Binder, negative electrode including the same, and rechargeable battery

Abstract

Provided is an adhesive for a rechargeable battery, a negative electrode including the adhesive, and a rechargeable battery including the adhesive. The adhesive includes a copolymer, and the copolymer includes: a plurality of first components, each first component having a linear or branched structure, each first component including 1-1 units derived from a monovinyl aromatic monomer and 1-2 units derived from a conjugated diene monomer; and a second component, derived from vinylsilsesquioxane or a derivative thereof, constituting a core node of the copolymer. In the copolymer, the plurality of first components are respectively bonded to vinyl groups of the one second component.

Description

Technical Field

[0001] One or more embodiments of the present disclosure relate to a binder, and more particularly, to a binder for a rechargeable battery, a negative electrode including the binder, and a rechargeable battery including the binder. Background Art

[0002] Rechargeable lithium batteries (e.g., lithium-ion batteries) have many advantages such as high energy density, long cycle life, high nominal voltage, low self-discharge rate, small size, and light weight, and are widely used in the field of consumer electronics. With the rapid development of electric vehicles and mobile electronic devices in recent years, people's demands for the safety performance, cycle performance, etc. of rechargeable lithium batteries are getting higher and higher, and the emergence of new rechargeable lithium batteries with comprehensively improved performance is expected.

[0003] The electrode binder is an important auxiliary functional material and an essential material in rechargeable lithium batteries. Although its content in the electrode is small, it is the main source of the mechanical properties of the entire electrode, has an important impact on the production process of the electrode and the electrochemical performance of the battery, and plays an irreplaceable role. The main function of the electrode binder is to bond the electrode active material, the conductive agent and the current collector together to stabilize the structure of the electrode material and shorten the lithium ion transmission path.

[0004] Compared with ordinary binders, the electrode binder is required not only to have bonding performance, but also to be able to withstand the swelling and corrosion of the electrolyte, and at the same time ensure that the lithium ion transmission path is not affected.

[0005] In the prior art, conventional lithium ion electrode binders mainly include polyvinyl alcohol, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR) polymers, fluorinated rubber, polyurethane, polyacrylic acid, etc. Among them, the SBR binder is widely used in lithium ion batteries due to its stable performance and price advantage. However, due to the defects of the SBR binder itself, sodium carboxymethyl cellulose (CMC) is usually used in combination with SBR as the electrode binder.

[0006] On the other hand, in recent years, silicon-based negative electrode materials have attracted attention due to their higher theoretical capacity. However, the silicon-based negative electrode material will undergo a large volume change during the insertion / extraction of lithium, so the negative electrode active material layer will expand and contract more significantly during charging and discharging, which will lead to the deterioration of the electrode performance.

[0007] The above information disclosed in this background art section is only used to enhance the understanding of the background art of the present disclosure, and thus may include information that does not constitute the prior art. Summary of the Invention

[0008] Embodiments of the present disclosure relate to a binder for a rechargeable battery that can improve battery performance.

[0009] Embodiments of the present disclosure relate to a negative electrode including the binder.

[0010] Embodiments of the present disclosure relate to a rechargeable battery including the binder.

[0011] However, the present disclosure is not limited to the above aspects and can be variously extended without departing from the technical spirit of the present disclosure.

[0012] Embodiments of the present disclosure provide a binder for a rechargeable battery, the binder for a rechargeable battery including a copolymer, the copolymer including: a plurality of first components having a linear or branched structure, each first component including 1-1 units derived from a monovinyl aromatic monomer and 1-2 units derived from a conjugated diene monomer; and a second component derived from vinylsilsesquioxane or a derivative thereof, constituting a core node of the copolymer. In the copolymer, the plurality of first components are respectively bonded to vinyl groups of the one second component.

[0013] In an embodiment of the present disclosure, a ratio of the number of the first components to the number of the second components in the copolymer is from about 2:1 to about 8:1.

[0014] In an embodiment of the present disclosure, a ratio of the number of the first components to the number of the second components in the copolymer is from about 2:1 to about 5:1.

[0015] In an embodiment of the present disclosure, a ratio of the number of the first components to the number of the second components in the copolymer is from about 3:1 to about 4:1.

[0016] In an embodiment of the present disclosure, a ratio of the number of the first components to the number of the second components in the copolymer is about 3.5:1.

[0017] In an embodiment of the present disclosure, a number average molecular weight of the first component is from about 50,000 to about 250,000.

[0018] In an embodiment of the present disclosure, a number average molecular weight of the copolymer is from about 200,000 to about 1,200,000.

[0019] In an embodiment of the present disclosure, the first component includes a block copolymer of 1-1 units and 1-2 units.

[0020] In an embodiment of the present disclosure, based on the total weight of the first component, the content of the 1-1 unit is in the range of about 12 wt% to about 25 wt%, and the content of the 1-2 unit is in the range of about 75 wt% to about 88 wt%.

[0021] In an embodiment of the present disclosure, the binder further includes a crosslinking agent, and the crosslinking agent includes units derived from amino sesquisiloxane or its derivatives.

[0022] In an embodiment of the present disclosure, the crosslinking agent is N-phenylamino-sesquisiloxane or its derivatives.

[0023] In an embodiment of the present disclosure, the copolymer is crosslinked by a crosslinking agent to form a polymer having a semi-interpenetrating polymer network structure.

[0024] In an embodiment of the present disclosure, the polymer having a semi-interpenetrating polymer network structure includes: a network-structured polymer formed by crosslinking the copolymer with a crosslinking agent; and the copolymer, independent of the network-structured polymer.

[0025] In an embodiment of the present disclosure, in the binder, the content (by weight) of the crosslinking agent is about 1.5% or less of the weight of the copolymer.

[0026] In an embodiment of the present disclosure, the crosslinking degree of the copolymer is not higher than about 40%.

[0027] In an embodiment of the present disclosure, the first component further includes 1-3 units derived from a carboxyl group-containing unsaturated olefin monomer.

[0028] In an embodiment of the present disclosure, based on the total weight of the first component, the content of the 1-3 unit is in the range of about 3 wt% or less.

[0029] In an embodiment of the present disclosure, the carboxyl group-containing unsaturated olefin monomer is selected from at least one of (meth)acrylic acid or its anhydride, maleic acid or its anhydride, and vinylbenzoic acid or its anhydride.

[0030] In an embodiment of the present disclosure, the carboxyl group-containing unsaturated olefin monomer is maleic acid or maleic anhydride.

[0031] In an embodiment of the present disclosure, the monovinyl aromatic monomer is selected from at least one of styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 2,4-dimethylstyrene, vinylnaphthalene, vinyltoluene, vinyldimethylbenzene, adamantylstyrene, vinylanthracene, vinylbiphenyl, and 1,1-diphenylethylene.

[0032] In an embodiment of the present disclosure, the monovinyl aromatic monomer is styrene.

[0033] In an embodiment of the present disclosure, the conjugated diene monomer includes butadiene and optionally isoprene.

[0034] In an embodiment of the present disclosure, the conjugated diene monomer is butadiene.

[0035] In an embodiment of the present disclosure, the conjugated diene monomer includes butadiene and isoprene.

[0036] In an embodiment of the present disclosure, based on the total weight of 1-2 units, the content of the units derived from the isoprene monomer is 0 wt% to 25 wt%.

[0037] In an embodiment of the present disclosure, the binder does not include sodium carboxymethyl cellulose.

[0038] In an embodiment of the present disclosure, the present disclosure also provides a method for preparing a binder for a rechargeable battery, the method comprising the following steps: adding a monovinyl aromatic reaction monomer to a solvent, adding an initiator to initiate a polymerization reaction; adding a conjugated diene reaction monomer to the reaction solution, and continuing the reaction to form a copolymer of a first component; adding vinylsilsesquioxane or its derivative, and reacting it with the copolymer of the first component to form a copolymer in which a second component derived from vinylsilsesquioxane or its derivative is a core node and the first component is bonded to the second component.

[0039] In an embodiment of the present disclosure, the effective addition amount of the initiator is 2 to 8 times the effective addition amount of vinylsilsesquioxane or its derivative.

[0040] In an embodiment of the present disclosure, the effective addition amount of the initiator is 2 to 5 times the effective addition amount of vinylsilsesquioxane or its derivative.

[0041] In an embodiment of the present disclosure, the effective addition amount of the initiator is 3 to 4 times the effective addition amount of vinylsilsesquioxane or its derivative.

[0042] In an embodiment of the present disclosure, the effective addition amount of the initiator is 3.5 times the effective addition amount of vinylsilsesquioxane or its derivative.

[0043] The present disclosure also provides a negative electrode, the negative electrode including the binder as described above.

[0044] The present disclosure also provides a rechargeable battery, the rechargeable battery including: the negative electrode as described above; a positive electrode; and a separator disposed between the negative electrode and the positive electrode.

[0045] According to one or more embodiments, a binder that can improve the performance and safety of a battery, a negative electrode including the binder, and a rechargeable battery are provided.

[0046] The effects of the present disclosure are not limited to those mentioned herein, and those skilled in the art will clearly understand other effects through the description of the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The drawings are included to provide a further explanation of the present disclosure, and are incorporated into and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, are used to explain the principles of the present disclosure.

[0048] Figure 1 is a schematic diagram showing the bonding mechanism of the binder in the electrode.

[0049] Figure 2 is a schematic structural diagram of a rechargeable battery according to an embodiment of the present disclosure.

[0050] Figure 3 is a schematic structural diagram of an electrode assembly according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0051] The present disclosure may be modified in many alternative forms, and thus specific embodiments will be illustrated in the drawings and described in more detail. However, it should be understood that the specific embodiments are not intended to limit the present disclosure to the particular forms disclosed, but are intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure.

[0052] Hereinafter, embodiments of the present disclosure will be described in more detail. However, these embodiments are merely examples, and the present disclosure is not limited thereto, and the present disclosure is defined by the scope of the claims. The terms used herein are only for describing the embodiments and are not intended to limit the present disclosure. Unless the context clearly indicates otherwise, the singular forms include the plural forms.

[0053] As used herein, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are also intended to include the plural forms. Further, when describing the embodiments of the present disclosure, the use of "may" refers to "one or more embodiments of the present disclosure".

[0054] As used herein, the terms "substantially", "about", and similar terms are used as approximate terms and not as degree terms, and are intended to account for the inherent deviations of measured or calculated values that would be recognized by those of ordinary skill in the art.

[0055] As used herein, the term "a combination thereof" can refer to a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, a reaction product, etc.

[0056] It should be understood that terms such as "comprising / variations thereof", "including / variations thereof" or "having / variations thereof" are intended to indicate the presence of the recited features, quantities, steps, elements or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, quantities, steps, elements or combinations thereof.

[0057] In the drawings, for clarity, the thickness of layers, films, panels, regions, etc. may be exaggerated, and throughout the present disclosure, like reference numerals represent like elements, and for the sake of brevity, their repeated description may not be provided. It will be understood that when an element such as a layer, film, region or substrate is referred to as "on" another element, it can be directly on the said another element, or there may also be intervening elements. In contrast, when an element is referred to as "directly on" another element, there are no intervening elements between them.

[0058] "Thickness" can be measured, for example, with a micrometer or by images taken with an optical microscope (such as a scanning electron microscope).

[0059] Furthermore, any numerical range recited herein is intended to include all sub-ranges having the same numerical precision included within the recited range. For example, the range "1.0 to 10.0" is intended to include all sub-ranges between the recited minimum value 1.0 and the recited maximum value 10.0 (and including the recited minimum value 1.0 and the recited maximum value 10.0), that is, having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0, such as, for example, 2.4 to 7.6. Any maximum numerical limit recited herein is intended to include all lower numerical limits contained therein, and any minimum numerical limit recited in this specification is intended to include all higher numerical limits contained therein. Thus, the applicant reserves the right to modify this specification (including the claims) to expressly recite any sub-ranges included within the ranges expressly recited herein.

[0060] "Thickness" can be measured by images taken with an optical microscope or a scanning electron microscope.

[0061] Hereinafter, binders according to embodiments of the present disclosure will be described.

[0062] Embodiments of the present disclosure provide an adhesive for a rechargeable battery. The adhesive can be used for the electrodes of a rechargeable battery. Specifically, it can be an adhesive in the electrodes for adhering electrode active materials and conductive materials to a current collector. The adhesive can include a copolymer. That is, the main component of the adhesive can be the copolymer described below alone. In some embodiments, the main component of the adhesive can further include other components (e.g., crosslinking agents). It can be understood that the adhesive can also include other minor components and inevitable impurities and other components. The copolymer includes a first component and a second component. Specifically, in a copolymer macromolecule, there are at least two first components and one second component. The first component has a linear or branched structure and constitutes the arms of the copolymer. The second component constitutes the core node of the copolymer. In other words, the copolymer can be a star copolymer having at least two arms. The first component includes 1-1 units derived from monovinyl aromatic monomers and 1-2 units derived from conjugated diene monomers. The second component is derived from vinyl sesquisiloxane or its derivatives. In some embodiments, the second component can be a part formed by one molecule of vinyl sesquisiloxane or its derivative molecule.

[0063] In some embodiments of the present disclosure, the monovinyl aromatic monomers can include at least one of styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 2,4-dimethylstyrene, vinylnaphthalene, vinyltoluene, vinyldimethylbenzene, adamantylstyrene, vinylanthracene, vinylbiphenyl, 1,1-diphenylethylene.

[0064] In some embodiments of the present disclosure, the conjugated diene monomers can include butadiene and optionally isoprene.

[0065] That is, the first component can be a copolymer of monovinyl aromatic and conjugated diene. The "copolymer" here can be an alternating copolymer, a random copolymer or a block copolymer. That is, the first component can include an alternating copolymer, a random copolymer or a block copolymer of monovinyl aromatic and conjugated diene. In some embodiments of the present disclosure, the first component can include a block copolymer of monovinyl aromatic and conjugated diene.

[0066] In the following description, there may be involved the theoretical basis for the excellent effects of the adhesive according to some embodiments of the present disclosure. It can be understood that these theoretical bases are only for helping to understand the present disclosure and are not intended to limit the present disclosure in any way. That is, the effects of the adhesive of the present disclosure are not limited by these theoretical bases, that is, it can be not based on these theoretical bases, or can also be based on theoretical bases other than these theoretical bases.

[0067] A copolymer of styrene as a monovinyl aromatic hydrocarbon and butadiene as a conjugated diene is a styrene-butadiene rubber (SBR) polymer. SBR is a commonly used binder for lithium battery electrodes, especially the negative electrode. The SBR used in this field is usually formed by free radical emulsion polymerization, which is a random copolymer of styrene and butadiene.

[0068] However, SBR is prone to swelling in the electrolyte. Moreover, if SBR is used alone as a binder, it is difficult to prepare a slurry because SBR does not have a suspension and dispersion function, and the slurry will settle. Therefore, sodium carboxymethyl cellulose (CMC) and SBR are usually used in combination as an electrode binder in this field. However, CMC has the defect of relatively large brittleness. For example, the electrode active material layer made of the binder containing CMC is prone to cracking during the charge and discharge of the battery. Especially when there is a relatively large volume change in the electrode material during the charge and discharge of the battery, the binder containing CMC is more likely to increase the risk of rupture of the electrode active material layer.

[0069] In recent years, silicon-based negative electrode materials (i.e., Si-based active materials) have received attention due to their higher theoretical capacity. However, although silicon-based negative electrode materials can significantly improve the energy density of lithium batteries, they will undergo a relatively large volume change during the insertion / extraction of lithium. Therefore, the electrode active material layer will expand and contract more significantly during charging and discharging, which will lead to the deterioration of electrode performance.

[0070] Therefore, if the CMC-SBR composite binder is applied to an electrode using a silicon-based negative electrode material, in the case where there is a relatively large volume change in the electrode active material layer, the risk of rupture of the electrode active material layer due to the relatively large brittleness of CMC will be more prominent. However, as mentioned above, if SBR is used alone as a binder, it is difficult to prepare a slurry because SBR does not have a suspension and dispersion function, and the slurry will settle. Moreover, SBR is prone to swelling in the electrolyte. When the volume of the silicon-based negative electrode material expands, the volume of the electrode active material layer will also expand more significantly, which will lead to a relatively significant increase in the volume of the electrode assembly, affecting battery performance and posing a safety hazard.

[0071] Therefore, the present disclosure proposes a solution to this problem. Specifically, the embodiments of the present disclosure obtain a star copolymer including a first component as an arm and a second component as a core by performing an addition reaction between a copolymer of a monovinyl aromatic hydrocarbon and a conjugated diene and vinylsilsesquioxane or its derivative, wherein the first component includes a 1-1 unit derived from a monovinyl aromatic hydrocarbon monomer and a 1-2 unit derived from a conjugated diene monomer, and the second component is derived from vinylsilsesquioxane or its derivative.

[0072] In some embodiments of the present disclosure, the vinyl silsesquioxane or its derivative may be, for example, octavinyl silsesquioxane or its derivative.

[0073] Silsesquioxane refers to polyhedral oligomeric silsesquioxane, a novel organic-inorganic hybrid nanostructured material. Its internal inorganic framework is a hexahedral cage structure composed of Si-O-Si or Si-O bonds. Each corner contains a Si atom, and each face is composed of Si-O-Si eight-membered rings, with strong structural symmetry. Multiple organic groups can be attached to each Si atom on the outside. Therefore, a typical molecular formula can be depicted as (CH3SiO 1.5 )n, where n is usually 8, and can also be 10, 12, etc. R can be H and active or inactive groups, such as epoxy groups, amino groups, carboxyl groups, alkenyl groups, alkyl groups, hydroxyl groups, aryl groups, etc. The structure of a typical cage-type polyhedral oligomeric silsesquioxane is shown in Formula 1 below.

[0074] [Formula 1]

[0075]

[0076] When R in Formula 1 is vinyl, it is vinyl silsesquioxane. Specifically, when all R are vinyl, it is octavinyl silsesquioxane. In the embodiments of the present disclosure, a part (for example, two or more) of R in Formula 1 can be vinyl, while other R in Formula 1 can be H or other groups.

[0077] For the copolymer of monovinylarene and conjugated diene, the unsaturated double bond at the chain end can undergo an addition reaction with the vinyl group of vinyl silsesquioxane in the presence of an anionic polymerization active center, thereby binding the chain-like copolymer of monovinylarene and conjugated diene to vinyl silsesquioxane.

[0078] Therefore, in the embodiments of the present disclosure, monovinylarene and conjugated diene are first copolymerized by living anionic polymerization to form the first component that will serve as an arm, and then the first component reacts with vinyl silsesquioxane that will serve as the second component in the presence of an active center, thereby forming a copolymer including the first component and the second component. The preparation method will be further described in detail later.

[0079] In the following description, for the sake of simplicity, styrene will be used as an example of monovinylarene, and butadiene and / or isoprene will be used as examples of conjugated dienes. It can be understood that the present disclosure is not limited thereto, and other types of monovinylarenes as described above are applicable to the inventive concept of the present disclosure.

[0080] The copolymer having the above structure can first improve the problem that SBR is prone to swelling in the electrolyte. Since the sesquioxane has a strong three-dimensional structure, it can enhance the volume stability and structural stability of the copolymer. In addition, due to the more stable and firm structure of the sesquioxane, it can tightly connect multiple long-chain first components together, avoiding the problem that the chain segments of the first components are too long and prone to breakage or entanglement under the same molecular weight. Therefore, the copolymer with vinyl sesquioxane as the core can have better toughness than pure chain-like SBR. Especially when applied to a silicon-based anode with large volume changes, the copolymer with vinyl sesquioxane as the core in the embodiments of the present disclosure can avoid the breakage of molecular chains caused by too long molecular chain segments.

[0081] Secondly, the sesquioxane has a cage structure. Therefore, the copolymer of the present disclosure can improve the electrolyte absorption capacity of the binder through the cage structure of the sesquioxane, which is beneficial to the migration of lithium ions in the electrode.

[0082] The main role of the binder in the electrode is to bond components such as the electrode active material and the conductive agent in the electrode active material layer to the metal current collector. Figure 1 The schematic diagram of the mechanism of the binder is shown. As Figure 1 shown, the mechanism of action of the binder can be understood as: the chain-like polymer binder binds and fixes the spherical electrode active material to the metal current collector like a "rope". Therefore, combined Figure 1 with this, if the binder is just a simple linear polymer, the fixing effect on the electrode active material is relatively weak. In the present application, the copolymer in the binder can be a star-shaped polymer including a first component and a second component. The copolymer with this structure spreads on the electrode active material and can firmly fix the electrode active material like a "net".

[0083] Although some linear polymers can generate some "binding points" with each other to form a structure similar to a network, these "binding points" are easily disconnected under the frequent volume changes of the electrode active material, resulting in the deterioration of the adhesion of the binder. In the embodiments of the present application, the binding bond between the first component and the second component combined through an addition reaction is relatively more stable and not easily broken. In addition, the second component derived from vinyl sesquioxane has a strong three-dimensional structure, which can tightly connect the first component combined with it like a "knot" and can firmly fix the electrode active material attached to it. Therefore, compared with the SBR binder and the CMC-SBR binder, the binder of the present disclosure can have better stability, can prevent the structure and volume of the electrode active material from changing too much during charge and discharge, prevent the electrode active material from falling off, and improve the cycle stability of the electrode.

[0084] As described above, the silsesquioxane can carry multiple (e.g., 12 or 8) reactive groups. Therefore, in the case of octavinylsilsesquioxane, theoretically, 8 first components can combine with 1 second component. That is to say, in some embodiments of the present disclosure, the copolymer can include 2 to 8 first components and 1 second component. In other words, in some embodiments of the present disclosure, the ratio of the number of the first component to the second component in the copolymer can be 2:1 to 8:1.

[0085] In some embodiments of the present disclosure, the ratio of the number of the first component to the second component in the copolymer can be 2:1 to 5:1. That is to say, the number of arms of the copolymer is in the range of 2 to 5. It can be understood that the range of 2:1 to 5:1 here refers to the ratio calculated by gel permeation chromatography (GPC) test. That is to say, when a large number of copolymer macromolecules are taken as a reference, the ratio of the number of the first component to the second component is 2:1 to 5:1. It can be understood that in some (very small number) individual copolymer molecules, the ratio of the number of the first component to the second component can be outside the range of 2:1 to 5:1. For the vast majority of individual copolymer molecules, the ratio of the number of the first component to the second component is 2:1 to 5:1. That is to say, for the vast majority of individual copolymer molecules, they can have 2, 3, 4 or 5 arms, that is, the ratio of the number of the first component to the second component is 2, 3, 4 or 5. Of course, if calculated based on a large number of copolymer molecules, the ratio of the number of the first component to the second component is any value between 2 and 5 (i.e., not necessarily an integer).

[0086] In some embodiments of the present invention, the ratio of the number of the first component to the second component in the copolymer is 2:1 to 5:1, specifically, 2.5:1 to 4.5:1, more specifically, 3:1 to 4:1, and more specifically, 3.5:1. That is to say, in some embodiments of the present invention, the vast majority of copolymer macromolecules can have one second component and 2 to 5 first components, and more specifically, can have one second component and 3 or 4 first components.

[0087] The copolymer with such a structure can better exhibit structural stability while ensuring the electrical properties of the electrode. As described above, the copolymer in the binder of the present disclosure can fix the electrode active material like a "net". In this case, if the number of the first component in the copolymer is less than 2, the copolymer is more like a linear polymer, and it is difficult to achieve the effect of a "net". On the contrary, if the number of the first component in the copolymer is too large, that is, greater than 5, the movement space of the first component will be restricted due to steric hindrance effects, which will cause some chain-like first components to be difficult to wind well around the electrode active material. On the one hand, this will cause this part of the first component to be difficult to play its role as a binder, resulting in waste of materials; on the other hand, too many first components will block the lithium ion transport channels, leading to deterioration of the electrical properties of the electrode.

[0088] In addition, in order for the binder to have good adhesion and be suitable for preparing the active material slurry, it is required that the copolymer has a suitable molecular weight and at the same time the chain-like first component has a suitable length. Therefore, if the number of the first component in the copolymer is too large, then in order to control the molecular weight of the copolymer from being too large, the length of the molecular chain of the first component needs to be shortened, which may lead to a decrease in the adhesion of the binder. On the contrary, if the appropriate length of the first component is to be satisfied, it will result in too large a molecular weight of the copolymer, which is difficult to dissolve in the solvent during the preparation of the active material slurry, and cracks are likely to appear in the prepared electrode active material layer.

[0089] In some embodiments of the present disclosure, the number average molecular weight Mn of the first component can be in the range of about 50,000 to about 250,000. When the number average molecular weight of the first component is within the above range, the copolymer including it can exhibit excellent binding properties. If the number average molecular weight Mn of the first component is less than 50,000, the formed molecular chain is shorter, the entanglement effect on the electrode active material is weaker, and moreover, the viscosity of the formed copolymer is too low, resulting in poor binding properties of the binder. If the number average molecular weight Mn of the first component is greater than 250,000, the copolymer formed by it is difficult to dissolve in the solvent when preparing the slurry of the negative electrode active material composition, increasing the difficulty of the preparation process, and the too long molecular chain segment will also increase the internal resistance of the battery.

[0090] More specifically, in some embodiments of the present disclosure, the number average molecular weight Mn of the first component can be about 70,000 to about 230,000, about 90,000 to about 210,000, about 110,000 to about 190,000, about 130,000 to about 170,000, about 150,000.

[0091] In some embodiments of the present disclosure, the number-average molecular weight Mn of a copolymer including a first component and a second component may be from about 200,000 to about 1,200,000. When the number-average molecular weight of the copolymer is within the above range, it may exhibit excellent adhesion properties. If the number-average molecular weight Mn of the copolymer is less than 200,000, the viscosity of the copolymer formed thereby is too low, resulting in poor adhesion of the binder. If the number-average molecular weight Mn of the copolymer is greater than 1,200,000, the copolymer formed thereby is difficult to dissolve in a solvent when preparing a slurry of the negative electrode active material composition, increasing the difficulty of the preparation process; moreover, the electrode active material layer including the copolymer is prone to cracking.

[0092] More specifically, in some embodiments of the present disclosure, the number-average molecular weight Mn of a copolymer including a first component and a second component may be from about 200,000 to about 1,200,000, from about 300,000 to about 1,000,000, from about 400,000 to about 800,000, from about 450,000 to about 700,000, from about 500,000 to about 600,000, about 550,000.

[0093] That is to say, in some embodiments of the present disclosure, by setting the molecular weight of the first component, the ratio of the number of the first component to the second component, and the molecular weight of the copolymer within appropriate ranges, the performance of the binder can be effectively improved. For example, in some embodiments of the present application, the ratio of the number of the first component to the second component in the copolymer is from 3:1 to 4:1, the number-average molecular weight Mn of the first component is from about 130,000 to about 170,000, and the number-average molecular weight Mn of the copolymer is from about 500,000 to about 600,000. Within the above range, the binder can exhibit excellent adhesion and other properties.

[0094] In some embodiments of the present disclosure, the first component includes a block copolymer of 1-1 units and 1-2 units. In this case, the 1-1 units derived from monovinyl aromatic monomers form a hard block to provide strength; the 1-2 units derived from conjugated diene monomers form a soft block to provide elasticity and adhesion.

[0095] As described above, the first component of the present application is formed by living anionic polymerization. For example, homopolymerization of monovinyl aromatic hydrocarbons can be carried out first, and then conjugated diene monomers can be added to form a block copolymer of the two with the homopolymer of monovinyl aromatic hydrocarbons. Alternatively, monovinyl aromatic hydrocarbons and conjugated dienes can also be added simultaneously during polymerization. In this case, due to the difference in reactivity ratios between monovinyl aromatic hydrocarbons and conjugated dienes, the polymerization sequence of the two will be different. Generally, monovinyl aromatic hydrocarbons will first affinity with the initiator to form active centers, and then monovinyl aromatic hydrocarbons will first polymerize into chains to form a block containing basically only it. Then, conjugated dienes can be added to the active centers at the chain ends of the monovinyl aromatic hydrocarbon block to form a conjugated diene block. This will be further described in detail later.

[0096] After that, vinyl silsesquioxane or its derivatives can be added while maintaining the existence of active centers, so that the first component reacts with it to form a copolymer.

[0097] The first component with the above structure can further improve the mechanical properties of the copolymer, so that the binder of the present disclosure has better adhesion performance.

[0098] In some embodiments of the present disclosure, based on the total amount of 100 wt% of the 1-1 units and 1-2 units in the first component, the content of the 1-1 units is in the range of 12 wt% to 25 wt%, and the content of the 1-2 units is in the range of 75 wt% to 88 wt%. In other words, the mass ratio of the 1-1 units to the 1-2 units in the first component is in the range of 12:88 to 25:75.

[0099] When the contents of the 1-1 units and 1-2 units in the first component are within the above ranges, the copolymer can have excellent adhesion, elasticity and strength. If the content of the 1-1 units is less than 12 wt% or the content of the 1-2 units is higher than 88 wt%, the content of the hard block in the first component is too low, resulting in insufficient strength and poor structural stability of the electrode. If the content of the 1-1 units is higher than 25 wt% or the content of the 1-2 units is less than 75 wt%, the content of the soft block in the first component is too low, resulting in poor adhesion, excessive rigidity and poor elasticity of the copolymer.

[0100] In addition, in the polymerization reaction of the present disclosure, the monomers can basically react completely. Therefore, in the present disclosure, the weight percentages of the above-mentioned 1-1 units and 1-2 units in the first component are basically the same as the weight percentages of the 1-1 units and 1-2 units added during the preparation of the first component. That is to say, throughout the text, the weight percentages of the respective components or units in the copolymer can be regarded as equal to the weight percentages of the respective components or corresponding monomers added during the preparation of the copolymer.

[0101] In some embodiments of the present disclosure, the 1-2 units may include units derived from butadiene monomers and optionally units derived from isoprene monomers. That is to say, the block formed by the 1-2 units (i.e., the conjugated diene block) can be a block formed by butadiene, or a block formed by both butadiene and isoprene, that is, it can be a random chain, an alternating chain, or a block chain of butadiene and isoprene.

[0102] In some embodiments of the present disclosure, based on the total weight of the 1-2 units, the content of the units derived from isoprene monomers can be from 0 wt% to 25 wt%. If the content of the units derived from isoprene monomers exceeds 25%, it will have an adverse effect on the adhesion of the binder.

[0103] In some embodiments of the present disclosure, the first component further includes 1-3 units derived from carboxyl-containing unsaturated olefin monomers.

[0104] The addition of the 1-3 units can further improve the adhesion of the binder. Since SBR is prone to swelling in the electrode liquid and then gelation occurs, which will affect the adhesion of the binder and lead to deterioration of the structural stability of the electrode. By further including the 1-3 units, the adhesion between the gelled part of the binder and the metal current collector can be improved, thereby improving the adhesion of the binder.

[0105] In some embodiments of the present disclosure, the carboxyl-containing unsaturated olefin monomer can be selected from at least one of (meth)acrylic acid or its anhydride, maleic acid or its anhydride, and vinylbenzoic acid or its anhydride.

[0106] In some embodiments of the present disclosure, the carboxyl-containing unsaturated olefin can be maleic acid or maleic anhydride.

[0107] In some embodiments of the present disclosure, based on the total weight of the first component, the content of the 1-3 units can be in the range of 3 wt% or less. If the content of the 1-3 units in the first component is higher than 3 wt%, it will cause difficulties in the preparation process.

[0108] More specifically, in some embodiments of the present disclosure, the content of the 1-3 units can be in the range of 0.5 wt% to 2.5 wt%, in the range of 1.0 wt% to 2.0 wt%, in the range of 1.2 wt% to 1.80 wt%, in the range of 1.4 wt% to 1.6 wt%, or be 1.5 wt%.

[0109] In some embodiments of the present disclosure, the binder may further include a crosslinking agent, and the crosslinking agent may include units of amino sesquisiloxane or its derivatives. For example, the crosslinking agent may be N-phenylamino-sesquisiloxane or its derivatives.

[0110] The copolymer is crosslinked by the crosslinking agent to form a polymer having a semi-interpenetrating polymer network structure.

[0111] The polymer having a semi-interpenetrating polymer network structure includes: a network-structured polymer formed by crosslinking a copolymer with a crosslinking agent; and a copolymer independent of the network-structured polymer.

[0112] For example, a polymer having a semi-interpenetrating polymer network (semi-IPN) structure may include a network-structured polymer formed by crosslinking a copolymer with a crosslinking agent and a copolymer independent of the network-structured polymer.

[0113] Since the copolymer is crosslinked with the crosslinking agent to form a polymer having a semi-interpenetrating polymer network structure, the adhesion, mechanical properties, chemical resistance, swelling resistance, etc. of the binder can be improved compared to the case where the copolymer exists alone.

[0114] In some embodiments of the present disclosure, the weight of the crosslinking agent may be about 1.5% or less of the weight of the copolymer. Specifically, the weight of the crosslinking agent may be 1.2% or less, 1.0% or less, 0.8% or less, 0.6% or less, 0.4% or less, 0.2% or less, 0.1% or less, or 0.05% or less of the weight of the copolymer.

[0115] In some embodiments of the present disclosure, the crosslinking degree of the copolymer (or binder) is not higher than about 40%. Since it is not necessary to use too much crosslinking agent, for example, as described above, the weight of the crosslinking agent may be 1.5% or less of the weight of the copolymer, so the crosslinking degree of the copolymer of the present disclosure can be in the range of about 40% or less. If the crosslinking degree of the copolymer is higher than 40%, the rigidity of the binder is too high, making it difficult to prepare the negative electrode slurry.

[0116] In some embodiments of the present disclosure, the crosslinking degree of the copolymer is in the range of about 5% to about 35%, in the range of about 10% to about 30%, in the range of about 15% to about 25%, in the range of about 18% to about 22%, or about 20%.

[0117] In addition, the inventors have found that when the ratio of the amount of the first component to the second component in the copolymer is in the range of 2:1 to 5:1 or in the range of 3:1 to 4:1, the binder including the copolymer and the crosslinking agent has relatively more excellent properties. This may be because when the copolymer has a structure with 2 to 5 arms or 3 to 4 arms, it can more suitably form a semi-interpenetrating polymer network structure with the crosslinking agent.

[0118] The embodiments of the present disclosure also provide a method for preparing a binder for a rechargeable battery, the method including the following steps: adding a monovinyl aromatic reaction monomer into a solvent, adding an initiator to initiate a polymerization reaction; adding a conjugated diene reaction monomer into the reaction solution, and continuing the reaction to generate a copolymer of the first component; adding vinylsilsesquioxane or its derivative, and making it react with the copolymer of the first component to generate a copolymer in which the second component derived from vinylsilsesquioxane or its derivative is used as a core node and the first component is bonded to the second component.

[0119] Alternatively, the monovinyl aromatic reaction monomer and the conjugated diene reaction monomer can also be added into the solvent simultaneously, and then an initiator is added to initiate the polymerization reaction. In this case, due to the difference in the reactivity ratios of the monovinyl aromatic and the conjugated diene, the polymerization sequence of the two is different.

[0120] The copolymer in the binder of the present disclosure can be prepared by living anionic polymerization. Specifically, the living anionic polymerization can be carried out under anhydrous and anaerobic conditions by using a schlenk system. Anionic polymerization initiators and suitable solvents known in the art can be used. For example, according to a predetermined ratio, the monovinyl aromatic monomer and the conjugated diene monomer are added into the solvent and kept under anhydrous and anaerobic conditions, and then an appropriate amount of initiator can be added according to the designed molecular weight. Here, the appropriate amount of initiator includes the effective addition amount of the initiator and the amount of this part of the initiator used to remove the remaining water and oxygen in the reaction system. That is to say, in the present disclosure, the "effective addition amount" refers to the amount of the initiator or monomer that finally actually participates in the polymerization reaction. At a suitable temperature, the monovinyl aromatic monomer and the conjugated diene monomer will undergo anionic polymerization (the first-step reaction) under the initiation of the initiator to generate a block copolymer, that is, the first component. After the first-step reaction is completed, an appropriate amount of vinylsilsesquioxane or its derivative can be added as the second component according to the set ratio of the amount of the first component to the second component. Since there are anionic active centers in the first component, vinylsilsesquioxane or its derivative can continue to react with the first component by an addition reaction (the second-step reaction) to generate a copolymer including the first component and the second component. After the reaction is complete, a terminator can be added to terminate the reaction.

[0121] In some embodiments of the present disclosure, the effective addition amount of the initiator is about 2 to about 8 times, about 2 to about 5 times, about 3 to about 4 times, or about 3.5 times the effective addition amount of vinyl sesquisiloxane or its derivatives.

[0122] In some embodiments of the present disclosure, when the first component further includes 1-3 units derived from a carboxyl group-containing unsaturated olefin monomer, an appropriate amount of the carboxyl group-containing unsaturated olefin monomer can be added to the system after the above two-step reaction is completed. The carboxyl group-containing unsaturated olefin monomer can be grafted onto the first component through a radical polymerization reaction between the carboxyl group-containing unsaturated olefin monomer and the 1-1 units and 1-2 units in the first component, forming a first component including 1-3 units derived from the carboxyl group-containing unsaturated olefin monomer.

[0123] In some embodiments of the present disclosure, when the first component further includes 1-3 units derived from a carboxyl group-containing unsaturated olefin monomer, an appropriate amount of the carboxyl group-containing unsaturated olefin monomer can also be added to the system immediately after the completion of the first step of the above reaction, so that it is grafted onto the first component through radical polymerization with the 1-1 units and 1-2 units.

[0124] During the preparation process, the addition ratio of the monovinyl aromatic monomer and the conjugated diene monomer, the quantitative ratio of the first component to the second component, and the content of the 1-3 units in the first component are controlled within the ranges described above, which will not be elaborated here.

[0125] In some embodiments of the present disclosure, when the binder further includes a crosslinking agent, the above copolymer and the crosslinking agent can be mixed to obtain a binder. Specifically, the copolymer and the crosslinking agent can be mixed by using an interpenetrating network polymer preparation technique, and a suitable initiator is added to partially crosslink the two to prepare a binder.

[0126] The rechargeable battery of the embodiments of the present disclosure will be described below.

[0127] As Figure 2 shown, the embodiments of the present disclosure also provide a rechargeable battery 1, which may include: an electrode assembly 10, including: a positive electrode 20; a negative electrode 30; and a separator 40 between the positive electrode 2 and the negative electrode 30; an electrolyte (not shown), the electrode assembly 10 being immersed in the electrolyte; and a housing 50 for accommodating the electrode assembly 10 and the electrolyte. The rechargeable battery 1 may further include a battery cover 60 for sealing the housing 50.

[0128] As Figure 3As shown, the negative electrode 30 includes a negative electrode current collector 31 and a negative electrode active material layer 32 formed on the negative electrode current collector 31. The positive electrode 20 includes a positive electrode current collector 21 and a positive electrode active material layer 22 formed on the positive electrode current collector 21. At least one of the negative electrode active material layer 32 and the positive electrode active material layer 22 includes the binder for a rechargeable battery described above. In some embodiments of the present disclosure, the negative electrode active material layer includes the binder for a rechargeable battery described above.

[0129] Hereinafter, a rechargeable battery according to an embodiment of the present disclosure will be further described.

[0130] According to an embodiment of the present disclosure, the negative electrode 30 for a rechargeable battery includes a negative electrode current collector 31 and a negative electrode active material layer 32 formed on the negative electrode current collector 31.

[0131] The material of the negative electrode current collector 31 is not particularly limited. For example, it may be a copper foil.

[0132] The negative electrode active material layer 32 includes the binder, the negative electrode active material, and a conductive agent described above.

[0133] According to an embodiment of the present disclosure, based on the total weight of the negative electrode active material layer of 100 wt%, the content of the binder may be in the range of about 0.5 wt% to about 6 wt%, further, it may be in the range of about 0.65 wt% to about 4 wt%, still further, it may be in the range of about 0.8 wt% to about 3 wt%, still further, it may be in the range of about 1 wt% to about 2.5 wt%, still further, it may be about 1.5 wt%. When the content of the binder is greater than or equal to 0.5 wt%, a negative electrode having excellent close contact properties and capable of suppressing the swelling of the negative electrode to have good cycle performance can be obtained. On the other hand, when the content of the binder is less than or equal to 6 wt%, the cycle performance of the battery can be improved without excessively increasing the electrode resistance.

[0134] The conductive agent may include at least one of the following: carbonaceous materials: carbon black, fine graphite particles, natural graphite, artificial graphite, acetylene black, Ketjen black, carbon fiber, carbon nanotube; metal materials: metal powders, metal fibers, or metal tubes of copper, nickel, aluminum, or silver; conductive polymers: polyphenylene derivatives. However, the disclosure is not limited thereto, and any conductive agent may be used as long as it is used in the art.

[0135] Based on the total weight of the negative electrode active material layer being 100 wt%, the content of the conductive agent can be in the range of about 1 wt% to about 10 wt%, and further, it can be in the range of about 1 wt% to about 5 wt%. When the content of the conductive agent in the negative electrode active material layer is within the above range, the negative electrode can have improved electrical conductivity, and a lithium battery including the negative electrode can have improved cycling characteristics.

[0136] The negative electrode active material can include an active material containing silicon atoms. Examples of the active material containing silicon atoms can include silicon microparticles, silicon oxide (SiO x (0 < x ≤ 2)), a composite material of silicon oxide and conductive carbon, a composite material of a silicon-containing material and conductive carbon, and an alloy containing silicon (for example, an alloy material of silicon and aluminum). That is, in some embodiments of the present application, the negative electrode active material can be a silicon-based negative electrode active material.

[0137] Based on the total weight of the negative electrode active material layer being 100 wt%, the content of the negative electrode active material can be in the range of about 82 wt% to about 98 wt%, and further, it can be in the range of about 90 wt% to about 97 wt%, and still further, it can be in the range of about 94 wt% to about 96 wt%.

[0138] When the content of the negative electrode active material is greater than or equal to about 82 wt%, the electrode resistance will not increase excessively, and a negative electrode with good cycling performance can be obtained. At the same time, when the content of the negative electrode active material is less than or equal to about 98 wt%, a negative electrode with excellent close contact properties and good cycling performance can be obtained.

[0139] For example, the negative electrode 30 can be manufactured by the following manufacturing method. The negative electrode active material, the conductive agent, and the binder are dry-mixed to prepare a negative electrode material mixture. Subsequently, the negative electrode material mixture is dispersed in a suitable organic solvent to prepare a negative electrode material mixture slurry, and the prepared negative electrode material mixture slurry is coated on the negative electrode current collector 31, and dried and pressed to prepare a negative electrode 30 including a negative electrode active material layer 32 and a negative electrode current collector 31.

[0140] The negative electrode for a rechargeable battery according to an embodiment of the present disclosure includes the above-mentioned binder and negative electrode active material. Therefore, a negative electrode with improved cycling characteristics while maintaining good close contact properties can be obtained.

[0141] According to an embodiment of the present disclosure, the positive electrode 20 for a rechargeable battery includes a positive electrode current collector 21 and a positive electrode active material layer 22 formed on the positive electrode current collector 21, and the positive electrode active material layer 22 includes a positive electrode active material, a conductive agent, and a binder.

[0142] The positive electrode active material is not particularly limited as long as it is a solid solution oxide containing lithium, for example, a material capable of electrochemically intercalating and deintercalating lithium ions. The solid solution oxide may include, for example, Li a Mn x Co y Ni z O2(1.15 ≤ a ≤ 1.43, 0.45 ≤ x ≤ 0.6, 0.10 ≤ y ≤ 0.15, 0.20 ≤ z ≤ 0.28), LiMn x Co y Ni z O2(0.3 ≤ x ≤ 0.85, 0.10 ≤ y ≤ 0.3, 0.10 ≤ z ≤ 0.3), LiMn 1.5 Ni 0.5 O4, etc.

[0143] The conductive agent can be the same as the conductive agent of the negative electrode described above.

[0144] The binder for the positive electrode can be, for example, polyvinylidene fluoride, ethylene - propylene - diene terpolymer, styrene - butadiene rubber, acrylonitrile - butadiene rubber, fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, etc. The positive electrode binder is not particularly limited as long as it can bind the positive electrode active material and the conductive agent to the positive electrode current collector.

[0145] For example, the positive electrode 20 can be manufactured by the following manufacturing method. The positive electrode active material, the conductive agent, and the positive electrode binder are dry - mixed to prepare a positive electrode material mixture. Subsequently, the positive electrode material mixture is dispersed in a suitable organic solvent to prepare a positive electrode material mixture slurry, and the prepared positive electrode material mixture slurry is coated on the positive electrode current collector 21, and dried and pressed to prepare a positive electrode including a positive electrode active material layer 22 and a positive electrode current collector 21.

[0146] The separator 40 is not particularly limited. The separator 40 can be any commonly used separator in a rechargeable lithium battery, which can separate the positive electrode 20 and the negative electrode 30 and provide a transmission channel for lithium ions.

[0147] For example, the separator 40 may have a low resistance to ion transport and excellent or suitable impregnability for the electrolyte solution. For example, in one or more embodiments, the separator may be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof. In some embodiments, the separator may be in the form of a non-woven fabric or a woven fabric. For example, in some embodiments, in a lithium-ion battery, polyolefin polymers (such as polyethylene and polypropylene) separators may be mainly used. To ensure heat resistance or mechanical strength, a coated separator including a ceramic component or a polymer material may be used. In some embodiments, the separator may have a single-layer or multi-layer structure.

[0148] The electrolyte is not particularly limited. The electrolyte may be, for example, an organic electrolyte. For example, an organic electrolyte is prepared by dissolving a lithium salt in an organic solvent.

[0149] As the organic solvent, any organic solvent may be used as long as it is used in the art. The organic solvent may be, for example, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, or a mixture thereof.

[0150] As the lithium salt, any lithium salt may be used as long as it is used in the art. The lithium salt may be, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2)(1 ≤ x ≤ 20, 1 ≤ y ≤ 20), LiCl, LiI, or a mixture thereof.

[0151] The binder of the present disclosure and the rechargeable battery including the binder will be further described below with specific examples.

[0152] Example 1

[0153] (Preparation of the Binder)

[0154] Prepare an anhydrous and deoxygenated environment using a Schlenk system. Add 225 g of cyclohexane and 4.5 g of styrene to a 1 L reaction flask equipped with magnetic stirring. Stir well, and slowly add n-butyllithium to the solution using a syringe until the solution turns slightly yellow and the color no longer fades. Then, raise the temperature to 50 °C and add 0.167×10 -3 mol of n-butyllithium to initiate the polymerization reaction. After reacting for 1 h, introduce 20.5 g of purified butadiene into the reaction solution, maintain the temperature at 50 °C, and continue the reaction for 2 h. At this point, the styrene and butadiene monomers have basically reacted completely, and a styrene-butadiene block copolymer is obtained. Raise the temperature to 70 °C, add 0.48×10 -4 mol of purified octavinylsilsesquioxane to carry out the coupling reaction. After reacting for 2 h, add isopropanol to terminate the coupling reaction (the molar ratio of isopropanol to n-butyllithium is 1:1) to obtain the copolymer.

[0155] Pour the reaction solution into ethanol for precipitation to obtain a white colloidal copolymer as the binder.

[0156] Use GPC to measure the molecular weight of the copolymer. The number-average molecular weight of the first unit structure is approximately 156,000, the number-average molecular weight of the copolymer is approximately 542,000, and the ratio of the number of the first unit structure to the second unit structure in the copolymer is approximately 3.47.

[0157] (Manufacture of the negative electrode)

[0158] Mix the silicon-based negative electrode active material (silicon content: 60 wt%), graphite, and the above binder in a weight ratio of 96:2:2 with toluene to prepare a negative electrode slurry with a solid content of 40 wt%, and stir well. Uniformly coat the negative electrode slurry on one surface of a negative electrode current collector copper foil with a thickness of 10 μm, dry at room temperature, and then vacuum dry at 120 °C under vacuum conditions, and press to prepare the negative electrode.

[0159] (Manufacture of the positive electrode)

[0160] Disperse LiNi 0.91 Co 0.05 Al 0.04 O2, acetylene black, and polyvinylidene fluoride in a solid weight ratio of 97:1.4:1.6 in an N-methylpyrrolidone (NMP) solvent to prepare a slurry with a solid content of 45 wt%, and stir well. Uniformly coat the positive electrode slurry on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, dry at room temperature, and then dry at 120 °C under vacuum conditions, and press to prepare the positive electrode.

[0161] (Manufacture of the separator)

[0162] Use a polypropylene separator (Celgard 3510) as the separator.

[0163] (Manufacture of electrolyte solution)

[0164] Dissolve 1.15 M LiPF6 in ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and ethyl propionate (EP) (volume ratio 3:1:1:3) to obtain the electrolyte solution.

[0165] (Manufacture of coin-type battery)

[0166] Manufacture a coin-type battery using the positive electrode, negative electrode, separator, and electrolyte solution prepared as described above.

[0167] Example 2

[0168] Except for adding 0.55×10 -4 mol octavinylsilsesquioxane to the reaction solution for a coupling reaction, manufacture a coin-type battery in the same manner as in Example 1.

[0169] Example 3

[0170] Except for adding 0.41×10 -4 mol octavinylsilsesquioxane to the reaction solution for a coupling reaction, manufacture a coin-type battery in the same manner as in Example 1.

[0171] Example 4

[0172] Except for adding 0.82×10 -4 mol octavinylsilsesquioxane to the reaction solution for a coupling reaction, manufacture a coin-type battery in the same manner as in Example 1.

[0173] Example 5

[0174] Except for adding 0.33×10 -4 mol octavinylsilsesquioxane to the reaction solution for a coupling reaction, manufacture a coin-type battery in the same manner as in Example 1.

[0175] Example 6

[0176] Except for adding 0.20×10 -4 mol octavinylsilsesquioxane to the reaction solution for a coupling reaction, manufacture a coin-type battery in the same manner as in Example 1.

[0177] Example 7

[0178] A coin-type battery was fabricated in the same manner as in Example 1, except that the amount of styrene added was adjusted to 3 g and the amount of butadiene added was adjusted to 22 g.

[0179] Example 8

[0180] A coin-type battery was fabricated in the same manner as in Example 1, except that the amount of styrene added was adjusted to 6.25 g and the amount of butadiene added was adjusted to 18.75 g.

[0181] Example 9

[0182] A coin-type battery was fabricated in the same manner as in Example 1, except that the reaction monomers were adjusted to 4.5 g of styrene, 18.45 g of butadiene, and 2.05 g of isoprene.

[0183] Example 10

[0184] A coin-type battery was fabricated in the same manner as in Example 1, except that the reaction monomers were adjusted to 4.5 g of styrene, 15.375 g of butadiene, and 5.125 g of isoprene.

[0185] Example 11

[0186] The difference from Example 1 is that after the coupling reaction was completed, the copolymer was transferred to 400 mL of toluene solvent, 0.38 g of maleic anhydride and 0.03 g of azobisisobutyronitrile were added, and after stirring for 1 h, the temperature was raised to 90 °C. After reacting for 1 h, heating was stopped to obtain a copolymer in which the first unit structure further included 1-3 units.

[0187] Example 12

[0188] A coin-type battery was fabricated in the same manner as in Example 11, except that 0.77 g of maleic anhydride and 0.05 g of azobisisobutyronitrile were added.

[0189] Example 13

[0190] The difference from Example 9 is that after the coupling reaction was completed, the copolymer was transferred to 400 mL of toluene solvent, 0.38 g of maleic anhydride and 0.03 g of azobisisobutyronitrile were added, and after stirring for 1 h, the temperature was raised to 90 °C. After reacting for 1 h, heating was stopped to obtain a copolymer in which the first unit structure further included 1-3 units.

[0191] Example 14

[0192] The difference from Example 13 is that 0.51 g of maleic anhydride and 0.04 g of azobisisobutyronitrile were added.

[0193] Example 15

[0194] Except that the addition amount (effective addition amount) of n-butyllithium is adjusted to 0.5×10 -3 mol, and the addition amount of octavinylsilsesquioxane is adjusted to 0.125×10 -3 mol, a coin-type battery is manufactured in the same manner as in Example 1.

[0195] Example 16

[0196] Except that the addition amount (effective addition amount) of n-butyllithium is adjusted to 0.25×10 -3 mol, and the addition amount of octavinylsilsesquioxane is adjusted to 0.07×10 -3 mol, a coin-type battery is manufactured in the same manner as in Example 1.

[0197] Example 17

[0198] Except that the addition amount (effective addition amount) of n-butyllithium is adjusted to 0.125×10 -3 mol, and the addition amount of octavinylsilsesquioxane is adjusted to 0.35×10 -4 mol, a coin-type battery is manufactured in the same manner as in Example 1.

[0199] Example 18

[0200] Except that the addition amount (effective addition amount) of n-butyllithium is adjusted to 0.1×10 -3 mol, and the addition amount of octavinylsilsesquioxane is adjusted to 0.28×10 -4 mol, a coin-type battery is manufactured in the same manner as in Example 1.

[0201] Example 19

[0202] It is different from Example 1 in that after obtaining the copolymer, the copolymer is mixed with N-phenylamino-silsesquioxane as a crosslinking agent, and the two are partially crosslinked using a palladium catalyst to prepare a binder. Among them, the weight of N-phenylamino-silsesquioxane is 0.5% of the weight of the copolymer.

[0203] Example 20

[0204] It is different from Example 19 in that the weight of N-phenylamino-silsesquioxane is 1.0% of the weight of the copolymer.

[0205] Example 21

[0206] The difference from Example 19 is that the weight of N-phenylamino-sesquisiloxane is 1.5% of the weight of the copolymer.

[0207] Example 22

[0208] The difference from Example 13 is that after obtaining the copolymer, the copolymer is mixed with N-phenylamino-sesquisiloxane as a crosslinking agent, and the two are partially crosslinked using a palladium catalyst to prepare a binder. Among them, the weight of N-phenylamino-sesquisiloxane is 1.0% of the weight of the copolymer.

[0209] Example 23

[0210] A coin-type battery is manufactured in the same manner as in Example 1, except that the weight ratio of the silicon-based anode active material (silicon content: 60 wt%), graphite, and binder is adjusted to 96.5:2:1.5.

[0211] Comparative Example 1

[0212] The difference from Example 1 is that a combination binder of sodium carboxymethyl cellulose (CMC) and styrene-butadiene copolymer (SBR) (a linear polymer with a number average molecular weight of 500,000) is used instead of the binder in Example 1, and a negative electrode slurry is prepared with the silicon-based anode active material (silicon content: 60 wt%), graphite, CMC, and SBR in a weight ratio of 96:2:1.2:0.8.

[0213] Comparative Example 2

[0214] Except for adding 1.2×10 -4 mol of octavinyl sesquisiloxane to the reaction solution for a coupling reaction, a coin-type battery is manufactured in the same manner as in Example 1.

[0215] Comparative Example 3

[0216] Except for adjusting the addition amount (effective addition amount) of n-butyllithium to 0.75×10 -3 mol and adjusting the addition amount of octavinyl sesquisiloxane to 0.2×10 -3 mol, a coin-type battery is manufactured in the same manner as in Example 1.

[0217] Comparative Example 4

[0218] Except for adjusting the addition amount (effective addition amount) of n-butyllithium to 0.12×10 -3 mol and adjusting the addition amount of octavinyl sesquisiloxane to 0.27×10-4 Outside of 1 mol, coin-type batteries were manufactured in the same manner as in Example 1.

[0219] Comparative Example 5

[0220] Except that the addition amount (effective addition amount) of n-butyllithium was adjusted to 0.12×10 -3 mol, and the addition amount of octavinylsilsesquioxane was adjusted to 0.27×10 -4 mol, coin-type batteries were manufactured in the same manner as in Example 1.

[0221] Comparative Example 6

[0222] Except that the addition amount of styrene was adjusted to 2.0 g and the addition amount of butadiene was adjusted to 23 g, coin-type batteries were manufactured in the same manner as in Example 1.

[0223] Comparative Example 7

[0224] Except that the addition amount of styrene was adjusted to 7.5 g and the addition amount of butadiene was adjusted to 17.5 g, coin-type batteries were manufactured in the same manner as in Example 1.

[0225] Comparative Example 8

[0226] Except that 1.04 g of maleic anhydride and 0.08 g of azobisisobutyronitrile were added, coin-type batteries were manufactured in the same manner as in Example 11

[0227] Comparative Example 9

[0228] The difference from Example 17 is that the weight of N-phenylamino-silsesquioxane is 2.0% of the weight of the copolymer.

[0229] Evaluation of Binder, Anode Slurry, Anode and Rechargeable Battery

[0230] (Copolymer molecular weight)

[0231] The molecular weights of the copolymers of Examples 1 to 18 and Comparative Examples 2 to 8 were measured by gel permeation chromatography, and the analysis results of the number-average molecular weight Mn of the first component in the copolymer and the number-average molecular weight Mn of the copolymer are shown in Table 1.

[0232] (Viscosity)

[0233] The copolymers of Examples 1 to 18 and Comparative Examples 2 to 8 were dissolved in toluene, and the viscosities of the solutions with a solid content of 7 wt% were measured at 25°C. The results are shown in Table 1.

[0234] (Crosslinking Degree Test)

[0235] Test the crosslinking degree of the binders in Test Examples 19 to 22 and Comparative Example 9. The crosslinking degree of the binder was tested by the immersion dissolution method. Take 1 g of the binder sample, soak it in acetone or carbon tetrachloride solvent for 7 days, then take out the sample, dry and weigh it to obtain the mass (w1) of the sample after immersion. Calculate the crosslinking degree according to the weight change before and after immersion. Crosslinking degree = w1 × 100%. The results are shown in Table 2.

[0236] (Coating Performance)

[0237] Coat the negative electrode slurries of Examples 1 to 23 and Comparative Examples 1 to 9 on copper foils respectively, and dry to obtain the negative electrode active material layer. Check whether the negative electrode active material layer is cracked to evaluate the coating performance. The results are shown in Table 3.

[0238] The coating performance evaluation was carried out according to the following evaluation criteria.

[0239] ○: No cracks occurred

[0240] ×: Cracks occurred

[0241] (Swelling Degree Test)

[0242] Cut the binders of Examples 1 to 23 and Comparative Examples 1 to 9 into samples of 10 mm × 20 mm, weigh the mass (w0) of the sample before immersion, then soak the sample in the electrolyte at 60 °C for 48 hours, dry the solvent on the surface of the sample, and weigh the mass (w2) of the sample after swelling. Each sample was weighed three times during the test. Swelling degree = (w2 - w0) / w0 × 100%. The results are shown in Table 3.

[0243] (Adhesion)

[0244] Dry the negative electrodes of Examples 1 to 23 and Comparative Examples 1 to 9 in an oven at 60 °C for 15 h, cut them into strip samples of 10 mm × 20 mm, paste the samples on a 30 mm × 60 cm steel plate through double-sided tape, roll them 8 times with a small stick, fix the steel plate in the lower clamp of the tensile machine, clamp the sample with the upper clamp, and stretch it by 5 mm at a constant rate of 5 mm / min. The included angle between the pulled part of the sample and the steel plate in space is 180°. Finally, the average value of the pulling force in the stable area is recorded as the adhesion of the negative electrode active material layer. The results are shown in Table 3.

[0245] (DC Internal Resistance (DR-IR))

[0246] At 25 °C, the rechargeable lithium battery was charged at a constant current of 0.7C until fully charged, cut off at 0.02C, and left to stand for 10 minutes; after discharging at a constant current of 0.5C for 30 seconds, it was charged at a constant current of 0.5C for 30 seconds and left to stand for 10 minutes; after discharging at a constant current of 1.0C for 30 seconds, it was charged at a constant current of 0.5C for 1 minute and left to stand for 10 minutes; after discharging at a constant current of 2.0C for 30 seconds, it was charged at a constant current of 0.5C for 2 minutes and left to stand for 10 minutes; after discharging at a constant current of 3.0C for 30 seconds, it was charged at a constant current of 0.5C for 3 minutes and left to stand for 10 minutes; the DC-IR was calculated based on the ratio of the average voltage change (ΔV) and the average current change (ΔI) during discharging at a constant current at each C-rate (where R = ΔV / ΔI), and its average value was used as the measured value. The results are shown in Table 3.

[0247] (Capacity retention rate after 100 cycles)

[0248] The rechargeable battery cells of Examples 1 to 23 and Comparative Examples 1 to 9 were respectively charged at a constant current of 0.1CA to 4.3V based on the designed capacity in a 25 °C thermostat, and then charged at a constant voltage of 4.3V to 0.05CA. Then, the battery was discharged at a constant current of 0.1CA to 2.5V.

[0249] Subsequently, in a 25 °C thermostat, under the conditions of a charging cut-off voltage of 4.3V and a discharging cut-off voltage of 2.5V, the cell was charged at a constant current of 0.2CA, charged at a constant voltage of 0.05CA, and discharged at a constant current of 0.2CA. This was regarded as one cycle, and thus measured relative to the initial discharge capacity.

[0250] Subsequently, under the conditions of a charging cut-off voltage of 4.3V and a discharging cut-off voltage of 2.5V, the rechargeable battery cell was charged at a constant current of 0.5CA at 25 °C, charged at a constant voltage of 0.05CA, and discharged at a constant current of 0.5CA, and repeated 100 cycles for the cycle life test.

[0251] Subsequently, after 100 cycles, the battery was charged at a constant current of 0.2CA, charged at a constant voltage of 0.05CA, and discharged at 0.2CA to measure the discharge capacity. Then, the discharge capacity was divided by the initial discharge capacity to obtain the capacity retention rate after 100 cycles. The results are shown in Table 3.

[0252] (Negative electrode swelling rate after 100 cycles)

[0253] The battery cells of Examples 1 to 23 and Comparative Examples 1 to 9 after undergoing the above 100 cycles were disassembled, and the negative electrodes were taken out. The thickness of the negative electrodes was measured in micrometers and then compared with the thickness of the negative electrodes before the first charge to evaluate the swelling rate of the negative electrodes after 100 cycles. The results are shown in Table 3.

[0254] Here, the swelling rate of the negative electrode was calculated according to [(thickness of the negative electrode after charging - thickness of the negative electrode before charging) / thickness of the negative electrode before charging] × 100%.

[0255] (Peeling of the negative electrode active material layer after 100 cycles)

[0256] For the negative electrodes of Examples 1 to 23 and Comparative Examples 1 to 9, the negative electrodes after undergoing the above 100 cycles were visually inspected and evaluated according to the following criteria. The results are shown in Table 3.

[0257] ○: No negative electrode active material layer peeled off from the copper foil. △: Part of the negative electrode active material layer peeled off from the copper foil. ×: All of the negative electrode active material layer peeled off from the copper foil.

[0258] (Table 1)

[0259]

[0260]

[0261] In Table 1, the wt% of Unit 1-1, Unit 1-2, and Unit 1-3 is the weight percentage of Unit 1-1, Unit 1-2, and Unit 1-3 in the first component. The wt% of Ip is the weight percentage of isoprene in Unit 1-2. The molecular weight of the first component and the molecular weight of the copolymer are number average molecular weights.

[0262] (Table 2)

[0263] Crosslinking Agent Content (%) Degree of Crosslinking (%) Example 19 0.5 12 Example 20 1.0 24 Example 21 1.5 35 Example 22 1.0 25 Comparative Example 9 2.0 43

[0264] Table 2 shows the crosslinking agent content in the binders of Examples 19 to 22 and Comparative Example 9. The crosslinking agent content (%) refers to the percentage of the weight of the crosslinking agent to the weight of the copolymer. It can be seen from Table 2 that as the content of the crosslinking agent increases, the degree of crosslinking increases. For Comparative Example 9, the degree of crosslinking has reached 43%.

[0265] (Table 3)

[0266]

[0267]

[0268] Table 3 shows some test performances of the binders, negative electrodes, and rechargeable batteries of Examples 1 to 23 and Comparative Examples 1 to 9.

[0269] As can be seen from Table 3, compared with the CMC-SBR composite binder of Comparative Example 1, the binders of Examples 1 to 23 have a lower degree of swelling. Compared with the negative electrode using the CMC-SBR composite binder of Comparative Example 1, the swelling rate of the negative electrodes of Examples 1 to 23 using the binder according to the present disclosure after 100 cycles is lower. This shows that the binder of the present disclosure has improved swelling resistance, and the negative electrode including it has improved volume stability and structural stability. Compared with the negative electrode using the CMC-SBR composite binder of Comparative Example 1, the capacity retention rate of the negative electrodes of Examples 1 to 23 using the binder according to the present disclosure after 100 cycles is relatively low, indicating that the binder of the present disclosure also improves the life of the rechargeable battery. Compared with the negative electrode using the CMC-SBR composite binder of Comparative Example 1, the DC internal resistance of the negative electrodes of Examples 1 to 5 is relatively low, indicating that using the binder according to the present disclosure can improve the lithium battery transmission efficiency and reduce the battery internal resistance.

[0270] The adhesion of the negative electrodes of Comparative Examples 2 and 3 is poor, and a certain degree of peeling occurs in the negative electrode active material layer after 100 cycles. This shows that if the ratio of the amount of the first component to the second component in the copolymer is too low or the relative molecular weight of the first component is too low, it will lead to deterioration of adhesion, affect the adhesion of the negative electrode active material layer to the current collector, and will also lead to deterioration of the negative electrode swelling rate and capacity retention rate.

[0271] The capacity retention rate, negative electrode swelling rate, and DC internal resistance of the negative electrode of Comparative Example 4 are poor. This may be because the relative molecular weight of the first component in its copolymer is too large, the molecular chain is long, and some molecular chains will break after multiple cycles, resulting in an increase in the negative electrode swelling rate. At the same time, this will also lead to a decrease in the adhesion to the electrode active material, resulting in a decrease in the capacity retention rate of the negative electrode. In addition, the first component with a larger molecular weight hinders the transmission of lithium ions to a certain extent.

[0272] The binder of Comparative Example 5 cannot fabricate a negative electrode, which may be because the relative molecular weight of its copolymer is too large, making it difficult to dissolve in the solvent when preparing the negative electrode slurry and difficult to prepare the negative electrode slurry.

[0273] The binder of Comparative Example 6 has a large degree of swelling, and the negative electrode also has a high swelling rate. This may be because the content of 1-1 units in its first component is too low, and the content of the hard block is low, resulting in poor volume stability of the negative electrode.

[0274] Comparative Example 7 has a lower adhesion, which may be because the content of 1-2 units in its first component is too low and the content of the soft block is low.

[0275] There are too many 1-3 units in the copolymer of Comparative Example 8, and adhesion is likely to occur during the preparation of the negative electrode slurry, so the negative electrode cannot be prepared.

[0276] There is too much cross-linking agent in the binder of Comparative Example 9, resulting in too high rigidity of the binder and making it difficult to prepare the negative electrode slurry.

[0277] Examples 11 to 14 show relatively high adhesion because the addition of 1-3 units improves the adhesion of the binder. Similarly, Examples 19 to 22 also show relatively high adhesion because the addition of the cross-linking agent improves the adhesion of the binder.

[0278] In addition, by comparing Examples 1 to 6, it can be found that the DC internal resistance of Example 6 is relatively high because the number of the first components in the copolymer is too large, which hinders the lithium ion transport channels to a certain extent. The adhesion of Example 4 is relatively low, indicating that the copolymer containing about 2 first components has limited improvement in adhesion.

[0279] In addition, in Example 23, a relatively lower binder weight ratio (1.5 wt%) was adopted, and the obtained binder, the prepared negative electrode and the rechargeable battery also showed excellent swelling resistance, volume stability, capacity retention rate and DC internal resistance. This shows that the binder according to the present disclosure can still have the ability to improve battery performance with a relatively small amount.

[0280] According to the embodiments of the present disclosure, the binder for a rechargeable battery may include a copolymer, the copolymer may include a plurality of first components and one second component combined with the plurality of first components, the first component includes 1-1 units derived from monovinyl aromatic monomers and 1-2 units derived from conjugated diene monomers, and the second component is derived from vinyl sesquisiloxane or its derivatives. The ratio of the number of the first component to the second component may be 2:1 to 5:1. The first component may further include 1-3 units derived from carboxyl-containing unsaturated olefin monomers. In addition, the binder may further include a cross-linking agent.

[0281] The above binder can at least have improved swelling resistance, thereby improving the volume stability and structural stability of the electrode including the same.

[0282] Although the present disclosure has been described in connection with currently considered practical exemplary embodiments, it will be understood that the present disclosure is not limited to the disclosed embodiments, but on the contrary, is intended to cover one or more suitable modifications and equivalent arrangements included within the spirit and scope of the appended claims and their equivalents.

Claims

1. A binder for the negative electrode of a rechargeable battery, characterized in that, The binder includes a copolymer, and the copolymer includes: A plurality of first components, each first component having a linear or branched structure, each first component including 1-1 units derived from monovinyl aromatic monomers and 1-2 units derived from conjugated diene monomers; and A second component, derived from vinylsilsesquioxane or its derivatives, constituting the core node of the copolymer, wherein, in the copolymer, the plurality of first components are respectively bonded to the vinyl groups of the one second component, The ratio of the number of the first components to the second component in the copolymer is 3:1 to 5:1, The number average molecular weight of the copolymer is in the range of 400,000 to 800,000, and Based on the total weight of 100 wt% of the first component, the content of 1-1 units is in the range of 12 wt% to 25 wt%, and the content of 1-2 units is in the range of 75 wt% to 88 wt%.

2. The binder for the negative electrode of a rechargeable battery according to claim 1, characterized in that, The binder further includes a crosslinking agent, and the crosslinking agent includes units derived from amino silsesquioxane or its derivatives.

3. The binder for the negative electrode of a rechargeable battery according to claim 1, characterized in that, The first component further includes 1-3 units derived from carboxyl-containing unsaturated olefin monomers.

4. The binder for the negative electrode of a rechargeable battery according to claim 3, characterized in that, The carboxyl-containing unsaturated olefin monomer is selected from at least one of (meth)acrylic acid or its anhydride, maleic acid or its anhydride, and vinylbenzoic acid or its anhydride.

5. The binder for the negative electrode of a rechargeable battery according to claim 1, characterized in that, The monovinyl aromatic monomer is selected from at least one of styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 2,4-dimethylstyrene, vinylnaphthalene, vinyltoluene, vinylxylene, adamantylstyrene, vinylanthracene, vinylbiphenyl, 1,1-diphenylethylene.

6. A negative electrode, characterized in that, The negative electrode includes the binder for the negative electrode of a rechargeable battery according to any one of claims 1 to 5.

7. A rechargeable battery, the rechargeable battery includes: The negative electrode according to claim 6; A positive electrode; And A separator, between the negative electrode and the positive electrode.

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