A negative electrode binder, a method for preparing the same, and an application thereof

Abstract

The present application relates to a kind of negative electrode binder and its preparation method and application, and the present application belongs to electrochemistry technical field.The preparation raw material of the negative electrode binder includes N-vinyl pyrrolidone monomer, fluorinated acrylic ester monomer, polyoxyethylene ether monomer and latent crosslinking monomer;The latent crosslinking monomer includes acrylamide compound.The negative electrode binder provided by the present application is time-controllable self-crosslinking copolymer binder, which has excellent bonding performance, and the negative electrode plate made of it has high peel strength, low internal resistance and good capacity cycle stability, thereby meeting the needs of solid-state battery high voltage, large rate charge and discharge and other requirements well, and has strong practicability.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, and in particular to a negative electrode binder, its preparation method, and its application. Background Technology

[0002] Silicon anode materials boast a theoretical specific capacity of up to 4200 mAh / g (approximately 10 times that of graphite anodes) and a low lithium intercalation potential (~0.4 V vs. Li / Li). + Silicon, with its abundant reserves in the Earth's crust, is considered a key technological path for solid-state batteries to achieve an energy density exceeding 350 Wh / kg. However, the commercial application of silicon anodes still faces fundamental technological bottlenecks: the lithium insertion / extraction process is accompanied by a lattice expansion rate of over 300%, triggering a series of cascading failure mechanisms. First, the repeated expansion and contraction of active material particles leads to their own pulverization and breakage, disrupting the physical contact with conductive agents and current collectors. Second, traditional binders such as polyvinylidene fluoride (PVDF) and sodium carboxymethyl cellulose / styrene-butadiene rubber (CMC / SBR) are prone to chain segment slippage, plastic deformation, or even fracture failure under this mechanical stress, failing to maintain the integrity of the electrode structure. More seriously, in solid-state battery systems, the solid-solid contact interface between silicon particles and solid electrolyte continuously degrades due to volume changes, interrupting ion conduction pathways and causing a sharp increase in interface impedance, ultimately leading to rapid capacity decay and a cycle life of less than 100 cycles.

[0003] Currently used binders on the market, such as sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA) binders, still have some shortcomings, such as insufficient bonding strength, poor dispersibility, and poor suspension performance, resulting in low peel strength, high internal resistance, and poor cycle performance of the manufactured negative electrode sheets. Furthermore, existing silicon-based negative electrode materials and binders have not completely solved problems such as volume expansion, poor conductivity, and insufficient adhesion during cycling, making it difficult to meet the requirements of high-performance lithium-ion batteries. At the same time, none of the aforementioned binders have solved the problems of poor conductivity and inability to withstand high voltage, making it difficult to meet the requirements of solid-state batteries for high voltage and high-rate charge / discharge.

[0004] Therefore, developing a negative electrode binder with excellent bonding properties that can meet the requirements of high voltage and high-rate charge and discharge of solid-state batteries has become an urgent problem to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a negative electrode binder, its preparation method, and its application. The negative electrode binder is a time-controllable self-crosslinking copolymer binder with excellent bonding performance. When applied to solid-state batteries, it can effectively meet the requirements of high voltage and high-rate charge / discharge, demonstrating strong practicality.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a negative electrode binder, wherein the raw materials for preparing the negative electrode binder include N-vinylpyrrolidone monomer, fluoroacrylate monomer, polyoxyethylene ether monomer and latent crosslinking monomer;

[0008] The latent crosslinking monomers include acrylamide compounds.

[0009] This invention optimizes the design of raw materials for preparing the negative electrode binder. It copolymerizes latent crosslinking monomers with N-vinylpyrrolidone monomers, polyoxyethylene ether monomers, and fluorinated acrylate monomers to construct a hybrid network that combines rigidity and flexibility with dynamic and static characteristics. This network can intelligently respond to the cyclic strain of silicon particle expansion and contraction. The negative electrode binder exhibits excellent bonding performance, and the resulting negative electrode sheet has high peel strength, low internal resistance, and good capacity cycle stability. Therefore, it can well meet the requirements of high voltage and high-rate charge and discharge of solid-state batteries, making it highly practical.

[0010] Furthermore, the negative electrode binder provided by the present invention has the following advantages:

[0011] I. Molecular-level temporal control is possible: By adopting a "protection-activation" strategy, the two-stage decoupling of polymerization and curing is achieved. It can achieve structural design of copolymer molecules (negative electrode binder) without crosslinking during the polymerization stage. In the preparation of negative electrode sheets, the negative electrode binder can achieve precise temporal control of efficient curing through thermal triggering after coating. This overcomes the dilemma of the traditional self-crosslinking polymer in terms of the trade-off between storage stability and reactivity. In other words, it effectively solves the technical bottleneck of traditional crosslinking binders being prone to gelation in the slurry stage and uneven crosslinking in the electrode.

[0012] II. It can construct a stress-response intelligent network: by integrating permanent cross-linking and dynamic covalent bonds, the negative electrode binder can be applied to the electrode to give the electrode active stress dissipation capability, thereby giving the silicon negative electrode of solid-state battery intelligent response capability of stress self-adaptation and interface self-repair.

[0013] III. It can achieve interface molecular stitching: By using latent crosslinking monomers, a two-way functional group (N-alkoxy and acrylamide group) design is introduced, which upgrades the resulting negative electrode binder from "bonding" to "stitching", thereby achieving the purpose of silicon-current collector integrated structure design.

[0014] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0015] As a preferred embodiment of the present invention, the raw materials for preparing the negative electrode binder include the following components in parts by weight:

[0016] 20-35 parts of N-vinylpyrrolidone monomer;

[0017] 15-30 parts of fluoroacrylate monomer;

[0018] 30-50 parts of polyoxyethylene ether monomer;

[0019] 3-8 parts of latent crosslinking monomer.

[0020] This invention designs the raw materials for preparing the negative electrode binder. By using a combination of specific amounts of N-vinylpyrrolidone monomer, fluoroacrylate monomer, polyoxyethylene ether monomer, and latent crosslinking monomer, the resulting negative electrode binder can have excellent bonding strength, dispersibility, and suspension properties. The negative electrode sheet made from it has high peel strength, low internal resistance, and good cycle performance.

[0021] Furthermore, when the content of latent crosslinking monomers is low, the crosslinking network structure is sparse, which reduces both peel strength and capacity cycling retention. When the content of latent crosslinking monomers is high, the crosslinking is too high and the structure is dense, which is not conducive to the ion transport of polyether chains, resulting in increased internal resistance and decreased ionic conductivity.

[0022] The weight percentage of N-vinylpyrrolidone in the raw materials for preparing the negative electrode binder provided by the present invention can be 20 parts, 22 parts, 24 parts, 26 parts, 28 parts, 30 parts, 32 parts or 35 parts, as well as specific values ​​between the above-mentioned values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0023] The weight percentage of fluoroacrylate monomer in the raw materials for preparing the negative electrode binder provided by the present invention can be 15 parts, 17 parts, 20 parts, 22 parts, 24 parts, 26 parts, 28 parts or 30 parts, as well as specific values ​​between the above-mentioned values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0024] The weight percentage of polyoxyethylene ether monomer in the raw materials for preparing the negative electrode binder provided by the present invention can be 30 parts, 32 parts, 34 parts, 36 parts, 38 parts, 40 parts, 42 parts, 44 parts, 46 parts, 48 ​​parts or 50 parts, as well as specific values ​​between the above-mentioned values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0025] The weight percentage of the latent crosslinking monomer in the raw materials for preparing the negative electrode binder provided by the present invention can be 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, 5.5 parts, 6 parts, 6.5 parts, 7 parts, 7.5 parts, or 8 parts, as well as specific values ​​between the above-mentioned values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0026] As a preferred embodiment of the present invention, the fluoroacrylate monomer includes any one or a combination of at least two of hexafluorobutyl acrylate, octafluoropentyl acrylate, or dodecafluoroheptyl acrylate.

[0027] As a preferred embodiment of the present invention, the polyoxyethylene ether monomer includes any one or a combination of at least two of ethylene glycol monovinyl polyoxyethylene ether (EPEG), allyl polyoxyethylene ether (APEG), isopentenyl polyoxyethylene ether (TPEG) or methyl allyl polyoxyethylene ether (HPEG).

[0028] As a preferred embodiment of the present invention, the molecular weight of the polyoxyethylene ether monomer is 1000-3000, for example, it can be 1000, 1200, 1400, 1600, 1800, 2000, 2200, 2400, 2600, 2800 or 3000, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0029] This invention optimizes the molecular weight of polyoxyethylene ether monomers to achieve a synergistic effect between grafting reactivity and chain segment mobility, effectively balancing the adhesion strength and conductivity of the synthesized negative electrode binder. When the molecular weight of the polyoxyethylene ether monomer is low, it hinders the formation of effective chain segment entanglement and ion transport channels, leading to a decrease in the ionic conductivity of the resulting material. Conversely, when the molecular weight of the polyoxyethylene ether monomer is high, the significant steric hindrance greatly reduces its reactivity and grafting efficiency during polymerization, resulting in insufficient density of effective adhesive groups in the polymer, thereby weakening the overall adhesion strength of the obtained negative electrode binder.

[0030] It should be noted that the molecular weight of the polyoxyethylene ether monomer in this invention refers to the average relative molecular mass measured by A.3 in Appendix A of GB 1886.302-2021.

[0031] As a preferred embodiment of the present invention, the polyoxyethylene ether monomer is 30-40 parts by weight, for example, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 or 40 parts, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0032] This invention optimizes the weight percentage of polyoxyethylene ether monomers to achieve an optimal balance between the conductivity and mechanical strength of the resulting negative electrode binder. When the weight percentage is low, the introduced polyether chain density is insufficient, failing to form a continuous and interconnected effective ion transport network within the polymer matrix, leading to decreased ionic conductivity and affecting the battery's rate performance. When the weight percentage is high, its long-chain flexible structure exerts a significant "plasticizing effect" on the polymer matrix, significantly reducing the overall glass transition temperature of the binder system, thereby weakening its cohesive strength and modulus, failing to meet the high strength requirements for maintaining structural integrity during cycling.

[0033] As a preferred embodiment of the present invention, the structural formula of the acrylamide compound is as follows: ;

[0034] R1 is selected from H or C1-C3 alkyl groups;

[0035] R2 is selected from substituted or unsubstituted C1-C3 alkyl groups, wherein the substituted group is selected from C1-C3 alkyl or C6-C18 aryl.

[0036] Among them, C1-C3 can be C1, C2 or C3, and C6-C18 can be C6, C9, C10, C11, C12, C14, C15, C16 or C18.

[0037] Preferably, the acrylamide compound includes any one or a combination of at least two of N-n-butoxymethacrylamide, N-isobutoxymethacrylamide, or N-methoxymethacrylamide.

[0038] Preferably, the raw materials for preparing the negative electrode binder also include an initiator.

[0039] Preferably, the initiator includes azo initiators and / or organic peroxide initiators.

[0040] Preferably, the azo initiator includes any one or a combination of at least two of azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN), or azobisisovalerate (AMBN).

[0041] Preferably, the organic peroxide initiator includes any one or a combination of at least two of tert-butyl peroxypentanoate, benzoyl peroxide (BPO), or lauroyl peroxide (LPO).

[0042] Preferably, the mass of the initiator is 0.5-3% of the total mass of the monomer, for example, it can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8% or 3%, and specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0043] It should be noted that the "total mass of monomers" refers to the sum of the weight parts of N-vinylpyrrolidone monomer, fluoroacrylate monomer, polyoxyethylene ether monomer, and latent crosslinking monomer.

[0044] Preferably, the raw materials for preparing the negative electrode binder further include a solvent, wherein the solvent includes water.

[0045] Preferably, the mass concentration of the polyoxyethylene ether monomer in the solvent is 40-60%, for example, it can be 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58% or 60%, and specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0046] In a second aspect, the present invention provides a method for preparing the negative electrode binder as described in the first aspect, the method comprising the following steps:

[0047] The negative electrode binder is obtained by mixing polyoxyethylene ether monomer with an optional solvent, adding N-vinylpyrrolidone monomer, fluoroacrylate monomer, latent crosslinking monomer and optional initiator.

[0048] In this invention, the polyoxyethylene ether monomer has low activity. By preferentially mixing the polyoxyethylene ether monomer with the solvent before adding other raw material monomers, the grafting rate of the polyoxyethylene ether can be improved, thereby better copolymerizing with other monomers. This facilitates the design optimization of the molecular structure of the negative electrode binder, resulting in higher peel strength, lower internal resistance, and better capacity cycle stability when applied to batteries.

[0049] Preferably, the mixing process further includes a step of heating to 60-80°C, for example, 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C or 80°C, as well as specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0050] Preferably, the N-vinylpyrrolidone monomer, fluoroacrylate monomer, latent crosslinking monomer, and optional initiator are added at a time of 2-6 h, for example, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, or 6 h, as well as specific values ​​between the above-mentioned time points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0051] Preferably, the reaction is carried out in a protective gas atmosphere, the protective gas including any one or a combination of at least two of nitrogen, argon or helium.

[0052] The reaction includes a heat preservation reaction, the heat preservation reaction time is 1-3 h, for example, it can be 1 h, 1.2 h, 1.5 h, 1.8 h, 2 h, 2.2 h, 2.5 h, 2.8 h or 3 h, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific point values ​​included in the range.

[0053] Thirdly, the present invention provides a negative electrode sheet, the negative electrode sheet comprising a silicon-carbon negative electrode material, conductive carbon black, water, and the negative electrode binder described in the first aspect.

[0054] Preferably, the negative electrode sheet is prepared by the following method, which includes the following steps:

[0055] The silicon-carbon anode material, conductive carbon black, anode binder and water are mixed and coated onto the surface of a substrate, and then dried to obtain the anode sheet.

[0056] Preferably, the drying temperature is ≥100℃ and the drying time is 10-60 min.

[0057] The curing temperature of the negative electrode binder provided by this invention is perfectly matched with the existing electrode drying process, requiring no additional equipment, and has good process compatibility. It also solves the problem of the sensitivity of solid electrolytes to humidity (the curing process can be completed in a protective gas atmosphere).

[0058] The drying temperature can be 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃ or 150℃, and the time can be 10 min, 20 min, 30 min, 40 min, 50 min or 60 min, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, this invention will not exhaustively list the specific values ​​included in the range. Furthermore, the drying temperature is preferably 100-130℃.

[0059] In the preparation process of the negative electrode sheet provided by the present invention, when the drying temperature of the electrode sheet rises to 100-130℃, the latent crosslinking monomer groups, such as N-alkoxy groups, undergo alcohol elimination reaction to generate N-hydroxymethyl active intermediates in situ. Subsequently, they undergo rapid condensation with adjacent amide groups to form stable methylene bridges, thereby enabling the negative electrode binder to solidify and crosslink to form a three-dimensional crosslinked solidified network structure.

[0060] The negative electrode binder provided by this invention can achieve a solvation layer peeling effect during the preparation of the negative electrode sheet. In the slurry formed by mixing silicon-carbon negative electrode material, conductive carbon black, negative electrode binder and water, polar groups are wrapped by hydrogen bonds, which can effectively inhibit pre-crosslinking. Then, during the drying process, the water solvent evaporates, the molecular chain segments are released from binding, the effective collision probability increases sharply, and the crosslinking reaction is initiated. This is conducive to realizing the intelligent response capability of stress self-adaptation and interface self-repair of silicon negative electrode in solid-state battery.

[0061] In the preparation process of the negative electrode sheet provided by this invention, the interfacial catalytic effect can be well achieved, and the Cu contained in the oxide layer on the surface of the copper foil... 2+ / Cu + It can act as a coordination center to promote the hydrolysis and condensation of crosslinking groups, thereby achieving "preferential crosslinking at the current collector interface" and enhancing the adhesion between the negative electrode binder and the copper foil.

[0062] It should be noted that in the laboratory preparation process of the negative electrode sheet of the present invention, in order to obtain a fully dried negative electrode sheet, the drying time can be extended according to the actual situation, and is not limited to 10-60 min.

[0063] Fourthly, the present invention provides an application of the negative electrode sheet as described in the third aspect in an energy storage device.

[0064] Preferably, the electrochemical energy storage device includes a solid-state battery.

[0065] Compared with the prior art, the present invention has at least the following beneficial effects:

[0066] The negative electrode binder provided by this invention is prepared by copolymerizing latent crosslinking monomers with N-vinylpyrrolidone monomers, polyoxyethylene ether monomers, and fluorinated acrylate monomers to construct a hybrid network that combines rigidity and flexibility with dynamic and static characteristics. This network can achieve intelligent response to the cyclic strain of silicon particles during expansion and contraction. The negative electrode binder exhibits excellent bonding performance, and the resulting negative electrode sheet has high temperature peel strength (25.9-37.1 N / m), good capacity cycle stability (capacity retention rate of 80-90% after 500 cycles), and low internal resistance (15-45 mΩ). Therefore, it can well meet the requirements of high voltage and high-rate charge and discharge of solid-state batteries, and has strong practicality. Detailed Implementation

[0067] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0068] Unless otherwise specified, the materials and equipment involved in the following detailed embodiments are all conventional materials and equipment in the art and will not affect the technical effects of the present invention.

[0069] Unless otherwise specified, all reagents and raw materials used in the following examples and comparative examples are commercially available products. Some raw material information is as follows:

[0070] Methyl allyl polyoxyethylene ether (HPEG) 1: purchased from Shanghai Dongda Chemical HPEG-2400;

[0071] Methyl allyl polyoxyethylene ether (HPEG) 2: purchased from Shanghai Dongda Chemical HPEG-600;

[0072] Methyl allyl polyoxyethylene ether (HPEG) 3: purchased from Shanghai Dongda Chemical HEPG-1000;

[0073] Methyl allyl polyoxyethylene ether (HPEG) 4: purchased from Shanghai Dongda Chemical HPEG-3000;

[0074] Methyl allyl polyoxyethylene ether (HPEG) 5: purchased from Shanghai Dongda Chemical HPEG-4000;

[0075] Ethylene glycol monovinyl polyoxyethylene ether (EPEG): Purchased from Liaoning Aoke Chemical Co., Ltd. EPEG-3000;

[0076] Allyl polyoxyethylene ether (APEG): purchased from Haian Petrochemical APEG-2400;

[0077] Isopentenyl alcohol polyoxyethylene ether (TPEG): purchased from Shanghai Dongda Chemical TPEG-2400.

[0078] Example 1

[0079] This embodiment provides a negative electrode binder and its preparation method. The raw materials for preparing the negative electrode binder include the following components in parts by weight:

[0080] N-Vinylpyrrolidone (NVP) 25 parts;

[0081] 20 parts of hexafluorobutyl acrylate;

[0082] 1 35 parts of methyl allyl polyoxyethylene ether;

[0083] 6 parts of N-butoxymethylacrylamide;

[0084] Azobisisovalerate (AMBN) 1 part;

[0085] 35 parts of deionized water.

[0086] The preparation method specifically includes the following steps:

[0087] After mixing methyl allyl polyoxyethylene ether 1 with deionized water, the mixture was heated to 70°C. Under a nitrogen atmosphere, NVP, hexafluorobutyl acrylate, N-butoxymethacrylamide, and AMBN were added. The total addition time was controlled to be 4 h. After the addition was completed, the mixture was kept at the temperature for 2 h to obtain the negative electrode binder.

[0088] Example 2

[0089] This embodiment provides a negative electrode binder and its preparation method. The raw materials for preparing the negative electrode binder include the following components in parts by weight:

[0090] N-Vinylpyrrolidone (NVP) 20 parts;

[0091] 15 parts of octafluoroamyl acrylate;

[0092] 40 parts of ethylene glycol monovinyl polyoxyethylene ether (EPEG);

[0093] 8 parts of N-isobutoxymethacrylamide;

[0094] 0.5 parts of tert-butyl peroxypentanoate;

[0095] 60 parts of deionized water.

[0096] The preparation method specifically includes the following steps:

[0097] After mixing EPEG with deionized water, the mixture was heated to 60°C. Under a nitrogen atmosphere, NVP, octafluoropentyl acrylate, N-isobutoxymethacrylamide, and tert-butyl peroxypentanoate were added. The total addition time was controlled to be 2 h. After the addition was completed, the reaction was kept at the temperature for 3 h to obtain the negative electrode binder.

[0098] Example 3

[0099] This embodiment provides a negative electrode binder and its preparation method. The raw materials for preparing the negative electrode binder include the following components in parts by weight:

[0100] N-Vinylpyrrolidone (NVP) 35 parts;

[0101] 25 parts of hexafluorobutyl acrylate;

[0102] 150 parts of allyl polyoxyethylene ether;

[0103] 4 parts of N-butoxymethylacrylamide;

[0104] Two parts of azobisisobutyronitrile (AIBN);

[0105] 35 parts of deionized water.

[0106] The preparation method specifically includes the following steps:

[0107] Allyl polyoxyethylene ether 1 was mixed with deionized water and heated to 75°C. Under a nitrogen atmosphere, NVP, hexafluorobutyl acrylate, N-butoxymethylacrylamide and AIBN were added. The total addition time was controlled to be 5 h. After the addition was completed, the reaction was kept at the temperature for 2 h to obtain the negative electrode binder.

[0108] Example 4

[0109] This embodiment provides a negative electrode binder and its preparation method. The raw materials for preparing the negative electrode binder include the following components in parts by weight:

[0110] N-Vinylpyrrolidone (NVP) 30 parts;

[0111] 30 parts of dodecafluoroheptyl acrylate;

[0112] Isopentenyl alcohol polyoxyethylene ether (TPEG) 30 parts;

[0113] 3 parts of N-methoxymethylacrylamide;

[0114] Benzoyl peroxide (BPO) 2.7 parts;

[0115] 45 parts of deionized water.

[0116] The preparation method specifically includes the following steps:

[0117] After mixing TPEG with deionized water, the mixture was heated to 80°C. Under a nitrogen atmosphere, NVP, dodecafluoroheptyl acrylate, N-methoxymethylacrylamide, and BPO were added. The addition time was controlled to be 6 h. After the addition was completed, the mixture was kept at the temperature for 1 h to obtain the negative electrode binder.

[0118] Example 5

[0119] This embodiment provides a negative electrode binder and its preparation method. The only difference between this embodiment and Example 1 is that the weight of N-butoxymethacrylamide is adjusted from 6 parts to 2 parts. All other raw materials, contents and preparation methods are the same as in Example 1.

[0120] Example 6

[0121] This embodiment provides a negative electrode binder and its preparation method. The only difference between this embodiment and Example 1 is that the weight of N-butoxymethacrylamide is adjusted from 6 parts to 3 parts. All other raw materials, contents and preparation methods are the same as in Example 1.

[0122] Example 7

[0123] This embodiment provides a negative electrode binder and its preparation method. The only difference between this embodiment and Example 1 is that the weight of N-butoxymethacrylamide is adjusted from 6 parts to 8 parts. All other raw materials, contents and preparation methods are the same as in Example 1.

[0124] Example 8

[0125] This embodiment provides a negative electrode binder and its preparation method. The only difference between this embodiment and Example 1 is that the weight of N-butoxymethacrylamide is adjusted from 6 parts to 9 parts. All other raw materials, contents and preparation methods are the same as in Example 1.

[0126] Example 9

[0127] This embodiment provides a negative electrode binder and its preparation method. The only difference between this embodiment and Example 1 is that the methyl allyl polyoxyethylene ether 1 in Example 1 is replaced with an equal weight amount of methyl allyl polyoxyethylene ether 2. All other raw materials, contents and preparation methods are the same as in Example 1.

[0128] Example 10

[0129] This embodiment provides a negative electrode binder and its preparation method. The only difference between this embodiment and Example 1 is that the methyl allyl polyoxyethylene ether 1 in Example 1 is replaced with an equal weight amount of methyl allyl polyoxyethylene ether 3. All other raw materials, contents and preparation methods are the same as in Example 1.

[0130] Example 11

[0131] This embodiment provides a negative electrode binder and its preparation method. The only difference between this embodiment and Example 1 is that the methyl allyl polyoxyethylene ether 1 in Example 1 is replaced with an equal weight amount of methyl allyl polyoxyethylene ether 4. All other raw materials, contents and preparation methods are the same as in Example 1.

[0132] Example 12

[0133] This embodiment provides a negative electrode binder and its preparation method. The only difference between this embodiment and Example 1 is that the methyl allyl polyoxyethylene ether 1 in Example 1 is replaced with an equal weight amount of methyl allyl polyoxyethylene ether 5. All other raw materials, contents and preparation methods are the same as in Example 1.

[0134] Example 13

[0135] This embodiment provides a negative electrode binder and its preparation method. The only difference between this embodiment and Example 1 is that the weight parts of methyl allyl polyoxyethylene ether 1 are adjusted from 35 parts to 25 parts. All other raw materials, contents and preparation methods are the same as in Example 1.

[0136] Example 14

[0137] This embodiment provides a negative electrode binder and its preparation method. The only difference between this embodiment and Example 1 is that the weight parts of methyl allyl polyoxyethylene ether 1 are adjusted from 35 parts to 30 parts. All other raw materials, contents and preparation methods are the same as in Example 1.

[0138] Example 15

[0139] This embodiment provides a negative electrode binder and its preparation method. The only difference between this embodiment and Example 1 is that the weight parts of methyl allyl polyoxyethylene ether 1 are adjusted from 35 parts to 40 parts. The other raw materials, contents and preparation methods are the same as in Example 1.

[0140] Example 16

[0141] This embodiment provides a negative electrode binder and its preparation method. The only difference between this embodiment and Example 1 is that the weight parts of methyl allyl polyoxyethylene ether 1 are adjusted from 35 parts to 45 parts. The other raw materials, contents and preparation methods are the same as in Example 1.

[0142] Example 17

[0143] This embodiment provides a negative electrode binder and its preparation method, which differs from Embodiment 1 only in the preparation method. The preparation method includes the following steps:

[0144] Under a nitrogen atmosphere, NVP, hexafluorobutyl acrylate, methyl allyl polyoxyethylene ether 1, N-butoxymethylacrylamide and AMBN were mixed and reacted at 70°C for 6 h to obtain the negative electrode binder.

[0145] Comparative Example 1

[0146] This comparative example provides a negative electrode binder and its preparation method. The only difference between this example and Example 1 is that the hexafluorobutyl acrylate in Example 1 is replaced with an equal weight of n-butyl acrylate. All other raw materials, contents, and preparation methods are the same as in Example 1.

[0147] Comparative Example 2

[0148] This comparative example provides a negative electrode binder and its preparation method. The only difference between this example and Example 1 is that N-butoxymethacrylamide in Example 1 is replaced with an equal amount of methacrylamide. All other raw materials, contents, and preparation methods are the same as in Example 1.

[0149] Comparative Example 3

[0150] This comparative example provides a negative electrode binder consisting of lithium polyacrylate binder (purchased from Shandong Taihe Technology) and styrene-butadiene emulsion.

[0151] Negative electrode sheets were prepared using the negative electrode binders from Examples 1-17 and Comparative Examples 1-2, respectively. The specific preparation methods included the following steps:

[0152] The negative electrode binder was diluted with deionized water to a solid content of 40%, and then mixed evenly in a mass ratio of silicon-carbon negative electrode material: conductive carbon black: binder (solid content 40%): water = 100:2:5:100 to obtain a slurry. The slurry was then poured onto copper foil for coating and dried in a vacuum drying oven at 120℃ for 30 minutes to obtain the negative electrode sheet. After drying, the electrode sheet was rolled to ensure consistent compaction density. The silicon-carbon negative electrode material used was BTR BAS-2A.

[0153] In addition, the negative electrode binder of Comparative Example 3 was used to prepare a negative electrode sheet. The specific preparation method includes the following steps:

[0154] A slurry was prepared by mixing silicon-carbon anode material, conductive carbon black, lithium polyacrylate binder, styrene-butadiene emulsion, and water in a mass ratio of 100:2:5:1:100. This slurry was then poured onto copper foil for coating and dried in a vacuum drying oven at 120°C for 30 minutes to obtain the anode sheet. After drying, the electrode sheet was rolled to ensure consistent compaction density. The silicon-carbon anode material used was BTR BAS-2A.

[0155] The negative electrode sheets prepared with the negative electrode binder in Examples 1-17 and Comparative Examples 1-3 were cut into 14 mm round sheets using a punching machine. These were then transferred to a glove box for lithium battery assembly. The positive electrode of the lithium battery was NCM811, the separator was Celgard 2400 lithium battery separator, and the electrolyte was EC / DEC / LiPF6 (the volume ratio of ethylene carbonate EC to diethyl carbonate DEC was 1:1, and the concentration of LiPF6 was 1 mol / L). The assembled lithium batteries were tested for electrode peel strength, cycle capacity, internal resistance, and other performance characteristics. The test methods / standards are as follows:

[0156] (1) Peel strength: According to GB 2792-2014 Test method for peel strength of adhesive tape, the peel force of the negative electrode sheet was tested by the 180° peel method. The peel force of the prepared negative electrode sheet was tested by the INSTRON tensile tester at 23℃ and 50% humidity.

[0157] (2) Capacity retention rate: At 45°C, the lithium battery was charged to 4.2 volts at a current of 1C. After the voltage reached 4.2 volts, it was charged at a constant voltage of 4.2 volts with a cutoff current of 0.05C. After resting for 5 minutes, it was discharged to 3 volts at a current of 0.5C. The discharge capacity of the battery was recorded. Then the above charge and discharge steps were repeated to test the capacity retention rate after 500 cycles.

[0158] (3) Internal resistance: The fully charged button battery was left to stand at room temperature for 1 hour to stabilize its voltage. Then, a constant current discharge pulse with a 1C rate and a duration of 10 seconds was applied using a test device with pulse discharge function. The instantaneous voltage drop value ΔV and discharge current I at the start of the pulse were accurately recorded. The result was obtained by calculating the DC internal resistance ≈ ΔV / I using the formula DC internal resistance ≈ ΔV / I.

[0159] The test results are shown in Table 1.

[0160] Table 1

[0161]

[0162] According to the test results in Table 1:

[0163] (1) As can be seen from Examples 1 to 17, the negative electrode sheet prepared by the present invention through copolymerization of specific latent crosslinking monomers with N-vinylpyrrolidone monomers, polyoxyethylene ether monomers and fluorinated acrylate monomers has the characteristics of high peel strength (25.9-37.1 N / m), good capacity cycle stability (capacity retention rate of 80-90% after 500 cycles) and low internal resistance (15-45 mΩ), thus well meeting the requirements of high voltage and high rate charge and discharge of solid-state batteries, and has strong practicality.

[0164] (2) By comparing Example 1 with Examples 5-8, it can be seen that the weight fraction of the latent crosslinking monomer in Example 5 is relatively low, and the peel strength and capacity cycle retention of the negative electrode sheet formed by the negative electrode binder are significantly reduced. In Example 8, the weight fraction of the latent crosslinking monomer is relatively high, and the internal resistance and ionic conductivity of the negative electrode sheet formed by the negative electrode binder are significantly increased. This shows that by adjusting and optimizing the weight fraction of the latent crosslinking monomer, the present invention can further control the adhesion strength and conductivity of the negative electrode binder, thereby obtaining a negative electrode sheet with better overall performance such as higher peel strength and lower internal resistance.

[0165] (3) By comparing Example 1 with Examples 9-12, it can be seen that the molecular weight of the polyoxyethylene ether monomer in Example 9 is relatively low, and the internal resistance and ionic conductivity of the negative electrode sheet formed by the negative electrode binder are significantly increased. In Example 12, the molecular weight of the polyoxyethylene ether monomer is relatively high, and the peel strength of the negative electrode sheet formed by the negative electrode binder is significantly reduced. This shows that by adjusting and optimizing the molecular weight of the polyoxyethylene ether monomer, the present invention can further control the adhesion strength and conductivity of the negative electrode binder, thereby obtaining a negative electrode sheet with higher peel strength, lower internal resistance and better cycle stability.

[0166] (4) By comparing Example 1 with Examples 13-16, it can be seen that the weight fraction of polyoxyethylene ether monomer in Example 13 is relatively low, resulting in increased internal resistance, decreased ionic conductivity, and decreased peel strength of the negative electrode sheet formed by the resulting negative electrode binder. In Example 16, the weight fraction of polyoxyethylene ether monomer is relatively high, resulting in decreased peel strength and capacity cycle retention of the negative electrode sheet formed by the resulting negative electrode binder. This indicates that by adjusting and optimizing the weight fraction of polyoxyethylene ether monomer, the present invention can further control the adhesion strength and conductivity of the negative electrode binder, thereby obtaining a negative electrode sheet with higher peel strength, lower internal resistance, and better cycle stability.

[0167] (5) By comparing Example 1 and Example 17, it can be seen that the negative electrode adhesive of Example 17 was prepared by directly mixing the raw material components. The peel strength and capacity cycle retention of the resulting negative electrode adhesive were significantly reduced, and the internal resistance was significantly increased. This shows that by using the method of preferentially mixing polyoxyethylene ether monomer with solvent and then adding other raw material monomers, the present invention can make the resulting negative electrode adhesive have higher peel strength, better cycle stability and higher ionic conductivity.

[0168] (6) By comparing Example 1 with Comparative Example 1, it can be seen that the conventional acrylate monomer without fluorine was used in Comparative Example 1. The peel strength and capacity cycle retention of the resulting negative electrode binder were reduced, and the internal resistance was increased. This shows that the use of the specific fluorinated acrylate monomer of the present invention can further improve the peel strength, cycle stability and ionic conductivity of the resulting negative electrode binder.

[0169] (7) By comparing Example 1 and Comparative Example 2, it can be seen that Comparative Example 2 uses methacrylamide, that is, it does not use the latent crosslinking monomer of the present invention. The peel strength and capacity cycle retention of the obtained negative electrode binder are significantly reduced, and the internal resistance is significantly increased. This shows that the use of the latent crosslinking monomer of the present invention can further improve the peel strength, cycle stability and ionic conductivity of the obtained negative electrode binder.

[0170] (8) By comparing Examples 1-17 with Comparative Example 3, it can be seen that Comparative Example 3 uses a commercially available negative electrode binder, which has a measured peel strength of 21.1 N / m, a capacity cycle retention rate of only 71.1%, and an internal resistance as high as 93 mΩ. This indicates that its ionic conductivity is poor and its cycle stability is poor. This clearly shows that compared with the prior art, the negative electrode binder provided by the present invention has excellent ionic conductivity and capacity cycle stability while maintaining excellent adhesion performance. It has better overall performance and is more practical.

[0171] In summary, by optimizing the raw material composition and preparation method of the negative electrode binder, this invention can further improve the adhesion strength and conductivity of the negative electrode binder, resulting in a negative electrode sheet with better peel strength (31.7-36.3 N / m) and capacity cycle retention (86-90%), and lower internal resistance (15-32 mΩ). This better meets the requirements of high voltage and high-rate charge and discharge of solid-state batteries, making it highly practical.

[0172] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A negative electrode binder, characterized in that, The raw materials for preparing the negative electrode binder include the following components in parts by weight: 20-35 parts of N-vinylpyrrolidone monomer; 15-30 parts of fluoroacrylate monomer; 30-50 parts of polyoxyethylene ether monomer; 3-8 parts of latent crosslinking monomer; The latent crosslinking monomer includes acrylamide compounds; the structural formula of the acrylamide compound is as follows: ； R1 is selected from H or C1-C3 alkyl groups; R2 is selected from substituted or unsubstituted C1-C3 alkyl groups, wherein the substituted group is selected from C1-C3 alkyl or C6-C18 aryl; The molecular weight of the polyoxyethylene ether monomer is 1000-3000.

2. The negative electrode binder according to claim 1, characterized in that, The fluoroacrylate monomers include any one or a combination of at least two of hexafluorobutyl acrylate, octafluoropentyl acrylate or dodecafluoroheptyl acrylate. The polyoxyethylene ether monomer includes any one or a combination of at least two of ethylene glycol monovinyl polyoxyethylene ether, allyl polyoxyethylene ether, isopentenyl polyoxyethylene ether, or methyl allyl polyoxyethylene ether.

3. The negative electrode binder according to claim 1, characterized in that, The polyoxyethylene ether monomer is present in parts by weight of 30-40.

4. The negative electrode binder according to claim 1, characterized in that, The raw materials for preparing the negative electrode binder also include an initiator; The initiator includes azo initiators and / or organic peroxide initiators; The azo initiator includes any one or a combination of at least two of azobisisobutyronitrile, azobisisoheptanenitrile, or azobisisovalerate. The organic peroxide initiator includes any one or a combination of at least two of tert-butyl peroxypentanoate, benzoyl peroxide, or lauroyl peroxide. The initiator accounts for 0.5-3% of the total mass of the monomers; The raw materials for preparing the negative electrode binder also include a solvent, which includes water; The polyoxyethylene ether monomer has a mass concentration of 40-60% in the solvent.

5. A method for preparing a negative electrode binder as described in any one of claims 1-4, characterized in that, The preparation method includes the following steps: The negative electrode binder is obtained by mixing polyoxyethylene ether monomer with an optional solvent, adding N-vinylpyrrolidone monomer, fluoroacrylate monomer, latent crosslinking monomer and optional initiator.

6. The method for preparing the negative electrode binder according to claim 5, characterized in that, The mixing process also includes a step of heating to 60-80°C; The N-vinylpyrrolidone monomer, fluoroacrylate monomer, latent crosslinking monomer, and optional initiator are added at a time of 2-6 h. The reaction is carried out in a protective gas atmosphere, which includes any one or a combination of at least two of nitrogen, argon, or helium. The reaction includes a heat preservation reaction, the heat preservation reaction time being 1-3 h.

7. A negative electrode sheet, characterized in that, The raw materials for preparing the negative electrode sheet include silicon-carbon negative electrode material, conductive carbon black, water, and the negative electrode binder as described in any one of claims 1-4; The negative electrode sheet is prepared by the following method, which includes the following steps: The silicon-carbon anode material, conductive carbon black, anode binder and water are mixed and coated onto the surface of a substrate, and then dried to obtain the anode sheet. The drying temperature is ≥100℃, and the drying time is 10-60 min.

8. The application of the negative electrode sheet as described in claim 7 in an electrochemical energy storage device; The electrochemical energy storage device includes a solid-state battery.

Images