Secondary battery and electric device

Abstract

This application provides a secondary battery and an electrical device. The secondary battery includes a negative electrode sheet. The negative electrode sheet includes a negative current collector, an active material layer, and a hydrophobic layer arranged sequentially. The hydrophobic layer is disposed on the side of the active material layer opposite to the negative current collector; the hydrophobic layer contains quinone-enriched thiophene copolymer particles, the quinone-enriched thiophene copolymer particles accounting for 80%~90% of the mass of the hydrophobic layer, and the contact angle of the quinone-enriched thiophene copolymer particles with the electrolyte is greater than 150°. This improves the cycle performance of the secondary battery.

Description

Technical Field

[0001] The exemplary embodiments of this application generally relate to the field of batteries, and particularly to secondary batteries and electrical devices. Background Technology

[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and environmental friendliness, have become the core energy source for portable electronic devices, electric vehicles, and large-scale energy storage systems. As a key component of lithium-ion batteries, the performance of the anode material directly affects the overall electrochemical performance of the battery. Currently, graphite is considered one of the ideal anode materials for lithium-ion batteries due to its low cost, moderate lithium intercalation potential, excellent cycle stability, and high theoretical specific capacity. Summary of the Invention

[0003] In a first aspect of this application, a secondary battery is provided. The secondary battery includes a negative electrode sheet, which comprises a negative current collector, an active material layer, and a hydrophobic layer disposed sequentially. The hydrophobic layer is disposed on the side of the active material layer opposite to the negative current collector. The hydrophobic layer contains quinone-enriched thiophene copolymer particles, the quinone-enriched thiophene copolymer particles accounting for 80% to 90% of the mass of the hydrophobic layer, and the contact angle of the quinone-enriched thiophene copolymer particles with the electrolyte is greater than 150°.

[0004] A lyophobic layer, composed primarily of quinone-enriched thiophene copolymer, is deposited on the surface of the active material layer of the negative electrode. This effectively prevents direct contact and side reactions between the electrolyte (e.g., carbonate electrolytes) and the negative electrode active material. This contributes to the formation of a more stable and uniform solid electrolyte interface (SEI) film on the surface of the lyophobic layer. Simultaneously, this lyophobic layer exhibits excellent conductivity for lithium ions, ensuring high ion conductivity of the negative electrode.

[0005] In quinone-enriched thiophene copolymers, the thiophene units (-C4H2S-) and benzoquinone units (-C6H4O2-) form a conjugated structure, and the carbonyl groups of the benzoquinone units are embedded within the polymer under the guidance of internal hydrogen bonding and other forces. This gives the quinone-enriched thiophene copolymer a non-polar surface characteristic. This characteristic provides strong interfacial tension against polar organic electrolytes (e.g., carbonate electrolytes), inhibiting electrolyte penetration into the active material layer and potential side reactions. After tableting, the quinone-enriched thiophene copolymer exhibits a contact angle with the electrolyte exceeding 150°. This strong hydrophobic property effectively protects the active material layer from electrolyte intrusion, thereby reducing the risk of graphite interlayer delamination and improving the cycle performance of the secondary battery.

[0006] Meanwhile, quinone-enriched thiophene copolymers can also construct excellent ion transport channels, enabling rapid and stable lithium-ion transfer between the electrolyte and the active material layer. Specifically, lithium ions in the electrolyte phase are dispersed in a solvated form in a carbonate-based electrolyte solvent, and are encapsulated by carbonate solvent molecules through oxygen atom coordination. During the approach of lithium ions to the hydrophobic layer, lithium ions can undergo partial desolvation by electrostatic attraction with conjugated structures or heteroatoms (e.g., O, S) in the quinone-enriched thiophene copolymer, allowing them to enter the hydrophobic layer (e.g., into the ion transport channels of the quinone-enriched thiophene copolymer). Lithium ions in the hydrophobic layer can migrate through continuous channels between quinone-enriched thiophene copolymer particles, or through the conduction effect of polymer segments (Li... + Under the coordination of the functional groups and heteroatoms of the polymer, the ions migrate between conjugated chain segments and transfer to the active material layer, thereby enabling the active material layer to obtain a continuous and uniform ion flow.

[0007] In some embodiments, the secondary battery provided in this application maintains a graphite interlayer spacing of 0.335 nm after 500 charge-discharge cycles (SEM verification shows structural integrity > 95%), and the capacity retention rate of the secondary battery after 500 charge-discharge cycles is not less than 88%.

[0008] In some embodiments, the hydrophobic layer contains a conductive agent, and the conductive agent accounts for 4% to 10% of the mass of the hydrophobic layer.

[0009] In some embodiments, the mass percentage of the conductive agent, based on the total mass of the hydrophobic layer, can be a range defined by one or any two of the following values: 4 wt%, 6 wt%, 8 wt%, or 10 wt%.

[0010] The conductive agent is uniformly dispersed among the quinone-enriched thiophene copolymer particles, thereby constructing a channel suitable for ion transport. This channel effectively alleviates the problem of lithium-ion migration being hindered by the excessive repulsion of the electrolyte by the hydrophobic layer due to its hydrophobic properties. While preventing the electrolyte solvent from penetrating the hydrophobic layer, it ensures that ions can smoothly pass through the hydrophobic layer during charging and discharging. Furthermore, this structural design does not damage the core hydrophobic structure of the hydrophobic layer, and significantly reduces ion migration resistance, thereby reducing the resistance of the negative electrode.

[0011] In some embodiments, the conductive agent may be at least one of Super P carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, graphene, and conductive ceramic powder.

[0012] In some embodiments, the contact angle between the hydrophobic layer and the electrolyte is greater than 110°.

[0013] The quinone-enriched thiophene copolymer particles, after being mixed with a conductive agent, form a hydrophobic layer that still exhibits good hydrophobic properties towards the electrolyte. This effectively protects the active material layer and reduces electrolyte intrusion into it.

[0014] In some embodiments, the contact angle of the hydrophobic layer with the electrolyte can be one or a range defined by any two of the following values: 110°, 120°, 130°, 140°, or 150°.

[0015] It should be noted that in some embodiments, the electrolyte in the secondary battery provided in this application includes a carbonate-based electrolyte. That is, the quinone-based enriched thiophene copolymer exhibits strong hydrophobic properties to carbonate-based electrolytes. For example, when the quinone-based enriched thiophene copolymer is prepared into a tablet, the contact angle of the quinone-based enriched thiophene copolymer with propylene carbonate (PC) can be controlled to be above 150°. The hydrophobic layer prepared from the quinone-based enriched thiophene copolymer can have a contact angle of above 110° with propylene carbonate.

[0016] Furthermore, the quinone-enriched thiophene copolymer also exhibits good hydrophobicity to other carbonate solvents such as ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC). Therefore, in some embodiments, the electrolyte can also be a composition composed of ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) mixed in a predetermined ratio. The hydrophobic layer can provide effective barrier to such composite carbonate electrolytes, thereby protecting the active material layer.

[0017] In some embodiments, the porosity of the hydrophilic layer is 40% to 70%.

[0018] The highly porous structure of the hydrophore can form a rich and interconnected pore network, shortening the Li... + The diffusion path. By controlling the porosity of the hydrophobic layer within an appropriate range (e.g., 40%~70%), it can ensure the protective structure of the hydrophobic layer for the electrolyte, effectively preventing the electrolyte from penetrating through the hydrophobic layer to the active material layer. On the other hand, it can improve the transport efficiency of lithium ions in the hydrophobic layer.

[0019] In some embodiments, the porosity of the lyophobic layer may be a value or a range defined by any two of the following: 40%, 45%, 50%, 55%, 60%, 65%, or 70%.

[0020] In some embodiments, the quinone-enriched thiophene copolymer particles comprise structural units derived from thiophene and structural units derived from p-benzoquinone, wherein the molar ratio of the structural units derived from thiophene to those derived from p-benzoquinone is (1.5~2.5):1.

[0021] In some embodiments, thiophene (Th) and p-benzoquinone (BQ) can be polymerized under the action of an initiator to obtain a quinone-enriched thiophene copolymer (PTh-BQ). The obtained polymer can be coated onto the surface of the active material layer. In some embodiments, the active material layer and the hydrophobic layer can be simultaneously coated onto the surface of the negative electrode current collector, thereby weakening the interface boundary between the hydrophobic layer and the active material layer and improving the bonding strength between the hydrophobic layer and the active material layer.

[0022] In some embodiments, the quinone-enriched thiophene copolymer particles may further include structural units derived from naphthoquinone and / or anthraquinone. The molar ratio of structural units containing thiophene rings to structural units containing carbonyl groups in the quinone-enriched thiophene copolymer is (1.5~2.5):1. Similarly, naphthoquinone and / or anthraquinone can be used as monomers and polymerized with thiophene under the action of an initiator to obtain quinone-enriched thiophene copolymers.

[0023] In some embodiments, in quinone-enriched thiophene copolymer particles, carbonyl groups are at least partially located inside the quinone-enriched thiophene copolymer particles, and thiophene rings are at least partially located on the surface of the quinone-enriched thiophene copolymer particles.

[0024] By controlling the molar ratio of thiophene to benzoquinone, the structure of the copolymer can be optimized, thereby improving the hydrophobic properties of the polymer. In some embodiments, the carbonyl group derived from p-benzoquinone in the polymer can be embedded inside the polymer under the influence of hydrogen bonding, while the nonpolar thiophene ring is exposed on the polymer surface. This structure ensures the stability of the polymer structure while also making the polymer surface nonpolar, thus exhibiting good hydrophobicity to polar electrolytes (e.g., propylene carbonate).

[0025] In some embodiments, the molar ratio of the structural unit derived from thiophene to the structural unit derived from p-benzoquinone can be a value of 1.5, 1.8, 2, 2.3, or 2.5, or a range defined by any two of these values.

[0026] In some embodiments, the number-average molecular weight of the quinone-enriched thiophene copolymer is 50 kDa to 60 kDa.

[0027] In some embodiments, the number-average molecular weight of the quinone-enriched thiophene copolymer may be a value defined by one or any two of the following: 50 kDa, 52 kDa, 54 kDa, 56 kDa, 58 kDa, or 60 kDa.

[0028] By controlling the molecular weight of quinone-enriched thiophene copolymers, a denser physical entanglement network is formed between polymer chains. This entanglement network enhances the coupling strength between polymer chain segments, effectively suppressing relative slippage and thus improving the tensile strength and toughness of the material. This tensile strength and toughness effectively resist volume changes and mechanical stresses during the charging and discharging process of the negative electrode, preventing coating cracking or peeling and ensuring the long-term stable operation of the negative electrode.

[0029] In some embodiments, the tortuosity τ of the active material layer is 3.5 to 4.5.

[0030] In some embodiments, the active material layer comprises graphite and multi-walled carbon nanotubes (CNTs). The CNTs are vertically oriented to the graphite layer under conditions such as stirring or magnetic field induction, meaning the long axis of the CNTs forms an approximately 90° angle with the graphite layer. The vertically oriented CNTs can form directional pillars between multiple graphite layers, thereby channeling the pores in the active material layer into interconnected channels perpendicular to the graphite layers. Lithium ions can rapidly enter different graphite layers and complete lithium intercalation through these channels. This significantly reduces ion migration resistance, allowing lithium ions to rapidly migrate to their target location within the active material layer. Furthermore, the vertically oriented CNTs can form through-conductive pathways between graphite layers, allowing electrons to migrate between them. Compared to randomly wound CNTs, vertically oriented CNTs shorten the electron transport path, reduce contact resistance, and allow electrons to more efficiently reach the active material surface from the current collector and react electrochemically with lithium ions. In other words, multi-walled carbon nanotubes can simultaneously facilitate ion transport and electron transport, enabling efficient transport of electrons and lithium ions and improving battery rate performance and cycle stability.

[0031] In addition, the high permeability of the active material layer to ions allows ions to be evenly distributed in all areas of the electrode, avoiding excessively high or low local concentrations, thereby significantly reducing concentration polarization.

[0032] In some embodiments, the tortuosity of the active material layer may be a value defined by one or any two of 3.5, 3.8, 4.0, 4.2, or 4.5.

[0033] In some embodiments, the parameters of multi-walled carbon nanotubes can meet at least one of the above parameter standards: purity above 95%, outer diameter of 8~15nm, length of 40~60μm, and specific surface area of ​​120~160 m² / g.

[0034] In some embodiments, the specific capacity of graphite is 350 mAh / g.

[0035] In some embodiments, the compaction density of the active material layer is 1.6 g / cm³. 3 ~1.8 g / cm 3 The porosity of the active material layer is 35%~45%.

[0036] By controlling the compaction density and porosity of the active material layer, the packing density of the active material can be increased, significantly increasing the content of active material per unit volume, thereby improving the battery energy density. Furthermore, controlling the porosity of the active material layer within the range of 35%–45% and / or controlling the compaction density of the active material layer at 1.6 g / cm³... 3 ~1.8 g / cm 3 Within this range, it also helps to form a stable ion conduction network inside the active material layer, thereby optimizing the ion transport efficiency of the negative electrode sheet.

[0037] In some embodiments, the compaction density of the active material layer may be 1.60 g / cm³. 3 1.65 g / cm 3 1.70 g / cm 3 1.75 g / cm 3 1.80 g / cm 3 The range of values ​​defined by one or any two values ​​in the range.

[0038] In some embodiments, the porosity of the active material layer can be 35%, 37%, 40%, 43%, or 45%. In some embodiments, the mass ratio of the active material layer to the hydrophobic layer is (3~5):1.

[0039] By controlling the mass ratio of the active material layer to the hydrophobic layer, the negative electrode sheet can have sufficient active material while ensuring that the hydrophobic layer completely covers the active material layer. In this way, the energy density of the secondary battery is improved while maintaining the protective capability of the hydrophobic layer against the active material layer.

[0040] In some embodiments, the mass ratio of the active material layer to the hydrophobic layer can be one of 3, 3.5, 4, 4.5, or 5, or a range defined by any two of these values.

[0041] In some embodiments, the surface resistivity of the negative electrode is less than or equal to 5 Ω / cm. 2 .

[0042] In a second aspect of this application, an electrical appliance is provided. The electrical appliance includes a secondary battery provided according to the first aspect of this application, the secondary battery serving as a power source for the electrical appliance.

[0043] In some embodiments, the electrical equipment can be application devices such as vehicles, mobile phones, portable devices, laptops, ships, spacecraft, electric toys, and power tools. Vehicles can be new energy vehicles, including pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles; spacecraft include airplanes, rockets, space shuttles, and spacecraft; electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers. This application does not impose special limitations on the above-mentioned devices.

[0044] It should be understood that the content described in this content section is not intended to limit the key or essential features of the embodiments of this application, nor is it intended to restrict the scope of this application. Other features of this application will become readily apparent from the following description. Detailed Implementation

[0045] The embodiments of this application will now be described in more detail. It should be understood that this application can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to provide a more thorough and complete understanding of this application. It should be understood that the embodiments of this application are for illustrative purposes only and are not intended to limit the scope of protection of this application.

[0046] It should be noted that the headings of any section / subsection provided herein are not limiting. Various embodiments are described throughout this document, and embodiments of any type may be included under any section / subsection. Furthermore, embodiments described in any section / subsection may be combined in any way with any other embodiments described in the same section / subsection and / or different sections / subsections.

[0047] In the description of embodiments of this application, the term "comprising" and similar terms should be understood as open-ended inclusion, i.e., "including but not limited to". The term "based on" should be understood as "at least partially based on". The term "one embodiment" or "the embodiment" should be understood as "at least one embodiment". The term "some embodiments" should be understood as "at least some embodiments". Other explicit and implicit definitions may also be included below. The terms "first", "second", etc., may refer to different or the same objects. Other explicit and implicit definitions may also be included below.

[0048] The secondary battery provided in this application embodiment has an active material layer and a hydrophobic layer sequentially disposed on the surface of the negative electrode current collector. The hydrophobic layer includes quinone-enriched thiophene copolymer particles. The quinone-enriched thiophene copolymer has strong hydrophobicity to the electrolyte, which reduces the penetration of the electrolyte into the active material layer and hinders the co-intercalation of solvent molecules such as propylene carbonate between graphite layers, thus reducing the risk of graphite collapse. The hydrophobic layer can preferentially form (e.g., under 0.9V conditions) a dense solid electrolyte interface (SEI) film, thereby protecting the active material layer, reducing the erosion of the active material layer by electrolyte side reactions, and thus improving the cycle performance of the battery. In addition, the high porosity and conductive agent in the hydrophobic layer can also construct an efficient lithium-ion transport channel, shorten the lithium-ion diffusion path, and improve ionic conductivity.

[0049] The secondary battery provided in this application will be further described below with reference to specific embodiments.

[0050] Preparation of quinone-enriched thiophene copolymers Preparation Example 1 S1, 0.017 mol of thiophene (CAS: 110-02-1) and 0.0085 mol of p-benzoquinone (CAS: 106-51-4) were added to 20 ml of chloroform (CHCl3) (the molar ratio of thiophene to p-benzoquinone was 2:1). Then, 1.036 mg of anhydrous ferric chloride (FeCl3) was added as an initiator, and 1 wt% of perfluoroalkylsilane (based on the total mass of thiophene and p-benzoquinone) was added. The mixture was then initially mixed under a nitrogen atmosphere.

[0051] S2 was reacted at 0°C for 4 hours with continuous stirring at a speed of 1000 rpm during the reaction.

[0052] S3, transfer the reactants to an environment of -20°C to cool and let stand for 12 hours.

[0053] S4, after washing and vacuum drying, yields quinone-enriched thiophene copolymer particles.

[0054] Preparation Example 2 The difference from Preparation Example 1 is that in Preparation Example 2, the amount of thiophene used is 0.01955 mol, the amount of p-benzoquinone used is 0.0085 mol (the molar ratio of thiophene to p-benzoquinone is 2.3:1), and the amount of anhydrous ferric chloride used as the initiator is 1.140 mg.

[0055] Preparation Example 3 The difference from Preparation Example 1 is that in Preparation Example 3, the amount of thiophene used is 0.02125 mol, the amount of p-benzoquinone used is 0.0085 mol (the molar ratio of thiophene to p-benzoquinone is 2.5:1), and the amount of anhydrous ferric chloride used as the initiator is 1.121 mg.

[0056] Preparation Example 4 The difference from Preparation Example 1 is that in Preparation Example 4, the amount of thiophene used is 0.02238 mol, the amount of p-benzoquinone used is 0.0085 mol (the molar ratio of thiophene to p-benzoquinone is 2.8:1), and the amount of anhydrous ferric chloride used as the initiator is 1.254 mg.

[0057] Preparation Example 5 The difference from Preparation Example 1 is that in Preparation Example 5, the amount of thiophene used is 0.0255 mol, the amount of p-benzoquinone used is 0.0085 mol (the molar ratio of thiophene to p-benzoquinone is 3:1), and the amount of anhydrous ferric chloride used as the initiator is 1.381 mg.

[0058] Preparation of secondary batteries Example 1 1) Preparation of negative electrode sheet The negative electrode current collector is a double-sided carbon-coated copper foil with a thickness of 6μm and a carbon coating thickness of 1μm on each side.

[0059] Preparation of liquid-phobic slurry The liquefying layer slurry was obtained by dispersing quinone-enriched thiophene copolymer particles, a conductive agent (conductive carbon black), and polyvinylidene fluoride (PVDF) binder in a dispersion medium of N-methylpyrrolidone (NMP) prepared in Preparation Example 1. The solid content of the liquefying layer slurry was 35 wt%. The mass ratio of quinone-enriched thiophene copolymer particles, conductive carbon black, and PVDF in the liquefying layer slurry was 20:1:4. After coating and drying, the N-methylpyrrolidone, serving as the dispersion medium, evaporated, thereby forming a liquefying layer. The quinone-enriched thiophene copolymer particles accounted for 80 wt% of the mass of the liquefying layer, the conductive carbon black accounted for 4 wt%, and the balance was the binder PVDF.

[0060] The preparation method of the liquid-repellent slurry is as follows: Super P carbon black was added to N-methylpyrrolidone, and the conductive carbon black was dispersed in N-methylpyrrolidone by ultrasonication at a power of 500 W for 30 min. Then, quinone-enriched thiophene copolymer particles prepared in Preparation Example 1 were added and stirred for 2 hours at a stirring speed of 200 rpm. Finally, polyvinylidene fluoride was added and stirred for 1 hour at a stirring speed of 1500 rpm to obtain a liquid-phobic slurry.

[0061] Preparation of active material layer slurry The active material layer slurry was obtained by dispersing graphite, multi-walled carbon nanotubes (CNTs), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), and sodium carboxymethyl cellulose (CMC) in an aqueous solution of sodium dodecylbenzenesulfonate (sodium dodecylbenzenesulfonate concentration was 1 wt%). The solid content of the active material layer slurry was 50.5 wt%. The mass ratio of graphite, multi-walled carbon nanotubes, styrene-butadiene rubber, polyacrylonitrile, and sodium carboxymethyl cellulose in the active material layer slurry was 96.7:0.7:1.5:0.5:0.6.

[0062] The preparation method of the active material layer slurry is as follows: Multi-walled carbon nanotubes were dispersed in an aqueous solution of sodium dodecylbenzenesulfonate, followed by the addition of graphite, sodium carboxymethyl cellulose, and styrene-butadiene rubber. The mixture was then ball-milled for 4 hours using a cycle of 15 min forward rotation, 5 min standing, and 10 min reverse rotation to obtain an active material layer slurry.

[0063] Coating of active material layer slurry and hydrophobic layer slurry The active material layer slurry and the hydrophobic layer slurry are sequentially coated onto two opposite surfaces of the negative electrode current collector, with the hydrophobic layer slurry positioned on the side of the active material layer slurry facing away from the negative electrode current collector. After drying, the active material layer and the hydrophobic layer are formed. The active material layer and the hydrophobic layer are sequentially deposited on the surface of the negative electrode current collector to obtain the negative electrode sheet. The coating weight areal density ratio of the hydrophobic layer to the active material layer is 3:7, and the mass ratio of the hydrophobic layer to the active material layer is 3:9.

[0064] 2) Preparation of positive electrode sheet The positive current collector is a double-sided carbon-coated aluminum foil with a thickness of 6μm and a carbon coating thickness of 1μm on each side.

[0065] Lithium iron phosphate, multi-walled carbon nanotubes (CNTs), and polyvinylidene fluoride binder were mixed at a mass ratio of 97.55:0.65:1.8 and added to the solvent N-methylpyrrolidone (NMP). The mixture was stirred under vacuum until homogeneous to obtain a positive electrode slurry. The solid content of the positive electrode slurry was 70%. The positive electrode slurry was uniformly coated on both sides of the positive electrode current collector aluminum foil and dried. After drying, the foil was rolled to obtain the positive electrode sheet.

[0066] 3) Preparation of electrolyte In a glove box with an argon atmosphere containing less than 10 ppm of water, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0067] 4) Assembly of secondary batteries A bare cell is obtained by stacking a positive electrode, a 9µm thick polyethylene separator, and a negative electrode in sequence and winding them. The bare cell is placed in an outer packaging shell, vacuum dried, and then injected with electrolyte. After standing, formation, shaping, and capacity testing, a secondary battery is obtained.

[0068] Examples 2-5 The difference from Example 1 is that the lipolytic layer slurry in Examples 2-5 uses quinone-enriched thiophene copolymer particles prepared in Preparation Examples 2-5, respectively.

[0069] Examples 6-8 The difference from Example 3 is that the mass percentage of quinone-enriched thiophene copolymer particles in the lyophobic layer is different.

[0070] Examples 9-11 The difference from Example 7 is that the mass percentage of the conductive agent in the hydrophobic layer is different.

[0071] Examples 12-15 The difference from Example 9 is that the mass ratio of the active material layer to the hydrophobic layer is different.

[0072] Examples 16 and 17 The difference from Example 13 is that the mass ratio of graphite to multi-walled carbon nanotubes in the active material layer slurry is different.

[0073] Examples 1-17 are shown in Table 1. Table 1

[0074] Note that the copolymers mentioned in Table 1 are the quinone-enriched thiophene copolymer particles prepared in the preparation examples above.

[0075] Comparative Example 1 The difference from Example 13 is that the active material layer of the negative electrode sheet is not coated with a hydrophobic layer on the side facing away from the negative electrode current collector.

[0076] Comparative Example 2 The difference from Example 13 is that the quinone-enriched thiophene copolymer particles in the hydrophobic layer slurry of the negative electrode are replaced with polyaniline particles.

[0077] Performance testing 1) Detection of the hydrophobic properties of propylene carbonate by quinone-enriched thiophene copolymer and hydrophobic layer.

[0078] 1.1) The quinone-enriched thiophene copolymer particles prepared in Examples 1-5 were compressed into tablets with a diameter of 2.5 cm using a tablet press at a pressure of 10 MPa. The tablets were placed on a sample stage, and a drop of propylene carbonate was dropped into the center of the tablet. Images of the side of the droplet were taken using a contact angle meter (Dataphysics OCA 25 model) with a CCD camera, and the contact angle α1 of the quinone-enriched thiophene copolymer to propylene carbonate was calculated.

[0079] 1.2) A drop of propylene carbonate was dropped at the center of the negative electrode prepared in Examples 1-17 and Comparative Examples 1 and 2. Images of the side of the drop were taken using a CCD camera of a contact angle measuring instrument, and the contact angle α2 of the lyophobic layer with propylene carbonate was calculated.

[0080] 2) Detection of the number-average molecular weight of quinone-enriched thiophene copolymers.

[0081] The number-average molecular weight of the quinone-enriched thiophene copolymer was determined and calculated using a high-performance liquid chromatography (Agilent 1260) system. The quinone-enriched thiophene copolymer was dissolved in N-methylpyrrolidone and added to a chromatographic column for elution. The column was a polystyrene-divinylbenzene (PS-DVB) gel column (5 μm, 300 × 7.5 mm, separation range 10³–10⁻⁶). 6 Da), column temperature: 30±0.1℃, mobile phase: chromatographic grade tetrahydrofuran (THF), containing 0.1 wt% LiBr.

[0082] The eluent concentration change was detected using a differential refractive index detector (RI), the elution peak shape and retention time of the sample were recorded, and the number-average molecular weight was calculated.

[0083] 3) The molar ratio k of the quinone-enriched thiophene copolymer derived from thiophene and the structural units derived from p-benzoquinone.

[0084] Using X-ray photoelectron spectroscopy (model: ThermoFisher Scientific K-Alpha): the molar ratio k of structural units derived from thiophene and structural units derived from p-benzoquinone was indirectly calculated by the ratio of S elements (from thiophene) and O elements (mainly from quinone groups).

[0085] 4) Detection of the compaction density ρ of the electrode sheet Cut the electrode sheets into samples with regular geometric shapes and measure the sample dimensions. Weigh the samples and calculate the electrode areal density based on the sample mass and sample area.

[0086] The compaction density ρ of the electrode sheet = electrode sheet surface density / electrode sheet thickness.

[0087] 5) Detection of porosity φ The porosity φ1 of the active material layer and the porosity φ2 of the lyophobic layer were determined using a fully automated mercury porosimeter. Samples with only the active material layer and samples with only the lyophobic layer were placed in the sample cell of the mercury porosimeter, and the porosity φ was calculated.

[0088] φ=V 孔总 / V 表 ×100%.

[0089] 6) Detection of the tortuosity τ of the active material layer.

[0090] The negative electrode sheets prepared in Examples 1-17 and Comparative Examples 1 and 2 were assembled into coin-type symmetrical cells. The resting time of the symmetrical cells was ≥12h. Test parameters: disturbance voltage 5mV, test frequency 5MHz~200mHz, and 6 test frequencies in each frequency band.

[0091] Data processing: The inflection point and the next four points are fitted, and the Warburg coefficient σ is obtained based on the fitting slope.

[0092] Based on formula Calculate the effective diffusion coefficient D eff In the formula, R is the gas constant, T is the thermodynamic temperature, A is the electrode area, n is the number of electrons per mole of reaction, F is the Faraday constant, and C is the volume concentration of the active material in the electrode.

[0093] Then based on the formula Determine the tortuosity τ of the active material. In the formula, ε is the porosity of the electrode material, and D0 is the diffusion coefficient of lithium ions in the bulk electrolyte.

[0094] 7) Detection of the surface resistance R of the negative electrode plate.

[0095] A film resistance meter (model BER1300 (IEST Energy Technology)) with an electrode diameter of 14 mm was used. The negative electrode sheets from Examples 1-17 and Comparative Examples 1 and 2 were cut into rectangular samples of 5 cm × 10 cm. The sample was placed on the sample stage of the resistance meter with the hydrophobic layer facing the test surface. The film resistance meter was started and pressure was applied to 25 MPa. After holding the pressure for 25 seconds, the sheet resistance of the negative electrode sheet was collected and calculated.

[0096] 8) Detect the cycle capacity retention rate of the secondary battery.

[0097] In a 25℃ testing environment, the test battery was constant-capacity at 0.2C for 3 cycles to obtain the average capacity C0. It was then charged at a constant rate of 4C0 to 3.65V and allowed to rest for 10 minutes. It was then discharged at a constant rate of 4C0 to 2.5V and allowed to rest for 10 minutes. After 500 cycles, the battery's cycle capacity retention was calculated. Cycle capacity retention = Discharge capacity at 500th cycle / Average capacity × 100%.

[0098] The detection results of the quinone-enriched thiophene copolymers prepared in Examples 1-5 are shown in Table 2.

[0099] Table 2

[0100] The detection results of Examples 1-17 and Comparative Examples 1 and 2 are shown in Table 3.

[0101] Table 3

[0102] Note: In Table 3, " / " indicates that the item was not detected.

[0103] Referring to Tables 1-3, the secondary batteries provided in Examples 1-17 effectively block the wetting of the negative electrode sheet by setting a hydrophobic layer with quinone-rich thiophene copolymer as the main active component on the surface of the active material layer of the negative electrode sheet. This reduces the side reactions between the electrolyte and the negative electrode active material, thereby reducing the risk of delamination of the graphite interlayer structure in the active material layer and improving the cycle performance of the secondary battery.

[0104] The tablets prepared from quinone-enriched thiophene copolymers in Examples 1-5 exhibited contact angles (a1) of over 150° with propylene carbonate, indicating that the quinone-enriched thiophene copolymers possess good hydrophobicity to carbonate electrolytes. The negative electrode sheets in Examples 1-17 showed contact angles (a2) of over 110° with propylene carbonate. This means that the hydrophobic layer effectively resists the intrusion of electrolyte solvents, thereby protecting the active material layer, reducing side reactions between the active material layer and the electrolyte solvent, and improving the cycle performance of the secondary battery. The secondary batteries in Examples 1-17 achieved a capacity retention rate of over 88% after 500 cycles, and the secondary battery in Example 8 achieved a capacity retention rate of over 96% after 500 cycles.

[0105] Comparative Example 1, due to the lack of a hydrophobic layer treatment on the surface of the active material layer of the negative electrode, exhibited a significant decrease in capacity after multiple cycles. Examples 1-17 showed significantly better capacity retention after 500 cycles compared to Comparative Example 1. Comparative Example 2 used polyaniline particles as the main effective component of the hydrophobic layer; however, compared to the quinone-enriched thiophene copolymer provided in Examples 1-17, the polyaniline particles exhibited poor hydrophobic properties towards the electrolyte. The contact angle of the negative electrode in Examples 1-17 to propylene carbonate was significantly higher than that in Comparative Example 2, and the secondary batteries of Examples 1-17 showed better 500-cycle performance than Comparative Example 2. Furthermore, the hydrophobic layer formed by the quinone-enriched thiophene copolymer also demonstrated superior electrical performance compared to the hydrophobic layer of Comparative Example 2; the sheet resistance of the negative electrode prepared in Examples 1-17 was lower than that of Comparative Example 2.

[0106] Referring to Preparation Examples 1-5, by adjusting the amounts of thiophene and p-benzoquinone, the molar ratio of thiophene-derived structural units to p-benzoquinone-derived structural units in the synthesized quinone-enriched thiophene copolymers was changed, thereby altering the hydrophobic properties of the quinone-enriched thiophene copolymers. Referring to Table 2, as the molar ratio (k) of thiophene-derived and p-benzoquinone-derived structural units increases, the contact angle of the quinone-enriched thiophene copolymer with propylene carbonate also increases, meaning the quinone-enriched thiophene copolymer exhibits better hydrophobicity to carbonate electrolyte solvents. Furthermore, as the molar ratio (k) of thiophene-derived and p-benzoquinone-derived structural units increases, the number-average molecular weight of the quinone-enriched thiophene copolymer decreases, which may lead to changes in the porosity of the hydrophobic layer of the prepared negative electrode.

[0107] Because the quinone-based enriched thiophene copolymers of Preparation Examples 1-5 were used to prepare the negative electrode sheets, the contact angle of the negative electrode sheets with propylene carbonate and the porosity of the liquid-phobic layer in Examples 1-5 changed accordingly. Furthermore, the sheet resistance of the negative electrode sheets and the cycle capacity retention of the secondary battery also changed accordingly. In some embodiments, a suitable quinone-based enriched thiophene copolymer from the preparation examples can be selected as the liquid-phobic layer of the negative electrode sheet according to actual needs, so that the secondary battery can be adapted to different electrical performance requirements or cycle performance requirements. This application will not elaborate on this further.

[0108] Referring to Examples 3 and 6-8, variations in the mass percentage of quinone-enriched thiophene copolymer particles in the hydrophobic layer may alter the contact angle of the negative electrode with propylene carbonate and the porosity of the hydrophobic layer, further affecting the sheet resistance of the negative electrode and improving the cycle performance of the secondary battery. In Example 8, with the quinone-enriched thiophene copolymer comprising 80% of the hydrophobic layer, the sheet resistance of the negative electrode was 2.2 Ω / cm.2 The secondary battery retains 96% of its capacity after 500 cycles.

[0109] Referring to Examples 7 and 9-11, changes in the mass percentage of the conductive agent in the hydrophobic layer may affect the sheet resistance of the negative electrode. As the mass percentage of the conductive agent increases, the sheet resistance of the negative electrode decreases. Furthermore, increasing the mass percentage of the conductive agent may also reduce the cycle capacity retention of the secondary battery. Therefore, a suitable mass percentage of the conductive agent can be selected based on the specific application scenario of the secondary battery to achieve a balance between at least the sheet resistance of the negative electrode and the cycle capacity retention of the secondary battery.

[0110] Referring to Examples 9 and 12-15, as the mass ratio of the active material layer to the hydrophobic layer of the negative electrode is adjusted, the hydrophobic properties of the negative electrode to the electrolyte (e.g., the contact angle α2 of the negative electrode to propylene carbonate) change accordingly, which may affect the sheet resistance of the negative electrode and the cycle capacity retention of the secondary battery. In Example 9, the mass ratio of the active material layer to the hydrophobic layer is 3, the contact angle α2 of the negative electrode to propylene carbonate in Example 9 is 130°, and the sheet resistance of the negative electrode in Example 9 is 2.2 Ω / cm. 2 The secondary battery retains 94% of its capacity after 500 cycles.

[0111] Referring to Examples 13, 16, and 17, variations in the mass ratio of graphite to multi-walled carbon nanotubes in the active material layer slurry can affect the porosity and tortuosity of the active material layer. By controlling the mass ratio of graphite to multi-walled carbon nanotubes within a certain range, the porosity of the active material layer can be controlled within the range of 35% to 45%, and / or the tortuosity of the active material layer can be controlled within the range of 3.5 to 4.5. Furthermore, the sheet resistance of the negative electrode and the cycle capacity retention rate of the secondary battery can be altered.

[0112] The various implementations of this application have been described above. The foregoing description is exemplary and not exhaustive, nor is it limited to the disclosed implementations. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described implementations. The terminology used herein is chosen to best explain the principles, practical applications, or improvements to technology in the market, or to enable others skilled in the art to understand the various implementations disclosed herein.

Claims

1. A secondary battery, characterized in that, It includes a negative electrode sheet, wherein the negative electrode sheet comprises a negative current collector, an active material layer and a liquid-repellent layer arranged sequentially, and the liquid-repellent layer is disposed on the side of the active material layer opposite to the negative current collector; The hydrophobic layer contains quinone-enriched thiophene copolymer particles, which account for 80% to 90% of the mass of the hydrophobic layer, and the contact angle of the quinone-enriched thiophene copolymer particles with the electrolyte is greater than 150°.

2. The secondary battery according to claim 1, characterized in that, The hydrophobic layer contains a conductive agent, and the conductive agent accounts for 4% to 10% of the mass of the hydrophobic layer.

3. The secondary battery according to claim 1, characterized in that, The contact angle of the hydrophobic layer with the electrolyte is greater than 110°.

4. The secondary battery according to claim 1, characterized in that, The porosity of the hydrophobic layer is 40%~70%.

5. The secondary battery according to claim 1, characterized in that, The quinone-enriched thiophene copolymer particles comprise structural units derived from thiophene and structural units derived from p-benzoquinone, wherein the molar ratio of the structural units derived from thiophene to the structural units derived from p-benzoquinone is (1.5~2.5):

1.

6. The secondary battery according to claim 1, characterized in that, In the quinone-enriched thiophene copolymer particles, carbonyl groups are at least partially located inside the quinone-enriched thiophene copolymer particles, and thiophene rings are at least partially located on the surface of the quinone-enriched thiophene copolymer particles.

7. The secondary battery according to claim 1, characterized in that, The number-average molecular weight of the quinone-enriched thiophene copolymer is 50 kDa to 60 kDa.

8. The secondary battery according to claim 1, characterized in that, The tortuosity τ of the active material layer is 3.5~4.

5.

9. The secondary battery according to claim 1, characterized in that, The compaction density of the active material layer is 1.6~1.8 g / cm³. 3 The porosity of the active material layer is 35%~45%.

10. The secondary battery according to claim 1, characterized in that, The mass ratio of the active material layer to the hydrophobic layer is (3~5):

1.

11. The secondary battery according to claim 1, characterized in that, The surface resistivity of the negative electrode is less than or equal to 5 Ω / cm. 2 .

12. An electrical appliance, characterized in that, The device includes the secondary battery as described in any one of claims 1-11, wherein the secondary battery serves as the power supply for the electrical equipment.

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