An electrode sheet and its preparation method, a secondary battery, a battery assembly, and an electrical device.

Abstract

This invention provides an electrode sheet and its preparation method, a secondary battery, a battery assembly, and an electrical device. The electrode sheet includes a current collector and an electrode active layer disposed on at least one functional surface of the current collector. The electrode active layer includes a wetting agent, a solid electrolyte, and an active material. The wetting agent includes an ionic liquid, and the concentration of the wetting agent in the electrode active layer increases along the direction away from the current collector. This invention can improve the solid-solid contact problem within the electrode sheet of a solid-state battery, helping to reduce the battery's overpotential and improve cycle capacity retention.

Description

Technical Field

[0001] This invention relates to the field of secondary batteries, specifically to an electrode sheet and its preparation method, a secondary battery, a battery assembly, and an electrical device. Background Technology

[0002] Compared to liquid batteries, solid-state batteries offer higher safety due to the use of solid electrolytes.

[0003] However, solid-state batteries suffer from solid-solid interface contact issues, leading to increased overpotential and exacerbated cycle stability degradation. Specifically, this manifests as poor wettability at the solid-solid contact interfaces between active material particles within the electrode active layer and between active material particles and solid electrolyte particles. Insufficient physical contact between active material particles and the solid electrolyte easily forms ion migration barriers, resulting in discontinuous ion transport paths and increased interfacial impedance. Furthermore, insufficient chemical compatibility between active material particles and the solid electrolyte can easily induce interfacial side reactions. All of these problems contribute to increased battery overpotential and exacerbated cycle stability degradation.

[0004] Therefore, improving the solid-solid contact problem of solid-state batteries, effectively reducing battery overpotential, and improving battery cycle capacity retention are the key research areas in this field. Summary of the Invention

[0005] This invention provides an electrode sheet and its preparation method, a secondary battery, a battery assembly, and an electrical device, which can improve the solid-solid contact problem within the electrode sheet of a solid-state battery, help reduce the overpotential of the battery, and improve the cycle capacity retention rate.

[0006] The present invention provides an electrode sheet comprising an electrode current collector and an electrode active layer disposed on at least one side of the electrode current collector, the electrode active layer comprising a wetting agent, the concentration of the wetting agent in the electrode active layer increasing in the direction away from the electrode current collector.

[0007] Optionally, the increasing trend of the concentration of the wetting agent in the electrode active layer along the direction away from the electrode current collector includes: the increasing trend of the concentration of the wetting agent in the electrode active layer along the direction away from the electrode current collector.

[0008] Optionally, the electrode active layer sequentially includes regions C, B, and A along the direction away from the electrode current collector; the region of 0-1 / 3 thickness of the electrode active layer is designated as region A, the region of 1 / 3-2 / 3 thickness is designated as region B, and the region of 2 / 3-3 / 3 thickness is designated as region C; the ratio of the mass of the wetting agent in region A to the total mass of the wetting agent in the electrode active layer is 50%-70%; the ratio of the mass of the wetting agent in region B to the total mass of the wetting agent in the electrode active layer is 20%-35%; and the ratio of the mass of the wetting agent in region C to the total mass of the wetting agent in the electrode active layer is 10%-20%.

[0009] Optionally, in the thickness direction of the electrode sheet, the electrode active layer includes N stacked sub-electrode active layers, where N is greater than or equal to 2, and in any two adjacent sub-electrode active layers, the concentration of the wetting agent in the sub-electrode active layer farther from the electrode current collector is greater than the concentration of the wetting agent in the sub-electrode active layer closer to the electrode current collector.

[0010] Optionally, the wetting agent includes an ionic liquid.

[0011] Optionally, the ionic liquid includes cations and anions, wherein the cations include one or more of imidazole cations, heterocyclic organic cations, quaternary ammonium cations, pyridine cations, pyrrole cations, and piperidine cations, and the anions include one or more of fluorosulfonylimide anions, tetrafluoroborate anions, and sulfonate anions.

[0012] Optionally, the wetting agent comprises a complex of lithium salt and ionic liquid.

[0013] Optionally, the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalate-borate), lithium difluorooxalate-borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

[0014] Optionally, the mass ratio of the lithium salt to the ionic liquid is 1:(8-10).

[0015] Optionally, the electrode active layer further includes a solid electrolyte, wherein the mass ratio of the wetting agent to the solid electrolyte is 1% to 20%.

[0016] Optionally, the solid electrolyte includes one or more of sulfide electrolytes, oxide electrolytes, and chloride electrolytes.

[0017] Optionally, the electrode sheet is a positive electrode sheet; preferably, the electrode active layer includes a positive electrode active material, which includes one or more of binary materials, ternary materials, and phosphate materials, wherein the binary material includes one or more of lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide, the phosphate material includes one or more of lithium iron phosphate, lithium cobalt phosphate, lithium manganese phosphate, and lithium nickel phosphate, and the ternary material includes one or more of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

[0018] Optionally, the electrode sheet is a negative electrode sheet; preferably, the electrode active layer includes a negative electrode active material, which includes one or more of lithium metal, graphite, hard carbon, tin, silicon, silicon carbide, titanium dioxide, soft carbon, silicon oxide, lithium titanate, red phosphorus, and black phosphorus.

[0019] The present invention provides a method for preparing an electrode sheet as described above, comprising: forming an electrode active layer on at least one side of an electrode current collector to obtain the electrode sheet.

[0020] Optionally, the process of forming the electrode active layer on at least one side of the electrode current collector includes: forming an electrode active layer precursor on at least one side of the electrode current collector; applying a coating liquid containing the wetting agent to the surface of the electrode active layer precursor, and then drying it at 50°C to 100°C for 0.5h to 3.0h to form the electrode active layer, thereby obtaining the electrode sheet.

[0021] Optionally, the process of forming the electrode active layer on at least one side of the electrode current collector includes: preparing N portions of electrode active slurry, where N is greater than or equal to 2; wherein each of the N portions of electrode active slurry contains the wetting agent, and the concentration of the wetting agent in any two portions of the electrode active slurry is different; sequentially coating the N portions of electrode active slurry onto at least one side of the electrode current collector in order of increasing concentration of the wetting agent in the electrode active slurry to form N stacked sub-electrode active layers, thereby forming the electrode active layer and obtaining the positive electrode sheet.

[0022] The present invention provides a secondary battery comprising an electrode sheet as described above or an electrode sheet prepared according to the electrode sheet preparation method described above.

[0023] Optionally, the secondary battery is a solid-state battery or a semi-solid-state battery.

[0024] Optionally, the battery includes a positive electrode plate, a negative electrode plate, and a separator membrane between the positive electrode plate and the negative electrode plate; the separator membrane includes a second solid electrolyte.

[0025] The present invention provides a battery assembly comprising at least two secondary batteries as described above.

[0026] The present invention provides an electrical device, including a secondary battery or a battery assembly as described above, wherein the secondary battery or the battery assembly serves as the power supply for the electrical device.

[0027] This invention provides an electrode sheet and its preparation method, a secondary battery, a battery assembly, and an electrical device. The concentration of the wetting agent in the electrode active layer increases along the direction away from the electrode current collector. This not only effectively utilizes the wetting agent's ability to improve the wettability of the solid-solid contact interface, allowing the wetting agent to improve the wettability of the solid-solid contact interface between active material particles, thereby improving the ion transport path and reducing interfacial impedance, but also places a lower content of wetting agent in the electrode sheet region near the electrode current collector along the electrode sheet thickness direction. This strengthens the contact between particles in this region, helping the electrode sheet to maintain good electronic conductivity. This effectively solves the problem that the wetting agent in the electrode sheet region near the electrode current collector may block the electronic conduction path. Moreover, the increasing content of the wetting agent is more compatible with the active material particles, which is beneficial for further reducing the battery overpotential and improving the battery's cycle capacity retention rate. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a cross-sectional schematic diagram of the electrode sheet provided in an embodiment of the present invention. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Existing technologies aim to reduce interfacial impedance and address the aforementioned issues by adding wetting agents (interfacial wetting agents), such as polymers, ionic liquids, or electrolytes, to the electrode sheets (composite electrodes) of solid-state batteries. However, these technologies still fail to effectively solve the solid-solid contact problem in solid-state batteries. For example, the wetting agent may only cover the surface of the electrode sheet and has difficulty penetrating into the interior, preventing it from optimizing the solid-solid interfacial contact between active particles and between active particles and the solid electrolyte within the electrode sheet. Alternatively, the wetting agent may be uniformly or randomly distributed within the electrode sheet, failing to target different areas of the electrode sheet. Targeted optimization of the differentiated interface issues (near current collector side / far current collector side) makes it difficult to form a coherent interface optimization network. Furthermore, there may be excessive wetting agent in certain areas inside the electrode sheet, which can block electron conduction paths and reduce the conductivity of the electrode sheet. In addition, if there is insufficient wetting agent in the electrode sheet far from the current collector, it will be difficult for the wetting agent to fully bridge the interface defects between the electrode sheet and the solid electrolyte layer, resulting in limited effect on reducing interface impedance. Consequently, it is impossible to effectively reduce the overpotential of the battery and improve the cycle capacity retention rate of the battery.

[0032] To overcome the deficiencies in the prior art, embodiments of the present invention provide an electrode sheet, including an electrode current collector and an electrode active layer disposed on at least one side of the electrode current collector. The electrode active layer includes a wetting agent, and the concentration of the wetting agent in the electrode active layer increases in the direction away from the electrode current collector.

[0033] According to research and analysis, the concentration of wetting agent in the electrode active layer increases along the direction away from the electrode current collector. This not only effectively leverages the wetting agent's ability to improve the wettability of the solid-solid contact interface, allowing it to improve the wettability of the solid-solid contact interface between active material particles, thereby improving ion transport paths and reducing interfacial impedance, but also, by placing a lower concentration of wetting agent in the electrode sheet region near the electrode current collector along the electrode sheet thickness direction, the contact between particles in this region is strengthened, helping the electrode sheet to maintain good electronic conductivity. This effectively solves the problem that wetting agent in the electrode sheet region near the electrode current collector may block the electronic conduction path. Moreover, the increasing concentration of wetting agent is more compatible with the active material particles, which is beneficial for further reducing the battery overpotential and improving the battery's cycle capacity retention rate.

[0034] Therefore, the embodiments of the present invention precisely match the concentration of wetting agent according to the functional and demand characteristics of different regions of the electrode sheet, which can improve the solid-solid contact problem in the electrode sheet, help reduce the overpotential of the battery, and improve the cycle capacity retention rate.

[0035] In solid-state batteries, the electrode active layer may also include a solid electrolyte. The concentration of wetting agent in the electrode active layer tends to increase along the direction away from the electrode current collector. This not only provides the advantages mentioned above, but also improves the wettability of the solid-solid contact interface between the active material particles and the solid electrolyte, thereby improving the ion transport path, reducing interfacial impedance, helping to reduce the battery's overpotential, and improving the battery's cycle capacity retention.

[0036] Furthermore, solid-state batteries may also include a solid electrolyte layer. The concentration of wetting agent in the electrode active layer increases along the direction away from the electrode current collector, matching the wetting agent content distribution in the electrode sheet with the different needs of different regions within the electrode sheet. This not only strengthens the contact between particles in the region near the electrode current collector, helping the electrode sheet to maintain good electronic conductivity, but also improves the interfacial wettability of particles within the electrode sheet. In addition, it can effectively bridge interfacial defects between the electrode sheet and the solid electrolyte layer, effectively reducing interfacial impedance, thereby helping to reduce battery overpotential and improve battery cycle capacity retention.

[0037] In some embodiments, the increasing trend of the concentration of the wetting agent in the electrode active layer along the direction away from the electrode current collector includes: the increasing trend of the concentration of the wetting agent in the electrode active layer along the direction away from the electrode current collector (such as a gradient increasing trend).

[0038] The concentration of wetting agent in the electrode active layer gradually increases along the direction away from the electrode current collector (such as a gradient increase trend), making the content of wetting agent in the electrode active layer change in a continuous gradient. This can better improve the solid-solid contact problem within the electrode sheet of the solid-state battery. For example, it can improve the wettability of the solid-solid contact interface between active material particles and between active material particles and solid electrolyte. It can also fully bridge the interface defects between the electrode sheet and the solid electrolyte layer, effectively reducing the interface impedance. At the same time, in the electrode sheet thickness direction, a lower content of wetting agent is placed in the electrode sheet area near the electrode current collector, which helps the electrode sheet to maintain good electronic conduction performance. This effectively solves the problem that the wetting agent in the electrode sheet area near the electrode current collector may block the electronic conduction path, which helps to reduce the battery overpotential and improve the battery's cycle capacity retention rate.

[0039] In some embodiments, such as Figure 1 As shown, the electrode active layer, along the direction away from the electrode current collector, sequentially includes (or is divided into) region C, region B, and region A. That is, region C is close to the electrode current collector, region A is far from the electrode current collector, and region B is located between region C and region A.

[0040] Specifically, the region from 0 to 1 / 3 of the electrode active layer thickness is designated as region A, the region from 1 / 3 to 2 / 3 of the thickness is designated as region B, and the region from 2 / 3 to 3 / 3 of the thickness is designated as region C. The aforementioned thickness ranges are measured from the surface of the electrode active layer.

[0041] In Zone C (low content zone), the ratio of the mass of the wetting agent to the total mass of the wetting agent in the electrode active layer is 10% to 20%, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any combination thereof; in Zone B (medium content zone), the ratio of the mass of the wetting agent to the total mass of the wetting agent in the electrode active layer is 20% to 35%, for example, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or any combination thereof; in Zone A (high content zone), the ratio of the mass of the wetting agent to the total mass of the wetting agent in the electrode active layer can be 50% to 70%, for example, 50%, 55%, 60%, 65%, 70%, or any combination thereof.

[0042] By controlling the concentration of wetting agent in regions C, B, and A to meet the aforementioned range, the concentration of wetting agent in the electrode active layer increases in the direction away from the electrode current collector. A lower concentration of wetting agent in the region near the electrode current collector (region C) enhances the contact between particles in this area, reduces the obstruction of electron conduction paths by the wetting agent, and allows the electrode to maintain good electron conduction performance. A higher concentration of wetting agent in the intermediate region (region B), with a transitional wetting agent content between regions C and A, helps form a coherent ion transport network, achieving a synergistic improvement in the overall interface performance of the electrode, preventing local ion transport path interruptions, and improving ion transport efficiency. A higher concentration of wetting agent in the region away from the electrode current collector (region A) helps to fully bridge interface defects between the electrode and the solid electrolyte layer, effectively reducing interface impedance. By setting different amounts of wetting agent in different regions of the electrode sheet according to functional orientation, the content of wetting agent is matched with the severity of interface problems in the different regions. By adjusting the content of wetting agent in a differentiated manner, the interfacial wettability inside the electrode sheet and between the electrode sheet and the solid electrolyte layer can be controlled, which can suppress interfacial contact loss, suppress capacity decay, and also take into account the requirements of electronic conductivity and ion transport. This can simultaneously improve the interfacial compatibility and ion transport efficiency of the electrode-electrolyte, help reduce the overpotential of the battery, improve the cycle stability of the battery, and improve the cycle capacity retention rate of the battery.

[0043] In practice, the distribution of wetting agent content along the thickness direction of the electrode sheet can be tested using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). The testing principle is explained as follows: The electron beam of the scanning electron microscope bombards the surface of the electrode sheet cross-section, exciting secondary electron signals to form a high-resolution morphological image (resolution up to 1-5 nm). This high-resolution morphological image can be used to locate the current collector side (C region), intermediate transition region (B region), and electrolyte side (A region) of the electrode sheet cross-section; then, the electron beam of the energy dispersive X-ray spectroscopy is used to excite the electrode sheet cross-section. The inner-shell electrons of the atoms generate characteristic X-rays. These X-rays are captured and analyzed by an energy dispersive spectroscopy detector, which can be used to capture and analyze the types of specific elements in the wetting agent and their X-ray signal intensity. For example, when the wetting agent includes an ionic liquid, fluorine (F) and sulfur (S) in the ionic liquid can be used as specific elements. The X-ray signal intensity of these specific elements is positively correlated with the concentration of the ionic liquid (or wetting agent). Therefore, by testing the proportion of the X-ray signal intensity of the above-mentioned specific elements in different regions of the electrode sheet, the mass proportion of the wetting agent in different regions of the electrode sheet can be quantitatively characterized, so as to illustrate the distribution of the wetting agent in the electrode sheet.

[0044] The specific testing steps include:

[0045] (1) Sample preparation

[0046] Cutting: Cut the positive or negative electrode sheet along the direction perpendicular to the electrode current collector to obtain a sample with a cross-section in the thickness direction (e.g., the cross-section size can be 5mm×5mm). During the cutting process, care should be taken to avoid wetting agent migration caused by mechanical stress.

[0047] Gold plating treatment: A 5nm thick gold layer is sputtered onto the surface of the above cross section to eliminate the interference of charge accumulation on the electron beam.

[0048] Vacuum drying: The sample is placed in a vacuum drying oven (60℃, 12h) to dry it, so as to remove the residual solvent in the sample and prevent the residual solvent from evaporating and contaminating the chamber during the test.

[0049] (2) SEM-EDS test parameters

[0050] SEM conditions:

[0051] Accelerating voltage: 15kV (to balance penetration depth and resolution).

[0052] Working distance: 10mm.

[0053] Detector: Backscattered electron (BSE) mode, contrast reflects differences in element atomic number.

[0054] EDS conditions:

[0055] Surface scan region: In the above cross section, along the thickness direction of the electrode sheet (electrode current collector side → electrolyte layer side), it is divided into current collector side (C region), intermediate transition region (B region) and electrolyte side (A region). The sum of the dimensions of region A, region B and region C along the thickness direction of the electrode sheet is equal to the thickness of the electrode sheet (for example, the dimension of each region along the thickness direction of the electrode sheet is ≈30μm).

[0056] Scanning mode: Mapping area scan (step size 1μm, dwell time 50ms / point), synchronously acquiring the X-ray signal intensity of specific elements in the wetting agent, such as the X-ray signal intensity of element F (energy 0.677keV, corresponding to F-Kα line).

[0057] (3) Data processing

[0058] Extraction of X-ray signal intensity of specific elements in wetting agent: Use software (such as Oxford INCA) to integrate the X-ray signal intensity of specific elements in regions A, B, and C, and then calculate the average X-ray signal intensity (counts) of regions A, B, and C respectively.

[0059] Gradient quantitative calculation: Based on the proportion of X-ray signal intensity of a specific element, the distribution of wetting agent content in the thickness direction of the electrode sheet is characterized (verified). For example, the proportion of the X-ray signal intensity of a specific element in region A to the sum of the X-ray signal intensities of specific elements in regions A, B, and C represents the ratio of the mass of wetting agent in region A to the total mass of wetting agent in the active electrode layer; the proportion of the X-ray signal intensity of a specific element in region B to the sum of the X-ray signal intensities of specific elements in regions A, B, and C represents the ratio of the mass of wetting agent in region B to the total mass of wetting agent in the active electrode layer; and the proportion of the X-ray signal intensity of a specific element in region C to the sum of the X-ray signal intensities of specific elements in regions A, B, and C represents the ratio of the mass of wetting agent in region C to the total mass of wetting agent in the active electrode layer.

[0060] In some embodiments, in the thickness direction of the electrode sheet, the electrode active layer includes N stacked sub-electrode active layers, where N is greater than or equal to 2, and in any two adjacent sub-electrode active layers, the concentration of wetting agent in the sub-electrode active layer farther from the electrode current collector is greater than the concentration of wetting agent in the sub-electrode active layer closer to the electrode current collector.

[0061] In some embodiments, the wetting agent includes an ionic liquid.

[0062] Ionic liquids do not react with solid electrolytes (such as sulfide electrolytes) and can maintain high stability in the electrode sheet, thereby ensuring better reduction of battery overpotential and improving battery cycle capacity retention.

[0063] Ionic liquids include cations and anions.

[0064] Specifically, the cation may include one or more of imidazole cations, heterocyclic organic cations, quaternary ammonium cations, pyridine cations, pyrrole cations, and piperidine cations, and the anion may include one or more of fluorosulfonylimide anions, tetrafluoroborate anions, and sulfonate anions.

[0065] For example, the aforementioned ionic liquids may include 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (EMIMTFSI) or N-triethyl-N-hexyl quaternary ammonium bis(trifluoromethanesulfonyl)imide salt (N...). 2226 One or more of the following: -TFSI, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt BMIMTFSI, 1-methyl-1-propylpyrrolidine bis(trifluoromethanesulfonyl)imide salt Pyr13TFSI, and 1-ethyl-3-methylimidazolium tetrafluoroborate EtMeim-BF4.

[0066] In addition, wetting agents may include complexes of lithium salts and ionic liquids.

[0067] Complexes of lithium salts and ionic liquids can act as ion transport conductors, which can help to further improve the lithium conduction properties of wetting agents.

[0068] The lithium salt and ionic liquid complexes of the present invention can be analyzed and characterized by ion chromatography.

[0069] In addition, the lithium salt in the complex of lithium salt and ionic liquid can provide lithium ions, thereby improving the ion conduction performance of the electrode sheet, which in turn helps to reduce the overpotential of the battery and improve the cycle capacity retention rate of the battery.

[0070] Furthermore, the mass ratio of lithium salt to ionic liquid can be 1:(8 to 10), for example, 1:8, 1:9, 1:10 or any combination thereof.

[0071] In practice, the mass ratio of lithium salt to ionic liquid can be verified using ion chromatography, including the following steps:

[0072] 1) Cut the electrode sample into small pieces and immerse it in xylene. Sonicate it for a period of time (e.g., 30 minutes ± 10 minutes). The ultrasonic power can be 200W ± 20W and the frequency can be 40kHz ± 5kHz. Then, centrifuge the ultrasonically treated material at a speed of 8000rpm ± 100rpm for 10 minutes ± 1 minute to remove electrolytes (e.g., sulfide electrolytes), conductive agents, and electrode active particles. Collect the supernatant. Repeat the above steps twice, then combine the supernatants and concentrate them (e.g., concentrate to 1mL) to obtain the test solution for later use.

[0073] 2) Parameters of ion chromatography testing technology

[0074] Ion chromatography instrument: Dionex ICS-5000+ ion chromatography system (equipped with conductivity detector).

[0075] Chromatographic column:

[0076] Cation analysis: Dionex IonPac CS12A (4×250mm) separation column + CG12A guard column; Anion analysis: Dionex IonPac AS11-HC (4×250mm) separation column + AG11-HC guard column.

[0077] Mobile phase: cations (Li) + EtMeim + ): 20 mM methanesulfonic acid (MSA), flow rate 1.0 mL / min;

[0078] Anions (such as BF4) - FSI - Gradient elution program (0 min-10 min: 5 mM potassium hydroxide (KOH); 10 min-20 min: 30 mM potassium hydroxide (KOH)), flow rate 1.2 mL / min.

[0079] Detector: Suppressed conductivity detection (cation: CSRS 500 4mm; anion: ASRS 500 4mm).

[0080] Column temperature: 30℃; injection volume: 25μL.

[0081] 3) Quantitative analysis

[0082] Standard curve: Prepare standard solutions of lithium salt (e.g., LiFSI) and ionic liquid (e.g., EtMeim-BF4) (concentration range can be 0.1 mg / L to 10 mg / L) respectively, and establish a peak area-concentration calibration curve (R²). 2 ≥0.999).

[0083] Sample testing: Dilute the test solution to the linear range, inject and analyze, and record the Li values. + and anions in ionic liquids (such as FSI) - The peak area of ​​the lithium salt (such as LiFSI) was used to calculate the content of the lithium salt; and the content of the ionic liquid (such as EtMeim-BF4) was determined by total organic carbon (TOC) or nuclear magnetic resonance (NMR).

[0084] Specifically, lithium salts may include one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalate-borate), lithium difluorooxalate-borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

[0085] In some embodiments, the electrode active layer further includes a solid electrolyte.

[0086] As mentioned earlier, the concentration of wetting agent in the electrode active layer tends to increase in the direction away from the electrode current collector, which can improve the wettability of the solid-solid contact interface between the active material particles and the solid electrolyte, thereby improving the ion transport path, reducing the interface impedance, helping to reduce the overpotential of the battery, and improving the cycle capacity retention rate of the battery.

[0087] Specifically, the mass ratio of wetting agent to solid electrolyte can be 1% to 20%, for example, 1%, 5%, 10%, 15%, 20%, or any combination thereof.

[0088] By controlling the mass ratio of wetting agent to solid electrolyte to meet the above range, it is helpful to give full play to the wetting agent to improve the wettability of the contact interface between particles inside the electrode sheet, thereby helping to reduce the overpotential of the battery and improve the cycle capacity retention rate of the battery.

[0089] Solid electrolytes may include one or more of the following: sulfide electrolytes, oxide electrolytes, and chloride electrolytes.

[0090] Specifically, sulfide electrolytes can include LGPS-type sulfide electrolytes (such as Li...). 10 GeP2S 12 ), sulfide electrolytes of the sulfide type (such as Li6PS5Cl), and Thio-LISICON type electrolytes (such as Li 3.25 Ge 0.25 P 0.75 S4), at least one of amorphous sulfide electrolytes (such as 70Li2S·30P2S5(LPS)); oxide electrolytes may include perovskite electrolytes (such as Li 3x La 2 / 3-x TiO3(LLTO)), garnet-type electrolytes (such as Li7La3Zr2O) 12(LLZO)), NASICON-type electrolytes (such as Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (LATP)), LISICON-type electrolytes (such as Li 14 Zn(GeO4)4); the chloride electrolyte may include a Li-M-Cl ternary system electrolyte, M may include one or more of In, Zr, Al, Er, Y, Hf, for example, it may include at least one of Li3InCl6, Li2ZrCl6, LiAlCl4.

[0091] In some embodiments, the electrode sheet is a positive electrode sheet.

[0092] Correspondingly, the electrode active layer includes a positive electrode active material. The positive electrode active material may include one or more of binary materials, ternary materials, and phosphate materials.

[0093] The above binary material may include LiNi x A (1-x) O2, where A includes at least one of Co and Mn, 0 ≤ x ≤ 1. For example, the binary material may include one or more of lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), and lithium manganate (LiMnO2).

[0094] The phosphate material includes one or more of lithium iron phosphate (LiFePO4), lithium cobalt phosphate (LiCoPO4), lithium manganese phosphate (LiMnPO4), and lithium nickel phosphate (LiNiPO4).

[0095] The chemical formula of the ternary material may be LiNi m B n C (1-m-n) O2, where B and C each independently include at least one of Co, Al, and Mn, and B and C are different, 0 < m < 1, 0 < n < 1. For example, the ternary material may include one or more of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminate.

[0096] In some other embodiments, the electrode sheet is a negative electrode sheet.

[0097] Correspondingly, the electrode active layer is a negative electrode active material, and the negative electrode active material includes one or more of lithium metal, graphite, hard carbon, tin, silicon, silicon carbide, titanium dioxide, soft carbon, silicon oxide, lithium titanate, red phosphorus, and black phosphorus.

[0098] It is understandable that the above electrode active layer may further include a conductive agent.

[0099] Conductive agents include one or more of acetylene black, conductive carbon black (Super P), conductive graphite (Super S), graphene, carbon fiber, carbon nanotubes, and Ketjen black.

[0100] The present invention also provides a method for preparing the above-mentioned electrode sheet, comprising: forming the above-mentioned electrode active layer on at least one side of the electrode current collector to obtain the electrode sheet.

[0101] The above preparation method is simple.

[0102] In some embodiments, the process of forming an electrode active layer on at least one side of the electrode current collector includes: forming an electrode active layer precursor on the surface of the electrode current collector; applying a coating liquid containing a wetting agent to the surface of the electrode active layer precursor, and then drying it at 50°C to 100°C for 0.5h to 3h to form an electrode active layer, thereby obtaining an electrode sheet.

[0103] According to research and analysis, after coating the electrode active layer precursor with a coating solution containing a wetting agent, the coating solution (including the wetting agent and organic solvent) is immersed in the electrode active layer precursor. As the immersion depth (the dimension along the thickness direction of the electrode sheet) varies, the concentration of the wetting agent in different regions of the electrode sheet will vary. That is, the wetting agent content is higher in the region near the electrode current collector. During the drying process at 50℃~100℃ for 0.5h~3.0h, the organic solvent will evaporate, and the wetting agent will gradually transfer from the region near the electrode current collector to the region away from the electrode current collector (i.e., near the surface of the electrode active layer) along with the organic solvent. This causes the concentration of the wetting agent in the electrode active layer to increase in the direction away from the electrode current collector, thereby preparing the electrode sheet of the embodiment of the present invention.

[0104] For example, the drying temperature can be a range of 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C or any two of these, and the drying time can be a range of 0.5h, 1.0h, 1.5h, 2.0h, 2.5h, 3.0h or any two of these.

[0105] The process of forming the electrode active layer precursor on the surface of the electrode current collector can be carried out by dry or wet methods, and the embodiments of the present invention do not particularly limit this.

[0106] In some embodiments, the method for preparing the electrode sheet specifically includes:

[0107] Electrode active material, conductive agent, and solid electrolyte are dispersed in a solution containing a binder and mixed evenly by mechanical stirring to obtain an electrode slurry. The electrode slurry is then coated onto at least one side of an electrode current collector (such as an aluminum current collector or a copper current collector) and dried, for example, at 80℃±10℃ for 10-12 hours, to form an electrode active layer precursor on the surface of the electrode current collector. A coating liquid containing a wetting agent is then coated (sprayed) onto the surface of the electrode active layer precursor and dried at 50℃-100℃ for 0.5-3.0 hours to form the aforementioned electrode active layer, resulting in an electrode sheet.

[0108] A coating solution containing a wetting agent can be prepared by the following process: mixing a system including an ionic liquid and an organic solvent until homogeneous to obtain a coating solution containing a wetting agent.

[0109] Organic solvents may include one or more of acetonitrile (ACN), N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), anisole (AN), butyl butyrate (BB), isobutyl isobutyrate (IIB), and xylene (XYL).

[0110] The aforementioned systems, which include ionic liquids and organic solvents, may also include lithium salts.

[0111] Ionic liquids can coordinate with lithium salts to form lithium-ionic liquid complexes. Specifically, the lone pair of electrons on the anion in the ionic liquid can act as an electron donor (Lewis base), reacting with the lithium ion (Li). + The empty orbitals of the lithium salt undergo coordination (Lewis acid-base interaction) to form a complex of lithium salt and ionic liquid. This lithium salt-ionic liquid complex can act as an ion transport conductor, helping to improve the lithium conductivity of the wetting agent.

[0112] The adhesive may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyisobutylene (PIB), styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene-butene-styrene block copolymer (SEBS), styrene-butadiene rubber (SBR), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), and polyacrylic acid (PAA).

[0113] In addition, the process of applying the coating liquid containing wetting agent to the surface of the electrode active layer precursor may include: applying (spraying) the coating liquid containing wetting agent to the surface of the electrode active layer precursor at least once (multiple times or multiple layers).

[0114] The drying process described above, at 50℃~100℃ for 0.5h~3.0h, can be carried out by heating and drying. In practice, the drying process can be carried out in a forced-air drying oven.

[0115] Furthermore, the coating liquid containing the wetting agent may also include lithium salt.

[0116] The functions and types of lithium salts are the same as before, and will not be repeated here.

[0117] In other embodiments, the process of forming an electrode active layer on at least one side of the electrode current collector includes: preparing N portions of electrode active slurry, where N is greater than or equal to 2; wherein each of the N portions of electrode active slurry contains a wetting agent, and the concentration of the wetting agent in any two portions of electrode active slurry is different; and sequentially coating the N portions of electrode active slurry onto at least one side of the electrode current collector in order of increasing concentration of the wetting agent in the electrode active slurry to form N stacked sub-electrode active layers, thereby forming an electrode active layer and obtaining a positive electrode sheet.

[0118] This invention also provides a secondary battery, comprising the electrode sheet described above or an electrode sheet prepared according to the method described above.

[0119] Based on the aforementioned electrode sheet, the secondary electrode exhibits lower overvoltage and higher cycle capacity retention, which will not be elaborated further here.

[0120] Specifically, the secondary battery can be a solid-state battery or a semi-solid-state battery.

[0121] The aforementioned battery (solid-state battery or semi-solid-state battery) may include a positive electrode plate, a negative electrode plate, and a separator between the positive electrode plate and the negative electrode plate; the separator includes a second solid electrolyte.

[0122] It is understandable that the concentration of wetting agent in the above-mentioned positive electrode sheet and / or negative electrode sheet tends to increase in the direction away from the electrode current collector, thereby enabling the battery to have lower overvoltage and higher cycle capacity retention.

[0123] The present invention also provides a battery assembly comprising at least two of the above-described secondary batteries.

[0124] The present invention also provides an electrical device, including the above-mentioned secondary battery or battery assembly, wherein the secondary battery or battery assembly serves as the power supply for the electrical device.

[0125] The aforementioned electrical equipment may include at least one of electric vehicles, portable electronic devices, wearable devices, household appliances, and industrial equipment.

[0126] Specifically, electric vehicles may include at least one of electric cars, electric bicycles, and electric scooters; portable electronic devices may include at least one of smartphones, laptops, and tablets; wearable devices may include at least one of smartwatches and fitness trackers; home appliances may include at least one of robotic vacuum cleaners and portable audio equipment; and industrial equipment may include drones.

[0127] The present invention will be further described below through specific embodiments and comparative examples. Unless otherwise specified, the reagents, materials and instruments used below are all conventional reagents, materials and instruments, all of which are commercially available, and the reagents and materials involved can also be synthesized by conventional synthetic methods.

[0128] Example 1

[0129] Preparation of positive electrode

[0130] 1) Disperse NCM811 (positive electrode active material), Super P (conductive agent), and sulfide electrolyte Li6PS5Cl in a solution containing SBR (binder) to obtain a positive electrode slurry; wherein the mass ratio of NCM811, Li6PS5Cl, Super P, and SBR is 80:20:0.5:0.5;

[0131] 2) Then the positive electrode slurry is coated on both sides of the aluminum current collector and dried at 80°C for 10 hours to form a positive electrode active layer precursor on the surface of the electrode current collector;

[0132] 3) A wetting agent is obtained by mixing 1-ethyl-3-methylimidazolium tetrafluoroborate (EtMeim-BF4) and lithium salt (LiFSI, lithium bis(fluorosulfonyl)imide); wherein the mass ratio of lithium salt (LiFSI, lithium bis(fluorosulfonyl)imide) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EtMeim-BF4) is 1:9.

[0133] 4) Disperse the wetting agent in xylene to obtain a coating solution containing the wetting agent. Coat (spray) the coating solution onto the surface of the positive electrode active layer precursor, so that the coating solution is immersed in the positive electrode active layer precursor. Then dry at 80°C for 2 hours to form the positive electrode active layer and obtain the positive electrode sheet.

[0134] The mass ratio of wetting agent to Li6PS5Cl is 5wt%.

[0135] Example 2

[0136] This embodiment is basically the same as Embodiment 1, except that:

[0137] The mass ratio of wetting agent to sulfide electrolyte Li6PS5Cl was adjusted to 20wt%; other conditions remained unchanged.

[0138] Example 3

[0139] This embodiment is basically the same as Embodiment 1, except that:

[0140] The mass ratio of wetting agent to sulfide electrolyte Li6PS5Cl was adjusted to 1 wt%; other conditions remained unchanged.

[0141] Example 4

[0142] This embodiment is basically the same as Embodiment 1, except that:

[0143] The mass ratio of wetting agent to sulfide electrolyte Li6PS5Cl was adjusted to 5wt%.

[0144] Meanwhile, adjust the drying temperature and time in step 4) to 90℃ and 30min respectively.

[0145] Example 5

[0146] This embodiment is basically the same as Embodiment 1, except that:

[0147] The wetting agent does not contain lithium salt LiFSI (lithium bis(fluorosulfonyl)imide), that is, the wetting agent only includes 1-ethyl-3-methylimidazolium tetrafluoroborate EtMeim-BF4; other conditions remain unchanged.

[0148] Example 6

[0149] This embodiment is basically the same as Embodiment 1, except that:

[0150] Change the type of ionic liquid to N 2226 -TFSI; and the mass ratio of lithium salt to ionic liquid is 1:8; other conditions remain unchanged.

[0151] Example 7

[0152] This embodiment is basically the same as Embodiment 1, except that:

[0153] Change the type of ionic liquid N 2226 -TFSI; and the mass ratio of lithium salt to ionic liquid is 1:10; other conditions remain unchanged.

[0154] Example 8

[0155] This embodiment provides a method for preparing a negative electrode sheet, which is basically the same as the previous embodiment, except that graphite (negative electrode active material) is used instead of NCM811 (positive electrode active material); other conditions remain unchanged.

[0156] Comparative Example 1

[0157] Preparation of positive electrode:

[0158] 1) Disperse NCM811 (positive electrode active material), Super P (conductive agent), and sulfide electrolyte Li6PS5Cl in a solution containing SBR (binder) to obtain a positive electrode slurry; wherein the mass ratio of NCM811, Li6PS5Cl, Super P, and SBR is 80:20:0.5:0.5;

[0159] 2) Then the positive electrode slurry is coated on both sides of the aluminum current collector and dried at 80°C for 10 hours to obtain the positive electrode sheet.

[0160] Comparative Example 2

[0161] This comparative example is basically the same as Example 1, except that:

[0162] 4) Disperse the wetting agent in xylene to obtain a coating solution containing the wetting agent. Immerse the positive electrode active layer precursor in the coating solution so that the coating solution wets the positive electrode active layer precursor. Then dry at 45°C for 3 hours to form the positive electrode active layer and obtain the positive electrode sheet.

[0163] Comparative Example 3

[0164] This comparative example is basically the same as comparative example 2, except that;

[0165] The mass ratio of wetting agent to sulfide electrolyte Li6PS5Cl was 20wt%; other conditions remained unchanged.

[0166] Experimental Example 1

[0167] The positive or negative electrode sheets of each embodiment and comparative example were divided into three regions along the thickness direction, sequentially named regions C, B, and A, away from the electrode current collector. Then, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) was used to verify the gradient distribution of the wetting agent content along the thickness direction of the electrode sheet. The testing process specifically included:

[0168] (1) Sample preparation

[0169] Cutting: Cut the positive or negative electrode sheet of each embodiment and comparative example along the direction perpendicular to the electrode current collector to obtain a sample with the cross-section in the thickness direction. During the cutting process, care should be taken to avoid wetting agent migration caused by mechanical stress.

[0170] Gold plating treatment: A 5nm thick gold layer is sputtered onto the surface of the above cross section to eliminate the interference of surface charge accumulation on the electron beam.

[0171] Vacuum drying: The sample is placed in a vacuum drying oven (60℃, 12h) to dry it, so as to remove the residual solvent in the sample and prevent the residual solvent from evaporating and contaminating the chamber during the test.

[0172] (2) SEM-EDS test parameters

[0173] SEM conditions:

[0174] Accelerating voltage: 15kV (to balance penetration depth and resolution).

[0175] Working distance: 10mm.

[0176] Detector: Backscattered electron (BSE) mode, contrast reflects differences in element atomic number.

[0177] EDS conditions:

[0178] Surface scan region: In the above cross section, along the thickness direction of the electrode sheet (electrode current collector side → electrolyte layer side), it is divided into current collector side (C region), intermediate transition region (B region) and electrolyte side (A region). The sum of the dimensions of region A, region B and region C along the thickness direction of the electrode sheet is equal to the thickness of the electrode sheet.

[0179] Scanning mode: Mapping area scan (step size 1μm, dwell time 50ms / point), synchronously acquiring the X-ray signal intensity of F element in the wetting agent (energy 0.677keV, corresponding to F-Kα line).

[0180] (3) Data processing

[0181] Extraction of X-ray signal intensity of element F in wetting agent: The X-ray signal intensity of element F in regions A, B and C was integrated using software (Oxford INCA), and then the average X-ray signal intensity (counts) of regions A, B and C was calculated.

[0182] Gradient quantitative calculation: The distribution of wetting agent content along the thickness direction of the electrode sheet is characterized (verified) based on the proportion of X-ray signal intensity of element F. Specifically, the proportion of X-ray signal intensity of element F in region A (F intensity in region A) to the sum of X-ray signal intensities of element F in regions A, B, and C represents the ratio of the mass of wetting agent in region A to the total mass of wetting agent in the electrode active layer; the proportion of X-ray signal intensity of element F in region B (F intensity in region B) to the sum of X-ray signal intensities of element F in regions A, B, and C represents the ratio of the mass of wetting agent in region B to the total mass of wetting agent in the electrode active layer; and the proportion of X-ray signal intensity of element F in region C (F intensity in region C) to the sum of X-ray signal intensities of element F in regions A, B, and C represents the ratio of the mass of wetting agent in region C to the total mass of wetting agent in the electrode active layer.

[0183] The test results are shown in Table 1.

[0184] Table 1. Test results of wetting agent content in the electrode sheets of each embodiment and comparative example.

[0185]

[0186] Data Analysis:

[0187] In all embodiments, the X-ray signal intensity of element F in region A was higher than that in region C (the difference was 3-5 times). In Example 3, because region A had the highest proportion of wetting agent (61.6%), the gradient trend of the X-ray signal intensity of element F in the three regions was the steepest. In Example 5, the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate EtMeim-BF4 was used directly as a wetting agent without introducing additional lithium salt. The overall X-ray signal intensity of element F was slightly lower than that in Example 1, but the gradient trend of the X-ray signal intensity of element F in the three regions was still as expected.

[0188] In Comparative Example 1 (without wetting agent), the X-ray signal intensity of element F was background noise (approximately 200 counts), and there was no gradient distribution of the X-ray signal intensity of element F in the three regions. In Comparative Examples 2-3 (uniform distribution), the X-ray signal intensity of element F was uniformly distributed in the three regions (the proportion of wetting agent in region A was approximately 33%), which was in stark contrast to the examples. In Comparative Example 3, due to the higher total amount of wetting agent (20 wt%), the overall X-ray signal intensity of element F was higher than that of Comparative Example 2.

[0189] Furthermore, in Example 1, the X-ray signal intensity of F element in region A accounted for 52.1% of the total of the three regions, which was directly related to its low overpotential (40mV) and high cycle capacity retention (78%). This indicates that region A contains a high content of wetting agent, which can effectively optimize the interface between the electrode sheet and the electrolyte layer to compensate for the interface defects formed by the uniform distribution of wetting agent within the electrode sheet. In contrast, in Comparative Example 2, the X-ray signal intensity of F element in region A accounted for only 33.5% of the total of the three regions, resulting in insufficient interface wetting. Consequently, the overpotential of its pouch cell increased to 52mV, and the cycle capacity retention decreased to 72%. In Example 2 (total wetting agent content of 20wt%), the X-ray signal intensity of F element in region A reached 4850 counts, and the overpotential was further reduced to 35mV. This demonstrates that the gradient design of wetting agent content within the electrode sheet can accommodate higher wetting agent content without blocking electron conduction.

[0190] Experimental Example 2

[0191] The mass ratio of lithium salt to ionic liquid in the positive or negative electrode of each embodiment and comparative example was tested, specifically including:

[0192] 1) After cutting the electrode sample into small pieces, immerse it in xylene and sonicate it for 30 minutes at a power of 200W and a frequency of 40kHz. Then, centrifuge the ultrasonically treated material at a speed of 8000rpm for 10 minutes to remove electrolytes, conductive agents, and electrode active particles from the ultrasonically treated material. Collect the supernatant. Repeat the above steps twice, then combine the supernatants and concentrate them to 1mL to obtain the test solution for later use.

[0193] 2) Parameters of ion chromatography testing technology

[0194] Ion chromatography instrument: Dionex ICS-5000+ ion chromatography system (equipped with conductivity detector).

[0195] Chromatographic column:

[0196] Cation analysis: Dionex IonPac CS12A (4×250mm) separation column + CG12A guard column; Anion analysis: Dionex IonPac AS11-HC (4×250mm) separation column + AG11-HC guard column.

[0197] Mobile phase: cations (Li) + EtMeim + ): 20 mM methanesulfonic acid (MSA), flow rate 1.0 mL / min;

[0198] Anions (such as BF4) - FSI - Gradient elution program (0 min-10 min: 5 mM KOH; 10 min-20 min: 30 mM KOH), flow rate 1.2 mL / min.

[0199] Detector: Suppressed conductivity detection (cation: CSRS 500 4mm; anion: ASRS 500 4mm).

[0200] Column temperature: 30℃; injection volume: 25μL.

[0201] 3) Quantitative analysis

[0202] Standard curve: Prepare standard solutions of lithium salt (e.g., LiFSI) and ionic liquid (e.g., EtMeim-BF4) (concentration range of 0.1 mg / L to 10 mg / L) respectively, and establish a peak area-concentration calibration curve (R²). 2 ≥0.999).

[0203] Sample testing: Dilute the test solution to the linear range, inject and analyze, and record the Li values. + and anions in ionic liquids (such as FSI)- The peak area of ​​the lithium salt (such as LiFSI) was used to calculate the content of the lithium salt; and the content of the ionic liquid (such as EtMeim-BF4) was determined by total organic carbon (TOC) or nuclear magnetic resonance (NMR).

[0204] The test results are shown in Table 2.

[0205] Table 2 shows the mass ratio of lithium salt to ionic liquid in the positive or negative electrode of each embodiment and comparative example.

[0206]

[0207] The deviations between the measured and designed values ​​of the mass ratio of lithium salt and ionic liquid in each embodiment and comparative example are ≤1.5%, indicating that the above-mentioned extraction and content analysis methods for lithium salt and ionic liquid are reliable.

[0208] The test results of each embodiment show that the concentration of the wetting agent in the electrode active layer increases along the direction away from the electrode current collector (gradient distribution) and does not affect the mass ratio of lithium salt and ionic liquid. In Example 5, no lithium salt (LiFSI) was added, but trace amounts of Li were detected. + (0.2%) may be due to lithium salt residue or background interference in the electrode sheet.

[0209] Experimental Example 3

[0210] The following parameters of the positive or negative electrode sheets of each embodiment and comparative example were tested:

[0211] 1. Assemble the positive or negative electrode sheets into a solid-state battery.

[0212] 1) After transferring the Li6PS5Cl electrolyte onto the silicon negative electrode sheet (11*21cm), it was stacked with the positive electrode sheets of Examples 1 to 8 and Comparative Examples 1 to 3 respectively. The number of positive electrode sheets was 10 and the number of negative electrode sheets was 11. Then, it was encapsulated with aluminum-plastic film and subjected to isostatic pressing at 300MPa to assemble into the soft-pack batteries of Examples 1 to 8 and Comparative Examples 1 to 3.

[0213] 2) After transferring the Li6PS5Cl electrolyte onto the NCM811 positive electrode sheet (11*21cm), it is stacked with the negative electrode sheet of Example 9. The number of positive electrode sheets is 10 and the number of negative electrode sheets is 11. Then, it is packaged with aluminum-plastic film and subjected to isostatic pressure of 300MPa to assemble the soft pack battery of Example 9.

[0214] 2. Test the cycle capacity retention and overvoltage of the above-mentioned soft-pack batteries.

[0215] Ten pouch cells from each embodiment and comparative example were placed in a LAND CT 2001C secondary battery performance testing system and tested at a constant temperature of 45°C. The tests included:

[0216] 1) Charge-discharge cycle test:

[0217] Charge-discharge cycles were performed at a constant current of 0.2C, with a charging cutoff voltage of 4.2V and a discharging cutoff voltage of 2.5V. Each cycle included the following steps:

[0218] a. Charge at constant current to 4.2V;

[0219] b. Charge at constant voltage until the current drops to 0.05C;

[0220] c. Let stand for 10 minutes;

[0221] d. Discharge at a constant current to 2.5V;

[0222] e. Let it stand for 10 minutes before starting the next cycle.

[0223] The number of cycles was set to 200. The discharge capacity of the 1st and 200th cycles was recorded. The ratio of the discharge capacity of the 200th cycle to the discharge capacity of the 1st cycle was calculated, which is the capacity retention rate after 200 cycles.

[0224] 2) Overpotential test:

[0225] Constant current charging and discharging were performed at 45℃ at rates of 0.5C and 1C, and the average value of the voltage difference in the plateau region of the charging and discharging curve was recorded as the overpotential.

[0226] The test results of 10 batteries from each embodiment and comparative example were taken as the arithmetic mean, and the standard deviation was controlled within ±5%.

[0227] Table 3. Overvoltage and cycle capacity retention rates of the pouch cells in each embodiment and comparative example.

[0228]

[0229] Data Analysis:

[0230] The overvoltage of the pouch cells in each embodiment was lower than that of the pouch cells in the comparative example, and the cycle capacity retention rate of the pouch cells in each embodiment was higher than that of the pouch cells in the comparative example. This indicates that the concentration of wetting agent in the electrode active layer increases along the direction away from the electrode current collector, which helps to reduce the overvoltage of the battery and improve the cycle capacity retention rate. Compared with the overvoltage of the comparative example, the overvoltage of the embodiments was reduced by more than 30%, and the capacity retention rate was improved by 15% to 23%, which essentially solved the imbalance problem of overvoltage and cycle performance of the battery caused by uniform distribution of wetting agent or absence of wetting agent.

[0231] Taking Example 1 as an example, its overpotential at 0.5C rate is 40mV, and its capacity retention rate after 200 cycles reaches 78%. In contrast, Comparative Example 1, due to the absence of wetting agent, has an overpotential that rises to 65mV and a capacity retention rate of only 62%.

[0232] Under the same interfacial wetting agent content, the performance of a gradient-distributed interfacial wetting agent is superior to that of a uniformly distributed one: for example, Example 1 had a lower overpotential at 0.5C than Control Example 2, and a higher capacity retention rate after 200 cycles; Example 2 had a lower overpotential at 0.5C than Control Example 3, and a higher capacity retention rate after 200 cycles. It is evident that the difference in overpotential and cycle capacity retention rate stems from the wetting agent content mechanism of the gradient design. The high-content wetting agent region far from the electrode current collector effectively bridges the interfacial defects between the electrode sheet and the solid electrolyte layer, reducing ion transport impedance, while the low-content region near the electrode current collector avoids excessive wetting agent blocking the electron conduction path, thereby synergistically optimizing ion and electron transport efficiency. Furthermore, when the mass ratio of wetting agent to solid electrolyte in the electrode sheet is increased to 20%, interfacial ion transport can be further optimized. As shown in Example 2, the overpotential is further reduced to 35mV, and the capacity retention rate after 200 cycles is increased to 85%.

[0233] Compared with Example 1, the proportion of wetting agent on the fluid side of the far collector electrode in Example 4 is increased to 70%, the overpotential of the corresponding pouch cell is reduced to 38mV, and the capacity retention rate after 200 cycles is increased to 80%, which proves that expanding the content gradient of wetting agent is beneficial to further improve the interface between the electrode sheet / solid electrolyte layer and the interfacial wettability between particles inside the electrode sheet.

[0234] In addition, Example 5 directly used the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EtMeim-BF4) as an interface wetting agent, which improved the capacity retention rate to 81%, verifying that pure ionic liquids can also bring benefits to the battery's overvoltage and cycle capacity retention rate without the addition of lithium salts.

[0235] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrode sheet, characterized by, The device includes an electrode current collector and an electrode active layer disposed on at least one side of the electrode current collector. The electrode active layer includes a wetting agent, and the concentration of the wetting agent in the electrode active layer increases in the direction away from the electrode current collector.

2. The electrode pad of claim 1, wherein The concentration of the wetting agent in the electrode active layer increasing along the direction away from the electrode current collector includes: the concentration of the wetting agent in the electrode active layer gradually increasing along the direction away from the electrode current collector.

3. The electrode sheet according to claim 1 or 2, characterized by The electrode active layer includes regions C, B, and A sequentially along the direction away from the electrode current collector; the region between 0 and 1 / 3 of the thickness of the electrode active layer is denoted as region A, the region between 1 / 3 and 2 / 3 of the thickness is denoted as region B, and the region between 2 / 3 and 3 / 3 of the thickness is denoted as region C. The ratio of the mass of the wetting agent in region A to the total mass of the wetting agent in the electrode active layer is 50% to 70%. The ratio of the mass of the wetting agent in region B to the total mass of the wetting agent in the electrode active layer is 20% to 35%. The ratio of the mass of the wetting agent in region C to the total mass of the wetting agent in the electrode active layer is 10% to 20%.

4. The electrode sheet according to any one of claims 1 to 3, characterized by In the thickness direction of the electrode sheet, the electrode active layer includes N stacked sub-electrode active layers, where N is greater than or equal to 2. In any two adjacent sub-electrode active layers, the concentration of the wetting agent in the sub-electrode active layer farther from the electrode current collector is greater than the concentration of the wetting agent in the sub-electrode active layer closer to the electrode current collector.

5. The electrode sheet according to any one of claims 1 to 4, characterized by The wetting agent includes an ionic liquid.

6. The electrode pad of claim 5, wherein The ionic liquid comprises cations and anions. The cations include one or more of imidazole cations, heterocyclic organic cations, quaternary ammonium cations, pyridine cations, pyrrole cations, and piperidine cations. The anions include one or more of fluorosulfonylimide anions, tetrafluoroborate anions, and sulfonate anions.

7. The electrode sheet according to any one of claims 1 to 6, characterized by The wetting agent comprises a complex of lithium salt and ionic liquid.

8. The electrode pad of claim 7, wherein The lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

9. The electrode sheet according to claim 7 or 8, characterized in that, The mass ratio of the lithium salt to the ionic liquid is 1:(8-10).

10. The electrode sheet according to any one of claims 1-9, characterized in that, The electrode active layer further includes a solid electrolyte, and the mass ratio of the wetting agent to the solid electrolyte is 1% to 20%.

11. The electrode sheet according to claim 10, characterized in that, The solid electrolyte includes one or more of sulfide electrolytes, oxide electrolytes, and chloride electrolytes.

12. The electrode sheet according to any one of claims 1 to 11, characterized by The electrode sheet is a positive electrode sheet; Preferably, the electrode active layer includes a positive electrode active material, which includes one or more of binary materials, ternary materials, and phosphate materials. The binary materials include one or more of lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide. The phosphate materials include one or more of lithium iron phosphate, lithium cobalt phosphate, lithium manganese phosphate, and lithium nickel phosphate. The ternary materials include one or more of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

13. The electrode sheet according to any one of claims 1 to 12, characterized by The electrode sheet is a negative electrode sheet; Preferably, the electrode active layer includes a negative electrode active material, which includes one or more of lithium metal, graphite, hard carbon, tin, silicon, silicon carbide, titanium dioxide, soft carbon, silicon oxide, lithium titanate, red phosphorus, and black phosphorus.

14. A method of producing the electrode sheet according to any one of claims 1 to 13, characterized by, include: The electrode active layer is formed on at least one side of the electrode current collector to obtain the electrode sheet.

15. The method of claim 14, wherein, The process of forming the electrode active layer on at least one side of the electrode current collector includes: An electrode active layer precursor is formed on at least one side of the electrode current collector; The coating solution containing the wetting agent is applied to the surface of the electrode active layer precursor, and then dried at 50°C to 100°C for 0.5h to 3.0h to form the electrode active layer, thereby obtaining the electrode sheet.

16. The method of claim 14, wherein, The process of forming the electrode active layer on at least one side of the electrode current collector includes: Prepare N portions of electrode active slurry, where N is greater than or equal to 2; wherein each of the N portions of electrode active slurry contains the wetting agent, and the concentration of the wetting agent in any two portions of the electrode active slurry is different; According to the order of increasing concentration of the wetting agent in the electrode active slurry, N parts of the electrode active slurry are sequentially coated on at least one side of the electrode current collector to form N stacked sub-electrode active layers, thereby forming the electrode active layer and obtaining the positive electrode sheet.

17. A secondary battery characterized by comprising: The electrode sheet includes the electrode sheet according to any one of claims 1-13 or the electrode sheet prepared according to any one of claims 14-16.

18. The secondary battery according to claim 17, characterized by The secondary battery is a solid-state battery or a semi-solid-state battery.

19. The secondary battery according to claim 17 or 18, characterized in that, The battery includes a positive electrode plate, a negative electrode plate, and a separator membrane between the positive electrode plate and the negative electrode plate; the separator membrane includes a second solid electrolyte.

20. A battery assembly comprising: The battery assembly includes at least two secondary batteries as described in any one of claims 17-19.

21. An electrical device, comprising: The device includes a secondary battery as described in any one of claims 17-19 or a battery assembly as described in claim 20, wherein the secondary battery or the battery assembly serves as a power supply for the electrical device.

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