A method of evaluating the interface condition of a lithium-ion battery electrode sheet, a separator structure, and a battery electrode sheet-separator structure

Abstract

The application discloses a kind of methods for evaluating lithium ion battery pole piece interface condition, diaphragm structure and battery pole piece-diaphragm structure, belong to lithium ion battery field.It includes the following steps:S1, coating: functional coating is carried out to battery diaphragm, and functional coating material is coating slurry containing solid electrolyte Li 1+x Al x Ti 2x (PO4)3, x=0.01-0.5;S2, manufacturing battery;S3, evaluation: battery is disassembled, and the interface state of pole piece is judged by observing the interface of functional diaphragm close to negative pole side.The application utilizes the property that solid electrolyte LATP is reduced and discolored at low potential, and the slurry containing LATP is coated on the surface of diaphragm close to negative pole side, to realize the quick and intuitive evaluation of pole piece interface state.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, and more specifically, relates to a method for evaluating the interface condition of lithium-ion battery electrodes, a separator structure, and a battery electrode-separator structure. Background Technology

[0002] Since their commercialization nearly 30 years ago, lithium-ion batteries have been widely used in consumer electronics, electric vehicles, and energy storage due to their high energy density, environmental friendliness, and long lifespan. To meet increasingly demanding performance requirements, continuous optimization of lithium-ion battery materials and structures is essential. Interface issues have been a major challenge in optimizing lithium-ion membrane batteries, particularly the negative electrode interface. Only a negative electrode interface with good contact with the separator and a uniform and stable SEI film can guarantee excellent battery performance. However, in reality, various factors prevent the negative electrode interface from achieving the expected uniformity and stability. For example, gases generated during battery formation can form bubbles at the electrode interface. These bubbles hinder electrolyte wetting, thus impeding lithium-ion transport, increasing migration paths, and creating dark areas in uncontacted regions. Lithium may also deposit around these dark areas (which do not participate in electrochemical reactions), affecting overall battery performance such as capacity, rate performance, and cycle life, and in severe cases, potentially leading to safety accidents.

[0003] Researchers are exploring various methods to optimize lithium-ion battery interfaces, such as optimizing the positive and negative electrode plates, battery assembly processes, and battery formation and capacity testing processes. These optimization methods all rely on the effective assessment of the lithium-ion battery electrode interface condition; therefore, how to effectively assess the lithium-ion battery electrode interface condition is crucial. Existing methods for assessing the lithium-ion battery electrode interface condition mainly include observing the electrode interface state through battery disassembly, indirect assessment through battery performance testing, and characterization methods such as CT scanning to observe the electrode state. These methods all have certain limitations in assessing the electrode interface, either due to long assessment cycles or a lack of intuitiveness and effectiveness. Therefore, there is an urgent need to provide a more effective method for assessing the lithium-ion battery electrode interface condition. For example, patent CN109342952A discloses a method for evaluating the interface between the electrode and electrolyte of a lithium-ion battery, including the following steps: Assembling multiple single-layer soft-pack full cells using positive and negative electrode sheets from the same batch, coated on one side; after standing, charging two cells to a fully charged state and discharging them to an empty state respectively after formation; disassembling the fully charged and empty full cells in a glove box and removing the positive and negative electrode sheets; removing residual electrolyte from the positive and negative electrode sheets; assembling the negative electrode sheet in the fully charged state and the negative electrode sheet in the empty state into a negative electrode symmetrical battery; after standing, performing a cycle test under constant current and temperature. Assembling the positive electrode sheet in the empty state and the positive electrode sheet in the fully charged state into a positive electrode symmetrical battery; after standing, performing a cycle test under constant current and temperature. Cycling the positive and negative electrode symmetrical batteries to different cycle numbers and performing impedance tests. Patent CN105652214A discloses an evaluation method for the interface between the negative electrode and electrolyte in a lithium-ion battery, comprising: selecting a batch of negative electrode sheets with single-sided coating, using a certain electrolyte, and assembling them into a symmetrical battery; after standing for a period of time, applying a constant current to the symmetrical battery and conducting a cycle performance test; plotting the change curve of the polarization voltage of the symmetrical battery with test time; analyzing and judging the stability of the SEI film formed at the interface between the batch of negative electrode sheets and the electrolyte, as well as the compatibility between the active material of the batch of negative electrode sheets and the electrolyte; selecting the same batch of negative electrode sheets with single-sided coating, using other different types of electrolytes, assembling them into a symmetrical battery, and repeating the above steps. Patent CN112068002A discloses a method for rapidly evaluating ceramic composite electrodes. The method includes: assembling electrodes coated with ceramic coatings of different thicknesses into a first symmetrical battery, assembling blank electrodes into a second symmetrical battery, and obtaining electrical performance information for both; assembling electrodes coated with ceramic coatings of different thicknesses into a first single-cell pouch battery, assembling blank electrodes into a second single-cell pouch battery, simulating an abuse environment, and obtaining safety information for both; and evaluating the performance of electrodes coated with ceramic coatings of different thicknesses based on the electrical performance information of the first and second symmetrical batteries, the safety information of the first and second single-cell pouch batteries, and the safety information of the second single-cell pouch batteries.

[0004] Lithium aluminum titanium phosphate (LATP) exhibits high lithium-ion conductivity, enhancing lithium-ion transport efficiency. Compared to other materials, LATP possesses structural stability, strong chemical stability, and excellent cycle performance, making it commonly used in electrodes and separators to improve the ionic conductivity of the positive electrode and reduce battery internal resistance. For example, patent CN114171848A describes a method where a slurry is directly coated onto the electrode; patent CN104103873A describes a method where a solid electrolyte is plated onto a porous ceramic substrate to isolate the lithium metal negative electrode and the porous positive electrode, thereby improving ion conductivity; and patent WO2021184768A1 describes a method where LATP is coated onto the electrode surface to reduce the reactivity between the solid sulfide electrolyte layer and the positive electrode material, thus reducing the surface charge layer effect and ensuring rapid lithium-ion migration. Patent CN113540688A describes a method of uniformly coating a dispersion onto a separator substrate using porous extrusion. After drying, a separator coating material is obtained. The excellent thermodynamic properties of LATP are used to regulate the transport of lithium ions, especially at low temperatures, and to improve the adhesion between LATP and the positive and negative electrode sheets. However, the patent does not address the application of LATP in evaluating the interface condition of lithium-ion battery electrodes. Summary of the Invention

[0005] 1. The problem to be solved

[0006] To address the problems of long evaluation cycles and lack of intuitiveness and effectiveness in existing methods for assessing the interface condition of lithium-ion battery electrodes, this invention provides a method for assessing the interface condition of lithium-ion battery electrodes, which enables rapid and intuitive assessment of the battery electrode interface condition.

[0007] 2. Technical Solution

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0009] A coating slurry comprising a solid electrolyte, a binder, a dispersant, and a wetting agent in a mass percentage of (92-99.97):(0.01-3):(0.01-3):(0.01-2).

[0010] The coating slurry is an aqueous dispersion slurry, which also includes deionized water. The solid content of the coating slurry is 20-40 wt%. Alternatively, an oil-based dispersion system can be used, wherein the dispersed phase is DMC (dimethyl carbonate), acetone, or NMP (N-methylpyrrolidone), with a solid content of 20-40 wt%, sufficient to disperse the solid electrolyte, binder, dispersant, and wetting agent in the slurry. This invention controls the solid content of the slurry to 20-40 wt%. By adjusting the ratio of solid electrolyte, binder, dispersant, and wetting agent, the resulting slurry has low viscosity, allowing for a thinner coating on the separator. The thickness of the functional coating is controlled between 0.5 μm and 5 μm. If the coating is too thin, the interfacial reaction sensitivity is poor; if the coating is too thick, the battery permeability is poor and it does not meet battery design requirements. By controlling the mass percentages of solid electrolyte, binder, dispersant, and wetting agent at (92-99.97):(0.01-3):(0.01-3):(0.01-2), the resulting functional coating-coated diaphragm exhibits good air permeability, peel strength, and heat shrinkage properties. Good air permeability is achieved by controlling the mass ratio, particle size distribution, and proportion of additives in the solid electrolyte; good peel strength and heat shrinkage properties are achieved by controlling the type and ratio of binder.

[0011] The solid electrolyte is a NASCION-type solid electrolyte material, and the NASCION-type solid electrolyte is: Li 1+x Al x Ti 2x (PO4)3, where x is between 0.01 and 0.5. Controlling x within this range is crucial. The amount of Li doping affects the ionic conductivity and reducibility of the electrolyte. If the Li doping amount is too low (x is too small), the electrolyte's ionic conductivity and reducibility are poor, the interface reaction is slow, and the blackening phenomenon is delayed. If the Li doping amount is too high (x is too large), lattice distortion is likely to occur. Preferably, x is 0.3. The particle size of the solid electrolyte is between 10 nm and 20 μm, and the shape is an irregular polygon. Preferably, the particle size is controlled between 0.1 nm and 5 μm. If the particles are too small, they are prone to clogging the pores of the separator, affecting the battery's permeability. If the particles are too large, the coating uniformity cannot be ensured, the coating thickness will be too thick, and the specific surface area of ​​large electrolyte particles is small, resulting in a slow reaction and low sensitivity.

[0012] Preferably, the adhesive is styrene-butadiene rubber, and one or more of polyvinylpyrrolidone, acrylate or polyvinyl alcohol may also be used.

[0013] Preferably, the dispersant is sodium dodecylbenzene sulfate, but polyacrylate or compounds containing amino aromatic groups, such as amino aromatic ethers or amino aromatic esters, may also be used.

[0014] Preferably, the wetting agent is a polyether organosilicon copolymer, including polyether siloxane, polyether-modified polydimethylsiloxane, etc.

[0015] The present invention also discloses a method for preparing the above-mentioned coating slurry, comprising the following steps:

[0016] A dispersion is obtained by stirring and dispersing a solid electrolyte, a dispersant, and water for 1-3 hours, preferably at a stirring speed of 1000-2000 rpm; a binder is added to the dispersion and stirred and dispersed for 0.5-2 hours to obtain a slurry, preferably at a stirring speed of 100-500 rpm; a wetting agent is added to the slurry and stirred for 0.1-0.5 hours, and the slurry is filtered to obtain a coating slurry, preferably with a filter mesh of 100-200 mesh.

[0017] Preferably, the above preparation process is carried out at a temperature of 20-40°C, and the dispersion process can be carried out using a high-speed disperser, such as a dual planetary high-speed disperser.

[0018] The present invention also discloses a separator structure, including a base membrane and at least one functional coating applied to the side near the negative electrode of the battery. To enhance the separator performance, the base membrane may be coated with at least one reinforcing layer, such as an alumina ceramic coating, a silica coating, or a hydrated aluminum hydroxide coating. In addition, other materials may be coated, and the resulting material serves as the substrate for the functional coating.

[0019] The preparation method of the diaphragm structure includes the following steps: uniformly coating the diaphragm structure surface with a coating slurry using a high-precision coating machine; the coating method is micro-gravure roller coating; and the main material of the coating slurry is the solid electrolyte lithium titanium aluminum phosphate (Li). 1+ x Al x Ti 2x (PO4)3, LATP), the coating method is single-sided coating.

[0020] Preferably, the coating speed is 25-50 m / min and the drying temperature is 40-70℃.

[0021] Preferably, the coating thickness of the functional coating is 0.5µm-5µm.

[0022] The membrane structure can be the membrane structure of the present invention, that is, including a base membrane and at least one functional coating, or it can be an existing membrane structure.

[0023] The separator structure is used to prepare a battery electrode-separator structure, which includes a positive electrode, a negative electrode, a base film, and a functional coating applied to the surface of the base film near the negative electrode.

[0024] A reinforcing layer, such as an alumina ceramic coating, a silica coating, or a hydrated aluminum hydroxide coating, can also be applied. The reinforcing layer can be applied to the base film surface near the positive electrode of the battery, or simultaneously applied to the base film surface near the negative electrode of the battery, to enhance the strength of the base film.

[0025] By observing the degree and uniformity of blackening of the separator on the negative electrode side, the battery interface state is observed. The greater the degree of blackening of the functional separator, the better the contact between the functional coating and the electrode sheet, and the better the battery interface state. The more uniform the degree of blackening of the functional separator, the more uniform the battery interface.

[0026] The method for evaluating the interface condition of lithium-ion battery electrodes using the above-prepared separator structure specifically includes the following steps:

[0027] S1. Coating: According to the battery design requirements, the selected lithium-ion battery separator is functionally coated to obtain a functional separator. The coating material is a mixture containing solid electrolyte Li. 1+x Al x Ti 2x (PO4)3 coating slurry, x = 0.01-0.5;

[0028] S2. Manufacturing batteries: During the normal production process of batteries, a certain number of batteries are manufactured using the functional separator from step S1. Except for the separator, other materials and process conditions are consistent with those of batteries produced in normal production.

[0029] S3. Evaluation: Disassemble the battery and observe the interface of the functional separator on the negative electrode side to determine the state of the electrode interface.

[0030] The principle behind the aforementioned evaluation method is as follows: Solid electrolyte LATP has the characteristic of being reduced at low potentials. After reduction, LATP changes from white to black. When LATP is coated on the surface of the separator and comes into contact with the negative electrode in a lithium-ion battery, the negative electrode potential decreases after charging, causing LATP to be reduced and the separator to turn black on the negative electrode side. This reduction and blackening is highly sensitive to the contact condition and interfacial pressure between the separator and the negative electrode in lithium-ion batteries; the better the contact and the greater the pressure, the easier it is for LATP to be reduced and turn black. Simultaneously, defects on the positive and negative electrode sheets, such as particles, scratches, and excessive compaction, affect lithium-ion intercalation and also influence the decrease in the negative electrode potential, thus being reflected in the functional separator, allowing for a direct assessment of the electrode state. Utilizing this characteristic, the electrode interface state can be determined by directly observing the negative electrode side interface of the separator after disassembling the battery.

[0031] The method for evaluating the interface condition of lithium-ion battery electrodes of the present invention is applicable to all lithium-ion batteries, such as wound square aluminum-cased batteries, stacked pouch batteries, and cylindrical aluminum-cased batteries.

[0032] 3. Beneficial effects

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] This invention utilizes the property of the solid electrolyte LATP to change color when reduced at low potential. A coating slurry containing LATP is coated onto the separator near the negative electrode, enabling rapid assessment of the electrode interface state. Compared with the prior art, which assesses the electrode interface state by obtaining electrochemical performance, the assessment cycle is long and not intuitive or effective. This invention achieves rapid and intuitive assessment of the battery electrode interface state. Attached Figure Description

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that these drawings are designed for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless specifically indicated, these drawings are intended only to conceptually illustrate the structural construction described herein and are not necessarily drawn to scale.

[0036] Figure 1 This is a schematic diagram of the diaphragm structure in Embodiment 1 of the present invention;

[0037] Figure 2 This is a schematic diagram of the diaphragm structure in Embodiment 2 of the present invention;

[0038] Figure 3 This is the battery electrode-separator structure obtained in Example 2 of the present invention;

[0039] Figure 4 This is a schematic diagram of the diaphragm structure in Embodiment 3 of the present invention;

[0040] In the diagram: 1. Base film; 2. Alumina ceramic coating; 3. Functional coating; 4. Battery negative electrode; 5. Battery positive electrode. Detailed Implementation

[0041] The following detailed description of exemplary embodiments of the invention is taken with reference to the accompanying drawings, which form part of the description and illustrate exemplary embodiments in which the invention may be practiced. While these exemplary embodiments have been described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be implemented and various changes may be made to the invention without departing from the spirit and scope thereof. The more detailed description of embodiments of the invention below is not intended to limit the scope of the claimed invention, but is merely illustrative and not restrictive of the description of the features and characteristics of the invention, to suggest the best mode for carrying out the invention, and is sufficient to enable those skilled in the art to practice the invention. Therefore, the scope of the invention is defined only by the appended claims.

[0042] The following detailed description and exemplary embodiments of the invention can be better understood in conjunction with the accompanying drawings, wherein the elements and features of the invention are identified by reference numerals.

[0043] The battery manufacturing process utilizes existing battery manufacturing technologies and includes the following steps:

[0044] S1. Electrode Manufacturing: The positive electrode material, negative electrode material, conductive agent, binder, and other additives are dispersed in an oil-based / water-based system. The slurry is then coated onto aluminum or copper foil using a transfer or spray coating method. The electrode sheet is rolled to the designed thickness and then die-cut to the required size to obtain the positive electrode sheet and negative electrode sheet. The positive electrode material can be lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide, etc., the negative electrode material can be graphite, silicon suboxide, etc., and the conductive agent can be carbon black, carbon nanotubes, etc.

[0045] S2. Cell Assembly: The positive electrode sheet, negative electrode sheet and separator are wound or stacked into bare cells using a lithium-ion battery winding machine, stacking machine, etc. At the same time, a certain number of bare cells using functional separators are wound or stacked. During the winding or stacking process, it is ensured that the functional coating of the separator and the negative electrode sheet of the battery are in contact.

[0046] S3. Battery Assembly: The bare cell is sealed by welding tabs, inserting into an aluminum shell, welding the top cover, and then baking at high temperature to remove moisture. Then, the designed amount of electrolyte is injected to obtain a complete cell; wherein, the aluminum-plastic film can be an aluminum-plastic film.

[0047] S4. Battery formation and capacity testing: The cells that have been filled with electrolyte are formed to activate the battery, and the basic performance of the battery is determined by capacity testing, and finally the finished battery is obtained.

[0048] Example 1

[0049] Example 1 provides a method for evaluating the interface condition of lithium-ion battery electrodes, using a functional separator to evaluate the interface condition of a wound square aluminum-cased battery.

[0050] The specific steps are as follows:

[0051] S1. Coating: According to the battery design requirements, the selected lithium-ion battery separator is functionally coated to obtain a functional separator. The coating material is a mixture containing solid electrolyte Li. 1+x Al x Ti 2x (PO4)3 coating slurry, where x = 0.01;

[0052] S2. Battery manufacturing: During the normal production process of the battery, a certain number of cores are wound using the functional separator from step S1 during the winding process. During the winding process, ensure that the functional coating of the separator and the negative electrode of the battery are aligned. The subsequent assembly, liquid injection, formation and capacity testing processes are consistent with those of normal batteries. Except for the separator, other materials are consistent with those of normally produced batteries.

[0053] S3. Evaluation: If it is necessary to evaluate the battery electrode interface condition under a certain production process, select a battery using a functional separator under the same conditions, disassemble the battery, and observe the interface of the separator on the negative electrode side to determine the electrode interface condition. If necessary, take photos of the separator interface with a camera for intuitive comparison of the interface condition under different evaluation process conditions. The main criteria for judgment are the degree of blackening and the uniformity of blackening on the negative electrode side of the separator.

[0054] The composition ratio, process parameters, and coating process of the coating slurry are shown in Tables 1-3.

[0055] The coating slurry comprises a solid electrolyte, a binder, a dispersant, and a wetting agent, wherein the solid electrolyte is Li. 1+ x Al x Ti 2x The electrolyte is (PO4)3, where x = 0.01, and the particle size is 1.0 μm. The binder is styrene-butadiene rubber, the dispersant is sodium dodecylbenzene sulfate, and the wetting agent is polyether siloxane. The mass percentage of the solid electrolyte, binder, dispersant, and wetting agent is 94:2:2:1. The coating slurry is an aqueous dispersion slurry, which also includes deionized water, and the solid content of the coating slurry is 21 wt%.

[0056] The preparation method of the above-mentioned coating slurry includes the following steps:

[0057] The solid electrolyte, dispersant, and water were stirred and dispersed for 1.3 hours to obtain a dispersion at a stirring speed of 1200 rpm.

[0058] Add a binder to the dispersion and stir for 0.6 hours to obtain a slurry. The stirring speed is 200 rpm.

[0059] Add wetting agent to the slurry and stir for 0.3 hours. Filter to obtain the coating slurry with a filter screen of 200 mesh.

[0060] The above process was carried out at a temperature of 25°C.

[0061] The preparation method of the diaphragm structure includes the following steps: uniformly coating the diaphragm structure surface with a coating slurry using a high-precision coating machine; the coating method is micro-gravure roller coating; and the main material of the coating slurry is the solid electrolyte lithium titanium aluminum phosphate (Li). 1+ x Alx Ti 2x (PO4)3, x = 0.01), the coating method is single-sided coating.

[0062] Preferably, the coating speed is 30 m / min and the drying temperature is 65°C.

[0063] Preferably, the coating thickness of the functional coating is 2 μm.

[0064] The separator structure includes a base film, an alumina ceramic coating, and a functional coating, wherein the alumina ceramic coating and the functional coating are respectively coated on both sides of the base film. The resulting battery electrode-separator structure includes a base film, an alumina ceramic coating, a functional coating, and battery electrodes, wherein the alumina ceramic coating and the functional coating are respectively coated on both sides of the base film. The battery electrodes include a negative electrode and a positive electrode, wherein the negative electrode is disposed on the surface of the functional coating, and the positive electrode is disposed on the surface of the alumina ceramic coating.

[0065] The selected separator structure is 9+3+2, where 9 represents a 9µm PE wet-process lithium-ion battery separator base film, 3 represents a 3µm alumina ceramic coating applied to the surface of the base film, and 2 represents a 2µm thick functional coating containing LATP solid electrolyte applied to the surface of the base film opposite the alumina ceramic coating. 9+3 is the separator structure used in conventional batteries.

[0066] The selected battery system is lithium iron phosphate / graphite, with a nominal battery capacity of 60Ah.

[0067] A schematic diagram of the diaphragm structure in this embodiment is shown below. Figure 1 As shown.

[0068] Example 2

[0069] Example 2 provides a method for evaluating the interface condition of lithium-ion battery electrodes, using a specially designed functional separator to evaluate the interface condition of a stacked pouch cell.

[0070] The specific steps are as follows:

[0071] S1. Coating: According to the battery design requirements, the selected lithium-ion battery separator is functionally coated to obtain a functional separator. The coating material is a mixture containing solid electrolyte Li. 1+x Al x Ti 2x (PO4)3 coating slurry, where x = 0.5;

[0072] S2. Battery manufacturing: During the normal production process of the battery, a certain number of cells are assembled using the functional separator from step S1 during the stacking process. During the stacking process, ensure that the functional coating of the separator and the negative electrode of the battery are aligned. Subsequent assembly, liquid injection, formation and capacity testing processes are consistent with those of normal batteries. Except for the separator, other materials are consistent with those of normally produced batteries.

[0073] S3. Evaluation: If it is necessary to evaluate the battery electrode interface condition under a certain production process, select a battery using a functional separator under the same conditions, disassemble the battery, and observe the interface of the separator on the negative electrode side to determine the electrode interface condition. If necessary, take photos of the separator interface with a camera for intuitive comparison of the interface condition under different evaluation process conditions. The main criteria for judgment are the degree of blackening and the uniformity of blackening on the negative electrode side of the separator.

[0074] The composition ratio, process parameters, and coating process of the coating slurry are shown in Tables 1-3.

[0075] The coating slurry comprises a solid electrolyte, a binder, a dispersant, and a wetting agent, wherein the solid electrolyte is Li. 1+ x Al x Ti 2x The electrolyte is (PO4)3, where x = 0.5, and the particle size is 0.7 μm. The binder is acrylate, the dispersant is polyacrylate, and the wetting agent is polyether siloxane. The mass percentages of the solid electrolyte, binder, dispersant, and wetting agent are 95:3:1.5:0.5. The coating slurry is an aqueous dispersion slurry, which also includes deionized water. The solid content of the coating slurry is 31 wt%.

[0076] The preparation method of the above-mentioned coating slurry includes the following steps:

[0077] Solid electrolyte, dispersant and water were stirred and dispersed for 1.5 h to obtain a dispersion at a stirring speed of 1600 rpm; binder was added to the dispersion and stirred and dispersed for 1.5 h to obtain a slurry at a stirring speed of 300 rpm; wetting agent was added to the slurry and stirred for 0.2 h, and then filtered to obtain a coating slurry with a filter mesh of 200 mesh.

[0078] The above process was carried out at a temperature of 25°C.

[0079] The preparation method of the diaphragm structure includes the following steps: uniformly coating the diaphragm structure surface with a coating slurry using a high-precision coating machine; the coating method is micro-gravure roller coating; and the main material of the coating slurry is the solid electrolyte lithium titanium aluminum phosphate (Li). 1+ x Al x Ti 2x (PO4)3, x=0.5), the coating method is single-sided coating.

[0080] Preferably, the coating speed is 40 m / min and the drying temperature is 65°C.

[0081] Preferably, the coating thickness of the functional coating is 1 μm.

[0082] The separator structure includes a base film, two layers of alumina ceramic coating, and a functional coating. The alumina ceramic coating is coated on both sides of the base film, and the functional coating is coated on one side of the functional coating surface. The resulting battery electrode-separator structure includes a base film, two layers of alumina ceramic coating, and a functional coating. The alumina ceramic coating is coated on both sides of the base film, and the functional coating is coated on one side of the functional coating surface. The battery electrode includes a negative electrode and a positive electrode. The negative electrode is disposed on the functional coating surface, and the positive electrode is disposed on the alumina ceramic coating surface.

[0083] The selected functional separator coating structure is 12+3+3+1, where 12 represents a 12µm PE wet-process lithium-ion battery separator base film, 3 represents a 3µm alumina ceramic coating coated on both sides of the base film, and 1 represents a 1µm thick LATP solid electrolyte coating coated on the surface of the ceramic coating. 12+3+3 is the separator structure used in conventional batteries.

[0084] The selected battery system is lithium nickel cobalt manganese oxide / graphite, with a nominal battery capacity of 80Ah.

[0085] A schematic diagram of the diaphragm structure in this embodiment is shown below. Figure 2 As shown in the diagram, the battery electrode-separator structure is as follows: Figure 3 As shown.

[0086] Example 3

[0087] Example 3 provides a method for evaluating the interface condition of lithium-ion battery electrodes, using a specially designed functional separator to evaluate the interface condition of a cylindrical aluminum-cased battery.

[0088] The specific steps are as follows:

[0089] S1. Coating: According to the battery design requirements, the selected lithium-ion battery separator is functionally coated to obtain a functional separator. The coating material is a mixture containing solid electrolyte Li. 1+x Al x Ti 2x (PO4)3 coating slurry, where x = 0.2;

[0090] S2. Battery Manufacturing: During normal battery production, a certain number of cores are assembled using the functional separator from step S1 during the lamination process. During winding, it is ensured that the functional coating of the separator and the negative electrode sheet of the battery are aligned. Subsequent assembly, electrolyte injection, formation, and capacity testing processes are consistent with those of normal batteries, and all materials except the separator are consistent with those used in normal production batteries.

[0091] S3. Evaluation: If it is necessary to evaluate the battery electrode interface condition under a certain production process, select a battery using a functional separator under the same conditions, disassemble the battery, and observe the interface of the separator on the negative electrode side to determine the electrode interface condition. If necessary, take photos of the separator interface with a camera for intuitive comparison of the interface condition under different evaluation process conditions. The main criteria for judgment are the degree of blackening and the uniformity of blackening on the negative electrode side of the separator.

[0092] The composition ratio, process parameters, and coating process of the coating slurry are shown in Tables 1-3.

[0093] The coating slurry comprises a solid electrolyte, a binder, a dispersant, and a wetting agent, wherein the solid electrolyte is Li. 1+ x Al x Ti 2x The electrolyte is (PO4)3, where x = 0.2, and the particle size is 0.3 μm. The binder is polyvinyl alcohol, the dispersant is polyacrylate, and the wetting agent is polyether siloxane. The mass percentages of the solid electrolyte, binder, dispersant, and wetting agent are 97:2:0.8:0.2. The coating slurry is an aqueous dispersion slurry, which also contains deionized water, and the solid content of the coating slurry is 21 wt%.

[0094] The preparation method of the above-mentioned coating slurry includes the following steps:

[0095] Solid electrolyte, dispersant and water were stirred and dispersed for 2 hours to obtain a dispersion at a stirring speed of 2000 rpm. A binder was added to the dispersion and stirred and dispersed for 2 hours to obtain a slurry at a stirring speed of 500 rpm. A wetting agent was added to the slurry and stirred for 0.5 hours. The slurry was then filtered to obtain a coating slurry with a screen mesh of 200 mesh.

[0096] The above process was carried out at a temperature of 25°C.

[0097] The preparation method of the diaphragm structure includes the following steps: uniformly coating the diaphragm structure surface with a coating slurry using a high-precision coating machine; the coating method is micro-gravure roller coating; and the main material of the coating slurry is the solid electrolyte lithium titanium aluminum phosphate (Li). 1+ x Al x Ti2x (PO4)3, x=0.2), the coating method is single-sided coating.

[0098] Preferably, the coating speed is 50 m / min and the drying temperature is 70°C.

[0099] Preferably, the coating thickness of the functional coating is 1 μm.

[0100] The separator structure includes a base membrane and a functional coating layer, the functional coating layer being coated on one side of the base membrane. The resulting battery electrode-separator structure includes a base membrane and a functional coating layer, the functional coating layer being coated on one side of the base membrane. The battery electrode includes a negative electrode and a positive electrode, the negative electrode being disposed on the surface of the functional coating, and the positive electrode being disposed on the surface of the base membrane.

[0101] The selected functional separator coating structure is 14+1, where 14 represents a 14µm PE wet-process lithium-ion battery separator base film, and 1 represents a 1µm thick LATP solid electrolyte coating applied to the surface of the separator base film. 14 represents a separator used in conventional batteries.

[0102] The selected battery system is lithium nickel cobalt manganese oxide / graphite, with a nominal battery capacity of 15Ah.

[0103] A schematic diagram of the diaphragm structure in this embodiment is shown below. Figure 4 As shown.

[0104] Table 1. Components of the coating slurry in various embodiments of the present invention

[0105]

[0106] Table 2. Preparation process parameters of the coating slurry in various embodiments of the present invention.

[0107]

[0108] Table 3 Coating process parameters in various embodiments of the present invention

[0109] Coating speed (m / min) 30 40 50 Drying temperature (°C) 65 65 70 Coating thickness (µm) 2 1 1

Claims

1. A method for evaluating the interface condition of lithium-ion battery electrodes, characterized in that, Includes the following steps: S1, coating: functional coating is performed on the battery separator, the coating slurry includes solid electrolyte, binder, dispersant and wetting agent, the mass percentage is (92-99.97):(0.01-3):(0.01-3):(0.01-2); the solid electrolyte is Li 1+ x Al x Ti 2x (PO4)3, x=0.01-0.5, the particle size of the solid electrolyte is 10nm-20um, the coating thickness is 0.5um-5um; the coating slurry containing LATP is coated on the separator close to the negative electrode sheet side; S2, Manufacturing batteries; S3. Evaluation: Disassemble the battery and observe the interface of the functional separator on the negative electrode side to determine the state of the electrode interface. Observe the degree and uniformity of blackening of the separator on the negative electrode side to determine the state of the battery interface.

2. The method for evaluating the interface condition of lithium-ion battery electrodes according to claim 1, characterized in that, In step S1, the coating method is micro-gravure roller coating, and the coating form is single-sided coating.

3. The method for evaluating the interface condition of lithium-ion battery electrodes according to claim 1, characterized in that, The coating slurry is an aqueous dispersion slurry, which also includes deionized water, and the solid content of the coating slurry is 20-40 wt%.

4. The method for evaluating the interface condition of lithium-ion battery electrodes according to claim 3, characterized in that, The adhesive is one or more of styrene-butadiene rubber, polyvinylpyrrolidone, acrylates, or polyvinyl alcohol; the dispersant is one or more of sodium dodecylbenzene sulfate, polyacrylate, or compounds containing amino aromatic esters; and the wetting agent is a polyether silicone copolymer.

5. The method for evaluating the interface condition of lithium-ion battery electrodes according to claim 4, characterized in that, The method for preparing the coating slurry includes the following steps: Solid electrolyte, dispersant and water are stirred and dispersed to obtain a dispersion; binder is added to the dispersion and stirred evenly to obtain a slurry; wetting agent is added to the slurry and stirred evenly, and then filtered to obtain a coating slurry.

6. A separator structure prepared by a method for evaluating the interface condition of lithium-ion battery electrodes according to any one of claims 1-5, characterized in that, It includes a base film and at least one functional coating layer, the functional coating being coated on the surface of the base film, the thickness of the functional coating being 0.5um-5um.

7. The separator structure prepared by the method for evaluating the interface condition of lithium-ion battery electrodes according to claim 6, characterized in that, It also includes a reinforcing layer coated on the surface of the base film.

8. A battery electrode-separator structure comprising a separator structure prepared by the method for evaluating the interface condition of lithium-ion battery electrodes as described in any one of claims 6-7, characterized in that, It also includes battery electrode sheets, which include a positive electrode sheet and a negative electrode sheet, and the functional coating is applied to the surface of a base film near the negative electrode sheet.

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