Method and device for testing ionic conductivity of lithium ion electrode material

Abstract

The invention relates to the technical field of ionic conductivity testing, in particular to a lithium ion electrode material ionic conductivity testing method and device, and the testing method comprises the following steps: preparing a composite electrode, assembling a symmetrical battery, testing and calculating the ionic conductivity, and correcting the ionic conductivity. According to the method, a real battery environment is simulated through the symmetrical battery and the electrolyte, and errors caused by neglect of pore distribution in a traditional method are solved by combining SEM actual measurement porosity and Achie model correction, so that a test result is more accurate; the device supports rapid replacement of the electrode plates, constant-voltage clamping ensures test consistency, the single test time is short, and the accuracy rate is high.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ion conductivity testing, in particular to a lithium ion electrode material ion conductivity testing method and testing device. BACKGROUND

[0002] Electrode materials (including positive electrode materials and negative electrode materials) are important components of lithium ion batteries. As lithium ion donors and acceptors, the transmission of lithium ions between the positive and negative electrodes determines the electrical performance of lithium ion batteries. Therefore, testing the ion conductivity of electrode materials can study the lithium ion transmission characteristics of different electrode materials under different compaction densities and surface densities, achieve better material matching in the battery design process, and improve the performance of lithium ion batteries.

[0003] The prior art CN118130899A discloses a solid-state electrolyte powder material ion conductivity testing method. The solid-state electrolyte powder material is made into sheet materials with different densities, and the surface of the sheet materials is polished smooth. Several blocking electrodes are added, the ion conductivity is calculated by testing the resistance of each blocking electrode. Since the internal pores of the material will reduce the effective ion conductivity, a function model is established for different densities ε and corresponding ion conductivities σ to calculate the actual material ion conductivity. The electrode preparation and testing steps of this invention are complicated, the actual internal environment of the battery cannot be established, and only the density represents the porosity of the material, resulting in a large error in the final result. Therefore, there is an urgent need for a method that can quickly and accurately test the ion conductivity of lithium ion electrode materials. SUMMARY

[0004] The present application aims to provide a lithium ion electrode material ion conductivity testing method and testing device to solve the problems raised in the background.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solution: an electrode material ion conductivity testing method, comprising the following steps: S1: preparing a composite electrode: mixing electrode materials, conductive agents, and binders in a certain proportion to form a slurry, uniformly coating the slurry on a current collector, baking the coated electrode sheet, compacting after baking, punching into a composite electrode sheet, and testing the coating layer thickness (L); S2: assembling a symmetrical battery: inserting two identical electrode sheets into an aluminum plastic film battery shell, separating them with a separator, injecting electrolyte, and assembling a symmetrical battery. Apply a constant clamping force through a pressing device and let it stand for 4-6 hours to allow the electrolyte to fully soak. S4: Test and calculate ion conductivity: test the electrode material electrochemical impedance spectroscopy (EIS), by fitting the Nyquist curve, decompose the material ion impedance (Rion) and interface impedance (Rint), calculate the ion conductivity σi=L / (Rion×A), wherein L is the thickness of the electrode material, and A is the area of the electrode material; S5: Correct ion conductivity: make a scanning electron microscope (SEM) on the cross section of the electrode, calculate the porosity of the composite electrode ϕ, and correct σ eff =σ i ⋅ϕ m , m is an empirical constant, and finally the ion conductivity of the electrode material is obtained.

[0006] Preferably, the mixing ratio in S1 simulates the actual ratio.

[0007] Preferably, the positive electrode material in S1 is coated on the carbon-coated aluminum foil, and the negative electrode material is coated on the copper foil.

[0008] Preferably, in S1, the coated electrode sheet is baked at 85°C for 4h.

[0009] Preferably, in S2, the constant clamping force is 1N·m.

[0010] Preferably, the ion conductivity testing device for electrode material used is composed of a sliding rail, an aluminum plastic film battery case, an extrusion plate, and a pressure sensor.

[0011] Preferably, the top of the extrusion plate is provided with an insulating silica gel pad, and the thickness of the insulating silica gel pad is 2mm.

[0012] Preferably, the extrusion plate seals the opening of the battery case by constant pressure clamping, and the pressure sensor monitors the clamping force in real time.

[0013] Preferably, the diaphragm is a polyethylene film PE or a polypropylene film PP.

[0014] Compared with the prior art, the beneficial effects of the present application are: Accuracy is improved: by simulating the real battery environment with a symmetrical battery + electrolyte, combining the measured porosity ϕ by SEM and the correction by Archie's model, the error caused by ignoring the pore distribution in the traditional method is solved, and the test result is more accurate; High efficiency and convenience: the device supports quick replacement of electrode sheets, constant pressure clamping ensures test consistency, single test time is short, and accuracy is high. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 It is a structure schematic diagram of the electrode material ion conductivity testing device; Figure 2 It is a structure diagram of the symmetrical battery; Figure 3 is a cross-sectional view of a symmetric battery; Figure 4 is an EIS impedance spectrum; In the figure, slide rail-1, extrusion plate-2, pressure sensor-3, insulating silica gel pad-4, aluminum plastic film battery shell-5, symmetric battery-6, current collector-7, separator-8, slurry-9. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0017] Please refer to Figure 1 The present application provides a technical solution: an electrode material ionic conductivity testing device, which is composed of a slide rail 1, an aluminum plastic film battery shell 5, an extrusion plate 2, and a pressure sensor 3. The top of the extrusion plate 2 is provided with an insulating silica gel pad 4, and the thickness of the insulating silica gel pad 4 is 2 mm. The inside of the aluminum plastic film battery shell 5 is divided into two areas by a separator 8, and the separator 8 is a polyethylene film PE or a polypropylene film PP.

[0018] The extrusion plate 2 seals the opening of the battery shell by constant pressure clamping, and the pressure sensor 3 monitors the clamping force in real time.

[0019] An electrode material ionic conductivity testing method, comprising the following steps: First, a composite electrode is prepared, and an electrode material (a positive electrode material or a negative electrode material), a conductive agent, and a binder are mixed in a certain proportion to form a slurry 9 simulating the actual proportioning of the electrode, and then uniformly coated on a current collector 7, the positive electrode material is coated on a carbon-coated aluminum foil, and the negative electrode material is coated on a copper foil. The coated electrode sheet is baked at 85°C for 4h; the baked electrode sheet is compacted, and then punched into a 121mm*91mm composite electrode sheet and the coating layer thickness (L) is tested.

[0020] The two punched composite electrode sheets are inserted into the two areas of the aluminum plastic film battery shell 5 respectively, and the middle is separated by a separator 8. 5g of electrolyte is added into the battery shell to form a symmetric battery 6 simulating the actual internal operating environment of the battery; two extrusion plates are used to clamp the symmetric battery, and the clamping force is set to 1N·m to make the electrode sheet closely adhere to the separator; the upper insulating silica gel pad of the extrusion plate can seal the upper opening of the aluminum plastic film battery shell to prevent the electrolyte from evaporating; then the electrolyte is fully soaked at room temperature for 4h-6h.

[0021] The electrode material is tested by electrochemical impedance spectroscopy (EIS). The material ion impedance (R ion ) and interface impedance (R int ) are decomposed by fitting the Nyquist curve, and the ion conductivity σ i =L / (R ion ×A) is calculated, where L is the thickness of the electrode material, and A is the area of the electrode material.

[0022] Then the electrode cross section is scanned by scanning electron microscopy (SEM), the porosity of the composite electrode is calculated, and the σ eff =σ i ⋅ϕ m is corrected by Archie's law, where m is an empirical constant, and finally the ion conductivity of the electrode material is obtained. Example 1

[0023] The positive electrode material lithium iron phosphate LFP, conductive carbon black SP, and binder PVDF are prepared into a slurry at a ratio of 97:1:2, uniformly coated on a carbon-coated aluminum foil, and the coated electrode is baked at 85°C for 4h. The baked electrode is compacted, then punched into a 121mm*91mm composite electrode and the coating layer thickness (L=91um) is tested. The electrode is assembled into a symmetrical battery, and the electrochemical impedance spectroscopy (EIS) of the symmetrical battery is tested. The material ion impedance (R ion ) and interface impedance (R int ) are decomposed by fitting the Nyquist curve, the ion impedance (R ion ) is 8.49mΩ, and the ion conductivity σ i =L / (R ion ×A)=9.65*10 -3 S / cm is calculated. Then the electrode cross section is scanned by scanning electron microscopy (SEM), the porosity of the composite electrode is calculated, and the σ eff =σ i ⋅ϕ m is corrected by Archie's law, where m=1.5, and finally the ion conductivity of the electrode material is obtained σ eff =2.11*10 -3 S / cm. Example 2

[0024] The cathode material lithium iron phosphate LFP, conductive carbon black SP and conductive paste CNT, and binder PVDF were made into a slurry at a ratio of 96.5:1:0.5:2 and evenly coated on carbon-coated aluminum foil. The coated electrode was baked at 85°C for 4 hours. The baked electrode was compacted and then punched into a 121mm*91mm composite electrode sheet and the coating thickness was tested (L=93um). The electrode was assembled into a symmetrical battery, which was placed on a test device and the electrochemical impedance spectroscopy (EIS) of the symmetrical battery was tested. By fitting the Nyquist curve, the material ionic impedance (R ion ) and interface impedance (R int ), ionic resistance (R ion ) is 8.45 mΩ, and the ionic conductivity σ is calculated. i =L / (R ion ×A)=9.70*10 -3 S / cm; Scanning electron microscopy (SEM) was then performed on the electrode cross section to calculate the porosity of the composite electrode ϕ = 35.67%, and σ was corrected using Archie's law. eff =σ i ⋅ϕ m , m=1.5, and finally the ionic conductivity σ of the electrode material is obtained eff =2.07*10 -3 S / cm.

[0025] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations that come within the meaning and range of equivalents of the claims are intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0026] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for testing the ionic conductivity of an electrode material, characterized by: The following steps are involved: S1: preparing a composite electrode: mixing electrode materials, a conductive agent, and a binder in a certain proportion to form a slurry (9), uniformly coating the slurry on a current collector (7), baking the coated electrode, compacting the electrode after baking, punching the composite electrode sheet, and measuring the coating layer thickness (L); S2: Symmetrical battery assembly: insert two identical electrode sheets into the aluminum-plastic film battery case (5), separate them with a diaphragm (8), inject electrolyte to form a symmetrical battery (6), apply a constant clamping force through the extrusion device, and let it stand for 4-6 hours to allow the electrolyte to fully penetrate: S4: Test and calculate ionic conductivity: Test the electrochemical impedance spectroscopy (EIS) of the electrode material and decompose the material ionic impedance (R ion ) and interface impedance (R int ), calculate the ionic conductivity σ i =L / (R ion ×A), where L is the thickness of the electrode material and A is the area of ​​the electrode material; S5: Correction of ionic conductivity: Scanning electron microscopy (SEM) of the electrode cross section was performed to calculate the porosity ϕ of the composite electrode and to correct σ using Archie's law. eff =σ i ⋅ϕ m , m is an empirical constant, and the ionic conductivity of the electrode material is finally obtained.

2. The method for testing the ionic conductivity of an electrode material according to claim 1, wherein: The mixing ratio in S1 simulates the actual ratio.

3. The method for testing the ionic conductivity of an electrode material according to claim 2, wherein: In S1, the positive electrode material is coated on carbon-coated aluminum foil, and the negative electrode material is coated on copper foil.

4. The method for testing the ionic conductivity of an electrode material according to claim 1, wherein: In S1, the coated electrode is baked at 85°C for 4 hours.

5. The method for testing ionic conductivity of electrode materials according to claim 1, wherein: In S2, the constant clamping force is 1 N·m.

6. The method for testing the ionic conductivity of an electrode material according to claim 1, wherein: The electrode material ionic conductivity testing device used is composed of a slide rail (1), an aluminum-plastic film battery shell (5), an extrusion plate (2), and a pressure sensor (3).

7. The method for testing the ionic conductivity of an electrode material according to claim 6, wherein: An insulating silicone pad (4) is provided on the top of the extruded plate (2), and the thickness of the insulating silicone pad (4) is 2 mm.

8. The method for testing the ionic conductivity of an electrode material according to claim 7, wherein: The extrusion plate (2) seals the battery shell opening by clamping at a constant pressure, and the pressure sensor (3) monitors the clamping force in real time.

9. The method for testing the ionic conductivity of an electrode material according to claim 1, wherein: The diaphragm (8) is a polyethylene film PE or a polypropylene film PP.

Images