CN113138221B - Method for optimizing proportion representation SEI film impedance of conductive agent and binder - Google Patents
Method for optimizing proportion representation SEI film impedance of conductive agent and binder Download PDFInfo
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Abstract
The invention discloses a method for optimizing the proportion of a conductive agent and a binder to represent SEI (solid electrolyte interface) film impedance, relates to the technical field of lithium ion battery detection and representation, and aims to solve the problems that battery impedance test based on the traditional formula proportion can only obtain a semi-circle of a high-frequency area with overlapped SEI film impedance and electronic conductance impedance, a semi-circle of a low-frequency area related to a charge transfer process and an oblique line of a very low-frequency area related to solid phase diffusion. The invention optimizes the proportion of the conductive agent and the binder, particularly needs to increase the content of the conductive agent and the binder in the electrode, prepares the battery which can distinguish the semicircle related to the SEI film impedance and the semicircle of the electronic conductance impedance related to the lithium ion deintercalation process, and solves the problems that the battery impedance test of the traditional formula proportion can only obtain the high-frequency region semicircle overlapped by the SEI film impedance and the electronic conductance impedance, the low-frequency region semicircle related to the charge transfer process and the extremely low-frequency region oblique line related to the solid phase diffusion.
Description
Technical Field
The invention relates to the technical field of lithium ion battery detection characterization, in particular to a method for optimizing the proportion of a conductive agent and a binder to characterize the impedance of an SEI film.
Background
The lithium ion battery is widely applied to the fields of energy storage, power automobiles, ships and the like due to the characteristics of long cycle life, high energy density, no pollution of green energy and the like. However, the capacity of the battery decreases after long cycling and operation, which is mainly related to the increased polarization of the battery during long cycling. Therefore, it is necessary to investigate the cause of the increase in polarization of the lithium ion battery so that the occurrence of polarization of the battery can be avoided or reduced. In order to realize the research on the polarization of the battery, various research means must be developed and applied, and Electrochemical Impedance Spectroscopy (EIS) is one of the most powerful tools for researching the polarization of the battery, and therefore, the EIS is widely applied to research on the de-intercalation process in the active material of the lithium ion electrode.
At present, impedance research on batteries in the formation process is more, for example, patent CN109461980A discloses an impedance monitoring method for representing the SEI film formation process, and tests battery impedance show a stepping method for impedance test in the first cathode polarization process of graphite/negative electrode, and meanwhile, the silicon carbon negative electrode can also form an SEI film, which has the same impedance change; the change of resistance of the SEI film during film formation can be deeply understood and used for revealing the formation mechanism of the SEI film. However, in most cases, only a high-frequency region semicircle related to the SEI film impedance, a medium-frequency region semicircle related to the charge transfer process, and a very low-frequency region diagonal line related to the solid phase diffusion appear in the EIS impedance spectrum, and the semicircle reflecting the SEI film impedance may overlap with the semicircle related to the electron conductance impedance of the electrode active material during the lithium ion deintercalation process, so that it is necessary to separate the semicircle reflecting the SEI film impedance from the semicircle reflecting the electron conductance impedance in order to know the change of the SEI film impedance during the formation or charging and discharging processes, and thus, it is necessary to improve the process of manufacturing the electrode sheet. Therefore, the method for simply and effectively evaluating the impedance of the lithium battery has strong practical significance.
Disclosure of Invention
The invention aims to solve the technical problem that the battery impedance test of the traditional formula proportion can only obtain the semi-circle of the high-frequency region with overlapped SEI film impedance and electronic conductance impedance, the semi-circle of the low-frequency region related to the charge transfer process and the oblique line of the very low-frequency region related to solid phase diffusion.
The invention solves the technical problems through the following technical means:
a method for optimizing the proportion of a conductive agent and a binder to characterize the resistance of an SEI film, comprising the steps of:
(1) mixing negative graphite, a binder and a conductive agent in proportion, and then sequentially carrying out slurry mixing, coating, baking and rolling processes to obtain a 100% SOC negative pole piece, wherein the weight percentage of the negative graphite is 80-87.5%, the weight percentage of the binder is 2.5-10.5%, the weight percentage of the conductive agent is 2-10%, and the sum of the three is 100%;
(2) respectively cutting the 100% SOC negative pole piece obtained in the step (1) and a lithium copper composite belt with the thickness of 100 microns in a drying room with dew point control, and assembling the cut 100% SOC negative pole piece, the cut lithium copper composite belt and electrolyte into a single-layer soft package half-cell;
(3) performing full discharge test on the single-layer soft package half cell assembled in the step (2) on a test cabinet by adopting a multiplying power of 0.01-0.05C, and discharging to 0.005V to obtain a half cell in a full discharge state;
(4) disassembling the fully-placed half-cell obtained in the step (3) in a glove box, taking out a 100% SOC lithium-embedded negative electrode plate, cleaning the negative electrode plate in dimethyl carbonate, and drying in a vacuum oven;
(5) taking a lithium copper composite belt with the width of 0.5-1mm as a reference electrode, and assembling the 100% SOC negative pole piece, the 0% SOC negative pole piece and the reference electrode which are cut in the step (2) into a negative symmetric battery three-electrode, wherein the reference electrode is positioned between the 100% SOC negative pole piece and the 0% SOC negative pole piece, a negative reference is formed between the 100% SOC negative pole piece and the reference electrode, a positive reference is formed between the 0% SOC negative pole piece and the reference electrode, and a full battery is formed between the 100% SOC negative pole piece and the 0% SOC negative pole piece;
(6) and (4) applying a constant current of 0.01-0.05C to the three electrodes of the negative electrode symmetrical battery in the step (5), wherein the voltage range is-2V, and monitoring the impedance of the negative parametron, the positive parametron and the full battery respectively by using a multi-channel recorder.
The invention optimizes the proportion of the conductive agent and the binder, particularly needs to increase the content of the conductive agent and the binder in the electrode, prepares the battery which can distinguish the semicircle related to the SEI film impedance and the semicircle of the electronic conductance impedance related to the lithium ion deintercalation process, and solves the problems that the battery impedance test of the traditional formula proportion can only obtain the high-frequency region semicircle overlapped by the SEI film impedance and the electronic conductance impedance, the low-frequency region semicircle related to the charge transfer process and the extremely low-frequency region oblique line related to the solid phase diffusion.
Preferably, the binder in the step (1) is oil-based polyvinylidene fluoride (PVDF).
Preferably, the conductive agent in step (1) comprises one of carbon black SP, graphite KS-6 or carbon nanotubes.
Preferably, the slurry mixing time in the step (1) is 20-30min, the coating thickness is 150-250 μm, the baking temperature is 95-105 ℃, the baking time is 2-4h, the rolled thickness is 20-30 μm, and the rolled baking time is 20-24 h.
Preferably, the dew point of the drying room in step (2) is ≦ 40 ℃.
Preferably, the area of the lithium copper composite tape in the step (2) is greater than the area of the 100% SOC negative electrode piece, and the ratio of the area of the lithium copper composite tape to the area of the 100% SOC negative electrode piece is 1.08-1.2.
Preferably, the main solvent component of the electrolyte in the step (2) is composed of EC, EMC and DEC, wherein the weight percentage of EC is 0% to 60%, the weight percentage of EMC is 0% to 70%, the weight percentage of DEC is 0% to 40%, and the sum of the three is 100%.
Preferably, the temperature of the vacuum oven in the step (4) is 80-100 ℃, and the drying time is 10-15 min.
Preferably, in the step (5), the tab of the reference electrode, the tab of the 100% SOC negative electrode piece and the tab of the 0% SOC negative electrode piece are located on the same side or are placed at a right angle with the tab of the 100% SOC negative electrode piece and the tab of the 0% SOC negative electrode piece.
Preferably, the area of the 100% SOC negative electrode piece in the step (5) is greater than the area of the 0% SOC negative electrode piece, and the ratio of the area of the 100% SOC negative electrode piece to the area of the 0% SOC negative electrode piece is 1.08-1.2.
The invention has the following beneficial effects: the invention optimizes the proportion of the conductive agent and the binder, particularly relates to a battery which needs to increase the content of the conductive agent and the binder in an electrode and can separate a semicircle related to SEI film impedance and a semicircle related to electronic conductance impedance in a lithium ion de-intercalation process, and solves the problems that battery impedance tests in the traditional formula proportion can only obtain the SEI film impedance and the semicircle of a high frequency region overlapped with the electronic conductance impedance, the semicircle of a low frequency region related to a charge transfer process and an oblique line of a very low frequency region related to solid phase diffusion.
Drawings
FIG. 1 is a schematic diagram of an impedance test according to embodiment 1 of the present invention;
FIG. 2 shows the results of the impedance test of the positive reference in example 1 of the present invention at a low temperature of-20 ℃;
FIG. 3 shows the results of the impedance test of the positive reference in example 2 of the present invention at a low temperature of-20 ℃;
FIG. 4 shows the results of the impedance test of the positive reference in example 3 of the present invention at a low temperature of-20 ℃;
FIG. 5 shows the results of the impedance test of comparative example 1 of the present invention against a reference at a low temperature of-20 ℃.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Test materials, reagents and the like used in the following examples are commercially available unless otherwise specified.
Those skilled in the art who do not specify any particular technique or condition in the examples can follow the techniques or conditions described in the literature in this field or follow the product specification.
Example 1
A method for optimizing the ratio of a conductive agent to a binder for SEI film resistance characterization, comprising the steps of:
(1) mixing negative graphite, PVDF and SP in a ratio of 80:10:10, and then sequentially carrying out slurry mixing, coating, baking and rolling processes to obtain a 100% SOC negative pole piece; the slurry mixing, coating, baking and rolling process comprises the following steps: the slurry mixing time in a slurry mixing machine is 30min, the thickness of the slurry coated on a coating machine is 200 mu m, the slurry is baked for 3h in an oven at 100 ℃ after coating, then the slurry is rolled on a roller press, the thickness after rolling is 30 mu m, and the 100% SOC negative pole piece obtained after 24h of baking after rolling is stored in a glove box for standby;
(2) cutting the 100% SOC negative pole piece obtained in the step (1) into a plurality of pole pieces with the length of 4.2cm and the width of 5.3cm in a drying room (the dew point is less than or equal to-40 ℃) with dew point control, then compositely cutting lithium copper with the thickness of 100 mu m into a lithium copper composite belt with the length of 4.5cm and the width of 5.5cm, and then assembling the cut 100% SOC negative pole piece, the lithium copper composite belt and electrolyte (the components are EC: EMC: DEC: 30:50:20) into a plurality of groups of single-layer soft package half batteries;
(3) carrying out full discharge test on a plurality of groups of single-layer soft package half batteries on a test cabinet by adopting the multiplying power of 0.04C, and discharging to 0.005V to obtain full discharge half batteries;
(4) disassembling the fully-discharged half-cell obtained in the step (3) in a glove box, taking out a 100% SOC lithium-embedded negative electrode sheet, cleaning the negative electrode in dimethyl carbonate (DMC), and drying in a vacuum oven at 80 ℃ for 10 min;
(5) a lithium-copper composite belt with the width of 1mm is used as a reference electrode, and then the 100% SOC negative pole piece, the 0% SOC negative pole piece and the reference electrode which are cut in the step (2) are assembled into a negative symmetric battery three-electrode, wherein the reference electrode is positioned between the 100% SOC negative pole piece and the 0% SOC negative pole piece, a tab of the reference electrode, a tab of the 100% SOC negative pole piece and a tab of the 0% SOC negative pole piece are positioned on the same side, a negative reference is positioned between the 100% SOC negative pole piece and the reference electrode, a positive reference is positioned between the 0% SOC negative pole piece and the reference electrode, a full battery is positioned between the 100% SOC negative pole piece and the 0% SOC negative pole piece, and the assembly schematic diagram is shown in fig. 1;
(6) and (4) applying a constant current of 0.04C to the three electrodes of the negative electrode symmetrical battery in the step (5), wherein the voltage range is-2V, and monitoring the impedance of the negative reference, the positive reference and the full battery respectively by using a multichannel recorder.
Fig. 2 is a test result of the positive reference impedance of the present example at a low temperature of-20 c, and it can be seen from the result of fig. 2 that the characteristic spectrum of three semicircles and one oblique line are clearly seen in the positive reference impedance of the low SOC, in which the frequency region semicircles are related to the electron conductivity of the electrode active material, indicating that the impedance and the electron conductivity impedance of the SEI film can be effectively distinguished by a method of changing the ratio of the binder and the conductive agent.
Example 2
A method for optimizing the proportion of a conductive agent and a binder to characterize the resistance of an SEI film, comprising the steps of:
(1) mixing negative graphite, PVDF and SP in a ratio of 87.5:10:2.5, and then sequentially carrying out slurry mixing, coating, baking and rolling processes to obtain a 100% SOC negative pole piece; the slurry mixing, coating, baking and rolling process comprises the following steps: the slurry mixing time in a slurry mixing machine is 30min, the coating thickness on a coating machine is 200 mu m, the coating is baked for 3h in an oven at 100 ℃, then the rolling is carried out on a roller press, the rolled thickness is 30 mu m, and the 100% SOC negative pole piece obtained by baking for 24h after the rolling is stored in a glove box for later use;
(2) cutting the 100% SOC negative pole piece obtained in the step (1) into a plurality of pole pieces with the length of 4.2cm and the width of 5.3cm in a drying room (the dew point is less than or equal to-40 ℃) with dew point control, then compositely cutting lithium copper with the thickness of 100 mu m into a lithium copper composite belt with the length of 4.5cm and the width of 5.5cm, and then assembling the cut 100% SOC negative pole piece, the lithium copper composite belt and electrolyte (the components are EC: EMC: DEC: 30:50:20) into a plurality of groups of single-layer soft package half batteries;
(3) carrying out full discharge test on a plurality of groups of single-layer soft package half batteries on a test cabinet by adopting the multiplying power of 0.04C, and discharging to 0.005V to obtain half batteries in a full discharge state;
(4) disassembling the fully-discharged half-cell obtained in the step (3) in a glove box, taking out a 100% SOC lithium-embedded negative electrode sheet, cleaning the negative electrode in dimethyl carbonate (DMC), and drying in a vacuum oven at 80 ℃ for 10 min;
(5) taking a lithium-copper composite belt with the width of 1mm as a reference electrode, and assembling the 100% SOC negative pole piece, the 0% SOC negative pole piece and the reference electrode which are cut in the step (2) into a negative symmetric battery three-electrode, wherein the reference electrode is positioned between the 100% SOC negative pole piece and the 0% SOC negative pole piece, a tab of the reference electrode, a tab of the 100% SOC negative pole piece and a tab of the 0% SOC negative pole piece are positioned on the same side, a negative reference is formed between the 100% SOC negative pole piece and the reference electrode, a positive reference is formed between the 0% SOC negative pole piece and the reference electrode, and a full battery is formed between the 100% SOC negative pole piece and the 0% SOC negative pole piece;
(6) applying a constant current of 0.04C to the three electrodes of the negative electrode symmetrical battery in the step (5), wherein the voltage range is-2V, and monitoring the impedance of the negative parametron, the positive parametron and the full battery respectively by using a multi-channel recorder;
fig. 3 is a result of the test of the positive reference impedance at a low temperature of-20 c according to the present embodiment, and it can be seen from the result of fig. 3 that the positive reference impedance at a low SOC shows a characteristic spectrum of three distinct semicircles and one oblique line, wherein the frequency region semicircles are related to the electron conductivity of the electrode active material, indicating that the impedance of the SEI film can be effectively distinguished from the electron conductivity impedance by changing the ratio of the binder to the conductive agent.
Example 3
A method for optimizing the proportion of a conductive agent and a binder to characterize the resistance of an SEI film, comprising the steps of:
(1) mixing negative graphite, PVDF and SP in a ratio of 87.5:2.5:10, and then sequentially carrying out slurry mixing, coating, baking and rolling processes to obtain a 100% SOC negative pole piece; the slurry mixing, coating, baking and rolling process comprises the following steps: the slurry mixing time in a slurry mixing machine is 30min, the thickness of the slurry coated on a coating machine is 200 mu m, the slurry is baked for 3h in an oven at 100 ℃ after coating, then the slurry is rolled on a roller press, the thickness after rolling is 30 mu m, and the 100% SOC negative pole piece obtained after 24h of baking after rolling is stored in a glove box for standby;
(2) cutting the 100% SOC negative pole piece obtained in the step (1) into a plurality of pole pieces with the length of 4.2cm and the width of 5.3cm in a drying room (the dew point is less than or equal to-40 ℃) with dew point control, then compositely cutting lithium copper with the thickness of 100 mu m into a lithium copper composite belt with the length of 4.5cm and the width of 5.5cm, and then assembling the cut 100% SOC negative pole piece, the lithium copper composite belt and electrolyte (the components are EC: EMC: DEC: 30:50:20) into a plurality of groups of single-layer soft package half batteries;
(3) carrying out full discharge test on a plurality of groups of single-layer soft package half batteries on a test cabinet by adopting the multiplying power of 0.04C, and discharging to 0.005V to obtain full discharge half batteries;
(4) disassembling the fully-discharged half-cell obtained in the step (3) in a glove box, taking out a 100% SOC lithium-embedded negative electrode sheet, cleaning the negative electrode in dimethyl carbonate (DMC), and drying in a vacuum oven at 80 ℃ for 10 min;
(5) taking a lithium-copper composite belt with the width of 1mm as a reference electrode, and assembling the 100% SOC negative pole piece, the 0% SOC negative pole piece and the reference electrode which are cut in the step (2) into a negative symmetric battery three-electrode, wherein the reference electrode is positioned between the 100% SOC negative pole piece and the 0% SOC negative pole piece, a tab of the reference electrode, a tab of the 100% SOC negative pole piece and a tab of the 0% SOC negative pole piece are positioned on the same side, a negative reference is formed between the 100% SOC negative pole piece and the reference electrode, a positive reference is formed between the 0% SOC negative pole piece and the reference electrode, and a full battery is formed between the 100% SOC negative pole piece and the 0% SOC negative pole piece;
(6) applying a constant current of 0.04C to the three electrodes of the negative electrode symmetrical battery in the step (5), wherein the voltage range is-2V, and monitoring the impedance of the negative parametron, the positive parametron and the full battery respectively by using a multi-channel recorder;
fig. 4 is a test result of the positive reference impedance of the present example at a low temperature of-20 ℃, and it can be seen from the result of fig. 4 that the positive reference impedance of the low SOC shows a characteristic spectrum of three distinct semicircles and one oblique line, wherein the frequency region semicircles are related to the electron conductivity of the electrode active material, indicating that the impedance of the SEI film can be effectively distinguished from the electron conductivity impedance by changing the ratio of the binder to the conductive agent.
Comparative example 1
(1) Mixing negative graphite, PVDF and SP in a ratio of 98:1:1, and then sequentially carrying out slurry mixing, coating, baking and rolling processes to obtain a 100% SOC negative pole piece; the slurry mixing, coating, baking and rolling process comprises the following steps: the slurry mixing time in a slurry mixing machine is 30min, the coating thickness on a coating machine is 200 mu m, the coating is baked for 3h in an oven at 100 ℃, then the rolling is carried out on a roller press, the rolled thickness is 30 mu m, and the 100% SOC negative pole piece obtained by baking for 24h after the rolling is stored in a glove box for later use;
(2) cutting the 100% SOC negative pole piece obtained in the step (1) into a plurality of pole pieces with the length of 4.2cm and the width of 5.3cm in a drying room (the dew point is less than or equal to-40 ℃) with dew point control, then compositely cutting lithium copper with the thickness of 100 mu m into a lithium copper composite belt with the length of 4.5cm and the width of 5.5cm, and then assembling the cut 100% SOC negative pole piece, the lithium copper composite belt and electrolyte (the components are EC: EMC: DEC: 30:50:20) into a plurality of groups of single-layer soft package half batteries;
(3) carrying out full discharge test on a plurality of groups of single-layer soft package half batteries on a test cabinet by adopting the multiplying power of 0.04C, and discharging to 0.005V to obtain full discharge half batteries;
(4) disassembling the fully-discharged half-cell obtained in the step (3) in a glove box, taking out a 100% SOC lithium-embedded negative electrode sheet, cleaning the negative electrode in dimethyl carbonate (DMC), and drying in a vacuum oven at 80 ℃ for 10 min;
(5) taking a lithium-copper composite belt with the width of 1mm as a reference electrode, and assembling the 100% SOC negative pole piece, the 0% SOC negative pole piece and the reference electrode which are cut in the step (2) into a negative symmetric battery three-electrode, wherein the reference electrode is positioned between the 100% SOC negative pole piece and the 0% SOC negative pole piece, a tab of the reference electrode, a tab of the 100% SOC negative pole piece and a tab of the 0% SOC negative pole piece are positioned on the same side, a negative reference is formed between the 100% SOC negative pole piece and the reference electrode, a positive reference is formed between the 0% SOC negative pole piece and the reference electrode, and a full battery is formed between the 100% SOC negative pole piece and the 0% SOC negative pole piece;
(6) applying a constant current of 0.04C to the three electrodes of the negative electrode symmetrical battery in the step (5), wherein the voltage range is-2V, and monitoring the impedance of the negative parametron, the positive parametron and the full battery respectively by using a multi-channel recorder;
fig. 5 is a test result of the positive reference impedance of the present comparative example at a low temperature of-20 c, and it can be seen from the result of fig. 5 that the positive reference impedance of low SOC shows a characteristic spectrum of two semicircles and one oblique line, in which the semicircles in the low frequency region are impedances related to charge transfer, indicating that the lower ratio of the binder and the conductive agent cannot effectively distinguish the impedance of the SEI film from the electron conductance impedance.
The above examples are only intended to illustrate the technical solution of the present invention, and not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A method for optimizing the proportion of a conductive agent and a binder to characterize the resistance of an SEI film, comprising the steps of:
(1) mixing negative graphite, a binder and a conductive agent in proportion, and then sequentially carrying out slurry mixing, coating, baking and rolling processes to obtain a 100% SOC negative pole piece, wherein the weight percentage of the negative graphite is 80-87.5%, the weight percentage of the binder is 2.5-10.5%, the weight percentage of the conductive agent is 2-10%, and the sum of the three is 100%;
(2) respectively cutting the 100% SOC negative pole piece obtained in the step (1) and a lithium copper composite belt with the thickness of 100 microns in a drying room with dew point control, and assembling the cut 100% SOC negative pole piece, the cut lithium copper composite belt and electrolyte into a single-layer soft package half-cell;
(3) performing full discharge test on the single-layer soft package half battery assembled in the step (2) on a test cabinet by adopting a multiplying power of 0.01-0.05C, and discharging to 0.005V to obtain a half battery in a full discharge state;
(4) disassembling the fully-discharged half-cell obtained in the step (3) in a glove box, taking out a 100% SOC lithium-embedded negative electrode sheet, cleaning the negative electrode sheet in dimethyl carbonate, and drying in a vacuum oven;
(5) taking a lithium-copper composite belt with the width of 0.5-1mm as a reference electrode, and assembling the 100% SOC negative pole piece, the 0% SOC negative pole piece and the reference electrode which are cut in the step (2) into a negative symmetric battery three-electrode, wherein the reference electrode is positioned between the 100% SOC negative pole piece and the 0% SOC negative pole piece, the space between the 100% SOC negative pole piece and the reference electrode is called negative reference, the space between the 0% SOC negative pole piece and the reference electrode is called positive reference, and the space between the 100% SOC negative pole piece and the 0% SOC negative pole piece is called full battery;
(6) and (4) applying a constant current of 0.01-0.05C to the three electrodes of the negative electrode symmetrical battery in the step (5), wherein the voltage range is-2V, and monitoring the impedance of the negative parametron, the positive parametron and the full battery respectively by using a multi-channel recorder.
2. The method for optimizing the proportion of the conductive agent and the binder for representing the SEI film impedance as claimed in claim 1, wherein: the binder in the step (1) is oil-based polyvinylidene fluoride.
3. The method for optimizing the proportion of the conductive agent and the binder for representing the SEI film impedance as claimed in claim 1, wherein: the conductive agent in the step (1) comprises one of carbon black SP, graphite KS-6 or carbon nano tubes.
4. The method for optimizing the proportion of the conductive agent and the binder for representing the SEI film impedance as claimed in claim 1, wherein: the slurry mixing time in the step (1) is 20-30min, the coating thickness is 150-.
5. The method for optimizing the proportion of the conductive agent and the binder for representing the SEI film impedance as claimed in claim 1, wherein: the dew point of the drying room in the step (2) is less than or equal to-40 ℃.
6. The method for optimizing the proportion of the conductive agent and the binder for representing the SEI film impedance as claimed in claim 1, wherein: in the step (2), the area of the lithium-copper composite belt is larger than the area of the 100% SOC negative pole piece, and the ratio of the area of the lithium-copper composite belt to the area of the 100% SOC negative pole piece is 1.08-1.2.
7. The method for optimizing the proportion of the conductive agent and the binder for representing the SEI film impedance as claimed in claim 1, wherein: the main solvent component of the electrolyte in the step (2) comprises EC, EMC and DEC, wherein the weight percentage of EC is 0-60%, the weight percentage of EMC is 0-70%, the weight percentage of DEC is 0-40%, and the sum of the EC, EMC and DEC is 100%.
8. The method for optimizing the proportion of the conductive agent and the binder for representing the SEI film impedance as claimed in claim 1, wherein: the temperature of the vacuum oven in the step (4) is 80-100 ℃, and the drying time is 10-15 min.
9. The method for optimizing the proportion of the conductive agent and the binder for representing the SEI film impedance as claimed in claim 1, wherein: and (5) the tab of the reference electrode in the step (5) is positioned on the same side with the tab of the 100% SOC negative pole piece and the tab of the 0% SOC negative pole piece or is positioned at a right angle with the tab of the 100% SOC negative pole piece and the tab of the 0% SOC negative pole piece.
10. The method for optimizing the proportion of the conductive agent and the binder for representing the SEI film impedance as claimed in claim 1, wherein: in the step (5), the area of the 100% SOC negative pole piece is larger than that of the 0% SOC negative pole piece, and the ratio of the area of the 100% SOC negative pole piece to that of the 0% SOC negative pole piece is 1.08-1.2.
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