Screening method of lithium primary battery electrolyte

Abstract

The invention provides a screening method of a lithium primary battery electrolyte. The method comprises the following steps: putting three electrodes into an electrolyte to be detected, and carrying out n-circle scanning by using cyclic voltammetry; the current of the first circle is defined as I1, and the current of the nth circle is defined as In; if I1 is larger than or equal to In, it is judged that an SEI film formed by the to-be-detected electrolyte is stable; and if I1 is less than In, judging that the SEI film formed by the electrolyte to be detected is unstable. According to the method, the stability of the SEI film formed by the electrolyte and the lithium metal is judged by utilizing the cyclic voltammetry, so that the stability of the battery electrolyte is judged, and the electrolyte capable of stabilizing in the lithium primary battery is screened out; according to the electrochemical testing method, the stability of the electrolyte can be judged in advance, the stable electrolyte is screened out in advance for testing the full performance of the battery cell, and production and testing resources can be greatly saved.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular to a method for screening electrolytes for lithium primary batteries. Background Art

[0002] Lithium primary batteries use metallic lithium as the negative electrode and play a vital role in portable electronic devices, electric vehicles, and energy storage systems. After the lithium primary battery is injected with electrolyte, the electrolyte components react with lithium metal to form an SEI film, which has an important influence on the performance of the lithium primary battery before and after high-temperature storage. The formation of the SEI film can protect lithium metal from further corrosion and prevent the components in the electrolyte from directly contacting lithium metal, thereby reducing side reactions inside the battery and extending the service life of the battery. On the other hand, if the generated SEI film is unstable, or its components decompose at high temperatures, then the metallic lithium will continue to react with the electrolyte, consuming lithium ions and electrolyte solvents in the battery system. This will not only cause a significant decrease in the capacity retention rate of the battery after storage, but also reduce the rate performance of the battery at high power output, seriously affecting the long-term stability and reliability of the battery.

[0003] In existing production technologies, to determine whether the SEI film formed by the electrolyte components and lithium metal has good performance, it is usually necessary to produce finished battery cells and store them in a high-temperature environment for a period of time, and then compare the changes in electrical performance before and after storage, or disassemble the battery to observe the SEI film coverage on the surface of lithium metal. Although this process can accurately reflect the actual performance of the battery, it takes 2 to 3 months to produce finished battery cells and verify the high-temperature storage performance, and requires a lot of testing resources. Summary of the invention

[0004] The main purpose of the present application is to provide a method for screening lithium primary battery electrolytes to solve the problem in the prior art that it is difficult to directly screen out an electrolyte that can form a stable SEI film with lithium metal.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a method for screening lithium primary battery electrolyte is provided, wherein three electrodes are placed in the electrolyte to be tested, and cyclic voltammetry is used to perform n-cycle scanning; the three electrodes include a working electrode, a reference electrode and a lithium counter electrode, and n is 2 to 10; the current of the first cycle is defined as I1, and the current of the nth cycle is defined as I n ; If I1≥I n , judge that the SEI film formed by the electrolyte to be tested is stable; if I1<I n , judging that the SEI film formed by the electrolyte to be tested is unstable.

[0006] Furthermore, the screening method also includes a secondary screening step: calculating the stability coefficient Φ of the electrolyte to be tested, Φ=|I1-I n|÷I1; when I1≥I n When Φ is smaller, the SEI film formed by the electrolyte to be tested is more stable; when I1<I n When Φ is larger, the SEI film formed by the electrolyte to be tested is more unstable.

[0007] Furthermore, the working electrode is a Pt electrode, and the reference electrode is a lithium electrode.

[0008] Furthermore, the working electrode, the reference electrode and the lithium counter electrode were placed in the electrolyte to be tested and allowed to stand for 1 to 3 hours. After the voltage change was ≤0.01 V / min, cyclic voltammetry was used to perform n-cycle scanning.

[0009] Furthermore, during the scanning process, the voltage is first scanned from the open circuit voltage to 0 V, and then scanned from 0 V to the open circuit voltage.

[0010] Furthermore, the scanning speed is 0.04-0.06 mV / s.

[0011] Furthermore, the number of scanning cycles n is 3 to 6; and / or the scanning temperature is 20±3°C.

[0012] Furthermore, the electrolyte to be tested is a non-aqueous electrolyte, which includes a solvent and a supporting electrolyte, and the weight ratio of the solvent to the supporting electrolyte is (9-11):1.

[0013] Further, the solvent of the non-aqueous electrolyte includes one or more of ethylene glycol dimethyl ether, γ-butyrolactone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

[0014] Further, the supporting electrolyte of the non-aqueous electrolyte includes one or more of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate and lithium tetrafluorooxalatophosphate.

[0015] By applying the technical solution of the present application, the stability of the SEI film formed by the electrolyte and lithium metal is determined by cyclic voltammetry, and then the stability of the battery electrolyte is determined, and an electrolyte that can act stably in the lithium primary battery is screened out. The present application uses an electrochemical testing method to determine the stability of the electrolyte in advance, and pre-screens a stable electrolyte for testing the full performance of the battery cell, which can greatly save production and testing resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings constituting part of the present application are used to provide a further understanding of the present application. The exemplary embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0017] Figure 1 A diagram of a test device according to Embodiment 1 of the present application is shown;

[0018] Figure 2 shows the CV curve diagram of each electrolyte according to Example 1 of the present application;

[0019] Figure 3 Shown are photos of the electrolytes disassembled after storage according to Example 1 of the present application. DETAILED DESCRIPTION

[0020] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0021] As described in the background of this application, it is difficult to directly screen out an electrolyte that can form a stable SEI film with lithium metal in the prior art. In order to solve the above problem, in a typical embodiment of this application, a method for screening lithium primary battery electrolyte is provided, wherein three electrodes are placed in the electrolyte to be tested, and cyclic voltammetry is used to perform n-cycle scanning; the three electrodes include a working electrode, a reference electrode, and a lithium counter electrode, and n is 2 to 10; the current of the first cycle is defined as I1, and the current of the nth cycle is defined as I n ; If I1≥I n , judge that the SEI film formed by the electrolyte to be tested is stable; if I1<I n , judging that the SEI film formed by the electrolyte to be tested is unstable.

[0022] As an important electrochemical test method, cyclic voltammetry is widely used in the field of electrochemistry, especially in the research of lithium batteries. It is often used to study the reversibility of electrode reactions, electrode reaction mechanisms and electrode reaction kinetic parameters. During the research process, the inventor unexpectedly found that the change in current density of the cyclic voltammetry curve (CV curve) with the increase in the number of scans can reflect the stability of the electrolyte.

[0023] Specifically, the working electrode, reference electrode and lithium counter electrode are placed in the electrolyte to be tested, and cyclic voltammetry is used to perform n-cycle scanning in the electrochemical workstation. The electrolyte has corresponding reaction currents at different voltages, and the reaction current has different change trends as the scanning voltage changes in each cycle.

[0024] If the current I1 of the first circle ≥ the current I of the nth circle n , indicating that as the number of cycles increases, the reaction current decreases, and the SEI film effectively passivates the contact reaction between lithium metal and electrolyte. Therefore, it can be judged that the SEI film formed by the electrolyte to be tested and lithium metal is stable, and the electrolyte to be tested is stable.

[0025] If the current I1 of the first circle is less than the current I n, indicating that as the number of cycles increases, the reaction current increases, the electrolyte system is unstable with lithium metal and will continue to react. Therefore, it is judged that the SEI film formed by the electrolyte to be tested and lithium metal is unstable, and the electrolyte to be tested is unstable.

[0026] This application uses cyclic voltammetry to determine the stability of the SEI film formed by the electrolyte and lithium metal, and then determine the stability of the battery electrolyte, and screen out the electrolyte that can act stably in the lithium primary battery. Through electrochemical testing methods, the stability of the electrolyte can be judged in advance, and stable electrolytes can be pre-screened for full performance testing of the battery cell, saving production and testing resources. This method provides an effective way to solve the problem of lithium corrosion, and is expected to reduce battery self-discharge and enhance the storage stability of the battery.

[0027] According to the test method of the present application, lithium corrosion can be avoided and the self-discharge of the battery cell can be reduced by selecting a suitable electrolyte type, thereby improving the storage stability of the battery and extending the service life of the battery. This method provides an effective way to optimize battery design, which helps to improve battery performance and reduce the self-discharge caused by lithium corrosion. Therefore, when selecting a battery electrolyte, a cyclic voltammetry test can be performed to screen out a reliable electrolyte in advance. This method is simple to operate and increases the storage stability and safety of the battery cell. This can not only significantly shorten the R&D cycle and reduce R&D costs, but also provide new possibilities for performance optimization of lithium primary batteries.

[0028] By accurately calculating the stability coefficient, the stability of the electrolyte to be tested can be further quantified and finely evaluated. In some embodiments, the screening method further includes a secondary screening step: calculating the stability coefficient Φ of the electrolyte to be tested, Φ = |I1-I n |÷I1; when I1≥I n When Φ is smaller, the SEI film formed by the electrolyte to be tested is more stable; when I1<I n When Φ is larger, the SEI film formed by the electrolyte to be tested is more unstable.

[0029] Using the first and last loop currents for evaluation and calculating the stability coefficient can provide a clear quantitative indicator, making the stability evaluation of the electrolyte more objective and accurate, and the higher the value of the screening results.

[0030] When I1≥I n When Φ is smaller, it means that on the basis of the decrease of reaction current with the increase of cycle number, I1 and I n The smaller the gap between them, that is, the smaller the decrease in current density in the last cycle compared to the first cycle, it indicates that the SEI film has a better passivation effect in the early stage of formation, and the more effectively it can prevent further reaction between lithium metal and electrolyte, and the more stable the electrolyte to be tested is.

[0031] When I1<I n When Φ is larger, it means that on the basis of the increase in reaction current with the increase in the number of cycles, I1 and I n The larger the gap between them, that is, the greater the increase in current density in the last cycle compared to the first cycle, it indicates that the initial reaction between the electrolyte and lithium metal did not form sufficient passivation, and the SEI film failed to effectively prevent the continuous reaction between lithium metal and the electrolyte, which may cause the instability of the SEI film and the decline in electrical performance during the use of the battery. The more unstable the electrolyte to be tested is.

[0032] By introducing the stability factor Φ, not only can potential stable electrolyte formulas be quickly identified, but potential instability factors can also be eliminated in the early research and development stage. The stability of the electrolyte can be evaluated more accurately, and stable and unstable electrolytes can be accurately ranked, thereby accelerating the research and development process, reducing invalid testing and waste of resources, and being more conducive to the design and optimization of lithium primary batteries.

[0033] To further improve the accuracy and reliability of cyclic voltammetry testing of electrolyte stability, in some embodiments, the working electrode is a Pt electrode and the reference electrode is a lithium electrode. This electrode combination can provide a more stable electrochemical environment, making the test results more reliable, and is suitable for electrolyte stability testing in laboratories and industrial environments.

[0034] Platinum electrodes are the most ideal choice for cyclic voltammetry tests due to their excellent chemical stability and conductivity. They can provide a stable electrochemical platform for monitoring the reaction characteristics of electrolytes at different voltages. As a reference electrode, lithium electrodes can more accurately reflect the electrochemical state of lithium metal in electrolytes, which is essential for studying the formation and stability of SEI films. The use of platinum electrodes can further improve the stability of electrode materials during the test, avoid interference of the electrode itself with the test results, and improve the accuracy of cyclic voltammetry tests. At the same time, as a reference electrode, lithium electrodes can directly reflect the electrochemical behavior of lithium metal and improve the reliability of test results.

[0035] The combination of platinum electrode and lithium electrode is suitable for testing a variety of electrolyte formulas. Whether it is based on cyclic carboxylic acid esters, cyclic carbonates, or ether solvent systems, accurate reaction current data can be obtained, which enhances the versatility and adaptability of the test method. By using stable Pt electrodes and reference lithium electrodes, the analysis of test results becomes more intuitive and accurate, so that electrolytes with unstable performance when forming SEI films can be identified more quickly, the screening process of electrolytes can be optimized, and R&D efficiency can be improved.

[0036] In some embodiments, the working electrode, the reference electrode, and the lithium counter electrode are placed in the electrolyte to be tested, and allowed to stand for 1 to 3 hours. After the voltage change is ≤0.01V / min, indicating that a stable state has been reached, cyclic voltammetry is then used to perform n-circle scans. The standing process helps to form a preliminary SEI film, thereby more accurately evaluating the actual performance of the electrolyte in the battery. After standing for 1 to 3 hours, the electrode and the electrolyte can be fully contacted and reach electrochemical equilibrium. The voltage change is ≤0.01V / min, which allows the test to start in a more stable electrochemical environment.

[0037] The above pretreatment steps can further reduce the transient effects in the initial stage and improve the accuracy and comparability of the test data. By setting the rest time and the stable voltage change, the timing of the test start can be more accurately controlled, reducing unnecessary waiting time, while also reducing data deviations caused by system instability, thereby efficiently utilizing test resources and reducing overall test costs. By combining rest pretreatment with cyclic voltammetry, the stability of test conditions, test efficiency and data reliability can be further improved, thereby more quickly and accurately screening out stable lithium primary battery electrolytes to further reduce the risk of reduced battery capacity retention and reduced rate performance.

[0038] In order to further improve the accuracy and reliability of evaluating the stability of the SEI film, so as to be more conducive to screening out a stable electrolyte, in some embodiments, during the scanning process, the open circuit voltage is first scanned to 0V, and then scanned from 0V to the open circuit voltage. Among them, the open circuit voltage refers to the voltage when the three electrodes are placed in the electrolyte and stabilized for 1 to 3 hours and the voltage change is ≤0.01mV / s. By controlling the scanning voltage and speed, the reaction characteristics of the electrolyte at different potentials can be more comprehensively understood. The above scanning voltage range basically covers all electrochemically active areas when the electrolyte is in contact with lithium metal, so that the test can more comprehensively capture the reaction characteristics of the electrolyte at different potentials, especially the key potential interval of SEI film formation, which helps to accurately evaluate the stability of the electrolyte SEI film.

[0039] In order to make the electrode reaction process more fully proceed, to observe more subtle electrochemical reaction characteristics, and to improve the accuracy of test data, in some embodiments, the scanning speed is 0.04-0.06mV / s. The above parameter setting is more helpful to capture the initial reaction details of SEI film formation and the current response with potential changes, thereby providing a more detailed basis for the evaluation of electrolyte stability, which is more conducive to the screening and optimization of lithium primary battery electrolytes.

[0040] In some embodiments, the number of scanning cycles n is 3 to 6; and / or the scanning temperature is 20±3°C. Multi-cycle scanning can more fully reveal the dynamic reaction process of the electrolyte at different potentials, especially for the observation of the formation and stability of the SEI film, and cover enough reaction cycles to evaluate the stability of the SEI film over time, without excessive scanning resulting in waste of resources and test redundancy. The above test temperature range can more accurately reflect the behavior of the electrolyte in a conventional use environment, improve the repeatability and reliability of the test results, make the evaluation of the stability of the SEI film closer to the actual application situation, and enhance the practical value of the electrolyte screening method.

[0041] Regarding the type of electrolyte, in some embodiments, the electrolyte to be tested is a non-aqueous electrolyte, and the non-aqueous electrolyte includes a solvent and a supporting electrolyte; and / or, the weight ratio of the solvent to the supporting electrolyte is (9-11): 1. The non-aqueous electrolyte has high electrochemical stability, a wide potential window, and good lithium ion conductivity. Its selection and ratio directly affect the performance of the lithium primary battery. The above electrolyte formula is more suitable for screening by the method of the present application, and is suitable for performance improvement and cost control of lithium primary batteries.

[0042] Under the above-mentioned weight ratio of solvent and supporting electrolyte, each component in the non-aqueous electrolyte can more effectively participate in the formation process of the SEI film, so that the cyclic voltammetry method can more accurately capture the electrochemical behavior characteristics of the SEI film, and provide a more reliable data basis for evaluating the stability of the SEI film and the compatibility of the electrolyte. The appropriate ratio of solvent and supporting electrolyte also helps to maintain the electrochemical stability and lithium ion conductivity of the electrolyte, reduce abnormal fluctuations during the test, and improve the repeatability and consistency of the cyclic voltammetry test in multiple scans and different voltage ranges. The non-aqueous electrolyte of the present application and the optimized weight ratio of solvent and supporting electrolyte are highly matched with the screening method based on cyclic voltammetry of the present application, which can not only more accurately evaluate the stability of the electrolyte, but also significantly improve the efficiency and reliability of the test.

[0043] Based on similar reasons, in some embodiments, the solvent of the non-aqueous electrolyte includes one or more of cyclic carboxylic acid esters, cyclic carbonates and ether substances. Specifically, the cyclic carboxylic acid ester includes γ-butyrolactone (γ-GBL), the cyclic carbonate includes propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) One or more, the ether substance includes ethylene glycol dimethyl ether (DME). Further, the solvent of the non-aqueous electrolyte includes cyclic carboxylic acid esters and ether substances, and the volume ratio of the two is 1: (1 to 2); or the solvent of the non-aqueous electrolyte includes cyclic carbonates and ether substances, and the volume ratio of the two is 1: (1 to 2). The selection of these solvents can affect the formation of the SEI film. The most suitable solvent combination for lithium primary batteries can be determined through testing, which is suitable for the formulation optimization of lithium primary battery electrolytes.

[0044] In some embodiments, the supporting electrolyte of the non-aqueous electrolyte includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(oxalatoborate) (LiBOB), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiODFB), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiPO2F2) and lithium tetrafluorooxalatophosphate (LiFOP). The selection of supporting electrolyte is crucial to the electrochemical performance of lithium primary batteries. This method can screen out the most suitable supporting electrolyte, which is more conducive to the performance improvement and safety enhancement of lithium primary battery electrolytes.

[0045] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0046] Example 1

[0047] Provide 8 kinds of electrolytes to be tested for screening:

[0048] The 1# electrolyte contains lithium tetrafluoroborate as the main salt, γ-butyrolactone (γ-GBL) and ethylene glycol dimethyl ether (DME) (volume ratio 1:1) as solvents, and the mass ratio of the main salt to the solvent is 1:9;

[0049] The 2# electrolyte contains lithium tetrafluoroborate as the main salt, ethylene carbonate (EC) and ethylene glycol dimethyl ether (DME) (volume ratio 1:1) as solvents, and the mass ratio of the main salt to the solvent is 1:9.5;

[0050] The 3# electrolyte contains lithium hexafluorophosphate as the main salt, propylene carbonate (PC) and ethylene glycol dimethyl ether (DME) (volume ratio 1:1) as solvents, and the mass ratio of the main salt to the solvent is 1:9.5;

[0051] The 4# electrolyte contains lithium hexafluorophosphate as the main salt, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio 1:1) as solvents, and the mass ratio of the main salt to the solvent is 1:10.5;

[0052] The 5# electrolyte contains lithium difluorooxalate borate as the main salt, ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1:2) as solvents, and the mass ratio of the main salt to the solvent is 1:9.5;

[0053] The 6# electrolyte contains lithium difluorooxalate borate as the main salt, ethylene carbonate (EC) and ethylene glycol dimethyl ether (DME) (volume ratio 1:1) as solvents, and the mass ratio of the main salt to the solvent is 1:10;

[0054] The 7# electrolyte contains lithium bis(oxalatoborate) as the main salt, γ-butyrolactone (γ-GBL) and ethylene glycol dimethyl ether (DME) (volume ratio 1:2) as solvents, and the mass ratio of the main salt to the solvent is 1:9;

[0055] The 8# electrolyte uses lithium disoxalatoborate as the main salt, propylene carbonate (PC) and ethylene glycol dimethyl ether (DME) (volume ratio 1:1) as solvents, and the mass ratio of the main salt to the solvent is 1:10.

[0056] The working electrode (Pt electrode), the reference electrode (lithium electrode) and the counter electrode (lithium electrode) form a three-electrode. The three electrodes are placed in the electrolyte to be tested and left to stand for 2 hours. After the voltage stabilizes (voltage change ≤ 0.01V / min), a cyclic voltammetry test is performed using an electrochemical workstation. See the test device diagram for details. Figure 1 .

[0057] Cyclic voltammetry was used to scan from open circuit voltage to 0 V, and then from 0 V to open circuit voltage; number of scans: 4 (I n i.e. I4); scanning speed: 0.05mV / s; temperature: 20±3°C.

[0058] The CV curves of each electrolyte are shown in Figure 2 , where the horizontal coordinate of each curve is voltage E, in V, and the vertical coordinate is current I, in mA. It can be seen that:

[0059] As the number of cycles of 1#, 2#, 4#, 6#, 7#, and 8# electrolytes increases, the reaction current decreases continuously (I1>I n ), indicating that the SEI film formed by the electrolyte system and lithium metal effectively passivates the contact reaction between lithium metal and electrolyte, the SEI film is stable, and the electrolyte to be tested is stable. The stability coefficient Φ of the above electrolyte is calculated, and the results are shown in Table 1. When I1≥I nWhen Φ is smaller, the SEI film formed by the tested electrolyte is more stable, and the tested electrolyte is more stable. It can be seen that the stability of the above electrolytes is ranked as 6#>8#>4#>7#>2#>1#.

[0060] As the number of cycles of 3# and 5# electrolytes increases, the reaction current increases continuously (I1<I n ), indicating that the electrolyte system is unstable with lithium metal and will continue to react, the SEI film is unstable, and the electrolyte to be tested is unstable. The stability coefficient Φ of the electrolyte is calculated, and the results are shown in Table 1. When I1<I n When Φ is larger, the SEI film formed by the tested electrolyte is more unstable, and the tested electrolyte is more unstable. It can be seen that the stability ranking of the above electrolytes is 5#>3#.

[0061] Therefore, 1#, 2#, 4#, 6#, 7#, and 8# electrolytes are selected as stable electrolytes for lithium primary batteries, among which 6# electrolyte is the most stable stable electrolyte for lithium primary batteries.

[0062] Verification results:

[0063] Electrolytes 1# to 8# are made into lithium primary batteries by the following methods: (1) The positive electrode active material MnO2, the conductive agent SP and the binder PVDF are mixed in a mass ratio of 90:5:5 to form a high-viscosity slurry, which is coated on an aluminum foil, dried at 85°C, and then rolled and die-cut to obtain a positive electrode sheet. (2) In a glove box filled with argon, the electrolyte raw materials are mixed in proportion to obtain electrolytes 1# to 8#. (3) The lithium ribbon is cut into corresponding sizes to obtain a metal lithium negative electrode sheet. (4) The positive electrode sheet, the metal lithium negative electrode sheet and the separator (PE) are assembled into a battery cell by winding, and the prepared electrolytes are injected into the battery cell, and the battery is obtained after sealing.

[0064] The battery was disassembled after being stored at 60°C for 100 days. See the disassembly photos after storage. Figure 3 , the percentage of lithium surface corrosion / roughness / discoloration / graying / byproduct coverage area is shown in Table 1.

[0065] The battery was placed at a constant temperature of 25°C for more than 5 hours, and the battery was discharged at a rate of 0.05C until the battery reached a cut-off voltage of 2V. The battery capacity was tested, and the capacity of the new battery was compared with that of the battery after storage. The capacity retention rate was calculated. The results are shown in Table 1.

[0066] Table 1

[0067]

[0068]

[0069] Depend on Figure 2 , Figure 3As shown in Table 1, the current density of 1#, 2#, 4#, 6#, 7#, and 8# electrolytes gradually decreases with the increase of cycles. When the battery is disassembled, it is found that the lithium interface is smoother, there are fewer by-products, the self-discharge of the battery cell is smaller, and the capacity retention rate is higher. The current density of 3# and 5# electrolytes gradually increases with the increase of cycles. When the battery is disassembled, it is found that the lithium interface is rougher, there are more by-products, the self-discharge of the battery cell is larger, and the capacity retention rate is lower. It can be seen that the screening results of this application are consistent with the actual disassembly situation and the battery capacity retention rate test situation, and can quickly and accurately screen out the electrolyte system that can form a stable SEI film with the lithium electrode in the early stage of the battery.

[0070] It should be noted that the method of the present invention can screen out electrolytes that can form a stable SEI film, and exclude electrolytes that cannot form a stable SEI film, but for multiple stable electrolytes with similar stability, the order according to the stability coefficient and the order according to the capacity retention rate may not be exactly the same. This is because the charging and discharging of the battery is a relatively complex chemical reaction process. When the electrolyte stability is not much different, the capacity retention rate may fluctuate at a similar level, but the screened stable electrolytes (such as 1#, 2#, 4#, 6#, 7#, 8# electrolytes of the present invention) can all meet the use of the battery, which is understandable to those skilled in the art and is acceptable in the battery research and development and production process, and will not be repeated here.

[0071] As can be seen from the above, the present application uses cyclic voltammetry to determine the stability of the SEI film formed by the electrolyte and lithium metal, and then determines the stability of the battery electrolyte, and screens out electrolytes that can act stably in lithium primary batteries. The present application uses electrochemical testing methods to determine the stability of the electrolyte in advance, and pre-screens stable electrolytes for full performance testing of the battery cell, which can greatly save production and testing resources.

[0072] The above is only a part of the embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for screening a lithium primary battery electrolyte, characterized in that: Put three electrodes into the electrolyte to be tested, and perform n-cycle scanning using cyclic voltammetry; the three electrodes include a working electrode, a reference electrode and a lithium counter electrode, and n is 2 to 10; Define the current of the first circle as I1 and the current of the nth circle as I n ; If I1≥I n , judging that the SEI film formed by the electrolyte to be tested is stable; If I1<I n , it is judged that the SEI film formed by the electrolyte to be tested is unstable.

2. The screening method according to claim 1, characterized in that The screening method also includes the step of secondary screening: Calculate the stability coefficient Φ of the electrolyte to be tested, Φ=|I1-I n |÷I1; When I1≥I n When Φ is smaller, it is judged that the SEI film formed by the electrolyte to be tested is more stable; When I1<I n When Φ is larger, it is judged that the SEI film formed by the electrolyte to be tested is more unstable.

3. The screening method according to claim 1 or 2, characterized in that The working electrode is a Pt electrode, and the reference electrode is a lithium electrode.

4. The screening method according to any one of claims 1 to 3, characterized in that The working electrode, the reference electrode and the lithium counter electrode are placed in the electrolyte to be tested, and allowed to stand for 1 to 3 hours. After the voltage change is ≤0.01 V / min, the cyclic voltammetry method is used to perform n-cycle scanning.

5. The screening method according to any one of claims 1 to 4, characterized in that During the scanning process, the voltage is first scanned from the open circuit voltage to 0 V, and then scanned from 0 V to the open circuit voltage.

6. The screening method according to any one of claims 1 to 5, characterized in that The scanning speed is 0.04-0.06 mV / s.

7. The screening method according to any one of claims 1 to 6, characterized in that The number of scanning circles n is 3 to 6; And / or the scanning temperature is 20±3°C.

8. The screening method according to any one of claims 1 to 7, characterized in that The electrolyte to be tested is a non-aqueous electrolyte, which includes a solvent and a supporting electrolyte, and the weight ratio of the solvent to the supporting electrolyte is (9-11):

1.

9. The screening method according to claim 8, characterized in that The solvent of the non-aqueous electrolyte includes one or more of ethylene glycol dimethyl ether, γ-butyrolactone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

10. The screening method according to claim 8 or 9, characterized in that The supporting electrolyte of the non-aqueous electrolyte includes one or more of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate and lithium tetrafluorooxalatophosphate.

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