An electrolyte and a lithium-ion battery using the same.

Abstract

This invention provides an electrolyte and a lithium-ion battery using the same, comprising additive A and additive B; additive A has the general structural formula [formula missing], wherein at least one of R1, R2, and R3 is an olefinic group; additive B has the general structural formula [formula missing], wherein R4 is a C1-C4 alkyl group. This electrolyte exhibits good stability and can form high-performance CEI and SEI films at the positive and negative electrodes of the lithium-ion battery, thereby effectively reducing the probability of electrolyte decomposition under high-voltage application conditions and significantly improving the high-voltage performance of the lithium-ion battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically, it relates to an electrolyte and a lithium-ion battery using the same. Background Technology

[0002] With the increasing demands for energy density in lithium-ion batteries from pure electric vehicles, hybrid vehicles, and portable energy storage devices, there is a growing expectation to develop lithium-ion batteries with higher energy and power densities to achieve longer driving range and energy storage for electric devices. Increasing the operating voltage is one method to improve the energy density of lithium-ion batteries. However, at high operating voltages, the electrolyte needs to have good oxidation resistance and a stable electrochemical window to ensure stable cycling of the lithium-ion battery under high voltage.

[0003] However, commercial lithium-ion battery electrolytes are generally composed of carbonate organic solvents and lithium hexafluorophosphate (LiPF6). The carbonate solvents are mainly composed of chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), as well as cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC). However, the oxidation potential of the above organic solvents is low, and they are prone to oxidation and decomposition under high voltage, making them difficult to exist stably. This leads to a decrease in the performance of lithium-ion batteries containing these solvents in the electrolyte.

[0004] The withstand voltage of commercial electrolytes can typically be improved in the following ways:

[0005] (1) Increasing the lithium salt concentration in the electrolyte containing carbonate solvents increases the number of complexes between lithium ions and solvent molecules, enhances the antioxidant properties of the complexed solvent molecules, and improves the stability of the electrolyte. In addition, compared with traditional electrolytes, high-concentration electrolytes have enhanced flame retardancy, thus improving the safety of the battery.

[0006] (2) Replace carbonate solvents with new high-voltage electrolyte solvents. New solvents include sulfones, nitriles, ionic liquids and fluorinated electrolytes. These new electrolyte systems can meet the high voltage requirements to a certain extent.

[0007] (3) By adding high voltage electrolyte additives to traditional carbonate electrolytes, the additives can preferentially decompose on the positive electrode surface to form a CEI film during battery cycling, which can protect the integrity of high voltage electrode materials to a certain extent and reduce the side reactions caused by the contact between high voltage positive electrode and electrolyte.

[0008] While the aforementioned methods can improve the high-voltage tolerance of electrolytes to some extent, they all have limitations. High lithium salt concentrations lead to high costs and low safety in electrolytes. Sulfone solvents and ionic liquids, due to their relatively high melting points, experience performance degradation at low temperatures. Poor compatibility between nitriles and graphite anodes also limits the practical application of new solvent-based electrolyte systems. In contrast, high-voltage multifunctional additives can simply and effectively improve the high-voltage tolerance of electrolytes. However, currently available high-voltage electrolyte additives all have a single positive electrode film-forming function, and their types are relatively limited. Therefore, developing novel and practical multifunctional high-voltage electrolyte additives remains an urgent problem to be solved. Summary of the Invention

[0009] This invention provides an electrolyte and a lithium-ion battery using the same. The electrolyte has good stability and can form high-performance CEI and SEI films at the positive and negative electrodes of the lithium-ion battery, respectively. This effectively reduces the probability of electrolyte decomposition under high-voltage conditions and improves the high-voltage performance of the lithium-ion battery.

[0010] According to a first aspect of the present invention, an electrolyte is provided, characterized in that it comprises additive A and additive B; the general structural formula of additive A is as follows: Among them, at least one of R1, R2, and R3 is an olefinic group; the general structural formula of additive B is R4 is a C1 to C4 alkyl group.

[0011] In the electrolyte provided by this invention, the combination of additives A and B effectively improves the stability of the electrolyte. On the one hand, the addition of these two additives inhibits the decomposition of the electrolyte under high-temperature conditions. On the other hand, these two additives are easily oxidized and reduced to form structurally stable CEI and SEI films on the surfaces of the positive and negative electrodes, thereby effectively reducing side reactions between the electrolyte and the positive and negative electrodes. Both additives A and B contain nitrogen atoms. Nitrogen atoms with lone pairs of electrons can complex with transition metal ions dissolved from the positive electrode active material, preventing transition metal ions from migrating to the negative electrode and damaging the negative electrode SEI film. In addition, the combination of additives A and B can effectively remove PF5, HF, CO2, and H2O generated in the electrolyte during the operation of the lithium-ion battery, effectively reducing the risk of corrosion of internal battery components by these materials, improving the cycle performance of the lithium-ion battery, and extending the service life of the lithium-ion battery.

[0012] Preferably, additive A is selected from... (CAS101-37-1) (CAS 87024-56-4) (CAS 50729-70-9) (CAS 30358-11-3) (CAS 3922-50-7) At least one of (CAS16715-84-7).

[0013] Preferably, additive A is Selecting materials with the above molecular structure as additive A can enhance the complexation effect on transition metal ions dissolved from the positive electrode, further inhibit the damage of transition metal ions in the electrolyte to the negative electrode SEI film, and further improve the removal effect of HF in the electrolyte.

[0014] Preferably, additive B is selected from... (CAS 81606-79-3) (CAS 91040-87-8) (CAS1248902-14-8) At least one of (CAS1490391-62-2).

[0015] Preferably, the general structural formula of additive B is as follows: Among them, R5 and R6 are independently selected from hydrogen, C1-C10 straight-chain or branched alkyl or alkoxy groups, and C1-C10 straight-chain or branched alkyl or alkoxy groups that are halogenated or unsubstituted. Using materials with the above molecular structure as additive B can further improve the removal efficiency of HF from the electrolyte.

[0016] Preferably, the molar mass of additive A is 190–300, and the molar mass of additive B is 100–180. In the electrolyte, the mass ratio of additive A to additive B satisfies the condition that the mass of additive A : mass of additive B = 0.5–0.8 : 1. In this scheme, by optimizing the ratio of additive A and additive B, the stability of both the positive electrode CEI film and the negative electrode SEI film of the lithium-ion battery is taken into account, thereby improving the working stability of the lithium-ion battery.

[0017] Preferably, the sum of the masses of additive A and additive B accounts for 0.6 wt.% to 2 wt.% of the mass of the electrolyte.

[0018] Preferably, the electrolyte further includes at least one of sulfur-containing additives, carbonate additives, and lithium salt additives; the sulfur-containing additives include at least one of vinyl sulfate (DTD), 1,3-propanesulfonyl lactone (PS), and 1,3-propenesulfonyl lactone (PST); the carbonate additives include vinylene carbonate (VC); and the lithium salt additives include at least one of lithium difluorosulfonylimide (LiFSI), lithium difluorophosphate (LiPO2F2), lithium oxalate borate (LiBOB), and lithium difluorodioxalate phosphate (LiODFP).

[0019] Preferably, the sulfur-containing additive includes PST, and in the electrolyte, the mass ratio of additive A to 1,3-propenesulfonyl lactone is 0.3–1:0.5–2. Based on the combined use of additive A and additive B in the electrolyte, further adding PST as a sulfur-containing additive in the electrolyte formulation can effectively improve the high-temperature performance of lithium-ion batteries.

[0020] Preferably, the electrolyte includes an organic solvent component, the organic solvent component accounting for 80 wt.% to 90 wt.% of the electrolyte mass. The organic solvent component includes cyclic carbonates, linear carbonates, and linear carboxylic acid esters, with a mass ratio of cyclic carbonate:linear carbonate:linear carboxylic acid ester = 10–25:50–80:5–20. In the above scheme, by selecting and controlling the proportions of the organic solvent components suitable for additives A and B, the high-temperature cycle characteristics of the lithium-ion battery can be further improved.

[0021] Preferably, the cyclic carbonate includes fluoroethylene carbonate (FEC), the chain carbonate includes diethyl carbonate, and the chain carboxylic acid ester includes ethyl difluorocarbonate.

[0022] Preferably, in the electrolyte, the mass ratio of fluoroethylene carbonate: ethylene carbonate: diethyl carbonate: ethyl difluorocarbonate is 5-15: 5-15: 60-80: 10-20.

[0023] According to a second aspect of the present invention, a lithium-ion battery is provided, the lithium-ion battery comprising the electrolyte as described above.

[0024] Specific implementation methods

[0025] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0026] Example 1

[0027] Based on the mass percentage of the components, the electrolyte formulation used in this embodiment is as follows: Additive A 0.3%, Additive B 0.4%, VC 0.2%, LiODFP 0.5%, PST 1%, Lithium hexafluorophosphate (LiPF6) 15%, and the balance being organic solvent components. The organic solvent components in the above electrolyte formulation consist of fluoroethylene carbonate, ethylene carbonate, and diethyl carbonate, wherein the mass fractions of fluoroethylene carbonate, ethylene carbonate, ethyl difluorophosphate, and diethyl carbonate are 10%, 10%, 15%, and 65%, respectively. Additive B in the above electrolyte formulation is... Different experimental groups were set up with additive A in the formula as the variable, and they were labeled as: experimental group 1-1, experimental group 1-2, experimental group 1-3, experimental group 1-4, and experimental group 1-5. The additive A used in each of the above experimental groups is shown in Table 1.

[0028] Table 1. Experimental group numbers and corresponding additive A used in this embodiment.

[0029]

[0030] Each experimental group prepared materials according to their respective electrolyte formulations. First, the materials used to prepare the organic solvent components were mixed evenly to obtain the organic solvent components. Then, under an argon atmosphere at 10°C, the formulated amounts of VC, PST, LiODFP, additive A, additive B, and LiPF6 were added to the organic solvent components. The temperature was maintained at 10°C, and the resulting mixture was stirred thoroughly until the solid materials were fully dissolved to obtain a homogeneous solution, thus preparing the electrolyte.

[0031] Example 2

[0032] The electrolyte formulation used in this embodiment, calculated by the mass percentage of the components, is as follows: Additive A 0.3%, Additive B 0.4%, VC 0.2%, LiODFP 0.5%, PST 1%, Lithium hexafluorophosphate (LiPF6) 15%, and the remainder being organic solvent components. The organic solvent components in the above electrolyte formulation have the same composition as those in the electrolyte formulation used in Example 1. Additive A in the above electrolyte formulation is triazine compound I from Table 1. Different experimental groups were set up using additive B as a variable, labeled as Experimental Group 2-1 and Experimental Group 2-2, respectively. The additive B used in each experimental group is shown in Table 2. Furthermore, since the experimental groups set up in this embodiment use the same type of additive A as Experimental Group 1-1 of Example 1, and the difference lies in the additive B in the electrolyte formulation, Experimental Group 1-1 of Example 1 is also included in Table 2 for comparison.

[0033] Table 2. Experimental group numbers and corresponding additive B used in this embodiment.

[0034]

[0035] Each experimental group prepared materials according to their respective electrolyte formulations. First, the materials used to prepare the organic solvent components were mixed evenly to obtain the organic solvent components. Then, under an argon atmosphere at 10°C, the formulated amounts of VC, PST, LiODFP, additive A, additive B, and LiPF6 were added to the organic solvent components. The temperature was maintained at 10°C, and the resulting mixture was stirred thoroughly until the solid materials were fully dissolved to obtain a homogeneous solution, thus preparing the electrolyte.

[0036] Comparative Example 1

[0037] This comparative example sets up control groups 1-1, 1-2, and 1-3 to prepare electrolytes. The specific formulations and methods for preparing electrolytes in each control group are as follows.

[0038] Control group 1-1:

[0039] Using the electrolyte formulation used in experimental group 1-1 of Example 1 as a reference, the difference between the electrolyte formulation used in control group 1 and the electrolyte formulation used in experimental group 1-1 is that the additive A used is... (hereinafter referred to as "triazine compound VI"), in the electrolyte formulation used in control group 1, triazine compound VI was used to replace triazine compound I in the electrolyte formulation of experimental group 1-1 by an equal mass as additive A in the electrolyte formulation. Apart from this, all other materials in the electrolyte formulation used in control group 1 were consistent with those used in the electrolyte formulation of experimental group 1-1 in terms of materials and proportions. Materials were prepared according to the electrolyte formulation used in control group 1, and the electrolyte was prepared according to the method used in experimental group 1-1.

[0040] Control groups 1-2:

[0041] Using the electrolyte formulation of experimental group 2-1 in Example 2 as a reference, the difference between the electrolyte formulation of control group 2 and that of experimental group 2-1 is that the additive B used is... (hereinafter referred to as "triazole compound IV"), in the electrolyte formulation used in control group 2, triazole compound IV replaced triazole compound I in the electrolyte formulation of experimental group 2-1 by an equal mass as additive B in the electrolyte formulation. Apart from this, all other materials in the electrolyte formulation used in control group 2 were consistent with those used in the electrolyte formulation of experimental group 2-1 in terms of materials and proportions. Materials were prepared according to the electrolyte formulation used in control group 2, and the electrolyte was prepared according to the method used in experimental group 2-1.

[0042] Control groups 1-3:

[0043] Based on the mass percentage of the components, the electrolyte formulation used in control group 6 is as follows: VC 0.2%, LiODFP 0.5%, PST 1%, LiPF6 15%, with the balance being organic solvent components. In the above electrolyte formulation, the organic solvent components used have the same composition as those included in the electrolyte formulation used in Example 1.

[0044] Prepare the materials according to the electrolyte formula. First, mix the materials used to prepare the organic solvent component evenly to obtain the organic solvent component. Then, under an argon atmosphere at 10°C, add the formulated amounts of VC, PST, LiODFP, and LiPF6 to the organic solvent component. Keep the temperature at 10°C and stir the resulting mixture thoroughly until the solid material is fully dissolved to obtain a homogeneous solution, thus preparing the electrolyte.

[0045] Preparation Example 1

[0046] The electrolyte used in this preparation example for preparing lithium-ion batteries is the electrolyte prepared in Example 1, Example 2, and Comparative Example 1.

[0047] The method for preparing a lithium-ion battery in this example is as follows:

[0048] Graphite was used as the negative electrode active material. A negative electrode slurry was prepared by mixing graphite, conductive agent acetylene black, binder CMC, and SBR in a mass ratio of 94:1:2:3. The negative electrode slurry was coated onto a copper foil current collector and vacuum dried to obtain a negative electrode sheet. NCM523 was used as the positive electrode active material. A positive electrode slurry was prepared by mixing NCM523, conductive agent acetylene black, and binder PVDF in a mass ratio of 94:3:3. The positive electrode slurry was coated onto an aluminum foil current collector and vacuum dried to obtain a positive electrode sheet. The electrolytes prepared in Examples 1, 2, and the comparative example were used to assemble the above-mentioned positive electrode sheet, negative electrode sheet, and Celgard 2400 separator into a soft-pack battery.

[0049] Test Example 1

[0050] 1. Electrolyte HF content test

[0051] (1) Test object

[0052] The electrolytes prepared according to Example 1, Example 2, and Comparative Example 1.

[0053] (2) Test method

[0054] The electrolyte was stored at 45°C, and the HF content in the electrolyte was tested by ice-water titration at the start of the experiment and after 15 days of storage. The HF content measured at the start of the experiment was recorded as HF-0d, and the HF content measured after 15 days of storage was recorded as HF-15d.

[0055] 2. Cycle performance testing of lithium-ion batteries

[0056] (1) Test object

[0057] The lithium-ion battery prepared in Example 1 was used as the test object.

[0058] (2) Test method

[0059] Room temperature cycle test: Place the lithium-ion battery at 25℃ and record the initial capacity, labeled A1. Cycle the lithium-ion battery 2000 times at a 5C / 5C rate and record the capacity under this condition, labeled A2. The capacity retention rate of the lithium-ion battery after 2000 cycles at room temperature is calculated as follows:

[0060] Room temperature cycling capacity retention rate (%) = A2 / A1 × 100%.

[0061] High-temperature cycling test: The lithium-ion battery was placed at 45℃, and the initial capacity was recorded and marked as A3. The lithium-ion battery was cycled 2000 times at a 5C / 5C rate, and the capacity of the lithium-ion battery under this condition was recorded and marked as A4. The capacity retention rate of the lithium-ion battery after 2000 high-temperature cycles is calculated as follows:

[0062] High-temperature cycling capacity retention (%) = A4 / A3 × 100%.

[0063] 3. High-Temperature Storage Performance Testing of Lithium-ion Batteries

[0064] (1) Test object

[0065] The lithium-ion battery prepared in Example 1 was used as the test object.

[0066] (2) Test method

[0067] The lithium-ion battery was charged at a constant current of 1.0C (nominal capacity) to a voltage of 4.4V, then charged at a constant voltage of 4.4V until the current ≤0.05C. After resting for 10 minutes, it was discharged at a constant current of 1C to 2.8V. This constituted one charge-discharge cycle. The tested lithium-ion battery was subjected to 5 charge-discharge cycles at 25℃ with a charge-discharge rate of 1C, and then fully charged at a 1C rate. The capacity Q0 and volume V0 of the lithium-ion battery were recorded. The fully charged battery was stored at 60℃ for 90 days, and the volume V1 and 1C discharge capacity Q1 of the lithium-ion battery were recorded. Then, the lithium-ion battery was charged and discharged at 25℃ with a 1C rate for 5 weeks, and the 1C discharge capacity Q2 was recorded. The experimental data such as the battery's high-temperature storage capacity retention rate, capacity recovery rate, and volume change rate were calculated. The calculation formulas used are as follows:

[0068] Capacity retention rate (%) = Q1 / Q0 × 100%;

[0069] Capacity recovery rate (%) = Q2 / Q0 × 100%;

[0070] Volume change rate (%) = (V1-V0) / V0×100%.

[0071] 4. Test Results

[0072] The test results for this test case are shown in Table 3.

[0073] The electrolytes prepared in control groups 1-3 contained neither triazine nor triazole compounds. The test results showed that these electrolytes had significantly higher HF content than tested in this test example. Furthermore, among all the lithium-ion batteries tested in this example, those using electrolytes from control groups 1-3 exhibited significant deficiencies in both high-temperature storage performance and room-temperature / high-temperature cycle performance.

[0074] Compared with the electrolytes provided in control groups 1-3, the electrolytes provided in experimental groups 1-1, 1-2, 1-3, 1-4, 1-5, 2-1, and 2-2 all contained the general structural formula [structure missing]. Additive A (where at least one of R1, R2, and R3 is an olefinic group) and the general structural formula is Additive B (where R4 is an alkyl group). Based on the combination of additives A and B: First, it inhibits the decomposition of the electrolyte under high-temperature conditions; second, the two additives readily form structurally stable CEI and SEI films on the surfaces of the positive and negative electrodes, thereby effectively reducing side reactions between the electrolyte and the positive and negative electrodes; third, additives A and B inhibit the dissolution of transition metal ions from the positive electrode active material, thus preventing transition metal ions from migrating to the negative electrode and damaging the negative electrode SEI film; fourth, the combination of the two additives can effectively remove PF5, HF, CO2, and H2O generated in the electrolyte during the operation of the lithium-ion battery. In summary, the combined application of additives A and B can improve the high-temperature storage performance and cycle performance of lithium-ion batteries using these electrolytes to a certain extent.

[0075] The electrolytes prepared in control groups 1-1 and 1-2 both contained triazine and triazole compounds. However, compared with the performance of lithium-ion batteries using the electrolytes from experimental groups 1-1, 1-2, 1-3, 1-4, 1-5, 2-1, and 2-2, respectively, and the performance of lithium-ion batteries using these electrolytes, the performance of the electrolytes from control groups 1-1 and 1-2 still showed significant deficiencies. Specifically, the triazine compound in the electrolyte from control group 1-1 did not contain an olefin group, meaning the triazine compound used in preparing the electrolyte in control group 1-1 was not additive A. Similarly, the triazole compound in the electrolyte from control group 1-2 did not contain a cyano group, meaning the triazole compound used in preparing the electrolyte in control group 1-2 was not additive B. Therefore, although the electrolytes prepared in control groups 1-1 and 1-2 both contained triazine and triazole compounds, the triazine and triazole compounds used in these two electrolytes did not simultaneously conform to the general structural formulas of additives A and B. Thus, the combination of additives A and B was not actually involved in the preparation of these two electrolytes. The test results of this example demonstrate that, for electrolytes, not any combination of triazine and triazole compounds can achieve the same effect as the combination of additives A and B.

[0076] The electrolytes prepared in experimental groups 1-1, 1-2, 1-3, 1-4, and 1-5 differed primarily in the specific type of additive A. Among these electrolytes, the electrolyte provided in experimental group 1-1 exhibited the lowest HF content under the same test conditions in this test example. Furthermore, in lithium-ion batteries using these electrolytes, the lithium-ion battery using the electrolyte from experimental group 1-1 demonstrated the best high-temperature performance and cycle performance in this test example. Additive A in the electrolyte of experimental group 1-1 is a triazine compound I, with the following structure: Based on the application of additive B, the use of triazine compound I as additive A can better complex the transition metal ions dissolved from the positive electrode of lithium-ion batteries, preventing the transition metal ions from migrating to the negative electrode and damaging the SEI film.

[0077] The difference in the formulation of the electrolytes prepared in Experimental Groups 1-1, 2-1, and 2-2 lies in the specific type of additive B. Lithium-ion batteries using these electrolytes all achieved excellent high-temperature performance and excellent cycle performance. Among the electrolytes, the electrolyte provided in Experimental Group 1-1 showed the lowest HF content under the same test conditions in this test example.

[0078] Table 3. Statistical analysis of test results for Test Example 1

[0079]

[0080]

[0081] Comparative Example 2

[0082] As described above, the electrolytes provided in each experimental group in Example 1 were all electrolytes using a combination of additives A and B. Among these electrolytes, the electrolyte provided in experimental group 1-1 of Example 1 and the lithium-ion battery using it achieved the best overall performance among similar test objects in Test Example 1. Based on the test results in Test Example 1, this comparative example uses experimental group 1-1 of Example 1 as a control, and sets up control groups 1-4 and 1-5 to prepare electrolytes. The specific formulations and methods of preparing the electrolytes for these two control groups are as follows.

[0083] Control groups 1-4:

[0084] Based on the mass percentage of the components, the electrolyte formulation used in control group 4 is as follows: Additive A 0.7%, VC 0.2%, LiODFP 0.5%, PST 1%, LiPF6 15%, with the balance being organic solvent components. In the above electrolyte formulation, the organic solvent components used have the same composition as those included in the electrolyte formulation used in Example 1, and the additive A used is the same as that in experimental group 1-1 of Example 1, both being triazine compound I.

[0085] Prepare the materials according to the electrolyte formula. First, mix the materials used to prepare the organic solvent component evenly to obtain the organic solvent component. Then, under an argon atmosphere at 10°C, add the formulated amounts of VC, PST, LiODFP, additive A, and LiPF6 to the organic solvent component. Keep the temperature at 10°C and stir the resulting mixture thoroughly until the solid material is fully dissolved to obtain a homogeneous solution, thus preparing the electrolyte.

[0086] Control groups 1-5:

[0087] Based on the mass percentage of the components, the electrolyte formulation used in control group 5 is as follows: Additive B 0.7%, VC 0.2%, LiODFP 0.5%, PST 1%, LiPF6 15%, with the balance being organic solvent components. In the above electrolyte formulation, the organic solvent components used have the same composition as those included in the electrolyte formulation used in Example 1, and the additive B used is the same as that in experimental group 1-1 of Example 1, both being triazole compound I.

[0088] Prepare the materials according to the electrolyte formula. First, mix the materials used to prepare the organic solvent component evenly to obtain the organic solvent component. Then, under an argon atmosphere at 10°C, add the formulated amounts of VC, PST, LiODFP, additive B, and LiPF6 to the organic solvent component. Keep the temperature at 10°C and stir the resulting mixture thoroughly until the solid material is fully dissolved to obtain a homogeneous solution, thus preparing the electrolyte.

[0089] Preparation Example 2

[0090] The electrolyte used in this preparation example to prepare the lithium-ion battery is the electrolyte prepared in Comparative Example 2.

[0091] The method used to prepare the lithium-ion battery in this preparation example is consistent with the method used to prepare the lithium-ion battery in Preparation Example 1.

[0092] Test Example 2

[0093] 1. Electrolyte HF content test

[0094] (1) Test object

[0095] The electrolyte prepared in Comparative Example 2 was used as the test object.

[0096] (2) Test method

[0097] The method used in this test example to test the HF content of the electrolyte is consistent with the method used in Test Example 1.

[0098] 2. Cycle performance testing of lithium-ion batteries

[0099] (1) Test object

[0100] The lithium-ion battery prepared in Example 2 was used as the test object.

[0101] (2) Test method

[0102] The method used in this test example to test the cycle performance of lithium-ion batteries is consistent with the method used in Test Example 1.

[0103] 3. High-Temperature Storage Performance Testing of Lithium-ion Batteries

[0104] (1) Test object

[0105] The lithium-ion battery prepared in Example 2 was used as the test object.

[0106] (2) Test method

[0107] The method used in this test example to test the high-temperature storage performance of lithium-ion batteries is consistent with the method used in Test Example 1.

[0108] 3. Test Results

[0109] The test results for this test example are shown in Table 4. For ease of comparison, Table 4 also shows the test results of the electrolyte used in Experimental Group 1-1 of Example 1 and the lithium-ion battery made using it in Test Example 1. In the two control groups set up in Comparative Example 2, the electrolytes of Control Group 1-4 and Experimental Group 1-1 contain the same type of additive A, but the electrolytes of Control Group 1-4 do not contain additive B. The electrolytes of Control Group 1-5 and Experimental Group 1-1 contain the same type of additive B, but the electrolytes of Control Group 1-5 do not contain additive A. The test results of control group electrolytes 1-4 and 1-5, as well as lithium-ion batteries using these two electrolytes respectively, were compared in this test example. With the same amount of additive, control group electrolytes 1-4 containing additive A and the lithium-ion batteries using them performed better in all performance tests compared to similar test subjects. This indicates that, when used separately, additive A is more effective than additive B in improving the performance of the electrolyte and the lithium-ion batteries using it. However, compared to control group 1-4, experimental group 1-1 essentially used additive B to partially replace additive A in the electrolyte preparation process. The test results show that experimental group 1-1 electrolyte and the lithium-ion batteries using it outperformed similar test subjects in this test example in all performance tests. This demonstrates that when additive A and additive B are used together, they can synergistically enhance the overall performance of the electrolyte and the applied lithium-ion batteries.

[0110] In addition to experimental group 1 and experimental group 1-1, other experimental groups in Example 1 were used as controls. The comparative experiments were set up with reference to the variable settings of experimental group 1-1, control group 1-4, and control group 1-5. The performance differences that are consistent with the test results of this test case can also be obtained.

[0111] Table 4. Statistical results of test example 2

[0112]

[0113]

[0114] Example 3

[0115] In this embodiment, based on the test results of Test Example 1 and Test Example 2, the optimal ratio of additive A and additive B in the electrolyte formulation is further explored. Calculated according to the mass percentage of the components, the electrolyte formulation used in this embodiment is as follows: the total amount of additive A and additive B is 0.7%, VC 0.2%, LiODFP 0.5%, PST 1%, lithium hexafluorophosphate (LiPF6) 15%, and the remainder is organic solvent components. In this embodiment, using the ratio of additive A and additive B as a variable, and referring to experimental group 1-1 of Example 1, experimental groups 3-1, 3-2, 3-3, and 3-4 were set up. In the above experimental groups, additive A was always triazine compound I, and additive B was always triazole compound I. Table 5 shows the mass percentage and mass ratio of additive A and additive B in the electrolyte formulations used in the above experimental groups. For ease of comparison, Table 5 also shows the content of additive A and additive B in the electrolyte formulation used in experimental group 1-1 of Example 1.

[0116] Table 5. Variable settings among the electrolyte formulations used in each experimental group in Example 3

[0117] Group Additive A percentage Additive B percentage Additive A : Additive B (mass ratio) Experimental group 1-1 0.3％ 0.4％ 0.75:0.1 Experimental group 3-1 0.23％ 0.47％ 0.5:1 Experimental group 3-2 0.31％ 0.39％ 0.8:1 Experimental group 3-3 0.16％ 0.54％ 0.3:1 Experimental group 3-4 0.35％ 0.35％ 1:1

[0118] Experimental groups 3-1, 3-2, 3-3, and 3-4 prepared their materials according to their respective electrolyte formulations, and then prepared the electrolytes in the manner used in Experimental group 1-1 of Example 1.

[0119] Preparation Example 3

[0120] The electrolyte used in this preparation example to prepare the lithium-ion battery is the electrolyte prepared in Example 3.

[0121] The method used to prepare the lithium-ion battery in this preparation example is consistent with the method used to prepare the lithium-ion battery in Preparation Example 1.

[0122] Test Example 3

[0123] The test item conducted in this test case is the cycle performance test of lithium ions.

[0124] 1. Test Object

[0125] The lithium-ion battery prepared in Example 3 was used as the test object.

[0126] 2. Testing Methods

[0127] The method used in this test example to test the cycle performance of lithium-ion batteries is consistent with the method used in Test Example 1.

[0128] 3. Test Results

[0129] The test results of this test example are shown in Table 6. For easy comparison, Table 6 also shows the test results of the lithium-ion battery prepared using the electrolyte of Experimental Group 1-1 in Example 1 in Test Example 1.

[0130] The test results of this test case show that, among the test subjects, experimental groups 1-1, 3-1, and 3-2 provide better cycle performance for lithium-ion batteries. In the electrolyte formulation used in the test subjects, when the ratio of additive A to additive B in the formulation meets the requirement of additive A mass: additive B mass = 0.5–0.8, the stability of the positive electrode CEI film and the negative electrode SEI film of the lithium-ion battery can be further improved, thereby enhancing the working stability of the lithium-ion battery.

[0131] Aside from the use of triazine compounds as additive A and triazole compounds as additive B, when other triazine compounds shown in Table 1 are used as additive A and other triazole compounds shown in Table 2 are used as additive B, and different combinations of additive A / additive B are used in the preparation of the electrolyte, the cycle performance of the lithium-ion battery is better when the mass ratio of additive A to additive B is 0.5 to 0.8.

[0132] Table 6. Statistical results of lithium-ion battery cycle performance test in Test Example 3

[0133]

[0134]

[0135] Example 4

[0136] In this embodiment, the electrolyte formulation used in Experimental Group 1-1 of Example 1 is used as the basis, and the sulfur-containing additives in the electrolyte formulation are used as variables to set up Experimental Group 4-1, Experimental Group 4-2, and Experimental Group 4-3.

[0137] Experimental Group 4-1: PST in the electrolyte formulation of Experimental Group 1-1 was replaced by DTD at the same mass, and the resulting electrolyte formulation was used as the electrolyte formulation of Experimental Group 4-1.

[0138] Experimental group 4-2: PS was used to replace PST in the electrolyte formula of experimental group 1-1 by an equal mass, and the resulting electrolyte formula was used as the electrolyte formula of experimental group 4-2.

[0139] Experimental Group 4-3: The organic solvent component in the electrolyte formulation of Experimental Group 1-1 was replaced with PST in the electrolyte formulation of Experimental Group 1-1 by an equal mass, and the resulting electrolyte formulation was used as the electrolyte formulation of Experimental Group 4-3.

[0140] Experimental groups 4-1, 4-2, and 4-3 prepared their materials according to their respective electrolyte formulations, and then prepared the electrolytes in the manner used in Experimental group 1-1 of Example 1.

[0141] Preparation Example 4

[0142] The electrolyte used in this preparation example for preparing the lithium-ion battery is the electrolyte prepared in Example 4.

[0143] The method used to prepare the lithium-ion battery in this preparation example is consistent with the method used to prepare the lithium-ion battery in Preparation Example 1.

[0144] Test Example 4

[0145] 1. Cycle performance testing of lithium-ion batteries

[0146] (1) Test object

[0147] The lithium-ion battery prepared in Example 4 was used as the test object.

[0148] (2) Test method

[0149] The method used in this test example to test the cycle performance of lithium-ion batteries is consistent with the method used in Test Example 1.

[0150] 2. High-Temperature Storage Performance Testing of Lithium-ion Batteries

[0151] (1) Test object

[0152] The lithium-ion battery prepared in Example 4 was used as the test object.

[0153] (2) Test method

[0154] The method used in this test example to test the high-temperature storage performance of lithium-ion batteries is consistent with the lithium-ion battery cycle performance test method used in Test Example 1.

[0155] 3. Test Results

[0156] The test results of this test example are shown in Table 7. For ease of comparison, Table 7 also shows the test results of lithium-ion batteries prepared using the electrolyte of Experimental Group 1-1 of Example 1 in Test Example 1. The electrolytes prepared in Experimental Group 1-1 of Example 1, Experimental Group 4-1 of Example 4, and Experimental Group 4-2 of Example 4 all contain sulfur-containing additives, while the electrolyte prepared in Experimental Group 4-3 of Example 4 does not contain sulfur-containing additives. The test results of this test example show that the lithium-ion batteries using the electrolytes of Experimental Group 4-3, Experimental Group 4-1, and Experimental Group 4-2 of Example 4 all achieved basically equivalent levels in various product performance tests. Compared with the above lithium-ion batteries, the lithium-ion battery using the electrolyte of Experimental Group 1-1 of Example 1 showed certain advantages in various product performance tests measured in this test example. This demonstrates that for electrolyte systems containing additives A and B, not the addition of any single sulfur-containing additive can effectively improve the performance of lithium-ion batteries using these electrolytes. However, based on the combined use of additives A and B in the electrolyte, further adding PST as a sulfur-containing additive can effectively improve the performance of lithium-ion batteries using these electrolytes, particularly enhancing their high-temperature performance.

[0157] Table 7. Statistical results of test case 4

[0158]

[0159] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that: It includes additive A and additive B; the general structural formula of additive A is as follows: In this embodiment, at least one of R1, R2, and R3 is an olefinic group; the general structural formula of additive B is: In the electrolyte, R4 is a C1-C4 alkyl group; R5 and R6 are independently selected from hydrogen, C1-C10 straight-chain or branched alkyl or alkoxy groups, and C1-C10 halogenated or unsubstituted straight-chain or branched alkyl or alkoxy groups; in the electrolyte, the mass ratio of additive A to additive B satisfies the condition that the mass of additive A:mass of additive B = 0.5-0.8:1; the sum of the masses of additive A and additive B accounts for 0.6 wt.% to 2 wt.% of the mass of the electrolyte.

2. The electrolyte as described in claim 1, characterized in that, The additive A is .

3. The electrolyte as described in claim 1, characterized in that: The general structural formula of additive B is: .

4. The electrolyte as described in claim 1, characterized in that: The molar mass of additive A is 190-300, and the molar mass of additive B is 100-180.

5. The electrolyte according to any one of claims 1 to 4, characterized in that: The electrolyte also includes at least one of sulfur-containing additives, carbonate additives, and lithium salt additives; The sulfur-containing additive includes at least one of vinyl sulfate, 1,3-propanesulfonate lactone, and 1,3-propenesulfonate lactone. The carbonate additives include vinylene carbonate; The lithium salt additive includes at least one of lithium difluorosulfonylimide, lithium difluorophosphate, lithium dioxaborate, and lithium difluorodioxaborate.

6. The electrolyte as described in claim 5, characterized in that: The sulfur-containing additive includes 1,3-propenesulfonate lactone, and in the electrolyte, the mass ratio of additive A to 1,3-propenesulfonate lactone is 0.3-1:0.5-2.

7. The electrolyte according to any one of claims 1 to 4, characterized in that: The electrolyte includes an organic solvent component, the organic solvent component accounting for 80 wt.% to 90 wt.% of the mass of the electrolyte. The organic solvent component includes cyclic carbonates, chain carbonates, and chain carboxylic esters, and the cyclic carbonate : chain carbonate : chain carboxylic ester ratio is 10 to 25 : 50 to 80 : 5 to 20 by mass.

8. The electrolyte as described in claim 7, characterized in that: The cyclic carbonates include fluoroethylene carbonate and ethylene carbonate, the chain carbonates include diethyl carbonate, and the chain carboxylic acid esters include ethyl difluorocarbonate.

9. A lithium-ion battery, characterized in that: The lithium-ion battery includes the electrolyte as described in any one of claims 1 to 8.

Images