Multifunctional lithium ion battery electrolyte with high-voltage, fast-charging and low-temperature performances and application of multifunctional lithium ion battery electrolyte

Abstract

The invention discloses a multifunctional lithium ion battery electrolyte with high-voltage, fast-charge and low-temperature performances and application thereof, the electrolyte can improve the high-voltage, fast-charge and low-temperature performances of a battery, and the electrolyte belongs to the field of lithium ion battery electrolytes. The electrolyte is composed of a lithium salt, an organic solvent, a diluent and a proper amount of an additive. The electrolyte has relatively high ionic conductivity and Li < + > weak solvation environment, and can form a stable and rapid lithium-conducting interface layer on a positive and negative electrode interface, so that Li < + > can rapidly migrate in the battery, and the rapid charging and low-temperature performance of the battery is improved. Meanwhile, the formed inorganic-interface-rich film can effectively bear high cut-off voltage of the positive electrode and large volume expansion of the negative electrode, so that the battery can show stable circulation under the condition of high cut-off voltage.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrolytes for lithium secondary batteries, and in particular relates to a multifunctional lithium ion battery electrolyte capable of improving high voltage, fast charging and low temperature performance and its application. Background Art

[0002] The vigorous development of new energy vehicles and low-altitude flight economy has driven the performance upgrade of power batteries, which requires improving the energy density of batteries and having superior fast charging performance and low-temperature performance. The current traditional graphite system and low cut-off voltage (<4.3V) positive electrode limit the improvement of material capacity and overall battery voltage, and have gradually become difficult to meet the demand for high energy density. Therefore, achieving the coordinated use of high-capacity negative electrodes (such as silicon-carbon negative electrodes) and high-voltage positive electrodes is an effective way to develop the next generation of high-energy density batteries. However, the high-voltage and high-energy density electrode system needs to solve the core problem of interfacial side reactions (silicon volume expansion, high-voltage electrolyte decomposition). At the same time, how to maintain high-speed ion conduction in such a system to achieve excellent fast charging (>4C) and low-temperature performance is the key to meeting comprehensive needs.

[0003] At present, traditional carbonate electrolytes are difficult to meet so many requirements at the same time. Carbonate electrolytes are easily oxidized and decomposed to produce gas under high pressure, and the HF generated in them attacks the crystal structure of the positive electrode, causing a large loss of transition metal ions. In addition, ethylene carbonate (EC) and Li + The interaction is strong and the viscosity is high, so the high-speed conduction and desolvation resistance of lithium ions are large.

[0004] Promoting anion-derived interface films is a powerful means to solve the problem of interfacial side reactions. On the one hand, the derived inorganic-rich negative electrode interface can enhance the mechanical properties to alleviate the interface fragmentation problem caused by the large volume expansion of high-capacity negative electrodes; on the other hand, the same inorganic-rich positive electrode interface can prevent electrolyte oxidation and inhibit the dissolution of transition metal ions to maintain high-voltage stability. The anion-derived interface relies on a large proportion of contact ion pairs and ion aggregates formed in the electrolyte, which is not conducive to the improvement of ionic conductivity. At the same time, the anion-rich Li + The constraints of Li + How to coordinate the electrolyte components to achieve anion-derived interfacial film and Li + The rapid conduction of electricity is the key to developing high voltage, fast charging and low temperature performance. Summary of the Invention

[0005] In order to solve the problem that the above-mentioned lithium-ion batteries cannot simultaneously take into account the multiple performance aspects of high voltage, fast charging and low temperature, the present invention provides an electrolyte and its application that effectively improves the fast charging and low temperature performance of the battery and is compatible with high-voltage positive electrode and high-capacity negative electrode battery systems.

[0006] In order to achieve the above objectives, the present invention adopts the following technical solutions.

[0007] A multifunctional lithium-ion battery electrolyte that combines high-voltage, fast-charging, and low-temperature performance. The electrolyte consists of a lithium salt, an organic solvent, a diluent, and an additive. The molar ratio of the lithium salt to the organic solvent is 1:(4-6), the molar ratio of the lithium salt to the diluent is 1:(0-4), and the molar ratio of the lithium salt to the additive is 1:(0-0.5).

[0008] Preferably, the lithium salt is one or a combination of two or more of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluorosulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate (LiODFB) and lithium difluorophosphate, and more preferably lithium bis(fluorosulfonyl)imide (LiFSI).

[0009] Preferably, the organic solvent is one or a combination of two or more selected from the group consisting of linear carboxylates, linear carbonates, fluorinated linear carboxylates, and fluorinated linear carbonates; further preferably, the organic solvent is one or a combination of two or more selected from the group consisting of methyl acetate, ethyl acetate, methyl propionate, fluoromethyl acetate, fluoroethyl acetate, fluoromethyl propionate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluorodimethyl carbonate, fluorodiethyl carbonate, and fluoromethyl ethyl carbonate; and most preferably, methyl acetate.

[0010] Preferably, the diluent is one or more of a fluoroether, a fluoroalkane, or a halogen-containing phenyl derivative that is insoluble in lithium salts; further preferably, one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, 2,2,2-trifluoroethyl-1,1,2,2-tetrafluoroethyl ether, 3-fluorotoluene, 1,2-difluorobenzene, 3-fluorotrifluorotoluene and trifluoromethoxybenzene; most preferably, 1,2-difluorobenzene.

[0011] Preferably, the additive is one of fluoroethylene carbonate, lithium difluorooxalophosphate, lithium difluorophosphate, lithium hexafluorophosphate or a combination thereof, and more preferably is a combination of fluoroethylene carbonate, lithium difluorooxalophosphate and lithium hexafluorophosphate.

[0012] Preferably, the molar ratio of the lithium salt to the organic solvent is 1:5.

[0013] Preferably, the molar ratio of the lithium salt to the diluent is 1:3.

[0014] Preferably, the molar ratio of the lithium salt to the additive is 1:(0.1-0.4), more preferably 1:0.4.

[0015] Preferably, the molar ratio of the lithium salt, the organic solvent, the diluent, and the additive is 1:5:3:0.4.

[0016] A lithium-ion battery comprises a positive electrode, a negative electrode, a separator and any of the above multifunctional lithium-ion battery electrolytes having high voltage, fast charging and low temperature performance.

[0017] Preferably, the positive electrode is a nickel-cobalt-manganese ternary positive electrode, and the negative electrode is a silicon-carbon negative electrode.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] Compared with the traditional carbonate electrolyte, the electrolyte of the present invention has higher ionic conductivity. + The desolvation energy is significantly reduced, and the two together ensure the high-speed migration of lithium ions. In addition, the electrolyte can simultaneously derive stable and Li + The interfacial film with low diffusion activation energy ensures stable operation of the battery under high voltage. These improvements enable the silicon-carbon full battery to maintain stable cycling within the 2.5-4.6V range, with a 6C fast charge capability and good low-temperature performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The electrolytes of Examples 8-10 of the present invention are shown in the cycle curves of Si-C||NCM622 at 30°C, 500mA / g current density and 2.5-4.6V voltage range, and the specific capacity retention rate at 200 cycles (calculated based on the mass of the silicon-carbon negative electrode).

[0021] Figure 2 This is a charge and discharge curve diagram of the electrolyte of Example 8 of the present invention at different charge rates in Si-C||NCM811 at 30°C.

[0022] Figure 3 This is a charge and discharge curve diagram of Si-C||NCM622 at 30°C, 0°C, -10°C, -20°C, -30°C, -40°C, -50°C, and -60°C of the electrolyte of Example 8 of the present invention; wherein, the current density at 30°C to -50°C is 100mA / g, and the current density at -60°C is 50mA / g. DETAILED DESCRIPTION

[0023] The following further illustrates the specific implementation of the present invention with reference to examples and drawings, but the embodiments of the present invention are not limited thereto. Certain substances in the examples are described using the abbreviations in parentheses after the substances.

[0024] Comparative Example 1, Examples 1-10

[0025] The electrolyte solution was prepared at room temperature in a glove box with an oxygen content of <0.01ppm and a moisture content of <0.01ppm. The preparation process was as follows: the solvent and diluent were mixed uniformly in proportion, and then the lithium salt was added in proportion. After the lithium salt was completely dissolved, the additives were added in proportion. The above process was stirred uniformly using a stirrer throughout, and finally a clear and transparent electrolyte was obtained. The specific proportions of the examples and comparative examples are shown in the following table:

[0026] Table 1 Components of Comparative Examples and Examples

[0027]

[0028]

[0029] Note: Lithium hexafluorophosphate (LiPF6); ethylene carbonate (EC); diethyl carbonate (DEC); fluoroethylene carbonate (FEC); lithium bis(fluorosulfonyl)imide (LiFSI); 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE); methyl acetate (MA); lithium difluorooxalatophosphate (LiDFOB); (2,2,2-trifluoroethyl) ether (BTFE); 3-fluorotoluene (mFT); 1,2-difluorobenzene (DFB); 3-fluorotrifluorotoluene (mFTFT); trifluoromethoxybenzene (TFOMB).

[0030] Test 1: Determination of ionic conductivity of electrolyte at different temperatures

[0031] The electrolytes from Comparative Example 1 and Examples 1, 5-10 were each packaged in a centrifuge tube, and conductivity electrodes were placed in the tube. The tube was then placed in a thermostat to maintain a constant temperature. After maintaining the temperature for 1 hour at each temperature point, the ionic conductivity of the electrolytes was measured. The test results are shown in Table 2.

[0032] Table 2 Ionic conductivity of comparative examples and some examples

[0033]

[0034] Test 2: Low-temperature charge and discharge capacity retention rate determination

[0035] A full-cell Si-C||NCM622 was assembled using a silicon-carbon negative electrode and a nickel-cobalt-manganese ternary positive electrode NCM622 as the battery cell using Comparative Example 1 and Examples 1-10. After five formation cycles at 30°C, the battery was transferred to a -30°C environment. The full-cell was charged and discharged in the voltage range of 2.5-4.6V, using a constant current and constant voltage method for charging and a constant current method for discharging. The charge rate was 0.1C, and the discharge rate was cut off when the time reached 10h or the current was less than 0.05C. The low-temperature capacity retention rate was calculated by dividing the first discharge specific capacity at low temperature by the formation discharge specific capacity at 30°C.

[0036] Table 3 Low temperature capacity retention rate of comparative examples and examples at -30°C

[0037] Capacity retention rate at -30℃, 0.1C Comparative Example 1 29.3％ Example 1 79.0％ Example 2 77.5％ Example 3 79.6％ Example 4 80.5％ Example 5 80.8％ Example 6 81.1％ Example 8 81.5％ Example 9 80.4 Example 10 79.6％

[0038] Test 3: Cyclic stability determination

[0039] The cycling stability of the batteries composed of Examples 8-10 at room temperature was verified in Si-C||NCM622 full cells. The full cells were cycled in the voltage range of 2.5-4.6V and the cycle rate was 0.3C. The experimental results are shown in Figure 2. Figure 1 shown.

[0040] Test 4: Fast charging performance measurement

[0041] The fast charging performance of Example 8 was verified in Si-C||NCM811 batteries. The full battery was charged using a constant current and constant voltage method within the voltage range of 2.5-4.3V and discharged using a constant current method. Charging was performed at a corresponding rate, and the discharge rate was terminated when the time reached the corresponding cut-off time or the current was less than 0.05C. The experimental results are shown in Figure 1. Figure 2 shown.

[0042] Test 5: Determination of battery operating temperature limit range

[0043] The low temperature limit range that the battery composed of Example 8 can adapt to was verified in a Si-C||NCM622 full cell. The full cell was charged and discharged in the range of 30℃ to -60℃, and the low temperature capacity retention rate was calculated by dividing the initial discharge capacity at low temperature by the formation discharge capacity at 30℃. The experimental results are shown in Figure 2. Figure 3 .

[0044] As can be seen from Table 2, the electrolyte of the present invention can exhibit high ionic conductivity in a wide temperature range, ensuring the rapid conduction of lithium ions. The low-temperature capacity retention rate test shows the significant advantages of the electrolyte of the present invention in improving the capacity of the battery at low temperatures. Compared with the comparative example 1 which has only 29.3% capacity at -30°C, the electrolyte of the present invention can retain the capacity of the battery at around 80%. Furthermore, taking Example 8 as an example, the operating temperature limit of the electrolyte was tested, and the results showed that it can enable the battery to have the ability to charge and discharge in the range as low as -60°C ( Figure 3 At the same time, the fast charging performance of the electrolyte was verified in Ah-level soft-pack batteries. Under 6C fast charging (10 minutes charging time), the battery can exert 76.1% of its capacity ( Figure 2 The above test results collectively demonstrate the multifunctional advantages of the electrolyte in the present invention in terms of high voltage, fast charging and low temperature performance.

[0045] It will be understood that the terms (including technical and scientific terms) used in the present invention have the same meanings as those generally understood by those skilled in the art.

[0046] The specific embodiments described above are only some of the specific embodiments of the present invention, and are only used to further explain the technical solutions and effects of the present invention in detail, and are not intended to limit the present invention. Any changes and substitutions that can be easily conceived by those skilled in the art within the spirit and technical scope of the present invention should be included in the scope of protection of the present invention.

Claims

1. A multifunctional lithium-ion battery electrolyte that combines high voltage, fast charging and low temperature performance, characterized in that: The invention is composed of a lithium salt, an organic solvent, a diluent and an additive; the molar ratio of the lithium salt to the organic solvent is 1:(4-6), the molar ratio of the lithium salt to the diluent is 1:(0-4), and the molar ratio of the lithium salt to the additive is 1:(0-0.5).

2. The multifunctional lithium-ion battery electrolyte having high voltage, fast charge and low temperature performance as claimed in claim 1, characterized in that: The lithium salt is one or a combination of two or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate and lithium difluorophosphate.

3. The multifunctional lithium-ion battery electrolyte having high voltage, fast charge and low temperature performance as claimed in claim 1, characterized in that: The organic solvent is one or a combination of two or more of methyl acetate, ethyl acetate, methyl propionate, methyl fluoroacetate, ethyl fluoroacetate, methyl fluoropropionate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluorodimethyl carbonate, fluorodiethyl carbonate and fluoromethyl ethyl carbonate.

4. The multifunctional lithium-ion battery electrolyte having high voltage, fast charge and low temperature performance as claimed in claim 1, characterized in that: The diluent is one or a combination of two or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, 2,2,2-trifluoroethyl-1,1,2,2-tetrafluoroethyl ether, 3-fluorotoluene, 1,2-difluorobenzene, 3-fluorotrifluorotoluene and trifluoromethoxybenzene.

5. The multifunctional lithium-ion battery electrolyte having high voltage, fast charge and low temperature performance as claimed in claim 1, characterized in that: The additive is one or a combination of two or more of fluoroethylene carbonate, lithium difluorooxalophosphate, lithium difluorophosphate and lithium hexafluorophosphate.

6. The multifunctional lithium-ion battery electrolyte having high voltage, fast charge and low temperature performance as claimed in claim 1, characterized in that: The molar ratio of the lithium salt to the organic solvent is 1:

5.

7. The multifunctional lithium-ion battery electrolyte having high voltage, fast charge and low temperature performance as claimed in claim 1, characterized in that: The molar ratio of the lithium salt to the diluent is 1:

3.

8. The multifunctional lithium-ion battery electrolyte having high voltage, fast charge and low temperature performance as claimed in claim 1, characterized in that: The molar ratio of the lithium salt to the additive is 1:(0.05-0.5).

9. A lithium-ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and the multifunctional lithium-ion battery electrolyte having high voltage, fast charging and low temperature performance as described in any one of claims 1 to 8.

10. A lithium-ion battery according to claim 9, characterized in that: The positive electrode is a nickel-cobalt-manganese ternary positive electrode, and the negative electrode is a silicon-carbon negative electrode.

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