A high-pressure-resistant fireproof electrolyte, a preparation method and application thereof, and a lithium ion battery

Abstract

The application belongs to the technical field of lithium batteries, and particularly relates to a high-pressure-resistant fireproof electrolyte, a preparation method and application thereof, and a lithium ion battery. The application provides a high-pressure-resistant fireproof electrolyte, which comprises a lithium salt, a fluorinated cyano-based organic solvent and an electrolyte additive; the fluorinated cyano-based organic solvent has the following structure; wherein R1 and R2 independently comprise C1-C5 fluoroalkyl. The electrolyte has high oxidation stability and fireproof property, can form a lithium-rich solid electrolyte interface layer (SEI) at the negative electrode of the lithium ion battery, inhibit dendrite growth, and improve the cycle stability of the high-pressure lithium metal battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a high-voltage fire-resistant electrolyte, its preparation method and application, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are widely used in various aspects of daily life, including portable electronic devices and electric vehicles, due to their advantages such as high operating voltage, high energy density, low self-discharge rate, no memory effect, long cycle life, and no pollution. Traditional carbonate or ether-based electrolytes, under high voltage (>4.5V vs. Li...),... + The lithium metal anode is prone to oxidation and decomposition under the influence of cyano groups, leading to capacity decay and the risk of thermal runaway. Although existing cyano-based organic solvents have a wide electrochemical window, they have poor compatibility with lithium metal anodes: the strong reducing properties of cyano groups lead to the formation of unstable SEI, and α-H atoms initiate harmful substitution reactions.

[0003] Currently, the liquid electrolytes used in commercial lithium-ion batteries generally use lithium hexafluorophosphate (LiPF6) as the conductive salt and a mixture of high-viscosity, high-dielectric-constant ethylene carbonate (EC) and propylene carbonate (PC) with low-viscosity, low-dielectric-constant dimethyl carbonate (DMC), diethyl carbonate (DEC), or methyl ethyl carbonate (EMC) as the solvent. Although this type of liquid electrolyte has been widely used, it has the following defects that hinder its application in high-voltage lithium-ion batteries: (1) LiPF6 has poor thermal and chemical stability, especially at low temperatures it is prone to crystallization or solidification, and its viscosity increases, which leads to a sharp decrease in conductivity and a rapid increase in the interfacial impedance between the electrolyte and the electrode, causing the battery to fail to work; (2) When the system voltage is higher than 4.5V, conventional carbonate-based electrolyte solvents such as EC will decompose, resulting in a decrease in battery performance. Summary of the Invention

[0004] The purpose of this invention is to provide a high-pressure resistant fire-retardant electrolyte, its preparation method and application, and a lithium-ion battery. The electrolyte provided by this invention has high thermal stability and high-pressure lithium stability. When applied to lithium-ion batteries, it can improve their cycle life and storage life.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a high-pressure resistant and fire-retardant electrolyte, comprising lithium salt, fluorinated cyanide organic solvent and electrolyte additives;

[0007] The fluorinated cyano-based organic solvent has the following structure:

[0008] ;

[0009] Among them, R1 and R2 independently include C1-C5 fluoroalkyl groups.

[0010] Preferably, R1 and R2 independently include , and At least one of them.

[0011] Preferably, the fluorinated cyano-based organic solvent includes , and At least one of them.

[0012] Preferably, the lithium salt includes at least one of lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalate)borate, and lithium difluorooxalateborate.

[0013] Preferably, the electrolyte additive includes at least one of carbonate compounds, propane sulfonate lactone, and vinyl sulfate;

[0014] The carbonate compounds include at least one of vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylethylene carbonate.

[0015] Preferably, by mass percentage, the high-voltage fireproof electrolyte comprises 13-28% lithium salt, 65-85% fluorinated cyano-based organic solvent, and 4-17% electrolyte additives.

[0016] This invention also provides a method for preparing the high-pressure resistant fire-retardant electrolyte described in the above technical solution, comprising the following steps:

[0017] In a protective atmosphere, lithium salt, fluorinated cyanide organic solvent and electrolyte additives are mixed to obtain the high-voltage fire-retardant electrolyte.

[0018] Preferably, the mixing includes: mixing a fluorinated cyano-based organic solvent and an electrolyte additive, then adding a lithium salt and stirring; the mixing temperature is 40~60℃; the mixing speed is 300~600rpm; and the mixing time is 12~36h.

[0019] The present invention also provides the application of the high-voltage fire-resistant electrolyte described in the above technical solution or the high-voltage fire-resistant electrolyte prepared by the preparation method described in the above technical solution in lithium-ion batteries.

[0020] The present invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the high-voltage fire-resistant electrolyte described in the above technical solution or the high-voltage fire-resistant electrolyte prepared by the preparation method described in the above technical solution.

[0021] This invention provides a high-pressure resistant and fire-retardant electrolyte, comprising a lithium salt, a fluorinated cyanide organic solvent, and an electrolyte additive; the fluorinated cyanide organic solvent has the following structure:

[0022] ;

[0023] Among them, R1 and R2 independently include C1-C5 fluoroalkyl groups.

[0024] Traditional carbonate or ether-based electrolytes at high voltages (>4.5V vs. Li) + Lithium metal batteries are prone to oxidative decomposition under certain conditions (e.g., under Li-), leading to capacity decay and the risk of thermal runaway. While existing cyano-based organic solvents have a wide electrochemical window, they have poor compatibility with lithium metal anodes: the strong reducing properties of cyano groups lead to the formation of an unstable SEI, and α-H atoms initiate harmful substitution reactions. The high-voltage, fire-resistant lithium-ion battery electrolyte provided by this invention exhibits high oxidation stability (>4.9V) and fire resistance at low salt concentrations. It can form a lithium-rich solid electrolyte interphase (SEI) layer at the lithium-ion battery anode, inhibiting dendrite growth and improving the cycle stability of high-voltage lithium metal batteries (e.g., NCM811 cathodes) (capacity retention >90% after 200 cycles). It is suitable for lithium-ion batteries above 5.0V. Attached Figure Description

[0025] Figure 1 The figure shows the electrochemical flotation experiment results of the battery corresponding to the electrolyte in Example 3;

[0026] Figure 2 The fire resistance test results are for Example 3, Example 5, Comparative Example 1, and EC-DMC commercial electrolyte, respectively.

[0027] Figure 3 The image shows the cycle stability of the NCM811-Li button cell corresponding to Example 3. Detailed Implementation

[0028] This invention provides a high-pressure resistant and fire-retardant electrolyte, comprising lithium salt, fluorinated cyanide organic solvent and electrolyte additives;

[0029] The fluorinated cyano-based organic solvent has the following structure;

[0030] ;

[0031] Among them, R1 and R2 independently include C1-C5 fluoroalkyl groups.

[0032] In this invention, the independent R1 and R2 preferably include , and At least one of them.

[0033] In this invention, the fluorinated cyano-based organic solvent preferably includes (2,2-bis(3,3,3-trifluoromethyl)malononitrile), (2,2-bis(3,3,3-trifluoroethyl)malononitrile) and At least one of (2,2-bis(3,3,3-trifluoropropyl)malononitrile).

[0034] In this invention, fluorinated cyano-based organic solvents can dissolve lithium salts, increase ion transport, and thus improve the energy density of the battery, making them applicable to high-voltage, fire-resistant lithium-ion batteries. Fluorination of cyano-based organic solvents can increase the number of territorial sites, improving fire resistance.

[0035] In this invention, the lithium salt preferably includes at least one of lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalate-borate), and lithium difluorooxalate-borate. In this invention, the lithium salt mainly functions to provide an electrochemically active lithium-ion source, provide ionic conductivity, participate in the formation of a solid electrolyte membrane, and influence the stability of the electrolyte. After dissolution and dissociation, it releases lithium ions, which serve as charge carriers in the redox process during charging and discharging. As the main ionic conductor of the electrolyte, its concentration and degree of dissociation determine its ionic conductivity, affecting rate performance. Its anions (such as PF6)... - TFSI - The decomposition products undergo irreversible electrochemical reduction / oxidation during the first charge / discharge process, participating in the construction of the negative electrode SEI film and the positive electrode CEI film, stabilizing the electrode / electrolyte interface, and suppressing continuous side reactions. Their thermal stability, electrochemical window, and compatibility with the solvent / electrode directly determine the battery's safety and cycle life.

[0036] In this invention, the electrolyte additive preferably includes at least one selected from carbonate compounds, propane sulfonate lactone, and vinyl sulfate; the carbonate compound preferably includes at least one selected from vinylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate, and vinyl ethylene carbonate. In this invention, the electrolyte additive is mainly used in electrode / electrolyte interface engineering. It preferentially undergoes reduction / oxidation decomposition before the solvent, forming a dense passivation layer. Furthermore, it can inhibit the continuous decomposition of the electrolyte, reduce irreversible capacity loss, thereby improving the lithium-ion interface migration rate and enhancing rate performance.

[0037] In this invention, the high-voltage fire-retardant electrolyte preferably comprises, by mass percentage, 13-28% lithium salt, specifically 13%, 16%, 19%, 22%, 25%, or 28%; 65-85% fluorinated cyano-based organic solvent, specifically 65%, 67%, 69%, 71%, 73%, 75%, 77%, 79%, 81%, 83%, or 85%; and 4-17% electrolyte additives, specifically 4%, 6%, 8%, 10%, 12%, 14%, 16%, or 17%.

[0038] This invention also provides a method for preparing the high-pressure resistant fire-retardant electrolyte described in the above technical solution, comprising the following steps:

[0039] In a protective atmosphere, lithium salt, fluorinated cyanide organic solvent and electrolyte additives are mixed to obtain the high-voltage fire-retardant electrolyte.

[0040] In this invention, the protective atmosphere preferably comprises high-purity argon. In this invention, the mixing is preferably carried out in a glove box filled with a protective atmosphere, wherein the total moisture and oxygen content in the glove box is preferably below 5 ppm. In this invention, the mixing preferably includes: mixing a fluorinated cyanide organic solvent and an electrolyte additive, then adding a lithium salt and stirring; the mixing temperature is preferably 40-60°C; the mixing speed is preferably 300-600 rpm; and the mixing time is preferably 12-36 hours.

[0041] The present invention also provides the application of the high-voltage fire-resistant electrolyte described in the above technical solution or the high-voltage fire-resistant electrolyte prepared by the preparation method described in the above technical solution in lithium-ion batteries.

[0042] The present invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the high-voltage fire-resistant electrolyte described in the above technical solution or the high-voltage fire-resistant electrolyte prepared by the preparation method described in the above technical solution.

[0043] In this invention, the positive electrode material preferably includes lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, or the ternary material NCM811; the negative electrode material preferably includes graphite, silicon carbide, or metallic lithium. This invention does not impose any particular limitation on the assembly method of the lithium-ion battery; any method well-known to those skilled in the art can be used.

[0044] In this invention, the voltage of the lithium-ion battery is preferably 5.0V or higher.

[0045] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0046] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0047] Examples and Comparative Examples

[0048] In a glove box filled with high-purity argon, the total content of moisture and oxygen in the glove box is controlled below 5 ppm. After mixing the fluorinated cyano-based organic solvent and electrolyte additives, lithium salt is slowly added and stirred at 380 rpm at 60°C until the mixture is uniform, and the specific components and their contents are shown in Tables 1 and 2.

[0049] Performance testing

[0050] Test Example 1

[0051] The performance of the electrolytes in the examples and comparative examples was tested, specifically including ionic conductivity, electrochemical stability window, and cycle performance.

[0052] The ionic conductivity was calculated using impedance (EIS), and the steel battery was tested using assembled steel, with the steel sheets serving as the positive and negative electrodes of the battery.

[0053] The electrochemical stability window was calculated using the linear voltammetric scan (LSV) method. The assembled steel sheet was used to test the lithium battery, with the steel sheet serving as the positive electrode and the lithium metal sheet serving as the negative electrode.

[0054] Cyclic performance was tested by charge-discharge cycles at a 0.5C rate, and the battery capacity retention was recorded after 100 cycles. The test used an assembled full cell, with ternary NCM811 as the positive electrode and lithium metal as the negative electrode. The ternary NCM811 material is composed of 80% active material, 10% conductive carbon, and 10% binder.

[0055] Table 1. Formulation of electrolyte for the examples

[0056]

[0057] Table 2. Formulations of comparative electrolytes

[0058]

[0059] Table 3 Cycle performance of batteries assembled with electrolytes corresponding to Example 3 and Comparative Example 1

[0060]

[0061] As can be seen from Tables 1-3 above, the fluorinated cyano-based organic solvents in the high-voltage fire-resistant electrolyte provided by the present invention have high electrochemical stability, can exist stably in the electrolyte within the charge and discharge voltage range, and have good compatibility with the positive electrode material and lithium metal, which can significantly improve the cycle performance of the battery and increase the battery cycle life and storage life.

[0062] Test Example 2

[0063] The button cell corresponding to the electrolyte in Example 3 of Test Example 1 was tested;

[0064] Figure 1 The electrochemical flotation experiment results of the full cell prepared with high-voltage fire-retardant electrolyte (refer to the full cell in Test Example 1); by Figure 1 It is known that this electrolyte has a high electrochemical stability window and lithium stability, and can be used in high-voltage fireproof lithium-ion batteries above 4.3V.

[0065] Test the fire-retardant properties of the electrolyte. Figure 2 From left to right: Example 3, Example 5, Comparative Example 1, and fire resistance test of EC-DMC commercial electrolyte; Figure 2 It is evident that the electrolyte provided by this invention has a certain fire-retardant effect, especially compared with commercial electrolytes, the effect is significantly improved.

[0066] Figure 3 The circuit stability diagram is shown for the NCM811-Li coin cell corresponding to Example 3; by Figure 3 It can be seen that the NCM811-Li coin cell configured with this electrolyte still has a capacity retention rate of 90.1% after 200 cycles at a rate of 0.5C, proving that it has good cycle stability.

[0067] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A high-pressure resistant fire-retardant electrolyte, characterized in that, It is composed of lithium salt, fluorinated cyano-based organic solvents, and electrolyte additives; The fluorinated cyano-based organic solvent has the following structure: ； R1 and R2 are independent. , and At least one of them; The electrolyte additive is at least one of carbonate compounds, propane sulfonate lactone, and vinyl sulfate; the carbonate compound is at least one of vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinyl ethylene carbonate. The high-voltage fire-retardant electrolyte comprises, by weight percentage, 13-28% lithium salt, 65-85% fluorinated cyano-based organic solvent, and 4-17% electrolyte additives.

2. The high-pressure resistant fire-retardant electrolyte according to claim 1, characterized in that, The fluorinated cyanide organic solvent is , and At least one of them.

3. The high-pressure resistant fire-retardant electrolyte according to claim 1, characterized in that, The lithium salt includes at least one of lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalate)borate, and lithium difluorooxalateborate.

4. The method for preparing the high-pressure resistant fire-retardant electrolyte according to any one of claims 1 to 3, characterized in that, Includes the following steps: In a protective atmosphere, lithium salt, fluorinated cyanide organic solvent and electrolyte additives are mixed to obtain the high-voltage fire-retardant electrolyte.

5. The preparation method according to claim 4, characterized in that, The mixing process includes: mixing a fluorinated cyano-based organic solvent and an electrolyte additive, then adding a lithium salt and stirring; the mixing temperature is 40~60℃; the mixing speed is 300~600rpm; and the mixing time is 12~36h.

6. The application of the high-voltage fire-resistant electrolyte according to any one of claims 1 to 3 or the high-voltage fire-resistant electrolyte prepared by the preparation method according to claim 4 or 5 in lithium-ion batteries.

7. A lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The electrolyte is the high-pressure resistant fireproof electrolyte according to any one of claims 1 to 3 or the high-pressure resistant fireproof electrolyte prepared by the preparation method according to claim 4 or 5.

Images