Electrolyte and Lithium-ion Batteries

Abstract

The present invention relates to an electrolyte and a lithium-ion battery. The above-mentioned electrolyte comprises a solvent, a conductive lithium salt and an additive, and the additive has the following general formula: #imgabs0# wherein, R1 is selected from one of alkenyl, aldehyde group, haloalkyl, sulfonyl group and cyano group, and R2 is selected from one of fluorine element and C1-C 10 fluorinated alkyl. In the above-mentioned electrolyte, the oxidation potential of the additive is lower than that of the solvent, and a stable and uniform interfacial film can be formed on the surface of the positive electrode material during the first charge and discharge process, inhibiting the further decomposition of the electrolyte and the positive electrode material, reducing the dissolution of transition metal cations in the positive electrode material, stabilizing the material structure, and improving the cycle performance and safety performance of the battery.

Description

Technical Field

[0001] The present invention relates to the field of lithium batteries, and in particular to an electrolyte and a lithium ion battery. Background Art

[0002] As the first commercially used lithium-ion battery cathode material, lithium cobalt oxide has a high compaction density (4.2g / cm 3 ), and increasing the charging cut-off voltage of lithium cobalt oxide can significantly improve its energy density. For example, the energy density of lithium cobalt oxide is 740Wh / kg when the charging cut-off voltage is 4.45V, and the energy density increases to 840Wh / kg when the charging cut-off voltage is 4.55V, which makes the volume energy density of lithium cobalt oxide better than other materials, and has advantages in the use of portable devices with high volume requirements. Therefore, lithium cobalt oxide positive electrode materials still occupy a high market share in the 3C electronic product market. In order to extend the working time and service life of electronic products after charging, and increase the utilization rate of raw material cobalt, it is imperative to increase the energy density of lithium cobalt oxide. As mentioned above, increasing the charging cut-off voltage can significantly increase the energy density of lithium cobalt oxide. However, while increasing the voltage of the positive electrode material, the charge and discharge cycle performance of the battery is declining. This is mainly due to the instability of the electrolyte under high voltage, which causes the battery performance to decline. Summary of the invention

[0003] Based on this, it is necessary to provide an electrolyte that has good stability at high voltage and can improve the cycle performance of the battery.

[0004] In addition, it is also necessary to provide a lithium ion battery containing the electrolyte.

[0005] An electrolyte comprises: a solvent, a conductive lithium salt and an additive, wherein the additive has the following general formula:

[0006]

[0007] Wherein, R1 is selected from one of alkenyl, aldehyde, halogenated alkyl, sulfonyl and cyano, and R2 is selected from fluorine and C1-C 10 One of the fluoroalkyl groups.

[0008] In one embodiment, R1 is selected from one of C2-C6 alkenyl, C1-C6 aldehyde, C1-C6 haloalkyl, sulfonyl chloride and C1-C6 cyano; and / or,

[0009] R2 is selected from the group consisting of fluorine and C1-C4 fluoroalkyl.

[0010] In one embodiment, the additive comprises at least one of the following compounds:

[0011]

[0012] In one of the embodiments, in the electrolyte, the mass percentage of the additive is 0.5% to 7%.

[0013] In one of the embodiments, in the electrolyte, the mass percentage of the additive is 1% to 5%.

[0014] In one embodiment, the solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, butyrolactone, valerolactone, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate and propyl propionate.

[0015] In one embodiment, the conductive lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethylsulfonate, lithium difluorooxalatoborate, lithium dioxalatoborate and lithium difluorooxalatoborate.

[0016] In one of the embodiments, in the electrolyte, the concentration of the conductive lithium salt is 0.5 mol / L to 1.5 mol / L.

[0017] A lithium ion battery comprises a positive electrode, a negative electrode, a separator and the above electrolyte.

[0018] In one embodiment, the material of the positive electrode includes lithium cobalt oxide; and / or,

[0019] The material of the negative electrode includes metallic lithium; and / or,

[0020] The diaphragm is selected from one of a polyethylene diaphragm and a polypropylene diaphragm.

[0021] The above-mentioned electrolyte includes a solvent, a conductive lithium salt and an additive. The oxidation potential of the additive is lower than that of the solvent. The additive can be oxidized on the surface of the positive electrode material during the first charge and discharge process to form a stable and uniform interface film, inhibiting further decomposition of the electrolyte and the positive electrode material, reducing the dissolution of transition metal cations in the positive electrode material, stabilizing the material structure, and thereby improving the cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A comparison chart of the test of applying the electrolytes of Example 4 and Comparative Examples 1, 2 and 3 to high-voltage (4.5V) lithium cobalt oxide batteries and performing 300 cycles at 1C at room temperature;

[0023] Figure 2 The discharge medium voltage diagram of the electrolytes of Example 4 and Comparative Examples 1, 2 and 3 are respectively applied to a high-voltage (4.5V) lithium cobalt oxide battery;

[0024] Figure 3 The electron microscope images are of the electrolytes of Example 4 and Comparative Example 1 before and after being applied to high-voltage (4.5V) lithium cobalt oxide batteries. DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively below in conjunction with the specific embodiments. Preferred embodiments of the present invention are provided in the specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0027] "Alkyl" refers to a saturated hydrocarbon containing primary (normal) carbon atoms, secondary carbon atoms, tertiary carbon atoms, quaternary carbon atoms, or a combination thereof. Phrases containing this term, such as "C1-C 10 "Alkyl" refers to an alkyl group containing 1 to 10 carbon atoms, and each occurrence can be independently C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, C9 alkyl or C 10 Alkyl. Suitable examples include, but are not limited to, methyl (Me, -CH3), ethyl (Et, -CH2CH3), 1-propyl (n-Pr, n-propyl, -CH2CH2CH3), 2-propyl (i-Pr, i-propyl, -CH(CH3)2), 1-butyl (n-Bu, n-butyl, -CH2CH2CH2CH3), 2-methyl-1-propyl (i-Bu, i-butyl, -CH2CH(CH3)2), 2-butyl (s-Bu, s-butyl, -CH(CH3)CH2CH3), etc. Others, "C1-C6 alkyl", "C1-C4 alkyl", etc. have similar meanings and are not repeated here.

[0028] "Alkenyl" refers to a group containing at least one unsaturated site, i.e., a carbon-carbon sp 2A hydrocarbon containing a positive carbon atom, a secondary carbon atom, a tertiary carbon atom or a ring carbon atom of a double bond. A phrase containing this term, for example, "C2-C6 alkenyl" refers to an alkenyl group containing 2 to 6 carbon atoms, and each occurrence can be independently C2 alkenyl, C3 alkenyl, C4 alkenyl, C5 alkenyl or C6 alkenyl. Suitable examples include, but are not limited to, vinyl (-CH=CH2), allyl (-CH2CH=CH2), cyclopentenyl (-C5H7) and 5-hexenyl (-CH2CH2CH2CH2CH=CH2), etc.

[0029] "Halogen" or "halo" refers to F, Cl, Br or I.

[0030] "Aldehyde" refers to -CHO, "sulfonyl" refers to -S(=O)2-, and "cyano" refers to -CN.

[0031] Increasing the charge cut-off voltage can significantly increase the energy density of lithium cobalt oxide. However, due to the instability of traditional electrolytes, the higher the voltage, the easier it is for the electrolyte to oxidize and decompose, and deposit on the surface of the positive electrode material. At the same time, the oxidation decomposition reaction of the electrolyte will also promote the destruction of the positive electrode material, thereby affecting the cycle stability of the battery. Therefore, in order to continue to increase the cut-off voltage to obtain a higher energy density, the present application provides a high-voltage resistant electrolyte, so that the positive electrode / electrolyte surface interface remains stable under high voltage, thereby improving the cycle stability of the battery.

[0032] Specifically, an electrolyte according to an embodiment includes: a solvent, a conductive lithium salt and an additive, wherein the additive has the following general formula: The electrolyte can be applied to 4.5V high voltage lithium cobalt oxide system.

[0033] Wherein, R1 is selected from one of alkenyl, aldehyde, halogenated alkyl, sulfonyl and cyano. R2 is selected from fluorine and C1-C 10 One of the fluoroalkyl groups.

[0034] Further, R1 is selected from one of C2-C6 alkenyl, C1-C6 aldehyde, C1-C6 haloalkyl, sulfonyl chloride and C1-C6 cyano. Further, R1 is selected from one of C2-C3 alkenyl, C1-C3 aldehyde, C1-C3 haloalkyl, sulfonyl chloride and C1-C3 cyano. In a specific example, R1 is selected from one of -CH-CH=CH2, -CHO, -CF3, -S(=O)2-Cl, -CN and -CH2-CN.

[0035] Furthermore, R2 is selected from one of fluorine and C1-C4 fluoroalkyl. Preferably, R2 is fluorine.

[0036] In some embodiments, the additive includes at least one of the following compounds:

[0037]

[0038] Specifically, in the electrolyte, the mass percentage of the additive is 0.5% to 7%. In a specific example, in the electrolyte, the mass percentage of the additive is 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7% or a range consisting of any two of these values. Preferably, in the electrolyte, the mass percentage of the additive is 1% to 5%.

[0039] In one specific example, the additive is In the electrolyte, the mass percentage of the additive is 5%.

[0040] In one specific example, the additive is In the electrolyte, the mass percentage of the additive is 1%.

[0041] The oxidation potential of the above-mentioned additive is lower than that of the solvent. It can oxidize on the surface of the positive electrode material during the first charge and discharge process to form a stable and uniform interface film, inhibit further decomposition of the electrolyte and the positive electrode material, reduce the dissolution of transition metal cations in the positive electrode material, stabilize the material structure, and improve the cycle performance and safety performance of the battery.

[0042] Specifically, the solvent is a non-aqueous organic solvent. Further, the solvent is selected from at least one of ethylene carbonate (EC), propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), butyrolactone, valerolactone, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate and propyl propionate.

[0043] In a specific example, the solvent is a mixture of ethyl methyl carbonate, diethyl carbonate and ethylene carbonate. For example, the solvent is a mixture of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate in a mass ratio of 3:2:5.

[0044] Specifically, the conductive lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(trifluoromethylsulfonyl)imide (Li(CF3SO2)2N), lithium trifluoromethylsulfonate (LiSO2CF3), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB) and lithium difluorooxalatoborate (LiDFOP). Optionally, in a specific example, the conductive lithium salt is lithium hexafluorophosphate.

[0045] Further, in the electrolyte, the concentration of the conductive lithium salt is 0.5 mol / L to 1.5 mol / L. For example, the concentration of the conductive lithium salt is 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, or a range consisting of any two of these values. Preferably, in the electrolyte, the concentration of the conductive lithium salt is 1 mol / L.

[0046] In one embodiment, the preparation process of the electrolyte includes: purifying the solvent with a molecular sieve, then adding a conductive lithium salt to completely dissolve the conductive lithium salt, and finally adding a certain amount of the above additives. It is understood that the preparation process of the electrolyte is not limited to this, for example, the solvent, the conductive lithium salt and the additive can also be added at the same time and mixed evenly.

[0047] The above electrolyte has at least the following advantages:

[0048] (1) The above-mentioned electrolyte includes a solvent, a conductive lithium salt and an additive. The oxidation potential of the additive is lower than that of the solvent. The additive can be oxidized on the surface of the positive electrode material during the first charge and discharge process to form a stable and uniform interface film, thereby inhibiting further decomposition of the electrolyte and the positive electrode material, reducing the dissolution of transition metal cations in the positive electrode material, stabilizing the material structure, and improving the cycle performance and safety performance of the battery.

[0049] (2) In the above electrolyte, the amount of additives added is very small, the overall cost of the obtained electrolyte is low, and it has good application prospects.

[0050] The present application also provides a lithium ion battery of an embodiment, comprising the above electrolyte. The lithium ion battery also comprises a positive electrode, a negative electrode and a separator. For example, the lithium ion battery is a lithium cobalt oxide battery.

[0051] Specifically, the material of the positive electrode includes lithium cobalt oxide.

[0052] The material of the negative electrode includes metallic lithium.

[0053] The diaphragm is selected from one of a polyethylene diaphragm and a polypropylene diaphragm.

[0054] It is understandable that the above lists only several common materials for the positive electrode, the negative electrode and the separator, but is not limited thereto, and other materials commonly used in the art may also be used.

[0055] The above lithium-ion battery has good cycle performance and interface stability under high voltage.

[0056] In order to make the purpose and advantages of the present invention clearer, the electrolyte of the present invention and its effects are further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and shall not be used to limit the present invention.

[0057] Example 1

[0058] The electrolyte of this embodiment includes: a solvent, a conductive lithium salt and an additive. The solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:5. The lithium salt is lithium hexafluorophosphate with a concentration of 1 mol / L, and the additive is The mass percentage of the additive in the electrolyte is 0.5%.

[0059] The preparation process of the lithium ion battery of this embodiment is as follows:

[0060] (1) Preparation of electrolyte: Cyclic carbonate solvent EC, linear carbonate solvent DEC and EMC were mixed at a mass ratio of EC:DEC:EMC=3:2:5, and purified using molecular sieves. Then, lithium hexafluorophosphate was added to make the concentration of lithium hexafluorophosphate 1 mol / L. After the lithium hexafluorophosphate was completely dissolved, 0.5% by mass of additives were added.

[0061] (2) Preparation of positive electrode sheet: Lithium cobalt oxide, polytetrafluoroethylene binder (PVDF) and conductive agent acetylene black were dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1 to obtain a slurry, which was then evenly coated on the current collector aluminum foil. First, it was dried in an oven at 80°C for 1 hour, then transferred to 120°C for vacuum drying for 12 hours, and then rolled three times using a roller press to cut it into a 12 mm diameter electrode sheet for use.

[0062] (3) Preparation of lithium-ion batteries: The prepared lithium cobalt oxide electrode was used as the positive electrode, lithium foil as the negative electrode, and Celgard 2500 as the separator. 2025-type button cells were assembled in a high-purity argon glove box, and about 60 μL of the above-mentioned electrolyte was injected into each battery.

[0063] Example 2

[0064] The electrolyte of this embodiment includes: a solvent, a conductive lithium salt and an additive. The solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:5. The lithium salt is lithium hexafluorophosphate with a concentration of 1 mol / L, and the additive is The mass percentage of the additive in the electrolyte is 1%.

[0065] The preparation process of the lithium ion battery of this embodiment is similar to that of Embodiment 1, except that the mass percentage of the additive in the electrolyte is different. In this embodiment, the mass percentage of the additive in the electrolyte is 1%.

[0066] Example 3

[0067] The electrolyte of this embodiment includes: a solvent, a conductive lithium salt and an additive. The solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:5. The lithium salt is lithium hexafluorophosphate with a concentration of 1 mol / L, and the additive is The mass percentage of the additive in the electrolyte is 3%.

[0068] The preparation process of the lithium ion battery of this embodiment is similar to that of Embodiment 1, except that the mass percentage of the additive in the electrolyte is different. In this embodiment, the mass percentage of the additive in the electrolyte is 3%.

[0069] Example 4

[0070] The electrolyte of this embodiment includes: a solvent, a conductive lithium salt and an additive. The solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:5. The lithium salt is lithium hexafluorophosphate with a concentration of 1 mol / L, and the additive is The mass percentage of the additive in the electrolyte is 5%.

[0071] The preparation process of the lithium ion battery of this embodiment is similar to that of Embodiment 1, except that the mass percentage of the additive in the electrolyte is different. In this embodiment, the mass percentage of the additive in the electrolyte is 5%.

[0072] Example 5

[0073] The electrolyte of this embodiment includes: a solvent, a conductive lithium salt and an additive. The solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:5. The lithium salt is lithium hexafluorophosphate with a concentration of 1 mol / L, and the additive is The mass percentage of the additive in the electrolyte is 7%.

[0074] The preparation process of the lithium ion battery of this embodiment is similar to that of Embodiment 1, except that the mass percentage of the additive in the electrolyte is different. In this embodiment, the mass percentage of the additive in the electrolyte is 7%.

[0075] Example 6

[0076] The electrolyte of this embodiment includes: a solvent, a conductive lithium salt and an additive. The solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:5. The lithium salt is lithium hexafluorophosphate with a concentration of 1 mol / L, and the additive is The mass percentage of the additive in the electrolyte is 1%.

[0077] The preparation process of the lithium ion battery of this embodiment is similar to that of embodiment 1, except that the type and mass percentage of the additive in the electrolyte are different. In this embodiment, the additive is The mass percentage of the additive in the electrolyte is 1%.

[0078] Example 7

[0079] The electrolyte of this embodiment includes: a solvent, a conductive lithium salt and an additive. The solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:5. The lithium salt is lithium hexafluorophosphate with a concentration of 1 mol / L, and the additive is The mass percentage of the additive in the electrolyte is 1%.

[0080] The preparation process of the lithium ion battery of this embodiment is similar to that of embodiment 1, except that the type and mass percentage of the additive in the electrolyte are different. In this embodiment, the additive is The mass percentage of the additive in the electrolyte is 1%.

[0081] Example 8

[0082] The electrolyte of this embodiment includes: a solvent, a conductive lithium salt and an additive. The solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:5. The lithium salt is lithium hexafluorophosphate with a concentration of 1 mol / L, and the additive is The mass percentage of the additive in the electrolyte is 1%.

[0083] The preparation process of the lithium ion battery of this embodiment is similar to that of embodiment 1, except that the type and mass percentage of the additive in the electrolyte are different. In this embodiment, the additive is The mass percentage of the additive in the electrolyte is 1%.

[0084] Example 9

[0085] The electrolyte of this embodiment includes: a solvent, a conductive lithium salt and an additive. The solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:5. The lithium salt is lithium hexafluorophosphate with a concentration of 1 mol / L, and the additive is The mass percentage of the additive in the electrolyte is 1%.

[0086] The preparation process of the lithium ion battery of this embodiment is similar to that of embodiment 1, except that the type and mass percentage of the additive in the electrolyte are different. In this embodiment, the additive is The mass percentage of the additive in the electrolyte is 1%.

[0087] Example 10

[0088] The electrolyte of this embodiment includes: a solvent, a conductive lithium salt and an additive. The solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:5. The lithium salt is lithium hexafluorophosphate with a concentration of 1 mol / L, and the additive is The mass percentage of the additive in the electrolyte is 1%.

[0089] The preparation process of the lithium ion battery of this embodiment is similar to that of embodiment 1, except that the type and mass percentage of the additive in the electrolyte are different. In this embodiment, the additive is The mass percentage of the additive in the electrolyte is 1%.

[0090] Comparative Example 1

[0091] The electrolyte of Comparative Example 1 includes: a solvent and a conductive lithium salt. The solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:5. The lithium salt is lithium hexafluorophosphate with a concentration of 1 mol / L.

[0092] The preparation process of the lithium ion battery of Comparative Example 1 is similar to that of Example 1, except that the electrolyte of Comparative Example 1 does not contain any additive.

[0093] Comparative Example 2

[0094] The electrolyte of Comparative Example 2 includes: a solvent, a conductive lithium salt and an additive. The solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:5. The lithium salt is lithium hexafluorophosphate with a concentration of 1 mol / L, and the additive is 2,6-difluorobenzonitrile, and the mass percentage of the additive in the electrolyte is 1%.

[0095] The preparation process of the lithium ion battery of Comparative Example 2 is similar to that of Example 2, except that the additive in the electrolyte is different. In Comparative Example 2, the additive is 2,6-difluorobenzonitrile.

[0096] Comparative Example 3

[0097] The electrolyte of Comparative Example 3 includes: a solvent, a conductive lithium salt and an additive. The solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:5. The lithium salt is lithium hexafluorophosphate with a concentration of 1 mol / L, and the additive is 2,6-difluorobenzonitrile, and the mass percentage of the additive in the electrolyte is 5%.

[0098] The preparation process of the lithium ion battery of Comparative Example 3 is similar to that of Example 4, except that the additive in the electrolyte is different. In Comparative Example 3, the additive is 2,6-difluorobenzonitrile.

[0099] The following is the test part:

[0100] The lithium cobalt oxide batteries prepared in the examples and comparative examples were left to stand for 8 hours, and then placed in a blue electric charge and discharge instrument to perform a long cycle test of 1C cycle 300 cycles in the voltage range of 3.0 to 4.5 V. The test results are as follows:

[0101] Figure 1 The electrolytes prepared in Example 4 and Comparative Examples 1, 2 and 3 are respectively applied to high-voltage (4.5V) lithium cobalt oxide batteries for 300 cycles at room temperature and 1C. Figure 1 It can be seen that the electrolyte of Example 4 contains additives The cobalt oxide lithium battery has a capacity retention rate of 82.8% after 300 cycles at 3.0-4.5V, while the electrolyte of Comparative Example 1 does not contain additives, and the cobalt oxide lithium battery has a capacity retention rate of only 36.4% after 300 cycles at 3.0-4.5V. Comparative Examples 2 and 3 respectively add 1% and 5% 2,6-difluorobenzonitrile to the electrolyte, and the battery capacity retention rates of the cobalt oxide lithium battery after 300 cycles at 3.0-4.5V are 67.2% and 55.6%, respectively, which are lower than those of Example 4. It can be seen that the electrolyte containing additives The electrolyte has higher high-voltage resistance. This is mainly because the additives oxidize and polymerize on the surface of the positive electrode to form a stable interface film, which inhibits a series of side reactions occurring on the electrode surface under high voltage, thereby improving the cycle performance of the high-voltage lithium cobalt oxide battery.

[0102] Figure 2 The electrolytes prepared in Example 4 and Comparative Examples 1, 2 and 3 are respectively applied to the discharge medium voltage curves of high-voltage (4.5V) lithium cobalt oxide batteries. Figure 2 It can be seen that the discharge medium voltage of the lithium cobalt oxide battery of Comparative Example 1 dropped sharply from 3.890V to 3.202V after 300 charge and discharge cycles. The discharge medium voltage of the lithium cobalt oxide battery of Comparative Example 2 also dropped from 3.960V to 3.781V, and the discharge medium voltage of the lithium cobalt oxide battery of Comparative Example 3 also dropped from 3.958V to 3.648V, while the discharge medium voltage of the lithium cobalt oxide battery of Example 4 was very stable, and after 300 charge and discharge cycles, the discharge medium voltage of the battery could still be as high as 3.858V. This shows that the lithium cobalt oxide / electrolyte interface of the lithium cobalt oxide battery of Example 4 remains stable after 300 cycles, while the interface impedance of the lithium cobalt oxide battery of Comparative Example 1 grows rapidly due to the large amount of decomposition of the electrolyte.

[0103] Figure 3 Electron microscope images of the electrolytes prepared in Example 4 and Comparative Example 1 respectively applied to high voltage (4.5V) lithium cobalt oxide batteries. Figure 3 As can be seen from the figure, (a), (d) and (g) show that the surface of the original lithium cobalt oxide particles is smooth and has no covering. (b), (e) and (h) are the lithium cobalt oxide batteries prepared in Example 4 after 300 charge and discharge cycles, and the particle surface is covered with decomposition products of uneven thickness. As shown in (c), (f) and (i) of the lithium cobalt oxide battery of Comparative Example 1, there is a regular and uniform SEI on the surface of the lithium cobalt oxide material, which also shows that the electrode / electrolyte interface stability prepared in Example 4 is better than that of Comparative Example 1.

[0104] The capacity retention rate of the lithium cobalt oxide batteries of other embodiments and comparative examples after 300 cycles at 3.0-4.5V and the discharge medium voltage data of the batteries after 300 charge and discharge cycles are shown in Table 1 below:

[0105] Table 1

[0106]

[0107]

[0108] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0109] The above-described embodiments only express several implementation methods of the present invention, which is convenient for understanding the technical solutions of the present invention in detail, but cannot be understood as limiting the scope of protection of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided by the present invention are all within the protection scope of the claims attached to the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the contents of the attached claims, and the description and drawings can be used to interpret the contents of the claims.

Claims

1. An electrolyte, characterized in that: include: A solvent, a conductive lithium salt and an additive, wherein the additive has the following general formula: , Wherein, R1 is selected from one of C1~C6 aldehyde groups and sulfonyl chloride, R2 is selected from fluorine element, and in the electrolyte, the mass percentage of the additive is 1%~3%.

2. The electrolyte according to claim 1, characterized in that R1 is selected from one of -CHO and -S(=O)2-Cl.

3. The electrolyte according to claim 1, characterized in that The solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, butyrolactone, valerolactone, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate and propyl propionate.

4. The electrolyte according to claim 3, characterized in that The oxidation potential of the additive is lower than the oxidation potential of the solvent.

5. The electrolyte according to claim 3, characterized in that The solvent is a mixture of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate in a mass ratio of 3:2:

5.

6. The electrolyte according to claim 1, characterized in that The conductive lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethylsulfonate, lithium difluorooxalatoborate, lithium dioxalatoborate and lithium difluorooxalatoborate.

7. The electrolyte according to claim 1 or 6, characterized in that In the electrolyte, the concentration of the conductive lithium salt is 0.5 mol / L to 1.5 mol / L.

8. A lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and the electrolyte according to any one of claims 1 to 7.

9. The lithium-ion battery according to claim 8, characterized in that: The material of the positive electrode includes lithium cobalt oxide.

10. The lithium ion battery according to claim 8, characterized in that The material of the negative electrode includes metallic lithium.

11. The lithium ion battery according to claim 8, characterized in that: The diaphragm is selected from one of a polyethylene diaphragm and a polypropylene diaphragm.

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