Electrolyte additive, electrolyte containing electrolyte additive and lithium ion secondary battery

Abstract

The invention discloses an electrolyte additive, an electrolyte containing the electrolyte additive and a lithium ion secondary battery. The electrolyte additive comprises a substance shown as a formula (1), in the formula (1), R1 is hydrogen, substituted or unsubstituted phenyl, halogen, alkoxy or cyano; x is a sulfonyl group, a sulfoxide group or a carbonyl group; and R2 is hydrogen, halogen substituted or unsubstituted C1-6 alkyl, silyl or alkoxy. By using the electrolyte additive disclosed by the invention, the cycle performance of the battery is obviously improved, and the impedance and gas production of the battery are obviously reduced. # imgabs0 #

Description

Technical Field

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

[0002] As various electronic devices such as mobile phones have become widely used, there is a strong demand for miniaturization, weight reduction, and longer life of these electronic devices. Therefore, development of small, lightweight, and high-energy-density secondary batteries as power sources is underway.

[0003] Secondary batteries are not limited to electronic devices, but are also being studied for other uses, such as battery packs that can be detachably mounted on electronic devices, electric vehicles such as electric cars, power storage systems such as home power servers, and electric tools such as electric drills.

[0004] Compared with traditional lead-acid batteries and zinc-manganese batteries, lithium-ion batteries have the advantages of long service life, high output voltage, high energy density, low self-discharge, low environmental pollution and no memory effect. Nowadays, they have been widely used in portable electronic devices, electric vehicles, power tools and other fields. As one of the important components of lithium-ion batteries, the composition of electrolyte has an important influence on the overall performance of the battery.

[0005] Therefore, various studies have been conducted in the art on the composition of the electrolyte. For example, CN110945705A discloses a five-membered ring structure However, since the five-membered ring structure contains more fluorine atoms, it will decompose during the battery charging and discharging process to form excessive inorganic lithium salts such as LiF, resulting in increased battery impedance. In addition, compounds with more fluorine substitution have lower boiling points and are more volatile. Summary of the invention

[0006] The main purpose of the present invention is to provide an electrolyte additive, an electrolyte containing the same and a lithium ion secondary battery, so as to solve the problems of poor battery cycle performance, high battery impedance and high battery gas production in the prior art.

[0007] In order to achieve the above object, according to one aspect of the present invention, there is provided an electrolyte additive, the additive comprising a substance represented by the following formula (1):

[0008]

[0009] Among them, R 1 is hydrogen, substituted or unsubstituted phenyl, halogen, alkoxy or cyano;

[0010] X is a sulfone group, a sulfoxide group or a carbonyl group;

[0011] R2 is hydrogen, halogen substituted or unsubstituted C 1-6 Alkyl, silyl or alkoxy.

[0012] Furthermore, in the above electrolyte additive, R 1 is a substituted or unsubstituted phenyl group; R 2 is halogen substituted or unsubstituted C 1-6 Alkyl or alkoxy.

[0013] Furthermore, in the above electrolyte additive, R 1 is halogen substituted or C 1-3 Alkyl substituted phenyl.

[0014] Furthermore, in the above electrolyte additive, R 1 Select any one of the following:

[0015]

[0016] Furthermore, in the above electrolyte additive, the substance of formula (1) is selected from any one of the following items:

[0017]

[0018] According to another aspect of the present invention, an electrolyte is provided, comprising an organic solvent, a lithium salt and the electrolyte additive described in the present invention.

[0019] Further, in the above electrolyte, the amount of the additive is in the range of 0.1 parts by weight to 3.0 parts by weight based on 100 parts by weight of the organic solvent and the lithium salt.

[0020] Furthermore, in the above electrolyte, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dihexyl carbonate, ethyl methyl carbonate, methylpropyl carbonate and propyl propionate.

[0021] Furthermore, in the above electrolyte, the electrolyte also includes fluoroethylene carbonate.

[0022] According to another aspect of the present invention, a lithium-ion secondary battery is provided, comprising: a positive electrode, a negative electrode, a separator, and the electrolyte described in the present invention.

[0023] By using the electrolyte additive of the present invention, since the asymmetric difluorocyclopropene structure has high reaction activity during the cycle of battery charge and discharge, it is easier to decompose and form a stable solid electrolyte interface (SEI) film, which can protect the electrode material and prevent the electrolyte from directly contacting the electrode, and the asymmetric difluorocyclopropene structure can participate in the reaction at the positive and negative electrodes of the battery at the same time, and the generated SEI and positive electrode electrolyte interface (CEI) impedance are small, which significantly improves the battery cycle performance. In addition, the functional groups on both sides of the asymmetric difluorocyclopropene structure are different, compared with the compounds of symmetrical structures, the solubility of the electrolyte additive in non-aqueous electrolyte can be effectively improved. And the reaction product of the asymmetric difluorocyclopropene structure does not contain gas, so the gas production of the battery can be significantly reduced. DETAILED DESCRIPTION

[0024] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0025] As described in the background art, only five-membered unsaturated cyclic compounds are proposed as electrolyte additives in the prior art. However, since the five-membered unsaturated cyclic compound contains more fluorine atoms, it will decompose to form excessive inorganic lithium salts such as LiF during the battery charge and discharge process, resulting in increased battery impedance, and compounds with more fluorine substitution have lower boiling points and are volatile. Therefore, it is still necessary to develop an electrolyte additive that can overcome the problems in the prior art. In view of the problems in the prior art, according to a typical embodiment of the present invention, an electrolyte additive is provided, which comprises a substance represented by the following formula (1):

[0026]

[0027] Among them, R 1 is hydrogen, substituted or unsubstituted phenyl, halogen, alkoxy or cyano;

[0028] X is a sulfone group, a sulfoxide group or a carbonyl group;

[0029] R 2 is hydrogen, halogen substituted or unsubstituted C 1-6 Alkyl, silyl or alkoxy.

[0030] By using the electrolyte additive of the present invention, since the asymmetric difluorocyclopropene structure has high reaction activity during the cycle of battery charge and discharge, it is easier to decompose and form a stable solid electrolyte interface (SEI) film, which can protect the electrode material and prevent the electrolyte from directly contacting the electrode, and the asymmetric difluorocyclopropene structure can participate in the reaction at the positive and negative electrodes of the battery at the same time, and the generated SEI and positive electrode electrolyte interface (CEI) impedance are small, which significantly improves the battery cycle performance. In addition, the functional groups on both sides of the difluorocyclopropene structure are different, and compared with the compounds of symmetrical structures, the solubility of the electrolyte additive in the non-aqueous electrolyte can be effectively improved. And the reaction product of the asymmetric difluorocyclopropene structure does not contain gas, so the gas production of the battery can be significantly reduced.

[0031] The electrolyte additive of the present invention can provide fluoride ions after the ternary ring is opened to form lithium fluoride, and the double bond part can initiate polymerization at the same time, forming a protective film on the electrode surface, thereby improving the circulation. The addition of the X group adjusts the polymerization activity of the ternary ring opening and the double bond, and the polar electron-rich unit contained in the X group itself is easy to cooperate with the positively charged lithium ion, strengthens the coordination bond effect of the substituent part for the lithium ion, promotes the diffusion and transmission of the lithium ion, and improves the battery performance. In addition, the introduced X group can form a larger conjugated system with the double bond of difluorocyclopropene, increase structural stability, and can coordinately regulate the film-forming effect of the overall molecule in the battery, thereby improving the battery cycle, reducing the impedance and other performances.

[0032] definition

[0033] Alkoxy refers to a group formed by connecting an alkyl group to an oxygen atom (RO-), such as methoxy, ethoxy, propoxy, etc.

[0034] Phenyl is a hydrophobic aromatic functional group obtained from benzene (C6H6) with the molecular formula -C6H5.

[0035] Alkyl is the part of an alkane molecule that has one hydrogen atom removed. n H 2n+1 , n is an integer greater than or equal to 1, for example, n is an integer of 1-6, preferably n is an integer of 1-3, such as methyl, ethyl, propyl, etc.

[0036] Silane group is the part remaining after removing a hydrogen atom from the silane molecule, and its general formula is Si n H 2n+1 , n is an integer greater than or equal to 1, for example, n is an integer of 1-6, preferably n is an integer of 1-3, such as silyl, disilyl, etc.

[0037] Preferred R 1

[0038] R1 Preferably, R is hydrogen, substituted or unsubstituted phenyl, halogen (eg, F, Cl, Br or I), alkoxy or cyano (-CN). 1 Preferably, it is hydrogen, substituted or unsubstituted phenyl, halogen (such as F, Cl, Br or I), C 1-6 More preferably, R 1 is halogen substituted or C 1-3 Most preferably, R 1 is fluorine substituted or C 1-3 Phenyl substituted with alkyl (eg, methyl, ethyl, propyl), wherein the substituents on the benzene ring can be located at the ortho, meta, para, or a combination thereof of difluorocyclopropene, and the number of the substituents can be 1-5, such as 1, 2, or 3.

[0039] Preferred R 2

[0040] R 2 Preferably, C 1-6 More preferably, R 2 C is halogen substituted or unsubstituted 1-6 Alkyl or C 1-6 Most preferably, R 2 C is halogen substituted or unsubstituted 1-3 Alkyl or C 1-3 Alkoxy (e.g., methoxy, ethoxy, propoxy), wherein the number of substituents may be 1-3. 2 It may be methoxy or trifluoromethyl.

[0041] Preferably, in formula (1), R 1 is a substituted or unsubstituted phenyl group; R 2 is halogen substituted or unsubstituted C 1-6 By using a substance represented by formula (1) that satisfies this condition, the battery impedance can be further reduced and the battery gas generation can be significantly reduced.

[0042] Preferably, in formula (1), R 1 is halogen substituted or C 1-3 Most preferably, R 1 is fluorine substituted or C 1-3 Phenyl substituted with an alkyl group (e.g., methyl, ethyl, propyl). By using a substance represented by formula (1) that satisfies this condition, the battery impedance can be further reduced and the battery gas generation can be significantly reduced. Preferably, R 1 is fluorine substituted or C 1-3 Phenyl substituted with an alkyl group (eg, methyl, ethyl, propyl).

[0043] Preferably, in formula (1), R 1 Select any one of the following:

[0044]

[0045] By using a substance represented by formula (1) that satisfies this condition, the battery impedance can be further reduced and the battery gas generation can be significantly reduced.

[0046] Preferably, the substance of formula (1) is selected from any one of the following:

[0047] By using a substance represented by formula (1) that satisfies this condition, the battery impedance can be further reduced and the battery gas generation can be significantly reduced.

[0048] According to another aspect of the present invention, an electrolyte is provided, comprising an organic solvent, a lithium salt and the electrolyte additive described in the present invention.

[0049] By using the electrolyte additive of the present invention in the electrolyte, since the asymmetric difluorocyclopropene structure has high reaction activity during the battery charge and discharge cycle, it is easier to decompose and form a stable solid electrolyte interface (SEI) film, which can protect the electrode material and prevent the electrolyte from directly contacting the electrode, and the asymmetric difluorocyclopropene structure can participate in the reaction at the positive and negative electrodes of the battery at the same time, and the generated SEI and positive electrode electrolyte interface (CEI) impedance are small, which significantly improves the battery cycle performance. In addition, the functional groups on both sides of the difluorocyclopropene structure are different, and compared with the compounds of the symmetrical structure, the solubility of the electrolyte additive in the non-aqueous electrolyte can be effectively improved. In addition, the reaction product of the asymmetric difluorocyclopropene structure does not contain gas, so the gas production of the battery can be significantly reduced.

[0050] Preferably, in the above electrolyte, based on 100 parts by weight of the organic solvent and the lithium salt, the amount of the additive is in the range of 0.1 parts by weight to 3.0 parts by weight, preferably, the amount of the additive is in the range of 0.5 parts by weight to 2.0 parts by weight. Within this range, the electrolyte additive can be well dissolved in the organic solvent, thereby further reducing the battery impedance and significantly reducing the battery gas generation.

[0051] Specifically, in the above electrolyte, based on 100 parts by weight of the organic solvent and the lithium salt, the amount of the electrolyte additive can be 0.1 parts by weight, 0.5 parts by weight, 1.0 parts by weight, 1.1 parts by weight, 1.5 parts by weight, 2.0 parts by weight, 2.1 parts by weight, 2.5 parts by weight, or 3.0 parts by weight.

[0052] In addition to the electrolyte additive of the present invention, the electrolyte may further include other electrolyte additives. For example, the electrolyte may further include fluoroethylene carbonate (FEC), and the amount of fluoroethylene carbonate (FEC) may be in the range of 0.1 to 3.0 parts by weight based on 100 parts by weight of the organic solvent and the lithium salt.

[0053] Preferably, in the above-mentioned electrolyte, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dihexyl carbonate, ethyl methyl carbonate, methylpropyl carbonate and propyl propionate. The above is only an example of the organic solvent used in the present invention, but is not limited to this. Those skilled in the art can select suitable organic solvent according to actual needs.

[0054] The present invention does not impose any limitation on lithium salts, and any lithium salt commonly used in the art can be used in the present invention.

[0055] According to another aspect of the present invention, a lithium ion secondary battery is provided, comprising: a positive electrode, a negative electrode, a separator, and an electrolyte described in the present invention. The present invention does not impose any restrictions on the positive electrode, the negative electrode, and the separator, and the positive electrode, the negative electrode, and the separator commonly used in the art can be used in the present invention.

[0056] By using the electrolyte additive of the present invention in a lithium ion secondary battery, since the asymmetric difluorocyclopropene structure has high reaction activity during the battery charge and discharge cycle, it is easier to decompose and form a stable solid electrolyte interface (SEI) film, which can protect the electrode material and prevent the electrolyte from directly contacting the electrode, and the asymmetric difluorocyclopropene structure can participate in the reaction at the positive and negative electrodes of the battery at the same time, and the generated SEI and positive electrode electrolyte interface (CEI) impedance are small, which significantly improves the battery cycle performance. In addition, the functional groups on both sides of the difluorocyclopropene structure are different, and compared with the compounds of the symmetrical structure, the solubility of the electrolyte additive in the non-aqueous electrolyte can be effectively improved. And the reaction product of the asymmetric difluorocyclopropene structure does not contain gas, so the gas production of the battery can be significantly reduced.

[0057] Example

[0058] Preparation of positive electrode

[0059] The positive electrode active material is lithium nickel cobalt aluminum oxide NCA (specifically LiNi 0.8 Co 0.15 Al 0.05O2) (95.50g), conductive carbon black (2.50g), binder polyvinylidene fluoride (1.90g) and dispersant polyvinyl pyrrolidone (0.10g) were mixed to obtain a positive electrode mixture, and the positive electrode mixture was dispersed in N-methylpyrrolidone to obtain a positive electrode mixture slurry. Then, the positive electrode mixture slurry was uniformly coated on a positive electrode collector made of aluminum foil, which was dried and stamped to form a positive electrode sheet.

[0060] Preparation of negative electrode

[0061] A mixture of silicon oxide and graphite powder (95.85 g, where the weight ratio of silicon oxide to graphite is 9:1) of negative electrode active material, conductive carbon black (1.00 g), binder carboxymethyl cellulose and styrene butadiene latex (3.15 g) and an appropriate amount of water were stirred to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was then uniformly coated on a negative electrode collector made of copper foil, dried and stamped to form a negative electrode sheet.

[0062] Preparation of basic electrolyte

[0063] Ethylene carbonate (20.00 g), dimethyl carbonate (62.00 g), and lithium hexafluorophosphate (18.00 g) were mixed to prepare a basic electrolyte.

[0064] Preparation of the electrolyte of Example 1

[0065] Add 0.1 g of electrolyte additive C-0 to the basic electrolyte, mix well and set aside.

[0066] Preparation of the electrolyte of Example 2-5

[0067] The preparation of the electrolytes of Examples 2-5 is the same as that of Example 1, except that the amount of the electrolyte additive C-0 in Example 1 is changed to 0.5 g, 1.0 g, 2.0 g, and 3.0 g, respectively.

[0068] Preparation of the electrolyte of Example 6

[0069] The preparation of the electrolyte of Example 6 is the same as that of Example 1, except that the electrolyte additive C-0 in Example 1 is changed to C-1.

[0070] Preparation of the electrolyte of Examples 7-10

[0071] The preparation of the electrolytes of Examples 7 to 10 is the same as that of Example 6, except that the amount of the electrolyte additive C-1 in Example 6 is changed to 0.5 g, 1.0 g, 2.0 g, and 3.0 g, respectively.

[0072] Preparation of the electrolyte of Example 11

[0073] The preparation of the electrolyte of Example 11 differs from that of the electrolyte of Example 3 only in that 3.0 g of FEC is further added.

[0074] Preparation of the electrolyte of Example 12

[0075] The preparation of the electrolyte of Example 12 differs from that of the electrolyte of Example 8 only in that 3.0 g of FEC is further added.

[0076] Preparation of the electrolyte of Comparative Example 1

[0077] The preparation of the electrolyte of Comparative Example 1 is the same as that of the basic electrolyte.

[0078] Preparation of the electrolyte of Comparative Example 2

[0079] The preparation of the electrolyte of Comparative Example 2 is the same as that of the electrolytes of Examples 2 and 7, except that the electrolyte additive of the present invention is replaced by FEC.

[0080] Preparation of the electrolyte of Comparative Example 3

[0081] The preparation of the electrolyte of Comparative Example 3 is the same as that of the electrolytes of Examples 3 and 8, except that the electrolyte additive of the present invention is replaced by FEC.

[0082] Preparation of the electrolyte of Comparative Example 4

[0083] The preparation of the electrolyte of Comparative Example 4 is the same as that of the electrolytes of Examples 5 and 10, except that the electrolyte additive of the present invention is replaced by FEC.

[0084] Battery Assembly

[0085] Assemble CR2016 button cells in a dry laboratory. Use the positive electrode sheet obtained in the above steps as the positive electrode, the negative electrode sheet as the negative electrode, and the electrolyte prepared in the embodiment and the comparative example as the electrolyte. Assemble the positive electrode, the negative electrode, the separator and the battery shell of the button cell and inject the electrolyte. After the battery is assembled, let it stand for 12 hours to age, thereby obtaining an NCA button cell.

[0086] Battery performance test

[0087] 1. Use a charge and discharge instrument to test the battery's cycle performance and impedance.

[0088] The batteries in the embodiments and comparative examples were first subjected to a 0.1C charge and discharge cycle test at 23°C once, and the first discharge capacity (discharge capacity of the first cycle) was measured. Then, a cycle test of 0.5C charge and 5C discharge was performed 100 times at 60°C, and the discharge capacity of the 100th cycle was measured. Based on the following formula: Capacity retention rate after 100 cycles [%] = (discharge capacity of the 100th cycle / discharge capacity of the 1st cycle) × 100%, the capacity retention rate after 100 cycles (%) was calculated using the discharge capacity of the 1st cycle and the discharge capacity of the 100th cycle. Finally, a charge test at a rate of 0.5C was performed once at 60°C to determine the impedance value of the battery.

[0089] 2. Gas production test

[0090] After completing a 0.1C charge-discharge cycle test at 23°C, the volume of each battery was recorded through water as the initial volume; after performing a 0.5C charge and 5C discharge cycle test at 60°C for 100 times, the volume of each battery was recorded through water again as the final volume. The difference between the two volumes is the amount of gas generated by the battery.

[0091] The performance test results of the batteries of Examples 1-12 and Comparative Examples 1-4 are shown in Table 1 below.

[0092] Table 1

[0093]

[0094]

[0095] Note: The additive content is the weight percentage based on the total weight of the basic electrolyte.

[0096] As can be seen from Table 1, compared with Comparative Example 1 without adding the electrolyte additive, Examples 1-10 containing the electrolyte additive of the present invention significantly improved the cycle performance of the battery, while significantly reducing the battery impedance and gas production; compared with Comparative Examples 2-4 adding the electrolyte additive FEC, Examples 1-10 containing the electrolyte additive of the present invention maintained or improved the cycle performance of the battery, while significantly reducing the battery impedance and gas production.

[0097] In addition, it can be seen from Table 1 that, compared with Comparative Example 4 containing the same content of FEC, Examples 11-12 comprising the combination of the electrolyte additive of the present invention and FEC significantly improved the cycle performance of the battery, while significantly reducing the battery impedance and gas production.

[0098] Moreover, compared with Example 1, Example 8 shows that additive C-1 can significantly improve the cycle performance of the battery and reduce the battery impedance. This is because the structure of C-1 contains sulfone groups, and the sulfur and oxygen in the sulfone groups have high electronegativity and can react with Li + The SEI film formed by coordination is an organic lithium compound, which can promote the transmission of lithium ions.

[0099] By comparing the embodiments of the present invention with the comparative examples, it can be seen from the above experimental results that the above embodiments of the present invention achieve the following technical effects:

[0100] By using the electrolyte additive of the present invention in a lithium ion secondary battery, since the asymmetric difluorocyclopropene structure has high reaction activity during the battery charge and discharge cycle, it is easier to decompose and form a stable solid electrolyte interface (SEI) film, which can protect the electrode material and prevent the electrolyte from directly contacting the electrode, and the asymmetric difluorocyclopropene structure can participate in the reaction at the positive and negative electrodes of the battery at the same time, and the generated SEI and positive electrode electrolyte interface (CEI) impedance are small, which significantly improves the battery cycle performance. In addition, the functional groups on both sides of the difluorocyclopropene structure are different, and compared with the compounds of the symmetrical structure, the solubility of the electrolyte additive in the non-aqueous electrolyte can be effectively improved. And the reaction product of the asymmetric difluorocyclopropene structure does not contain gas, so the gas production of the battery can be significantly reduced.

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An electrolyte additive, characterized in that: The additive comprises a substance represented by the following formula (1): Among them, R 1 is hydrogen, substituted or unsubstituted phenyl, halogen, alkoxy or cyano; X is a sulfone group, a sulfoxide group or a carbonyl group; R 2 is hydrogen, halogen substituted or unsubstituted C 1-6 Alkyl, silyl or alkoxy.

2. The electrolyte additive according to claim 1, characterized in that: R 1 is a substituted or unsubstituted phenyl group; R 2 is halogen substituted or unsubstituted C 1-6 Alkyl or alkoxy.

3. The electrolyte additive according to claim 1 or 2, characterized in that: R 1 is halogen substituted or C 1-3 Alkyl substituted phenyl.

4. The electrolyte additive according to claim 1 or 2, characterized in that: R 1 Select any one of the following:

5. The electrolyte additive according to claim 1 or 2, characterized in that: The substance of formula (1) is selected from any one of the following: 6 . An electrolyte comprising an organic solvent, a lithium salt and the electrolyte additive according to any one of claims 1 to 5.

7. The electrolyte according to claim 6, characterized in that The amount of the additive is in the range of 0.1 parts by weight to 3.0 parts by weight based on 100 parts by weight of the organic solvent and the lithium salt.

8. The electrolyte according to claim 6 or 7, characterized in that The organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dihexyl carbonate, ethyl methyl carbonate, methylpropyl carbonate and propyl propionate.

9. The electrolyte according to claim 6 or 7, characterized in that The electrolyte further comprises fluoroethylene carbonate.

10. A lithium ion secondary battery, characterized in that: include: positive electrode, negative electrode, Diaphragm, and The electrolyte according to any one of claims 6 to 9.

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