Electrolyte for improving self-discharge, supercapacitor and aging process

Abstract

The present disclosure provides an electrolyte for improving self-discharge, a supercapacitor and an aging process, and belongs to the technical field of supercapacitors. The electrolyte comprises a lithium salt, an organic solvent, a sulfur-containing additive, a carbonate additive and a functional additive. The general structure of the functional additive is as follows: wherein R1 is selected from any one of hydrogen, an amino group and C1-C3 alkyl; and R2 is selected from any one of a substituted or unsubstituted phenyl group and a pyridine. The present disclosure realizes the synchronous optimization of the self-discharge rate and consistency of the supercapacitor by optimizing the additive, and has high performance (low K value), low cost (low additive dosage) and high adaptability (flexible parameters), thereby effectively solving the problem of poor consistency of the supercapacitor after formation and distribution.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of supercapacitors, and particularly relates to an electrolyte for improving self-discharge, a supercapacitor and an aging process. BACKGROUND

[0002] Supercapacitors have inherent high self-discharge rate characteristics, and especially have the problem of inconsistent self-discharge when used in groups, which seriously restricts the reliability and service life of the energy storage system. Specifically, to meet the demand for high voltage and large current output, supercapacitors need to be connected in series and parallel to form a module. However, the inconsistency of internal resistance and self-discharge rate caused by process deviation between single units is significantly amplified in group work, causing internal distribution imbalance, increasing management costs and shortening the overall service life. The complex side reactions caused by the high specific surface area active material inside the supercapacitor worsen the self-discharge, leading to poor consistency of single supercapacitors, thereby increasing the cost of enterprises. Therefore, solving the problem of poor consistency of supercapacitors after formation and distribution is a difficult problem currently faced. SUMMARY

[0003] The present disclosure aims to at least solve one of the technical problems existing in the prior art, and provides an electrolyte for improving self-discharge, a supercapacitor and an aging process.

[0004] In one aspect of the present disclosure, an electrolyte for improving self-discharge is provided, which comprises:

[0005] a lithium salt;

[0006] an organic solvent;

[0007] a sulfur-containing additive;

[0008] a carbonate additive;

[0009] a functional additive, the structure of the functional additive being as follows:

[0010] ;

[0011] wherein R1 is selected from any one of hydrogen, amino and C1-C3 alkyl; and R2 is selected from any one of substituted or unsubstituted phenyl and pyridine.

[0012] Optionally, the functional additive is selected from any one of the following structures:

[0013] Formula I-1;

[0014] Formula I-2;

[0015] Formula I-3;

[0016] Formula I-4.

[0017] Optionally, the functional additive has a mass percentage of 0.3-1% in the electrolyte.

[0018] Optionally, the sulfur-containing additive includes at least one of 1,3-propylene sulfite, 1,3-propane sulfite and ethylene sulfate;

[0019] The sulfur-containing additive has a mass percentage of 0.5-2% in the electrolyte.

[0020] Optionally, the carbonate additive includes vinylene carbonate;

[0021] The carbonate additive has a mass percentage of 0.3-0.5% in the electrolyte.

[0022] Optionally, the lithium salt is lithium hexafluorophosphate;

[0023] The lithium salt has a mass percentage of 10%-12.5% in the electrolyte.

[0024] Optionally, the organic solvent includes a cyclic carbonate and a chain carbonate.

[0025] Optionally, the cyclic carbonate includes at least one of fluoroethylene carbonate, vinylene carbonate and propylene carbonate;

[0026] The chain carbonate includes at least one of diethyl carbonate and dimethyl carbonate.

[0027] Another aspect of the present disclosure provides a supercapacitor, which includes a positive electrode, a negative electrode, an electrolyte and a separator, wherein

[0028] The electrolyte is the electrolyte described above.

[0029] Another aspect of the present disclosure provides an aging process of the supercapacitor described above, which includes: placing the supercapacitor after the cell assembly at 25-60℃ for 48h-240h.

[0030] The present disclosure provides an electrolyte for improving self-discharge, a supercapacitor and an aging process. The electrolyte includes: a lithium salt, an organic solvent, a sulfur-containing additive, a carbonate additive and a functional additive, and the functional additive has a general structure as follows: ; wherein R1 is selected from any one of hydrogen, amino, C1-C3 alkyl; R2 is selected from any one of substituted or unsubstituted phenyl, pyridine. The present disclosure realizes the synchronous optimization of self-discharge rate and consistency of supercapacitors by optimizing additives, synergistic effect of three additives, has high performance (low K value), low cost (low additive amount) and high adaptability (flexible parameters), and the above additives are also matched with aging process, effectively solving the problem of poor consistency of supercapacitors after formation and distribution. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 K value box plot of example 1, example 2, example 3, example 4 of the present disclosure;

[0032] Figure 2 K value box plot of example 2, example 5, example 6, example 7 of the present disclosure;

[0033] Figure 3 K value box plot of example 5, example 8, example 9, example 10 of the present disclosure;

[0034] Figure 4 K value box plot of example 5, example 11, example 12, example 13, example 14, example 15 of the present disclosure;

[0035] Figure 5 K value box plot of example 2, example 5, comparative example 1, comparative example 2, comparative example 3 of the present disclosure. DETAILED DESCRIPTION

[0036] In order for those skilled in the art to better understand the technical solutions of the present disclosure, the present disclosure will be described in further detail below in combination with the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present disclosure and are part of the embodiments of the present disclosure, but not all embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present disclosure.

[0037] In one aspect of the present disclosure, an electrolyte for improving self-discharge is provided, the electrolyte comprising: a lithium salt, an organic solvent, a sulfur-containing additive, a carbonate-based additive, and a functional additive, wherein the functional additive has the following general structure:

[0038] ;

[0039] wherein R1 is selected from any one of hydrogen, amino, C1-C3 alkyl; R2 is selected from any one of substituted or unsubstituted phenyl, pyridine.

[0040] In the present embodiment, R1 in the functional additive molecule is an electron-donating group, which contains lone pair electrons (such as the N atom of an amino group) that can preferentially undergo complexation reaction with high-valence metal ions on the positive electrode surface to form a stable coordination structure, inhibiting the dissolution of transition metal ions and thus reducing the self-discharge channel caused by metal ion migration. At high potentials, the R1 group (especially the amino group and hydrogen) can be preferentially oxidized and decomposed on the positive electrode surface over electrolyte solvents (such as carbonates), and form a uniform and stable positive electrode electrolyte interface film (CEI film) through radical polymerization. R2 is a substituted / unsubstituted phenyl or pyridyl group (containing an aromatic ring structure), whose conjugated system can enhance the adsorption capacity of the additive molecule on the positive electrode surface through π-π stacking or hydrophobic interaction, preventing the CEI film from being washed off by the electrolyte. The aromatic ring structure of R2 can adjust the oxidation polymerization rate of the additive, matching the aging process of the supercapacitor (such as specific aging temperature and time). By controlling the formation rate and thickness of the CEI film, the individual performance differences of the aged capacitors (such as capacity and internal resistance consistency) are reduced, and the production cost of the enterprise is reduced. That is, the functional additive of the present embodiment can match the subsequent aging process of the capacitor to solve the problem of poor consistency of supercapacitors.

[0041] In some preferred embodiments, the functional additive is selected from any one of the following structures:

[0042] Formula I-1;

[0043] Formula I-2;

[0044] Formula I-3;

[0045] Formula I-4.

[0046] It is particularly noted that the above structural formula I-2 has an amino group, a pyridyl group, and multiple strong coordination groups of cyano groups (-C≡N), which can preferentially form stable coordination structures with high-valence metal ions (such as Ni 3 + / 4+) complexation reaction occurs, forming a dense and stable positive electrode electrolyte interface film (CEI film) on the surface of the positive electrode. In addition, the additive can stabilize the surface lattice structure of the positive electrode material through complexation, effectively inhibiting the dissolution of transition metal ions and reducing the self-discharge channels caused thereby; at high voltage, the electrolyte is prone to oxidative decomposition on the surface of the positive electrode, and the functional additive can preferentially oxidize and polymerize on the surface of the positive electrode to form a stable CEI film, blocking direct contact between the electrolyte and the high-activity positive electrode material, inhibiting continuous oxidation gas production and the resulting voltage drop (self-discharge); at the same time, the aging process of the capacitor is optimized, and the aging temperature and aging time that affect the self-discharge of the supercapacitor are identified, so that the consistency of the supercapacitor after aging is greatly improved, reducing the cost of enterprises.

[0047] In other preferred embodiments, the mass percentage of the functional additive in the electrolyte is 0.3-1%, for example, 0.3%, 0.5%, 0.8%, 1%, etc. can be preferred.

[0048] In other preferred embodiments, the sulfur-containing additive includes at least one of 1,3-propylene sulfite (PST), 1,3-propane sulfite (PS), and vinyl sulfate (DTD); the mass percentage of the sulfur-containing additive in the electrolyte is 0.5-2%.

[0049] In other preferred embodiments, the acid ester additive includes vinylene carbonate (VC); the mass percentage of the carbonate additive in the electrolyte is 0.3-0.5%.

[0050] Note that the additive of the present embodiment includes three types, one of which is a functional additive containing amino, pyridine, and multiple strong coordination groups such as cyano (-C≡N), which can form a dense and stable positive electrode electrolyte interface film, inhibit the dissolution of transition metals, reduce the voltage drop caused by oxidation gas production, another type is a sulfur-containing additive that reduces to form a sulfur-containing SEI film on the negative electrode surface, improving the interface density and ion conductivity, and the third type is an acid ester additive that undergoes ring-opening polymerization on the positive and negative electrode surfaces to supplement the defects of the CEI / SEI film, enhance the interface integrity, and at the same time improve the oxidation / reduction stability of the electrolyte and reduce the side reactions at high voltage. That is, the three additives work together to perfect the interface structure, significantly reduce the self-discharge rate of the supercapacitor, and improve the consistency of the single unit.

[0051] In other preferred embodiments, the lithium salt is lithium hexafluorophosphate (LiPF6); the mass percentage of the lithium salt in the electrolyte is 10%-12.5%.

[0052] In other preferred embodiments, the organic solvent includes cyclic carbonates and chain carbonates.

[0053] As a further preferred solution, the cyclic carbonate includes at least one of fluoroethylene carbonate (FEC), ethylene carbonate (EC) and propylene carbonate (PC); the total mass of the cyclic carbonate is 15% to 25% of the total mass of the organic solvent, calculated on the basis of 100% of the total mass of the organic solvent.

[0054] As a further preferred solution, the chain carbonate includes at least one of diethyl carbonate (DEC) and dimethyl carbonate (DMC). The mass of the diethyl carbonate is 10% to 20% of the total mass of the organic solvent, and the mass of the dimethyl carbonate is 55% to 65% of the total mass of the organic solvent, calculated on the basis of 100% of the total mass of the organic solvent.

[0055] In another aspect of the present disclosure, a supercapacitor is provided, which includes a positive electrode, a negative electrode, an electrolyte and a separator; wherein the electrolyte is the electrolyte as described above, and the specific components are described above and will not be repeated here.

[0056] It should be noted that the present embodiment does not specifically limit the positive electrode and the negative electrode, for example, the positive electrode is prepared by stirring a certain proportion of activated carbon, ternary (NCM622), conductive agent Super P and adhesive polyvinylidene fluoride (PVDF) with an appropriate amount of N-methyl pyrrolidone (NMP) into a slurry, and coating on an aluminum foil. For the negative electrode, a certain proportion of activated carbon, Super P and PAA are stirred into a slurry with NMP, and coated on a copper foil. After drying, rolling, die cutting and other processes, the corresponding positive electrode sheet and negative electrode sheet are prepared. Then the positive and negative electrode sheets and the separator are wound, and finally the supercapacitor is prepared, and the electrolyte is injected, which needs to fully soak the electrode and the separator pores.

[0057] In another aspect of the present disclosure, an aging process for a supercapacitor is provided, which includes: placing the supercapacitor after the separation at 25-60°C for 48h-240h.

[0058] In some preferred embodiments, the standing temperature is preferably 40-55°C, and the standing time is preferably 72-144h.

[0059] The aging process of the present embodiment significantly improves the self-discharge rate and the consistency of the single body of the supercapacitor by optimizing the standing temperature and time, combined with specific electrolyte additives, thereby improving the self-discharge phenomenon.

[0060] The electrolyte for improving self-discharge will be further described below in combination with specific embodiments:

[0061] Example 1

[0062] The electrolyte formula used in this embodiment is as follows, calculated in terms of the mass percentage of components: functional additive (structural formula I-2 shown above): 0.3%, the structural formula of which is as described above, vinylene carbonate (VC): 0.5%, vinyl sulfonate (DTD): 0.5%, lithium hexafluorophosphate (LiPF6): 12%, and the balance being the organic solvent component, the mass percentage of the organic solvent in the electrolyte being 86.7%.

[0063] The organic solvent component in the electrolyte formula described above is composed of fluoroethylene carbonate, vinylene carbonate, propylene carbonate, diethyl carbonate, and dimethyl carbonate, wherein, calculated in terms of the total mass of the organic solvent being 100%, the mass percentage of fluoroethylene carbonate is 3%, the mass percentage of vinylene carbonate is 17%, the mass percentage of propylene carbonate is 4%, the mass percentage of diethyl carbonate is 20%, and the mass percentage of dimethyl carbonate is 56%.

[0064] In a glove box with water and oxygen content less than 0.1, the functional additive, vinylene carbonate, and vinyl sulfonate are added to the organic solvent in the above mass percentages, and then lithium hexafluorophosphate is added, and the mixture is stirred at a temperature of 10°C for 5h to obtain the electrolyte of this embodiment.

[0065] In this embodiment, the supercapacitor aging time is set to 72h, and the aging temperature is set to 40°C.

[0066] Example 2

[0067] The difference between this embodiment and Example 1 is only that the amount of functional additive added in the electrolyte is 0.5%, and the other conditions are the same as in Example 1.

[0068] Example 3

[0069] The difference between this embodiment and Example 1 is only that the amount of functional additive added in the electrolyte is 0.7%, and the other conditions are the same as in Example 1.

[0070] Example 4

[0071] The difference between this embodiment and Example 1 is only that the amount of functional additive added in the electrolyte is 1%, and the other conditions are the same as in Example 1.

[0072] Example 5

[0073] The electrolyte formula used in this embodiment is as follows, calculated in terms of the mass percentage of components: functional additive: 0.5%, vinylene carbonate (VC): 0.5%, vinyl sulfonate (DTD): 0.5%, lithium hexafluorophosphate (LiPF6): 12%, and the balance being the organic solvent component, the mass percentage of the organic solvent in the electrolyte being 86.5%.

[0074] The organic solvent component in the above electrolyte formula is composed of fluoroethylene carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate and dimethyl carbonate, wherein the mass percentage of fluoroethylene carbonate is 3%, the mass percentage of ethylene carbonate is 17%, the mass percentage of propylene carbonate is 4%, the mass percentage of diethyl carbonate is 20%, and the mass percentage of dimethyl carbonate is 56%, based on the total mass of the organic solvent being 100%.

[0075] In a glove box with less than 0.1 oxygen content, the functional additives, vinylene carbonate and vinyl sulfate were added to the organic solvent according to the above mass fraction, and then lithium hexafluorophosphate was added, and the mixture was stirred at 10℃ for 5h to obtain the electrolyte of the present embodiment.

[0076] In the present embodiment, the aging time of the supercapacitor is set to 96h, and the aging temperature is set to 40℃.

[0077] Example 6

[0078] The difference between the present embodiment and Example 5 is only that the aging time of the supercapacitor is set to 120h, and the others are the same as Example 5.

[0079] Example 7

[0080] The difference between the present embodiment and Example 5 is only that the aging time of the supercapacitor is set to 144h, and the others are the same as Example 5.

[0081] Example 8

[0082] The difference between the present embodiment and Example 5 is only that the aging temperature of the supercapacitor is set to 45℃, and the others are the same as Example 5.

[0083] Example 9

[0084] The difference between the present embodiment and Example 5 is only that the aging temperature of the supercapacitor is set to 50℃, and the others are the same as Example 5.

[0085] Example 10

[0086] The difference between the present embodiment and Example 5 is only that the aging temperature of the supercapacitor is set to 55℃, and the others are the same as Example 5.

[0087] Example 11

[0088] The difference between the present embodiment and Example 5 is only that the amount of the sulfur-containing additive DTD is increased to 1%, and the others are the same as Example 5.

[0089] Example 12

[0090] The difference between this embodiment and embodiment 5 is that the amount of the sulfur-containing additive DTD is increased to 1.5%, and the rest is the same as embodiment 5.

[0091] Embodiment 13

[0092] The difference between this embodiment and embodiment 5 is that the amount of the sulfur-containing additive DTD is increased to 2%, and the rest is the same as embodiment 5.

[0093] Embodiment 14

[0094] The difference between this embodiment and embodiment 5 is that the sulfur-containing additive DTD is replaced by 1,3-propane sulfone lactone, the amount is 0.5%, the standing time is 96h, the aging temperature is 55℃, and the rest is the same as embodiment 5.

[0095] Embodiment 15

[0096] The difference between this embodiment and embodiment 5 is that the sulfur-containing additive DTD is replaced by 1,3-propane sulfone lactone, the amount is 0.7%, and the rest is the same as embodiment 5.

[0097] Comparative Example 1

[0098] The electrolyte formula used in this embodiment is as follows: vinylene carbonate (VC): 0.5%, vinyl sulfate (DTD): 0.5%, lithium hexafluorophosphate (LiPF6): 12%, and the rest is the organic solvent component, the mass fraction of the organic solvent in the electrolyte is 87%.

[0099] The organic solvent component in the above electrolyte formula is composed of fluoroethylene carbonate, vinylene carbonate, propylene carbonate, diethyl carbonate and dimethyl carbonate, wherein, calculated based on the total mass of the organic solvent as 100%, the mass fraction of fluoroethylene carbonate is 3%, the mass fraction of vinylene carbonate is 17%, the mass fraction of propylene carbonate is 4%; the mass fraction of diethyl carbonate is 20%, and the mass fraction of dimethyl carbonate is 56%.

[0100] In a glove box with water and oxygen content less than 0.1, the functional additives, vinylene carbonate, vinyl sulfate are added to the organic solvent according to the above mass fraction, and then lithium hexafluorophosphate is added, stirred and mixed at 10℃ for 5h to obtain the electrolyte of this embodiment.

[0101] In this embodiment, the supercapacitor aging time is set to 72h, and the aging temperature is set to 40℃.

[0102] Comparative Example 2

[0103] The difference between the present comparative example and Comparative Example 1 is that only 0.5% functional additive is contained, the aging time of the supercapacitor is set to 24 h, the aging temperature is 40℃, and the rest is the same as Comparative Example 1.

[0104] Comparative Example 3

[0105] The difference between the present comparative example and Comparative Example 1 is that only 0.5% functional additive is contained, the aging time of the supercapacitor is set to 24 h, the aging temperature is 40℃, and the rest is the same as Comparative Example 1.

[0106] Further, the K value of each of the above examples and comparative examples is calculated, wherein the K value calculation method is as follows: (OCV1-OCV2) / (T2-T1), and the results are shown in Table 1. Figures 1 to 5

[0107] From Figure 1 It can be seen from Examples 1-4 that when the amount of functional additive is increased from 0.3% to 0.5%, the K value improves significantly, and when the amount of functional additive is increased from 0.5% to 1%, the K value does not improve much. Figure 2 It can be seen that as the standing time increases, the K value first decreases and then increases, indicating that the optimal aging time is 96 h. Figure 3 It can be seen that as the aging temperature increases, the K value becomes lower and lower, indicating that the higher the temperature, the more beneficial it is to improve self-discharge. Figure 4 It can be seen that the K value of Example 14 is the lowest, which may be due to the replacement of DTD with 1,3-propylene sulfite, which preferentially reduces on the surface of the negative electrode during the first charging of the supercapacitor, forming a dense and stable interfacial film, thereby improving self-discharge. Figure 5 It can be seen that Comparative Example 1 does not add functional additive, and the K value increases significantly, and Comparative Examples 2 and 3 contain functional additives, and are aged at 40℃ and 25℃ for 24 h, respectively, and the K value improvement effect is not obvious.

[0108] The present disclosure proposes an electrolyte, a supercapacitor and an aging process for improving self-discharge, which has the following beneficial effects compared with the prior art: the amino, pyridine and multiple cyano (-C≡N) strong coordination groups in the functional additive molecules of the present disclosure can preferentially react with high-valence metal ions (such as Ni 3+ / 4+ ​The complexation reaction occurs, a dense and stable positive electrolyte interface film (CEI) is formed on the surface of the positive electrode, in addition, the additive stabilizes the surface lattice structure of the positive electrode material by complexation, effectively inhibits the dissolution of transition metal ions, thereby reducing the self-discharge channel caused thereby; at high potential, the electrolyte is easy to oxidize and decompose on the surface of the positive electrode, the functional additive can be preferentially oxidized and polymerized on the surface of the positive electrode to form a stable CEI film, blocking the direct contact of the electrolyte with the high-activity positive electrode material, inhibiting the continuous oxidation gas and the voltage drop (self-discharge) caused thereby; at the same time, the aging process is optimized, the aging temperature and aging time which affect the self-discharge of the supercapacitor can be identified, so that the consistency of the supercapacitor after aging is greatly improved, and the enterprise cost is reduced.

[0109] It can be understood that the above embodiments are only exemplary embodiments adopted for illustrating the principles of the present disclosure, but the present disclosure is not limited thereto. Various modifications and improvements can be made by those of ordinary skill in the art without departing from the spirit and essence of the present disclosure, and these modifications and improvements are also considered to be within the protection scope of the present disclosure.

Claims

1. An electrolyte solution for improving self-discharge, characterized by comprising: The electrolyte comprises: a lithium salt; an organic solvent; a sulfur-containing additive; a carbonate additive; a functional additive, the general structure of which is as follows: ； wherein R1 is selected from any one of hydrogen, amino, C1-C3 alkyl; R2 is selected from any one of substituted or unsubstituted phenyl, pyridine.

2. The electrolyte according to claim 1, characterized in that, The functional additive is selected from any one of the following structures: Formula I-1; Formula I-2; Formula I-3; Formula I-4.

3. The electrolyte of claim 1, wherein The mass percentage of the functional additive in the electrolyte is 0.3-1%.

4. The electrolyte of claim 1, wherein The sulfur-containing additive comprises at least one of 1,3-propylene sulfite, 1,3-propane sulfite and ethylene sulfate; The mass percentage of the sulfur-containing additive in the electrolyte is 0.5-2%.

5. The electrolyte of claim 1, wherein The carbonate additive comprises vinylene carbonate; The mass percentage of the carbonate additive in the electrolyte is 0.3-0.5%.

6. The electrolyte of claim 1, wherein The lithium salt is lithium hexafluorophosphate; The mass percentage of the lithium salt in the electrolyte is 10%-12.5%.

7. The electrolyte of claim 1, wherein The organic solvent comprises a cyclic carbonate and a chain carbonate.

8. The electrolyte according to claim 7, characterized in that The cyclic carbonate comprises at least one of fluoroethylene carbonate, vinylene carbonate and propylene carbonate; The chain carbonate comprises at least one of diethyl carbonate and dimethyl carbonate.

9. An ultracapacitor, characterized by, The supercapacitor comprises a positive electrode, a negative electrode, an electrolyte and a separator; wherein The electrolyte is the electrolyte according to any one of claims 1-8.

10. An aging process of a supercapacitor, characterized by, The aging process comprises: placing the supercapacitor after the capacity test at 25-60℃ for 48h-240h; wherein The supercapacitor is the supercapacitor according to claim 9.

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