Electrolyte, secondary battery and electrical equipment

Abstract

The present application provides an electrolyte, a secondary battery and an electrical device. The pyrene additive in the electrolyte can enhance the wettability of the electrolyte to the electrode and effectively improve the negative electrode interface, thereby effectively extending the cycle life of the secondary battery.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to electrolytes, secondary batteries and electrical equipment. Background Art

[0002] Currently, people are increasingly relying on secondary battery-powered products, such as digital gadgets and new energy vehicles, and the market's requirements for secondary batteries are becoming increasingly stringent. Although secondary batteries are available in solid-state and semi-solid-state forms, liquid secondary batteries using electrolytes currently dominate the market. The electrolyte is a key component of liquid secondary batteries, not only transporting ions during the battery's charge and discharge cycles but also participating in the formation of the solid electrolyte interface (SEI) film during the battery's formation process. The SEI film also plays a crucial role in battery performance.

[0003] The wetting properties of the electrolyte on the electrodes not only affect the conduction of active ions in the battery, but also the film formation of the SEI film. Although the industry is currently trying to use various additives to improve the wetting properties of the electrolyte, or using film-forming agents to improve the film formation of the SEI film, these additives often have a relatively simple effect and may even have a negative impact on battery performance, with limited improvement in battery performance. Summary of the Invention

[0004] In view of this, the embodiments of the present application provide an electrolyte, a secondary battery and an electrical device. The pyrene additive in the electrolyte can enhance the wettability of the electrolyte to the electrode and effectively improve the negative electrode interface, thereby effectively extending the cycle life of the secondary battery.

[0005] In a first aspect, an embodiment of the present application provides an electrolyte solution comprising an electrolyte, an electrolyte salt, and a pyrene additive, wherein the pyrene additive has at least one of the following substituents:

[0006] Wherein, R is a substituted or unsubstituted alkyl group, and R1 and R2 each independently include at least one of an ester group, an alkoxy group, an alkyl ether group, an alkenyl ether group and a hydrogen atom.

[0007] When the above electrolyte is applied to a battery with a carbon-containing negative electrode, the polycyclic structure in the pyrene additive forms a π-π conjugation with the carbon material of the negative electrode; at the same time, due to the weak polarity of the pyrene group and the strong polarity of the silicon-oxygen bond in the substituent, this molecular structure with strong polarity at one end and weak polarity at the other end allows the pyrene additive to play a role similar to a "surfactant", improving the wettability of the electrolyte to the carbon-based negative electrode and improving the problem of local performance differences of the negative electrode caused by uneven electrolyte infiltration; at the same time, the sufficient infiltration of the electrolyte allows a well-uniform SEI film to be formed on the surface of the negative electrode during the formation process, which can effectively improve the stability of the SEI film during the charge and discharge process. More importantly, due to the presence of silicon-oxygen bonds, the pyrene additive molecules can react with water and H in HF that may be generated during the battery formation and charge and discharge cycles. + The reaction has the effect of removing water and acid, and inhibiting the decomposition of electrolyte salts in the electrolyte. Therefore, the above electrolyte can effectively extend the cycle life and comprehensive performance of the battery.

[0008] A second aspect of the embodiments of the present application provides a secondary battery comprising the electrolyte provided in the first aspect of the embodiments of the present application and a negative electrode plate, wherein the negative electrode plate comprises a negative electrode active material, wherein the negative electrode active material comprises a carbon material. Due to the use of the secondary battery provided in the embodiments of the present application, the electrolyte has good wettability of the electrodes during long cycles of the secondary battery, and the SEI film on the surface of the negative electrode plate of the secondary battery is uniform and stable, resulting in good overall performance and a long cycle life.

[0009] The third aspect of the present invention provides an electric device, comprising the secondary battery provided in the second aspect of the present invention. Since the secondary battery provided in the present invention can be used to power the electric device, the electric device has a good market prospect. DETAILED DESCRIPTION

[0010] The electrolyte is a key component of secondary batteries. It not only transports active ions and electrons during the battery's charge-discharge cycle but also participates in the formation of the SEI film during the battery's formation process. The performance of the SEI film is crucial to battery stability and other performance factors. An ideal SEI film should at least uniformly cover the surface of the negative electrode and exhibit good stability during the battery's charge-discharge cycle. This is beneficial for achieving optimal battery performance over long cycles. Furthermore, it is well known that good electrolyte wettability of the electrodes also improves battery performance, especially in the later stages of cycling when the electrolyte content decreases. This good electrolyte wettability can effectively reduce the risk of battery capacity drop. Currently, the industry is experimenting with adding various surfactants to the electrolyte to improve its wettability of the electrodes, or using film-forming agents to improve the SEI film. However, these additives often have limited effects or even negatively impact battery performance, resulting in limited improvements. Therefore, it is necessary to explore new approaches to electrolyte additives.

[0011] To solve the above technical problems, the present invention provides an electrolyte solution comprising an electrolyte, an electrolyte salt, and a pyrene additive, wherein the pyrene additive has at least one of the following substituents: That is, the pyrene additive is pyrene having at least one of the above-mentioned substituents;

[0012] Wherein, R is a substituted or unsubstituted alkyl group, and R1 and R2 each independently include at least one of an ester group, an alkoxy group, an alkyl ether group, an alkenyl ether group and a hydrogen atom.

[0013] In the embodiments of the present application, an alkyl ether group includes a group formed by removing a hydrogen atom from any carbon atom in an alkyl ether, and an alkenyl ether group includes a group formed by removing a hydrogen atom from any carbon atom in an alkenyl ether. Specifically, taking an alkyl ether group as an example, the following is explained in detail: an alkyl ether group can be a group formed by removing a hydrogen atom from any carbon atom in a monoalkyl ether, i.e., an alkyl ether group having one ether oxygen bond, for example, -CH2-O-CH3; an alkyl ether group can be a group formed by removing a hydrogen atom from any carbon atom in a dialkyl ether, i.e., an alkyl ether group having two ether oxygen bonds, for example, -CH2-O-CH2CH2-O-CH3; or an alkyl ether group can be a group formed by removing a hydrogen atom from any carbon atom in a polyalkyl ether, i.e., an alkyl ether group having three or more ether oxygen bonds, for example, -CH2CH2-O-CH2CH2-O-CH2CH2-O-CH3. Similarly, an alkenyl ether group can also contain one, two, or more ether oxygen bonds, and the following can be analogized with the case of an alkyl ether group, which will not be described in detail here.

[0014] When the above-mentioned electrolyte is applied to a battery with a carbon-based negative electrode, the delocalized π electron cloud can overlap between the polycyclic structure (pyrene group) in the pyrene additive and the large π polycyclic ring of the negative electrode carbon material, forming a π-π conjugated effect; at the same time, since the polarity of the pyrene group is relatively weak, and the polarity of the silicon-oxygen bond in the substituent is relatively strong, this molecular structure with strong polarity at one end and weak polarity at the other end enables the pyrene additive to play a role similar to that of a "surfactant", thereby improving the wettability of the electrolyte to the carbon-based negative electrode, so that the electrolyte can fully infiltrate and penetrate the negative electrode, and improve the problem of local performance differences of the negative electrode caused by uneven electrolyte infiltration; at the same time, since the electrolyte will also participate in or promote the formation of the SEI film on the surface of the negative electrode, the sufficient infiltration of the electrolyte enables a more uniform SEI film to be formed on the surface of the negative electrode during the formation process, which can effectively improve the stability of the SEI film during the charge and discharge process.

[0015] More importantly, due to the presence of silicon-oxygen bonds in the substituents, pyrene additive molecules can react with water and H in HF that may be generated during battery formation and charge-discharge cycles. + The reaction has the effect of removing water and acid, thereby reducing the risk of water and gas production during the battery cycle and formation process affecting the structural stability of the SEI film, and inhibiting the decomposition of electrolyte salts in the electrolyte, effectively extending the cycle life and comprehensive performance of the battery.

[0016] Furthermore, sufficient infiltration of the electrolyte can also reduce the risk of capacity drop in the late stage of battery cycle due to uneven current density distribution on the negative electrode surface and loss of active ions due to local dendrite growth. It can more fully avoid the extreme situation of dendrites growing indiscriminately and piercing the diaphragm to cause battery short circuit, thereby ensuring better safety performance of the battery.

[0017] In addition, the electrolyte has excellent wettability to the positive electrode of the battery and good compatibility with the positive electrode.

[0018] The electrolyte solution of the embodiment of the present application can be stored at 5°C-25°C away from light.

[0019] In some embodiments of the present application, the pyrene additive includes at least one structure as shown in formula (I) to formula (III),

[0020]

[0021] The above structure is easy to prepare, and has stable chemical properties, suitable steric hindrance, can be stably dissolved in the electrolyte system, can form a certain π-π conjugation with the carbon material, and has obvious strong polar end and weak polar end in the molecule, which has a good effect on improving the wettability of the electrolyte. Furthermore, the structures shown in the above formula (II) and formula (III) can achieve better water and acid removal effects. It should be noted that when the structure of the pyrene additive is as shown in formula (III), the two Rs in its two substituents may be the same or different, the two R1s may be the same or different, and the two R2s may be the same or different.

[0022] In some embodiments of the present application, a pyrene additive molecule contains multiple substituents as described above: In this way, the water and acid removal effects of the pyrene additive can be enhanced. Specifically, a pyrene additive molecule can contain two or three of the aforementioned substituents.

[0023] In some embodiments of the present application, R is a substituted or unsubstituted C1-C10 alkyl group. Controlling the number of carbon atoms in the alkyl group within the above range can, firstly, minimize steric hindrance and enhance flexibility of R, thereby ensuring better solubility of the pyrene additive in the electrolyte system; and secondly, minimize the polarity of R, thereby avoiding impacting the performance of the pyrene additive. Specifically, the number of carbon atoms in the substituted or unsubstituted alkyl group can be, but is not limited to, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0024] In some embodiments of the present application, R is a substituted or unsubstituted straight-chain alkyl group. In some specific embodiments, R is a substituted or unsubstituted C3-C10 straight-chain alkyl group. Further increasing the chain length of the straight-chain alkyl group can improve the flexibility of the R group, thereby slightly improving the solubility of the pyrene additive in the electrolyte system of the embodiment of the present application, which is more conducive to the application of the electrolyte. In other specific embodiments, R is a substituted or unsubstituted C3-C10 asymmetric branched alkyl group, so that R can have a certain polarity.

[0025] In some embodiments of the present application, for a single pyrene additive molecule, R is selected from any one of substituted or unsubstituted methyl, substituted or unsubstituted ethyl, substituted or unsubstituted propyl, substituted or unsubstituted n-butyl, substituted or substituted n-pentyl, substituted or substituted n-hexyl, substituted or substituted n-heptyl, substituted or substituted n-octyl, substituted or substituted n-nonyl, substituted or substituted n-decyl, etc.

[0026] In some embodiments of the present application, the substituent in the substituted alkyl group is selected from at least one of a halogen atom, an amino group, and a hydroxyl group. Among them, the halogen atom can be a fluorine atom, a chlorine atom, and a bromine atom. In some specific embodiments, when the substituent is an amino group and / or a hydroxyl group, the hydrophilicity of the pyrene additive molecule can be appropriately improved, which is beneficial for it to play a role similar to that of a "surfactant". In the embodiments of the present application, when R is a substituted alkyl group, it can be a single substitution or a polysubstitution. When it is a polysubstitution, the multiple substituents can be the same or different. In some embodiments of the present application, when the substituent is a hydroxyl group, R can be -CH2CH2OH; when the substituent is an amino group, R can be -CH2NH3; when the substituent is a halogen atom, R can be -CH2CH2Cl.

[0027] In the examples of this application, for the same substituent For example, R1 and R2 can be the same or different. For example, R1 and R2 can both be hydrogen atoms. When R1 and R2 are different, they can be the same or different substituents. For example, R1 and R2 can both be alkoxy groups, but one can be a methoxy group and the other an ethoxy group; or, one of R1 and R2 can be an alkoxy group and the other an ester group.

[0028] In some embodiments of the present application, when R1 and / or R2 are ester groups, the ester groups may be, but are not limited to, -CH2COOCH3, -COOCH3, -COOCH2CH3, -COOCH2CH2CH3, -CH2CH2COOCH3, or -CH2CH2CH3COOCH3. The ester group can improve the solubility of the pyrene additive molecules in the electrolyte system while maintaining good amphiphilicity. In some specific embodiments of the present application, the number of carbon atoms in the ester group is controlled to be 1-10. In this way, the steric hindrance of the pyrene additive molecules can be controlled within an appropriate range.

[0029] In some embodiments of the present application, when R1 and / or R2 are alkoxy groups, the alkoxy group may be, but is not limited to, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, 2-methoxyethoxy, etc. It is understandable that the oxygen atom in the alkoxy group is directly connected to the Si atom. Increasing the number of silicon-oxygen bonds can also enhance the water and acid removal effect of the pyrene additive molecule, thereby further improving the cycle performance of the final battery. In some embodiments of the present application, at least one of R1 and R2 is an alkoxy group.

[0030] In some specific embodiments, the number of carbon atoms in the alkoxy group is controlled to be 1-10. In this way, the steric hindrance and flexibility can be controlled to be appropriate, which is beneficial to the performance of the battery.

[0031] In some embodiments of the present application, when R1 and / or R2 are alkyl ether or alkenyl ether groups, the alkyl ether group may be, but is not limited to, -CH2OCH3, -CH2CH2OCH3, -CH2OCH2CH3, or -CH2CH2OCH2CH3; the alkenyl ether group may be, but is not limited to, -CH2CH=CHCH2-O-CH3, or -CH2CH=CHCH2-O-CH2CH3. It is understood that in pyrene additives, the carbon atoms of the alkyl ether and alkenyl ether groups are directly connected to the Si atom, and the carbon-silicon bond energy is higher, which can make the structure of the pyrene additive molecule more stable, facilitating the construction of a uniform and stable SEI film. In the embodiments of the present application, the alkyl ether and alkenyl ether groups may have only one ether oxygen atom or multiple ether oxygen atoms, for example, 2-3. This not only increases the solubility of the pyrene additive molecules in the electrolyte system, but also reduces the risk of side reactions between the ether oxygen atoms and other substances in the battery cell, thereby enhancing battery performance. In some embodiments, the alkyl ether group has 2-10 carbon atoms. In some embodiments, the alkenyl ether group has 3-10 carbon atoms. Similarly, this further enhances battery performance.

[0032] In some embodiments, one of R1 and R2 is an alkoxy group, and the other is an alkyl ether group or an alkenyl ether group. This allows for the combined advantages of both substitutions, improving the overall performance of the pyrene-based additive molecule. In some embodiments, one of R1 and R2 is an alkoxy group, and the other is an alkyl ether group, which facilitates preparation.

[0033] In some embodiments of the present application, the additive molecule pyrene additive includes at least one structure as shown in formula (A) to formula (D):

[0034]

[0035] In some embodiments of the present application, the preparation of the pyrene additive includes:

[0036] Magnesium and tetramethyl orthosilicate are added to tetrahydrofuran, nitrogen is introduced, and bromopyrene is added dropwise. The obtained mixture is then stirred at 50°C-100°C for 8h-16h. After stirring, the mixture is placed in an ice-water bath and NH4Cl is added for separation. After separation, methyl tert-butyl ether is used for multiple extractions, and the mixture is then washed with brine, dried with Na2SO4, and then spin-dried. Finally, the pyrene additive is obtained by vacuum distillation or chromatography.

[0037] In some embodiments of the present application, the mass proportion of pyrene additives in the electrolyte is 0.1%-4%. The appropriate mass proportion can effectively ensure that the electrolyte has better wetting performance on the electrode (especially the carbon-containing negative electrode), thereby improving the interface performance of the negative electrode as much as possible and improving the long-cycle stability of the battery; it will not affect the proportion of other substances in the electrolyte, and can also reduce the negative impact that may be caused by large-scale addition. Exemplarily, the mass proportion of pyrene additives in the electrolyte can be, but is not limited to, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, etc.

[0038] In some specific embodiments, the pyrene additive accounts for 0.1% to 2% by weight in the electrolyte. This effectively improves the electrolyte's wettability to the negative electrode while minimizing the risk of limited cycle performance gains due to side reactions between the pyrene additive and other components in the battery.

[0039] In some embodiments of the present application, the electrolyte further includes a flame retardant additive. Among them, the flame retardant additive includes but is not limited to at least one of trimethyl phosphate (TMP), diphenyl cresol phosphate (CDP) and diphenyl octyl phosphate (DPOF). The flame retardant additive can enhance the flame retardant properties of the electrolyte, thereby enhancing the safety performance of the final battery. In some specific embodiments, the mass content of the flame retardant additive in the electrolyte is ≤2%. Specifically, the mass content of the flame retardant additive in the electrolyte may be, but is not limited to, 0.1%, 0.2%, 0.5%, 1%, 1.2%, 1.5%, 1.8%, 2%, and the like.

[0040] In some embodiments of the present application, the solvent of the electrolyte includes but is not limited to ester solvents. Wherein, ester solvents include but are not limited to at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene methyl carbonate (EMC) and vinylene carbonate (VC). In some specific embodiments, the above-mentioned carbonate solvents include cyclic carbonate and linear carbonate simultaneously, and the cyclic carbonate includes ethylene carbonate, and the linear carbonate includes at least one of diethyl carbonate, dimethyl carbonate and methyl ethyl carbonate. The dielectric constant of cyclic carbonate is high, and the viscosity of linear carbonate is small, and the two are used in combination to help improve the ionic conductivity of the electrolyte.

[0041] In some specific embodiments, the solvent includes vinylene carbonate (VC), and the content of vinylene carbonate in the electrolyte is ≤3%, further ≤2%. VC can play the role of a film-forming agent, further optimize the film-forming performance of the SEI film, and during the charge and discharge cycle of the battery, when the carbon material (e.g., graphite) of the negative electrode breaks to produce a new end face, it promotes the formation of the SEI film at the end face, thereby improving the cycle performance of the battery. Specifically, the mass proportion of VC in the electrolyte can be, but is not limited to, 0.1%, 0.2%, 0.5%, 1%, 1.2%, 1.5%, 1.8%, 2%, etc.

[0042] The electrolyte of the embodiment of the present application can be used for lithium ion secondary batteries, sodium ion secondary batteries, or other alkali metal ion secondary batteries. Correspondingly, the electrolyte in the electrolyte can be selected according to the specific battery type, and can be selected from any corresponding electrolyte known to ordinary technicians in the field. Exemplarily, when used for lithium ion batteries, the electrolyte includes but is not limited to lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium sulfate (Li2SO4), lithium difluorooxalatoborate (abbreviated as LiDFOB), lithium dioxalatoborate (abbreviated as LiBOB), lithium bis(trifluoromethanesulfonic acid imide) (abbreviated as LiTFSI), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (abbreviated as LiTFA or LiOTF) and lithium perchlorate (LiClO4) at least one.

[0043] In some embodiments of the present application, the molar concentration of the electrolyte in the electrolyte is 0.8 mol / L-1.2 mol / L.

[0044] The present application also provides a secondary battery comprising the electrolyte provided in the present application and a negative electrode plate, wherein the negative electrode plate comprises a negative electrode active material, wherein the negative electrode active material comprises a carbon material. Due to the use of the secondary battery provided in the present application, the electrolyte has good wettability of the electrodes during long cycles of the secondary battery, and the SEI film on the surface of the negative electrode plate of the secondary battery is uniform and stable, resulting in good overall performance and a long cycle life.

[0045] In the embodiment of the present application, the secondary battery may be a lithium ion battery, a sodium ion battery, or other alkali metal ion battery.

[0046] In some embodiments of the present application, the above-mentioned negative electrode plate includes a current collector and a negative electrode active material layer arranged on at least one side surface of the current collector, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a carbon material.

[0047] In some embodiments of the present application, the carbon materials used as the negative electrode active material include, but are not limited to, carbon materials such as graphite, hard carbon, and mesocarbon microbeads (MCMB) that can be used as the negative electrode active material. In some specific embodiments, the negative electrode active material includes graphite. It can be understood that the negative electrode active material may also include other types of negative electrode active materials. In some specific embodiments, when the negative electrode active material further includes other types of negative electrode active materials, the mass ratio of the carbon material (e.g., graphite) used as the negative electrode active material in the negative electrode active material is ≥60%.

[0048] In some embodiments of the present application, the negative electrode active material layer further includes a binder. Optionally, the negative electrode active material layer further includes a conductive agent.

[0049] In the embodiments of the present application, the current collector of the negative electrode can be any current collector applicable to the negative electrode well-known to those skilled in the art. The binder and the conductive agent in the negative electrode active material layer can be materials well-known to those skilled in the art.

[0050] In some embodiments of the present application, the secondary battery includes a positive electrode plate, a negative electrode plate, and a separator and an electrolyte located between the positive electrode plate and the negative electrode plate. Among them, the above positive electrode plate is any positive electrode plate well-known in the art. In some embodiments, the above positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on at least one side thereof, where the positive electrode active material is any positive electrode active material well-known in the art. Exemplarily, for a lithium-ion battery, the above positive electrode active material includes, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium iron phosphate (LiFePO4), lithium cobalt phosphate (LiCoPO4), lithium manganese phosphate (LiMnPO4), lithium nickel phosphate (LiNiPO4), lithium manganate (LiMnO2), binary material LiNi x A (1-k) O2 (where A is selected from one of Co and Mn, 0 < k < 1), ternary material LiNimEnM ) (1-m-n) O2 (where E and M are independently selected from at least one of Co, Al, and Mn, and E and M are different, 0 < m < 1, 0 < n < 1).

[0051] In some embodiments of the present application, the positive electrode active material layer further includes a conductive agent and a binder. In the present application, the above binder and conductive agent are any binder and conductive agent selected from those well-known in the art. In some embodiments, the conductive agents of the positive electrode plate can be independently selected from at least one of acetylene black, Super P, Super S, graphene, carbon fiber, carbon nanotube, and Ketjen black.

[0052] In the embodiments of the present application, the above separator is any separator well-known in the art.

[0053] The present invention also provides an electric device including the secondary battery provided in the present invention. Since the electric device can be powered by the secondary battery provided in the present invention, the electric device has a good market prospect.

[0054] In some embodiments of the present application, the above-mentioned electrical equipment includes but is not limited to 3C electronic equipment, new energy vehicles, electric assisted bicycles, etc.

[0055] The technical solution of this application is further illustrated below with multiple embodiments.

[0056] Example 1

[0057] An electrolyte solution comprising the following components: EMC:EC:DMC:DEC (specifically, a mass ratio of 35:30:20:15), an electrolyte (specifically, lithium hexafluorophosphate), and a pyrene additive represented by formula (A). The pyrene additive has a mass content of 0.1% in the electrolyte solution. The concentration of lithium hexafluorophosphate is 1 mol / L.

[0058]

[0059] Example 2

[0060] The difference from Example 1 is that the electrolyte further contains 2 wt.% of vinylene carbonate.

[0061] Example 3

[0062] The difference from Example 2 is that the mass content of the pyrene additive in the electrolyte is 0.6%.

[0063] Example 4

[0064] The difference from Example 2 is that the mass content of the pyrene additive in the electrolyte is 1%.

[0065] Example 5

[0066] The difference from Example 2 is that the mass content of the pyrene additive in the electrolyte is 2%.

[0067] Example 6

[0068] The difference from Example 2 is that the mass content of the pyrene additive in the electrolyte is 4%.

[0069] Example 7

[0070] The difference from Example 2 is that the pyrene additive in the electrolyte is replaced with a pyrene additive as shown in formula (B).

[0071] Example 8

[0072] The difference from Example 2 is that the pyrene additive in the electrolyte is replaced with a pyrene additive as shown in formula (C).

[0073]

[0074] Example 9

[0075] The difference from Example 2 is that the pyrene additive in the electrolyte is replaced with a pyrene additive as shown in formula (D).

[0076]

[0077] Example 10

[0078] The difference from Example 2 is that the electrolyte further contains 2 wt.% of trimethyl phosphate (TMP).

[0079] In order to highlight the beneficial effects of the embodiments of the present application, the following comparative examples are provided.

[0080] Comparative Example 1

[0081] The only difference from Example 1 is that the electrolyte does not contain the pyrene additive provided in the example of this application.

[0082] Comparative Example 2

[0083] The only difference from Example 2 is that the electrolyte does not contain the pyrene additive provided in the example of this application.

[0084] Performance Testing

[0085] (1) Prepare test cells containing the electrolytes of the embodiment and the comparative example respectively: prepare positive electrode sheets, negative electrode sheets and separators (specifically polypropylene separators), wherein the positive electrode sheets include a positive electrode current collector (specifically aluminum foil) and a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material (specifically LiFePO4), a conductive agent (specifically Super P), and a binder (specifically polyvinylidene fluoride, PVDF) in a mass ratio of 100:5:5; the negative electrode sheets include a negative electrode current collector (specifically copper foil) and a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material (specifically graphite), a conductive agent (specifically Super P), and a binder (specifically polyvinylidene fluoride, PVDF) in a mass ratio of 100:1:5. P), a binder (specifically 1 part by weight of sodium carboxymethyl cellulose (CMC) + 1.6 parts by weight of styrene-butadiene rubber (SBR)); placing a diaphragm (specifically a polypropylene diaphragm with a thickness of 14 μm) between the positive electrode sheet and the negative electrode sheet to separate the positive and negative electrode sheets to obtain a battery cell; the electrolyte of each embodiment and comparative example is poured into the battery cell, and the battery cell is formed to obtain a soft-pack battery.

[0086] (2) Electrolyte wetting performance test

[0087] Prepare multiple positive electrode sheets in step (1), multiple negative electrode sheets in step (1), and multiple separators in step (1). On the flat surface of a static contact angle tester, the electrolytes of each embodiment and comparative example are dripped onto the above-mentioned specimens. In each round of testing, a drop of 4 μL of liquid is dripped onto the surface of the specimen. After the drop is stable, the contact angle between the electrolyte and the specimen is tested. Among them, when each electrolyte is dripped onto the positive electrode sheet specimen and the separator specimen, the drop is quickly absorbed, indicating that the wettability is very good. The static contact angle test results of each electrolyte on the surface of the negative electrode sheet sample are summarized in Table 1.

[0088] (3) Electrochemical performance test

[0089] The batteries of the above embodiments and comparative examples were capacity calibrated as follows: at 25±3°C, they were charged at a constant current and constant voltage of 0.25C to 3.5V, cut off at 0.02C, and left for 30 minutes; then discharged at a constant current of 0.25C to 2.0V and left for 30 minutes; the above was one cycle, and the discharge capacity of the third cycle was recorded as the nominal discharge capacity C0 of each battery.

[0090] Each battery was subjected to a cycling performance test: The batteries of the above examples and comparative examples were left for 3 hours, then charged to 3.5V at 0.5C0 constant current at 25±3°C, left for 30 minutes, and then discharged to 2.0V at 0.5C0 constant current, left for 30 minutes, for a total of 500 cycles. The capacity retention after 100, 300, and 500 cycles was recorded. The capacity retention after N cycles is calculated as: discharge capacity at the Nth cycle / discharge capacity at the first cycle × 100%. The results are summarized in Table 2.

[0091] Table 1

[0092] Case Negative electrode contact angle test value / ° Example 1 19.10 Example 2 18.96 Example 3 15.70 Example 4 14.35 Example 5 12.67 Example 6 11.32 Example 7 19.23 Example 8 19.42 Example 9 19.37 Example 10 18.87 Comparative Example 1 19.84 Comparative Example 2 19.58

[0093] Table 2

[0094]

[0095]

[0096] By comparing the data in Table 1 and Table 2, it can be found that the electrolyte provided in the embodiment of the present application has good wettability to the negative electrode, and the wettability of the electrolyte to the negative electrode improves with the increase of the content of the pyrene additive in the electrolyte.

[0097] When both the embodiment and comparative example electrolytes do not contain VC (Example 1 and Comparative Example 1), the cycle performance of the embodiment is better than that of Comparative Example 1. Further, when the embodiment and comparative example electrolytes (Examples 2-9 and Comparative Example 2) contain the same amount of VC, the electrolyte provided by the embodiment of the present application can improve the cycle performance of the battery to a certain extent, especially when the content of the pyrene additive in the electrolyte is within the further recommended range of 0.1%-2%, but the cycle performance of the battery (Examples 2-5) is better. Furthermore, when the flame retardant additive trimethyl phosphate is added to the electrolyte (Example 10), it will not affect the cycle performance of the battery, and can further improve the flame retardant properties of the battery.

[0098] The above is an exemplary embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made thereto without departing from the principles of the present application. These improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. An electrolyte, characterized in that: Including solvent, electrolyte salt and pyrene additive; The pyrene additive includes at least one structure as shown in formula (I) to formula (III): Formula (I), Formula (II), Formula (III); wherein R is a substituted or unsubstituted alkyl group, and R1 and R2 each independently include at least one of an ester group, an alkoxy group, an alkyl ether group, an alkenyl ether group, and a hydrogen atom; The mass proportion of the pyrene additive in the electrolyte is 0.1%-4%.

2. The electrolyte according to claim 1, characterized in that The R is a substituted or unsubstituted C1-C10 alkyl group.

3. The electrolyte according to claim 1, characterized in that The R is a substituted or unsubstituted straight-chain alkyl group.

4. The electrolyte according to claim 1, characterized in that The substituent in the substituted alkyl group is selected from one or more of a halogen atom, an amino group and a hydroxyl group.

5. The electrolyte according to claim 1, characterized in that At least one of R1 and R2 is an alkoxy group.

6. The electrolyte according to claim 1, characterized in that The pyrene additive includes at least one structure as shown in formula (A) to formula (D): Formula (A); Formula (B); Formula (C); Formula (D).

7. The electrolyte according to any one of claims 1 to 6, characterized in that The electrolyte further includes a flame retardant additive, wherein the flame retardant additive includes at least one of trimethyl phosphate, diphenyl cresol phosphate and diphenyl octyl phosphate; The mass proportion of the flame retardant additive in the electrolyte is ≤2%.

8. The electrolyte according to claim 1, characterized in that The solvent includes an ester solvent; the ester solvent includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, vinyl methyl carbonate and vinylene carbonate.

9. A secondary battery, characterized in that: The secondary battery comprises the electrolyte according to any one of claims 1 to 8 and a negative electrode plate, wherein the negative electrode plate comprises a negative electrode active material, and the negative electrode active material comprises a carbon material.

10. The secondary battery according to claim 9, wherein The carbon material includes graphite.

11. An electrical device, characterized in that: The electric device includes the secondary battery according to claim 9 or 10.

Images