Electrolyte, secondary battery and electric equipment

Abstract

The embodiment of the invention provides an electrolyte, a secondary battery and electric equipment, and the electrolyte provided by the embodiment of the invention comprises a lithium salt, an organic solvent and a first additive, the first additive includes a polyoxyethylene polyoxypropylene block copolymer, and the polyoxyethylene polyoxypropylene block copolymer includes a compound of formula (I). The polyoxyethylene group in the compound with the formula (I) is beneficial to reducing the interface impedance between an electrolyte and a pole piece and improving the rate capability of the secondary battery; the polyoxypropylene group in the compound with the formula (I) can also improve the stability of the electrolyte, so that the cycle performance of the secondary battery is improved, and the service life of the secondary battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to an electrolyte, a secondary battery, and an electrical device using the same. Background Art

[0002] With the wide application of secondary batteries in different fields (such as electric vehicles, drones, mobile devices, power tools, etc.), higher requirements are put forward for the charging and discharging time and power of secondary batteries.

[0003] In related technologies, high-rate secondary batteries improve the internal conductivity of secondary batteries by optimizing the active materials in the positive electrode plate and the negative electrode plate to achieve rapid charging of secondary batteries; however, during the operation of high-rate secondary batteries, large-rate current discharge needs to be continuously carried out, which will cause more intense side reactions inside the secondary batteries, exacerbate the rapid degradation of the internal structure of the secondary batteries, and further lead to the deterioration of the cycle performance and the shortening of the service life of the secondary batteries. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an electrolyte, a secondary battery, and an electrical device using the same, so as to solve the problems of deteriorated cycle performance and shortened service life of high-rate secondary batteries in related technologies.

[0005] To solve the above problems, the present invention is realized by the following technical solutions:

[0006] The present invention provides an electrolyte, which includes a lithium salt, an organic solvent, and a first additive; the first additive includes a polyoxyethylene-polyoxypropylene block copolymer, and the polyoxyethylene-polyoxypropylene block copolymer includes a compound having the formula (I):

[0007] HO(C 2 H 4 O) a (C 3 H 6 O) b (C 2 H 4 O) a H Formula (I);

[0008] Wherein, a represents the degree of polymerization of —C 2 H 4 O—, and a is any integer from 5 to 200; b represents the degree of polymerization of —C 3 H 6 O—, and b is any integer from 4 to 250.

[0009] Furthermore, in the electrolyte, in the compound having the formula (I), —(C 2 H 4O) a The relative molecular mass of —(C

[0010] is 100 - 2200. 3 H 6 O) b The relative molecular mass of —(C

[0011] is 100 - 2000.

[0012] Furthermore, in the electrolyte, the mass percentage of the first additive is 0.2 wt% - 1.5 wt%.

[0013] Furthermore, in the electrolyte, the electrolyte further includes a second additive, and the second additive includes at least one of vinylene carbonate, propylene sulfite, ethylene sulfate, ethylene vinylene carbonate, fluoroethylene carbonate, lithium bis(oxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorophosphate.

[0014] Furthermore, in the electrolyte, the organic solvent includes at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0015] Furthermore, in the electrolyte, the mass percentage of the organic solvent is 74 wt% - 85 wt%.

[0016] The present invention also provides a secondary battery, which includes a positive electrode sheet, a negative electrode sheet, and the electrolyte as described above.

[0017] The present invention also provides an electrical device, which includes the above secondary battery, and the secondary battery serves as the power supply of the electrical device.

[0018] Compared with the related art, the embodiments of the present invention have the following advantages:

[0019] The electrolyte provided by the embodiments of the present invention includes a lithium salt, an organic solvent, and a first additive; the first additive includes a polyoxyethylene - polyoxypropylene block copolymer, and the polyoxyethylene - polyoxypropylene block copolymer includes a compound having the formula (I); wherein, the polyoxyethylene group (—C 2 H 4O—) has strong hydrophilicity and can form hydrogen bonds with water molecules, making the first additive molecules easily and uniformly dispersed in water, improving the wettability of the electrolyte to the electrode sheet, being beneficial to reducing the interfacial impedance between the electrolyte and the electrode sheet, and improving the rate performance of the secondary battery; the polyoxypropylene group (—C 3 H 6 O—) in the compound of formula (I) shows certain hydrophobicity and can adsorb on the surface of the solid particles of the active material in the electrode sheet to form a stable emulsion or suspension, inhibit the decomposition reaction of the lithium salt, improve the stability of the electrolyte, reduce the degree of side reactions in the secondary battery, and be beneficial to improving the cycle performance of the secondary battery and extending the service life of the secondary battery; further, in the embodiments of the present invention, by controlling the degree of polymerization of —C 2 H 4 O— to be 5 to 200 and controlling the degree of polymerization of —C 3 H 6 O— to be 4 to 250, the hydrophilic-lipophilic balance value of the polyoxyethylene-polyoxypropylene block copolymer can be adjusted, which is beneficial to further improving the stability of the electrolyte, reducing the decomposition and volatilization of the electrolyte, thereby further improving the stability of the electrolyte and reducing the degree of side reactions in the secondary battery.

[0020] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present invention. Detailed embodiments

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0022] To make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with specific embodiments.

[0023] In the related art, high-rate secondary batteries improve the conductivity inside the secondary battery by optimizing the active materials in the positive electrode sheet and the negative electrode sheet to achieve rapid charging of the secondary battery; however, during the operation of high-rate secondary batteries, large-rate current discharge needs to be continuously carried out, which will cause more intense side reactions inside the secondary battery, exacerbate the rapid degradation of the internal structure of the secondary battery, and further lead to the deterioration of the cycle performance of the secondary battery and the shortening of the service life.

[0024] Embodiments of the present invention provide an electrolyte to solve the above problems. The electrolyte includes a lithium salt, an organic solvent, and a first additive. The first additive includes a polyoxyethylene-polyoxypropylene block copolymer, and the polyoxyethylene-polyoxypropylene block copolymer includes a compound having formula (I):

[0025] HO(C 2 H 4 O) a (C 3 H 6 O) b (C 2 H 4 O) a H Formula (I);

[0026] wherein, a represents the degree of polymerization of —C 2 H 4 O—, and a is any integer from 5 to 200; b represents the degree of polymerization of —C 3 H 6 O—, and b is any integer from 4 to 250.

[0027] Specifically, in the compound having formula (I), —C 2 H 4 O— can be represented by formula (II):

[0028] -CH 2 CH 2 O- Formula (II).

[0029] In the compound having formula (I), —C 3 H 6 O— can be represented by formula (III) or formula (IV):

[0030]

[0031] In embodiments of the present invention, in the compound having formula (I), the degree of polymerization a of —C 2 H 4 O— can be any integer from 5 to 200; exemplarily, a can be one of 5, 30, 50, 100, 120, 150, and 200, or any range value between any two of them.

[0032] In the compound having formula (I), the degree of polymerization b of —C 3 H 6 O— can be any integer from 4 to 250; exemplarily, b can be one of 4, 10, 50, 100, 150, 200, and 250, or any range value between any two of them.

[0033] In the embodiments of the present invention, —C 2 H 4 O— in the compound of formula (I) has strong hydrophilicity and can form hydrogen bonds with water molecules, making the first additive molecules easily disperse uniformly in water, improving the wettability of the electrolyte to the electrode sheet, facilitating the reduction of the interfacial impedance between the electrolyte and the electrode sheet, and improving the rate performance of the secondary battery; —C 3 H 6 O— in the compound of formula (I) shows certain hydrophobicity and can adsorb on the surface of the solid particles of the active material in the electrode sheet to form a stable emulsion or suspension, inhibit the decomposition reaction of the lithium salt, improve the stability of the electrolyte, reduce the degree of side reactions in the secondary battery, and facilitate the improvement of the cycle performance of the secondary battery and the extension of the service life of the secondary battery; further, in the embodiments of the present invention, by controlling the degree of polymerization of —C 2 H 4 O— to be 5 to 200 and the degree of polymerization of —C 3 H 6 O— to be 4 to 250, the hydrophilic-lipophilic balance value (HLB) of the polyoxyethylene-polyoxypropylene block copolymer can be adjusted, which is conducive to further improving the stability of the electrolyte, reducing the decomposition and volatilization of the electrolyte, thereby further improving the stability of the electrolyte and reducing the degree of side reactions in the secondary battery.

[0034] In addition, in the compound of formula (I), both —C 2 H 4 O— and —C 3 H 6 O— include ether bonds (—O—), and —C 2 H 4 O— and —C 3 H 6 O— including ether bonds can form a polymer molecular layer in the electrolyte, reduce the surface tension of the electrolyte, reduce the generation of bubbles in the electrolyte, improve the compatibility between the electrolyte and the electrode sheet, further improve the wettability of the electrolyte to the electrode sheet, reduce the interfacial resistance between the electrolyte and the electrode sheet, and improve the rate performance of the secondary battery.

[0035] Optionally, in the electrolyte provided by the embodiments of the present invention, in the compound of formula (I), the relative molecular mass of the polyoxyethylene block —(C 2 H 4 O) a — is 100 to 2200; specifically, in the compound of formula (I), —(C 2 H 4 O) aThe relative molecular mass of — can be one of 100, 300, 700, 1000, 1500, 1900, and 2200 or the range value of any two of them.

[0036] Optionally, in the electrolyte provided by the embodiments of the present invention, among the compounds having the formula (I), the polyoxypropylene block —(C 3 H 6 O) b — has a relative molecular mass of 100 to 2000; specifically, among the compounds having the formula (I), —(C 3 H 6 O) b — has a relative molecular mass that can be one of 100, 300, 600, 900, 1500, 1700, and 2000 or the range value of any two of them.

[0037] In the embodiments of the present invention, by controlling the relative molecular mass of —(C 2 H 4 O) a — within 100 to 2200, and / or by controlling the relative molecular mass of —(C 3 H 6 O) b — within 100 to 2000, the hydrophilic-lipophilic balance value of the polyoxyethylene-polyoxypropylene block copolymer can be adjusted more accurately, which is beneficial to further improving the stability of the electrolyte, reducing the decomposition and volatilization of the electrolyte, thereby reducing the degree of side reactions in the secondary battery, improving the cycle performance of the secondary battery, and prolonging the service life of the secondary battery.

[0038] Optionally, in the electrolyte provided by the embodiments of the present invention, the mass ratio of the first additive is 0.2 wt% to 1.5 wt%; specifically, in the electrolyte, the mass ratio of the first additive can be one of 0.2 wt%, 0.5 wt%, 0.7 wt%, 1 wt%, 1.3 wt%, and 1.5 wt% or the range value of any two of them. Within this range value, the effect of the polyoxyethylene-polyoxypropylene block copolymer in improving the rate performance and cycle performance of the secondary battery and prolonging the service life of the secondary battery can be further exerted.

[0039] Optionally, the electrolyte provided by the embodiments of the present invention further includes a second additive, and the second additive includes at least one of vinylene carbonate (VC), propylene sulfite (PS), 1,3,2-dioxathiolane 2,2-dioxide (DTD), vinylethylene carbonate (VEC), 4-fluoro-1,3-dioxolan-2-one (FEC), lithium bis(oxalate)borate (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis((trifluoromethyl)sulfonyl)azanide (LiTFSI), and lithium difluorophosphate (LiPO 2 F 2 ).

[0040] The above-mentioned second additive can form a stable solid electrolyte interface (SEI) film on the surface of the negative electrode sheet of the secondary battery. It synergizes with the first additive, can further improve the stability of the electrolyte, reduce the degree of side reactions in the secondary battery, improve the cycling performance of the secondary battery, and thus extend the service life of the secondary battery.

[0041] Optionally, in the electrolyte provided by the embodiments of the present invention, the mass ratio of the second additive is 5 wt% to 10 wt%; specifically, in the electrolyte, the mass ratio of the second additive can be one of 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, and 10 wt% or the range value of any two of them. Within this range value, the effect of the second additive in improving the stability of the electrolyte, improving the cycling performance of the secondary battery, and extending the service life of the secondary battery can be further exerted.

[0042] Optionally, in the electrolyte provided by the embodiments of the present invention, the organic solvent includes at least two of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0043] Among them, ethylene carbonate has a high film-forming potential on the negative electrode sheet and can participate in the formation of the SEI film on the surface of the graphite negative electrode sheet, reducing side reactions on the surface of the electrode sheet. Moreover, ethylene carbonate has a relatively high dielectric constant, which can improve the ionic conductivity of the electrolyte.

[0044] Propylene carbonate can enhance the stability of the secondary battery, protect the negative electrode sheet, reduce the polarity of the electrolyte, and thus reduce the possibility of secondary battery failure; in addition, propylene carbonate can also reduce the operating temperature of the secondary battery and improve the stability of the secondary battery during the charge and discharge cycle process.

[0045] Dimethyl carbonate can mix with electrolyte components with low polarity, such as ethylene carbonate and diethyl carbonate, to form a balanced dissolution, enabling the secondary battery to reach a stable state faster, and further improving the cycle life and rate performance of the secondary battery.

[0046] Diethyl carbonate, when used together with other solvents, such as ethylene carbonate and dimethyl carbonate, can improve the solubility of each component in the electrolyte.

[0047] Lithium difluorophosphate can further reduce the interfacial resistance between the electrolyte and the electrode sheet, reduce the internal impedance of the secondary battery, and improve the rate performance and cycle performance of the secondary battery.

[0048] Ethyl methyl carbonate mainly plays a role in providing an ion conduction channel in the electrolyte, promoting the transfer of ions in the electrolyte between the positive and negative electrode sheets, which is beneficial to improving the efficiency and rate performance of the electrochemical reaction of the secondary battery.

[0049] Optionally, in the electrolyte provided by the embodiments of the present invention, the mass ratio of the organic solvent is 74wt% - 85wt%; specifically, in the electrolyte, the mass ratio of the organic solvent can be one of 74wt%, 76wt%, 78wt%, 80wt%, 83wt%, and 85wt% or the range value of any two of them. Within this range value, it is beneficial to fully dissolve the lithium salt, the first additive, and the second additive, provide a necessary migration medium for lithium ions, improve the electrolyte conductivity, and thus improve the rate performance and cycle performance of the secondary battery and extend the service life of the secondary battery.

[0050] Optionally, in the electrolyte provided by the embodiments of the present invention, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), and lithium difluoro(oxalato)borate (LiODFB).

[0051] Among them, lithium hexafluorophosphate and lithium tetrafluoroborate have high ionic conductivity and good electrochemical stability, which can improve the stability of the electrolyte, reduce the degree of side reactions in the secondary battery, and further reduce the corrosion degree of the side reaction products on the electrode sheet, which is beneficial to improving the cycling performance of the secondary battery and extending the service life of the secondary battery; lithium difluoro(oxalato)borate has excellent high and low temperature performance and can maintain stable electrochemical performance within a wide temperature range; in addition, lithium difluoro(oxalato)borate as the lithium salt in the electrolyte can also provide high ionic conductivity and improve the overall electrochemical performance of the secondary battery.

[0052] Optionally, in the electrolyte provided by the embodiments of the present invention, the mass ratio of the lithium salt is 8wt% - 16wt%; specifically, in the electrolyte, the mass ratio of the lithium salt can be one or any range value between two of 8wt%, 10wt%, 11wt%, 13wt%, 15wt%, and 16wt%. Within this range, while improving the conductivity of the electrolyte, the viscosity of the electrolyte can be made moderate, effectively taking into account both the conductivity and viscosity of the electrolyte, and further exerting the effect of the lithium salt in improving the performance of the electrolyte.

[0053] It should be noted that in the electrolyte provided by the embodiments of the present invention, the sum of the mass ratios of the lithium salt, organic solvent, first additive, and second additive is 100wt%.

[0054] The present invention also provides a method for preparing an electrolyte, which includes: under the protection of an inert gas, mixing a lithium salt and an organic solvent to obtain a colorless transparent liquid; mixing the first additive, the second additive, and the colorless transparent liquid to obtain an electrolyte.

[0055] Among them, during the process of mixing the lithium salt and the organic solvent, since adding the lithium salt will cause the temperature of the electrolyte to rise and cause a certain degree of thermal decomposition of the lithium salt, it is necessary to control the temperature of the electrolyte during the addition of the lithium salt; specifically, when the temperature of the electrolyte rises by more than 2°C, stop adding the lithium salt, and when the temperature of the electrolyte rises by less than 2°C, continue to add the lithium salt.

[0056] Among them, the temperature control of the above electrolyte can be achieved by ice bath, dry ice circulation cooling, liquid nitrogen cooling, etc.

[0057] Optionally, in some embodiments, the above-mentioned organic solvent includes multiple solvents. Before mixing the lithium salt and the organic solvent, it is necessary to pre-mix the multiple solvents and remove water, and then under the protection of an inert gas, mix the lithium salt and the above-mentioned organic solvent to obtain the above-mentioned colorless transparent liquid; then mix the above-mentioned first additive, second additive with the above-mentioned colorless transparent liquid to obtain an electrolyte. Among them, the molecular sieve adsorption method can be used to remove water from the organic solvent.

[0058] The present invention also provides a secondary battery, wherein the secondary battery includes a positive electrode sheet, a negative electrode sheet and the above-mentioned electrolyte.

[0059] Among them, the lithium salt in the electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet.

[0060] The above-mentioned positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on the above-mentioned positive electrode current collector. The above-mentioned positive electrode active material layer includes a positive electrode active material, and the above-mentioned positive electrode active material includes a lithium ion transition metal oxide, a ternary positive electrode material, etc. The above-mentioned lithium ion transition metal oxide includes at least one of lithium cobalt oxide (LiCoO 2 ), lithium manganese oxide (LiMn 2 O 4 ), lithium iron phosphate (LiFePO 4 ), and the above-mentioned ternary positive electrode material can specifically be a high-nickel layered ternary positive electrode material.

[0061] Optionally, in some embodiments, the above-mentioned positive electrode sheet further includes a conductive agent and a binder. The above-mentioned conductive agent can include at least one of conductive carbon black, acetylene black (Super P), Ketjen black, carbon nanotubes, graphene, carbon fiber, and carbon microspheres. The above-mentioned binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0062] In some embodiments, the preparation method of the positive electrode sheet is as follows: Disperse the components for preparing the positive electrode sheet, such as the above-mentioned positive electrode active material, binder and any other components, in a solvent such as N-methylpyrrolidone (NMP) to form a positive electrode slurry; coat the positive electrode slurry on both sides of a positive electrode current collector such as aluminum foil; after processes such as baking, rolling, and slicing, the positive electrode sheet can be obtained.

[0063] Among them, the negative electrode plate includes a negative current collector and a negative active material layer provided on the negative current collector. The above-mentioned negative active material layer can adopt a negative active material for a secondary battery, and the negative active material includes any one or a combination of at least two of hard carbon, soft carbon, graphite, and silicon monoxide.

[0064] In the secondary battery provided by the embodiment of the present invention, the negative electrode plate further includes a conductive agent and a binder; optionally, the above-mentioned conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene, and the above-mentioned binder includes a carboxymethyl cellulose (CMC)-based binder and a resin-based binder.

[0065] Optionally, in some embodiments, the carboxymethyl cellulose-based binder includes one or more of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose; and / or the resin-based binder includes one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), and polyacrylonitrile (PAN).

[0066] In some embodiments, the preparation method of the negative electrode plate is as follows: Disperse the components for preparing the negative electrode plate, such as the above-mentioned negative active material, binder, and conductive agent, in a solvent such as deionized water to form a negative electrode slurry; coat the negative electrode slurry on both sides of a negative current collector such as copper foil; after processes such as baking, rolling, and cutting, the negative electrode plate can be obtained.

[0067] It can be understood that the secondary battery provided by the embodiment of the present invention further includes a separator.

[0068] In practical applications, stack the negative electrode plate, separator, and positive electrode plate in sequence and wind them to obtain a wound core, package the wound core to obtain a bare battery cell, bake the bare battery cell, and then perform liquid injection, formation, secondary packaging, and sorting to obtain the above-mentioned secondary battery.

[0069] The present invention also proposes an electrical device. Among them, the electrical device includes the above-mentioned secondary battery, and this secondary battery serves as the power supply of the electrical device.

[0070] For the above-mentioned secondary battery embodiments and electrical device embodiments, they include the above-mentioned electrolyte and can achieve the same technical effects. To avoid repetition, it will not be elaborated here. For relevant parts, refer to the partial description of the electrolyte embodiments.

[0071] In order to make the invention purpose, technical solution, and beneficial effects of the present invention clearer, the present invention will be further described below in conjunction with embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0072] The present invention will be described in detail below through embodiments.

[0073] Embodiment 1

[0074] (1) Preparation of electrolyte:

[0075] At room temperature, in a glove box filled with argon (H 2 O < 1 ppm, O 2 < 1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC) were mixed evenly to obtain an organic solvent; lithium hexafluorophosphate was added to the organic solvent successively, with continuous stirring and cooling with dry ice. When ensuring that the temperature of the electrolyte does not exceed 2 °C during the addition, lithium hexafluorophosphate can be added continuously to obtain a colorless transparent liquid; Pluronic F68 was added to the colorless transparent liquid as the first additive, and the second additives lithium difluorophosphate (LiPO 2 F 2 ), lithium bis(fluorosulfonyl)imide (LiFSI), vinylene sulfate (DTD), vinylene carbonate (VC), propylene sulfite (PS), and fluoroethylene carbonate (FEC) were added to the colorless transparent liquid, and stirred evenly to obtain the electrolyte; wherein, in the electrolyte, the mass ratio of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, vinylene sulfate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, and Pluronic F68 is 19.8:39.6:17.03:3.96:11.08:0.79:0.79:0.79:0.4:0.79:3.97:1.

[0076] (2) Preparation of positive electrode sheet:

[0077] The positive electrode active material Li(Ni 0.8 Mn 0.1 Co 0.1 )O 2 , conductive agent acetylene black, and binder polyvinylidene fluoride were mixed evenly according to the mass ratio of 95:3:2, and uniformly dispersed in 1-methyl-2-pyrrolidone to make a positive electrode slurry. The positive electrode slurry was coated on both sides of the aluminum foil, baked, rolled, and cut into pieces to obtain the positive electrode sheet.

[0078] (3) Preparation of negative electrode sheet

[0079] The negative electrode active material carbon-silicon composite material, conductive agent acetylene black, binder styrene-butadiene rubber, and carboxymethyl cellulose are mixed evenly according to a mass ratio of 95:2:1.5:1.5, and uniformly dispersed in deionized water to prepare a negative electrode paste. The negative electrode paste is coated on both sides of a copper foil, baked, roll-pressed, and cut into pieces to obtain a negative electrode plate.

[0080] (4) Preparation of secondary battery

[0081] The prepared positive electrode plate, separator, and negative electrode plate are stacked in sequence, with the separator placed in the middle of the positive and negative electrode plates. After winding, hot pressing and shaping, and tab welding, a bare battery core is obtained. The bare battery core is placed in an outer packaging aluminum-plastic film and baked in an oven at 85 ± 10 °C for 24 h. The electrolyte prepared in step (1) is injected into the dried battery, and after standing, forming, and grading, a 5.2 Ah ternary silicon-carbon system secondary battery is obtained.

[0082] Examples 2 - 3

[0083] The differences between Examples 2 - 3 and Example 1 are that in step (1), the mass ratios of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, vinylene sulfate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, and Pluronic F68 are 19.96:39.92:17.17:3.99:11.18:0.8:0.8:0.8:0.4:0.8:3.98:0.2 and 19.71:39.41:16.95:3.95:11.02:0.79:0.78:0.78:0.39:0.78:3.94:1.5, respectively.

[0084] Comparative Example 1

[0085] The difference between Comparative Example 1 and Example 1 is that in step (1), the electrolyte does not include the first additive, and in the electrolyte, the mass ratio of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, vinylene sulfate, vinylene carbonate, propylene sulfite, and fluoroethylene carbonate is 20:40:17.2:4:11.2:0.8:0.8:0.8:0.4:0.8:4.

[0086] The components and parameters of the electrolytes in Examples 1 - 3 and Comparative Example 1 are shown in Table 1.

[0087] Table 1

[0088]

[0089] Test method:

[0090] (1) Rate performance test:

[0091] First, at room temperature (25 ± 2 °C), discharge the secondary battery at a current of 1 / 3C to 2.8V and let it stand for 30 min. Then, charge the secondary battery at a current of 1 / 3C to 4.35V and perform constant voltage charging at 4.35V until the current ≤ 0.05C. Finally, after letting the secondary battery stand at room temperature for 30 min, discharge it to the cut-off voltage at different rates (1C, 3C, 5C, and 10C) respectively, and record the discharge capacity and capacity retention rate of the secondary battery at different rates.

[0092] (2) Cycle performance test:

[0093] First, at room temperature (25 ± 2 °C), charge the secondary battery from 1% SOC to 99% SOC at a charging current of 1C. Then, after letting the secondary battery stand for 30 min, discharge it at a current of 1C to the cut-off voltage and let it stand for 60 min. Conduct cycle tests until the number of cycles reaches 1500, or until the discharge capacity of the secondary battery is equal to 80% of the initial discharge capacity.

[0094] Perform rate performance tests on the secondary batteries prepared through Examples 1 to 3 and Comparative Example 1. The test data are shown in Table 2.

[0095] Table 2

[0096]

[0097] According to the test data in Table 2, it can be seen that as the mass percentage of the first additive in the electrolyte increases, both the discharge capacity and capacity retention rate of the secondary battery at different rates show an increasing trend. Specifically, the discharge capacity of the secondary battery prepared through Example 3 when discharged at a rate of 3C is 4.92 Ah, which is 4% higher than 4.73 Ah of Comparative Example 1. The capacity retention rate of the secondary battery prepared through Example 3 when discharged at a rate of 3C is 94.3%, which is 3.7% higher than 90.6% of Comparative Example 1. The discharge capacity of the secondary battery prepared through Example 3 when discharged at a rate of 5C is 4.39 Ah, which is 5.3% higher than 4.17 Ah of Comparative Example 1. The capacity retention rate of the secondary battery prepared through Example 3 when discharged at a rate of 5C is 84.13%, which is 4.2% higher than 79.9% of Comparative Example 1. The discharge capacity of the secondary battery prepared through Example 3 when discharged at a rate of 10C is 3.71 Ah, which is 13.5% higher than 3.27 Ah of Comparative Example 1. The capacity retention rate of the secondary battery prepared through Example 3 when discharged at a rate of 10C is 71.19%, which is 8.5% higher than 62.7% of Comparative Example 1.

[0098] The secondary batteries prepared through Examples 1 to 3 and Comparative Example 1 were subjected to a cycle performance test, and the test data are shown in Table 3.

[0099] Table 3

[0100]

[0101] According to the test data in Table 3, it can be seen that as the mass percentage of the first additive in the electrolyte increases, the cycle capacity retention rate of the secondary battery shows an increasing trend; specifically, when the number of cycles is 500, the capacity retention rate of the secondary battery prepared through Example 3 is 95.46%, which is 3.9% higher than the capacity retention rate of 91.55% of the secondary battery prepared through Comparative Example 1; when the number of cycles is 1000, the capacity retention rate of the secondary battery prepared through Example 3 is 90.45%, which is 5% higher than the capacity retention rate of 85.42% of the secondary battery prepared through Comparative Example 1; when the number of cycles is 1500, the capacity retention rate of the secondary battery prepared through Example 3 is 88.77%, which is 9.6% higher than the capacity retention rate of 79.13% of the secondary battery prepared through Comparative Example 1.

[0102] In summary, the electrolyte provided by the embodiments of the present invention includes a lithium salt, an organic solvent, and a first additive; the first additive includes a polyoxyethylene polyoxypropylene block copolymer, and the polyoxyethylene polyoxypropylene block copolymer includes a compound having the formula (I); wherein, —C 2 H 4 O— in the compound having the formula (I) has strong hydrophilicity and can form hydrogen bonds with water molecules, making the first additive molecules easily disperse uniformly in water, improving the wettability of the electrolyte to the electrode sheet, being beneficial to reducing the interfacial impedance between the electrolyte and the electrode sheet, and improving the rate performance of the secondary battery; —C 3 H 6 O— in the compound having the formula (I) shows certain hydrophobicity and can adsorb on the surface of the solid particles of the active material in the electrode sheet to form a stable emulsion or suspension, which can inhibit the decomposition reaction of the lithium salt, improve the stability of the electrolyte, reduce the degree of side reactions in the secondary battery, and is beneficial to improving the cycle performance of the secondary battery and extending the service life of the secondary battery; further, in the embodiments of the present invention, by controlling the degree of polymerization of —C 2 H 4 O— to be 5 to 200 and the degree of polymerization of —C 3 H 6 O— to be 4 to 250, the hydrophilic-lipophilic balance value of the polyoxyethylene polyoxypropylene block copolymer can be adjusted, which is beneficial to further improving the stability of the electrolyte, reducing the decomposition and volatilization of the electrolyte, thereby further improving the stability of the electrolyte and reducing the degree of side reactions in the secondary battery.

[0103] The above has introduced in detail an electrolyte, a secondary battery and an electrical device provided by the present invention. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. An electrolyte, characterized in that: The invention comprises a lithium salt, an organic solvent and a first additive; the first additive comprises a polyoxyethylene-polyoxypropylene block copolymer, and the polyoxyethylene-polyoxypropylene block copolymer comprises a compound having formula (I): HO(C2H4O) a (C3H6O) b (C2H4O) a Formula H (I); Wherein, a represents the degree of polymerization of -C2H4O-, and a is any integer from 5 to 200; b represents the degree of polymerization of -C3H6O-, and b is any integer from 4 to 250.

2. The electrolyte according to claim 1, characterized in that In the compound of formula (I), —(C 2 H 4 O) a —The relative molecular mass is 100~2200.

3. The electrolyte according to claim 1, characterized in that In the compound of formula (I), —(C 3 H 6 O) b —The relative molecular mass is 100~2000.

4. The electrolyte according to claim 1, characterized in that In the electrolyte, the mass percentage of the first additive is 0.2 wt % to 1.5 wt %.

5. The electrolyte according to claim 1, characterized in that The electrolyte also includes a second additive, which includes at least one of vinylene carbonate, propylene sulfite, vinyl sulfate, vinylene carbonate, fluoroethylene carbonate, lithium bis(oxalatoborate), lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide) and lithium difluorophosphate.

6. The electrolyte according to claim 5, characterized in that In the electrolyte, the mass percentage of the second additive is 5wt% to 10wt%.

7. The electrolyte according to claim 1, characterized in that The organic solvent includes at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

8. The electrolyte according to claim 1, characterized in that In the electrolyte, the mass proportion of the organic solvent is 74wt% to 85wt%.

9. A secondary battery, characterized in that: The secondary battery comprises a positive electrode sheet, a negative electrode sheet and the electrolyte according to any one of claims 1 to 8.

10. An electrical device, characterized in that: The electrical device comprises the secondary battery according to claim 9, and the secondary battery serves as a power supply for the electrical device.

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