A solvent, an electrolyte, a battery, a battery pack, and an electric device

Abstract

The present application provides an electrolyte, a battery, a battery pack, and an electric device, the electrolyte comprising a cyclic sulfite compound represented by formula 1 and / or a cyano phosphate cyclic compound represented by formula 2. The solvent provided by the present application can increase the total entropy value of the electrolyte, adjust the solvation structure of lithium ions, and reduce side reactions by inducing film formation at the electrode interface, thereby helping to improve the cycle stability of the battery at high temperature, the storage life, and the charging efficiency at low temperature.

Description

Technical Field

[0001] This invention belongs to the field of secondary batteries, specifically relating to a solvent, and more particularly to a solvent, electrolyte, battery, battery pack, and electrical equipment. Background Technology

[0002] Lithium-ion batteries are widely used in mobile electronic devices, electric vehicles, drones, and other fields due to their high energy density, long lifespan, and lack of memory effect. With the continuous development of products powered by lithium-ion batteries and the increasing demands for their performance and safety under higher or lower temperature conditions, lithium-ion batteries are facing greater challenges.

[0003] Existing electrolyte systems for lithium-ion batteries mainly include carbonate solvents. Carbonate solvents are prone to decomposition at high temperatures, producing gases and other byproducts, which increases the internal pressure of the battery and affects its high-temperature safety and storage life. At low temperatures, carbonate solvents face the problems of slow reaction kinetics and high lithium-ion desolvation energy, affecting the migration speed of lithium ions and thus affecting the low-temperature charging efficiency of the battery. Summary of the Invention

[0004] This invention provides a solvent that can increase the total entropy of the electrolyte, adjust the solvation structure of lithium ions, and reduce side reactions by inducing film formation at the electrode interface, thereby helping to improve the low-temperature conductivity and high-temperature stability of the electrolyte.

[0005] The present invention also provides an electrolyte that, since it includes the above-mentioned solvent, can simultaneously improve the high-temperature cycling performance, storage performance, and low-temperature charging efficiency of the battery.

[0006] The present invention also provides a battery, which, because it includes the above-mentioned electrolyte, has the advantages of high-temperature cycle stability, long storage life, and high low-temperature charging efficiency.

[0007] The present invention also provides a battery pack, which, since it includes at least two of the above-mentioned batteries, has the characteristics of high / low temperature resistance. Specifically, it can maintain good cycle performance and long storage life at high temperatures and maintain high charging efficiency at low temperatures.

[0008] The present invention also provides an electrical device, which includes the above-mentioned battery or battery pack and has good adaptability to high and low temperatures.

[0009] In a first aspect, the present invention provides a solvent comprising a cyclic sulfite compound of Formula 1 and / or a cyclic cyanophosphate compound of Formula 2.

[0010] Formula 1,

[0011] R1 and R2 are each independently any one of halogen, halogen-substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, and at least one of R1 and R2 includes a halogen atom.

[0012] The cyanophosphate cyclic compound includes the compound shown in Formula 2:

[0013] Equation 2,

[0014] R3 is any one of halogen, halogen-substituted alkyl, or halogen-substituted alkenyl.

[0015] In an alternative embodiment, R1 and R2 are each independently any one of a halogen-substituted or unsubstituted C1-C6 alkyl group or a substituted or unsubstituted C2-C6 alkenyl group.

[0016] And / or, R3 is any one of a halogen-substituted C1-C6 alkyl group or a halogen-substituted C2-C6 alkenyl group.

[0017] In an optional embodiment, at least one of R1 and R2 includes any one of fluorine atom, difluoromethyl, and trifluoromethyl.

[0018] And / or, the R3 includes any one of fluorine atoms, difluoromethyl, and trifluoromethyl.

[0019] In an optional embodiment, the mass ratio of the cyclic sulfite compound to the cyclic cyanophosphate compound ranges from (0.25-4):1.

[0020] In a second aspect, the present invention provides an electrolyte comprising the solvent described in the first aspect.

[0021] In an optional embodiment, the cyclic sulfite compound comprises 1-20% by mass, based on the total mass of the electrolyte.

[0022] And / or, based on the total mass of the electrolyte, the mass percentage of the cyanophosphate cyclic compound is 1-20%.

[0023] In an optional embodiment, the electrolyte further includes a second solvent and an electrolyte salt;

[0024] The second solvent includes at least one of carbonates and their derivatives, and carboxylic acid esters and their derivatives;

[0025] And / or, the electrolyte salt includes at least one of lithium salt, sodium salt, and potassium salt.

[0026] In an optional embodiment, the lithium salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium dioxaborate, lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxaborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and trimethylsilyl trifluoromethanesulfonate.

[0027] In an optional embodiment, the mass percentage of the electrolyte salt is 0.1% to 15% based on the total mass of the electrolyte;

[0028] And / or, based on the total mass of the electrolyte, the mass percentage of the second solvent in the electrolyte is 10%-90%.

[0029] In an optional embodiment, the electrolyte further includes an additive, wherein the additive includes at least one of: fluoroethylene carbonate, vinylene carbonate, ethylene sulfate, ethylene sulfite, 1,3-propanesulfonate lactone, 1,3-propenylsulfonate lactone, and ethylene ethylene carbonate.

[0030] In an alternative embodiment, the additive has a mass percentage content of 0.1%-5% in the electrolyte, based on the total mass of the electrolyte.

[0031] Thirdly, the present invention provides a battery comprising the electrolyte described in the second aspect.

[0032] Fourthly, the present invention provides a battery pack comprising at least two batteries as described in the third aspect.

[0033] Fifthly, the present invention provides an electrical device comprising the battery described in the third aspect or the battery pack described in the fourth aspect.

[0034] The solvent provided by this invention can increase the total entropy of the electrolyte, adjust the solvation structure of lithium ions, and reduce side reactions by inducing film formation at the electrode interface, thereby helping to improve the battery's cycle stability at high temperatures, storage life, and charging efficiency at low temperatures. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 The figures show the test results of low-temperature discharge power performance of Examples 1-13 and Comparative Examples 1-4 of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0038] In this application, references to "an embodiment," "an example," or "an example" mean that a specific feature, structure, or characteristic described in connection with that embodiment, example, or example is included in at least one embodiment of the invention. Therefore, the phrases "an embodiment," "an example," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination.

[0039] Traditional electrolytes using ethylene carbonate (EC) as a solvent face challenges due to their solvent-dominated solvation structure. These challenges include slow reaction kinetics at low temperatures, high lithium-ion desolvation energy, and severe interfacial side reactions at high temperatures.

[0040] To address the aforementioned problems, this invention discovers that introducing a solvent with a specific structure into the electrolyte can increase the total entropy of the electrolyte, adjust the solvation structure of lithium ions, and reduce side reactions by inducing film formation at the electrode interface. This improves the low-temperature performance of the electrolyte while simultaneously maintaining good room-temperature and high-temperature cycling performance. Specifically, this invention provides the following solution:

[0041] In a first aspect, the present invention provides a solvent comprising a cyclic sulfite compound of Formula 1 and / or a cyclic cyanophosphate compound of Formula 2.

[0042] Formula 1,

[0043] R1 and R2 are each independently any one of halogen, halogen-substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, and at least one of R1 and R2 includes a halogen atom.

[0044] The cyanophosphate cyclic compound includes the compound shown in Formula 2:

[0045] Equation 2,

[0046] R3 is any one of halogen, halogen-substituted alkyl, or halogen-substituted alkenyl.

[0047] In this invention, by introducing cyclic sulfite compounds and / or cyclic cyanophosphate compounds with specific structures into the solvent, the high-temperature cycle stability, storage life, and low-temperature charging efficiency of the battery can be effectively improved. The main reasons are as follows: the cyclic sulfite compounds and cyclic cyanophosphate compounds with specific structures can form a halogen-rich solvation structure with the specific solvent as the core. This solvation structure can significantly increase the entropy value of the electrolyte and reduce the energy barrier of the metal ion desolvation process, which helps to improve the low-temperature conductivity of the battery. At the same time, the above-mentioned solvent can also generate an interface film with high ionic conductivity and rich in inorganic matter on the electrode surface, inducing uniform metal deposition behavior, which helps to improve the high-temperature stability of the battery.

[0048] In detail, the aforementioned cyclic sulfite compound readily coordinates with Li-X (where X is at least one of F, Cl, Br, and I) and Li-O to form a solvation sheath of moderate strength. This promotes the desolvation of metal ions at low temperatures, reduces the migration resistance of metal ions in the solvent, and increases their mobility. Furthermore, the cyclic sulfite compound enhances charge balance and dispersion by extracting the electron cloud from S=O and transferring it to halogen atoms, reducing interfacial impedance and thus improving the ionic conductivity of the electrolyte at low temperatures, ensuring the battery's low-temperature performance. In addition, the cyclic sulfite compound exhibits moderate ring strain, enhancing reducing activity and preferentially forming inorganic interfacial films such as metal-rich fluorides and metal sulfites at the negative electrode, thereby suppressing interfacial side reactions and improving the battery's stability at high temperatures.

[0049] Cyclic cyanophosphate compounds can induce the formation of an interfacial film rich in metal halides and metal phosphides on the electrode surface, thereby suppressing side reactions at the electrode interface and improving the stability of the battery at high temperatures. On the other hand, since both cyano groups and halogens have strong electronegativity, this not only increases the oxidation potential of cyclic cyanophosphate compounds, making the electrolyte more stable in high-temperature environments and less prone to oxidation, but also reduces their binding energy with metal ions, thereby promoting the desolvation of metal ions at low temperatures, reducing the migration resistance of metal ions in the electrolyte, and increasing the migration rate of metal ions in the electrolyte, thus ensuring the charging efficiency of the battery at low temperatures.

[0050] To further improve the high-temperature stability and low-temperature charging efficiency of the battery, in some embodiments, the solvent includes cyclic sulfite compounds and cyclic cyanophosphate compounds. When the solvent simultaneously includes both cyclic sulfite compounds and cyclic cyanophosphate compounds, the entropy value of the electrolyte can be further increased, and the solvation structure of the metal ions can be adjusted, enabling the battery to possess both superior low-temperature charging performance and high-temperature cycling performance.

[0051] It is understood that the solvent of the present invention is not only applicable to lithium-ion batteries, but also to secondary batteries such as sodium-ion batteries, potassium-ion batteries, magnesium-ion batteries, and zinc-ion batteries.

[0052] In some embodiments, the halogen is at least one of fluorine, chlorine, bromine, and iodine.

[0053] In some embodiments, the alkyl group can be at least one of straight-chain alkyl, branched alkyl, cycloalkyl, etc.

[0054] In one specific embodiment, R1 and R2 are each independently any one of a halogen-substituted or unsubstituted C1-C6 alkyl group or a substituted or unsubstituted C2-C6 alkenyl group.

[0055] Among them, cyclic sulfite compounds with the above substituents not only have good solubility, which can further ensure that the electrolyte salt can be fully dissolved in them, but also have lower viscosity, which helps to further improve the migration rate of ions, thereby further improving the low-temperature conductivity and overall electrochemical performance of the electrolyte.

[0056] In one specific embodiment, R3 is any one of a halogen-substituted C1-C6 alkyl group or a halogen-substituted C2-C6 alkenyl group.

[0057] Among them, cyanophosphate cyclic compounds with the above substituents can have both good solubility and low viscosity, which can further ensure that the electrolyte salt can be fully dissolved in it, improve the migration rate of ions, and thus further improve the low-temperature conductivity and overall electrochemical performance of the electrolyte.

[0058] In some embodiments, the C1-C6 alkyl groups can be straight-chain alkyl groups of C1-C6 or branched-chain alkyl groups of C3-C6.

[0059] In one specific embodiment, at least one of R1 and R2 includes any one of fluorine atom, difluoromethyl, and trifluoromethyl.

[0060] Among them, the cyclic sulfite compounds with substituents have lower costs and can further reduce solvent viscosity, thereby further improving the low-temperature conductivity of the electrolyte and improving the low-temperature charging efficiency of the battery.

[0061] In one specific embodiment, R3 includes any one of fluorine atom, difluoromethyl, and trifluoromethyl.

[0062] Among them, the cyanophosphate cyclic compounds with substituents have lower costs and can further reduce solvent viscosity, thereby further improving the low-temperature conductivity of the electrolyte and improving the low-temperature charging efficiency of the battery.

[0063] The cyclic sulfite compounds shown in Formulas 1 and 2 can be prepared using conventional processes.

[0064] In some embodiments, the method for preparing the cyclic sulfite compound of formula 1-1 includes the following steps:

[0065] Equation 1-1, 2,2-Difluoro-1,1-ethylene glycol,

[0066] 2,2-Difluoro-1,1-ethylene glycol was subjected to a mono-substitution reaction with thionyl chloride to generate intermediate 1. Intermediate 1 was further subjected to a substitution reaction with thionyl chloride (-25°C) to generate a cyclic sulfite compound of the final formula 1-1.

[0067] In some embodiments, the method for preparing the cyclic sulfite compounds of formulas 1-2 includes the following steps:

[0068] Equation 1-2, Trifluoroacetaldehyde hydrate

[0069] Trifluoroacetaldehyde hydrate was subjected to a monosubstitution reaction with thionyl chloride to generate intermediate 2. Intermediate 2 was further subjected to a substitution reaction with thionyl chloride to generate the final cyclic sulfite compound of formula 1-2.

[0070] The cyanophosphate cyclic compound shown in Formula 2 can be prepared according to conventional processes. In some embodiments, the preparation method of the cyanophosphate cyclic compound shown in Formula 2-1 includes the following steps:

[0071] Equation 2-1,

[0072] A mixed system containing dichlorocyanophosphate, 3,3,3-trifluoro-1,2-propanediol and triethylamine was subjected to a one-step substitution reaction at 45 °C to obtain the cyclic cyanophosphate compound shown in Formula 2-1.

[0073] In some embodiments, the preparation method of the cyanophosphate cyclic compound shown in Formula 2-2 includes the following steps:

[0074] Equation 2-2,

[0075] A mixed system containing dichlorocyanophosphate, 3,3-difluoro-1,2-propanediol and triethylamine was subjected to a one-step substitution reaction at 45 °C to obtain the cyclic cyanophosphate compound shown in Formula 2-2.

[0076] In one specific embodiment, the mass ratio of the cyclic sulfite compound to the cyclic cyanophosphate compound is (0.25-4):1.

[0077] Among them, the cyclic sulfite compound and cyanophosphate cyclic compound in the above ratio can give full play to the advantages of both, synergistically increase the entropy value of the electrolyte, and adjust the solvation structure of metal ions, so that the battery can have better low-temperature charging performance and high-temperature cycling performance.

[0078] In a second aspect, the present invention provides an electrolyte comprising the solvent described in the first aspect.

[0079] Because the electrolyte includes the aforementioned solvents, it can simultaneously improve the battery's high-temperature cycling performance, storage performance, and low-temperature charging efficiency.

[0080] In one specific embodiment, the mass percentage of the cyclic sulfite compound is 1-20% based on the total mass of the electrolyte.

[0081] For example, the mass percentage of the cyclic sulfite compound in the electrolyte is any one of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range of both.

[0082] Among them, the cyclic sulfite compound with the mass percentage mentioned above can further increase the entropy value of the electrolyte and reduce the energy barrier of the metal ion desolvation process, thereby helping to further improve the low-temperature conductivity of the battery; at the same time, it can also generate a denser interface film with high ionic conductivity and rich in inorganic matter on the electrode surface, further improving the high-temperature stability of the battery.

[0083] In one specific embodiment, the mass percentage of the cyanophosphate cyclic compound is 1-20% based on the total mass of the electrolyte.

[0084] For example, the mass percentage of the cyanophosphate cyclic compound in the electrolyte is any one of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range of both.

[0085] As described above, the cyclic cyanophosphate compound at a mass percentage can, on the one hand, induce the formation of a denser interfacial film rich in metal halides and metal phosphides on the electrode surface, thereby suppressing side reactions at the electrode interface and improving the stability of the battery at high temperatures; on the other hand, it can further increase the oxidation potential of the phosphate ester and reduce the binding energy between the phosphate ester and lithium ions, promoting the desolvation of metal ions at low temperatures and improving the migration rate of metal ions in the electrolyte, thereby ensuring the charging efficiency of the battery at low temperatures.

[0086] In one specific embodiment, the electrolyte further includes a second solvent and an electrolyte salt;

[0087] The second solvent includes at least one of carbonates and their derivatives, and carboxylic esters and their derivatives.

[0088] The second solvent described above is completely miscible with the first solvent of the present invention. The carbonate solvent has a low viscosity and can serve as a solvent carrier for the electrolyte, helping to separate cations and anions in the electrolyte and transfer charge between electrodes. It also helps to improve the overall conductivity of the electrolyte, which is beneficial to the charge and discharge efficiency of the battery.

[0089] In one specific embodiment, the electrolyte salt includes at least one of lithium salt, sodium salt, and potassium salt.

[0090] It is understood that the solvent of the present invention is not only applicable to lithium-ion batteries, but also to secondary batteries such as sodium-ion batteries and potassium-ion batteries.

[0091] In one specific embodiment, the lithium salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium dioxaborate, lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxaborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and trimethylsilyl trifluoromethanesulfonate.

[0092] As described above, lithium salts can dissolve better in solvents to form electrolytes with high stability and good lithium conductivity, enabling lithium ions to migrate rapidly in the electrolyte and thus giving the battery superior low-temperature performance.

[0093] In one specific embodiment, the mass percentage of the electrolyte salt is 0.1-15% based on the total mass of the electrolyte.

[0094] The electrolyte salts with the mass percentages mentioned above dissolve better in the solvent and also ensure the appropriate viscosity of the electrolyte, which further guarantees the low-temperature performance of the battery.

[0095] For example, the mass percentage of lithium salt in the electrolyte is any one of 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range of both.

[0096] In one specific embodiment, based on the total mass of the electrolyte, the mass percentage of the second solvent in the electrolyte is 10%-90%.

[0097] For example, the mass percentage of the second solvent in the electrolyte is any one of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or a range of both.

[0098] The second solvent, as described above, at a mass percentage, helps to reduce the economic cost of the electrolyte and further ensures that the electrolyte viscosity is appropriate, allowing lithium ions to migrate rapidly in the electrolyte, thereby further improving the low-temperature charging performance of the battery.

[0099] In one specific embodiment, the electrolyte further includes additives, wherein the additives include at least one of the following: fluoroethylene carbonate, vinylene carbonate, ethylene sulfate, ethylene sulfite, 1,3-propanesulfonate lactone, 1,3-propenylsulfonate lactone, and ethylene ethylene carbonate.

[0100] Among them, the above-mentioned additives have good affinity for the negative electrode surface, which can help the first solvent to build a stable SEI film on the negative electrode surface, and further protect the negative electrode structure from corrosion by solvent molecules, HF, F- and other impurities in the electrolyte.

[0101] In one specific embodiment, the additive has a mass percentage content of 0.1%-5% in the electrolyte, based on the total mass of the electrolyte.

[0102] For example, the mass percentage of the additive in the electrolyte is any one of 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range of both.

[0103] When the electrolyte contains the additives mentioned above, it can better work with the first solvent to form a stable SEI film, thereby further improving the high-temperature stability of the battery.

[0104] Thirdly, the present invention provides a battery comprising the electrolyte described in the second aspect.

[0105] Because it includes the electrolyte mentioned above, this battery has the advantages of high-temperature cycle stability, long storage life, and high low-temperature charging efficiency.

[0106] In one specific embodiment, in addition to the electrolyte provided by this invention, the battery also includes a positive electrode, a negative electrode, and a separator. During the charging and discharging process, active metal ions repeatedly insert and extract between the positive and negative electrode, while the electrolyte acts as a conductor of ions between them. The separator is disposed between the positive and negative electrode, primarily to prevent short circuits between them, while simultaneously allowing ions to pass through.

[0107] This application does not limit the type of separator, and any separator material in existing batteries can be used. For example, separators include, but are not limited to, single-layer PP (polypropylene) membranes, single-layer PE (polyethylene) membranes, double-layer PP / PE membranes, double-layer PP / PP membranes, and triple-layer PP / PE / PP membranes.

[0108] This application does not limit the positive electrode active material in the positive electrode sheet. It can be the positive electrode active material commonly used in existing batteries. For example, the positive electrode active material includes, but is not limited to, at least one composite oxide of lithium and metals such as cobalt, manganese, nickel and combinations thereof.

[0109] This application does not limit the negative electrode active material in the negative electrode sheet. It can be a negative electrode active material commonly used in existing batteries. For example, the negative electrode active material includes, but is not limited to, at least one of graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode material, tin-based negative electrode material, etc.

[0110] The battery of the present invention can be manufactured according to conventional methods in the art. For example, the positive electrode, separator and negative electrode can be stacked in sequence and assembled into a cell by winding or stacking process. After packaging and baking, electrolyte is injected and then the battery is manufactured by hot pressing and other processes.

[0111] Fourthly, the present invention provides a battery pack comprising at least two batteries as described in the second aspect.

[0112] Since the battery pack includes at least two of the aforementioned batteries, it is characterized by high and low temperature resistance, specifically maintaining good cycle life and long storage life at high temperatures, and maintaining high charging efficiency at low temperatures.

[0113] Typically, a battery pack includes at least two of the aforementioned batteries, which are connected as individual cells to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods.

[0114] Fifthly, the present invention provides an electrical device comprising the battery described in the third aspect or the battery pack described in the fourth aspect.

[0115] Since the electrical equipment includes the aforementioned batteries or battery packs, it has good adaptability to high and low temperatures.

[0116] The electrical equipment used in the embodiments of the present invention can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no particular limitations on this.

[0117] The technical solution of the present invention will be further illustrated below with reference to specific embodiments. All parts, percentages and ratios recorded in the following embodiments are based on weight. All reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing. The instruments used in the embodiments are also commercially available.

[0118] Example 1

[0119] This example provides an electrolyte comprising a solvent composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), a cyclic sulfite compound, and a cyclic cyanophosphate compound, wherein the cyclic sulfite compound has the structure of Formula 1-1, and the cyclic cyanophosphate compound has the structure of Formula 2-1. Based on the total mass of the electrolyte, the solvent accounts for 87% of the mass of the electrolyte.

[0120] The lithium salt is a mixture of LiPF6 and LiFSI, and the mass percentage of the lithium salt is 6% LiPF6 + 4% LiFSI based on the total mass of the electrolyte.

[0121] The additive is vinylene carbonate (VC), and the mass percentage of VC in the electrolyte is 3% based on the total mass of the electrolyte.

[0122] Its preparation method includes the following steps:

[0123] In a glove box (H2O<0.5 ppm, O2<0.5 ppm), the additives, lithium salt and solvent were mixed in the mass ratio and stirred thoroughly according to the formula in Table 1 to obtain electrolyte C1.

[0124] Example 2

[0125] The electrolyte was prepared using the same method as in Example 1, except that electrolyte C2 was prepared according to the formula in Table 1.

[0126] Example 3

[0127] The electrolyte was prepared using the same method as in Example 1, except that electrolyte C3 was prepared according to the formula in Table 1.

[0128] Example 4

[0129] The electrolyte was prepared using the same method as in Example 1, except that electrolyte C4 was prepared according to the formula in Table 1.

[0130] Example 5

[0131] The electrolyte was prepared using the same method as in Example 1, except that electrolyte C5 was prepared according to the formula in Table 1.

[0132] Example 6

[0133] The electrolyte was prepared using the same method as in Example 1, except that electrolyte C6 was prepared according to the formula in Table 1.

[0134] Example 7

[0135] The electrolyte was prepared using the same method as in Example 1, except that electrolyte C7 was prepared according to the formula in Table 1.

[0136] Example 8

[0137] The electrolyte was prepared using the same method as in Example 1, except that electrolyte C8 was prepared according to the formula in Table 1.

[0138] Example 9

[0139] The electrolyte was prepared using the same method as in Example 1, except that electrolyte C9 was prepared according to the formula in Table 1.

[0140] Example 10

[0141] The electrolyte was prepared using the same method as in Example 1, except that electrolyte C10 was prepared according to the formula in Table 1.

[0142] Example 11

[0143] The electrolyte was prepared using the same method as in Example 1, except that electrolyte C11 was prepared according to the formula in Table 1.

[0144] Example 12

[0145] The electrolyte was prepared using the same method as in Example 1, except that electrolyte C12 was prepared according to the formula in Table 1.

[0146] Example 13

[0147] The electrolyte was prepared using the same method as in Example 1, except that electrolyte C13 was prepared according to the formula in Table 1.

[0148] Comparative Example 1

[0149] The electrolyte was prepared using the same method as in Example 1, except that electrolyte D1 was prepared according to the formula in Table 1.

[0150] Comparative Example 2

[0151] The electrolyte was prepared using the same method as in Example 1, except that electrolyte D2 was prepared according to the formula in Table 1.

[0152] Comparative Example 3

[0153] The electrolyte was prepared using the same method as in Example 1, except that electrolyte D3 was prepared according to the formula in Table 1.

[0154] Comparative Example 4

[0155] The electrolyte was prepared using the same method as in Example 1, except that electrolyte D4 was prepared according to the formula in Table 1.

[0156] Table 1

[0157]

[0158] Test case

[0159] Batteries were prepared using the electrolytes from the above embodiments and comparative examples, respectively, including the following steps:

[0160] Preparation of the positive electrode sheet: The positive electrode material is, for example, lithium iron phosphate; the binder is, for example, polyvinylidene fluoride; and the conductive agent is, for example, acetylene black. The positive electrode material, acetylene black, and polyvinylidene fluoride are mixed, for example, in a weight ratio of 95:3:2. An organic solvent is added and stirred until the system is homogeneous to obtain a positive electrode slurry. The organic solvent is, for example, N-methylpyrrolidone. The positive electrode slurry is uniformly coated onto aluminum foil, and the aluminum foil is dried, for example, in a forced-air drying oven or a vacuum drying oven. The dried aluminum foil is then cold-pressed to obtain the positive electrode sheet. Its single-sided areal density is 225 g / m³. 2 ;

[0161] Preparation of the negative electrode sheet: The negative electrode material is selected from graphite, the conductive agent is selected from acetylene black, the binder is selected from styrene-butadiene rubber, and the thickener is selected from sodium carboxymethyl cellulose. Graphite, acetylene black, styrene-butadiene rubber, and sodium carboxymethyl cellulose are mixed in a mass ratio of 96:2:1:1, deionized water is added, and the mixture is stirred thoroughly to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on copper foil, and after drying and cold pressing, a negative electrode sheet is obtained. Its single-sided areal density is 97.5 g / m². 2 ;

[0162] Battery Assembly: The following operations are performed under an environment with a dew point ≤ -40℃: The positive electrode sheet is die-cut to 72mm long and 61mm wide, and the negative electrode sheet is die-cut to 74mm long and 63mm wide. 15 positive electrode sheets, 16 negative electrode sheets, and the separator are stacked sequentially. After stacking, the sheets are placed in a suitably sized punched aluminum-plastic film packaging bag. Hot-press sealing is performed under the following conditions: 950kg pressure, 60℃ for 20 seconds. 12.5g of electrolyte is injected from the unsealed side. The final sealing area is then hot-pressed under a vacuum of -90KPa using a heat sealer. This completes the production of a small pouch battery with a designed capacity of 3Ah.

[0163] Formation / Capacity Testing: After the prepared batteries are left to rest, they are first charged at 0.05C for 4 hours at 25°C, then left to rest for 10 minutes, and then charged at a higher current of 0.2C to the cutoff voltage of 3.75V to form a stable and dense SEI film. After aging at 50°C for 72 hours, the batteries are first discharged at 1C constant current to 2.2V at 25°C, then charged at 1C constant current and constant voltage to 3.75V, and finally discharged at 1C constant current to 2.2V. Batteries with similar capacities are selected for testing.

[0164] The batteries prepared with the electrolytes of the above embodiments are designated as B1 to B13, and the batteries prepared with the electrolytes of the comparative examples are designated as RB1 to RB4.

[0165] Test case

[0166] The following tests were performed on the batteries in the test cases:

[0167] 1) Low-temperature power performance test:

[0168] The domestically produced Landian CT2001C test cabinet was used for testing. The low-temperature charging capability test conditions were as follows: the battery was charged at 3.45V constant voltage at 25℃, with a cutoff current of 0.05C; then discharged at 1C constant current to 2.0V; stored at -20℃ for 8 hours; charged at 3.45V constant voltage, with the upper limit current limited to 3C and the cutoff current at 0.05C; the battery was then returned to room temperature for 6 hours and discharged at 1C constant current to 2.0V. The corresponding charge and discharge capacity and time curves were recorded.

[0169] The battery was stored at -35℃ for 8 hours, charged at a constant voltage of 3.45V, with the upper limit current limited to 3C and the cutoff current to 0.05C. Afterward, the battery was allowed to return to room temperature for 6 hours, and then discharged at a constant current of 1C to 2.0V. The corresponding charge / discharge capacity and time curves were recorded. Ten battery groups were used for each example and comparative example, and the average value of the test results was taken.

[0170] The calculation formula is: Low temperature charging capacity @ 100% SOC = Low temperature charging capacity / 25℃ discharge capacity * 100%. The test results are shown in Table 2.

[0171] 2) Low-temperature discharge power performance test:

[0172] The domestically produced Landian CT2001C test cabinet was used for testing. The low-temperature discharge capability test conditions were as follows: the battery was charged at a constant voltage of 3.45V at room temperature, with the upper limit current limited to 3C and the cutoff current to 0.05C; it was placed in a -35℃ environment for 12 hours, followed by a 5C discharge for 1 second and a 2.5C discharge for 9 seconds; the corresponding discharge time curves were recorded, and the terminal voltage at the end of the discharge was selected. Ten sets of batteries were set up for each example and comparative example, and the average value of the test results was taken. The test results are as follows. Figure 1 As shown.

[0173] 3) High-temperature cycling performance test:

[0174] The domestically produced Landian CT2001C test cabinet was used for testing. The specific test conditions were as follows: the soft-pack battery was cycled 500 times at 1C current between 2.00V and 3.75V at 60℃; the initial discharge capacity was recorded; after 500 charge-discharge cycles, the discharge capacity of the 500th cycle was recorded; and the capacity retention rate of the battery after high-temperature cycling was calculated. Ten sets of batteries were set up for each example and comparative example, and the average value of the test results was taken.

[0175] The calculation formula is: Capacity retention rate (%) after 500 cycles = Discharge capacity after 500 cycles / Initial discharge capacity × 100%. The test results are shown in Table 3.

[0176] 4) High-temperature storage performance test:

[0177] The specific test conditions were as follows: the battery was stored in a 60°C constant temperature chamber for 30 days under a constant current and voltage of 3.75V at 1C until the current cutoff at 0.05C. The capacity retention rate of the battery after high-temperature storage was calculated. Ten sets of batteries were used in each example and comparative example, and the average value of the test results was taken.

[0178] The calculation formula is: 30D storage capacity recovery rate (%) = discharge capacity after 30 days of storage / initial discharge capacity × 100%. The test results are shown in Table 3.

[0179] Table 2

[0180]

[0181] As shown in Table 2, compared with the comparative example, the electrolyte in the embodiment helps to further improve the low-temperature charging performance of the battery.

[0182] Table 3

[0183]

[0184] As shown in Table 3, compared with the comparative example, the electrolyte in the embodiment helps to further improve the high-temperature storage performance and cycle performance of the battery.

[0185] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A solvent, characterized in that, Including the cyclic sulfite compounds shown in Formula 1 and / or the cyclic cyanophosphate compounds shown in Formula 2, Formula 1, Wherein, R1 and R2 are each independently either fluorine or fluorine-substituted alkyl groups; The cyanophosphate cyclic compound includes the compound shown in Formula 2: Equation 2, R3 is any one of fluorine or fluorine-substituted alkyl groups.

2. The solvent according to claim 1, characterized in that, R1 and R2 are each independently fluorinated C1-C6 alkyl groups; And / or, R3 is a fluorine-substituted C1-C6 alkyl group.

3. The solvent according to claim 2, characterized in that, At least one of R1 and R2 includes any one of fluorine atom, difluoromethyl, and trifluoromethyl; And / or, the R3 includes any one of fluorine atoms, difluoromethyl, and trifluoromethyl.

4. The solvent according to any one of claims 1-3, characterized in that, The mass ratio of the cyclic sulfite compound to the cyclic cyanophosphate compound is in the range of (0.25-4):

1.

5. An electrolyte, characterized in that, Includes the solvent described in any one of claims 1-4.

6. The electrolyte according to claim 5, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the cyclic sulfite compound is 1-20%; And / or, based on the total mass of the electrolyte, the mass percentage of the cyanophosphate cyclic compound is 1-20%.

7. The electrolyte according to claim 5 or 6, characterized in that, The electrolyte also includes a second solvent and an electrolyte salt; The second solvent includes at least one of carbonates and their derivatives, and carboxylic acid esters and their derivatives; And / or, the electrolyte salt includes at least one of lithium salt, sodium salt, and potassium salt.

8. The electrolyte according to claim 7, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium dioxaborate, lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxaborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and trimethylsilyl trifluoromethanesulfonate.

9. The electrolyte according to claim 7, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the electrolyte salt is 0.1% to 15%. And / or, based on the total mass of the electrolyte, the mass percentage of the second solvent in the electrolyte is 50%-90%.

10. The electrolyte according to claim 8, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the electrolyte salt is 0.1% to 15%. And / or, based on the total mass of the electrolyte, the mass percentage of the second solvent in the electrolyte is 50%-90%.

11. The electrolyte according to claim 5, characterized in that, The electrolyte further includes additives, wherein the additives include at least one of the following: fluoroethylene carbonate, ethylene carbonate, ethylene sulfate, ethylene sulfite, 1,3-propanesulfonate lactone, 1,3-propenylsulfonate lactone, and ethylene carbonate.

12. The electrolyte according to claim 7, characterized in that, The electrolyte further includes additives, wherein the additives include at least one of the following: fluoroethylene carbonate, ethylene carbonate, ethylene sulfate, ethylene sulfite, 1,3-propanesulfonate lactone, 1,3-propenylsulfonate lactone, and ethylene carbonate.

13. The electrolyte according to any one of claims 6, 8-10, characterized in that, The electrolyte further includes additives, wherein the additives include at least one of the following: fluoroethylene carbonate, ethylene carbonate, ethylene sulfate, ethylene sulfite, 1,3-propanesulfonate lactone, 1,3-propenylsulfonate lactone, and ethylene carbonate.

14. The electrolyte according to claim 11 or 12, characterized in that, Based on the total mass of the electrolyte, the additive has a mass percentage content of 0.1%-5% in the electrolyte.

15. The electrolyte according to claim 13, characterized in that, Based on the total mass of the electrolyte, the additive has a mass percentage content of 0.1%-5% in the electrolyte.

16. A battery, characterized in that, Includes the electrolyte as described in any one of claims 1-15.

17. A battery pack, characterized in that, It includes at least two batteries as described in claim 16.

18. An electrical appliance, characterized in that, Includes the battery of claim 16 or the battery pack of claim 17.

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