Solvent, electrolyte, battery, battery pack and electric equipment

Abstract

The invention provides an electrolyte, a battery, a battery pack and electric equipment. The electrolyte comprises a cyclic sulfite compound as shown in a formula 1 and / or a cyano phosphate cyclic compound as shown in a formula 2. According to the solvent provided by the invention, the total entropy value of an electrolyte can be increased, the solvation structure of lithium ions can be adjusted, and side reactions are reduced by inducing film formation on an electrode interface, so that the cycle stability and the storage life of a battery at a high temperature and the charging efficiency at a low temperature can be improved.

Description

Technical Field

[0001] The present invention belongs to the field of secondary batteries, and specifically relates to a solvent, and in particular to a solvent, an electrolyte, a battery, a battery pack, and an electrical device. Background Art

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

[0003] The electrolyte system of existing lithium-ion batteries mainly includes carbonate solvents. Among them, carbonate solvents are prone to decomposition at high temperatures, producing gases and other byproducts, which lead to increased internal pressure of the battery and affect the high-temperature safety and storage life of the battery; at low temperatures, carbonate solvents face the problems of slow reaction kinetics and high lithium ion desolvation energy, which affects the migration speed of lithium ions and thus the low-temperature charging efficiency of the battery. Summary of the Invention

[0004] The present invention provides a solvent that can increase the total entropy of an electrolyte, regulate 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. Since the electrolyte includes the above-mentioned solvent, it can simultaneously improve the high-temperature cycle, storage performance and low-temperature charging efficiency of the battery.

[0006] The present invention also provides a battery. Since the battery includes the above-mentioned electrolyte, the battery 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. Since the battery pack includes at least two of the above-mentioned batteries, the battery pack has the characteristics of high / low temperature resistance. Specifically, it can maintain good cycleability 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 high and low temperature adaptability.

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

[0010]

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

[0012] The cyanophosphate cyclic compound includes a compound represented by Formula 2:

[0013]

[0014] Here, R3 is any one of halogen, halogen-substituted alkyl, and 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 and a halogen-substituted C2-C6 alkenyl group.

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

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

[0019] In an optional embodiment, the mass ratio of the cyclic sulfite compound to the cyanophosphate cyclic compound is in the range of (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, based on the total mass of the electrolyte, the mass percentage of the cyclic sulfite compound is 1-20%;

[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 comprises a second solvent and an electrolyte salt;

[0024] Wherein, the second solvent comprises at least one of carbonate and its derivatives, carboxylate and its 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 bis(oxalatoborate), lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide) and trimethylsilyl trifluoromethanesulfonate.

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

[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, vinyl sulfate, vinyl sulfite, 1,3-propane sultone, 1,3-propene sultone, and vinyl ethylene carbonate.

[0030] In an optional embodiment, based on the total mass of the electrolyte, the mass percentage of the additive in the electrolyte is 0.1%-5%.

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

[0032] In a fourth aspect, the present invention provides a battery pack comprising at least two batteries according to the third aspect.

[0033] In a fifth aspect, 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 the present 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 cycle stability and storage life of the battery at high temperatures and the charging efficiency at low temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the following briefly introduces the drawings required for use in the embodiments of the present invention or related technologies. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0036] Figure 1 Graph showing the low-temperature discharge power performance test results of Examples 1-13 of the present invention and Comparative Examples 1-4. DETAILED DESCRIPTION

[0037] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0038] Throughout this application, references to "one embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment, embodiment, or example is included in at least one embodiment of the present invention. Therefore, appearances of the phrases "one embodiment," "an embodiment," "an example," or "an example" in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable combinations and / or subcombinations in one or more embodiments or examples.

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

[0040] To address the above issues, the present invention discovered 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, thereby improving the low-temperature performance of the electrolyte while also taking into account both room-temperature and high-temperature cycle performance. Specifically, the present invention provides the following solutions:

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

[0042]

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

[0044] The cyanophosphate cyclic compound includes a compound represented by Formula 2:

[0045]

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

[0047] In the present invention, by introducing a cyclic sulfite compound and / or a cyanophosphate cyclic compound of a specific structure 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 include: the cyclic sulfite compound and the cyanophosphate cyclic compound of the specific structure can form a halogen-rich solvation structure with a 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 a high ionic conductivity and inorganic-rich interface film on the electrode surface, inducing uniform metal deposition behavior, which helps to improve the high-temperature stability of the battery.

[0048] Specifically, the cyclic sulfite compound readily coordinates with Li-X (X is at least one of F, Cl, Br, and I) and Li-O, forming a moderately strong solvation sheath. This promotes the desolvation of metal ions at low temperatures, reduces the resistance to metal ion migration in the solvent, and improves the mobility of metal ions in the solvent. Furthermore, the cyclic sulfite compound extracts the electron cloud of S=O and transfers it to the halogen atom, enhancing the balanced charge dispersion and reducing the interfacial impedance of the electrode, thereby improving the ionic conductivity of the electrolyte at low temperatures and ensuring the low-temperature performance of the battery. Furthermore, the cyclic sulfite compound has moderate ring tension, enhances reduction activity, and preferentially forms an inorganic interfacial film rich in metal fluoride and metal sulfite at the negative electrode, thereby suppressing interfacial side reactions and improving the stability of the battery at high temperatures.

[0049] On the one hand, cyanophosphate cyclic compounds can induce the formation of an interfacial film rich in metal halides and metal phosphides on the electrode surface, thereby inhibiting side reactions at the electrode interface and improving the stability of the battery at high temperatures. On the other hand, since both cyano and halogen have strong electronegativity, this not only increases the oxidation potential of the cyanophosphate cyclic compound, making the electrolyte more stable in a high-temperature environment and less susceptible to oxidation, but also reduces its 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 improving the mobility of metal ions in the electrolyte, thereby 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 a cyclic sulfite compound and a cyclic cyanophosphate compound. When the solvent includes both a cyclic sulfite compound and a cyclic cyanophosphate compound, the entropy of the electrolyte can be further increased, the solvation structure of the metal ions can be adjusted, and the battery can achieve both superior low-temperature charging performance and high-temperature cycling performance.

[0051] It can be 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 may be at least one of a linear alkyl group, a branched alkyl group, a cycloalkyl group, and the like.

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

[0055] Among them, the cyclic sulfite compound having the above substituents not only has good solubility, which can further ensure that the electrolyte salt can be fully dissolved therein, but also has a lower viscosity, which helps to further increase the migration speed 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 and a halogen-substituted C2-C6 alkenyl group.

[0057] Among them, the cyanophosphate cyclic compound having the above substituents can have both good solubility and low viscosity, which can further ensure that the electrolyte salt can be fully dissolved therein, increase the migration speed 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 group may be a C1-C6 straight-chain alkyl group or a C3-C6 branched-chain alkyl group.

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

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

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

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

[0063] The cyclic sulfite compound represented by Formula 1 and Formula 2 can be prepared according to a conventional process.

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

[0065]

[0066] The intermediate product 1 is generated by performing a single substitution reaction on 2,2-dichloro-1,1-ethanediol with phosphorus dichloride cyanide, and the final cyclic sulfite compound of Formula 1-1 is generated by further performing a substitution reaction on the intermediate product 1 with phosphorus dichloride cyanide (-25°C).

[0067] In some embodiments, the method for preparing the cyclic sulfite compound of Formula 1-2 includes the following process:

[0068]

[0069] The intermediate product 2 is generated by performing a single substitution reaction on trifluoroacetaldehyde hydrate with phosphorus dichloride cyanide, and the final cyclic sulfite compound of Formula 1-2 is generated by further performing a substitution reaction on the intermediate product 2 with phosphorus dichloride cyanide.

[0070] The cyclic cyanophosphate compound represented by Formula 2 can be prepared according to a conventional process, and in some embodiments, the method for preparing the cyclic cyanophosphate compound represented by Formula 2-1 includes the following process:

[0071]

[0072] A one-step substitution reaction is performed on a mixture containing phosphorus dichlorocyanide, 3,3,3-trifluoro-1,2-propanediol, and triethylamine at 45°C to obtain the cyclic cyanophosphate compound represented by Formula 2-1.

[0073] In some embodiments, the method for preparing the cyclic cyanophosphate compound represented by Formula 2-2 includes the following process:

[0074]

[0075] A one-step substitution reaction is performed on a mixture containing phosphorus dichlorocyanide, 3,3-difluoro-1,2-propanediol, and triethylamine at 45°C to obtain the cyclic cyanophosphate compound represented by Formula 2-2.

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

[0077] The cyclic sulfite compound and the cyanophosphonate cyclic compound in the above ratio can fully exert the advantages of both, synergistically increase the entropy of the electrolyte, adjust the solvation structure of the metal ions, and can make the battery have more excellent low-temperature charging performance and high-temperature cycle performance.

[0078] In a second aspect, the present application provides an electrolyte comprising the solvent of the first aspect.

[0079] Since the electrolyte comprises the above solvent, it can simultaneously improve the high-temperature cycle, storage, and low-temperature charging efficiency of the battery.

[0080] In a 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 consisting of any two of them.

[0082] The cyclic sulfite compound with the above mass percentage can further increase the entropy of the electrolyte, reduce the energy barrier of the desolvation process of the metal ions, thereby further improving the low-temperature conductivity of the battery; at the same time, it can also generate a more dense interface film rich in inorganic matter on the electrode surface, further improving the high-temperature stability of the battery.

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

[0084] For example, the mass percentage of the cyanophosphonate 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 consisting of any two of them.

[0085] The cyanophosphonate cyclic compound with the above mass percentage can on the one hand induce the formation of a more dense interface film rich in metal halide and metal phosphide on the electrode surface, thereby inhibiting the side reaction at the electrode interface and improving the stability of the battery at high temperature; on the other hand, it can further increase the oxidation potential of the phosphonate and reduce the binding energy between the phosphonate and lithium ions, promote the desolvation of the metal ions at low temperature, and improve the mobility of the metal ions in the electrolyte, thereby ensuring the charging efficiency of the battery at low temperature.

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

[0087] Wherein, the second solvent includes at least one of carbonate and its derivatives, carboxylic acid ester and its 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 be used as a solvent carrier for the electrolyte, helping to separate cations and anions in the electrolyte and transfer charges between the electrodes. At the same time, it helps to improve the conductivity of the entire electrolyte, which is beneficial to the charge and discharge efficiency of the battery.

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

[0090] It can be 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 a specific embodiment, the lithium salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalatoborate), lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide) and trimethylsilyl trifluoromethanesulfonate.

[0092] In the above-described embodiment, the lithium salt can be better dissolved in the solvent to form an electrolyte with high stability and good lithium conductivity, so that lithium ions can migrate quickly in the electrolyte, thereby making the battery exhibit better low-temperature performance.

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

[0094] The electrolyte salt with the above-mentioned mass percentage can be better dissolved in the solvent and can make the viscosity of the electrolyte appropriate, which can further ensure the low-temperature performance of the battery.

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

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

[0097] Illustratively, in the electrolyte, the mass percentage of the second solvent is any value among 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc., or a range consisting of both values.

[0098] The second solvent in the above-mentioned mass percentage is beneficial to reducing the economic cost of the electrolyte and can further ensure that the viscosity of the electrolyte is appropriate, so that lithium ions can migrate quickly in the electrolyte, thereby further improving the low-temperature charging performance of the battery.

[0099] In a specific embodiment, the electrolyte further includes an additive, wherein the additive includes at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinyl sulfite, 1,3-propane sultone, 1,3-propene sultone, and vinyl ethylene carbonate.

[0100] Among them, the above-mentioned additives have good affinity for the negative electrode surface, can assist the first solvent in building 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 a specific embodiment, based on the total mass of the electrolyte, the mass percentage of the additive in the electrolyte is 0.1%-5%.

[0102] Illustratively, in the electrolyte, the mass percentage of the additive is any value among 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc., or a range consisting of both values.

[0103] When the electrolyte includes the additive in the above-mentioned content, it can better construct a stable SEI film together with the first solvent, thereby further improving the high-temperature stability of the battery.

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

[0105] Due to the inclusion of the above-mentioned electrolyte, the battery has the advantages of high-temperature cycle stability, long storage life, and high low-temperature charging efficiency.

[0106] In one embodiment, in addition to the electrolyte provided by the present invention, the battery also includes a positive electrode sheet, a negative electrode sheet, and a separator. During the battery's charge and discharge process, active metal ions are intercalated and released between the positive and negative electrodes, and the electrolyte acts as an ion conductor between the positive and negative electrodes. The separator is disposed between the positive and negative electrodes, primarily preventing short circuits between the positive and negative electrodes while allowing ions to pass through.

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

[0108] The present application does not limit the positive electrode active material in the positive electrode sheet, which can be a 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 a metal selected from the group consisting of cobalt, manganese, nickel, and combinations thereof.

[0109] The present application does not limit the negative electrode active material in the negative electrode sheet, which 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 microbeads, silicon-based negative electrode materials, tin-based negative electrode materials, etc.

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

[0111] In a fourth aspect, the present invention provides a battery pack comprising at least two batteries according to the second aspect.

[0112] Since the battery pack includes at least two of the above batteries, the battery pack 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.

[0113] Generally, a battery pack includes at least two of the above-mentioned batteries, which are connected as single cells to form a battery pack. The batteries can be electrically connected by conventional methods in the art, such as series connection, parallel connection, or a combination of these connection methods.

[0114] In a fifth aspect, 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 battery or battery pack, it has good high and low temperature adaptability.

[0116] The electrical equipment in the embodiments of the present invention can be conventional electrical equipment in this field, such as power equipment (such as electric vehicles, electric cars), electronic equipment (such as mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (such as watches, bracelets, VR glasses, etc.), energy storage power stations, etc., without special restrictions.

[0117] The technical solutions of the present application are further illustrated below in combination with specific examples. All the parts, percentage contents and ratios recorded in the following examples are based on weight, and all the reagents used in the examples are commercially available or synthesized according to conventional methods and can be directly used without further treatment, and the instruments used in the examples are commercially available.

[0118] Example 1

[0119] This example provides an electrolyte, which comprises a solvent composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), a cyclic sulfite compound and a cyano phosphate cyclic compound, wherein the cyclic sulfite compound has a structure of formula 1-1, and the cyano phosphate cyclic compound has a structure of formula 2-1. The mass percentage of the solvent in the electrolyte is 87% based on the total 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] A preparation method thereof comprises the following steps:

[0123] The additive, the lithium salt and the solvent are mixed in a glove box (H2O < 0.5 ppm, O2 < 0.5 ppm) according to the mass ratio, and the electrolyte C1 is obtained by fully stirring and mixing according to the formulation in Table 1.

[0124] Example 2

[0125] The electrolyte is prepared in the same way as in Example 1, except that the electrolyte C2 is prepared according to the formulation in Table 1.

[0126] Example 3

[0127] The electrolyte is prepared in the same way as in Example 1, except that the electrolyte C3 is prepared according to the formulation in Table 1.

[0128] Example 4

[0129] The electrolyte is prepared in the same way as in Example 1, except that the electrolyte C4 is prepared according to the formulation in Table 1.

[0130] Example 5

[0131] The electrolyte is prepared in the same way as in Example 1, except that the electrolyte C5 is prepared according to the formulation in Table 1.

[0132] Example 6

[0133] An electrolyte was prepared in the same manner as Example 1, except that electrolyte C6 was prepared according to the formulation in Table 1.

[0134] Example 7

[0135] An electrolyte was prepared in the same manner as Example 1, except that electrolyte C7 was prepared according to the formulation in Table 1.

[0136] Example 8

[0137] An electrolyte was prepared in the same manner as Example 1, except that electrolyte C8 was prepared according to the formulation in Table 1.

[0138] Example 9

[0139] An electrolyte was prepared in the same manner as Example 1, except that electrolyte C9 was prepared according to the formulation in Table 1.

[0140] Example 10

[0141] An electrolyte was prepared in the same manner as Example 1, except that electrolyte C10 was prepared according to the formulation in Table 1.

[0142] Example 11

[0143] An electrolyte was prepared in the same manner as Example 1, except that electrolyte C11 was prepared according to the formulation in Table 1.

[0144] Example 12

[0145] An electrolyte was prepared in the same manner as Example 1, except that electrolyte C12 was prepared according to the formulation in Table 1.

[0146] Example 13

[0147] An electrolyte was prepared in the same manner as Example 1, except that electrolyte C13 was prepared according to the formulation in Table 1.

[0148] Comparative Example 1

[0149] An electrolyte was prepared in the same manner as Example 1, except that electrolyte D1 was prepared according to the formulation in Table 1.

[0150] Comparative Example 2

[0151] An electrolyte was prepared in the same manner as Example 1, except that electrolyte D2 was prepared according to the formulation in Table 1.

[0152] Comparative Example 3

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

[0154] Comparative Example 4

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

[0156] Table 1

[0157]

[0158]

[0159] Test Example

[0160] The electrolyte of each of the above examples and comparative examples was used to prepare a battery, including the following steps:

[0161] Preparation of the positive electrode sheet: the positive electrode material is, for example, lithium iron phosphate, the binder is, for example, selected from polyvinylidene fluoride, and the conductive agent is, for example, selected from acetylene black. The positive electrode material, acetylene black and polyvinylidene fluoride are mixed, for example, in a ratio of 95:3:2 by weight, and then an organic solvent is added and stirred until the system is uniform to obtain a positive electrode slurry. The organic solvent is, for example, selected from N-methyl pyrrolidone. The positive electrode slurry is uniformly coated on an aluminum foil, and the aluminum foil is dried, for example, in a forced air drying oven or a vacuum drying oven, and then the dried aluminum foil is cold-pressed, and the like, to obtain a positive electrode sheet. The single-sided area density of the positive electrode sheet is 225 g / m 2 ;

[0162] Preparation of the negative electrode sheet: the negative electrode material is, for example, selected from graphite, the conductive agent is, for example, selected from acetylene black, the binder is, for example, selected from styrene-butadiene rubber, and the thickening agent is, for example, selected from sodium carboxymethyl cellulose. The graphite, acetylene black, styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed, for example, in a mass ratio of 96:2:1:1, and then deionized water is added and stirred to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on a copper foil, and then dried and cold-pressed to obtain a negative electrode sheet. The single-sided area density of the negative electrode sheet is 97.5 g / m 2 ;

[0163] Assembly of the battery: the following operations were performed in an environment with a dew point ≤-40°C: the positive electrode sheet was die-cut to 72 mm long and 61 mm wide, and the negative electrode sheet was die-cut to 74 mm long and 63 mm wide. Fifteen positive electrode sheets, sixteen negative electrode sheets and a separator were sequentially stacked. After stacking, the stack was placed in a packaging bag made of aluminum plastic film with a suitable size. Hot-pressing packaging was performed under the following process conditions: a pressure of 950 kg and a temperature of 60°C for 20 seconds. 12.5 g of electrolyte was injected from the side that was not yet sealed. The final sealing area was hot-pressed and sealed under a vacuum of-90 KPa using a heat sealer, and a small soft-pack battery was obtained after completion. The design capacity of the battery was 3 Ah.

[0164] Formation / priming: the prepared battery was first charged at 0.05C current for 4h at 25℃ environment, after 10min rest, then charged to cut-off voltage 3.75V at 0.2C larger current to form stable and compact SEI film. After 72h aging at 50℃, the battery was first discharged at 1C constant current to 2.2V at 25℃ environment, then charged to 3.75V at 1C constant current and constant voltage, and finally discharged to 2.2V at 1C constant current. The batteries with similar capacity were selected for testing.

[0165] The batteries prepared from the electrolytes of the above examples were denoted as B1-B13, and the batteries prepared from the electrolytes of the comparative examples were denoted as RB1-RB4.

[0166] Test Example

[0167] The batteries of the test example were subjected to the following tests:

[0168] 1) Low-temperature power performance test:

[0169] The test was performed using a domestic blue electricity model CT2001C test cabinet, and the low-temperature charging capacity test conditions were as follows: the battery was charged at 3.45V constant voltage at 25℃, and the cut-off current was 0.05C; then discharged at 1C constant current to 2.0V, stored at-20℃ environment for 8h, charged at 3.45V constant voltage, and the upper limit current was limited to 3C, and the cut-off current was 0.05C; the battery was returned to normal temperature and rested for 6h, and discharged at 1C constant current to 2.0V, and the corresponding charge and discharge capacity and time curve were recorded;

[0170] The test was performed using a domestic blue electricity model CT2001C test cabinet, and the low-temperature charging capacity test conditions were as follows: the battery was charged at 3.45V constant voltage at 25℃, and the cut-off current was 0.05C; then discharged at 1C constant current to 2.0V, stored at-20℃ environment for 8h, charged at 3.45V constant voltage, and the upper limit current was limited to 3C, and the cut-off current was 0.05C; the battery was returned to normal temperature and rested for 6h, and discharged at 1C constant current to 2.0V, and the corresponding charge and discharge capacity and time curve were recorded;

[0171] The calculation formula was: low-temperature charging capacity @100% SOC = low-temperature charging capacity / 25℃ discharging capacity*100%, and the test results were shown in Table 2.

[0172] 2) Low-temperature discharge power performance test:

[0173] The test was performed using a domestic blue electricity model CT2001C test cabinet, and the low-temperature discharge capacity test conditions were as follows: the battery was charged at 3.45V constant voltage at 25℃, and the cut-off current was 0.05C; then discharged at 1C constant current to 2.0V, stored at-20℃ environment for 8h, charged at 3.45V constant voltage, and the upper limit current was limited to 3C, and the cut-off current was 0.05C; the battery was returned to normal temperature and rested for 6h, and discharged at 1C constant current to 2.0V, and the corresponding charge and discharge capacity and time curve were recorded; Figure 1 The test was performed using a domestic blue electricity model CT2001C test cabinet, and the low-temperature discharge capacity test conditions were as follows: the battery was charged at 3.45V constant voltage at 25℃, and the cut-off current was 0.05C; then discharged at 1C constant current to 2.0V, stored at-20℃ environment for 8h, charged at 3.45V constant voltage, and the upper limit current was limited to 3C, and the cut-off current was 0.05C; the battery was returned to normal temperature and rested for 6h, and discharged at 1C constant current to 2.0V, and the corresponding charge and discharge capacity and time curve were recorded;

[0174] 3) High temperature cycle performance test:

[0175] The test was conducted using a domestically produced Blue Electric model CT2001C test cabinet. 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°C; the initial discharge capacity was recorded. After 500 cycles of charge and discharge, the discharge capacity at the 500th cycle was recorded, and the capacity retention rate of the battery after high-temperature cycling was calculated. Ten groups of batteries were set for each set of examples and comparative examples, and the test results were averaged.

[0176] 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.

[0177] 4) High temperature storage performance test:

[0178] The specific test conditions are: 1C constant current and constant voltage, 3.75V to 0.05C current cutoff, and the battery is placed in a 60℃ constant temperature box for 30 days. The capacity retention rate of the battery after high temperature storage is calculated. Each group of examples and comparative examples is set up with 10 groups of batteries, and the test results are averaged.

[0179] The calculation formula is: storage 30D capacity recovery rate (%) = discharge capacity after 30 days of storage / initial discharge capacity × 100%. The test results are shown in Table 3.

[0180] Table 2

[0181]

[0182] It can be seen from Table 2 that, compared with the comparative example, the electrolyte of the embodiment helps to further improve the low-temperature charging performance of the battery.

[0183] Table 3

[0184]

[0185]

[0186] It can be seen from Table 3 that, compared with the comparative example, the electrolyte of the embodiment helps to further improve the high-temperature storage performance and cycle performance of the battery.

[0187] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 It includes a cyclic sulfite compound represented by Formula 1 and / or a cyanophosphate cyclic compound represented by Formula 2, wherein R1 and R2 are each independently any one of halogen, halogen-substituted or unsubstituted alkyl, and substituted or unsubstituted alkenyl, and at least one of R1 and R2 includes a halogen atom; The cyanophosphate cyclic compound includes a compound represented by Formula 2: Here, R3 is any one of halogen, halogen-substituted alkyl, and halogen-substituted alkenyl.

2. The solvent according to claim 1, characterized in that R1 and R2 are each independently a halogen-substituted or unsubstituted C1-C6 alkyl group, or a substituted or unsubstituted C2-C6 alkenyl group; And / or, R3 is any one of a halogen-substituted C1-C6 alkyl group and a halogen-substituted C2-C6 alkenyl group.

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

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

1.

5. An electrolyte, characterized in that The invention comprises the solvent according to any one of claims 1 to 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 further includes a second solvent and an electrolyte salt; Wherein, the second solvent comprises at least one of carbonate and its derivatives, carboxylate and its 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 bis(oxalatoborate), lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide) and trimethylsilyl trifluoromethanesulfonate.

9. The electrolyte according to claim 7 or 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 10%-90%.

10. The electrolyte according to any one of claims 5 to 9, characterized in that: The electrolyte further includes an additive, wherein the additive includes at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinyl sulfite, 1,3-propane sultone, 1,3-propene sultone, and vinyl ethylene carbonate.

11. The electrolyte according to claim 10, characterized in that Based on the total mass of the electrolyte, the mass percentage of the additive in the electrolyte is 0.1%-5%.

12. A battery, characterized in that: The electrolyte comprising any one of claims 1 to 11.

13. A battery pack, characterized in that: Comprising at least two batteries according to claim 12.

14. An electrical device, characterized in that: A battery according to claim 12 or a battery pack according to claim 13.

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