Electrolyte, lithium ion battery and electronic product

Abstract

The invention discloses an electrolyte, a lithium ion battery and an electronic product. The electrolyte comprises electrolyte salt and a solvent; wherein the concentration of the electrolyte salt is 0.1 mol / L-5 mol / L, and the ether solvent comprises one or more of dimethoxymethane, diethoxymethane, 1, 2-diethoxyethane, 1, 3-dioxolane, 1, 3-dioxane, 1, 4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, diethyl ether, cyclopentyl methyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether. According to the electrolyte provided by the invention, the ether solvents are reasonably screened, and the ether solvents with relatively weak lithium salt dissolving capacity are selected, so that the electrolyte forms contact ion pairs and aggregation ion pairs at low concentration, and then anion derivative interface chemistry is introduced, and the obtained electrolyte reduces co-intercalation behaviors and is relatively good in stability at low temperature; the method is suitable for low-temperature environments.

Description

Technical Field

[0001] The present application relates to the field of lithium-ion batteries, and in particular to an electrolyte, a lithium-ion battery and an electronic product. Background Art

[0002] Since the commercial application of lithium-ion batteries (LIBs), they have been widely used in small smart wearable devices, mobile electronic devices, electric vehicles and grid energy storage. At present, the traditional carbonate-based electrolyte is mainly prepared by dissolving lithium hexafluorophosphate (LiPF6) in a mixed solution of ethylene carbonate (EC) and chain carbonates (such as ethyl methyl carbonate / EMC, dimethyl carbonate / DMC, diethyl carbonate / DEC, etc.). Among them, because EC has an extremely high freezing point (36.4℃) and EC accounts for a high proportion (25-50%) in commercial electrolytes (such as 1.0 M LiPF6-EC-DMC), commercial electrolytes freeze at temperatures below -20℃, which makes LIBs difficult to operate at low temperatures, the performance drops sharply, and there are safety issues such as lithium dendrite growth, which seriously hinders the use and promotion of 3C electronic equipment and new energy vehicles in cold areas (such as northern my country, where the temperature is below zero for a long time in winter). Secondly, LIBs are also used in military equipment, polar exploration and space fields, and their operating scenarios are more complex and extreme. For example, the operating temperature in military equipment can be as low as -40°C; the temperature in polar exploration and space fields is even lower.

[0003] Since traditional low-concentration (~1 mol / L) ether electrolytes (such as ethylene glycol dimethyl ether / DME) have extremely low freezing points and high ionic conductivity, they are also suitable for low-temperature electrolytes. However, traditional low-concentration ether electrolytes have problems such as solvent co-embedded graphite and poor oxidation stability, which hinder their development in low-temperature lithium-ion batteries. Among them, some studies have solved the problems of low-concentration ether electrolytes by preparing local high-concentration ether electrolytes. Local high-concentration electrolytes are prepared by adding diluents to high-concentration electrolytes. However, high-concentration electrolytes have high viscosity, low ionic conductivity, and poor wettability with diaphragms, positive and negative electrodes, resulting in poor low-temperature performance of the battery. Summary of the invention

[0004] Based on this, it is necessary to provide an electrolyte, a lithium-ion battery and an electronic product that reduce the co-embedded behavior and have better stability at low temperatures.

[0005] The present application provides an electrolyte solution, including an electrolyte salt and an ether solvent;

[0006] The concentration of the electrolyte salt is 0.1 mol / L to 5 mol / L, and the ether solvent includes one or more of dimethoxymethane, diethoxymethane, 1,2-diethoxyethane, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, ethyl ether, cyclopentyl methyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

[0007] In one embodiment, the ether solvent includes a first solvent or a second solvent and a third solvent in a volume ratio of (1~2): 1, the first solvent and the second solvent each independently include one or more of diethoxymethane, 1,2-diethoxyethane and dimethoxymethane, and the third solvent includes one or more of 1,3-dioxolane, 1,4-dioxane and 1,3-dioxane.

[0008] In one embodiment, the electrolyte salt includes a lithium salt.

[0009] In one embodiment, the lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium difluoroborate, lithium perchlorate, lithium hexafluoroarsenate and lithium trifluoromethanesulfonate.

[0010] In one embodiment, the concentration of the lithium salt in the electrolyte is 0.1 mol / L~5 mol / L.

[0011] Furthermore, the present application also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator and the above-mentioned electrolyte, wherein the separator is arranged between the positive electrode and the negative electrode, and the positive electrode, the negative electrode and the separator are immersed in the electrolyte.

[0012] In one embodiment, the positive electrode includes a positive electrode collector and a positive electrode active layer formed on at least one side of the positive electrode collector, the material of the positive electrode active layer includes a positive electrode active material, and the positive electrode active material includes one or more of nickel cobalt lithium manganese oxide ternary material, lithium nickel manganese oxide and lithium cobalt oxide.

[0013] In one embodiment, the positive electrode active material loading on the positive electrode is 1.5 mg / cm 2 ~3.0mg / cm 2 .

[0014] In one embodiment, the negative electrode includes one of a graphite electrode and a lithium metal electrode.

[0015] Furthermore, the present application provides an electronic product, whose power supply device is the above-mentioned lithium-ion battery.

[0016] The electrolyte provided in the present application is prepared by rationally screening ether solvents and selecting ether solvents with weaker ability to dissolve lithium salts, so that the electrolyte forms contact ion pairs and aggregated ion pairs at low concentrations, and then introduces anion-derived interface chemistry. The obtained electrolyte has reduced co-embedding behavior and better stability at low temperatures, and is suitable for use in low-temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on these drawings without creative work.

[0018] In order to more completely understand the present application and its beneficial effects, the following description will be given in conjunction with the accompanying drawings. In the following description, the same figure numbers represent the same parts.

[0019] Figure 1 The graphs are the cycle performance of Li||graphite batteries using the electrolyte of Example 1 and the electrolyte of Comparative Example 1 at 25°C and 0.5 C rate, respectively.

[0020] Figure 2 The graphs are Li||graphite battery cycle performance diagrams at 25°C and 0.5 C rate using the electrolyte of Example 1, the electrolyte of Example 2, and the electrolyte of Example 3, respectively.

[0021] Figure 3 The graphs are rate performance diagrams of Li||graphite batteries using the electrolyte of Example 1 and the electrolyte of Comparative Example 2 at 25°C.

[0022] Figure 4 a is a graph of the specific capacity of Li||graphite battery using the electrolyte of Example 1 and the electrolyte of Comparative Example 2 at different temperatures and 0.1C rate, Figure 4 b is a graph showing the low temperature cycle performance of a Li|| graphite battery using the electrolyte of Example 1 and the electrolyte of Comparative Example 2 at -20°C and 0.2 C rate, respectively.

[0023] Figure 5 The graphs are graphs of the graphite||NCM811 battery cycle performance at 25°C and 0.5 C rate using the electrolyte of Example 1, the electrolyte of Comparative Example 1, the electrolyte of Comparative Example 2, and the electrolyte of Comparative Example 3, respectively.

[0024] Figure 6 This is a graph showing the cycle performance of a graphite||NCM811 battery using the electrolyte of Example 1 at -20°C and 0.1C rate. DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are given in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0027] The term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of the related listed items, wherein the any and all combinations include any combination of two related listed items, any more related listed items, or all related listed items. For example, "A and / or B" includes three parallel solutions: A, B, and "a combination of A and B".

[0028] In this article, unless otherwise specified, "one or more" means any one of the listed items or any combination of the listed items. Similarly, "one or more" and other expressions that mean "one or more" are also understood in the same way unless otherwise specified.

[0029] In this document, "further", "further", "particularly", "for example", "such as", "example", "for example", etc. are used for descriptive purposes, indicating that the previous and subsequent technical solutions are related in terms of the content covered, but should not be understood as limiting the previous technical solution, nor can they be understood as limiting the scope of protection of this document. In this document, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0030] Herein, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If multiple "optional" items appear in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "optional" item is independent of each other. In this application, descriptions such as "optionally contain", "optionally include", etc. mean "contain or not contain". "Optional component X" means that component X exists or does not exist, or means that component X is contained or not contained.

[0031] In this document, the terms "first", "second", "third", "fourth", etc. in "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", etc. are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0032] In this article, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0033] Herein, when it comes to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​within the numerical interval is considered to be continuous and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when a numerical interval only refers to integers within the numerical interval, including the two endpoint integers of the numerical range, and each integer between the two endpoints, is equivalent to directly listing each integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be combined. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all sub-ranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows broadly including numerical interval types such as percentage intervals, ratio intervals, and ratio intervals.

[0034] Herein, the term "room temperature" or "normal temperature" generally refers to 4°C~35°C, for example, 20°C±5°C. In some embodiments herein, "room temperature" or "normal temperature" refers to 10°C~30°C. In some embodiments herein, "room temperature" or "normal temperature" refers to 20°C~30°C.

[0035] In this article, if there are multiple steps involved in the method flow, unless there is a clear different description in this article, there is no strict order restriction for the execution of these steps, and they can be executed in other orders than described. Moreover, any step can include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be executed in turn, alternating or simultaneously with other steps or parts of sub-steps or stages of other steps.

[0036] The present application provides an electrolyte solution comprising an electrolyte salt and an ether solvent; wherein the concentration of the electrolyte salt is 0.1 mol / L~5 mol / L, and the ether solvent comprises one or more of dimethoxymethane, diethoxymethane, 1,2-diethoxyethane, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, ethyl ether, cyclopentyl methyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

[0037] In a specific example, the ether solvent includes a first solvent or a second solvent and a third solvent in a volume ratio of (1~2): 1, the first solvent and the second solvent each independently include one or more of diethoxymethane, 1,2-diethoxyethane and dimethoxymethane, and the third solvent includes one or more of 1,3-dioxolane, 1,4-dioxane and 1,3-dioxane.

[0038] Furthermore, the ether solvent may be one of diethoxymethane, 1,2-diethoxyethane and dimethoxymethane, and the ether solvent may also be the second solvent and the third solvent in a volume ratio of but not limited to 1:1, 1.5:1 or 2:1.

[0039] In one specific example, the electrolyte salt includes a lithium salt.

[0040] In a specific example, the lithium salt includes one or more of lithium bis(fluorosulfonyl)imide salt, lithium hexafluorophosphate salt, lithium bis(trifluoromethanesulfonyl)imide salt, lithium difluorooxalate borate salt, lithium tetrafluoroborate salt, lithium difluoroborate salt, lithium perchlorate salt, lithium hexafluoroarsenate salt, and lithium trifluoromethanesulfonate.

[0041] In a specific example, the concentration of the lithium salt in the electrolyte is 0.1 mol / L to 5 mol / L. Further, the concentration of the lithium salt in the electrolyte may be, but is not limited to, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L or 5 mol / L.

[0042] The electrolyte provided in the present application is prepared by rationally screening ether solvents and selecting ether solvents with weaker ability to dissolve lithium salts, so that the electrolyte forms contact ion pairs and aggregated ion pairs at low concentrations, and then introduces anion-derived interface chemistry. The obtained electrolyte has reduced co-embedding behavior and better stability at low temperatures, and is suitable for use in low-temperature environments.

[0043] Furthermore, the present application also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator and the above-mentioned electrolyte, wherein the separator is arranged between the positive electrode and the negative electrode, and the positive electrode, the negative electrode and the separator are immersed in the electrolyte.

[0044] In a specific example, the positive electrode includes a positive electrode collector and a positive electrode active layer formed on at least one side surface of the positive electrode collector, the material of the positive electrode active layer includes a positive electrode active material, and the positive electrode active material includes one or more of nickel cobalt lithium manganese oxide ternary material, lithium nickel manganese oxide and lithium cobalt oxide.

[0045] Furthermore, the material composition of the positive electrode active layer includes a positive electrode active material, a first binder and a first conductive agent in a mass ratio of (75~90): (5~12): (3~15). Specifically, the first binder may be but is not limited to polyvinylidene fluoride, and the first conductive agent may be but is not limited to acetylene black.

[0046] In a specific example, the loading of the positive electrode active material on the positive electrode is 1.5 mg / cm 2 ~3.0 mg / cm 2 .

[0047] Specifically, the loading amount of the positive electrode active material on the positive electrode can be, but is not limited to, 1.5 mg / cm -2 , 2 mg / cm 2 , 2.5 mg / cm 2 or 3 mg / cm 2 .

[0048] Furthermore, the positive electrode current collector may be, but is not limited to, aluminum foil or copper foil.

[0049] In a specific example, the negative electrode includes one of a graphite electrode and a lithium metal electrode.

[0050] It can be understood that the negative electrode can use only metallic lithium as the negative electrode, or it can be a graphite electrode. Specifically, the graphite electrode includes a negative electrode current collector and a negative electrode active layer formed on at least one side of the negative electrode current collector. The material of the negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes graphite. The loading amount of the negative electrode active material on the negative electrode is 0.5 mg / cm 2 ~2.0 mg / cm 2 .

[0051] Specifically, the loading amount of the negative electrode active material on the negative electrode can be, but is not limited to, 0.5 mg / cm 2 , 1 mg / cm 2 , 1.5mg / cm 2 or 2 mg / cm 2 .

[0052] Furthermore, the material composition of the negative electrode active layer includes a negative electrode active material, a second binder and a second conductive agent in a mass ratio of (85~90): (5~12): (3~8). Specifically, the second binder may be but is not limited to polyvinylidene fluoride, and the second conductive agent may be but is not limited to acetylene black.

[0053] Furthermore, the present application provides an electronic product, whose power supply device is the above-mentioned lithium-ion battery.

[0054] The present application is further described in detail below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are preferably referred to the guidance given in the present application, and can also be based on the experimental manuals or conventional conditions in the art, can also be based on the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0055] In the following specific embodiments, the measured parameters of raw material components may have slight deviations within the range of weighing accuracy unless otherwise specified. For temperature and time parameters, acceptable deviations caused by instrument test accuracy or operation accuracy are allowed. "Normal temperature" refers to 25°C; "normal pressure" refers to 100KPa or 101KPa.

[0056] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0057] Example 1

[0058] This embodiment provides a formula of a low-temperature and high-voltage lithium-ion battery electrolyte, which is as follows:

[0059] Step 1) At 25° C., in a glove box with a water content and an oxygen content of less than 0.01 ppm, diethoxymethane and 1,3-dioxolane are uniformly mixed in a volume ratio of 1:1 to obtain a diethoxymethane:1,3-dioxolane (1:1) uniform mixed liquid.

[0060] Step 2) Add lithium bis(fluorosulfonyl)imide to the above-mentioned diethoxymethane:1,3-dioxolane (1:1) uniform mixture and stir to fully dissolve and mix evenly to prepare a 1 mol / L lithium bis(fluorosulfonyl)imide / diethoxymethane:1,3-dioxolane (1:1) electrolyte.

[0061] Example 2

[0062] This embodiment provides a formula of a low-temperature and high-voltage lithium-ion battery electrolyte, which is as follows:

[0063] Step 1) At 25° C., in a glove box with a water content and an oxygen content of less than 0.01 ppm, diethoxymethane and 1,3-dioxolane are uniformly mixed in a volume ratio of 1:1 to obtain a diethoxymethane:1,3-dioxolane (1:1) uniform mixed liquid.

[0064] Step 2) Add lithium bis(fluorosulfonyl)imide to the above-mentioned diethoxymethane:1,3-dioxolane (1:1) uniform mixture and stir to fully dissolve and mix evenly to prepare a 2 mol / L lithium bis(fluorosulfonyl)imide / diethoxymethane:1,3-dioxolane (1:1) electrolyte.

[0065] Example 3

[0066] This embodiment provides a formula of a low-temperature and high-voltage lithium-ion battery electrolyte, which is as follows:

[0067] Step 1) At 25° C., in a glove box with a water content and an oxygen content of less than 0.01 ppm, diethoxymethane and 1,3-dioxolane are uniformly mixed in a volume ratio of 1:1 to obtain a diethoxymethane:1,3-dioxolane (1:1) uniform mixed liquid.

[0068] Step 2) Add lithium bis(fluorosulfonyl)imide to the above-mentioned diethoxymethane:1,3-dioxolane (1:1) uniform mixture and stir to fully dissolve and mix evenly to prepare 0.5 mol / L lithium bis(fluorosulfonyl)imide / diethoxymethane:1,3-dioxolane (1:1) electrolyte.

[0069] Example 4

[0070] This embodiment provides a formula of a low-temperature and high-voltage lithium-ion battery electrolyte, which is as follows:

[0071] Step 1) At 25° C., in a glove box with a water content and an oxygen content of less than 0.01 ppm, dimethoxymethane and 1,3-dioxolane are uniformly mixed in a volume ratio of 1:1 to obtain a uniform mixture of dimethoxymethane:1,3-dioxolane (1:1).

[0072] Step 2) Add lithium bis(fluorosulfonyl)imide to the above-mentioned uniform mixture of dimethoxymethane:1,3-dioxolane (1:1), stir to fully dissolve and mix evenly, to prepare a 1 mol / L lithium bis(fluorosulfonyl)imide / dimethoxymethane:1,3-dioxolane (1:1) electrolyte.

[0073] Example 5

[0074] This embodiment provides a formula of a low-temperature and high-voltage lithium-ion battery electrolyte, which is as follows:

[0075] Step 1) At 25° C., in a glove box with a water content and an oxygen content of less than 0.01 ppm, dimethoxymethane and 1,4-dioxane are mixed uniformly in a volume ratio of 2:1 to obtain a uniform mixture of dimethoxymethane:1,4-dioxane (2:1).

[0076] Step 2) Add lithium bis(fluorosulfonyl)imide to the above-mentioned uniform mixture of dimethoxymethane:1,4-dioxane (2:1), stir to fully dissolve and mix evenly, to prepare a 1 mol / L lithium bis(fluorosulfonyl)imide / dimethoxymethane:1,4-dioxane (2:1) electrolyte.

[0077] Example 6

[0078] This embodiment provides a formula of a low-temperature and high-voltage lithium-ion battery electrolyte, which is as follows:

[0079] Step 1) At 25° C., in a glove box with a water content and an oxygen content of less than 0.01 ppm, 1,2-diethoxyethane and 1,3-dioxolane are uniformly mixed in a volume ratio of 1:1 to obtain a uniform mixed liquid of 1,2-diethoxyethane:1,3-dioxolane (1:1).

[0080] Step 2) Add lithium bis(fluorosulfonyl)imide to the above-mentioned uniform mixture of 1,2-diethoxyethane:1,3-dioxolane (1:1), stir to fully dissolve and mix evenly, to prepare a 1 mol / L lithium bis(fluorosulfonyl)imide / 1,2-diethoxyethane:1,3-dioxolane (1:1) electrolyte.

[0081] Comparative Example 1

[0082] Step 1) At 25° C., in a glove box with a water content and an oxygen content of less than 0.01 ppm, ethylene glycol dimethyl ether and 1,3-dioxolane are mixed uniformly in a volume ratio of 1:1 to obtain a uniform mixture of ethylene glycol dimethyl ether:1,3-dioxolane (1:1).

[0083] Step 2) Add lithium bis(fluorosulfonyl)imide to the above-mentioned uniform mixture of ethylene glycol dimethyl ether:1,3-dioxolane (1:1), stir to fully dissolve and mix evenly, to prepare a 1 mol / L lithium bis(fluorosulfonyl)imide / ethylene glycol dimethyl ether:1,3-dioxolane (1:1) electrolyte.

[0084] Comparative Example 2

[0085] A common commercial electrolyte for lithium-ion batteries was selected: 1 mol / L LiPF6 in EC:DMC (1:1), and lithium hexafluorophosphate was dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1 to prepare an electrolyte with a concentration of 1 mol / L.

[0086] Comparative Example 3

[0087] Step 1) In a glove box at 25° C. with a water content and an oxygen content of less than 0.01 ppm, ethylene carbonate and ethylene glycol dimethyl ether are mixed uniformly in a volume ratio of 1:1 to obtain a uniform mixture of ethylene carbonate:ethylene glycol dimethyl ether (1:1).

[0088] Step 2) Add lithium bis(fluorosulfonyl)imide to the above-mentioned uniform mixture of ethylene carbonate:ethylene glycol dimethyl ether (1:1), stir to fully dissolve it and mix it evenly, to prepare a 1 mol / L lithium bis(fluorosulfonyl)imide / ethylene carbonate:ethylene glycol dimethyl ether (1:1) electrolyte.

[0089] The electrolytes prepared in the examples and comparative examples were used to assemble Li||graphite batteries and graphite||NCM811 batteries, and electrochemical performance tests were performed.

[0090] Preparation method of graphite electrode: Graphite, polyvinylidene fluoride (PVDF) binder, and acetylene black are mixed in a ratio of 87:8:5, dispersed by N-methylpyrrolidone (NMP) solution to obtain a uniform slurry, and the slurry is coated on the copper foil using a 50 μm scraper. First, the electrode is placed in a 60°C forced air oven for 6 h to remove most of the NMP solvent, and then the electrode is placed in a 120°C vacuum drying oven and vacuum dried overnight. Use a tablet press to make it into a 12 mm diameter and an active material loading of 1.4 mg / cm 2 Store the disc in a glove box.

[0091] Preparation method of nickel cobalt manganese oxide 811 (NCM811) electrode: NCM811, polyvinylidene fluoride (PVDF) binder, and acetylene black are mixed in a ratio of 80:8:12, dispersed by N-methylpyrrolidone (NMP) solution to obtain a uniform slurry, and the slurry is coated on aluminum foil using a 100 μm scraper. First, place the electrode in a 60°C forced air oven for 6 h to remove most of the NMP solvent, and then place the electrode in a 120°C vacuum drying oven and vacuum dry overnight. Use a tablet press to make it into a 12 mm diameter and 3.0 mg / cm active material loading. 2 The discs were stored in a glove box.

[0092] Assembly method of Li|| graphite battery: at 25°C, in a glove box, use metal lithium as the negative electrode; the prepared graphite pole piece as the positive electrode; PP2500 as the separator; the comparative electrolyte and the electrolyte system prepared in this application as the electrolyte, and assemble the Li|| graphite battery. After the assembled battery is left at room temperature for 10 hours, the charge and discharge test is performed.

[0093] The assembly method of graphite||NCM811 battery: at 25°C, in a glove box, the prepared graphite pole piece is used as the negative electrode; the prepared NCM811 pole piece is used as the positive electrode; PP2500 is used as the separator; the comparative electrolyte and the electrolyte system prepared in the present application are used as the electrolyte, and the graphite||NCM811 battery is assembled. After the assembled battery is left to stand at room temperature for 10 hours, the charge and discharge test is performed.

[0094] Test results

[0095] At 25°C and 0.5 C rate, the cycle performance of Li||graphite battery using the electrolyte of Example 1 and the electrolyte of Comparative Example 1 was tested. The results are as follows: Figure 1 As shown. Figure 1 It can be seen from the results that due to the co-embedding behavior of ethylene glycol dimethyl ether (DME), the battery using the electrolyte of Comparative Example 1 only exhibits an extremely low specific capacity, while the battery using the electrolyte of Example 1 can be stably cycled for 300 cycles, with a specific capacity of 350 mAh g at a rate of 0.5 C. -1 , the capacity retention rate is 93.3%, and the average coulombic efficiency is 99.9%. This fully proves that the weakly solvated electrolyte provided by the present application can effectively solve the bottleneck problem of conventional chain ether solvents co-embedded in graphite, making the battery stable and normal cycle.

[0096] At 25°C and 0.5 C rate, the cycle performance of Li||graphite batteries using the electrolytes of Example 1, Example 2, and Example 3 was tested. The results are as follows: Figure 2 As shown. Figure 2 It can be seen that the all-ether weakly solvated electrolyte at different concentrations also allows the graphite negative electrode to circulate stably, which once again shows that the electrolyte design strategy of the present application can effectively solve the bottleneck problem of ether solvent co-embedded in graphite and broaden the application scope of ether electrolytes.

[0097] At 25°C, the rate performance of Li||graphite battery using the electrolyte of Example 1 and the electrolyte of Comparative Example 2 was tested. The results are as follows: Figure 3 As shown in Table 1. Figure 3 As can be seen from the data in Table 1, compared with the electrolyte in Comparative Example 2, the battery using the electrolyte in Example 1 has better rate performance, which proves that the electrolyte system has fast charge and discharge capabilities.

[0098] The specific capacity of Li||graphite batteries using different electrolytes was tested at different temperatures (25°C, 0°C, -10°C, -20°C and -30°C) and 0.1 C rate. The results are as follows Figure 4 The a is shown in Table 2. Figure 4As can be seen from a and Table 2, within the tested temperature range, the specific capacity of the battery using the electrolyte of Example 1 is much higher than that of the battery using the electrolyte of Comparative Example 2. The batteries using the electrolyte of Example 1 have a high specific capacity and capacity retention rate at the tested temperature, which shows that the electrolyte has a very high potential for low-temperature application. At -20°C and 0.2 C rate, the low-temperature cycle performance of Li|| graphite batteries using different electrolytes was tested. The results are as follows Figure 4 As shown in b. Figure 4 It can be seen from b that the electrolyte of Example 1 can make the battery cycle stably at -20°C and make the battery have a higher specific capacity, which shows that the electrolyte system designed in the present application can make the battery have excellent low-temperature long-cycle performance.

[0099] At 25°C and 0.5 C rate, the cycling performance of graphite||NCM811 batteries using different electrolytes was tested. The results are as follows: Figure 5 As shown in Table 3. Figure 5 As shown, since the electrolyte of comparative example 1 will have serious graphite co-embedded behavior, the full battery assembled using it has an extremely low specific capacity. At the same time, due to the poor oxidation stability of the electrolyte of comparative example 2, the coulombic efficiency of the full battery assembled using it is discontinuously decayed when it is cycled to 250 cycles. The capacity retention rate of the battery after 300 cycles is 46.9%, and the average coulombic efficiency is 98.1%. The battery capacity using the electrolyte of comparative example 3 decays rapidly and the cycle performance is poor. In contrast, the capacity retention rate of the battery using the electrolyte of embodiment 1 after 300 cycles is 74.5%, and the average coulombic efficiency is 99.5%. In addition, it can be seen from Table 3 that compared with comparative example 2, the battery using the electrolyte of embodiments 1-6 has higher cycle stability under high voltage conditions. It is well known that conventional ether electrolytes are difficult to match with high-voltage ternary positive electrode materials due to their poor oxidation stability and other problems. This application uses weakly solvated ether solvents to make the full ether electrolyte match with high-voltage ternary positive electrode materials, which helps to improve the energy density of the battery.

[0100] The cycle performance of the graphite||NCM811 battery of Example 1 was tested at -20°C and 0.1 C rate. The results are as follows Figure 6 As shown in the figure, the battery using the electrolyte designed in this application can be stably cycled at -20°C and has a high capacity of up to 144.8 mAh g -1 The specific capacity, capacity retention rate is 99.6%, and average coulombic efficiency is 99.0%. This shows that the all-ether weakly solvated electrolyte designed in this application can be used in low-temperature LIBs, and can match high-voltage positive electrode materials, effectively improve battery energy density and broaden the temperature application range of lithium-ion batteries.

[0101] Table 1 Rate performance of Li||graphite batteries with different electrolytes at 25°C

[0102]

[0103] Table 2 Performance of Li||graphite batteries using different electrolytes at different temperatures and 0.1 C rate

[0104]

[0105] Table 3 Performance of graphite||NCM811 batteries using different electrolytes at 25°C and 0.5 C rate

[0106]

[0107] The present application provides a weakly solvated electrolyte of all-ether solvents, which realizes the formation of anion-rich solvation structure at low concentrations, forms anion-derived SEI film rich in inorganic components on the graphite surface, and effectively solves the co-embedding problem of ether solvents in graphite electrodes, which can make Li|| graphite batteries have excellent room temperature and low temperature long cycle and rate performance. Secondly, the electrolyte can match high-voltage ternary positive electrode materials, so that the graphite||NCM811 battery shows excellent long cycle stability at room temperature and low temperature conditions, which provides an effective solution for matching high-voltage ternary materials with all-ether electrolytes, and effectively improves the low temperature and high voltage resistance performance of lithium-ion batteries.

[0108] The above embodiments only express several implementation methods of the present application, which is convenient for understanding the technical solution of the present application in detail, but it cannot be understood as limiting the scope of protection of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the protection scope of the present application. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided in the present application are all within the protection scope of the claims attached to the present application. Therefore, the protection scope of the patent of this application shall be based on the content of the attached claims, and the description and drawings can be used to explain the content of the claims.

Claims

1. An electrolyte, characterized in that: Including electrolyte salts and ether solvents; The concentration of the electrolyte salt is 0.1 mol / L~5 mol / L, and the ether solvent includes one or more of dimethoxymethane, diethoxymethane, 1,2-diethoxyethane, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, ethyl ether, cyclopentyl methyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

2. The electrolyte according to claim 1, characterized in that The ether solvent includes a first solvent or a second solvent and a third solvent in a volume ratio of (1~2): 1, the first solvent and the second solvent each independently include one or more of diethoxymethane, 1,2-diethoxyethane and dimethoxymethane, and the third solvent includes one or more of 1,3-dioxolane, 1,4-dioxane and 1,3-dioxane.

3. The electrolyte according to claim 1 or 2, characterized in that The electrolyte salt includes a lithium salt.

4. The electrolyte according to claim 3, characterized in that The lithium salt includes one or more of lithium bis(fluorosulfonyl)imide salt, lithium hexafluorophosphate salt, lithium bis(trifluoromethanesulfonyl)imide salt, lithium difluorooxalatoborate salt, lithium tetrafluoroborate salt, lithium difluoroborate salt, lithium perchlorate salt, lithium hexafluoroarsenate salt and lithium trifluoromethanesulfonate.

5. The electrolyte according to claim 3, characterized in that The concentration of the lithium salt in the electrolyte is 0.1 mol / L~5 mol / L.

6. A lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and the electrolyte according to any one of claims 1 to 5, wherein the separator is arranged between the positive electrode and the negative electrode, and the positive electrode, the negative electrode and the separator are immersed in the electrolyte.

7. The lithium ion battery according to claim 6, characterized in that The positive electrode includes a positive electrode collector and a positive electrode active layer formed on at least one side of the positive electrode collector. The material of the positive electrode active layer includes a positive electrode active material. The positive electrode active material includes one or more of a nickel cobalt lithium manganese oxide ternary material, lithium nickel manganese oxide and lithium cobalt oxide.

8. The lithium ion battery according to claim 7, characterized in that The positive electrode active material loading on the positive electrode is 1.5 mg / cm 2 ~3.0 mg / cm 2 .

9. The lithium ion battery according to any one of claims 6 to 8, characterized in that The negative electrode includes one of a graphite electrode and a lithium metal electrode.

10. An electronic product, characterized in that: The power supply device is a lithium-ion battery as described in any one of claims 6 to 9.

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