Solution for preparing electrolyte and preparation method therefor, electrolyte and preparation method therefor, lithium-ion battery, and electric device

Abstract

Provided are a solution for preparing an electrolyte and a preparation method therefor, an electrolyte and a preparation method therefor, a lithium-ion battery, and an electric device. The solution comprises a non-aqueous solvent and magnesium nitrate, wherein the non-aqueous solvent comprises an ester solvent; and the water content a of the solution satisfies: a<100 ppm. The solution contains magnesium nitrate dissolved therein and has an extremely low water content. An electrolyte prepared from the solution can contain magnesium nitrate and has the advantages of a low water content and a low probability of deterioration; and when being used in a lithium-ion battery, the electrolyte is conducive to improving the cycle life of the lithium-ion battery.

Description

Solution for preparing electrolyte and preparation method thereof, electrolyte and preparation method thereof, lithium ion battery and power-consuming device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410051672.9 filed on January 12, 2024, entitled “Solution for preparing electrolyte and preparation method thereof, electrolyte and preparation method thereof, lithium-ion battery and electrical device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the field of batteries, and more specifically, to a solution for preparing an electrolyte and a preparation method thereof, an electrolyte and a preparation method thereof, a lithium-ion battery, and an electrical device. Background Art

[0004] Electrolyte is a key component of lithium-ion batteries. The conduction of lithium ions between the positive and negative electrodes depends on the electrolyte. Therefore, the electrolyte has an important influence on the electrochemical performance and cycle life of lithium-ion batteries.

[0005] Adding magnesium nitrate as an additive to the electrolyte helps inhibit lithium dendrite growth, helping to improve the safety and cycle performance of lithium-ion batteries. However, magnesium nitrate has a high content of crystalline water and is usually stable in the form of magnesium nitrate hexahydrate. Directly adding magnesium nitrate to the electrolyte introduces a large amount of water, causing the electrolyte to deteriorate and thus affecting the electrochemical performance and cycle life of the lithium-ion battery. Therefore, how to reduce the water content of the electrolyte containing magnesium nitrate is a technical problem that needs to be solved urgently.

[0006] Summary of the Invention

[0007] The present application is made in view of the above-mentioned technical problems, and its purpose is to provide a solution for preparing an electrolyte and a preparation method thereof, an electrolyte and a preparation method thereof, a lithium-ion battery and an electrical device. The solution has dissolved magnesium nitrate and has an extremely low water content. The electrolyte prepared by the solution can include magnesium nitrate and has the advantages of low water content and not easy to deteriorate.

[0008] In a first aspect, a solution for preparing an electrolyte is provided, wherein the solution comprises a non-aqueous solvent and magnesium nitrate, wherein the non-aqueous solvent comprises an ester solvent; and the water content a of the solution satisfies: a<100ppm.

[0009] In an embodiment of the present application, magnesium nitrate has been dissolved in a solution used to prepare an electrolyte, and the water content of the solution is controlled within a range of less than 100 ppm. The electrolyte prepared by using the solution not only contains magnesium nitrate, which is beneficial for inducing uniform deposition of lithium ions and inhibiting the growth of lithium dendrites; but also has a very low water content and meets application requirements, and the water content of the electrolyte will not exceed the standard due to the introduction of magnesium nitrate into the electrolyte. Thus, it is helpful to prepare an electrolyte with low water content and containing magnesium nitrate, improve the problem that the electrolyte containing magnesium nitrate is easy to deteriorate, and help improve the cycle life of lithium-ion batteries.

[0010] In one possible implementation, a<50 ppm.

[0011] In a possible implementation, the mass content b of the magnesium nitrate in the solution satisfies: 0.7%≤b≤14%.

[0012] In one possible implementation, 0.7%≤b≤13.8%.

[0013] In the embodiments of the present application, by controlling the mass content of magnesium nitrate in the solution within an appropriate range, the subsequently prepared electrolyte can contain sufficient magnesium ions while reducing the effect of the additive on the impedance of the lithium-ion battery.

[0014] In one possible implementation, the ester solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, and 1,4-butyrolactone.

[0015] In a possible implementation, the ester solvent includes at least one of ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, and dimethyl carbonate.

[0016] In a possible implementation, the solution includes impurity metal ions, and the impurity metal ions include other metal ions other than lithium ions and magnesium ions.

[0017] In one possible implementation, the concentration c of the impurity metal ions in the solution satisfies: c<50 mg / L. In one possible implementation, the solution further comprises: a dehydrating agent, the dehydrating agent comprising at least one of molecular sieves, silica gel, and aluminum oxide.

[0018] In a possible implementation, the molecular sieve includes at least one of a lithium molecular sieve, a potassium molecular sieve, a sodium molecular sieve, and a calcium molecular sieve.

[0019] In a second aspect, a method for preparing a solution in any possible implementation of the first aspect is provided, the preparation method comprising: drying magnesium nitrate hexahydrate to obtain a dry sample; dissolving the dry sample in a non-aqueous solvent to obtain an intermediate solution; and adding a desiccant to the intermediate solution to remove water to obtain the solution.

[0020] In a possible implementation, the drying process includes at least one of a baking process and a freeze-drying process.

[0021] In one possible implementation, the drying treatment of magnesium nitrate hexahydrate to obtain a dry sample includes: heating the magnesium nitrate hexahydrate to 290°C at normal pressure, and the holding time t satisfies: 1h≤t≤1.2h; or heating the magnesium nitrate hexahydrate to 290°C at normal pressure, and the holding time t satisfies: t≥2h; or heating the magnesium nitrate hexahydrate to 260°C in a vacuum environment, and the holding time t satisfies: 0.5h≤t≤0.8h; and sealing and storing the sample when the sample is cooled to 60°C to 120°C to obtain the dry sample.

[0022] In a possible implementation, the heating rate of the heating is 4° C. / min to 10° C. / min.

[0023] In a possible implementation, the dehydrating agent includes at least one of molecular sieve, silica gel, and aluminum oxide; optionally, the molecular sieve includes at least one of lithium molecular sieve, potassium molecular sieve, sodium molecular sieve, and calcium molecular sieve.

[0024] In a possible implementation, the molecular sieve includes a lithium molecular sieve.

[0025] In a possible implementation, a mass ratio m1:m2 of the dehydrating agent to the non-aqueous solvent in which the dried sample is dissolved satisfies: 1:10≤m1:m2≤2:10.

[0026] In a possible implementation, the adding of a dehydrating agent to remove water includes: replacing the dehydrating agent after a first time to continue removing water, the first time being 8 hours to 12 hours; and repeating the step of replacing the dehydrating agent at least 4 times.

[0027] In a third aspect, an electrolyte is provided, wherein the electrolyte is prepared from the solution in any possible implementation of the first aspect, or the solution prepared by the preparation method in any possible implementation of the second aspect.

[0028] In a possible implementation, the water content of the electrolyte is less than or equal to 50 ppm.

[0029] In a possible implementation, the water content of the electrolyte is less than or equal to 20 ppm.

[0030] In a fourth aspect, a method for preparing an electrolyte is provided, the method comprising: adding an electrolyte salt to the solution in the first aspect or the solution prepared by the preparation method in the second aspect to obtain the electrolyte.

[0031] In a fifth aspect, a lithium-ion battery is provided, wherein the lithium-ion battery comprises the electrolyte in the third aspect, or the electrolyte prepared by the method in the fourth aspect.

[0032] In one possible implementation, the lithium-ion battery is a lithium metal battery.

[0033] In a sixth aspect, an electrical device is provided, wherein the electrical device includes the lithium-ion battery in the fifth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0035] FIG1 is a schematic flow chart of a method for preparing a solution for preparing an electrolyte.

[0036] FIG2 is a schematic flow chart of a method for preparing an electrolyte.

[0037] FIG3 is a schematic diagram of a battery cell.

[0038] FIG4 is a schematic diagram of a battery module.

[0039] FIG5 is a schematic diagram of a battery.

[0040] FIG6 is another schematic diagram of a battery. DETAILED DESCRIPTION

[0041] Below, the embodiments of the lithium-ion battery and the electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0042] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] In the description of this application, it should be noted that, unless otherwise specified, "plurality" means more than two; terms such as "upper," "lower," "left," "right," "inner," and "outer" indicating directions or positional relationships are merely for the purpose of facilitating the description of this application and simplifying the description, and do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting this application. Furthermore, terms such as "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0044] Unless otherwise specified, in this application, the phrase "A and / or B" means "A, B, or both A and B". More specifically, the condition "A and / or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0045] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0046] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0047] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0048] As mentioned, "non-aqueous solvent" refers to solvents other than water. In the field of lithium-ion batteries, common non-aqueous solvents include ester solvents, ether solvents, sulfone solvents (including sulfoxides), etc.

[0049] Where mentioned, “water content” refers to the mass fraction of water in a solution, which can be expressed as (m 水 / m 溶液 )×100%.

[0050] As mentioned, "lithium-type molecular sieves" refer to molecular sieves that can undergo ion exchange with lithium ions. The lithium ions in the lithium-type molecular sieve can exchange with other metals or metal ions in solution, forming a metal ion-type molecular sieve. For example, a lithium-type molecular sieve can be represented by the general formula Li2O·nAl2O3·mSiO2, where n and m are the molar numbers of SiO2 and Al2O3 in the molecular sieve. Adjusting the values ​​of n and m can produce molecular sieves with different pore sizes.

[0051] As mentioned, the "X" in "X-type molecular sieve" represents the ions in the molecular sieve that can be ion-exchanged. For example, the potassium ions in the potassium-type molecular sieve can be exchanged with other metals in the solution to form a metal ion-type molecular sieve. For example, the potassium-type molecular sieve can be 2 / 3K2O·1 / 3Na2O·Al2O3·2SiO2; the sodium-type molecular sieve can be Na2O·Al2O3·2SiO2; and the calcium-type molecular sieve can be 3 / 4CaO·1 / 4Na2O·Al2O3·2SiO2.

[0052] Next, embodiments of the present application are introduced.

[0053] In recent years, secondary batteries have been widely used in power tools, electronic products, electric vehicles, aerospace and other fields due to their high energy density and long service life, and have thus achieved great development. Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charge and discharge process of the battery, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. Among them, the electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, which allows active ions to pass through while preventing the positive and negative electrodes from short-circuiting, so that the electrochemical reaction of the secondary battery proceeds normally.

[0054] Take lithium-ion batteries, for example. They are a typical secondary battery. Because they rely on the chemical reaction of lithium ions intercalating and deintercalating between the positive and negative electrodes for charging and discharging, they are also called rocking-chair batteries. During the charging process, lithium ions are released from the positive electrode active material, transferred through the electrolyte to the negative electrode, and then embedded in the negative electrode active material. During the discharge process, lithium ions are released from the negative electrode active material, transferred through the electrolyte to the positive electrode, and then embedded in the positive electrode active material.

[0055] It should be understood that the "lithium insertion" and "intercalation" processes described in this application refer to the process in which lithium ions are embedded in the positive electrode active material or the negative electrode active material due to an electrochemical reaction, and the "de-lithiumization", "de-lithiumization" and "de-intercalation" processes described in this application refer to the process in which lithium ions are removed from the positive electrode active material or the negative electrode active material due to an electrochemical reaction.

[0056] Magnesium nitrate is an additive in lithium-ion battery electrolytes. By introducing magnesium ions into the electrolyte, it helps inhibit lithium dendrite growth, which is beneficial to the safety and cycling performance of lithium-ion batteries. Typically, magnesium nitrate is added directly to the electrolyte as an electrolyte additive. Because most electrolyte salts in electrolytes are easily hydrolyzed, electrolytes are actually highly sensitive to moisture. For example, the hydrolysis of electrolyte salts such as lithium hexafluorophosphate produces substances such as hydrogen fluoride and phosphorus trifluoride, which can cause the electrolyte to deteriorate and become ineffective. Magnesium nitrate, on the other hand, contains a large amount of water of crystallization and is typically stable in the form of magnesium nitrate hexahydrate. The introduction of magnesium nitrate into the electrolyte inevitably introduces a large amount of moisture, making the electrolyte susceptible to deterioration or failure, thereby affecting the cycle life of the lithium-ion battery.

[0057] In view of this, the embodiments of the present application provide a solution for preparing an electrolyte and a preparation method thereof, an electrolyte and a preparation method thereof, a lithium-ion battery and an electrical device. The electrolyte prepared by the solution not only contains magnesium nitrate, but also has the advantages of low water content and not easy to deteriorate. Therefore, it helps to improve the stability of the electrolyte containing magnesium nitrate, and further helps to improve the cycle life of the lithium-ion battery.

[0058] First, a solution for preparing an electrolyte is provided, the solution comprising a non-aqueous solvent and magnesium nitrate, wherein the non-aqueous solvent comprises an ester solvent; the water content a of the solution satisfies: a<100ppm; optionally, a<50ppm.

[0059] Specifically, a can be any value less than 100 ppm; further, a can be any value less than 50 ppm. In this embodiment, by introducing magnesium nitrate into the solution and controlling the water content of the solution to be less than 100 ppm, and then preparing the electrolyte through the solution, an electrolyte containing magnesium nitrate but with a low water content can be prepared, so that the water content of the electrolyte will not exceed the standard due to the dissolution of magnesium nitrate. Therefore, the electrolyte containing magnesium nitrate prepared by the solution has the advantages of being stable and not easy to deteriorate, which can help improve the cycle life of lithium-ion batteries. In other words, the solution can also be considered as a "semi-finished product" of the electrolyte. If water is directly removed from the prepared electrolyte dissolved with magnesium nitrate, the dehydration process may have an adverse effect on the electrolyte, for example, decomposition of lithium salts and deterioration of additives. Compared with the solution of directly removing water from the electrolyte, the electrolyte "semi-finished product" in this embodiment is used to prepare the electrolyte. The higher water content caused by dissolving magnesium nitrate has been controlled in the "semi-finished product", so that the electrolyte does not need to be dehydrated in the future to target the high water content caused by magnesium nitrate, thereby reducing the risk of lithium salt decomposition and additive deterioration in the electrolyte.

[0060] In one embodiment, the mass content b of magnesium nitrate in the solution satisfies: 0.7%≤b≤14%; alternatively, 0.7%≤b≤13.8%.

[0061] Specifically, b can be 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 13.8%, 14%, or its value is within the range obtained by combining any two of the above values.

[0062] In this embodiment, on the one hand, the mass content of magnesium nitrate in the solution cannot be too low. If the mass content of magnesium nitrate is too low, the electrolyte prepared subsequently will not have enough magnesium nitrate, and it will not be able to inhibit lithium dendrites. On the other hand, the mass content of magnesium nitrate in the solution cannot be too high. If the mass content of magnesium nitrate is too high, it will not be conducive to the full dissolution of magnesium nitrate in the electrolyte and will introduce too many magnesium ions into the electrolyte, which will have a certain impact on the efficient transmission of lithium ions. Therefore, by controlling the mass content of magnesium nitrate in the solution within the range of 0.7% to 14%, it is possible to have sufficient magnesium nitrate in the electrolyte prepared subsequently while reducing the impact on the impedance of the lithium ion battery.

[0063] In one embodiment, the ester solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, and 1,4-butyrolactone; optionally, the ester solvent includes at least one of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC), and dimethyl carbonate (DMC).

[0064] Specifically, non-aqueous solvents may include ester solvents, ether solvents, sulfone solvents, and the like. Among them, ether solvents include 1,2-dimethoxypropane (DME), tetrahydrofuran (THF), and other substances; sulfone solvents include tetramethylene sulfone (TMS), and other substances. Ester solvents, ether solvents, and sulfone solvents can all be used as solvents for electrolytes, and can be flexibly selected according to different battery systems. Among them, ester solvents have good solubility and electrochemical stability. When used as solvents for electrolytes, they can provide lithium-ion batteries with higher ionic conductivity and electrochemical stability, and are therefore widely used in lithium-ion batteries.

[0065] In this embodiment, by selecting an ester solvent as the non-aqueous solvent of the solution, the electrolyte prepared by using the solution can also have good ionic conductivity and electrochemical stability.

[0066] It should be understood that the non-aqueous solvent may be at least partially identical to the solvent of the electrolyte. For example, the non-aqueous solvent in the solution and the solvent in the electrolyte may both be DEC, or both may be a mixture of DEC and DMC. For another example, the non-aqueous solvent in the solution may be DEC, while DMC is also introduced during the preparation of the electrolyte, such that the solvent of the electrolyte ultimately becomes a mixture of DEC and DMC.

[0067] In one embodiment, the solution includes impurity metal ions, and the impurity metal ions include other metal ions besides lithium ions and magnesium ions.

[0068] It should be understood that in order to control the water content of the solution, after dissolving magnesium nitrate, the solution needs to be dehydrated, for example, by removing water with a water removing agent. The water removing agent may introduce other ions other than magnesium ion or lithium ion into the solution, thereby introducing some other metal ions in the process of preparing the solution, so that there are impurity metal ions in the prepared solution. For example, sodium ion, potassium ion, calcium ion, iron ion, copper ion, etc.

[0069] In one embodiment, the concentration c of the impurity metal ions in the solution satisfies: c<50 mg / L.

[0070] Specifically, c can be any value less than 50 mg / L. In this embodiment, the concentration of impurity metal ions in the solution can be indirectly affected by controlling the amount of the water scavenger, so that the impurity metal ion content in the solution is low, which helps to reduce the impurity metal ion content in the subsequently prepared electrolyte.

[0071] In one embodiment, the solution further comprises: a dehydrating agent; the dehydrating agent comprises at least one of molecular sieves, silica gel, and aluminum oxide.

[0072] The above-mentioned dehydrating agent removes water based on the principle of adsorbing water molecules. Therefore, after adding the dehydrating agent to the solution for dehydration, the dehydrating agent in the solution can be removed by separation methods such as filtration to obtain a solution with a lower water content.

[0073] In one embodiment, the molecular sieve includes at least one of a lithium molecular sieve, a potassium molecular sieve, a sodium molecular sieve, and a calcium molecular sieve; alternatively, the molecular sieve includes a lithium molecular sieve.

[0074] In this embodiment, by selecting a molecular sieve as a dehydrating agent, it is helpful to efficiently remove water from the solution. Among them, the lithium-type molecular sieve can be a substance that satisfies the general formula Li2O·nAl2O3·mSiO2. It can be seen from the general formula that the ions that can undergo ion exchange in the lithium-type molecular sieve are lithium ions. Lithium-type molecular sieves are similar to other types of molecular sieves. In addition to being able to adsorb water molecules, ion exchange may also occur, which will introduce lithium ions into the solution. Therefore, compared with other types of molecular sieves, by using lithium-type molecular sieves as a dehydrating agent, in addition to being able to efficiently remove water, even if ion exchange occurs, only lithium ions will be introduced into the solution instead of other impurity metal ions. Therefore, it is beneficial to reduce the impurity metal ions in the solution while efficiently removing water.

[0075] Next, the preparation method of the above solution is introduced.

[0076] FIG1 is a schematic flow chart of a method for preparing a solution for preparing an electrolyte according to an embodiment of the present application. As shown in FIG1 , the preparation method 100 includes:

[0077] S101, drying magnesium nitrate hexahydrate to obtain a dry sample;

[0078] S102, dissolving the dried sample in a non-aqueous solvent to obtain an intermediate solution;

[0079] S103, adding a dehydrating agent to the intermediate solution to remove water, so as to obtain a solution for preparing an electrolyte.

[0080] Specifically, before magnesium nitrate hexahydrate is dissolved in a non-aqueous solvent, it is first dried to obtain a sample having a preliminary dehydration effect. This step can remove most of the crystal water in magnesium nitrate hexahydrate, which is beneficial to improving the efficiency of subsequent water removal. Adding a water scavenger to the intermediate solution to remove water can further adsorb the water molecules in the solution, thereby obtaining a solution having been dissolved with magnesium nitrate and having a very low water content.

[0081] The method of this embodiment can produce the solution used to prepare the electrolyte in the aforementioned embodiments, i.e., the "semi-finished" electrolyte. Using this solution to prepare the electrolyte effectively addresses the issue of excessive water content in the electrolyte containing dissolved magnesium nitrate, which can easily deteriorate and become ineffective. Thus, the solution prepared by the method provided in this embodiment helps improve the stability of the electrolyte, thereby increasing the cycle life of the lithium-ion battery.

[0082] It should be understood that after the water removal is completed, the water removal agent in the solution can be removed by filtration or other methods commonly used by those skilled in the art to obtain the solution for preparing the electrolyte, which is not limited in this embodiment of the present application.

[0083] Optionally, in S101, the drying process includes at least one of a baking process and a freeze-drying process.

[0084] Specifically, the magnesium nitrate hexahydrate can be dried to be initially dehydrated by various methods such as drying, freeze drying (lyophilization), etc. After the drying process, the dried sample includes magnesium nitrate dihydrate.

[0085] Optionally, in S101, drying the magnesium nitrate hexahydrate to obtain a dry sample includes: (1) heating the magnesium nitrate hexahydrate to 290° C. at normal pressure, with a holding time t satisfying: 1 h ≤ t ≤ 1.2 h; or (2) heating the magnesium nitrate hexahydrate to 290° C. at normal pressure, with a holding time t satisfying: t ≥ 2 h; or (3) heating the magnesium nitrate hexahydrate to 260° C. in a vacuum environment, with a holding time t satisfying: 0.5 h ≤ t ≤ 0.8 h. After holding the temperature, the sample is cooled to 60° C. to 120° C. and sealed for storage to obtain a dry sample.

[0086] Specifically, the drying process can be achieved by using equipment such as an oven, a vacuum oven, and a muffle furnace. The drying process needs to remove as much water as possible while preventing the decomposition of magnesium nitrate hexahydrate. Considering the requirements for equipment and water removal efficiency, the drying process preferably adopts solution (1).

[0087] In schemes (1) and (3), the holding time must be controlled within the range of 1 h to 1.2 h and 0.5 h to 0.8 h, respectively. On the one hand, sufficient holding time allows the removal of as much water as possible from the magnesium nitrate hexahydrate; on the other hand, too long a holding time may cause the magnesium nitrate to decompose or hydrolyze, thereby generating impurities. Therefore, by controlling the holding time within an appropriate range, the water in the magnesium nitrate can be removed as much as possible, and the possibility of introducing impurities into the magnesium nitrate can be reduced.

[0088] When drying magnesium nitrate hexahydrate, there is a cooling process after the heating and holding process. Unless otherwise specified, this cooling process is a natural cooling process, that is, after the drying is completed, the dried sample and the instrument are not treated in any way, and the sample is allowed to cool naturally at room temperature.

[0089] In this embodiment, the sample is sealed and stored when the temperature drops to about 80° C., which can reduce the possibility of part of the magnesium nitrate absorbing water repeatedly during the cooling process of the sample, so that the dried sample contains as little water as possible, thereby improving the subsequent water removal efficiency.

[0090] Optionally, the heating rate of the drying process is 4°C / min to 10°C / min; optionally, the heating rate is 5°C / min.

[0091] Optionally, the freeze-drying treatment includes: placing the magnesium nitrate hexahydrate in liquid nitrogen for pre-freeze-drying, then placing the pre-freeze-dried magnesium nitrate hexahydrate in a freeze dryer, vacuuming for 2 hours, and freeze-drying at a temperature of -60°C for at least 12 hours.

[0092] The types of dewatering agents have been introduced in detail in the previous article and will not be repeated here.

[0093] Optionally, a mass ratio m1:m2 of the dehydrating agent to the non-aqueous solvent in which the dry sample is dissolved satisfies: 1:10≤m1:m2≤2:10.

[0094] Specifically, m1:m2 can be 1:10, 1.1:10, 1.2:10, 1.3:10, 1.4:10, 1.5:10, 1.6:10, 1.7:10, 1.8:10, 1.9:10, 2:10, or its value is within the range obtained by combining any two of the above values.

[0095] Optionally, in S103 , adding a dehydrating agent to the intermediate solution to remove water includes: replacing the dehydrating agent after a first time to continue removing water, the first time being 8 hours to 12 hours; and repeating the above step of replacing the dehydrating agent at least 4 times.

[0096] Specifically, step S103 may be repeated multiple times. For example, when using molecular sieves for water removal, the molecular sieves may be replaced every first time, and the water removal step may be repeated multiple times to reduce the water content in the solution.

[0097] Typically, a lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. Next, we will provide a detailed introduction to the positive electrode sheet, negative electrode sheet, separator, and electrolyte in a lithium-ion battery.

[0098] [Electrolyte]

[0099] The electrolyte conducts ions between the positive and negative electrodes. The electrolyte includes an electrolyte salt and a solvent. The electrolyte provided herein is prepared from the above solution or the solution prepared by the preparation method 100.

[0100] In one embodiment, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0101] In one embodiment, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0102] In one embodiment, the electrolyte may further include other additives, which may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives that improve the battery's overcharge performance, additives that improve the battery's high or low temperature performance, etc.

[0103] FIG2 is a schematic flow chart of a method for preparing an electrolyte according to an embodiment of the present application. As shown in FIG2 , the preparation method 200 includes:

[0104] S201, adding an electrolyte salt to a solution for preparing an electrolyte to obtain the electrolyte.

[0105] Generally speaking, an electrolyte salt such as a lithium salt is first added to a solvent, and then magnesium nitrate, an additive, is added to the mixed solution to obtain an electrolyte. Magnesium nitrate is usually stably present in the form of magnesium nitrate hexahydrate, so magnesium nitrate hexahydrate is usually added to the mixed solution. Then, water removal is performed. After the magnesium nitrate hexahydrate has dissolved in the electrolyte, even if water removal is started at this point, the water in the electrolyte will inevitably react with the electrolyte salt or other additives in the electrolyte due to the long water removal time, causing the electrolyte to deteriorate. Even if the magnesium nitrate hexahydrate is first dried, it is impossible to completely remove the water therein, and the magnesium nitrate added to the electrolyte will still lead to the above-mentioned problems.

[0106] In the present embodiment, the dried magnesium nitrate is first dissolved in a non-aqueous solvent, and the solution is dehydrated to obtain a "semi-finished" electrolyte solution with an extremely low water content. An electrolyte salt is then dissolved in this solution to obtain an electrolyte solution with an extremely low water content that meets application requirements. The present embodiment incorporates the dehydration step during the preparation of the solution, eliminating the electrolyte salt at this point. This effectively prevents deterioration of the electrolyte during the dehydration process.

[0107] In one embodiment, the method 200 further includes: adding a solvent to the solution for preparing the electrolyte. As mentioned above, the solvent may be the same as the non-aqueous solvent or may be different from the non-aqueous solvent.

[0108] [Negative electrode]

[0109] The negative electrode sheet generally includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material.

[0110] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0111] In one embodiment, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0112] In one embodiment, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0113] In one embodiment, the negative electrode film layer further includes a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0114] In one embodiment, the negative electrode film layer further includes a conductive agent, which can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0115] In one embodiment, the negative electrode film layer further includes other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0116] In one embodiment, the negative electrode sheet can be prepared by forming a negative electrode slurry using the aforementioned components for preparing the negative electrode sheet. For example, the negative electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form the negative electrode slurry. The negative electrode slurry is then coated onto the negative electrode current collector. After drying and cold pressing, the negative electrode sheet is obtained.

[0117] [Positive electrode]

[0118] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0119] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0120] In one embodiment, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0121] In one embodiment, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and at least one of its modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and at least one of a composite material of lithium iron manganese phosphate and carbon. The battery will be accompanied by the deintercalation and consumption of Li during the charging and discharging process, and the molar content of Li in the positive electrode active material is different when the battery is discharged to different states. In the enumeration of positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li will change after the charge and discharge cycle. In the enumeration of positive electrode active materials in this application, the molar content of O is only an ideal state value. The release of lattice oxygen will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0122] In one embodiment, the positive electrode film layer further includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0123] In one embodiment, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0124] In one embodiment, the positive electrode sheet can be prepared by separately forming a positive electrode slurry from the components used to prepare the positive electrode sheet. For example, the first positive electrode active material and / or the second positive electrode active material, a conductive agent, a binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is then coated on a positive electrode current collector. After drying and cold pressing, the positive electrode sheet can be obtained.

[0125] [Isolator]

[0126] In one embodiment, the battery further includes a separator. The present application has no particular limitation on the type of separator. For example, any known porous structure separator with good chemical and mechanical stability can be selected.

[0127] In one embodiment, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0128] In one embodiment, the negative electrode sheet, the positive electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0129] In one embodiment, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0130] In one embodiment, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0131] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG3 shows a battery cell 300 having a square structure as an example.

[0132] It should be understood that the battery cell 300 may include the lithium-ion battery in the aforementioned embodiment.

[0133] Figure 4 illustrates an example battery module 400. Referring to Figure 4 , in battery module 400, multiple battery cells 300 may be arranged sequentially along the length of the battery module 400. Of course, any other arrangement is also possible. Furthermore, the multiple battery cells 300 may be secured using fasteners. The multiple battery cells 300 may be of the same chemical system or of different chemical systems.

[0134] Optionally, in one embodiment, the battery module 400 may further include a housing having an accommodation space, and the plurality of battery cells 300 may be accommodated in the accommodation space.

[0135] Optionally, in one embodiment, the battery modules 400 may be assembled into a battery. The battery may contain one or more battery modules 400. The specific number may be selected by those skilled in the art according to the application and capacity of the battery.

[0136] Figures 5 and 6 illustrate an example battery pack 500. Referring to Figures 5 and 6, the battery pack 500 may include a battery box and multiple battery modules 400 disposed within the battery box. The battery box includes an upper case 501 and a lower case 502. The upper case 501 can be placed over the lower case 502 to form an enclosed space for accommodating the battery modules 400. The multiple battery modules 400 can be arranged in any manner within the battery box.

[0137] It should be understood that the battery cells 300 can first be assembled into the battery module 400, and the battery pack 500 can be assembled from the battery module 400. Alternatively, the battery pack 500 can be directly assembled from the battery cells 300, omitting the intermediate form of the battery module 400.

[0138] In addition, the present application also provides an electrical device, which includes the lithium-ion battery in the aforementioned embodiment.

[0139] In another embodiment, an electrical device includes at least one of the battery cells 300, battery modules 400, or battery packs 500 provided herein. The battery cells 300, battery modules 400, or battery packs 500 can be used as a power source for the electrical device or as an energy storage unit for the electrical device. Electrical devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0140] As an electric device, the number of battery cells 300 , battery modules 400 , or battery packs 500 can be selected according to its usage requirements.

[0141] As an example of an electric device, the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module can be used.

[0142] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0143] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0144] [Examples 1-12 and Comparative Examples 1-2]

[0145] Example 1

[0146] (1) Preparation of negative electrode sheet

[0147] The negative electrode active material graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) were dissolved in deionized water at a mass ratio of 96:2:1:1 and mixed thoroughly to produce a negative electrode slurry. The slurry was then evenly coated onto the negative electrode current collector copper foil. The negative electrode sheets were then cold pressed and slit.

[0148] (2) Preparation of positive electrode sheet

[0149] The positive electrode active material, lithium nickel cobalt manganese oxide, the conductive agent, acetylene black, and the binder, polyvinylidene fluoride (PVDF), were dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 96:2:2 and mixed thoroughly to produce a positive electrode slurry. The slurry was then evenly coated onto the positive electrode current collector, aluminum foil. The positive electrode sheets were then cold pressed and slit.

[0150] (3) Preparation of electrolyte

[0151] Commercially available magnesium nitrate hexahydrate was placed in an oven and heated to 290°C at a rate of 5°C / min for 1 hour. The oven was then naturally cooled to approximately 80°C, removed while hot, and sealed for storage. Approximately 62g of the sealed, dried sample was uniformly dissolved in 1L of EMC (equivalent to b = 7.4%). Approximately 160g of lithium molecular sieves (equivalent to m1:m2 = 1.5:10; d = 1.5 / 11) were then added to remove water. After approximately 8-12 hours, the lithium molecular sieves were replaced with new ones. The dehydration step was repeated four times, and the lithium molecular sieves were filtered out to obtain a solution for preparing an electrolyte. Testing of the solution revealed a water content of 57ppm and an impurity metal ion concentration of 27mg / L.

[0152] The solution was mixed evenly with EMC in a volume ratio of 3:7, and then 1 mol / L lithium hexafluorophosphate (LiPF6) was added and dispersed evenly to obtain the electrolyte of Example 1. The water content of the electrolyte was measured to be less than 20 ppm.

[0153] (4) Preparation of lithium-ion batteries

[0154] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order so that the separator is between the positive electrode sheet and the negative electrode sheet and can isolate the positive electrode sheet from the negative electrode sheet; then the stacked components are wound and placed in a shell, and after drying, the electrolyte is injected, and after packaging, formation, and standing, the lithium-ion battery of Example 1 is obtained.

[0155] Example 2

[0156] Compared with Example 1, in the solution of Example 2, the non-aqueous solvent is DEC, b=10.6%, and the final measured values ​​are a=58 ppm, c=29 mg / L.

[0157] Example 3

[0158] Compared with Example 1, in the solution of Example 3, the non-aqueous solvent is a mixture of EC and EMC, wherein the volume ratio of EC to EMC is 3:7, b=5.3%, and the final measured values ​​of a=52 ppm and c=26 mg / L.

[0159] Example 4

[0160] Compared with Example 1, in the solution of Example 4, the non-aqueous solvent is a mixture of EC, EMC and DEC, wherein the volume ratio of EC, EMC and DEC is 3:7:5, b = 1.4%, and when preparing this solution, the water removal step is repeated 3 times, and finally a = 63 ppm and c = 22 mg / L are measured.

[0161] Example 5

[0162] Compared with Example 1, in the solution of Example 5, b=0.7%. When preparing this solution, the water removal step was repeated 3 times, and finally a=39 ppm and c=20 mg / L were measured.

[0163] Example 6

[0164] Compared with Example 1, in the solution of Example 6, b=13.8%. When preparing this solution, the water removal step was repeated 6 times, and finally a=76 ppm and c=34 mg / L were measured.

[0165] Example 7

[0166] Compared with Example 1, in the solution of Example 7, m1:m2=0.8:10. When preparing this solution, the water removal step was repeated 7 times, and finally a=71 ppm and c=35 mg / L were measured.

[0167] Example 8

[0168] Compared with Example 1, in the solution of Example 8, m1:m2=1:10. When preparing this solution, the water removal step was repeated 6 times, and finally a=56 ppm and c=32 mg / L were measured.

[0169] Example 9

[0170] Compared with Example 1, in the solution of Example 9, m1:m2=2:10. When preparing the solution, the water removal step was repeated 3 times, and finally a=65 ppm and c=41 mg / L were measured.

[0171] Example 10

[0172] Compared with Example 1, in the solution of Example 10, m1:m2=2.2:10. When preparing this solution, the water removal step was repeated 3 times, and finally a=46 ppm and c=57 mg / L were measured.

[0173] Example 11

[0174] Compared with Example 1, in the solution of Example 11, silica gel was used as a dehydrating agent. When preparing the solution, the dehydration step was repeated 5 times, and finally a=83 ppm and c=30 mg / L were measured.

[0175] Example 12

[0176] Compared with Example 1, in the solution of Example 12, aluminum oxide was used as a dehydrating agent. When preparing the solution, the dehydration step was repeated 5 times, and finally a=77 ppm and c=45 mg / L were measured.

[0177] Comparative Example 1

[0178] Compared with Example 1, in the electrolyte of Comparative Example 1, magnesium nitrate hexahydrate without drying treatment was directly added to the electrolyte, the solvent of the electrolyte was EMC, and the mass content of magnesium nitrate in the electrolyte was 7.4%.

[0179] Comparative Example 2

[0180] Compared with Example 1, in the electrolyte of Comparative Example 2, dried magnesium nitrate hexahydrate was directly added to the electrolyte, the solvent of the electrolyte was EMC, and the mass content of magnesium nitrate in the electrolyte was 7.4%.

[0181] Product parameters of Examples 1-12 and Comparative Examples 1-2.

[0182] Table 1: Products and performance parameters of Examples 1-12 and Comparative Examples 1-2

[0183] In Table 1, "Non-aqueous Solvent" represents the type of non-aqueous solvent in the solution used to prepare the electrolyte; "Dehydrating Agent" represents the type of dehydrating agent used in preparing the aforementioned solution; "m1:m2" represents the mass ratio of the dehydrating agent to the intermediate solution used in preparing the aforementioned solution; "a" represents the water content in the aforementioned solution; "b" represents the mass content of magnesium nitrate in the aforementioned solution; and "c" represents the concentration of impurity metal ions in the aforementioned solution; "Number of Dehydration Times" represents the number of times the dehydrating agent was used in the process of preparing the aforementioned solution; and "Number of Cycles" represents the number of cycles measured during the cycle test of the lithium-ion batteries in the aforementioned Examples and Comparative Examples.

[0184] According to the comparative analysis of the embodiment and the comparative example, it can be seen that: in the embodiment, the lithium-ion battery electrolyte is prepared using the solution for preparing the electrolyte provided by the present application; while in the comparative example, the electrolyte of the lithium-ion battery directly introduces magnesium nitrate into the electrolyte, or directly introduces dried magnesium nitrate into the electrolyte, so that the water content a of the electrolyte is much higher than that of the embodiment, which seriously threatens the cycle performance of the lithium-ion battery. The number of cycles in the comparative example also proves this. Therefore, it is shown that by using the solution for preparing the electrolyte provided by the present application, an electrolyte with extremely low water content can be prepared, which effectively improves the problem of electrolyte deterioration caused by excessive water content of the electrolyte and helps to improve the cycle performance of the lithium-ion battery.

[0185] By comparing and analyzing the implementations 1-4, it can be seen that as the mass content of magnesium nitrate in the solution increases, the cycle performance of the lithium-ion battery increases accordingly. The possible principle is that the magnesium ions introduced into the electrolyte can effectively induce the uniform deposition of lithium ions, thereby inhibiting lithium dendrites, which contributes to the cycle performance of the lithium-ion battery to a certain extent. This effect is enhanced within a certain concentration range as the magnesium ion concentration increases. Further combined with the data of Example 6, it can be seen that the magnesium ion concentration cannot be too high. The possible principle is that too much magnesium ions have a greater impact on the impedance of the lithium-ion battery, which is not conducive to the cycle performance of the lithium-ion battery. It can be seen from the data of Examples 4 and 5 that although the magnesium ion concentration in Example 5 is lower than that in Example 4, at the same time, the water content in the solution of Example 5 is also much lower than that in Example 4. According to the fact that the cycle performance of Example 5 is better than that of Example 4, the effect of the water content of the electrolyte on the cycle performance of the lithium-ion battery is greater than the effect of the magnesium ion concentration on the cycle performance. This once again illustrates the importance of controlling the water content of the electrolyte.

[0186] By comparative analysis of Examples 7-10, it can be seen that the dewatering agent dosage of Example 7 is too little, and it is necessary to carry out 7 dewaterings to control the water content to 71ppm, the dewatering efficiency is too low and the dewatering effect is not good. The dewatering agent dosage of Example 10 is too much. Although the dewatering efficiency is high and the water content in the solution is only 46ppm, the dewatering agent dosage is too much and easily introduces more impurity metal ions. The concentration of impurity metal ions is higher than that of other embodiments, which affects the cycle performance of the lithium ion battery and makes the cycle performance of Example 10 inferior to that of other embodiments. The dewatering agent dosage of Examples 8-9 is appropriate, so that the dewatering efficiency is higher, the solution water content is lower, and the impurity metal ion content is lower, and the lithium ion battery has a cycle performance better than that of Examples 7 and 10.

[0187] Examples 11-12 respectively demonstrate the use of silica gel and alumina as dewatering agents. It can be seen that in Examples 11-12, by using an appropriate amount of dewatering agent, it is possible to have a higher dewatering efficiency and make the solution have a lower water content, thereby making the electrolyte have a lower water content, and also solving the problem of electrolyte deterioration due to high water content, so that the lithium-ion battery has good cycle performance. Among them, when the amount of dewatering agent is the same and the number of dewatering times is the same, the water content of Example 11 is higher than that of Example 12, indicating that the dewatering efficiency of silica gel is better than that of alumina. However, the concentration of impurity metal ions in Example 11 is lower than that of Example 12, indicating that the use of silica gel as a dewatering agent, although the dewatering effect is slightly better than that of alumina, will introduce more impurity metal ions, making the cycle performance of Example 12 inferior to that of Example 11.

[0188] The following is a brief introduction to the test methods for the physical and chemical parameters and performance parameters involved in the embodiments of this application. It should be understood that the following test methods are only examples, and other test methods known in the art can also be used for testing.

[0189] 1. Water content test in solution

[0190] The water content in the sample (solution) to be tested can be obtained by performing a standard test using the Karl Fischer liquid moisture test method.

[0191] 2. Test of metal ion concentration in solution

[0192] ICP can be used to test the concentration of metal ions in a solution. Specifically, the test solution is atomized by a nebulizer system to form an aerosol. This aerosol is then carried into the plasma by a carrier gas. Under high temperature and an inert argon atmosphere, it evaporates, vaporizes, dissociates, and ionizes, transforming it into positively charged ions. These ions then enter a mass spectrometer through an ion collection system and are separated according to their mass-to-charge ratio. The intensity of each ion mass spectrum peak is proportional to the corresponding ion concentration in the sample, enabling quantitative analysis of each element. This test then determines the concentration of metal ions in the solution.

[0193] 3. Test method for cycle life of lithium-ion batteries

[0194] Lithium-ion batteries were tested at 25°C using the following process: charging at a constant current rate of 1C to 4.3V, then charging at a constant voltage at 4.3V until the current dropped to 0.05C. After the battery rested for 30 minutes, it was discharged at a constant current rate of 1C to 2.5V, and then rested for another 30 minutes. The same cycle test was then repeated until the discharge capacity dropped below 80% of the initial discharge capacity. The number of cycles at this point was recorded.

[0195] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A solution for preparing an electrolyte, characterized in that, The solution includes: a non-aqueous solvent and magnesium nitrate, wherein the non-aqueous solvent includes an ester solvent; The water content a of the solution satisfies: a < 100 ppm.

2. The solution according to claim 1, wherein a < 50 ppm.

3. The solution according to claim 1 or 2, characterized in that, The mass content b of magnesium nitrate in the solution satisfies: 0.7% ≤ b ≤ 14%.

4. The solution according to any one of claims 1-3, characterized in that, The ester solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone.

5. The solution according to claim 4, wherein, The ester solvent includes at least one of ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, dimethyl carbonate.

6. The solution according to any one of claims 1-5, characterized in that, The solution includes impurity metal ions, and the impurity metal ions include metal ions other than lithium ions and magnesium ions.

7. The solution according to claim 6, wherein, The concentration c of the impurity metal ions in the solution satisfies: c < 50 mg / L.

8. The solution according to any one of claims 1-7, characterized in that, The solution further includes: a water remover, and the water remover includes at least one of molecular sieve, silica gel, and aluminum oxide.

9. The solution according to claim 8, characterized in that, The molecular sieve includes at least one of lithium-type molecular sieve, potassium-type molecular sieve, sodium-type molecular sieve, and calcium-type molecular sieve.

10. A method for preparing a solution according to any one of claims 1-9, characterized in that, The preparation method includes: performing a drying treatment on magnesium nitrate hexahydrate to obtain a dried sample; dissolving the dried sample in a non-aqueous solvent to obtain an intermediate solution; adding a water remover to the intermediate solution to remove water to obtain the solution.

11. The preparation method according to claim 10, characterized in that, The drying treatment includes at least one of drying by baking and freeze-drying.

12. The preparation method according to claim 10 or 11, characterized in that, The performing a drying treatment on magnesium nitrate hexahydrate to obtain a dried sample includes: heating the magnesium nitrate hexahydrate to 290 °C under normal pressure, and the holding time t satisfies: 1 h ≤ t ≤ 1.2 h; or heating the magnesium nitrate hexahydrate to 180 °C under normal pressure, and the holding time t satisfies: t ≥ 2 h; or heating the magnesium nitrate hexahydrate to 260 °C in a vacuum environment, and the holding time t satisfies: 0.5 h ≤ t ≤ 0.8 h; sealing and storing the sample when it is cooled to 60 °C - 120 °C to obtain the dried sample.

13. The preparation method according to claim 12, characterized in that, The heating rate of the heating is 4 °C / min - 10 °C / min.

14. The preparation method according to any one of claims 10-13, characterized in that, The water remover includes at least one of molecular sieve, silica gel, and aluminum oxide.

15. The preparation method according to claim 14, characterized in that, The molecular sieve includes at least one of lithium-type molecular sieve, potassium-type molecular sieve, sodium-type molecular sieve, and calcium-type molecular sieve.

16. The preparation method according to claim 14 or 15, characterized in that, The mass ratio m1:m2 of the water remover to the intermediate solution satisfies: 1:10 ≤ m1:m2 ≤ 2:

10.

17. The preparation method according to any one of claims 10-16, characterized in that, The adding a water remover to the intermediate solution to remove water includes: replacing the water remover after a first time to continue removing water, and the first time is 8 h - 12 h; repeating the step of replacing the water remover at least 4 times.

18. An electrolyte, characterized in that, The electrolyte is prepared from the solution described in any one of claims 1 - 9, or from the solution prepared by the preparation method described in any one of claims 10 - 17.

19. The electrolyte according to claim 18, wherein The water content of the electrolyte is less than or equal to 50 ppm.

20. The electrolyte according to claim 19, wherein The water content of the electrolyte is less than or equal to 20 ppm.

21. A method for preparing an electrolyte, characterized in that, The preparation method includes: An electrolyte salt is added to the solution according to any one of claims 1-9 or the solution prepared by the method according to any one of claims 10-17 to obtain the electrolyte solution.

22. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte solution according to any one of claims 18-20 or the electrolyte solution prepared by the method according to claim 21.

23. An electrical device, characterized in that, The electrical device includes the lithium-ion battery according to claim 22.

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