Additive of lithium metal electrolyte, lithium metal electrolyte and lithium metal battery

Abstract

The invention discloses an additive of a lithium metal electrolyte, the lithium metal electrolyte and a lithium metal battery, and relates to the technical field of lithium ion batteries, the structural general formula of the additive of the lithium metal electrolyte is # imgabs0 #, R1, R2, R3, R4, R5 and R6 are respectively selected from any one of hydrogen, halogen atoms, alkane with the carbon atom number of 1-5, unsaturated alkyl with the carbon atom number of 2-5 and phenyl; the lithium metal electrolyte comprises the additive, a lithium salt, an organic solvent and a conventional additive. The electrolyte prepared by using the additive can form a compact, stable and low-impedance SEI film, so that the growth of lithium dendrites is effectively inhibited, and the safety and cycle performance of the prepared lithium metal battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and particularly relates to an additive for a lithium metal electrolyte, a lithium metal electrolyte and a lithium metal battery. Background Art

[0002] The development of high energy density in new energy power batteries is the core driving force for improving the cruising range of electric vehicles, and its realization depends on the collaborative breakthroughs in material innovation, process optimization and system integration. The trend of high nickel content in cathode materials (such as ternary materials like NCM811 and NCA) has become the mainstream, and their high specific capacity characteristics provide key support for the improvement of energy density. Lithium metal as an anode material has become an important direction for future development due to its extremely high theoretical specific capacity (3860 mAh / g). Its application can significantly improve the battery energy density, and through combination with advanced processes, it can effectively inhibit the growth of lithium dendrites and improve the cycle stability. Although lithium metal batteries still face challenges in large-scale preparation, interface engineering, etc., their significant advantages in energy density make them an important development direction for the next generation of power batteries. With the continuous improvement of material preparation processes, breakthroughs in interface optimization technologies and the improvement of manufacturing systems, lithium metal batteries are expected to achieve industrial applications in the future and provide core technical support for the sustainable development of the new energy vehicle industry.

[0003] Lithium metal batteries are regarded as the core technical direction of the next generation of high specific energy batteries due to their extremely high theoretical energy density, but their commercialization process is limited by bottleneck problems such as short cycle life and poor safety. Currently, lithium metal batteries mainly have problems such as an increased risk of battery short circuit caused by the disordered growth of lithium dendrites, side reactions and loss of active substances caused by the instability of the electrode-electrolyte interface, and significant performance degradation of traditional electrolytes in high and low temperature environments. The root cause of these problems lies in the insufficient interfacial compatibility between the electrolyte and the lithium metal anode, making it difficult to form a stable solid electrolyte interface film (SEI).

[0004] The patent document with the publication number CN202311805981.2 discloses an additive for a lithium metal battery electrolyte, a lithium metal battery electrolyte and a lithium metal battery. This method provides a new type of additive containing a nitrate functional group, which can achieve the same effect as lithium nitrate and can generate a rich LiN on the surface of the lithium metal anode x O yThe solid electrolyte interface with Li3N improves the uniformity of lithium deposition and extraction on the lithium metal anode, inhibits the generation of lithium dendrites, thereby enhancing the long cycle life and safety performance of lithium metal batteries. This patent also provides other additives that can assist in forming a denser and lower-impedance SEI, and at the same time form a film on the cathode to prevent solvent oxidation. However, this patent only improves lithium deposition from the aspect of the low-impedance SEI film, and does not optimize the lithium ion transport mode from the solvation structure aspect to improve the uniformity of lithium deposition, which may lead to a reduction in the cycle performance and safety performance of lithium metal batteries.

[0005] A patent document with the publication number CN202010485377.6 discloses an electrolyte and a lithium metal battery. This method provides a nitroaniline compound additive. This additive has a stable structure. At the same time, the electron-withdrawing effect of the nitro group and the conjugation effect of the benzene ring can form lithium nitride substances by reduction at low potentials. The dense and highly conductive lithium nitride SEI film can reduce the polarization of the electrode and prevent the continuous reduction of the solvent, thereby reducing the volume expansion of the lithium metal electrode, reducing the polarization of the lithium metal battery, and extending the cycle life of the lithium metal battery. However, the solvent system provided by this patent uses a single ether solvent. Although ether has good anti-reduction characteristics, it is easily oxidized and decomposed at high voltages, resulting in rapid loss of active lithium. At the same time, the dielectric constant of ether is relatively low, and the dissociation of lithium salts is difficult, resulting in insufficient effective lithium in the electrolyte, thus affecting the deposition behavior of lithium ions at the lithium metal interface; in addition, the nitroaniline compound additive is easily reduced to form an organic component of a high molecular weight polymer SEI film due to its stable structure, resulting in an increase in impedance and further affecting the uniform deposition of lithium ions. Summary of the Invention

[0006] Based on the problems of short cycle life and poor safety of lithium metal batteries in the prior art, the purpose of the present invention is to provide an additive for lithium metal electrolytes, a lithium metal electrolyte, and a lithium metal battery. By optimizing the solvation structure of the electrolyte and synergistically regulating with the additive to affect the lithium ion transport mode and lithium deposition / stripping behavior, a dense, stable, and low-impedance SEI film is formed, effectively inhibiting the growth of lithium dendrites and improving the safety and cycle performance of lithium metal batteries.

[0007] The present invention is achieved through the following technical solutions:

[0008] In the first aspect, the present application provides an additive for a lithium metal electrolyte, and the structural general formula of the additive is:

[0009]

[0010] Wherein, R1, R2, R3, R4, R5, and R6 are respectively selected from any one of hydrogen, halogen atoms, alkyl groups with 1 to 5 carbon atoms, unsaturated hydrocarbon groups with 2 to 5 carbon atoms, and phenyl groups.

[0011] This additive can be reduced on the surface of the negative electrode earlier than the solvent to form a SEI film rich in LiF. This film has high mechanical strength, a dense and flexible structure, can withstand the volume change of the electrode material during charge and discharge, reduce the rupture and peeling of the film, and maintain the long-term stability of the electrode. In addition, this additive can be oxidized to form a dense CEI film before the solvent, prevent the continued oxidation of the ether solvent, and improve the cycle performance of the battery.

[0012] Further, part or all of the alkyl group, unsaturated hydrocarbon group, and phenyl group are substituted by halogen atoms.

[0013] Further, the structural formula of the additive includes any one of the following.

[0014] In a second aspect, the present application provides a lithium metal electrolyte, including the above-mentioned additive. For the sake of distinction, the above-mentioned additive is named additive A here. The addition amount of additive A is 0.1% - 5% of the total mass of the electrolyte; it also includes a lithium salt, an organic solvent, and a conventional additive B. The addition amount of the conventional additive B is 0.1% - 3% of the total mass of the electrolyte. The conventional additive B includes any one or a combination of ethylene carbonate, fluoroethylene carbonate, vinylene ethylene carbonate, ethylene sulfate, methylene methanedisulfonate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, and propenylsulfonic acid lactone.

[0015] When additive A is used in combination with the conventional additive B, it can assist additive A to form a denser and more stable SEI film, form inorganic components rich in elements such as S, F, B, and P, further reduce the film formation impedance, and improve the comprehensive performance of the lithium metal battery.

[0016] Further, the lithium salt includes any one or a combination of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium borate, lithium perchlorate, lithium bis(pentafluoroethylsulfonylimide), lithium bis(trifluoromethylsulfonylimide), and lithium bis(fluorosulfonylimide).

[0017] Further, the addition amount of the lithium salt is 15% - 25% of the total mass of the electrolyte.

[0018] Further, the organic solvent includes an ether and a cyclic high dielectric constant mixed solvent. The weight ratio of the ether solvent to the cyclic high dielectric constant solvent is 2.5 - 5.5. Preferably, it is 3 - 5.

[0019] The electrolyte solvent uses an ether-based and cyclic high dielectric constant mixed solvent. The ether-based solvent has a relatively stable structure, good reduction stability, is not easily reduced at the low potential of the lithium metal negative electrode. At the same time, the ether-based solvent and Li +The weakened interaction helps the desolvation of lithium ions at the interface of the lithium metal anode, thereby promoting the uniform deposition of lithium and improving the Coulomb efficiency; the cyclic high-dielectric-constant solvent can effectively dissociate the electrolyte salt, improve the ionic conductivity, and ensure sufficient effective lithium transport. In addition, the mixed use of the two solvents can adjust the Li + solvation structure and reduce the activation energy of lithium ion desolvation, thereby significantly improving the charge transfer kinetics during the lithium deposition process.

[0020] Furthermore, the addition amount of the organic solvent is 67% to 84% of the total mass of the electrolyte, preferably 70% to 80%.

[0021] Furthermore, the ether solvent includes any one or a combination of ethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, triethylene glycol dimethyl ether, methyl butyl ether, n-butyl ether, and ethylene oxide. Preferably, it is any one or a combination of ethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, and triethylene glycol dimethyl ether.

[0022] Furthermore, the cyclic high-dielectric-constant solvent includes any one of ethylene carbonate, propylene carbonate, vinylene sulfite, propylene sulfite, butylene sulfite, and sulfolane. Preferably, it is any one of ethylene carbonate, propylene carbonate, vinylene sulfite, and propylene sulfite.

[0023] In a third aspect, the present application provides a method for preparing a lithium metal electrolyte, including the following steps:

[0024] In an inert gas environment (a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm)), two or more organic solvents are mixed evenly;

[0025] The mixed solvent is cooled, then a lithium salt is added. After the lithium salt is completely dissolved, additive A and conventional additive B are added, and after stirring evenly and dissolving sufficiently, the electrolyte is obtained.

[0026] Furthermore, the cooling temperature of the mixed solvent is controlled at 0 to 10 °C.

[0027] In a fourth aspect, the present application provides a lithium metal battery, including the above lithium metal electrolyte or the lithium metal electrolyte prepared by the above preparation method.

[0028] The lithium metal battery includes a positive electrode material, a negative electrode material, a separator, and the above electrolyte. The positive electrode material is any one of lithium cobaltate, lithium manganate, lithium-rich manganese-based, ternary nickel cobalt manganese lithium, lithium iron phosphate, and lithium manganese iron phosphate, preferably lithium cobaltate, lithium-rich manganese-based, and ternary nickel cobalt manganese lithium; the negative electrode material is lithium metal, lithium alloy, and lithium-carbon composite material, preferably lithium metal; the separator material is polyethylene, polypropylene, and their coated separators.

[0029] The preparation steps of the positive electrode plate are as follows: the positive electrode material, conductive agent and binder are mixed evenly according to the mass ratio of 96:2:2, and then they are dispersed in N-methyl-2-pyrrolidone (NMP) to obtain the positive electrode slurry. Then the slurry is evenly coated on both sides of the aluminum foil, and after drying, rolling and die-cutting, the positive electrode plate is obtained.

[0030] The preparation steps of the negative electrode plate are as follows: lithium metal and the current collector copper are pressed together to form a lithium foil, and after die-cutting, the negative electrode plate is obtained. The thickness of the lithium foil is 50 - 200 μm.

[0031] The preparation steps of the lithium metal battery are as follows: the positive electrode plate, separator and negative electrode plate are stacked in sequence, ensuring that the separator separates the positive electrode plate and the negative electrode plate, and the negative electrode plate completely wraps the positive electrode plate. Then the stacked battery core is put into an aluminum-plastic film packaging bag, and then the electrolyte prepared above is injected into the battery core. Subsequently, after processes such as sealing, formation, aging, and secondary sealing and grading, a lithium metal battery with a capacity of 15000 mAh is manufactured.

[0032] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0033] (1) The novel additive provided by the present invention can be reduced on the surface of the negative electrode earlier than the solvent to form a SEI film rich in LiF. The film has high mechanical strength, a dense and flexible structure, can withstand the volume change of the electrode material during charge and discharge, reduce the rupture and peeling of the film, and maintain the long-term stability of the electrode. In addition, the additive can be oxidized on the surface of the positive electrode to form a dense CEI film, prevent the continuous oxidation and decomposition of the ether solvent, and improve the cycle performance of the battery.

[0034] (2) In the lithium metal electrolyte of the present invention, two mixed solvents, an ether solvent and a cyclic high-dielectric constant solvent, are used in combination. It has good reduction stability to prevent the continuous reduction and decomposition of the solvent. At the same time, the cyclic high-dielectric constant solvent can effectively dissociate the electrolyte salt to ensure sufficient effective lithium transport. In addition, the combination of the two solvents can adjust the lithium ion solvation structure and reduce the activation energy of lithium ion desolvation, thus significantly improving the charge transfer kinetics during the lithium deposition process.

[0035] (3) The novel additive provided by the present invention is used in combination with a conventional additive, which can assist the novel additive to form a denser and more stable SEI film, forming an inorganic component rich in elements such as S, F, B, and P, further reducing the film formation impedance, and improving the comprehensive performance of the lithium metal battery. Specific embodiments

[0036] To make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. The illustrative embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0037] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known materials or methods have not been described in detail to avoid obscuring the present invention.

[0038] Throughout the specification, the mention of "one embodiment", "an embodiment", "one example" or "an example" means that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present invention. Thus, the phrases "one embodiment", "an embodiment", "one example" or "an example" appearing throughout the specification do not necessarily all refer to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable combination and / or sub-combination in one or more embodiments or examples. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0039] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The range defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" have been fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. In addition, when it is stated that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0040] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or may include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can 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.

[0041] Example 1

[0042] This example provides a method for preparing a lithium metal battery. The specific preparation steps are as follows:

[0043] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene glycol dimethyl ether and ethylene carbonate are mixed evenly according to 55% and 20% of the total weight of the electrolyte respectively. Then the mixed solvent is cooled in an environment of 5°C, and then 20% of lithium hexafluorophosphate based on the total weight of the electrolyte is slowly added. After complete dissolution, 3% of additive A (molecular formula I is as follows) based on the total weight of the electrolyte is added. Subsequently, vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 1% of the total weight of the electrolyte) are added. After stirring evenly and dissolving sufficiently, the electrolyte is obtained.

[0044]

[0045] S2. Preparation of the positive electrode sheet: Lithium cobaltate as the positive electrode material, conductive carbon black Super - P, and binder polyvinylidene fluoride (PVDF) are mixed evenly according to a mass ratio of 96:2:2. Then they are dispersed in N - methyl - 2 - pyrrolidone (NMP) to obtain a positive electrode slurry. Then the slurry is evenly coated on both sides of the aluminum foil, and after drying and rolling, the positive electrode sheet is obtained.

[0046] S3. Preparation of the negative electrode sheet: Lithium metal and the current collector copper are pressed together to form a lithium foil, and after die - cutting, the negative electrode sheet is obtained. The thickness of the lithium foil is 150 μm.

[0047] S4. Preparation of the lithium metal battery: The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, ensuring that the separator separates the positive electrode sheet and the negative electrode sheet, and the negative electrode sheet completely wraps the positive electrode sheet. Then the stacked battery core is put into an aluminum - plastic film packaging bag. Subsequently, the above - prepared electrolyte is injected into the battery core, and then through processes such as sealing, formation, aging, and secondary sealing and grading, a lithium - ion battery with a capacity of 15000 mAh is manufactured.

[0048] Example 2

[0049] This embodiment provides a method for preparing a lithium metal battery, which is different from that of Embodiment 1 in that the additive A used in preparing the electrolyte in this embodiment is The steps are as follows:

[0050] S1. Preparation of the electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), mix ethylene glycol dimethyl ether and ethylene carbonate evenly according to 55% and 20% of the total weight of the electrolyte respectively. Then cool the mixed solvent in a 5°C environment, and slowly add 20% of lithium hexafluorophosphate based on the total weight of the electrolyte. After complete dissolution, add 3% of additive A (molecular formula II is as follows) based on the total weight of the electrolyte. Subsequently, add vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 1% of the total weight of the electrolyte), and stir evenly and dissolve thoroughly to obtain the electrolyte.

[0051]

[0052] Steps S2 to S4 are the same as those in Embodiment 1.

[0053] Embodiment 3

[0054] This embodiment provides a method for preparing a lithium metal battery, which is different from that of Embodiment 1 in that the additive A used in preparing the electrolyte in this embodiment is The steps are as follows:

[0055] S1. Preparation of the electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), mix ethylene glycol dimethyl ether and ethylene carbonate evenly according to 55% and 20% of the total weight of the electrolyte respectively. Then cool the mixed solvent in a 5°C environment, and slowly add 20% of lithium hexafluorophosphate based on the total weight of the electrolyte. After complete dissolution, add 3% of additive A (molecular formula III is as follows) based on the total weight of the electrolyte. Subsequently, add vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 1% of the total weight of the electrolyte), and stir evenly and dissolve thoroughly to obtain the electrolyte.

[0056]

[0057] Steps S2 to S4 are the same as those in Embodiment 1.

[0058] Embodiment 4

[0059] This embodiment provides a method for preparing a lithium metal battery, which is different from that of Embodiment 1 in that the additive A used in preparing the electrolyte in this embodiment is The steps are as follows:

[0060] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene glycol dimethyl ether and ethylene carbonate are mixed evenly at 55% and 20% of the total weight of the electrolyte respectively. Then, the mixed solvent is cooled in an environment of 5°C, and then 20% of lithium hexafluorophosphate based on the total weight of the electrolyte is slowly added. After complete dissolution, additive A (molecular formula IV is as follows) accounting for 3% of the total weight of the electrolyte is added. Subsequently, vinylene carbonate and fluoroethylene carbonate (the addition amount of each is 1% of the total weight of the electrolyte) are added. After stirring evenly and dissolving fully, the electrolyte is obtained.

[0061]

[0062] Steps S2 - S4 are the same as those in Example 1.

[0063] Example 5

[0064] This example provides a method for preparing a lithium metal battery. The difference from Example 1 is that additive A used in the preparation of the electrolyte in this example is The steps are as follows:

[0065] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene glycol dimethyl ether and ethylene carbonate are mixed evenly at 55% and 20% of the total weight of the electrolyte respectively. Then, the mixed solvent is cooled in an environment of 5°C, and then 20% of lithium hexafluorophosphate based on the total weight of the electrolyte is slowly added. After complete dissolution, additive A (molecular formula V is as follows) accounting for 3% of the total weight of the electrolyte is added. Subsequently, vinylene carbonate and fluoroethylene carbonate (the addition amount of each is 1% of the total weight of the electrolyte) are added. After stirring evenly and dissolving fully, the electrolyte is obtained.

[0066]

[0067] Steps S2 - S4 are the same as those in Example 1.

[0068] Example 6

[0069] This example provides a method for preparing a lithium metal battery. The difference from Example 1 is that additive A used in the preparation of the electrolyte in this example is The steps are as follows:

[0070] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), mix ethylene glycol dimethyl ether and ethylene carbonate evenly at 55% and 20% of the total weight of the electrolyte respectively. Then cool the mixed solvent in an environment of 5°C, and slowly add lithium hexafluorophosphate accounting for 20% of the total weight of the electrolyte. After complete dissolution, add additive A (molecular formula VI is as follows) accounting for 3% of the total weight of the electrolyte. Subsequently, add vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 1% of the total weight of the electrolyte), and after stirring evenly and dissolving sufficiently, the electrolyte is obtained.

[0071]

[0072] Steps S2 - S4 are the same as those in Example 1.

[0073] Example 7

[0074] This example provides a method for preparing a lithium metal battery. Different from Example 1, the dosage of additive A added in step S1 of this example is 0.1%. The specific preparation steps are as follows:

[0075] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), mix ethylene glycol dimethyl ether and ethylene carbonate evenly at 56.5% and 21.4% of the total weight of the electrolyte respectively. Then cool the mixed solvent in an environment of 5°C, and slowly add lithium hexafluorophosphate accounting for 20% of the total weight of the electrolyte. After complete dissolution, add additive A (molecular formula I is as follows) accounting for 0.1% of the total weight of the electrolyte. Subsequently, add vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 1% of the total weight of the electrolyte), and after stirring evenly and dissolving sufficiently, the electrolyte is obtained.

[0076]

[0077] Steps S2 - S4 are the same as those in Example 1.

[0078] Example 8

[0079] This example provides a method for preparing a lithium metal battery. Different from Example 1, the dosage of additive A added in step S1 of this example is 5%. The specific preparation steps are as follows:

[0080] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene glycol dimethyl ether and ethylene carbonate are mixed evenly at 53% and 20% of the total weight of the electrolyte respectively. Then, the mixed solvent is cooled in an environment of 5°C, and then 20% of lithium hexafluorophosphate based on the total weight of the electrolyte is slowly added. After complete dissolution, 5% of additive A (molecular formula I is as follows) based on the total weight of the electrolyte is added. Subsequently, vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 1% of the total weight of the electrolyte) are added. After stirring evenly and dissolving sufficiently, the electrolyte is obtained.

[0081]

[0082] Steps S2 - S4 are the same as those in Example 1.

[0083] Example 9

[0084] This example provides a method for preparing a lithium metal battery. Different from Example 1, in step S1 of this example, tetrahydrofuran and propylene carbonate are mixed evenly at 64% and 16% of the total weight of the electrolyte respectively. The specific preparation steps are as follows:

[0085] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), tetrahydrofuran and propylene carbonate are mixed evenly at 64% and 16% of the total weight of the electrolyte respectively. Then, the mixed solvent is cooled in an environment of 5°C, and then 17% of lithium hexafluorophosphate based on the total weight of the electrolyte is slowly added. After complete dissolution, 1% of additive A (molecular formula I is as follows) based on the total weight of the electrolyte is added. Subsequently, vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 1% of the total weight of the electrolyte) are added. After stirring evenly and dissolving sufficiently, the electrolyte is obtained.

[0086]

[0087] Steps S2 - S4 are the same as those in Example 1.

[0088] Example 10

[0089] This example provides a method for preparing a lithium metal battery. Different from Example 1, in step S1 of this example, 1,3 - dioxolane and ethylene sulfite are mixed evenly at 58% and 12% of the total weight of the electrolyte respectively. The specific preparation steps are as follows:

[0090] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), mix 1,3-dioxolane and vinylene sulfite evenly according to 58% and 12% of the total weight of the electrolyte respectively. Then cool the mixed solvent in an environment of 5°C, and slowly add lithium hexafluorophosphate accounting for 20% of the total weight of the electrolyte. After complete dissolution, add additive A (molecular formula I is as follows) accounting for 5% of the total weight of the electrolyte. Subsequently, add vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 2.5% of the total weight of the electrolyte), and stir evenly and dissolve fully to obtain the electrolyte.

[0091]

[0092] Steps S2 - S4 are the same as those in Example 1.

[0093] Example 11

[0094] This example provides a method for preparing a lithium metal battery. Different from Example 1, in step S1 of this example, triglyme and propylene sulfite are mixed evenly according to 56% and 19% of the total weight of the electrolyte respectively. The specific preparation steps are as follows:

[0095] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), mix triglyme and propylene sulfite evenly according to 56% and 19% of the total weight of the electrolyte respectively. Then cool the mixed solvent in an environment of 5°C, and slowly add lithium hexafluorophosphate accounting for 20% of the total weight of the electrolyte. After complete dissolution, add additive A (molecular formula I is as follows) accounting for 3% of the total weight of the electrolyte. Subsequently, add vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 1% of the total weight of the electrolyte), and stir evenly and dissolve fully to obtain the electrolyte.

[0096]

[0097] Steps S2 - S4 are the same as those in Example 1.

[0098] Example 12

[0099] This example provides a method for preparing a lithium metal battery. Different from Example 1, in step S1 of this example, 1,3-dioxolane, tetrahydrofuran, and ethylene carbonate are mixed evenly according to 22%, 40%, and 13% of the total weight of the electrolyte respectively. The specific preparation steps are as follows:

[0100] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), mix 1,3-dioxolane, tetrahydrofuran, and ethylene carbonate evenly according to 22%, 40%, and 13% of the total weight of the electrolyte respectively. Then cool the mixed solvent in a 5°C environment, and slowly add lithium hexafluorophosphate accounting for 20% of the total weight of the electrolyte. After complete dissolution, add additive A (molecular formula I is as follows) accounting for 3% of the total weight of the electrolyte. Subsequently, add vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 1% of the total weight of the electrolyte), and stir evenly and dissolve thoroughly to obtain the electrolyte.

[0101]

[0102] Steps S2 - S4 are the same as those in Example 1.

[0103] Example 13

[0104] This example provides a method for preparing a lithium metal battery. Different from Example 1, in step S1 of this example, ethylene glycol dimethyl ether, tetrahydrofuran, and propylene carbonate are mixed evenly according to 43%, 20%, and 15% of the total weight of the electrolyte respectively. The specific preparation steps are as follows:

[0105] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), mix ethylene glycol dimethyl ether, tetrahydrofuran, and propylene carbonate evenly according to 43%, 20%, and 15% of the total weight of the electrolyte respectively. Then cool the mixed solvent in a 5°C environment, and slowly add lithium hexafluorophosphate accounting for 20% of the total weight of the electrolyte. After complete dissolution, add additive A (molecular formula I is as follows) accounting for 1% of the total weight of the electrolyte. Subsequently, add vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 0.5% of the total weight of the electrolyte), and stir evenly and dissolve thoroughly to obtain the electrolyte.

[0106]

[0107] Steps S2 - S4 are the same as those in Example 1.

[0108] Example 14

[0109] This example provides a method for preparing a lithium metal battery. Different from Example 1, in this example, the lithium salt used in step S1 is lithium bis(fluorosulfonylimide) accounting for 18% of the total weight of the electrolyte. The specific preparation steps are as follows:

[0110] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene glycol dimethyl ether and ethylene carbonate are mixed evenly at 55% and 20% of the total weight of the electrolyte respectively. Then the mixed solvent is cooled in an environment of 5 °C, and then 18% of lithium bis(fluorosulfonylimide) based on the total weight of the electrolyte is slowly added. After complete dissolution, additive A (molecular formula I is as follows) accounting for 3% of the total weight of the electrolyte is added. Subsequently, vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 2% of the total weight of the electrolyte) are added. After stirring evenly and dissolving fully, the electrolyte is obtained.

[0111]

[0112] Steps S2 - S4 are the same as those in Example 1.

[0113] Example 15

[0114] This example provides a method for preparing a lithium metal battery. Different from Example 1, in this example, the lithium salt in step S1 uses 22% of lithium bis(fluorosulfonylimide) based on the total weight of the electrolyte. The specific preparation steps are as follows:

[0115] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene glycol dimethyl ether and ethylene carbonate are mixed evenly at 55% and 20% of the total weight of the electrolyte respectively. Then the mixed solvent is cooled in an environment of 5 °C, and then 22% of lithium bis(fluorosulfonylimide) based on the total weight of the electrolyte is slowly added. After complete dissolution, additive A (molecular formula I is as follows) accounting for 1% of the total weight of the electrolyte is added. Subsequently, vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 1% of the total weight of the electrolyte) are added. After stirring evenly and dissolving fully, the electrolyte is obtained.

[0116]

[0117] Steps S2 - S4 are the same as those in Example 1.

[0118] Example 16

[0119] This example provides a method for preparing a lithium metal battery. Different from Example 1, in this example, the lithium salt in step S1 uses 20% of lithium bis(trifluoromethylsulfonyl)imide based on the total weight of the electrolyte. The specific preparation steps are as follows:

[0120] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene glycol dimethyl ether and ethylene carbonate are respectively mixed evenly at 55% and 20% of the total weight of the electrolyte. Then, the mixed solvent is cooled in an environment of 5°C, and then 20% of bis(trifluoromethylsulfonyl)imide of the total weight of the electrolyte is slowly added. After complete dissolution, 3% of additive A (molecular formula I is as follows) of the total weight of the electrolyte is added. Subsequently, vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 1% of the total weight of the electrolyte) are added. After stirring evenly and dissolving sufficiently, the electrolyte is obtained.

[0121]

[0122] Steps S2 - S4 are the same as those in Example 1.

[0123] Example 17

[0124] This example provides a method for preparing a lithium metal battery. Different from Example 1, in this example, the lithium salt in step S1 is lithium bis(fluorosulfonyl)imide at 18% of the total weight of the electrolyte. The specific preparation steps are as follows:

[0125] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene glycol dimethyl ether and ethylene carbonate are respectively mixed evenly at 55% and 20% of the total weight of the electrolyte. Then, the mixed solvent is cooled in an environment of 5°C, and then 18% of lithium bis(fluorosulfonyl)imide of the total weight of the electrolyte is slowly added. After complete dissolution, 3% of additive A (molecular formula I is as follows) of the total weight of the electrolyte is added. Subsequently, vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 2% of the total weight of the electrolyte) are added. After stirring evenly and dissolving sufficiently, the electrolyte is obtained.

[0126]

[0127] Steps S2 - S4 are the same as those in Example 1.

[0128] Example 18

[0129] This example provides a method for preparing a lithium metal battery. Different from Example 1, in this example, the conventional additives used in step S1 are ethylene sulfate and fluoroethylene carbonate (the addition amounts are both 0.5% of the total weight of the electrolyte). The specific preparation steps are as follows:

[0130] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene glycol dimethyl ether and ethylene carbonate are mixed evenly at 55% and 20% of the total weight of the electrolyte respectively. Then the mixed solvent is cooled in an environment of 5°C, and then 20% of lithium hexafluorophosphate based on the total weight of the electrolyte is slowly added. After complete dissolution, 4% of additive A (molecular formula I is as follows) based on the total weight of the electrolyte is added. Subsequently, vinylene sulfate and fluoroethylene carbonate (the addition amounts are both 0.5% of the total weight of the electrolyte) are added. After stirring evenly and dissolving sufficiently, the electrolyte is obtained.

[0131]

[0132] Steps S2 - S4 are the same as those in Example 1.

[0133] Example 19

[0134] This example provides a preparation method of a lithium metal battery. Different from Example 1, the conventional additives used in step S1 of this example are lithium difluorooxalate borate and vinylene carbonate (the addition amounts are both 0.75% of the total weight of the electrolyte). The specific preparation steps are as follows:

[0135] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene glycol dimethyl ether and ethylene carbonate are mixed evenly at 55% and 20% of the total weight of the electrolyte respectively. Then the mixed solvent is cooled in an environment of 5°C, and then 20% of lithium hexafluorophosphate based on the total weight of the electrolyte is slowly added. After complete dissolution, 3.5% of additive A (molecular formula I is as follows) based on the total weight of the electrolyte is added. Subsequently, lithium difluorooxalate borate and vinylene carbonate (the addition amounts are both 0.75% of the total weight of the electrolyte) are added. After stirring evenly and dissolving sufficiently, the electrolyte is obtained.

[0136]

[0137] Steps S2 - S4 are the same as those in Example 1.

[0138] Example 20

[0139] This example provides a preparation method of a lithium metal battery. Different from Example 1, the conventional additives used in step S1 of this example are lithium difluorooxalate phosphate and fluoroethylene carbonate (the addition amounts are both 1.5% of the total weight of the electrolyte). The specific preparation steps are as follows:

[0140] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene glycol dimethyl ether and ethylene carbonate are mixed evenly at 55% and 20% of the total weight of the electrolyte respectively. Then, the mixed solvent is cooled in an environment of 5°C, and then 20% of lithium hexafluorophosphate based on the total weight of the electrolyte is slowly added. After complete dissolution, 2% of additive A (molecular formula I is as follows) based on the total weight of the electrolyte is added. Subsequently, lithium difluoro(oxalato)phosphate and fluoroethylene carbonate (the addition amounts are both 1.5% of the total weight of the electrolyte) are added. After stirring evenly and dissolving sufficiently, the electrolyte is obtained.

[0141]

[0142] Steps S2 - S4 are the same as those in Example 1.

[0143] Example 21

[0144] This example provides a method for preparing a lithium metal battery. Different from Example 1, the conventional additive used in step S1 of this example is vinylene sulfate (the addition amount is 2.5% of the total weight of the electrolyte). The specific preparation steps are as follows:

[0145] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene glycol dimethyl ether and ethylene carbonate are mixed evenly at 55% and 20% of the total weight of the electrolyte respectively. Then, the mixed solvent is cooled in an environment of 5°C, and then 20% of lithium hexafluorophosphate based on the total weight of the electrolyte is slowly added. After complete dissolution, 2.5% of additive A (molecular formula I is as follows) based on the total weight of the electrolyte is added. Subsequently, vinylene sulfate (the addition amount is 2.5% of the total weight of the electrolyte) is added. After stirring evenly and dissolving sufficiently, the electrolyte is obtained.

[0146]

[0147] Steps S2 - S4 are the same as those in Example 1.

[0148] Example 22

[0149] This example provides a method for preparing a lithium metal battery. Different from Example 1, the conventional additives used in step S1 of this example are vinylene carbonate and vinylene sulfate (the addition amounts are both 1% of the total weight of the electrolyte). The specific preparation steps are as follows:

[0150] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene glycol dimethyl ether and ethylene carbonate are mixed evenly at 55% and 20% of the total weight of the electrolyte respectively. Then, the mixed solvent is cooled in an environment of 5 °C, and then 20% of lithium hexafluorophosphate based on the total weight of the electrolyte is slowly added. After complete dissolution, additive A (molecular formula I is as follows) accounting for 3% of the total weight of the electrolyte is added. Subsequently, vinylene carbonate and vinylene sulfate (the addition amounts are both 1% of the total weight of the electrolyte) are added. After stirring evenly and dissolving sufficiently, the electrolyte is obtained.

[0151]

[0152] Steps S2 - S4 are the same as those in Example 1.

[0153] Comparative Example 1

[0154] This comparative example provides a method for preparing a lithium - metal battery. Different from Example 1, in step S1 of this example, additive A is not added. The specific preparation steps are as follows:

[0155] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene glycol dimethyl ether and ethylene carbonate are mixed evenly at 55% and 20% of the total weight of the electrolyte respectively. Then, the mixed solvent is cooled in an environment of 5 °C, and then 20% of lithium hexafluorophosphate based on the total weight of the electrolyte is slowly added. After complete dissolution, vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 2.5% of the total weight of the electrolyte) are added. After stirring evenly and dissolving sufficiently, the electrolyte is obtained.

[0156] Steps S2 - S4 are the same as those in Example 1.

[0157] Comparative Example 2

[0158] This comparative example provides a method for preparing a lithium - metal battery. Different from Example 1, in step S1 of this example, the mixed solvent is not used. The specific preparation steps are as follows:

[0159] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), 75% of ethylene glycol dimethyl ether solvent based on the total weight of the electrolyte is cooled in an environment of 5 °C, and then 20% of lithium hexafluorophosphate based on the total weight of the electrolyte is slowly added. After complete dissolution, additive A (molecular formula I is as follows) accounting for 3% of the total weight of the electrolyte is added. Subsequently, vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 1% of the total weight of the electrolyte) are added. After stirring evenly and dissolving sufficiently, the electrolyte is obtained.

[0160]

[0161] Steps S2 - S4 are the same as those in Example 1.

[0162] Comparative Example 3

[0163] This comparative example provides a method for preparing a lithium - metal battery. Different from Example 1, in step S1 of this example, no mixed solvent and additive A were used. The specific preparation steps are as follows:

[0164] S1. Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), 75% of the ethylene glycol dimethyl ether solvent by the total weight of the electrolyte was placed in an environment at 5 °C for cooling, and then 20% of lithium hexafluorophosphate by the total weight of the electrolyte was slowly added. After complete dissolution, vinylene carbonate and fluoroethylene carbonate (the addition amounts are both 2.5% of the total weight of the electrolyte) were added. After stirring evenly and dissolving sufficiently, the electrolyte was obtained.

[0165] Steps S2 - S4 are the same as those in Example 1.

[0166] The conductivity of the lithium - metal electrolytes prepared by the methods of Examples 1 - 22 and Comparative Examples 1 - 3 was tested, and the cycling performance of the prepared lithium - metal batteries was also tested. The conductivity was tested using a conductivity tester; Room - temperature cycling: The divided - capacity batteries were charged and discharged cyclically at a current of 1C at room temperature of 25 °C and high temperature of 45 °C, and the cut - off voltage range was 2.5 - 4.5V. The capacity retention rate and the internal resistance of the battery after cycling were counted. The test results are shown in Table 1.

[0167] Table 1

[0168]

[0169]

[0170] It can be seen from the test data in Table 1 that in Examples 1 - 22, an ether - based and cyclic high - dielectric - constant mixed solvent was used, and the additives were a combination of a new additive A and conventional additives. The solvent had good reduction stability, was not easily reduced at the low potential of the lithium - metal negative electrode, and at the same time ensured the effective dissociation of the electrolyte salt, had sufficient effective lithium - transport ability. In addition, the mixed use could regulate Li +The solvation structure is formed, and the activation energy of lithium ion desolvation is reduced, thereby significantly improving the charge transfer kinetics during the lithium deposition process. The novel additive A can be reduced on the negative electrode surface earlier than the solvent to form a SEI film rich in LiF. This film has a dense and flexible structure, with a good elastic modulus, which can reduce the rupture and peeling of the film and maintain the long-term stability of the electrode. Secondly, the additive A can be oxidized to form a dense CEI film to prevent the continued oxidation of the ether solvent. In addition, the use of conventional additives can assist in forming a dense and low-impedance SEI film, comprehensively improving the cycle performance of the battery. It can be seen from the test data that it has good lithium ion transmission ability and excellent cycle performance; in Comparative Example 1, the novel additive A was not used, resulting in a less dense film and a high impedance. At the same time, it affected the uniform transmission of lithium ions in the SEI film, and the data showed that the cycle performance was weakened; in Comparative Example 2, the mixed solvent was not used, the conductivity was significantly reduced, and at the same time, it also affected the lithium ion desolvation energy, resulting in a significant weakening of the cycle performance; in Comparative Example 3, the mixed solvent system and the novel additive were not used, and the conductivity and cycle performance were significantly weakened, proving that the novel additive and the lithium metal electrolyte provided by this application can effectively improve the uniform deposition of lithium ions on the metal surface, prevent the consumption of active lithium, and at the same time prevent the side reactions of the positive and negative electrodes, improving the cycle performance of the lithium metal battery.

[0171] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered by the scope of the claims and the description of the present invention.

Claims

1. An additive for a lithium metal electrolyte, characterized in that, The general structural formula of the additive is as follows: Among them, R1, R2, R3, R4, R5, and R6 are each independently selected from any one of hydrogen, a halogen atom, an alkyl group having 1 to 5 carbon atoms, an unsaturated hydrocarbon group having 2 to 5 carbon atoms, and a phenyl group.

2. The additive for a lithium metal electrolyte according to claim 1, wherein, The alkyl group, unsaturated hydrocarbon group, and phenyl group are partially or completely substituted by halogen atoms.

3. An additive for a lithium metal electrolyte according to claim 1, characterized in that, The structural formula of the additive includes Any one of them.

4. A lithium metal electrolyte, characterized in that, It includes the additive in any one of claims 1 to 3.

5. A lithium metal electrolyte according to claim 4, characterized in that, The lithium metal electrolyte further includes a lithium salt, an organic solvent, and a conventional additive. The conventional additive includes any one or a combination of ethylene carbonate, fluoroethylene carbonate, vinylene ethylene carbonate, ethylene sulfate, methylene methanedisulfonate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, and propenylsulfonic acid lactone.

6. A lithium metal electrolyte according to claim 5, characterized in that, The addition amount of the additive in any one of claims 1 to 3 is 0.1% to 5% of the total mass of the electrolyte, and the addition amount of the conventional additive is 0.1% to 3% of the total mass of the electrolyte.

7. A lithium metal electrolyte according to claim 5, characterized in that, The lithium salt includes any one or a combination of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium borate, lithium perchlorate, lithium bis(pentafluoroethylsulfonylimide), lithium bis(trifluoromethylsulfonylimide), and lithium bis(fluorosulfonylimide).

8. A lithium metal electrolyte according to claim 5, wherein The addition amount of the lithium salt is 15% to 25% of the total mass of the electrolyte.

9. A lithium metal electrolyte according to claim 5, wherein, The organic solvent includes an ether and a cyclic high dielectric constant mixed solvent, and the weight ratio of the ether solvent to the cyclic high dielectric constant solvent is 2.5 to 5.

5.

10. A lithium metal electrolyte according to claim 5, characterized in that, The addition amount of the organic solvent is 67% to 84% of the total mass of the electrolyte.

11. A lithium metal electrolyte according to claim 9, characterized in that, The ether solvent includes any one or a combination of ethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, triethylene glycol dimethyl ether, methyl butyl ether, n-butyl ether, and ethylene oxide.

12. A lithium metal electrolyte according to claim 9, characterized in that, The cyclic high dielectric constant solvent includes any one of ethylene carbonate, propylene carbonate, ethylene sulfite, propylene sulfite, butene sulfite, and sulfolane.

13. A method for preparing a lithium metal electrolyte, characterized in that, It includes the following steps: In an inert gas environment, two or more organic solvents are mixed evenly. The mixed solvent is cooled, and then a lithium salt is added. After the lithium salt is completely dissolved, an additive in any one of claims 1 to 3 and a conventional additive are added. After stirring evenly and dissolving sufficiently, an electrolyte is obtained.

14. The preparation method of a lithium metal electrolyte according to claim 13, characterized in that, The cooling temperature of the mixed solvent is controlled at 0 to 10 °C.

15. A lithium metal battery, characterized in that, It includes the lithium metal electrolyte according to any one of claims 4 to 12 or the lithium metal electrolyte prepared by the preparation method according to any one of claims 13 to 14.

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