Battery and preparation method thereof

Abstract

The invention provides a battery and a preparation method thereof. The preparation method comprises the following steps: S1, preparing a first dry battery cell from a positive plate, a diaphragm and a lithium metal negative plate; s2, injecting a first electrolyte into the first dry battery cell, then sequentially standing and circulating to form a protective film on the surface of the lithium metal negative plate, and then removing the residual first electrolyte to obtain a second dry battery cell; s3, injecting a second electrolyte into the second dry cell to obtain a battery; wherein the first electrolyte comprises a first lithium salt, a first organic solvent and a cyclic ether compound; and the second electrolyte comprises a second lithium salt and a second organic solvent. The first lithium salt and the cyclic ether compound are adopted to pre-form a layer of inorganic and organic composite protective film on the surface of the negative electrode of the battery, so that generation of lithium dendrites in the charging and discharging process is inhibited, and the cycle performance and the safety performance of the battery are improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a battery and a method for preparing the same. Background Technology

[0002] With the development of technology, the demand for battery energy density is increasing. Lithium metal anodes have advantages such as ultra-high theoretical capacity (3860 mAh / g) and low redox potential (-3.04 V vs SHE), and have become a research hotspot in the field of high-energy-density batteries. However, the cycling stability of lithium metal anodes in batteries still faces the following challenges: (1) During cycling, Li + (1) Uneven deposition leads to induced dendrite growth, which poses a safety hazard to the battery; (2) Lithium metal can react irreversibly with almost all common electrolytes, forming a thick solid electrolyte interphase (SEI) film on the surface of lithium metal. This not only consumes electrolyte and active lithium but also increases the internal resistance of the battery, thus shortening the battery life; (3) Lithium metal expands in volume during charging and discharging, causing the SEI to break and expose fresh lithium, triggering side reactions that cause a sharp drop in coulombic efficiency and a significant decrease in battery cycle life.

[0003] To address these issues, researchers have explored strategies such as electrolyte optimization, anode modification, solid-state electrolytes, separator modification, and three-dimensional framework current collectors. Some studies have proposed using carbonate additives to form polymer films to increase the flexibility of the electrolyte interphase (SEI); however, the porous nature of these films negatively impacts battery cycle performance. Other studies have proposed coating the lithium anode with polymer films, but issues such as uneven coating, difficulty in thickness control, complex processes, and challenges in mass production hinder the practical application of lithium metal batteries. Summary of the Invention

[0004] The main objective of this invention is to provide a battery and its preparation method to solve the problem of poor cycle stability of batteries in the prior art.

[0005] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a battery, the method comprising: step S1, preparing a first dry cell by forming a positive electrode, a separator, and a lithium metal negative electrode; step S2, injecting a first electrolyte into the first dry cell and then sequentially allowing it to stand and circulate to form a protective film on the surface of the lithium metal negative electrode, and then removing the remaining first electrolyte to obtain a second dry cell; step S3, injecting a second electrolyte into the second dry cell to obtain a battery; wherein the first electrolyte comprises a first lithium salt, a first organic solvent, and a cyclic ether compound; and the second electrolyte comprises a second lithium salt and a second organic solvent.

[0006] Furthermore, the mass percentage of cyclic ether compounds in the first electrolyte is 2-5%.

[0007] Furthermore, the cyclic ether compound is selected from any one or more of 1,3,5-trioxane, 1,3-dioxolane, 1,2,4-trioxane and 1,4-dioxane.

[0008] Further, in step S2, the settling temperature is 20~30℃; and / or, the settling time is 24~48h; and / or, the cycling temperature is 20~30℃; and / or, the cycling rate is 0.1~0.2C; and / or, the number of cycles is 2~3; and / or, the cycling voltage range is 2.75~4.3V.

[0009] Furthermore, in step S2, the temperature for removing the remaining first electrolyte is 50~65℃; and / or the time for removing the remaining first electrolyte is 4~8h.

[0010] Further, the concentration of the first lithium salt in the first electrolyte is 0.1~0.3 mol / L; and / or, the concentration of the second lithium salt in the second electrolyte is 1.0~1.5 mol / L.

[0011] Furthermore, the first lithium salt and the second lithium salt are each independently selected from lithium bisfluorosulfonylimide and / or lithium bistrifluoromethanesulfonylimide.

[0012] Furthermore, both the first organic solvent and the second organic solvent are ether solvents; preferably, the ether solvent is selected from any one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and ethylene glycol diethyl ether.

[0013] Furthermore, the positive electrode is selected from any one or more of lithium iron phosphate positive electrode, lithium manganese iron phosphate positive electrode, and NCM811 positive electrode.

[0014] A second aspect of the present invention provides a battery prepared by the aforementioned preparation method.

[0015] By applying the technical solution of this invention, this application first injects a first electrolyte into a first dry cell for settling and cycling. The cyclic ether compounds in the first electrolyte have a high reduction potential and can be reduced on the negative electrode surface. The cyclic ether molecules gain electrons on the negative electrode surface, opening their rings to form free radical anions. These free radical anions rapidly undergo polymerization to form oligomeric or polyether-based organic lithium compounds. This polymer film is relatively flexible, which can alleviate SEI film rupture and reduce dendrite formation during cycling. Simultaneously, the first lithium salt in the first electrolyte can be reduced and decomposed to form an inorganic layer on the negative electrode surface, which helps improve ionic conductivity and induces uniform ion deposition. Therefore, using the first lithium salt and cyclic ether compounds to pre-form an inorganic-organic composite protective film on the negative electrode surface of the battery helps improve the flexibility and conductivity of the SEI layer, reduces fresh lithium exposure, suppresses lithium dendrite formation during charging and discharging, and improves the battery's cycle performance and safety performance. Detailed Implementation

[0016] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0017] As described in the background section, existing batteries suffer from poor cycle stability. To address this problem, a first aspect of the present invention provides a method for preparing a battery, comprising: step S1, preparing a first dry cell by forming a positive electrode, a separator, and a lithium metal negative electrode; step S2, injecting a first electrolyte into the first dry cell and then sequentially allowing it to stand and cycle to form a protective film on the surface of the lithium metal negative electrode, and then removing the remaining first electrolyte to obtain a second dry cell; step S3, injecting a second electrolyte into the second dry cell to obtain a battery; wherein the first electrolyte comprises a first lithium salt, a first organic solvent, and a cyclic ether compound; and the second electrolyte comprises a second lithium salt and a second organic solvent.

[0018] This application involves first injecting a first electrolyte into a first dry cell for settling and cycling. The cyclic ether compounds in the first electrolyte have a high reduction potential and can be reduced at the negative electrode surface. The cyclic ether molecules gain electrons at the negative electrode surface, opening their rings to form free radical anions. These free radical anions rapidly polymerize to form oligomeric or polyether-based organic lithium compounds. This polymer film is relatively flexible, mitigating SEI film rupture and reducing dendrite formation during cycling. Simultaneously, the first lithium salt in the first electrolyte can be reduced and decomposed, forming an inorganic layer on the negative electrode surface, which helps improve ionic conductivity and induces uniform ion deposition. Therefore, using the first lithium salt and cyclic ether compounds to pre-form an inorganic-organic composite protective film on the negative electrode surface of the battery helps improve the flexibility and conductivity of the SEI layer, reduces fresh lithium exposure, suppresses lithium dendrite formation during charging and discharging, and improves the battery's cycle performance and safety.

[0019] Furthermore, the mass percentage of cyclic ether compounds in the first electrolyte is 2-5%.

[0020] Controlling the mass percentage of cyclic ether compounds in the first electrolyte within the above-mentioned range helps to form a denser and more uniform film, thereby improving the interfacial stability of the electrode and reducing the formation of lithium dendrites.

[0021] Furthermore, the first electrolyte comprises lithium bis(fluorosulfonyl)imide, 1,3,5-trioxane, and ethylene glycol dimethyl ether.

[0022] Lithium bis(fluorosulfonyl)imide decomposes on the negative electrode surface to form a stable inorganic layer. This inorganic layer improves the conductivity and ionic conductivity of the SEI film and reduces the formation of lithium dendrites. 1,3,5-Trioxane is reduced on the negative electrode surface to form a polymer film, increasing the flexibility of the SEI film. Ethylene glycol dimethyl ether enhances the stability of the electrolyte, provides a good lithium-ion transport environment, and also contributes to the formation of the polymer film. Together with lithium bis(fluorosulfonyl)imide and 1,3,5-trioxane, they form a more stable and uniform protective film, thereby further improving the cycle stability of the battery.

[0023] Furthermore, the cyclic ether compound is selected from any one or more of 1,3,5-trioxane, 1,3-dioxolane, 1,2,4-trioxane and 1,4-dioxane.

[0024] Controlling the types of cyclic ether compounds within the above-mentioned range helps to enable cyclic ether compounds to form a stable and flexible film layer, effectively resisting SEI film rupture and reducing lithium dendrite formation.

[0025] Further, in step S2, the settling temperature is 20~30℃; and / or, the settling time is 24~48h; and / or, the cycling temperature is 20~30℃; and / or, the cycling rate is 0.1~0.2C; and / or, the number of cycles is 2~3; and / or, the cycling voltage range is 2.75~4.3V.

[0026] Controlling the settling temperature and time within the aforementioned range helps the first electrolyte to fully wet the first dry cell, which in turn improves the stability and quality of the subsequent protective film formation. Controlling the cycling temperature, rate, number of cycles, and voltage within the aforementioned range helps control the thickness of the protective film, improving its uniformity and stability, thereby enhancing the battery's cycle stability.

[0027] Furthermore, in step S2, the temperature for removing the remaining first electrolyte is 50~65℃; and / or the time for removing the remaining first electrolyte is 4~8h.

[0028] Controlling the temperature and time for removing the remaining first electrolyte within the above range helps to improve the removal efficiency of the first electrolyte while reducing the generation of side reactions.

[0029] Further, the concentration of the first lithium salt in the first electrolyte is 0.1~0.3 mol / L; and / or, the concentration of the second lithium salt in the second electrolyte is 1.0~1.5 mol / L.

[0030] Controlling the concentration of the first lithium salt within the aforementioned range helps to enhance the synergistic effect between the first lithium salt and the cyclic ether compound, thereby improving the flexibility of the protective film and consequently enhancing the cycle stability of the battery. Controlling the concentration of the second lithium salt in the second electrolyte within the aforementioned range helps to improve the ionic conductivity of the second electrolyte, reduce internal resistance, and increase coulombic efficiency.

[0031] To further improve the cycle stability of the battery, the first lithium salt and the second lithium salt are each independently selected from lithium bisfluorosulfonylimide and / or lithium bistrifluoromethanesulfonylimide.

[0032] Furthermore, both the first organic solvent and the second organic solvent are ether solvents; furthermore, the ether solvent is selected from any one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and ethylene glycol diethyl ether.

[0033] Controlling the types of the first and second organic solvents within the aforementioned range helps to improve the uniformity of the dispersion of each component in the first and second electrolytes, thereby contributing to the improvement of the stability of the first and second electrolytes.

[0034] Furthermore, the positive electrode is selected from any one or more of lithium iron phosphate positive electrode, lithium manganese iron phosphate positive electrode, and NCM811 positive electrode.

[0035] The positive electrode sheet of this application can be obtained by purchasing or by using existing technology, and the positive electrode sheet can also be selected from other types commonly found in the art.

[0036] A second aspect of the present invention provides a battery prepared by the aforementioned preparation method.

[0037] Since the battery described above is prepared by the method of this application, it has high cycle stability.

[0038] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0039] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0040] Example 1

[0041] Step S1: NCM811 is used as the positive electrode active material. NCM811, super conductive carbon black, and polyvinylidene fluoride binder are mixed and slurried in a mass ratio of 96:2:2 and then coated to obtain an NCM811 positive electrode sheet. Lithium metal is used as the negative electrode sheet. The NCM811 positive electrode sheet, polyethylene separator, and lithium metal negative electrode sheet are stacked to prepare the first dry cell.

[0042] Step S2: Lithium difluorosulfonylimide, ethylene glycol dimethyl ether, and 1,3,5-trioxane are mixed to obtain a first electrolyte. The concentration of lithium difluorosulfonylimide in the first electrolyte is 0.2 mol / L, and the mass percentage of 1,3,5-trioxane in the first electrolyte is 2%. The first electrolyte is injected into a first dry cell and left to stand at 25°C for 24 hours. The cell is then circulated at 25°C at a rate of 0.1C for 2 cycles, with a voltage range of 2.75~4.3V. The cell is then baked in a vacuum oven at 50°C for 8 hours to remove the remaining first electrolyte, resulting in a second dry cell.

[0043] In step S3, lithium bisfluorosulfonylimide and ethylene glycol dimethyl ether are mixed to obtain a second electrolyte. The concentration of lithium bisfluorosulfonylimide in the second electrolyte is 1.2 mol / L. The second electrolyte is injected into the second dry cell for encapsulation to obtain the battery.

[0044] Example 2

[0045] The difference from Example 1 is that the mass percentage of 1,3,5-trioxane in the first electrolyte is 5%;

[0046] Step S1: NCM811 is used as the positive electrode active material. NCM811, super conductive carbon black, and polyvinylidene fluoride binder are mixed and slurried in a mass ratio of 96:2:2 and then coated to obtain an NCM811 positive electrode sheet. Lithium metal is used as the negative electrode sheet. The NCM811 positive electrode sheet, polyethylene separator, and lithium metal negative electrode sheet are stacked to prepare the first dry cell.

[0047] Step S2: Lithium difluorosulfonylimide, ethylene glycol dimethyl ether, and 1,3,5-trioxane are mixed to obtain a first electrolyte. The concentration of lithium difluorosulfonylimide in the first electrolyte is 1.2 mol / L, and the mass percentage of 1,3,5-trioxane in the first electrolyte is 5%. The first electrolyte is injected into a first dry cell and left to stand at 25°C for 24 hours. The cell is then circulated at 25°C for 2 cycles at a rate of 0.1C, with a voltage range of 2.75~4.3V. The cell is then baked in a vacuum oven at 50°C for 8 hours to remove the remaining first electrolyte, resulting in a second dry cell.

[0048] In step S3, lithium bisfluorosulfonylimide and ethylene glycol dimethyl ether are mixed to obtain a second electrolyte. The concentration of lithium bisfluorosulfonylimide in the second electrolyte is 1.2 mol / L. The second electrolyte is injected into the second dry cell for encapsulation to obtain the battery.

[0049] Example 3

[0050] The difference from Example 1 is that the mass percentage of 1,3,5-trioxane in the first electrolyte is 10%;

[0051] Step S1: NCM811 is used as the positive electrode active material. NCM811, super conductive carbon black, and polyvinylidene fluoride binder are mixed and slurried in a mass ratio of 96:2:2 and then coated to obtain an NCM811 positive electrode sheet. Lithium metal is used as the negative electrode sheet. The NCM811 positive electrode sheet, polyethylene separator, and lithium metal negative electrode sheet are stacked to prepare the first dry cell.

[0052] Step S2: Lithium difluorosulfonylimide, ethylene glycol dimethyl ether, and 1,3,5-trioxane are mixed to obtain a first electrolyte. The concentration of lithium difluorosulfonylimide in the first electrolyte is 1.2 mol / L, and the mass percentage of 1,3,5-trioxane in the first electrolyte is 10%. The first electrolyte is injected into a first dry cell and left to stand at 25°C for 24 hours. The cell is then circulated at 25°C for 2 cycles at a rate of 0.1C, with a voltage range of 2.75~4.3V. The cell is then baked in a vacuum oven at 50°C for 8 hours to remove the remaining first electrolyte, resulting in a second dry cell.

[0053] In step S3, lithium bisfluorosulfonylimide and ethylene glycol dimethyl ether are mixed to obtain a second electrolyte. The concentration of lithium bisfluorosulfonylimide in the second electrolyte is 1.2 mol / L. The second electrolyte is injected into the second dry cell for encapsulation to obtain the battery.

[0054] Example 4

[0055] The difference from Example 1 is that 1,4-dioxane is used instead of 1,3,5-trioxane;

[0056] Step S1: NCM811 is used as the positive electrode active material. NCM811, super conductive carbon black, and polyvinylidene fluoride binder are mixed and slurried in a mass ratio of 96:2:2 and then coated to obtain an NCM811 positive electrode sheet. Lithium metal is used as the negative electrode sheet. The NCM811 positive electrode sheet, polyethylene separator, and lithium metal negative electrode sheet are stacked to prepare the first dry cell.

[0057] Step S2: Lithium difluorosulfonylimide, ethylene glycol dimethyl ether, and 1,4-dioxane are mixed to obtain a first electrolyte. The concentration of lithium difluorosulfonylimide in the first electrolyte is 0.2 mol / L, and the mass percentage of 1,4-dioxane in the first electrolyte is 2%. The first electrolyte is injected into a first dry cell and left to stand at 25°C for 24 hours. The cell is then circulated at 25°C for 2 cycles at a rate of 0.1C, with a voltage range of 2.75~4.3V. The cell is then baked in a vacuum oven at 50°C for 8 hours to remove the remaining first electrolyte, resulting in a second dry cell.

[0058] In step S3, lithium bisfluorosulfonylimide and ethylene glycol dimethyl ether are mixed to obtain a second electrolyte. The concentration of lithium bisfluorosulfonylimide in the second electrolyte is 1.2 mol / L. The second electrolyte is injected into the second dry cell for encapsulation to obtain the battery.

[0059] Example 5

[0060] The difference from Example 1 is that 1,3-dioxolane is used instead of 1,3,5-trioxane;

[0061] Step S1: NCM811 is used as the positive electrode active material. NCM811, super conductive carbon black, and polyvinylidene fluoride binder are mixed and slurried in a mass ratio of 96:2:2 and then coated to obtain an NCM811 positive electrode sheet. Lithium metal is used as the negative electrode sheet. The NCM811 positive electrode sheet, polyethylene separator, and lithium metal negative electrode sheet are stacked to prepare the first dry cell.

[0062] Step S2: Lithium difluorosulfonylimide, ethylene glycol dimethyl ether, and 1,3-dioxolane are mixed to obtain a first electrolyte. The concentration of lithium difluorosulfonylimide in the first electrolyte is 0.2 mol / L, and the mass percentage of 1,3-dioxolane in the first electrolyte is 2%. The first electrolyte is injected into a first dry cell and left to stand at 25°C for 24 hours. The cell is then circulated at 25°C for 2 cycles at a rate of 0.1C, with a voltage range of 2.75~4.3V. The cell is then baked in a vacuum oven at 50°C for 8 hours to remove the remaining first electrolyte, resulting in a second dry cell.

[0063] In step S3, lithium bisfluorosulfonylimide and ethylene glycol dimethyl ether are mixed to obtain a second electrolyte. The concentration of lithium bisfluorosulfonylimide in the second electrolyte is 1.2 mol / L. The second electrolyte is injected into the second dry cell for encapsulation to obtain the battery.

[0064] Example 6

[0065] The difference from Example 1 is that 1,2,4-trioxane is used instead of 1,3,5-trioxane;

[0066] Step S1: NCM811 is used as the positive electrode active material. NCM811, super conductive carbon black, and polyvinylidene fluoride binder are mixed and slurried in a mass ratio of 96:2:2 and then coated to obtain an NCM811 positive electrode sheet. Lithium metal is used as the negative electrode sheet. The NCM811 positive electrode sheet, polyethylene separator, and lithium metal negative electrode sheet are stacked to prepare the first dry cell.

[0067] Step S2: Lithium difluorosulfonylimide, ethylene glycol dimethyl ether, and 1,2,4-trioxane are mixed to obtain a first electrolyte. The concentration of lithium difluorosulfonylimide in the first electrolyte is 0.2 mol / L, and the mass percentage of 1,2,4-trioxane in the first electrolyte is 2%. The first electrolyte is injected into a first dry cell and left to stand at 25°C for 24 hours. The cell is then circulated at 25°C for 2 cycles at a rate of 0.1C, with a voltage range of 2.75~4.3V. The cell is then baked in a vacuum oven at 50°C for 8 hours to remove the remaining first electrolyte, resulting in a second dry cell.

[0068] In step S3, lithium bisfluorosulfonylimide and ethylene glycol dimethyl ether are mixed to obtain a second electrolyte. The concentration of lithium bisfluorosulfonylimide in the second electrolyte is 1.2 mol / L. The second electrolyte is injected into the second dry cell for encapsulation to obtain the battery.

[0069] Example 7

[0070] The difference from Example 1 is that in step S1, NCM811 is used as the positive electrode active material, and NCM811, super conductive carbon black and polyvinylidene fluoride binder are mixed and slurried in a mass ratio of 96:2:2 and then coated to obtain an NCM811 positive electrode sheet; lithium metal is used as the negative electrode sheet, and the NCM811 positive electrode sheet, polyethylene separator and lithium metal negative electrode sheet are stacked to prepare the first dry cell.

[0071] Step S2: Lithium bis(trifluoromethanesulfonyl)imide, diethylene glycol dimethyl ether, and 1,3,5-trioxane are mixed to obtain a first electrolyte. The concentration of lithium bis(trifluoromethanesulfonyl)imide in the first electrolyte is 0.1 mol / L, and the mass percentage of 1,3,5-trioxane in the first electrolyte is 2%. The first electrolyte is injected into a first dry cell and left to stand at 20°C for 48 hours. The cell is then circulated at 20°C for 3 cycles at a rate of 0.2C, with a voltage range of 2.75~4.3V. The cell is then baked in a vacuum oven at 60°C for 6 hours to remove the remaining first electrolyte, resulting in a second dry cell.

[0072] Step S3: Lithium bis(trifluoromethanesulfonyl)imide and diethylene glycol dimethyl ether are mixed to obtain a second electrolyte. The concentration of lithium bis(trifluoromethanesulfonyl)imide in the second electrolyte is 1.0 mol / L. The second electrolyte is injected into the second dry cell for encapsulation to obtain the battery.

[0073] Example 8

[0074] The difference from Example 1 is that in step S1, NCM811 is used as the positive electrode active material, and NCM811, super conductive carbon black and polyvinylidene fluoride binder are mixed and slurried in a mass ratio of 96:2:2 and then coated to obtain an NCM811 positive electrode sheet; lithium metal is used as the negative electrode sheet, and the NCM811 positive electrode sheet, polyethylene separator and lithium metal negative electrode sheet are stacked to prepare the first dry cell.

[0075] Step S2: Lithium difluorosulfonylimide, ethylene glycol diethyl ether, and 1,3,5-trioxane are mixed to obtain a first electrolyte. The concentration of lithium difluorosulfonylimide in the first electrolyte is 0.3 mol / L, and the mass percentage of 1,3,5-trioxane in the first electrolyte is 2%. The first electrolyte is injected into a first dry cell and left to stand at 30°C for 32 hours. The cell is then circulated at 30°C for 2 cycles at a rate of 0.1C, with a voltage range of 2.75~4.3V. The cell is then baked in a vacuum oven at 65°C for 4 hours to remove the remaining first electrolyte, resulting in a second dry cell.

[0076] In step S3, lithium bisfluorosulfonylimide and ethylene glycol diethyl ether are mixed to obtain a second electrolyte. The concentration of lithium bisfluorosulfonylimide in the second electrolyte is 1.5 mol / L. The second electrolyte is injected into the second dry cell for encapsulation to obtain the battery.

[0077] Comparative Example 1

[0078] The difference from Example 1 is that the addition of 1,3,5-trioxane was omitted, resulting in the final battery.

[0079] Performance testing

[0080] Cyclic performance was tested using a charge-discharge test cabinet at an ambient temperature of 25℃. The voltage range was 2.75~4.3V, with 0.5C charging and 1C discharging. For cells that experienced overcharging, the number of cycles was recorded until the capacity retention rate reached 80%. For cells that were overcharged, the number of cycles at the point of overcharging was recorded. The test results are shown in Table 1.

[0081] Table 1

[0082]

[0083] As can be seen from the above description, the embodiments of the present invention achieve the following beneficial effects:

[0084] This application involves first injecting a first electrolyte into a first dry cell for settling and cycling. The cyclic ether compounds in the first electrolyte have a high reduction potential and can be reduced at the negative electrode surface. The cyclic ether molecules gain electrons at the negative electrode surface, opening their rings to form free radical anions. These free radical anions rapidly polymerize to form oligomeric or polyether-based organic lithium compounds. This polymer film is relatively flexible, mitigating SEI film rupture and reducing dendrite formation during cycling. Simultaneously, the first lithium salt in the first electrolyte can be reduced and decomposed, forming an inorganic layer on the negative electrode surface, which helps improve ionic conductivity and induces uniform ion deposition. Therefore, using the first lithium salt and cyclic ether compounds to pre-form an inorganic-organic composite protective film on the negative electrode surface of the battery helps improve the flexibility and conductivity of the SEI layer, reduces fresh lithium exposure, suppresses lithium dendrite formation during charging and discharging, and improves the battery's cycle performance and safety.

[0085] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a battery, characterized in that, The preparation method includes: Step S1: The positive electrode, separator, and lithium metal negative electrode are prepared into the first dry cell; Step S2: After injecting the first electrolyte into the first dry cell, the cells are allowed to stand and circulate sequentially to form a protective film on the surface of the lithium metal negative electrode. Then, the remaining first electrolyte is removed to obtain the second dry cell. Step S3: Inject the second electrolyte into the second dry cell to obtain the battery; The first electrolyte comprises a first lithium salt, a first organic solvent, and a cyclic ether compound; the second electrolyte comprises a second lithium salt and a second organic solvent.

2. The preparation method according to claim 1, characterized in that, The cyclic ether compounds in the first electrolyte account for 2-5% of the total mass.

3. The preparation method according to claim 1 or 2, characterized in that, The cyclic ether compounds are selected from any one or more of 1,3,5-trioxane, 1,3-dioxolane, 1,2,4-trioxane and 1,4-dioxane.

4. The preparation method according to any one of claims 1 to 3, characterized in that, In step S2, the settling temperature is 20~30℃; and / or the settling time is 24~48h. And / or, the temperature of the cycle is 20~30℃; and / or, the cycle rate is 0.1~0.2℃; and / or, the number of cycles is 2~3; and / or, the voltage range of the cycle is 2.75~4.3V.

5. The preparation method according to any one of claims 1 to 4, characterized in that, In step S2, the temperature for removing the remaining first electrolyte is 50~65℃; and / or the time for removing the remaining first electrolyte is 4~8h.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The concentration of the first lithium salt in the first electrolyte is 0.1~0.3 mol / L; and / or, the concentration of the second lithium salt in the second electrolyte is 1.0~1.5 mol / L.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The first lithium salt and the second lithium salt are each independently selected from lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide.

8. The preparation method according to any one of claims 1 to 7, characterized in that, Both the first organic solvent and the second organic solvent are ether solvents; preferably, the ether solvent is selected from any one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and ethylene glycol diethyl ether.

9. The preparation method according to any one of claims 1 to 8, characterized in that, The positive electrode is selected from any one or more of lithium iron phosphate positive electrode, lithium manganese iron phosphate positive electrode, and NCM811 positive electrode.

10. A battery, characterized in that, The battery is prepared by the preparation method according to any one of claims 1 to 9.

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