Potential control method for in-situ formation of solid electrolyte interface phase

Abstract

The invention discloses a potential control method for in-situ formation of a solid electrolyte interface phase, which comprises the following steps: (1) connecting a negative-electrode-free metal lithium battery into an electrochemical workstation, carrying out linear potential scanning, and determining the decomposition potential of each component in the electrolyte; the negative-electrode-free metal lithium battery comprises the electrolyte, a copper current collector, a diaphragm and a lithium positive electrode, the electrolyte comprises a solvent, a lithium salt and an additive; and (2) connecting the cathode-free metal lithium battery in the step (1) into a battery test system, setting a constant voltage according to the decomposition potential determined in the step (1), and performing potential control to induce formation of a solid electrolyte interface phase. A potential control method is utilized to induce electrolyte decomposition to form a solid electrolyte interface phase in situ, so that the consumption of an active substance separated from a positive electrode in the circulation process is reduced, and the coulombic efficiency of the battery in the initial circulation stage is improved.

Description

Technical Field

[0001] The present application relates to a potential control method for in-situ formation of a solid electrolyte interphase, belonging to the technical field of metal lithium batteries. Background Art

[0002] The development of electric vehicles has promoted the exploration of secondary batteries with high energy density and high safety. Metallic lithium has a low reduction potential (-3.04 V vs. SHE) and a high theoretical specific capacity (3860 mAh g -1 ), and is considered to be one of the most promising anode materials for high energy density energy storage devices. However, during the actual battery test process, the thickness of metallic lithium used exceeds 400 μm, which greatly reduces the actual energy density. The contradiction between the reduction of energy density by thick lithium and the high cost of thin lithium has promoted the development of lithium metal batteries without an anode.

[0003] Generally, a lithium metal battery without an anode consists of a fully charged cathode, an electrolyte, a separator, and a copper current collector. However, the copper current collector has a lithiumophobic property, which causes uneven initial lithium nucleation and serious growth of dendrites, resulting in internal short circuit of the battery and potential safety hazards. Secondly, during the battery cycling process, the decomposition products of the solvent and lithium salt in the electrolyte form a solid electrolyte interphase (SEI) on the copper current collector, which has poor mechanical stability and will continuously break and reform during the deposition and dissolution process of metallic lithium, causing continuous consumption of the active material and the electrolyte. At the same time, the thick solid electrolyte interphase wraps the metallic lithium, causing it to lose electrical contact with the copper current collector and become "dead lithium". Compared with lithium batteries containing anode materials, lithium metal batteries without an anode lose the protection of the anode host material or lithium compensation from the anode side. Any irreversible loss of active lithium (such as the continuous formation of the solid electrolyte interphase and the formation of dead lithium) during the cycling process will directly manifest as a decrease in battery capacity, reducing the first-cycle Coulombic efficiency and the cycling efficiency after stabilization of the battery. Currently, the interface regulation strategies for current collectors include inducing the formation of a stable solid electrolyte interphase through electrolyte design and constructing an artificial solid electrolyte interphase by coating a functional thin layer on the surface of the current collector. However, high cost and complex processes limit the development of the above two types of interface regulation strategies. Therefore, it is particularly important to study and design a low-cost, simple-process method for in-situ construction of a solid electrolyte interphase (SEI) with low interface impedance and high stability. Summary of the Invention

[0004] In view of this, the purpose of this application is to provide an interfacial regulation strategy for current collectors that can improve the Coulombic efficiency and cycling stability of batteries. This application utilizes the differences in the reduction decomposition potentials of solvents, lithium salts, and additives in the electrolyte to induce different components in the electrolyte to in-situ form a solid electrolyte interface phase with low interfacial impedance and high stability on the surface of the copper current collector by controlling the electrode potential of the copper current collector and the constant voltage holding time. Before battery cycling, a solid electrolyte interface phase is in-situ formed by inducing the decomposition of the electrolyte through a potential control method, reducing the consumption of active substances released from the positive electrode during cycling, and improving the Coulombic efficiency in the initial cycling stage of the battery. Additionally, this method can induce the decomposition of different components in the electrolyte by controlling the magnitude of the copper current collector potential, adjust the composition and structure of the solid electrolyte interface phase, reduce the interfacial impedance, and improve the interfacial stability, which is beneficial for Li+ transport and prevents the continuous fragmentation and reorganization of the solid electrolyte interface phase, thereby improving the Coulombic efficiency of the battery. This method in-situ forms the solid electrolyte interface phase by applying a constant potential to the assembled battery, which effectively simplifies the preparation process compared to non-in-situ modification of the copper current collector and endows this method with the potential for commercial application.

[0005] In one aspect of this application, a method for in-situ forming a solid electrolyte interface phase is provided, and the method includes:

[0006] (1) Connect a lithium metal battery without a negative electrode to an electrochemical workstation, perform a linear potential sweep, and determine the decomposition potentials of each component in the electrolyte;

[0007] Wherein, the lithium metal battery without a negative electrode includes the electrolyte, a copper current collector, a separator, and a lithium positive electrode; the electrolyte includes a solvent, a lithium salt, and an additive;

[0008] (2) Connect the lithium metal battery without a negative electrode in step (1) to a battery test system, set a constant voltage according to the decomposition potential determined in step (1), and perform potential control to induce the formation of the solid electrolyte interface phase.

[0009] Optionally, the constant voltage is 0 - 1.5V.

[0010] Optionally, the constant voltage is 0.2 - 1.0V.

[0011] Optionally, the constant voltage is independently selected from any value of 0V, 0.1V, 0.2V, 0.5V, 0.8V, 1.0V, 1.3V, 1.5V or a range value between any two of the above.

[0012] Optionally, the holding time of the constant voltage is 0 - 20h.

[0013] Optionally, the holding time of the constant voltage is 10 - 16h.

[0014] Optionally, the holding time of the constant voltage is independently selected from any value among 0 h, 5 h, 10 h, 12 h, 16 h, 18 h, 20 h or a range value between any two of the above.

[0015] Optionally, the scanning rate of the linear potential sweep is 0.1 - 10 mV s -1 , and the scanning voltage range is 2.5 V - 0 V.

[0016] Optionally, the scanning rate of the linear potential sweep is independently selected from any value among 0.1 mV s -1 , 1 mV s -1 , 2 mV s -1 , 5 mV s -1 , 8 mV s -1 , 10 mV s -1 or a range value between any two of the above.

[0017] Optionally, the scanning voltage is independently selected from any value among 2.5 V - 0.5 V, 1.3 V - 0.1 V, 0.5 V - 0 V or a range value between any two of the above.

[0018] Optionally, in step (1), the non-aqueous anode lithium metal battery is obtained by the following method:

[0019] Under an inert atmosphere, a lithium salt, an additive, and a solvent are mixed and stirred to obtain the electrolyte, and the electrolyte is assembled with the copper current collector, the separator, and the lithium cathode to obtain the non-aqueous anode lithium metal battery.

[0020] Optionally, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluoromethanesulfonyl)imide (LiFSI);

[0021] In the electrolyte, the concentration of the lithium salt is 0.5 - 5 mol / L.

[0022] Optionally, the concentration of the lithium salt is independently selected from any value among 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L or a range value between any two of the above.

[0023] Optionally, the additive is selected from at least one of lithium nitrate (LiNO3), vinyl ethylene carbonate (VEC), cyclotriphosphazene (FPPN), ethoxypentafluorocyclotriphosphazene (PFPN), pentafluoro(phenoxy)cyclotriphosphazene (HFPN), and 1,1,1,3,3,3-hexafluoroisopropyl-p-toluenesulfonate (HFST).

[0024] Optionally, in the electrolyte, the content of the additive is 0 to 5 wt %.

[0025] Optionally, the additive content is 0.5-3wt%.

[0026] Optionally, the additive content is independently selected from any value among 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt% or a range between any two of the above.

[0027] Optionally, the solvent is 1,3-dioxolane (DOL)

[0028] As a specific implementation manner, the copper current collector has a diameter of 14 mm and a thickness of 13 μm.

[0029] Optionally, the membrane is Celgard 3501.

[0030] As a specific implementation, the lithium positive electrode has a diameter of 10 mm and a thickness of 700 μm.

[0031] Optionally, the inert atmosphere is selected from at least one of argon and nitrogen.

[0032] As a specific implementation manner, the inert gas is high-purity argon gas with a purity greater than 99.999%, wherein the oxygen and water contents are less than 0.01 ppm.

[0033] Optionally, the stirring time is 0 to 8 hours.

[0034] Optionally, the stirring time is independently selected from any value of 1 h, 2 h, 4 h, 6 h, 8 h, or a range between any two of the above values.

[0035] As a specific embodiment, a potential control method for in-situ formation of a solid electrolyte interface phase, the potential control method comprises the following steps:

[0036] (1) mixing a solvent, a lithium salt, and an additive under an inert atmosphere, and stirring them thoroughly to obtain an electrolyte;

[0037] (2) Under the protection of an inert atmosphere, a copper current collector, an electrolyte, a separator, and a positive electrode are assembled in sequence to form a non-aqueous anode metal lithium battery;

[0038] (3) The assembled non-aqueous anode metal lithium battery in (2) is connected to an electrochemical workstation for linear potential scanning;

[0039] (4) The assembled non-aqueous anode metal lithium battery in (2) is connected to a battery testing system, and a constant voltage is set according to the decomposition potential determined in (3) to perform potential-controlled induction for the formation of a solid electrolyte interphase.

[0040] Among them, the positive electrode is metallic lithium.

[0041] In this application, for the range values of data, the endpoint values are all included. Except for the constant voltage and the scanning voltage, when other parameters are 0, the 0 value is not taken.

[0042] The beneficial effects that this application can produce include:

[0043] 1) Before battery cycling, this application uses a potential control method to induce in-situ formation of a solid electrolyte interphase by decomposing the electrolyte, reducing the consumption of active substances released from the positive electrode during cycling, and improving the Coulombic efficiency in the initial cycling stage of the battery.

[0044] 2) This application can induce the decomposition of different components in the electrolyte by controlling the potential magnitude and potential holding time of the copper current collector, adjust the composition and structure of the solid electrolyte interphase, reduce the interfacial impedance, and improve the interfacial stability. It is beneficial for Li + transport, and prevent continuous fragmentation and reorganization of the solid electrolyte interphase, thereby improving the Coulombic efficiency of the battery.

[0045] 3) This application can form a desired functional solid electrolyte interphase by changing the electrolyte components and adjusting the composition in the solid electrolyte interphase.

[0046] 4) This method induces the in-situ formation of a solid electrolyte interphase by applying a constant potential to the assembled battery. Compared with the non-in-situ copper current collector interface regulation strategy, it effectively simplifies the preparation process, making this method have the potential for commercial application. Description of the Drawings

[0047] Figure 1 It is a linear potential scanning diagram of the electrolyte components in the embodiment of this application;

[0048] Figure 2 It is the performance characterization curves of the surface of the copper electrode after potential control in Example 1, Example 4, and Example 5 of this application. Among them, Figure (a) is an EIS spectrum diagram, and Figure (b) is a DRT spectrum diagram;

[0049] Figure 3 These are the XPS spectra of the Cu surface composition after potential control in Example 1, Example 4, and Example 5 of this application. Among them, (a) is for Example 1, (b) is for Example 4, and (c) is for Example 5;

[0050] Figure 4 These are the lithium deposition morphologies at the first cycle of the battery after potential control in Example 1, Comparative Example 1, Example 4, and Example 5 of this application. The scale bar is 1 μm;

[0051] Figure 5 These are the XPS spectra of the surface composition of the battery after 5 cycles of potential control in Example 1, Example 4, and Example 5 of this application. Among them, (a) is for Example 1, (b) is for Example 4, and (c) is for Example 5;

[0052] Figure 6 These are the Coulombic efficiency diagrams of Example 1, Comparative Example 1, Example 4, and Example 5 of this application;

[0053] Figure 7 These are the Coulombic efficiency diagrams of Example 2, Comparative Example 2, Example 6, and Example 7 of this application;

[0054] Figure 8 These are the Coulombic efficiency diagrams of Example 2 and Example 8 of this application;

[0055] Figure 9 These are the Coulombic efficiency diagrams of Example 3, Comparative Example 3, Example 9, and Example 10 of this application. Detailed implementation manners

[0056] The following details this application in conjunction with examples, but this application is not limited to these examples.

[0057] Unless otherwise specified, the raw materials in the examples of this application are all purchased through commercial channels.

[0058] The analysis methods in the examples of this application are as follows:

[0059] Use the Shanghai Chenhua CHI604 electrochemical workstation (frequency range 3 MHz to 0.1 Hz, oscillation center 0 V vs. Li + / Li) to perform EIS tests, and use Matlab and DRTtool for DRT analysis;

[0060] Use an X-ray photoelectron spectrometer (X-ray photoelectron spectroscopy, XPS, Thermo ESCALAB250Xi) with a monochromatic Al Kα X-ray source to analyze the surface components of the samples.;

[0061] The morphology of lithium deposition in the first cycle of the battery after potential control was observed by scanning electron microscopy (Scanning electron microscopy, SEM, JEOL 6360LV@15kV and JSM 7800F@3kV).

[0062] Example 1

[0063] In an argon gas atmosphere, 10 mL of DOL, 2.8708 g of LiTFSI, 1.8708 g of LiFSI, and 0.1549 g of PFPN were uniformly mixed for 2 h to prepare an electrolyte. The obtained electrolyte was injected into a lithium metal-free battery with metallic lithium as the positive electrode (diameter 10 mm, thickness 700 μm), Celgard 3501 as the separator, and a copper current collector (diameter 14 mm, thickness 13 μm) as the negative electrode. The lithium metal-free battery was connected to an electrochemical workstation for LSV testing, where the scan rate was 0.1 mV s -1 , and the scanning voltage was OCV to 0 V vs. Li + / Li to determine the decomposition potential of each component. The lithium metal-free battery was placed in a Neware electrochemical test system, and the potential of the copper current collector was controlled at 0.5 V and maintained for 12 h to form a solid electrolyte interface layer. The battery after potential control was placed in a BlueTEC electrochemical test system for constant current charge and discharge testing.

[0064] Example 2

[0065] In an argon gas atmosphere, 10 mL of DOL, 2.8708 g of LiTFSI, 1.8708 g of LiFSI, and 0.3132 g of PFPN were uniformly mixed for 2 h to prepare an electrolyte. The obtained electrolyte was injected into a lithium metal-free battery with metallic lithium as the positive electrode (diameter 10 mm, thickness 700 μm), Celgard 3501 as the separator, and a copper current collector (diameter 14 mm, thickness 13 μm) as the negative electrode. The lithium metal-free battery was connected to an electrochemical workstation for LSV testing, where the scan rate was 0.1 mV s -1 , and the scanning voltage was OCV to 0 V vs. Li + / Li to determine the decomposition potential of each component. The lithium metal-free battery was placed in a Neware electrochemical test system, and the potential of the copper current collector was controlled at 0.5 V and maintained for 12 h to form a solid electrolyte interface layer. The battery after potential control was placed in a BlueTEC electrochemical test system for constant current charge and discharge testing.

[0066] Example 3

[0067] In an argon gas atmosphere, 10 mL of DOL, 2.8708 g of LiTFSI, 1.8708 g of LiFSI, and 0.1549 g of HFST were uniformly mixed for 2 h to prepare an electrolyte. The obtained electrolyte was injected into a lithium metal-free battery with metallic lithium as the positive electrode (diameter 10 mm, thickness 700 μm), Celgard 3501 as the separator, and a copper current collector (diameter 14 mm, thickness 13 μm) as the negative electrode. The lithium metal-free battery was connected to an electrochemical workstation for LSV testing, where the scan rate was 0.1 mV s -1 , and the scanning voltage was OCV to 0 V vs. Li + / Li to determine the decomposition potential of each component. The lithium metal-free battery was placed in a Neware electrochemical test system, and the potential of the copper current collector was controlled at 0.5 V and maintained for 12 h to form a solid electrolyte interface layer. The battery after potential control was placed in a Blue Energy electrochemical test system for constant current charge-discharge testing.

[0068] Comparative Example 1

[0069] In an argon gas atmosphere, 10 mL of DOL, 2.8708 g of LiTFSI, 1.8708 g of LiFSI, and 0.1549 g of PFPN were uniformly mixed for 2 h to prepare an electrolyte. The obtained electrolyte was injected into a lithium metal-free battery with metallic lithium as the positive electrode (diameter 10 mm, thickness 700 μm), Celgard 3501 as the separator, and a copper current collector (diameter 14 mm, thickness 13 μm) as the negative electrode. The lithium metal-free battery was connected to an electrochemical workstation for LSV testing, where the scan rate was 0.1 mV s -1 , and the scanning voltage was OCV to 0 V vs. Li + / Li to determine the decomposition potential of each component. The lithium metal-free battery was allowed to stand for 12 h to form a solid electrolyte interface layer. Subsequently, the battery was placed in a Blue Energy electrochemical test system for constant current charge-discharge testing.

[0070] Example 4

[0071] In an argon gas atmosphere, 10 mL of DOL, 2.8708 g of LiTFSI, 1.8708 g of LiFSI, and 0.1549 g of PFPN were uniformly mixed for 2 h to prepare an electrolyte. The obtained electrolyte was injected into a lithium metal-free battery with metallic lithium as the positive electrode (diameter 10 mm, thickness 700 μm), Celgard 3501 as the separator, and a copper current collector (diameter 14 mm, thickness 13 μm) as the negative electrode. The lithium metal-free battery was connected to an electrochemical workstation for LSV testing, where the scan rate was 0.1 mV s -1 , and the scanning voltage was OCV to 0 V vs. Li + / Li, determine the decomposition potential of each component. Place the non-aqueous lithium metal battery in a Neware electrochemical test system, control the potential of the copper current collector at 1.3 V, and maintain it for 12 h to form a solid electrolyte interface layer. The battery after potential control is placed in a Blue Power electrochemical test system for constant current charge and discharge testing.

[0072] Example 5

[0073] In an argon gas atmosphere, 10 mL of DOL, 2.8708 g of LiTFSI, 1.8708 g of LiFSI, and 0.1549 g of PFPN were uniformly mixed for 2 h to prepare an electrolyte. The obtained electrolyte was injected into a non-aqueous lithium metal battery with metallic lithium as the positive electrode (diameter 10 mm, thickness 700 μm), Celgard 3501 as the separator, and a copper current collector (diameter 14 mm, thickness 13 μm) as the negative electrode. The non-aqueous lithium metal battery was connected to an electrochemical workstation for LSV testing, where the scan rate was 0.1 mV s -1 , and the scanning voltage was OCV to 0 V vs. Li + / Li, determine the decomposition potential of each component. Place the non-aqueous lithium metal battery in a Neware electrochemical test system, control the potential of the copper current collector at 0.1 V, and maintain it for 12 h to form a solid electrolyte interface layer. The battery after potential control is placed in a Blue Power electrochemical test system for constant current charge and discharge testing.

[0074] Comparative Example 2

[0075] In an argon gas atmosphere, 10 mL of DOL, 2.8708 g of LiTFSI, 1.8708 g of LiFSI, and 0.3132 g of PFPN were uniformly mixed for 2 h to prepare an electrolyte. The obtained electrolyte was injected into a non-aqueous lithium metal battery with metallic lithium as the positive electrode (diameter 10 mm, thickness 700 μm), Celgard 3501 as the separator, and a copper current collector (diameter 14 mm, thickness 13 μm) as the negative electrode. The non-aqueous lithium metal battery was connected to an electrochemical workstation for LSV testing, where the scan rate was 0.1 mV s -1 , and the scanning voltage was OCV to 0 V vs. Li + / Li, determine the decomposition potential of each component. Place the non-aqueous lithium metal battery in a Neware electrochemical test system, let the battery stand for 12 h to form a solid electrolyte interface layer. The battery after potential control is placed in a Blue Power electrochemical test system for constant current charge and discharge testing.

[0076] Example 6

[0077] In an argon gas atmosphere, 10 mL of DOL, 2.8708 g of LiTFSI, 1.8708 g of LiFSI, and 0.3132 g of PFPN were uniformly mixed for 2 h to prepare an electrolyte. The obtained electrolyte was injected into a lithium metal-free battery with a lithium metal as the positive electrode (diameter: 10 mm, thickness: 700 μm), Celgard 3501 as the separator, and a copper current collector (diameter: 14 mm, thickness: 13 μm) as the negative electrode. The lithium metal-free battery was connected to an electrochemical workstation for LSV testing, with a scan rate of 0.1 mV s -1 , and the scanning voltage was OCV to 0 V vs. Li + / Li to determine the decomposition potential of each component. The lithium metal-free battery was placed in a Neware electrochemical test system, and the potential of the copper current collector was controlled at 1.3 V and maintained for 12 h to form a solid electrolyte interface layer. The battery after potential control was placed in a BlueTEC electrochemical test system for constant current charge and discharge testing.

[0078] Example 7

[0079] In an argon gas atmosphere, 10 mL of DOL, 2.8708 g of LiTFSI, 1.8708 g of LiFSI, and 0.3132 g of PFPN were uniformly mixed for 2 h to prepare an electrolyte. The obtained electrolyte was injected into a lithium metal-free battery with a lithium metal as the positive electrode (diameter: 10 mm, thickness: 700 μm), Celgard 3501 as the separator, and a copper current collector (diameter: 14 mm, thickness: 13 μm) as the negative electrode. The lithium metal-free battery was connected to an electrochemical workstation for LSV testing, with a scan rate of 0.1 mV s -1 , and the scanning voltage was OCV to 0 V vs. Li + / Li to determine the decomposition potential of each component. The lithium metal-free battery was placed in a Neware electrochemical test system, and the potential of the copper current collector was controlled at 0.1 V and maintained for 12 h to form a solid electrolyte interface layer. The battery after potential control was placed in a BlueTEC electrochemical test system for constant current charge and discharge testing.

[0080] Example 8

[0081] In an argon gas atmosphere, 10 mL of DOL, 2.8708 g of LiTFSI, 1.8708 g of LiFSI, and 0.3132 g of PFPN were uniformly mixed for 2 h to prepare an electrolyte. The obtained electrolyte was injected into a lithium metal-free battery with a lithium metal as the positive electrode (diameter: 10 mm, thickness: 700 μm), Celgard 3501 as the separator, and a copper current collector (diameter: 14 mm, thickness: 13 μm) as the negative electrode. The lithium metal-free battery was connected to an electrochemical workstation for LSV testing, with a scan rate of 0.1 mV s -1, the scanning voltage is OCV to 0 V vs. Li + / Li, to determine the decomposition potential of each component. Place the lithium metal battery without a negative electrode in a Neware electrochemical test system, control the potential of the copper current collector at 0.5 V, and maintain it for 20 h to form a solid electrolyte interface layer. The battery after potential control is placed in a BlueTEC electrochemical test system for constant current charge and discharge testing.

[0082] Comparative Example 3

[0083] In an argon gas atmosphere, 10 mL of DOL, 2.8708 g of LiTFSI, 1.8708 g of LiFSI, and 0.1549 g of HFST are uniformly mixed for 2 h to prepare an electrolyte. The obtained electrolyte is injected into a lithium metal battery without a negative electrode with metallic lithium as the positive electrode (diameter 10 mm, thickness 700 μm), Celgard 3501 as the separator, and a copper current collector (diameter 14 mm, thickness 13 μm) as the negative electrode. The lithium metal battery without a negative electrode is connected to an electrochemical workstation for LSV testing, where the scanning rate is 0.1 mV s -1 , the scanning voltage is OCV to 0 V vs. Li + / Li, to determine the decomposition potential of each component. Place the lithium metal battery without a negative electrode in a Neware electrochemical test system, let it stand for 12 h to form a solid electrolyte interface layer. The battery after potential control is placed in a BlueTEC electrochemical test system for constant current charge and discharge testing.

[0084] Example 9

[0085] In an argon gas atmosphere, 10 mL of DOL, 2.8708 g of LiTFSI, 1.8708 g of LiFSI, and 0.1549 g of HFST are uniformly mixed for 2 h to prepare an electrolyte. The obtained electrolyte is injected into a lithium metal battery without a negative electrode with metallic lithium as the positive electrode (diameter 10 mm, thickness 700 μm), Celgard 3501 as the separator, and a copper current collector (diameter 14 mm, thickness 13 μm) as the negative electrode. The lithium metal battery without a negative electrode is connected to an electrochemical workstation for LSV testing, where the scanning rate is 0.1 mV s -1 , the scanning voltage is OCV to 0 V vs. Li + / Li, to determine the decomposition potential of each component. Place the lithium metal battery without a negative electrode in a Neware electrochemical test system, control the potential of the copper current collector at 1.3 V, and maintain it for 12 h to form a solid electrolyte interface layer. The battery after potential control is placed in a BlueTEC electrochemical test system for constant current charge and discharge testing.

[0086] Example 10

[0087] In an argon gas atmosphere, 10 mL of DOL, 2.8708 g of LiTFSI, 1.8708 g of LiFSI, and 0.1549 g of HFST were uniformly mixed for 2 h to prepare an electrolyte. The obtained electrolyte was injected into a non-aqueous lithium metal battery with metallic lithium as the positive electrode (diameter: 10 mm, thickness: 700 μm), Celgard 3501 as the separator, and a copper current collector (diameter: 14 mm, thickness: 13 μm) as the negative electrode. The non-aqueous lithium metal battery was connected to an electrochemical workstation for LSV testing, where the scan rate was 0.1 mV s -1 , and the scanning voltage was OCV~0 V vs. Li + / Li to determine the decomposition potential of each component. The non-aqueous lithium metal battery was placed in a Neware electrochemical test system, and the potential of the copper current collector was controlled at 0.1 V and maintained for 12 h to form a solid electrolyte interface layer. The battery after potential control was placed in a BlueTEC electrochemical test system for constant current charge-discharge testing.

[0088] Analysis of experimental results

[0089] In the examples, the reduction decomposition potential of the electrolyte was determined by linear scanning of the electrolyte. Referring to Figure 1 , it was divided into three segments: 0~0.2 V, 0.2~1.0 V, and 1.0~1.5 V. According to the results of linear potential scanning, the constant voltage values for potential control were set.

[0090] After the potential control of Examples 4, 5, and 1 was carried out, the surface of the copper electrode was analyzed by Figure 2 (a) EIS spectra. By comparing the EIS spectra of Examples 4, 5, and 1, it can be concluded that the surface of the copper electrode in Example 1 has a smaller interfacial impedance. At the same time, by comparing Figure 2 (b) the DRT spectra, it can be seen that the surface of the electrode in Example 1 has a smaller Li + desolvation impedance (R2), Li + transport impedance (R3) in the solid electrolyte interface phase, and charge transfer impedance (R4), which is beneficial to the rapid lithium ion transport and electrochemical reaction kinetics at the electrode interface; the reason for this phenomenon is that the constant voltage value in Example 1 is conducive to the formation of more Li + with high Li + conductivity; while the content of Li3N components with high Li + conductivity in Example 4 is relatively low, and the content of the organic component P-N with low Li + conductivity in Example 5 is relatively high, which is not conducive to the transport of Li Figure 3 at the interface and the occurrence of electrode reactions, which is consistent with the

[0091] XPS spectra of the Cu surface composition after potential control in Example 1, Example 4, and Example 5 ( Figure 3 ), it can be seen that the nitrogen-containing components in Example 1 are mainly PFPN, Li3N, and LiN formed by the complete decomposition of the lithium salt x O y - , NO2 - and other high-ion-conductivity products. In Example 4, the incomplete decomposition of PFPN and the lithium salt, and the violent decomposition of the solvent (DOL) in Example 5 result in a significant decrease in the high-ion-conductivity LiN x O y - , NO2 - compared with Example 1. Therefore, Example 1 is more conducive to the formation of a high-ion-conductivity SEI, improving interfacial lithium-ion transport and electrochemical reaction kinetics

[0092] Comparing the initial lithium metal deposition morphologies of Comparative Example 1, Example 4, Example 5, and Example 1 ( Figure 4 ), it can be seen that the lithium metal deposition morphology in Example 1 is more flat and dense; while the lithium metal deposition morphology in Comparative Example 1 is composed of a large number of lithium metal particles piled up, loose and porous, which means that applying potential control can significantly improve the lithium metal deposition morphology. Due to the different electrode potentials applied at the potential-controlled interfaces in Example 4, Example 5, and Example 1, there are significant differences in the deposition morphologies. Dendritic lithium deposition even appears in Example 4, proving that the solid electrolyte interface phase with a low interfacial impedance generated by the potential value in Example 1 is more conducive to the formation of a uniform and flat lithium deposition morphology.

[0093] Comparing the XPS spectra of the electrode surface composition after five constant-current charge-discharge cycles of the batteries in Example 4, Example 5, and Example 1 ( Figure 5 ), it can be seen that from the outside to the inside of the solid electrolyte interface phase in Example 1, the organic components represented by C-O-C and the unstable Li2CO3 component gradually decrease, and the inorganic components such as Li2O gradually increase, indicating that the solid electrolyte interface phase in Example 1 is a bilayer structure. In Example 4 and Example 5, from the outside to the inside, the solid electrolyte interface phase is always dominated by unstable Li2CO3 and ROCO2-Li. Therefore, the constant voltage value in Example 1 is more conducive to the formation of a stable bilayer SEI, preventing continuous fragmentation and reorganization during cycling, and having a better protective effect.

[0094] Performing constant-current charge-discharge tests on Comparative Example 1, Example 4, Example 5, and Example 1, with a current density of 1 mA cm -2 , and the results are as Figure 6 shown. From Figure 6It can be seen that the initial Coulombic efficiency of Example 1 is as high as 93.6%, and the Coulombic efficiency of the subsequent battery cycles quickly stabilizes at 98.7%. In contrast, Comparative Example 1 and Example 4 show low initial Coulombic efficiencies of 82.8% and 87.0% respectively. During the subsequent constant current charge-discharge process, the Coulombic efficiency slowly increases and only reaches a stable value (98.1%, 98.2%) after 20 cycles. Although Example 5 shows a high initial Coulombic efficiency of 93.6%, the Coulombic efficiency of the battery significantly decreases after long-term cycling, which can well verify Figure 2 and Figure 5 the characterization results, that is, under the potential value condition of Example 1, potential control is carried out, and the generated SEI has low interfacial impedance and high stability, which can significantly improve the initial Coulombic efficiency, uniform the deposition morphology of metallic lithium, and play a continuous protective role during the subsequent cycling process, improving the Coulombic efficiency after stabilization and cycling stability.

[0095] Based on the principle of potential control, the appropriate electrode potential is selected to induce different degrees of decomposition of electrolyte components to form a good solid electrolyte interface phase. With the components of the electrolyte remaining unchanged and the additive content adjusted, the same law should be followed under the same constant voltage condition.

[0096] Comparing Figure 7 Comparative Example 2, Example 6, Example 7 and Example 2, the same law as that of Comparative Example 1, Example 4, Example 5 and Example 1 can be obtained. Although the additive concentration is increased, under the constant potential value condition of Example 2, the initial Coulombic efficiency of the battery can still be significantly improved to 92.7%, and the Coulombic efficiency after stabilization is 98.7%. Without potential control, Comparative Example 2 shows a low initial Coulombic efficiency of 89.0% and a slow process of Coulombic efficiency stabilization. Although Example 6 and Example 7 have relatively high initial Coulombic efficiencies, the subsequent constant current charge-discharge process shows relatively low Coulombic efficiencies. It is proved that when the components of the electrolyte remain unchanged and the additive content increases, the Coulombic efficiency of the battery can still be improved under the condition of appropriate constant potential value.

[0097] Based on the fact that potential control induces the decomposition of electrolyte components to form a solid electrolyte interface phase, the constant potential time affects the quality of the solid electrolyte and thus affects the Coulombic efficiency of the battery. By comparing Example 8 and Example 2 (see Figure 8 ), it can be concluded that when the constant voltage control time of Example 8 is extended, the Coulombic efficiency decreases instead, indicating that the constant voltage control time needs to be within an appropriate range. In this study, the potential control time is preferably 10 - 16 h.

[0098] In addition, by changing the types of additives in the electrolyte (Example 3, Comparative Example 3, Example 9, Example 10), the battery Coulombic efficiency still shows the same performance improvement law (see Figure 9 ).

[0099] The improvement of the Coulombic efficiency in the examples is mainly achieved by taking advantage of the differences in the decomposition potentials of the components in the electrolyte. Before the battery cycling of the assembled lithium metal battery without a negative electrode, through a potential control method, an appropriate constant voltage value and an appropriate constant voltage control time are selected to induce the decomposition of the components in the electrolyte, and a solid electrolyte interface phase with low interfacial impedance and high stability is formed in-situ. On the one hand, it is beneficial to the Li+ transport, and on the other hand, the high stability can be maintained during the battery cycling. Therefore, the Coulombic efficiency of the first cycle and the cycling stability of the battery can be significantly improved.

[0100] As described above, only several embodiments of the present application are presented, and no any form of limitation is imposed on the present application. Although the present application is disclosed with preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, makes some changes or modifications using the disclosed technical content, which are equivalent to equivalent embodiments and all fall within the scope of the technical solution.

Claims

1. A method for in-situ formation of a solid electrolyte interphase, characterized in that, The method includes: (1) Connect the non-aqueous cathode metal lithium battery to an electrochemical workstation, perform linear potential scanning, and determine the decomposition potential of each component in the electrolyte; Among them, the non-aqueous cathode metal lithium battery includes the electrolyte, copper current collector, separator, and lithium cathode; the electrolyte includes a solvent, a lithium salt, and an additive; (2) Connect the non-aqueous cathode metal lithium battery in step (1) to a battery test system, set a constant voltage according to the decomposition potential determined in step (1), and perform potential control to induce the formation of a solid electrolyte interface phase.

2. The method according to claim 1, characterized in that, The constant voltage is 0 to 1.5 V; Preferably, the constant voltage is 0.2 to 1.0 V.

3. The method according to claim 1, characterized in that, The holding time of the constant voltage is 0 to 20 h; Preferably, the holding time of the constant voltage is 10 to 16 h.

4. The method according to claim 1, characterized in that, The scanning rate of the linear potential sweep is 0.1 to 10 mV s -1 , and the scanning voltage range is 2.5 V to 0 V.

5. The method according to claim 1, characterized in that, In step (1), the non-aqueous cathode metal lithium battery is obtained by the following method: Under an inert atmosphere, mix the lithium salt, additive, and solvent, and stir to obtain the electrolyte. Assemble the electrolyte with the copper current collector, separator, and lithium cathode to obtain the non-aqueous cathode metal lithium battery.

6. The method according to claim 5, characterized in that, The lithium salt is selected from at least one of lithium hexafluoroborate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluoromethanesulfonyl)imide; In the electrolyte, the concentration of the lithium salt is 0.5 to 5 mol / L.

7. The method according to claim 5, characterized in that, The additive is selected from at least one of lithium nitrate, vinylene carbonate, cyclotriphosphazene, ethoxy pentafluorocyclotriphosphazene, pentafluoro(phenoxy)cyclotriphosphazene, and 1,1,1,3,3,3-hexafluoroisopropyl tosylate; In the electrolyte, the content of the additive is 0 to 5 wt%; Preferably, the content of the additive is 0.5 to 3 wt%.

8. The method according to claim 5, characterized in that, The solvent is 1,3-dioxolane.

9. The method according to claim 5, characterized in that, The separator is Celgard 3501.

10. The method according to claim 5, characterized in that, The inert atmosphere is selected from at least one of argon and nitrogen; The stirring time is 0 to 8 h.

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