A preparation method and application of LiBr@Li electrode based on LiBr interface protection layer

Abstract

The application relates to a preparation method and application of a LiBr@Li electrode based on a LiBr interface protection layer, and relates to a preparation method and application of a lithium electrode. The application aims to solve the problems of uneven lithium deposition, lithium dendrite growth, increased side reactions, low coulomb efficiency, poor cycle performance and short service life of existing lithium metal batteries in the charging and discharging process due to uneven distribution of lithium ions on the electrode surface. The lithium metal electrode is modified by adopting a LiBr interface protection layer. LiBr has good ion conductivity and can accelerate lithium ion transmission. Meanwhile, the chemical structure of LiBr is stable, can maintain stability in a wide voltage window, prevents continuous decomposition of electrolyte, improves the overall stability of the battery, effectively inhibits lithium dendrite growth, can reduce the interface energy between lithium metal and electrolyte, reduces side reactions, greatly improves the coulomb efficiency of the battery, and significantly improves the cycle performance of the battery and prolongs the service life.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method and application of a lithium electrode. BACKGROUND

[0002] The high theoretical specific capacity (3860 mAh g -1 ) and the lowest electrode potential (-3.04 V vs standard hydrogen electrode) of lithium metal make lithium metal batteries (LMB) have the potential to become a new type of high-energy-density energy storage device. However, the development of lithium metal batteries faces many challenges. First, during the cycling process, the deposition of lithium metal is in a non-uniform state, and dendrite growth is not controlled, which can easily lead to battery failure, and there are also safety hazards in organic electrolyte systems. Second, lithium metal has ultra-high chemical activity, which is prone to irreversible reactions with electrolyte and positive electrode material, causing rapid capacity decay of the battery. In addition, due to the lack of a host structure in the lithium metal electrode, infinite volume change occurs during battery operation, and the deposition / stripping of lithium ions also presents a non-uniform phenomenon, which further promotes the growth of dendrites. These problems, in combination, will lead to continuous loss of lithium and electrolyte, the formation of "dead lithium", and ultimately result in a decrease in battery coulombic efficiency (CE) and battery failure.

[0003] To solve these problems, researchers have proposed various strategies, including the use of solid electrolytes, the addition of electrolyte additives, the construction of artificial SEI, and the creation of a three-dimensional host. Among them, modifying the lithium metal battery electrode interface and constructing an artificial SEI layer are considered to be an effective way to simultaneously alleviate volume change and inhibit dendrite growth. By carefully designing and regulating the composition, structure, and performance of the artificial SEI, the interface characteristics of the lithium metal electrode can be significantly optimized, which is expected to promote the practical application of lithium metal batteries.

[0004] In terms of constructing an artificial SEI, existing technologies mainly include chemical vapor deposition (CVD), physical vapor deposition (PVD), and solution methods. Although chemical vapor deposition can accurately control the composition and thickness of the SEI layer, it has a complex process, high cost, and is difficult to apply on a large scale. In addition, impurities may be introduced during the deposition process, affecting the stability of the SEI layer. Physical vapor deposition can prepare high-quality SEI layers, but the equipment is expensive, the yield is low, and the adhesion to the substrate during the deposition process is limited, causing the SEI layer to easily fall off. The solution method is relatively simple to operate and has a lower cost, but the uniformity of the prepared SEI layer is poor, and it is difficult to precisely control its microstructure, which limits its effectiveness in inhibiting lithium dendrite growth and alleviating volume change. These problems in existing technologies limit the further development and commercial application of lithium metal batteries. SUMMARY

[0005] The purpose of the present application is to solve the problems of uneven lithium deposition, lithium dendrite growth, increased side reactions, low coulombic efficiency, poor cycle performance and short service life caused by uneven distribution of lithium ions on the electrode surface during the charging and discharging process of existing lithium metal batteries, and to provide a preparation method and application of LiBr@Li electrode based on LiBr interfacial protection layer.

[0006] The present application uses LiBr interfacial protection layer to modify the lithium metal electrode. LiBr has good ionic conductivity, which can accelerate lithium ion transmission. At the same time, it has stable chemical structure and can maintain stability in a wide voltage window, prevent electrolyte from continuous decomposition and improve the overall stability of the battery. LiBr can quickly and uniformly spread on the lithium metal electrode due to its small lattice energy, forming a dense protective film. This film not only can precisely regulate lithium ion deposition and effectively inhibit lithium dendrite growth, but also can reduce the interface energy between lithium metal and electrolyte, reduce side reactions and greatly improve the coulombic efficiency of the battery, thereby significantly improving the cycle performance of the battery and prolonging the service life.

[0007] A preparation method of LiBr@Li electrode based on LiBr interfacial protection layer, which is completed according to the following steps:

[0008] I. In an argon-filled glove box, tris(2,3-dibromopropyl) isocyanurate is added to an organic solvent, and magnetically stirred for a period of time to obtain a tris(2,3-dibromopropyl) isocyanurate solution;

[0009] II. In an argon-filled glove box, the tris(2,3-dibromopropyl) isocyanurate solution is uniformly drop-coated on one surface of a lithium sheet, and after a period of reaction, the lithium sheet is washed in an organic solvent to remove unreacted tris(2,3-dibromopropyl) isocyanurate solution, and finally the lithium sheet is dried in a room temperature environment to obtain a LiBr@Li electrode based on LiBr interfacial protection layer.

[0010] A LiBr@Li electrode based on LiBr interfacial protection layer is applied in a lithium metal battery.

[0011] Principles and advantages of the present application:

[0012] The application focuses on constructing an artificial SEI layer rich in LiBr; LiBr spreads rapidly and uniformly on the surface of a lithium metal electrode to form an extremely dense artificial SEI; this SEI film is just like an intelligent protective barrier, which precisely regulates the deposition behavior of lithium ions: in the nucleation stage, the LiBr layer changes the deposition mode of lithium, making it more uniform, which is conducive to the dense growth of lithium; and can provide a large number of uniformly distributed active sites for lithium deposition, effectively reducing the nucleation barrier; it can also significantly reduce the interfacial energy between lithium metal and electrolyte, reducing the occurrence of side reactions; during the charge and discharge cycle, the LiBr layer can well adapt to the volume change of lithium due to its good flexibility and stability, stabilize the electrode interface, and greatly inhibit the generation of lithium dendrites. The design idea of the application is innovative and unique, the experimental operation is relatively simple, and the comprehensive performance of the lithium metal battery is effectively improved, which opens up a new way for promoting its practical application.

[0013] Secondly, the electrochemical performance of the LiBr@Li electrode based on the LiBr interface protection layer obtained by the application is tested, and the results show that the symmetric battery assembled by the LiBr@Li electrode based on the LiBr interface protection layer can be stably cycled for more than 700h under the current density of 5mAcm -2 and the surface capacity of 1mAhcm -2 , which indicates that the LiBr@Li electrode based on the LiBr interface protection layer provided by the application has excellent lithium deposition / stripping stability; when assembled with a lithium iron phosphate (LiFePO4) anode, the LiBr@Li electrode based on the LiBr interface protection layer shows a high discharge specific capacity of 76mAhg -1 and a capacity retention rate of 73% after 4500 cycles at an initial capacity of 102mAhg -1 at 5C, which indicates that the LiBr@Li electrode based on the LiBr interface protection layer provided by the application has a high cycle life. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 SEM image, wherein a is the SEM image of the untreated lithium sheet, and b is the SEM image of the LiBr@Li electrode based on the LiBr interface protection layer prepared in Example 1;

[0015] Figure 2 XPS image of the LiBr@Li electrode based on the LiBr interface protection layer prepared in Example 1, wherein a is Li1s, and b is Br 3d;

[0016] Figure 3 Li∥Li symmetric battery and LiBr@Li∥LiBr@Li symmetric battery at a current density of 2mAcm -2The in-situ optical characterization maps of lithium deposition under the Li||Li symmetric cell and the LiBr@Li||LiBr@Li symmetric cell, wherein a, b, c and d are Li||Li symmetric cells, and e, f, g and h are LiBr@Li||LiBr@Li symmetric cells;

[0017] Figure 4 The constant current charge-discharge curves of the Li||Li symmetric cell and the LiBr@Li||LiBr@Li symmetric cell;

[0018] Figure 5 The cycle performance of the Li||LFP full cell and the LiBr@Li||LFP full cell;

[0019] Figure 6 The cycle performance of the Li||NCM811 full cell and the LiBr@Li||NCM811 full cell. DETAILED DESCRIPTION

[0020] Embodiment I: A preparation method of a LiBr@Li electrode based on a LiBr interfacial protection layer is provided, which is completed according to the following steps:

[0021] I. In an argon-filled glove box, tris(2,3-dibromopropyl) isocyanurate is added to an organic solvent, and magnetically stirred for a period of time to obtain a tris(2,3-dibromopropyl) isocyanurate solution;

[0022] II. In an argon-filled glove box, the tris(2,3-dibromopropyl) isocyanurate solution is uniformly drop-coated on one surface of a lithium sheet, and after a period of reaction, the lithium sheet is washed in an organic solvent to remove unreacted tris(2,3-dibromopropyl) isocyanurate solution, and finally the lithium sheet is dried in a room temperature environment to obtain a LiBr@Li electrode based on a LiBr interfacial protection layer.

[0023] Embodiment II: The difference between this embodiment and Embodiment I is that the water content in the argon-filled glove box in step I is precisely controlled to be <0.01 ppm, and the oxygen content is <0.01 ppm. The other steps are the same as those in Embodiment I.

[0024] Embodiment III: The difference between this embodiment and either of Embodiments I or II is that the organic solvent in step I is N-methylpyrrolidone, dimethylformamide or tetrahydrofuran. The other steps are the same as those in Embodiments I or II.

[0025] Embodiment IV: The difference between this embodiment and any one of Embodiments I to III is that the mass-to-volume ratio of tris(2,3-dibromopropyl) isocyanurate to organic solvent in step I is (0.01 g-0.03 g):1 mL. The other steps are the same as those in Embodiments I to III.

[0026] Specific embodiment five: the difference between this embodiment and one of the specific embodiments one to four is that the magnetic stirring speed in step one is 200 r / min to 500 r / min, and the magnetic stirring time is 5 min to 10 min.

[0027] The other steps are the same as specific embodiments one to four.

[0028] Specific embodiment six: the difference between this embodiment and one of the specific embodiments one to five is that the organic solvent in step two is N-methyl pyrrolidone, dimethylformamide or tetrahydrofuran. The other steps are the same as specific embodiments one to five.

[0029] Specific embodiment seven: the difference between this embodiment and one of the specific embodiments one to six is that the volume to surface area ratio of tris(2,3-dibromopropyl) isocyanurate solution to lithium piece in step two is 30 mL:150 mm 2 . The other steps are the same as specific embodiments one to six.

[0030] Specific embodiment eight: the difference between this embodiment and one of the specific embodiments one to seven is that the reaction time in step two is 1 min to 2 min. The other steps are the same as specific embodiments one to seven.

[0031] Specific embodiment nine: the difference between this embodiment and one of the specific embodiments one to eight is that the drying time in step two is 3 h to 4 h. The other steps are the same as specific embodiments one to eight.

[0032] Specific embodiment ten: this embodiment is the application of LiBr@Li electrode based on LiBr interface protection layer in lithium metal battery.

[0033] The beneficial effects of the present application are verified by the following examples:

[0034] Example 1: a preparation method of LiBr@Li electrode based on LiBr interface protection layer, specifically completed by the following steps:

[0035] I. In an argon-filled glove box, 0.02 g of tris(2,3-dibromopropyl) isocyanurate was added to 1 mL of N-methyl pyrrolidone (NMP), and magnetic stirring was carried out at a magnetic stirring speed of 200 r / min for 10 min to obtain a tris(2,3-dibromopropyl) isocyanurate solution;

[0036] The water content in the argon-filled glove box in step one is accurately controlled to be <0.01 ppm, and the oxygen content is <0.01 ppm;

[0037] 2. In an argon-filled glove box, 30 mL of tris(2,3-dibromopropyl) isocyanurate solution was uniformly drop-coated onto one surface of a lithium sheet. After reacting for 1 min, the lithium sheet was washed in N-methylpyrrolidone (NMP) to remove unreacted tris(2,3-dibromopropyl) isocyanurate solution. Finally, the lithium sheet was dried at room temperature for 3 h to obtain a LiBr@Li electrode based on a LiBr interface protective layer.

[0038] The volume ratio of the tris(2,3-dibromopropyl)isocyanurate solution to the surface area of ​​the lithium sheet in step two is 30 mL: 150 mm². 2 .

[0039] Figure 1 The figures are SEM images, where a is the SEM image of the untreated lithium sheet and b is the SEM image of the LiBr@Li electrode based on the LiBr interface protective layer prepared in Example 1.

[0040] from Figure 1 As can be seen from image a, the surface of lithium metal is smooth. From... Figure 1 As can be seen from b, the surface of the LiBr@Li electrode based on the LiBr interface protective layer has a uniform and dense coating.

[0041] Figure 2 XPS images of the LiBr@Li electrode based on the LiBr interface protective layer prepared in Example 1, where a represents Li1s and b represents Br3d.

[0042] from Figure 2 As can be seen from a, Li 1s at 56.6 eV belongs to the LiBr@Li electrode based on the LiBr interface protective layer; from Figure 2 As shown in b, the peak at 69.0 eV in the Br 3d spectrum belongs to the LiBr@Li electrode based on the LiBr interface protective layer; XPS shows that after the in-situ reaction, an artificial SEI layer rich in LiBr was successfully prepared on the lithium metal surface.

[0043] Assemble symmetrical cells:

[0044] In an Ar-filled glovebox, a coin cell assembly with model 2032, a commercial polypropylene separator (Celgard 2500) with a diameter of 18 mm, and a stainless steel spacer (SS) with a thickness of 1 mm were assembled. The assembly was stacked in the order of negative electrode shell, battery spring, SS, LiBr@Li electrode prepared in Example 1, commercial polypropylene separator, LiBr@Li electrode prepared in Example 1, and positive electrode shell. 30 μL of commercial electrolyte (purchased from Solstice, detailed composition: 1.0 M LiTFSI in DOL:DME = 1:1 vol% with 2.0% LiNO3) was added to the interface between the LiBr@Li electrode and the commercial polypropylene separator for wetting. Then, the assembly was pressed to 50 kgcm -2 on a manual coin cell sealer and taken out after 5 s, at which time the battery assembly was complete.

[0045] A Li∥Li symmetric cell was assembled using lithium sheet according to the same method as above.

[0046] To visually demonstrate the advantage of the protective layer in the process of lithium plating, Li∥Li symmetric cells and LiBr@Li∥LiBr@Li symmetric cells were tested by in-situ optical microscopy at a current density of 2 mAcm -2 . Figure 3 As shown in (a, b), after 30 min, a large number of lithium dendrites appeared on the surface of the bare lithium metal electrode, and the battery short-circuited. This indicates that due to the tip of the lithium metal surface, the space charge effect and the uneven Li + distribution, lithium metal tends to deposit unevenly on the surface without protection, and the deposition is uneven, concentrated in the nucleation position at the initial time. In contrast, the LiBr@Li electrode prepared in Example 1 based on the LiBr interface protective layer showed a relatively uniform surface within 10 h of lithium deposition time, indicating that the artificial SEI of the LiBr@Li electrode prepared in Example 1 based on the LiBr interface protective layer is conducive to the formation of compact and uniform lithium deposition morphology, avoiding the growth of dendrites, and is conducive to the safety of lithium metal batteries.

[0047] To reveal the advantage of the LiBr layer, a symmetric cell was assembled using the LiBr@Li electrode prepared in Example 1 as the working electrode and lithium sheet as the counter electrode for charge-discharge testing, and the results are shown in Figure 4 . At a current density of 5 mAcm -2 and a capacity of 1 mAhcm -2Under the same area capacity, the voltage polarization of bare Li||Li cell gradually increased from 200 hours, and LiBr@Li||LiBr@Li symmetric cell showed lower voltage polarization than bare Li||Li cell and could maintain stable cycling for at least 700 hours. This indicates the superiority of the LiBr-rich artificial SEI layer.

[0048] In order to further explore the potential value of LiBr@Li electrode based on LiBr interfacial protection layer prepared in Example 1 in practical application, lithium metal full cells were prepared by assembling lithium iron phosphate (LiFePO4, LFP) positive electrode and lithium nickel cobalt manganese oxide (NCM811) positive electrode with different negative electrodes, and comparative study on their electrochemical performance was carried out.

[0049] The assembly method of LiBr@Li||LFP full cell is as follows:

[0050] In an Ar-filled glove box, 2032 type coin cell components, 18 mm diameter commercial polypropylene separator (Celgard 2500) and 1 mm thick stainless steel gasket (SS) were selected for assembly. In order, the negative electrode shell, the battery spring, the SS, the LiBr@Li electrode prepared in Example 1, the commercial polypropylene separator, the lithium iron phosphate (LiFePO4, LFP) positive electrode or the lithium nickel cobalt manganese oxide (NCM811) positive electrode, and the positive electrode shell were stacked and assembled. 50 μL of commercial electrolyte (purchased from Celgard Company, product details: 1.0 M LiPF6 in EC:DEC:DMC = 1:1:1 vol% with 5.0% FEC) was added to the interface between the LiBr@Li electrode and the commercial polypropylene separator for wetting; then it was pressed to 50 kgcm -2 on a manual coin cell sealing machine and taken out after 5 s, at which time the battery assembly was completed.

[0051] According to the same method, lithium metal full cells were prepared by assembling lithium sheet as negative electrode with lithium iron phosphate (LiFePO4, LFP) positive electrode and lithium nickel cobalt manganese oxide (NCM811) positive electrode, and comparative study on their electrochemical performance was carried out.

[0052] In the experiment with LFP as the positive electrode, the active material mass loading of the LFP electrode was ~ 5.1 mgcm -2 . From Figure 5 the experimental data, LiBr@Li||LFP full cell showed an initial discharge capacity of 102 mAhg -2 at a charge-discharge rate of 5C. After 4500 cycles, the discharge capacity of the battery could still be maintained at 76 mAhg -2, and the capacity retention rate is as high as 73%, showing good cycle stability. In contrast, the capacity of the traditional Li||LFP full battery decreases rapidly with the increase of cycle number.

[0053] In the experiment with NCM811 as the positive electrode, the active material mass loading of the NCM811 electrode is ~ 8.7 mg cm -2 . Also from Figure 6 It can be seen that the initial discharge capacity of the LiBr@Li||NCM811 full battery is up to 164 mAh g -2 at a charge-discharge rate of 2C. After 350 cycles, the discharge capacity is 98 mAh g -2 , and the capacity retention rate is 60%, also showing a high capacity retention ability. In sharp contrast, the capacity of the Li||NCM811 full battery also shows a rapid decay during the cycle.

[0054] The above experimental results fully show that the LiBr@Li electrode for lithium metal batteries provided by the application has excellent performance in terms of discharge specific capacity and cycle life, and has significant application advantages and broad market prospects.

Claims

1. A method for preparing LiBr@Li electrode based on LiBr interfacial protection layer, characterized by The preparation method is specifically completed according to the following steps: I. In an argon-filled glove box, tri(2,3-dibromopropyl) isocyanurate is added to an organic solvent, and magnetic stirring is performed for a period of time to obtain a tri(2,3-dibromopropyl) isocyanurate solution; II. In an argon-filled glove box, the tri(2,3-dibromopropyl) isocyanurate solution is uniformly drop-coated on one surface of a lithium sheet, and after reaction for a period of time, the lithium sheet is washed in an organic solvent to remove unreacted tri(2,3-dibromopropyl) isocyanurate solution, and finally the lithium sheet is dried at room temperature to obtain a LiBr@Li electrode based on a LiBr interfacial protection layer.

2. The method for preparing LiBr@Li electrode based on LiBr interfacial protection layer according to claim 1, characterized in that The water content in the argon-filled glove box in step I is accurately controlled to be <0.01 ppm, and the oxygen content is <0.01 ppm.

3. The method of claim 1, wherein the method is characterized by The organic solvent in step I is N-methylpyrrolidone, dimethylformamide or tetrahydrofuran.

4. The method of claim 1, wherein the method is characterized by The mass / volume ratio of tri(2,3-dibromopropyl) isocyanurate to organic solvent in step I is (0.01 g-0.03 g): 1 mL.

5. The method of claim 1, wherein the method is characterized by The speed of magnetic stirring in step I is 200 r / min-500 r / min, and the time of magnetic stirring is 5 min-10 min.

6. The method of claim 1, wherein the method is characterized by The organic solvent in step II is N-methylpyrrolidone, dimethylformamide or tetrahydrofuran.

7. The method of claim 1, wherein the method is characterized by The volume of the solution of tris(2,3-dibromopropyl) isocyanurate described in step two to one surface area of lithium pieces is 30 mL : 150 mm 2 .

8. The method of claim 1, wherein the method is characterized by The reaction time in step II is 1 min-2 min.

9. The method of claim 1, wherein the method is characterized by The drying time in step II is 3 h-4 h.

10. Use of a LiBr@Li electrode based on a LiBr interfacial protection layer prepared according to the preparation method of claim 1, characterized in that A LiBr@Li electrode based on a LiBr interfacial protection layer is applied in a lithium metal battery.

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