Preparation method and application of LiBr (at) Li electrode based on LiBr interface protection layer

Abstract

The invention discloses a preparation method and application of a LiBr-coated Li electrode based on a LiBr interface protective layer, and relates to a preparation method and application of a lithium electrode. The invention aims to solve the problems of non-uniform lithium deposition, lithium dendrite growth, side reaction increase, low coulombic efficiency, poor cycle performance and short service life caused by non-uniform distribution of lithium ions on the surface of an electrode in the charging and discharging process of the existing lithium metal battery. The LiBr interface protection layer is adopted to modify the lithium metal electrode, and LiBr has good ionic conductivity and can accelerate lithium ion transmission; meanwhile, the chemical structure is stable and can be kept stable in a wide voltage window, continuous decomposition of an electrolyte is prevented, and the overall stability of the battery is improved; lithium dendrite growth is effectively inhibited, the interface energy of lithium metal and electrolyte can be reduced, side reactions are reduced, and the coulombic efficiency of the battery is greatly improved, so that the cycle performance of the battery is remarkably improved, and the service life of the battery is prolonged.

Description

Technical Field

[0001] The invention relates to a preparation method and application of a lithium electrode. Background Art

[0002] The high theoretical specific capacity of lithium metal (3860 mAh g -1 ) and the lowest electrode potential (-3.04V vs standard hydrogen electrode) make lithium metal batteries (LMBs) potentially a new type of high energy density energy storage device. However, the development of lithium metal batteries faces many challenges. First, during the cycle, the deposition of lithium metal is uneven, and the dendrite growth is uncontrolled, which can easily lead to battery failure, and there are also safety hazards in the organic electrolyte system. Secondly, lithium metal has ultra-high chemical activity and is prone to irreversible reactions with electrolytes and positive electrode materials, causing rapid decay of battery capacity. In addition, due to the lack of a main structure of lithium metal electrodes, there will be infinite volume changes during battery operation, and the deposition / stripping of lithium ions is also uneven, resulting in frequent rupture and regeneration of the solid electrolyte interface layer (SEI), further promoting dendrite growth. The combined effect of these problems will lead to continuous loss of lithium and electrolyte, the formation of "dead lithium", and ultimately reduce the coulombic efficiency (CE) of the battery and battery failure.

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

[0004] In terms of constructing artificial SEI, the existing technologies mainly include chemical vapor deposition (CVD), physical vapor deposition (PVD) and solution method. Although chemical vapor deposition can accurately control the composition and thickness of the SEI layer, its process is complicated, the cost is high, it is difficult to apply on a large scale, and impurities may be introduced during the deposition process, affecting the stability of the SEI layer. Physical vapor deposition can produce a high-quality SEI layer, but the equipment is expensive and the output is low. At the same time, the adhesion to the substrate during the deposition process is limited, which makes the SEI layer easy to fall off. The solution method is relatively simple to operate and low in cost, but the uniformity of the prepared SEI layer is poor, and it is difficult to accurately control its microstructure. The effect is limited in inhibiting the growth of lithium dendrites and alleviating volume changes. The problems existing in these existing technologies have limited the further development and commercial application of lithium metal batteries. Summary of the invention

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

[0006] The present invention adopts a LiBr interface protection layer to modify the lithium metal electrode. LiBr has good ionic conductivity and can accelerate lithium ion transmission. At the same time, the chemical structure is stable and can remain stable in a wide voltage window, preventing the electrolyte from continuously decomposing and improving the overall stability of the battery. Due to its small lattice energy, LiBr can spread quickly and evenly on the lithium metal electrode to form a dense protective film. This film can not only accurately control lithium ion deposition and effectively inhibit the growth of lithium dendrites, but also reduce the interface energy between lithium metal and electrolyte, reduce side reactions, and greatly improve the battery Coulomb efficiency, thereby significantly improving the battery cycle performance and extending the service life.

[0007] A method for preparing a LiBr@Li electrode based on a LiBr interface protection layer is specifically completed by the following steps:

[0008] 1. Add tris(2,3-dibromopropyl)isocyanurate to an organic solvent in a glove box filled with argon gas, and stir magnetically for a period of time to obtain a tris(2,3-dibromopropyl)isocyanurate solution;

[0009] 2. In a glove box filled with argon, tri(2,3-dibromopropyl)isocyanurate solution is evenly dropped on one surface of a lithium sheet. After a period of reaction, the lithium sheet is placed in an organic solvent for cleaning to remove the unreacted tri(2,3-dibromopropyl)isocyanurate solution. Finally, the lithium sheet is dried at room temperature to obtain a LiBr@Li electrode based on a LiBr interface protective layer.

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

[0011] Principles and advantages of the present invention:

[0012] 1. The present invention focuses on constructing an artificial SEI layer rich in LiBr; LiBr spreads rapidly and evenly on the surface of the lithium metal electrode to form an extremely dense artificial SEI; this SEI film is 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. It can also provide a large number of evenly distributed active sites for the deposition of lithium, effectively reducing the nucleation barrier; it can also significantly reduce the interfacial energy between lithium metal and electrolyte, and reduce the occurrence of side reactions; during the charge and discharge cycle, the LiBr layer can rely on its good flexibility and stability to adapt well to the volume change of lithium, stabilize the electrode interface, and greatly inhibit the generation of lithium dendrites. The design concept of the present invention is innovative and unique, and the experimental operation is relatively simple. It effectively improves the comprehensive performance of lithium metal batteries and opens up new ways to promote their practical applications;

[0013] Second, the electrochemical performance of the LiBr@Li electrode based on the LiBr interface protection layer obtained in the present invention was tested. The results showed that at 5 mA cm -2 The current density is 1 mAh cm -2 The symmetrical battery assembled with the LiBr@Li electrode based on the LiBr interface protection layer can stably cycle for more than 700 h at a surface capacity of 1.54 W, indicating that the LiBr@Li electrode based on the LiBr interface protection layer provided by the present invention 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 has an initial capacity of 102 mAh g at 5C. -1 After 4500 cycles, it showed 76 mAhg -1 The high discharge specific capacity and 73% capacity retention rate indicate that the LiBr@Li electrode based on the LiBr interface protection layer provided by the present invention has a high cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0016] Figure 3 For Li∥Li symmetric battery and LiBr@Li∥LiBr@Li symmetric battery at current density: 2mAcm -2In-situ optical characterization of lithium deposition under the above conditions, where 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 and discharge curves of Li∥Li symmetric battery and LiBr@Li∥LiBr@Li symmetric battery;

[0018] Figure 5 Cycling performance of Li∥LFP full battery and LiBr@Li||LFP full battery;

[0019] Figure 6 Cycling performance of Li∥NCM811 full battery and LiBr@Li||NCM811 full battery. DETAILED DESCRIPTION

[0020] Specific implementation method 1: This implementation method is a preparation method of a LiBr@Li electrode based on a LiBr interface protection layer, which is specifically completed in the following steps:

[0021] 1. Add tris(2,3-dibromopropyl)isocyanurate to an organic solvent in a glove box filled with argon gas, and stir magnetically for a period of time to obtain a tris(2,3-dibromopropyl)isocyanurate solution;

[0022] 2. In a glove box filled with argon, tri(2,3-dibromopropyl)isocyanurate solution is evenly dropped on one surface of a lithium sheet. After a period of reaction, the lithium sheet is placed in an organic solvent for cleaning to remove the unreacted tri(2,3-dibromopropyl)isocyanurate solution. Finally, the lithium sheet is dried at room temperature to obtain a LiBr@Li electrode based on a LiBr interface protective layer.

[0023] Specific implementation method 2: This implementation method is different from specific implementation method 1 in that the water content in the glove box filled with argon gas in step 1 is precisely controlled to be less than 0.01 ppm, and the oxygen content is less than 0.01 ppm. The other steps are the same as those in specific implementation method 1.

[0024] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the organic solvent in step 1 is N-methylpyrrolidone, dimethylformamide or tetrahydrofuran. The other steps are the same as those in specific embodiment 1 or 2.

[0025] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the mass ratio of tris(2,3-dibromopropyl)isocyanurate to the volume ratio of the organic solvent in step 1 is (0.01 g to 0.03 g): 1 mL. The other steps are the same as those in specific embodiments 1 to 3.

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

[0027] The other steps are the same as those in Specific Embodiments 1 to 4.

[0028] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the organic solvent in step 2 is N-methylpyrrolidone, dimethylformamide or tetrahydrofuran. The other steps are the same as those in specific embodiments 1 to 5.

[0029] Specific embodiment 7: The difference between this embodiment and specific embodiments 1 to 6 is that the volume ratio of the tris(2,3-dibromopropyl)isocyanurate solution described in step 2 to the surface area of ​​the lithium sheet is 30mL:150mm 2 The other steps are the same as those in Specific Embodiments 1 to 6.

[0030] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that the reaction time in step 2 is 1 to 2 minutes. The other steps are the same as those in specific embodiments 1 to 7.

[0031] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the drying time in step 2 is 3 hours to 4 hours. The other steps are the same as those in specific embodiments 1 to 8.

[0032] Specific embodiment 10: This embodiment is an application of a LiBr@Li electrode based on a LiBr interface protection layer in a lithium metal battery.

[0033] The following examples are used to verify the beneficial effects of the present invention:

[0034] Example 1: A method for preparing a LiBr@Li electrode based on a LiBr interface protection layer is specifically completed by the following steps:

[0035] 1. In a glove box filled with argon, 0.02 g of tris(2,3-dibromopropyl)isocyanurate was added to 1 mL of N-methylpyrrolidone (NMP), and the mixture was stirred for 10 min at a magnetic stirring speed of 200 r / min to obtain a tris(2,3-dibromopropyl)isocyanurate solution;

[0036] The water content in the glove box filled with argon described in step 1 is precisely controlled to be less than 0.01 ppm, and the oxygen content is less than 0.01 ppm;

[0037] Second, in a glove box filled with argon, 30 mL of tris (2,3-dibromopropyl) isocyanurate solution was evenly dropped on one surface of the lithium sheet. After reacting for 1 min, the lithium sheet was placed in N-methylpyrrolidone (NMP) for cleaning to remove the unreacted tris (2,3-dibromopropyl) isocyanurate solution. Finally, the lithium sheet was placed at room temperature and dried 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 in step 2 to the surface area of ​​the lithium sheet is 30 mL:150 mm 2 .

[0039] Figure 1 : are SEM images, in which a is a SEM image of an untreated lithium sheet, and b is a SEM image of a LiBr@Li electrode based on a LiBr interface protection layer prepared in Example 1;

[0040] from Figure 1 In a, we can see that the surface of metallic lithium is smooth. Figure 1 In b, it can be seen that the surface of the LiBr@Li electrode based on the LiBr interface protection layer has a uniform and dense coating.

[0041] Figure 2 This is the XPS image of the LiBr@Li electrode based on the LiBr interface protection layer prepared in Example 1, where a is Li1s and b is Br 3d;

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

[0043] Assemble the symmetrical battery:

[0044] In a glove box filled with Ar gas, a button cell assembly of model 2032, a commercial polypropylene diaphragm (Celgard 2500) with a diameter of 18 mm, and a stainless steel gasket (SS) with a thickness of 1 mm were selected for assembly. The negative electrode shell, battery shrapnel, SS, LiBr@Li electrode prepared in Example 1, commercial polypropylene diaphragm, LiBr@Li electrode prepared in Example 1, and positive electrode shell were stacked and assembled in the order of each other, and 30 μL of commercial electrolyte (the commercial electrolyte was purchased from Celud Company, detailed product composition: 1.0M LiTFSI in DOL:DME=1:1vol%with 2.0%LiNO3) was dripped at the interface where the LiBr@Li electrode and the commercial polypropylene diaphragm contacted each other for wetting; then the pressure was pressed to 50 kgcm on a manual button cell sealing machine. -2 , and hold it for 5s before taking it out. The battery assembly is now complete.

[0045] The Li∥Li symmetric battery was assembled using lithium sheets in the same manner as above.

[0046] In order to intuitively demonstrate the advantages of the protective layer during lithium electroplating, Li∥Li symmetric cells and LiBr@Li∥LiBr@Li symmetric cells were tested at a current density of 2 mA cm -2 In situ optical microscopy tests were carried out under the conditions of Figure 3 (a, b) show that after 30 min, lithium dendrites appeared on the surface of the exposed lithium metal electrode, causing the battery to short-circuit. This indicates that the sharp edges of the lithium metal surface, the space charge effect, and the uneven Li + Distribution, lithium metal tends to be deposited unevenly on the surface without protection, and the deposition is uneven, focusing on the initial nucleation position for growth. In contrast, the LiBr@Li electrode based on the LiBr interface protection layer prepared in Example 1 presents a fairly uniform surface within 10 h of lithium deposition time, indicating that the artificial SEI of the LiBr@Li electrode based on the LiBr interface protection layer prepared in Example 1 is conducive to the formation of a compact and uniform lithium deposition morphology, avoiding the growth of dendrites, and is beneficial to the safety of lithium metal batteries.

[0047] To reveal the advantages of the LiBr layer, the LiBr@Li electrode based on the LiBr interface protection layer prepared in Example 1 was used as the working electrode, and the lithium sheet was used as the counter electrode to assemble a symmetrical battery for charge and discharge tests. The results are as follows: Figure 4 As shown, at 5mAcm -2 The current density is 1 mAh cm -2At an area capacity of 1.34 W, the voltage polarization of the bare Li||Li battery gradually increases from 200 h, and the LiBr@Li||LiBr@Li symmetric battery exhibits lower voltage polarization than the bare Li||Li battery and can maintain stable cycling for at least 700 h. This shows the superiority of the LiBr-rich artificial SEI layer.

[0048] In order to further explore the potential value of the LiBr@Li electrode based on the LiBr interface protection layer prepared in Example 1 in practical applications, lithium iron phosphate (LiFePO4, LFP) positive electrode and lithium nickel cobalt manganese oxide (NCM811) positive electrode were assembled with different negative electrodes to prepare lithium metal full batteries, and their electrochemical properties were compared.

[0049] The assembly method of LiBr@Li||LFP full battery is completed in the following steps:

[0050] In a glove box filled with Ar gas, a button cell assembly of model 2032, a commercial polypropylene diaphragm (Celgard 2500) with a diameter of 18 mm, and a stainless steel gasket (SS) with a thickness of 1 mm were selected for assembly. The negative electrode shell, battery shrapnel, SS, LiBr@Li electrode prepared in Example 1, commercial polypropylene diaphragm, lithium iron phosphate (LiFePO4, LFP) positive electrode or nickel cobalt manganese oxide (NCM811) positive electrode, and positive electrode shell were stacked and assembled in the order of the negative electrode shell, and 50 μL of commercial electrolyte (the commercial electrolyte was purchased from Cluder, detailed product composition: 1.0M LiPF6 in EC:DEC:DMC=1:1:1vol%with 5.0% FEC) was dripped at the interface where the LiBr@Li electrode and the commercial polypropylene diaphragm contacted each other for wetting; then the button cell was pressed to 50 kgcm on a manual button cell sealing machine. -2 , and hold it for 5s before taking it out. The battery assembly is now complete.

[0051] According to the same method, the lithium sheet was used as the negative electrode and assembled with the lithium iron phosphate (LiFePO4, LFP) positive electrode and the lithium nickel cobalt manganese oxide (NCM811) positive electrode to prepare a lithium metal full battery, and a comparative study was carried out on its electrochemical properties.

[0052] In the experiment with LFP as the positive electrode, the active material mass loading of the LFP electrode was ∼5.1 mg cm -2 .from Figure 5 The experimental data show that the LiBr@Li||LFP full battery exhibits a charge and discharge rate of 102 mAh g at a charge and discharge rate of 5C. -2 After 4500 cycles, the battery's discharge capacity can still be maintained at 76 mAhg -2, the capacity retention rate is as high as 73%, showing good cycling 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 NCM811 electrode was ~8.7 mg cm -2 . Also from Figure 6 It can be seen that the initial discharge capacity of LiBr@Li||NCM811 full battery can reach 164mAhg at a charge and discharge rate of 2C. -2 After 350 cycles, the discharge capacity is 98 mAh g -2 , the capacity retention rate reaches 60%, which also reflects 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 demonstrate that the LiBr@Li electrode for lithium metal batteries provided by the present invention exhibits 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 a LiBr@Li electrode based on a LiBr interface protection layer, characterized in that The preparation method is specifically completed according to the following steps:

1. Add tris(2,3-dibromopropyl)isocyanurate to an organic solvent in a glove box filled with argon gas, and stir magnetically for a period of time to obtain a tris(2,3-dibromopropyl)isocyanurate solution; 2. In a glove box filled with argon, tri(2,3-dibromopropyl)isocyanurate solution is evenly dropped on one surface of a lithium sheet. After a period of reaction, the lithium sheet is placed in an organic solvent for cleaning to remove the unreacted tri(2,3-dibromopropyl)isocyanurate solution. Finally, the lithium sheet is dried at room temperature to obtain a LiBr@Li electrode based on a LiBr interface protective layer.

2. The method for preparing a LiBr@Li electrode based on a LiBr interface protection layer according to claim 1, characterized in that The water content in the glove box filled with argon in step 1 is precisely controlled to be less than 0.01 ppm, and the oxygen content is less than 0.01 ppm.

3. The method for preparing a LiBr@Li electrode based on a LiBr interface protection layer according to claim 1, characterized in that The organic solvent described in step 1 is N-methylpyrrolidone, dimethylformamide or tetrahydrofuran.

4. The method for preparing a LiBr@Li electrode based on a LiBr interface protection layer according to claim 1, characterized in that The mass ratio of tris(2,3-dibromopropyl)isocyanurate described in step 1 to the volume ratio of the organic solvent is (0.01 g to 0.03 g):1 mL.

5. The method for preparing a LiBr@Li electrode based on a LiBr interface protection layer according to claim 1, characterized in that The speed of the magnetic stirring in step 1 is 200 r / min to 500 r / min, and the time of the magnetic stirring is 5 min to 10 min.

6. The method for preparing a LiBr@Li electrode based on a LiBr interface protection layer according to claim 1, characterized in that The organic solvent in step 2 is N-methylpyrrolidone, dimethylformamide or tetrahydrofuran.

7. The method for preparing a LiBr@Li electrode based on a LiBr interface protection layer according to claim 1, characterized in that The volume ratio of the tris(2,3-dibromopropyl)isocyanurate solution in step 2 to the surface area of ​​the lithium sheet is 30 mL:150 mm 2 .

8. The method for preparing a LiBr@Li electrode based on a LiBr interface protection layer according to claim 1, characterized in that The reaction time in step 2 is 1 min to 2 min.

9. The method for preparing a LiBr@Li electrode based on a LiBr interface protection layer according to claim 1, characterized in that The drying time described in step 2 is 3h to 4h.

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

Images