A LiI / LiNO3 composite electrolyte for Li-O2 batteries and its application method

Abstract

The application discloses a LiI / LiNO3 composite electrolyte applied to a Li-O2 battery and a use method thereof, the LiI / LiNO3 composite electrolyte comprises a main body liquid and an additive liquid, the main body liquid comprises a LiI solution and a LiTFSI solution, the concentration of the LiI solution is 0.5mol / L-1.5mol / L, the concentration of the LiTFSI solution is 0.5mol / L-1.5mol / L, the volume proportion of the LiI solution in the main body liquid is 70%-90%, the additive liquid comprises a LiNO3 solution, the concentration of the LiNO3 solution is 0.5mol / L-1.5mol / L, and the volume proportion of the additive liquid in the electrolyte is 5%-25%. The use method of the LiI / LiNO3 composite electrolyte is that the main body liquid and the additive liquid are respectively and uniformly dropped on a battery diaphragm of the Li-O2 battery, the total volume of the electrolyte is determined according to the area of the battery diaphragm, and 40muL-60muL of the electrolyte is needed for each square centimeter of the battery diaphragm. The electrolyte can effectively prolong the service life of the Li-O2 battery by adding the LiI to reduce the charging potential of the battery and by adding the LiNO3 to stabilize the discharging process of the battery.

Description

Technical Field

[0001] This invention relates to a LiI / LiNO3 composite electrolyte for use in Li-O2 batteries and its application method, belonging to the field of lithium metal battery technology. Background Technology

[0002] With societal development, energy storage devices are increasingly being used across various industries. The demand for high-performance energy storage devices is also growing. Simultaneously, to alleviate concerns about the battery life of electronic products, the energy storage industry is demanding higher energy density from storage batteries. Among various types of batteries, lithium-air batteries, using lithium metal as the negative electrode, are considered a strong candidate for next-generation energy storage batteries due to their high energy density. However, it is undeniable that despite their extremely high specific capacity, lithium-air batteries still have issues to address regarding battery life, operational stability, and environmental requirements. Among these, battery life is the key factor determining whether lithium-air batteries can be practically applied.

[0003] Optimizing various components of a Li-O2 battery can improve its lifespan. This is mainly attributed to the fact that optimizing the electrodes and electrolyte, and adding redox mediators, helps the battery achieve a more stable electrochemical operating environment, thereby extending its lifespan. Among various methods, adding redox mediators has the most direct and efficient effect on adjusting the charge-discharge reaction environment of Li-O2 batteries. Redox mediators can regulate the charge-discharge overpotential, promote product decomposition, and help form a stable passivation layer on the lithium electrode. Commonly used redox mediators include 2,2,6,6-tetramethyl-1-piperidinoxy (TEMPO), tetrathionyl fulvalene (TTF), and lithium halogen salts. Among these, LiI, as a type of lithium halogen salt, has received widespread attention due to its excellent charging potential regulation. Tao Liu et al. pointed out that in Li-O2 batteries with added LiI, the formation and decomposition of LiOH can effectively ensure the cycle stability of the Li-O2 battery. Based on this, Raman spectroscopy, nuclear magnetic resonance spectroscopy, and molecular dynamics were used to study the role of LiI in the operation of Li-O2 batteries, as well as the mechanism of LiOH formation and decomposition. Some researchers also believe that LiI forms I3 during battery charging and discharging. - Substances such as [list of substances] can lead to electrolyte degradation. It is noted that a small amount of water can mitigate nucleophilic attacks in the battery, while increased water content leads to the inactivation of LiI's catalytic effect. It is important to note that although LiI can significantly regulate the battery's charging potential, it has little impact on the battery's discharge plateau. In summary, while existing organic Li-O2 battery electrolytes can ensure stable battery operation, their functionality is limited, and they have a high probability of volatilization and decomposition during charge and discharge, which is one of the main factors contributing to the short lifespan of Li-O2 batteries. Summary of the Invention

[0004] The purpose of this invention is to provide a LiI / LiNO3 composite electrolyte for Li-O2 batteries and its application method. This electrolyte reduces the charging potential of the battery by adding LiI and stabilizes the discharge process of the battery by adding LiNO3, thereby effectively improving the service life of Li-O2 batteries.

[0005] The technical solution adopted by the present invention to achieve its purpose is: a LiI / LiNO3 composite electrolyte for Li-O2 batteries, comprising a main electrolyte and an additive electrolyte;

[0006] The host solution comprises a LiI (lithium iodide) solution and a LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) solution, wherein the concentration of the LiI solution is 0.5 mol / L-1.5 mol / L and the concentration of the LiTFSI solution is 0.5 mol / L-1.5 mol / L; the volume percentage of the LiI solution in the host solution is 70%-90%.

[0007] The additive solution includes a LiNO3 (lithium nitrate) solution with a concentration of 0.5 mol / L to 1.5 mol / L.

[0008] The volume percentage of the added liquid in the electrolyte is 5%-25%. Furthermore, the concentration of LiI solution in the main solution of the present invention is 0.8 mol / L-1.2 mol / L, and the concentration of LiTFSI solution is 0.8 mol / L-1.2 mol / L.

[0009] Furthermore, the concentration of the LiNO3 solution added in this invention is 0.8 mol / L-1.2 mol / L.

[0010] Furthermore, the volume percentage of the added liquid in the electrolyte of the present invention is 10%-20%.

[0011] Furthermore, the volume percentage of LiI solution in the host liquid of the present invention is 75%-85%.

[0012] Furthermore, the solvents for the LiI solution, LiTFSI solution, and LiNO3 solution described in this invention are ether solvents, sulfone solvents, or ester solvents.

[0013] Furthermore, in the main solution of the present invention, the concentration of LiI solution is 1 mol / L, the concentration of LiTFSI solution is 1 mol / L, the concentration of LiNO3 solution in the additive solution is 1 mol / L, the volume ratio of LiI solution in the main solution is 80%, and the volume ratio of the additive solution in the electrolyte is 20%.

[0014] Furthermore, the solvents for the LiI solution, LiTFSI solution, and LiNO3 solution described in this invention are ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or dimethyl sulfoxide.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] The electrolyte of this invention uses LiI solution and LiTFSI solution as the main liquid and LiNO3 solution as the additive liquid. LiI, as a redox medium, effectively reduces the overpotential of the battery during charging, ensuring the stability of the electrode-electrolyte environment during battery charging. LiNO3, as an electrolyte additive, helps the lithium anode to form a more stable metal passivation layer, reduces the battery's discharge overpotential, and further improves the stability of the electrochemical reaction. In summary, LiI and LiNO3 play a significant regulatory role in the charge and discharge potential of Li-O2 batteries.

[0017] This invention, by adjusting the concentration and volume ratio of LiI and LiTFSI solutions in the main electrolyte, the concentration of the added LiNO3 solution, and the volume ratio of the added solution in the electrolyte, yields an organic electrolyte that effectively ensures the stability of Li-O2 battery operation and improves its lifespan. Furthermore, both LiI and LiNO3 are readily available lithium salts, making the cost of the electrolyte in this invention controllable.

[0018] In order to achieve its inventive objective, the present invention also provides a method for using the above-mentioned LiI / LiNO3 composite electrolyte applied to Li-O2 batteries. Specifically, the main electrolyte and the additive liquid are uniformly dropped onto the battery separator of the Li-O2 battery. The total volume of the electrolyte is determined according to the area of ​​the battery separator, and 40μL-60μL of electrolyte is required per square centimeter of battery separator.

[0019] Furthermore, in the method of using the composite electrolyte of the present invention, the specific method of uniformly adding the main solution and the additive solution to the battery separator of the Li-O2 battery is as follows: first, the additive solution is added to the battery separator of the Li-O2 battery, and after standing for 5-30 minutes, the main solution is added to the battery separator of the Li-O2 battery. When assembling the battery, the side of the battery separator with the electrolyte added is attached to the carbon paper positive electrode, and the other side is attached to the lithium negative electrode. The present invention adds the additive solution first, and after standing for 5-30 minutes, adds the main solution. This ensures that the additive solution added first is stably dispersed on the battery separator closer to the lithium metal electrode, which is beneficial for forming a stable passivation layer on the lithium metal negative electrode during discharge, and better reduces the discharge overpotential of the battery.

[0020] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. Attached Figure Description

[0021] Figure 1 This is a cycle life curve of the Li-O2 battery in Embodiment 1 of the present invention.

[0022] Figure 2 This is a cycle life curve of the Li-O2 battery in Embodiment 2 of the present invention.

[0023] Figure 3 This is a cycle life curve of a Li-O2 battery, which is a comparative example of the present invention.

[0024] Figure 4 This is a cycle life curve of the Li-O2 battery, which is a comparative example of the present invention.

[0025] Figure 5 This is a cycle life curve of a three-Li-O2 battery, which is a comparative example of the present invention. Detailed Implementation

[0026] Example

[0027] A LiI / LiNO3 composite electrolyte for use in Li-O2 batteries, comprising a bulk electrolyte and additives;

[0028] The host liquid comprises a LiI solution and a LiTFSI solution, wherein the concentration of the LiI solution is 0.5 mol / L-1.5 mol / L and the concentration of the LiTFSI solution is 0.5 mol / L-1.5 mol / L; the volume percentage of the LiI solution in the host liquid is 70%-90%, preferably 75%-85%.

[0029] The additive solution includes a LiNO3 solution with a concentration of 0.5 mol / L to 1.5 mol / L.

[0030] The volume percentage of the added liquid in the electrolyte is 5%-25%, preferably 10%-20%.

[0031] The preferred concentrations of the LiI solution, LiTFSI solution, and LiNO3 solution in the main solution are 0.8 mol / L to 1.2 mol / L, 0.8 mol / L to 1.2 mol / L, and 0.8 mol / L to 1.2 mol / L, respectively.

[0032] In this example, the solvents for the LiI solution, LiTFSI solution, and LiNO3 solution are ether solvents, sulfone solvents, or ester solvents.

[0033] More preferably, in this example, the concentration of LiI solution in the main electrolyte is 1 mol / L, the concentration of LiTFSI solution is 1 mol / L, and the concentration of LiNO3 solution in the additive solution is 1 mol / L. The volume percentage of LiI solution in the main electrolyte is 80%, and the volume percentage of the additive solution in the electrolyte is 20%. The solvents for the LiI solution, LiTFSI solution, and LiNO3 solution are ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or dimethyl sulfoxide.

[0034] A method for using the aforementioned LiI / LiNO3 composite electrolyte in a Li-O2 battery specifically includes uniformly dripping the main solution and the additive solution onto the battery separator of the Li-O2 battery. The total volume of the electrolyte is determined according to the area of ​​the battery separator, with 40 μL-60 μL of electrolyte required per square centimeter of battery separator. The preferred method for uniformly dripping the main solution and the additive solution onto the battery separator of the Li-O2 battery is as follows: first, the additive solution is dripped onto the battery separator of the Li-O2 battery, and after standing for 5 min-30 min, the main solution is then dripped onto the battery separator of the Li-O2 battery.

[0035] Example 1

[0036] A LiI / LiNO3 composite electrolyte for use in Li-O2 batteries includes a main electrolyte and an additive electrolyte; the main electrolyte includes a LiI solution and a LiTFSI solution, wherein the concentration of the LiI solution is 1 mol / L and the concentration of the LiTFSI solution is 1 mol / L; the volume percentage of the LiI solution in the main electrolyte is 80%.

[0037] The additive solution is a LiNO3 solution with a concentration of 1 mol / L;

[0038] The volume ratio of the added liquid in the electrolyte is 20%.

[0039] The solvent for the LiI solution, LiTFSI solution, and LiNO3 solution is tetraethylene glycol dimethyl ether.

[0040] The above-mentioned LiI / LiNO3 composite electrolyte was applied to the Li-O2 battery. It was added dropwise onto the battery separator of the Li-O2 battery. First, the additive liquid was added dropwise onto the battery separator of the Li-O2 battery, and after standing for 15 minutes, the main liquid was added dropwise onto the battery separator of the Li-O2 battery.

[0041] The preparation method of the Li-O2 battery described in this example is as follows:

[0042] The Li-O2 battery cathode uses pure carbon material, with carbon nanotubes / graphene as the catalyst coating. First, a composite catalyst material is prepared by weighing appropriate masses of porous carbon material and catalyst powder using an electronic balance, mixing them at a graphene:carbon nanotube mass ratio of 3:1. PTFE aqueous solution is used as a binder, and appropriate amounts of N-methyl-2-pyrrolidone (NMP) solution and ultrapure water are used as dispersants. During electrode preparation, the catalyst powder and binder are mixed at a mass ratio of 9:1, and an appropriate amount of dispersant is added. The mixture is stirred in a magnetic stirrer for 12 hours. The mixture is stirred into a uniform, viscous slurry. The catalyst slurry is then coated onto carbon paper using an infrared drying plate coating machine and placed in a vacuum drying oven at 100℃ for 12 hours. Finally, a hydraulic slicer is used to cut the slurry into 16mm diameter cathode discs, with a catalyst loading of 1mg / cm³. 2 In this example, the separator of the Li-O2 battery is a glass fiber membrane. The glass fiber membrane is placed in a constant temperature drying oven and dried at 100°C for 8 hours.

[0043] The battery assembly was carried out in a glove box under an argon atmosphere. The glass fiber membrane of the Li-O2 battery had an area of ​​2 cm². 2 The total electrolyte volume was controlled at 100 μL. The electrolyte was added dropwise onto the glass fiber membrane of the Li-O2 battery, as described above. After addition, the lithium sheet, glass fiber membrane, and positive electrode were sequentially loaded into the battery mold, with the catalyst-coated side of the electrode in contact with the glass fiber membrane. The battery was then sealed using a hydraulic sealing machine. After assembly, a stable three-phase interface needed to be formed between the electrolyte and the electrodes. Therefore, the battery was placed in a glove box for 24 hours before charge-discharge and electrochemical tests were conducted.

[0044] Example 2

[0045] A LiI / LiNO3 composite electrolyte for use in Li-O2 batteries includes a main electrolyte and an additive electrolyte; the main electrolyte includes a LiI solution and a LiTFSI solution, wherein the concentration of the LiI solution is 1 mol / L and the concentration of the LiTFSI solution is 1 mol / L; the volume percentage of the LiI solution in the main electrolyte is 80%.

[0046] The additive solution is a LiNO3 solution with a concentration of 1 mol / L;

[0047] The volume percentage of the added liquid in the electrolyte is 10%.

[0048] The solvent for the LiI solution, LiTFSI solution, and LiNO3 solution is tetraethylene glycol dimethyl ether.

[0049] The above-mentioned LiI / LiNO3 composite electrolyte was applied to the Li-O2 battery. It was dropped onto the battery separator of the Li-O2 battery, and the total volume of the electrolyte was controlled to be 100 μL. First, the additive solution was dropped onto the battery separator of the Li-O2 battery, and after standing for 15 min, the main solution was dropped onto the battery separator of the Li-O2 battery.

[0050] The Li-O2 battery used in this example is the same as that in Example 1.

[0051] Comparative Example 1

[0052] An electrolyte for use in Li-O2 batteries, wherein the electrolyte is a 1 mol / L LiTFSI solution, and the solvent of the LiTFSI solution is tetraethylene glycol dimethyl ether.

[0053] The above electrolyte was applied to a Li-O2 battery by being dropped onto the battery separator of the Li-O2 battery, with the electrolyte volume controlled at 100 μL.

[0054] The Li-O2 battery used in this example is the same as that in Example 1.

[0055] Comparative Example 2

[0056] An electrolyte for use in Li-O2 batteries, wherein the electrolyte is a LiI solution with a concentration of 1 mol / L, and the solvent of the LiI solution is tetraethylene glycol dimethyl ether.

[0057] The above electrolyte was applied to a Li-O2 battery by being dropped onto the battery separator of the Li-O2 battery, with the electrolyte volume controlled at 100 μL.

[0058] The Li-O2 battery used in this example is the same as that in Example 1.

[0059] Comparative Example 3

[0060] A LiI / LiNO3 composite electrolyte for use in Li-O2 batteries includes a main electrolyte and an additive electrolyte; the main electrolyte includes a LiI solution and a LiTFSI solution, wherein the concentration of the LiI solution is 1 mol / L and the concentration of the LiTFSI solution is 1 mol / L; the volume percentage of the LiI solution in the main electrolyte is 80%.

[0061] The additive solution is a LiNO3 solution with a concentration of 1 mol / L;

[0062] The volume ratio of the added liquid in the electrolyte is 30%.

[0063] The solvent for the LiI solution, LiTFSI solution, and LiNO3 solution is tetraethylene glycol dimethyl ether.

[0064] The above-mentioned LiI / LiNO3 composite electrolyte was applied to the Li-O2 battery. It was dropped onto the battery separator of the Li-O2 battery, and the total volume of the electrolyte was controlled to be 100 μL. First, the additive solution was dropped onto the battery separator of the Li-O2 battery, and after standing for 15 min, the main solution was dropped onto the battery separator of the Li-O2 battery.

[0065] The Li-O2 battery used in this example is the same as that in Example 1.

[0066] Li-O2 batteries obtained with electrolytes from Examples 1, 2, 1, 2, and 3 were subjected to charge-discharge tests. The tests were conducted using a CT2001A model from Wuhan Landian Electronics Co., Ltd., and controlled by a supporting computer software system that allowed for setting the battery's discharge current, battery potential, and protection potential. Gas supply was provided using an oxygen tank, pressure reducing valve, and mass flow meter, allowing for control of gas flow and pressure. The test subject was an organic electrolyte lithium-oxygen battery. The charge-discharge capacity was set to 1 mAh, the specific capacity to be 500 mAh / g, the constant charge-discharge current to be 0.2 mA, and the current density to be 0.1 mA / cm². 2 Set the battery charging protection voltage to 5V and the discharging protection voltage to 2V. Figures 1 to 5 The graphs show the cycle life curves of Li-O2 batteries in Examples 1, 2, 1, 2, and 3 of this invention.

[0067] from Figure 1 It can be seen that when the electrolyte of Example 1 was applied to the Li-O2 battery, the battery ultimately completed 220 charge-discharge cycles, and the battery exhibited good cycle stability and a relatively stable charge-discharge plateau during the first 80% of its operating time. Therefore, it is evident that using a composite solution of LiI and LiTFSI as the main electrolyte, with the addition of 20% by volume of LiNO3 solution, can significantly improve the stability and lifespan of the Li-O2 battery.

[0068] from Figure 2 As can be seen, when the electrolyte of Example 2 is applied to the Li-O2 battery, the initial charging potential of the battery is maintained at around 3.05V, the initial charge-discharge potential difference is reduced to 0.25V, and the discharge plateau maintains stable operation for more than 150 cycles. It is worth noting that the battery's charging potential shows a certain increase at the end of the discharge phase compared to the battery without added electrolyte (Comparative Example 2). This indicates that the addition of LiNO3 solution has a certain impact on the regulation of charging potential by LiI. In summary, using a composite solution of LiI and LiTFSI solution as the main electrolyte, with the addition of 10% volume of LiNO3 solution as the electrolyte, improves the stability and lifespan of the Li-O2 battery.

[0069] Figure 3The figure shows the cyclic charge-discharge performance of a Li-O2 battery using LiTFSI solution as the electrolyte. As can be seen from the figure, the battery's charging potential reaches 4.5V, while the discharging potential stabilizes at around 2.6V, indicating a large potential difference between charge and discharge. The battery operates relatively stably for the first 60 cycles, but its performance declines significantly in subsequent cycles. By the 78th cycle, the charge / discharge termination potential is close to the set protection potential, indicating a significant performance degradation.

[0070] Figure 4 The figure shows the cyclic charge-discharge characteristics of a Li-O2 battery using LiI solution as the electrolyte. The figure shows that compared to... Figure 3 The minimum overpotential difference during battery charge-discharge was close to 0.3V, indicating a significant improvement in cycle efficiency. However, while the battery exhibited relatively stable charge-discharge performance in the first 40 cycles, the discharge potential began to decrease significantly afterward. By the 140th cycle, the discharge cutoff potential had fallen below 2.0V, marking the end of the battery's lifespan. This suggests that using LiI solution as the organic electrolyte in lithium-oxygen batteries can improve cycle charge-discharge performance to some extent compared to LiTFSI solution, but the improvement is limited.

[0071] from Figure 5 It can be seen that as the volume ratio of the added LiNO3 solution increases, the charge and discharge life of the battery decreases. Figure 5 The study showed that adding 30% LiNO3 by volume to the LiI electrolyte increased the charging potential of the lithium-oxygen battery, increased the charge-discharge potential difference, and significantly reduced the battery cycle life to 65 cycles, resulting in a significant deterioration in battery charge-discharge performance and cycle life. Therefore, only a certain proportion of LiNO3 solution can improve the stability and lifespan of Li-O2 batteries.

Claims

1. A method for improving the stability of the solid-liquid two-phase charge-discharge reaction in Li-O2 batteries, characterized in that: The battery separator of a Li-O2 battery is treated with a LiI / LiNO3 composite electrolyte consisting of a main electrolyte and an additive solution. The treatment process is as follows: the main electrolyte and the additive solution are uniformly dropped onto the battery separator of the Li-O2 battery. The total volume of electrolyte depends on the area of ​​the battery separator, with 40μL-60μL of electrolyte required per square centimeter of battery separator. The main electrolyte includes a LiI solution and a LiTFSI solution, with the LiI solution concentration being 0.5mol / L-1.5mol / L and the LiTFSI solution concentration being 0.5mol / L-1.5mol / L. The volume percentage of the LiI solution in the main electrolyte is 70%-90%. The additive solution includes a LiNO3 solution with a LiNO3 solution concentration of 0.5mol / L-1.5mol / L. The volume percentage of the additive solution in the electrolyte is 5%-25%.

2. The method for improving the stability of the solid-liquid two-phase charge-discharge reaction of a Li-O2 battery according to claim 1, characterized in that: The concentration of LiI solution in the main solution is 0.8 mol / L-1.2 mol / L, and the concentration of LTFSI solution is 0.8 mol / L-1.2 mol / L.

3. The method for improving the stability of the solid-liquid two-phase charge-discharge reaction of a Li-O2 battery according to claim 1, characterized in that: The concentration of the added LiNO3 solution is 0.8 mol / L-1.2 mol / L.

4. The method for improving the stability of the solid-liquid two-phase charge-discharge reaction of a Li-O2 battery according to claim 1, characterized in that: The volume percentage of the added liquid in the electrolyte is 10%-20%.

5. The method for improving the stability of the solid-liquid two-phase charge-discharge reaction of a Li-O2 battery according to claim 4, characterized in that: The volume percentage of LiI solution in the main liquid is 75%-85%.

6. The method for improving the stability of the solid-liquid two-phase charge-discharge reaction of a Li-O2 battery according to claim 1, characterized in that: The solvents for the LiI solution, LiTFSI solution, and LiNO3 solution are ether solvents, sulfone solvents, or ester solvents.

7. The method for improving the stability of the solid-liquid two-phase charge-discharge reaction of a Li-O2 battery according to claim 1, characterized in that: The main electrolyte contains 1 mol / L LiI solution, 1 mol / L LiTFSI solution, and 1 mol / L LiNO3 solution. The volume percentage of the main electrolyte is 80% LiI solution, and the volume percentage of the electrolyte is 20% LiNO3 solution.

8. The method for improving the stability of the solid-liquid two-phase charge-discharge reaction of a Li-O2 battery according to claim 7, characterized in that: The solvents for the LiI solution, LiTFSI solution, and LiNO3 solution are ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or dimethyl sulfoxide.

9. The method for improving the stability of the solid-liquid two-phase charge-discharge reaction of a Li-O2 battery according to claim 1, characterized in that; The specific method for uniformly adding the main liquid and the additive liquid to the battery separator of the Li-O2 battery is as follows: first, add the additive liquid to the battery separator of the Li-O2 battery, let it stand for 5 min to 30 min, and then add the main liquid to the battery separator of the Li-O2 battery.

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