Electrolyte for lithium-oxygen battery and self-catalytic lithium-oxygen battery

Abstract

The application provides a kind of electrolyte for lithium-oxygen battery and self-catalytic lithium-oxygen battery, the electrolyte for lithium-oxygen battery includes the following components: aprotic solvent, solute is 0.5-2mol / L lithium salt, 0.01-0.1 mol / L acetylacetone manganese;The aprotic solvent includes at least 60vol% dimethyl sulfoxide.In the application, acetylacetone manganese is used as a positive electrolyte additive in Li-O2 battery, which can significantly enhance the reaction kinetics of lithium-oxygen battery, realize low overpotential, and long cycle excellent life, has very high practical value, can become a kind of cheap, high-efficiency metal-oxygen or metal-air battery positive electrode additive, for building high-performance battery system.

Description

Technical Field

[0001] This invention belongs to the technical field, specifically relating to an electrolyte for lithium-oxygen batteries and a self-catalytic lithium-oxygen battery. Background Technology

[0002] Due to its approximately 3500 Wh / kg -1 Due to their high specific capacity, lithium-oxygen batteries (Li-O2 batteries) are considered promising candidates for advanced energy conversion and storage devices. However, lithium-oxygen batteries face significant challenges related to slow kinetics, stemming from the insulating properties of discharge products, complex gas-solid-liquid three-phase interface variations, and various side reactions. These slow kinetics lead to high overpotentials and limited cycle life in lithium-oxygen batteries. To address these issues, three main strategies have been explored over the past decade: the integration of cathode electrocatalysts, the use of redox mediators, and the development of modified Li2O2.

[0003] The modified Li₂O₂ structure possesses the desired enhanced ionic and electronic conductivity while promoting formation and decomposition processes, potentially introducing a novel discharge-charge mechanism for batteries. In previous work, our group developed a self-catalytic Li-O₂ battery system, providing an innovative approach for the structural design of electrocatalyst active sites and discharge products in Li-O₂ batteries. Transition metal-doped Li₂O₂ (M-Li) was synthesized by in-situ doping transition metal elements into the discharge product Li₂O₂. 2-x O2), its conductivity is higher than that of pure Li2O2. MO x The site serves as an autocatalytic active center, promoting Li 2-x The decomposition of O2 minimizes the introduction of multiphase interfaces, effectively enhancing the reaction process. The self-catalytic Li-O2 battery can have its performance enhanced through structural tuning, exhibiting a capacity of approximately 35000 mAh g⁻¹. -1 High specific capacitance and low overpotential of 0.76 V, and 3000 mA g -1 The rapid charging process is beneficial. However, its impact on the stability of highly active mesophases (such as superoxide in Li-O2 batteries) is limited, posing a significant challenge to improving the cycle stability of autocatalytic Li-O2 batteries.

[0004] As a liquid-phase catalyst, redox mediators play a crucial role in improving battery energy efficiency and cycle stability by capturing the mesophase, promoting electron transfer, and facilitating structural transformation. Between the discharge products and the electrodes, redox mediators act as charge carriers, mitigating polarization, promoting the decomposition of discharge products, and reducing overpotential during the OER process. Existing technologies have disclosed some reports on the use of redox mediators as electrolyte additives in lithium-oxygen batteries.

[0005] Patent CN113258137A discloses an electrolyte additive for improving the electrochemical performance of lithium-oxygen batteries, with the following chemical structure: However, its improvement on the performance of lithium-oxygen batteries is not significant, and the manufacturing process is relatively complex.

[0006] CN106785036A discloses an electrolyte additive for lithium-air batteries, comprising one or more of iodobenzene, iodobenzene, and iodobenzene. This additive can contact discharge products, reducing charging overpotential, and interacts with the discharge intermediate lithium superoxide and the discharge product lithium peroxide, stabilizing these two substances and suppressing side reactions. Therefore, it improves charging polarization and cycle performance. However, its structural stability is poor; the charging capacity significantly decreases after less than 130 cycles, and it does not offer any original optimization for the positive electrode reaction process of lithium-oxygen batteries.

[0007] CN109193030A discloses a lithium-oxygen battery electrolyte using molybdenum pentachloride as the redox medium, comprising a soluble lithium salt as the solute, a proton-free solvent, and molybdenum pentachloride as an additive; wherein the solute concentration in the electrolyte is 0.1~1 mol / L; and the concentration of molybdenum pentachloride in the electrolyte is 0.01~0.1 mol / L. However, the molybdenum ions contained in the electrolyte are unstable to the lithium anode, and molybdenum is an oxygen-loving element. Therefore, this battery system also exhibits extremely poor cycle stability, only 45 cycles, and high overpotential and severe polarization. During charge and discharge, the molybdenum ions mainly function by transferring electrons through the redox reaction of molybdenum, without effectively regulating the insulating lithium peroxide itself, resulting in a very limited main function. Under such oxygen-rich conditions, it is easily deactivated by attacks from oxygen ions, superoxide ions, etc.

[0008] CN116780051A discloses an electrolyte additive for lithium-oxygen batteries, which is a crown ether compound, suitable for Li... + It exhibits strong adsorption capacity, increases the statistical capacity of lithium peroxide, effectively alleviates positive electrode passivation, and relieves blockage problems. Furthermore, the generated complex adsorbs O2 through electrostatic attraction. -Active ions help avoid side reactions. However, this method does not fundamentally optimize the insulation properties of products in lithium-oxygen batteries; it only stabilizes oxygen-rich intermediates but does not significantly improve the overall battery reaction kinetics.

[0009] While the aforementioned patents have partially optimized the reaction pathway of lithium-oxygen batteries, resulting in some improvement in battery stability and catalytic activity, they have failed to fundamentally solve the critical problem of slow kinetics due to the lack of changes to the intrinsic physical and chemical properties of the insulating product structure at the positive electrode. The novel additive disclosed in this invention, through rigorous screening and comprehensive consideration of the liquid-phase reaction mechanism and the characteristics of the solid-phase products at the positive electrode, utilizes a molecular-ionic coexisting Mn(acac)3 additive system. This achieves multiple effects, including molecular intermediate stability and autocatalytic properties of the solid-phase products. In particular, it addresses the inherent weakness of lithium peroxide's electronic insulation, endowing it with excellent electrochemical activity, significantly improving the reaction kinetics and cycle stability of lithium-oxygen batteries, and achieving ultra-low overpotential and ultra-long lifespan.

[0010] Ma et al. introduced vanadium acetylacetone (V(acac)3) into Li-O2 batteries. During discharge, V(acac)3 binds to and stabilizes the superoxide intermediate, thereby accelerating ORR kinetics. During charging, V(acac)3 acts as a redox mediator, enabling Li2O2 to be oxidized at lower voltages. The battery using V(acac)3 exhibited high rate performance, low overpotential, and long cycle life at 200 mAg. -1 It can achieve 100 cycles. Zhou et al. introduced Ir(acac)3 into a Li-O2 battery. This compound can react with O2 to form an intermediate complex (Ir(acac)3-O2). - Ir(acac)3 modulates the ORR pathway and stabilizes superoxide radicals. During charging, Ir(acac)3 acts as a redox mediator, promoting the decomposition of Li2O2 through reaction with superoxide intermediates. Batteries using Ir(acac)3 exhibit lower overpotential and higher discharge capacity (17446 mAh g⁻¹). -1 ) and improved cycling performance (at 100 mA g) -1 (More than 130 cycles). However, the presence of the aforementioned V(acac)3 or Ir(acac)3 redox mediators leads to the formation of toroidal discharge products in Li-O2 batteries, which are difficult to completely decompose during charging, resulting in high overpotentials and hindering the enhancement of rate performance and fast charging characteristics. Therefore, the simultaneous coupling of autocatalysis and redox within the same battery system is expected to further promote the development of high-performance Li-O2 battery systems. Summary of the Invention

[0011] To overcome the challenge of further improving the performance of electrolytes in existing lithium-oxygen batteries, this invention uses manganese acetylacetonate as a cathode additive in Li-O2 batteries. On one hand, the transition metal acetylacetonate, as a weak electrolyte, allows partial cation dissociation, which is then integrated into the discharge products through doping during discharge, thus acting as a self-catalytic active site. On the other hand, the undissociated acetylacetonate molecules act as a liquid-phase redox mediator, capturing and stabilizing the intermediate phase. Results show that the electrolyte of this invention, using the combination of manganese acetylacetonate and DMSO solvent, can significantly enhance the reaction kinetics of lithium-oxygen batteries, achieving a low overpotential of 0.43 V at 1 A g. -1 The system exhibits stability exceeding 250 cycles at current densities. Furthermore, when combined with an optimized reaction environment and a pre-loaded solid-phase electrocatalyst, the system achieves stability at 1 A g / L. -1 It exhibits an excellent lifespan of 3850 cycles, demonstrating high practical value. It can serve as a low-cost, high-efficiency cathode additive for metal-oxygen or metal-air batteries, used in constructing high-performance battery systems. Specifically, this invention achieves the above objectives through the following technical solutions:

[0012] An electrolyte for a lithium-oxygen battery comprises the following components: an aprotic solvent, a lithium salt of 0.5-2 mol / L as solute, and manganese acetylacetone of 0.01-0.1 mol / L; wherein the aprotic solvent comprises at least 50 vol% dimethyl sulfoxide.

[0013] Preferably, the aprotic solvent comprises at least 60 vol% dimethyl sulfoxide; more preferably, the aprotic solvent comprises at least 66 vol% dimethyl sulfoxide.

[0014] Preferably, the electrolyte used in the lithium-oxygen battery is a positive electrode electrolyte.

[0015] Further, the aprotic solvent is dimethyl sulfoxide or a mixture of dimethyl sulfoxide and organic solvent A, wherein organic solvent A is selected from at least one of 1,3-dioxolane, ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, propylene carbonate, ethylene carbonate, N,N-dimethylacetamide, dimethylformamide, and ethyl methyl sulfone.

[0016] Preferably, the aprotic solvent is a mixture of dimethyl sulfoxide and organic solvent A in a volume ratio of 1-4:1; more preferably, the aprotic solvent is a mixture of dimethyl sulfoxide and 1,3-dioxolane in a volume ratio of 2-4:1. Solvents compounded according to the above ratios better utilize the combined solvent's advantages. The inventors have discovered that compounding DOL and DMSO can complement each other's advantages while reducing their respective disadvantages. DOL and DMSO, as electrolyte components, each have their unique properties and advantages / disadvantages. DOL (1,3-dioxolane) has a low freezing point and viscosity, making it suitable for use at low temperatures, but it is prone to polymerization. DMSO (dimethyl sulfoxide) has a high dielectric constant and donor number, promoting the generation of trisulfide radicals, but its cycle efficiency is high in the first 10 weeks, after which it may decrease. Compounding DOL and DMSO can complement each other's advantages while reducing their respective disadvantages. Through compounding, the excellent kinetic performance of DOL at low temperatures can be utilized, while DMSO can improve the cycle efficiency and stability of the battery.

[0017] Furthermore, the lithium salt is selected from at least one of lithium trifluoromethanesulfonate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium nitrate.

[0018] The present invention also provides a lithium-oxygen battery, comprising a lithium negative electrode, a positive electrode, a separator, and the aforementioned electrolyte. Those skilled in the art will understand that the lithium-oxygen battery also includes a lithium-air battery.

[0019] Furthermore, the positive electrode is KB and platinum-carbon coated carbon paper, and the diaphragm is a glass fiber diaphragm.

[0020] The present invention also protects the use of manganese acetylacetonate as an additive in the positive electrode electrolyte of lithium-oxygen batteries; the positive electrode electrolyte of lithium-oxygen batteries contains 0.01-0.1 mol / L manganese acetylacetonate, 0.5-2 mol / L lithium salt, and an aprotic solvent, wherein the aprotic solvent includes at least 50 vol% dimethyl sulfoxide; preferably, the aprotic solvent includes at least 60 vol% dimethyl sulfoxide.

[0021] Furthermore, the aprotic solvent is dimethyl sulfoxide or a mixture of dimethyl sulfoxide and organic solvent A, wherein organic solvent A is selected from at least one of 1,3-dioxolane, ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, propylene carbonate, ethylene carbonate, N,N-dimethylacetamide, dimethylformamide, and ethyl methyl sulfone.

[0022] Preferably, the aprotic solvent is a mixture of dimethyl sulfoxide and organic solvent A in a volume ratio of 1-4:1; more preferably, the aprotic solvent is a mixture of dimethyl sulfoxide and 1,3-dioxolane in a volume ratio of 1-4:1.

[0023] This invention uses manganese acetylacetonate as an additive, dissolved in a basic electrolyte to prepare a functional electrolyte for assembling a lithium-oxygen battery. Through battery charge-discharge operation, positive electrode materials with self-catalytic active sites, i.e., discharge products, can be repeatedly generated and decomposed on the positive electrode. These catalytically active sites can be implanted into the discharge products for catalytic action. Simultaneously, the metal sites doped into the discharge products have excellent regulatory characteristics on the electronic structure of the products themselves, transforming them from insulators to semiconductors or conductors, exhibiting certain metallic properties, and fundamentally accelerating the positive electrode reaction kinetics. Furthermore, the acetylacetonate, existing in molecular form, can directly interact with superoxide ions, enhancing its stability and making it easier to disproportionate and convert to lithium peroxide, reducing the occurrence of side reactions. The application of novel additives in this invention gives the electrolyte solution excellent electrochemical performance, playing a fundamental role in improving the performance of metal-oxygen batteries. Attached Figure Description

[0024] Figure 1 These are the UV spectra of the functional electrolyte with and without KO2 added in step 2 of Example 1;

[0025] Figure 2 This is the XPS spectrum of the positive electrode of the lithium-oxygen battery in Example 1 under fully discharged state;

[0026] Figure 3 The images show the capacity-limited cycle charge-discharge curves (a) and the corresponding overpotential and energy efficiency (b) of the Li-O2 battery.

[0027] Figure 4 The image is an electron microscope image of the discharge products after the battery in Example 1 has been running. It can be seen that the product has a film-like morphology.

[0028] Figure 5 These are electron microscope images of the discharge products of the battery in Comparative Example 3 after operation;

[0029] Figure 6 This is an electron microscope image of the discharge products of the battery in Comparative Example 4 after operation. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0031] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0032] Example 1

[0033] 1. Mix porous carbon material and commercial platinum carbon material with (1%) polyvinylidene fluoride solution or Nafion solution at an appropriate mass ratio (45%:45%:10%), add an appropriate amount of pyrrolidone solvent, sonicate until well dispersed, and coat evenly on a substrate. Bake at 100 degrees Celsius for 12 hours to prepare an air electrode.

[0034] 2. Preparation of electrolyte: Dissolve the additive manganese acetylacetone (0.1 M) and lithium salt LiCF3SO3 (1 M) in DMSO to prepare the functional electrolyte; dissolve the lithium salt LiCF3SO3 (1 M) in DMSO to prepare the basic electrolyte.

[0035] 3. Using the air electrode prepared above as the positive electrode, lithium metal as the negative electrode, basic electrolyte as the negative electrolyte, and functional electrolyte as the positive electrolyte, a self-catalytic metal-oxygen battery is assembled.

[0036] Figure 1 These are the UV spectra of the functional electrolyte in step 2 of Example 1 with and without the addition of KO2. It can be seen that potassium superoxide (KO2) generates O2 in DMSO. - Subsequently, it was introduced into a 1 M LiCF3SO3 / DMSO electrolyte containing Mn(acac)3 ( Figure 1 Saturated KO2 / DMSO solution was injected into a Li-containing container. + After contact with the electrolyte, the peak intensity at 292 nm increases rapidly and broadens to longer wavelengths, indicating a strong interaction with superoxide. Therefore, Mn(acac)3 can directly interact with the discharge product intermediates superoxide and lithium superoxide, thereby stabilizing them and preventing them from attacking the electrolyte solution or carbon materials, thus avoiding numerous side reactions. Currently, this interaction requires the presence of DMSO in the solvent.

[0037] Figure 2 This is the XPS spectrum of the positive electrode of the lithium-oxygen battery in Example 1 under fully discharged state. The XPS analysis revealed the content of different elements on the electrode. The atomic ratio of Mn to Li in the discharge products was approximately 2:98, indicating that Mn... 2+ Doping is incorporated into the discharge product Li2O2, and Mn is involved in the reaction process. 2+ The doping level is significantly lower than that of Li + .

[0038] To evaluate the battery performance of this system, it was assembled into coin cells and tested in a high-purity oxygen atmosphere (Li-O2 evaluation system). All current densities and specific capacities were calculated based on the mass of the loaded materials. The test system pressure was 0.1 MPa atm, the test system temperature was room temperature, the test system was a Newwell tester, and the constant current charge-discharge voltage range was 2.0–4.5 V. Cyclic testing was conducted at 1000 mA g. -1 The experiment was conducted at a current density of [value missing]. Figure 3 The figures (a) show the capacity-limited cycle charge-discharge curves (C / D) of a Li-O2 battery, along with the corresponding overpotential and energy efficiency (b). It can be seen that at 1000 mA g / dL... -1 At high current densities, the self-catalytic Li-O2 battery system with added Mn(acac)3 can operate for more than 3850 cycles, and its charging and discharging capacities can still reach 500 mAh g⁻¹ during the cycles. -1 To achieve the longest reported lifespan. In the discharge-charge curve ( Figure 3 a) and the corresponding parameters in the bar chart ( Figure 3 (b) The median discharge voltage remained above 2.7V for 2000 cycles; the median charge voltage gradually increased in the first 200 cycles, reached a stable state at 500 cycles, and remained consistent for the first 2000 cycles. The battery's energy efficiency decreased from an initial 75.2% to 62.5%. In the system without Mn(acac)3 additive, the battery could operate for a maximum of 30 cycles. The above analysis shows that the introduction of Mn(acac)3 significantly improves the cycle stability of Li-O2 batteries, fully demonstrating the practical value and significance of Li-O2 batteries.

[0039] Example 2

[0040] The other conditions are the same as in Example 1, except that in step 2, the solvent DMSO is replaced with a mixed solvent of DMSO and DOL in a volume ratio of 2:1 in the preparation of the functional electrolyte.

[0041] Example 3

[0042] The other conditions are the same as in Example 1, except that in step 2, the solvent DMSO is replaced with a mixed solvent of DMSO and DOL in a volume ratio of 4:1 in the preparation of the functional electrolyte.

[0043] Example 4

[0044] The other conditions are the same as in Example 1, except that in step 2, the solvent DMSO is replaced with a mixture of DMSO and ethylene glycol dimethyl ether in a volume ratio of 2:1 in the preparation of the functional electrolyte.

[0045] Example 5

[0046] The other conditions are the same as in Example 1, except that in step 2, the solvent DMSO is replaced with a mixture of DMSO and ethylene carbonate in a volume ratio of 2:1 in the preparation of the functional electrolyte.

[0047] Example 6

[0048] The other conditions are the same as in Example 1, except that in step 2, the solvent DMSO is replaced with a mixture of DMSO and DOL in a volume ratio of 1:1 in the preparation of the functional electrolyte.

[0049] Comparative Example 1

[0050] The other conditions are the same as in Example 1, except that in step 2, manganese acetylacetone is replaced with iron acetylacetone of equal molar concentration in the preparation of the functional electrolyte.

[0051] Comparative Example 2

[0052] The other conditions are the same as in Example 1, except that in step 2, manganese acetylacetone is replaced with nickel acetylacetone of equal molar concentration in the preparation of the functional electrolyte.

[0053] Comparative Example 3

[0054] The other conditions are the same as in Example 1, except that in step 2, manganese acetylacetone is replaced with vanadium acetylacetone of equal molar concentration in the preparation of the functional electrolyte.

[0055] Comparative Example 4

[0056] The other conditions are the same as in Example 1, except that in step 2, manganese acetylacetone is replaced with iridium acetylacetone at an equimolar concentration in the preparation of the functional electrolyte.

[0057] Comparative Example 5

[0058] The other conditions are the same as in Example 1, except that in step 2, the solvent DMSO is replaced with DOL in the preparation of the functional electrolyte.

[0059] Figure 4 The image shows an electron microscope photograph of the discharge products after the battery in Example 1 has been running, which can be seen to have a film-like morphology. Figure 5 These are electron microscope images of the discharge products of the battery in Comparative Example 3 after operation. Figure 6 This is an electron microscope image of the discharge products of the battery in Comparative Example 4 after operation. Figure 5 , Figure 6It can be seen that using V(acac)3 or Ir(acac)3 as additives in the positive electrode electrolyte of lithium-oxygen batteries results in cyclic morphologies of the discharge products. Typically, with increasing discharge capacity, the electrode is covered by cyclic Li2O2 via a solution-mediated pathway. These cyclic product morphologies are difficult to completely decompose during charging, leading to high overpotentials. In this invention, the introduction of Mn(acac)3 during discharge promotes the adsorption and growth of reaction intermediates LiO2 and Li2O2 molecules on the KB electrode. This is a surface-mediated pathway, and the discharge products exhibit film and / or sheet-like structures. These structures are more easily formed and decomposed during charge and discharge, thus endowing the lithium-oxygen battery with low overpotential and high cycle performance. The electrochemical performance data of the lithium-oxygen batteries in the above embodiments and comparative examples are listed in Table 1 below.

[0060] Table 1 Electrochemical performance data of lithium-oxygen batteries

[0061] .

[0062] This invention prepares an electrolyte for the positive electrode of a lithium-oxygen battery by dissolving manganese acetylacetonate in a basic electrolyte solution, and assembles the lithium-oxygen battery using the basic electrolyte solution as the negative electrode electrolyte. Through battery charge-discharge operation, positive electrode materials with self-catalytic active sites, i.e., discharge products, can be repeatedly generated and decomposed on the positive electrode. These catalytically active sites can be implanted into the discharge products for catalytic action. Simultaneously, the metal sites doped into the discharge products have excellent regulatory characteristics on the electronic structure of the discharge products themselves, transforming them from insulators to semiconductors or conductors, exhibiting certain metallic properties, and fundamentally accelerating the positive electrode reaction kinetics. Furthermore, manganese acetylacetonate, existing in molecular form, can directly interact with superoxide ions, enhancing its stability and making it easier to disproportionate and convert to lithium peroxide, reducing the occurrence of side reactions. The application of additives in this invention gives the electrolyte solution excellent electrochemical performance, playing a fundamental role in improving the performance of lithium-oxygen batteries. This new method is based on common commercial raw materials, optimizes the battery system's operating mechanism through normal battery reactions, is simple and easy to implement, uses inexpensive and readily available raw materials, and has excellent performance, demonstrating great practical value and economic prospects.

Claims

1. An electrolyte for a lithium-oxygen battery, characterized by comprising: It includes the following components: an aprotic solvent, a lithium salt of 0.5-2 mol / L as solute, and manganese acetylacetone of 0.01-0.1 mol / L; the aprotic solvent is a mixture of dimethyl sulfoxide and 1,3-dioxolane in a volume ratio of 2-4:

1.

2. The electrolyte for a lithium-oxygen battery according to claim 1, characterized by, The lithium salt is selected from at least one of lithium trifluoromethanesulfonate, lithium perchlorate, lithium bis(trifluoromethanesulfonylimide), lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium nitrate.

3. A self-catalyzing lithium-oxygen battery, characterized in that, It includes a lithium anode, a cathode, a separator, and an electrolyte for a lithium-oxygen battery as described in any one of claims 1 or 2.

4. The self-catalyzing lithium-oxygen battery of claim 3, wherein, The positive electrode is KB and platinum-carbon coated carbon paper, and the diaphragm is a glass fiber diaphragm.

5. The use of manganese acetylacetone as an additive in the positive electrode electrolyte of a self-catalytic lithium-oxygen battery, characterized in that... The positive electrode electrolyte of the lithium-oxygen battery contains 0.01-0.1 mol / L manganese acetylacetone, 0.5-2 mol / L lithium salt, and an aprotic solvent, wherein the aprotic solvent is a mixture of dimethyl sulfoxide and 1,3-dioxolane in a volume ratio of 1-4:1.

Images