Electrolyte additive, electrolyte, preparation method thereof and lithium-sulfoxyl chloride secondary battery

Abstract

The application provides an electrolyte additive, which is a nitrate compound with a chemical structure as shown in general formula I; by introducing the nitrate additive into a base electrolyte, an organic solvent and a lithium salt, the nitrate additive can be preferentially reduced on the surface of a negative electrode to form a solid electrolyte interface with high density and high mechanical strength, which can not only block the corrosion of a byproduct of a side reaction on the negative electrode, but also inhibit the growth of lithium dendrites, reduce the loss of active lithium and the consumption of electrolyte, and improve the cycle life and low-temperature performance of a battery. Meanwhile, the electrolyte additive can also improve the problems of discharge capacity attenuation and voltage polarization increase of the battery after long-time standing, and has good practicability.

Description

Technical Field

[0001] This invention relates to the field of secondary battery and electrolyte technology, and particularly to an electrolyte additive, an electrolyte and its preparation method, and a lithium-thionyl chloride secondary battery. Background Technology

[0002] The lithium-thionyl chloride (LTC) secondary battery is a novel high-energy-density secondary battery based on the primary LTC battery. The primary LTC battery boasts high energy density (710 Wh / kg), high operating voltage (3.4 V), and extremely low self-discharge, making it widely used in military and aerospace fields. Furthermore, the LTC-based electrolyte has an extremely low melting point (-110℃) and a high boiling point (78.8℃), demonstrating excellent performance in extreme high and low temperature environments. The LTC secondary battery also possesses high energy density, high operating voltage, and excellent wide-temperature performance, overcoming the limitation of the non-rechargeable nature of LTC. Therefore, the LTC secondary battery shows promising application prospects in high-energy-density and extreme environmental service conditions. However, it also faces many challenges in practical applications, particularly the inability of the solid electrolyte interface formed by traditional electrolytes to effectively protect the negative electrode.

[0003] In lithium-thionyl chloride secondary batteries, the traditional solid electrolyte interface is mainly composed of inorganic components, such as LiCl, which has low mechanical strength and is prone to cracking during charge and discharge, leading to phase separation between the solid electrolyte interface and the electrode interface. This not only induces the growth of lithium dendrites but also ensures continuous contact between the electrolyte and the lithium anode, resulting in the loss of active lithium, electrolyte consumption, and continuous thickening of the passivation layer. Consequently, the battery suffers from short cycle life, poor cycle stability, and slow kinetic performance.

[0004] Therefore, how to regulate the solid electrolyte interface on the negative electrode side to protect the negative electrode and thus achieve better battery performance has become a key scientific and technological challenge restricting the development of lithium-thionyl chloride secondary batteries. To address this issue, there is an urgent need to develop a solid electrolyte interface with high mechanical strength and high ionic conductivity to fundamentally improve interfacial contact and structural stability, thereby significantly enhancing the battery's cycle life and kinetic performance. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides an electrolyte additive, an electrolyte, a method for preparing the electrolyte, and a lithium-thionyl chloride secondary battery. This invention introduces a nitrate additive into the basic electrolyte, organic solvent, and lithium salt. This additive preferentially reduces the electrolyte on the negative electrode surface, forming a dense, high-mechanical-strength solid electrolyte interface. This interface not only prevents corrosion of the negative electrode by byproducts but also inhibits lithium dendrite growth, reduces active lithium loss and electrolyte consumption, thereby improving the battery's cycle life and low-temperature performance. Simultaneously, this electrolyte additive also improves problems such as capacity decay and increased voltage polarization after prolonged static storage, demonstrating significant practicality.

[0006] The primary objective of this invention is to provide an electrolyte additive, which is a nitrate compound with a chemical structure as shown in general formula I. ; General Formula I Wherein, R is any one of Li, Na, K, Cu, C3H7, and [Li(15-crown-5)].

[0007] Furthermore, R is preferably Li.

[0008] A second objective of this invention is to provide an electrolyte comprising an organic solvent, an additive, and a lithium salt, wherein the additive is the electrolyte additive described above.

[0009] Specifically, the lithium salt is lithium tetrachloroaluminate or lithium difluorooxalate borate, and the organic solvent is thionyl chloride or methyl acetate.

[0010] Specifically, the concentration of the electrolyte additive in the electrolyte is 0.05~0.5 mol / L.

[0011] Furthermore, the concentration of the electrolyte additive in the electrolyte is preferably 0.1 mol / L.

[0012] Specifically, the concentration of the lithium salt in the electrolyte is 1~3 mol / L.

[0013] The third objective of this invention is to provide a method for preparing an electrolyte, which includes the following steps: under a protective atmosphere, lithium salts are mixed and dissolved in an organic solvent, then electrolyte additives are added, and the mixture is magnetically stirred until homogeneous to obtain an electrolyte.

[0014] The fourth objective of this invention is to provide a lithium-thionyl chloride secondary battery, which includes a positive electrode, an electrolyte, a separator, and a negative electrode, wherein the electrolyte contains the electrolyte additives described above.

[0015] Specifically, the positive electrode comprises a porous carbon material; the negative electrode is lithium metal.

[0016] Compared with the prior art, the beneficial effects of the present invention include: (1) This invention provides a high-performance lithium-thionyl chloride secondary battery electrolyte system that innovatively introduces nitrate compounds as multifunctional additives; the nitrate additives play a decisive role on the negative electrode side, and their anions (NO3) - It possesses a low unoccupied molecular orbital (LUMO) energy level, enabling it to preferentially undergo reduction reactions on the lithium metal anode surface during the initial battery cycle, forming Li3N and LiN-containing compounds. x O y A dense, high-mechanical-strength solid electrolyte interphase (SEI) effectively protects the negative electrode. This SEI layer possesses two core characteristics: first, its density and high mechanical strength physically block the continuous corrosion of the lithium negative electrode by thionyl chloride and its reduction products, significantly reducing irreversible loss of active lithium and side reaction consumption of the electrolyte; second, its high ionic conductivity facilitates rapid and uniform lithium-ion transport. The SEI effectively inhibits the rampant growth of lithium dendrites and guides uniform lithium deposition / stripping. Its high DN value reduces solvent coordination, and Li... + Rapid desolvation improves ionic conductivity, enabling Li... + Rapid and uniform distribution and deposition improve the morphology of lithium deposition and enhance battery cycle stability; (2) The nitrate additive in this invention also contributes key benefits at the positive electrode side and the entire electrolyte system level, NO3 - It possesses a high highest occupied molecular orbital (HOMO) energy level, allowing it to preferentially oxidize at the positive electrode potential and participate in the formation of a protective positive electrode electrolyte interface (CEI). The CEI can mitigate the corrosion and passivation of carbon cathode materials by intermediate products such as chlorine and polysulfides, thereby protecting the cathode structure and improving reaction reversibility. Furthermore, NO3... - The introduction of nitrate can also promote the reversible kinetics of thionyl chloride reduction products, which helps to reduce charging overpotential and alleviate voltage hysteresis. At the system level, the oxidizing property of nitrate helps to remove reducing impurities in the electrolyte and improve the chemical stability of the system. Its interaction with LiAlCl4 may also optimize the solvation structure of lithium ions.

[0017] (3) In the electrolyte provided by the present invention, LiAlCl4 acts as a conductive lithium salt, which dissociates into Li during charging and discharging. +This lithium salt participates in the deposition / stripping reaction of lithium metal in the negative electrode. It exhibits excellent solubility in thionyl chloride solvent, and the in-situ generated complex components enhance ion dissociation, constructing a high-ionic-conductivity electrolyte to ensure high-rate battery performance. The AlCl3 generated by trace disproportionation in the system can participate in the formation of an aluminum-containing passivation film on the lithium negative electrode surface, synergistically inhibiting lithium dendrite growth and the continuous corrosion side reaction of thionyl chloride on lithium metal. Thionyl chloride, as the main solvent, can efficiently dissolve the lithium salt and construct continuous ion transport channels. During discharge, lithium metal in the negative electrode undergoes lithium stripping oxidation, which is reduced on the catalytic carbon matrix surface of the positive electrode, generating Li, S, and SO2, constituting the main source of battery discharge capacity. Simultaneously, SOCl2 forms a complex with trace amounts of AlCl3, optimizing the Lewis acid-base balance of the electrolyte and stabilizing the electrolyte chemical environment. Nitrate compounds, as functional additives, can be preferentially reduced on the lithium negative electrode surface upon dissociation, generating Li3N and LiN-rich compounds. x O y The dense, high-ionic-conductivity SEI effectively suppresses lithium dendrite growth and improves lithium deposition / stripping coulombic efficiency; simultaneously, it optimizes the physicochemical properties of the positive electrode interface, alleviates positive electrode passivation caused by irreversible deposition of discharge products, reduces electrolyte consumption, suppresses negative electrode SEI thickening, reduces cycle overpotential, and improves battery cycle reversibility; furthermore, NO3 - The solvation environment is reconstructed, and the dissociation equilibrium of chloroaluminate is regulated. In summary, LiAlCl4 ensures the high ionic conductivity of the system and participates in the initial construction of the negative electrode interface; SOCl2 serves as a solvent and provides ion transport medium and capacity source for electrochemically reactive materials; nitrate additives simultaneously modify the chemical composition of the positive and negative electrode interfaces; the ternary components synergistically counteract each other, effectively suppressing electrolyte side reactions and positive and negative electrode passivation, improving the overall electrochemical performance of the battery, broadening the battery's applicable operating temperature range, and achieving long-term battery storage characteristics.

[0018] (4) Through the complementary film formation and synergistic stabilization effects of additives and base electrolytes during charge and discharge processes, a composite solid electrolyte interface (SEI) and positive electrode electrolyte interface (CEI) with fast ion conduction, high mechanical strength, and stable structure are jointly constructed. When this electrolyte is applied to lithium-thionyl chloride secondary batteries, the cycle life and coulombic efficiency of the battery are significantly improved, the wide temperature range adaptability (especially at low temperatures) is improved, and the capacity decay and voltage polarization problems after long-term static storage are effectively alleviated, thus achieving a key performance breakthrough for this high-energy-density battery system from "single use" to stable "secondary cycle". Attached Figure Description

[0019] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0020] Figure 1 (a) and (d) are SEM images of the negative electrode side cross sections of the secondary batteries prepared in Example 1 and Comparative Example 1 of the present invention, respectively. Figure 1 (b) and (c) are SEM images of the negative electrode surface in the secondary battery prepared in Comparative Example 1 of the present invention at different rates. Figure 1 (e, f) are SEM images of the negative electrode surface in the secondary battery prepared in Example 1 of the present invention at different rates; Figure 2 (ab) are the S2p comparison spectrum of the XPS energy spectrum of the negative electrode surface in the secondary battery prepared in Example 1 and Comparative Example 1, respectively, and the N1s spectrum of the XPS energy spectrum of the negative electrode surface in the secondary battery prepared in Example 1. Figure 3 (a) is a comparison of the impedance test results of the secondary batteries prepared in Example 1 and Comparative Example 1 after 10 charge-discharge cycles and after being left to stand. Figure 3 (bc) are impedance test diagrams of the secondary batteries prepared in Example 1 and Comparative Example 1 of the present invention before and after 10 charge-discharge cycles and after being left to stand. Figure 3 (d) is a comparison diagram of the electrochemical impedance of the secondary batteries prepared in Example 1 and Comparative Example 1 of the present invention; Figure 4 Comparison chart of the long-cycle performance test of the secondary batteries prepared in Example 1 and Comparative Examples 1-5 at a low temperature of -40°C and a current density of 1000 mA / g. Figure 5 The graph shows a comparison of the long-cycle performance of the secondary batteries prepared in Examples 1-3, 10-12 and Comparative Example 1 at a low temperature of -40°C and a current density of 1000 mA / g. Figure 6 Comparative graphs showing the long-cycle performance of the secondary batteries prepared in Examples 1 and 7-9 of this invention at a low temperature of -40°C and a current density of 1000 mA / g. Figure 7 This is a comparison chart showing the cycling performance of the secondary batteries prepared in Example 1 and Comparative Example 1 of this invention after being left to stand for three days, at 25°C and a current density of 1000 mA / g. Figure 8 This is a comparison diagram of the LUMO and HOMO energy levels of the electrolyte additives prepared in Example 1 and Comparative Examples 2-5 of the present invention; Figure 9 This is a comparison chart of the DN values ​​of the electrolyte additives prepared in Example 1 and Comparative Examples 2-5 of the present invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the present invention.

[0022] Example 1 Preparation of electrolyte: In an argon-filled glove box, where the water and oxygen content is below 0.01 ppm, lithium tetrachloroaluminate and lithium nitrate were sequentially dissolved in thionyl chloride. The mixture was stirred at room temperature on a magnetic stirrer to obtain the electrolyte prepared in Example 1. The electrolyte contained 0.1 mol / L lithium nitrate and 1.8 mol / L lithium tetrachloroaluminate. The chemical structural formula of lithium nitrate is: ; Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80°C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 1, denoted as 0.1 M LiNO3.

[0023] Example 2 Preparation of electrolyte: In an argon-filled glove box, where the water and oxygen content is less than 0.01 ppm, lithium tetrachloroaluminate and sodium nitrate were dissolved sequentially in thionyl chloride and stirred on a magnetic stirrer at room temperature to obtain the electrolyte prepared in Example 2. The concentration of sodium nitrate in the electrolyte was 0.1 mol / L and the concentration of lithium tetrachloroaluminate was 1.8 mol / L.

[0024] Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80°C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 2, denoted as 0.1 M NaNO3.

[0025] Example 3 Preparation of electrolyte: In an argon-filled glove box, where the water and oxygen content is less than 0.01 ppm, lithium tetrachloroaluminate and potassium nitrate were dissolved sequentially in thionyl chloride and stirred on a magnetic stirrer at room temperature to obtain the electrolyte prepared in Example 3. The concentration of potassium nitrate in the electrolyte was 0.1 mol / L and the concentration of lithium tetrachloroaluminate was 1.8 mol / L.

[0026] Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone in a mortar for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80°C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 3, denoted as 0.1 M KNO3.

[0027] Example 4 Preparation of electrolyte: In an argon-filled glove box, where the water and oxygen content is less than 0.01 ppm, lithium tetrachloroaluminate and lithium nitrate were dissolved sequentially in thionyl chloride and stirred on a magnetic stirrer at room temperature to obtain the electrolyte prepared in Example 4. The concentration of lithium nitrate in this electrolyte was 0.05 mol / L and the concentration of lithium tetrachloroaluminate was 2.5 mol / L.

[0028] Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80°C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 4.

[0029] Example 5 Preparation of electrolyte: In an argon-filled glove box, where the water and oxygen content is less than 0.01 ppm, lithium tetrachloroaluminate and lithium nitrate were sequentially dissolved in thionyl chloride and stirred on a magnetic stirrer at room temperature to obtain the electrolyte prepared in Example 5. The concentration of lithium nitrate in the electrolyte was 0.3 mol / L and the concentration of lithium tetrachloroaluminate was 3 mol / L.

[0030] Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone in a mortar for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80°C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 5.

[0031] Example 6 Preparation of electrolyte: In an argon-filled glove box, where the water and oxygen content is less than 0.01 ppm, lithium tetrachloroaluminate and lithium nitrate were sequentially dissolved in thionyl chloride and stirred on a magnetic stirrer at room temperature to obtain the electrolyte prepared in Example 6. The concentration of lithium nitrate in the electrolyte was 0.5 mol / L and the concentration of lithium tetrachloroaluminate was 1.8 mol / L.

[0032] Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80°C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 6.

[0033] Example 7 Preparation of electrolyte: In an argon-filled glove box, where the water and oxygen content is less than 0.01 ppm, lithium tetrachloroaluminate and lithium nitrate were dissolved sequentially in methyl acetate and stirred on a magnetic stirrer at room temperature to obtain the electrolyte prepared in Example 7. The concentration of lithium nitrate in the electrolyte was 0.1 mol / L and the concentration of lithium tetrachloroaluminate was 1.8 mol / L.

[0034] Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80°C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 7.

[0035] Example 8 Preparation of electrolyte: In an argon-filled glove box, where the water and oxygen content is less than 0.01 ppm, lithium difluorooxalate borate and lithium nitrate were sequentially dissolved in thionyl chloride and stirred on a magnetic stirrer at room temperature to obtain the electrolyte prepared in Example 8. The concentration of lithium nitrate in the electrolyte was 0.1 mol / L and the concentration of lithium tetrachloroaluminate was 1.8 mol / L.

[0036] Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80°C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 7.

[0037] Example 9 Preparation of electrolyte: In an argon-filled glove box, where the water and oxygen content is less than 0.01 ppm, lithium difluorooxalate borate and lithium nitrate were sequentially dissolved in methyl acetate and stirred on a magnetic stirrer at room temperature to obtain the electrolyte prepared in Example 9. The electrolyte contained lithium nitrate at a concentration of 0.1 mol / L and lithium tetrachloroaluminate at a concentration of 1.8 mol / L.

[0038] Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone in a mortar for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80°C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 9.

[0039] Example 10 Preparation of electrolyte: In an argon-filled glove box, where the water and oxygen content is less than 0.01 ppm, lithium tetrachloroaluminate and copper nitrate were dissolved sequentially in thionyl chloride and stirred on a magnetic stirrer at room temperature to prepare the electrolyte prepared in Example 10. The concentration of copper nitrate in the electrolyte was 0.1 mol / L and the concentration of lithium tetrachloroaluminate was 1.8 mol / L.

[0040] Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80°C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 10, denoted as 0.1 M Cu(NO3)2.

[0041] Example 11 Preparation of electrolyte: In an argon-filled glove box, where the water and oxygen content is less than 0.01 ppm, lithium tetrachloroaluminate and isopropyl nitrate were sequentially dissolved in thionyl chloride, and stirred on a magnetic stirrer at room temperature to prepare the electrolyte prepared in Example 10. The electrolyte contained isopropyl nitrate at a concentration of 0.1 mol / L and lithium tetrachloroaluminate at a concentration of 1.8 mol / L.

[0042] Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80°C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 11, denoted as 0.1M C3H7NO3.

[0043] Example 12 Preparation of electrolyte: In an argon-filled glove box, where the water and oxygen content is less than 0.01 ppm, lithium tetrachloroaluminate and lithium nitrate (15-crown-5) were sequentially dissolved in thionyl chloride and stirred on a magnetic stirrer at room temperature to obtain the electrolyte prepared in Example 12. The concentration of lithium nitrate (15-crown-5) in the electrolyte was 0.1 mol / L and the concentration of lithium tetrachloroaluminate was 1.8 mol / L.

[0044] Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80°C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 11, denoted as [Li(15-crown-5)]NO3.

[0045] Comparative Example 1 The difference from Example 1 is that no nitrate additive is added.

[0046] Preparation of electrolyte: In an argon-filled glove box with water and oxygen content below 0.01 ppm, lithium tetrachloroaluminate was dissolved in thionyl chloride and stirred on a magnetic stirrer at room temperature to prepare the electrolyte prepared in Comparative Example 1, in which the concentration of lithium tetrachloroaluminate was 1.8 mol / L.

[0047] Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80°C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Comparative Example 1, denoted as LiNO3-free.

[0048] Comparative Example 2 The difference from Example 1 is that lithium bis(fluorosulfonyl)imide (LiFSI) is used instead of nitrate additives.

[0049] Preparation of electrolyte: In an argon-filled glove box with water and oxygen content below 0.01 ppm, lithium tetrachloroaluminate and LiFSI were dissolved sequentially in thionyl chloride. The mixture was stirred on a magnetic stirrer at room temperature to prepare the electrolyte prepared in Comparative Example 1, in which the concentration of lithium tetrachloroaluminate was 1.8 mol / L and the concentration of LiFSI was 0.1 mol / L.

[0050] Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80 °C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Comparative Example 2, denoted as 0.1 M LiFSI.

[0051] Comparative Example 3 The difference from Example 1 is that lithium hexafluorophosphate (LiPF6) is used instead of nitrate additives.

[0052] Preparation of electrolyte: In an argon-filled glove box with water and oxygen content below 0.01 ppm, lithium tetrachloroaluminate and LiPF6 were sequentially dissolved in thionyl chloride. The mixture was stirred on a magnetic stirrer at room temperature to obtain the electrolyte prepared in Comparative Example 1, in which the concentration of lithium tetrachloroaluminate was 1.8 mol / L and the concentration of LiPF6 was 0.1 mol / L.

[0053] Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80 °C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Comparative Example 3, labeled as 0.1 M LiPF6.

[0054] Comparative Example 4 The difference from Example 1 is that lithium perchlorate (LiClO4) is used instead of nitrate additives.

[0055] Preparation of electrolyte: In an argon-filled glove box with water and oxygen content below 0.01 ppm, lithium tetrachloroaluminate and LiClO4 were sequentially dissolved in thionyl chloride. The mixture was stirred on a magnetic stirrer at room temperature to obtain the electrolyte prepared in Comparative Example 4, in which the concentration of lithium tetrachloroaluminate was 1.8 mol / L and the concentration of LiClO4 was 0.1 mol / L.

[0056] Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80°C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Comparative Example 4, labeled as 0.1 M LiClO4.

[0057] Comparative Example 5 The difference from Example 1 is that lithium bis(fluorosulfonyl)imide (LiTFSI) is used instead of nitrate additives.

[0058] Preparation of electrolyte: In an argon-filled glove box with water and oxygen content below 0.01 ppm, lithium tetrachloroaluminate and LiTFSI were sequentially dissolved in thionyl chloride. The mixture was stirred on a magnetic stirrer at room temperature to prepare the electrolyte prepared in Comparative Example 5, in which the concentration of lithium tetrachloroaluminate was 1.8 mol / L and the concentration of LiTFSI was 0.1 mol / L.

[0059] Battery fabrication: Ordered mesoporous carbon material CMK-3 powder, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1 and ground in N-methylpyrrolidone for 30 min to obtain a positive electrode slurry. The positive electrode slurry was then impregnated onto a stainless steel sheet with a diameter of 15.5 mm and dried overnight in a vacuum oven at 80°C to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, a 47 μm glass fiber separator, and a lithium metal sheet were assembled in sequence into a button cell, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Comparative Example 5, labeled as 0.1 M LiTFSI.

[0060] Performance testing Figure 1 (a) and (d) are SEM images of the negative electrode side cross sections of the secondary batteries prepared in Example 1 and Comparative Example 1 of the present invention, respectively. Figure 1 (b) and (c) are SEM images of the negative electrode surface in the secondary battery prepared in Comparative Example 1 of the present invention at different rates. Figure 1 (e) and (f) are SEM images of the negative electrode surface in the secondary battery prepared in Example 1 of this invention at different magnification rates; Figure 1(d) It can be observed that the cross-sectional SEM morphology of the negative electrode side is smooth after the addition of lithium nitrate; from the surface SEM, it can be seen that the SEI without lithium nitrate in Comparative Example 1 is loose and porous with poor structural stability; while the SEI derived from lithium nitrate in Example 1 is more uniform and dense with high mechanical strength. Figure 2 (ab) are the S 2p comparison spectra of the XPS energy spectrum of the negative electrode surface in the secondary battery prepared in Example 1 and Comparative Example 1, respectively, and the N 1s spectrum of the XPS energy spectrum of the negative electrode surface in the secondary battery prepared in Example 1. Figure 2 This demonstrates the difference in material composition on the negative electrode surface before and after the addition of lithium nitrate, from... Figure 2 As can be seen, the addition of LiNO3 forms a mixture containing Li3N and LiN. x O y The inorganic dense SEI layer; the S 2p spectrum of the negative electrode with added lithium nitrate shows that it does not contain S, SCl2, or S2Cl2, indicating that the dense SEI can block S and Cl byproducts, while the SEI without lithium nitrate is loose and porous, and byproducts coming from the positive electrode will accumulate in the electrode pores.

[0061] Figure 3 (a) is a comparison of the impedance test results of the secondary batteries prepared in Example 1 and Comparative Example 1 after 10 charge-discharge cycles and after being left to stand. Figure 3 (bc) are impedance test diagrams of the secondary batteries prepared in Example 1 and Comparative Example 1 of the present invention before and after 10 charge-discharge cycles and after being left to stand. Figure 3 (d) is a comparison diagram of the electrochemical impedance of the secondary batteries prepared in Example 1 and Comparative Example 1 of the present invention; Figure 3 This study demonstrates the impedance comparison of two batteries before and after the addition of lithium nitrate. The experimental design involved subjecting the assembled batteries to 10 charge-discharge cycles followed by a long-term resting period, and then measuring the impedance of the batteries before and after the resting period. The battery with added lithium nitrate showed almost no change in impedance before and after the resting period, while the battery without added lithium nitrate showed an increase in impedance, and R... SEI R ct Significantly increased. Figure 4 Comparison chart of the long-cycle performance test of the secondary batteries prepared in Example 1 and Comparative Examples 1-5 at a low temperature of -40°C and a current density of 1000 mA / g. Figure 4The results of long-term cycling performance tests at a current density of 1000 mA / g were presented for batteries containing conventional 1.8 mol / L lithium tetrachloroaluminate (Comparative Example 1) and lithium-thionyl chloride secondary battery electrolytes prepared in Examples 1 and 2-3, respectively, with the addition of three different additives. The batteries containing 0.1 mol / L lithium difluorosulfonylimide and 0.1 mol / L lithium hexafluorophosphate showed improved electrochemical performance compared to the conventional 1.8 mol / L lithium tetrachloroaluminate battery, but had shorter cycle life and poorer cycle stability. The battery with 0.1 mol / L lithium nitrate exhibited excellent cycle stability and a long cycle life, achieving stable cycling over 500 cycles. Figure 5 The graph shows a comparison of the long-cycle performance of the secondary batteries prepared in Examples 1-3, 10-12 and Comparative Example 1 at a low temperature of -40°C and a current density of 1000 mA / g. Figure 5 The results of long-term cycling performance tests at a current density of 1000 mA / g were presented for batteries containing conventional 1.8 mol / L lithium tetrachloroaluminate and lithium-thionyl chloride secondary battery electrolytes with the addition of three different nitrate additives, at a low temperature of -40°C. Batteries containing 0.1 mol / L sodium nitrate, 0.1 mol / L potassium nitrate, and 0.1 mol / L potassium nitrate all showed significantly improved electrochemical performance compared to the conventional 1.8 mol / L lithium tetrachloroaluminate battery, addressing the issues of short cycle life and poor cycle stability. However, the battery with 0.1 mol / L lithium nitrate exhibited the best cycle stability and long cycle life, achieving stable cycling over 500 cycles. Figure 6 Comparative graphs showing the long-cycle performance of the secondary batteries prepared in Examples 1 and 7-9 of this invention at a low temperature of -40°C and a current density of 1000 mA / g. Figure 6 The study compared the long-cycle performance of different types of lithium salts and solvents after the addition of lithium nitrate, showing that the combination of lithium tetrachloroaluminate as lithium salt and thionyl chloride as solvent was optimal. Figure 7 This is a comparison chart showing the cycling performance of the secondary batteries prepared in Example 1 and Comparative Example 1 of this invention after being left to stand for three days, at 25°C and a current density of 1000 mA / g. Figure 7 The comparison of cycle performance of batteries with and without lithium nitrate after being left to stand for 3 days was shown. The SEI derived from lithium nitrate has excellent properties and effectively protects the negative electrode during the standing period, thus maintaining the discharge capacity of the battery during recycle. Figure 8 The diagram shows a comparison of the LUMO and HOMO energy levels of the electrolyte additives prepared in Example 1 and Comparative Examples 2-5 of this invention. Nitrate ions have a lower LUMO energy level, making them more likely to accept electrons and exhibiting stronger oxidizing properties. They can preferentially be reduced on the negative electrode side to form Li3N and LiN-containing compounds. x O yThe high mechanical strength, inorganic density, and high ionic conductivity of the SEI (electrolyte interface) improve the cycle stability and kinetic performance of the battery. Nitrate ions have a high HOMO energy level and can be preferentially oxidized at the positive electrode potential, participating in the formation of a protective positive electrode electrolyte interface (CEI). The CEI can mitigate the corrosion and passivation of carbon cathode materials by intermediate products such as chlorine and polysulfides, thereby protecting the cathode structure and improving reaction reversibility. Figure 9 This is a comparison chart of the DN values ​​of the electrolyte additives prepared in Example 1 and Comparative Examples 2-5 of the present invention; Figure 9 The DN values ​​of different electrolyte additives are shown. Nitrate has the highest DN value, indicating that more nitrate enters Li. + The solvation sheath reduces solvent coordination and preferentially reduces on the negative electrode side, forming a Li3N and LiN-containing structure. x O y The high mechanical strength, inorganic density, and high ionic conductivity of SEI inhibit the side reactions of SOCl2 and improve the cycle stability of the battery.

[0062] In summary, this invention introduces nitrate additives into the basic electrolyte, organic solvent, and lithium salt, enabling preferential reduction on the negative electrode surface to form a dense, high-mechanical-strength solid electrolyte interface. This interface not only prevents corrosion of the negative electrode by by-reaction products but also inhibits lithium dendrite growth, reduces active lithium loss and electrolyte consumption, thereby improving battery cycle life and low-temperature performance. Furthermore, this electrolyte additive also improves issues such as capacity decay and increased voltage polarization after prolonged static storage. Notably, when the electrolyte additive is lithium nitrate at a concentration of 0.1 mol / L, the resulting battery exhibits the most superior cycle stability and longest cycle life.

[0063] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. An electrolyte additive, characterized in that, The additive is a nitrate compound with a chemical structure as shown in general formula I. ； General Formula I Wherein, R is any one of Li, Na, K, Cu, C3H7, and [Li(15-crown-5)].

2. The electrolyte additive according to claim 1, characterized in that, The R is preferably Li.

3. An electrolyte, characterized in that, It comprises an organic solvent, an electrolyte additive, and a lithium salt, wherein the electrolyte additive is the electrolyte additive as described in claim 1.

4. The electrolyte according to claim 3, characterized in that, The lithium salt is lithium tetrachloroaluminate or lithium difluorooxalate borate, and the organic solvent is thionyl chloride or methyl acetate.

5. The electrolyte according to claim 3, characterized in that, The concentration of the electrolyte additive in the electrolyte is 0.05~0.5 mol / L.

6. The electrolyte according to claim 3, characterized in that, The concentration of the lithium salt in the electrolyte is 1~3 mol / L.

7. The electrolyte according to claim 3, characterized in that, The preferred concentration of the electrolyte additive in the electrolyte is 0.1 mol / L.

8. A method for preparing any one of the electrolytes as described in claims 2 to 7, the method comprising the following steps: Under a protective atmosphere, lithium salts are mixed and dissolved in an organic solvent, then electrolyte additives are added, and the mixture is magnetically stirred until homogeneous to obtain the electrolyte.

9. A lithium-thionyl chloride secondary battery, characterized in that, The lithium-thionyl chloride secondary battery includes a positive electrode, an electrolyte, a separator, and a negative electrode, wherein the electrolyte contains the electrolyte additive as described in claim 1.

10. The secondary battery according to claim 9, characterized in that, The positive electrode contains porous carbon material; the negative electrode is lithium metal.

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