Local high-concentration electrolyte, preparation method thereof and lithium-thionyl chloride secondary battery

Abstract

The invention provides a local high-concentration electrolyte which is composed of a lithium salt, a high-corrosion thionyl chloride solvent and an ester diluent according to a specific proportion, and a similar high-concentration characteristic solution environment is formed by regulating and controlling a local solvation structure of lithium ions. On the basis of ensuring high mobility of lithium ions, chemical corrosion of a high-corrosion thionyl chloride solvent to the lithium metal negative electrode is effectively inhibited, an interface is induced to form a compact and stable SEI film, the reversibility of the lithium metal negative electrode is improved, and the cycle life of the lithium metal negative electrode is prolonged. The lithium-thionyl chloride secondary battery electrolyte system provided by the invention has chemical stability, conductivity and process compatibility, and is suitable for development and application of rechargeable chlorine batteries with high energy density and wide temperature range.

Description

Technical Field

[0001] This invention relates to the field of secondary battery materials and electrolytes, and particularly to a locally high-concentration electrolyte, its preparation method, and a lithium-thionyl chloride secondary battery. Background Technology

[0002] With the increasing demand for high-energy-density energy storage systems in portable devices, electric vehicles, and specialized fields such as military and aerospace, lithium metal batteries are widely considered to have significant development potential in next-generation energy storage technologies due to their ultra-high theoretical specific capacity and low electrode potential. As an important system within this category, lithium-chlorine / chloride batteries offer advantages such as high theoretical energy density, high output voltage, abundant resources, and good stability, making them particularly suitable for long-life and wide-temperature-range applications, and have received increasing attention in recent years.

[0003] However, lithium-thionyl chloride battery systems primarily rely on highly corrosive thionyl chloride electrolytes (such as thionyl chloride, aluminum chloride / chlorine mixtures). These electrolytes are prone to strong side reactions when in contact with the lithium metal anode, generating large amounts of irreversible products (such as lithium chloride, lithium sulfite, etc.), leading to problems such as electrode / electrolyte interface instability, lithium dendrite growth, and rapid capacity decay. Therefore, current rechargeable lithium-chlorine batteries still suffer from severe bottlenecks in interface stability and cycle life. Furthermore, these highly corrosive thionyl chloride electrolyte systems have high viscosity and poor low-temperature conductivity, preventing effective discharge at -20°C or even lower temperatures, thus limiting their application in extreme environments.

[0004] In recent years, to alleviate the corrosiveness of highly corrosive thionyl chloride electrolytes and improve their low-temperature performance, researchers have proposed a design strategy of "locally high-concentration electrolytes." This strategy introduces non-coordinating diluents (such as dichloroethane and fluorinated ethers) into the high-concentration lithium salt and main solvent system. Without disrupting the original solvation structure, this strategy modulates the electrolyte's microstructure, thereby reducing the overall viscosity, expanding the electrochemical stability window, and improving lithium-ion migration efficiency. The use of fluorinated diluents such as dichloroethane effectively regulates solvent polarity and intermolecular interactions, giving the system superior low-temperature fluidity and strong interfacial film-forming ability.

[0005] Although locally high-concentration electrolytes have alleviated the severe side reactions between lithium metal and highly corrosive thionyl chloride electrolytes to some extent and exhibited superior thermal stability and film-forming properties compared to traditional electrolytes, several limitations remain. First, most current locally high-concentration electrolyte systems struggle to maintain sufficiently high ionic conductivity below -40°C, severely restricting their practicality in extremely cold environments. Second, some non-coordinating diluents exhibit poor microscopic compatibility with chlorine-based solvents, easily leading to phase separation or solvation structural instability, thus affecting the interfacial stability of the electrolyte over long-term use. Furthermore, most current research focuses on lithium metal anodes or graphite-based materials, with limited research on the compatibility of silicon-based high-capacity anodes in chlorine systems, lacking a systematic design and process implementation path that can be practically applied to high-energy-density lithium-chlorine secondary batteries.

[0006] Therefore, there is an urgent need to develop a lithium-chlorine battery electrolyte system that combines low-temperature operability, high interfacial stability, and strong resistance to side reactions, in order to solve the bottleneck problems of existing chlorine batteries in terms of low-temperature start-up, cycle stability, and safety, thereby promoting their practical application in extreme environment energy storage scenarios. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a locally high-concentration electrolyte, its preparation method, and a lithium-thionyl chloride secondary battery. The electrolyte provided by this invention is composed of lithium salt, highly corrosive thionyl chloride solvent, and ester diluent in a specific ratio. By regulating the local solvation structure of lithium ions, a near-high-concentration characteristic solution environment is formed. While ensuring high lithium ion mobility, it effectively inhibits the chemical corrosion of the lithium metal anode by the highly corrosive thionyl chloride solvent and induces the formation of a dense and stable SEI film at the interface, thereby improving the reversibility and cycle life of the lithium metal anode.

[0008] The primary objective of this invention is to provide a locally high-concentration electrolyte, which comprises aluminum salt, lithium salt, thionyl chloride, and ester diluent.

[0009] Specifically, the aluminum salt is aluminum chloride.

[0010] Specifically, the lithium salt is one or more of lithium difluorosulfonate imine, lithium bis(trifluoromethanesulfonyl)imine, lithium trifluoromethanesulfonate, lithium difluorooxalate borate, and lithium tetrafluoroborate.

[0011] Specifically, the ester diluent is one or more of ethyl acetate, methyl acetate, propyl acetate, butyl acetate, triethyl phosphate, trimethyl phosphate, and propylene carbonate.

[0012] Specifically, the total molar concentration of aluminum salts in the locally high-concentration electrolyte is 2~6 mol / L.

[0013] Specifically, the total molar concentration of lithium salt in the locally high-concentration electrolyte is 0.1 mol / L.

[0014] Specifically, the volume ratio of thionyl chloride to ester diluent in the locally high-concentration electrolyte is (9~1):1.

[0015] The second objective of this invention is to provide a method for preparing a locally high-concentration electrolyte, which includes the following steps: under a protective atmosphere, aluminum salt and lithium salt are mixed and dissolved in thionyl chloride, then an ester diluent is added, and the mixture is magnetically stirred until homogeneous to obtain a locally high-concentration electrolyte.

[0016] The third 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 is the locally high-concentration lithium chloride battery electrolyte described above.

[0017] Specifically, the positive electrode comprises a porous carbon material; the negative electrode is lithium metal.

[0018] Compared with the prior art, the beneficial effects of the present invention include: (1) This invention provides a locally high-concentration electrolyte for lithium-thionyl chloride secondary batteries. The electrolyte is composed of four core components in a specific ratio: lithium salt, aluminum salt, thionyl chloride active solvent, and ester non-coordination diluent. The high-concentration aluminum chloride and lithium salt compete for coordination in thionyl chloride, jointly constructing a high-strength local solvation sheath layer rich in complex anions surrounding lithium ions. The locally high-concentration lithium ion solvation structure is maintained by lithium salt and aluminum chloride, ensuring efficient coordination and migration channels for lithium ions. The ester diluent acts as an inert medium, penetrating into the sheath layer without disintegrating it, thereby reducing the solution viscosity macroscopically and maintaining a "quasi-high concentration" environment microscopically. This forms a synergistic effect of "low viscosity and high local concentration", enabling the electrolyte to maintain high ionic conductivity in a wide temperature range of -60 to 25 °C, solving the problem of slow lithium ion migration and electrochemical lag in traditional chlorine-based electrolytes at low temperatures, and improving low-temperature start-up capability. (2) The diluent used in this invention has good compatibility with chlorine-based active solvents. By introducing a non-coordinating diluent to construct a locally high-concentration lithium-chlorine electrolyte system, the chemical corrosion of the lithium anode by highly corrosive thionyl chloride is significantly reduced, the generation of irreversible byproducts is reduced, and the chemical stability between the electrolyte and the anode is effectively improved. The viscosity of the electrolyte decreases and the flash point increases, reducing the risk of flammability. At the same time, the diluent regulates the Lewis acidity and alkalinity to inhibit the generation of highly reactive intermediates, thereby improving the thermal stability and operational safety of the battery from the source. (3) When the locally high-concentration electrolyte provided by this invention is applied to lithium-thionyl chloride secondary batteries, the locally high-concentration system can induce a stable lithium-ion solvation structure, which, together with the surface passivation layer, forms a dense and uniform negative electrode passivation film, inhibiting lithium dendrite growth and achieving high coulombic efficiency and excellent cycle stability. It significantly inhibits the chemical corrosion of the lithium metal negative electrode by thionyl chloride from the source and induces the formation of a dense and stable solid electrolyte interphase (SEI) film, greatly improving the reversibility and cycle life of the negative electrode. In addition, the electrolyte prepared by this invention can also be applied to different lithium-chlorine battery systems (such as lithium / thionyl chloride, lithium / chlorine, lithium tetrachloroaluminate, etc.), further endowing different lithium-chlorine battery systems with excellent wide-temperature performance, high safety, and practical engineering potential and operational safety. 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 The electrolytes prepared in Example 1 and Comparative Example 1 of this invention are respectively 23 Comparison of Al NMR test results; Figure 2 The electrolytes prepared in Example 1 and Comparative Example 1 of this invention are respectively 7 Comparison of Li NMR test results; Figure 3 The graph shows a comparison of the specific capacity and coulombic efficiency of the secondary batteries prepared in Example 1 and Comparative Example 1 of this invention. Figure 4 These are Tafel comparison images of the secondary batteries prepared in Example 1 and Comparative Example 1 of the present invention, respectively; Figure 5 This is a comparison of the charge-discharge specific capacity test curves of the secondary batteries prepared in Example 1 and Comparative Example 1 of this invention at the 100th and 70th cycles, respectively. 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 less than 0.01 ppm, 4 mmol of aluminum chloride and 0.1 mmol of lithium difluorosulfonate were dissolved in a mixed solution of 1 mL of thionyl chloride and ethyl acetate (the volume ratio of thionyl chloride to ethyl acetate was 3:1). The prepared electrolyte was placed on a magnetic stirrer at room temperature and stirred for 1 h to obtain the locally high-concentration electrolyte prepared in Example 1, which is denoted as the 25% ethyl acetate system electrolyte.

[0023] 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, polypropylene separator, and lithium metal sheet were assembled into a button cell in sequence, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 1.

[0024] Example 2 Preparation of electrolyte: In an argon-filled glove box with water and oxygen content below 0.01 ppm, 2 mmol of aluminum chloride and 0.1 mmol of lithium bis(trifluoromethanesulfonyl)imide were dissolved in a mixed solution of 1 mL of thionyl chloride and methyl acetate (the volume ratio of thionyl chloride to methyl acetate was 6:1). The prepared electrolyte was stirred on a magnetic stirrer at room temperature for 1 h to obtain the locally high-concentration electrolyte prepared in Example 2.

[0025] 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 ℃ to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, polypropylene separator, and lithium metal sheet were assembled into a button cell in sequence, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 2.

[0026] Example 3 Preparation of electrolyte: In an argon-filled glove box with water and oxygen content below 0.01 ppm, 3 mmol of aluminum chloride and 0.1 mmol of lithium trifluoromethanesulfonate were dissolved in a mixed solution of 1 mL of thionyl chloride and propyl acetate (the volume ratio of thionyl chloride to propyl acetate was 7:1). The prepared electrolyte was placed on a magnetic stirrer and stirred for 1 h at room temperature to obtain the locally high-concentration electrolyte prepared in Example 3.

[0027] 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 ℃ to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, polypropylene separator, and lithium metal sheet were assembled into a button cell in sequence, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 3.

[0028] Example 4 Preparation of electrolyte: In an argon-filled glove box with water and oxygen content below 0.01 ppm, 5 mmol of aluminum chloride and 0.1 mmol of lithium difluorooxalate borate were dissolved in a mixed solution of 1 mL of thionyl chloride and butyl acetate (the volume ratio of thionyl chloride to butyl acetate was 9:1). The prepared electrolyte was stirred on a magnetic stirrer at room temperature for 1 h to obtain the locally high-concentration electrolyte prepared in Example 4.

[0029] 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, polypropylene separator, and lithium metal sheet were assembled into a button cell in sequence, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 4.

[0030] Example 5 Preparation of electrolyte: In an argon-filled glove box with water and oxygen content below 0.01 ppm, 6 mmol of aluminum chloride and 0.1 mmol of lithium tetrafluoroborate were dissolved in a mixed solution of 1 mL of thionyl chloride and triethyl phosphate (the volume ratio of thionyl chloride to triethyl phosphate was 3:1). The prepared electrolyte was placed on a magnetic stirrer and stirred for 1 h at room temperature to obtain the locally high-concentration electrolyte prepared in Example 5.

[0031] 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 ℃ to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, polypropylene separator, and lithium metal sheet were assembled into a button cell in sequence, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 5.

[0032] Example 6 Preparation of electrolyte: In an argon-filled glove box with water and oxygen content below 0.01 ppm, 3 mmol of aluminum chloride and 0.1 mmol of lithium difluorosulfonate were dissolved in a mixed solution of 1 mL of thionyl chloride and propylene carbonate (the volume ratio of thionyl chloride to propylene carbonate was 7:1). The prepared electrolyte was stirred on a magnetic stirrer at room temperature for 1 h to obtain the locally high-concentration electrolyte prepared in Example 6.

[0033] 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, polypropylene separator, and lithium metal sheet were assembled into a button cell in sequence, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Example 6.

[0034] Comparative Example 1 The difference from Example 1 is that no ester additives are added.

[0035] Preparation of electrolyte: In an argon-filled glove box with water and oxygen content below 0.01 ppm, 4 mmol aluminum chloride and 0.1 mmol lithium difluorosulfonate were dissolved in 1 mL thionyl chloride. The prepared electrolyte was placed on a magnetic stirrer at room temperature and stirred for 1 h to obtain the electrolyte prepared in Comparative Example 1, denoted as the 4 M aluminum chloride system electrolyte.

[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 ℃ to obtain a CMK-3 positive electrode sheet. The CMK-3 positive electrode sheet, polypropylene separator, and lithium metal sheet were assembled into a button cell in sequence, and an appropriate amount of the electrolyte prepared above was added to obtain the lithium-thionyl chloride secondary battery prepared in Comparative Example 1.

[0037] Performance testing The lithium-thionyl chloride secondary batteries prepared in Examples 1-6 were placed in a constant temperature environment of -40 °C for 1 hour and then subjected to cycle testing using a Blue Electric charge-discharge tester. Constant current charge-discharge tests were conducted at 1C within a voltage range of 2 to 5 V.

[0038] Figure 1 The electrolytes prepared in Example 1 and Comparative Example 1 of this invention are respectively 23 Comparison of Al NMR test results; from Figure 1 It can be seen that, 23The Al NMR spectrum provides direct evidence for changes in the solvated structure. In the electrolyte with 25% ethyl acetate, the chemical shift of the Al signal was 93.95 ppm, while it was 97.14 ppm in the 4M aluminum chloride system. The shift towards the higher field (93.95 ppm) indicates that the addition of the ester diluent altered the aggregated state or coordination structure of aluminum chloride. This promoted the formation of more uniform and stable ion pairs or complexes, and reduced the local aggregation of strongly Lewis acidic Al species, which is beneficial for forming a more uniform interfacial passivation layer and improving the chemical stability of the electrolyte. Figure 2 The electrolytes prepared in Example 1 and Comparative Example 1 of this invention are respectively 7 Comparison of Li NMR test results; from Figure 2 It can be seen that, 7 Li NMR results further corroborate the formation of locally solvated structures. In the 25% ethyl acetate electrolyte system provided in Example 1 of this invention, Li + The chemical shift was -1.65 ppm, compared to -1.71 ppm in the 4M aluminum chloride electrolyte system provided in Comparative Example 1 of this invention, indicating a shift towards a higher field. This change suggests that the introduction of ester diluents subtly modulates the structure of the primary solvation sheath of lithium ions, possibly reducing the tight interaction between lithium ions and strongly coordinating anions, and forming a solvation structure that is more conducive to the rapid desolvation and migration of lithium ions.

[0039] Figure 3 The graph shows a comparison of the specific capacity and coulombic efficiency of the secondary batteries prepared in Example 1 and Comparative Example 1 of this invention. Figure 3 Two electrolyte systems were demonstrated at -60 °C and 0.1 A g. -1 Comparison of long-term cycling performance under specific conditions. The battery prepared based on the electrolyte system with 25% ethyl acetate provided in Example 1 of this invention exhibits significantly higher initial specific capacity and excellent capacity retention. More importantly, its coulombic efficiency rapidly increases during cycling and stabilizes at a high level close to 100%, indicating that the deposition / dissolution process of the lithium anode is highly reversible and side reactions are effectively suppressed. In contrast, the system without the addition of 25% ethyl acetate has lower capacity and faster decay, with larger fluctuations in coulombic efficiency. This result directly confirms that the locally high-concentration solvation structure constructed with ethyl acetate can significantly improve the battery's capacity performance and cycling stability at extreme low temperatures. Figure 4 These are Tafel comparison images of the secondary batteries prepared in Example 1 and Comparative Example 1 of the present invention, respectively; Figure 4 The battery prepared using the 25% ethyl acetate electrolyte system provided in Example 1 of this invention has an exchange current density of approximately 5.08 mA cm⁻¹. -2 The concentration is significantly higher than that of the 4 M aluminum chloride system (approximately 0.06 mA cm⁻¹). -2The significant increase in exchange current density indicates that the ester diluent, while effectively reducing the overall viscosity of the electrolyte, synergistically forms a locally high-concentration solvation structure with lithium salt and aluminum chloride. This significantly optimizes the transport and charge transfer kinetics of lithium ions at the electrode / electrolyte interface, greatly reducing electrochemical polarization. This reveals the core reason for the system's efficient low-temperature charge-discharge capability from a kinetic perspective. Figure 5 This is a comparison of the charge-discharge specific capacity test curves of the secondary batteries prepared in Example 1 and Comparative Example 1 of this invention at the 100th and 70th cycles, respectively. Figure 5 The two batteries were compared at -40 °C and 1 A g. -1 Under these conditions, typical charge-discharge curves after long cycling are shown. Even after 100 cycles, the battery prepared with the 25% ethyl acetate electrolyte system provided in Example 1 of this invention maintains a clear voltage plateau and small voltage polarization in its charge-discharge curve, indicating good electrode reaction reversibility and structural stability. In contrast, the battery prepared with the 4 M aluminum chloride system in Comparative Example 1 of this invention shows a significant increase in polarization and a shortened voltage plateau in its charge-discharge curve by cycle 70. This result directly demonstrates that electrolyte systems regulated by ester diluents can more effectively maintain the stability and reversibility of electrode reactions under wide temperature range and high-rate long cycling conditions.

[0040] In summary, the present invention provides a locally high-concentration electrolyte composed of four core components—lithium salt, aluminum salt, thionyl chloride active solvent, and ester-based non-coordinating diluent—in a specific ratio. Aluminum chloride and lithium salt synergistically compete for coordination in thionyl chloride, and the ester-based diluent acts as an inert medium, reducing the solution viscosity macroscopically and maintaining a "quasi-high concentration" environment microscopically. This creates a synergistic effect of "low viscosity and high local concentration," enabling the electrolyte to maintain high ionic conductivity over a wide temperature range of -60 to 25 °C. This solves the problem of slow lithium-ion migration and electrochemical lag in traditional chlorine-based electrolytes at low temperatures, improves low-temperature start-up capability, and endows the chlorine battery system with excellent wide-temperature performance and high safety.

[0041] 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. A locally high-concentration electrolyte, characterized in that, The electrolyte includes aluminum salts, lithium salts, thionyl chloride, and ester diluents.

2. The electrolyte according to claim 1, characterized in that, The aluminum salt is aluminum chloride.

3. The electrolyte according to claim 1, characterized in that, The lithium salt is one or a combination of lithium difluorosulfonate imine, lithium bis(trifluoromethanesulfonyl)imine, lithium trifluoromethanesulfonate, lithium difluorooxalate borate, and lithium tetrafluoroborate.

4. The electrolyte according to claim 1, characterized in that, The ester diluent is one or a combination of ethyl acetate, methyl acetate, propyl acetate, butyl acetate, triethyl phosphate, trimethyl phosphate, and propylene carbonate.

5. The electrolyte according to claim 1, characterized in that, The total molar concentration of aluminum salts in the locally high-concentration electrolyte is 2~6 mol / L.

6. The electrolyte according to claim 1, characterized in that, The total molar concentration of lithium salt in the locally high-concentration electrolyte is 0.1 mol / L.

7. The electrolyte according to claim 1, characterized in that, The volume ratio of thionyl chloride to ester diluent in the locally high-concentration electrolyte is (9~1):

1.

8. A method for preparing a locally high-concentration electrolyte, characterized in that, The preparation method includes the following steps: under a protective atmosphere, aluminum salt and lithium salt are mixed and dissolved in thionyl chloride, then an ester diluent is added, and the mixture is magnetically stirred until homogeneous to obtain a locally high-concentration 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 is the locally high-concentration lithium chloride battery electrolyte as described in any one of claims 1-8.

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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