Local eutectic electrolyte, preparation method thereof and electrochemical device

Abstract

The invention relates to a local eutectic electrolyte, a preparation method thereof and an electrochemical device, and the local eutectic electrolyte comprises a eutectic solvent and a diluent, the eutectic solvent comprises a metal salt and an organic solvent. The invention also comprises a preparation method of the local eutectic electrolyte. The electrochemical device at least comprises a cathode, an anode, a diaphragm and a local eutectic electrolyte. The local eutectic electrolyte is formed by blending the metal salt, the organic solvent and the diluent in specific types and proportions. The electrolyte has the characteristics of low viscosity, wide electrochemical stability window, low flammability or non-flammability, high lithium ion transfer number, good ionic conductivity, wide temperature range and the like. Therefore, the material can be well and practically applied to electrochemical devices, especially supercapacitors, batteries and sensors.

Description

Technical Field

[0001] The present invention relates to the field of lithium batteries, and in particular to a local eutectic electrolyte, a preparation method thereof, and an electrochemical device. Background Art

[0002] Liquid electrolytes are widely used in most electrochemical devices, such as supercapacitors, batteries, and sensors. Electrolytes should have the characteristics of wide operating temperature window, high ionic conductivity, low viscosity, wide electrochemical stability window, non-flammability, and low cost. However, conventional liquid electrolytes cannot meet all of the above requirements. For example: 1) Commercial lithium-ion battery electrolytes are highly flammable; 2) Ionic liquid electrolytes have high viscosity and poor lithium ion transfer numbers; 3) High-concentration electrolytes may have poor low-temperature performance due to salt precipitation. Therefore, the search for new electrolytes suitable for electrochemical devices should continue.

[0003] CN113707938A discloses an electrolyte based on a ternary low eutectic solvent, which has low viscosity and high conductivity, has the effect of inhibiting dendrites under the action of additives, and has good cycle performance. However, it requires the action of additives.

[0004] CN118676431A discloses an electrolyte based on a low eutectic solvent that can be used in electrochemical devices. The preparation method based on molecular plastic crystal can obtain good conductivity at low temperature, but the electrolyte still has the characteristics of high viscosity and poor conductivity.

[0005] CN118281286A discloses a partially diluted high-concentration electrolyte and a preparation method thereof, which comprises a non-aqueous organic solvent, a lithium salt and a diluent. The solvent component used is highly safe and can significantly increase the life of the lithium metal battery. However, the safety of the electrolyte component used is still not enough.

[0006] CN116525943A discloses a double halide ion liquid electrolyte, which has high room temperature ion conductivity and lithium ion transfer number, and can reduce the viscosity of the system and improve the wetting performance on the one hand, and reduce the freezing point of the electrolyte as a whole on the other hand, which can provide a certain low temperature working ability. However, in some occasions, the viscosity, lithium ion transfer number and ion conductivity of the electrolyte do not meet the requirements.

[0007] Moreover, the currently disclosed electrolyte systems mostly use highly volatile substances such as ethers, ketones, and lipids as solvents, which have poor safety, low decomposition pressure, and serious dendrite problems. Additives are often used to suppress the dendrite problem. Summary of the invention

[0008] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a local eutectic electrolyte with lower viscosity, higher lithium ion transfer number and better ion conductivity.

[0009] The second technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for preparing a local eutectic electrolyte with low viscosity, high lithium ion transfer number and good ion conductivity.

[0010] The third technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide an electrochemical device.

[0011] The technical solution adopted by the present invention to solve the technical problem is a local eutectic electrolyte, which includes: a eutectic solvent (DES) and a diluent.

[0012] The low eutectic solvent comprises: a metal salt and an organic solvent.

[0013] The deep eutectic solvent is represented by Formula I:

[0014] Cat + X - Y z (Ⅰ)

[0015] In formula Ⅰ, Cat + is the cation of the metal salt; X - is the anion of the metal salt; Y is a solid organic solvent at ≤30°C; Z is the molar ratio of the organic solvent to the metal salt, ranging from 0 to 10.0 (preferably 0.5 to 5), to ensure that the lithium salt is fully dissolved.

[0016] The deep eutectic solvent is in liquid state at a temperature > 20° C. The Lewis acid of the metal salt and the Lewis base of the organic solvent interact with each other through coordination.

[0017] Further, Cat + At least one of the following: lithium (Li + ), sodium (Na + ), potassium (K + ), magnesium (Mg 2+ ), calcium (Ca 2+ ), aluminum (Al 3+ )、Zn 2+ ).

[0018] Furthermore, the anion X - At least one of the following: bis(trifluoromethylsulfonyl) (TFSI - ), bis(fluorosulfonyl imide) - ), hexafluorophosphate (PF6 - ), hexafluoroborate (BF4- ), bis(oxalatoborate) (BOB - ), difluorooxalate borate (DFOB - ), fluorosulfonyl-trifluoromethanesulfonyl imide (FTFSI - ), bis(pentafluoroethanesulfonyl)imide (BETI - ), perchlorate (ClO4 - ), potassium trifluorosulfonate (OTF - ), nitrate (NO3 - ), carbonate (CO3 2- ), sulfate (SO4 2- ), chloride ion (Cl - ).

[0019] Furthermore, the metal salt is a lithium salt, more preferably at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium nitrate, lithium perchlorate, lithium chloride, lithium bis(trifluoromethanesulfonyl imide) and lithium bis(fluorosulfonyl imide).

[0020] Further, the organic solvent Y is at least one of sulfide, sulfoxide, sulfone, sulfonamide, nitrile, dinitrile, carbonate, and acetamide. Preferably, the organic solvent is at least one of N,N-dimethylmethanesulfonamide, dimethyl sulfone, ethyl methyl sulfone, cyclopentane, malononitrile, and succinonitrile.

[0021] An organic solvent Y, wherein the sulfide is represented by formula II; the sulfoxide is represented by formula III; the sulfone is represented by formula IV; the sulfonamide is represented by formula V; the butyronitrile is represented by formula VI; the carbonate is represented by formula VII; and the acetamide is represented by formula VIII.

[0022]

[0023] Further, the local eutectic electrolyte is a local eutectic solvent, represented by Formula IX:

[0024] AB m (IX)

[0025] Wherein, A is a low eutectic solvent; B is a diluent; and m is a molar ratio of the diluent to the metal salt in the low eutectic solvent, and the value range is 0 to 10.0 (preferably 0.5 to 5).

[0026] Further, the diluent B is at least one of ether, carbonate, acetamide, nitrile, phosphate, sulfide, sulfoxide, sulfite, sulfone, and sulfate. Preferably, the diluent is at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,2-trifluoroethyl trifluoromethanesulfonate, and 2,2,2-trifluoroethyl trifluoromethanesulfonate.

[0027] Furthermore, the metal salt (Cat + X- The solubility of the metal salt in the diluent (B) should be at least 10 times smaller than the solubility of the metal salt in the organic solvent (Y). This allows the deep eutectic solvent to maintain the solvation structure of the deep eutectic solvent after the diluent is added.

[0028] diluent, wherein the ether is represented by formula X; the carbonate is represented by formula XI; the acetamide is represented by formula XII; the nitrile is represented by formula XIII; the phosphate is represented by formula XIV; the sulfide is represented by formula XV; the sulfoxide or sulfite is represented by formula XVI; and the sulfone or sulfate is represented by formula XVII.

[0029]

[0030] A method for preparing a local eutectic electrolyte comprises the following steps:

[0031] S1. Mixing a metal salt and an organic solvent in a certain molar ratio, stirring at an appropriate temperature until a clear and transparent electrolyte is obtained to obtain a mixture;

[0032] S2. Mix the mixture obtained in step S1 with a diluent in a certain molar ratio, and stir at an appropriate temperature to obtain a clear and transparent electrolyte, which is a local eutectic electrolyte.

[0033] Preferably, in steps S1 and S2, the stirring temperature is controlled at 30-40°C.

[0034] Preferably, each of the above steps needs to be carried out under an argon environment, and the water content and oxygen content are below 0.2 ppm.

[0035] An electrochemical device comprises the local eutectic electrolyte of the present invention.

[0036] An electrochemical device comprises at least a cathode, an anode, a diaphragm and a local eutectic electrolyte.

[0037] The present invention provides a novel electrolyte, which comprises a non-protonic "deep eutectic solvent (DES)" and a diluent. This electrolyte is called a "local deep eutectic solvent (LDES)". The local deep eutectic solvent (LDES) is used as an electrolyte for electrochemical devices. Through Lewis acid-base interaction, a metal salt (Lewis acid) and an organic solvent (Lewis base) are mixed to prepare a non-protonic DES. The solvent used in the present invention is usually a non-protonic solvent, such as sulfones, amides, and carbonates. This is because the functional groups therein can better interact with metal salts, especially lithium salts, through Lewis acid-base coordination to achieve good compatibility, and at the same time, its volatility and flammability are poor, so this DES is safer. In order to solve the shortcomings of high viscosity and poor wettability of non-protonic DES, a diluent is added to form LDES. The diluent has poor solvation ability for metal salts, so the microscopic solvation structure of non-protonic DES can still be maintained in LDES. Therefore, LDES has both the advantages of DES and overcomes the disadvantages of DES, and is suitable as an advanced electrolyte for electrochemical devices.

[0038] The electrochemical device of the present invention includes an anode, a cathode, a separator and a local eutectic electrolyte, and may further have a current collector for each anode and cathode. Exemplary electrochemical devices include, but are not limited to, primary batteries, rechargeable batteries, double-layer capacitors, supercapacitors, and sensors. In some embodiments, exemplary rechargeable batteries include, but are not limited to: lithium ion batteries, lithium metal batteries, lithium oxygen batteries, lithium air batteries, lithium sulfur batteries, lithium selenium batteries; sodium ion batteries, sodium oxygen batteries, sodium sulfur batteries; potassium ion batteries, potassium oxygen batteries; magnesium ion batteries; aluminum ion batteries, etc.

[0039] The present invention blends metal salts of specific types and proportions with organic solvents and diluents to form a local eutectic electrolyte. The electrolyte has the characteristics of low viscosity, wide electrochemical stability window, low or non-flammable, high lithium ion transfer number, good ion conductivity, wide temperature range, etc. It can be better used in electrochemical devices, especially supercapacitors, batteries and sensors.

[0040] The present invention blends metal salts of specific types and proportions with organic solvents and diluents, which not only further improves the safety, but also forms a unique solvation structure, thereby effectively inhibiting the dendrite problem and providing the possibility for its commercialization.

[0041] The electrolyte of the present invention has the effect of inhibiting dendrites without the need for additives, has better electrochemical stability, has a higher decomposition voltage, and has more advantages in the application field of high-voltage electrolytes. At the same time, the electrolyte of the present invention can achieve a relatively high coulombic efficiency.

[0042] The electrolyte of the present invention does not include a proton solvent, which avoids hydrogen evolution at a low potential under the anode, thereby providing it with a wider electrochemical stability window. Compared with high-concentration electrolytes or locally high-concentration electrolytes, the electrolyte of the present invention has a wider temperature range and can operate at a lower temperature. Compared with ionic liquid electrolytes, the present invention has low viscosity, a high lithium ion transfer number and good ionic conductivity. Compared with commercial lithium ion electrode electrolytes, the electrolyte of the present invention exhibits lower flammability and more uniform lithium deposition. The electrolyte of the present invention is safer, has lower cost, and is suitable for industrial production and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The test results of the electrolyte ion conductivity of Examples 1-6;

[0044] Figure 2 The test results of the coulombic efficiency of the electrolytes of Examples 1-6;

[0045] Figure 3 The coulombic efficiency curve of the lithium copper battery assembled by the electrolyte of Example 3;

[0046] Figure 4 The linear sweep voltammetry curves of Examples 1-6 are shown in FIG. Specific implementation methods

[0048] The present invention is further described in detail below in conjunction with specific embodiments.

[0049] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0050] Example 1

[0051] The method for preparing the local eutectic electrolyte of this embodiment specifically includes the following steps:

[0052] S1. Heat the solvent N,N-dimethylmethanesulfonamide (DMMSA) to melt it, take 15 mmol DMMSA (1.8476 g), weigh 5 mmol (0.9354 g) lithium bis(fluorosulfonyl)imide (LiFSI), mix the two, and stir at 30° C. for 3 hours until a clear solution is formed to obtain a mixture (LiFSI / 3DMMSA);

[0053] S2. Take 0.5566 g (1 mmol LiFSI / 3DMMSA) of the mixture obtained in step S1 (the amount of substance is calculated based on the content of lithium salt) and mix it with 4 mmol (0.9283 g) of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and stir at 30° C. for 3 hours until a uniform solution is formed to obtain a clear and transparent electrolyte, which is a local low eutectic electrolyte (1 mmol LiFSI / 3DMMSA / 4TTE).

[0054] All the above steps need to be carried out in an argon environment, and the water content and oxygen content need to be below 0.2 ppm.

[0055] Example 2

[0056] The method for preparing the local eutectic electrolyte of this embodiment specifically includes the following steps:

[0057] S1. Heat the solvent ethyl methanesulfonate (EMS) to melt it, take 15 mmol EMS (1.6224 g), weigh 5 mmol (0.9354 g) lithium bis(fluorosulfonyl)imide (LiFSI), mix the two and stir at 30° C. for 2 hours until a clear solution is formed to obtain a mixture (LiFSI / 3EMS);

[0058] S2. Take 0.5476 g (1 mmol LiFSI / 3EMS) of the mixture obtained in step S1 (the amount of substance is calculated based on the content of lithium salt) and mix it with 4 mmol (0.9283 g) of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and stir it at 30° C. for 2 hours until a uniform solution is formed to obtain a clear and transparent electrolyte, which is a local low eutectic electrolyte (1 mmol LiFSI / 3EMS / 4TTE).

[0059] All the above steps need to be carried out in an argon environment, and the water content and oxygen content need to be below 0.2 ppm.

[0060] Example 3

[0061] The method for preparing the local eutectic electrolyte of this embodiment specifically includes the following steps:

[0062] S1. Heat the solvent cyclopentane sulfone (TMS) to melt it, take 15 mmol TMS (1.8624 g) into a vial, weigh 5 mmol (0.9354 g) lithium bis(fluorosulfonyl)imide (LiFSI), mix the two and stir at 30° C. for 2 hours until a clear solution is formed to obtain a mixture (LiFSI / 3TMS);

[0063] S2. Take 0.5596 g (1 mmol LiFSI / 3TMS) of the mixture obtained in step S1 (the amount of substance is calculated based on the content of lithium salt) and mix it with 4 mmol (0.9283 g) of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and stir it at 30° C. for 2 hours until a uniform solution is formed to obtain a clear and transparent electrolyte, which is a local low eutectic electrolyte (1 mmol LiFSI / 3TMS / 4TTE).

[0064] All the above steps need to be carried out in an argon environment, and the water content and oxygen content need to be below 0.2 ppm.

[0065] Example 4

[0066] The method for preparing the local eutectic electrolyte of this embodiment specifically includes the following steps:

[0067] S1. Heat the solvent sulfolane (TMS) to melt it, take 15 mmol TMS (1.8025 g), weigh 5 mmol (0.4687 g) lithium tetrafluoroborate (LiBF4), mix the two and stir at 30°C for 2 hours until a clear solution is formed to obtain a mixture (LiBF4 / 3TMS);

[0068] S2. Take 0.4662 g (1 mmol LiBF4 / 3TMS) of the mixture obtained in step S1 (the amount of substance is calculated based on the content of lithium salt) and mix it with 4 mmol (0.9283 g) of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and stir it at 30°C for 2 hours until a uniform solution is formed to obtain a clear and transparent electrolyte, which is a local low eutectic electrolyte (1 mmol LiBF4 / 3TMS / 4TTE).

[0069] All the above steps need to be carried out in an argon environment, and the water content and oxygen content need to be below 0.2 ppm.

[0070] Example 5

[0071] The method for preparing the local eutectic electrolyte of this embodiment specifically includes the following steps:

[0072] S1. Heat the solvent N,N-dimethylmethanesulfonamide (DMMSA) to melt it, take 15 mmol DMMSA (1.8476 g) into a vial, weigh 5 mmol (0.9354 g) lithium bis(fluorosulfonyl)imide (LiFSI), mix the two and stir at 30°C for 2 hours until a clear solution is formed to obtain a mixture (LiFSI / 3TMS);

[0073] S2. Take 0.5566 g (1 mmol LiFSI / 3TMS) of the mixture obtained in step S1 (the amount of substance is calculated based on the content of lithium salt) and mix it with 4 mmol (0.9284 g) of 2,2,2-trifluoroethyl trifluoromethanesulfonate (TTS), and stir at 30° C. for 2 hours until a uniform solution is formed to obtain a clear and transparent electrolyte, which is a local low eutectic electrolyte (1 mmol LiFSI / 3DMMSA / 4TTS).

[0074] All the above steps need to be carried out in an argon environment, and the water content and oxygen content need to be below 0.2 ppm.

[0075] Example 6

[0076] The method for preparing the local eutectic electrolyte of this embodiment specifically includes the following steps:

[0077] S1. Heat the solvent N,N-dimethylmethanesulfonamide (DMMSA) to melt it, take 10 mmol DMMSA (1.2317 g) into a vial, weigh 15 mmol (2.8061 g) lithium bis(fluorosulfonyl)imide (LiFSI), mix the two and stir at 30° C. for 2 hours until a clear solution is formed to obtain a mixture (1.5LiFSI / DMMSA);

[0078] S2. Take 0.4038 g (1 mmol 1.5LiFSI / DMMSA) of the mixture obtained in step S1 (the amount of substance is calculated based on the content of lithium salt) and mix it with 1 mmol (0.2311 g) 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and stir at 30° C. for 2 hours until a uniform solution is formed to obtain a clear and transparent electrolyte, which is a local low eutectic electrolyte (1 mmol 1.5LiFSI / DMMSA / TTE).

[0079] All the above steps need to be carried out in an argon environment, and the water content and oxygen content need to be below 0.2 ppm.

[0080] Performance testing experiment

[0081] 1. Assemble a symmetrical steel sheet battery, use Celgard 2325 as a separator, use the electrolyte obtained in Examples 1-6 as an electrolyte, and measure the ionic conductivity of the experimental system. The test principle of ionic conductivity is as shown in Formula III:

[0082]

[0083] In the formula, L is the distance between the symmetrical steel sheets (in cm), which is the thickness of the diaphragm 2.5*10 -3 cm, A is the area of ​​the steel sheet (in cm2 ), the diameter of the steel sheet is 16.2 mm, so the area A is 2.06 cm 2 ; R b The value of the abscissa corresponding to the intersection of the impedance spectrum and the abscissa in the impedance test (unit: Ω). The calculated result is located at Figure 1 middle, Figure 1 The test results of the ionic conductivity of the electrolytes of Examples 1 to 6 are shown in Table 1. It is worth noting that the ionic conductivity measured in this way is usually ten times smaller than the actual ionic conductivity due to the influence of the diaphragm. This shows that the electrolytes obtained in our experiments have relatively excellent ionic conductivity.

[0084] 2. Assemble a lithium-copper battery, using a lithium sheet as the negative electrode, a copper sheet as the positive electrode, Celgard 2325 as the separator, and the electrolyte of Examples 1-6 as the electrolyte, and measure the coulombic efficiency of the experimental system.

[0085] The coulombic efficiency test adopts the average coulombic efficiency method. The specific method is as follows: assemble the lithium copper battery, first plate 5mAh cm on the Cu -2 of Li and stripped to 1 V for one initial cycle, plating 5 mAh cm on Cu -2 The Li is used as a lithium reservoir, with a repetitive rate of 1 mAh cm -2 Li stripping / plating, after 9 cycles, all Li is stripped to 1V, calculated as formula (IV):

[0086]

[0087] Q in the formula 循环，剥 , Q 循环，镀 , Q 剥 , Q 镀 , representing the stripping and plating capacity during the cycle, the initial cycle stripping capacity and the plating capacity respectively. The results of the coulombic efficiency determination are located at Figure 2 . Figure 2 The test results of the coulombic efficiency of the electrolytes of Examples 1-6 show that the electrolytes obtained by the present invention have a high coulombic efficiency, which means that the battery can maintain a high energy utilization rate after multiple charge and discharge cycles. Figure 3 This is a curve of the coulombic efficiency of the lithium-copper battery assembled with the electrolyte of Example 3. In the figure, the surface capacity after 9 cycles is almost the same as the surface capacity before the cycle, which indicates that the coulombic efficiency of the experimental system is high. It also indicates that the stability during the cycle is good and the dendrite problem is alleviated.

[0088] 3. Using lithium sheet as negative electrode, steel sheet as counter electrode, Celgard2325 as separator, and the electrolyte of Examples 1-6 as electrolyte, the electrochemical stability window of the electrolyte was tested at a scan rate of 1 mV / s. The results of the test are listed in Figure 4 . Figure 4 The linear sweep voltammetry curves of Examples 1 to 6 show the electrochemical oxidation window of the electrolyte. The oxidation voltage higher than 5.0 V indicates that the electrolyte of the present invention has a better development space in the field of high-voltage electrolytes.

Claims

1. A local eutectic electrolyte, characterized in that: include: Deep eutectic solvents and diluents; The deep eutectic solvent comprises: a metal salt and an organic solvent; The deep eutectic solvent is represented by Formula I: Cat + X - Y z (Ⅰ) In Formula I, Cat + is the cation of the metal salt; X - is the anion of the metal salt; Y is an organic solvent in solid form at ≤30°C; Z is the molar ratio of the organic solvent to the metal salt, ranging from 0 to 10.0; The local eutectic electrolyte is a local eutectic solvent, represented by Formula IX: AB m (Ⅸ) Wherein, A is a low eutectic solvent; B is a diluent; and m is a molar ratio of the diluent to the metal salt in the low eutectic solvent, and the value ranges from 0 to 10.

0.

2. The local eutectic electrolyte according to claim 1, characterized in that: Cat + At least one of the following: Lithium + , sodium Na + Potassium + , magnesium Mg 2+ Calcium 2+ 、Aluminum 3+ 、Zn 2+ .

3. The local eutectic electrolyte according to claim 1 or 2, characterized in that: Anion X - It is at least one of the following: bistrifluoromethylsulfonyl, bisfluorosulfonyl imide, hexafluorophosphate, hexafluoroborate, bisoxalatoborate, difluorooxalatoborate, fluorosulfonyl-trifluoromethanesulfonyl imide, bispentafluoroethanesulfonyl imide, perchlorate, trifluoropotassium sulfonate, nitrate, carbonate, sulfate, and chloride.

4. The local eutectic electrolyte according to claim 1 or 2, characterized in that: The metal salt is a lithium salt, and / or the organic solvent Y is at least one of sulfide, sulfoxide, sulfone, sulfonamide, nitrile, dinitrile, carbonate, and acetamide; and / or the diluent B is at least one of ether, carbonate, acetamide, nitrile, phosphate, sulfide, sulfoxide, sulfite, sulfone, and sulfate.

5. The local eutectic electrolyte according to claim 4, characterized in that: The lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium nitrate, lithium perchlorate, lithium chloride, lithium bis(trifluoromethanesulfonyl imide), and lithium bis(fluorosulfonyl imide); and / or the organic solvent is at least one of N,N-dimethylmethanesulfonamide, dimethyl sulfone, ethyl methyl sulfone, cyclopentane, malononitrile, and succinonitrile.

6. The local eutectic electrolyte according to claim 4, characterized in that: The diluent is at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,2-trifluoroethyl trifluoromethanesulfonate, and 2,2,2-trifluoroethyl trifluoromethanesulfonate.

7. The local eutectic electrolyte according to claim 1 or 2, characterized in that: The solubility of the metal salt in the diluent is at least 10 times less than the solubility of the metal salt in the organic solvent.

8. A method for preparing the local eutectic electrolyte according to any one of claims 1 to 7, characterized in that: The specific steps include: S1. Mixing a metal salt and an organic solvent in a certain molar ratio, stirring at an appropriate temperature until a clear and transparent electrolyte is obtained to obtain a mixture; S2. Mix the mixture obtained in step S1 with a diluent in a certain molar ratio, and stir at an appropriate temperature to obtain a clear and transparent electrolyte, which is a local eutectic electrolyte.

9. The method for preparing a local eutectic electrolyte according to claim 8, characterized in that: In steps S1 and S2, the stirring temperature is controlled at 30-40°C.

10. An electrochemical device, characterized in that: Comprising the local eutectic electrolyte as claimed in any one of claims 1 to 7.

Images