Sodium-ion battery electrolyte and sodium-ion battery prepared from same

Abstract

The invention discloses a sodium-ion battery electrolyte and a sodium-ion battery prepared from the sodium-ion battery electrolyte. The electrolyte has the characteristics of high boiling point, wide liquid state range temperature and good stability. A sodium salt with a trifluoro substituent group is matched with a conventional sodium salt according to a proper proportion, so that the problems of low ion mobility and difficulty in desolvation of the sodium ion battery caused by only using propylene carbonate as a solvent are solved. The sodium ion battery prepared from the electrolyte has excellent high-temperature and low-temperature cycle performance and high-temperature storage performance, and the safety of the battery is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a sodium ion battery electrolyte and a sodium ion battery prepared therefrom. Background Art

[0002] Cyclic carbonate is an organic solvent with high dielectric constant, wide temperature range and excellent performance. As a non-protonic polar organic solvent, it can dissolve a variety of organic substances and inorganic salts due to its high dielectric constant. It is a widely used electrolyte solvent. Ethylene carbonate is a crystalline solid at room temperature (25°C), which requires heating and melting before use. Usually, linear carbonate or carboxylic acid ester solvents are used for mutual matching. More importantly, ethylene carbonate is easily reduced and has low electrochemical stability. Batteries are prone to gasification when used in harsh environments, causing battery failure, fire or even explosion. Propylene carbonate (PC, C 4 H 6 O 3 ) has the characteristics of low melting point, high boiling point, wide liquid temperature range (-48.8℃~242℃), wide electrochemical window, good chemical stability, and strong solubility, which has significant advantages in sodium ion batteries. Despite this, single propylene carbonate as an organic solvent for electrolyte still faces the problems of high low-temperature viscosity, low ion mobility, and difficulty in desolvation, which leads to increased polarization of the battery cell and inability to charge and discharge normally at low temperatures. Therefore, the existing sodium ion battery electrolyte is still mainly a composite combination of at least two cyclic carbonates. However, this composite electrolyte can usually only be used within a narrow temperature range, otherwise it is easy to cause the battery cell to fail due to excessively low temperature and cannot be used. At the same time, its safety is insufficient at high temperatures. Since high and low temperature performance cannot be taken into account at the same time, the development of wide-temperature batteries with high safety and excellent cycle performance has always been widely concerned by people. It is necessary to provide a technical solution to the above problems. Summary of the invention

[0003] The object of the present invention is to overcome the deficiencies of the prior art and provide a sodium ion battery electrolyte, which has a wide operating temperature range and good electrical conductivity and uses only propylene carbonate as an electrolyte solvent.

[0004] Another object of the present invention is to provide a method for preparing the sodium ion battery electrolyte.

[0005] Another object of the present invention is to provide a sodium ion battery.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A sodium ion battery electrolyte, comprising a sodium salt, an organic solvent and an additive; the sodium salt comprises a first sodium salt and a second sodium salt;

[0008] The first sodium salt is a sodium salt other than a trifluoro substituent, and the second sodium salt is a sodium salt with a trifluoro substituent;

[0009] The mass ratio of the first sodium salt to the second sodium salt is 8-10:0.1-1;

[0010] The organic solvent is propylene carbonate.

[0011] The inventors found that a sodium salt with an appropriate amount of trifluoro substituents can be used as a diluent for sodium salts, which not only improves the antioxidant properties of the ion solvation structure, but also makes it easier to enter the metal ion solvation structure and modify it. At the same time, the introduction of trifluoro substituents can more effectively reduce the electronegativity of the carbonyl oxygen on the electrolyte solvent molecule than monofluoro and difluoro substitutions, and the effect of sodium ions and carbonyl groups is weakened, ensuring that even at low temperatures, sodium ions can be promoted to dissolve, reduce the desolvation energy of the sodium ion migration process, and greatly improve the low-temperature electrical performance of the battery. The trifluoro substituent has a relatively moderate interaction strength with sodium ions than the multi-fluorine substituent, can effectively enter the sodium ion solvation structure, will not excessively reduce the conductivity of the electrolyte, and has a lower cost advantage. Therefore, with the cooperation of the sodium salt of the trifluoro substituent, the high temperature and wide performance of propylene carbonate can be better utilized, the use temperature width of the electrolyte can be improved, and the prepared sodium ion battery has excellent high temperature and low temperature cycle performance and high temperature storage performance, and the safety of the battery is greatly improved.

[0012] Preferably, the first sodium salt is any one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium fluoromalonate borate, sodium bis(oxalatoborate), sodium difluorooxalatoborate or sodium difluorophosphate.

[0013] Preferably, the second sodium salt is any one or more of sodium trifluoromethanesulfinate, sodium trifluoroalkylcarboxylate, sodium 3,3,3-trifluoropropane-1-trifluoroborate, sodium tridecafluoroheptanoate, sodium trifluorobenzoate, sodium trifloxysulfuron, sodium fomesafen, or sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate or their alkyl substituents.

[0014] The alkyl carboxylic acid in the sodium trifluoroalkyl carboxylate can be selected from C1-C8 alkyl carboxylic acids, namely formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid or octanoic acid.

[0015] Preferably, in the sodium ion battery electrolyte, the concentration of sodium salt is 5wt% to 35wt%.

[0016] Preferably, the mass percentage of the organic solvent in the sodium ion battery electrolyte is 50wt% to 90wt%.

[0017] More preferably, the mass percentage of the organic solvent in the sodium ion battery electrolyte is 60wt% to 85wt%.

[0018] Preferably, the mass percentage of the additive in the sodium ion battery electrolyte is not greater than 15wt%.

[0019] More preferably, the mass percentage of the additive in the sodium ion battery electrolyte is 3wt% to 10wt%.

[0020] Preferably, the additive includes any one or more of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, hexamethylene diisocyanate, vinyl sulfate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, 1,3-propane sultone, propenyl-1,3-propane sultone, pentafluoro(phenoxy)cyclotriphosphazene, tetrafluoroethyl tetrafluoropropyl ether, pyridine, ethylene glycol dibutyl ether, propylene sulfite, 4-methylethylene sulfate, succinonitrile or adiponitrile.

[0021] The method for preparing the sodium ion battery electrolyte comprises the following steps:

[0022] S1. dissolving the first sodium salt in an organic solvent to obtain a first mixed solution;

[0023] S2. Adding a second sodium salt to the first mixed solution to obtain a second mixed solution;

[0024] S3. Add additives to the second mixed solution and stir evenly to obtain the sodium ion battery electrolyte.

[0025] More specifically, the organic solvent is dried before being added. The drying may be carried out by Molecular sieves are used.

[0026] A sodium ion battery uses the sodium ion battery electrolyte as its electrolyte.

[0027] More specifically, the sodium ion battery includes a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte.

[0028] The positive electrode plate described in the present invention can be commercially available or homemade.

[0029] Specifically, the positive electrode sheet includes a positive electrode active material, a conductive agent, a binder, and the like.

[0030] The positive electrode active material can be selected from one or more mixed systems of layered oxide type, polyanion type (such as sodium vanadium phosphate, sodium ferric sulfate, sodium ferric phosphate pyrophosphate), Prussian blue or Prussian white.

[0031] The conductive agent is a commonly used carbon conductive agent, which can be selected from one or more of conductive graphite, carbon black, carbon fiber, carbon nanotube or graphene.

[0032] The binder is a common binder and can be selected from one or more of polyvinylidene fluoride, polyacrylic acid, polyacrylonitrile, polyimide or polytetrafluoroethylene.

[0033] The negative electrode sheet includes a negative electrode active material, a conductive agent, a binder, and the like.

[0034] The negative electrode active material may be amorphous carbon such as hard carbon or soft carbon.

[0035] The conductive agent is a commonly used carbon conductive agent, which can be selected from one or more of conductive graphite, carbon black, carbon fiber, carbon nanotube or graphene.

[0036] The binder is a common binder and can be selected from one or more of polyacrylic acid, polyacrylonitrile, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride and polytetrafluoroethylene.

[0037] The diaphragm can be selected from one of PP, PE, PP and PE multilayer composite diaphragm, ceramic layer modified diaphragm, PMMA coated diaphragm, aramid modified diaphragm or oxide solid electrolyte coated diaphragm.

[0038] The preparation method of the sodium ion battery specifically comprises the following steps: S1, winding a positive electrode sheet, a separator and a negative electrode sheet to obtain a bare cell, and then encapsulating to obtain a dry cell; S2, injecting the sodium ion battery electrolyte into the dry cell, and obtaining the sodium ion battery through formation and volume separation.

[0039] In some specific embodiments, the positive electrode sheet can be prepared by the following preparation method:

[0040] The positive electrode material (such as Na 4 Fe(PO 4 ) 2 P 2 O 7 ), a conductive agent (e.g. a mixture of SP and CNT in a mass ratio of 1:1), and a binder (e.g. polytetrafluoroethylene) are dispersed in an N-methylpyrrolidone (NMP) solvent in a mass ratio of 94:3:3, and stirred evenly by a planetary mixer to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on both sides of an aluminum foil by a coating machine, and a positive electrode sheet is obtained after baking, rolling, and slitting, and finally dried in vacuum for standby use.

[0041] In some specific embodiments, the negative electrode plate can be prepared by the following preparation method:

[0042] The negative electrode material (such as hard carbon), conductive agent (SP), and binder (CMC and SBR mass ratio of 1:1) are mixed together at a mass ratio of 94:3:3, dispersed in deionized water, and stirred evenly with a planetary mixer to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on both sides of the aluminum foil with a coating machine, and the negative electrode sheets are obtained after baking, rolling, and slitting, and finally vacuum dried for standby use.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The present invention provides an electrolyte containing only a single organic solvent as a solvent, and the electrolyte has the characteristics of high boiling point, wide liquid temperature range and good stability. The electrolyte is matched with a sodium salt with a trifluoro substituent in a suitable ratio with a conventional sodium salt, which overcomes the problems of low ion mobility and difficult desolvation of sodium ion batteries caused by using only propylene carbonate as a solvent. The sodium ion battery prepared by the electrolyte has excellent high-temperature and low-temperature cycle performance and high-temperature storage performance, and the safety of the battery is greatly improved. DETAILED DESCRIPTION

[0045] The present invention is further described in detail below in conjunction with specific examples, which are only used to explain the present invention and are not used to limit the scope of the present invention. The test methods used in the following examples are conventional methods unless otherwise specified; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0046] The positive electrode sheets used in the examples and comparative examples were prepared by the following preparation method:

[0047] The positive electrode material Na 4 Fe(PO 4 ) 2 P 2 O 7 , a conductive agent (a mixture of SP and CNT in a mass ratio of 1:1), and a binder (PVDF) are dispersed in an N-methylpyrrolidone (NMP) solvent in a mass ratio of 94:3:3, and are stirred evenly by a planetary mixer to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on both sides of an aluminum foil by a coater, and a positive electrode sheet is obtained after baking, rolling, and slitting, and finally dried in vacuum for standby use.

[0048] The negative electrode sheets used in the examples and comparative examples were prepared by the following preparation method:

[0049] The negative electrode material (such as hard carbon), conductive agent (SP), and binder (carboxymethyl cellulose CMC and styrene-butadiene rubber SBR in a mass ratio of 1:1) are mixed together in a mass ratio of 94:3:3, dispersed in deionized water, and stirred evenly with a planetary mixer to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on both sides of the aluminum foil with a coater, and the negative electrode sheet is obtained after baking, rolling, and slitting, and finally vacuum dried for standby use.

[0050] In the embodiments and comparative examples, the method for preparing the sodium ion battery electrolyte comprises the following steps:

[0051] S1. dissolving the first sodium salt in an organic solvent to obtain a first mixed solution;

[0052] S2. Adding a second sodium salt to the first mixed solution to obtain a second mixed solution;

[0053] S3. Add additives to the second mixed solution and stir evenly to obtain the sodium ion battery electrolyte.

[0054] The preparation method of the sodium ion battery specifically comprises the following steps: S4, winding the positive electrode sheet, the separator and the negative electrode sheet to obtain a bare cell, and then encapsulating to obtain a dry cell; S5, injecting the sodium ion battery electrolyte into the dry cell, and obtaining the sodium ion battery through formation and volume separation.

[0055] Example 1

[0056] A sodium ion battery electrolyte, comprising a sodium salt, an organic solvent and an additive; the sodium salt comprises a first sodium salt and a second sodium salt;

[0057] The organic solvent is propylene carbonate;

[0058] The first sodium salt is NaPF 6 、NaFSI;NaPF 6 The mass ratio with NaFSI is 1:2;

[0059] The second sodium salt is sodium trifluoromethanesulfinate;

[0060] The mass ratio of the first sodium salt to the second sodium salt is 6:0.25;

[0061] The total mass of sodium salt is 14% of the mass of electrolyte;

[0062] The additives are fluoroethylene carbonate, vinyl sulfate, and 1,3-propane sultone, with a mass ratio of 2:1:1;

[0063] The total mass of additives is 4% of the battery electrolyte;

[0064] The total mass of solvents is 82% of the battery electrolyte.

[0065] The electrolyte is used to prepare a sodium ion battery.

[0066] Example 2

[0067] A sodium ion battery electrolyte, comprising a sodium salt, an organic solvent and an additive; the sodium salt comprises a first sodium salt and a second sodium salt;

[0068] The organic solvent is propylene carbonate;

[0069] The first sodium salt is NaPF 6 、NaPO 2 F 2 ;NaPF 6 With NaPO 2 F 2 The mass ratio is 13:1;

[0070] The second sodium salt is sodium trifluoromethanesulfinate;

[0071] The mass ratio of the first sodium salt to the second sodium salt is 6:0.25;

[0072] The total mass of sodium salt is 15% of the mass of electrolyte;

[0073] The additives are fluoroethylene carbonate, vinyl sulfate, and 1,3-propane sultone, with a mass ratio of 2:1:1;

[0074] The total mass of additives is 5% of the battery electrolyte;

[0075] The total mass of the solvent is 80% of the battery electrolyte.

[0076] The electrolyte is used to prepare a sodium ion battery.

[0077] Example 3

[0078] A sodium ion battery electrolyte, comprising a sodium salt, an organic solvent and an additive; the sodium salt comprises a first sodium salt and a second sodium salt;

[0079] The organic solvent is propylene carbonate;

[0080] The first sodium salt is NaPF 6 ;

[0081] The second sodium salt is sodium trifluoromethanesulfinate;

[0082] The mass ratio of the first sodium salt to the second sodium salt is 10:0.5;

[0083] The total mass of sodium salt is 14% of the mass of electrolyte; the additives are fluoroethylene carbonate, vinyl sulfate, and 1,3-propane sultone, with a mass ratio of 2:1:1;

[0084] The total mass of additives is 4% of the battery electrolyte;

[0085] The total mass of solvents is 82% of the battery electrolyte.

[0086] The electrolyte is used to prepare a sodium ion battery.

[0087] Example 4

[0088] A sodium ion battery electrolyte, comprising a sodium salt, an organic solvent and an additive; the sodium salt comprises a first sodium salt and a second sodium salt;

[0089] The organic solvent is propylene carbonate;

[0090] The first sodium salt is NaPF 6 ;

[0091] The second sodium salt is sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate;

[0092] The mass ratio of the first sodium salt to the second sodium salt is 6:0.5;

[0093] The total mass of sodium salt is 14% of the mass of electrolyte, and the additives are fluoroethylene carbonate, vinyl sulfate, and 1,3-propane sultone, with a mass ratio of 2:1:1;

[0094] The total mass of additives is 4% of the battery electrolyte;

[0095] The total mass of solvents is 82% of the battery electrolyte.

[0096] The electrolyte is used to prepare a sodium ion battery.

[0097] Example 5

[0098] A sodium ion battery electrolyte, comprising a sodium salt, an organic solvent and an additive; the sodium salt comprises a first sodium salt and a second sodium salt;

[0099] The organic solvent is propylene carbonate;

[0100] The first sodium salt is NaPF 6 ;

[0101] The second sodium salt is sodium trifluoroacetate;

[0102] The mass ratio of the first sodium salt to the second sodium salt is 6.5:0.5;

[0103] The total mass of sodium salt is 16.8% of the mass of electrolyte. The additives are fluoroethylene carbonate, vinyl sulfate, and 1,3-propane sultone, with a mass ratio of 2:1:1.

[0104] The total mass of additives is 3.2% of the battery electrolyte;

[0105] The total mass of the solvent is 80% of the battery electrolyte.

[0106] The electrolyte is used to prepare a sodium ion battery.

[0107] Example 6

[0108] A sodium ion battery electrolyte, comprising a sodium salt, an organic solvent and an additive; the sodium salt comprises a first sodium salt and a second sodium salt;

[0109] The organic solvent is propylene carbonate;

[0110] The first sodium salt is NaPF 6 ;

[0111] The second sodium salt is trifloxysulfuron sodium;

[0112] The mass ratio of the first sodium salt to the second sodium salt is 6.5:0.25;

[0113] The total mass of sodium salt is 14% of the mass of electrolyte; the additives are fluoroethylene carbonate, vinyl sulfate, and 1,3-propane sultone, with a mass ratio of 1:1:1;

[0114] The total mass of additives is 4% of the battery electrolyte;

[0115] The total mass of solvents is 82% of the battery electrolyte.

[0116] The electrolyte is used to prepare a sodium ion battery.

[0117] Example 7

[0118] A sodium ion battery electrolyte, comprising a sodium salt, an organic solvent and an additive; the sodium salt comprises a first sodium salt and a second sodium salt;

[0119] The organic solvent is propylene carbonate;

[0120] The first sodium salt is NaPF 6 、NaFSI;NaPF 6 The mass ratio with NaFSI is 1:2;

[0121] The second sodium salt is sodium 3,3,3-trifluoropropane-1-trifluoroborate;

[0122] The mass ratio of the first sodium salt to the second sodium salt is 6.5:0.25;

[0123] The total mass of sodium salt is 28% of the mass of electrolyte, and the additives are fluoroethylene carbonate, vinyl sulfate, and 1,3-propane sultone, with a mass ratio of 1:1:0.5;

[0124] The total mass of additives is 4% of the battery electrolyte;

[0125] The total mass of solvent is 68% of the battery electrolyte.

[0126] The electrolyte is used to prepare a sodium ion battery.

[0127] Comparative Example 1

[0128] A sodium ion battery electrolyte comprising a sodium salt, an organic solvent and an additive;

[0129] The organic solvent is propylene carbonate;

[0130] The sodium salt is NaPF 6 ;

[0131] The total mass of sodium salt is 14% of the mass of electrolyte, and the additives are fluoroethylene carbonate, vinyl sulfate, and 1,3-propane sultone, with a mass ratio of 2:1:1;

[0132] The total mass of additives is 4% of the battery electrolyte;

[0133] The total mass of solvents is 82% of the battery electrolyte.

[0134] The electrolyte is used to prepare a sodium ion battery.

[0135] Comparative Example 2

[0136] A sodium ion battery electrolyte, comprising a sodium salt, an organic solvent and an additive; the sodium salt comprises a first sodium salt and a second sodium salt;

[0137] The organic solvent is ethylene carbonate and propylene carbonate in a mass ratio of 3:7;

[0138] The first sodium salt is NaPF 6 ;

[0139] The second sodium salt is sodium trifluoromethanesulfinate;

[0140] The mass ratio of the first sodium salt to the second sodium salt is 10:0.5;

[0141] The total mass of sodium salt is 14% of the mass of electrolyte, and the additives are fluoroethylene carbonate, vinyl sulfate, and 1,3-propane sultone, with a mass ratio of 2:1:1;

[0142] The total mass of additives is 4% of the battery electrolyte;

[0143] The total mass of solvents is 82% of the battery electrolyte.

[0144] The electrolyte is used to prepare a sodium ion battery.

[0145] Performance Testing

[0146] 1. Test Method

[0147] (1) Battery cycle performance test:

[0148] High temperature cycle test:

[0149] After the battery was placed in a constant temperature oven at 60°C for 3 hours, it was charged to 3.45V at a constant current of 1C, then charged at a constant voltage until the current dropped to 0.05C, and then discharged to 1.5V at a constant current of 1C. This cycle was repeated, and the initial capacity of the battery and the discharge capacity of the last cycle (800th cycle) were recorded. Capacity retention rate = discharge capacity of the last cycle (800th cycle) / initial capacity × 100%.

[0150] -10 degrees low temperature cycle test:

[0151] After the battery is placed in a low-temperature cabinet at a constant temperature of -10°C for 3 hours, it is charged to 3.45V at a constant current of 0.33C, then charged at a constant voltage until the current reaches 0.05C, and then discharged to 1.5V at a constant current of 0.5C. This cycle is repeated, and the initial capacity of the battery and the discharge capacity of the last cycle (500th cycle) are recorded. Capacity retention rate = discharge capacity of the last cycle (500th cycle) / initial capacity × 100%.

[0152] (2) Battery storage performance test: 85℃ high temperature storage:

[0153] Standard charge: Charge the battery at 25°C at a constant current of 0.5C to 3.45V, cut off at 0.02C, and then discharge at a constant current of 0.2C to 1.5V. Record the initial thickness, initial capacity and internal resistance R1 of the battery cell.

[0154] Charge to 3.45V according to the standard method, place in an oven at a constant temperature of 85℃ for 28 days, wait for the battery to cool to room temperature, and then measure the cell thickness and internal resistance R2 after 28 days. The capacity discharged to 1.5V at a current of 0.2C is recorded as the remaining capacity. The stored cell is charged to 3.45V at a constant current of 0.5C, cut off at 0.02C, and then discharged to 1.5V at a constant current of 0.2C, which is recorded as the recovered capacity.

[0155] Residual value = remaining capacity / initial capacity × 100%,

[0156] Recovery value = recovery capacity / initial capacity × 100%,

[0157] Thickness expansion rate = (thickness after storage - thickness before storage) / thickness before storage × 100%,

[0158] Internal resistance growth rate=(internal resistance after storage-internal resistance before storage) / internal resistance before storage×100%.

[0159] The above cycle and high temperature storage performance test results are shown in Table 1.

[0160] (3) Battery safety performance test:

[0161] Hot Plate Safety Test:

[0162] Charge the battery cell at 1C to 3.45V at 25℃, and cut off at 0.02C. Then place the battery cell on the graphene heating plate and heat it until the bottom temperature of the battery cell is about 280℃. Keep it above 280℃ for 30-40 minutes, and observe the voltage change and whether the battery cell expands or fails.

[0163] Thermal shock safety test:

[0164] The fully charged cell is placed in an air circulation heating furnace with an initial temperature of 25±3℃, heated to 170±2℃ at a heating rate of 5±2℃ / min and maintained for 30min. It passes if there is no fire or explosion.

[0165] The above hot plate and thermal shock safety test results are shown in Table 2.

[0166] 2. Test results

[0167] Table 1 High temperature cycle and storage performance

[0168]

[0169] Table 2 Hot plate, thermal shock safety test

[0170] serial number Hot Plate Test Results Thermal shock test results Example 1 3.39V, not expanded The battery cell has not expanded or exploded. Example 2 3.42V, not expanded The battery cell has not expanded or exploded. Example 3 3.41V, not expanded The battery cell has not expanded or exploded. Example 4 3.41V, not expanded The battery cell has not expanded or exploded. Example 5 3.42V, not expanded The battery cell has not expanded or exploded. Example 6 3.39V, not expanded The battery cell has not expanded or exploded. Example 7 3.40V, not expanded The battery cell has not expanded or exploded. Comparative Example 1 3.39V, not expanded The battery cell swells and smokes, but there is no explosion Comparative Example 2 0V, not expanded The battery cell swells and smokes, but there is no explosion

[0171] It can be seen from Table 1 and Table 2 that the sodium ion battery prepared by the sodium ion battery electrolyte provided by the present invention has excellent high-temperature and low-temperature cycle performance and high-temperature storage performance, and the safety of the battery is greatly improved.

[0172] It can be seen from Comparative Example 1 that if no sodium salt with a trifluoro substituent is added, there are defects such as poor low-temperature cycle performance and reduced thermal shock safety performance, indicating that the combined electrolyte with the addition of a sodium salt with a trifluoro substituent and pure propylene carbonate as a single solvent has excellent wide temperature performance.

[0173] It can be seen from Comparative Example 2 that the use of ethylene carbonate and propylene carbonate as a mixed solvent has the defects of poor high temperature performance, easy gas generation at high temperature, low safety performance at high temperature, and insufficient low temperature performance. It can be seen from the hot plate and thermal shock safety tests that the voltage of the embodiment and comparative example 1 is still stable at around 3.40V and above, and the battery cell has not failed, while the voltage of comparative example 2 has dropped to 0V and the battery cell has expanded and smoked, and the internal short circuit of the battery cell has caused a complete failure phenomenon, which shows that the pure PC-based electrolyte has a high thermal stability and the safety performance of the sodium ion battery is good.

[0174] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A sodium ion battery electrolyte, characterized in that: It comprises a sodium salt, an organic solvent and an additive; the sodium salt comprises a first sodium salt and a second sodium salt; The first sodium salt is a sodium salt other than a trifluoro substituent, and the second sodium salt is a sodium salt with a trifluoro substituent; The mass ratio of the first sodium salt to the second sodium salt is 8-10:0.1-1; The organic solvent is propylene carbonate.

2. The sodium ion battery electrolyte according to claim 1, characterized in that: The first sodium salt is any one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium fluoromalonate borate, sodium bis(oxalatoborate), sodium difluorooxalatoborate or sodium difluorophosphate.

3. The sodium ion battery electrolyte according to claim 1, characterized in that: The second sodium salt is any one or more of sodium trifluoromethanesulfinate, sodium trifluoroalkylcarboxylate, sodium 3,3,3-trifluoropropane-1-trifluoroborate, sodium tridecafluoroheptanoate, sodium trifluorobenzoate, sodium trifloxysulfuron, sodium fomesafen, or sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate or their alkyl substituents.

4. The sodium ion battery electrolyte according to claim 1, characterized in that: In the sodium ion battery electrolyte, the mass percentage of sodium salt is 5wt% to 35wt%.

5. The sodium ion battery electrolyte according to claim 1, characterized in that: The mass percentage of the organic solvent in the sodium ion battery electrolyte is 50wt% to 90wt%.

6. The sodium ion battery electrolyte according to claim 5, characterized in that: The mass percentage of the organic solvent in the sodium ion battery electrolyte is 60wt% to 85wt%.

7. The sodium ion battery electrolyte according to claim 1, characterized in that: The mass percentage of the additive in the sodium ion battery electrolyte is no more than 15wt%.

8. The sodium ion battery electrolyte according to claim 1, characterized in that: The additive includes any one or more of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, hexamethylene diisocyanate, vinyl sulfate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, 1,3-propane sultone, propenyl-1,3-propane sultone, pentafluoro(phenoxy)cyclotriphosphazene, tetrafluoroethyl tetrafluoropropyl ether, pyridine, ethylene glycol dibutyl ether, propylene sulfite, 4-methylethylene sulfate, succinonitrile or adiponitrile.

9. The method for preparing the sodium ion battery electrolyte according to any one of claims 1 to 8, characterized in that: The steps include: S1. dissolving the first sodium salt in an organic solvent to obtain a first mixed solution; S2. Adding a second sodium salt to the first mixed solution to obtain a second mixed solution; S3. Add additives to the second mixed solution and stir evenly to obtain the sodium ion battery electrolyte.

10. A sodium ion battery, characterized in that: The sodium ion battery electrolyte according to any one of claims 1 to 8 is used as the electrolyte.

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