Lithium / Thionyl Chloride Battery Electrolyte

Abstract

The invention discloses a lithium thionyl chloride battery electrolyte. The electrolyte comprises thionyl chloride, electrolyte salt and additives. The additives comprise a first additive and a second additive. The preparation method comprises: distilling thionyl chloride and collecting fractions; weighing the electrolyte salt and dissolving it in the thionyl chloride fraction; purifying the first additive; purifying the second additive; weighing the purified first additive and the purified second additive, and adding them into a thionyl chloride solution of the electrolyte salt to obtain the lithium thionyl chloride battery electrolyte. The first additive and the second additive in the lithium thionyl chloride battery electrolyte of the invention work synergistically, so that the lithium / thionyl chloride battery achieves good discharge voltage and discharge capacity, significantly improves the voltage hysteresis phenomenon of the lithium / thionyl chloride battery, and the lithium thionyl chloride battery prepared by the electrolyte has good cycle performance and high safety.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, in particular to a lithium thionyl chloride battery electrolyte. Background Art

[0002] Lithium / thionyl chloride (Li / SOCl2) battery is a lithium battery with lithium as anode, carbon as cathode carrier, and thionyl chloride (SOCl2) solution of anhydrous lithium tetrachloroaluminate as electrolyte. Lithium / thionyl chloride battery has the characteristics of high specific energy, high specific power, stable discharge voltage, long storage life, etc., and is widely used in military and civilian industries such as aerospace, underwater weapons, navigation equipment, geological exploration, instrumentation, etc. Lithium / thionyl chloride battery is currently the battery with the highest specific energy and specific power in the battery field. The overall reaction mechanism of lithium thionyl chloride battery is: 4Li+2SOCl2→4LiCl+S+SO2, sulfur and sulfur dioxide are dissolved in excess thionyl chloride electrolyte, and during discharge, a certain degree of pressure will be generated due to the production of sulfur dioxide. During storage, once the lithium negative electrode comes into contact with the electrolyte, it reacts with the thionyl chloride electrolyte to generate LiCl, and the lithium negative electrode is protected by the LiCl film formed on it. This passivation film is beneficial to extend the storage life of the battery, but it will cause voltage hysteresis at the beginning of discharge. The voltage hysteresis phenomenon is particularly obvious when the battery is discharged in a low temperature environment after being stored at high temperature for a long time.

[0003] In order to eliminate the voltage hysteresis of lithium / thionyl chloride batteries, most of them adopt the methods of improving the current collection form of the cathode and anode, or improving the impurity content and molar concentration of the electrolyte to reduce the internal resistance of the battery; adding electronic components inside or outside the battery to put the battery in a weak discharge state to weaken the formation of the passivation film; adding metal phthalocyanine compounds or sulfides to the cathode and electrolyte to improve the voltage hysteresis performance. Some of the above methods can improve certain properties of lithium / thionyl chloride batteries to a certain extent, but some of them "sacrifice" the capacity of lithium / thionyl chloride batteries at the expense of weakening other properties of lithium / thionyl chloride batteries.

[0004] Electrolyte is one of the three elements that make up lithium thionyl chloride batteries. Its physical and chemical properties play a vital role in the performance of battery materials. It is of great significance to develop electrolyte materials that match cathode and anode materials. Summary of the invention

[0005] The object of the present invention is to provide a lithium thionyl chloride battery electrolyte and a preparation method thereof, so as to solve the problems in the prior art.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A lithium thionyl chloride battery electrolyte comprises thionyl chloride, electrolyte salt and additive, wherein the molar concentration of the thionyl chloride solution of the electrolyte salt is 0.1-1 mol / L, and the mass of the additive is 0.01-0.5% of the total mass of the electrolyte. If the amount of the additive added is too small, the phenomenon of battery voltage hysteresis cannot be alleviated, and if the amount of the additive added is too large, the gram capacity of the material will be affected, and waste will be caused, and the phenomenon of battery voltage hysteresis cannot be alleviated.

[0008] As an optimization, the additive includes a first additive and a second additive, and the structural formula of the first additive is:

[0009] ;

[0010] Wherein, X is a halogen; R1 is a nitrile group, an amine group, a hydroxyl group or a nitro group; R2 and R3 are both hydrogen, a mono-substituted or poly-substituted C1-C6 alkyl group, an aryl group, a C1-C6 alkoxy group or a halogenated C1-C6 alkoxy group; R4 is a C1-C6 alkyl group or a C1-C6 alkyl group mono-substituted or poly-substituted by a halogen.

[0011] As an optimization, the structural formula of the second additive is:

[0012] ;

[0013] Wherein, X1 is a halogen; R 11 , R 21 , R 31 are C1-C10 alkyl, halogenated C1-C10 alkyl, C1-C10 alkoxy or halogenated C1-C10 alkoxy; R 41 It is a heterocyclic group which is unsubstituted or substituted by a C1-C6 alkyl group, and the heterocyclic ring contains one or more of O, N, and S elements.

[0014] As an optimization, the electrolyte salt is one or more of lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate), lithium trifluoromethanesulfonate, tri(trifluoromethylsulfonyl)methyl lithium, lithium hexafluorophosphate, lithium trioxalate phosphate, lithium difluorobis(oxalate phosphate), and lithium tetrafluorooxalate phosphate. The main disadvantage of Li / SOCl2 battery is its voltage hysteresis phenomenon, which is more serious when used at room temperature after high temperature storage. The main reason for the voltage hysteresis of Li / SOCl2 battery is that lithium tetrachloroaluminate (LiAlCl4) electrolyte salt is used in the battery system. The electrolyte solution containing this salt produces a spontaneous chemical reaction at the lithium anode, and the product is LiCl. LiCl is covered on the surface of the lithium anode in the form of a thin film, which hinders the contact between lithium and the electrolyte solution, and finally leads to voltage hysteresis. The present invention uses the above electrolyte salt instead of lithium tetrachloroaluminate (LiAlCl4) electrolyte salt to prepare lithium thionyl chloride battery electrolyte, which can effectively reduce the battery voltage hysteresis phenomenon.

[0015] As an optimization, the mass of the first additive is 0.005-0.3% of the total mass of the electrolyte, and the mass of the second additive is 0.005-0.2% of the total mass of the electrolyte.

[0016] A method for preparing a lithium thionyl chloride battery electrolyte, the preparation method comprising the following steps:

[0017] (1) distilling thionyl chloride and collecting fractions;

[0018] (2) weighing an electrolyte salt and placing it in the thionyl chloride fraction obtained in step (1), and adjusting the volume to obtain a thionyl chloride solution of the electrolyte salt;

[0019] (3) Purification of the first additive: extracting the first additive with acetone to obtain a first additive extract, distilling the extract to obtain the first additive, and drying to obtain a purified first additive;

[0020] (4) Purification of the second additive: The second additive is purified by using a sublimation purification device:

[0021] (a) adding molten salt into the heating chamber through the feed inlet, and heating the molten salt using a first molten salt heating rod and a second molten salt heating rod;

[0022] (b) the second additive is loaded into a sublimation loading boat, silica gel is spread on the second additive, and then placed in a cylindrical tube, and after closing the end door, a vacuum pump is used to evacuate the vacuum cooling tube, and the purification of the second additive is completed after a period of time;

[0023] (5) Weigh the purified first additive obtained in step (3) and the purified second additive obtained in step (4), and then add them to the thionyl chloride solution of the electrolyte salt obtained in step (2), and stir continuously until they are completely dissolved to obtain a lithium thionyl chloride battery electrolyte.

[0024] As an optimization, a method for preparing a lithium thionyl chloride battery electrolyte comprises the following steps:

[0025] (1) Place thionyl chloride in a flask, heat it for distillation, and collect the fraction at 70-80°C; distilling thionyl chloride is for the purpose of purification;

[0026] (2) weighing an electrolyte salt, dissolving the electrolyte salt in the thionyl chloride fraction obtained in step (1) under an inert atmosphere, and adjusting the volume to obtain a thionyl chloride solution of the electrolyte salt having a molar concentration of 0.1-1 mol / L;

[0027] (3) Purification of the first additive: extracting the first additive with acetone to obtain a first additive extract, distilling the extract to obtain the first additive, and drying to obtain the purified first additive; the extraction temperature is 30-45° C., the extraction time is 1-4 hours, and the distillation is carried out by reduced pressure distillation at 40-80° C.;

[0028] (4) Purification of the second additive: The second additive is purified by using a sublimation purification device: the purification method has a short process flow and is easy to operate. The purity of the purified second additive is greater than 99%;

[0029] (a) adding molten salt into the heating chamber through the feed port, and heating the molten salt by using the first molten salt heating rod and the second molten salt heating rod to make the temperature reach 200-250°C;

[0030] (b) The second additive is loaded into a sublimation loading boat, silica gel is spread on the second additive, and then placed in a cylindrical tube. After closing the end door, the vacuum degree is pumped to 0.03-0.08KPa by a vacuum pump through a vacuum cooling tube. After 6-15 hours, the second additive is purified; the silica gel mainly plays a decolorizing role;

[0031] (5) Weigh the purified first additive obtained in step (3) and the purified second additive obtained in step (4), and then add them to the thionyl chloride solution of the electrolyte salt obtained in step (2), and stir continuously until they are completely dissolved to obtain a lithium thionyl chloride battery electrolyte.

[0032] The first additive and the second additive are purified to reduce impurities, and the lithium thionyl chloride battery electrolyte prepared by using them can more effectively alleviate the phenomenon of battery voltage hysteresis.

[0033] As an optimization, the molten salt in step (a) is a mixture of equal masses of sodium nitrite and potassium nitrite.

[0034] As an optimization, in step (3), the extract is transferred to an oscillator before distillation and oscillated at 100-300 r / min for 30-60 min. The purpose of oscillation is to make the first additive and acetone mix more evenly.

[0035] As an optimization, steps (1), (2) and (3) are all performed in a dry environment with a relative humidity of ≤0.5-1%. The electrolyte of lithium thionyl chloride batteries reacts violently with water, and even a very small amount of water can easily react with it to produce HCl gas, causing severe corrosion. Therefore, the experimental operation should be performed in a dry environment when preparing the electrolyte.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] First, the first additive and the second additive in the lithium thionyl chloride battery electrolyte of the present invention have good anti-thionyl chloride passivation characteristics through synergistic effect. The first additive and the second additive inhibit the formation of a "passivation film" on the surface of the metal lithium anode through the action of thionyl chloride, a cathode active substance in the lithium / thionyl chloride battery, so that the lithium / thionyl chloride battery has a good discharge voltage and discharge capacity, and the voltage hysteresis phenomenon of the lithium / thionyl chloride battery is significantly improved.

[0038] Secondly, the first additive and the second additive in the lithium thionyl chloride battery electrolyte of the present invention have good resistance to nucleophilic attack, and the synergistic effect of the two can effectively inhibit the loss of Li2O, stabilize the structure of the lithium-rich positive electrode material, and effectively alleviate the occurrence of battery voltage hysteresis. At the same time, the lithium thionyl chloride battery electrolyte of the present invention has good antioxidant properties and is non-flammable. Therefore, the lithium thionyl chloride battery prepared from the electrolyte has good cycle performance and high safety.

[0039] Third, the preparation method of the lithium thionyl chloride battery electrolyte of the present invention is simple, easy to operate, scientific in formula, low in raw material cost, strong in practicability, and has broad application prospects.

[0040] Fourthly, in the preparation method of the lithium thionyl chloride battery electrolyte of the present invention, thionyl chloride is distilled and the first additive and the second additive are purified, so that the prepared lithium thionyl chloride battery electrolyte has less impurity content and better performance of the electrolyte. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] Embodiment 1:

[0043] A lithium thionyl chloride battery electrolyte comprises thionyl chloride, lithium bis(fluorosulfonyl)imide and an additive, wherein the molar concentration of the thionyl chloride solution of the electrolyte salt is 0.1 mol / L, the mass of the additive is 0.01% of the total mass of the electrolyte, and the additive comprises a first additive and a second additive, wherein the mass of the first additive is 0.005% of the total mass of the electrolyte, and the mass of the second additive is 0.005% of the total mass of the electrolyte.

[0044] The structural formula of the first additive is:

[0045] ;

[0046] Wherein, X is Cl; R1 is a nitrile group; R2 and R3 are both hydrogen; and R4 is a methyl group.

[0047] The structural formula of the second additive is:

[0048] ;

[0049] Where X1 is Cl; R 11 , R 21 , R 31 All are methyl; R 41 It is a pyrrole heterocyclic group.

[0050] A method for preparing a lithium thionyl chloride battery electrolyte, the preparation method comprising the following steps:

[0051] (1) In a dry environment with a relative humidity of ≤0.5%, place thionyl chloride in a flask, heat it for distillation, and collect the fraction at 70°C;

[0052] (2) Under a dry environment with a relative humidity of ≤0.5%, weigh an electrolyte salt, and dissolve the electrolyte salt in the thionyl chloride fraction obtained in step (1) under an inert atmosphere, and adjust the volume to obtain a thionyl chloride solution of the electrolyte salt with a molar concentration of 0.1 mol / L;

[0053] (3) Purification of the first additive: The first additive is extracted with acetone to obtain a first additive extract, the extract is transferred to an oscillator, and oscillated at 100 r / min for 30 min, and the extract is distilled to remove the acetone to obtain a first additive crude extract, and finally the supernatant is removed and dried to obtain a purified first additive; the extraction temperature is 30° C., the extraction time is 1 h, and the distillation is carried out at 40° C. by reduced pressure distillation;

[0054] (4) Purification of the second additive: The second additive is purified by using a sublimation purification device:

[0055] (a) adding molten salt into the heating chamber through the feed port, wherein the molten salt is a mixture of sodium nitrite and potassium nitrite of equal mass, and heating the molten salt by using a first molten salt heating rod and a second molten salt heating rod to make the temperature reach 200° C.;

[0056] (b) The second additive is loaded into a sublimation loading boat, silica gel is spread on the second additive, and then placed in a cylindrical tube. After closing the end door, the vacuum degree is evacuated to 0.03 KPa by a vacuum pump through a vacuum cooling tube, and the purification of the second additive is completed after 6 hours;

[0057] (5) Under a dry environment with a relative humidity of ≤0.5%, weigh the purified first additive obtained in step (3) and the purified second additive obtained in step (4), and then add them to the thionyl chloride solution of the electrolyte salt obtained in step (2), and stir continuously until they are completely dissolved to obtain a lithium thionyl chloride battery electrolyte.

[0058] Embodiment 2:

[0059] A lithium thionyl chloride battery electrolyte comprises thionyl chloride, lithium bis(oxalatoborate) and an additive, wherein the molar concentration of the thionyl chloride solution of the electrolyte salt is 0.4 mol / L, the mass of the additive is 0.1% of the total mass of the electrolyte, and the additive comprises a first additive and a second additive, wherein the mass of the first additive is 0.05% of the total mass of the electrolyte, and the mass of the second additive is 0.05% of the total mass of the electrolyte.

[0060] The structural formula of the first additive is:

[0061] ;

[0062] Wherein, X is Br; R1 is an amino group; R2 and R3 are both chloromethyl groups; and R4 is an ethyl group.

[0063] The structural formula of the second additive is:

[0064] ;

[0065] Wherein, X1 is Br; R 11 , R 21 , R 31 All are chloromethyl; R 41 It is a furan heterocyclic group.

[0066] A method for preparing a lithium thionyl chloride battery electrolyte, the preparation method comprising the following steps:

[0067] (1) In a dry environment with a relative humidity of ≤0.6%, place thionyl chloride in a flask, heat it for distillation, and collect the fraction at 72°C;

[0068] (2) Under a dry environment with a relative humidity of ≤0.6%, weigh an electrolyte salt, and dissolve the electrolyte salt in the thionyl chloride fraction obtained in step (1) under an inert atmosphere, and adjust the volume to obtain a thionyl chloride solution of the electrolyte salt with a molar concentration of 0.4 mol / L;

[0069] (3) Purification of the first additive: The first additive is extracted with acetone to obtain a first additive extract, the extract is transferred to an oscillator, and oscillated at 150 r / min for 35 min, and the extract is distilled to remove the acetone to obtain a first additive crude extract, and finally the supernatant is removed and dried to obtain a purified first additive; the extraction temperature is 32° C., the extraction time is 1.5 h, and the distillation is carried out at 50° C. by reduced pressure distillation;

[0070] (4) Purification of the second additive: The second additive is purified by using a sublimation purification device:

[0071] (a) adding molten salt into the heating chamber through the feed port, wherein the molten salt is a mixture of sodium nitrite and potassium nitrite of equal mass, and heating the molten salt by a first molten salt heating rod and a second molten salt heating rod to a temperature of 210° C.;

[0072] (b) The second additive is loaded into a sublimation loading boat, silica gel is spread on the second additive, and then placed in a cylindrical tube. After closing the end door, the vacuum degree is evacuated to 0.04 KPa by a vacuum pump through a vacuum cooling tube, and the purification of the second additive is completed after 8 hours;

[0073] (5) Under a dry environment with a relative humidity of ≤0.6%, weigh the purified first additive obtained in step (3) and the purified second additive obtained in step (4), and then add them to the thionyl chloride solution of the electrolyte salt obtained in step (2), and stir continuously until they are completely dissolved to obtain a lithium thionyl chloride battery electrolyte.

[0074] Embodiment 3:

[0075] A lithium thionyl chloride battery electrolyte comprises thionyl chloride, lithium trifluoromethanesulfonate and an additive, wherein the molar concentration of the thionyl chloride solution of the electrolyte salt is 0.6 mol / L, the mass of the additive is 0.2% of the total mass of the electrolyte, and the additive comprises a first additive and a second additive, wherein the mass of the first additive is 0.1% of the total mass of the electrolyte, and the mass of the second additive is 0.2% of the total mass of the electrolyte.

[0076] The structural formula of the first additive is:

[0077] ;

[0078] Wherein, X is I; R1 is hydroxyl; R2 and R3 are both phenyl; and R4 is chloromethyl.

[0079] The structural formula of the second additive is:

[0080] ;

[0081] Among them, X1 is I; R11 , R 21 , R 31 All are methoxy; R 41 It is a thiophene heterocyclic group.

[0082] A method for preparing a lithium thionyl chloride battery electrolyte, the preparation method comprising the following steps:

[0083] (1) In a dry environment with a relative humidity of ≤0.7%, place thionyl chloride in a flask, heat it for distillation, and collect the fraction at 74°C;

[0084] (2) Under a dry environment with a relative humidity of ≤0.7%, weigh an electrolyte salt, and dissolve the electrolyte salt in the thionyl chloride fraction obtained in step (1) under an inert atmosphere, and adjust the volume to obtain a thionyl chloride solution of the electrolyte salt with a molar concentration of 0.6 mol / L;

[0085] (3) Purification of the first additive: The first additive is extracted with acetone to obtain a first additive extract, the extract is transferred to an oscillator, and oscillated at 200 r / min for 40 min, and the extract is distilled to remove the acetone to obtain a first additive crude extract, and finally the supernatant is removed and dried to obtain a purified first additive; the extraction temperature is 34° C., the extraction time is 2 h, and the distillation is carried out at 60° C. by reduced pressure distillation;

[0086] (4) Purification of the second additive: The second additive is purified by using a sublimation purification device:

[0087] (a) adding molten salt into the heating chamber through the feed port, wherein the molten salt is a mixture of sodium nitrite and potassium nitrite of equal mass, and heating the molten salt by using a first molten salt heating rod and a second molten salt heating rod to make the temperature reach 220° C.;

[0088] (b) The second additive is loaded into a sublimation loading boat, silica gel is spread on the second additive, and then placed in a cylindrical tube. After closing the end door, the vacuum degree is evacuated to 0.05 KPa by a vacuum pump through a vacuum cooling tube, and the purification of the second additive is completed after 10 hours;

[0089] (5) Under a dry environment with a relative humidity of ≤0.7%, weigh the purified first additive obtained in step (3) and the purified second additive obtained in step (4), and then add them to the thionyl chloride solution of the electrolyte salt obtained in step (2), and stir continuously until they are completely dissolved to obtain a lithium thionyl chloride battery electrolyte.

[0090] Embodiment 4:

[0091] A lithium thionyl chloride battery electrolyte comprises thionyl chloride, tris(trifluoromethylsulfonyl)methyl lithium, lithium hexafluorophosphate and an additive, wherein the molar concentration of the thionyl chloride solution of the electrolyte salt is 0.8 mol / L, the mass of the additive is 0.4% of the total mass of the electrolyte, and the additive comprises a first additive and a second additive, wherein the mass of the first additive is 0.2% of the total mass of the electrolyte, and the mass of the second additive is 0.2% of the total mass of the electrolyte.

[0092] The structural formula of the first additive is:

[0093] ;

[0094] Wherein, X is F; R1 is nitro; R2 and R3 are both methoxy; and R4 is propyl.

[0095] The structural formula of the second additive is:

[0096] ;

[0097] Among them, X1 is F; R 11 , R 21 , R 31 All are chloromethoxy; R 41 It is a 3-methylpyridine heterocyclic group.

[0098] A method for preparing a lithium thionyl chloride battery electrolyte, the preparation method comprising the following steps:

[0099] (1) In a dry environment with a relative humidity of ≤0.8%, place thionyl chloride in a flask, heat it for distillation, and collect the fraction at 78°C;

[0100] (2) Under a dry environment with a relative humidity of ≤0.8%, weigh an electrolyte salt, and dissolve the electrolyte salt in the thionyl chloride fraction obtained in step (1) under an inert atmosphere, and adjust the volume to obtain a thionyl chloride solution of the electrolyte salt with a molar concentration of 0.8 mol / L;

[0101] (3) Purification of the first additive: The first additive is extracted with acetone to obtain a first additive extract, the extract is transferred to an oscillator, and oscillated at 250 r / min for 50 min, and the extract is distilled to remove the acetone to obtain a first additive crude extract, and finally the supernatant is removed and dried to obtain a purified first additive; the extraction temperature is 40° C., the extraction time is 3 h, and the distillation is carried out at 70° C. by reduced pressure distillation;

[0102] (4) Purification of the second additive: The second additive is purified by using a sublimation purification device:

[0103] (a) adding molten salt into the heating chamber through the feed port, wherein the molten salt is a mixture of sodium nitrite and potassium nitrite of equal mass, and heating the molten salt by a first molten salt heating rod and a second molten salt heating rod to a temperature of 240° C.;

[0104] (b) The second additive is loaded into a sublimation loading boat, silica gel is spread on the second additive, and then placed in a cylindrical tube. After closing the end door, the vacuum degree is evacuated to 0.07 KPa by a vacuum pump through a vacuum cooling tube, and the purification of the second additive is completed after 12 hours;

[0105] (5) Under a dry environment with a relative humidity of ≤0.8%, weigh the purified first additive obtained in step (3) and the purified second additive obtained in step (4), and then add them to the thionyl chloride solution of the electrolyte salt obtained in step (2), and stir continuously until they are completely dissolved to obtain a lithium thionyl chloride battery electrolyte.

[0106] Embodiment 5:

[0107] A lithium thionyl chloride battery electrolyte comprises thionyl chloride, lithium trioxalate phosphate, lithium difluorodioxalate phosphate and an additive, wherein the molar concentration of the thionyl chloride solution of the electrolyte salt is 1 mol / L, the mass of the additive is 0.5% of the total mass of the electrolyte, and the additive comprises a first additive and a second additive, wherein the mass of the first additive is 0.3% of the total mass of the electrolyte, and the mass of the second additive is 0.2% of the total mass of the electrolyte.

[0108] The structural formula of the first additive is:

[0109] ;

[0110] Wherein, X is Cl; R1 is an amino group; R2 and R3 are both tolyl groups; and R4 is a chloroethyl group.

[0111] The structural formula of the second additive is:

[0112] ;

[0113] Where X1 is Cl; R 11 , R 21 , R 31 All are chloropropyl; R 41 It is a 2-chlorofuran heterocyclic group.

[0114] A method for preparing a lithium thionyl chloride battery electrolyte, the preparation method comprising the following steps:

[0115] (1) In a dry environment with a relative humidity of ≤1%, place thionyl chloride in a flask, heat it for distillation, and collect the fraction at 80°C;

[0116] (2) Under a dry environment with a relative humidity of ≤1%, weigh an electrolyte salt, and dissolve the electrolyte salt in the thionyl chloride fraction obtained in step (1) under an inert atmosphere, and adjust the volume to obtain a thionyl chloride solution of the electrolyte salt with a molar concentration of 1 mol / L;

[0117] (3) Purification of the first additive: The first additive is extracted with acetone to obtain a first additive extract, the extract is transferred to an oscillator, and oscillated at 300 r / min for 60 min, and the extract is distilled to remove the acetone to obtain a first additive crude extract, and finally the supernatant is removed and dried to obtain a purified first additive; the extraction temperature is 45° C., the extraction time is 4 h, and the distillation is carried out at 80° C. by reduced pressure distillation;

[0118] (4) Purification of the second additive: The second additive is purified by using a sublimation purification device:

[0119] (a) adding molten salt into the heating chamber through the feed port, wherein the molten salt is a mixture of sodium nitrite and potassium nitrite of equal mass, and heating the molten salt by using a first molten salt heating rod and a second molten salt heating rod to make the temperature reach 250° C.;

[0120] (b) The second additive is loaded into a sublimation loading boat, silica gel is spread on the second additive, and then placed in a cylindrical tube. After closing the end door, the vacuum degree is evacuated to 0.08 KPa by a vacuum pump through a vacuum cooling tube, and the purification of the second additive is completed after 15 hours;

[0121] (5) Under a dry environment with a relative humidity of ≤0.5-1%, weigh the purified first additive obtained in step (3) and the purified second additive obtained in step (4), and then add them to the thionyl chloride solution of the electrolyte salt obtained in step (2), and stir continuously until they are completely dissolved to obtain a lithium thionyl chloride battery electrolyte.

[0122] Comparative Example:

[0123] The commercially available lithium / thionyl chloride battery electrolyte is a thionyl chloride solution of lithium tetrachloroaluminate as the electrolyte. Thionyl chloride is both a solvent and a positive electrode active substance. The electrolyte salt is lithium tetrachloroaluminate, and the lithium salt concentration is 1.7 mol / L.

[0124] Effect example:

[0125] Make a lithium / thionyl chloride battery:

[0126] At room temperature, graphite positive electrode material, conductive agent carbon black (SP), and adhesive polyvinylidene fluoride (PVDF) are slurried in a ratio of 8:1:1, with the solvent being N-methyl-2-pyrrolidone (NMP) and the solid content being 25%, and are evenly coated on a 0.02 mm thick aluminum foil, and then dried, rolled, and cut to form a carbon positive electrode sheet;

[0127] The positive electrode uniformly adopts a carbon positive electrode sheet, the negative electrode adopts a metal lithium electrode, and the electrolyte adopts the lithium / thionyl chloride battery electrolyte prepared in Examples 1 to 5 of the present invention and the electrolyte in the comparative example to respectively prepare a lithium / thionyl chloride battery. The battery is cycled at 3.87V and 0.05C for 200 cycles, and the battery is subjected to charge and discharge tests. The test results are shown in Table 1. The battery is subjected to charge and discharge tests at any rate between 0.025-2C, and the test results are shown in Table 2.

[0128] Table 1 Battery charge and discharge performance test results

[0129]

[0130] From the test data in Table 1, it can be seen that after 200 cycles of charge and discharge of the batteries of the lithium / thionyl chloride battery electrolytes prepared in Examples 1 to 5 of the present invention, the capacity retention rate is above 90%, with the highest being 93.7%, and the average discharge voltages are 3.36V, 3.34V, 3.32V, 3.35V, and 3.37, respectively. After 200 cycles of charge and discharge of the battery of the comparative example lithium / thionyl chloride battery electrolyte, the capacity retention rate is 76.3%, and the average discharge voltage is 3.12V. The results show that the cycle performance of the battery using the lithium / thionyl chloride battery electrolyte prepared in Examples 1 to 5 of the present invention is better than that of the battery using the comparative example lithium / thionyl chloride battery electrolyte, and the voltage hysteresis phenomenon is also significantly improved.

[0131] Table 2 Battery charge and discharge performance test results at different rates

[0132]

[0133] From the test data in Table 2, it can be seen that the platform voltage and capacity of the battery using the lithium / thionyl chloride battery electrolyte prepared in Example 1 of the present invention are higher than the platform voltage of the battery using the lithium / thionyl chloride battery electrolyte of the comparative example. The results show that the battery using the lithium / thionyl chloride battery electrolyte prepared in Example 1 of the present invention has good discharge voltage and discharge capacity.

[0134] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A lithium thionyl chloride battery electrolyte, comprising thionyl chloride, lithium trioxalate phosphate, lithium difluorodioxalate phosphate and an additive, wherein the molar concentration of the thionyl chloride solution of the electrolyte salt is 1 mol / L, the mass of the additive is 0.5% of the total mass of the electrolyte, and the additive comprises a first additive and a second additive, wherein the mass of the first additive is 0.3% of the total mass of the electrolyte, and the mass of the second additive is 0.2% of the total mass of the electrolyte; The structural formula of the first additive is: ； in, X is Cl; R1 is an amino group; R2 and R3 are both tolyl groups; R4 is a chloroethyl group; The structural formula of the second additive is: ； Where X1 is Cl; R 11 , R 21 , R 31 All are chloropropyl; R 41 is a 2-chlorofuran heterocyclic group; The preparation method of the lithium thionyl chloride battery electrolyte comprises the following steps: (1) In a dry environment with a relative humidity of ≤1%, place thionyl chloride in a flask, heat it for distillation, and collect the fraction at 80°C; (2) Under a dry environment with a relative humidity of ≤1%, weigh an electrolyte salt, and dissolve the electrolyte salt in the thionyl chloride fraction obtained in step (1) under an inert atmosphere, and adjust the volume to obtain a thionyl chloride solution of the electrolyte salt with a molar concentration of 1 mol / L; (3) Purification of the first additive: The first additive is extracted with acetone to obtain a first additive extract, the extract is transferred to an oscillator, and oscillated at 300 r / min for 60 min, and the extract is distilled to remove the acetone to obtain a first additive crude extract, and finally the supernatant is removed and dried to obtain a purified first additive; the extraction temperature is 45° C., the extraction time is 4 h, and the distillation is carried out at 80° C. by reduced pressure distillation; (4) Purification of the second additive: The second additive is purified by using a sublimation purification device: (a) adding molten salt into the heating chamber through the feed port, wherein the molten salt is a mixture of sodium nitrite and potassium nitrite of equal mass, and heating the molten salt by using a first molten salt heating rod and a second molten salt heating rod to make the temperature reach 250° C.; (b) The second additive is loaded into a sublimation loading boat, silica gel is spread on the second additive, and then placed in a cylindrical tube. After closing the end door, the vacuum degree is evacuated to 0.08 KPa by a vacuum pump through a vacuum cooling tube, and the purification of the second additive is completed after 15 hours; (5) Under a dry environment with a relative humidity of ≤0.5-1%, weigh the purified first additive obtained in step (3) and the purified second additive obtained in step (4), and then add them to the thionyl chloride solution of the electrolyte salt obtained in step (2), and stir continuously until they are completely dissolved to obtain a lithium thionyl chloride battery electrolyte.

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