An electrolyte for a lithium / thionyl chloride battery

Abstract

The present invention discloses a lithium thionyl chloride battery electrolyte. The electrolyte comprises thionyl chloride, an electrolyte salt, and additives. The additives include a first additive and a second additive. The preparation method is as follows: distill thionyl chloride and collect the distillate; weigh the electrolyte salt and dissolve it in the thionyl chloride distillate; purify the first additive; purify the second additive; weigh the purified first additive and the purified second additive, and add them to the 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 present invention act synergistically, enabling the lithium / thionyl chloride battery to achieve good discharge voltage and discharge capacity, significantly improving the voltage hysteresis phenomenon of the lithium / thionyl chloride battery, and the lithium thionyl chloride battery prepared from this electrolyte has good cycle performance and high safety.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and specifically to an electrolyte for a lithium thionyl chloride battery. Background Art

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

[0003] In order to eliminate the voltage hysteresis phenomenon of the lithium / thionyl chloride battery, most methods are to improve the current collection form of the cathode and anode, or improve the impurity content and molar concentration of the electrolyte to reduce the internal resistance of the battery; install electronic components inside or outside the battery to make the battery in a weak discharge state to weaken the formation of the passivation film; add metal phthalocyanine compounds or sulfides to the cathode and electrolyte to improve the voltage hysteresis performance. Some of the above methods can improve certain performances of the lithium / thionyl chloride battery to a certain extent, but some of them weaken some other performances of the lithium / thionyl chloride battery at the cost of "sacrificing" the capacity of the lithium / thionyl chloride battery.

[0004] The electrolyte is one of the three elements constituting the lithium thionyl chloride battery, and its physical and chemical properties play a crucial role in the performance of battery materials. Developing an electrolyte material that matches the cathode and anode materials is of great significance. Summary of the Invention

[0005] The purpose of the present invention is to provide an electrolyte for a lithium thionyl chloride battery and its preparation method to solve the problems in the prior art.

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

[0007] A lithium thionyl chloride battery electrolyte includes thionyl chloride, an electrolyte salt, and an additive. The molar concentration of the electrolyte salt in the thionyl chloride solution 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 addition amount of the additive is too small, it cannot reduce the phenomenon of battery voltage hysteresis. If the addition amount of the additive is too large, it will affect the specific capacity of the material and cause waste, and still cannot reduce the phenomenon of battery voltage hysteresis.

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

[0009] ;

[0010] Wherein, X is a halogen; R1 is a nitrile group, an amino group, a hydroxyl group, or a nitro group; R2 and R3 are both hydrogen, a mono-substituted or multi-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 multi-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 all C1-C10 alkyl groups, halogenated C1-C10 alkyl groups, C1-C10 alkoxy groups, or halogenated C1-C10 alkoxy groups; R 41 is a heterocyclic group that is unsubstituted or substituted by a C1-C6 alkyl group, and the heterocycle contains one or more of the elements O, N, and S.

[0014] As an optimization, the electrolyte salt is one or more of lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, lithium trifluoromethanesulfonate, lithium tris(trifluoromethylsulfonyl)methyl, lithium hexafluorophosphate, lithium trioxalato phosphate, lithium difluorodioxalato phosphate, and lithium tetrafluoroxalato phosphate. The main drawback of the Li / SOCl2 battery is its voltage hysteresis phenomenon, which is particularly severe when the battery is stored at high temperature and then used at room temperature. The main reason for the voltage hysteresis of the Li / SOCl2 battery is the use of lithium tetrachloroaluminate (LiAlCl4) electrolyte salt in the battery system. The electrolyte solution containing this salt undergoes a spontaneous chemical reaction with the lithium anode, and the product is LiCl. LiCl covers the surface of the lithium anode in the form of a thin film, preventing the contact between lithium and the electrolyte solution, and ultimately leading to voltage hysteresis. The present invention uses the above electrolyte salts to replace lithium tetrachloroaluminate (LiAlCl4) electrolyte salt to prepare a lithium thionyl chloride battery electrolyte, which can effectively reduce the phenomenon of battery voltage hysteresis.

[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 preparation method of a lithium thionyl chloride battery electrolyte, the preparation method comprising the following steps:

[0017] (1) Distill thionyl chloride and collect the distillate;

[0018] (2) Weigh the electrolyte salt and place it in the thionyl chloride distillate obtained in step (1), make up the volume to obtain a thionyl chloride solution of the electrolyte salt;

[0019] (3) Purification of the first additive: Extract the first additive with acetone to obtain an extraction solution of the first additive, then distill the extraction solution to obtain the first additive, and dry it to obtain the purified first additive;

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

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

[0022] (b) Load the second additive into the sublimation loading boat, spread silica gel on the second additive, then place it in a cylindrical tube, close the end door and evacuate it with a vacuum pump through a vacuum cooling tube. After a period of time, the purification of the second additive is completed;

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

[0024] As an optimization, a preparation method of a lithium thionyl chloride battery electrolyte, the preparation method comprising the following steps:

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

[0026] (2) Weigh the electrolyte salt, and under an inert atmosphere condition, dissolve the above-mentioned electrolyte salt in the thionyl chloride distillate obtained in step (1), make up the volume to obtain a thionyl chloride solution of the electrolyte salt with a molar concentration of 0.1 - 1 mol / L;

[0027] (3)Purification of the first additive: The first additive is extracted with acetone to obtain an extraction solution of the first additive. Then, the extraction solution is distilled to obtain the first additive, and the purified first additive is obtained after drying. The extraction temperature is 30 - 45°C, and the extraction time is 1 - 4 h. The distillation is carried out by vacuum distillation at 40 - 80°C.

[0028] (4)Purification of the second additive: The purification of the second additive is carried out using a sublimation purification device. The process flow of this purification method is short, the operation is simple, and the purity of the purified second additive is greater than 99%.

[0029] (a)The molten salt is added into the heating chamber through the feed port, and the molten salt is heated by 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 the sublimation loading boat, silica gel is spread on the second additive, and then it is placed in a cylindrical tube. After closing the end door, the vacuum is pumped to 0.03 - 0.08 KPa through the vacuum cooling tube by a vacuum pump, and the purification of the second additive is completed after 6 - 15 h. The silica gel mainly plays a role in decolorization.

[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 continuously stir until completely dissolved to obtain the lithium thionyl chloride battery electrolyte.

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

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

[0034] As an optimization, before distillation in step (3), the extraction solution is transferred to a shaker and shaken at 100 - 300 r / min for 30 - 60 min. The purpose of shaking is to make the first additive mix more evenly with acetone.

[0035] As an optimization, steps (1), (2), and (3) are all carried out in a dry environment with a relative humidity ≤ 0.5 - 1%. The reaction between the lithium thionyl chloride battery electrolyte and water is very intense. Even a very small amount of water is likely to react with it, generating HCl gas and causing serious corrosion. Therefore, experimental operations should be carried out in a dry environment when preparing the electrolyte.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] First, the synergistic effect of the first additive and the second additive in the electrolyte of the lithium thionyl chloride battery of the present invention has good characteristics of resisting passivation by thionyl chloride. Through the action of thionyl chloride, the cathode active material in the lithium / thionyl chloride battery, the formation of the "passivation film" on the surface of the lithium metal anode is inhibited, enabling the lithium / thionyl chloride battery to achieve good discharge voltage and discharge capacity, and significantly improving the voltage hysteresis phenomenon of the lithium / thionyl chloride battery.

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

[0039] Third, the preparation method of the electrolyte of the lithium thionyl chloride battery of the present invention is simple, easy to operate, scientifically formulated, low in raw material cost, strong in practicability, and has a wide application prospect.

[0040] Fourth, in the preparation method of the electrolyte of the lithium thionyl chloride battery of the present invention, thionyl chloride is distilled, and the first additive and the second additive are purified, so that the prepared electrolyte of the lithium thionyl chloride battery has less impurity content and more excellent electrolyte performance. Detailed Embodiments

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0042] Example 1:

[0043] A lithium thionyl chloride battery electrolyte includes thionyl chloride, lithium bis(fluorosulfonyl)imide and additives. The molar concentration of the thionyl chloride solution of the electrolyte salt is 0.1 mol / L, and the mass of the additives is 0.01% of the total mass of the electrolyte. The additives include 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] Among them, X is Cl; R1 is a nitrile group; both R2 and R3 are hydrogen; R4 is a methyl group.

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

[0048] ;

[0049] Among them, X1 is Cl; R 11 、R 21 、R 31 are all methyl groups; R 41 is a pyrrole heterocyclic group.

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

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

[0052] (2) In a dry environment with a relative humidity ≤ 0.5%, weigh the electrolyte salt, and under an inert atmosphere condition, dissolve the above electrolyte salt in the thionyl chloride fraction prepared in step (1), and make up 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: Use acetone to leach the first additive to obtain a first additive leaching solution, transfer the leaching solution to a shaker, shake it at 100 r / min for 30 min, then distill the leaching solution to remove acetone to obtain a first additive crude extract, and finally remove the supernatant and dry it to obtain the purified first additive; the leaching temperature is 30 °C, the leaching time is 1 h, and the distillation is carried out by vacuum distillation at 40 °C;

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

[0055] (a) Add the molten salt into the heating chamber through the feed port. The molten salt is a mixture of sodium nitrite and potassium nitrite with equal mass. Use the first molten salt heating rod and the second molten salt heating rod to heat the molten salt to make the temperature reach 200 °C;

[0056] (b) Load the second additive into the sublimation loading boat, spread silica gel on the second additive, then put it into a cylindrical tube, close the end door, and use a vacuum cooling tube to pump the vacuum degree to 0.03 KPa by a vacuum pump, and complete the purification of the second additive after 6 h;

[0057] (5) In a dry environment with a relative humidity ≤ 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 continuously stir until completely dissolved to obtain the electrolyte solution of the lithium thionyl chloride battery.

[0058] Example 2:

[0059] An electrolyte solution for a lithium thionyl chloride battery, comprising thionyl chloride, lithium bis(oxalato)borate, and an additive. The molar concentration of the thionyl chloride solution of the electrolyte salt is 0.4 mol / L, and the mass of the additive is 0.1% of the total mass of the electrolyte solution. The additive includes a first additive and a second additive, wherein the mass of the first additive is 0.05% of the total mass of the electrolyte solution, and the mass of the second additive is 0.05% of the total mass of the electrolyte solution.

[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; 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 are both chloromethyl groups; R 41 is a furan heterocyclic group.

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

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

[0068] (2) In a dry environment with a relative humidity ≤ 0.6%, weigh the electrolyte salt, and under an inert atmosphere condition, dissolve the above-mentioned electrolyte salt in the thionyl chloride fraction prepared in step (1), and make up 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 was extracted with acetone to obtain an extraction solution of the first additive. The extraction solution was transferred to a shaker and shaken at 150 r / min for 35 min. Then, the extraction solution was distilled to remove acetone, obtaining a crude extract of the first additive. Finally, the supernatant was removed and dried to obtain the purified first additive; the extraction temperature was 32 °C, the extraction time was 1.5 h, and the distillation was carried out by vacuum distillation at 50 °C;

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

[0071] (a)The molten salt was added to the heating chamber through the feed port. The molten salt was a mixture of sodium nitrite and potassium nitrite with equal masses. The first molten salt heating rod and the second molten salt heating rod were used to heat the molten salt to a temperature of 210 °C;

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

[0073] (5)In a dry environment with a relative humidity ≤ 0.6%, the purified first additive obtained in step (3) and the purified second additive obtained in step (4) were weighed, and then added to the thionyl chloride solution of the electrolyte salt obtained in step (2), and continuously stirred until completely dissolved, obtaining the electrolyte solution of the lithium thionyl chloride battery.

[0074] Example 3:

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

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

[0077] ;

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

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

[0080] ;

[0081] Wherein, X1 is I; R11 and R 21 and R 31 are both methoxy groups; R 41 is a thiophene heterocyclic group.

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

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

[0084] (2) In a dry environment with a relative humidity ≤ 0.7%, weigh the electrolyte salt, and under an inert atmosphere condition, dissolve the above electrolyte salt in the thionyl chloride fraction prepared in step (1), make up 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: Extract the first additive with acetone to obtain an extraction solution of the first additive. Transfer the extraction solution to a shaker, shake it at 200 r / min for 40 min, then distill the extraction solution to remove acetone to obtain a crude extract of the first additive. Finally, remove the supernatant and dry it to obtain the purified first additive; the extraction temperature is 34 °C, the extraction time is 2 h, and the distillation is carried out by vacuum distillation at 60 °C;

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

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

[0088] (b) Load the second additive into the sublimation loading boat, spread silica gel on the second additive, then place it in a cylindrical tube. After closing the end door, use a vacuum cooling tube to evacuate the vacuum degree to 0.05 KPa by a vacuum pump, and complete the purification of the second additive after 10 h;

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

[0090] Example 4:

[0091] A lithium thionyl chloride battery electrolyte, comprising thionyl chloride, lithium tris(trifluoromethanesulfonyl)methide, lithium hexafluorophosphate and an additive. The molar concentration of the electrolyte salt in the thionyl chloride solution is 0.8 mol / L. The mass of the additive is 0.4% of the total mass of the electrolyte. The additive includes 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; R4 is propyl.

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

[0096] ;

[0097] Wherein, X1 is F; R 11 , R 21 , R 31 are all chloromethoxy; R 41 is 3-methylpyridine heterocyclic group.

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

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

[0100] (2) In a dry environment with a relative humidity ≤ 0.8%, weigh the electrolyte salt, and under an inert atmosphere condition, dissolve the above electrolyte salt in the thionyl chloride fraction prepared in step (1), and make up 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: Extract the first additive with acetone to obtain a first additive extract. Transfer the extract to a shaker, shake at 250 r / min for 50 min, then distill the extract to remove acetone to obtain a first additive crude extract, and finally remove the supernatant and dry to obtain the purified first additive; The extraction temperature is 40 °C, the extraction time is 3 h, and the distillation is carried out by vacuum distillation at 70 °C;

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

[0103] (a) Add molten salt into the heating chamber through the feeding port. The molten salt is a mixture of sodium nitrite and potassium nitrite with equal mass. Use the first molten salt heating rod and the second molten salt heating rod to heat the molten salt until the temperature reaches 240 °C.

[0104] (b) Load the second additive into the sublimation loading boat, spread silica gel on the second additive, then place it into the cylindrical tube. After closing the end door, evacuate to a vacuum degree of 0.07 KPa through the vacuum cooling tube by a vacuum pump, and complete the purification of the second additive after 12 h.

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

[0106] Example 5:

[0107] A lithium thionyl chloride battery electrolyte includes thionyl chloride, lithium tris(oxalato)phosphate, lithium difluoro(oxalato)phosphate and additives. The molar concentration of the thionyl chloride solution of the electrolyte salt is 1 mol / L, the mass of the additives is 0.5% of the total mass of the electrolyte, the additives include 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] Among them, X is Cl; R1 is an amino group; R2 and R3 are both tolyl groups; R4 is a chloroethyl group.

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

[0112] ;

[0113] Among them, X1 is Cl; R 11 , R 21 , R 31 are all chloropropyl groups; R 41 is a 2-chlorofuran heterocyclic group.

[0114] A preparation method of a lithium thionyl chloride battery electrolyte, the preparation method includes the following steps:

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

[0116] (2) In a dry environment with a relative humidity ≤ 1%, weigh the electrolyte salt. Under an inert atmosphere condition, dissolve the above-mentioned electrolyte salt in the thionyl chloride fraction prepared in step (1), and make up 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: Extract the first additive with acetone to obtain an extraction solution of the first additive. Transfer the extraction solution into a shaker, shake it at 300 r / min for 60 min, then distill the extraction solution to remove acetone to obtain a crude extract of the first additive. Finally, remove the supernatant and dry it to obtain the purified first additive; the extraction temperature is 45 °C, the extraction time is 4 h, and the distillation is carried out by vacuum distillation at 80 °C;

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

[0119] (a) Add the molten salt into the heating chamber through the feed port. The molten salt is a mixture of sodium nitrite and potassium nitrite with equal mass. Use the first molten salt heating rod and the second molten salt heating rod to heat the molten salt to make the temperature reach 250 °C;

[0120] (b) Load the second additive into the sublimation loading boat, spread silica gel on the second additive, then put it into the cylindrical tube. After closing the end door, evacuate the vacuum degree to 0.08 KPa through the vacuum cooling tube by a vacuum pump, and complete the purification of the second additive after 15 h;

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

[0122] Comparative example:

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

[0124] Example of effect:

[0125] Fabricate a lithium / thionyl chloride battery:

[0126] At room temperature, the graphite positive electrode material, conductive agent carbon black (SP), and binder polyvinylidene fluoride (PVDF) were homogenized in a ratio of 8:1:1. The solvent was N-methyl-2-pyrrolidone (NMP), and the solid content was 25%. It was uniformly coated on an aluminum foil with a thickness of 0.02 mm, and after drying, rolling, and slicing, a carbon positive electrode sheet was made;

[0127] The positive electrode uniformly used the carbon positive electrode sheet, the negative electrode used a metallic lithium electrode, and the lithium / thionyl chloride battery electrolytes prepared in Examples 1 to 5 of the present invention and the electrolytes in the comparative examples were used in turn to fabricate lithium / thionyl chloride batteries. The batteries were cycled 200 times at a rate of 0.05C at 3.87V, and the charge-discharge tests of the batteries were carried out. The test results are shown in Table 1. At any rate between 0.025C and 2C, the charge-discharge tests of the batteries were carried out, and the test results are shown in Table 2.

[0128] Table 1 Test results of charge-discharge performance of the battery

[0129]

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

[0131] Table 2 Test results of charge-discharge performance of the battery at different rates

[0132]

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

[0134] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention.

Claims

1. A lithium thionyl chloride battery electrolyte, comprising thionyl chloride, lithium bis(oxalato)borate and additives. The molar concentration of the thionyl chloride solution of the electrolyte salt is 0.4 mol / L, and the mass of the additives is 0.1% of the total mass of the electrolyte. The additives include 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; The structural formula of the first additive is: ； Among them, X is Br; R1 is an amino group; R2 and R3 are both chloromethyl groups; R4 is an ethyl group; The structural formula of the second additive is: ； Among them, X1 is Br; R 11 , R 21 , R 31 are all chloromethyl groups; R 41 is a furan 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 ≤ 0.6%, place thionyl chloride in a flask, heat it for distillation, and collect the fraction at 72 °C; (2) In a dry environment with a relative humidity ≤ 0.6%, weigh the electrolyte salt. Under an inert atmosphere, dissolve the above electrolyte salt in the thionyl chloride fraction prepared in step (1), and make up the volume to obtain a thionyl chloride solution of the electrolyte salt with a molar concentration of 0.4 mol / L; (3) Purification of the first additive: Extract the first additive with acetone to obtain an extraction solution of the first additive. Transfer the extraction solution to a shaker, shake it at 150 r / min for 35 min, then distill the extraction solution to remove acetone to obtain a crude extract of the first additive. Finally, remove the supernatant and dry it to obtain the purified first additive; the extraction temperature is 32 °C, the extraction time is 1.5 h, and the distillation is carried out by vacuum distillation at 50 °C; (4) Purification of the second additive: The purification of the second additive is carried out using a sublimation purification device: (a) Add the molten salt into the heating chamber through the feed port. The molten salt is a mixture of sodium nitrite and potassium nitrite with equal mass. Heat the molten salt using the first molten salt heating rod and the second molten salt heating rod to make the temperature reach 210 °C; (b) Load the second additive into the sublimation loading boat, spread silica gel on the second additive, then place it in a cylindrical tube. After closing the end door, evacuate the vacuum to 0.04 KPa through the vacuum cooling tube by a vacuum pump, and complete the purification of the second additive after 8 h; (5) In a dry environment with a relative humidity ≤ 0.6%, weigh the purified first additive obtained in step (3) and the purified second additive obtained in step (4), then add them to the thionyl chloride solution of the electrolyte salt obtained in step (2), and continuously stir until completely dissolved to obtain the lithium thionyl chloride battery electrolyte.

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