Electrolyte additive capable of improving flame retardance and application of electrolyte additive in sodium-ion battery

Abstract

The invention discloses an electrolyte additive capable of improving flame retardance and application of the electrolyte additive in a sodium-ion battery, and relates to the technical field of sodium-ion batteries. The method comprises the following specific steps: preparing a traditional electrolyte with a sodium salt concentration of 0.8-1.2 M, selecting two or more than two of electrolytes EC, PC and EMC for preparation, and naming the traditional electrolyte as a basic electrolyte; an additive A and an additive B with different concentrations are added into a basic electrolyte to serve as electrolyte additives, and the sodium-ion battery electrolyte containing the additives with different concentrations is prepared. The electrochemical performance, the safety and the thermal stability of the sodium ion battery are effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of sodium ion batteries, in particular to an improved flame retardant electrolyte additive and application thereof in sodium ion batteries. Background Art

[0002] Sodium-ion batteries are considered to be a promising next-generation low-cost power system, but they use a flammable organic solvent system and are prone to combustion and explosion under conditions of abuse. To solve this problem, we have developed a new type of non-flammable sodium battery electrolyte. By adding a highly efficient phosphazene flame retardant to conventional sodium batteries, the sodium battery electrolyte becomes non-flammable. This flame retardant can also improve the electrochemical performance and safety of the sodium manganate positive electrode and hard carbon negative electrode of the sodium battery.

[0003] As we all know, battery safety is the premise of battery research and development, and the following situations often cause safety problems of lithium / sodium ion batteries: (1) During the cycle of ion batteries, dendrites often grow, which then penetrate the diaphragm and cause safety problems; (2) Metal lithium / sodium is not only active but also has a low melting point (the melting point of lithium is 187°C and the melting point of sodium is 97.7°C). With the occurrence of thermal runaway effect, the temperature of the battery system rises, the metal melts, and safety problems arise; (3) Battery operation is often accompanied by energy conversion (chemical energy and electrical energy) and heat generation, which causes the ambient temperature to rise. As for liquid electrolytes, they generally have the disadvantages of being volatile, having a low flash point, and being easy to leak. When the temperature reaches a certain level, it is easy to cause safety problems such as battery combustion and explosion. In order to solve these safety problems, people have taken some measures: (1) adding film-forming additives to promote the formation of SEI and CEI films and inhibit the growth of lithium / sodium dendrites; (2) replacing the leaky liquid electrolyte with a solid electrolyte or gel polymer electrolyte; (3) adding flame retardant additives to enhance the flame retardant properties of the battery.

[0004] As the main component of the battery's internal circulation, the electrolyte plays an important role in conducting ions and participating in the redox reaction on the positive and negative electrode surfaces. At present, the most commonly used electrolyte for sodium-ion batteries is ester organic electrolyte. Because it contains a large amount of organic flammable solvents, it will explode when the battery has thermal runaway, which brings great safety hazards to the battery. Compared with lithium, sodium has higher reactivity, and safety is more important for sodium-ion batteries. In addition, the operation of the battery is a delicate system process, and its safety depends not only on the electrolyte itself, but also on the compatibility between electrode materials. Good interface stability is conducive to preventing side reactions between electrolytes and electrodes, ensuring the normal progress of the entire charging and discharging process.

[0005] Flame retardant additives can increase the flash point of the original electrolyte and inhibit the spread of fire. They are generally divided into inorganic / organic flame retardant additives. Inorganic flame retardants have the characteristics of high ion conductivity, non-flammability, and high transmission capacity for lithium / sodium ions. Organic flame retardant additives have the advantages of suitable physical properties, good compatibility, and a wide variety of types and low cost. Among them, phosphorus / phosphonate compounds are the most effective and commonly used type of organic flame retardant additives, which can effectively play a flame retardant effect in ion batteries. Summary of the invention

[0006] The present invention provides a method for delaying the initial combustion time of a battery, reducing the self-extinguishing time and the heat release. First, a phosphorus-based flame retardant is used as an additive, and the phosphorus-based condensed phase flame retardant achieves a flame retardant effect by delaying or preventing the thermal decomposition of the polymer in the condensed phase. When the flame retardant material burns, the phosphorus-based flame retardant is thermally decomposed to generate phosphoric acid, metaphosphoric acid, pyrophosphoric acid, polyphosphoric acid and other substances, which promote the dehydration and carbonization of the combustibles and adhere to the surface of the material to form a protective layer; at the same time, the phosphorus-rich glassy substance generated by its thermal decomposition covers the surface of the residual carbon, which can isolate the air and improve the density of the residual carbon surface. The residual carbon layer has poor thermal conductivity. While hindering the release of combustible gases, it can weaken the heat feedback intensity of the flame to the substrate, thereby achieving the purpose of flame retardancy.

[0007] The specific operation includes the following steps:

[0008] An improved flame retardant electrolyte additive and its application in a sodium ion battery, characterized in that the electrolyte comprises: sodium salt, electrolyte, additive A and additive B.

[0009] Furthermore, the additive A includes at least one of triphenyl phosphate (TPP) and resorcinol bis(diphenyl phosphate) (RDP) compounds having a structure shown in Formula 1.

[0010]

[0011] Furthermore, the preparation steps of the additive B are as follows:

[0012] a) mixing 0.06-0.5 parts of biphenyl-4,4'-dithiol, 2-5 parts of maleimidoferrocene, CAS: 96483-68-0, and 2-5 parts of dimethylamine in 220-400 parts of toluene by weight, and reacting at a temperature range of 60 to 70° C. and at normal pressure for 80-160 minutes;

[0013] b) then adding 25-50 parts of diphenyl aminophosphorate, reacting at a temperature range of 60 to 70° C. under normal pressure for 60 to 120 minutes, and after the reaction is completed, removing the toluene solvent by reduced pressure distillation to obtain additive B.

[0014] Furthermore, the total amount of the sodium salt, additive A and additive B is 1-20 wt % based on the total mass of the electrolyte.

[0015] Furthermore, the sodium salt is sodium hexafluorophosphate (NaPF6) or sodium perchlorate (NaClO4), and the concentration of the sodium salt is 0.8-1.2M.

[0016] Furthermore, the electrolyte is two or more of ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC).

[0017] Furthermore, the positive electrode of the sodium ion battery is a sodium manganate positive electrode.

[0018] Furthermore, the negative electrode of the sodium ion battery is hard carbon (HC).

[0019] Furthermore, the preparation method of the electrolyte is:

[0020] (1) preparing a conventional electrolyte with a sodium salt concentration of 0.8-1.2 M, selecting two or more of the electrolytes EC, PC, and EMC for preparation, and naming it as a basic electrolyte;

[0021] (2) Additive A and additive B of different concentrations were added to the basic electrolyte as electrolyte additives to prepare sodium ion battery electrolytes containing additives of different concentrations.

[0022] The present invention provides a sodium ion battery electrolyte with improved first-cycle coulombic efficiency, which is prepared by the above-mentioned preparation method.

[0023] The reaction mechanism of the additive B provided by the present invention is:

[0024] Under the influence of light or heat, the sulfhydryl group (-SH) of biphenyl-4,4'-dithiol can be homolytically split to form sulfhydryl radicals (S·). These radicals are highly reactive and can initiate subsequent chain reactions. In the reaction between diphenylphosphoamidate and maleimidoferrocene, the amino group acts as a nucleophilic group to attack the β carbon (i.e., on the side of the >C=C< double bond) in the maleimide molecule, resulting in a Michael-type addition. This addition mode allows the nitrogen atom with a higher electron density to be added to the relatively electron-deficient double bond, initiating the growth of the polymerization chain. In the sulfhydryl-ene addition process, the newly generated carbon-centered radical can continue to react with the sulfhydryl groups in other biphenyl-4,4'-dithiol molecules to form stable products.

[0025] The technical effects of the additive B provided by the present invention are:

[0026] 1. Improvement of flame retardant performance

[0027] Due to the presence of phosphate groups, the compound can quickly form a protective barrier under high temperature conditions, isolating oxygen and combustion sources, thereby significantly slowing down the burning rate of the material. When heated, phosphate esters will decompose to produce phosphoric acid, which further promotes the formation of a carbonized layer on the surface of the material, enhancing the flame retardant effect.

[0028] 2. Enhanced thermal stability and mechanical strength

[0029] The introduction of biphenyl and ferrocene groups not only increases the molecular weight and structural complexity of the material, but also provides additional thermal stability and mechanical strength. The rigid structure of the biphenyl group and the unique electronic properties of ferrocene work together to improve the material's high temperature resistance and mechanical properties.

[0030] 3. Improved security

[0031] In lithium battery applications, using diphenyl phosphate containing ferrocene and biphenyl as an electrolyte additive can effectively reduce the risk of fire when the battery overheats and improve the safety performance of the battery. This material can respond quickly when the battery is abnormal, inhibit or delay the spread of fire, and provide additional protection for system safety.

[0032] Technical effects:

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The present invention provides a method for improving battery safety. By optimizing the proportion of additives in the electrolyte, the combustion of the battery caused by short circuit and other reasons is suppressed, the self-extinguishing time is reduced, and the electrochemical cycle stability and safety are improved. A phosphorus-based condensed phase flame retardant is used as an electrolyte additive. The flame retardant achieves a flame retardant effect by delaying or preventing the thermal decomposition of the polymer in the condensed phase. When the flame retardant material burns, phosphoric acid, metaphosphoric acid, pyrophosphoric acid, polyphosphoric acid and other substances generated by the phosphorus-based flame retardant under thermal decomposition promote the dehydration and carbonization of the combustible material, adhere to the surface of the material, and form a protective layer; at the same time, the phosphorus-rich glassy substance generated by its thermal decomposition covers the surface of the residual carbon, which can isolate the air and improve the density of the residual carbon surface. The residual carbon layer has poor thermal conductivity. While hindering the release of combustible gases, it can weaken the heat feedback intensity of the flame to the substrate, thereby achieving the purpose of flame retardancy. Ultimately, the electrochemical performance and safety of the sodium ion battery are improved.

[0035] (2) The preparation process provided by the present invention is relatively simple, the dosage is small, and the overall performance of the sodium ion battery is improved with a small amount of additives. The product performance is relatively good and has certain competitive advantages. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with specific embodiments. The following embodiments are only used to illustrate the present invention and are not intended to limit the scope of application of the present invention. Without departing from the spirit and essence of the present invention, modifications or replacements made to the inventive method, steps or conditions all belong to the scope of the present invention.

[0037] Test Example 1: Electrochemical Performance Test

[0038] Battery assembly: The positive electrode materials of Examples 1-4 and Comparative Examples 1-2 are all sodium manganate positive electrodes, the conductive material is CNT, and the binder is PVDF; they are weighed according to a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) is added to make a viscous glue, which is coated on aluminum foil and baked in a vacuum drying oven at 120°C for 12 hours to obtain a positive electrode sheet.

[0039] Hard carbon negative electrode material is used as the active material, and the mass ratio of active material: ultrafine carbon powder (SP): polyvinylidene fluoride is 90:5:5. N-methylpyrrolidone (NMP) is added to make a viscous glue, which is coated on aluminum foil and baked in a vacuum drying oven at 120°C for 12 hours to obtain a negative electrode sheet.

[0040] PE film is used as separator.

[0041] The layered oxide sodium manganate cathode-HC battery was tested in the voltage range of 2.0V-3.9V, first discharged at a rate of 0.1C to a voltage of 2.0V, and then charged at 0.1C to 3.9V.

[0042] Test Example 2: Self-extinguishing time test

[0043] The fully discharged sodium manganate positive electrode-HC battery was disassembled in a glove box, and the sodium manganate positive electrode and HC negative electrode were prepared respectively. They were then taken out and ignited immediately, and the combustion time was recorded.

[0044] Test Example 3: Thermal Stability Test

[0045] The fully discharged sodium manganate positive electrode-HC battery was disassembled in a glove box to obtain the sodium manganate positive electrode and HC negative electrode. Then the sodium manganate positive electrode, HC negative electrode, TPP-containing electrolyte, RDP-containing electrolyte and two groups of basic electrolytes were taken out and immediately subjected to DSC testing with a test temperature range of -50-400°C and a heating rate of 5°C / s. The exothermic energy was observed.

[0046] Example 1

[0047] The present invention provides a method for improving a flame retardant electrolyte additive, comprising the following components:

[0048] This embodiment provides a sodium ion battery electrolyte, the formula of which is: 20g ethylene carbonate (EC) solvent, 20g propylene carbonate (PC) solvent, 20g ethyl methyl carbonate (EMC), and 10.08g sodium hexafluorophosphate. Then, different contents of additives TPP and additive B are prepared according to Table 1. The raw materials are mixed evenly to prepare an electrolyte.

[0049] The preparation steps of the additive B are as follows:

[0050] a) 0.06 g of biphenyl-4,4'-dithiol, 2 g of maleimidoferrocene, CAS: 96483-68-0, and 2 g of dimethylamine were mixed in 220 g of toluene and reacted at 60° C. and normal pressure for 160 minutes;

[0051] b) then adding 25 g of diphenyl aminophosphorate, reacting at a temperature of 60° C. and normal pressure for 120 minutes. After the reaction is completed, removing the toluene solvent by reduced pressure distillation to obtain additive B.

[0052] Table 1

[0053]

[0054]

[0055] Test results:

[0056]

[0057] Example 2

[0058] The present invention provides a method for improving a flame retardant electrolyte additive, comprising the following components:

[0059] This embodiment provides a sodium ion battery electrolyte, the formula of which is: 20g propylene carbonate (PC) solvent, 20g ethyl methyl carbonate (EMC), 10.08g sodium hexafluorophosphate. Then, different contents of additives TPP and additive B are prepared according to Table 2. The raw materials are mixed evenly to prepare the electrolyte.

[0060] The preparation steps of the additive B are as follows:

[0061] a) 0.2 g of biphenyl-4,4'-dithiol, 3 g of maleimidoferrocene, CAS: 96483-68-0, and 3 g of dimethylamine were mixed in 280 g of toluene and reacted at 65° C. and normal pressure for 120 minutes;

[0062] b) then adding 35 g of diphenyl aminophosphorate, reacting at a temperature of 65° C. and normal pressure for 100 minutes. After the reaction is completed, removing the toluene solvent by reduced pressure distillation to obtain additive B.

[0063] Table 2

[0064] Recipe Name Propylene carbonate Ethyl methyl carbonate <![CDATA[NaPF6]]> TPP Additive B Recipe 1 30g 30g 10.08g 3ml 0.2g Recipe 2 30g 30g 10.08g 6ml 0.4g Recipe 3 30g 30g 10.08g 9ml 0.6g Recipe 4 30g 30g 10.08g 12ml 0.8g

[0065] Test results:

[0066]

[0067] Example 3

[0068] The present invention provides a method for improving a flame retardant electrolyte additive, comprising the following components:

[0069] This embodiment provides a sodium ion battery electrolyte, the formula of which is: 20g propylene carbonate (PC) solvent, 20g ethyl methyl carbonate (EMC), 10.08g sodium hexafluorophosphate. Then, different contents of additives RDP and additive B are prepared according to Table 3. The raw materials are mixed evenly to prepare the electrolyte.

[0070] The preparation steps of the additive B are as follows:

[0071] a) 0.35 g of biphenyl-4,4'-dithiol, 4 g of maleimidoferrocene, CAS: 96483-68-0, and 4 g of dimethylamine were mixed in 350 g of toluene and reacted at 65° C. and normal pressure for 100 minutes;

[0072] b) then adding 45 g of diphenyl aminophosphorate, reacting at a temperature of 65° C. and normal pressure for 80 minutes. After the reaction is completed, removing the toluene solvent by reduced pressure distillation to obtain additive B.

[0073] Table 3

[0074] Recipe Name Propylene carbonate Ethyl methyl carbonate <![CDATA[NaPF6]]> RDP Additive B Recipe 1 30g 30g 10.08g 3ml 0.2g Recipe 2 30g 30g 10.08g 6ml 0.4g Recipe 3 30g 30g 10.08g 9ml 0.6g Recipe 4 30g 30g 10.08g 12ml 0.8g

[0075] Test results:

[0076]

[0077]

[0078] Example 4

[0079] The present invention provides a method for improving a flame retardant electrolyte additive, comprising the following components:

[0080] This embodiment provides a sodium ion battery electrolyte, the formula of which is: 20g ethylene carbonate (EC) solvent, 20g propylene carbonate (PC) solvent, 20g ethyl methyl carbonate (EMC), and 10.08g sodium hexafluorophosphate. Then, different contents of additives RDP and additive B are prepared according to Table 4. The raw materials are mixed evenly to prepare an electrolyte.

[0081] The preparation steps of the additive B are as follows:

[0082] a) 0.5 g of biphenyl-4,4'-dithiol, 5 g of maleimidoferrocene, CAS: 96483-68-0, and 5 g of dimethylamine were mixed in 400 g of toluene and reacted at a temperature range of 70° C. and normal pressure for 160 minutes;

[0083] b) then adding 50 g of diphenyl aminophosphorate, reacting at a temperature of 70° C. and normal pressure for 120 minutes, and after the reaction is completed, removing the toluene solvent by reduced pressure distillation to obtain additive B.

[0084] Table 4

[0085] Recipe Name Propylene carbonate Ethyl methyl carbonate Ethylene carbonate <![CDATA[NaPF6]]> RDP Additive B Recipe 1 20g 20g 20g 10.08g 3ml 0.2g Recipe 2 20g 20g 20g 10.08g 6ml 0.4g Recipe 3 20g 20g 20g 10.08g 9ml 0.6g Recipe 4 20g 20g 20g 10.08g 12ml 0.8g

[0086] Test results:

[0087]

[0088]

[0089] Comparative Example 1

[0090] The present invention provides a method for improving a flame retardant electrolyte additive, comprising the following components:

[0091] This embodiment provides a sodium ion battery electrolyte, the formula of which is: 20g ethylene carbonate (EC) solvent, 20g propylene carbonate (PC) solvent, 20g ethyl methyl carbonate (EMC), and 10.08g sodium hexafluorophosphate. The raw materials are mixed evenly to prepare the electrolyte.

[0092] Test results:

[0093]

[0094] Comparative Example 2

[0095] The present invention provides a method for improving a flame retardant electrolyte additive, comprising the following components:

[0096] This embodiment provides a sodium ion battery electrolyte, the formula of which is as follows: 20g of propylene carbonate (PC) solvent, 20g of ethyl methyl carbonate (EMC), and 10.08g of sodium hexafluorophosphate. The raw materials are mixed evenly to prepare the electrolyte.

[0097] Test results:

[0098]

[0099] It can be concluded from the test results of the examples that the method effectively improves the electrochemical performance, safety and thermal stability of sodium ion batteries by adding phosphorus-based condensed phase flame retardants to the electrolyte. At the same time, the test results also show that the optimized ratio of the additive has a significant effect on improving the overall battery performance.

[0100] The specific implementation of the present invention is described in detail, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be thought of by a person skilled in the art within the technical scope disclosed by the present invention without creative work should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope defined in the claims.

Claims

1. An improved flame retardant electrolyte additive and its application in sodium ion batteries, characterized in that: The electrolyte comprises: sodium salt, electrolyte, additive A and additive B.

2. According to claim 1, an improved flame retardant electrolyte additive and its use in sodium ion batteries, characterized in that: The additive A includes at least one of triphenyl phosphate (TPP) and resorcinol bis(diphenyl phosphate) (RDP) having a structure shown in Formula 1.

3. The flame retardant electrolyte additive and its application in sodium ion batteries according to claim 1, characterized in that: The preparation steps of the additive B are as follows: a) mixing 0.06-0.5 parts of biphenyl-4,4'-dithiol, 2-5 parts of maleimide ferrocene and 2-5 parts of dimethylamine in 220-400 parts of toluene by weight, and reacting at a temperature range of 60 to 70° C. and normal pressure for 80-160 minutes; b) then adding 25-50 parts of diphenyl aminophosphorate, reacting at a temperature range of 60 to 70° C. under normal pressure for 60 to 120 minutes, and after the reaction is completed, removing the toluene solvent by reduced pressure distillation to obtain additive B.

4. The flame retardant electrolyte additive and its application in sodium ion batteries according to claim 1, characterized in that: The total amount of the sodium salt, additive A and additive B is 1-20 wt % based on the total mass of the electrolyte.

5. The flame retardant electrolyte additive and its application in sodium ion batteries according to claim 1, characterized in that: The sodium salt is sodium hexafluorophosphate (NaPF6) or sodium perchlorate (NaClO4), and the concentration of the sodium salt is 0.8-1.2M.

6. The flame retardant electrolyte additive and its application in sodium ion batteries according to claim 1, characterized in that: The electrolyte is two or more of ethylene carbonate (EC), propylene carbonate (PC) and ethyl methyl carbonate (EMC).

7. The flame retardant electrolyte additive and its application in sodium ion batteries according to claims 1-6, characterized in that: The preparation method of the electrolyte: (1) preparing a conventional electrolyte with a sodium salt concentration of 0.8-1.2 M, selecting two or more of the electrolytes EC, PC, and EMC for preparation, and naming it as a basic electrolyte; (2) Additive A and additive B of different concentrations were added to the basic electrolyte as electrolyte additives to prepare sodium ion battery electrolytes containing additives of different concentrations.

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