Flame-retardant microcapsule, preparation method thereof, and flame-retardant electrolyte

Abstract

The present invention belongs to the field of lithium-ion battery electrolytes and provides a flame-retardant microcapsule comprising a capsule core and a shell layer covering the capsule core; the capsule core is formed by dissolving triphenyl phosphate in toluene; the shell layer comprises a conductive polymer and a thermally responsive polymer; the thermally responsive polymer is a water-soluble polymer, and the melting point of the thermally responsive polymer is 100-200°C; the conductive polymer is a water-soluble conductive polyaniline formed after modification of polyaniline; the weight ratio of the thermally responsive polymer to the conductive polymer satisfies: 1:3-4. The flame-retardant microcapsules of the present application, when added to the electrolyte, can release the flame retardant in time in the event of thermal runaway, avoid battery combustion, and effectively ensure the electrochemical properties of the electrolyte. The present invention also provides a method for preparing the above-mentioned flame-retardant microcapsules and a flame-retardant electrolyte containing the above-mentioned flame-retardant microcapsules.

Description

Technical Field

[0001] The present invention belongs to the field of lithium batteries, and in particular relates to a flame-retardant microcapsule and a preparation method thereof, and a flame-retardant electrolyte. Background Art

[0002] Lithium-ion batteries are the core of the development of new energy vehicles. They are also an indispensable component of electronic devices such as mobile phones, power tools, and digital cameras. Lithium-ion batteries are composed of positive electrode materials, negative electrode materials, electrolytes, diaphragms, conductive agents, binders, and packaging materials. When charging, the positive electrode Li + and Li in the electrolyte + The Li2O3 electrolyte gathers toward the negative electrode, obtains electrons, and is reduced to Li2O3 embedded in the carbon material of the negative electrode. During discharge, the Li2O3 embedded in the carbon material of the negative electrode loses electrons and enters the electrolyte. The Li2O3 electrolyte in the electrolyte + Move to the positive electrode and use chemical reaction to realize the discharge process.

[0003] When lithium-ion batteries are used, extremely high safety requirements are placed on them. However, lithium-ion batteries have poor thermal stability and are prone to thermal runaway under certain conditions. The highly flammable electrolyte is the main cause of thermal runaway in lithium-ion batteries. Therefore, reducing the flammability of the electrolyte is the key to solving the thermal runaway problem of lithium-ion batteries.

[0004] The existing technology mainly adopts the method of adding flame retardants to the electrolyte to achieve the flame retardant effect of the electrolyte. However, many flame retardants are easily co-embedded and reductively decomposed in the graphite negative electrode, affecting its flame retardant stability. At the same time, it is easy to cause the cycle performance of the battery to deteriorate and affect the electrochemical performance of the battery. In order to resolve the contradiction between flame retardant performance and electrochemical performance, researchers have developed "flame retardant microcapsules". By coating a layer of polymer shell on the surface of the flame retardant, the polymer shell melts when the electrolyte temperature rises, and the flame retardant coated inside is released to exert a flame retardant effect. Through the microcapsule structure, the stable presence of the flame retardant in the electrolyte is achieved, and the impact of the addition of the flame retardant on the electrochemical performance of the battery can be reduced.

[0005] However, existing flame-retardant microcapsules either have problems such as the shell material melting point being too high, the flame retardant material being introduced too late, resulting in flame retardant failure (such as patent CN108815787A), or the shell material having poor conductivity affecting the electrochemical performance of the battery (such as patent CN110215642A), making it difficult to achieve an effective balance between the two.

[0006] Patent CN111463488A discloses a double-sided microcapsule flame retardant, in order to achieve the dual effects of timely response of flame retardant materials and good conductive properties. The microcapsule flame retardant includes a core composed of a flame retardant and a shell that wraps the core. The shell includes a first shell composed of a conductive polymer and a second shell composed of a thermally responsive copolymer. The first shell and the second shell are close together on both sides and wrap the core. The double-sided flame retardant shell material contains both a conductive polymer and a thermally responsive polymer, which will not affect the conductivity of the electrolyte, and is beneficial to reducing the negative impact of the flame retardant capsule on the electrochemical performance of the lithium battery.

[0007] However, the surface material of the flame-retardant microcapsules in the prior art is half conductive polymer and half thermally responsive copolymer, which is uneven. Therefore, its flame-retardant response time and conductive performance cannot achieve the expected effect. In addition, the preparation process of the flame-retardant microcapsules is complicated and the process control requirements are strict, which is not convenient for industrial promotion. Summary of the Invention

[0008] The first object of the present invention is to provide a flame retardant microcapsule that can release the flame retardant in time when thermal runaway occurs, thereby preventing the battery from burning and effectively ensuring the electrochemical properties of the electrolyte.

[0009] The second object of the present invention is to provide a method for preparing the flame retardant microcapsules, which can prepare flame retardant microcapsules with good coverage and good particle size uniformity through a simple method.

[0010] The third object of the present invention is to provide an electrolyte containing the flame retardant microcapsules, which has good flame retardant effect and electrochemical performance and can respond promptly to thermal runaway.

[0011] In order to achieve the above object, the technical solution adopted by the present invention is:

[0012] A flame-retardant microcapsule comprises a capsule core and a shell layer covering the capsule core; the capsule core is formed by dissolving triphenyl phosphate in toluene; the shell layer comprises a conductive polymer and a thermoresponsive polymer; the thermoresponsive polymer is a water-soluble polymer, and the melting point of the thermoresponsive polymer is 100-200°C, preferably 100-140°C; the conductive polymer is a water-soluble conductive polyaniline formed by modifying polyaniline; both the thermoresponsive polymer and the conductive polymer are insoluble in toluene; and the weight ratio of the thermoresponsive polymer to the conductive polymer satisfies the following ratio: 1:3-4.

[0013] When thermal runaway begins, the shell of a lithium-ion battery needs to rupture quickly to release the flame-retardant material inside to retard the flame in time, thereby effectively preventing combustion. If the shell material contains a high content of thermoresponsive polymers that can melt at low temperatures, it can quickly disintegrate at temperatures of 130-160°C when thermal runaway begins. However, thermoresponsive polymers that can melt at low temperatures generally have weak electrical conductivity, which will inevitably affect the electrochemical performance of the battery. If the shell material contains a high content of conductive polymers, it can promote the improvement of electrochemical performance. However, polymers with high electrical conductivity generally have high melting points, making it difficult to achieve the effect of rapid disintegration at the onset of thermal runaway.

[0014] Based on this, the present application first designs a high content of conductive polymer in the shell material to ensure its conductive performance. At the same time, in addition to triphenyl phosphate (flame-retardant TPP), the present application also designs the core of the capsule to contain solvent toluene. Toluene begins to vaporize at 110°C. When thermal runaway starts (130-160°C), toluene has begun to vaporize. As toluene vaporizes, the air pressure inside the microcapsule increases sharply. Only a small amount of melting point is needed for the shell to quickly disintegrate under the internal atmospheric pressure, which helps to promote the release of flame-retardant TPP in the capsule core, so that the flame-retardant TPP can quickly participate in the flame retardancy of the electrolyte, thereby effectively preventing the battery from burning.

[0015] In addition, after the initiation of thermal runaway, the vaporized toluene and the liquid flame-retardant TPP are evenly dispersed, and the bubbles formed can more easily carry the liquid flame-retardant TPP and disperse it faster into the electrolyte.

[0016] The present application utilizes the aqueous and oily properties between the water-soluble shell material and the water-insoluble core material to easily form flame-retardant microcapsules with good coating performance. The flame-retardant microcapsules can be stably dispersed in the lithium battery electrolyte (ethylene carbonate). The shell material of the microcapsule is immiscible with the lithium battery electrolyte and does not melt under normal operating conditions (around 80°C), thereby ensuring that the above-mentioned microcapsule structure will not be destroyed during normal operation of the lithium battery.

[0017] The design of the flame-retardant microcapsules of the present application can not only effectively promote the improvement of electrochemical performance, but also achieve a rapid response to thermal runaway, thereby achieving a better flame retardant effect.

[0018] Specifically, the thermoresponsive polymer of the present application is selected from at least one of sodium alginate, polyamide, polyurea, polyacrylamide, or polyurethane. These polymers can meet the requirements of water solubility and melting point between 100 and 200°C by controlling the degree of polymerization.

[0019] Specifically, the weight ratio of the shell layer to the capsule core of the present application satisfies: 1.5-2.5:1, which can achieve a more stable coating effect.

[0020] Specifically, the weight ratio of triphenyl phosphate to toluene in the present application satisfies: 1:0.5~1, which can ensure that triphenyl phosphate forms a stable solution and that toluene can generate a pressure sufficient to break through the shell after vaporization, while also ensuring the content of flame retardant components as much as possible.

[0021] The present application also provides a method for preparing the flame retardant microcapsules, comprising the following steps:

[0022] S1 dissolves the thermoresponsive polymer and the conductive polymer in water to form a shell solution, wherein the weight ratio of the thermoresponsive polymer and the conductive polymer to water satisfies: 1:3-4;

[0023] S2 dissolves triphenyl phosphate in toluene in a certain proportion to form a capsule core solution;

[0024] S3 uniformly disperses the core solution obtained in step S2 in the shell solution obtained in step S1 according to a certain proportion, and adds an emulsifier to fully disperse the solution to form an oil-in-water emulsion;

[0025] S4: sending the oil-in-water emulsion obtained in step S3 into a spray drying chamber for spray drying to obtain flame-retardant microcapsules;

[0026] S5: drying the flame retardant microcapsules obtained in step S4 at 60-80° C. in vacuum until constant weight is reached.

[0027] The present application uses a spray drying method to prepare oil-in-water microcapsules whose shell materials are two water-soluble polymers and whose core materials are two oil-soluble polymers. Compared with the in situ polymerization method and the coaxial EHD droplet injection method, the spray drying method of the present application can prepare the microcapsules of the present application more simply and efficiently, and the prepared microcapsules have good coating properties and good particle size uniformity.

[0028] To be more specific, the inlet air temperature of the spray drying chamber of the present application is 120-130°C; the outlet air temperature is 60-80°C; although the melting point of the thermally responsive polymer of the shell is preferably 100-140°C, since the spray drying process ends very quickly and the main component of the shell material is a conductive polymer with a melting point of about 400°C, the inlet air temperature of the present application is selected to be 120-130°C. Experiments show that at this temperature, basically no adhesion is formed between the particles, and the granulation properties are good and the particle uniformity is good.

[0029] More specifically, in step S3, the amount of emulsifier added is 1-1.5%; the emulsifier is selected from at least one of polyoxyethylene fatty acid esters, polyoxyethylene lauryl ether, and polyoxyethylene cetyl ether. In the presence of the emulsifier, stable oil-in-water particles are more easily formed.

[0030] The present application also provides a flame retardant electrolyte, including lithium salt, solvent and flame retardant microcapsules, wherein the addition amount of the flame retardant microcapsules is 1 to 15%; specifically, the solvent contains ethylene carbonate, more specifically, the solvent is EC / DMC / EMC (volume ratio is 1:1:1).

[0031] The beneficial effects of the present invention are:

[0032] The present invention realizes the rapid response and release of flame retardant materials when thermal runaway occurs through the structural design of flame retardant microcapsules and the design of capsule core and capsule wall materials, thereby avoiding the flame retardant failure caused by combustion due to the late participation of flame retardant materials, and at the same time ensuring the improvement of the electrochemical performance of the electrolyte. DETAILED DESCRIPTION

[0033] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the present invention will be further described below in conjunction with specific examples. In the embodiments, if specific conditions are not specified, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. The reagents used or those without indicating the manufacturer are conventional products that can be purchased commercially. All features disclosed in this specification, except mutually exclusive features and / or steps, can be combined in any way.

[0034] The following examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0035] The water-soluble conductive polyaniline used in the following examples was purchased from Hubei Shuaiyan Ligao Biopharmaceutical Co., Ltd. Product Name: Water-soluble conductive polyaniline; Product Properties: Dark green solid powder at room temperature, boiling point 869.2±65.0°C at 760 mmHg, melting point >350°C.

[0036] Example 1

[0037] This embodiment provides a method for preparing flame-retardant microcapsules, comprising the following steps:

[0038] S1: weighing sodium alginate and water-soluble conductive polyaniline in a weight ratio of 1:3 and dissolving them in water to form a shell solution, wherein the weight ratio of the sum of the weights of the sodium alginate and the water-soluble conductive polyaniline to the weight of water satisfies: 1:3;

[0039] S2: dissolving triphenyl phosphate in toluene at a weight ratio of triphenyl phosphate to toluene of 1:0.5 to form a capsule core solution;

[0040] S3: Weighing the shell solution and the core solution separately at a shell-to-core weight ratio of 1.5:1; then evenly dispersing the core solution in the shell solution, adding 1.5% of an emulsifier, polyoxyethylene fatty acid ester, and homogenizing at 5000 rpm for three times to form an oil-in-water emulsion after sufficient dispersion;

[0041] S4: feeding the oil-in-water emulsion obtained in step S3 into a spray drying chamber for spray drying to obtain flame-retardant microcapsules; the specific parameters of the spray drying are: feed flow rate: 30 mL / min; feed temperature: 100° C.; the air inlet temperature of the spray drying chamber is controlled at 120° C.-130° C.; and the air outlet temperature is controlled at 60-80° C.;

[0042] S5: drying the flame retardant microcapsules obtained in step S4 at 60-80° C. in vacuum until constant weight is reached.

[0043] The flame-retardant microcapsules prepared by the preparation method of this embodiment are denoted as Z1.

[0044] Example 2

[0045] This embodiment provides a method for preparing flame-retardant microcapsules, which differs from the preparation method in Example 1 in that the weight ratio of sodium alginate to water-soluble conductive polyaniline in this embodiment is 1:4.

[0046] The flame-retardant microcapsules prepared by the preparation method of this embodiment are denoted as Z2.

[0047] Example 3

[0048] This embodiment provides a method for preparing flame-retardant microcapsules, which differs from the preparation method in Example 1 in that the weight ratio of triphenyl phosphate to toluene in this embodiment is 1:1.

[0049] The flame-retardant microcapsules prepared by the preparation method of this embodiment are denoted as Z3.

[0050] Example 4

[0051] This embodiment provides a method for preparing flame-retardant microcapsules, which differs from the preparation method in Example 1 in that the weight ratio of the shell layer to the capsule core in this embodiment is 2:1.

[0052] The flame-retardant microcapsules prepared by the preparation method of this example are denoted as Z4.

[0053] Example 5

[0054] This embodiment provides a method for preparing flame-retardant microcapsules, which differs from the preparation method in Example 1 in that the weight ratio of the shell layer to the capsule core in this embodiment is 2.5:1.

[0055] The flame-retardant microcapsules prepared by the preparation method of this example are denoted as Z5.

[0056] Example 6

[0057] This embodiment provides a flame-retardant electrolyte, comprising: LiPF6, a solvent, and flame-retardant microcapsules Z1; the solvent is EC / DMC / EMC (volume ratio is 1:1:1); LiPF6 is dissolved in the solvent to form a solution with a lithium salt concentration of 1 mol / L, and the flame-retardant microcapsules are uniformly dispersed in the above solution, and the amount of flame-retardant microcapsules added is 10% of the total mass of the electrolyte.

[0058] Example 7

[0059] This embodiment provides a flame-retardant electrolyte, comprising: LiPF6, a solvent, and flame-retardant microcapsules Z2; the solvent is EC / DMC / EMC (volume ratio of 1:1:1); LiPF6 is dissolved in the solvent to form a solution with a lithium salt concentration of 1 mol / L, and the flame-retardant microcapsules are uniformly dispersed in the above solution, and the amount of flame-retardant microcapsules added is 10% of the total mass of the electrolyte.

[0060] Example 8

[0061] This embodiment provides a flame-retardant electrolyte, comprising: LiPF6, a solvent, and flame-retardant microcapsules Z3; the solvent is EC / DMC / EMC (volume ratio of 1:1:1); LiPF6 is dissolved in the solvent to form a solution with a lithium salt concentration of 1 mol / L, and the flame-retardant microcapsules are uniformly dispersed in the above solution, and the amount of flame-retardant microcapsules added is 10% of the total mass of the electrolyte.

[0062] Example 9

[0063] This embodiment provides a flame-retardant electrolyte, comprising: LiPF6, a solvent, and flame-retardant microcapsules Z4; the solvent is EC / DMC / EMC (volume ratio of 1:1:1); LiPF6 is dissolved in the solvent to form a solution with a lithium salt concentration of 1 mol / L, and the flame-retardant microcapsules are uniformly dispersed in the above solution, and the amount of flame-retardant microcapsules added is 10% of the total mass of the electrolyte.

[0064] Example 10

[0065] This embodiment provides a flame-retardant electrolyte, comprising: LiPF6, a solvent, and flame-retardant microcapsules Z5; the solvent is EC / DMC / EMC (volume ratio of 1:1:1); LiPF6 is dissolved in the solvent to form a solution with a lithium salt concentration of 1 mol / L, and the flame-retardant microcapsules are uniformly dispersed in the above solution, and the amount of flame-retardant microcapsules added is 10% of the total mass of the electrolyte.

[0066] Comparative Example 1

[0067] This comparative example provides a method for preparing flame-retardant microcapsules. The difference from the preparation method of Example 1 is that no toluene is added to the capsule core of this comparative example. The flame-retardant microcapsules prepared using the preparation method of this comparative example are denoted as CK1.

[0068] Comparative Example 2

[0069] This comparative example provides a method for preparing flame-retardant microcapsules. The difference from the preparation method of Example 1 is that water-soluble conductive polyaniline is not added to the shell material of this comparative example. The flame-retardant microcapsules prepared using the preparation method of this comparative example are designated as CK2.

[0070] Comparative Example 3

[0071] This comparative example provides a flame-retardant electrolyte, comprising: LiPF6, a solvent, and flame-retardant microcapsules CK1; the solvent is EC / DMC / EMC (volume ratio of 1:1:1); LiPF6 is dissolved in the solvent to form a solution with a lithium salt concentration of 1 mol / L, and the flame-retardant microcapsules are uniformly dispersed in the above solution, and the amount of flame-retardant microcapsules added is 10% of the total mass of the electrolyte.

[0072] Comparative Example 4

[0073] This comparative example provides a flame-retardant electrolyte, comprising: LiPF6, a solvent, and flame-retardant microcapsules CK2; the solvent is EC / DMC / EMC (volume ratio of 1:1:1); LiPF6 is dissolved in the solvent to form a solution with a lithium salt concentration of 1 mol / L, and the flame-retardant microcapsules are uniformly dispersed in the above solution, and the amount of flame-retardant microcapsules added is 10% of the total mass of the electrolyte.

[0074] Comparative Example 5

[0075] This comparative example provides a flame retardant electrolyte, comprising: LiPF6 and a solvent; the solvent is EC / DMC / EMC (volume ratio is 1:1:1); LiPF6 is dissolved in the solvent to form a solution with a lithium salt concentration of 1 mol / L.

[0076] Experimental Example 1 Electrochemical Performance Test

[0077] Preparation of lithium-ion batteries

[0078] (1) Preparation of positive electrode sheet

[0079] Lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4), Super-P and polyvinylidene fluoride (PVDF) containing NMP as a binder were mixed in a mass ratio of 8:1:1, and ball milled at 300 rpm for 5 hours to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on one side of a clean aluminum foil surface, dried, and cut into pieces to obtain a positive electrode sheet for testing.

[0080] (2) Preparation of negative electrode sheet

[0081] Lithium sheet is used as negative electrode.

[0082] (3) Preparation of button batteries

[0083] In a glove box filled with argon where the moisture and oxygen levels were less than 10 ppm, the positive electrode sheet in (1) and the negative electrode sheet in (2) were added to the electrolytes prepared in Examples 6-10 and Comparative Examples 3-5, respectively, and Celgard 2400 was used as a separator to assemble CR2032 button cells.

[0084] Electrochemical performance test

[0085] The button cell was pre-cycled three times at room temperature by charging at a constant current of 0.2C to 5.2V and then discharging at a constant current to 3.5V. The battery was then cycled for 100 cycles by charging at a constant current of 1C to 5.2V and then discharging at a constant current to 3.5V. The high-temperature cycle performance data are shown in Table 1.

[0086] Table 1 Battery performance of each embodiment and comparative example

[0087] electrolyte Flame retardant microcapsules Battery performance-100 cycles capacity retention Example 6 Z1 85.21％ Example 7 Z2 90.85％ Example 8 Z3 85.03％ Example 9 Z4 90.14％ Example 10 Z5 84.36％ Comparative Example 3 CK1 85.36％ Comparative Example 4 CK2 76.76％ Comparative Example 5 0 80.15％

[0088] From the results in Table 1, it can be seen that the electrochemical performance of Examples 6-10 is better than that of Comparative Example 5. That is to say, after adding the flame-retardant microcapsules of the present application, the electrochemical performance of the battery is not negatively affected, and the electrochemical performance is also improved due to the addition of the conductive polymer.

[0089] Comparison of the results of Comparative Example 4 and Example 6 shows that the electrochemical performance of the flame-retardant microcapsules without conductive material added to the shell layer deteriorates. This is because the thermally responsive polymer of the shell layer itself has poor conductivity, which can easily cause the conductivity of the electrolyte to deteriorate and the electrochemical performance of the battery to deteriorate.

[0090] Experimental Example 2: Battery Safety Performance Test

[0091] A lithium-ion battery was prepared using the same method as in Experimental Example 1.

[0092] (1) Penetration test: The lithium-ion battery is charged to 100% SOC at a constant current of 0.1C at 25±3°C, and a needle with a diameter of 8mm is used to penetrate the lithium-ion battery for the needle penetration test;

[0093] (2) Overcharge test: At 25±3°C, charge the lithium-ion battery to 100% SOC at a constant current of 0.5C, and then overcharge it from 100% SOC to 200% SOC.

[0094] The safety test criteria for lithium-ion batteries are: no explosion, no fire, and no combustion are considered passed. The number of lithium-ion batteries that passed the safety test was counted. Table 2 shows the safety test results of lithium-ion batteries prepared in various examples and comparative examples:

[0095] Table 2 Flame retardant properties of various embodiments and comparative examples

[0096]

[0097] It can be seen from Table 2 that after adding the flame retardant microcapsules of the present application, its flame retardant performance is significantly better than that of Comparative Example 5 in which no flame retardant microcapsules are added, and the flame retardant microcapsules of the present application have better flame retardant effects than the flame retardant microcapsules of the prior art.

[0098] Comparison of the results of Comparative Example 3 and Example 1 shows that when toluene is not added to the capsule core, the shell disintegrates slowly, which in turn causes the flame retardant material to be unable to quickly participate in the flame retardant reaction, causing the entire battery to be easily destroyed by thermal runaway.

[0099] In summary, the flame-retardant microcapsules of the present application are added to the electrolyte, which can not only greatly promote the improvement of the electrochemical performance of the battery, but also have a good flame-retardant effect.

[0100] The present invention is not limited to the above-mentioned embodiments. Anyone should be aware that any structural changes made under the guidance of the present invention, and any technical solutions that are the same or similar to those of the present invention, fall within the scope of protection of the present invention.

Claims

1. A flame retardant microcapsule, characterized in that: The invention comprises a capsule core and a shell layer covering the capsule core; the capsule core is formed by dissolving triphenyl phosphate in toluene; the shell layer comprises a conductive polymer and a thermoresponsive polymer; The thermally responsive polymer is a water-soluble polymer, and the melting point of the thermally responsive polymer is 100-140° C.; the conductive polymer is a water-soluble conductive polyaniline formed by modifying polyaniline; The weight ratio of the thermoresponsive polymer to the conductive polymer satisfies: 1:3-4; The thermally responsive polymer is selected from at least one of sodium alginate, polyamide, polyurea, polyacrylamide or polyurethane; The weight ratio of the shell layer to the capsule core satisfies: 1.5~2.5:

1.

2. The flame retardant microcapsule according to claim 1, characterized in that The weight ratio of the triphenyl phosphate to the toluene satisfies: 1:0.5~1.

3. The method for preparing the flame-retardant microcapsules according to any one of claims 1 to 2, characterized in that: The steps include: S1 dissolving the thermoresponsive polymer and the conductive polymer in water to form a shell solution, wherein the weight ratio of the thermoresponsive polymer and the conductive polymer to water satisfies: 1:3-4; S2 dissolve triphenyl phosphate in toluene in a certain proportion to form a capsule core solution; S3: uniformly dispersing the core solution obtained in step S2 into the shell solution obtained in step S1 according to a certain proportion, and adding an emulsifier to emulsify the solution to form an oil-in-water emulsion; S4 sending the oil-in-water emulsion obtained in step S3 into a spray drying chamber for spray drying to obtain flame retardant microcapsules; S5 Dry the flame retardant microcapsules obtained in step S4 at 60-80° C. to a constant weight.

4. The method for preparing flame-retardant microcapsules according to claim 3, characterized in that: In step S4, the air inlet temperature of the spray drying chamber is 120-130°C.

5. The method for preparing flame-retardant microcapsules according to claim 4, characterized in that: In step S3, the amount of the emulsifier added is 1-1.5%; the emulsifier is selected from at least one of polyoxyethylene fatty acid esters, polyoxyethylene lauryl ether and polyoxyethylene cetyl ether.

6. A flame retardant electrolyte, characterized in that: The invention comprises a lithium salt, a solvent and the flame retardant microcapsules according to any one of claims 1 to 2.

7. The flame retardant electrolyte according to claim 6, characterized in that The added amount of the flame retardant microcapsules is 1-15%.

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