Lithium battery electrolyte

Abstract

The invention belongs to the field of lithium batteries, and discloses a lithium battery electrolyte which comprises the following components in parts by weight: 22-28 parts of a flame retardant, 10-12 parts of lithium salt, 50-62 parts of a solvent, 3-5 parts of an interface regulator, 1-3 parts of a special functional aid and 0.5-2 parts of a novel synergist, the flame retardant is a mixture composed of ammonium polyphosphate with the polymerization degree of 500-1000 and perfluorohexanone with the purity of more than or equal to 99.5% according to the weight ratio of 2: 1-3: 1; the lithium salt is a mixture of lithium hexafluorophosphate and lithium bis (fluorosulfonyl) imide in a weight ratio of (1: 1)-(2: 1); the invention aims to overcome the defects in the prior art, and provides the lithium battery electrolyte and the preparation method thereof, the electrolyte has excellent flame retardant property, good ionic conductivity and cycling stability, and the preparation method is simple and easy to implement and suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a lithium battery electrolyte. BACKGROUND

[0002] With the rapid development of new energy industry, lithium batteries are widely used in electric vehicles, portable electronic devices and other fields due to their high energy density, long cycle life and other advantages. However, the safety problem of lithium batteries has always been a key factor restricting their development, and the flammability of electrolyte is one of the important reasons for battery fire and explosion.

[0003] In the prior art, in order to improve the flame retardant performance of the electrolyte, a flame retardant is usually added to the electrolyte, but there are often the following problems: some flame retardants can reduce the ionic conductivity of the electrolyte, affecting the electrochemical performance of the battery; some flame retardants have poor compatibility with other components in the electrolyte, resulting in a decrease in the stability of the electrolyte; and the flame retardant effect of some flame retardant solutions is not ideal, which is difficult to meet the high safety requirement.

[0004] Therefore, it is of great significance to develop a lithium battery electrolyte with excellent flame retardant performance and good electrochemical performance. SUMMARY

[0005] The present application aims to overcome the shortcomings of the prior art and provide a flame-retardant lithium battery electrolyte and a preparation method thereof. The electrolyte has excellent flame retardant performance, good ionic conductivity and cycle stability, and the preparation method is simple and easy to implement, suitable for industrial production.

[0006] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme: The technical scheme provided by the present application is: a lithium battery electrolyte, comprising the following components by weight: 22-28 parts of a flame retardant, 10-12 parts of a lithium salt, 50-62 parts of a solvent, 3-5 parts of an interface modifier, 1-3 parts of a special functional additive, and 0.5-2 parts of a new synergist; the flame retardant is a mixture of ammonium polyphosphate with a polymerization degree of 500-1000 and perfluorohexanone with a purity of ≥99.5% at a weight ratio of 2:1-3:1; the lithium salt is a mixture of lithium hexafluorophosphate and lithium bisfluorosulfonylimide at a weight ratio of 1:1-2:1.

[0007] Further, the solvent is a mixture of dimethyl carbonate, ethylene carbonate and ethyl trifluoroacetate at a volume ratio of 3:2:1-4:3:1, and the purity of the ethylene carbonate is ≥99.9% and the water content is ≤10ppm; the volume ratio of dimethyl carbonate, ethylene carbonate and ethyl trifluoroacetate in the solvent is preferably 3:2:1.

[0008] Further, the interface regulator is a mixture of vinylene carbonate and lithium pyrophosphate with particle size ≤5 μm in a weight ratio of 2:1-3:1, and the weight ratio of the vinylene carbonate to the lithium pyrophosphate is preferably 2.5:1.

[0009] Further, the special functional auxiliary agent is a mixture of benzotriazole and polydimethylsiloxane with viscosity of 50-100 mPa · s in a weight ratio of 1:1-2:1, and the purity of the benzotriazole is ≥99%; and the weight ratio of the benzotriazole to the polydimethylsiloxane is preferably 1.5:1.

[0010] Further, the novel synergist is a mixture of anatase nano-titanium dioxide with particle size of 20-50 nm and specific surface area of 50-80 m 2 / g and ethylene carbonate with water content of ≤15 ppm in a weight ratio of 1:1-3:1, and the weight ratio of the nano-titanium dioxide to the ethylene carbonate is preferably 2:1.

[0011] Further, the weight ratio of the ammonium polyphosphate to the perfluorohexanone is 2.5:1; the weight ratio of the lithium hexafluorophosphate to the lithium bisfluorosulfonylimide is 1.5:1, and the water content of the lithium hexafluorophosphate is ≤20 ppm.

[0012] The application also provides a preparation method of the lithium battery electrolyte, for preparing the lithium battery electrolyte, comprising the following steps: (1) preparing a mixed solvent: uniformly mixing dimethyl carbonate and ethylene carbonate in a glove box at 25°C and humidity of ≤30%, and then adding ethyl trifluoroacetate through a constant-pressure dropping funnel at a rate of 5 mL / min, while maintaining the stirring speed of a magnetic stirrer at 80-100 r / min, mixing for 1-1.5 hours, and monitoring the water content of the solvent in real time by using a Karl Fischer moisture meter to ensure that the water content is ≤20 ppm; (2) preparing an interface regulator: grinding and mixing vinylene carbonate and lithium pyrophosphate in aagate mortar at a rotating speed of 300-400 r / min for 15-20 minutes, passing through a 200-mesh stainless steel screen, and collecting the undersize as the interface regulator; (3) preparing a special functional auxiliary agent: mixing benzotriazole with purity of ≥99% and anhydrous ethanol (purity ≥99.9%) in a mass ratio of 1:5-1:8, stirring in a 40°C water bath until completely dissolved, and then adding polydimethylsiloxane with viscosity of 50-100 mPa · s, and stirring and mixing at 50-60°C and a stirring speed of 150 r / min for 30 minutes to obtain a uniform transparent liquid; (4) Preparation of a new synergist: add the anatase nano-titanium dioxide with a particle size of 20-50 nm and ethylene carbonate with a water content of ≤15 ppm into a beaker in proportion, use a probe-type ultrasonic instrument with a power of 200-300 W (the probe is inserted into the liquid surface by 1-2 cm), and ultrasonic for 10-15 minutes under the condition of a working / intermittent time ratio of 3s / 2s, and immediately after ultrasonic, detect the particle size distribution by using a dynamic light scattering instrument to ensure that D90≤100 nm, and if it does not meet the standard, extend the ultrasonic for 5 minutes; (5) Preparation of an electrolyte: add the mixed solvent obtained in step (1) into a double-layer glass reaction kettle equipped with a nitrogen protection device (the purity of nitrogen is ≥99.999%, and the flow is 200-300 mL / min), open the constant temperature water bath to control the temperature at 30-40℃, and stir at a speed of 100-120 r / min by using a mechanical stirrer, add lithium salt and flame retardant in sequence, stir until the solution is clear, then add the interface regulator obtained in step (2), the special functional additive obtained in step (3) and the new synergist obtained in step (4), continue to stir for 2-3 hours, and finally collect the filtrate by using a 0.2-0.5 μm polytetrafluoroethylene microporous filter membrane to reduce pressure filtration (the vacuum degree is 0.08-0.1 MPa), and the collected filtrate is a lithium battery electrolyte.

[0013] The beneficial effects of the technical solution are: (1) The ammonium polyphosphate is matched with perfluorohexanone (weight ratio 2:1-3:1) to form a "solid-phase flame retardant + gas-phase fire extinguishing" synergistic mechanism, the ammonium polyphosphate decomposes to generate phosphate ester substances at high temperature, which covers the electrode surface to form a flame-retardant barrier to inhibit the volatilization of combustible materials; the perfluorohexanone interrupts the chain reaction by capturing combustion free radicals, and the combination of the two makes the electrolyte pass the UL94 V-0 level test, and the self-extinguishing time is ≤3s after ignition, which is more than 70% shorter than the existing phosphate ester single flame-retardant system (self-extinguishing time ≥10s), and in the 130℃ hot box test, the battery has no smoke and fire phenomenon, while in the prior art, the battery starts to smoke at 100℃ or above.

[0014] (2) The solvent can offset the viscosity increase caused by the flame retardant, so that the electrolyte has an electrical conductivity of 11-13 mS / cm at 25℃, which is higher than the 8-10 mS / cm of the existing composite flame-retardant electrolyte; at the same time, the synergistic effect of ethylene carbonate and lithium salt (weight ratio of new synergist 2:1) makes the lithium salt exist in a stable solvated structure in the electrolyte, and the lithium salt decomposition rate is ≤5% after 150h storage at 60℃, which is much lower than the 15%-20% in the prior art, solving the technical problem that high flame retardancy and high ionic conductivity are difficult to achieve.

[0015] (3) The interface regulator can form a lithium-phosphorus-oxygen-containing composite SEI film on the electrode surface, the film has low impedance (initial impedance ≤ 50 Ω) and high stability, and the impedance increases only by 80% after 1C cycle for 1000 times, while the impedance of the existing electrolyte increases by more than 300% after cycle; the metal complexation of benzotriazole in the special functional additive and the flexible isolation layer of polydimethylsiloxane synergize, further inhibit the dissolution of the electrode material, so that the capacity retention rate of the battery is 88%-92% after 1C cycle for 1200 times, which is significantly improved compared with the existing flame-retardant electrolyte (70%-80%).

[0016] (4) The introduction of nano-titanium dioxide (particle size 20-50 nm) promotes lithium ion migration through size effect, and the conductivity of the electrolyte remains above 5 mS / cm at-20℃, so that the capacity retention rate of the battery at-20℃ is above 75%, while the capacity retention rate of the existing flame-retardant electrolyte is only 50%-60%; in the needle test (diameter 3mm steel needle, speed 50mm / s), the battery using the electrolyte of the present application has no fire and no explosion, and the maximum surface temperature is ≤ 150℃, which is much lower than the 250℃ or more of the prior art, and the risk of thermal runaway is greatly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0017] Fig. 1 The data comparison table of each embodiment of the lithium battery electrolyte proposed in the present application is shown in the following table: Fig. 2 The difference comparison table of each embodiment of the lithium battery electrolyte proposed in the present application is shown in the following table: DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present application will be described in detail below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0019] The specific implementation process is as follows: Embodiment 1: Please refer to Figs. 1-2 The present application provides a technical solution: a lithium battery electrolyte, which comprises the following components by weight: 110g of flame retardant, 50g of lithium salt, 250g of solvent, 15g of interface regulator, 5g of special functional additive, and 2.5g of new synergist. The electrolyte is prepared by the following method: 2 The electrolyte is prepared by the following method: The electrolyte is prepared by the following method: (1) Preparation of mixed solvent: dimethyl carbonate and ethylene carbonate are mixed at a volume ratio of 3:2 at 25°C and 25% humidity in a glove box, and then ethyl trifluoroacetate (volume is 1 / 6 of the total volume of dimethyl carbonate and ethylene carbonate) is slowly added through a constant pressure dropping funnel at a rate of 5 mL / min, while a magnetic stirrer is used to maintain a stirring speed of 80 r / min, and the mixture is mixed for 1 hour. During this period, a Karl Fischer moisture meter is used to monitor the moisture of the solvent in real time, and the moisture is measured to be 15 ppm; (2) Preparation of interface modifier: vinylene carbonate and lithium pyrophosphate are ground and mixed in aagate mortar at a speed of 300 r / min for 15 minutes, then passed through a 200 mesh stainless steel screen, and the undersize material is collected as the interface modifier; (3) Preparation of special functional additive: 99% purity benzotriazole and anhydrous ethanol (99.9% purity) are mixed at a mass ratio of 1:5, and after stirring to complete dissolution in a 40°C water bath, polydimethylsiloxane with a viscosity of 50 mPa·s (1:1 by weight with benzotriazole) is added, and the mixture is stirred at 50°C and 150 r / min for 30 minutes to obtain a uniform transparent liquid; (4) Preparation of new synergist: anatase type nano-titanium dioxide with a particle size of 20 nm and ethylene carbonate with a moisture content of 12 ppm are added to a beaker at a weight ratio of 1:1, and a probe ultrasonic instrument with a power of 200 W is used to ultrasonic for 10 minutes under the condition of working / intermittent time ratio of 3s / 2s. After ultrasonic, the particle size distribution is detected by dynamic light scattering instrument immediately, and D90 is 80 nm; (5) Preparation of electrolyte: 250 g of the mixed solvent obtained in step (1) was added to a double-layer glass reaction kettle equipped with a nitrogen protection device (nitrogen purity 99.999%, flow rate 200 mL / min), a constant temperature water bath was started to control the temperature at 30°C, a mechanical stirrer was used to stir at a speed of 100 r / min, 50 g of lithium salt (lithium hexafluorophosphate and lithium bisfluorosulfonylimide in a weight ratio of 1:1) was added, 110 g of flame retardant (ammonium polyphosphate and perfluorohexanone in a weight ratio of 2:1) was added, stirring was performed for 30 min until the solution was clear, then 15 g of the interfacial modifier obtained in step (2), 5 g of the special functional additive obtained in step (3) and 2.5 g of the novel synergist obtained in step (4) were added, and stirring was continued for 2 h, finally, the filtrate was collected by filtering (vacuum degree 0.08 MPa) through a polytetrafluoroethylene microporous filter membrane with a pore size of 0.2 μm under reduced pressure, and the filtrate was the flame-retardant lithium battery electrolyte; The base formula of the embodiment exhibits good comprehensive performance through reasonable proportioning and process control; the flame retardant (ammonium polyphosphate and perfluorohexanone, 2:1) is used to achieve V-0 level flame retardation (self-extinguishing time 2.8 s); the optimized collocation of lithium salt and solvent makes the 25°C conductivity reach 11.2 mS / cm, meeting the ion conduction requirement; the moisture (15 ppm) and dispersion process are strictly controlled during preparation, the interfacial modifier is ground and sieved, and the novel synergist is ultrasonically dispersed (D90=80 nm), which guarantees the system stability; the capacity retention rate is 88.3% after 1C cycle for 1200 times, the capacity retention rate at -20°C is 75.2%, and the lithium salt decomposition rate during 60°C storage is 4.8%, all of which are better than those of the traditional electrolyte; although the proportion of the flame retardant and the synergist is relatively low, the performance under extreme conditions is slightly inferior to that of other embodiments, but the feasibility of the "composite flame retardant + interfacial regulation" route has been verified, laying a foundation for subsequent optimization.

[0020] Example 2: Please refer to Figs. 1-2 The present application provides a technical solution: a lithium battery electrolyte, which comprises the following components in weight parts: flame retardant 125 g, lithium salt 55 g, solvent 275 g, interfacial modifier 20 g, special functional additive 10 g, and novel synergist 6 g. The flame retardant is a mixture of ammonium polyphosphate with a degree of polymerization of 800 and perfluorohexanone with a purity of 99.6% in a weight ratio of 2.5:1; the lithium salt is a mixture of lithium hexafluorophosphate (moisture content 18 ppm) and lithium bisfluorosulfonylimide in a weight ratio of 1.5:1; the solvent is a mixture of dimethyl carbonate, ethylene carbonate (purity 99.9%, moisture content 9 ppm) and trifluoroacetic acid ethyl ester in a volume ratio of 3:2:1; the interfacial modifier is a mixture of vinylene carbonate and lithium pyrophosphate with a particle size of 3 μm in a weight ratio of 2.5:1; the special functional additive is a mixture of benzotriazole (purity 99%) and polydimethylsiloxane with a viscosity of 80 mPa·s in a weight ratio of 1.5:1; the novel synergist is lithium bisfluorosulfonylimide with a particle size of 35 nm and a specific surface area of 65 m2 / g.2 a mixture of 2.0 g of anatase nano-titanium dioxide and 1.0 g of ethylene carbonate with a moisture content of 13 ppm, in a weight ratio of 2:1; The preparation method of the electrolyte is as follows: (1) Preparation of mixed solvent: dimethyl carbonate and ethylene carbonate were mixed uniformly at a volume ratio of 3:2 at 25°C in a glove box with a humidity of 28%, and then ethyl trifluoroacetate (volume 1 / 6 of the total volume of dimethyl carbonate and ethylene carbonate) was slowly added through a constant pressure dropping funnel at a rate of 5 mL / min, while a magnetic stirrer was used to maintain a stirring speed of 90 r / min, and the mixture was mixed for 1.2 hours, during which a Karl Fischer moisture meter was used to monitor the moisture of the solvent in real time, and the moisture was measured to be 18 ppm; (2) Preparation of interfacial modifier: vinylene carbonate and lithium pyrophosphate were ground and mixed in aagate mortar at a speed of 350 r / min for 18 minutes, passed through a 200 mesh stainless steel screen, and the undersize was collected as the interfacial modifier; (3) Preparation of special functional additive: benzotriazole with a purity of 99% and anhydrous ethanol (purity 99.9%) were mixed at a mass ratio of 1:6, and after stirring to complete dissolution in a 40°C water bath, polydimethylsiloxane with a viscosity of 80 mPa·s (weight ratio of 1:1.5 to benzotriazole) was added, and the mixture was stirred at 55°C and 150 r / min for 30 minutes to obtain a uniform transparent liquid; (5) Preparation of electrolyte: 275 g of the mixed solvent obtained in step (1) was added to a double-layer glass reaction kettle equipped with a nitrogen protection device (nitrogen purity 99.999%, flow rate 250 mL / min), the constant temperature water bath was turned on to control the temperature at 35°C, a mechanical stirrer was used to stir at a speed of 110 r / min, and then lithium salt 55 g (lithium hexafluorophosphate and lithium bisfluorosulfonylimide at a weight ratio of 1.5:1), flame retardant 125 g (ammonium polyphosphate and perfluorohexanone at a weight ratio of 2.5:1) were added in turn, and the solution was stirred for 35 minutes until it was clear, then the interfacial modifier obtained in step (2) 20 g, the special functional additive obtained in step (3) 10 g and the novel synergist obtained in step (4) 6 g were added, and the stirring was continued for 2.5 hours, finally a 0.4 μm polytetrafluoroethylene microporous filter membrane was used to filter under reduced pressure (vacuum degree 0.09 MPa) through a sand core funnel, and the filtrate was collected as the flame-retardant lithium battery electrolyte; The embodiment optimizes the proportion of each component, especially adjusts the weight ratio of ammonium polyphosphate to perfluorohexanone in the flame retardant to 2.5:1, and sets the weight ratio of lithium hexafluorophosphate to lithium bisfluorosulfonylimide in the lithium salt to 1.5:1, so that the comprehensive performance of the electrolyte is better; through testing, the conductivity of the electrolyte is 12.3 mS / cm at 25℃, the self-extinguishing time of the UL94 vertical burning test is 2.1 s, reaching the V-0 level standard; the capacity retention rate is 90.5% after 1C cycle for 1200 times, and the low-temperature capacity retention rate is 78% at-20℃; the synergistic effect of each component is remarkable, the composite SEI film formed by the interfacial modifier effectively inhibits the impedance growth, the special functional additive further improves the electrode stability, and the new synergist optimizes the ion migration ability while ensuring the flame retardance.

[0021] Embodiment 3 Please refer to Figs. 1-2 The application provides a technical scheme of a lithium battery electrolyte, which comprises the following components in the following weight parts: 130 g of a flame retardant, 57.5 g of a lithium salt, 290 g of a solvent, 22.5 g of an interfacial modifier, 12.5 g of a special functional additive, and 9 g of a new synergist. The flame retardant is a mixture of ammonium polyphosphate with a polymerization degree of 900 and perfluorohexanone with a purity of 99.7% in a weight ratio of 2.8:1; the lithium salt is a mixture of lithium hexafluorophosphate (water content: 19 ppm) and lithium bisfluorosulfonylimide in a weight ratio of 1.8:1; the solvent is a mixture of dimethyl carbonate, ethylene carbonate (purity: 99.9%, water content: 9.5 ppm) and ethyl trifluoroacetate in a volume ratio of 4:3:1; the interfacial modifier is a mixture of vinylene carbonate and lithium pyrophosphate with a particle size of 3.5 μm in a weight ratio of 2.8:1; the special functional additive is a mixture of benzotriazole (purity: 99%) and polydimethylsiloxane with a viscosity of 90 mPa·s in a weight ratio of 1.8:1; and the new synergist is a mixture of anatase nano-titanium dioxide with a particle size of 40 nm and a specific surface area of 70 m 2 / g and ethylene carbonate with a water content of 13.5 ppm in a weight ratio of 2.5:1. The preparation method of the electrolyte is as follows: (1) Preparation of a mixed solvent: dimethyl carbonate and ethylene carbonate are mixed uniformly in a glove box at 25℃ and a humidity of 29%, and then ethyl trifluoroacetate (volume: 1 / 8 of the total volume of dimethyl carbonate and ethylene carbonate) is slowly added through a constant-pressure dropping funnel at a rate of 5 mL / min, while a magnetic stirrer is used to maintain a stirring speed of 95 r / min, the mixture is mixed for 1.4 hours, and a Karl Fischer moisture meter is used to monitor the water content of the solvent in real time, and the water content is measured to be 19 ppm. (2) Preparation of interface modifier: vinylene carbonate and lithium pyrophosphate were mixed in a marble mortar at a rotation speed of 380 r / min for 19 minutes, and then sieved through a 200-mesh stainless steel screen. The undersize was collected as the interface modifier; (3) Preparation of special functional additive: benzotriazole with a purity of 99% and anhydrous ethanol (purity 99.9%) were mixed at a mass ratio of 1:7. After stirring in a 40°C water bath until complete dissolution, polydimethylsiloxane with a viscosity of 90 mPa·s (benzotriazole:polydimethylsiloxane = 1:1.8 by weight) was added. The mixture was stirred at 58°C and 150 r / min for 30 minutes to obtain a uniform transparent liquid; (4) Preparation of new synergist: anatase-type nanometer titanium dioxide with a particle size of 40 nm and ethylene carbonate with a water content of 13.5 ppm were added to a beaker at a weight ratio of 2.5:1. A probe-type ultrasonic instrument (probe inserted 1.8 cm below the liquid surface) with a power of 280 W was used for ultrasonic treatment for 14 minutes under the condition of a working / intermittent time ratio of 3s / 2s. The particle size distribution was detected immediately after ultrasonic treatment using a dynamic light scattering instrument, and the D90 was 95 nm; (5) Preparation of electrolyte: 290 g of the mixed solvent obtained in step (1) was added to a double-layer glass reactor equipped with a nitrogen protection device (nitrogen purity 99.999%, flow rate 280 mL / min). The constant temperature water bath was turned on to control the temperature at 38°C, and the mechanical stirrer was used to stir at a rotation speed of 115 r / min. Lithium salt 57.5 g (lithium hexafluorophosphate and lithium bisfluorosulfonylimide = 1.8:1 by weight), flame retardant 130 g (ammonium polyphosphate and perfluorohexanone = 2.8:1 by weight) were added in sequence. The solution was stirred for 38 minutes until it was clear. Then, the interface modifier obtained in step (2) 22.5 g, the special functional additive obtained in step (3) 12.5 g, and the new synergist obtained in step (4) 9 g were added. The stirring was continued for 2.8 hours. Finally, the electrolyte for lithium battery was obtained by reducing pressure filtration (vacuum degree 0.095 MPa) through a sand core funnel using a 0.45 μm polytetrafluoroethylene microporous filter membrane, and the filtrate was collected; In this embodiment, the solvent system is in a volume ratio of 4:3:1, and the addition amount of the flame retardant and the functional additive is appropriately increased to further enhance the flame retardation performance and the interface stability. The test results show that the heat release rate of the electrolyte is reduced by 8% compared to that of Example 2, and the lithium salt decomposition rate after 150 h of storage at 60°C is only 4.2%, which reflects excellent thermal stability. The capacity retention rate after 1200 cycles at 1C is 89.2%, which is slightly lower than that of Example 2, but performs better in the 130°C hot box test without any abnormal phenomenon. This indicates that a higher proportion of flame retardant and functional additive has a significant effect on improving safety, and the increase in the proportion of nanometer titanium dioxide in the new synergist still has a significant promoting effect on ion migration, with a conductivity of 5.3 mS / cm at -20°C.

[0022] Example 4: Please refer to Figs. 1-2 The application provides a technical scheme of a lithium battery electrolyte, which comprises the following components in parts by weight: 140g of a flame retardant, 60g of a lithium salt, 310g of a solvent, 25g of an interface regulator, 15g of a special functional additive and 10g of a novel synergist. The flame retardant is a mixture of ammonium polyphosphate with a polymerization degree of 1000 and perfluorohexanone with a purity of 99.8% at a weight ratio of 3:1; the lithium salt is a mixture of lithium hexafluorophosphate (water content of 20ppm) and lithium bisfluorosulfonylimide at a weight ratio of 2:1; the solvent is a mixture of dimethyl carbonate, ethylene carbonate (purity of 99.9%, water content of 10ppm) and ethyl trifluoroacetate at a volume ratio of 4:3:1; the interface regulator is a mixture of vinylene carbonate and lithium pyrophosphate with a particle size of 5μm at a weight ratio of 3:1; the special functional additive is a mixture of benzotriazole (purity of 99%) and polydimethylsiloxane with a viscosity of 100mPa·s at a weight ratio of 2:1; and the novel synergist is a mixture of anatase nano-titanium dioxide with a particle size of 50nm and a specific surface area of 80m 2 / g and ethylene carbonate with a water content of 15ppm at a weight ratio of 3:1. The preparation method of the electrolyte is as follows: (1) Preparation of a mixed solvent: dimethyl carbonate and ethylene carbonate are mixed uniformly at a volume ratio of 4:3 in a glove box at 25℃ and a humidity of 30%, and then ethyl trifluoroacetate (volume is 1 / 8 of the total volume of dimethyl carbonate and ethylene carbonate) is slowly added through a constant-pressure dropping funnel at a rate of 5mL / min, while a magnetic stirrer is used to keep the stirring speed at 100r / min, the mixture is mixed for 1.5 hours, and a Karl Fischer moisture meter is used to monitor the water content of the solvent in real time during the mixing process, and the water content is measured to be 20ppm; (2) Preparation of an interface regulator: vinylene carbonate and lithium pyrophosphate are ground and mixed in aagate mortar at a rotating speed of 400r / min for 20 minutes, and then the mixture is passed through a 200-mesh stainless steel screen, and the undersize material is collected as the interface regulator; (3) Preparation of a special functional additive: benzotriazole with a purity of 99% and anhydrous ethanol (purity of 99.9%) are mixed at a mass ratio of 1:8, and then the mixture is stirred in a 40℃ water bath until it is completely dissolved, and then polydimethylsiloxane with a viscosity of 100mPa·s (weight ratio of 1:2 with respect to benzotriazole) is added, and the mixture is stirred and mixed at 60℃ and a stirring speed of 150r / min for 30 minutes, so as to obtain a uniform transparent liquid; (4) Preparation of a novel synergist: anatase nano-titanium dioxide with a particle size of 50nm and ethylene carbonate with a water content of 15ppm are added to a beaker at a weight ratio of 3:1, a probe-type ultrasonic instrument (probe is inserted into the liquid surface below 2cm) with a power of 300W is used to ultrasonically treat the mixture for 15 minutes under the condition that the working / intermittent time ratio is 3s / 2s, and then a dynamic light scattering instrument is used to detect the particle size distribution immediately after ultrasonic treatment, and the D90 is 100nm. (5) Preparation of electrolyte: 310 g of the mixed solvent obtained in step (1) was added to a double-layer glass reactor equipped with a nitrogen protection device (nitrogen purity 99.999%, flow rate 300 mL / min), a constant temperature water bath was started to control the temperature at 40℃, a mechanical stirrer was started to stir at a speed of 120 r / min, 60 g of lithium salt (lithium hexafluorophosphate and lithium bisfluorosulfonylimide, weight ratio 2:1) was added, 140 g of flame retardant (ammonium polyphosphate and perfluorohexanone, weight ratio 3:1) was added, and the solution was stirred for 40 min until it was clear, then 25 g of the interfacial modifier obtained in step (2), 15 g of the special functional additive obtained in step (3), and 10 g of the novel synergist obtained in step (4) were added, and the stirring was continued for 3 h, finally, the filtrate was collected by reducing pressure filtration (vacuum degree 0.1 MPa) through a polytetrafluoroethylene microporous filter membrane with a pore size of 0.5 μm, and the filtrate was the flame-retardant lithium battery electrolyte; The upper limit proportion of each component was used in this example, the content of the flame retardant and the lithium salt was relatively high, and the purpose was to maximize the flame retardation performance and ion conduction basis; tests showed that the self-extinguishing time of the electrolyte in the UL94 vertical burning test was 1.8 s, and the flame retardation effect was optimal; but the conductivity at 25℃ was 11.2 mS / cm, which was slightly lower than that of examples 2 and 3, which was due to the slight increase in viscosity caused by the high proportion of flame retardant; the capacity retention rate after 1C cycle for 1200 times was 88.3%, and the low temperature capacity retention rate at-20℃ was 75.5%, both of which were at a good level; it is worth noting that the highest surface temperature of the needle test was only 142℃, and the safety was outstanding, which indicated that the high proportion of ammonium polyphosphate and perfluorohexanone compounded in the inhibition of thermal runaway played a significant role, and the synergism of the interfacial modifier and the special functional additive could still effectively maintain the cycle stability.

[0023] Example 5: Please refer to Figs. 1-2 The present application provides a technical solution: a lithium battery electrolyte, which comprises the following components by weight: 120 g of flame retardant, 52.5 g of lithium salt, 265 g of solvent, 17.5 g of interfacial modifier, 7.5 g of special functional additive, and 5 g of novel synergist; The flame retardant is a mixture of ammonium polyphosphate with a polymerization degree of 600 and perfluorohexanone with a purity of 99.5% in a weight ratio of 2.2:1; the lithium salt is a mixture of lithium hexafluorophosphate (water content 16 ppm) and lithium bisfluorosulfonylimide in a weight ratio of 1.2:1; the solvent is a mixture of dimethyl carbonate, ethylene carbonate (purity 99.9%, water content 8.5 ppm) and trifluoroacetic acid ethyl ester in a volume ratio of 3:2:1; the interfacial modifier is a mixture of vinylene carbonate and lithium pyrophosphate with a particle size of 3 μm in a weight ratio of 2.2:1; the special functional additive is a mixture of benzotriazole (purity 99%) and polydimethylsiloxane with a viscosity of 60 mPa·s in a weight ratio of 1.2:1; the novel synergist is a mixture of lithium bis(fluorosulfonyl)imide with a particle size of 25 nm and a specific surface area of 55 m 2a mixture of 265 g of the mixed solvent obtained in step (1), 52.5 g of lithium salt (lithium hexafluorophosphate and lithium bisfluorosulfonylimide in a weight ratio of 1.2:1), 120 g of flame retardant (ammonium polyphosphate and perfluorohexanone in a weight ratio of 2.2:1), 17.5 g of the interfacial modifier obtained in step (2), 7.5 g of the special functional additive obtained in step (3), and 5 g of the new synergist obtained in step (4) were added into a double-layered glass reactor equipped with a nitrogen protection device (nitrogen purity 99.999%, flow rate 220 mL / min), and stirred at a constant temperature of 32°C for 2.2 hours. The electrolyte was obtained by filtering the solution through a polytetrafluoroethylene microporous filter membrane (0.3 μm) at a reduced pressure (vacuum degree 0.085 MPa) through a sand core funnel. The electrolyte was prepared as follows: (1) Preparation of mixed solvent: dimethyl carbonate and ethylene carbonate were mixed at a volume ratio of 3:2 at 25°C in a glove box with a humidity of 26%, and then ethyl trifluoroacetate (volume 1 / 6 of the total volume of dimethyl carbonate and ethylene carbonate) was slowly added through a constant pressure dropping funnel at a rate of 5 mL / min, while a magnetic stirrer was used to maintain a stirring speed of 85 r / min. The mixture was stirred for 1.1 hours, during which a Karl Fischer moisture meter was used to monitor the moisture content of the solvent in real time, and the moisture content was measured to be 16 ppm. (2) Preparation of interfacial modifier: vinylene carbonate and lithium pyrophosphate were ground in aagate mortar at a speed of 320 r / min for 16 minutes, and then passed through a 200-mesh stainless steel screen. The undersize was collected as the interfacial modifier. (3) Preparation of special functional additive: benzotriazole with a purity of 99% and anhydrous ethanol (purity 99.9%) were mixed at a mass ratio of 1:5.5, and then stirred in a 40°C water bath until completely dissolved. Then, polydimethylsiloxane with a viscosity of 60 mPa·s (weight ratio of benzotriazole:1:1.2) was added, and the mixture was stirred at 52°C and 150 r / min for 30 minutes to obtain a uniform transparent liquid. (4) Preparation of new synergist: 25-nm anatase-type nanometer titanium dioxide and ethylene carbonate with a moisture content of 12.5 ppm were mixed in a beaker at a weight ratio of 1.5:1. A probe-type ultrasonic instrument (probe inserted 1.2 cm below the liquid surface) with a power of 220 W was used to ultrasonicate the mixture for 11 minutes under the conditions of a working / intermittent time ratio of 3 s / 2 s. The particle size distribution was detected immediately after ultrasonication using a dynamic light scattering instrument, and the D90 was 82 nm. (5) Preparation of electrolyte: 265 g of the mixed solvent obtained in step (1) was added into a double-layered glass reactor equipped with a nitrogen protection device (nitrogen purity 99.999%, flow rate 220 mL / min), and a constant temperature water bath was opened to control the temperature at 32°C. A mechanical stirrer was used to stir at a speed of 105 r / min. Lithium salt (lithium hexafluorophosphate and lithium bisfluorosulfonylimide in a weight ratio of 1.2:1) 52.5 g, flame retardant (ammonium polyphosphate and perfluorohexanone in a weight ratio of 2.2:1) 120 g were added in sequence, and the solution was stirred for 32 minutes until it was clear. Then, the interfacial modifier obtained in step (2) 17.5 g, the special functional additive obtained in step (3) 7.5 g, and the new synergist obtained in step (4) 5 g were added, and the stirring was continued for 2.2 hours. Finally, the electrolyte for the flame-retardant lithium battery was obtained by filtering the solution through a polytetrafluoroethylene microporous filter membrane (0.3 μm) at a reduced pressure (vacuum degree 0.085 MPa) through a sand core funnel. The present embodiment selects a moderate component ratio, and the comprehensive performance is balanced. Test data show that the conductivity is 12.1 mS / cm at 25°C, the self-extinguishing time is 2.3 s in the UL94 vertical burning test, the capacity retention rate is 90.1% after 1C cycle for 1200 times, and the low-temperature capacity retention rate is 77.2% at -20°C. Each performance index has no obvious short board, which reflects the stability of the synergistic effect of each component under the ratio. The lower proportion of the flame retardant makes the electrolyte viscosity moderate, and the ion migration is smooth. The reasonable proportion of the interfacial modifier and the new synergist can still ensure good interfacial stability and low-temperature performance, and is suitable for application scenarios with balanced comprehensive performance.

[0024] Embodiment 6: Please refer to Figs. 1-2 The present application provides a technical solution: a lithium battery electrolyte, comprising the following components by weight: 135 g of flame retardant, 59 g of lithium salt, 300 g of solvent, 24 g of interfacial modifier, 14 g of special functional additive, and 9.5 g of new synergist. The flame retardant is a mixture of ammonium polyphosphate with a polymerization degree of 950 and perfluorohexanone with a purity of 99.7% in a weight ratio of 2.9:1; the lithium salt is a mixture of lithium hexafluorophosphate (water content 19 ppm) and lithium bisfluorosulfonylimide in a weight ratio of 1.9:1; the solvent is a mixture of dimethyl carbonate, ethylene carbonate (purity 99.9%, water content 9.8 ppm) and ethyl trifluoroacetate in a volume ratio of 4:3:1; the interfacial modifier is a mixture of vinylene carbonate and lithium pyrophosphate with a particle size of 4.5 μm in a weight ratio of 2.9:1; the special functional additive is a mixture of benzotriazole (purity 99%) and polydimethylsiloxane with a viscosity of 95 mPa·s in a weight ratio of 1.9:1; the new synergist is a mixture of anatase nano-titanium dioxide with a particle size of 45 nm and a specific surface area of 78 m 2 / g and ethylene carbonate with a water content of 14.5 ppm in a weight ratio of 2.8:1; The preparation method of the electrolyte is as follows: (1) Preparation of mixed solvent: dimethyl carbonate and ethylene carbonate are mixed uniformly in a glove box at 25°C and 29% humidity in a volume ratio of 4:3, and then ethyl trifluoroacetate (volume is 1 / 8 of the total volume of dimethyl carbonate and ethylene carbonate) is slowly added through a constant pressure dropping funnel at a rate of 5 mL / min, while a magnetic stirrer is used to maintain a stirring speed of 98 r / min, and mixed for 1.45 hours. During the mixing process, a Karl Fischer moisture meter is used to monitor the water content of the solvent in real time, and the water content is measured to be 19 ppm; (2) Preparation of interfacial modifier: vinylene carbonate and lithium pyrophosphate are ground and mixed in aagate mortar at a speed of 390 r / min for 19.5 minutes, then passed through a 200 mesh stainless steel screen, and the undersize material was collected as the interfacial modifier; (3) Preparation of special functional additives: 99% pure benzotriazole was mixed with 99.9% pure anhydrous ethanol at a mass ratio of 1:7.8, stirred in a 40°C water bath until completely dissolved, then 95 mPa·s viscosity polydimethylsiloxane (1:1.9 by weight of benzotriazole) was added, and stirred at 59°C and 150 r / min for 30 minutes to obtain a uniform transparent liquid; (4) Preparation of new synergist: 45 nm particle size anatase nano-titanium dioxide was added to a beaker with 14.5 ppm water content ethylene carbonate at a weight ratio of 2.8:1, a 290 W probe-type ultrasonic instrument (probe inserted 1.9 cm below the liquid surface) was used, and the working / intermittent time ratio was 3s / 2s. Ultrasonic for 14.5 minutes, then use dynamic light scattering instrument to detect particle size distribution, D90 is 98 nm; (5) Preparation of electrolyte: 300g of the mixed solvent obtained in step (1) was added to a double-layer glass reactor equipped with a nitrogen protection device (nitrogen purity 99.999%, flow rate 290mL / min), the constant temperature water bath was turned on to control the temperature at 39°C, and the mechanical stirrer was used to stir at a speed of 118r / min. Add lithium salt 59g (lithium hexafluorophosphate and lithium bisfluorosulfonylimide at a weight ratio of 1.9:1), flame retardant 135g (ammonium polyphosphate and perfluorohexanone at a weight ratio of 2.9:1), stir for 39 minutes until the solution is clear, then add the interface modifier obtained in step (2) 24g, the special functional additive obtained in step (3) 14g and the new synergist obtained in step (4) 9.5g, continue to stir for 2.9 hours, finally through the sand core funnel using 0.48μm polytetrafluoroethylene microporous filter membrane reduced pressure filtration (vacuum degree 0.098MPa), collect the filtrate, which is the flame-retardant lithium battery electrolyte; The proportions of the components in this example are close to the upper limit, and are intended to test the performance under high proportions of components; the test results show that the conductivity at 25°C is 11.5mS / cm, the self-extinguishing time in UL94 vertical burning test is 1.9s, and the flame retardant performance is excellent; the capacity retention rate after 1C cycle for 1200 times is 88.7%, and the low temperature capacity retention rate at-20°C is 76.3%; the lithium salt decomposition rate after 60°C storage for 150h is 4.5%, the thermal stability is good, the surface maximum temperature in the needle test is 145°C, and the safety is high; compared with example 4, it is slightly better in conductivity and low temperature performance, which is due to the reasonable proportioning of solvents and new synergists, which can still maintain good ion migration ability under high proportion of flame retardant, and is suitable for scenes with high safety requirements and certain tolerance to other performances.

[0025] Comparative example 1 A lithium battery electrolyte, which is different from example 2 in that it does not contain a new synergist, and the rest of the components and preparation methods are the same as example 2; The preparation method of the electrolyte is as follows: (1)-(4) steps, only not to prepare the new synergist, the rest of the steps with example 2; (5) preparation of electrolyte: the mixed solvent 275g obtained in step (1) is added to a double layer glass reactor equipped with nitrogen protection device (nitrogen purity 99.999%, flow rate 250ml / min), the constant temperature water bath is opened to control the temperature at 35℃, the mechanical stirrer is used to stir at 110r / min, lithium salt 55g (lithium hexafluorophosphate and lithium bisfluorosulfonylimide weight ratio 1.5:1), flame retardant 125g (ammonium polyphosphate and perfluorohexanone weight ratio 2.5:1) are added in turn, stirring for 35 minutes until the solution is clear, then adding the interface modifier 20g obtained in step (2), special functional additive 10g obtained in step (3), continue to stir for 2.5 hours, finally through the sand core funnel with 0.4μm polytetrafluoroethylene microporous filter membrane under reduced pressure (vacuum degree 0.09MPa), the filtrate is collected as lithium battery electrolyte; Due to the lack of new synergist, the test shows that the electrolyte conductivity at 25℃ is reduced to 9.8mS / cm, which is 20.3% lower than that of example 2, because there is no nano titanium dioxide to promote ion migration and ethylene carbonate to optimize the solvation structure; The capacity retention rate after 1C cycle for 1200 times is only 75.2%, which is far lower than 90.5% of example 2, and the lithium salt decomposition rate reaches 18.3% after 60℃ storage for 150h, the thermal stability decreases significantly; The self-extinguishing time of UL94 vertical burning test is prolonged to 4.5s, which does not reach the V-0 level standard, which shows that the new synergist is indispensable in improving the comprehensive performance of electrolyte, especially the ion migration, cycle stability and thermal stability.

[0026] Comparative example 2 A kind of lithium battery electrolyte, the difference between example 2 is that the flame retardant is only ammonium polyphosphate (degree of polymerization 800), does not contain perfluorohexanone, the rest of the components and preparation method are the same with example 2; The preparation method of the electrolyte is as follows: (1)-(4) steps with example 2; (5) Preparation of electrolyte: the mixed solvent obtained in step (1) 275 g was added to a double-layer glass reactor equipped with a nitrogen protection device (nitrogen purity 99.999%, flow rate 250 mL / min), a constant temperature water bath was opened to control the temperature at 35°C, a mechanical stirrer was used to stir at a speed of 110 r / min, lithium salt 55 g (lithium hexafluorophosphate and lithium bisfluorosulfonylimide in a weight ratio of 1.5:1) was added, and flame retardant 125 g (only ammonium polyphosphate) was added, stirred for 35 minutes until the solution was clear, then interface modifier 20 g obtained in step (2), special functional additive 10 g obtained in step (3) and novel synergist 6 g obtained in step (4) were added, and stirring was continued for 2.5 hours, finally 0.4 μm polytetrafluoroethylene microporous filter membrane was used to reduce pressure filtration (vacuum degree 0.09 MPa) through a sand core funnel, and the filtrate was collected as the lithium battery electrolyte; This example only uses ammonium polyphosphate as a flame retardant, and the self-extinguishing time of UL94 vertical burning test reaches 7.2 s, which cannot pass the V-0 level test, and the flame retardant effect is far inferior to that of Example 2, indicating that the synergistic flame retardant effect of perfluoromethyl ketone and ammonium polyphosphate is crucial; In addition, the electrolyte appears a slight fire phenomenon in the needle test, the highest surface temperature reaches 260°C, and the safety is poor; At the same time, due to the lack of gas phase fire extinguishing effect of perfluoromethyl ketone, the side reaction of electrode and electrolyte is intensified at high temperature, and the capacity retention rate is 76.5% after 1200 cycles at 1C, which is lower than that of Example 2, verifying the necessity of the composite flame retardant system.

[0027] Comparative Example 3 A lithium battery electrolyte, which is different from Example 2 in that: the interface modifier is only vinylene carbonate, and does not contain lithium pyrophosphate, and the rest of the components and preparation method are the same as Example 2; The preparation method of the electrolyte is as follows: (1), (3), (4) steps are the same as Example 2; (2) Preparation of interface modifier: only take vinylene carbonate as the interface modifier; (5) Preparation of electrolyte: the mixed solvent obtained in step (1) 275 g was added to a double-layer glass reactor equipped with a nitrogen protection device (nitrogen purity 99.999%, flow rate 250 mL / min), a constant temperature water bath was opened to control the temperature at 35°C, a mechanical stirrer was used to stir at a speed of 110 r / min, lithium salt 55 g (lithium hexafluorophosphate and lithium bisfluorosulfonylimide in a weight ratio of 1.5:1) was added, and flame retardant 125 g (polyphosphate and perfluoromethyl ketone in a weight ratio of 2.5:1) was added, stirred for 35 minutes until the solution was clear, then interface modifier 20 g obtained in step (2), special functional additive 10 g obtained in step (3) and novel synergist 6 g obtained in step (4) were added, and stirring was continued for 2.5 hours, finally 0.4 μm polytetrafluoroethylene microporous filter membrane was used to reduce pressure filtration (vacuum degree 0.09 MPa) through a sand core funnel, and the filtrate was collected as the lithium battery electrolyte; The interface regulator does not contain lithium pyrophosphate, and a stable lithium-phosphorus-oxygen composite SEI film cannot be formed. The initial impedance reaches 85 Ω, which is 70% higher than 50 Ω of Example 2. After 1C cycle for 1200 times, the impedance increases to 320 Ω, which is 3.5 times of the impedance after cycle of Example 2, and the capacity retention rate is only 68.3%. This shows that lithium pyrophosphate plays a significant role in reducing interface impedance and improving the stability of SEI film. Single vinylene carbonate cannot meet the interface stability requirements of long-term cycle, further highlighting the rationality of the interface regulator compound in the present application.

[0028] Through systematic testing and data analysis of the six examples and three comparative examples, it can be clearly found that the technical scheme of the flame-retardant lithium battery electrolyte proposed in the present application has achieved a breakthrough in the core indicators of flame-retardant performance, electrochemical performance, interface stability and safety, fully embodying its creativity and significant progress compared with the prior art. This progress is not a simple superposition of single components, but through the precise proportioning and synergistic effect of each component, a new electrolyte performance optimization system is constructed, solving the technical problem of "difficulty in achieving high flame retardancy and high electrochemical performance simultaneously" which has long plagued the field. From the perspective of flame retardant performance and safety, the test data of Examples 1-6 show highly consistent excellent performance, while the comparative examples show obvious defects. Example 2, as a typical representative of balanced performance, has a self-extinguishing time of only 2.1 s in the UL94 vertical burning test, which is much lower than 4.5 s of Comparative Example 1 (missing new synergist) and 7.2 s of Comparative Example 2 (single flame retardant), and all examples achieve V-0 level flame retardant standard, while Comparative Examples 1 and 2 do not meet the standard. This difference is due to the "ammonium polyphosphate-perfluorohexanone-new synergist" ternary flame retardant system invented by the present application: the phosphate ester solid barrier formed by the decomposition of ammonium polyphosphate at high temperature cooperates with the fluorine-containing free radical gas phase fire suppression released by perfluorohexanone, and the new synergist enhances the dispersibility of the flame retardant by optimizing the solvation structure, and the physical barrier effect of nano titanium dioxide delays heat transfer. In the needle test, the surface temperature of the battery of Example 2 is only 148℃, and there is no fire and explosion phenomenon, while the surface temperature of Comparative Example 2 rises to 260℃ and there is a slight fire due to the lack of gas phase inhibition effect of perfluorohexanone. The 60℃ hot box test further confirms that the examples can still maintain stability at 130℃ environment, while Comparative Examples 1 and 2 show smoke at 110℃ and 105℃ respectively, fully proving that the present application has improved the safety threshold of lithium battery by more than 25% through the composite flame retardant mechanism and thermal stability optimization; this leap in safety is not at the expense of other performance, but through the synergy of each component to achieve the trinity protection of "flame retardant-heat dissipation-stability", which is in sharp contrast to the performance imbalance caused by single flame retardant in the comparative examples; The difference between the examples and the comparative examples is also significant in terms of electrochemical performance and cycle stability, highlighting the scientific nature of the component design of the present application; the 25°C electrical conductivity of Example 2 reaches 12.3 mS / cm, which is 25.5% higher than that of Comparative Example 1 (lacking the new synergist) of 9.8 mS / cm, and even higher than that of Comparative Example 3 (single interface modifier) of 10.5 mS / cm; this high electrical conductivity is due to the synergistic effect of the new synergist and the solvent system: the particle size effect of nano-titanium dioxide (20-50 nm) provides additional migration channels for lithium ions, and the matching of the specific surface area (50-80 m 2 / g) and the anatase crystal form reduces the lithium ion migration resistance by more than 15%; the mixed solvent shell formed by ethylene carbonate and ethylene carbonate retains high dielectric constant (promotes lithium salt dissociation) and reduces overall viscosity through the low viscosity property of trifluoroacetic acid ethyl ester; Comparative Example 1 lacks this system, and the lithium salt dissociation degree decreases by 20%, directly leading to a decrease in electrical conductivity; in the cycle performance test, the capacity retention rate of Example 2 is still 90.5% after 1C cycle for 1200 times, while that of Comparative Example 3 (single interface modifier) is only 68.3%, and that of Comparative Example 1 is as low as 75.2%; the core of this difference lies in the "lithium pyrophosphate-vinylene carbonate-benzotriazole" interface regulation system designed by the present application: lithium pyrophosphate reacts with lithium ions on the electrode surface to form a stable SEI film bottom layer containing Li3PO4, the organic layer formed by the polymerization of vinylene carbonate provides flexibility, and benzotriazole inhibits transition metal dissolution by complexing metal ions; Electrochemical impedance spectroscopy (EIS) shows that the charge transfer impedance of Example 2 after cycling only increases by 80%, while that of Comparative Example 3 increases by 350%, proving that this interface system can effectively inhibit the impedance increase during the cycle process; in the low temperature performance test, the capacity retention rate of Example 2 at -20°C is 78%, which is 25.8% higher than that of Comparative Example 1 of 62%, which benefits from the ion conduction channels maintained by nano-titanium dioxide at low temperature, solving the pain point of poor low temperature performance of traditional flame-retardant electrolyte; From the comprehensive performance synergy and industrialization value, the technical scheme of the application realizes the balance and leap of multiple performances, has remarkable creativity and practical value; it can be found through comparing the parameters of different embodiments that when the weight ratio of ammonium polyphosphate and perfluorohexanone is 2.5:1, and the weight ratio of nano titanium dioxide and ethylene carbonate in the new synergist is 2:1 (such as example 2), the best performance balance point can be obtained: at this time, the flame retardancy (self-extinguishing time 2.1s), conductivity (12.3mS / cm), cycle life (90.5%) and low temperature performance (78%) form the optimal combination, and the indicators present positive synergy instead of mutual restriction; this synergistic effect completely disappears in the comparative examples - comparative example 1 lacks a new synergist, resulting in a decrease in conductivity and cycle performance; comparative example 2 uses a single flame retardant, resulting in the dual defects of insufficient flame retardancy and cycle performance decay; more breakthrough is that the application takes into account the industrialization feasibility while improving performance: all raw materials are industrial grade products, and the cost is reduced by 30% compared with the perfluoro solvent system; the process design of "step-by-step pretreatment-nitrogen protection-precision filtration" in the preparation process can realize large-scale production through the existing electrolyte production line, and the repeated test of the six examples shows that the performance fluctuation error is less than 3%, proving that the scheme has good process stability; compared with the preparation method of the existing flame-retardant electrolyte which needs special equipment, the process compatibility of the application is stronger, and the equipment investment cost is reduced by more than 40%; this "high performance-low cost-easy production" triple advantage makes the application not only achieve a technical breakthrough at the laboratory level, but also has the potential to quickly convert into an industrial product, which is an important embodiment of its creativity - solving technical problems while providing a feasible industrialization path. In summary, through component innovation and synergistic design, the application breaks through the performance bottleneck of traditional flame-retardant electrolyte, and its creativity is reflected in three aspects: first, a "solid-gas-physical barrier" three-in-one composite flame-retardant system is constructed, solving the problem of low efficiency of single flame retardant; second, a performance optimization mechanism of "new synergist-interface modifier" synergy is developed, achieving the balance of high flame retardancy and high electrochemical performance; third, a preparation process compatible with industrial production is designed, enabling the laboratory performance advantage to be converted into industrial competitiveness; compared with the comparative examples and the prior art, the electrolyte of the application improves the 1C cycle life by 15%-20%, improves the flame retardant grade from V-1 to V-0, improves the low temperature performance by more than 20%, and reduces the cost by 30%, fully realizing the synergistic optimization of "safety-performance-cost", and providing a key material solution for the development of high safety lithium batteries.

[0029] The test method is as follows: 25℃ conductivity test: Conductivity meter (model: DDS-307A) was used for testing; before testing, the electrode of the conductivity meter was calibrated in 0.01 mol / L potassium chloride standard solution (standard conductivity is 1413 μS / cm at 25°C); 10 mL of the electrolyte to be tested was taken into a clean glass sample cell, the electrode was inserted into the electrolyte (ensuring that the electrode was completely immersed and did not touch the container wall), after constant temperature in a 25°C constant temperature water bath for 30 minutes, the conductivity value was read, the test was repeated for 3 times, and the average value was taken as the final result; UL94 vertical burning test: The test was carried out according to the UL94-2013 standard; the electrolyte was injected into a quartz sample tank with a thickness of 3 mm (the sample amount was 80% of the tank volume), the sample tank was vertically fixed on the burning test frame, a bunsen burner (flame height 20 mm, blue flame) was used to burn at the center of the bottom of the sample tank for 10 seconds, the flame was removed, and the self-extinguishing time was recorded; if the sample did not extinguish within 30 seconds, it was burned again for 10 seconds, and the second self-extinguishing time was recorded; if both the self-extinguishing times were ≤10 seconds, and there was no burning drop to ignite the cotton 300 mm below, it was determined as V-0 level; 1C cycle 1200 times capacity retention test: the electrolyte was injected into a CR2032 type button cell (positive electrode: LiCoO2, negative electrode: graphite, separator: Celgard2400), which was assembled in a glove box (argon atmosphere, water and oxygen content ≤0.1 ppm); a battery test system (model: NEWARE BTS-5V2A) was used for testing, the test conditions were: 25°C environment, charged to 4.2V at 1C rate (constant current and constant voltage, cutoff current 0.05C), rested for 5 minutes, then discharged to 3.0V at 1C rate, the first discharge capacity was recorded; the above charging and discharging process was repeated for 1200 times, the 1200th discharge capacity was recorded; capacity retention rate = (1200th discharge capacity / first discharge capacity) x 100%, 3 parallel batteries were tested, and the average value was taken; -20°C capacity retention test: the test object was the above-mentioned CR2032 type button cell, after being placed in a -20°C low temperature box for 2 hours, a 5V2A test system was used to charge to 4.2V at 0.2C rate (constant current and constant voltage, cutoff current 0.05C), rested for 5 minutes, then discharged to 3.0V at 0.2C rate, the -20°C discharge capacity was recorded; the battery was restored to 25°C, and the normal temperature discharge capacity was tested under the same charging and discharging system; low temperature capacity retention rate = (-20°C discharge capacity / normal temperature discharge capacity) x 100%, 3 parallel batteries were tested, and the average value was taken; 60°C storage for 150h lithium salt decomposition rate test: 5 mL of the electrolyte to be tested was placed in a sealed polytetrafluoroethylene container, and stored in a 60°C constant temperature box for 150h; before and after storage, ion chromatography (model: Dionex ICS-1100) was used to test the free fluoride ion (F⁻ ) concentration (characteristic product of lithium salt decomposition); lithium salt decomposition rate = (F ⁻ concentration after storage) / theoretical total F ⁻ concentration) x 100%, theoretical total F ⁻ concentration is calculated according to the amount of lithium salt, and the average value of three tests is taken; Puncture test surface maximum temperature test: the electrolyte is injected into a soft package battery (specification: 50mm x 50mm x 3mm, positive electrode: LiNi0.5Co0.2Mn0.3O2, negative electrode: graphite, capacity: 1000mAh), and the packaging is completed in a dry room (humidity ≤2%); a puncture test device (steel needle diameter 3mm, needle tip angle 30°) is used to vertically puncture the center position of the battery at a speed of 50mm / s, an infrared thermal imager (model: FLIRE60) is used to monitor the change of the surface temperature of the battery in real time, the maximum temperature within 30 minutes after puncture is recorded, and the average value of three parallel batteries is taken; Initial impedance and impedance test after 1C cycle for 1200 times: an electrochemical workstation (model: CHI660E) is used to test the impedance of CR2032 type button cell, the test frequency range is 100kHz-0.01Hz, and the amplitude is 5mV; the initial impedance is the test result after the battery is assembled and placed for 24 hours; the impedance after 1C cycle for 1200 times is the test result after the cycle test is completed and placed for 24 hours, the diameter of the semicircle in the impedance spectrum is read as the charge transfer impedance value, three parallel batteries are tested, and the average value is taken; 130℃ hot box test: the soft package battery (same as the puncture test specification) is placed in a hot box, heated to 130℃ at a rate of 5℃ / min, and kept at constant temperature for 30 minutes, whether the battery appears smoke, fire, explosion and other phenomena is observed, the time and state of abnormal phenomenon are recorded, and the most serious phenomenon is taken as the result.

[0030] The above is only an embodiment of the present application, and the specific technical solutions or characteristics in the scheme are not described in detail. It should be noted that for those skilled in the art, without departing from the technical solutions of the present application, some modifications and improvements can be made, which should also be considered as the protection scope of the present application, and these will not affect the effect and practicality of the patent. The protection scope claimed in this application should be subject to the content of its claims, and the specific embodiments in the description can be used to explain the content of the claims.

Claims

1. A lithium battery electrolyte, characterized by, The components include the following weight parts: flame retardant 22-28 parts, lithium salt 10-12 parts, solvent 50-62 parts, interface modifier 3-5 parts, special functional additive 1-3 parts, and new synergist 0.5-2 parts; The flame retardant is a mixture of ammonium polyphosphate with a polymerization degree of 500-1000 and perfluorohexanone with a purity of ≥99.5% at a weight ratio of 2:1-3:1; The lithium salt is a mixture of lithium hexafluorophosphate and lithium bisfluorosulfonylimide at a weight ratio of 1:1-2:

1.

2. The lithium battery electrolyte according to claim 1, wherein, The solvent is a mixture of dimethyl carbonate, ethylene carbonate and ethyl trifluoroacetate at a volume ratio of 3:2:1-4:3:1, and the purity of the ethylene carbonate is ≥99.9% and the water content is ≤10ppm; the volume ratio of dimethyl carbonate, ethylene carbonate and ethyl trifluoroacetate in the solvent is preferably 3:2:

1.

3. The lithium battery electrolyte of claim 1, wherein, The interface modifier is a mixture of vinylene carbonate and lithium pyrophosphate with a particle size of ≤5μm at a weight ratio of 2:1-3:1, and the weight ratio of the vinylene carbonate and lithium pyrophosphate is preferably 2.5:

1.

4. The lithium battery electrolyte of claim 1, wherein, The special functional additive is a mixture of benzotriazole and polydimethylsiloxane with a viscosity of 50-100mPa•s at a weight ratio of 1:1-2:1, and the purity of the benzotriazole is ≥99%; the weight ratio of the benzotriazole and polydimethylsiloxane is preferably 1.5:

1.

5. The lithium battery electrolyte of claim 1, wherein, The new synergist is a mixture of anatase nanotitanium dioxide with a particle size of 20-50 nm and a specific surface area of 50-80 m 2 / g and ethylene carbonate with a water content of < 15 ppm in a weight ratio of 1 : 1 to 3 : 1, the weight ratio of nanotitanium dioxide to ethylene carbonate preferably being 2 :

1.

6. The lithium battery electrolyte of claim 1, wherein, The weight ratio of the ammonium polyphosphate and perfluorohexanone is 2.5:1; the weight ratio of the lithium hexafluorophosphate and lithium bisfluorosulfonylimide is 1.5:1, and the water content of the lithium hexafluorophosphate is ≤20ppm.

7. A method for preparing a lithium battery electrolyte, characterized by, The method for preparing the lithium battery electrolyte of any one of claims 1-6 comprises the following steps: (1) preparing a mixed solvent: mixing dimethyl carbonate and ethylene carbonate in a glove box at 25℃ and humidity ≤30% in proportion, then adding ethyl trifluoroacetate at a rate of 5mL / min through a constant pressure dropping funnel, while maintaining the stirring speed of a magnetic stirrer at 80-100r / min, mixing for 1-1.5 hours, and monitoring the water content of the solvent in real time with a Karl Fischer moisture meter during the mixing to ensure that the water content is ≤20ppm; (2) preparing an interface modifier: grinding and mixing vinylene carbonate and lithium pyrophosphate in aagate mortar at a speed of 300-400r / min for 15-20 minutes, passing through a 200-mesh stainless steel screen, and collecting the undersize as the interface modifier; (3) preparing a special functional additive: mixing benzotriazole with a purity of ≥99% and anhydrous ethanol (purity ≥99.9%) in a mass ratio of 1:5-1:8, stirring in a 40℃ water bath until completely dissolved, then adding polydimethylsiloxane with a viscosity of 50-100mPa•s, and stirring and mixing at 50-60℃ and 150r / min for 30 minutes to obtain a uniform transparent liquid; (4) Preparation of a new synergist: add the anatase type nano-titanium dioxide with a particle size of 20-50 nm and ethylene carbonate with a water content of ≤15 ppm into a beaker in proportion, use a probe type ultrasonic instrument with a power of 200-300 W (the probe is inserted into the liquid surface below 1-2 cm), and ultrasonic for 10-15 minutes under the condition of a working / intermittent time ratio of 3 s / 2 s, immediately detect the particle size distribution by using a dynamic light scattering instrument after ultrasonic, ensure that D90≤100 nm, if it does not meet the standard, extend the ultrasonic for 5 minutes; (5) Preparation of an electrolyte: add the mixed solvent obtained in step (1) into a double-layer glass reaction kettle equipped with a nitrogen protection device (the purity of nitrogen is ≥99.999%, and the flow is 200-300 mL / min), open the constant temperature water bath to control the temperature to be 30-40℃, use a mechanical stirrer to stir at a rotating speed of 100-120 r / min, add lithium salt and flame retardant in sequence, stir until the solution is clear, then add the interface regulator obtained in step (2), the special functional additive obtained in step (3) and the new synergist obtained in step (4), continue to stir for 2-3 hours, finally, collect the filtrate by using a 0.2-0.5 μm polytetrafluoroethylene microporous filter membrane to perform pressure reduction filtration (the vacuum degree is 0.08-0.1 MPa) through a sand core funnel, and the collected filtrate is the lithium battery electrolyte.

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