High-safety non-flammable environment-friendly parking lithium iron battery

Abstract

The invention relates to the technical field of lithium iron batteries, and discloses a lithium iron battery comprising a positive pole piece, a negative pole piece, a diaphragm and an organic electrolyte, the positive pole piece comprises a positive current collector and a positive active material arranged on the surface of the positive current collector, and the negative pole piece comprises a negative current collector and a negative active material arranged on the surface of the negative current collector; the positive electrode active material is lithium iron phosphate; the negative electrode active material is graphite; and the organic electrolyte additive is composed of tetramethyl tetraphenyl cyclotetrasiloxane and ethylene carbonate. According to the high-safety non-flammable environment-friendly lithium iron battery for the parking vehicle, the flammability can be effectively reduced under the condition that the electrolyte viscosity, the conductivity, the battery cycle performance and the like are not influenced; the flame retardant is added into the electrolyte, so that a voltage stability window is not damaged, the electrolyte can be inhibited from generating more gas under a high-temperature condition, and the cycle performance and the safety performance of the battery are obviously improved.

Description

Technical Field

[0001] The invention relates to the technical field of iron-lithium batteries, in particular to a highly safe, non-flammable and environmentally friendly iron-lithium battery for parking. Background Art

[0002] Iron-lithium battery, whose full name is lithium iron phosphate lithium-ion battery, is a type of battery in the lithium battery family. Its positive electrode material is mainly lithium iron phosphate material, so it is also called iron-lithium battery. Iron-lithium battery has the following advantages: high efficiency output, good temperature performance, fast charging, environmental protection, etc. Its performance is particularly suitable for power applications, such as: large electric vehicles, power tools, small medical instruments and equipment and portable instruments, etc.

[0003] The rapid development of industry and economy has brought about problems such as the shortage of non-renewable energy and environmental pollution. Therefore, the development and utilization of new green and renewable energy has become a hot research field in the field of chemical power sources. Iron-lithium ion batteries are widely used in our daily lives due to their advantages such as high voltage, high energy density, long cycle life, small memory effect, and green environmental protection. For example, they are used in portable traditional electronic devices, power tools, new energy vehicles, energy storage power stations, etc., becoming one of the most promising and competitive high-tech products. With the large-scale expansion and application of iron-lithium ion batteries, various safety issues have also arisen. In recent years, accidents related to thermal runaway of iron-lithium ion batteries have been reported from time to time, which has also affected the large-scale application of iron-lithium ion batteries to a certain extent. The thermal runaway phenomenon of iron-lithium ion batteries has attracted attention from all walks of life and has put forward higher requirements for the safety performance of iron-lithium ion batteries. Based on this, a highly safe, non-flammable and environmentally friendly iron-lithium battery for parking is proposed. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the deficiencies in the prior art, the present invention provides a highly safe, non-flammable, environmentally friendly iron-lithium battery for parking, which has the advantages of being able to reduce the probability of spontaneous combustion of the iron-lithium battery, and solves the problem of the iron-lithium battery being prone to spontaneous combustion during use.

[0006] (II) Technical solution

[0007] To achieve the above object, the present invention provides the following technical solution: comprising a positive electrode sheet, a negative electrode sheet, a separator and an organic electrolyte, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material disposed on the surface of the positive electrode current collector, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material disposed on the surface of the negative electrode current collector;

[0008] The positive electrode active material is lithium iron phosphate; the negative electrode active material is graphite; the organic electrolyte additive consists of tetramethyltetraphenylcyclotetrasiloxane and vinyl ethylene carbonate; the mass percentage of tetramethyltetraphenylcyclotetrasiloxane is 0.6-1%; the mass percentage of vinyl ethylene carbonate is 0.5-1.5%; the 25°C conductivity of the electrolyte is 9.10mS / cm~9.20mS / cm; the 25°C viscosity of the electrolyte is 5mPa.s~7mPa.s, and the organic electrolyte contains an organic solvent, a lithium salt, an electrolyte additive and a flame retardant additive.

[0009] Preferably, the particle size D50 of the positive electrode active material is 2-4 μm.

[0010] Preferably, the particle size D50 of the negative electrode active material is 8 to 11 μm.

[0011] Preferably, the diaphragm is polyethylene with a thickness of 15 um, and the porosity of the diaphragm is 45-55%.

[0012] Preferably, the compaction density of the positive electrode sheet is 2.2 g / cm 3 ~2.6g / cm 3 .

[0013] Preferably, the flame retardant additive is diphenyl cresol phosphate, and the mass fraction of the flame retardant additive is 5% to 10%.

[0014] A method for preparing a highly safe, non-flammable, environmentally friendly lithium iron battery for parking comprises the following steps:

[0015] 1) Preparation of negative electrode sheet: The negative electrode active material, the conductive agent CNT, and the binder CMC are uniformly mixed in a mass ratio of 90:5:5, and then dispersed in deionized water to obtain a negative electrode slurry, the negative electrode slurry is coated on a copper foil, and dried at 110° C. in a vacuum environment for 12 h to obtain a negative electrode sheet, and the negative electrode sheet is cold-pressed to tightly stack the particles to obtain a negative electrode sheet.

[0016] 2) Preparation of positive electrode sheet: The positive electrode active material, conductive agent SP, and binder PVDF are uniformly mixed in a mass ratio of 92:4:4, and then dispersed in NMP to obtain a positive electrode slurry, the positive electrode slurry is coated on an aluminum foil, and dried at 90°C in a vacuum environment for 24 hours to obtain a positive electrode sheet, and the electrode sheet is cold-pressed to make the particles densely stacked to obtain a positive electrode sheet.

[0017] 3) Assembling the battery: Assemble the above-mentioned positive electrode sheet, negative electrode sheet and separator into a single-electrode soft-pack battery, and inject a sufficient amount of organic electrolyte.

[0018] 4) Formation: After injection, the battery is left to stand at room temperature for 12 hours. After the electrolyte completely soaks the electrodes, it is charged at 0.15C for 4 hours at a temperature of 25°C to form an SE I film at the negative electrode. After the generated gas is removed, it is charged at 0.33C to the upper limit voltage, and then charged at a constant voltage of 0.05C.

[0019] (III) Beneficial effects

[0020] Compared with the prior art, the present invention provides a highly safe, non-flammable, environmentally friendly lithium iron battery for parking, which has the following beneficial effects:

[0021] This highly safe, non-flammable, environmentally friendly iron-lithium battery for parking can effectively reduce flammability without affecting the electrolyte viscosity, conductivity, battery cycle performance, etc.; by adding flame retardants to the electrolyte, the voltage stability window will not be damaged, and the electrolyte can be inhibited from producing more gas under high temperature conditions, significantly improving the battery's cycle performance and safety performance. DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Embodiment 1:

[0024] 1) Preparation of negative electrode sheet: The negative electrode active material, the conductive agent CNT, and the binder CMC are uniformly mixed in a mass ratio of 90:5:5, and then dispersed in deionized water to obtain a negative electrode slurry, the negative electrode slurry is coated on a copper foil, and dried at 110°C in a vacuum environment for 12 hours to obtain a negative electrode sheet, and the negative electrode sheet is cold-pressed to make the particles densely stacked to obtain a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material disposed on the surface of the negative electrode current collector, the negative electrode active material is graphite, the particle size D50 of the negative electrode active material is 8 μm, and the compaction density of the negative electrode sheet is 1.5 g / cm 3 .

[0025] 2) Preparation of positive electrode sheet: The positive electrode active material, conductive agent SP, and binder PVDF are mixed uniformly in a mass ratio of 92:4:4, and then dispersed in NMP to obtain a positive electrode slurry, the positive electrode slurry is coated on an aluminum foil, and dried at 90°C in a vacuum environment for 24 hours to obtain a positive electrode sheet, and the sheet is cold-pressed to make the particles densely stacked to obtain a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material disposed on the surface of the positive electrode current collector, the positive electrode active material is lithium iron phosphate, the particle size D50 of the positive electrode active material is 2 μm, and the compaction density of the positive electrode sheet is 2.2 g / cm 3 .

[0026] 3) Assembling the battery: Assemble the above-mentioned positive electrode plate, negative electrode plate and separator into a single-pole soft-pack battery, and inject a sufficient amount of organic electrolyte, the organic electrolyte additive consists of tetramethyltetraphenylcyclotetrasiloxane and vinyl ethylene carbonate; the mass percentage of tetramethyltetraphenylcyclotetrasiloxane is 0.6%; the mass percentage of vinyl ethylene carbonate is 0.5%; the conductivity of the electrolyte at 25°C is 9.10mS / cm; the viscosity of the electrolyte at 25°C is 5mPa.s, the organic electrolyte comprises an organic solvent, a lithium salt, an electrolyte additive and a flame retardant additive, the separator is polyethylene with a thickness of 15um, the porosity of the separator is 45, the flame retardant additive is diphenyl phosphate, and the mass fraction of the flame retardant additive is 5%.

[0027] 4) Formation: After injection, the battery is left to stand at room temperature for 12 hours. After the electrolyte completely soaks the electrodes, it is charged at 0.15C for 4 hours at a temperature of 25°C to form an SE I film at the negative electrode. After the generated gas is removed, it is charged at 0.33C to the upper limit voltage, and then charged at a constant voltage of 0.05C.

[0028] The experiment proved that when the mass fraction of the flame retardant additive was 5%, it had a good flame retardant effect. When the particle size D50 of the negative electrode active material was 8 μm and the compaction density of the negative electrode sheet was 1.5 g / cm 3 The particle size D50 of the positive electrode active material is 2 μm, and the compaction density of the positive electrode sheet is 2.2 g / cm 3 When the electrolyte can function normally, the mass percentage of tetramethyltetraphenylcyclotetrasiloxane is 0.6%; the mass percentage of vinyl ethylene carbonate is 0.5%, which can improve the conductivity of the electrolyte.

[0029] Embodiment 2:

[0030] 1) Preparation of negative electrode sheet: The negative electrode active material, the conductive agent CNT, and the binder CMC are uniformly mixed in a mass ratio of 90:5:5, and then dispersed in deionized water to obtain a negative electrode slurry, the negative electrode slurry is coated on a copper foil, and dried at 110°C in a vacuum environment for 12 hours to obtain a negative electrode sheet, and the negative electrode sheet is cold-pressed to make the particles densely stacked to obtain a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material disposed on the surface of the negative electrode current collector, the negative electrode active material is graphite, the particle size D50 of the negative electrode active material is 9 μm, and the compaction density of the negative electrode sheet is 1.6 g / cm 3 .

[0031] 2) Preparation of positive electrode sheet: The positive electrode active material, conductive agent SP, and binder PVDF are mixed uniformly in a mass ratio of 92:4:4, and then dispersed in NMP to obtain a positive electrode slurry, the positive electrode slurry is coated on an aluminum foil, and dried at 90°C in a vacuum environment for 24 hours to obtain a positive electrode sheet, and the sheet is cold-pressed to make the particles densely stacked to obtain a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material disposed on the surface of the positive electrode current collector, the positive electrode active material is lithium iron phosphate, the particle size D50 of the positive electrode active material is 3 μm, and the compaction density of the positive electrode sheet is 2.4 g / cm 3 .

[0032] 3) Assembling the battery: Assemble the above-mentioned positive electrode plate, negative electrode plate and separator into a single-pole soft-pack battery, and inject a sufficient amount of organic electrolyte, the organic electrolyte additive consists of tetramethyltetraphenylcyclotetrasiloxane and vinyl ethylene carbonate; the mass percentage of tetramethyltetraphenylcyclotetrasiloxane is 0.8%; the mass percentage of vinyl ethylene carbonate is 1%; the conductivity of the electrolyte at 25°C is 9.15mS / cm; the viscosity of the electrolyte at 25°C is 6mPa.s, the organic electrolyte comprises an organic solvent, a lithium salt, an electrolyte additive and a flame retardant additive, the separator is a polyethylene with a thickness of 15um, the porosity of the separator is 50%, the flame retardant additive is diphenyl cresol phosphate, and the mass fraction of the flame retardant additive is 8%.

[0033] 4) Formation: After injection, the battery is left to stand at room temperature for 12 hours. After the electrolyte completely soaks the electrodes, it is charged at 0.15C for 4 hours at a temperature of 25°C to form an SE I film at the negative electrode. After the generated gas is removed, it is charged at 0.33C to the upper limit voltage, and then charged at a constant voltage of 0.05C.

[0034] The experiment proved that the flame retardant effect was better when the mass fraction of the flame retardant additive was 8% than when the mass fraction of the flame retardant additive was 5%. When the particle size D50 of the negative electrode active material was 9μm and the compaction density of the negative electrode sheet was 1.6g / cm 3 The particle size D50 of the positive electrode active material is 3 μm, and the compaction density of the positive electrode sheet is 2.4 g / cm 3When the mass percentage of tetramethyltetraphenylcyclotetrasiloxane is 0.8% and the mass percentage of vinyl ethylene carbonate is 1%, the conductivity of the electrolyte can be further improved.

[0035] Embodiment three:

[0036] 1) Preparation of negative electrode sheet: The negative electrode active material, the conductive agent CNT, and the binder CMC are uniformly mixed in a mass ratio of 90:5:5, and then dispersed in deionized water to obtain a negative electrode slurry, the negative electrode slurry is coated on a copper foil, and dried at 110°C in a vacuum environment for 12 hours to obtain a negative electrode sheet, and the negative electrode sheet is cold-pressed to make the particles densely stacked to obtain a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material disposed on the surface of the negative electrode current collector, the negative electrode active material is graphite, the particle size D50 of the negative electrode active material is 11 μm, and the compaction density of the negative electrode sheet is 1.7 g / cm 3 .

[0037] 2) Preparation of positive electrode sheet: The positive electrode active material, conductive agent SP, and binder PVDF are mixed uniformly in a mass ratio of 92:4:4, and then dispersed in NMP to obtain a positive electrode slurry, the positive electrode slurry is coated on an aluminum foil, and dried at 90°C in a vacuum environment for 24 hours to obtain a positive electrode sheet, and the sheet is cold-pressed to make the particles densely stacked to obtain a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material disposed on the surface of the positive electrode current collector, the positive electrode active material is lithium iron phosphate, the particle size D50 of the positive electrode active material is 4 μm, and the compaction density of the positive electrode sheet is 2.6 g / cm 3 .

[0038] 3) Assembling the battery: Assemble the above-mentioned positive electrode plate, negative electrode plate and separator into a single-pole soft-pack battery, and inject a sufficient amount of organic electrolyte, the organic electrolyte additive consists of tetramethyltetraphenylcyclotetrasiloxane and vinyl ethylene carbonate; the mass percentage of tetramethyltetraphenylcyclotetrasiloxane is 1%; the mass percentage of vinyl ethylene carbonate is 1.5%; the conductivity of the electrolyte at 25°C is 9.20mS / cm; the viscosity of the electrolyte at 25°C is 7mPa.s, the organic electrolyte comprises an organic solvent, a lithium salt, an electrolyte additive and a flame retardant additive, the separator is a polyethylene with a thickness of 15um, the porosity of the separator is 55%, the flame retardant additive is diphenyl phosphate, and the mass fraction of the flame retardant additive is 10%.

[0039] 4) Formation: After injection, the battery is left to stand at room temperature for 12 hours. After the electrolyte completely soaks the electrodes, it is charged at 0.15C for 4 hours at a temperature of 25°C to form an SE I film at the negative electrode. After the generated gas is removed, it is charged at 0.33C to the upper limit voltage, and then charged at a constant voltage of 0.05C.

[0040] The experiment proved that the flame retardant effect was best when the mass fraction of the flame retardant additive was 10%, when the particle size D50 of the negative electrode active material was 11 μm, and the compaction density of the negative electrode sheet was 1.7 g / cm 3 The particle size D50 of the positive electrode active material is 4 μm, and the compaction density of the positive electrode sheet is 2.6 g / cm 3 The conductivity of the electrolyte is relative to the particle size D50 of the negative electrode active material is 9 μm, and the compaction density of the negative electrode sheet is 1.6 g / cm 3 The particle size D50 of the positive electrode active material is 3 μm, and the compaction density of the positive electrode sheet is 2.4 g / cm 3 When the mass percentage of tetramethyltetraphenylcyclotetrasiloxane is 0.8%, the conductivity decreases; when the mass percentage of tetramethyltetraphenylcyclotetrasiloxane is 1%; and the mass percentage of vinyl ethylene carbonate is 1.5%, the effect of improving the conductivity of the electrolyte is no longer obvious.

[0041] It should be noted that NMP is N-methylpyrrolidone; its Chinese alias is 1-methyl-2-pyrrolidone; N-methyl-2-pyrrolidone is a colorless, transparent, oily liquid with a slight amine smell, low volatility, and good thermal and chemical stability; the "C" in 0.33C represents the battery discharge rate.

[0042] The beneficial effects of the present invention are: it can effectively reduce the flammability without affecting the viscosity, conductivity, battery cycle performance, etc. of the electrolyte; by adding a flame retardant to the electrolyte, the voltage stability window will not be damaged, and the electrolyte can be inhibited from producing more gas under high temperature conditions, thereby significantly improving the battery's cycle performance and safety performance, and solving the problem of the easy spontaneous combustion of iron-lithium batteries during use.

[0043] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A highly safe, non-flammable, environmentally friendly lithium iron battery for parking, characterized by: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator and an organic electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material disposed on the surface of the positive electrode current collector, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material disposed on the surface of the negative electrode current collector; The positive electrode active material is lithium iron phosphate; the negative electrode active material is graphite; the organic electrolyte additive is composed of tetramethyltetraphenylcyclotetrasiloxane and vinyl ethylene carbonate; the mass percentage of tetramethyltetraphenylcyclotetrasiloxane is 0.6-1%; the mass percentage of vinyl ethylene carbonate is 0.5-1.5%; the 25°C conductivity of the electrolyte is 9.10mS / cm~9.20mS / cm; the 25°C viscosity of the electrolyte is 5mPa.s~7mPa.s, and the organic electrolyte contains an organic solvent, a lithium salt, an electrolyte additive and a flame retardant additive.

2. A highly safe, non-flammable, environmentally friendly lithium iron battery for parking according to claim 1, characterized in that: The particle size D50 of the positive electrode active material is 2 to 4 μm.

3. A highly safe, non-flammable, environmentally friendly lithium iron battery for parking according to claim 1, characterized in that: The particle size D50 of the negative electrode active material is 8 to 11 μm.

4. A highly safe, non-flammable, environmentally friendly lithium iron battery for parking according to claim 1, characterized in that: The diaphragm is polyethylene with a thickness of 15 μm and a porosity of 45-55%.

5. The highly safe, non-flammable, environmentally friendly lithium iron battery for parking according to claim 1, characterized in that: The compaction density of the positive electrode sheet is 2.2 g / cm 3 ~2.6g / cm 3 .

6. A highly safe, non-flammable, environmentally friendly lithium iron battery for parking according to claim 1, characterized in that: The compaction density of the negative electrode sheet is 1.5 g / cm 3 ~1.7g / cm 3 .

7. The highly safe, non-flammable, environmentally friendly lithium iron battery for parking according to claim 1, characterized in that: The flame retardant additive is diphenyl cresol phosphate, and the mass fraction of the flame retardant additive is 5% to 10%.

8. A method for preparing a highly safe, non-flammable, environmentally friendly lithium iron battery for parking according to claims 1-7, characterized in that: The following steps are involved: 1) Preparation of negative electrode sheet: The negative electrode active material, the conductive agent CNT, and the binder CMC are uniformly mixed in a mass ratio of 90:5:5, and then dispersed in deionized water to obtain a negative electrode slurry, the negative electrode slurry is coated on a copper foil, and dried at 110° C. in a vacuum environment for 12 h to obtain a negative electrode sheet, and the negative electrode sheet is cold-pressed to tightly stack the particles to obtain a negative electrode sheet. 2) Preparation of positive electrode sheet: The positive electrode active material, conductive agent SP, and binder PVDF are uniformly mixed in a mass ratio of 92:4:4, and then dispersed in NMP to obtain a positive electrode slurry, the positive electrode slurry is coated on an aluminum foil, and dried at 90°C in a vacuum environment for 24 hours to obtain a positive electrode sheet, and the electrode sheet is cold-pressed to make the particles densely stacked to obtain a positive electrode sheet. 3) Assembling the battery: Assemble the above-mentioned positive electrode sheet, negative electrode sheet and separator into a single-electrode soft-pack battery, and inject a sufficient amount of organic electrolyte. 4) Formation: After injection, let the battery stand at room temperature for 12 hours. After the electrolyte completely soaks the electrodes, charge it at 0.15C for 4 hours at a temperature of 25°C to form a SEI film at the negative electrode. After removing the generated gas, charge it at 0.33C to the upper limit voltage, and then charge it at a constant voltage of 0.05C.