阅读说明：本技术 一种方形铝壳低温倍率型锂离子电池及其制备方法 (Square aluminum shell low-temperature rate lithium ion battery and preparation method thereof ) 是由 张秦怡 邵乐 胡朝文 米吉福 张贵录 路通 胡秋晨 于 2021-07-30 设计创作，主要内容包括：本发明提供一种方形铝壳低温倍率型锂离子电池及其制备方法,由正极活性物质、导电炭黑SP、碳纳米管导电浆料、PVDF聚偏氟乙烯粘结剂、分散剂和氮甲基吡咯烷酮(NMP)制备正极浆料并形成侧边留箔正极极片；由负极活性材料、导电炭黑SP、羧甲基纤维素纳CMC、增稠剂丁苯橡胶SBR和水混合得到负极浆料并形成侧边留箔负极极片；将正极极片和负极极片制成全极耳方形极组并制备得到方形铝壳锂离子电池；将方形铝壳锂离子电池在高温老化后进行化成,制得方形铝壳低温倍率型锂离子电池；本发明利用简单的制备工艺,通过材料的合理选型搭配及电池化成工艺特殊处理,得到兼具低温和倍率性能的长寿命方形铝壳低温倍率型锂离子电池,制备工艺可靠稳定,适合生产。(The invention provides a square aluminum shell low-temperature multiplying power type lithium ion battery and a preparation method thereof, wherein positive electrode slurry is prepared by a positive electrode active substance, conductive carbon black SP, carbon nano tube conductive slurry, PVDF (polyvinylidene fluoride) binder, a dispersing agent and N-methyl pyrrolidone (NMP) and a side edge foil-left positive electrode piece is formed; mixing a negative active material, conductive carbon black SP, carboxymethyl cellulose sodium CMC, thickening agent SBR and water to obtain negative slurry and forming a side-edge foil-remained negative pole piece; preparing a positive pole piece and a negative pole piece into a full-lug square pole group and preparing a square aluminum shell lithium ion battery; forming the square aluminum shell lithium ion battery after high-temperature aging to obtain the square aluminum shell low-temperature multiplying power type lithium ion battery; the invention utilizes simple preparation process, obtains the long-service-life square aluminum shell low-temperature multiplying power type lithium ion battery with low temperature and multiplying power performance by reasonable type selection and collocation of materials and special treatment of battery formation process, has reliable and stable preparation process and is suitable for production.)

1. A preparation method of a square aluminum shell low-temperature rate lithium ion battery is characterized by comprising the following specific steps:

s1, mixing the positive active substance, the conductive carbon black, the carbon nanotube conductive slurry, the polyvinylidene fluoride binder and the dispersant to obtain a first precursor, adding N-methyl pyrrolidone into the first precursor to adjust the viscosity to obtain positive slurry, coating the positive slurry on an aluminum foil, and forming a positive pole piece with a foil left on the side edge through coating, rolling and slitting;

s2, mixing the negative active material, conductive carbon black, sodium carboxymethyl cellulose and thickening agent styrene butadiene rubber to obtain a second precursor, adding water into the second precursor to adjust viscosity to obtain negative slurry, coating the negative slurry on a copper foil, and rolling and slitting to form a negative pole piece with a foil left on the side edge;

s3, separating the positive pole piece and the negative pole piece obtained in the steps S1 and S2 by a lithium ion battery diaphragm, connecting the positive pole piece and the negative pole piece into a square aluminum shell through winding and ultrasonic welding to prepare a full-lug square pole group, injecting lithium ion battery electrolyte into the pole group, pre-forming and exhausting, sealing and cleaning to obtain a square aluminum shell lithium ion battery;

and S4, aging the square aluminum shell lithium ion battery obtained in the step S3 at a high temperature, forming, placing the formed battery in an environment of 45-50 ℃ for 2-4 h after being fully charged at normal temperature, cooling at 0-5 ℃, and discharging at normal temperature to obtain the square aluminum shell low-temperature rate lithium ion battery.

2. The method for preparing the square aluminum-shell low-temperature rate lithium ion battery according to claim 1, wherein in step S1, 93 wt% -96 wt% of the positive electrode active material, 1.2 wt% -2.5 wt% of the conductive carbon black SP, 0.4 wt% -1.6 wt% of the carbon nanotube conductive paste, 1.0 wt% -3.5 wt% of the PVDF polyvinylidene fluoride binder, and 0.1 wt% -0.2 wt% of the dispersant are mixed by weight to obtain the first precursor.

3. The method of any one of claims 1 or 2, wherein in step S1, the positive electrode active material is prepared by hydrothermal carbon-coating nano LFP material, and has a particle size of 3 μm to 8 μm and a specific surface area of 10m²/g～14m²And the positive active material is nano lithium iron phosphate or a lithium iron composite.

4. The method for preparing a square aluminum-shell low-temperature rate lithium ion battery according to claim 1, wherein in step S1, the carbon nanotube conductive paste is CNT or a mixture of CNT and graphene; the dispersing agent is a copolymer of styrene and acrylic ester; the dosage of the N-methyl pyrrolidone is 45 wt% -50 wt% of the anode slurry.

5. The method for preparing a square aluminum-shell low-temperature rate lithium ion battery according to claim 1, wherein in step S2, 94 wt% -96 wt% of negative active material, 1.0 wt% -2.5 wt% of conductive carbon black, 1.0 wt% -1.5 wt% of sodium carboxymethyl cellulose and 1.5 wt% -2.5 wt% of thickener styrene butadiene rubber are mixed to obtain a second precursor.

6. The method for preparing the square aluminum-shell low-temperature rate lithium ion battery according to claim 1, wherein in step S2, the water is used in an amount of 47 wt% to 50 wt% of the negative electrode slurry.

7. The method for preparing the square aluminum-shell low-temperature rate lithium ion battery according to claim 1, wherein in step S2, the particle size of the negative electrode active material is 7 μm to 13 μm, and the negative electrode active material is hard carbon-coated nano small-particle-size graphite or modified artificial graphite.

8. The method for preparing the square aluminum shell low-temperature rate lithium ion battery according to claim 1, wherein in step S3, the lithium ion battery separator is a water-based or oil-based rubber-coated ceramic separator, and the lithium ion battery separator has a thickness of 12 to 20 μm; the electrolyte of the lithium ion battery is an amorphous electrolyte of lithium hexafluorophosphate, and the concentration of the electrolyte is 1.0-1.5 mol/L.

9. The method according to claim 8, wherein in step S3, the solvent of the amorphous electrolyte solution of lithium hexafluorophosphate is a mixture of EC and a chain carboxylate solvent, and the chain carboxylate solvent comprises at least one of poly (ethylene glycol) dimethyl ether, ethyl acetate, ethyl propionate, methyl acetate and methyl butyrate.

10. A square aluminum-shell low-temperature rate lithium ion battery, which is characterized by being prepared according to the preparation method of any one of claims 1 to 9.

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly belongs to a square aluminum shell low-temperature rate lithium ion battery and a preparation method thereof.

Background

The lithium iron phosphate battery becomes the energy source first choice of the power battery due to high safety and long cycle life, but the conductivity of the battery electrolyte is reduced at low temperature, the interface impedance is increased, and an SEI (solid electrolyte interphase) film is poor, so that the overall impedance of the battery is increased, and in addition, the conductivity of the material is poor, so that the application of the lithium iron phosphate battery is limited in severe cold regions and under special working conditions, and the improvement of the low-temperature performance is a key factor for expanding the application of the lithium iron phosphate battery.

The anode materials of the existing low-temperature batteries are basically lithium cobaltate or ternary materials, the battery structure has more flexible packaging laminated sheets and cylinders, the capacity and the multiplying power of the cylinders are limited, the heat dissipation is not good, the flexible packaging laminated sheet structure is unstable, and the battery structure is not beneficial to large-scale PACK grouping; the material system adopts anode and cathode materials to modify and optimize the electrolyte composition, so that the low-temperature performance of the lithium iron phosphate can be obviously improved, but the improvement space is limited; the performance of an SEI film is improved by adding a film forming additive and the like, so that the low-temperature performance of the battery is improved, but other performance discounts can be brought; and the low-temperature performance of the battery is improved by designing a self-heating device, but the problem of low temperature difference of the battery cannot be fundamentally solved.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a square aluminum shell low-temperature multiplying power type lithium ion battery and a preparation method thereof, aiming at improving the low-temperature performance of the lithium iron phosphate battery, the formed battery is placed at high temperature and then rapidly cooled by adopting a gluing ceramic diaphragm and amorphous electrolyte through the selection optimization of anode and cathode materials by a simple process, and the long-service-life square aluminum shell low-temperature multiplying power type lithium ion battery with low-temperature and multiplying power performance is effectively prepared.

In order to achieve the purpose, the invention provides the following technical scheme: a preparation method of a square aluminum shell low-temperature rate lithium ion battery comprises the following specific steps:

s1, mixing the positive active substance, the conductive carbon black, the carbon nanotube conductive slurry, the polyvinylidene fluoride binder and the dispersant to obtain a first precursor, adding N-methyl pyrrolidone into the first precursor to adjust the viscosity to obtain positive slurry, coating the positive slurry on an aluminum foil, and forming a positive pole piece with a foil left on the side edge through coating, rolling and slitting;

s2, mixing the negative active material, conductive carbon black, sodium carboxymethyl cellulose and thickening agent styrene butadiene rubber to obtain a second precursor, adding water into the second precursor to adjust viscosity to obtain negative slurry, coating the negative slurry on a copper foil, and rolling and slitting to form a negative pole piece with a foil left on the side edge;

s3, separating the positive pole piece and the negative pole piece obtained in the steps S1 and S2 by a lithium ion battery diaphragm, connecting the positive pole piece and the negative pole piece into a square aluminum shell through winding and ultrasonic welding to prepare a full-lug square pole group, injecting lithium ion battery electrolyte into the pole group, pre-forming and exhausting, sealing and cleaning to obtain a square aluminum shell lithium ion battery;

and S4, aging the square aluminum shell lithium ion battery obtained in the step S3 at a high temperature, forming, placing the formed battery in an environment of 45-50 ℃ for 2-4 h after being fully charged at normal temperature, cooling at 0-5 ℃, and discharging at normal temperature to obtain the square aluminum shell low-temperature rate lithium ion battery.

Further, in step S1, 93 wt% to 96 wt% of the positive electrode active material, 1.2 wt% to 2.5 wt% of the conductive carbon black SP, 0.4 wt% to 1.6 wt% of the carbon nanotube conductive slurry, 1.0 wt% to 3.5 wt% of the PVDF polyvinylidene fluoride binder, and 0.1 wt% to 0.2 wt% of the dispersant are mixed by weight to obtain the first precursor.

Further, in step S1, the positive active material is prepared by a hydrothermal carbon-coated nano LFP material, and has a particle size of 3 μm to 8 μm and a specific surface area of 10m²/g～14m²And the positive active material is nano lithium iron phosphate or a lithium iron composite.

Further, in step S1, the carbon nanotube conductive paste is CNT or a mixture of CNT and graphene; the dispersing agent is a copolymer of styrene and acrylic ester; the dosage of the N-methyl pyrrolidone is 45 wt% -50 wt% of the anode slurry.

Further, in step S2, 94 wt% to 96 wt% of the negative active material, 1.0 wt% to 2.5 wt% of the conductive carbon black, 1.0 wt% to 1.5 wt% of sodium carboxymethyl cellulose, and 1.5 wt% to 2.5 wt% of the thickener styrene butadiene rubber are mixed by weight to obtain the second precursor.

Further, in step S2, the water is used in an amount of 47 wt% to 50 wt% of the negative electrode slurry.

Further, in step S2, the negative electrode active material has a particle size of 7 to 13 μm, and the negative electrode active material is hard carbon-coated nano small particle size graphite or modified artificial graphite.

Further, in step S3, the lithium ion battery separator is a water-based or oil-based adhesive ceramic separator, and the thickness of the lithium ion battery separator is 12 μm to 20 μm; the electrolyte of the lithium ion battery is an amorphous electrolyte of lithium hexafluorophosphate, and the concentration of the electrolyte is 1.0-1.5 mol/L.

Further, in step S3, the solvent of the amorphous electrolyte solution of lithium hexafluorophosphate is a mixture of EC and a chain carboxylic ester solvent, and the chain carboxylic ester solvent includes at least one of poly (ethylene glycol) dimethyl ether, ethyl acetate, ethyl propionate, methyl acetate, and methyl butyrate.

The invention also provides a square aluminum shell low-temperature rate lithium ion battery which is prepared according to the preparation method.

Compared with the prior art, the invention has at least the following beneficial effects:

the invention provides a square aluminum shell low-temperature rate lithium ion battery.A material system suitable for low-temperature rate is verified and optimized through DOE experiments, a nano lithium iron phosphate/hard carbon coated graphite/amorphous electrolyte system is preferably selected, and the lithium iron phosphate square lithium ion battery with low-temperature rate is prepared through reasonable model selection matching of materials;

the battery formation adopts a method of rapid cooling after high-temperature treatment, which is beneficial to the rapid stability of an SEI film, does not need to add an additional film-forming agent, can ensure the quality of the SEI film and improve the cycle stability of the lithium ion battery, and the prepared square aluminum shell low-temperature rate lithium ion battery has lower internal resistance of the battery, excellent low-temperature and rate discharge performance (-40 ℃/3C capacity retention > 88% @2.0V, 25 ℃/10C capacity retention > 98%), and good cycle life (25 ℃ 1C 100% DOD 500 weeks > 97%). Furthermore, the positive active substance is prepared by a hydrothermal method, so that the particle size is uniform, the specific surface area of the material is large, the conductivity is good, and meanwhile, a small amount of dispersant is added for homogenizing to obtain stable and uniform slurry with low resistivity, so that the capacity exertion of the battery and the good consistency of the battery are ensured; the square aluminum shell low-temperature rate lithium ion battery prepared by the simple process has the advantages of small integral internal resistance, good heat dissipation, excellent low-temperature rate performance, stable battery performance, strong manufacturability, stable battery structure, higher safety and easiness in realizing large-scale PACK grouping, and is suitable for industrial production.

Drawings

FIG. 1 is a schematic view of the-40 ℃ low-temperature discharge curve of the low-temperature rate battery of the present invention;

FIG. 2 is a schematic view of the normal temperature rate discharge curve of the low temperature rate battery of the present invention;

FIG. 3 is a schematic view of a normal temperature 1C cycle curve of the low-temperature rate battery of the present invention;

Detailed Description

The invention is further described with reference to the following figures and detailed description.

The invention provides a square aluminum shell low-temperature rate lithium ion battery and a preparation method thereof, wherein the preparation method comprises the following steps: s1, mixing 93-96 wt% of positive electrode active substance, 1.2-2.5 wt% of conductive carbon black SP, 0.4-1.6 wt% of carbon nanotube conductive slurry, 1.0-3.5 wt% of PVDF polyvinylidene fluoride binder and 0.1-0.2 wt% of dispersant to obtain a first precursor, adding N-methyl pyrrolidone (NMP) into the first precursor to obtain positive electrode slurry, wherein the amount of the N-methyl pyrrolidone (NMP) is 45-50 wt% of the positive electrode slurry, coating the positive electrode slurry on an aluminum foil, and forming a side foil-retained positive electrode piece through coating, rolling and slitting;

s2, mixing 94-96 wt% of a negative electrode active material, 1.0-2.5 wt% of conductive carbon black SP, 1.0-1.5 wt% of carboxymethyl cellulose sodium CMC, 1.5-2.5 wt% of a thickening agent styrene butadiene rubber SBR to obtain a second precursor, adding water into the second precursor to obtain negative electrode slurry, wherein the amount of the water accounts for 47-50 wt% of the negative electrode slurry, coating the negative electrode slurry on a copper foil, and rolling and slitting to form a negative electrode piece with a side edge remaining foil;

s3, separating the positive and negative pole pieces obtained in the steps S1 and S2 by a lithium ion battery diaphragm, and winding and ultrasonically welding the positive and negative pole pieces into a shell to prepare a full-lug square pole group;

s4, injecting 1.0-1.5mol/L lithium ion battery electrolyte into the pole group obtained in the step S3 after the pole group is qualified by baking moisture test (the water content of the positive pole piece is less than or equal to 200ppm, and the water content of the negative pole piece is less than or equal to 250ppm), pre-forming and exhausting, sealing and cleaning to obtain the square aluminum shell lithium ion battery;

s5, forming the square aluminum shell lithium ion battery obtained in the step S4 after high-temperature aging, placing the formed battery in an environment of 45-50 ℃ for 2-4 h after being fully charged at normal temperature, cooling at 0-5 ℃, and discharging at normal temperature to obtain the square aluminum shell low-temperature multiplying power type lithium ion battery;

in step S1, the positive electrode active material is prepared by a hydrothermal carbon-coated nano LFP material, the particle size is 3-8 μm, and the specific surface area is 10-14 m²And/g, the anode active material is nano lithium iron phosphate or a lithium iron composite.

In step S1, the aluminum foil is a carbon-coated aluminum foil;

in step S1, the carbon nanotube conductive paste is CNT (carbon nanotube) or a mixture of CNT and graphene.

In the step S1, the dispersing agent is a copolymer of styrene and acrylic ester, which can effectively improve the dispersion stability of the high specific surface material;

in the step S2, the negative active material is hard carbon-coated nano small-particle-size graphite or modified artificial graphite, and the particle size of the negative active material is 7-13 μm;

in the step S3, the lithium ion battery diaphragm is a water-based/oil-based glue-coated ceramic diaphragm, the thickness of the lithium ion battery diaphragm is 12-20 μm, the glue-coated diaphragm can effectively reduce wrinkles of the interface of the full-lug battery, and the battery interface is ensured to be good and a lithium ion migration channel is smooth;

in step S4, the lithium ion battery electrolyte is an amorphous electrolyte of lithium hexafluorophosphate, the solvent is a mixture of EC (ethylene carbonate) and a chain carboxylic ester solvent, and the chain carboxylic ester solvent contains at least one of poly (ethylene glycol) dimethyl ether, ethyl acetate, ethyl propionate, methyl acetate, and methyl butyrate. The amorphous electrolyte has low viscosity and good conductivity at low temperature, has good compatibility with anode and cathode materials, and can effectively improve the low-temperature performance of the battery;

in step S5, after formation, the method of rapid cooling after high temperature treatment is beneficial to rapid stabilization of a Solid Electrolyte Interface (film)), and no additional film forming agent is needed, so that the quality of the SEI film can be ensured, and the cycle stability of the lithium ion battery can be improved.

The square aluminum shell low-temperature rate lithium ion battery has lower internal resistance, excellent low-temperature and rate discharge performance (-40 ℃/3C; 25 ℃/10C) and good cycle life (25 ℃ 1C 100% DOD 500 cycle > 97%).

Example 1

S1, mixing 94.5 wt% of nano lithium iron phosphate, 1.5 wt% of conductive carbon black SP1.5wt%, 1.3 wt% of carbon nanotube conductive slurry (CNT), 2.5 wt% of PVDF polyvinylidene fluoride binder and 0.2 wt% of dispersant to obtain a first precursor, mixing the first precursor with N-methyl pyrrolidone (NMP) to prepare positive electrode slurry, wherein the amount of the N-methyl pyrrolidone (NMP) is 47 wt% of the positive electrode slurry, coating the positive electrode slurry on a carbon-coated aluminum foil, and forming a side foil-retained positive electrode plate through coating, rolling and slitting;

s2, mixing 95.2 wt% of hard carbon coated small-particle-size nano graphite, 1.5 wt% of conductive carbon black SP1.5wt%, 1.3wt% of carboxymethyl cellulose sodium CMC1.3wt% and 2.0 wt% of thickening agent styrene butadiene rubber SBR2 to obtain a second precursor, mixing the second precursor with water to prepare negative electrode slurry, wherein the amount of the water is 48 wt% of the negative electrode slurry, coating the negative electrode slurry on a carbon-coated copper foil, and rolling and slitting to form a side-edge foil-remaining negative electrode piece;

s3, separating the positive and negative pole pieces obtained in the steps S1 and S2 by a 20-micron water-based glue coating ceramic diaphragm, and winding and ultrasonically welding the positive and negative pole pieces into a shell to prepare a full-lug square pole group;

s4, injecting lithium hexafluorophosphate (EC and poly (ethylene glycol) dimethyl ether cosolvent) amorphous electrolyte with the concentration of 1.0mol/L into the pole group obtained in the step S3 after the pole group is tested to be qualified through baking moisture, pre-forming and exhausting, sealing and cleaning to obtain the square aluminum shell lithium ion battery;

s5, aging the square aluminum shell lithium ion battery obtained in the step S4 at a high temperature of 40 +/-5 ℃ for 24 hours, forming, placing the formed battery in a 45 ℃ environment for 4 hours after full electricity at normal temperature, then transferring the battery to a 0 ℃ low-temperature environment for cooling, and recovering discharge at normal temperature to obtain the square aluminum shell low-temperature multiplying power type lithium ion battery;

as shown in fig. 1, which is a schematic diagram of a low-temperature discharge curve at-40 ℃ of the square aluminum-shell low-temperature rate lithium ion battery prepared in example 1 of the present invention, it can be seen from the diagram that when the discharge is cut off by 2.0V, the discharge capacity is maintained to be greater than 76% at-40 ℃/1C, and the pull-down voltage is greater than 2.5V; the discharge capacity of the battery at 40 ℃ below zero/3 ℃ is kept to be larger than 88%, the pull-down voltage is larger than 2.1V, and the platform voltage is larger than 2.5V, which shows that the battery has good low-temperature starting performance.

As shown in fig. 2, which is a schematic diagram of a normal-temperature rate discharge curve of the square aluminum-shell low-temperature rate lithium ion battery prepared in example 1 of the present invention, test data show that the discharge capacity retention rate of the battery at normal temperature of 10C is greater than 98%, and the temperature rise of the battery is less than or equal to 27 ℃, which indicates that the battery has good conductivity, small rate discharge polarization, and good high-rate discharge performance.

As shown in fig. 3, which is a schematic diagram of a normal-temperature 1C cycle curve of the square aluminum-shell low-temperature rate lithium ion battery prepared in example 1 of the present invention, it is seen that the battery has a full charge-discharge cycle at normal temperature, the capacity of 500 cycles is maintained to be greater than 97%, the battery cycle life is expected to be more than 2000 times, and the low-temperature battery has excellent cycle performance.

Example 2

S1, mixing 94.6 wt% of nano lithium iron phosphate, 1.5 wt% of conductive carbon black SP1.5wt%, 1.3 wt% of carbon nanotube conductive slurry (CNT + graphene), 2.5 wt% of PVDF polyvinylidene fluoride binder and 0.1 wt% of dispersant to obtain a first precursor, mixing the first precursor with N-methyl pyrrolidone (NMP) to prepare positive electrode slurry, wherein the amount of N-methyl pyrrolidone (NMP) is 48 wt% of that of the positive electrode slurry, coating the positive electrode slurry on a carbon-coated aluminum foil, and forming a side foil-retained positive electrode plate through coating, rolling and slitting;

s2, mixing 94 wt% of modified artificial graphite, 2.2 wt% of conductive carbon black SPC, 1.5 wt% of carboxymethyl cellulose sodium CMCm and 2.0 wt% of thickening agent styrene butadiene rubber SBR2, mixing the second precursor and the thickening agent SBR2.0 to obtain a second precursor, preparing negative electrode slurry by mixing the second precursor, coating the negative electrode slurry on copper foil, rolling and slitting to form a negative electrode plate with a side edge remaining foil;

s3, separating the positive and negative pole pieces obtained in the steps S1 and S2 by an oily glue-coated ceramic diaphragm of 20 microns, and winding and ultrasonically welding the positive and negative pole pieces into a shell to prepare a full-lug square pole group;

s4, injecting lithium hexafluorophosphate (EC, poly (ethylene glycol) dimethyl ether and ethyl acetate cosolvent) amorphous electrolyte with the concentration of 1.5mol/L into the pole group obtained in the step S3 after the pole group is tested to be qualified through baking moisture, pre-forming and exhausting, sealing and cleaning to obtain the square aluminum shell lithium ion battery;

s5, aging the square aluminum shell lithium ion battery obtained in the step S4 at a high temperature of 40 +/-5 ℃ for 24 hours, forming, placing the formed battery in an environment of 50 ℃ after being fully charged at a normal temperature, standing for 2 hours, transferring the battery into a low-temperature environment of 0 ℃ for cooling, recovering at the normal temperature, discharging to obtain the square aluminum shell low-temperature multiplying power type lithium ion battery, and testing the performance of the battery, wherein the battery performance data table 1 shows that when the discharge is stopped at 2.0V, the discharge capacity of the battery at 40 ℃/1C is kept to be more than 76%, the pull-down voltage is more than 2.4V, the battery is fully charged and discharged at the normal temperature, and the capacity of 500 weeks is kept to be more than 94%; compared with the example 1, in the example 2, the formation treatment process is changed under the condition that the system proportion is similar, the battery after formation is subjected to high-temperature treatment at a temperature of 50 ℃/2h from high-temperature shelf at a temperature of 45 ℃/4h, the influence on the low-temperature performance of the battery is small, but the cycle performance is reduced by 3 points, which indicates that the high-temperature shelf for a short time is not beneficial to the stability of an SEI film, so the cycle performance is reduced to some extent.

Example 3

S1, mixing 93 wt% of nano lithium iron phosphate, 2.5 wt% of conductive carbon black SP2, 1.6 wt% of carbon nano tube conductive slurry (CNT), 2.6 wt% of PVDF polyvinylidene fluoride binder and 0.2 wt% of dispersant to obtain a first precursor, mixing the first precursor with N-methyl pyrrolidone (NMP) to prepare positive electrode slurry, wherein the amount of the N-methyl pyrrolidone (NMP) is 50 wt% of the positive electrode slurry, coating the positive electrode slurry on a carbon-coated aluminum foil, and forming a side-edge foil-retained positive electrode plate through coating, rolling and slitting;

s2, mixing 96 wt% of hard carbon coated small-particle-size nano graphite, 1.2 wt% of conductive carbon black SPC, 1.1 wt% of carboxymethyl cellulose sodium CMC1.7 wt% and 1.7 wt% of styrene butadiene rubber serving as a thickening agent to obtain a second precursor, mixing the second precursor and the second precursor to prepare negative electrode slurry, coating the negative electrode slurry on a carbon-coated copper foil, and rolling and slitting to form a negative electrode plate with a side edge remaining foil;

s3, separating the positive and negative pole pieces obtained in the steps S1 and S2 by a 20-micron water-based glue coating ceramic diaphragm, and winding and ultrasonically welding the positive and negative pole pieces into a shell to prepare a full-lug square pole group;

s4, injecting lithium hexafluorophosphate (EC, poly (ethylene glycol) dimethyl ether, ethyl propionate and methyl acetate cosolvent) amorphous electrolyte with the concentration of 1.2mol/L into the pole group obtained in the step S3 after being tested to be qualified through baking moisture, sealing and cleaning after pre-formation and exhaust, and obtaining the square aluminum shell lithium ion battery;

s5, aging the battery obtained in the step S4 at a high temperature of 40 +/-5 ℃ for 24 hours, forming, placing the formed battery in an environment of 45 ℃ after full charge at a normal temperature, standing for 4 hours, transferring to a low-temperature environment of 5 ℃ for cooling, and recovering discharge at the normal temperature to prepare the square aluminum shell low-temperature rate type lithium ion battery, wherein the battery performance test shows that the battery performance data table 1 shows that when the discharge is cut off to 2.0V, the discharge capacity of the battery at 40 ℃/1C is kept to be more than 77%, the pull-down voltage is more than 2.5V, the battery is charged and discharged at the normal temperature in a full charge and discharge cycle, and the capacity is kept to be more than 97% in 500 weeks; compared with the embodiment 1 and the embodiment 2, the embodiment 3 increases the total conductive paste content, the low-temperature performance of the battery is improved, the improvement of the content of the conductive agent is beneficial to reducing the integral internal resistance of the battery, and the high-temperature short-time standing is also beneficial to stabilizing an SEI film and influencing the cycle performance of the battery.

Example 4

S1, mixing 93.6 wt% of a lithium iron composite, 1.2 wt% of conductive carbon black SP1.2 wt%, 1.6 wt% of carbon nanotube conductive slurry (CNT), 3.5 wt% of PVDF polyvinylidene fluoride binder and 0.1 wt% of a dispersing agent to obtain a first precursor, mixing the first precursor with N-methyl pyrrolidone (NMP) to prepare positive electrode slurry, wherein the amount of the N-methyl pyrrolidone (NMP) is 45 wt% of that of the positive electrode slurry, coating the positive electrode slurry on a carbon-coated aluminum foil, and forming a side foil-retained positive electrode plate through coating, rolling and slitting;

s2, mixing 94 wt% of hard carbon coated nano small-particle-size graphite, 2.5 wt% of conductive carbon black SP2, 1.0 wt% of carboxymethyl cellulose sodium CMCx and 2.5 wt% of thickening agent styrene butadiene rubber SBR2 to obtain a second precursor, mixing the second precursor and the second precursor to prepare negative electrode slurry, coating the negative electrode slurry on a carbon-coated copper foil, and rolling and slitting to form a side-edge foil-remaining negative electrode piece;

s3, separating the positive and negative pole pieces obtained in the steps S1 and S2 by an oily glue-coated ceramic diaphragm of 16 microns, and winding and ultrasonically welding the positive and negative pole pieces into a shell to prepare a full-lug square pole group;

s4, injecting lithium hexafluorophosphate (EC, poly (ethylene glycol) dimethyl ether and methyl butyrate cosolvent) amorphous electrolyte with the concentration of 1.0mol/L into the pole group obtained in the step S3 after the pole group is tested to be qualified through baking moisture, pre-forming and exhausting, sealing and cleaning to obtain the square aluminum shell lithium ion battery;

s5, aging the square aluminum shell lithium ion battery obtained in the step S4 at a high temperature of 40 +/-5 ℃ for 24 hours, forming, placing the formed battery in an environment of 45 ℃ after being fully charged at a normal temperature, standing for 4 hours, transferring the battery into a low-temperature environment of 0 ℃ for cooling, and recovering discharge at the normal temperature to obtain the square aluminum shell low-temperature multiplying power type lithium ion battery, wherein the battery performance data table 1 shows that when the discharge is stopped at 2.0V, the discharge capacity of the battery at 40 ℃/1C is kept to be more than 74%, the pull-down voltage is more than 2.2V, the battery is fully charged and discharged at the normal temperature, and the capacity is kept to be more than 95% in 500 weeks; in example 4, the separator having a thickness of 16 μm was used, the thickness of the separator was decreased, and the low-temperature performance and the cycle performance of the battery were decreased, as compared to examples 1 and 3, and the thickness of the separator may affect the low-temperature capacity retention and the pull-down voltage of the battery.

Example 5

S1, mixing 96 wt% of a lithium iron compound, 2.4 wt% of conductive carbon black SP2, 0.4 wt% of carbon nanotube conductive slurry (CNT + graphene), 1.0 wt% of PVDF polyvinylidene fluoride binder and 0.2 wt% of a dispersing agent to obtain a first precursor, mixing the first precursor and N-methyl pyrrolidone (NMP) to prepare positive electrode slurry, wherein the amount of the N-methyl pyrrolidone (NMP) is 50 wt% of that of the positive electrode slurry, coating the positive electrode slurry on a carbon-coated aluminum foil, and forming a side foil-retained positive electrode piece through coating, rolling and slitting;

s2, mixing 96 wt% of modified artificial graphite, 1 wt% of conductive carbon black SP, 1.5 wt% of carboxymethyl cellulose sodium CMCx and 1.5 wt% of thickening agent styrene butadiene rubber SBR1, mixing the second precursor and the thickening agent SBR1.5wt% to obtain a second precursor, preparing negative electrode slurry by mixing the second precursor, coating the negative electrode slurry on copper foil, rolling and slitting to form a negative electrode piece with a side edge remaining foil;

s3, separating the positive and negative pole pieces obtained in the steps S1 and S2 by a 12-micron water-based glue coating ceramic diaphragm, and winding and ultrasonically welding the positive and negative pole pieces into a shell to prepare a full-lug square pole group;

s4, injecting lithium hexafluorophosphate (EC, methyl acetate and ethyl acetate cosolvent) amorphous electrolyte with the concentration of 1.5mol/L into the pole group obtained in the step S3 after the pole group is tested to be qualified through baking moisture, pre-forming and exhausting, sealing and cleaning to obtain the square aluminum shell lithium ion battery;

s5, aging the square aluminum shell lithium ion battery obtained in the step S4 at a high temperature of 40 +/-5 ℃ for 24 hours, forming, placing the formed battery in an environment of 45 ℃ after being fully charged at a normal temperature, standing for 4 hours, transferring the battery into a low-temperature environment of 3 ℃ for cooling, recovering at the normal temperature, discharging to obtain the square aluminum shell low-temperature multiplying power type lithium ion battery, and testing the performance of the battery, wherein the battery performance data table 1 shows that when the discharge is stopped at 2.0V, the discharge capacity of the battery is kept to be more than 75 percent at 40 ℃/1C, the pull-down voltage is more than 2.7V, the battery is fully charged and discharged at the normal temperature, and the capacity is kept to be more than 96 percent at 500 weeks; compared with example 4, in example 5, the 12-micron-thick diaphragm is adopted, the low-temperature performance and the cycling performance of the battery are respectively increased by 1 percentage point, comparing examples 1 and 3(20 μm diaphragm) and example 4(16 μm diaphragm), analyzing the low-temperature performance and cycle performance data of the battery, wherein the results of comparing examples 1 and 3(20 μm diaphragm) > example 5(12 μm diaphragm) > example 4(16 μm diaphragm) indicate that the diaphragm thickness is not a factor really influencing the low-temperature performance of the battery, and further comparing the physicochemical parameters of the three diaphragms, the air permeability and the porosity of the diaphragm are main factors influencing the performance of the battery, and comprehensively, the porosity of the 20 μm diaphragm is large, so that the electrolyte infiltration is facilitated, and therefore, the low-temperature discharge capacity retention rate is better, and the 12 mu m diaphragm has lower air permeability, better conductivity and small battery polarization, so the pull-down voltage of the battery is higher under low-temperature discharge.

In view of the stable performance of the low-temperature rate lithium ion battery, the material systems of examples 2 to 5 can obtain similar battery performance effects, so that specific curve graphs of other examples are not shown, and only key performance data are subjected to comparative analysis.

Comparative example 1

After a 26650-3.35Ah cylindrical low-temperature battery sold in a certain battery manufacturer is taken to be subjected to constant volume with the battery of the invention, the low-temperature-40 ℃/1C discharge and the normal-temperature 1C cycle performance are tested under the same condition, and the measured data are shown in Table 1: the discharge capacity of the low-temperature cylindrical battery at 40 ℃ below zero/1C is kept to be more than 64 percent, the pull-down voltage is more than 2.5 percent, the full charge and discharge cycle of the battery at the normal temperature of 1C is 500 weeks, the capacity is kept to be more than 94 percent, and the performance of the battery is more deviated than that of the battery, which shows that the performance of the low-temperature multiplying power type square aluminum shell battery is superior to that of the low-temperature cylindrical battery.

Comparative example 2

After the lithium iron phosphate 3613065-20Ah square aluminum shell low-temperature battery of a certain battery manufacturer sold in the market and the battery of the invention are subjected to constant volume, the low-temperature-40 ℃/1C discharge and the normal-temperature 1C cycle performance are tested under the same conditions, and the measured data are shown in Table 1: the discharge capacity of the 20Ah square battery is kept to be more than 69 percent at 40 ℃/1C, the pull-down voltage is more than 2.2, the full charge and discharge cycle of the battery is 500 weeks at the normal temperature of 1C, the capacity is kept to be more than 95 percent, and the performance is more deviated than that of the battery, which shows that the performance of the low-temperature multiplying power type square aluminum shell battery is superior to that of the square aluminum shell battery with the same structure in the market.

TABLE 1 table of performance data for each of the examples and comparative examples