A positive electrode slurry, a positive electrode sheet and a battery of a low-temperature power type lithium ion battery

Abstract

A positive electrode slurry, a positive electrode sheet and a battery of a low-temperature power lithium ion battery, the low-temperature power lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator; the positive electrode slurry of the positive electrode sheet comprises the following components and weight percentages: positive electrode active material 95%-97.5%, positive electrode conductive agent 1.5%-3%, positive electrode binder 1%-2%; the positive electrode sheet is prepared by wet coating through dispersing the above-mentioned components in N-methyl pyrrolidone solvent; the positive electrode active material is a lithium nickel cobalt manganese oxide ternary material, the particle size distribution D50 is 3.0-3.5 µm, the specific surface area is 1.5-2.0 m 2 / g; the positive electrode conductive agent is composed of conductive graphite and carbon nanotubes, the weight percentage of conductive graphite is 50%-70%; the positive electrode binder is polyvinylidene fluoride; the low-temperature performance of the positive electrode material is effectively improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium ion batteries, and particularly relates to a positive electrode slurry, a positive electrode sheet and a battery of a low-temperature power type lithium ion battery. BACKGROUND

[0002] In a low-temperature environment, the charging and discharging performance of a lithium ion battery is not ideal due to polarization. When a commonly used lithium ion battery works at-10 DEG C, the maximum charging and discharging capacity and the terminal voltage thereof are greatly reduced compared with those at room temperature. When the environmental temperature drops to-20 DEG C, the available capacity can even be reduced to 1 / 3 of that at room temperature 25 DEG C. When the environmental temperature is lower, some lithium batteries cannot even perform charging and discharging activities and enter a "dead battery" state.

[0003] A lithium ion battery for an automobile start-stop system is disclosed in Chinese Patent (Publication No. CN106876714A, Publication Date 2017.6.20), which comprises a lithium iron phosphate positive electrode active material and a particle size (D50<3 mu m). However, the specific energy of the positive electrode material active substance is low, and the low-temperature discharging platform is low, which cannot meet the demand of high power of the start-stop auxiliary cell at low temperature. The new energy market demand is huge, and 12 / 48V start-stop and auxiliary systems are widely concerned by the market. Such power type lithium ion batteries have high demand for the low-temperature performance of the positive electrode material. SUMMARY

[0004] The purpose of the present application is to overcome the above-mentioned deficiencies of the prior art, and to provide a positive electrode slurry, a positive electrode sheet and a battery of a low-temperature power type lithium ion battery, which effectively improve the low-temperature performance of the positive electrode material.

[0005] The technical solution of the present application is: a low-temperature power type lithium ion battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator; the following dosages are mass percentages unless otherwise specified;

[0006] The positive electrode slurry of the positive electrode sheet comprises the following components and weight percentages: positive electrode active material 95%-97.5%, positive electrode conductive agent 1.5%-3%, and positive electrode binder 1%-2%; the positive electrode sheet is prepared by dispersing the above-mentioned components in N-methyl pyrrolidone (NMP) solvent and then coating by a wet method.

[0007] The positive electrode active material is a lithium nickel cobalt manganese oxide ternary material (NCM523), the particle size distribution D50 of which is 3.0-3.5 mu m, and the specific surface area is 1.5-2.0 m 2 / g; the positive electrode conductive agent is composed of conductive graphite and carbon nanotubes, and the weight percentage of the conductive graphite is 50%-70%; the positive electrode binder is polyvinylidene fluoride (PVDF);

[0008] 1) the preparation method of the positive electrode tab comprises the following steps:

[0009] (1) the positive electrode active material, conductive graphite and positive electrode binder are added into a stirring cylinder for stirring; carbon nanotubes are dispersed in N-methyl pyrrolidone solvent to obtain a carbon nanotube conductive slurry, the weight percentage of the carbon nanotubes is 3-10%, and the weight percentage of the N-methyl pyrrolidone solvent is 90-97%; then, the carbon nanotube conductive slurry with a weight percentage of 40±4% is added into the stirring cylinder for stirring; thereafter, the remaining carbon nanotube conductive slurry and N-methyl pyrrolidone solvent are added into the stirring cylinder for continuous stirring; then, an appropriate amount of N-methyl pyrrolidone solvent is sequentially added into the stirring cylinder, and the positive electrode slurry is obtained after stirring, with the solid content ratio controlled to be 60%-65%;

[0010] (2) the positive electrode slurry is uniformly coated on both sides of the positive electrode current collector carbon-coated aluminum foil to obtain a wet electrode plate, with the single-side coating area density controlled to be 65-110 g / m 2 ; (3) the wet electrode plate is transferred to a baking room, and dried at a baking temperature of 100-120℃ to obtain a positive electrode tab with a compacted density of 2.8-3.5 g / cm 3 ;

[0011] 2) negative electrode tab preparation: the formula of the negative electrode slurry comprises the following components with the mass percentage: 90-94% of artificial graphite, 1-5% of soft carbon, 1-3% of conductive agent, 1-2% of sodium carboxymethyl cellulose, 1-2% of butadiene-styrene rubber, and the balance of deionized water; the artificial graphite, soft carbon, conductive agent, sodium carboxymethyl cellulose, butadiene-styrene rubber and deionized water are added into a stirring cylinder for wet stirring at a self-rotation speed of 2000-2500 r / min and a public rotation speed of 15-25 r / min, and the solid content ratio is controlled to be 50%-55%; then, the wet electrode plate is obtained by uniformly coating on the negative electrode copper foil current collector; the wet electrode plate is transferred to a baking room, and dried at a baking temperature of 90-95℃; thereafter, the dried electrode tab is rolled to obtain a negative electrode tab with a compacted density of 1.2-1.8 g / cm 3 and a surface density of 40-50 g / cm 2 .

[0012] 3) the positive electrode tab, the negative electrode tab and the polypropylene separator coated with aluminum oxide ceramic are assembled in an aluminum plastic film, electrolyte is injected, and then the sealing, formation, and capacity procedures are performed to obtain a finished product battery cell; thereafter, the finished product battery cell is subjected to rate performance test under different temperatures and different pulse current conditions.

[0013] The electrolyte is composed of carbonate solvents, lithium salts and additives.

[0014] The carbonic acid lipid solvent is composed of 5-15% mass percentage of ethylene carbonate, 30-35% mass percentage of dimethyl carbonate and 30-35% mass percentage of methyl ethyl carbonate; the lithium salt is composed of 10-15% mass percentage of lithium hexafluorophosphate and 5-10% mass percentage of lithium bisfluorosulfonylimide; the additive is composed of 1-2% mass percentage of lithium difluoroborate oxalate, 1-3% mass percentage of tributyl borate and 1-2% mass percentage of vinylene carbonate.

[0015] The separator is one of a single-side alumina ceramic coated polypropylene separator and a single-side alumina ceramic coated polyethylene separator.

[0016] The lithium ion battery includes a start-stop lithium ion battery and an auxiliary lithium ion battery.

[0017] The negative electrode slurry is composed of the following components in mass percentage: 90% artificial graphite, 5% soft carbon, 2% conductive agent, 1% sodium carboxymethyl cellulose, 2% butadiene rubber, and the balance is deionized water.

[0018] An anode slurry of a positive electrode sheet of a low-temperature power type lithium ion battery, the anode slurry of the positive electrode sheet comprising the following components and weight percentages: anode active material 95%-97.5%, anode conductive agent 1.5%-3%, anode binder 1%-2%; the anode active material is lithium nickel cobalt manganese oxide ternary material (NCM523), the particle size distribution D50 is 3.0-3.5 μm, and the specific surface area is 1.5-2.0 m2 / g; the anode conductive agent is composed of conductive graphite and carbon nanotubes, and the weight percentage of conductive graphite is 50%-70%; the anode binder is polyvinylidene fluoride (PVDF).

[0019] A preparation method of the anode slurry as described above, comprising the following steps:

[0020] The positive electrode active material, conductive graphite and positive electrode binder are added into a stirring cylinder, and dry powder stirring is performed at a revolution speed of 15-30 r / min for 30-60 min; carbon nanotube conductive slurry is obtained by dispersing carbon nanotubes in N-methyl pyrrolidone (NMP) solvent, the weight percentage of carbon nanotubes in the carbon nanotube conductive slurry is 3-10%, and the weight percentage of N-methyl pyrrolidone (NMP) solvent is 90-97%; the carbon nanotube conductive slurry is divided into two parts A and B, then part A of the carbon nanotube conductive slurry with a weight percentage of 40±4% is added into the stirring cylinder, and wet stirring is performed at a revolution speed of 200-300 r / min and a revolution speed of 15-25 r / min for 30-60 min; then the remaining part B of the carbon nanotube conductive slurry and N-methyl pyrrolidone (NMP) solvent are added into the stirring cylinder, and stirring is continued at a revolution speed of 15-25 r / min for 4-8 h; then, an appropriate amount of N-methyl pyrrolidone (NMP) solvent is added into the stirring cylinder in sequence, and the stirring cylinder is controlled to rotate at a revolution speed of 4000-5000 r / min and a revolution speed of 10-25 r / min, and stirring is performed for 8-12 h to obtain a positive electrode slurry, and the solid content ratio is controlled to be 60%-65%.

[0021] A preparation method of a positive electrode sheet of a low-temperature power type lithium ion battery, which adopts the positive electrode slurry as described above, and includes the following steps:

[0022] The positive electrode slurry as described above is uniformly coated on both sides of a positive electrode current collector carbon-coated aluminum foil to obtain a wet electrode plate, and the single-sided coating area density is controlled to be 65-110 g / m 2 ;

[0023] The wet electrode plate is transferred to a baking room, and drying is performed at a baking temperature of 100-120℃ to obtain a positive electrode sheet with a compacted density of 2.8-3.5 g / cm 3 .

[0024] The inventors have found that proper particle size selection has a great influence on the performance of the battery cell, and reducing the particle size of the material and shortening the migration path of lithium ions are effective ways to improve the low-temperature performance of the positive electrode material. However, too small particle size will increase the specific surface area of the material, thereby increasing the side reaction between the material and the electrolyte and reducing the low-temperature performance of the positive electrode material. In addition, by adding graphite conductive agent and two-dimensional carbon nanotube conductive agent with different structures to build a cross-linked network of electron transport, and by improving the stirring method to improve the dispersibility of the conductive agent and the positive electrode active material and promote the effective contact between the conductive agent and the positive electrode active material, the electron transport path of the positive electrode material can be enhanced, thereby improving the low-temperature performance of the positive electrode material. Therefore, for the selection and application of the positive electrode material of the power lithium ion battery, the particle size and specific surface area of the positive electrode material need to be regulated, and an electron transport network matching the material needs to be built to synergistically optimize the ion and electron transport paths, thereby meeting the requirements of 12V or 48V start-stop power supply.

[0025] The positive electrode material of the application preferably NCM523, the particle size range is controlled in D50 3.0-3.5um, the specific surface area is 1.5-2.0m 2 / g, the particle size is smaller, the specific surface area is larger, the performance of the battery cell in this range reaches the optimal value, and the advantages of the particle size and the specific surface area improve the mass transfer efficiency of the positive electrode material and the electrolyte. On the other hand, the application preferably builds an electron transport network with graphite conductive agent and two-dimensional carbon nanotube, wherein the proportion of conductive graphite is 50-70%, the addition sequence and stirring speed of the conductive agent are adjusted to improve the dispersibility of the positive electrode particles and the conductive agent, and the electron transport path on the positive electrode material side is improved. The synergistic effect of the above mass transfer efficiency and electron transport capacity improves the rate performance of the battery cell in a low-temperature environment, which is beneficial to the use of high-power battery cells, especially low-temperature start-stop and auxiliary power supply. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The electron microscope morphology pictures of the positive electrode materials under the conditions of Comparative Example 1, Comparative Example 2 and Example 1 are shown in the following table:

[0027] Figure 2 The low-temperature rate performance of the battery cells assembled with different positive electrode materials under different pulse discharge conditions at-30℃ is shown in the following table:

[0028] Figure 3 The low-temperature rate performance of the battery cells assembled with different positive electrode materials under 25C pulse discharge conditions at-20℃ is shown in the following table. DETAILED DESCRIPTION

[0029] The application will be further described below in conjunction with the examples.

[0030] The positive electrode slurry of the positive electrode tab comprises the following components and weight percentages: positive electrode active material 95%-97.5%, positive electrode conductive agent 1.5%-3%, and positive electrode binder 1%-2%; the positive electrode tab is prepared by wet blade coating of the above components dispersed in N-methyl pyrrolidone solvent;

[0031] The positive electrode active material is a lithium nickel cobalt manganese oxide ternary material with a particle size distribution D50 of 3.0-3.5 μm and a specific surface area of 1.5-2.0 m 2 / g; the positive electrode conductive agent is composed of conductive graphite and carbon nanotubes, with the weight percentage of conductive graphite being 50%-70%; the positive electrode binder is polyvinylidene fluoride;

[0032] 1) The preparation method of the positive electrode tab comprises the following steps:

[0033] (1) The positive electrode active material, conductive graphite, and positive electrode binder are added to a stirring cylinder for stirring; carbon nanotubes are dispersed in N-methyl pyrrolidone solvent to obtain a carbon nanotube conductive slurry, with the weight percentage of carbon nanotubes being 3-10% and the weight percentage of N-methyl pyrrolidone solvent being 90-97%; then 40±4% of the carbon nanotube conductive slurry by weight is added to the stirring cylinder for stirring; thereafter, the remaining carbon nanotube conductive slurry and N-methyl pyrrolidone solvent are added to the stirring cylinder for continuous stirring; then, an appropriate amount of N-methyl pyrrolidone solvent is added to the stirring cylinder in sequence, and the positive electrode slurry is obtained after stirring, with the solid content ratio being controlled at 60%-65%;

[0034] (2) The positive electrode slurry is uniformly coated on both sides of the positive electrode current collector carbon-coated aluminum foil to obtain a wet electrode plate, with the single-sided coating area density being controlled at 65-110 g / m 2 ; (3) The wet electrode plate is transferred to a baking chamber, and dried at a baking temperature of 100-120°C to obtain a positive electrode tab with a compacted density of 2.8-3.5 g / cm 3 ;

[0035] 2) Preparation of the negative electrode tab: the formula of the negative electrode slurry contains the following components with the following mass percentages: 90-94% of artificial graphite, 1-5% of soft carbon, 1-3% of conductive agent, 1-2% of sodium carboxymethyl cellulose, 1-2% of butadiene-styrene rubber, and the balance being deionized water; the artificial graphite, soft carbon, conductive agent, sodium carboxymethyl cellulose, butadiene-styrene rubber, and deionized water are added to a stirring cylinder for stirring to obtain a negative electrode slurry, with the solid content ratio being controlled at 50%-55%; then the negative electrode slurry is uniformly coated on the negative electrode copper foil current collector to obtain a wet electrode plate, which is transferred to a baking chamber and dried at a baking temperature of 90-95°C; thereafter, the dried electrode tab is rolled to obtain a negative electrode tab with a compacted density of 1.2-1.8 g / cm 3 and a surface density of 40-50 g / cm2 The negative electrode plate;

[0036] 3) Assemble the positive electrode, negative electrode and separator in an aluminum-plastic film, inject electrolyte, and then perform sealing, formation and capacity testing to obtain the finished battery cell; subsequently, test the rate performance of this finished battery cell under different temperature and pulse current conditions.

[0037] The electrolyte is composed of a carbonate solvent, a lithium salt, and additives. The carbonate solvent consists of 5-15% by mass of ethylene carbonate, 30-35% by mass of dimethyl carbonate, and 30-35% by mass of ethyl methyl carbonate; the lithium salt consists of 10-15% by mass of lithium hexafluorophosphate and 5-10% by mass of lithium difluorosulfonylimide; the additives consist of 1-2% by mass of lithium difluorooxalate borate, 1-3% by mass of tributyl borate, and 1-2% by mass of vinylene carbonate.

[0038] Example 1

[0039] The mass ratio of NCM523, conductive graphite, carbon nanotubes, and PVDF in the positive electrode slurry of the positive electrode sheet is 96:1.2:1:1.8.

[0040] 1. The preparation method of the positive electrode sheet includes the following steps: (1) NCM523 (D50=3.2μm), conductive graphite and PVDF are added to the stirring tank in a mass ratio of 96:1.2:1.8 and the dry powder is stirred at a speed of 20r / min for 30min; carbon nanotubes are dispersed in N-methylpyrrolidone (NMP).

[0041] Carbon nanotube conductive slurry was prepared in solvent, and the mass percentage of carbon nanotubes in the carbon nanotube conductive slurry was adjusted to 5%. Then, 40% of the mass of carbon nanotube conductive slurry was added to a stirring tank and wetted and stirred for 30 min at a rotation speed of 300 r / min and a revolution speed of 25 r / min. After that, the remaining carbon nanotube conductive slurry and N-methylpyrrolidone (NMP) solvent were added to the stirring tank and stirred for 4 h at a revolution speed of 25 r / min. Then, an appropriate amount of NMP solvent was added to the stirring tank one by one, and the stirring tank speed was controlled at a rotation speed of 4000 r / min and a revolution speed of 15 r / min. After stirring for 12 h, a positive electrode slurry was obtained and the solid content was controlled at 63%. (2) The positive electrode slurry was uniformly coated on both sides of the positive electrode current collector carbon-coated aluminum foil to obtain a wet electrode plate and the single-sided coating surface density was controlled at 75 g / m. 2 ;

[0042] (3) The above wet electrode plates were transferred to the baking room and dried at a temperature controlled at 120℃ to obtain a compacted density of 3.0 g / cm³. 3the positive electrode of the positive electrode plate.

[0043] 2. The method for preparing the negative electrode plate comprises the following steps: the negative electrode slurry is composed of 90% by mass fraction of artificial graphite, 5% of soft carbon, 2% of conductive agent, 1% of sodium carboxymethyl cellulose and 2% of butadiene rubber and deionized water, the rate of wet stirring is controlled at 2000 r / min of rotation and 25 r / min of revolution, and the solid content ratio is controlled at 53%, then uniformly coated on the negative electrode copper foil current collector to obtain a wet electrode plate, the wet electrode plate is transferred to a baking room, and the baking temperature is controlled at 90℃ for drying;

[0044] After that, the dried electrode plate is rolled to obtain a negative electrode plate with a compacted density of 1.2 g / cm 3 and a surface density of 40 g / cm 2 ;

[0045] 3. The lithium ion electrolyte is composed of a solvent, a lithium salt and an additive, the solvent is composed of vinyl carbonate, dimethyl carbonate and methyl ethyl carbonate in a mass ratio of 15:30:30; the lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonylimide in a mass ratio of 15:5; the additive is composed of lithium difluoro oxalate borate, tributyl borate and vinylene carbonate in a mass ratio of 2:2:1;

[0046] 4. The positive electrode plate, the negative electrode plate and the polypropylene separator coated with alumina ceramic of 1-3 are assembled in an aluminum plastic film, the electrolyte composed of the solvent, the lithium salt and the additive is injected, then the sealing, formation and capacity test procedures are carried out to obtain a finished product battery. Subsequently, the finished product battery is subjected to rate performance test under different temperature and different pulse current conditions.

[0047] Example 2

[0048] The mass ratio of NCM523 (D50 = 3.5 μm), conductive graphite, carbon nanotube and PVDF in the positive electrode slurry of the positive electrode plate is 97.5:0.75:0.75:1.

[0049] 1. The preparation method of the positive electrode tab comprises the following steps: (1) NCM523 (D50=3.5 μm), conductive graphite, and PVDF are added into a stirring cylinder at a mass ratio of 97.5:0.75:1, dry powder stirring is carried out at a rotation speed of 25 r / min for 40 min; carbon nanotube conductive slurry is prepared by dispersing carbon nanotubes in N-methyl pyrrolidone (NMP) solvent, the mass percentage of carbon nanotubes in the carbon nanotube conductive slurry is adjusted to 6%; then 40% of the mass of the conductive slurry is poured into the stirring cylinder, wet stirring is carried out at a rotation speed of 300 r / min and a revolution speed of 20 r / min for 30 min; then the remaining carbon nanotube conductive slurry and N-methyl pyrrolidone (NMP) solvent are added into the stirring cylinder, stirring is continued at a revolution speed of 25 r / min for 4 h; then, a proper amount of NMP solvent is added into the stirring cylinder in sequence, the stirring cylinder is controlled at a rotation speed of 5000 r / min and a revolution speed of 25 r / min, and the positive electrode slurry is obtained after stirring for 8 h, the solid content ratio is controlled at 65%; (2) the positive electrode slurry is uniformly coated on both sides of the positive current collector carbon-coated aluminum foil to obtain a wet electrode plate, the single-sided coating area density is controlled at 80 g / m 2 ; (3) the wet electrode plate is transferred to a baking room, drying is carried out at a baking temperature of 100℃, and the positive electrode tab with a compacted density of 2.8 g / cm 3 is obtained.

[0050] 2. The preparation method of the negative electrode tab comprises the following steps: the negative electrode slurry is composed of 92% of artificial graphite, 3% of soft carbon, 3% of conductive agent, 1% of sodium carboxymethyl cellulose, 1% of butadiene rubber, and deionized water, the wet stirring rate is controlled at 2000 r / min and 25 r / min, the solid content ratio is controlled at 55%, and then the wet electrode plate is obtained by uniformly coating on the negative copper foil current collector; the wet electrode plate is transferred to a baking room, and drying is carried out at a baking temperature of 90℃;

[0051] then the dried electrode tab is rolled to obtain the negative electrode tab with a compacted density of 1.5 g / cm 3 and an area density of 45 g / cm 2 ;

[0052] 3. The lithium ion electrolyte is composed of a solvent, a lithium salt, and an additive, the solvent is composed of vinyl carbonate, dimethyl carbonate, and methyl ethyl carbonate at a mass ratio of 5:35:35; the lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonylimide at a mass ratio of 15:5; the additive is composed of lithium difluoro oxalate borate, tributyl borate, and vinylene carbonate at a mass ratio of 2:1.5:1.5;

[0053] 4. The positive electrode plate, negative electrode plate and polyethylene separator coated with alumina ceramic of 1-3 are assembled in an aluminum plastic film, the electrolyte composed of solvent, lithium salt and additive is injected, and then the sealing, formation, and capacity process are carried out to obtain the finished product battery. Subsequently, the finished product battery is subjected to rate performance test under different temperature and different pulse current conditions.

[0054] Example 3

[0055] The mass ratio of NCM523 (D50 = 3.0 μm), conductive graphite, carbon nanotube and PVDF in the positive electrode slurry of the positive electrode plate is 97:1:1:1.

[0056] 1. The preparation method of the positive electrode plate comprises the following steps: (1) NCM523 (D50 = 3.0 μm), conductive graphite and PVDF are added to a stirring cylinder at a mass ratio of 97:1:1, dry powder stirring is carried out at a rotation speed of 30 r / min for 30 min; carbon nanotube conductive slurry is prepared by dispersing carbon nanotubes in N-methyl pyrrolidone (NMP) solvent, and the mass percentage of carbon nanotubes in the carbon nanotube conductive slurry is adjusted to 8%; then 40% of the conductive slurry is poured into the stirring cylinder, and wet stirring is carried out at a rotation speed of 300 r / min and a revolution speed of 25 r / min for 30 min; thereafter, the remaining carbon nanotube conductive slurry and N-methyl pyrrolidone (NMP) solvent are added to the stirring cylinder, and stirring is continued at a revolution speed of 25 r / min for 8 h; then, an appropriate amount of NMP solvent is added to the stirring cylinder in sequence, and the stirring cylinder is controlled at a rotation speed of 4000 r / min and a revolution speed of 15 r / min, and after stirring for 12 h, a positive electrode slurry is obtained, and the solid content ratio is controlled at 60%; (2) the positive electrode slurry is uniformly coated on both sides of the positive electrode current collector carbon-coated aluminum foil to obtain a wet electrode plate, and the single-sided coating area density is controlled at 75 g / m 2 ; (3) the wet electrode plate is transferred to a baking room, and dried at a baking temperature of 110°C to obtain a positive electrode plate with a compacted density of 3.5 g / cm 3 .

[0057] 2. The preparation method of the negative electrode plate comprises the following steps: the negative electrode slurry is composed of 94% of artificial graphite, 1% of soft carbon, 2% of conductive agent, 1% of sodium carboxymethyl cellulose and 2% of butadiene rubber and deionized water, the wet stirring rate is controlled at 2000 r / min and 25 r / min,

[0058] and the solid content ratio is 55%, and then uniformly coated on the negative electrode copper foil current collector to obtain a wet electrode plate, and the wet electrode plate is transferred to a baking room and dried at a baking temperature of 95°C; thereafter, the dried electrode plate is rolled to obtain a negative electrode plate with a compacted density of 1.8 g / cm 3 and a surface density of 48 g / cm2 negative electrode tab;

[0059] 3. The lithium ion electrolyte is composed of a solvent, a lithium salt and an additive, the solvent is composed of vinyl carbonate, dimethyl carbonate and methyl ethyl carbonate in a mass ratio of 15:30:30; the lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonylimide in a mass ratio of 10:10; the additive is composed of lithium difluoro(oxalato)borate, tributyl borate and vinylene carbonate in a mass ratio of 2:2:1;

[0060] 4. The positive electrode tab, the negative electrode tab and the polypropylene separator coated with alumina ceramic of 1-3 are assembled in an aluminum plastic film, the electrolyte composed of the above-mentioned solvent, lithium salt and additive is injected, and then the sealing, formation and capacity process are carried out to obtain a finished product battery. Subsequently, the finished product battery is subjected to rate performance test under different temperature and different pulse current conditions.

[0061] Comparative Example 1

[0062] The present comparative example provides a low-temperature power type lithium ion battery, comprising a positive electrode tab, a negative electrode tab, an electrolyte and a separator;

[0063] 1. The preparation method of the positive electrode tab comprises the following steps: (1) NCM523 (D50 = 2.2 μm), conductive graphite and PVDF are added to a stirring cylinder in a mass ratio of 96:1.2:1.8, dry powder stirring is carried out at a rotation speed of 30 r / min for 30 min; 1% of carbon nanotube is dispersed in N-methyl pyrrolidone (NMP) solvent to prepare a carbon nanotube conductive slurry, and the mass percentage of carbon nanotube is adjusted to 6%; then 40% of the conductive slurry is poured into the stirring cylinder, and wet stirring is carried out at a rotation speed of 300 r / min and a revolution speed of 25 r / min for 30 min; thereafter, the remaining mass of the carbon nanotube conductive slurry and N-methyl pyrrolidone (NMP) solvent is added to the stirring cylinder, and stirring is continued at a revolution speed of 25 r / min for 4 h; then, an appropriate amount of NMP solvent is added to the stirring cylinder in sequence, and the stirring cylinder is controlled at a rotation speed of 4000 r / min and a revolution speed of 15 r / min, and the positive electrode slurry is obtained after stirring for 12 h, and the solid content ratio is controlled at 63%; (2) the positive electrode slurry is uniformly coated on both sides of the positive electrode current collector carbon-coated aluminum foil to obtain a wet electrode plate, and the single-sided coating area density is controlled at 75 g / m 2 ; (3) the wet electrode plate is transferred to a baking chamber, and the baking temperature is controlled at 120℃

[0064] drying to obtain a positive electrode tab with a compacted density of 3.0 g / cm 3 ;

[0065] 2. The preparation method of the negative electrode tab comprises the following steps: the negative electrode slurry is composed of 90%

[0066] Artificial graphite, 5% soft carbon, 2% conductive agent, 1% carboxymethyl cellulose sodium and 2% butadiene rubber and deionized water are composed, the rate of wet stirring is controlled at 2000 r / min and 25 r / min, and the solid content ratio is controlled at 53%, then uniformly coated on the negative copper foil current collector to obtain a wet negative plate, the wet negative plate is transferred to a baking chamber, and the baking temperature is controlled at 90°C for drying; then the dried negative plate is rolled to obtain a negative plate with a compacted density of 1.2 g / cm 3 and a surface density of 40 g / cm 2 ;

[0067] 3. The lithium ion electrolyte is composed of a solvent, a lithium salt and an additive, the solvent is composed of vinyl carbonate, dimethyl carbonate and methyl ethyl carbonate in a mass ratio of 15:30:30; the lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonylimide in a mass ratio of 15:5; the additive is composed of lithium difluoro oxalate borate, tributyl borate and vinylene carbonate in a mass ratio of 2:2:1;

[0068] 4. The positive plate, the negative plate and the polypropylene separator coated with alumina ceramic of 1-3 are assembled in an aluminum plastic film, the electrolyte composed of the solvent, the lithium salt and the additive is injected, then the sealing, formation and capacity test procedures are carried out to obtain a finished product battery. Then, the finished product battery is tested for rate performance under different temperatures and different pulse current conditions.

[0069] Comparative Example 2

[0070] The embodiment provides a low-temperature power type lithium ion battery, which comprises a positive plate, a negative plate, an electrolyte and a separator.

[0071] 1. The preparation method of the positive plate comprises the following steps: (1) NCM523 (D50=5.4 μm), conductive graphite and PVDF are added into a stirring cylinder in a mass ratio of 96:1.2:1.8, dry powder stirring is carried out at a rotation speed of 25 r / min for 30 min; 1% of carbon nanotubes by mass are dispersed in N-methyl pyrrolidone (NMP) solvent to prepare a carbon nanotube conductive slurry, and the mass percentage of the carbon nanotubes is adjusted to 6%; then the conductive slurry is poured into the stirring cylinder, and wet stirring is carried out at a rotation speed of 300 r / min and 25 r / min for 4.5 h; then, appropriate NMP solvent is added into the stirring cylinder in sequence, and the stirring cylinder is controlled at a rotation speed of 4000 r / min and 15 r / min, and the positive slurry is obtained after stirring for 12 h, and the solid content ratio is controlled at 63%; (2) the positive slurry is uniformly coated on the carbon-coated aluminum foil positive current collector on both sides to obtain a wet negative plate, and the single-sided coating surface density is controlled at 75 g / m 2; (3) transferring the wet cathode plate to a baking room and drying at a baking temperature of 120℃ to obtain a cathode plate with a compacted density of 3.0 g / cm 3 .

[0072] 2. The preparation method of the negative electrode plate comprises the following steps: the negative electrode slurry is composed of 90% by mass fraction of artificial graphite, 5% of soft carbon, 2% of conductive agent, 1% of sodium carboxymethyl cellulose and 2% of butadiene rubber and deionized water, the stirring rate of wet mixing is controlled at 2000 r / min of self-rotation and 25 r / min of revolution,

[0073] and the solid content ratio is controlled at 53%, and then uniformly coated on a negative copper foil current collector to obtain a wet cathode plate, and the wet cathode plate is transferred to a baking room and dried at a baking temperature of 90℃; after that, the dried cathode plate is rolled to obtain a negative electrode plate with a compacted density of 1.2 g / cm 3 and a surface density of 40 g / cm 2 .

[0074] 3. The lithium ion electrolyte is composed of a solvent, a lithium salt and an additive, the solvent is composed of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate in a mass ratio of 15:30:30; the lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonylimide in a mass ratio of 15:5; and the additive is composed of lithium difluoro(oxalato)borate, tributyl borate and vinylene carbonate in a mass ratio of 2:2:1.

[0075] 4. The positive electrode plate, the negative electrode plate and the polypropylene separator coated with alumina ceramic of 1-3 are assembled in an aluminum plastic film, the electrolyte composed of the solvent, the lithium salt and the additive is injected, and then a sealing, formation and capacity process is performed to obtain a finished product battery. Subsequently, the finished product battery is subjected to rate performance test under different temperature and different pulse current conditions.

[0076] Figure 1 It is the electron microscope morphology picture of the positive electrode material under the conditions of Comparative Example 1, Comparative Example 2 and Example 1. (a) The positive electrode material of Comparative Example 1, D50 is 2.2 μm; (b) The positive electrode material of Example 1, D50 is 3.2 μm; (c) The positive electrode material of Comparative Example 2, D50 is 5.4 μm.

[0077] Figure 2 It is the low-temperature rate performance performance diagram of the battery assembled with different positive electrode materials under different pulse discharge conditions at -30℃. Under the condition of -30℃ and 270A maximum pulse discharge, the discharge lower limit voltage value of the battery of Example 1 is 2.62V, which is higher than the lower limit voltage value 2.48V of Comparative Example 1 and the lower limit voltage 2.40V of Comparative Example 2.

[0078] Figure 3The low temperature rate performance of the battery cells assembled with different positive electrode materials under the condition of -20℃, 25C pulse discharge is shown in the figure. Under the condition of -20℃, 425A continuous pulse discharge, the discharge lower limit voltage value of the battery cell of Example 1 is 2.59V, and the battery cells of Comparative Example 1 and Comparative Example 2 can not meet the start-stop requirements of the automobile because the lower limit voltage value is lowered to 2.0V within 2s.

Claims

1. A low-temperature power lithium ion battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, characterized in that, the positive electrode slurry of the positive electrode sheet comprises the following components and weight percentages: positive electrode active material 95%-97.5%, positive electrode conductive agent 1.5%-3%, positive electrode binder 1%-2%; the positive electrode sheet is prepared by wet blade coating with the above components dispersed in N-methyl pyrrolidone solvent; The positive electrode active material is a lithium nickel cobalt manganese oxide ternary material, the particle size distribution D50 is 3.0-3.5 µm, the specific surface area is 1.5-2.0 m 2 / g; the positive electrode conductive agent is composed of conductive graphite and carbon nanotubes, the weight percentage of conductive graphite accounts for 50%-70%; the positive electrode binder is polyvinylidene fluoride; 1) the preparation method of the positive electrode sheet comprises the following steps: (1) the positive active material, conductive graphite and positive electrode binder are added into a stirring tank for stirring; carbon nanotubes are dispersed in N-methyl pyrrolidone solvent to obtain a carbon nanotube conductive slurry, the weight percentage of the carbon nanotubes being 3-10%, and the weight percentage of the N-methyl pyrrolidone solvent being 90-97%; then, the carbon nanotube conductive slurry with a weight percentage of 40±4% is added into the stirring tank for stirring; thereafter, the remaining carbon nanotube conductive slurry and N-methyl pyrrolidone solvent are added into the stirring tank for continuous stirring; then, an appropriate amount of N-methyl pyrrolidone solvent is added into the stirring tank in sequence, and a positive electrode slurry is obtained after stirring, with the solid content ratio being controlled at 60%-65%; (2) the positive electrode slurry is uniformly coated on both sides of a carbon-coated aluminum foil serving as a positive electrode current collector to obtain a wet positive plate, with the single-side coating area density being controlled at 65-110 g / m 2 ; (3) the wet positive plate is transferred to a baking room, and dried at a baking temperature of 100-120℃ to obtain a positive electrode tab with a compacted density of 2.8-3.5 g / cm 3 ; 2) negative electrode tab preparation: the formulation of the negative electrode slurry comprises the following components in mass percentage: 90-94% artificial graphite, 1-5% soft carbon, 1-3% conductive agent, 1-2% sodium carboxymethyl cellulose, 1-2% butadiene-styrene rubber, and the balance is deionized water, artificial graphite, soft carbon, conductive agent, sodium carboxymethyl cellulose, butadiene-styrene rubber and deionized water are added to a stirring cylinder for stirring to obtain a negative electrode slurry, and the solid content ratio is controlled to be 50%-55%, then the negative electrode slurry is uniformly coated on the negative copper foil current collector to obtain a wet electrode plate, the wet electrode plate is transferred to a baking room, and the baking temperature is controlled at 90-95°C for drying; thereafter, the dried electrode plate is rolled to obtain a negative electrode tab with a compaction density of 1.2-1.8 g / cm 3 and a surface density of 40-50 g / cm 2 ​ 3) the positive electrode sheet, the negative electrode sheet and the separator are assembled in an aluminum plastic film, the electrolyte is injected, and then the sealing, formation and capacity distribution processes are carried out to obtain a finished battery cell; Subsequently, the finished battery cell is subjected to rate performance test under different temperature and different pulse current conditions.

2. The cryogenic power lithium-ion battery of claim 1, wherein, The electrolyte is composed of carbonate solvents, lithium salts and additives.

3. The cryogenic power lithium-ion battery of claim 2, wherein, The carbonate solvents are composed of 5-15% by mass of ethylene carbonate, 30-35% by mass of dimethyl carbonate and 30-35% by mass of methyl ethyl carbonate; the lithium salts are composed of 10-15% by mass of lithium hexafluorophosphate and 5-10% by mass of lithium bisfluorosulfonylimide; the additives are composed of 1-2% by mass of lithium difluoroboric oxalate, 1-3% by mass of tributyl borate and 1-2% by mass of vinylene carbonate.

4. The cryogenic power-type lithium-ion battery of claim 1, wherein, The separator is one of a single-sided alumina ceramic coated polypropylene separator or a single-sided alumina ceramic coated polyethylene separator.

5. The cryogenic power-type lithium-ion battery of claim 1, wherein, The lithium ion battery includes a start-stop lithium ion battery and an auxiliary lithium ion battery.

6. The cryogenic power lithium-ion battery of claim 1, wherein, The negative electrode slurry is composed of the following components by mass percentage: 90% artificial graphite, 5% soft carbon, 2% conductive agent, 1% sodium carboxymethyl cellulose, 2% butadiene rubber, and the balance is deionized water.

7. The cryogenic power lithium-ion battery of claim 1, wherein, In the preparation of the negative electrode sheet, the artificial graphite, soft carbon, conductive agent, sodium carboxymethyl cellulose, butadiene rubber and deionized water are stirred by wet stirring, and the wet stirring rate is controlled at 2000-2500 r / min of autorotation and 15-25 r / min of revolution.

8. A positive slurry for a positive electrode sheet of a low-temperature power lithium ion battery, characterized by The positive electrode slurry of the positive electrode tab comprises the following components and weight percentages: positive electrode active material 95%-97.5%, positive electrode conductive agent 1.5%-3%, and positive electrode binder 1%-2%; the positive electrode active material is a lithium nickel cobalt manganese oxide ternary material, the particle size distribution D50 of which is 3.0-3.5 µm, and the specific surface area is 1.5-2.0 m 2 / g; the positive electrode conductive agent is composed of conductive graphite and carbon nanotubes, and the weight percentage of the conductive graphite is 50%-70%; and the positive electrode binder is polyvinylidene fluoride.

9. A method of producing the positive electrode slurry according to claim 8, characterized by, comprising the following steps: The positive electrode active material, conductive graphite and positive electrode binder are added into a stirring cylinder, and dry powder stirring is carried out at a rotation speed of 15-30 r / min for 30-60 min; carbon nanotubes are dispersed in N-methyl pyrrolidone solvent to obtain a carbon nanotube conductive slurry, the weight percentage of the carbon nanotubes is 3-10%, and the weight percentage of the N-methyl pyrrolidone solvent is 90-97%; then, the carbon nanotube conductive slurry with a weight percentage of 40%±4 is added into the stirring cylinder, and wet stirring is carried out at a rotation speed of 200-300 r / min and a revolution speed of 15-25 r / min for 30-60 min; thereafter, the remaining carbon nanotube conductive slurry and N-methyl pyrrolidone solvent are added into the stirring cylinder, and stirring is continuously carried out at a revolution speed of 15-25 r / min for 4-8 h; then, an appropriate amount of N-methyl pyrrolidone solvent is added into the stirring cylinder in sequence, and the stirring cylinder is controlled to rotate at a rotation speed of 4000-5000 r / min and a revolution speed of 10-25 r / min, and the positive electrode slurry is obtained after stirring for 8-12 h, and the solid content ratio is controlled to be 60%-65%.

10. A method for preparing a cathode sheet of a low-temperature power lithium ion battery, using the cathode slurry according to claim 8, characterized in that, comprising the steps of: The positive electrode slurry is uniformly coated on both sides of the positive current collector coated carbon aluminum foil to obtain a wet plate, and the single-side coating density is controlled to be 65-110 g / m 2 ; The wet cathode plate is transferred to a baking room, and the baking temperature is controlled at 100-120°C for drying, to obtain a positive electrode plate with a compacted density of 2.8-3.5 g / cm 3 .

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