CN110739485A - low-temperature lithium ion batteries - Google Patents

Abstract

The invention belongs to the field of lithium batteries, and particularly relates to low-temperature lithium ion batteries, wherein a positive plate comprises a positive current collector and a positive active material layer, the positive active material layer comprises a 4.4V lithium cobaltate material, a positive conductive agent and a positive binder, a negative plate comprises a negative current collector and a negative active material layer, the negative active material layer comprises a hard carbon-coated secondary particle artificial graphite material, a negative conductive agent, a dispersing agent and a negative binder, an electrolyte comprises 10-20% of lithium hexafluorophosphate, 10-20% of ethyl propionate, 10-20% of diethyl carbonate, 15-30% of ethylene carbonate, 15-30% of propyl propionate, 3-10% of fluoroethylene carbonate, 2-3% of propylene sulfite, 0.5-2.5% of ethylene glycol monobutyl ether and 0.5-2.5% of 2, 2' -dipyridyl disulfide.

Description

low-temperature lithium ion batteries

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to low-temperature lithium ion batteries.

Background

At present, the low-temperature performance of the lithium ion battery is relatively poor, and particularly in a low-temperature environment below-20 ℃, the charging of the lithium ion battery becomes extremely difficult, lithium dendrites are precipitated, the internal of the battery can be short-circuited, the discharge performance of the battery is greatly reduced, and the subsequent electrochemical performance is greatly reduced, so that the research on the use of the lithium ion battery in a cold environment is urgent.

, the main reasons for the poor performance of the battery in low temperature environment are 1) the viscosity of the electrolyte increases and even the icing phenomenon occurs in low temperature environment, and the conductivity is greatly reduced, 2) the migration speed of lithium ions in the anode and cathode materials is slowed, and 3) the diffusion on the electrode/electrolyte interface and the charge transfer rate are slowed, that is, the transmission rate of lithium ions may be reduced due to the properties of the anode material, the cathode material and the electrolyte.

Disclosure of Invention

The invention aims to provide low-temperature lithium ion batteries which have good charge and discharge performance and higher energy density under low-temperature conditions aiming at the defects of the prior art.

In order to achieve the purpose, the invention adopts the following technical scheme:

kinds of low temperature lithium ion battery, including positive plate, negative plate, diaphragm and electrolyte;

the positive plate comprises a positive current collector and a positive active substance layer arranged on the surface of the positive current collector, wherein the positive active substance layer comprises a 4.4V lithium cobaltate material, a positive conductive agent and a positive binder;

the negative plate comprises a negative current collector and a negative active substance layer arranged on the surface of the negative current collector, wherein the negative active substance layer comprises a hard carbon-coated secondary particle artificial graphite material, a negative conductive agent, a dispersing agent and a negative binder;

the electrolyte comprises 10-20% of lithium hexafluorophosphate, 10-20% of ethyl propionate, 10-20% of diethyl carbonate, 15-30% of ethylene carbonate, 15-30% of propyl propionate, 3-10% of fluoroethylene carbonate, 2-3% of propylene sulfite, 0.5-2.5% of ethylene glycol monobutyl ether and 0.5-2.5% of 2, 2' -dipyridyl disulfide.

The improvements of the low-temperature lithium ion battery are that the surface density of the positive electrode active material layer is 145-150 g/m²The compacted density of the positive active material layer is 3.6-4.2 g/m³. In a reasonable surface density range, the surface density is reduced, the porosity of the material is increased, the larger the electrolyte adsorption amount of active substances per unit mass is, and the solution contact resistance is reduced; the surface density is small, and the thickness of the pole piece is thickIn addition, , the thickness of the pole piece is correspondingly reduced, which is beneficial to the migration of lithium ions in active material, but when the compaction density is too high, the infiltration capacity of the material to the electrolyte is poor, the contact resistance is increased, and the negative effect on the battery performance is generated.

The improvements of the low-temperature lithium ion battery are that the surface density of the negative electrode active material layer is 75-80 g/m²The compacted density of the negative electrode active material layer is 1.3-1.8 g/m³。

The improvements of the low-temperature lithium ion battery are that the mass ratio of the 4.4V lithium cobaltate material to the positive electrode conductive agent to the positive electrode binder is (95-98): 1-3: 1-2.

The improvements of the low-temperature lithium ion battery are that the mass ratio of the hard carbon-coated secondary particle artificial graphite material to the negative electrode conductive agent to the dispersing agent to the negative electrode binder is (95-98): (0.5-1.5): (1-1.5): 1-2.

The improvements of the low-temperature lithium ion battery are that the 4.4V lithium cobaltate material is formed by mixing at least two kinds of spheroidal particles with different particle diameters, the median particle diameter of the 4.4V lithium cobaltate material is 12-18 mu m, and the specific surface area is 0.25-0.3 m²The tap density is 2.5-3.0 g/cm³Wherein the particle size of the spheroidal particles with large particle size is 32-38 μm, and the particle size of the spheroidal particles with small particle size is 2-5 μm. The particles with different particle sizes are mixed, wherein the small particle size particles are beneficial to reducing the lithium ion transmission distance and improving the low-temperature performance, and the large particle size particles are beneficial to improving the cycle performance of the battery due to increasing the compaction density.

improvements of the low-temperature lithium ion battery provided by the invention are that the median particle size of the hard carbon-coated secondary artificial graphite particle material is 12-18 mu m, and the specific surface area of the hard carbon-coated secondary artificial graphite particle material is1.0 to 1.4m²The tap density is 0.8-1.2 g/cm³. The adoption of the hard carbon coating is favorable for improving the stability of the cathode active material under the low-temperature condition and improving the low-temperature performance of the battery.

improvements of the low-temperature lithium ion battery are that the positive electrode conductive agent comprises at least of conductive carbon black, conductive graphite, graphene, carbon nanotubes and carbon fibers, and the positive electrode binder comprises polyvinylidene fluoride.

The improvements of the low-temperature lithium ion battery are that the negative electrode conductive agent comprises at least of conductive carbon black, conductive graphite, carbon fiber, carbon nano tube and graphene, the negative electrode binder comprises at least of acrylonitrile multipolymer, styrene butadiene rubber, sodium carboxymethyl cellulose and polyacrylic acid, and the dispersant is sodium carboxymethyl cellulose.

The improvements of the low-temperature lithium ion battery comprise a base film, an adhesive layer and a ceramic layer, wherein the ceramic layer is adhered to the surface of the base film through the adhesive layer, and the base film is at least selected from a polypropylene film, a polypropylene/polyethylene/polypropylene composite film, nylon cloth, glass fiber, a polyvinyl alcohol film and asbestos paper.

Compared with the prior art, the low-temperature lithium ion battery has the beneficial effects that in the aspect of , the hard carbon coated secondary particle artificial graphite material is used as a negative electrode active substance, the direct current internal resistance (DCR) of the material is reduced, and the low-temperature performance of the battery is improved, in the aspect of , the composition and the content of each component of the electrolyte are improved, wherein propyl propionate is beneficial to infiltration and is beneficial to improvement of low-temperature discharge and low-temperature cycle lithium precipitation, ethyl propionate has low viscosity, high dielectric constant and good infiltration and is beneficial to improvement of the low-temperature charging performance of the battery core, diethyl carbonate has high dielectric constant and is beneficial to improvement of conductivity, and 2, 2' -dipyridyl disulfide is beneficial to improvement of the low-temperature charging performance, so that the conductivity and the low-temperature charging performance of the electrolyte are obviously improved.

Drawings

FIG. 1 is a diagram showing an analysis of the lithium deposition in the example of the present invention.

FIG. 2 is a diagram showing an analysis of lithium deposition in comparative example 1 of the present invention.

FIG. 3 is a diagram showing an analysis of lithium deposition in comparative example 2 of the present invention.

FIG. 4 is a diagram showing an analysis of lithium deposition in comparative example 3 of the present invention.

FIG. 5 is a graph showing the discharge rate of example 1 of the present invention.

FIG. 6 is a graph showing the cycle of example 1 of the present invention.

Detailed Description

The present invention will be described in further detail with reference to specific embodiments and the accompanying drawings, but the embodiments of the invention are not limited thereto.

Example 1

The low-temperature lithium ion battery comprises a positive plate, a negative plate, a diaphragm and electrolyte;

the positive plate comprises a positive current collector and a positive active material layer arranged on the surface of the positive current collector, and the surface density of the positive active material layer is 148g/m²The positive electrode active material layer had a compacted density of 4.0g/m³The positive active material layer comprises the following components in a mass ratio of 97.5: 1.5: 1 of 4.4V lithium cobaltate material, a positive electrode conductive agent and a positive electrode binder; the 4.4V lithium cobaltate material is formed by mixing at least two kinds of spheroidal particles with different particle diameters, the median particle diameter of the 4.4V lithium cobaltate material is 15 mu m, and the specific surface area is 0.27m²(g) tap density of 2.7g/cm³Wherein, the particle diameter of the spheroidal particle with large particle diameter is 35 μm, and the particle diameter of the spheroidal particle with small particle diameter is 3 μm; the conductive agent is carbon nano tube and conductive carbon black (mass ratio is 7:8), the carbon nano tube is LB-117-44, the conductive carbon black is conventional Super-P, and the binder is polyvinylidene fluoride (Solef 5130).

The negative plate comprises a negative current collector and a negative active material layer arranged on the surface of the negative current collectorThe surface density of the negative electrode active material layer was 78.5g/m²The compacted density of the negative electrode active material layer was 1.6g/m³The negative electrode active material layer includes, by mass, 96.5: 1: 1.3: 1.2, coating a secondary particle artificial graphite material with hard carbon, a negative electrode conductive agent, a dispersing agent and a negative electrode binder; the hard carbon-coated secondary artificial graphite particle material has a median particle diameter of 15 μm and a specific surface area of 1.2m²(g) tap density of 1.0g/cm³(ii) a The negative electrode conductive agent comprises conductive carbon black (conventional Super-P), the negative electrode binder is SBR (model 6913), and the dispersing agent is sodium carboxymethyl cellulose (model 2200).

The diaphragm comprises a base film, an adhesive layer and a ceramic layer, wherein the ceramic layer is adhered to the surface of the base film through the adhesive layer, the base film is a polypropylene film, and the adhesive layer is PVDF.

The electrolyte comprises 15% of lithium hexafluorophosphate, 15% of ethyl propionate, 15% of diethyl carbonate, 23% of ethylene carbonate, 22% of propyl propionate, 5% of fluoroethylene carbonate, 2% of propylene sulfite, 1.5% of ethylene glycol monobutyl ether and 1.5% of 2, 2' -dipyridyl disulfide.

The preparation method of the low-temperature lithium ion battery of the embodiment comprises the following steps:

preparing a positive plate: uniformly dispersing a positive binder and a positive conductive agent, adding a 4.4V lithium cobaltate material, mixing to obtain positive active material slurry with the viscosity of 6000-8000 mpa.s, coating the positive active material slurry on the surface of a positive current collector, drying and rolling to obtain a positive plate;

preparing a negative plate: dissolving a dispersing agent in deionized water, adding a negative electrode conductive agent, adding a hard carbon coated secondary particle artificial graphite material after uniform dispersion, adjusting the viscosity of the slurry to 2500mpa.s, adding a negative electrode binder to prepare a negative electrode active substance slurry, coating the negative electrode active substance slurry on the surface of a negative electrode current collector, drying and rolling to prepare a negative electrode sheet;

preparing an electrolyte: and (3) in a glove box, controlling the humidity and the oxygen content to be below 0.1ppm, and uniformly mixing the components to obtain the electrolyte.

The diaphragm is prepared by coating adhesive layers of 2 μm on the surface of a base film, and coating ceramic layers of 2 μm on the surface of the adhesive layers.

And preparing the obtained positive plate, negative plate and diaphragm into a battery with a required model by adopting a winding mode, and then preparing the battery into a low-temperature lithium ion battery through the working procedures of casing, baking, injecting electrolyte, forming, grading and the like.

Example 2

The difference from example 1 is:

the surface density of the positive electrode active material layer was 145g/m²The positive electrode active material layer had a compacted density of 3.6g/m³. The surface density of the negative electrode active material layer was 75g/m²The compacted density of the negative electrode active material layer was 1.3g/m³。

The rest is the same as embodiment 1, and the description is omitted here.

Example 3

The difference from example 1 is:

the surface density of the positive electrode active material layer was 150g/m²The positive electrode active material layer had a compacted density of 4.2g/m³. The surface density of the negative electrode active material layer was 80g/m²The compacted density of the negative electrode active material layer was 1.8g/m³。

The rest is the same as embodiment 1, and the description is omitted here.

Example 4

The difference from example 1 is:

the 4.4V lithium cobaltate material is formed by mixing at least two kinds of spheroidal particles with different particle diameters, the median particle diameter of the 4.4V lithium cobaltate material is 12 mu m, and the specific surface area is 0.25m²(g) tap density of 2.5g/cm³Wherein the spherical-like particles having a large particle diameter have a particle diameter of 32 μm, and the spherical-like particles having a small particle diameter have a particle diameter of 2 μm.

The rest is the same as embodiment 1, and the description is omitted here.

Example 5

The difference from example 1 is:

the 4.4V lithium cobaltate material is formed by mixing at least two kinds of spheroidal particles with different particle diameters, the median particle diameter of the 4.4V lithium cobaltate material is 18 mu m, and the specific surface area is0.3m²(g) tap density of 3.0g/cm³Wherein the spherical-like particles having a large particle diameter have a particle diameter of 38 μm and the spherical-like particles having a small particle diameter have a particle diameter of 5 μm.

The rest is the same as embodiment 1, and the description is omitted here.

Example 6

The difference from example 1 is:

the hard carbon-coated secondary artificial graphite particle material has a median particle diameter of 12 μm and a specific surface area of 1.0m²(g), tap density 0.8g/cm³。

The rest is the same as embodiment 1, and the description is omitted here.

Example 7

The difference from example 1 is:

the hard carbon-coated secondary artificial graphite particle material has a median particle diameter of 18 μm and a specific surface area of 1.4m²(g) tap density of 1.2g/cm³。

The rest is the same as embodiment 1, and the description is omitted here.

Example 8

The difference from example 1 is:

the electrolyte comprises 20% of lithium hexafluorophosphate, 12% of ethyl propionate, 20% of diethyl carbonate, 15% of ethylene carbonate, 15% of propyl propionate, 10% of fluoroethylene carbonate, 3% of propylene sulfite, 2.5% of ethylene glycol monobutyl ether and 2.5% of 2, 2' -dipyridyl disulfide.

The rest is the same as embodiment 1, and the description is omitted here.

Example 9

The difference from example 1 is:

the electrolyte comprises 12% of lithium hexafluorophosphate, 20% of ethyl propionate, 12% of diethyl carbonate, 30% of ethylene carbonate, 20% of propyl propionate, 3% of fluoroethylene carbonate, 2% of propylene sulfite, 0.5% of ethylene glycol monobutyl ether and 0.5% of 2, 2' -dipyridyl disulfide.

The rest is the same as embodiment 1, and the description is omitted here.

Example 10

The difference from example 1 is:

the electrolyte comprises 18% of lithium hexafluorophosphate, 18% of ethyl propionate, 18% of diethyl carbonate, 20% of ethylene carbonate, 20% of propyl propionate, 3% of fluoroethylene carbonate, 2% of propylene sulfite, 0.5% of ethylene glycol monobutyl ether and 0.5% of 2, 2' -dipyridyl disulfide.

The rest is the same as embodiment 1, and the description is omitted here.

Comparative example 1

The difference from example 1 is:

the positive active material is lithium iron phosphate.

The rest is the same as embodiment 1, and the description is omitted here.

Comparative example 2

The difference from example 1 is:

the negative active material is graphite.

The rest is the same as embodiment 1, and the description is omitted here.

Comparative example 3

The difference from example 1 is:

the electrolyte is 2 wt% of fluorinated propylene carbonate, 11 wt% of lithium hexafluorophosphate and 87% of organic solvent (the mass ratio of propylene carbonate to ethylene carbonate to ethyl methyl carbonate to ethyl formate is 1: 4: 4: 4).

The rest is the same as embodiment 1, and the description is omitted here.

Performance testing

The lithium ion battery prepared above was subjected to the following performance tests:

1) the battery is placed at the temperature of 25 ℃, 0 ℃, 5 ℃, 10 ℃ and 20 ℃, the battery is charged and discharged by currents of 0.1C, 0.2C, 0.3C, 0.5C, 0.7C, 1.0C, 1.2C, 1.5C, 2.0C, 2.5C and 3.0C respectively, the battery is disassembled after 5 weeks of circulation, and whether the lithium precipitation phenomenon exists in the battery is observed. The lithium deposition of the batteries of examples 1-10 is shown in FIG. 1, the lithium deposition of the battery of comparative example 1 is shown in FIG. 2, the lithium deposition of the battery of comparative example 2 is shown in FIG. 3, and the lithium deposition of the battery of comparative example 3 is shown in FIG. 4.

2) The discharge capacity of the battery is taken as a reference, the battery is placed at the temperature of 60 ℃, 0 ℃, 10 ℃ and 20 ℃ to discharge with the current of 0.5 ℃, and the discharge rate of the battery is calculated according to the discharge capacity of the battery. Specific results are shown in table 1. The discharge rate curve of example 1 is shown in fig. 5.

3) The battery was charged at a temperature of 0 ℃ with a current of 2C and discharged with a current of 1C, and the capacity retention ratio of the battery was calculated after 100 cycles. The specific results are shown in table 2, and the cycle curves of example 1 are shown in fig. 6.

Table 1 discharge rate test results

TABLE 2 Capacity Retention test results

Firstly, as can be seen from comparison of fig. 1 to 4, the low-temperature lithium ion battery prepared by the invention is charged and discharged at a low temperature of-20 ℃ with a current of 0.2C, and no lithium precipitation phenomenon is found after disassembly, while the lithium ion battery of comparative examples 1 to 3 is charged and discharged at a low temperature of-10 ℃ with a current of 0.2C, and the lithium precipitation phenomenon is found after disassembly, so that the low-temperature lithium ion battery prepared by the invention has good low-temperature performance.

Secondly, as can be seen from table 1 and fig. 5, compared with the lithium ion battery prepared by the comparative example, the low temperature lithium ion battery prepared by the invention has higher discharge rate (based on the discharge capacity of the battery at 25 ℃) at 0 ℃, -10 ℃ and even-20 ℃), that is, the low temperature lithium ion battery of the invention has good discharge performance in low temperature environment.

Finally, as can be seen from table 2 and fig. 6, compared with the lithium ion battery prepared by the comparative example, the low-temperature lithium ion battery prepared by the present invention has high initial capacity and higher capacity retention rate at 0 ℃, that is, the low-temperature lithium ion battery of the present invention not only has higher energy density, but also has good cycle stability in a low-temperature environment.

Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention shall fall within the protection scope of the present invention.

Claims (10)

1, kinds of low temperature lithium ion battery, wherein it comprises positive plate, negative plate, diaphragm and electrolyte;

the positive plate comprises a positive current collector and a positive active substance layer arranged on the surface of the positive current collector, wherein the positive active substance layer comprises a 4.4V lithium cobaltate material, a positive conductive agent and a positive binder;

the negative plate comprises a negative current collector and a negative active substance layer arranged on the surface of the negative current collector, wherein the negative active substance layer comprises a hard carbon-coated secondary particle artificial graphite material, a negative conductive agent, a dispersing agent and a negative binder;

the electrolyte comprises 10-20% of lithium hexafluorophosphate, 10-20% of ethyl propionate, 10-20% of diethyl carbonate, 15-30% of ethylene carbonate, 15-30% of propyl propionate, 3-10% of fluoroethylene carbonate, 2-3% of propylene sulfite, 0.5-2.5% of ethylene glycol monobutyl ether and 0.5-2.5% of 2, 2' -dipyridyl disulfide.

2. The low temperature lithium ion battery of claim 1, wherein: the surface density of the positive electrode active material layer is 145-150 g/m²The positive electrode activityThe compacted density of the material layer is 3.6-4.2 g/m³。

3. The low temperature lithium ion battery of claim 1, wherein: the surface density of the negative electrode active material layer is 75-80 g/m²The compacted density of the negative electrode active material layer is 1.3-1.8 g/m³。

4. The low temperature lithium ion battery of claim 1, wherein: the mass ratio of the 4.4V lithium cobaltate material to the positive electrode conductive agent to the positive electrode binder is (95-98): 1-3): (1-2).

5. The low temperature lithium ion battery of claim 1, wherein: the mass ratio of the hard carbon-coated secondary particle artificial graphite material to the negative electrode conductive agent to the dispersing agent to the negative electrode binder is (95-98): (0.5-1.5): (1-1.5): (1-2).

6. The low temperature lithium ion battery of claim 1, wherein: the 4.4V lithium cobaltate material is formed by mixing at least two kinds of spheroidal particles with different particle diameters, the median particle diameter of the 4.4V lithium cobaltate material is 12-18 mu m, and the specific surface area is 0.25-0.3 m²The tap density is 2.5-3.0 g/cm³Wherein the particle size of the spheroidal particles with large particle size is 32-38 μm, and the particle size of the spheroidal particles with small particle size is 2-5 μm.

7. The low temperature lithium ion battery of claim 1, wherein: the hard carbon-coated secondary artificial graphite particle material has a median particle diameter of 12-18 mu m and a specific surface area of 1.0-1.4 m²The tap density is 0.8-1.2 g/cm³。

8. The low-temperature lithium ion battery according to claim 1, wherein the positive electrode conductive agent comprises at least of conductive carbon black, conductive graphite, graphene, carbon nanotubes and carbon fibers, and the positive electrode binder comprises polyvinylidene fluoride.

9. The low-temperature lithium ion battery of claim 1, wherein the negative electrode conductive agent comprises at least of conductive carbon black, conductive graphite, carbon fiber, carbon nanotube and graphene, the negative electrode binder comprises at least of acrylonitrile multipolymer, styrene-butadiene rubber, sodium carboxymethyl cellulose and polyacrylic acid, and the dispersant is sodium carboxymethyl cellulose.

10. The low-temperature lithium ion battery of claim 1, wherein the separator comprises a base film, an adhesive layer and a ceramic layer, the ceramic layer is adhered to the surface of the base film through the adhesive layer, and the base film is at least selected from a polypropylene film, a polypropylene/polyethylene/polypropylene composite film, nylon cloth, glass fiber, a polyvinyl alcohol film and asbestos paper.

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