Methods for improving the power density of lithium-ion batteries

Abstract

The present invention discloses a method for improving the power density of a lithium-ion battery, comprising the following steps: when preparing the positive and / or negative electrode sheets of the lithium battery, uniformly mixing an active material, a conductive agent, and a binder to form a slurry; uniformly coating the slurry on a foil current collector; drying the coating layer; rolling the coated composite electrode; first placing the electrode sheet in a low-temperature environment for a predetermined period of time; and then returning the electrode sheet to room temperature to obtain a high-power electrode sheet. The present invention improves the rate performance of a lithium-ion battery by reducing the tortuosity of the electrode sheet, shortening the mass transfer path, and lowering the lithium ion diffusion impedance. This method does not require controlling the particle size of the electrode material or the thickness of the electrode sheet, thereby improving the power density while maintaining process simplicity and the battery's energy density.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a method for improving the power density of lithium-ion batteries. Background Art

[0002] Lithium-ion batteries are currently one of the most commonly used energy storage devices, offering advantages such as high specific energy, high voltage, long cycle life, and environmental friendliness. However, with the widespread application and accelerating replacement of lithium-ion batteries, consumers are demanding higher power densities. These include fast-charging technology for electronic products like mobile phones, high-power output and fast-charging technology for electric vehicles, and the high-load capacity of drones. These applications all require lithium-ion batteries to possess higher power density.

[0003] Currently, there are several methods for increasing the power density of lithium-ion batteries. The first is to reduce the particle size of the battery material. This effectively shortens the distance for ion diffusion, thereby improving rate performance. However, this approach can have a series of impacts on the electrode manufacturing process. First, it can cause material dispersion problems during the homogenization process. Simply increasing the stirring speed makes it difficult to evenly disperse small particles. Second, the large specific surface energy of small particles can lead to severe agglomeration, affecting coating consistency and operability. Therefore, this method is prone to problems such as difficulty in homogenization and processing. The second method is to reduce the coating thickness of the electrode sheet. This method can significantly shorten the diffusion path of liquid-phase ions and improve the battery's rate performance, but it also reduces the active material loading and lowers the battery's energy density. The third method is to reduce the electrode sheet's compaction density. This method can increase the spacing between the material particles, improve the electrode sheet's electrolyte absorption capacity, widen and increase the lithium ion transmission path, and facilitate the rapid movement of lithium ions under high current. However, there is an optimal range for compaction density. Excessively low compaction density is not conducive to contact between particles, negatively affecting the electrode sheet's electronic conductivity and reducing the battery's volumetric energy density. Summary of the Invention

[0004] The purpose of the present invention is to address the technical defects existing in the prior art and provide a method for improving the power density of lithium-ion batteries. By utilizing the physical property that the thermal expansion coefficients of the components in the electrode slurry are different, the micromorphology of the electrode is regulated by changing the temperature field, the tortuosity of the electrode is reduced, and the infiltration of the electrolyte is promoted, thereby improving the power density of the lithium-ion battery.

[0005] The technical solution adopted to achieve the purpose of the present invention is:

[0006] A method for improving the power density of a lithium-ion battery comprises the following steps:

[0007] When preparing the positive electrode and / or negative electrode of a lithium battery, the active material, conductive agent and binder are evenly mixed to prepare a slurry, the slurry is evenly coated on the foil current collector to form a coating layer, the coating layer is dried, the electrode electrode with the dried coating layer is rolled, the rolled electrode electrode is placed in a low-temperature environment for a predetermined time, and the electrode electrode is placed in a normal temperature environment to return to room temperature to obtain a high-power electrode.

[0008] Among them, the low-temperature environment is -60 to 0°C, preferably -60 to -18°C, and more preferably -20 to -18°C. The predetermined time in the low-temperature environment is 0 to 24 hours, preferably 1 to 24 hours, and more preferably 1 to 15 hours, depending on the temperature of the low-temperature environment. The lower the temperature, the shorter the standing time. The normal temperature environment is 20 to 30°C.

[0009] The present invention improves the rate performance of lithium-ion batteries by reducing the tortuosity of the electrode sheet, shortening the mass transfer path, and lowering the lithium ion diffusion impedance. This method does not require regulating the particle size of the electrode material and the thickness of the electrode sheet, thereby ensuring the simplicity of the process and the energy density of the battery while improving the power density. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 The figure is a flow chart of a method for improving the power density of a lithium-ion battery according to the present invention.

[0011] Figure 2 These are SEM images of Example 1, Example 2 and Comparative Example 1.

[0012] Figure 3 The electrochemical impedance spectroscopy diagrams of the button batteries corresponding to Example 1, Example 2 and Comparative Example 1 are shown.

[0013] Figure 4 These are SEM images of Example 3, Example 4 and Comparative Example 2. DETAILED DESCRIPTION

[0014] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0015] The present invention utilizes the physical property that the thermal expansion coefficients of the organic polymer binder and the inorganic components in the electrode components are quite different. By changing the temperature field, the components shrink asynchronously, increasing the porosity of the electrode sheet, reducing the tortuosity of the electrode sheet, shortening the lithium ion diffusion path, and thereby improving the wettability of the electrolyte to the electrode sheet, and ultimately improving the power density of the battery.

[0016] like Figure 1 As shown, a method for improving the power density of a lithium-ion battery comprises the following steps:

[0017] When preparing the positive electrode and / or negative electrode of a lithium battery, the active material, conductive agent and binder are evenly mixed to prepare a slurry, the slurry is evenly coated on the foil current collector to form a coating layer, the coating layer is dried, the electrode electrode with the dried coating layer is rolled, the rolled electrode electrode is placed in a low-temperature environment for a predetermined time, and the electrode electrode is placed in a normal temperature environment to return to room temperature to obtain a high-power electrode.

[0018] Among them, the low-temperature environment is -60 to 0°C, preferably -60 to -18°C, and more preferably -20 to -18°C. The predetermined time in the low-temperature environment is 0 to 24 hours, preferably 1 to 24 hours, and more preferably 1 to 15 hours, depending on the temperature of the low-temperature environment. The lower the temperature, the shorter the standing time. The normal temperature environment is 20 to 30°C.

[0019] Example 1

[0020] The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi 0.9 Co 0.05 Mn 0.05 The positive electrode slurry was prepared by uniformly mixing the conductive agent carbon black (Super-P) and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 97:1:2. The viscosity of the positive electrode slurry was 6000-8000 mPa·s. The positive electrode slurry was evenly coated on the aluminum foil current collector and the coating layer was dried at a temperature of 120°C for 3 minutes. The surface density of the electrode was 45 mg / cm 2 The coated composite layer electrode was rolled. The thickness of the composite electrode after rolling was 140 μm and the compaction density was 3.5 g / cm 3 ; Place the electrode in a low temperature environment of -18℃ and let it stand for 1 hour, then place the electrode in an ambient temperature of 25℃ and return to room temperature to obtain a new high-power electrode.

[0021] Example 2

[0022] The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi 0.9 Co 0.05 Mn 0.05 The positive electrode slurry was prepared by uniformly mixing the conductive agent carbon black (Super-P) and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 97:1:2. The viscosity of the positive electrode slurry was 6000-8000 mPa·s. The positive electrode slurry was evenly coated on the aluminum foil current collector and the coating layer was dried at a temperature of 120°C for 3 minutes. The surface density of the electrode was 45 mg / cm 2 The coated composite layer electrode was rolled. The thickness of the composite electrode after rolling was 140 μm and the compaction density was 3.5 g / cm 3; Place the electrode in a low temperature environment of -18℃ and let it stand for 15 hours, then place the electrode in an ambient temperature of 25℃ and restore it to room temperature to obtain a new high-power electrode.

[0023] Comparative Example 1

[0024] The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi 0.9 Co 0.05 Mn 0.05 The positive electrode slurry was prepared by uniformly mixing the conductive agent carbon black (Super-P) and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 97:1:2. The viscosity of the positive electrode slurry was 6000-8000 mPa·s. The positive electrode slurry was evenly coated on the aluminum foil current collector and the coating layer was dried at a temperature of 120°C for 3 minutes. The surface density of the electrode was 45 mg / cm 2 The coated composite layer electrode was rolled. The thickness of the composite electrode after rolling was 140 μm and the compaction density was 3.5 g / cm 3 .

[0025] The experimental results show that:

[0026] The bulk resistance of Example 1 is 2.212Ω·cm, and the interface resistance is 0.132Ω·cm 2 , the porosity is 21.14%; the bulk resistance of implementation 2 is 1.822Ω·cm, and the interface resistance is 0.106Ω·cm 2 , the porosity is 24.36%; the volume resistance of comparative example 1 is 2.501Ω·cm, and the interface resistance is 0.241Ω·cm 2 , the porosity is 14.95%.

[0027] Figure 2 These are SEM images of Example 1, Example 2 and Comparative Example 1.

[0028] It can be seen from the figure that the pores in Examples 1 and 2 are more than that in Comparative Example 1.

[0029] Figure 3 The electrochemical impedance spectra of the button cells corresponding to Example 1, Example 2, and Comparative Example 1 are shown. It can be seen from the figure that the impedance of the button cells assembled using Examples 1 and 2 is lower than that of Comparative Example 1.

[0030] Table 1 is a comparative data of electrolyte infiltration rate of Example 1, Example 2 and Comparative Example 1. It can be seen from the table that the electrolyte absorption time of Example 1 and Example 2 is shorter than that of Comparative Example 1.

[0031] Table 2 shows the rate performance comparison data of the button cells corresponding to Example 1, Example 2, and Comparative Example 1. As can be seen from the table, the capacity retention rate of Examples 1 and 2 at high current is higher than that of Comparative Example 1.

[0032] Example 3

[0033] The negative electrode slurry was prepared by uniformly mixing the negative electrode active material graphite, the conductive agent carbon black (Super-P), the binder sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) in a mass ratio of 97:1:1:1. The viscosity of the negative electrode slurry was 2000-2600 mPa·s. The negative electrode slurry was evenly coated on the copper foil current collector, and the coating layer was dried at a drying temperature of 140°C for 5 minutes. The surface density of the electrode sheet was 17.53 mg / cm 2 The coated composite layer electrode was rolled. The thickness of the composite electrode after rolling was 106 μm and the compaction density was 1.75 g / cm 3 First, place the electrode in a low temperature environment of -20℃ and let it stand for 1 hour, then place the electrode in an ambient temperature of 20-30℃ and restore it to room temperature to obtain a new high-power electrode.

[0034] Example 4

[0035] The negative electrode slurry was prepared by uniformly mixing the negative electrode active material graphite, the conductive agent carbon black (Super-P), the binder sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) in a mass ratio of 97:1:1:1. The viscosity of the negative electrode slurry was 2000-2600 mPa·s. The negative electrode slurry was evenly coated on the copper foil current collector, and the coating layer was dried at a drying temperature of 140°C for 5 minutes. The surface density of the electrode sheet was 17.53 mg / cm 2 The coated composite layer electrode was rolled. The thickness of the composite electrode after rolling was 106 μm and the compaction density was 1.75 g / cm 3 First, place the electrode in a low temperature environment of -20℃ and let it stand for 15 hours, then place the electrode in an ambient temperature of 20-30℃ and restore it to room temperature to obtain a new high-power electrode.

[0036] Comparative Example 2

[0037] The negative electrode slurry was prepared by uniformly mixing the negative electrode active material graphite, the conductive agent carbon black (Super-P), the binder sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) in a mass ratio of 97:1:1:1. The viscosity of the negative electrode slurry was 2000-2600 mPa·s. The negative electrode slurry was evenly coated on the copper foil current collector, and the coating layer was dried at a drying temperature of 140°C for 5 minutes. The surface density of the electrode sheet was 17.53 mg / cm 2 The coated composite layer electrode was rolled. The thickness of the composite electrode after rolling was 106 μm and the compaction density was 1.75 g / cm 3 .

[0038] The experimental results show that:

[0039] The bulk resistance of Example 3 is 0.072Ω·cm and the interface resistance is 0.015Ω·cm 2 , the porosity is 21.49%; the bulk resistance of Example 4 is 0.047Ω·cm, and the interface resistance is 0.008Ω·cm 2 , the porosity is 23.21%; the volume resistance of comparative example 2 is 0.106Ω·cm, and the interface resistance is 0.117Ω·cm 2 , the porosity is 20.26%.

[0040] Figure 4 These are SEM images of Example 3, Example 4 and Comparative Example 2.

[0041] It can be seen from the figure that the pores of Examples 3 and 4 are more than that of Comparative Example 2.

[0042] Table 3 is the comparative data of electrolyte infiltration rate of Example 3, Example 4 and Comparative Example 2.

[0043] It can be seen from the table that the liquid absorption time of Examples 3 and 4 is shorter than that of Comparative Example 2.

[0044] Table 1. Comparative data of electrolyte infiltration rate

[0045]

[0046] Table 2. Comparison of button cell rate performance

[0047]

[0048] Table 3. Comparative data of electrolyte infiltration rate

[0049]

[0050] The present invention utilizes the physical property that the thermal expansion coefficients of the components in the electrode slurry are different. The micromorphology of the electrode sheet is controlled by temperature field changes, the porosity of the electrode sheet is increased, and the tortuosity is reduced, which is conducive to the rapid and full infiltration of the electrolyte, shortens the lithium ion transmission path, promotes the shuttle of lithium ions between the positive and negative electrodes, and reduces the ion diffusion resistance. It can improve the power density of the lithium-ion battery while ensuring the energy density, and meet the demand for high power density of lithium-ion batteries in consumer electronics, electric vehicles, drones and other fields. It has the advantages of simplicity, speed, efficiency and low cost.

[0051] The basic principles, main features and advantages of the present invention are shown and described above. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0052] The embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being defined by the appended claims rather than the foregoing description, and all changes that come within the meaning and range of equivalents of the claims are therefore intended to be embraced therein.

[0053] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for improving the power density of a lithium-ion battery, characterized in that: The following steps are involved: When preparing a positive electrode or negative electrode of a lithium-ion battery, the active material, the conductive agent, and the binder are uniformly mixed to prepare a slurry, the slurry is uniformly coated on a foil current collector to form a coating layer, the coating layer is dried, the electrode electrode with the dried coating layer is rolled, the rolled electrode electrode is placed in a low-temperature environment of -60 to -18°C for a predetermined time, and the electrode electrode is placed in a normal temperature environment to return to room temperature to obtain a high-power electrode; the predetermined low-temperature environment time is 1 to 24 hours, and the normal temperature environment temperature is 20 to 30°C; When preparing a positive electrode sheet for a lithium-ion battery, lithium nickel cobalt manganese oxide, carbon black and polyvinylidene fluoride are mixed in a mass ratio of 97:1:2 to prepare a positive electrode slurry; When preparing a negative electrode sheet of a lithium-ion battery, graphite, carbon black, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed in a mass ratio of 97:1:1:1 to prepare a negative electrode slurry.

2. The method for improving the power density of a lithium-ion battery according to claim 1, wherein: When drying the coating layer, the drying temperature for the positive electrode sheet is 120° C. and the drying time is 3-5 minutes, and the drying temperature for the negative electrode sheet is 140° C. and the drying time is 5 minutes.

3. The method for improving the power density of a lithium-ion battery according to claim 2, wherein: The surface density of the positive electrode is 45 mg / cm 2 The thickness of the positive electrode sheet after rolling is 140μm and the compaction density is 3.5g / cm 3 ; The surface density of the negative electrode is 17.53 mg / cm 2 The thickness of the negative electrode sheet after rolling is 106μm and the compaction density is 1.75 g / cm 3 .

4. The method for improving the power density of a lithium-ion battery according to claim 1, wherein: The viscosity of the positive electrode slurry is 6000~8000mPa·s, and the viscosity of the negative electrode slurry is 2000~2600mPa·s.

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