Lithium ion battery negative electrode, fast-charging lithium ion battery and method for predicting performance of fast-charging lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and relates to a lithium ion battery negative electrode, a fast-charging lithium ion battery and a method for predicting the performance of the fast-charging lithium ion battery. The lithium ion battery negative electrode comprises a current collector and an active layer covering the surface of the current collector, wherein the active layer is composed of a negative electrode active material, a conductive agent and a binder; wherein the negative pole piece meets the following conditions: the parameter 2 is between 9 * 10 <-15 > and 35 * 10 <-15 >, the parameter 2 is the value of the quotient of the parameter 1 and the particle size of the negative active material, and the parameter 1 is the value of the product of the porosity of the negative pole piece and the lithium ion diffusion coefficient of the negative active material. The dynamic performance of the negative electrode of the lithium ion battery can be improved, the internal resistance of the battery is reduced, and the fast charging performance and cycle performance of the battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and relates to a lithium ion battery negative electrode, a fast-charge lithium ion battery, and a method for predicting the performance of a fast-charge lithium ion battery. Background Art

[0002] Currently, the charging efficiency of lithium-ion batteries has become one of the main bottlenecks restricting the popularization of electric vehicles. Traditional charging strategies are often accompanied by battery performance degradation and safety hazards when facing the demand for fast charging. Therefore, improving the fast charging capability of batteries while ensuring their safety and cycle life is an important direction for the development of lithium-ion battery technology.

[0003] Using a diaphragm with high porosity and high ionic conductivity to reduce the internal resistance of the battery and improve the charging efficiency is one of the current development directions of the fast charging technology of lithium-ion batteries. The internal resistance of lithium-ion batteries includes: ohmic internal resistance Rs, charge transfer impedance Rct, and diffusion impedance Rw. Reducing impedance is an effective way to improve the fast charging capability of lithium-ion batteries. According to the inventor's research, at present, the kinetic performance of the negative electrode of lithium-ion batteries is poor, resulting in a high internal resistance of lithium-ion batteries, thereby affecting the fast charging performance and cycle performance of lithium-ion batteries. Summary of the invention

[0004] In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide a lithium ion battery negative electrode, a fast-charging lithium ion battery and a method for predicting the performance of a fast-charging lithium ion battery. The present invention can improve the kinetic performance of the lithium ion battery negative electrode, reduce the internal resistance of the battery, and improve the fast-charging performance and cycle performance of the battery.

[0005] In order to achieve the above object, the technical solution of the present invention is:

[0006] In a first aspect, a negative electrode plate of a lithium ion battery comprises a current collector and an active layer covering the surface of the current collector, wherein the active layer is composed of a negative electrode active material, a conductive agent and a binder; wherein the negative electrode plate satisfies the following conditions: parameter 2 is within 9×10 -15 Up to 35×10 -15 The parameter 2 is the value of the quotient of the parameter 1 and the particle size of the negative electrode active material, and the parameter 1 is the product value of the porosity of the negative electrode sheet and the lithium ion diffusion coefficient of the negative electrode active material.

[0007] The porosity of the negative electrode sheet mainly affects the ohmic impedance Rs and diffusion impedance Rw of the lithium-ion battery. Too high a porosity will increase the electronic impedance and ionic impedance of the negative electrode material, affecting the rate and cycle performance of the battery cell. Too low a porosity will reduce the electronic impedance of the negative electrode, but will reduce the ion transfer rate, thus affecting the rate performance of the lithium-ion battery. Therefore, the appropriate porosity can balance the electronic transfer and ion transfer during the pre-lithiation process and improve the fast charging performance of the lithium-ion battery.

[0008] The lithium ion diffusion coefficient of the negative electrode active material mainly affects the charge transfer impedance Rct of the lithium ion battery. The larger the Ks, the more conducive it is to the deintercalation of lithium ions. The smaller the Ks, the less conducive it is to the deintercalation of lithium ions, and the higher the risk of lithium deposition on the negative electrode surface.

[0009] The present invention unexpectedly discovered through research that by regulating the particle size of the negative electrode active material, the porosity of the negative electrode sheet, and the lithium ion diffusion coefficient of the negative electrode active material to meet the above requirements, the impedance of the lithium ion battery can be effectively reduced, and the cycle performance of the lithium ion battery can be effectively improved.

[0010] In a second aspect, a fast-charging lithium-ion battery comprises a positive electrode plate, an electrolyte, a separator and the above-mentioned negative electrode plate of the lithium-ion battery.

[0011] According to the negative electrode plate of the lithium ion battery provided by the first aspect of the present invention, it can be known that when the negative electrode plate meets the corresponding requirements, it can improve the kinetic performance of the negative electrode of the lithium ion battery, reduce the internal resistance of the battery, and improve the fast charging performance and cycle performance of the battery; and the requirements met by the negative electrode plate are related to the particle size of the negative electrode active material, the porosity of the negative electrode plate, and the lithium ion diffusion coefficient of the negative electrode active material. Therefore, the requirements met by the negative electrode plate can be used to predict whether the internal resistance, fast charging performance and cycle performance of the negative electrode plate or even the lithium ion battery can meet the requirements, that is, in the third aspect, the present invention provides a method for predicting the performance of a fast-charging lithium ion battery, obtaining the porosity of the negative electrode plate, the lithium ion diffusion coefficient of the negative electrode active material and the particle size of the negative electrode active material; calculating the product value of the porosity of the negative electrode plate and the lithium ion diffusion coefficient of the negative electrode active material as parameter 1, calculating the value of the quotient of parameter 1 and the particle size of the negative electrode active material as parameter 2, and judging whether parameter 2 is within 9×10 -15 Up to 35×10 -15 between.

[0012] The method provided by the present invention can predict the performance of a fast-charging lithium-ion battery through the parameters of the negative electrode plate and the negative electrode active material, thereby reducing the cost of experimental research and development and improving the research and development efficiency of fast-charging lithium-ion batteries.

[0013] The beneficial effects of the present invention are:

[0014] 1. The present invention has found that the negative electrode kinetics of lithium-ion batteries can be adjusted by simultaneously adjusting the particle size of negative electrode active materials, the lithium ion diffusion coefficient of negative electrode active materials and the porosity of negative electrode plates, thereby adjusting and reducing the internal resistance of the battery, the fast charging performance of the battery and the cycle performance. Based on this, the present invention further provides requirements based on the particle size of negative electrode active materials, the lithium ion diffusion coefficient of negative electrode active materials and the porosity of negative electrode plates, thereby improving the negative electrode kinetics of lithium-ion batteries, reducing the internal resistance of the battery, and improving the fast charging performance and cycle performance of the battery.

[0015] 2. The present invention can predict the electrochemical properties of fast-charge lithium-ion batteries, such as internal resistance, fast-charge performance and cycle performance, by detecting the particle size of the negative electrode active material, the lithium ion diffusion coefficient of the negative electrode active material and the porosity of the negative electrode plate, thereby reducing the R&D investment cost of fast-charge lithium-ion batteries. DETAILED DESCRIPTION

[0016] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0017] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0018] In view of the poor kinetic performance of the negative electrode of the existing lithium ion battery, which leads to a high internal resistance of the lithium ion battery and affects the fast charging performance and cycle performance of the lithium ion battery, the present invention proposes a lithium ion battery negative electrode and a fast charging lithium ion battery.

[0019] A typical embodiment of the present invention provides a negative electrode plate for a lithium ion battery, comprising a current collector and an active layer covering the surface of the current collector, wherein the active layer is composed of a negative electrode active material, a conductive agent and a binder; wherein the negative electrode plate satisfies the following conditions: parameter 2 is within 9×10 -15 Up to 35×10 -15 The parameter 2 is the value of the quotient of the parameter 1 and the particle size of the negative electrode active material, and the parameter 1 is the product value of the porosity of the negative electrode sheet and the lithium ion diffusion coefficient of the negative electrode active material.

[0020] Specifically, the unit of the particle size of the negative electrode active material is μm, and the unit of the lithium ion diffusion coefficient of the negative electrode active material is m 2 / s.

[0021] More specifically, the requirements for the negative electrode are:

[0022] 9<(θ*Ks*10 15 ) / D<35 (1)

[0023] Wherein, Ks is the lithium ion diffusion coefficient of the negative electrode active material, in m 2 / s;

[0024] D is the particle size of the negative electrode active material in the negative electrode sheet, in μm;

[0025] θ is the porosity of the negative electrode sheet.

[0026] In some embodiments, the negative electrode active material is graphite. Studies have shown that when graphite is used as the negative electrode active material, the prepared negative electrode sheet can better improve the negative electrode dynamics of the lithium ion battery after meeting the above conditions, reduce the internal resistance of the battery, and improve the fast charging performance and cycle performance of the battery.

[0027] In some embodiments, the particle size of the negative electrode active material is D 50 . D 50 It is the particle size corresponding to when the cumulative particle size distribution percentage reaches 50%, which can also be called the median diameter or median particle size. 50 The thickness of the negative electrode sheet is 8 to 20 μm, preferably 8 to 16 μm. Studies have shown that the performance of lithium-ion batteries using negative electrode sheets under this condition is better.

[0028] In some embodiments, the porosity of the negative electrode plate is 28-38%. Studies have shown that under this condition, the electron transmission and ion transmission in the pre-lithiation process can be better balanced, and the fast charging performance of the lithium-ion battery can be better improved.

[0029] The preparation method of the negative electrode sheet provided by the present invention is a general preparation method of the negative electrode sheet, for example, the negative electrode active material, the conductive agent, the binder and the thickener are dispersed in a solvent, the negative electrode slurry is obtained by mechanical mixing, and then coated on the current collector, and the negative electrode sheet is obtained by rolling and drying. In some embodiments, the mass ratio of the negative electrode active material, the conductive agent, the binder and the thickener is 94-97:0.5-3:1-3:1-3. Specifically, the solvent is water. Using water as a solvent can reduce environmental pollution compared with other solvents.

[0030] The current collector of the present invention can be a current collector commonly used in the negative electrode of a lithium ion battery. In some embodiments, the current collector used in the negative electrode plate is at least one of copper foil, carbon-coated copper foil, carbon paper and copper-plated polymer film.

[0031] The conductive agent of the present invention can be a conductive agent commonly used in the negative electrode of a lithium ion battery. In some embodiments, the conductive agent includes one or more of carbon black, conductive graphite, carbon nanotubes, and graphene.

[0032] Another embodiment of the present invention provides a fast-charging lithium-ion battery, comprising a positive electrode plate, an electrolyte, a separator and the above-mentioned negative electrode plate of the lithium-ion battery.

[0033] The electrolyte of the present invention is any electrolyte of a lithium ion battery. The diaphragm of the present invention is any diaphragm of a lithium ion battery.

[0034] The active material of the positive electrode plate of the present invention is any positive electrode active material of a lithium ion battery. In some embodiments, the active material of the positive electrode plate is lithium iron phosphate.

[0035] The third embodiment of the present invention provides a method for predicting the performance of a fast-charged lithium-ion battery, obtaining the porosity of the negative electrode sheet, the lithium ion diffusion coefficient of the negative electrode active material, and the particle size of the negative electrode active material; calculating the product of the porosity of the negative electrode sheet and the lithium ion diffusion coefficient of the negative electrode active material as parameter 1, calculating the quotient of parameter 1 and the particle size of the negative electrode active material as parameter 2, and judging whether parameter 2 is within 9×10 -15 Up to 35×10 -15 between.

[0036] Specifically, the unit of the particle size of the negative electrode active material is μm, and the unit of the lithium ion diffusion coefficient of the negative electrode active material is m 2 / s.

[0037] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in combination with specific embodiments and comparative examples.

[0038] Example 1

[0039] A negative electrode sheet for a lithium-ion battery is prepared by dispersing an artificial graphite negative electrode active material, a conductive agent (SP), a binder (SDR) and a thickener (CMC) in water in a mass ratio of 96%:1%:1.8%:1.2% to prepare a negative electrode slurry, coating the obtained negative electrode slurry on a copper foil, and rolling to obtain a negative electrode sheet; wherein the D 50 The thickness is 12 μm, and the lithium ion diffusion coefficient Ks is 6*10 -13 m 2 / s, and the porosity of the negative electrode sheet was made to be 29.1% by controlling the rolling thickness.

[0040] Example 2

[0041] A negative electrode sheet for a lithium-ion battery is prepared by dispersing an artificial graphite negative electrode active material, a conductive agent (SP), a binder (SDR) and a thickener (CMC) in water in a mass ratio of 96%:1%:1.8%:1.2% to prepare a negative electrode slurry, coating the obtained negative electrode slurry on a copper foil, and rolling to obtain a negative electrode sheet; wherein the D 50 The thickness is 8 μm, and the lithium ion diffusion coefficient Ks is 6*10 -13 m 2 / s, and the porosity of the negative electrode sheet was made to be 29.1% by controlling the rolling thickness.

[0042] Example 3

[0043] A negative electrode sheet for a lithium-ion battery is prepared by dispersing an artificial graphite negative electrode active material, a conductive agent (SP), a binder (SDR) and a thickener (CMC) in water in a mass ratio of 96%:1%:1.8%:1.2% to prepare a negative electrode slurry, coating the obtained negative electrode slurry on a copper foil, and rolling to obtain a negative electrode sheet; wherein the D 50 The thickness is 12 μm, and the lithium ion diffusion coefficient Ks is 6*10 -13 m 2 / s, and the porosity of the negative electrode sheet was made to be 25.4% by controlling the rolling thickness.

[0044] Example 4

[0045] A negative electrode sheet for a lithium-ion battery is prepared by dispersing an artificial graphite negative electrode active material, a conductive agent (SP), a binder (SDR) and a thickener (CMC) in water in a mass ratio of 96%:1%:1.8%:1.2% to prepare a negative electrode slurry, coating the obtained negative electrode slurry on a copper foil, and rolling to obtain a negative electrode sheet; wherein the D 50 is 12μm, and the lithium ion diffusion coefficient Ks is 10*10 -13 m 2 / s, and the porosity of the negative electrode sheet was made to be 29.1% by controlling the rolling thickness.

[0046] Comparative Example 1

[0047] A negative electrode sheet for a lithium-ion battery is prepared by dispersing an artificial graphite negative electrode active material, a conductive agent (SP), a binder (SDR) and a thickener (CMC) in water in a mass ratio of 96%:1%:1.8%:1.2% to prepare a negative electrode slurry, coating the obtained negative electrode slurry on a copper foil, and rolling to obtain a negative electrode sheet; wherein the D 50 The thickness is 12 μm, and the lithium ion diffusion coefficient Ks is 2*10 -13 m 2 / s, and the porosity of the negative electrode sheet was made to be 29.1% by controlling the rolling thickness.

[0048] Comparative Example 2

[0049] A negative electrode sheet for a lithium-ion battery is prepared by dispersing an artificial graphite negative electrode active material, a conductive agent (SP), a binder (SDR) and a thickener (CMC) in water in a mass ratio of 96%:1%:1.8%:1.2% to prepare a negative electrode slurry, coating the obtained negative electrode slurry on a copper foil, and rolling to obtain a negative electrode sheet; wherein the D 50 The lithium ion diffusion coefficient Ks is 6*10 -13 m 2 / s, and the porosity of the negative electrode sheet was made to be 29.1% by controlling the rolling thickness.

[0050] Performance Test:

[0051] Lithium-ion battery assembly:

[0052] A lithium ion battery was made by combining the negative electrode sheets of the lithium ion batteries prepared in the above-mentioned embodiments and comparative examples with the positive electrode sheets of lithium iron phosphate, an electrolyte (configured according to the mass ratio of LiPIF6:LFSI:EC:EMC:DMC:VC:DTD of 11.5:254:33.7:25.4:2:0.5) and a PE separator.

[0053] Cycle test: Cycle test is carried out in accordance with the cycle life test requirements of GB / T 31484-2015 "Cycle life requirements and test methods for power batteries for electric vehicles", and the capacity retention rate is measured after 600 cycles of 25°C room temperature cycles and 300 cycles of 45°C high temperature cycles.

[0054] DC internal resistance test: At 25°C, the obtained lithium-ion secondary battery was implanted in copper wire and then lithium-plated. The SOC was adjusted to 50%, and the battery was discharged at 2C pulse current for 30s. The voltage drop of the positive electrode to the reference electrode before and after discharge was recorded, and the DC internal resistance of the positive electrode was obtained according to R=U / I.

[0055] Rate performance: Charge the single cell according to the requirements of GB / T 31486-2015 "Requirements and test methods for cycle life of power batteries for electric vehicles" and test the discharge capacity retention rate at 2C rate;

[0056] Specifically, the relevant parameters of Examples 1 to 4 and Comparative Examples 1 to 2 and the performance test results under the same conditions are shown in Table 1 below.

[0057] Table 1 Comparison of physical properties of embodiments and comparative examples

[0058]

[0059] Among them, parameter 2 is the value calculated according to the following formula

[0060] Parameter 2 = (θ*Ks*10 15 ) / D

[0061] Wherein, Ks is the lithium ion diffusion coefficient of the negative electrode active material, in m 2 / s;

[0062] D is the particle size of the negative electrode active material in the negative electrode sheet, in μm;

[0063] θ is the porosity of the negative electrode sheet.

[0064] As can be seen from Table 1, Examples 1 to 4 can effectively improve the rate performance and cycle performance of lithium-ion batteries and improve the risk of lithium plating in the battery cell within the scope of the present invention. Compared with Example 1, in Example 2, the particle size of the active material is reduced, the transmission path of lithium ions is shortened, and the electrochemical polarization and concentration polarization resistance are reduced, thereby effectively improving the fast charging performance of the battery cell. In Example 3, the porosity of the negative electrode plate is reduced, and the material contact in the plate is more sufficient, so that the electronic impedance of the plate is reduced, and the rate performance of the battery cell is improved.

[0065] In Comparative Example 1, due to the low diffusion coefficient of the negative electrode active material, the charge transfer impedance increases, which is not conducive to the rapid insertion of lithium ions and increases the internal resistance of the battery. In Comparative Example 2, graphite with a larger particle size is used, the lithium ion migration path increases, the polarization increases, and it is not conducive to the rate performance of the battery cell.

[0066] Example 5

[0067] A method for predicting fast-charge lithium-ion battery performance comprises the following steps:

[0068] 1. Detection of D of artificial graphite 50 , denoted as D (unit: μm).

[0069] 2. Detect the lithium ion diffusion coefficient of artificial graphite, denoted as Ks (unit: m 2 / s).

[0070] 3. Detect the porosity of the prepared lithium-ion battery negative electrode sheet, denoted as θ.

[0071] 4. Substitute the data obtained in steps 1-3 into (θ*Ks*10 15 ) / D to obtain the value, which is recorded as parameter 2.

[0072] 5. Determine whether parameter 2 is between 9 and 35.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A negative electrode plate for a lithium-ion battery, comprising a current collector and an active layer covering the surface of the current collector, wherein the active layer is composed of a negative electrode active material, a conductive agent and a binder; wherein: The negative electrode plate meets the following conditions: parameter 2 is 9×10 -15 Up to 35×10 -15 The parameter 2 is the value of the quotient of the parameter 1 and the particle size of the negative electrode active material, and the parameter 1 is the product value of the porosity of the negative electrode sheet and the lithium ion diffusion coefficient of the negative electrode active material.

2. The negative electrode plate of a lithium-ion battery as claimed in claim 1, characterized in that: The unit of the particle size of the negative electrode active material is μm, and the unit of the lithium ion diffusion coefficient of the negative electrode active material is m 2 / s.

3. The negative electrode plate of a lithium-ion battery as claimed in claim 1, characterized in that: The negative electrode active material is graphite.

4. The negative electrode plate of a lithium-ion battery as claimed in claim 1, characterized in that: The particle size of the negative electrode active material is D 50 Preferably, D 50 It is 8 to 20 μm, preferably 8 to 16 μm.

5. The negative electrode plate of a lithium-ion battery as claimed in claim 1, characterized in that: The porosity of the negative electrode sheet is 28-38%.

6. The negative electrode plate of a lithium-ion battery as claimed in claim 1, characterized in that: The mass ratio of the negative electrode active material, the conductive agent and the binder is 94-97:0.5-3:1-3.

7. The negative electrode plate of a lithium-ion battery as claimed in claim 1, characterized in that: The current collector used in the negative electrode plate is at least one of copper foil, carbon-coated copper foil, carbon paper and copper-plated polymer film; Alternatively, the conductive agent includes one or more of carbon black, conductive graphite, carbon nanotubes, and graphene.

8. A fast-charge lithium-ion battery, characterized in that: The invention comprises a positive electrode plate, an electrolyte, a diaphragm and a negative electrode plate of a lithium ion battery as claimed in any one of claims 1 to 7.

9. The fast-charge lithium-ion battery according to claim 8, characterized in that: The active material of the positive electrode is lithium iron phosphate.

10. A method for predicting the performance of a fast-charged lithium-ion battery, characterized in that: Obtain the porosity of the negative electrode sheet, the lithium ion diffusion coefficient of the negative electrode active material, and the particle size of the negative electrode active material; calculate the product of the porosity of the negative electrode sheet and the lithium ion diffusion coefficient of the negative electrode active material as parameter 1, calculate the quotient of parameter 1 and the particle size of the negative electrode active material as parameter 2, and determine whether parameter 2 is within 9×10 -15 Up to 35×10 -15 between.

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