Lithium ion battery preparation method, battery and electrochemical device

Abstract

The invention provides a lithium ion battery preparation method, a battery and an electrochemical device. According to the scheme, a pole piece material in a preset particle size interval is firstly screened, the sphericity degree is adjusted, then a pole piece is prepared, and performance and structure parameters are adjusted. And then preparing positive and negative electrode compacted pole pieces with different compaction densities, making a symmetrical battery, carrying out an electrochemical impedance test, and preparing the battery after determining the target positive and negative electrode compaction densities. The method has remarkable advantages, the cycle life of the pole piece and the volume energy density of the battery can be effectively prolonged, and the damage to the charge-discharge structure and the performance degradation of the electrode are reduced by optimizing the material characteristics and the process; the pole piece structure and composition are reasonably designed, and the active substance content and utilization rate are improved. The compaction density of positive and negative plates is accurately regulated, the positive and negative matching performance is improved, polarization is reduced, and the charging and discharging efficiency and stability are improved. Compared with the conventional technology, the method has the remarkable advantages of high controllability, wide range, long service life, stable effect and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a method for preparing a lithium-ion battery, a battery and an electrochemical device. Background Art

[0002] In recent years, the new energy vehicle market has flourished, gradually becoming the mainstream development direction of the automotive industry. Consumer demand for new energy vehicles is growing, but range and charging anxiety have become the main factors affecting their purchasing decisions.

[0003] Against this backdrop, high-energy-density fast-charging technology has become a mainstream development trend in the lithium-ion battery market. Fast-charging technology can significantly reduce battery charging times, effectively addressing consumers' anxiety about recharging, and improving the convenience and user experience of new energy vehicles. High energy density is a key factor in increasing battery energy density, which directly increases the range of new energy vehicles, satisfying consumers' demand for longer driving range.

[0004] In lithium battery production, compaction density is a key metric for electrode production. It refers to the mass of active material per unit volume of the electrode sheet after roller compaction. Generally speaking, a higher compaction density means more active material can be accommodated within the same volume, thereby increasing the battery's capacity. This is because a higher compaction density reduces the electrode sheet's porosity, increases the contact area between the active materials, and improves lithium ion transport efficiency. However, in actual production, blindly pursuing a high compaction density is not a good strategy. When the compaction density is too high, the electrode sheet's porosity is excessively reduced, making it difficult for the electrolyte to penetrate the electrode sheet, thus hindering the transport and insertion / extraction of lithium ions. This not only fails to improve the battery's specific capacity, but can also severely reduce its specific capacity, cycling performance, and fast-charging capability. Specifically, this results in increased internal resistance and significant heat generation during charge and discharge, shortened battery life, and safety issues such as lithium plating during fast charging.

[0005] In addition, with the development of lithium battery technology, in order to further improve the performance of the battery, a composite system that mixes two or even more materials is often used. In this composite system, different materials have different physical properties such as particle size and specific surface area. These differences will lead to uneven distribution of materials during the mixing process, which in turn affects the compaction effect of the electrode and the overall performance of the battery. For example, materials with larger particle sizes may form larger gaps during the compaction process, while materials with smaller particle sizes may fill these gaps. However, if the compaction process is unreasonable, it will lead to uneven distribution of materials, affecting the performance of the battery. Therefore, how to choose the appropriate compaction density, especially in the composite system, and accurately design the compaction process to optimize the overall performance of lithium-ion batteries has become an urgent problem to be solved in the current lithium battery industry. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the problem in the prior art that the comprehensive performance of lithium-ion batteries is difficult to improve, and to provide a lithium-ion battery preparation method, a battery and an electrochemical device.

[0007] In order to solve the above technical problems, the present invention provides a method for preparing a lithium-ion battery, which comprises: step S1, screening a first prepared positive electrode active material having a material particle size within a preset particle size range from a plurality of positive electrode active materials; step S2, adjusting the sphericity of the first prepared positive electrode active material to a preset sphericity range to obtain a second prepared positive electrode active material; step S3, obtaining a target positive electrode active material by adjusting the material performance parameters and structural performance parameters of the second prepared positive electrode active material; step S4, using the target positive electrode active material to prepare a plurality of positive electrode compacted sheets and negative electrode compacted electrode sheet, and the number of positive electrode compacted electrode sheets and negative electrode compacted electrode sheets of any compaction density is multiple; step S5, preparing the multiple positive electrode compacted electrode sheets with the same compaction density into a positive electrode symmetrical battery, and at the same time preparing the multiple negative electrode compacted electrode sheets with the same compaction density into a negative electrode symmetrical battery; step S6, performing electrochemical impedance spectroscopy on the positive electrode symmetrical battery and the negative electrode symmetrical battery with different compaction densities, respectively, and obtaining the target positive electrode compaction density and the target negative electrode compaction density according to the electrochemical impedance spectroscopy results; step S7, preparing a lithium-ion battery according to the target positive electrode compaction density and the target negative electrode compaction density.

[0008] In one embodiment of the present invention, in step S3, the method for adjusting the material performance parameters of the second prepared positive electrode active material is: setting the material performance parameters of the positive electrode active material to X=D×(w×100)×Pd / a, and making 0.001≤X≤500, wherein D is the material particle size, w is the proportion of active material in the electrode sheet, and 75%≤w≤99%; a is the electrode thickness, and 45μm≤a≤500μm; Pd is the pre-compacted density of the electrode sheet, and 1.5g / cc≤Pd≤4.6g / cc.

[0009] In one embodiment of the present invention, in step S1, the method for screening the material particle size is: setting the material particle size D=Dv50+Dv90, wherein Dv50 is the cumulative particle size of 50% volume distribution, and its interval range is 0.8-25μm, and Dv90 is the cumulative particle size of 90% volume distribution, and its interval range is 6-40μm.

[0010] In one embodiment of the present invention, in step S3, the method for adjusting the structural performance parameters of the second prepared positive electrode active material is: setting the structural performance parameters of the positive electrode active material to Y=a×b×c / (Rmax-Rmin), and limiting 0.003≤Y≤10 6 , wherein a is the thickness of the pole piece material, and 45μm≤a≤500μm, b is the porosity of the pole piece material, and 15%≤b≤40%, c is the pore density ratio of the pole piece material, and 0.02μm≤c≤150μm, Rmax is the maximum pore size of the non-closed pores of the pole piece material, and 5μm≤Rmax≤20μm; Rmin is the minimum pore size of the non-closed pores of the pole piece material, and 0.01μm≤Rmin<5μm.

[0011] In one embodiment of the present invention, in step S2, the method for adjusting the sphericity of the first prepared positive electrode active material to a preset sphericity range is: setting the preset sphericity ψ = (V / S) 1 / 3 The preset range of sphericity ψ is 0.2~0.995, where V is the volume of the measured material and S is the specific surface area of the measured material.

[0012] In one embodiment of the present invention, the pole piece structural performance parameter Y is adjusted by laser drilling technology and / or pole piece rolling processing.

[0013] In one embodiment of the present invention, in step S4, positive electrode compacted sheets with different compaction densities are prepared by adjusting the rolling pressure and the rolling gap.

[0014] In one embodiment of the present invention, step S6 includes: step S61, performing electrochemical impedance tests on the positive symmetrical batteries with different compaction densities to obtain ohmic impedances and solid-phase diffusion impedances in the plurality of positive symmetrical batteries, and simultaneously performing electrochemical impedance tests on the negative symmetrical batteries with different compaction densities to obtain ohmic impedances and solid-phase diffusion impedances in the plurality of negative symmetrical batteries; step S62, integrating the ohmic impedance and solid-phase diffusion impedance curves of the plurality of positive symmetrical batteries to obtain the positive symmetrical battery having the slowest growth rate of the ohmic impedance curve during the increase of the solid-phase diffusion impedance curve, to obtain a target positive electrode compaction density; and integrating the ohmic impedance and solid-phase diffusion impedance curves of the plurality of negative symmetrical batteries to obtain the negative symmetrical battery having the slowest growth rate of the ohmic impedance curve during the increase of the solid-phase diffusion impedance curve, to obtain a target negative electrode compaction density.

[0015] The present invention also provides a battery, which is prepared using the above-mentioned lithium ion battery preparation method.

[0016] The present invention also provides an electrochemical device, which is prepared using the above-mentioned lithium ion battery preparation method.

[0017] The above technical solution of the present invention has the following advantages over the prior art: The present invention relates to a lithium-ion battery preparation method, battery, and electrochemical device. By precisely defining and adjusting the pole piece material, it explores a completely new preparation and processing method in a complex composite material system.

[0018] This method can effectively improve the cycle life and volume energy density of the electrode. On the one hand, during the cycle use of the electrode, by optimizing the material properties and preparation process, the structural damage and performance degradation of the electrode material during the charge and discharge process are reduced, thereby significantly extending the service life of the electrode and ensuring that the battery can maintain good performance after multiple charge and discharge cycles. On the other hand, by rationally designing the structure and material composition of the electrode, the content and utilization rate of active materials per unit volume are increased, thereby improving the volume energy density of the battery and meeting the market demand for high-energy-density batteries. Most importantly, the present invention can significantly improve the matching of the positive and negative electrodes by precisely controlling the compaction density of the positive and negative electrodes, reduce polarization inside the battery, improve the battery's charge and discharge efficiency and stability, and avoid battery performance degradation and safety hazards caused by mismatch between the positive and negative electrodes. Compared with conventional battery processing technologies at this stage, the present invention has the advantages of high controllability, wide application range, long application life, stable operation effect and high matching, and is expected to bring new breakthroughs and changes to the development of the industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings.

[0020] Figure 1 is a flow chart of a method for preparing a lithium-ion battery in a preferred embodiment of the present invention; Figure 2 yes Figure 1 Surface morphology of the electrode material in the lithium-ion battery preparation method shown; Figure 3 yes Figure 1 Ohmic impedance and solid phase diffusion impedance curves in the positive electrode symmetrical battery in the lithium ion battery preparation method shown; Figure 4 yes Figure 1 The ohmic impedance and solid-phase diffusion impedance curves of the negative electrode symmetrical battery in the lithium-ion battery preparation method shown. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0022] Example 1:

[0023] See also Figure 1 As shown, this embodiment provides a method for preparing a lithium ion battery, which includes: Step S1, screening a first prepared positive electrode active material whose material particle size is within a preset particle size range from a plurality of positive electrode active materials: Further, this embodiment specifically includes: in step S1, the method for screening the material particle size is: setting the material particle size D=Dv50+Dv90, wherein Dv50 is the cumulative particle size of 50% volume distribution, which is preferably 20μm, and Dv90 is the cumulative particle size of 90% volume distribution, which is preferably 25μm.

[0024] Based on this, this embodiment can shorten the diffusion path of lithium ions in the electrode material by controlling the particle size and distribution of the electrode material, increasing the diffusion rate of lithium ions, thereby improving the battery's charge and discharge efficiency and rate performance. Furthermore, the smaller particle size increases the contact area between the electrode material and the electrolyte, facilitating the insertion and extraction reactions of lithium ions.

[0025] Furthermore, limiting the particle size within a preset range can ensure the uniformity of the electrode material, thereby helping to improve the uniformity of the electrode's compaction density and the consistency of its electrochemical performance, reducing local current density unevenness caused by excessive particle size differences, and thus improving the safety and cycle stability of the battery.

[0026] Step S2: adjusting the sphericity of the first prepared positive electrode active material to a preset sphericity range to obtain a second prepared positive electrode active material; Figure 2 As shown, further, this embodiment specifically includes: in step S2, the method of adjusting the sphericity of the first prepared positive electrode active material to a preset sphericity range is: setting the preset sphericity ψ= (V / S) 1 / 3 The preset range of sphericity ψ is 0.2~0.995, where V is the volume of the measured material and S is the specific surface area of the measured material.

[0027] Specifically, electrode materials with a sphericity ψ limited to the range of 0.2-0.995 have better stacking properties. This allows nearly spherical particles to pack more tightly together during compaction, improving the electrode density and, in turn, the battery's volumetric energy density. Furthermore, the spherical particles have a smoother surface, which facilitates the penetration and diffusion of the electrolyte within the electrode, allowing for better contact between the electrolyte and the electrode material, improving lithium ion transmission efficiency, and reducing the battery's internal resistance.

[0028] Step S3: Obtain a target positive electrode active material by adjusting the material performance parameters and structural performance parameters of the second prepared positive electrode active material. Furthermore, in step S3 of this embodiment, the method for adjusting the material performance parameters of the second prepared positive electrode active material is: setting the material performance parameters of the positive electrode active material to X=D×(w×100)×Pd / a, and making 0.001≤X≤500, wherein D is the material particle size, w is the proportion of active material in the electrode sheet, which is preferably 80%; a is the electrode thickness, which is preferably 300 μm; Pd is the pre-compacted density of the electrode sheet, which is preferably 3.0 g / cc. Based on this, X in this embodiment is 36.

[0029] Correspondingly, in step S3, the method for adjusting the structural performance parameters of the second prepared positive electrode active material is: setting the structural performance parameters of the positive electrode active material to Y=a×b×c / (Rmax-Rmin), and limiting 0.003≤Y≤10 6 , where a is the thickness of the electrode material, preferably 200 μm, b is the porosity of the electrode material, preferably 30%, c is the pore size density ratio of the electrode material, preferably 50 μm, Rmax is the maximum diameter of the non-closed pores of the electrode material, preferably 10 μm, and Rmin is the minimum diameter of the non-closed pores of the electrode material, preferably 3 μm. Based on this, Y in this embodiment is 85.7. Furthermore, in this embodiment, the electrode structure performance parameter Y is adjusted through laser drilling technology and / or electrode roll pressing.

[0030] Furthermore, for the material performance parameter X, this application comprehensively considers multiple factors such as material particle size, active material ratio, pre-compacted density, and electrode thickness. By controlling X within the range of 0.001-500, the relationship between these factors can be balanced, so that the battery can achieve better comprehensive performance in terms of capacity, energy density, charge and discharge performance, etc. Specifically, a reasonable active material ratio w and pre-compacted density Pd can improve the utilization rate of the active material, while an appropriate electrode thickness a can ensure the effective diffusion of lithium ions, avoiding the difficulty of lithium ion diffusion and increased internal resistance caused by excessively thick electrodes.

[0031] Correspondingly, for the structural performance parameter Y, this application controls Y to be between 0.003 and 10 6 Within the range of , the microstructure of the electrode can be optimized to provide a good channel for the penetration of the electrolyte and the transmission of lithium ions. Among them, the appropriate porosity b and pore size distribution can ensure the uniform distribution of the electrolyte inside the electrode, reduce local polarization, and improve the charge and discharge stability and cycle life of the battery. In addition, this embodiment adjusts the electrode structure performance parameter Y through laser drilling technology and / or electrode rolling processing, and has good process adjustability. Therefore, the microstructural parameters such as the porosity, pore size and distribution of the electrode can be accurately controlled according to actual needs to meet the requirements of different battery performance.

[0032] Step S4, using the target positive electrode active material to prepare a plurality of positive electrode compacted pole pieces and negative electrode compacted pole pieces with different compaction densities, and the number of positive electrode compacted pole pieces and negative electrode compacted pole pieces with any compaction density is multiple. Furthermore, in this embodiment, positive electrode compacted pole pieces with different compaction densities are prepared by adjusting the rolling pressure and the rolling gap. Furthermore, in this embodiment, pole pieces with different compaction densities are prepared by adjusting the rolling pressure and the rolling gap, and the effect of compaction density on battery performance can be systematically studied. Different compaction densities will affect the performance indicators of the pole piece, such as porosity, internal resistance, and lithium ion diffusion rate. By preparing a plurality of pole pieces with different compaction densities, the compaction density that best suits the battery system can be found, thereby improving the overall performance of the battery.

[0033] Specifically, in this embodiment, positive electrode compacted sheets having compaction densities of 2.6 g / cc, 2.7 g / cc, 2.8 g / cc, 2.85 g / cc, 2.9 g / cc, 3.05 g / cc, 3.25 g / cc, and 3.35 g / cc were prepared, and negative electrode compacted sheets having compaction densities of 1.0 g / cc, 1.3 g / cc, 1.5 g / cc, 1.55 g / cc, 1.6 g / cc, 1.75 g / cc, and 1.85 g / cc were prepared. In different embodiments, positive and negative electrode compacted sheets having different density gradients can be provided according to actual use requirements, and the present invention does not impose specific limitations on this.

[0034] Step S5: The positive electrode sheets with the same compaction density are prepared into a positive symmetrical battery, and the negative electrode sheets with the same compaction density are prepared into a negative symmetrical battery. Furthermore, in this embodiment, the positive and negative symmetrical batteries can eliminate the complex interactions between the positive and negative electrodes, focusing the research on the electrochemical performance of a single electrode, thereby more accurately studying the effect of compaction density on electrode performance.

[0035] Step S6: Electrochemical impedance spectroscopy (EIS) is performed on the symmetrical positive and negative electrodes at different compaction densities to determine target positive and negative electrode compaction densities from the various compaction densities. The core purpose of this step is to screen target positive and negative electrode compaction densities from the various compaction densities by performing electrochemical impedance spectroscopy (EIS) on the symmetrical positive and negative electrodes at different compaction densities. This ensures that the positive and negative electrodes of the lithium-ion battery achieve optimal performance matching in actual operation, thereby improving the overall battery performance, such as charge and discharge efficiency, energy density, and cycle life.

[0036] Specifically, step S6 in this embodiment includes: Step S61: Electrochemical impedance spectroscopy (EIS) is performed on the positive symmetrical cells with different compaction densities to obtain the ohmic impedance and solid-phase diffusion impedance of the multiple positive symmetrical cells. Simultaneously, EIS is performed on the negative symmetrical cells with different compaction densities to obtain the ohmic impedance and solid-phase diffusion impedance of the multiple negative symmetrical cells. It should be noted that ohmic impedance reflects the resistance of the electronic conductors (such as the current collector and electrode materials) and ionic conductors (such as the electrolyte) within the battery, while solid-phase diffusion impedance reflects the ease with which lithium ions diffuse within the solid phase of the electrode material. By measuring these two impedances, the electron conduction and lithium ion diffusion processes within the battery electrodes at different compaction densities can be accurately understood.

[0037] Step S62: Integrate the ohmic impedance and solid-phase diffusion impedance curves of the plurality of positive symmetrical cells to obtain the positive symmetrical cell with the slowest ohmic impedance curve growth rate during the increase of the solid-phase diffusion impedance curve, thereby obtaining a target positive electrode compaction density. Integrate the ohmic impedance and solid-phase diffusion impedance curves of the plurality of negative symmetrical cells to obtain the negative symmetrical cell with the slowest ohmic impedance curve growth rate during the increase of the solid-phase diffusion impedance curve, thereby obtaining a target negative electrode compaction density. Specifically, during battery charge and discharge, electron conduction and lithium ion diffusion are two key processes, and their synergistic effect determines battery performance. Solid-phase diffusion impedance reflects the ease of lithium ion diffusion, while ohmic impedance reflects the resistance to electron conduction. By selecting the compaction density at which the ohmic impedance growth rate is slowest when the solid-phase diffusion impedance increases, it is possible to minimize the resistance to electron conduction while ensuring lithium ion diffusion performance, thereby achieving a balance between electron conduction and ion diffusion performance. This also helps improve battery cycling stability and extend battery life.

[0038] Further, see Figure 3 As shown, too low or too high a compaction density will cause differences in ohmic impedance and diffusion impedance. Among them, if the ohmic impedance is too high, the electrical contact is poor, and there is also the risk of double-layer capacitance phenomenon (abnormal arc model of diffusion impedance) caused by abnormal contact between the active material and the current collector. Therefore, considering the perspectives of electrical contact and lithium ion solid phase diffusion, the positive electrode compaction density in this embodiment is preferably 2.85g / cc. Similarly, see Figure 4 As shown, the negative electrode compaction density is preferably 1.5 g / cc.

[0039] Step S7: preparing a lithium-ion battery according to the target positive electrode compaction density and the target negative electrode compaction density.

[0040] Example 2:

[0041] This embodiment provides another method for preparing a lithium-ion battery, the main design ideas and principles of which are the same as those of the first embodiment, and will not be described in detail here. In this embodiment, only the positive electrode active materials screened by the material performance parameter X and the structural performance parameter Y in step S3 are different. Specifically, in this embodiment, adjusting the performance parameter X of the electrode material is specifically as follows: screening out positive electrode active materials whose X meets 0.001~500, and X=(Dv50+Dv90)×(w×100)×Pd / a, wherein Dv50 is preferably 25; Dv90 is preferably 40; w is the proportion of active material in the electrode, which is preferably 99%; a is the electrode thickness, which is preferably 500μm; Pd is the pre-compacted density of the electrode, which is preferably 4.6g / cc. Based on this, X in this embodiment is 59.225.6.

[0042] Correspondingly, in step S3, the electrode structure performance parameter Y is adjusted as follows: to select the electrode structure performance parameter Y that meets the range of 0.003 to 10 6 positive electrode active material, and Y=a×b×c / (Rmax-Rmin), wherein a is the thickness of the electrode material, and is preferably 500 μm, b is the porosity of the electrode material, and is preferably 40%, c is the pore density ratio of the electrode material, and is preferably 150 μm, Rmax is the minimum pore size of the non-closed pores of the electrode material, and is preferably 20 μm; Rmin is the maximum pore size of the non-closed pores of the electrode material, and is preferably 5 μm. Based on this, Y in this embodiment is 2000.

[0043] Example 3:

[0044] This embodiment provides another method for preparing a lithium-ion battery, the main design ideas and principles of which are the same as those of the first embodiment, and will not be described in detail here. In this embodiment, only the positive electrode active materials screened by the material performance parameter X and the structural performance parameter Y in step S3 are different. Specifically, in this embodiment, adjusting the performance parameter X of the electrode material is specifically as follows: screening out positive electrode active materials whose X meets 0.001~500, and X=(Dv50+Dv90)×(w×100)×Pd / a, wherein Dv50 is preferably 0.8; Dv90 is preferably 6; w is the proportion of the electrode active material, which is preferably 75%, a is the electrode thickness, which is preferably 45μm; Pd is the pre-compacted density of the electrode, which is preferably 1.5g / cc. Based on this, X in this embodiment is 17.0. In different embodiments, the Dv50 interval can be configured to be 0.8-25μm, the Dv90 interval can be configured to be 6-40μm, the electrode active material proportion w interval can be configured to be 75%~99%; the electrode thickness a interval can be configured to be 45μm~500μm; the electrode pre-compaction density Pd interval can be configured to be 1.5g / cc~4.6g / cc.

[0045] Correspondingly, in step S3, the electrode structure performance parameter Y is adjusted as follows: to select the electrode structure performance parameter Y that meets the range of 0.003 to 10 6positive electrode active material, and Y=a×b×c / (Rmax-Rmin), wherein a is the thickness of the electrode material, and is preferably 45 μm, b is the porosity of the electrode material, and is preferably 15%, c is the pore density ratio of the electrode material, and is preferably 0.02 μm, Rmax is the minimum pore size of the non-closed pores of the electrode material, and is preferably 5 μm; Rmin is the maximum pore size of the non-closed pores of the electrode material, and is preferably 0.01 μm. Based on this, Y in this embodiment is 0.03. In different embodiments, the thickness a of the pole piece material can be configured to range from 45 μm to 500 μm, the porosity b of the pole piece material can be configured to range from 15% to 40%, the pore density ratio c of the pole piece material can be configured to range from 0.02 μm to 150 μm, the maximum pore size Rmax of the non-closed pores of the pole piece material can be configured to range from 5 μm to 20 μm; the minimum pore size Rmin of the non-closed pores of the pole piece material can be configured to range from 0.01 μm to 5 μm.

[0046] Example 4:

[0047] This embodiment provides a battery, which is prepared using the lithium-ion battery preparation method described in the first embodiment.

[0048] Embodiment 5:

[0049] This embodiment provides an electrochemical device, which is prepared using the lithium-ion battery preparation method described in the first embodiment.

[0050] In summary, the present invention demonstrates outstanding performance improvements and innovative advantages in the field of lithium-ion batteries. It can effectively enhance the cycle life and volume energy density of the electrode. When the electrode is recycled, the present invention greatly reduces the structural damage and performance degradation of the electrode material during the charge and discharge process by deeply optimizing the material properties and preparation process. This significantly extends the service life of the electrode, ensuring that the battery can maintain excellent performance even after multiple charge and discharge cycles. At the same time, the present invention improves the content and utilization efficiency of active substances per unit volume by rationally planning the electrode structure and material composition, thereby effectively improving the volume energy density of the battery, fully meeting the market's urgent demand for high-energy-density batteries. What is particularly critical is that the present invention can accurately control the compaction density of the positive and negative electrode sheets, greatly improving the matching between the positive and negative electrodes. This measure can significantly reduce the polarization phenomenon inside the battery, improve the efficiency and stability of battery charge and discharge, and effectively avoid problems such as battery performance degradation and safety hazards caused by mismatch between the positive and negative electrodes.

[0051] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium ion battery, characterized in that: include: Step S1, screening a first preliminary positive electrode active material having a particle size within a preset particle size range from a plurality of positive electrode active materials; Step S2, adjusting the sphericity of the first prepared positive electrode active material to a preset sphericity range to obtain a second prepared positive electrode active material; Step S3, obtaining a target positive electrode active material by adjusting the material performance parameters and structural performance parameters of the second prepared positive electrode active material; Step S4: using the target positive electrode active material to prepare a plurality of positive electrode compacted sheets and negative electrode compacted sheets with different compaction densities, wherein the number of positive electrode compacted sheets and negative electrode compacted sheets with any compaction density is multiple; Step S5, preparing a positive electrode symmetrical battery by compacting multiple positive electrode sheets with the same compaction density, and preparing a negative electrode symmetrical battery by compacting multiple negative electrode sheets with the same compaction density; Step S6, performing electrochemical impedance spectroscopy on the positive electrode symmetrical battery and the negative electrode symmetrical battery with different compaction densities, respectively, and obtaining a target positive electrode compaction density and a target negative electrode compaction density according to the electrochemical impedance spectroscopy test results; Step S7: preparing a lithium-ion battery according to the target positive electrode compaction density and the target negative electrode compaction density.

2. The method for preparing a lithium-ion battery according to claim 1, wherein: In step S3, the method for adjusting the material performance parameters of the second prepared positive electrode active material is as follows: setting the material performance parameters of the positive electrode active material to X=D×(w×100)×Pd / a, and making 0.001≤X≤500, wherein D is the material particle size, w is the proportion of active material in the electrode sheet, and 75%≤w≤99%; a is the electrode thickness, and 45μm≤a≤500μm; Pd is the pre-compacted density of the electrode sheet, and 1.5g / cc≤Pd≤4.6g / cc.

3. The method for preparing a lithium ion battery according to claim 1 or 2, wherein: In step S1, the method for screening the material particle size is: setting the material particle size D=Dv50+Dv90, wherein Dv50 is the cumulative particle size of 50% volume distribution, and its interval range is 0.8-25μm, and Dv90 is the cumulative particle size of 90% volume distribution, and its interval range is 6-40μm.

4. The method for preparing a lithium-ion battery according to claim 1, wherein: In step S3, the method for adjusting the structural performance parameters of the second prepared positive electrode active material is: setting the structural performance parameters of the positive electrode active material to Y=a×b×c / (Rmax-Rmin), and limiting 0.003≤Y≤10 6 , wherein a is the thickness of the pole piece material, and 45μm≤a≤500μm, b is the porosity of the pole piece material, and 15%≤b≤40%, c is the pore density ratio of the pole piece material, and 0.02μm≤c≤150μm, Rmax is the maximum pore size of the non-closed pores of the pole piece material, and 5μm≤Rmax≤20μm; Rmin is the minimum pore size of the non-closed pores of the pole piece material, and 0.01μm≤Rmin<5μm.

5. The method for preparing a lithium-ion battery according to claim 1, wherein: In step S2, the method for adjusting the sphericity of the first prepared positive electrode active material to a preset sphericity range is: setting the preset sphericity ψ = (V / S) 1 / 3 The preset range of sphericity ψ is 0.2~0.995, where V is the volume of the measured material and S is the specific surface area of the measured material.

6. The method for preparing a lithium-ion battery according to claim 5, wherein: The pole piece structural performance parameter Y is adjusted by laser drilling technology and / or pole piece rolling processing.

7. The method for preparing a lithium-ion battery according to claim 1, wherein: In step S4, positive electrode compacted sheets with different compaction densities are prepared by adjusting the rolling pressure and the rolling gap.

8. The method for preparing a lithium-ion battery according to claim 1, wherein: Step S6 includes: Step S61: performing electrochemical impedance tests on the positive symmetrical batteries with different compaction densities to obtain ohmic impedances and solid-phase diffusion impedances in the plurality of positive symmetrical batteries. At the same time, performing electrochemical impedance tests on the negative symmetrical batteries with different compaction densities to obtain ohmic impedances and solid-phase diffusion impedances in the plurality of negative symmetrical batteries. Step S62: Integrate the ohmic impedance and solid-phase diffusion impedance curves of the plurality of positive symmetrical batteries to obtain the positive symmetrical battery whose ohmic impedance curve increases the slowest during the increase of the solid-phase diffusion impedance curve, so as to obtain a target positive electrode compaction density; integrate the ohmic impedance and solid-phase diffusion impedance curves of the plurality of negative symmetrical batteries to obtain the negative symmetrical battery whose ohmic impedance curve increases the slowest during the increase of the solid-phase diffusion impedance curve, so as to obtain a target negative electrode compaction density.

9. A battery, characterized in that: The lithium ion battery is prepared by the lithium ion battery preparation method according to any one of claims 1 to 8.

10. An electrochemical device, characterized in that: The lithium ion battery is prepared by the lithium ion battery preparation method according to any one of claims 1 to 8.

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