Battery cell pole piece and preparation method thereof
By repeatedly rolling the cell electrodes to break down large particles of lithium iron phosphate, the problem of declining initial capacity and rate performance of lithium iron phosphate batteries was solved, thereby improving initial capacity and cycle performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2022-08-18
- Publication Date
- 2026-03-31
AI Technical Summary
Existing technologies that increase the compaction density of lithium iron phosphate batteries lead to a decrease in their initial capacity and rate performance, especially a low initial capacity that gradually increases during cycling, affecting battery production and assembly results.
By repeatedly rolling the cell electrodes and adjusting the pressure value to break up large lithium iron phosphate particles, the lithium ion diffusion distance is reduced, and the initial capacity is increased. This includes the gradual adjustment of the first, second, and third pressure values to ensure the breakage and shedding of both large and small lithium iron phosphate particles.
It significantly improves the initial capacity and rate performance of the cell electrodes, enhances cycle performance, reduces capacity ramp-up, increases battery yield, and lowers production costs.
Smart Images
Figure CN121769020A_ABST
Abstract
Description
[0001] This application is a divisional application of the parent application with application number "CN202210992880.X", application date "2022.08.18", and title "Method for increasing the initial capacity of battery cell electrode and battery cell electrode". Technical Field
[0002] This application relates to the field of battery technology, and in particular to a cell electrode and its preparation method. Background Technology
[0003] Lithium iron phosphate (LFP), as the most important cathode material for lithium batteries, is increasingly widely used in electric vehicles. To further improve the energy density of LFP, developing high-compact-density LFP materials has become a major development direction. Currently, the compaction density of LFP powder can reach >2.50 g / cc, and some manufacturers have even achieved 2.70 g / cc. High compaction density is typically achieved by mixing particles of different sizes. This mixing can be achieved naturally through temperature gradients during sintering, or by preparing LFP of different particle sizes and then mixing them. The compaction density is increased by utilizing the close packing of particles of different sizes in space. Typical results are shown below. Figure 1 As shown.
[0004] While high-density LFP (Low-Package Photopolymer) can improve battery energy density, it introduces a larger particle size, significantly reducing both capacity and rate capability. In particular, its initial capacity is considerably lower, with a gradual increase in capacity during subsequent cycles. This initial low-capacity phenomenon, followed by capacity ramp-up, is a key factor. Figure 2 As shown, this has caused great trouble for battery manufacturers in cell capacity assessment and has also had a significant impact on battery pack assembly.
[0005] Currently, there are generally two main methods to improve capacity ramp-up: the first is to dope LFP particles to improve their rate performance, and the second is to precisely control the size of LFP materials for blending. Both methods suffer from drawbacks such as complex preparation methods, high equipment requirements, and high costs. To address these issues, this invention proposes a method for improving the initial capacity of battery cell electrodes and a battery cell electrode itself. Summary of the Invention
[0006] The purpose of this invention is to provide a battery cell electrode sheet and its preparation method, which can improve the capacity ramp-up problem that exists in the production and preparation process of battery cell electrodes sheet.
[0007] To achieve the above objectives, the present invention provides a method for increasing the initial capacity of battery cell electrodes, comprising the following steps: The cell electrode sheet is rolled using a first pressure value to bring the cell electrode sheet to the ultimate compaction state. The cell electrode sheets under extreme compaction state are scanned, and the cell electrode sheets containing large-particle lithium iron phosphate are selected; Adjust the pressure of the roller to increase the pressure from the first pressure value to the second pressure value; The second pressure value is used to roll the cell electrode containing the large lithium iron phosphate particles to break the large lithium iron phosphate particles, thereby increasing the initial capacity of the cell electrode. The compaction density of the battery cell electrode sheet in the extreme compaction state is between 2.65 and 2.70 g / cc; the particle size of the large particles in the high-compacted LFP is between 1 and 2 μm.
[0008] Optionally, the first pressure value is between 6.0 and 8.0 tons.
[0009] Optionally, under the extreme compaction state, the resistance of the cell electrode is between 40 and 200 mΩ.
[0010] Optionally, the second pressure value is between 8.0 and 9.0 tons, and the second pressure value includes 8 tons.
[0011] Optionally, in the crushed state of the large-particle lithium iron phosphate, the compaction density of the cell electrode is between 2.70 and 2.71 g / cc, and the resistance of the cell electrode is between 67 and 350 mΩ.
[0012] Optionally, the cell electrode includes lithium iron phosphate, a binder, and a conductive agent, wherein the lithium iron phosphate and the conductive agent are polymerized together by the binder; After the cell electrode containing the large lithium iron phosphate particles is rolled using the second pressure value; Continue to increase the pressure of the roller press, so that the pressure of the roller press changes from the second pressure value to the third pressure value; The third pressure value is used to roll the battery cell electrode sheet after the large lithium iron phosphate particles are crushed again, so that the small lithium iron phosphate particles are crushed and the binder and the conductive agent are detached from the battery cell electrode sheet. The small particles in the lithium iron phosphate are less than 1 μm in size.
[0013] Optionally, the third pressure value is greater than 9 tons, and the third pressure value includes 9 tons.
[0014] Optionally, when the small lithium iron phosphate particles are crushed, the compaction density of the cell electrode is between 2.70 and 2.71 g / cc, and the resistance of the cell electrode exceeds 350 mΩ.
[0015] Optionally, a cell electrode sheet is prepared using the method described above for increasing the initial capacity of the cell electrode sheet.
[0016] The beneficial effects of the method for improving the initial capacity of battery cell electrodes and the battery cell electrodes provided by this invention are as follows: By increasing the pressure of the cell electrode rolling, the large lithium iron phosphate particles in the cell electrode are broken, thereby reducing the diffusion distance between lithium ions and the contact internal resistance, which increases the initial capacity of the cell electrode and improves the capacity ramp-up phenomenon in the subsequent cell electrode production process. Moreover, this method is simple and easy to operate, and can not only improve the initial capacity and rate performance of the cell electrode, but also improve the cycle performance of the cell electrode. Attached Figure Description
[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0018] Figure 1 This is a schematic diagram of the laser particle size distribution and scanning electron microscope of the high-pressure lithium iron phosphate material in this invention; Figure 2 This is a schematic diagram illustrating the specific capacity ramp-up of the high-pressure lithium iron phosphate material in this invention; Figure 3 This is a flowchart illustrating an embodiment of the present invention; Figure 4 This is a schematic diagram of the compaction window for the cell electrode rolling process in this invention; Figure 5 This is a scanning electron microscope (SEM) diagram of the electrode sheet of the battery cell in the present invention when it is not under extreme compaction. Figure 6 This is a scanning electron microscope (SEM) diagram of the large-particle lithium iron phosphate particles in the broken state described in this invention. Figure 7 This is a schematic diagram showing the capacity ramp-up under different roller pressure conditions in this invention. Detailed Implementation
[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art. The terms "comprising" and similar expressions used herein mean that the element or object preceding the word covers the element or object listed following the word and its equivalents, but do not exclude other elements or objects.
[0020] To address the problems existing in the prior art, one embodiment of the present invention provides a method for increasing the initial capacity of battery cell electrodes, see reference. Figure 3 As shown, it includes the following steps: S01: The battery cell electrode sheet is rolled using a first pressure value to bring it to its ultimate compaction state.
[0021] During the production process of the battery cell electrode sheet, it needs to be rolled to continuously increase its compaction density. In this step, the battery cell electrode sheet is rolled using the first pressure value, which allows it to quickly reach its ultimate compaction state. At this ultimate compaction state, the compaction density of the battery cell electrode sheet is between 2.65 and 2.70 g / cc. It should be noted that the ultimate compaction state of the battery cell electrode sheet is the maximum compaction density that the battery cell electrode sheet can achieve, and at this density, large lithium iron phosphate particles do not break.
[0022] S02: Scan the cell electrode sheet under extreme compaction state and select the cell electrode sheet containing large particles of lithium iron phosphate.
[0023] Specifically, a scanning electron microscope (SEM) is used to scan the cross-section of the battery cell electrode sheet under extreme compaction, and the battery cell electrode sheets with good cross-sectional condition and unbroken large lithium iron phosphate particles are selected. In this step, the large lithium iron phosphate particles have a particle size between 1 and 2 μm.
[0024] S03: Adjust the pressure of the roller to increase the pressure from the first pressure value to the second pressure value.
[0025] At the first pressure value, the cell electrode reaches its maximum limit, at which point the large lithium iron phosphate particles do not break. The first pressure value is then increased to the second pressure value. The pressure of the second pressure value exceeds the maximum pressure the cell electrode can withstand. When the second pressure value is applied to the cell electrode, it will cause the cell electrode to break, and correspondingly, the large lithium iron phosphate particles within the cell electrode will also break.
[0026] S04: The cell electrode containing the large lithium iron phosphate particles is subjected to the second pressure value to crush the large lithium iron phosphate particles, thereby increasing the initial capacity of the cell electrode.
[0027] As shown in S03, after the battery cell electrode is rolled at the second pressure value, the battery cell electrode breaks, and the large lithium iron phosphate particles within the battery cell electrode also break. After the large lithium iron phosphate particles break, the diffusion distance of lithium ions becomes shorter, reducing the contact internal resistance and increasing the capacity of the battery cell electrode. The battery cell electrode prepared under the second pressure value has a significantly higher initial capacity than the battery cell electrode prepared without the second pressure value. Thus, during subsequent production of the battery cell electrode, the battery cell electrode prepared under the second pressure value can effectively improve the capacity ramp-up phenomenon. Furthermore, during the crushing process of the large lithium iron phosphate particles, the small lithium iron phosphate particles remain intact due to their higher pressure resistance.
[0028] In this embodiment, the first pressure value is between 6.0 tons and 8.0 tons. Under the extreme compaction state, the resistance of the cell electrode is between 40mΩ and 200mΩ.
[0029] In the compaction experiment of the battery cell electrode, the compaction density of the battery cell electrode increases with the pressure applied to it. (See [reference needed]) Figure 4 As shown. From Figure 4 As can be seen, when the provided roller pressure is between 6.0 and 8.0 tons, the compaction density of the battery cell electrode reaches between 2.65 g / cc and 2.70 g / cc. At this point, the battery cell electrode reaches the ultimate compaction state.
[0030] Furthermore, when the first pressure value is between 6.0 tons and 8.0 tons, the large lithium iron phosphate particles do not break, and both the binder and the conductive agent detach from the cell electrode. (See reference...) Figure 5 As shown.
[0031] Furthermore, in this embodiment, the first pressure value is selected as 7 tons. When the first pressure value is selected as 7 tons, the compaction density of the battery cell electrode is 2.70 g / cc, and the resistance of the battery cell electrode is 120 mΩ. See Table 1 for details.
[0032] Table 1: Resistance of battery cell electrodes under different rolling pressures In this embodiment, the second pressure value is between 8.0 and 9.0 tons, and includes 8 tons. Under the crushed state of the large-particle lithium iron phosphate, the compaction density of the cell electrode is between 2.70 g / cc and 2.71 g / cc. At this time, the resistance of the cell electrode is between 67 mΩ and 350 mΩ, as shown in Table 1.
[0033] When the second pressure value is between 8.0 tons and 9.0 tons, the cell electrode is subjected to the rolling process. At this time, the large lithium iron phosphate particles break under the rolling pressure, while the small lithium iron phosphate particles do not break. The binder and the conductive agent both detach from the cell electrode, thus increasing the electrode resistance. (See reference...) Figure 7 As shown. By Figure 6 As can be seen, after the large lithium iron phosphate particles are broken, the diffusion distance of lithium ions becomes shorter, and the internal resistance of the cell electrode decreases, thereby improving the initial capacity of the cell electrode. In the subsequent preparation process of the cell electrode, the capacity ramp-up phenomenon can be effectively improved.
[0034] Furthermore, the second pressure value is selected as 8 tons. Under this pressure, the large particles of lithium iron phosphate are broken. As shown in Table 1, at this time, the compaction density of the cell electrode is 2.71 g / cc, and the resistance of the cell electrode is 68 mΩ.
[0035] In this embodiment, the battery cell electrode sheet includes lithium iron phosphate, a binder, and a conductive agent, wherein the lithium iron phosphate and the conductive agent are polymerized together by the binder. After the battery cell electrode sheet containing the large lithium iron phosphate particles is rolled using the second pressure value, the rolling pressure is further increased to change from the second pressure value to a third pressure value. The battery cell electrode sheet after the large lithium iron phosphate particles have been broken down is rolled again using the third pressure value to break down the small lithium iron phosphate particles, causing the binder and the conductive agent to detach from the battery cell electrode sheet. The small particles of lithium iron phosphate have a particle size of less than 1 μm.
[0036] To better verify that the initial capacity of the battery cell electrode reaches its optimal value when the second pressure value is applied, this embodiment also provides an experiment of rolling the battery cell electrode under the third pressure value.
[0037] Specifically, the third pressure value is greater than 9 tons, and the third pressure value includes 9 tons. When the small-particle lithium iron phosphate is crushed, the compaction density of the cell electrode is between 2.70 g / cc and 2.71 g / cc, at which point the resistance of the cell electrode exceeds 350 mΩ.
[0038] Under the third pressure value, both the large and small lithium iron phosphate particles break down under rolling pressure, and the binder and the conductive agent detach from the battery cell electrode.
[0039] Furthermore, the third pressure value is selected as 9 tons. Under this pressure, both the large and small lithium iron phosphate particles break down under rolling pressure, and the binder and conductive agent detach from the battery cell electrode. As can be seen from Table 1, at this point, the compaction density of the battery cell electrode is 2.71 g / cc, and the resistance of the battery cell electrode is 350 mΩ.
[0040] In summary, at the first pressure value, neither the large nor small lithium iron phosphate particles broke under the rolling pressure, and both the binder and the conductive agent detached from the cell electrode. At the second pressure value, the large lithium iron phosphate particles broke under the rolling pressure, while the small lithium iron phosphate particles did not, and both the binder and the conductive agent detached from the cell electrode. At the third pressure value, neither the large nor small lithium iron phosphate particles broke under the rolling pressure, and both the binder and the conductive agent detached from the cell electrode. Comparing the resistance of the cell electrode under the three different pressure values, it can be seen that the resistance is lowest at the second pressure value, meaning that the capacity of the cell electrode is highest at the second pressure value. Increasing the initial capacity of the cell electrode at the second pressure value can effectively improve the subsequent capacity ramp-up phenomenon. (See [reference needed]). Figure 7 As shown.
[0041] The present invention provides another embodiment, specifically a battery cell electrode sheet, which is prepared using the method described above for increasing the initial capacity of the battery cell electrode sheet.
[0042] The present invention also provides a comparative embodiment in which all other processes are the same as the method for increasing the initial capacity of the battery cell electrode, except that the 7-ton rolling mill is used to prepare the battery cell electrode. Hereinafter, the battery cell electrode prepared using the method for increasing the initial capacity of the battery cell electrode will be referred to as battery cell electrode A; the battery cell electrode prepared in the comparative embodiment will be referred to as battery cell electrode B.
[0043] The electrical performance of the battery cell electrodes obtained by the two embodiments described above was tested, see reference. Figure 7 As shown, the 2C capacity retention rate of cell electrode A is 92.2%, and that of cell electrode B is 88.3%. The initial capacity of cell electrode A is significantly higher than that of Comparative Example 1, reaching its maximum after 6 cycles with a capacity ramp-up rate of 2.4%, and a capacity retention rate of 94.8% after 1000 cycles. In contrast, cell electrode B only reaches 5.08 Ah after 30 cycles, with a capacity ramp-up rate of 5.4% and a capacity retention rate of 90.2% after 1000 cycles. See Table 2 for details. Table 2:
[0044] Table 2: Results of Electrical Performance Tests for Cell Electrodes The above results indicate that the battery electrode prepared by the method described above not only improves the initial capacity and rate performance, but also enhances the cycle performance. Specifically, this is because the micro-cracks in the lithium iron phosphate particles increase the specific surface area and shorten the diffusion path, making lithium insertion / extraction easier. This improvement on the capacity ramp-up problem of lithium iron phosphate batteries from the battery electrode end effectively increases the battery yield and reduces manufacturing costs.
[0045] In this invention, by increasing the pressure of the cell electrode rolling process, the large lithium iron phosphate particles in the cell electrode are broken, thereby reducing the diffusion distance between lithium ions and the contact resistance, which increases the initial capacity of the cell electrode and improves the capacity ramp-up phenomenon in the subsequent cell electrode production process. Moreover, this method is simple and easy to operate, and can not only improve the initial capacity and rate performance of the cell electrode, but also improve the cycle performance of the cell electrode.
[0046] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.
Claims
1. A method of making an electrode tab of a battery cell, the method comprising: The method comprises: rolling the electrode sheet of the battery cell with a first pressure value to make the electrode sheet of the battery cell reach an ultimate compaction state; the first pressure value is between 6.0 tons and 8.0 tons; the electrode sheet of the battery cell comprises lithium iron phosphate, a binder and a conductive agent, wherein the lithium iron phosphate and the conductive agent are aggregated together through the binder; the compaction density of the electrode sheet of the battery cell in the ultimate compaction state is between 2.65 g / cc and 2.70 g / cc; for the electrode sheet of the battery cell in the ultimate compaction state, the electrode sheet containing large-particle lithium iron phosphate is selected, the particle size of the large-particle lithium iron phosphate being between 1 μm and 2 μm; the electrode sheet containing the large-particle lithium iron phosphate is rolled with the second pressure value to make the large-particle lithium iron phosphate be broken into small-particle lithium iron phosphate, the compaction density of the electrode sheet being between 2.70 g / cc and 2.71 g / cc, the second pressure value being between 6.0 tons and 8.0 tons, and the second pressure value including 8 tons.
2. The method of claim 1, wherein the method further comprises: The ultimate compaction state of the electrode sheet of the battery cell is the maximum compaction density that the electrode sheet of the battery cell can reach, and at the density, the large-particle lithium iron phosphate is not broken.
3. The method of claim 1, wherein the method further comprises: The resistance of the electrode sheet of the battery cell in the ultimate compaction state is between 40 mΩ and 200 mΩ.
4. The method of claim 1, wherein the method further comprises: The resistance of the electrode sheet of the battery cell in the large-particle lithium iron phosphate broken state is between 67 mΩ and 350 mΩ.
5. The method of claim 1, wherein the method further comprises: For the electrode sheet of the battery cell in the ultimate compaction state, the electrode sheet containing large-particle lithium iron phosphate further comprises: scanning the cross section of the electrode sheet of the battery cell in the ultimate compaction state by using a scanning electron microscope, and selecting the electrode sheet of the battery cell with a good cross section state and unbroken large-particle lithium iron phosphate.
6. The method of claim 1, wherein the method further comprises: The method further comprises: re-rolling the electrode sheet of the battery cell after the large-particle lithium iron phosphate is broken with a third pressure value to make the small-particle lithium iron phosphate be broken, and the binder and the conductive agent are both dropped from the electrode sheet of the battery cell; the particle size of the smaller particles in the lithium iron phosphate compacted by using the third pressure value is less than 1 μm, the third pressure value is greater than 9 tons, and the third pressure value includes 9 tons.
7. The method of claim 6, wherein the method further comprises: In the broken state of the smaller particle lithium iron phosphate, the compaction density of the electrode sheet of the battery cell is between 2.70 g / cc and 2.71 g / cc, and the resistance of the electrode sheet of the battery cell is more than 350 mΩ.
8. An electrode tab of a battery cell, characterized by The electrode sheet of the battery cell is obtained by using the preparation method of the electrode sheet of the battery cell in any one of claims 1-7.