Method for obtaining pole piece compaction density and surface density and method for selecting pole piece foil

Abstract

The present invention discloses a method for obtaining the compaction density and surface density of an electrode piece and a method for screening electrode piece foil. The acquisition method of the present invention performs pre-charging, forming and overcharging treatments on cells with the same material foil and the same ratio of different compaction densities to positive and negative electrode surface densities. The compaction density and surface density that cause a sudden change in the electrode foil breaking ratio and the electrode light transmittance ratio can be obtained more accurately through the electrode foil breaking ratio and the electrode light transmittance ratio. The screening method of the present invention uses the compaction density and surface density of the cell when the electrode foil breaking and the electrode light transmittance ratio suddenly change during the pre-charging, forming and overcharging treatments of the cell to make cells with different foil materials, so that different foil materials have obvious effects on the electrode foil breaking and electrode light transmittance of the cell, and can select foil materials with low risks of electrode foil breaking and electrode light transmittance from different foil materials as the electrode piece of the cell. The method of the present invention can measure the effects of different foil materials on the broken foil of the cell electrode piece using a small number of cells, thereby reducing the screening time of the foil materials and reducing the screening cost.

Description

Technical Field

[0001] The invention belongs to the research field of battery performance improvement technology, and particularly relates to a method for obtaining the compaction density and surface density of a pole piece and a method for screening pole piece foils. Background Art

[0002] The electrode sheet is the core of the battery. The electrode sheets inside the battery cell mainly have two structures: winding and stacking. Due to the winding and stacking of the electrode sheets, there is stress in the internal structure of the battery cell. In addition, the mutual extrusion between particles and particles in the material, and between particles and foil materials, will cause the phenomenon of electrode sheet foil breaking inside the battery cell. In particular, for cylindrical 18650 batteries with internal electrode sheets as winding structures, due to the bending of the electrode sheet foil itself, there is a high risk of negative electrode sheet foil breaking or positive electrode light transmission inside the battery cell. The broken foil or light transmission of the electrode sheet directly affects the performance and safety of the battery cell. Therefore, preventing the broken foil of the electrode sheet has become an important task to improve the reliability of the battery cell. As the factor that directly affects the broken foil and light transmission of the battery cell electrode sheet, the screening of the foil material used to manufacture the battery cell electrode sheet plays an important role in improving the broken foil and light transmission of the battery cell electrode sheet.

[0003] During the preparation process of battery cell production, it is necessary to screen the pole pieces of different foil materials. These foil materials come from different manufacturers, and their models, production processes and structures may be different. Selecting the foil material with the least impact on the pole piece foil breakage and light transmittance to produce the battery cell can improve the reliability of the battery cell to a certain extent. Furthermore, if you want to improve the pole piece foil breakage and light transmittance of the battery cell that is already in production, you also need to compare and screen the used foil materials with the newly introduced foil materials, and then decide whether to replace the existing foil materials.

[0004] Since the probability of electrode foil breaking and light transmission is relatively small during mass production, conventional methods are used to screen different foil materials, which requires a large number of cells to be tested for electrode foil breaking and light transmission. In the test results, the number of electrode foil breaking and light transmission is relatively small, and it is impossible to draw a conclusion from the test data on what kind of electrode material can effectively improve the electrode foil breaking and light transmission. Therefore, when selecting the electrode foil material for the battery cell, it is difficult to screen the electrode foil material for the battery cell through the electrode foil breaking and light transmission test, and thus it is impossible to select the foil material that can improve the electrode foil breaking and light transmission of the battery cell. Summary of the invention

[0005] In order to solve the shortcomings of the prior art, the present invention provides a method for obtaining the compaction density and surface density of a pole piece and a method for screening a pole piece foil. A battery cell with different pole piece compaction densities and the same positive and negative pole surface density ratio is made using the same material foil, and the battery cell is sequentially pre-charged, formed, and overcharged. The electrode foil breaking ratio and the electrode light transmittance ratio of the battery cell during the pre-charging, forming, and overcharging treatments are counted, and the battery cell compaction density and surface density when the electrode foil breaking ratio and the pole piece light transmittance ratio suddenly change are obtained. The method for obtaining the pole piece compaction density and surface density of the present invention pre-charges, forms, and overcharges the battery cell made of the same material foil, so that the battery cell is in an environment of current change and voltage change, and obtains a more accurate compaction density and surface density that cause the electrode foil breaking ratio and the electrode light transmittance ratio to suddenly change through the electrode foil breaking ratio and the electrode light transmittance ratio.

[0006] The screening method of the electrode foil of the present invention uses foils of different materials, combined with compaction density and surface density that cause a sudden change in the electrode foil breaking ratio and the electrode light transmittance ratio to make different battery cells, and uses a method for obtaining the compaction density and surface density of the battery cell electrode sheet to count the electrode foil breaking ratio and the electrode light transmittance ratio of the battery cells with different foil materials, and screens out the battery cell electrode sheet foil with the smallest electrode foil breaking ratio and electrode light transmittance ratio among the battery cells with different foil materials. The method of the present invention can effectively screen out foils that can improve the electrode foil breaking and electrode light transmittance conditions, and then manufacture battery cells with the foils screened by the method of the present invention to improve the reliability and performance of the battery cells. The method of the present invention can screen out foils with less impact on the electrode foil breaking by testing a small number of battery cells, and the method of the present invention reduces the screening time and reduces the screening cost of the battery cell electrode sheet foil.

[0007] The technical effects to be achieved by the present invention are achieved through the following solutions:

[0008] A method for obtaining the compaction density and surface density of a pole piece comprises the following steps:

[0009] Step 1: Using foil of the same material to manufacture battery cells with different compaction densities of battery cell pole pieces and the same ratio of positive and negative electrode surface density; preferably, battery cells with different compaction densities of pole pieces have different surface densities.

[0010] The different compaction density of the pole piece means that at least one of the compaction density of the positive pole and the compaction density of the negative pole of the manufactured battery cell is different. The same ratio of the positive and negative electrode surface density means that the surface density of the manufactured battery cell can be different or the same, but the ratio of the positive and negative electrode surface density of the battery cell must be the same. That is, when the surface density of the negative electrode of the battery cell changes, the surface density of the positive electrode will change in the same proportion as the surface density of the negative electrode, and the positive and negative electrode surface density ratio after the change is the same as the positive and negative electrode surface density ratio before the change.

[0011] The value of N / P in the battery cell is constant. N / P is the ratio of the product of the negative electrode active material gram capacity, the negative electrode surface density and the negative electrode active material content ratio to the product of the positive electrode active material gram capacity, the positive electrode surface density and the positive electrode active material content ratio. When the negative electrode active material gram capacity, the negative electrode active material content, the positive electrode active material gram capacity and the positive electrode active material content remain unchanged, the change in the ratio of the negative electrode surface density to the positive electrode surface density will affect the N / P parameter value. The positive and negative electrode surface density ratio remains unchanged to ensure that the negative electrode excess coefficient N / P remains unchanged, reducing the impact of the negative electrode excess coefficient on the experiment.

[0012] Step 2: pre-charging, forming, and overcharging the battery cell in sequence, and testing the AC internal resistance of the battery cell during the pre-charging and forming processes;

[0013] The cell internal resistance test method includes AC internal resistance test and DC internal resistance test. The cell internal resistance test of the present invention is preferably AC internal resistance test. During the DC internal resistance test, the cell needs to be cyclically charged and discharged, which will affect the internal performance of the cell and further affect subsequent tests. In order to reduce the impact on subsequent tests, the internal resistance test is preferably AC internal resistance test.

[0014] Step three: select the battery cell sample 1 with higher AC internal resistance during the pre-charging process for disassembly, select the battery cell sample 2 with higher AC internal resistance during the formation process for disassembly, and select the battery cell sample 3 with a set voltage value during the overcharging process for disassembly.

[0015] Step 4: Count the electrode foil breakage ratio and electrode light transmittance ratio of the battery sample 1, the battery sample 2, and the battery sample 3.

[0016] Step 5: When the electrode foil breaking ratio and the electrode light transmittance ratio suddenly change, the compaction density and the surface density of the battery cell are obtained.

[0017] During the mass production of battery cells, due to the relatively mature production process of batteries, electrode foil breakage and electrode light transmission rarely occur. For the test of the broken foil of the battery cell pole piece, a large number of battery cells are needed to verify the influence of the foil material on the broken foil of the battery cell pole piece, and the number of electrode foil breakage and electrode light transmission in the test is relatively small, so it is difficult to verify the influence of the foil material on the broken foil of the battery cell pole piece, and it is impossible to screen out the foil material that can improve the broken foil condition of the battery cell pole piece. In the method for obtaining the compaction density and surface density of the battery cell pole piece of the present invention, the compaction density and surface density when the electrode foil breakage ratio and the electrode light transmission ratio suddenly change during the pre-charging, formation, and overcharging processes are first obtained. The compaction density and surface density of the pole piece are used to make battery cells with different foil materials, and the method for obtaining the compaction density and surface density of the battery cell pole piece of the present invention is used to count the electrode foil breakage ratio and the electrode light transmission ratio of the battery cells with different foil materials, and the battery cell pole piece foil with the smallest electrode foil breakage ratio and electrode light transmission ratio is screened out in the battery cells with different foil materials.

[0018] In combination with the compaction density and surface density obtained in the method for obtaining the compaction density and surface density of the battery cell pole piece of the present invention, battery cells with different foil materials are made. On the one hand, when the compaction density and surface density of the pole piece are achieved, the battery cell pole piece is more likely to break and transmit light, and the number of broken foils and the number of light transmissions can be significantly increased, and a large number of battery cells are not required for testing. On the other hand, when the compaction density and surface density of the pole piece are achieved, although the electrode foil breaking and electrode light transmission are more obvious, most of the foil breaking and light transmission phenomena will not occur when testing the battery cell, resulting in the inability to distinguish the magnitude of the influence of the foil material on the electrode foil breaking and electrode light transmission from the number of foil breaking and light transmission of the battery cell pole piece. Since the compaction density and surface density are too large, the battery cell pole piece is extremely prone to foil breaking and light transmission. When testing battery cells with different foil materials, it will be impossible to distinguish the influence of different foil materials on the battery cell pole piece because the number of foil breaking and light transmission of the battery cells with different foil materials is too large, and the ratio of the number of foil breaking and light transmission of the battery cells with different foil materials is almost the same.

[0019] The battery cells are pre-charged, formed, and overcharged, and the electrodes are tested through the current and voltage changes in the battery cells. After the test, the battery cells with higher internal resistance are disassembled, and the proportion of broken electrode foil and electrode light transmittance is counted. When there is a problem with the battery cell structure, it is mainly judged by its internal resistance value, and its internal resistance will increase when the battery cell has broken foil, so the battery cell with higher internal resistance is selected for disassembly. The reason for the increase in the internal resistance of the battery cell is not necessarily caused by the broken foil of the electrode piece, but the broken foil of the electrode piece will cause the internal resistance of the battery cell to increase. Therefore, it cannot be judged that the electrode piece in the battery cell has broken foil based solely on the high resistance value of the battery cell. Further disassembly is required to determine whether the electrode piece in the battery cell has broken foil.

[0020] Furthermore, the foil material is one of aluminum foil, copper foil, nickel foil, iron foil and tin foil.

[0021] Furthermore, the foil material is copper foil.

[0022] Furthermore, the negative electrode compaction density of the battery cell is 1.40-1.85 g / cm 3 .

[0023] Furthermore, the negative electrode surface density of the battery cell is 150-300 g / m 2 .

[0024] Furthermore, the positive electrode surface density of the battery cell is 350-550 g / m 2 .

[0025] The negative electrode compaction density of the battery cell is 1.40-1.85g / cm 3 , the negative electrode surface density is 150-300 g / m 2 , the positive electrode surface density is 350-550 g / m 2When the compaction density and surface density of the negative electrode of the battery cell pole piece are within the above range, the compaction density and surface density are closer to the pole piece compaction density and surface density that can cause the number of broken foils of the battery cell pole piece to begin to increase significantly, and the cell compaction density and surface density when the electrode broken foil ratio and the electrode light transmittance ratio suddenly change during pre-charging, formation and overcharging can be obtained with fewer cells, and the compaction density and surface density in the above range are both within the normal use range of the battery cell electrode, and the pole piece compaction density and surface density begin to change within the normal use range, which can reduce the number of experimental cells and reduce the time for foil screening.

[0026] Furthermore, the battery cells with higher AC internal resistance are arranged from high to low AC internal resistance, and 10-30 battery cells are selected starting from the highest AC internal resistance.

[0027] Furthermore, the charging termination voltage of the battery cell is U 1 , the maximum withstand voltage is U 2 The voltage range of the overcharge process is set to U 1 -U 2 Preferably, when the battery cell is a 18650 cylindrical battery cell, the voltage value range is set to 4.2V-4.4V.

[0028] Furthermore, during the overcharging process, 2-4 voltage values ​​are selected in a set voltage value interval as the voltage of the battery cell during the overcharging process.

[0029] During the use of the battery, the battery may be overcharged due to the influence of the charging voltage. Therefore, overcharging is used as a test step, and the battery cells are overcharged with different voltage values ​​to test the electrode foil breakage and electrode transmittance ratio of the electrode after overcharging, to ensure that the foil selected in the subsequent battery cell electrode foil screening method can maintain good performance under overcharging conditions.

[0030] A method for screening a battery cell electrode foil comprises the following steps:

[0031] S01, using the above-mentioned method for obtaining the compaction density and surface density of the battery cell electrode piece to obtain the compaction density and surface density of the battery cell electrode piece;

[0032] S02, using foils of different materials and combining the compaction density and surface density obtained in S01, to manufacture cells of different foils;

[0033] S03, replace step 1 in the method for obtaining the compaction density and surface density of the battery cell electrode sheet with S02, use this method to count the electrode broken foil ratio and electrode transmittance ratio of the battery cells with different foil materials, and screen out the battery cell electrode sheet foil with the smallest electrode broken foil ratio and electrode transmittance ratio among the battery cells with different foil materials.

[0034] The present invention has the following advantages:

[0035] 1. The method for obtaining the compaction density and surface density of the electrode piece of the present invention performs pre-charging, formation and overcharging treatments on battery cells of the same material foil but different compaction densities and surface densities, so that the battery cells are in an environment of current and voltage changes. The compaction density and surface density that cause a sudden change in the electrode foil breaking ratio and the electrode transmittance ratio can be obtained more accurately through the electrode foil breaking ratio and the electrode transmittance ratio.

[0036] 2. The screening method of the electrode foil of the present invention uses the compaction density and surface density of the battery cell when the ratio of electrode foil breaking and electrode light transmission suddenly changes during the pre-charging, formation and overcharging process to make battery cells with different foil materials, so that the influence of different foil materials on electrode foil breaking and electrode light transmission is obvious, and the foil with low risk of electrode foil breaking and electrode light transmission can be selected from different foil materials as the electrode of the battery cell. The method of the present invention can measure the influence of different foil materials on the breaking of the battery cell electrode sheet with a small number of battery cells, reduce the screening time of the foil materials, and reduce the screening cost. DETAILED DESCRIPTION

[0037] In order to better explain the method of the present invention and make the steps and advantages of the method of the present invention more prominent, the present invention is described in detail below in conjunction with embodiments.

[0038] In the following embodiments, three different types A, B, and C of 18650 cylindrical cells produced by Shenzhen BAK Power Battery Co., Ltd. are used as experimental objects, but the method of the present invention does not limit the manufacturer, type, and model of the cell for obtaining the compaction density and the surface density and for foil screening. That is, the method of the present invention is not limited to the 18650 cylindrical cell produced by Shenzhen BAK Power Battery Co., Ltd. This method is applicable to cells produced by other manufacturers and square, soft-pack, and other types of cells.

[0039] In the method for obtaining compaction density and surface density of the present invention, the battery cells made of the same foil material may have different pole piece compaction densities in at least one of the properties of the positive electrode compaction density and the negative electrode compaction density. Their surface densities may be the same or different, but the ratio of the positive and negative electrode surface densities is the same. Since the expansion of the negative electrode foil has a greater impact on the foil material, the battery cells with different negative electrode compaction density, the same positive electrode compaction density, different surface density, and the same positive and negative electrode compaction density ratio are used for experiments in the following embodiments, but the method of the present invention is not limited to this. The experimental battery cells of the method of the present invention include battery cells with different positive and negative electrode compaction densities made of the same foil material, and the same surface density; including battery cells with different positive electrode compaction density, the same negative electrode compaction density, different surface density, and the same positive and negative electrode surface density ratio made of the same foil material, etc.

[0040] Embodiment 1

[0041] This embodiment uses cylindrical battery cell 18650-A as the experimental object.

[0042] The method of the present invention is used to obtain the compaction density and surface density of the battery cell electrode sheet, and the steps are as follows:

[0043] Step 1

[0044] The same foil material is used to make cells with different compaction density and surface density of the cell pole piece. The cells are grouped. The compaction density of the negative electrode piece of the first group of cells is 1.55 g / cm 3 , surface density is 240g / m 2 The compaction density of the negative electrode sheets of the subsequent groups of cells increases to the maximum compaction density of the sheet with this attribute, 1.96 g / cm 3 When the value exceeds this value, it is difficult for the electrode to absorb liquid. The incremental value of the negative electrode is 1.55 g / cm 3 ×3%, its surface density also increases, the increment value is 240g / m 2 ×5%; the surface density of the positive electrode of the first group of cells is 400g / m 2 The surface density of the positive electrode of the subsequent group of cells increases by 400g / m 2 ×5%, the compaction density of the positive electrode sheet remains unchanged. The cell grouping design is shown in the following table:

[0045]

[0046] The cell grouping scheme is shown in the following table:

[0047]

[0048] The battery cells are manufactured according to the negative electrode compaction density, negative electrode surface density and positive electrode surface density in the above table. The ratio of the negative electrode surface density to the positive electrode surface density remains unchanged. Other parameters and materials used remain unchanged. The number of battery cells in each group is 50.

[0049] The compaction density and surface density of the negative electrode sheet both increase, while the surface density of the positive electrode sheet also increases, while the compaction density of the positive electrode remains unchanged. The purpose of this design is that the expansion of the negative electrode has a greater impact on the foil. When obtaining the compaction density and surface density of the battery cell, in order to reduce the impact of the negative electrode excess coefficient on the test, only the surface density of the positive electrode sheet increases, ensuring that the surface density ratio of the two types of electrode sheets remains unchanged, thereby ensuring that the N / P parameter value remains unchanged and reducing the impact on the test. N / P is the ratio of the product of the gram capacity of the negative electrode active material, the surface density of the negative electrode and the content ratio of the negative electrode active material to the product of the gram capacity of the positive electrode active material, the surface density of the positive electrode and the content ratio of the positive electrode active material. When the gram capacity of the negative electrode active material, the content of the negative electrode active material, the gram capacity of the positive electrode active material and the content of the positive electrode active material remain unchanged, the change in the ratio of the negative electrode surface density to the positive electrode surface density will affect the N / P parameter value.

[0050] Step 2 and Step 3

[0051] The grouped battery cells are pre-charged, and the internal resistance of the battery cells in different groups is tested after pre-charging. From each group, the battery sample 1 with higher AC internal resistance during the pre-charging process is selected for disassembly. The number of battery cells in the battery sample 1 is 15, and the number of electrode foil breakage and electrode light transmittance in each group is recorded.

[0052] The remaining cells in each group are formed, and after formation, AC internal resistance tests are performed on the cells in different groups. Cell sample 2 with higher AC internal resistance during the formation process is selected from each group for disassembly. The number of cells in cell sample 2 is 15, and the number of electrode foil breakage and electrode light transmission in each group is recorded.

[0053] The remaining cells in each group are overcharged in groups. The charging termination voltage U of the 18650-A cylindrical cell is 1 is 4.2V, the maximum withstand voltage U 2 The voltage value of each group is set to 4.25 V and 4.30 V, and the cell sample 3 with the set voltage value of 4.25 V and 4.30 V during overcharging is selected for disassembly. The number of cells in the cell sample 3 is 20. The number of electrode foil breakage and electrode light transmission in each group is recorded.

[0054] Step 4

[0055] The electrode foil breakage ratio and electrode light transmittance ratio of battery sample 1, battery sample 2, and battery sample 3 are statistically analyzed, and the statistical results are shown in the following table:

[0056]

[0057] It can be seen from the table that the electrode foil breakage ratio and the electrode light transmittance ratio have obvious mutations in the battery cell group No. 4.

[0058] Step 5

[0059] When the electrode foil breaking ratio and the electrode light transmittance ratio suddenly change, the compaction density and surface density of the battery cell are obtained, that is, the compaction density and surface density of the battery cell with sequence number 4 are obtained, and the compaction density of the negative electrode is 1.69 g / cm 3 The negative electrode surface density is 276 g / m 2 The positive electrode surface density is 460 g / m 2 .

[0060] The method of the present invention is used to screen the cell pole sheet foil of the cylindrical cell 18650-A model, and the steps are as follows:

[0061] S01: The compaction density of the negative electrode of the battery cell obtained by the above method is 1.69 g / cm 3 The negative electrode surface density is 276 g / m 2 The positive electrode surface density is 460 g / m 2 .

[0062] S02: The foil material used for cylindrical battery cell 18650-A model is copper foil 1. Now, the influence of copper foil 2 and copper foil 3 on electrode foil breakage and electrode light transmittance is tested and compared with the influence of copper foil 1 on electrode foil breakage and electrode light transmittance. The battery cell is made of copper foil 1, copper foil 2 and copper foil 3 in combination with the obtained battery cell compaction density and surface density. The foil materials are copper foil 1, copper foil 2 and copper foil 3. Copper foil 2, copper foil 3 and copper foil 1 are produced by different manufacturers, and their production processes and structures are different. The number of battery cells made of these three foil materials is 50 respectively.

[0063] S03: Pre-charge, form and overcharge the manufactured copper foil 1-pole cell, copper foil 2-pole cell and copper foil 3-pole cell. The group number of the copper foil 1-pole cell is 1, the group number of the copper foil 2-pole cell is 2, and the group number of the copper foil 3-pole cell is 3. The copper foil 1-pole cell group is the control group, and the others are the experimental groups. The electrode foil breakage ratio and electrode light transmittance ratio generated during the pre-charge, formation and overcharge process are counted. The statistics are shown in the following table:

[0064]

[0065] It can be seen from the above table that during the pre-charging, formation and overcharging process, the electrode foil breaking and light transmission ratio of the copper foil 1 electrode cell is significantly lower than that of the copper foil 2 electrode cell and the copper foil 3 electrode cell. Using copper foil 2 and copper foil 3 to make the electrode of the cylindrical battery 18650-A model will not improve the electrode foil breaking and light transmission of the battery cell, so foil 1 is selected as the electrode foil of the cylindrical battery 18650-A model.

[0066] Embodiment 2

[0067] This embodiment uses cylindrical battery cell 18650-B as the experimental object.

[0068] The method of the present invention is used to obtain the compaction density and surface density of the battery cell electrode sheet, and the steps are as follows:

[0069] Step 1

[0070] The same foil material is used to make cells with different compaction density and surface density of the cell pole piece. The cells are grouped. The compaction density of the negative electrode piece of the first group of cells is 1.60 g / cm 3 , surface density is 250g / m 2 The compaction density of the negative electrode sheets of the subsequent groups of cells increases to a maximum value of 1.84 g / cm 3 When this value is exceeded, it is difficult for the negative electrode to absorb liquid. The incremental value of the compacted density of the negative electrode is 1.60 g / cm 3 ×2%, its surface density also increases, the increment is 250g / m 2 ×4%; the surface density of the positive electrode of the first group of cells is 420g / m 2 The surface density of the positive electrode of the subsequent group of cells increases by 420g / m 2 ×4%, the compaction density of the positive electrode sheet remains unchanged. The battery cell grouping scheme is shown in the following table:

[0071]

[0072] The battery cells are manufactured according to the negative electrode compaction density, negative electrode surface density and positive electrode surface density in the above table. The ratio of the negative electrode surface density to the positive electrode surface density remains unchanged. Other parameters and materials used remain unchanged. The number of battery cells in each group is 45.

[0073] Step 2 and Step 3

[0074] The grouped battery cells are pre-charged, and the internal resistance of the battery cells in different groups is tested after pre-charging. From each group, the battery sample 1 with higher AC internal resistance during the pre-charging process is selected for disassembly. The number of battery cells in the battery sample 1 is 15, and the number of electrode foil breakage and electrode light transmittance in each group is recorded.

[0075] The remaining cells in each group are formed, and after formation, AC internal resistance tests are performed on the cells in different groups. Cell sample 2 with higher AC internal resistance during the formation process is selected from each group for disassembly. The number of cells in cell sample 2 is 15, and the number of electrode foil breakage and electrode light transmission in each group is recorded.

[0076] The remaining cells in each group are overcharged in groups. The charging termination voltage U of the 18650-B cylindrical cell is 1 is 4.2V, the maximum withstand voltage U 2The voltage value of each group is set to 4.20V and 4.30V, and the cell sample 3 with the set voltage value of 4.20V and 4.30V during overcharging is selected for disassembly. The number of cells in the cell sample 3 is 15. The number of electrode foil breakage and electrode light transmission in each group is recorded.

[0077] Step 4

[0078] The electrode foil breaking ratio and electrode light transmission ratio of battery sample 1, battery sample 2, and battery sample 3 were counted. The statistical results are shown in the following table:

[0079]

[0080] It can be seen from the table that the electrode foil breakage ratio and the electrode light transmittance ratio have obvious mutations in the battery cell group with serial number 7.

[0081] Step 5

[0082] When the electrode foil breaking ratio and the electrode light transmittance ratio suddenly change, the compaction density and surface density of the battery cell are obtained, that is, the compaction density and surface density of the battery cell with sequence number 7 are obtained, and the compaction density of the negative electrode is 1.792g / cm 3 The negative electrode surface density is 310 g / m 2 The positive electrode surface density is 520.4 g / m 2 .

[0083] The method of the present invention is used to screen the cell pole foil material of the cylindrical cell 18650-B model, and the steps are as follows:

[0084] S01: The compaction density of the negative electrode of the battery cell obtained by the above method is 1.792g / cm 3 The negative electrode surface density is 310 g / m 2 The positive electrode surface density is 520.4 g / m 2 .

[0085] S02: The foil material used for cylindrical battery cell 18650-B model is copper foil 4. Now we test the influence of copper foil 5 and copper foil 6 on electrode foil breakage and electrode light transmittance, and compare it with the influence of copper foil 4 on electrode foil breakage and electrode light transmittance. The battery cell is made of copper foil 4, copper foil 5 and copper foil 6 in combination with the obtained battery cell compaction density and surface density. The foil materials are copper foil 4, copper foil 5 and copper foil 6. Copper foil 5, copper foil 6 and copper foil 4 are produced by different manufacturers, and their production processes and structures are different. The number of battery cells made of these three foil materials is 50 respectively.

[0086] S03: Pre-charge, form and overcharge the manufactured copper foil 4-pole sheet battery cells, copper foil 5-pole sheet battery cells and copper foil 6-pole sheet battery cells. The group number of the copper foil 4-pole sheet battery cells is 1, the group number of the copper foil 5-pole sheet battery cells is 2, and the group number of the copper foil 6-pole sheet battery cells is 3. The copper foil 1-pole sheet battery group is the control group, and the others are the experimental groups. The electrode foil breakage ratio and electrode light transmittance ratio generated during the pre-charge, formation and overcharge charging process are counted. The statistics are shown in the following table:

[0087]

[0088] It can be seen from the above table that: during the pre-charging, formation and overcharging process, the electrode foil breaking and light transmittance ratio of the copper foil 5 electrode sheet battery cell is significantly lower than that of the copper foil 4 electrode sheet battery cell. The electrode foil breaking and light transmittance ratio of the copper foil 6 electrode sheet battery cell is higher than that of the copper foil 4 electrode sheet battery cell. Using copper foil 5 to make the electrode sheet of the cylindrical battery cell 18650-B model can improve the situation of the electrode foil breaking of the battery cell, but using copper foil 6 to make the electrode sheet of the cylindrical battery cell 18650-B model will not improve the situation of the electrode foil breaking of the battery cell, so foil 5 is selected as the electrode foil material for the cylindrical battery cell 18650-B model.

[0089] Embodiment 3

[0090] This embodiment uses cylindrical battery cell 18650-C as the experimental object.

[0091] The method of the present invention is used to obtain the compaction density and surface density of the battery cell electrode sheet, and the steps are as follows:

[0092] Step 1

[0093] The same foil material is used to make cells with different compaction density and surface density of the cell pole piece. The cells are grouped. The compaction density of the negative electrode piece of the first group of cells is 1.70 g / cm 3 , surface density is 200g / m 2 The compaction density of the negative electrode sheets of the subsequent groups of cells increases to a maximum value of 1.85 g / cm 3 When the value exceeds this value, it is difficult for the negative electrode to absorb liquid. The incremental value of the compacted density of the negative electrode is 1.70 g / cm 3 ×3%, its surface density also increases, the increment is 200g / m 2 ×6%; the surface density of the positive electrode of the first group of cells is 420g / m 2 The surface density of the positive electrode of the subsequent group of cells increases by 420g / m 2 ×6%, the compaction density of the positive electrode sheet remains unchanged. The battery cell grouping scheme is shown in the following table:

[0094]

[0095] The battery cells are manufactured according to the negative electrode compaction density, negative electrode surface density and positive electrode surface density in the above table. The ratio of the negative electrode surface density to the positive electrode surface density remains unchanged. Other parameters and materials used remain unchanged. The number of battery cells in each group is 60.

[0096] Step 2 and Step 3

[0097] The grouped battery cells are pre-charged, and the internal resistance of the battery cells in different groups is tested after pre-charging. From each group, the battery sample 1 with higher AC internal resistance during the pre-charging process is selected for disassembly. The number of battery cells in the battery sample 1 is 20, and the number of electrode foil breakage and electrode light transmittance in each group is recorded.

[0098] The remaining cells in each group are formed, and after formation, AC internal resistance tests are performed on the cells in different groups. Cell sample 2 with higher AC internal resistance during the formation process is selected from each group for disassembly. The number of cells in cell sample 2 is 20, and the number of broken electrode foils and light-transmitting electrodes in each group is recorded.

[0099] The remaining cells in each group are overcharged in groups. The charging termination voltage U of the 18650-C cylindrical cell is 1 is 4.2V, the maximum withstand voltage U 2 The voltage value of each group is set to 4.25V, 4.30V, and 4.35V, and the cell sample 3 with the set voltage value of 4.25V, 4.30V, and 4.35V during overcharging is selected for disassembly. The number of cells in the cell sample 3 is 20. The number of electrode foil breakage and electrode light transmission in each group is recorded.

[0100] Step 4

[0101] The electrode foil breaking ratio and electrode light transmission ratio of battery sample 1, battery sample 2, and battery sample 3 were counted. The statistical results are shown in the following table:

[0102]

[0103] It can be seen from the table that the electrode foil breaking ratio and electrode light transmission ratio have obvious mutations in the battery group with serial number 3. Compared with the battery group with serial number 2, the electrode foil breaking ratio and electrode light transmission ratio of the battery group have increased significantly. The compaction density of the solid battery electrode piece is the median of the compaction density of group number 2 and group number 3. Similarly, the surface density of the battery electrode piece is the median of the compaction density of group number 2 and group number 3. The compaction density of the negative electrode piece of the battery is 1.777 g / cm 3 The negative electrode surface density is 218 g / m 2 The ratio of the positive electrode surface density to the negative electrode surface density remains unchanged, so its surface density is 457.8 g / m 2In view of the fact that the broken foil ratio and light transmittance ratio of the battery cells in group number 3 have increased significantly, the screening values ​​of the negative electrode compaction density and surface density are taken as the median of group number 2 and group number 3 in order to obtain more accurate values ​​of the compaction density and surface density of the battery cells, thereby ensuring the accuracy of subsequent screening.

[0104] It can also be seen from the above table that the changes in the compaction density and surface density of the negative electrode sheet of the cylindrical battery 18650-C model battery have a greater impact on the electrode sheet breaking and light transmission. In order to obtain more accurate compaction density and surface density of the battery with a sudden change in the ratio of electrode breaking and light transmission, the incremental values ​​of the compaction density and surface density of the negative electrode should be selected as small values ​​during the experiment. In this embodiment, the incremental value of the compaction density of the negative electrode sheet is 1.70 g / cm 3 ×3%, the incremental value of the negative electrode surface density is 200g / m 2 ×6%, from the experimental battery cell pole piece foil situation, the negative pole piece compaction density linear increase value should be selected than 1.70 g / cm 3 ×3% smaller value, the negative electrode sheet surface density increment value should be selected to be greater than 200g / m 2 ×6% smaller value makes the selected compaction density and surface density screening values ​​more accurate. In this embodiment, the median of the compaction density and surface density of group number 2 and group number 3 is selected to increase the accuracy of the compaction density and surface density obtained.

[0105] Step 5

[0106] When the electrode foil breaking ratio and the electrode light transmittance ratio suddenly change, the compaction density and surface density of the battery cell are obtained, that is, the median of the compaction density and surface density of the battery cells with sequence numbers 2 and 3 is obtained, and the compaction density of the negative electrode sheet is 1.777 g / cm 3 The negative electrode surface density is 218 g / m 2 The positive electrode surface density is 457.8 g / m 2 .

[0107] The method of the present invention is used to screen the cell pole sheet foil of the cylindrical cell 18650-C model, and the steps are as follows:

[0108] S01: The compaction density of the negative electrode sheet of the battery cell obtained by the above method is 1.777 g / cm 3 The negative electrode surface density is 218 g / m 2 The positive electrode surface density is 457.8 g / m 2 .

[0109] S02: The foil material used for cylindrical battery cell 18650-C model is copper foil 7. Now, the influence of copper foil 8, copper foil 9, and copper foil 10 on electrode foil breakage and electrode light transmittance is tested and compared with the influence of copper foil 4 on electrode foil breakage and electrode light transmittance. The battery cell is made of copper foil 7, copper foil 8, copper foil 9, and copper foil 10 in combination with the obtained battery cell compaction density and surface density. The foil materials are copper foil 7, copper foil 8, copper foil 9, and copper foil 10. Copper foil 7, copper foil 8, copper foil 9, and copper foil 10 are produced by different manufacturers, and their production processes and structures are different. The number of battery cells made of these four foil materials is 60 respectively.

[0110] S03: Pre-charge, form and overcharge the manufactured copper foil 7-pole sheet battery cells, copper foil 8-pole sheet battery cells, copper foil 9-pole sheet battery cells and copper foil 10-pole sheet battery cells. The group number of the copper foil 7-pole sheet battery cells is 1, the group number of the copper foil 8-pole sheet battery cells is 2, the group number of the copper foil 9-pole sheet battery cells is 3, and the group number of the copper foil 10-pole sheet battery cells is 4. The copper foil 7-pole sheet battery group is the control group, and the others are experimental groups. The proportion of electrode foil breakage and the proportion of electrode light transmittance generated during the pre-charging, forming and overcharging process are counted. The statistics are shown in the following table:

[0111]

[0112] It can be seen from the above table that: during the pre-charging, formation and overcharging process, the electrode foil breaking and light transmittance ratio of the copper foil 8 electrode sheet battery cell and the copper foil 10 electrode sheet battery cell is significantly lower than that of the copper foil 7 electrode sheet battery cell; the electrode foil breaking and light transmittance ratio of the copper foil 9 electrode sheet battery cell is higher than that of the copper foil 7 electrode sheet battery cell. Using copper foil 8 and foil 10 to make the electrode sheet of the cylindrical battery cell 18650-C model can improve the situation of the electrode foil breaking of the battery cell, but using copper foil 9 to make the electrode sheet of the cylindrical battery cell 18650-C model will not improve the situation of the electrode foil breaking of the battery cell. Comparing foil 8 with foil 10, the electrode foil breaking and light transmittance ratio of foil 10 is smaller, so foil 10 is selected as the electrode foil of the cylindrical battery cell 18650-C model.

[0113] In the exemplified embodiments, the compaction density and surface density of the negative electrode plate and the surface density of the positive electrode are used as variables. However, the method of the present invention can also use the compaction density and surface density of the positive electrode plate and the surface density of the negative electrode as incremental variables. The test effect is the same as that of the negative electrode plate. In the test process, the compaction density and surface density of the electrode plate with different properties are selected as variables according to the specific situation.

[0114] By using the first, second and third embodiments of the method of the present invention, a small number of battery cells can be used to screen out foil materials with little effect on the broken foil of the battery cell pole piece from different foil materials, so that the foil materials can be used to produce the battery cell pole piece, thereby improving the performance and reliability of the battery cell. The method of the present invention can not only be used to screen the battery cell pole piece foil materials, but also to verify the effect of improving the broken foil of the battery cell pole piece. For example, the pole piece compaction density and surface density that cause a significant increase in the number of broken foil of the battery cell pole piece can be screened out, and the pole piece compaction density and surface density can be used to make battery cells with different pole piece winding shapes or different pole piece stacking methods, and verify whether the change in the pole piece winding shape or the pole piece stacking method has the effect of improving the broken foil of the battery cell pole piece.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention rather than to limit them. Although the embodiments of the present invention have been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the embodiments of the present invention can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for obtaining the compaction density and surface density of a pole piece, It is characterized in that The steps include: Step 1: Using the same material foil to make battery cells with different compaction densities of battery cell pole pieces and the same positive and negative electrode surface density ratio; Step 2: pre-charging, forming, and overcharging the battery cell in sequence, and testing the AC internal resistance of the battery cell during the pre-charging and forming processes; Step 3: Select the battery sample 1 with higher AC internal resistance during the pre-charging process for disassembly, select the battery sample 2 with higher AC internal resistance during the formation process for disassembly, and select the battery sample 3 with a set voltage value during the overcharging process for disassembly; Step 4: Counting the electrode foil breaking ratio and electrode light transmission ratio of the battery sample 1, the battery sample 2, and the battery sample 3; Step 5: When the electrode foil breaking ratio and the electrode light transmittance ratio suddenly change, the compaction density and the surface density of the battery cell are obtained.

2. The method for obtaining the compaction density and surface density of the pole piece according to claim 1, Features: The foil material is one of aluminum foil, copper foil, nickel foil, iron foil and tin foil.

3. The method for obtaining the compaction density and surface density of the pole piece according to claim 2, Features: The foil material is copper foil.

4. The method for obtaining the compaction density and surface density of the pole piece according to claim 1, Features: The negative electrode compaction density of the battery cell is 1.40-1.85 g / cm 3 .

5. The method for obtaining the compaction density and surface density of the pole piece according to claim 1, Features: The negative electrode surface density of the battery cell is 150-300 g / m 2 .

6. The method for obtaining the compaction density and surface density of the pole piece according to claim 1, Features: The positive electrode surface density of the battery cell is 350-550 g / m 2 .

7. The method for obtaining the compaction density and surface density of the pole piece according to claim 1, Features: The battery cells with higher AC internal resistance are arranged from high to low AC internal resistance, and 10-30 battery cells are selected starting from the highest AC internal resistance.

8. The method for obtaining the compaction density and surface density of the pole piece according to claim 1, Features: The charging termination voltage of the battery cell is U 1 , the maximum withstand voltage is U 2 The voltage interval of the voltage value set during the overcharging process is U 1 -U 2 .

9. The method for obtaining the compaction density and surface density of the pole piece according to claim 8, Features: During the overcharging process, 2-4 voltage values ​​are selected in the voltage interval of the set voltage value as the set voltage value during the overcharging process.

10. A method for screening electrode foil, It is characterized in that The steps include: S01, obtaining the compaction density and surface density of the electrode sheet of the battery cell by using the method for obtaining the compaction density and surface density of the electrode sheet as described in any one of claims 1 to 7; S02, using foils of different materials and combining the compaction density and surface density obtained in S01, to manufacture battery cells of different foils; S03, replacing step 1 in the method for obtaining the compacted density and surface density of the electrode sheet according to any one of claims 1-7 with S02, using this method to count the electrode broken foil ratio and electrode transmittance ratio of the battery cells with different foil materials, and screening out the battery cell electrode sheet foil with the smallest electrode broken foil ratio and electrode transmittance ratio among the battery cells with different foil materials.

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