Method for preparing battery pole piece, battery pole piece and battery

Abstract

The application provides a battery pole piece preparation method and a battery pole piece, and relates to the technical field of secondary batteries.The battery pole piece preparation method and the battery pole piece provided by the application have the following characteristics: the average porosity of the negative active material coating on the negative center region of the negative pole foil is a first porosity; the average porosity of the negative active material coating on the negative OH region of the negative pole foil is a second porosity; the second porosity is greater than the first porosity; in the discharge process of a lithium ion battery, the movement speed of lithium ions in the active material coating of the negative OH region of the negative pole foil can be improved, so that the amount of lithium ions in the negative OH region of the negative pole foil returning to the positive pole is increased when the discharge cut-off condition is reached, and then the capacity loss phenomenon caused by the discharge of lithium ions in the prior art is relieved.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to a method for preparing a battery electrode, the battery electrode, and a battery. Background Technology

[0002] During the charging process of a lithium-ion battery, if there are no sites on the negative electrode to accept lithium ions, lithium plating will occur on the surface of the negative electrode. Therefore, in the initial design stage, the capacity of the negative electrode often needs to be over-designed, such as an overhang design.

[0003] In this context, "overhang" refers to the portion of the active material coating on the negative electrode that extends beyond the active material coating on the positive electrode. In other words, the active material coating on the negative electrode is larger than that on the positive electrode. This overhang provides additional lithium intercalation sites during lithium-ion battery charging, thereby reducing the risk of lithium plating on the negative electrode to some extent.

[0004] The inventors of this application have discovered that during the resting phase after charging of a lithium-ion battery, lithium in the central region of the negative electrode (i.e., the non-overhang region) diffuses to the edge region (i.e., the overhang region; abbreviated as OH region) under the influence of the concentration gradient. However, during the subsequent discharge process, especially when the current density is high, as lithium in the negative electrode active material coating returns to the positive electrode, only a small portion of the lithium ions in the OH region return to the positive electrode when the discharge cutoff condition is reached, resulting in capacity loss.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a battery electrode, a battery electrode, and a battery, which aims to alleviate the capacity loss phenomenon caused by lithium-ion discharge in the prior art.

[0007] A first aspect of the present invention provides a method for preparing a battery electrode, comprising the following steps: providing a negative electrode foil, wherein the surface of the negative electrode foil is divided into a connected negative electrode central region and a first OH region; providing a negative electrode coating material, applying the negative electrode coating material to the negative electrode central region and the first OH region of the negative electrode foil; treating the negative electrode coating material applied to the negative electrode foil to form a negative electrode active material coating; wherein the average porosity of the negative electrode active material coating located in the negative electrode central region of the negative electrode foil is a first porosity; the average porosity of the negative electrode active material coating located in the first OH region of the negative electrode foil is a second porosity; the second porosity is greater than the first porosity.

[0008] A second aspect of the present invention provides a battery electrode sheet, comprising: a negative electrode foil having a surface divided into a connected negative electrode central region and an OH region; and a negative electrode active material coating formed on the negative electrode foil, wherein the average porosity of the negative electrode active material coating located in the negative electrode central region of the negative electrode foil is a first porosity, and the average porosity of the negative electrode active material coating located in the negative electrode OH region of the negative electrode foil is a second porosity, the second porosity being greater than the first porosity.

[0009] A third aspect of the present invention provides a battery comprising the battery electrode sheet described above.

[0010] The battery electrode preparation method, battery electrode, and battery provided by this invention utilize a first porosity for the average porosity of the negative electrode active material coating located in the negative electrode center region of the negative electrode foil, and a second porosity for the average porosity of the negative electrode active material coating located in the negative electrode OH region of the negative electrode foil. The second porosity is greater than the first porosity. Consequently, during the discharge process of the lithium-ion battery, the movement speed of lithium ions in the active material coating in the negative electrode OH region of the negative electrode foil can be increased. This increases the amount of lithium ions returning to the positive electrode in the negative electrode OH region of the negative electrode foil when the discharge cutoff condition is reached, thereby mitigating the capacity loss phenomenon caused by lithium-ion discharge in the prior art. Attached Figure Description

[0011] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0012] Figure 1 This is a schematic diagram of the structure of the battery negative electrode sheet provided by the present invention;

[0013] Figure 2 This is a schematic diagram of the structure of the positive electrode sheet of the battery provided by the present invention.

[0014] Icons: 10 - Negative electrode OH region; 12 - First OH region; 14 - Second OH region; 20 - Negative electrode center region; 30 - Positive electrode edge region; 32 - First edge region; 34 - Second edge region; 40 - Positive electrode center region. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the present invention clearer, the following description will be provided in conjunction with the embodiments of the present invention and the accompanying drawings. Figure 1 and Figure 2The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention can be arranged and designed in various different configurations.

[0016] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0017] A first aspect of the present invention provides a method for preparing a battery electrode, comprising the following steps: providing a negative electrode foil, wherein the surface of the negative electrode foil is divided into a connected negative electrode central region 20 and a first OH region 12; providing a negative electrode coating material, applying the negative electrode coating material to the negative electrode central region 20 and the first OH region 12 of the negative electrode foil; treating the negative electrode coating material applied to the negative electrode foil to form a negative active material coating; wherein the average porosity of the negative active material coating located on the negative electrode central region 20 of the negative electrode foil is a first porosity; the average porosity of the negative active material coating located on the first OH region 12 of the negative electrode foil is a second porosity; the second porosity is greater than the first porosity.

[0018] The battery electrode preparation method provided by this invention, during the discharge process of a lithium-ion battery, because the average porosity of the negative electrode active material coating on the first OH region 12 of the negative electrode foil is greater than the average porosity of the negative electrode active material coating on the central region 20 of the negative electrode foil (that is, the second porosity is greater than the first porosity), can increase the movement speed of lithium ions in the active material coating of the first OH region 12 of the negative electrode foil, thereby increasing the amount of lithium ions returning to the positive electrode in the first OH region 12 of the negative electrode foil when the discharge cutoff condition is reached, thereby alleviating the capacity loss phenomenon caused by lithium ion discharge in the prior art.

[0019] Specifically, in the prior art, when the porosity of the active material coating on the negative electrode center region and the negative electrode first OH region is the same, when the lithium battery is charging, since there is no corresponding positive electrode active material coating position in the negative electrode first OH region, most of the lithium ions in the negative electrode first OH region are lithium ions from the negative electrode center region moving towards the negative electrode first OH region (this is based on the fact that the lithium ion concentration in the negative electrode center region is greater than that in the negative electrode first OH region, and the lithium ions migrate due to the influence of the concentration gradient). When the lithium battery is discharging, fewer lithium ions migrate out of the negative electrode first OH region, resulting in capacity loss. For ease of description later, in the prior art, the amount of lithium ions migrating into the negative electrode first OH region when the lithium battery is charging will be denoted as A; and the amount of lithium ions migrating out of the negative electrode first OH region when the lithium battery is discharging will be denoted as B.

[0020] In the technical solution of this application, when the porosity of the active material coating on the negative electrode central region 20 and the negative electrode first OH region 12 is inconsistent, when the lithium battery is charged, since there is no corresponding positive electrode active material coating position in the negative electrode first OH region 12, most of the lithium ions in the negative electrode first OH region 12 are obtained by lithium ions in the negative electrode central region 20 moving to the negative electrode first OH region 12 (this is based on the fact that the lithium ion concentration in the negative electrode central region 20 is greater than that in the negative electrode first OH region 12, and the lithium ions migrate due to the influence of the concentration gradient; it is also based on the fact that the porosity of the active material coating in the negative electrode central region 20 is less than that in the negative electrode first OH region 12, and more lithium ions move to the negative electrode first OH region 12). When the lithium battery is discharged, the lithium ions migrating out of the negative electrode first OH region 12 are affected by the fact that the porosity of the active material coating in the negative electrode central region 20 is less than that in the negative electrode first OH region 12, and more lithium ions migrate out of the negative electrode first OH region 12, thereby alleviating the capacity loss phenomenon.

[0021] For ease of description later, in the technical solution of this application, when the lithium battery is charging, the amount of lithium ions that originally migrate into the first OH region 12 of the negative electrode due to the influence of the lithium ion concentration gradient is denoted as C, and the amount of lithium ions that migrate into the first OH region 12 of the negative electrode due to the influence of the porosity of the active material coating of the central region 20 of the negative electrode being less than the porosity of the active material coating of the first OH region 12 of the negative electrode is denoted as D; when the lithium battery is discharging, the amount of lithium ions that originally need to migrate out of the first OH region 12 of the negative electrode is denoted as E, and the amount of lithium ions that migrate out of the first OH region 12 of the negative electrode due to the influence of the porosity of the active material coating of the central region 20 of the negative electrode being less than the porosity of the active material coating of the first OH region 12 of the negative electrode is denoted as F.

[0022] As verified by the inventors of this application, (AB) > (C + DEF). Therefore, the technical solution of this application can alleviate the capacity loss phenomenon caused by lithium-ion discharge in the prior art.

[0023] It should be noted that since the coating on the negative electrode is in a fluid state after application, the porosity of the negative electrode active material coating formed on the negative electrode central region 20 of the negative electrode foil may be different at different locations, and the porosity of the negative electrode active material coating on the first OH region 12 of the negative electrode foil may also be different at different locations. Therefore, the above content uses the description related to "average porosity", where average porosity refers to the porosity value of the active material coating in the corresponding region.

[0024] It should also be noted that this application uses lithium-ion batteries as an example for illustration, but the technical solution of this application is not limited to lithium-ion batteries. Other types of cells, such as sodium-ion batteries, can also adopt the technical solution of this application. Furthermore, the provided negative electrode coating material includes a first negative electrode coating material and a second negative electrode coating material; applying the negative electrode coating material to the negative electrode center region 20 and the first OH region 12 of the negative electrode foil material specifically includes: applying the first negative electrode coating material to the negative electrode center region 20 of the negative electrode foil material and applying the second negative electrode coating material to the first OH region 12 of the negative electrode foil material; processing the negative electrode coating material applied to the negative electrode foil material to form a negative active material coating, specifically including: processing the first negative electrode coating material applied to the negative electrode center region 20 of the negative electrode foil material and the second negative electrode coating material applied to the first OH region 12 of the negative electrode foil material to form a negative active material coating with a first porosity and a negative active material coating with a second porosity.

[0025] In this way, a negative electrode active material coating with an average porosity of the first porosity located on the negative electrode center region 20 of the negative electrode foil can be formed based on different negative electrode coatings, and a negative electrode active material coating with an average porosity of the second porosity located on the negative electrode first OH region 12 of the negative electrode foil can be formed. This is beneficial for achieving a second porosity greater than the first porosity. At the same time, it can minimize the occurrence of situations where other steps after the coating step need to be "differently treated for the negative electrode center region 20 and the first OH region 12 of the negative electrode foil" during the electrode preparation process, thereby reducing the complexity of the process.

[0026] It should be noted that in other embodiments, the same negative electrode coating material can be applied to both the negative electrode center region and the first OH region of the negative electrode foil. Different treatments can be applied to the negative electrode center region and the first OH region of the negative electrode foil in subsequent steps after the coating step (e.g., applying the same amount of pore-forming agent, but using different temperatures for different regions during heat treatment to cause different degrees of decomposition of the pore-forming agent in different regions, thereby achieving different porosities in different regions). It should be noted that this approach requires relatively strict temperature treatment for different regions, making the process more complex and costly. This will result in a second porosity greater than the first porosity.

[0027] In some examples, the negative electrode active material, binder, conductive agent and solvent are mixed to form the first negative electrode coating; the negative electrode active material, binder, conductive agent, solvent and pore-forming agent are mixed to form the second negative electrode coating.

[0028] In other examples, a negative electrode coating is provided; a portion of the negative electrode coating is taken to form a first negative electrode coating, and another portion of the negative electrode slurry is taken and a pore-forming agent is added to form a second negative electrode coating. In this way, the negative electrode active material, binder, conductive agent and solvent in the mixed negative electrode coating can be mixed in the same step, thereby reducing the complexity of the process.

[0029] Therefore, this application distinguishes between the first and second negative electrode coatings based on whether or not a pore-forming agent is added. In other words, the second negative electrode coating contains an additional pore-forming agent compared to the first negative electrode coating. Of course, in some embodiments, the first negative electrode coating may contain a certain amount of pore-forming agent, while the second negative electrode coating may contain a greater amount of pore-forming agent than the first. This application does not limit the timing of adding the pore-forming agent.

[0030] Furthermore, the pore-forming agent is made of a component that can decompose into gas upon heating. In this way, during the subsequent heat treatment of the negative electrode sheet to be coated, the additional pore-forming agent added to the second negative electrode to be coated decomposes into gas upon heating, so as to use the gas to form a negative electrode active material coating with a large porosity on the first OH region 12 of the negative electrode foil.

[0031] Preferably, the pore-forming agent is at least one of ammonium chloride, ammonium oxalate, ammonium hydrogen oxalate, and p-toluenesulfonyl hydrazine.

[0032] Based on the above, it can be understood that processing the second negative electrode coating material applied to the first OH region 12 of the negative electrode foil can specifically include heat treatment of the second negative electrode coating material applied to the first OH region 12 of the negative electrode foil to cause the pore-forming agent to decompose by heat.

[0033] It should be noted that in this step, the heat treatment can be performed separately on the second negative electrode coating on the first OH region 12 of the negative electrode foil, thus reducing the impact on the first negative electrode coating on the negative electrode center region 20 of the negative electrode foil. Of course, the heat treatment can also be performed on the negative electrode coating on the entire negative electrode foil, thus reducing the complexity of the process.

[0034] Furthermore, by heat-treating the second negative electrode coating applied to the first OH region 12 of the negative electrode foil after rolling, the pore-forming agent is decomposed by heat, which can avoid the rolling process from affecting the porosity of the negative electrode active material coating on the first OH region 12 of the negative electrode foil.

[0035] The pore-forming agent accounts for 2%-8% of the mass fraction of the coating on the second negative electrode. The inventors of this application have discovered that, by combining the specific components of the aforementioned pore-forming agent, the following 1.2 ≤ P can be ensured. OH / P NOH ≤2.0, and will not affect the desired function of other components in the second negative electrode coating.

[0036] Furthermore, the surface of the negative electrode foil also has a second OH region 14, and the first OH region 12, the negative electrode central region 20, and the second OH region 14 are sequentially connected along the width direction of the negative electrode foil; the negative electrode coating to be applied is applied to the second OH region 14 of the negative electrode foil and treated to form a negative electrode active material coating; wherein, the average porosity of the negative electrode active material coating located in the second OH region 14 of the negative electrode foil is the same as the second porosity.

[0037] It should be noted that the treatment of the second OH region 14 on the surface of the negative electrode foil can be the same as the treatment of the first OH region 12 on the surface of the negative electrode foil described above. In addition, the treatment of the second OH region 14 on the surface of the negative electrode foil can be carried out together with the treatment of the first OH region 12 on the surface of the negative electrode foil to reduce the complexity of the process, which will not be described in detail here.

[0038] Furthermore, it should be noted that, based on the fact that the first OH region 12, the negative electrode center region 20, and the second OH region 14 are sequentially connected along the width direction of the negative electrode foil, the negative electrode sheet involved in this application is particularly suitable for wound battery cells. More preferably, in one example, each edge region on the surface of the negative electrode foil is a first OH region, and each edge region here undergoes the same treatment as the first OH region described above. This is applicable to stacked battery cells, and will not be elaborated further here.

[0039] Furthermore, 1.2 ≤ P OH / P NOH ≤2.0;

[0040] Among them, P OHFor the second porosity, P NOH The first porosity;

[0041] The inventors of this application discovered that P OH / P NOH When P is below 1.2, OH and P NOH The difference is small, and the improvement on the lithium-ion migration rate in the OH region is limited, still resulting in a high reversible capacity loss and easy lithium plating at the edge of the negative electrode; when P OH / P NOH At a porosity above 2.0, lithium ions in the OH region already possess excellent kinetic properties. Further increasing the porosity has little effect on improving the lithium ion migration rate and can easily damage the electrode structure.

[0042] Among them, P OH / P NOH Typical, but not limited to, values ​​are 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0. In some preferred embodiments of the invention, P... OH / P NOH A value of 1.5 yields the best results.

[0043] Optionally, the first porosity ranges from 27% to 42%; the second porosity ranges from 40% to 75%. For example, in one instance, the porosity of the negative electrode active material coating located in the negative electrode central region 20 of the negative electrode foil accounts for 30% of its total volume; the porosity of the negative electrode active material coating located in the first OH region 12 of the negative electrode foil accounts for 45% of its total volume.

[0044] Preferably, the width of the first OH region 12 is 0.2mm-5mm, more preferably 1mm-3mm; preferably, the width of the second OH region 14 is 0.2mm-5mm, more preferably 1mm-3mm. The width of the first OH region is typically, but not limited to, 0.2mm, 0.4mm, 0.8mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 4mm, or 5mm.

[0045] The width of the second OH region is typically, but not limited to, 0.2 mm, 0.4 mm, 0.8 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 4 mm or 5 mm.

[0046] Furthermore, the above preparation method further includes the following steps: providing a positive electrode foil, wherein the positive electrode foil is divided into a connected positive electrode central region 40 and a positive electrode edge region 30; providing a positive electrode coating material, and applying the positive electrode coating material to the positive electrode central region 40 and the positive electrode edge region 30 of the positive electrode foil; treating the positive electrode coating material applied to the positive electrode foil to form a positive active material coating; wherein the average porosity of the positive active material coating located in the positive electrode central region 40 of the positive electrode foil is a third porosity; the average porosity of the positive active material coating located in the positive electrode edge region 30 of the positive electrode foil is a fourth porosity; the third porosity is greater than the fourth porosity. Thus, during the discharge process of a lithium battery, the lateral diffusion rate of lithium ions from the active material coating in the positive electrode edge region 30 to the active material coating in the positive electrode center region 40 can be accelerated. This prevents the active material coating in the positive electrode edge region 30 from excessively intercalating lithium due to receiving additional lithium ions from the negative electrode OH region 10 during the discharge process, thereby preventing the corresponding region of the negative electrode from receiving excessive lithium and producing lithium plating during the subsequent charging process. It should be noted that the specific means to achieve a third porosity greater than the fourth porosity can refer to the specific means described above for achieving a second porosity greater than the first porosity.

[0047] It should also be noted that when the positive electrode and the negative electrode in this application jointly form a battery, the positive electrode edge region 30 and the positive electrode center region 40 are both set corresponding to the negative electrode center region 20, and the positive electrode edge region 30 is located at the edge of the positive electrode center region 40.

[0048] In one example, the positive electrode edge region 30 includes a first edge region 32 and a second edge region 34, which are sequentially connected along the width of the positive electrode foil. This type of positive electrode foil is particularly suitable for forming a wound bare cell together with the negative electrode foil whose surface is divided into a first OH region 12, a negative electrode center region 20, and a second OH region 14.

[0049] In one example, a positive electrode active material, a binder, a conductive agent, and a solvent are mixed to form a first positive electrode coating; a positive electrode active material, a binder, a conductive agent, a solvent, and a pore-forming agent are mixed to form a second positive electrode coating; or, a positive electrode coating is provided; a portion of the positive electrode coating is taken to form the first positive electrode coating, and another portion of the positive electrode slurry is taken and a pore-forming agent is added to form the second positive electrode coating.

[0050] The second positive electrode coating is applied to the positive electrode center area of ​​the positive electrode foil, and the first positive electrode coating is applied to the positive electrode edge area of ​​the positive electrode foil.

[0051] The second positive electrode coating material applied to the positive electrode center region of the positive electrode foil and the first positive electrode coating material applied to the positive electrode edge region of the positive electrode foil are processed to form an active material coating with a fourth porosity in the first positive electrode coating material, and the pore-forming agent of the second positive electrode coating material is decomposed by heat to form a positive active material coating with a third porosity in the second positive electrode coating material.

[0052] The pore-forming agent is made from a component that can decompose into a gas upon heating; the pore-forming agent is at least one of ammonium chloride, ammonium oxalate, ammonium hydrogen oxalate, and p-toluenesulfonyl hydrazine, and the pore-forming agent accounts for 3%-7% of the mass fraction of the coating on the second positive electrode. The inventors of this application have discovered that this ensures the achievement of 0.5 ≤ P. CE / P ED ≤0.9, and will not affect the desired function of other components in the second positive electrode coating.

[0053] Furthermore, 0.5 ≤ P CE / P ED ≤0.9,

[0054] Among them, P ED For the third porosity, P CE The fourth porosity;

[0055] P CE / P ED When the porosity is below 0.5, as the porosity of the cathode center increases further, the proportion of active material in the cathode as a whole will decrease, resulting in a reduction in battery capacity.

[0056] P CE / P ED When it is above 0.9, due to P CE and P ED The difference is small, the improvement in the transport rate of lithium ion lateral diffusion is small, and there is still some lithium plating in the negative electrode region corresponding to the positive electrode edge region 30.

[0057] P CE / P ED Typical but not restrictive values ​​are 0.5, 0.6, 0.7, 0.75, 0.8, or 0.9.

[0058] Preferably, P CE / P ED It is 0.75;

[0059] Preferably, the width of the positive electrode central region 40 accounts for 90%-98% of the width of the positive electrode active material coating. When the positive electrode edge region 30 includes a first edge region 32 and a second edge region 34, the width of the positive electrode edge region 30 is the sum of the widths of the first edge region 32 and the second edge region 34. This ensures that excess lithium ions accumulated in the positive electrode edge region 30 during cycling can quickly diffuse to the positive electrode central region 40.

[0060] A second aspect of the present invention provides a battery electrode sheet, comprising: a negative electrode foil having a surface divided into a connected negative electrode central region 20 and a negative electrode OH region 10; and a negative electrode active material coating formed on the negative electrode foil, wherein the average porosity of the negative electrode active material coating located on the negative electrode central region 20 of the negative electrode foil is a first porosity, and the average porosity of the negative electrode active material coating located on the negative electrode OH region 10 of the negative electrode foil is a second porosity, the second porosity being greater than the first porosity.

[0061] The battery electrode provided by the present invention has a negative electrode central region 20 and a negative electrode OH region 10 on the negative electrode foil. The porosity of the negative electrode active material coating in the negative electrode OH region 10 is greater than that in the negative electrode central region 20, which improves the transport speed of lithium ions in the negative electrode OH region 10, avoids reversible capacity loss caused by incomplete discharge, reduces lithium plating on the negative electrode, and extends the service life of the battery.

[0062] Furthermore, the device includes a positive electrode foil with a surface divided into a connected positive electrode central region 40 and a positive electrode edge region 30; and a positive electrode active material coating formed on the positive electrode foil, wherein the average porosity of the positive electrode active material coating located in the positive electrode central region 40 of the positive electrode foil is a third porosity, and the average porosity of the positive electrode active material coating located in the positive electrode edge region 30 of the positive electrode foil is a fourth porosity, with the third porosity being greater than the fourth porosity. This further helps to prevent the formation of lithium plating on the negative electrode.

[0063] It should be noted that the structures of the negative electrode foil and negative electrode active material coating provided in this embodiment are the same as those of the negative electrode foil and negative electrode active material coating prepared by the above-described preparation method of this application, such as having the same porosity ratio, etc., which will not be repeated here. The structures of the positive electrode foil and positive electrode active material coating provided in this embodiment are the same as those of the positive electrode foil and positive electrode active material coating prepared by the above-described preparation method of this application, such as having the same ratio of the width of the positive electrode central region to the width of the positive electrode active material coating, which will not be repeated here.

[0064] A third aspect of the present invention provides a battery comprising the battery electrode sheet described above.

[0065] The battery electrode preparation method, battery electrode, and battery provided by this invention utilize a first porosity for the average porosity of the negative electrode active material coating located in the negative electrode center region of the negative electrode foil, and a second porosity for the average porosity of the negative electrode active material coating located in the negative electrode OH region of the negative electrode foil. The second porosity is greater than the first porosity. During the discharge process of the lithium-ion battery, the movement speed of lithium ions in the active material coating of the negative electrode OH region of the negative electrode foil can be increased, thereby increasing the amount of lithium ions returning to the positive electrode in the negative electrode OH region of the negative electrode foil when the discharge cutoff condition is reached, thus alleviating the capacity loss phenomenon caused by lithium ion discharge in the prior art.

[0066] The following detailed description of some embodiments of the present invention is provided in conjunction with examples. Unless otherwise specified, the following embodiments and features can be combined with each other. Unless otherwise specified, the raw materials used in the following embodiments and comparative examples were all commercially available.

[0067] Example 1

[0068] This embodiment provides a battery electrode, the preparation process of which is as follows:

[0069] 1. Mix and stir 95 parts by weight of graphite, 1 part by weight of sodium carboxymethyl cellulose, 2 parts by weight of styrene-butadiene rubber, 1 part by weight of conductive carbon black, 1 part by weight of carbon nanotubes and 110 parts by weight of deionized water to prepare a first slurry (the above-mentioned first negative electrode coating); mix and stir 95 parts by weight of graphite, 1 part by weight of sodium carboxymethyl cellulose, 2 parts by weight of styrene-butadiene rubber, 1 part by weight of conductive carbon black, 1 part by weight of carbon nanotubes, 2 parts by weight of ammonium oxalate and 112 parts by weight of deionized water to prepare a second slurry (the above-mentioned second negative electrode coating).

[0070] 2. Using an 8μm thick copper foil as the negative electrode foil, the first slurry and the second slurry are coated on the negative electrode center region and the negative electrode OH region, respectively. The width of the negative electrode OH region is 3mm. After coating, the negative electrode sheet is dried at 88℃ to obtain a semi-finished negative electrode sheet.

[0071] 3. Mix and stir 93 parts by weight of NCM622, 5 parts by weight of conductive carbon black, 2 parts by weight of polyvinylidene fluoride and 100 parts by weight of N-methylpyrrolidone to prepare a third slurry (the first positive electrode coating material mentioned above); mix and stir 93 parts by weight of NCM622, 5 parts by weight of conductive carbon black, 2 parts by weight of polyvinylidene fluoride, 5.8 parts by weight of p-toluenesulfonyl hydrazine and 105.8 parts by weight of N-methylpyrrolidone to prepare a fourth slurry (the second positive electrode coating material mentioned above).

[0072] 4. Using 13μm thick aluminum foil as the positive electrode foil, the third and fourth slurries are coated on the edge region and the center region of the positive electrode, respectively. The width of the center region of the positive electrode accounts for 96%. After coating, it is dried at 92℃ to obtain the positive electrode sheet semi-finished product.

[0073] 5. Roll the negative electrode semi-finished product obtained in step 2 and the positive electrode semi-finished product obtained in step 4, and then heat treat them at 170℃ to obtain the positive electrode and negative electrode.

[0074] Example 2

[0075] This embodiment provides a battery electrode sheet. Unlike embodiment 1, the second slurry is formulated with 95 parts by weight of graphite, 1 part by weight of sodium carboxymethyl cellulose, 2 parts by weight of styrene-butadiene rubber, 1 part by weight of conductive carbon black, 1 part by weight of carbon nanotubes, 8.7 parts by weight of ammonium oxalate, and 120 parts by weight of deionized water. The other raw materials and methods are the same as in embodiment 1, and will not be repeated here.

[0076] Example 3

[0077] This embodiment provides a battery electrode sheet. Unlike embodiment 1, the second slurry is formulated with 95 parts by weight of graphite, 1 part by weight of sodium carboxymethyl cellulose, 2 parts by weight of styrene-butadiene rubber, 1 part by weight of conductive carbon black, 1 part by weight of carbon nanotubes, 4.6 parts by weight of ammonium oxalate, and 115 parts by weight of deionized water. The other raw materials and methods are the same as in embodiment 1, and will not be repeated here.

[0078] Example 4

[0079] This embodiment provides a battery electrode sheet. Unlike embodiment 3, the fourth slurry is formulated with 93 parts by weight of NCM622, 5 parts by weight of conductive carbon black, 2 parts by weight of polyvinylidene fluoride, 7.5 parts by weight of p-toluenesulfonyl hydrazine, and 107.5 parts by weight of N-methylpyrrolidone. The other raw materials and methods are the same as in embodiment 3, and will not be repeated here.

[0080] Example 5

[0081] This embodiment provides a battery electrode sheet. Unlike embodiment 3, the fourth slurry is formulated with 93 parts by weight of NCM622, 5 parts by weight of conductive carbon black, 2 parts by weight of polyvinylidene fluoride, 3.1 parts by weight of p-toluenesulfonyl hydrazine, and 103.1 parts by weight of N-methylpyrrolidone. The other raw materials and methods are the same as in embodiment 3, and will not be repeated here.

[0082] Comparative Example 1

[0083] This embodiment provides a battery electrode sheet. Unlike embodiment 3, the fourth slurry has the same formulation as the third slurry, while the other raw materials and methods are the same as in embodiment 3, and will not be repeated here.

[0084] Comparative Example 2

[0085] This comparative example provides a battery electrode sheet. Unlike Example 3, the second slurry has the same formulation as the first slurry, while the other raw materials and methods are the same as in Example 3, and will not be repeated here.

[0086] Comparative Example 3

[0087] This comparative example provides a battery electrode sheet. Unlike Comparative Example 1, the second slurry has the same formulation as the first slurry, while the other raw materials and methods are the same as those in Comparative Example 1, and will not be repeated here.

[0088] Experimental Example 1

[0089] The porosity of the positive and negative electrode sheets obtained in Examples 1-5 and Comparative Examples 1-3 was measured using a fully automated mercury porosimeter from Mack Corporation, USA. The test areas included the negative electrode OH region, the negative electrode center region, the positive electrode center region, and the positive electrode edge region. The corresponding porosities were P0, ... OH P NOH P ED and P CE The results are shown in Table 1.

[0090] Table 1

[0091]

[0092]

[0093] Experimental Example 2

[0094] The pouch cells prepared in Examples 1-5 and Comparative Examples 1-3 were charged and discharged according to method A below, and the discharge capacity was recorded:

[0095] 1. Charge at a constant current of 1.8C to 4.25V;

[0096] 2. Charge at the upper limit cutoff voltage until the current is less than 0.01C (ensure that the SOC of the negative overhang and non-overhang regions is the same);

[0097] 3. Discharge at a constant current of 1.8C to 2.8V;

[0098] 4. Discharge at a constant voltage of 2.8V for 100 hours (to ensure that all active lithium ions in the negative electrode overhang region are removed).

[0099] The pouch cells prepared in Examples 1-5 and Comparative Examples 1-3 were charged and discharged according to method B below, and the discharge capacity was recorded:

[0100] 1. Discharge at a constant voltage of 2.8V for 100 hours (ensuring complete discharge of the negative electrode and the absence of active lithium ions in the OH region);

[0101] 2. Charge at a constant current of 1.8C to 4.25V;

[0102] 3. Discharge at a constant current of 1.8C to 2.8V;

[0103] 4. Discharge at a constant voltage of 2.8V for 100 hours (the purpose is to recover the capacity loss caused by polarization).

[0104] The obtained data is shown in Table 2.

[0105] Table 2

[0106]

[0107] Q in Table 2 总 Q represents the total discharge capacity of the CC-CV circuit. CC Q represents the capacity of the constant current discharge section. CV For the discharge constant voltage range capacity, Q OH This refers to the reversible capacity loss caused by the OH region.

[0108] The purpose of Examples 1B-5B and Comparative Examples 1B-3B is to obtain the reversible capacity loss caused by polarization during discharge. Therefore, the reversible capacity loss caused by the negative electrode OH region is obtained by subtracting the capacity of the constant voltage discharge section in Examples 1A-5A and Comparative Examples 1A-3A from the capacity of the constant voltage discharge section in Examples 1B-5B and Comparative Examples 1B-3B.

[0109] The data in the table show that the reversible capacity loss caused by the OH region of the negative electrode in Examples 1-3 was 3.4%, 2.5%, and 2.4%, respectively, all lower than the 5.8% in Comparative Example 2. This indicates that increasing the porosity of the OH region of the negative electrode can significantly reduce the reversible capacity loss caused by the OH region. The data in Comparative Examples 1 and 3 also corroborate this conclusion. Furthermore, the reversible capacity loss percentages of the OH region of the negative electrode in Examples 3-5 and Comparative Example 1 are basically the same, indicating that increasing the porosity of the central region of the positive electrode does not significantly improve the reversible capacity loss of the OH region of the negative electrode, but it will cause a decrease in battery capacity.

[0110] Experimental Example 3

[0111] The soft-pack batteries obtained in Examples 1-5 and Comparative Examples 1-3 were subjected to 300 charge-discharge cycles. The cells were disassembled and the interfaces were observed. The results are shown in Table 3.

[0112] Table 3

[0113] Example 1 Lithium-free Example 2 Lithium-free Example 3 Lithium-free Example 4 Lithium-free Example 5 Slight lithium plating Comparative Example 1 Slight lithium plating Comparative Example 2 Lithium-free Comparative Example 3 Lithium plating

[0114] Comparing Examples 3-5 and Comparative Example 1, it is evident that increasing the porosity of the central region of the positive electrode significantly improves the degree of lithium deposition at the negative electrode corresponding to the edge of the positive electrode. Data from Comparative Examples 2 and 3 also corroborate this conclusion. Furthermore, data from Comparative Examples 1 and 3 indicate that increasing the porosity of the OH region of the negative electrode also improves the lithium deposition at the negative electrode corresponding to the edge of the positive electrode.

[0115] It should be noted that, in the above embodiments and comparative examples, apart from the different conditions listed above, the remaining steps should be kept the same or tend to be the same in order to control the quantity. Furthermore, it is understood that, in the heat treatment step of the preparation process, the pore-forming agent added to the slurry should be fully decomposed.

[0116] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a battery electrode, characterized in that, Includes the following steps: A negative electrode foil is provided, wherein the surface of the negative electrode foil is divided into a connected negative electrode central region and a first overhang region, the first overhang region being a first OH region; A negative electrode coating material is provided, and the negative electrode coating material is applied to the negative electrode center region and the first OH region of the negative electrode foil. The negative electrode coating material applied to the negative electrode foil is treated to form a negative electrode active material coating. The average porosity of the negative electrode active material coating located in the negative electrode center region of the negative electrode foil is a first porosity; the average porosity of the negative electrode active material coating located in the first OH region of the negative electrode foil is a second porosity; the second porosity is greater than the first porosity; the first porosity ranges from 27% to 42%; the second porosity ranges from 53.7% to 75%. A positive electrode foil is provided, wherein the positive electrode foil is divided into a connected positive electrode central region and a positive electrode edge region; A positive electrode coating material is provided, and the positive electrode coating material is applied to the positive electrode center region and the positive electrode edge region of the positive electrode foil. The positive electrode coating material applied to the positive electrode foil is treated to form a positive active material coating. The average porosity of the positive electrode active material coating located in the positive electrode center region of the positive electrode foil is the third porosity. The average porosity of the positive electrode active material coating located in the positive electrode edge region of the positive electrode foil is the fourth porosity. The third porosity is greater than the fourth porosity; 0.5≤P CE / P ED ≤0.75, where P ED For the third porosity, P CE This is the fourth porosity.

2. The preparation method according to claim 1, characterized in that, The provided negative electrode coating material includes a first negative electrode coating material and a second negative electrode coating material; Applying the negative electrode coating material to the negative electrode center region and the first OH region of the negative electrode foil material specifically includes: applying the first negative electrode coating material to the negative electrode center region of the negative electrode foil material, and applying the second negative electrode coating material to the first OH region of the negative electrode foil material; The negative electrode coating material applied to the negative electrode foil is processed to form a negative active material coating. Specifically, this includes processing a first negative electrode coating material applied to the negative electrode center region of the negative electrode foil and a second negative electrode coating material applied to the first OH region of the negative electrode foil, so that the first negative electrode coating material forms a negative active material coating with a first porosity and the second negative electrode coating material forms a negative active material coating with a second porosity.

3. The preparation method according to claim 2, characterized in that, A first negative electrode coating is formed by mixing a negative electrode active material, a binder, a conductive agent, and a solvent; a second negative electrode coating is formed by mixing a negative electrode active material, a binder, a conductive agent, a solvent, and a pore-forming agent. or, Provide a negative electrode coating material; take a portion of the negative electrode coating material to form a first negative electrode coating material, and take another portion of the negative electrode slurry and add a pore-forming agent to form a second negative electrode coating material.

4. The preparation method according to claim 3, characterized in that, The pore-forming agent is made from components that can decompose into gas when heated; The pore-forming agent is at least one of ammonium chloride, ammonium oxalate, ammonium hydrogen oxalate, and p-toluenesulfonyl hydrazine; The second negative electrode coating material applied to the first OH region of the negative electrode foil is processed, including rolling the second negative electrode coating material applied to the first OH region of the negative electrode foil and then heat-treating it so that the pore-forming agent is decomposed by heat. The pore-forming agent accounts for 2%-8% of the mass fraction of the second negative electrode coating.

5. The preparation method according to any one of claims 1-4, characterized in that, The surface of the negative electrode foil also has a second OH region, and the first OH region, the negative electrode center region and the second OH region are connected sequentially along the width direction of the negative electrode foil; The negative electrode coating material is applied to the second OH region of the negative electrode foil and then treated to form a negative electrode active material coating. The average porosity of the negative electrode active material coating located in the second OH region of the negative electrode foil is the same as the second porosity.

6. The preparation method according to claim 5, characterized in that, 1.2≤P OH / P NOH ≤2.0; Among them, P OH For the second porosity, P NOH The first porosity is defined as follows: the width of the first OH region is 0.2 mm to 5 mm; the width of the second OH region is 0.2 mm to 5 mm.

7. The preparation method according to claim 1, characterized in that, A first positive electrode coating is formed by mixing a positive electrode active material, a binder, a conductive agent, and a solvent; a second positive electrode coating is formed by mixing a positive electrode active material, a binder, a conductive agent, a solvent, and a pore-forming agent; or, a positive electrode coating is provided; a portion of the positive electrode coating is taken to form a first positive electrode coating, and another portion of the positive electrode slurry is taken and a pore-forming agent is added to form a second positive electrode coating. The second positive electrode coating is applied to the positive electrode center region of the positive electrode foil, and the first positive electrode coating is applied to the positive electrode edge region of the positive electrode foil. The second positive electrode coating material applied to the positive electrode center region of the positive electrode foil and the first positive electrode coating material applied to the positive electrode edge region of the positive electrode foil are treated to form an active material coating with a fourth porosity in the first positive electrode coating material, and the pore-forming agent of the second positive electrode coating material is decomposed by heat to form a positive active material coating with a third porosity in the second positive electrode coating material. The pore-forming agent is made from a component that can decompose into gas when heated; the pore-forming agent is at least one of ammonium chloride, ammonium oxalate, ammonium hydrogen oxalate and p-toluenesulfonyl hydrazine, and the pore-forming agent accounts for 3%-7% of the mass fraction of the second positive electrode coating.

8. The preparation method according to claim 1, characterized in that, The width of the positive electrode central region accounts for 90%-98% of the width of the positive electrode active material coating.

9. A battery electrode, characterized in that, It was prepared by the preparation method according to any one of claims 1 to 8; The battery electrode includes: The negative electrode foil has a surface divided into a connected negative electrode central region and an OH region. And, a negative active material coating formed on the negative electrode foil, wherein the average porosity of the negative active material coating located in the negative electrode center region of the negative electrode foil is a first porosity, and the average porosity of the negative active material coating located in the negative electrode OH region of the negative electrode foil is a second porosity, the second porosity being greater than the first porosity.

10. The battery electrode according to claim 9, characterized in that, It includes a positive electrode foil, the surface of which is divided into a connected positive electrode central region and a positive electrode edge region; And, a positive electrode active material coating formed on the positive electrode foil, wherein the average porosity of the positive electrode active material coating located in the positive electrode central region of the positive electrode foil is a third porosity, and the average porosity of the positive electrode active material coating located in the positive electrode edge region of the positive electrode foil is a fourth porosity, wherein the third porosity is greater than the fourth porosity.

11. A battery, characterized in that, Includes the battery electrode as described in claim 9 or 10.

Images