Coating method of positive pole piece, positive pole piece and battery monomer

Abstract

The embodiment of the invention provides a coating method of a positive pole piece, the positive pole piece and a battery monomer. The coating method comprises the following steps: a slurry homogenizing process: forming insulating slurry and active substance slurry; a coating step of coating at least one side of a current collector with the insulating slurry and the active material slurry at the same time through the coating step; the insulating slurry and the active material slurry form an insulating layer and an active material layer through the drying process, the value range of interfacial tension between the insulating slurry and the active material slurry is 1.0 mN / m to 30.0 mN / m, in the drying process, the value range of the drying temperature is 120 DEG C to 150 DEG C, and the value range of the active material layer is 0.5 mN / m to 0.5 mN / m. The coating method effectively relieves the problem that materials of the insulating layer and the active substance layer are mutually soluble or fall off and the like.

Description

Technical Field

[0001] Embodiments of this application relate to a coating method for a positive electrode sheet, as well as a positive electrode sheet and a battery cell. Background Technology

[0002] In the field of new energy, the development of secondary batteries is becoming increasingly important. However, in the process of preparing the positive electrode sheet of secondary batteries, when coating the current collector with an insulating layer and an active material layer, the interfacial tension between the insulating layer and the active material layer is not clearly controlled by appropriate methods, which leads to severe shrinkage of the active material layer and the phenomenon of mutual dissolution and powder runoff between the insulating layer and the active material layer. Summary of the Invention

[0003] This application forms a positive electrode sheet by forming an insulating layer and an active material layer on a current collector through a coating method including a homogenization process, a coating process, and a drying process. The above-mentioned problems are solved by controlling the interfacial tension between the insulating slurry and the active material slurry of the positive electrode sheet to be in the range of 1.0 mN / m to 30.0 mN / m.

[0004] Some embodiments of this application provide a coating method for a positive electrode sheet, including: a homogenization step: forming an insulating slurry and an active material slurry; a coating step: simultaneously coating the insulating slurry and the active material slurry on at least one side of a current collector; and a drying step: forming the insulating slurry and the active material slurry into an insulating layer and an active material layer by a drying step, wherein the interfacial tension between the insulating slurry and the active material slurry ranges from 1.0 mN / m to 30.0 mN / m, and the drying temperature in the drying step ranges from 120℃ to 150℃. This coating method effectively alleviates problems such as material missolution or detachment between the insulating layer and the active material layer.

[0005] In some embodiments, the initial drying temperature in the drying process is greater than or equal to 130°C.

[0006] In some embodiments, the solid content of the insulating slurry is 25%-35% by weight, and the viscosity of the insulating slurry is 1000cP-8000cP.

[0007] In some embodiments, the active material slurry has a solid content of 60%-70% by mass percentage, and the viscosity of the active material slurry is 3000 cP-6000 cP.

[0008] In some embodiments, the insulating slurry includes an inorganic insulating filler, and the active material slurry includes an active material. The particle size D50 of the inorganic insulating filler ranges from 0.7 μm to 2.0 μm, and the difference between the particle size D50 of the active material and the particle size D50 of the inorganic insulating filler ranges from 0.1 μm to 0.5 μm. Here, D50 represents the particle size of the inorganic insulating filler or the active material that reaches 50% of the volumetric particle size from the smallest particle size side in the volumetric particle size distribution.

[0009] In some embodiments, the areal density of the insulating layer is 80 g / m². 2 -90 g / m 2 The areal density of the active material layer is 200 g / m³. 2 -210 g / m 2 .

[0010] In some embodiments, the active material slurry includes a lithium phosphate material, and the insulating slurry includes an inorganic insulating filler, a binder, and a first additive. The first additive is used to increase the surface tension of the insulating slurry. The first additive is selected from one or more of polyethylene glycol, polypropylene glycol, and glycerin. The surface tension of the insulating slurry ranges from 10 mN / m to 50 mN / m.

[0011] In some embodiments, the active material slurry includes a lithium phosphate material and a second additive, the insulating layer includes an inorganic insulating filler and a binder, the second additive is used to reduce the surface tension of the active material slurry, and the second additive is selected from one or more of polyesters, polyethers, and polyurethanes.

[0012] Some other embodiments of this application provide a positive electrode sheet formed according to the above coating method, wherein, in the thickness direction of the current collector, the maximum thickness of the insulating layer is A μm, the maximum thickness of the active material layer is B μm, the value of A / B ranges from 0.2 to 0.5, and the difference between the maximum thickness of the active material layer and the maximum thickness of the insulating layer ranges from 20 μm to 85 μm.

[0013] Some embodiments of this application provide a battery cell, including: a housing having an upper opening; a top cover for closing the opening, the top cover including a terminal post; an electrode assembly disposed within the housing, the electrode assembly including the aforementioned positive electrode sheet, the electrode assembly being formed by winding or stacking the positive electrode sheet, a separator, and a negative electrode sheet, and having multiple tabs, the multiple tabs being bundled together and electrically connected to the terminal post. Attached Figure Description

[0014] Various aspects of the invention will be best understood from the following detailed description when read in conjunction with the accompanying drawings.

[0015] Figure 1 A schematic diagram is shown when the electronic device according to an embodiment of this application is a vehicle.

[0016] Figure 2 A battery pack according to an embodiment of this application is shown.

[0017] Figure 3 An exploded view of a battery cell according to an embodiment of this application is shown.

[0018] Figure 4 A schematic diagram of the structure of the positive electrode and the negative electrode in an electrode assembly according to some embodiments is shown.

[0019] Figure 5 A cross-sectional view of a positive electrode sheet according to some embodiments of this application is shown.

[0020] Figure 6A Some embodiments of this application are shown along Figure 5 The cross-sectional view taken from line AA.

[0021] Figure 6B Another embodiment of this application is shown along Figure 5 The cross-sectional view taken from line AA.

[0022] Figure 7 A flowchart of a coating method for a positive electrode sheet according to some embodiments is shown. Detailed Implementation

[0023] With the continuous development of new energy technologies, the application fields of battery cells are constantly expanding. However, there are currently many factors affecting the performance of battery cells, such as the problem of material missolution or detachment between the insulating layer and the active material layer in the positive electrode sheet. To address this issue, the applicant discovered that in the coating method of the positive electrode sheet, an insulating slurry and an active material slurry can be formed through a homogenization process, followed by a coating process and a drying process to form the insulating layer and the active material layer. The interfacial tension between the insulating slurry and the active material slurry is controlled within the range of 1.0 mN / m to 30.0 mN / m, and the drying temperature is controlled within the range of 120℃-150℃. This coating method can effectively alleviate the problems of material missolution or detachment between the insulating layer and the active material layer.

[0024] In some embodiments, the interfacial tension of this application can be determined using the ring method, in accordance with the GB / T6541-1986 standard. Specifically, the active material slurry is placed in the lower layer of a glass vessel, below a platinum ring. The ring is lowered to immerse the active material slurry in the ring. Then, an insulating slurry is added along the wall of the glass vessel to completely cover the ring. Afterward, the ring is raised to pull it away from the interface between the active material slurry and the insulating slurry, thereby obtaining the interfacial tension.

[0025] Furthermore, this application controls the interfacial tension between the insulating slurry and the active material slurry to a range of 1.0 mN / m to 30.0 mN / m, which allows for a wider range of drying temperatures in the drying process (the drying temperature range is controlled between 120℃ and 150℃). This enables compatibility with more drying processes, reduces the difficulty of temperature control in the drying process, lowers costs, improves the compatibility of the drying process, and allows for a wider temperature window, i.e., a better drying temperature window.

[0026] Furthermore, in this application, during the drying process, the initial drying temperature is greater than or equal to 130°C. If the initial temperature is less than 130°C, the drying capacity of the first stage in the drying process will be weakened. After the insulating slurry and the active material slurry enter the middle stage, the interfacial tension of the wet film of the insulating slurry and the active material slurry increases with the increase of temperature and solid content, causing mutual repulsion between the two phase interfaces of the insulating slurry and the active material slurry, resulting in shrinkage of the active material layer.

[0027] In some embodiments, the solid content of the insulating slurry is 25%-35%, and the viscosity of the insulating slurry is 1000cP-8000cP. The solid content of the active material slurry is 60%-70% by mass, and the viscosity of the active material slurry is 3000cP-6000cP. Furthermore, the insulating slurry includes an inorganic insulating filler, and the active material slurry includes an active material. The particle size D50 of the inorganic insulating filler ranges from 0.7μm to 2.0μm, and the difference between the particle size D50 of the active material and the particle size D50 of the inorganic insulating filler ranges from 0.1μm to 0.5μm. Here, D50 represents the particle size that, in a volume-based particle size distribution, the inorganic insulating filler or active material reaches 50% of the cumulative volume from the smallest particle size side. At the same solid content, larger particle size results in lower viscosity; at the same viscosity, larger particle size results in higher solid content; and at the same solid content, larger particle size results in lower viscosity. Therefore, viscosity, particle size, and solid content can be adjusted to modify the corresponding insulating slurry and active material slurry. In this application, limiting the viscosity, solid content, and particle size of the insulating slurry and active material slurry to the above ranges ensures compatibility with the temperature and air frequency in the drying process. In this application, the active material may include lithium iron phosphate, and the inorganic insulating filler may include ceramic materials such as boehmite.

[0028] Furthermore, to improve the energy density of the product, it is necessary to increase the areal density of the insulating layer and the active material layer (dry film). However, increasing the areal density makes it easier for the powder to dissolve and run off. To address this issue, this application controls the areal density of the insulating layer (dry film) to 80 g / m² by controlling the interfacial tension. 2 -90 g / m 2 The areal density of the active material layer (dry film) is controlled at 200 g / m². 2 -210 g / m 2 This increases the areal density of the insulating layer and the active material layer. This is because by synergistically matching the interfacial tension, that is, controlling the range of the interfacial tension between the insulating slurry and the active material slurry to 1.0 mN / m to 30.0 mN / m, the problem of mutual solubility and powder runoff between the materials of the insulating layer and the active material layer when the areal density is within the above-mentioned higher range can be effectively solved.

[0029] The coating method of this application and the positive electrode sheet, battery cell and electronic device formed therefrom are described in detail below with reference to specific embodiments.

[0030] refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of an electronic device in an embodiment of the present invention. The electronic device 1000 in this embodiment can be, for example, a vehicle, which may include a body 1100 and a battery pack. The battery pack may include one or more individual battery cells 1200. The battery pack is disposed inside the body 1100 to supply power to the vehicle and ensure its normal operation. In practical applications, the vehicle can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.

[0031] In other embodiments, the electronic device 1000 may be, for example, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, and a power tool, etc. This embodiment does not limit the type of the electronic device 1000.

[0032] refer to Figures 2 to 4 In this embodiment, the battery cell 1200 may include a housing 1210, a top cover 1220, and an electrode assembly 1230. The top cover 1220 has an adapter piece 1221 on the side facing the housing 1210. The housing 1210 has an internal accommodating space, and one end of the housing 1210 has an opening. The electrode assembly 1230 can be accommodated in the internal accommodating space of the housing 1210. The top cover 1220 can close onto the opening of the housing 1210 and is fixedly connected to the housing 1210, so that the interior of the housing 1210 is relatively sealed.

[0033] like Figure 4 As shown, the electrode assembly 1230 may include a positive electrode 100a, a negative electrode 100b, and a separator 200. The separator 200 is located between the positive electrode 100a and the negative electrode 100b to isolate them and prevent short circuits caused by contact between the positive electrode 100a and the negative electrode 100b. The positive electrode 100a, the separator 200, and the negative electrode 100b are simultaneously wound to form the electrode assembly 1230 in a wound state.

[0034] Figure 5 A schematic diagram of the positive electrode 100a formed by the above coating method is shown. Further, Figure 6A It shows along Figure 5 The image shows a side view of line AA of the positive electrode 100a. In some specific embodiments, combined with... Figure 5 and Figure 6A In the thickness direction H of the current collector, the maximum thickness of the insulating layer is A μm, and the maximum thickness of the active material layer is B μm, with the A / B ratio ranging from 0.2 to 0.5. As the thickness of the active material layer 103 increases, a suitable thickness for the insulating layer 102 is required. An excessively thick insulating layer 102 can cause the active material layer 103 to shrink due to interfacial tension, resulting in leakage of the current collector 101 and posing a safety risk. Therefore, in the thickness direction H of the current collector, the maximum thickness of the insulating layer 102 is A μm, and the maximum thickness of the active material layer is B μm. Controlling the A / B ratio to 0.2-0.5 can mitigate the aforementioned safety risk. In this application, the thicknesses of the insulating layer 102 and the active material layer 103 are their maximum thicknesses on one side of the current collector 101. This is because the active material layer 103 has a thinning area; therefore, to avoid controversy, the maximum thickness is used. Furthermore, the maximum thickness of the aforementioned insulating layer 102 and active material layer 103 is taken after the positive electrode sheet is prepared and dried, and also includes the thickness of the corresponding insulating layer and active material layer of the positive electrode sheet at 0% SOC (State of Charge) after the battery is disassembled.

[0035] Furthermore, in the current collector thickness direction H, the difference between the maximum thickness of the active material layer and the maximum thickness of the insulating layer ranges from 20 μm to 85 μm, specifically selected from 20 μm, 30 μm, 40 μm, 50 μm, and 80 μm. When the difference between the maximum thickness of the active material layer 103 and the maximum thickness of the insulating layer 102 is too large, it will further deteriorate the interfacial contact between the active material layer 103 and the insulating layer 102, causing gaps or large-area mutual fusion to easily occur between the insulating layer 102 and the active material layer 103. Moreover, an excessively large thickness difference between the active material layer 103 and the insulating layer 102 (>85 μm) will lead to interface defects (such as...) between the active material layer 103 and the insulating layer 102. Figure 6A A thickness step appears at interface S). During coating, when coating the other side of the positive electrode sheet, the already coated portion of the positive electrode sheet will adhere tightly to the steel roller. This thickness step at the interface can cause the tab blank area to curl or collapse, increasing the distance between the current collector 101 and the extrusion coating die, making it prone to air entrainment defects. When the thickness difference between the active material layer 103 and the insulating layer 102 is too small (<20μm), the insulating layer 102 will also come into contact with the rolling roller and be compressed during the subsequent rolling process to densify the positive electrode sheet. The compressed and densified insulating layer will have two adverse effects: first, the dense insulating layer is more likely to reflect laser light, which is not conducive to laser cutting; second, the hardness and brittleness of the insulating layer 102 will increase after compression, making it prone to positive electrode sheet breakage. Therefore, with the upgrading of battery cell products (such as capacity increasing from 280Ah to higher 600Ah), the thickness of the active material layer of the positive electrode sheet is continuously increasing. By controlling the thickness difference between the insulating layer 102 and the active material layer 103 (controlling this thickness difference within the range of 20μm to 85μm), the problem of poor overlap between the insulating layer and the active material layer can be effectively alleviated. In summary, with the upgrading of secondary battery products and the sharp increase in the positive electrode active material layer, the above-mentioned problems can be solved by controlling the thickness of the insulating layer and the active material layer. The coating method for the positive electrode sheet provided in this application eliminates the adhesive application step, therefore the insulating layer is coated thicker, and the areal density is greater than that when adhesive is applied.

[0036] In addition, such as Figure 5 and Figure 6A As shown, the positive electrode 100a provided in this application includes: an electrode body 110 and an electrode tab 120 protruding from the electrode body 110. The electrode tab 120 is connected to one side of the electrode body 110 along a first direction, such as... Figure 5As shown, the direction from the tab 120 to the electrode body 110 is the first direction D. An insulating layer 102 is provided at the connection area between the tab 120 and the electrode body 110. The tab 120 includes a tab blank area 121 and a portion of the insulating layer 102 (such as the second insulating layer 105). Another portion of the insulating layer 102 (such as the first insulating layer 104) is placed in the electrode body 110. Figure 5 This is an illustrative embodiment, and the second insulating layer 105 may also extend into the electrode body 110.

[0037] Combination Figure 5 and Figure 6A As shown, the electrode body 110 includes: a current collector 101; an insulating layer 102 and an active material layer 103. The active material layer 103 and the insulating layer 102 are disposed adjacent to each other on the same side surface of the current collector 101. In the first direction D, a portion of the insulating layer 102 and a portion of the active material layer 103 overlap to form a first overlapping region Q1. By controlling the interfacial tension between the insulating slurry and the active material slurry to be in the range of 1.0 mN / m to 30.0 mN / m, problems such as material missolution or detachment in the first overlapping region Q1 of the insulating layer 102 and the active material layer 103 can be effectively alleviated. In this application, controlling the interfacial tension between the insulating slurry and the active material slurry to be in the range of 1.0 mN / m to 30.0 mN / m is a proven golden range that can simultaneously balance good overlap and suppress shrinkage. The interfacial tension between the insulating slurry and the active material slurry is too low (<1.0 mN / m): In the first overlapping region Q1, the molecules or microparticles of the two slurries (insulating slurry and active material slurry) diffuse and penetrate more easily. This causes the originally clear physical boundary to become blurred or even disappear and become miscible before drying and curing. During subsequent drying, rolling, or battery cycling, the bonding force in the first overlapping region Q1 weakens, making it very easy for the insulating layer or active material layer to detach from the interface, thus leading to a short circuit risk at the tab 120 of the positive electrode 100a. The interfacial tension is too high (>30.0 mN / m): Such high interfacial tension means that the two liquids tend to be incompatible and repel each other. The insulating slurry cannot effectively wet the edge of the active material layer, which tends to shrink and coalesce to minimize the contact area, ultimately causing obvious interfacial separation and gaps between the two phases in the first overlapping region. Furthermore, it can cause poor overlap between the insulating layer 102 and the active material layer 103, making it easy to peel off at the edge.

[0038] Furthermore, by controlling the interfacial tension between the insulating slurry and the active material slurry to a range of 1.0 mN / m to 30.0 mN / m, the reliable overlap and shrinkage suppression of the insulating layer 102 and the active material layer 103 in the first overlapping region Q1 can be improved. Controlling the interfacial tension within this window increases the clarity and stability of the interface (S) at the first overlapping region between the insulating layer 102 and the active material layer 103, effectively mitigating problems such as material missolution or detachment in the first overlapping region of the insulating layer and the active material layer. In addition, the positive electrode sheet provided in this application can further improve its production yield and stability, thereby enhancing the long-term reliability and durability of the corresponding battery cell.

[0039] In some embodiments, see Figure 5 and Figure 6A The insulating layer 102 may further include a first insulating portion 104 and a second insulating portion 105 connected in sequence. The first insulating portion 104 is located between the second insulating portion 105 and the active material layer 103. The maximum thickness of the first insulating portion 104 is greater than the maximum thickness of the second insulating portion 105. The orthogonal projection of the first overlapping region Q1 along the current collector thickness direction H is located within the range of the first insulating portion 104. In an embodiment, when the insulating layer 102 includes two types of insulating portions, the first insulating portion 104 at the root can serve as a tab support, and the second insulating portion 105 is thinner, facilitating the tab 120 to bend and bend. In this case, the first overlapping region Q1 is within the first insulating portion 104 and not within the second insulating portion 105, which allows the second insulating portion 105 to bend better and prevents the second insulating portion 105 in the overlapping area from falling off after bending.

[0040] Reference Figure 5 The tab 120 includes a transition region R on the side near the electrode body 110. Along the first direction D, the minimum distance between the transition region of the tab 120 and the first overlapping region Q1 is greater than 0 mm. In this application, the interfacial tension between the insulating slurry and the active material slurry is within the above-mentioned range (the value range is limited to 1.0 mN / m to 30.0 mN / m), avoiding at least a partial projection of the first overlapping region Q1 onto the transition region R, thus ensuring that the interfacial tension of the first overlapping region Q1 within the above-mentioned range can effectively avoid the problem of cutting and falling off.

[0041] Furthermore, the applicant discovered that the interfacial tension between the insulating grout and the active material grout is related to the surface tension of both the insulating grout and the active material grout. Factors affecting the interfacial tension include the magnitude of surface tension, polarity matching, and interfacial structure. In some embodiments, ignoring the effect of polarity, the interfacial tension increases with the increase of the surface tension difference between the two phases. Based on theory and experimental measurements, when only a surface tension difference exists, and the surface tension difference is very small, interfacial separation is unlikely to occur between the insulating layer 102 and the active material layer 103. Since the interfacial tension exceeding the threshold between the insulating grout and the active material grout at high temperatures is the main reason for the shrinkage of the active material, it is recommended to control the surface tension of the insulating grout at the level of the surface tension of the active material grout to reduce the interfacial tension through surface tension control.

[0042] In some embodiments, the active material slurry includes lithium phosphate (LFP) material (active material), and the insulating slurry includes inorganic insulating filler, binder, and a first additive. The first additive is used to increase the surface tension of the insulating slurry. The first additive can be selected from one or more of polyethylene glycol, polypropylene glycol, and glycerin. The surface tension of the insulating slurry ranges from 10 mN / m to 50 mN / m. In embodiments, for the LFP cathode, because of its high surface tension, it is necessary to increase the surface tension of the insulating slurry. In some embodiments, the surface tension of the insulating slurry is controlled within the range of 10 mN / m to 50 mN / m, which can improve the interfacial tension between the insulating slurry and the active material slurry, making it less likely for interfacial separation to occur between the insulating layer 102 and the active material layer 103. In addition, adding the first additive to the insulating slurry does not affect the energy density of the active material slurry. Furthermore, the insulating layer 102 has a relatively small width, which makes it easier to control. The surface tension is measured using the ring method, in accordance with GB / T6541-1986 standard, specifically referring to the above interfacial tension test method.

[0043] In some other embodiments, the active material slurry includes a lithium phosphate (LFP) material and a second additive, and the insulating slurry includes an inorganic insulating filler and a binder. The second additive is used to reduce the surface tension of the active material slurry and is selected from one or more polyesters, polyethers, and polyurethanes. In the embodiments, for the LFP cathode, because of its high surface tension, reducing the surface tension of the active material slurry improves the interfacial tension between the insulating slurry and the active material slurry. In some embodiments, polyesters include, but are not limited to, polyethylene glycol-poly(D,L-lactide), polyethers include, but are not limited to, polyethylene glycol monomethyl ether, and polyurethanes include, but are not limited to, ethoxycarbamates. In some embodiments, the surface tension of the active material slurry ranges from 10 mN / m to 50 mN / m.

[0044] Furthermore, the aforementioned configuration of the active material slurry and insulating slurry further avoids the back-roller adhesive application method during positive electrode coating. This solves the problem in the prior art where, to improve yield, the positive electrode of the battery cell needs to use back-roller adhesive application to ensure the overlap of the inorganic insulating filler-lithium iron (active material) in the insulating layer and to prevent shrinkage of the lithium iron film area. This method can cause problems such as fluctuations in the edge surface density of the positive electrode due to fluctuations in the adhesive application position, which may lead to lithium plating risks.

[0045] In some embodiments, the surface tension difference between the insulating slurry and the active material slurry can be reduced so that the interfacial tension between the insulating slurry and the active material slurry falls within the range of 1.0 mN / m to 30.0 mN / m. In some embodiments, the surface tension difference between the insulating slurry and the active material slurry is in the range of 0.1 mN / m to 1.1 mN / m.

[0046] In some embodiments, see Figure 6B , Figure 6B It shows along Figure 5 The other side view of line AA. The second side surface of the current collector 101 opposite to the first side surface includes an active material layer 103 and an insulating layer 102. The active material layer 103 and the insulating layer 102 are disposed adjacent to each other in the first direction D. Part of the insulating layer 102 and part of the active material layer 103 overlap to form a second overlapping region Q2. In the second overlapping region Q2, the interfacial tension between the insulating slurry and the active material slurry ranges from 1.0 mN / m to 30.0 mN / m. In the thickness direction H of the current collector, the orthographic projections of the first overlapping region Q1 and the second overlapping region Q2 at least partially overlap. In this application, the orthographic projections of the first overlapping region Q1 and the second overlapping region Q2 in the current collector thickness direction H at least partially overlap, which helps to ensure that the front and back sides of the first overlapping region Q1 and the second overlapping region Q2 correspond and are not completely misaligned. This helps to ensure that the interface morphology of the active material layer 103 and the insulating layer 102 in the first overlapping region Q1 and the second overlapping region Q2 is similar, so that the control range of the interface tension can be compatible with both sides. At the same time, the misalignment size of the edge of the active material layer after drying can be controlled within a small range (<0.5mm), improving the uniformity of the electrode size.

[0047] Other embodiments of this application provide a battery cell including a housing 1210 with an opening at the top; a top cover 1220 for covering the opening, the top cover 1220 including a terminal post; and an electrode assembly 1230 disposed within the housing 1210. The electrode assembly 1230 includes the aforementioned positive electrode 100a and negative electrode 100b. The electrode assembly 1230 is formed by winding or stacking the positive electrode 100a, the separator 200, and the negative electrode 100b. Multiple tabs are provided, and after being bundled together, they are electrically connected to the terminal post. By controlling the interfacial tension between the insulating slurry and the active material slurry to a range of 1.0 mN / m to 30.0 mN / m, damage to the interface caused by the bundling of the tabs can be avoided, preventing foil leakage and thus improving safety.

[0048] Furthermore, the battery cell can be a lithium-ion battery, a sodium-ion battery, a sodium-lithium-ion battery, etc., and this application is not limited to this. In some embodiments, the battery is a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0049] The coating method for the positive electrode is as follows: See Figure 7 A coating method for a positive electrode sheet 100a is provided, including a homogenization process, a coating process, and a drying process. Specifically, the homogenization process involves forming an insulating slurry and an active material slurry (stirred under vacuum until the system is homogeneous); the coating process involves simultaneously coating the insulating slurry and the active material slurry onto at least one side of the current collector; and the drying process involves forming an insulating layer and an active material layer from the insulating slurry and the active material slurry through a drying process. In this method, the simultaneous coating of the insulating slurry and the active material slurry achieves simultaneous drying. The positive electrode sheet is then obtained through cold pressing, slitting, and cutting.

[0050] Specifically, in some embodiments, the homogenization process for forming the insulating slurry includes: adding a binder, a first additive, and an inorganic insulating filler to an appropriate amount of NMP (N-methylpyrrolidone) to prepare an insulating slurry with a solid content of 30%. Specifically, this involves: dissolving and diluting the binder in the insulating slurry to form a binder solution; adding insulating material powder (inorganic insulating filler) to the binder solution; stirring and dispersing; adding the first additive; stirring and dispersing again to obtain the insulating slurry; and measuring the viscosity of the insulating slurry.

[0051] The process of forming an active material slurry through homogenization includes: mixing the corresponding positive electrode active material (lithium iron phosphate), conductive agent and binder in a mass ratio of 96-98:1-2:1-2, adding a solvent (such as N-methylpyrrolidone), and stirring under vacuum until the system is homogeneous to prepare an active material slurry with a solid content of 70%.

[0052] The coating process includes: vacuum degassing of the insulating slurry and the active material slurry; pumping the insulating slurry and the active material slurry to the coating die head using a screw pump; and simultaneously coating the insulating slurry and the active material slurry using a slit extrusion die head through the coating pad flow channel, coating the insulating slurry and the active material slurry onto the current collector to obtain a wet insulating film and a wet active material film, and performing corresponding tests on the wet insulating film and the wet active material film (such as the thickness). Furthermore, the drying process includes: raising the temperature of the wet insulating film and the wet active material film; evaporating the solvent in the wet insulating film and the wet active material film. Specifically, when using an oven, the positive electrode sheet is rapidly heated in the initial oven (such as the first and second ovens in a 6-section oven), and in the intermediate oven (such as the third and fourth ovens in a 6-section oven), the positive electrode sheet enters the rapid solvent evaporation stage. In the final oven (such as the 5th and 6th sections of a 6-section oven), the positive electrode enters a slow solvent evaporation stage. Afterward, the positive electrode is cooled; that is, after exiting the oven, it passes through cooling rollers to obtain the insulating layer and the active material layer. The insulating layer and the active material layer are then inspected (e.g., their thickness).

[0053] In summary, this application forms a positive electrode 100a using the above coating method. As mentioned above, the interfacial tension between the insulating slurry and the active material slurry is controlled within the range of 1.0 mN / m to 30.0 mN / m. In the drying process, the drying temperature is controlled within the range of 120℃-150℃, which can effectively alleviate problems such as material missolution or detachment between the insulating layer and the active material layer.

[0054] Furthermore, this application controls the interfacial tension between the insulating slurry and the active material slurry to a range of 1.0 mN / m to 30.0 mN / m, which allows for a wider range of drying temperatures in the drying process (the drying temperature range is controlled between 120℃ and 150℃), enabling compatibility with more drying processes, reducing the difficulty of temperature control in the drying process, lowering costs, improving the compatibility of the drying process, and matching a wider temperature window.

[0055] Furthermore, in this application, during the drying process, the initial drying temperature is greater than or equal to 130°C. If the initial temperature is less than 130°C, the drying capacity of the first stage in the drying process will be weakened. After the insulating slurry and the active material slurry enter the middle stage, the interfacial tension of the wet film of the insulating slurry and the active material slurry increases with the increase of temperature and solid content, causing mutual repulsion between the two phase interfaces of the insulating slurry and the active material slurry, resulting in shrinkage of the active material layer. In some embodiments, the solid content of the insulating slurry is 25%-35%, and the viscosity of the insulating slurry is 1000cP-8000cP. The solid content of the active material slurry is 60%-70% by mass, and the viscosity of the active material slurry is 3000cP-6000cP. Furthermore, the insulating slurry includes an inorganic insulating filler, and the active material slurry includes an active material. The particle size D50 of the inorganic insulating filler ranges from 0.7μm to 2.0μm, and the difference between the particle size D50 of the active material and the particle size D50 of the inorganic insulating filler ranges from 0.1μm to 0.5μm. Here, D50 represents the particle size that, in a volume-based particle size distribution, the inorganic insulating filler or active material reaches 50% of the cumulative volume from the smallest particle size side. At the same solid content, the larger the particle size, the lower the viscosity; at the same viscosity, the larger the particle size, the higher the solid content; and at the same solid content, the larger the particle size, the lower the viscosity. In this application, the viscosity, solid content, and particle size of the insulating slurry and the active material slurry are limited to the above ranges, which can be compatible with the temperature and air frequency in the drying process.

[0056] In some embodiments, the thickness of the insulating wet film is 7.00 mm-8.00 mm, and the areal density of the insulating wet film is 190 g / m³. 2 -200 g / m 2 The thickness of the insulating layer (i.e., the dry film of the insulating layer) is 7.00mm-8.00mm, and the areal density of the wet film of the insulating layer is 80g / m³. 2 -90 g / m 2 In some embodiments, the thickness of the active material layer wet film is 370mm-380mm, and the areal density of the active material layer wet film is 300g / m³. 2 -310 g / m 2 The thickness of the active material layer (i.e., the dry film of the active material layer) is 370mm-380mm, and the areal density of the active material layer is 200g / m³. 2 -210 g / m 2 .

[0057] Positive electrode sheet: As described above, the insulating slurry includes: inorganic insulating filler, binder, and optionally a first additive. The first additive is used to increase the surface tension of the insulating slurry. The first additive is selected from one or more of polyethylene glycol, polypropylene glycol, glycerin, etc., and the surface tension of the insulating slurry ranges from 10 mN / m to 50 mN / m. Active material slurry includes: lithium phosphate material, binder, and optionally a second additive. The insulating layer includes inorganic insulating filler and binder. The second additive is used to reduce the surface tension of the active material slurry. The second additive is selected from one or more of polyesters, polyethers, polyurethanes, etc. Polyesters include, but are not limited to, polyethylene glycol-poly(D,L-lactide); polyethers include, but are not limited to, polyethylene glycol monomethyl ether; polyurethanes include, but are not limited to, ethoxycarbamates. In some embodiments, the surface tension of the active material slurry ranges from 10 mN / m to 50 mN / m. In some embodiments, either the first additive or the second additive may be included, but in some other embodiments, both the first additive and the second additive may be included. For the binder, it can typically be selected from polyimide, polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers. In some embodiments, polyimide can be used as the binder.

[0058] In the aforementioned positive electrode sheet, the interfacial tension between the insulating slurry and the active material slurry ranges from 1.0 mN / m to 30.0 mN / m. This effectively mitigates problems such as material missolution or detachment between the insulating layer and the active material layer.

[0059] In addition, in the thickness direction of the current collector, the maximum thickness of the insulating layer is A μm, the maximum thickness of the active material layer is B μm, the value of A / B ranges from 0.2 to 0.5, and the difference between the maximum thickness of the active material layer and the maximum thickness of the insulating layer ranges from 20 μm to 85 μm, specifically selected from 20 μm, 30 μm, 40 μm, 50 μm, and 80 μm.

[0060] Specifically, in some embodiments, the insulating paste and the active material paste also include a conductive agent and a solvent (such as N-methylpyrrolidone). The conductive agent is a reagent used to ensure good charge-discharge performance of the electrode. Conductive carbon, such as carbon black, can be used as the conductive agent, or any suitable conductive agent.

[0061] For the current collector of the positive electrode, materials that do not cause chemical changes and have high conductivity can be used without restriction. Commonly used materials include stainless steel, aluminum, nickel, titanium, or calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. To enhance the adhesion of the positive electrode active material, micro-embossing can be formed on the surface of the current collector. Current collectors can be used in various forms, such as films, sheets, foils, meshes, or porous bodies.

[0062] Negative electrode sheet: In some alternative embodiments, the negative electrode sheet can be prepared using methods conventional in the art. For example, the following method can be used: mixing negative electrode active material, binder, conductive agent and optionally thickener in a certain weight ratio, adding solvent and mixing evenly to obtain a negative electrode slurry; then uniformly coating the negative electrode slurry onto a negative electrode current collector; air-drying at room temperature and then transferring to an oven for further drying, followed by cold pressing, slitting and cutting to obtain the negative electrode sheet.

[0063] The negative electrode active material can be any negative electrode active material conventionally used in the art to prepare negative electrode sheets, and can be selected from at least one of graphene, artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon suboxide, and silicon carbide; the binder plays a role in improving the adhesion between the negative electrode active materials and the adhesion between the negative electrode active materials and the negative electrode current collector, and its type is not particularly limited. Specific examples of binders may include styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyvinylidene fluoride hexafluoropropylene copolymer (PVDF co HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof can be used.

[0064] There are no particular limitations on the conductive agent, as long as it is conductive and does not cause chemical changes in the battery. For example, specific materials that can be used include: graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black (SP), acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives, etc. Furthermore, a thickener such as carboxymethyl cellulose (CMC) can be used, but there are no specific limitations.

[0065] For the negative electrode current collector, the negative electrode current collector can be a current collector conventionally used for negative electrodes in the art, and can be a common current collector or a composite current collector. The negative electrode current collector can be made of a non-chemically reactive and conductive material without limitation. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum-cadmium alloys can be used, or copper, stainless steel, or aluminum-cadmium alloys surface-treated with carbon, nickel, titanium, or silver. Furthermore, to enhance the adhesion of the negative electrode active material, micro-embossing can be formed on the surface of the negative electrode current collector. The negative electrode current collector can be used in various forms, such as a membrane, sheet, foil, mesh, or porous body.

[0066] Separator: The separator placed between the positive and negative electrode plates uses an insulating film with high ion permeability and high mechanical strength. The separator typically has a thickness of 9 μm-18 μm; a pore size of 5 μm-300 μm; an air permeability of 180 s / 100 mL-380 s / 100 mL; and a porosity of 30% to 50%. As a separator, it is chemically resistant and hydrophobic, and is usually made of sheets or nonwoven fabrics made of: olefin polymers such as polypropylene or polyethylene films; glass fibers; or, further, using the aforementioned sheets or nonwoven fabrics as a base film, coated with a coating.

[0067] Electrolyte: In this application, the electrolyte may be a conventional electrolyte used in lithium-ion batteries, generally including non-aqueous solvents, lithium salts and additives.

[0068] In some embodiments, the non-aqueous solvent may be a conventional non-aqueous solvent in the art, preferably an ester solvent, and more preferably a carbonate solvent. The carbonate solvent may be one or more of ethylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC).

[0069] In some embodiments, the additive may be one or more selected from vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene ethylene carbonate (VEC), vinyl sulfate (DTD), vinylene sulfate, 1,3-propane sulfonyl lactone (PS), propylene sulfonate lactone, and 1,4-butane sulfonate lactone. The conventional amount of the additive in the electrolyte is 1%-4% of the electrolyte, for example, 2%.

[0070] In some embodiments, the lithium salt may be a conventional lithium salt in the art, such as at least one selected from LiPF6, LiBF4, LiN(SO2F)2 (abbreviated as LiFSI), LiClO4, LiAsF6, LiB(C2O4)2 (abbreviated as LiBOB), LiBF2(C2O4) (abbreviated as LiDFOB), LiN(SO2RF)2, and LiN(SO2F)(SO2RF). The concentration of the lithium salt may be conventional in the art, and the lithium salt is preferably present in the electrolyte at a concentration of 5%-20%, typically 1 mol / L-2 mol / L.

[0071] In this application, the preparation method of the electrolyte can be conventional in the art, generally involving mixing a non-aqueous solvent, lithium salt, and additives.

[0072] Battery cell (taking lithium-ion battery as an example): The above positive electrode, separator, and negative electrode are stacked in sequence, with the separator between the positive and negative electrodes to provide isolation. Then, they are wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a battery cell such as a lithium-ion battery is obtained.

[0073] In this application, the electronic device includes the aforementioned battery cell, and the electronic device can be the vehicle described above, or it can be a mobile phone, portable device, laptop, ship, spacecraft, electric toy, power tool, etc. The vehicle can be a gasoline-powered car, a natural gas-powered car, or a new energy vehicle; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.; spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc.; electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc.; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. It can also be an energy storage electronic device that stores energy and then discharges it externally. This application does not impose any special limitations on the aforementioned electronic devices.

[0074] The present application is further illustrated below by way of embodiments, but these embodiments are not intended to limit the scope of the present application. Unless otherwise specified, all embodiments below are performed at room temperature (25°C), and experimental methods without specific conditions are performed according to conventional methods and conditions in the art, or as selected according to the product manual.

[0075] Example 1

[0076] Preparation of the positive electrode sheet:

[0077] (1) Homogenization process: The insulating slurry is prepared by adding 4.16 kg of polyimide, 0.3 kg of polyethylene glycol (the first additive), and 17 kg of boehmite (an inorganic insulating filler) to an appropriate amount of NMP (N-methylpyrrolidone) to prepare an insulating slurry with a solid content of 30%. Preparation process: Add the polyimide binder solution to a mixing tank, then spray in 6.4 kg of NMP solvent, stirring for 10 min. Add 17 kg of boehmite powder in three batches, spray in 6.4 kg of NMP solvent, and stir for 30 min to disperse at a temperature ≤50℃. Add 0.6 kg of polyethylene glycol (the first additive), disperse, and stir for 30 min. Viscosity is measured; when the viscosity of the insulating slurry is 6880 cP, it is shipped to a buffer tank. The content of polyethylene glycol (the first additive) can be adjusted to achieve a surface tension of 40 mN / m for the prepared insulating slurry.

[0078] The active material slurry is prepared as follows: Lithium iron phosphate (LFP), polyvinylidene fluoride (PVDF), and conductive carbon are mixed in a mass ratio of 97:2:1. A solvent (such as N-methylpyrrolidone) is added, and the mixture is stirred under vacuum until the system is homogeneous, yielding an active material slurry with a solid content of 70%. In this application, 20 kg of lithium iron phosphate is used as the LFP. Furthermore, a second additive, such as a polyester, for example polyethylene glycol-poly(D,L-lactide), can be added to the active material slurry to achieve a surface tension of 40 mN / m.

[0079] (2) Coating process: This can be divided into the following steps: After vacuum degassing, the insulating slurry and active material slurry are slowly stirred and stored in a buffer tank. The insulating slurry and active material slurry are pumped to the coating die head by a screw pump. A slit extrusion die head is used for simultaneous coating. Through the gasket flow channel design between the upper and lower dies, the insulating slurry and active material slurry are extruded from the die head and coated onto the current collector (copper foil) in close contact with the steel roller. The insulating layer is coated on both sides of the active material layer. The current collector thickness is 12μm. The current collector conveyor belt continuously carries away the insulating layer and the active material layer. The dimensions such as thickness and areal density of the wet film of the insulating layer and the wet film of the active material layer in the wet film state of the positive electrode sheet are optionally detected by a CCD (charge-coupled device camera) and a X-ray areal density meter.

[0080] (3) Baking Process: The oven is 30m long (or any suitable length, such as 60m), divided into 6 sections, each 5m long. The parameters for each section are shown in Table 1. The baking process can be divided into the following stages: In the first and second oven sections, the insulating slurry and active material slurry of the positive electrode sheet are rapidly heated. In the third and fourth oven sections, the insulating slurry and active material slurry of the positive electrode sheet enter the rapid solvent evaporation stage. In the fifth and sixth oven sections, the insulating slurry and active material slurry of the positive electrode sheet enter the slow solvent evaporation stage. After exiting the oven, the positive electrode sheet is cooled by cooling rollers. The cooled positive electrode sheet is then inspected by a CCD and X-ray areal density meter to determine the dimensions and areal density of the insulating layer and active material layer in the dry film state. The positive electrode sheet is then slit and cut to obtain the final product.

[0081] Table 1 Oven Parameter Settings

[0082]

[0083] Among them, circulating air represents the frequency of the airflow blowing onto the positive electrode plate, while exhaust air represents the frequency of the airflow that is expelled. The exhaust air has a higher frequency than the circulating air.

[0084] Preparation of negative electrode sheet

[0085] The negative electrode active material graphite, conductive agent SP, thickener CMC, and binder SBR are mixed in a mass ratio of 96:1:1.2:1.8 with deionized water in a vacuum mixer until the system is homogeneous, thus obtaining a negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector copper foil, dried at room temperature, and then transferred to an oven for further drying. Finally, the negative electrode sheet is obtained through cold pressing, slitting, and cutting.

[0086] Preparation of electrolyte

[0087] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. Finally, 2% VC was added as a film-forming additive.

[0088] Preparation of the separating membrane

[0089] A 12μm thick polyethylene film was selected as the separator.

[0090] Preparation of lithium-ion batteries

[0091] Stack the above-mentioned positive electrode sheet, separator membrane, and negative electrode sheet in sequence, with the separator membrane placed between the positive and negative electrode sheets to play an isolation role, and then wind them to obtain a bare battery cell; place the bare battery cell in an outer packaging case, inject electrolyte after drying, and obtain a lithium-ion battery through processes such as vacuum packaging, standing, formation, and shaping.

[0092] Measurement of interfacial tension and surface tension: The interfacial tension of this application and the following surface tension can be measured by the ring method, and the measurement is carried out in accordance with the standard of GB / T6541-1986. Specifically, place the active material slurry in the lower layer of a glassware, place it under a platinum ring, lower the ring to immerse the active material slurry in the ring, then add an insulating slurry along the wall of the glassware to completely cover the ring, and then lift the ring to pull it off from the interface between the active material slurry and the insulating slurry, so as to obtain the interfacial tension. The measurement method of the surface tension is similar to that of the interfacial tension, and this surface tension can be the interfacial tension between the insulating slurry or the active material slurry and air.

[0093] Measurement of the gap between the insulating layer and the active material layer of the positive electrode sheet: The maximum distance of the gap existing between the insulating layer and the corresponding active material layer in the first direction.

[0094] Judgment of the gap: Whether there is a gap can be determined with 0.3mm as the boundary. A gap greater than 0.3mm is regarded as having a gap, and a gap less than 0.3mm is regarded as having no gap.

[0095] Judgment of mutual dissolution and powder running:

[0096] Slight mutual dissolution: The maximum width of the mixed material between the insulating layer and the active material layer is >0mm and ≤0.5mm;

[0097] No mutual dissolution: The maximum width of the mixed material between the insulating layer and the active material layer is 0mm.

[0098] Judgment of whether the shrinkage is serious: The thickness of the central dressing area of the active material layer of the positive electrode sheet is C, and the junction of the active material layer and the insulating layer of the positive electrode sheet is point E. If the dressing thickness of the active material layer at point E < 0.1×C, it is considered that there is a problem of shrinkage of the active material layer. The position where the dressing thickness of the active material layer reaches 0.1×C is point F, and the distance from E to F is defined as the shrinkage width W. W = 0 means no shrinkage, 0 < W ≤ 1.0mm means slight shrinkage, and W > 1mm means obvious shrinkage.

[0099] Thickness measurement: Measure with a micrometer.

[0100] Viscosity detection: The viscosity is tested according to GB / T 10247-2008: Specifically, the rotational method of GB / T10247-2008.

[0101] Areal density detection:

[0102] Insulation layer density: Take 10 insulation layer coating samples with a length of 20mm and a width of 5mm (total area a0 = 1000mm²). 2 The insulation coating (including the current collector) is weighed on a balance to obtain the weight w1. The total area a0 is multiplied by the current collector density ρ2 and the current collector thickness h2 to obtain the current collector weight w2. The net weight of the insulation layer w = w1 - w2. The surface density of the insulation layer (the surface density of this application is the surface density of a single side) m1 = w / (a0 × 2).

[0103] Density of active material layers: Eight circular active material layer samples with a diameter of 50 mm were taken (total area a1 = 157 cm²). 2 The material is placed on a balance and weighed to obtain the weight w3 of the double active material layer (including the current collector). The total area a1 is multiplied by the current collector density ρ2 and the current collector thickness h2 to obtain the current collector weight w4. The net weight of the double active material layer w0 = w3 - w4. The surface density of the active material layer (the surface density of this application is the surface density of a single side) m2 = w0 / (a1×2).

[0104] In the following embodiments, the interfacial tension or surface tension of the insulating slurry and the active material slurry can be adjusted by adding a first additive to the insulating slurry and / or adding a second additive to the active material slurry, or by controlling the content of the first additive and / or the second additive. The first additive is used to increase the surface tension of the insulating slurry, and the first additive may be selected from one or more of polyethylene glycol, polypropylene glycol, and glycerin. The second additive is used to reduce the surface tension of the active material slurry, and the second additive may be selected from one or more of polyesters, polyethers, and polyurethanes. Polyesters include, but are not limited to, polyethylene glycol-poly(D,L-lactide), polyethers include, but are not limited to, polyethylene glycol monomethyl ether, and polyurethanes include, but are not limited to, ethoxycarbamates.

[0105] In some embodiments, the interfacial tension or surface tension of the insulating slurry and the active material slurry can be adjusted by regulating the solid content, viscosity, or particle size D50 of the corresponding materials. As described above, the solid content of the insulating slurry is 25%-35%, and the viscosity of the insulating slurry is 1000cP-8000cP. By mass percentage, the solid content of the active material slurry is 60%-70%, and the viscosity of the active material slurry is 3000cP-6000cP. Furthermore, the insulating slurry includes inorganic insulating fillers, and the active material slurry includes active material materials. The particle size D50 of the inorganic insulating fillers ranges from 0.7μm to 2.0μm, and the difference between the particle size D50 of the active material materials and the particle size D50 of the inorganic insulating fillers ranges from 0.1μm to 0.5μm. Here, D50 represents the particle size of the inorganic insulating fillers or active material materials that reaches 50% of the volumetric particle size from the smallest particle size side in the volumetric particle size distribution. At the same solid content, the larger the particle size, the lower the viscosity; at the same viscosity, the larger the particle size, the higher the solid content; and at the same solid content, the larger the particle size, the lower the viscosity. In this application, the viscosity, solid content, and particle size of the insulating slurry and the active material slurry are limited to the above ranges, which can be compatible with the temperature and air frequency in the drying process.

[0106] In addition, the areal density of the insulating layer is 80 g / m². 2 -90 g / m 2 The areal density of the active material layer is 200 g / m³. 2 -210 g / m 2 By synergistically matching the aforementioned interfacial tensions, the problem of material missolution and powder runoff between the insulating layer and the active material layer when the areal density is within the aforementioned high range can be effectively solved.

[0107] Examples 2 to 10 and Comparative Examples 1 to 2

[0108] The methods in Examples 2 to 10 and Comparative Examples 1 to 2 are the same as those in Example 1, with the different parameters shown in Table 2 below.

[0109] Table 2 shows the relevant parameters and test results for Examples 1-10 and Comparative Examples 1-2.

[0110]

[0111]

[0112] As can be seen from Examples 1 to 10, controlling the interfacial tension between the insulating slurry and the active material slurry within the range of 1.0 mN / m to 30.0 mN / m can improve the reliable overlap of the insulating layer and the active material layer and suppress shrinkage. Controlling the interfacial tension within this window increases the clarity and stability of the interface between the insulating layer and the active material layer, which can effectively alleviate problems such as material missolution or detachment between the insulating layer and the active material layer.

[0113] Furthermore, comparing Example 1 with Comparative Example 1 reveals that when the interfacial tension is too low (e.g., less than 1.0 mN / m), the molecules or microparticles of the insulating slurry and active material slurry diffuse and permeate more easily. This causes the originally clear physical boundaries to become blurred or even disappear and become miscible before drying and curing. During subsequent drying, rolling, or battery cycling, the bonding force between the insulating layer and the active material layer weakens, making it very easy for the insulating layer or active material layer material to detach from the interface, thus leading to a short circuit risk at the tab of the positive electrode. Comparing Example 1 with Comparative Example 2 reveals that when the interfacial tension is too high (>30.0 mN / m), the two liquids tend to be incompatible and repel each other. The insulating slurry cannot effectively wet the edges of the active material layer, which tends to shrink and coalesce to minimize the contact area, ultimately resulting in obvious interfacial separation and gaps between the insulating slurry and the active material slurry phases. Furthermore, when the interfacial tension is greater than 30 mN / m, significant shrinkage failure of the lithium iron phosphate slurry (active material slurry) will occur, that is, poor integration with the insulating slurry.

[0114] Example 11

[0115] The method in Example 11 is the same as that in Example 1, except that the parameters are the oven parameters, which are shown in Table 3 below.

[0116] Table 3 Oven parameters in Example 11

[0117]

[0118]

[0119] Table 4. Relevant parameters and test results from Examples 1 and 11

[0120]

[0121] Comparing Example 1 with Example 11, it can be seen that in the drying process, the initial drying temperature should be greater than or equal to 130°C. If the initial temperature is less than 130°C, the drying capacity in the first stage of the drying process will be weakened. After the insulating slurry and the active material slurry enter the middle stage, the wet film interfacial tension of the insulating slurry and the active material slurry increases with the increase of temperature and solid content, causing mutual repulsion between the two phase interfaces of the insulating slurry and the active material slurry, which will affect the shrinkage of the active material layer. Setting the initial drying temperature to be greater than or equal to 130°C can better control the wet film interfacial tension of the insulating slurry and the active material slurry, and can also reduce costs.

[0122] The foregoing outlines features of several embodiments to enable those skilled in the art to better understand aspects of the invention. Those skilled in the art should understand that they can readily use this invention as a basis to design or modify other processes and structures for implementing the same purposes and / or achieving the same advantages as the embodiments described herein. Those skilled in the art should also recognize that such equivalent constructions do not depart from the spirit and scope of the invention, and that various changes, substitutions, and modifications can be made to them herein without departing from the spirit and scope of the invention.

Claims

1. A coating method for a positive electrode sheet, characterized in that, include: Homogenization process: forming insulating slurry and active material slurry; Coating process: The insulating slurry and the active material slurry are simultaneously coated on at least one side of the current collector through a coating process; and Drying process: The drying process forms the insulating slurry and the active material slurry into an insulating layer and an active material layer, respectively. The interfacial tension between the insulating slurry and the active material slurry ranges from 1.0 mN / m to 30.0 mN / m, and the drying temperature in the drying process ranges from 120℃ to 150℃.

2. The coating method according to claim 1, characterized in that, In the drying process, the initial drying temperature is greater than or equal to 130°C.

3. The coating method according to claim 1, characterized in that, The insulating slurry has a solid content of 25%-35% by mass percentage and a viscosity of 1000cP-8000cP.

4. The coating method according to claim 1, characterized in that, The active substance slurry has a solid content of 60%-70% by mass percentage, and the viscosity of the active substance slurry is 3000cP-6000cP.

5. The coating method according to claim 1, characterized in that, The insulating slurry includes inorganic insulating fillers, and the active material slurry includes active material. The particle size D50 of the inorganic insulating filler ranges from 0.7 μm to 2.0 μm, and the difference between the particle size D50 of the active material and the particle size D50 of the inorganic insulating filler ranges from 0.1 μm to 0.5 μm. Wherein, D50 represents the particle size that, in the volume-based particle size distribution, the inorganic insulating filler or the active material reaches 50% of the cumulative volume from the smallest particle size side.

6. The coating method according to claim 1, characterized in that, The areal density of the insulating layer is 80 g / m³. 2 -90 g / m 2 The areal density of the active material layer is 200 g / m³. 2 -210 g / m 2 .

7. The coating method according to claim 1, characterized in that, The active material slurry includes lithium phosphate material, and the insulating slurry includes inorganic insulating filler, binder and first additive. The first additive is used to increase the surface tension of the insulating slurry. The first additive is selected from one or more of polyethylene glycol, polypropylene glycol and glycerin. The surface tension of the insulating slurry ranges from 10 mN / m to 50 mN / m.

8. The coating method according to claim 1, characterized in that, The active material slurry includes a lithium phosphate material and a second additive. The insulating layer includes an inorganic insulating filler and a binder. The second additive is used to reduce the surface tension of the active material slurry. The second additive is selected from one or more of polyester, polyether, and polyurethane.

9. A positive electrode sheet, characterized in that, Formed by the method according to any one of claims 1-8, wherein, in the thickness direction of the current collector, the maximum thickness of the insulating layer is A μm, the maximum thickness of the active material layer is B μm, the value of A / B ranges from 0.2 to 0.5, and the difference between the maximum thickness of the active material layer and the maximum thickness of the insulating layer ranges from 20 μm to 85 μm.

10. A single battery cell, characterized in that, include: The casing has an opening at the top; A top cover for closing the opening, the top cover including a pole; An electrode assembly is disposed within the housing. The electrode assembly includes a positive electrode sheet according to claim 9. The electrode assembly is formed by winding or stacking the positive electrode sheet, the diaphragm, and the negative electrode sheet. The number of tabs is multiple, and the multiple tabs are bundled together and electrically connected to the electrode post.

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