Sodium battery diaphragm

Abstract

The utility model discloses a sodium battery diaphragm which comprises a base membrane, a first ceramic particle coating and a second ceramic particle coating, wherein the first ceramic particle coating and the second ceramic particle coating are arranged on the surface of the same side of the base membrane; the porosity of the second ceramic particle coating is greater than that of the first ceramic particle coating; when the diaphragm is in a winding state, the diaphragm is provided with straight areas and corner areas which are alternately arranged in the winding direction of the diaphragm, the straight areas of the base membrane are coated with the first ceramic particle coating, and the corner areas of the base membrane are coated with the second ceramic particle coating. According to the utility model, the first ceramic particle coating and the second ceramic particle coating are respectively coated on the base membrane, so that the heat resistance and the puncture resistance of the diaphragm are obviously improved; besides, the corner area is coated with the second ceramic particle coating with higher porosity, so that the corner area has a higher pore structure, enough gaps can be kept at the corner position to accommodate electrolyte, and the phenomenon of sodium precipitation at the corner is avoided.

Description

Technical Field

[0001] The utility model belongs to the technical field of sodium ion batteries, and in particular relates to a sodium battery separator. Background Art

[0002] As a new type of secondary battery, sodium-ion batteries (Na-ion batteries) show great potential for large-scale energy storage due to their abundant raw materials and low cost. However, Na-ion batteries still face several technical challenges in practical application, among which the stability of cycling performance is an urgent issue to be addressed.

[0003] During the cycling of sodium-ion batteries, both the positive and negative electrodes expand and contract as sodium ions are inserted and extracted. This volume change continues throughout the battery's lifecycle, significantly impacting its structural stability and performance. This issue is particularly prominent in wound batteries.

[0004] The corners of wound sodium-ion batteries are a particular area of ​​stress concentration. During cycling, the distance between the positive and negative electrodes is compressed and reduced due to the continuous expansion and contraction of the electrodes. This compression effect causes the electrolyte to be continuously squeezed out, resulting in a significant decrease in the electrolyte content at the corners of the core in the later stages of the cycle. This electrolyte deficiency can lead to a series of problems, the most serious of which is the precipitation of metallic sodium, a phenomenon known as sodium precipitation.

[0005] Sodium precipitation not only reduces battery capacity and efficiency but can also pose safety risks. Furthermore, uneven deformation of the electrode corners and uneven electrolyte distribution can lead to abnormal cell thickness in the later stages of cycling. This thickness anomaly not only affects the battery's appearance and structural integrity but can also lead to serious consequences such as internal short circuits.

[0006] Therefore, there is an urgent need to provide a technical solution to the above problems. Utility Model Content

[0007] The purpose of the utility model is to provide a sodium battery separator to address the shortcomings of the existing technology, so as to solve the technical problem that the corners of the existing sodium battery core are easily compressed and reduced, resulting in poor electrolyte infiltration at the corners and easy sodium precipitation.

[0008] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0009] A sodium battery separator comprises a base membrane, and a first ceramic particle coating and a second ceramic particle coating provided on the same side surface of the base membrane; wherein the porosity of the second ceramic particle coating is greater than the porosity of the first ceramic particle coating;

[0010] When the diaphragm is in a wound state, the diaphragm has straight areas and corner areas alternately arranged along its winding direction, the first ceramic particle coating is applied to the straight areas of the base film, and the second ceramic particle coating is applied to the corner areas of the base film.

[0011] The first and second ceramic particle coatings are applied to the base film to improve the heat resistance and puncture resistance of the separator. Furthermore, applying the second ceramic particle coating to the corners of the base film, with a porosity greater than that of the first, allows for sufficient clearance at the corners of the wound cell. The pore structure of the second ceramic coating allows for electrolyte storage, preventing the electrolyte from being squeezed out of the corners due to expansion of the positive and negative electrodes during circulation, thus preventing sodium precipitation at the corners and effectively improving abnormal thickness of the cell in the later stages of cycling.

[0012] Preferably, the first ceramic particle coating and the second ceramic particle coating each include ceramic particles and a binder, wherein the ceramic particles may be alumina, silica, or zirconium oxide, and the binder may be polyvinylidene fluoride or polymethyl methacrylate. The pore structure of the ceramic particle coating can be prepared by adding a pore-forming agent to the ceramic particle coating slurry, wherein the pore-forming agent evaporates during the drying process to form the pore structure. The pore-forming agent may be sodium bicarbonate, and the porosity can be controlled by controlling the content of the pore-forming agent in the ceramic particle coating slurry.

[0013] Preferably, the porosity of the first ceramic coating is 50-60%, and the porosity of the second ceramic coating is 70-90%.

[0014] Preferably, the thickness of the second ceramic particle coating layer is smaller than the thickness of the first ceramic particle coating layer.

[0015] Preferably, the thickness of the first ceramic particle coating layer is 5 to 10 μm, and the thickness of the second ceramic particle coating layer is 1 to 5 μm.

[0016] Preferably, the width of the second ceramic coating at each corner area of ​​the base film increases with the increase in the number of winding turns.

[0017] Preferably, both sides of the base film are coated with a first ceramic particle coating layer and a second ceramic particle coating layer.

[0018] Preferably, the base film is a PP film, a PE film or a PI film.

[0019] Preferably, the base film has a thickness of 10 to 15 μm.

[0020] Compared with the existing technology, the beneficial effects of the present invention are as follows: the present invention provides a sodium battery separator, comprising a base membrane, and a first ceramic particle coating and a second ceramic particle coating provided on the same side surface of the base membrane; and the porosity of the second ceramic particle coating is greater than the porosity of the first ceramic particle coating; when the separator is in a wound state, the separator has straight areas and corner areas alternately arranged along its winding direction, the first ceramic particle coating is applied to the straight areas of the base membrane, and the second ceramic particle coating is applied to the corner areas of the base membrane. By respectively applying the first ceramic particle coating and the second ceramic particle coating on the base membrane, the present invention significantly improves the heat resistance and puncture resistance of the separator; wherein, the introduction of ceramic particles enables the separator to maintain stability in a high temperature environment, reducing the risk of battery overheating; at the same time, the ceramic coating improves the mechanical strength of the separator and reduces the risk of puncture. In addition, the porosity of the second ceramic particle coating is greater than that of the first ceramic particle coating, which makes the corner area have a higher porosity structure. This design ensures that the corner position can maintain sufficient gap to accommodate the electrolyte, effectively preventing the electrolyte from being squeezed out of the corner, avoiding the sodium precipitation phenomenon in the corner, and improving the thickness abnormality problem in the later stage of the battery cell cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic structural diagram of the sodium battery separator of the present utility model.

[0022] In the figure: 1, base film; 2, first ceramic particle coating; 3, second ceramic particle coating. DETAILED DESCRIPTION

[0023] In order to make the technical solutions and advantages of the present invention clearer, the present invention and its beneficial effects will be described in further detail below in conjunction with specific implementation methods and the accompanying drawings, but the implementation methods of the present invention are not limited thereto.

[0024] like Figure 1 As shown, the present application provides a sodium battery separator, comprising a base film 1, and a first ceramic particle coating 2 and a second ceramic particle coating 3 provided on the same side surface of the base film 1; and the porosity of the second ceramic particle coating 3 is greater than the porosity of the first ceramic particle coating 2;

[0025] When the diaphragm is in a wound state, the diaphragm has straight areas and corner areas alternately arranged along its winding direction, the first ceramic particle coating 2 is coated on the straight areas of the base membrane 1, and the second ceramic particle coating 3 is coated on the corner areas of the base membrane 1.

[0026] The present application not only improves the heat resistance and puncture resistance of the separator by coating the first ceramic particle coating 2 and the second ceramic particle coating 3 on the base film 1, but also cleverly solves the problem of the corners of the sodium battery core. Specifically, the separator provided by the present application has the following advantages:

[0027] a) Improved heat resistance: The ceramic particle coating can remain stable at high temperatures, preventing the separator from shrinking and improving battery safety.

[0028] b) Enhanced puncture resistance: The ceramic particle coating increases the mechanical strength of the diaphragm and reduces the risk of internal short circuits.

[0029] c) Preventing sodium precipitation at corners: By coating the corner area with a second ceramic particle coating 3 with higher porosity, more space is created to accommodate the electrolyte; this not only alleviates the problem of electrolyte extrusion caused by electrode expansion or extrusion, but also effectively prevents the occurrence of sodium precipitation.

[0030] d) Improved cycle performance: Due to the more uniform distribution of electrolyte at the corners, the thickness anomaly of the battery after long-term cycling is significantly improved, extending the battery life.

[0031] In one embodiment of the present application, the first ceramic particle coating 2 and the second ceramic particle coating 3 each include ceramic particles and a binder, wherein the ceramic particles may be alumina, silica, or zirconium oxide, and the binder may be polyvinylidene fluoride or polymethyl methacrylate. The pore structure of the ceramic particle coating can be prepared by adding a pore-forming agent to the ceramic particle coating slurry, wherein the pore-forming agent evaporates during the drying process to form a pore structure, wherein the pore-forming agent may be sodium bicarbonate, and the porosity can be controlled by controlling the content of the pore-forming agent in the ceramic particle coating slurry.

[0032] In one embodiment of the present application, the porosity of the first ceramic coating is 50-60%, and the porosity of the second ceramic coating is 70-90%, which ensures the mechanical strength of the straight area and provides sufficient electrolyte storage space in the corner area.

[0033] In one embodiment of the present application, the thickness of the second ceramic particle coating 3 is less than that of the first ceramic particle coating 2. This allows the corner area to reserve more space for accommodating the electrolyte, further avoiding the problem of poor wettability caused by squeezing the corner area.

[0034] In one embodiment of the present application, the thickness of the first ceramic particle coating layer 2 is 5 to 10 μm, and the thickness of the second ceramic particle coating layer 3 is 1 to 5 μm.

[0035] In one embodiment of the present application, the width of the second ceramic coating at each corner of the base film 1 increases as the number of windings increases. This design, which increases the coating width at the corners as the number of windings increases, takes into account the difference in curvature between the inner and outer rings and better adapts to stress distribution at different locations.

[0036] In one embodiment of the present application, both sides of the base film 1 are coated with a first ceramic particle coating 2 and a second ceramic particle coating 3. Coating both sides of the base film 1 with ceramic particle coatings can further improve the mechanical strength and heat resistance of the separator, while increasing the storage capacity of the electrolyte.

[0037] In one embodiment of the present application, the base film 1 is a PP film, a PE film or a PI film, wherein the PP film, the PE film or the PI film as the base film 1 material has good mechanical properties and chemical stability.

[0038] In one embodiment of the present application, the base film 1 has a thickness of 10 to 15 μm, which can ensure a balance between strength and flexibility, and is beneficial to improving the energy density of the battery.

[0039] Based on the disclosure and teachings of the above description, those skilled in the art will be able to make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above. Any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention fall within the scope of protection of the present invention. In addition, although certain specific terms are used in this description, these terms are for convenience only and do not constitute any limitation on the present invention.

Claims

1. A sodium battery separator, characterized in that: The invention comprises a base film, and a first ceramic particle coating and a second ceramic particle coating provided on the same side surface of the base film; wherein the porosity of the second ceramic particle coating is greater than the porosity of the first ceramic particle coating; When the diaphragm is in a wound state, the diaphragm has straight areas and corner areas alternately arranged along its winding direction, the first ceramic particle coating is applied to the straight areas of the base film, and the second ceramic particle coating is applied to the corner areas of the base film.

2. The sodium battery separator according to claim 1, characterized in that: The porosity of the first ceramic particle coating layer is 50-60%, and the porosity of the second ceramic particle coating layer is 70-90%.

3. The sodium battery separator according to claim 1, characterized in that: The thickness of the second ceramic particle coating layer is smaller than the thickness of the first ceramic particle coating layer.

4. The sodium battery separator according to claim 3, characterized in that: The thickness of the first ceramic particle coating layer is 5 to 10 μm, and the thickness of the second ceramic particle coating layer is 1 to 5 μm.

5. The sodium battery separator according to claim 1, characterized in that: The width of the second ceramic particle coating layer at each corner area of ​​the base film increases with the increase in the number of winding turns.

6. The sodium battery separator according to claim 1, characterized in that: Both sides of the base film are coated with a first ceramic particle coating layer and a second ceramic particle coating layer.

7. The sodium battery separator according to claim 1, characterized in that: The base film is a PP film, a PE film or a PI film.

8. The sodium battery separator according to claim 1, characterized in that: The base film has a thickness of 10 to 15 μm.

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