Diaphragm and battery

Abstract

The invention relates to the technical field of lithium ion batteries, and provides a diaphragm and a battery. The diaphragm comprises a base material and a ceramic layer covering at least one side surface of the base material; in a given direction parallel to the surface of the base material, the ceramic layer comprises a plurality of T1 regions and a plurality of T2 regions which are alternately arranged in sequence; in the thickness direction of the base material, the thickness of the ceramic layer in the T1 area is marked as D1, the thickness of the ceramic layer in the T2 area is marked as D2 [mu] m, D = D1 / D2, and D is larger than or equal to 1.5 and smaller than or equal to 4; the porosity of the base material is recorded as P%, and P and D meet the condition that D / P is larger than or equal to 2.73 and smaller than or equal to 11.43. The diaphragm can improve the wettability of electrolyte, is favorable for maintaining the stability of an interface at the later period of battery cycle expansion, and prolongs the cycle life of the battery; and the influence of non-uniform charge distribution on the surface of the electrode caused by uneven surface of the diaphragm can be improved, so that the migration rate of lithium ions is accelerated, and the fast charging performance of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a separator and a battery. Background Art

[0002] Lithium-ion batteries are now widely used in many technological fields such as 3C consumer products and electric vehicles, showing strong market application potential. As market competition becomes increasingly fierce, the demand for battery performance is also increasing, which directly drives the continuous evolution of battery technology towards higher capacity and faster charging power. Silicon (Si) has a high theoretical specific capacity, and the theoretical specific capacity of full lithiumization can reach 4200mAh / g (about 10 times that of graphite). It is considered to be one of the most promising negative electrode materials. However, because the lithium storage mechanism of silicon-containing negative electrodes is an alloying reaction mechanism, silicon will undergo severe volume expansion during the lithiation process. During the battery charge and discharge cycle, repeated volume changes will cause the structure of the electrode material to collapse, resulting in active Li + Therefore, how to effectively alleviate the volume expansion problem of silicon-containing negative electrodes during the lithiation process has become a key problem that needs to be solved in the current lithium-ion battery technology field. Summary of the invention

[0003] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art, and to provide a diaphragm, in which the ceramic layer of the diaphragm has a T1 region and a T2 region arranged at intervals, and there is a thickness difference between the ceramic layer of the T1 region and the ceramic layer of the T2 region, and a plurality of concave-convex structures that can optimize the distribution of the electrolyte are formed on the surface of the diaphragm, which can improve the electrolyte wettability inside the electrode sheet, improve the film formation uniformity and stability of the SEI film of the negative electrode sheet, and help maintain the stability of the interface in the late stage of battery cycle expansion, and extend the cycle life of the battery; the uneven surface of the diaphragm can improve the electrolyte wettability to a certain extent, but it is easy to cause uneven charge distribution on the electrode surface, affecting the insertion and extraction speed of lithium ions, thereby reducing the fast charging performance of the battery. The present application can improve the influence of uneven charge distribution on the electrode surface caused by the uneven surface of the diaphragm by controlling the thickness ratio of the ceramic layer in the T1 region and the ceramic layer in the T2 region and reasonably matching it with the porosity of the substrate, thereby accelerating the migration rate of lithium ions and improving the fast charging performance of the battery.

[0004] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides a diaphragm, which includes a substrate and a ceramic layer covering the surface of at least one side of the substrate; in a given direction parallel to the surface of the substrate, the ceramic layer includes a plurality of T1 regions and a plurality of T2 regions arranged alternately in sequence; in the thickness direction of the substrate, the thickness of the ceramic layer in the T1 region is denoted as D1μm, the thickness of the ceramic layer in the T2 region is denoted as D2μm, D=D1 / D2, D satisfies: 1.5≤D≤4; the porosity of the substrate is denoted as P%, and P and D satisfy: 2.73≤D / P≤11.43.

[0005] A second aspect of the present invention provides a battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator is the separator provided in the first aspect of the present invention.

[0006] The present invention adopts the above technical solution to achieve the following beneficial effects:

[0007] The diaphragm provided by the present invention has a ceramic layer arranged on the surface of at least one side of a substrate, and the ceramic layer has T1 regions and T2 regions arranged alternately at intervals, and there is a thickness difference between the ceramic layer in the T1 region and the ceramic layer in the T2 region, so that a plurality of concave-convex structures that can optimize the distribution of the electrolyte are formed on the surface of the diaphragm, which can improve the wettability of the electrolyte, and is beneficial to maintaining the stability of the interface in the late stage of battery cycle expansion, thereby extending the cycle life of the battery; further controlling the ratio of the thickness of the ceramic layer in the T1 region and the ceramic layer in the T2 region to the porosity of the substrate to meet a specific range can improve the influence of the uneven charge distribution on the electrode surface caused by the uneven surface of the diaphragm, thereby effectively improving the migration rate of lithium ions and improving the fast charging performance of the battery.

[0008] The endpoints and any values ​​of the range disclosed in this article are not limited to the precise range or value, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. Herein, in the absence of special instructions, data ranges include endpoints. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 Shown is a schematic diagram of a first structure of a diaphragm ceramic layer in an example of the present invention.

[0010] Figure 2 Shown is a second structural schematic diagram of the diaphragm ceramic layer in an example of the present invention.

[0011] Figure 3 Shown is a third structural schematic diagram of the diaphragm ceramic layer in an example of the present invention.

[0012] Figure 4 Shown is a schematic diagram of a cross-sectional structure of a diaphragm in an example of the present invention.

[0013] Figure 5 Shown is an optical microscope image of the surface of the ceramic layer of the diaphragm in one example of the present invention.

[0014] Figure 6 Shown is a scanning electron microscope (SEM) image of a cross section of a diaphragm in an example of the present invention.

[0015] Reference numerals: 1-T1 region; 2-T2 region; 3-substrate. DETAILED DESCRIPTION

[0016] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0017] Unless otherwise defined, all scientific and technical terms used in the present invention have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention relates.

[0018] The first aspect of the present invention provides a diaphragm, which includes a substrate and a ceramic layer covering the surface of at least one side of the substrate; in a given direction parallel to the surface of the substrate, the ceramic layer includes a plurality of T1 regions and a plurality of T2 regions arranged alternately in sequence; in the thickness direction of the substrate, the thickness of the ceramic layer in the T1 region is denoted as D1μm, the thickness of the ceramic layer in the T2 region is denoted as D2μm, D=D1 / D2, D satisfies: 1.5≤D≤4; the porosity of the substrate is denoted as P%, and P and D satisfy: 2.73≤D / P≤11.43.

[0019] The diaphragm provided by the present invention has a ceramic layer on at least one side of the substrate, the ceramic layer includes a T1 region and a T2 region arranged alternately in sequence, and since the thickness of the ceramic layer in the T1 region is higher than the thickness of the ceramic layer in the T2 region, a series of sequentially spaced "convex portions" are formed on the surface of the ceramic layer, and a "depressed portion" is correspondingly formed in the T2 region. Such a plurality of "striped" regularly arranged concave-convex structures (for example Figure 5 and Figure 6As shown), additional liquid storage space can be formed on the surface of the diaphragm, which improves the wettability of the electrolyte inside the battery, reduces the concentration gradient of the electrolyte inside the battery, and is beneficial to maintaining the stability of the contact interface between the diaphragm and the electrode in the later stage of battery cycle expansion, thereby extending the cycle life of the battery. However, the uneven surface of the diaphragm can easily lead to uneven charge distribution on the electrode surface, affecting the insertion and extraction speed of lithium ions, thereby reducing the fast charging performance of the battery. A higher base membrane porosity can provide more transmission channels for lithium ions and reduce the migration resistance of lithium ions. By controlling the thickness ratio of the ceramic layer in the T1 region and the ceramic layer in the T2 region to meet the above range with the porosity of the substrate, the transmission path of lithium ions in the diaphragm can be further optimized, the migration rate of lithium ions can be accelerated, and the charge distribution on the electrode surface can be improved through the migration and aggregation of lithium ions, thereby increasing the insertion and extraction speed of lithium ions in the active material and improving the fast charging performance of the battery.

[0020] Illustratively, the thickness ratio (D) of the ceramic layer in the T1 region and the ceramic layer in the T2 region may be 1.5, 2, 2.5, 3, 3.5, 4 or any value in the range consisting of any two of the above values.

[0021] Exemplarily, the ratio of the thickness ratio of the ceramic layer in the T1 region and the ceramic layer in the T2 region to the porosity of the substrate (D / P) can be, for example, 2.73, 3, 5, 7, 9, 11, 11.43 or any point value in the range consisting of any two of the above point values.

[0022] The present invention controls the ratio of the thickness ratio of the ceramic layer in the T1 region and the ceramic layer in the T2 region to the porosity of the substrate to satisfy the range of 2.73≤D / P≤11.43, which can avoid the situation where the thickness ratio of the ceramic layer in the T1 region and the ceramic layer in the T2 region is too small when D / P is less than 2.73, and the depression formed by the ceramic layer in the T2 region is too shallow, and it is impossible to optimize the infiltration of the electrolyte in the width direction and the thickness direction of the electrode piece, resulting in insufficient electrolyte infiltration in the electrode piece away from the edge area in the width direction, and the formed interface film is too thin to maintain the stability of the interface in the late stage of battery cycle expansion, thereby reducing the cycle life of the battery. Alternatively, it may be that the porosity of the substrate is too large, which may lead to a decrease in the liquid retention capacity of the diaphragm, and has little effect on improving the uneven charge distribution on the electrode surface caused by the uneven surface of the diaphragm. In addition, due to the surface roughness problem of the silicon negative electrode, the diaphragm is easily pierced during winding or the diaphragm is easily made too thin and damaged when squeezed, resulting in a short circuit in the battery. It can also avoid the situation that when D / P>11.43, the thickness ratio of the ceramic layer in the T1 region and the ceramic layer in the T2 region is too large, and the depression formed by the ceramic layer in the T2 region is too deep. On the one hand, the uneven charge distribution on the electrode surface is aggravated, and the impact of the uneven charge distribution cannot be improved by adjusting the porosity of the base film, which reduces the insertion and extraction speed of lithium ions, thereby reducing the rate performance of the battery; on the other hand, the continuity of the ceramic layer is reduced, the bonding force between the diaphragm and the electrode is weakened, and the stress at the contact interface between the diaphragm and the electrode is too concentrated, which worsens the interface problem and accelerates the formation of black spots at the negative electrode interface, which is easy to cause lithium precipitation problems, or the porosity of the substrate may be too small, providing too few lithium ion transmission channels, increasing the internal resistance of the battery, and reducing the charging and discharging efficiency of the battery.

[0023] It should be noted that when calculating the value of the D / P formula, the porosity P of the substrate is converted into a decimal and entered. For example, when D is 4 and P (%) is 35, D / P = 4 / (35×0.01) = 11.43.

[0024] It should be noted that the "given direction" mentioned in the present invention can be understood as including three situations: along the TD direction of the diaphragm (the TD direction of the diaphragm is the transverse direction of the diaphragm), along the MD direction of the diaphragm (the winding direction of the diaphragm, also called the machine direction), and oblique setting (not parallel to the TD direction and the MD direction).

[0025] In some embodiments, along the TD direction of the diaphragm, the ceramic layer includes a plurality of T1 regions and a plurality of T2 regions that are alternately arranged in sequence. Figure 1 As shown, the T1 region 1 and the T2 region 2 in the diaphragm ceramic layer are alternately arranged in sequence along the TD direction of the diaphragm, and the minimum angle A1 between the T1 region 1 and the T2 region 2 and the TD direction of the diaphragm is 0°≤A1≤90°.

[0026] In some embodiments, along the MD direction of the separator, the ceramic layer includes a plurality of T1 regions and a plurality of T2 regions that are alternately arranged in sequence. Figure 2 As shown, the T1 region 1 and the T2 region 2 in the diaphragm ceramic layer are alternately arranged in sequence along the MD direction of the diaphragm, and the minimum angle A2 between the T1 region 1 and the T2 region 2 and the MD direction of the diaphragm is 0°≤A2≤90°.

[0027] In some embodiments, in any direction parallel to the substrate surface but not parallel to the TD direction and the MD direction of the separator, the ceramic layer includes a plurality of T1 regions and a plurality of T2 regions alternately arranged in sequence. Figure 3 As shown, the T1 region 1 and the T2 region 2 in the diaphragm ceramic layer are alternately arranged in an oblique direction in sequence, and the minimum angle A3 between the T1 region 1 and the T2 region 2 and the MD direction or TD direction of the diaphragm is 0°<A3<90°.

[0028] In some embodiments, ceramic layers are provided on both sides of the substrate.

[0029] In some embodiments, a ceramic layer is provided on one side surface of the substrate. When the ceramic layer is provided on only one side surface of the substrate, the ceramic layer preferably faces the positive electrode sheet. The presence of the diaphragm ceramic layer will weaken the adhesion between the diaphragm and the electrode sheet to a certain extent. Due to the characteristics of the positive and negative electrode materials, the adhesion of the ceramic layer when facing the positive electrode sheet is stronger than the adhesion of the ceramic layer when facing the negative electrode sheet. The ceramic layer preferably faces the positive electrode sheet to ensure the bonding strength between the diaphragm and the electrode sheet, maintain the structural integrity of the battery, and also help reduce the internal stress during the battery charging and discharging process, further extending the cycle life of the battery.

[0030] In some embodiments, the porosity (P%) of the substrate satisfies: 30≤P≤60, and the porosity of the substrate can be, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60% or any point value in the range composed of the above two point values. The porosity of the substrate is the ratio of the volume of the micropores in the substrate to the total volume of the substrate, which directly affects the electrochemical properties of the substrate, including air permeability, liquid absorption rate, electrochemical impedance, etc. Controlling the porosity of the substrate to further meet the above range can further accelerate the migration rate of lithium ions and improve the fast charging performance of the battery.

[0031] In the present application, when obtaining the performance parameters of the substrate (such as porosity, elongation at break, puncture strength), the method of removing the ceramic layer from the diaphragm sample is not particularly limited, and examples include: using tape to stick and peel the ceramic layer from the substrate; or immersing the diaphragm sample in water or other solvents that can dissolve the ceramic layer, applying ultrasonic cleaning, and drying at room temperature.

[0032] Exemplarily, the ceramic layer is pasted and peeled off from the substrate using an adhesive tape until the residual rate of the ceramic layer on the substrate is less than 5%, and the porosity of the obtained substrate can be measured, for example, using a true density test method (such as a dry method, a volume method). The porosity of the substrate is calculated by measuring the apparent density of the substrate and the raw material density. Among them, the raw material density refers to the true density of the material used to make the substrate, such as polyethylene (PE), polypropylene (PP), etc. The calculation formula is: porosity = (raw material density-apparent density) / raw material density × 100%.

[0033] In some embodiments, D1 satisfies: 0.5≤D1≤5, and the thickness of the ceramic layer in the T1 region can be, for example, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm or any point value in the range consisting of any two of the above point values.

[0034] In some embodiments, D2 satisfies: 0.5≤D2≤5, and the thickness of the ceramic layer in the T2 region can be, for example, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm or any point value in the range formed by any two of the above point values, preferably 0.2≤D2≤3.

[0035] The thickness of the ceramic layer in the T1 region and the ceramic layer in the T2 region determines the depth of the recessed area of ​​the ceramic layer, which in turn affects the distribution of the electrolyte inside the battery and the interface stability between the diaphragm and the pole piece, as well as the uniformity of the charge distribution on the electrode surface. By further controlling the thickness of the ceramic layer in the T1 region and the ceramic layer in the T2 region to meet the above range, on the one hand, the concentration gradient of the electrolyte can be further reduced, so that the electrolyte infiltration is more sufficient, the lithium ion conductivity is improved, and the stability of the contact interface between the diaphragm and the pole piece is improved, and the black spot lithium precipitation at the negative electrode interface is inhibited, thereby improving the expansion of the battery and extending the cycle life of the battery; on the other hand, the unevenness of the charge distribution on the electrode surface can be prevented from being too serious, which will excessively affect the fast charging performance of the battery.

[0036] In the present invention, the thickness D1 of the ceramic layer in the T1 region can be interpreted as the maximum vertical distance from the surface of the ceramic layer on the side away from the substrate to the surface of the substrate in the T1 region, such as Figure 4 As shown in D1; the thickness D2 of the ceramic layer in the T2 region can be interpreted as the minimum vertical distance from the surface of the ceramic layer away from the substrate to the substrate surface in the T2 region, as shown in Figure 4 As shown in D2.

[0037] In some embodiments, along the given direction, the shortest distance from one side boundary to the other side boundary of the ceramic layer in the T1 region (for ease of understanding, it can also be described as the "width" of the T1 region) is recorded as L1μm, and the shortest distance from one side boundary to the other side boundary of the ceramic layer in the T2 region (corresponding to the "width" of the T2 region) is recorded as L2μm, L=L1 / L2, L satisfies: 0.5≤L≤3, and the value of L can be, for example, any point value in the range of 0.5, 1, 1.5, 2, 2.5, 3. The ratio of the width of the ceramic layer in the T1 region to the width of the ceramic layer in the T2 region determines the proportion of the protrusion (T1 region) and the depression (T2 region) of the ceramic layer on the surface of the diaphragm. When the size of the diaphragm is constant, the larger L is, the larger the proportion of the protrusion in the ceramic layer is, and conversely, the smaller L is, the larger the proportion of the depression in the ceramic layer is. By controlling the size of L, the ceramic layer can form a suitable electrolyte storage space on the surface of the diaphragm, which is beneficial to the infiltration of the electrolyte, further improving the battery interface problems and improving the black spot lithium precipitation. At the same time, it will not excessively affect the lithium ion utilization rate and conductivity of the diaphragm, thereby excessively reducing the fast charging performance of the battery.

[0038] In some embodiments, L1 satisfies: 6≤L1≤100, and the shortest distance from one side boundary to the other side boundary of the ceramic layer in the T1 region can be, for example, 6μm, 8μm, 10μm, 15μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, or any point value in the range consisting of any two of the above point values.

[0039] In some embodiments, L2 satisfies: 6.7≤L2≤50, and the shortest distance from one side boundary to the other side boundary of the ceramic layer in the T2 region can be, for example, 6.7μm, 7μm, 8μm, 9μm, 10μm, 20μm, 30μm, 40μm, 50μm, or any point value in the range consisting of any two of the above point values.

[0040] When the size of the diaphragm is constant, the width of the ceramic layer in the T1 region and the width of the ceramic layer in the T2 region determine the number of concave-convex structures on the diaphragm surface composed of the T1 region (protrusion) and the T2 region (depression). Further controlling the size of the ratio L of L1 and L2 can form a suitable number of concave-convex structures on the diaphragm surface, avoiding the situation where the size of L1 is too small or the size of L2 is too large, which affects the continuity of the diaphragm ceramic layer, resulting in insufficient adhesion at the contact interface between the diaphragm and the electrode, and easily causes black spots and lithium precipitation at the negative electrode interface during the battery cycle expansion process, worsening the interface problem, and ultimately causing a decrease in the battery cycle performance. It may also excessively affect the lithium ion utilization and conductivity of the diaphragm, and significantly reduce the fast charging performance of the battery.

[0041] Depend on Figure 4It can be seen that the shortest distance L1 from one side boundary to the other side boundary of the ceramic layer in the T1 region can be understood as the length of the shortest straight section of the ceramic layer along the given direction (i.e., the direction in which the T1 region and the T2 region are alternately arranged in sequence) on the surface of the side of the ceramic layer away from the substrate; relative to L1, the shortest distance L2 from one side boundary to the other side boundary of the ceramic layer in the T2 region is determined by the shape of the recessed portion formed by the ceramic layer in the T2 region. Taking the example of an arc-shaped recessed portion of the ceramic layer, L2 can be understood as the shortest tangent distance from the intersection point of the arc boundary on one side of the T2 region to the arc boundary on the opposite side along the given direction on the surface of the ceramic layer away from the substrate, as shown by L2 in the figure.

[0042] In some embodiments, the T1 region and T2 region of the diaphragm ceramic layer can be manufactured using a gravure roller. Specifically, the structure of the gravure roller can be adjusted to set periodic concave and convex regions on the gravure roller, thereby obtaining the T1 region and T2 region of the ceramic layer with specific thickness and width. Figure 4 The figure shows a schematic diagram of a cross-sectional structure of a diaphragm in an example of the present invention, wherein T1 region 1 and T2 region 2 are alternately arranged in sequence, and along the thickness direction of the substrate 3, there is a thickness difference between T1 region 1 and T2 region 2, a convex portion is formed in the T1 region, and a concave portion is formed in the T2 region, thereby forming a plurality of concave-convex structures regularly arranged in a "striped" manner on the surface of the diaphragm.

[0043] Exemplarily, the thickness D1 and width L1 of the ceramic layer in the T1 region and the thickness D2 and width L2 of the T2 region in the present invention can be measured by observation under a scanning electron microscope. For example, a number of T1 regions and T2 regions can be randomly selected from the ceramic layer (for example, an integer number of 5, 10, 20, etc. of T1 regions / T2 regions can be selected), and the thickness and width of the ceramic layer in the selected T1 region and the ceramic layer in the T2 region are measured respectively, and the average values ​​of each are taken to obtain D1, D2, L1, and L2.

[0044] In some embodiments, the elongation at break of the substrate in the TD direction is recorded as E TD %, L and E TD Satisfy: 0.3≤L / E TD ≤6, L / E TD The value of can be, for example, 0.3, 0.5, 0.8, 1, 2, 3, 4, 5, 6 or any point value in the range of the above two points. The elongation at break of the substrate in the TD direction is an important indicator for measuring the ductility of the substrate under the action of tensile force, which determines the stability of the overall structure of the diaphragm and directly affects the cycle performance of the battery. The present invention controls L and E TD The ratio of the two makes the proportion of the ceramic layer T1 area (convex part) and the T2 area (concave part) on the diaphragm surface and the elongation at break of the substrate in the TD direction within an appropriate range, which can avoid L / ETD When <0.3, it means L is too small and / or E TD If L is too small, the ceramic layer depression will occupy a large proportion of the diaphragm surface, and the continuity of the ceramic layer will be reduced, resulting in uneven charge distribution on the electrode surface, affecting the insertion and extraction speed of lithium ions, thereby reducing the fast charging performance of the battery; E TD If the size is too large, the diaphragm will be easily deformed during battery assembly and use, affecting the structural stability and electrochemical performance of the battery. TD >6, meaning L is too large and / or E TD When E is too small and L is too large, the recessed space provided by the ceramic layer T2 region is too small. Although the uniformity of charge distribution on the electrode surface can be improved, the ion transmission efficiency will be reduced, which is also not conducive to improving the interface problem. TD If the value is too small, the flexibility and ductility of the diaphragm are poor, and the ability to resist deformation caused by external force is weak, which is not conducive to alleviating the mechanical stress caused by volume expansion during the battery charging and discharging process. There is a risk of diaphragm rupture, which can easily cause battery short circuit and deteriorate the battery winding yield. L / E TD The value of is in an appropriate range, which can effectively improve the battery's cycle performance and interface stability.

[0045] It should be noted that when calculating L / E TD When the value of the formula is, the elongation at break of the substrate in the TD direction E TD Convert to a decimal and substitute, for example, L is 0.5, E TD When (%) is 100, L / E TD =0.5 / (100×0.01)=0.5.

[0046] In some embodiments, E TD Satisfy: 50 ≤ E TD ≤150, the elongation at break of the substrate in the TD direction can be, for example, 50%, 80%, 100%, 120%, 150% or any point value in the range formed by any two of the above point values. Further limiting the elongation at break of the substrate in the TD direction to the above range can further stabilize the overall structure of the diaphragm, and cooperate with the geometric structure of the diaphragm ceramic layer to better stabilize the contact interface between the diaphragm and the pole piece, thereby improving the cycle performance and safety performance of the battery.

[0047] In some embodiments, the elongation at break of the substrate in the MD direction is recorded as E MD %E MD Satisfy: 50 ≤ E MD≤300, the elongation at break of the substrate in the MD direction can be, for example, 50%, 100%, 150%, 200%, 250%, 300% or any point value in the range of any two of the above points. Controlling the elongation at break of the substrate in the MD direction to meet the above range can make the substrate have appropriate flexibility and ductility in the MD direction, avoiding E MD <50, the elongation of the substrate is poor. During the winding process and use, the diaphragm will be subjected to the tensile force and bending force from the winding equipment, which may cause cracks or ruptures. Avoid E MD When the value is greater than 300, the substrate is easily deformed excessively by external forces, which is not conducive to the stability of the overall structure of the diaphragm.

[0048] For example, the ceramic layer is peeled off from the substrate using an adhesive tape until the residual rate of the ceramic layer on the substrate is less than 5%, and the elongation at break of the obtained substrate in the TD direction and the elongation at break of the substrate in the MD direction can be measured by a tensile testing machine. The specific test method may include the following steps: the substrate is prepared into a sample with a width of 15 mm along the TD or MD direction, the initial distance between the clamps of the tensile testing machine is set to 50 mm, and the test is conducted at a tensile speed of 100±10 mm / min until the substrate breaks, and the distance between the clamps at the time of break is recorded as L TD mm or L MD mm, elongation at break of substrate in TD direction = (L TD -50) / 50×100%; elongation at break of substrate in MD direction = (L MD -50) / 50×100%.

[0049] In some embodiments, the peel strength between the ceramic layer and the substrate is 30N / m-200N / m, for example, 30N / m, 50N / m, 80N / m, 100N / m, 150N / m, 200N / m or any point value in the range of any two of the above points. The peel strength between the ceramic layer and the substrate satisfies the above range, which can improve the overall structural stability of the diaphragm and avoid the difficulty in diaphragm processing due to too high peel strength, and the ceramic layer and the substrate are easily delaminated and fall off due to too low peel strength due to the influence of external force.

[0050] Exemplarily, the peel strength between the ceramic layer and the substrate can be measured by a tensile testing machine. The specific test method may include the following steps: take a stainless steel plate of a certain size, paste a double-sided tape in the center, and tear off the paper layer; take a diaphragm sample coated with a ceramic layer, and fit one side of the diaphragm to the upper surface of the double-sided tape; take a 15mm wide 3M peeling tape, and the adhesive layer is close to the upper surface of the diaphragm coated with the ceramic layer (the side not bonded with the double-sided tape); use a rubber roller to roll back and forth naturally on the 3M peeling tape to ensure that the adhesive in the 3M peeling tape is evenly distributed; use a 180° peeling method, and use a tensile testing machine to perform a peeling test at a peeling speed of 100mm / min, then the peel strength between the ceramic layer and the substrate = peeling force / peeling tape width × 100%.

[0051] In some embodiments, the ceramic layer includes ceramic particles, a binder, and a dispersant.

[0052] In some embodiments, based on the total mass of the ceramic layer, the mass of the ceramic particles accounts for 40%-96%, for example, it can be 40%, 50%, 60%, 70%, 80%, 90%, 96% or any point value in the range consisting of any two of the above point values.

[0053] The ceramic particles can be selected from, for example, boehmite (γ-AlOOH), alumina (Al 2 O 3 ), barium sulfate (BaSO 4 ), magnesium oxide (MgO), magnesium hydroxide (Mg(OH) 2 ), silicon dioxide (SiO 2 ), tin dioxide (SnO 2 ), titanium oxide (TiO 2) , calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO 2 ), yttrium oxide (Y 2 O 3 ), nickel oxide (NiO), cerium oxide (CeO 2 ), zirconium titanate (SrTiO 3) 、Barium titanate (BaTiO 3 ), magnesium fluoride (MgF 2 )

[0054] In some embodiments, based on the total mass of the ceramic layer, the mass proportion of the binder is 3%-60%, for example, it can be 3%, 5%, 8%, 10%, 20%, 30%, 40%, 50%, 60% or any point value in the range consisting of any two of the above points.

[0055] In the present invention, the binder in the ceramic layer is not specifically limited. For example, conventional binders in the art can be selected, including but not limited to one or more of polyvinylidene fluoride, copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene or polyhexafluoropropylene.

[0056] In some embodiments, based on the total mass of the ceramic layer, the mass proportion of the dispersant is 0.7%-1.5%, for example, it can be 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or any point value in the range consisting of any two of the above points.

[0057] In the present invention, the dispersant in the ceramic layer is not specifically limited, and the dispersant may be any conventional dispersant in the art, including but not limited to at least one of polyamide, polyvinyl alcohol, polyurethane, and polyvinyl pyrrolidone.

[0058] In some embodiments, the substrate further satisfies at least one of the following conditions:

[0059] (i) the thickness of the substrate is 4 μm-20 μm;

[0060] (ii) the pore size distribution of the substrate is 10 nm-100 nm;

[0061] (iii) The puncture strength of the substrate is denoted as N gf, where N satisfies: 200≤N≤400.

[0062] In (i), the thickness of the substrate can be, for example, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, or any point value in the range formed by the above two points. Controlling the thickness of the substrate to meet the above range can ensure that the overall performance of the diaphragm meets the requirements of different application scenarios, while avoiding the decrease in mechanical properties of the diaphragm due to the substrate being too thin, which may cause the positive and negative electrodes to contact and cause a short circuit in the battery, and avoiding the substrate being too thick, which may cause the lithium ion transmission path to be too long and reduce the fast charging performance of the battery.

[0063] In (ii), the pore size distribution of the substrate can be, for example, 10 nm, 20 nm, 50 nm, 80 nm, 100 nm, or any point value in the range of any two of the above points. The pore size distribution of the substrate satisfies the above range, which can ensure the efficient transmission of lithium ions and improve the fast charging performance of the battery.

[0064] In (iii), the puncture strength of the substrate can be, for example, 200 gf, 250 gf, 300 gf, 350 gf, 400 gf, or any point value in the range formed by any two of the above points. When the puncture strength of the substrate is within the above range, it can effectively resist the mechanical stress that may be generated inside the battery, prevent the diaphragm from being punctured and causing a short circuit between the positive and negative electrodes, ensure the safety and cycle stability of the battery, and extend the battery life.

[0065] Exemplarily, the puncture strength test method of the substrate may include the following steps: flatten the substrate in a fixture and clamp it, take a puncture needle with a diameter of Φ=1.0 mm and a spherical tip R=0.5 mm and puncture perpendicularly to the surface of the substrate at a rate of 100±10 mm / min until the substrate is pierced, and record the maximum puncture force, which is the puncture strength of the substrate.

[0066] A second aspect of the present invention provides a battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator is the separator provided by the first aspect of the present invention.

[0067] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one side of the surface of the negative electrode current collector, the negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes silicon particles; based on the total mass of the negative electrode active material, the mass proportion of the silicon element is denoted as G%, and G satisfies: 10≤G≤20. The mass proportion of the silicon element can be, for example, 10%, 12%, 14%, 16%, 18%, 20%, or any point value in the range composed of any two of the above point values.

[0068] Silicon-containing negative electrode sheets can significantly increase the energy density of batteries, provide a fast channel for lithium ion migration during charging and discharging, and improve the low-temperature discharge capacity of batteries. However, silicon particles will undergo severe volume changes during electrochemical reactions (volume changes of up to 320%). This severe volume expansion and contraction will cause damage to the structure of the electrode material, greatly affecting the thickness expansion and interface stability of the battery during the cycle. The present invention controls the proportion of silicon elements in the negative electrode active material within the above range, which can fully utilize the advantages of silicon particles in significantly improving the energy density of batteries, providing a fast channel for lithium ion migration, and improving the low-temperature discharge capacity of batteries, and can effectively avoid the destruction of the electrode material structure caused by excessive volume expansion of silicon particles, thereby well controlling the thickness expansion of the battery during the cycle, maintaining the stability of the battery interface, and ultimately improving the overall performance and cycle life of the battery.

[0069] For example, in the negative electrode active material, the mass proportion of silicon element can be obtained by acid treating the negative electrode active material and then performing ICP analysis and calculation. Alternatively, the test method for the mass proportion of silicon element can be tested by thermogravimetric analysis, for example, using Shimadzu DTG-60 thermogravimetric analyzer for testing, and the test conditions are: sample amount 5 mg, air as atmosphere, heating rate 10℃ / min from room temperature to 900℃ and constant temperature for 40min. The relationship between the mass proportion of silicon element (x) and the final weight residual percentage (y) of the entire test is: x=7y / 15.

[0070] In some embodiments, the particle size Dv50 of the silicon particles is recorded as V nm, V satisfies: 10≤V≤50, and the particle size Dv50 of the silicon particles can be, for example, 10nm, 20nm, 30nm, 40nm, 50nm, or any point value in the range composed of the above two point values. Controlling the particle size Dv50 of the silicon particles within the above range is helpful to form a uniform and stable microstructure in the negative electrode sheet, which can increase the contact area between the silicon particles and the electrolyte, improve the efficiency of lithium ion insertion and extraction, and alleviate the volume change of the silicon particles during the charge and discharge process, reduce the structural stress concentration caused by the excessively large particle size and the agglomeration of the silicon particles caused by the excessively small particle size, thereby improving the charge and discharge performance, cycle stability and energy density of the battery.

[0071] The particle size Dv50 of the silicon particles can be measured by a laser particle size test method, for example, using a Malvern particle size tester for measurement.

[0072] In some embodiments, the silicon particles include one or more of elemental silicon, silicon oxygen, silicon carbon, silicon nitrogen, and silicon alloys.

[0073] In some embodiments, the width ratio L of the ceramic layer in the T1 region and the ceramic layer in the T2 region, the thickness ratio D of the ceramic layer in the T1 region and the ceramic layer in the T2 region, and the silicon content G in the negative electrode active material satisfy: The value of can be, for example, 5, 8, 10, 20, 30, 40, 50, 60, 70 or any point value in the range of the above two point values. Since L and D represent the proportion of the protrusions and depressions of the ceramic layer on the surface of the diaphragm and the depth of the depressions of the ceramic layer, respectively, the comprehensive feature of the product of L and D can be used to quantitatively describe the morphology of the concave-convex structure on the surface of the diaphragm, and jointly determine the distribution of the electrolyte inside the battery. By controlling the ratio of (L×D) to the silicon content (G) in the negative electrode active material to meet the above range, the "striped" interlaced concave-convex structure of the ceramic layer can, on the one hand, improve the infiltration of the electrolyte and the film thickness of the SEI in the central area of ​​the negative electrode sheet, so that it is not easy to locally rupture when the silicon particles cyclically expand, thereby improving the cycle performance of the battery; on the other hand, it can provide a suitable gap to buffer the volume expansion of the silicon particles in the negative electrode sheet, thereby improving the cycle expansion and improving the cycle performance of the battery; on the third hand, it can keep the charge distribution on the electrode surface suitable for the volume expansion of the silicon particles, increase the lithium insertion and delithiation rate of the silicon particles, and thus improve the battery's cycle fast charging performance. At the same time, avoid When the size of the diaphragm is constant, the proportion of the recessed part in the ceramic layer is too large or the depth of the recessed part is too shallow, which is not conducive to the infiltration of the electrolyte and the alleviation of the volume expansion of the silicon particles; or the negative electrode is doped with too much silicon, the diaphragm has poor resistance to puncture, and the roughness of the silicon particles may cause damage to the diaphragm, which is easy to cause a short circuit in the battery process; it can also avoid When the size of the diaphragm is constant, if the depression in the ceramic layer is too deep or the thickness of the protrusion is too large, although the wettability of the electrolyte can be improved, it will lead to uneven charge distribution on the electrode surface, affecting the insertion and extraction speed of lithium ions, thereby reducing the fast charging performance of the battery; or the silicon content is too low, which is not conducive to improving the battery energy density.

[0074] It should be noted that in the calculation When the value of the formula is used, the silicon content G is converted into a decimal and inserted. For example, when L is 0.5, D is 4, and G (%) is 10,

[0075] In some embodiments, the width ratio L of the ceramic layer in the T1 region and the ceramic layer in the T2 region, the puncture strength N of the substrate, and the particle size Dv50 V of the silicon particles satisfy: The value of can be, for example, 16, 20, 30, 40, 50, 60, 70, 80 or any point value in the range formed by any two of the above point values. The arrangement of the concave-convex structure of the ceramic layer (the proportion of the protrusions and depressions on the surface of the diaphragm) and the puncture strength of the substrate jointly determine the stability of the diaphragm and the uniformity of the charge distribution on the surface of the pole piece. The particle size Dv50 of the silicon particles affects the volume change of the silicon particles during the charging and discharging process of the battery. Using (L×N) as a quantitative parameter for the stability of the diaphragm and controlling the ratio of (L×N) to the particle size Dv50 (V) of the silicon particles to meet the above range can effectively improve the short-circuit problem in the battery process caused by the change in the roughness of the silicon particles, as well as the rate of lithium insertion and extraction during the cycle of the silicon particles, further improving the cycle performance of the battery and improving cycle expansion; it can avoid 16. When the diaphragm size is constant, if the ceramic layer depression accounts for too large a proportion of the diaphragm surface, the substrate's needle puncture strength is too low, or the silicon particle size is too large, the risk of short circuit in the battery manufacturing process will increase. When the size of the diaphragm is constant, the proportion of the recessed part of the ceramic layer on the surface of the diaphragm is too small, the puncture strength of the substrate is too large, or the particle size of the silicon particles is too small, the liquid storage performance of the diaphragm is reduced, the lithium ion transmission performance of the battery is weakened, and the battery's charge and discharge capacity deviation is caused.

[0076] In some embodiments, the conductivity of the electrolyte is recorded as σmS / cm, σ satisfies: 3≤σ≤15, and the conductivity of the electrolyte can be, for example, 3mS / cm, 5mS / cm, 7mS / cm, 9mS / cm, 11mS / cm, 13mS / cm, 15mS / cm or any point value in the range composed of the above two point values. The conductivity of the electrolyte reflects the electrical conductivity of the electrolyte and directly affects the migration rate of lithium ions and the performance of the battery. Controlling the conductivity of the electrolyte within the above range can optimize the migration rate of lithium ions, improve the impact of uneven charge distribution on the electrode surface caused by the uneven surface of the diaphragm, improve the fast charging performance of the battery, avoid the conductivity of the electrolyte being too low, the migration rate of lithium ions is slowed down, and the battery performance is reduced; avoid the conductivity of the electrolyte being too high, which may cause internal short circuit or overheating of the battery, affecting the safety of the battery.

[0077] Exemplarily, the conductivity of the electrolyte can be tested by a conductivity meter, which may include the following steps: clean the conductivity electrode to ensure that there is no dirt on the electrode surface; pour the electrolyte sample into the measuring container to ensure that the electrode is completely immersed in the solution; connect the conductivity meter, apply an appropriate voltage, and measure the current passing through the electrode; read the conductivity value displayed by the conductivity meter and record it.

[0078] The thickness D1 of the ceramic layer in the T1 region, the thickness D2 of the ceramic layer in the T2 region, the width L1 of the ceramic layer in the T1 region, the width L2 of the ceramic layer in the T2 region and the conductivity σ of the electrolyte satisfy the formula: The value of can be, for example, 0.5, 1, 2, 3, 4, 5, 6, 7 or any point value in the range of the above two point values. In the region consisting of a single T1 region and a single T2 region, It represents the ratio of the depth of the depressed portion formed in the T2 region to the thickness of the T1 region. It represents the ratio of the width of the T2 region (the width of the formed depressed portion) to the total width of the T1 region and the T2 region. It can be expressed as the spatial area ratio of the depression formed by the ceramic layer in the T2 region within the region composed of a single T1 region and a single T2 region of the ceramic layer. The size of the depression directly affects the wettability of the electrolyte and is related to the lithium ion transmission rate of the diaphragm and the uniformity of charge distribution on the surface of the electrode. The present invention further defines Meeting the above range and correlating the area ratio of the recessed portion of the ceramic layer with the conductivity of the electrolyte can avoid When the conductivity of the electrolyte is too low, or when the thickness of the ceramic layer in the T1 region and the ceramic layer in the T2 region remain unchanged, the thickness of the ceramic layer in the T1 region is relatively low, and the formed depression is too shallow, or, for example, when the width of the ceramic layer in the T2 region remains unchanged, the width of the ceramic layer in the T1 region is too large, and the width of the ceramic layer in the T2 region is relatively low, and the width of the formed depression is too narrow, resulting in a relatively low area of ​​the depression in the ceramic layer, which is not conducive to the battery's liquid storage and lithium ion transmission, and ultimately leads to deviations in the battery's cycle performance; avoid When the conductivity of the electrolyte is too high, or for example, when the thickness of the ceramic layer in the T2 region remains unchanged, the thickness of the ceramic layer in the T1 region is too high, and the formed depression is too deep, or for example, when the width of the ceramic layer in the T2 region remains unchanged, the width of the ceramic layer in the T1 region is too small, and the width of the ceramic layer in the T2 region accounts for a relatively high proportion, and the width of the formed depression is too wide, resulting in a relatively high proportion of the area of ​​the depression in the ceramic layer. Although the lithium ion conductivity of the battery can be improved, the strength deviation of the diaphragm may aggravate the interface problem, easily produce black spots at the negative electrode interface, precipitate lithium dendrites, and increase the risk of short circuit; and the charge distribution unevenness on the electrode surface is aggravated, reducing the fast charging performance.

[0079] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0080] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0081] The present invention is described in detail below in conjunction with specific embodiments, which are used to understand but not to limit the present invention.

[0082] Example 1-1

[0083] 1. Diaphragm preparation

[0084] (1) mixing a ceramic material, a binder, a dispersant and a solvent to obtain a ceramic slurry;

[0085] (2) The ceramic slurry obtained in step (1) is coated on one side of the substrate by roller coating, and after high temperature baking, a base film layer coated with a ceramic layer on one side or a substrate coated with a ceramic layer on both sides is obtained. The T1 region and the T2 region of the ceramic layer are arranged in sequence along the TD direction of the separator, and the surface of the separator ceramic layer is opposite to the surface of the positive electrode sheet.

[0086] The substrate is a polyethylene microporous membrane, the thickness of the substrate is 9 μm, the porosity is 35%, the puncture strength is 400 gf, and the elongation at break in the TD direction is 50%.

[0087] Ceramic material is Al 2 O 3 The binder is polymethyl methacrylate, the dispersant is polyethylene oxide, and the solvent is water; the mass ratio of the ceramic material, the binder, the dispersant and the solvent is 35:4:1:60.

[0088] The width L1 of the T1 region is 7.5 μm, and the thickness D1 is 2 μm; the width L2 of the T2 region is 15 μm, and the thickness D2 is 0.5 μm.

[0089] 2. Battery preparation

[0090] (1) Preparation of positive electrode

[0091] Conductive carbon (Super-P) and activated carbon are mixed in a mass ratio of 1:1 as a conductive agent. Polyvinylidene fluoride (PVDF) is used as a binder, and lithium cobalt oxide is used as an active material. According to the ratio of 97.5% active material, 1.35% conductive agent and 1.15% binder, they are dissolved in N-methylpyrrolidone solvent and mixed evenly. After that, the obtained positive electrode slurry is evenly coated on both sides of the aluminum foil current collector and dried to form a positive electrode film. Finally, the production of lithium-ion battery positive electrode sheets is completed through the steps of cold pressing, cutting into sheets and welding electrode ears.

[0092] (2) Preparation of negative electrode sheet

[0093] Si-C is used as the negative electrode active material (the silicon content in Si-C is 10%), and the particle size Dv50 of the silicon particles is 50nm. The active material is mixed with Super-P conductive agent, sodium carboxymethyl cellulose (CMC) thickener and styrene-butadiene rubber (SBR) binder, wherein the mass ratio of the negative electrode active material, conductive agent, thickener and binder is 97.2:0.6:1:1.2. These materials are dissolved in deionized water and stirred thoroughly to form a negative electrode slurry. Then, the negative electrode slurry is evenly coated on both sides of the copper foil current collector and dried to form a negative electrode film. Finally, the preparation of the negative electrode sheet of the lithium-ion battery is completed by cold pressing, cutting into sheets and welding the electrode ears.

[0094] (3) Preparation of electrolyte

[0095] LiPF 6 As lithium salt, ethylene carbonate, diethyl carbonate, methyl ethyl carbonate and vinylene carbonate were mixed in a mass ratio of 8:85:5:2 to form a mixed solvent. Subsequently, the lithium salt and the solvent were mixed in a mass ratio of 8:92 to form an electrolyte. The conductivity σ of the electrolyte used was 10 mS / cm.

[0096] (4) Preparation of batteries

[0097] The separator is the separator prepared in step (1), and the prepared positive electrode sheet, negative electrode sheet and manufactured separator are wound and assembled into a battery cell. After drying, liquid injection and packaging, a lithium-ion secondary battery is obtained.

[0098] 3. Battery performance test:

[0099] i) Cyclic performance test

[0100] The thickness and capacity of the battery at 30% SOC were tested at 25°C; the temperature of the incubator was adjusted to 25°C, the battery was left standing for 60 minutes, discharged at 10C to the lower cut-off voltage, left standing for 5 minutes, charged at 3C to the upper cut-off voltage, and maintained at a constant voltage of 0.05C; the battery was left standing for 30 minutes, and the thickness and capacity of the battery were measured at the first full charge; the temperature was adjusted to 10°C and the following steps were performed: (1) discharged at 10C to the lower cut-off voltage; (2) left standing for 30 minutes; (3) charged at 3C to the upper cut-off voltage, maintained at a constant voltage of 0.05C, and left standing for 5 minutes; (4) Steps (1) to (4) were cycled for 600T, and the thickness and capacity of the battery were tested every 100T under full charge.

[0101] Thickness expansion ratio = (battery thickness after cycle number - initial thickness) / initial thickness × 100%.

[0102] Capacity retention rate = battery capacity after different cycles / initial capacity × 100%.

[0103] The thickness expansion rate and capacity retention rate of the battery after 600T cycles are taken as the test results in the present invention and recorded in the corresponding embodiment table below.

[0104] ii) Lithium precipitation test

[0105] When the battery cycle reaches 600T, it is charged at 3C to the upper cut-off voltage, and the voltage is constant to 0.05C, and then it is disassembled. Confirm the lithium deposition on the interface. According to the lithium deposition situation, the lithium deposition degree is given in order from light to heavy. ★ represents no lithium deposition at all, ★★ represents mild lithium deposition, ★★★ represents moderate lithium deposition, and ★★★★ represents severe lithium deposition.

[0106] iii) 25℃ rate charging

[0107] At the test temperature of 25±3℃, the battery cell packaging test: stand for 5 minutes; discharge at 0.5C to the lower cut-off voltage; stand for 30 minutes; charge at a rate of 5C to the upper cut-off voltage, and record the capacity at this time as [CC-capacity]; continue to charge at a constant voltage to 0.05C, and record the capacity at this time as [CC-CV capacity]; calculate the constant current charging ratio = [CC-capacity] / [CC-CV capacity]×100%.

[0108] iv) Short circuit rate

[0109] After the battery goes through the winding process and before the liquid injection process, a voltage higher than normal operation (usually 100V) is applied to the two side ears of the battery, and the insulation of the core is judged by testing the resistance. When the core resistance is ≤2MΩ, it means that the core is short-circuited. Test 100 batteries and calculate the short-circuit rate.

[0110] Example 1 and Example 2 as well as Comparative Examples 1-4 are carried out with reference to Example 1-1, and the main differences are shown in Table 1. Among them, the porosity P of the substrate in Example 1 changes. The ratio (D) of the thickness (D1) of the ceramic layer in the T1 region to the thickness (D2) in the T2 region in Example 2 changes. The diaphragm in Comparative Example 1 is a conventional diaphragm, and there is no thickness difference in the ceramic layer. In Comparative Example 2, D is too large, and the value of D / P is not within the protection range. Comparative Example 3 is a conventional diaphragm, there is no thickness difference in the ceramic layer and the porosity of the substrate is too large, and the value of D / P is not within the protection range. In Comparative Example 4, the values ​​of D1, D2, P, and D are all within the protection range, but the value of D / P is not within the protection range.

[0111] Table 1

[0112]

[0113]

[0114] As can be seen from Table 1, the diaphragm provided by the present invention is provided with a ceramic layer on at least one side surface of the substrate, the ceramic layer has T1 regions and T2 regions arranged alternately at intervals, there is a thickness difference between the T1 region and the T2 region, and a plurality of concave-convex structures that can optimize the distribution of the electrolyte are formed on the surface of the diaphragm, which can improve the wettability of the electrolyte, is beneficial to maintain the stability of the interface in the late stage of battery cycle expansion, and improves the cycle capacity retention rate of the battery; further controlling the ratio of the thickness ratio of the T1 region and the T2 region to the porosity of the substrate to meet a specific range can improve the influence of uneven charge distribution on the electrode surface caused by the uneven surface of the diaphragm, thereby effectively improving the migration rate of lithium ions, improving the fast charging performance of the battery, and reducing the risk of lithium plating and short circuit of the battery.

[0115] The examples 3 and 4 were carried out in accordance with the example 1-1, and the main differences are shown in Table 2. Among them, the elongation at break E of the substrate in the TD direction of the example 3 group is TD Size change, E TD The size of can be adjusted by changing the molecular weight of the raw materials used in the preparation of the substrate and the stretching and shaping process. In Example 4, the size of the ratio L between the width L1 of the T1 region and the width L2 of the T2 region of the ceramic layer is changed.

[0116] Table 2

[0117]

[0118]

[0119] As shown in Table 2, the present invention adjusts the elongation at break E of the substrate in the TD direction. TD size, the ratio L of the width L1 of the ceramic layer T1 region to the width L2 of the ceramic layer T2 region, and the ratio L between L and E TD The ratio can further improve the battery's cycle capacity retention rate and fast charging performance, and reduce the risk of battery lithium plating and short circuit.

[0120] The fifth embodiment is carried out in accordance with the first embodiment, and the main differences are shown in Table 3. The fifth embodiment adjusts the width ratio L between the T1 region and the T2 region, the thickness ratio D between the T1 region and the T2 region, or the silicon content G to obtain The value of changes.

[0121] Table 3

[0122]

[0123] As shown in Table 3, the present invention establishes a relationship between the width ratio L of the T1 region and the T2 region, the thickness ratio D of the T1 region and the T2 region, and the silicon content G in the negative electrode active material, and controls When the value of meets a specific range, the battery's cycle capacity retention rate and fast charging performance can be further improved, while reducing the battery's thickness expansion and short circuit risks during the cycle.

[0124] The sixth embodiment was carried out in accordance with the first embodiment, and the main differences are shown in Table 4. The sixth embodiment was carried out by adjusting the width ratio L of the T1 region and the T2 region, the puncture strength N of the substrate or the DV50 of the silicon particles. The value of changes.

[0125] Table 4

[0126]

[0127] As shown in Table 4, the present invention establishes a relationship between the width ratio L of the T1 region and the T2 region, the puncture strength N of the substrate, and the DV50 of the silicon particles, and defines The value range can further improve the battery's cycle capacity retention rate and fast charging performance, while reducing the battery's thickness expansion and short circuit risks during the cycle.

[0128] The Example 7 group was carried out in accordance with the Example 1-1, and the main differences are shown in Table 5. Among them, the Example 7 group changed the thickness D1 of the T1 region, the thickness D2 of the T2 region, the width L1 of the T1 region, the width L2 of the T2 region or the conductivity σ of the electrolyte to make The value of

[0129] Table 5

[0130]

[0131]

[0132] As can be seen from Table 5, the present invention establishes a relationship between the thickness D1 of the T1 region, the thickness D2 of the T2 region, the width L1 of the T1 region, the width L2 of the T2 region and the conductivity σ of the electrolyte, and the formula is satisfied: The battery's cycle capacity retention rate and fast charging performance can be further improved, while the battery's thickness expansion and short circuit risks during the cycle can be reduced.

[0133] It should be noted that, in this article, the terms "comprise", "include" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise one..." do not exclude the presence of other identical elements in the process, method, article or device including the element. In addition, it should be pointed out that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved, for example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0134] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A diaphragm, characterized in that: The diaphragm includes a substrate and a ceramic layer covering at least one side of the substrate; in a given direction parallel to the surface of the substrate, the ceramic layer includes a plurality of T1 regions and a plurality of T2 regions alternately arranged in sequence; In the thickness direction of the substrate, the thickness of the ceramic layer in the T1 region is recorded as D1 μm, and the thickness of the ceramic layer in the T2 region is recorded as D2 μm, D=D1 / D2, and D satisfies: 1.5≤D≤4; The porosity of the substrate is denoted as P%, and P and D satisfy: 2.73≤D / P≤11.

43.

2. The diaphragm according to claim 1, characterized in that Along the given direction, the shortest distance from one side boundary to the other side boundary of the ceramic layer in the T1 region is recorded as L1 μm, and the shortest distance from one side boundary to the other side boundary of the ceramic layer in the T2 region is recorded as L2 μm, L=L1 / L2, L satisfies: 0.5≤L≤3; and / or, L1 satisfies: 6≤L1≤100; and / or, L2 satisfies: 6.7≤L2≤50; And / or, D1 satisfies: 0.5≤D1≤5; And / or, D2 satisfies: 0.5≤D2≤5; And / or, P satisfies: 30≤P≤60.

3. The diaphragm according to claim 2, characterized in that The elongation at break of the substrate in the TD direction is recorded as E TD %, L and E TD Satisfy: 0.3≤L / E TD ≤6; Preferably, E TD Satisfy: 50 ≤ E TD ≤150; And / or, the elongation at break of the substrate in the MD direction is recorded as E MD %E MD Satisfy: 50 ≤ E MD ≤300.

4. The diaphragm according to any one of claims 1 to 3, characterized in that: The ceramic layer includes ceramic particles, a binder and a dispersant; Preferably, based on the total mass of the ceramic layer, the mass of the ceramic particles accounts for 40%-96%; Preferably, based on the total mass of the ceramic layer, the mass proportion of the binder is 3%-60%; Preferably, based on the total mass of the ceramic layer, the mass proportion of the dispersant is 0.7%-1.5%; And / or, the peel strength between the ceramic layer and the substrate is 30 N / m-200 N / m.

5. The diaphragm according to any one of claims 1 to 3, characterized in that: The substrate also satisfies at least one of the following conditions: (i) the thickness of the substrate is 4 μm-20 μm; (ii) the pore size distribution of the substrate is 10 nm-100 nm; (iii) The puncture strength of the substrate is denoted as N gf, where N satisfies: 200≤N≤400.

6. A battery, characterized in that: The battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, and the separator is the separator according to any one of claims 1 to 5.

7. The battery according to claim 6, characterized in that The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active layer comprises a negative electrode active material, and the negative electrode active material comprises silicon particles; Based on the total mass of the negative electrode active material, the mass percentage of silicon is recorded as G%, and G satisfies: 10≤G≤20; And / or, the particle size Dv50 of the silicon particles is denoted as V nm, and V satisfies: 10≤V≤50.

8. The battery according to claim 7, characterized in that L, D and G meet the following conditions:

9. The battery according to claim 7, characterized in that L, N and V meet the following conditions:

10. The battery according to claim 7, characterized in that The conductivity of the electrolyte is denoted as σmS / cm, where σ satisfies: 3≤σ≤15; D1, D2, L1, L2 and σ satisfy

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