Pole piece and battery cell

Abstract

The embodiment of the invention provides a pole piece and a battery cell. The pole piece comprises a current collector, a first active material layer and a second active material layer, the current collector is provided with a first surface and a second surface which are oppositely arranged along the thickness direction of the pole piece, and the first active material layer and the second active material layer are respectively arranged on the first surface and the second surface. At least one surface of the first active material layer and the second active material layer is provided with a bright area, the bright area comprises a plurality of spaced bright area strips, a dark area strip is formed between every two adjacent bright area strips, and a plurality of grooves are at least formed in the bright area. The grooves are formed in the bright area of the pole piece, so that the side reaction layer formed on the surface of the active material layer in the pre-lithiation process can be removed. Therefore, the side reaction layer can be prevented from influencing the combination of the pole piece and the diaphragm when the battery cell is formed, the interface quality of the lithium supplement pole piece and the diaphragm can be improved, the hardness of the battery is increased, and the internal resistance of the battery is reduced, so that the energy density and the cycle life of the lithium supplement battery are ensured.

Description

Technical Field

[0001] The present application relates to the field of batteries, and specifically, to an electrode sheet and an electric core. Background Art

[0002] With the rapid development of fields such as electronic devices and electric vehicles, the demand for lithium-ion batteries with characteristics such as high capacity, long life, good stability, high power density, low price, and environmental friendliness is gradually increasing.

[0003] The electric core of a lithium-ion battery mainly consists of a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. As one of the core components of a lithium-ion battery, the negative electrode sheet plays a key role in the above-mentioned performance of the battery.

[0004] Currently, in related technologies, to increase the capacity of a lithium-ion battery, silicon can be doped into the negative active material of the negative electrode sheet. However, correspondingly, there is a problem that the actual capacity of the lithium-ion battery is low due to the low initial coulombic efficiency (ICE) of the battery. To improve this problem, the negative electrode or the positive electrode is usually pre-lithiated to improve the initial coulombic efficiency of the battery.

[0005] However, currently, there are some negative effects brought about by the pre-lithiation of the electrode sheet, which deteriorate the battery performance. Summary of the Invention

[0006] In view of this, embodiments of the present application provide an electrode sheet and an electric core to improve the problem that the negative effects brought about by the pre-lithiation of the electrode sheet of a lithium-ion battery deteriorate the battery performance.

[0007] In a first aspect, the present application provides an electrode sheet. The electrode sheet includes a current collector, a first active material layer, and a second active material layer. Along the thickness direction of the electrode sheet, the current collector has a first surface and a second surface that are oppositely arranged, and the first active material layer and the second active material layer are respectively arranged on the first surface and the second surface. Here, at least one surface of the first active material layer and the second active material layer has a bright area, the bright area includes a plurality of spaced bright area strips, a dark area strip is formed between adjacent bright area strips, and a plurality of grooves are formed at least on the bright area, the extending direction of the grooves is the same as the extending direction of the bright area strips; the bright area includes a recessed portion that is recessed inward, and the grooves are located at the bottom of the recessed portion.

[0008] Based on the electrode sheet provided in the first aspect, in a possible implementation manner, the groove has a first depth h1, h1 is 0.1 μm to 6 μm; and / or, the groove has a first width w1, w1 ≥ 30 μm; and / or, the distance between the grooves is d1, d1 is 30 μm to 100 μm.

[0009] In this application, the bright area and bright area stripes refer to the areas with high brightness in the pictures obtained by using a laser scanning confocal microscope at a certain magnification, for example, 4 times to 1000 times. The dark area stripes refer to the areas with low brightness in the pictures obtained by using a laser scanning confocal microscope at a certain magnification, for example, 4 times to 1000 times. For example, the surface topography image of the negative electrode can be obtained by using a laser scanning confocal microscope (Olympus, LEXT 0LS3100), and the bright area stripes and dark area stripes can be distinguished according to the image.

[0010] Based on the electrode provided in the first aspect, in a possible implementation, the extending direction of the groove has an included angle α with the extending direction of the bright area stripes, and α < 60°.

[0011] Based on the electrode provided in the first aspect, in a possible implementation, the bright area stripes have a second width w2, where w2 is 100 μm to 1000 μm, and / or, there is a second spacing d2 between adjacent bright area stripes, where d2 is 100 μm to 1000 μm, and the width w1 of the groove is less than d2; preferably, w2 is 200 μm to 500 μm, and / or, d2 is 200 μm to 500 μm.

[0012] Based on the electrode provided in the first aspect, in a possible implementation, the width w1 of the groove is less than the second width d2 between adjacent bright area stripes.

[0013] Based on the electrode provided in the first aspect, in a possible implementation, the area where the bright area stripes are located forms a first area, and the area between the bright area stripes forms a second area; along the thickness direction, the top of the first area and the top of the second area have a height difference h2 with the surface of the current collector, the groove has a depth h1, and h1 < h2, and / or, the area of the first area is S1, the area of the second area is S2, and the value range of S1 / S2 is 0.7 to 1.3.

[0014] Based on the electrode provided in the first aspect, in a possible implementation, grooves are formed on at least 70% of the bright area stripes.

[0015] Based on the electrode provided in the first aspect, in a possible implementation, the bright area stripes include a side reaction layer around the groove, and the thickness of the side reaction layer is less than the depth of the groove; and / or, the components of the side reaction layer include at least one of metallic lithium, lithium oxide, lithium hydroxide, and lithium fluoride; and / or, calculated by mass content percentage, the ratio of the content of fluorine element and oxygen element on the surface of the electrode satisfies: F / O < 0.4.

[0016] In a second aspect, this application provides an electric cell, and this electric cell includes any one of the above electrodes.

[0017] Based on the battery cell provided in the second aspect, in a possible implementation, the three-point hardness global bending load F of the battery cell satisfies: F≥90N.

[0018] According to the electrode sheet provided in the embodiments of the present application, by providing grooves in the bright area (pre-lithiation treatment part) of the electrode sheet, the side reaction layer formed on the surface of the active material layer during pre-lithiation, such as the negative electrode active material layer surface of the negative electrode sheet, can be removed. Therefore, when forming the battery cell, the influence of the side reaction layer on the bonding between the electrode sheet and the separator can be avoided, the interface quality between the lithium supplementing electrode sheet and the separator can be improved, the hardness of the battery can be increased, the internal resistance of the battery can be reduced, thereby ensuring the energy density and cycle life of the lithium supplementing battery.

[0019] In addition, by providing grooves on the surface of the electrode sheet, the specific surface area of the electrode sheet can be increased, thereby improving the wetting effect of the electrolyte on the surface of the electrode sheet, and the electrolyte can also be stored, which helps ion migration and thus delays the aging of the battery. Description of the Drawings

[0020] Figure 1 Schematic diagram of the structure of the lithium supplementing electrode sheet in the related art.

[0021] Figure 2 For Figure 1 Cross-sectional view of the lithium supplementing electrode sheet along B’-B’ in

[0022] Figure 3 For Figure 1 Partial longitudinal-sectional microscopic structure diagram of the active material layer at the lithium supplementing position of the electrode sheet in

[0023] Figure 4 Schematic diagram of the structure of the electrode sheet according to an embodiment of the present application.

[0024] Figure 5 For Figure 4 Cross-sectional view of the electrode sheet along A-A in

[0025] Figure 6 For Figure 4 Cross-sectional view of the electrode sheet along B-B in

[0026] Figure 7 Schematic diagram of the structure of the electrode sheet according to another embodiment of the present application.

[0027] Figure 8 For Figure 7 Microscopic structure diagram of the surface of the active material layer of the electrode sheet before the groove is opened in

[0028] Figure 9 For Figure 7 Microscopic structure diagram of the surface of the active material layer of the electrode sheet after the groove is opened in

[0029] Figure 10Schematic comparison diagram of the initial Coulomb efficiency of the battery according to an embodiment of the present application and that of the comparative example battery.

[0030] Figure 11 Schematic comparison diagram of the battery capacity of the battery according to an embodiment of the present application and that of the comparative example battery.

[0031] Figure 12 Schematic diagram of the cell structure according to an embodiment of the present application.

[0032] Figure 13 For Figure 12 Cross-sectional view of the cell along D-D in

[0033] Figure 14 Schematic diagram of the cell structure according to another embodiment of the present application.

[0034] Figure 15 Schematic diagram of the battery structure according to an embodiment of the present application.

[0035] Figure 16 Schematic diagram of the battery structure according to another embodiment of the present application.

[0036] Figure 17 Schematic diagram of the test method for the three-electricity hardness test.

[0037] Reference numerals: 1000. Battery; 100. Cell; 101. Bending part; 101a. First bending part; 101b. Second bending part; 102. Flat part; 10. Positive electrode sheet; 20 / 20'. Negative electrode sheet / electrode sheet; 21 / 21'. Negative current collector / current collector; 21a / 21a'. First surface; 21b / 21b'. Second surface; 22a / 22a'. First negative active material layer / first active material layer; 22b / 22b'. Second negative active material layer / second active material layer; 221 / 221'. Negative active material base layer; 222 / 222'. Prelithiation layer; 223 / 223'. Side reaction layer; 23. Groove; 24. First region, 25. Second region; 200. Housing; 30. Separator; 301. Indenter; 302. Support. Detailed implementation manners

[0038] With the rapid development of industries such as new energy vehicles and electronic communication equipment, consumers' demand for lithium-ion batteries with characteristics of high capacity, long life, stability, and high power density is increasing day by day. As one of the important components of the battery cell, the electrode is one of the key factors determining the above performance.

[0039] To improve the performance of batteries, silicon anodes with higher specific capacity compared to traditional graphite anodes are a hot direction in battery development. However, batteries prepared with silicon anodes have the problem of low initial Coulomb efficiency, which in turn leads to low actual capacity utilization.

[0040] Currently known, in order to improve the initial Coulomb efficiency of the above-mentioned batteries, the electrode can be pre-lithiated to improve the initial Coulomb efficiency of the battery and ensure the utilization of battery capacity. For example, taking lithium supplementation of the negative electrode as an example, techniques such as lithium foil lithium supplementation or electrolytic lithium salt aqueous solution can be used for pre-lithiation. However, while supplementing lithium to the electrode, some negative effects that deteriorate the battery are brought about.

[0041] Taking lithium foil lithium supplementation of the negative electrode sheet as an example, when supplementing lithium, the rolled thin lithium strip is directly compounded with the silicon anode. For example, the lithium strip and the silicon anode are mechanically pressed to obtain a relatively tight contact interface, providing a necessary electron path. Then, due to the potential difference between lithium and the silicon anode itself, in the liquid phase environment of the injected electrolyte, the pre-lithiation of the silicon anode is achieved through the spontaneous reaction of lithium and silicon. However, for actual metallic lithium as an additional lithium source, its actual lithium supplementation capacity is not fully utilized. During pre-lithiation, there are some side reactions.

[0042] The utilization rate of metallic lithium actually participating in the pre-lithiation reaction is limited, and a part (about 20% - 40%) of the lithium undergoes side reactions, such as the oxidation of lithium and side reactions generated by the contact of lithium with the electrolyte. These side reactions form lithium oxides (Li2O), lithium fluorides (LiF), lithium hydroxides (LiOH), lithium silicates, and carbonates, etc. of lithium. At the same time, or due to the disconnection of the electron path, part of the metallic lithium loses its reactivity and becomes dead lithium. The products of the side reactions ultimately form a side reaction product shell layer attached to the surface of the negative electrode active material layer.

[0043] Taking Figure 1 and Figure 2 the negative electrode sheet 20' shown as an example, along the thickness direction of the negative electrode sheet 20', the negative electrode current collector 21' has a first surface 21a' and a second surface 21b' arranged oppositely, and the first negative electrode active material layer 22a' and the second negative electrode active material layer 22b' are respectively arranged on the first surface 21a' and the second surface 21a'. After lithium supplementation, each of the first negative electrode active material layer 22a' and the second negative electrode active material layer 22b' is composed of a negative electrode active material matrix layer 221', a pre-lithiation layer 222', and a side reaction layer 223'. Referring to Figure 3 , on the surface of the pre-lithiated electrode, a side reaction layer of 1μm - 3μm is formed.

[0044] Due to the existence of the side reaction layer, the effective contact between the negative electrode interface and the separator is isolated, resulting in a certain degree of unqualified peeling force or even non - adhesion between the separator and the negative electrode after the formation and sorting of the lithium - supplement battery. Furthermore, it may lead to poor cell hardness, the whole being too soft and easy to deform, reducing the ED yield. At the same time, it may cause the deterioration of the electrode interface and worsen the cycle performance problem of the battery.

[0045] In order to improve the above - mentioned situation and at least partially solve the above - mentioned problems, the embodiments of the present application provide a wound electrode body and a battery. Next, the embodiments of the present application will be described in conjunction with Figures 4 to 16 to illustrate the embodiments of the present application.

[0046] It should be understood that there can be multiple implementation manners of the present application and should not be construed as being limited to the embodiments described herein. The embodiments described herein are only for a more thorough and clear understanding of the present application.

[0047] Exemplary electrode

[0048] Referring to Figures 4 to 9 , in a first aspect, the present application provides a pole piece 20. The pole piece 20 includes a current collector 21, a first active material layer 22a, and a second active material layer 22b. Along the thickness direction of the pole piece 20, the current collector 21 has a first surface 21a and a second surface 21b which are oppositely arranged, and the first active material layer 22a and the second active material layer 22b are respectively disposed on the first surface 21a and the second surface 21b.

[0049] There are bright regions on at least one surface of the first active material layer 22a and the second active material layer 22b, and a plurality of grooves 23 are formed at least on the bright regions. That is, at least one of the first active material layer 22a and the second active material layer 22b is pre - lithiated, and a plurality of grooves 23 are formed at least at the pre - lithiated parts. For example, the first active material layer 22a or the second active material layer 22b can be pre - lithiated, or both the first active material layer 22a and the second active material layer 22b can be pre - lithiated simultaneously. The grooves 23 can be only located at the pre - lithiated parts or can also be located at other parts simultaneously. The formation method of the grooves can be, for example, laser grooving or mechanical grooving.

[0050] The bright regions include multiple spaced bright region strips (i.e., prelithiation strips), and dark region strips (i.e., non-lithium-complementary regions) are formed between adjacent bright region strips. That is, the prelithiation treatment is an intermittent prelithiation treatment, and the prelithiated parts have multiple bright region strips distributed at intervals. That is, intermittent lithium supplementation is performed on the surface of the active material layer to avoid the side reaction layer 223 completely covering the active material layer. Combining with the grooves 23 can further improve the bonding effect and interface quality between the electrode sheet 20 and the separator, improve the hardness of the battery, reduce the internal resistance of the battery, so as to ensure the energy density and cycle life of the prelithiated battery, etc.

[0051] For the descriptions of the bright regions, bright region strips, dark regions, and dark region strips in this article, please refer to the above descriptions and will not be elaborated here.

[0052] It should be noted that the prelithiation process is a technology known in the art and will not be elaborated here.

[0053] For example, taking the electrode sheet 20 as the negative electrode sheet 20 as an example, refer to Figures 4 to 7 , the negative electrode sheet 20 includes a negative current collector 21, a first negative electrode active material layer 22a, and a second negative electrode active material layer 22b. Along the thickness direction of the negative electrode sheet 20, the negative current collector 21 has a first surface 21a and a second surface 21b arranged oppositely, and the first negative electrode active material layer 22a and the second negative electrode active material layer 22b are respectively arranged on the first surface 21a and the second surface 21b. At least one of the first negative electrode active material layer 22a and the second negative electrode active material layer 22b is subjected to intermittent prelithiation treatment, and multiple grooves 23 are formed at least at the prelithiated parts. Among them, the extending direction of the grooves is substantially the same as the extending direction of the bright region strips formed after prelithiation; in addition, on the electrode sheet after prelithiation treatment, a recessed part that is recessed inward will be formed at the prelithiated region (i.e., the bright region strips), and the grooves are formed at the bottom of the recessed part, that is, the grooves are located at the bottom of the recessed part, so that the negative electrode active material under the bright region strips is exposed, so as to contact the electrolyte and achieve a normal lithium deintercalation effect, improving the energy density.

[0054] According to the electrode sheet 20 provided by the embodiment of the present application, by providing grooves 23 at the prelithiated parts of the electrode sheet 20, the side reaction layer 223 formed on the surface of the active material layer during the prelithiation process, such as the surface of the negative electrode active material base layer 221 of the negative electrode sheet 20, can be removed. Therefore, when forming the battery cell 100, the influence of the side reaction layer 223 on the bonding between the electrode sheet 20 and the separator can be avoided, the interface quality between the prelithiated electrode sheet 20 and the separator can be improved, the hardness of the battery can be increased, and the internal resistance of the battery can be reduced, so as to ensure the energy density and cycle life of the prelithiated battery.

[0055] In addition, grooves 23 are provided on the surface of the electrode sheet 20, which can increase the specific surface area of the electrode sheet 20, thereby improving the wetting effect of the electrolyte on the surface of the electrode sheet 20. Moreover, the grooves can store the electrolyte, which is helpful for ion migration and thus delays the aging of the battery.

[0056] Those skilled in the art can understand that the electrode sheet 20 of the present application can be applicable to the electrode sheet 20 that needs to remove the prelithiation negative reaction layer, and is not limited to the negative electrode sheet 20. Hereinafter, for the convenience of description, the negative electrode sheet 20 is taken as an example to describe the technical solution of the electrode sheet 20 of the present application.

[0057] It should be noted that the grooves 23 can be formed by various processing methods, such as laser grooving.

[0058] Reference Figure 4 and Figure 7 In one example, the groove 23 has a first depth h1, and h1 is 0.1 μm to 6 μm, such as 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm or 4.5 μm, etc.

[0059] By setting the depth of the groove 23 within this range, the side reaction layer 223 formed on the surface of the active material layer after prelithiation removal can be avoided. When forming the battery cell 100, the side reaction layer 223 will not affect the bonding between the electrode sheet 20 and the separator. This can improve the interfacial quality between the lithium supplement electrode sheet 20 and the separator, increase the hardness of the battery, reduce the internal resistance of the battery, and thus ensure the energy density and cycle life of the lithium supplement battery. At the same time, if the depth of the groove 23 is too shallow, the side reaction layer 223 cannot be effectively removed, which may affect the local CB value and pose a risk of lithium precipitation. At the same time, it may also affect the hardness, energy density and cycle life of the battery. Then, if the depth of the groove 23 is too deep, too much active material will be removed, affecting the capacity of the battery.

[0060] Reference Figure 5 and Figure 6 It can be seen that in the lithium supplement area not covered by the groove 23, the first negative electrode active material layer 22a and the second negative electrode active material layer 22b are each composed of a negative electrode active material base layer 221, a prelithiation layer 222 and a side reaction layer 223. In the lithium supplement area covered by the groove 23, the first negative electrode active material layer 22a and the second negative electrode active material layer 22b are each composed of a negative electrode active material base layer 221 and a prelithiation layer 222.

[0061] Continuing to refer to Figure 4 and Figure 7 In one example, the groove 23 has a first width w1, and w1≥30 μm, such as 35 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm, etc.

[0062] Setting the width of the groove 23 within this range can avoid the side reaction layer 223 formed on the surface of the active material layer after prelithiation removal. When forming the battery cell 100, the side reaction layer 223 can be prevented from affecting the bonding between the electrode sheet 20 and the separator, improving the interface quality between the lithium - supplementing electrode sheet 20 and the separator, increasing the hardness of the battery, reducing the internal resistance of the battery, and thus ensuring the energy density and cycle life of the lithium - supplemented battery. At the same time, if the width of the groove 23 is too narrow, the side reaction layer 223 cannot be effectively removed, which may affect the local CB value and pose a risk of lithium deposition. At the same time, it may also affect the hardness, energy density and cycle life of the battery.

[0063] Next, referring to Figure 4 and Figure 7 In one example, there is a first spacing d1 between the grooves 23, and d1 is 30 μm to 100 μm, such as 35 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm, etc. In this way, it can be avoided that the spacing between the grooves 23 is too small, resulting in heat concentration during the formation of the grooves 23 and affecting the strength of the electrode sheet 20. At the same time, it can be avoided that the spacing is too large, which cannot effectively remove the side reaction layer 223 and cannot effectively improve the bonding between the electrode sheet 20 and the separator, causing corresponding negative effects.

[0064] In one example, any two or all of the following conditions can be simultaneously satisfied: the groove 23 has a first depth h1, where h1 is 0.1 μm to 6 μm; the groove 23 has a first width w1, where w1 ≥ 30 μm; and there is a first spacing d1 between the grooves 23, where d1 is 30 μm to 100 μm.

[0065] In one example, the extending direction of the groove 23 and the extending direction of the bright - area strip have an included angle α, and α < 60° (such as 0°, 5°, 10°, 20°, 30°, 40°, 50°, etc.), so that the groove 23 can remove more of the side reaction layer 223, and thus better achieve the effect brought by the groove 23 removing the side reaction layer 223.

[0066] Referring to Figure 9 In a preferred example, the extending direction of the groove 23 is the same as the extending direction of the bright - area strip. When the extending direction of the groove 23 is the same as the extending direction of the bright - area strip, the groove 23 can remove more of the side reaction layer 223, and thus better achieve the effect brought by the groove 23 removing the side reaction layer 223.

[0067] It can be understood that the above - mentioned same extending direction of the groove 23 and the bright - area strip means that the extending direction of the groove 23 and the extending direction of the bright - area strip can have a deviation of ±15%.

[0068] It can also be understood that the extending direction of the bright area strip can be parallel to the length direction of the electrode sheet 20, perpendicular to the length direction of the electrode sheet 20, or have other included angles therebetween, which is not limited in this application.

[0069] Return reference Figure 7 , in some examples, the bright area strip can have a second width w2, and w2 is 100 μm to 1000 μm, such as 150 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm or 900 μm, etc. In this way, a good prelithiation effect can be ensured, and the first Coulombic efficiency of the battery can be effectively improved. If the bright area strip is too narrow, the prelithiation effect will be poor, and the effect of improving the first Coulombic efficiency will be poor. If the bright area strip is too wide, the width of the side reaction layer 223 will be wide, which will affect the combination of the electrode sheet 20 and the separator to a certain extent, and thus bring corresponding negative effects.

[0070] There is a second spacing d2 between adjacent bright area strips, and d2 is 100 μm to 1000 μm, such as 150 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm or 900 μm, etc. In this way, while ensuring the prelithiation effect, an appropriate amount of active material can be left for combination with the separator to improve the combination interface between the separator and the electrode sheet 20. If the spacing between the bright area strips is too small, the width of the side reaction layer 223 will be wide, which will affect the combination of the electrode sheet 20 and the separator to a certain extent, and thus bring corresponding negative effects. If the spacing between the bright area strips is too large, the prelithiation effect will be poor, and the effect of improving the first Coulombic efficiency will be poor.

[0071] Furthermore, the bright area strip has a second width w2, and w2 is 200 μm to 500 μm. There is a second spacing d2 between the bright area strips, and d2 is 200 μm to 500 μm. In this way, a good prelithiation effect can be ensured, the first Coulombic efficiency of the battery can be effectively improved, and at the same time, the combination interface between the separator and the electrode sheet 20 can be better improved.

[0072] The width W1 of the groove 23 < d2 to avoid removing too much active material layer, which may affect the local CB value, there is a risk of lithium precipitation, and at the same time, it may affect the hardness, energy density and cycle life of the battery.

[0073] Reference Figure 8 , the area where the bright area strip is located forms a first area 24 (i.e., Figure 7 the bright area in Figure 7The dark areas), and the two are arranged at intervals on the surface of the negative electrode sheet 20. Along the thickness direction, the top of the first region 24 and the top of the second region 25 have a height difference h2 from the surface of the current collector 21, and the groove 23 has a depth h1, where h1 < h2, so as to avoid excessive removal of the active material and affect the capacity of the battery, such as affecting the local CB value of the negative electrode sheet 20 and bringing the risk of lithium deposition here.

[0074] In some examples, the area of the first region 24 is S1, and the area of the second region 25 is S2. The value range of S1 / S2 is 0.7 to 1.3, such as 0.8, 0.9, 1.0, 1.1, or 1.2, etc. Controlling the area ratio of the first region and the second region within this range, in cooperation with the groove 23, can ensure the prelithiation effect to effectively improve the first Coulombic efficiency of the battery. At the same time, it is avoided that the area of the first region 24 is too large, so that too many side reaction layer 223 covers the first region 24 and deteriorates the performance of the negative electrode interface, affecting the cycle performance of the battery 1000. On the other hand, it can be avoided that the area of the first region 24 is too small to effectively compensate for lithium and cannot effectively improve the first Coulombic efficiency of the battery 1000.

[0075] In one example, it can be simultaneously satisfied that the region where the bright area strip is located forms the first region 24, and the region between the bright area strips forms the second region 25. The two are arranged at intervals on the surface of the negative electrode sheet 20. Along the thickness direction, the top of the first region 24 and the top of the second region 25 have a height difference h2 from the surface of the current collector 21, and the groove 23 has a depth h1, where h1 < h2. The area of the first region 24 is S1, and the area of the second region 25 is S2. The value range of S1 / S2 is 0.7 to 1.3.

[0076] In some embodiments, in the above-mentioned electrode sheet 20, grooves 23 are formed on at least 70% of the bright area strips (i.e., the parts subjected to prelithiation treatment), that is, the removal amount of the side reaction layer 223 is at least 70% of its area, so as to ensure the repeated removal of the side reaction layer 223, and further better realize the effect brought by the groove 23 removing the side reaction layer 223.

[0077] In some examples, refer to Figure 3 and Figure 6 ., the bright area strip may include the side reaction layer 223. The composition of the side reaction layer 223 may include at least one of metallic lithium, lithium oxide, lithium hydroxide, and lithium fluoride. The side reaction layer 223 is located around the groove. By forming a groove in the side reaction layer, the thickness of the side reaction layer is less than the depth of the groove, so that the negative electrode active material layer below the side reaction layer is exposed to participate in the reaction, thereby improving the adhesion between the separator and the negative electrode sheet.

[0078] In some examples, calculated by mass percentage, the ratio of the content of fluorine element to the content of oxygen element on the surface of the electrode sheet 20 satisfies: F / O < 0.4. By providing grooves 23 on the surface of the electrode sheet 20, the side reaction layer is effectively removed. Here, the composition can be obtained by line scanning with a scanning electron microscope.

[0079] As described above, the above-mentioned electrode sheet 20 can be a negative electrode sheet 20.

[0080] As follows Figures 4 to 11 , taking the negative electrode sheet 20 as an example, the electrode sheet 20 of the present application will be illustrated by way of example.

[0081] Referring to Figures 4 to 7 , the negative electrode sheet 20 may include a negative electrode current collector 21, a first negative electrode active material layer 22a, and a second negative electrode active material layer 22b. Along the thickness direction of the negative electrode sheet 20, the negative electrode current collector 21 may have a first surface 21a and a second surface 21b arranged oppositely, and the first negative electrode active material layer 22a and the second negative electrode active material layer 22b are respectively arranged on the first surface 21a and the second surface 21b. The first negative electrode active material layer 22a and the second negative electrode active material layer 22b are pre-lithiated, for example, by intermittent pre-lithiation, and a plurality of grooves 23 may be formed in the first negative electrode active material layer 22a and the second negative electrode active material layer 22b, and the extending direction of the grooves 23 is the same as the extending direction of the bright area strip.

[0082] Referring to Figure 7 , the bright area strip has a second width w2, and w2 is 100 μm to 1000 μm. There is a second spacing d2 between the bright area strips, and d2 is 100 μm to 1000 μm. Further, the bright area strip has a second width w2, and w2 is 200 μm to 500 μm. There is a second spacing d2 between the bright area strips, and d2 is 200 μm to 500 μm.

[0083] Referring to Figure 4 and Figure 7 , the groove 23 may have a first depth h1, and h1 is 0.1 μm to 6 μm. The groove 23 may have a first width w1, w1 ≥ 30 μm, and the width w1 of the groove 23 is less than d2. There may be a first spacing d1 between the grooves 23, and d1 is 30 μm to 100 μm.

[0084] Referring to Figure 8 and Figure 9 , the area where the bright area strip is located forms a first area 24, and the area between the bright area strips forms a second area 25. Referring to Figure 7 Along the thickness direction, the top of the first area 24 and the top of the second area 25 have a height difference h2 from the surface of the current collector 21, and the groove 23 has a depth h1, and h1 < h2.

[0085] Grooves 23 are formed on at least 70% of the prelithiated parts.

[0086] Exemplary battery cell

[0087] In a second aspect, the present application provides an electric cell 100, which includes the above-mentioned electrode sheet 20.

[0088] Reference Figure 12 and Figure 13 , taking the wound electric cell 100 as an example, the electric cell 100 may include a positive electrode sheet 10, a negative electrode sheet 20, and a separator 30. The positive electrode sheet 10 and the negative electrode sheet 20 are separated by the separator 30 and wound around the winding center E-E to form a wound electrode body 100 having a flat portion 102 and two bending portions 101a, 101b. The two bending portions 101a, 101b are distributed at opposite ends of the flat portion 102 in the width direction. The two bending portions 101a, 101b are collectively referred to as the bending portion 101.

[0089] Reference Figure 14 , in another embodiment, the electric cell 100 is a stacked cell including a positive electrode sheet 10, a negative electrode sheet 20, and a separator 30.

[0090] The positive electrode sheet 10 may include a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector. By way of example only, the positive electrode current collector may be a strip-shaped metal foil, and the positive electrode active layer may contain a positive electrode active material capable of reversibly absorbing and releasing charge carriers. In addition, they may further include a conductive material, a binder, and various additive components, etc.

[0091] By way of example only, the metal foil mentioned here may be aluminum foil, and the positive electrode active material mentioned may be a lithium transition metal composite oxide such as lithium nickel cobalt manganese composite oxide, lithium cobalt oxide, etc.

[0092] Exemplarily, the above-mentioned binder may include one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyimide or polyethylene.

[0093] Exemplarily, the above-mentioned conductive material may include one or more of conductive ceramics, carbon black, graphite, graphene, polyaniline, polypyrrole, Ketjen black, acetylene black, and carbon nanotubes.

[0094] Exemplarily, the above-mentioned additive components such as solvents may include one or more of N-methylpyrrolidone, water, ethanol, and polyethylene glycol.

[0095] Return to reference Figure 4 and Figure 7, the negative electrode sheet 20 may include a negative electrode current collector 21 and a negative electrode active material layer provided on the negative electrode current collector 21 (i.e., the first negative electrode active material layer 22a and the second negative electrode active material layer 22b).

[0096] The negative electrode active material layer includes a negative electrode active material and a silicon-carbon material. For example, the negative electrode active material includes one or more of graphite, soft carbon, hard carbon, mesophase microspheres, and a silicon-carbon material. For example, the silicon-carbon material includes one or more of elemental silicon, silicon-based alloys, silicon oxides, and silicon-carbon composite materials. Exemplarily, the silicon-carbon material may be granular silicon formed by graphite and silicon, and the granular silicon may be formed by plating silicon on graphite particles.

[0097] In addition, the negative electrode active material may further include one or more of a binder, a conductive agent, and a solvent.

[0098] Exemplarily, the binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, polyacrylic acid, sodium carboxymethyl cellulose, polyimide, or polyethylene.

[0099] Exemplarily, the conductive agent includes one or more of conductive ceramics, carbon black, graphite, graphene, polyaniline, polypyrrole, Ketjen black, acetylene black, and carbon nanotubes.

[0100] Exemplarily, the solvent includes one or more of N-methylpyrrolidone, water, ethanol, and polyethylene glycol.

[0101] For example, the negative electrode current collector 21 is a copper foil or any other foil material. Exemplarily, the negative electrode current collector 21 may be a copper foil.

[0102] The battery cell 100 of the present application correspondingly has the corresponding effects of the above-mentioned electrode sheet 20, which will not be elaborated here.

[0103] The three-point hardness full-range travel bending load F of the battery cell may satisfy: F≥90N.

[0104] Here, the three-point hardness full-range travel bending load of the battery cell refers to the bending load of the battery cell obtained by using an electronic universal testing machine to support both ends of the battery cell at a constant indenter pressing speed and testing under a set full range of travel.

[0105] It can be understood that the battery cell 100 of the present application is not limited to the above-mentioned wound battery cell 100 and may also be set in other shapes, such as a stacked type.

[0106] Exemplarily, the main process of prelithiation in this article can be as follows. According to the designed lithium compensation amount and the corresponding equivalent lithium compensation thickness. Before prelithiation, a pair-roll mill (or laminator) is used, and the roll gap is set to be the negative electrode sheet thickness ±10 μm. Under the pressure of about 1 ton, the lithium foil is pressed onto the surface of the negative electrode active material layer 222 of the negative electrode sheet 20. Then, an electrical short circuit is formed when the negative electrode sheet 20 and the lithium foil are infiltrated by the electrolyte, realizing the prelithiation of the negative electrode sheet.

[0107] It should be noted that those skilled in the art can adjust the roll gap and load according to the composite effect of the lithium strip and the negative electrode sheet 20. The composite effect should ensure that the lithium strip can be completely transferred to the negative electrode sheet 20 and has an appropriate bonding force (the lithium strip will not separate from the negative electrode sheet).

[0108] Other prelithiation processes and related parameters can refer to the conventional settings in the art and will not be elaborated here.

[0109] Exemplary battery 1000

[0110] Reference Figure 15 and 16 , the embodiment of the present application also provides a battery 1000. The battery 1000 includes the above-mentioned battery cell 100.

[0111] Continuing to refer to Figure 15 and Figure 16 , the battery 1000 may include a battery cell 100 and a housing 200. An accommodation cavity may be provided in the housing 200, and one or more battery cells 100 may be accommodated in the accommodation cavity.

[0112] As Figure 15 shown, exemplarily, the housing 200 may be square. That is to say, the battery 1000 may be a square battery 1000. The material of the housing 200 may be the same as the materials used in the past and is not particularly limited. For example, the housing 200 may be made of metal, particularly, it may be made of aluminum (alloy) or iron (alloy), etc.

[0113] As Figure 16 shown, exemplarily, the housing 200 is flat and made of a relatively soft material, such as aluminum plastic film. That is to say, in this embodiment, the battery 1000 may be a soft-pack battery 1000.

[0114] It can be expected that in other examples of the embodiment of the present application, the battery 1000 may also be implemented as other types other than the square battery 1000 and the soft-pack battery 1000.

[0115] It should be noted that the structures of other aspects of the battery 1000 may be the same as those of the conventional battery 1000. For the sake of simplicity, the embodiments of the present application will not elaborate on this anymore.

[0116] Taking the wound-type battery cell as an example, the above-mentioned battery 1000 can be manufactured into a wound-type electrode body 100 according to a conventional winding structure, with the positive electrode sheet 10, the negative electrode sheet 20, and the separator 30, and then made into the battery 1000 through steps such as encapsulation, liquid injection, formation, secondary sealing, and grading. The electrolyte is a commercially available conventional electrolyte, and no special requirements are imposed on this in the present application.

[0117] The battery 1000 provided by the embodiments of the present application has the corresponding effects of the above-mentioned battery cell 100. For details, please refer to the above text and will not be elaborated here.

[0118] It should be noted that in the present disclosure, the "battery 1000" refers to a power storage device that can be repeatedly charged and discharged, and it can be interpreted as the concept of a "secondary battery". In the embodiments of the present application, the concept of a "secondary battery" can include lithium-ion secondary batteries, etc.

[0119] It should be understood that the term "including" and its variations used in the embodiments of the present application are open-ended, that is, "including but not limited to". The term "according to" means "at least partially according to". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least another embodiment". The term "a plurality of" means "more than one", which means covering two, three, or more cases.

[0120] It should be understood that although terms such as "first" or "second" may be used in the embodiments of the present application to describe various elements, for example, the first surface and the second surface, these elements are not defined by these terms, and these terms are only used to distinguish one element from another. The protection scope of the embodiments of the present application is not limited to the above embodiments. Any person skilled in the art can think of changes or substitutions within the technical scope disclosed in the embodiments of the present application, and all should be covered within the protection scope of the embodiments of the present application. Therefore, the protection scope of the embodiments of the present application shall be subject to the protection scope of the claims.

[0121] The present application will be described in detail below with reference to specific embodiments, and these embodiments are for understanding rather than limiting the present application.

[0122] The materials, reagents, etc. used in the following embodiments can be obtained from commercial channels without special instructions. The processing procedures and techniques involved are conventional technical means without special instructions.

[0123] Example 1

[0124] Preparation of the negative electrode sheet 20: The negative electrode active material (i.e., the negative electrode active material, including 20 wt% of silicon oxide material and 80 wt% of graphite), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and conductive carbon black are dispersed in deionized water (which can also be water) as a solvent in a mass percentage of 95.8:0.85:1.3:2.05, and mixed evenly to obtain a slurry. The prepared negative electrode slurry is evenly coated on a copper foil, dried at 100 °C + 10 °C, and then rolled and slit to obtain the negative electrode sheet 20. The negative electrode active material is a mixture of carbon-coated artificial graphite material and silicon-carbon material, where the content of the silicon-carbon material is 50 wt%, and the silicon-carbon material is a silicon-carbon negative electrode material composed of nano-silicon and graphite, with a silicon content of 40 wt%. Along the thickness direction of the negative electrode sheet 20, the thicknesses of the negative electrode active material layers 222 on both sides of the negative electrode current collector 21 are 102 μm respectively, and the negative electrode current collector is a copper foil with a thickness of 6 μm. The negative electrode lithium supplement amount is 0.23 mg / cm 2 , the second width w2 of the bright area strip is 300 μm, and the second spacing d2 between the bright area strips is 300 μm. Laser-machined grooves 23 are formed on the first active material layer and the second active material layer. The width of the groove 23 is 50 μm, the depth is 3 μm, and the spacing between the grooves 23 is 58 μm. The pre-lithiation process used is the above-mentioned known lithium foil pre-lithiation, which will not be elaborated here. The designed lithium supplement amount is 0.23 mg / cm 2 , and the corresponding equivalent lithium supplement thickness is 4.2 μm. Before lithium supplementation, a pair of roll mills (or laminators) are used, and the roll gap is set to the thickness of the negative electrode sheet. Under the action of a pressure of 1 ton, a lithium foil with a thickness of 4.2 μm is pressed onto the surface of the negative electrode active material layer 222 of the negative electrode sheet 20, and then an electrical short circuit is formed under the infiltration of the negative electrode sheet 20 and the lithium foil in the electrolyte to achieve the pre-lithiation of the negative electrode sheet.

[0125] Preparation of the positive electrode sheet 10: The positive electrode active material nickel cobalt manganese (NCM811), the binder polyvinylidene fluoride, and the conductive agent carbon black are mixed in a mass percentage ratio of 97:2:2, and an appropriate amount of N-methylpyrrolidone is added as a solvent and stirred evenly to make an electrode slurry. The prepared positive electrode slurry is evenly coated on an aluminum foil and rolled and slit to form the positive electrode sheet 10. Along the thickness direction of the positive electrode sheet 10, the thicknesses of the positive electrode active material layers on both sides of the positive electrode current collector are 129 ± 3 μm respectively, and the positive electrode current collector is an aluminum foil with a thickness of 10 μm.

[0126] Then, according to the conventional winding structure, the positive electrode sheet 10, the negative electrode sheet 20, and the separator 30 are made into a wound battery 1000, and then the battery 1000 is made through steps such as encapsulation, liquid injection, formation, secondary sealing, and grading. Here, the electrolyte is a conventional commercially available electrolyte. The positive electrode sheet 10 has two more tabs 13 than the negative electrode sheet 20, and the two tabs 13 are located in the overlapping area of the first paste application area 14 and the second empty foil area 17.

[0127] Comparative Example 1

[0128] The difference between Comparative Example 1 and Example 1 is that the groove 23 is not provided.

[0129] Figure 10 It is a comparison chart of the initial Coulomb efficiency between the battery with the groove 23 provided on the surface of the negative electrode sheet 20 after prelithiation treatment and the battery only with prelithiation treatment. It can be seen that by providing the groove 23 on the surface of the negative electrode sheet 20 after prelithiation treatment, the initial Coulomb efficiency of the battery can be further improved. Figure 11 It is a comparison chart of the capacities between the battery with the groove 23 provided on the surface of the negative electrode sheet 20 after prelithiation treatment and the battery only with prelithiation treatment. It can be seen that by providing the groove 23 on the surface of the negative electrode sheet 20 after prelithiation treatment, the capacity of the battery can be further improved.

[0130] The composition of the bright area (the first region 24) and the dark area (the second region 25) of Example 1 was subjected to line scanning by a scanning electron microscope, and Table 1 shows the composition results obtained by the line scanning. It can be seen that the content of F element on the surface of the treated negative electrode sheet 20 is significantly reduced, and F / O < 0.4. It indicates that after the surface treatment, side reaction products such as LiF on the surface of the negative electrode sheet 20 are significantly reduced, avoiding excessive shielding of the negative electrode interface by the side reaction layer 223, and thus avoiding deterioration of the battery performance, such as the performance of battery capacity and cycle performance.

[0131] The batteries prepared in Example 1 and Comparative Example 1 were subjected to a three-point hardness full-range travel test. Under the full-range condition, the bending resistance of the battery prepared in Comparative Example 1 was 81 N to 89 N, and the bending resistance of the battery prepared in Example 1 was 92 N to 98 N. It can be seen that by providing the groove 23, the separator 30 can be well adhered to the negative electrode sheet 20, improving the hardness of the battery cell to a certain extent, and thus improving the bending resistance performance of the battery cell.

[0132] Method for three-point hardness full-range travel test: The equipment for the three-point hardness test is an electronic universal testing machine. The number of samples in each group is 9, the width of the sample is 63 mm, the test result takes the average value of 9 samples, the full-range travel is 5 mm, and the pressing speed of the indenter is 1 mm / min. Specifically refer to Figure 17 , the head of the indenter 301 is U-shaped, upward supports 302 are provided at both ends of the battery cell, and the distance between the two supports 302 is 50 mm. During the test, the indenter vertically moves downward uniformly until the entire travel is completed, and the force value returned by the sensor (i.e., the full-range travel bending load of the three-point hardness test) is recorded.

[0133] It should be noted that the size of the full-range travel and the distance between the supports 302 can be adjusted according to the size of the battery cell 100.

[0134] Table 1 Component line scan results of Example 1

Claims

1. A pole piece, characterized in that: It includes a current collector, a first active material layer and a second active material layer. Along the thickness direction of the electrode sheet, the current collector has a first surface and a second surface that are arranged opposite to each other. The first active material layer and the second active material layer are arranged on the first surface and the second surface respectively. At least one of the first active material layer and the second active material layer has a bright area on its surface, the bright area includes a plurality of spaced bright area strips, a dark area strip is formed between adjacent bright area strips, and a plurality of grooves are formed at least on the bright area, and the extending direction of the grooves is the same as the extending direction of the bright area strips; The bright area includes a concave portion that is concave inwardly, and the groove is located at the bottom of the concave portion.

2. The pole piece according to claim 1, characterized in that: The groove has a first depth h1, and the depth h1 is 0.1 μm to 6 μm; and / or The groove has a first width w1, wherein w1≥30 μm; and / or There is a first distance d1 between the grooves, and the distance d1 is 30 μm to 100 μm.

3. The pole piece according to claim 1, characterized in that: An extending direction of the groove and an extending direction of the bright area strip form an included angle α, where α is less than 60°.

4. The pole piece according to claim 1, characterized in that: The bright area strip has a second width w2, wherein w2 is 150 μm to 1000 μm, and / or, There is a second spacing d2 between adjacent bright area strips, and d2 is 150 μm to 1000 μm; preferably, w2 is 200 μm to 500 μm, and / or d2 is 200 μm to 500 μm.

5. The pole piece according to any one of claims 1 to 4, characterized in that: The width w1 of the groove is smaller than the second width d2 between adjacent bright area strips.

6. The pole piece according to any one of claims 1 to 4, characterized in that: The area where the bright area strips are located forms a first area, and the area between the bright area strips forms a second area; along the thickness direction, the top of the first area and the top of the second area have a height difference h2, and the groove has a depth h1, h1<h2, and / or The area of ​​the first region is S1, the area of ​​the second region is S2, and the value range of S1 / S2 is 0.7 to 1.

3.

7. The pole piece according to any one of claims 1 to 4, characterized in that: At least 70% of the bright area strips are formed with the grooves.

8. The pole piece according to any one of claims 1 to 4, characterized in that: The bright area strip includes a side reaction layer located around the groove, and the thickness of the side reaction layer is less than the depth of the groove; and / or the components of the side reaction layer include at least one of metallic lithium, lithium oxide, lithium hydroxide and lithium fluoride; and / or, calculated as a percentage of mass content, the ratio of the content of fluorine element and oxygen element on the surface of the electrode satisfies: F / O<0.

4.

9. A battery cell comprising the pole piece according to any one of claims 1 to 8. 10 . The battery cell according to claim 9 , wherein the full-range stroke bending load F of the battery cell in a three-point hardness test satisfies: F ≥ 90N.

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