Negative plate and battery

Abstract

The utility model discloses a negative plate and a battery. The negative plate provided by the utility model comprises a current collector, a negative tab and an active material layer, the current collector includes a first end and a second end. The negative tab is arranged at the second end. The active material layer is coated on the surface of the current collector, the active material layer comprises a silicon-based layer and one or more graphite layers, and the sum of the surface densities of all the graphite layers is gradually increased from the first end to the second end. According to the negative plate disclosed by the embodiment of the utility model, the graphite layer is non-uniformly coated in order to ensure the cycling stability and reduce the expansion of the silicon material, and the surface density of the graphite in the active substance layer closer to the tab is higher, so that the conductivity of the tab is improved by utilizing the good conductivity of the graphite; and the polarization phenomenon is reduced.

Description

TECHNICAL FIELD

[0001] The utility model relates to negative plate preparation technical field, concretely relates to a negative plate and battery. BACKGROUND

[0002] Battery is the core component in new energy technology, and the energy density of the battery is the technology that needs to pursue constantly, however, the traditional graphite negative electrode has approached the theoretical capacity density, therefore, in order to further improve the energy density of the negative electrode, high capacity density silicon-based material is selected to be added to the active material layer of the negative electrode based on graphite, but the negative plate with silicon-based and graphite in the prior art has the problem of easy polarization phenomenon near the tab. SUMMARY

[0003] The utility model discloses at least one of the technical problems in the prior art is solved.The utility model provides a negative plate, which can reduce the probability of polarization phenomenon near the tab of the negative plate.

[0004] The utility model further provides a battery with the negative plate.

[0005] The negative plate according to the first aspect of the utility model comprises a current collector, a negative tab and an active material layer.The current collector comprises a first end and a second end.The negative tab is arranged at the second end.The active material layer is coated on the surface of the current collector, and the active material layer comprises a silicon-based layer and one or more graphite layers, and the sum of the area densities of all the graphite layers gradually increases from the first end to the second end.

[0006] The negative plate according to the utility model has at least the following beneficial effects: the polarization phenomenon of the tab refers to the phenomenon that the electrode potential deviates from the equilibrium potential when the current passes through the electrode, when the current passes through the electrode, the distribution of the current density on the electrode is not uniform due to the existence of the current collector, and the current density in the part close to the tab is relatively high because the current needs to be concentrated to pass through the tab for transmission. High current density can accelerate the electrode reaction rate, which may cause more serious electrochemical polarization, and in the prior art, the silicon-based layer is added in the active material layer to further reduce the area density of graphite and the electron conduction rate, so that the polarization phenomenon is more likely to occur. The negative plate of the utility model embodiment uniformly coats the graphite layer to ensure the cycle stability and reduce the expansion of the silicon material, the area density of graphite in the active material layer close to the tab position is larger, the good conductivity of graphite is utilized to increase the conductivity of the tab, and when the current density is increased, the polarization phenomenon is reduced.

[0007] According to some embodiments of the present application, the areal density of the silicon-based layer gradually decreases from the first end to the second end.

[0008] According to some embodiments of the present application, the silicon-based layer is arranged on the current collector, and the graphite layer is arranged on the side surface of the silicon-based layer away from the current collector.

[0009] According to some embodiments of the present application, the same side of the current collector is provided with two graphite layers, and the two graphite layers are respectively a first graphite layer and a second graphite layer.

[0010] According to some embodiments of the present application, the areal density of the first graphite layer gradually increases from the first end to the second end, and / or the areal density of the second graphite layer gradually increases.

[0011] According to some embodiments of the present application, the sum of the areal density of the first graphite layer and the areal density of the second graphite layer is a first areal density, 0.32 mg / cm 2 ≤ first areal density ≤ 2.89 mg / cm 2 ; and / or the areal density of the silicon-based layer is a second areal density, 0.64 mg / cm 2 ≤ second areal density ≤ 5.78 mg / cm 2 .

[0012] According to some embodiments of the present application, the active material layer comprises a first segment, a second segment, a third segment, a fourth segment and a fifth segment which are equal in length and arranged in sequence along the length direction.

[0013] According to some embodiments of the present application, the material of the silicon-based layer is one of silicon-carbon graphite composite material, silicon-oxygen graphite composite material and silicon alloy composite material.

[0014] According to some embodiments of the present application, in the active material layer per unit area, the weight proportion of the silicon-based layer is 10% to 90%.

[0015] The battery according to the second aspect of the present application comprises the negative plate according to any one of the first aspect of the present application.

[0016] The battery according to the embodiment of the utility model has at least the following beneficial effects: high current density can cause the electrode reaction rate to accelerate, thereby possibly causing more serious electrochemical polarization, and in the prior art, in order to improve the energy density, a silicon-based layer is added in the active material layer, the surface density of graphite is further reduced, the electron conduction rate is reduced, and therefore polarization is more likely to occur. The negative plate of the embodiment of the utility model is unevenly coated with the graphite layer, the surface density of the graphite in the active material layer closer to the position of the tab is greater, the good conductivity of the graphite is utilized to increase the conductivity of the tab, when the current density is increased, the phenomenon of polarization is reduced, and the performance and service life of the battery are improved.

[0017] Additional aspects and advantages of the utility model will be partially given in the following description, some will become apparent from the following description, or be understood through the practice of the utility model. BRIEF DESCRIPTION OF DRAWINGS

[0018] The utility model will be further explained in combination with the drawings and embodiments, wherein:

[0019] Figure 1 It is the sectional view of the first embodiment of the negative plate in an embodiment of the utility model;

[0020] Figure 2 It is the sectional view of the second embodiment of the negative plate in an embodiment of the utility model.

[0021] Reference signs: negative plate 100, current collector 101, first end 102, second end 103, negative tab 104, active material layer 105, silicon-based layer 106, graphite layer 107, first graphite layer 108, second graphite layer 109, first section 110, second section 111, third section 112, fourth section 113, fifth section 114. DETAILED DESCRIPTION

[0022] The embodiments of the utility model are described in detail below, and the examples of the embodiments are shown in the drawings, wherein the same or similar reference signs represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the utility model, and cannot be understood as limiting the utility model.

[0023] In the description of the utility model, it is understood that the orientation description, such as up, down, front, back, left, right and the like, is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the utility model and simplifying the description, and cannot be understood as indicating or implying that the indicated device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the utility model.

[0024] In the description of the utility model, the meaning of several is one or more, the meaning of multiple is two or more, greater than, less than, exceed and the like are understood as not including the number, above, below, within and the like are understood as including the number. If it is described to the first, the second is only used for distinguishing the purpose of technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or implicitly indicating the sequence of indicated technical features.

[0025] In the description of the utility model, unless otherwise explicitly limited, the words such as setting, installation, connection should be understood in a broad sense, and the specific meaning of the above words in the utility model can be reasonably determined by the person skilled in the art in combination with the specific content of the technical scheme.

[0026] In the description of the utility model, the description of reference terms "one embodiment", "some embodiments", "illustrative embodiment", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the utility model. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0027] Reference Figure 1 and Figure 2According to the negative plate 100 of the first aspect embodiment of the present application, the surface density of the graphite layer 107 in the active material layer 105 gradually increases from the first end 102 to the second end 103, so that the polarization phenomenon of the electrode is reduced.

[0028] It should be noted that, with reference to the drawings Figure 1 In some embodiments of the present application, the area of each layer is equal when viewed from top to bottom, that is, each layer penetrates the entire active material layer 105 along the length direction, and the thickness of the silicon-based layer 106 and each graphite layer 107 in the active material layer 105 is different when viewed along the side section direction, so as to change the surface density. It should be noted that the surface density of each substance in the coating refers to the mass of the substance in a unit area of the coating surface, for example, if the surface density of the graphite is 2.89 mg / cm 2 , it means that the area of the upper surface of one side of the current collector 101 from top to bottom is 1 cm 2The mass of the graphite in the part of the active material layer 105 is 2.89 mg. Therefore, it should be noted that, in some embodiments of the utility model, when the active material layer 105 is processed, the flow of the spray head is controlled, the flow is reduced by a certain proportion when the silicon-based layer 106 is sprayed from the first end 102 to the second end 103, so that the weight of the sprayed silicon-based material is reduced, and the flow is increased by a certain proportion when the graphite layer 107 is sprayed from the first end 102 to the second end 103, so that the weight of the sprayed graphite is increased, so as to realize the change of the area density of the silicon-based layer 106 or the graphite layer 107, and the change of the area density is uniform and continuous.

[0029] It should be noted that, in some embodiments of the utility model, by controlling the flow of the spray head, the area density of the sprayed material gradually changes according to the preset, and finally the area density of the active material layer 105 is uniform, and the uniformity of the area density helps to form a more uniform current distribution, reduces the phenomenon of excessive local current or insufficient local current due to uneven area density, thereby reducing the internal resistance of the battery, and in addition, has the advantages of improving the discharge specific capacity, improving the cycle performance and the like.

[0030] It should be noted that, with reference to Figure 1 In some embodiments of the utility model, the upper surface of the finally formed active material layer 105 is in a plane, and the flat upper surface of the active material layer 105 helps to form a more uniform electrolyte distribution, so that the transmission of lithium ions in the electrode is more smooth. This helps to reduce the phenomenon of excessive local lithium ion concentration or insufficient local lithium ion concentration due to uneven electrolyte distribution, thereby improving the charge and discharge efficiency of the battery. The flat upper surface of the active material layer 105 helps to form a more compact conductive network, so that the transmission of electrons in the electrode is more efficient. This helps to reduce the internal resistance of the battery, improve the power output and energy density of the battery, and also reduces the mechanical stress caused by the uneven surface, thereby prolonging the cycle life of the battery.

[0031] It should be noted that, in some embodiments of the utility model, the arrangement of the silicon-based and the graphite is as shown in Figure 1 and Figure 2 The structure is layered, or the silicon-based can be mixed in the graphite according to a certain proportion, so that the area density of the graphite gradually increases as the position closer to the negative electrode lug 104.

[0032] It should be noted that, in some embodiments of the utility model, Figure 1 and Figure 2is a cross-sectional view of the negative electrode sheet 100 during the manufacturing process, thus in a horizontal state, in actual use, the negative electrode sheet 100 can be used in a stacked electrode or a wound electrode, without affecting its performance, and the flat surface shown in the figure can also be crimped or folded during the process of processing into an electrode.

[0033] Reference Figure 1 and Figure 2 In some embodiments of the present application, the areal density of the silicon-based layer 106 gradually decreases from the first end 102 to the second end 103. Since the current needs to be concentrated through the tab for transmission, the current density in this area is relatively high, and the conductive performance of the silicon-based material is lower than that of graphite, so the silicon-based layer 106 with high areal density is arranged away from the tab, and the areal density of the silicon-based layer 106 closer to the tab is lower, which can reduce the influence of the silicon-based layer 106 on the charge and discharge rate, while also retaining the advantages of high capacity density of silicon-based materials. The design that the content of the silicon-based layer 106 in the active material layer 105 is lower closer to the negative tab 104 can reduce the influence of volume expansion on the negative tab 104, optimize lithium ion transmission, reduce stress concentration, and improve battery safety.

[0034] Reference Figure 2 In some embodiments of the present application, the silicon-based layer 106 is arranged on the current collector 101, and the graphite layer 107 is arranged on the side surface of the silicon-based layer 106 away from the current collector 101. The silicon-based layer 106 has extremely high theoretical lithium storage capacity, far exceeding that of traditional graphite negative electrode materials, which enables the battery to store more energy, thereby improving the energy storage density of the battery. However, the expansion coefficient of silicon is also high, so the arrangement in the active material layer 105 can make the battery more severely expand and contract during the cycle process, leading to peeling of the negative electrode coating of the battery from the foil in the later cycle stage, further showing abnormal phenomena such as purple discoloration and increased internal resistance of the negative electrode sheet 100. If the silicon-based layer 106 is exposed on the outermost surface, the volume expansion effect of the silicon-based material will directly act on the outer surface of the active material layer 105. This can exacerbate the rupture and shedding of the active material layer 105, thereby reducing the performance and cycle life of the battery. Graphite has small volume change during charge and discharge and good stability, and covering the graphite layer 107 on the side surface of the silicon-based layer 106 away from the current collector 101 can effectively alleviate the stress phenomenon caused by the expansion of silicon, maintain the stability of the electrode structure, and thus improve the cycle stability and capacity retention rate of the battery.

[0035] Reference Figure 1In some embodiments of the utility model, two graphite layers 107 are arranged on the same side of the current collector 101, the two graphite layers 107 are respectively a first graphite layer 108 and a second graphite layer 109, the second graphite layer 109 is arranged on the current collector 101, the silicon-based layer 106 is arranged on the side surface of the second graphite layer 109 away from the current collector 101, and the first graphite layer 108 is arranged on the side surface of the silicon-based layer 106 away from the current collector 101. The second graphite layer 109 is additionally arranged between the silicon-based layer 106 and the current collector 101, so that the influence of the volume expansion of the silicon-based layer 106 on the overall structure of the negative plate 100 can be further alleviated, and the second graphite layer 109 arranged between the silicon-based layer 106 and the current collector 101 can form a conductive bridge, so that the current can flow more smoothly through the negative electrode, thereby improving the performance of the battery.

[0036] Reference Figure 1 In some embodiments of the utility model, the area density of the first graphite layer 108 gradually increases from the first end 102 to the second end 103, and / or the area density of the second graphite layer 109 gradually increases. Increasing the content of the graphite layer 107 near the negative tab 104 can more effectively collect and conduct the current, effectively reduce the probability of polarization phenomenon, and improve the battery performance and cycle life.

[0037] In some embodiments of the utility model, the sum of the area density of the first graphite layer 108 and the area density of the second graphite layer 109 is a first area density, 0.32 mg / cm 2 ≤ the first area density ≤ 2.89 mg / cm 2 ; and / or the area density of the silicon-based layer 106 is a second area density, 0.64 mg / cm 2 ≤ the second area density ≤ 5.78 mg / cm 2 . The density of the graphite layer 107 and the density of the silicon-based layer 106 affect the overall performance of the battery. When the first area density is greater than 2.89 mg / cm 2 , the content of the graphite layer 107 is too high, the excessive graphite layer 107 leads to excessive conductivity, and under the condition that the overall size of the active material layer 105 is constant, increasing the content of the graphite layer 107 will also reduce the content of the silicon-based layer 106, which fails to fully utilize the lithium storage performance of the silicon-based layer 106, thereby affecting the energy density of the battery; when the first area density is less than 0.32 mg / cm 2 , the graphite content is too low, which may lead to insufficient conductivity of the negative plate 100, affect the charging performance of the battery, and fail to effectively buffer the volume expansion of the silicon-based layer 106. When the second area density is greater than 5.78 mg / cm 2When the content of the silicon-based layer 106 is too high, since the silicon-based layer will expand and shrink greatly during the charging and discharging process, too high content of the silicon-based layer 106 can cause the destruction of the structure of the negative plate 100 and the rapid decay of the battery performance, and too high content of the silicon-based layer 106 can also reduce the conductivity and charging and discharging efficiency of the battery; when the second area density is less than 0.64 mg / cm 2 When the content of the silicon-based layer 106 is too low, the overall lithium storage capacity of the active material layer 105 is reduced, and the endurance and energy density of the battery are reduced.

[0038] Reference Figure 1 In some embodiments of the present application, the active material layer 105 includes a first segment 110, a second segment 111, a third segment 112, a fourth segment 113 and a fifth segment 114 which are sequentially arranged along the length direction and have equal lengths. In the fourth segment 113 and the fifth segment 114, the material of the first graphite layer 108 and the second graphite layer 109 is one of natural flake graphite, graphitized mesocarbon microbeads, and soft carbon coated artificial graphite. The fourth segment 113 and the fifth segment 114 are closer to the position of the negative tab 104, and the current density is higher. The material of natural flake graphite, graphitized mesocarbon microbeads, and soft carbon coated artificial graphite is high-rate graphite, which has a faster charging and discharging rate. Therefore, selecting the material of the first graphite layer 108 and the second graphite layer 109 at this position as the above material can better play the charging and discharging performance of graphite.

[0039] In some embodiments of the present application, the material of the silicon-based layer 106 is one of silicon-carbon-graphite composite material, silicon-oxygen-graphite composite material, and silicon alloy composite material. The silicon-based layer 106 is arranged in the active material layer 105 of the negative electrode and mainly plays a role of lithium storage. The silicon-carbon-graphite composite material, the silicon-oxygen-graphite composite material, and the silicon alloy composite material all have high energy density and good lithium storage performance, which can effectively improve the capacity density of the battery. It should be noted that the above composite material means that the material can also have other materials, for example, the main components of the silicon-carbon-graphite composite material are silicon and carbon, and the main components of the silicon-oxygen-graphite composite material are silicon, graphite, and oxygen, etc.

[0040] In some embodiments of the utility model, in the active material layer 105 per unit area, the weight proportion of silicon-based layer 106 is 10%~90%. The active material layer 105 per unit area refers to the upper surface of the single-sided active material layer 105 of the current collector 101, and the weight proportion of the silicon-based layer 106 in the part of the active material layer 105 is between 10% and 90%, including 10% and 90%. Such design is to make the content of silicon-based layer 106 in each part of the active material layer 105 moderate, and the content of silicon-based layer 106 too high may cause the destruction of the negative plate 100 structure and the rapid attenuation of the battery performance, and the content of silicon-based layer 106 too high also reduces the conductivity and charge-discharge efficiency of the battery, and the content of silicon-based layer 106 too low reduces the overall lithium storage capacity of the active material layer 105, reduces the endurance and energy density of the battery.

[0041] According to the battery of the second aspect of the utility model, the negative plate 100 of any one of the first aspect of the utility model is included. In this way, high current density may cause the electrode reaction rate to accelerate, thereby possibly causing more serious electrochemical polarization, and in the prior art, in order to improve the energy density, the silicon-based layer 106 is added in the active material layer 105, and the surface density of graphite is further reduced, and the electron conduction rate is reduced, so that polarization phenomenon is more likely to occur. The negative plate 100 of the embodiment of the utility model, in order to ensure the cycle stability and reduce the expansion of the silicon material, the graphite layer 107 is unevenly coated, the surface density of the graphite in the active material layer 105 closer to the lug position is larger, thereby utilizing the good conductivity of the graphite, increasing the conductivity of the lug, when the current density is increased, the polarization phenomenon is reduced, and the performance and service life of the battery are improved.

[0042] The embodiments of the utility model are described in detail above in combination with the drawings, but the utility model is not limited to the above-mentioned embodiments, and within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the purpose of the utility model. In addition, the embodiments of the utility model and the features in the embodiments can be combined with each other without conflict.

Claims

1. A negative electrode sheet, characterized by, The battery comprises: a current collector comprising a first end and a second end; a negative tab provided at the second end; an active material layer coated on a surface of the current collector, the active material layer comprising a silicon-based layer and one or more graphite layers, the sum of the area densities of all the graphite layers gradually increasing from the first end to the second end.

2. The negative electrode sheet according to claim 1, characterized by The area density of the silicon-based layer gradually decreases from the first end to the second end.

3. The negative electrode sheet according to claim 1, characterized by The silicon-based layer is provided on one side surface of the current collector, and the graphite layer is provided on the other side surface of the silicon-based layer away from the current collector.

4. The negative electrode sheet according to claim 1, characterized by The same side of the current collector is provided with two graphite layers, which are a first graphite layer and a second graphite layer respectively, the second graphite layer is provided on the surface of the current collector, the silicon-based layer is provided on one side surface of the second graphite layer away from the current collector, and the first graphite layer is provided on one side surface of the silicon-based layer away from the current collector.

5. The negative electrode sheet according to claim 4, characterized by The area density of the first graphite layer gradually increases from the first end to the second end, and / or the area density of the second graphite layer gradually increases from the first end to the second end.

6. The negative electrode sheet according to claim 4, characterized by The sum of the areal density of the first graphite layer and the areal density of the second graphite layer is a first areal density, 0.32 mg / cm 2 ≤ first areal density ≤ 2.89 mg / cm 2 ; and / or the silicon-based layer has an areal density of a second areal density, 0.64 mg / cm 2 ≤ second areal density ≤ 5.78 mg / cm 2 .

7. The negative electrode sheet according to claim 4, characterized by The active material layer comprises a first segment, a second segment, a third segment, a fourth segment and a fifth segment which are equal in length and arranged in sequence along the length direction, in the fourth segment and the fifth segment, the materials of the first graphite layer and the second graphite layer are one of natural flake graphite, graphitized mesocarbon microbeads and soft carbon coated artificial graphite.

8. The negative electrode sheet according to claim 1, characterized by The material of the silicon-based layer is one of silicon-carbon-graphite composite material, silicon-oxygen-graphite composite material and silicon alloy composite material.

9. The negative electrode sheet according to claim 1, wherein In the active material layer per unit area, the weight percentage of the silicon-based layer is 10% to 90%.

10. A battery characterized by The battery comprises the negative tab as claimed in any one of claims 1 to 9.

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