Composite current collector, pole piece and electrochemical device

Abstract

The utility model discloses a composite current collector, the composite current collector comprises a middle layer and a composite layer covered on the surface of the middle layer, the middle layer is a hot melting layer, the composite layer comprises a conductive layer and a connecting layer, and the conductive layer is connected with the two side surfaces of the hot melting layer through the connecting layer. A traditional metal current collector is replaced by the composite current collector, and the hot melting layer is arranged in the composite current collector, so that when an internal short circuit occurs in the battery, the hot melting layer in the current collector quickly absorbs heat and is partially melted by virtue of a large amount of heat generated by the internal short circuit; and the molten hot melting layer flows and wraps the edge of the damaged part of the conductive layer and the surface of a puncture object, so that the conductive layer is recovered to be isolated from other parts, an internal short circuit is prevented from continuing to occur, and the stability and the safety of the lithium ion battery are improved. In addition, the utility model also discloses a pole piece and an electrochemical device.

Description

Technical Field

[0001] The utility model relates to the field of lithium - ion batteries, and particularly to a composite current collector, a pole piece and an electrochemical device. Background Art

[0002] With the wide application of lithium - ion batteries in consumer electronics and electric vehicles, the requirements for the weight energy density and volume energy density of lithium - ion batteries are gradually increasing, and the subsequent safety problems of battery cells have attracted more and more public attention.

[0003] At present, the current collectors in lithium - ion batteries mainly include metal foil current collectors and composite current collectors with metal layers plated on both sides of a polymer layer. When mechanical safety, foreign object impact, external acupuncture, extrusion, etc. occur in the battery cell, the existing conventional metal foil current collectors and composite current collectors will be damaged, resulting in direct contact between the positive electrode and the negative electrode, causing internal short - circuit of the battery cell, and the internal temperature of the battery rises sharply, which will not only affect the normal use of the battery and reduce the battery life, but also pose great safety hazards. Summary of the Utility Model

[0004] The main purpose of the utility model is to propose a composite current collector, aiming to solve the problem of easy short - circuit in the battery cell.

[0005] To achieve the above purpose, the utility model proposes a composite current collector, which includes an intermediate layer and a composite layer covering the surface of the intermediate layer. The intermediate layer is a heat - melting layer, and the composite layer includes a conductive layer and a connection layer. The conductive layer is connected to the two side surfaces of the heat - melting layer through the connection layer.

[0006] In some embodiments, the connection layer is an organic support layer or a bonding layer, and the organic support layer or the bonding layer is disposed between the heat - melting layer and the conductive layer.

[0007] In some embodiments, the thickness of the heat - melting layer is 1μm - 5μm.

[0008] In some embodiments, the thickness of the organic support layer is 1μm - 10μm.

[0009] In some embodiments, the material of the conductive layer is metal, and the thickness of the conductive layer is 0.05μm - 2μm.

[0010] In some embodiments, the initial melting temperature of the heat - melting layer is 80°C - 130°C.

[0011] In some embodiments, the material of the heat - melting layer is one or more of imidazole, benzotriazole, 2 - methylimidazole, o - phenylenediamine, urea, malonic acid, glutaric acid, suberic acid, cyclopentanedicarboxylic acid and their derivatives.

[0012] The present utility model further provides a pole piece, which includes any one of the current collectors described in the foregoing embodiments, and an active material layer is provided on at least one outer surface of the composite current collector.

[0013] In some embodiments, the thickness of the composite current collector is less than the thickness of the active material layer.

[0014] The present utility model further provides an electrochemical device, which includes a positive pole piece, a negative pole piece, a separator and an electrolyte, and the positive pole piece and / or the negative pole piece is the pole piece described in any one of the foregoing embodiments.

[0015] By using a composite current collector to replace the traditional metal current collector and providing a heat-melting layer in the composite current collector, when an internal short circuit occurs inside the battery, with the help of a large amount of heat generated by the internal short circuit, the heat-melting layer in the current collector quickly absorbs heat and partially melts. The melted heat-melting layer flows and wraps the edge of the damaged part of the conductive layer and the surface of the puncturing object, so that the conductive layer is restored to a state of being isolated from other components, preventing the internal short circuit from continuing to occur, and improving the stability and safety of the lithium-ion battery. Description of the Drawings

[0016] Figure 1 It is a cross-sectional view of another embodiment of the current collector of the present utility model;

[0017] Figure 2 It is a cross-sectional view of an embodiment of the pole piece of the present utility model.

[0018] Reference Numerals:

[0019] 100, heat-melting layer; 200, conductive layer; 300, connecting layer; 400, active material layer. Detailed Embodiments

[0020] Next, the solutions in the embodiments of the present utility model will be clearly and completely described in conjunction with the drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all of the embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present utility model.

[0021] It should be noted that all the directional indications (such as up, down, left, right, front, back...) in the embodiments of the present utility model are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the drawings). If the specific posture changes, the directional indications will also change accordingly.

[0022] It should also be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or there may be an intermediate element present at the same time. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intermediate element present at the same time.

[0023] In addition, in the present utility model, the descriptions involving "first", "second", etc. are only for descriptive purposes and should not be construed as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present utility model.

[0024] The present utility model provides a composite current collector. Referring to Figure 1 , the composite current collector includes an intermediate layer and a composite layer covering the surface of the intermediate layer. The intermediate layer is a hot-melt layer 100, and the composite layer includes a conductive layer 200 and a connecting layer 300. The conductive layer 200 is connected to both side surfaces of the hot-melt layer 100 through the connecting layer 300.

[0025] As a conductive medium inside the battery, the current collector provides a channel for current transmission. In the prior art, the current collector is generally a metal foil, which can collect the current generated by the battery active material to form a larger current for external output. In this embodiment, the composite current collector is in a long strip shape as a whole and is composed of a composite material, including two conductive layers 200 and a hot-melt layer 100 sandwiched between the two conductive layers 200. Among them, the conductive layer 200 has good electrical conductivity and plays a role in ensuring the effective transmission of current inside the battery. It can be made of a metal conductive material or a carbon-based conductive material. The metal conductive material can be at least one of aluminum, copper, nickel, titanium, silver, nickel-copper alloy, and aluminum-zirconium alloy. The carbon-based conductive material can be at least one of graphite, acetylene black, graphene, and carbon nanotubes.

[0026] The hot-melt layer 100 is disposed between the conductive layers 200 and is usually made of a polymer material with a relatively low initial melting temperature. The initial melting temperature refers to the initial temperature at which a solid melts its physical state from solid to liquid. The conductive layer 200 and the hot-melt layer 100 are connected together through the connecting layer 300. Exemplarily, when the conductive layer 200 is a copper foil, a viscous substance is coated on one side of the copper foil as the connecting layer 300 to bond the copper foil to the hot-melt layer 100.

[0027] Compared with conventional metal current collectors, the composite current collector in this embodiment has a smaller mass under the same volume; and the hot-melt layer 100 in the composite current collector can, when an internal short circuit occurs in the lithium-ion battery, partially melt and wrap the conductive layer 200 by means of the heat rapidly increased due to the internal short circuit, so as to isolate the positive electrode sheet and the negative electrode sheet, thereby preventing the internal short circuit from continuing to occur. At the same time, it can also prevent the burrs at the edge of the conductive layer 200 from piercing the separator after thermal expansion, affecting the use of the lithium-ion battery.

[0028] As Figure 1 shown, in some embodiments, the connection layer 300 is an organic support layer or an adhesive layer, and the organic support layer or the adhesive layer is disposed between the hot-melt layer 100 and the conductive layer 200.

[0029] Among them, the adhesive layer serves to connect and fix the conductive layer and the hot-melt layer together. Specifically, through an adhesive process, an adhesive is coated on the conductive layer and / or the hot-melt layer to bond the two together.

[0030] An organic support layer can also be used to replace the adhesive layer, which serves to support and stabilize the conductive layer 200, providing a stable base so that the conductive layer 200 can be evenly distributed and maintain the required arrangement state. Moreover, there are various connection methods between the conductive layer 200 and the organic support layer. For example, when the conductive layer 200 is a metal, it can be disposed on the organic support layer by means of evaporation plating, electroplating, etc., without the need for bonding, avoiding problems such as uneven distribution of the adhesive or poor corrosion resistance of the adhesive, and prolonging the service life of the lithium-ion battery.

[0031] As Figure 1 shown, in some embodiments, the thickness of the hot-melt layer 100 is 1 μm to 5 μm. Specifically, the thickness of the hot-melt layer 100 can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc. In this embodiment, since the hot-melt layer 100 is used to absorb the heat generated during an internal short circuit of the lithium-ion battery and wrap the edge of the conductive layer 200 after melting, the hot-melt layer 100 cannot be too thin. If the thickness of the hot-melt layer 100 is less than 1 μm, the amount is too small and the fluidity is insufficient to play the role of wrapping the edge of the metal layer; if the thickness of the hot-melt layer 100 is greater than 5 μm, it will occupy the space of the active material layer in the electrode sheet, reducing the energy density of the lithium-ion battery. Preferably, the thickness of the hot-melt layer 100 is controlled to be 2 μm, so that the hot-melt layer 100 can melt and cover the edge of the conductive layer 200 while not occupying too much space and avoiding too low an energy density of the lithium-ion battery.

[0032] In some embodiments, the thickness of the organic support layer is 1 μm to 10 μm. By selecting a polymer material to form the support layer, since the density of the polymer material is usually less than that of the conductive layer 200, compared with the traditional metal composite current collector, the mass of the composite current collector in this embodiment is smaller under the same volume, which can improve the weight energy density of the battery.

[0033] When the thickness of the support layer is less than 1 μm, the support layer is too thin, which has little effect on the structure of the composite current collector. And due to the low mechanical strength, it is easy to break during the processing of the electrode sheet and cannot play a good supporting role. When the thickness of the support layer is greater than 10 μm, the support layer is too thick, which will occupy the setting space of the conductive layer 200 and the hot melt layer 100, increasing the volume of the composite current collector. In this embodiment, the thickness of the support layer is usually selected to be 3 μm to ensure that the influence of the support layer on the volume of the composite current collector is not significant, and at the same time, the conductive layer 200 can be smoothly set on the support layer, improving the mechanical strength and stability of the composite current collector.

[0034] As Figure 1 shown, in some embodiments, the material of the conductive layer 200 is metal, and the thickness of the conductive layer 200 is 0.05 μm to 2 μm. Exemplarily, if the conductive layer 200 is a copper foil and the thickness of the conductive layer 200 is controlled to be 0.05 μm, at this time the conductive layer 200 is relatively thin, occupying less space, and more active materials can be set under the same volume, and the energy density of the lithium-ion battery made is greater. However, if the thickness is less than 0.05 μm, the too-thin copper foil has a large resistance, making the internal temperature of the battery higher and affecting the service life of the battery. When the thickness of the conductive layer 200 is controlled to be 2 μm, at this time the conductive layer 200 is relatively thick, playing a better supporting role, and the small resistance makes the battery not easy to heat up. But when the thickness is greater than 2 μm, the greater the thickness of the conductive layer 200, the smaller the available space for other parts, and the less active materials in the battery, resulting in a decrease in the energy density of the lithium-ion battery.

[0035] In some embodiments, the initial melting temperature of the hot melt layer 100 is 80 °C to 130 °C.

[0036] By controlling the specific composition of the hot-melt layer 100, the initial melting temperature of the hot-melt layer 100 can be adjusted. When the initial melting temperature of the hot-melt layer 100 is controlled at 80 °C, the hot-melt layer 100 can quickly enter the molten state, so as to timely wrap the edge of the conductive layer 200. Since the formation process temperature of the battery core in a lithium-ion battery is about 80 °C, if the initial melting temperature of the hot-melt layer 100 is too low, it is easy to cause the hot-melt layer 100 to melt during the production process of the lithium-ion battery, affecting the normal process flow. If the initial melting temperature of the hot-melt layer 100 is higher than 130 °C, even if an internal short circuit occurs in the lithium-ion battery, the generated heat is not enough to quickly melt the hot-melt layer 100, and it cannot timely wrap the conductive layer 200 and isolate the positive and negative electrode plates. Therefore, in this embodiment, the initial melting temperature of the hot-melt layer 100 is usually controlled at 95 °C, which can avoid the melting of the hot-melt layer 100 during the manufacturing process of the lithium-ion battery, and can also quickly melt when an internal short circuit occurs in the lithium-ion battery, preventing the internal short circuit from continuing.

[0037] In some embodiments, the material of the hot-melt layer 100 is one or more of imidazole, benzotriazole, 2-methylimidazole, o-phenylenediamine, urea, malonic acid, glutaric acid, suberic acid, cyclopentanedicarboxylic acid and their derivatives.

[0038] The present utility model further provides a pole piece. Referring to Figure 2 , the pole piece includes the composite current collector in the foregoing embodiment, and an active material layer 400 is provided on at least one outer surface of the composite current collector. Since the pole piece in this embodiment adopts all the technical solutions of all the above embodiments, it has at least all the technical effects brought by the technical solutions of the above embodiments, which will not be elaborated here one by one. The active material layer 400 is provided on at least one surface of the composite current collector, that is, at least one layer of the active material layer 400 is connected to the conductive layer 200. The active material layer 400 is usually provided on the surface of the conductive layer 200 by coating or rolling, and its coverage area and compaction density can be selected according to needs.

[0039] As Figure 2 shown, in some embodiments, the thickness of the composite current collector is less than the thickness of the active material layer 400. Since the capacity of the battery is mainly determined by the content of the active material in the active material layer 400, ensuring that the thickness of the composite current collector is less than the thickness of the active material layer 400 can ensure that the thickness of the composite current collector is small, and while having good electrical conductivity, the volume of the lithium-ion battery is small, that is, the energy density of the lithium-ion battery is improved.

[0040] The present utility model further provides an electrochemical device, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The positive electrode sheet and / or the negative electrode sheet is the electrode sheet of any one of the foregoing embodiments. Since the electrochemical device in this embodiment adopts all the technical solutions of all the above embodiments, it has at least all the technical effects brought by the technical solutions of the above embodiments, which will not be elaborated herein one by one. It can be understood that there may be multiple positive electrode sheets, negative electrode sheets and separators, and the three can be stacked to form a battery cell structure in the electrochemical device, or wound to form a wound core structure.

[0041] The above are only partial or preferred embodiments of the present utility model. Whether in terms of text or drawings, the scope of protection of the present utility model cannot be limited thereby. Any equivalent structural transformation made by using the content of the specification and drawings of the present utility model under the overall concept of the present utility model, or any direct / indirect application in other related technical fields is included in the scope of protection of the present utility model.

Claims

1. A composite current collector, characterized in that: The composite current collector includes an intermediate layer and a composite layer covering the surface of the intermediate layer, the intermediate layer is a hot melt layer, the composite layer includes a conductive layer and a connecting layer, and the conductive layer is connected to the two side surfaces of the hot melt layer through the connecting layer.

2. The composite current collector according to claim 1, characterized in that: The connecting layer is an organic supporting layer or an adhesive layer, and the organic supporting layer or the adhesive layer is arranged between the hot-melt layer and the conductive layer.

3. The composite current collector according to claim 2, characterized in that: The thickness of the hot melt layer is 1 μm to 5 μm.

4. The composite current collector according to claim 3, characterized in that: The thickness of the organic support layer is 1 μm to 10 μm.

5. The composite current collector according to any one of claims 1 to 4, characterized in that: The conductive layer is made of metal, and has a thickness of 0.05 μm to 2 μm.

6. The composite current collector according to claim 5, characterized in that: The initial melting temperature of the hot melt layer is 80°C to 130°C.

7. A pole piece, characterized in that: The pole piece comprises the composite current collector according to any one of claims 1 to 6, and at least one outer surface of the composite current collector is provided with an active material layer.

8. The pole piece according to claim 7, characterized in that: The thickness of the composite current collector is smaller than the thickness of the active material layer.

9. An electrochemical device, characterized in that: It comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet and / or the negative electrode sheet is the electrode sheet as described in any one of claims 7-8.

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