Composite current collector

Abstract

The application discloses a kind of composite current collectors, comprising: support layer, the support layer is made of polymer material;Conductive layer, the conductive layer is arranged on support layer;Conductive layer includes brittle layer and metal layer of multilayer alternately arranged;The ratio of the thickness of each metal layer and adjacent brittle layer is 3.5-15:1;The ratio of the elongation at break of metal layer and brittle layer is 6.8-12.2:1.The application sets up the brittle material with very low elongation at break and good brittleness on the surface of the metal layer of conductive layer, when being driven to stretch by external action such as puncture, due to the effect of brittle material, metal layer can directly fracture and break, and form open circuit;Greatly reduce the risk of internal short circuit thermal runaway of lithium ion battery when being subjected to abnormal conditions such as extrusion, collision or puncture.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a composite current collector. BACKGROUND

[0002] With the rapid development of new energy and electronic technology, the cycle life, safety performance and energy density of batteries have become the top priority. As a very important part of the battery, the current collector is used to collect the current generated by the battery active material to form a larger current for external output, and its performance will directly affect the cycle life, energy density and safety of the battery. Currently, copper foil and aluminum foil are commonly used as current collectors for positive and negative electrode sheets in lithium batteries and sodium batteries. Such current collectors have high cost and weight, which is not conducive to the control of battery cost and the improvement of energy density.

[0003] The composite current collector has obvious advantages compared to the traditional foil current collector. The composite current collector usually has a "sandwich" structure, with a polymer macromolecular layer in the middle and metal conductive layers on both sides. Because the metal layer on the surface of the composite current collector is thin and the internal polymer layer is light, it can effectively reduce the overall weight of the current collector, thereby increasing the energy density of the lithium ion battery.

[0004] Lithium ion batteries are prone to internal short circuit when subjected to abnormal conditions such as compression, collision or puncture, which can cause the battery to catch fire or even explode. The current composite current collector has an insulating polymer support layer, which can block electron transmission when punctured. However, when a nail or internal puncture occurs, the metal layer on the surface of the polymer support layer still has some conductive ability, and the battery temperature still shows an upward trend, which poses a certain risk of thermal runaway. Therefore, it is necessary to further improve the structure of the composite current collector to improve its thermal safety performance. SUMMARY

[0005] In order to improve the thermal safety performance of the composite current collector, the present application provides a composite current collector. The above-mentioned object can be achieved by the following technical solutions:

[0006] A composite current collector, comprising:

[0007] a support layer, the support layer comprising a polymer material;

[0008] a conductive layer disposed on the support layer; the conductive layer comprises a plurality of layers of brittle layers and metal layers arranged alternately;

[0009] The thickness ratio of each metal layer to the adjacent brittle layer is 3.5-15:1;

[0010] The elongation at break ratio of each metal layer to the adjacent brittle layer is 6.8-12.2:1.

[0011] Optionally, the thickness of each brittle layer is 1-15 nm; and the thickness of each metal layer is 10-100 nm.

[0012] Preferably, the conductive layer comprises at least three brittle layers and at least three metal layers.

[0013] Optionally, the tensile strength of the support layer is less than that of the conductive layer.

[0014] Optionally, the binding force between each metal layer and the adjacent brittle layer is greater than that between the support layer and the conductive layer.

[0015] Optionally, the thickness of each brittle layer increases successively with the distance of the brittle layer from the support layer.

[0016] Optionally, the surface of the conductive layer in contact with the support layer is a brittle layer.

[0017] Optionally, the surface of the conductive layer away from the support layer is a brittle layer.

[0018] Optionally, the hardness of the brittle layer is greater than that of the metal layer.

[0019] Optionally, the metal layer is made of at least one of aluminum, lithium, and nickel.

[0020] Optionally, the brittle material is a ceramic inorganic material.

[0021] Optionally, the brittle layer is made of at least one of aluminum oxide, silicon oxide, titanium oxide, silicon carbide, aluminum nitride, and silicon nitride.

[0022] Optionally, the support layer is made of at least one of PP, PET, and PI.

[0023] The above-mentioned method for preparing the composite current collector comprises the following steps:

[0024] The brittle layer and the metal layer are alternately deposited on the support layer by magnetron sputtering to form the conductive layer.

[0025] The deposition method is magnetron sputtering, or at least one of evaporation, PVD, and CVD.

[0026] Optionally, before the deposition of the brittle layer and the metal layer, the surface of the support layer is roughened to improve the binding force between the support layer and the conductive layer.

[0027] Optionally, the conditions for deposition by magnetron sputtering are as follows: the metal target is moved towards the brittle material target, the magnetron sputtering power density is 50 W / cm2, the vacuum degree is 0.1 Pa, the protective gas is argon, the flow rate is 50 mL / min, and the deposition time is 4.5 s each time.

[0028] Optionally, the application further provides the use of the composite current collector in the preparation of a battery.

[0029] The technical scheme of the application has the following advantages:

[0030] The brittle material layer is arranged on the surface of the metal layer of the conductive layer, and when the brittle material layer is driven to stretch due to external effects such as puncture, the metal layer can directly break and crumble due to the effect of the brittle material, thereby forming an open circuit, and the risk of internal short-circuit thermal runaway of the lithium ion battery under abnormal conditions such as extrusion, collision or puncture is greatly reduced.

[0031] In order to meet the overcurrent capacity of the current collector, the conductive layer needs to reach a certain thickness, and it is more difficult for the thicker conductive layer to stretch and deform to generate cracks. Therefore, the conductive layer is designed as a multi-layer structure in the present scheme, and the metal layer and the brittle layer are both multi-layer and arranged alternately. When each brittle layer breaks and crumbles, it only needs to act on its adjacent metal layer to drive it to break together to realize point short-circuit. Through the multi-layer and alternating arrangement, the short-circuit points not only exist in the two-dimensional direction in the plane, but also increase the short-circuit points in the thickness direction, forming a multi-point open circuit in the three-dimensional space, and further reducing the risk of internal short-circuit thermal runaway of the battery under external force impact. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical scheme in the specific embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the description of the specific embodiments or the prior art. Obviously, the drawings described below are some embodiments of the application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0033] Figure 1 is a schematic diagram of the puncture experiment.

[0034] The marks in the figure are: negative electrode sheet 1; diaphragm 2; positive electrode sheet 3; nail 4. DETAILED DESCRIPTION

[0035] The detailed description of the various exemplary embodiments of the application should not be considered as limiting the application, but should be understood as a more detailed description of some aspects, characteristics and embodiments of the application. It should be understood that the terms described in the application are only for the description of the particular embodiments, and are not used to limit the application.

[0036] In addition, for numerical ranges recited herein, every integer value within the range is specifically contemplated. In this written description and in the claims, words such as "comprise," "include," "have," and "contain" are not meant to be limiting. The use of the term "about" in relation to a value means that the value includes the exact value, but also other values that are close to the exact value. The term "about" is intended to encompass values that are within a reasonable range of the exact value, such as a range that would be understood by one of ordinary skill in the art to be close to the exact value.

[0037] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" or variants thereof are open-ended, and include one or more steps, elements, integers, articles, components or members, but do not preclude the addition of one or more other steps, elements, integers, articles, components, members or groups thereof.

[0038] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application.

[0039] A composite current collector in the present application comprises:

[0040] A support layer made of a polymer material;

[0041] An electrically conductive layer disposed on the support layer; the electrically conductive layer comprises a plurality of brittle layer metal layers arranged alternately;

[0042] The ratio of the thickness of each metal layer to the adjacent brittle layer is 3.5-15:1;

[0043] The ratio of the elongation at break of the metal layer to the brittle layer is 6.8-12.2:1.

[0044] The thickness of the brittle layer is 1-15 nm; the thickness of the metal layer is 10-100 nm.

[0045] The electrically conductive layer comprises at least 3 brittle layers and at least 3 metal layers.

[0046] When the battery is impacted by external force, the current collector may be punctured, stretched, etc. Due to the presence of the high-molecular support layer with good ductility and high toughness in the composite current collector, when being stretched and punctured, the surface conductive layer can be deformed synchronously with the high-molecular support layer subjected to tensile deformation. However, the ductility of the conductive layer is relatively weak, and cracks may be generated due to stretching. These cracks can achieve disconnection and reduce the risk of thermal runaway of the battery. However, due to the high toughness of the high-molecular support layer, even if the metal layer on the surface is cracked, it cannot be completely disconnected. Therefore, the brittle material with low elongation at break and high brittleness is arranged on the surface of the metal layer. When being stretched, the metal layer can not only be stretched, but also directly cracked and broken to form a disconnection due to the effect of the brittle material. In addition, in order to meet the flow capacity of the current collector, the conductive layer needs to reach a certain thickness, and it is more difficult to stretch and deform to generate cracks when the thickness is thicker. Therefore, the conductive layer is designed as a multi-layer structure in the present scheme, and the metal layer and the brittle layer are both multi-layered and arranged alternately. The thickness of each metal layer is relatively thin, and when each brittle layer is cracked and broken, it only needs to act on the adjacent metal layer to drive it to crack together to achieve point short circuit. Furthermore, through the multi-layered and alternating arrangement, the short circuit points not only exist in the two-dimensional plane direction, but also increase the short circuit points in the thickness direction to form multi-point disconnection in three-dimensional space, thereby further reducing the risk of internal short circuit thermal runaway of the battery when being impacted by external force.

[0047] The ratio of the elongation at break of the metal layer to the brittle layer should be greater than a certain value, and the brittle layer should be easy to crack and open circuit. However, the ratio should not be too large. If the ratio is too large, the brittle layer is too fragile, and it cannot guarantee the normal processing and use of the battery pole piece, or the ductility of the metal layer is too good, and it cannot crack together under the action of the brittle layer. Therefore, the ratio of the elongation at break of the metal layer to the brittle layer, especially the ratio of the elongation at break of the innermost metal layer close to the support layer to the innermost brittle layer, should be 6.8-12.2:1.

[0048] The ratio of the thickness of the metal layer to the adjacent brittle layer should not be too small. If the ratio is too small, the ductility of the conductive layer tends to be brittle, and the difference in ductility between the support layer is too large. During the rolling process of the pole piece, a large number of wrinkles may be generated at the junction of the slurry coating area and the empty foil area due to uneven stress, which affects the lug welding. The ratio should not be too large. If the ratio is too large, the brittle layer is too thin, and micro-cracks may be generated during the processing and use of the pole piece. In addition, when the brittle layer is too thin and the metal layer is too thick, the brittle layer cracking may not drive the metal layer to crack together.

[0049] The tensile strength of the support layer is less than the tensile strength of the conductive layer. The bonding force between each metal layer and the adjacent brittle layer is greater than the bonding force between the support layer and the conductive layer.

[0050] When the support layer has a sufficient bonding force with the conductive layer, the tensile deformation of the support layer can transmit the force to the conductive layer, and drive the brittle layer in the conductive layer to stretch and break, otherwise, the support layer and the conductive layer may be directly peeled off due to uneven extension, and the circuit of the conductive layer cannot be broken; and since the tensile force is transmitted from the support layer to the brittle layer, and then transmitted to the adjacent metal layer outside the brittle layer after the brittle layer is broken, the bonding force between the metal layer and the adjacent inner brittle layer is greater than the bonding force between the support layer and the conductive layer, so that the brittle layer can drive the adjacent outer metal layer to break synchronously when the brittle layer breaks.

[0051] The bonding force between the support layer and the conductive layer can be realized by selecting high-attachment-force film deposition methods such as magnetron sputtering ion beam deposition, or roughening the surface of the support layer by laser cleaning to control and improve the bonding force, or the attachment force of general ceramic materials on the polymer-based film is better than that of metal materials, and a ceramic brittle layer can be arranged at the innermost layer; the bonding force between the brittle layer and the metal layer can be improved by one-step film coating; the elongation at break of the metal layer can be controlled by selecting different types of metals or alloys; and the elongation at break of the brittle layer can be controlled by selecting different types of ceramic substances or mixing a plurality of ceramic substances.

[0052] The hardness of the brittle layer is greater than that of the metal layer. The thickness of each layer of the brittle layer increases successively with the distance of the brittle layer from the support layer. First, when the composite current collector is subjected to external force impact and deformation such as puncture and stretching, the support layer is stretched and deformed to drive the brittle layer close to the support layer to break and crumble, and then a breaking reaction chain is initiated to generate force on the brittle layer away from the support layer, and the brittle layer close to the support layer is thinner and more likely to achieve stepwise breaking.

[0053] Second, when the composite current collector is applied in a battery, it will undergo electrode slurry coating and rolling processes, and the upper layer of the current collector is subjected to the extrusion of electrode particles. If the brittle layer of the upper layer is thinner than the lower layer and the hardness of the upper layer is not high enough, the brittle layer of the upper layer is prone to produce fine cracks during the rolling process. The increased cracks of the upper layer increase the contact area between the electrolyte and the current collector, and the increased electrolyte increases the risk of corrosion of the current collector.

[0054] Preferably, the surface of the conductive layer in contact with the support layer is a brittle layer. That is, the brittle layer directly contacts the support layer, which is more likely to initiate a breaking reaction chain.

[0055] Preferably, the surface of the conductive layer away from the support layer is a brittle layer. The brittle layer of the uppermost layer is the thickest and has a higher hardness, which can protect the brittle layer of the lower layer from producing cracks during the processing of electrode rolling.

[0056] The metal layer is aluminum, lithium, nickel, or the like.

[0057] The brittle layer is a ceramic inorganic substance, and the maximum thickness of the brittle layer is not higher than 15 nm. The ceramic inorganic substance has good brittleness, and has chemical performance temperature and is not easy to be corroded by electrolyte, and can also play a role in protecting the base film. However, the conductivity of the ceramic inorganic substance is poor, so the thickness of the brittle layer needs to be set to be relatively thin, so that the current collector can still excite the directional movement of the electrons in the metal layer under the electric potential difference. The brittle layer cannot provide a large resistance due to the small thickness, and the conductivity will not change too much, so as not to affect the conductivity of the current collector.

[0058] The brittle layer is a ceramic inorganic substance, such as one or more of alumina, silicon oxide, titanium oxide, silicon carbide, aluminum nitride and silicon nitride.

[0059] The support layer is a high molecular polymer, such as PP, PET, PI.

[0060] The test method of the elongation at break of the brittle layer metal layer in each embodiment is as follows:

[0061] The brittle layer test sample is prepared, the same support layer as in the embodiment is selected, and the same plating method is selected to prepare the same brittle layer as the bottom layer (the layer closest to the contact with the support layer) on the upper and lower surfaces of the support layer to obtain the brittle layer sample.

[0062] The metal layer test sample is prepared, the same support layer as in the embodiment is selected, and the same plating method is selected to prepare the same metal layer as the bottom layer (the layer closest to the contact with the support layer) on the upper and lower surfaces of the support layer to obtain the metal layer sample.

[0063] The brittle layer sample and the metal layer sample are both punched and cut into a 10 mm wide sample to be tested; a universal testing machine is used for tensile testing at normal temperature and pressure (25℃, 0.1MPa), the initial position is set so that the sample length between the clamps is 50 mm long, the tensile speed is 50 mm / min, and the device displacement y (mm) when the brittle layer or the metal layer produces a crack is recorded, and finally the elongation at break is calculated as (y / 50) x 100%

[0064] Example 1

[0065] The embodiment provides a composite current collector and a preparation method thereof. The composite current collector comprises a support layer and a conductive layer, the conductive layer is arranged on the support layer, and the conductive layer comprises a plurality of brittle layers and metal layers arranged alternately. The material of the support layer is PET, the material of the metal layer is aluminum, and the material of the brittle layer is titanium oxide. There are five metal layers and five brittle layers, the innermost layer (the layer closest to the contact between the conductive layer and the support layer) is a metal layer, and the outermost layer (the layer farthest away from the support layer) is a brittle layer. The thickness of each metal layer is 30 nm, and the thickness of each brittle layer is 3 nm.

[0066] Preparation method: a PET film with a thickness of 6 μm is placed in a magnetron sputtering machine, and the brittle layer and the metal layer are alternately deposited on both sides of the thickness direction of the PET film. The specific process conditions are as follows:

[0067] 1) The target arrangement mode is set to 8 aluminum targets plus 1 titanium oxide target (purity is 99.95%), the PET film is brought to the direction from the aluminum target to the titanium oxide target, the magnetron sputtering power density is 50 W / cm2, the vacuum degree is 0.1 Pa, the protective gas is argon, the flow rate is 50 mL / min, and the first deposition time is 4.5 s;

[0068] 2) Repeat the above step 5 times, and each deposition time is 4.5 s.

[0069] After testing, the metal layer of Example 1 has an elongation at break of 18.1%, and the brittle layer has an elongation at break of 1.8%.

[0070] Example 2

[0071] The composite current collector provided by the embodiment comprises a support layer and a conductive layer, the conductive layer is arranged on the support layer, and the conductive layer comprises a plurality of brittle layers and metal layers arranged alternately, wherein the support layer is PET, the metal layer is aluminum, and the brittle layer is titanium oxide.

[0072] Preparation method: a PET film with a thickness of 6 μm is placed in a magnetron sputtering machine, and the brittle layer and the metal layer are alternately deposited on both sides of the thickness direction of the PET film. The specific process conditions are as follows:

[0073] 1) The target arrangement mode is set to 8 aluminum targets plus 1 titanium oxide target (purity is 99.95%), the PET film is brought to the direction from the aluminum target to the titanium oxide target, the magnetron sputtering power density is 50 W / cm2, the vacuum degree is 0.1 Pa, the protective gas is argon, the flow rate is 50 mL / min, and the first deposition time is 2.5 s;

[0074] 2) Repeat the above step 5 times, and each deposition time is 0.5 s more than the first time.

[0075] Five layers of metal layers and brittle layers are obtained, the innermost is the metal layer, and the outermost is the brittle layer. The thicknesses of the metal layers from the inside to the outside are 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, and 40 nm, respectively, and the thicknesses of the brittle layers from the inside to the outside are 1 nm, 3 nm, 5 nm, 7 nm, 9 nm, and 11 nm, respectively. Compared with Example 1, the thicknesses of the metal layers and the brittle layers have an increasing trend. After testing, the metal layer of Example 2 has an elongation at break of 14.5%, and the brittle layer has an elongation at break of 1.3%.

[0076] Example 3

[0077] The embodiment provides a composite current collector and a preparation method thereof, the composite current collector comprises a support layer and a conductive layer, the conductive layer is arranged on the support layer, and the conductive layer comprises brittle layer metal layers arranged alternately in multiple layers.

[0078] The preparation method is as follows: a PET film with a thickness of 6 μm is placed in a magnetron sputtering machine, and the brittle layer and the metal layer are alternately deposited on both sides of the thickness direction of the PET film, and the specific process conditions are as follows:

[0079] 1) the target material arrangement mode is set to one titanium oxide target plus eight aluminum targets (the purity is 99.95 %), the PET film is carried in the direction from the titanium oxide target to the aluminum target, the magnetron sputtering power density is 50 W / cm 2 , the vacuum degree is 0.1 Pa, the protective gas is argon, the flow rate is 50 mL / min, and the first deposition time is 4.5 s;

[0080] 2) the above step is repeated five times, and the deposition time is 4.5 s each time.

[0081] Five metal layers and five brittle layers are obtained, the innermost side is the brittle layer, and the outermost side is the metal layer. The thickness of each metal layer is 30 nm, and the thickness of each brittle layer is 3 nm. Test results show that the elongation at break of the metal layer of the embodiment 3 is 18.2 %, and the elongation at break of the brittle layer is 1.7 %.

[0082] Embodiment 4

[0083] The embodiment provides a composite current collector and a preparation method thereof, the composite current collector comprises a support layer and a conductive layer, the conductive layer is arranged on the support layer, and the conductive layer comprises brittle layer metal layers arranged alternately in multiple layers.

[0084] The preparation method is as follows: a PET film with a thickness of 6 μm is placed in a magnetron sputtering machine, and the brittle layer and the metal layer are alternately deposited on both sides of the thickness direction of the PET film, and the specific process conditions are as follows:

[0085] 1) the surface of the PET is subjected to laser etching, so that the surface roughness is improved, and the bonding force is improved.

[0086] 2) the target material arrangement mode is set to one titanium oxide target, eight aluminum targets and one titanium oxide target arranged in sequence (the purity is 99.95 %), the PET film is carried in the direction from the aluminum target to the titanium oxide target, the magnetron sputtering power density is 50 W / cm2, the vacuum degree is 0.1 Pa, the protective gas is argon, the flow rate is 50 mL / min, and the first deposition time is 5 s; 3) the above step is repeated five times, and the deposition time is 5 s each time.

[0087] The metal layer and the brittle layer are each five layers, the innermost side is the brittle layer, and the outermost side is the metal layer. The thickness of each metal layer is 30 nm, and the thickness of each brittle layer is 3 nm. Testing shows that the elongation at break of the metal layer of Example 5 is 13.7%, and the elongation at break of the brittle layer is 2%.

[0088] Example 5

[0089] The composite current collector provided by the embodiment and a preparation method thereof, the composite current collector comprises a support layer and a conductive layer, the conductive layer is arranged on the support layer, and the conductive layer comprises a plurality of layers of brittle layers and metal layers arranged alternately, wherein the support layer is PET, the metal layer is copper, and the brittle layer is silicon carbide.

[0090] Preparation method: a PET film with a thickness of 6 μm is placed in a magnetron sputtering machine, and the brittle layer and the metal layer are alternately deposited on both sides of the thickness direction of the PET film. The specific process conditions are as follows:

[0091] 3) The target arrangement mode is set to one silicon carbide target plus eight copper targets (the purity of each is 99.95%), the PET film is moved in the direction from the silicon carbide target to the copper target, the magnetron sputtering power density is 50 W / cm2, the vacuum degree is 0.1 Pa, the protective gas is argon, the flow rate is 50 mL / min, and the first deposition time is 4.5 s;

[0092] 4) The above step is repeated five times, and the deposition time of each time is 4.5 s.

[0093] The metal layer and the brittle layer are each five layers, the innermost side is the brittle layer, and the outermost side is the metal layer. The thickness of each metal layer is 30 nm, and the thickness of each brittle layer is 3 nm. Testing shows that the elongation at break of the metal layer of Example 5 is 13.7%, and the elongation at break of the brittle layer is 2%.

[0094] Example 6

[0095] The composite current collector provided by the embodiment and a preparation method thereof, the composite current collector comprises a support layer and a conductive layer, the conductive layer is arranged on the support layer, and the conductive layer comprises a plurality of layers of brittle layers and metal layers arranged alternately, wherein the support layer is PET, the metal layer is copper, and the brittle layer is silicon carbide.

[0096] Preparation method: a PET film with a thickness of 6 μm is placed in a magnetron sputtering machine, and the brittle layer and the metal layer are alternately deposited on both sides of the thickness direction of the PET film. The specific process conditions are as follows:

[0097] 5) The target arrangement mode is set to one aluminum oxide target plus eight lithium targets (the purity of each is 99.95%), the PET film is moved in the direction from the aluminum oxide target to the lithium target, the magnetron sputtering power density is 50 W / cm 2, the vacuum degree is 0.1 Pa, the protective gas is argon, the flow rate is 50 mL / min, and the first deposition time is 4.5 s;

[0098] 6) Repeat the above step 5 times, and the deposition time of each time is 4.5 s.

[0099] Five layers of metal layers and five layers of fragile layers are obtained, and the innermost side is the fragile layer and the outermost side is the metal layer. The thickness of each metal layer is 30 nm, and the thickness of each fragile layer is 3 nm. It is tested that the elongation at break of the metal layer of Example 6 is 20.7%, and the elongation at break of the fragile layer is 1.7%.

[0100] Example 7

[0101] The composite current collector provided by the embodiment and a preparation method thereof, the composite current collector comprises a support layer and a conductive layer, the conductive layer is arranged on the support layer, and the conductive layer comprises a plurality of layers of fragile layers and metal layers arranged alternately, wherein the support layer is selected from PP, the metal layer is aluminum, and the fragile layer is titanium oxide.

[0102] Preparation method: a PP film with a thickness of 6 μm is placed in a magnetron sputtering machine, and the fragile layers and the metal layers are alternately deposited on both sides of the thickness direction of the PP film, and the specific process conditions are as follows:

[0103] 1) The target material arrangement mode is set to 8 aluminum targets plus one titanium oxide target (the purity of each is 99.95%), the PP film is moved in the direction from the aluminum target to the titanium oxide target, the magnetron sputtering power density is 50 W / cm 2 , the vacuum degree is 0.1 Pa, the protective gas is argon, the flow rate is 50 mL / min, and the first deposition time is 4.5 s;

[0104] 2) Repeat the above step 5 times, and the deposition time of each time is 4.5 s.

[0105] Five layers of metal layers and five layers of fragile layers are obtained, and the innermost side is the metal layer and the outermost side is the fragile layer. The thickness of each metal layer is 30 nm, and the thickness of each fragile layer is 3 nm. It is tested that the elongation at break of the metal layer of Example 7 is 18%, and the elongation at break of the fragile layer is 1.8%.

[0106] Comparative Example 1

[0107] The support layer is selected from PET, the metal layer is iron, and the fragile layer is zirconium oxide. In the comparative example, the metal layer with a lower elongation at break and the fragile layer with a higher elongation at break are used.

[0108] Preparation method: a PET film with a thickness of 6 μm is placed in a magnetron sputtering machine, and the fragile layers and the metal layers are alternately deposited on both sides of the thickness direction of the PET film, and the specific process conditions are as follows:

[0109] 1) Set the target arrangement for 8 iron target plus one zirconia target (purity of 99.95%), PET film from the direction of the iron target to the zirconia target, magnetron sputtering power density of 50 W / cm 2 , vacuum degree of 0.1 Pa, protective gas is argon, flow rate of 50 mL / min, the first deposition time of 4.5 s;

[0110] 2) Repeat the above steps 5 times, and the deposition time is 4.5 s each time.

[0111] Get five layers of metal layer and brittle layer, the innermost is the metal layer, and the outermost is the brittle layer. Each layer of metal layer is 30 nm thick, and the brittle layer is 3 nm thick. Test shows that the metal layer of Comparative Example 1 has a breaking elongation of 12.2%, and the brittle layer has a breaking elongation of 2.1%.

[0112] Comparative Example 2

[0113] The support layer is PET, the metal layer is aluminum, and the brittle layer is titanium oxide.

[0114] Preparation method: place a PET film with a thickness of 6 μm in a magnetron sputtering machine, and perform alternating deposition of the brittle layer and the metal layer on both sides of the PET film in the thickness direction, and the specific process conditions are as follows:

[0115] 1) In the first magnetron sputtering machine, set the target arrangement for 9 aluminum targets (purity of 99.95%), magnetron sputtering power density of 60 W / cm2, vacuum degree of 0.1 Pa, protective gas is argon, flow rate of 50 mL / min, deposition time of 20 s;

[0116] 2) Turn into the second magnetron sputtering machine, set the target arrangement for 1 titanium oxide target (purity of 99.95%), magnetron sputtering power density of 50 W / cm 2 , vacuum degree of 0.1 Pa, protective gas is argon, flow rate of 50 mL / min, deposition time of 1 s;

[0117] Get 1 layer of metal layer and brittle layer, the inner side is the metal layer, and the outer side is the brittle layer. The metal layer is 160 nm thick, and the brittle layer is 5 nm thick. Test shows that the metal layer of Comparative Example 2 has a breaking elongation of 18.2%, and the brittle layer has a breaking elongation of 1.8%.

[0118] Comparative Example 3

[0119] The support layer is PET, the metal layer is aluminum, and the brittle layer is titanium oxide.

[0120] Preparation method: place a PET film with a thickness of 6 μm in a magnetron sputtering machine, and perform alternating deposition of the brittle layer and the metal layer on both sides of the PET film in the thickness direction, and the specific process conditions are as follows:

[0121] 1) Set the target arrangement to 4 aluminum targets plus 4 titanium oxide targets (both with a purity of 99.95%), and the PET film is sputtered from the aluminum target to the titanium oxide target, the magnetron sputtering power density is 50 W / cm 2 , the vacuum degree is 0.1 Pa, the protective gas is argon, the flow rate is 50 mL / min, and the first deposition time is 4.5 s;

[0122] 2) Repeat the above step 5 times, and the deposition time of each time is 4.5 s. Five layers of metal layers and brittle layers are obtained, the innermost is the metal layer, and the outermost is the brittle layer. The thickness of each metal layer is 16 nm, and the thickness of each brittle layer is 14 nm. Compared with Example 1, the thickness ratio of the metal layer and the brittle layer is too small, and the two are step-by-step plated, and the bonding force is weak. After testing, the metal layer of the comparative example 3 has an elongation at break of 18.1%, and the brittle layer has an elongation at break of 1.8%.

[0123] Bonding force test

[0124] The test method is as follows: the above-mentioned composite current collector is selected as the sample to be tested, the width h is 0.02 m, at normal temperature and pressure (25℃, 0.1 MPa), 3M double-sided tape is uniformly pasted on one side of the stainless steel plate, and then the sample to be tested is uniformly pasted on the other side of the double-sided tape. The sample to be tested is peeled off using a high-iron tension machine, and the surface of the support layer on one side is tested after peeling. If the element ratio of the metal element in the brittle layer on the surface of the support layer is less than 5%, it is considered that the bonding force between the metal layer and the brittle layer is greater than the bonding force between the brittle layer and the support layer. After testing, the bonding force between the metal layer and the brittle layer in each example is greater than the bonding force between the brittle layer and the support layer.

[0125] Battery performance test:

[0126] Battery preparation method:

[0127] Preparation of the pole piece and the battery:

[0128] 1) Preparation of the positive pole piece

[0129] The positive pole piece is prepared by mixing the ternary active material NCM811, conductive carbon black and the binder PVDF in a weight ratio of 92:4:4 in NMP to obtain a positive pole slurry. The positive pole slurry is coated on the composite current collector sample, dried and rolled to obtain the positive pole piece. The compaction density of the positive active material layer is 3.3 g / cm 3 .

[0130] 2) Preparation of the negative pole piece

[0131] The negative active material artificial graphite, binder SBR, dispersant CMC and conductive carbon black were mixed in water in a weight ratio of 96:2:1.2:0.8, and the negative electrode slurry was obtained after being fully stirred and mixed uniformly. The negative electrode slurry was coated on the composite current collector sample, dried and rolled, and then die-cut to obtain the negative electrode sheet. The compaction density of the negative active material layer was 1.55 g / cm 3 .

[0132] 3) Separator

[0133] The PE film was selected as the separator.

[0134] 4) Preparation of electrolyte

[0135] Ethylene carbonate (EC) and methyl ethyl carbonate (EMC) were mixed in a volume ratio of 4:6 as the solvent, and lithium salt LiPF6 was selected as the solute, and the concentration was 1 mol / L.

[0136] 5) Preparation of battery

[0137] The above positive electrode sheet, separator and negative electrode sheet were stacked in order, and the battery cell was obtained after winding. The battery cell was placed in the battery shell, and the above electrolyte was added. After packaging, standing, formation, and capacity distribution processes, the sample lithium battery was obtained.

[0138] Puncture test method:

[0139] As shown in Figure 1 , the puncture test was used to simulate the abnormal condition of the battery in the present application, and the change of the battery after the nail was observed. The schematic diagram of the puncture test in the present application is shown in the figure. The nail 4 penetrates one layer of positive electrode sheet 3, one layer of separator 2 and one layer of negative electrode sheet 1 of the battery.

[0140] The mechanical puncture uses a steel needle with a diameter of 8 mm, which is stabbed at a speed of 25 mm / s towards the large face of the experimental sample battery. A temperature monitoring point is arranged at a distance of 1.5 cm from the puncture position on the large face of the sample battery, and the temperature change of the battery within 2 hours after the steel needle contacts the battery is detected and read in real time by the temperature sensor.

[0141] Puncture displacement test method:

[0142] When the puncture displacement of the support layer material is lower, the deformation amount of the current collector and the corresponding electrode sheet and battery when mechanical damage occurs is also smaller, and the probability of battery short circuit and thermal runaway is also lower, and the safety of the battery is higher.

[0143] The puncture displacement test was performed using a tensile testing machine. The circular sample composite current collector with a diameter of 4 cm was fixed on the sample loading platform of the tensile testing machine, the horizontal plane of the sample was kept perpendicular to the moving direction of the steel nail, and the cross section of the steel nail was 1 mm 2A steel nail is driven at a speed of 50 mm / min to the center of the sample, and the displacement of the steel nail from the time the steel nail contacts the sample to the time the sample is pierced is measured and recorded, which is the puncture displacement of the sample.

[0144] Test results comparison:

[0145] Table 1 battery performance test results of batteries prepared using the composite current collectors of examples and comparative examples

[0146] No. Puncture displacement (mm) Maximum rate of temperature rise °C / min Maximum temperature rise °C Example 1 4.2 0.01 25.9 Example 2 3.7 0 25.2 Example 3 3.8 0 25.1 Example 4 3.5 0 25.1 Example 5 3.2 0 25.1 Example 6 4.8 0.01 25.8 Example 7 3.7 0 25.2 Comparative Example 1 5.1 0.33 36.5 Comparative Example 2 6.3 0.41 38.6 Comparative Example 3 7.9 0.57 42.1

[0147] From the above experimental results, it can be seen that the battery prepared using the composite current collector of the present application can effectively inhibit the risk of internal short circuit thermal runaway when abnormality such as puncture occurs. According to the effect comparison of various examples and comparative examples, it can be seen that if the elongation at break of the brittle layer is too large or the brittle layer and the metal layer are not alternately arranged, the effect of inhibiting short circuit thermal runaway will be reduced.

[0148] Obviously, the above examples are only examples for clearly illustrating but not limiting the embodiments. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, it is not necessary and also impossible to enumerate all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method of making a composite current collector, characterized by, The composite current collector comprises: a support layer comprising a polymer material; a conductive layer disposed on the support layer; the conductive layer comprises a plurality of layers of brittle layers and metal layers arranged alternately; the ratio of the thickness of each metal layer to the adjacent brittle layer is 3.5-15:1; the ratio of the elongation at break of each metal layer to the adjacent brittle layer is 6.8-12.2:1; the thickness of each brittle layer is 1-15 nm; the thickness of each metal layer is 10-100 nm; the bonding force between each metal layer and the adjacent brittle layer is greater than the bonding force between the support layer and the conductive layer; the preparation method comprises the following steps: alternately depositing a plurality of layers of brittle layers and metal layers on the support layer to form a conductive layer; The deposition method is magnetron sputtering; the magnetron sputtering power density is 50 W / cm 2 , and the vacuum degree is 0.1 Pa.

2. The production method according to claim 1, characterized by, the conductive layer comprises at least 3 brittle layers and at least 3 metal layers.

3. The preparation method according to claim 1, characterized in that, The tensile strength of the support layer is less than the tensile strength of the conductive layer.

4. The method of claim 1, wherein, The thickness of each brittle layer increases successively with the distance of the brittle layer from the support layer.

5. The preparation method according to claim 1, characterized in that, The surface of the conductive layer in contact with the support layer is a brittle layer.

6. The preparation method according to claim 1, characterized in that, The surface of the conductive layer away from the support layer is a brittle layer.

7. The preparation method according to claim 1, characterized in that, The metal layer is made of at least one of aluminum, lithium, and nickel; and / or, The brittle layer is made of at least one of aluminum oxide, silicon oxide, titanium oxide, silicon carbide, aluminum nitride, and silicon nitride; and / or, The support layer is made of at least one of PP, PET, and PI; and / or, The hardness of the brittle layer is greater than that of the metal layer.

8. Use of the composite current collector prepared by the preparation method of any one of claims 1-7 in the preparation of a battery.

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