CN115275211A

CN115275211A - Composite current collector and preparation method thereof, electrode pole piece, battery and terminal

Info

Publication number: CN115275211A
Application number: CN202110486544.3A
Authority: CN
Inventors: 邓耀明; 张新枝; 高云雷; 陈涛; 阳东方; 谢封超
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2021-04-30
Filing date: 2021-04-30
Publication date: 2022-11-01

Abstract

The application provides a composite current collector, including polymer substrate and set up the first conducting layer on polymer substrate one side surface or set up first conducting layer and the second conducting layer on polymer substrate relative both sides surface, wherein, polymer substrate's percentage elongation is sigma, and thickness is D2, and the thickness of first conducting layer is D1¹The thickness of the second conductive layer is D1²Defining parameters: β 1= (0.03 × D1)¹)/(σ×D2)，β2＝(0.03×D1²) V (. Sigma.. Times.D2), and both of β 1 and β 2 are in the range of 0.01 to 0.3. The conductive layer in the composite current collector has strong adhesive force on the polymer substrate, the composite current collector has high structural stability, and the composite current collector can be used for preparing electrode plates and batteries of lithium ion batteries, so that the safety performance and the energy density of the batteries can be effectively improved. The application also provides a preparation method of the composite current collector, and a battery electrode plate, a battery and a terminal which adopt the composite current collector.

Description

Composite current collector and preparation method thereof, electrode pole piece, battery and terminal

Technical Field

The application relates to the technical field of batteries, in particular to a composite current collector and a preparation method thereof, an electrode plate, a battery and a terminal.

Background

The lithium ion battery has the advantages of high energy density, long cycle life, low self-discharge point and the like, so that the lithium ion battery is widely applied to the fields of electric automobiles, electronic equipment (such as mobile phones, tablet computers, energy storage equipment and the like) and the like. The common current collector in the lithium ion battery is generally a metal foil, for example, the current collector on the positive electrode side is generally an aluminum foil, and the current collector on the negative electrode side is generally a copper foil, but the density of the metal foil is high, and the specific gravity of the metal foil in the battery is large, so that the energy density of the battery is not favorably improved; and when the battery is subjected to abnormal conditions such as extrusion, collision or puncture, internal short circuit of the battery is easily caused, and further thermal runaway occurs, and the composite current collector formed by the insulating polymer substrate bearing the metal conducting layer is considered to be one of effective means for reducing the internal short circuit of the battery and improving the energy density of the battery.

However, the difference between the phase interface and the elongation of the metal conductive layer and the insulating polymer substrate is large, so that the adhesion of the metal conductive layer on the insulating polymer substrate is poor, the metal layer is easy to shift and even fall off, and the safety problem of the battery cannot be effectively solved.

Disclosure of Invention

In view of this, the present application provides a composite current collector, which can significantly improve the bonding force between a conductive layer and a polymer substrate by controlling the thickness and the elongation of the polymer substrate and the thickness of the conductive layer disposed thereon to satisfy a certain proportional relationship, so that the composite current collector has better structural stability and can effectively improve the safety of a battery.

In a first aspect, embodiments of the present application provide a composite current collector, including a polymer substrate, and a first conductive layer disposed on one side surface of the polymer substrate or a first conductive layer and a second conductive layer disposed on two opposite side surfaces of the polymer substrate, where the first conductive layer and the second conductive layer partially cover or completely cover the surface of the polymer substrate;

wherein the thickness of the first conductive layer is denoted as D1¹The thickness of the second conductive layer is marked as D1²The elongation of the polymer substrate is denoted as σ, the thickness of the polymer substrate is denoted as D2, and the parameters are defined as: β 1= (0.03 × D1)¹)/(σ×D2)，β2＝(0.03×D1²) V (σ × D2), and both the β 1 and the β 2 are in the range of 0.01 to 0.3.

According to the composite current collector provided by the first aspect of the embodiment of the application, the thickness and the elongation of the polymer substrate and the thickness of the conducting layer arranged on the polymer substrate are regulated to meet a certain proportional relation, so that the composite current collector is not easy to generate phase displacement between the conducting layer and the polymer substrate in the processes of rolling, high-temperature standing after battery liquid injection and the like, and the adhesive force between the conducting layer and the polymer substrate can be effectively improved. Furthermore, when the battery is extruded, collided or punctured, the composite current collector can effectively play a role of avoiding the internal short circuit of the battery, so that the safety performance of the battery can be effectively improved.

In the embodiment of the present application, the value range of σ is 3% to 300%.

In the embodiments of the present application, D1¹And said D1²The value range of (a) is 30nm-2 μm. The conductive layer with proper thickness can realize high-strength adhesion on the polymer substrate, and is also beneficial to maintaining effective electronic conduction of the composite current collector under high mechanical deformation.

In an embodiment of the present application, the polymer constituting the polymer substrate has a solubility parameter of 10 to 22 (J/cm)³)^0.5. Polymers with higher solubility parameters may facilitate high strength adhesion of the conductive layer thereto.

In embodiments of the present application, the difference in solubility parameters between the polymer and the battery electrolyte is from 5 to 15 (J/cm)³)^0.5. At this time, the process of the present invention,the polymer substrate of the composite current collector is also not easily swelled by the battery electrolyte.

In the embodiments of the present application, a surface tension coefficient of the polymer substrate facing the first conductive layer is greater than or equal to 38 dynes/cm, or a surface tension coefficient of the polymer substrate facing the first conductive layer and a surface tension coefficient of the polymer substrate facing the second conductive layer are both greater than or equal to 38 dynes/cm. A surface with a large surface tension coefficient facilitates the adhesion of the conductive layer thereon.

In some embodiments of the present application, the surface of the polymer substrate facing the first conductive layer carries polar groups, or both the surface of the polymer substrate facing the first conductive layer and the surface facing the second conductive layer carry polar groups. The polar group can further improve the adhesion of the conductive layer on the polymer substrate.

In some embodiments of the present application, the polymer substrate further comprises a conductive additive. The proper amount of the conductive additive can reduce the surface resistance of the composite current collector, and further is beneficial to reducing the self-heat generation of the battery under the normal work.

In an embodiment of the present application, the conductive additive includes at least one of a metal conductive material and a carbon-based conductive material; the metal conductive material comprises one or more of nickel, copper, aluminum, titanium, silver and alloys thereof, and the carbon-based conductive material comprises one or more of carbon nanotubes, graphene, graphite, acetylene black and amorphous carbon.

In some embodiments of the present application, the conductive additive comprises no more than 5% by weight of the polymer substrate. At this time, the problem that the mass ratio of the conductive additive is too high, so that the resistance of the polymer substrate is too low, and the safety of the battery under abnormal operation is not improved can be avoided.

In some embodiments of the present application, the polymeric substrate further has a porous structure. At this time, the surface density of the polymer substrate can be further reduced, thereby being beneficial to improving the energy density of the battery.

In the embodiment of the application, the thickness of the composite current collector is 3-20 μm.

In the embodiment of the application, the surface density of the composite current collector is 0.5mg/cm²-4mg/cm². At this time, the area density of the composite current collector is lower, which is more helpful for improving the energy density of the battery.

In an embodiment of the present application, the elongation of the composite current collector under a 30 ton roll is greater than 0 and less than or equal to 10%. At the moment, the surface density change of the composite current collector before and after rolling is not overlarge, and the actual surface density of the electrode plate manufactured by the composite current collector is closer to the design value, so that the controllable design of battery performance parameters is facilitated.

In the embodiment of the application, the peel strength of the first conductive layer, the second conductive layer and the polymer substrate is more than 15N/m.

In a second aspect, an embodiment of the present application provides a method for preparing a composite current collector, including the following steps:

forming a first conductive layer on one side surface of a polymer substrate, or forming a first conductive layer and a second conductive layer on two opposite side surfaces of the polymer substrate to obtain a composite current collector; wherein the first and second electrically conductive layers partially cover or completely cover the surface of the polymer substrate,

wherein the elongation of the polymer substrate is denoted as σ, the thickness of the polymer substrate is denoted as D2, and the thickness of the first conductive layer is denoted as D1¹The thickness of the second conductive layer is marked as D1²Defining parameters: β 1= (0.03 × D1)¹)/(σ×D2)，β2＝(0.03×D1²) V (σ × D2), and both the β 1 and the β 2 are in the range of 0.01 to 0.3.

In the embodiment of the present application, the first conductive layer and the second conductive layer are independently formed on the polymer substrate by one or more methods selected from mechanical rolling, bonding, liquid phase coating, vapor deposition, electroplating, and electroless plating.

In some embodiments of the present application, before forming the first conductive layer or before forming the first conductive layer and the second conductive layer, the method further comprises: and performing at least one of corona treatment, plasma surface treatment and compound surface modification treatment on the surface of the polymer substrate on which the first conductive layer is to be formed or the surfaces on which the first conductive layer and the second conductive layer are to be formed. These treatments increase the number of polar groups on the surface of the polymer substrate, increase its surface tension, and further improve the adhesion of the conductive layer thereon.

The preparation method of the composite current collector provided by the second aspect of the embodiment of the application is simple in process, and the prepared composite current collector is stable in structure, is suitable for preparing an electrode plate, and can effectively play a role in improving the safety and the energy density of a battery.

In a third aspect, an embodiment of the present application further provides an electrode tab, where the electrode tab includes the composite current collector described in the first aspect of the present application, and an electrode active material layer formed on the first conductive layer or on the first conductive layer and the second conductive layer of the composite current collector. The application provides a battery electrode piece is arranged in the battery, can help effectively promoting the security and the energy density of battery.

In a fourth aspect, an embodiment of the present application further provides a battery, where the battery includes a positive electrode plate, a negative electrode plate, and a diaphragm and an electrolyte between the positive electrode plate and the negative electrode plate, where the positive electrode plate and/or the negative electrode plate includes the electrode plate according to the third aspect of the embodiment of the present application. The battery provided by the present application can have high safety and high energy density.

In some embodiments of the present application, the positive electrode plate is the electrode plate. Because the positive pole piece adopts the electrode pole piece, when the battery is extruded, collided or punctured, the most dangerous internal short circuit problem of the battery caused by abnormal contact between the aluminum foil and the negative active material (such as graphite) can be effectively solved.

In a fifth aspect, embodiments of the present application further provide a terminal, where the terminal includes a housing, a main board located inside the housing, and a battery according to the fourth aspect of the embodiments of the present application, where the electrochemical battery is used to supply power to the terminal. The terminal can be an electronic product such as a mobile phone, a notebook, a tablet personal computer, a portable machine, an intelligent wearable product and the like.

Drawings

Fig. 1 is a schematic structural diagram of a terminal according to an embodiment of the present application;

fig. 2 is a schematic structural diagram of a lithium ion battery provided in an embodiment of the present application;

fig. 3a is a schematic structural diagram of a composite current collector provided in an embodiment of the present application;

fig. 3b is another schematic structural diagram of a composite current collector provided in an embodiment of the present application;

fig. 4 is a schematic view of a nail penetration experiment in a simulation in which a foreign substance penetrates into a battery.

Detailed Description

The embodiments of the present application will be described in detail below with reference to the drawings.

Referring to fig. 1, fig. 1 is a schematic structural diagram of a terminal 100 according to an embodiment of the present disclosure. The terminal 100 may be an electronic product such as a mobile phone, a tablet computer, a notebook computer, a Virtual Reality (VR) terminal device, a wearable device, a vehicle-mounted device, and an energy storage device. In the embodiment of the present application, the terminal 100 is described as an example of a mobile phone.

As shown in fig. 1, the terminal 100 includes a housing 101 assembled at the outside of the terminal, and a circuit board and a battery (not shown in the figure) located inside the housing 101, wherein the battery is the lithium secondary battery 100 provided in the above-mentioned embodiment of the present application, the housing 101 may include a display screen assembled at the front side of the terminal and a rear cover assembled at the rear side, the battery may be fixed at the inner side of the rear cover, and the battery is electrically connected to the circuit board for supplying power to the circuit board of the terminal 100.

Fig. 2 shows a schematic diagram of a structure of a battery used in the terminal 100. The battery 200 includes a positive electrode tab 10, a negative electrode tab 20, and a separator 30 and an electrolyte (not shown) between the positive electrode tab 10 and the negative electrode tab 20. The positive electrode tab 10 may include a positive electrode collector 11 and a positive electrode active material layer 12 disposed on at least one side surface of the positive electrode collector 11, and the negative electrode tab 20 includes a negative electrode collector 21 and a negative electrode active material layer 22 disposed on at least one side surface of the negative electrode collector 21. The positive electrode current collector 11 and/or the negative electrode current collector 21 may be a composite current collector provided in the embodiments of the present application. The battery of the present application may be wound or stacked. The battery of the present application may be any of a lithium secondary battery, a sodium secondary battery, a potassium secondary battery, a magnesium secondary battery, a zinc secondary battery, and the like.

Fig. 3a and fig. 3b respectively show a schematic structural diagram of a composite current collector provided in an embodiment of the present application. In fig. 3a, the composite current collector 300 includes a polymer substrate 301 and a first conductive layer 302 disposed on one side surface of the polymer substrate 301. In fig. 3b, the composite current collector 300 includes a polymer substrate 301 and first and second conductive layers 302 and 302' disposed on opposite side surfaces of the polymer substrate 301. The first and second conductive layers 302, 302' may be used for subsequent deposition of electrode active materials thereon to make electrode pads.

In this application, the thickness of the first conductive layer 302 is denoted as D1¹The thickness of the second conductive layer 302' is denoted as D1²The elongation of the polymer substrate 301 is denoted as σ and the thickness of the polymer substrate 301 is denoted as D2, the following parameters being defined in the present application: β 1= (0.03 × D1)¹)/(σ×D2)，β2＝(0.03×D1²) V (σ × D2), and both of the β 1 and the β 2 are in the range of 0.01 to 0.3

Wherein σ is given as a percentage, D1¹、D1²Unified with the unit of D2, β 1 and β 2 are the self-defined parameters of the present application. The thickness D1 of the first conductive layer 302 is set to be equal to or greater than the thickness D1¹And a thickness D1 of the second conductive layer 302²May be equal or different.

The composite current collector 300 provided by the embodiment of the application can effectively improve the adhesive force between the conductive layer and the polymer substrate 301 by regulating and controlling the thickness and the elongation of the polymer substrate 301 and the thickness of the conductive layer arranged on the polymer substrate 301 to meet the defined proportional relationship, so that the composite current collector 300 is not easy to cause phase displacement between the conductive layer and the polymer substrate 301 in the processes of rolling, high-temperature standing after battery liquid injection and the like, and further is not easy to cause the conductive layer to fall off and lose efficacy. Furthermore, the safety performance of the battery adopting the composite current collector under the abnormal conditions of extrusion, collision, puncture and the like can be effectively improved. For example, in the case of simulating the abnormal condition of the battery by the nail penetration test shown in fig. 4, on one hand, since the conductive layers 302 and 302 'in the composite current collector are not easy to fall off from the polymer substrate 301, and the thickness thereof is significantly reduced compared with the thickness of the conventional current collectors such as aluminum foil and copper foil, the chances of electrical connection between nails and the conductive layers 302 and 302', the negative electrode material layer 22, the negative electrode current collector 21, etc. can be reduced, thereby reducing the probability of thermal runaway due to short circuit inside the battery, and reducing the probability of thermite reaction when the conductive layer in the positive electrode side current collector is aluminum; on the other hand, the polymer substrate 301 has certain toughness and deformability, and can wrap the nail to some extent to perform a heat insulation function, so that the safety performance of the battery is improved.

In addition, since the polymer substrate 301 is generally lower in density than metal, the composite current collector 300 is lower in density than conventional battery current collectors such as aluminum foil and copper foil, and a battery made of the composite current collector is also lower in weight, so that the energy density of the battery is improved. In addition, the conductive layer in the composite current collector 300 is not easy to fall off and lose efficacy, and accordingly, the conductive layer attached with the electrode active material layer is not easy to fall off, and the cycle stability of the electrode plate is improved.

Therefore, the composite current collector provided by the embodiment of the application has the advantages of light weight and high interlayer bonding force, can effectively improve the mechanical abuse test results of the battery such as nail penetration and impact, and can effectively improve the safety performance and the mass energy density of the battery.

In fig. 4, only the composite current collector is illustrated as the current collector of the positive electrode tab 10. In other embodiments of the present application, the composite current collector 300 may also be used as the negative electrode current collector 21.

In the embodiment of the present application, the values of the parameters β 1 and β 2 defined above may be specifically 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.1, 0.15, 0.2, 0.25, or the like. In some embodiments, both β 1 and β 2 range from 0.01 to 0.06. At this time, the conductive layer has stronger adhesion with the polymer substrate 301, and the probability of relative displacement therebetween is smaller.

In the embodiment of the present application, the thickness D1 of the conductive layer¹、D1²The value ranges of (A) are all within 30nm-3 mu m. The conductive layer of suitable thickness can realize high strength adhesion on polymer substrate 301, still is favorable to keeping the effective electron conduction of composite current collector 300 under high mechanical deformation to guarantee the whole longer cycle life of electrode sheet. Specifically, D1¹、D1²May be independently 50nm, 100nm, 200nm, 600nm, 800nm, 1 μm, 1.2 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or the like. In some embodiments, D1¹And D1²The value range of (A) is 30nm-2.5 μm. In other embodiments, D1¹And D1²The value range of (A) is 300nm-2 μm. In still other embodiments, D1¹And D1²The value range of (A) is 1.2-3 μm.

In the embodiment of the present application, the elongation σ of the polymer substrate 301 ranges from: sigma is more than or equal to 3 percent and less than or equal to 300 percent. Elongation σ can be used to describe the plastic properties of a material, which refers to the percentage of the total deformation Δ L of a gauge length segment after tensile failure of a polymer substrate specimen, to the original gauge length L. The elongation can be measured by the test method described in GB/T33143-2016. The elongation σ of the polymer substrate 301 is affected not only by the polymer in its components but also by various factors such as the preparation process of the polymer substrate, the presence or absence of a porous structure in the structure, and the like. But the elongation σ is independent of the stretching direction when the polymer substrate 301 is subjected to the elongation test. In some embodiments of the present application, the value range of σ is: sigma is more than or equal to 5 percent and less than or equal to 180 percent.

In the present embodiment, the thickness D2 of the polymer substrate 301 may be 1 μm to 15 μm. A polymer substrate of suitable thickness avoids a negative impact on the volumetric energy density of the cell. In some embodiments, the thickness D2 of the polymer substrate 301 may be 1 μm to 10 μm. In other embodiments, the thickness D2 may be 2 μm to 6 μm.

The method for implementing the applicationWherein the polymer constituting the polymer substrate 301 has a solubility parameter of 10 to 22 (J/cm)³)^0.5. The solubility parameter of the polymer can reflect the polarity strength of the polymer, generally, a polar substance with a larger solubility parameter is more favorable for the adhesion of a metal conductive layer thereon, but when the solubility parameter of the polymer is too high, the polar substance is easily swelled by a strong-polarity electrolyte, so that the interface layers of the polymer substrate 301 and the conductive layer are deactivated, the bonding force between the two is reduced, and the composite current collector 300 and the structure of the positive electrode plate 10 and/or the negative electrode plate 20 using the composite current collector 300 are damaged, thereby increasing the internal impedance of the battery and deteriorating the performance of the battery. The polymer is controlled to have a solubility parameter of 10 to 22 (J/cm)³)^0.5It is possible to prevent the polymer substrate 301 from being swelled by the electrolyte while ensuring the conductive layer to be firmly attached to the polymer substrate 301.

In the present embodiment, the difference in solubility parameters between the polymer constituting the polymer substrate 301 and the battery electrolyte is 5 to 15 (J/cm)³)^0.5. At this time, the difference between the solubility parameters of the polymer and the battery electrolyte is appropriate, and the polymer substrate is not easily swelled by the battery electrolyte, so that the damage to the overall structure of the composite current collector 300 can be avoided.

In the present embodiment, the polymer comprising the polymer substrate 301 is selected from polyethylene (e.g., having a solubility parameter of 16.5 (J/cm)³)^0.5) Polypropylene (e.g., having a solubility parameter of 17.0 (J/cm)³)^0.5) Polybutene (e.g., having a solubility parameter of 16.5 (J/cm)³)^0.5) Polymethylpentene (e.g., having a solubility parameter of 16.7 (J/cm)³)^0.5) Polyvinylidene fluoride (e.g., having a solubility parameter of 19.2 (J/cm)³)^0.5) Polytetrafluoroethylene (e.g., having a solubility parameter of 12.7 (J/cm)³)^0.5) A polyester terephthalate (e.g., having a solubility parameter of 20.1 (J/cm)³)^0.5) Polyurethane (e.g., having a solubility parameter of 20.4 (J/cm)³)^0.5) Polyimide (e.g., having a solubility parameter of 21.2 (J/cm)³)^0.5) Polyamides (e.g., having a solubility parameter of 18.9 (J/cm)³)^0.5) Poly (p-phenylene terephthalamide) (i.e., aramid, e.g., having a solubility parameter of 19.2 (J/cm)³)^0.5) And copolymers thereof, but are not limited thereto.

In the present embodiment, the density of the polymer substrate 301 is less than the density of the conductive layer 302. Like this, the area density of the composite current collector 300 that this application embodiment provided is also lower, can also promote the weight energy density of battery when promoting battery safety performance. Wherein, the smaller the density of the polymer substrate 301, the greater the improvement benefit on the energy density of the battery. In addition, the polymer substrate 301 has certain flexibility, so that the conductive layer 302 on the surface of the polymer substrate can be well supported and protected, and the pole piece fracture phenomenon common in the conventional current collector is not easy to generate. In embodiments of the present application, the polymer substrate 301 may have a density of 0.9g/cm³-3g/cm³. In some embodiments, the density of the polymer substrate 301 is 0.9g/cm³-2.6g/cm³。

In the embodiment of the present application, the areal density of the composite current collector 300 is 0.5g/cm²-4g/cm². At this time, the area density of the composite current collector is lower, which is more helpful for improving the energy density of the battery. In some embodiments, the areal density of the composite current collector 300 is 1g/cm²-2.6g/cm². And at this time, the mechanical properties of the composite current collector are still more excellent.

In some embodiments, the surface tension coefficient of the polymer substrate 301 facing the first conductive layer 302 is greater than or equal to 38 dynes/cm, or the surface tension coefficient of the polymer substrate 301 facing the first conductive layer 302 and the surface tension coefficient of the polymer substrate facing the second conductive layer 302' is greater than or equal to 38 dynes/cm. At this time, the surface of the polymer substrate 301 is more advantageous for forming a conductive layer having a high bonding force thereto.

In some embodiments of the present application, the surface of polymer substrate 301 facing first electrically conductive layer 302 or the surfaces facing first and second electrically conductive layers 302 and 302' may also be treated with at least one of corona treatment, plasma surface treatment, compound surface modification treatment, and the like. These surface treatment methods can increase the number of polar groups on the surface of the polymer substrate 301, increase the surface tension thereof, and further improve the adhesion of the conductive layer on the polymer substrate 301.

Among them, the compound used for surface modification may include acid anhydrides (such as maleic anhydride), higher fatty acids and salts thereof, epoxides, compounds having sulfonic acid groups, compounds having phosphoric acid groups, silane coupling agents, and the like. Wherein, the corona treatment is to generate low-temperature plasma by corona discharge on the surface of the treated substrate with high frequency and high voltage, and the plasma can penetrate into the surface of the substrate to oxidize and polarize the molecules of the treated surface so as to increase the adhesion of the surface of the substrate. Generally, the corona treatment can be used to impart hydroxyl groups, carboxyl groups, etc. to the surface of the substrate, and the specific examples are determined according to the material of the substrate. The plasma surface treatment refers to the interaction between plasma of non-polymeric gas (such as nitrogen, hydrogen, oxygen, ammonia, carbon monoxide, etc.) and the surface of the polymer substrate to form new functional groups on the surface of the substrate. Generally, a polymer material is subjected to plasma treatment with a non-polymerizable gas such as the above, and then contacted with air, to introduce carboxyl groups, hydroxyl groups, carbonyl groups, amino groups, and the like into the surface.

Thus, in some embodiments of the present application, the surface of the polymer substrate 301 facing the first conductive layer 302 or the surfaces facing the first conductive layer 302 and the second conductive layer 302' carry polar groups. The polar groups may promote adhesion of the conductive layer on the polymer substrate 301. Wherein the polar group may include at least one of a carboxyl group, a hydroxyl group, a carbonyl group, an amino group, an epoxy group, a sulfonic acid group, a phosphoric acid group, and the like.

In some embodiments of the present application, there is also a transition layer between the polymer substrate 301 and the conductive layer 302 and/or the conductive layer 302'. In some embodiments, the transition layer comprises an adhesive layer. The transition layer may further improve the bonding force between the conductive layer and the polymer substrate 301.

In some embodiments of the present application, the polymer substrate 301 further comprises a conductive additive. That is, the constituent material of the polymer substrate 301 includes the aforementioned polymer and conductive additive. The proper amount of conductive additive can improve the conductive capability of the polymer substrate 301, and is beneficial to reducing the surface resistance of the composite current collector 300, so that the internal resistance of the battery is reduced, and the self-heat generation of the battery under normal work is reduced. In the present embodiment, the mass ratio of the conductive additive in the polymer base 301 is not more than 5%. This prevents the polymer substrate 301 from having too low resistance due to too high an amount of conductive additive added, which is detrimental to improving the safety of the battery under abnormal operation. The conductive additive may be one or more selected from a metal conductive material and a carbon-based conductive material described below.

In other embodiments of the present application, the polymer substrate 301 also has a porous structure. The polymer substrate 301 with the porous structure can further reduce the surface density of the composite current collector 300, and is more beneficial to improving the energy density of the battery. In this case, the material of the polymer substrate 301 may be all polymers, or may be a mixture or composite of a polymer and a conductive additive.

Further, the porosity of the polymer substrate 301 is 10% to 50%, and the pore size is 30nm to 80nm. A polymer substrate 301 with suitable porosity and pore size can have a certain mechanical strength and good load bearing effect on the conductive layer at a lower density. In some embodiments, the polymer substrate 301 has a porosity of 20% to 40% and a pore size of 30nm to 60nm.

In the present embodiment, the constituent materials of the first conductive layer 302 and the second conductive layer 302' are independently selected from at least one of a metal conductive material and a carbon-based conductive material. Wherein the metal conductive material comprises one or more of nickel, copper, aluminum, titanium, silver and alloys thereof (such as nickel-copper alloy, aluminum-zirconium alloy and the like); the carbon-based conductive material comprises one or more of carbon nano tubes, graphene, graphite, acetylene black, amorphous carbon and the like.

The first conductive layer 302 and the second conductive layer 302' can be independently prepared on the polymer substrate 301 by one or more methods of vapor deposition, electroplating, electroless plating, liquid phase method, thermal spraying, and the like. The vapor deposition method, the liquid phase method and the thermal spraying method are particularly suitable for preparing the conductive layer made of the carbon-based conductive material; the vapor deposition method, electroplating and chemical plating are particularly suitable for preparing the conductive layer made of metal conductive materials.

In the embodiment of the present application, the thickness of the composite current collector 300 may be 3 μm to 20 μm. The composite current collector with proper thickness can perform effective and stable electronic conduction under high mechanical deformation, and can also enable the volume energy density of the battery to be higher. Compared with a pure metal foil, the thickness of the composite current collector can be thinner (for example, less than 10 μm), and the reduction of the energy density of the battery is facilitated. In some embodiments, the thickness of the composite current collector 300 is 5 μm to 16 μm, for example 5 μm to 11 μm.

In the embodiment of the present application, the sheet resistance of the composite current collector 300 is 16m Ω/□ -200m Ω/□. In some embodiments, the sheet resistance of the composite current collector 300 is 20m Ω/□ -100m Ω/□. The composite current collector with proper square resistance can prevent the short-circuit resistance of the battery from being too small under abnormal conditions, so that the short-circuit current and the short-circuit heat generation quantity are not too large, and the safety performance of the battery is improved; in addition, the composite current collector with proper square resistance can also prevent the self-generated heat of the battery under normal work from being too high, and improve the work efficiency of the battery.

In the present embodiment, the elongation of the composite current collector 300 is less than or equal to 10% at a roll pressure of 30 tons. Among them, 30 ton roll pressing is a common pressure to which the composite current collector is subjected during the preparation of the electrode sheet and the battery. Under the 30-ton rolling, the elongation of the composite current collector is low, which means that the plastic deformation degree of the composite current collector is not high, and the change of the surface density before and after the rolling is not overlarge, so that when the composite current collector loaded with the electrode active material is pressed, the deviation of the actual surface density of the obtained electrode pole piece from a design value is not overlarge, and the distribution state of the electrode active material on the composite current collector is not greatly changed. In some embodiments, the composite current collector 300 has an elongation of 2 to 10%, for example 3% to 9%, at a roll pressure of 30 tons.

In the present embodiment, the peel strength of each conductive layer from the polymer substrate 301 in the composite current collector 300 is greater than 15N/m. The higher peel strength represents that the bonding force between the conductive layer and the polymer substrate 301 is strong, and phase displacement is not easily generated between the conductive layer and the polymer substrate, so that the composite current collector can stably exert the functions of conducting electrons and improving the safety and energy density of the battery. In some embodiments, the peel strength is greater than or equal to 20N/m, and in other embodiments, the peel strength is greater than or equal to 30N/m, or even greater than or equal to 40N/m.

Correspondingly, the embodiment of the application also provides a preparation method of the composite current collector, which comprises the following steps:

forming a first conductive layer on one side surface of a polymer substrate, or forming a first conductive layer and a second conductive layer on two opposite side surfaces of the polymer substrate to obtain a composite current collector;

wherein the first and second electrically conductive layers partially or completely cover the surface of the polymeric substrate, the first electrically conductive layer having a thickness denoted D1¹The thickness of the second conductive layer is marked as D1²The elongation of the polymer substrate is denoted as σ, the thickness of the polymer substrate is denoted as D2, and the parameters are defined as: β 1= (0.03 × D1)¹)/(σ×D2)，β2＝(0.03×D1²) V (σ × D2), and both the β 1 and the β 2 are in the range of 0.01 to 0.3.

In embodiments of the present application, the polymeric substrate may be provided directly, or the polymeric substrate may be formed in situ on a rigid substrate (e.g., by coating) and then peeled from the rigid substrate. The rigid substrate can be made of stainless steel, glass and the like.

In the present embodiment, each of the conductive layers may be formed on the polymer substrate 301 by one or more methods selected from mechanical rolling, bonding, liquid phase coating, vapor deposition, electroplating, electroless plating, and liquid phase coating. The specific parameters of the preparation process can be set according to actual needs.

Wherein, the mechanical rolling method can be carried out by the following steps: the foil of conductive layer material and the surface of the polymeric substrate are heated while hot air is being blown to heat the surfaces of the two materials to a temperature (e.g., 160-180 c) and then the two are brought together and placed in a mechanical roller and pressure is applied to tightly bond the two. When the conductive layer is prepared on the polymer substrate 301 by bonding, a bonding agent may be coated on the surface of the polymer substrate, and after drying, an adhesive layer may be formed between the polymer substrate and the conductive layer 302, and the adhesive layer may serve as a transition layer therebetween. The liquid phase coating method may include any one of spraying, brushing, dipping, spin coating, and the like, and is suitable for preparing a conductive layer made of a carbon-based conductive material.

The vapor deposition method may include a physical vapor deposition method and a chemical vapor deposition method. The physical vapor deposition method may include at least one of a laser pulse deposition method, a sputtering method, an evaporation method, and the like; examples of the sputtering method include magnetron sputtering, radio frequency sputtering, and the like; the evaporation method may specifically include at least one of vacuum evaporation, thermal evaporation, electron beam evaporation, and the like. The chemical vapor deposition process may include one or more of hot filament chemical vapor deposition, plasma enhanced chemical vapor deposition, and the like. Wherein, the physical vapor deposition method is more suitable for manufacturing the metal conductive layer. Specifically, the process flow of vacuum evaporation generally comprises: and (3) placing the polymer substrate subjected to surface cleaning treatment in a vacuum plating chamber, melting and evaporating the high-purity metal wire placed in the metal evaporation chamber, and finally depositing the evaporated metal vapor on the surface of the polymer substrate through a cooling system in the vacuum plating chamber to form a conductive layer. Wherein, the technological process of the magnetron sputtering method is generally as follows: and placing a polymer substrate in the magnetron sputtering chamber, vacuumizing the sputtering chamber, starting a magnetron sputtering power supply to enable high-purity inert gas introduced into the sputtering chamber to generate glow discharge, and bombarding the target material so that target atoms sputtered from the target material are deposited on the polymer substrate to be coated.

In some embodiments, each of the conductive layers described above can be independently prepared on the polymer substrate 301 using one or more of a liquid phase coating method, a vapor deposition method, electroplating, electroless plating, and the like. At the moment, the conducting layer is deposited on the polymer substrate in situ, so that stronger binding force between the conducting layer and the polymer substrate can be ensured, and the composite current collector can be ensured to have higher structural stability.

In an embodiment of the present invention, the constituent material of each conductive layer includes at least one of a metal conductive material and a carbon-based conductive material. Wherein the metal conductive material comprises one or more of nickel, copper, aluminum, titanium, silver and alloys thereof (such as nickel-copper alloy, aluminum-zirconium alloy and the like); the carbon-based conductive material comprises one or more of carbon nano tubes, graphene, graphite, acetylene black, amorphous carbon and the like. The vapor deposition method and the liquid phase coating method are particularly suitable for preparing the conductive layer made of the carbon-based conductive material. The vapor deposition method, electroplating and chemical plating are particularly suitable for preparing the conductive layer made of the metal conductive material. That is, the conductive layer at this time is a vapor deposition layer, an electroplating layer, or an electroless plating layer. In some embodiments, the metal conductive layer is preferably prepared by an electroplating method, and a physical vapor deposition method such as a magnetron sputtering method, a vacuum evaporation method, or the like. When the composite current collector of the embodiment of the application is used for a lithium ion battery, the current collector containing the metal aluminum, silver and carbon conductive layers can be used for a positive electrode, and the current collector containing the copper, nickel, titanium and carbon conductive layers can be used for a negative electrode.

In some embodiments of the present application, before forming the first conductive layer on the polymer substrate, the method of preparing further comprises: and (3) subjecting the surface of the polymer substrate, on which the first conductive layer is to be formed, to at least one of corona treatment, plasma surface treatment and compound surface modification treatment. In other embodiments of the present application, before forming the first conductive layer and the second conductive layer on the polymer substrate, the method further comprises: and subjecting the surface of the polymer substrate on which the first conductive layer and the second conductive layer are to be formed to at least one of corona treatment, plasma surface treatment and compound surface modification treatment. These treatments increase the number of polar groups on the surface of the polymer substrate 301, increase the surface tension thereof, and further improve the adhesion of the conductive layer on the polymer substrate 301.

The preparation method of the composite current collector provided by the embodiment of the application is simple in process, the prepared composite current collector is stable in structure, and the effects of improving the safety and the energy density of a battery can be effectively exerted.

It should be noted that, after the electrode active material layer is formed on each conductive layer in the subsequent step, the composite current collector 300 and the electrode active material layer thereon form an electrode plate. The electrode active material layer may be formed on the conductive layer 302, 302' by coating, pressing, and may include conventional materials such as a binder, a conductive agent, and the like, in addition to the electrode active material. The electrode active material in the electrode active material layer is a material that can store energy by deintercalating ions, including one of lithium ions, sodium ions, potassium ions, magnesium ions, and aluminum ions. The electrode active material may be a positive electrode active material or a negative electrode active material. If the electrode plate is used as a positive electrode plate, the electrode active material layer is specifically a positive electrode active material layer; if the electrode plate is used as a negative electrode plate, the electrode active material layer is specifically a negative electrode active material layer. For a lithium ion battery, the positive active material may specifically be at least one of lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium vanadyl phosphate, lithium cobaltate, lithium manganate, lithium nickelate, lithium vanadate, lithium manganese nickelate, lithium nickel manganate, lithium manganese rich-based material, lithium nickel cobalt manganese manganate, lithium nickel cobalt aluminate, and the like. The negative active material of the lithium ion battery may include metallic lithium, graphite, hard carbon, silicon-based materials (including elemental silicon, silicon alloys, silicon oxides, silicon-carbon composites), tin-based materials (including elemental tin, tin oxides, tin-based alloys), lithium titanate (Li)₄Ti₅O₁₂) And TiO₂And the like.

The examples of the present application are further described below in terms of various examples. The present embodiments are not limited to the following specific examples. The present invention can be modified and implemented as appropriate within the scope not changing the main right of the present application.

Example 1

A preparation method of a composite current collector comprises the following steps:

a8.4 μm thick Polyethylene terephthalate (PET) film was selected, the film had an elongation of 15% and the solubility parameter of the PET film was 20.1 (J/cm)³)^0.5(ii) a Cleaning the surface of the film substrate (such as removing dust on the surface of the film by using a brush), and controlling the water content of the film substrate to be lower than 0.1% and the surface tension coefficient to be 38 dyne/cm;

and (2) placing the PET film subjected to surface cleaning treatment in a vacuum plating chamber, melting and evaporating high-purity aluminum wires in a metal evaporation chamber at the high temperature of 1300-2000 ℃, evaporating the evaporated aluminum steam through a cooling system in the vacuum plating chamber, and finally evaporating and depositing on two surfaces of the PET film to form aluminum conducting layers, wherein the thickness of each aluminum conducting layer is controlled to be 1.3 mu m, so that the composite current collector is obtained.

A schematic cross-sectional view of the composite current collector prepared in example 1 of the present application is shown in fig. 3 b. The composite current collector comprises a PET film substrate and aluminum conducting layers arranged on the two opposite side surfaces of the PET film substrate. The composite current collector prepared in example 1 had a thickness of 11 μm and the parameter β = (0.03 × 1.3)/(15% × 8.4) =0.031 as defined above.

Preparation of positive pole piece of lithium ion battery

Mixing a positive active material lithium cobaltate, conductive carbon black and a binding agent polyvinylidene fluoride in N-methyl pyrrolidone according to a weight ratio of 97.5, stirring uniformly to obtain positive slurry, uniformly coating the positive slurry on two surfaces of the composite current collector prepared in the embodiment 1 of the application (namely, coating the positive slurry on two aluminum conductive layers) by adopting coating equipment, drying the positive slurry by using an oven to remove the N-methyl pyrrolidone, forming a positive active material layer on the aluminum conductive layers to obtain an unpressed positive pole piece, and carrying out cold pressing, slitting and tab welding on the unpressed positive pole piece to obtain the lithium ion battery positive pole piece.

Preparation of lithium ion battery negative pole piece

Stirring and uniformly mixing the artificial graphite serving as the negative electrode active material, carboxymethyl cellulose serving as a thickener and styrene butadiene rubber serving as a binder in deionized water according to the weight ratio of 97.3 to 1.7 to obtain negative electrode slurry, uniformly coating the negative electrode slurry on two sides of a copper foil by adopting coating equipment, drying the copper foil by using an oven, and then carrying out cold pressing, slitting and tab welding to obtain a negative electrode piece.

Preparation of lithium ion battery full cell

Taking the prepared lithium ion battery cathode pole piece, the prepared lithium ion battery anode pole piece and Celgard2400 as a diaphragm, and using 1mol/L LiPF₆The volume ratio of EC (ethylene carbonate) + DEC (diethyl carbonate) + PP (propyl propionate) (EC, DEC, PP is 3).

Example 2

selecting a Polyethylene (PE) film with the thickness of 2.5 microns, wherein the film has a porous structure, the porosity of the film is 37%, the pore size distribution is 35nm-60nm, the elongation of the film is 180% when the film is tested, and the solubility parameter of the PE is 16.5 (J/cm)³)^0.5(ii) a Cleaning the surface of the film substrate, controlling the water content of the film substrate to be lower than 0.1%, and measuring the surface tension coefficient of the film substrate to be 38 dyne/cm;

and (2) placing the PE film subjected to surface cleaning treatment in a vacuum plating chamber, performing evaporation deposition on two opposite surfaces of the PE film to form aluminum conducting layers according to the vacuum evaporation process described in embodiment 1, and controlling the thickness of each aluminum conducting layer to be 1.5 micrometers to obtain the composite current collector.

The thickness of the composite current collector prepared in example 2 of the present application was 5.5 μm, and the parameter β = (0.03 × 1.5)/(180% × 2.5) =0.01 as defined above.

According to the battery preparation method described in example 1, the composite current collector of example 2 was used to prepare a positive electrode sheet and a lithium ion battery.

Example 3

selecting a polytetrafluoroethylene film with the thickness of 8 mu m, wherein the elongation of the film is 15 percent, and the solubility parameter of the polytetrafluoroethylene is 12.7 (J/cm)³)^0.5(ii) a Cleaning the surface of the film substrate, and controlling the water content of the film substrate to be lower than 0.1%;

performing corona treatment on the polytetrafluoroethylene film subjected to surface cleaning treatment to improve the surface tension of the polytetrafluoroethylene film, and measuring that the surface tension coefficient after the corona treatment is 39 dyne/cm (wherein the surface tension coefficient of the polytetrafluoroethylene film without the corona treatment is about 20 dyne/cm); and then placing the polytetrafluoroethylene film in a vacuum plating chamber, and performing evaporation deposition on two opposite surfaces of the polytetrafluoroethylene film to form aluminum conducting layers according to the vacuum evaporation process described in embodiment 1, wherein the thickness of each aluminum conducting layer is controlled to be 1.26 mu m, so that the composite current collector is obtained.

The composite current collector prepared in example 3 of the present application had a thickness of 10.52 μm and the parameter β = (0.03 × 1.26)/(15% × 8) =0.031 as defined above.

According to the battery preparation method described in example 1, the composite current collector of example 3 was used to prepare a positive electrode sheet and a lithium ion battery.

Example 4

a PET film 8.4 μm thick having an elongation of 15%, a surface tension coefficient of 39 dynes/cm and a solubility parameter of 20.1 (J/cm)³)^0.5；

After the surface of the PET film substrate is cleaned, the PET film substrate is subjected to surface modification treatment by adopting a 3wt% maleic anhydride aqueous solution, then the PET film substrate is baked at 80 ℃ and then washed and dried, and the water content of the PET film subjected to surface modification treatment is controlled to be lower than 0.1%; measuring the surface tension coefficient of the obtained product after surface modification treatment to be 41 dyne/cm;

and (2) placing the PET film subjected to the surface modification treatment in a vacuum plating chamber, performing evaporation deposition on two opposite surfaces of the PET film to form aluminum conducting layers according to the vacuum evaporation process described in embodiment 1, and controlling the thickness of each aluminum conducting layer to be 1.3 microns to obtain the composite current collector.

The thickness of the composite current collector prepared in example 4 of the present application was 11 μm, and the parameter β = (0.03 × 1.3)/(15% × 8.4) =0.031 as defined above.

According to the battery preparation method described in example 1, the composite current collector of example 4 was used to prepare a positive electrode sheet and a lithium ion battery.

Example 5

A method of preparing a composite current collector, which differs from example 4 in that: the PET film is also doped with 2wt% of Ag powder. The Ag powder-doped PET film can be obtained by coating a mixed slurry containing Ag powder and PET on a rigid substrate such as stainless steel, glass and the like, drying and uncovering the film. The elongation of the Ag powder-doped PET film is 15%, and the surface tension coefficient of the Ag powder-doped PET film modified by the maleic anhydride is 40 dyne/cm;

according to the battery preparation method described in example 1, the composite current collector of example 5 was used to prepare a positive electrode sheet and a lithium ion battery.

Example 6

A method of preparing a composite current collector, which differs from example 1 in that: the thickness of the selected PET film is 3 μm, and the elongation is 5%; the conductive aluminum layers formed on the opposite surfaces of the PET film were each 1.25 μm.

The thickness of the composite current collector prepared in example 6 of the present application was 5.5 μm, and the parameter β = (0.03 × 1.25)/(5% × 3) =0.25 as defined above.

According to the battery preparation method described in example 1, the composite current collector of example 6 was used to prepare a positive electrode sheet and a lithium ion battery.

Example 7

A method of preparing a composite current collector, which differs from example 2 in that: the selected PE film has no porous structure; the elongation of the PE film was 30%.

The thickness of the composite current collector prepared in example 7 of the present application was 5.5 μm, and the parameter β = (0.03 × 1.5)/(30% × 2.5) =0.06 as defined above.

According to the battery preparation method described in example 1, the positive electrode sheet and the lithium ion battery were prepared using the composite current collector of example 7.

Example 8

A method of preparing a composite current collector, which differs from example 1 in that: the conductive layers disposed on opposite side surfaces of the PET film were each Ti, and the thickness of both conductive layers was 0.9 μm, with the parameter β =0.021 defined above.

According to the battery preparation method described in example 1, the composite current collector of example 8 is used to prepare a positive electrode plate and a lithium ion battery.

Example 9

A composite current collector comprises a Polyimide (PI) film and Cu conducting layers arranged on two opposite side surfaces of the PI film; wherein the PI film has a thickness of 5 μm and a solubility parameter of 21.2 (J/cm)³)^0.5Elongation of 15%, surface tension coefficient of 42 dyne/cm; the Cu conductive layers were formed by magnetron sputtering, and each Cu conductive layer had a thickness of 1 μm, and the parameter β =0.04 defined above.

The composite current collector provided in example 9 is used to manufacture a battery negative electrode plate, a graphite material layer is formed on a Cu conductive layer of the composite current collector, and the obtained negative electrode plate and a positive electrode plate manufactured by using the composite current collector of example 4 are assembled into a lithium ion battery.

In addition, in order to highlight the beneficial effect of this application technical scheme, set up the following comparative example.

Comparative example 1

An aluminum foil with the thickness of 11 mu m is selected as a current collector of the battery anode. According to the battery preparation method described in example 1, the aluminum foil of comparative example 1 was used to prepare a positive electrode sheet and a lithium ion battery.

Comparative example 2

A composite current collector comprises a PET film and aluminum conducting layers arranged on the surfaces of two opposite sides of the PET film; wherein the thickness of the PET film is 5 μm, the elongation is 15%, the aluminum conductive layers are formed by vacuum evaporation, and the thickness of each aluminum conductive layer is 30nm. But the parameter β = (0.03 × 30 nm)/(15% × 5 × 1000 nm) =0.0012 as defined above. The beta is not in the range of 0.02-0.5 in the present application.

According to the battery production method described in example 1, the aluminum foil of comparative example 2 was used to produce a positive electrode sheet and a lithium ion battery.

In order to strongly support the beneficial effects brought by the technical scheme of the embodiment of the application, the current collectors of the embodiments and the comparative examples are subjected to square resistance, surface density, elongation and peeling strength tests, and the lithium ion batteries prepared in the embodiments and the comparative examples are subjected to energy density, rate performance and cycle performance tests, and safety tests such as nail penetration, impact, plane extrusion and the like. The results are summarized in table 1 below.

The surface density test method of the current collector comprises the following steps: a small piece of foil material was arbitrarily cut from each current collector of each example and comparative example, and the foil material was cut into 9 samples to be measured in the transverse direction and the longitudinal direction by a die cutter, wherein each sample had an area of 1540.25mm²And then weighing the samples respectively by using a ten-thousandth balance to obtain the weight average value of the samples to be measured, and taking the ratio of the weight average value to the area of the samples to be measured as the surface density of the current collector.

Elongation testing of the current collector: cut out three parallel sample respectively with each mass flow body, the sample is the bar, and the size is: the width is 15mm, length 100mm (the sample length of cutting is greater than 50mm in order to make things convenient for anchor clamps to cliied the mass flow body sample), fix each bar sample respectively on the anchor clamps of multi-functional pulling force machine to make upper and lower anchor clamps be located the length direction of bar sample, adopt multi-functional pulling force machine to carry out tensile test to each bar sample, and set up the length between upper and lower anchor clamps before the test to be L₀50mm, starting the stretching of the specimen at a stretching speed of 100mm/min, the distance between the two clamps until the specimen has just been snapped off being recorded as L₁Then the elongation of the sample = (L)₁-L₀)/L₀。

And (3) testing the peeling force of the conductive layer of the current collector: according to the method described in GB/T1457-2005, three parallel samples were cut from each current collector, the samples were in the form of strips and the dimensions were: the width is 15mm, the length is 100mm, then a stainless steel plate with the surface roughness of 50 +/-25 nm is scrubbed by alcohol dust-free cloth, then a double faced adhesive tape is used for fixing a conducting layer of a sample to be tested on the stainless steel plate, 2kg of manual pinch roller is used for rolling back and forth for 2 times, the stainless steel plate fixed with the sample to be tested is installed on a machine clamp, 180-degree stripping is carried out by adopting a multifunctional tensile machine, the stretching speed of the multifunctional tensile machine is set to be 100mm/min, stripping testing is started, the testing is stopped until the conducting layer of a current collector to be tested is completely stripped from a polymer layer, and the stripping force value is read.

The method for testing the energy density of the battery comprises the following steps: charging each lithium ion battery to the full charge voltage of 4.45V at 0.2C multiplying power, charging at constant voltage to the cutoff current of 0.025C, and standing for 10min; discharging to rated lower limit voltage of 3.0V by adopting 0.2C multiplying power, recording the capacity and energy of the battery, and weighing the weight of the battery by adopting a balance. Wherein the mass energy density of the battery is equal to the ratio of the battery energy to the battery mass.

The method for testing the rate capability of the battery comprises the following steps: at the ambient temperature of 25 +/-3 ℃, standing for 5 minutes after each lithium ion battery is discharged to 3.0V at the rate of 0.7C; charging to full charge voltage of 4.45V at 0.2C, charging to cutoff current of 0.025C at constant voltage, standing for 5 minutes, discharging to 3.0V at 0.2C, and recording the discharge capacity at 0.2C at normal temperature. The cell was fully charged in the manner previously described and tested for discharge capacity at 0.5C. The discharge rate performance of the battery is measured by the ratio of 0.5C discharge capacity to 0.2C discharge capacity.

The method for testing the cycle performance of the battery comprises the following steps: under the temperature of 25 +/-3 ℃, each lithium ion battery is subjected to constant current charging at the rate of 1.1C to the charging limiting voltage of 4.2V, then is subjected to constant voltage charging at the voltage of 4.2V to the cutoff current of 0.7C, is subjected to constant current charging at the current of 0.7C to the charging cutoff voltage of 4.45V, is subjected to constant voltage charging at the voltage of 4.45V to the cutoff current of 0.025C, and is kept for 5min; and then discharging at a constant current of 1.0C until the discharge cut-off voltage reaches 3.0V, standing for 5min, and recording as a charge-discharge cycle. After the charge-discharge cycle for 400 weeks, the ratio of the discharge capacity of the battery at the 400 th cycle to the discharge capacity of the battery at the first cycle was calculated, and the ratio was used as the capacity retention rate after the battery cycle for 400 weeks.

The nail penetration experiment of the battery: and (3) fully charging the battery according to a standard charging mode (specifically, after the battery is charged to the full charging voltage at 0.2C, the battery is charged to the cut-off current at a constant voltage and is cut off at 0.025C), and then carrying out a nail penetration test within 24 h. The method comprises the steps of firstly placing a battery on a plane, vertically puncturing the battery at a speed of 150mm/s by using a steel nail with a diameter of 3mm, continuously keeping the battery punctured by the steel nail for 5min or stopping testing when the temperature of the battery is reduced to 50 ℃, if the battery is not ignited or not exploded, indicating that the battery passes the test, testing 5 parallel samples, and taking the ratio of the number of the samples passing the test to the total number of the test samples as the passing rate of the puncturing test.

Impact test of the battery: and after the battery is fully charged according to the standard charging mode, performing impact test within 24 h. The cells were first placed on a flat surface and a steel post 15.8 + -0.1 mm in diameter was centered on the cell so that the longitudinal axis of the post was parallel to the flat surface on which the cells were placed. The steel column can be fixed by using clamps on the left and right sides of the steel column, but the steel column cannot be fixed by using articles with a buffering function, such as sponge, below the steel column. An impact weight of 9.1 + -0.46 kg was freely dropped from a height of 610 + -25 mm onto the test cell. If the battery is not ignited and not exploded after being impacted, the battery passes the impact test, 5 parallel samples are tested, and the ratio of the number of the samples passing the test to the total number of the test samples is used as the impact test passing rate.

Plane compression test of battery: and (3) fully charging the battery according to the standard charging mode, and then carrying out a plane extrusion experiment within 12-24 h. The largest face of the cell was squeezed parallel to the table, the plane of the cell was squeezed perpendicularly with a metal block, and the pressure was released when it reached 13 ± 1kN, and each sample was tested only once in one direction. If the battery is not ignited and not exploded after being extruded, the battery passes the plane extrusion test. The impact test pass rate was determined as the ratio of the number of samples that passed the test to the total number of samples tested, 5 parallel samples were tested.

TABLE 1 summary of test results for each example and comparative example

As can be known from table 1, compared with a simple metal foil as a current collector (comparative example 1), the composite current collector provided by the present application has a lower surface density, and is helpful for improving the energy density and safety performance of the battery. However, when the thickness and elongation of the polymer substrate in the composite current collector and the thickness of the conductive layer disposed thereon do not satisfy the proportional relationship defined in the present application (comparative example 2), the peel strength between the conductive layer and the polymer substrate is low, and the safety performance of the battery is also significantly reduced.

In addition, the surface of the aluminum conductive layer of each composite current collector in the examples of the present application was coated with a positive electrode slurry of a positive electrode active material lithium cobaltate, and the positive electrode slurry was dried and cold-pressed to make the density of the lithium cobaltate active layer on the aluminum conductive layer to 4.1g/cm³Then, the obtained positive electrode piece is immersed in electrolyte (the electrolyte composition is 1mol/L LiPF)₆The volume ratio of EC, DEC and PP of EC + DEC + PP mixed solution in (3). If the composite current collector of comparative example 2 is subjected to the same test, the conductive layer thereof is rapidly foamed and peeled. The result shows that the conductive layer attached to the polymer substrate is relatively stable in the high-temperature standing process after the electrolyte is injected into the composite current collector, and the strong bonding force between the conductive layer and the polymer substrate is further proved.

The composite current collector provided by the embodiment of the application has the advantages of strong binding force between the conductive layer and the polymer substrate, stable structure, excellent mechanical property and low surface density, and the battery prepared by adopting the composite current collector has excellent electrochemical property and particularly outstanding safety performance.

The foregoing merely represents exemplary embodiments of the present application and the description is more specific and detailed, but is not to be construed as limiting the scope of the claims. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A composite current collector comprising a polymeric substrate, and a first electrically conductive layer disposed on one surface of the polymeric substrate or a first electrically conductive layer and a second electrically conductive layer disposed on opposite surfaces of the polymeric substrate, the first electrically conductive layer and the second electrically conductive layer partially covering or completely covering the surface of the polymeric substrate;

2. The composite current collector of claim 1, wherein σ ranges from 3% to 300%.

3. The composite current collector of claim 1, wherein D1 is¹And said D1²The range of (b) is 30nm-2 μm.

4. The composite current collector of any one of claims 1 to 3, wherein the polymer constituting the polymer substrate has a solubility parameter ranging from 10 to 22 (J/cm)³)^0.5。

5. The composite current collector of claim 4, wherein the difference in solubility parameters of the polymer and the battery electrolyte is from 5 to 15 (J/cm)³)^0.5。

6. The composite current collector of any one of claims 1 to 5, wherein a surface tension coefficient of the surface of the polymer substrate facing the first conductive layer is greater than or equal to 38 dynes/cm, or a surface tension coefficient of both the surface of the polymer substrate facing the first conductive layer and the surface facing the second conductive layer is greater than or equal to 38 dynes/cm.

7. The composite current collector of claim 6, wherein a surface of the polymer substrate facing the first conductive layer carries polar groups, or wherein both a surface of the polymer substrate facing the first conductive layer and a surface facing the second conductive layer carry polar groups.

8. The composite current collector of any one of claims 1 to 7, wherein the polymer substrate further comprises a conductive additive.

9. The composite current collector of claim 8, wherein the conductive additive comprises at least one of a metal conductive material and a carbon-based conductive material; the metal conductive material comprises one or more of nickel, copper, aluminum, titanium, silver and alloys thereof, and the carbon-based conductive material comprises one or more of carbon nanotubes, graphene, graphite, acetylene black and amorphous carbon.

10. The composite current collector of claim 8, wherein the conductive additive is present in the polymer substrate at a mass fraction of no more than 5%.

11. The composite current collector of any one of claims 1 to 10, wherein the polymer substrate further has a porous structure.

12. The composite collector of any of claims 1 to 11, wherein the composite collector has a thickness ranging from 3 μ ι η to 20 μ ι η.

13. The composite current collector of any one of claims 1 to 12, wherein the areal density of the composite current collectorIs 0.5mg/cm²-4 mg/cm²。

14. The composite current collector of any one of claims 1 to 13, wherein the composite current collector has an elongation greater than 0 and less than or equal to 10% at a roll pressure of 30 tons.

15. The composite current collector of any one of claims 1 to 14, wherein the peel strength of the first electrically conductive layer, the second electrically conductive layer, and the polymer substrate are each greater than 15N/m.

16. The preparation method of the composite current collector is characterized by comprising the following steps of:

17. The method of preparing a composite current collector of claim 16, wherein prior to forming the first conductive layer or prior to forming the first and second conductive layers, the method further comprises: and subjecting the surface of the polymer substrate on which the first conductive layer is to be formed or the surfaces on which the first conductive layer and the second conductive layer are to be formed to at least one of corona treatment, plasma surface treatment and compound surface modification treatment.

18. An electrode sheet comprising the composite current collector of any one of claims 1 to 15 and an electrode active material layer formed on the first conductive layer or on the first conductive layer and the second conductive layer.

19. A battery comprising a positive electrode tab, a negative electrode tab, and a separator and an electrolyte between the positive and negative electrode tabs, wherein the positive and/or negative electrode tabs comprise the electrode tab of claim 18.

20. A terminal comprising a housing, a motherboard located within the housing, and a battery as claimed in claim 19 for powering the terminal.