Composite current collector, preparation method thereof, negative electrode and lithium ion battery

Abstract

The invention provides a composite current collector and a preparation method thereof, a negative electrode and a lithium ion battery. The composite current collector comprises a current collector body and a heating layer stacked on at least one surface of the current collector body in the thickness direction, wherein the heating layer comprises a conductive agent and a binder; and the coverage rate of the heating layer on the surface of the current collector body is less than 100%. According to the invention, the heating layer is directly integrated on the current collector, so that the heating layer is used as a self-heating layer at a low temperature, uniform Joule heat can be directly generated in the electrode when current flows through, the overall temperature of the battery is rapidly increased, and the rate capability and cycling stability of the lithium ion battery at the low temperature are further improved; meanwhile, the influence on the impedance of the battery at room temperature is small, good electrochemical performance is kept, and the chemical stability is good.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a composite current collector, a preparation method thereof, a negative electrode and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries (LIBs) have become the main power source for electric vehicles and electronic devices due to their high energy density, good rate capability and cycle stability. However, the performance of LIBs in low-temperature environments is limited, mainly due to the decrease in the electrical conductivity of lithium ions in the electrolyte, the increase in solvation or desolvation energy, the increase in charge transfer resistance at the electrode or electrolyte interface, and the slow diffusion of lithium ions in the active material. These factors lead to an increase in internal polarization, a decrease in voltage, and may cause lithium metal deposition and dendrite growth problems, further reducing the performance and safety of the battery.

[0003] The lithium deposition phenomenon of lithium batteries at low temperatures seriously hinders the application of lithium batteries in cold regions. The current solution is generally to add a heating layer outside the lithium battery, but the traditional external heating layer has problems such as large thermal resistance, slow response and poor uniformity, and additionally increases the volume of the battery. Therefore, it is crucial to improve the performance of LIBs at low temperatures while considering low energy consumption. SUMMARY

[0004] The main purpose of the present application is to provide a composite current collector, a preparation method thereof, a negative electrode and a lithium ion battery, to solve the problem of poor performance of lithium ion batteries at low temperatures in the related art.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a composite current collector is provided, which comprises a current collector body and a heating layer stacked on at least one surface of the current collector body in the thickness direction of the current collector body; wherein the heating layer comprises a conductive agent and a binder; the coverage of the heating layer on the surface of the current collector body is <100%.

[0006] Further, the coverage of the heating layer on the surface of the current collector body is 40-60%; and / or, the conductive agent is selected from any one or more of Super P conductive agent, acetylene black and ketjen black; and / or, the binder is selected from any one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, sodium alginate, polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene copolymer; and / or, the mass ratio of the conductive agent and the binder is 85:15-95:5.

[0007] Further, the conductive agent further comprises carbon nanotubes, and the mass fraction of the carbon nanotubes in the conductive agent is 10-50%.

[0008] Further, the heating layer comprises a plurality of spaced patterned regions; wherein the shape of the patterned regions is selected from any one or more of a circle, a square, a triangle and a pentacle; the edge distance between each adjacent patterned region is 0.3-0.8mm, and the center distance between each adjacent patterned region is 1.3-1.8mm.

[0009] Further, the thickness of the heating layer is 8-12μm; and / or, the thickness of the current collector body is 4.5-12μm; and / or, the thickness ratio of the heating layer to the current collector body is 1-2.7:1.

[0010] Further, the resistivity of the heating layer is 1-50Ω·cm; and / or, the current collector body is an aluminum foil and / or a copper foil.

[0011] According to another aspect of the present application, there is provided a preparation method of the above-mentioned composite current collector, comprising: step S1, mixing raw materials comprising a conductive agent, a binder and a solvent to obtain a slurry; and step S2, coating the slurry on at least one side surface of the current collector body and drying to form a heating layer, thereby obtaining the composite current collector; wherein the coverage of the heating layer on the surface of the current collector body is <100%.

[0012] Further, in the above-mentioned step S1, the solvent is water and / or ethanol; and / or, the solid content of the slurry is 6-10%; and / or, in step S2, the coating method is spraying; and / or, the drying temperature is 50-80℃, and the drying time is 20-60min.

[0013] According to still another aspect of the present application, there is provided a negative electrode comprising a current collector, which is the above-mentioned composite current collector.

[0014] According to still another aspect of the present application, there is provided a lithium ion battery comprising a positive electrode, a negative electrode and a separator, wherein the negative electrode is the above-mentioned negative electrode.

[0015] By applying the technical solution of the application, the heating layer (composite carbon layer) is directly integrated into the current collector, so that it can generate uniform Joule heat inside the electrode when current flows, thereby rapidly increasing the overall temperature of the battery, and improving the rate performance and cycle stability of the lithium ion battery at low temperature. At the same time, the impedance of the battery at room temperature is small, the electrochemical performance is good, and the chemical stability is good. The thin and light heating layer of the application includes a light conductive agent and a binder. At room temperature, the resistance of the heating layer is small enough compared to the impedance of the entire battery, so it will not significantly increase the internal resistance of the battery or reduce its room temperature performance. In addition, when the current flows through the battery at low temperature, the current also flows through the heating layer (which has a higher resistivity than the metal current collector) with resistance. According to Joule's law, the current flowing through the heating layer with resistance will generate heat. Controlling the coverage of the heating layer on the surface of the current collector body to be less than 100% can ensure that it does not completely block the conductive contact between the current collector and the active material, allowing the current to pass while generating heat. This heat is generated directly inside the battery (self-heating), thereby rapidly and effectively increasing the temperature of the core area of the battery. In addition, the use of the composite current collector of the application can simultaneously consider lower energy consumption on the basis of rapidly improving the performance of the lithium ion battery at low temperature. DETAILED DESCRIPTION

[0016] It should be noted that the embodiments in the application and the features in the embodiments can be combined with each other without conflict. The application will be described in detail below with reference to the embodiments.

[0017] As analyzed in the background art of the application, the prior art has the problem that the performance of the lithium ion battery at low temperature is poor. In order to solve the above problem, the application provides a composite current collector and a preparation method thereof, a negative electrode, and a lithium ion battery.

[0018] In a typical embodiment of the application, a composite current collector is provided, which includes a current collector body and a heating layer laminated on at least one surface of the current collector body in the thickness direction; wherein the heating layer includes a conductive agent and a binder; the coverage of the heating layer on the surface of the current collector body is less than 100%.

[0019] The application can make the current flow to directly generate uniform Joule heat inside the electrode, thereby quickly raising the overall temperature of the battery, and improving the rate performance and cycle stability of the lithium ion battery at low temperature. Meanwhile, the application has little effect on the impedance of the battery at room temperature, maintains good electrochemical performance, and has good chemical stability. The thin heating layer of the application includes a lightweight conductive agent and a binder, and its resistance is small enough relative to the impedance of the entire battery at room temperature, so it will not significantly increase the internal resistance of the battery or reduce its normal temperature performance. In addition, when the current flows through the battery at low temperature, the current also flows through the heating layer with resistance (its resistivity is higher than that of the metal current collector). According to Joule's law, the current flowing through the heating layer with resistance will generate heat. Controlling the coverage of the heating layer on the surface of the current collector body to be less than 100% can ensure that it will not completely block the conductive contact between the current collector and the active material, allowing the current to pass while generating heat. This heat is directly generated inside the battery (self-heating), thereby quickly and effectively raising the temperature of the core area of the battery. In addition, the use of the composite current collector of the application can improve the performance of the lithium ion battery at low temperature while considering the lower energy consumption.

[0020] In an embodiment of the application, the coverage of the heating layer on the surface of the current collector body is 40-60%; and / or, the conductive agent is selected from any one or more of Super P conductive agent, acetylene black and ketjen black; and / or, the binder is selected from any one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, sodium alginate, polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene copolymer; and / or, the mass ratio of the conductive agent and the binder is 85:15-95:5.

[0021] Controlling the coverage of the heating layer on the surface of the current collector body to be 40-60% helps to achieve rapid and uniform temperature rise, thereby improving the low temperature performance of the battery while maintaining the effective transmission of electrons, so that the electrons are still smoothly transmitted from the active material to the external circuit while self-heating. In addition, it also helps to achieve uniform and reasonable distribution of the heating layer on the current collector, reduces the current density unevenness caused by the edge effect, thereby reducing the risk of lithium precipitation and short circuit, and further improving the safety of the battery. In addition, the coverage of the heating layer on the surface of the current collector body can be 40%, 45%, 50%, 55% or 60%. Of course, the coverage of the heating layer on the surface of the current collector body can be any point value within the above range.

[0022] Controlling the type of conductive agent within the above range helps to improve the electrical conductivity of the electrode, thereby facilitating faster movement of lithium ions within the electrode at low temperatures, reducing charge transfer impedance. Controlling the type of binder within the above range helps to enhance the mechanical strength of the electrode, thereby reducing the occurrence of peeling or cracking of the electrode material during charging and discharging, thereby improving the cycle stability and safety of the battery.

[0023] Controlling the mass ratio of the conductive agent and the binder within the above range helps to quickly raise the overall temperature of the battery, thereby further improving the rate performance and cycle stability of the lithium ion battery at low temperatures, while maintaining the electrochemical performance at room temperature. At the same time, it also helps to optimize the interface properties between the electrode material and the composite current collector, including adhesion and contact resistance, thereby improving the cycle performance and rate capability of the battery. In addition, the mass ratio of the conductive agent and the binder can be 85:15, 87:13, 90:10, 92:17 or 95:5, of course, the mass ratio of the conductive agent and the binder can be any ratio within the above range.

[0024] In an embodiment of the present application, the conductive agent further includes carbon nanotubes, and the mass ratio of the carbon nanotubes in the conductive agent is 10-50%.

[0025] Carbon nanotubes have good electrical conductivity and high aspect ratio, which helps to form an efficient conductive network in the electrode material. When the conductive agent includes carbon nanotubes, the carbon nanotubes are used in combination with the above-mentioned conductive agents (Super P conductive agent, acetylene black and ketchen black), and the mass ratio of the carbon nanotubes in the conductive agent is controlled within the above range, which not only helps to promote lithium ion diffusion, thereby improving the rate performance and low temperature adaptability of the battery, but also helps to improve the efficiency of the conductive network, thereby improving the electronic conductivity of the electrode. In addition, the mass ratio of the carbon nanotubes in the conductive agent can be 10%, 20%, 30%, 40% or 50%, of course, the mass ratio of the carbon nanotubes in the conductive agent can be any one point value within the above range.

[0026] In an embodiment of the present application, the heating layer includes a plurality of spaced patterned regions; wherein the shape of the patterned regions is selected from any one or more of a circle, a square, a triangle and a pentagram; the edge distance between each adjacent patterned region is 0.3-0.8mm, and the center distance between each adjacent patterned region is 1.3-1.8mm.

[0027] The shape of the control pattern region, the edge interval distance and the center interval distance between adjacent control pattern regions are within the above ranges, which helps to distribute the current more evenly inside the electrode, thereby generating uniform Joule heat and reducing material damage or performance degradation caused by local overheating, so as to quickly and uniformly heat the battery at low temperature. At the same time, the design of the edge interval and the center interval helps to keep the electronic conduction path between the heating layer and the current collector body from being completely blocked, thereby helping lithium ions to effectively reach the active material from the electrolyte during charging, reducing the occurrence of lithium precipitation and short circuit. In addition, the edge interval distance between adjacent control pattern regions can be 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm or 0.8 mm, of course, the edge interval distance between adjacent control pattern regions can be any point value within the above range. The center interval distance between adjacent control pattern regions can be 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm or 1.8 mm, of course, the center interval distance between adjacent control pattern regions can be any point value within the above range.

[0028] Optionally, the shape of the control pattern region is a circle, and the diameter of the circle is 0.5-1.5 mm, optionally 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm or 1.5 mm. The shape of the control pattern region is a square, and the side length of the square is 0.5-1.5 mm, optionally 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm or 1.5 mm. The shape of the control pattern region is a triangle, and the side length of the triangle is 0.5-1.5 mm, optionally 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm or 1.5 mm. The shape of the control pattern region is a pentagram, and the side length of the pentagram is 0.25-0.75 mm, optionally 0.25 mm, 0.35 mm, 0.45 mm, 0.55 mm, 0.65 mm or 0.75 mm. Controlling the shape and spacing of the control pattern region helps to balance the heating effect and electrical conductivity, so that the heating layer can provide sufficient heat source while maintaining good electrical conductivity performance, thereby better improving the rate performance and cycle stability of the battery. At the same time, by controlling the distribution and size of the control pattern region, it helps to reduce unnecessary energy consumption, thereby improving the heating efficiency. The layout of the control pattern region also helps to enhance the compatibility between the heating layer and the electrode material, reducing the occurrence of cracks or peeling during battery assembly or long-term use.

[0029] In an embodiment of the present application, the thickness of the heating layer is 8-12 μm; and / or, the thickness of the current collector body is 4.5-12 μm; and / or, the thickness ratio of the heating layer and the current collector body is 1-2.7:1.

[0030] Controlling the thickness of the current collector body within the above range helps to provide sufficient conductive path, thus effectively collecting current, and helps to distribute heat evenly. Meanwhile, a certain mechanical strength is maintained to support the electrode material, thus improving stability. In addition, the thickness of the current collector body can be 4.5 μm, 6 μm, 8 μm, 10 μm or 12 μm, of course, the thickness of the current collector body can be any point value within the above range.

[0031] Within the electrode, the thickness of the heating layer affects the uniform generation of Joule heat. A heating layer that is too thin can not generate enough heat throughout the electrode plane, while a heating layer that is too thick can cause local overheating. Controlling the thickness of the heating layer within the above range helps to heat evenly and effectively, thus improving the performance of the battery under low temperature conditions. Meanwhile, it also helps to maintain the resistance characteristics of the heating layer, reducing energy loss due to excessive resistance. In addition, the thickness of the heating layer can be 8 μm, 9 μm, 10 μm, 11 μm or 12 μm, of course, the thickness of the heating layer can be any point value within the above range.

[0032] Controlling the thickness ratio of the heating layer and the current collector body within the above range helps to improve the structural strength of the composite current collector, and the heating layer provides a self-heating function while not affecting the basic conductive performance of the current collector. Meanwhile, it also helps to more accurately control the temperature rise during heating, thus enabling the battery to quickly reach the ideal working temperature when starting at low temperature. In addition, the thickness ratio of the heating layer and the current collector body can be 1:1, 1.5:1, 2:1, 2.5:1 or 2.7:1, of course, the thickness ratio of the heating layer and the current collector body can be any ratio within the above range.

[0033] In an embodiment of the present application, the resistivity of the heating layer is 1-50 Ω·cm; and / or, the current collector body is an aluminum foil and / or a copper foil.

[0034] The resistivity has a certain influence on the Joule heat generated when the current passes through the heating layer. If the resistivity is too low, the heating layer generates insufficient heat to quickly raise the battery temperature; if it is too high, it can generate too much heat at a lower current, causing local overheating and even damaging the battery components. Controlling the resistivity of the heating layer within the above range effectively generates heat at low temperature and has little effect on the battery impedance at normal temperature (i.e., the heating layer has high conductivity and is thin and light). Controlling the type of current collector body within the above range helps to better composite the heating layer to form a composite current collector. In addition, the resistivity of the heating layer can be 1 Ω·cm, 5 Ω·cm, 10 Ω·cm, 20 Ω·cm, 30 Ω·cm, 40 Ω·cm or 50 Ω·cm, of course, the resistivity of the heating layer can be any point value within the above range.

[0035] In another typical embodiment of the present application, a preparation method of the composite current collector is provided, which comprises: step S1, mixing raw materials including a conductive agent, a binder and a solvent to obtain a slurry; and step S2, coating the slurry on at least one side surface of a current collector body and drying to form a heating layer, thereby obtaining the composite current collector; wherein the coverage of the heating layer on the surface of the current collector body is < 100%.

[0036] The composite current collector prepared by the preparation method of the present application can directly integrate the heating layer into the current collector, directly generate uniform Joule heat in the electrode when the current flows, thereby rapidly increasing the overall temperature of the battery, and improving the rate performance and cycle stability of the lithium ion battery at low temperature while maintaining the electrochemical performance at room temperature. In addition, controlling the coverage of the heating layer on the surface of the current collector body in the above range can ensure that the interface between the composite current collector and the composite electrode is not completely blocked, thereby retaining the electron conduction channel. In addition, the preparation method of the present application is simple and easy to operate.

[0037] In an embodiment of the present application, in step S1, the solvent is water and / or ethanol; and / or, the solid content of the slurry is 6-10%; and / or, in step S2, the coating method is spraying; and / or, the drying temperature is 50-80℃, and the drying time is 20-60min.

[0038] Controlling the type of solvent in the above range helps the conductive agent and the binder to be dispersed in the solvent to obtain a uniform slurry, thereby facilitating subsequent coating. Controlling the solid content of the slurry in the above range helps the subsequent slurry to be uniformly coated on the surface of the current collector body and reduces the nozzle blockage during spraying. In addition, the solid content of the slurry can be 6%, 7%, 8%, 9% or 10%. Of course, the solid content of the slurry can be any point value in the above range.

[0039] Controlling the drying temperature and drying time in the above range helps to promote the uniform solidification of the conductive agent and the binder to form a stable heating layer, thereby improving the mechanical strength and electrochemical stability of the composite current collector. In addition, the drying temperature can be 50℃, 60℃, 70℃ or 80℃, and the drying time can be 20min, 30min, 40min, 50min or 60min. Of course, the drying temperature and time can be any point value in the above range.

[0040] In another typical embodiment of the present application, a negative electrode is provided, which comprises a current collector, and the current collector is the composite current collector described above.

[0041] The negative electrode comprising the composite current collector described above has good rate performance and cycle stability at low temperature.

[0042] In another typical embodiment of the present application, a lithium ion battery is provided, comprising a positive electrode, a negative electrode and a separator, the negative electrode being the negative electrode described above.

[0043] The lithium ion battery comprising the negative electrode described above has good rate performance and cycle stability at low temperature, while maintaining good electrochemical performance at room temperature.

[0044] The beneficial effects of the present application will be further illustrated below in conjunction with examples.

[0045] Example 1

[0046] Super P conductive agent and binder carboxymethyl cellulose sodium (CMC) were added to a solvent deionized water in a mass ratio of 90:10 to obtain a slurry with a solid content of 8%. The slurry was sprayed on one side surface of a current collector body copper foil with a thickness of 6 μm to form a plurality of patterned areas, the patterned areas being circular with a radius of 0.5 mm, the edge distance between circles being 0.5 mm, the center distance between circles being 1.5 mm, the sprayed thickness being 10 μm, and the sprayed current collector being dried at 65 °C for 40 min to form a heating layer, thereby obtaining a composite current collector, wherein the coverage of the heating layer on the surface of the current collector body is 50%.

[0047] Example 2

[0048] The difference from Example 1 is that the conductive agent is acetylene black, and finally a composite current collector is obtained.

[0049] Example 3

[0050] The difference from Example 1 is that the conductive agent is Ketjen black, and finally a composite current collector is obtained.

[0051] Example 4

[0052] The difference from Example 1 is that the conductive agent is carbon nanotubes and Super P conductive agent, the mass ratio of carbon nanotubes and Super P conductive agent being 1:1, and finally a composite current collector is obtained.

[0053] Example 5

[0054] The difference from Example 1 is that the conductive agent is carbon nanotubes and acetylene black, the mass ratio of carbon nanotubes and acetylene black being 1:1, and finally a composite current collector is obtained.

[0055] Example 6

[0056] The difference from Example 1 is that the conductive agent is carbon nanotubes and Ketjen black, the mass ratio of carbon nanotubes and Ketjen black being 1:1, and finally a composite current collector is obtained.

[0057] Example 7

[0058] The difference from Example 1 is that the slurry is sprayed on one side surface of the current collector body copper foil into a plurality of patterned areas, the patterned areas are squares with a side length of 1 mm, the edge spacing distance between the squares is 0.5 mm, the center spacing distance between the squares is 1.5 mm, and after spraying, the heating layer is dried to form a composite current collector, wherein the coverage of the heating layer on the surface of the current collector body is 40%.

[0059] Example 8

[0060] The difference from Example 1 is that the slurry is sprayed on one side surface of the current collector body copper foil into a plurality of patterned areas, the patterned areas are equilateral triangles with a side length of 1 mm, the center spacing distance between the equilateral triangles is 1.8 mm, and after spraying, the heating layer is dried to form a composite current collector.

[0061] Example 9

[0062] The difference from Example 1 is that the slurry is sprayed on one side surface of the current collector body copper foil into a plurality of patterned areas, the patterned areas are regular pentagons with a side length of 0.5 mm, the center spacing distance between the regular pentagons is 1.35 mm, and after spraying, the heating layer is dried to form a composite current collector.

[0063] Example 10

[0064] The difference from Example 1 is that the conductive agent is carbon nanotubes, and a composite current collector is finally obtained.

[0065] Example 11

[0066] The difference from Example 1 is that the mass ratio of Super P conductive agent to binder sodium carboxymethyl cellulose is 95:5, and a composite current collector is finally obtained.

[0067] Example 12

[0068] The difference from Example 1 is that the mass ratio of Super P conductive agent to binder sodium carboxymethyl cellulose is 80:20, and a composite current collector is finally obtained.

[0069] Example 13

[0070] The difference from Example 1 is that the coverage of the heating layer on the surface of the current collector body is 60%, and a composite current collector is finally obtained.

[0071] Example 14

[0072] The difference from Example 1 is that the coverage of the heating layer on the surface of the current collector body is 35%, and a composite current collector is finally obtained.

[0073] Example 15

[0074] The difference from Example 1 is that the thickness of the heating layer is 12 pm, the thickness of the current collector body is 6 pm, and the thickness ratio of the heating layer and the current collector body is 2:1, and finally a composite current collector is obtained.

[0075] Example 16

[0076] The difference from Example 1 is that the thickness of the heating layer is 5 pm, the thickness of the current collector body is 6 pm, and the thickness ratio of the heating layer and the current collector body is 5:6, and finally a composite current collector is obtained.

[0077] Example 17

[0078] The difference from Example 1 is that the conductive agent is graphene, and finally a composite current collector is obtained.

[0079] Comparative Example 1

[0080] The difference from Example 1 is that the slurry is sprayed on the entire surface of one side of the current collector body to form a heating layer, the area of the heating layer is the same as the area of the current collector body, and finally a composite current collector is obtained.

[0081] Comparative Example 2

[0082] The difference from Example 1 is that the current collector body surface is not sprayed with slurry, and finally a composite current collector is obtained.

[0083] Test method:

[0084] Preparation of lithium ion battery: NCM811, polyvinylidene fluoride (PVDF) and acetylene black were added into solvent 1-methyl-2-pyrrolidone (NMP) according to a mass ratio of 8:1:1 to obtain a positive electrode slurry. The positive electrode slurry was coated on an aluminum foil and dried at 90°C for 8h, and the electrode was punched into a circular sheet with a diameter of 13mm to obtain a positive electrode. Graphite, Super P, sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) were added into deionized water according to a mass ratio of 93:3:2:2 to obtain a negative electrode slurry. The negative electrode slurry was coated on the composite current collector of the examples and comparative examples, dried at 60°C for 1h, and the electrode was punched into a circular sheet with a diameter of 13mm to obtain a negative electrode.

[0085] A polypropylene separator (Celgard 2400) was used as a separator, and a solution of 1 mol / L lithium hexafluorophosphate (LiPF6) dissolved in ethylene carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate (EMC) (mass ratio of 1:1:1) was used as an electrolyte.

[0086] The above positive electrode, negative electrode and separator were assembled into a CR2032 type button cell in a glove box (oxygen and water content ≤0.1 ppm), injected with electrolyte and sealed, and a lithium ion battery was assembled.

[0087] Electrochemical performance test:

[0088] The lithium ion battery was placed at room temperature 25℃ for 10h, and electrochemical test was performed by using Wuhan Lan electric CT2001A type battery test system, and the test voltage range was set to 2.8-4.3V (vs. Li+ / Li).

[0089] (1) The shell temperature after 10 cycles and 20 cycles at-10℃, 0.5C was recorded, and the thermocouple was attached to the surface of the battery steel shell, and the instantaneous temperature at the end of charging and discharging was recorded;

[0090] (2) The impedance was tested at room temperature 25℃.

[0091] The above test results are shown in Table 1.

[0092] Table 1

[0093]

[0094]

[0095] As can be seen from Table 1, compared with Comparative Example 2, the shell temperature of the lithium ion battery of the embodiment of the present application has a significant temperature rise. Although the temperature rise in the early stage is more obvious, the composite current collector of Comparative Example 1 is fully covered by the heating layer on the surface of the current collector body, and a short circuit occurs at 50 cycles. Because the lithium ion is reduced to metallic lithium on the surface of the negative electrode during charging and needs to be in direct contact with the current collector and the electrolyte interface, the heating layer is fully covered, forcing the ion to bypass to the uncovered area, resulting in a dramatic increase in local current density, thereby causing edge lithium precipitation, and finally puncturing the separator to cause a short circuit.

[0096] Compared with Comparative Example 2, although the lithium ion battery of the embodiment of the present application has a slight increase in impedance at room temperature, the influence is small, and the lithium ion battery of the present application has a significant decrease in impedance after 20 cycles at-10℃ due to the self-heating operation, and compared with Comparative Example 2, the shell temperature of the lithium ion battery of the present application is significantly increased after using the heating layer.

[0097] In Example 10, only carbon nanotubes are used as the conductive agent in the heating layer, and pure carbon nanotubes are difficult to disperse, have high cost and low resistivity, resulting in poor heating efficiency.

[0098] In Example 17, graphene is used as the conductive agent in the heating layer. Graphene has good conductivity, but is high in cost, difficult to uniformly disperse and pattern deposit on a large scale, and the sheet structure hinders ion transmission to some extent. Pure graphene has low resistivity, resulting in poor heat generation effect.

[0099] From the above description, it can be seen that the above-mentioned embodiments of the present application achieve the following technical effects:

[0100] The heating layer (composite carbon layer) is directly integrated into the current collector in the present application, which can generate uniform Joule heat directly inside the electrode when current flows through it at low temperature, thereby rapidly increasing the overall temperature of the battery, and improving the rate performance and cycle stability of the lithium ion battery at low temperature. At the same time, the impedance of the battery at room temperature is small, maintaining good electrochemical performance, and the chemical stability is good. The light and thin heating layer of the present application includes light conductive agents and binders, and its resistance is small enough relative to the impedance of the entire battery at room temperature, so it will not significantly increase the internal resistance of the battery or reduce its normal temperature performance. In addition, when the current passes through the battery at low temperature, the current will also flow through the heating layer with resistance (its resistivity is higher than that of the metal current collector). According to Joule's law, the current flowing through the heating layer with resistance will generate heat. Controlling the coverage of the heating layer on the surface of the current collector body to be <100% can ensure that it will not completely block the conductive contact between the current collector and the active material, allowing the current to pass while generating heat. This heat is generated directly inside the battery (self-heating), thereby rapidly and effectively increasing the temperature of the core area of the battery. In addition, the use of the composite current collector of the present application can simultaneously consider lower energy consumption on the basis of rapidly improving the performance of the lithium ion battery at low temperature.

[0101] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Those skilled in the art can make various modifications and changes to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A composite current collector, characterized in that, The composite current collector includes a current collector body and a heating layer stacked on at least one surface of the current collector body in the thickness direction; wherein the heating layer includes a conductive agent and a binder; the coverage of the heating layer on the surface of the current collector body is <100%.

2. The composite current collector according to claim 1, characterized in that, The heating layer has a coverage of 40-60% on the surface of the current collector body; and / or, the conductive agent is selected from any one or more of Super P conductive agent, acetylene black, and Ketjen black; and / or, the binder is selected from any one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, sodium alginate, polyvinylidene fluoride, and polyvinylidene fluoride-hexafluoropropylene copolymer; and / or, the mass ratio of the conductive agent to the binder is 85:15 to 95:

5.

3. The composite current collector according to claim 1 or 2, characterized in that, The conductive agent also includes carbon nanotubes, and the mass percentage of the carbon nanotubes in the conductive agent is 10-50%.

4. The composite current collector according to any one of claims 1 to 3, characterized in that, The heating layer includes multiple spaced graphic regions; wherein the shape of the graphic regions is selected from any one or more of circles, squares, triangles and pentagrams; the edge spacing between adjacent graphic regions is 0.3 to 0.8 mm, and the center spacing between adjacent graphic regions is 1.3 to 1.8 mm.

5. The composite current collector according to any one of claims 1 to 4, characterized in that, The thickness of the heating layer is 8–12 μm; and / or the thickness of the current collector body is 4.5–12 μm; and / or the thickness ratio of the heating layer to the current collector body is 1–2.7:

1.

6. The composite current collector according to any one of claims 1 to 5, characterized in that, The resistivity of the heating layer is 1 to 50 Ω·cm; and / or the current collector body is aluminum foil and / or copper foil.

7. A method for preparing the composite current collector according to any one of claims 1 to 6, characterized in that, The preparation method includes: Step S1 involves mixing raw materials including a conductive agent, a binder, and a solvent to obtain a slurry; and Step S2: The slurry is coated onto at least one side surface of the current collector body and then dried to form a heating layer, thereby obtaining the composite current collector; The heating layer has a coverage rate of <100% on the surface of the current collector body.

8. The preparation method according to claim 7, characterized in that, In step S1, the solvent is water and / or ethanol; and / or, the solid content of the slurry is 6-10%; And / or, in step S2, the coating method is spraying; and / or, the drying temperature is 50-80°C, and the drying time is 20-60 min.

9. A negative electrode, comprising a current collector, characterized in that, The current collector is a composite current collector as described in any one of claims 1 to 6.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that, The negative electrode is the negative electrode as described in claim 9.

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