Lithium ion battery positive electrode with high thermal stability and preparation method thereof

Abstract

The invention discloses a lithium ion battery positive electrode with high thermal stability. The lithium ion battery positive electrode comprises a composite current collector and a positive electrode active material coating, wherein at least one surface of the composite current collector is coated with the positive electrode active material coating; the composite current collector comprises a first aluminum foil layer, a second aluminum foil layer and a heat-resistant buffer material layer arranged between the first aluminum foil layer and the second aluminum foil layer; the heat-resistant buffer material layer is made of ceramic silica gel foam, a plurality of trapezoidal protrusions are arranged on the surfaces of the two sides of the heat-resistant buffer material layer, the first aluminum foil layer and the second aluminum foil layer are each provided with a plurality of trapezoidal grooves embedded with the trapezoidal protrusions, the width of the cross section of each trapezoidal protrusion is gradually increased from inside to outside, and the width of the cross section of each trapezoidal groove is gradually increased from inside to outside. The width of the cross section of the trapezoid groove is gradually reduced from inside to outside, and an interlocking structure is formed between the first aluminum foil layer and the second aluminum foil layer through matching of the trapezoid protrusion and the trapezoid groove. The lithium ion battery positive electrode provided by the invention has excellent thermal stability, high interface bonding strength and high mechanical reliability.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to a lithium ion battery positive electrode with high thermal stability and a preparation method thereof. Background Art

[0002] Since its commercialization in the 1990s, lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, energy storage systems, etc. due to their excellent properties such as high energy density, long cycle life, and low self-discharge rate. However, with the continuous expansion of the application fields of lithium-ion batteries, the requirements for their safety, reliability, and high-temperature performance are also increasing.

[0003] The positive electrode of a lithium-ion battery is one of the key components of the battery, and its performance directly affects key indicators such as the battery's capacity, rate, cycle life, and safety. The positive electrode is generally composed of a current collector and an active material layer, in which the current collector not only carries and collects current, but also has an important influence on the battery's internal resistance, coulomb efficiency, and cycle stability. At present, aluminum foil is mostly used as the current collector for lithium-ion battery positive electrodes, but single-layer aluminum foil has problems such as insufficient mechanical strength and poor high-temperature stability, which limits the safety and reliability of the battery.

[0004] In order to improve the performance of the positive electrode current collector, the industry has proposed a technical solution of using a composite current collector, that is, using polymer materials such as PET or PP as the base film, and depositing metal layers (such as copper, aluminum, etc.) on both sides through vacuum coating, lamination and other processes to form a composite current collector with a metal layer-base film-metal layer sandwich structure. This composite current collector not only has the high conductivity of the metal layer and the flexibility of the polymer base film, but also can improve the corrosion resistance and environmental resistance of the current collector through the barrier effect of the base film, which is expected to comprehensively improve the comprehensive performance of the positive electrode of lithium-ion batteries.

[0005] However, the existing composite current collectors still have some problems that need to be solved in practical applications. First, the thermal stability of polymer base films such as PET and PP is limited, and they are easy to soften, deform, melt or decompose under high temperature conditions, resulting in the composite current collector being unable to maintain good mechanical properties and structural integrity. In particular, when thermal runaway occurs inside the battery, the existing composite current collector cannot provide effective heat insulation and flame retardant protection, and it is difficult to prevent or delay the spread of thermal runaway, which seriously threatens the safety of the battery. Secondly, the interface bonding strength between the metal layer and the polymer base film is insufficient, and interface failure problems such as delamination and peeling are prone to occur during the long-term charge and discharge cycle of the battery, resulting in a decrease in the conductivity of the current collector, accelerating the battery capacity decay and shortening the life. Furthermore, the mechanical properties and stress transfer capabilities of the existing composite current collectors need to be improved, and it is difficult to effectively absorb and buffer the mechanical stress inside or outside the battery. It is easy to deform, break or break under extreme conditions such as vibration, extrusion, and falling, inducing safety hazards such as internal short circuits.

[0006] Therefore, there is an urgent need to develop a new lithium-ion battery positive electrode with excellent thermal stability, high interface bonding strength and high mechanical reliability to comprehensively improve the safety, reliability and high-temperature performance of the lithium-ion battery positive electrode. Summary of the invention

[0007] The main purpose of the present invention is to provide a new type of lithium-ion battery positive electrode with excellent thermal stability, high interface bonding strength and high mechanical reliability in view of the deficiencies of the prior art, so as to comprehensively improve the safety, reliability and high temperature performance of the lithium-ion battery positive electrode. The positive electrode not only maintains excellent mechanical strength, rigidity and deformation resistance under high temperature conditions, but also has good heat insulation and flame retardant properties, which can block heat transfer and inhibit exothermic reactions in the early stage of battery thermal runaway, thereby preventing or delaying the occurrence of thermal runaway to the greatest extent. At the same time, the positive electrode can also provide sufficiently high interface bonding strength and fatigue life, ensure long-term reliable connection between aluminum foil and base film, and maintain a stable conductive network. In addition, the positive electrode also has excellent buffering energy absorption capacity and uniformity of stress distribution, effectively reducing local stress concentration and improving the vibration and impact resistance of the battery.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] A lithium-ion battery positive electrode with high thermal stability, comprising a composite current collector and a positive electrode active material coating coated on at least one surface of the composite current collector; the composite current collector comprises a first aluminum foil layer, a second aluminum foil layer, and a heat-resistant buffer material layer arranged between the first aluminum foil layer and the second aluminum foil layer;

[0010] The heat-resistant buffer material layer is a ceramic silicone foam, which comprises the following components in weight proportion: 30-40 parts of vinyl silicone oil, 10-20 parts of white carbon black, 20-50 parts of nano-ceramic powder, 0.1-1.0 parts of ethynyl cyclohexanol, 1-10 parts of hydrogen-containing silicone oil, 1-10 parts of hydroxy silicone oil, 0.1-1.0 parts of platinum catalyst, 10-20 parts of β-eucryptite, and 1-8 parts of halloysite nanotubes;

[0011] A plurality of trapezoidal protrusions are provided on both side surfaces of the heat-resistant buffer material layer, and a plurality of trapezoidal grooves are provided on the first aluminum foil layer and the second aluminum foil layer for engaging with the trapezoidal protrusions. The cross-sectional width of the trapezoidal protrusions gradually increases from the inside to the outside, and the cross-sectional width of the trapezoidal grooves gradually decreases from the inside to the outside. An interlocking structure is formed between the first aluminum foil layer and the second aluminum foil layer through the cooperation of the trapezoidal protrusions and the trapezoidal grooves.

[0012] Preferably, the height of the trapezoidal protrusion is g, the depth of the trapezoidal groove is h, the cross-sectional width of the trapezoidal protrusion is w, the cross-sectional width of the trapezoidal groove is d, the thickness of the heat-resistant buffer material layer is G, and the thickness of the first aluminum foil layer and the second aluminum foil layer are both H, wherein g, h, w, d, G and H satisfy the relationship: g=h, w=d, 0.1G≤g≤0.3G, 0.2H≤h≤0.4H, H<G.

[0013] Preferably, the sum of the forward projection areas of all trapezoidal protrusions on the surface of one side of the heat-resistant buffer material layer is S1, and the forward projection area of ​​the heat-resistant buffer material layer is S; wherein S1 and S satisfy the relationship: 0.5S≤S1≤0.7S.

[0014] Preferably, the preparation method of the ceramic silica foam is as follows:

[0015] Step S1, adding vinyl silicone oil, white carbon black, nano ceramic powder and β-eucryptite into a kneader, kneading into a mass at 130-150° C., cooling, and obtaining a base rubber;

[0016] Step S2, stirring and mixing the hydroxy silicone oil and the halloysite nanotubes to obtain a foaming mixture; wherein the stirring and mixing speed is 23000-26000 r / min, and the mixing time is 10-25 s;

[0017] Step S3, adding the foaming mixture, ethynyl cyclohexanol, hydrogen-containing silicone oil, and platinum catalyst into the base rubber, mixing evenly, to obtain a rubber material;

[0018] Step S4, vulcanizing and foaming the rubber material by a molding process to obtain the ceramicized silicone foam.

[0019] Preferably, one or more pressure sensors are embedded in the heat-resistant buffer material layer to monitor the pressure borne by various regions of the positive electrode in real time.

[0020] Preferably, a first temperature control material layer is provided between the first aluminum foil layer and the heat-resistant buffer material layer, and a second temperature control material layer is provided between the second aluminum foil layer and the heat-resistant buffer material layer; the shapes of the first temperature control material layer and the second temperature control material layer are both adapted to the shape of the trapezoidal raised surface of the heat-resistant buffer material layer; the phase change temperatures of the first temperature control material layer and the second temperature control material layer are both 57-62°C.

[0021] Preferably, the first temperature control material layer and the second temperature control material layer both include the following compositions in weight proportions: 45-55 parts of octadecanoic acid glycerol, 20-25 parts of palmitic acid, 10-15 parts of polyethylene glycol 4000, 3-5 parts of carbon nanotubes, 2-3 parts of boron nitride nanosheets, 1-2 parts of expanded graphite, and 0.5-1 parts of nano-magnesium oxide.

[0022] Preferably, the preparation method of the first temperature control material layer or the second temperature control material layer is as follows:

[0023] (1) Stearyl glycerol and palmitic acid are mixed according to a ratio, heated to melt in an oil bath at 85-95° C., and stirred evenly;

[0024] (2) adding polyethylene glycol 4000 to the molten mixture of step (1) and continuing to stir until it is completely dissolved;

[0025] (3) dispersing carbon nanotubes and boron nitride nanosheets in N-methylpyrrolidone and ultrasonically treating for 30 minutes;

[0026] (4) slowly adding the suspension of step (3) into the molten mixture of step (2), and stirring at high speed for 45 minutes;

[0027] (5) adding expanded graphite and nano magnesium oxide, and continuing high-speed stirring for 20 minutes to obtain a temperature control material layer slurry;

[0028] (6) Spraying the temperature control material layer slurry onto the outer surface of the heat-resistant buffer material layer and drying it to obtain a first temperature control material layer or a second temperature control material layer of a desired shape and thickness.

[0029] Preferably, a first modified thermally conductive silicone is provided between the first aluminum foil layer and the heat-resistant buffer material layer, and a second modified thermally conductive silicone is provided between the second aluminum foil layer and the heat-resistant buffer material layer; the shapes of the first modified thermally conductive silicone and the second modified thermally conductive silicone are both adapted to the shape of the trapezoidal raised surface of the heat-resistant buffer material layer; the porosity of the first modified thermally conductive silicone and the second modified thermally conductive silicone are both 65% to 85%; the first aluminum foil layer and the heat-resistant buffer material layer are bonded and connected by the first modified thermally conductive silicone; the second aluminum foil layer and the heat-resistant buffer material layer are bonded and connected by the second modified thermally conductive silicone.

[0030] In addition, the present invention also provides a method for preparing the lithium ion battery positive electrode with high thermal stability, comprising the following steps:

[0031] 1) preparing a ceramic silicone foam rubber material according to the above-mentioned ceramic silicone foam preparation method;

[0032] 2) vulcanizing and foaming the ceramic silicone foam rubber material through a molding process to obtain a heat-resistant buffer material layer with trapezoidal protrusions on both sides of the surface;

[0033] 3) spraying an aluminum foil layer of the same thickness on the surface of the heat-resistant buffer material layer by magnetron sputtering, and drying to obtain a composite current collector;

[0034] 4) coating the positive electrode active material coating slurry on at least one surface of the composite current collector and drying it to obtain the positive electrode of the lithium ion battery.

[0035] Compared with the prior art, the present invention has at least the following beneficial effects:

[0036] 1) The present invention adopts a composite current collector structure comprising a first aluminum foil layer, a second aluminum foil layer and a heat-resistant buffer material layer arranged between the two aluminum foil layers, wherein the heat-resistant buffer material layer is made of ceramic silicone foam with specific components and proportions; the material design gives the composite current collector excellent high temperature resistance, flame retardancy and mechanical buffering properties; under high temperature thermal runaway conditions, the ceramic silicone foam can maintain good mechanical strength and structural integrity, play a role in heat insulation and flame retardancy, effectively delay the occurrence and spread of thermal runaway, and greatly improve the thermal stability and safety of the positive electrode.

[0037] 2) The present invention designs an interlocking structure in which trapezoidal protrusions and trapezoidal grooves are embedded between the heat-resistant buffer material layer and the aluminum foil layer; this structure greatly increases the interface contact area and mechanical bite force, and significantly improves the interface bonding strength and shear resistance; the interlocking structure can effectively resist the interface shear stress, prevent interface delamination or peeling, ensure the interface connection reliability and conductivity stability of the composite current collector in long-term charge and discharge cycles, and improve the cycle life and mechanical fatigue performance of the positive electrode.

[0038] 3) In addition, the porous buffer structure of the ceramic silicone foam, combined with the interlocking design of protrusions and grooves, gives the composite current collector excellent buffering energy absorption and pressure equalization properties; the positive electrode can effectively absorb and dissipate internal or external impact and vibration energy, protecting the battery from mechanical stress damage; at the same time, the interlocking structure makes the stress distribution inside the positive electrode more uniform, reducing the risk of local deformation or damage caused by stress concentration, and greatly improving the battery's vibration and impact resistance and mechanical stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a schematic cross-sectional structure diagram of a positive electrode in one embodiment of the present invention;

[0040] Figure 2 Schematic diagram of the structure of a composite current collector of a positive electrode in one embodiment of the present invention;

[0041] Figure 3It is a structural exploded diagram of a composite current collector of a positive electrode in one embodiment of the present invention;

[0042] Figure 4 is a schematic cross-sectional structure diagram of a positive electrode in another embodiment of the present invention;

[0043] Figure 5 is a structural exploded view of a composite current collector of a positive electrode in another embodiment of the present invention;

[0044] Figure 6 This is a structural exploded view of a composite current collector of a positive electrode in yet another embodiment of the present invention.

[0045] In the figure: 1. composite current collector; 11. first aluminum foil layer; 12. second aluminum foil layer; 13. heat-resistant buffer material layer; 14. trapezoidal protrusion; 15. trapezoidal groove; 16. first temperature control material layer; 17. second temperature control material layer; 18. first modified thermally conductive silica gel; 19. second modified thermally conductive silica gel; 2. positive electrode active material coating; 3. pressure sensor. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] Please see attached Figures 1 to 3 The present embodiment provides a lithium-ion battery positive electrode with high thermal stability, comprising a composite current collector 1 and a positive electrode active material coating 2 coated on at least one surface of the composite current collector 1; the composite current collector 1 comprises a first aluminum foil layer 11, a second aluminum foil layer 12, and a heat-resistant buffer material layer 13 disposed between the first aluminum foil layer 11 and the second aluminum foil layer 12; wherein the composite current collector 1 is connected to a positive electrode tab;

[0048] The heat-resistant buffer material layer 13 is a ceramic silicone foam, which includes the following components in weight ratio: 30-40 parts of vinyl silicone oil, 10-20 parts of white carbon black, 20-50 parts of nano-ceramic powder, 0.1-1.0 parts of ethynyl cyclohexanol, 1-10 parts of hydrogen-containing silicone oil, 1-10 parts of hydroxy silicone oil, 0.1-1.0 parts of platinum catalyst, 10-20 parts of β-eucryptite, and 1-8 parts of halloysite nanotubes;

[0049] A plurality of trapezoidal protrusions 14 are provided on both side surfaces of the heat-resistant buffer material layer 13, and a plurality of trapezoidal grooves 15 are provided on the first aluminum foil layer 11 and the second aluminum foil layer 12 for engaging with the trapezoidal protrusions 14. The cross-sectional width of the trapezoidal protrusions 14 gradually increases from the inside to the outside, and the cross-sectional width of the trapezoidal grooves 15 gradually decreases from the inside to the outside. An interlocking structure is formed between the first aluminum foil layer 11 and the second aluminum foil layer 12 through the cooperation of the trapezoidal protrusions 14 and the trapezoidal grooves 15.

[0050] The ceramic silicone foam provided by the present invention not only has good elasticity under normal working conditions, but also can play a good buffering role for the composite current collector 1; and at high temperatures, the ceramic silicone foam can quickly form a foam ceramic body with a self-supporting structure, and can maintain a high degree of pore structure retention rate, thereby exerting excellent heat insulation and flame retardant effects, and it can withstand the burning of flames above 1300°C for a long time, can effectively block the transfer of fire and temperature, effectively inhibit the combustion reaction inside the battery, and hinder the spread and propagation of flames. For example, when the temperature inside the battery rises abnormally, the ceramic silicone foam plays a role in heat insulation and insulation, delays the accumulation and transfer of heat, buys precious time for the activation of battery safety protection measures, and effectively prevents or delays the occurrence of thermal runaway accidents; when the battery has abnormal conditions such as internal short circuit, overcharge, over discharge, etc., the ceramic silicone foam can prevent the chain reaction caused by the combustion of the electrolyte and reduce the risk of battery fire or explosion.

[0051] Among them, vinyl silicone oil is the main polymer matrix, which provides the required elasticity and flexibility in the foaming system; it can form a cross-linked structure by reacting with hydrogen-containing silicone oil, thereby enhancing the mechanical strength of the material. Silica is used as a reinforcing agent. Silica increases the tear strength and wear resistance of the composite material, while improving the compression resistance of silicone rubber, making the material less likely to deform even under higher loads. Nano-ceramic powder acts as a flame retardant. At high temperatures, nano-ceramic powder can promote the formation of a hard ceramic layer on the surface of the material, effectively preventing the further spread of flames and heat. Ethylene cyclohexanol is used as an inhibitor. This compound can control the rate of polymerization and avoid structural instability caused by too fast a reaction. Hydrogen-containing silicone oil acts as a cross-linking agent and reacts with vinyl silicone oil to form a silicone rubber network structure, enhancing the overall mechanical properties and thermal stability of the material. Hydroxyl silicone oil acts as a foaming agent in this system. Hydroxyl silicone oil decomposes and produces gas when heated to form a foam structure, thereby providing good cushioning properties and low density. Platinum catalyst catalyzes the addition cross-linking reaction of vinyl silicone oil and hydrogen silicone oil, improving the efficiency and uniformity of the reaction and ensuring the consistency of material performance. β-eucryptite, as a ceramic-forming agent, can promote the transformation of silicone rubber into ceramic body at high temperature, enhancing the high temperature resistance and structural stability of the material. Halloysite nanotubes, as a pore structure stabilizer, can form a uniformly distributed support structure in the material, enhance the stability of the pore structure, and avoid collapse under high temperature or mechanical pressure.

[0052] Therefore, through these specific components and their synergistic effects, the ceramicized silicone foam of the present invention not only maintains excellent elasticity and flexibility, but also significantly improves the performance of the material under extreme conditions. Moreover, at high temperatures, the material can quickly form a self-supporting foam ceramic body, greatly improving the heat insulation and flame retardancy. This foam ceramic body can maintain its structural integrity and flame retardancy when subjected to high temperatures or direct flame irradiation, unlike traditional silicone foams that may crack, deform, collapse or even pulverize under the same conditions, thereby losing its protective ability.

[0053] In one implementation of the present application, the height of the trapezoidal protrusion 14 is g, the depth of the trapezoidal groove 15 is h, the cross-sectional width of the trapezoidal protrusion 14 is w, the cross-sectional width of the trapezoidal groove 15 is d, the thickness of the heat-resistant buffer material layer 13 is G, and the thickness of the first aluminum foil layer 11 and the second aluminum foil layer 12 are both H, wherein g, h, w, d, G and H satisfy the relationship: g = h, w = d, 0.1G ≤ g ≤ 0.3G, 0.2H ≤ h ≤ 0.4H, H < G. When the above relationship is satisfied between the protrusion height, the groove depth, the protrusion width, the groove width, and the heat-resistant buffer layer and the aluminum foil layer thickness, it is possible to ensure sufficient mechanical interlocking strength and buffering performance while taking into account the lightweight and thin design of the composite current collector 1, while improving the mechanical reliability of the positive electrode, reducing the volume and weight of the positive electrode, and improving the energy density of the battery.

[0054] In one implementation of the present application, the height g of the trapezoidal protrusion 14 is 1.6 to 6.4 μm, the depth h of the trapezoidal groove 15 is 1.6 to 6.4 μm, the cross-sectional width w of the trapezoidal protrusion 14 is 50 to 500 μm, the cross-sectional width d of the trapezoidal groove 15 is 50 to 500 μm, the thickness G of the heat-resistant buffer material layer 13 is 16 to 21.4 μm, and the thickness H of the first aluminum foil layer 11 and the second aluminum foil layer 12 are both 8 to 16 μm.

[0055] In one implementation of the present application, the sum of the forward projection areas of all the trapezoidal protrusions 14 on one side of the heat-resistant buffer material layer 13 is S1, and the forward projection area of ​​the heat-resistant buffer material layer 13 is S; wherein S1 and S satisfy the relationship: 0.5S≤S1≤0.7S. This can provide a sufficiently large interlocking contact area to ensure the reliability of the interface bonding, and can also avoid the excessively large projection area that leads to insufficient buffer deformation space of the heat-resistant buffer layer, while ensuring the interlocking strength and maintaining the good buffering energy absorption performance of the composite current collector 1.

[0056] In one implementation of the present application, the preparation method of ceramic silicone foam is as follows:

[0057] Step S1, adding vinyl silicone oil, white carbon black, nano ceramic powder and β-eucryptite into a kneader, kneading into a mass at 130-150° C., cooling, and obtaining a base rubber;

[0058] Step S2, stirring and mixing the hydroxy silicone oil and the halloysite nanotubes to obtain a foaming mixture; wherein the stirring and mixing speed is 23000-26000 r / min, and the mixing time is 10-25 s;

[0059] Step S3, adding the foaming mixture, ethynyl cyclohexanol, hydrogen-containing silicone oil, and platinum catalyst into the base rubber, mixing evenly, to obtain a rubber material;

[0060] Step S4, vulcanizing and foaming the rubber material by a molding process to obtain ceramic silicone foam.

[0061] Among them, the ceramic silicone foam prepared in this application has the following advantages:

[0062] 1) Excellent mechanical properties and elasticity: Due to the cross-linked structure of vinyl silicone oil and hydrogen silicone oil, plus the reinforcement effect of white carbon black, the silicone foam of the present invention has good elasticity and resistance to mechanical stress, so that it can maintain its original shape and function after long-term use or repeated compression.

[0063] 2) Highly efficient flame retardant and heat insulation capabilities: The addition of nano-ceramic powder and β-eucryptite enables the material to quickly form a protective ceramic layer when exposed to high temperature or flame. This layer of structure can not only effectively isolate the flame, but also reduce heat transfer and protect the internal structure from damage.

[0064] 3) Highly stable foam structure: The foam structure is formed by the gas generated by the decomposition of hydroxy silicone oil, and its stability is enhanced by halloysite nanotubes, so that the foam is not easy to collapse even at high temperatures and maintains a high pore structure retention rate.

[0065] 4) Excellent heat resistance: The controlled polymerization rate of ethynyl cyclohexanol and the efficient catalytic effect of platinum catalyst ensure the uniform formation and stability of the silicone rubber network structure, thereby maintaining performance in extremely high temperature environments.

[0066] In one implementation according to the present application, Figure 4 As shown, one or more pressure sensors 3 are embedded in the heat-resistant buffer material layer 13 to monitor the pressure of each area of ​​the positive electrode in real time. By embedding the pressure sensor 3 in the heat-resistant buffer material layer 13, real-time monitoring and mapping of the pressure distribution in different areas of the positive electrode can be achieved, local stress anomalies can be discovered and located in time, data support can be provided for battery safety protection and fault diagnosis, and the intelligence level and reliability of the battery management system can be greatly improved.

[0067] In one implementation according to the present application, Figure 5 As shown, a first temperature control material layer 16 is further arranged between the first aluminum foil layer 11 and the heat-resistant buffer material layer 13, and a second temperature control material layer 17 is further arranged between the second aluminum foil layer 12 and the heat-resistant buffer material layer 13; the shapes of the first temperature control material layer 16 and the second temperature control material layer 17 are both adapted to the shape of the surface of the trapezoidal protrusion 14 of the heat-resistant buffer material layer 13; the phase change temperatures of the first temperature control material layer 16 and the second temperature control material layer 17 are both 57-62°C.

[0068] In one implementation of the present application, the first temperature control material layer 16 and the second temperature control material layer 17 both include the following compositions in weight proportions: 45-55 parts of octadecanoic acid glycerol, 20-25 parts of palmitic acid, 10-15 parts of polyethylene glycol 4000, 3-5 parts of carbon nanotubes, 2-3 parts of boron nitride nanosheets, 1-2 parts of expanded graphite, and 0.5-1 parts of nano-magnesium oxide.

[0069] Among them, octadecanoic acid glycerol and palmitic acid are used as the main phase change materials to provide high-temperature phase change capability, and the mixed use can adjust the phase change temperature range; polyethylene glycol 4000 adjusts the phase change temperature, increases the heat capacity of the material, and improves the heat storage capacity; carbon nanotubes significantly improve the thermal conductivity of the material and improve the rapid distribution of heat in the phase change material; boron nitride nanosheets further enhance heat conduction and improve the thermal stability of the material; expanded graphite increases the specific surface area of ​​the material, improves the heat exchange efficiency, and improves the thermal conductivity and flame retardancy of the material; nano magnesium oxide enhances the thermal stability and flame retardancy of the material and improves the structural integrity of the material at high temperatures. The phase change temperature of the temperature control material layer is 57℃~62℃. When it reaches the phase change temperature, it can quickly absorb heat, effectively adjust the battery temperature, and improve the heat and high temperature resistance of the battery.

[0070] In one implementation of the present application, the preparation method of the first temperature control material layer 16 or the second temperature control material layer 17 is as follows:

[0071] (1) Stearyl glycerol and palmitic acid are mixed according to a ratio, heated to melt in an oil bath at 85-95° C., and stirred evenly;

[0072] (2) adding polyethylene glycol 4000 to the molten mixture of step (1) and continuing to stir until it is completely dissolved;

[0073] (3) dispersing carbon nanotubes and boron nitride nanosheets in N-methylpyrrolidone and ultrasonically treating for 30 minutes;

[0074] (4) slowly adding the suspension of step (3) into the molten mixture of step (2), and stirring at high speed for 45 minutes;

[0075] (5) adding expanded graphite and nano magnesium oxide, and continuing high-speed stirring for 20 minutes to obtain a temperature control material layer slurry;

[0076] (6) The temperature control material layer slurry is sprayed onto the outer surface of the heat-resistant buffer material layer 13 and dried to obtain the first temperature control material layer 16 or the second temperature control material layer 17 of the desired shape and thickness.

[0077] In one implementation according to the present application, Figure 6As shown, a first modified thermally conductive silicone 18 is further arranged between the first aluminum foil layer 11 and the heat-resistant buffer material layer 13, and a second modified thermally conductive silicone 19 is further arranged between the second aluminum foil layer 12 and the heat-resistant buffer material layer 13; the shapes of the first modified thermally conductive silicone 18 and the second modified thermally conductive silicone 19 are both adapted to the shape of the surface of the trapezoidal protrusion 14 of the heat-resistant buffer material layer 13; the porosity of the first modified thermally conductive silicone 18 and the second modified thermally conductive silicone 19 are both 65% to 85%; the first aluminum foil layer 11 and the heat-resistant buffer material layer 13 are bonded and connected by the first modified thermally conductive silicone 18; the second aluminum foil layer 12 and the heat-resistant buffer material layer 13 are bonded and connected by the second modified thermally conductive silicone 19.

[0078] A modified thermally conductive silica gel with a porosity of 65% to 85% is embedded between the first and second aluminum foil layers 12 and the heat-resistant buffer material layer 13, which not only has good thermal conductivity, but also has a good energy absorption and buffering effect, further preventing stress concentration from causing deformation, fracture or damage of the composite current collector 1, thereby significantly improving the mechanical stability and reliability of the battery; in addition, the modified thermally conductive silica gel can also bond and fix the first and second aluminum foil layers 12 and the heat-resistant buffer material layer 13, and its thermal conductivity can reach 6-10W / (m·k), which can accelerate the heat conduction and dissipation of the battery at high temperature and avoid local overheating.

[0079] The preparation method of the modified thermally conductive silica gel is as follows:

[0080] 1) Boron nitride and KH570 silane coupling agent are dispersed in 100 ml of aqueous solution at a mass ratio of 10:1, and the concentrations are 40 mg / ml and 4 mg / ml respectively. The mixed dispersion is placed in a water bath ultrasound at 0°C for 40 minutes, then centrifuged to remove excess solvent, and freeze-dried to obtain modified boron nitride powder.

[0081] 2) The modified boron nitride powder and graphene were dispersed in a mixed solvent of alcohol and water in a mass ratio of 1:5, with concentrations of 1.2 mg / ml and 6 mg / ml, respectively. 2 mg / ml carbon nanotubes were added at the same time, and ultrasonic cell crusher was used for 10 min at a power of 1200 W to obtain graphene slurry.

[0082] 3) The polyurethane sponge foam was immersed in a 2 mol / L NaOH solution, treated in 40°C warm water for 3.5 h, and then placed in a 5 mg / ml anilinemethyltriethoxysilane aqueous solution and immersed for 24 h to obtain a modified polyurethane porous foam.

[0083] 4) The modified polyurethane porous foam structure was immersed in the uniform graphene slurry prepared above, and ultrasonicated in a water bath for 20 minutes at 0°C. It was dried at 60°C, and then heated from 60°C to 200°C at a heating rate of 15°C per minute, and then heated from 200°C to 380°C at a heating rate of 3°C per minute for 30 minutes, and the porous material was removed to obtain a three-dimensional porous graphene-boron nitride composite material.

[0084] 5) The three-dimensional porous graphene-boron nitride composite material obtained above was immersed in silica gel (Wacker SEMICOSIL9212), evacuated to remove bubbles, sprayed on the outer surface of the heat-resistant buffer material layer 13, placed in a 120° C. oven, and cured for 15 minutes to obtain modified thermally conductive silica gel.

[0085] In addition, the present invention also provides a method for preparing the lithium ion battery positive electrode with high thermal stability, comprising the following steps:

[0086] 1) preparing a ceramic silicone foam rubber material according to the above-mentioned ceramic silicone foam preparation method;

[0087] 2) vulcanizing and foaming the ceramic silicone foam rubber material through a molding process to obtain a heat-resistant buffer material layer 13 with trapezoidal protrusions 14 on both sides of the surface; wherein the molding process is to pour the ceramic silicone foam rubber material into a mold with trapezoidal grooves 15 on both sides;

[0088] 3) Spraying an aluminum foil layer of the same thickness on the surface of the heat-resistant buffer material layer 13 by magnetron sputtering, and drying to obtain a composite current collector 1;

[0089] 4) The positive electrode active material coating 2 slurry is coated on at least one surface of the composite current collector 1 and dried to obtain the positive electrode of the lithium ion battery.

[0090] The positive electrode active material coating 2 generally includes a positive electrode active material, a binder and a conductive agent, wherein the types and amounts of the positive electrode active material, the binder and the conductive agent in the positive electrode active material coating 2, as well as the thickness of the positive electrode active material coating 2, etc. can all be conventionally selected in the art. For example, as some specific examples, the positive electrode active material in the positive electrode active material coating 2 may include but is not limited to lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, etc., the binder may include but is not limited to polyvinylidene fluoride, styrene butadiene rubber, polyvinyl alcohol, polyurethane, etc., and the conductive agent may include but is not limited to carbon nanofibers, carbon nanotubes, conductive carbon black, graphene, etc. The surface density of the positive electrode active material coating 2 may be 10 to 12 mg / cm2.

[0091] The embodiments of the present application are described in detail below. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. The reagents or instruments used without indicating the manufacturer are all conventional products that can be obtained commercially.

[0092] Example 1

[0093] Preparation of positive electrode:

[0094] The positive electrode of the lithium-ion battery of this embodiment includes a composite current collector 1 and a positive electrode active material coating 2 coated on a surface of the composite current collector 1; the composite current collector 1 includes a first aluminum foil layer 11, a second aluminum foil layer 12 and a heat-resistant buffer material layer 13 arranged between the first aluminum foil layer 11 and the second aluminum foil layer 12.

[0095] Among them, the heat-resistant buffer material layer 13 is ceramic silicone foam, and the ceramic silicone foam includes the following components in weight proportion: 35 parts of vinyl silicone oil, 15 parts of white carbon black, 30 parts of nano-ceramic powder, 0.5 parts of ethynyl cyclohexanol, 5 parts of hydrogenated silicone oil, 5 parts of hydroxyl silicone oil, 0.5 parts of platinum catalyst, 15 parts of β-eucryptite, and 4 parts of halloysite nanotubes.

[0096] Among them, multiple trapezoidal protrusions 14 are provided on both side surfaces of the heat-resistant buffer material layer 13, and multiple trapezoidal grooves 15 embedded with the trapezoidal protrusions 14 are provided on the first aluminum foil layer 11 and the second aluminum foil layer 12. The cross-sectional width of the trapezoidal protrusions 14 gradually increases from the inside to the outside, and the cross-sectional width of the trapezoidal grooves 15 gradually decreases from the inside to the outside. An interlocking structure is formed between the first aluminum foil layer 11 and the second aluminum foil layer 12 through the cooperation of the trapezoidal protrusions 14 and the trapezoidal grooves 15.

[0097] Among them, the height of the trapezoidal protrusion 14 is g, the depth of the trapezoidal groove 15 is h, the cross-sectional width of the trapezoidal protrusion 14 is w, the cross-sectional width of the trapezoidal groove 15 is d, the thickness of the heat-resistant buffer material layer 13 is G, and the thickness of the first aluminum foil layer 11 and the second aluminum foil layer 12 are both H, wherein g, h, w, d, G and H satisfy the relationship: g=h, w=d, 0.1G≤g≤0.3G, 0.2H≤h≤0.4H, H<G; the sum of the forward projection areas of all the trapezoidal protrusions 14 on the surface of one side of the heat-resistant buffer material layer 13 is S1, and the forward projection area of ​​the heat-resistant buffer material layer 13 is S; wherein S1 and S satisfy the relationship: 0.5S≤S1≤0.7S.

[0098] Specifically, in this embodiment, the height g of the trapezoidal protrusion 14 is 3μm, the depth h of the trapezoidal groove 15 is 3μm, the cross-sectional width of the trapezoidal protrusion 14 is 100μm on the short side and 300μm on the long side, the cross-sectional width of the trapezoidal groove 15 is 100μm on the short side and 300μm on the long side, the thickness G of the heat-resistant buffer material layer 13 is 15μm, the thickness H of the first aluminum foil layer 11 and the second aluminum foil layer 12 are both 10μm; and S1 / S=0.6.

[0099] The preparation method of the positive electrode sheet is as follows:

[0100] 1) preparing a ceramic silicone foam rubber material according to the above-mentioned ceramic silicone foam preparation method;

[0101] 2) vulcanizing and foaming the ceramic silicone foam rubber material through a molding process to obtain a heat-resistant buffer material layer 13 having trapezoidal protrusions 14 on both sides of the surface;

[0102] 3) Spraying an aluminum foil layer of the same thickness on the surface of the heat-resistant buffer material layer 13 by magnetron sputtering, and drying to obtain a composite current collector 1;

[0103] 4) The positive electrode active material lithium nickel cobalt manganese oxide, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride are dispersed in a solvent NMP (N-methylpyrrolidone) in a mass ratio of 95:2:3, stirred evenly to obtain a positive electrode active material coating 2 slurry, coated on a surface of the composite current collector 1, and dried to obtain the lithium ion battery positive electrode sheet.

[0104] Preparation of negative electrode sheet:

[0105] Hard carbon, carbon black and aqueous carboxymethyl cellulose are dispersed in water at a mass ratio of 95:2:3 to form a uniformly dispersed slurry, the slurry is evenly coated on the surface of the current collector copper foil, and then transferred to a vacuum drying oven for complete drying to obtain a negative electrode sheet.

[0106] Preparation of electrolyte:

[0107] Ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 1:1, and then FEC (fluoroethylene carbonate) is added at a volume percentage of 5%. Then, the fully dried lithium salt LiPF6 is dissolved in a mixed organic solvent at a concentration ratio of 1 mol / L to prepare an electrolyte.

[0108] Preparation of isolation film: A PET / PP composite film with a thickness of 20 microns was selected.

[0109] Preparation of lithium-ion batteries:

[0110] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and the electrolyte is added, and a lithium-ion battery is assembled according to conventional processes.

[0111] Example 2

[0112] Different from Example 1, a first temperature control material layer 16 is further arranged between the first aluminum foil layer 11 and the heat-resistant buffer material layer 13 in the composite current collector 1 of the positive electrode of this embodiment, and a second temperature control material layer 17 is further arranged between the second aluminum foil layer 12 and the heat-resistant buffer material layer 13; the shapes of the first temperature control material layer 16 and the second temperature control material layer 17 are both adapted to the shape of the surface of the trapezoidal protrusion 14 of the heat-resistant buffer material layer 13; the phase change temperatures of the first temperature control material layer 16 and the second temperature control material layer 17 are both 57-62°C.

[0113] The first temperature control material layer 16 and the second temperature control material layer 17 both include the following compositions in weight proportions: 50 parts of octadecyl glycerol, 22 parts of palmitic acid, 13 parts of polyethylene glycol 4000, 4 parts of carbon nanotubes, 2 parts of boron nitride nanosheets, 1 part of expanded graphite, and 1 part of nano magnesium oxide.

[0114] The preparation method of the first temperature control material layer 16 or the second temperature control material layer 17 is as follows:

[0115] (1) Stearyl glycerol and palmitic acid are mixed according to a ratio, heated to melt in an oil bath at 85-95° C., and stirred evenly;

[0116] (2) adding polyethylene glycol 4000 to the molten mixture of step (1) and continuing to stir until it is completely dissolved;

[0117] (3) dispersing carbon nanotubes and boron nitride nanosheets in N-methylpyrrolidone and ultrasonically treating for 30 minutes;

[0118] (4) slowly adding the suspension of step (3) into the molten mixture of step (2), and stirring at high speed for 45 minutes;

[0119] (5) adding expanded graphite and nano magnesium oxide, and continuing high-speed stirring for 20 minutes to obtain a temperature control material layer slurry;

[0120] (6) The temperature control material layer slurry is sprayed onto the outer surface of the heat-resistant buffer material layer 13 and dried to obtain the first temperature control material layer 16 or the second temperature control material layer 17 of the desired shape and thickness.

[0121] The rest is the same as in Example 1 and will not be described again here.

[0122] Example 3

[0123] Different from Example 1, in the composite current collector 1 of the positive electrode of this embodiment, a first modified thermally conductive silicone 18 is further arranged between the first aluminum foil layer 11 and the heat-resistant buffer material layer 13, and a second modified thermally conductive silicone 19 is further arranged between the second aluminum foil layer 12 and the heat-resistant buffer material layer 13; the shapes of the first modified thermally conductive silicone 18 and the second modified thermally conductive silicone 19 are both adapted to the shape of the surface of the trapezoidal protrusion 14 of the heat-resistant buffer material layer 13; the porosity of the first modified thermally conductive silicone 18 and the second modified thermally conductive silicone 19 are both 75%; the first aluminum foil layer 11 and the heat-resistant buffer material layer 13 are bonded and connected by the first modified thermally conductive silicone 18; the second aluminum foil layer 12 and the heat-resistant buffer material layer 13 are bonded and connected by the second modified thermally conductive silicone 19.

[0124] The preparation method of the modified thermally conductive silica gel is as follows:

[0125] 1) Boron nitride and KH570 silane coupling agent are dispersed in 100 ml of aqueous solution at a mass ratio of 10:1, and the concentrations are 40 mg / ml and 4 mg / ml respectively. The mixed dispersion is placed in a water bath ultrasound at 0°C for 40 minutes, then centrifuged to remove excess solvent, and freeze-dried to obtain modified boron nitride powder.

[0126] 2) The modified boron nitride powder and graphene were dispersed in a mixed solvent of alcohol and water in a mass ratio of 1:5, with concentrations of 1.2 mg / ml and 6 mg / ml, respectively. 2 mg / ml carbon nanotubes were added at the same time, and ultrasonic cell crusher was used for 10 min at a power of 1200 W to obtain graphene slurry.

[0127] 3) The polyurethane sponge foam was immersed in a 2 mol / L NaOH solution, treated in 40°C warm water for 3.5 h, and then placed in a 5 mg / ml anilinemethyltriethoxysilane aqueous solution and immersed for 24 h to obtain a modified polyurethane porous foam.

[0128] 4) The modified polyurethane porous foam structure was immersed in the uniform graphene slurry prepared above, and ultrasonicated in a water bath for 20 minutes at 0°C. It was dried at 60°C, and then heated from 60°C to 200°C at a heating rate of 15°C per minute, and then heated from 200°C to 380°C at a heating rate of 3°C per minute for 30 minutes, and the porous material was removed to obtain a three-dimensional porous graphene-boron nitride composite material.

[0129] 5) The three-dimensional porous graphene-boron nitride composite material obtained above was immersed in silica gel (Wacker SEMICOSIL9212), evacuated to remove bubbles, sprayed on the outer surface of the heat-resistant buffer material layer 13, placed in a 120° C. oven, and cured for 15 minutes to obtain modified thermally conductive silica gel.

[0130] The rest is the same as in Example 1 and will not be described again here.

[0131] Comparative Example 1

[0132] Different from Example 1, the composite current collector 1 of the positive electrode in this comparative example adopts a three-layer composite current collector 1 of aluminum foil-PET-aluminum foil.

[0133] The rest is the same as in Example 1 and will not be described again here.

[0134] The following electrochemical performance tests were performed on the positive electrode sheets and lithium-ion batteries of the above-mentioned embodiments and comparative examples, respectively. The test results are shown in Table 1.

[0135] 1) Ductility test: Under the same pressure (20 tons), the positive electrode sheets prepared in the embodiment and the comparative example were rolled to observe whether there was brittle fracture or cracking on the surface of the electrode sheet. If any of the above phenomena occurred, it means that the ductility is poor.

[0136] 2) Needle penetration test: Use a 10mm diameter steel needle at a speed of 3mm / s to pierce the battery and stay inside the battery for 10 minutes to observe whether there is any reaction, sparks or fire.

[0137] 3) High temperature cycle test: The cycle capacity retention rate (%) of the above lithium-ion battery during 300 charge and discharge cycles at high temperature (60°C) is tested at a charge and discharge voltage of 2.5V to 3.65V and a charge and discharge rate of 1C / 1C. That is, the discharge capacity of the lithium-ion battery in the first cycle at the corresponding temperature is set to 1, and the ratio of the discharge capacity during continuous charge and discharge cycles under the same conditions to the discharge capacity of the first cycle is the capacity retention rate (%) under the number of cycles.

[0138] Table 1

[0139]

[0140] It can be seen from the test results in Table 1 that, compared with the positive electrode prepared by the existing composite current collector, the positive electrode of the present invention has better ductility, can effectively prevent the positive electrode from brittle fracture or cracking, and the lithium ion battery prepared using the positive electrode of the present invention has better thermal stability and safety performance.

[0141] By comparing Example 1 and Example 2, it can be seen that when a temperature control material layer is further provided inside the composite current collector of the positive electrode, the heat resistance and high temperature resistance of the battery can be further improved, indicating that the temperature control material layer can accelerate the heat conduction and dissipation of the battery at high temperature, avoid local overheating, and thus improve the battery cycle performance.

[0142] By comparing Example 1 and Example 3, it can be seen that when modified thermally conductive silicone is further provided inside the composite current collector of the positive electrode, it helps to further improve the high-temperature cycle performance of the battery, which means that the modified thermally conductive silicone not only has a good energy absorption and buffering effect, but can also adjust the stress uniformly distributed on the surface of the pole piece, and can accelerate heat dispersion, thereby improving the high-temperature resistance of the battery.

[0143] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0144] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A lithium ion battery positive electrode with high thermal stability, characterized in that: It comprises a composite current collector and a positive electrode active material coating coated on at least one surface of the composite current collector; the composite current collector comprises a first aluminum foil layer, a second aluminum foil layer and a heat-resistant buffer material layer arranged between the first aluminum foil layer and the second aluminum foil layer; The heat-resistant buffer material layer is a ceramic silicone foam, which comprises the following components in weight proportion: 30-40 parts of vinyl silicone oil, 10-20 parts of white carbon black, 20-50 parts of nano-ceramic powder, 0.1-1.0 parts of ethynyl cyclohexanol, 1-10 parts of hydrogen-containing silicone oil, 1-10 parts of hydroxy silicone oil, 0.1-1.0 parts of platinum catalyst, 10-20 parts of β-eucryptite, and 1-8 parts of halloysite nanotubes; A plurality of trapezoidal protrusions are provided on both side surfaces of the heat-resistant buffer material layer, and a plurality of trapezoidal grooves are provided on the first aluminum foil layer and the second aluminum foil layer for engaging with the trapezoidal protrusions. The cross-sectional width of the trapezoidal protrusions gradually increases from the inside to the outside, and the cross-sectional width of the trapezoidal grooves gradually decreases from the inside to the outside. An interlocking structure is formed between the first aluminum foil layer and the second aluminum foil layer through the cooperation of the trapezoidal protrusions and the trapezoidal grooves.

2. The lithium-ion battery positive electrode with high thermal stability according to claim 1, characterized in that: The height of the trapezoidal protrusion is g, the depth of the trapezoidal groove is h, the cross-sectional width of the trapezoidal protrusion is w, the cross-sectional width of the trapezoidal groove is d, the thickness of the heat-resistant buffer material layer is G, and the thickness of the first aluminum foil layer and the second aluminum foil layer are both H, wherein g, h, w, d, G and H satisfy the relationship: g=h, w=d, 0.1G≤g≤0.3G, 0.2H≤h≤0.4H, H<G.

3. The lithium ion battery positive electrode with high thermal stability according to claim 1 or 2, characterized in that: The sum of the forward projection areas of all the trapezoidal protrusions on the surface of one side of the heat-resistant buffer material layer is S1, and the forward projection area of ​​the heat-resistant buffer material layer is S; wherein S1 and S satisfy the relationship: 0.5S≤S1≤0.7S.

4. The lithium-ion battery positive electrode with high thermal stability according to claim 1, characterized in that: The preparation method of the ceramic silica gel foam is as follows: Step S1, adding vinyl silicone oil, white carbon black, nano ceramic powder and β-eucryptite into a kneader, kneading into a mass at 130-150° C., cooling, and obtaining a base rubber; Step S2, stirring and mixing the hydroxy silicone oil and the halloysite nanotubes to obtain a foaming mixture; wherein the stirring and mixing speed is 23000-26000 r / min, and the mixing time is 10-25 s; Step S3, adding the foaming mixture, ethynyl cyclohexanol, hydrogen-containing silicone oil, and platinum catalyst into the base rubber, mixing evenly, to obtain a rubber material; Step S4, vulcanizing and foaming the rubber material by a molding process to obtain the ceramicized silicone foam.

5. The lithium-ion battery positive electrode with high thermal stability according to claim 1, characterized in that: One or more pressure sensors are embedded in the heat-resistant buffer material layer to monitor the pressure borne by various regions of the positive electrode in real time.

6. The lithium-ion battery positive electrode with high thermal stability according to claim 1, characterized in that: A first temperature control material layer is also arranged between the first aluminum foil layer and the heat-resistant buffer material layer, and a second temperature control material layer is also arranged between the second aluminum foil layer and the heat-resistant buffer material layer; the shapes of the first temperature control material layer and the second temperature control material layer are both adapted to the shape of the trapezoidal raised surface of the heat-resistant buffer material layer; the phase change temperatures of the first temperature control material layer and the second temperature control material layer are both 57-62°C.

7. The lithium-ion battery positive electrode with high thermal stability according to claim 6, characterized in that: The first temperature control material layer and the second temperature control material layer both include the following components in weight proportion: 45-55 parts of octadecanoic acid glycerol, 20-25 parts of palmitic acid, 10-15 parts of polyethylene glycol 4000, 3-5 parts of carbon nanotubes, 2-3 parts of boron nitride nanosheets, 1-2 parts of expanded graphite, and 0.5-1 parts of nano magnesium oxide.

8. The lithium-ion battery positive electrode with high thermal stability according to claim 7, characterized in that: The preparation method of the first temperature control material layer or the second temperature control material layer is as follows: (1) Stearyl glycerol and palmitic acid are mixed according to a ratio, heated to melt in an oil bath at 85-95° C., and stirred evenly; (2) adding polyethylene glycol 4000 to the molten mixture of step (1) and continuing to stir until it is completely dissolved; (3) dispersing carbon nanotubes and boron nitride nanosheets in N-methylpyrrolidone and ultrasonically treating for 30 minutes; (4) slowly adding the suspension of step (3) into the molten mixture of step (2), and stirring at high speed for 45 minutes; (5) adding expanded graphite and nano magnesium oxide, and continuing high-speed stirring for 20 minutes to obtain a temperature control material layer slurry; (6) Spraying the temperature control material layer slurry onto the outer surface of the heat-resistant buffer material layer and drying it to obtain a first temperature control material layer or a second temperature control material layer of a desired shape and thickness.

9. The lithium-ion battery positive electrode with high thermal stability according to claim 1, characterized in that: A first modified thermally conductive silicone is also arranged between the first aluminum foil layer and the heat-resistant buffer material layer, and a second modified thermally conductive silicone is also arranged between the second aluminum foil layer and the heat-resistant buffer material layer; the shapes of the first modified thermally conductive silicone and the second modified thermally conductive silicone are both adapted to the shape of the trapezoidal raised surface of the heat-resistant buffer material layer; the porosity of the first modified thermally conductive silicone and the second modified thermally conductive silicone are both 65% to 85%; the first aluminum foil layer and the heat-resistant buffer material layer are bonded and connected by the first modified thermally conductive silicone; the second aluminum foil layer and the heat-resistant buffer material layer are bonded and connected by the second modified thermally conductive silicone.

10. A method for preparing a lithium-ion battery positive electrode with high thermal stability according to any one of claims 1 to 9, characterized in that: The following steps are involved: 1) preparing a ceramic silicone foam rubber material according to the preparation method of the ceramic silicone foam according to claim 4; 2) vulcanizing and foaming the ceramic silicone foam rubber material through a molding process to obtain a heat-resistant buffer material layer with trapezoidal protrusions on both sides of the surface; 3) spraying an aluminum foil layer of the same thickness on the surface of the heat-resistant buffer material layer by magnetron sputtering, and drying to obtain a composite current collector; 4) coating the positive electrode active material coating slurry on at least one surface of the composite current collector and drying it to obtain the positive electrode of the lithium ion battery.

Images