Secondary battery and electronic equipment

Abstract

The invention relates to a secondary battery and electronic equipment, and belongs to the technical field of electrochemistry. The secondary battery comprises an electrode assembly and an aluminum-plastic film, wherein the aluminum-plastic film comprises a base film and a coating; the base film is provided with a first surface and a second surface which are oppositely arranged in the thickness direction of the base film, and the first surface of the base film faces the electrode assembly; the coating is arranged on the second surface of the base membrane, and the coating comprises porous hydrogel dry glue and a phase change material. According to the secondary battery, the temperature of the secondary battery in the rapid charging and discharging process can be effectively reduced, and meanwhile, excellent cycle performance is kept.

Description

Technical Field

[0001] This application relates to the field of electrochemical technologies, and particularly to a secondary battery and an electronic device. Background Art

[0002] Aluminum plastic film is a commonly used packaging material for soft-pack batteries or blade batteries, mainly used to isolate the external environment to protect the internal electrodes. For example, the aluminum plastic film used for soft-pack batteries is structurally divided into an outer nylon layer, an intermediate aluminum foil layer, and an inner polypropylene film layer; among them, the nylon layer can improve the stamping formability of the aluminum foil layer and prevent the aluminum foil from oxidizing, and the aluminum foil layer mainly blocks the permeation of water vapor and oxygen while endowing the aluminum plastic film with good cold stamping formability, and the polypropylene film layer mainly has a packaging function to make the aluminum plastic film have a sealing property. However, this type of aluminum plastic film is difficult to meet the requirements of high-energy-density batteries, and it is easy to cause the temperature of the battery monomer to rise rapidly during rapid charging or discharging, resulting in heat accumulation and spreading to other battery monomers, which will not only increase the risk of battery thermal runaway, but also seriously affect the cycle performance of the battery. Summary of the Invention

[0003] The purpose of this application is to overcome the deficiencies of the prior art and provide a secondary battery and an electronic device.

[0004] To achieve the above purpose, the technical solution adopted in this application is as follows:

[0005] A first aspect of this application provides a secondary battery, including an electrode assembly and an aluminum plastic film, and the aluminum plastic film includes a base film and a coating; the base film has a first surface and a second surface that are oppositely arranged in its thickness direction, and the first surface of the base film faces the electrode assembly; the coating is provided on the second surface of the base film, and the coating includes a porous hydrogel dry gel and a phase change material.

[0006] For the secondary battery provided in this application, the outer surface of the internal electrode assembly is wrapped by an aluminum plastic film with a coating. The coating of the aluminum plastic film includes a hydrogel dry gel skeleton with a porous structure. This hydrogel dry gel skeleton has a large specific surface area and certain water absorption capacity, can absorb moisture in the external environment to block moisture permeation, and can also evaporate the absorbed moisture during the battery heating process to achieve good cooling; moreover, a phase change material is uniformly dispersed in the hydrogel dry gel skeleton. The phase change material can not only absorb the heat inside the battery to lower the battery temperature, but also absorb the heat of adjacent batteries to block the heat diffusion and transfer to reduce the risk of thermal runaway, thereby significantly improving the cycle performance of the battery.

[0007] In some embodiments of the present application, the thickness of the aluminum-plastic film is 60 μm to 120 μm. By controlling the thickness of the aluminum-plastic film within the above range, the thickness of the aluminum-plastic film with a coating can be made equivalent to that of a conventional aluminum-plastic film (without a coating), which can not only maintain the basic functions of the aluminum-plastic film but also endow it with good heat absorption function, thereby effectively reducing the heat transfer rate and improving the cycle performance of the battery.

[0008] In some embodiments of the present application, the base film includes a stacked polypropylene layer and aluminum foil layer, and the coating is provided on the surface of the aluminum foil layer. The coating is directly provided on the surface of the aluminum foil layer, which can better absorb the heat from the inside of the battery, more effectively reduce the temperature of the battery, and improve the heat absorption efficiency; at the same time, it is also beneficial to reduce the overall thickness of the aluminum-plastic film and increase the energy density of the battery.

[0009] In some embodiments of the present application, the ratio of the thickness of the coating to the thickness of the base film is 0.2 to 0.4. By controlling the ratio of the thickness of the coating to the thickness of the base film within the above range, the aluminum-plastic film can better balance mechanical strength and heat absorption performance.

[0010] In some embodiments of the present application, the base film includes a polypropylene layer, an aluminum foil layer, and a protective layer stacked in sequence, and the coating is provided on the surface of the protective layer; the protective layer includes a nylon layer and / or a PET layer.

[0011] In some embodiments of the present application, the ratio of the thickness of the coating to the thickness of the base film is 0.1 to 0.4. By controlling the ratio of the thickness of the coating to the thickness of the base film within the above range, the aluminum-plastic film can better balance mechanical strength and heat absorption performance.

[0012] In some embodiments of the present application, the surface roughness Ra of the protective layer is 0.4 μm to 6.3 μm. By controlling the surface roughness of the protective layer within the above range, a large number of pits or micropores can be formed on the surface of the protective layer, and the porous hydrogel dry glue in the coating can partially fill these pits or micropores to form a "mortise and tenon" structure, thereby enhancing the adhesion of the coating and improving the bonding performance between the coating and the base film, effectively preventing the coating from peeling off.

[0013] In some embodiments of the present application, the porous hydrogel dry glue includes at least one of polyethylene glycol, polyacrylic acid, polyvinyl alcohol, polylactic acid-glycolic acid, polyacrylamide, collagen, chitosan, alginate, agarose, and gelatin. Using the above materials as the porous hydrogel dry glue can better improve the compatibility between the coating and the base film, and thus improve the bonding performance between the coating and the base film.

[0014] In some embodiments of the present application, the phase change material includes at least one of paraffin-based phase change materials, fatty acid-based phase change materials, polyol-based phase change materials, hydrated salts, metal alloys, microcapsule phase change materials, and graphene composite phase change materials. Using the above materials as the phase change material can better improve the compatibility between the coating and the base film, and thus improve the adhesion performance between the coating and the base film.

[0015] In some embodiments of the present application, the coating further includes inorganic materials, and the inorganic materials include at least one of silicon oxide, zirconium oxide, aluminum oxide, niobium oxide, titanium oxide, and boehmite. When the coating contains inorganic materials, on the one hand, the inorganic materials can be used as reinforcing fillers for the porous hydrogel xerogel to improve the mechanical strength of the porous hydrogel xerogel. On the other hand, the inorganic materials dispersed in the porous hydrogel xerogel can also play a role in heat dispersion or heat transfer, quickly transferring heat to the adjacent phase change material, enabling the phase change material to absorb heat more quickly and fully, and thus better reducing the temperature of the battery.

[0016] In some embodiments of the present application, the elongation at break of the aluminum-plastic film is ≥100%. By keeping the elongation at break of the aluminum-plastic film greater than or equal to 100%, it not only has good processing performance during processing such as stamping and hemming, but also has good tensile and puncture resistance properties to better ensure the reliability and stability of the battery in actual applications.

[0017] The second aspect of the present application provides an electronic device, which includes the secondary battery provided by the first aspect of the present application.

[0018] Compared with the prior art, the beneficial effects of the present application are as follows:

[0019] For the secondary battery provided by the present application, the outer surface of the internal electrode assembly is wrapped by an aluminum-plastic film with a coating. The coating of the aluminum-plastic film includes a hydrogel xerogel skeleton with a porous structure. The hydrogel xerogel skeleton has a large specific surface area and certain water absorption capacity, can absorb moisture in the external environment to block the permeation of moisture, and at the same time can evaporate the absorbed moisture during the battery heating process to achieve good temperature reduction; moreover, a phase change material is also dispersed in the hydrogel xerogel skeleton. The phase change material can not only absorb the heat inside the battery to reduce the battery temperature, but also absorb the heat of adjacent batteries to block the diffusion and transfer of heat to reduce the risk of thermal runaway, and thus significantly improve the cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other embodiments can also be obtained based on these drawings.

[0021] Figure 1 It is a schematic cross-sectional structure diagram of an aluminum-plastic film of a secondary battery according to one embodiment of the present application;

[0022] Figure 2 It is a schematic cross-sectional structure diagram of an aluminum-plastic film of a secondary battery according to another embodiment of the present application. Specific embodiments

[0023] To better illustrate the purpose, technical solutions and advantages of the present application, the following will further illustrate the present application in combination with specific embodiments and comparative examples. The purpose is to understand the content of the present application in detail, rather than a limitation to the present application. All other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present application. The experimental reagents and instruments involved in the implementation of the present application are all common ordinary reagents and instruments unless otherwise specified.

[0024] It should be noted that in the specific embodiments of the present application, lithium-ion batteries are used as examples of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0025] The first aspect of the present application provides a secondary battery, including an electrode assembly and an aluminum-plastic film. The aluminum-plastic film includes a base film and a coating; the base film has a first surface and a second surface arranged oppositely in its thickness direction, and the first surface of the base film faces the electrode assembly; the coating is provided on the second surface of the base film, and the coating includes a porous hydrogel dry gel and a phase change material.

[0026] For the secondary battery provided by the present application, the outer surface of the internal electrode assembly is wrapped by an aluminum-plastic film with a coating. The coating of the aluminum-plastic film includes a hydrogel dry gel skeleton with a porous structure. This hydrogel dry gel skeleton has a large specific surface area and certain water absorption, can absorb moisture in the external environment to block the penetration of moisture, and at the same time can evaporate the absorbed moisture during the heating process of the battery to achieve good cooling; moreover, a phase change material is evenly dispersed in the hydrogel dry gel skeleton. The phase change material can not only absorb the heat inside the battery to reduce the battery temperature, but also absorb the heat of adjacent batteries to block the heat diffusion and transfer to reduce the risk of thermal runaway, thereby significantly improving the cycle performance of the battery.

[0027] It should be noted that the porous hydrogel dry gel refers to a polymer skeleton with a porous structure formed after the hydrogel removes the water therein through drying (such as freeze-drying, etc.); the hydrogel can be composed of synthetic polymers and water, or composed of natural polymers and water, or obtained by polymerizing polymerization monomers in water.

[0028] The present application has no particular limitation on the phase change material, as long as it can achieve the purpose of the present application. For example, the phase change material can include, but is not limited to, organic phase change materials, inorganic phase change materials, composite phase change materials, etc. Optionally, the organic phase change material includes at least one of paraffin-based phase change materials (such as C18-C50 alkanes), fatty acid-based phase change materials (such as lauric acid), and polyol-based phase change materials (such as erythritol); the inorganic phase change material includes at least one of hydrated salts (such as sodium sulfate decahydrate) and metal alloys (such as Bi-Sn-Pb); the composite phase change material includes at least one of microcapsule phase change materials (such as paraffin / silica core-shell structure) and graphene composite phase change materials. The mass percentage content of the phase change material in the coating is preferably 5% to 30%, specifically it can be 5%, 7%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30% or a range composed of any two of these values. By regulating the mass percentage content of the phase change material in the coating within the above range, the coating can have a good thermal buffering effect, reduce the heating rate during the charge and discharge process of the battery, and at the same time ensure the mechanical strength and barrier properties of the aluminum-plastic film.

[0029] The present application has no particular limitation on the type of secondary battery, and it can include any device that undergoes an electrochemical reaction. The secondary battery in the present application can include, but is not limited to, lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, lithium-ion polymer secondary batteries (lithium-ion polymer batteries), etc.

[0030] In some embodiments of the present application, the thickness of the aluminum-plastic film is 60 μm to 120 μm. For example, the thickness of the aluminum-plastic film can be 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm or a range composed of any two of these values. By regulating the thickness of the aluminum-plastic film within the above range, the thickness of the aluminum-plastic film including the coating can be made equivalent to the thickness of a conventional aluminum-plastic film (without coating), which can not only maintain the basic functions of the aluminum-plastic film but also enable it to have a good heat absorption function, thereby effectively reducing the heat transfer rate and improving the cycle performance of the battery.

[0031] In some embodiments of the present application, the base film includes a stacked polypropylene layer and an aluminum foil layer, and the coating is disposed on the surface of the aluminum foil layer. The coating is directly disposed on the surface of the aluminum foil layer, which can better absorb the heat from the inside of the battery, more effectively reduce the temperature of the battery, and improve the heat absorption efficiency. At the same time, it is also beneficial to reduce the overall thickness of the aluminum-plastic film and improve the energy density of the battery.

[0032] In some embodiments of the present application, the ratio of the thickness of the coating to the thickness of the base film is 0.2 to 0.4. For example, the ratio of the thickness of the coating to the thickness of the base film is 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38, 0.4 or a range composed of any two of these values. By adjusting the ratio of the thickness of the coating to the thickness of the base film within the above range, the aluminum-plastic film can better balance mechanical strength and heat absorption performance.

[0033] In some embodiments of the present application, the base film includes a polypropylene layer, an aluminum foil layer, and a protective layer stacked in sequence, and the coating is disposed on the surface of the protective layer; the protective layer includes a nylon layer and / or a PET (polyethylene terephthalate) layer.

[0034] In some embodiments of the present application, the ratio of the thickness of the coating to the thickness of the base film is 0.1 to 0.4 (for example, it can be 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38, 0.4 or a range composed of any two of these values); and / or, the surface roughness Ra (Ra represents the arithmetic mean roughness) of the protective layer is 0.4 μm to 6.3 μm (for example, it can be 0.4 μm, 0.7 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.3 μm or a range composed of any two of these values). By adjusting the ratio of the thickness of the coating to the thickness of the base film within the above range, the aluminum-plastic film can better balance mechanical strength and heat absorption performance; at the same time, by adjusting the surface roughness of the protective layer within the above range, a large number of pits or micropores can be formed on the surface of the protective layer, and the porous hydrogel dry gel in the coating can partially fill these pits or micropores to form a "mortise and tenon" structure, thereby enhancing the adhesion of the coating and improving the bonding performance between the coating and the base film, effectively preventing the coating from peeling off. The surface roughness Ra is calculated by using a stylus profilometer to directly contact the measured surface with a probe and record the vertical movement data of the surface profile.

[0035] In some embodiments of the present application, the porous hydrogel dry gel comprises at least one of polyethylene glycol, polyacrylic acid, polyvinyl alcohol, polylactic acid-glycolic acid, polyacrylamide, collagen, chitosan, alginate (such as sodium alginate, potassium alginate, calcium alginate, etc.), agarose, and gelatin. Using the above materials as the porous hydrogel dry gel can better improve the compatibility between the coating and the base film, and thus improve the adhesion performance between the coating and the base film.

[0036] In some embodiments of the present application, the phase change material comprises at least one of paraffin-based phase change materials, fatty acid-based phase change materials, polyol-based phase change materials, hydrated salts, metal alloys, microcapsule phase change materials, and graphene composite phase change materials. Using the above materials as the phase change material can better improve the compatibility between the coating and the base film, and thus improve the adhesion performance between the coating and the base film.

[0037] In some embodiments of the present application, the coating further comprises an inorganic material, and the inorganic material comprises at least one of silicon oxide, zirconium oxide, aluminum oxide, niobium oxide, titanium oxide, and boehmite. When the coating contains an inorganic material, on the one hand, the inorganic material can be used as a reinforcing filler for the porous hydrogel dry gel to improve the mechanical strength of the porous hydrogel dry gel. On the other hand, the inorganic material dispersed in the porous hydrogel dry gel can also play a role in heat dispersion or heat transfer, quickly transferring heat to the adjacent phase change material, enabling the phase change material to absorb heat more quickly and fully, and thus better reducing the temperature of the battery.

[0038] In some embodiments of the present application, the particle size D of the inorganic material V50 is preferably from 10 nm to 200 nm. For example, the particle size D of the inorganic material V50 can be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 100 nm, 150 nm, 200 nm or a range composed of any two of these values. By adjusting the particle size D of the inorganic material V50 within the above range, strong interfacial bonding can be formed through hydrogen bonds, van der Waals forces or chemical bonds between the inorganic material and the molecular chains of the porous hydrogel dry gel, thereby improving the mechanical properties (such as tensile strength, modulus) of the porous hydrogel dry gel and improving the mechanical strength of the coating. Among them, the particle size D v50 refers to the particle size at which, in the particle size distribution based on the volume of the material, starting from the small particle size, the cumulative volume reaches 50%.

[0039] In some embodiments of the present application, the mass percentage content of the inorganic material in the coating is preferably 1% to 10%. For example, the mass percentage content of the inorganic material in the coating can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range composed of any two of these values. By controlling the mass percentage content of the inorganic material in the coating within the above range, it is more conducive to improving the mechanical strength of the coating and promoting heat transfer to better improve battery heating.

[0040] In some embodiments of the present application, the elongation at break of the aluminum-plastic film is ≥100%. For example, the elongation at break of the aluminum-plastic film can be 100%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, or a range composed of any two of these values. By maintaining the elongation at break of the aluminum-plastic film greater than or equal to 100%, it not only has good processing performance during processing such as stamping and hemming, but also has good tensile and puncture resistance properties to better ensure the reliability and stability of the battery in practical applications.

[0041] In some embodiments of the present application, the surface roughness Ra (Ra represents the arithmetic mean roughness) of the coating is 0.1 μm to 2 μm. For example, the surface roughness of the coating can be 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2 μm, or a range composed of any two of these values. To a certain extent, the surface roughness of the coating affects its contact with moisture in the external environment. By keeping the surface roughness of the coating within the above range, it is more conducive to the coating absorbing moisture in the external environment, thereby better blocking moisture penetration and absorbing heat during high-rate charge and discharge of the battery. The surface roughness Ra is calculated by using a stylus profilometer to directly contact the measured surface and record the vertical movement data of the surface profile.

[0042] In the secondary battery of the present application, the electrode assembly includes a negative electrode sheet, and the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material, a negative electrode binder, and a negative electrode dispersant. The present application does not particularly limit the mass ratio of the negative electrode active material, the negative electrode binder, and the negative electrode dispersant in the negative electrode material layer. Those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0043] The "negative electrode material layer located on at least one surface of the negative electrode current collector" mentioned above means that the negative electrode material layer can be located on one surface of the negative electrode current collector along its thickness direction, or on both surfaces of the negative electrode current collector along its thickness direction. The "surface" can be the entire area of the surface of the negative electrode current collector, or a partial area of the surface of the negative electrode current collector. There is no special limitation in this application, as long as the purpose of this application can be achieved.

[0044] There is no special limitation on the negative electrode current collector in this application, as long as the purpose of this application can be achieved. For example, the negative electrode current collector can include, but is not limited to, copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, carbon-coated aluminum foil, carbon-coated copper foil, lithium-copper composite current collector, carbon-copper composite current collector, nickel-copper composite current collector, titanium-copper composite current collector, etc. There is no special limitation on the thickness of the negative electrode current collector and the negative electrode material layer located on the surface of the negative electrode current collector in this application, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 3 μm to 8 μm, and the thickness of the single-sided negative electrode material layer is 0 μm to 100 μm.

[0045] There is no special limitation on the type of the negative electrode active material in this application, as long as the purpose of this application can be achieved. For example, the negative electrode active material can include, but is not limited to, natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithiated TiO2-Li4Ti5O with a spinel structure 12 , lithium metal, structured lithium metal, at least one of Li-Al alloy.

[0046] There is no special limitation on the types of the negative electrode binder and the negative electrode dispersant in this application, as long as the purpose of this application can be achieved. For example, the negative electrode binder can include, but is not limited to, polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose, potassium hydroxymethyl cellulose, etc.; the negative electrode dispersant can include, but is not limited to, carboxymethyl cellulose, sodium carboxymethyl cellulose, etc.

[0047] The electrode assembly in the secondary battery of this application further includes a positive electrode plate, and the positive electrode plate includes a positive electrode current collector and a positive electrode material layer located on at least one surface of the positive electrode current collector. The positive electrode material layer contains a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent. There is no special limitation on the mass ratio of the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent in the positive electrode material layer in this application, and those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved.

[0048] The above-mentioned "positive electrode material layer located on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be located on one surface of the positive electrode current collector along its thickness direction, or on two surfaces of the positive electrode current collector along its thickness direction. The "surface" can be the entire area of the positive electrode current collector surface or a partial area of the positive electrode current collector surface. There is no special limitation in this application, as long as the purpose of this application can be achieved.

[0049] There is no special limitation on the positive electrode current collector in this application, as long as the purpose of this application can be achieved. For example, the positive electrode current collector can include, but is not limited to, copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, carbon-coated aluminum foil, carbon-coated copper foil, lithium-copper composite current collector, carbon-copper composite current collector, nickel-copper composite current collector, titanium-copper composite current collector, etc. There is no special limitation on the thickness of the positive electrode current collector and the positive electrode material layer located on the surface of the positive electrode current collector in this application, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 7 μm to 13 μm, and the thickness of the single-sided negative electrode active material layer is 10 μm to 100 μm.

[0050] There is no special limitation on the type of the positive electrode active material in this application, as long as the purpose of this application can be achieved. For example, the positive electrode active material includes, but is not limited to, at least one of lithium cobaltate, lithium nickel cobalt manganese oxide (NCM811, NCM622, NCM523, NCM111), lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel-type lithium manganate, spinel-type lithium nickel manganate, lithium titanate.

[0051] There is no special limitation on the types of the positive electrode binder and the positive electrode conductive agent in this application, as long as the purpose of this application can be achieved. For example, the positive electrode binder can include, but is not limited to, polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose, potassium hydroxymethyl cellulose, etc.; the positive electrode conductive agent can include, but is not limited to, conductive carbon black, carbon nanotubes, carbon fibers, flake graphite, Ketjen black, graphene, metal materials (copper, nickel, aluminum or silver), conductive polymers (polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole), etc.

[0052] In the secondary battery of the present application, the electrode assembly further includes a separator, which is used to separate the positive electrode sheet and the negative electrode sheet to prevent internal short circuit of the secondary battery. The separator allows electrolyte ions to pass through freely and does not affect the progress of the electrochemical charge and discharge process. The present application places no particular limitation on the separator, as long as it can achieve the purpose of the present application. For example, the material of the separator may include, but is not limited to, polyolefins mainly composed of polyethylene and polypropylene, polyesters (such as polyethylene terephthalate film), cellulose, polyimide, polyamide, spandex, aramid, etc.; the types of the separator may include woven films, non-woven films, microporous films, composite films, rolled films, spun films, etc.

[0053] The separator of the present application may include a base film and a coating located on at least one surface of the base film. The base film may be a non-woven fabric or a composite film having a porous structure. For example, the base film may use a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, a polypropylene-polyethylene-polypropylene porous composite film, etc.; the coating may be a polymer layer, an inorganic layer, or a mixture layer formed by a polymer and an inorganic substance. The inorganic particles in the coating may include at least one of alumina, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate.

[0054] In the secondary battery of the present application, the electrode assembly further includes an electrolyte, which includes a lithium salt and an organic solvent. The present application places no particular limitation on the mass percentage content of the lithium salt and the organic solvent in the electrolyte, as long as it can achieve the purpose of the present application. For example, based on the mass of the electrolyte, in a low-concentration electrolyte (i.e., a conventional electrolyte), the mass percentage content of the lithium salt is 8% to 15%, and the mass percentage content of the organic solvent is 70% to 85%; in a high-concentration electrolyte, the mass percentage content of the lithium salt is 30% to 50%, and the mass percentage content of the organic solvent is 50% to 70%.

[0055] The present application places no particular limitation on the type of the lithium salt, as long as it can achieve the purpose of the present application. Lithium salts known in the art may be used. For example, the lithium salt may include, but is not limited to, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, etc. The present application places no particular limitation on the organic solvent, as long as it can achieve the purpose of the present application. For example, the organic solvent may include carbonate compounds, carboxylate compounds, ether compounds, or other organic solvents (such as dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphate esters), etc.

[0056] The second aspect of the present application provides an electronic device, which includes the secondary battery provided by the first aspect of the present application. The specific type of the electronic device is not particularly limited in the present application. For example, the electronic device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo earphone, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0057] To clearly understand the technical solution of the present application, the present application will be further described in detail below with specific examples and comparative examples. These examples should not be construed as limiting the scope claimed by the present application.

[0058] Test methods and equipment

[0059] 1. Heat absorption performance test of aluminum plastic film

[0060] Attach the aluminum plastic film to the surface of the heating plate (the polypropylene layer in the aluminum plastic film is in contact with the surface of the heating plate), and attach a temperature-sensitive wire to the coating surface on the side of the aluminum plastic film away from the heating plate. Then, increase the temperature of the heating plate from room temperature to T1 (50 °C) at a heating rate of 10 °C / min. At this time, the temperature measured by the temperature-sensitive wire is T2. The heat absorption performance of the aluminum plastic film is evaluated by the temperature difference between the two sides of the aluminum plastic film (ΔT = T1 - T2). The larger the value of ΔT, the better the heat absorption performance of the aluminum plastic film.

[0061] 2. Battery surface temperature test

[0062] Let the soft-pack lithium-ion battery stand in a constant-temperature oven at 40 °C for 30 minutes, discharge it to the cut-off voltage (3V) at a current of 0.2C (C is calculated based on the standard capacity), stand for 5 minutes, and then charge it to the cut-off voltage (4.45V) at a current of 3C, and record the highest temperature on the surface of the soft-pack lithium-ion battery at the end of charging.

[0063] 3. Elongation at break test of aluminum plastic film

[0064] Use the ASTM D882 standard (plastic film tensile test standard). The length of the sample before stretching is L0. Using a universal material testing machine, the stretching rate is 50 mm / min. Stretch the sample until it breaks, and the length at break is L1. The elongation at break = (L1 - L0) / L0 × 100%.

[0065] 4. Cycle performance test

[0066] The soft-pack lithium-ion battery is left standing in a constant-temperature oven at 25°C for 30 minutes, discharged at a current of 0.2C (where C is calculated based on the standard capacity) to the cut-off voltage (3V), and left standing for 5 minutes. Then, it is charged at a current of 3C to the cut-off voltage (4.45V), CVed to 0.025C, left standing for 5 minutes, and then discharged at a current of 1C to the cut-off voltage (3V), and left standing for 5 minutes (this is one charge-discharge cycle process). Record the first-cycle discharge capacity C0 of the soft-pack lithium-ion battery. After that, cycle 300 times according to the above cycle process, and record the cycle discharge capacity C1 of the 300th cycle. The 300-cycle capacity retention rate = C1 / C0 × 100%.

[0067] Example 1

[0068] <Preparation of Aluminum-Plastic Film>

[0069] Mix acrylamide, initiator ammonium persulfate, phase change material, inorganic material, and water evenly to form a coating slurry. Then, evenly coat the coating slurry on the surface of the nylon layer in the base film (polypropylene layer / aluminum foil layer / nylon layer, where the thickness of the polypropylene layer is 20μm, the thickness of the aluminum foil layer is 30μm, and the thickness of the nylon layer is 25μm), and in-situ polymerize and cure (acrylamide polymerizes to form polyacrylamide), and dry to obtain the aluminum-plastic film. The cross-sectional structure schematic diagram of the aluminum-plastic film is as Figure 1 shown.

[0070] <Preparation of Negative Electrode Plate>

[0071] Mix the negative electrode active material (graphite), styrene-butadiene rubber (SBP), and sodium carboxymethyl cellulose (CMC) in a weight ratio of 97:2:1 and stir well in an appropriate amount of deionized water to form a uniform negative electrode slurry, where the solid content of the negative electrode slurry is 40wt%. Coat the negative electrode slurry on one side surface of the negative electrode current collector copper foil, dry it at 85°C, and then after cold pressing, slicing, and slitting, dry it in a vacuum at 120°C for 12h to obtain a single-sided coated negative electrode plate. Repeat the above steps on the other side surface of the copper foil in the above single-sided coated negative electrode plate to obtain a negative electrode plate with a double-sided coated negative electrode material layer. Then, after cold pressing, slicing, and slitting, dry it in a vacuum at 120°C for 12h to obtain a negative electrode plate with a specification of 78mm × 875mm for use. Among them, the compaction density of the negative electrode material layer after cold pressing is 1.7g / cm 3 .

[0072] <Preparation of Positive Electrode Plate>

[0073] The cathode active material lithium cobalt oxide (LiCoO₂), conductive carbon black (Super P), and cathode binder (polyvinylidene fluoride PVDF) are mixed at a mass ratio of 97:1.4:1.6, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a cathode slurry with a solid content of 72 wt%. After vacuum stirring evenly, the cathode slurry is obtained. The cathode slurry is evenly coated on one side surface of a cathode current collector aluminum foil with a thickness of 12 μm and dried at 85 °C to obtain a cathode electrode sheet with a single-sided coated cathode material layer. When coating, the coating weight of the cathode material layer is 19 mg / cm 2 。Then repeat the above steps on the other side surface of the aluminum foil to obtain a cathode electrode sheet with a double-sided coated cathode material layer. After cold pressing, slicing, and slitting, it is dried under vacuum conditions at 85 °C for 4 h to obtain a cathode electrode sheet with a specification of 74 mm × 867 mm for use. Among them, the compaction density of the cathode material layer after cold pressing is 4.2 g / cm 3 。

[0074] <Preparation of electrolyte>

[0075] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed evenly according to a weight ratio of EC:EMC:DEC = 30:50:20 to obtain a base solvent. Then, lithium salt lithium hexafluorophosphate (LiPF₆) is added to the above base solvent and mixed evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, the mass percentage content of the lithium salt is 12.5%, and the balance is the base solvent.

[0076] <Preparation of separator>

[0077] A porous polyethylene (PE) film with a thickness of 7 μm (provided by Celgard) is used as the separator.

[0078] <Preparation of lithium-ion full cell>

[0079] The cathode electrode sheet, separator, anode electrode sheet, and separator are stacked in sequence, with the separator placed in the middle between the cathode electrode sheet and the anode electrode sheet to play an isolation role, and then wound to obtain an electrode assembly. After welding the tab, the electrode assembly is placed in an aluminum-plastic film packaging bag (made of the above-mentioned aluminum-plastic film), dried at 80 °C, injected with electrolyte, and then subjected to vacuum packaging, standing, formation, shaping, and capacity testing processes to obtain a soft-pack lithium-ion battery, which is the lithium-ion full cell.

[0080] Example 2

[0081] Except that it is different from Example 1 in the <preparation of aluminum-plastic film>, the rest is the same as Example 1.

[0082] The preparation of the aluminum-plastic film is as follows: Polyvinyl alcohol, a phase change material, an inorganic material, and water are mixed evenly to form a coating slurry, and then the coating slurry is evenly coated on the surface of the nylon layer in a base film (a polypropylene layer / an aluminum foil layer / a nylon layer, where the thickness of the polypropylene layer is 20 μm, the thickness of the aluminum foil layer is 30 μm, and the thickness of the nylon layer is 25 μm), and then dried to obtain the aluminum-plastic film.

[0083] Example 3

[0084] Except that it is different from Example 1 in the preparation of the aluminum-plastic film, the rest is the same as Example 1.

[0085] The preparation of the aluminum-plastic film is as follows: Sodium alginate, a phase change material, an inorganic material, and water are mixed evenly to form a coating slurry, and then the coating slurry is evenly coated on the surface of the nylon layer in a base film (a polypropylene layer / an aluminum foil layer / a nylon layer, where the thickness of the polypropylene layer is 20 μm, the thickness of the aluminum foil layer is 30 μm, and the thickness of the nylon layer is 25 μm), and then dried to obtain the aluminum-plastic film.

[0086] Examples 4 to 5

[0087] Except that it is different from Example 1 in the type of the phase change material in the preparation of the aluminum-plastic film, the rest is the same as Example 1.

[0088] Examples 6 to 7

[0089] Except that it is different from Example 1 in the mass percentage content of the phase change material in the coating in the preparation of the aluminum-plastic film, the rest is the same as Example 1.

[0090] Examples 8 to 9

[0091] Except that it is different from Example 1 in the type of the inorganic material in the preparation of the aluminum-plastic film, the rest is the same as Example 1.

[0092] Examples 10 to 11

[0093] Except that it is different from Example 1 in the particle size of the inorganic material in the preparation of the aluminum-plastic film, the rest is the same as Example 1.

[0094] Examples 12 to 13

[0095] Except that it is different from Example 1 in the mass percentage content of the inorganic material in the coating in the preparation of the aluminum-plastic film, the rest is the same as Example 1.

[0096] Examples 14 to 15

[0097] Except that by adjusting the thickness of the coating in the aluminum-plastic film, the ratio of the thickness of the coating to the thickness of the base film is different from that in Example 1, the rest is the same as Example 1.

[0098] Example 16

[0099] Except that the composition of the coating in <Preparation of Aluminum-Plastic Film> is different from that in Example 1 (there is no inorganic material in the coating), the rest is the same as in Example 1.

[0100] Example 17

[0101] Except that the base film of the aluminum-plastic film, the thickness of the base film, the thickness of the coating, and the ratio of the thickness of the coating to the base film in <Preparation of Aluminum-Plastic Film> are different from those in Example 1, the rest is the same as in Example 1; the schematic cross-sectional structure diagram of the aluminum-plastic film is as Figure 2 shown.

[0102] Comparative Example 1

[0103] Except that the structure of the aluminum-plastic film in <Preparation of Aluminum-Plastic Film> is different from that in Example 1 (there is no coating in the aluminum-plastic film), the rest is the same as in Example 1.

[0104] Comparative Example 2

[0105] Except that the composition of the coating in <Preparation of Aluminum-Plastic Film> is different from that in Example 1 (there is no phase change material in the coating), the rest is the same as in Example 1.

[0106]

[0107] According to the data in Table 1, it can be seen that the temperature difference between the two sides of the aluminum-plastic film in Examples 1 to 17 is greater than or equal to 7.5 °C and the elongation at break remains above 110%. At the same time, the maximum temperature during the charging process of the soft-pack battery at 40 °C and 3C current is less than 46.5 °C, and the cycle capacity retention rate after 300 cycles is greater than 93%. This indicates that the secondary battery of the present application can effectively reduce its temperature during fast charge and discharge and maintain excellent cycle performance. According to the data of Comparative Example 1, it can be seen that when using a conventional aluminum-plastic film (without a coating), the problem of temperature rise of the secondary battery during fast charging cannot be effectively solved; according to the data of Comparative Example 2, it can be found that when the coating of the aluminum-plastic film contains porous hydrogel dry glue but does not contain a phase change material, although the temperature of the secondary battery during fast charging can be reduced to a certain extent, the improvement effect is limited.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A secondary battery, comprising an electrode assembly and an aluminum-plastic film, characterized in that: The aluminum-plastic film includes a base film and a coating; the base film has a first surface and a second surface arranged opposite to each other in its thickness direction, and the first surface of the base film faces the electrode assembly; the coating is arranged on the second surface of the base film, and the coating includes a porous hydrogel dry glue and a phase change material.

2. The secondary battery according to claim 1, wherein: The thickness of the aluminum-plastic film is 60 μm to 120 μm.

3. The secondary battery according to claim 1, wherein: The base film comprises a polypropylene layer and an aluminum foil layer which are stacked, and the coating is arranged on the surface of the aluminum foil layer.

4. The secondary battery according to claim 3, characterized in that: The ratio of the thickness of the coating layer to the thickness of the base film is 0.2 to 0.

4.

5. The secondary battery according to claim 1, wherein: The base film comprises a polypropylene layer, an aluminum foil layer and a protective layer which are stacked in sequence, and the coating is arranged on the surface of the protective layer; the protective layer comprises a nylon layer and / or a PET layer.

6. The secondary battery according to claim 5, characterized in that: The ratio of the thickness of the coating layer to the thickness of the base film is 0.1 to 0.4; and / or the surface roughness Ra of the protective layer is 0.4 μm to 6.3 μm.

7. The secondary battery according to any one of claims 1 to 6, characterized in that: The porous hydrogel dry glue includes at least one of polyethylene glycol, polyacrylic acid, polyvinyl alcohol, polylactic acid-glycolic acid, polyacrylamide, collagen, chitosan, alginate, agarose, and gelatin; and / or the phase change material includes at least one of paraffin phase change material, fatty acid phase change material, polyol phase change material, hydrated salt, metal alloy, microcapsule phase change material, and graphene composite phase change material.

8. The secondary battery according to any one of claims 1 to 6, characterized in that: The coating also includes an inorganic material, and the inorganic material includes at least one of silicon oxide, zirconium oxide, aluminum oxide, niobium oxide, titanium oxide, and boehmite.

9. The secondary battery according to claim 1, wherein: The elongation at break of the aluminum-plastic film is ≥100%.

10. An electronic device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 9.

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