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, the electrode assembly comprises a positive pole piece, a negative pole piece and a diaphragm, the positive pole piece, the negative pole piece and the diaphragm are wound, and the diaphragm is located between the positive pole piece and the negative pole piece; the electrode assembly comprises a straight area and bending areas located at the two opposite ends of the straight area. A coating is arranged between the positive pole piece and / or the negative pole piece in the bending area and the diaphragm; the coating comprises a metal organic framework material. The bending area of the secondary battery has high electrolyte retention property, and lithium precipitation at a corner interface of the bending area can be effectively improved, so that the cycle performance of the battery is improved, and the safety risk of the battery is reduced.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a secondary battery and electronic device. Background Technology

[0002] Pouch batteries are characterized by their lightweight, high energy density, and high safety, and are widely used in consumer electronics, new energy vehicles, and energy storage systems. Pouch battery cells are mainly divided into wound cells and stacked cells. During the winding process, wound cells form flat and bent areas. The bent areas are easily compressed, often resulting in a lack of electrolyte. This not only leads to lithium plating in the bent areas but also degrades the battery's cycle performance. Summary of the Invention

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

[0004] To achieve the above objectives, 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. The electrode assembly includes a positive electrode, a negative electrode, and a separator wound together, with the separator located between the positive and negative electrode. The electrode assembly includes a flat region and bent regions located at opposite ends of the flat region. A coating is provided between the positive and / or negative electrode in the bent region and the separator. The coating comprises a metal-organic framework material.

[0006] The secondary battery of this application has a coating containing a metal-organic framework (MOF) between the positive and / or negative electrode sheets in the internal bending region and the separator. This coating can effectively improve the contact performance between the electrode sheets and the separator. Moreover, the MOF in the coating has a porous structure, which, compared with conventional porous materials, can absorb and store electrolyte in the bending region, thereby improving the electrolyte retention performance in the bending region and promoting ion conduction in this region. This not only improves lithium plating in the bending region to reduce safety risks, but also significantly improves the cycle performance of the battery.

[0007] In some embodiments of this application, the average particle size of the metal-organic framework material is between 10 nm and 100 nm. By controlling the average particle size of the metal-organic framework material within the above range, the uniform dispersion of the metal-organic framework material in the coating can be promoted, thereby enabling the coating to have a uniformly distributed microporous structure and suitable porosity, thus improving the adsorption of electrolyte by the coating and increasing the electrolyte retention rate in the bending area of ​​the electrode assembly.

[0008] In some embodiments of this application, the average thickness of the coating is between 0.5 μm and 2 μm. By controlling the average thickness of the coating within this range, not only can the battery have a higher volumetric energy density, but the electrolyte retention capacity of the coating can also be effectively improved, thereby reducing the risk of lithium plating caused by insufficient electrolyte in the bending area of ​​the electrode assembly during battery cycling expansion.

[0009] In some embodiments of this application, the metal-organic framework material contains element A, which includes at least one of Zn, Cu, Cr, Al, Fe, Ni, Mn, and Co; the mass percentage content of element A is 0.1% to 1% based on the mass of the coating. Element A is a characteristic element of the metal-organic framework material. By controlling the mass percentage content of element A within the above range, the content of the metal-organic framework material in the coating can be adjusted, thereby achieving optimal electrolyte retention and volumetric energy density.

[0010] In some embodiments of this application, the coating further includes a ceramic material containing element B, which includes at least one of Li, Al, Ti, Zr, O, S, P, and Cl. Including a ceramic material in the coating not only maintains a high electrolyte retention rate but also effectively improves the ionic conductivity of the coating and enhances the contact performance between the electrode and the separator, promoting uniform lithium ion deposition, further reducing the risk of lithium plating in the bending area of ​​the electrode assembly, and thus improving the battery's safety performance.

[0011] In some embodiments of this application, the mass percentage ratio of element B to element A is between 0 and 1, depending on the quality of the coating. By controlling the mass percentage ratio of element B to element A in the coating within the above range, not only can the electrolyte retention in the bending area of ​​the electrode assembly be maintained to reduce the risk of lithium plating due to interfacial impedance, but the safety performance of the battery can also be further optimized.

[0012] In some embodiments of this application, the metal-organic framework material is composed of metal ions and organic ligands; the metal ions include at least one of zinc ions, cobalt ions, copper ions, iron ions, nickel ions, and zirconium ions; the organic ligands include at least one of 2-methylimidazole, 1,3,5-benzenetricarboxylic acid, and terephthalic acid.

[0013] In some embodiments of this application, the porosity of the coating is 10% to 50%; the difference between the porosity of the coating and the porosity of the diaphragm in the flat region is 5% to 40%. By adjusting the porosity of the coating within the above range, the coating can achieve optimal electrolyte retention; and by adjusting the difference between the porosity of the coating and the porosity of the diaphragm in the flat region to meet the above conditions, the interfacial impedance between the coating and the diaphragm can be better balanced.

[0014] In some embodiments of this application, the positive electrode in the bending region includes a positive electrode material layer comprising a metal-organic framework (MOF) material; and / or, the negative electrode in the bending region includes a negative electrode material layer comprising a MOF material. The positive electrode material layer is disposed on one surface of the positive current collector, and the negative electrode material layer is disposed on one surface of the negative current collector. When the positive and / or negative electrode material layers contain MOF materials, it can better promote the absorption and storage of electrolyte in the bending region of the electrode assembly, and also improve the wettability of the electrolyte on the electrode. Simultaneously, the porous structure of the MOF material and the electrolyte within the pores facilitate rapid lithium-ion transport.

[0015] A second aspect of this application provides an electronic device that includes the secondary battery provided in the first aspect of this application.

[0016] Compared with the prior art, the beneficial effects of this application are as follows:

[0017] The secondary battery provided in this application has a coating containing a metal-organic framework (MOF) between the positive and / or negative electrode sheets in the internal bending region and the separator. This coating can effectively improve the contact performance between the electrode sheets and the separator. Moreover, the MOF in the coating has a porous structure, which, compared with conventional porous materials, can absorb and store electrolyte in the bending region, thereby improving the electrolyte retention performance in the bending region and promoting ion conduction in this region. This not only improves lithium plating in the bending region to reduce safety risks, but also significantly improves the cycle performance of the battery. Detailed Implementation

[0018] To better illustrate the purpose, technical solution, and advantages of this application, the following description, in conjunction with specific embodiments and comparative examples, aims to provide a detailed understanding of the content of this application, rather than limiting it. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this application. Unless otherwise specified, the experimental reagents and instruments involved in the implementation of this application are all commonly used reagents and instruments.

[0019] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0020] The first aspect of this application provides a secondary battery including an electrode assembly comprising a positive electrode, a negative electrode, and a separator wound together, the separator being located between the positive and negative electrode; the electrode assembly includes a flat region and bent regions located at opposite ends of the flat region; a coating is provided between the positive and / or negative electrode in the bent region and the separator; the coating comprises a metal-organic framework material.

[0021] The secondary battery provided in this application has a coating containing a metal-organic framework (MOF) between the positive and / or negative electrode sheets in the internal bending region and the separator. This coating can effectively improve the contact performance between the electrode sheets and the separator. Moreover, the MOF in the coating has a porous structure, which, compared with conventional porous materials, can absorb and store electrolyte in the bending region, thereby improving the electrolyte retention performance in the bending region and promoting ion conduction in this region. This not only improves lithium plating in the bending region to reduce safety risks, but also significantly improves the cycle performance of the battery.

[0022] It should be noted that the coating between the positive and / or negative electrode sheets and the separator in the aforementioned bending region can be located on the surface of the positive electrode sheet, the surface of the negative electrode sheet, or the surface of the separator; it can also exist as an independent layered structure, which is stacked between the electrode sheet and the separator during the winding process of the electrode assembly. The coating includes at least a metal-organic framework material and a binder, the binder serving to connect the metal-organic framework materials to each other and to fix the metal-organic framework materials to the surface of the electrode sheet or separator.

[0023] The aforementioned electrode assembly generally includes two straight regions and two bent regions. The two straight regions are arranged in parallel to each other, one bent region is connected between the two ends on one side of the two straight regions, and the other bent region is connected between the two ends on the other side of the two straight regions.

[0024] This application does not impose any particular limitation on the type of secondary battery, which may include any device in which an electrochemical reaction occurs. The secondary battery in this application may include, but is not limited to, lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, and lithium-ion polymer secondary batteries (lithium-ion polymer batteries).

[0025] In some embodiments of this application, the average particle size of the metal-organic framework material is from 10 nm to 100 nm. For example, the average particle size of the metal-organic framework material can be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, or a range of any two of these values. Preferably, the average particle size of the metal-organic framework material is from 10 nm to 50 nm. By controlling the average particle size of the metal-organic framework material within the above range, the uniform dispersion of the metal-organic framework material in the coating can be promoted, thereby enabling the coating to have a uniformly distributed microporous structure and suitable porosity, thereby improving the adsorption of electrolyte by the coating and increasing the electrolyte retention rate in the bending area of ​​the electrode assembly.

[0026] In some embodiments of this application, the pore size of the metal-organic framework material is from 1 nm to 5 nm. For example, the pore size of the metal-organic framework material can be 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, or a range of any two values ​​therein. By controlling the pore size of the metal-organic framework material within the above range, not only can the electrolyte be rapidly adsorbed during the electrolyte injection process of the battery cell using capillary action, but the adsorbed electrolyte can also be stored, thereby significantly improving the electrolyte retention rate in the bending area of ​​the electrode assembly, so that the bending area will not be in a state of electrolyte deficiency even when subjected to compression.

[0027] In some embodiments of this application, the average thickness of the coating is from 0.5 μm to 2 μm. For example, the average thickness of the coating can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, or a range of any two of these values. By controlling the average thickness of the coating within the above range, not only can the battery possess a higher volumetric energy density, but the electrolyte retention capacity of the coating can also be effectively improved, thereby reducing the risk of lithium plating caused by insufficient electrolyte in the bending area of ​​the electrode assembly during battery cycling expansion.

[0028] In some embodiments of this application, the metal-organic framework material includes element A, which includes at least one selected from Zn, Cu, Cr, Al, Fe, Ni, Mn, and Co; the mass percentage content of element A is 0.1% to 1% based on the mass of the coating. For example, based on the mass of the coating, the mass percentage content of element A in the coating can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a range consisting of any two of these values. Element A is a characteristic element of the metal-organic framework material. By controlling the mass percentage content of element A within the above range, the content of the metal-organic framework material in the coating can be adjusted, thereby achieving optimal electrolyte retention and volumetric energy density.

[0029] In some embodiments of this application, the coating further includes a ceramic material containing element B, specifically at least one selected from Li, Al, Ti, Zr, O, S, P, and Cl. Including a ceramic material in the coating not only maintains a high electrolyte retention rate but also effectively improves the coating's ionic conductivity and enhances the contact performance between the electrode and the separator, promoting uniform lithium-ion deposition and further reducing the risk of lithium plating in the bending areas of the electrode assembly, thereby improving battery safety. For example, the ceramic material can be at least one selected from LATP, LLZO, LiPSCl, and LGPS.

[0030] In some embodiments of this application, the ratio of the mass percentage of element B to the mass percentage of element A is between 0 and 1, depending on the quality of the coating. For example, the ratio of the mass percentage of element B to the mass percentage of element A can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range consisting of any two of these values. By controlling the mass percentage ratio of element B to element A in the coating within the above range, not only can the electrolyte retention in the bending area of ​​the electrode assembly be maintained to reduce the risk of lithium plating due to interfacial impedance, but the safety performance of the battery can also be further optimized.

[0031] In some embodiments of this application, the metal-organic framework material is composed of metal ions and organic ligands; the metal ions include at least one selected from zinc ions, cobalt ions, copper ions, iron ions, nickel ions, and zirconium ions; the organic ligands include at least one selected from 2-methylimidazole, 1,3,5-benzenetricarboxylic acid, and terephthalic acid (H2BDC). For example, the metal-organic framework material can be at least one selected from ZIF-8, ZIF-67, Cu-BTC, Fe-BTC, MOF-5, Ni-MOF, MIL-100, and UiO-66.

[0032] In some embodiments of this application, the porosity of the coating is 10% to 50%; the difference between the porosity of the coating and the porosity of the diaphragm in the flat region is 5% to 40%. For example, the porosity of the coating is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any combination of two of these values; the difference between the porosity of the coating and the porosity of the diaphragm in the flat region can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any combination of two of these values. By adjusting the porosity of the coating within the above range, the coating can achieve optimal electrolyte retention; and by adjusting the difference between the porosity of the coating and the porosity of the diaphragm in the flat region to meet the above conditions, the interfacial resistance between the coating and the diaphragm can be better balanced.

[0033] In some embodiments of this application, the positive electrode in the bending region includes a positive electrode material layer (the positive electrode material layer includes a positive electrode active material, a binder, a conductive agent, a dispersant, etc.), and the positive electrode material layer includes a metal-organic framework material; and / or, the negative electrode in the bending region includes a negative electrode material layer (the negative electrode material layer includes a negative electrode active material, a binder, a conductive agent, a dispersant, etc.), and the negative electrode material layer includes a metal-organic framework material. The positive electrode material layer is disposed on the surface of one side of the positive electrode current collector, and the negative electrode material layer is disposed on the surface of one side of the negative electrode current collector. When the positive electrode material layer and / or the negative electrode material layer contain a metal-organic framework material, it can better promote the absorption and storage of electrolyte in the bending region of the electrode assembly, and it is also beneficial to improve the wettability of the electrolyte to the electrode. At the same time, the porous structure of the metal-organic framework material and the electrolyte in the pore structure are conducive to the rapid transport of lithium ions.

[0034] The negative electrode in the electrode assembly of the secondary battery of this application includes a negative electrode current collector and a negative electrode material layer located on at least one side surface of the negative electrode current collector. The negative electrode material layer comprises a negative electrode active material, a negative electrode binder, and a negative electrode dispersant. This application does not impose any particular limitation on 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 them according to actual needs, as long as the purpose of this application can be achieved.

[0035] The aforementioned "negative electrode material layer located on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be located on one surface of the negative electrode current collector along its own thickness direction, or it can be located on two surfaces of the negative electrode current collector along its own thickness direction. The "surface" can be the entire area of ​​the negative electrode current collector surface, or it can be a part of the negative electrode current collector surface. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0036] This application does not impose any particular limitation on the negative electrode current collector, as long as it achieves the purpose of this application. For example, the negative electrode current collector may include, but is not limited to, copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, 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. This application does not impose any particular limitation on the thickness of the negative electrode current collector and the negative electrode material layer on the surface of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector may be 6 μm to 12 μm, and the thickness of the single-sided negative electrode material layer may be 30 μm to 100 μm.

[0037] This application does not specifically limit the type of negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, and SiO2. x(0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithiated TiO2-Li4Ti5O with spinel structure 12 , lithium metal, structured lithium metal, at least one of Li-Al alloy.

[0038] This application places no particular restrictions on the types of the negative electrode binder and the negative electrode dispersant, as long as the objectives of this application can be achieved. For example, the negative electrode binder may include, but is not limited to, polyacrylate, polyimide, polyamide, polyamide-imide, 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 may include, but is not limited to, carboxymethyl cellulose, sodium carboxymethyl cellulose, etc.

[0039] In the secondary battery of this application, the positive electrode plate in the electrode assembly 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. This application places no particular restrictions 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. Those skilled in the art can select according to actual needs as long as the objectives of this application can be achieved.

[0040] 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 can be located on both 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. This application places no particular restrictions as long as the objectives of this application can be achieved.

[0041] This application places no particular restrictions on the positive electrode current collector as long as the objectives of this application can be achieved. For example, the positive electrode current collector may 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. This application places no particular restrictions 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 as long as the objectives of this application can be achieved. For example, the thickness of the positive electrode current collector can be 6 μm to 15 μm, and the thickness of the single-sided positive electrode material layer can be 30 μm to 100 μm.

[0042] This application does not specifically limit the type of positive electrode active material, as long as it can achieve the purpose of this application. For example, positive electrode active materials include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide (NCM811, NCM622, NCM523, NCM111), lithium nickel manganese aluminum oxide, 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 manganese oxide, spinel-type lithium nickel manganese oxide, and lithium titanate.

[0043] This application does not impose any particular restrictions on the types of positive electrode binders and positive electrode conductive agents, as long as they can achieve the purpose of this application. For example, positive electrode binders may include, but are not limited to, polyacrylates, polyimides, polyamides, polyamide-imides, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose, potassium hydroxymethyl cellulose, etc.; positive electrode conductive agents may include, but are not limited to, conductive carbon black, carbon nanotubes, carbon fibers, flake graphite, Ketjen black, graphene, metallic materials (copper, nickel, aluminum, or silver), conductive polymers (polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole), etc.

[0044] The electrode assembly of the secondary battery in this application also includes a separator, which separates the positive and negative electrode plates to prevent internal short circuits in the secondary battery. The separator allows electrolyte ions to pass freely without affecting the electrochemical charging and discharging process. This application does not impose any particular limitations on the separator, as long as it can achieve the purpose of this application. For example, the material of the separator can include, but is not limited to, polyethylene, polyolefins mainly composed of polypropylene, polyesters (such as polyethylene terephthalate membranes), cellulose, polyimide, polyamide, spandex, aramid, etc.; the type of separator can include woven membranes, nonwoven membranes, microporous membranes, composite membranes, rolled membranes, spun membranes, etc.

[0045] The diaphragm of this application may include a base membrane and a coating on at least one surface of the base membrane. The base membrane may be a nonwoven fabric or composite membrane with a porous structure. For example, the base membrane may be a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, a polypropylene-polyethylene-polypropylene porous composite membrane, 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, silicon oxide, magnesium oxide, 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, and barium sulfate.

[0046] The electrode assembly of the secondary battery in this application also includes an electrolyte, which comprises a lithium salt and an organic solvent. This application does not impose any particular limitation on the mass percentage of the lithium salt and organic solvent in the electrolyte, as long as the purpose of this application is achieved. For example, based on the mass of the electrolyte, the mass percentage of the lithium salt can be 10% to 40%, and the mass percentage of the organic solvent can be 60% to 90%.

[0047] This application does not impose any particular limitation on the type of lithium salt, as long as it achieves the purpose of this application. Lithium salts known in the art can be used, such as lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, etc. This application does not impose any particular limitation on the organic solvent, as long as it achieves the purpose of this application. For example, the organic solvent can include carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents (such as dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphate esters).

[0048] The second aspect of this application provides an electronic device that includes the secondary battery provided in the first aspect of this application. This application does not particularly limit the specific types of electronic devices; for example, electronic devices may include, but are not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0049] To clearly understand the technical solution of this application, the following detailed description of this application is provided in conjunction with specific embodiments and comparative examples. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0050] Test methods and equipment

[0051] 1. Average particle size testing of metal-organic framework materials

[0052] The coating was sliced ​​using focused ion beam (FIB) and characterized using a high-resolution transmission electron microscope (HRTEM, model Talos F200X). A measurement location was randomly selected, and the particle size of the metal-organic framework material within the selected area (100,000x magnification) was measured and statistically analyzed. The arithmetic mean was then calculated to obtain the average particle size of the metal-organic framework material.

[0053] 2. Mass percentage test of elements A and B in the coating

[0054] The surface EDS test of the coating was performed using an X-ray energy dispersive spectrometer (model Hitachi SU8220) at a test voltage of 10KV. The test area was magnified 3000 times and the entire area was scanned by EDS.

[0055] 3. Average coating thickness test

[0056] The electrode was processed by ion polishing and then characterized by scanning electron microscopy (SEM). Within the same selected area, the thickness of the coating was measured at five randomly selected locations. The arithmetic mean of the coating thickness at the five different locations was calculated to obtain the average thickness of the coating.

[0057] 4. Porosity testing of coatings and diaphragms

[0058] The porosity of the coating and the diaphragm can be tested according to GB / T33052-2016. Cut the sample into a suitable size and measure the volume V1 of the sample. Place the sample in a bottle containing hexadecane for a certain period of time so that the pores in the sample are completely filled with hexadecane and calculate the volume of hexadecane absorbed, V2. Porosity (%) = (V2 / V1) × 100%.

[0059] 5. Lithium plating test of the battery

[0060] After formation, the soft-pack lithium-ion battery was placed in a constant temperature chamber at 25℃±1℃ for 30 minutes. It was first charged to 4.5V with a current of 2C and then placed for 5 minutes. Then it was discharged to 3V with a current of 0.5C. This is one charge-discharge cycle, and a total of 10 cycles were performed. After the cycle was completed, it was charged to 4.5V with a current of 2C again. The charge-discharge test was then stopped, and the cell was disassembled to observe the lithium plating state.

[0061] 6. Battery cycle performance test

[0062] After formation, the pouch lithium-ion battery was placed in a constant temperature chamber at 25℃±1℃ for 30 minutes. It was then charged to 4.5V at 0.5C and placed for 5 minutes. Next, it was discharged to 3V at 0.5C. This constitutes one charge-discharge cycle. The initial cycle discharge capacity C0 of the pouch lithium-ion battery was recorded. This cycle was then repeated 100 times, and the cycle discharge capacity C1 of the 100th cycle was recorded. The 100-cycle capacity retention rate = C1 / C0 × 100%.

[0063] 7. Battery rate performance test

[0064] After formation, the soft-pack lithium-ion batteries were placed in a constant temperature chamber at 25℃±1℃ for 30 minutes and then subjected to the following charge-discharge cycles: First, they were charged to 4.5V at a current of 0.5C, placed for 5 minutes, and then discharged to 3V at a current of 0.5C, recording the discharge capacity C0; then, they were charged to 4.5V at a current of 0.5C, placed for 5 minutes, and then discharged to 3V at a current of 1C, recording the discharge capacity C1; then, they were charged to 4.5V at a current of 0.5C, placed for 5 minutes, and then discharged to 3V at a current of 2C, recording the discharge capacity C2; finally, they were charged to 4.5V at a current of 0.5C, placed for 5 minutes, and then discharged to 3V at a current of 3C, recording the discharge capacity C3. The capacity retention rate under 3C discharge conditions = C3 / C0 × 100%.

[0065] Example 1

[0066] <Preparation of Metal-Organic Framework Materials>

[0067] An ethanol solution of zinc nitrate (4 mmol) was added to an ethanol solution of 2-methylimidazole (8 mmol), and the mixture was sonicated for 0.5 h. The mixture was then heated at 65 °C for 2 days and cooled to room temperature. The mixture was washed with pure ethanol and dried under a nitrogen atmosphere to obtain the metal-organic framework material (ZIF-8).

[0068] <Preparation of Negative Electrode Sheets>

[0069] The negative electrode active material (graphite), styrene-butadiene rubber (SBP) and sodium carboxymethyl cellulose (CMC) were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 97:2:1 to form a uniform negative electrode slurry with a solid content of 40 wt%.

[0070] The negative electrode slurry was coated onto one side of the copper foil of the negative electrode current collector and dried at 85°C. After cold pressing, cutting, and slitting, it was dried under vacuum at 120°C for 12 hours to obtain a single-sided coated negative electrode sheet. The above steps were repeated on the other side of the copper foil in the single-sided coated negative electrode sheet to obtain a double-sided coated negative electrode sheet. This was then cold-pressed, cut, and slitting, and dried under vacuum at 120°C for 12 hours to obtain a negative electrode sheet with dimensions of 78mm × 875mm for later use. The compaction density of the negative electrode material layer after cold pressing was 1.7 g / cm³. 3 .

[0071] The above-mentioned metal-organic framework material, PVDF and NMP are mixed in a mass ratio of 60:30:10 to form a coating slurry. The coating slurry is then uniformly coated on the surface of the negative electrode material layer of the above-mentioned negative electrode sheet to obtain a negative electrode sheet with a coating.

[0072] <Preparation of the positive electrode>

[0073] Lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and positive electrode binder (polyvinylidene fluoride (PVDF)) were mixed at a mass ratio of 97:1.4:1.6. N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode slurry with a solid content of 72 wt%. The slurry was then uniformly stirred under vacuum. The positive electrode slurry was then uniformly coated onto one side of a 12 μm thick aluminum foil used as a positive electrode current collector and dried at 85 °C to obtain a single-sided coated positive electrode sheet. The coating weight of the positive electrode material layer was 19 mg / cm³. 2 Then, the above steps are repeated on the other side of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After cold pressing, cutting, and slitting, it is dried under vacuum at 85℃ for 4 hours to obtain a positive electrode sheet with dimensions of 74mm × 867mm for later use. The compaction density of the positive electrode material layer after cold pressing is 4.2 g / cm³. 3 .

[0074] <Preparation of Electrolyte>

[0075] In an argon-atmospheric glove box with a water content of less than 10 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed uniformly at a weight ratio of EC:EMC:DEC = 30:50:20 to obtain a base solvent. Then, lithium hexafluorophosphate (LiPF6) and fluoroethylene carbonate (FEC) were added to the base solvent and mixed uniformly to obtain the electrolyte. Based on the mass of the electrolyte, the lithium salt content was 12.5% ​​by mass, the FEC content was 5% by mass, and the remainder was the base solvent.

[0076] <Preparation of the diaphragm>

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

[0078] <Preparation of Lithium-ion Full Batteries>

[0079] The positive electrode, separator, and coated negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. This is then wound to form the electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag, dried at 80°C, and then injected with electrolyte. Following vacuum sealing, settling, formation, shaping, and capacity testing, a soft-pack lithium-ion battery is obtained, which is a lithium-ion full battery.

[0080] Examples 2 to 3

[0081] Except for the difference in the average particle size of the metal-organic framework material compared to Example 1, which was achieved by adjusting the synthesis temperature in the <Preparation of Metal-Organic Framework Materials> section, the rest of the steps are the same as in Example 1. Lowering the reaction temperature can reduce the average particle size of the metal-organic framework material, while raising the reaction temperature can increase the average particle size of the metal-organic framework material.

[0082] Example 4

[0083] Except for the preparation of metal-organic framework materials, which differs from Example 1, the rest is the same as Example 1.

[0084] The preparation of the metal-organic framework material was as follows: At room temperature, a nickel nitrate solution (concentration 0.01 mol / L, solvent: water) was added to a terephthalic acid solution (concentration 0.01 mol / L, solvent: N,N-dimethylformamide), with a volume ratio of nickel nitrate solution to terephthalic acid solution of 2:1. After dissolving and stirring for 1.5 h, a precursor solution was obtained. Then, the precursor solution was subjected to a solvothermal reaction at 120 °C for 12 h to obtain a green precipitate. The green precipitate was washed by centrifugation and filtered using N,N-dimethylformamide and anhydrous ethanol, respectively, and dried below 65 °C to obtain the metal-organic framework material (Ni-MOF).

[0085] Example 5

[0086] Except for the preparation of metal-organic framework materials, which differs from Example 1, the rest is the same as Example 1.

[0087] Preparation of the metal-organic framework material: 5.60 mmol of Zn(NO3)2·6H2O and 2.12 mmol of terephthalic acid were dissolved in 80 mL of DMF solvent to obtain a mixture. The mixture was then placed in a polytetrafluoroethylene-lined autoclave, sealed, and heated to 403 K for 4 hours. After cooling to room temperature, the sample powder was collected by centrifugation and washed with DMF to remove unreacted zinc nitrate. After washing with methanol and drying, the metal-organic framework material (MOF-5) was obtained.

[0088] Examples 6 to 7

[0089] Except for the difference in the mass percentage of metal-organic framework material in the coating in the <Preparation of Negative Electrode Sheet> compared to Example 1, the rest is the same as in Example 1.

[0090] Example 8

[0091] Except for the addition of ceramic material (LATP) to the coating slurry in the <Preparation of Negative Electrode Sheet>, and the difference in the mass percentage of ceramic material in the coating compared to Example 1, the rest is the same as in Example 1.

[0092] Example 9

[0093] Except for the addition of ceramic material (LLZO) to the coating slurry in the <Preparation of Negative Electrode Sheet>, and the difference in the mass percentage of ceramic material in the coating compared to Example 1, the rest is the same as Example 1.

[0094] Examples 10 to 11

[0095] Except for the difference in the mass percentage of ceramic material in the coating in the <Preparation of Negative Electrode Sheet> compared to Example 8, the rest is the same as in Example 8.

[0096] Examples 12 to 14

[0097] Except for the difference in the average thickness of the coating in <Preparation of Negative Electrode Sheet> compared to Example 1, the rest is the same as in Example 1.

[0098] Example 15

[0099] Except for the addition of metal-organic framework material (ZIF-8) to the positive electrode slurry in the <Preparation of Positive Electrode Sheet>, and the difference in the mass percentage of metal-organic framework material in the positive electrode material layer compared to Example 1, the rest is the same as in Example 1.

[0100] Example 16

[0101] Except for the addition of metal-organic framework material (ZIF-8) to the negative electrode slurry in the <Preparation of Negative Electrode Sheet>, and the difference in the mass percentage of metal-organic framework material in the negative electrode material layer compared to Example 1, the rest is the same as in Example 1.

[0102] Example 17

[0103] Except for the addition of metal-organic framework material (ZIF-8) to the positive electrode slurry in the <Preparation of Positive Electrode Sheet>, and the difference in the mass percentage of metal-organic framework material in the positive electrode material layer compared to Example 1; except for the addition of metal-organic framework material (ZIF-8) to the negative electrode slurry in the <Preparation of Negative Electrode Sheet>, and the difference in the mass percentage of metal-organic framework material in the negative electrode material layer compared to Example 1; the rest are the same as Example 1.

[0104] Comparative Example 1

[0105] Except for the section on "Preparation of Negative Electrode Sheet", in which the metal-organic framework material in the coating is replaced with the same mass of activated carbon, the rest is the same as in Example 1.

[0106] Comparative Example 2

[0107] Except for the section on "Preparation of Positive Electrode Sheet", in which the metal-organic framework material in the coating is replaced with the same mass of carbon aerogel, the rest is the same as in Example 1.

[0108] Table 1

[0109]

[0110] Table 2

[0111]

[0112]

[0113] Table 3

[0114]

[0115]

[0116] In Tables 2 and 3, " / " indicates that there are no relevant parameters.

[0117] According to the data in Tables 1, 2 and 3, the soft-pack lithium-ion batteries in Examples 1 to 17 did not experience lithium plating, and the capacity retention rate after 100 cycles was greater than or equal to 94%, while the capacity retention rate under 3C discharge conditions was greater than or equal to 90%. This indicates that the secondary battery of this application can effectively improve lithium plating at the corner interface of the bending area, and at the same time has good cycle performance and excellent rate performance.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A secondary battery, comprising an electrode assembly, the electrode assembly including a positive electrode, a negative electrode, and a separator wound together, the separator being located between the positive electrode and the negative electrode; characterized in that, The electrode assembly includes a flat region and bent regions located at opposite ends of the flat region; a coating is provided between the positive electrode and / or negative electrode in the bent region and the separator; the coating comprises a metal-organic framework material.

2. The secondary battery as described in claim 1, characterized in that, The average particle size of the metal-organic framework material is 10 nm to 100 nm.

3. The secondary battery as described in claim 1, characterized in that, The average thickness of the coating is 0.5 μm to 2 μm.

4. The secondary battery as described in claim 1, characterized in that, The metal-organic framework material contains element A, which includes at least one of Zn, Cu, Cr, Al, Fe, Ni, Mn, and Co; the mass percentage of element A is 0.1% to 1% based on the mass of the coating.

5. The secondary battery as described in claim 4, characterized in that, The coating also includes a ceramic material containing element B, which includes at least one of Li, Al, Ti, Zr, O, S, P, and Cl.

6. The secondary battery as described in claim 5, characterized in that, Based on the coating quality, the ratio of the mass percentage of element B to the mass percentage of element A is between 0 and 1.

7. The secondary battery as described in claim 1, characterized in that, The metal-organic framework material is composed of metal ions and organic ligands; The metal ions include at least one of zinc ions, cobalt ions, copper ions, iron ions, nickel ions, and zirconium ions; The organic ligand includes at least one of 2-methylimidazole, 1,3,5-benzenetricarboxylic acid, and terephthalic acid.

8. The secondary battery as described in claim 1, characterized in that, The porosity of the coating is 10% to 50%; the difference between the porosity of the coating and the porosity of the diaphragm in the flat region is 5% to 40%.

9. The secondary battery as described in claim 1, characterized in that, The positive electrode sheet in the bending region includes a positive electrode material layer, which comprises a metal-organic framework material; and / or... The negative electrode sheet in the bending region includes a negative electrode material layer, which includes a metal-organic framework material.

10. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 9.

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