Foam and preparation method thereof, battery and electric equipment

Abstract

The invention provides foam and a preparation method thereof, a battery and electric equipment. The foam has the most frequent pore size of 23-50 microns and the pore size distribution of 5-91 microns. The foam provided by the invention can guarantee the cycle performance under the condition that internal stress or shearing force is generated due to non-uniform stress on the large surface of the pole core.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and particularly to a foam, a preparation method thereof, a battery, and an electrical device. Background Art

[0002] Foam is a material obtained by foaming plastic particles, and has a series of characteristics such as high elasticity, light weight, fast pressure-sensitive fixation, and convenient use, and is widely used in battery systems. In a battery system, the porous structure of the foam can effectively absorb and retain the electrolyte, reduce the free flow of the electrolyte by absorbing the electrolyte, and reduce the leakage risk.

[0003] Patent document CN218242213U discloses a battery cell structure, which includes a foam, and the porosity of the foam is between 30% and 75%; a battery cell unit, the battery cell unit is a battery cell body or composed of at least two battery cell bodies connected in parallel, and the foam is bonded to the surface of the bare battery cell, and the battery cell body is a cylindrical or square battery cell body. This foam can fully absorb the electrolyte, so that the foam can reduce the loss of the electrolyte during the battery processing. In addition, as the battery cell cycles, the electrolyte absorbed in the foam is released, so as to ensure that there is enough electrolyte during the battery cell cycle, extend the service life of the battery, and improve the problem of large-area blackboard diving of the negative electrode plate caused by the depletion of the electrolyte.

[0004] However, in the existing battery cells, when the initial pre-tightening force exceeds a certain value, local stress will be too large. Even if the foam is bonded to the surface of the bare battery cell, it will still cause the electrolyte to be extruded locally and unable to flow back, resulting in the drying up of the electrolyte and cyclic diving.

[0005] Therefore, it is urgent to develop a new type of foam to ensure the cycling performance in the case of uneven stress or shear force on the large surface of the electrode core. Summary of the Invention

[0006] The present invention provides a foam, which has a special pore size distribution and can ensure the cycling performance in the case of uneven stress or shear force generated on the electrode core when used in a battery.

[0007] The present invention also provides a preparation method of the foam, the preparation method is simple to operate, and the prepared foam has excellent cycling performance.

[0008] The present invention also provides a battery, which includes the above-mentioned foam, and thus has good cycling performance.

[0009] The present invention also provides an electrical device, which includes the above-mentioned battery and has excellent use performance.

[0010] On the one hand, the present invention provides a foam, the most frequent pore size of the foam is 23-50 μm, and the pore size distribution is 5-91 μm.

[0011] For the foam as described above, the maximum pore size of the foam is A, and the minimum pore size of the foam is B, satisfying 42 μm ≤ A - B ≤ 71 μm.

[0012] For the foam as described above, the porosity of the foam is 30% - 90%.

[0013] For the foam as described above, the thickness of the foam is 0.3 mm - 3 mm.

[0014] For the foam as described above, the foam is selected from at least one of polyurethane foam, polyvinyl alcohol foam, polyacrylamide, polyethylene glycol, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl methyl ether, and polyvinyl caprolactam.

[0015] On another aspect, the present invention provides a preparation method of the foam as described above, comprising the following steps:

[0016] 1) Quick-freezing a mixed solution containing a polymer at -50°C to -20°C for 0.5 - 2 h to obtain a precursor;

[0017] 2) Performing a solvent removal treatment on the precursor under a vacuum degree of 20 Pa to 150 Pa to obtain the foam;

[0018] Wherein, the polymer includes at least one of polyurethane, polyvinyl alcohol, polyacrylamide, polyethylene glycol, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl methyl ether, and polyvinyl caprolactam.

[0019] For the preparation method as described above, in step 2), the heating rate of the solvent removal treatment is 2.5 - 10°C / h, the temperature is -10 - 0°C, and the time is 10 - 14 h.

[0020] For the preparation method as described above, the mass concentration of the polymer in the mixed solution is 10% - 50%.

[0021] For the preparation method as described above, the mixed solution is prepared by a preparation method including the following steps:

[0022] Mixing the polymer and the solvent and then stirring in a water bath at 30°C to 50°C, the stirring rate is 100 - 600 rpm, and the time is 10 - 60 min.

[0023] On another aspect, the present invention provides a battery, including the foam as described above or the foam prepared by the preparation method as described above.

[0024] The battery as described above, the battery includes a first surface, a second surface, and a third surface;

[0025] Wherein, the first surface and the second surface are arranged opposite to each other, and the third surface is between the first surface and the second surface;

[0026] The battery cover plate is arranged on the first surface, and the foam is arranged on the third surface.

[0027] On the other hand, the present invention provides an electrical device, including the battery as described above.

[0028] The foam provided by the present invention has a special pore size distribution, and improves the ability to continuously release the expansion space during the cycling process through smaller pore sizes and a uniformly distributed pore structure, reduces the expansion force performance in the battery life termination state, and further ensures the cycling performance in the case of uneven stress and shear force on the large surface of the electrode core. Description of the Drawings

[0029] Figure 1 It is a schematic side view of the battery structure provided by a specific embodiment of the present invention;

[0030] Figure 2 It is a schematic top view of the battery structure provided by a specific embodiment of the present invention;

[0031] Figure 3 It is the compression curve of the foam provided by Examples 1-4 and Comparative Example 1 of the present invention;

[0032] Figure 4 It is the cycling expansion force curve of the batteries provided by Example 1, Comparative Example 1 and the control group of the present invention.

[0033] Description of the Reference Numerals:

[0034] 1 - housing; 2 - foam; 3 - common foam; 4 - bare electrode core; 5 - battery cover plate; A - first surface; B - second surface; C - third surface. Detailed Embodiments

[0035] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0036] Currently, the common way to use the foam in a battery is to wrap the bare battery cell with the foam. However, the existing foam cannot maintain its original pore size distribution under internal stress and shear stress, and even problems such as aging may occur. During the cycling process, when uneven stress is generated on the large surface of the electrode core, resulting in internal stress or shear stress, it will cause wrinkles and lithium deposition in the gaps between the electrode sheets, consuming a large amount of electrolyte and thus leading to cycling degradation.

[0037] Therefore, by optimizing the pore size distribution of the foam, the ability to continuously release the expansion space during the cycling process can be enhanced, improving the cycling performance of the battery.

[0038] On the one hand, the present invention provides a foam, the most frequent pore size of the foam is 23 - 50 μm, and the pore size distribution is 5 - 91 μm.

[0039] The foam is a porous material composed of a large number of tiny bubbles or pores. The pore size distribution of the foam can be analyzed by common methods in the art, such as microscopy imaging method, gas adsorption method, mercury intrusion method, etc.

[0040] In a specific embodiment, the mercury intrusion method is used to analyze the pore size distribution of the foam, including the following steps:

[0041] ① Sample preparation: Place the dry sample directly in a sealed sample chamber.

[0042] ② Instrument preparation: Calibrate the mercury intrusion porosimeter to ensure the correct operation of the pressure sensor and the volume recorder. Set the experimental parameters and adjust the pressure range and step according to the characteristics of the sample.

[0043] ③ Testing process: At low pressure (usually starting from a few hundred pascals), mercury begins to gradually invade the larger pores and cracks on the surface of the sample; as the pressure increases (which can reach the order of hundreds of megapascals), mercury gradually invades smaller pores.

[0044] ④ Data acquisition: The mercury intrusion data within the entire pressure range will be recorded to generate a pressure - volume curve. Through this curve, the pore volume distribution can be analyzed.

[0045] ⑤ Data analysis: Use the Washburn equation to convert the pressure - volume data into pore size distribution. This equation assumes that mercury enters the sample through cylindrical pores and uses the surface tension and contact angle of mercury to calculate the pore size.

[0046] Analysis software is usually used to automatically process these data and generate a graph of pore volume versus pore size. The starting point and ending point of the peak in the graph are taken as the minimum and maximum pore sizes, and the pore size corresponding to the highest peak intensity is the most frequent pore size.

[0047] Among them, the most frequent pore size of the foam refers to the pore size with the highest frequency in the pore size distribution of the foam. Specifically, the most frequent pore size of the foam includes but is not limited to 23μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, or the range composed of any two of them.

[0048] The pore size distribution in the present invention refers to the range formed by the minimum pore size and the maximum pore size in the foam. Specifically, the pore size distribution includes but is not limited to 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 91μm, or the range composed of any two of them.

[0049] The foam provided by the present invention has a special pore size distribution. When the most frequent pore size and the pore size distribution of the foam meet the above ranges, it can not only effectively absorb and relieve internal stress and shear stress through the special pore size distribution, protect the electrode material, and prevent cracking and pulverization caused by volume change during charge and discharge, but also the special pore size distribution can disperse local stress and shear stress to a larger area, and still provide a continuous compressible space within the compression stress range of the foam, reducing the concentrated stress on a single electrode area when the stress is too large in the later stage of battery cycling, reducing mechanical damage to the material, so that when the battery is under internal stress or shear stress, the electrolyte can successfully flow back, avoiding electrolyte dryness and cyclic voltage drop.

[0050] Further, in a specific embodiment of the present invention, the maximum pore size of the foam is A, and the minimum pore size of the foam is B, satisfying 42μm ≤ A - B ≤ 71μm.

[0051] Specifically, the difference between the maximum pore size and the minimum pore size of the foam includes but is not limited to 42μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 71μm, or the range composed of any two of them.

[0052] When the difference between the maximum pore size and the minimum pore size of the foam meets the above range, the pore size distribution range is relatively wide, which can more effectively disperse and absorb local stress. Among them, the larger pore size can provide additional buffer space, while the smaller pore size helps to maintain the overall strength and stability of the material. At the same time, the diversity of pore size distribution can further optimize the retention and flow of the electrolyte. Among them, the larger pore size helps the rapid distribution of the electrolyte, while the smaller pore size helps to retain the electrolyte, ensuring good ionic conductivity still under stress conditions.

[0053] As a porous structure, the porosity of the foam has a significant impact on various properties of the foam, such as its cushioning performance and liquid absorption capacity.

[0054] In a specific embodiment, the porosity of the foam is 30% - 90%.

[0055] In the present invention, the porosity of the foam refers to the ratio between the pore volume and the total volume, and can be calculated by the following formula:

[0056] Porosity = (pore volume / total volume) × 100%.

[0057] The porosity can be measured by methods such as gas adsorption method, liquid impregnation method, microscope image analysis, etc. Specifically, the porosity of the foam in the present invention includes but is not limited to 30%, 40%, 50%, 60%, 70%, 80%, 90% or the range composed of any two of them.

[0058] When the porosity of the foam is within the above range, the foam can maintain a certain flexibility while providing sufficient structural support, making it easier for the foam to return to its original shape after being subjected to local stress or deformation, and maintaining the function of the foam. Moreover, the porosity within the above range can ensure the effective management of the retention and flow of the electrolyte in battery applications, thereby improving ion conductivity and enhancing the cycling performance of the battery.

[0059] When the foam is applied to a battery, it needs to have a suitable thickness to exert its stress dispersion ability and support and protection functions. In a specific embodiment of the present invention, the thickness of the foam is 0.3 mm - 3 mm.

[0060] Specifically, the thickness of the foam includes but is not limited to 0.3 mm, 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm or the range composed of any two of them.

[0061] When the thickness of the foam is within the above range, it can provide more cushioning space, reduce stress concentration, and is more conducive to the recovery of the foam after being subjected to mechanical stress, maintaining its functions and performance, and extending the service life of the battery.

[0062] Furthermore, in a specific embodiment of the present invention, the foam is selected from at least one of polyurethane foam, polyvinyl alcohol foam, polyacrylamide, polyethylene glycol, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl methyl ether, and polyvinyl caprolactam.

[0063] The above types of foams have good cushioning effects, strong chemical resistance, and are more stable.

[0064] On the other hand, the present invention provides a preparation method of the foam as described above, including the following steps:

[0065] 1) The mixed solution including the polymer is subjected to quick freezing treatment at -50°C to -20°C for 0.5 to 2 hours to obtain a precursor;

[0066] 2) The solvent of the precursor is removed under a vacuum degree of 20 Pa to 150 Pa to obtain the foam;

[0067] Wherein, the polymer includes at least one of polyurethane, polyvinyl alcohol, polyacrylamide, polyethylene glycol, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl methyl ether, and polyvinyl caprolactam.

[0068] The preparation method provided by the present invention can prepare a foam with a most frequent pore diameter of 23 - 50 μm and a pore size distribution of 5 - 91 μm.

[0069] Specifically, in step 1), the mixed solution including the polymer is stirred evenly, and then the mixed solution is poured into a mold and quickly cooled to -50°C to -20°C for quick freezing treatment for 0.5 to 2 hours to form smaller and evenly distributed ice crystals in the mold to obtain a precursor.

[0070] The temperature of the quick freezing treatment includes but is not limited to -50°C, -45°C, -40°C, -35°C, -30°C, -25°C, -20°C or the range composed of any two of them, and the time includes but is not limited to 0.5 h, 1 h, 1.5 h, 2 h or the range composed of any two of them.

[0071] The present invention does not limit the device for quick freezing treatment, and common devices in the art can be selected for quick freezing treatment. For example, a freeze dryer is used to quickly cool to -50°C to -20°C, and the mold is placed in the freezing cavity of the freeze dryer for 0.5 - 2 hours to obtain a precursor.

[0072] During the quick freezing treatment, the lower the temperature, the faster the freezing speed, which will result in small and evenly distributed ice crystals, while slow freezing may produce large and uneven ice crystal structures. A faster freezing speed can be selected, such as -5 to -10°C / min.

[0073] It can be understood that the mixed solution also includes a solvent. The present invention does not limit the specific type of the solvent, and common solvents in the art can be selected, such as water, ethanol, acetone, methyl ether, DMF, and NMP.

[0074] In a specific embodiment, the polymer is selected as aqueous polyurethane (solid content is 50%), and the solvent is water.

[0075] In step 2), the precursor is subjected to solvent removal treatment under a vacuum of 20 Pa to 150 Pa, so that the residual solvent in the precursor sublimes, and the solvent is removed without damaging the foam structure, forming a stable foam.

[0076] The present invention does not limit the device and specific operation of the solvent removal treatment. In a specific embodiment, a vacuum pump is used to reduce the chamber pressure of the freezing chamber, so that the vacuum includes but is not limited to 20 Pa, 30 Pa, 40 Pa, 50 Pa, 60 Pa, 70 Pa, 80 Pa, 90 Pa, 100 Pa, 110 Pa, 120 Pa, 130 Pa, 140 Pa, 150 Pa or the range composed of any two of them.

[0077] Among them, in order to make the solvent sublime more evenly, the temperature and time of the solvent removal treatment can be further controlled to make the pore size distribution more suitable.

[0078] In a specific embodiment, the heating rate of the solvent removal treatment is 2.5 to 10 °C / h, the temperature is -10 to 0 °C, and the time is 10 to 14 h.

[0079] Specifically, the heating rate includes but is not limited to 2.5 °C / h, 3 °C / h, 4 °C / h, 5 °C / h, 6 °C / h, 7 °C / h, 8 °C / h, 9 °C / h, 10 °C / h or the range composed of any two of them. The temperature of the solvent removal treatment includes but is not limited to -10 °C, -8 °C, -6 °C, -4 °C, -2 °C, 0 or the range composed of any two of them. The time includes but is not limited to 10 h, 10.5 h, 11 h, 11.5 h, 12 h, 12.5 h, 13 h, 13.5 h, 14 h or the range composed of any two of them.

[0080] When the heating rate, temperature and time of the solvent removal treatment meet the above ranges, it is beneficial to obtain a more uniform pore structure and improve the performance of the foam.

[0081] During the preparation of the foam, the concentration of the polymer in the mixed solution has a great influence on the porosity. In a specific embodiment, the mass concentration of the polymer in the mixed solution is 10% to 50%.

[0082] Specifically, the mass concentration of the polymer in the mixed solution includes but is not limited to 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or the range composed of any two of them.

[0083] Higher polymer concentrations generally result in smaller pore sizes and denser foam structures, improving the mechanical stability of the foam, while lower concentrations produce larger pore sizes and more open structures, enhancing the electrolyte absorption capacity of the foam. Mass concentrations within the above ranges enable the foam to have a more excellent pore size distribution and improve foam performance.

[0084] In a specific embodiment, to obtain a uniformly mixed solution, the mixed solution is prepared by a preparation method including the following steps:

[0085] The polymer is mixed with the solvent and then stirred in a water bath at 30°C to 50°C, with a stirring rate of 100 - 600 rpm and a time of 10 - 60 min.

[0086] Specifically, the temperature of the water bath stirring includes but is not limited to 30°C, 35°C, 40°C, 45°C, 50°C or the range composed of any two of them, the stirring rate includes but is not limited to 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm or the range composed of any two of them, and the time includes but is not limited to 10 min, 20 min, 30 min, 40 min, 50 min, 60 min or the range composed of any two of them.

[0087] Another aspect of the present invention provides a battery, including the foam as described above or the foam prepared by the preparation method as described above.

[0088] Since the battery provided by the present invention includes the foam as described above or the foam prepared by the preparation method as described above, the battery can still maintain good cycling performance during cycling.

[0089] Further, in a specific embodiment of the present invention, as Figure 1 shown, the battery includes a first surface A, a second surface B, and a third surface C;

[0090] Among them, the first surface A and the second surface B are oppositely arranged, and the third surface C is between the first surface A and the second surface B;

[0091] The battery cover plate 5 is arranged on the first surface A, and the foam 2 is arranged on the third surface C.

[0092] The third surface in the present invention refers to the circumferential surface between the first surface and the second surface. If the battery is a cylindrical battery, the third surface refers to the arc surface of the cylindrical battery; if the battery is a square battery, the third surface refers to the square circumferential surface between the battery cover plate and the bottom of the square battery.

[0093] Among them, Figure 2This is a top view schematic diagram of the battery structure in another specific embodiment of the present invention. The foam 2 can control the pressure on the large surface of the electrode core, ensure a certain restraint force at the initial stage of cycling, and maintain the uniform force on the electrode plates in the cycling state of the electrode core, without the phenomenon of gaps caused by electrode plate wrinkles; at the same time, it provides a continuous compressible space during the cycling process to prevent the compression curve of the foam 2 from quickly reaching the non-linear growth region and reduce the expansion force of the module in the EOL state. At the same time, the foam 2 provides the functions of liquid absorption and insulation.

[0094] The battery cover plate 5 includes a cover plate, an aluminum block, an insulating sheet, a sealing ring, a pole column, a spacer, an explosion-proof valve, an explosion-proof valve protection sheet, etc., and is connected to the electrode tab of the electrode core through a lead-out electrode sheet.

[0095] It can be understood that, as Figure 1 shown, the battery further includes a housing 1, a common foam 3, and a bare battery cell 4, wherein the housing 1 is a single-sided through-hole housing, and the housing can be prepared by common methods in the art, such as stamping or welding.

[0096] The present invention does not limit the material of the housing 1, and common materials in the art can be selected, such as aluminum or steel.

[0097] The housing 1 can play a role in physically protecting and supporting the internal structure of the battery, preventing the influence of the external environment on the inside of the battery.

[0098] The common foam 3 can be a common foam in the art. The common foam 3 is arranged on the second surface B and is mainly used to support the bare battery cell. The common foam 3 with a suitable pore size distribution can be selected according to actual needs. In a specific embodiment, the porosity of the common foam 3 is 20%-40%, the thickness is 0.3 mm - 0.5 mm, the pore size distribution is 5 μm - 91 μm, the pore size difference is 42 μm - 71 μm, and the most frequent pore size is 23 μm - 50 μm.

[0099] Taking into account the stronger support effect required for the electrode core and the bottom insulation requirement under the Z-axis vibration condition of the battery cell, a common foam with a thickness of 0.3 mm and a porosity of 20% is preferably selected.

[0100] The bare battery cell 4 is formed by winding or laminating a positive electrode sheet, a negative electrode sheet, and a separator, and can lead out an electrode tab for electrical connection with the battery cover plate 5.

[0101] The present invention does not limit the dimensions of each part in the battery and the battery assembly method. In a specific embodiment, the lithium-ion battery is a square aluminum shell battery, with a width of 148 mm, a shoulder height of 103 mm, a thickness of 52 mm, a large surface thickness of the housing of 0.5 mm, a side thickness of 0.55 mm, and a bottom thickness of 1.2 mm.

[0102] The bare battery cell 4 is an LFP system electrode core with a width of 145 mm, a height of 90 mm, and a thickness of 47 mm.

[0103] The battery cover plate 5 is subjected to FtT welding, then inserted into the shell, and after insertion, the shell and cover are welded.

[0104] The housing 1 is made of an aluminum shell. The aluminum shell needs to be pasted with a foam 2 first. For example, a foam 2 with a thickness of 1 mm and a porosity of 90% is pasted on the housing 1; a foam 3 with a thickness of 0.5 mm, a porosity of 20%, a length of 147 mm, and a width of 50.9 mm is pasted on the housing 1.

[0105] More specifically, the complete battery is obtained through processes such as baking, liquid injection, formation, aging, and grading.

[0106] On the other hand, the present invention provides an electrical device including the battery as described above.

[0107] The present invention does not limit the specific type of the electrical device, and it can include any device that requires a battery for power supply, such as electric vehicles, mobile phones, smart homes, robots, drones, electronic cigarettes, speakers, etc.

[0108] The electrical device provided by the present invention includes the above battery, so it has good performance in use.

[0109] Hereinafter, the foam provided by the present invention will be introduced in detail through specific examples.

[0110] Example 1

[0111] The preparation method of the foam provided by the present invention includes the following steps:

[0112] 1. First, add 20 g of waterborne polyurethane (PU, solid content 50%, purchased from Anhui Dawei Huatai New Materials Technology Co., Ltd., AH-K100-1 model anionic waterborne polyurethane, density 1.06 g / cm 3 , molecular weight 10,000 - 100,000) to 100 g of water, and perform water bath stirring at 30 °C with a stirring rate of 300 rpm for 10 min to obtain a mixed solution;

[0113] 2. Pour the above mixed solution into a mold, and quickly cool it to -50 °C using a freeze dryer. Place the mold in the freezing chamber of the freeze dryer for 0.5 h to quickly solidify the solution into a solid to obtain a precursor;

[0114] 3. Use a vacuum pump to reduce the air pressure in the chamber, adjust the heating temperature of the freezing chamber at 10 °C / h, heat it up to -10 °C, with a vacuum degree of 150 Pa, and a duration of 12 h to obtain the foam.

[0115] Example 2

[0116] The preparation method of the foam provided by the present invention comprises the following steps:

[0117] 1. First, add 20 g of aqueous polyurethane (PU, solid content 50%, purchased from Anhui Dawei Huatai New Materials Technology Co., Ltd., AH-K100-1 model anionic aqueous polyurethane, density 1.06 g / cm 3 , molecular weight 10,000 - 100,000) to 100 g of water, carry out water bath stirring at 30 °C, the stirring rate is 300 rpm, and the stirring time is 10 min to obtain a mixed solution;

[0118] 2. Pour the above mixed solution into a mold, quickly cool it to -40 °C using a freeze dryer, place the mold in the freezing chamber of the freeze dryer for 0.5 h, and make the solution quickly solidify into a solid to obtain a precursor;

[0119] 3. Use a vacuum pump to reduce the air pressure in the chamber, adjust the heating temperature of the freezing chamber to 7.5 °C / h, heat it up to -10 °C, the vacuum degree is 100 Pa, and the duration is 12 h to obtain the foam.

[0120] Example 3

[0121] The preparation method of the foam provided by the present invention comprises the following steps:

[0122] 1. First, add 20 g of aqueous polyurethane (PU, solid content 50%, purchased from Anhui Dawei Huatai New Materials Technology Co., Ltd., AH-K100-1 model anionic aqueous polyurethane, density 1.06 g / cm 3 , molecular weight 10,000 - 100,000) to 100 g of water, carry out water bath stirring at 30 °C, the stirring rate is 300 rpm, and the stirring time is 10 min to obtain a mixed solution;

[0123] 2. Pour the above mixed solution into a mold, quickly cool it to -30 °C using a freeze dryer, place the mold in the freezing chamber of the freeze dryer for 0.5 h, and make the solution quickly solidify into a solid to obtain a precursor;

[0124] 3. Use a vacuum pump to reduce the air pressure in the chamber, adjust the heating temperature of the freezing chamber to 5 °C / h, heat it up to -10 °C, the vacuum degree is 50 Pa, and the duration is 12 h to obtain the foam.

[0125] Example 4

[0126] The preparation method of the foam provided by the present invention comprises the following steps:

[0127] 1. First, add 20 g of aqueous polyurethane (PU, solid content 50%, purchased from Anhui Dawei Huatai New Material Technology Co., Ltd., anionic aqueous polyurethane of model AH-K100-1, density 1.06 g / cm 3 , molecular weight 10,000 - 100,000) to 100 g of water, and carry out water bath stirring at 30 °C with a stirring rate of 300 rpm for 10 min to obtain a mixed solution;

[0128] 2. Pour the above mixed solution into a mold, quickly cool it to -20 °C using a freeze dryer, place the mold in the freezing chamber of the freeze dryer for 0.5 h to quickly solidify the solution into a solid to obtain a precursor;

[0129] 3. Use a vacuum pump to reduce the air pressure in the chamber, adjust the heating temperature of the freezing chamber at 2.5 °C / h to heat it up to -10 °C, with a vacuum degree of 150 Pa and a duration of 12 h to obtain a foam.

[0130] Example 5

[0131] The preparation method of the foam provided by the present invention includes the following steps:

[0132] 1. First, add 10 g of polyvinyl alcohol (PVA) to 100 g of ethanol, and carry out water bath stirring at 30 °C with a stirring rate of 300 rpm for 10 min to obtain a mixed solution;

[0133] 2. Pour the above mixed solution into a mold, quickly cool it to -50 °C using a freeze dryer, place the mold in the freezing chamber of the freeze dryer for 0.5 h to quickly solidify the solution into a solid to obtain a precursor;

[0134] 3. Use a vacuum pump to reduce the air pressure in the chamber, adjust the heating temperature of the freezing chamber at 10 °C / h to heat it up to 0 °C, with a vacuum degree of 100 Pa and a duration of 14 h to obtain a foam.

[0135] Example 6

[0136] The preparation method of the foam provided in this example is basically the same as that of Example 1, except that in step 3), the heating rate for solvent removal treatment is 12 °C / h, the temperature is -12 °C, and the time is 8 h.

[0137] Comparative Example 1

[0138] The foam provided in this comparative example is a commercial foam purchased from Chongqing Jinling Printing Co., Ltd.

[0139] Comparative Example 2

[0140] The preparation method of the foam provided in this comparative example is basically the same as that of Example 1, except that:

[0141] In step 2), the temperature of the quick-freezing treatment is -10°C and the time is 3 h.

[0142] Comparative Example 3

[0143] The method for preparing the foam provided in this comparative example is basically the same as that in Example 1, except that:

[0144] In step 3), the solvent removal treatment is not carried out under vacuum conditions.

[0145] Test Example

[0146] 1. Pore size test

[0147] The pore size of the foams provided in all examples and comparative examples was tested using the mercury intrusion method, including the following steps:

[0148] ① Sample preparation: Place the dried sample directly in a sealed sample chamber.

[0149] ② Instrument preparation: Calibrate the mercury intrusion porosimeter to ensure the correct operation of the pressure sensor and the volume recorder. Set the experimental parameters and adjust the pressure range and step according to the characteristics of the sample.

[0150] ③ Test process: At low pressure (usually starting from a few hundred pascals), mercury begins to gradually penetrate into the larger pores and cracks on the surface of the sample; as the pressure increases (which can reach the order of several hundred megapascals), mercury gradually penetrates into smaller pores.

[0151] ④ Data acquisition: The mercury intrusion data within the entire pressure range is recorded to generate a pressure-volume curve. Through this curve, the pore volume distribution can be analyzed.

[0152] ⑤ Data analysis: Use the Washburn equation to convert the pressure-volume data into pore size distribution: This equation assumes that mercury enters the sample through cylindrical pores and uses the surface tension and contact angle of mercury to calculate the pore size.

[0153] Analysis software is usually used to automatically process this data and generate a graph of pore volume versus pore size. The starting and ending points of the peak in the graph are taken as the minimum and maximum pore sizes, and the pore size corresponding to the highest peak intensity is taken as the most frequent pore size. The specific test results are shown in Table 1.

[0154] Table 1

[0155]

[0156]

[0157] 2. Compression performance test

[0158] The compression performance of the foams provided in all the examples and comparative examples was tested, including the following steps:

[0159] ① Sample preparation: Ensure that the surface of the sample is flat to ensure uniform stress.

[0160] ② Equipment calibration: Use a universal material testing machine to ensure accurate calibration of the load cell and displacement sensor of the equipment.

[0161] ③ Test condition setting:

[0162] Define the test speed: a strain rate of 10% / min (0.1 mm / min was used in this case), and set the duration under a constant load to 1 min.

[0163] ④ Test execution:

[0164] Place the sample on the lower fixture of the testing machine, and adjust the upper fixture to slightly touch the upper surface of the sample. Start the test, squeeze the sample at the set speed, and record the force-displacement data. End the test after the sample reaches the predetermined compression rate (e.g., 80% deformation).

[0165] ⑤ Data acquisition and analysis: Record the change of force with displacement during the whole test process to generate a compression curve. Convert the force-displacement data into a stress-strain curve.

[0166] The test results are shown in Table 2.

[0167] Table 2

[0168]

[0169]

[0170] Among them, Figure 3 are the compression curves of the foams provided in Examples 1-4 and Comparative Example 1. It can be seen from Figure 3 that under the same pressure, the compression amount of the foams provided in Examples 1-4 is significantly higher than that of the foam provided in Comparative Example 1, indicating that the foams provided in Examples 1-4 have good buffering ability and can provide a stable and sustainable compression space.

[0171] 3. Cycling performance test

[0172] Lithium-ion batteries were successively made using the foams provided in all the examples and comparative examples for cycling tests.

[0173] Among them, the schematic diagram of the lithium-ion battery is as shown in Figure 1 and includes a housing 1, a foam 2, a common foam 3 (polyurethane foam, purchased from Chongqing Jinling Printing Co., Ltd.), a bare battery cell 4, and a battery cover plate 5. The preparation process includes the following steps:

[0174] The lithium-ion battery is a square aluminum shell battery with a width of 148 mm, a shoulder height of 103 mm, a thickness of 52 mm, a thickness of 0.5 mm for the large surface of the shell, a thickness of 0.55 mm for the side surface, and a thickness of 1.2 mm for the bottom surface. The bare battery core 4 is an LFP system battery core. The positive electrode plate of the battery core is composed of lithium iron phosphate particles, binder (PVDF), and conductive agent (carbon nanotubes and carbon black). The negative electrode plate uses artificial graphite, binder (SBR), and dispersant (CMC). The separator uses a PE + ceramic + glue separator. The positive current collector uses carbon-coated aluminum foil, and the negative current collector uses copper foil. The width of the battery core is 145 mm, the height is 90 mm, and the thickness is 47 mm. The bare battery core 4 is welded to the battery cover plate 5 by FtT welding, and then put into the shell. After putting into the shell, the shell and cover are welded. The shell 1 is made of aluminum shell. The thickness of the foam 2 provided in the examples and comparative examples is 1 mm, which is pasted on the large surface and the side surface of the aluminum shell, that is, the third surface C; the common foam 3 uses a PU foam with a thickness of 0.5 mm, a porosity of 20%, a length of 147 mm, and a width of 50.9 mm, which is pasted on the bottom surface of the aluminum shell, that is, the second surface B. The above sequence is to paste the common foam 3 on the second surface B first, and then paste the foam 2 on the third surface C.

[0175] Subsequently, it needs to go through processes such as baking, liquid injection, formation, aging, and grading to obtain a battery with a cell capacity of 87 Ah.

[0176] At the same time, a control group is set up, and the foam 2 is not set in the batteries of the control group.

[0177] The cycle performance of the prepared batteries is tested: the test temperature is 55 °C, the test current is charged to 3.65 V at 1C and discharged to 2.2 V at 1C, and the voltage range is 2.2 - 3.65 V. The battery core is constrained by a constant-gap steel plate expansion force fixture with a gap of 52 mm. The specific test results are shown in Table 3.

[0178] Table 3

[0179] Serial number Number of circulation turns Capacity retention rate / % Maximum expansion force / N Example 1 500 85.4 2557 Example 2 500 84.5 2669 Example 3 500 83.3 2823 Example 4 500 82.9 3048 Example 5 500 85.2 2588 Example 6 500 81.3 3544 Comparative example 1 400 79.8 5247 Comparative example 2 450 80.0 5156 Comparative example 3 100 91.2 66 Control group 100 90.4 52

[0180] Among them, Figure 4 are the high-temperature expansion force cycle curves provided by Example 1, Comparative Example 1, and the control group. From Figure 4It can be seen that the control group experienced a plunge after 80 cycles. The reason is that in the state without foam, the inner core of the electrode was initially not restricted by the aluminum shell and was in a state without pre-tightening force. As the electrode core expanded and contracted during charging and discharging, a large gap was generated between the electrode sheets, resulting in lithium deposition. Subsequently, a side reaction occurred with the electrolyte, generating a large amount of gas, thus causing the plunge phenomenon. Since the thickness of the internal battery cell increased with the large generation of gas, it can be seen from the expansion force curve that the expansion force increased slightly after the plunge. Compared with the control group, the number of cycles with a faster decline in Example 1 was around the 400th cycle, and the corresponding expansion force was about 2000 N. For Comparative Example 1, the number of cycles with a faster decline was around the 200th cycle, and the corresponding expansion force was about 2400 N. It can be seen from this that when the expansion force increased to a certain value, it would bring about a failure mode of cycle decay and plunge due to excessive force. The growth rate of the expansion force in Example 1 was lower than that in Comparative Example 1. It was found that during the cycling process, the foam in Example 1 could continuously provide the expansion space required by the electrode core, thereby delaying the arrival of the expansion force inflection point and further improving the cycle performance of the battery.

[0181] 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 them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A foam, characterized in that: The most frequent pore size of the foam is 23-50 μm, and the pore size distribution is 5-91 μm.

2. The foam according to claim 1, characterized in that The maximum pore size of the foam is A, and the minimum pore size of the foam is B, satisfying 42 μm≤AB≤71 μm.

3. The foam according to claim 1 or 2, characterized in that: The porosity of the foam is 30%-90%.

4. The foam according to any one of claims 1 to 3, characterized in that: The thickness of the foam is 0.3mm-3mm.

5. The foam according to any one of claims 1 to 4, characterized in that: The foam is selected from at least one of polyurethane, polyvinyl alcohol, polyacrylamide, polyethylene glycol, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl methyl ether and polyvinyl caprolactam.

6. A method for preparing the foam according to any one of claims 1 to 5, characterized in that: The following steps are involved: 1) performing quick freezing treatment on the mixed solution including the polymer at -50°C to -20°C for 0.5 to 2 hours to obtain a precursor; 2) performing a solvent removal treatment on the precursor at a vacuum degree of 20Pa to 150Pa to obtain the foam; Wherein, the polymer includes at least one of polyurethane, polyvinyl alcohol, polyacrylamide, polyethylene glycol, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl methyl ether and polyvinyl caprolactam.

7. The preparation method according to claim 6, characterized in that: In step 2), the heating rate of the solvent removal treatment is 2.5 to 10°C / h, the temperature is -10 to 0°C, and the time is 10 to 14h.

8. The preparation method according to claim 6 or 7, characterized in that: The mass concentration of the polymer in the mixed solution is 10% to 50%.

9. The preparation method according to any one of claims 6 to 8, characterized in that: The mixed solution is prepared by a preparation method comprising the following steps: After the polymer and the solvent are mixed, they are stirred in a water bath at 30° C. to 50° C., with a stirring rate of 100-600 rpm for 10 to 60 minutes.

10. A battery, characterized in that: The invention comprises the foam described in any one of claims 1 to 5 or the foam prepared by the preparation method described in any one of claims 6 to 9.

11. The battery according to claim 10, characterized in that The battery comprises a first side, a second side, and a third side; Wherein, the first surface is arranged opposite to the second surface, and the third surface is between the first surface and the second surface; The battery cover is arranged on the first surface, and the foam is arranged on the third surface.

12. An electrical equipment, characterized in that: A battery comprising the battery according to claim 10 or 11.

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