Flexible anisotropic conductive hydrated salt phase change gel as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of phase change materials, and particularly relates to flexible anisotropic conductive hydrated salt phase change gel as well as a preparation method and application thereof. The flexible anisotropic conductive hydrated salt phase change gel comprises hydrogel and hydrated salt adsorbed in a semi-interpenetrating three-dimensional network structure of the hydrogel, the hydrogel is prepared from the following raw materials in parts by weight: 1 to 15 parts of hydrophilic modified conductive filler, 4 to 15 parts of gel polymer, 1 to 7 parts of polysaccharide substance and 75 to 94 parts of water. The flexible anisotropic conductive hydrated salt phase change gel material disclosed by the invention has high phase change latent heat, high decomposition heat storage and anisotropic conductivity, can realize high-efficiency heat dissipation and temperature control through phase change at high temperature, and can be decomposed to absorb heat when thermal runaway occurs so as to inhibit generation and spreading of thermal runaway; at low temperature, the material can be electrified in one direction to heat the battery, and insulation can be maintained in the other direction, so that the full-temperature-range heat management of the lithium ion battery is realized, and the safety is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of phase change materials, and particularly relates to a flexible anisotropic conductive hydrated salt phase change gel and a preparation method and application thereof. Background Art

[0002] During the application process of lithium batteries, full-temperature thermal management is crucial for their performance and safety. Full-temperature thermal management refers to solving the performance degradation and safety problems of lithium batteries when working at extreme temperatures through low-temperature heating, high-temperature heat dissipation, and ultra-high-temperature thermal runaway protection measures. Because phase change materials can absorb or release latent heat during the phase change process, they have become an important tool for lithium battery thermal management to cope with extreme temperature environments.

[0003] Inorganic hydrated salt phase change materials can absorb a large amount of heat through phase change and thermochemical decomposition, and have the ability to efficiently absorb heat and cool down at high temperatures and prevent ultra-high-temperature thermal runaway. Related technologies have disclosed a hydrated salt thermochemical energy storage composite material, which is composed of a hydrated salt, a highly thermally conductive porous adsorbent material, and a reinforcing material. However, the constructed isotropic conductive three-dimensional continuous rigid framework structure has poor mechanical properties and is easy to break. During the driving process of an automobile, the hydrated salt thermochemical energy storage composite material is prone to mechanical collision with the battery to generate fragments and contact the electrode plate, leading to battery short circuit, and it is difficult to meet the actual safety requirements. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a flexible anisotropic conductive hydrated salt phase change gel and a preparation method and application thereof. The flexible anisotropic conductive hydrated salt phase change gel of the present invention can meet the requirements of full-temperature thermal management of lithium-ion batteries, has good mechanical properties, can resist compression and bending and is not easy to break, can stably fit the battery surface, provide buffering and shock absorption effects, and meet the actual safety requirements.

[0005] The present invention provides a flexible anisotropic conductive hydrated salt phase change gel, which includes a hydrogel and a hydrated salt adsorbed in the semi-interpenetrating three-dimensional network structure of the hydrogel;

[0006] The hydrogel includes the following raw materials for preparation in parts by weight: 1-15 parts of a hydrophilic modified conductive filler, 4-15 parts of a hydrogel polymer, 1-7 parts of a polysaccharide substance, and 75-94 parts of water;

[0007] In the flexible anisotropic conductive hydrated salt phase change gel, the hydrophilic modified conductive filler is distributed in a decreasing manner from the gel surface layer to the center.

[0008] Preferably, the hydrated salt includes one or more of disodium hydrogen phosphate dodecahydrate, sodium acetate trihydrate, sodium sulfate decahydrate, calcium chloride hexahydrate, magnesium nitrate hexahydrate, lithium nitrate trihydrate, and potassium alum dodecahydrate.

[0009] Preferably, the hydrophilic modified conductive filler includes one or more of hydrophilic modified expanded graphite, hydrophilic modified graphene, hydrophilic modified carbon nanotubes, hydrophilic modified carbon nanosheets, hydrophilic modified MXenes, and hydrophilic modified copper powder.

[0010] Preferably, the hydrophilic modified conductive filler is obtained by modifying the conductive filler with a non-ionic surfactant, and the mass ratio of the conductive filler to the non-ionic surfactant is 100:(1-10).

[0011] Preferably, the hydrogel polymer includes one or more of polyvinyl alcohol, gelatin, polyacrylamide, curdlan, sodium polyacrylate, and carboxymethyl cellulose.

[0012] Preferably, the polysaccharide includes one or more of chitosan, sodium alginate, alginic acid, gellan gum, and pectin.

[0013] Preferably, the hydrogel comprises the following raw materials in parts by weight: 10 parts of hydrophilic modified expanded graphite, 8 parts of polyvinyl alcohol, 4 parts of sodium alginate, and 78 parts of water;

[0014] Or it includes: 5 parts of hydrophilic modified graphene, 12 parts of gelatin, 6 parts of chitosan, and 77 parts of water;

[0015] Or it includes: 3 parts of hydrophilic modified carbon nanotubes, 7 parts of curdlan, 5 parts of gellan gum, and 85 parts of water.

[0016] The present invention also provides a method for preparing the flexible anisotropic conductive hydrated salt phase change gel described in the above technical solution, including the following steps:

[0017] Mix and heat the hydrogel polymer, polysaccharide, hydrophilic modified conductive filler, and water to obtain a pre-gel dispersion;

[0018] Remove the bubbles from the pre-gel dispersion, and perform freeze-thaw treatment to obtain a hydrogel;

[0019] Immerse the hydrogel in a hydrated salt solution to obtain the flexible anisotropic conductive hydrated salt phase change gel.

[0020] Preferably, the hydrated salt solution is a saturated hydrated salt solution, and the immersion time is 24-48 h.

[0021] The present invention also provides the application of the flexible anisotropic conductive hydrated salt phase change gel described in the above technical solution or the flexible anisotropic conductive hydrated salt phase change gel obtained by the above preparation method in the full-temperature range thermal management of lithium batteries.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention provides a flexible anisotropic conductive hydrated salt phase change gel, which comprises a hydrogel and a hydrated salt adsorbed in the semi-interpenetrating three-dimensional network structure of the hydrogel; the hydrogel comprises the following raw materials in parts by weight for preparation: 1-15 parts of a hydrophilic modified conductive filler, 4-15 parts of a hydrogel polymer, 1-7 parts of a polysaccharide substance, and 75-94 parts of water;

[0024] In the flexible anisotropic conductive hydrated salt phase change gel, the hydrophilic modified conductive filler is distributed in a decreasing manner from the gel surface layer to the center.

[0025] The present invention combines a hydrated salt and a hydrogel to prepare a flexible anisotropic conductive hydrated salt phase change gel material. The hydrophilic gel carrier can better carry the hydrated salt. By utilizing the three-dimensional continuous flexible structure, toughness and deformability of the hydrogel, it not only solves the problem that the phase change material based on the hydrated salt is fragile, but also can adapt to the volume expansion generated during the charge and discharge process of today's high-capacity and high-power lithium-ion batteries. The hydrated salt simultaneously has the ability of phase change and endothermic decomposition. It conducts efficient heat dissipation and temperature control at high temperatures, and decomposes endothermically during thermal runaway to inhibit the occurrence and spread of thermal runaway. The hydrogel polymer and the polysaccharide substance are crosslinked to form a semi-interpenetrating three-dimensional network structure, which has the function of adsorbing the hydrated salt, so that the hydrated salt will not leak from the material even in the molten state. The hydrophilic modified conductive filler is interspersed in the three-dimensional network formed by the hydrogel polymer and the polysaccharide substance in a gradient dispersion form, with a dense surface layer and a sparse center, forming a certain conductive path, which can enhance the conductivity of the material and enable the material to have the ability of low-temperature heating by electricity, and can meet the requirements of full-temperature-range thermal management of lithium-ion batteries.

[0026] The flexible anisotropic conductive hydrated salt phase change gel material of the present invention has an anisotropic conductive network microscopically and presents a three-layer structure macroscopically. The modified conductive filler is uniformly distributed in the upper and lower surface layers, and a conductive path can be formed transversely, while only a small amount of modified conductive filler is scattered in the middle layer. The material of the present invention shows anisotropic conductive characteristics, exhibits high conductivity transversely and low conductivity longitudinally, can be heated by electricity at low temperatures, and can reduce the risk of short circuit between batteries. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0028] Figure 1 DSC diagram of the material prepared in Example 1;

[0029] Figure 2The physical diagram of the hydrated salt gel prepared in Example 1;

[0030] Figure 3 The schematic diagram of the anisotropic conductivity of the material prepared in Example 1;

[0031] Figure 4 The transverse and longitudinal resistivity diagrams of the materials prepared in Example 1 and Comparative Example 1 in the molten or crystalline state;

[0032] Figure 5 The schematic structural diagram of the arrangement of the square battery and the material in Test Example 3;

[0033] Figure 6 The temperature change curves of different battery packs at different detection times in Test Example 3;

[0034] Figure 7 The temperature change curves of the battery packs of Example 1(a) and Comparative Example 3(b) at different detection times when thermal runaway occurs in Test Example 4;

[0035] Figure 8 The temperature change curves of the battery pack at different detection times when the material prepared in Example 1 is electrically heated at -20°C in Test Example 5. Detailed implementation mode

[0036] The present invention provides a flexible anisotropic conductive hydrated salt phase change gel, which comprises a hydrogel and a hydrated salt adsorbed in the semi-interpenetrating three-dimensional network structure of the hydrogel;

[0037] The hydrogel comprises the following raw materials in parts by weight: 1-15 parts of a hydrophilic modified conductive filler, 4-15 parts of a hydrogel polymer, 1-7 parts of a polysaccharide substance, and 75-94 parts of water;

[0038] In the flexible anisotropic conductive hydrated salt phase change gel, the hydrophilic modified conductive filler is distributed decreasingly from the gel surface layer to the center.

[0039] In the present invention, unless otherwise specified, the materials and equipment used are all commercially available products in the art.

[0040] In the present invention, the hydrophilic modified conductive filler preferably comprises one or more of hydrophilic modified expanded graphite, hydrophilic modified graphene, hydrophilic modified carbon nanotubes, hydrophilic modified carbon nanosheets, hydrophilic modified MXenes, and hydrophilic modified copper powder.

[0041] In the present invention, the hydrophilic modified conductive filler is preferably prepared by a method comprising the following steps:

[0042] Mix a non-ionic surfactant, ethanol, and a conductive filler, perform ultrasonic treatment, and dry to obtain the hydrophilic modified conductive filler.

[0043] In the present invention, the non-ionic surfactant preferably includes one or more of Triton X-100, OP-10, polyoxyethylene lauryl ether, Tween-20, Tween-40, Tween-60, and Span-60. The present invention has no special requirements for the dosage of the ethanol, and it is only necessary to disperse the surfactant and the conductive filler.

[0044] In the present invention, the conductive filler preferably includes one or more of expanded graphite, graphene, carbon nanotubes, carbon nanosheets, MXenes, and copper powder.

[0045] In the present invention, the mass ratio of the conductive filler to the non-ionic surfactant is preferably 100:(1-10), and specifically can be 100:1, 100:2, or 100:3.

[0046] In the present invention, the time of the ultrasonic treatment is preferably 10-30 min, and specifically can be 10 min, 20 min, or 30 min. During the ultrasonic treatment, the hydrophilic groups in the non-ionic surfactant can be grafted onto the conductive filler, so that the conductive filler is modified into a hydrophilic modified conductive filler.

[0047] In the present invention, the temperature of the drying is preferably 80-100 °C, and specifically can be 80 °C, 85 °C, 90 °C, or 100 °C, and the time is preferably 24-48 h, and specifically can be 24 h, 36 h, or 48 h.

[0048] In the present invention, the mixing of the non-ionic surfactant, ethanol, and conductive filler is preferably as follows: first, the non-ionic surfactant is dispersed in excessive ethanol, and then the conductive filler is added.

[0049] In the present invention, the weight parts of the hydrophilic modified conductive filler in the preparation raw materials are preferably 2-12 parts, and specifically can be 3 parts, 5 parts, or 10 parts. The hydrophilic modified conductive filler is dispersed and interspersed in the three-dimensional network formed by the hydrogel polymer and the polysaccharide substance to form a conductive path, which can enhance the conductivity of the material and enable the material to have the ability of low-temperature power-on heating.

[0050] In the present invention, the hydrogel polymer preferably includes one or more of polyvinyl alcohol, gelatin, polyacrylamide, curdlan, sodium polyacrylate, and carboxymethyl cellulose.

[0051] Based on the weight parts of the hydrophilic modified conductive filler, the weight parts of the hydrogel polymer in the preparation raw materials are preferably 7-12 parts, and specifically can be 7 parts, 8 parts, or 12 parts.

[0052] In the present invention, the polysaccharide substance preferably includes one or more of chitosan, sodium alginate, alginic acid, gellan gum, and pectin.

[0053] Based on the weight parts of the hydrophilic modified conductive filler, the weight parts of the polysaccharide substance in the preparation raw materials are preferably 2 - 6 parts, specifically 4 parts, 5 parts, or 6 parts. The hydrogel polymer and the polysaccharide substance will crosslink during the freeze-thaw process to form a semi-interpenetrating three-dimensional network structure, which has the function of adsorbing hydrated salts, so that the hydrated salts will not leak from the material even in the molten state.

[0054] In the present invention, the water is preferably deionized water; based on the weight parts of the hydrophilic modified conductive filler, the weight parts of water in the preparation raw materials are preferably 77 - 85 parts, specifically 77 parts, 78 parts, or 85 parts.

[0055] In the present invention, the hydrated salt preferably includes one or more of disodium hydrogen phosphate dodecahydrate, sodium acetate trihydrate, sodium sulfate decahydrate, calcium chloride hexahydrate, magnesium nitrate hexahydrate, lithium nitrate trihydrate, and potassium alum dodecahydrate. The hydrated salt has the ability of phase change and endothermic decomposition, can dissipate heat and control temperature efficiently at high temperature, and decomposes endothermically to inhibit the occurrence and spread of thermal runaway when thermal runaway occurs.

[0056] In the present invention, the hydrogel preferably includes the following weight parts of preparation raw materials: 10 parts of hydrophilic modified expanded graphite, 8 parts of polyvinyl alcohol, 4 parts of sodium alginate, and 78 parts of water;

[0057] Or includes: 5 parts of hydrophilic modified graphene, 12 parts of gelatin, 6 parts of chitosan, and 77 parts of water;

[0058] Or includes: 3 parts of hydrophilic modified carbon nanotubes, 7 parts of curdlan gum, 5 parts of gellan gum, and 85 parts of water.

[0059] The present invention also provides a preparation method of the flexible anisotropic conductive hydrated salt phase change gel described in the above technical solution, including the following steps:

[0060] Mix and heat the hydrogel polymer, polysaccharide substance, hydrophilic modified conductive filler, and water to obtain a pre-gel dispersion;

[0061] Remove the bubbles from the pre-gel dispersion, and perform freeze-thaw to obtain a hydrogel;

[0062] Immerse the hydrogel in a hydrated salt solution to obtain the flexible anisotropic conductive hydrated salt phase change gel.

[0063] The present invention mixes and heats the hydrogel polymer, polysaccharide substance, hydrophilic modified conductive filler, and water to obtain a pre-gel dispersion.

[0064] In the present invention, the heating temperature is preferably 60 to 100 °C, specifically it can be 60 °C, 80 °C, 90 °C or 100 °C, and the time is preferably 4 to 6 h, specifically it can be 4 h, 5 h or 6 h. Preferably, stirring is accompanied during heating, and the rotation speed of the stirring is preferably 300 to 500 r / min, specifically it can be 300 r / min, 400 r / min or 500 r / min. During the heating and stirring process, the hydrogel polymer and the polysaccharide dissolve, and the hydrophilic modified conductive filler is uniformly dispersed to obtain a pre-gel dispersion.

[0065] After obtaining the pre-gel dispersion, the present invention removes the bubbles from the pre-gel dispersion and performs freeze-thawing to obtain a hydrogel.

[0066] In the present invention, the method for removing bubbles is preferably static placement, and the static placement time is preferably 15 to 60 min, specifically it can be 15 min, 30 min or 60 min.

[0067] In the present invention, the freeze-thawing includes freezing and thawing. The freezing temperature is preferably -30 to -10 °C, specifically it can be -30 °C, -20 °C or -10 °C; the thawing is preferably carried out at room temperature. The freeze-thawing time is preferably 8 to 24 h, specifically it can be 8 h, 16 h or 24 h. During the freeze-thawing process, the hydrogel polymer and the polysaccharide crosslink to form a semi-interpenetrating continuous three-dimensional network structure and gelate, solidifying the liquid pre-gel dispersion into a solid hydrogel.

[0068] After obtaining the hydrogel, the present invention impregnates the hydrogel in a hydrated salt solution to obtain the flexible anisotropic conductive hydrated salt phase change gel.

[0069] In the present invention, the hydrated salt solution is preferably a saturated hydrated salt solution, and the impregnation time is preferably 24 to 48 h, specifically it can be 24 h, 36 h or 48 h. During the impregnation process, the ions in the saturated hydrated salt solution enter the hydrogel through osmosis, combine with the water molecules in the hydrogel network to form a hydrated salt, and are adsorbed in the three-dimensional network structure of the hydrogel.

[0070] The present invention also provides the application of the flexible anisotropic conductive hydrated salt phase change gel described in the above technical solution or the flexible anisotropic conductive hydrated salt phase change gel obtained by the above preparation method in the full-temperature-range thermal management of lithium batteries.

[0071] The present invention uses a flexible anisotropic conductive hydrated salt phase change gel to construct a thermal management system for the entire temperature range. The flexible anisotropic conductive hydrated salt phase change gel material simultaneously has a high phase change latent heat, high decomposition heat storage, and anisotropic conductivity. It can achieve efficient heat dissipation and temperature control during phase change at high temperatures, absorb heat during thermal runaway to inhibit the occurrence and spread of thermal runaway, and can not only energize and heat the battery in one direction at low temperatures but also maintain insulation in another direction, thereby realizing thermal management of lithium-ion batteries over the entire temperature range and improving safety.

[0072] The flexible anisotropic conductive hydrated salt phase change gel material of the present invention is flexible and not easily broken, can stably adhere to the battery surface, adapt to the volume change of the battery during charging and discharging, provide shock absorption and anti-collision functions, and further improve the safety and reliability of the battery system.

[0073] To further illustrate the present invention, the flexible anisotropic conductive hydrated salt phase change gel provided by the present invention, its preparation method and application will be described in detail below in conjunction with the drawings and embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0074] In the following examples and comparative examples, the parts of each component are by weight.

[0075] Example 1

[0076] First, prepare the modified conductive filler for later use. Disperse 0.05 part of TritonX-100 in an excess of ethanol, add 1 part of expanded graphite, mix and sonicate for 20 min, and dry at 80 °C for 48 h to obtain modified expanded graphite.

[0077] Then, use the above-mentioned modified expanded graphite to prepare a flexible anisotropic conductive hydrated salt phase change gel. The raw materials include the following parts by weight: 10 parts of modified expanded graphite, 8 parts of polyvinyl alcohol, 4 parts of sodium alginate, 78 parts of deionized water, and a saturated solution of disodium hydrogen phosphate dodecahydrate.

[0078] The preparation method includes the following steps:

[0079] S1. Heat polyvinyl alcohol, sodium alginate, and modified expanded graphite in deionized water at 90 °C, stir at a speed of 400 r / min for 5 h, and obtain a pre-gel dispersion after mixing;

[0080] S2. Let the pre-gel dispersion stand for 30 min, and obtain a hydrogel after freeze-thawing at -10 °C for 16 h (including freezing and thawing, with the same time);

[0081] S3. Immerse the hydrogel in a saturated solution of disodium hydrogen phosphate dodecahydrate for 36 h, wipe it dry, and obtain the material.

[0082] Example 2

[0083] First, prepare the modified conductive filler for later use. Disperse 0.01 part of Tween-20 in excessive ethanol, add 1 part of graphene, mix them and ultrasonicate for 10 min, then dry at 85 °C for 36 h to obtain the modified graphene.

[0084] Then, use the above-mentioned modified graphene to prepare the flexible anisotropic conductive hydrated salt phase change gel, which includes the following raw materials in parts by weight: 5 parts of modified graphene, 12 parts of gelatin, 6 parts of chitosan, 77 parts of deionized water, and saturated sodium sulfate decahydrate solution.

[0085] The preparation method includes the following steps:

[0086] S1. Heat gelatin, chitosan and modified graphene in deionized water at 60 °C, stir at a speed of 500 r / min for 4 h, and obtain a pre-gel dispersion after mixing;

[0087] S2. Let the pre-gel dispersion stand for 60 min, and obtain a hydrogel after freeze-thawing at -20 °C for 8 h;

[0088] S3. Immerse the hydrogel in the saturated sodium sulfate decahydrate solution for 48 h, wipe it dry, and obtain the said material.

[0089] Example 3

[0090] First, prepare the modified conductive filler for later use. Disperse 0.02 part of OP-10 in excessive ethanol, add 1 part of carbon nanotubes, mix them and ultrasonicate for 10 min, then dry at 90 °C for 24 h to obtain the modified carbon nanotubes.

[0091] Then, use the above-mentioned modified carbon nanotubes to prepare the anisotropic flexible conductive hydrated salt phase change gel. It includes the following raw materials in parts by weight: 3 parts of modified carbon nanotubes, 7 parts of curdlan, 5 parts of gellan gum, 85 parts of deionized water, and saturated sodium acetate trihydrate solution.

[0092] The preparation method includes the following steps:

[0093] S1. Heat curdlan, gellan gum and modified carbon nanotubes in deionized water at 80 °C, stir at a speed of 300 r / min for 6 h, and obtain a pre-gel dispersion after mixing;

[0094] S2. Let the pre-gel dispersion stand for 15 min, and obtain a hydrogel after freeze-thawing at -30 °C for 24 h;

[0095] S3. Immerse the hydrogel in the saturated sodium acetate trihydrate solution for 24 h, wipe it dry, and obtain the said material.

[0096] Comparative Example 1

[0097] The difference between this comparative example and Example 1 is that no modified conductive filler is added, and the remaining steps are the same.

[0098] That is, it includes the following raw materials in parts by weight: 8 parts of polyvinyl alcohol, 4 parts of sodium alginate, 88 parts of deionized water, and a saturated solution of disodium hydrogen phosphate dodecahydrate.

[0099] Comparative Example 2

[0100] The difference between this comparative example and Example 1 is that the conductive filler is not modified, and the remaining steps are the same.

[0101] That is, it includes the following raw materials in parts by weight: 10 parts of expanded graphite, 8 parts of polyvinyl alcohol, 4 parts of sodium alginate, 78 parts of deionized water, and a saturated solution of disodium hydrogen phosphate dodecahydrate.

[0102] Test Example 1

[0103] The materials prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were tested for their melting point, latent heat of fusion, and decomposition enthalpy using DSC according to the following method. The results are listed in Table 1; the DSC program is as follows: Hold at 0 °C for 1 min; Heat at a rate of 5 °C / min to 190 °C; Hold at 190 °C for 1 min.

[0104] Table 1 Performance parameters of the materials prepared in Examples 1 to 3 and Comparative Examples

[0105]

[0106] Figure 1 It is the thermoanalysis curve (DSC) diagram of the material prepared in Example 1. Combining Table 1 and Figure 1 It can be seen that the materials prepared in Examples 1 to 3 and Comparative Examples 1 to 2 have a certain latent heat of fusion before 55 °C, which can keep the lithium-ion battery within an appropriate temperature range during operation. They have a relatively large decomposition enthalpy value in the range of 80 - 120 °C, which can control the surrounding batteries within 120 °C when thermal runaway occurs in the lithium-ion battery, preventing the spread of thermal runaway.

[0107] Test Example 2

[0108] The materials prepared in Example 1 and Comparative Example 1 were tested for their electrical conductivity, including the test results of the resistivity in the transverse and longitudinal directions in the molten and crystalline states.

[0109] Figure 2 It is the physical diagram of the hydrated salt gel prepared in Example 1. From Figure 2It can be seen that the hydrated salt gel material presents a three-layer structure. Specifically, the modified conductive fillers are evenly distributed in the upper and lower layers, which can form a conductive path in the transverse direction, while only a small amount of modified conductive fillers are scattered in the middle layer. The reason may be that during the freeze-thaw curing process of the hydrogel, the transformation from liquid to solid does not occur instantaneously. The modified expanded graphite has a large free movement space in the initial stage of gelation and is gradually captured by the gel over time. The regions at the upper and lower ends start to solidify first due to the influence of the temperature gradient, resulting in the modified expanded graphite being captured and fixed in these regions first. The middle layer solidifies more slowly and captures less modified expanded graphite, thus forming the phenomenon of less modified expanded graphite in the middle layer. The hydrated salt gel material exhibits anisotropic conductive properties, showing high conductivity in the transverse direction and low conductivity in the longitudinal direction. It can not only be electrified and heated at low temperatures but also reduce the risk of short circuit between batteries.

[0110] Figure 3 Schematic diagram of the anisotropic conductivity of the material prepared in Example 1.

[0111] Figure 4 As per Figure 2 The transverse and longitudinal resistivity diagrams of the materials prepared in Example 1 and Comparative Example 1 tested in the molten and crystalline states according to the transverse and longitudinal directions shown. It can be seen from Figure 4 that the material in Example 1 has certain conductivity in the transverse direction and shows certain insulation in the longitudinal direction, that is, it has anisotropic conductivity. While the material without added modified conductive filler (Comparative Example 1) shows low conductivity in both the transverse and longitudinal directions, that is, it presents insulation and cannot be electrified to generate heat, thus unable to achieve the function of heating the battery at low temperatures.

[0112] Test Example 3

[0113] The lithium-ion battery pack was tested for thermal management according to the following method: A square lithium-ion battery pack with three 51Ah batteries connected in series was used as the test object, and the distance between adjacent batteries was 2 mm. The materials prepared in Example 1 with a thickness of 2 mm and the materials prepared in Comparative Example 1 with a thickness of 2 mm were respectively placed between the batteries, and the battery pack with no material placed between the batteries was denoted as Comparative Example 3. The temperature of the middle battery in the battery pack was measured at different times using a thermocouple under a 2C discharge rate.

[0114] Figure 5 Schematic diagram of the structural arrangement of the square battery and the material.

[0115] Figure 6 Temperature change curves of different battery packs in Comparative Example 1, Comparative Example 3, and Example 1 at different detection times. It can be seen from Figure 6It can be seen that in Comparative Example 3, the temperature curve continued to rise without any cooling measures, while the curves of Comparative Example 1 and Example 1 showed a stage with a smaller slope, which was caused by the material continuously absorbing the latent heat of fusion. Eventually, the maximum temperature was reduced from 62.2 °C in Comparative Example 3 to 51.7 °C and 47.7 °C. Example 1 could control the battery pack below the safe operating temperature of lithium-ion batteries, i.e., 50 °C, showing excellent high-temperature battery cooling effect.

[0116] Test Example 4

[0117] The following method was used to conduct the battery thermal runaway test on the lithium-ion battery pack: The arrangement of the materials and the batteries in Example 1 and Comparative Example 3 was the same as that in Test Example 3. After the battery was fully charged, it was placed in an explosion-proof box for a nail penetration test. A nail penetration machine was used to penetrate 20 mm into the negative electrode of the middle battery in the battery pack to trigger thermal runaway. Thermocouples were used to record the temperature changes of the batteries at the centers of both sides of each battery.

[0118] Figure 7 Figure shows the temperature change curves of the battery packs in Comparative Example 3 and Example 1 at different detection times during battery thermal runaway. From Figure 7 It can be seen that in Comparative Example 3, without any cooling measures, the temperature of each battery increased sharply during the thermal runaway of the middle battery, triggering the spread of thermal runaway. When the thermal runaway occurred in the middle battery in Example 1, the material continuously absorbed the heat released by the thermal runaway battery through the latent heat of fusion, sensible heat absorption, and decomposition heat absorption, reducing the maximum temperature of the thermal runaway of the middle battery from 1028 °C to within 597 °C, and reducing the maximum temperature of the surrounding batteries from 995 °C to no higher than 147 °C, preventing the occurrence of thermal runaway spread and showing excellent battery thermal runaway protection effect.

[0119] Test Example 5

[0120] The following method was used to conduct the low-temperature electric heating test on the lithium-ion battery pack: The arrangement of the materials and the batteries was the same as that in Test Example 3. The material was connected to the power supply using conductive adhesive and a copper plate to form a closed circuit. The battery and the material were simultaneously placed in a constant temperature box at -20 °C and cooled to -20 °C. The material was energized at a constant voltage of 5 V for 5 min, and a thermocouple was used to measure the temperature at the center of the middle battery at different times.

[0121] Figure 8 Figure shows the temperature change curves of the battery pack at different detection times during the electric heating of the material prepared in Example 1 at -20 °C. From Figure 8 It can be seen that the material in Example 1 was heated from -18.4 °C to 15.2 °C at a power of 7.5 W, and the heating rate could reach 5.4 °C / min, showing good low-temperature electric heating battery effect.

[0122] The flexible conductive hydrated salt gel material of Embodiment 1 of the present invention simultaneously has a high phase change latent heat of 174.9 J / g, a high decomposition enthalpy value of 1120 J / g, and the ability of anisotropic conductivity, and has the ability to realize low-temperature electric heating, high-temperature heat dissipation, and ultra-high-temperature heat absorption to inhibit the occurrence and spread of battery thermal runaway, that is, it can achieve integrated full-temperature thermal management of the battery. The flexible conductive hydrated salt gel material of Embodiment 1 of the present invention is formed by a polymer network adsorbing hydrated salts. At room temperature, the compressive strength and flexural strength can reach 203 kPa and 2330 kPa respectively; it can be bent arbitrarily at high temperatures, and the compressive strength reaches 1 kPa. It has both flexibility and certain mechanical strength, can resist compression and bending and is not easily broken, can stably fit the battery surface, adapt to the volume change of the battery during charging and discharging and heating, and provide buffering and shock absorption effects.

[0123] Although the above embodiments have made a detailed description of the present invention, they are only a part of the embodiments of the present invention, rather than all embodiments. People can also obtain other embodiments according to the embodiments of the present invention without creative labor, and these embodiments all belong to the protection scope of the present invention.

Claims

1. A flexible anisotropic conductive hydrated salt phase change gel, characterized in that, It includes a hydrogel and a hydrated salt adsorbed in the semi-interpenetrating three-dimensional network structure of the hydrogel; The hydrogel comprises the following raw materials for preparation in parts by weight: 1-15 parts of a hydrophilic modified conductive filler, 4-15 parts of a hydrogel polymer, 1-7 parts of a polysaccharide substance, and 75-94 parts of water; In the flexible anisotropic conductive hydrated salt phase change gel, the hydrophilic modified conductive filler is distributed decreasingly from the gel surface layer to the center.

2. The flexible anisotropic conductive hydrated salt phase change gel according to claim 1, wherein The hydrated salt includes one or more of disodium hydrogen phosphate dodecahydrate, sodium acetate trihydrate, sodium sulfate decahydrate, calcium chloride hexahydrate, magnesium nitrate hexahydrate, lithium nitrate trihydrate, and potassium alum dodecahydrate.

3. The flexible anisotropic conductive hydrated salt phase change gel according to claim 1, characterized in that, The hydrophilic modified conductive filler includes one or more of hydrophilic modified expanded graphite, hydrophilic modified graphene, hydrophilic modified carbon nanotubes, hydrophilic modified carbon nanosheets, hydrophilic modified MXenes, and hydrophilic modified copper powder.

4. The flexible anisotropic conductive hydrated salt phase change gel according to claim 1 or 3, characterized in that The hydrophilic modified conductive filler is obtained by modifying the conductive filler with a non-ionic surfactant, and the mass ratio of the conductive filler to the non-ionic surfactant is 100:(1-10).

5. The flexible anisotropic conductive hydrated salt phase change gel according to claim 1, wherein The hydrogel polymer includes one or more of polyvinyl alcohol, gelatin, polyacrylamide, curdlan, sodium polyacrylate, and carboxymethyl cellulose.

6. The flexible anisotropic conductive hydrated salt phase change gel according to claim 1, characterized in that, The polysaccharide substance includes one or more of chitosan, sodium alginate, alginic acid, gellan gum, and pectin.

7. The flexible anisotropic conductive hydrated salt phase change gel according to claim 1, characterized in that, The hydrogel comprises the following raw materials for preparation in parts by weight: 10 parts of hydrophilic modified expanded graphite, 8 parts of polyvinyl alcohol, 4 parts of sodium alginate, and 78 parts of water; Or it includes: 5 parts of hydrophilic modified graphene, 12 parts of gelatin, 6 parts of chitosan, and 77 parts of water; Or it includes: 3 parts of hydrophilic modified carbon nanotubes, 7 parts of curdlan, 5 parts of gellan gum, and 85 parts of water.

8. The preparation method of the flexible anisotropic conductive hydrated salt phase change gel according to any one of claims 1 to 7, characterized in that, It includes the following steps: Mix and heat the hydrogel polymer, the polysaccharide substance, the hydrophilic modified conductive filler, and water to obtain a pre-gel dispersion; Remove bubbles from the pre-gel dispersion and perform freeze-thawing to obtain a hydrogel; Immerse the hydrogel in a hydrated salt solution to obtain the flexible anisotropic conductive hydrated salt phase change gel.

9. The preparation method according to claim 8, characterized in that The hydrated salt solution is a saturated hydrated salt solution, and the immersion time is 24-48 h.

10. Application of the flexible anisotropic conductive hydrated salt phase change gel according to any one of claims 1-7 or the flexible anisotropic conductive hydrated salt phase change gel obtained by the preparation method according to claim 8 or 9 in the full-temperature-range thermal management of a lithium battery.

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