Battery cells and their preparation methods, battery devices, electrical devices, energy storage devices

Abstract

This application relates to the field of batteries, specifically to battery cells and their preparation methods, battery devices, power-consuming devices, and energy storage devices. In the preparation method of the battery cell of this application, the steps for preparing the composite separator include: subjecting a grafted modified polymer base film to free radical activation treatment, thereby giving the surface of the grafted modified polymer base film hydroxyl groups; mixing the free radical activated grafted modified polymer base film with a suspension of nano-silica, and performing an anchoring treatment, thereby anchoring the nano-silica to the grafted modified polymer base film through some hydroxyl groups; mixing the anchored grafted modified polymer base film with a tetraalkoxysilane crosslinking liquid and an organic framework material, and performing crosslinking bonding, thereby bridging some hydroxyl groups and the organic framework material through tetraalkoxysilane segments to prepare the composite separator. The composite separator prepared in this application has high mechanical stability, ion transport efficiency, and electrolyte wetting performance, which is beneficial for improving the cycle life of the battery cell.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to battery cells and their preparation methods, battery devices, power-consuming devices, and energy storage devices. Background Technology

[0002] Battery cells offer significant advantages in energy storage and are compatible with various new energy devices. Within a battery cell, the separator, as the core component separating the positive and negative electrodes and blocking electron conduction, plays a crucial role in preventing internal short circuits. Polymer separators have mature manufacturing processes and good chemical stability, making them a widely used base membrane material. However, polymer separators have low surface energy and poor hydrophilicity, resulting in poor wettability with the electrolyte and increased ion transport resistance, which in turn affects the rate performance and cycle stability of the battery cell. Currently, methods for modifying polymer separators mainly include surface modification and composite modification. However, composite separators prepared by traditional modification methods still suffer from weak interfacial bonding, failing to effectively improve ion transport efficiency and thus limiting the improvement of the cycle stability of the battery cell. Summary of the Invention

[0003] Based on this, this application provides a battery cell and its preparation method, a battery device, an electrical device, and an energy storage device to solve the problem that composite separators prepared by traditional processes have weak interfacial bonding and cannot effectively improve ion transport efficiency, thereby restricting the improvement of the cycle stability performance of battery cells.

[0004] A first aspect of this application provides a method for preparing a battery cell, the battery cell comprising a positive electrode, a negative electrode, and a composite separator, the composite separator being disposed between the positive electrode and the negative electrode, the preparation steps of the composite separator including:

[0005] The grafted modified polymer base film is subjected to free radical activation treatment to give the surface of the grafted modified polymer base film hydroxyl groups; the grafted modified polymer base film includes a polymer base film and silane coupling agent segments and polyether polyol segments grafted onto the surface of the polymer base film;

[0006] The grafted modified polymer base film after free radical activation treatment and the suspension of nano-silica were mixed and anchored, and the nano-silica was anchored to the grafted modified polymer base film through some of the hydroxyl groups.

[0007] The anchored grafted modified polymer base film is mixed with a tetraalkoxysilane crosslinking liquid and an organic framework material, and crosslinked and bonded to bridge some of the hydroxyl groups and the organic framework material through tetraalkoxysilane segments to prepare a composite membrane.

[0008] In some embodiments, the step of free radical activation treatment of the grafted modified polymer base film includes: using a solution of an organic peroxide initiator to perform free radical activation treatment on the grafted modified polymer base film.

[0009] In the solution of the organic peroxide initiator, the mass fraction of the organic peroxide initiator is 1% to 4%; the organic peroxide initiator includes one or more of benzoyl peroxide, dicumyl peroxide, and di-tert-butyl peroxide.

[0010] In some embodiments, the suspension of nano-silica comprises the nano-silica and an aminosilane coupling agent, and the preparation method has one or more of the following characteristics:

[0011] (1) The average particle size of the nano-silica is 80nm~120nm;

[0012] (2) In the suspension of nano-silica, the mass fraction of nano-silica is 2.5%~3.5%;

[0013] (3) The mass ratio of the polymer base film to the nano-silica is 1:(0.05~0.2);

[0014] (4) The aminosilane coupling agent includes one or more of γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane;

[0015] (5) In the suspension of nano-silica, the mass fraction of the aminosilane coupling agent is 0.1%~0.3%.

[0016] In some embodiments, the tetraalkoxysilane crosslinking liquid comprises a tetraalkoxysilane and a basic catalyst, and the preparation method has one or more of the following characteristics:

[0017] (1) The tetraalkoxysilane includes one or more of tetraethoxysilane and tetramethoxysilane;

[0018] (2) The alkaline catalyst includes one or more of ammonia and triethylamine;

[0019] (3) In the tetraalkoxysilane crosslinking liquid, the mass fraction of the tetraalkoxysilane is 10%~14%;

[0020] (4) The mass ratio of the polymer base film to the mass ratio of the tetraalkoxysilane in the tetraalkoxysilane crosslinking solution is 1:(0.05~0.2).

[0021] In some embodiments, the organic framework material includes one or more of metal-organic framework materials and covalent organic framework materials, and the preparation method has one or more of the following characteristics:

[0022] (1) The mass ratio of the polymer base film to the organic framework material is 1:(0.02~0.06);

[0023] (2) The metal ions in the metal-organic framework material include one or more of zirconium ions, copper ions and zinc ions;

[0024] (3) The organic ligands in the metal-organic framework material include one or more of terephthalic acid ligands and biphenyl ligands;

[0025] (4) The covalent organic framework material includes one or more of borate ester covalent organic framework materials and triazine covalent organic framework materials.

[0026] In some embodiments, the free radical activation treatment step includes: carrying out the reaction at 80°C to 90°C under a protective gas atmosphere.

[0027] In some embodiments, the anchoring process is performed at a temperature of 50°C to 60°C.

[0028] In some embodiments, the crosslinking bonding temperature is 40°C to 50°C.

[0029] In some embodiments, the polymer-based film is made of one or more of polypropylene, polyethylene, and polyester.

[0030] In some embodiments, the average pore size of the polymer-based membrane is 0.3 μm to 0.7 μm.

[0031] In some embodiments, the thickness of the polymer base film is 20 μm to 30 μm.

[0032] In some embodiments, the porosity of the polymer-based membrane is 40% to 50%.

[0033] In some embodiments, the mass ratio of the polymer base film to the silane coupling agent segment is 1:(0.02~0.05).

[0034] In some embodiments, the mass ratio of the polymer base film to the polyether polyol segments is 1:(0.5~0.6).

[0035] In some embodiments, the preparation step of the grafted modified polymer base film is further included, comprising: plasma treatment of the polymer base film; grafting treatment of the plasma-treated polymer base film with silane coupling agent modification liquid and polyether polyol modification liquid in sequence to prepare the grafted modified polymer base film; the surface of the grafted modified polymer base film has silane coupling agent segments and polyether polyol segments.

[0036] In some embodiments, the silane coupling agent in the silane coupling agent modified liquid includes one or more of γ-glycidoxypropyltrimethoxysilane, (3-glycidoxypropyl)methyldimethoxysilane, and (3-glycidoxypropyl)methyldiethoxysilane.

[0037] In some embodiments, the polyether polyol in the polyether polyol modified liquid includes one or more of polyethylene glycol and polypropylene glycol.

[0038] In some embodiments, the process parameters for grafting using the silane coupling agent modified liquid include a temperature of 40°C to 50°C.

[0039] In some embodiments, the process parameters for grafting using the polyether polyol modified liquid include a temperature of 60°C to 70°C.

[0040] A second aspect of this application provides a battery cell comprising a positive electrode, a negative electrode, and a composite separator; the composite separator is disposed between the positive electrode and the negative electrode, the composite separator comprising a grafted modified polymer base film, the grafted modified polymer base film comprising a polymer base film and silane coupling agent segments and polyether polyol segments grafted onto the surface of the polymer base film; the composite separator further comprises nano-silica, tetraalkoxysilane segments, and an organic framework material; the nano-silica is anchored to the grafted modified polymer base film via siloxane bonds; the tetraalkoxysilane segments are fixed to the grafted modified polymer base film via siloxane bonds, and the tetraalkoxysilane segments bridge the organic framework material.

[0041] In some embodiments, the silane coupling agent segment includes one or more of γ-glycidoxypropyltrimethoxysilane segment, (3-glycidoxypropyl)methyldimethoxysilane segment, and (3-glycidoxypropyl)methyldiethoxysilane segment.

[0042] In some embodiments, the polyether polyol segment includes one or more of polyethylene glycol segments and polypropylene glycol segments.

[0043] In some embodiments, the tetraalkoxysilane segment includes one or more of tetraethoxysilane segments and tetramethoxysilane segments.

[0044] In some embodiments, the organic framework material includes one or more of metal-organic framework materials and covalent organic framework materials.

[0045] In some embodiments, the polymer-based film is made of one or more of polypropylene, polyethylene, and polyester.

[0046] In some embodiments, the average pore size of the polymer-based membrane is 0.3 μm to 0.7 μm.

[0047] In some embodiments, the thickness of the polymer base film is 20 μm to 30 μm.

[0048] In some embodiments, the porosity of the polymer-based membrane is 40% to 50%.

[0049] A third aspect of this application provides a battery device comprising a plurality of battery cells prepared by any of the preparation methods of the first aspect of this application or comprising a plurality of battery cells as described in any of the second aspects of this application, wherein the battery device comprises one or more of a battery module, a battery pack, and an energy storage battery.

[0050] A fourth aspect of this application provides an electrical device including a battery device as described in a third aspect of this application.

[0051] A fifth aspect of this application provides an energy storage device, including a battery device as described in a third aspect of this application.

[0052] The method for preparing the battery cell provided in this application has at least the following beneficial effects:

[0053] In the method for preparing the battery cell provided in this application, the silane coupling agent segments and polyether polyol segments on the surface of the grafted modified polymer base film are subjected to free radical activation treatment. This promotes cross-linking reactions and full extension of each segment, exposing the silanol groups originally encapsulated by the segments, the terminal hydroxyl groups of the polyether polyol, or the hydroxyl groups present on the surface of the polymer base film. The free radical activation treatment can also induce polyether polyol segment breakage and molecular chain rearrangement, further generating hydroxyl groups in situ, thereby enriching the grafted modified polymer base film with hydroxyl groups. This provides a foundation for subsequent anchoring of nano-silica and cross-linking bonding of tetraalkoxysilane cross-linking liquid and organic framework materials.

[0054] A nano-silica suspension was used to anchor a hydroxyl-rich grafted modified polymer base membrane. Some of the hydroxyl groups formed covalent bonds such as silicon-oxygen bonds with the silanol groups on the surface of the nano-silica, which anchored the nano-silica particles to the surface of the polymer base membrane. This effectively filled the micro-defects on the membrane surface and improved the thermal stability and structural density of the membrane. In addition, silica can also improve the wettability of the electrolyte on the membrane surface.

[0055] Crosslinking bonding is achieved using a tetraalkoxysilane crosslinking solution and an organic framework material. The tetraalkoxysilane acts as a molecular bridging agent, utilizing the hydroxyl groups on the polymer base membrane surface to simultaneously connect the polymer base membrane and the organic framework material. The organic framework material, combined with bonded and anchored nano-silica, silane coupling agent segments grafted onto the base membrane surface, and polyether polyol segments, constructs an organic-inorganic composite crosslinking network, effectively mitigating the problems of functional layer detachment and weak interfacial bonding. Furthermore, the uniform doping of the organic framework material within the crosslinking network, along with its synergistic effect with the organic-inorganic composite crosslinking network, optimizes the membrane's pore structure and ion transport channels, thereby improving the wettability, thermal stability, and electrochemical performance of the composite membrane.

[0056] The preparation method provided in this application achieves surface activation modification of the polymer-based membrane, anchoring of inorganic nano-silica, and cross-linking bonding of the organic framework material through sequential free radical activation treatment, anchoring treatment, and cross-linking bonding treatment. The organic-inorganic composite cross-linked structure constructed on the surface of the composite membrane improves the mechanical and thermal stability of the composite membrane, enhances electrolyte wetting performance, and thus improves the cycle stability of the battery cells. Furthermore, this preparation method offers strong controllability of process steps, is less likely to damage the intrinsic structure of the polymer-based membrane, and is suitable for large-scale mass production. Attached Figure Description

[0057] Figure 1 A process flow diagram illustrating the fabrication process of a composite membrane provided as an example in this application. Detailed Implementation

[0058] The following detailed description, in conjunction with specific embodiments, provides a more complete and clear account of the battery cell, its preparation method, battery device, power consumption device, and energy storage device of this application. This application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0059] In a battery cell, the separator is the main component that isolates the positive and negative electrodes and conducts ions. Currently, polymer separators such as polypropylene (PP) are widely used. However, polymer separators suffer from poor hydrophilicity and poor electrolyte wettability. To improve the wettability of polymer separators with the electrolyte, they are usually modified. Currently, the main method for modifying polymer separators is composite modification, which involves forming a functional material layer on the surface of the polymer separator. However, due to insufficient adhesion between the functional material layer and the polymer separator surface, delamination and other problems easily occur during long-term cycling, resulting in limited improvement in cycle stability. Other methods utilize acid and alkali etching to modify the surface of the polymer separator to increase its surface polarity, but this method easily damages the separator, reducing its stability.

[0060] Traditional modification methods suffer from weak interfacial bonding, low stability, and insufficient durability, thus failing to improve the cycle stability of battery cells. A first aspect of this application provides a method for preparing a battery cell, the battery cell comprising a positive electrode, a negative electrode, and a composite separator. The composite separator is disposed between the positive and negative electrode. See also... Figure 1 The preparation steps of the composite membrane include:

[0061] S10. The grafted modified polymer base film is subjected to free radical activation treatment to give the surface of the grafted modified polymer base film hydroxyl groups. The grafted modified polymer base film includes a polymer base film and silane coupling agent segments and polyether polyol segments grafted onto the surface of the polymer base film.

[0062] S20. The grafted modified polymer base film after free radical activation treatment and the suspension of nano-silica are mixed and anchored to the grafted modified polymer base film through some hydroxyl groups.

[0063] S30. The anchored grafted modified polymer base film is mixed with tetraalkoxysilane crosslinking liquid and organic framework material, and crosslinked and bonded to bridge some hydroxyl groups and organic framework material through tetraalkoxysilane segments to prepare a composite membrane.

[0064] The preparation method provided in this application achieves surface activation modification of the polymer base film, anchoring of inorganic nano-silica, and cross-linking bonding of the organic framework material through sequential free radical activation treatment, anchoring treatment, and cross-linking bonding treatment. The organic-inorganic composite cross-linked structure constructed on the surface of the composite separator has good interfacial adhesion with the polymer base film, which improves the thermal stability and electrolyte wetting performance of the composite separator, thereby enhancing the cycle stability of the battery cells. Moreover, the preparation method has strong process controllability, does not easily damage the intrinsic structure of the polymer base film, and is suitable for large-scale mass production.

[0065] In step S10, "grafted modified polymer base film" refers to a modified film with a polymer base film as the matrix and functional segments grafted onto the surface of the polymer base film. Further, the grafted modified polymer base film of this application includes a polymer base film and silane coupling agent segments and polyether polyol segments grafted onto the surface of the polymer base film. As an example, the silane coupling agent segments include one or more of γ-glycidyl etheroxypropyltrimethoxysilane segments, (3-glycidyl etheroxypropyl)methyldimethoxysilane segments, and (3-glycidyl etheroxypropyl)methyldiethoxysilane segments. The polyether polyol segments include one or more of polyethylene glycol segments and polypropylene glycol segments.

[0066] Furthermore, the preparation steps of the grafted modified polymer-based film include:

[0067] a1. Plasma treatment of the polymer base film.

[0068] a2. Graft-modified polymer base films were prepared by sequentially grafting plasma-treated polymer base films using silane coupling agent modification solution and polyether polyol modification solution. The surface of the graft-modified polymer base film contains silane coupling agent segments and polyether polyol segments.

[0069] As an example, the polymer-based membrane is made of one or more of polypropylene, polyethylene, and polyester. The average pore size of the polymer-based membrane is 0.3 μm to 0.7 μm. The average pore size of the polymer-based membrane refers to the average diameter of the pores in the membrane. The average pore size can be determined using the bubble pressure method or the mercury porosimetry method. Exemplarily, the average pore size of the polymer-based membrane is 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, or 0.7 μm, or any two of the above values ​​as endpoints. The thickness of the polymer-based membrane is 20 μm to 30 μm. The thickness of the polymer-based membrane includes, but is not limited to, 20 μm, 22 μm, 24 μm, 25 μm, 26 μm, 28 μm, or 30 μm, or any two of the above values ​​as endpoints. In some examples, the porosity of the polymer-based membrane is 40% to 50%. The porosity of the polymer-based membrane includes, but is not limited to, 40%, 43%, 45%, 48%, or 50%, or any two of the above point values ​​as endpoints within the range.

[0070] In some examples, the process of cleaning and drying the polymer base film is included before the plasma treatment step. For example, the cleaning and drying steps involve sequentially ultrasonically cleaning the polymer base film with acetone, ethanol, and deionized water for 10-30 minutes each, followed by vacuum drying at 60°C-80°C for 2-4 hours.

[0071] Step a1, the plasma treatment of the polymer base film includes: using an argon and oxygen mixture with a volume ratio of (2~4):1, and treating for 3 to 10 minutes at a plasma power of 80W~120W and a treatment distance of 8mm~12mm. By using the aforementioned plasma treatment with the argon-oxygen mixture, a large number of oxygen-containing polar groups are introduced onto the surface of the polymer base film. The siloxane groups in the silane coupling agent and the hydroxyl groups in the polyether polyol can form covalent bonds with the oxygen-containing polar groups on the surface of the polymer base film, thereby grafting the silane coupling agent segments and polyether polyol segments onto the surface of the polymer base film and improving the grafting bonding force. For example, the volume ratio of argon to oxygen in the mixture includes, but is not limited to, 2:1, 3:1, or 4:1, or any two of the above values ​​as endpoints. The plasma power includes, but is not limited to, 80W, 90W, 95W, 100W, 105W, 115W, or 120W, or any two of the above values ​​as endpoints. The processing distance includes, but is not limited to, 8mm, 10mm or 12mm, or any two of the above point values ​​as endpoint values ​​within the range.

[0072] In step a2, the silane coupling agent in the silane coupling agent modified solution includes one or more of γ-glycidoxypropyltrimethoxysilane, (3-glycidoxypropyl)methyldimethoxysilane, and (3-glycidoxypropyl)methyldiethoxysilane. Further, the silane coupling agent in the silane coupling agent modified solution is γ-glycidoxypropyltrimethoxysilane.

[0073] Furthermore, the silane coupling agent modified solution comprises a silane coupling agent and an alcohol solvent in a mass ratio of 1:(18~22). The alcohol solvent includes, but is not limited to, one or more of methanol, ethanol, and isopropanol. Even further, the pH of the silane coupling agent modified solution is 3~5. A pH within the above range facilitates the hydrolysis of the silane coupling agent to generate silanol groups; the alcohol solvent, when formulated with a specific mass ratio and exhibiting good solubility for the silane coupling agent, can fully wet the plasma-treated polymer base film, promoting the reaction between the silanol groups and the active sites of the polymer base film, and strengthening the grafting bond. Without limitation, methods for setting the pH of the silane coupling agent modified solution to 3~5 include, but are not limited to, adding an aqueous hydrochloric acid solution. As an example, the mass fraction of the aqueous hydrochloric acid solution includes, but is not limited to, 0.3wt%~0.8wt%.

[0074] In some examples, step a2, the grafting treatment using a silane coupling agent modified solution is performed by immersing the plasma-treated polymer base film in the silane coupling agent modified solution. Further, the process parameters for the grafting treatment using the silane coupling agent modified solution include: a temperature of 40℃~50℃; and a grafting time of 4h~10h.

[0075] To ensure the silane coupling agent segments are grafted onto the surface of the polymer base film and to avoid segment agglomeration and pore blockage of the polymer base film caused by a slightly high grafting amount, in some examples, the mass ratio of the polymer base film to the silane coupling agent segments in the grafted modified polymer base film prepared in step a2 is 1:(0.02~0.05). Exemplarily, the mass ratio of the polymer base film to the silane coupling agent segments includes, but is not limited to, 1:0.02, 1:0.025, 1:0.03, 1:0.035, 1:0.04, or 1:0.05, or any two of the above values ​​as endpoints.

[0076] In step a2, the polyether polyol in the polyether polyol modification solution includes one or more of polyethylene glycol and polypropylene glycol. Further, the number-average molecular weight of the polyether polyol is 1500-3000. Exemplarily, the number-average molecular weight of the polyether polyol includes, but is not limited to, 1500, 1800, 2000, 2100, 2200, 2500, 2800, or 3000, or any two of the above values ​​as endpoints. Even further, the number-average molecular weight of the polyether polyol is 1800-2200. The aforementioned polyether polyol has a suitable segment length, which can form flexible segments on the surface of the polymer base film and retain terminal hydroxyl groups, providing active sites for subsequent free radical activation and crosslinking reactions. Further, the polyether polyol modification solution includes a polyether polyol and a solvent in a mass ratio of 1:(8-12). The solvent includes, but is not limited to, one or more of methanol, ethanol, and isopropanol.

[0077] In some examples, step a2 involves grafting with a polyether polyol modified solution by immersing the polymer base film, after grafting with the silane coupling agent modified solution, into the polyether polyol modified solution. To improve both the grafting efficiency and the activity of the active sites, in some examples, the process parameters for grafting with the polyether polyol modified solution include: a temperature of 60℃~70℃; and a grafting time of 6h~10h. The temperature for grafting with the polyether polyol modified solution includes, but is not limited to, 60℃, 63℃, 65℃, 68℃, or 70℃, or any two of the above values ​​as endpoints.

[0078] To provide active sites for the grafting of polyether polyol segments onto the surface of the polymer base film and to maintain the porosity and ion conductivity of the polymer base film, in some examples, the mass ratio of the polymer base film to the polyether polyol segments in the grafted modified polymer base film prepared in step a2 is 1:(0.5~0.6). Exemplarily, the mass ratio of the polymer base film to the polyether polyol segments includes, but is not limited to, 1:0.5, 1:0.52, 1:0.53, 1:0.54, 1:0.55, 1:0.56, 1:0.58, or 1:0.6, or any two of the above values ​​as endpoints.

[0079] In step S10, "free radical activation treatment" refers to the step of generating free radicals using an initiator and then using these free radicals to activate and modify the grafted polymer base film. Exemplarily, the initiator is an organic peroxide initiator. More exemplaryly, the organic peroxide initiator includes one or more of benzoyl peroxide, dicumyl peroxide, and di-tert-butyl peroxide.

[0080] In some examples, step S10, the step of performing free radical activation treatment on the grafted modified polymer base film, includes: performing free radical activation treatment on the grafted modified polymer base film using a solution of an organic peroxide initiator. Further, the method of performing free radical activation treatment on the grafted modified polymer base film using a solution of an organic peroxide initiator is as follows: immersing the grafted modified polymer base film in the solution of the organic peroxide initiator for free radical activation treatment.

[0081] In the solution of the organic peroxide initiator, the mass fraction of the organic peroxide initiator is 1% to 4%. Exemplarily, the mass fraction of the organic peroxide initiator includes, but is not limited to, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 3%, 3.5%, or 4%, or any two of the above values ​​as endpoints. The solvent in the solution of the organic peroxide initiator includes, but is not limited to, one or more of methanol, ethanol, and isopropanol. In some examples, in step S10, the mass ratio of the organic peroxide initiator to the silane coupling agent segment in the grafted modified polymer base film is (0.7 to 1.2):1. Exemplarily, the mass ratio of the organic peroxide initiator to the silane coupling agent segment in the grafted modified polymer base film includes, but is not limited to, 0.8:1, 0.9:1, 1:1, 1.1:1, or 1.2:1, or any two of the above values ​​as endpoints. Furthermore, the mass ratio of the organic peroxide initiator to the silane coupling agent segment in the grafted modified polymer base film is (0.9~1.2):1.

[0082] In some examples, the free radical activation treatment step includes: reacting at 70°C to 90°C under a protective gas atmosphere. Further, the free radical activation treatment step includes: reacting at 80°C to 90°C under a protective gas atmosphere. The temperature of the free radical activation treatment includes, but is not limited to, 80°C, 83°C, 85°C, 88°C, or 90°C, or any two of the above values ​​as endpoints. The protective gas includes, but is not limited to, one or more of argon and nitrogen. The free radical activation treatment time is 2h to 5h. When the grafted modified polymer base film is subjected to free radical activation treatment, the grafted functional segments such as silane coupling agent segments and polyether polyol segments extend, exposing the silanol groups of the silane coupling agent segments, the terminal hydroxyl groups of the polyether polyol, or the hydroxyl groups present on the surface of the polymer base film. Accompanying the free radical activation treatment are the breakage of polyether polyol segments and silane coupling agent segments, molecular chain rearrangement, etc., making the surface of the grafted modified polymer base film rich in hydroxyl groups. The hydroxyl-rich structure on the surface of the grafted modified polymer base film provides active sites for the anchoring of nano-silica in step S20 and the cross-linking bonding of the tetraalkoxysilane cross-linking liquid and organic framework material in step S30; and the hydroxyl-rich structure can improve the polarity of the polymer base film and enhance its wettability.

[0083] In step S20, the suspension of nano-silica includes nano-silica and an aminosilane coupling agent. The nano-silica in the suspension can dehydrate and condense with the hydroxyl groups on the surface of the grafted modified polymer base film, anchoring the nano-silica to the grafted modified polymer base film through silicon-oxygen bonds. Adding the aminosilane coupling agent to the nano-silica suspension allows it to act as a cross-linking bridge, bonding the polymer base film and nano-silica at both ends, thus strengthening the interfacial bonding between the inorganic nano-silica and the organic polymer base film and simultaneously improving anchoring stability.

[0084] For example, the average particle size of the nano-silica is 80 nm to 120 nm. The average particle size of the nano-silica includes, but is not limited to, 80 nm, 90 nm, 95 nm, 98 nm, 100 nm, 105 nm, 110 nm, or 120 nm, or any two of the above values ​​as endpoints. The aminosilane coupling agent includes one or more of γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane. Further, the aminosilane coupling agent includes γ-aminopropyltriethoxysilane.

[0085] In some examples, the mass fraction of nano-silica in the suspension is 2.5% to 3.5%. Exemplarily, the mass fraction of nano-silica includes, but is not limited to, 2.5%, 2.8%, 3%, 3.05%, 3.07%, 3.1%, 3.3%, or 3.5%, or any two of the above values ​​as endpoints. The mass fraction of aminosilane coupling agent in the suspension is 0.1% to 0.3%. The mass fraction of aminosilane coupling agent includes, but is not limited to, 0.1%, 0.14%, 0.15%, 0.16%, 0.2%, 0.25%, or 0.3%, or any two of the above values ​​as endpoints.

[0086] The suspension of nano-silica also includes a surfactant. The surfactant includes, but is not limited to, one or more of sodium dodecylbenzenesulfonate and sodium fatty alcohol polyoxyethylene ether sulfate. The mass fraction of the surfactant in the suspension of nano-silica is 0.3% to 0.8%. Exemplarily, the mass fraction of the surfactant includes, but is not limited to, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, or 0.8%, or any two of the above values ​​as endpoints. The solvent included in the suspension of nano-silica is water.

[0087] In some examples, the preparation steps of the nano-silica suspension include: mixing nano-silica, an aminosilane coupling agent, a surfactant, and water, followed by ultrasonic dispersion to prepare the nano-silica suspension. Exemplarily, the ultrasonic dispersion power is 150W~250W. As an example, the ultrasonic dispersion power includes, but is not limited to, 150W, 180W, 190W, 200W, 210W, 240W, or 250W, or any two of the above values ​​as endpoints. The ultrasonic dispersion time is 40min~50min. The surfactant and preparation method, in combination, can reduce the surface tension of the suspension system, prevent the nano-silica particles from agglomerating and settling, and improve the stability of the suspension in use. Furthermore, the above suspension can improve the wetting and penetration of the polymer base film, which is beneficial for the anchoring of nano-silica on the polymer base film surface.

[0088] In step S20, the method of mixing the free radical activated grafted modified polymer base film and the nano-silica suspension is as follows: the free radical activated grafted modified polymer base film is immersed in the nano-silica suspension. In some examples, the anchoring treatment temperature is 50℃~90℃. Further, the anchoring treatment temperature is 50℃~60℃. Exemplarily, the anchoring treatment temperature includes, but is not limited to, 50℃, 53℃, 55℃, 58℃ or 60℃, or any two of the above values ​​as endpoints. The anchoring treatment time is 3h~8h. The process parameters of the anchoring treatment and the nano-silica suspension are combined to wet and anchor the silica nanoparticles on the surface of the polymer base film, forming a stable organic-inorganic interface structure, thereby effectively preventing ceramic particles from falling off and improving the structural stability of the composite membrane.

[0089] In some examples, the mass ratio of the polymer base film to the nano-silica is 1:(0.05~0.2). For example, the mass ratio of the polymer base film to the nano-silica may include, but is not limited to, 1:0.05, 1:0.08, 1:0.1, 1:0.12, 1:0.15, or 1:0.2, or any two of the above values ​​as endpoints. Further, the mass ratio of the polymer base film to the nano-silica is 1:(0.09~0.12).

[0090] A nano-silica suspension was used to anchor hydroxyl-rich grafted polymer-based membranes. Some hydroxyl groups formed covalent bonds such as silicon-oxygen bonds with the silanol groups on the surface of the nano-silica, thereby enhancing interfacial adhesion and anchoring the nano-silica particles to the polymer-based membrane surface. Furthermore, the anchoring of silica further improves the electrolyte wettability of the membrane surface and reduces the interfacial impedance of the battery cells.

[0091] In some examples, before mixing the anchored grafted modified polymer base film with the tetraalkoxysilane crosslinking liquid and the organic framework material in step S30, the process further includes: vacuum drying the organic framework material. Exemplarily, the vacuum drying temperature is 110°C to 130°C. The vacuum drying time is 6 hours to 10 hours. The vacuum drying temperature includes, but is not limited to, 110°C, 115°C, 120°C, 125°C, or 130°C, or any two of these values ​​as endpoints. Vacuum drying can remove moisture and impurities from the pores of the organic framework material, improving the subsequent anchoring and composite modification effects.

[0092] In some examples, in step S30, the tetraalkoxysilane crosslinking liquid includes a tetraalkoxysilane and an alkaline catalyst. The tetraalkoxysilane molecule has multiple siloxane groups, some of which can form siloxane chemical bonds with hydroxyl groups on the grafted modified polymer base film, while other siloxane groups can connect with organic framework materials. The tetraalkoxysilane plays a multi-component bridging role, which is beneficial for improving the bonding force of the multiphase composite interface. Exemplarily, the tetraalkoxysilane includes one or more of tetraethoxysilane and tetramethoxysilane. The alkaline catalyst includes one or more of ammonia and triethylamine. The pH of the tetraalkoxysilane crosslinking liquid is 8-10. Understandably, the alkaline catalyst can be added according to the pH of the tetraalkoxysilane crosslinking liquid.

[0093] Alkaline catalysts can regulate the pH of the tetraalkoxysilane crosslinking solution and promote the hydrolysis and crosslinking of tetraalkoxysilane molecules. This crosslinking structure can further fix nano-silica. Furthermore, this crosslinking structure can bridge the hydroxyl groups on the polymer-based film surface with the organic framework material, forming a stable chemical bond structure among the three. This enhances the bonding stability of nano-silica, tetraalkoxysilane segments, and the organic framework material, strengthening the overall anchoring and adhesion effect.

[0094] In step S30, the mass fraction of tetraalkoxysilane in the tetraalkoxysilane crosslinking liquid is 10% to 14%. As an example, the mass fraction of tetraalkoxysilane includes, but is not limited to, 10%, 11%, 12%, 13%, or 14%, or any two of the above values ​​as endpoints. Further, the mass fraction of tetraalkoxysilane is 11% to 13%. The tetraalkoxysilane crosslinking liquid also includes an organic solvent. The organic solvent includes, but is not limited to, one or more of methanol, ethanol, and isopropanol.

[0095] In step S30, the organic framework material includes one or more of metal-organic framework materials and covalent organic framework materials. As an example, the metal ion in the metal-organic framework material includes one or more of zirconium ions, copper ions, and zinc ions. The organic ligand in the metal-organic framework material includes one or more of terephthalic acid ligands and biphenyl ligands. Further, the metal ion in the metal-organic framework material is a zirconium ion. The organic ligand in the metal-organic framework material is a terephthalic acid ligand. Metal-organic framework materials include, but are not limited to, UIO-66.

[0096] Covalent organic framework materials include one or more of borate ester covalent organic framework materials and triazine covalent organic framework materials. As examples, borate ester covalent organic framework materials include, but are not limited to, one or more of COF-1 and COF-5. Triazine covalent organic framework materials include, but are not limited to, one or more of CTF-1 and CTF-2.

[0097] Introducing organic framework materials into composite membranes allows the porous framework structure and surface-active groups of the organic framework materials to optimize the pore structure and ion transport efficiency of the membrane.

[0098] In some of these examples, the average particle size of the organic framework material is 150 nm to 250 nm. Further, the mass ratio of the polymer base film to the organic framework material is 1:(0.02 to 0.06). As examples, the mass ratio of the polymer base film to the organic framework material includes, but is not limited to, 1:0.02, 1:0.03, 1:0.04, 1:0.05, or 1:0.06, or any two of the above values ​​as endpoints.

[0099] In some examples, the mass ratio of the polymer base film to the tetraalkoxysilane in the tetraalkoxysilane crosslinking solution is 1:(0.05~0.2). As examples, the mass ratio of the polymer base film to the tetraalkoxysilane in the tetraalkoxysilane crosslinking solution includes, but is not limited to, 1:0.05, 1:0.08, 1:0.1, 1:0.12, 1:0.13, 1:0.15, 1:0.18, or 1:0.2, or any two of the above values ​​as endpoints. Further, the mass ratio of the polymer base film to the tetraalkoxysilane in the tetraalkoxysilane crosslinking solution is 1:(0.11~0.15).

[0100] In some examples, in step S30, the anchored grafted modified polymer base film is mixed with the tetraalkoxysilane crosslinking liquid and the organic framework material by ultrasonic dispersion. Further, the ultrasonic dispersion time is 15 min to 30 min.

[0101] In some examples, in step S30, the crosslinking temperature is 40℃~100℃. Further, the crosslinking temperature is 40℃~50℃. The crosslinking temperature includes, but is not limited to, 40℃, 43℃, 45℃, 48℃, or 50℃, or any two of the above values ​​as endpoints. Further, the crosslinking time is 6h~12h.

[0102] In step S30, a cross-linking bonding treatment is performed using a tetraalkoxysilane cross-linking liquid and an organic framework material. The tetraalkoxysilane acts as a molecular bridging agent, utilizing the hydroxyl groups on the surface of the polymer base membrane to simultaneously connect the polymer base membrane and the organic framework material. The organic framework material, combined with bonded and anchored nano-silica, silane coupling agent segments grafted onto the base membrane surface, and polyether polyol segments, forms an organic-inorganic composite cross-linking network, effectively alleviating the problems of easy functional layer detachment and weak interfacial bonding. Furthermore, the organic framework material, incorporated into the cross-linking network, synergistically optimizes the membrane's pore structure and ion transport channels, thus improving the wettability, thermal stability, and electrochemical performance of the composite membrane.

[0103] A second aspect of this application provides a battery cell including a positive electrode, a negative electrode, and a composite separator. The composite separator is disposed between the positive and negative electrode. The composite separator includes a grafted modified polymer base film, which comprises a polymer base film and silane coupling agent segments and polyether polyol segments grafted onto the surface of the polymer base film. The composite separator also includes nano-silica, tetraalkoxysilane segments, and an organic framework material. The nano-silica is anchored to the grafted modified polymer base film via silicon-oxygen bonds. The tetraalkoxysilane segments are fixed to the grafted modified polymer base film via silicon-oxygen bonds, and the tetraalkoxysilane segments bridge the organic framework material.

[0104] Understandably, the battery cell described in the second aspect of this application can be prepared by the preparation method of the first aspect of this application. In the composite separator of this application, the grafted modified polymer base membrane includes a polymer base membrane and silane coupling agent segments and polyether polyol segments grafted onto the surface of the polymer base membrane. The hydroxyl groups on the surface of the silane coupling agent segments and / or polyether polyol segments and / or polymer base membrane enable nano-silica to be anchored to the grafted modified polymer base membrane via siloxane bonds, and enable the tetraalkoxysilane segments to be fixed to the grafted modified polymer base membrane via siloxane bonds, and the tetraalkoxysilane segments bridge the organic framework material. In this composite separator, the polymer base membrane and other materials have good bonding force, the thermal stability and electrolyte wetting performance of the composite separator are improved, which is beneficial to improving the cycle stability of the battery cell.

[0105] As an example, the polymer-based membrane is made of one or more of polypropylene, polyethylene, and polyester. The average pore size of the polymer-based membrane is 0.3 μm to 0.7 μm. The thickness of the polymer-based membrane is 20 μm to 30 μm. The porosity of the polymer-based membrane is 40% to 50%.

[0106] As examples, silane coupling agent segments include one or more of γ-glycidoxypropyltrimethoxysilane segments, (3-glycidoxypropyl)methyldimethoxysilane segments, and (3-glycidoxypropyl)methyldiethoxysilane segments. Polyether polyol segments include one or more of polyethylene glycol segments and polypropylene glycol segments. Tetraalkoxysilane segments include one or more of tetraethoxysilane segments and tetramethoxysilane segments. Organic framework materials include one or more of metal-organic framework materials and covalent organic framework materials.

[0107] As examples, the mass ratio of polymer-based film to silane coupling agent segments is 1:(0.02~0.05). The mass ratio of polymer-based film to polyether polyol segments is 1:(0.5~0.6). The mass ratio of polymer-based film to nano-silica is 1:(0.05~0.2). The mass ratio of polymer-based film to organic framework material is 1:(0.02~0.06). The mass ratio of polymer-based film to tetraalkoxysilane segments is 1:(0.05~0.2).

[0108] As an example, in the composite membrane, the tetraalkoxysilane segments have a cross-linked structure. Further, the degree of cross-linking of the tetraalkoxysilane segments is 50% to 65%. For example, the degree of cross-linking of the tetraalkoxysilane segments may include, but is not limited to, 50%, 53%, 55%, 56%, 58%, 60%, 62%, or 65%, or any two of the above values ​​as endpoints.

[0109] As an example, in the composite membrane, the chemical bonding rate between the organic framework material and the tetraalkoxysilane segment is 78% to 90%. The chemical bonding rate between the organic framework material and the tetraalkoxysilane segment can be, but is not limited to, 80%, 84%, 88%, or any two of the above values ​​as endpoints.

[0110] "Degree of crosslinking of tetraalkoxysilane segments" refers to the molar percentage of silicon atoms forming Si-O-Si bridges in the total silicon-oxygen structure after hydrolysis and condensation of tetraalkoxysilane. "Chemical bonding rate between organic framework materials and tetraalkoxysilane segments" refers to the percentage of the mass of tetraalkoxysilane segments bonded to the organic framework material relative to the total mass of the tetraalkoxysilane segments. Both "degree of crosslinking of tetraalkoxysilane segments" and "chemical bonding rate between organic framework materials and tetraalkoxysilane segments" can be determined through... 29 The results were obtained by combining nuclear magnetic resonance spectroscopy (NMR) with X-ray photoelectron spectroscopy (XPS) of Si solid-state. 29 Si solid-state nuclear magnetic resonance spectroscopy is used to quantitatively calculate the degree of crosslinking of silicon-oxygen networks, while X-ray photoelectron spectroscopy is used to quantitatively obtain the interfacial chemical bonding rate by fitting characteristic bonding peaks.

[0111] As an example, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. As an example, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0112] The positive electrode film layer includes a positive electrode active material, a binder, and a conductive agent. Exemplarily, the positive electrode active material includes one or more of lithium iron phosphate, lithium manganese iron phosphate, and lithium nickel iron phosphate. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0113] In some examples, the negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material. The negative current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0114] As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.

[0115] As an example, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). As an example, the negative electrode film layer may also optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0116] A third aspect of this application provides a battery device comprising a plurality of battery cells prepared by any of the methods described in the first aspect of this application, or comprising a plurality of battery cells prepared by the second aspect of this application. The battery device includes one or more of a battery module, a battery pack, and an energy storage battery.

[0117] A fourth aspect of this application provides an electrical device including a battery device as described in the third aspect of this application. In the electrical device, the battery device is used as a power source.

[0118] A fifth aspect of this application provides an energy storage device, including the battery device as described in the third aspect of this application. The energy storage device can be, but is not limited to, an energy storage container, an energy storage cabinet, an energy storage power station, an energy storage battery pack, or a portable energy storage system. The energy storage device provided in this application is suitable for long-term energy storage. As an example, the aforementioned energy storage device can support continuous discharge of the battery for 4 hours, 8 hours, or even longer, meeting the structural stability requirements of high-capacity batteries.

[0119] The following are specific examples. Unless otherwise specified, the raw materials used in the examples are all commercially available products.

[0120] Example 1

[0121] (1) Plasma treatment of polymer-based films:

[0122] A polypropylene (PP) base film with a thickness of 25 μm, an average pore size of 0.5 μm, and a porosity of 45% was selected. The PP base film was ultrasonically cleaned sequentially with acetone, ethanol, and deionized water for 20 min each, followed by vacuum drying at 70℃ for 3 h to obtain the cleaned PP base film. The cleaned PP base film was then placed in a plasma treatment device using a 3:1 volume ratio of argon and oxygen mixed gas at a plasma power of 100 W and a treatment distance of 10 mm for 5 min to obtain the plasma-treated polymer base film.

[0123] (2) Graft-modified polymer base films were prepared by sequentially using silane coupling agent modified solution and polyether polyol modified solution for grafting treatment:

[0124] γ-glycidoxypropyltrimethoxysilane KH560 (silane coupling agent) and ethanol were mixed at a mass ratio of 1:19. A 0.5 wt.% hydrochloric acid aqueous solution was added to adjust the pH to 4, yielding a silane coupling agent modified solution. The plasma-treated polymer base film was immersed in the silane coupling agent modified solution and grafted at 45°C for 5 h. After the reaction, the film was washed four times with ethanol and vacuum dried at 70°C for 3 h to obtain a silane coupling agent segment grafted modified polymer base film (mass ratio of polymer base film to silane coupling agent segment was 1:0.025). Gravimetric analysis showed that the grafting rate of the silane coupling agent segments in the silane coupling agent segment grafted modified polymer base film was 92%.

[0125] The silane coupling agent-modified polymer base film was then immersed in a polyether polyol modification solution and grafted at 65°C for 8 hours to prepare the grafted modified polymer base film (the mass ratio of polymer base film to polyether polyol segments was 1:0.55). The polyether polyol modification solution consisted of polyethylene glycol (PEG-2000) with a number average molecular weight of 2000 and ethanol. The mass ratio of polyethylene glycol to ethanol was 1:9.

[0126] (3) Free radical activation treatment of the grafted modified polymer-based film:

[0127] Benzoyl peroxide (BPO) was selected as the organic peroxide initiator. A solution of the organic peroxide initiator was prepared by mixing BPO and ethanol (the mass fraction of BPO in the solution was 2%, and the mass ratio of BPO to silane coupling agent segments was 1.2:1). The grafted modified polymer base film was immersed in the organic peroxide initiator solution and subjected to free radical activation treatment at 85°C for 3 hours under a nitrogen atmosphere. After the reaction, the film was washed four times with ethanol and dried under vacuum at 70°C for 3 hours.

[0128] (4) The grafted modified polymer base film after free radical activation treatment and the suspension of nano-silica were mixed and anchored:

[0129] A suspension of nano-silica was prepared by mixing nano-silica with an average particle size of 100 nm, γ-aminopropyltriethoxysilane KH550, sodium dodecylbenzenesulfonate, and deionized water, and ultrasonically dispersing the mixture for 45 min at an ultrasonic dispersion power of 200 W. The mass fraction of nano-silica in the suspension was 3.2%, the mass fraction of γ-aminopropyltriethoxysilane was 0.16%, and the mass fraction of sodium dodecylbenzenesulfonate was 0.5%. A grafted modified polymer film, after free radical activation treatment, was immersed in the nano-silica suspension and anchored at 55 °C for 5 h. After the reaction, the film was washed four times with deionized water and vacuum dried at 70 °C for 3 h to prepare a silica anchoring modification intermediate. In this intermediate, the mass ratio of the polymer film to nano-silica was 1:0.1.

[0130] (5) The anchored grafted modified polymer base film is mixed with tetraalkoxysilane crosslinking liquid and organic framework material for crosslinking bonding:

[0131] Tetraethoxysilane (TEOS), ammonia, and ethanol were stirred until homogeneous to prepare a tetraalkoxysilane crosslinking solution (pH 9, TEOS mass fraction 12%). The mass ratio of the polymer base membrane to the tetraalkoxysilane in the crosslinking solution was 1:0.12. The anchored grafted modified polymer base membrane was immersed in the tetraalkoxysilane crosslinking solution, and metal-organic framework material UIO-66 (average particle size 200 nm, vacuum dried at 120℃ for 8 h) was added. The mass ratio of the polymer base membrane to UIO-66 was 1:0.04, followed by ultrasonic dispersion for 20 min. Crosslinking and bonding were then carried out at 45℃ for 8 h. After the reaction, the membrane was washed four times with ethanol and vacuum dried at 70℃ for 6 h to prepare the composite separator. 29 According to the detection of Si solid-state nuclear magnetic resonance spectroscopy combined with X-ray photoelectron spectroscopy, the crosslinking degree of tetraethoxysilane TEOS in the composite membrane is 60%, and the chemical bonding rate of UIO-66 and the crosslinking network of tetraethoxysilane TEOS is 88%.

[0132] Example 2

[0133] Example 2 is basically the same as Example 1, the main difference being that step (3) of Example 2 is different from that of Example 1. Step (3) of Example 2 is as follows:

[0134] (3) Free radical activation treatment of the grafted modified polymer-based film:

[0135] Benzoyl peroxide (BPO) was selected as the organic peroxide initiator. A solution of the organic peroxide initiator was prepared by mixing BPO and ethanol (the mass fraction of BPO in the solution was 1.2%, and the mass ratio of BPO to silane coupling agent segments was 0.8:1). The grafted modified polymer base film was immersed in the organic peroxide initiator solution and subjected to free radical activation treatment at 85°C for 3 hours under a nitrogen atmosphere. After the reaction, the film was washed four times with ethanol and dried under vacuum at 70°C for 3 hours.

[0136] Example 3

[0137] Example 3 is basically the same as Example 1, the main difference being that step (4) is different in Example 3 and Example 1. Step (4) of Example 3 is as follows:

[0138] (4) The grafted modified polymer base film after free radical activation treatment and the suspension of nano-silica were mixed and anchored:

[0139] Nano-sized silica with an average particle size of 100 nm, γ-aminopropyltriethoxysilane KH550, sodium dodecylbenzenesulfonate, and deionized water were mixed and ultrasonically dispersed for 45 min at an ultrasonic dispersion power of 200 W to prepare a suspension of nano-sized silica. The mass fraction of nano-sized silica in the suspension was adjusted to 3.07%, the mass fraction of γ-aminopropyltriethoxysilane to 0.16%, and the mass fraction of sodium dodecylbenzenesulfonate to 0.5%. The grafted modified polymer base film after free radical activation treatment was immersed in the above suspension and anchored at 55 °C for 5 h. After the reaction, it was washed 4 times with deionized water and vacuum dried at 70 °C for 3 h to prepare a silica anchoring modified intermediate. In this intermediate, the mass ratio of polymer base film to nano-sized silica was 1:0.08.

[0140] Example 4

[0141] Example 4 is basically the same as Example 1, the main difference being that step (5) of Example 4 is different from that of Example 1. Step (5) of Example 4 is as follows:

[0142] (5) The anchored grafted modified polymer base film is mixed with tetraalkoxysilane crosslinking liquid and organic framework material for crosslinking bonding:

[0143] Tetraethoxysilane (TEOS), ammonia, and ethanol were stirred until homogeneous to prepare a tetraalkoxysilane crosslinking solution (pH 9, TEOS mass fraction 10%). The mass ratio of the polymer base membrane to the tetraalkoxysilane in the crosslinking solution was 1:0.1. The anchored grafted modified polymer base membrane was immersed in the tetraalkoxysilane crosslinking solution, and metal-organic framework material UIO-66 (average particle size 200 nm, vacuum dried at 120℃ for 8 h) was added. The mass ratio of the polymer base membrane to UIO-66 was 1:0.04, followed by ultrasonic dispersion for 20 min. Crosslinking and bonding were then carried out at 45℃ for 8 h. After the reaction, the membrane was washed four times with ethanol and vacuum dried at 70℃ for 6 h to prepare the composite separator. 29 According to the detection of Si solid-state nuclear magnetic resonance spectroscopy combined with X-ray photoelectron spectroscopy, the crosslinking degree of tetraethoxysilane TEOS in the composite membrane is 55%, and the chemical bonding rate of UIO-66 and the crosslinking network of tetraethoxysilane TEOS is 84%.

[0144] Example 5

[0145] Example 5 is basically the same as Example 1, the main difference being that step (5) in Example 5 is:

[0146] (5) The anchored grafted modified polymer base film is mixed with tetraalkoxysilane crosslinking liquid and organic framework material for crosslinking bonding:

[0147] Tetraethoxysilane (TEOS), ammonia, and ethanol were stirred until homogeneous to prepare a tetraalkoxysilane crosslinking solution (pH 9, TEOS mass fraction 12%). The mass ratio of the polymer base membrane to the tetraalkoxysilane in the crosslinking solution was 1:0.1. The anchored grafted modified polymer base membrane was immersed in the tetraalkoxysilane crosslinking solution, and metal-organic framework material UIO-66 (average particle size 200 nm, vacuum dried at 120℃ for 8 h) was added. The mass ratio of the polymer base membrane to UIO-66 was 1:0.04, followed by ultrasonic dispersion for 20 min. Crosslinking and bonding were then carried out at 45℃ for 8 h. After the reaction, the membrane was washed four times with ethanol and vacuum dried at 70℃ for 6 h to prepare the composite separator. 29 According to the detection of Si solid-state nuclear magnetic resonance spectroscopy combined with X-ray photoelectron spectroscopy, the crosslinking degree of tetraethoxysilane TEOS in the composite membrane is 60%, and the chemical bonding rate of UIO-66 and the crosslinking network of tetraethoxysilane TEOS is 88%.

[0148] Example 6

[0149] Example 6 is basically the same as Example 1. The main difference is that step (5) of Example 6 is different from that of Example 1. In Example 6, borate ester type covalent organic framework material COF-5 with an average particle size of 200nm is used to replace UIO-66 in Example 1.

[0150] through 29 According to the detection of Si solid-state nuclear magnetic resonance spectroscopy combined with X-ray photoelectron spectroscopy, the crosslinking degree of tetraethoxysilane TEOS in the composite membrane is 56%, and the chemical bonding rate of UIO-66 with the crosslinking network of tetraethoxysilane TEOS is 80%.

[0151] Example 7

[0152] Example 7 is basically the same as Example 1, except that the temperature for free radical activation treatment in step (3) of Example 7 is 75°C.

[0153] Example 8

[0154] Example 8 is basically the same as Example 1, except that the temperature for anchoring treatment in step (4) of Example 8 is 85°C.

[0155] Example 9

[0156] Example 9 is basically the same as Example 1, except that the temperature for cross-linking bonding in step (5) of Example 9 is 95°C.

[0157] Comparative Example 1

[0158] Comparative Example 1 is basically the same as Example 1, except that Comparative Example 1 uses a polypropylene PP base membrane with a thickness of 25 μm, an average pore size of 0.5 μm, and a porosity of 45% as the diaphragm.

[0159] Comparative Example 2

[0160] Comparative Example 2 is basically the same as Example 1, the main difference being that Comparative Example 2 does not include step (2). In Comparative Example 2, the plasma-treated polymer base film is directly immersed in a solution of an organic peroxide initiator and subsequent steps are performed. The steps of Comparative Example 2 are as follows:

[0161] Plasma treatment of polymer-based films: Same as in Example 1.

[0162] Free radical activation treatment of graft-modified polymer-based films:

[0163] Benzoyl peroxide (BPO) was selected as the organic peroxide initiator. A solution of the organic peroxide initiator (2% by mass) was prepared by mixing BPO and ethanol. The plasma-treated polymer substrate film was immersed in the organic peroxide initiator solution and subjected to free radical activation treatment at 85°C for 3 hours under a nitrogen atmosphere. After the reaction, the film was washed four times with ethanol and then vacuum-dried at 70°C for 3 hours.

[0164] The polymer-based film after free radical activation treatment was mixed with a suspension of nano-silica for anchoring treatment: same as in Example 1. 29 According to the detection of Si solid-state nuclear magnetic resonance spectroscopy combined with X-ray photoelectron spectroscopy, the crosslinking degree of tetraethoxysilane TEOS in the composite membrane is only 38%, and the chemical bonding rate of UIO-66 and the crosslinking network of tetraethoxysilane TEOS is only 52%.

[0165] Comparative Example 3

[0166] Comparative Example 3 is basically the same as Example 1. The main difference is that Comparative Example 3 does not include step (3). In Comparative Example 3, the grafted modified polymer base film is directly immersed in the suspension of nano-silica and the subsequent steps are carried out.

[0167] through 29 According to the detection of Si solid-state nuclear magnetic resonance spectroscopy combined with X-ray photoelectron spectroscopy, the crosslinking degree of tetraethoxysilane TEOS in the composite membrane is only 41%, and the chemical bonding rate of UIO-66 with the crosslinking network of tetraethoxysilane TEOS is only 56%.

[0168] Comparative Example 4

[0169] Comparative Example 4 is basically the same as Example 1. The main difference is that Comparative Example 4 does not include step (4). In Comparative Example 4, the grafted modified polymer base film after free radical activation treatment is directly immersed in tetraalkoxysilane crosslinking liquid and subsequent steps are performed.

[0170] through 29 According to the detection of Si solid-state nuclear magnetic resonance spectroscopy combined with X-ray photoelectron spectroscopy, the crosslinking degree of tetraethoxysilane TEOS in the composite membrane is 53%, and the chemical bonding rate of UIO-66 with the crosslinking network of tetraethoxysilane TEOS is 72%.

[0171] Comparative Example 5

[0172] Comparative Example 5 is basically the same as Example 1, the main difference being that step (5) in Comparative Example 5 does not include the organic framework material UIO-66. Step (5) of Comparative Example 5 is as follows:

[0173] (5) The anchored grafted modified polymer base film is mixed with tetraalkoxysilane crosslinking liquid and crosslinked together:

[0174] Tetraethoxysilane (TEOS), ammonia, and ethanol were stirred until homogeneous to prepare a tetraalkoxysilane crosslinking solution (pH 9, TEOS mass fraction 12%). The mass ratio of the polymer base membrane to the tetraalkoxysilane in the crosslinking solution was 1:0.1. The anchored grafted modified polymer base membrane was immersed in the tetraalkoxysilane crosslinking solution and then ultrasonically dispersed for 20 min. Crosslinking was then carried out at 45 °C for 8 h. After the reaction, the membrane was washed four times with ethanol and vacuum dried at 70 °C for 6 h to prepare the composite separator.

[0175] Comparative Example 6

[0176] Comparative Example 6 is basically the same as Example 1, the main difference being that step (5) of Comparative Example 6 does not include the tetraalkoxysilane crosslinking liquid. Step (5) of Comparative Example 6 is as follows:

[0177] (5) The anchored grafted modified polymer base film is mixed with the organic framework material and cross-linked:

[0178] The anchored grafted modified polymer-based membrane was immersed in a mixture of ammonia and ethanol at pH 9, and metal-organic framework material UIO-66 (average particle size 200 nm, vacuum dried at 120 °C for 8 h) was added. The mass ratio of polymer-based membrane to UIO-66 was 1:0.04, followed by ultrasonic dispersion for 20 min. The reaction was then carried out at 45 °C for 8 h. After the reaction, the membrane was washed four times with ethanol and vacuum dried at 70 °C for 6 h to prepare the composite membrane.

[0179] Performance testing:

[0180] The composite membranes prepared in the above embodiments and comparative examples were subjected to the following tests:

[0181] (1) Adhesion: The peel strength of the composite membrane was tested by the standard GB / T 2792-1998 test method to characterize the degree of interfacial bonding between the modified functional layer and the polymer base membrane. The unit is N / 25mm.

[0182] (2) Liquid absorption rate: Cut the composite diaphragm into 5 samples of 100×100mm size, weigh them, immerse each sample in conventional electrolyte for 10 minutes, remove the samples, blot the electrolyte on the surface with filter paper, weigh them again, and calculate the percentage increase in mass after immersion in electrolyte, which is the liquid absorption rate. The average liquid absorption rate of the 5 samples is the liquid absorption rate.

[0183] (3) Heat shrinkage rate: The heat shrinkage rate of the composite diaphragm at 120℃×1h was tested according to standard GB / T 12027-2004.

[0184] (4) Cyclic performance test: The lithium iron phosphate (LiFePO4) positive electrode, the above-mentioned composite separator and graphite negative electrode are assembled into a battery cell. The battery is charged and discharged at 0.5C constant current and constant voltage at room temperature of 25℃, with a voltage test range of 2.5 to 3.65V, and 500 charge-discharge cycles are performed. The capacity retention rate of the battery after 500 cycles is tested and calculated.

[0185] The corresponding test results are shown in Table 1.

[0186] Table 1

[0187]

[0188] Comparative Example 1 used a polypropylene (PP) base membrane as the separator. The composite separator preparation process in Comparative Example 2 did not include the grafting treatment steps with silane coupling agent modified liquid and polyether polyol modified liquid; therefore, the polymer base membrane did not have silane coupling agent segments and polyether polyol segments. The composite separator preparation process in Comparative Example 3 did not include the free radical activation treatment step. Comparative Example 4 did not include the nano-silica anchoring treatment step. Organic framework materials were not used in the crosslinking bonding step of Comparative Example 5, and tetraalkoxysilane crosslinking liquid was not used in the crosslinking bonding step of Comparative Example 6. Compared to Examples 1-9, the composite separators prepared in Comparative Examples 1-6 exhibited weaker peel strength, lower liquid absorption rate, and poorer thermal stability, failing to provide good cycle stability for the battery cells.

[0189] In Examples 1 through 9, the main difference between Example 1 and Example 2 lies in the different mass fractions of benzoyl peroxide (BPO) in the solution during the free radical activation treatment step, resulting in different mass ratios of benzoyl peroxide (BPO) to silane coupling agent segments. As shown in Table 1, in Example 1, when the mass ratio of benzoyl peroxide (BPO) to silane coupling agent segments is within the range of (0.9~1.2):1, the composite separator exhibits higher peel strength, higher liquid absorption rate, and better thermal stability, which is more conducive to improving the cycle stability of the battery cells.

[0190] The main difference between Example 1 and Example 3 lies in the different mass ratios of the polymer-based film and the nano-silica. A comparison of the two shows that in Example 1, when the mass ratio of the polymer-based film to the nano-silica is in the range of 1:(0.09~0.12), the composite separator exhibits higher peel strength, higher liquid absorption rate, and better thermal stability, which is more conducive to improving the cycle stability of the battery cells.

[0191] The main difference between Examples 1 and 4 lies in the different mass fractions of tetraethoxysilane (TEOS), which in turn leads to different mass ratios of the polymer base film and tetraethoxysilane in the tetraethoxysilane crosslinking solution. A comparison shows that when the mass fraction of TEOS in the tetraethoxysilane crosslinking solution is 11%–13%, and the mass ratio of the polymer base film to the tetraethoxysilane in the crosslinking solution is 1:(0.11–0.15), the composite separator exhibits higher peel strength, higher liquid absorption rate, and better thermal stability, thus improving the cycle stability of the battery cells.

[0192] The main difference between Example 1 and Example 5 lies in the different mass ratios of the polymer base film and the tetraalkoxysilane in the tetraalkoxysilane crosslinking solution. In Example 1, the mass ratio of the polymer base film to the tetraalkoxysilane in the tetraalkoxysilane crosslinking solution is 1:(0.11~0.15), resulting in a composite separator with higher peel strength, higher liquid absorption rate, and better thermal stability, which is more conducive to improving the cycle stability of the battery cells.

[0193] The main difference between Example 1 and Example 6 lies in the type of organic framework material used. Example 1 uses a metal-organic framework material, which results in a composite separator with higher peel strength, higher liquid absorption rate, and better thermal stability, thus improving the cycle stability of the battery cells.

[0194] The main difference between Example 1 and Example 7 lies in the temperature of the free radical activation treatment. The main difference between Example 1 and Example 8 lies in the temperature of the anchoring treatment. The main difference between Example 1 and Example 9 lies in the temperature of the crosslinking bonding. As can be seen from the above comparison, the composite separator prepared in Example 1, with a free radical activation treatment temperature of 80℃~90℃, an anchoring treatment temperature of 50℃~60℃, and a crosslinking bonding temperature of 40℃~50℃, exhibits higher peel strength, higher liquid absorption rate, and better thermal stability, which is more conducive to improving the cycle stability of the battery cell.

[0195] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0196] The embodiments described above are merely illustrative of several implementation methods of this application, intended to facilitate a detailed understanding of the technical solutions of this application, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent application should be determined by the content of the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a battery cell, the battery cell comprising a positive electrode, a negative electrode, and a composite separator, wherein the composite separator is disposed between the positive electrode and the negative electrode, characterized in that, The preparation steps of the composite membrane include: The grafted modified polymer base film is subjected to free radical activation treatment to give the surface of the grafted modified polymer base film hydroxyl groups; the grafted modified polymer base film includes a polymer base film and silane coupling agent segments and polyether polyol segments grafted onto the surface of the polymer base film; The grafted modified polymer base film after free radical activation treatment and the suspension of nano-silica were mixed and anchored, and the nano-silica was anchored to the grafted modified polymer base film through some of the hydroxyl groups. The anchored grafted modified polymer base film is mixed with a tetraalkoxysilane crosslinking liquid and an organic framework material, and crosslinked and bonded to bridge some of the hydroxyl groups and the organic framework material through tetraalkoxysilane segments to prepare a composite membrane.

2. The method for preparing a single battery cell according to claim 1, characterized in that, The steps of free radical activation treatment of the grafted modified polymer-based film include: A solution of an organic peroxide initiator was used to perform free radical activation treatment on the grafted modified polymer-based film; In the solution of the organic peroxide initiator, the mass fraction of the organic peroxide initiator is 1% to 4%; the organic peroxide initiator includes one or more of benzoyl peroxide, dicumyl peroxide, and di-tert-butyl peroxide.

3. The method for preparing a single battery cell according to claim 1, characterized in that, The suspension of nano-silica comprises nano-silica and an aminosilane coupling agent, and the preparation method has one or more of the following characteristics: (1) The average particle size of the nano-silica is 80nm~120nm; (2) In the suspension of nano-silica, the mass fraction of nano-silica is 2.5%~3.5%; (3) The mass ratio of the polymer base film to the nano-silica is 1:(0.05~0.2); (4) The aminosilane coupling agent includes one or more of γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane; (5) In the suspension of nano-silica, the mass fraction of the aminosilane coupling agent is 0.1%~0.3%.

4. The method for preparing a single battery cell according to claim 1, characterized in that, The tetraalkoxysilane crosslinking liquid comprises a tetraalkoxysilane and a basic catalyst, and the preparation method has one or more of the following characteristics: (1) The tetraalkoxysilane includes one or more of tetraethoxysilane and tetramethoxysilane; (2) The alkaline catalyst includes one or more of ammonia and triethylamine; (3) In the tetraalkoxysilane crosslinking liquid, the mass fraction of the tetraalkoxysilane is 10%~14%; (4) The mass ratio of the polymer base film to the mass ratio of the tetraalkoxysilane in the tetraalkoxysilane crosslinking solution is 1:(0.05~0.2).

5. The method for preparing a single battery cell according to claim 1, characterized in that, The organic framework material includes one or more of metal-organic framework materials and covalent organic framework materials, and the preparation method has one or more of the following characteristics: (1) The mass ratio of the polymer base film to the organic framework material is 1:(0.02~0.06); (2) The metal ions in the metal-organic framework material include one or more of zirconium ions, copper ions and zinc ions; (3) The organic ligands in the metal-organic framework material include one or more of terephthalic acid ligands and biphenyl ligands; (4) The covalent organic framework material includes one or more of borate ester covalent organic framework materials and triazine covalent organic framework materials.

6. The method for preparing a single battery cell according to claim 1, characterized in that, The steps of free radical activation treatment include: carrying out the reaction at 80°C to 90°C under a protective gas atmosphere; and / or, The anchoring treatment temperature is 50℃~60℃; and / or, The cross-linking bonding temperature is 40℃~50℃.

7. The method for preparing a single battery cell according to claim 1, characterized in that, The polymer-based film is made of one or more of polypropylene, polyethylene, and polyester; and / or, The polymer-based film has an average pore size of 0.3 μm to 0.7 μm; and / or, The thickness of the polymer-based film is 20 μm to 30 μm; and / or, The polymer-based membrane has a porosity of 40% to 50%; and / or, The mass ratio of the polymer base film to the silane coupling agent segment is 1:(0.02~0.05); and / or, The mass ratio of the polymer base film to the polyether polyol segment is 1:(0.5~0.6).

8. The method for preparing a battery cell according to any one of claims 1 to 7, characterized in that, It also includes the preparation step of the grafted modified polymer-based film, including: Plasma treatment of polymer-based films; A grafted modified polymer base film was prepared by sequentially grafting a silane coupling agent modified solution and a polyether polyol modified solution onto a plasma-treated polymer base film; the surface of the grafted modified polymer base film has silane coupling agent segments and polyether polyol segments.

9. The method for preparing a battery cell according to claim 8, characterized in that, The silane coupling agent in the modified silane coupling agent solution includes one or more of γ-glycidoxypropyltrimethoxysilane, (3-glycidoxypropyl)methyldimethoxysilane, and (3-glycidoxypropyl)methyldiethoxysilane; and / or, The polyether polyol in the modified polyether polyol solution includes one or more of polyethylene glycol and polypropylene glycol.

10. The method for preparing a battery cell according to claim 8, characterized in that, The process parameters for grafting using the silane coupling agent modified solution include: a temperature of 40℃~50℃; and / or, The process parameters for grafting using the polyether polyol modified liquid include: a temperature of 60℃~70℃.

11. A battery cell, comprising a positive electrode, a negative electrode, and a composite separator; wherein the composite separator is disposed between the positive electrode and the negative electrode, characterized in that, The composite membrane includes a grafted modified polymer base membrane, which comprises a polymer base membrane and silane coupling agent segments and polyether polyol segments grafted onto the surface of the polymer base membrane. The composite membrane further includes nano-silica, tetraalkoxysilane segments, and organic framework materials; the nano-silica is anchored to the grafted modified polymer base membrane via silicon-oxygen bonds; The tetraalkoxysilane segments are fixed to the grafted modified polymer base film via siloxane bonds, and the tetraalkoxysilane segments bridge the organic framework material.

12. The battery cell according to claim 11, characterized in that, The silane coupling agent segments include one or more selected from γ-glycidoxypropyltrimethoxysilane segments, (3-glycidoxypropyl)methyldimethoxysilane segments, and (3-glycidoxypropyl)methyldiethoxysilane segments; and / or, The polyether polyol segments include one or more of polyethylene glycol segments and polypropylene glycol segments; and / or, The tetraalkoxysilane segment includes one or more of tetraethoxysilane segments and tetramethoxysilane segments; and / or, The organic framework material includes one or more of metal-organic framework materials and covalent organic framework materials; and / or, The polymer-based film is made of one or more of polypropylene, polyethylene, and polyester; and / or, The polymer-based film has an average pore size of 0.3 μm to 0.7 μm; and / or, The thickness of the polymer-based film is 20 μm to 30 μm; and / or, The porosity of the polymer-based membrane is 40%~50%.

13. A battery device, characterized in that, The battery device comprises one or more of the following: battery modules, battery packs, and energy storage batteries. The battery device includes multiple battery cells prepared by any one of the preparation methods described in claims 1 to 10, or multiple battery cells as described in any one of claims 11 to 12.

14. An electrical appliance, characterized in that, Includes the battery device as described in claim 13.

15. An energy storage device, characterized in that, Includes the battery device as described in claim 13.

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