Acrylonitrile-modified SEI film, anode and its preparation method

Abstract

This invention provides an acrylonitrile-modified anode polymer SEI film, an anode, and a method for preparing the same, relating to the field of lithium battery manufacturing technology. This invention prepares a novel composite polymer solid electrolyte using a simple and rapid method. It involves solution copolymerization of polyacrylonitrile and acrylate monomers, followed by the addition of inorganic nanoparticles. By introducing various coordination groups, such as carbon-oxygen double bonds (C=O) and ether-oxygen bonds (C-O-C) in polyacrylic acid esters, and carbon-nitrogen triple bonds (CN) in acrylonitrile, the conductivity and thermo-electrochemical stability of the composite solid polymer electrolyte are improved. Further coating this electrolyte onto the anode surface as an artificial SEI film can alleviate the repeated decomposition of conventional SEI films at high temperatures, potentially improving the high-temperature storage, high-temperature cycling performance, and safety performance of the battery cell.

Description

Technical Field

[0001] This invention relates to the field of lithium battery manufacturing technology, and in particular to an acrylonitrile-modified anode polymer SEI film, the anode, and its preparation method. Background Technology

[0002] In existing technologies, the formation of conventional SEI films depends on the irreversible reduction of electrolyte components (lithium salt, solvent, additives): lithium salt (such as...) LiTFSI is reduced on the negative electrode surface to generate Inorganic components; reduced by electrolyte solvent (such as ethylene carbonate EC, dimethyl carbonate DMC) to produce alkyl lithium carbonate ( ), lithium carbonate ( Organic components such as organic matter; the above products spontaneously accumulate to form an "inner inorganic phase" ( Main phase) + outer organic phase ( It has a double-layered structure (mainly) and is porous and uneven in shape.

[0003] Its common components can be divided into two main categories: inorganic and organic. Among the inorganic components, lithium fluoride (LiF) has a high melting point and excellent mechanical strength, serving as the framework for the film and suppressing lithium dendrites; lithium carbonate (… Lithium oxide provides basic ion conduction; Lithium carbonate (LiF) has high ionic conductivity and can improve lithium-ion transport efficiency in synergy with LiF. Among organic components, alkyl lithium carbonate (LiF) It possesses good flexibility, allowing it to adapt to electrode volume expansion; polycarbonate exhibits outstanding thermal stability and adhesion, providing significant stress buffering. Existing technologies for improving the performance of conventional SEI films in lithium-ion batteries primarily involve adding specific functional molecules to the electrolyte to induce the formation of a dense layer rich in stable components in the SEI film, and using pre-lithiation methods to assist film formation. For example, adding fluoroethylene carbonate (FEC) and vinylene carbonate (VC) preferentially reduces and decomposes to generate an inorganic layer containing LiF, improving the conductivity of the SEI film and polymerizing on the electrode surface to form a flexible organic layer that buffers volume changes.

[0004] Although ordinary SEI films can achieve the basic functions of "electronic insulation and ion conduction", they have insurmountable defects in performance and application scenarios due to their "spontaneous formation" nature, as follows:

[0005] (a) Composition and structure are uncontrollable:

[0006] The composition ratio of ordinary SEI membranes (such as LiF and...) The content ratio of inorganic phase is significantly affected by environmental factors such as electrolyte formulation, temperature, and voltage, and is prone to problems such as "uneven distribution of inorganic phase" and "excessive decomposition of organic phase". For example, in a high-temperature environment (>60℃), the content of inorganic phase in ordinary SEI membranes is significantly affected by environmental factors such as electrolyte formulation, temperature, and voltage, and is prone to problems such as "uneven distribution of inorganic phase" and "excessive decomposition of organic phase". Easily decomposed into and This results in a loose membrane structure, which cannot continuously block the side reactions between the electrolyte and the negative electrode.

[0007] (ii) Imbalance between ionic conductivity and mechanical strength:

[0008] The ionic conductivity of ordinary SEI membranes is typically only It cannot meet the requirements of high-rate batteries (such as 5C fast-charging batteries). Transmission requirements; at the same time, its mechanical strength is extremely low (Young's modulus 1~10GPa), and during the lithium metal anode cycling process, it is prone to stress fracture caused by lithium dendrite growth, which leads to dendrite penetration of the separator.

[0009] (III) Shortcomings in cycle stability and lifespan:

[0010] Ordinary SEI films undergo a dynamic process of "continuous rupture-regeneration" during charge-discharge cycles. Each regeneration consumes active lithium and electrolyte, leading to rapid capacity decay. Current technology data shows that lithium metal batteries using ordinary SEI films generally experience a capacity decay of over 30% after 500 cycles, and the initial coulombic efficiency (ICE) is below 85%, far from meeting the industry requirement of "capacity retention of ≥80% after 1500 cycles" for power batteries.

[0011] (iv) Poor adaptability over a wide temperature range:

[0012] At low temperatures (< -20℃), the organic phase in ordinary SEI films easily crystallizes, leading to a sharp drop in ionic conductivity (< The battery cannot discharge normally; under high temperature (>80℃) conditions, its organic phase is easily oxidized and decomposed, releasing CO, Gases can cause the battery cells to swell. Summary of the Invention

[0013] In order to simultaneously improve the conductivity, heat resistance and electrochemical stability of the anode polymer SEI film, this application provides an acrylonitrile-modified anode polymer SEI film, an anode and a method for preparing the same.

[0014] In a first aspect, this application provides a method for preparing an acrylonitrile-modified negative electrode polymer SEI film, comprising the following preparation steps:

[0015] Polymer monomers containing carbon-carbon double bonds are dispersed in an organic solvent to form a prepolymer solution;

[0016] A thermal initiator is added to a prepolymer solution, and a polymerization reaction is carried out under an inert gas atmosphere to obtain a polymer dispersion.

[0017] Then, nanoparticles are added, stirred and mixed evenly, and then coated on the surface of the negative electrode material. After drying, an acrylonitrile-modified negative electrode polymer SEI film is obtained.

[0018] The polymer monomers include at least two or more of acrylonitrile, polyethylene glycol diacrylate, vinylene carbonate, pentaerythritol tetraacrylate, and trimethylolpropane triacrylate.

[0019] Furthermore, the polymer monomer is a composition of acrylonitrile and polyethylene glycol diacrylate (PEGDA) in a mass ratio of 1-5:1.

[0020] Furthermore, the mass concentration of the polymer monomer in the prepolymer solution is 8-12 wt%.

[0021] Furthermore, the initiator accounts for 2-7% of the polymer monomer mass.

[0022] Furthermore, the polymerization temperature during the polymerization reaction is 55-75 ℃, and the polymerization time is 8-30 h.

[0023] Furthermore, the mass ratio of the nanoparticles to the polymer monomer is 0.01-0.1:1, and the nanoparticles are nano-silica and / or nano-titanium dioxide.

[0024] Furthermore, the nanoparticles are a composition of nano-titanium dioxide and nano-silica in a mass ratio of 0.15-0.35:0.15-0.25.

[0025] Lewis acid nanoparticles, by virtue of their Lewis acidity, can constrain the movement of anions on the one hand, and reduce the strong Lewis basicity of ether oxygen bonds on the other hand, thus making the binding effect of ether oxygen bond groups on lithium ions less, and making the transport of lithium ions in polymers easier.

[0026] about Dielectric constant ratio Strong, in this system and Both can improve electrical conductivity, but they have far fewer hydroxyl groups, making them more difficult to disperse well in polymers.

[0027] Furthermore, the preparation of the polymer SEI film also includes lithium salt, which is derived from the addition of lithium salt to the polymer dispersion or from the infiltration of lithium salt into the electrolyte in a lithium battery.

[0028] Preferably, the lithium salt content in the obtained composite polymer SEI film ranges from 20-40 wt% of the monomer mass.

[0029] Secondly, this application provides a nitrile-modified SEI film for lithium batteries, prepared using the method described in this application, with a conductivity of... Its thermal decomposition temperature is greater than 300 ℃.

[0030] Preferably, the conductivity of the negative electrode polymer SEI film is... The decomposition voltage is greater than 5.1V, and the thermal decomposition temperature is 300~320℃.

[0031] Thirdly, this application provides a negative electrode comprising an acrylonitrile-modified negative electrode polymer SEI film as described in this application or a negative electrode polymer SEI film obtained by the preparation method described in this application.

[0032] Beneficial effects: 1. This invention prepares a new composite polymer solid electrolyte through a simple and rapid method. It involves solution copolymerization of acrylonitrile and acrylate monomers, and then composited with inorganic nanoparticles. By introducing various coordination groups such as carbon-oxygen double bonds and ether-oxygen bonds (C=O, COC) in acrylates and carbon-nitrogen triple bonds (CN) in acrylonitrile, the conductivity and thermo-electrochemical stability of the composite solid polymer electrolyte are improved. Furthermore, it is coated on the surface of the negative electrode as an artificial SEI film, which can alleviate the repeated decomposition of conventional SEI films at high temperatures and is expected to improve the high-temperature storage, high-temperature cycling performance and safety performance of the battery cell.

[0033] 2. The acrylonitrile used in this application provides a highly polar cyano group ( To promote lithium-ion transport and enhance interfacial adhesion, polyethylene glycol diacrylate, as a bifunctional crosslinking agent, constructs a flexible three-dimensional polymer network to buffer volumetric strain; the two, in synergy with nano-titanium dioxide, form a composite polymer collective with both good ion conductivity and mechanical elasticity; further employing... Nanoparticles with a specific mass ratio A relatively high proportion It provides the main body with additional lithium-ion conduction pathways and an electrochemically inert framework, while a specific ratio of ,prevent Aggregation optimizes the transport pathway layout; and its surface hydroxyl groups strengthen the connection between the inorganic and organic phases, preventing thermal delamination. Ultimately, a tight "organic-inorganic interpenetrating structure" is formed between the polymer network and the inorganic particles: the polymer network provides a uniformly dispersed carrier for the nanoparticles and imparts overall toughness, while the highly dispersed nanoparticles significantly improve the ionic conductivity, thermal stability, and electrochemical window of the composite membrane, thereby synergistically constructing an advanced artificial SEI membrane that can simultaneously meet the requirements of high ionic conductivity, heat resistance, wide potential stability, and mechanical stability.

[0034] 3. This invention, by modifying acrylate-based polymers, broadens the electrochemical window of the composite polymer electrolyte SEI membrane to 5 V and increases the conductivity to [missing value]. With a thermal stability of 200 °C, it can be used as a negative electrode surface coating to improve the high-temperature storage and high-temperature cycling performance of the battery cell. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of the artificial SEI film obtained by the preparation method of Example 1 of the present invention on the negative electrode;

[0036] Figure 2 The image above shows the thermogravimetric curve of the artificial SEI membrane obtained by the preparation method in Example 1 of this invention.

[0037] Figure 3 The figures are electrochemical window test curves of the artificial SEI membrane obtained by the preparation method in Example 1 of this invention.

[0038] Figure label:

[0039] 1. Negative electrode; 2. Artificial SEI membrane; 3. Nanoparticles. Detailed Implementation

[0040] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] SEI: Solid electrolyte interface film, refers to a stable solid film formed on the electrode surface after the reduction reaction between the electrolyte and electrode materials (such as graphite in the negative electrode) during the first charge and discharge of the battery. This film can prevent further decomposition of the electrolyte while allowing lithium ions to pass through, and is crucial to the cycle life and safety of the battery.

[0042] Artificial SEI: An artificial solid electrolyte interphase (SEI) is a protective layer artificially constructed on the surface of electrode materials (especially metal anodes such as lithium, sodium, and zinc). It aims to replace or optimize the naturally formed SEI film during the first charge and discharge cycle of the battery, addressing its instability and susceptibility to breakage, thereby significantly improving the overall performance of the battery.

[0043] PEGDA: Polyethylene glycol diacrylate. This invention uses the 400MW specification. Its ether oxygen bond (COC) can provide lithium ion transport channels, and the double bond is used for cross-linking to form a three-dimensional network. The purity is ≥98% to avoid impurities affecting polymerization.

[0044] Composite polymers refer to high-performance material systems with multiphase structures formed by uniformly dispersing or combining one or more functional components (dispersed phases) with different physical and chemical properties in a polymer (resin) matrix through physical, chemical or material processing methods.

[0045] Example 1: A method for preparing an acrylonitrile-modified SEI film as a negative electrode polymer, comprising the following preparation steps:

[0046] (1) 2g of acrylonitrile AN and 8g of polyethylene glycol diacrylate PEGDA (400 MW, C=CC(=O)OC(CO)nOC(=O)C=C) were ultrasonically dispersed in 55g of acetonitrile solution.

[0047] (2) Weigh 0.5 g of azobisisobutyronitrile and add it to the above mixture, and stir magnetically until it is completely dissolved.

[0048] (3) The mixed solution is protected by nitrogen gas and the container is sealed and kept at 65°C for 20 h to obtain polymer dispersion.

[0049] (4) Further add a certain amount of lithium salt (30 wt% of monomer content) to the above polymer dispersion and continue stirring for 2 h.

[0050] (5) The obtained uniformly mixed composite polymer dispersion is coated on the surface of the negative electrode material and then gently and slowly dried to obtain an acrylonitrile-modified negative electrode polymer SEI film.

[0051] Example 2: A method for preparing an acrylonitrile-modified negative electrode polymer SEI film, which differs from Example 1 in that the ratio of polymer monomers is different; the specific steps are as follows:

[0052] (1) 5.7g acrylonitrile AN and 4.3g polyethylene glycol diacrylate PEGDA (400 MW) were ultrasonically dispersed in 110g acetonitrile solution.

[0053] (2) Weigh 0.5 g of azobisisobutyronitrile and add it to the above mixture, and stir magnetically until it is completely dissolved.

[0054] (3) The mixed solution is protected by nitrogen gas and the container is sealed and kept at 65°C for 20 h to obtain polymer dispersion.

[0055] (4) Further add a certain amount of lithium salt (30 wt% of monomer content) to the above polymer dispersion and continue stirring for 2 h.

[0056] (5) The obtained uniformly mixed composite polymer dispersion is coated on the surface of the negative electrode material and then gently and slowly dried to obtain an acrylonitrile-modified negative electrode polymer SEI film.

[0057] Example 3: A method for preparing an acrylonitrile-modified negative electrode polymer SEI film, which differs from Examples 1 and 2 in that the ratio of polymer monomers is different; the specific steps are as follows:

[0058] (1) 8 g acrylonitrile AN and 2 g polyethylene glycol diacrylate PEGDA (400 MW) were ultrasonically dispersed in 110 g acetonitrile solution.

[0059] (2) Weigh 0.25 g of azobisisobutyronitrile and add it to the above mixture. Stir magnetically until it is completely dissolved.

[0060] (3) The mixed solution is protected by nitrogen gas and the container is sealed and kept at 65°C for 20 h to obtain polymer dispersion.

[0061] (4) Further add a certain amount of lithium salt (30 wt% of monomer content) to the above polymer dispersion and continue stirring for 2 h.

[0062] (5) The obtained uniformly mixed composite polymer dispersion is coated on the surface of the negative electrode material and then gently and slowly dried to obtain an acrylonitrile-modified negative electrode polymer SEI film.

[0063] Example 4: A method for preparing an acrylonitrile-modified anode polymer SEI film, which differs from Example 3 in that: nanofillers are added. The specific steps are as follows:

[0064] (1) 5.7 g acrylonitrile AN and 4.3 g polyethylene glycol diacrylate PEGDA (400 MW) were ultrasonically dispersed in 110 g acetonitrile solution.

[0065] (2) Weigh 0.5 g of azobisisobutyronitrile and add it to the above mixture, and stir magnetically until it is completely dissolved.

[0066] (3) The mixed solution is protected by nitrogen gas and the container is sealed and kept at 65°C for 20 h to obtain polymer dispersion.

[0067] (4) Further, a quantitative amount of lithium salt (30 wt% of monomer content) and 0.1 g of nano-silica ( ， Particles with an average particle size of 50 nm were ultrasonically dispersed into the polymer dispersion and stirred vigorously for 12 h.

[0068] (5) The obtained uniformly mixed composite polymer dispersion is coated on the surface of the negative electrode material and then gently and slowly dried to obtain an acrylonitrile-modified inorganic composite negative electrode polymer SEI film.

[0069] Example 5: A method for preparing an acrylonitrile-modified anode polymer SEI film, differing from Example 3 in that: SiO2 nanofiller is added; the specific steps are as follows:

[0070] (1) 5.7 g acrylonitrile AN and 4.3 g polyethylene glycol diacrylate PEGDA (400 MW) were ultrasonically dispersed in 110 g acetonitrile solution.

[0071] (2) Weigh 0.5 g of azobisisobutyronitrile and add it to the above mixture, and stir magnetically until it is completely dissolved.

[0072] (3) The mixed solution is protected by nitrogen gas and the container is sealed and kept at 65°C for 20 h to obtain polymer dispersion.

[0073] (4) Further, a quantitative amount of lithium salt (30 wt% of monomer content) and 0.5 g of nano-silica ( ， Particles with an average particle size of 50 nm were ultrasonically dispersed into the polymer dispersion and stirred vigorously for 12 h.

[0074] (5) The obtained uniformly mixed composite polymer dispersion is coated on the surface of the negative electrode material and then gently and slowly dried to obtain an acrylonitrile-modified inorganic composite negative electrode polymer SEI film.

[0075] Example 6: A method for preparing an acrylonitrile-modified anode polymer SEI film, differing from Example 3 in that: SiO2 nanofiller is added; the specific steps are as follows:

[0076] (1) 5.7 g acrylonitrile AN and 4.3 g polyethylene glycol diacrylate PEGDA (400 MW) were ultrasonically dispersed in 110 g acetonitrile solution.

[0077] (2) Weigh 0.5 g of azobisisobutyronitrile and add it to the above mixture, and stir magnetically until it is completely dissolved.

[0078] (3) The mixed solution is protected by nitrogen gas and the container is sealed and kept at 65°C for 20 h to obtain polymer dispersion.

[0079] (4) Further, a quantitative amount of lithium salt (30 wt% of monomer content) and 1 g of nano-silica ( ， Particles with an average particle size of 50 nm were ultrasonically dispersed into the polymer dispersion and stirred vigorously for 12 h.

[0080] (5) The obtained uniformly mixed composite polymer dispersion is coated on the surface of the negative electrode material and then gently and slowly dried to obtain an acrylonitrile-modified inorganic composite negative electrode polymer SEI film.

[0081] Example 7: A method for preparing an acrylonitrile-modified anode polymer SEI film, which differs from Example 3 in that: nanofillers are added. The specific steps are as follows:

[0082] (1) 5.7 g acrylonitrile AN and 4.3 g polyethylene glycol diacrylate PEGDA (400 MW) were ultrasonically dispersed in 110 g acetonitrile solution.

[0083] (2) Weigh 0.5 g of azobisisobutyronitrile and add it to the above mixture, and stir magnetically until it is completely dissolved.

[0084] (3) The mixed solution is protected by nitrogen gas and the container is sealed and kept at 65°C for 20 h to obtain polymer dispersion.

[0085] (4) Further, a quantitative amount of lithium salt (30 wt% of monomer content) and 0.3 g of nano titanium dioxide ( ， Particles with an average particle size of 35 nm were ultrasonically dispersed into the polymer dispersion and stirred vigorously for 12 h.

[0086] (5) The obtained uniformly mixed composite polymer dispersion is coated on the surface of the negative electrode material and then gently and slowly dried to obtain an acrylonitrile-modified inorganic composite negative electrode polymer SEI film.

[0087] Example 8: A method for preparing an acrylonitrile-modified anode polymer SEI film, which differs from Example 3 in that: nanofillers are added. The specific steps are as follows:

[0088] (1) 5.7 g acrylonitrile AN and 4.3 g polyethylene glycol diacrylate PEGDA (400 MW) were ultrasonically dispersed in 110 g acetonitrile solution.

[0089] (2) Weigh 0.5 g of azobisisobutyronitrile and add it to the above mixture, and stir magnetically until it is completely dissolved.

[0090] (3) The mixed solution is protected by nitrogen gas and the container is sealed and kept at 65°C for 20 h to obtain polymer dispersion.

[0091] (4) Further, a quantitative amount of lithium salt (30 wt% of monomer content) and 0.5 g of nano titanium dioxide ( ， Particles with an average particle size of 35 nm were ultrasonically dispersed into the polymer dispersion and stirred vigorously for 12 h.

[0092] (5) The obtained uniformly mixed composite polymer dispersion is coated on the surface of the negative electrode material and then gently and slowly dried to obtain an acrylonitrile-modified inorganic composite negative electrode polymer SEI film.

[0093] Example 9: A method for preparing an acrylonitrile-modified anode polymer SEI film, which differs from Example 3 in that: nanofillers are added. The specific steps are as follows:

[0094] (1) 5.7 g acrylonitrile AN and 4.3 g polyethylene glycol diacrylate PEGDA (400 MW) were ultrasonically dispersed in 110 g acetonitrile solution.

[0095] (2) Weigh 0.5 g of azobisisobutyronitrile and add it to the above mixture, and stir magnetically until it is completely dissolved.

[0096] (3) The mixed solution is protected by nitrogen gas and the container is sealed and kept at 65°C for 20 h to obtain polymer dispersion.

[0097] (4) Further, a quantitative amount of lithium salt (30 wt% of monomer content) and 0.9 g of nano titanium dioxide ( ， Particles with an average particle size of 35 nm were ultrasonically dispersed into the polymer dispersion and stirred vigorously for 12 h.

[0098] (5) The obtained uniformly mixed composite polymer dispersion is coated on the surface of the negative electrode material and then gently and slowly dried to obtain an acrylonitrile-modified inorganic composite negative electrode polymer SEI film.

[0099] Example 10: A method for preparing an acrylonitrile-modified anode polymer SEI film, which differs from Example 3 in that: nanofillers are added. The specific steps are as follows:

[0100] (1) 5.7 g acrylonitrile AN and 4.3 g polyethylene glycol diacrylate PEGDA (400 MW) were ultrasonically dispersed in 110 g acetonitrile solution.

[0101] (2) Weigh 0.5 g of azobisisobutyronitrile and add it to the above mixture, and stir magnetically until it is completely dissolved.

[0102] (3) The mixed solution is protected by nitrogen gas and the container is sealed and kept at 65°C for 20 h to obtain polymer dispersion.

[0103] (4) Further, a quantitative amount of lithium salt (30 wt% of monomer content), 0.15 g and 0.35 g The particles were ultrasonically dispersed into the aforementioned polymer dispersion and stirred vigorously for 12 h.

[0104] (5) The obtained uniformly mixed composite polymer dispersion is coated on the surface of the negative electrode material and then gently and slowly dried to obtain an acrylonitrile-modified inorganic composite negative electrode polymer SEI film.

[0105] Example 11, a method for preparing an acrylonitrile-modified anode polymer SEI film, differs from Example 3 in that: nanofillers are added. The specific steps are as follows:

[0106] (1) 5.7 g acrylonitrile AN and 4.3 g polyethylene glycol diacrylate PEGDA (400 MW) were ultrasonically dispersed in 110 g acetonitrile solution.

[0107] (2) Weigh 0.5 g of azobisisobutyronitrile and add it to the above mixture, and stir magnetically until it is completely dissolved.

[0108] (3) The mixed solution is protected by nitrogen gas and the container is sealed and kept at 65°C for 20 h to obtain polymer dispersion.

[0109] (4) Further, a quantitative amount of lithium salt (30 wt% of monomer content) and 0.25 g and 0.25 g The particles were ultrasonically dispersed into the aforementioned polymer dispersion and stirred vigorously for 12 h.

[0110] (5) The obtained uniformly mixed composite polymer dispersion is coated on the surface of the negative electrode material and then gently and slowly dried to obtain an acrylonitrile-modified inorganic composite negative electrode polymer SEI film.

[0111] Example 12, a method for preparing an acrylonitrile-modified anode polymer SEI film, differs from Example 3 in that: nanofillers are added. The specific steps are as follows:

[0112] (1) 5.7 g acrylonitrile AN and 4.3 g polyethylene glycol diacrylate PEGDA (400 MW) were ultrasonically dispersed in 110 g acetonitrile solution.

[0113] (2) Weigh 0.5 g of azobisisobutyronitrile and add it to the above mixture, and stir magnetically until it is completely dissolved.

[0114] (3) The mixed solution is protected by nitrogen gas and the container is sealed and kept at 65°C for 20 h to obtain polymer dispersion.

[0115] (4) Further, a quantitative amount of lithium salt (30 wt% of monomer content) and 0.35 g and 0.15 g The particles were ultrasonically dispersed into the aforementioned polymer dispersion and stirred vigorously for 12 h.

[0116] (5) The obtained uniformly mixed composite polymer dispersion is coated on the surface of the negative electrode material and then gently and slowly dried to obtain an acrylonitrile-modified inorganic composite negative electrode polymer SEI film.

[0117] Performance testing:

[0118] Several tests were performed on the crosslinked polymer SEI film prepared above, including ionic conductivity testing (results are shown in Table 1) and thermal stability testing (results are shown in Table 1 and...). Figure 2 Electrochemical stability test (test results are shown in Table 1 and...) Figure 3 Results showed that the modified cross-linked polymer composite SEI film had higher conductivity, good thermal stability and a wider electrochemical window.

[0119] Table 1 compares the conductivity levels of typical polymer systems in composite polymer SEI films. It can be seen that the conductivity of single PEGDA and acrylonitrile polymers is not ideal, while the conductivity of composite copolymer systems with specific monomer ratios can reach... The conductivity level.

[0120] Table 1. Performance list of the prepared SEI films

[0121]

[0122] from Figure 1 Thermogravimetric analysis (TGA) curves of the composite SEI film show that it possesses thermal stability far exceeding that of conventional SEI films, exhibiting significant decomposition only above 300℃, which is more conducive to extending the high-temperature lifespan of the battery. From Figure 2 Electrochemical window test curves of the composite SEI film show that it exhibits good electrochemical stability, with significant decomposition only occurring above 5.26 V, meeting the normal operating environment requirements of mainstream electrode combinations. Applying it as an SEI film on the negative electrode surface is expected to improve the high-temperature storage performance and high-temperature cycling performance of the battery.

[0123] from Figure 2 The thermogravimetric analysis curve of the composite SEI film shows that it has thermal stability far exceeding that of conventional SEI films. It only shows significant decomposition above 300℃, which is more conducive to extending the high-temperature life of the battery.

[0124] from Figure 3Electrochemical window test curves of the composite SEI film show good electrochemical stability, with significant decomposition only occurring above 5.26 V, meeting the normal operating environment requirements of mainstream electrode combinations. A stainless steel|electrolyte|stainless steel symmetric cell (SS|SPE|SS) was used, and the electrochemical stability of the electrolyte film was tested using linear sweep voltammetry (LSV), observing the SEI film redox decomposition voltage at high and low voltages.

[0125] The coordinating groups include the carbon-oxygen double bonds and ether-oxygen bonds (C=O, COC) in acrylates, and the carbon-nitrogen triple bonds (CN) in acrylonitrile. These groups coordinate with lithium ions for synergistic transport and conduction. This effect is difficult to achieve with metal oxides, which transport lithium ions through lattice vacancies. This mechanism differs from that of polymer groups. The ability of multiple groups to coordinate and decoordinate with lithium ions synergistically promotes lithium ion transport and increases conductivity.

[0126] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing an acrylonitrile-modified SEI film as a negative electrode polymer, characterized in that, The preparation steps include the following: Polymer monomers containing carbon-carbon double bonds are dispersed in an organic solvent to form a prepolymer solution; A thermal initiator is added to a prepolymer solution, and a polymerization reaction is carried out under an inert gas atmosphere to obtain a polymer dispersion. Then, nanoparticles are added, stirred and mixed evenly, and then coated on the surface of the negative electrode material. After drying, an acrylonitrile-modified negative electrode polymer SEI film is obtained. The polymer monomers include at least two or more of acrylonitrile, polyethylene glycol diacrylate, vinylene carbonate, pentaerythritol tetraacrylate, and trimethylolpropane triacrylate.

2. The method for preparing an acrylonitrile-modified SEI negative electrode membrane according to claim 1, characterized in that, The polymer monomers are a composition of acrylonitrile and polyethylene glycol diacrylate in a mass ratio of 1-5:

1.

3. The method for preparing an acrylonitrile-modified negative electrode polymer SEI film according to claim 1 or 2, characterized in that, The prepolymer solution contains polymer monomers at a mass concentration of 8-12 wt%.

4. The method for preparing an acrylonitrile-modified negative electrode polymer SEI film according to claim 3, characterized in that, The initiator accounts for 2-7% of the polymer monomer mass.

5. A method for preparing an acrylonitrile-modified negative electrode polymer SEI film according to any one of claims 1-2, 4, characterized in that, The polymerization temperature during the polymerization reaction is 55-75 ℃, and the polymerization time is 8-30 h.

6. The method for preparing an acrylonitrile-modified negative electrode polymer SEI film according to claim 5, characterized in that, The mass ratio of the nanoparticles to the polymer monomer is 0.01-0.1:1, and the nanoparticles are nano-silica and / or nano-titanium dioxide.

7. A method for preparing an acrylonitrile-modified negative electrode polymer SEI film according to any one of claims 1-2, 4, and 6, characterized in that, The nanoparticles are a composition of nano-titanium dioxide and nano-silica in a mass ratio of 0.15-0.35:0.15-0.

25.

8. The method for preparing an acrylonitrile-modified negative electrode polymer SEI film according to claim 7, characterized in that, The preparation of the polymer SEI film also includes lithium salt, which is derived from the addition of lithium salt to the polymer dispersion or from the infiltration of lithium salt into the electrolyte in a lithium battery.

9. An acrylonitrile-modified SEI negative electrode membrane obtained by the preparation method according to any one of claims 1-8, characterized in that, electrical conductivity Its thermal decomposition temperature is greater than 300 ℃.

10. A negative electrode, characterized in that, The acrylonitrile-modified negative electrode polymer SEI film as described in claim 9 or the acrylonitrile-modified negative electrode polymer SEI film obtained by the preparation method as described in any one of claims 1-8.

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