A negative electrode material coated with a double-conductive-layer SEI film for energy storage and a preparation method thereof

Abstract

The application relates to a negative electrode material coated with a double-conductive-layer SEI film for energy storage and a preparation method thereof, and belongs to the technical field of artificial SEI film preparation, at least one of the problems such as low ion conductivity and electron conductivity of the SEI film, poor thermal stability, low thermal storage temperature and the like in the prior art is solved. The application provides a preparation method of the negative electrode material coated with the double-conductive-layer SEI film, first, ion liquid monomers, polymer monomers, an initiator and a lithium salt are uniformly mixed and fully dissolved to obtain a casting solution; the casting solution, an active material and inorganic nano particles are uniformly mixed, coating and solidification are carried out under an initiation condition, and the negative electrode material coated with the double-conductive-layer SEI film is obtained after drying. The negative electrode material prepared by the method has good conductivity and thermal stability, the electron conductivity is increased by more than 30%, the explosion pressure of the prepared battery cell / battery is reduced by more than 13%, the environmental temperature is reduced by more than 27.5%, the time to reach the maximum pressure is prolonged by more than 90%, and the in-situ expansion thickness is reduced by 10-30%.

Description

Technical Field

[0001] This invention relates to the field of artificially constructed SEI film preparation technology, and in particular to a negative electrode material for energy storage coated with a double conductive SEI film and its preparation method. Background Technology

[0002] In recent years, with the booming development of electric vehicles, numerous electric vehicle fires have occurred, making electric vehicle safety a major public concern. During the charging and discharging process, if heat dissipation is insufficient or internal short circuits occur, a large amount of heat will be generated, potentially leading to thermal runaway. Therefore, increasing the storage temperature of the battery cell is one way to address thermal runaway in power battery cells. Thermal runaway often begins with the decomposition of the SEI film on the negative electrode. The dissolution of the SEI film exposes the lithium-intercalated carbon components within the negative electrode directly to the electrolyte. The lithium-intercalated carbon reacts exothermically with the electrolyte, causing a temperature rise and triggering the thermal runaway process.

[0003] Currently, existing artificially constructed anode SEI films generally suffer from defects such as low ionic and electronic conductivity, poor thermal stability, and low thermal storage temperature. Therefore, it is necessary to develop an anode SEI film with high conductivity, good thermal stability, and excellent safety performance. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide an anode material coated with a double conductive layer SEI film for energy storage and its preparation method, in order to solve at least one of the problems of low ionic conductivity and electronic conductivity, poor thermal stability, and low thermal storage temperature of existing artificially constructed SEI films for anodes.

[0005] This invention provides a method for preparing a negative electrode material coated with a double conductive layer SEI film, comprising the following steps:

[0006] First, the ionic liquid monomer, polymer monomer, initiator and lithium salt are mixed evenly and fully dissolved to obtain a copolymer solution. The copolymer solution is then diluted with an organic solution to obtain a casting solution.

[0007] The casting solution, active material and inorganic nanoparticles are mixed evenly, coated and cured under light or heat initiation conditions, and then dried to obtain a negative electrode material coated with a double conductive layer SEI film.

[0008] The main reactants in the copolymer solution include ionic liquid monomers, polymer monomers, and lithium salts.

[0009] The composition of the main reactants, by mass percentage, is as follows: 50-85% ionic liquid monomer, 5-25% polymer monomer, and 10-30% lithium salt, totaling 100%.

[0010] The amount of initiator added is 0.5% to 2% of the sum of the mass of the ionic liquid monomer and the polymer monomer; the molecular weight of the polymerized solid electrolyte is >300,000.

[0011] Preferably, the active material and inorganic nanoparticles are premixed before being mixed with the casting solution. The premixing operation is as follows:

[0012] The active material and inorganic nanoparticles were added to a dual planetary stirrer and mixed. The dual planetary stirrer rotated at a speed of 500–3000 rpm and revolved at a speed of 5–50 rpm for 10–60 min.

[0013] Specifically, the ionic liquid monomer is an imidazole-based reactive ionic liquid monomer containing a double bond, and the polymer monomer is an acrylate-based reactive polymer monomer containing a double bond.

[0014] Specifically, the ionic liquid monomer is one or more of the following: 1-methylimidazolium tetrafluoroborate, 1-ethylimidazolium tetrafluoroborate, 1-butylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-2,3-dimethylimidazolium hexafluorophosphate, 1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)imide, 1-methyl-3-ethylimidazolium bis(fluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium trifluoroacetate, 1-vinyl-3-ethylimidazolium tetrafluoroborate, 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide, 1-vinyl-3-butylimidazolium tetrafluoroborate, and 1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide.

[0015] Specifically, the polymer monomer is one or more of polyethylene glycol diacrylate, polyethylene glycol methyl ether methacrylate, glycidyl methacrylate, methyl methacrylate, hydroxyethyl methacrylate, butyl methacrylate, n-butyl acrylate, and tert-butyl acrylate.

[0016] The lithium salt is one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalate-borate), lithium bis(trifluoromethanesulfonyl)imide, and lithium di(fluorooxalate-borate).

[0017] Furthermore,

[0018] When the initiation condition is light, the initiator is a photoinitiator, which is one or a combination of two or more of 2-hydroxy-2-methylphenylacetone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 1-hydroxycyclohexylphenyl ketone.

[0019] When the initiation condition is heating, the initiator is a thermal initiator, which is one or a combination of two or more of azobisisobutyronitrile, azobisisoheptanenitrile, diisopropylbenzene peroxide, potassium persulfate, and ammonium persulfate.

[0020] Specifically, the mass content of the copolymer solution in the casting solution is 0.5-5%; wherein the organic solvent is one or more of acetone, N,N-dimethylformamide, dimethylacetamide, N-methylpyrrolidone and acetonitrile.

[0021] Specifically, the mixing ratio of the active material and the inorganic nanoparticles is: 98-99.5 wt.% active material and 0.5-2.0 wt.% inorganic nanoparticles;

[0022] The active material is any one or a combination of two or more of the following: graphite, hard carbon, soft carbon, lithium titanate, silicon carbide, and silicon oxide.

[0023] The inorganic nanoparticles are one or more of the following: conductive carbon black with a particle size of 10–300 nm, single-walled carbon nanotubes with a diameter of 1–5 nm, and multi-walled carbon nanotubes with a diameter of 5–100 nm.

[0024] Specifically, the ratio of the sum of the masses of active materials and inorganic nanoparticles to the mass of the casting solution is 1:0.9~1.

[0025] Specifically,

[0026] The photo-initiation conditions are to irradiate the mixed reaction system with an ultraviolet lamp with a wavelength of 350nm to 405nm for 30 to 90 minutes;

[0027] The thermal initiation conditions are to heat the mixed reaction system at 40–80°C for 36–72 hours.

[0028] The present invention also provides a negative electrode material coated with a double conductive layer SEI film, wherein the negative electrode material is prepared by the preparation method described above.

[0029] The present invention also provides an electrode, a battery, an electrochemical device, an electrical device, and an energy storage device, wherein the electrode, battery, electrochemical device, electrical device, and energy storage device include the aforementioned negative electrode material;

[0030] Preferably, the battery is selected from either a solid-state battery or a semi-solid-state battery.

[0031] Furthermore, the explosion pressure of the semi-solid battery is reduced by no less than 13%, the ambient temperature is reduced by no less than 27.5%, and the time to reach the maximum pressure is extended by at least 90%.

[0032] Among them, the conductivity of the negative electrode sheet is increased by ≥50%.

[0033] Furthermore, the in-situ expansion thickness of the cell containing the negative electrode sheet is reduced by 10-30%.

[0034] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0035] 1. The negative electrode double conductive layer SEI film prepared by the present invention has high conductivity, good thermal stability, significantly improved thermal storage temperature, and greatly improved safety performance.

[0036] In summary, this invention utilizes imidazole-based reactive ionic liquids containing double bonds and acrylate-based reactive polymer monomers containing double bonds in an in-situ polymerization reaction to generate a polyionic liquid-based solid electrolyte in situ on the negative electrode surface, thus constructing a stable artificial SEI membrane (i.e., a solid electrolyte membrane) at the negative electrode. Simultaneously, inorganic conductive materials are used to composite it, constructing a micro-conductive layer on its surface.

[0037] The specific explanation is as follows:

[0038] Solid electrolyte membrane (SEI membrane) can be uniformly and densely coated on the surface of negative electrode material particles. It works together with inorganic nanoparticles (with good conductivity) to build continuous electron and ion transport channels, thereby improving the ion transport efficiency and electron conduction of the electrode, enabling more active materials to fully participate in the electrochemical reaction, and thus improving the overall performance of the battery.

[0039] The introduction of inorganic nanoparticles can also reduce electrode internal resistance and decrease ohmic polarization heat during charging and discharging. Lower internal resistance reduces heat generation during cell charging and discharging, indirectly lowering cell temperature, reducing thermal runaway, and further reducing explosion pressure, thus improving battery thermal stability. Simultaneously, it can reduce structural damage caused by volume expansion during charging and discharging, stabilize the negative electrode interface, reduce internal battery pressure, and improve battery safety performance.

[0040] Compared to organic conductive polymers, inorganic nano-ions exhibit higher electron mobility, enabling rapid electron conduction. They also possess higher electrical conductivity and better chemical and thermal stability, allowing them to withstand higher temperatures and chemical environmental changes during battery charging and discharging without easily decomposing or deteriorating. Furthermore, they possess higher hardness and strength, enhancing the structural stability of the negative electrode. During battery cycling, they help maintain the electrode's shape and structure, reducing electrode deformation and breakage caused by volume changes, thus improving battery safety and reliability.

[0041] Solid electrolyte membranes (SEI membranes) possess a copolymer framework (a framework formed by the polymerization of ionic liquid monomers and polymer monomers). Due to their flexibility and fracture resistance, they can serve as a protective layer for the negative electrode, suppressing the volume expansion of the negative electrode and side reactions with carbonate electrolytes. This cross-linked artificial SEI membrane exhibits good thermal stability, is non-flammable, has high ionic conductivity, and good flexibility and processability.

[0042] It is worth emphasizing that the molecular weight of the final solid electrolyte polymer should be >300,000; otherwise, the polymer cross-linking degree will be low, the polymer chain length will be short, and the strength of the copolymer framework structure will be insufficient. This will prevent the polymer from mitigating the volume expansion of the negative electrode material, or the mitigation effect will be extremely weak, thus affecting the safety performance of the negative electrode material. Furthermore, the in-situ expansion thickness of the cell containing the negative electrode sheet will be reduced by 10-30%. (e.g.) Figure 5 (As shown)

[0043] The negative electrode material coated with the aforementioned SEI film was used to make a negative electrode sheet, which was then stacked with a high-nickel ternary positive electrode (NCM811) to form a 2.5Ah pouch cell, and subjected to hot box and explosion pressure tests. Both explosion pressure and ambient temperature decreased significantly, with electronic conductivity increasing by ≥50%, explosion pressure decreasing by ≥13%, ambient temperature decreasing by ≥27.5% (degrees Celsius), and the time to reach maximum pressure increasing by ≥90%.

[0044] It is worth emphasizing that the final SEI membrane structure and performance are closely related to the selection of polymeric monomers (ionic monomers, polymeric monomers, types and sizes of inorganic nanoparticles, etc.) and the control of process conditions. It is the result of the synergistic effect of multiple factors. Adjusting the type or content of any component or modifying process parameters alone will have unpredictable effects on the SEI membrane structure and performance. For example, if the type of polymeric monomer is adjusted, even with the same polymerization reaction conditions and even if a similar molecular weight is obtained, the final SEI membrane will still fail to achieve the technical effects described in this invention due to changes in the crosslinking structure and composite process; the same applies to process conditions.

[0045] 2. The preparation method provided by this invention is simple, the process conditions are mild, the relevant equipment and instruments are readily available, the operation difficulty is moderate, and it is suitable for large-scale production and widespread promotion.

[0046] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0047] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0048] Figure 1 This is a schematic diagram of the negative electrode double conductive layer SEI film structure.

[0049] Figure 2 TEM images of the negative electrode materials in the examples and comparative examples;

[0050] Figure 3 The explosion pressure diagrams are for the embodiment and comparative examples of battery cell explosion pressure tests.

[0051] Figure 4 The diagram shows the ambient temperature of the cell explosion pressure test environment for both the example and comparative embodiments.

[0052] Figure 5 The diagram shows the in-situ expansion of the battery cells during cycling, as shown in the examples and comparative examples. Detailed Implementation

[0053] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0054] Polyionic liquids are a new type of polymer containing a large number of repeating ionic liquid units. They not only have the good flexibility and easy processing properties of polymers, but also the non-flammability, excellent thermal stability, and good electrochemical and chemical stability of ionic liquids. They are ideal materials for constructing artificial SEI membranes. However, pure polyionic liquid-based materials have poor ionic and electronic conductivity.

[0055] This invention further incorporates polymer monomers to copolymerize polyionic liquids (using ionic monomers as raw materials to obtain polyionic liquids after reaction) and inorganic nanoparticles to improve their ionic and electronic conductivity. Furthermore, the polymer monomers and inorganic nanoparticles also reduce internal resistance and improve electrode flexibility and mechanical stability, as detailed below.

[0056] Generally, SEI films are considered to have a bilayer structure: an inorganic inner layer (closer to the negative electrode material) mainly composed of inorganic compounds such as LiF, Li₂CO₃, Li₂O, and LiPF₃; this layer is dense with few pores, possessing high mechanical strength and good ionic conductivity, effectively blocking electron transport while allowing lithium ions to pass through. The organic outer layer (closer to the electrolyte) is mainly composed of organic compounds; this layer is relatively porous and loose, allowing electrolyte permeation, and may undergo further chemical changes during subsequent cycles.

[0057] This invention provides a method for preparing a negative electrode material coated with a double conductive layer SEI film, comprising the following steps:

[0058] First, the ionic liquid monomer, polymer monomer, initiator and lithium salt are mixed evenly and fully dissolved to obtain a copolymer solution. The copolymer solution is then diluted with an organic solution to obtain a casting solution.

[0059] The casting solution, active material and inorganic nanoparticles are mixed evenly to obtain a mixed reaction system. The system is then coated and cured under light or heat initiation conditions. After drying, a double conductive layer SEI film / artificial SEI film is obtained on the surface of the negative electrode material.

[0060] The main reactants in the copolymer solution include ionic liquid monomers, polymer monomers, and lithium salts.

[0061] The composition of the main reactants, by mass percentage, is as follows: 50-85% ionic liquid monomer, 5-25% polymer monomer, and 10-30% lithium salt, totaling 100%.

[0062] The amount of initiator added is 0.5% to 2% of the sum of the mass of the ionic liquid monomer and the polymer monomer; the molecular weight of the solid electrolyte polymer after polymerization is >300,000.

[0063] Specifically, the ionic liquid monomer is an imidazole-based reactive ionic liquid monomer containing a double bond, and the polymer monomer is an acrylate-based reactive polymer monomer containing a double bond.

[0064] This invention utilizes an imidazole-based reactive ionic liquid containing double bonds and an acrylate-based reactive polymer monomer containing double bonds, which undergo in-situ polymerization to generate a polyionic liquid-based solid electrolyte on the negative electrode surface, thus constructing a stable artificial SEI film at the negative electrode. Simultaneously, an inorganic conductive material is used to composite it, constructing a micro-conductive layer on its surface.

[0065] Preferably, the active material and inorganic nanoparticles are premixed before being mixed with the casting solution. The premixing operation is as follows:

[0066] The active material and inorganic nanoparticles are added to a dual planetary stirrer and mixed. The dual planetary stirrer rotates at a speed of 500–3000 rpm and revolves at a speed of 5–50 rpm for 10–60 minutes. Premixing the active material and conductive nanoparticles ensures that the conductive particles are uniformly dispersed around the active material particles.

[0067] Specifically, the ionic liquid monomer is one or more of the following: 1-methylimidazolium tetrafluoroborate, 1-ethylimidazolium tetrafluoroborate, 1-butylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-2,3-dimethylimidazolium hexafluorophosphate, 1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)imide, 1-methyl-3-ethylimidazolium bis(fluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium trifluoroacetate, 1-vinyl-3-ethylimidazolium tetrafluoroborate, 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide, 1-vinyl-3-butylimidazolium tetrafluoroborate, and 1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide. These ionic liquid monomers all possess the characteristics of an ionic liquid based on imidazolium cations, exhibiting good lithium salt solubility, high chemical stability, good chemical conductivity, and high-temperature resistance.

[0068] Specifically, the polymer monomer is one or more of polyethylene glycol diacrylate, polyethylene glycol methyl ether methacrylate, glycidyl methacrylate, methyl methacrylate, hydroxyethyl methacrylate, butyl methacrylate, n-butyl acrylate, and tert-butyl acrylate.

[0069] Furthermore, the polymer monomers selected in this invention all possess carbon-carbon double bond functional groups, enabling them to undergo polymerization reactions under photoinitiator or thermal initiator conditions, producing polymers with a certain molecular weight. The polymer monomers all have low glass transition temperatures, exhibiting good flexibility and elasticity at both room and high temperatures, which can improve the flexibility and mechanical stability of the electrode and mitigate volume changes in the negative electrode material.

[0070] The lithium salt is one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium di(fluorooxalato)borate. The lithium salt is formed by lithium ions and corresponding anions bonded together by ionic bonds. In the electrolyte, it can ionize into lithium ions and corresponding anions. During the initial charge and discharge process, the anions of these lithium salts may participate in the formation of a solid electrolyte interphase (SEI) film on the electrode surface. Furthermore, they all possess a relatively wide electrochemical window, and within a certain voltage range, they are not prone to redox reactions and can remain stable within the battery's operating voltage range.

[0071] Furthermore, when the initiation condition is light irradiation, the initiator is a photoinitiator, which is one or a combination of two or more of 2-hydroxy-2-methylphenylacetone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 1-hydroxycyclohexylphenyl ketone.

[0072] When the initiation condition is heating, the initiator is a thermal initiator, which is one or a combination of two or more of azobisisobutyronitrile, azobisisoheptanenitrile, diisopropylbenzene peroxide, potassium persulfate, and ammonium persulfate.

[0073] Specifically, the mass content of the copolymer solution in the casting solution is 0.5-5%; wherein the organic solvent is one or more of acetone, N,N-dimethylformamide, dimethylacetamide, N-methylpyrrolidone and acetonitrile.

[0074] Specifically, the mixing ratio of the active material and the inorganic nanoparticles is: 98-99.5 wt.% active material and 0.5-2.0 wt.% inorganic nanoparticles;

[0075] The active material is any one or a combination of two or more of the following: graphite, hard carbon, soft carbon, lithium titanate, silicon carbide, and silicon oxide.

[0076] The inorganic nanoparticles are one or more of the following: conductive carbon black with a particle size of 10–300 nm, single-walled carbon nanotubes with a diameter of 1–5 nm, and multi-walled carbon nanotubes with a diameter of 5–100 nm.

[0077] Specifically, the ratio of the sum of the masses of active materials and inorganic nanoparticles to the mass of the casting solution is 1:0.9~1.

[0078] Furthermore, inorganic nanoparticles can effectively reduce electrode internal resistance and decrease ohmic polarization heat during charging and discharging. Lower internal resistance reduces heat generation during battery operation, indirectly alleviating temperature rise issues, reducing explosion pressure, and mitigating thermal runaway, thus contributing to improved battery thermal stability. Graphene, carbon fiber, and carbon nanotubes are particularly preferred materials, as these materials can also reduce structural damage caused by volume expansion during charging and discharging, stabilize the negative electrode interface, reduce internal battery pressure, and improve battery safety.

[0079] Specifically,

[0080] The photo-initiation conditions are to irradiate the mixed reaction system with an ultraviolet lamp with a wavelength of 350nm to 405nm for 30 to 90 minutes;

[0081] The thermal initiation conditions are heating the mixed reaction system at 40–80°C for 36–72 hours.

[0082] Excessive reaction time leads to continuous monomer polymerization, increasing the polymer's molecular weight. Overly long reaction times can cause excessive cross-linking of polymer chains, forming a three-dimensional network structure, making the material hard and brittle, losing its original flexibility. Furthermore, longer reaction times make the polymerization reaction more complex, increasing the amount of polymers with different chain lengths and resulting in a wider molecular weight distribution. This can lead to inhomogeneity in polymer properties, affecting mechanical properties and thermal stability. Conversely, insufficient reaction time results in incomplete monomer reaction, low monomer conversion, and unreacted monomers remaining in the product. Insufficient polymerization leads to a lower molecular weight polymer. Low molecular weight polymers can cause abnormal properties such as glass transition temperature, resulting in poor thermal stability and insufficient flexibility.

[0083] It is worth emphasizing that the molecular weight of the final solid electrolyte polymer should be >300,000. Otherwise, the degree of cross-linking will be low, the polymer chain length will be short, and the strength of the copolymer framework structure will be insufficient. This will not be able to mitigate the volume expansion of the negative electrode material or the mitigation effect will be extremely weak, thus affecting the safety performance of the negative electrode material.

[0084] Furthermore, the in-situ expansion thickness of the cell containing the negative electrode sheet is reduced by 10-30%.

[0085] Excessively high temperatures can cause the initiator to decompose too quickly, generating a large number of free radicals. These free radicals rapidly initiate monomer polymerization, making the reaction rate too fast and potentially leading to uncontrolled polymerization and runaway polymerization. High temperatures also increase the chain transfer reaction rate, causing premature termination of polymer chains and reducing the polymer's molecular weight. Furthermore, the uneven reaction rate and complexity of chain transfer reactions at high temperatures increase the differences in chain growth, resulting in a wider molecular weight distribution and affecting the uniformity of polymer properties. In addition, high temperatures may trigger side reactions, generating impurities and reducing product purity. Conversely, excessively low temperatures result in slow initiator decomposition, generating fewer free radicals, and insufficient activation energy for monomers, leading to a slow polymerization rate. This prolongs the production cycle, reduces production efficiency, and increases production costs. A slow reaction rate means that monomers cannot be fully converted into polymers within a given reaction time, resulting in low monomer conversion rates and unreacted monomers remaining in the product, affecting polymer properties and wasting raw materials. Low temperatures can also lead to uneven distribution of the initiator in the reaction system, causing significant differences in monomer polymerization in localized areas and resulting in uneven molecular weight distribution. The polymer molecular weight may be higher in some regions and lower in others, affecting the overall stability of the polymer's properties.

[0086] Furthermore, after the reaction is complete, the material is vacuum dried at room temperature until the organic solvent is completely evaporated, resulting in the coated negative electrode material powder.

[0087] Furthermore, both photoinitiators and thermal initiators initiate polymerization reactions by breaking and forming carbon-carbon double bonds, thereby connecting ionic liquid monomers and polymer monomer molecules to form high molecular weight polymers.

[0088]

[0089] The ionic liquid monomer and polymer monomer components eventually form a copolymer backbone, while the inorganic nanoparticle components are uniformly dispersed on the surface of the negative electrode active material and compounded by the copolymer, acting as a conductive agent in the copolymer.

[0090] R1 groups include, but are not limited to, polyethylene glycol groups, alkyl groups, hydroxyl groups, epoxy alkyl groups, etc.

[0091] The R2 group is BF4. - PF6 - N(SO2CF3)2 - N(SO2F)2 - CF3COO - One or more of them.

[0092] Furthermore, the inorganic nanoparticles do not form a copolymer backbone, but are composited in the copolymer backbone in a uniformly dispersed form.

[0093] The present invention also provides a negative electrode material coated with a double conductive layer SEI film, wherein the negative electrode material is prepared by the preparation method described above.

[0094] The present invention also provides an electrode, a battery, an electrochemical device, an electrical device, and an energy storage device, wherein the electrode, battery, electrochemical device, electrical device, and energy storage device include the aforementioned negative electrode material;

[0095] Preferably, the battery is selected from either a solid-state battery or a semi-solid-state battery.

[0096] Furthermore, the explosion pressure of the semi-solid battery is reduced by no less than 13%, the ambient temperature is reduced by no less than 27.5%, and the time to reach the maximum pressure is extended by at least 90%.

[0097] Among them, the conductivity of the negative electrode sheet is increased by ≥50%.

[0098] Furthermore, the in-situ expansion thickness of the cell containing the negative electrode sheet is reduced by 10-30%.

[0099] For example, new energy batteries can be manufactured according to the following method:

[0100] Negative electrode preparation:

[0101] By mass percentage, the negative electrode material loaded with the SEI film (90%–98 wt%), conductive agent 1 (0.5–2 wt%), and thickener (0.2%–0.8 wt%) are premixed and stirred on a dual planetary stirrer. After stirring is complete, conductive agent 2 (0.1–0.5 wt%), binder 1 (1%–5 wt%), and deionized water are added and stirring continues. After stirring is complete, conductive agent 2, binder 1, and deionized water are added again and stirring continues. After stirring is complete, deionized water is added to adjust the viscosity to 3000–8000 cp. After stirring is complete, binder 2 (1%–5 wt%) is finally added, and the slurry preparation is complete. Finally, the slurry is coated using a transfer coating method to prepare the negative electrode sheet.

[0102] The conductive additive 1 and conductive additive 2 include any one or a combination of two or more of conductive carbon black, SUPER-P, KS-6, carbon nanotubes, graphene, and VGCF carbon fiber. All of the above conductive agents possess good electrical conductivity.

[0103] The adhesives 1 and 2 comprise any one or a combination of two or more of polyvinylidene fluoride, polyacrylic acid, styrene-butadiene rubber, polyamide, polyvinyl alcohol, polyethyleneimine, and polyimide. All of the above adhesives possess the ability to form strong and tough bonding forces between active material particles and between the active material and the current collector.

[0104] Battery fabrication:

[0105] The negative electrode and positive electrode stack are assembled into a soft-pack battery with a capacity of 1.5 to 5.5 Ah.

[0106] Specifically, an appropriate amount of electrolyte is injected according to the actual situation. The injection coefficient is generally between 2.5 and 3.5 g / Ah. The main components of the electrolyte are diethyl carbonate, ethylene carbonate, propylene carbonate and propyl propionate.

[0107] Specifically, the active material of the cathode material is any one or a combination of two or more cathode materials such as lithium iron phosphate, lithium manganese oxide, lithium cobalt oxide, and ternary materials, but is not limited thereto.

[0108] Specifically, the negative electrode material after coating was characterized by TEM+EDS testing, and the soft-pack battery cells after stacking (examples and comparative examples) were charged to full charge and subjected to hot box and explosion pressure tests.

[0109] The hot box test conditions are:

[0110] a)RT to 100℃at 5℃ / min,for 30min;

[0111] b)100℃to 120℃at 5℃ / min,for 30min;

[0112] c)120℃to 140℃at 5℃ / min,for 30min;

[0113] d)140℃to 150℃at 5℃ / min,for 30min;

[0114] e)150℃to 160℃at 5℃ / min,for 30min;

[0115] f)160℃to 170℃at 5℃ / min,for 30min.

[0116] g)170℃to 180℃at 5℃ / min,for 30min.

[0117] The explosion pressure test conditions are: RT to 200℃ at 5℃ / s.

[0118] Example 1:

[0119] Mix 0.5g of 1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide salt, 0.25g of polyethylene glycol diacrylate, 0.25g of lithium bis(trifluoromethanesulfonyl)imide, and 0.00375g of thermal initiator azobisisobutyronitrile, and stir on a magnetic stirrer until the lithium salt and initiator are completely dissolved to form a transparent, clear solution.

[0120] Then, it was diluted with acetonitrile solution to a concentration of 0.5%; 199g of silicon carbide material, 1.0g of conductive carbon black and 200g of 0.5% acetonitrile solution were stirred with a double planetary stirrer under the following conditions: 500rpm, revolution at 20rpm, time for 20min.

[0121] After coating, the mixed material was cured in situ at 60°C for 36 hours, and then vacuum dried to obtain an SEI film coated on the surface of the negative electrode material. The number-average molecular weight of the prepared solid electrolyte polymer was approximately 320,000. Finally, the negative electrode sheet was prepared and stacked with a high-nickel ternary positive electrode (NCM811) to form a 2.5Ah pouch cell.

[0122] The soft pack exploded at a pressure of 99.86 kPa, with an explosion time of 2.3 s. The ambient temperature after the explosion was 107.7 ℃, and the electrode conductivity was 3.5 S / cm.

[0123] Example 2:

[0124] Mix 0.55g of 1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide salt, 0.25g of polyethylene glycol diacrylate, 0.2g of lithium bis(trifluoromethanesulfonyl)imide, and 0.0075g of thermal initiator azobisisobutyronitrile, and stir on a magnetic stirrer until the lithium salt and initiator are completely dissolved to form a transparent, clear solution;

[0125] Then, it was diluted with acetonitrile solution to a concentration of 1.0%; 199g of silicon-carbon material, 1.0g of single-walled carbon nanotubes and 200g of 1.0% acetonitrile solution were stirred with a double planetary stirrer under the following conditions: 500rpm, revolution at 20rpm, and time of 20min.

[0126] After coating, the mixed material was cured in situ at 60°C for 40 hours, and then vacuum dried to obtain an SEI film coated on the surface of the negative electrode material. The number-average molecular weight of the prepared solid electrolyte polymer was approximately 325,000. Finally, the negative electrode sheet was prepared and stacked with a high-nickel ternary positive electrode (NCM811) to form a 2.5Ah pouch cell.

[0127] The soft pack exploded at a pressure of 98.12 kPa, with an explosion time of 2.4 s. The ambient temperature after the explosion was 106.1 ℃, and the electrode conductivity was 3.33 S / cm.

[0128] Example 3:

[0129] Mix 0.65g of 1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide salt, 0.15g of polyethylene glycol diacrylate, 0.2g of lithium bis(trifluoromethanesulfonyl)imide, and 0.005g of thermal initiator azobisisobutyronitrile, and stir on a magnetic stirrer until the lithium salt and initiator are completely dissolved to form a transparent, clear solution.

[0130] Then, it was diluted with acetonitrile solution to a concentration of 0.5%; 199g of silicon-carbon material, 1g of multi-walled carbon nanotubes and 200g of 0.5% acetonitrile solution were stirred with a double planetary stirrer under the following conditions: 500rpm, revolution at 20rpm, time for 20min.

[0131] After coating, the mixed material was cured in situ at 60°C for 72 hours, and then vacuum dried to obtain an SEI film coated on the surface of the negative electrode material. The number-average molecular weight of the prepared solid electrolyte polymer was approximately 350,000. Finally, the negative electrode sheet was prepared and stacked with a high-nickel ternary positive electrode (NCM811) to form a 2.5Ah pouch cell.

[0132] The soft pack exploded at a pressure of 97.79 kPa, with an explosion time of 2.5 s. The ambient temperature after the explosion was 106.25 ℃, and the electrode conductivity was 3.33 S / cm.

[0133] Example 4:

[0134] Mix 0.85g of 1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide salt, 0.05g of polyethylene glycol diacrylate, 0.1g of lithium bis(trifluoromethanesulfonyl)imide, and 0.015g of thermal initiator azobisisobutyronitrile, and stir on a magnetic stirrer until the lithium salt and initiator are completely dissolved to form a transparent, clear solution.

[0135] Then, it was diluted with acetonitrile solution to a concentration of 0.5%; 197g of silicon carbide material, 3.0g of conductive carbon black and 200g of 0.5% acetonitrile solution were stirred with a double planetary stirrer under the following conditions: 500rpm, revolution at 20rpm, time for 20min.

[0136] After coating, the mixed material was cured in situ at 60°C for 36 hours, and then vacuum dried to obtain an SEI film coated on the surface of the negative electrode material. The number-average molecular weight of the prepared solid electrolyte polymer was approximately 308,000. Finally, the negative electrode sheet was prepared and stacked with a high-nickel ternary positive electrode (NCM811) to form a 2.5Ah pouch cell.

[0137] The soft pack exploded at a pressure of 93.4 kPa, with an explosion time of 2.8 s. The ambient temperature after the explosion was 102.15 ℃, and the electrode conductivity was 5.0 S / cm.

[0138] Example 5:

[0139] Mix 0.85 g of 1-vinyl-3-butylimidazolium tetrafluoroborate, 0.05 g of polyethylene glycol methyl ether methacrylate, 0.1 g of lithium bis(trifluoromethanesulfonyl)imide, and 0.0075 g of thermal initiator azobisisobutyronitrile, and stir on a magnetic stirrer until the lithium salt and initiator are completely dissolved to form a transparent, clear solution;

[0140] Then, it was diluted with acetonitrile solution to a concentration of 0.5%; 198.5g of silicon-carbon material, 1.5g of single-walled carbon nanotubes and 200g of 0.5% acetonitrile solution were stirred with a double planetary stirrer under the following conditions: 500rpm, revolution at 20rpm, and time of 20min.

[0141] After coating, the mixed material was cured in situ at 60°C for 48 hours, and then vacuum dried to obtain an SEI film coated on the surface of the negative electrode material. The number-average molecular weight of the prepared solid electrolyte polymer was approximately 315,000. Finally, the negative electrode sheet was prepared and stacked with a high-nickel ternary positive electrode (NCM811) to form a 2.5Ah pouch cell.

[0142] The soft pack exploded at a pressure of 85.74 kPa, with an explosion time of 3.3 s. The ambient temperature after the explosion was 91.6 ℃, and the electrode conductivity was 4.35 S / cm.

[0143] Comparative Example 1

[0144] Mix 0.5g of 1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide salt, 0.25g of polyethylene glycol diacrylate, 0.25g of lithium bis(trifluoromethanesulfonyl)imide, and 0.00375g of thermal initiator azobisisobutyronitrile, and stir on a magnetic stirrer until the lithium salt and initiator are completely dissolved to form a transparent, clear solution.

[0145] Then, it was diluted with acetonitrile solution to a concentration of 0.5%; 199g of silicon carbide material, 1.0g of conductive carbon black and 200g of 0.5% acetonitrile solution were stirred with a double planetary stirrer under the following conditions: 500rpm, revolution at 20rpm, time for 20min.

[0146] After coating, the mixed material was cured in situ at 60°C for 12 hours, and then vacuum dried to obtain an SEI film coated on the surface of the negative electrode material. The number-average molecular weight of the prepared solid electrolyte polymer was approximately 100,000. Finally, the negative electrode sheet was prepared and stacked with a high-nickel ternary positive electrode (NCM811) to form a 2.5Ah pouch cell.

[0147] The soft pack exploded at a pressure of 106.25 kPa, with an explosion time of 1.9 s. The ambient temperature after the explosion was 139.3 ℃, and the electrode conductivity was 3.33 S / cm.

[0148] Comparative Example 2

[0149] 0.5 g of 1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide salt, 0.25 g of polyethylene glycol diacrylate, 0.25 g of lithium bis(trifluoromethanesulfonyl)imide, 0.00375 g of thermal initiator azobisisobutyronitrile, 199 g of silicon-carbon material, and 1.0 g of conductive carbon black were directly added to the slurry obtained during the homogenization process of the negative electrode sheet. After the electrode sheet was prepared, it was placed in situ for curing at 60°C for 36 h. After vacuum drying, an SEI film was obtained coating the surface of the negative electrode material. The number-average molecular weight of the prepared solid electrolyte polymer was approximately 300,000. Finally, it was stacked with a high-nickel ternary cathode (NCM811) to form a 2.5 Ah soft-pack battery.

[0150] The soft pack exploded at a pressure of 109.45 kPa, with an explosion time of 1.6 s. The ambient temperature after the explosion was 137.1 ℃, and the electrode conductivity was 3.18 S / cm.

[0151] Comparative Example 3

[0152] Mix 0.5g of 1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide salt, 0.25g of polyethylene glycol diacrylate, 0.25g of lithium bis(trifluoromethanesulfonyl)imide, and 0.00375g of thermal initiator azobisisobutyronitrile (AIBN). Stir on a magnetic stirrer until the lithium salt and initiator are completely dissolved, forming a transparent, clear solution. Then dilute the solution with acetonitrile solution to a concentration of 0.5%. Finally, add 1.0g of polypyrrole and stir thoroughly until the polypyrrole is completely dissolved.

[0153] 199g of silicon carbide material and 200g of 0.5% acetonitrile solution were stirred using a double planetary stirrer under the following conditions: 500 rpm, revolution at 20 rpm, and time of 20 min.

[0154] After coating, the mixed material was cured in situ at 60°C for 36 hours. Finally, a negative electrode sheet was prepared and stacked with a high-nickel ternary positive electrode (NCM811) to form a 2.5Ah pouch cell.

[0155] The soft pack exploded at a pressure of 111.17 kPa, with an explosion time of 1.4 s. The ambient temperature after the explosion was 142.6 ℃, and the electrode conductivity was 2.5 S / cm.

[0156] Comparative Example 4

[0157] A 2.5Ah soft-pack battery is assembled using silicon-carbon material (powder) to form a negative electrode sheet and a high-nickel ternary positive electrode (NCM811) stack.

[0158] The soft pack exploded at a pressure of 114.84 kPa, with an explosion time of 1.2 s. The ambient temperature after the explosion was 148.7 ℃, and the electrode conductivity was 2.2 S / cm.

[0159] like Figure 2 As shown, in Examples 1-5, a thin and transparent coating layer can be clearly observed at the edge of the active material under TEM, while no coating layer is observed at the edge of the comparative example, indicating that the polymer solid electrolyte / SEI film is successfully coated on the surface of the active material.

[0160] Comparative examples and embodiments show that by copolymerizing ionic liquid-based monomers and acrylic monomers, and simultaneously introducing inorganic nanoparticles, an artificial SEI film that conducts both ions and electrons can be constructed on the surface of silicon-carbon materials.

[0161] The content of ionic liquid monomers has a significant impact on its thermal stability; appropriately increasing the content of ionic liquid monomers can improve thermal stability.

[0162] The in-situ curing time has a key effect on its molecular weight. A curing time of more than 36 hours can produce solid electrolytes with a molecular weight of more than 300,000. Moreover, the molecular weight gradually increases with the increase of curing time.

[0163] like Figure 5 As shown, the artificial SEI film (negative electrode material) with double conductive layer prepared by the present invention has a significant effect on inhibiting / mitigating the volume expansion of the battery cell. Compared with the comparative example, the thickness of the battery cell in situ expansion is reduced by 10-30%, and the reduction ratio is more significant compared with conventional existing technologies.

[0164] The curing time of Comparative Example 1 is shorter. The shorter curing time prevents the formation of a cross-linked network structure, resulting in a lower molecular weight and poor suppression of expansion of the negative electrode.

[0165] Comparative Example 2 uses a direct blending method, but the polymer fails to build an artificial SEI film on the surface of the negative electrode active material. The polymer dispersed in the slurry will further affect the construction of the electron transport network in the electrode, resulting in high internal resistance of the cell and affecting the thermal stability of the cell.

[0166] In Comparative Example 3, the use of organic conductive polymers to replace inorganic nanoparticles resulted in a significant decrease in thermal stability. Although organic conductive polymers also possess a certain degree of stability, they may be affected by electrolyte erosion, redox reactions, and other factors, leading to changes in the polymer's structure and properties. This reduces the effectiveness of limiting the volume expansion of the negative electrode material, thereby lowering the thermal stability of the battery cell. Furthermore, organic conductive polymers have poor conductivity, especially when the degree of polymerization of the SEI film increases and the number-average molecular weight increases, the disadvantage of insufficient conductivity becomes more pronounced.

[0167] Comparative Example 4 was tested using commercially available common negative electrode materials, and the performance data was poor.

[0168] In summary, Examples 1-5 showed a significant decrease in both explosion pressure and ambient temperature. After testing in a hot chamber and under explosion pressure (compared to Comparative Example 4, prior art), the explosion pressure decreased by at least 13%, the ambient temperature decreased by at least 27.5%, and the time to reach maximum pressure was extended by at least 90%. This is because the constructed artificial SEI film possesses high thermal stability and non-flammability. During the thermal runaway phase of the battery cell, it can increase the decomposition temperature of the negative electrode SEI film, further improving the thermal stability of the battery cell. Simultaneously, the conductivity of the artificial SEI film (referring to the conductivity of the negative electrode sheet) increased by ≥50%, and the in-situ expansion thickness of the battery cell containing the negative electrode sheet decreased by 10-30%.

[0169] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a negative electrode material coated with a double conductive layer SEI film, characterized in that: First, the ionic liquid monomer, polymer monomer, initiator and lithium salt are mixed evenly and fully dissolved to obtain a copolymer solution. The copolymer solution is then diluted with an organic solution to obtain a casting solution. The casting solution, active material and inorganic nanoparticles are mixed evenly, coated and cured under light or heat initiation conditions, and then dried to obtain a negative electrode material coated with a double conductive layer SEI film. The main reactants in the copolymer solution include ionic liquid monomers, polymer monomers, and lithium salts. The composition of the main reactants, by mass percentage, is as follows: 50-85% ionic liquid monomer, 5-25% polymer monomer, and 10-30% lithium salt, totaling 100%. The amount of initiator added is 0.5% to 2% of the sum of the mass of the ionic liquid monomer and the polymer monomer; the molecular weight of the polymerized solid electrolyte is >300,000.

2. The preparation method according to claim 1, characterized in that, The active material and inorganic nanoparticles are premixed before being mixed with the casting solution. The premixing process is as follows: The active material and inorganic nanoparticles were added to a dual planetary stirrer and mixed. The dual planetary stirrer rotated at a speed of 500–3000 rpm and revolved at a speed of 5–50 rpm for 10–60 min.

3. The preparation method according to claim 1, characterized in that, The ionic liquid monomer is one or more of the following: 1-methylimidazolium tetrafluoroborate, 1-ethylimidazolium tetrafluoroborate, 1-butylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-2,3-dimethylimidazolium hexafluorophosphate, 1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)imide, 1-methyl-3-ethylimidazolium bis(fluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium trifluoroacetate, 1-vinyl-3-ethylimidazolium tetrafluoroborate, 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide, 1-vinyl-3-butylimidazolium tetrafluoroborate, and 1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide.

4. The preparation method according to claim 1, characterized in that, The polymer monomer is one or more of polyethylene glycol diacrylate, polyethylene glycol methyl ether methacrylate, glycidyl methacrylate, methyl methacrylate, hydroxyethyl methacrylate, butyl methacrylate, n-butyl acrylate, and tert-butyl acrylate. The lithium salt is one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalate-borate), lithium bis(trifluoromethanesulfonyl)imide, and lithium di(fluorooxalate-borate).

5. The preparation method according to claim 1, characterized in that: When the initiation condition is light, the initiator is a photoinitiator, which is one or a combination of two or more of 2-hydroxy-2-methylphenylacetone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 1-hydroxycyclohexylphenyl ketone. When the initiation condition is heating, the initiator is a thermal initiator, which is one or a combination of two or more of azobisisobutyronitrile, azobisisoheptanenitrile, diisopropylbenzene peroxide, potassium persulfate, and ammonium persulfate.

6. The preparation method according to claim 1, characterized in that, The mass content of the copolymer solution in the casting solution is 0.5-5%; wherein the organic solvent is one or more of acetone, N,N-dimethylformamide, dimethylacetamide, N-methylpyrrolidone and acetonitrile.

7. The preparation method according to claim 1 or 2, characterized in that, The mixing ratio of the active material and inorganic nanoparticles is: 98-99.5 wt.% active material and 0.5-2.0 wt.% inorganic nanoparticles. The active material is any one or a combination of two or more of the following: graphite, hard carbon, soft carbon, lithium titanate, silicon carbide, and silicon oxide. The inorganic nanoparticles are one or more of the following: conductive carbon black with a particle size of 10–300 nm, single-walled carbon nanotubes with a diameter of 1–5 nm, and multi-walled carbon nanotubes with a diameter of 5–100 nm.

8. The preparation method according to claim 1, characterized in that: The photo-initiation conditions are to irradiate the mixed reaction system with an ultraviolet lamp with a wavelength of 350nm to 405nm for 30 to 90 minutes; The thermal initiation conditions are to heat the mixed reaction system at 40–80°C for 36–72 hours.

9. A negative electrode material coated with a double conductive layer SEI film, characterized in that, The negative electrode material is prepared by the preparation method according to any one of claims 1 to 8.

10. An electrode, battery, electrochemical device, electrical equipment, or energy storage device, characterized in that, The electrode, battery, electrochemical device, electrical equipment, and energy storage device include the negative electrode material as described in claim 9; Preferably, the battery is selected from either a solid-state battery or a semi-solid-state battery.

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