Polyurethane cushion sheet for solid-state battery and method for preparing the same

Abstract

The application discloses a kind of polyurethane buffer sheets for solid-state battery, by controlling the regulation and control pressure variable index M of polyurethane buffer sheet, so that ultra-thin buffer sheet can meet the demand of high energy density, and can inhibit the additional deformation caused by the SEI thickening of solid-state battery in the whole life cycle of battery, maintain stable stress regulation ability.The material maintains good stress retention ability during repeated compression, ensures the stability of the interface contact state of the battery during long-term use, and the preparation method of the polyurethane buffer sheet for solid-state battery is also disclosed.

Description

Technical Field

[0001] This invention relates to a polymer foam sheet, specifically to a polyurethane buffer sheet and its preparation method, which is particularly suitable for buffer sheets in solid-state batteries. Background Technology

[0002] While lithium-ion battery technology has made significant progress with the rapid development of electric vehicles, traditional liquid lithium-ion batteries are approaching their theoretical energy density limits. Furthermore, the flammable and explosive properties of their liquid electrolytes pose serious safety hazards. In contrast, solid-state batteries, with their higher safety performance and potential energy density advantages, are considered an important direction for the next generation of battery technology. However, solid-state batteries face severe technical challenges in practical applications: silicon anode materials undergo volume expansion and contraction exceeding 250% during charging and discharging. This dramatic "breathing effect" causes continuous changes in internal stress, easily leading to silicon particle crushing, electrode cracking, and ultimately rapid performance degradation. More critically, the solid-solid interface between components in all-solid-state batteries makes them extremely sensitive to stacking stress: insufficient stacking stress leads to poor interface contact and a significant increase in internal resistance; while excessive stacking stress generates excessive shear force within the battery, which, combined with the repeated expansion and contraction of the electrode materials, further exacerbates the risk of electrode cracking or tearing. This uneven stress distribution is particularly pronounced in batteries with multi-layer stacked structures.

[0003] The commonly used flat-plate pressurization method in industrial applications struggles to achieve uniform pressure distribution, easily leading to localized stress concentration. While laboratory studies have attempted to alleviate stress by adding flexible buffer materials to the outside of pouch cells, the aluminum-plastic film interface between the battery and the buffer material causes a tearing effect during pressurization, negatively impacting the battery's initial efficiency and cycle performance. Research indicates that the cycle life of both liquid and solid-state lithium-ion batteries is significantly affected by stacking stress. Although liquid batteries exhibit better liquid-solid interface conformity and require relatively lower initial stacking stress, the solid-solid interface characteristics of solid-state batteries necessitate higher stacking stress to ensure good interfacial contact. Ideally, the compressive stress of the buffer material remains constant, unaffected by changes in compressive strain. However, in reality, the rigidity of the solid electrolyte in solid-state batteries places more stringent demands on interfacial contact: on one hand, sufficient stacking stress must be maintained to ensure tight solid-solid interface contact; on the other hand, it must accommodate the dynamic deformation of the battery during charging and discharging. This balance faces multiple challenges in practical applications. As the number of cycles increases, electrode material degradation and the continuous thickening of the SEI film constantly alter the stress distribution within the battery. Furthermore, the use of ultra-thin buffer materials to achieve higher energy density further compresses the space for stress regulation. Adding to the complexity, solid-state batteries undergo continuous structural evolution throughout their lifespan: initially, buffer materials need to provide sufficient contact pressure; in the mid-term, they must adapt to electrode volume fluctuations; and in the later stages, they must cope with additional deformation caused by material aging. Existing buffer materials often fall short in some aspects, either failing to provide sufficient initial contact pressure or losing their stress regulation capabilities during long-term cycling. This performance shortcoming directly restricts the reliability and lifespan of solid-state batteries. Summary of the Invention

[0004] In view of the deficiencies in the existing technology, the purpose of this invention is to provide a polyurethane buffer sheet that, while providing buffering performance to ensure the safety of solid-state batteries when subjected to impact, can also take into account the unique application scenarios of solid-state batteries, so as to meet the requirements of solid-state batteries for high energy density and long cycle life.

[0005] In order to solve the above problems, the inventors conducted in-depth research and found that when a polyurethane buffer sheet is designed that has a relatively high initial stress at a relatively thin thickness and does not generate excessive internal stress over a large deformation range, the above problems can be solved.

[0006] The specific plan is as follows: In a first aspect, the present invention discloses a polyurethane buffer sheet for solid-state batteries. The polyurethane buffer sheet, in its uncompressed state, has a thickness ranging from 0.02 to 1 mm. In the stress-strain curve of the buffer material, the polyurethane buffer sheet, as the deformation increases from 0, sequentially exhibits three regions: the Hooke's region, the smooth region, and the exponential expansion region (e.g.,...). Figure 1 As shown in the figure, these three regions have the following characteristics: Hooke's zone: The stress σ and deformation ε have a basically linear relationship; Smooth region: As the deformation ε increases, the stress σ increases more slowly, and the stress-strain curve transitions from linear to smooth. In the exponential growth region: the curve becomes steeper, and the stress increases sharply with the increase of deformation; In the stress-strain curve of the buffer material, the critical point between the Hooke's zone and the smooth zone is defined as A, and the critical point between the smooth zone and the exponentially increasing zone is defined as B. εA, εB, σA, and σB are the strain and stress values ​​corresponding to A and B, respectively. The polyurethane buffer sheet satisfies the compressive strain index M of 0.3 ≤ M ≤ 0.9, where the compressive strain index M satisfies the following formula: .

[0007] In one embodiment, the polyurethane buffer sheet simultaneously satisfies the following relationship in the stress-strain curve of the buffer material: (1) 10%≤ε A ≤25%; (2) 35%≤ε B ≤90%; (3) σ A ≥0.2MPa; (4) σ B ≤5MPa.

[0008] In one of the schemes, the preferred pressure transformer index M is 0.4≤M≤0.8, further is 0.45≤M≤0.8, further is 0.5≤M≤0.85; further is 0.55≤M≤0.8; further is 0.5≤M≤0.8; further is 0.5≤M≤0.8; further is 0.55≤M≤0.8; further is 0.6≤M≤0.8.

[0009] In one embodiment, the polyurethane buffer sheet, in its uncompressed state, has a density ρ 缓 The range is 250-750 kg / m 3 Preferred density ρ 缓 300-700 kg / m 3 Furthermore, it is 350-600 kg / m³. 3Further, it is 350-550 kg / m³. 3 .

[0010] In one embodiment, the preferred polyurethane buffer sheet σ A ≥0.25MPa; further optimization of σ A ≥0.3MPa; further optimization of σ A ≥0.4MPa; further optimization of σ A ≥0.5MPa.

[0011] In one embodiment, the preferred polyurethane buffer sheet σ B ≤4.5MPa; further optimization of σ B ≤4MPa; Further optimization of σ B ≤3.5MPa; further optimization of σ B ≤3MPa; further preferred σB≤2.5MPa; further preferred σ B ≤2MPa; Further optimization of σ B ≤1.5MPa.

[0012] In one embodiment, the thickness variation of the polyurethane buffer sheet is controlled within 10% of the thickness; further, the thickness variation is controlled within 8%, further, within 6%, further, within 4%, and further, within 2%.

[0013] In one embodiment, the cyclic compressive stress retention rate of the polyurethane buffer sheet is ≥80%. Preferably, the cyclic compressive stress retention rate of the polyurethane buffer sheet is ≥85%, further preferably ≥90%, and even more preferably ≥95%.

[0014] In a second aspect, the present invention discloses a method for preparing a polyurethane buffer sheet for solid-state batteries, comprising the following steps: (1) Preparation of A material: Mix polyols of different viscosities with additives including at least nucleating agents and stabilizers, and stir evenly to obtain A material mixture.

[0015] (2) Bubble injection: Physical foaming gas is introduced into material A and mixed at a gas-liquid volume ratio of (30-400):100. The density of the gas-liquid mixture of material A after mixing is controlled to be 0.2-1 g / cm³, and the maximum bubble size Dmax in the gas-liquid mixture of material A is ≤20μm. (3) Mixing of A and B components: The gas-liquid mixture of component A and the polyisocyanate component B from step (2) are mixed, wherein the viscosity of the reaction mixture is controlled within the range of 100-600 mPa·s. Furthermore, the α value is controlled to satisfy 1066 (mgKOH / g) ≤ α ≤ 1600 (mgKOH / g). The α value is defined as: α = (OHV) （A） *m （A） ) / ([NCO]% （B） *m （B） ) OHV (A) The hydroxyl value of component A is defined as follows:

[0016] Where m （A） The OHV of a single material is the total mass of mixture A. （i） It can be obtained by testing according to GB / T 12008.3-2009 (Method A); [NCO]% （B） The NCO content of material B can be obtained by testing according to GB / T 12009.4-2016 (Method A); m （B） This refers to the total mass of material B. (4) Spraying: The reaction mixture from step (3) is atomized by a spray gun and sprayed onto a carrier substrate with a surface difference of ≤0.1μm, while controlling the atomized particle size to be ≤5μm; (5) Coating: The carrier substrate sprayed with the reaction system mixture is passed through a slit device with a slit gap flatness of ≤0.03μm to adjust the thickness and thickness difference of the mixture; (6) Curing: The coated mixture is cured at 100-150℃ to obtain a polyurethane buffer sheet for solid-state batteries.

[0017] In one of the schemes, in the preparation of material A, polyols of different viscosities are poured into the mixing tank in order of viscosity from low to high. When the amount of polyol added reaches 1 / 3 to 2 / 3 of the total amount, stirring is started. After stirring evenly, the remaining polyol, stabilizer and catalyst are added, the speed is increased and stirring is evenly. The prepared material is sealed and allowed to stand to obtain the mixture of material A.

[0018] In one of the schemes, the sealing and standing treatment step in step (1) is specifically as follows: the A material mixture prepared in step (1) is sealed under nitrogen protection and placed in a constant temperature and humidity room for 0.5-6 hours, with a constant temperature of 18-30℃ and humidity <30%RH.

[0019] In one of the schemes, the preferred α value range is 1200 (mgKOH / g) ≤ α ≤ 1467 (mgKOH / g); a further α value range satisfies 1266 (mgKOH / g) ≤ α ≤ 1400 (mgKOH / g).

[0020] In one embodiment, the polyol mixture satisfies a viscosity range of 150-1000 mPa·s, with a preferred polyol mixture satisfying a viscosity range of 150-800 mPa·s, and a further polyol mixture satisfying a viscosity range of 250-700 mPa·s. The average functionality satisfies a range of 2-5, and the average hydroxyl value satisfies a range of 150-400 mg KOH / g, with a preferred range of 200-400 mg KOH / g, and a further range of 250-350 mg KOH / g.

[0021] In one embodiment, the viscosity of the polyisocyanate is in the range of 20-1000 mPa·s, preferably 20-800 mPa·s, more preferably 20-600 mPa·s, further preferably 20-400 mPa·s, even more preferably 20-250 mPa·s, and most preferably 20-150 mPa·s; the average functionality of the polyisocyanate is 2.0-2.8, preferably 2.1-2.8, more preferably 2.2-2.8, and even more preferably 2.3-2.8; the NCO content of the polyisocyanate is 15-35%, preferably 17-33%, more preferably 19-33%, even more preferably 21-33%, even more preferably 23-33%, and most preferably 25-33%.

[0022] In one embodiment, the viscosity range of the mixture is preferably 200-500 mPa·s after mixing for 3-20 minutes.

[0023] In one embodiment, the stabilizer is a foam stabilizer, preferably a silicone-based polyurethane foam stabilizer, with a content of 0.1-10 wt% based on the total content of the polymer raw materials.

[0024] In one embodiment, the catalyst comprises an organometallic catalyst or an organoamine compound, wherein the organometallic catalyst is selected from one or more organonitrile compounds, organobismuth compounds, and organocobalt compounds, and the organoamine compound comprises acid-terminated amines or quaternary ammonium salts of organoamines, specifically selected from triethylenediamine (TEDA), bis(dimethylaminoethyl) ether and its analogues, cyclohexylmethyl tertiary amines, pentamethyldialkyltriamine, tetramethylalkyldiamine, 2,4,6-tris(dimethylaminomethyl)phenol, 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine, tris(dimethylaminopropyl)amine, N,N-dimethylbenzylamine, N,N-dimethyl(hexadecyl)amine, dimethylethanolamine, dimethylaminoethoxyethanol, trimethylhydroxyethylpropanediamine, trimethylhydroxyethylethylenediamine, N,N-bis(dimethylaminopropyl)isopropanolamine, 1,8-diazabicyclo[5,4,0]undecene-7 (DBU), 1,5 One or more of the following: diazabicyclo[4,3,0]nonene 5 (DBN), 1,8-diazabicyclo[5,3,0]decene 7 (DBD), and 1,4-diazabicyclo[3,3,0]octene 4 (DBO).

[0025] In one of the embodiments, optional other additives may also be included, which are selected from one or more of the following: nucleating agents, viscosity modifiers, antioxidants, colorants, crosslinking agents, dispersants, ultraviolet absorbers, leveling agents, foaming agents, superdispersing additives, and water-absorbing agents.

[0026] In one of the schemes, the physical foaming gas in step (2) includes nitrogen, compressed air, and carbon dioxide, preferably nitrogen.

[0027] In one of the schemes, in step (4), the surface difference of the carrier substrate is ≤0.1μm.

[0028] In one of the schemes, in step (5), the thickness of the reaction mixture is controlled at 0.02-1.5 mm, and the thickness difference after curing is within 10%.

[0029] In one of the schemes, after step (6) is cured, it also goes through the processes of winding, slitting and packaging.

[0030] In a third aspect, the present invention also discloses the application of the polyurethane buffer sheet shown in a solid-state battery.

[0031] The beneficial effects of this invention are: This invention improves the compatibility of polyurethane buffer sheets with solid-state batteries by controlling the modulating voltage coefficient M of the polyurethane buffer sheet. Specifically, this is reflected in: First, when the critical stress value σA of the Hooke region and smooth region of the polyurethane buffer sheet is controlled at ≥0.2MPa, the polyurethane buffer sheet can ensure the initial compressive stress when compressed to the Hooke region, which effectively solves the problem of increased interface resistance caused by insufficient initial contact pressure of traditional buffer materials. Secondly, within the range of M and the critical strain regions εA and εB defined in this invention, the smooth area of ​​the polyurethane buffer sheet can maintain a stable stress plateau, thereby adapting to the volume expansion of the solid-state battery during charging and discharging without causing stress abrupt changes and avoiding damage to the internal structure. Finally, the critical compressive stress σB in the smooth area and finger-increase area of ​​the polyurethane buffer sheet is controlled at ≤5MPa, which can prevent the internal components of the solid-state battery from being damaged due to excessive pressure.

[0032] This precise control of the stress-strain curve allows the ultra-thin buffer sheet to meet high energy density requirements while suppressing additional deformation, including that caused by the thickening of the SEI in solid-state batteries, throughout the battery's entire lifespan, maintaining stable stress regulation capabilities. Furthermore, the material maintains excellent stress retention during repeated compression, ensuring the stability of the interface contact state during long-term battery use. Practical applications demonstrate that using the buffer material of this invention can significantly improve the cycle performance and safety of solid-state batteries. Attached Figure Description

[0033] Figure 1 The diagram shows stress-strain curves for existing technologies and embodiments of the present invention. It should be noted that εA, εB, σA, and σB are not read as specific values ​​in the diagram.

[0034] Figure 2 This is a schematic diagram of the first derivative of the stress-strain curve in Embodiment 1 of the present invention, and the location of point A is determined based on this diagram.

[0035] Figure 3 This is a schematic diagram of the stress-strain curve of Embodiment 1 of the present invention, and the location of point B is determined based on this diagram. Detailed Implementation

[0036] Although the invention has been described to a certain extent, it is apparent that appropriate variations can be made to the various conditions without departing from the spirit and scope of the invention. It is understood that the invention is not limited to the described embodiments, but falls within the scope of the claims, which include equivalent substitutions for each of the elements.

[0037] [Pressure Transformation Index M] The stress-strain curve of polyurethane cushioning material during compression exhibits three continuous characteristic regions, such as... Figure 1As shown: First is the Hooke's zone, also known as the linear elastic zone, where the stress-strain relationship is approximately linear, with deformation ranging from 0% to εA. This stage is primarily dominated by the elastic bending of the cell walls, and the elastic modulus depends on the cell structure itself. As compression progresses, the material enters the smoothing zone, also called the stress plateau zone, where deformation extends from εA to εB. In this stage, stress increases slowly with increasing strain, the cells gradually collapse, and the cell walls yield, exhibiting a clear stress relaxation phenomenon. Finally, there is the exponential growth zone, also known as the densification zone, where stress increases exponentially with strain, Poisson's ratio approaches 0.5, and the material volume exhibits incompressible characteristics. At this point, the cell structure is completely compacted, and the material density is close to the bulk density of the resin.

[0038] In solid-state battery applications, existing buffer materials have significant shortcomings. During the initial compression stage, i.e. the Hooke's region, traditional materials often cannot provide sufficient contact stress, leading to poor contact at the battery interface. During the operating stage, due to the insufficient range of the smooth region, the stress response of the material is unstable under large deformation, making it difficult to adapt to changes in electrode volume. In the high compression stage, the material is prone to sudden stress changes, and this nonlinear growth can easily damage the electrode and create an unfavorable coupling with the battery's breathing effect.

[0039] From a microscopic perspective, point A marks the starting point of compression of the foam from its free state. At this stage, the foam deformation is small, and gaps exist between the cells. In the initial stage of compression, normal cells gradually converge. At this time, the stress mainly comes from the force on the cell walls during the initial flattening process, and the deformation and stress change are basically proportional. Furthermore, some cells with larger openings or thinner walls generate almost no additional stress during compression. When compression exceeds point A and enters the smooth zone, the cells at point A have become ellipsoidal. With continued compression, the line connecting the two foci of the ellipsoid is perpendicular to the direction of force, and the top surface arc tends to be smoother, resulting in a lower force value. As the compression increases, the top surface arc becomes smoother, and the force growth rate slows down. However, because the cells gradually converge, the interaction forces increase, and the overall stress still rises slowly, while the derivative of the stress curve gradually decreases or remains essentially unchanged. Once compression exceeds point B, the gaps between the cells decrease significantly, lateral stress begins to dominate, and the stress caused by cell flattening becomes negligible. After the gas inside the bubbles is squeezed out, the material gradually loses its buffering effect and enters a state of compression close to that of a solid or elastomer, and the stress increases exponentially.

[0040] The method for determining points A and B in the diagram is as follows: Point A: Linear fitting is performed on discrete points within the rapidly decreasing region of the first derivative smoothed curve of the SS curve (referred to as the first derivative curve) starting from 0 (e.g., the compression amount is between 1% and 5% in Example 1). The fitted line is A1. A tangent line is drawn to the curve at the lowest point of the first derivative curve, designated as A2. The intersection of the fitted line A1 and the tangent line A2 is designated as A3. The point corresponding to the abscissa of the SS curve corresponding to the abscissa of A3 is defined as point A. See [link to relevant documentation]. Figure 2 .

[0041] Point B: Draw the tangent line to the SS curve from point A as B1. Take the point on the SS curve where the Y-value is 2500 kPa and draw the tangent line to the SS curve as B2. The intersection of B1 and B2 is defined as point B. 2500 kPa is an empirical position; in the SS curve, the tangent lines drawn from points above 2500 kPa are not significantly different. Therefore, we uniformly determine the point at 2500 kPa as the tangent line to the SS curve. See [link / reference]. Figure 3 .

[0042] The polyurethane buffer sheet proposed in this invention has a specific compressive strain index M, the formula of which is: .

[0043] Wherein εA and εB are the critical strain values ​​between the Hooke's zone and the smooth zone, and between the smooth zone and the exponentially increasing zone, respectively, and σA and σB are the corresponding critical stress values. The exponent M is controlled within the range of 0.35 to 0.9. When the M value is below 0.35, the material stress increases too quickly, and the deformation capacity is insufficient. To meet performance requirements, the material thickness often needs to be increased, thereby reducing the battery energy density. When the M value exceeds 0.9, although the deformation capacity is improved, the initial contact stress is insufficient, which easily leads to poor interface contact and increased internal resistance. Through extensive experimental verification, the preferred M value range of this invention includes 0.35 to 0.85, more preferably 0.4 to 0.8, further preferably 0.45 to 0.8, even more preferably 0.5 to 0.8, and most preferably 0.55 to 0.8, to ensure that the material has sufficient deformation buffering capacity while providing suitable initial contact stress.

[0044] Furthermore, the polyurethane buffer sheet must simultaneously meet the following parameter conditions on the stress-strain curve: εA is between 10% and 25%. This range ensures that the material has an appropriate linear elastic response in the initial compression stage, enabling it to quickly establish effective contact under small deformations, avoiding insufficient initial stress due to excessively high εA, or premature termination of the Hooke zone due to excessively low εA.

[0045] εB is controlled between 35% and 90%. The late-smoothing end strain gives the material better deformation adaptability, allowing it to maintain stress stability during electrode volume changes and avoiding premature densification.

[0046] σA is not less than 0.2 MPa. Higher initial plateau stress helps to establish sufficient interfacial contact in the battery stack, reduce contact resistance, and improve battery performance consistency.

[0047] σB should not exceed 5 MPa. This upper limit can effectively prevent a sharp increase in stress under high compression conditions, thereby avoiding mechanical damage to the electrode and mitigating the adverse coupling with the battery breathing effect.

[0048] By coordinating the M value with the four key parameters mentioned above, it is possible to achieve multiple requirements such as initial contact, platform stability, and high compression safety without increasing the material thickness, thus meeting the comprehensive needs of solid-state batteries for deformation adaptability and stress retention rate of buffer materials during long-term cycling.

[0049] [Thickness and thickness range] The thickness design of the polyurethane buffer sheet is a key parameter affecting the energy density of solid-state batteries. Through in-depth research, this invention has determined that the optimal thickness range for the polyurethane buffer sheet is 0.02-1 mm. When the thickness is below 0.02 mm, the material's deformation capacity during compression is limited, potentially leading to interlayer fracture. Conversely, when the thickness exceeds 1 mm, unnecessary structural redundancy is created, reducing the battery's energy density. It should be noted that the 1 mm upper limit is based on energy density optimization considerations and does not imply that manufacturing products with higher thicknesses is impossible. In fact, manufacturing products with higher thicknesses is easier to achieve, especially considering feasibility factors in industrial production.

[0050] To ensure consistent product performance, this invention implements strict control over the thickness variation, keeping it within 10% of the original thickness. This stringent tolerance control guarantees: 1) the accuracy and stability of thickness during production; 2) the reliability of performance in practical applications; and 3) the quality consistency between different batches of products. Through graded optimization, the variation is further optimized to be within 9%, 8%, 7%, 6%, 5%, 4%, 3%, and 2%. Research shows that when the thickness variation exceeds 10%, it leads to uneven stress distribution inside the battery, causing local resistance differences and ultimately affecting the battery's cycle performance. This precise thickness control is one of the key technical features of this invention.

[0051] [density] The density of polyurethane buffer sheets is one of the key parameters affecting their compressive performance. The density range of the polyurethane buffer sheets of this invention is 250-750 kg / m³, which ensures that the material has both good compressive performance and structural stability. When the density is below 250 kg / m³, the material faces two main problems: First, to achieve the stress requirement of ≥200 kPa at 25% compression, the hard segment content, mainly composed of isocyanate and chain extender, must be increased. This leads to intensified microphase separation, forming a significant double glass transition zone, causing the material to exhibit slow rebound characteristics and reduce the rebound rate. Second, if the original formulation is maintained, the 25% compressive stress may be far below 200 kPa. To achieve the required stress, the compression must be increased to 35%-50%. This either requires increasing the material thickness, thus affecting the energy density, or leads to poor interfacial contact, thus increasing internal resistance.

[0052] When the density exceeds 750 kg / m³, the material rapidly reaches a densified state during compression, exhibiting incompressible properties similar to a solid. To obtain sufficient deformation, the thickness also needs to be increased, which is detrimental to improving energy density.

[0053] The preferred density range is 300-700 kg / m³ 3 Furthermore, the density range is selected as 350-650 kg / m³. 3 A further density range of 350-600 kg / m³ was selected. 3 A further density range of 350-550 kg / m³ was selected. 3 .

[0054] By controlling the balance of the ratio of hard segments (mainly isocyanate / chain extender) to soft segments (mainly polyether polyol, polyester polyol, polyacrylate polyol, etc.) in polyurethane materials, and by controlling the foaming process, the above density range can be obtained.

[0055] Cyclic compressive stress retention rate The polyurethane buffer pad of this invention has a cyclic compressive stress retention rate of over 80%. Cyclic stress loss in polymer materials is the result of fatigue or stress relaxation under certain cyclic stress. The greater the cyclic compressive stress loss, the lower the compressive stress retention rate, which is a key factor related to the cycle stability and safety of solid-state batteries. When the cyclic compressive stress retention rate of the polyurethane buffer pad is below 80%, the stress in the material becomes lower under the same compression after repeated charge-discharge cycles. To some extent, low stress can lead to weak adhesion between the solid and solid interfaces inside the battery, increasing the interfacial resistance and affecting the battery's cycle life and service life. Preferably, the cyclic compressive stress retention rate of the polyurethane buffer pad is above 85%, further preferably above 90%, and even more preferably above 95%.

[0056] [raw material] The polyurethane buffer sheet of this invention is prepared by crosslinking polymerization of isocyanate and a compound containing active hydrogen. Its raw material system includes essential components and optional components. The essential components are polyols, polyisocyanates, stabilizers, nucleating agents, and catalysts; optional components include viscosity modifiers, leveling agents, antioxidants, foaming agents, superdispersants, water-absorbing agents, and color pastes, etc. Those skilled in the art can rationally select and combine these components according to actual process and performance requirements. The specific types selected are conventional components in the art, and their dosages are conventional dosages foreseeable in the art.

[0057] (1) Polyols Regarding the selection of polyols, one or more types of polyols suitable for polyurethane foam preparation can be used, including but not limited to polyester polyols, polyether polyols, polyacrylate polyols, polyolefin polyols, bio-based polyols, epoxy resins, polyether ester diols, and amine polymers such as amino-terminated polyethers and urethane polyols. Specifically, polyester polyols encompass adipic acid-based polyester diols, aromatic polyester polyols, dimer polyester diols, polycaprolactone polyols, and polycarbonate diols. Adipic acid-based polyester diols include various structures such as polyethylene adipate diol, propylene adipate diol, and butyl adipate diol; aromatic polyester polyols can be prepared by condensation reactions of phthalic acid, terephthalic acid, isophthalic acid or their derivatives with diols such as ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, and neopentanediol; polycaprolactone polyols further include polycaprolactone diol and polycaprolactone triol, and can be further subdivided into polycaprolactone polyols starting with BDO, NPG, HDO, DEG, EG, DMPA, and TMP based on the type of initiator; polycarbonate diols include various structures such as polyhexene carbonate diol, poly-1,6-hexanediol carbonate diol, and polybutylene carbonate diol.

[0058] Polyether polyols include polypropylene oxide polyols, polymeric polyols, polytetrahydrofuran and its copolymers, polyethylene oxide polyols, polytrimethylene polyether glycols, and aromatic polyether polyols. Polypropylene oxide polyols encompass difunctional to octafunctional polyethers based on different initiators, such as EO / PO copolyethers using ethylene glycol, propylene glycol, butanediol, glycerol, pentaerythritol, xylitol, sorbitol, and sucrose as initiators. Polymeric polyols are grafted polyether polyols, typically containing styrene-acrylonitrile copolymers, which can improve foam load-bearing capacity. Polytetrahydrofuran copolymers can be classified into molecular weight grades from 250 to 3000 based on their degree of polymerization.

[0059] To balance material performance and process feasibility, preferred polyols include polyoxypropylene polyol, polytetrahydrofuran diol, polymeric polyol, polycaprolactone diol, and polycaprolactone triol. Especially under conditions of room temperature and cost control, the use of polyoxypropylene polyol, polymeric polyol, polycaprolactone diol, and polycaprolactone triol is further recommended.

[0060] In one preferred embodiment, the polyol system used in this invention comprises the following four types of components: Polyol component 1: viscosity of 200-500 mPa·s, functionality of 1.5-3, hydroxyl value of 100-400 mgKOH / g; Polyol component 2: viscosity of 300-800 mPa·s, functionality of 2.5-3.5, hydroxyl value of 100-400 mgKOH / g; Polyol component 3: viscosity of 300-3000 mPa·s, functionality of 2.5-3.5, hydroxyl value of 20-100 mgKOH / g; Polyol component 4: viscosity of 500-5000 mPa·s, functionality of 2-8, and hydroxyl value of 20-80 mgKOH / g.

[0061] The aforementioned polyol components can be single compounds or mixtures of multiple polyols. The polyol system may contain only component 1 or component 2, or it may be a mixture of component 1 and / or component 2 with component 3 and / or component 4. The overall polyol mixture should have a viscosity of 150-1000 mPa·s, preferably 150-800 mPa·s, more preferably 250-700 mPa·s; based on this, the average functionality of the polyol is 2-5, preferably 2.3-4.5, more preferably 2.5-4.2. During the preparation of material A, the mixture of multiple polyols is poured into the mixing tank in order of increasing viscosity.

[0062] (2) Polyisocyanates In terms of the selection of polyisocyanates, aromatic, aliphatic, or alicyclic isocyanates can be used. Aromatic isocyanates include toluene diisocyanate, phenyl diisocyanate, diphenylmethane diisocyanate, and phenylenediamine diisocyanate; aliphatic isocyanates include hexamethylene diisocyanate, pentamethylene diisocyanate, and trimethylhexamethylene diisocyanate; alicyclic isocyanates include isophorone diisocyanate, hydrogenated TDI, hydrogenated TMXDI, and norbornene diisocyanate.

[0063] Considering processing performance, cost, and operational safety, diphenylmethane diisocyanate and its modified products are preferred, such as liquefied MDI, pure MDI, polymeric MDI, MDI50, polymethylene polyphenyl isocyanate, and carbodiimide-modified MDI. To obtain higher initial compressive stress and control costs, the selected polyisocyanate should preferably have a functionality of 2.0-2.8, a viscosity of 20-1000 mPa·s, and an NCO content of 15-35%. The preferred functionality range is 2.1-2.8, more preferably 2.2-2.8, and even more preferably 2.3-2.8. To improve processing convenience, the viscosity is preferably 20-800 mPa·s, more preferably 20-600 mPa·s, even more preferably 20-400 mPa·s, still more preferably 20-250 mPa·s, and most preferably 20-150 mPa·s. In terms of cost control, the NCO content is preferably 17-33%, more preferably 19-33%, further preferably 21-33%, even more preferably 23-33%, and most preferably 25-33%.

[0064] To achieve the performance described in this invention and ensure processing feasibility, the viscosity of the A / B reaction system mixture after mixing polyol and polyisocyanate should be maintained at 100-1000 mPa·s for 3-20 minutes. Preferably, this viscosity maintenance time is 5-30 minutes, more preferably 10-60 minutes; the mixed viscosity is further preferably 200-500 mPa·s. During polyurethane foaming, the initial viscosity and time-varying behavior of the mixture directly determine the material's flow characteristics and the stability of the bubbles. If the viscosity is too low, the material is prone to excessive flow in the mold, resulting in uneven density and difficulty in controlling the thickness of the molded parts. Simultaneously, insufficient bubble wall strength makes it easy for the bubbles to merge or rupture during foaming, forming irregular large pores, ultimately damaging the stability of the buffer stress plateau. If the viscosity is too high, the material has poor flowability, making it difficult to completely fill complex mold cavities, easily causing localized material shortages. It also hinders the normal growth and expansion of bubbles, leading to a denser cell structure and narrowing the strain range εB-εA in the smooth zone. Setting the viscosity hold-up time window to 3-20 minutes is to match the actual production process cycle. This window needs to be long enough to complete the entire process from mixing and pouring to mold filling; however, it cannot be too long, otherwise the system reaction will be too slow, leading to low production efficiency or bubble structure collapse. Further optimizing the viscosity to 200-500 mPa·s, coupled with a hold-up time of 10-60 minutes, is to ensure that while obtaining a uniform and fine cell structure, the material has good moldability and the ability to replicate the mold outline, thereby guaranteeing the consistency of the final product's geometric dimensions and the repeatability of its mechanical properties.

[0065] To simultaneously meet product performance and processing requirements, the α value should satisfy 1066 (mgKOH / g) ≤ α ≤ 1600 (mgKOH / g), with a preferred α value range of 1200 (mgKOH / g) ≤ α ≤ 1467 (mgKOH / g); a further preferred α value range is 1266 (mgKOH / g) ≤ α ≤ 1400 (mgKOH / g). The parameter α is essentially a functional expression of the isocyanate index, directly determining the molar ratio of -NCO and -OH groups. When the α value is too low, it indicates a relative excess of isocyanate. Excess -NCO groups participate in the formation of rigid crosslinking points such as biuret and urethane, leading to excessively high crosslinking density and increased hardness. While this may increase the initial stress σA, it makes the material brittle, shortens the smooth zone, and significantly increases the stress σB in the densified zone, even exceeding the upper limit of 5 MPa, increasing the risk of electrode damage. Conversely, when the α value is too high, it means that the polyol is relatively excessive, and there are a large number of unreacted flexible hydroxyl segments in the system. This will lead to insufficient crosslinking density, resulting in a low initial modulus of the material, which cannot provide sufficient initial contact stress (σA is difficult to reach above 0.2 MPa). At the same time, the material has weak resistance under pressure, and the stress level in the plateau region is low and may be unstable, making it impossible to effectively maintain stable contact at the battery interface. By optimizing α in the range of 1066-1600 (mgKOH / g), especially the more preferred range of 1266-1400 (mgKOH / g), the polyurethane network can form a moderate crosslinking structure and phase separation. This ensures that the molecular segments have sufficient mobility to provide a broad and smooth stress plateau through the gradual collapse of the pores under pressure, while also providing the necessary rigidity to ensure that sufficient initial contact stress can be generated even with small deformations (Hooke's region).

[0066] (3) Stabilizer In the preparation process of the polyurethane buffer sheet described in this invention, a foam stabilizer is required to regulate the cell structure and maintain the stability of the foaming system. This stabilizer belongs to the surfactant category in terms of physicochemical properties, including both non-silicone and silicon compounds. Considering cell uniformity and molding effect, a silicon-based polyurethane foam stabilizer is preferred.

[0067] The amount of stabilizer used is based on the total mass of the polyol and ranges from 0.1% to 10%. This upper limit is not set because exceeding 10% makes it impossible to produce a buffer sheet that meets performance requirements, but rather because excessive amounts of silicon-based stabilizers may cause surface precipitation, affect interfacial properties, and result in uneconomical costs. On the other hand, an amount below 0.1% may lead to insufficient dispersion of the stabilizer in the system, affecting the uniformity and stability of the cell structure. Therefore, a further preferred stabilizer amount is 0.5% to 8%.

[0068] (4) Catalyst To regulate the reaction rate during polyurethane synthesis, especially to meet the specific requirements of atomization processes on the system's curing behavior, a catalyst needs to be added to the formulation. Suitable catalysts include organometallic catalysts and amine catalysts.

[0069] Organometallic catalysts can be categorized into organoiron, organonickel, organotin, organobismuth, organolead, organocobalt, organozirconium, and organozinc metal compounds. Amine catalysts include triethylenediamine, bis(dimethylaminoethyl) ether, cyclohexylmethyl tertiary amine, pentamethyldialkyltriamine, tetramethylalkyldiamine, 2,4,6-tris(dimethylaminomethyl)phenol, 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine, tris(dimethylaminopropyl)amine, N,N-dimethylbenzylamine, N,N-dimethylhexadecylamine, dimethylethanolamine, dimethylaminoethoxyethanol, trimethylhydroxyethylpropanediamine, trimethylhydroxyethylethylenediamine, N,N-bis(dimethylaminopropyl)isopropanolamine, and bicyclic amidine compounds such as 1,8-diazabicyclo[5.4.0]undecene-7, 1,5-diazabicyclo[4.3.0]nonene-5, 1,8-diazabicyclo[5.3.0]decene-7, and 1,4-diazabicyclo[3.3.0]octene-4.

[0070] Based on environmental protection requirements and actual catalytic activity, organonitrogen, organobismuth, or organocobalt compounds with moderate activity under low-temperature conditions are preferred among organometallic catalysts; for amine catalysts, acid-terminated amines or organoamine quaternary ammonium salts can be selected to achieve stable control of the reaction process and reliable assurance of the final product performance.

[0071] (5) Other adjuvants In the preparation of polyurethane buffer sheets for solid-state batteries, other additives can be selectively added according to actual preparation requirements, including one or more of the following: nucleating agents, viscosity modifiers, antioxidants, colorants, crosslinking agents, dispersants, UV absorbers, leveling agents, foaming agents, superdispersants, and water absorbents. Each additive is added to the preparation mixture at appropriate times according to conventional dosage ratios to synergistically ensure the structural performance and application suitability of the polyurethane buffer sheet. Specifically, nucleating agents can refine the cell size, improve the uniformity of cell distribution, and enhance the mechanical stability of the buffer sheet; viscosity modifiers can flexibly control the viscosity of the reaction system to adapt to the requirements of bubble injection, spraying, and coating processes, ensuring processing continuity; antioxidants can inhibit the oxidative degradation of polyurethane molecular chains, delay material aging, and extend the service life of the buffer sheet; colorants can give the product a specific appearance without affecting the core buffering and mechanical properties; crosslinking agents can increase the crosslinking density of molecular chains and optimize the material's compressive strength and resilience; dispersants and superdispersants can promote the uniform dispersion of each component and avoid local performance deviations. UV absorbers can resist UV radiation and prevent material performance degradation; leveling agents can improve coating and molding effects and enhance the surface smoothness of the buffer sheet. Foaming agents can assist in the formation of stable cell structures from physical foaming gases and supplement and regulate cell morphology; water-absorbing agents can adsorb trace amounts of moisture in the system, avoiding adverse effects of moisture on polyurethane reactions and solid-state battery performance.

[0072] [Preparation Method] The method for preparing a polyurethane buffer sheet for solid-state batteries according to the present invention includes the following steps: (1) Preparation of material A Before preparing material A, the polyol is further heated to 80-100℃, and an antioxidant is optionally added for stirring and dispersion. Then, it is distilled under reduced pressure in a sealed tank for 1-5 hours to precisely control the moisture content of the raw materials, ensuring a controllable foaming process and stable final product performance. The polyol is then cooled to room temperature, and all materials are placed in a dry environment at 23±3℃ and relative humidity below 30% for at least 24 hours to ensure that the raw material temperature and moisture content meet the process requirements.

[0073] Add the polyols gradually to the mixing tank according to their viscosity, from low to high. When the added amount reaches 1 / 3 to 2 / 3 of the total mass of polyols, start stirring and control the speed at 200-400 rpm. Optional nucleating agents, viscosity modifiers, or water-absorbing agents can be added. After the addition is complete, continue stirring for 10-20 minutes. Then, add the remaining polyols, stabilizers, and catalysts within 1-3 minutes, and gradually increase the stirring speed to 1000-1500 rpm, continuing stirring for 15-30 minutes. The prepared material needs to be sealed and allowed to stand, if necessary, under nitrogen protection, and allowed to stand for 1-3 hours in a constant temperature and humidity environment of 23±3℃ and humidity below 30% to obtain mixture A.

[0074] (2) Bubble injection The foaming gas is mixed with the aforementioned mixture A in a high-speed, small-gap mixing chamber at a gas-liquid volume ratio of (30-400):100 to form a gas-liquid mixture that maintains a liquid flow state in appearance. Its density is controlled at 0.2-1 g / cm³, preferably 0.5-1 g / cm³, and the density change within 10 minutes does not exceed 120% of the initial value, wherein the maximum bubble size Dmax does not exceed 20 μm.

[0075] (3) Mixing of A and B materials The gas-liquid mixture of material A and the polyisocyanate component of material B in step (2) are mixed in proportion, and optionally, other additives are added to form a reaction system. The viscosity of the reaction system mixture is controlled in the range of 100-600 mPa·s, and the α value of the reaction system satisfies 1066 (mgKOH / g) ≤ α ≤ 1600 (mgKOH / g). The α value is defined as: α = (OHV) （A） *m （A） ) / ([NCO]% （B） *m （B） ) OHV(A) is defined as the mixed hydroxyl value of material A, and the mixed hydroxyl value is defined as follows:

[0076] Where m （A） The OHV of a single material is the total mass of mixture A. （i） It can be obtained by testing according to GB / T 12008.3-2009 (Method A); [NCO]% （B） The NCO content of material B can be obtained by testing according to GB / T 12009.4-2016 (Method A); m （B） This represents the total mass of material B.

[0077] The α value satisfies 1066 (mgKOH / g) ≤ α ≤ 1600 (mgKOH / g), wherein the preferred α value range is 1200 (mgKOH / g) ≤ α ≤ 1467 (mgKOH / g); and a further α value range satisfies 1266 (mgKOH / g) ≤ α ≤ 1400 (mgKOH / g).

[0078] In addition to the antioxidants, nucleating agents, viscosity modifiers or water absorbers mentioned above, other additives may also include one or more of the following: colorants, crosslinking agents, dispersants, ultraviolet absorbers, leveling agents, foaming agents, and superdispersing additives.

[0079] (4) Spraying: The above A / B mixture is transported to the spray gun nozzle by air pressure for atomization and spraying onto the carrier substrate. At the same time, the surface difference of the carrier substrate is less than 0.1μm. The carrier substrate acts as a carrier for polyurethane and also as a "soft mold" for polyurethane cushioning pad, constraining the thickness of the polyurethane cushioning pad and controlling the thickness difference of the polyurethane cushioning pad.

[0080] The spray gun or nozzle atomizes the A / B reaction mixture using high-pressure gas. The atomized particle size must be ≤5μm. The spray width and shape can be adjusted by changing the shape and size of the nozzle. To achieve high flatness and minimal thickness variation, the spray gun is mounted on a movable platform. The platform moves laterally to achieve reciprocating spraying, promoting uniformity and consistency. By adjusting the distance and speed of the spray gun platform's movement, the interval between the nth and n+1th sprays at the same location must not exceed 0.5s to avoid inconsistent reaction rates affecting surface appearance and thickness variation.

[0081] (5) Coating: In the coating stage, the carrier film runs on the drive roller at a certain speed, and the A / B reaction mixture is continuously sprayed onto the carrier film. Then, the thickness is adjusted by a slit device. The flatness of the slit gap meets the range of ±0.03μm, so as to control the thickness and thickness difference. Considering the application scenario of polyurethane buffer sheet and taking into account that gas may escape during the subsequent curing process, which may cause the thickness to become thinner, the thickness of the reaction mixture is controlled at 0.02-1.5mm, and the thickness difference after curing is within 10%.

[0082] (6) Curing: The curing process involves the A / B mixture, after the coating stage, being conveyed into the oven via drive rollers. Under the action of a catalyst, the A / B mixture reacts rapidly to form a cured product. The curing temperature is 100-150°C, and the curing time under heating conditions is 3-20 minutes.

[0083] After the curing step is completed, the polyurethane buffer sheet for solid-state batteries is obtained. It then undergoes processes such as winding, slitting, and encapsulation. Since these processes do not affect the performance of the buffer sheet material itself, they will not be described in detail here.

[0084] The following description uses several embodiments related to the present invention, but it is not intended to limit the present invention to these embodiments.

[0085] Example 1: Raw material pretreatment: Polypropylene glycol (viscosity 210 mPa·s, functionality 2, hydroxyl value 240 mgKOH / g), polypropylene triol (viscosity 500 mPa·s, functionality 3, hydroxyl value 270 mgKOH / g), and high primary hydroxyl content, high EO-terminated polyether triol (viscosity 1500 mPa·s, functionality 3, hydroxyl value 35 mgKOH / g) were heated at 85℃ in a mass ratio of 20:40:40, followed by vacuum distillation at -0.095 MPa for 2 hours in a sealed tank. After cooling to room temperature, all materials were placed in a constant temperature and humidity environment of 25℃ and 25% relative humidity for 24 hours.

[0086] Preparation of Material A: Add the pretreated polyols to the mixing tank in order of increasing viscosity. When the added amount reaches 50% of the total mass, start stirring and maintain a stirring speed of 300 rpm for 15 minutes. Then, add the remaining polyols within 2 minutes, increasing the stirring speed to 1200 rpm and continuing stirring for 20 minutes. Simultaneously, add 5% (by mass) of silicone-based polyurethane foam stabilizer and 0.15% (by mass) of organic bismuth compound catalyst. The prepared materials are then allowed to stand for 2 hours under nitrogen protection at 25°C and 25% humidity to obtain mixed material A.

[0087] Bubble injection: High-purity nitrogen gas is mixed with mixed material A in a high-speed, small-gap mixing chamber at a gas-liquid volume ratio of 150 / 100 to form a gas-liquid mixture, and the maximum bubble size Dmax is controlled to be no greater than 20μm.

[0088] A / B material mixing: The gas-liquid mixture of material A was mixed with modified diphenylmethane diisocyanate with a viscosity of 150 mPa·s, a functionality of 2.3, and an NCO content of 21.5% at a ratio of α=1302 mgKOH / g. The viscosity of the mixture in the reaction system was controlled to be 350 mPa·s (measured 5 min after mixing).

[0089] Spraying operation: The A / B mixture is delivered to the spray gun nozzle by air pressure and atomized, with the atomized particle size controlled at 3μm, and sprayed onto a carrier substrate with a surface difference of ≤±0.05μm. The spray gun is mounted on a movable platform, and the lateral reciprocating motion ensures that the interval between two sprays at the same position is ≤0.3s.

[0090] Coating process: The carrier substrate coated with the reactive mixture is passed through a slit device with a slit gap flatness within ±0.03μm to control the coating thickness to 0.75mm.

[0091] Curing: The coated mixture is cured at 135°C for 7 minutes, and then wound, slit, and packaged to obtain the target polyurethane buffer sheet.

[0092] Example 2 Raw material pretreatment: Polypropylene glycol (viscosity 300 mPa·s, functionality 2, hydroxyl value 240 mgKOH / g), polypropylene triol (viscosity 500 mPa·s, functionality 3, hydroxyl value 270 mgKOH / g), and high primary hydroxyl content, high EO-terminated polyether triol (viscosity 1500 mPa·s, functionality 3, hydroxyl value 35 mgKOH / g) were heated at 85℃ in a mass ratio of 30:60:10, followed by vacuum distillation at -0.095 MPa for 2 hours in a sealed tank. After cooling to room temperature, all materials were placed in a constant temperature and humidity environment of 25℃ and 25% relative humidity for 24 hours.

[0093] Preparation of Material A: Add the pretreated polyols to the mixing tank in order of increasing viscosity. When the added amount reaches 50% of the total mass, start stirring at 300 rpm. Simultaneously add 0.2% (by mass) of polyether-modified polysiloxane viscosity modifier. After adding the materials, continue stirring for 15 minutes. Then, add the remaining polyols within 2 minutes, increasing the stirring speed to 1200 rpm and stirring for another 20 minutes. At the same time, add 8% (by mass) of silicone-based polyurethane foam stabilizer and 0.1% (by mass) of organic bismuth compound catalyst. The prepared materials are then allowed to stand for 2 hours at 25°C and 25% humidity under nitrogen protection to obtain Mixture A.

[0094] Bubble injection: High-purity nitrogen gas is mixed with mixed material A in a high-speed, small-gap mixing chamber at a gas-liquid volume ratio of 200 / 100 to form a gas-liquid mixture, and the maximum bubble size Dmax is controlled to be no greater than 20μm.

[0095] A / B material mixing: The gas-liquid mixture of material A was mixed with modified diphenylmethane diisocyanate with a viscosity of 150 mPa·s, a functionality of 2.3, and an NCO content of 21.5% at a ratio of α=1302 mgKOH / g, and the viscosity of the reaction system mixture was controlled to be 240 mPa·s (measured 5 min after mixing).

[0096] Spraying operation: The A / B mixture is delivered to the spray gun nozzle by air pressure and atomized, with the atomized particle size controlled at 3μm, and sprayed onto a carrier substrate with a surface difference of ≤±0.05μm. The spray gun is mounted on a movable platform, and the lateral reciprocating motion ensures that the interval between two sprays at the same position is ≤0.3s.

[0097] Coating process: The carrier substrate coated with the reactive mixture is passed through a slit device with a slit gap flatness within ±0.03μm to control the coating thickness to 0.05mm.

[0098] Curing: The coated mixture is cured at 135°C for 7 minutes, and then wound, slit, and packaged to obtain the target polyurethane buffer sheet.

[0099] Example 3 Raw material pretreatment: Polypropylene glycol (viscosity 210 mPa·s, functionality 2, hydroxyl value 240 mgKOH / g), polypropylene triol (viscosity 500 mPa·s, functionality 3, hydroxyl value 270 mgKOH / g), and high primary hydroxyl content, high EO-terminated polyether triol (viscosity 1500 mPa·s, functionality 3, hydroxyl value 35 mgKOH / g) were heated at 85℃ in a mass ratio of 20:40:40, followed by vacuum distillation at -0.095 MPa for 2 hours in a sealed tank. After cooling to room temperature, all materials were placed in a constant temperature and humidity environment of 25℃ and 25% relative humidity for 24 hours.

[0100] Preparation of Material A: Add the pretreated polyols to the mixing tank in order of viscosity from low to high. When the added amount reaches 50% of the total mass, start stirring and control the speed at 300 rpm for 15 minutes. Then, add the remaining polyols within 2 minutes, increase the stirring speed to 1200 rpm and continue stirring for 20 minutes. Simultaneously, add 5% of a silicone-based polyurethane foam stabilizer and 0.2% of an organic bismuth compound catalyst, based on the total mass of the polyols. After preparation, let the mixture stand for 2 hours at 25°C and 25% humidity under nitrogen protection to obtain Mixture A.

[0101] Bubble injection: High-purity nitrogen gas is mixed with mixed material A in a high-speed, small-gap mixing chamber at a gas-liquid volume ratio of 100 / 100 to form a gas-liquid mixture, and the maximum bubble size Dmax is controlled to be no greater than 20μm.

[0102] A / B material mixing: The gas-liquid mixture of material A was mixed with modified diphenylmethane diisocyanate with a viscosity of 150 mPa·s, a functionality of 2.1, and an NCO content of 21.5% at a ratio of α=1302 mgKOH / g. The viscosity of the mixture in the reaction system was controlled to be 350 mPa·s (measured 5 min after mixing).

[0103] Spraying operation: The A / B mixture is delivered to the spray gun nozzle by air pressure and atomized, with the atomized particle size controlled at 3μm, and sprayed onto a carrier substrate with a surface difference of ≤±0.05μm. The spray gun is mounted on a movable platform, and the lateral reciprocating motion ensures that the interval between two sprays at the same position is ≤0.3s.

[0104] Coating process: The carrier substrate coated with the reactive mixture is passed through a slit device with a slit gap flatness within ±0.03μm to control the coating thickness to 1.4mm.

[0105] Curing: The coated mixture is cured at 135°C for 7 minutes, and then wound, slit, and packaged to obtain the target polyurethane buffer sheet.

[0106] Example 4 Raw material pretreatment: Polypropylene glycol (viscosity 300 mPa·s, functionality 2, hydroxyl value 240 mgKOH / g), high EO-terminated polyether triol (viscosity 1500 mPa·s, functionality 3, hydroxyl value 35 mgKOH / g), and polypropylene triol (viscosity 300 mPa·s, functionality 3, hydroxyl value 350 mgKOH / g) were heated at 85℃ in a mass ratio of 10:30:60, followed by vacuum distillation at -0.095 MPa for 2 hours in a sealed tank. After cooling to room temperature, all materials were placed in a constant temperature and humidity environment of 25℃ and 25% relative humidity for 24 hours.

[0107] Preparation of Material A: Add the pretreated polyols to the mixing tank in order of increasing viscosity. When the added amount reaches 50% of the total mass, start stirring and maintain a stirring speed of 300 rpm for 15 minutes. Then, add the remaining polyols within 2 minutes, increasing the stirring speed to 1200 rpm and continuing stirring for 20 minutes. Simultaneously, add 3% (by mass) of silicone-based polyurethane foam stabilizer and 0.15% (by mass) of organic amine catalyst. After preparation, allow the mixture to stand for 2 hours at 25°C and 25% humidity under nitrogen protection to obtain Mixture A.

[0108] Bubble injection: High-purity nitrogen gas is mixed with mixed material A in a high-speed, small-gap mixing chamber at a gas-liquid volume ratio of 200 / 100 to form a gas-liquid mixture, and the maximum bubble size Dmax is controlled to be no greater than 20μm.

[0109] A / B material mixing: The gas-liquid mixture of material A was mixed with modified diphenylmethane diisocyanate with a viscosity of 160 mPa·s, a functionality of 2.5, and an NCO content of 30% at a ratio of α=1302 mgKOH / g. The viscosity of the mixture in the reaction system was controlled to be 400 mPa·s (measured 5 min after mixing).

[0110] Spraying operation: The A / B mixture is delivered to the spray gun nozzle by air pressure and atomized, with the atomized particle size controlled at 3μm, and sprayed onto a carrier substrate with a surface difference of ≤±0.05μm. The spray gun is mounted on a movable platform, and the lateral reciprocating motion ensures that the interval between two sprays at the same position is ≤0.3s.

[0111] Coating process: The carrier substrate coated with the reactive mixture is passed through a slit device with a slit gap flatness within ±0.03μm to control the coating thickness to 0.75mm.

[0112] Curing: The coated mixture is cured at 135°C for 7 minutes, and then wound, slit, and packaged to obtain the target polyurethane buffer sheet.

[0113] Example 5 Raw material pretreatment: Polypropylene glycol (viscosity 300 mPa·s, functionality 2, hydroxyl value 240 mgKOH / g), polypropylene triol (viscosity 500 mPa·s, functionality 3, hydroxyl value 270 mgKOH / g), polyether triol (viscosity 1500 mPa·s, functionality 3, hydroxyl value 35 mgKOH / g), and high-viscosity, low-hydroxyl-value polyether polyol (viscosity 2500 mPa·s, functionality 3, hydroxyl value 28 mgKOH / g) were heated at 85℃ in a mass ratio of 20:20:40:20, followed by vacuum distillation at -0.095 MPa for 2 hours in a sealed tank. After cooling to room temperature, all materials were placed in a constant temperature and humidity environment of 25℃ and 25% relative humidity for 24 hours.

[0114] Preparation of Material A: Add the pretreated polyols to the mixing tank in order of increasing viscosity. When the added amount reaches 50% of the total mass, start stirring at 300 rpm. Simultaneously add 0.2% (by mass) of polyether-modified polysiloxane viscosity modifier. After the addition is complete, continue stirring for 15 minutes. Then, add the remaining polyols within 2 minutes, increase the stirring speed to 1200 rpm, and continue stirring for 20 minutes. At the same time, add 3% (by mass) of silicone-based polyurethane foam stabilizer and 0.15% (by mass) of organic amine catalyst. The prepared material is then allowed to stand for 2 hours at 25°C and 25% humidity under nitrogen protection to obtain Mixture A.

[0115] Bubble injection: High-purity nitrogen gas is mixed with mixed material A in a high-speed, small-gap mixing chamber at a gas-liquid volume ratio of 200 / 100 to form a gas-liquid mixture, and the maximum bubble size Dmax is controlled to be no greater than 20μm.

[0116] A / B material mixing: The gas-liquid mixture of material A was mixed with modified diphenylmethane diisocyanate with a viscosity of 150 mPa·s, a functionality of 2.1, and an NCO content of 21.5% at a ratio of α=1302 mgKOH / g. The viscosity of the mixture in the reaction system was controlled to be 350 mPa·s (measured 5 min after mixing).

[0117] Spraying operation: The A / B mixture is delivered to the spray gun nozzle by air pressure and atomized, with the atomized particle size controlled at 3μm, and sprayed onto a carrier substrate with a surface difference of ≤±0.05μm. The spray gun is mounted on a movable platform, and the lateral reciprocating motion ensures that the interval between two sprays at the same position is ≤0.3s.

[0118] Coating process: The carrier substrate coated with the reactive mixture is passed through a slit device with a slit gap flatness within ±0.03μm to control the coating thickness to 0.75mm.

[0119] Curing: The coated mixture is cured at 135°C for 7 minutes, and then wound, slit, and packaged to obtain the target polyurethane buffer sheet.

[0120] Example 6 Raw material pretreatment: Polypropylene glycol (viscosity 300 mPa·s, functionality 2, hydroxyl value 240 mgKOH / g), high EO-terminated polyether triol (viscosity 1500 mPa·s, functionality 3, hydroxyl value 35 mgKOH / g), and polypropylene triol (viscosity 300 mPa·s, functionality 3, hydroxyl value 350 mgKOH / g) were heated at 85°C in a mass ratio of 10:30:60. A hindered phenolic antioxidant (0.1% of the total mass of polyols) was added and stirred to disperse the mixture. Subsequently, the mixture was distilled under reduced pressure at -0.095 MPa for 2 hours in a sealed container. After cooling to room temperature, all materials were placed in a constant temperature and humidity environment at 25°C and 25% relative humidity for 24 hours.

[0121] Preparation of Material A: Add the pretreated polyols to the mixing tank in order of viscosity from low to high. When the added amount reaches 50% of the total mass, start stirring. Simultaneously add 0.15% of the total polyol mass of fumed silica nucleating agent. After the addition is complete, control the stirring speed at 300 rpm for 15 minutes. Then, add the remaining polyols within 2 minutes, increase the stirring speed to 1200 rpm and continue stirring for 20 minutes. At the same time, add 8% of the total polyol mass of silicone-based polyurethane foam stabilizer and 0.15% of the total polyol mass of organic amine catalyst. The prepared material is then allowed to stand for 2 hours at 25°C and 25% humidity under nitrogen protection to obtain Mixture A.

[0122] Bubble injection: High-purity nitrogen gas is mixed with mixed material A in a high-speed, small-gap mixing chamber at a gas-liquid volume ratio of 300 / 100 to form a gas-liquid mixture, and the maximum bubble size Dmax is controlled to be no greater than 20μm.

[0123] A / B material mixing: The gas-liquid mixture of material A was mixed with modified diphenylmethane diisocyanate with a viscosity of 150 mPa·s, a functionality of 2.1, and an NCO content of 21.5% at a ratio of α=1100 mgKOH / g, and the viscosity of the reaction system mixture was controlled to be 240 mPa·s (measured 5 min after mixing).

[0124] Spraying operation: The A / B mixture is delivered to the spray gun nozzle by air pressure and atomized, with the atomized particle size controlled at 3μm, and sprayed onto a carrier substrate with a surface difference of ≤±0.05μm. The spray gun is mounted on a movable platform, and the lateral reciprocating motion ensures that the interval between two sprays at the same position is ≤0.3s.

[0125] Coating process: The carrier substrate coated with the reactive mixture is passed through a slit device with a slit gap flatness within ±0.03μm to control the coating thickness to 0.75mm.

[0126] Curing: The coated mixture is cured at 120°C for 7 minutes, and then wound, slit, and packaged to obtain the target polyurethane buffer sheet.

[0127] Example 7 Raw material pretreatment: Polypropylene glycol (viscosity 210 mPa·s, functionality 2, hydroxyl value 240 mgKOH / g), polypropylene triol (viscosity 500 mPa·s, functionality 3, hydroxyl value 270 mgKOH / g), and high primary hydroxyl content, high EO-terminated polyether triol (viscosity 1500 mPa·s, functionality 3, hydroxyl value 35 mgKOH / g) were heated at 85℃ in a mass ratio of 20:40:40, followed by vacuum distillation at -0.095 MPa for 2 hours in a sealed tank. After cooling to room temperature, all materials were placed in a constant temperature and humidity environment of 25℃ and 25% relative humidity for 24 hours.

[0128] Preparation of Material A: Add the pretreated polyols to the mixing tank in order of increasing viscosity. When the added amount reaches 50% of the total mass, start stirring and maintain a stirring speed of 300 rpm for 15 minutes. Then, add the remaining polyols within 2 minutes, increasing the stirring speed to 1200 rpm and continuing stirring for 20 minutes. Simultaneously, add 5% (by mass) of silicone-based polyurethane foam stabilizer and 0.15% (by mass) of organic bismuth compound catalyst. The prepared materials are then allowed to stand for 2 hours under nitrogen protection at 25°C and 25% humidity to obtain mixed material A.

[0129] Bubble injection: High-purity nitrogen gas is mixed with mixed material A in a high-speed, small-gap mixing chamber at a gas-liquid volume ratio of 50 / 100 to form a gas-liquid mixture, and the maximum bubble size Dmax is controlled to be no greater than 20μm.

[0130] A / B material mixing: The gas-liquid mixture of material A was mixed with modified diphenylmethane diisocyanate with a viscosity of 150 mPa·s, a functionality of 2.3, and an NCO content of 21.5% at a ratio of α=1500 mgKOH / g, and the viscosity of the reaction system mixture was controlled to be 350 mPa·s (measured 5 min after mixing).

[0131] Spraying operation: The A / B mixture is delivered to the spray gun nozzle by air pressure and atomized, with the atomized particle size controlled at 3μm, and sprayed onto a carrier substrate with a surface difference of ≤±0.05μm. The spray gun is mounted on a movable platform, and the lateral reciprocating motion ensures that the interval between two sprays at the same position is ≤0.3s.

[0132] Coating process: The carrier substrate coated with the reactive mixture is passed through a slit device with a slit gap flatness within ±0.03μm to control the coating thickness to 0.2mm.

[0133] Curing: The coated mixture is cured at 135°C for 7 minutes, and then wound, slit, and packaged to obtain the target polyurethane buffer sheet.

[0134] Comparative Example 1 Raw material pretreatment: Polypropylene glycol (viscosity 300 mPa·s, functionality 2, hydroxyl value 240 mgKOH / g), high EO-terminated polyether triol (viscosity 1500 mPa·s, functionality 3, hydroxyl value 35 mgKOH / g), and polypropylene triol (viscosity 300 mPa·s, functionality 3, hydroxyl value 350 mgKOH / g) were heated at 85℃ in a mass ratio of 10:30:60, followed by vacuum distillation at -0.095 MPa for 2 hours in a sealed tank. After cooling to room temperature, all materials were placed in a constant temperature and humidity environment of 25℃ and 25% relative humidity for 24 hours.

[0135] Preparation of Material A: Add the pretreated polyols to the mixing tank in order of viscosity from low to high. When the added amount reaches 50% of the total mass, start stirring and control the speed at 300 rpm for 15 minutes. Then, add the remaining polyols within 2 minutes, increase the stirring speed to 1200 rpm and continue stirring for 20 minutes. Simultaneously, add 5% of the total polyol mass of silicone-based polyurethane foam stabilizer and 0.15% of the organic amine compound catalyst. After preparation, let the mixture stand for 2 hours at 25°C and 25% humidity under nitrogen protection to obtain Mixture A.

[0136] Bubble injection: High-purity nitrogen gas is mixed with mixed material A in a high-speed, small-gap mixing chamber at a gas-liquid volume ratio of 100 / 100 to form a gas-liquid mixture, and the maximum bubble size Dmax is controlled to be no greater than 20μm.

[0137] A / B material mixing: The gas-liquid mixture of material A was mixed with modified diphenylmethane diisocyanate with a viscosity of 150 mPa·s, a functionality of 2.1, and an NCO content of 21.5% at a ratio of α=900 mgKOH / g, and the viscosity of the mixture in the reaction system was controlled to be 290 mPa·s (measured 5 min after mixing).

[0138] Spraying operation: The A / B mixture is delivered to the spray gun nozzle by air pressure and atomized, with the atomized particle size controlled at 3μm, and sprayed onto a carrier substrate with a surface difference of ≤±0.05μm. The spray gun is mounted on a movable platform, and the lateral reciprocating motion ensures that the interval between two sprays at the same position is ≤0.3s.

[0139] Coating process: The carrier substrate coated with the reactive mixture is passed through a slit device with a slit gap flatness within ±0.03μm to control the coating thickness to 0.75mm.

[0140] Curing: The coated mixture is cured at 135°C for 7 minutes, and then wound, slit, and packaged to obtain the target polyurethane buffer sheet.

[0141] Comparative Example 2 Raw material pretreatment: Polypropylene glycol (viscosity 210 mPa·s, functionality 2, hydroxyl value 240 mgKOH / g), polypropylene triol (viscosity 500 mPa·s, functionality 3, hydroxyl value 270 mgKOH / g), and high primary hydroxyl content, high EO-terminated polyether triol (viscosity 1500 mPa·s, functionality 3, hydroxyl value 35 mgKOH / g) were heated at 85℃ in a mass ratio of 20:40:40, followed by vacuum distillation at -0.095 MPa for 2 hours in a sealed tank. After cooling to room temperature, all materials were placed in a constant temperature and humidity environment of 25℃ and 25% relative humidity for 24 hours.

[0142] Preparation of Material A: Add the pretreated polyols to the mixing tank in order of increasing viscosity. When the added amount reaches 50% of the total mass, start stirring and maintain a stirring speed of 300 rpm for 15 minutes. Then, add the remaining polyols within 2 minutes, increasing the stirring speed to 1200 rpm and continuing stirring for 20 minutes. Simultaneously, add 5% (by mass) of silicone-based polyurethane foam stabilizer and 0.15% (by mass) of organic bismuth compound catalyst. The prepared materials are then allowed to stand for 2 hours under nitrogen protection at 25°C and 25% humidity to obtain mixed material A.

[0143] Bubble injection: High-purity nitrogen gas is mixed with mixed material A in a high-speed, small-gap mixing chamber at a gas-liquid volume ratio of 100 / 100 to form a gas-liquid mixture, and the maximum bubble size Dmax is controlled to be no greater than 20μm.

[0144] A / B material mixing: The gas-liquid mixture of material A was mixed with modified diphenylmethane diisocyanate with a viscosity of 150 mPa·s, a functionality of 2.3, and an NCO content of 21.5% at a ratio of α=1700 mgKOH / g, and the viscosity of the mixture in the reaction system was controlled to be 430 mPa·s (measured 5 min after mixing).

[0145] Spraying operation: The A / B mixture is delivered to the spray gun nozzle by air pressure and atomized, with the atomized particle size controlled at 3μm, and sprayed onto a carrier substrate with a surface difference of ≤±0.05μm. The spray gun is mounted on a movable platform, and the lateral reciprocating motion ensures that the interval between two sprays at the same position is ≤0.3s.

[0146] Coating process: The carrier substrate coated with the reactive mixture is passed through a slit device with a slit gap flatness within ±0.03μm to control the coating thickness to 0.75mm.

[0147] Curing: The coated mixture is cured at 135°C for 7 minutes, and then wound, slit, and packaged to obtain the target polyurethane buffer sheet.

[0148] Comparative Example 3 Raw material pretreatment: Polypropylene glycol (viscosity 210 mPa·s, functionality 2, hydroxyl value 240 mgKOH / g), polypropylene triol (viscosity 500 mPa·s, functionality 3, hydroxyl value 270 mgKOH / g), and high primary hydroxyl content, high EO-terminated polyether triol (viscosity 1500 mPa·s, functionality 3, hydroxyl value 35 mgKOH / g) were heated at 85℃ in a mass ratio of 20:40:40, followed by vacuum distillation at -0.095 MPa for 2 hours in a sealed tank. After cooling to room temperature, all materials were placed in a constant temperature and humidity environment of 25℃ and 25% relative humidity for 24 hours.

[0149] Preparation of Material A: Add the pretreated polyols to the mixing tank in order of increasing viscosity. When the added amount reaches 50% of the total mass, start stirring and maintain a stirring speed of 300 rpm for 15 minutes. Then, add the remaining polyols within 2 minutes, increasing the stirring speed to 1200 rpm and continuing stirring for 20 minutes. Simultaneously, add 8% (by mass) of silicone-based polyurethane foam stabilizer and 0.5% (by mass) of organic bismuth compound catalyst. The prepared materials are then allowed to stand for 2 hours at 25°C and 25% humidity under nitrogen protection to obtain mixed material A.

[0150] Bubble injection: High-purity nitrogen gas is mixed with mixed material A in a high-speed, small-gap mixing chamber at a gas-liquid volume ratio of 200 / 100 to form a gas-liquid mixture, and the maximum bubble size Dmax is controlled to be no greater than 20μm.

[0151] A / B material mixing: The gas-liquid mixture of material A was mixed with modified diphenylmethane diisocyanate with a viscosity of 150 mPa·s, a functionality of 2.3, and an NCO content of 21.5% at a ratio of α=1100 mgKOH / g, and the viscosity of the mixture in the reaction system was controlled to be 320 mPa·s (measured 5 min after mixing).

[0152] Spraying operation: The A / B mixture is delivered to the spray gun nozzle by air pressure and atomized, with the atomized particle size controlled at 3μm, and sprayed onto a carrier substrate with a surface difference of ≤±0.05μm. The spray gun is mounted on a movable platform, and the lateral reciprocating motion ensures that the interval between two sprays at the same position is ≤0.3s.

[0153] Coating treatment: The coating thickness is controlled at 0.75mm, and the flatness of the slit gap is not controlled.

[0154] Curing: The coated mixture is cured at 155°C for 7 minutes, and then wound, slit, and packaged to obtain the target polyurethane buffer sheet.

[0155] Comparative Example 4 Raw material pretreatment: Polypropylene glycol (viscosity 210 mPa·s, functionality 2, hydroxyl value 240 mgKOH / g), polypropylene triol (viscosity 500 mPa·s, functionality 3, hydroxyl value 270 mgKOH / g), and high primary hydroxyl content, high EO-terminated polyether triol (viscosity 1500 mPa·s, functionality 3, hydroxyl value 35 mgKOH / g) were heated at 85℃ in a mass ratio of 20:40:40, followed by vacuum distillation at -0.095 MPa for 2 hours in a sealed tank. After cooling to room temperature, all materials were placed in a constant temperature and humidity environment of 25℃ and 25% relative humidity for 24 hours.

[0156] Preparation of Material A: Add the pretreated polyols to the mixing tank in order of increasing viscosity. When the added amount reaches 50% of the total mass, start stirring and maintain a stirring speed of 300 rpm for 15 minutes. Then, add the remaining polyols within 2 minutes, increasing the stirring speed to 1200 rpm and continuing stirring for 20 minutes. Simultaneously, add 0.5% of a silicone-based polyurethane foam stabilizer and 0.03% of an organic bismuth compound catalyst, based on the total mass of the polyols. After preparation, allow the mixture to stand for 2 hours at 25°C and 25% humidity under nitrogen protection to obtain Mixture A.

[0157] Bubble injection: High-purity nitrogen gas is mixed with mixed material A in a high-speed, small-gap mixing chamber at a gas-liquid volume ratio of 300 / 100 to form a gas-liquid mixture, and the maximum bubble size Dmax is controlled to be no greater than 20μm.

[0158] A / B material mixing: The gas-liquid mixture of material A was mixed with modified diphenylmethane diisocyanate with a viscosity of 150 mPa·s, a functionality of 2.3, and an NCO content of 21.5% at a ratio of α=1500 mgKOH / g, and the viscosity of the mixture in the reaction system was controlled to be 390 mPa·s (measured 5 min after mixing).

[0159] Spraying operation: The A / B mixture is delivered to the spray gun nozzle by air pressure and atomized, with the atomized particle size controlled at 3μm, and sprayed onto a carrier substrate with a surface difference of ≤±0.05μm. The spray gun is mounted on a movable platform, and the lateral reciprocating motion ensures that the interval between two sprays at the same position is ≤0.3s.

[0160] Coating process: The carrier substrate coated with the reactive mixture is passed through a slit device with a slit gap flatness within ±0.03μm to control the coating thickness to 0.75mm.

[0161] Curing: The coated mixture is cured at 90°C for 7 minutes, and then wound, slit, and packaged to obtain the target polyurethane buffer sheet.

[0162] Comparative Example 5 Raw material pretreatment: Polypropylene glycol (viscosity 210 mPa·s, functionality 2, hydroxyl value 240 mgKOH / g), polypropylene triol (viscosity 500 mPa·s, functionality 3, hydroxyl value 270 mgKOH / g), and high primary hydroxyl content, high EO-terminated polyether triol (viscosity 1500 mPa·s, functionality 3, hydroxyl value 35 mgKOH / g) were heated at 85℃ in a mass ratio of 20:40:40, followed by vacuum distillation at -0.095 MPa for 2 hours in a sealed tank. After cooling to room temperature, all materials were placed in a constant temperature and humidity environment of 25℃ and 25% relative humidity for 24 hours.

[0163] Preparation of Material A: Add the pretreated polyols to the mixing tank in order of increasing viscosity. When the added amount reaches 50% of the total mass, start stirring and maintain a stirring speed of 300 rpm for 15 minutes. Then, add the remaining polyols within 2 minutes, increasing the stirring speed to 1200 rpm and continuing stirring for 20 minutes. Simultaneously, add 0.1% of a silicone-based polyurethane foam stabilizer and 0.15% of an organic amine catalyst, based on the total mass of the polyols. After preparation, allow the mixture to stand for 2 hours at 25°C and 25% humidity under nitrogen protection to obtain Mixture A.

[0164] Bubble injection: High-purity nitrogen gas is mixed with mixed material A in a high-speed, small-gap mixing chamber at a gas-liquid volume ratio of 100 / 100 to form a gas-liquid mixture, and the maximum bubble size Dmax is controlled to be no greater than 20μm.

[0165] A / B material mixing: The gas-liquid mixture of material A was mixed with modified diphenylmethane diisocyanate with a viscosity of 150 mPa·s, a functionality of 2.3, and an NCO content of 21.5% at a ratio of α=1302 mgKOH / g. The viscosity of the mixture in the reaction system was controlled to be 350 mPa·s (measured 5 min after mixing).

[0166] Spraying operation: The A / B mixture is delivered to the spray gun nozzle by air pressure and atomized, with the atomized particle size controlled at 3μm, and sprayed onto a carrier substrate with a surface difference of ≤±0.05μm. The spray gun is mounted on a movable platform, and the lateral reciprocating motion ensures that the interval between two sprays at the same position is ≤0.3s.

[0167] Coating process: The carrier substrate coated with the reactive mixture is passed through a slit device with a slit gap flatness within ±0.03μm to control the coating thickness to 0.75mm.

[0168] Curing: The coated mixture is cured at 125°C for 7 minutes, and then wound, slit, and packaged to obtain the target polyurethane buffer sheet.

[0169] Comparative Example 6 Raw material pretreatment: Polypropylene glycol (viscosity 210 mPa·s, functionality 2, hydroxyl value 240 mgKOH / g), polypropylene triol (viscosity 500 mPa·s, functionality 3, hydroxyl value 270 mgKOH / g), and high primary hydroxyl content, high EO-terminated polyether triol (viscosity 1500 mPa·s, functionality 3, hydroxyl value 35 mgKOH / g) were heated at 85℃ in a mass ratio of 20:40:40, followed by vacuum distillation at -0.095 MPa for 2 hours in a sealed tank. After cooling to room temperature, all materials were placed in a constant temperature and humidity environment of 25℃ and 25% relative humidity for 24 hours.

[0170] Preparation of Material A: Add the pretreated polyols to the mixing tank in order of increasing viscosity. When the added amount reaches 50% of the total mass, start stirring and maintain a stirring speed of 300 rpm for 15 minutes. Then, add the remaining polyols within 2 minutes, increasing the stirring speed to 1200 rpm and continuing stirring for 20 minutes. Simultaneously, add 5% (by mass) of silicone-based polyurethane foam stabilizer and 0.15% (by mass) of organic bismuth compound catalyst. The prepared materials are then allowed to stand for 2 hours under nitrogen protection at 25°C and 25% humidity to obtain mixed material A.

[0171] Bubble injection: High-purity nitrogen gas is mixed with mixed material A in a high-speed, small-gap mixing chamber at a gas-liquid volume ratio of 10 / 100 to form a gas-liquid mixture, and the maximum bubble size Dmax is controlled to be no greater than 20μm.

[0172] A / B material mixing: The gas-liquid mixture of material A was mixed with modified diphenylmethane diisocyanate with a viscosity of 150 mPa·s, a functionality of 2.3, and an NCO content of 21.5% at a ratio of α=1302 mgKOH / g. The viscosity of the mixture in the reaction system was controlled to be 350 mPa·s (measured 5 min after mixing).

[0173] Spraying operation: The A / B mixture is delivered to the spray gun nozzle by air pressure and atomized, with the atomized particle size controlled at 3μm, and sprayed onto a carrier substrate with a surface difference of ≤±0.05μm. The spray gun is mounted on a movable platform, and the lateral reciprocating motion ensures that the interval between two sprays at the same position is ≤0.3s.

[0174] Coating process: The carrier substrate coated with the reactive mixture is passed through a slit device with a slit gap flatness within ±0.03μm to control the coating thickness to 0.75mm.

[0175] Curing: The coated mixture is cured at 140℃ for 7 minutes, and then wound, slit, and packaged to obtain the target polyurethane buffer sheet.

[0176] Comparative Example 7 Raw material pretreatment: Polypropylene glycol (viscosity 300 mPa·s, functionality 2, hydroxyl value 112 mgKOH / g), polypropylene triol (viscosity 500 mPa·s, functionality 3, hydroxyl value 270 mgKOH / g), polyether triol (viscosity 1500 mPa·s, functionality 3, hydroxyl value 35 mgKOH / g), and high-viscosity, low-hydroxyl-value polyether polyol (viscosity 2500 mPa·s, functionality 3, hydroxyl value 28 mgKOH / g) were heated at 85℃ in a mass ratio of 60:10:10:20, followed by vacuum distillation in a sealed tank at -0.095 MPa for 2 hours. After cooling to room temperature, all materials were placed in a constant temperature and humidity environment of 25℃ and 25% relative humidity for 24 hours.

[0177] Preparation of Material A: Add the pretreated polyols to the mixing tank in order of increasing viscosity. When the added amount reaches 50% of the total mass, start stirring at 300 rpm. Simultaneously add 0.2% (by mass) of polyether-modified polysiloxane viscosity modifier. After the addition is complete, continue stirring for 15 minutes. Then, add the remaining polyols within 2 minutes, increase the stirring speed to 1200 rpm, and continue stirring for 20 minutes. At the same time, add 3% (by mass) of silicone-based polyurethane foam stabilizer and 0.15% (by mass) of organic amine catalyst. The prepared material is then allowed to stand for 2 hours at 25°C and 25% humidity under nitrogen protection to obtain Mixture A.

[0178] Bubble injection: High-purity nitrogen gas is mixed with mixed material A in a high-speed, small-gap mixing chamber at a gas-liquid volume ratio of 200 / 100 to form a gas-liquid mixture, and the maximum bubble size Dmax is controlled to be no greater than 20μm.

[0179] A / B material mixing: The gas-liquid mixture of material A was mixed with modified diphenylmethane diisocyanate with a viscosity of 150 mPa·s, a functionality of 2.1, and an NCO content of 21.5% at a ratio of α=1302 mgKOH / g. The viscosity of the mixture in the reaction system was controlled to be 550 mPa·s (measured 5 min after mixing).

[0180] Spraying operation: The A / B mixture is delivered to the spray gun nozzle by air pressure and atomized, with the atomized particle size controlled at 3μm, and sprayed onto a carrier substrate with a surface difference of ≤±0.05μm. The spray gun is mounted on a movable platform, and the lateral reciprocating motion ensures that the interval between two sprays at the same position is ≤0.3s.

[0181] Coating process: The carrier substrate coated with the reactive mixture is passed through a slit device with a slit gap flatness within ±0.03μm to control the coating thickness to 1.5mm.

[0182] Curing: The coated mixture is cured at 135°C for 7 minutes, and then wound, slit, and packaged to obtain the target polyurethane buffer sheet.

[0183] Comparative Example 8 Raw material pretreatment: Polypropylene glycol (viscosity 300 mPa·s, functionality 2, hydroxyl value 112 mgKOH / g), polypropylene triol (viscosity 500 mPa·s, functionality 3, hydroxyl value 270 mgKOH / g), polyether triol (viscosity 1500 mPa·s, functionality 3, hydroxyl value 35 mgKOH / g), high primary hydroxyl content, high EO-terminated polyether triol (viscosity 1500 mPa·s, functionality 3, hydroxyl value 35 mgKOH / g), and high viscosity, low hydroxyl value polyether polyol (viscosity 2500 mPa·s, functionality 3, hydroxyl value 28 mgKOH / g) were heated at 85℃ in a mass ratio of 20:20:20:40, followed by vacuum distillation at -0.095 MPa for 2 hours in a sealed tank. After cooling to room temperature, all materials were placed in a constant temperature and humidity environment of 25℃ and 25% relative humidity for 24 hours.

[0184] Preparation of Material A: Add the pretreated polyols to the mixing tank in order of increasing viscosity. When the added amount reaches 50% of the total mass, start stirring at 300 rpm. Simultaneously add 0.2% (by mass) of polyether-modified polysiloxane viscosity modifier. After the addition is complete, continue stirring for 15 minutes. Then, add the remaining polyols within 2 minutes, increase the stirring speed to 1200 rpm, and continue stirring for 20 minutes. At the same time, add 3% (by mass) of silicone-based polyurethane foam stabilizer and 0.15% (by mass) of organic amine catalyst. The prepared material is then allowed to stand for 2 hours at 25°C and 25% humidity under nitrogen protection to obtain Mixture A.

[0185] Bubble injection: High-purity nitrogen gas is mixed with mixed material A in a high-speed, small-gap mixing chamber at a gas-liquid volume ratio of 300 / 100 to form a gas-liquid mixture, and the maximum bubble size Dmax is controlled to be no greater than 20μm.

[0186] A / B material mixing: The gas-liquid mixture of material A was mixed with modified diphenylmethane diisocyanate with a viscosity of 150 mPa·s, a functionality of 2.1, and an NCO content of 21.5% at a ratio of α=1302 mgKOH / g. The viscosity of the mixture in the reaction system was controlled to be 1500 mPa·s (measured 5 min after mixing).

[0187] Spraying operation: The A / B mixture is delivered to the spray gun nozzle by air pressure and atomized, with the atomized particle size controlled at 3μm, and sprayed onto a carrier substrate with a surface difference of ≤±0.05μm. The spray gun is mounted on a movable platform, and the lateral reciprocating motion ensures that the interval between two sprays at the same position is ≤0.3s.

[0188] Coating process: The carrier substrate coated with the reactive mixture is passed through a slit device with a slit gap flatness within ±0.03μm to control the coating thickness to 0.2mm.

[0189] Curing: The coated mixture is cured at 135°C for 7 minutes, and then wound, slit, and packaged to obtain the target polyurethane buffer sheet.

[0190] Test method: 1-Plotting compressive stress-strain curves and determining characteristic points Perform the test according to GB / T18942.1 and read the compressive stress-strain curve.

[0191] (1) Data processing and curve plotting (1.1) Stress σ calculation: σ=F / A0, where F is the real-time load (N) and A0 is the initial cross-sectional area of ​​the sample (m²).

[0192] (1.2) Strain ε calculation: ε = Δh / h0 × 100%, where Δh is the real-time displacement (mm) and h0 is the initial average thickness of the sample (mm).

[0193] (1.3) Plot the curve: plot the compressive stress-strain curve with strain ε as the abscissa and stress σ as the ordinate.

[0194] (2) Determination of characteristic parameters (points A and B) Determining point A (the critical point between the Hooke's zone and the smooth zone): In the initial stage of the curve, a linear fit is performed, typically within the range of 0% to 5% strain. Point A is defined as the point where the fitted line deviates significantly from the measured curve. This can be achieved by taking the point where the tangent modulus decreases to 80% of the initial modulus, or by using the "offset method" (offsetting the strain axis by a specific value from the origin, such as 1% strain, and drawing a parallel line). Record the strain εA and stress σA corresponding to point A.

[0195] Determining point B (the critical point between the smooth region and the exponential growth region): Point B is defined as the turning point where the smooth zone ends and the stress begins to rise sharply. It can be determined using the following method: Second derivative method: Find the second derivative of the stress-strain curve, and point B corresponds to the first significant peak point of its second derivative.

[0196] Record the strain εB and stress σB corresponding to point B.

[0197] Calculation of the pressure transformer index M: After obtaining εA, εB, σA, and σB, substitute them into the formula to calculate: .

[0198] 2-Hydroxy value determination The determination was performed according to Method A of GB / T 12008.3-2009.

[0199] 3-NCO content determination, α value determination The determination was performed according to Method A of GB / T 12009.4-2016.

[0200] 4-Viscosity The determination was performed according to Method B of GB / T 12008.7-2010.

[0201] 5-Density Perform the procedure according to GB / T6343. Cut at least three regularly shaped specimens free of visible defects from the finished product. Measure the dimensions of the specimens using a measuring instrument with an accuracy of not less than 0.02 mm and calculate their volume V (cm³). Weigh the specimens using an analytical balance with an accuracy of 0.0001 g, and determine their mass m (g). Calculate the density using the formula ρ = m / V × 10³, and express the result in kg / m³. Take the arithmetic mean of all specimens.

[0202] 6-Cyclic compressive stress retention rate The compressive stress test method was performed according to GB / T18942.1, combined with the cyclic durability requirements. Specimen preparation was the same as for the 1-compressive stress-strain curve. Before the test, a prestress of (100±10) Pa was applied to the specimen and then zeroed. The specimen was compressed to 50% strain at a rate of 50% of its initial thickness per minute, and then unloaded, completing one cycle. This process was repeated 1000 times at a frequency of 1 Hz. The compressive stress values ​​σ1 and σ2 at 50% strain were recorded in the first and 1000th cycles. 1000 The cyclic compressive stress retention rate is calculated using the formula (σ... 1000 Calculate using ( / σ1)×100%.

[0203] 7-Battery capacity retention rate The procedure was performed according to GB / T18287. The solid-state battery integrating the polyurethane buffer sheet of this invention was charged at a constant current and constant voltage of 0.5C to the upper limit voltage at an ambient temperature of 20±5°C, with a cutoff current of 0.05C; subsequently, it was discharged at a constant current of 0.5C to the cutoff voltage. This constitutes one charge-discharge cycle. The discharge capacity C0 of the first cycle was recorded. The battery was subjected to this charge-discharge cycle repeatedly, and the discharge capacity C of the 500th cycle was recorded. 500 Battery capacity retention rate is calculated using the formula (C). 500 Calculate using ( / C0)×100%.

[0204] 8. Thickness and thickness range Proceed in accordance with GB / T 6342-1996.

[0205] The indicators of Examples 1-7 and Comparative Examples 1-8 are shown in the table below:

[0206] It can be seen that the polyurethane buffer sheet of the present invention falls within the range of the adjustable pressure change index M, and εA, εB, σA, σB are significantly better than M in terms of appearance, thickness flatness, cyclic compressive stress retention rate and battery capacity retention rate in Examples 1-7 within the defined range, and in Comparative Examples 1-8 where εA, εB, σA, σB are not within the defined range. This proves that the buffer material designed in the present invention can significantly improve the cycle performance and safety of solid-state batteries.

[0207] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A polyurethane buffer sheet for solid-state batteries, characterized in that, The thickness of the polyurethane buffer sheet in the uncompressed state ranges from 0.02 to 1 mm; the stress-strain curve of the polyurethane buffer sheet shows the Hooke region, the smooth region and the exponential region in sequence as the deformation increases from 0. The critical point between the Hooke region and the smooth region is A, and the critical point between the smooth region and the exponential region is B. εA, εB, σA and σB are the strain and stress values ​​corresponding to A and B, respectively. The polyurethane buffer sheet satisfies the condition that the compressive stress index M is 0.3 ≤ M ≤ 0.9, where the compressive stress index M satisfies the following formula: 。 2. The polyurethane buffer sheet according to claim 1, characterized in that, The polyurethane buffer sheet simultaneously satisfies the following relationship: (1)10%≤ε A ≤25%; (2)35%≤ε B ≤90%; (3)σ A ≥0.2MPa; (4)s B ≤5MPa.

3. The polyurethane buffer sheet according to claim 1, characterized in that, The pressure transformer index M satisfies 0.4≤M≤0.

8.

4. The polyurethane buffer sheet according to claim 1, characterized in that, The polyurethane buffer sheet, in its uncompressed state, has a density ρ 缓 The range is 250-750 kg / m 3 .

5. The polyurethane buffer sheet according to claim 1, characterized in that, The thickness variation of the polyurethane buffer sheet is controlled within 10% of the thickness.

6. The polyurethane buffer sheet according to claim 1, characterized in that, The cyclic compressive stress retention rate of the polyurethane buffer sheet is ≥80%.

7. A method for preparing a polyurethane buffer sheet for solid-state batteries as described in claims 1-6, characterized in that, Includes the following steps: (1) Preparation of A material: Mix polyols of different viscosities with additives including at least nucleating agents and stabilizers, and stir evenly to obtain a mixture of A material; (2) Bubble injection: Physical foaming gas is introduced into material A and mixed at a gas-liquid volume ratio of (30-400):

100. The density of the gas-liquid mixture of material A after mixing is controlled to be 0.2-1 g / cm³, and the maximum bubble size Dmax in the gas-liquid mixture of material A is ≤20μm. (3) Mixing of A and B components: The gas-liquid mixture of component A and the polyisocyanate component B from step (2) are mixed, wherein the viscosity of the reaction mixture is controlled within the range of 100-600 mPa·s. Furthermore, the α value is controlled to satisfy 1066 (mgKOH / g) ≤ α ≤ 1600 (mgKOH / g). The α value is defined as: α = (OHV) （A） *m （A） ) / ([NCO]% （B） *m （B） ) OHV (A) The hydroxyl value of component A is defined as follows: Where m （A） The hydroxyl value (OHV) of a single material is the total mass of mixture A. （i） It can be obtained by testing according to the method in GB / T 12008.3-2009A; [NCO]% （B） The NCO content of material B can be obtained by testing according to method A in GB / T 12009.4-2016. m （B） This refers to the total mass of material B. (4) Spraying: The reaction mixture from step (3) is atomized by a spray gun and sprayed onto a carrier substrate with a surface difference of ≤0.1μm, while controlling the atomized particle size to be ≤5μm; (5) Coating: The carrier substrate sprayed with the reaction system mixture is passed through a slit device with a slit gap flatness of ≤0.03μm to adjust the thickness and thickness difference of the mixture; (6) Curing: The coated mixture is cured at 100-150℃ to obtain a polyurethane buffer sheet for solid-state batteries.

8. The preparation method according to claim 7, characterized in that, In the preparation of material A, polyols of different viscosities are poured into the mixing tank in order of increasing viscosity. When the amount of polyol added reaches 1 / 3 to 2 / 3 of the total amount, stirring is started. After stirring evenly, the remaining polyol, stabilizer and catalyst are added and stirred evenly. The prepared material is then sealed and allowed to stand to obtain the mixture of material A.

9. The preparation method according to claim 8, characterized in that, The specific steps of the sealing and settling process are as follows: the A material mixture prepared in step (1) is sealed under nitrogen protection and placed in a constant temperature and humidity room for 0.5-6 hours, with a constant temperature of 18-30℃ and a humidity of <30%RH.

10. The preparation method according to claim 7, characterized in that, The α value ranges from 1200 (mgKOH / g) ≤ α ≤ 1467 (mgKOH / g).

11. The preparation method according to claim 7, characterized in that, The polyol mixture meets the viscosity range of 150-1000 mPa·s.

12. The preparation method according to claim 7, characterized in that, The viscosity range of the polyisocyanate is 20-1000 mPa·s, and the viscosity range of the mixture after mixing for 3-20 minutes is 200-500 mPa·s.

13. The preparation method according to claim 7, characterized in that, In step (4), the surface difference of the carrier substrate is ≤0.1μm, and in step (5), the thickness of the mixture is controlled between 0.02-1.5mm, and the thickness difference after curing is within 10%.

14. The application of a polyurethane buffer sheet as described in any one of claims 1-6 in a solid-state battery.

Images