Battery cell, method for manufacturing the same, battery device, electric device, and energy storage device

Abstract

The embodiment of the application relates to the field of sodium ion batteries, and provides a battery monomer, a preparation method of the battery monomer, a battery device, a power utilization device and an energy storage device. The gel polymer electrolyte in the battery monomer has a gradient-decreasing elastic modulus along a thickness direction: a high-modulus layer close to a positive plate side provides effective mechanical constraint for deformation of Prussian blue positive electrode particles, and a low-modulus flexible buffer layer close to a diaphragm side absorbs and dissipates macro stress, active matching of an interface stress field generated by a "breathing effect" of the Prussian blue positive electrode is realized, and the cycle stability of a Prussian blue-based sodium ion battery is significantly improved.

Description

Technical Field

[0001] This application relates to the field of batteries, and in particular to a battery cell and its preparation method, a battery device, an electrical device, and an energy storage device. Background Technology

[0002] Sodium-ion batteries have become an ideal candidate technology for large-scale energy storage due to their abundant resources, low cost, and excellent low-temperature performance. Among them, Prussian blue analogues (PBA, whose general formula can be represented as Na) are particularly valuable. x M[M'(CN)6] y •nH₂O (where M and M' are transition metal ions) cathode materials are considered one of the most promising cathode systems for industrialization due to their open three-dimensional cubic framework structure, high theoretical specific capacity, and excellent rate performance. However, during charge and discharge, PBA materials undergo sodium ion insertion / extraction, lattice water / coordination environment rearrangement, local lattice distortion, and possible phase transition evolution, leading to periodic changes in lattice parameters and significant volume changes (i.e., the "breathing effect"). This dynamic volume change induces strong alternating mechanical stress at the electrode / electrolyte interface, causing cathode particle pulverization, debonding from the current collector, and conductive network breakage. It also promotes repeated rupture and reconstruction of the electrolyte interface, ultimately leading to capacity decay and a sharp increase in impedance, severely limiting its long-cycle stability.

[0003] Therefore, there is an urgent need for a novel interface engineering solution that can actively match the gradient stress field of the PBA "breathing effect" and has both mechanical constraint and ion transport capabilities, in order to break through the existing technical bottlenecks and realize the practical application of high cycle life sodium-ion batteries. Summary of the Invention

[0004] This application provides a battery cell and its preparation method, a battery device, an electrical device, and an energy storage device to solve the problem of poor cycle performance of Prussian blue cathode materials in the prior art due to the "breathing effect".

[0005] According to some embodiments of this application, a first aspect of this application provides a battery cell including a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte is disposed at least between the positive electrode and the separator. The electrolyte is a gel polymer electrolyte, and: by weight, the gel polymer electrolyte includes 15 to 60 parts of polymer matrix, 40 to 85 parts of liquid phase component, 0.01 to 1.8 parts of photoinitiator, and 0 to 10 parts of functional additives; the polymer matrix includes cross-linked polymers and linear polymers, and the weight ratio of cross-linked polymers to linear polymers is denoted as W; in the gel polymer electrolyte, the W value on the side closer to the positive electrode is greater than the W value on the side closer to the separator.

[0006] In some embodiments, the elastic modulus of the gel polymer electrolyte near the positive electrode is greater than that of the gel polymer electrolyte near the separator.

[0007] In some embodiments, the polymer matrix comprises 25 to 45 parts by weight of the gel polymer electrolyte; and / or, the crosslinked polymer comprises 5 wt% to 95 wt% by weight of the polymer matrix; and / or, the linear polymer comprises 5 wt% to 95 wt% by weight of the polymer matrix.

[0008] In some embodiments, the thickness direction of the gel polymer electrolyte is denoted as z, the total thickness is L, and z=0 is denoted on the positive electrode side and z=L is denoted on the separator side; in the thickness range from z=0 to z=0.3L~0.4L, the mass fraction of cross-linked polymer in the polymer matrix is ​​50wt%~95wt%; the mass fraction of linear polymer is 5wt%~50wt%; in the thickness range from z=0.3L~0.4L to z=0.6L~0.7L, the mass fraction of cross-linked polymer in the polymer matrix is ​​30wt%~70wt%, and the mass fraction of linear polymer is 30wt%~70wt%; in the thickness range from z=0.6L~0.7L to z=L, the mass fraction of cross-linked polymer in the polymer matrix is ​​5wt%~50wt%; the mass fraction of linear polymer is 50wt%~95wt%.

[0009] In some embodiments, the total thickness of the gel polymer electrolyte is 10 μm to 100 μm; and / or, at 25 ± 2 °C, the sodium ion conductivity of the gel polymer electrolyte is ≥ 0.3 mS / cm; and / or, at 25 ± 2 °C, the electrochemical stability window of the gel polymer electrolyte is ≥ 4.0 V vs. Na / Na. + ; and / or, within a thickness range of z=0 to z=0.3L~0.4L, the elastic modulus of the gel polymer electrolyte at 25±2℃ is 5MPa~200MPa; within a thickness range of z=0.6L~0.7L to z=L, the elastic modulus of the gel polymer electrolyte at 25±2℃ is 0.05MPa~10MPa.

[0010] In some embodiments, the crosslinked polymer is poly(ethylene glycol) diacrylate and / or poly(ethylene glycol) dimethacrylate; and / or, the number-average molecular weight of the crosslinked polymer is 400 g / mol to 1000 g / mol; the linear polymer is poly(ethylene oxide); and / or, the weight-average molecular weight of the linear polymer is 1 × 10⁻⁶. 5 g / mol ~ 1×10 6 g / mol.

[0011] In some embodiments, the liquid phase comprises 55 to 75 parts by weight of the gel polymer electrolyte; and / or, the liquid phase component includes a solvent and a sodium salt, wherein the concentration of the sodium salt in the solvent is 0.5 mol / L to 2.0 mol / L.

[0012] In some embodiments, the solvent is a carbonate solvent; and / or, the sodium salt is selected from one or more of sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, and sodium perchlorate.

[0013] In some embodiments, the content of the photoinitiator is 0.5wt% to 3wt% based on 100% of the total weight of the crosslinked polymer; and / or, the photoinitiator is a free radical photoinitiator.

[0014] In some embodiments, the battery cell uses a Prussian blue analogue as the positive electrode active material, the chemical formula of which is Na. x M[M'(CN)6] y ·nH2O, wherein M is selected from one or more of Fe, Mn, Ni, and Co, M' is selected from one or more of Fe, Mn, and Co, x is 0~2, y is 0.7~1.0, and n is 0~6.

[0015] According to some embodiments of this application, a second aspect of this application provides a method for preparing a battery cell, including a process of setting an electrolyte between a positive electrode and a separator. The process of setting the electrolyte includes: step S1, preparing at least two prepolymer solutions; each prepolymer solution includes a cross-linked polymer, a linear polymer, a liquid phase component, and a photoinitiator, and the W content in each prepolymer solution is different; step S2, coating all the prepolymer solutions onto one side surface of the positive electrode to form a wet film; along the direction away from the positive electrode, the W content in the wet film shows a gradient decreasing trend; step S3, performing UV curing treatment on the wet film to form a gel polymer electrolyte on one side surface of the positive electrode.

[0016] In some embodiments, step S1 includes: preparing prepolymer solution A and prepolymer solution B; prepolymer solution A contains 15wt%~30wt% of crosslinked polymer, 0.2~5wt% of linear polymer, 0.05wt%~1wt% of photoinitiator, and the remainder is liquid phase; prepolymer solution B contains 2wt%~10wt% of crosslinked polymer, 5~20wt% of linear polymer, 0.01wt%~0.3wt% of photoinitiator, and the remainder is liquid phase.

[0017] In some embodiments, in step S2, the coating method is dual-channel gradient coating, and the dual-channel gradient coating includes: feeding prepolymer solution A and prepolymer solution B into a slit coating die through adjacent feeding channels, with prepolymer solution A close to the positive electrode and prepolymer solution B away from the positive electrode; then, forming a liquid film with continuous component transition at the die cavity or outlet using laminar flow, and coating the liquid film onto one side surface of the positive electrode to form a wet film; or, the coating method is sequential coating, and the sequential coating includes: coating prepolymer solution A onto one side surface of the positive electrode to form a first film; after standing treatment, coating prepolymer solution B onto the side surface of the first film away from the positive electrode to form a second film, thereby obtaining a wet film.

[0018] In some embodiments, in step S3, the UV curing process uses a UV wavelength of 350nm~405nm; and / or, the UV curing intensity is 10mW / cm². 2 ~200mW / cm 2 The total curing time is 1 min to 30 min; and / or, the UV curing treatment is carried out in a protective atmosphere at a temperature of 25℃ to 50℃; the protective atmosphere is nitrogen and / or argon; and / or, the UV curing treatment is implemented by one or more of the following methods: digital light processing control, spatial light modulator control, partitioned shading and step-by-step exposure, and light absorber-assisted unilateral irradiation.

[0019] In some embodiments, in step S3, the thickness direction of the wet film is denoted as z1, the total thickness is denoted as L1, and z1=0 is denoted on the positive electrode side. Furthermore, the UV curing process is implemented by digital light processing or spatial light modulator control. The UV curing process includes applying a light intensity of 50 mW / cm² within a thickness range from z1=0 to z=0.3L1~0.4L1 using digital light processing or a spatial light modulator. 2 ~200mW / cm 2 UV light was applied and cured for 5-15 minutes; within the thickness range from z1=0.6L1~0.7L1 to z1=L1, a light intensity of 10mW / cm was applied. 2 ~50mW / cm 2 The UV curing process involves irradiating and curing the wet film with UV light for 3 to 10 minutes; alternatively, the UV curing process can be implemented by partitioned shading and step-by-step exposure. The UV curing process includes: using a shading plate with a width of 0.5L1 to 0.7L1, first exposing the area of ​​the wet film near the positive electrode for 5 to 15 minutes, then removing the shading plate and exposing the entire wet film for 5 to 15 minutes; the light intensity of the first exposure is 50 mW / cm². 2 ~200mW / cm 2 The light intensity of the second exposure was 10 mW / cm².2 ~50mW / cm 2 Alternatively, the UV curing process can be achieved by unilateral irradiation assisted by a light absorber. Step S1 further includes adding 0.05wt%~1wt% of a light absorber to prepolymer solution A and prepolymer solution B respectively. The UV curing process includes unidirectional irradiation of the free surface of the gel polymer electrolyte (i.e., the side away from the positive electrode) with a light intensity of 30mW / cm. 2 ~150mW / cm 2 The UV light utilizes the natural attenuation of light intensity as the wet film thickness forms a cross-linking gradient.

[0020] In some embodiments, step S3 further includes immersing the UV-cured wet film in an electrolyte solution for a duration of 5 to 30 minutes.

[0021] According to some embodiments of this application, a third aspect of this application provides a battery device, including one or more of a battery module, a battery pack, and an energy storage battery, wherein the battery device includes the aforementioned battery cell; or, the battery device includes a battery cell prepared by the aforementioned battery cell preparation method.

[0022] According to some embodiments of this application, a fourth aspect of this application provides an electrical device, including a means for providing electrical energy, wherein the means for providing electrical energy includes the battery device described above.

[0023] According to some embodiments of this application, a fifth aspect of this application provides an energy storage device, including a means for storing electrical energy, wherein the means for storing electrical energy includes the battery device described above.

[0024] The technical solution provided in this application has at least the following advantages: it adopts a gradient modulus gel polymer electrolyte and controls the weight ratio gradient distribution of cross-linked polymers and linear polymers in the thickness direction. The high cross-linking density constraint structure near the positive electrode and the low modulus semi-interpenetrating network buffer layer near the separator achieve the purpose of actively matching the spatial gradient stress field generated by the "breathing effect" of the Prussian blue positive electrode. This achieves the technical effect of suppressing positive electrode particle pulverization and interface cracking, and improving battery cycle stability and rate performance. Attached Figure Description

[0025] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the drawings in the accompanying drawings do not constitute a limitation on scale. In order to more clearly illustrate the technical solutions in the embodiments of this application or in the conventional art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a process flow diagram of setting up the gel polymer electrolyte in the embodiments of this application. Detailed Implementation

[0027] As the background technology shows, Prussian blue cathodes, due to their open framework structure, undergo periodic volume changes (i.e., the "breathing effect") during sodium ion insertion / extraction, accompanied by lattice water / coordination environment rearrangement, local lattice distortion, and possible phase transition evolution. This effect leads to dynamic alternating stress on the cathode particle surface, resulting in a series of problems such as cathode material pulverization, desorption from the current collector, conductive network damage, and repeated cracking of the electrode / electrolyte interface, severely limiting the cycle life and rate performance of Prussian blue-based sodium-ion batteries. Existing technologies mainly focus on research and improvement in the following directions:

[0028] The first type of technology involves bulk modification strategies for cathode materials. Researchers have attempted to reduce lattice defects and water of crystallization content by controlling the synthesis conditions of Prussian blue, or by using metal ion doping (such as Mn, Co, Ni, etc.) to stabilize the crystal structure and reduce the magnitude of volume changes. In addition, coating the surface of Prussian blue particles with carbon materials, oxides, or polymer protective layers is also a common modification method, aiming to provide a physical protective barrier for the particles.

[0029] The second type of technology involves optimizing traditional liquid electrolytes. By adjusting the solvent composition, lithium salt type and concentration, or introducing functional additives, efforts are made to form a more stable cathode-electrolyte interphase (CEI) film on the cathode surface to mitigate electrolyte decomposition and interfacial side reactions. Some studies employ a high-concentration electrolyte strategy to improve interfacial stability.

[0030] The third type of technology involves the application of gel polymer electrolytes (GPE). Compared to liquid electrolytes, GPE offers better mechanical properties and safety, and can provide a certain degree of physical constraint on the electrode surface. Existing GPE technologies mostly employ a homogeneous structure design, meaning that the composition and crosslinking density of the polymer matrix are essentially consistent throughout the entire thickness direction. Mechanical strength and ionic conductivity are balanced by selecting appropriate polymer types (such as PEO, PVDF-HFP, PMMA, etc.) and plasticizers.

[0031] The fourth type of technology involves the introduction of solid-state electrolytes. Some studies explore the use of inorganic solid-state electrolytes or organic-inorganic composite solid-state electrolytes to replace liquid electrolytes, utilizing the high modulus properties of solid-state electrolytes to provide rigid constraint on the electrodes.

[0032] While the aforementioned existing technologies have made some progress in improving the electrochemical performance of Prussian blue cathodes, they still have fundamental limitations in addressing the interfacial mechanical challenges posed by the "breathing effect":

[0033] First, bulk modification strategies for cathode materials cannot fundamentally solve the interfacial stress problem. Although doping or structural optimization can reduce the volume change of Prussian blue to some extent, they cannot completely eliminate the "breathing effect," and residual volume changes will still accumulate interfacial damage during long-term cycling. The surface coating layer is usually a homogeneous thin film structure, which is prone to fatigue cracking under cyclic alternating stress, and the rigid constraint of the coating layer may be mismatched with the volume change of the particles, thus exacerbating stress concentration.

[0034] Secondly, liquid electrolytes cannot provide effective mechanical support. Traditional liquid electrolytes themselves lack mechanical strength and cannot provide any constraint on the expansion and deformation of the cathode particles. Although the chemical stability of the CEI film can be improved through additive optimization, the CEI film, as a nanoscale thin layer, has limited mechanical strength and cannot withstand the stress generated by the volume changes of Prussian blue particles at the micrometer level. Repeated cracking and rebuilding during cycling are inevitable.

[0035] Furthermore, traditional homogeneous GPEs present an inherent contradiction between mechanical properties and ion conduction. Existing gel polymer electrolytes mostly employ a uniform modulus design: increasing crosslinking density to enhance mechanical strength significantly reduces the degree of freedom of polymer chain movement and ionic conductivity; conversely, decreasing crosslinking density to ensure ion transport results in insufficient mechanical constraint. More importantly, homogeneous modulus GPEs cannot adapt to the spatially non-uniform distribution of the stress field on the Prussian blue cathode surface—stress is highest near the particle surface and gradually decreases outwards. Homogeneous GPEs can only "passively withstand" this gradient stress field, easily leading to stress concentration and interfacial delamination at the hard / soft interface.

[0036] Furthermore, while rigid solid electrolytes possess high mechanical strength, they exhibit poor interfacial compatibility with Prussian blue. The rigidity of inorganic solid electrolytes makes them difficult to adapt to changes in the volume of cathode particles, leading to a gradual deterioration of interfacial contact during cycling and a sharp increase in interfacial impedance. Voids and defects at the solid-solid interface also significantly impact ion transport efficiency.

[0037] In summary, the common shortcoming of existing technologies is the lack of a design concept for targeted mechanical matching of the dynamic and non-uniform stress field generated by the "breathing effect" of Prussian blue cathode. This results in the interface stability problem not being fundamentally solved, which restricts the further improvement of the cycle life of Prussian blue-based sodium-ion batteries.

[0038] To address the problem of periodic volume changes (i.e., "breathing effect") caused by lattice water / coordination environment rearrangement, local lattice distortion, and possible phase transition evolution during the charging and discharging process of Prussian blue analog cathodes in sodium-ion batteries, which leads to mechanical mismatch at the cathode interface and deterioration of cycle stability, the first aspect of this application provides a battery cell including a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte is disposed at least between the positive electrode and the separator. The electrolyte is a gel polymer electrolyte, and: by weight, the gel polymer electrolyte includes 15 to 60 parts of polymer matrix, 40 to 85 parts of liquid phase component, 0.01 to 1.8 parts of photoinitiator, and 0 to 10 parts of functional additives; the polymer matrix includes cross-linked polymers and linear polymers, and the weight ratio of cross-linked polymers to linear polymers is denoted as W; in the gel polymer electrolyte, the W value on the side closer to the positive electrode is greater than the W value on the side closer to the separator.

[0039] As mentioned earlier, the stress generated by Prussian blue cathode particles during charging and discharging exhibits a spatial distribution characteristic—the stress is strongest near the particle surface and gradually decreases outwards. Based on this characteristic, this invention designs a gradient modulus GPE structure to match it: the inner layer (near the cathode side) uses a high-crosslink density PEGDA network to form a high-modulus phase, which is tightly bonded to the cathode particles, providing effective mechanical constraint on particle expansion and deformation, and inhibiting pulverization and shedding; the outer layer (near the separator side) uses a semi-interpenetrating network (semi-IPN) structure formed by crosslinked polymers and linear polymers, with a significantly reduced modulus, which acts as a flexible damping layer to absorb and dissipate the macroscopic stress transmitted by the inner layer, protecting the interface integrity between the GPE and the separator / negative electrode. Compared with the homogeneous design of existing technologies, the gradient modulus GPE provided by this invention has the following technical advantages: the continuously changing modulus gradient avoids the stress concentration commonly found at the interface of hard / soft materials, allowing the mechanical stress generated by the "breathing effect" to be smoothly dispersed within the GPE layer; the high modulus constraint of the inner layer and the flexible buffer of the outer layer form a synergistic complement, which can both suppress excessive deformation of the cathode particles and tolerate a certain degree of interface displacement; at the same time, through the coordinated design of polymer composition and crosslinking degree, sufficient sodium ion transport capacity of the overall GPE layer is maintained while achieving the modulus gradient.

[0040] Therefore, this invention proposes a gel polymer electrolyte with a gradient modulus decreasing from the inside (near the positive electrode) to the outside (near the separator), aiming to actively match and effectively buffer the interfacial stress field generated by the "breathing effect" of the Prussian blue positive electrode. The high-modulus inner layer provides mechanical constraint on the positive electrode particles, inhibiting their excessive expansion and pulverization; the low-modulus outer layer acts as a flexible damping layer to absorb and dissipate macroscopic stress, maintaining interfacial integrity. Through this mechanical gradient design, the cycle stability of Prussian blue-based sodium-ion batteries at medium to high rates is significantly improved while ensuring sodium-ion transport performance, providing reliable technical support for large-scale energy storage applications. Specifically:

[0041] The mechanical constraint effect of the high W value region (near the positive electrode side): Cross-linked polymers form a three-dimensional cross-linked network, and its network density is positively correlated with the W value. A high W value near the positive electrode indicates high polymer cross-linking density, low chain segment freedom, and high elastic modulus in this region. When the Prussian blue positive electrode undergoes local expansion due to periodic volume changes during charging and discharging, this high-modulus layer can apply directional mechanical constraint to the surface of the positive electrode particles, inhibiting excessive expansion and relative displacement between particles, thereby effectively mitigating the initiation of microcracks and particle pulverization caused by volume changes. The stress dissipation effect of the low W value region (near the separator side): Linear polymers do not form cross-linked networks, and their long-chain structure endows the material with high flexibility and low modulus. A low W value near the separator indicates low cross-linking density, active chain segment movement, and low modulus in this region, forming a flexible buffer layer. When the positive electrode expansion stress is transmitted to the interior of GPE through the high modulus layer, the low modulus region can absorb and dissipate macroscopic stress energy, reduce the concentrated propagation of stress to the separator / negative electrode interface, and prevent the overall layered structure of GPE from delamination or peeling due to stress accumulation.

[0042] Because the W value decreases continuously in the thickness direction, stress concentration and interface debonding caused by abrupt changes in modulus, as seen in traditional multilayer structures, are avoided. This gradient design enables the non-uniform stress field generated by the "breathing effect" to be smoothly transmitted and gradually attenuated within the GPE, maintaining the integrity of the electrode / electrolyte interface without compromising the ion transport path.

[0043] In general, the technical solution provided by this invention has the following advantages:

[0044] Firstly, the interface stability is significantly improved: the gradient modulus structure effectively suppresses the pulverization, shedding and interface cracking of Prussian blue cathode particles, maintains the integrity of the conductive network and the stability of interface contact, and improves the cycle life of the battery.

[0045] Secondly, it has an outstanding stress buffering effect: the continuous modulus gradient enables a smooth transition and effective dissipation of stress, avoiding the accumulation of fatigue damage caused by stress concentration.

[0046] Third, it has good applicability at medium and high rates: while ensuring mechanical properties, it maintains good ion transport capabilities and meets the electrochemical kinetic requirements of high-rate (e.g., 1~5C rate) cycling.

[0047] In practical applications, to avoid ambiguity, the distance between the positive electrode and the separator is denoted as d. When the distance between any point in the gel polymer electrolyte and the positive electrode is less than 0.5d, it is considered to be closer to the positive electrode; and when the distance between any point in the gel polymer electrolyte and the separator is less than 0.5d, it is considered to be closer to the separator.

[0048] In some embodiments, the elastic modulus of the gel polymer electrolyte near the positive electrode is greater than that near the separator. This preferred method designs a mechanical gradient structure for the GPE, specifically targeting the "breathing effect" stress mode of the Prussian blue positive electrode. Specifically, the inner high-modulus cross-linked network is tightly bonded to the positive electrode material particles, suppressing particle expansion and pulverization; the outer low-modulus semi-IPN structure acts as a damping layer to dissipate macroscopic stress. This, in turn, promotes a more synergistic interface system between the GPE and the positive electrode, thereby significantly improving the cycle stability of the battery.

[0049] In some embodiments, W decreases gradually from the positive electrode side to the separator side; the elastic modulus of the gel polymer electrolyte also decreases gradually from the positive electrode side to the separator side. In this preferred embodiment, the gradual decrease in W value means that the crosslinking density decreases continuously along the thickness direction, which directly leads to a continuous decrease in the elastic modulus. This continuous gradient avoids the existence of discrete interlayer interfaces, thereby eliminating stress concentration points caused by abrupt changes in stiffness in traditional multilayer structures, allowing the mechanical stress generated by the "breathing effect" to be smoothly transmitted and dissipated step by step within the GPE without resistance. Furthermore, this significantly improves the dynamic stability of the interface and extends the cycle life of the battery cell.

[0050] In some embodiments, the polymer matrix comprises 25 to 45 parts by weight of the gel polymer electrolyte; and / or, the crosslinked polymer comprises 5 wt% to 95 wt% by weight of the polymer matrix; and / or, the linear polymer comprises 5 wt% to 95 wt% by weight of the polymer matrix. These preferred ranges ensure that the polymer matrix proportion in the GPE is sufficient to form a continuous and stable network structure, reducing structural collapse or ion channel interruption due to excessively low content.

[0051] In some embodiments, the thickness direction of the gel polymer electrolyte is denoted as z, the total thickness is L, and z=0 is denoted on the positive electrode side and z=L is denoted on the separator side; within the thickness range of z=0 to z=0.3L~0.4L, the mass fraction of cross-linked polymer in the polymer matrix is ​​50wt%~95wt%, preferably 70wt%~90wt%; the mass fraction of linear polymer is 5wt%~50wt%, preferably 10wt%~30wt%; within the thickness range of z=0.3L~0.4L to z=0.6L~0.7L... The mass fraction of cross-linked polymer in the polymer matrix is ​​30wt%~70wt%, preferably 40wt%~60wt%, and the mass fraction of linear polymer is 30wt%~70wt%, preferably 40wt%~60wt%. In the thickness range from z=0.6L~0.7L to z=L, the mass fraction of cross-linked polymer in the polymer matrix is ​​5wt%~50wt%, preferably 10wt%~30wt%, and the mass fraction of linear polymer is 50wt%~95wt%, preferably 70wt%~90wt%.

[0052] In the aforementioned preferred embodiment, within the thickness range of z=0 to z=0.3L~0.4L, the higher content of cross-linked polymers results in a high-crosslink density three-dimensional network structure in this region, exhibiting a high elastic modulus. Within the thickness range of z=0.6L~0.7L to z=L, the higher content of linear polymers results in a semi-IPN structure where low-crosslinked polymer networks and linear polymer chains interpenetrate, significantly reducing the modulus and exhibiting flexibility and elasticity. Within the thickness range of z=0.3L~0.4L to z=0.6L~0.7L, i.e., the intermediate transition region, located between the inner and outer layers, the content of cross-linked and linear polymers varies monotonically or nearly monotonically along the z-direction, causing the modulus to continuously decrease from the inner to the outer layer, forming a smooth gradient transition and avoiding stress concentration at the hard / soft interface. Meanwhile, by rationally designing the thickness ratio of each layer and the content of its components, Pareto optimization of mechanical stability and ionic conductivity was better achieved at the overall GPE level—obtaining a sufficient modulus gradient to match interfacial stress while maintaining the overall ionic conductivity at a practical level to meet the requirements of medium-to-high rate cycling. Ultimately, this resulted in a battery cell with better performance, especially superior long-cycle stability.

[0053] Furthermore, within the thickness range of z=0 to z=0.3L~0.4L, W ranges from 1 to 19; within the thickness range of z=0.3L~0.4L to z=0.6L~0.7L, W ranges from 0.4 to 2.3; and within the thickness range of z=0.6L~0.7L to z=L, W ranges from 0.05 to 1. This gradient design of W values ​​further enhances the significance of the modulus difference between the inner and outer layers of the GPE, and the numerical range is more reasonable. This ensures clear functional differentiation while maintaining superior structural integrity, resulting in a gel polymer electrolyte with more stable structural and mechanical properties.

[0054] It should be noted that the mass fractions of the two polymers and the W values ​​within the thickness range of z=0.3L~0.4L to z=0.6L~0.7L are average values.

[0055] In some embodiments, the total thickness of the gel polymer electrolyte is 10 μm to 100 μm, preferably 20 μm to 50 μm, to better balance mechanical support and low ion transport impedance. At 25 ± 2 °C, the sodium ion conductivity of the gel polymer electrolyte is ≥0.3 mS / cm, more preferably ≥0.5 mS / cm, thus better meeting the requirements for high-rate applications. At 25 ± 2 °C, the electrochemical stability window of the gel polymer electrolyte is ≥4.0 V vs. Na / Na. + This allows for better compatibility with cathode materials.

[0056] Meanwhile, within a thickness range of z=0 to z=0.3L~0.4L, the elastic modulus of the gel polymer electrolyte at 25±2℃ is 5MPa~200MPa, preferably 20MPa~100MPa; within a thickness range of z=0.6L~0.7L to z=L, the elastic modulus of the gel polymer electrolyte at 25±2℃ is 0.05MPa~10MPa, preferably 0.1MPa~5MPa. Let E_inner be the elastic modulus of the gel polymer electrolyte within the thickness range of z=0 to z=0.3L~0.4L, and E_outer be the elastic modulus within the thickness range of z=0.6L~0.7L to z=L; E_inner / E_outer ≥ 5, more preferably E_inner / E_outer ≥ 10. The aforementioned optimization of modulus-related parameters enables the gradient GPE provided by this invention to achieve mechanical matching without sacrificing electrochemical performance, further realizing synergistic optimization of mechanics and electrochemistry.

[0057] In some embodiments, the crosslinking polymer is poly(ethylene glycol) diacrylate (PEGDA) and / or poly(ethylene glycol) dimethacrylate (PEGDMA). The acrylate groups at both ends of the PEGDA molecule can undergo free radical polymerization under the action of a photoinitiator, forming a three-dimensional crosslinked network, which endows GPE with better mechanical strength and structural stability. Preferably, the crosslinking polymer has a number-average molecular weight of 400 g / mol to 1000 g / mol, meaning that its molecular chains are shorter, its reactivity is higher, and its crosslinking point density is larger, resulting in a denser and more rigid network structure. This significantly improves the elastic modulus of the GPE near the positive electrode side, more effectively confining the local expansion in the "breathing effect" of the Prussian blue positive electrode.

[0058] In some embodiments, the linear polymer is poly(ethylene oxide) (PEO); and / or, the weight-average molecular weight of the linear polymer is 1 × 10⁻⁶. 5 g / mol ~ 1×10 6 g / mol. Among them, the long-chain structure of high molecular weight PEO can form a more stable semi-IPN structure with the PEGDA network, which can reduce the local modulus while maintaining structural integrity, and provide ether oxygen segment coordination channels for sodium ion transport, thereby further optimizing the performance of the obtained battery cell.

[0059] Further, in some embodiments, the crosslinked polymer is poly(ethylene glycol) diacrylate; and / or, the linear polymer is poly(ethylene oxide); more preferably, the number-average molecular weight of the crosslinked polymer is 700 ± 50 g / mol; and / or, the weight-average molecular weight of the linear polymer is 5 × 10⁻⁶ g / mol. 5 g / mol ~ 7 × 10 5 g / mol. In this preferred embodiment, when the number-average molecular weight of PEGDA is 700±50 g / mol, its crosslinking network density and chain segment fluidity achieve a better balance—ensuring both high modulus of the inner layer to effectively constrain the cathode particles and avoiding excessive crosslinking that could lead to decreased solvent absorption or ion channel blockage; when the PEO Mw is 5×10 5 g / mol ~ 7 × 10 5 At g / mol, the degree of long-chain entanglement and ether oxygen density can better synergistically enhance sodium ion mobility, resulting in higher overall conductivity of GPE. Simultaneously, it ensures sufficient tear resistance and interfacial adhesion of the outer layer even at low crosslinking density. The combination of these two specific polymers maximizes the synergistic effect of mechanical and ion transport properties in the resulting gel polymer electrolyte, significantly improving the cycle stability of the battery cell.

[0060] In some embodiments, the liquid phase is preferably 55 to 75 parts by weight of the gel polymer electrolyte to facilitate more complete dissolution of the sodium salt and allow the polymer matrix to swell sufficiently, forming a more uniform gel network without dry areas. Furthermore, to ensure that the GPE maintains its gradient mechanical structure while also promoting efficient migration of sodium ions in both the inner highly cross-linked region and the outer lowly cross-linked region, thereby further improving the rate performance of the battery cell, the liquid phase component preferably includes a solvent and a sodium salt, with the sodium salt concentration in the solvent being 0.5 mol / L to 2.0 mol / L, more preferably 0.8 mol / L to 1.5 mol / L.

[0061] In some embodiments, the solvent is a carbonate solvent, which has a high dielectric constant and moderate polarity, enabling more effective dissociation of the sodium salt and stabilization of the sodium ion solvation shell, thereby improving ionic conductivity. Preferably, the sodium salt is selected from one or more of sodium trifluoromethanesulfonate (NaOTf), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), and sodium perchlorate (NaClO4). Among these, NaOTf exhibits superior electrochemical stability and better film-forming ability within the aforementioned concentration range, while also showing better compatibility with the PBA cathode.

[0062] Furthermore, the carbonate solvent includes ethylene carbonate (EC) and diethyl carbonate (DEC), wherein the volume ratio of ethylene carbonate to diethyl carbonate is preferably (3~7):(7~3), more preferably (4~6):(6~4), and even more preferably (0.8~1.2):(0.8~1.2). This progressively preferred solvent system combines the high dielectric constant of EC (promoting salt dissociation) with the low viscosity of DEC (enhancing ion migration rate), resulting in better sodium ion transport kinetics in the GPE, thereby further improving the various electrical properties of the battery cell. Even more preferably, the carbonate solvent also includes propylene carbonate and / or ethyl methyl carbonate, which, as a co-solvent, can further improve the low-temperature performance and interfacial wettability of the GPE.

[0063] In some embodiments, to promote a more efficient and complete crosslinking reaction, achieve a more precise construction of the high crosslinking density of the GPE inner layer, and facilitate the effective formation of the gradient modulus, preferably, the content of the photoinitiator is 0.5wt% to 3wt% based on 100% of the total weight of the crosslinked polymer; and / or, the photoinitiator is a free radical photoinitiator. Specifically, the photoinitiator is selected from one or more of 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropanone, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

[0064] To more effectively suppress linear polymer crystallization and improve the low-temperature ionic conductivity of GPE, the preferred functional additives are selected from one or more of succinic anhydride, polyethylene glycol, and ionic liquids. The number-average molecular weight of the polyethylene glycol is preferably 200-1000; the ionic liquid is specifically selected from one or more of N-butyl-N-methylpyrrolidone bis(fluorosulfonyl)imide, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0065] In some embodiments, the battery cell uses a Prussian blue analogue as the positive electrode active material, the chemical formula of which is Na. x M[M'(CN)6] y ·nH₂O, wherein M is selected from one or more of Fe, Mn, Ni, and Co, M' is selected from one or more of Fe, Mn, and Co, x is 0~2, y is 0.7~1.0, and n is 0~6. Further, the preferred chemical formula of the Prussian blue analogue is Na. x Fe[Fe(CN)6], where x is 0.5~2. Within this chemical formula range, its crystal structure is more stable, its specific capacity is higher, and its reversibility is better, enabling it to form a more stable mechano-electrochemical synergistic system with gradient GPE.

[0066] In practical applications, besides Prussian blue analogues, layered oxides (such as Na) can also be used as the positive electrode. x Positive electrode materials include MO2 series and polyanionic types (such as Na3V2(PO4)3, NaFePO4). Negative electrode materials can include hard carbon, soft carbon, sodium metal, and sodium alloys. The separator can be commercial polypropylene (PP) separator, polyethylene (PE) separator, PP / PE / PP three-layer composite separator, or ceramic-coated separator. The battery system provided by this invention can utilize a reasonable combination of any one or more of the above materials. The operating temperature range of the resulting battery is generally 0~55℃, preferably 10~55℃. The rated operating voltage is 2.0~3.9V vs. Na / Na. + The design range is 1~5 C.

[0067] According to some embodiments of this application, a second aspect of this application provides a method for preparing a battery cell, such as... Figure 1As shown, the process includes setting an electrolyte between a positive electrode and a separator. The process includes: step S1, preparing at least two prepolymer solutions; each prepolymer solution includes a cross-linked polymer, a linear polymer, a liquid phase component, and a photoinitiator, and the W content in each prepolymer solution is different; step S2, coating all the prepolymer solutions onto one side surface of the positive electrode to form a wet film; along the direction away from the positive electrode, the W content in the wet film decreases in a gradient trend; step S3, performing UV curing treatment on the wet film to form a gel polymer electrolyte on one side surface of the positive electrode.

[0068] Regarding the GPE in the aforementioned battery cells, this invention provides a corresponding preparation method. In the preparation process, at least two prepolymer solutions with different W values ​​are prepared, coated to form a W-gradient wet film, and then UV-cured to form the GPE. Through multi-component solution coating, the spatial distribution of components can be precisely controlled, allowing the W value to continuously decrease along the thickness direction, enabling industrial-scale preparation without complex equipment. Furthermore, the preparation method provided by this invention employs UV curing technology, which is simple and controllable, with flexible and diverse gradient control methods, possessing the potential for industrial-scale expansion.

[0069] In some embodiments, step S1 includes: preparing prepolymer solution A and prepolymer solution B; prepolymer solution A contains 15wt%~30wt% crosslinked polymer, 0.2~5wt% linear polymer, 0.05wt%~1wt% photoinitiator, and the remainder is liquid phase; prepolymer solution B contains 2wt%~10wt% crosslinked polymer, 5~20wt% linear polymer, 0.01wt%~0.3wt% photoinitiator, and the remainder is liquid phase. In the formulations of the two prepolymer solutions, prepolymer solution A has a high W value and prepolymer solution B has a low W value, thereby stably constructing a gradient structure with a high modulus inner layer and a low modulus outer layer. At the same time, the differences between the two solution components are significant but not extreme, allowing for a smooth transition between layers during coating, and also promoting higher efficiency and structural uniformity in gradient formation.

[0070] To minimize the impact of moisture and thus better maintain the stability of the cathode structure and the integrity of the GPE electrochemical window, it is preferable that the preparation processes of both prepolymer solution A and prepolymer solution B are carried out under a protective atmosphere, with the H2O content in the protective atmosphere ≤10ppm. Specifically, the protective atmosphere can be argon.

[0071] In step S1 above, it is preferable to dissolve the linear polymer in prepolymer solution A and prepolymer solution B at a temperature of 40°C to 60°C, so as to promote more complete dissolution of the linear polymer, reduce GPE structural defects caused by undissolved particles, and at the same time avoid polymer degradation, thereby further improving the component uniformity of gradient GPE.

[0072] In some embodiments, step S2 involves a dual-channel gradient coating process, which includes: feeding prepolymer solution A and prepolymer solution B into a slit coating die through adjacent feed channels, with prepolymer solution A closer to the positive electrode and prepolymer solution B further away; then, forming a continuously transitioning liquid film at the die cavity or outlet using laminar flow, and coating the liquid film onto one side surface of the positive electrode to form a wet film. In this preferred embodiment, dual-channel gradient coating is used to form a continuously transitioning wet film using laminar flow. This process is direct, efficient, and scalable, effectively promoting a continuous decrease in the W value with thickness, eliminating discrete interfaces, and ultimately yielding a GPE with superior performance.

[0073] In other embodiments, step S2 involves sequential coating, which includes: coating prepolymer solution A onto one side surface of the positive electrode to form a first film; and after a settling period, coating prepolymer solution B onto the side surface of the first film away from the positive electrode to form a second film, thereby obtaining a wet film. In this preferred embodiment, by step-by-step coating and settling, solutions A and B undergo controllable molecular-level diffusion at the interface, forming a quasi-gradient structure with continuous component transition. During the settling process, some linear polymers and solvents are allowed to migrate slowly between the two layers, thereby further reducing interfacial abruptness and stress concentration caused by direct stacking of hard / soft layers, thus stably achieving a thickness transition from high to low W values.

[0074] In some embodiments, in step S3, the UV light wavelength used for the UV curing treatment is preferably 350 nm to 405 nm, more preferably 365 ± 5 nm, thereby more efficiently initiating the free radical polymerization of the crosslinked polymer and achieving a more stable crosslinked network construction. The preferred UV curing light intensity is 10 mW / cm². 2 ~200mW / cm 2 The total curing time is 1 min to 30 min, more preferably 5 min to 15 min, to facilitate sufficient cross-linking in the inner layer of GPE while maintaining moderate cross-linking in the outer layer. This reduces embrittlement caused by insufficient or excessive cross-linking, resulting in battery cells with more stable cycle performance. To more effectively suppress oxygen polymerization and improve the uniformity and integrity of the cross-linking reaction, UV curing is preferably carried out in a protective atmosphere at a temperature of 25°C to 50°C; the protective atmosphere is preferably nitrogen and / or argon.

[0075] In practical applications, UV curing is achieved through one or more of the following methods: digital light processing control, spatial light modulator control, zoned shading and step-by-step exposure, and light absorber-assisted unilateral irradiation. More specifically:

[0076] In step S3, the thickness direction of the wet film is denoted as z1, the total thickness is denoted as L1, and z1=0 is denoted on the positive electrode side, and:

[0077] In some embodiments, the UV curing process is implemented by digital light processing or spatial light modulator control. The UV curing process includes applying light with an intensity of 50 mW / cm² within a thickness range from z1=0 to z=0.3L1~0.4L1 using digital light processing or a spatial light modulator. 2 ~200mW / cm 2 UV light was applied and cured for 5-15 minutes; within the thickness range from z1=0.6L1~0.7L1 to z1=L1, a light intensity of 10mW / cm was applied. 2 ~50mW / cm 2 The cells are then irradiated with UV light and cured for 3 to 10 minutes. This preferred approach directly controls the cumulative light dose to different depth regions through optimized light intensity and time. High light intensity combined with long irradiation significantly increases the cross-linking density of the inner layer, forming a high-modulus region; low light intensity combined with short irradiation results in a lower degree of cross-linking in the outer layer, maintaining flexibility. This achieves non-contact and precise spatial modulus design, ultimately optimizing the cycle performance of the resulting battery cell.

[0078] In some embodiments, the UV curing process is implemented by partitioned shading and step-by-step exposure. The UV curing process includes: using a shading plate with a width of 0.5L1~0.7L1, first exposing the area of ​​the wet film near the positive electrode for 5min~15min, then removing the shading plate and exposing the entire wet film for 5min~15min; the light intensity of the first exposure is 50mW / cm². 2 ~200mW / cm 2 The light intensity of the second exposure was 10 mW / cm². 2 ~50mW / cm 2 The preferred scheme described above achieves phased control of energy input through a physical mask, allowing the inner layer to receive a higher total light dose and the outer layer to receive a lower total light dose, thereby forming a crosslinking density gradient. This scheme does not require a complex optical system; gradient curing can be achieved simply through mechanical shielding, resulting in stronger process compatibility and the ability to stably obtain a structure with a highly crosslinked inner layer and a low-crosslinked outer layer.

[0079] In some embodiments, the UV curing treatment is implemented by unidirectional irradiation assisted by a light absorber. Step S1 further includes adding 0.05wt%~1wt% of a light absorber to prepolymer solution A and prepolymer solution B respectively. The UV curing treatment includes unidirectional irradiation of the free surface of the gel polymer electrolyte (i.e., the side away from the positive electrode) with a light intensity of 30mW / cm². 2 ~150mW / cm 2The UV light is used to create a crosslinking gradient by utilizing the natural attenuation of light intensity with the thickness of the wet film. Preferably, the light absorber is selected from one or more of benzotriazole UV absorbers and benzophenone UV absorbers. In the above preferred embodiment, UV light is unidirectionally irradiated from the free surface of the gel polymer electrolyte (i.e., the side away from the positive electrode). The light absorber causes the UV light intensity to naturally attenuate along the thickness direction. Since the concentration of crosslinked polymers in the prepolymer solution near the positive electrode is significantly higher than that near the membrane (approximately 3-4 times), even if the UV dose is lower near the positive electrode, its absolute crosslinking density is still much higher than that near the membrane, and the contribution of the component gradient to the modulus gradient is dominant. The role of the light absorber is to prevent the low content of crosslinked polymers near the membrane from being over-crosslinked, thereby maintaining the low modulus characteristics and flexible buffering function of the outer layer. This solution does not require additional light control equipment, significantly simplifying equipment requirements.

[0080] In the aforementioned implementation schemes, while achieving a polymer composition gradient based on the spatial gradient change in the weight ratio of the two polymers, a crosslinking density gradient is further achieved during the preparation process through spatial modulation of the UV light dose. The superposition and synergistic enhancement of these two gradient mechanisms allow for more precise control of the modulus distribution curve of the GPE in the thickness direction. More importantly, this dual control results in a continuous gradient transition rather than discrete layering, thus avoiding stress concentration at the hard / soft interface. This allows the stress generated by the "breathing effect" to be smoothly dispersed within the GPE, significantly optimizing the cycle stability of the battery cells.

[0081] In some embodiments, step S3 further includes wetting the UV-cured wet film in an electrolyte solution for 5 to 30 minutes. Since the GPE curing process may result in uneven local pore size due to polymer network shrinkage, the preferred wetting conditions described above can fill micropores, improve ion channel connectivity, further homogenize the distribution of residual solvent and sodium salt within the GPE, and promote interfacial wetting between the GPE and the cathode material, thereby further enhancing the sodium ion conductivity of the resulting GPE.

[0082] In practical applications, the electrolyte includes a solvent and a sodium salt, with the sodium salt concentration in the solvent ranging from 0.5 mol / L to 2.0 mol / L. The solvent is a carbonate-based solvent. More preferably, the composition of the electrolyte used for wetting is consistent with the liquid phase composition of the GPE, so as to facilitate solvent exchange or component migration during wetting without chemical potential differences, reducing cracking or modulus imbalance caused by the expansion / contraction of the GPE structure. This more effectively achieves interface stability and structural integrity, ultimately resulting in a superior gradient structure.

[0083] In addition, Prussian blue cathode sheets may optionally undergo surface pretreatment before coating the prepolymer solution, including but not limited to: vacuum drying to remove surface moisture, slight compaction to improve surface smoothness, plasma treatment to enhance surface polarity and wettability, or coating with an extremely thin undercoat to improve the adhesion between the prepolymer and the cathode material.

[0084] The assembly of the battery includes: assembling the prepared Prussian blue positive electrode sheet with a gradient GPE layer, the separator, and the hard carbon negative electrode in sequence; using a stacking or winding process to make the cell; and then, after conventional processes such as aluminum-plastic film encapsulation, vacuum drying, replenishing electrolyte (if necessary), and formation aging, obtaining the finished sodium-ion battery.

[0085] According to some embodiments of this application, a third aspect of this application provides a battery device, including one or more of a battery module, a battery pack, and an energy storage battery. The battery device includes the aforementioned battery cell; or, the battery device includes a battery cell prepared by the aforementioned battery cell preparation method. The battery cell provided by this invention, through a gradient modulus gel polymer electrolyte, effectively alleviates the interfacial alternating stress caused by periodic volume changes during sodium ion insertion / extraction at the Prussian blue cathode, thereby significantly reducing the cumulative damage at the electrode / electrolyte interface, and thus enabling the battery device to have a longer cycle life.

[0086] According to some embodiments of this application, a fourth aspect of this application provides an electrical device, including a means for providing electrical energy, wherein the means for providing electrical energy includes the aforementioned battery device. The GPE in the battery cell provided by this invention can effectively suppress the pulverization of positive electrode particles and interface cracking, significantly improving cycle stability, and enabling the electrical device containing the battery to have better capacity retention and service life under long-term, high-power operation conditions.

[0087] According to some embodiments of this application, a fifth aspect of this application provides an energy storage device, including a means for storing electrical energy, wherein the means for storing electrical energy includes the aforementioned battery device. The battery cells provided by this invention can maintain excellent capacity retention during multiple cycles and have a stable operating voltage window, meeting the core requirements of energy storage systems for long-term cycling, low degradation, and high safety.

[0088] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0089] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0090] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0091] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0092] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0093] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0094] In the accompanying drawings corresponding to the embodiments of this application, the thickness and area of ​​the layers are enlarged for better understanding and ease of description. When describing a component (such as a layer, film, region, or substrate) on or on the surface of another component, the component may be "directly" located on the surface of the other component, or there may be a third component between the two components. Conversely, when describing a component on the surface of another component, or when another component is formed or disposed on the surface of a component, it indicates that there is no third component between the two components. Furthermore, when describing a component as being "generally" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor is it formed on a portion of the edge of the entire surface.

[0095] In the description of the embodiments of this application, when a component "includes" another component, other components are not excluded unless otherwise stated, and other components may be further included. Furthermore, when a component such as a layer, film, region, or plate is referred to as being "on / located" on another component, it can be "directly on" the other component (i.e., located on the surface of the other component with no other components between them), or another component may be present therein. Moreover, when a component such as a layer, film, region, or plate is "directly located" on another component, or when a component such as a layer, film, region, or plate is located on the surface of another component, it indicates that no other components are located therein.

[0096] The terminology used in the description of the various embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various embodiments and the appended claims, the term "part" is also intended to include the plural form unless the context clearly indicates otherwise. Components include layers, films, regions, or plates, etc.

[0097] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0098] Example 1

[0099] A method for preparing a Prussian blue-based sodium-ion battery:

[0100] This embodiment uses a Prussian blue positive electrode sheet, wherein the positive electrode active material is Na. x Fe[Fe(CN)6], where x is 1.8. Before preparing the electrolyte layer, it can be pretreated by vacuum drying at 120℃ for 2 hours.

[0101] (1) Prepare two prepolymer solutions:

[0102] Prepolymer solution A (high modulus side formulation): Based on the total mass of the solution, the content of poly(ethylene glycol) diacrylate (PEGDA, number average molecular weight of 700 g / mol) is 22 wt%, and the content of poly(ethylene oxide) (PEO, weight average molecular weight of 6 × 10⁻⁶) is 10⁻⁶. 5 The content of PEGDA is 2wt%, and the remainder is a mixed solvent of ethylene carbonate and diethyl carbonate (EC / DEC=1:1) (containing dissolved sodium trifluoromethanesulfonate, concentration 1.0mol / L) and photoinitiator 2,2-dimethoxy-2-phenylacetophenone (DMPA) (1.5wt% of the mass of PEGDA).

[0103] Prepolymer solution B (low modulus side formulation): Based on the total mass of the solution, the content of poly(ethylene glycol) diacrylate (PEGDA) is 5wt%, the content of poly(ethylene oxide) (PEO) is 15wt%, and the rest is consistent with that of prepolymer solution A.

[0104] The preparation processes of prepolymer solution A and prepolymer solution B were both carried out under argon gas with an H2O content ≤10ppm. Simultaneously, the PEO powder should be pre-dissolved in a portion of the solvent at 40℃~60℃, and stirred thoroughly until homogeneous and transparent before being mixed with other components.

[0105] (2) Dual-channel gradient coating: Prepolymer solution A and prepolymer solution B are fed into the slit coating die through adjacent feeding channels, with prepolymer solution A close to the positive electrode and prepolymer solution B far away from the positive electrode. Then, a liquid film with continuous component transition is formed in the inner cavity or outlet of the die using laminar flow. The liquid film is coated on one side surface of the positive electrode to form a wet film.

[0106] (3-1) The wet film is cured in argon gas at 30℃ using ultraviolet light with a wavelength of 365nm, causing PEGDA to undergo free radical polymerization to form a cross-linked network and a gel polymer electrolyte (GPE). A spatial gradient of light dose is introduced during the curing process to enhance the modulus gradient effect. Specific method:

[0107] First, denote the thickness direction of the wet film as z1, the total thickness as L1, and note that z1=0 on the positive electrode side. Then, using digital light processing (DLP), apply light with an intensity of 100 mW / cm² within the thickness range from z1=0 to z=0.35L1. 2 UV light was applied and cured for 10 minutes; within a thickness range from z1=0.65L1 to z1=L1, light with an intensity of 25mW / cm² was applied using digital light processing or a spatial light modulator. 2 Expose to UV light and cure for 5 minutes.

[0108] (3-2) Prepare an electrolyte with the same liquid phase composition as the prepolymer solution A, and briefly immerse the positive electrode with the GPE layer in it (15 min) to homogenize the distribution of solvent and sodium salt inside the GPE and improve the interfacial wettability between GPE and the positive electrode material.

[0109] (4) The prepared Prussian blue positive electrode with gradient GPE layer is assembled with the separator and hard carbon negative electrode in sequence, and the cell is made by stacking or winding process. After conventional processes such as aluminum-plastic film encapsulation, vacuum drying, replenishing electrolyte (if necessary), formation and aging, the finished sodium-ion battery is obtained.

[0110] In the resulting battery, a 35 μm thick GPE layer is disposed between the positive electrode and the separator, which includes 34 wt% polymer matrix (of which PEGDA is 16.5 wt% and PEO is 17.5 wt%), 65 wt% liquid phase component, 0.25 wt% photoinitiator and 0.75 wt% functional additives.

[0111] Let z be the thickness direction of the gel polymer electrolyte, and L be the total thickness. Let z=0 on the positive electrode side and z=L on the separator side. In the thickness direction, the contents of PEGDA and PEO satisfy the following:

[0112] Within a thickness range from z=0 to z=0.35L, PEGDA is 85wt%, PEO is 15wt%, and the ratio W is 5.67.

[0113] Within a thickness range of z = 0.35L to 0.65L, PEGDA is 45wt% and PEO is 55wt%, with a ratio W of 0.82.

[0114] Within a thickness range from z=0.65L to z=L, PEGDA is 15wt%, PEO is 85wt%, and the ratio W is 0.18.

[0115] Example 2

[0116] A method for preparing a Prussian blue-based sodium-ion battery:

[0117] This embodiment uses a Prussian blue positive electrode sheet, which is consistent with that of Embodiment 1.

[0118] (1) Prepare two prepolymer solutions:

[0119] Prepolymer solution A (high modulus side formulation): Based on the total mass of the solution, the content of poly(ethylene glycol) diacrylate (PEGDA, number average molecular weight of 700 g / mol) is 25 wt%, and the content of poly(ethylene oxide) (PEO, weight average molecular weight of 6 × 10⁻⁶) is 25 wt%. 5The content of PEGDA is 1 wt%, and the remainder is a mixed solvent of ethylene carbonate and diethyl carbonate (EC / DEC=1:1) (containing dissolved sodium trifluoromethanesulfonate, concentration 1.0 mol / L) and photoinitiator 2-hydroxy-2-methyl-1-phenylpropanone (Darocur 1173) (2.0 wt% of PEGDA mass).

[0120] Prepolymer solution B (low modulus side formulation): Based on the total mass of the solution, the content of poly(ethylene glycol) diacrylate (PEGDA) is 4wt%, the content of poly(ethylene oxide) (PEO) is 18wt%, and the rest is consistent with that of prepolymer solution A.

[0121] The preparation processes of prepolymer solution A and prepolymer solution B were both carried out under argon gas with an H2O content ≤10ppm. Simultaneously, the PEO powder should be pre-dissolved in a portion of the solvent at 40℃~60℃, and stirred thoroughly until homogeneous and transparent before being mixed with other components.

[0122] (2) Sequential coating: Prepolymer solution A is coated on one side surface of the positive electrode to form a first film with a thickness of about 12 μm to 14 μm; after a standing treatment of 3 min, prepolymer solution B is coated on the side surface of the first film away from the positive electrode to form a second film with a thickness of about 16 μm to 18 μm, thus obtaining a wet film.

[0123] (3-1) The ultraviolet light wavelength and curing conditions were as described in Example 1, specifically using zoned shading and step-by-step exposure:

[0124] First, denote the thickness direction of the wet film as z1, the total thickness as L1, and note that z1=0 on the positive electrode side. Using a light-shielding plate with a width of 0.6L1, first expose the area of ​​the wet film near the positive electrode side to light for 8 minutes at a light intensity of 80mW / cm². 2 The first exposure was performed, followed by removal of the light-blocking plate, and the entire wet film was exposed for 5 minutes at a light intensity of 20 mW / cm². 2 The second exposure.

[0125] (3-2) is consistent with Example 1.

[0126] (4) Consistent with Example 1.

[0127] In the resulting battery, a 30 μm thick GPE layer is disposed between the positive electrode and the separator, which includes 33 wt% polymer matrix (of which PEGDA is 16.3 wt% and PEO is 16.7 wt%), 66 wt% liquid phase component, 0.33 wt% photoinitiator and 0.67 wt% functional additives.

[0128] Let z be the thickness direction of the gel polymer electrolyte, and L be the total thickness. Let z=0 on the positive electrode side and z=L on the separator side. In the thickness direction, the contents of PEGDA and PEO satisfy the following:

[0129] Within a thickness range from z=0 to z=0.4L, PEGDA is 88wt% and PEO is 12wt%, with a ratio W of 7.33.

[0130] In the thickness range of z=0.4L to 0.65L, PEGDA is 40wt% and PEO is 60wt%, with a ratio W of 0.67.

[0131] Within a thickness range from z=0.65L to z=L, PEGDA is 12wt% and PEO is 88wt%, with a ratio W of 0.14.

[0132] Example 3

[0133] A method for preparing a Prussian blue-based sodium-ion battery:

[0134] This embodiment uses a Prussian blue positive electrode sheet, which is consistent with that of Embodiment 1.

[0135] (1) Prepare two prepolymer solutions:

[0136] Prepolymer solution A (high modulus side formulation): Based on the total mass of the solution, the content of poly(ethylene glycol) diacrylate (PEGDA, number average molecular weight of 700 g / mol) is 20 wt%, and the content of poly(ethylene oxide) (PEO, weight average molecular weight of 6 × 10⁻⁶) is 10 wt%. 5 The content of PEGDA is 3wt%, the content of light absorber 2-hydroxy-4-methoxybenzophenone (UV-9) is 0.3wt%, and the remainder is a mixed solvent of ethylene carbonate and diethyl carbonate (EC / DEC=1:1) (containing dissolved sodium trifluoromethanesulfonate, concentration 1.0mol / L) and photoinitiator bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (Irgacure 819) (1.0wt% of PEGDA mass).

[0137] Prepolymer solution B (low modulus side formulation): Based on the total mass of the solution, the content of poly(ethylene glycol) diacrylate (PEGDA) is 6wt%, the content of poly(ethylene oxide) (PEO) is 12wt%, the content of light absorber 2-hydroxy-4-methoxybenzophenone (UV-9) is 0.15wt%, and the rest is consistent with prepolymer solution A.

[0138] The preparation processes of prepolymer solution A and prepolymer solution B were both carried out under argon gas with an H2O content ≤10ppm. Simultaneously, the PEO powder should be pre-dissolved in a portion of the solvent at 40℃~60℃, and stirred thoroughly until homogeneous and transparent before being mixed with other components.

[0139] (2) Dual-channel gradient coating: consistent with Example 1.

[0140] (3-1) The ultraviolet light wavelength and curing conditions were as described in Example 1, specifically using a light absorber-assisted unilateral irradiation: UV light with an intensity of 80 mW / cm² was unidirectionally irradiated from the free surface of the gel polymer electrolyte (i.e., the side away from the positive electrode), utilizing the natural decay of light intensity with the thickness of the wet film to form a crosslinking gradient. The total curing time was controlled at 12 min, and the curing temperature was 35 °C. Since the concentration of crosslinked polymer in prepolymer solution A was significantly higher than that in prepolymer solution B (approximately 3 to 4 times), even under lower UV dose conditions, the absolute crosslinking density near the positive electrode side was still much higher than that near the membrane side, and the contribution of the component gradient to the modulus gradient was dominant.

[0141] (3-2) is consistent with Example 1.

[0142] (4) Consistent with Example 1.

[0143] In the resulting battery, a 40 μm thick GPE layer is disposed between the positive electrode and the separator, which includes 31 wt% polymer matrix (of which PEGDA is 14.9 wt% and PEO is 16.1 wt%), 68 wt% liquid phase component, 0.15 wt% photoinitiator and 0.85 wt% functional additives.

[0144] Let z be the thickness direction of the gel polymer electrolyte, and L be the total thickness. Let z=0 on the positive electrode side and z=L on the separator side. In the thickness direction, the contents of PEGDA and PEO satisfy the following:

[0145] Within a thickness range from z=0 to z=0.35L, PEGDA is 80wt%, PEO is 20wt%, and the ratio W is 4.00.

[0146] Within a thickness range of z = 0.35L to 0.7L, PEGDA is 42wt% and PEO is 58wt%, with a ratio W of 0.72.

[0147] Within the thickness range from z=0.7L to z=L, PEGDA is 18wt%, PEO is 82wt%, and the ratio W is 0.22.

[0148] Example 4

[0149] The results are largely the same as in Example 1, except that the total thickness of the GPE layer is changed to 20 μm. The thinner GPE layer reduces the ion transport impedance, but the mechanical buffering effect is slightly weakened.

[0150] Example 5

[0151] The results are largely the same as in Example 1, except that the total GPE thickness is changed to 50 μm. The thicker GPE layer enhances the mechanical buffering effect, but the increased ion transport path leads to a slight decrease in conductivity.

[0152] Example 6

[0153] The experiment is largely the same as in Example 1, except that the sodium salt is changed from sodium trifluoromethanesulfonate (NaOTf) to sodium bis(fluorosulfonyl)imide (NaFSI), while maintaining the concentration at 1.0 mol / L. NaFSI has a higher degree of ionic dissociation, which is beneficial for improving conductivity.

[0154] Example 7

[0155] The study was largely the same as in Example 1, except that the sodium salt concentration was increased from 1.0 mol / L to 1.5 mol / L. The higher salt concentration increased the number of charge carriers, but also increased the solution viscosity.

[0156] Example 8

[0157] The method is basically the same as in Example 1, except that the solvent system is changed from EC / DEC = 1:1 (volume ratio) to EC / DEC = 3:7 (volume ratio). The increased DEC ratio reduces the solvent viscosity, which is beneficial for ion migration.

[0158] Example 9

[0159] The results are largely the same as in Example 1, except that the number-average molecular weight of PEGDA is changed from 700 g / mol to 400 g / mol. The lower molecular weight PEGDA has shorter chain segments and a higher density of crosslinking points, forming a denser network structure. This significantly improves the elastic modulus of the inner layer, but reduces the ionic conductivity.

[0160] Example 10

[0161] This is basically the same as Example 1, except that the weight-average molecular weight of PEO is 6 × 10⁻⁶. 5 g / mol changed to 1×10 5 g / mol. Lower molecular weight PEO chains exhibit reduced entanglement and increased outer layer flexibility, but the mechanical integrity of the semi-IPN structure is slightly reduced.

[0162] Example 11

[0163] The results are largely the same as in Example 1, except that 3 wt% succinate (SN) is added as a functional additive to prepolymer solutions A and B, respectively. SN can effectively inhibit the crystallization of PEO and improve the room temperature ionic conductivity of GPE.

[0164] Example 12

[0165] The method is basically the same as in Example 1, except that 5 wt% of N-butyl-N-methylpyrrolidone bis(fluorosulfonyl)imide salt (Pyr) is added to prepolymer solutions A and B respectively. 14 FSI (Fluorescent Silicate) ionic liquids are used as functional additives. Ionic liquids can broaden the electrochemical stability window and improve interfacial compatibility.

[0166] Comparative Example 1

[0167] Homogeneous high-modulus GPE was used: the polymer matrix contained 90wt% PEGDA and 10wt% PEO, uniformly distributed throughout the thickness direction without a gradient structure. The solvent, sodium salt, photoinitiator, and curing conditions remained consistent with Example 1, but UV curing was performed using a uniform light intensity of 100 mW / cm². 2 Full irradiation for 10 minutes. The resulting GPE has a total thickness of 35 μm, an overall elastic modulus of approximately 95 MPa, and an ionic conductivity of 0.31 mS / cm.

[0168] Comparative Example 2

[0169] Homogeneous low-modulus GPE was used: the polymer matrix contained 15wt% PEGDA and 85wt% PEO, uniformly distributed throughout the thickness direction without a gradient structure. All other conditions remained consistent with Comparative Example 1. The resulting GPE had a total thickness of 35μm, an overall elastic modulus of approximately 1.8MPa, and a sodium ion conductivity of 0.89mS / cm.

[0170] Comparative Example 3

[0171] The GPE prepolymer solution A / B with only component gradient and no UV gradient was used. The composition was the same as in Example 1, and the dual-channel gradient coating method was the same as in Example 1. However, the UV curing was performed with a uniform light intensity of 50 mW / cm². 2 Full irradiation for 8 minutes, without localized dose adjustment. The resulting GPE total thickness is 35 μm, E_inner is approximately 45 MPa, E_outer is approximately 3.5 MPa, and E_inner / E_outer = 12.9.

[0172] Comparative Example 4

[0173] A conventional liquid electrolyte (1.0 mol / L NaOTf dissolved in EC / DEC = 1:1) is used, and no gel polymer electrolyte layer is placed between the positive electrode and the separator. The positive electrode material, negative electrode material, separator, and battery assembly process are consistent with those in Example 1. The liquid electrolyte does not have mechanical restraint capabilities and cannot provide any mechanical support for the expansion and deformation of the positive electrode particles.

[0174] Comparative Example 5

[0175] The design is essentially the same as in Example 1, except that the gradient directions are reversed: prepolymer solution A (high PEGDA content) is located away from the positive electrode, while prepolymer solution B (high PEO content) is located closer to the positive electrode. That is, the side closer to the positive electrode has a low modulus, and the side closer to the separator has a high modulus. This reverse gradient design keeps the high-modulus region away from the surface of the positive electrode particles, which requires mechanical constraint, while the low-modulus region cannot effectively constrain the stress generated by the positive electrode breathing effect.

[0176] Test methods

[0177] Sodium ion conductivity of the gel polymer electrolyte: obtained by electrochemical impedance spectroscopy (EIS) based on the symmetrical barrier electrode structure of SS|GPE|SS.

[0178] Electrochemical stability window of gel polymer electrolyte: Based on the SS|GPE|Na half-cell structure, it was obtained by linear sweep voltammetry (LSV) at a scan rate of 1 mV / s and a test temperature of 25 ± 2 ℃.

[0179] The elastic modulus E_inner of the gel polymer electrolyte in the thickness range from z=0 to z=0.3L~0.4L is obtained by cutting GPE into cross-sectional samples along the thickness direction, performing quasi-static indentation tests on the cross-section using a nanoindenter (Berkovich diamond indenter), with a maximum load of 1~10mN and the same loading-holding-unloading rate. At least 5 indentation points are taken near the positive electrode side (z=0~0.3L region), and the reduced elastic modulus is calculated according to the Oliver-Pharr method and the average value is taken. The test temperature is 25±2℃.

[0180] The elastic modulus E_outer of the gel polymer electrolyte is obtained by testing the average reduced elastic modulus of at least 5 indentation points in the thickness range from z=0.6L~0.7L to z=L, according to the same test method as E_inner. The difference is that the indentation position is near the diaphragm side (in the z=0.7L~L region).

[0181] Electrical performance testing of battery samples: The batteries were first activated by 3 cycles at a 0.1C rate under a constant temperature environment of 25±2℃, and then at a 1C rate (1C corresponds to the theoretical specific capacity of the positive electrode active material) at 2.0~3.9V (vs. Na / Na).+ A constant current charge-discharge cycle test was performed within the voltage range, and the ratio of the discharge capacity of the 500th cycle to the discharge capacity of the 1st cycle (1C) was recorded. This ratio is the capacity retention rate (%) after 500 cycles.

[0182] The test results are shown in Table 1.

[0183] Table 1

[0184]

[0185] As can be seen from the above description, the embodiments of the present invention use a gradient modulus gel polymer electrolyte and achieve the purpose of actively matching the spatial gradient stress field generated by the "breathing effect" of the Prussian blue cathode by regulating the weight ratio gradient distribution of cross-linked polymer and linear polymer in the thickness direction, thereby suppressing cathode particle pulverization and interface cracking, and ultimately significantly improving the cycle stability and rate performance of the battery.

[0186] Specifically, in each embodiment: the gradient modulus GPEs provided in Examples 1-12 all exhibited significantly better cycling stability than the comparative examples. Examples 1-3 verified the effectiveness of three different UV curing methods; Examples 4 and 5 showed that good gradient effects could be achieved within the GPE thickness range of 20-50 μm; Examples 6-8 verified the applicability of different sodium salt and solvent systems; Examples 9 and 10 verified the applicability of PEGDA and PEO with different molecular weights; Examples 11 and 12 verified the further optimization effect of functional additives on performance. Comparative Examples 1 and 2 showed that homogeneous GPE, regardless of whether it was high or low modulus, could not effectively match the stress generated by the breathing effect; Comparative Example 3 showed that a dual gradient (component + UV) was superior to a single component gradient; Comparative Example 4 showed that the liquid electrolyte could not provide mechanical support; Comparative Example 5 showed that a reverse gradient not only failed to improve but actually deteriorated cycling performance.

[0187] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of this application. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A battery cell, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is disposed at least between the positive electrode and the separator, characterized in that, The electrolyte is a gel polymer electrolyte, and: By weight, the gel polymer electrolyte comprises 15 to 60 parts of polymer matrix, 40 to 85 parts of liquid phase component, 0.01 to 1.8 parts of photoinitiator and 0 to 10 parts of functional additives. The polymer matrix includes a cross-linked polymer and a linear polymer, and the weight ratio of the cross-linked polymer to the linear polymer is denoted as W; in the gel polymer electrolyte, the W value on the side closer to the positive electrode is greater than the W value on the side closer to the separator.

2. The battery cell according to claim 1, characterized in that, The elastic modulus of the gel polymer electrolyte closer to the positive electrode is greater than that of the gel polymer electrolyte closer to the separator.

3. The battery cell according to claim 2, characterized in that, Based on the weight parts of the gel polymer electrolyte, the polymer matrix comprises 25 to 45 parts by weight; and / or, In the polymer matrix, the mass fraction of the crosslinked polymer is 5 wt% to 95 wt%; and / or, In the polymer matrix, the mass fraction of the linear polymer is 5 wt% to 95 wt%.

4. The battery cell according to any one of claims 1 to 3, characterized in that, Let z be the thickness direction of the gel polymer electrolyte, L be the total thickness, and let z=0 on the positive electrode side and z=L on the diaphragm side. Within a thickness range of z=0 to z=0.3L~0.4L, the mass fraction of the cross-linked polymer in the polymer matrix is ​​50wt%~95wt%; the mass fraction of the linear polymer is 5wt%~50wt%. Within a thickness range of z = 0.3 L ~ 0.4 L to z = 0.6 L ~ 0.7 L, the mass fraction of the cross-linked polymer in the polymer matrix is ​​30 wt% ~ 70 wt%, and the mass fraction of the linear polymer is 30 wt% ~ 70 wt%. Within a thickness range from z=0.6L to 0.7L to z=L, the mass fraction of the cross-linked polymer in the polymer matrix is ​​5wt% to 50wt%; the mass fraction of the linear polymer is 50wt% to 95wt%.

5. The battery cell according to claim 4, characterized in that, The total thickness of the gel polymer electrolyte is 10 μm to 100 μm; and / or, At 25±2℃, the sodium ion conductivity of the gel polymer electrolyte is ≥0.3 mS / cm; and / or, At 25±2℃, the electrochemical stability window of the gel polymer electrolyte is ≥4.0V vs. Na / Na. + ; and / or, Within a thickness range of z=0 to z=0.3L~0.4L, the elastic modulus of the gel polymer electrolyte at 25±2℃ is 5MPa~200MPa. The elastic modulus of the gel polymer electrolyte is 0.05 MPa to 10 MPa in the thickness range from z=0.6L to 0.7L to z=L at 25±2℃.

6. The battery cell according to any one of claims 1 to 3, characterized in that, The cross-linked polymer is one or more of poly(ethylene glycol) diacrylate and / or poly(ethylene glycol) dimethacrylate; and / or, the number average molecular weight of the cross-linked polymer is 400 g / mol to 1000 g / mol; The linear polymer is poly(ethylene oxide); and / or, the weight-average molecular weight of the linear polymer is 1 × 10⁻⁶. 5 g / mol ~ 1×10 6 g / mol.

7. The battery cell according to any one of claims 1 to 3, characterized in that, Based on the weight parts of the gel polymer electrolyte, the liquid phase comprises 55 to 75 parts by weight; and / or, The liquid phase component includes a solvent and a sodium salt, wherein the concentration of the sodium salt in the solvent is 0.5 mol / L to 2.0 mol / L.

8. The battery cell according to claim 7, characterized in that, The solvent is a carbonate solvent; and / or the sodium salt is selected from one or more of sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, and sodium perchlorate.

9. The battery cell according to any one of claims 1 to 3, characterized in that, The content of the photoinitiator is 0.5wt% to 3wt% based on the total weight of the crosslinked polymer (100%); and / or the photoinitiator is a free radical photoinitiator.

10. The battery cell according to any one of claims 1 to 3, characterized in that, The battery cell uses a Prussian blue analogue as the positive electrode active material, and the chemical formula of the Prussian blue analogue is Na. x M[M'(CN)6] y ·nH2O, wherein M is selected from one or more of Fe, Mn, Ni, and Co, M' is selected from one or more of Fe, Mn, and Co, x is 0~2, y is 0.7~1.0, and n is 0~6.

11. A method for preparing a battery cell according to any one of claims 1 to 10, comprising the process of disposing of the electrolyte between the positive electrode and the separator, characterized in that, The process of setting the electrolyte includes: Step S1: Prepare at least two prepolymer solutions; each prepolymer solution includes the crosslinked polymer, the linear polymer, the liquid phase component, and the photoinitiator, and the W content is different in each prepolymer solution; Step S2: All of the prepolymer solution is coated onto one side surface of the positive electrode to form a wet film; along the direction away from the positive electrode, the W in the wet film shows a gradient decreasing trend; Step S3: Perform UV curing treatment on the wet film to form the gel polymer electrolyte on one side surface of the positive electrode.

12. The method for preparing a battery cell according to claim 11, characterized in that, Step S1 includes: preparing prepolymer solution A and prepolymer solution B; prepolymer solution A contains 15wt%~30wt% of the crosslinked polymer, 0.2~5wt% of the linear polymer, 0.05wt%~1wt% of the photoinitiator, and the remainder is the liquid phase; prepolymer solution B contains 2wt%~10wt% of the crosslinked polymer, 5~20wt% of the linear polymer, 0.01wt%~0.3wt% of the photoinitiator, and the remainder is the liquid phase.

13. A battery device comprising one or more of a battery module, a battery pack, and an energy storage battery, characterized in that, The battery device comprises a battery cell according to any one of claims 1 to 10; or, the battery device comprises a battery cell prepared by the method for preparing the battery cell according to claim 11 or 12.

14. An electrical appliance, comprising means for providing electrical energy, characterized in that, The device for providing electrical energy includes the battery device of claim 13.

15. An energy storage device, comprising means for storing electrical energy, characterized in that, The device for storing electrical energy includes the battery device of claim 13.

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