Flexible lithium ion battery

Abstract

The invention provides a flexible lithium ion battery, and belongs to the technical field of battery manufacturing. The flexible lithium ion battery comprises a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode is a three-dimensional network electrode, a fabric electrode, a LiV3O8 composite electrode or an MXene composite electrode. According to the invention, a brand new flexible battery solution is provided by organically combining electrode material doping modification, gel electrolyte preparation, multi-material synergism and structure optimization. Compared with the prior art, the flexible lithium ion battery disclosed by the invention is comprehensively improved in the aspects of energy density, cycle life, mechanical flexibility, safe reliability and the like, the specific capacity is improved by 20-50%, the coulombic efficiency is close to 100%, and the capacity retention rate after 100 cycles is improved by about 10% while the similar free deformation capability is maintained; the gt is still kept after 500 times of circulation under the repeated bending test; and the capacity is 95%.

Description

Technical Field

[0001] This invention relates to the field of battery manufacturing technology, and in particular to a flexible lithium-ion battery. Background Technology

[0002] With the development of wearable devices, flexible displays, and implantable medical devices, there is an urgent need for flexible energy devices that can be bent, rolled, and even stretched. Traditional lithium-ion batteries use rigid metal current collectors and liquid electrolytes, which are prone to separation of electrode materials from the current collector when bent or folded, leading to capacity decay and even short circuit risks. In recent years, to obtain flexible batteries, researchers have proposed improvement schemes from both material and structural aspects: First, doping and modification of electrode materials. By doping or surface functionalizing electrode materials, conductivity and cycle stability can be improved. For example, nitrogen-doped carbon materials can introduce more defects and active sites into carbon materials, effectively improving lithium-ion storage capacity and rate performance. Nitrogen-doped carbon nanofiber films can serve as self-supporting anodes, providing high specific capacity and stable cycle performance while maintaining good flexibility. Furthermore, two-dimensional transition metal carbides / nitrides (MXenes), due to their high conductivity and mechanical flexibility, are used to construct flexible electrodes or as conductive additives to form self-supporting conductive films. Furthermore, combining nano-metal oxides with conductive polymers (such as polyaniline and polypyrrole) can leverage the advantages of each: metal oxides provide high specific capacity, while conductive polymers construct conductive networks and improve material flexibility. For example, literature reports that polyaniline (PANI) coating LiV3O8 nanoparticles can form a continuous conductive network, allowing for full utilization of the active material, with initial capacity and cycle life significantly superior to unmodified LiV3O8. Therefore, doping and surface modification of electrode materials are important directions for improving the performance of flexible batteries. II. Novel Gel / Solid Electrolytes: Liquid electrolytes pose leakage and safety hazards in flexible batteries, while all-solid-state electrolytes have low ionic conductivity. Therefore, developing gel electrolytes with high ionic conductivity and flexibility has become a research hotspot. One approach is to adsorb liquid electrolytes into a polymer matrix to form a gel, such as embedding ionic liquids and lithium salts into polymer networks like polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyethylene glycol (PEO), and polyacrylonitrile (PAN) to create ion-gel membranes. These gel electrolytes exhibit solid film properties at room temperature, possessing a certain mechanical strength and serving as both a separator and a support structure. However, they contain liquid components such as ionic liquids, resulting in ion mobility close to that of liquid electrolytes. For example, US Patent 20140059820A1 discloses an ionic liquid gel electrolyte that uses PVDF-HFP as a matrix and embeds ionic liquids and lithium salts, combining the mechanical flexibility of solids with the high ionic conductivity of liquids. Furthermore, by introducing crosslinkable monomers into the polymer and performing photo / thermal curing, a three-dimensional crosslinked gel electrolyte structure can be obtained, further improving mechanical strength, preventing flow at high temperatures, and maintaining good ionic conductivity. These novel gel / solid electrolyte technologies enhance the safety and stability of flexible batteries under repeated deformation and puncture conditions.

[0003] III. Synergistic Enhancement through Multi-Material Composites: Combining multiple active or functional materials can achieve complementary and synergistic performance enhancement. For example, lithium vanadium oxide (such as LiV3O8) has a high theoretical specific capacity but poor conductivity and is prone to dissolving some active materials during cycling. When combined with conductive polymers, the conductive polymers provide electron conduction pathways and form a protective layer on the particle surface to buffer the electrolyte's corrosion and dissolution of the active materials, thereby improving capacity utilization and cycle life. Similarly, simultaneously mixing high-capacity active materials with highly stable materials in the cathode can balance energy density and cycle life. Regarding binders, novel polymer binders such as sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and conductive polymer-based binders offer stronger adhesion or elasticity compared to traditional PVDF, reducing electrode cracking during repeated bending. Simultaneously, combining flexible support current collectors (such as carbon cloth and metal fiber felt) with active materials can significantly improve the electrode's mechanical strength and deformation resistance. For example, coating active material slurry onto flexible carbon fiber fabric can produce freely bendable electrodes. The carbon fabric current collector is lightweight and conductive, reducing the burden on energy density imposed by traditional metal foils and preventing coating peeling during deformation. Therefore, the optimized combination of multiple materials is an effective strategy for achieving high-performance flexible batteries.

[0004] IV. Flexible Structure Design Innovation: The design of the battery structure affects its flexibility and performance. Existing flexible battery structures include fibrous batteries, thin-film batteries, and folding / kirigami structures. For example, Chinese patent CN118645704B uses several slender fibrous positive and negative electrodes arranged side by side in the package, achieving free design of the battery shape. Other examples include "scorpion tail" structures and serpentine circuit board traces, which improve the battery's bending ability in a single direction through specific geometric designs. However, for more complex multi-directional bending and even stretching, more ingenious three-dimensional structures are needed. For instance, in 2020, the KIST research team in South Korea reported a micro-honeycomb electrode framework: using graphene and carbon nanotubes to construct a concave honeycomb porous skeleton, and then radially compressing it to form an accordion-like folding structure. This structure endows the originally brittle electrode material with stretchable elasticity, thus creating a lithium-ion battery that can stretch by 50%. This battery uses a cross-linked gel electrolyte and elastic encapsulation, with all components participating in energy storage and no inert rubber components. Therefore, it retains over 95% of its capacity after 500 cycles of tensile strain at 50%, achieving an areal capacity of up to 5.05 mAh / cm². 2 Its performance is comparable to that of conventional rigid batteries.

[0005] While the aforementioned technologies have made some progress in the field of flexible batteries, several shortcomings remain: First, many existing flexible batteries focus only on improving the flexibility of the structural design, without fundamentally changing the specific capacity and stability of the electrode materials themselves. This results in low battery energy density and significant performance degradation after repeated bending cycles. Patent CN118645704B achieves free battery shape design using aramid fiber current collectors, but its positive electrode active material is still traditional lithium cobalt oxide (theoretical capacity approximately 140 mAh / g), and the negative electrode is graphite, limiting energy density. Furthermore, its electrode coating uses common PVDF and other binders, which may lead to coating cracking or peeling under long-term repeated deformation. Additionally, the high flexibility design incorporating elastomers often sacrifices some active material content, which is detrimental to high energy output. Therefore, researching a flexible lithium-ion battery is of great significance. Summary of the Invention

[0006] The purpose of this invention is to provide a flexible lithium-ion battery to solve the problem of poor performance of flexible lithium-ion batteries in the prior art.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The present invention provides a flexible lithium-ion battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode is a three-dimensional network electrode, a fabric electrode, a LiV3O8 composite electrode or an MXene composite electrode.

[0008] Preferably, the method for preparing the three-dimensional network electrode is as follows: the aluminum foil is micro-mesh-processed, and then coated with a mixed slurry to obtain the positive electrode.

[0009] Preferably, the aperture of the microgrid is 0.1~0.3mm and the spacing between the apertures is 0.5~1.5mm.

[0010] Preferably, the MXene composite electrode is prepared by mixing lithium iron phosphate, a conductive agent and a binder, adding MXene slurry to obtain a paste, and then rolling it into a sheet to obtain a positive electrode.

[0011] Preferably, the LiV3O8 composite electrode is prepared by mixing PANI-coated LiV3O8 composite material, conductive agent and binder, and adding carbon nanotubes to form a positive electrode sheet.

[0012] Preferably, the fabric electrode is prepared by: (1) Polyvinylidene fluoride and thermoplastic polyurethane are mixed in a solvent, and acrylic acid and an initiator are added to prepare an adhesive; (2) Mix the active material, conductive agent and binder, and then coat them onto carbon fiber fabric to obtain the positive electrode.

[0013] Preferably, the negative electrode is prepared by immersing a nitrogen-doped carbon fiber membrane in an ethanol solution of niobium pentachloride and nickel chloride, removing it, and then carrying out a reduction reaction to obtain a modified negative electrode.

[0014] Preferably, the electrolyte is prepared by mixing PVDF-HFP powder and solvent, adding ionic liquid, photoinitiator and crosslinking monomer, casting into a film and then crosslinking and curing to obtain the electrolyte.

[0015] Preferably, the electrolyte is prepared by dissolving polyacrylonitrile and polyethylene oxide in a solvent, adding ionic liquid and carbonate electrolyte, then adding silicate nanofibers to obtain a mixed solvent, and finally casting to obtain the electrolyte.

[0016] Preferably, the negative electrode is prepared by mechanically meshing a copper foil and then coating the copper foil with a negative electrode slurry to obtain the negative electrode.

[0017] The beneficial effects of this invention are: This invention provides a novel flexible battery solution by organically combining electrode material doping modification, gel electrolyte preparation, multi-material synergy, and structural optimization. Compared with existing technologies, the flexible lithium-ion battery of this invention achieves comprehensive improvements in energy density, cycle life, mechanical flexibility, and safety reliability. While maintaining similar free deformation capabilities, it increases specific capacity by 20-50%, achieves a coulombic efficiency close to 100%, and improves capacity retention by approximately 10% after 100 cycles. It also retains >95% of its capacity after 500 cycles under repeated bending tests.

[0018] The flexible lithium-ion battery of this invention can be widely used in wearable devices, flexible displays, electronic skin and biomedicine, etc., to meet the urgent need for high-performance energy in future flexible electronics. Detailed Implementation

[0019] The present invention provides a flexible lithium-ion battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode is a three-dimensional network electrode, a fabric electrode, a LiV3O8 composite electrode or an MXene composite electrode.

[0020] In this invention, the method for preparing the three-dimensional network electrode is as follows: the aluminum foil is micro-mesh-processed, and then coated with a mixed slurry to obtain the positive electrode.

[0021] In this invention, the aperture of the micro-mesh processing is 0.1~0.3mm, preferably 0.2mm, and the spacing between the holes is 0.5~1.5mm, preferably 0.8~1.2mm, and more preferably 1.0mm.

[0022] In this invention, the MXene composite electrode is prepared by mixing lithium iron phosphate, a conductive agent and a binder, adding MXene slurry to obtain a paste, and then rolling it into a sheet to obtain a positive electrode.

[0023] In this invention, the LiV3O8 composite electrode is prepared by mixing PANI-coated LiV3O8 composite material, conductive agent and binder, and adding carbon nanotubes to form a positive electrode sheet.

[0024] In this invention, the fabric electrode is prepared by: (1) Polyvinylidene fluoride and thermoplastic polyurethane are mixed in a solvent, and acrylic acid and an initiator are added to prepare an adhesive; (2) Mix the active material, conductive agent and binder, and then coat them onto carbon fiber fabric to obtain the positive electrode.

[0025] In this invention, the negative electrode is prepared by immersing a nitrogen-doped carbon fiber film in an ethanol solution of niobium pentachloride and nickel chloride, removing it, and then performing a reduction reaction to obtain a modified negative electrode.

[0026] In this invention, the concentration of niobium pentachloride in the ethanol solution of niobium pentachloride and nickel chloride is 0.001~0.010 mol / L, preferably 0.002~0.008 mol / L, more preferably 0.003~0.006 mol / L; the concentration of nickel chloride is 0.001~0.005 mol / L, preferably 0.02~0.004 mol / L.

[0027] In this invention, the electrolyte is prepared by mixing PVDF-HFP powder and solvent, adding ionic liquid, photoinitiator and crosslinking monomer, casting into a film and then crosslinking and curing to obtain the electrolyte.

[0028] In this invention, the electrolyte is prepared by dissolving polyacrylonitrile and polyethylene oxide in a solvent, adding ionic liquid and carbonate electrolyte, then adding silicate nanofibers to obtain a mixed solvent, and finally casting to obtain the electrolyte.

[0029] In this invention, the negative electrode is prepared by mechanically meshing a copper foil and then coating the copper foil with a negative electrode slurry to obtain the negative electrode.

[0030] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0031] Example 1

[0032] Positive electrode preparation: Aluminum foil is laser-drilled to create a micro-mesh structure, with a hole diameter of 0.2 mm and a hole spacing of 1 mm; Ti3C2T... x MXene slurry was obtained by mixing PVDF-HFP at a mass ratio of 8:2. The prepared MXene slurry was then coated onto micro-mesh-treated aluminum foil (coating thickness of 0.2 mm) to obtain pretreated aluminum foil.

[0033] NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O2) is mixed with acetylene black conductive agent and PVDF binder in a mass ratio of 90:5:5 in N-methylpyrrolidone (NMP) solvent and stirred to form a slurry. The slurry is then coated onto pretreated aluminum foil and dried to obtain the positive electrode, resulting in an active material NCM811 loading of 15 mg / cm³. 2 .

[0034] Anode preparation: Polyacrylonitrile was dissolved in N,N-dimethylformamide to obtain an electrospinning solution with a concentration of 10 wt%. The spinning parameters were: voltage 20 kV, distance between the needle and the receiver 15 cm, flow rate of the spinning solution 0.18 mL / h, spinning temperature 25 °C, and humidity 50% RH, to obtain a fiber membrane (diameter 400 nm). The fiber membrane was carbonized in an ammonia atmosphere at 800 °C for 2 h to obtain a nitrogen-doped carbon fiber membrane with a nitrogen doping amount of 6 wt%. The nitrogen-doped carbon fiber membrane was immersed in an ethanol solution of niobium pentachloride and nickel chloride (niobium pentachloride concentration 0.003 mol / L, nickel chloride concentration 0.002 mol / L) for 20 min. After immersion, it was removed and reduced at 600 °C for 10 min to deposit Nb / Ni particles on the surface of the nitrogen-doped carbon fiber membrane, thus obtaining the modified anode, denoted as Nb-Ni@NC.

[0035] Preparation of gel electrolyte: PVDF-HFP powder and acetone were mixed to obtain a 10 wt% solution. 1-Ethyl-3-methylimidazolium tetrafluoroborate and lithium bis(trifluoromethanesulfonyl)imide salt were added (the molar ratio of 1-ethyl-3-methylimidazolium tetrafluoroborate and lithium bis(trifluoromethanesulfonyl)imide was 1:0.8). The amount of ionic liquid added accounted for 60% of the mass of PVDF-HFP powder. Then, 1 wt% of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and 4 wt% of the crosslinking monomer hexafluorobutyl bis(glycidyl) ether were added. The resulting mixture was stirred evenly under an argon atmosphere and then cast onto a polypropylene substrate to form a film. The film was crosslinked and cured by UV irradiation for 10 min. After peeling off the substrate, the gel electrolyte membrane was obtained.

[0036] Example 1 describes a process where an MXene slurry is coated onto the positive electrode, resulting in a more robust coating and a richer conductive network. Depositing alloy metal particles onto the negative electrode provides additional active sites and pseudocapacitive contributions, and also enhances the electronic conduction pathway.

[0037] Flexible lithium-ion battery assembly: The positive and negative electrodes described above are cut into 30mm × 30mm diameter electrodes. The gel electrolyte membrane is cut into a 30mm diameter circle. The gel electrolyte membrane is sandwiched between the positive and negative electrodes and stacked in alignment to form a sandwich-structured cell. Then, a 100μm thick aluminum-plastic composite film is used as the encapsulation shell, and the cell is placed inside. The shell is sealed under vacuum using a heat sealer, leaving only the opening for the lead-out tabs. One aluminum lead-out tab for the positive electrode and one nickel lead-out tab for the negative electrode are led out. After encapsulation, two drops of liquid electrolyte (1mol / L LiPF6 electrolyte solution, solvent EC / DMC, where the volume ratio of EC to DMC is 1:1) are added to the cell through the injection port to fully wet the gel membrane. Finally, the injection port is sealed to obtain a flexible lithium-ion battery.

[0038] The flexible lithium-ion battery of Example 1 was left to stand at room temperature for 24 hours, then charged to 4.2V at a constant current and constant voltage of 0.1C, with a constant voltage cutoff current of 0.01C; discharged to 3.0V at 0.2C, and cycled 3 times for activation. After that, the electrochemical performance and flexibility of the flexible lithium-ion battery were tested.

[0039] Initial capacity and rate performance: The flexible lithium-ion battery of Example 1 exhibited an initial discharge specific capacity of 175 mAh / g (based on the mass of the positive electrode active material) at 0.2C discharge, which is close to 95% of the theoretical capacity of NCM811 material. At 0.5C, 1C, and 2C discharges, the capacity remained at 150 mAh / g, 140 mAh / g, and 125 mAh / g, respectively, demonstrating good rate performance. This is because nitrogen doping of carbon in the negative electrode increases the lithium-ion diffusion rate, and the flexible lithium-ion battery has low internal resistance, achieving an initial coulombic efficiency of over 99% after 3 cycles.

[0040] Cycle life: The flexible lithium-ion battery of Example 1 was subjected to long-term cycle testing under 1C charge-discharge conditions. The results showed that the capacity retention rate was 91.8% after 500 cycles, with an average capacity decay of only 0.016% per cycle. The flexible lithium-ion battery of Example 1 exhibits excellent cycle stability, which is attributed to the stable structure of the nitrogen-doped carbon fiber film (small volume change during lithium intercalation) and the gel electrolyte suppressing lithium plating and side reactions.

[0041] Flexibility performance: Flexible lithium-ion batteries were encapsulated on PET plastic sheets and subjected to mechanical tests at room temperature with different bending radii and cycles.

[0042] Repeated bending test: The flexible lithium-ion battery was repeatedly bent to a radius R = 3 mm (approximately 180° bend) and then flattened. This bending process was repeated 1000 times. There was no significant change in battery capacity before and after the test; after 1000 cycles, the capacity remained above 99%, and the internal resistance increased by less than 5%. The battery appearance showed no wrinkling or damage, and no electrode layer peeling was observed. This demonstrates that the flexible lithium-ion battery of Example 1 exhibits excellent bending resistance.

[0043] Safety Performance: Needle penetration and puncture tests were conducted. A 2 mm diameter steel needle was used to penetrate a fully charged flexible lithium-ion battery. The battery voltage dropped momentarily but did not catch fire or emit smoke. After the needle was removed, the battery voltage partially recovered. This is because the gel electrolyte binds the liquid within the polymer, preventing significant electrolyte leakage during puncture. Furthermore, the nitrogen-doped carbon fiber film provides conductive continuity, preventing the formation of hot spots. The flexible lithium-ion battery was stored at 85°C for 2 hours without bulging or leakage, and showed no significant performance degradation, indicating good high-temperature resistance of the electrolyte and encapsulation.

[0044] Example 2

[0045] Positive electrode preparation: Ti3AlC2 was etched in a 40% HF solution for 48 hours to obtain MXene slurry, wherein the mass-to-volume ratio of Ti3AlC2 to HF solution was 1 g:20 mL. Lithium iron phosphate (LiFePO4) was mixed with conductive carbon black and PTFE binder at a mass ratio of 90:5:5, and then the MXene slurry was added (the amount of MXene slurry added accounted for 10% of the mass of lithium iron phosphate). The mixture was ground to obtain a uniform paste, which was then rolled into a positive electrode sheet with a thickness of 100 μm and vacuum dried at 80 °C.

[0046] Negative electrode preparation: Graphite, CMC-SBR aqueous binder, and conductive carbon black were mixed at a mass ratio of 95:2.5:2.5 to obtain a slurry. Then, an aqueous suspension of graphene oxide was added (ensuring the graphene oxide content was 1% of the graphite mass). This mixture was then coated onto a 50 μm thick copper foil and dried to obtain the negative electrode. The graphite loading on the negative electrode was 6 mg / cm³. 2 .

[0047] Preparation of gel electrolyte: A blend of polyacrylonitrile and polyethylene oxide (with a mass ratio of 7:3) was used as the polymer matrix and dissolved in N-methylpyrrolidone to form a 10% solution. Then, an ionic liquid and a carbonate electrolyte were added, with a mass ratio of 1:1. The ionic liquid was N-methyl-N-butylpyrrolidone-bis(trifluoromethanesulfonyl)imide (Pyr... 14The TFSI carbonate electrolyte has an EC to DC volume ratio of 1:1, and the mass ratio of the blend, ionic liquid, and carbonate electrolyte is 1:0.5:0.5. After thorough mixing to form a transparent sol, sodium silicate nanofibers (5% of the transparent sol mass) are added to obtain a mixed sol. This mixed sol is then cast into a glass mold and dried at 60°C to obtain a 50 μm thick gel electrolyte membrane. This gel electrolyte membrane remains flexible and does not exhibit brittleness at -20°C, and its room temperature ionic conductivity is 2.1 × 10⁻⁶. -3 S / cm, does not fracture under 300% tensile strain, ionic conductivity of 1×10 at -10℃ -4 S / cm.

[0048] The positive and negative electrodes are cut into circular pieces with a diameter of 25mm. In an argon glove box, the positive electrode, gel electrolyte membrane and negative electrode are stacked in sequence and placed into an aluminum-plastic film bag. The tabs are then sealed to obtain a flexible lithium-ion battery with a rated capacity of about 20mAh.

[0049] Performance tests were conducted on the flexible lithium-ion battery of Example 2: Initial specific capacity: At 0.1C discharge, the discharge specific capacity of the flexible lithium-ion battery cathode reaches 155 mAh / g, which is close to 91% of the theoretical capacity of LFP (170 mAh / g). The initial coulombic efficiency of the flexible lithium-ion battery is 88%, which is due to the loss of solid electrolyte membrane (SEI) formation in the graphite-prepared anode during the first week, but it increases to >95% in the second week.

[0050] Cycling performance: After 1000 cycles at 0.5C, the capacity retention reached 94.5%, demonstrating an extremely long cycle life. This is mainly attributed to the structural stability of LFP itself, and the MXene network, which improves the uniformity of electron / ion channels and slows down activity decay.

[0051] Fast charging capability: The flexible lithium-ion battery of Example 2 can be charged to 80% capacity in 1 hour and 30 minutes at 1C and 2C respectively, and shows no abnormalities after 500 cycles. The 2C rate discharge capacity is approximately 130 mAh / g (84% of the 0.1C capacity), indicating that the MXene-enhanced cathode significantly reduces high-rate polarization, which has a significant improvement effect on materials with low conductivity such as LFP.

[0052] Flexibility Test: The flexible lithium-ion battery of Example 2 was wound onto a cylindrical rod with a diameter of 10 mm and left to stand for 1 hour, then laid flat. The capacity remained unchanged. The battery was bent 180° and clamped at R=5 mm, and cyclically bent at 0.2C for 50 cycles. The capacity showed no significant decrease, and the performance remained stable after unfolding. Drop and Torsion Test: The battery was dropped freely from a height of 1 m 5 times, and the voltage remained normal. The battery was manually twisted ±30° repeatedly 20 times, and no internal short circuit occurred. This indicates that the flexible lithium-ion battery of Example 2 can operate safely under all-directional flexible stress.

[0053] Safety Performance: The flexible lithium-ion battery of Example 2 remained intact and leak-free after being stored at 60°C for 24 hours. During the nail penetration test, the flexible lithium-ion battery of Example 2 showed no violent reaction, only slight localized heating, and continued to operate stably for a period of time. This demonstrates that the gel electrolyte membrane prepared from ionic liquid gel has a significant safety advantage.

[0054] The flexible lithium-ion battery of Example 2 can operate normally within a temperature range of -10 to 60°C, demonstrating good environmental adaptability. The flexible lithium-ion battery of Example 2 is suitable for long-life, high-safety energy storage scenarios.

[0055] Example 3

[0056] Cathode preparation: V₂O₅ was dissolved in hydrogen peroxide and water to form a metavanadate solution. Lithium hydroxide was then added, and the mixture was hydrothermally reacted at 180°C for 12 h. After washing and drying, nanosheet-like LiV₃O₈ powder was obtained. The LiV₃O₈ powder was dispersed in a 1 mol / L hydrochloric acid solution, and aniline monomer was added, with a mass ratio of aniline monomer to LiV₃O₈ powder of 1:2. The mixture was stirred in an ice bath, and ammonium persulfate solution was slowly added dropwise in 20 mL increments. The polymerization reaction was carried out for 30 min, and the resulting dark green solid was filtered. After washing with ethanol and vacuum drying, PANI-coated LiV₃O₈ composite material was obtained. Thermogravimetric analysis of the PANI-coated LiV₃O₈ composite material showed that the PANI content was 12 wt%. Scanning electron microscopy revealed that polyaniline formed a coating layer with a thickness of 5-10 nm, and a bridging network was formed between the particles. This structure is beneficial for improving the conductivity of LiV₃O₈.

[0057] PANI-coated LiV3O8 composite material, Super P conductive carbon black, and binder (polyvinylidene fluoride and polyacrylic acid mixed in a 1:1 mass ratio, with 5% carbon nanotubes added by the total mass of polyvinylidene fluoride and polyacrylic acid) were mixed, wherein the mass ratio of PANI-coated LiV3O8 composite material, Super P conductive carbon black, and binder was 85:5:10, to obtain a mixed slurry. The above mixed slurry was then used to form a positive electrode sheet with a thickness of 50 μm, and the loading of PANI-coated LiV3O8 composite material was 10 mg / cm³. 2 .

[0058] Anode preparation: 5 parts SiO x Powder (x≈1) and 95 parts graphite were mixed, and 10 parts CMC-SBR were added to make a slurry. The slurry was coated onto copper foil and dried to obtain the negative electrode sheet. x The total loading of powder and graphite was 5 mg / cm³. 2 The initial reversible capacity of the above-mentioned negative electrode is 390 mAh / g, which is 5% higher than that of the negative electrode prepared from pure graphite.

[0059] Using a commercially available PE-PP three-layer microporous membrane as a separator, LiPF6 and a mixed solvent (mass ratio of EC / DEC / FEC = 1:1:0.1) were mixed, and then trimethyl phosphate (the amount of trimethyl phosphate added accounted for 10% of the total mass of the electrolyte) was added to obtain an electrolyte with a LiPF6 concentration of 1 mol / L.

[0060] Battery assembly: The positive electrode is cut into 35 mm × 40 mm sizes, and the negative electrode is slightly larger than the positive electrode. A negative electrode is placed on each side of the positive electrode to form a "negative electrode-positive electrode-negative electrode" sandwich structure. A separator is sandwiched between the positive and negative electrodes to form a cell. The cell is placed in an aluminum-plastic film package and vacuum sealed in a dry chamber. Then, 500 μL of electrolyte is injected, and after standing and soaking, it is sealed to obtain a flexible square battery.

[0061] Performance tests were conducted on the square flexible lithium-ion battery of Example 3: Initial capacity and energy density: The square flexible lithium-ion battery of Example 3 was charged and discharged at 0.1C within a voltage range of 2.8~4.0V, and the first-week discharge capacity was measured to be 220 mAh / g (based on the mass of the positive electrode active material LiV3O8). Considering that the theoretical capacity of LiV3O8 is approximately 280 mAh / g (2.5~4.0V), this indicates that PANI coating significantly improves the utilization rate of the active material. Converted to the overall battery energy density (including the weight of all components), it is approximately 265 Wh / kg. A small amount of SiO2 was added during the preparation of the negative electrode. x It is beneficial to improve the overall capacity of flexible lithium-ion batteries.

[0062] Cycle stability: After 500 charge-discharge cycles at 0.5C, the capacity of the flexible prismatic battery in Example 3 slowly decreased from the initial 210 mAh / g to 160 mAh / g, with a capacity retention of approximately 76%. The capacity remained above 90% during the first 100 cycles, and then decreased by approximately 0.05% per cycle thereafter, demonstrating good cycle stability.

[0063] Rate performance: The flexible square battery of Example 3 discharged at 1C and 2C with capacities of 190 mAh / g and 170 mAh / g, respectively, equivalent to 86% and 77% of the 0.1C capacity. There was a slight decrease at higher rates, but the overall capacity remained high. This was mainly due to the slightly slower diffusion rate of LiV3O8 itself; however, the PANI conductive network ensured good internal conductivity of the electrodes even at 2C.

[0064] Flexibility Performance: The square flexible lithium-ion battery of Example 3 was fixed in a U-shaped groove with a radius of curvature R = 4 mm. It was bent and fixed while undergoing 100 charge-discharge cycles. The battery capacity decreased slightly from 165 mAh / g to 160 mAh / g, a decrease of <3%, demonstrating its good performance under small-radius bending. The battery was then removed and laid flat, and 20 more 180° folding experiments were performed. Afterward, the capacity showed no significant change. High-magnification imaging of the battery cross-section during the folding process revealed no coating peeling or current collector breakage. This is related to the use of a high-toughness adhesive, and the carbon nanotubes in the adhesive layer also enhance the tensile strength of the coating, allowing it to stretch along with the foil without breaking when the battery is bent.

[0065] Safety Performance: The flexible square battery of Example 3 contains a flame-retardant electrolyte additive, trimethyl phosphate. After fully charging the battery, it was heated in a flame for 5 seconds and then removed from the flame. The battery did not burn; only the encapsulation slightly melted and broke, but it did not explode. In the same experiment, a flexible lithium-ion battery without trimethyl phosphate would have produced an open flame due to electrolyte combustion. Furthermore, since LiV3O8 has higher thermal stability than LiCoO2 (no oxygen release) and the negative electrode does not contain pure lithium, the battery only showed slight swelling during high-temperature storage (80°C, 8h), and its performance basically recovered after cooling. All of this demonstrates that the flexible square battery of Example 3 has good safety characteristics.

[0066] Example 4

[0067] Positive electrode preparation: A flexible carbon fiber fabric with a thickness of 200 μm (area density of 5 mg / cm²) was used as the positive electrode current collector. Polyvinylidene fluoride (PVDF) and thermoplastic polyurethane (TPU) were mixed at a mass ratio of 1:1 and dissolved in N,N-dimethylformamide to form a viscous solution. Acrylic acid (5% of the total mass of the binder solution) and ammonium persulfate initiator (1% of the mass of acrylic acid) were added and stirred evenly to obtain the binder solution, wherein the concentration of PVDF+TPU was 5%. NCM523 powder (LiN) was added. C M The conductive carbon black (Super P) and the above binder solution were mixed at a mass ratio of 90:5:15 to obtain a uniform slurry. The slurry was directly coated and penetrated into the pores of the carbon cloth current collector. The three-dimensional framework structure of the carbon cloth enhanced the adhesion of the coating. The coating amount was controlled so that the positive electrode active material loading was 10 mg / cm² after drying. The electrode was hot-pressed at 120℃ for 3 min to allow partial interpenetrating crosslinking of PVDF and TPU (acrylic acid participated in the PVDF grafting reaction), forming a tough double-network structure. The resulting carbon cloth positive electrode was grayish-black, the coating did not peel off when bent, and it was elastic. The binder of the positive electrode adopted a double-network elastomer. The slurry had both plasticity and crosslinkability, and the two polymers intertwined to form a bicontinuous phase.

[0068] Negative electrode preparation: A copper foil (9 μm thick) was mechanically meshed: a diamond-shaped mesh was imprinted with a line width of 0.5 mm, a hole spacing of 1 mm, and a hole depth of 50%, forming a grooved texture. A slurry was prepared by mixing graphene, conductive carbon black, and CMC-SBR water-based binder at a mass ratio of 93:2:5. This slurry was then applied to the meshed copper foil, allowing the coating to mechanically adhere to the copper foil surface. After drying, the negative electrode was obtained with a loading of 4 mg / cm². The meshing treatment of the copper foil enhances its flexibility and coating adhesion, resulting in a negative electrode sheet with a visible mesh pattern that is less prone to cracking during bending.

[0069] Electrolyte: The gel electrolyte of Example 1 was used.

[0070] The prepared positive and negative electrodes were cut into 30mm×30mm sheets and assembled into a single-layer cell according to the positive electrode / gel electrolyte / negative electrode. Then, they were packaged into a soft-pack battery with a thickness of 2mm and a capacity of 45 mAh.

[0071] Performance testing: At room temperature, the initial discharge capacity at 0.2C is 150 mAh / g (theoretically approximately 160 mAh / g for NCM523), with an initial efficiency of approximately 96%, indicating that the introduction of binder and carbon cloth did not significantly affect the activity. After 50 cycles, the capacity remained at 147 mAh / g, with a capacity retention of 98%, demonstrating that the dual-network binder ensured initial cycling stability.

[0072] Flexibility Comparison Test: The pouch cell of Example 4 was compared with a set of comparative cells using conventional current collectors and binders through bending tests. The positive electrode of the comparative cells was NCM523 coated with aluminum foil (PVDF binder), and the negative electrode was graphite coated with conventional copper foil (CMC-SBR bonding). Both sets of cells were packaged under the same conditions. Bending fatigue test was performed: the cells were fixed in a bent state with a radius R=5mm, and then charged and discharged 100 times at a 0.5C rate. After that, the capacity change was tested after straightening. The pouch cell of Example 4 retained 99% of its capacity after bending and charging and discharging, while the comparative cells only retained about 85%. Moreover, disassembly revealed that the positive electrode coating of the comparative cells had obvious peeling at the edge, and the negative electrode copper foil had irreversible wrinkles. In contrast, the carbon cloth positive electrode of Example 4 was intact, and although the negative electrode copper foil was deformed, no cracks appeared due to the mesh structure. Next, an extreme folding test was performed: both sets of cells were folded 180° and held for 1 hour. The soft-pack battery in Example 4 showed only a slight drop in open-circuit voltage of 0.02V during folding, and the voltage rebounded after unfolding, with no significant capacity decay. In contrast, the comparative battery experienced a rapid voltage drop of 0.1V and slight short-circuit signs (internal resistance fluctuations) during folding, and its capacity decreased by approximately 10% after unfolding, indicating internal damage. These comparisons clearly demonstrate that the combination of flexible carbon cloth current collector and elastic binder significantly improves the battery's bending resistance. The three-dimensional fiber structure of the carbon cloth disperses the stress on the electrodes during bending, while the dual-network binder firmly adheres the active material to the fibers, preventing stress concentration-induced cracks.

[0073] Safety Performance: The pouch cell in Example 4 retained its electrodes even under extreme mechanical deformation, reducing the risk of short circuits. Furthermore, unlike metal foil, the carbon cloth does not develop sharp edges at bends that could pierce the separator, further enhancing safety. In a simulated extreme condition, the pouch cell of Example 4 was forcibly wound around a 2 mm diameter rod. Although some wrinkles appeared in the cell, it could still charge and discharge normally after being removed (with a slight 5% capacity reduction) without any internal short circuits. With a battery using aluminum foil current collectors, such an operation would almost certainly result in a short circuit. In fire tests, the flame-retardant properties of the carbon cloth also provided a slight benefit (the carbon cloth only carbonized without melting or dripping during combustion), contributing slightly to overall safety.

[0074] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A flexible lithium-ion battery, characterized in that, The application relates to a battery, which comprises a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode is a three-dimensional network electrode, a fabric electrode, a LiV3O8 composite electrode or a MXene composite electrode.

2. The flexible lithium-ion battery of claim 1, wherein, The three-dimensional network electrode is prepared by performing micro-mesh processing on an aluminum foil, and then coating a mixed slurry to obtain the positive electrode.

3. The flexible lithium-ion battery of claim 2, wherein, The micro-mesh processing has a pore diameter of 0.1-0.3 mm and a pore spacing of 0.5-1.5 mm.

4. The flexible lithium-ion battery of claim 1, wherein, The MXene composite electrode is prepared by mixing a lithium iron phosphate, a conductive agent and a binder, adding a MXene slurry to obtain a paste, and then calendering into a sheet to obtain the positive electrode.

5. The flexible lithium-ion battery of claim 1, wherein, The LiV3O8 composite electrode is prepared by mixing a PANI-coated LiV3O8 composite material, a conductive agent and a binder, and adding carbon nanotubes to obtain a positive electrode sheet.

6. The flexible lithium-ion battery of claim 1, wherein, The fabric electrode is prepared by: (1) mixing polyvinylidene fluoride and thermoplastic polyurethane in a solvent, adding acrylic acid and an initiator to obtain a binder; (2) mixing an active material, a conductive agent and the binder, and then coating the mixture on a carbon fiber fabric to obtain the positive electrode.

7. The flexible lithium-ion battery of claim 2 or 3, wherein, The negative electrode is prepared by immersing a nitrogen-doped carbon fiber membrane in an ethanol solution of niobium pentachloride and nickel chloride, taking out the membrane and then performing a reduction reaction to obtain the modified negative electrode.

8. The flexible lithium-ion battery of claim 7, wherein, The electrolyte is prepared by mixing PVDF-HFP powder and a solvent, adding an ionic liquid, a photoinitiator and a crosslinking monomer, and then performing crosslinking and solidification after casting a film to obtain the electrolyte.

9. The flexible lithium-ion battery of claim 4, wherein, The electrolyte is prepared by dissolving polyacrylonitrile and polyethylene oxide in a solvent, adding an ionic liquid and a carbonate electrolyte, adding silicate nanofibers to obtain a mixed solvent, and finally casting to obtain the electrolyte.

10. The flexible lithium-ion battery of claim 6, wherein, The negative electrode is prepared by performing mechanical mesh processing on a copper foil, and then coating a negative electrode slurry on the copper foil to obtain the negative electrode.