A stretchable yarn-shaped battery and its preparation method

Abstract

The present invention discloses a stretchable yarn-type battery and a preparation method thereof, belonging to the technical field of flexible batteries. In the present invention, the semi-prepolymer method is used to uniformly disperse CNT in the polyurethane soft segment and then polymerize, so that CNT is selectively dispersed in the soft phase region. A highly elastic conductive nanofiber electrofilm is prepared by electrospinning as a current collector, which can not only establish a conductive network inside and on the surface of the yarn to achieve high conductivity of the yarn, but also achieve a strong loading capacity of the active substance. At the same time, PUA is used as the solid component of the gel electrolyte, and tributyl phosphate is used as the solvent, providing good stretchability and good environmental stability for the electrolyte. Lithium bis(trifluoromethanesulfonyl)imide and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide are added to improve the ionic conductivity of the electrolyte. Finally, the prepared stretchable lithium-ion battery has good flexibility and capacity retention performance, and has broad application prospects in the field of flexible electronics.

Description

Technical Field

[0001] The present invention relates to a stretchable yarn-shaped battery and a preparation method thereof, belonging to the technical field of flexible batteries. Background Art

[0002] As an emerging technology, flexible electronics is a technology for constructing electronic / photoelectric devices on a flexible substrate. Flexible / wearable electronic products, with their unique mechanical flexibility, high portability, light weight and other characteristics, have not only changed traditional consumer electronic products, but also brought many new fields such as artificial skin, implantable medical devices, epidermal sensors, etc. into social life, leading the next electronic revolution.

[0003] Among various flexible / wearable electronic products, stretchable electronic devices are the most demanding and challenging. Stretchable electronic devices not only need to have the ability to bend, fold, twist, compress, stretch or even deform into any shape, but also need to maintain excellent electrical performance, reliability and integration. The functionalization of stretchable electronic devices requires high-performance energy storage devices. Since the existing energy storage devices on the market are generally rigid and cannot be stretched, they cannot meet the requirements of stretchable electronic products for portability and stretchability. Therefore, there is an urgent need to develop reliable energy storage devices with high elasticity and high electrochemical performance.

[0004] Among various energy storage devices, lithium-ion batteries and supercapacitors represent two leading electrochemical energy storage technologies, both of which are necessary for powering wearable electronic devices. Lithium-ion batteries are the most widely used commercial portable energy storage devices; lithium-ion batteries have outstanding advantages such as high energy density (up to 180 Wh kg-1), high voltage, and no memory effect, and are the mainstream of research on personalized electronic products.

[0005] In the prior art, the preparation of stretchable linear lithium-ion batteries is usually to directly disperse lithium salts on a carbon nanotube film to prepare a carbon nanotube / lithium salt composite fiber, and then wind the composite fiber around an elastic rubber, coat a gel electrolyte, and finally encapsulate it into a stretchable linear lithium-ion battery; however, this type of linear lithium-ion battery still has poor flexibility; there is also a serious problem that the active material falls off during stretching; the elastic limit of the active material is usually <0.1%, which is a rigid material and cannot adapt to elastic deformation. External stretching will cause cracks and gradually crack and powder in the active material layer, and even fall off from the current collector, thus reducing the electrical contact between the active materials and between the active material and the current collector, seriously hindering electron transport, and ultimately causing rapid capacity decay, resulting in problems such as battery capacity decline and poor cycle performance, and cannot meet the requirements of stretchable yarn batteries as "soft" electronic devices. Summary of the Invention

[0006] The object of the present invention is to solve the problems existing in the stretchable linear lithium-ion battery in the prior art, such as poor flexibility, easy decline of battery capacity after multiple stretches, and poor cycle performance.

[0007] The present invention provides a stretchable yarn-shaped battery and a preparation method thereof. The stretchable lithium-ion battery prepared by this method exhibits good flexibility and capacity retention performance. Specifically, the semi-prepolymer method is used to uniformly disperse CNT in the polyurethane soft segment first and then polymerize it, so that CNT is selectively dispersed in the soft phase region. A highly elastic conductive nanofiber membrane is prepared by electrospinning as the current collector of the stretchable lithium-ion battery. PUA is used as an elastomer to provide good stretching performance. Moreover, the high specific surface area of the nanofiber and the capillary effect of its aggregate can achieve efficient adsorption of active materials, which can not only establish a conductive network inside and on the surface of the yarn to achieve high conductivity of the yarn, but also realize high loading of active substances. And because the active material layer is inside the yarn, the active substances cannot fall off during stretching. During the preparation of the gel electrolyte, ionic liquid and tributyl phosphate are used as a mixed solvent. The ionic liquid and lithium salt improve the ionic conductivity of the gel electrolyte. The non-volatile and water-repellent characteristics of tributyl phosphate provide good environmental stability for the gel electrolyte. The gel electrolyte is cast on the electrode yarn and cured by ultraviolet light to form a highly elastic gel electrolyte with good environmental stability. In addition, a carbon fiber yarn wound with graphite in a spring shape is used as the anode. The spring-like structure can reduce the elongation of the fiber itself during stretching to avoid the shedding of active substances. The overall yarn battery is a coaxial structure, providing a larger, tighter and more effective interface area.

[0008] The first object of the present invention is to provide a preparation method of a stretchable yarn-shaped battery, and the method comprises the following steps:

[0009] (1) Preparation of silver / carbon nanotube / polyurethane film

[0010] Carbon nanotubes (CNT) are added to polypropylene glycol (PPG) and ultrasonically dispersed, then diphenylmethane diisocyanate (MDI-50) is added for reaction. After the reaction is completed, it is cooled, and N,N-dimethylformamide (DMF) is added to dissolve it into a solution. Then, a 2 mol / L ethylenediamine / N,N-dimethylformamide (EDA / DMF) solution is added to the solution for polymerization reaction to form a polyurethane (PU) spinning solution. The polyurethane solution is electrospun to prepare a CNT / PU spinning film, and then the CNT / PU spinning film is silver-plated to form an Ag / CNT / PU film;

[0011] (2) Electrode preparation

[0012] The active material, conductive agent, and binder are ground and mixed in proportion, and water is added to form a positive electrode slurry, which is coated on the Ag / CNT / PU film prepared in step (1), dried, and then twisted and wound into a positive electrode yarn;

[0013] Graphite, conductive agent, and binder are ground and mixed in proportion, and water is added to form a negative electrode slurry, which is coated on carbon filaments and dried to obtain a negative electrode yarn;

[0014] (3) Preparation of gel electrolyte

[0015] 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM]TF2N) and tributyl phosphate (TBP) are mixed in proportion, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and polyurethane acrylate (PUA) are added and stirred until dissolved; then a crosslinking agent and a photoinitiator are added, and ultraviolet irradiation is used for curing to form a gel to obtain a gel electrolyte;

[0016] (4) Battery assembly

[0017] The gel electrolyte prepared in step (3) is cast on the positive and negative electrode yarns prepared in step (2) and cured, and then the negative electrode yarn is wound around the positive electrode yarn to assemble a battery.

[0018] In one embodiment, the dosage of the carbon nanotubes in step (1) accounts for 7-9% of the mass of the spinning solution; preferably 8%.

[0019] In one embodiment, the reaction conditions in step (1) are: 80-90 °C, and the time is 3-5 h.

[0020] In one embodiment, the mass ratio of the polypropylene glycol to diphenylmethane diisocyanate in step (1) is 4:1.5-2.

[0021] In one embodiment, the mass ratio of the polypropylene glycol to ethylenediamine in step (1) is 0.058-0.06.

[0022] In one embodiment, the silver plating in step (1) is specifically carried out by using a magnetron sputtering device to deposit silver on the CNT / PU spinning film; the vacuum degree of the magnetron sputtering device is 6×10 -4 -7×10 -4 Pa, the working gas pressure is 0.6-1 Pa, and the time is 10-20 min.

[0023] In one embodiment, the active material in step (2) includes one or more of lithium iron phosphate, lithium manganate, and lithium cobaltate; the conductive agent includes carbon black or / and carbon nanotubes; the binder includes carboxymethyl chitosan and / or carboxymethyl cellulose

[0024] In one embodiment, the mass ratio of the active material, conductive agent and binder in step (2) is 8:1:1.

[0025] In one embodiment, the mass ratio of the graphite, conductive agent and binder in step (2) is 8:1:1.

[0026] In one embodiment, the mass ratio of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide to tributyl phosphate in step (3) is 1-2:1; preferably 1.5:1.

[0027] In one embodiment, the addition amount of lithium bis(trifluoromethanesulfonyl)imide accounts for 10-30% of the mass of the solvent (total mass of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and tributyl phosphate); preferably 20%.

[0028] In one embodiment, the addition amount of polyurethane acrylate in step (3) accounts for 30-60% of the total solution mass.

[0029] In one embodiment, the crosslinking agent in step (3) is any one of 1,6-hexanediol diacrylate (HDDA) and 2-hydroxyethyl methacrylate (HEMA); the initiator is any one of 1-hydroxycyclohexyl phenyl ketone (photoinitiator 184), 2-hydroxy-2-methylpropiophenone (HMPP), and benzoin dimethyl ether (BDK).

[0030] In one embodiment, the ultraviolet irradiation power in step (3) is 450-500 W, and the irradiation time is 100-140 s.

[0031] The second object of the present invention is to provide a stretchable yarn-shaped battery prepared by the method described above.

[0032] The third object of the present invention is to provide the application of the stretchable yarn-shaped battery described above in flexible electronic products and wearable electronic products.

[0033] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0034] (1) The present invention uses polyurethane with excellent mechanical properties as the current collector, and improves the conductivity of polyurethane by adding inorganic conductive materials and magnetron sputtering silver layer. CNT is added during the PU prepolymerization process, so that CNT is selectively dispersed in the soft phase region of polyurethane. Due to the one-dimensional slender tubular structure of CNT, during the stretching process, even if the silver layer cracks, CNT can play a bridging role, retaining a large number of contact sites and maintaining the stability of the conductive network; solving the problem of poor conductivity of polymers, and realizing maintaining good conductivity under large tensile deformation.

[0035] (2) In the present invention, the active material and the conductive material are uniformly loaded into the current collector yarn. This not only enables the establishment of a conductive network inside and on the surface of the yarn to achieve high conductivity of the yarn, but also realizes high loading of the active material. Moreover, due to the twisting and winding, the active material layer is inside the yarn. When stretched, the volume changes in the longitudinal direction, generating pressure inside the yarn, which compacts the active material, avoiding the problem that external stretching can cause cracks in the active material layer, gradually crack and powder, and even fall off from the current collector, thereby reducing the electrical contact between the active materials and between the active material and the current collector, seriously hindering electron transport, and ultimately causing rapid capacity decay.

[0036] (3) The present invention uses PUA as the solid component of the gel electrolyte, providing good tensile properties for the electrolyte. By adding an appropriate amount of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIMTFSI), the ionic conductivity of the electrolyte is enhanced. At the same time, using tributyl phosphate (TBP) as the solvent, based on its characteristics of being non-volatile and non-absorbent, the electrolyte obtains good environmental stability. Description of the Drawings

[0037] Figure 1 It is the tensile curve graph of the polyurethane film prepared in Example 2 of the present invention;

[0038] Figure 2 It is the resistivity change curve graph of the carbon nanotube / polyurethane film prepared in Example 2 of the present invention and the silver / carbon nanotube / polyurethane film prepared in Example 1 after 100 cycles of 200% cyclic stretching;

[0039] Figure 3 It is the tensile curve graph of the gel electrolyte prepared in Example 3 of the present invention;

[0040] Figure 4 It is the ionic conductivity curve of the gel electrolyte prepared in Example 3 of the present invention.

[0041] Figure 5 It is the performance test graph of the stretchable yarn battery prepared in Example 1 after 100 cycles;

[0042] Figure 6 It is the performance test graph of the yarn battery stretched by 150% in Example 1 after 100 cycles. Detailed Embodiments

[0043] The present invention will be further described below in conjunction with the embodiments, but the implementation manners of the present invention are not limited thereto.

[0044] Test Methods

[0045] 1. Ionic Conductivity Test

[0046] Referring to the "Test Method for Thin Film Ionic Conductivity of Power Batteries" (NB / T 10827-2021), a stainless steel sheet │ gel electrolyte │ stainless steel sheet type blocking electrode system is adopted. The parameter settings are as follows: high frequency 106 Hz, low frequency 1 Hz, amplitude 0.01 V.

[0047] 2. Cycling and rate performance testing

[0048] Cycling performance testing: The battery model used is the CR2032 button cell. The charge and discharge cut-off voltages of the LiFePO4 material are 2.7 V - 4.2 V. In addition, the rate performance of the battery is obtained by changing the charge and discharge current density. Discharge the voltage to 2.7 V and charge the voltage to 4.2 V; set the charge and discharge current to 170 (the theoretical specific capacity of the active material, here the theoretical specific capacity of lithium iron phosphate is used) * current density (0.1) * mass of the active substance (0.0053 g) = 0.09 mA, and obtain the specific capacity / cycle number curve with 100 cycles to analyze its cycling performance.

[0049] 3. Tensile and fracture testing:

[0050] Use an electronic universal tensile testing machine to perform tensile performance testing on the battery: Randomly select 10 points on the sample, try to make these 10 points evenly distributed on the sample, measure the diameters of these 10 points, and take the average value as the diameter of the sample. Clamp both ends of the sample on the gripper of the universal tensile testing machine, and the sample is straightened without elongation: With the lower gripper stationary, the upper gripper moves upward at a speed of 2 mm / min, and the temperature of the test room is set to a constant temperature of 26 °C.

[0051] Example 1

[0052] A method for preparing a stretchable yarn-shaped battery, the method comprising the following steps:

[0053] The first step: Preparation of silver / carbon nanotube / polyurethane film

[0054] After dehydrating 4 g of polypropylene glycol (PPG), 8 wt% carbon nanotubes (CNT, relative to the spinning solution) were added and ultrasonically dispersed for 4 h. Then, 1.83 g of diphenylmethane diisocyanate (MDI-50) was added, and the mixture was stirred and heated at 50 °C for 45 min, followed by raising the temperature to 90 °C and reacting for 3 h. After the reaction, it was cooled and 20 ml of N,N-dimethylformamide (DMF) was added and stirred for 12 h to completely dissolve the precursor. Then, 10 ml of ethylenediamine DMF solution (2 mol / L) was added to carry out the polymerization reaction of polyurethane (PU). After the reaction, it was continuously stirred to form a uniform spinning solution. The solution was electrospun under the conditions of applying 20 kV, a pushing liquid speed of 1 ml / h, and a collection distance of 15 cm to prepare the CNT / PU membrane. The electrospun CNT / PU membrane was sputtered with silver at a power of 30 W for 10 min to prepare the Ag / CNT / PU membrane;

[0055] Step 2: Electrode preparation

[0056] Using lithium iron phosphate (LFP) as the active material, carbon black as the conductive agent, and carboxymethyl chitosan as the binder, they were ground and mixed at a mass ratio of 8:1:1. An appropriate amount of deionized water was added and stirred to make the positive electrode slurry, which was coated on the Ag / CNT / PU membrane, vacuum dried, and then twisted and wound into the positive electrode yarn;

[0057] The carbon filaments were ultrasonically treated in deionized water for 3 h to remove surface impurities and then dried at 80 °C. Graphite, carbon black, and carboxymethyl chitosan were mixed and ground at a mass ratio of 8:1:1, and an appropriate amount of deionized water was added and stirred to form a uniform slurry, which was coated on the carbon filaments and vacuum dried at 60 °C for 12 h as the negative electrode yarn;

[0058] Step 3: Gel electrolyte preparation

[0059] 1.5 g of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM]TF2N) and 1 g of tributyl phosphate (TBP) were taken and stirred and mixed (the ratio of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide to tributyl phosphate, i.e., the TB ratio, was 1.5:1). 20% (by mass ratio of the total mass of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and tributyl phosphate) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added and stirred until completely dissolved. Polyurethane acrylate (PUA) with a mass ratio of 0.5 to the solvent (total mass of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and tributyl phosphate) was added and stirred until uniform, and then 0.175 g of cross-linking agent 1,6-hexanediol diacrylate (HDDA) and 0.085 g of photoinitiator 1-hydroxycyclohexyl phenyl ketone (photoinitiator 184) were added and continuously stirred to form a uniform viscous solution, which was cured by ultraviolet irradiation at 500 W for 140 s to form a gel as the battery electrolyte;

[0060] Step 4: Battery assembly

[0061] The gel electrolyte was cast on the positive and negative electrode yarns respectively and cured, and the negative electrode yarn coated with a layer of gel electrolyte was wound around the positive electrode yarn coated with the electrolyte layer to assemble the battery.

[0062] Example 2 Optimization of the preparation of carbon nanotube / polyurethane film

[0063] 1. Preparation of polyurethane film (PU film)

[0064] After dehydrating 4 g of polypropylene glycol (PPG), 1.83 g of diphenylmethane diisocyanate (MDI-50) was added, and the mixture was stirred and heated at 50 °C for 45 min and then heated to 90 °C for 3 h. After the reaction, it was cooled and 20 ml of N,N-dimethylformamide (DMF) was added and stirred for 12 h to completely dissolve the precursor. Then 10 ml of ethylenediamine DMF solution (2 mol / L) was added for the polymerization reaction of polyurethane (PU). After the reaction, stirring was continued to form a uniform spinning solution. The solution was electrospun to prepare a PU film under the conditions of applying 20 kV, a pushing liquid speed of 1 ml / h, and a collection distance of 15 cm.

[0065] 2. Preparation of carbon nanotube / polyurethane film (CNT9 / PU)

[0066] After dehydrating 4 g of polypropylene glycol (PPG), 9 wt% carbon nanotubes (CNT, relative to the spinning solution) were added and ultrasonically dispersed for 4 h. Then 1.83 g of diphenylmethane diisocyanate (MDI-50) was added, and the mixture was stirred and heated at 50 °C for 45 min and then heated to 90 °C for 3 h. After the reaction, it was cooled and 20 ml of N,N-dimethylformamide (DMF) was added and stirred for 12 h to completely dissolve the precursor. Then 10 ml of ethylenediamine DMF solution (2 mol / L) was added for the polymerization reaction of polyurethane (PU). After the reaction, stirring was continued to form a uniform spinning solution. The solution was electrospun to prepare a CNT / PU film under the conditions of applying 20 kV, a pushing liquid speed of 1 ml / h, and a collection distance of 15 cm.

[0067] 3. Preparation of carbon nanotube / polyurethane film (CNT8 / PU)

[0068] After dehydrating 4 g of polypropylene glycol (PPG), 8 wt% carbon nanotubes (CNT, relative to the spinning solution) were added and ultrasonically dispersed for 4 h. Then 1.83 g of diphenylmethane diisocyanate (MDI-50) was added, and the mixture was stirred and heated at 50 °C for 45 min and then heated to 90 °C for 3 h. After the reaction, it was cooled and 20 ml of N,N-dimethylformamide (DMF) was added and stirred for 12 h to completely dissolve the precursor. Then 10 ml of ethylenediamine DMF solution (2 mol / L) was added for the polymerization reaction of polyurethane (PU). After the reaction, stirring was continued to form a uniform spinning solution. The solution was electrospun to prepare a CNT / PU film under the conditions of applying 20 kV, a pushing liquid speed of 1 ml / h, and a collection distance of 15 cm.

[0069] 4. Preparation of Carbon Nanotube / Polyurethane Film (CNT7 / PU)

[0070] After dehydrating 4 g of polypropylene glycol (PPG), 7 wt% carbon nanotubes (CNT, relative to the spinning solution) were added and ultrasonically dispersed for 4 h. Then, 1.83 g of diphenylmethane diisocyanate (MDI-50) was added, and the mixture was stirred and heated at 50 °C for 45 min and then reacted at 90 °C for 3 h. After the reaction, it was cooled and 20 ml of N,N-dimethylformamide (DMF) was added and stirred for 12 h to completely dissolve the precursor. Then, 10 ml of ethylenediamine DMF solution (2 mol / L) was added to carry out the polymerization reaction of polyurethane (PU). After the reaction, it was continuously stirred to form a uniform spinning solution. The solution was electrospun to prepare the CNT / PU film under the conditions of applying 20 kV, a pushing liquid speed of 1 ml / h, and a collection distance of 15 cm.

[0071] Optimization of Gel Electrolyte Preparation in Example 3

[0072] 1. Preparation of Gel Electrolytes (TB1L0PUA, TB 1.5 L0PUA and TB2L0PUA)

[0073] 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM]TF2N) and tributyl phosphate (TBP) were respectively adjusted and stirred and mixed according to mass ratios of 1:1, 1.5:1, and 2:1. Polyurethane acrylate (PUA) with a mass ratio of 0.5 to the total mass of the solvents (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and tributyl phosphate) was added and stirred until uniform, and then 0.175 g of crosslinking agent 1,6-hexanediol diacrylate (HDDA) and 0.085 g of photoinitiator 1-hydroxycyclohexyl phenyl ketone (photoinitiator 184) were added and continuously stirred to form a uniform viscous solution, which was cured by 500 W ultraviolet irradiation for 140 s to obtain gel electrolytes TB1L0PUA, TB 1.5 L0PUA and TB2L0PUA respectively.

[0074] 2. Preparation of Gel Electrolytes (TB 1.5 L 0.1 PUA, TB 1.5 L 0.2 PUA and TB 1.5 L 0.3 PUA)

[0075] Take 1.5 g of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM]TF2N) and 1 g of tributyl phosphate (TBP), stir and mix them, and then stir and mix them with 0.25 g, 0.5 g, and 0.75 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) respectively until completely dissolved. Add polyurethane acrylate (PUA) with a mass ratio of 0.5 to the total mass of the solvents (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and tributyl phosphate), stir until homogeneous, then add 0.175 g of crosslinking agent 1,6-hexanediol diacrylate (HDDA) and 0.85 g of photoinitiator 1-hydroxycyclohexyl phenyl ketone (photoinitiator 184), and continue to stir to form a homogeneous viscous solution. Cure it into a gel by irradiating with 500 W ultraviolet light for 140 s to obtain gel electrolytes TB respectively. 1.5 L 0.1 PUA, TB 1.5 L 0.2 PUA and TB 1.5 L 0.3 PUA.

[0076] Performance measurement

[0077] 1. Measure the tensile fracture properties of the PU membrane, CNT7 / PU membrane, CNT8 / PU membrane, and CNT9 / PU membrane prepared in Example 2. The results are as Figure 1 shown:

[0078] From Figure 1 it can be seen that compared with the pure PU nanofiber membrane, the breaking strength of the CNT / PU nanofiber membrane has increased, and the elongation at break has decreased. This is because the CNTs are dispersed in the soft phase region, hindering the movement of molecular chains, and the elongation of the soft chain segments provides good elongation for the polyurethane. Therefore, the elongation at break decreases. However, CNTs have a high aspect ratio and tend to be uniformly dispersed in the polyurethane nanofibers, which can transfer and bear part of the external force, and CNTs themselves have strong stiffness. Therefore, the breaking strength of CNT / PU has increased. But when the content of CNTs continues to increase after reaching a certain level, not only the elongation at break decreases, but the breaking strength also decreases. This is because a large number of local agglomerations of CNTs cause defects.

[0079] 2. Measure the conductivity performance of the Ag / CNT8 / PU membrane in Example 1 and the CNT7 / PU membrane, CNT8 / PU membrane, and CNT9 / PU membrane in Example 2. The results are as Figure 2 shown:

[0080] From Figure 2As can be seen from the data in Table 1, by comparing the resistances of polyurethane films with different CNT contents under repeated stretching, it can be known that the initial resistances of CNT7 / PU and CNT8 / PU are smaller than that of CNT9 / PU. This is because the CNTs in CNT9 / PU agglomerate, resulting in uneven dispersion and defects in the conductive network, thus leading to a larger initial resistance. After stretching, the polyurethane fibers elongate, and during this process, the CNTs also move. The number of CNT contact points in CNT7 / PU decreases after stretching, while the CNTs in CNT8 / PU overlap with each other and can maintain a complete conductive network after stretching. Although there are more CNTs in CNT9 / PU, due to the defects in the conductive network caused by agglomeration, the resistance increases significantly under stretching. After sputtering the silver layer, the conductive performance of the polyurethane fiber film is greatly improved. The Ag layer not only reduces the resistance under non-stretched conditions but also increases more contact sites on the fiber surface under stretching. The resistivity before and after stretching is below 0.03, which is of the same order of magnitude as the resistivity of copper (0.017). At the same time, it has excellent tensile resilience and conductive performance and can be used as a current collector for elastic electrodes.

[0081] Table 1. Test data of conductive performance

[0082]

[0083] 3. The tensile performance and fracture performance of the gel electrolyte prepared in Example 3 were measured, and the results are as Figure 3 shown:

[0084] From Figure 3 it can be seen that by comparing TB1L0PUA, TB 1.5 L0PUA, and TB2L0PUA, it is found that the strength and elongation at break first increase and then decrease. This is because [BMIM]TF2N has a plasticizing effect on PUA, so an appropriate addition ratio improves the mechanical properties. However, TBP also has excellent plasticization on the polymer in the organic-inorganic ion gel system. When the content of [BMIM]TF2N continues to increase, the content of TBP decreases. When the influence of [BMIM]TF2N on PUA is less than the influence of the decrease in TBP on the plasticization of PUA, the mechanical properties of the gel electrolyte decline. By comparing the addition of different contents of LiTFSI, it is found that the lithium salt helps to improve the mechanical properties of the gel electrolyte. LiTFSI has a plasticizing effect on PUA, but when the addition of LiTFSI is excessive, an interaction between PUA and the lithium salt will occur, hindering the movement of polymer segments, so the fracture strength and elongation at break decrease.

[0085] 4. The ionic conductivity of the gel electrolyte prepared in Example 3 was measured, and the results are as Figure 4 and Table 2 shown:

[0086] From Figure 4As can be seen from the data in Table 2, the migration of lithium ions in the gel electrolyte mainly depends on the movement of ions along the polymer segments and the migration of ions in the ionic liquid. According to the formula

[0087] σ = d / (R×A)

[0088] σ - ionic conductivity, S / cm; d - thickness of the gel electrolyte, cm; R - intrinsic resistance, Ω; A - electrode area, cm 2 ;

[0089] the ionic conductivity can be calculated. The ionic conductivity first increases and then decreases. This is because the mobile Li + mainly comes from [BMIM]TF2N. Therefore, when [BMIM]TF2N is increased first, the ionic conductivity increases. However, when a critical value is reached, increasing the ratio of the ionic liquid further will cause the ratio of tributyl phosphate to decrease. Tributyl phosphate can reduce the viscosity of the ionic liquid, making the migration of lithium ions easier and increasing the ionic conductivity of the system. The addition of LiTFSI can increase the content of lithium ions. When the addition amount of LiTFSI continues to increase, Li + interacts with the ether bond and carbonyl group in PUA and is difficult to move, so the ionic conductivity decreases.

[0090] Table 2. Ionic conductivity data

[0091]

[0092] 5. The cycle performance of the stretchable yarn-shaped battery prepared in Example 1 was measured, and the results are as Figure 5 and 6 shown. As can be seen from Figure 5 , the initial capacity of the yarn battery is 89.77 mAh / g, and the capacity after 100 cycles at 0.2C is 57.89 mAh / g, with a capacity retention rate of 66%. For the unconventional yarn full battery, the initial capacity is close to that of the coin cell (95 mAh / g), and the capacity retention rate is relatively ideal.

[0093] As can be seen from Figure 6 , after the fiber battery is cycled at 0.2C under 150% stretching, the initial capacity is 82.02 mAh / g, and the decrease in the initial capacity compared to the non-stretched state is not obvious. This is because of the stretching hysteresis phenomenon of the stretchable material. After stretching for a period of time, the capacity begins to decrease and then remains stable. The capacity after 100 cycles is 39.57 mAh / g, and the capacity retention rate is 48.25%. This shows that the yarn battery has good capacity retention rate and stability under large stretching.

Claims

1. A preparation method of a stretchable yarn-shaped battery, characterized in that, The method includes the following steps: (1) Preparation of silver / carbon nanotube / polyurethane film The carbon nanotubes are added to polypropylene glycol and ultrasonically dispersed, then diphenylmethane diisocyanate is added for reaction. After the reaction is completed, it is cooled, and N,N-dimethylformamide is added to dissolve it into a solution. Ethylenediamine / N,N-dimethylformamide solution is added to the solution for polymerization reaction to form a polyurethane spinning solution. The CNT / PU spinning film is prepared by electrospinning, and then the CNT / PU spinning film is silver-plated to form the Ag / CNT / PU film; (2) Electrode preparation The active material, conductive agent, and binder are ground and mixed in proportion, and water is added to form a positive electrode paste, which is coated on the Ag / CNT / PU film prepared in step (1). After drying, it is twisted and wound into a positive electrode yarn; Graphite, conductive agent, and binder are ground and mixed in proportion, and water is added to form a negative electrode paste, which is coated on carbon filaments and dried to be used as a negative electrode yarn; (3) Preparation of gel electrolyte 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and tributyl phosphate are mixed, and lithium bis(trifluoromethanesulfonyl)imide and polyurethane acrylate are added and stirred until dissolved; then a crosslinking agent and a photoinitiator are added, and it is cured by ultraviolet irradiation to form a gel, that is, a gel electrolyte is formed; (4) Battery assembly The gel electrolyte prepared in step (3) is respectively cast on the positive and negative electrode yarns prepared in step (2) and cured, and then the negative electrode yarn is wound around the positive electrode yarn to assemble a battery.

2. The preparation method according to claim 1, characterized in that, The dosage of the carbon nanotubes described in step (1) accounts for 7-9% of the mass percentage of the spinning solution.

3. The preparation method according to claim 1, wherein The active material described in step (2) includes one or more of lithium iron phosphate, lithium manganate, and lithium cobaltate; the conductive agent includes carbon black or / and carbon nanotubes; the binder includes carboxymethyl chitosan and / or carboxymethyl cellulose.

4. The preparation method according to claim 1, characterized in that, The mass ratio of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide to tributyl phosphate described in step (3) is 1-2:

1.

5. The preparation method according to claim 1, characterized in that, The addition amount of lithium bis(trifluoromethanesulfonyl)imide accounts for 10-30% of the total mass of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and tributyl phosphate.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the active material, conductive agent, and binder described in step (2) is 8:1:

1.

7. The preparation method according to claim 1, characterized in that, The mass ratio of graphite, conductive agent, and binder described in step (2) is 8:1:

1.

8. The preparation method according to claim 1, wherein, The silver plating in step (1) is specifically carried out by using a magnetron sputtering device to deposit silver on the CNT / PU spinning film; the vacuum degree of the magnetron sputtering device is 6×10 -4 -7×10 -4 Pa, the working pressure is 0.6 - 1 Pa, and the time is 10 - 20 min.

9. A stretchable yarn-shaped battery prepared by the preparation method according to any one of claims 1-8.

10. Application of the stretchable yarn-shaped battery according to claim 9 in flexible electronic products and wearable electronic products.

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