High ionic conductivity and strong liquid absorption performance nanofiber separator and preparation method and application

Abstract

The application discloses a kind of high ionic conductivity and strong liquid absorption performance nanofiber diaphragm and preparation method and application, preparation method includes: (1) lithium nitrate salt is dissolved, and is configured into lithium nitrate solution;(2) nanofiber diaphragm film is pressed into electrode sheet and is dried in vacuum drying oven;(3) at the temperature of 100-120 DEG C, nanofiber diaphragm after processing in step (2) is immersed in LiNO3 solution in step (1) and is soaked, and they are fully mixed, and lithium nitrate is coated and filled on nanometer diaphragm;(4) nanofiber diaphragm obtained after processing in step (3) is dried under the condition of 40~100 DEG C, and the high ionic conductivity and strong liquid absorption performance nanofiber diaphragm are obtained.The middle layer of nanofiber diaphragm treated by LiNO3 in the application helps to maintain the integrity of lithium metal and diaphragm interface, reduces the side reaction in battery, and prolongs the cycle life of battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal batteries, and particularly relates to a nanofiber separator with high ionic conductivity and strong liquid absorption performance, its preparation method and application. Background Technology

[0002] Lithium-ion batteries, with their superior characteristics such as high energy density, long cycle life, and low self-discharge rate, have become an indispensable core power component for modern portable electronic devices (including mobile phones, laptops, tablets, etc.), electric vehicles, and large-scale energy storage systems. As these application areas continue to expand and technologies iterate, the expectations for lithium-ion battery performance are becoming increasingly stringent. Taking electric vehicles as an example, their requirements for lithium-ion batteries not only lie in higher power density to achieve fast charging and strong power output, but also in ensuring long driving range. This means that all components inside the battery, especially the separator, must effectively ensure the stable operation and safety of the battery during the efficient transfer of lithium ions.

[0003] As a key component of lithium-ion batteries (LIBs), the negative electrode in most commercially available LIBs currently uses graphite as the negative electrode material, its main function being to accept and collect lithium ions originating from the positive electrode. However, the development of traditional lithium-ion batteries based on graphite negative electrodes has approached its theoretical capacity limit (372 mAh / g). In contrast, lithium metal batteries, with their theoretical capacity as high as 3860 mAh / g and a low reduction potential of -3.04V (compared to the standard hydrogen electrode), have begun to attract global attention from researchers. However, the high reactivity of lithium metal leads to serious safety hazards caused by dendrite growth and low coulombic efficiency in lithium metal batteries (LMBs) during cycling. Currently, several mainstream solutions have emerged, such as designing functional electrolytes, constructing special three-dimensional current collectors, and modifying artificial solid electrolyte membranes, all with the core objective of overcoming the lithium dendrite growth problem. The design and modification of lithiophilic interlayers are also widely used in the field of lithium metal batteries (LMBs). For LMBs, employing a lithiophilic interlayer is a key measure to suppress dendrite growth and fully leverage the high capacity advantage of lithium metal batteries. This requires the interlayer to possess excellent ion conduction properties and high electrolyte wettability to achieve liquid retention and rapid ion conduction, as well as strong chemical stability to avoid side reactions with the electrolyte. Furthermore, the unique lithiophilic mechanism of the interlayer is a core element for achieving dendrite-free lithium metal anodes. The lithiophilic interlayer is closely related to the manufacturing cost and battery efficiency of lithium metal batteries; it is no exaggeration to say that the presence or absence of the interlayer directly affects the performance and lifespan of LMBs.

[0004] Lithium-ion batteries (LIBs) are a type of high-energy-density battery. LiCoO2 (LCO), as the first generation of commercially available lithium-ion battery cathode materials, still dominates the market for lithium-ion rechargeable battery cathode materials. Co in LCO is a scarce strategic metal, leading to its high cost. Meanwhile, Li[Ni]... 1-2x Co x Mn x O2 (NCM) cathode materials primarily consist of Ni, Co, and Mn, with a relatively low Co content. Furthermore, with technological advancements, high-nickel, low-cobalt ternary materials are emerging, further reducing costs and making them more economically advantageous for large-scale applications. NCM materials exhibit superior cycle performance compared to LCO. After multiple charge-discharge cycles, their capacity decay is relatively slow, maintaining a high specific capacity and extending battery life. This reduces the frequency and cost of battery replacement, making them particularly suitable for applications with high cycle life requirements, such as electric vehicles. Its working principle is as follows: During charging, an oxidation reaction occurs at the cathode, e... - Through the external circuit, Li flows from the positive to the negative electrode, inside the battery... + The electrolyte travels from the positive electrode to the negative electrode, where a reduction reaction occurs. Conversely, during discharge, a reduction reaction occurs at the positive electrode. - Through the external circuit, Li flows from the negative terminal to the positive terminal, inside the battery... + The electrolyte travels from the negative electrode to the positive electrode, where an oxidation reaction occurs.

[0005] In lithium-ion batteries (LIBs), the energy density and lithium storage capacity of the anode are the main factors affecting battery performance, and the corresponding component is the lithium metal anode (LMA). Conventional LMAs are mainly composed of pure lithium foil. During cycling, LMAs face safety hazards caused by lithium dendrite growth and low coulombic efficiency (CE). When nanofiber membranes are used as an interlayer, the addition of the interlayer affects the ion and electron transfer efficiency to some extent. Summary of the Invention

[0006] This invention provides a nanofiber separator with high ionic conductivity and strong liquid absorption performance, as well as its preparation method, to solve the problems of lithium dendrite growth and low coulombic efficiency caused by the obstruction of ionic conductivity in the current application of the intermediate layer of lithium metal batteries, thereby solving the problem of high energy density lithium metal batteries moving towards practical application.

[0007] To achieve the above objectives, this invention provides the application of nanofiber membranes and lithium nitrate solution in the preparation of nanofiber membranes with high ionic conductivity and strong liquid absorption properties. The nanofiber membrane is composed of a skeleton fiber layer, a nanofiber layer, and a polymer network layer stacked from bottom to top. The skeleton fiber layer is composed of interwoven micron-sized fibers and short chemical fibers, the nanofiber layer is composed of interwoven nanofibers containing hydroxyl functional groups, and the polymer network layer is composed of interwoven polymers. The nanofiber portions extend into the skeleton fiber layer, and the polymer portions extend into the nanofiber layer. In the nanofiber membrane, the skeleton fiber proportion is 11-15 wt%, the nanofiber proportion is 80-84 wt%, and the polymer network proportion is 5 wt%. The lithium nitrate solution is a 0.5 mol / L to 2 mol / L aqueous solution of lithium nitrate; The nanofiber membrane is pressed into an electrode sheet and dried in a vacuum drying oven. It is then immersed in the lithium nitrate solution, thoroughly mixed, and dried at 40–100°C to obtain the nanofiber membrane with high ionic conductivity and strong liquid absorption performance.

[0008] The nanofiber membrane comprises 15 wt% skeletal fibers, 80 wt% nanofibers, and 5 wt% polymer network. The membrane has a thickness of 12-18 μm, a porosity of 80-86%, and an ionic conductivity of 0.70-0.80 mS / cm. -1 The concentration of the lithium nitrate aqueous solution is 1 mol / L.

[0009] The nanofibers have a diameter of 5-100 nm; the microfibers have a diameter of 0.5-1 μm and a length of 10-1000 μm; the chemical short fibers have a diameter of 1-6 μm and a length of 1-12 mm; the nanofibers are at least one of nanocellulose fibers and fibrillated Tencel fibers; the microfibers are at least one of split-fiber chemical short fibers, pulp, and microcellulose fibers; the chemical short fibers are at least one of PET fibers, PAN fibers, PBO fibers, PA fibers, PI fibers, and aramid short fibers; and the polymer is at least one of aramid, polyacrylonitrile, polyvinylidene fluoride, and polymethyl methacrylate.

[0010] Another object of the present invention is to provide a method for preparing a nanofiber membrane with high ionic conductivity and strong liquid absorption performance, the steps of which include: Step 1. Dissolve lithium nitrate to prepare an aqueous solution of lithium nitrate; Step 2. Press the nanofiber membrane into electrode sheets and dry them in a vacuum drying oven; Step 3. Immerse the nanofiber membrane treated in Step 2 in the LiNO3 solution from Step 1 at a temperature of 100-120℃. Mix the two thoroughly and coat the nanofiber membrane with lithium-loving nitrate. Step 4. The nanofiber membrane obtained in step 3 is dried at 40-100°C to obtain the nanofiber membrane with high ionic conductivity and strong liquid absorption performance.

[0011] In step 1, the concentration of the lithium nitrate solution is 0.5 mol / L to 2 mol / L.

[0012] The concentration of the lithium nitrate solution in step 1 is 1 mol / L.

[0013] In step 2, the nanofiber membrane is immersed in LiNO3 solution for 20-60 minutes.

[0014] In step 2, the thickness of the nanofiber membrane is 12 μm-18 μm.

[0015] The nanofiber membrane is composed of a skeleton fiber layer, a nanofiber layer, and a polymer network layer stacked from bottom to top. The skeleton fiber layer is composed of interwoven micron-sized fibers and short chemical fibers, the nanofiber layer is composed of interwoven nanofibers containing hydroxyl functional groups, and the polymer network layer is composed of interwoven polymers. The nanofibers extend into the skeleton fiber layer, and the polymers extend into the nanofiber layer. In the nanofiber membrane, the skeleton fiber accounts for 11-15 wt%, the nanofiber accounts for 80-84 wt%, and the polymer network accounts for 5 wt%.

[0016] The nanofiber membrane comprises 15 wt% skeletal fibers, 80 wt% nanofibers, and 5 wt% polymer network. The membrane has a thickness of 12-18 μm, a porosity of 80-86%, and an ionic conductivity of 0.70-0.80 mS / cm. -1 .

[0017] A nanofiber membrane with high ionic conductivity and strong liquid absorption is prepared by the method described above. The nanofiber membrane with high ionic conductivity and strong liquid absorption comprises a nanofiber membrane and a lithium nitrate salt coated on the membrane. The weight of the lithium nitrate salt is 1.2 to 1.4% of the weight of the nanofiber membrane.

[0018] A lithium-ion battery includes a shell, a positive electrode, a negative electrode, an electrolyte, and an intermediate layer. The intermediate layer is a nanofiber membrane with high ionic conductivity and strong liquid absorption prepared by the method described above. The thickness of the nanofiber membrane with high ionic conductivity and strong liquid absorption is 15 μm. Beneficial effects: This invention provides a method for preparing a nanofiber membrane with high ionic conductivity and strong liquid absorption. The prepared nanofiber membrane, as the intermediate layer of the battery, has the following advantages: (1) The lithium-affinity properties of the coating layer, combined with the high porosity of the nanofiber membrane, can improve the ionic conductivity and liquid absorption of the lithium metal negative electrode. At the same time, this invention explores the nanofiber membrane treated with the optimal concentration of LiNO3, so as to maximize the ionic conductivity and liquid absorption; (2) LiNO3 solution is simple and easy to prepare, which can realize the mass production of materials with high ionic conductivity and strong liquid absorption, greatly reducing the cost of commercial application of lithium metal batteries; (3) A stable interface layer can be formed at the contact interface between the electrode and the intermediate layer. This interface layer can inhibit the growth of lithium dendrites and extend the cycle life of the battery. Attached Figure Description

[0019] Figure 1 The present invention provides a liquid absorption strength test for the nanofiber membrane, wherein (a) is the liquid absorption capacity test of Example 1, (b) is the liquid absorption capacity test of Example 2, (c) is the liquid absorption capacity test of Example 3, (d) is the liquid absorption capacity test of Example 4, and (e) is the liquid absorption capacity test of Comparative Example 2. Figure 2 The nanofiber separators prepared in Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2 of this invention serve as the intermediate layer of the lithium metal anode and Li[Ni] 0.8 Co 0.1 Mn 0.1 Electrochemical impedance spectroscopy (EIS) testing of full cells assembled from O2; Figure 3 The nanofiber separators prepared in Examples 1, 2, 3, and Comparative Example 2 of this invention serve as the intermediate layer of the lithium metal anode and are used in conjunction with Li[Ni] 0.8 Co 0.1 Mn 0.1 XPS characterization results of the intermediate layer of a full cell assembled from O2 under 15 discharge cycles; Figure 4 The nanofiber separators prepared in Examples 2, 1, and 2 of this invention serve as the intermediate layer of the lithium metal anode and are used in conjunction with Li[Ni] 0.8 Co 0.1 Mn 0.1 Electrochemical cycling test of a full cell assembled with O2. Detailed Implementation

[0020] The technical solution of the present invention will be described below through specific embodiments.

[0021] Comparative Example 1 The preparation method of the nanofiber membrane includes the following steps: (1) The nanofiber membrane is formed by stacking a skeleton fiber layer, a nanofiber layer and a polymer network layer from bottom to top; the skeleton fiber layer is formed by interlacing micron fibers and chemical short fibers, the nanofiber layer is formed by interlacing nanofibers containing hydroxyl functional groups, and the polymer network layer is formed by interlacing polymers; the nanofibers extend into the skeleton fiber layer and the polymers extend into the nanofiber layer.

[0022] The microfiber is at least one of the following: split short chemical fibers, pulp, and microfiber cellulose fibers; the diameter of the microfiber is 0.5-1 μm and the length is 10-1000 μm.

[0023] The chemical staple fiber is at least one of PET fiber, PAN fiber, PBO fiber, PA fiber, PI fiber, and aramid staple fiber. The diameter of the chemical staple fiber is 1-6 μm and the length is 1-12 mm.

[0024] Nanofibers are at least one of nanocellulose fibers and fibrillated Tencel fibers.

[0025] The polymer is at least one of aramid, polyacrylonitrile, polyvinylidene fluoride, and polymethyl methacrylate.

[0026] (2) In step (1), the skeleton fiber accounts for 15wt%, the nanofiber accounts for 80wt%, and the polymer network accounts for 5wt%.

[0027] (3) Further, the nanofiber membrane has a thickness of 12 μm-18 μm, a porosity of 80-86%, and an ionic conductivity of 0.70-0.80 mS / cm. -1 .

[0028] (4) Before use, the wet membrane is filtered, squeezed and cut into small round pieces with a diameter of 16 mm, and placed in a vacuum drying oven at 60 ℃ for 12 h to completely remove the moisture in the air to obtain a nanofiber membrane with a thickness of 15 μm.

[0029] Comparative Example 2 A method for preparing a nanofiber separator loaded with AgNO3 for use as an interlayer in a lithium metal battery, comprising the following steps: (1) Weigh 2g of AgNO3 particles using an analytical balance and prepare a 1mol / L AgNO3 solution with deionized water.

[0030] (2) A nanofiber membrane with a thickness of 15 μm purchased from Ningbo Rouchuang Nanotechnology Co., Ltd. (prepared using the method of Comparative Example 1) was pressed and cut into small round pieces with a diameter of 16 mm, and placed in a vacuum drying oven at 60 °C for 12 h to completely remove moisture from the air. (3) At 80 °C, the nanofiber membrane with a thickness of 15 μm in step (2) was soaked in the AgNO3 solution of step (1) for 30 minutes. (4) The nanofiber membrane from step (3) was placed in an 80 ℃ oven to dry the moisture, and then placed in a 60 ℃ vacuum drying oven for 12 h to completely remove the moisture in the air. It was then stored in a vacuum drying oven. After drying, the membrane gained 1.3% more weight than the original membrane.

[0031] Example 1 A method for preparing a nanofiber membrane with high ionic conductivity and strong liquid absorption properties, comprising the following steps: (1) Weigh 1g of LiNO3 particles using an analytical balance and prepare a 0.5 mol / L LiNO3 solution with deionized water.

[0032] (2) The nanofiber membrane prepared in Comparative Example 1 was pressed and cut into small round pieces with a diameter of 16 mm, and placed in a vacuum drying oven at 60 ℃ for 12 h to completely remove moisture from the air; the surface of the nanofiber is rich in hydroxyl groups, which can adsorb lithium nitrate to form a new pore structure.

[0033] (3) At 80 °C, the nanofiber membrane with a thickness of 15 μm in step (2) was soaked in the LiNO3 solution of step (1) for 30 minutes. (4) The nanofiber membrane from step (3) was placed in an 80 ℃ oven to dry the moisture, and then placed in a 60 ℃ vacuum drying oven for 12 h to completely remove the moisture in the air. It was then stored in a vacuum drying oven. After drying, the membrane gained 1% weight compared to the original membrane.

[0034] Example 2 A method for preparing a nanofiber membrane with high ionic conductivity and strong liquid absorption properties, comprising the following steps: (1) Weigh 2g of LiNO3 particles using an analytical balance and prepare a 1mol / L LiNO3 solution with deionized water.

[0035] (2) The nanofiber membrane prepared in Comparative Example 1 was pressed and cut into small round pieces with a diameter of 16 mm, and placed in a vacuum drying oven at 60 ℃ for 12 h to completely remove moisture from the air. (3) At 80 °C, the nanofiber membrane with a thickness of 15 μm in step (2) was soaked in the LiNO3 solution of step (1) for 30 minutes. (4) The nanofiber membrane from step (3) was placed in an 80 ℃ oven to dry the moisture, and then placed in a 60 ℃ vacuum drying oven for 12 h to completely remove the moisture in the air. It was then stored in a vacuum drying oven. After drying, the membrane gained 1.2% more weight than the original membrane.

[0036] Example 3 A method for preparing a nanofiber membrane with high ionic conductivity and strong liquid absorption properties, comprising the following steps: (1) Weigh 4 LiNO3 particles using an analytical balance and prepare a 2 mol / L LiNO3 solution with deionized water.

[0037] (2) The nanofiber membrane prepared in Comparative Example 1 was pressed and cut into small round pieces with a diameter of 16 mm, and placed in a vacuum drying oven at 60 ℃ for 12 h to completely remove moisture from the air. (3) At 80 °C, the nanofiber membrane with a thickness of 15 μm in step (2) was soaked in the LiNO3 solution of step (1) for 30 minutes. (4) The nanofiber membrane from step (3) was placed in an 80 ℃ oven to dry the moisture, and then placed in a 60 ℃ vacuum drying oven for 12 h to completely remove the moisture in the air. It was then stored in a vacuum drying oven. After drying, the membrane gained 1.4% more weight than the original membrane.

[0038] Example 4 (1) A method for preparing a nanofiber membrane, the steps of which are the same as those of Comparative Example 1, except that the proportion of nanocellulose in the nanofiber membrane is different.

[0039] (2) The proportion of the backbone fiber is 25wt%, the proportion of nanofiber is 70wt%, and the proportion of polymer network is 5wt%.

[0040] (3) Further, the nanofiber membrane has a thickness of 14 μm-20 μm, a porosity of 68-74%, and an ionic conductivity of 0.51-0.59 mS / cm. -1 .

[0041] (4) Before use, the wet membrane is filtered, squeezed and cut into small round pieces with a diameter of 16 mm, and placed in a vacuum drying oven at 60 ℃ for 12 h to completely remove the moisture in the air to obtain a nanofiber membrane with a thickness of 15 μm.

[0042] Example 5 (1) A method for preparing a nanofiber membrane, the steps of which are the same as those of Comparative Example 1, except that the proportion of nanocellulose in the nanofiber membrane is different.

[0043] (2) The proportion of backbone fiber is 20wt%, nanofiber is 75wt%, and polymer network is 5wt%.

[0044] (3) Further, the nanofiber membrane has a thickness of 14 μm-20 μm, a porosity of 69-75%, and an ionic conductivity of 0.58-0.63 mS / cm. -1 .

[0045] (4) Before use, the wet membrane is filtered, squeezed and cut into small round pieces with a diameter of 16 mm, and placed in a vacuum drying oven at 60 ℃ for 12 h to completely remove the moisture in the air to obtain a nanofiber membrane with a thickness of 15 μm.

[0046] Example 6 (1) A method for preparing a nanofiber membrane, the steps of which are the same as those of Comparative Example 1, except that the proportion of nanocellulose in the nanofiber membrane is different.

[0047] (2) The proportion of backbone fiber is 10wt%, nanofiber is 85wt%, and polymer network is 5wt%.

[0048] (3) Further, the nanofiber membrane has a thickness of 11-18 μm, a porosity of 81-88%, and an ionic conductivity of 0.61-0.68 mS / cm. -1 .

[0049] (4) Before use, the wet membrane is filtered, squeezed and cut into small round pieces with a diameter of 16 mm, and placed in a vacuum drying oven at 60 ℃ for 12 h to completely remove the moisture in the air to obtain a nanofiber membrane with a thickness of 15 μm.

[0050] The membranes prepared in Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2 were subjected to performance tests, and the results are shown in Table 1.

[0051] Table 1. Ionic conductivity and liquid absorption height of ultrathin nanofiber membranes under the action of LiNO3.

[0052] As shown in Table 1, when using ultrathin nanofiber membranes treated with different concentrations of LiNO3 to form the intermediate layer, it is not necessarily better to have more LiNO3. The best effect is achieved when the LiNO3 loading on the nanofiber membrane reaches the optimal level, so that the nanofiber membrane can achieve the best ionic conductivity and liquid absorption height. When the LiNO3 loading on the nanofiber membrane is moderate, the ionic conductivity, liquid absorption height and membrane pore size distribution complement each other and reach the optimal level simultaneously.

[0053] The nanofiber membranes from Examples 4-6 were treated with different concentrations of LiNO3 solution as described in Examples 1-3 to prepare nanofiber membranes of the same thickness but with different LiNO3 loading weights, exhibiting high ionic conductivity and strong liquid absorption properties. Ionic conductivity, membrane porosity, and pore size distribution were measured, and the results are shown in Table 2. The nanofiber content affects LiNO3 adsorption. When using ultrathin nanofiber membranes treated with different concentrations of LiNO3 as intermediate layers, a higher LiNO3 content is not necessarily better. The best effect is achieved when the LiNO3 loading of the nanofiber membrane is optimal. This is mainly because the hydroxyl groups loaded on the nanofiber directly affect LiNO3 adsorption, and the optimal nanofiber content leads to the best effect, resulting in the best ionic conductivity of the nanofiber membrane. When the LiNO3 loading of the nanofiber membrane is moderate, the ionic conductivity, membrane porosity, and membrane pore size distribution complement each other and simultaneously reach their optimal values.

[0054] Table 2 Ionic conductivity and porosity of ultrathin nanofiber membranes under LiNO3 action

[0055] Table 3. Ionic conductivity and porosity of nanofiber membranes from Comparative Examples 1 to 3 after 15 cycles under LiNO3 treatment.

[0056] Table 3 shows that the porosity and other properties of the nanofiber membrane decreased to varying degrees after cycling, while the ionic conductivity increased. This may be because LiNO3, under electrochemical action, generated new substances with higher ionic conductivity, altering the pore structure distribution and ionic conductivity of the membrane. Low LiNO3 concentration affects the amount of new substances with higher ionic conductivity generated; however, excessive generation of these substances significantly reduces the membrane's porosity and pore size, thus slowing down the rate at which lithium ions pass through the membrane and lowering the ionic conductivity. Therefore, more LiNO3 content is not necessarily better; the optimal LiNO3 loading on the nanofiber membrane yields the best results, ensuring that the nanofiber membrane achieves optimal ionic conductivity and porosity during cycling.

[0057] The nanofiber separators prepared in Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2 were combined with lithium metal anodes and Li[Ni]0.8 Co 0.1 Mn 0.1 An O2 cathode and an electrolyte (DME / DOL (1:1, v / v) 1 M LiTFSI) were assembled into a full cell for electrochemical impedance spectroscopy (EIS) testing. The Nyquist curve is shown below. Figure 2 As shown, the charge transfer impedance Rct of the battery in Example 2 is lower than that in Examples 1, 3, Comparative Example 1, and Comparative Example 2. This means that the Li through the interface film... + Reduced transport resistance effectively promotes lithium-ion migration in the interlayer, enhancing ionic conductivity. In electrochemical impedance spectroscopy, a lower charge transfer impedance (Rct) is generally associated with better electrochemical performance because it signifies less resistance to charge transfer during the electrochemical reaction, thereby improving the battery's charge-discharge efficiency and rate performance.

[0058] In the above steps, the nanofiber membrane, after being soaked in LiNO3 solution, exhibits good ionic conductivity and liquid absorption performance. LiNO3 is a strong electrolyte, which will dissociate a large number of lithium ions (Li) during lithium deposition. + ) and nitrate ions (NO3) - XPS analysis was performed on the nanofiber separators and lithium metal anodes, Li[Ni] fabricated in Example 1 and Comparative Example 2, and their interaction with these materials. 0.8 Co 0.1 Mn 0.1 The characteristics of a full cell assembled with an O2 cathode and an electrolyte (DME / DOL (1:1, v / v) 1 M LiTFSI) after charge and discharge, such as... Figure 3 The findings show that, compared to Examples 1, 3, and Comparative Example 2, the nanofiber separator in Example 2 exhibits a more significant formation of a Li3N-rich solid electrolyte interphase (SEI) layer and highly ionicly conductive Li2O on the lithium anode-facing surface, thus stabilizing subsequent lithium deposition / stripping. Simultaneously, the Li2O peak positions in Examples 3 and Comparative Example 2 show a leftward shift, indicating the formation of a more stable Li2O layer on the nanofiber separator surface. This may be detrimental to lithium ion migration, as higher binding energies mean more difficulty in extracting lithium ions from Li2O, potentially affecting battery cycle performance. Unfavorable charge transfer can lead to reduced lithium adsorption energy, thus impacting lithium deposition / stripping in subsequent cycles. Compared to Example 2, the LiNO3-modified nanofiber separator demonstrates superior performance compared to the AgNO3-modified nanofiber separator. This difference is attributed to the uneven lithium deposition / stripping process on the separator in Comparative Example 2, resulting in the accumulation of dead lithium.

[0059] After treating nanofiber membranes with LiNO3 solutions of different concentrations, when the nanofiber membranes are immersed in the LiNO3 solution, on the one hand, the additional lithium ions increase the ion concentration in the electrolyte near the membrane, promoting the migration of lithium ions in the intermediate layer and improving ionic conductivity; on the other hand, NO3... - The presence of ions interacts with other ions in the electrolyte, promoting the dissociation of lithium salts and further enhancing ionic conductivity. Simultaneously, the formation of a Li3N-rich SEI and highly ionicly conductive Li2O facilitates uniform lithium metal deposition / stripping. It is also noteworthy that the LiNO3-coated nanofiber separator exhibits strong liquid absorption and retention capabilities, optimizing the microenvironment for ion transport and effectively improving the overall ionic conductivity of the separator. The LiNO3-formed SEI film possesses certain electrochemical stability and interfacial activity. When present in the interlayer of the nanofiber separator, it forms a stable interfacial layer at the interface between the lithium metal anode and the interlayer. This interfacial layer inhibits the growth of lithium dendrites, a potentially detrimental phenomenon in lithium-ion batteries during cycling. Lithium dendrites can puncture the separator, leading to short circuits and severely impacting battery safety and lifespan. By suppressing lithium dendrite growth, the LiNO3-treated nanofiber separator interlayer helps maintain the integrity of the lithium metal-separator interface, reducing internal side reactions and extending battery cycle life.

[0060] The chemical properties of nanofiber membranes change after treatment with LiNO3 solution. This is because the LiNO3 solution can introduce polar NO3 groups onto the membrane surface. - The LiNO3 solution alters the charge distribution on the membrane surface, transforming it from a relatively hydrophobic state to a more hydrophilic one. Lithium ions from LiNO3 may adsorb onto the membrane surface, giving it a positive charge. Anions from the electrolyte are then attracted to this surface, promoting contact and adsorption between the electrolyte and the membrane, thus improving the membrane's liquid absorption capacity. From a physical structure perspective, the LiNO3 solution can regulate the pore structure of the nanofiber membrane during soaking. It may prevent pore collapse or blockage during membrane preparation, making the pores more open. Simultaneously, it can also create a more rational pore size distribution, facilitating electrolyte filling and storage. The membrane pores treated with LiNO3 solution can better absorb and contain the electrolyte, thereby increasing its liquid absorption capacity.

[0061] It should be understood that the above description of the preferred embodiments is quite detailed, but it should not be considered as a limitation on the scope of protection of this invention. Those skilled in the art, under the guidance of this invention, can make substitutions or modifications without departing from the scope of protection of the claims of this invention, and all such substitutions or modifications fall within the scope of protection of this invention. The scope of protection of this invention should be determined by the appended claims.

Claims

1. A method for preparing a nanofiber membrane with high ionic conductivity and strong liquid absorption performance, characterized in that the steps include... include: Step 1. Dissolve lithium nitrate to prepare an aqueous solution of lithium nitrate; Step 2. Press the nanofiber diaphragm into an electrode sheet and dry it in a vacuum drying oven; Step 3. Immerse the nanofiber membrane treated in Step 2 in the lithium nitrate aqueous solution in Step 1 at a temperature of 80-120℃. Mix the two thoroughly and the lithium-loving nitrate will coat and fill the nanofiber membrane. Step 4. The nanofiber membrane obtained after treatment in step 3 is dried at 40-100°C to obtain the nanofiber membrane with high ionic conductivity and strong liquid absorption performance. The concentration of the lithium nitrate aqueous solution in step 1 is 1 mol / L; In step 3, the nanofiber membrane is immersed in lithium nitrate aqueous solution for 20-60 minutes. The nanofiber membrane is formed by stacking a skeleton fiber layer, a nanofiber layer, and a polymer network layer from bottom to top. The skeleton fiber layer is made of interwoven micron-sized fibers and short chemical fibers. The nanofiber layer is made of interwoven nanofibers containing hydroxyl functional groups. The polymer network layer is made of interwoven polymers. The nanofiber portion extends into the skeleton fiber layer, and the polymer portion extends into the nanofiber layer. The nanofiber membrane comprises 15 wt% skeletal fibers, 80 wt% nanofibers, and 5 wt% polymer network. The membrane has a thickness of 12 μm-18 μm, a porosity of 80-86%, and an ionic conductivity of 0.70-0.80 mS·cm. -1 .

2. A nanofiber membrane with high ionic conductivity and strong liquid absorption, prepared by the method described in claim 1, characterized in that, The membrane comprises a nanofiber membrane and lithium nitrate coated on the membrane, wherein the weight of the lithium nitrate is 1.2 to 1.4% of the weight of the nanofiber membrane.

3. A lithium-ion battery, characterized in that, It includes a shell, a positive electrode, a negative electrode, an electrolyte, and an intermediate layer, wherein the intermediate layer is the nanofiber membrane with high ionic conductivity and strong liquid absorption as described in claim 2, and the thickness of the nanofiber membrane with high ionic conductivity and strong liquid absorption is 15 μm.

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