Lithium ion battery positive plate capable of releasing lithium nitrate, diaphragm-free lithium ion battery and preparation method

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a lithium ion battery positive plate capable of releasing lithium nitrate, a diaphragm-free lithium ion battery and a preparation method. The surface of the positive plate of the lithium ion battery is coated with a hollow mesoporous silica insulating coating capable of releasing lithium nitrate, so that the battery completely abandons a traditional polyolefin diaphragm. The coating can store lithium nitrate by utilizing a hollow cavity of the hollow mesoporous silica while realizing physical isolation of the electrode, and a lithium nitrate additive is released by virtue of a mesoporous channel, so that the cycling stability of the battery is improved. According to the invention, the hollow mesoporous silica capable of releasing lithium nitrate is prepared into the self-supporting functional coating by using the flexible bonding effect of the binder. According to the structure, the thermal stability of the battery is remarkably improved, and the risk of high-temperature thermal shrinkage short circuit is reduced. Lithium nitrate in the hollow mesoporous silica is released into the electrolyte and participates in forming a nitrate-containing and high-strength solid electrolyte interface film or a positive electrode electrolyte interface film, so that the cycle life is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a lithium-ion battery positive electrode that can release lithium nitrate, a membrane-free lithium-ion battery, and a preparation method thereof. Background Technology

[0002] Lithium-ion batteries (LIBs), with their high energy density, have been widely used in consumer electronics, electric vehicles, and energy storage systems (ESS). With the expansion of application scenarios, higher requirements are being placed on battery energy density, cycle life, and safety. Among these, the separator, as a core component, directly affects battery performance and safety by isolating the physical contact between the positive and negative electrodes and regulating lithium-ion transport. Currently, commercially available separators are mainly made of porous polyethylene (PE), polypropylene (PP), or their composite membranes (such as a PP / PE / PP three-layer structure), which have advantages in chemical stability and mechanical strength. However, these separator materials suffer from poor thermal stability, high interfacial impedance, and poor electrolyte wettability, leading to a decline in battery cycle performance and safety. To overcome these bottlenecks, the industry mainly adopts methods such as coating with ceramic layers (e.g., Al2O3, SiO2) to improve electrolyte wettability and reduce interfacial impedance; thinning the separator can reduce battery impedance and increase battery energy density, but thinning reduces the mechanical strength of the separator and makes the coating prone to peeling off and clogging pores; using polyvinylidene fluoride- co Polymer matrices such as hexafluoropropylene (PVDF-HFP) can improve electrolyte wettability, but their thermal stability is not fundamentally improved, and the improvement in ionic conductivity is limited. Therefore, there is an urgent need to develop a new technology to avoid the problems of low energy density, short cycle life, and poor safety in lithium-ion batteries caused by the separator. Summary of the Invention

[0003] This invention aims to simultaneously solve the problems of limited energy density, insufficient cycle life, and high thermal safety risk in traditional lithium-ion batteries through electrode-electrolyte interface reconstruction and separator replacement technology. The core innovations are: (1) abandoning the traditional separator, constructing a self-supporting coating on the surface of the positive electrode that has both physical isolation and lithium nitrate release functions (thickness of only 1-50 μm, which is highly adjustable compared to the 16-25 μm of commercial separators); (2) addressing the problem of low solubility of lithium nitrate in organic electrolytes, loading lithium nitrate into hollow mesoporous silica (HMSNs) to realize the release of lithium nitrate from the pores, participate in the formation of a high-strength nitrogen-containing interface film (CEI / SEI), suppress side reactions and improve cycle stability; (3) the inorganic framework structure of HMSNs gives the coating excellent thermal stability, fundamentally eliminating the risk of high-temperature short circuit.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A lithium-ion battery positive electrode sheet has an insulating coating on its surface, which includes hollow mesoporous silica particles (LiNO3@HMSNs) loaded with lithium nitrate and a binder; the coating has both electrode isolation and lithium nitrate release functions. Specifically, the coating is used to physically isolate the electrode and release lithium nitrate through mesoporous channels.

[0005] Preferably, the HMSNs have a pore size of 2-50 nm and a shell thickness of 5-200 nm.

[0006] Preferably, the lithium nitrate loading in the hollow mesoporous silica particles is 10 wt%-60 wt%.

[0007] Preferably, the cathode is any one of lithium iron phosphate, lithium cobalt oxide, or lithium nickel cobalt manganese oxide.

[0008] Preferably, the adhesive is PVDF or PVDF-HFP adhesive.

[0009] More preferably, the mass ratio of PVDF to HMSNs is 1:(5~20).

[0010] Preferably, the thickness of the coating is 1-50 µm.

[0011] Preferably, the method for preparing lithium nitrate-loaded hollow mesoporous silica particles includes the following steps: Step 1: Preparation of silica (SiO2) nanoparticles Tetraethoxysilane (TEOS) and ammonia were added to a mixed solution of ethanol and water, and the mixture was stirred at a constant temperature for 2 hours. After the reaction was completed, the white product was washed 4 times each with ethanol and deionized water to obtain silica nanoparticles. Step 2: Synthesis of SiO2@CTAB-SiO2 core-shell structured nanoparticles Silica nanoparticles were dispersed in deionized water and ultrasonically dispersed to obtain a dispersion. The dispersion was added to a mixed solution containing surfactant, deionized water, ethanol and concentrated ammonia. After stirring at room temperature, TEOS was quickly added and the reaction continued. After the reaction was completed, the white product was collected by centrifugation and washed 4 times each with ethanol and water. The product was labeled as SiO2@CTAB-SiO2. Step 3: Preparation of HMSNs SiO2@CTAB-SiO2 was redispersed in deionized water to obtain a dispersion, which was ultrasonicated for 20 minutes and vigorously stirred until the particles were uniformly dispersed. Sodium carbonate was added, and the mixture was heated and stirred to react. After centrifugation, the product was washed thoroughly with water and dispersed in a mixture of methanol and hydrochloric acid. The mixture was refluxed at a certain temperature and then centrifuged again. The product was washed thoroughly with deionized water and ethanol in sequence. The final product was labeled as HMSNs. Step 4: Preparation of HMSNs adsorbed with lithium nitrate HMSNs were loaded into an aqueous lithium nitrate solution, stirred, and dried to obtain HMSNs loaded with lithium nitrate (LiNO3@HMSNs).

[0012] More preferably, in step 1, the mass concentration of ammonia is 25%-30%, the volume ratio of TEOS to ammonia is 1:(0.5~2), the volume ratio of ethanol to water in the mixed solution of ethanol and water is (5~10):1, and the volume ratio of TEOS to the mixed solution is (20~100):1.

[0013] More preferably, in step 1, the reaction time is 1-5 h and the reaction temperature is 20-50 ℃.

[0014] More preferably, in step 2, the concentration of silica nanoparticles in the dispersion is 2~10 g / L, and the mass-to-volume ratio of the dispersion to the surfactant, deionized water, ethanol, concentrated ammonia, and TEOS in the mixed solution is (100~200) mg : (20~50) mL : (10~50) mL : (0.1~1.0) mL : (0.1~5) mL.

[0015] More preferably, in step 2, the reaction time is 2 to 10 hours.

[0016] More preferably, the surfactant in step 2 is hexadecyltrimethylammonium bromide or a silane coupling agent.

[0017] More preferably, in step 3, the concentration of SiO2@CTAB-SiO2 in the dispersion is 5~20 g / L; the concentration of hydrochloric acid in the mixed solution of methanol and hydrochloric acid is 20~38%, and the mass ratio of hydrochloric acid in the mixed solution is 1~5%; the mass ratio of the dispersion, sodium carbonate, and the mixed solution of methanol and hydrochloric acid is (5~20):(0.2~0.6):(20~100).

[0018] In a further preferred embodiment, in step 3, after adding sodium carbonate, the heating and stirring temperature is 30-80 ℃, and the reaction time is 5-10 h.

[0019] In a further preferred embodiment, step 3 involves a reflux time of 5–30 h and a reflux temperature of 50–100 ℃.

[0020] More preferably, the concentration of the lithium nitrate aqueous solution in step 4 is 10-90 g / L; More preferably, in step 4, the mass-to-volume ratio of HMSNs to lithium nitrate solution is 1 g : (10~100) mL.

[0021] In a further preferred embodiment, in step 4, HMSNs are immersed in an aqueous lithium nitrate solution, stirred for 5-24 hours, then vacuumed, released, filtered, and the product is dried at 25-100 °C to obtain lithium nitrate-loaded HMSNs.

[0022] The method for preparing a lithium-ion battery positive electrode sheet comprises the following steps: (a) Mix LiNO3@HMSNs, PVDF, and N-methylpyrrolidone and stir until homogeneous to obtain a coating slurry; (b) The coating slurry is applied to the surface of the positive electrode and dried to obtain a positive electrode sheet coated with LiNO3@HMSNs.

[0023] Preferably, in step (a), the LiNO3@HMSNs, binder and N-methylpyrrolidone are mixed and pulped at a mass ratio of (50~95): (5~50): (50~200); Preferably, in step (b), the drying method is to dry at 100 °C for 12 h.

[0024] A membraneless lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte, but does not include a separator; the positive electrode is physically isolated by a coating. The negative electrode is selected from graphite, silicon-carbon composite material, or metallic lithium. The electrolyte contains lithium salt and an organic solvent.

[0025] Compared with the prior art, the beneficial effects of the present invention are reflected in: This invention utilizes a composite coating of lithium-ion battery cathode materials (HMSNs) and a binder to completely eliminate the need for traditional polyolefin separators, potentially increasing the battery's volumetric energy density. The invention leverages the flexible bonding effect of the binder to create a self-supporting functionalized coating with high porosity from the HMSNs. This structure significantly improves the battery's thermal stability and reduces the risk of short circuits due to high-temperature thermal shrinkage. While achieving physical isolation between the electrodes, the coating also stores lithium nitrate within the hollow cavities (50-200 nm) of the HMSNs and releases it through mesoporous channels (2-50 nm). This lithium nitrate release participates in the formation of a stable nitrogen-containing interface film, significantly improving the battery's cycle stability. Attached Figure Description

[0026] Figure 1 These are TEM images of HMSNs in Embodiment 1 of the present invention; Figure 2 This is a graph showing the BET test results of HMSNs in Embodiment 1 of the present invention; Figure 3 This is a graph showing the BET test results of LiNO3@HMSNs in Embodiment 1 of the present invention; Figure 4This is a schematic diagram illustrating the fabrication of the positive electrode sheet coated with LiNO3@HMSNs according to the present invention; Figure 5 This is a surface SEM image of the lithium iron phosphate cathode sheet in Example 1 of the present invention; Figure 6 This is a SEM image of the surface of the positive electrode coated with LiNO3@HMSNs in Embodiment 1 of the present invention; Figure 7 This is a SEM image of the cross-section of the positive electrode coated with LiNO3@HMSNs in Embodiment 1 of the present invention; Figure 8 This is a graph showing the weight changes of different positive electrode sheets after being immersed in water for 24 hours in Example 1 of the present invention; Figure 9 This is a rate performance diagram of the half-cell in Embodiment 1 of the present invention at 0.2-4.0 C. Figure 10 This is a cycle performance diagram of the half-cell at 1.0 C in Embodiment 1 of the present invention; Figure 11 This is a SEM image of the cross-section of the positive electrode coated with LiNO3@HMSNs in Embodiment 2 of the present invention; Figure 12 This is a cycle performance diagram of the half-cell at 1.0 C in Embodiment 2 of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be described in detail below through specific embodiments and examples. It should be noted that systematic examples can make the innovative advantages and technical features of the present invention more explicit. It should be particularly noted that the provided embodiments are merely illustrative examples of technical principles and do not constitute a limitation on the scope of the claims of the present invention. Those skilled in the art should understand that, under the premise of strictly following the core design concept and claims of the present invention, adaptive adjustments or equivalent substitutions can be made to the specific implementation details and manifestations of the technical solution, and such technical modifications all fall within the protection scope of the patent claims of this invention.

[0028] Unless otherwise specified, the experimental methods mentioned in this document refer to the general experimental procedures in this field; unless otherwise specified, the reagents and materials mentioned refer to conventional chemical preparations that can be obtained through standardized commercial channels; and the experimental apparatus and instruments mentioned all adopt conventional experimental instruments that conform to industry standards.

[0029] Example 1 A method for preparing a positive electrode sheet for a membrane-free lithium-ion battery capable of releasing lithium nitrate includes the following steps: A method for preparing lithium nitrate-loaded hollow mesoporous silica particles includes the following steps: Step 1: Preparation of silica (SiO2) nanoparticles Tetraethoxysilane (TEOS, 10 mL) and concentrated ammonia (25%, wt%) (10 mL) were added to an ethanol / water mixture (428 mL ethanol + 60 mL water), and the mixture was gently stirred at 30 °C for 2 hours. After the reaction was completed, the white product was washed four times each with ethanol and deionized water, and finally ultrasonically dispersed in deionized water for later use. Step 2: Synthesis of SiO2@CTAB-SiO2 core-shell structured nanoparticles 100 mg of silica nanoparticles were dispersed in 20 mL of deionized water and sonicated for 30 minutes. The dispersion was then added to a mixed solution containing 150 mg of hexadecyltrimethylammonium bromide (CTAB), 30 mL of deionized water, 30 mL of ethanol, and 0.55 mL of concentrated ammonia. After stirring at room temperature for 30 minutes, 0.25 mL of TEOS was quickly added, and the reaction was continued for 6 hours. The white product (300 mg) was collected by centrifugation, washed four times each with ethanol and water, and redispersed in 20 mL of deionized water for later use. The product was labeled as SiO2@CTAB-SiO2. Step 3: Preparation of HMSNs A 20 mL solution of SiO2@CTAB-SiO2 with a concentration of 15 g / L was ultrasonicated for 20 minutes and stirred vigorously for 4 hours. Sodium carbonate (Na2CO3, 470 mg) was added, and the mixture was stirred at 50 °C for 10 hours. After centrifugation, the product was washed thoroughly with water. The product was dispersed in a methanol / hydrochloric acid mixture (50 g methanol + 4 g hydrochloric acid); refluxed at 80 °C for 24 hours; after centrifugation, the product was washed thoroughly with deionized water and ethanol, respectively. The final product was labeled as HMSNs.

[0030] TEM analysis of HMSNs yielded the following results: Figure 1 As shown, a spherical structure with a hollow structure and a shell thickness of about 50 nm with many pores can be seen, which can promote the rapid migration of lithium ions.

[0031] A BET test was performed on HMSNs, and the results are as follows: Figure 2 As shown, the pore size of the spheres is between 2 and 5 nm.

[0032] Specific surface area analysis of HMSNs microspheres was performed, and the results are as follows: Figure 3 As shown in the figure, it can be seen that the HMSNs before adsorption have many pores, especially the pores with a diameter of 2-5 nm, which have the highest pore area of ​​1.17 cm². 3 g -1 nm -1After lithium nitrate is adsorbed into the pores of HMSNs, the pore area of ​​the micropores almost disappears, leaving only a very small number of pores around 30 nm. The results indicate that lithium nitrate adsorbs into the pores of HMSNs, blocking them.

[0033] Step 4: Take 5.0 g of HMSNs and pour it into 100 mL of 90 g / L lithium nitrate aqueous solution. Stir for 12 hours, then vacuum, release the gas, filter, dry at 80 ℃ for 12 hours, and take it out to obtain LiNO3@HMSNs nanomaterials.

[0034] A method for preparing a lithium-ion battery positive electrode sheet, the preparation process is shown in the schematic diagram below. Figure 4 As shown, the steps are as follows: (a) Take 5.0 g of LiNO3@HMSNs nanospheres, 1.0 g of PVDF, and a certain amount of NMP and stir them evenly to prepare a polymer-coated inorganic nanoparticle cathode coating slurry, and store it for later use.

[0035] Preparation of positive electrode slurry: Lithium iron phosphate, binder PVDF, and conductive agent acetylene black were dried in a vacuum oven for 12 hours. 2.0 g of lithium iron phosphate and 0.25 g of acetylene black were weighed and ground evenly. 5% PVDF was then added and the mixture was ground for another 30 minutes. NMP was used as the solvent. After grinding evenly, the mixture was stored for later use.

[0036] (b) The above-mentioned positive electrode slurry is coated using a coating machine, dried, and rolled to obtain a lithium iron phosphate positive electrode sheet. Then, another layer of the above-mentioned polymer-coated inorganic nanosphere particle positive electrode coating slurry is coated on top, and dried in a vacuum oven at 100 °C for 12 hours to obtain a positive electrode sheet coated with LiNO3@HMSNs, as shown in the schematic diagram. Figure 3 As shown, the LiNO3@HMSNs composite coating acts as a separator to prevent short circuits between the positive and negative electrodes, while the released lithium nitrate participates in the formation of a stable nitrogen-containing interface film.

[0037] SEM images of the surface of the uncoated LiNO3@HMSNs lithium iron phosphate cathode are shown below. Figure 5 As shown, the lithium iron phosphate particles are relatively large, and the positive electrode surface is very rough. SEM analysis of the positive electrode coated with LiNO3@HMSNs yielded the following results: Figure 6 , 7 As shown, the coating thickness is about 2 µm, and the positive electrode surface is protected by the coating, making it relatively smooth and flat.

[0038] A membrane-free lithium-ion battery is prepared by the following method: The positive electrode used was the lithium iron phosphate positive electrode sheet coated with LiNO3@HMSNs prepared above, and the negative electrode was lithium metal. The electrical performance of the prepared button cell was tested by lithium sheet-electrolyte-positive electrode. The electrolyte used was a commercial lithium-ion electrolyte (1.0 M LiPF6 in EC:EMC=1:1 vol%).

[0039] In the lithium nitrate adsorption capacity test, lithium iron phosphate cathode sheets, HMSNs-coated / lithium iron phosphate cathode sheets, and LiNO3@HMSNs-coated / lithium iron phosphate cathode sheets were formed into discs with a diameter of 12 mm. After weighing, they were immersed in 100 ml of deionized water solvent for 24 hours, then removed and weighed again. The lithium nitrate content could be calculated from the change in mass before and after the immersion. Figure 8 It can be seen that the mass change of the lithium iron phosphate cathode sheet and the HMSNs coating / lithium iron phosphate cathode sheet before and after immersion is small, and the areal density of the LiNO3@HMSNs coating is approximately 2.2 mg cm³. -2 The areal capacity of lithium nitrate is approximately 0.4 mg cm³. -2 The content of lithium nitrate in the coating is approximately 18 wt%.

[0040] The solubility of lithium nitrate in the electrolyte is very low, about 6 g / L. The amount of electrolyte added to a single button cell is about 0.08 mL, and the maximum amount of lithium nitrate dissolved is 0.48 µg. The electrode is about 10 mg, and about 400 µg of lithium nitrate can be released. Therefore, the amount of lithium nitrate in the layer is much higher than the amount of lithium nitrate that can be dissolved in the electrolyte, so the amount of lithium nitrate is sufficient.

[0041] Comparative Example 1 Commercial lithium iron phosphate cathode sheets were selected for the positive electrode, and a common Celgard 2325 separator was used. Lithium metal was selected for the negative electrode. The electrical performance of the prepared button cell was tested by passing the negative electrode-separator-electrolyte-positive electrode. A commercial lithium-ion electrolyte (1.0 M LiPF6, EC:EMC=1:1 Vol%) was selected as the electrolyte.

[0042] Comparative Example 2 Take 5.0 g of HMSNs nanospheres, 1.0 g of PVDF, and a certain amount of NMP, stir evenly to prepare a polymer-coated inorganic nanoparticle cathode coating slurry, and store it for later use.

[0043] Preparation of positive electrode slurry: Lithium iron phosphate, binder PVDF, and conductive agent acetylene black were dried in a vacuum oven for 12 hours. 2.0 g of lithium iron phosphate and 0.25 g of acetylene black were weighed and ground evenly. 5% PVDF was then added and the mixture was ground for another 30 minutes. NMP was used as the solvent. After grinding evenly, the mixture was stored for later use.

[0044] The above-mentioned positive electrode slurry was coated using a coating machine, dried, and rolled to obtain a lithium iron phosphate positive electrode sheet. Then, a layer of the above-mentioned polymer-coated inorganic nanosphere particle positive electrode coating slurry was coated on top, and dried in a vacuum oven at 100 °C for 12 hours to obtain a positive electrode sheet coated with HMSNs. The positive electrode used was the lithium iron phosphate positive electrode sheet coated with HMSNs prepared above, and the negative electrode was lithium metal. The electrical performance of the prepared button cell was tested using a lithium sheet-electrolyte-positive electrode method. The electrolyte used was a commercially available lithium-ion electrolyte (1.0 M LiPF6 in EC:EMC = 1:1 vol%).

[0045] Depend on Figure 6 It can be clearly observed that the surface of the lithium iron phosphate cathode is smoother after coating. Figure 7 The cross-sectional view clearly shows that the coating is approximately 2 µm thick, much smaller than the thickness of commercial separators (commercial separators are typically 20-40 µm thick). Therefore, replacing the separator with a coating can further improve the energy density of the battery. The rate performance of the batteries prepared in Example 1, Comparative Examples 1 and 2 is compared. Figure 9 ), Cyclic performance ( Figure 10 Test them separately, by Figure 9 It is known that coated lithium iron phosphate batteries have higher capacity at high rates. The 2-micron coating significantly reduces the distance between the positive and negative electrodes, thus shortening the lithium-ion transport distance and improving transport efficiency during battery charging and discharging. The spherical stacking of HMSNs creates larger and more numerous pores than commercial separators, effectively enhancing the lithium-ion transport channels. Figure 9 The rate performance data shows that at low rates (0.2 C), the discharge capacities of the three types of batteries are similar. However, at high rate cycles (4 C), the battery with more pores and a shorter transmission distance has a higher cycle capacity than the battery using a commercially available separator. This is evident from the long-cycle performance curves (…). Figure 10 It can be seen that the capacity of batteries assembled with commercial separators decays relatively quickly. Batteries assembled using positive electrode sheets coated with HMSNs show a significant increase in discharge capacity after 200 cycles, and batteries assembled using positive electrode sheets coated with LiNO3@HMSNs show an even greater increase in discharge capacity. This demonstrates that the HMSNs coating can fill the pores on the positive electrode surface, creating a more uniform positive electrode surface, thus increasing cycle stability. The LiNO3@HMSNs coating can release nitrate ions, which participate in the formation of the electrode-electrolyte interface film, constructing a high-strength interface film containing nitrogen, thus further increasing its cycle stability.

[0046] Example 2 A method for preparing a membraneless lithium-ion battery positive electrode that releases lithium nitrate differs from Example 1 in that the thickness of the positive electrode coating is different.

[0047] By adjusting the distance between the scraper and the positive electrode surface, an inorganic nanosphere coating was applied to the surface of the lithium iron phosphate positive electrode. The coating width was designed to encompass the entire positive electrode active layer and aluminum foil, with a coating thickness of approximately 10 µm. The positive electrode coating was first characterized, and then a battery was assembled using the positive electrode sheet for electrochemical performance testing. Figure 11 The SEM image of the positive electrode cross-section shows a coating thickness of approximately 10 µm, still significantly thinner than that of commercially available separators. The assembled battery's cycle performance is as follows... Figure 12 As shown, the increase in thickness does not adversely affect the battery's cycle stability; the battery can stably cycle for over 300 times while still maintaining a capacity of 141 mAh g. -1 .

[0048] Example 3 Unlike Example 1, a graphite anode was chosen instead of a lithium sheet.

[0049] Example 4 Unlike Example 1, a ternary cathode was chosen instead of lithium iron phosphate.

[0050] Example 5 Unlike Example 1, PVDF-HFP was chosen as the adhesive.

Claims

1. A positive electrode sheet for a lithium-ion battery, characterized in that, The surface of the positive electrode is coated with an insulating coating, which includes hollow mesoporous silica particles and a binder. Lithium nitrate is loaded into the pores of the hollow mesoporous silica particles.

2. The lithium-ion battery positive electrode sheet according to claim 1, characterized in that, The hollow mesoporous silica particles have a pore size of 2-50 nm and a shell thickness of 5-200 nm; preferably, the lithium nitrate loading in the hollow mesoporous silica particles is 10 wt%-60 wt%.

3. The lithium-ion battery positive electrode sheet according to claim 1, characterized in that, The positive electrode active material of the positive electrode sheet is selected from lithium iron phosphate, lithium cobalt oxide, and lithium nickel cobalt manganese oxide; preferably, the binder is selected from polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene copolymer; preferably, the mass ratio of the binder to the hollow mesoporous silica particles is 1: (5~20); preferably, the thickness of the coating is 1-50 µm.

4. The lithium-ion battery positive electrode sheet according to claim 1, characterized in that, A method for preparing lithium nitrate-loaded hollow mesoporous silica particles includes the following steps: Step 1: Preparation of silica nanoparticles Tetraethoxysilane and ammonia were added to a mixed solution of ethanol and water, and the mixture was stirred at a constant temperature. After the reaction was completed, the white product was washed four times each with ethanol and deionized water to obtain silica nanoparticles. Step 2: Synthesis of SiO2@CTAB-SiO2 core-shell structured nanoparticles Silica nanoparticles were dispersed in deionized water and ultrasonically dispersed to obtain a dispersion. The dispersion was added to a mixed solution containing surfactant, deionized water, ethanol and concentrated ammonia. After stirring at room temperature, TEOS was quickly added and the reaction continued. After the reaction was completed, the white product was collected by centrifugation and washed 4 times each with ethanol and water. The product was labeled as SiO2@CTAB-SiO2. Step 3: Preparation of HMSNs SiO2@CTAB-SiO2 was redispersed in deionized water to obtain a dispersion, which was ultrasonicated for 20 minutes and vigorously stirred until the particles were uniformly dispersed. Sodium carbonate was added, and the mixture was heated and stirred to react. After centrifugation, the product was washed thoroughly with water and dispersed in a mixture of methanol and hydrochloric acid. The mixture was refluxed at a certain temperature and then centrifuged again. The product was washed thoroughly with deionized water and ethanol in sequence. The final product was labeled as HMSNs. Step 4: Preparation of HMSNs loaded with lithium nitrate HMSNs were immersed in an aqueous lithium nitrate solution and stirred, then dried to obtain lithium nitrate-loaded HMSNs.

5. The lithium-ion battery positive electrode sheet according to claim 4, characterized in that, A method for preparing hollow mesoporous silica particles loaded with lithium nitrate, wherein in step 1, the mass concentration of ammonia is 25%-30%, the volume ratio of TEOS to ammonia is 1:(0.5~2), the volume ratio of ethanol to water in the mixed solution of ethanol and water is (5~10):1, and the volume ratio of TEOS to the mixed solution is (20~100):

1. Preferably, in step 1, the reaction time is 1-5 h and the reaction temperature is 20-50 ℃.

6. The lithium-ion battery positive electrode sheet according to claim 4, characterized in that, A method for preparing hollow mesoporous silica particles loaded with lithium nitrate, wherein in step 2, the concentration of silica nanoparticles in the dispersion is 2~10 g / L, and the mass-to-volume ratio of the dispersion to the surfactant, deionized water, ethanol, concentrated ammonia, and TEOS in the mixed solution is (100~200) mg : (20~50) mL : (10~50) mL : (0.1~1.0) mL : (0.1~5) mL; Preferably, in step 2, the reaction time is 2 to 10 hours; Preferably, the surfactant in step 2 is hexadecyltrimethylammonium bromide or a silane coupling agent.

7. The lithium-ion battery positive electrode sheet according to claim 4, characterized in that, A method for preparing hollow mesoporous silica particles loaded with lithium nitrate, step 3, the concentration of SiO2@CTAB-SiO2 in the dispersion is 5~20 g / L; In the methanol and hydrochloric acid mixed solution, the hydrochloric acid concentration is 20-38%, and the mass percentage of hydrochloric acid in the mixed solution is 1-5%; the mass ratio of the dispersion, sodium carbonate, and methanol and hydrochloric acid mixed solution is (5-20):(0.2-0.6):(20-100). Preferably, in step 3, after adding sodium carbonate, the heating and stirring temperature is 30-80 ℃, and the reaction time is 5-10 h; Preferably, in step 3, the reflux time is 5~30 h; the reflux temperature is 50-100 ℃.

8. The lithium-ion battery positive electrode sheet according to claim 4, characterized in that, A method for preparing hollow mesoporous silica particles loaded with lithium nitrate, wherein the concentration of the lithium nitrate aqueous solution in step 4 is 10-90 g / L; Preferably, in step 4, the mass-to-volume ratio of HMSNs to lithium nitrate aqueous solution is 1 g : (10~100) mL; Preferably, in step 4, HMSNs are immersed in an aqueous lithium nitrate solution, stirred for 5-24 hours, then vacuumed, released, filtered, and the product is dried at 25-100 °C to obtain lithium nitrate-loaded HMSNs.

9. A method for preparing a lithium-ion battery positive electrode sheet according to any one of claims 1-8, characterized in that, Includes the following steps: (a) Mix LiNO3@HMSNs, binder and N-methylpyrrolidone in a mass ratio of (50~95): (5~50): (50~200) to form a pulp; (b) The slurry is coated on the surface of the positive electrode and dried at 100 °C for 12 hours to form an insulating coating.

10. A membrane-free lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The positive electrode is the positive electrode sheet according to any one of claims 1-8; the battery does not contain a separator, and the insulating coating provides physical isolation between the positive and negative electrodes; the negative electrode is selected from graphite, silicon-carbon composite material or metallic lithium; the electrolyte contains lithium salt and organic solvent.

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