A flexible solid-state lithium-ion battery and its preparation method

Abstract

This invention discloses a flexible solid-state lithium-ion battery and its preparation method, belonging to the field of lithium-ion battery technology. The flexible solid-state lithium-ion battery includes a solid positive electrode, a solid negative electrode, and a solid electrolyte; the solid positive electrode is a lithium foil coated with a diamond film; the solid negative electrode includes a diamond film-coated composite negative electrode, a conductive agent, a lithium salt, and a binder; the solid electrolyte includes a polyethylene oxide solid polymer electrolyte or a polyvinylidene fluoride solid polymer electrolyte; the composite negative electrode is prepared from coal gangue, boric acid, and chitosan. The preparation process of this invention is simple, and the raw materials used are readily available, making it suitable for widespread application.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and more specifically relates to a flexible solid-state lithium-ion battery and its preparation method. Background Technology

[0002] With the advancement of technology, electronic devices are constantly evolving towards thinner, lighter, more diverse, and more flexible designs. The rise of smart hardware such as foldable phones and wearable devices has created an urgent demand for flexible energy storage devices to match them. Traditional rigid lithium-ion batteries cannot meet the usage requirements of these devices under bending, folding, and other deformable conditions, thus limiting the further development of flexible electronic devices.

[0003] As a result, flexible solid-state lithium-ion batteries have been developed in all aspects. Existing flexible solid-state lithium-ion batteries have the following defects: 1. Interface problems: (1) Excessive interface impedance: The solid electrolyte and electrode material are in solid-solid contact, and the effective contact between the electrode and the electrolyte is weak. The ion transport kinetics in solid materials are low, resulting in a large interface impedance, which will affect the charging and discharging efficiency and performance of the battery. (2) Insufficient interface stability: During the charging and discharging process of the battery, the electrode material may undergo volume changes, which will cause stress at the interface between the electrode and the electrolyte. Long-term use may cause cracks and separation at the interface, affecting the cycle life and safety of the battery. 2. Performance: (1) Low ionic conductivity: Compared with liquid electrolytes, the ionic conductivity of solid electrolytes is generally not high, which makes the internal resistance of the battery larger, the charging and discharging speed slower, and the overall rate performance lower, limiting its application in high-power demand scenarios, such as fast charging of electric vehicles. (2) Energy density needs to be improved: Although solid-state batteries theoretically have high energy density, the energy density of flexible solid-state lithium-ion batteries currently under research and development and in production still falls short of expectations, making it difficult to meet the needs of some devices with extremely high battery life requirements. Therefore, developing a flexible solid-state lithium-ion battery with high ionic conductivity, high energy density, excellent interface stability, and low interface impedance is of great significance for the development of flexible solid-state batteries. Summary of the Invention

[0004] The purpose of this invention is to provide a flexible solid-state lithium-ion battery and its preparation method, so as to solve the problems existing in the prior art and realize the preparation of a flexible solid-state lithium-ion battery with high ionic conductivity, high energy density, excellent interface stability and low interface impedance.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of this invention is to provide a flexible solid-state lithium-ion battery, which includes a solid positive electrode, a solid negative electrode, and a solid electrolyte; the solid positive electrode is a lithium foil coated with a diamond film; the solid negative electrode includes a composite negative electrode coated with a diamond film, a conductive agent, a lithium salt, and a binder; the solid electrolyte includes a polyoxyethylene solid polymer electrolyte or a polyvinylidene fluoride solid polymer electrolyte; the composite negative electrode is prepared from coal gangue, boric acid, and chitosan.

[0007] Preferably, the preparation of the composite negative electrode includes the following steps:

[0008] 1) Coal gangue is sequentially carbonized and activated to obtain porous carbon;

[0009] 2) Dissolve boric acid and chitosan in an alcohol-water solution to obtain a mixture; place the obtained porous carbon in the mixture for impregnation, and then heat treat it to obtain the composite negative electrode.

[0010] This invention prepares a composite negative electrode using coal gangue, a common solid waste. This invention transforms waste into a valuable resource by utilizing the abundant phosphorus, sulfur, and silicon elements in coal gangue to prepare porous carbon doped with phosphorus, sulfur, and silicon. Phosphorus doping into the porous carbon alters the electronic structure and surface properties of the carbon material, increasing the degree of defects and thus providing more lithium-ion storage sites, which is beneficial for improving the battery's specific capacity. Simultaneously, phosphorus can enhance the compatibility between the porous carbon and the electrolyte, promoting lithium-ion transport at the electrode / electrolyte interface and improving the battery's rate performance and cycle stability. Sulfur doping can... Increasing the interlayer spacing of carbon materials is beneficial for lithium-ion storage and the intercalation and deintercalation processes between carbon layers, thereby improving the rate performance of lithium-ion batteries and significantly enhancing both specific capacity and cycle performance. Silicon and carbon have similar chemical properties, but silicon atoms have a larger radius than carbon atoms. Silicon doping into porous carbon can increase the interlayer spacing of carbon materials, providing more favorable channels for lithium-ion intercalation and deintercalation, thus improving the lithium-ion diffusion rate and the rate performance of the battery. At the same time, silicon has a high theoretical specific capacity, and appropriate silicon doping can also increase the specific capacity of the anode material, thereby improving the energy density of the battery.

[0011] This invention further loads boric acid and chitosan onto porous carbon. Since the porous carbon is activated, its surface contains numerous active groups (hydroxyl, carboxyl, etc.), significantly improving the loading effect of boric acid and chitosan. After heat treatment, boron and nitrogen are doped into the porous carbon, thus preparing a multi-element (phosphorus, sulfur, silicon, boron, and nitrogen) doped porous carbon material. Boron doping can regulate the band structure of the porous carbon, improving its conductivity and electrochemical activity. The presence of boron atoms can create localized non-uniform charge distribution in the carbon material, which is beneficial for attracting lithium ions, increasing the adsorption energy and diffusion rate of lithium ions, thereby improving the charge-discharge performance and rate performance of the battery. Furthermore, boron doping can enhance the structural stability of the porous carbon, reducing volume changes during charge-discharge processes and improving the cycle life of the battery. The introduction of nitrogen atoms can disrupt the π-conjugated electron system of carbon atoms, thereby providing a larger electrochemical active area and more active sites, which can synergistically promote charge transfer between carbon atoms and heteroatoms, improving the conductivity and specific capacity of the carbon layer material.

[0012] The composite anode prepared by this invention has excellent electrochemical performance, which enables the prepared flexible solid-state lithium-ion battery to have high ionic conductivity and high energy density.

[0013] In addition, this invention ensures that the flexible solid-state lithium-ion battery has excellent interface stability and low interface impedance by depositing diamond films on the positive and negative electrode surfaces. During the deposition of the diamond film, under the action of hydrogen, methane, ethanol and anisole will generate CH3, CH2, H and O. Most of CH3 forms the diamond phase, while CH2 and a small part of CH3 form the non-diamond phase. The generated H and O etch the non-diamond phase to a certain extent. After subsequent calcination, the formed diamond film can have a uniform pore structure. It will not affect the insertion and extraction of lithium ions, and will also avoid the problem of mass reduction of electrode materials due to volume change. At the same time, the diamond film can also play the following roles: (1) Improve the surface performance of the electrode: The diamond film has high hardness and Chemical stability: Depositing a diamond film on the electrode surface can make the electrode surface smoother and reduce the roughness and defects of the electrode surface. This helps the electrolyte to contact the electrode better, improves the uniformity and tightness of the contact, and thus increases the effective contact area; (2) Enhance the conductivity of the electrode: Diamond has a certain conductivity. Covering the electrode with a diamond film can improve the conductivity of the electrode, reduce the resistance of the electrode, and make the charge transfer between the electrode and the electrolyte easier. This is conducive to the transmission of lithium ions between the electrode and the electrolyte, and indirectly enhances the effective contact between the two; (3) Improve the bonding strength between the electrolyte and the electrode: The surface of the diamond film contains abundant active groups, which can ensure that the electrolyte and the electrode material are tightly bonded, significantly improve the interface stability, and reduce the interface impedance.

[0014] Preferably, the particle size of the coal gangue is 200~300μm.

[0015] Preferably, the carbonization is carried out in an inert gas atmosphere, the inert gas including nitrogen; the carbonization temperature is 800~900℃, and the carbonization time is 1~3h; the activation includes: treating the carbonized product in an acid solution, the acid solution including one or more of acetic acid, hydrochloric acid and sulfuric acid, and the treatment time is 1~2h.

[0016] Preferably, the alcohol in the aqueous alcohol solution includes one or more of ethylene glycol, glycerol, and butanediol; the mass fraction of each substance in the mixture is: chitosan 2-4%, boric acid 2-4%, alcohol 60-85%, and the remainder is water.

[0017] Preferably, the immersion time is 5-8 hours; the heat treatment temperature is 100-150°C, and the heat treatment time is 40-80 minutes.

[0018] Preferably, the conductive agent includes acetylene black, graphene, or carbon fiber; the lithium salt includes lithium perchlorate and / or lithium tetrafluoroborate; and the binder includes polyvinylidene fluoride.

[0019] The second technical solution of the present invention provides a method for preparing the flexible solid-state lithium-ion battery, comprising the following steps:

[0020] (1) The composite negative electrode, conductive agent, lithium salt, binder and solvent are mixed to obtain electrode slurry. The electrode slurry is coated on copper foil to obtain negative electrode sheet. A diamond film is deposited on the negative electrode sheet and calcined to obtain solid negative electrode.

[0021] (2) Take lithium foil, deposit a diamond film on the surface of the lithium foil and calcine it to obtain a solid positive electrode;

[0022] (3) The solid negative electrode, solid electrolyte and solid positive electrode are stacked and assembled to obtain the flexible solid lithium-ion battery.

[0023] Preferably, the solvent includes N-methylpyrrolidone; the mass-to-volume ratio of the composite negative electrode, conductive agent, lithium salt, binder and solvent is 8~9g:1~2g:1~3g:2~3g:20~40mL; and the coating thickness is 30~60μm.

[0024] Preferably, the deposition parameters are independently set as follows: the deposition is carried out under a hydrogen atmosphere, the carbon source is methane, ethanol, and anisole, the volume ratio of methane, ethanol, and anisole is 5~6:0.5~0.8:0.1~0.2, the carbon source flow rate is 15~30 sccm, the surface temperature of the negative electrode and lithium foil during deposition is 700~800℃, the deposition pressure is 5~6 kPa, and the deposition time is 1~2 h; the calcination temperature is independently set at 800~900℃, and the calcination time is 30~80 min.

[0025] The present invention discloses the following technical effects:

[0026] 1. This invention prepares porous carbon materials doped with multiple elements (phosphorus, sulfur, silicon, boron and nitrogen) through a specific process. Using these materials as anode materials can enable the preparation of flexible solid-state lithium-ion batteries with high ionic conductivity and high energy density.

[0027] 2. The present invention can significantly improve the solid-solid interface stability and reduce the interface impedance by depositing diamond thin films on the surface of solid positive and solid negative electrodes.

[0028] 3. The preparation process described in this invention is simple, and the raw materials used are simple and readily available, making it suitable for widespread application. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0032] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0033] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0034] Example 1

[0035] Preparation of composite anode:

[0036] 1) Coal gangue with a particle size of 200 μm was first placed in a carbonization furnace for carbonization. Before carbonization, the air in the carbonization furnace was purged with nitrogen. The carbonization temperature was 850℃ and the carbonization time was 2h. Then the carbonization product was taken out and air-cooled to room temperature. After that, it was placed in a 35% hydrochloric acid aqueous solution for 1h for activation. It was washed 3 times with deionized water and dried to obtain porous carbon.

[0037] 2) Prepare a mixed solution with the following mass fractions of substances: chitosan 2%, boric acid 2%, ethylene glycol 85%, and the remainder being deionized water; immerse the obtained porous carbon in the mixed solution for 6 hours, and then heat-treat it at 120℃ for 1 hour to obtain a composite negative electrode;

[0038] Fabrication of flexible solid-state lithium-ion batteries:

[0039] (1) The obtained composite negative electrode, graphene, lithium tetrafluoroborate, polyvinylidene fluoride and N-methylpyrrolidone were mixed in a ratio of 8g:1g:2g:2g:35mL to obtain an electrode slurry. The electrode slurry was coated on a copper foil with a coating thickness of 40μm to obtain a negative electrode sheet. A diamond film was deposited on the negative electrode sheet and then calcined at 800℃ for 40min to obtain a solid negative electrode.

[0040] (2) Take lithium foil, deposit a diamond film on the surface of the lithium foil and calcine it at 850°C for 30 min to obtain a solid positive electrode;

[0041] (3) A flexible solid-state lithium-ion battery is obtained by stacking and assembling a solid negative electrode, a solid electrolyte and a solid positive electrode;

[0042] The deposition parameters in steps (1) and (2) are as follows: the deposition is carried out in a hydrogen atmosphere, the carbon source is methane, ethanol and anisole, the volume ratio of methane, ethanol and anisole is 5:0.5:0.1, the flow rate of the carbon source is 20 sccm, the surface temperature of the negative electrode and lithium foil during deposition is 750℃, the deposition pressure is 5 kPa, and the deposition time is 1 h.

[0043] The obtained flexible solid-state lithium-ion battery was subjected to charge-discharge tests at 25°C, 0.05C current, and charge-discharge cutoff voltage of 0.005~2.0V. The results showed that after 20 cycles, the discharge capacity was above 452mAh / g, and the capacity retention rate reached 100%.

[0044] The obtained flexible solid-state lithium-ion battery was fully charged at 25℃, 0.05C current, and charge / discharge cutoff voltage of 4.2~3.0V. After being bent 800 times, a charge / discharge test was conducted. The results showed that the battery charged and discharged normally, and the capacity remained above 99.5%.

[0045] Example 2

[0046] Preparation of composite anode:

[0047] 1) Coal gangue with a particle size of 250μm was first placed in a carbonization furnace for carbonization. Before carbonization, the air in the carbonization furnace was purged with nitrogen. The carbonization temperature was 800℃ and the carbonization time was 1.5h. Then the carbonization product was taken out and air-cooled to room temperature. After that, it was placed in a 35% hydrochloric acid aqueous solution for 1h for activation. It was washed three times with deionized water and dried to obtain porous carbon.

[0048] 2) Prepare a mixed solution with the following mass fractions of substances: chitosan 3%, boric acid 2%, ethylene glycol 70%, and the remainder being deionized water; immerse the obtained porous carbon in the mixed solution for 6 hours, and then heat-treat it at 120℃ for 1 hour to obtain a composite negative electrode;

[0049] Fabrication of flexible solid-state lithium-ion batteries:

[0050] (1) The obtained composite negative electrode, graphene, lithium tetrafluoroborate, polyvinylidene fluoride and N-methylpyrrolidone were mixed in a ratio of 8.5g:1g:2g:2g:40mL to obtain an electrode slurry. The electrode slurry was coated on a copper foil with a coating thickness of 35μm to obtain a negative electrode sheet. A diamond film was deposited on the negative electrode sheet and then calcined at 800℃ for 40min to obtain a solid negative electrode.

[0051] (2) Take lithium foil, deposit a diamond film on the surface of the lithium foil and calcine it at 850°C for 30 min to obtain a solid positive electrode;

[0052] (3) The solid negative electrode, solid electrolyte and solid positive electrode are stacked and assembled to obtain the flexible solid lithium-ion battery;

[0053] The deposition parameters in steps (1) and (2) are as follows: the deposition is carried out in a hydrogen atmosphere, the carbon source is methane, ethanol and anisole, the volume ratio of methane, ethanol and anisole is 5:0.7:0.2, the flow rate of the carbon source is 20 sccm, the surface temperature of the negative electrode and lithium foil during deposition is 700℃, the deposition pressure is 5 kPa, and the deposition time is 1.5 h.

[0054] The obtained flexible solid-state lithium-ion battery was subjected to charge-discharge tests at 25°C, 0.05C current, and charge-discharge cutoff voltage of 0.005~2.0V. The results showed that after 20 cycles, the discharge capacity was above 439mAh / g, and the capacity retention rate reached 100%.

[0055] The obtained flexible solid-state lithium-ion battery was fully charged at 25℃, 0.05C current, and charge / discharge cutoff voltage of 4.2~3.0V. After being bent 800 times, a charge / discharge test was conducted. The results showed that the battery charged and discharged normally, and the capacity remained above 99.4%.

[0056] Comparative Example 1

[0057] The difference from Example 1 is that the addition of boric acid is omitted in the preparation of the composite negative electrode, otherwise it is the same as Example 1.

[0058] The obtained flexible solid-state lithium-ion battery was subjected to charge-discharge tests at 25°C, 0.05C current, and charge-discharge cutoff voltage of 0.005~2.0V. The results showed that after 20 cycles, the discharge capacity was above 324mAh / g, and the capacity retention rate reached 95%.

[0059] The obtained flexible solid-state lithium-ion battery was fully charged at 25℃, 0.05C current, and charge / discharge cutoff voltage of 4.2~3.0V. After being bent 800 times, a charge / discharge test was conducted. The results showed that the battery charged and discharged normally, and the capacity remained above 85.2%.

[0060] Comparative Example 2

[0061] The difference from Example 1 is that the addition of chitosan was omitted in the preparation of the composite negative electrode, otherwise it is the same as Example 1.

[0062] The obtained flexible solid-state lithium-ion battery was subjected to charge-discharge tests at 25°C, 0.05C current, and charge-discharge cutoff voltage of 0.005~2.0V. The results showed that after 20 cycles, the discharge capacity was above 339mAh / g, and the capacity retention rate reached 95%.

[0063] The obtained flexible solid-state lithium-ion battery was fully charged at 25℃, 0.05C current, and charge / discharge cutoff voltage of 4.2~3.0V. After being bent 800 times, a charge / discharge test was conducted. The results showed that the battery charged and discharged normally, and the capacity remained above 86.1%.

[0064] Comparative Example 3

[0065] The difference from Example 1 is that step 1) is omitted in the preparation of the composite negative electrode, and "porous carbon" in step 2) is replaced with "graphene". The rest is the same as in Example 1.

[0066] The obtained flexible solid-state lithium-ion battery was subjected to charge-discharge tests at 25°C, 0.05C current, and charge-discharge cutoff voltage of 0.005~2.0V. The results showed that after 20 cycles, the discharge capacity was above 298mAh / g, and the capacity retention rate reached 89.2%.

[0067] The obtained flexible solid-state lithium-ion battery was fully charged at 25℃, 0.05C current, and charge / discharge cutoff voltage of 4.2~3.0V. After being bent 800 times, a charge / discharge test was conducted. The results showed that the battery charged and discharged normally, and the capacity remained above 76.5%.

[0068] Comparative Example 4

[0069] The difference from Example 1 is that the deposition of diamond film is omitted in the preparation of flexible solid-state lithium-ion battery, otherwise it is the same as Example 1.

[0070] The obtained flexible solid-state lithium-ion battery was subjected to charge-discharge tests at 25°C, 0.05C current, and charge-discharge cutoff voltage of 0.005~2.0V. The results showed that after 20 cycles, the discharge capacity was above 384mAh / g, and the capacity retention rate reached 98%.

[0071] The obtained flexible solid-state lithium-ion battery was fully charged at 25℃, 0.05C current, and charge / discharge cutoff voltage of 4.2~3.0V. After being bent 800 times, a charge / discharge test was conducted. The results showed that the battery charged and discharged normally, and the capacity remained above 68.1%.

[0072] The weather resistance of the batteries obtained in the above embodiments and comparative examples was tested by low-temperature freezing tests and high-temperature treatment tests:

[0073] Test method:

[0074] Low-temperature freezing test: The battery was placed in a freezer at -30°C for 1 hour, then removed and connected to an LED bulb via a wire. The LED bulb was then observed to see if it could function normally. The results showed that the batteries obtained in Examples 1-2 and Comparative Examples 1-3 all enabled the LED bulb to function normally, while the LED bulb connected to the battery in Comparative Example 4 did not light up.

[0075] High-temperature treatment test: The battery was wrapped in plastic film and placed in hot water at 45°C for 1 hour. After treatment, the battery was removed and connected to an LED bulb through a wire. The LED bulb was then observed to see if it could work normally. The results showed that the batteries obtained in Examples 1-2 and Comparative Examples 1-2 could make the LED bulb work normally. However, the LED bulb connected to the battery obtained in Comparative Example 3 remained lit for 5 minutes and then went out. The LED bulb connected to the battery obtained in Comparative Example 4 did not light up.

[0076] Therefore, the battery obtained by the present invention has excellent weather resistance.

[0077] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0078] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A flexible solid-state lithium-ion battery, characterized in that, The flexible solid-state lithium-ion battery includes a solid positive electrode, a solid negative electrode, and a solid electrolyte; the solid positive electrode is a lithium foil coated with a diamond film; the solid electrolyte includes a polyoxyethylene solid polymer electrolyte or a polyvinylidene fluoride solid polymer electrolyte; the solid negative electrode is prepared by mixing a composite negative electrode, a conductive agent, a lithium salt, a binder, and a solvent to obtain an electrode slurry, coating the electrode slurry onto a copper foil to obtain a negative electrode sheet, depositing a diamond film on the negative electrode sheet and calcining it to obtain a solid negative electrode; the composite negative electrode is prepared from coal gangue, boric acid, and chitosan; The preparation of the composite negative electrode includes the following steps: 1) Coal gangue is sequentially carbonized and activated to obtain porous carbon; 2) Boric acid and chitosan are dissolved in an alcohol-water solution to obtain a mixture; the obtained porous carbon is immersed in the mixture and then heat-treated to obtain the composite negative electrode; the composite negative electrode is a porous carbon material doped with phosphorus, sulfur, silicon, boron and nitrogen. The solid cathode is prepared by taking lithium foil, depositing a diamond film on the surface of the lithium foil and calcining it to obtain a solid cathode. The deposition parameters are independent as follows: it is carried out under a hydrogen atmosphere, the carbon source is methane, ethanol and anisole, the volume ratio of methane, ethanol and anisole is 5~6:0.5~0.8:0.1~0.2, the carbon source flow rate is 15~30 sccm, the surface temperature of the negative electrode and lithium foil during deposition is 700~800℃, the deposition pressure is 5~6 kPa, and the deposition time is 1~2 h; the calcination temperature is independent as follows: 800~900℃, and the calcination time is 30~80 min.

2. The flexible solid-state lithium-ion battery according to claim 1, characterized in that, The particle size of the coal gangue is 200~300μm.

3. The flexible solid-state lithium-ion battery according to claim 1, characterized in that, The carbonization is carried out under a nitrogen atmosphere; the carbonization temperature is 800~900℃, and the carbonization time is 1~3h; the activation includes: treating the carbonized product in an acid solution, the acid solution including one or more of acetic acid, hydrochloric acid and sulfuric acid, for 1~2h.

4. The flexible solid-state lithium-ion battery according to claim 1, characterized in that, The alcohol in the aqueous solution includes one or more of ethylene glycol, glycerol, and butanediol; the mass fraction of each substance in the mixture is: chitosan 2-4%, boric acid 2-4%, alcohol 60-85%, and the remainder is water.

5. The flexible solid-state lithium-ion battery according to claim 1, characterized in that, The immersion time is 5-8 hours; the heat treatment temperature is 100-150℃ and the heat treatment time is 40-80 minutes.

6. The flexible solid-state lithium-ion battery according to claim 1, characterized in that, The conductive agent includes acetylene black, graphene, or carbon fiber; the lithium salt includes lithium perchlorate and / or lithium tetrafluoroborate; and the binder includes polyvinylidene fluoride.

7. The method for preparing the flexible solid-state lithium-ion battery according to any one of claims 1 to 6, characterized in that, Includes the following steps: (1) The composite negative electrode, conductive agent, lithium salt, binder and solvent are mixed to obtain electrode slurry. The electrode slurry is coated on copper foil to obtain negative electrode sheet. A diamond film is deposited on the negative electrode sheet and calcined to obtain solid negative electrode. (2) Take lithium foil, deposit a diamond film on the surface of the lithium foil and calcine it to obtain a solid positive electrode; (3) The solid negative electrode, solid electrolyte and solid positive electrode are stacked and assembled to obtain the flexible solid lithium-ion battery.

8. The preparation method according to claim 7, characterized in that, The solvent includes N-methylpyrrolidone; the mass-volume ratio of the composite negative electrode, conductive agent, lithium salt, binder and solvent is 8~9g:1~2g:1~3g:2~3g:20~40mL; the coating thickness is 30~60μm.

9. The preparation method according to claim 7, characterized in that, The deposition parameters are independent as follows: it is carried out under a hydrogen atmosphere, the carbon source is methane, ethanol and anisole, the volume ratio of methane, ethanol and anisole is 5~6:0.5~0.8:0.1~0.2, the carbon source flow rate is 15~30 sccm, the surface temperature of the negative electrode and lithium foil during deposition is 700~800℃, the deposition pressure is 5~6 kPa, and the deposition time is 1~2 h; the calcination temperature is independent as follows: 800~900℃, and the calcination time is 30~80 min.