A production method of a solid-state battery with high safety, flame retardancy, and long cycle performance

Abstract

The present invention provides a solid-state battery with high safety, flame retardancy and long cycle performance, and a production method thereof. The production method includes the following steps: mixing 1,3-dioxolane, an initiator, a flame retardant, a lithium salt and a solvent to form an electrolyte solution for standby; mixing a variety of lithium compounds, a conductive agent and a binder evenly to form a slurry, coating the slurry on an aluminum foil with a protective film, and drying to obtain a positive electrode plate. The positive electrode plate and a negative electrode plate are processed into a battery core by a stacking or winding process; injecting a part of the electrolyte solution into the battery core, controlling the humidity within 20% RH and the pressure within 1-3 MPa, standing at a specific temperature below 60 °C for 5-8 h to form a first layer of gel, adding a second layer of electrolyte after standing for 5 h, and then obtaining a solid-state battery through high-temperature treatment, hot pressing and standing. The solid-state battery of the present invention has high safety and long cycle stability.

Description

Technical Field

[0001] The present invention relates to the field of solid-state battery manufacturing, and more particularly, to a production method of a solid-state battery with high safety, flame retardancy, and long cycle performance. Background Art

[0002] In view of the safety hazards and other problems caused by lithium batteries during use, solid-state electrolytes replacing liquid electrolytes have been widely studied, which significantly improves the safety performance of batteries and is of great significance in the history of lithium battery development.

[0003] In the prior art, so far, researchers have discovered a variety of solid-state electrolytes, including inorganic solid-state electrolytes and solid polymer electrolytes.

[0004] Among them, oxide solid-state electrolytes and hydride solid-state electrolytes are typical representatives of inorganic solid-state electrolytes. Polymer solid-state electrolytes include polymer electrolytes and gel polymer electrolytes.

[0005] Compared with all-solid polymer electrolytes, gel polymer electrolytes are considered to be more ideal polymer electrolytes because of their higher ionic conductivity than all-solid electrolytes. However, the main problems currently faced by gel polymer electrolytes are as follows: 1. Low ionic conductivity, resulting in low battery working efficiency and low energy upper limit, thus affecting the overall performance of the battery. 2. Poor thermal stability: It is prone to problems such as dehydration, decomposition, and melting at high temperatures. These thermal stability problems reduce the reliability and service life of the battery and limit the application of polymer solid-state electrolytes in high-temperature environments. 3. Poor interfacial stability: The interface between the polymer solid-state electrolyte and the positive and negative electrode materials is unstable, easily causing the migration and polarization of the electrolyte. This interfacial instability will lead to the attenuation of battery performance and affect the cycle stability and service life of the battery.

[0006] In view of this, the present invention is specifically proposed. Summary of the Invention

[0007] The object of the present invention is to provide a production method of a solid-state battery with high safety, flame retardancy, and long cycle performance. In the preparation process of the polymer solid-state electrolyte, this production method introduces an inorganic component as the second layer of electrolyte for enhancement. By means of the two-layer composite electrolyte, while reducing the polymer crystallinity, it promotes the dissociation of lithium salts, thereby improving the conductivity of the polymer electrolyte. And by adding inorganic components, it can further improve the thermal stability by enhancing the specific surface area, as well as enhance the stability between interfaces, reducing the possibility of causing the migration and polarization of the electrolyte.

[0008] In order to achieve the above object of the present invention, the following technical solutions are specifically adopted:

[0009] The present invention provides a production method of a solid-state battery with high safety, flame retardancy and long cycle performance, comprising the following steps:

[0010] Mix 1,3-dioxolane, an initiator, a flame retardant, a lithium salt and a solvent to form an electrolyte solution for standby;

[0011] Mix a variety of lithium compounds, a conductive agent and a binder evenly to form a slurry, coat the slurry on an aluminum foil with a protective film, and dry to obtain a positive electrode plate. The positive electrode plate and a negative electrode plate formed by combining graphite and carbon silicon are processed into a battery core through a stacking or winding process;

[0012] Inject a part of the electrolyte solution into the battery core, control the humidity within 20%RH and the pressure within 1-3MPa, and stand at a specific temperature below 60°C for 5-8h to form a first-layer gel. After standing for 5h, add a second-layer electrolyte including cellulose and inorganic fillers, and then obtain a solid-state battery through high-temperature treatment, hot pressing and standing.

[0013] Through research, it is found that inorganic solid electrolytes have a relatively high electrochemical window, but inorganic solid electrolytes have a large interfacial impedance and poor mechanical processability. Although polymer electrolytes have good flexibility, they have a low ionic conductivity at room temperature. Therefore, the present invention combines the two through the limitation of a specific production method to prepare a high-performance electrolyte to solve a series of problems such as low ionic conductivity, poor mechanical strength and poor interfacial stability. Especially in the second half of in-situ polymerization, the addition of an electrolyte containing inorganic components is used to enhance the performance of the battery in all aspects. The reason for choosing to add the electrolyte containing inorganic components only in the second half of the polymerization reaction is that adding it on the premise that the polymer gel state formed in the process of in-situ polymerization has been initially formed can ensure that the first-layer gel has been initially formed, and the addition of the second-layer electrolyte will not affect the gel state of the first layer, and can also achieve the effect of improving the battery performance through the composite form of the polymer and the inorganic components. Therefore, through practice, it is found that the timing of adding the second-layer electrolyte is also very important, which can make the two-layer electrolytes form a good composite state and will not affect each other's gel states.

[0014] Therefore, during the actual operation in the specific production process, the prepared electrolyte solution is first filled into the prepared battery core. After the system undergoes in-situ polymerization to form a gel under specific temperature, humidity, and pressure conditions, the reinforcing components such as cellulose and inorganic fillers for forming the second-layer electrolyte are added only after standing for more than 5 hours. The purpose is to form a composite two-layer electrolyte by the mutual combination of the added inorganic components and the gel, so as to enhance each other among the components and improve the electrochemical performance, mechanical performance, flame retardancy, etc. of the electrolyte, thereby enhancing the overall stability of the battery. After the solid electrolyte is formed, a series of high-temperature treatments, hot pressing, and standing treatments are required subsequently to achieve an ideal bonding effect.

[0015] In the above production method, the specific temperature is generally controlled below 60°C, and more preferably, the temperature is controlled between 20 - 50°C.

[0016] Preferably, the so-called high-temperature treatment refers to high-temperature curing treatment to ensure its complete curing and stable performance. The recommended curing temperature is 60°C to 90°C. This process can effectively improve the ionic conductivity of the electrolyte and enhance the overall stability of the battery.

[0017] After the battery production is completed, the battery should be left standing at room temperature to promote the stability and performance maturity of the materials. The recommended standing temperature is 25°C, and the standing time is sufficient for the chemical reactions inside the battery to reach a stable state, thereby ensuring the long-term reliability and performance of the battery.

[0018] In the above solution, the initiator can be selected from one or several of azobisisobutyronitrile, 1,3,2-dioxolothiophene-2,2-dioxide, azobisisoheptonitrile, and aluminum trifluoromethanesulfonate.

[0019] The solvent can be selected from one or more of dimethyl carbonate (DMC), ethylene carbonate (EC), or propylene carbonate (PC).

[0020] The flame retardant can be selected as triethyl phosphate, brominated epoxy resin, brominated polystyrene, melamine, etc.

[0021] The lithium salt can be one or more of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethylsulfonyl)imide (LiFSI), and lithium perchlorate (LiClO4).

[0022] Both the positive electrode plate and the negative electrode plate used in the processing and preparation of the battery core are conventional. The various lithium positive electrodes used in the preparation of the positive electrode plate include one or more of lithium iron phosphate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminate. The binder is one or more of carboxymethyl cellulose, polyacrylic acid, and polytetrafluoroethylene. The conductive agent can be conductive graphite or graphene. The coating temperature is preferably controlled at about 25°C. Within this temperature range, the viscosity and fluidity of the coating can reach the best state, promoting the uniform distribution and curing effect of the slurry.

[0023] In the above solution, the mass ratio of the three components of the lithium compound, binder, and conductive agent used to prepare the positive electrode plate to the electrolyte solution is preferably controlled at 96:1.5:2.5:0.5. The reason for controlling this ratio is to optimize the battery performance and ensure the electrochemical activity and structural stability of the electrode material.

[0024] For the components of the second electrolyte selected for enhancement, preferably, specifically including: by mass, 6 - 10 parts of electrolyte solution, 0.1 - 1 part of cellulose, and 0.2 - 0.7 part of inorganic filler.

[0025] Preferably, as a further feasible solution, by mass, 7 - 9 parts of electrolyte solution, 0.3 - 0.8 part of cellulose, and 0.3 - 0.6 part of inorganic filler.

[0026] More preferably, 8 parts of electrolyte solution, 1.5 parts of cellulose, and 0.5 part of inorganic filler.

[0027] A part of the prepared electrolyte solution is directly injected into the battery core, and the other part is used as a component of the second electrolyte to be compounded with cellulose and inorganic filler and added together.

[0028] When selecting the components of the second electrolyte in the present invention, it is specifically selected to match cellulose, inorganic filler, and electrolyte solution with each other to improve the battery performance. Because the addition of cellulose can utilize the polar groups on cellulose to complex with lithium ions to achieve ion migration, thereby improving the ion conductivity by increasing the migration rate of lithium ions. And the addition of cellulose can also improve the mechanical strength of the gel electrolyte, making its mechanical strength good after curing. The addition of inorganic filler promotes the dissociation of lithium salt while reducing the polymer crystallinity, thereby enhancing the ion conductivity of the electrolyte. Therefore, the reason for selecting the above components as the components of the second electrolyte layer is that each component does not play a single role, but interacts with each other after compounding to achieve the optimal performance in terms of the thermal stability, conductivity, and mechanical properties of the battery.

[0029] Preferably, as a further feasible solution, the inorganic filler is at least one or more of diatomaceous earth and oxide electrolyte, preferably a mixture of diatomaceous earth and magnesium oxide, and the mass ratio of the two is 0.2:1.

[0030] On the one hand, the addition of the inorganic filler is to improve the conductivity. On the other hand, if the addition amount is unreasonable, it may affect the mechanical strength after curing itself. Therefore, in order to balance the effects of both aspects, the best combination of the inorganic filler is the mixture of diatomaceous earth and magnesium oxide. The reason for choosing diatomaceous earth is that it can utilize its porous structure to adsorb the electrolyte, thereby better achieving the effect of improving the battery performance. Similarly, its porous structure enhances the specific surface area and porosity, thereby further improving the thermal stability of the electrolyte itself. However, attention needs to be paid to the mass ratio between it and magnesium oxide. The best mass ratio of the two is 0.2:1. The reason for such a designed dosage is that through specific practices, it is found that if the added diatomaceous earth has a porous structure and the addition amount is too large, it will affect the mechanical properties of the battery itself, and the gel state cannot reach the best. Therefore, the addition amounts of both need to be controlled appropriately, especially the addition amount of diatomaceous earth cannot be too large. As an oxide electrolyte with excellent performance, the addition amount of magnesium oxide can be slightly larger.

[0031] Preferably, as a further feasible solution, the cellulose mainly consists of cellulose acetate propionate and hydroxypropyl methylcellulose;

[0032] Preferably, the mass ratio of cellulose acetate propionate and hydroxypropyl methylcellulose is (3 - 7):1, and it can also be 4:1, 5:1, 6:1, etc.

[0033] When selecting cellulose in the present invention, through the screening of various celluloses, it is found that after the compounding of cellulose acetate propionate and hydroxypropyl methylcellulose, the effect of enhancing the battery performance is the most excellent. In fact, when screening cellulose, since carboxymethyl cellulose is generally used as an adhesive, experiments were also carried out in the specific experiment process. However, it is found that its effect of enhancing the conductive performance of the battery is not very excellent. The reason may be that after the transformation of these two celluloses, cellulose acetate propionate and hydroxypropyl methylcellulose, a long-chain structure can be formed, and this structure can better improve the gelation ability, thereby improving its mechanical properties and conductive properties. Therefore, the cellulose formed into a long chain after transformation has a better effect. Therefore, through specific experiments, it is found that compounding the above two celluloses in a certain mass ratio can achieve the best effect of improving the battery performance.

[0034] Preferably, as a further feasible solution, the protective film is coated on the aluminum foil of the positive electrode by wet coating. The protective film mainly consists of the following components: by mass, 6-9 parts of a mixture of graphene and carbon nanoparticles, 0.5-3 parts of cobalt-chromium alloy powder, and 1-2 parts of a binder.

[0035] In the process of preparing the protective film in the present invention, the protective film is first coated on the aluminum foil of the positive electrode by a wet process, and then the slurry is coated on the protective film. Among the components of the above protective film, the electrical conductivity and thermal conductivity of the battery itself are improved by the compounding of the mixture of graphene and carbon nanoparticles and alloy powder particles. The main function of the protective film is to achieve high electrical conductivity and high thermal conductivity, which can timely conduct away the heat generated by the aggregated current, play a good flame retardant effect, and also achieve a good anti-puncture effect. The binder in the above protective film components can use oil-based PVDF.

[0036] Among the components of the above protective film, the addition of the mixture of graphene and carbon nanoparticles can achieve the effects of high electrical conductivity and high thermal conductivity on the one hand, and on the other hand, it can also reduce the possibility of thermal runaway of the positive electrode plate after being compounded with cobalt-chromium alloy powder, playing the role of improving the stability, safety of the whole battery, enhancing the electrical conductivity and extending its service life. The reason for choosing cobalt-chromium alloy powder for the alloy powder is that cobalt and chromium are not easily oxidized themselves, thereby slowing down the structural change on the surface of the active material of the positive electrode active material caused by too high voltage and improving the stability of the positive electrode material.

[0037] Preferably, as a further feasible solution, the carbon nanoparticles include at least one of carbon nanofibers, carbon nanotubes, and nano carbon powder, preferably a mixture of carbon nanotubes and nano carbon powder, and the mass ratio of the two is 1:1.

[0038] Preferably, as a further feasible solution, in the mixture of graphene and carbon nanoparticles, the mass percentage of graphene is between 50-80%.

[0039] Carbon nanoparticles and graphene are mixed and added together. On the one hand, it is to achieve good thermal conductivity and electrical conductivity. On the other hand, the addition is because the uniform distribution of carbon nanoparticles in the film layer reduces the possibility of graphene agglomeration, thus affecting the performance. It makes the interfacial bonding between the protective film layer and the positive plate closer, relieves the internal stress of the film layer, increases the critical safety thickness of the film layer, and improves the bonding strength between the film layer and the substrate. It is also beneficial to enhance the overall mechanical strength of the battery after curing, and can also isolate the direct contact between the positive active material and the relatively unstable additives and solvents in the electrolyte, improving the overall safety of the battery. Given that graphene has excellent thermal conductivity and electrical conductivity, its mass percentage needs to be higher. The carbon nanoparticles are preferably added in the form of a composite of carbon nanotubes and nano-carbon powder, and the mass ratio of the two is 1:1. Because in this way, the mutual matching effect of the two carbon nanoparticles increases the uniformity of the film layer, and is also more conducive to the exertion of the thermal conductivity and electrical conductivity effects, improving the thermal conductivity and electrical conductivity efficiency.

[0040] In terms of the addition amount, the addition amount of the cobalt-chromium alloy powder should not be too large, otherwise it will cause large fluctuations in the mechanical properties of the battery. Preferably, as a further implementable solution, in the cobalt-chromium alloy powder, the mass proportion of chromium is at least above 50%, and the total mass proportion of cobalt-chromium is at least above 80%. Because the content of cobalt-chromium needs to be ensured in the alloy powder, it is best to limit the amounts of the two in the alloy powder according to the above ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. Moreover, throughout the drawings, the same reference numerals are used to represent the same components.

[0042] Figure 1 Internal structure diagram of the solid-state battery prepared in Example 3 of the present invention;

[0043] Figure 2 Picture of the battery internal core package in Example 3 of the present invention;

[0044] Figure 3 Process of puncturing and dissecting the solid-state battery prepared in Example 3 of the present invention;

[0045] Figure 4 Result of dissecting the punctured battery of the solid-state battery prepared in Example 3 of the present invention;

[0046] Figure 5 Cycling test results of the solid-state battery in Example 6 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The embodiments of the present invention will be described in detail below with reference to the examples, but those skilled in the art will appreciate that the following examples are intended only to illustrate the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0048] Example 1

[0049] The production method of large-capacity solid-state batteries is carried out in the following steps:

[0050] 1) Dissolve 1,3-dioxolane and triethyl phosphate in dimethyl carbonate solvent at a volume ratio of 0.1:1 and mix well. Then, add 0.3 mol / L azobisisobutyronitrile and 0.5 mol / L lithium hexafluorophosphate and stir thoroughly to form an electrolyte solution for use.

[0051] 2) 6g of a mixture of graphene and carbon nanoparticles (1.5g of carbon nanotubes, 1.5g of nano-carbon powder, and 3g of graphene), 3g of a cobalt-chromium alloy powder, and 2g of a binder oil-based PVDF are mixed to form a mixed powder. In the cobalt-chromium alloy powder, the mass proportion of chromium is 50%, and the total mass proportion of cobalt-chromium is 80%. A certain amount of the prepared mixed powder is taken out according to actual conditions and coated on aluminum foil using a wet process to form an aluminum foil with a protective film. Then, a lithium compound lithium iron phosphate, a conductive agent conductive graphite, and a binder carboxymethyl cellulose are mixed evenly to form a slurry, which is coated on the aluminum foil with the protective film. The coating temperature is 25°C, and the mass ratio of the lithium compound, binder, and conductive agent is 96:1.5:2.5. Drying is performed to obtain a positive electrode plate;

[0052] 3) The positive electrode plate coated with the protective film and the negative electrode plate formed by the graphite + carbon silicon composite are processed into a battery core through a lamination process;

[0053] 4) injecting a portion of the electrolyte solution in step 1) into the battery core, controlling the humidity within 20% RH and the pressure within 1 MPa, and allowing to stand at a specific temperature of 20°C for 5 hours to form a first layer of gel. After standing for 5 hours, a second layer of electrolyte comprising cellulose and an inorganic filler is added to the formed gel, wherein the second layer of electrolyte is prepared by uniformly mixing 7 g of electrolyte solution, 0.8 g of cellulose, and 0.3 g of diatomaceous earth, and adding the corresponding amount, wherein the cellulose is cellulose acetate propionate and hydroxypropyl methylcellulose in a mass ratio of 3:1, ensuring that the mass ratio of the total mass of the electrolyte solution in the system to the lithium iron phosphate is 0.5:96.

[0054] 5) After adding the second layer of electrolyte, let it stand for 3 h, then perform high-temperature curing treatment at 90 °C, hot pressing, and standing at 25 °C, and then weld the tabs and encapsulate to obtain a solid-state battery.

[0055] Example 2

[0056] The production method of a solid-state battery with high safety, flame retardancy, and long cycle performance is carried out according to the following steps:

[0057] 1) Mix 1,3-dioxolane and brominated epoxy resin in a volume ratio of 0.1:1, dissolve and mix them evenly with ethylene carbonate as the solvent, then add 0.4 mol / L of azobisisobutyronitrile and 0.5 mol / L of lithium bis(trifluoromethanesulfonyl)imide, and stir well to form an electrolyte solution for standby;

[0058] 2) Combine 9 g of a mixture of graphene and carbon nanoparticles (0.9 g of carbon nanofibers, 0.9 g of carbon nanotubes, and 7.2 g of graphene), 0.5 g of cobalt-chromium alloy powder, and 1 g of binder oil-based PVDF to form a mixed powder. In the cobalt-chromium alloy powder, the mass ratio of chromium is 60%, and the total mass ratio of cobalt and chromium is 85%. Take a certain amount of the prepared mixed powder according to the actual situation and coat it on the aluminum foil by the wet process to form an aluminum foil with a protective film. Then, mix lithium nickel cobalt manganese oxide, conductive agent conductive graphite, and binder polyacrylic acid evenly to form a slurry and coat it on the aluminum foil with a protective film. The coating temperature is 25 °C, and the mass ratio of the lithium compound, binder, and conductive agent is 96:1.5:2.5. Dry to obtain the positive electrode plate.

[0059] 3) Process the positive electrode plate after laminating and the negative electrode plate formed by compounding graphite and carbon silicon through the lamination process to prepare a battery core.

[0060] 4) Inject a part of the electrolyte solution in step 1) into the battery core, control the humidity within 20%RH and the pressure within 3 MPa, and let it stand at a specific temperature of 50 °C for 5 h to form the first layer of gel. After standing for 5 h, add the second layer of electrolyte including cellulose and inorganic fillers to the formed gel. The second layer of electrolyte is prepared by mixing 9 g of electrolyte solution, 0.3 g of cellulose, and 0.6 g of a mixture of diatomaceous earth and magnesium oxide with a mass ratio of 0.2:1, and take out the corresponding amount for addition. The cellulose is a mixture of cellulose acetate propionate and hydroxypropyl methylcellulose with a mass ratio of 7:1, ensuring that the mass ratio of the total electrolyte solution in the system to lithium iron phosphate is 0.5:96.

[0061] 5) After adding the second layer of electrolyte, let it stand for 2 h, then perform high-temperature curing treatment at 60 °C, hot pressing, and standing at 25 °C, and then weld the tabs and encapsulate to obtain a solid-state battery.

[0062] Example 3

[0063] The production method of a solid-state battery with high safety, flame retardancy and long cycle performance is carried out in the following steps:

[0064] 1) Dissolve 1,3-dioxolane and trichloromelamine in ethylene carbonate solvent at a volume ratio of 0.1:1 and mix them evenly. Then, add 0.4 mol / L of 1,3,2-dioxazolidinone-2,2-dioxide and 0.5 mol / L of lithium perchlorate and stir thoroughly to form an electrolyte solution for use.

[0065] 2) 8g of a mixture of graphene and carbon nanoparticles (1.6g of carbon nanofibers, 1.6g of carbon nanotubes, and 4.8g of graphene), 1g of a cobalt-chromium alloy powder, and 1.5g of a binder oil-based PVDF are mixed to form a mixed powder. In the cobalt-chromium alloy powder, chromium accounts for 60% by mass, and the total mass of cobalt and chromium accounts for 85%. A certain amount of the prepared mixed powder is taken out according to actual conditions and coated on aluminum foil using a wet process to form an aluminum foil with a protective film. A lithium compound, lithium nickel cobalt manganese oxide, a conductive agent, conductive graphite, and a binder, polyacrylic acid, are mixed evenly to form a slurry, which is then coated on the aluminum foil with the protective film. The coating temperature is 25°C, and the mass ratio of the lithium compound, binder, and conductive agent is 96:1.5:2.5. The mixture is dried to obtain a positive electrode plate;

[0066] 3) The coated positive plate and the negative plate formed by the graphite + carbon silicon composite are processed into a battery core through a lamination process;

[0067] 4) injecting a portion of the electrolyte solution in step 1) into the battery core, controlling the humidity within 20% RH and the pressure within 2 MPa, and allowing to stand at a specific temperature of 40°C for 5 hours to form a first layer of gel. After standing for 5 hours, a second layer of electrolyte comprising cellulose and an inorganic filler is added to the formed gel, wherein the second layer of electrolyte is prepared by uniformly mixing 8 g of electrolyte solution, 1.5 g of cellulose, and 0.5 g of a mixture of diatomaceous earth and magnesium oxide in a mass ratio of 0.2:1, and adding the corresponding amount, wherein the cellulose is cellulose acetate propionate and hydroxypropyl methylcellulose in a mass ratio of 6:1, ensuring that the mass ratio of the total mass of the electrolyte solution in the system to the lithium iron phosphate is 0.5:96.

[0068] 5) After adding the reinforcing components, the battery is left to stand for 3 hours, and then undergoes high-temperature curing treatment at 70°C, hot pressing, and standing at 25°C. The tabs are then welded and packaged to obtain a solid-state battery.

[0069] Figure 1 The internal structure diagram of the solid-state battery of this embodiment is shown in FIG. Two samples of the solid-state battery were selected for cycle testing to evaluate their long-term performance. The specific test results are shown in FIG.Figure 5 This test not only verifies the cycle stability of the battery, but also ensures its high performance and long life in practical applications. Figure 3 It can be seen that after the needle puncture test, the battery maintains a high level of safety, with no burning or thick smoke. Figure 4 It can be seen that after the battery is dissected after puncture, the current collector is characterized uniformly and the bonding surface is good. Figure 2 The figure shows the solid-state representation of the battery core pack after the electrolyte solidifies.

[0070] Example 4

[0071] The specific operating steps are the same as those in Example 3, except that the second layer electrolyte is prepared by uniformly mixing 6 g of electrolyte solution, 1 g of cellulose, and 0.2 g of a mixture of diatomaceous earth and magnesium oxide in a mass ratio of 0.2:1, and then taking out a corresponding amount to add, wherein the cellulose is cellulose acetate propionate and hydroxypropyl methylcellulose in a mass ratio of 6:1.

[0072] Example 5

[0073] The specific operating steps are the same as those in Example 3, except that the second layer electrolyte is prepared by uniformly mixing 10 g of electrolyte solution, 0.1 g of cellulose, and 0.7 g of a mixture of diatomaceous earth and magnesium oxide in a mass ratio of 0.2:1, and then adding the corresponding amount, wherein the cellulose is cellulose acetate propionate and hydroxypropyl methylcellulose in a mass ratio of 6:1.

[0074] Example 6

[0075] The specific operation steps are consistent with those of Example 3, except that the mixture of graphene and carbon nanoparticles is replaced by only adding graphene.

[0076] Example 7

[0077] The specific operation steps are the same as those in Example 3, except that the carbon nanoparticles are only one type of carbon nanofiber.

[0078] Example 8

[0079] The specific operation steps are the same as those in Example 3, except that 2 g of graphene, 3 g of carbon nanofibers, and 3 g of carbon nanotubes are used.

[0080] Example 9

[0081] The specific operation steps are the same as those in Example 3, except that no cobalt-chromium alloy powder is added.

[0082] Example 10

[0083] The specific operation steps are the same as those in Example 3, with the difference that 0.5 g of the mixture of diatomite and magnesium oxide with a mass ratio of 0.2:1 is replaced by 0.5 g of diatomite.

[0084] Example 11

[0085] The specific operation steps are the same as those in Example 3, with the difference that the mass ratio of diatomite to magnesium oxide is 3:1.

[0086] Example 12

[0087] The cellulose is cellulose acetate propionate.

[0088] Example 13

[0089] The cellulose is obtained by mixing cellulose acetate propionate and hydroxypropyl methylcellulose in a mass ratio of 1:1.

[0090] Experimental Example 1

[0091] The batteries prepared by the production methods of the above-mentioned various examples and comparative examples were subjected to performance tests. The specific test results are shown in Table 1 below. The first column is the capacity of the assembled battery during testing, and the second column is the capacity retention rate after 500 cycles.

[0092] In addition, overcharge experiments were conducted on the batteries of each example: The batteries were placed in a battery explosion-proof test chamber, and a DC regulated power supply was used. The output port of the battery was connected to the input port of the DC regulated power supply. Controlled at 160 °C for 60 minutes, record the maximum voltage at which the battery of each example does not catch fire or explode during overcharge. The specific results are shown in Table 1 below.

[0093] Table 1 Test Results

[0094]

[0095] It can be seen from the results in Table 1 above that for the batteries assembled in each example, comparing their capacitance, flame retardant performance of the battery itself, and mechanical properties, it is found that Example 3 performs best in each performance index. Because although considering safety, other Examples 1-2, 4-13 can basically pass the needle puncture test, but due to the change of conditions, their flame retardant performance, mechanical properties, and electrochemical properties cannot perform as well as the performance indexes of Example 3. Especially, the maximum overcharge voltage of Example 3 can reach 5 V. The normal battery voltage is 4.4 V, and overcharge is definitely prone to catching fire and explosion. However, the solid-state battery produced by the solution of the present invention can reach a maximum overcharge voltage of 5 V without catching fire or explosion, indicating its good flame retardant performance. Therefore, from the aspect of the battery stability itself, the effect of Example 3 is the best.

[0096] Figures 2 - 5The experimental results of the battery acupuncture and charge-discharge cycles of Example 3 are shown. Since the solutions of Examples 2-5 are also controlled within the scope of the solution of the present invention, it can be known from the experimental data in Table 1 above that the battery capacity results, as well as the mechanical properties and flame retardant properties of the battery itself, can also achieve good results. The conclusion drawn from the experimental data of Examples 1-5 is that as long as the battery produced by the solution of the present invention can achieve a large capacity retention rate, it also has good chemical stability, a good gel state, and the mechanical properties and flame retardant properties of the produced battery can also achieve excellent effects.

[0097] By comparing the experimental data of Examples 6-9 with that of Example 3, it is found that during the process of coating the protective film, it is best that none of the added graphene, carbon nanoparticles, and cobalt-chromium alloy powder can be missing. If carbon nanoparticles are not added, it will affect the uniformity of the film itself, so the capacity retention rate of Example 6 itself will be affected. Although the influence on the mechanical properties is not great, the influence on the flame retardant properties and the capacity retention rate is relatively large. In Example 7, because the carbon nanoparticles are not added in a combined manner, the uniformity of its film is not very good. In Example 8, because the amount of graphene does not reach an optimal addition, it affects its poor thermal and electrical conductivity. Of course, if the amount of graphene added is too large, it is easier to agglomerate and its uniformity will also be affected. Therefore, the addition amount of graphene is preferably neither too high nor too low. In addition, the conductivity can be improved after the alloy powder is combined. If it is not added, the conductivity will be affected, so the capacity retention rate of Example 9 will also be affected.

[0098] Examples 10-13 are for comparing the component screening of the second electrolyte. It can be seen from the data of each example that the added diatomaceous earth, magnesium oxide, and cellulose are all of specific significance for improving the performance. In Example 10, since magnesium oxide is not added, its electrical conductivity cannot reach an optimal effect, and its mechanical properties will also be affected. In Example 11, since the addition amount of diatomaceous earth is too large, the mechanical properties will also be affected. In Example 12, since the cellulose is only limited to one type, and in Example 13, since the two celluloses are not controlled within an optimal mass ratio range, the performance of the battery will be affected to a certain extent. Because the above two celluloses are two celluloses that are found through practice to have an excellent enhancing effect in combination, and can better improve the gel ability, thereby improving the electrical and mechanical properties. Therefore, it is best to combine them in a certain mass ratio to achieve the optimal effect.

[0099] In addition, the mechanical properties are represented by the tensile strength and the elastic modulus because both of these indicators are related to the use stability and service life of the battery. Good tensile strength means that the battery is not easily broken, has better safety and service life, while a better elastic modulus means that the battery has better shape stability and strong anti-deformation ability. Of course, neither of these two indicators is the larger the better. It is only necessary to ensure that they are as large as possible within a better range to improve the mechanical properties of the battery itself. Therefore, the solution of the present invention improves the performance of the entire battery after curing by adopting a two-layer electrolyte composite method.

[0100] Although the invention has been illustrated and described with reference to specific embodiments, it should be appreciated that many other changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, this means that all such changes and modifications that fall within the scope of the invention are included in the appended claims.

Claims

1. A production method of a solid-state battery with high safety, flame retardancy and long cycle performance, characterized in that, It includes the following steps: Mix 1,3-dioxolane, an initiator, a flame retardant, a lithium salt and a solvent to form an electrolyte solution for standby; Mix a variety of lithium compounds, a conductive agent and a binder evenly to form a slurry, coat it on an aluminum foil with a protective film, and dry to obtain a positive electrode plate. Process the positive electrode plate and a negative electrode plate formed by graphite + carbon silicon composite through a stacking or winding process to prepare a battery core; Inject a part of the electrolyte solution into the battery core, control the humidity within 20%RH and the pressure within 1-3MPa, stand at a specific temperature between 20-50°C below 60°C for 5-8h to form a first-layer gel. After standing for 5h, add a second-layer electrolyte including cellulose and inorganic filler, and then obtain a solid-state battery through high-temperature treatment, hot pressing and standing; The second-layer electrolyte includes: by mass, 6-10 parts of electrolyte solution, 0.1-1 part of cellulose, and 0.2-0.7 part of inorganic filler; the cellulose is mainly composed of cellulose acetate propionate and hydroxypropyl methylcellulose, and the mass ratio of cellulose acetate propionate to hydroxypropyl methylcellulose is (3-7):1; The inorganic filler is a mixture of diatomite and magnesium oxide, and the mass ratio of the two is 0.2:1; The protective film is coated on the aluminum foil of the positive electrode by a wet method. The protective film is mainly composed of the following components: by mass, 6-9 parts of a mixture of graphene and carbon nanoparticles, 0.5-3 parts of cobalt-chromium alloy powder, and 1-2 parts of binder; The carbon nanoparticles are a mixture of carbon nanotubes and nano carbon powder, and the mass ratio of the two is 1:

1.

2. The production method according to claim 1, characterized in that, The second-layer electrolyte includes: by mass, 7-9 parts of electrolyte solution, 0.3-0.8 part of cellulose, and 0.3-0.6 part of inorganic filler.

3. The production method according to claim 1, characterized in that, In the mixture of graphene and carbon nanoparticles, the mass percentage of graphene is between 50-80%.

4. The production method according to claim 1, characterized in that, In the cobalt-chromium alloy powder, the mass proportion of chromium is ≥50%, and the total mass proportion of cobalt-chromium is ≥80%.

5. The production method according to claim 1, characterized in that, The temperature of the high-temperature treatment is between 60-90°C.

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