A bipolar composite current collector and its preparation method, and a solid-state lithium secondary battery

Abstract

This invention relates to the field of secondary battery technology, specifically to a bipolar composite current collector and its preparation method, as well as a solid-state lithium secondary battery. The method includes the following steps: Step 1: Polyethylene oxide and lithium bis(fluorosulfonyl)imide are added to N,N-dimethylformamide and vacuum dried at 80-100°C for 10-14 hours, then cooled to obtain a solid polymer electrolyte; Step 2: Positive electrode active material, solid polymer electrolyte, conductive agent, and binder are sequentially added to N-methylpyrrolidone and mixed evenly to obtain a positive electrode slurry; this slurry is coated onto the outer surface of the metal Al layer of the bipolar composite current collector and dried to obtain the positive electrode material; this is used as an intermediate product; the intermediate product is then wound or stacked to obtain a solid-state lithium secondary battery composed of the bipolar composite current collector.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a bipolar composite current collector and its preparation method, as well as a solid-state lithium secondary battery. Background Technology

[0002] With the continued growth of the new energy vehicle market, the requirements for battery performance are increasing, and composite current collectors, as a novel material, have attracted much attention. Although composite current collectors have improved battery performance to some extent, bipolar current collectors, with their superior performance, are gradually becoming a potential product in the future market.

[0003] In the prior art, Adv. Funct. Mater. 2024, 34, 2310925 reported an ultralight bipolar composite current collector. Although it achieved an ultralight design, the adhesion between the metal layer and the insulating polymer film was insufficient, which led to the metal layer being prone to detachment under certain environments. The manufacturing process was also more complex and the safety performance was poor. CN202311349176.3 provides a novel bipolar composite current collector and its preparation process, which improves the adhesion, but it is not simple enough and has an excessively large mass.

[0004] The solid polymer battery of this invention adopts key technologies such as solid polymer electrolyte, negative electrode-free design, and optimized interface engineering, and exhibits advantages such as high safety, high energy density, long cycle life, environmental friendliness, and design flexibility.

[0005] Therefore, it is particularly necessary to prepare a solid-state lithium secondary battery composed of a bipolar composite current collector. Summary of the Invention

[0006] The purpose of this invention is to provide a bipolar composite current collector and its preparation method, as well as a solid-state lithium secondary battery, to solve the problems raised in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing a bipolar composite current collector includes the following steps:

[0009] Step 1: (1) A layer of alloy is magnetron sputtered on one side of the polymer layer to form an intermediate alloy layer; an aluminum metal seed layer is sputtered on the intermediate alloy layer, and then aluminum is electroplated to form a positive electrode metal layer to obtain a metal Al layer.

[0010] (2) A layer of alloy is also magnetron sputtered on the other side of the polymer layer to form an intermediate alloy layer; a copper metal seed layer is sputtered on the intermediate alloy layer, and then copper is electroplated to form a negative electrode metal layer to obtain a metal Cu layer.

[0011] Step 2: The Al and Cu metal layers are subjected to roughening roller grinding to obtain a bipolar composite current collector.

[0012] More preferably, the polymer layer is a polymer film of 1~15μm; the material of the polymer film includes one or more of polyethylene terephthalate, polypropylene, polytetrafluoroethylene, polyimide, polyethylene, and polyethylene naphthalate.

[0013] The intermediate alloy layer includes metal A and metal B; metal A includes one of copper, silver, magnesium, aluminum, and indium; metal B includes one of germanium, platinum, zinc, gold, tin, lead, cadmium, antimony, bismuth, gallium, carbon, silicon, and boron.

[0014] Ideally, the thickness of the Cu metal layer is 0.5~10μm; the thickness of the Al metal layer is 1~20μm; and the thickness of the intermediate alloy layer is 15~20nm.

[0015] Furthermore, the metal alloy layer includes a copper-tin alloy layer with a mass ratio of 1~5:5~9.

[0016] In a more optimized manner, the roughening degree of the roughened roller pressing structure in the roughening roller grinding process is 0.1~10Ra, preferably 1~5Ra.

[0017] A more optimized method for preparing a bipolar composite current collector is characterized in that the structure of the bipolar composite current collector, from top to bottom, comprises a metal Al layer, an intermediate alloy layer, a polymer layer, another intermediate alloy layer, and a metal Cu layer.

[0018] In a more optimized manner, the bipolar composite current collector is applied to a solid-state lithium secondary battery; the structure of the solid-state lithium secondary battery, from top to bottom, includes a solid polymer electrolyte, a positive electrode material, and a bipolar composite current collector.

[0019] In a more optimized manner, the preparation method of the solid-state lithium secondary battery includes the following steps:

[0020] Step 1: Add polyethylene oxide and lithium difluorosulfonyl imide to N,N-dimethylformamide, vacuum dry at 80~100℃ for 10~14 hours, cool to obtain solid polymer electrolyte;

[0021] Step 2: Add the positive electrode active material, solid polymer electrolyte, conductive agent, and binder to N-methylpyrrolidone in sequence and mix evenly to obtain a positive electrode slurry; coat the outer surface of the metal Al layer of the bipolar composite current collector, dry it, and obtain the positive electrode material; use this as an intermediate product;

[0022] Step 3: The intermediate products are wound or stacked to obtain solid-state lithium secondary batteries.

[0023] In a more optimized manner, the molar ratio of polyethylene oxide to lithium bis(fluorosulfonyl)imide in the raw materials of the solid polymer electrolyte is 8-20:1.

[0024] The raw materials of the positive electrode slurry include the following components: positive electrode active material, solid polymer electrolyte, conductive agent, and binder in a mass ratio of 6:2:1:1.

[0025] In a more optimized manner, the method for preparing the adhesive includes the following steps:

[0026] Step 1: (1) Add carboxymethyl guar gum and epoxy polyethylene glycol acrylate to a 25-40% ethanol aqueous solution, add potassium hydroxide aqueous solution and ethyl phosphate, react at 60-80℃ for 10-15 hours, purify, dry to obtain modified guar gum for later use; (2) Under nitrogen atmosphere, add 2,3,5,6-pyridinetetramine trihydrochloride, ethyl isocyanate acrylate and dibutyltin dilaurate to xylene solvent, react at 70-80℃ for 2-3 hours, filter, purify to obtain alkenylpyridine for later use;

[0027] Step 2: Add carboxymethyl cellulose, potassium persulfate, and sodium sulfite to deionized water and react at 40-50℃ for 60-90 min. Add acrylamide, butyl methacrylate, modified guar gum, and alkenylpyridine and react at 40-50℃ for 3-4 hours. Add potassium hydroxide aqueous solution and react at 90-95℃ for 60-90 min. Then cool to 40-50℃ and add disodium hydrogen phosphate and react for 3-4 hours. Wash, precipitate, and dry to obtain the adhesive.

[0028] More preferably, the raw materials of the adhesive include the following components by weight: 5-6 parts carboxymethyl cellulose, 0.2-0.6 parts potassium persulfate, 0.2-0.6 parts sodium sulfite, 50-60 parts deionized water, 25-30 parts acrylamide, 0.1-0.4 parts butyl methacrylate, 4-5 parts modified guar gum, 2-3 parts alkenylpyridine, 0.5-1 parts potassium hydroxide aqueous solution, and 2-3 parts disodium hydrogen phosphate.

[0029] In a more optimized manner, the raw materials of the modified guar gum include the following components: by mass, 7-8 parts carboxymethyl guar gum, 6-7 parts epoxy-based polyethylene glycol acrylate, 35-45 parts 25-40% aqueous ethanol solution, 0.5-1 parts potassium hydroxide aqueous solution, and 2-3 parts ethyl phosphate.

[0030] More preferably, the raw material for the alkenylpyridine comprises the following components: by mass parts, 7-8 parts of 2,3,5,6-pyridinetetraamine trihydrochloride, 6-7 parts of ethyl isocyanate acrylate, 0.05-0.1 parts of dibutyltin dilaurate, and 35-45 parts of xylene solvent.

[0031] In the proposed scheme, the number average molecular weight of epoxy-based polyethylene glycol acrylate is 600-900.

[0032] First, guar gum is modified to form a graft copolymer, and phosphate groups and unsaturated groups are introduced to increase the migration channels of lithium ions and improve lithium ion mobility. Then, multiple unsaturated bonds and pyridine groups are introduced through the reaction of amino groups with isocyanates. The pyridine groups can increase the intermolecular interaction forces and improve the heat resistance and chemical stability of the binder, while the unsaturated bonds can be used for subsequent polymerization reactions to form a hyperbranched structure, which helps to form more ion channels and facilitates lithium ion migration. The hyperbranched structure also reduces the linear arrangement of molecular chains and reduces the risk of thermal expansion. Then, a hyperbranched three-dimensional network structure is formed with polymers such as carboxymethyl cellulose and monomers such as acrylamide and butyl methacrylate, which produce a synergistic effect. The monomers improve the flexibility and water resistance, and the pores and channels in the three-dimensional network structure provide more pathways and channels for lithium ion migration, further improving the lithium ion migration rate and battery performance. The tight arrangement of polymer chains and the formation of cross-linked structures reduce the risk of thermal expansion. Finally, the introduction of phosphate groups again enhances the interaction between the binder and the cathode material through coordination bonds with lithium ions, thereby increasing the bonding strength and allowing the electrode material to adhere more firmly to the current collector, thus improving the cycle stability and lifespan of the battery.

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

[0034] 1. Bipolar composite current collectors can serve as current collectors for both positive and negative electrodes, reducing the number of components, simplifying battery structure, facilitating space utilization and battery design, and improving battery energy density.

[0035] 2. The process of preparing bipolar composite current collectors simplifies battery manufacturing, reduces pollution, and enables large-scale production. This helps to further reduce production costs and enhance the product's market competitiveness.

[0036] 3. By preparing bipolar composite current collectors, compatibility with various battery materials and systems can be achieved. Simultaneously, they can serve as a negative electrode-free material in negative electrode-free lithium batteries, helping to reduce lithium nucleation overpotential, achieve uniform lithium deposition, and further improve the overall battery performance. Furthermore, due to their bipolar nature, battery cells can be stacked, reducing the use of current collectors, negative electrode materials, and outer packaging, significantly reducing costs and simplifying the battery assembly process.

[0037] 4. The binder is composed of modified guar gum, carboxymethyl cellulose, and other polymeric compounds, forming a complex three-dimensional network structure that provides mechanical support, ensures electrode stability, accommodates volume changes, and provides more pathways for lithium-ion migration, thereby improving migration rate and battery performance. The pyridine structure and phosphate groups strongly interact with lithium ions, promoting migration and enhancing battery performance. Grafting and branching of unsaturated groups enhance the compactness and stability of the network structure, improving strength, solvent resistance, and thermal stability, while also strengthening adhesion to electrode materials, thus improving battery cycle stability and lifespan. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of a bipolar all-solid-state battery assembled with a bipolar composite current collector;

[0039] Figure 2 A schematic diagram of a bipolar all-solid-state lithium secondary battery assembled with a bipolar composite current collector;

[0040] Figure 3 This is a charge-discharge curve of a bipolar all-solid-state lithium secondary battery assembled with a bipolar composite current collector, prepared in Example 4, measured at 0.1C at room temperature. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Pre-preparation: The specific preparation process of the bipolar composite current collector is as follows:

[0043] Step 1: (1) A layer of alloy is magnetron sputtered on one side of the polymer layer as an intermediate alloy layer. The power is set to 5kW, the argon flow rate is 50mL / min, the coating vacuum degree is 0.08Pa, and the coating time is 1s. Then, aluminum is electroplated on the intermediate alloy layer to form a positive electrode metal layer, and a metal Al layer is obtained. The specific process conditions are as follows: the electroplating solution includes 100g / L copper sulfate, 120g / L sulfuric acid, 46mg / L HCl (hydrochloric acid), 15mg / L sodium 3-mercapto-1-propanesulfonate, 0.6mg / L 2-mercaptopyridine, 100mg / L polyethylene glycol (average molecular weight is 10000), the temperature of the electroplating solution is 25℃, and the average cathode current density is 1.5A / dm³. 2, The electroplating time is 5 min; (2) A layer of alloy is also magnetron sputtered on the other side of the polymer layer to form an intermediate alloy layer; a copper metal seed layer is sputtered on the intermediate alloy layer, and then water electroplating is performed to deposit copper to form a negative electrode metal layer, thus obtaining a metal Cu layer.

[0044] Step 2: Set the roughness of the metal Al layer and the metal Cu layer to 1Ra and perform roughening roller grinding to obtain the bipolar composite current collector.

[0045] Example 1: A solid-state lithium secondary battery, comprising the following steps:

[0046] Referring to the above pre-preparation process, the prepared bipolar composite current collector is used in the battery assembly process. In this embodiment, the current collector has a polyethylene terephthalate film as the polymer layer with a thickness of 4.5 micrometers, a copper-tin alloy layer as the intermediate metal layer with a thickness of 15 nanometers, an aluminum layer as the positive electrode metal layer, and a copper layer as the negative electrode metal layer. The aluminum layer has a thickness of 1 micrometer, and the copper layer has a thickness of 0.5 micrometers. The positive electrode active material is lithium iron phosphate, and the electrolyte is polyethylene oxide. The process of assembling it into a battery is as follows:

[0047] Step 1: Add polyethylene oxide and lithium difluorosulfonyl imide to N,N-dimethylformamide, with a molar ratio of polyethylene oxide to lithium difluorosulfonyl imide of 16:1. Dry under vacuum at 90°C for 12 hours, then cool to obtain a solid polymer electrolyte.

[0048] Step 2: Add 60 parts of positive electrode active material, 20 parts of solid polymer electrolyte, 10 parts of conductive agent, and 10 parts of binder to N-methylpyrrolidone and mix evenly to obtain a positive electrode slurry; coat it onto the outer surface of the metal Al layer of the bipolar composite current collector, dry it, and obtain the positive electrode material; use this as an intermediate product.

[0049] Step 3: The intermediate products are wound or stacked to obtain solid-state lithium secondary batteries.

[0050] Example 2: A method for preparing a bipolar composite current collector and a solid-state lithium secondary battery, comprising the following steps:

[0051] Referring to the above pre-preparation process, the prepared bipolar composite current collector is used in the battery assembly process. In this embodiment, the polymer substrate layer is a polyethylene terephthalate film with a thickness of 4.5 micrometers, the intermediate metal layer is a copper-tin alloy layer with a thickness of 15 nanometers, the positive electrode metal layer and the negative electrode metal layer are aluminum and copper layers, respectively, with the aluminum layer having a thickness of 2 micrometers and the copper layer having a thickness of 1 micrometer. The positive electrode active material is lithium iron phosphate, and the electrolyte is polyethylene oxide. The process of assembling it into a battery is as follows:

[0052] Step 1: Add polyethylene oxide and lithium difluorosulfonyl imide to N,N-dimethylformamide, with a molar ratio of polyethylene oxide to lithium difluorosulfonyl imide of 16:1. Dry under vacuum at 90°C for 12 hours, then cool to obtain a solid polymer electrolyte.

[0053] Step 2: Add 60 parts of positive electrode active material, 20 parts of solid polymer electrolyte, 10 parts of conductive agent, and 10 parts of binder to N-methylpyrrolidone and mix evenly to obtain a positive electrode slurry; coat it onto the outer surface of the metal Al layer of the bipolar composite current collector, dry it, and obtain the positive electrode material; use this as an intermediate product.

[0054] Step 3: The intermediate products are wound or stacked to obtain solid-state lithium secondary batteries.

[0055] Example 3: A method for preparing a bipolar composite current collector and a solid-state lithium secondary battery, comprising the following steps:

[0056] Referring to the above pre-preparation process, the prepared bipolar composite current collector is used in the battery assembly process. In this embodiment, the polymer substrate layer is a polyethylene terephthalate film with a thickness of 6 micrometers, the intermediate metal layer is a copper-tin alloy layer with a thickness of 15 nanometers, the positive electrode metal layer and the negative electrode metal layer are aluminum and copper layers, respectively, with the aluminum layer having a thickness of 2 micrometers and the copper layer having a thickness of 1 micrometer. The positive electrode active material is lithium iron phosphate, and the electrolyte is polyethylene oxide. The process of assembling it into a battery is as follows:

[0057] Step 1: Add polyethylene oxide and lithium difluorosulfonyl imide to N,N-dimethylformamide, with a molar ratio of polyethylene oxide to lithium difluorosulfonyl imide of 16:1. Dry under vacuum at 90°C for 12 hours, then cool to obtain a solid polymer electrolyte.

[0058] Step 2: Add 60 parts of positive electrode active material, 20 parts of solid polymer electrolyte, 10 parts of conductive agent, and 10 parts of binder to N-methylpyrrolidone and mix evenly to obtain a positive electrode slurry; coat it onto the outer surface of the metal Al layer of the bipolar composite current collector, dry it, and obtain the positive electrode material; use this as an intermediate product.

[0059] Step 3: The intermediate products are wound or stacked to obtain solid-state lithium secondary batteries.

[0060] Example 4: A method for preparing a bipolar composite current collector and a solid-state lithium secondary battery, comprising the following steps:

[0061] Referring to the above pre-preparation process, the prepared bipolar composite current collector is used in the battery assembly process. In this embodiment, the polymer substrate layer is a polyethylene terephthalate film with a thickness of 4.5 micrometers, the intermediate metal layer is a copper-tin alloy layer with a thickness of 15 nanometers, the positive electrode metal layer and the negative electrode metal layer are aluminum and copper layers, respectively, with the aluminum layer having a thickness of 1 micrometer and the copper layer having a thickness of 0.5 micrometers. The positive electrode active material is lithium iron phosphate, and the electrolyte is polyethylene oxide. The process of assembling it into a battery is as follows:

[0062] Step 1: Add polyethylene oxide and lithium difluorosulfonyl imide to N,N-dimethylformamide, with a molar ratio of polyethylene oxide to lithium difluorosulfonyl imide of 16:1. Dry under vacuum at 90°C for 12 hours, then cool to obtain a solid polymer electrolyte.

[0063] Step 2: Add 60 parts of positive electrode active material, 20 parts of solid polymer electrolyte, 10 parts of conductive agent, and 10 parts of binder to N-methylpyrrolidone and mix evenly to obtain a positive electrode slurry; coat it onto the outer surface of the metal Al layer of the bipolar composite current collector, dry it, and obtain the positive electrode material; use this as an intermediate product.

[0064] Step 3: The intermediate product is wound or stacked to obtain a solid-state lithium secondary battery; two solid-state battery cells are stacked to ensure that all surfaces are tightly fitted; finally, the compacted solid-state battery cells are encapsulated in a button cell to obtain a high-voltage bipolar all-solid-state battery.

[0065] Example 5: Based on Example 1, a branched adhesive is selected, with all other aspects remaining unchanged, including the following steps:

[0066] Referring to the above pre-preparation process, the prepared bipolar composite current collector is used in the battery assembly process. In this embodiment, the polymer substrate layer is a polyethylene terephthalate film with a thickness of 4.5 micrometers, the intermediate metal layer is a copper-tin alloy layer with a thickness of 15 nanometers, the positive electrode metal layer and the negative electrode metal layer are aluminum and copper layers, respectively, with the aluminum layer having a thickness of 1 micrometer and the copper layer having a thickness of 0.5 micrometers. The positive electrode active material is lithium iron phosphate, and the electrolyte is polyethylene oxide. The specific preparation process is as follows:

[0067] Step 1: (1) Add 7.5 parts of carboxymethyl guar gum and 6.5 parts of epoxy polyethylene glycol acrylate to 40 parts of 35% ethanol aqueous solution, add 0.8 parts of potassium hydroxide aqueous solution and 2.5 parts of ethyl phosphate, react at 70℃ for 12 hours, purify, dry, and obtain modified guar gum for later use; (2) Under nitrogen atmosphere, add 7.5 parts of 2,3,5,6-pyridinetetramine trihydrochloride, 6.5 parts of isocyanate ethyl acrylate and 0.08 parts of dibutyltin dilaurate to 40 parts of xylene solvent, react at 75℃ for 2.5 hours, filter, and purify. , to obtain alkenylpyridine, for later use; (3) 5.5 parts carboxymethyl cellulose, 0.3 parts potassium persulfate and 0.3 parts sodium sulfite were added to 55 parts deionized water and reacted at 45°C for 75 min. 28 parts acrylamide, 0.3 parts butyl methacrylate, 4.5 parts modified guar gum and 2.5 parts alkenylpyridine were added and reacted at 45°C for 3.5 hours. 0.8 parts potassium hydroxide aqueous solution were added and reacted at 92°C for 75 min. Then the temperature was lowered to 45°C and 2.5 parts disodium hydrogen phosphate were added and reacted for 3.5 hours. The mixture was washed, precipitated, and dried to obtain the adhesive;

[0068] Step 2: Add polyethylene oxide and lithium difluorosulfonyl imide to N,N-dimethylformamide, with a molar ratio of polyethylene oxide to lithium difluorosulfonyl imide of 16:1. Dry under vacuum at 90°C for 12 hours, then cool to obtain a solid polymer electrolyte.

[0069] Step 3: Add 60 parts of positive electrode active material, 20 parts of solid polymer electrolyte, 10 parts of conductive agent, and 10 parts of binder to N-methylpyrrolidone and mix evenly to obtain a positive electrode slurry; coat it onto the outer surface of the metal Al layer of the bipolar composite current collector, dry it, and obtain the positive electrode material; use this as an intermediate product.

[0070] Step 4: The intermediate products are wound or stacked to obtain solid-state lithium secondary batteries.

[0071] Comparative Example 1: Based on Example 1, the roughness was set to 0.05Ra and roughening roller grinding was performed. The other specific steps were the same as in Example 1.

[0072] Comparative Example 2: Based on Example 5, alkenylpyridine was not added, but the other specific steps were the same as in Example 5.

[0073] Performance Testing: The prepared solid-state lithium secondary battery composed of bipolar composite current collector was subjected to constant current charge-discharge testing within a voltage range of 2.7~3.8 V using a NEWARE battery testing system. The discharge specific capacity was tested at room temperature and 0.1C (1C is 170mAh / g), and the capacity retention rate after 200 cycles was recorded. The data obtained are shown in Table 1 below:

[0074]

[0075] Conclusions: The bipolar composite current collector prepared in this paper can serve as both a positive and negative electrode current collector, thereby improving battery energy density. The preparation of the bipolar composite current collector simplifies battery manufacturing processes, reduces pollution, and facilitates large-scale production, thus lowering costs. This current collector is compatible with various battery materials and can be used as a negative electrode-free material, further reducing costs and simplifying assembly. The preparation of a binder composed of polymeric compounds promotes lithium-ion migration, enhances the compactness and stability of the network structure, and improves battery cycle stability and lifespan.

[0076] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A solid-state lithium secondary battery, characterized by: The preparation method of the solid-state lithium secondary battery comprises the following steps: Step 1: polyethylene oxide, lithium bisfluorosulfonylimide salt is added to N,N dimethylformamide, vacuum dried at 80~100℃ for 10~14 hours, cooled, to obtain a solid-state polymer electrolyte; Step 2: the positive electrode active material, the solid-state polymer electrolyte, the conductive agent, and the binder are sequentially added to N-methylpyrrolidone and mixed uniformly to obtain a positive electrode slurry; the positive electrode slurry is coated on the outer surface of the metal Al layer of the bipolar composite current collector and dried to obtain a positive electrode material; the positive electrode material is used as an intermediate product; Step 3: the intermediate product is wound or laminated to obtain a solid-state lithium secondary battery; The preparation method of the binder comprises the following steps: Step 1: (1) carboxymethyl guar gum and epoxy polyethylene glycol acrylate are added to 25~40% ethanol aqueous solution, and potassium hydroxide aqueous solution and ethyl phosphate are added and reacted at 60~80℃ for 10~15 hours, purified, dried, to obtain modified guar gum for standby; (2) under nitrogen atmosphere, 2,3,5,6-pyridine tetramine trihydrochloride, isocyanate acrylate ethyl, and dibutyl tin dilaurate are added to xylene solvent and reacted at 70~80℃ for 2~3 hours, filtered, purified, to obtain alkenyl pyridine for standby; Step 2: carboxymethyl cellulose, potassium persulfate, and sodium sulfite are added to deionized water and reacted at 40~50℃ for 60~90min, acrylamide, butyl methacrylate, modified guar gum, and alkenyl pyridine are added and reacted at 40~50℃ for 3~4 hours, potassium hydroxide aqueous solution is added and reacted at 90~95℃ for 60~90min, then cooled to 40~50℃ and then added with disodium hydrogen phosphate and reacted for 3~4 hours, washed, precipitated, and dried, to obtain a binder; The preparation method of the bipolar composite current collector comprises the following steps: Step 1: (1) one side of the high molecular layer is magnetron sputtered with an alloy layer as an intermediate alloy layer; an aluminum metal seed layer is sputtered on the intermediate alloy layer, and then water electroplating is performed to deposit aluminum to form a positive electrode metal layer, to obtain a metal Al layer; (2) the other side of the high molecular layer is also magnetron sputtered with an alloy layer as an intermediate alloy layer; a copper metal seed layer is sputtered on the intermediate alloy layer, and then water electroplating is performed to deposit copper to form a negative electrode metal layer, to obtain a metal Cu layer; Step 2: the metal Al layer and the metal Cu layer are subjected to roughening roll grinding treatment to obtain a bipolar composite current collector. 2.The solid-state lithium secondary battery of claim 1, wherein: The high molecular layer is a high molecular film with a thickness of 1~15μm; the material of the high molecular film comprises one or more of polyethylene terephthalate, polypropylene, polytetrafluoroethylene, polyimide, polyethylene, and ethylene glycol naphthalene dicarboxylate; The intermediate alloy layer comprises metal A and metal B; the metal A comprises one of copper, silver, magnesium, aluminum, and indium; the metal B comprises one of germanium, platinum, zinc, gold, tin, lead, cadmium, antimony, bismuth, and gallium. 3.The solid-state lithium secondary battery of claim 1, wherein: The thickness of the metal Cu layer is 0.5~10μm; the thickness of the metal Al layer is 1~20μm; and the thickness of the intermediate alloy layer is 15~20nm. 4.The solid-state lithium secondary battery of claim 1, wherein: The roughness of the metal after the roughing roller grinding treatment is 0.1-10 Ra. 5.The solid-state lithium secondary battery of claim 1, wherein: The bipolar composite current collector comprises, from top to bottom, a metal Al layer, an intermediate alloy layer, a polymer layer, an intermediate alloy layer and a metal Cu layer. 6.The solid-state lithium secondary battery of claim 1, wherein: The molar ratio of polyethylene oxide and lithium bisfluorosulfonylimide in the raw material of the solid-state polymer electrolyte is 8-20:

1. The raw material of the positive electrode slurry comprises the following components: positive electrode active material, solid-state polymer electrolyte, conductive agent and binder in a mass ratio of 6:2:1:

1. 7.The solid-state lithium secondary battery of claim 1, wherein: The raw material of the binder comprises the following components: 5-6 parts of carboxymethyl cellulose, 0.2-0.6 parts of potassium persulfate, 0.2-0.6 parts of sodium sulfite, 50-60 parts of deionized water, 25-30 parts of acrylamide, 0.1-0.4 parts of butyl methacrylate, 4-5 parts of modified guar gum, 2-3 parts of alkenylpyridine, 0.5-1 parts of potassium hydroxide aqueous solution and 2-3 parts of disodium hydrogen phosphate.

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