High-energy-density fast-charging polymer soft package battery

Abstract

The invention discloses a high-energy-density fast-charging polymer soft package battery, which comprises a positive electrode, a negative electrode, a diaphragm, an electrolyte and a packaging body, the positive electrode is composed of core-shell composite particles prepared from lithium cobalt oxide and a lithium-rich manganese-based material through a spray drying method, the negative electrode is a lithium titanate coated three-dimensional porous graphene skeleton loaded silicon carbon composite material, and the lithium titanate coated three-dimensional porous graphene skeleton loaded silicon carbon composite material is a lithium titanate coated three-dimensional porous graphene skeleton loaded silicon carbon composite material. The electrolyte comprises lithium bis (trifluoromethylsulfonyl) imide, fluoroethylene carbonate and 1, 3-propane sultone, and the packaging body sequentially comprises a polyether-ether-ketone high-temperature-resistant layer, a nanometer aluminum oxide enhanced aluminum foil and a modified polypropylene heat sealing layer from inside to outside. Through modification of positive and negative electrode materials, optimization of an electrolyte and improvement of a packaging process, the energy density, the fast charging performance, the safety, the cycle life and other aspects are remarkably improved, and the defects of a traditional soft package battery are effectively overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of battery preparation, and specifically to a high energy density fast charging polymer soft-pack battery. Background Art

[0002] With the rapid development of new energy vehicles, portable electronic devices and energy storage systems, the market has put forward higher requirements for the energy density, fast charging performance and safety of lithium-ion batteries. However, traditional soft-pack lithium batteries still have the following defects:

[0003] Positive electrode material: Traditional lithium cobaltate (LiCoO2) is prone to structural collapse at high voltages (>4.3V), resulting in capacity attenuation; although lithium-rich manganese-based materials have high capacities, they have problems such as low initial efficiency and voltage attenuation. Negative electrode material: Silicon-based materials cause electrode pulverization due to volume expansion (>300%), and graphite materials have low energy density (theoretical capacity 372 mAh / g), making it difficult to meet the fast charging requirements. Electrolyte: Conventional electrolytes are prone to oxidation and decomposition at high voltages, and have insufficient ability to form SEI films on silicon-based negative electrodes. Encapsulation process: Traditional aluminum-plastic film encapsulation is prone to liquid leakage due to insufficient heat sealing strength and has poor high-temperature resistance (<120°C). Summary of the Invention

[0004] In order to overcome the deficiencies of the prior art solutions, the present invention provides a high energy density fast charging polymer soft-pack battery, which can effectively solve the problems raised in the background art.

[0005] The technical solution adopted by the present invention to solve its technical problems is:

[0006] A high energy density fast charging polymer soft-pack battery, including a positive electrode, a negative electrode, a separator, an electrolyte and a package. The positive electrode is composed of core-shell composite particles prepared by spray drying of lithium cobaltate and lithium-rich manganese-based materials. The positive electrode includes a core layer and a shell layer. The core layer is lithium cobaltate with a particle size of 3-8 μm, and the shell layer is a lithium-rich manganese-based material with a thickness of 0.5-2 μm. A double-phase coating layer is provided on the surface of the shell layer. The double-phase coating layer includes an inner layer with a thickness of 5-15 nm and an outer layer with a thickness of 10-30 nm. The inner layer is LiAlO2, and the outer layer is Li3PO4;

[0007] The negative electrode is a silicon-carbon composite material supported by a three-dimensional porous graphene framework coated with lithium titanate, where the porosity of the graphene framework is 75-85%, the pore size distribution is 10-200 nm, the silicon-carbon particles are embedded in the pores of the graphene framework by chemical vapor deposition, and the thickness of the lithium titanate coating layer on the surface is 2-5 nm;

[0008] The electrolyte includes lithium bis(trifluoromethanesulfonyl)imide, fluoroethylene carbonate, and 1,3-propane sultone. The concentration of lithium bis(trifluoromethanesulfonyl)imide is 1.2 - 1.8 mol / L, the volume ratio of fluoroethylene carbonate to 1,3-propane sultone is (5:1) - (8:1), and 0.1 - 0.5 wt% of lithium fluoride is added as a negative electrode SEI film promoter;

[0009] The encapsulation body consists of a polyetheretherketone high-temperature resistant layer with a thickness of 10 - 20 μm and a melting point ≥ 343°C, a nano-aluminum oxide reinforced aluminum foil with a thickness of 30 - 50 μm and a tensile strength ≥ 150 MPa, and a modified polypropylene heat-sealing layer with a melt index of 25 - 35 g / 10 min. The edge of the encapsulation body adopts a laser-induced metallization welding and gradient temperature hot pressing composite sealing process with a power of 250 - 400 W and a scanning speed of 5 - 10 mm / s. The gradient temperature hot pressing is divided into three sections: 80°C → 120°C → 150°C, and the pressure in each section is 0.5 - 1.5 MPa.

[0010] As a further description of the above technical solution, in the core-shell composite cathode material, 0.5 - 1.2 at% of zirconium element is doped in the lithium-rich manganese-based shell layer, and a transition layer is provided between the LiAlO2 and Li3PO4 layers of the biphasic coating layer. The transition layer is a late transition metal with a thickness of 2 - 5 nm.

[0011] As a further description of the above technical solution, the preparation method of the three-dimensional porous graphene framework includes the following steps:

[0012] Step S1: Mix graphene oxide and polystyrene microspheres with a particle size of 50 - 200 nm in a mass ratio of (1:2) - (1:5), and react for 6 - 12 hours under supercritical CO2 conditions to form a composite template;

[0013] Step S2: Heat-treat at 900 - 1100°C for 3 - 6 hours under argon protection to remove the PS template and obtain a porous graphene framework;

[0014] Step S3: Deposit a lithium titanate layer on the surface of the framework by atomic layer deposition method, with a deposition temperature of 200 - 250°C and 50 - 100 cycles.

[0015] As a further description of the above technical solution, 0.05 - 0.2 wt% of cyano triethoxysilane is added to the electrolyte as a positive electrode CEI film modifier, and the ionic conductivity of the electrolyte at 25°C is ≥ 12 mS / cm and the viscosity ≤ 35 mPa·s.

[0016] As a further description of the above technical solution, the surface of the PEEK layer of the encapsulation body is provided with V-shaped micro-grooves arranged in a staggered manner. The depth of the V-shaped micro-grooves is 5-15 μm, and the spacing is 20-50 μm. And an interfacial bonding force of ≥8 N / cm of C-O-Al chemical bonding interface is formed between the aluminum foil layer and the PEEK layer through plasma activation treatment.

[0017] As a further description of the above technical solution, the tab of the battery uses a copper-graphene composite tape. The Cu content of the copper-graphene composite tape is ≥98%, and the graphene content is 1-2%. A stepped buffer structure is provided at the connection between the tab and the current collector. The stepped buffer structure includes:

[0018] A copper-nickel alloy layer welded to the current collector. The thickness of the copper-nickel alloy layer is 50-80 μm. A polyimide tape covering the copper-nickel alloy layer. The thickness of the polyimide tape is 20-40 μm, and the temperature resistance grade is ≥200 °C. The outermost layer is a silicon-aluminum fiber-reinforced epoxy resin layer.

[0019] As a further description of the above technical solution, the preparation method of the battery includes the following steps:

[0020] Step S1, positive electrode preparation: Mix the core-shell composite positive electrode material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of (95:2.5:2.5), add N-methylpyrrolidone to make a slurry, and coat it on the aluminum foil;

[0021] After drying in a vacuum drying oven at 120 °C for 12 hours, roll pressing is performed at a pressure of 10-15 MPa to obtain a positive electrode sheet with a compaction density ≥3.4 g / cm 3 of the positive electrode sheet;

[0022] Step S2, negative electrode preparation: Mix the silicon-carbon composite particles, sodium carboxymethyl cellulose, and styrene-butadiene rubber in a mass ratio of (96:2:2), coat it on the copper foil, and after drying at 80 °C for 6 hours, use microwave radiation treatment with a power of 800-1200 W and a time of 30-60 s to enhance the bonding force;

[0023] Step S3, battery assembly: Assemble the positive and negative electrode sheets and the ceramic-coated separator into an electric core through a stacking process;

[0024] In a drying room with a humidity ≤1%, a three-stage liquid injection process is used:

[0025] First, inject 40% of the total amount of the electrolyte, let it stand for 2 hours, and then infiltrate it under a negative pressure of -0.08 MPa;

[0026] Second, inject 30% of the electrolyte, and perform a small current charge and discharge at 0.5 C once to promote penetration;

[0027] Inject the remaining electrolyte three times, pressurize to 1.0 MPa at 50 °C and hold for 4 hours;

[0028] After laser welding and encapsulation, perform a gradient forming process:

[0029] The first stage: Constant current charge at 0.02C to 3.0V and stand for 12 hours;

[0030] The second stage: Charge at 0.05C to 3.8V and age at 45 °C for 48 hours;

[0031] The third stage: Charge and discharge cyclically at 0.1C for 3 times, and detect the electrode structure stability by X-ray diffraction after each cycle.

[0032] As a further description of the above technical solution, nitrogen is introduced for protection during the microwave radiation treatment, the microwave frequency is 2.45 GHz ± 50 MHz, and the peel strength of the treated negative electrode sheet is ≥ 1.5 N / cm.

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

[0034] A high energy density fast charging polymer soft-pack battery of the present invention has at least one of the following beneficial effects during use:

[0035] Combined with the stability of lithium cobaltate and the high capacity of lithium-rich manganese-based materials, while zirconium doping and the double-phase coating layer solve the problems of unstable structure and voltage decay of lithium-rich manganese-based materials. Through the supercritical CO2 templating method + ALD deposition of lithium titanate layer, the efficient loading of silicon-carbon particles and the suppression of volume expansion are realized. Microwave treatment improves the crosslinking degree of the binder and increases the peel strength. Optimizing the electrolyte formulation improves the ionic conductivity and the stability of the SEI / CEI film. Adding cyano triethoxysilane promotes the uniform formation of the positive electrode CEI film and reduces the interfacial impedance. Structurally, combining V-shaped microgrooves and plasma-activated interfaces improves the bonding force, reduces the water and oxygen permeability, and improves the high-temperature resistance and sealing performance of the package. Laser-induced metallization welding combined with gradient hot pressing further increases the peel strength. The copper-graphene composite tape and the stepped buffer structure designed for the tab effectively reduce the occurrence of tab fracture during cycling. Description of the Drawings

[0036] Figure 1 It is a schematic diagram of the overall structure of a high energy density fast charging polymer soft-pack battery of the present invention;

[0037] Figure 2 It is a schematic diagram of the partial decomposition structure of a high energy density fast charging polymer soft-pack battery of the present invention;

[0038] Figure 3Schematic diagram of the battery preparation process of a high-energy-density fast-charging polymer soft-pack battery according to the present invention;

[0039] Figure 4 Schematic diagram of the preparation process of the three-dimensional porous graphene framework of a high-energy-density fast-charging polymer soft-pack battery according to the present invention;

[0040] Figure 5 Schematic diagram of the three-stage liquid injection process flow of a high-energy-density fast-charging polymer soft-pack battery according to the present invention;

[0041] Figure 6 Schematic diagram of the execution gradient formation process flow of a high-energy-density fast-charging polymer soft-pack battery according to the present invention.

[0042] Reference numerals in the figure:

[0043] 1. Encapsulation body; 101. V-shaped microgroove; 102. Positive electrode; 103. Separator; 104. Negative electrode. Detailed implementation manners

[0044] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

[0045] As Figures 1-6 shown, the present invention provides a high-energy-density fast-charging polymer soft-pack battery, including a positive electrode, a negative electrode, a separator, an electrolyte and an encapsulation body. The positive electrode is composed of core-shell composite particles prepared by a spray drying method from lithium cobaltate and lithium-rich manganese-based materials. The positive electrode includes a core layer and a shell layer. The core layer is lithium cobaltate with a particle size of 3-8 μm, and the shell layer is a lithium-rich manganese-based material with a thickness of 0.5-2 μm. A dual-phase coating layer is provided on the surface of the shell layer. The dual-phase coating layer includes an inner layer with a thickness of 5-15 nm and an outer layer with a thickness of 10-30 nm. The inner layer is LiAlO2, and the outer layer is Li3PO4.

[0046] The positive electrode of this embodiment uses LiCoO2 as the core (3-8 μm), a lithium-rich manganese-based material as the shell (0.5-2 μm), combines a dual-phase coating layer (inner layer LiAlO2 + outer layer Li3PO4) and a post-transition metal transition layer to improve the high-voltage stability (the capacity retention rate is ≥95% after 1000 cycles at 4.5V). 0.5-1.2 at% Zr is doped in the lithium-rich manganese-based shell layer 4+ , inhibiting the generation of oxygen vacancies and reducing the voltage decay rate (≤0.3 mV / cycle).

[0047] The negative electrode is a silicon-carbon composite material supported by a three-dimensional porous graphene framework coated with lithium titanate. The porosity of the graphene framework is 75-85%, the pore size distribution is 10-200 nm, silicon-carbon particles are embedded in the pores of the graphene framework by chemical vapor deposition, and the thickness of the lithium titanate coating layer on the surface is 2-5 nm.

[0048] In this embodiment, the negative electrode uses a three-dimensional porous graphene framework with a porosity of 75-85% and a pore size distribution of 10-200 nm. By using the supercritical CO2 template method + ALD deposition of a lithium titanate layer (2-5 nm), efficient loading of silicon-carbon particles (Si / C = 1:1 - 1:3) and suppression of volume expansion (expansion rate ≤ 5%) are achieved. Under microwave irradiation of 800-1200 W for 30-60 seconds, the crosslinking degree of the binder (CMC / SBR) is increased by 40%, and the peel strength is ≥ 1.5 N / cm.

[0049] The electrolyte includes lithium bis(trifluoromethanesulfonyl)imide, fluoroethylene carbonate, and 1,3-propane sultone. The concentration of lithium bis(trifluoromethanesulfonyl)imide is 1.2-1.8 mol / L, the volume ratio of fluoroethylene carbonate to 1,3-propane sultone is (5:1)-(8:1), and 0.1-0.5 wt% of lithium fluoride is added as a negative electrode SEI film promoter.

[0050] In this embodiment, the electrolyte formulation is optimized as LiTFSI (1.2-1.8 mol / L) + FEC / PS (5:1-8:1) + LiF (0.1-0.5 wt%), which synergistically improves the ionic conductivity (≥ 12 mS / cm) and the stability of the SEI / CEI film. 0.05-0.2 wt% of cyanoethyltriethoxysilane promotes the uniform formation of the positive electrode CEI film and reduces the interfacial impedance (≤ 15 Ω·cm 2 )

[0051] The encapsulation body consists of a polyetheretherketone high-temperature resistant layer with a thickness of 10-20 μm and a melting point ≥ 343 °C, a nano-aluminum oxide reinforced aluminum foil with a thickness of 30-50 μm and a tensile strength ≥ 150 MPa, and a modified polypropylene heat-sealing layer with a melt index of 25-35 g / 10 min. The edge of the encapsulation body uses a laser-induced metallization welding and gradient temperature hot pressing composite sealing process with a power of 250-400 W and a scanning speed of 5-10 mm / s. The gradient temperature hot pressing is divided into three stages: 80 °C → 120 °C → 150 °C, and the pressure in each stage is 0.5-1.5 MPa.

[0052] In this embodiment, the PEEK layer (10-20 μm) + nano-Al2O3 reinforced aluminum foil (30-50 μm) + modified PP heat-sealing layer, combined with V-shaped micro-grooves (5-15 μm deep) and a plasma-activated interface (C-O-Al bond, bonding force ≥ 8 N / cm), has a water and oxygen transmission rate ≤ 0.005 g / m 2 / day, Laser-induced metallization welding (250 - 400W) combined with gradient hot pressing (80°C → 150°C, 0.5 - 1.5MPa), the peel strength ≥ 18N / mm. Among them, the extremely ear copper-graphene composite tape (Cu ≥ 98%, graphene 1 - 2%) is paired with a stepped buffer structure (copper-nickel alloy layer + polyimide tape + aluminosilicate fiber layer), and the ear breakage rate during the cycle ≤ 0.1%.

[0053] This embodiment uses a core-shell structure with lithium cobaltate as the core and lithium-rich manganese-based material as the shell, and combines a double-phase coating layer (LiAlO2 and Li3PO4) and a LiAl 0.5 P 0.5 O2 transition layer, improving the high-voltage stability (capacity retention rate ≥ 95% after 1000 cycles at 4.5V). By doping zirconium elements in the lithium-rich manganese-based shell layer, the generation of oxygen vacancies is inhibited, and the voltage decay rate is reduced (≤ 0.3mV / cycle). This structure combines the stability of lithium cobaltate and the high capacity of lithium-rich manganese-based materials, while zirconium doping and the double-phase coating layer solve the problems of unstable structure and voltage decay of lithium-rich manganese-based materials.

[0054] A silicon-carbon composite material is loaded on a three-dimensional porous graphene framework coated with lithium titanate. The graphene framework provides a conductive network and accommodates the volume expansion of the silicon-carbon material. Through the supercritical CO2 templating method + ALD deposition of the lithium titanate layer, efficient loading of silicon-carbon particles and suppression of volume expansion (expansion rate ≤ 5%) are achieved. Microwave treatment improves the crosslinking degree of the binder and increases the peel strength.

[0055] The electrolyte formula is optimized as the combination of LiTFSI + FEC / PS + LiF, which synergistically improves the ionic conductivity (≥ 12mS / cm) and the stability of the SEI / CEI film. Adding cyano triethoxysilane promotes the uniform formation of the CEI film on the positive electrode and reduces the interfacial impedance.

[0056] An encapsulation structure of a PEEK layer + nano-aluminum oxide reinforced aluminum foil + modified PP heat-sealing layer is adopted, combined with V-shaped micro-grooves and a plasma-activated interface, to improve the bonding strength, reduce the water and oxygen permeability, and improve the high-temperature resistance and sealing performance of the package. Laser-induced metallization welding combined with gradient hot pressing further increases the peel strength. The copper-graphene composite tape and the stepped buffer structure designed for the ear effectively reduce the occurrence of ear breakage during the cycle.

[0057] Further, in the core-shell composite cathode material, 0.5 - 1.2at% of zirconium elements are doped in the lithium-rich manganese-based shell layer, and a transition layer is provided between the LiAlO2 and Li3PO4 layers of the double-phase coating layer. The transition layer is a late transition metal with a thickness of 2 - 5nm.

[0058] Further, the preparation method of the three-dimensional porous graphene framework includes the following steps:

[0059] Step S1: Mix graphene oxide and polystyrene microspheres with a particle size of 50 - 200 nm in a mass ratio of (1:2) - (1:5), and react under supercritical CO2 conditions for 6 - 12 hours to form a composite template;

[0060] Step S2: Remove the PS template by heat treatment at 900 - 1100 °C for 3 - 6 hours under argon protection to obtain a porous graphene framework;

[0061] Step S3: Deposit a lithium titanate layer on the surface of the framework by atomic layer deposition, with a deposition temperature of 200 - 250 °C and 50 - 100 deposition cycles.

[0062] Further, 0.05 - 0.2 wt% of cyano triethoxysilane is added to the electrolyte as a positive electrode CEI film modifier, and the ionic conductivity of the electrolyte at 25 °C is ≥12 mS / cm and the viscosity is ≤35 mPa·s.

[0063] Further, the surface of the PEEK layer of the encapsulation body is provided with V-shaped microgrooves arranged in a staggered manner. The depth of the V-shaped microgrooves is 5 - 15 μm, the spacing is 20 - 50 μm, and an interfacial bonding force ≥8 N / cm of C-O-Al chemical bonding interface is formed between the aluminum foil layer and the PEEK layer through plasma activation treatment.

[0064] Further, the tab of the battery uses a copper-graphene composite strip. The Cu content of the copper-graphene composite strip is ≥98%, and the graphene content is 1 - 2%. A stepped buffer structure is provided at the connection between the tab and the current collector. The stepped buffer structure includes:

[0065] A copper-nickel alloy layer welded to the current collector, with a thickness of the copper-nickel alloy layer being 50 - 80 μm, a polyimide tape covering the copper-nickel alloy layer, with a thickness of the polyimide tape being 20 - 40 μm and a temperature resistance grade ≥200 °C, and an outermost layer of aluminum silicate fiber reinforced epoxy resin layer.

[0066] Further, the preparation method of the battery includes the following steps:

[0067] Step S1, positive electrode preparation: Mix the core-shell composite positive electrode material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of (95:2.5:2.5), add N-methylpyrrolidone to make a slurry, and coat it on the aluminum foil;

[0068] After drying in a vacuum drying oven at 120 °C for 12 hours, roll press at a pressure of 10 - 15 MPa to obtain a positive electrode sheet with a compaction density ≥3.4 g / cm 3 of the positive electrode sheet;

[0069] Synthesis of core-shell material: Dispersed LiCoO2 particles (D50 = 5 μm) in an ethanol solution containing LiNO3, Mn(NO3)2, and Ni(NO3)2, and formed a lithium-rich manganese-based shell layer (thickness 1 μm) by spray drying. Coated LiAlO2 (10 nm) and Li3PO4 (20 nm) in sequence by sol-gel method, and generated a LiAl 0.5 P 0.5 O2 transition layer (3 nm). Preparation of electrode: Mixed the core-shell material, SP, and PVDF at a ratio of 95:2.5:2.5, coated on aluminum foil (coating amount 18 mg / cm 2 ), and the compaction density was 3.5 g / cm 3 after rolling, and the electrode resistance ≤ 2 Ω·cm.

[0070] Step S2, Preparation of negative electrode: Mixed silicon-carbon composite particles with sodium carboxymethyl cellulose and styrene-butadiene rubber at a mass ratio of (96:2:2), coated on copper foil, and after drying at 80 °C for 6 hours, used microwave radiation treatment with a power of 800 - 1200 W and a time of 30 - 60 s to enhance the adhesion;

[0071] Three-dimensional graphene framework: Reacted GO with PS microspheres (1:3) in supercritical CO2 (32 °C, 7.4 MPa) for 8 hours, removed the template by heat treatment at 1000 °C for 4 hours, and deposited a lithium titanate layer (200 °C, 80 cycles) by ALD, with a thickness of 3 nm. Silicon-carbon composite negative electrode: Loaded SiOx / C (1:2) particles into the pores of the framework, coated on copper foil (coating amount 10 mg / cm 2 ), and the peel strength was 1.8 N / cm after microwave treatment (1000 W, 45 s).

[0072] Step S3, Battery assembly: Assembled the positive and negative electrodes and the ceramic-coated separator into an electric core by the stacking process;

[0073] In a dry room with humidity ≤ 1%, adopted a three-stage liquid injection process:

[0074] First injected 40% of the total amount of electrolyte, left to stand for 2 hours and then infiltrated under a negative pressure of -0.08 MPa;

[0075] Second injected 30% of the electrolyte, and performed a small current charge and discharge at 0.5C once to promote penetration;

[0076] Third injected the remaining electrolyte, pressurized to 1.0 MPa at 50 °C and maintained for 4 hours;

[0077] After laser welding and encapsulation, performed a gradient formation process:

[0078] The first stage: Constant current charge at 0.02C until 3.0V, and then stand for 12 hours;

[0079] The second stage: Charge at 0.05C until 3.8V, and age at 45°C for 48 hours;

[0080] The third stage: Charge and discharge cyclically at 0.1C for 3 times, and detect the structural stability of the electrode by X-ray diffraction after each cycle.

[0081] The positive and negative electrode plates and the Al2O3 ceramic separator (thickness 5μm) are laminated into a 10Ah soft-pack battery cell. The three-stage liquid injection process: 40% + 30% + 30% of the electrolyte is injected step by step, and after pressure penetration, it is sealed.

[0082] Further, nitrogen is introduced for protection during the microwave radiation treatment, and the microwave frequency is 2.45GHz ± 50MHz. The peel strength of the treated negative electrode plate is ≥ 1.5N / cm.

[0083] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights.

Claims

1. A high energy density fast charging polymer soft-pack battery, comprising a positive electrode, a negative electrode, a separator, an electrolyte and a package, characterized in that, The positive electrode is composed of core-shell composite particles prepared by a spray drying method from lithium cobaltate and lithium-rich manganese-based material. The positive electrode includes a core layer and a shell layer. The core layer is lithium cobaltate with a particle size of 3 - 8 μm, and the shell layer is a lithium-rich manganese-based material with a thickness of 0.5 - 2 μm. A dual-phase coating layer is provided on the surface of the shell layer. The dual-phase coating layer includes an inner layer with a thickness of 5 - 15 nm and an outer layer with a thickness of 10 - 30 nm. The inner layer is LiAlO₂, and the outer layer is Li₃PO₄; The negative electrode is a silicon-carbon composite material supported by a three-dimensional porous graphene framework coated with lithium titanate. The porosity of the graphene framework is 75 - 85%, and the pore size distribution is 10 - 200 nm. The silicon-carbon particles are embedded into the pores of the graphene framework by chemical vapor deposition, and the thickness of the lithium titanate coating layer on the surface is 2 - 5 nm; The electrolyte includes lithium bis(trifluoromethanesulfonyl)imide, fluoroethylene carbonate, and 1,3 - propane sultone. The concentration of lithium bis(trifluoromethanesulfonyl)imide is 1.2 - 1.8 mol / L, the volume ratio of fluoroethylene carbonate to 1,3 - propane sultone is (5:1) - (8:1), and 0.1 - 0.5 wt% of lithium fluoride is added as a negative electrode SEI film promoter; The encapsulation body consists of a polyether ether ketone high-temperature resistant layer with a thickness of 10 - 20 μm and a melting point ≥ 343 °C, a nano-aluminum oxide reinforced aluminum foil with a thickness of 30 - 50 μm and a tensile strength ≥ 150 MPa, and a modified polypropylene heat-sealing layer with a melt index of 25 - 35 g / 10 min. The edge of the encapsulation body adopts a laser-induced metallization welding and gradient temperature hot pressing composite sealing process with a power of 250 - 400 W and a scanning speed of 5 - 10 mm / s. The gradient temperature hot pressing is divided into three stages: 80 °C → 120 °C → 150 °C, and the pressure in each stage is 0.5 - 1.5 MPa.

2. The high-energy density fast-charging polymer soft-pack battery according to claim 1, wherein: In the core-shell composite positive electrode material, 0.5 - 1.2 at% of zirconium element is doped in the lithium-rich manganese-based shell layer, and a transition layer is provided between the LiAlO₂ and Li₃PO₄ layers of the dual-phase coating layer. The transition layer is a late transition metal with a thickness of 2 - 5 nm.

3. A high-energy density fast-charging polymer soft-pack battery according to claim 1, characterized in that: The preparation method of the three-dimensional porous graphene framework includes the following steps: Step S1: Mix graphene oxide and polystyrene microspheres with a particle size of 50 - 200 nm in a mass ratio of (1:2) - (1:5), and react for 6 - 12 hours under supercritical CO₂ conditions to form a composite template; Step S2: Heat-treat at 900 - 1100 °C for 3 - 6 hours under argon protection to remove the PS template and obtain a porous graphene framework; Step S3: Deposit a lithium titanate layer on the surface of the framework by atomic layer deposition, with a deposition temperature of 200 - 250 °C and 50 - 100 deposition cycles.

4. A high-energy density fast-charging polymer soft-pack battery according to claim 1, characterized in that: 0.05 - 0.2 wt% of cyano triethoxysilane is added to the electrolyte as a positive electrode CEI film modifier, and the ionic conductivity of the electrolyte at 25 °C is ≥ 12 mS / cm, and the viscosity ≤ 35 mPa·s.

5. A high energy density fast charging polymer soft-pack battery according to claim 1, characterized in that: The surface of the PEEK layer of the encapsulation body is provided with V-shaped micro-grooves arranged in a staggered manner. The depth of the V-shaped micro-grooves is 5 - 15 μm, and the spacing is 20 - 50 μm. And an interfacial bonding force of ≥8 N / cm C-O-Al chemical bonding interface is formed between the aluminum foil layer and the PEEK layer through plasma activation treatment.

6. The high-energy density fast-charging polymer soft-pack battery according to claim 1, wherein: The tab of the battery uses a copper-graphene composite strip. The Cu content of the copper-graphene composite strip is ≥98%, and the graphene content is 1 - 2%. A stepped buffer structure is provided at the connection between the tab and the current collector. The stepped buffer structure includes: A copper-nickel alloy layer welded to the current collector. The thickness of the copper-nickel alloy layer is 50 - 80 μm. A polyimide tape covering the copper-nickel alloy layer. The thickness of the polyimide tape is 20 - 40 μm, and the temperature resistance grade is ≥200 °C. The outermost layer is a silicon-aluminum fiber reinforced epoxy resin layer.

7. A high-energy density fast-charging polymer soft-pack battery according to claim 1, characterized in that: The preparation method of the battery includes the following steps: Step S1, positive electrode preparation: Mix the core-shell composite positive electrode material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of (95:2.5:2.5), add N-methylpyrrolidone to make a slurry, and coat it on the aluminum foil. After drying at 120 °C for 12 hours in a vacuum drying oven, roll pressing is carried out at a pressure of 10 - 15 MPa to obtain a positive electrode sheet with a compaction density ≥ 3.4 g / cm 3 ; Step S2, negative electrode preparation: Mix the silicon-carbon composite particles, sodium carboxymethyl cellulose, and styrene-butadiene rubber in a mass ratio of (96:2:2), coat it on the copper foil, and after drying at 80 °C for 6 hours, perform microwave radiation treatment with a power of 800 - 1200 W and a time of 30 - 60 s to enhance the adhesion. Step S3, battery assembly: Assemble the positive and negative electrode sheets and the ceramic-coated separator into an electric core through a stacking process. In a drying room with a humidity ≤1%, a three-stage liquid injection process is adopted: First, inject 40% of the total amount of the electrolyte, let it stand for 2 hours, and then infiltrate it under a negative pressure of -0.08 MPa. Second, inject 30% of the electrolyte, charge and discharge at a small current of 0.5C for 1 time to promote penetration. Third, inject the remaining electrolyte, pressurize it to 1.0 MPa at 50 °C and maintain it for 4 hours. After laser welding and encapsulation, perform a gradient formation process: The first stage: Constant current charge at 0.02C to 3.0V, and let it stand for 12 hours. The second stage: Charge at 0.05C to 3.8V, and age it at 45 °C for 48 hours. The third stage: Cyclic charge and discharge at 0.1C for 3 times, and detect the electrode structure stability by X-ray diffraction after each cycle.

8. A high-energy density fast-charging polymer soft-pack battery according to claim 7, characterized in that: During the microwave radiation treatment, nitrogen is introduced for protection, and the microwave frequency is 2.45 GHz ± 50 MHz. The peel strength of the treated negative electrode sheet is ≥1.5 N / cm.

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