Lithium ion battery and preparation method thereof

Abstract

The invention relates to a lithium ion battery and a preparation method thereof. The lithium ion battery includes: a positive electrode; the negative electrode comprises a titanium-based oxide; the composite diaphragm is located between the positive electrode and the negative electrode, the composite diaphragm comprises a base membrane and a PTFE porous membrane, and the PTFE porous membrane is located between the base membrane and the negative electrode. According to the lithium ion battery provided by the technical scheme of the invention, the negative electrode comprises the titanium-based oxide, the composite diaphragm comprises the base membrane and the PTFE porous membrane, and the PTFE porous membrane is in direct contact with the negative electrode. And the titanium-based oxide does not react with PTFE and has good compatibility, so that the thermal stability and the safety of the battery are remarkably improved. The composite diaphragm is simple in structure and excellent in high-temperature resistance, high-temperature shrinkage is effectively prevented, and the risk of thermal runaway is reduced. Meanwhile, the battery has high rate capability and long cycle life, and is easy to industrially prepare.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a lithium-ion battery and its preparation method. Background Technology

[0002] Lithium-ion batteries are widely used in consumer electronics, electric vehicles, and energy storage systems. As a key internal component of the battery, the separator not only needs to isolate the positive and negative electrodes to prevent short circuits, but also needs to maintain structural stability and prevent thermal runaway when the battery overheats abnormally. The choice of negative electrode material is crucial to battery performance. Titanium-based oxides (such as lithium titanate) offer high safety, long cycle life, and excellent rate performance as negative electrode materials, but they require good compatibility with the separator.

[0003] Currently, commercial lithium-ion battery separators are mostly microporous membranes made of polyolefin materials (such as PP and PE). While these materials possess good mechanical properties and electrochemical stability, their melting points are relatively low (PE approximately 135℃, PP approximately 165℃), resulting in poor heat resistance. When the battery generates abnormal heat due to overcharging, short circuits, or fast charging, the polyolefin separator is prone to large-area melting and shrinkage, leading to direct contact between the positive and negative electrodes, potentially causing short circuits, fires, or even explosions—serious safety issues. This is especially true in power battery applications that demand high energy density and high-power fast charging, where internal heat generation is more significant, placing higher demands on the separator's thermal stability and compatibility with the negative electrode. Therefore, developing a high-safety lithium-ion battery that uses a separator compatible with titanium-based oxide negative electrodes, has a simple structure, good thermal stability, and is easy to industrialize is of great importance. Summary of the Invention

[0004] Therefore, it is necessary to provide a lithium-ion battery with a simple structure, good thermal stability, and easy industrialization preparation method.

[0005] A lithium-ion battery, characterized in that the lithium-ion battery comprises: positive electrode; Anode, said anode comprising titanium-based oxide; and A composite separator is located between the positive electrode and the negative electrode. The composite separator includes a base membrane and a PTFE porous membrane, and the PTFE porous membrane is located between the base membrane and the negative electrode.

[0006] The lithium-ion battery of this invention comprises a titanium-based oxide as the negative electrode and a composite separator comprising a base film and a PTFE porous film, with the PTFE porous film in direct contact with the negative electrode. The titanium-based oxide does not react with PTFE, exhibiting good compatibility and significantly improving the battery's thermal stability and safety. The composite separator has a simple structure, excellent high-temperature resistance, effectively preventing high-temperature shrinkage and reducing the risk of thermal runaway. Furthermore, this battery possesses high rate performance and long cycle life, and is easily industrialized.

[0007] In one embodiment, the titanium-based oxide includes Li4Ti5O 12 One or a mixture of TiO2, Bi2Ti2O7, Zn2Ti3O8, SrTiO3, LiNbTiO4, Nb2Ti2O7, Li2TiSiO5 and Ti4O7.

[0008] In one embodiment, the thickness of the PTFE porous membrane is 10 micrometers to 30 micrometers, and the pore size of the PTFE porous membrane is 0.8 micrometers to 1.5 micrometers.

[0009] In one embodiment, the composite membrane further includes a ceramic coating located between the base membrane and the PTFE porous membrane.

[0010] In one embodiment, the thickness of the ceramic coating is 0.5 micrometers to 5 micrometers; The ceramic coating comprises several ceramic particles and a binder; The ceramic particles are selected from one or a mixture of more than one of oxide ceramics, nitride ceramics and carbide ceramics; The binder accounts for 1% to 15% of the mass fraction of the ceramic coating, and the binder includes one or a mixture of water-based binders and oil-based binders.

[0011] In one embodiment, the ceramic coating and the PTFE porous membrane are symmetrically disposed on both sides of the base membrane, wherein the ceramic coating is located between the base membrane and the PTFE porous membrane.

[0012] In one embodiment, the base film is a polyolefin film, polyester film, polyimide film, aramid film, or nonwoven fabric base film; and / or The composite separator also includes an adhesive layer, which is located between the base membrane and the positive electrode.

[0013] A method for preparing any of the above-mentioned lithium-ion batteries includes the following steps: A positive electrode, a negative electrode, and a composite separator are provided, wherein the negative electrode comprises a titanium-based oxide, and the composite separator comprises a base membrane and a PTFE porous membrane; and The composite separator is placed between the positive electrode and the negative electrode, so that the PTFE porous membrane is in direct contact with the negative electrode, and the lithium-ion battery is assembled.

[0014] The lithium-ion battery fabrication method of this invention is simple. The negative electrode comprises a titanium-based oxide, and the composite separator comprises a base film and a PTFE porous film, with the PTFE porous film in direct contact with the negative electrode. The titanium-based oxide does not react with PTFE, exhibiting good compatibility and significantly improving the battery's thermal stability and safety. The composite separator has a simple structure, excellent high-temperature resistance, effectively preventing high-temperature shrinkage and reducing the risk of thermal runaway. Simultaneously, this battery possesses high rate performance and long cycle life, and is easily industrialized.

[0015] In one embodiment, the composite membrane further includes a ceramic coating comprising a plurality of ceramic particles and a binder, and the method for preparing the composite membrane includes the following steps: A ceramic slurry is prepared by uniformly mixing several ceramic particles, a binder, and a solvent; and The ceramic slurry is coated onto at least one surface of the base film, followed by drying to form a ceramic coating; and A composite membrane is obtained by combining a base membrane with a ceramic coating with a PTFE porous membrane.

[0016] In one embodiment, the drying temperature is 50°C to 120°C; The compounding method is roller pressing, with a pressing temperature of 60℃~130℃ and a pressing pressure of 0.5MPa~5MPa.

[0017] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a lithium-ion battery according to the first embodiment of the present invention; Figure 2 This is a schematic diagram of a lithium-ion battery according to the second embodiment of the present invention; Figure 3 This is a schematic diagram of a lithium-ion battery according to the third embodiment of the present invention; Figure 4 This is a schematic diagram of a lithium-ion battery according to the fourth embodiment of the present invention; Figure 5 This is a flowchart of the preparation method of the lithium-ion battery according to one embodiment of the present invention. Detailed Implementation

[0019] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] In this invention, PE is the abbreviation for Polyethylen, PP is the abbreviation for Polypropylene, and PTFE is the abbreviation for Polytetrafluoroethylene.

[0022] In this invention, the nonwoven fabric base film can be a nonwoven fabric base film of any material, including but not limited to a film made of polyester fiber, acrylic fiber, spandex, or any one or more of these fibers.

[0023] Please see Figure 1 The lithium-ion battery 100 of the first embodiment of the present invention includes a positive electrode 110, a negative electrode 120 and a composite separator 130.

[0024] The positive electrode 110 includes a positive electrode current collector and a positive electrode active material layer coated thereon. The active material layer includes a positive electrode active substance and may also include a conductive agent and / or a binder as needed. Any known positive electrode active substance may be used in this application without departing from the inventive concept of this application.

[0025] The negative electrode 120 comprises a titanium-based oxide. Specifically, the negative electrode includes a negative electrode current collector and a negative electrode active material layer coated thereon, the active material layer comprising a negative electrode active material, which includes a titanium-based oxide. Of course, conductive agents and / or binders may also be added to the negative electrode 120 as needed.

[0026] The composite membrane 130 is located between the positive electrode 110 and the negative electrode 120. The composite membrane 130 includes a base membrane 131 and a PTFE porous membrane 132, and the PTFE porous membrane 132 is located between the base membrane 131 and the negative electrode 120.

[0027] It should be noted that the PTFE porous membrane 132 is an independent pre-fabricated membrane, rather than a functional layer formed in situ on the surface of the base membrane through coating or other methods. It is a microporous film formed from raw materials through processes such as extrusion and stretching, and its microscopic structure has a three-dimensional network porous morphology composed of interconnected fibrous structures.

[0028] The lithium-ion battery 100 of this embodiment uses a titanium-based oxide as the negative electrode 120, and a composite separator 130 comprising a base film 131 and a PTFE porous film 132, with the PTFE porous film 132 in direct contact with the negative electrode 120. The titanium-based oxide does not react with PTFE, exhibiting good compatibility and significantly improving the battery's thermal stability and safety. The composite separator 130 has a simple structure, excellent high-temperature resistance, effectively preventing high-temperature shrinkage and reducing the risk of thermal runaway. Simultaneously, this battery possesses high rate performance and long cycle life, and is easy to industrialize.

[0029] Based on the aforementioned embodiments, titanium-based oxides include Li4Ti5O. 12 It is a mixture of one or more of the following: TiO2, Bi2Ti2O7, Zn2Ti3O8, SrTiO3, LiNbTiO4, Nb2Ti2O7, Li2TiSiO5, and Ti4O7. These types of titanium-based oxides do not react with PTFE, exhibiting good compatibility and significantly improving the thermal stability and safety of the battery.

[0030] Based on the aforementioned embodiments, the active material of the negative electrode may also include alloy-based negative electrode materials or phosphorus-based negative electrode materials. The alloy-based negative electrode materials include tin (Sn)-based materials (such as elemental tin, tin alloys, tin oxide, and their composite materials) or antimony (Sb)-based materials (such as elemental antimony, antimony alloys, and their composite materials). The phosphorus-based negative electrode materials include elemental phosphorus (such as black phosphorus, red phosphorus), phosphorus-carbon composite materials (such as P / C), or complexes of phosphorus with other elements. It is understood that when the above-mentioned alloy-based or phosphorus-based high-capacity negative electrode materials are used, their combination with the specific structure of the "base membrane-PTFE porous membrane" composite separator (with the PTFE porous membrane facing the negative electrode) described in this invention can effectively suppress the impact and damage to the separator caused by electrode volume changes or side reactions during cycling, thereby improving the battery's interface stability and long-cycle performance. Therefore, any lithium-ion battery formed by using the composite separator structure of this invention and combined with the above-mentioned negative electrode active materials falls within the protection scope of this invention.

[0031] Based on the aforementioned embodiments, the thickness of the PTFE porous membrane 132 is 10 micrometers to 30 micrometers, and the pore size of the PTFE porous membrane 132 is 0.8 micrometers to 1.5 micrometers. By controlling the thickness and pore size of the PTFE porous membrane 132 within this range, it can be ensured that it has sufficiently high porosity and excellent electrolyte retention, thereby providing unobstructed migration channels for lithium ions and reducing the internal resistance of the battery. At the same time, the PTFE porous membrane 132 of this thickness can also maintain good flexibility and mechanical strength, and does not affect the overall processability of the separator after being composited with the ceramic coating 130. Furthermore, the thickness of the PTFE porous membrane 132 may be, but is not limited to, 10 micrometers, 15 micrometers, 20 micrometers, 25 micrometers, or 30 micrometers, as well as specific values ​​between the above values; the pore size of the PTFE porous membrane 132 may be, but is not limited to, 0.8 micrometers, 0.9 micrometers, 1.0 micrometers, 1.1 micrometers, 1.2 micrometers, 1.3 micrometers, 1.4 micrometers, or 1.5 micrometers, as well as specific values ​​between the above values.

[0032] Based on the aforementioned embodiments, the base membrane 131 is a polyolefin (such as PE, PP, PE / PP, PE / PP / PE, PP / PE / PP) membrane, polyester (PET) membrane, polyimide (PI) membrane, aramid membrane, or nonwoven fabric base membrane. Furthermore, the base membrane 131 can also be a composite membrane of the above materials. Selecting these commercially available and technologically mature membranes as the base membrane not only ensures that the separator possesses good mechanical strength, electrochemical stability, and inherent thermal shutdown function, but also makes the composite separator easily integrated into the existing battery manufacturing industry chain, possessing excellent mass production feasibility and cost-effectiveness.

[0033] It is understood that this invention does not impose any restrictions on the material of the base film. Any film that can be used as a lithium battery separator substrate, including known base films modified by various physical or chemical methods, falls within the protection scope of this invention.

[0034] Based on the aforementioned embodiments, the areal density of the nonwoven fabric base film is 3 g / m³. 2 ~20g / m 2 The porosity of the nonwoven fabric-based membrane is 50%~95%, the thickness is 10 micrometers~50 micrometers, and the air permeability is 20cm. 3 / cm 2 / s~233cm 3 / cm 2The tensile strength of the nonwoven fabric base membrane ranges from 10 N / 50 mm to 132 N / 50 mm. By controlling the areal density, porosity, thickness, air permeability, and tensile strength of the nonwoven fabric base membrane within the aforementioned ranges, the base membrane is ensured to have a moderate weight and thickness while maintaining high porosity and good air permeability. This is beneficial for electrolyte wetting and rapid lithium-ion transport, while sufficient tensile strength ensures the mechanical integrity of the separator during battery assembly and use, preventing tearing and deformation.

[0035] Furthermore, the areal density of the nonwoven fabric-based film can be, but is not limited to, 3 g / m³. 2 4g / m 2 5g / m 2 6g / m 2 7g / m 2 8g / m 2 9g / m 2 10g / m 2 11g / m 2 12g / m 2 13g / m 2 14g / m 2 15g / m 2 16g / m 2 17g / m 2 18g / m 2 19g / m 2 Or 20g / m 2 The porosity of the nonwoven fabric base membrane can be, but is not limited to, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%. The thickness of the nonwoven fabric base membrane can be, but is not limited to, 10 micrometers, 12 micrometers, 20 micrometers, 25 micrometers, 30 micrometers, 35 micrometers, 40 micrometers, 45 micrometers, or 50 micrometers. The air permeability of the nonwoven fabric base membrane can be, but is not limited to, 20 cm². 3 / cm 2 / s、30cm 3 / cm 2 / s、40cm 3 / cm 2 / s、50cm 3 / cm 2 / s、80cm 3 / cm 2 / s、130cm 3 / cm 2 / s、132cm 3 / cm 2 / s、150cm 3 / cm 2 / s、180cm 3 / cm 2 / s or 233cm 3 / cm 2 / s, the tensile strength of the nonwoven base film can be, but is not limited to, 10N / 50mm, 30N / 50mm, 50N / 50mm, 80N / 50mm, 130N / 50mm or 132N / 50mm, and specific values ​​between the above values.

[0036] Based on the aforementioned embodiments, the areal density of the nonwoven fabric base film is 5 g / m³. 2 ~14g / m 2 The porosity of the nonwoven fabric-based membrane is 70%~90%, the thickness is 12 micrometers~25 micrometers, and the air permeability is 40cm. 3 / cm 2 / s~130cm 3 / cm 2 The tensile strength of the nonwoven fabric-based membrane is 30N / 50mm to 80N / 50mm. These optimized parameter ranges further balance the relationship between lightweight, high porosity, thinness, and mechanical strength of the composite separator, enabling it to maintain excellent ionic conductivity while possessing better thermal stability and durability, making it particularly suitable for lithium-ion batteries with high energy density and high power requirements.

[0037] Please see Figure 2 The lithium-ion battery 200 of the second embodiment of the present invention includes a positive electrode 210, a negative electrode 220 and a composite separator 230.

[0038] The negative electrode 220 comprises a titanium-based oxide. Specifically, the negative electrode includes a negative electrode current collector and a negative electrode active material layer coated thereon, the active material layer comprising a negative electrode active material, which includes a titanium-based oxide. Of course, conductive agents and / or binders may also be added to the negative electrode 220 as needed.

[0039] The composite membrane 230 is located between the positive electrode 210 and the negative electrode 220. The composite membrane 230 includes a base membrane 231 and a PTFE porous membrane 232, and the PTFE porous membrane 232 is located between the base membrane 231 and the negative electrode 220.

[0040] Furthermore, in this embodiment, the composite membrane 230 also includes a ceramic coating 233, which is located between the base membrane 231 and the PTFE porous membrane 232.

[0041] This basic three-layer structure achieves synergistic effects through functional layering: the base membrane 231 provides excellent mechanical support and closed-cell characteristics; the ceramic coating 233 endows the separator with excellent thermal stability and rigidity, preventing high-temperature shrinkage; and the surface PTFE porous membrane 232 provides extremely high porosity and excellent electrolyte wettability, ensuring low ion transport resistance. The synergistic effect of the ceramic coating 233 and the PTFE porous membrane 232 significantly improves the high-temperature resistance and thermal dimensional stability of the composite separator 230, effectively preventing high-temperature shrinkage and enhancing battery safety. The combination of the base membrane 231, ceramic coating 233, and PTFE porous membrane 232 significantly improves the overall performance of the composite separator 230, giving it high safety, excellent electrochemical performance, and mechanical integrity.

[0042] In this embodiment of the lithium-ion battery 200, the titanium-based oxide in the negative electrode 220 does not react with the PTFE in the PTFE porous membrane 232, exhibiting good compatibility and significantly improving the thermal stability and safety of the battery.

[0043] Based on the aforementioned embodiments, the thickness of the ceramic coating 233 is 0.5 micrometers to 5 micrometers. Controlling the thickness of the ceramic coating 233 within this optimized range ensures sufficient thermal stability and mechanical reinforcement of the composite diaphragm 230 while avoiding problems such as decreased overall porosity, reduced ionic conductivity, or reduced flexibility due to excessive coating thickness, thus achieving an optimal balance between the diaphragm's thermal safety and electrochemical performance. Furthermore, the thickness of the ceramic coating 233 can be, but is not limited to, 0.5 micrometers, 1 micrometer, 2 micrometers, 3 micrometers, 4 micrometers, or 5 micrometers, or specific values ​​between these values.

[0044] Based on the aforementioned embodiments, the ceramic coating 233 includes a plurality of ceramic particles and a binder. The binder in the ceramic coating 233 bonds the plurality of ceramic particles together, ensuring a strong bond between the ceramic coating 233 and the base membrane 231 and the PTFE porous membrane 232, while avoiding damage to the membrane structure from high temperatures. Furthermore, the process is simple and suitable for continuous production.

[0045] The ceramic particles are selected from one or a mixture of oxide ceramics, nitride ceramics, and carbide ceramics. These ceramic particles can maintain their physical and chemical stability within the operating temperature range of lithium-ion batteries and the temperature range where the separator undergoes thermal shrinkage, thereby improving the heat resistance, mechanical strength, and safety of the composite separator.

[0046] It is understood that a wide variety of ceramic particles can be used in this invention. For example, oxide ceramics include silicon dioxide, boehmite, alumina, zirconium oxide, titanium oxide, magnesium oxide, zinc oxide, aluminum hydroxide, etc.; nitride ceramics include boron nitride, silicon nitride, etc.; carbides include silicon carbide, titanium carbide, zirconium carbide, tungsten carbide, boron carbide, etc. These materials have excellent electrochemical stability and heat resistance, and are preferred solutions in this invention. In addition, ceramic-based solid electrolytes (such as lithium lanthanum zirconium oxide LLZO, lithium lanthanum titanium oxide LLTO, etc.) can also be used as a special type of ceramic particle because they possess lithium-ion conductivity. In summary, all ceramic particle materials that can meet the basic requirements of electrochemical stability and heat resistance and can be applied to lithium-ion battery systems fall within the protection scope of this invention.

[0047] Introducing these highly heat-resistant ceramic particles can greatly enhance the thermal insulation and thermal dimensional stability of the coating, making the composite separator less prone to melting and shrinkage at high temperatures, thereby effectively preventing battery thermal runaway. If ceramic-based solid electrolyte particles are added, the ionic conductivity can be enhanced to a certain extent and the penetration of lithium dendrites can be suppressed, further improving the safety and rate performance of the battery.

[0048] The binder accounts for 1% to 15% of the mass of the ceramic coating 233, and the binder includes one or more of water-based binders and oil-based binders.

[0049] By controlling the binder content within this range, a strong bond can be formed between ceramic particles and between the ceramic coating 233 and the base film 231, preventing coating detachment. At the same time, excessive binder can be avoided from clogging the pores between ceramic particles. This maintains the stability of the coating structure while maximizing the preservation of its porous structure, ensuring good electrolyte permeability and ionic conductivity. Furthermore, the mass fraction of the binder in the ceramic coating 233 can be, but is not limited to, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%, as well as specific values ​​between these values.

[0050] This application does not impose any special restrictions on the specific type of binder. Any binder component suitable for battery systems can be used in this invention without departing from the inventive concept of this application.

[0051] For example, the water-based adhesive includes any one or a mixture of several of the following: cellulose acetate (CA), methylcellulose (MC), sodium carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), styrene-butadiene rubber (SBR), nitrile rubber (NBR), styrene-ethylene-butene-styrene copolymer (SEBS), styrene-butadiene-styrene copolymer (SBS), polyvinyl alcohol (PVA), polyacrylamide (PAM), polyacrylic acid (PAA), sodium polyacrylate (NaPAA), lithium polyacrylate (LiPAA), polyacrylic acid copolymers (such as polyacrylic acid-polyacrylonitrile copolymer, polyacrylate-polyacrylonitrile copolymer), polyurethane (PU), polyethylene oxide (PEO), polyimide, ethylene-vinyl acetate copolymer, epoxy resin, sodium alginate, and lithium alginate.

[0052] For example, the oily adhesive includes any one or a mixture of several of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride copolymers (such as PVDF-HFP copolymer, PVDF-TFE copolymer).

[0053] The above examples are merely illustrative and are not intended to limit the scope of protection of this invention.

[0054] Preferably, the binder is an oil-based binder, which has excellent bonding properties. It not only ensures a strong bond between ceramic particles and between the ceramic coating 233 and the base film 231, but also forms a good bond between the ceramic coating 233 and the PTFE porous membrane 232, giving the battery higher overall hardness and interface smoothness. Specifically, when PVDF-HFP is used as the binder, during hot-pressing assembly, the PVDF-HFP layer is activated by heat, releasing a small amount of PVDF components, which promotes a tighter bond between the ceramic coating 233 and the base film 231, and between the ceramic coating 233 and the PTFE porous membrane 232 at the interface. After subsequent cold pressing, the binder is re-cured, further eliminating interlayer voids and enhancing the structural integrity and interface stability of the composite separator.

[0055] Please see Figure 3 The lithium-ion battery 300 of the third embodiment of the present invention includes a positive electrode 310, a negative electrode 320 and a composite separator 330.

[0056] The negative electrode 320 comprises a titanium-based oxide. Specifically, the negative electrode includes a negative electrode current collector and a negative electrode active material layer coated thereon, the active material layer comprising a negative electrode active material, which includes a titanium-based oxide. Of course, conductive agents and / or binders may also be added to the negative electrode 320 as needed.

[0057] The composite membrane 330 is located between the positive electrode 310 and the negative electrode 320. The composite membrane 330 includes a base membrane 331 and a PTFE porous membrane 332, and the PTFE porous membrane 332 is located between the base membrane 331 and the negative electrode 320.

[0058] In this embodiment of the lithium-ion battery 300, the titanium-based oxide in the negative electrode 320 does not react with the PTFE in the PTFE porous membrane 332, exhibiting good compatibility and significantly improving the battery's thermal stability and safety.

[0059] Furthermore, in this embodiment, the composite separator 330 also includes an adhesive layer 333, which is located between the base film 331 and the positive electrode 310. Adding an adhesive layer 333 between the base film 331 and the positive electrode 310 can greatly enhance the adhesion between the composite separator 330 and the positive electrode 310, reduce interface slippage and gaps between the electrode and the separator during charging and discharging, thereby reducing interface impedance, improving current distribution uniformity, and effectively suppressing polarization during cycling, which helps to improve the rate performance and cycle life of the battery.

[0060] Further, the adhesive layer 333 comprises one or a mixture of water-based and oil-based adhesives. Preferably, the adhesive in the adhesive layer 333 is an oil-based adhesive, which includes any one or a mixture of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride copolymers (such as PVDF-HFP copolymer, PVDF-TFE copolymer).

[0061] It should be noted that the lithium-ion battery of the present invention is not limited to the above embodiments. A ceramic coating and a PTFE porous membrane may also be symmetrically disposed on both sides of the base film, wherein the ceramic coating is located between the base film and the PTFE porous membrane.

[0062] Please see Figure 4 The lithium-ion battery 400 of the fourth embodiment of the present invention includes a positive electrode 410, a negative electrode 420 and a composite separator 430.

[0063] The negative electrode 420 comprises a titanium-based oxide. Specifically, the negative electrode includes a negative electrode current collector and a negative electrode active material layer coated thereon, the active material layer comprising a negative electrode active material, which includes a titanium-based oxide. Of course, conductive agents and / or binders may also be added to the negative electrode 420 as needed.

[0064] The composite membrane 430 is located between the positive electrode 410 and the negative electrode 420. The composite membrane 430 includes a base membrane 431, a PTFE porous membrane 432, and a ceramic coating 433 located between the base membrane 431 and the PTFE porous membrane 432.

[0065] In this embodiment of the lithium-ion battery 400, the titanium-based oxide in the negative electrode 420 does not react with the PTFE in the PTFE porous membrane 432, exhibiting good compatibility and significantly improving the battery's thermal stability and safety.

[0066] Furthermore, in this embodiment, a ceramic coating 433 and a PTFE porous membrane 432 are respectively disposed between the base membrane 431 and the negative electrode 420 and the positive electrode 410. Specifically, the two ceramic coatings 433 are located on both sides of the base membrane 431, and the ceramic coatings 433 include a plurality of ceramic particles and a binder. The PTFE porous membrane 432 is located on the side of the ceramic coating 433 away from the base membrane 431, and is in direct contact with the positive electrode 410 and the negative electrode 420 respectively.

[0067] This embodiment employs a double-sided symmetrical structure design, ensuring that both sides of the composite separator 430 have identical thermal stability and interfacial characteristics, completely eliminating the stress asymmetry or uneven thermal shrinkage problems that may result from single-sided coating. This structure is particularly suitable for applications with extremely high safety requirements, and eliminates the need to distinguish between the front and back sides during battery assembly, improving production efficiency and reliability.

[0068] The lithium-ion battery of this invention comprises a titanium-based oxide as the negative electrode and a composite separator comprising a base film and a PTFE porous film, with the PTFE porous film in direct contact with the negative electrode. The titanium-based oxide does not react with PTFE, exhibiting good compatibility and significantly improving the battery's thermal stability and safety. The composite separator has a simple structure, excellent high-temperature resistance, effectively preventing high-temperature shrinkage and reducing the risk of thermal runaway. Furthermore, this battery possesses high rate performance and long cycle life, and is easily industrialized.

[0069] Please see Figure 5 The method for preparing the lithium-ion battery according to one embodiment of the present invention includes the following steps: S10 provides a positive electrode, a negative electrode, and a composite separator, wherein the negative electrode includes a titanium-based oxide, and the composite separator includes a base membrane and a PTFE porous membrane.

[0070] S20. The composite separator is placed between the positive and negative electrodes, so that the PTFE porous membrane is in direct contact with the negative electrode, and the lithium-ion battery is assembled.

[0071] In one embodiment, the composite membrane further includes a ceramic coating located between the base membrane and the PTFE porous membrane, the ceramic coating comprising a plurality of ceramic particles and a binder.

[0072] The method for preparing the composite diaphragm in this embodiment is as follows: S11. Mix a number of ceramic particles, binder and solvent evenly to obtain ceramic slurry; S12. Apply ceramic slurry to at least one surface of the base film, and then dry it to form a ceramic coating. S13. The base membrane with ceramic coating is combined with a PTFE porous membrane to obtain a composite membrane.

[0073] In one embodiment, in step S11, the mass fraction of the ceramic particles in the ceramic slurry is 20% to 70%. Further, the mass fraction of the ceramic particles in the ceramic slurry can be, but is not limited to, 20%, 30%, 40%, 50%, 60%, or 70%, or specific values ​​between these values.

[0074] In one embodiment, the drying temperature in step S12 is 50°C to 120°C. Further, the drying temperature may be, but is not limited to, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, or 120°C, or specific values ​​between these values.

[0075] In one embodiment, the composite process in step S13 is roller pressing, with a pressing temperature of 60°C to 130°C and a pressing pressure of 0.5 MPa to 5 MPa. Under these temperatures and pressures, the binder (such as PVDF) in the ceramic coating can be effectively activated, thereby forming a strong and stable bonding interface between the base film and the PTFE porous film. Further, the pressing temperature can be, but is not limited to, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, or 130°C, and specific values ​​between these values. Further, the pressing pressure can be, but is not limited to, 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, or 5 MPa, and specific values ​​between these values.

[0076] The lithium-ion battery fabrication method of this invention is simple. The negative electrode comprises a titanium-based oxide, and the composite separator comprises a base film and a PTFE porous film, with the PTFE porous film in direct contact with the negative electrode. The titanium-based oxide does not react with PTFE, exhibiting good compatibility and significantly improving the battery's thermal stability and safety. The composite separator has a simple structure, excellent high-temperature resistance, effectively preventing high-temperature shrinkage and reducing the risk of thermal runaway. Simultaneously, this battery possesses high rate performance and long cycle life, and is easily industrialized.

[0077] It is understood that the description of the electrode structure in this application is a typical example, but the scope of protection is not limited thereto and also covers other structural forms known in the art. The active material includes known single materials, coating materials, doped materials, nanocomposites, and derivatives obtained through other optimization methods. Meanwhile, the conductive agent, binder, current collector, and other components include conventional and functionalized forms. Any known combination of materials and structural design that does not depart from the core concept of this invention is applicable to this application and will not be elaborated upon here.

[0078] Referring to the above embodiments, in order to make the technical solution of the present invention more specific, clear and easy to understand, examples of the technical solution of the present invention are given below. However, it should be noted that the content to be protected by the present invention is not limited to the following embodiments.

[0079] Example 1 Preparation of the negative electrode: Li4Ti5O 12 Super-P and CMC+SBR are added to deionized water at a mass ratio of 95:2:3. After mixing, the mixture is coated onto copper foil using a coating machine and dried to obtain the negative electrode.

[0080] The composite membrane is made by hot rolling a PE base membrane and a 15-micron thick PTFE porous membrane with a pore size of 1.0 micron, with the PTFE porous membrane facing the negative electrode.

[0081] Preparation of the positive electrode: NCM, super-p and PVDF are added to the solvent NMP in a mass ratio of 96:2:2. After mixing, the mixture is coated onto aluminum foil using a coating machine and dried to obtain the positive electrode.

[0082] The positive electrode, negative electrode, and composite separator prepared in the above steps are stacked and then injected with electrolyte (1 mol / LiPF6 + EC + DMC electrolyte) to form a lithium-ion battery.

[0083] Example 2 The lithium-ion battery was prepared according to the method of Example 1, except that the 15-micrometer-thick PTFE porous membrane with a pore size of 1.0 micrometer was replaced with a 10-micrometer-thick PTFE porous membrane with a pore size of 0.6 micrometer.

[0084] Example 3 The lithium-ion battery was prepared according to the method of Example 1, except that the 15-micrometer-thick PTFE porous membrane with a pore size of 1.0 micrometer was replaced with a 25-micrometer-thick PTFE porous membrane with a pore size of 1.6 micrometer.

[0085] Example 4 Lithium-ion batteries were prepared according to the method in Example 1, except that Li4Ti5O was used. 12 Replace with an equal amount of TiO2.

[0086] Example 5 The preparation of the negative and positive electrodes is the same as in Example 1.

[0087] Preparation of composite membrane: Based on Example 1, alumina ceramic particles and PVDF-HFP binder were mixed at a mass ratio of 92:8, and NMP solvent was added to prepare ceramic slurry. The ceramic slurry was coated on PE base membrane and dried at 60°C to form a 2-micron thick ceramic coating. Subsequently, the side containing the ceramic coating was rolled and composited with a PTFE porous membrane at 90°C and 2MPa pressure.

[0088] The positive electrode, negative electrode, and composite separator prepared in the above steps are stacked and then injected with electrolyte (1 mol / LiPF6 + EC + DMC electrolyte) to form a lithium-ion battery.

[0089] Example 6 The preparation of the negative and positive electrodes is the same as in Example 1.

[0090] Preparation of composite membrane: Boehmite ceramic particles and CMC / SBR binder were mixed at a mass ratio of 90:10, and NMP solvent was added to prepare a ceramic slurry. The ceramic slurry was coated on both sides of the PP base membrane. After drying at 65°C, a ceramic coating with a thickness of 1.5 micrometers was formed on both sides of the base membrane. At 85°C and 2.5MPa pressure, a PTFE porous membrane with a thickness of 12 micrometers and a pore size of 0.8 micrometers was then laminated on both sides of the base membrane.

[0091] Comparative Example 1 Lithium-ion batteries were prepared according to the method in Example 1, except that Li4Ti5O was used. 12 Replace it with an equal amount of graphite anode active material.

[0092] Battery cycle test: Temperature: 25℃±2℃ ① Charge to the termination voltage at 1C or the specified current, cut off current 0.05C, and let stand for 30 minutes; ② Discharge at 1C until the final discharge voltage (2.75V), record the discharge capacity, and let stand for 30 minutes; Repeat steps ① to ②, and record the discharge capacity in the 1000th cycle; Capacity retention rate after 1000 cycles = discharge capacity of the 1000th cycle / initial discharge capacity * 100%.

[0093] The test results are as follows: Table 1 Test results of Examples 1-6 and Comparative Example 1 Table 1 shows that for the use of Li4Ti5O 12The examples using a negative electrode and a PE / PTFE composite separator, and Comparative Example 1 using a graphite negative electrode, were subjected to cycle tests. The results showed that the batteries prepared in the examples maintained a capacity retention of better than 83% after 1000 cycles at 1C rate, significantly higher than the 73.5% of Comparative Example 1. This is mainly due to the Li4Ti5O... 12 The operating potential (approximately 1.55 V vs. Li) + The titanium oxide anode (PDE) has a higher reduction potential than PTFE, avoiding the side reaction of membrane reduction. In contrast, the graphite anode in Comparative Example 1 has a lower operating potential (approximately 0.1 V) than the PTFE reduction potential, leading to continuous interfacial side reactions and lithium loss. Therefore, in this application, the titanium oxide anode and the PTFE porous membrane achieve a synergistic effect through potential compatibility, resulting in a significant improvement in battery cycle life.

[0094] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0095] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery includes: positive electrode; Anode, said anode comprising titanium-based oxide; and A composite separator is located between the positive electrode and the negative electrode. The composite separator includes a base membrane and a PTFE porous membrane, and the PTFE porous membrane is located between the base membrane and the negative electrode.

2. The lithium-ion battery according to claim 1, characterized in that, The titanium-based oxide includes Li4Ti5O 12 One or a mixture of TiO2, Bi2Ti2O7, Zn2Ti3O8, SrTiO3, LiNbTiO4, Nb2Ti2O7, Li2TiSiO5 and Ti4O7.

3. The lithium-ion battery according to claim 1, characterized in that, The thickness of the PTFE porous membrane is 10 micrometers to 30 micrometers, and the pore size of the PTFE porous membrane is 0.8 micrometers to 1.5 micrometers.

4. The lithium-ion battery according to claim 1, characterized in that, The composite membrane also includes a ceramic coating, which is located between the base membrane and the PTFE porous membrane.

5. The lithium-ion battery according to claim 4, characterized in that, The thickness of the ceramic coating is 0.5 micrometers to 5 micrometers; The ceramic coating comprises several ceramic particles and a binder; The ceramic particles are selected from one or a mixture of more than one of oxide ceramics, nitride ceramics and carbide ceramics; The binder accounts for 1% to 15% of the mass fraction of the ceramic coating, and the binder includes one or a mixture of water-based binders and oil-based binders.

6. The lithium-ion battery according to claim 4, characterized in that, The ceramic coating and the PTFE porous membrane are symmetrically disposed on both sides of the base membrane, wherein the ceramic coating is located between the base membrane and the PTFE porous membrane.

7. The lithium-ion battery according to claim 1, characterized in that, The base film is a polyolefin film, polyester film, polyimide film, aramid film, or non-woven fabric base film; and / or The composite separator also includes an adhesive layer, which is located between the base membrane and the positive electrode.

8. A method for preparing a lithium-ion battery according to any one of claims 1 to 7, characterized in that, Includes the following steps: A positive electrode, a negative electrode, and a composite separator are provided, wherein the negative electrode comprises a titanium-based oxide, and the composite separator comprises a base membrane and a PTFE porous membrane; and The composite separator is placed between the positive electrode and the negative electrode, so that the PTFE porous membrane is in direct contact with the negative electrode, and the lithium-ion battery is assembled.

9. The method for preparing a lithium-ion battery according to claim 8, characterized in that, The composite membrane further includes a ceramic coating, which comprises a plurality of ceramic particles and a binder. The preparation method of the composite membrane includes the following steps: A ceramic slurry is prepared by uniformly mixing several ceramic particles, a binder, and a solvent; and The ceramic slurry is coated onto at least one surface of the base film, and then dried to form a ceramic coating. as well as A composite membrane is obtained by combining a base membrane with a ceramic coating with a PTFE porous membrane.

10. The method for preparing a lithium-ion battery according to claim 9, characterized in that, The drying temperature is 50℃~120℃; The compounding method is roller pressing, with a pressing temperature of 60℃~130℃ and a pressing pressure of 0.5MPa~5MPa.

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