A lithium battery metal shell with a composite flame-retardant functional layer and a lithium ion battery

Abstract

This invention relates to a lithium battery metal casing with a composite flame-retardant functional layer and a lithium-ion battery. The metal casing includes a casing body and an insulating layer disposed on the inner wall of the casing body. Several recesses are formed on the inner surface of the casing body, and these recesses are filled with a flame-retardant functional material. The flame-retardant functional material is at least one of a flame retardant and a phase change heat-absorbing material. The insulating layer is a low-melting-point polymer film. When thermal runaway occurs inside the battery, the high temperature causes the internal insulating film to rupture, and the flame-retardant functional material rapidly vaporizes and is released from the recesses. During vaporization, it absorbs a large amount of heat, lowers the temperature, and simultaneously forms an insulating layer that isolates oxygen in the air from contact with the combustible material, thereby preventing the continuation of combustion.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a lithium battery metal casing with a composite flame-retardant functional layer and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, long cycle life, high charge and discharge efficiency and low self-discharge rate, have been widely used in new energy vehicles, portable electronic devices, energy storage systems and other fields, and have become the mainstream electrochemical energy storage device.

[0003] Currently, lithium-ion battery casings are mostly made of metal, such as aluminum or steel. These metal casings offer advantages such as high mechanical strength, good sealing, and mature processing technology, effectively protecting core components like electrodes and electrolytes from external impacts and environmental influences. However, metal casings have significant shortcomings in flame retardancy and heat insulation. When a battery experiences thermal runaway, the metal casing is insufficient to prevent heat conduction and flame spread, easily leading to cascading failures of adjacent batteries within the battery module or pack. This can result in fires, explosions, and other safety accidents, severely limiting the application of lithium-ion batteries in high-safety-requirement scenarios.

[0004] To improve the safety performance of lithium-ion batteries, existing technologies mostly adopt external protection solutions for battery packs, which mainly include strengthening the structural strength of the module or battery pack shell, adding flame-retardant coatings or heat insulation layers to the outer surface of the shell, as shown in references 1 and 2.

[0005] Reference 1: Chinese patent document with publication number CN210576154U.

[0006] Reference 1 describes an explosion-proof and flame-retardant structure for a lithium battery, including a supporting shell, an explosion-proof protective ring, a cooling and flame-retardant layer, a lithium battery pack, and a cooling and protective core. The cooling and protective core is disposed through the center of the supporting shell. The lithium battery pack is arranged around the cooling and protective core inside the supporting shell. The cooling and flame-retardant layer is wrapped around the lithium battery pack, and the explosion-proof protective ring is arranged around the cooling and flame-retardant layer. This lithium battery structure can effectively cool the internal lithium battery pack, ensuring the normal operating temperature of the lithium battery. It can also provide automatic fire extinguishing and protection against damage caused by flying explosives, effectively improving the service life and performance of the lithium battery and protecting people's lives and property. This utility model belongs to the field of lithium battery protection technology, specifically referring to an explosion-proof and flame-retardant structure for lithium batteries that can cool down the lithium battery, cope with sudden accidents of spontaneous combustion and explosion of lithium batteries, and protect the health and property safety of users.

[0007] Reference 2: Chinese patent document with publication number CN223680152U.

[0008] Reference 2 describes a flame-retardant lithium battery, comprising an explosion-proof casing and a lithium battery core. The lithium battery core is housed within the explosion-proof casing, and a heat dissipation layer is wrapped around its exterior. A flame-retardant strip is wrapped around the surface of the heat dissipation layer away from the lithium battery core, and this strip is a multi-layered flame-retardant composite. A heat insulation layer is wrapped around the surface of the flame-retardant strip away from the heat dissipation layer, and this heat insulation layer is connected to the inner wall of the explosion-proof casing. A top cover is mounted on the top of the explosion-proof casing via an assembly mechanism. A positive electrode post is mounted on the top of the lithium battery core via a positive electrode sheet, with the upper end of the positive electrode post positioned on top of the top cover. Through this series of structural features, the battery exhibits excellent heat dissipation, flame retardancy, and heat insulation performance. The multi-layered flame-retardant strip not only possesses good flame retardancy but also strong adhesion, providing strong structural strength and tensile strength. The assembly between the explosion-proof casing and the top cover is leak-proof and sealed.

[0009] However, the aforementioned external protection solutions have many inherent drawbacks: strengthening the outer shell structure requires additional metal or composite material components, which significantly increases the overall weight and volume of the battery pack and reduces the energy density of the battery system; the external flame-retardant coating or heat insulation layer can hinder heat dissipation during normal battery operation, which can easily lead to heat accumulation inside the battery and affect the battery cycle life and charge / discharge performance. Summary of the Invention

[0010] The purpose of this invention is to solve the above-mentioned technical problems existing in the prior art and to provide a lithium battery metal casing and a lithium-ion battery with a composite flame-retardant functional layer.

[0011] To address the shortcomings of the aforementioned technical problems, the present invention adopts the following technical solution: A lithium battery metal casing with a composite flame-retardant functional layer, the metal casing comprising a casing body and an insulating layer disposed on the inner wall of the casing body; The inner surface of the shell body has several recesses, which are filled with flame-retardant material. The flame-retardant functional material is at least one of flame retardant and phase change heat-absorbing material; The insulating layer is a low-melting-point polymer film.

[0012] As a further optimization of the lithium battery metal casing with a composite flame-retardant functional layer of the present invention: the plurality of recesses are arranged periodically and regularly on the inner surface of the casing body, and the periodically and regularly arranged recesses form a grid-like groove array.

[0013] As a further optimization of the lithium battery metal casing with a composite flame-retardant functional layer of the present invention: the plurality of recesses are arranged periodically and regularly on the inner surface of the casing body, and the periodically and regularly arranged recesses form a honeycomb pit array.

[0014] As a further optimization of the lithium battery metal casing with a composite flame-retardant functional layer of the present invention: the plurality of recesses form a non-periodic, randomly interconnected porous foam-like structure on the inner surface of the casing body.

[0015] As a further optimization of the lithium battery metal casing with a composite flame-retardant functional layer of the present invention: the plurality of recesses include wavy or serpentine channels extending on the inner surface of the casing body.

[0016] As a further optimization of the lithium battery metal casing with a composite flame-retardant functional layer of the present invention: the flame retardant is at least one of organophosphorus flame retardants, nitrogen flame retardants, phosphorus-halogen flame retardants and perfluoroketone compounds.

[0017] As a further optimization of the lithium battery metal casing with a composite flame-retardant functional layer of the present invention: the phase change heat-absorbing material is an organic phase change material, an inorganic phase change material, or a composite phase change material.

[0018] As a further optimization of the lithium battery metal casing with a composite flame-retardant functional layer of the present invention: the material of the low melting point polymer film is polyethylene, polypropylene, polyester, polyamide, thermoplastic polyurethane or ethylene-vinyl acetate copolymer.

[0019] As a further optimization of the lithium battery metal casing with a composite flame-retardant functional layer of the present invention: the thickness of the low melting point polymer film is 3-20 μm, and the polymer film is configured such that the polymer film ruptures when the ambient temperature reaches or exceeds a temperature threshold.

[0020] A lithium battery with a composite flame-retardant functional layer includes the aforementioned metal casing and a cell and electrolyte disposed within the metal casing. The cell includes a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode.

[0021] This invention offers the following advantages: It focuses on the first line of defense at the battery level. When thermal runaway occurs inside the battery, the high temperature causes the internal insulating film to rupture, and the flame retardant rapidly vaporizes and is released from the grooved network. During vaporization, it absorbs a large amount of heat, lowering the temperature and simultaneously forming an insulating layer that prevents oxygen in the air from contacting the combustible material, thereby stopping the continued combustion. This invention modifies the battery casing itself, giving it high mechanical strength, flame retardancy, and heat insulation properties. Therefore, when thermal runaway occurs in a single battery, it can effectively delay or block the propagation of thermal runaway from one cell to adjacent cells, which is of great significance for improving the overall safety level of lithium-ion batteries and systems. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the metal casing of the present invention; Marked in the image: 1. Shell body; 2. Recessed part; 3. Flame-retardant functional material; 4. Insulation layer. Detailed Implementation

[0023] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0024] <Lithium battery metal casing with composite flame-retardant functional layer> A lithium battery metal casing with a composite flame-retardant functional layer can directly place heat-absorbing or flame-retardant materials in the position closest to the battery heat source, thereby achieving early and rapid suppression of thermal runaway and delaying heat transfer during thermal runaway, thus significantly improving the safety performance of the battery.

[0025] like Figure 1 As shown: The metal casing includes a casing body 1 and an insulating layer 4 disposed on the inner wall of the casing body 1.

[0026] The shell body 1 is made of conventional metal materials, such as aluminum or stainless steel, with a thickness of 0.1-1.0 mm, mainly providing mechanical strength and structural support for the shell.

[0027] The inner surface of the shell body 1 has several recesses 2, and the recesses 2 are filled with flame-retardant material 3.

[0028] The specific structural forms of the recessed portion 2 can be as follows: Structure Form 1: Several recesses are arranged periodically and regularly on the inner surface of the shell body, and the periodically and regularly arranged recesses form a grid-like groove array.

[0029] Structure Form Two: Several recesses are arranged periodically and regularly on the inner surface of the shell body, and the periodically and regularly arranged recesses form a honeycomb-shaped pit array.

[0030] Structure Type 3: Several recesses form a non-periodic, randomly interconnected porous foam-like structure on the inner surface of the shell body.

[0031] Structural Form Four: Several recesses include wavy or serpentine channels extending on the inner surface of the shell body.

[0032] The above structure can be formed in the following ways: such as chemical etching, laser etching, micro-stamping, etc., to directly process the groove network on the inner wall of the shell; or 3D printing technology can be used to directly manufacture the shell with complex internal channels.

[0033] For example, a high-precision CNC machine tool equipped with a micro-milling cutter or a V-shaped engraving cutter can be used. Based on a preset digital model, the tool path is controlled by a computer program to directly mill a grid-like groove with designed spacing, depth, and width on the first surface of a metal substrate.

[0034] For example, a layer of photoresist is uniformly coated on the surface of a metal substrate. Ultraviolet light exposure is performed using a photomask with a pre-designed grid pattern, causing a chemical reaction in certain areas of the photoresist. After treatment with a developer, the photoresist in specific areas is removed, exposing the underlying metal surface and forming a grid-like exposed pattern. The substrate is then immersed in a specific chemical etchant (such as FeCl3 solution for etching copper) or subjected to electrochemical etching. The exposed metal areas are selectively dissolved, forming grooves. The raised areas not protected by the photoresist are retained. After etching, a stripping solution is used to remove the remaining photoresist, resulting in a clean metal substrate with a grid-like groove array.

[0035] For example, creating a precision mold with a raised grid pattern. The mold and the metal sheet are formed in one step using a stamping press, or a grid-like array of grooves is imprinted on the surface of the metal sheet during continuous rolling.

[0036] Flame-retardant functional materials are at least one of flame retardants and phase change heat-absorbing materials. When a battery experiences abnormal temperature rise such as thermal runaway, this functional material can quickly suppress the heat source and delay the temperature rise through the synergistic effect of chemical flame retardancy and physical heat absorption.

[0037] The flame retardant is at least one of organophosphorus flame retardants, nitrogen-based flame retardants, phosphorus-halogen flame retardants, and perfluoroketone compounds.

[0038] Organophosphorus flame retardants include, for example, triphenyl phosphate (TPP), resorcinol bis(diphenyl phosphate) (RDP), bisphenol A bis(diphenyl phosphate) (BDP), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and their derivatives. These flame retardants primarily work by thermally decomposing to generate phosphoric acid compounds, promoting charring on the substrate surface and isolating heat and oxygen.

[0039] Nitrogen-based flame retardants: Examples include melamine (MEL), melamine cyanurate (MCA), and ammonium polyphosphate (APP, which also exhibits a phosphorus-nitrogen synergistic effect). When heated, they decompose to produce large amounts of non-flammable gases (such as ammonia and nitrogen), diluting oxygen and flammable gases and carrying away heat.

[0040] Phosphorus-halogen flame retardants: for example, tri(2-chloroethyl) phosphate (TCEP) and tri(2-chloropropyl) phosphate (TCPP). These flame retardants combine the dual mechanisms of gas-phase flame retardancy (halogen free radical capture) and condensed-phase flame retardancy (phosphoric acid char formation), resulting in high flame retardant efficiency.

[0041] Perfluoroketone compounds: for example, perfluoro-2-methyl-3-pentanone (commercial name FK-5-1-12), perfluoro-3-methyl-2-butanone, or perfluorohexanone (fire extinguishing agent). These novel clean gas-liquid two-phase flame retardants can efficiently capture free radicals in the combustion chain reaction after being heated and volatilized, and are insulating, non-toxic, and leave no residue.

[0042] Phase change endothermic materials can be organic, inorganic, or composite. These materials undergo a solid-liquid phase change near a set temperature threshold (e.g., 100℃-130℃), achieving isothermal heat absorption by absorbing a large amount of latent heat.

[0043] Organic phase change materials include paraffin-based, fatty acid-based, and alcohol-based phase change materials.

[0044] Paraffins include n-octadecane, n-eicosane, n-docosahexadecane, and mixtures thereof. They have high latent heat of phase transition, stable chemical properties, and do not exhibit supercooling.

[0045] Fatty acids include lauric acid, palmitic acid, and stearic acid. Alcohols include pentaerythritol and neopentyl glycol.

[0046] Inorganic phase change materials, such as sodium acetate trihydrate and calcium chloride hexahydrate, have high latent heat and relatively good thermal conductivity, but may suffer from supercooling and phase separation issues, requiring the addition of nucleating agents and thickeners.

[0047] The filling process for flame-retardant functional materials can at least adopt the following methods: Functional materials are mixed with liquid carriers (such as silicone oil, polymer solutions, water-based binders) and necessary additives (dispersants, leveling agents) to form a uniform paste or slurry with suitable viscosity and thixotropy.

[0048] The paste is applied in large quantities to the surface of the metal substrate.

[0049] Using a stiff squeegee or precision coating squeegee, scrape across the substrate surface at a set gap height and angle at a uniform speed. The pressure of the squeegee forces the high-viscosity paste to be "squeezed in" and completely fill the grooves.

[0050] For grooves with a large aspect ratio or pastes that are prone to air bubbles, the substrate can be moved into a vacuum chamber after coating and a vacuum can be drawn briefly to remove air bubbles from the grooves.

[0051] Depending on the slurry system, heat curing, UV curing, or room temperature drying are performed to set the paste.

[0052] The insulating layer is a low-melting-point polymer film. The low-melting-point polymer film is made of polyethylene, polypropylene, low-melting-point polyester, low-melting-point polyamide, thermoplastic polyurethane, or ethylene-vinyl acetate copolymer. The thickness of the low-melting-point polymer film is 3-20 μm, and the polymer film is configured to rupture when the ambient temperature reaches or exceeds a certain temperature threshold.

[0053] The normal function of the insulating layer is to provide reliable electrical insulation, while also acting as a physical barrier to protect the underlying functional composite material layer from oxidation, deliquescence, or mechanical wear. The insulating layer serves the following purposes: 1) It seals the material within the pores to prevent leakage, while also possessing resistance to electrolyte corrosion, long-term stability, and not reacting with the electrolyte; 2) It prevents the battery cell from contacting the casing, thus eliminating the need for a protective film. When a battery experiences thermal abuse due to a malfunction, causing an abnormal rise in local temperature and reaching a preset temperature threshold (Ts), the film mechanically ruptures within a very short time (e.g., 1-10 seconds), losing its continuity and insulation. After the insulating film ruptures, perfluoroketone compounds rapidly vaporize and are released from the grooved network. During vaporization, a large amount of heat is absorbed, lowering the temperature and forming an insulating layer that prevents oxygen in the air from contacting the combustible material, thereby stopping the continued combustion.

[0054] The insulating layer and the housing body can be bonded together by thermoforming or using high-performance adhesives to ensure strong interlayer bonding. For example, a low-melting-point polymer film can be cut and placed on a metal substrate filled with flame-retardant functional material. A small amount of adhesive with a temperature resistance below Ts can be used for local bonding. The film can then be thermoformed at a temperature below the film's Ts (e.g., 80% Ts) and under certain pressure to form a strong bond between the film and the metal raised platform and the surface of some functional materials.

[0055] On the one hand, this invention places flame-retardant functional materials within the battery casing. In the event of localized overheating or thermal runaway of the battery cell, heat can be rapidly transferred to the functional materials through the casing, triggering a rapid phase change that absorbs heat or releases flame retardants. The released flame retardants can penetrate the cell interface or gas-phase mass transfer pathways, suffocating the flame and blocking the chain reaction, thus intervening in the early stages of thermal runaway with extremely high efficiency. On the other hand, the flame-retardant functional materials are sealed within the casing structure, physically isolated from the electrolyte and electrode materials, fundamentally avoiding any interference with battery cycle life, impedance, and other performance characteristics.

[0056] Lithium batteries with composite flame-retardant functional layers A lithium battery with a composite flame-retardant functional layer includes a metal casing as described in Example 1, a cell and an electrolyte disposed within the metal casing, wherein the cell includes a positive electrode, a negative electrode and a separator between the positive electrode and the negative electrode.

[0057] This lithium-ion battery upgrades the traditional passively protected metal casing into an intelligent composite structure with heat sensing, active triggering, and multi-functional synergistic suppression capabilities.

[0058] The battery's metal casing is not a single solid; its substrate has a regularly arranged recessed structure, which is filled with a composite functional material of flame retardant and phase change heat-absorbing material. The surface of the substrate is covered with an extremely thin thermally responsive insulating polymer film.

[0059] When the battery is operating normally, the casing primarily serves as a structural support and heat dissipation unit. The insulating film on its surface ensures electrical insulation between the cell and the casing and seals and protects the flame-retardant materials. When the battery begins to experience thermal runaway due to internal short circuits, overcharging, or other faults: heat from the runaway area is transferred to the casing. When the local temperature reaches the preset rupture threshold of the insulating film (e.g., 100-150°C), the film rapidly melts and ruptures within seconds, exposing the underlying composite functional materials. The exposed phase change material immediately absorbs a large amount of latent heat, forming a temporary temperature plateau within the critical temperature range, drastically slowing the rate of temperature rise inside the battery and buying valuable time for the safety system to respond. Simultaneously, the released flame retardant rapidly diffuses to the heat source area, directly inhibiting the violent combustion reactions of the electrolyte and active materials through chemical actions such as capturing free radicals, diluting oxygen, or promoting char formation.

[0060] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A lithium battery metal can having a composite flame retardant functional layer, characterized in that, The metal casing includes a casing body and an insulating layer disposed on the inner wall of the casing body; The inner surface of the shell body has several recesses, which are filled with flame-retardant material. The flame-retardant functional material is at least one of flame retardant and phase change heat-absorbing material; The insulating layer is a low-melting-point polymer film.

2. The lithium battery metal shell with a composite flame-retardant functional layer according to claim 1, characterized in that, The recesses are arranged periodically and regularly on the inner surface of the housing body, forming a grid-like groove array.

3. The lithium battery metal casing with a composite flame-retardant functional layer as described in claim 1, characterized in that, The recesses are arranged periodically and regularly on the inner surface of the shell body, and the periodically and regularly arranged recesses form a honeycomb pit array.

4. The lithium battery metal casing with a composite flame-retardant functional layer as described in claim 1, characterized in that, The recesses on the inner surface of the shell body form a non-periodic, randomly interconnected porous foam-like structure.

5. The lithium battery metal casing with a composite flame-retardant functional layer as described in claim 1, characterized in that: The recesses include wavy or serpentine channels extending on the inner surface of the housing body.

6. The lithium battery metal casing with a composite flame-retardant functional layer as described in claim 1, characterized in that: The flame retardant is at least one of organophosphorus flame retardants, nitrogen-based flame retardants, phosphorus-halogen flame retardants, and perfluoroketone compounds.

7. The lithium battery metal casing with a composite flame-retardant functional layer as described in claim 1, characterized in that: The phase change heat-absorbing material is an organic phase change material, an inorganic phase change material, or a composite phase change material.

8. The lithium battery metal casing with a composite flame-retardant functional layer as described in claim 1, characterized in that: The low-melting-point polymer film is made of polyethylene, polypropylene, low-melting-point polyester, low-melting-point polyamide, thermoplastic polyurethane, or ethylene-vinyl acetate copolymer.

9. A lithium battery metal casing with a composite flame-retardant functional layer as described in claim 8, characterized in that: The low-melting-point polymer film has a thickness of 3-20 μm and is configured to rupture when the ambient temperature reaches or exceeds a temperature threshold.

10. A lithium battery with a composite flame-retardant functional layer, comprising a metal casing as described in any one of claims 1-9, a battery cell and an electrolyte disposed within the metal casing, wherein the battery cell comprises a positive electrode, a negative electrode and a separator between the positive electrode and the negative electrode, and the electrolyte is filled within the metal casing.

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