A lithium metal anode, its preparation method, and a lithium metal battery

Abstract

This invention discloses a method for preparing a lithium metal anode, comprising: preparing a polymer substrate, wherein the polymer substrate is an in-situ composite film of thermoplastic polyester and flame retardant; subjecting the polymer substrate to atmospheric pressure oxygen-blocking plasma treatment; preparing a first metal layer on the surface of the polymer substrate; subjecting the first metal layer to atmospheric pressure nitrogen-blocking plasma treatment; and preparing a lithium metal layer on the surface of the first metal layer. This invention also discloses a lithium metal anode obtained by the above-described method. Furthermore, this invention discloses a lithium metal battery comprising the above-described lithium metal anode, which, depending on the cathode material, can be a primary lithium metal battery or a secondary lithium metal battery. This invention can effectively improve the energy density of lithium metal batteries while possessing excellent safety performance.

Description

Technical Field

[0001] This invention relates to a lithium metal anode, its preparation method, and a lithium metal battery, belonging to the field of lithium metal battery technology. Background Technology

[0002] After dominating the consumer electronics market, lithium-ion batteries are rapidly expanding their applications in electric vehicles and energy storage. However, the energy density requirements of various emerging fields cannot be met by traditional lithium batteries based on lithium-ion intercalation chemistry. In this context, lithium metal batteries, renowned for their high energy density, are once again attracting attention as a next-generation advanced energy storage technology. This is because lithium metal anodes have low energy density (0.54 g / cm³). 3 ) and a very low standard reduction potential (-3.045V SHE).

[0003] However, practical research has revealed numerous difficulties hindering the widespread application of primary or secondary batteries using pure lithium strips as the negative electrode. High-energy-density lithium metal primary or secondary batteries typically have an N / P ratio of less than 2, or even lower. Therefore, the pure lithium strip negative electrode used is generally very thin, usually less than 150 μm, and its soft texture makes it unsuitable for battery fabrication. Due to the extremely high chemical reactivity of lithium metal, it continuously consumes the electrolyte, leading to the continuous pulverization of lithium metal, forming dead lithium, and increasing battery impedance. Furthermore, the hostless nature of pure lithium strips means that primary lithium metal batteries are prone to disconnection of the conductive path at the end of discharge or in the later stages of cycling in secondary lithium metal batteries, resulting in a sharp deterioration in battery performance. Simultaneously, it easily forms lithium dendrites, causing safety issues. To address these problems, lithium metal is often combined with copper foil current collectors and used as the negative electrode to avoid the failure of the negative electrode's current-collecting conductivity due to lithium metal consumption. However, copper foil is typically 6 μm to 12 μm thick and relatively heavy, which is detrimental to improving the energy density of lithium metal batteries. Other researchers have proposed using polymer substrates as current collectors to construct lithium metal anodes, thereby reducing the weight of the current collector. However, they have not considered the significant difference in thermal expansion coefficients between lithium metal and polymer materials, which leads to low contact stability between the polymer substrate and lithium metal. Furthermore, they have not considered the problems that polymer thermal decomposition can exacerbate battery combustion during battery thermal failure, resulting in reduced lithium metal anode performance and potential safety hazards. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned defects and provide a lithium metal anode, a preparation method, and a lithium metal battery, solving the problem of low contact stability between existing polymer current collectors and lithium metal, and the need for further improvement in safety, thereby improving the cycle stability and safety of lithium metal batteries.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A method for preparing a lithium metal anode, comprising:

[0007] A polymer material substrate is prepared, wherein the polymer material substrate is an in-situ composite film of thermoplastic polyester and flame retardant;

[0008] Polymer substrates were subjected to atmospheric pressure oxygen barrier plasma treatment.

[0009] A first metal layer was prepared on the surface of a polymer substrate after treatment with oxygen-blocking plasma under atmospheric pressure.

[0010] The first metal layer was subjected to atmospheric pressure nitrogen barrier plasma treatment;

[0011] A second metal layer is prepared on the surface of the first metal layer after treatment with nitrogen medium barrier plasma under atmospheric pressure; the second metal layer is a lithium metal layer.

[0012] Furthermore, the preparation method of the polymer material substrate is as follows:

[0013] A prepolymer solution of thermoplastic polyester was obtained using a solution method;

[0014] A flame retardant is added to the prepolymer solution to obtain a mixed solution;

[0015] The mixed solution is prepared into a composite film using a blade coating method or a casting method;

[0016] The composite film is dried at 60℃~80℃ and then cured at 100℃~300℃ to obtain a polymer material substrate.

[0017] Furthermore, the conditions for oxygen dielectric barrier plasma treatment under atmospheric pressure are a discharge power of 10kW to 50kW and a discharge time of 10s to 120s; the conditions for nitrogen dielectric barrier plasma treatment under atmospheric pressure are a discharge power of 30kW to 80kW and a discharge time of 30s to 150s.

[0018] Furthermore, the method for preparing the first metal layer on the surface of the polymer substrate is to first perform vacuum plating, followed by electrolytic plating;

[0019] The vacuum plating is vacuum evaporation, magnetron sputtering, or ion plating.

[0020] In the first metal layer, the thickness of vacuum deposition is 3nm to 30nm;

[0021] The method for preparing a second metal layer on the surface of a first metal layer after treatment with nitrogen medium barrier plasma under atmospheric pressure is electrochemical plating, vacuum electroplating, or lamination.

[0022] Furthermore, the thermoplastic polyester includes one or more of polyimide, polyurethane, polyethylene terephthalate, polybutylene terephthalate, poly(1,4-cyclohexanediol) terephthalate, polyethylene naphthalate, polybutylene naphthalate, or polyarylate.

[0023] Flame retardants include one or more of the following: organohalogen flame retardants or organophosphorus flame retardants;

[0024] Organic halogen flame retardants include one or more of the following: decabromobiphenyl acid, tetrabromobisphenol A, decabromodiphenyl ether, brominated polystyrene, decabromodiphenyl ethane, or chlorinated paraffin.

[0025] Organophosphorus flame retardants are one or more of phosphate esters or phosphites.

[0026] Furthermore, in the polymer matrix, the mass ratio of flame retardant to thermoplastic polyester is 1:10 to 2:5.

[0027] Furthermore, the first metal layer is one or more of copper, aluminum, silver, titanium, tin, or metal alloys.

[0028] The metal alloy is an alloy formed by adding other metal elements to one or more of the following metals: copper, aluminum, silver or tin. The other metal elements are one or more of the following: gold, tungsten, platinum, iron, cobalt, nickel, magnesium, zinc or chromium.

[0029] The mass of other metallic elements shall not exceed 5% of the mass of the main metallic element.

[0030] Furthermore, the thickness of the polymer substrate is 5μm to 15μm;

[0031] The thickness of the first metal layer is 50 nm to 900 nm;

[0032] The thickness of the second metal layer is 50 μm to 150 μm.

[0033] A lithium metal anode, obtained by the above-mentioned method for preparing lithium metal anode, comprises a polymer material substrate, a first metal layer, and a second metal layer;

[0034] The polymer substrate is an in-situ composite film of thermoplastic polyester and flame retardant;

[0035] The second metal layer is a lithium metal layer;

[0036] The first metal layer is attached to one or both sides of the polymer substrate, and the second metal layer is attached to the surface of the first metal layer.

[0037] Furthermore, the tensile strength of the polymer substrate is 25 N / mm². 2~50N / mm 2 Self-extinguishing time is 0, heat resistance temperature range is 230℃~350℃, and thermal expansion coefficient is 5×10. -5 / ℃~2×10 -6 / ℃, longitudinal and transverse thermal expansion and contraction at 100℃ for 1h <1.0%.

[0038] A lithium metal battery includes a positive electrode, a separator, and the aforementioned lithium metal negative electrode;

[0039] The lithium metal battery includes a primary lithium metal battery and a secondary lithium metal battery.

[0040] The positive electrode of a lithium metal primary battery is one of carbon fluoride, chromium oxide, or manganese dioxide;

[0041] The positive electrode of the lithium metal secondary battery is one or more of the following: layered lithium nickel cobalt manganese oxide with a nickel mass percentage greater than 80%, layered lithium nickel cobalt aluminum oxide with a nickel mass percentage greater than 80%, layered lithium cobalt oxide, spinel-type lithium nickel manganese oxide, and olivine-type lithium iron manganese phosphate.

[0042] Compared with the prior art, the present invention has at least one of the following advantages:

[0043] (1) This invention creatively proposes a lithium metal battery based on a polymer material substrate, which is beneficial to reduce the weight of the lithium metal anode and improve the energy density of the high specific energy lithium metal battery.

[0044] (2) The polymer material substrate of the present invention is formed by in-situ curing of flame retardant and thermoplastic polyester, and the flame retardant additive is dissolved in the prepolymer solution, which solves the problem of low dispersibility and easy leakage of flame retardant additive in polyester, effectively reduces the self-extinguishing time of polymer material, improves the flame retardant properties of polymer material, and is conducive to reducing short circuit current and short circuit heat generation, and improving the safety performance of battery.

[0045] (3) The polymer material base layer of the present invention has strong tensile strength. When the battery is subjected to abuse such as cutting or nail penetration, the polymer material base layer can effectively wrap the burrs of the lithium-based metal layer, increase the short-circuit resistance, and even cut off the conductive path in the nail penetration area, thereby improving the safety performance of the battery;

[0046] (4) The first metal layer designed in this invention serves as a transition layer. In addition to improving the conductivity of the current collector, it also improves the contact stability between the polymer substrate and the lithium metal layer. It also provides metal nucleation sites for lithium metal during repeated deposition, which helps to improve the uniformity of lithium deposition, reduce the probability of lithium dendrite formation, improve the cycle stability of lithium metal batteries, and improve the safety of the batteries.

[0047] (5) The present invention uses oxygen medium barrier plasma under atmospheric pressure to treat polymer material substrate, causing the covalent bonds on the surface of polymer material substrate to break, and introducing polar oxygen-containing functional groups such as hydroxyl, carbonyl, and carboxyl groups at the new break sites, thereby forming an active and dense cross-linked layer surface, which effectively improves the interfacial compatibility between the substrate and the first metal layer, improves the bonding strength between the two, and thus improves the cycle stability of lithium metal battery.

[0048] (6) The nitrogen medium barrier plasma treatment of the surface of the first metal layer proposed in this invention under atmospheric pressure to form nitrogen-doped three-dimensional porous copper oxide nanosheets is beneficial to the formation of metal bonds and covalent bonds between the first metal and lithium metal, thereby improving the adhesion between the first metal layer and the second lithium metal layer, and thus improving the cycle stability of the lithium metal battery. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the cross-sectional structure of the lithium metal anode of the present invention;

[0050] Figure 2 This is a schematic diagram of a preferred embodiment of the method for preparing a lithium metal anode according to the present invention.

[0051] Figure 3 This is the XPS spectrum of the polymer material substrate after atmospheric pressure oxygen barrier plasma treatment in Example 1 of the present invention;

[0052] Figure 4 This is an electron microscope image of the copper plating layer in Embodiment 1 of the present invention after treatment with nitrogen barrier plasma under atmospheric pressure;

[0053] Figure 5 This is the XPS spectrum of the polymer substrate of Comparative Example 2 of the present invention, which was not treated with oxygen-blocking plasma under atmospheric pressure. Detailed Implementation

[0054] The features and advantages of the present invention will become clearer and more apparent from the following detailed description.

[0055] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0056] This invention provides a lightweight lithium metal anode that improves the cycle stability and safety of lithium metal batteries, as well as its preparation method and primary and secondary lithium metal batteries using the lithium metal anode.

[0057] like Figure 1 In a first aspect, the present invention provides a lithium metal anode, comprising: a polymer substrate 1, a first metal layer 2, and a second lithium metal layer 3. The polymer substrate is an in-situ composite film of thermoplastic polyester and organic flame retardant additives.

[0058] In a lithium metal anode, the first metal layer and the second lithium metal layer can be attached to one or both sides of a polymer substrate.

[0059] In a preferred embodiment, the thickness of the polymer substrate is 2 μm to 30 μm. If the polymer substrate is too thin, its mechanical strength is insufficient, making the lithium metal anode prone to breakage during processing and battery cycling, failing to provide support and protection for the lithium metal layer, thus leading to deterioration of battery performance. If the polymer substrate is too thick, the lithium metal anode will have excessively high volume and mass, which is detrimental to improving the volumetric energy density and gravimetric energy density of the lithium metal battery. Preferably, the thickness of the polymer substrate is 5 μm to 15 μm.

[0060] The tensile strength of the polymer substrate is 10 N / mm². 2 ~100N / mm 2 If the tensile strength of the polymer substrate is too low, it is prone to excessive elongation or deformation during use and is easily broken, leading to metal layer breakage or peeling. If the tensile strength of the polymer substrate is too high, the solderability of the material deteriorates, making it difficult to effectively weld the tabs of the lithium metal anode. Preferably, the tensile strength of the polymer substrate is 25 N / mm². 2 ~50N / mm 2 .

[0061] The self-extinguishing time of the polymer substrate is 0. This means that the polymer substrate is non-flammable. In the event of thermal runaway or fire, it can prevent the large-scale spread of combustion. At the same time, the polymer substrate can produce non-flammable gases such as hydrogen halides and carbon dioxide, which play a role in flame retardancy and improve the safety of lithium metal batteries.

[0062] The long-term heat resistance temperature range of the polymer substrate is 200℃ to 500℃. If the long-term heat resistance temperature of the polymer substrate is too low, it may deform during use, failing to provide support and protection for the metal layer, thus affecting the cycle stability of the battery. If the long-term heat resistance temperature of the polymer substrate is too high, it will easily lead to poor processability, which is not conducive to the formation of thin films. Preferably, the long-term heat resistance temperature range of the polymer substrate is 230℃ to 350℃.

[0063] The coefficient of thermal expansion of the polymer substrate is 1×10⁻⁶. -4 / ℃~1×10 -7 / ℃. Since batteries generate heat during use or operate in high-temperature environments, if the coefficient of thermal expansion of the polymer substrate is too low, thermal expansion may occur during use, generating thermal stress. This reduces the adhesion between the substrate and the metal layer, easily leading to cracks or peeling of the metal layer, damaging the conductive path, and failing to provide support and protection for the metal layer, thus affecting the battery's cycle stability. If the coefficient of thermal expansion of the polymer substrate is too high, or if the long-term heat resistance temperature of the polymer substrate is too high, it can easily lead to poor processability, making it unsuitable for thin film fabrication. Preferably, the coefficient of thermal expansion of the polymer substrate is 5 × 10⁻⁶. -5 / ℃~2×10 -6 / ℃.

[0064] The longitudinal and transverse thermal expansion and contraction of the polymer substrate after being kept at 100℃ for 1 hour is <1.0%. The polymer substrate should have appropriate thermal expansion and contraction. If the thermal expansion and contraction of the polymer substrate is large, the large thermal stress between it and the metal layer during use will make the metal layer prone to cracking or peeling, resulting in the interruption of the conductive path and thus affecting the cycle stability of the battery.

[0065] In a preferred embodiment, the thermoplastic polyester includes one or more of polyimide PI, polyurethane PU, polyethylene terephthalate, polybutylene terephthalate, 1,4-cyclohexanediol terephthalate, polyethylene naphthalate, polybutylene naphthalate or polyarylate.

[0066] Organic flame retardant additives include organic halogenated flame retardants, such as one or more of decabromobiphenyl acid, tetrabromobisphenol A, decabromodiphenyl ether, brominated polystyrene, decabromodiphenyl ethane, or chlorinated paraffin, or organophosphorus flame retardants, such as one or more of phosphate esters and phosphites.

[0067] In a preferred embodiment, the mass ratio of flame retardant additive to thermoplastic polyester in the polymer substrate is 1:10 to 2:5. Within a suitable range, the ratio of polyester to flame retardant additive ensures that the polymer substrate has a self-extinguishing time of 0 while maintaining appropriate mechanical strength. If the ratio is too low, the insufficient content of flame retardant additive results in an excessively long self-extinguishing time, potentially leading to safety issues with the lithium metal battery. If the ratio is too high, the excessive content of flame retardant additive leads to insufficient mechanical strength in the polymer substrate, making it prone to breakage, cracking or peeling of the metal layer, and damage to the conductive path. This prevents the substrate from providing support and protection for the metal layer, thus affecting the battery's cycle stability.

[0068] In a preferred embodiment, the first metal layer comprises one or more of copper, aluminum, silver, titanium, and tin. Small amounts of other elemental metals may also be added to form a metal alloy with one or more of the aforementioned metal matrix to improve the electrical conductivity and surface tension of the metal layer. The added elemental metals include one or more of gold, tungsten, platinum, iron, cobalt, nickel, magnesium, zinc, and chromium, and the addition ratio is controlled to be within 5% of the mass fraction of the metal matrix. Preferably, the first metal layer is copper.

[0069] In a preferred embodiment, the thickness of the first metal layer is 50 nm to 900 nm. If the thickness of the first metal layer is too high, it will increase the mass of the lithium metal anode, which is not conducive to improving the energy density of the lithium metal battery. If the thickness of the first metal layer is too thin, a continuous conductive network layer cannot be formed on the surface of the polymer substrate, and it cannot play the role of current collection and conduction and improve the contact stability between the polymer substrate and lithium metal. When the lithium metal primary battery is at the end of discharge or the lithium metal secondary battery is in the cycle process, due to the consumption of a large amount of active lithium, the conductivity of the lithium metal anode will be significantly reduced, resulting in a rapid deterioration of the lithium metal battery performance.

[0070] The thickness of the second lithium metal layer is 30 μm to 180 μm, preferably 50 μm to 150 μm.

[0071] In a second aspect, the present invention provides a method for preparing a lithium metal anode, such as... Figure 2 In a preferred embodiment, the preparation method of the present invention includes:

[0072] (1) The polymer material substrate is prepared by solution prepolymerization to obtain a prepolymer solution. Then, the flame retardant additive is added to the prepolymer solution and dissolved. After mixing evenly, a composite film is made by scraping or casting. The composite film is dried at 60℃~80℃ and then cured at 100℃~300℃ to obtain the polymer material substrate.

[0073] (2) After the polymer substrate is treated with oxygen-blocking plasma under atmospheric pressure, a first metal layer is prepared on the surface of the polymer substrate by vacuum electroplating followed by electrolytic electroplating. The vacuum electroplating can be achieved through vacuum evaporation, magnetron sputtering, or ion plating. The electroplating utilizes the principle of electrolysis to form the metal coating. The thickness of the vacuum electroplated layer is 3 nm to 30 nm.

[0074] (3) After the first metal layer is treated with nitrogen barrier plasma under atmospheric pressure, a second metal layer is prepared on the surface of the first metal layer by electrochemical plating, vacuum electroplating, or lamination. Among them, the vacuum electroplating can be achieved by vacuum evaporation, magnetron sputtering, or ion plating.

[0075] In a preferred embodiment, the atmospheric pressure oxygen barrier plasma treatment conditions are a discharge power of 10kW to 50kW and a discharge time of 10s to 120s. If the discharge power or discharge time is too high during atmospheric pressure oxygen barrier plasma treatment, the discharge energy will be too high, easily damaging the surface matrix of the polymer material. If the discharge power or discharge time is too low, the discharge energy will be too low, making it impossible to form a dense cross-linked layer on the polymer material surface, thus failing to effectively improve the contact strength between the polymer material substrate and the first metal layer.

[0076] In a preferred embodiment, the nitrogen dielectric barrier plasma treatment conditions under atmospheric pressure are a discharge power of 30kW to 80kW and a discharge time of 30s to 150s. If the discharge power or discharge time is too high or too long during nitrogen dielectric barrier plasma treatment under atmospheric pressure, the discharge energy will be too high, easily damaging the surface energy of the first metal layer. If the discharge power or discharge time is too low or too short, the discharge energy will be too low, making it impossible to form continuous nitrogen-doped three-dimensional porous copper oxide nanosheets on the surface of the first metal layer, and thus failing to construct sufficient induced lithium deposition active sites, which is detrimental to the contact stability between the first and second metal layers.

[0077] In a third aspect, the present invention provides a lithium metal battery, comprising a positive electrode, a separator, and the aforementioned lithium metal negative electrode. The positive electrode can be one of carbon fluoride, chromium oxide, and manganese dioxide, used to manufacture a primary lithium metal battery. Alternatively, the positive electrode can be one or more of the following: layered lithium nickel cobalt manganese oxide with a nickel mass percentage greater than 80%; layered lithium nickel cobalt aluminum oxide with a nickel mass percentage greater than 80%; layered lithium cobalt oxide; spinel-type lithium nickel manganese oxide; and olivine-type lithium iron manganese phosphate, used to manufacture a secondary lithium metal battery.

[0078] This invention uses a polymer material as the substrate for the metal layer, which supports and protects the lithium-based metal layer. Because the density of the polymer substrate is significantly lower than that of conventional copper foil current collectors, it contributes less to increasing the weight of the lithium metal anode, thus improving the energy density of high-energy-density lithium metal batteries. Simultaneously, when an internal short circuit occurs, the flame-retardant properties of the polymer substrate increase the short-circuit resistance, reduce the short-circuit current and heat generation, and may even interrupt the conductive path of the internal short circuit, thereby improving battery safety. Alternatively, when the battery experiences abnormal conditions such as nail penetration, the high tensile strength of the polymer substrate allows it to effectively encapsulate the burrs in the lithium-based metal layer, increasing the short-circuit resistance and even interrupting the conductive path at the point of penetration. In this way, the damage caused by nail penetration is limited to the puncture site, forming a point-break, allowing the battery to operate normally for a certain period. The first metal layer, designed as a transition layer, not only improves the conductivity of the current collector but also enhances the contact stability between the polymer substrate and the lithium metal layer. It also provides metal nucleation sites for lithium metal during repeated deposition, which helps improve the uniformity of lithium deposition and reduce the probability of lithium dendrite formation.

[0079] In this invention, flame retardant additives and polymers are in-situ cured to form a composite film in a polymer substrate. The flame retardant additives are dissolved in a prepolymer solution, which solves the problem of low dispersibility and easy leakage of flame retardant additives in polyester. This effectively reduces the self-extinguishing time of the polymer material, improves the flame retardant properties of the polymer material, and helps to improve the safety of lithium metal anodes.

[0080] This invention proposes using atmospheric pressure oxygen dielectric barrier plasma to treat polymer substrates, thereby constructing a dense, active, cross-linked polymer substrate surface. This is because the plasma generated by atmospheric pressure oxygen dielectric barrier discharge can oxidize the polymer substrate surface, easily exciting oxygen to form active groups such as oxygen atoms, oxygen cations, and oxygen anions. This causes the covalent bonds on the polymer substrate surface to break, and polar oxygen-containing functional groups such as hydroxyl, carbonyl, and carboxyl groups are introduced at the new breakage sites, thus forming an active surface. This active surface forms chemical bonds with the metal surface, thereby improving interfacial compatibility and increasing the contact strength between the polymer substrate and the metal layer.

[0081] The present invention proposes a nitrogen-medium barrier plasma treatment of the surface of the first metal layer under atmospheric pressure, thereby constructing nitrogen-doped three-dimensional porous copper oxide nanosheets on the surface of the first metal layer. This increases the active sites for inducing lithium deposition, which is beneficial for the formation of metallic bonds and covalent bonds between the first metal and lithium metal, thereby improving the contact strength between the first metal layer and the second lithium metal layer.

[0082] Example 1

[0083] The method for preparing the lithium metal anode in this embodiment is as follows:

[0084] (1) A polyimide prepolymer solution was prepared by solution prepolymerization. Then, the decabromodiphenyl ethane flame retardant additive was added to the prepolymer solution and dissolved. The ratio of decabromodiphenyl ethane to polyimide was 3:20. After mixing evenly, a composite film was prepared by scraping. The composite film was dried at 60°C and then cured at 200°C to obtain a polymer material substrate.

[0085] (2) After the polymer substrate is treated with oxygen barrier plasma under atmospheric pressure, the discharge power is 20kW and the discharge time is 60s. Then, copper is deposited at 20nm by vacuum evaporation and 480nm by electrolytic copper plating.

[0086] (3) After the copper plating layer is treated with nitrogen barrier plasma under atmospheric pressure, the discharge power is 30kW and the discharge time is 80s. Electrochemical lithium plating with a thickness of 90μm is used to form a lithium metal anode.

[0087] The first metal layer and the second metal layer are attached to both sides of the polymer material substrate;

[0088] The thickness of the aforementioned polymer substrate is 6 μm, and its tensile strength is 35 N / mm. 2 Self-extinguishing time is 0, heat resistance temperature range is 312℃, and coefficient of thermal expansion is 1×10⁻⁶. -5 The longitudinal and transverse thermal expansion and contraction of the material after being kept at 100℃ for 1 hour is 0.8%.

[0089] The positive electrode material is lithium nickel cobalt manganese oxide (NCM811), and the separator is a PE separator, assembled into a 1Ah lithium metal secondary battery. The battery was subjected to energy density, 0.1C charge / 0.2C discharge cycle and nail penetration safety tests, and the test results are shown in Table 1. Figure 3 The XPS spectrum of the polymer substrate after atmospheric pressure oxygen barrier plasma treatment is shown. In the figure, C2 represents CO or C-OH chemical bonds, C3 represents C=O or OCO chemical bonds, and C4 represents OC=O or COOH chemical bonds. As can be seen from the figure, a large number of oxygen-containing groups are present on the surface after plasma treatment. Figure 4 This image shows an electron microscope (EMS) image of the copper plating layer after treatment with nitrogen barrier plasma at atmospheric pressure. The image reveals a rough surface layer with flaky structures.

[0090] Example 2

[0091] The method for preparing the lithium metal anode in this embodiment is as follows:

[0092] (1) A polyurethane prepolymer solution was prepared by solution prepolymerization. Then, a phosphate flame retardant additive was added to the prepolymer solution and dissolved. The ratio of phosphate to polyurethane was 1:10. After mixing evenly, a composite film was prepared by scraping. The composite film was dried at 60°C and then cured at 200°C to obtain a polymer material substrate.

[0093] (2) After the polymer substrate is treated with oxygen barrier plasma under atmospheric pressure, the discharge power is 20kW and the discharge time is 60s. Then, copper is deposited at 3nm by vacuum evaporation and 70nm by electrolytic copper plating. (3) After the copper plating layer is treated with nitrogen barrier plasma under atmospheric pressure, the discharge power is 30kW and the discharge time is 80s. Lithium is electrochemically plated to a thickness of 50μm to form a lithium metal anode.

[0094] The first metal layer and the second metal layer are attached to both sides of the polymer material substrate;

[0095] The thickness of the aforementioned polymer substrate is 8 μm, and its tensile strength is 39 N / mm. 2 Self-extinguishing time is 0, heat resistance temperature range is 264℃, and coefficient of thermal expansion is 7×10. -6 The longitudinal and lateral thermal expansion and contraction of the battery after holding at 100℃ for 1 hour is 0.9%. Fluorocarbon material is used for the positive electrode, and PE membrane is used for the separator. The battery is assembled into a 1Ah lithium metal primary battery. Energy density and nail penetration safety tests were performed on the battery, and the results are shown in Table 1.

[0096] Example 3

[0097] The method for preparing the lithium metal anode in this embodiment is as follows:

[0098] (1) A polyethylene terephthalate prepolymer solution was prepared by solution prepolymerization. Then, brominated polystyrene flame retardant additive was added to the prepolymer solution and dissolved. The ratio of polyethylene terephthalate to brominated polystyrene was 2:5. After mixing evenly, a composite film was prepared by scraping. The composite film was dried at 60°C and then cured at 200°C to obtain a polymer material substrate.

[0099] (2) After the polymer substrate was treated with oxygen barrier plasma under atmospheric pressure, the discharge power was 30kW and the discharge time was 80s. Then, copper was deposited at 30nm by vacuum evaporation and 870nm by electrolytic plating.

[0100] (3) After the copper plating layer is treated with nitrogen barrier plasma under atmospheric pressure, the discharge power is 50kW and the discharge time is 120s. Electrochemical lithium plating with a thickness of 150μm is used to form a lithium metal anode.

[0101] The first metal layer and the second metal layer are attached to both sides of the polymer material substrate;

[0102] The thickness of the aforementioned polymer substrate is 10 μm, and its tensile strength is 42 N / mm. 2 Self-extinguishing time is 0, heat resistance temperature range is 294℃, and coefficient of thermal expansion is 9×10. -6 The longitudinal and transverse thermal expansion and contraction of the material after being kept at 100℃ for 1 hour is 0.85%.

[0103] The positive electrode was made of olivine-type lithium iron manganese phosphate, and the separator was made of PE membrane, assembled into a 1Ah lithium metal secondary battery. The battery was subjected to energy density, 0.1C charge / 0.2C discharge cycle and nail penetration safety tests, and the test results are shown in Table 1.

[0104] Comparative Example 1

[0105] The difference between this comparative example and Example 1 is that conventional copper foil is used instead of the polymer material substrate and the first metal layer. The thickness of the copper foil in this comparative example is equal to the total thickness of the polymer material substrate and the first metal layer in Example 1.

[0106] As shown in Table 1, the energy density of the lithium metal battery in this comparative example is lower than that of the lithium metal battery obtained in Example 1. Under conditions of abuse involving nail penetration, the battery in this comparative example caught fire and burned.

[0107] Comparative Example 2

[0108] The difference between this comparative example and Example 1 is that the polymer substrate is not treated with atmospheric pressure oxygen medium blocking plasma.

[0109] The test results show that without treatment with oxygen-blocking plasma under atmospheric pressure, oxygen-containing functional groups cannot be introduced into the surface of the polymer substrate. The bonding strength between the polymer substrate and the first metal layer is poor, resulting in a decrease in the cycle performance of the resulting lithium metal secondary battery. Figure 5 The images show the XPS spectra of polymer substrates that have not undergone atmospheric pressure oxygen barrier plasma treatment. As can be seen from the figures, the untreated surface does not contain a large number of oxygen-containing groups.

[0110] Comparative Example 3

[0111] The difference between this comparative example and Example 1 is that the surface of the first metal layer is not treated with atmospheric pressure nitrogen medium blocking plasma.

[0112] The test results show that the surface of the first metal layer without plasma strengthening treatment cannot form metallic bonds and covalent bonds with lithium metal, resulting in a decrease in the cycle performance of the lithium metal battery.

[0113] Table 1 Performance Test Results

[0114]

[0115]

[0116] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0117] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for preparing a lithium metal anode, characterized in that, include: A polymer material substrate is prepared, wherein the polymer material substrate is an in-situ composite film of thermoplastic polyester and flame retardant; Polymer substrates were subjected to atmospheric pressure oxygen barrier plasma treatment. A first metal layer was prepared on the surface of a polymer substrate after treatment with oxygen-blocking plasma under atmospheric pressure. The first metal layer was subjected to atmospheric pressure nitrogen barrier plasma treatment; A second metal layer is prepared on the surface of a first metal layer after treatment with nitrogen-mediated barrier plasma under atmospheric pressure; the second metal layer is a lithium metal layer. The preparation method of the polymer substrate is as follows: A prepolymer solution of thermoplastic polyester was obtained using a solution method; A flame retardant is added to the prepolymer solution to obtain a mixed solution; The mixed solution is prepared into a composite film using a blade coating method or a casting method; The composite film is dried at 60℃~80℃ and then cured at 100℃~300℃ to obtain a polymer material substrate; The atmospheric pressure oxygen dielectric barrier plasma treatment conditions are a discharge power of 10 kW to 50 kW and a discharge time of 10 s to 120 s; the atmospheric pressure nitrogen dielectric barrier plasma treatment conditions are a discharge power of 30 kW to 80 kW and a discharge time of 30 s to 150 s. The method for preparing the first metal layer on the surface of a polymer substrate is to first vacuum plate and then electrolytic plate. The vacuum plating is vacuum evaporation, magnetron sputtering, or ion plating. In the first metal layer, the thickness of vacuum deposition is 3nm ~ 30nm; The method for preparing a second metal layer on the surface of the first metal layer after treatment with nitrogen medium barrier plasma under atmospheric pressure is electrochemical plating, vacuum electroplating or lamination. The tensile strength of the polymer substrate is 25 N / mm. 2 ~50 N / mm 2 Self-extinguishing time is 0, heat resistance temperature range is 230℃~350℃, and thermal expansion coefficient is 5×10. -5 / ℃~2×10 -6 / ℃, longitudinal and transverse thermal expansion and contraction at 100℃ for 1 hour are <1.0%; The first metal layer is one or more of the following: copper, aluminum, silver, titanium, tin, or metal alloys. The metal alloy is an alloy formed by adding other metal elements to one or more of the following metals: copper, aluminum, silver or tin. The other metal elements are one or more of the following: gold, tungsten, platinum, iron, cobalt, nickel, magnesium, zinc or chromium. The mass of other metallic elements shall not exceed 5% of the mass of the main metallic component; The thickness of the polymer substrate is 5μm~15μm; The thickness of the first metal layer is 50nm~900nm; The thickness of the second metal layer is 50μm~150μm.

2. The method for preparing a lithium metal anode according to claim 1, characterized in that, Thermoplastic polyesters include one or more of polyimide, polyurethane, polyethylene terephthalate, polybutylene terephthalate, 1,4-cyclohexanediol terephthalate, polyethylene naphthalate, polybutylene naphthalate or polyarylate. Flame retardants include one or more of the following: organohalogen flame retardants or organophosphorus flame retardants; Organic halogen flame retardants include one or more of the following: decabromobiphenyl acid, tetrabromobisphenol A, decabromodiphenyl ether, brominated polystyrene, decabromodiphenyl ethane, or chlorinated paraffin. Organophosphorus flame retardants are one or more of phosphate esters or phosphites.

3. The method for preparing a lithium metal anode according to claim 1, characterized in that, In the polymer matrix, the mass ratio of flame retardant to thermoplastic polyester is 1:10 to 2:

5.

4. A lithium metal anode, characterized in that, The lithium metal anode is prepared by any one of claims 1-3, comprising a polymer substrate, a first metal layer, and a second metal layer. The polymer substrate is an in-situ composite film of thermoplastic polyester and flame retardant; The second metal layer is a lithium metal layer; The first metal layer is attached to one or both sides of the polymer substrate, and the second metal layer is attached to the surface of the first metal layer.

5. A lithium metal battery, characterized in that, Includes a positive electrode, a separator, and a lithium metal negative electrode as described in claim 4; The lithium metal battery includes a primary lithium metal battery and a secondary lithium metal battery. The positive electrode of a lithium metal primary battery is one of carbon fluoride, chromium oxide, or manganese dioxide; The positive electrode of the lithium metal secondary battery is one or more of the following: layered lithium nickel cobalt manganese oxide with a nickel mass percentage greater than 80%, layered lithium nickel cobalt aluminum oxide with a nickel mass percentage greater than 80%, layered lithium cobalt oxide, spinel-type lithium nickel manganese oxide, and olivine-type lithium iron manganese phosphate.

Images