An ultrathin lithium metal composite negative electrode, a preparation method therefor and applications thereof

Abstract

The application relates to the technical field of lithium batteries, in particular to an ultrathin lithium metal composite negative electrode and a preparation method and application thereof, the method comprising the following steps: mixing a low-melting-point salt and lithium metal, heating to a molten state, and reacting to generate a molten-state composite lithium metal material; transferring the molten-state composite lithium metal material to a copper foil, uniformly coating the molten-state composite lithium metal material, cooling to room temperature, and obtaining the ultrathin lithium metal composite negative electrode. The spontaneous reaction of the dopant and the lithium metal is utilized to realize efficient synchronous chemical modification of the lithium metal negative electrode in a bulk phase / surface during a molten reaction process, the wettability of the lithium to the copper foil is improved to realize coating of the ultrathin lithium negative electrode, in-situ doping of the inorganic fast-ion-conductor component and the lithium-metal-alloy component is realized, and the rapid construction of the rich grain boundary interface is realized, lithium ion rapid conduction is realized, the uneven deposition and dendritic growth of the lithium are inhibited, and the coulomb efficiency is improved, and the electrochemical performance of the lithium metal negative electrode is improved.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to an ultrathin lithium metal composite anode, its preparation method and application. Background Technology

[0002] Since their introduction to the market, lithium-ion batteries have profoundly changed human society through their widespread application in portable electronics and electric vehicles. With the continuous emergence of new application scenarios and demands, the development of next-generation consumer electronics and electric vehicles urgently requires the development of new battery systems with higher energy densities. Lithium metal, due to its ultra-high theoretical specific capacity (3680 mAh g / g), is a suitable candidate for this technology. -1 Lithium metal is considered the holy grail of high-energy-density battery anode materials due to its low reduction potential (-3.04V, relative to the standard hydrogen electrode). However, lithium metal is highly reactive, has low strength, and high viscosity. Furthermore, a series of problems, such as low coulombic efficiency, short cycle life, and internal short circuits caused by lithium dendrite growth and high reactivity with electrolytes, severely restrict the practical application of lithium metal anodes.

[0003] Currently, to achieve optimal cycle performance, commercially available lithium foil typically has a thickness of 50 μm or more. While replenishing active lithium, it also acts as a current collector. During battery cycling, metallic lithium is continuously consumed, generating deactivated dead lithium until the electrode completely pulverizes at the end of its life, losing electrical connection and ceasing its current-collecting function. However, the areal capacity of the positive electrode is relatively low, typically only 2–4 mAh cm⁻¹. -2 No more than 6mAh cm -2 The required lithium metal anode only needs to be about 30 μm thick to achieve the necessary capacity matching. Furthermore, with lithium supplementation at the anode, the required thickness will be even smaller (<20 μm). Currently, commercially available lithium foil thicknesses range from 50 μm to 750 μm, which is severely excessive and significantly reduces the high specific capacity advantage of lithium metal anodes, leading to a significant decrease in battery energy density. However, ultrathin lithium metal strips (<20 μm) still face many challenges in terms of preparation and performance. Due to its limited mechanical strength, lithium metal strips with a thickness of less than 50 μm are prone to breakage, requiring copper foil current collectors for reinforcement. However, the natural lithium-phobicity of copper foil results in insufficient self-wetting of lithium metal with copper, making it difficult for molten lithium metal to spread uniformly on the copper foil surface. Therefore, the controllable preparation and rapid modification of ultrathin lithium metal anodes are of significant practical importance for improving lithium utilization efficiency in batteries and enhancing the energy density and cycle performance of the entire battery.

[0004] Existing methods for preparing lithium metal anodes involve pre-preparing an organic transition layer as a lithiophilic layer to improve the wettability of molten lithium to the substrate. However, the wettability of the organic coating to molten lithium remains insufficient, and side reactions between the organic coating and molten lithium are prone to occur at high temperatures. Under current technological advancements, achieving the fabrication of uniform, ultrathin lithium anodes remains challenging. Summary of the Invention

[0005] This application provides an ultrathin lithium metal composite anode, its preparation method, and its application, solving the technical problem in the prior art where the self-wetting property of lithium metal and copper is insufficient, and molten lithium is difficult to spread uniformly on the surface of copper foil.

[0006] To solve the above-mentioned technical problems, in a first aspect, embodiments of this application provide a method for preparing an ultrathin lithium metal composite anode, comprising the following steps: first, mixing a low-melting-point salt and lithium metal and heating to a molten state to react and generate a molten composite lithium metal material; then, transferring the molten composite lithium metal material onto a copper foil, uniformly coating the molten composite lithium metal material, and cooling to room temperature to obtain an ultrathin lithium metal composite anode.

[0007] In some exemplary embodiments, the anion of the low-melting-point salt includes inorganic nitrate, chlorine, nitrogen, phosphorus, fluorine, sulfur, or organic bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, hexafluorophosphate, difluorooxalateborate, tetrafluoroborate, difluorophosphate, bis(oxalateborate), and trifluoromethanesulfonate.

[0008] In some exemplary embodiments, the cation of the low-melting-point salt includes one or more of magnesium, zinc, aluminum, gallium, indium, silver, tin, bismuth, germanium, antimony, or organic 1-ethyl-3-methylimidazolium cation, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium cation, and N-methyl-N-propylpyrrolidine cation.

[0009] In some exemplary embodiments, when a low-melting-point salt is mixed with lithium metal and heated, a redox reaction occurs, generating an inorganic fast-ion conductor and a lithium-metal alloy within the lithium metal anode, thereby increasing the wettability of lithium on the copper foil.

[0010] In some exemplary embodiments, the inorganic fast ion conductor includes one or more of lithium fluoride, lithium nitride, lithium sulfide, or lithium phosphide.

[0011] In some exemplary embodiments, the thickness of the lithium metal layer in the ultrathin lithium metal composite anode is 1 μm to 20 μm.

[0012] In some exemplary embodiments, the thickness of the copper foil is 5 μm to 20 μm.

[0013] In some exemplary embodiments, the molten composite lithium metal material is uniformly coated and cooled to room temperature by natural cooling or blowing air.

[0014] Secondly, this application also provides an ultrathin lithium metal composite anode, which is prepared using the preparation method of the ultrathin lithium metal composite anode material described in the above embodiments.

[0015] Thirdly, this application also provides an application of the ultrathin lithium metal composite negative electrode described in the above embodiments in liquid lithium metal batteries and solid lithium metal batteries.

[0016] The technical solution provided in this application has at least the following advantages:

[0017] This application provides an ultrathin lithium metal composite anode and its preparation method and application. The preparation method includes the following steps: First, a low-melting-point salt and lithium metal are mixed and heated to a molten state to react and generate a molten composite lithium metal material; then, the molten composite lithium metal material is transferred onto a copper foil, uniformly coated, and cooled to room temperature to obtain an ultrathin lithium metal composite anode.

[0018] This application addresses the technical problem of insufficient self-wetting properties of lithium metal and copper in existing technologies, making it difficult for molten lithium to spread uniformly on the copper foil surface. On one hand, this application utilizes the rapid reaction between highly reducing and reactive lithium metal and low-melting-point salts, and the self-doping of the reaction products significantly improves the wettability of lithium metal on the copper foil surface. On the other hand, unlike organic / inorganic modifications only on the copper foil surface, this application involves doping modification of the lithium metal substrate itself, supporting the rapid and uniform coating of ultra-thin lithium metal layers with controllable thickness from 1μm to 20μm. Furthermore, this application cleverly utilizes the spontaneous reaction between dopants and lithium metal to achieve efficient and simultaneous chemical modification of the lithium metal anode phase / surface during the molten reaction process. This enables in-situ doping of inorganic fast ion conductors (lithium fluoride, lithium nitride, lithium sulfide, lithium phosphide, etc.) and lithium-metal alloy components, as well as the rapid construction of rich crystal interfaces. This method is efficient, simple, and uses inexpensive raw materials. Moreover, the preparation method of this application is universal and can be applied to low-melting-point salts that can react with lithium metal, such as organic salts and inorganic salts. Attached Figure Description

[0019] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments, and unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0020] Figure 1 A schematic flowchart illustrating a method for preparing an ultrathin lithium metal composite anode according to an embodiment of this application;

[0021] Figure 2 This is a SEM image of a lithium metal composite layer with a thickness of 1 μm uniformly coated on a copper substrate with a thickness of 10 μm, as described in Example 1 of this application.

[0022] Figure 3 This is a SEM image of a 2μm thick lithium metal composite layer uniformly coated on a 10μm thick copper substrate, as shown in Example 2 of this application.

[0023] Figure 4 This is a SEM image of a lithium metal composite layer with a thickness of 5 μm uniformly coated on a copper substrate with a thickness of 10 μm, as described in Example 3 of this application.

[0024] Figure 5 This is a SEM image of a lithium metal composite layer with a thickness of 8 μm uniformly coated on a copper substrate with a thickness of 10 μm, as shown in Example 4 of this application.

[0025] Figure 6 This is a SEM image of a lithium metal composite layer with a thickness of 10 μm uniformly coated on a copper substrate with a thickness of 10 μm, as shown in Example 5 of this application.

[0026] Figure 7 This is a SEM image of a 20 μm thick lithium metal composite layer uniformly coated on a 10 μm thick copper substrate, as described in Example 6 of this application.

[0027] Figure 8 This is a physical image of a lithium metal composite layer with a thickness of 10 μm uniformly coated on a copper substrate with a thickness of 10 μm, as shown in Embodiment 5 of this application.

[0028] Figure 9 A physical image of the unmodified lithium metal melt coating provided in the comparative example for this application;

[0029] Figure 10 This is a lithium iron phosphate-based full cell performance diagram of a 10μm lithium metal composite layer sample formed on a 10μm thick copper substrate in Example 5 of this application. Detailed Implementation

[0030] As can be seen from the background technology, the existing methods for preparing lithium metal anodes suffer from insufficient self-wetting properties between lithium metal and copper, making it difficult for molten lithium to spread uniformly on the copper foil surface.

[0031] One related technology proposes using at least one of the following lithiophilic elements, alloys, and metallic inorganic compounds as raw materials to first prepare an inorganic transition layer on a substrate via magnetron sputtering, thermal evaporation, or slurry coating; then, molten lithium metal is coated onto the surface of the inorganic transition layer to form an ultrathin lithium metal layer. However, this process involves multiple steps, is cumbersome, costly, and may suffer from adverse phenomena such as gas discharge, affecting the deposition quality of the modified layer. Furthermore, while evaporation and sputtering methods can directly and controllably grow certain specific lithiophilic component layers, the equipment requirements are too demanding, making large-scale processing difficult and limiting commercialization prospects.

[0032] Another related technique proposes pre-preparing an organic transition layer as a lithiophilic layer to improve the wettability of molten lithium to the substrate. However, the wettability of the organic coating to molten lithium is still insufficient, and side reactions between the organic coating and molten lithium are prone to occur at high temperatures. Under current technological advancements, achieving uniform, ultrathin lithium anode fabrication remains challenging.

[0033] Therefore, the problems to be solved by this application are: 1. In the prior art, the self-wetting property of lithium metal and copper is insufficient, and molten lithium is difficult to spread evenly on the copper foil surface; 2. The controllable coating and uniformity of lithium metal at various thickness gradients of 20μm and below; 3. Improving the uniformity and stability of lithium deposition in lithium metal anodes during cycling, and suppressing the formation and growth of lithium dendrites.

[0034] To address the aforementioned technical problems, this application provides an ultrathin lithium metal composite anode, its preparation method, and its application. The preparation method includes the following steps: First, a low-melting-point salt and lithium metal are mixed and heated to a molten state to react and generate a molten composite lithium metal material. Then, the molten composite lithium metal material is transferred onto a copper foil, uniformly coated, and cooled to room temperature to obtain the ultrathin lithium metal composite anode. This application utilizes the spontaneous reaction between dopants and lithium metal to achieve efficient and simultaneous chemical modification of the lithium metal anode bulk phase / surface during the molten reaction process. This enables in-situ doping of inorganic fast ion conductors (lithium fluoride, lithium nitride, lithium sulfide, lithium phosphide, etc.) and lithium-metal alloy components, as well as the rapid construction of rich crystal interfaces. It is efficient, simple, and uses inexpensive raw materials. Moreover, the preparation method of this application is universally applicable; low-melting-point salts that can react with lithium metal, such as organic and inorganic salts, are all feasible.

[0035] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0036] See Figure 1 This application provides a method for preparing an ultrathin lithium metal composite anode, comprising the following steps:

[0037] Step S1: Mix low-melting-point salt and lithium metal and heat to a molten state to react and generate a molten composite lithium metal material.

[0038] Step S2: Transfer the molten composite lithium metal material onto a copper foil, uniformly coat the molten composite lithium metal material, and cool it to room temperature to obtain an ultrathin lithium metal composite anode.

[0039] The method for preparing an ultrathin lithium metal composite anode provided in this application involves heating and melting lithium metal with a low-melting-point salt, allowing the two to react rapidly in a molten state. The resulting molten composite lithium metal material is then transferred onto a copper foil. The self-doping of the reaction products effectively improves the wettability of lithium metal on the copper foil surface, supporting the rapid and uniform coating of ultrathin lithium metal layers with controllable thickness (1μm–20μm). Furthermore, the presence of inorganic fast-ion conductor components, lithium-metal alloy components, and crystal interfaces in the reaction products facilitates rapid lithium-ion conduction on the lithium metal surface and in the bulk phase, suppressing uneven lithium deposition and lithium dendrite growth, effectively improving coulombic efficiency and cycle stability. This application has low equipment requirements, short preparation time, enables ultrathin coating of lithium metal with controllable thickness, high uniformity, and good cycle stability, and is expected to contribute to the high-performance application of lithium metal batteries.

[0040] The method for preparing the ultrathin lithium metal composite anode provided in this application involves first heating a low-melting-point salt and lithium metal to a molten state and mixing them thoroughly to react; then transferring the molten composite lithium metal material after the reaction onto a copper foil, maintaining the heating to keep the composite lithium metal material in a molten state, and uniformly coating the lithium metal in this state; and finally cooling to room temperature to obtain the ultrathin lithium metal composite anode.

[0041] In some embodiments, the anions of the low-melting-point salt include inorganic nitrate, chlorine, nitrogen, phosphorus, fluorine, sulfur, or organic bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, hexafluorophosphate, difluorooxalateborate, tetrafluoroborate, difluorophosphate, bis(oxalateborate), and trifluoromethanesulfonate.

[0042] In some embodiments, the cation of the low-melting-point salt includes one or more of magnesium, zinc, aluminum, gallium, indium, silver, tin, bismuth, germanium, antimony, or organic 1-ethyl-3-methylimidazolium cation, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium cation, and N-methyl-N-propylpyrrolidine cation.

[0043] In some embodiments, when a low-melting-point salt is mixed with lithium metal and heated, a redox reaction occurs, generating an inorganic fast-ion conductor and a lithium-metal alloy within the lithium metal anode, thereby increasing the wettability of lithium on the copper foil.

[0044] Specifically, this application utilizes a low-melting-point salt (molten salt) to carry out a redox reaction with lithium metal, generating a lithium-metal alloy rich in inorganic fast ion conductors within the lithium metal anode, thereby increasing the wettability of lithium on copper foil and solving the problem of non-wetting between molten lithium and the substrate in the preparation of ultrathin lithium foil.

[0045] In some embodiments, the inorganic fast ion conductor includes one or more of lithium fluoride, lithium nitride, lithium sulfide, or lithium phosphide.

[0046] Moreover, by cleverly utilizing the spontaneous reaction between dopants and lithium metal, efficient and simultaneous chemical modification of the lithium metal anode phase / surface is achieved during the melting reaction process. This enables in-situ doping of inorganic fast ion conductor components and lithium-metal alloy components, as well as the rapid construction of rich crystal interfaces, thereby achieving rapid lithium ion conduction, suppressing uneven lithium deposition and dendritic growth, improving coulombic efficiency, and enhancing the electrochemical performance of the lithium metal anode.

[0047] The method for preparing ultrathin lithium metal composite anodes provided in this application, through self-doping modification of lithium metal, can better control the thickness of the coated lithium layer and maintain its uniformity, and can prepare uniform lithium foils with thickness gradients below 20 μm.

[0048] In some embodiments, the thickness of the lithium metal layer in the ultrathin lithium metal composite anode is 1 μm to 20 μm. For example, the thickness of the lithium metal layer in the ultrathin lithium metal composite anode can be 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 15 μm, or 20 μm. Preferably, the thickness of the lithium metal layer in the ultrathin lithium metal composite anode is 10 μm.

[0049] This application utilizes the rapid reaction between highly reducing and reactive lithium metal and low-melting-point salts, and the self-doping of the reaction products can significantly improve the wettability of lithium metal on copper foil surfaces. Moreover, unlike organic / inorganic modifications that only affect the copper foil surface, the preparation method provided in this application allows for the rapid and uniform coating of ultrathin lithium metal layers with controllable thickness, ranging from 1 μm to 20 μm, through the doping modification of the lithium metal substrate itself.

[0050] In some embodiments, the thickness of the copper foil is 5 μm to 20 μm. For example, the thickness of the copper foil is 5 μm, 10 μm, 15 μm, or 20 μm. Preferably, the thickness of the copper foil is 10 μm.

[0051] In some embodiments, the molten composite lithium metal material is uniformly coated and cooled to room temperature by natural cooling or blowing air.

[0052] For example, this application may utilize various heating auxiliary methods, including: hot table heating, infrared lamp heating, etc.

[0053] This application also provides an ultrathin lithium metal composite anode, which is prepared using the preparation method of the ultrathin lithium metal composite anode material described in the above embodiments.

[0054] This application obtains ultrathin lithium metal composite anodes of Examples 1 to 6 by uniformly coating lithium metal composite layers of different thicknesses (1 μm to 20 μm) on a copper substrate with a thickness of 10 μm. SEM images of each example are shown below. Figures 2 to 8 As shown, unmodified lithium metal was used as a comparative example (physical image shown). Figure 9 (As shown), and in conjunction with the lithium iron phosphate-based full cell performance diagram of the sample with a 10 μm lithium metal composite layer formed on a 10 μm thick copper substrate in Example 5 (as shown in the figure). Figure 10 As shown in the figure, the experimental results show that the battery performance of the ultrathin lithium metal composite anode obtained by uniformly coating a 10μm lithium metal composite layer on a 10μm thick copper substrate is optimal.

[0055] This application also provides the application of ultrathin lithium metal composite anodes. The modified lithium metal anodes prepared in this application are applicable to both liquid lithium metal batteries and solid lithium metal batteries.

[0056] Based on the above technical solutions, this application provides an ultrathin lithium metal composite anode and its preparation method and application. The preparation method includes the following steps: First, a low-melting-point salt and lithium metal are mixed and heated to a molten state to react and generate a molten composite lithium metal material; then, the molten composite lithium metal material is transferred to a copper foil, uniformly coated, and cooled to room temperature to obtain an ultrathin lithium metal composite anode.

[0057] This application addresses the technical problem of insufficient self-wetting properties of lithium metal and copper in existing technologies, making it difficult for molten lithium to spread uniformly on the copper foil surface. On one hand, this application utilizes the rapid reaction between highly reducing and reactive lithium metal and low-melting-point salts, and the self-doping of the reaction products significantly improves the wettability of lithium metal on the copper foil surface. On the other hand, unlike organic / inorganic modifications only on the copper foil surface, this application involves doping modification of the lithium metal substrate itself, supporting the rapid and uniform coating of ultra-thin lithium metal layers with controllable thickness from 1μm to 20μm. Furthermore, this application cleverly utilizes the spontaneous reaction between dopants and lithium metal to achieve efficient and simultaneous chemical modification of the lithium metal anode phase / surface during the molten reaction process. This enables in-situ doping of inorganic fast ion conductors (lithium fluoride, lithium nitride, lithium sulfide, lithium phosphide, etc.) and lithium-metal alloy components, as well as the rapid construction of rich crystal interfaces. This method is efficient, simple, and uses inexpensive raw materials. Moreover, this application is universal and can be applied to low-melting-point salts that can react with lithium metal, such as organic salts and inorganic salts.

[0058] Those skilled in the art will understand that the above-described embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail may be made without departing from the spirit and scope of this application. Any person skilled in the art can make their own modifications and alterations without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A method for preparing an ultrathin lithium metal composite anode, characterized in that, Includes the following steps: Low-melting-point salts and lithium metal are mixed and heated to a molten state to react and generate a molten composite lithium metal material. The molten composite lithium metal material is transferred onto a copper foil, uniformly coated, and cooled to room temperature to obtain an ultrathin lithium metal composite anode. When low-melting-point salts are mixed with lithium metal and heated, a redox reaction occurs, generating an inorganic fast-ion conductor and a lithium-metal alloy within the lithium metal anode, thereby increasing the wettability of lithium on copper foil. The thickness of the composite lithium metal material layer in the ultrathin lithium metal composite anode is 1μm~20μm.

2. The method for preparing the ultrathin lithium metal composite anode according to claim 1, characterized in that, The anions of the low-melting-point salt include inorganic nitrate, chlorine, nitrogen, phosphorus, fluorine, and sulfur, or organic bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, hexafluorophosphate, difluorooxalateborate, tetrafluoroborate, difluorophosphate, bis(oxalateborate), and trifluoromethanesulfonate.

3. The method for preparing the ultrathin lithium metal composite anode according to claim 1, characterized in that, The cations of the low-melting-point salt include one or more of the following: magnesium, zinc, aluminum, gallium, indium, silver, tin, bismuth, germanium, antimony, or organic 1-ethyl-3-methylimidazolium cation, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium cation, and N-methyl-N-propylpyrrolidine cation.

4. The method for preparing the ultrathin lithium metal composite anode according to claim 1, characterized in that, The inorganic fast ion conductor includes one or more of lithium fluoride, lithium nitride, lithium sulfide, or lithium phosphide.

5. The method for preparing the ultrathin lithium metal composite anode according to claim 1, characterized in that, The thickness of the copper foil is 5μm to 20μm.

6. The method for preparing the ultrathin lithium metal composite anode according to claim 1, characterized in that, The molten composite lithium metal material is uniformly coated and then cooled to room temperature by natural cooling or blowing air.

7. An ultrathin lithium metal composite anode, characterized in that, It was prepared using the preparation method of the ultrathin lithium metal composite anode as described in any one of claims 1 to 6.

8. The application of the ultrathin lithium metal composite negative electrode as described in claim 7 in liquid lithium metal batteries and solid lithium metal batteries.

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