A composite lithium negative electrode with multilayer lithium-rich alloy, preparation method and application

Abstract

The present invention belongs to the field of lithium battery technology and discloses a composite lithium negative electrode with a multilayer lithium-rich alloy, a preparation method and an application thereof. The negative electrode current collector is sequentially provided with multiple layers of lithium-rich alloy layers of different compositions, each layer of the alloy is composed of a lithium-rich dual-phase alloy with a thickness of 1 to 50 μm. The lithium-rich dual-phase alloy is a lithium alloy Li-R formed by Li and a metal / non-metal R, wherein the metal R refers to at least one of B, Cu, Al, Sn, Sb, Zn, Mg, Ca, Ba, Ag, In, Bi, Ge, Ga, Au, and Pt. The lithium-rich alloy contains a lithium single phase and Li x R intermetallic compound phase or solid solution phase. Li x The R intermetallic compound phase or solid solution phase can interconnect to form a three-dimensional skeleton structure. The multilayer structure can effectively mitigate the structural collapse problem in lithium alloy anodes. The melt-forming film method is simple to produce and can easily produce low-cost, high-performance multilayer lithium alloy composite anodes.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a composite lithium negative electrode having multiple layers of lithium-rich alloy, a preparation method and applications thereof. Background Art

[0002] Currently, metallic lithium is considered the "holy grail" of lithium battery anodes due to its low redox potential and ultra-high theoretical capacity. However, during cycling, side reactions between metallic lithium and the electrolyte inevitably occur, leading to electrolyte consumption and capacity loss. Furthermore, safety risks such as uncontrollable lithium dendrite growth and significant volume changes restrict the development and application of metallic lithium anodes. Among the many modification strategies for metallic lithium anodes, the use of lithium alloy composite anodes and optimized current collector structure design are the most widely used.

[0003] At present, most of the research on lithium alloy composite negative electrodes uses melting and other methods to mix lithium and metal R evenly, and then forms a single layer of lithium-rich Li-R alloy through alloying reaction. Among them, the lithium alloy Li-R contains a single phase of metal Li and Li x R intermetallic compound or solid solution phase, and Li x The R phase can form a built-in three-dimensional skeleton structure in situ by means of phase separation, providing space for the deposition / dissolution of metallic lithium. x The R phase has a certain affinity for lithium, which restricts the nucleation and growth of metallic lithium, further improving the electrochemical performance of lithium-rich alloys. However, in existing technologies, such single-layer lithium-rich alloy anodes lack a lithium affinity gradient due to their simple structure, resulting in the easy deposition of metallic lithium on the anode surface and the growth of lithium dendrites, which need to be addressed urgently.

[0004] The above analysis, combined with current research in the field of lithium-rich alloy anodes, reveals that lithium-rich alloys formed with lithium-phobic elements such as Cu and Ni have relatively large nucleation barriers for lithium and tend to induce dendrite growth. However, for metals R with a strong lithiophilic affinity, such as Au, Ag, Al, Zn, and Mg, the nucleation barrier is relatively small, inducing dense, conformal growth of metallic lithium. In general, the problems and drawbacks of the existing technology are: existing composite lithium anodes have a single structure and lack a lithiophilic gradient, resulting in the easy deposition of metallic lithium on the anode surface, which tends to induce dendrite growth after multiple cycles. Summary of the Invention

[0005] In response to the problems existing in the prior art, the present invention provides a composite lithium negative electrode having multiple layers of lithium-rich alloy, a preparation method and applications.

[0006] The present invention is achieved by: a composite lithium negative electrode having multiple layers of lithium-rich alloy comprising:

[0007] The negative electrode is sequentially provided with multiple layers of lithium-rich alloy layers of different compositions, each layer of alloy is composed of a lithium-rich dual-phase alloy with a thickness of 1 to 50 μm. The lithium-rich dual-phase alloy is a lithium alloy Li-R formed by Li and metal / non-metal R, wherein the metal R refers to at least one of B, Cu, Al, Sn, Sb, Zn, Mg, Ca, Ba, Ag, In, Bi, Ge, Ga, Au, and Pt. The Li-R alloy contains lithium single phase and Li x R intermetallic compound phase or solid solution phase, in which Li x The R intermetallic compound phase or solid solution phase can connect with each other to form a three-dimensional skeleton structure, which slows down the volume change during the cycle and improves the electrochemical performance.

[0008] Furthermore, each layer is made of a lithium-rich alloy, wherein the bottom layer is the first layer, and the second layer, the third layer, and so on are arranged upward from the first layer.

[0009] Furthermore, the lithium affinity of each layer of lithium-rich alloy is not stronger than the lithium affinity of the underlying lithium-rich alloy.

[0010] Furthermore, the negative electrode current collector is copper foil, nickel foil, or stainless steel foil, more preferably copper foil.

[0011] The present invention also provides a method for preparing a composite lithium negative electrode having multiple layers of lithium-rich alloy, the specific steps of which are as follows:

[0012] Step 1: Mix metallic lithium and metal / non-metal R evenly and heat to obtain a molten alloy liquid;

[0013] Step 2: evenly distributing the molten alloy liquid onto the negative electrode current collector, followed by rapid cooling to obtain a first alloy layer on the negative electrode current collector;

[0014] Step 3: Evenly distribute another molten alloy liquid on the first alloy layer to prepare the second alloy layer, and continue upwards to complete the preparation of the lithium-rich alloy layer.

[0015] Furthermore, the temperature of the negative electrode current collector is 2-800°C, and the optimal temperature is 20-540°C.

[0016] Furthermore, the method for uniformly distributing the molten alloy liquid includes any one of a melt coating method, a melt casting method, a melt spraying method, a melt rolling method, and a melt strip spinning method.

[0017] Furthermore, the heating temperature of the molten alloy liquid is 230-1000°C, and the optimal temperature is 450-740°C.

[0018] Furthermore, the molten alloy layer is rapidly cooled to room temperature at a rate of 100 to 6000° C. / min.

[0019] Another object of the present invention is to provide a negative electrode plate of a lithium battery using a composite lithium negative electrode having a multi-layer lithium-rich alloy, which includes a multi-layer lithium alloy composite negative electrode.

[0020] Another object of the present invention is to provide a lithium battery using a composite lithium negative electrode having a multi-layer lithium-rich alloy, which includes a positive electrode plate, an electrolyte, and a negative electrode plate.

[0021] Furthermore, the positive electrode plate is composed of at least one of the following compounds: LiCoO2, LiFePO4, Li4Ti5O 12 、LiMn2O4、LiNi 0.5 Mn 0.5 O2、LiNi x Co y Mn( 1-x-y )O2、LiNi 0.8 Co 0.15 Al 0.05 O2, xLiMO2·(1-x)Li2MnO3; among which, 0 <x<1,0<y<1。

[0022] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0023] First, in view of the technical problems existing in the above-mentioned prior art and the difficulty of solving these problems, this paper closely combines the technical solutions to be protected by the present invention and the results and data during the research and development process, and analyzes in detail and in depth how the technical solutions of the present invention solve the technical problems and some creative technical effects brought about by solving the problems. The specific description is as follows:

[0024] The multi-layer lithium-rich alloy composite negative electrode provided by the present invention comprises multiple lithium-rich alloy layers with a thickness of 1 to 50 μm, sequentially disposed on a negative electrode current collector, and serves as the negative electrode of a lithium battery. In this multi-layer lithium-rich alloy composite negative electrode, the alloying elements are selected so that each alloy layer has a lithium affinity for the upper lithium alloy layer that is not stronger than that for the lower lithium alloy layer, thereby creating a longitudinal lithium affinity gradient. The depth-wise distribution of lithium alloys with varying lithium affinity facilitates the bottom-up deposition of lithium ions, effectively suppressing uneven lithium deposition on the electrode surface and thereby inhibiting the growth of lithium dendrites.

[0025] From the perspective of structural stability, compared with single-layer alloys, the repeated lithium extraction / insertion behavior is accompanied by volume changes and structural collapse during the alloying / de-alloying process; the multi-layer alloy composite negative electrode provided by the present invention will inevitably undergo interdiffusion between layers, and a ternary lithium alloy will be formed between adjacent layers, which helps to improve the mechanical stability of the interlayer skeleton structure, effectively reduce the risk of collapse of the overall skeleton structure, extend the cycle life of the battery, and improve the electrochemical performance of the battery.

[0026] In the preparation method of the multilayer composite negative electrode provided by the present invention, a simple high-temperature melting method is used, utilizing the excellent rheological properties and wettability of molten lithium alloy at high temperature and the easy and uniform spreading characteristics to achieve the preparation of multilayer lithium alloy layers with controllable thickness and tight bonding.

[0027] In the preparation method of the multi-layer composite negative electrode provided by the present invention, the molten alloy layer is rapidly cooled at a rate of 100 to 6000°C / min, thereby achieving rapid cooling of the alloy layer and controlling the phase separation process to obtain Li x R three-dimensional framework phase and metallic lithium.

[0028] Second, considering the technical solution as a whole or from the perspective of the product, the technical effects and advantages of the technical solution to be protected by the present invention are described in detail as follows:

[0029] Compared with existing lithium alloy negative electrode modification technologies, the present invention provides a novel modification method based on existing technologies. By selecting alloying elements, the lithium affinity of the upper lithium alloy layer is controlled to be no stronger than that of the lower lithium alloy layer, thereby constructing a composite multilayer alloy layer with a lithium affinity gradient. This can effectively mitigate the problems of lithium dendrite growth and structural collapse caused by changes in the three-dimensional skeleton volume that exist in metal lithium and lithium alloy negative electrodes. The production process is easy to implement, enabling the preparation of low-cost, high-performance multilayer alloy composite negative electrodes. Metal lithium batteries based on multilayer lithium alloy composite negative electrodes have higher first-cycle coulombic efficiency and longer cycle life.

[0030] Third, as auxiliary evidence for the inventiveness of the claims of the present invention, it is also reflected in the following important aspects:

[0031] At present, in the research field of alloyed negative electrodes, the research on lithium-rich alloys as composite metal lithium negative electrodes is still in its initial stage, and the lithium-rich alloy systems that have been studied more are all non-inert alloys, whose skeletons can reversibly deintercalate lithium, which will cause the skeleton to produce a certain volume change, which is not conducive to the stability of the electrode structure. For inert alloys, the constraint effect on the deposition of metallic lithium is limited. Metallic lithium is easy to deposit on the surface and tends to induce the growth of dendrites, which affects the life of lithium batteries. Based on this, the present invention starts from the root of solving the problem and constructs a multi-layer lithium-rich alloy composite negative electrode with a lithium-affinity gradient. The lithium-affinity gradient from bottom to top induces the deposition of lithium ions from bottom to top, avoiding the growth of lithium dendrites, and the multi-component lithium alloy formed by the mutual diffusion between the multi-layer alloys helps to improve the mechanical stability of the skeleton, effectively solving the problems currently faced in the field of lithium-rich alloy negative electrodes, such as low cycle life and easy growth of lithium dendrites. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the structure of a multi-layer lithium-rich alloy composite negative electrode provided by an embodiment of the present invention;

[0033] Figure 2 is a coulomb data diagram of a lithium battery provided by an embodiment of the present invention;

[0034] Figure 3 This is a cross-sectional SEM image of a double-layer lithium-rich alloy composite negative electrode provided by an embodiment of the present invention;

[0035] Figure 4 is a cycle performance diagram of a lithium symmetrical battery provided by an embodiment of the present invention;

[0036] In the figure: 1 is the negative electrode current collector; 2 is the first lithium-rich alloy layer; 3 is the second lithium-rich alloy layer; 4 is the third lithium-rich alloy layer. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0038] In order to enable those skilled in the art to fully understand how to implement the present invention, this section provides an explanatory embodiment that expands on the technical solutions of the claims.

[0039] like Figure 1-Figure 4 As shown, an embodiment of the present invention provides a composite lithium negative electrode having multiple layers of lithium-rich alloy, comprising:

[0040] The composite lithium negative electrode is a multi-layer lithium-rich alloy layer with different compositions sequentially arranged on the current collector. Each layer of alloy is composed of a lithium-rich bidirectional alloy with a thickness of 1 to 50 μm. The lithium-rich biphasic alloy is a lithium alloy Li-R formed by Li and metal / non-metal R, wherein the metal R refers to at least one of B, Cu, Al, Sn, Sb, Zn, Mg, Ca, Ba, Ag, In, Bi, Ge, and Ga. The Li-R alloy contains a lithium single phase and a Li-R intermetallic compound phase or solid solution phase. The Li-R intermetallic compound phase or solid solution phase can be interconnected to form a three-dimensional skeleton structure, thereby slowing down the volume change during the cycle and improving the electrochemical performance.

[0041] 1 is a negative electrode current collector, the bottom layer is a first lithium-rich alloy layer 2, the first lithium-rich alloy layer 2 is above the second lithium-rich alloy layer 3, and the second lithium-rich alloy layer 3 is above the third lithium-rich alloy layer 4.

[0042] An embodiment of the present invention provides a multi-layer lithium-rich alloy composite negative electrode with a lithium affinity gradient, which is used as a negative electrode plate in a lithium battery.

[0043] Example 1

[0044] This embodiment provides a double-layer alloy composite negative electrode, which includes a negative electrode current collector and two lithium alloy layers with different compositions and different thicknesses sequentially arranged on the negative electrode current collector.

[0045] The preparation method of the double-layer alloy composite negative electrode comprises:

[0046] (1) Metal Li and metal Al, or metal Li and metal Cu, are placed in two crucibles, respectively, and heated to 480°C to obtain a molten lithium-rich alloy;

[0047] (2) The stainless steel foil was heated to 480°C, and an ultra-thin molten Li-Al alloy layer was obtained by tape casting, which was then rapidly cooled to room temperature at a rate of 1000°C / min to obtain a first Li-Al alloy layer with a thickness of 30 μm.

[0048] (3) The stainless steel foil loaded with the first Li-Al alloy layer was heated to 250°C, and then a second Li-Cu alloy layer loaded on the Li-Al alloy layer was obtained by melt coating. The second Li-Cu alloy layer was rapidly cooled to room temperature at a rate of 2000°C / min to obtain a second Li-Cu alloy layer with a thickness of 10 μm and a double-layer lithium alloy composite negative electrode with a total thickness of 40 μm.

[0049] This embodiment also provides a lithium battery based on a double-layer lithium-rich alloy composite negative electrode, which includes a positive electrode plate, an electrolyte, and the above-mentioned double-layer lithium-rich alloy composite negative electrode plate. The preparation method of the lithium battery includes: assembling the above-mentioned double-layer alloy composite negative electrode plate, an ester electrolyte, a diaphragm, and a commercially purchased LiFePO4 positive electrode plate to obtain a lithium battery; assembling the above-mentioned double-layer alloy composite negative electrode plate, an ester electrolyte, a diaphragm, and the above-mentioned double-layer alloy as a positive electrode plate to obtain a lithium symmetrical battery.

[0050] Example 2

[0051] This embodiment provides a three-layer alloy composite negative electrode, the structure of which is similar to that of Example 1, and the preparation method includes:

[0052] (1) placing metallic Li and metallic Zn, metallic Li and metallic Al, and metallic Li and metallic Cu in three crucibles respectively and heating them to 600°C to obtain molten lithium-rich alloys;

[0053] (2) The stainless steel foil was heated to 280°C, and then the molten Li-Zn alloy was transferred to the stainless steel foil by a tape casting method to obtain an ultra-thin Li-Zn alloy layer. The ultra-thin Li-Zn alloy layer was then rapidly cooled to room temperature at a rate of 100°C / min to obtain a first Li-Zn alloy layer with a thickness of 20 μm.

[0054] (3) The stainless steel foil loaded with the first Li-Zn alloy layer was heated to 200°C, and the molten Li-Al alloy was evenly distributed on the surface of the Li-Zn alloy layer by melt spraying. The foil was then rapidly cooled to room temperature at a rate of 3000°C / min to obtain a second Li-Al alloy layer with a thickness of 10 μm.

[0055] (4) The stainless steel foil loaded with the double alloy layer was heated to 100°C, and the molten Li-Cu alloy was evenly distributed on the surface of the Li-Al alloy layer by melt spraying. The material was rapidly cooled to room temperature at a rate of 4500°C / min to obtain a third Li-Cu alloy layer with a thickness of 8 μm. The total thickness of the three-layer lithium alloy composite negative electrode material was 38 μm.

[0056] This embodiment also provides a lithium battery including a three-layer alloy composite negative electrode. The lithium battery includes a positive electrode plate, an electrolyte, and the three-layer alloy composite negative electrode plate. The preparation method of the lithium battery includes:

[0057] The above three-layer alloy composite negative electrode sheet, ester electrolyte, diaphragm, and commercially purchased LiFePO4 positive electrode sheet are assembled to obtain a lithium battery; the above three-layer alloy composite negative electrode sheet, ester electrolyte, diaphragm, and the above three-layer alloy as a positive electrode sheet are assembled to obtain a lithium symmetrical battery.

[0058] Instructions attached Figure 2This is the coulombic data graph corresponding to the lithium battery provided in Example 2 above. The coulombic efficiency test used a Li-Cu half-cell system, wherein the electrode material was a 10 mm disc cut from the three-layer Li-Zn-Al-Cu composite lithium-rich alloy prepared in Example 2 above as the counter electrode, and a 12 mm disc cut from commercial Cu foil as the working electrode. A CR2032 button cell model was used for the test in an ester electrolyte (1M LiTFSI (lithium bis(trifluoromethanesulfonyl imide)) dissolved in EC (ethylene carbonate) / DEC (diethyl carbonate), v / v = 1 / 1) with 5% FEC (fluoroethylene carbonate) added as an additive. A Celgard 2325 separator was used, and a constant surface current density (1 mA cm) was set. -2 ) for charge and discharge, discharge for a constant time (1 hour), and then charge to the cut-off voltage (1V). The results are shown in Figure 2 .Depend on Figure 2 It can be seen that the first-week coulombic efficiency of the above-mentioned three-layer alloy composite negative electrode reaches 94.53%, and the average coulombic efficiency reaches 97.09%, indicating that the three-layer alloy composite material is highly reversible during the cycle and lithium ions can be reversibly embedded and deintercalated inside the skeleton.

[0059] Example 3

[0060] This embodiment provides a double-layer alloy composite negative electrode, the structure of which is consistent with that of Example 1, and the preparation method includes:

[0061] (1) Li metal and In metal are placed in a crucible and heated to 230°C to obtain a molten alloy. Then, Li metal and Cu metal are placed in another crucible and heated to 400°C to obtain a molten lithium-rich alloy.

[0062] (2) The stainless steel foil was heated to 200°C, and then the molten Li-In alloy was transferred to the stainless steel foil. An ultra-thin molten Li-In alloy layer was obtained by rolling. The ultra-thin molten Li-In alloy layer was rapidly cooled to room temperature at a rate of 100°C / min to obtain a first Li-In alloy layer with a thickness of 4 μm.

[0063] (3) A stainless steel foil loaded with a first layer of Li-In alloy layer was placed in a 20°C environment, and then a molten Li-Cu alloy was prepared by melt spraying to obtain a second layer of Li-Cu alloy layer loaded on the Li-In alloy layer. The second layer was rapidly cooled to room temperature at a rate of 2000°C / min, so that the double-layer lithium alloy on the stainless steel foil was rapidly cooled to obtain a second layer of Li-Cu alloy layer with a thickness of 20 μm and a double-layer lithium alloy composite negative electrode with a total thickness of 24 μm.

[0064] This embodiment further provides a lithium battery comprising a double-layer alloy composite negative electrode, the lithium battery comprising a positive electrode plate, an electrolyte, and the double-layer alloy composite negative electrode plate. The preparation method of the lithium battery comprises:

[0065] The above-mentioned double-layer alloy composite negative electrode sheet, ester electrolyte, diaphragm, and commercially purchased LiFePO4 positive electrode sheet are assembled to obtain a lithium battery; the above-mentioned double-layer alloy composite negative electrode sheet, ester electrolyte, diaphragm, and the above-mentioned double-layer alloy as a positive electrode sheet are assembled to obtain a lithium symmetrical battery.

[0066] Instructions attached Figure 3 The SEM morphology of the cross section of the Li-In-Cu composite lithium-rich alloy prepared in Example 3 is shown in FIG. Figure 3 It can be seen that the double-layer alloy composite negative electrode prepared by the above method has uniform thickness and presents two different morphologies, namely, the Li-In alloy layer arranged above the negative electrode current collector serves as the first layer of lithium-rich alloy with a thickness of about 4 μm, and the Li-Cu alloy above the Li-In alloy serves as the second layer of lithium-rich alloy with a thickness of about 20 μm. Because the Li-Cu alloy is inert and provides an inert skeleton, the Li-In alloy, as a lithium-philic skeleton, is rich in lithium-philic sites, providing space and position for metallic lithium deposition, inducing lithium ions to deposit from the bottom up, and avoiding dense surface deposition and the formation of dendrites.

[0067] Example 4

[0068] This embodiment provides a double-layer alloy composite negative electrode, the structure of which is consistent with that of Example 1, and the preparation method includes:

[0069] (1) Metal Li and metal Mg, or metal Li and metal Cu are placed in two crucibles respectively and heated to 1000°C to obtain a molten lithium-rich alloy;

[0070] (2) The stainless steel foil was heated to 540°C, and then the molten Li-Mg alloy was transferred to the copper foil. An ultra-thin molten Li-Mg alloy layer was obtained by blade coating. The ultra-thin molten Li-Mg alloy layer was then rapidly cooled to room temperature at a rate of 900°C / min to obtain a first Li-Mg alloy layer with a thickness of 50 μm.

[0071] (3) The copper foil loaded with the first Li-Mg alloy layer was cooled to 2°C, and then the second Li-Cu alloy layer loaded on the Li-Mg alloy layer was obtained by the melt spinning method. The copper foil was rapidly cooled to room temperature at a rate of 6000°C / min, so that the double-layer lithium alloy on the stainless steel foil was rapidly cooled to obtain a second Li-Cu alloy layer with a thickness of 50 μm and a double-layer lithium alloy composite negative electrode with a total thickness of 100 μm.

[0072] This embodiment further provides a lithium battery comprising a double-layer alloy composite negative electrode, the lithium battery comprising a positive electrode plate, an electrolyte, and the double-layer alloy composite negative electrode plate. The preparation method of the lithium battery comprises:

[0073] The above-mentioned double-layer alloy composite negative electrode sheet, ester electrolyte, diaphragm, and commercially purchased LiFePO4 positive electrode sheet are assembled to obtain a lithium battery; the above-mentioned double-layer alloy composite negative electrode sheet, ester electrolyte, diaphragm, and the above-mentioned double-layer alloy as a positive electrode sheet are assembled to obtain a lithium symmetrical battery.

[0074] Instructions attached Figure 4 The cycling performance diagram of the lithium symmetric battery provided in Example 4 and Comparative Example 2 is shown. The cycling performance test was conducted using a Li-Li symmetric battery system, in which the electrode materials were all 10 mm discs cut from the single-layer Li-Cu lithium-rich alloy prepared in Example 4 and Comparative Example 2. The battery was tested using a CR 2032 button cell model in an ester electrolyte (1 M LiTFSI dissolved in EC / DEC, v / v = 1 / 1) with 5% FEC as an additive. A Celgard 2325 separator was used, and a constant areal current density (1 mA cm) was set. -2 ) for charging and discharging, charging and discharging were performed for the same time (1 hour), and the results are shown in Figure 4 .Depend on Figure 4 It can be seen that the symmetrical battery assembled with a double-layer composite lithium-rich alloy as the negative electrode can be stably cycled for more than 400 hours, while in Comparative Example 2, the single-layer Li-Cu alloy can only be cycled for 230 hours, and the polarization voltage of the multi-layer alloy composite negative electrode is also lower than that of the single-layer alloy, indicating that the lithium battery with a double-layer alloy composite negative electrode has better cycle performance, and the cycle life is significantly improved compared with the single-layer alloy layer. It can be seen that this multi-layer lithium-rich alloy negative electrode material with a lithium affinity gradient can greatly improve the cycle performance of the battery, while also reducing the voltage polarization of the battery.

[0075] Example 5

[0076] This embodiment provides a double-layer alloy composite negative electrode, the structure of which is consistent with that of Example 1, and the preparation method includes:

[0077] (1) Metal Li and metal Bi, and metal Li and metal B are placed in two crucibles respectively and heated to 800°C to obtain a molten lithium-rich alloy;

[0078] (2) The nickel foil was heated to 800°C, and the molten Li-Bi alloy was transferred to the stainless steel foil. An ultra-thin molten Li-Bi alloy layer was obtained by tape casting. The ultra-thin molten Li-Bi alloy layer was rapidly cooled to room temperature at a rate of 1200°C / min to obtain a first Li-Bi alloy layer with a thickness of 30 μm.

[0079] (3) A second Li-B alloy layer loaded on the Li-Bi alloy layer was obtained by melt spraying, and the double-layer lithium alloy on the nickel foil was rapidly cooled to room temperature at a rate of 4800°C / min to obtain a second Li-B alloy layer with a thickness of 1 μm and a double-layer lithium alloy composite negative electrode with a total thickness of 31 μm.

[0080] This embodiment further provides a lithium battery comprising a double-layer alloy composite negative electrode, the lithium battery comprising a positive electrode plate, an electrolyte, and the double-layer alloy composite negative electrode plate. The preparation method of the lithium battery comprises:

[0081] The above-mentioned double-layer alloy composite negative electrode sheet, ester electrolyte, diaphragm, and commercially purchased LiFePO4 positive electrode sheet are assembled to obtain a lithium battery; the above-mentioned double-layer alloy composite negative electrode sheet, ester electrolyte, diaphragm, and the above-mentioned double-layer alloy as a positive electrode sheet are assembled to obtain a lithium symmetrical battery.

[0082] Example 6

[0083] This embodiment provides a double-layer alloy composite negative electrode, the structure of which is consistent with that of Example 1, and the preparation method includes:

[0084] (1) placing metallic Li and metallic Ga, and metallic Li and metallic Ca in two crucibles respectively, and heating them to 480°C to obtain a molten lithium-rich alloy;

[0085] (2) heating the copper foil to 300°C, transferring the molten Li-Ga alloy onto the copper foil, and obtaining an ultra-thin molten Li-Ga alloy layer by a tape casting method. The ultra-thin molten Li-Ga alloy layer was then rapidly cooled to room temperature at a rate of 300°C / min to obtain a first Li-Ga alloy layer with a thickness of 1 μm.

[0086] (3) The copper foil loaded with the first Li-Ga alloy layer was heated to 120°C, and then a second Li-Ca alloy layer loaded on the Li-Ga alloy layer was obtained by a tape casting method. The copper foil was rapidly cooled to room temperature at a rate of 2000°C / min, so that the double-layer lithium alloy on the stainless steel foil was rapidly cooled to obtain a second Li-Ca alloy layer with a thickness of 50 μm and a double-layer lithium alloy composite negative electrode with a total thickness of 51 μm.

[0087] This embodiment further provides a lithium battery comprising a double-layer alloy composite negative electrode, the lithium battery comprising a positive electrode plate, an electrolyte, and the double-layer alloy composite negative electrode plate. The preparation method of the lithium battery comprises:

[0088] The above-mentioned double-layer alloy composite negative electrode sheet, ester electrolyte, diaphragm, and commercially purchased LiFePO4 positive electrode sheet are assembled to obtain a lithium battery; the above-mentioned double-layer alloy composite negative electrode sheet, ester electrolyte, diaphragm, and the above-mentioned double-layer alloy as a positive electrode sheet are assembled to obtain a lithium symmetrical battery.

[0089] Example 7

[0090] This embodiment provides a three-layer alloy composite negative electrode, whose structure is similar to that of Example 1, and the preparation method includes:

[0091] (1) Li and Ag, Li and Sn, and Li and Ba are placed in three crucibles, respectively, and heated to 740°C to obtain a molten lithium-rich alloy;

[0092] (2) heating the nickel foil to 540°C, transferring the molten Li-Ag alloy onto the nickel foil, and obtaining an ultrathin molten Li-Ag alloy layer by melt rolling, which was then rapidly cooled to room temperature at a rate of 800°C / min to obtain a first Li-Ag alloy layer with a thickness of 10 μm;

[0093] (3) The nickel foil loaded with the first Li-Ag alloy layer was heated to 400°C, and then a second Li-Sn alloy layer loaded on the Li-Ag alloy layer was obtained by a doctor blade coating method. The second Li-Sn alloy layer was then rapidly cooled to room temperature at a rate of 1700°C / min to rapidly cool the double-layer lithium alloy on the stainless steel foil, thereby obtaining a second Li-Sn alloy layer with a thickness of 30 μm.

[0094] (4) a third Li-Ba alloy layer supported on the Li-Sn alloy layer was obtained by melt spraying, and the layer was rapidly cooled to room temperature at a rate of 5000°C / min to obtain a third Li-Ba alloy layer with a thickness of 5 μm and a total thickness of 45 μm for a three-layer lithium alloy composite negative electrode material;

[0095] This embodiment also provides a lithium battery including a three-layer alloy composite negative electrode. The lithium battery includes a positive electrode plate, an electrolyte, and the three-layer alloy composite negative electrode plate. The preparation method of the lithium battery includes:

[0096] The above three-layer alloy composite negative electrode sheet, ester electrolyte, diaphragm, and commercially purchased LiFePO4 positive electrode sheet are assembled to obtain a lithium battery; the above three-layer alloy composite negative electrode sheet, ester electrolyte, diaphragm, and the above three-layer alloy as a positive electrode sheet are assembled to obtain a lithium symmetrical battery.

[0097] Comparative Example 1

[0098] This comparative example provides a lithium battery using a common metal lithium negative electrode, and the preparation method is as follows:

[0099] (1) Placing metallic Li in a crucible and heating it to 250°C to obtain molten metallic lithium;

[0100] (2) The stainless steel foil was heated to 250°C, and then the molten metal Li was transferred to the stainless steel foil. An ultra-thin Li layer was obtained by a tape casting method. The ultra-thin Li layer was cooled to room temperature at a rate of 100°C / min to obtain a metal Li layer with a thickness of 30 μm supported on the stainless steel foil.

[0101] (4) Assembling the above-mentioned single-layer metal lithium negative electrode sheet, ester electrolyte, diaphragm, and commercially purchased LiFePO4 positive electrode sheet to obtain a lithium battery; assembling the above-mentioned single-layer metal lithium negative electrode sheet, ester electrolyte, diaphragm, and the above-mentioned single-layer metal lithium as a positive electrode sheet to obtain a lithium symmetrical battery.

[0102] Comparative Example 2

[0103] This comparative example provides a lithium battery using a common Li-Cu alloy negative electrode plate, and the preparation method is as follows:

[0104] (1) Li metal and Cu metal are placed in a crucible and heated to 480°C to obtain a molten lithium-rich alloy;

[0105] (2) The stainless steel foil was heated to 480°C, and then the molten Li-Cu alloy was transferred to the stainless steel foil. An ultrathin molten Li-Cu alloy layer was obtained by blade coating. The ultrathin molten Li-Cu alloy layer was rapidly cooled to room temperature at a rate of 500°C / min to obtain a Li-Cu layer with a thickness of 30 μm supported on the stainless steel foil.

[0106] (4) Assembling the above-mentioned single-layer alloy composite negative electrode sheet, ester electrolyte, diaphragm, and commercially purchased LiFePO4 positive electrode sheet to obtain a lithium battery; assembling the above-mentioned single-layer alloy composite negative electrode sheet, ester electrolyte, diaphragm, and the above-mentioned single-layer alloy as a positive electrode sheet to obtain a lithium symmetrical battery.

[0107] The embodiments of the present invention have achieved some positive results during the development or use process, and indeed have great advantages over the existing technology. The following content describes them in conjunction with data, charts, etc. from the experimental process.

[0108] Figure 1 This is a schematic diagram of the structure of a multi-layer lithium-rich alloy composite provided in an application embodiment of the present invention, 1 is the negative electrode current collector, 2 is the first lithium-rich alloy layer, 3 is the second lithium-rich alloy layer, and so on, which are omitted here.

[0109] Figure 2 The three-layer Li-Zn-Al-Cu composite lithium-rich alloy prepared in Example 2 was used as the negative electrode, Cu foil was used as the counter electrode, and a half-cell prepared with a separator and an ester electrolyte was tested for coulombic efficiency. The current density during the test was 1 mA cm -2 , with an areal capacity of 1 mAh cm -2 , the results are shown in Figure 2 .Depend on Figure 2 It can be seen that the first-week coulombic efficiency of the three-layer alloy composite negative electrode reaches 94.53%, and the average coulombic efficiency reaches 97.09%.

[0110] Figure 3 The SEM morphology of the cross section of the Li-In-Cu composite lithium-rich alloy prepared in Example 3 is shown in FIG. Figure 3 It can be seen that the double-layer alloy composite negative electrode prepared by the above method has uniform thickness and presents two different morphologies, namely two different lithium alloy layers.

[0111] Figure 4 The double-layer Li-Mg-Cu composite lithium-rich alloy prepared in Example 4 was used as the positive and negative electrodes, and a symmetrical battery prepared with a separator and an ester electrolyte was tested for cycle performance. The current density during the test was 1 mA cm -2 , with a surface capacity of 1 mAh cm -2 , the results are shown in Figure 4 .Depend on Figure 4 It can be seen that the symmetrical battery can be cycled stably for more than 400 hours, while in Comparative Example 2, the single-layer Li-Cu alloy can only be cycled for 230 hours, indicating that the lithium battery with a double-layer alloy composite negative electrode has better cycle performance, and the cycle life is significantly improved compared to the single-layer alloy layer.

[0112] The lithium-ion batteries provided in Examples 1 to 7 and Comparative Examples 1 and 2 were subjected to charge and discharge tests using a Xinwei test system. The test results are shown in Table 1:

[0113] Table 1 Charge and discharge test results

[0114] sample First week Coulomb efficiency% Cycle performance h Example 1 94.98 400 Example 2 94.53 425 Example 3 96.72 375 Example 4 95.37 600 Example 5 95.14 470 Example 6 94.96 535 Example 7 95.21 450 Comparative Example 1 81.57 180 Comparative Example 2 91.32 230

[0115] As shown in Table 1, compared to the batteries prepared using ordinary metallic lithium or single-layer lithium alloy negative electrode sheets in Comparative Examples 1 and 2, the lithium batteries provided in Examples 1 to 7, which include multi-layer alloy composite negative electrodes, have higher first-cycle coulombic efficiency (up to 96.72%) and better cycle life (up to 600 hours or more). This shows that the multi-layer alloy composite negative electrode provided by the present invention, by sequentially providing multiple layers of lithium alloy layers of different compositions and thicknesses on the negative electrode current collector, effectively improves the stability of the negative electrode structure, improves interface problems, and increases the cycle life and coulombic efficiency of the lithium battery.

[0116] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A composite lithium negative electrode having multiple layers of lithium-rich alloy, characterized in that: The composite lithium negative electrode having multiple layers of lithium-rich alloy comprises: The lithium-rich dual-phase alloy is a lithium alloy Li-R formed by Li and metal / non-metal R, which contains lithium single phase and Li x R intermetallic compound phase or solid solution phase, in which Li x R intermetallic compound phases or solid solution phases can connect with each other to form a three-dimensional skeleton structure; The lithiophilicity of the upper lithium alloy is not stronger than that of the lower lithium alloy; The specific steps of the preparation method of the composite lithium negative electrode having multiple layers of lithium-rich alloy are as follows: Step 1: Mix metallic lithium and metal / non-metal R evenly and heat to obtain a molten alloy liquid; Step 2: evenly distributing the molten alloy liquid onto the negative electrode current collector, followed by rapid cooling to obtain a first alloy layer on the negative electrode current collector; Step 3: Introduce a second molten alloy liquid onto the first alloy layer to prepare a second alloy layer, then quickly cool it and repeat the process to complete the preparation of the multi-layer lithium-rich alloy.

2. The composite lithium negative electrode having a multilayer lithium-rich alloy according to claim 1, characterized in that Each layer is composed of a lithium-rich alloy layer with a thickness of 1 to 50 μm and a number of layers of 2 or more.

3. The composite lithium negative electrode having multiple layers of lithium-rich alloy according to claim 1, wherein: The metal R refers to at least one of B, Cu, Al, Sn, Sb, Zn, Mg, Ca, Ba, Ag, In, Bi, Ge, Ga, Au, and Pt.

4. The composite lithium negative electrode having a multilayer lithium-rich alloy according to claim 1, wherein: The negative electrode current collector is copper foil, nickel foil or stainless steel foil.

5. The composite lithium negative electrode having multiple layers of lithium-rich alloy according to claim 1, wherein: The negative electrode current collector is copper foil.

6. The composite lithium negative electrode having multiple layers of lithium-rich alloy according to claim 1, wherein: The heating temperature of the molten alloy liquid is 230-1000°C, and the temperature of the negative electrode current collector is 2-800°C.

7. The composite lithium negative electrode having multiple layers of lithium-rich alloy according to claim 1, wherein: The heating temperature of the molten alloy liquid is 450-740°C; the temperature of the negative electrode current collector is 20-540°C.

8. The composite lithium negative electrode having multiple layers of lithium-rich alloy according to claim 1, wherein: The molten alloy layer is rapidly cooled to room temperature at a rate of 100 to 6000° C. / min, wherein the preparation method of the alloy layer includes any one of melt coating, melt casting, melt spraying, melt calendering, and melt strip spinning.

9. The composite lithium negative electrode with multiple layers of lithium-rich alloy as claimed in any one of claims 1 to 8 is used as a negative electrode in a lithium battery.

10. The composite lithium negative electrode having multiple layers of lithium-rich alloy as claimed in any one of claims 1 to 8 is used in a lithium battery.

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