A core-shell material and a preparation method thereof, and a negative electrode material

Abstract

The present application relates to the technical field of battery, and particularly relates to a core-shell material, a preparation method thereof and a negative electrode material. The preparation method of the core-shell material comprises the following steps: providing metal raw materials of magnesium, copper, aluminum, zirconium and lithium; pretreating the metal raw materials into five-element alloy powder; placing the five-element alloy powder in an inert gas atmosphere or a micro-oxygen atmosphere; and sequentially performing temperature rising treatment and constant temperature annealing treatment on the five-element alloy powder. In the temperature rising treatment stage, the core layer Al3Zr and the shell layer Al3Li in the core-shell material are formed. After the core layer and the shell layer are formed, the zirconium atoms and the lithium atoms diffuse with each other at the interface between the core layer and the shell layer to form a transition layer Al3(Zr, Li). In the constant temperature annealing treatment stage, magnesium and copper form Mg2Cu3 phase which is directly bonded with the surface of the shell layer, and the copper atoms are directly bonded with the surface of the shell layer, so as to form the Al3Zr@Al3Li core-shell material. A preparation method of a core-shell material with mechanical strengthening and volume buffer is sought.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a core-shell material and a preparation method thereof, and a negative electrode material. BACKGROUND

[0002] With the surge in demand for high-energy-density batteries, lithium metal anodes have become a research hotspot due to their ultra-high theoretical capacity, but the severe volume expansion and uncontrollable dendrite growth during the cycling process seriously restrict their practical application. The existing technology usually introduces a buffer structure to relieve the expansion, but there are still significant defects: for example, the existing technology uses a traditional homogeneous alloy electrode, although the homogeneous alloy powder has a certain anti-expansion ability, but under the huge volume change of long-term cycling of the battery, the single alloy particle itself cracks and even pulverizes. In addition, the high-temperature sintering process is often used in the preparation process of the traditional homogeneous alloy electrode, which forms a process contradiction with the low melting point characteristics of lithium metal. Therefore, it is urgent to develop a material that has both mechanical strengthening and volume buffering functions, which is of decisive significance for promoting the industrialization of lithium metal anodes. SUMMARY

[0003] In order to solve the problem of low eutectic efficiency of the preparation method of the traditional core-shell material, the present application provides a core-shell material and a preparation method thereof, and a negative electrode material.

[0004] In order to solve the above technical problems, the present application provides the following technical solutions: a preparation method of a core-shell material, providing metal raw materials of magnesium, copper, aluminum, zirconium and lithium, pretreating the metal raw materials into a five-element alloy powder; placing the five-element alloy powder in an inert gas atmosphere or a micro-oxygen atmosphere, and sequentially performing temperature rising treatment and constant temperature annealing treatment on the five-element alloy powder; wherein the aluminum atoms of the five-element alloy powder are enriched to form a continuous phase of aluminum, the five-element alloy powder is heated in the temperature rising treatment stage, the zirconium atoms diffuse into the continuous phase of aluminum to form a core layer Al3Zr in the core-shell material, the lithium atoms diffuse into the continuous phase of aluminum to form a shell layer Al3Li in the core-shell material, and after the formation of the core layer and the shell layer, the zirconium atoms and the lithium atoms diffuse into each other at the interface between the core layer and the shell layer to form a transition layer Al3(Zr, Li); the heated five-element alloy powder is subjected to heat preservation and cooling in the constant temperature annealing treatment stage, when the five-element alloy powder is placed in an inert gas atmosphere, magnesium and copper form Mg2Cu3 phase which is directly bonded to the surface of the shell layer, and copper atoms are directly bonded to the surface of the shell layer, or when the five-element alloy powder is placed in a micro-oxygen atmosphere, magnesium and copper form Mg2Cu3 phase, the Mg2Cu3 phase is bonded to the surface of the shell layer through Mg-O bond, and copper atoms are bonded to the surface of the shell layer through Cu-O-Al bond, so as to form an Al3Zr@Al3Li core-shell material.

[0005] Preferably, the metal raw materials of magnesium, copper and aluminum are provided, the metal raw materials are prepared into a ternary alloy powder based on a preset smelting method; a metal zirconium powder is provided, the ternary alloy powder and the metal zirconium powder are mixed to form a quaternary alloy powder; a metal lithium powder is provided, the quaternary alloy powder is preheated under an inert gas atmosphere, and then the metal lithium powder is added to continue heating and cooling treatment to form a quinary alloy powder, wherein the particle size of the prepared alloy powder ranges from 10 to 110 μm; and the required particle size range is 10 to 30 μm.

[0006] Preferably, the preparation of the metal raw materials into a ternary alloy powder based on a preset smelting method comprises: providing metal raw materials of magnesium, copper and aluminum, wherein the mass ratio of magnesium, copper and aluminum in the metal raw materials is: 40-50%: 20-25%: 20-25%; the metal raw materials are sequentially placed in an inert atmosphere for smelting treatment to obtain a ternary alloy melt with a structure of (copper-aluminum-magnesium); the ternary alloy melt is atomized into an aerosol, and the aerosol is cooled to obtain a prepared alloy powder; and the prepared alloy powder is screened to obtain a ternary alloy powder of (copper-aluminum-magnesium) with a required particle size range.

[0007] Preferably, the smelting treatment comprises: introducing an inert gas under a vacuum environment with a pressure less than or equal to 10 -2 Mpa, heating from room temperature to 1000-1100℃ at a heating rate of 8-15℃ / min and maintaining for 0.5-1h, so that the metal copper, aluminum and magnesium are sequentially melted, and the molten metal copper, aluminum and magnesium are mixed by electromagnetic stirring at 20-30 Hz to obtain a ternary alloy melt.

[0008] Preferably, the mixing of the ternary alloy powder and the metal zirconium powder to form a quaternary alloy powder comprises: providing a metal zirconium powder, wherein the mass ratio of the ternary alloy powder and the metal zirconium powder is 95-99%: 1-5%; introducing an inert gas under an inert gas atmosphere to perform ball milling at a ball-to-material ratio of 8:1-12:1 and a speed of 30-60 rpm to obtain a (copper-aluminum-magnesium)-zirconium quaternary alloy powder.

[0009] Preferably, the formation of the quinary alloy powder specifically comprises: providing a metal lithium powder, preheating the quaternary alloy powder under an inert gas atmosphere to 170-180℃, then introducing an inert gas and adding the metal lithium powder, and mixing and cooling the quaternary alloy powder and the metal lithium powder heated from 170-180℃ to 185-220℃ to form a quinary alloy powder, wherein the mass ratio of the quaternary alloy powder and the metal lithium powder is 20-30%: 70-80%.

[0010] Preferably, the mixing and cooling process specifically comprises: stirring the mixture of the quaternary alloy powder and the lithium powder at a stirring speed of 50-150 rpm for 10-30 min by using a stirrer; and cooling the mixture from 185-220℃ to room temperature at a cooling rate of 5-15℃ / min after the stirring is stopped, so as to obtain the quinary alloy powder.

[0011] Preferably, the temperature rising process and the isothermal annealing process performed on the quinary alloy powder in sequence comprise: heating the quinary alloy powder to 170-190℃ at a heating rate of 3-8℃ / min at room temperature under an inert gas atmosphere to complete the temperature rising process, wherein during the temperature rising process, zirconium atoms diffuse into the continuous phase of aluminum to form a core layer Al3Zr in the core-shell material, lithium atoms diffuse into the continuous phase of aluminum to wrap the core layer Al3Zr and form a shell layer Al3Li in the core-shell material, and zirconium atoms and lithium atoms mutually diffuse at the interface of the core layer and the shell layer to form a transition layer Al3(Zr, Li); after the temperature rising process, the quinary alloy powder is kept at 170-190℃ for 8-15 hours to complete the isothermal annealing process; and after the isothermal annealing process, the quinary alloy powder is cooled to room temperature at a cooling rate of 3-8℃ / min at 170-190℃, wherein when the isothermal annealing process is completed and the cooling is started, Mg2Cu3 phase and copper atoms start to bond with the surface of the shell layer, and when the cooling is completed, Mg2Cu3 phase and copper atoms completely bond with the surface of the shell layer.

[0012] To solve the above technical problems, the present application provides another technical solution as follows: a core-shell material prepared by the preparation method of the core-shell material, the core-shell material comprising a core layer, a transition layer and a shell layer formed in sequence from inside to outside, and a bonding layer arranged on the shell layer; the bonding layer is arranged at the outer periphery of the shell layer and bonded with the shell layer; the core-shell material is Al3Zr@Al3Li, wherein the Al3Zr single crystal is the core layer of the core-shell material, the Al3Li single crystal is the shell layer of the core-shell material, and the Al3(Zr, Li) solid solution is the interface layer of the core-shell material; the bonding layer comprises Mg2Cu3 and Cu atoms, the Mg2Cu3 and the Cu atoms are respectively bonded with the surface of the shell layer, or the Mg2Cu3 is bonded with the surface of the shell layer through Mg-O bond, and the Cu atoms are bonded with the surface of the shell layer through Cu-O-Al bond.

[0013] To solve the above technical problems, the present application provides another technical solution as follows: a negative electrode material comprising a substrate layer, a buffer layer and a lithium-rich layer arranged in sequence, the substrate layer being a carbon fiber material, the lithium-rich layer comprising a first lithium metal matrix, the buffer layer comprising a second lithium metal matrix and buffer pores and the core-shell material distributed inside the second lithium metal matrix, and the substrate layer comprising a third lithium metal matrix and a modified carbon skeleton distributed inside the third lithium metal matrix.

[0014] Compared with the prior art, the core-shell material and the preparation method thereof and the negative electrode material have the following beneficial effects:

[0015] 1. The preparation method of the core-shell material provided by the embodiment of the present application comprises the following steps: providing metal raw materials of magnesium, copper, aluminum, zirconium and lithium, pretreating the metal raw materials into a five-element alloy powder; placing the five-element alloy powder in an inert gas atmosphere or a micro-oxygen atmosphere, and sequentially performing temperature rising treatment and constant temperature annealing treatment on the five-element alloy powder; wherein the aluminum atoms of the five-element alloy powder are enriched to form a continuous phase of aluminum, the five-element alloy powder is heated in the temperature rising treatment stage, the zirconium atoms diffuse into the continuous phase of aluminum to form a core layer Al3Zr in the core-shell material, the lithium atoms diffuse into the continuous phase of aluminum to form a shell layer Al3Li in the core-shell material, after the formation of the core layer and the shell layer, the zirconium atoms and the lithium atoms mutually diffuse at the interface between the core layer and the shell layer to form a transition layer Al3(Zr, Li); the heated five-element alloy powder is subjected to heat preservation and cooling in the constant temperature annealing treatment stage, when the five-element alloy powder is placed in the inert gas atmosphere, magnesium and copper form a Mg2Cu3 phase which is directly bonded to the surface of the shell layer, and copper atoms are directly bonded to the surface of the shell layer, or when the five-element alloy powder is placed in the micro-oxygen atmosphere, magnesium and copper form a Mg2Cu3 phase, the Mg2Cu3 phase is bonded to the surface of the shell layer through a Mg-O bond, and copper atoms are bonded to the surface of the shell layer through a Cu-O-Al bond, so as to form an Al3Zr@Al3Li core-shell material. The Al3Zr@Al3Li core-shell material prepared by the method of the embodiment has a unique core-shell structure, provides good mechanical support for the core layer, effectively resists external stress, the hard core layer can also effectively resist volume expansion and physically block dendrite penetration; the shell layer provides rich active sites for the embedding and extraction of lithium ions due to its high lithium content, which helps to improve the electrochemical activity of the material. At the same time, the existence of the transition layer Al3(Zr, Li) is like a “buffer zone”, which effectively relieves the stress between the core layer and the shell layer due to the difference in the thermal expansion coefficient, further improves the cycle stability of the material, and solves the problem of weak anti-expansion ability in the traditional homogeneous alloy electrode.

[0016] 2. The embodiment of the present application comprises the following steps: providing metal raw materials of magnesium, copper and aluminum, wherein the mass ratio of magnesium, copper and aluminum in the metal raw materials is 40-50%, 20-25% and 20-25% respectively; placing the metal raw materials in the order of copper, aluminum and magnesium in an inert atmosphere for smelting treatment to obtain a ternary alloy melt with a structure of (copper-aluminum-magnesium); performing atomization treatment on the ternary alloy melt to obtain an aerosol, and obtaining a preformed alloy powder through cooling treatment; and performing screening treatment on the preformed alloy powder to obtain a ternary alloy powder with a required particle size range (copper-aluminum-magnesium). The loading of "base layer Cu, middle layer Al and top layer Mg" can optimize the element diffusion path and ensure the uniformity of alloy composition.

[0017] 3. The embodiment of the present application comprises the following steps: introducing inert gas in a vacuum environment with a pressure less than or equal to 10 Mpa, and heating from room temperature to 1000-1100℃ at a heating rate of 8-15℃ / min and maintaining for 0.5-1h, so that the copper, aluminum and magnesium are sequentially melted, and the molten copper, aluminum and magnesium are mixed to obtain a ternary alloy melt. The layered smelting avoids alloy composition segregation caused by density difference. -2

[0018] 4. The particle size range of the preformed alloy powder is 10-110μm, and the required particle size range is 10-30μm. The 10-30μm powder can be partially melted during hot pressing, which can fill the pores of the carbon skeleton and avoid structural collapse caused by complete liquefaction.

[0019] 5. The embodiment of the present application comprises the following steps: providing a metal zirconium powder, wherein the mass ratio of the ternary alloy powder and the metal zirconium powder is 95-99%:1-5%; and placing the ternary alloy powder in an inert gas atmosphere to introduce inert gas, and performing ball milling treatment at a ball milling speed of 30-60 rpm and a ball-to-material ratio of 8:1-12:1 to obtain a (copper-aluminum-magnesium)-zirconium quaternary alloy powder. Zr is a key constituent element of the core layer, and its uniform dispersion directly determines the number and distribution of core phases. By limiting the mass ratio of Zr, the balance between strengthening effect and cost is achieved.

[0020] 6. The embodiment of the present application comprises the following steps: the mass ratio of the quaternary alloy powder and the metal lithium powder is 20-30%:70-80%; a stirrer is used to stir the mixture of the quaternary alloy powder and the metal lithium powder at a stirring speed of 50-150 rpm for 10-30 min; and the mixture is cooled from 185-220℃ to room temperature at a cooling rate of 5-15℃ / min after the stirring is stopped to obtain a quinary alloy powder. By introducing lithium elements at low temperature, the problems of Li loss and insufficient alloying caused by high-temperature lithiation are avoided.​

[0021] 7. The embodiment of the present application further provides a core-shell material, the core-shell material comprising a core layer, a transition layer and a shell layer formed in sequence from inside to outside, and a bonding layer arranged on the shell layer; the bonding layer is arranged at the outer periphery of the shell layer and is bonded with the shell layer; the core-shell material is Al3Zr@Al3Li, wherein the Al3Zr single crystal is the core layer of the core-shell material, the Al3Li single crystal is the shell layer of the core-shell material, the Al3(Zr, Li) solid solution is the interface layer of the core-shell material, and the bonding layer comprises Mg2Cu3 and Cu atoms, the Mg2Cu3 and the Cu atoms are respectively bonded with the surface of the shell layer, or the Mg2Cu3 is bonded with the surface of the shell layer through Mg-O bonding, and the Cu atom is bonded with the surface of the shell layer through Cu-O-Al bonding. The core-shell material of the embodiment solves the vicious cycle problem of "expansion-dendrite-failure" of the traditional lithium metal negative electrode. In the Al3Zr@Al3Li core-shell structure: the high modulus Al3Zr inner core can inhibit the volume expansion in the cycle process, and the flexible Al3Li outer shell buffers the stress through plastic deformation, and the two can synergistically greatly improve the electrode anti-expansion performance.

[0022] 8. The embodiment of the present application further provides a negative electrode material, comprising a substrate layer, a buffer layer and a lithium-rich layer arranged in sequence, the lithium-rich layer comprising a first lithium metal matrix, the buffer layer comprising a second lithium metal matrix and buffer pores and core-shell materials distributed in the second lithium metal matrix, and the substrate layer comprising a third lithium metal matrix and a modified carbon skeleton distributed in the third lithium metal matrix, and the second lithium metal matrix being arranged between the first lithium metal matrix and the third lithium metal matrix. The negative electrode material provided by the embodiment solves the technical contradiction that a single material cannot simultaneously have high capacity and low expansion. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0024] Figure 1 is a flowchart of the preparation method of the core-shell material provided by the first embodiment of the present application.

[0025] Figure 2 is a distribution diagram of the internal structure of the core-shell material provided by the second embodiment of the present application.

[0026] Figure 3 is a sectional view of the core-shell material along its diameter direction provided by the second embodiment of the present application.

[0027] Figure 4 Figure 3 is a structural schematic diagram of a negative electrode material provided by a third embodiment of the present application.

[0028] Explanation of the drawing:

[0029] 1, base layer; 2, buffer layer; 3, lithium-rich layer;

[0030] 11, first lithium metal matrix; 21, second lithium metal matrix; 22, buffer pore; 23, core-shell material; 31, third lithium metal matrix; 32, modified carbon skeleton. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0032] In the embodiments provided by the present application, it should be understood that "B corresponding to A" means that B is associated with A, and B can be determined according to A. However, it should also be understood that the determination of B according to A does not mean that B is determined only according to A, but B can also be determined according to A and / or other information.

[0033] It should be understood that "one embodiment" or "an embodiment" mentioned throughout the specification means that the specific features, structures or characteristics related to the embodiment are included in at least one embodiment of the present application. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. In addition, these specific features, structures or characteristics can be combined in one or more embodiments in any suitable manner. Those skilled in the art should also know that the embodiments described in the specification are all optional embodiments, and the actions and modules involved are not necessarily required by the present application.

[0034] In various embodiments of the present application, it should be understood that the size of the serial number of the above processes does not mean the inevitable sequence of execution, and the execution sequence of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0035] In the flowcharts and block diagrams of the drawings of the present application, the methods and possible implemented architectures, functions and operations according to various embodiments of the present application are illustrated. In this regard, each block in the flowchart or block diagram can represent a part of a step. It should also be noted that in some alternative implementations, the functions indicated in the blocks can also occur in a different order from that indicated in the drawings. For example, two blocks indicated in succession can actually be executed substantially in parallel, and sometimes they can be executed in reverse order, depending on the functions involved.

[0036] With the surge in demand for high energy density batteries, lithium metal anode has become a research hotspot due to its ultra-high theoretical capacity, but the severe volume expansion and uncontrollable dendrite growth during the cycle process seriously restrict its practical application. The existing technology usually introduces a buffer structure to relieve the expansion, but there are still significant defects.

[0037] For example, the homogeneous alloy electrode in the prior art introduces homogeneous alloy powder to enable the electrode to obtain certain anti-expansion ability. However, when the battery is cycled, the entire alloy powder particles will uniformly expand and shrink as a whole. The whole particle "breathes" when lithium is inserted and extracted. That is, when discharging, the whole particle expands, and a huge extrusion force is generated inside; when charging, the whole particle shrinks, and a tensile stress is generated inside. This repeated "extrusion-tension" cycle is like repeatedly bending a metal wire, which eventually leads to cracking or even pulverization of the single alloy particle itself. Therefore, such a homogeneous alloy electrode still generates a large stress on the electrode structure, and may still lead to particle pulverization or falling off from the current collector after long-term cycling. In addition, the high-temperature sintering process is often used in the preparation process of the traditional homogeneous alloy electrode, which is inconsistent with the low melting point characteristics of lithium metal. The smelting temperature is extremely high, the energy consumption is huge, and it is a great test for the equipment. At the same time, lithium is extremely easy to volatilize and oxidize at high temperature, resulting in inaccurate composition control and poor batch stability. Therefore, it is urgent to develop a kind of mechanical strengthening and volume buffer, which is of decisive significance to promote the industrialization of lithium metal anode.

[0038] Please refer to Figure 1 The first embodiment of the present application provides a preparation method of core-shell material, which comprises the following steps:

[0039] A1, providing metal raw materials of magnesium, copper, aluminum, zirconium and lithium, and pretreating the metal raw materials into a five-element alloy powder;

[0040] A2, placing the five-element alloy powder in an inert gas atmosphere or a micro-oxygen atmosphere, and sequentially performing temperature rising treatment and constant temperature annealing treatment on the five-element alloy powder;

[0041] The aluminum atoms of the five-element alloy powder are enriched to form a continuous phase of aluminum, the five-element alloy powder is heated in the temperature rising treatment stage, the zirconium atoms diffuse into the continuous phase of aluminum to form a core layer Al3Zr in the core-shell material, the lithium atoms diffuse into the continuous phase of aluminum to form a shell layer Al3Li in the core-shell material, and after the core layer and the shell layer are formed, the zirconium atoms and the lithium atoms diffuse into each other at the interface between the core layer and the shell layer to form a transition layer Al3(Zr, Li);

[0042] The heated five-element alloy powder is subjected to heat preservation and cooling in the constant temperature annealing treatment stage,

[0043] When the quinary alloy powder is placed in an inert gas atmosphere, magnesium and copper form Mg2Cu3 phase which directly bonds with the surface of the shell layer, and copper atoms directly bond with the surface of the shell layer,

[0044] Or, when the quinary alloy powder is placed in a micro-oxygen atmosphere, magnesium and copper form Mg2Cu3 phase, the Mg2Cu3 phase bonds with the surface of the shell layer through Mg-O bond, and copper atoms bond with the surface of the shell layer through Cu-O-Al bond, to form an Al3Zr@Al3Li core-shell material.

[0045] It should be noted that bonding refers to the process and result of two or more objects, usually solid surfaces, forming a strong connection at the contact interface through the interaction between atoms, molecules or ions at the interface. In this embodiment, the inert gas atmosphere refers to placing the material in a sealed environment with inert gas being introduced, wherein the inert gas cannot chemically react with the five metals, which can be argon, helium, neon, krypton, xenon. In the quinary alloy powder, aluminum elements form an enrichment region, i.e. a continuous phase mainly composed of aluminum atoms, which is usually referred to as "aluminum phase" or "continuous aluminum phase" hereinafter. During the temperature rising treatment stage, due to the different diffusion rates of element atoms, zirconium atoms, due to their relatively small atomic radius and high diffusion activity, preferentially diffuse into the continuous aluminum phase and react with aluminum atoms to form a core layer. At the same time, lithium atoms also diffuse into the continuous aluminum phase and combine with aluminum atoms to form a shell layer. During this process, the core layer and the shell layer are not completely independent, but at the interface between the core layer and the shell layer, zirconium atoms and lithium atoms interdiffuse to form a transition layer Al3(Zr, Li) with unique structure and performance. The existence of the transition layer not only enhances the bonding force between the core layer and the shell layer, but also effectively relieves the stress concentration problem caused by uneven element diffusion.

[0046] During the isothermal annealing stage, magnesium and copper elements react on the surface of the continuous phase of aluminum to form Mg2Cu3 phase and tightly bond with the surface of the shell layer. The formation of Mg2Cu3 phase further enhances the structural stability of the core-shell material. Copper atoms also bond with the surface of the shell layer during this stage, which helps to optimize the surface properties of the shell layer and improve its electrochemical performance. It should be noted that the micro-oxygen environment refers to the oxygen content required for the formation of Cu-O-Al bonds being less than 0.1 ppm and the oxygen content required for the formation of Mg-O bonds being less than 1 ppm. In the micro-oxygen environment, oxygen forms Mg-O bonds with Mg in the Mg2Cu3 phase and Cu-O-Al bonds with Al and Cu atomic nuclei in the shell layer. The Mg-O bonds and Cu-O-Al bonds function to bond the Mg2Cu3 phase and the shell layer and bond the Cu atoms and the shell layer. The Al3Zr@Al3Li core-shell material prepared by the method of the present embodiment has a unique core-shell structure. The core layer provides good mechanical support, effectively resisting external stress. The hard core layer can also effectively resist volume expansion and physically block dendrite penetration. The shell layer provides abundant active sites for lithium ion intercalation and deintercalation due to its high lithium content, which helps to improve the electrochemical activity of the material. At the same time, the existence of the transition layer Al3(Zr, Li) acts as a "buffer zone" to effectively relieve the stress between the core layer and the shell layer due to the difference in thermal expansion coefficient, further improving the cycle stability of the material. The design of this core-shell structure not only solves the problem of cracking and pulverization of homogeneous alloy electrodes during the cycling process due to the overall "breathing", but also achieves the dual effect of mechanical strengthening and volume buffering through the synergistic effect between the layers, providing strong material support for the industrial application of lithium metal anodes.

[0047] Specifically, the preparation method of the core-shell material further comprises the following steps:

[0048] S1, providing metal raw materials of magnesium, copper and aluminum, and preparing the metal raw materials into a ternary alloy powder based on a predetermined melting method;

[0049] S2, providing a metal zirconium powder, mixing the ternary alloy powder and the metal zirconium powder to form a quaternary alloy powder;

[0050] S3, providing a metal lithium powder, preheating the quaternary alloy powder under an inert gas atmosphere, then adding the metal lithium powder to continue heating and cooling treatment to form a quinary alloy powder; and

[0051] S4, placing the quinary alloy powder in an inert gas atmosphere or a micro-oxygen atmosphere, and sequentially performing temperature rising treatment and isothermal annealing treatment on the quinary alloy powder;

[0052] wherein the aluminum atoms of the quinary alloy powder are enriched to form a continuous phase of aluminum;

[0053] During the temperature rising treatment stage, zirconium atoms diffuse into the continuous phase of aluminum to form the core layer Al3Zr in the core-shell material, lithium atoms diffuse into the continuous phase of aluminum to form the shell layer Al3Li in the core-shell material, and after the formation of the core layer and the shell layer, zirconium atoms and lithium atoms diffuse into each other at the interface between the core layer and the shell layer to form a transition layer Al3(Zr, Li);

[0054] When the five-element alloy powder is placed in an inert gas atmosphere, during the constant temperature annealing treatment stage, magnesium and copper form the Mg2Cu3 phase which is directly bonded to the surface of the shell layer, and copper atoms are directly bonded to the surface of the shell layer; or

[0055] When the five-element alloy powder is placed in a micro-oxygen atmosphere, during the constant temperature annealing treatment stage, magnesium and copper form the Mg2Cu3 phase, the Mg2Cu3 phase is bonded to the surface of the shell layer through Mg-O bonds, and copper atoms are bonded to the surface of the shell layer through Cu-O-Al bonds, to form the Al3Zr@Al3Li core-shell material.

[0056] Specifically, the method adopts a distributed mixing process to realize the gradient diffusion and uniform distribution of elements from ternary alloy powder: (Mg-Al-Cu) alloy, to quaternary alloy powder: (Mg-Al-Cu)-Zr alloy, and then to five-element alloy powder: Li-(Mg-Al-Cu)-Zr. If multiple elements are directly mixed, it is easy to cause the phenomenon of "local enrichment-macroscopic segregation", that is, the concentration of a certain element in the alloy powder is much higher than the designed value in the microcosmic preparation process, forming element aggregation. While in the macroscopic electrode material, the element distribution presents a gradient difference, forming "composition stratification". The method realizes the uniform mixing of the five elements at the atomic scale through the distributed mixing process, lays a foundation for the formation of the core-shell structure, and is beneficial to the subsequent formation of the core-shell structure of the five-element alloy powder.

[0057] Further, the embodiment adopts step-by-step alloying to prepare the five-element alloy powder, and then the core-shell material is prepared by sequentially performing temperature rising treatment and isothermal annealing treatment on the five-element alloy powder. The three stages of temperature rising treatment and isothermal annealing treatment are important steps for forming the core-shell material. Specifically, in the process of steps S1 to S3, the main role is to prepare the five-element alloy powder as a precursor, specifically to prepare a microscopically inhomogeneous mixture, to prepare all elements for the subsequent reaction, and to fix them in the correct position. In the step-by-step alloying, the preparation of the ternary alloy powder can obtain the Mg-Al-Cu solid solution powder. That is, Al, Cu and Mg atoms are mixed at high temperature, and after cooling, a metastable solid solution is formed without independent intermetallic compounds. Zr is physically embedded and pressed on the surface of the (Mg-Al-Cu) solid solution powder. This process is only physical mixing, and Al3Zr is not formed. Zr element is placed beside the Al phase in the (Mg-Al-Cu) solid solution as a "seed", forming (Mg-Al-Cu)-Zr composite particles. Further, the Li powder is melted by heating to melt and wrap the alloy powder. A mixture of Li matrix and (Mg-Al-Cu)-Zr composite particles is formed. At this time, Al3Li has not been formed, and Li only exists as a matrix. The finally formed five-element alloy powder is an ideal precursor, that is, the Li matrix wraps the Al phase particles containing "Zr seeds", and the uniformity of each element in the five-element alloy powder is good, which completes the preliminary work for the subsequent temperature rising treatment stage of Zr diffusion into the Al phase and Li atom diffusion into the Al phase.

[0058] Specifically, in the heating treatment stage, Zr atoms in the region of Al element enrichment in the original powder particles obtain enough energy and start to diffuse in the Al phase particles. When the local Zr concentration in the Al phase reaches a critical value, the solubility of Zr atoms in the Al matrix decreases, so that the supersaturated Zr atoms will gather and precipitate. Because the growth rate is slow, the atoms have enough time to arrange neatly, thereby forming a single crystal, that is, a stable Al3Zr crystal nucleus will be formed and gradually grow. Also during the heating treatment stage, the shell layer usually occurs at the same time or later than the core layer. Li atoms have enough diffusion capacity at the annealing temperature, and Li atoms diffuse from the surrounding Li matrix to the particle surface and react with the Al phase on the particle surface layer. Specifically, they will react with the Al-rich phase wrapped around the core layer that does not participate in the reaction to generate Al3Li in situ, thereby completely coating the outer surface of the core layer to form a shell layer. Because the core layer grows inside and consumes the internal Al atoms, the Al atom concentration of the outer layer of the particle is reduced, creating conditions for the infiltration and reaction of Li, thereby ultimately forming a coated structure with the core layer as the inner layer and the shell layer as the outer layer. During the constant temperature treatment stage and the annealing treatment stage, usually at the end of the constant temperature treatment, Al3Zr and Al3Li at the interface of the two phases adjust slightly to realize the connection of the coherent or semi-coherent interface after constant temperature treatment to the end of annealing. During the annealing treatment stage, the interface structure further relaxes to form a firm metal bond as the temperature cools down. Specifically, after the core layer and the shell layer of the core-shell material are formed, a small amount of Zr atoms and Li atoms will diffuse into each other's lattices at the interface of the core and the shell, forming a compositionally graded solid solution layer, namely Al3(Zr, Li).

[0059] Further, in the step-by-step alloying preparation, that is, in step S3, lithium, copper and magnesium elements will form a Li-Mg-Cu matrix. In the constant temperature annealing treatment stage, magnesium and copper elements in the matrix will form Mg2Cu3 phase, which will bond with lithium on the shell layer, and the Mg2Cu3 phase will continue to grow and stabilize during the annealing process. Cu atoms diffuse from the matrix to the surface of the shell layer and enrich on the surface of the shell layer through surface segregation effect to form a bond.

[0060] It should be noted that in step S1, some natural oxide film such as Al2O3 may be left in the provided metal raw material magnesium, copper and aluminum. In the alloy distribution in the preparation of step alloying, a trace amount of oxygen may also be involved, forming a trace amount of oxide on the surface of the powder. Therefore, in addition to the Mg2Cu3 phase and Cu atoms bonded to the shell layer, the Mg2Cu3 phase may also be bonded to the surface of the shell layer through Mg-O bonds, and the Cu atoms may also be bonded to the surface of the shell layer through Cu-O-Al bonds. The core-shell material formed in this way is only different in the bonding layer, and the effect achieved is the same as that of the above-mentioned core-shell material, so it will not be described in detail here.

[0061] It should be noted that the thickness of the core-shell material mainly includes two aspects, one is the diffusion process, and the other is the raw material ratio. The diffusion process is related to temperature and time:

[0062] The time-related part is mainly associated with the diffusion distance formula:

[0063] x ≈ where x is the diffusion depth / thickness, D is the diffusion coefficient, and t is the time.

[0064] The temperature-related part is mainly associated with the Arrhenius formula:

[0065] D = D0 exp(-Q / RT), where D is the diffusion coefficient

[0066] Al3(Zr3Li) solid solution transition layer thickness: mainly related to temperature and time. The transition layer is the result of mutual diffusion of Zr and Li atoms in the Al matrix.

[0067] Therefore, the temperature determines the speed of atomic diffusion, and the time determines the depth of diffusion. Specifically, the thickness of the core layer (Al3Zr) is related to the time, temperature, and ratio. The growth of the core is a process of small particles dissolving and large particles growing. The longer the time, the larger the average size of the particles. The higher the temperature, the faster the growth rate. The total content of Zr in the raw material determines the number density of the core, which indirectly affects the final size. When the Zr content is fixed, the more the number of cores, the smaller the size of the individual core. The thickness of the shell layer (Al3Li) is also related to the ratio, time, and temperature. The thickness of the shell directly depends on the total amount of Li element available for reaction with Al to form Al3Li. The Li content is excessive, so how thick the shell can grow depends on the amount of Li atoms diffusing to the surface of the Al phase. This is also controlled by the diffusion law. The diffusion speed of Li atoms is faster than that of Zr, so under the same annealing conditions, the growth of the shell layer is also limited by the diffusion process. It should be understood that in this embodiment, by limiting the process parameters of the temperature rising treatment and the constant temperature annealing treatment, the diffusion of Zr and Li atoms is just allowed to be 2-5 nm. If the time is too short, the layer is incomplete, and if the time is too long, the element distribution is too uniform, losing the "core-shell" characteristics.

[0068] Further, in the step S1, the metal raw material is prepared into the ternary alloy powder based on a preset melting method, which comprises:

[0069] S11, providing metal raw materials of magnesium, copper and aluminum, wherein the mass ratio of magnesium, copper and aluminum in the metal raw materials is: 40-50%: 20-25%: 20-25%;

[0070] S12, the metal raw materials are placed in the inert atmosphere in the order of copper, aluminum and magnesium for melting treatment to obtain a ternary alloy melt with a structure of (copper-aluminum-magnesium);

[0071] S13, the ternary alloy melt is atomized into an aerosol, and the aerosol is cooled to obtain a pre-alloy powder; and

[0072] S14, the pre-alloy powder is screened to obtain a (copper-aluminum-magnesium) ternary alloy powder with a required particle size range.

[0073] It can be understood that the embodiment solves the problem of uneven core-shell coating caused by wide particle size distribution and low sphericity in the traditional powder preparation process by precisely controlling the raw material ratio and powder screening process. The composition and particle size of the ternary alloy powder are important factors for the formation of the core-shell structure, and the mass ratio of Mg, Cu and Al is (40-50%:20-25%:20-25%). Alternatively, the mass ratio of Mg, Cu and Al can also be (48-58%) : (18-23%) : (18-23%), (35-45%) : (25-30%) : (25-30%) or (42-46%) : (24-26%) : (24-26%). The mass ratio of Mg, Cu and Al is strictly controlled to ensure the formation of Mg2Cu3 bonding phase. The method optimizes the raw material ratio, so that Mg is dissolved in the Li matrix as an expansion inhibitor, Cu forms a conductive network, and Al is the main constituent element of the core-shell phase, and the three achieve the multifunctional integration of "inhibiting expansion, improving conductivity and building core-shell".

[0074] In addition, in the embodiment, the order of raw material input is Cu as the base layer, Al as the middle layer and Mg as the top layer. The loading sequence is mainly considered from the preparation process: the top layer Mg is a low melting point element, the melting point of Mg is 650°C, and the density of Mg is small, which is 1.74 g / cm³. It melts the fastest and floats naturally after melting to cover the liquid surface, isolating oxygen; the middle layer Al is a medium melting point, the melting point of Al is 660°C, which melts into Cu-Al pre-alloy downward and assists Mg melting upward; the base layer Cu is a high melting point element, the melting point of Cu is 1083°C, and Cu melts to form a liquid pool as an atomic diffusion skeleton. It should be noted that when Cu melts, Al has already melted and mixed with Cu, and Mg has also become liquid and covered on the surface of the molten pool to play a protective role. Specifically, if Cu is placed on the top layer, the unmelted Cu blocks the mixing process of the three metal elements, resulting in uneven composition. According to the loading of "base layer Cu, middle layer Al and top layer Mg", the element diffusion path can be optimized to ensure the uniformity of the alloy composition. The role of Cu is as a conductive skeleton. The role of Al is as a core-shell phase precursor: reacting with Zr to form a core layer and reacting with Li to form a shell layer. The role of Mg is an expansion inhibitor: solid solution in Li to form Mg-Li solid solution to inhibit the volume expansion of lithium deposition. The final form is a homogeneous ternary alloy melt, and the ternary alloy melt is not a layered structure. The ternary alloy melt forms a composition-uniform spherical powder after gas atomization.

[0075] Further, the particle size range of the pre-alloyed powder is 10-110 pm; and the required particle size range is 10-30 pm. Alternatively, the particle size range of the pre-alloyed powder can also be 10-30 pm, 20-50 pm, 70-100 pm or 40-80 pm; and the required particle size range is 10-30 pm. The required particle size range can also be 10-20 pm, 15-30 pm, 10-15 pm or 20-25 pm. Specifically, the conventional particle size of the sieved ternary alloy powder is mainly 10-110 pm, and the 10-30 pm segment needs to be obtained by precise sieving (yield less than or equal to 25%) due to its high sphericity and excellent core-shell structure adaptability. This screening is a key process control point for realizing uniform growth of core-shell phases and low expansion electrode structure. It should be understood that the powder is sieved in a glove box (where the gas environment is O2 / H2O < 0.1 ppm), and the 10-30 pm particle size segment is taken. The effect of the gas atomization powdering and precise sieving steps is to ensure the integrity of the core-shell structure.

[0076] Specifically, when the coarse powder is greater than 30 pm, the shell layer will be broken due to the excessively long diffusion path, and when the fine powder is less than 10 pm, the specific surface area will be too large to cause preferential oxidation of Li. This method atomizes by passing inert gas such as argon at 3-5 MPa to obtain a high-sphericity powder at a cooling rate greater than or equal to 10 4 K / s, and the 10-30 pm segment is selected by glove box sieving, and its specific surface area of 0.2-0.5 m² / g can ensure that the diffusion distance of Zr / Li elements during annealing is controlled at 2-5 nm, so that the core-shell coating rate is greater than 95%. In addition, this particle size range provides adaptability for subsequent gradient composite processes. Specifically, the 10-30 pm powder can be partially melted during hot pressing, and the Mg-Li eutectic point is approximately 430°C, which can fill the pore space of the carbon skeleton and avoid structural collapse caused by complete liquefaction. By limiting the particle size range of the powder, this embodiment solves the adaptability problem of core-shell structure growth and gradient composite process.

[0077] Further, the melting treatment in the above step S12 includes:

[0078] The pressure of the inert atmosphere is less than or equal to 10 -2 Mpa, and the temperature is raised from room temperature to 1000-1100°C at a temperature rise rate of 8-15°C / min and held for 0.5-1 h, so that the metal copper, aluminum and magnesium are sequentially melted, and the molten metal copper, aluminum and magnesium are stirred and mixed to obtain a ternary alloy melt. Specifically, the stirring and mixing method can be electromagnetic stirring, and the frequency can be 15-35 Hz.

[0079] Optionally, the heating rate can also be 8-10℃ / min, 9-13℃ / min or 10-15℃ / min. The temperature range after heating can also be 1000-1050℃, 1020-1100℃ or 1080-1100℃. The above holding time can also be 0.5-1h, 0.5-0.8h, or 0.6-1h. The frequency of electromagnetic stirring can also be 15-25Hz, 15-20Hz or 15-30Hz.

[0080] Understandably, the embodiment solves the composition segregation problem caused by insufficient element diffusion in traditional alloy preparation by optimizing the vacuum melting parameters. The melting point difference of the metal raw materials is specifically manifested in that the melting point of Cu is 1083℃, the melting point of Al is 660℃, and the melting point of Mg is 650℃, which easily leads to "stratified solidification", and the method realizes atomic-level mixing of elements through the charging sequence of "base layer Cu, middle layer Al, top layer Mg" and the stepwise heating strategy. It should be noted that the ternary alloy melt formed after mixing is not a layered structure.

[0081] If mixed melting, the vapor pressure of Mg is extremely high, and it will evaporate violently at 1050℃, and the melting point of Cu is much higher than that of Mg. If direct mixing, when Cu melts, Mg has been gasified almost completely.

[0082] If separately melted and then mixed, when the 1083℃ Cu melt is injected into the 650℃ Mg melt, the interface temperature exceeds 900℃ instantaneously, the vapor pressure of Mg increases by 1000 times, the melt splashes and explodes, and there is a risk of preparation. And after separate melting and mixing, the melt is easily exposed to air during transfer, MgO hard shell is generated on the surface of the Mg liquid, and the alloy is difficult to mix uniformly.

[0083] Specifically, first heat to 1000-1100℃ to completely melt the high-melting-point Cu to form a melt pool, and heat while electromagnetic stirring to promote the diffusion of Al and Mg to the Cu melt pool, which can effectively avoid gravity segregation caused by density difference.

[0084] Further, the vacuum degree is controlled to be less than or equal to 10 -2 Mpa and inert gas atmosphere, and inert gas is introduced, which can be 0.5-0.8 atm10 -2Mpa, the oxidation of active metals can be effectively inhibited. Specifically, Mg is easy to react with oxygen to form MgO inclusions in the molten state, and the method excludes air by pre-vacuuming and fills in argon to form a positive pressure protection, so that the oxygen content in the alloy ingot is low. This low-oxygen environment ensures the purity of the subsequent core-shell phase and avoids interface defects caused by oxide inclusions. In addition, the heating rate of 8~15 ℃ / min and the holding time of 0.5~1 h provide sufficient time for element diffusion. If the heating rate is too fast, it will lead to "large undercooling - insufficient grain refinement", and the slow heating and holding in the method ensure the composition uniformity of the ternary alloy ingot.

[0085] Further, in the step S2, mixing the ternary alloy powder and the metal zirconium powder to form a quaternary alloy powder comprises:

[0086] S21, providing a metal zirconium powder, wherein the mass ratio of the ternary alloy powder and the metal zirconium powder is 95~99%:1~5%;

[0087] S22, the ternary alloy powder is placed in an inert gas atmosphere and inert gas is introduced, ball milling is carried out at 30~60 rpm and a ball-to-material ratio of 8:1~12:1 to obtain a (copper-aluminum-magnesium)-zirconium quaternary alloy powder.

[0088] It can be understood that Zr, as a key constituent element of the core layer, its uniform dispersion directly determines the number and distribution of the core phase. Traditional mechanical mixing method is easy to cause Zr agglomeration, and the method adopts "low speed-high ball-to-material ratio" ball milling strategy, wherein the mass ratio of the ternary alloy powder and the metal zirconium powder can also be 95~98%:1~3%, 97~99%:4~5% or 95~96%:3~5%; the ball-to-material speed can also be 30~50 rpm, 40~55 rpm or 35~60 rpm, and the ball-to-material ratio can also be 8:1~10:1, 9:1~12:1 or 11:1~12:1. It should be understood that the embodiment breaks the Zr powder to the nanoscale by the impact and shearing action of the grinding ball and uniformly embeds it into the ternary alloy powder to form a quaternary alloy powder with a structure of (copper-aluminum-magnesium)-zirconium.

[0089] Further, during ball milling, the inert gas can be high-purity argon, and the ball milling time can be 1~4 h, 1~3 h or 3~4 h. The presence of inert gas avoids the oxidation and contamination of metal powder. Zr is easy to form ZrO2 passivation film in air, which hinders its reaction with Al. The method protects Zr by argon and strictly controls the ball milling time, so that the activity surface retention rate of Zr is greater than 90%, which ensures the in-situ generation of the core layer in the subsequent annealing process. Specifically, the ball milling time should not be too long to avoid excessive ball milling heat generation.

[0090] In addition, the mass ratio of 95-99:1-5 achieves a balance between strengthening effect and cost. If the Zr content is too low, the modulus cannot be effectively improved; if the content is too high, Zr agglomeration occurs, causing stress concentration. The present embodiment controls the volume fraction of the core layer by precise proportioning, thereby improving the modulus of the core-shell material and avoiding the problem of cyclic fracture caused by increased brittleness.

[0091] Further, in the step S3, forming the quinary alloy powder specifically includes:

[0092] The quaternary alloy powder is heated to 170-180°C under an inert gas atmosphere, then inert gas is introduced and metal lithium powder is added, the quaternary alloy powder and the metal lithium powder are heated from 170-180°C to 185-220°C, and then mixed and cooled to form the quinary alloy powder.

[0093] Understandably, in the process of introducing lithium, the present method adopts the control principle of distributed temperature control. First, the melting point of Li is only 180.5°C, and traditional high-temperature lithiation usually mixes lithium and alloy at a temperature higher than 250°C, which can cause Li vapor to escape and oxidize. In the present embodiment, the temperature is first raised to 170-180°C for preheating, and then the temperature is raised to 185-220°C, i.e. slightly higher than the melting point of lithium, so that the metal lithium is completely melted, and finally the temperature is controlled to be near the melting point of lithium, to ensure the full melting and diffusion of Li. In addition, the oxidation reaction is inhibited by filling inert gas during smelting. Specifically, the inert gas in the present embodiment can be argon or helium. The distributed temperature control in the present embodiment realizes "low-temperature lithiation" and improves the utilization rate of lithium metal.

[0094] Specifically, the temperature for preheating the quaternary alloy powder before adding lithium can be 170-175°C, 176-180°C or 176-179°C. The temperature for mixing the quaternary alloy powder and lithium metal can be 185-190°C, 200-220°C or 240-220°C. The temperature of 185-220°C is slightly higher than the melting point of lithium, but the temperature is not too high to avoid the loss of lithium vapor.

[0095] Specifically, the mixing and cooling treatment specifically includes: the mass ratio of the quaternary alloy powder to the metal lithium powder is 20-30:70-80%; the mixture of the quaternary alloy powder and the metal lithium powder is stirred at a stirring speed of 50-150 rpm for 10-30 min using a stirrer; after the stirring stops, the mixture is cooled from 185-220°C to room temperature at a cooling rate of 5-15°C / min to obtain the quinary alloy powder.

[0096] It can be understood that the embodiment solves the problems of Li loss and insufficient alloying caused by traditional high-temperature lithiation by optimizing the lithiation temperature and stirring parameters. Li has high chemical activity, and direct high-temperature mixing in the traditional process will cause more than 30% of Li to be lost in the form of steam. However, the present method adopts the strategy of “preheating-segmented heating”: first heat the quaternary alloy powder to 170-180℃, which is slightly lower than the melting point of Li, then add Li powder and heat to 185-220℃, which is in the Li melting range, and inhibit the volatilization of Li through temperature gradient.

[0097] Alternatively, the mass ratio of the quaternary alloy powder to the lithium powder can also be 20-25%: Li 75-80% or 28-30%: 70-72%; the stirring speed can also be 50-70 rpm, 60-120 rpm or 100-150 rpm, and the stirring time can also be 20-30 min or 20-25 min. The cooling rate can also be 5-10℃ / min or 9-12℃ / min.

[0098] Further, the stirring mode of the stirrer is closed propeller stirring, and the stirring promotes uniform contact of Li and alloy powder. Since Li is prone to form “droplet aggregation” after melting, the present method disperses Li droplets through the shearing action of the propeller, increases the solid-liquid reaction interface, and improves the conversion rate of lithiation reaction. This efficient alloying avoids the existence of free Li and reduces the risk of dendrite growth. In addition, the cooling rate is limited in the embodiment, and rapid cooling treatment inhibits the precipitation of coarse Li phase. Slow cooling will cause Li to segregate at the grain boundaries, but the present method controls the size of Li phase by rapid cooling, so that it is uniformly distributed in the matrix, and the plastic deformation ability of the material is improved.

[0099] Further in the step S4, in the embodiment, the temperature rising treatment and the isothermal annealing treatment are sequentially performed, and specifically include the following steps:

[0100] The quinary alloy powder is heated to 170-190℃ at a heating rate of 3-8℃ / min under an inert gas atmosphere at room temperature to complete the temperature rising treatment. During the temperature rising treatment, zirconium atoms diffuse into the continuous phase of aluminum to form the core layer in the core-shell material, lithium atoms diffuse into the continuous phase of aluminum to wrap the core layer and form the shell layer in the core-shell material, and zirconium atoms and lithium atoms mutually diffuse at the interface of the core layer and the shell layer to form a transition layer Al3(Zr, Li);

[0101] After the temperature rising treatment, the temperature is kept at 170-190℃ for 8-15 hours to complete the isothermal treatment;

[0102] After the constant temperature treatment, the temperature is cooled to room temperature at a cooling rate of 3-8 DEG C / min at 170-190 DEG C to complete the constant temperature annealing treatment, wherein when the constant temperature treatment is completed and the cooling starts, the Mg2Cu3 phase and copper atoms start to bond with the surface of the shell layer, and when the cooling is completed, the Mg2Cu3 phase and copper atoms are completely bonded with the surface of the shell layer.

[0103] In this embodiment, a slow heating rate of 3-8 DEG C / min provides sufficient power for atomic diffusion. The formation of Al3Zr has a high activation energy, and rapid heating can lead to incomplete reaction. This method ensures uniform distribution of Zr in the Al matrix by slow heating, avoiding local enrichment of the core-shell structure. Further, by 170-190 DEG C low temperature holding, the interface diffusion of Zr and Li atoms is promoted to form an Al3(Zr, Li) solid solution transition layer. The transition layer relieves stress through the gradient change of lattice parameters, improving the bonding strength of the core-shell structure. In addition, the holding time of 8-15 h balances the production efficiency and structural integrity. Short holding time can lead to insufficient transition layer thickness, and long holding time can cause grain coarsening. This method optimizes the holding time to control the grain size of the core-shell structure, ensuring mechanical strength and maintaining good plasticity.

[0104] Please refer to Figure 1 , Figure 2 and Figure 3 , the second embodiment of the present application also provides a core-shell material prepared by the preparation method of the core-shell material as described above.

[0105] It can be understood that the core-shell material described in this embodiment solves the vicious cycle problem of "expansion-dendrite-failure" of the traditional lithium metal negative electrode. In the Al3Zr@Al3Li core-shell structure: the high modulus Al3Zr inner core can inhibit the volume expansion during the cycle process, and the flexible Al3Li outer shell can buffer the stress through plastic deformation, and the two can greatly improve the electrode anti-expansion performance.

[0106] Further, the core-shell material comprises a core layer, a transition layer and a shell layer formed in sequence from inside to outside, and a bonding layer arranged on the shell layer; the bonding layer is arranged at the outer periphery of the shell layer and connected with the shell layer; wherein the Al3Zr single crystal is the core layer of the core-shell material, the Al3Li single crystal is the shell layer of the core-shell material, the Al3(Zr, Li) solid solution is the interface layer of the core-shell material, and the bonding layer comprises Mg2Cu3 and Cu atoms.

[0107] The Mg2Cu3 and Cu atoms are bonded with the surface of the shell layer respectively, or the Mg2Cu3 is bonded with the surface of the shell layer through Mg-O bond, and the Cu atoms are bonded with the surface of the shell layer through Cu-O-Al bond, and it should be noted that the oxygen atoms in the Mg-O bond and the Cu-O-Al bond are obtained in a micro-oxygen atmosphere.

[0108] The embodiment solves the technical problems of weak interface bonding and easy delamination of core-shell materials by designing a multi-layer interface structure. The core layer provides mechanical support, the shell layer guides lithium deposition, the transition layer Al3(Zr, Li) relieves lattice mismatch, and the bonding layer enhances interface bonding through chemical action. This four-level structure of "core-transition layer-shell-bonding layer" greatly improves the interface shear strength and solves the problem of interface debonding of traditional core-shell materials.

[0109] To demonstrate the performance of the core-shell material prepared in the embodiment, the ion conductivity, nanoindentation modulus, and cycle test of the same mass of the core-shell material prepared in the embodiment and Li-Mg-Cu-Al core-shell-free material are taken. Please refer to Table 1, alloy material performance test table:

[0110]

[0111] It should be understood that based on the data in Table 1, it can be seen that the shell layer in the core-shell material can provide a fast channel for lithium ion transmission, and its high lithium content feature significantly reduces the ion diffusion resistance; the nanoindentation modulus test can see that the core layer endows the material with excellent deformation resistance and suppresses the volume expansion during the cycle process; in addition, the transition layer Al3(Zr, Li) of the core-shell material buffers the stress at the core-shell interface, cooperates with the bonding effect of the Mg2Cu3 phase, effectively suppresses the dendrite growth, and improves the capacity retention rate to 95.8%. In summary, the Al3Zr@Al3Li core-shell structure realizes the synchronous optimization of mechanical properties and electrochemical properties through the cooperative design of "rigid inner core-flexible outer shell-interface transition layer", which provides an effective solution to the volume expansion and cycle failure problems of lithium metal anodes.

[0112] Please refer to Figure 4 The third embodiment of the present application provides a negative electrode material, which comprises a substrate layer 1, a buffer layer 2 and a lithium-rich layer 3 arranged in layers, the lithium-rich layer 3 comprising a first lithium metal matrix 11, the buffer layer 2 comprising a second lithium metal matrix 21 and buffer pores 22 distributed inside the second lithium metal matrix 21 and the above-mentioned core-shell material 23, and the substrate layer 1 comprising a third lithium metal matrix 31 and a modified carbon skeleton 32 distributed inside the third lithium metal matrix 31, the second lithium metal matrix 21 being sandwiched between the first lithium metal matrix and the third lithium metal matrix 31.

[0113] Specifically, the first lithium metal matrix 11, the second lithium metal matrix 21 and the third lithium metal matrix 31 in the embodiment are also referred to as "lithium metal network" and are Li-Mg-Cu matrix, which is a composite structure formed by continuous phase change. The "Al3Zr@Al3Li core-shell material" in the buffer layer 2 is uniformly dispersed in the second lithium metal matrix 21 as a reinforcing phase. Please refer to Figure 4The core-shell material 23 is embedded inside the second lithium metal matrix 21, and the core-shell material 23 is dispersed and the second lithium metal matrix 21 is continuous. In addition, the inside of the buffer layer 2 will retain certain pores, which provide crucial buffer pores 22 for volume expansion.

[0114] Specifically, the negative electrode material is prepared by stacking the modified carbon skeleton 32, the core-shell material 23 and the lithium metal material in the order from bottom to top, and then hot-pressing. During the hot-pressing process, the lithium in the lithium metal material and the core-shell material 23 melts to form a liquid phase, gradually infiltrates and bonds the surface of the core-shell, forming a uniform buffer layer. And the molten lithium infiltrates the surface pores of the underlying modified carbon skeleton 32, reacts with the modified carbon skeleton 32 to form a bond, and finally forms a solid whole similar to a sandwich structure. An interface layer is formed between the base layer 1 and the buffer layer 2, and between the buffer layer 2 and the lithium-rich layer 3. At the hot-pressing temperature, the molten lithium metal will infiltrate, corrode and partially dissolve the outermost shell layer of the core-shell material. At the same time, the elements in the core-shell material 23 will also diffuse into the lithium matrix. Thus, at the interface between the particles and the matrix, a compositionally graded, atomically mixed diffusion layer, i.e. an interface layer, is formed. This layer achieves high-strength metallurgical bonding from the particles to the matrix. It should be understood that the core layer and the shell layer are connected by a coherent interface, mainly bonded by metal bonds and part of covalent bonds, with high bonding energy and good stability. The shell layer and the lithium metal matrix are metallurgically bonded.

[0115] Specifically, the negative electrode material provided by the embodiment is a gradient design of "base layer 1-buffer layer 2-lithium-rich layer 3", which solves the technical contradiction that a single material cannot simultaneously have high capacity and low expansion. The structure realizes the synergistic integration of functions: the modified carbon skeleton in the base layer 1 acts as a mechanical skeleton to buffer the expansion of the lithium metal material; the core-shell material (Al3Zr@Al3Li) in the buffer layer 2 buffers the volume change through the "rigid core-flexible shell"; the surface lithium-rich layer 3, usually a metal lithium material, acts to supplement active lithium, similar to pre-lithiation, providing high capacity for the electrode material. The three form a functional gradient of "support-buffer-lithium storage". Specifically, the modified carbon skeleton 32 maintains a porosity of greater than or equal to 85%, providing deformation space for the expansion of the buffer layer 2. In the buffer layer 2, the core layer in the core-shell material 23 does not directly connect with Mg2Cu3 to form a network. They synergistically act together through the "lithium metal matrix" as a medium on a macroscopic scale to form an elastic-plastic dissipation network. The anti-expansion function is not achieved by direct connection of the core and Mg2Cu3, but by the following three-level dissipation mechanism: First level: the core layer has a very high modulus, providing mechanical support for the surrounding soft lithium matrix, greatly improving the overall stiffness of the individual composite particles, making them more difficult to be compressed and deformed. Second level: the Mg2Cu3 phase and the lithium metal matrix together form a "plastic deformation matrix" that wraps the core-shell material. The lithium matrix itself is relatively soft and will flow plastically, absorbing energy. The Mg2Cu3 phase, as a reinforcing phase, has a modulus much higher than lithium but has good elasticity. It will undergo reversible bending and deformation under cyclic stress, thereby absorbing and dissipating a large amount of strain energy. Third level: when the entire electrode expands, the stress is transmitted through the continuous lithium matrix. The stress first causes the soft lithium matrix to plastically deform. Subsequently, the stress is transmitted to the Mg2Cu3 phase, causing it to elastically deform. Finally, the stress is transmitted to the hardest core layer, which successfully resists most of the remaining stress, thereby suppressing the overall deformation.

[0116] In order to verify that the negative electrode material prepared in the embodiment has better performance, the following experimental tests are performed:

[0117] Example 1: Core-shell gradient composite electrode:

[0118] Step 1: Pretreatment of raw materials: Select high-purity metal raw materials according to the mass ratio (Mg: 47.2%, Al: 21.9%, Cu: 21.9%). Grind Mg with sandpaper, ultrasonic clean with 10% dilute acetic acid for 10 min, then rinse with deionized water, and vacuum dry at 60°C for 2h. Al and Cu are soaked in 5% oxalic acid solution for 5 min, then cleaned with ethanol, and vacuum dried at 80°C.

[0119] Step 2: Vacuum melting: Put the metal materials into the vacuum induction furnace for melting, the charging sequence is Cu at the bottom, Al in the middle, and Mg at the top, vacuumize to 0.05 Mpa and then fill high-purity argon. Heat from room temperature to 1050°C at a rate of 10°C / min, keep for 1 h, realize atomic-level mixing of liquid metal by 25 Hz electromagnetic stirring, and obtain alloy ingot.

[0120] Step 3: Gas atomization powdering: Atomize the molten alloy through a nozzle with d=0.5 mm, cool rapidly under 5 MPa argon pressure (where the cooling rate is greater than or equal to 104 K / s), and obtain ternary alloy powder with structure (copper-aluminum-magnesium). Screen the powder in a glove box (environment: O2 / H2O<0.1 ppm), and take the 10~30 μm particle size section.

[0121] Step 4: Zr strengthening phase pre-dispersion: Mix the ternary alloy powder and Zr powder (mass ratio of alloy powder 96%: Zr 4%), uniformly disperse in argon atmosphere by ball milling at a speed of 50 rpm and a ball-to-material ratio of 8:1 for 3 hours, and obtain quaternary alloy powder with structure (Mg-Al-Cu)-Zr.

[0122] Step 5: Low-temperature molten lithiumization: Preheat the quaternary alloy powder to 170°C, then add Li powder (mass ratio of alloy powder 25%: Li 75%), heat to 200°C in argon atmosphere, and mechanically stir for 20 min at a stirring speed of 60 rpm using a closed propeller. Immediately after stopping stirring, cool to room temperature at a cooling rate of 15°C / min, and obtain quinary alloy powder.

[0123] Step 5: Core-shell structure mechanical alloying: Put the quinary alloy powder into a tube furnace, heat from room temperature to 175°C at a rate of 5°C / min, keep at 175°C for 10 hours, and cool at a rate of 15°C / min in argon atmosphere at 175°C for 12 hours to form Al3Zr@Al3Li core-shell strengthening phase.

[0124] Step 6: Preparation of modified carbon skeleton: carbon fiber felt with porosity greater than or equal to 90% is used to deposit a nano-diamond lithium-lean layer by chemical vapor deposition at 800°C for 30 min and spray 2 mg / mL of a Ti3C2Tx lithiumophilic layer, where Ti3C2Tx is the general chemical formula of MXene material, Ti3C2 is the fixed stoichiometric ratio structure of MXene parent material, T represents -O, -OH, -F and other surface terminal groups, and x represents its non-stoichiometric composition. It should be noted that MXene material is a kind of two-dimensional transition metal carbide, nitride or carbonitride with terminal functional groups (-O, -OH, -F) on the surface, which is obtained by selective chemical etching of A atom layer in MAX phase material. They have metal-level conductivity, hydrophilicity, adjustable surface chemistry and good mechanical properties, and are a new type of multifunctional two-dimensional material with great application prospect. MAX phase is a new type of processable ceramic material composed of metal elements (M), main group elements (A) and carbon / nitrogen elements (X) with a hexagonal layered structure, combining the conductivity and thermal conductivity of metal with the high strength and high temperature resistance of ceramic. Ti3C2 is the fixed stoichiometric ratio structure of MXene material parent material, T represents -O, -OH, -F and other surface terminal groups, and x represents its non-stoichiometric composition, which means that the proportion of various atoms in the compound is not a simple integer ratio and can fluctuate within a certain range, such as Ti3C2O 1.3 (OH) 0.6 F 0.1 material, the value of x is not a single integer, but the sum of the number of all surface terminal groups. For example, x ≈ 2.0 (i.e. 1.3 + 0.6 + 0.1).

[0125] Step 7: Gradient composite: modified carbon skeleton, core-shell alloy powder metal lithium material stack (where the mass ratio is: modified carbon skeleton 30%; core-shell alloy powder 52%; metal lithium material 18%), heat pressed at 250°C / 5 MPa for 2 hours in a glove box, with a cooling rate of 10°C / min, to form a gradient structure composite electrode with a lithium-rich layer, a buffer layer and a substrate layer.

[0126] Comparative Example 1: Traditional homogeneous alloy electrode:

[0127] Li, Mg, Al, Cu are directly melted at a temperature of 1500°C (where the mass ratio of Li, Mg, Al, Cu is: Li 75%, Mg 12.5%, Al 6.25%, Cu 6.25%) and then broken and powdered to prepare a traditional homogeneous alloy electrode. This scheme has no gradient / core-shell design, the expansion rate test is the same as step 8 and the cycle stability verification is the same as step 9.

[0128] Comparative Example 2: Single-element reinforced alloy electrode:

[0129] Without performing the core-shell composite of steps 4-6, other conditions being the same, a single-element strengthened alloy electrode is prepared, the expansion rate test is the same as step 8, and the cycle stability verification is the same as step 9.

[0130] The corresponding test method is as follows:

[0131] In-situ expansion rate: An electrochemical in-situ expansion instrument is used to charge and discharge at 0.1C and record the thickness change of the electrodes in Experimental Example 1, Comparative Example 1 and Comparative Example 2 in real time.

[0132] Initial coulombic efficiency:

[0133] Capacity retention rate after 500 cycles: The electrodes in Experimental Example 1, Comparative Example 1 and Comparative Example 2 are directly hot-rolled to form self-supporting lithium metal strips (thickness less than or equal to 50 μm), CR2032 button half-cells are assembled, the test voltage is 0.005-1.5 V, the capacity retention rate is recorded after 1C current density cycling.

[0134] See Table 2, negative electrode material performance test table:

[0135]

[0136] As can be seen from Table 2, compared with traditional homogeneous alloy electrodes and single-element strengthened alloy electrodes, the core-shell material gradient composite electrode has a lower in-situ expansion rate, mainly in two aspects.

[0137] The first aspect is the Al3Zr@Al3Li core-shell structure: the high modulus core layer, with an elastic modulus of about 200 GPa, can provide rigid support, the flexible shell layer can buffer stress through plastic deformation, and the transition layer Al3(Zr, Li) solid solution can relieve the lattice mismatch of the core-shell. Specifically, in the Al3Zr@Al3Li core-shell material prepared by the method, Li provides a lithium source and constructs an ion channel. Mg inhibits dendrites and improves ductility; Al forms a core-shell phase skeleton, in which Al3Zr as the core layer can guide the deposition orientation, and Al3Li as the shell layer can also accelerate ion conduction; Zr improves the hardness of the core phase and induces lithium deposition; Cu forms Mg2Cu 3相与The surface of the shell layer is bonded or directly bonded with the surface of the shell layer. The Al3Zr@Al3Li core-shell material first inhibits dendrites, and secondly can resist swelling, and can also improve the cycle stability when used as a battery material. For inhibiting dendrites: the core can guide the directional deposition of lithium, eliminating random nucleation. It can accelerate the lateral diffusion of lithium ions and neutralize space charges. The Mg solid solution improves the surface layer lithium hardness and blocks the longitudinal penetration of dendrites, and can be used to resist swelling. Specifically, during the process of low-temperature molten lithium, Mg begins to melt into the molten Li to form a Mg-Li solid solution, and during the process of hot pressing, the lithium metal in the buffer layer is melted again. This process further homogenizes the distribution of Mg in Li, ensuring the composition uniformity of the β-Li(Mg) solid solution matrix formed after final solidification, and the Mg element is locked in the lithium matrix of the buffer layer 2 of the negative electrode material. In the battery charging and discharging cycle, lithium undergoes repeated deposition-dissolution, and the electrode volume changes accordingly. The Mg atoms melt into the Li lattice, causing lattice distortion, significantly improving the strength and hardness of the lithium metal. The harder lithium matrix is more resistant to dendrite penetration and plastic deformation. At the same time, the addition of Mg changes the deposition habit of lithium, making it more inclined to layer deposition rather than dendritic growth, thereby reducing the uncontrollable volume change that leads to swelling from the root. Finally, in combination with the Mg2Cu3 phase in the buffer layer, the core-shell material, and the like, the local stress is dispersed and dissipated. The Cu bonding layer forms an elastic buffer at the carbon skeleton interface, dispersing local stress. Li dynamic compensation drives dendrites to backfill through gradient concentration difference. For resisting swelling: the core-shell material provided in the embodiment can be used as a buffer layer in the battery negative electrode material, wherein the core layer forms an elastic network with the Mg2Cu3 phase, and plastic absorption of cycle strain.

[0138] The second aspect is a gradient composite layer: the modified carbon skeleton nanodiamond lithium-averse layer reserves expansion space to avoid structure collapse caused by excessive lithium penetration. Further, the core-shell material gradient composite electrode has a relatively optimal cycle life. The base layer is a carbon fiber material, and the lithium-philic layer or lithium-averse layer can be synergistically controlled: the Ti3C2Tx lithium-philic layer reduces the lithium nucleation overpotential, guiding uniform deposition, and experiments show that the capacity retention rate of Example 1 after 500 cycles is significantly higher than that of the comparative example. In addition, the core-shell material gradient composite electrode can inhibit dendrite growth, has a shell thickness of 5-10 nm, shortens the Li+ diffusion path, and avoids dendrite nucleation caused by excessive local ion concentration. This embodiment has the following beneficial effects through the synergistic design of "core-shell strengthening phase + gradient composite structure + interface layer": inhibiting electrode expansion: the high modulus core and flexible shell synergistically buffer volume changes, significantly reducing the structural stress during the cycle process; guiding uniform deposition: the lithium-philic shell layer provides directional nucleation sites, eliminating the risk of dendrite growth; improving cycle life: the unique interface design blocks the nanophase coarsening path, maintaining long-term structural stability; enhancing safety: the mechanically reinforced network blocks lithium dendrite penetration, preventing battery short circuits. Finally, the stable and long-cycle operation of high-energy density lithium metal batteries is realized, and the problems of expansion failure and safety hazards are comprehensively solved.

[0139] The above has introduced in detail a core-shell material and a preparation method thereof and a negative electrode material disclosed in the embodiments of the present application. The principles and implementation manners of the present application are described by applying specific examples in this paper. The above description of the embodiments is only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation manner and application range will be changed; in view of the above, the content of the specification should not be understood as a limitation of the present application; any modification, equivalent replacement and improvement within the principles of the present application should be included in the protection scope of the present application.

Claims

1. A method of preparing a core-shell material, characterized by: The preparation method of the core-shell material comprises the following steps: Providing metal raw materials of magnesium, copper and aluminum, and preparing the metal raw materials into a ternary alloy powder based on a preset smelting method, wherein the mass ratio of magnesium, copper and aluminum in the metal raw materials is 40-50%:20-25%:20-25%; Providing metal zirconium powder, and mixing the ternary alloy powder and the metal zirconium powder in a ball milling manner to form a quaternary alloy powder, wherein the mass ratio of the ternary alloy powder and the metal zirconium powder is 95-99%:1-5%; Providing metal lithium powder, and heating the quaternary alloy powder to 170-180℃ under an inert gas atmosphere, then introducing inert gas and adding the metal lithium powder, and mixing and cooling the quaternary alloy powder and the metal lithium powder heated from 170-180℃ to 185-220℃ to form a quinary alloy powder, wherein the mass ratio of the quaternary alloy powder and the metal lithium powder is 20-30%:70-80%; Placing the quinary alloy powder in an inert gas atmosphere, heating to 170-190℃ at a temperature rising rate of 3-8℃ / min at room temperature to complete the temperature rising process, wherein during the temperature rising process, zirconium atoms diffuse into the continuous phase of aluminum to form a core layer Al3Zr in the core-shell material, lithium atoms diffuse into the continuous phase of aluminum to wrap the core layer Al3Zr and form a shell layer Al3Li in the core-shell material, and zirconium atoms and lithium atoms mutually diffuse at the interface of the core layer and the shell layer to form a transition layer Al3(Zr,Li); and performing heat preservation and cooling on the heated quinary alloy powder during a constant temperature annealing process; After the temperature rising process, heat preservation is performed at 170-190℃ for 8-15 hours to complete the constant temperature process; After the constant temperature process, cooling is performed at 170-190℃ at a cooling rate of 3-8℃ / min to room temperature to complete the constant temperature annealing process; When the quinary alloy powder is placed in an inert gas atmosphere, the Mg2Cu3 phase and copper atoms begin to bond with the surface of the shell layer when the constant temperature process is completed and cooling begins, and the Mg2Cu3 phase and copper atoms completely bond with the surface of the shell layer when the cooling is completed; Or, when the quinary alloy powder is placed in a micro-oxygen atmosphere, magnesium and copper form the Mg2Cu3 phase, the Mg2Cu3 phase bonds with the surface of the shell layer through the Mg-O bond, and copper atoms bond with the surface of the shell layer through the Cu-O-Al bond, to form the Al3Zr@Al3Li core-shell material.

2. The method of claim 1, wherein: The preparation of the ternary alloy powder from the metal raw materials based on the preset smelting method comprises: Placing the metal raw materials in an inert atmosphere in the order of copper, aluminum and magnesium to perform smelting treatment to obtain a ternary alloy melt with a structure of (copper-aluminum-magnesium); Performing atomization treatment on the ternary alloy melt to obtain an aerosol, and obtaining a pre-alloy powder through cooling treatment of the aerosol; Performing screening treatment on the pre-alloy powder to obtain a ternary alloy powder (copper-aluminum-magnesium) with a required particle size range, wherein the particle size range of the pre-alloy powder is 10-110μm, and the required particle size range is 10-30μm.

3. The method of claim 2, wherein: The smelting treatment comprises: Control the inert atmosphere pressure less than or equal to 10 -2 Mpa, from room temperature to 1000~1100℃ at a heating rate of 8~15℃ / min and keep for 0.5~1h, so that the metal copper, aluminum and magnesium are melted in turn, and the molten liquid metal copper, aluminum and magnesium are stirred and mixed to obtain a ternary alloy melt.

4. The method of claim 1, wherein: The mixing of the ternary alloy powder and the metal zirconium powder in a ball milling manner to form a quaternary alloy powder comprises: The ternary alloy powder is placed in an inert gas atmosphere, inert gas is introduced, and ball milling is performed at a ball-to-powder ratio of 8:1-12:1 and 30-60 rpm to obtain a (copper-aluminum-magnesium)-zirconium quaternary alloy powder.

5. The method of claim 1, wherein: The mixing and cooling treatment specifically comprises: using a blender to stir the mixture of the quaternary alloy powder and the lithium powder at a stirring speed of 50-150 rpm for 10-30 min; after the stirring is stopped, the mixture is cooled from 185-220 DEG C to room temperature at a cooling rate of 5-15 DEG C / min to obtain a quinary alloy powder.

6. A core-shell material produced by the method for producing a core-shell material according to any one of claims 1 to 5, characterized by: The core-shell material comprises a core layer, a transition layer and a shell layer formed in sequence from inside to outside, and a bonding layer arranged on the shell layer; the bonding layer is arranged at the outer periphery of the shell layer and is bonded to the shell layer; The core-shell material is Al3Zr@Al3Li, wherein the Al3Zr single crystal is the core layer of the core-shell material, the Al3Li single crystal is the shell layer of the core-shell material, the Al3(Zr, Li) solid solution is the interface layer of the core-shell material, the bonding layer comprises Mg2Cu3 and Cu atoms, the Mg2Cu3 and the Cu atoms are respectively bonded to the surface of the shell layer, or the Mg2Cu3 is bonded to the surface of the shell layer through Mg-O bonds, and the Cu atoms are bonded to the surface of the shell layer through Cu-O-Al bonds.

7. A negative electrode material, characterized by: The lithium metal composite material comprises a substrate layer, a buffer layer and a lithium-rich layer arranged in sequence, the lithium-rich layer comprises a first lithium metal matrix, the buffer layer comprises a second lithium metal matrix and buffer pores distributed inside the second lithium metal matrix, and the core-shell material as claimed in claim 6, and the substrate layer comprises a third lithium metal matrix and a modified carbon skeleton distributed inside the third lithium metal matrix.

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