Fine grain reinforced lithium alloy powder negative electrode material as well as preparation method and application thereof

Abstract

The invention relates to a fine grain reinforced lithium alloy powder negative electrode material as well as a preparation method and application thereof. The preparation method of the lithium alloy powder negative electrode material comprises the following steps: proportioning lithium and at least one auxiliary element of Mg, Al and Zn according to the mass percentage of 5%-30%, carrying out induction suspension smelting for 2-10min at 5-20kW under the vacuum of less than or equal to 1Pa and the protection of argon, and cooling to form an alloy block; the preparation method comprises the following steps: firstly, preparing an alloy, then cutting the alloy into pieces in an extremely low-oxygen water glove box, adding 1-6% of polymethyl methacrylate and THF (tetrahydrofuran), filling the alloy into a freezing ball milling tank according to a ball-to-material ratio of (80: 1)-(200: 1), and carrying out ball milling for 20-30min at the temperature of-196 DEG C and the frequency of 20-30Hz to prepare fine-grain lithium alloy powder with the average particle size of 0.2-5mu m. The obtained powder can be tableted into a wafer negative electrode which is suitable for a lithium-copper half battery, a symmetrical battery and a lithium iron phosphate total battery. The material is fine in grain, high in purity and excellent in mechanical property, lithium nucleation overpotential can be reduced, dendritic crystal growth is inhibited, volume expansion stress is relieved, and the cycling stability and safety of the high-specific-energy lithium metal battery are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical energy storage, in particular to a fine-grain strengthened lithium alloy powder negative electrode material, a preparation method and applications thereof. BACKGROUND

[0002] Power transportation, portable electronics and large-scale energy storage scenarios continue to pursue higher energy density. The traditional graphite-based negative electrode of lithium-ion batteries has reached its theoretical limit. Even if combined with high-nickel ternary positive electrodes and Si-C composite negative electrodes, the specific energy of a single cell still hovers around 300Wh·kg -1 , and it is difficult to reach the medium and long-term goal of 500Wh·kg -1 . Compared with this, metal lithium has an ultra-high theoretical specific capacity of 3860mAh·g -1 , a minimum potential of -3.04V (vs SHE), and a lightweight feature (density 0.534g·cm -3 ), and is considered as a core negative electrode candidate to break through the energy bottleneck.

[0003] However, the surface chemical activity of metal lithium is extremely high. In a conventional carbonate or ether-based electrolyte, lithium continuously consumes solvents and forms a solid-state electrolyte interface film (SEI) during the deposition-stripping process. The film is mechanically fragile and prone to repeated rupture, and the fresh metal exposed continues to have side reactions, forming a closed loop and accelerating electrolyte depletion. The superposition of local ion concentration gradient and electric field tip effect promotes lithium to grow at high-curvature locations first, and eventually produces dendrites that penetrate the separator, "dead lithium" that is deactivated, and a sudden drop in capacity.

[0004] A multi-element strengthening strategy can significantly improve the yield strength and reduce the nucleation overpotential by introducing lithiumophilic elements into the lithium lattice, and has been proven to be able to inhibit dendrite growth to some extent. However, the alloy usually serves in bulk or rolled sheet form, and its macroscopic grain size still cannot coordinate the volume change of >300% under high surface capacity and high rate charging and discharging. Local internal stress concentration still leads to interface tearing, powdering and falling off, and polarization rising, and the cycle life is limited. The existing technology lacks attention to the relationship between the internal microstructure of lithium alloy and stress coupling, especially lacks a preparation method that can safely refine the alloy grains in an inert environment while maintaining high purity and process compatibility.

[0005] Therefore, the industry urgently needs a material and preparation method that can simultaneously relieve the volume expansion stress of lithium negative electrode, inhibit dendrite growth, and ensure high energy density and long cycle life. SUMMARY

[0006] The present application provides a fine-grain strengthened lithium alloy powder negative electrode material, a preparation method and applications thereof, aiming to solve the technical problem in the prior art that lithium alloy negative electrode materials are difficult to simultaneously inhibit volume expansion stress and dendrite growth, resulting in limited cycle life.

[0007] To achieve the above object, the technical scheme of the present application is as follows:

[0008] In a first aspect, the present application provides a preparation method of fine-grain strengthened lithium alloy powder negative electrode material, comprising the following steps:

[0009] a) proportioning lithium metal and one or more metal auxiliary elements according to mass percentage, so that the total mass of the auxiliary elements accounts for 5% - 30% of the mass of lithium metal, and then putting into a copper crucible after weighing under inert atmosphere;

[0010] b) placing the copper crucible at the center of the induction coil of a suspension melting device, vacuumizing to not higher than 1 Pa and filling with inert gas protection, and suspension melting under 5kW - 20kW induction power for 2min - 10min;

[0011] c) naturally cooling or controlling the cooling rate to room temperature at 1℃min -1 - 20℃min -1 ;

[0012] d) transferring the obtained alloy to an argon glove box with oxygen content and water content less than 0.01ppm, mechanically removing the surface oxide layer and packaging to obtain a multi-element solid solution strengthened lithium alloy block;

[0013] e) in the argon glove box, cutting the alloy block into 0.5mm - 2mm fragments, and weighing the alloy fragments and organic grinding aids and hard grinding beads together into a sealed cryogenic ball mill jar;

[0014] f) placing the ball mill jar in a vibrating cryogenic ball mill, pre-cooling at a frequency of 5Hz for 10min - 20min, and then ball milling at a frequency of 25Hz - 35Hz, with a total effective ball milling time of 20min - 30min, 4min - 6min for a cycle, and a cycle interval of 60s - 120s, and the whole process is kept under liquid nitrogen cooling condition at -196℃, to obtain fine-grain strengthened lithium alloy powder;

[0015] g) after the ball milling is completed, waiting for the jar body to warm up to room temperature, transferring the powder back into the argon glove box, sieving and collecting through a 300mesh - 600mesh sieve, and vacuum packaging and storing in inert atmosphere to obtain fine-grain strengthened lithium alloy powder negative electrode material with an average particle size of 1μm - 5μm.

[0016] Further, the metal auxiliary elements are selected from one or more of magnesium, aluminum and zinc, and the obtained alloy is Li-Mg, Li-Al, Li-Zn, Li-Mg-Al, Li-Mg-Zn or Li-Mg-Al-Zn alloy.

[0017] Further, the mass percentage of the auxiliary element in the alloy is:

[0018] Li-Mg-Zn alloy: Mg is 10% - 25%, Zn is 5% - 20%, and the balance is lithium;

[0019] Li-Mg-Al-Zn alloy: Mg is 5% - 20%, Al is 2% - 5%, Zn is 2% - 5%, and the balance is lithium.

[0020] Further, the organic grinding aid in step e) is composed of polymethyl methacrylate mixed with tetrahydrofuran, and the total addition amount is 1wt% - 6wt% of the mass of the alloy fragments.

[0021] Further, the hard grinding beads in step e) are hard tungsten steel grinding beads, and the ball-to-material ratio is 80:1 - 120:1.

[0022] In a second aspect, the present application provides a fine-grained strengthened lithium alloy powder negative electrode material, which is obtained by the above-mentioned preparation method, and the average particle size of the fine-grained strengthened lithium alloy powder negative electrode material is 1μm - 5μm.

[0023] In a third aspect, the present application provides an application of a fine-grained strengthened lithium alloy powder negative electrode material in a copper foil half-cell, and the copper foil half-cell comprises:

[0024] a) The lithium alloy powder is placed in a tabletting die, and is hot-pressed under an inert atmosphere at a pressure of 5MPa - 100MPa for 30s - 120s to form a thin foil with a thickness of 0.2mm as a working electrode;

[0025] b) A copper foil is used as a counter electrode and a current collector;

[0026] c) A Celgard2400 polypropylene porous membrane is used as a separator, and an electrolyte is LBC0045I(G);

[0027] d) A CR2032 type button cell is assembled in an argon glove box with H2O / O2 both below 0.1ppm, and is packaged under a pressure of 350-500psi.

[0028] In a fourth aspect, the present application provides an application of a fine-grained strengthened lithium alloy powder negative electrode material in a symmetric cell, and the symmetric cell comprises:

[0029] a) The lithium alloy powder is placed in a tabletting die, and is hot-pressed under an inert atmosphere at a pressure of 5MPa - 100MPa for 30s - 120s to form a thin foil with a thickness of 0.2mm as a working electrode;

[0030] b) Celgard 2400 polypropylene porous membrane as separator, electrolyte as LBC0045I(G);

[0031] c) Assemble CR2032 button cell in an argon glove box with H2O / O2 lower than 0.1ppm;

[0032] d) Package under 350-500psi pressure.

[0033] In a fifth aspect, the application provides an application of the fine-grain strengthened lithium alloy powder negative electrode material in a lithium iron phosphate full battery, wherein the lithium iron phosphate full battery comprises:

[0034] a) Put the lithium alloy powder into a tabletting die, and hot-press under an inert atmosphere at a pressure of 5MPa-100MPa for 30s-120s to form a thin foil with a thickness of 0.2mm as a negative electrode, and a positive electrode with an active material surface density of 3-4mgcm -2 and a LiFePO4 electrode with a mass ratio of LiFePO4:PVDF:SuperP of 8:1:1;

[0035] b) Celgard 2400 polypropylene porous membrane as separator, electrolyte as LBC0045I(G);

[0036] c) Assemble CR2032 button cell in an argon glove box with H2O / O2 lower than 0.1ppm;

[0037] d) Package under 350-500psi pressure.

[0038] Compared with the prior art, the application has the following beneficial effects:

[0039] The application refines the multi-element solid-solution lithium alloy to micro-nano particles through a deep cryogenic fine-grain process, significantly improves the yield strength and elastic uniformity of the material, enables the negative electrode to deform uniformly and reduce the internal stress and SEI rupture risk caused by volume expansion during large-area capacity and high-rate charging and discharging, provides a large number of uniform nucleation sites and shortens the ion diffusion path, effectively reduces the nucleation and deposition overpotential, thereby inhibits dendrite growth and reduces polarization, completes the whole ball milling process in liquid nitrogen deep cooling and inert atmosphere, avoids the introduction of oxidized impurities, maintains high purity and uniform composition, and the process parameters can be scaled up to batch production, the obtained powder can be directly tabletted, is compatible with existing button cell, laminated and other battery manufacturing processes, and the actual cycle life and coulombic efficiency are significantly better than those of pure lithium or conventional bulk alloy negative electrodes, and comprehensively reflect higher specific energy, safety and industrial applicability.

[0040] Of course, implementing each technical solution of the application does not necessarily need to achieve all the advantages described above. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings of other embodiments can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0042] Figure 1 XRD characterization diagram of each alloy component of the present application embodiment 1-2;

[0043] Figure 2 SEM images of each alloy component of the present application embodiment 1-2 under different magnifications; wherein, (a, b) Li powder SEM, (c, d) Li-Mg-Zn powder SEM, (e, f) Li-Mg-Al-Zn powder SEM;

[0044] Figure 3 EDS spectrum of Li-Mg-Al-Zn powder of the present application embodiment 2;

[0045] Figure 4 Mapping image of Li-Mg-Al-Zn powder of the present application embodiment 2;

[0046] Figure 5 Semi-cell lithium deposition discharge curve of different alloy powder components in the present application embodiment 3;

[0047] Figure 6 Impedance spectrum of symmetrical battery of different alloy powder components in the present application embodiment 4;

[0048] Figure 7 Cycling performance diagram of symmetrical battery of different alloy powder components in the present application embodiment 4 under different current densities; wherein, (a) 1 mA cm -2 , (b) 2 mA cm -2 , (c) 5 mA cm -2 , (d) 10 mA cm -2 ;

[0049] Figure 8 Microscopic morphology diagram of symmetrical battery of different alloy powder components in the present application embodiment 4 before and after 200 h of cycling; wherein, (a-b) Li-Mg-Zn powder before and after 200 h of cycling; (c-d) Li-Mg-Al-Zn powderMicro-morphology before and after 200h cycling;

[0050] Figure 9 Long cycle performance of Li powder ||LFP, Li-Mg-Zn powder ||LFP, Li-Mg-Al-Zn powder ||Long cycle performance of LFP; wherein, (a) long cycle performance at 1C; (b) long cycle performance at 5C;

[0051] Figure 10 Charge-discharge curves of different component electrodes in Example 5 of the present application at different cycle numbers;

[0052] Figure 11 Rate performance and charge-discharge curves of different component full cells in Example 5 of the present application;

[0053] Figure 12 ||Li-Mg-Al-Zn powder XPS analysis of electrodes before and after cycling; wherein, (a) high resolution curve of F1s before cycling; (b) high resolution curve of F1s after cycling; (c) high resolution curve of O1s before cycling; (d) high resolution curve of O1s after cycling; (e) high resolution curve of Li1s before cycling; (f) high resolution curve of Li1s after cycling. DETAILED DESCRIPTION

[0054] The application will be further described in details through specific embodiments combined with the drawings. In different embodiments, similar elements are marked with similar element reference numbers. In the following embodiments, many details are described in order to make the application better understood. However, those skilled in the art can easily recognize that some features can be omitted in different cases, or can be replaced by other elements, materials, methods. In some cases, some operations related to the application are not shown or described in the specification, in order to avoid the core part of the application being overwhelmed by too much description, and it is not necessary to describe these related operations in detail for those skilled in the art according to the description in the specification and general technical knowledge in the art.

[0055] In addition, the features, operations or characteristics described in the specification can be combined in any appropriate way to form various embodiments. At the same time, the steps or actions in the method description can also be sequentially adjusted or adjusted in a manner that is obvious to those skilled in the art. Therefore, the order in the specification and drawings is only for the purpose of clearly describing a certain embodiment, and does not mean that it is the necessary order, unless otherwise stated that a certain order must be followed.

[0056] Example 1:

[0057] The embodiment provides a preparation method of a Li-Mg-Zn fine-grain strengthened lithium alloy powder negative electrode material, and comprises the following steps:

[0058] Step a), under the protection of argon, lithium foil 1000 mg (purity ≥ 99.9%), magnesium particles 150 mg (purity ≥ 99.95%) and zinc foil 150 mg (purity 99.995%) are weighed in turn, quickly put into a copper crucible dried at 120 DEG C for 2 hours and covered.

[0059] Step b), the crucible is placed in the center of the coil of the induction suspension melting device, vacuumized to 1 Pa, and 99.999% argon is filled to 5*103 Pa; the induction power is set to 12 kW for continuous melting for 6 minutes, and the heating is stopped after the complete melting of the metal is observed.

[0060] Step c), the power is cut off, and the furnace cavity is naturally cooled to room temperature (≈25 DEG C), and the cooling time is about 30 minutes.

[0061] Step d), the cooled alloy ingot is transferred into an argon glove box with O2 / H2O<0.01 ppm, the oxide layer is removed by using #800 sandpaper, and the alloy is cut into fragments with a size of about 1 mm*1 mm, and the fragments are sealed and stored.

[0062] Step e), 1.0 g of the alloy fragments are weighed, 5 wt% polymethyl methacrylate (PMMA) and 1 mL of tetrahydrofuran (THF) are added, hard tungsten steel grinding beads are added according to a ball-to-material ratio of 100:1, the ball mill tank is tightly sealed after being loaded into a 50 mL cryogenic ball mill tank.

[0063] Step f), the ball mill tank is immersed in a liquid nitrogen (–196 DEG C) cooling tank, and pre-cooling is first carried out at a frequency of 5 Hz for 15 minutes; then, ball milling is carried out at a frequency of 30 Hz for 30 minutes, and a “5-minute grinding / 90-second interval” cycle mode is set to prevent local temperature rise, and the whole process is kept in a deep cooling state.

[0064] Step g), after the ball milling is completed, the tank body is naturally warmed to room temperature, and the tank body is re-transferred into an argon glove box, and is sieved through a 400-mesh sieve, so that a silver-gray Li-Mg-Zn fine-grain strengthened lithium alloy powder is obtained; and the powder is immediately loaded into an aluminum-plastic composite bag and vacuum packaged.

[0065] The obtained powder can be rolled or pressed into a 0.1-1 mm thick, Φ8-15 mm round sheet negative electrode, and is suitable for copper foil half-batteries, symmetric batteries and lithium iron phosphate full batteries.

[0066] Example 2:

[0067] The embodiment provides a preparation method of a Li-Mg-Al-Zn fine-grain strengthened lithium alloy powder negative electrode material, and comprises the following steps.

[0068] In step a), after the balance is zeroed on the operation table with continuous argon blowing, 1000 mg of lithium foil (purity ≥ 99.9%), 100 mg of magnesium particles (purity ≥ 99.95%), 100 mg of aluminum ingot (purity ≥ 99.9%) and 100 mg of zinc foil (purity 99.995%) are sequentially weighed, quickly put into a copper crucible dried at 120 DEG C for 2 hours in vacuum, and immediately covered tightly, and the whole weighing and charging process is controlled to be completed within 1 minute.

[0069] In step b), the charging crucible is placed in the center of the coil of the induction suspension melting device, vacuumized to 1 Pa, then 99.999% argon is filled to 5*103 Pa, the induction power is set to 15 kW, and suspension melting is performed for 7 minutes until the surface of the molten pool is bright and uniform, and then the heating is stopped.

[0070] In step c), the power is cut off to allow the furnace cavity to cool naturally, and after about 35 minutes, the crucible and the alloy ingot are cooled to room temperature.

[0071] In step d), the alloy ingot is transferred to an argon glove box with O2 / H2O both lower than 0.01 ppm by opening the furnace door, the surface oxide layer is removed by lightly grinding with #800 sandpaper, and then the alloy ingot is cut into 0.5 mm-2 mm fragments and 1.1 g is weighed for standby.

[0072] In step e), in the glove box, 1.1 g of alloy fragments is mixed with 5 wt% polymethyl methacrylate and 1 mL of tetrahydrofuran, hard tungsten steel grinding beads are added according to a ball-to-material ratio of 100:1, and then the mixture is loaded into a 50 mL cryogenic ball mill jar and sealed.

[0073] In step f), the ball mill jar is immersed in liquid nitrogen at -196 DEG C, pre-cooled at 5 Hz for 15 minutes, then switched to 30 Hz ball milling for 25 minutes, and the whole process is kept in a cryogenic environment to complete the fine-grain strengthening.

[0074] In step g), after the ball milling is completed, the jar body is warmed to room temperature under argon flow, the powder is poured back into the glove box, and silver-gray Li-Mg-Al-Zn fine-grain lithium alloy powder is obtained by sieving through a 400-500 mesh sieve, and immediately packaged in an aluminum-plastic composite bag for standby.

[0075] The obtained powder can be rolled or pressed into 0.1-1 mm thick, Φ8-15 mm round sheet negative electrodes, and is suitable for copper foil half-batteries, symmetric batteries and lithium iron phosphate full batteries.

[0076] The fine-grain strengthened lithium alloy powder negative electrode materials Li-Mg-Zn powder , Li-Mg-Al-Znpowder The relevant parameters were tested, and pure lithium powder Li powder As a control example, it is convenient to compare and analyze various parameters.

[0077] The phase composition of the prepared lithium alloy powder was observed by XRD. As Figure 1 shown, the XRD patterns of two alloy powder components were tested. Figure 1 The XRD patterns of the above alloy components and the original pure lithium powder are shown in the figure, and the diffraction angle is 10-80°. As Figure 1 can be seen, first, the three strong peaks corresponding to the Li standard card (PDF #01-1131) can accurately find the three strong peaks of Li in the alloy powder. The characteristic peaks of intermetallic compounds appear in the patterns of Li3-Al2 and Li-Zn alloys, such as Li3-Al2 showing characteristic peaks of Li3Al2 in the 15-20° interval, and Li-Zn showing characteristic peaks of LiZn at 25° and 48°, indicating that lithium alloy phases are introduced into the two alloy powders. In the patterns of ternary and quaternary alloys, in addition to the obvious Li3Al2 and LiZn characteristic peaks, the peaks in the 15-20° interval in the Li-Mg-Al-Zn component are speculated to be Mg4Zn7 alloy phase. In addition, the experimental peaks are highly consistent with the reference peaks, indicating that the phase of the sample is clear and the crystallinity is high.

[0078] Further SEM characterization of the prepared alloy nano-powder was carried out to determine the size of the alloy powder. As Figure 2 shown, at low magnification, the particle size of the prepared lithium powder is small, and there is obvious agglomeration, which may be caused by static electricity or van der Waals force. In Figure 2 (b), it can be seen that the size of Li powder is about 50-100 nm, the particle surface is smooth and has high flatness, which can provide a relatively larger specific surface area to promote the uniform distribution of local current and shorten the ion diffusion path. In Figure 2 (c) is the alloy powder of Li-Mg-Zn component, compared with Figure 2 (d) Li-Mg-Al-Zn component, the particle size of both is between 2-5 μm, and obvious bright spots can be found in the particles, which are speculated to be alloy components with high conductivity. The addition of Mg and Zn improves the flowability of the alloy, but the addition of Mg may cause local melting and recrystallization, resulting in larger particle size and wider particle size distribution. The addition of Al increases the strength of the alloy powder. With the addition of alloying elements, the particle morphology evolves from the agglomeration of lithium powder to regular and flat, indicating that alloying can control the particle size and surface properties. Further analysis needs to be combined with SEM / EDS to verify the composition of the alloy powder and the distribution of each element in the alloy particles.

[0079] As Figure 3The EDS element distribution map of Li-Mg-Al-Zn alloy powder taken under the 10 pm scale shows that Mg, Zn and Al elements exist in each alloy particle, and the distribution of the three elements is highly consistent with the morphology of the powder, indicating that the element distribution is relatively uniform, and no obvious segregation occurs. Due to the fine size of the alloy powder, it is easy to react with oxygen in the air, and partial oxidation may occur during the transfer of the sample. Combined with the mapping analysis of the middle alloy powder, the content of the three alloy elements is also relatively uniform, indicating that the preparation of the alloy powder not only ensures the small particle size but also obtains uniform element distribution. The multi-phase alloy structure can release the internal stress of lithium deposition, reduce stress concentration, and significantly improve the cycle stability of the electrode. Figure 4 The EDS element distribution map of Li-Mg-Al-Zn alloy powder taken under the 10 pm scale shows that Mg, Zn and Al elements exist in each alloy particle, and the distribution of the three elements is highly consistent with the morphology of the powder, indicating that the element distribution is relatively uniform, and no obvious segregation occurs. Due to the fine size of the alloy powder, it is easy to react with oxygen in the air, and partial oxidation may occur during the transfer of the sample. Combined with the mapping analysis of the middle alloy powder, the content of the three alloy elements is also relatively uniform, indicating that the preparation of the alloy powder not only ensures the small particle size but also obtains uniform element distribution. The multi-phase alloy structure can release the internal stress of lithium deposition, reduce stress concentration, and significantly improve the cycle stability of the electrode.

[0080] The fine-grain strengthened lithium alloy powder negative electrode material prepared in Examples 1-2 is applied to copper foil half-batteries, symmetric batteries and lithium iron phosphate full batteries to form the following Examples 3-5.

[0081] Example 3:

[0082] The fine-grain strengthened lithium alloy powder negative electrode material is applied to a copper foil half-battery, and the copper foil half-battery comprises:

[0083] a) placing Li-Mg-Zn powder , Li-Mg-Al-Zn powder in a tablet press mold, hot pressing under an inert atmosphere at a pressure of 5-100 MPa for 30-120 s to form a thin foil with a thickness of 0.2 mm as a working electrode;

[0084] b) using a copper foil as a counter electrode and a current collector;

[0085] c) using Celgard 2400 polypropylene porous membrane as a separator, and LBC0045I(G) as an electrolyte;

[0086] d) assembling a CR2032 type button cell in an argon glove box with H2O / O2 lower than 0.1 ppm, and packaging under a pressure of 350-500 psi, to finally form a copper foil half-battery, denoted as: Li-Mg-Zn powder ||Cu and Li-Mg-Al-Zn powder ||Cu.

[0087] For ease of comparison, pure lithium powder Li powder is used to form a copper foil half-battery, denoted as: Li powderr ||Cu.

[0088] The copper foil half-battery prepared in the above Example 3 is subjected to electrochemical performance testing:

[0089] Lithium metal nucleation and deposition overpotential is an important indicator to evaluate the lithium affinity of lithium metal negative electrode material. For example, Figure 5 In the present application, the lithium deposition discharge curves of the half-cells of three different electrodes of Li powderr ||Cu, Li-Mg-Zn powder ||Cu and Li-Mg-Al-Zn powder The lithium deposition discharge curves of the half-cells of the three different electrodes of Li -2 The current density of the half-cells is 1 mA cm From the figure, it can be seen that the deposition nucleation overpotential of Li powder is 147 mV, the deposition overpotential is 106 mV, and the deposition overpotential of Li-Mg-Zn powder is obviously lower than that of the other two alloy powder components in terms of low nucleation overpotential and low deposition potential. The nucleation overpotential of Li-Mg-Al-Zn is slightly smaller than that of Li-Mg-Zn, and the deposition overpotential is slightly better. Compared with the lithium powder electrode, Mg and Al can increase the mechanical strength of the alloy, reduce the volume expansion during lithium deposition / peeling, and nanocrystallization is more conducive to releasing internal stress and inhibiting the formation of lithium dendrites, thereby reducing the risk of short circuit. The addition of Zn further optimizes the interface stability and promotes uniform lithium ion distribution. The lithium affinity Zn powder network benefits from these favorable characteristics, further inhibits dendrite problems caused by excessive local current density.

[0090] Example 4:

[0091] The above fine-grained reinforced lithium alloy powder negative electrode material is applied to a symmetrical battery, which comprises:

[0092] a) Li-Mg-Zn powder , Li-Mg-Al-Zn powder is placed in a tabletting die and hot-pressed at a pressure of 5 MPa-100 MPa for 30 s-120 s under an inert atmosphere to form a thin foil with a thickness of 0.2 mm, which is used as a positive electrode and a negative electrode, respectively;

[0093] b) Celgard 2400 polypropylene porous membrane is used as a separator, and the electrolyte is LBC0045I(G);

[0094] c) CR2032 button cell is assembled in an argon glove box with H2O / O2 lower than 0.1 ppm;

[0095] d) Encapsulated under a pressure of 350-500 psi to form a symmetrical battery.

[0096] For ease of comparison, pure lithium powder Li powder is used to form a symmetrical battery.

[0097] The symmetrical battery prepared in the above example 4 is subjected to electrochemical performance test:

[0098] Figure 6 Example 4 Li powder , Li-Mg-Zn powder , Li-Mg-Al-Zn powder The symmetric cell impedance spectra are shown in Table 1. The ohmic resistance of the powder electrode has been greatly improved compared with the foil electrode in the first chapter. The interfacial resistance of Li-Mg-Zn powder and Li-Mg-Al-Zn powder has dropped to 10 Ω, and the ohmic resistance has been reduced by about 7.2 times. This result confirms the conclusion drawn from the nucleation and deposition potential, fully demonstrating that the modified electrode system has excellent charge transfer kinetics and structural stability. It is worth noting that this significant decrease in interfacial resistance is closely related to the increase in material mechanical properties and the optimized ion diffusion path.

[0099] Table 1 Symmetric cell impedance data of each component

[0100]

[0101] The inventors tested the current density of Example 4 at 1 mA cm -2 , 2 mA cm -2 , 5 mA cm -2 and 10 mA cm -2 , and the cycle performance at a surface capacity of 1 mAh cm -2 , 2 mAh cm -2 , 5 mAh cm -2 and 10 mAh cm -2 , and the test results are shown in Figure 7 At 1 mAh cm -2 and a current density of 1 mA cm -2 , the hysteresis voltage of the Li powder electrode is stable at 50 mV, while the hysteresis voltage of the Li-Mg-Al-Zn component is about 6 mV at the beginning of the cycle, and then runs stably at an extremely low hysteresis voltage of 8 mV. Similarly, the Li-Mg-Zn component symmetric cell also runs stably for more than 400 h at a lower hysteresis voltage of 15 mV, as shown in Figure 7 (a). Further increasing the current density to 2 mA cm -2 and the surface capacity to 2 mAh cm -2 , as shown in Figure 7(b), firstly, the lithium powder negative electrode has a long battery polarization process in the initial stage. As can be seen, the initial hysteresis voltage of the lithium powder reaches 100 mV or even higher. In contrast, the Li-Mg-Zn component and the Li-Mg-Al-Zn component greatly reduce the initial nucleation overpotential and the battery polarization process. The initial Li-Mg-Al-Zn has a hysteresis voltage of 17 mV, and the Li-Mg-Zn has a hysteresis voltage of 26 mV. After more than 450 h of cycling, the electrode still maintains a very low hysteresis voltage, and runs at about 17 mV and 25 mV, fully embodying the advantages of the electrode in cycle stability. Further increasing the current density to 5 mA cm -2 , the surface capacity test at 5 mA cm -2 , it can be seen that the lithium powder negative electrode not only has a high hysteresis voltage during 50 h of cycling, but also fails after 50 h. In contrast, the Li-Mg-Al-Zn component has only 31 mV of hysteresis voltage at the beginning of the cycle and falls back to 21 mV of hysteresis voltage in a very short time, and is stably cycled for more than 450 h. The Li-Mg-Zn also has this advantage, showing an initial hysteresis voltage of 50 mV at the beginning and stably running for 450 h in the subsequent cycle, while the test conditions are 10 mA cm -2 , 10 mA cm -2 , and 10 mA cm -2 , the lithium powder negative electrode cannot be cycled at a high current density, and fails after 50 h. The Li-Mg-Al-Zn component is cycled for more than 450 h under the test conditions of high current density and high surface capacity, and the hysteresis voltage is stably maintained at 10 mV, having a strong cycle stability advantage. This is due to the uniform dispersion of each alloy component in the powder particles of the alloy powder negative electrode, as well as the high specific surface area advantage to reduce the local current density, reduce the SEI interface impedance, inhibit the growth of lithium dendrites, thereby reducing the risk of short circuit and greatly prolonging the cycle life. As shown in Figure 8 , after 200 h of cycling of the alloy powder electrode at a current density of 1 mA cm -2 , the Li-Mg-Zn powder negative electrode, Figure 8 (a-b), and the Li-Mg-Al-Zn powder negative electrode Figure 8 (c-d), the electrode morphology before and after cycling is shown. The electrode material still maintains a fine powder size, and the dendrite growth and volume expansion are inhibited, which further confirms the practicality and structural stability of the lithium powder electrode. The high specific surface area provides a stable three-dimensional space for the electrode material, making it less susceptible to dendrite growth, reducing the risk of damaging the SEI film and piercing the separator to cause battery failure.

[0102] Example 5:

[0103] The fine-grain strengthened lithium alloy powder negative electrode material is applied to a lithium iron phosphate full battery, and the lithium iron phosphate full battery comprises:

[0104] a) Li-Mg-Zn powder , Li-Mg-Al-Zn powder is placed in a tablet pressing mold, and is hot-pressed at a pressure of 5 MPa-100 MPa for 30 s-120 s under an inert atmosphere to form a thin foil with a thickness of 0.2 mm as a negative electrode, and a positive electrode is a LiFePO4 electrode with an active material surface density of 3-4 mgcm -2 , and a mass ratio of LiFePO4: PVDF: SuperP of 8:1:1;

[0105] b) Celgard 2400 polypropylene porous film is used as a separator, and an electrolyte is LBC0045I(G);

[0106] c) A CR2032 button cell is assembled in an argon glove box with H2O / O2 both lower than 0.1 ppm;

[0107] d) The button cell is packaged under a pressure of 350-500 psi to finally form a lithium iron phosphate full battery, which is recorded as: Li-Mg-Zn powder ||LFP, Li-Mg-Al-Zn powder ||LFP.

[0108] For ease of comparison, pure lithium powder Li powder is used to form a lithium iron phosphate full battery, which is recorded as: Li powderr ||LFP.

[0109] The lithium iron phosphate full battery prepared in the above example 5 is subjected to electrochemical performance testing:

[0110] The performance of the lithium iron phosphate full battery prepared in the above example 5 is as shown in Figure 9 , and Figure 9 (a) shows the initial capacity of each alloy powder component at 1C, and the initial capacity of the Li-Mg-Al-Zn powder ||LFP full battery is 116 mAhg -1 , while the initial capacity of the Li-Mg-Zn powder ||LFP and Li powder ||LFP full batteries comes to the level of 106 mAhg -1 , and after 300 cycles, it can be found that the capacity and coulombic efficiency of the Li-Mg-Zn powder ||LFP full battery are greatly reduced at 270 cycles, and it is speculated that the battery has failed due to short circuit at this time, while the Li-Mg-Al-Zn powderThe LFP anode maintained a capacity of 111.8 mAh / g after more than 300 cycles. -1 The capacity retention rate was 96.4%, and the coulomb efficiency remained at 99.9%.

[0111] exist Figure 9 (b) further demonstrates the Li-Mg-Al-Zn powder The LFP full cell exhibits excellent performance, achieving an initial capacity of 80mAh g at a 5C current density. -1 It can cycle for more than 600 hours at its capacity and retain 95% of its capacity (75.9 mAh g). -1 ), and Li powder ||LFP full cells and Li-Mg-Zn powder All full-cell batteries exhibited excessive capacity degradation during long-term cycling, Li powder The LFP full cell retained only 43% of its capacity after 600 hours of cycling. Its performance was inferior to that of Li-Mg-Al-Zn. powder The long-cycle stability advantage of LFP.

[0112] exist Figure 10 The charge-discharge curves of different component electrodes from Example 5 were tested at different cycle numbers to evaluate the polarization phenomenon and capacity retention level of the full cell. First Figure 10 In (a), except for Li-Mg-Al-Zn powder The LFP component, along with the other two full cell groups, showed a clear degradation trend after 100 cycles. Figure 10 (bd) shows the charge-discharge curves of three full cells with different cycle numbers at a current density of 1C. It can be seen that Li-Mg-Al-Zn powder The LFP full cell exhibits less polarization change and the highest capacity retention among all components, demonstrating good overall cycle performance, while the Li... powder ||LFP and Li-Mg-Zn powder ||LFP full cells, on the other hand, experience a gradual decline in capacity retention during subsequent cycles.

[0113] Figure 11 The table shows the rate performance and charge-discharge curves of full cells with different components. It can be seen that Li-Mg-Al-Zn... powder The LFP full battery exhibits superior rate performance across the 0.1C to 10C range, with a capacity of 126mAhg. -1 114mAhg -1 105mAhg -1 94mAhg -1 73mAhg -1 In contrast, Li-Mg-Znpowder The capacity performance of the LFP full battery is relatively low, which is 121 mAhg -1 , 107 mAhg -1 , 97 mAhg -1 , 88 mAhg -1 , 67 mAhg -1 The charge-discharge curves at different rates further verify the polarization performance of the battery, as shown in Figure 11 (b-d), from which it can be seen that among the specific capacities at different rates, the Li-Mg-Al-Zn powder specific capacity of the LFP component remains the highest, and the advantage is more obvious as the rate increases. Not only does it have a lower voltage polarization curve, but also its specific capacity remains at a high level among the alloy powder components after the rate is continuously increased. In terms of the overall performance, the Li-Mg-Al-Zn powder full battery has more performance advantages.

[0114] The valence state information of the interface elements of the Li-Mg-Al-Zn powder powder electrode before and after the cycle is analyzed by XPS. As shown in Figure 12 . Figure 12 (a, b) is the F1s high-resolution curve of the Li-Mg-Al-Zn powder material before the cycle, from which it can be seen that the electrode only has the peaks of AlF3 (687.8 eV) and C6F6 (690.0 eV) at this time, and the electrode material has not reacted with the electrolyte at this time, and the binding energy is mainly the combination of the material itself and PMMA and the like, but the F1s curve after the cycle can show that the binding energy of LiF (685.1 eV) appears on the surface of the electrode at this time, and LiF can improve the ion transmission dynamics; as shown in Figure 12 (c, d), it can be seen that before the cycle, the material only has a single peak of Li2O (532.60 eV), and after the cycle, P2O5 (534.3 eV), OH - (533.31 eV) and O2 (531.0 eV) are generated, which are speculated to be the products of the reaction of the material with the electrolyte and the oxidation of the sample surface after contacting with air; Figure 12 (e, f) is the high-resolution curve of Li1s before and after the cycle, and it can be seen that the binding energy of LiN3 is generated after the cycle, and the existence of LiF and LiN3 is helpful to improve the electrochemical and mechanical properties of the SEI film.

[0115] In summary, the Li-Mg-Al-Zn alloy powder and the Li-Mg-Zn alloy powder of the application applied to the lithium alloy negative electrode have the following advantages:

[0116] Li-Mg-Al-Zn powder electrode material has lower nucleation overpotential (72 mV) and lower deposition overpotential (40 mV), and can be cycled over 450 cycles at a high current density of 10 mAcm -2 -2 powder The symmetrical electrode can be stably cycled over 450 h at a very low hysteresis voltage at a current density of 1 mAcm -2 , 2 mAcm -2 , 5 mAcm -2 and 10 mAcm -2 ; the Li-Mg-Al-Zn powder electrode matched with LFP full battery has more excellent long cycle performance and rate performance. Li-Mg-Al-Zn powder ||LFP full battery can be stably cycled over 350 cycles at a current density of 1 C, and the capacity retention rate is 96% (111.8 mAhcm -2 -2 -1 at 5 C.

[0117] The above application of specific examples to illustrate the present application, is only used to help understand the present application, and is not intended to limit the present application. For those skilled in the art to which the present application belongs, according to the idea of the present application, can make a number of simple deduction, deformation or replacement.

Claims

1. A method for the production of a fine-grain strengthened lithium alloy powder negative electrode material, characterized in that The method comprises the following steps: a) proportioning lithium metal and one or more metal auxiliary elements by mass percentage, so that the total mass of the auxiliary elements accounts for 5%-30% of the mass of lithium metal, and then putting them into a copper crucible after weighing under an inert atmosphere; b) placing the copper crucible in the center of the induction coil of a suspension smelting device, vacuumizing to not higher than 1 Pa and filling with inert gas protection, and suspension smelting for 2 min-10 min under an induction power of 5 kW-20 kW; c) natural cooling after the end of the smelting or controlled cooling to room temperature at 1 °C min -1 - 20 °C min -1 controlled cooling to room temperature; d) transferring the obtained alloy to an argon glove box with an oxygen content and a water content of less than 0.01 ppm, mechanically removing the surface oxide layer and packaging to obtain a multi-element solid solution strengthened lithium alloy block; e) in the argon glove box, cutting the alloy block into fragments of 0.5 mm-2 mm, and loading the alloy fragments, organic grinding aid and hard grinding beads into a sealed cryogenic ball mill jar; f) placing the ball mill jar in a vibrating cryogenic ball mill, pre-cooling at a frequency of 5 Hz for 10 min-20 min, and then ball milling at a frequency of 20 Hz-30 Hz, with a total effective ball milling time of 20 min-30 min, 4 min-6 min for one cycle, and a cycle interval of 60 s-120 s, and the whole process is kept under liquid nitrogen cooling condition at -196 ℃ to obtain a fine-grained strengthened lithium alloy powder; g) after the ball milling is completed, the jar body is warmed to room temperature, the powder is re-transferred into the argon glove box, is screened and collected through a 300 mesh-600 mesh screen, and is vacuum packaged and stored in an inert atmosphere to obtain a fine-grained strengthened lithium alloy powder negative electrode material with an average particle size of 1 μm-5 μm.

2. The method of claim 1, wherein the fine-grain strengthened lithium alloy powder negative electrode material is prepared by the steps of: The metal auxiliary elements are selected from one or more of magnesium, aluminum and zinc, and the obtained alloy is a Li-Mg, Li-Al, Li-Zn, Li-Mg-Al, Li-Mg-Zn or Li-Mg-Al-Zn alloy.

3. The method for preparing the fine-grained reinforced lithium alloy powder anode material according to claim 2, characterized in that, The mass percentage of the auxiliary elements in the alloy is: Li-Mg-Zn alloy: Mg is 5%-25%, Zn is 5%-20%, and the balance is lithium; Li-Mg-Al-Zn alloy: Mg is 5%-20%, Al is 2%-5%, Zn is 2%-5%, and the balance is lithium.

4. The method of producing a fine-grain strengthened lithium alloy powder negative electrode material according to any one of claims 1 to 3, characterized in that, The organic grinding aid in step e) is composed of polymethyl methacrylate and tetrahydrofuran, and the total addition amount accounts for 1 wt%-6 wt% of the mass of the alloy fragments.

5. The method of producing a fine-grain strengthened lithium alloy powder negative electrode material according to any one of claims 1 to 3, characterized in that, The hard grinding beads in step e) are hard tungsten steel grinding beads, and the ball-to-material ratio is 80:1-200:

1.

6. A fine-grain strengthened lithium alloy powder negative electrode material, characterized in that The fine-grained strengthened lithium alloy powder negative electrode material is obtained by the preparation method in any one of claims 1-5, and the average particle size of the fine-grained strengthened lithium alloy powder negative electrode material is 1 μm-5 μm.

7. Use of the fine-grain strengthened lithium alloy powder negative material according to claim 6 in a lithium-copper half-cell, characterized in that The copper foil half-cell comprises: a) placing the lithium alloy powder in a tabletting die, hot pressing under an inert atmosphere at a pressure of 5 MPa-100 MPa for 30 s-120 s to form a thin foil with a thickness of 0.2 mm as a working electrode; b) using a copper foil as a counter electrode and a current collector; c) using Celgard 2400 polypropylene porous membrane as a separator, and LBC0045I(G) as an electrolyte; d) Assemble CR2032 button cell in an argon glove box with both H2O / O2 below 0.1 ppm and encapsulate under 350-500 psi pressure.

8. Use of the fine-grain strengthened lithium alloy powder negative material according to claim 6 in a symmetric battery, characterized in that The symmetric battery comprises: a) Put the lithium alloy powder into a tabletting die and hot-press under inert atmosphere at a pressure of 5-100 MPa for 30-120 s to form a thin foil with a thickness of 0.2 mm as an anode and a cathode, respectively; b) Use Celgard 2400 polypropylene porous membrane as a separator and LBC0045I(G) as an electrolyte; c) Assemble CR2032 button cell in an argon glove box with both H2O / O2 below 0.1 ppm; d) Encapsulate under 350-500 psi pressure.

9. Use of the fine-grain strengthened lithium alloy powder negative material according to claim 6 in a lithium-iron-phosphate full cell, characterized in that, The lithium iron phosphate full battery comprises: a) The lithium alloy powder is placed in a tabletting die and hot-pressed under an inert atmosphere at a pressure of 5-100 MPa for 30-120 s to form a thin foil with a thickness of 0.2 mm as a negative electrode, and a positive electrode with an active material area density of 3-4 mg cm -2 and a LiFePO4 electrode with a mass ratio of LiFePO4: PVDF: Super P of 8: 1: 1; b) Use Celgard 2400 polypropylene porous membrane as a separator and LBC0045I(G) as an electrolyte; c) Assemble CR2032 button cell in an argon glove box with both H2O / O2 below 0.1 ppm; d) Encapsulate under 350-500 psi pressure.

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