A boron ore-derived composite lithium negative electrode material, and a preparation method and application thereof

Abstract

The application discloses a boron ore derived composite lithium negative electrode material and a preparation method and application thereof. A boron-containing ore is added into molten lithium for smelting, and a cast ingot is obtained after cooling. The cast ingot is sequentially subjected to rolling and tabletting, and a composite lithium negative electrode material is obtained. The composite lithium negative electrode material has a remarkable three-dimensional framework structure, which remarkably enhances the mechanical stability of the framework, and can effectively relieve the problems of lithium metal negative electrode dendrite growth, large volume fluctuation and poor mechanical processing performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery anode material technology, and specifically relates to a boron ore-derived composite lithium anode material, its preparation method, and its application. Background Technology

[0002] Currently dominant modern lithium-ion batteries cannot meet the urgent demand for higher energy density in next-generation energy storage devices. Lithium metal anode materials, due to their extremely low redox potential (-3.04V relative to the standard hydrogen potential) and ultra-high theoretical specific capacity (3860 mA hg), offer a solution. -1 Lithium metal anodes hold promise as energy storage devices for next-generation high-energy-density batteries. However, the widespread commercial application of lithium metal anodes currently faces several obstacles: First, the electrode material undergoes significant expansion and contraction during charging and discharging. This irreversible volume change leads to electrode pulverization, resulting in a sharp decline in battery performance and even failure. Second, the growth of lithium dendrites can puncture the separator, causing internal short circuits in the battery. This not only significantly shortens cycle life but also reduces coulombic efficiency, becoming a key obstacle to practical applications.

[0003] Based on their chemical composition, boron minerals worldwide can be classified into three categories: borosilicates, boroaluminate silicates, and borates. The main raw materials for the boron industry come from borate minerals. Although there are over a hundred types in this category, only about ten are exploitable, such as borax and sulphite. The main component of boromagnesite is magnesium borate monohydrate (Mg2(B2O5)(H2O)), the main component of boron-iron ore is (Mg,Fe)2Fe(BO3)O2, and the main component of borax is Na2B4O7·10H2O. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the first objective of this invention is to provide a method for preparing a boron ore-derived composite lithium anode material. This invention uses magnesium borate (Mg2B2O5), borax (Na2B4O7), boron ore ((Mg,Fe)2Fe(BO3)O2), and calcium borate (Ca(H2O)[B2BO4(OH)3]) as raw materials. These materials are mixed with metallic lithium, and a specific heating procedure is used in high-temperature smelting to prepare a Li-MBO (M=Mg, Na, Ca, Fe, etc.) composite material with a three-dimensional framework structure. The preparation method of this invention is simple, controllable, and suitable for industrial production.

[0005] The second objective of this invention is to provide a boron ore-derived composite lithium anode material prepared by the above-described preparation method. The composite lithium anode material provided by this invention has a significant three-dimensional framework structure, which significantly enhances the mechanical stability of the framework and can effectively alleviate the problems of dendrite growth, large volume fluctuation, and poor machinability of lithium metal anodes.

[0006] A third objective of this invention is to provide an application of a boron ore-derived composite lithium anode material prepared by the above-described preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a method for preparing a composite lithium anode material derived from boron ore. The method involves adding boron-containing minerals to molten lithium for melting, cooling to obtain an ingot, and then rolling and pressing the ingot into sheets to obtain the composite lithium anode material.

[0009] The smelting process is as follows: first, the temperature is raised to 300-350℃ and held for 0.5-3 hours; then, the temperature is gradually raised to 450-480℃; and finally, the temperature is raised to 500-600℃ and held for 2-6 hours.

[0010] During the gradient heating process, the temperature is maintained at 45-55℃ for 10-15 minutes at intervals.

[0011] The method for preparing boron ore-derived composite lithium anode material provided by this invention involves in-situ reaction of borate and lithium via vacuum melting to construct a three-dimensional network skeleton of interwoven Li-B fibers. Metallic lithium is uniformly filled in the three-dimensional network skeleton and forms a symbiotic nested composite structure with multi-element alloy phases M (M=Mg, Na, Ca, Fe, etc.) and Li2O particles. Through a multi-scale synergistic strengthening mechanism, the overall performance of the anode material is improved, significantly enhancing the cycle life of lithium batteries.

[0012] Experiments have shown that the heating program of this invention is crucial during the smelting process. Holding at 300–350°C for 0.5–3 hours allows the oxygen element to react with the molten lithium metal, generating lithium oxide particles that adhere to the borate matrix. Then, a gradient heating program is used. As the temperature increases, the borate containing elements M (M = Mg, Na, Ca, Fe, etc.) further reacts with the lithium metal, growing into a fibrous interwoven framework structure on the matrix and forming a symbiotic nested three-dimensional skeleton structure with the lithium oxide particles. Finally, the reaction is carried out at 500–600°C for 2–6 hours, promoting the formation of a three-dimensional network skeleton structure with high specific surface area and structural stability. Experiments have shown that using a gradient heating program in the middle stage can better ensure the full progress of each stage of the reaction and guarantee the formation of the three-dimensional skeleton structure.

[0013] In a preferred embodiment, the boron-containing mineral is selected from at least one of magnesium borate (Mg2B2O5), borax (Na2B4O7), boronite ((Mg,Fe)2Fe(BO3)O2), and calcite (Ca(H2O)[B2BO4(OH)3]). This invention selects borates containing the same metallic element (M=Mg, Na, Ca, Fe, etc.), whose atoms have the same or approximately the same number of protons and whose physicochemical properties are similar, ensuring the formation of a three-dimensional framework structure.

[0014] In a preferred embodiment, the boron-containing minerals are first vacuum dried at 100–200°C for 1–10 hours. Vacuum drying removes both free and bound water from the boron-containing minerals.

[0015] In a preferred embodiment, the molten lithium is obtained by heating the crucible to a temperature range of 200-300°C at a rate of 5-10°C / min, adding lithium metal, setting the rotation speed to 100-400 rpm, stirring and holding at the temperature for 20-30 minutes.

[0016] Experiments have shown that the stirring speed needs to be effectively controlled during the melting of lithium. If the speed is too high, a significant shear stress field will be generated inside the melt, and the imbalance between the inertial centrifugal force generated by fluid turbulence and surface tension will cause particle splashing. If the speed is too low, effective convection circulation cannot be formed inside the melt, especially below 250°C. Due to the different thermal conductivity of crucibles, metallic lithium may not be completely melted. Incompletely melted solid lithium precipitates in the melt, and these solid particles act as nucleation centers, accelerating the overall solidification process of the melt and seriously affecting the continuity of smelting.

[0017] In actual operation, lithium metal is first polished.

[0018] In a preferred embodiment, the mass ratio of molten lithium to boron-containing minerals is 50–90:10–50. In this invention, it is necessary to control the mass ratio of molten lithium to boron-containing minerals. If too much borate is added, the excess borate will not fully participate in the chemical reaction under high-temperature conditions, resulting in unreacted components remaining in the system. This leads to incomplete reaction during the heat treatment stage. These unreacted borates will cause powder splashing problems in subsequent stirring processes due to the shear force and fluid turbulence generated by mechanical stirring. If the amount of borate added is insufficient, a complete three-dimensional skeleton structure cannot be formed during the heat treatment stage. The formed skeleton structure will have defects or discontinuities, leading to a significant decrease in the performance of the composite material.

[0019] In a preferred embodiment, the melting is carried out under a protective atmosphere.

[0020] More preferably, the protective atmosphere is argon.

[0021] In a preferred embodiment, stirring continues during the melting process, and the stirring speed is controlled at 400-1100 rpm.

[0022] Further optimization involves controlling the stirring speed at 500-600 rpm during the heat preservation process at 300-350℃, controlling the stirring speed at 700-800 rpm during the gradient temperature rise to 450-480℃, and controlling the stirring speed at 1000-1100 rpm during the heat preservation process at 500-600℃.

[0023] Experiments have shown that gradually increasing the stirring rate can significantly improve the dispersion characteristics of borate solid particles in the melt, increase the uniformity of particle distribution, and reduce powder agglomeration. This optimized dispersion state provides favorable conditions for the construction of a three-dimensional network skeleton structure. The faster the stirring rate in the final stage of the reaction (500-600℃), the easier it is for the system to form a three-dimensional network with a well-defined pore structure, and its structural stability is better than that of the product under low stirring rate conditions.

[0024] In a preferred embodiment, the ingot is rolled to obtain a thin strip, which is then pressed into a sheet to obtain a composite lithium anode material. The thickness of the thin strip is 100–2000 μm.

[0025] The present invention also provides a boron ore-derived composite lithium anode material prepared by the above preparation method.

[0026] In a preferred embodiment, the microstructure of the composite lithium anode material is as follows: Li-B fibers intertwine with each other and are co-evolved and nested with multi-element alloy phases and Li2O particles to form a three-dimensional network skeleton structure, and metallic lithium is uniformly filled in the three-dimensional network skeleton structure, wherein the metal in the multi-element alloy phase is selected from at least one of Mg, Na, Ca, and Fe.

[0027] The composite lithium anode material prepared by this invention is a Li-MBO composite material, wherein M is selected from at least one of Mg, Na, Ca, and Fe. It forms a significant three-dimensional framework structure, which significantly enhances the mechanical stability of the framework and can effectively alleviate the problems of dendrite growth, large volume fluctuation, and poor machinability of lithium metal anodes.

[0028] The present invention also provides an application of a boron ore-derived composite lithium anode material, wherein the composite lithium anode material is used as an anode material in lithium-ion batteries.

[0029] Principles and advantages

[0030] On the one hand, this application proposes a method for heat-treating lithium alloys, innovatively constructing a highly stable three-dimensional network framework structure through the alloying reaction of lithium with magnesium borate. This three-dimensional network framework structure can serve as a carrier for lithium deposition / stripping, effectively suppressing volume changes during battery charging and discharging, reducing damage to the surface structure, and thus maintaining the long-term stability of the electrode interface.

[0031] On the other hand, this application also provides an alloy composition ratio optimization strategy and a heat treatment time control method, which clearly defines the process time window required to achieve the best treatment effect.

[0032] The lithium-based alloy material in this application, after being treated with a specific heat treatment process, possesses a highly stable three-dimensional framework structure, exhibiting excellent charge-discharge cycle stability. Secondary batteries prepared using this modified lithium alloy have a longer service life. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the experimental setup used in the embodiment.

[0034] Figure 2 The images show the surface microstructure of the LMBO-9:1-2h composite material in Example 1 at different magnifications, where (a) is the microstructure at a lower magnification and (b) is a magnified view of the particle aggregation area in (a).

[0035] Figure 3 The images show the surface microstructure of the LMBO-8:2-2h composite material in Example 2 at different magnifications, where (a) is the microstructure at a lower magnification and (b) is its magnified view.

[0036] Figure 4 The images show the surface microstructure of the LMBO-9:1-6h composite material in Example 3 at different magnifications, where (a) is the microstructure at a lower magnification and (b) is its magnified view.

[0037] Figure 5 The images show the surface microstructure of the LNBO-9:1-2h composite material in Example 4 at different magnifications, where (a) is the microstructure at a lower magnification and (b) is its magnified view.

[0038] Figure 6 Comparison of XRD diffraction patterns of LMBO-9:1-2h, LMBO-8:2-2h, and LMBO-9:1-6h composite lithium anode materials in Examples 1, 2, and 3.

[0039] Figure 7 The XRD diffraction pattern of the LNBO-9:1-2h composite lithium anode material in Example 4 is shown.

[0040] Figure 8 The images show the microstructure and elemental distribution of the three-dimensional framework of the LMBO-9:1-2h composite lithium anode material in Example 1. (a) is the microstructure of the three-dimensional framework of the composite lithium anode material, (b) is the distribution of Mg, (c) is the distribution of O, and (d) is the distribution of B.

[0041] Figure 9 The electrode discharge voltage-capacity curve of the LMBO-9:1-2h composite lithium anode material in Example 1 is shown.

[0042] Figure 10 The electrode discharge voltage-capacity curve of the LMBO-8:2-2h composite lithium anode material in Example 2 is shown.

[0043] Figure 11 The electrode discharge voltage-capacity curves of the LMBO-9:1-6h composite lithium anode material in Example 3 are shown.

[0044] Figure 12 The electrode discharge voltage-capacity curves of the LNBO-9:1-2h composite lithium anode material in Example 4 are shown.

[0045] Figure 13 The images show the three-dimensional framework morphology of the LMBO-9:1-2h composite lithium anode material after delithiation in Example 1. (a) is a sheet-like three-dimensional network framework structure, (b) is an enlarged view of a single three-dimensional framework structure, (c) is a partial enlarged view of the three-dimensional framework, and (d) is a further enlarged view based on (c).

[0046] Figure 14 Nyquist plots of symmetrical cells with different composite lithium anode materials.

[0047] Figure 15 Symmetric cells with different composite lithium anode materials at 1 mA / cm 2 1mAh / cm 2 Cyclic time-voltage plot under the given conditions.

[0048] Figure 16 Nyquist plots of full cells with different composite lithium anode materials.

[0049] Figure 17 The full-cell cycle performance of LMBO-9:1-2h|LFP in Example 1 is shown.

[0050] Figure 18 The Nyquist plot is shown for the pure Li anode symmetric cell in Comparative Example 1.

[0051] Figure 19 For the pure Li anode symmetric cell in Comparative Example 1 at 1 mA / cm 2 1mAh / cm2 Cyclic time-voltage plot under the given conditions.

[0052] Figure 20 The cycling performance of the pure Li|LFP full cell in Comparative Example 1 is shown.

[0053] Figure 21 The images show the microstructure of the LMBO composite material at different magnifications in Comparative Example 2; (a) shows the microstructure at a lower magnification, and (b) shows its magnified view. Detailed Implementation

[0054] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0055] Example 1: Preparation of LMBO-9:1-2h composite lithium anode material

[0056] 1. Prepare a Li-MBO (M=Mg, Na, Ca, Fe, etc.) composite material derived from boron ore, with a lithium ingot mass fraction of 90 wt% and a magnesium borate (Mg2B2O5) powder mass fraction of 10 wt%.

[0057] 2. A 0.1mm thick sheet metal can is used as a disposable crucible for heat treatment, placed inside a stainless steel crucible for easy reuse. The stainless steel crucible is cylindrical with an inner diameter of 53.5mm and a height of 150mm.

[0058] 3. Cut the metal ingot to a size that can be placed in the crucible inside an argon atmosphere glove box.

[0059] 4. Increase the temperature to 280℃ at a rate of 10℃ / min, then add polished lithium metal and set the rotation speed to 400 rpm to melt the lithium; add magnesium borate to the molten lithium in proportion, increase the temperature to 330℃, set the rotation speed to 600 rpm, and stir continuously for 2 hours; gradually increase the temperature to 480℃, holding at 50℃ for 10 minutes during this period, and set the rotation speed to 800 rpm; then increase the temperature to 550℃, set the rotation speed to 1100 rpm, stir and hold for 2 hours.

[0060] 5. After the heat treatment time is complete, turn off the furnace and remove the stirring rod. After the sample has cooled to room temperature naturally, use tweezers to remove the crucible lid and crucible, break the container, and peel out the ingot.

[0061] 6. The ingot is rolled into a 100μm thin strip by a roller press, and then pressed into a composite lithium anode material by a tablet press, named LMBO-9:1-2h.

[0062] The internal microstructure of the composite material was characterized by scanning electron microscopy (SEM). Figure 2 (a) shows the surface morphology of the composite material, with particles and some crystalline fibers uniformly distributed on the alloy matrix; (b) is a magnified view of the particle aggregation area. The phase composition of the sample was analyzed using X-ray diffraction (XRD). Based on the XRD pattern... Figure 6 The data shows that the LMBO-9:1-2h composite material is composed of Li, LiB, Li2O, and Li x Mg y B z O w It is composed of a microcrystalline glass phase.

[0063] Example 2: Preparation of LMBO-8:2-2h composite lithium anode material

[0064] 1. Prepare a Li-MBO (M=Mg, Na, Ca, Fe, etc.) composite material derived from boron ore, with a lithium ingot mass fraction of 80wt% and a magnesium borate (Mg2B2O5) powder mass fraction of 20wt%.

[0065] 2. A 0.1mm thick sheet metal can is used as a disposable crucible for heat treatment, placed inside a stainless steel crucible for easy reuse. The stainless steel crucible is cylindrical with an inner diameter of 53.5mm and a height of 150mm.

[0066] 3. Cut the metal ingot to a size that can be placed in the crucible inside an argon atmosphere glove box.

[0067] 4. Increase the temperature to 280℃ at a rate of 10℃ / min, then add polished lithium metal and set the rotation speed to 400 rpm to melt the lithium; add magnesium borate to the molten lithium in proportion, increase the temperature to 330℃, set the rotation speed to 600 rpm, and stir continuously for 2 hours; gradually increase the temperature to 480℃, holding at 50℃ for 10 minutes during this period, and set the rotation speed to 800 rpm; then increase the temperature to 550℃, set the rotation speed to 1100 rpm, stir and hold for 2 hours.

[0068] 5. After the heat treatment time is complete, turn off the furnace and remove the stirring rod. After the sample has cooled to room temperature naturally, use tweezers to remove the crucible lid and crucible, break the container, and peel out the alloy ingot.

[0069] 6. The ingot is rolled into a 100μm thin strip by a roller press, and then pressed into a composite lithium anode material by a tablet press, named LMBO-8:2-2h.

[0070] The internal microstructure of the composite material was characterized by scanning electron microscopy (SEM). Figure 3 ), where (a) shows the microstructure at a lower magnification, and it can be seen from the figure that the particles are uniformly distributed on the alloy matrix, and (b) is its magnified view; the phase of the sample was detected by X-ray diffraction (XRD), and according to the XRD spectrum ( Figure 6 The data shows that the LMBO-8:2-2h composite material is composed of Li, LiB, Li2O, and Li x Mg y B z O w It is composed of a microcrystalline glass phase.

[0071] Example 3: Preparation of LMBO-9:1-6h composite lithium anode material

[0072] 1. Prepare a Li-MBO (M=Mg, Na, Ca, Fe, etc.) composite material derived from boron ore, with a lithium ingot mass fraction of 90 wt% and a magnesium borate (Mg2B2O5) powder mass fraction of 10 wt%.

[0073] 2. A 0.1mm thick sheet metal can is used as a disposable crucible for heat treatment, placed inside a stainless steel crucible for easy reuse. The stainless steel crucible is cylindrical with an inner diameter of 53.5mm and a height of 150mm.

[0074] 3. Cut the metal ingot to a size that can be placed in the crucible inside an argon atmosphere glove box.

[0075] 4. Heat to 280℃ at a rate of 10℃ / min, then add polished lithium metal and set the rotation speed to 400 rpm to melt the lithium; add magnesium borate to the molten lithium in proportion, heat to 330℃, set the rotation speed to 600 rpm, and stir continuously for 2 hours; gradually increase the temperature to 480℃, holding at 50℃ for 10 minutes during this period, setting the rotation speed to 800 rpm, then heat to 550℃, setting the rotation speed to 1100 rpm, stirring and holding for 6 hours.

[0076] 5. After the heat treatment time is complete, turn off the furnace and remove the stirring rod. After the sample has cooled to room temperature naturally, use tweezers to remove the crucible lid and crucible, break the container, and peel out the alloy ingot.

[0077] 6. The ingot is rolled into a 100μm thin strip by a roller press, and then pressed into a composite lithium anode material by a tablet press, named LMBO-9:1-6h.

[0078] The internal microstructure of the composite material was characterized by scanning electron microscopy (SEM). Figure 4(a) shows the microstructure at a lower magnification, with particles and some large-diameter particles uniformly distributed on the alloy matrix; (b) is its magnified view. The phase composition of the sample was detected using X-ray diffraction (XRD). Figure 6 The data shows that the LMBO-9:1-6h composite material is composed of Li, LiB, Li2O, and Li x Mg y B z O w It is composed of a microcrystalline glass phase.

[0079] Example 4: Preparation of LNBO-9:1-2h composite lithium anode material

[0080] 1. Prepare a borax-derived Li-MBO (M=Mg, Na, Ca, Fe, etc.) composite material, with a lithium ingot mass fraction of 90 wt% and a borax (Na2B4O7) powder mass fraction of 10 wt%.

[0081] 2. A 0.1mm thick sheet metal can is used as a disposable crucible for heat treatment, placed inside a stainless steel crucible for easy reuse. The stainless steel crucible is cylindrical with an inner diameter of 53.5mm and a height of 150mm.

[0082] 3. Cut the metal ingot to a size that can be placed in the crucible inside an argon atmosphere glove box.

[0083] 4. Heat to 280℃ at a rate of 10℃ / min, then add polished lithium metal and set the rotation speed to 400 rpm to melt the lithium; add magnesium borate to the molten lithium in proportion, heat to 330℃, set the rotation speed to 600 rpm, and stir continuously for 2 hours; gradually increase the temperature to 480℃, holding at 50℃ for 10 minutes during this period, setting the rotation speed to 800 rpm, then heat to 550℃, setting the rotation speed to 1100 rpm, stirring and holding for 2 hours.

[0084] 5. After the heat treatment time is complete, turn off the furnace and remove the stirring rod. After the sample has cooled to room temperature naturally, use tweezers to remove the crucible lid and crucible, break the container, and peel out the alloy ingot.

[0085] 6. The ingot is rolled into a 100μm thin strip by a roller press, and then pressed into a composite lithium anode material by a tablet press, named LNBO-9:1-2h.

[0086] The internal microstructure of the composite material was characterized by scanning electron microscopy (SEM). Figure 5 (a) shows the microstructure at a lower magnification, revealing a smooth and flat alloy surface with some voids in the matrix structure. (b) is a magnified view of the sample. The phase composition of the sample was analyzed using X-ray diffraction (XRD). Based on the XRD pattern... Figure 7 The data shows that the LNBO-9:1-2h composite material is composed of Li, LiB, Li2O, and Li x Na y B z O w It is composed of a microcrystalline glass phase.

[0087] Example 5: Battery fabrication

[0088] 1. The electrolyte used was a Celgard 2400 membrane, 1 mol lithium di(trifluoromethanesulfonyl)imine (LiTFI) / 1,2-dimethoxyethane (DME) + 1,3-dioxocyclopentane (DOL) (volume ratio 1:1), and contained 2% Li2NO3 additive.

[0089] Using LMBO-9:1-2h from Example 1 as the positive and negative electrodes, a CR2016 coin cell symmetrical battery was assembled to obtain battery Sym-1;

[0090] Using LMBO-8:2-2h from Example 2 as the positive and negative electrodes, a CR2016 coin cell symmetrical battery was assembled to obtain battery Sym-2;

[0091] Using LMBO-9:1-6h from Example 3 as the positive and negative electrodes, a CR2016 coin cell symmetrical battery was assembled to obtain battery Sym-3;

[0092] Using LNBO-9:1-2h from Example 4 as the positive and negative electrodes, a CR2016 coin cell symmetrical battery was assembled to obtain battery Sym-4;

[0093] Sym-1, Sym-2, Sym-3, and Sym-4 were subjected to an A / cm range of 0.1 mA. 2 Constant current charging was performed at a current density until 0.5V, and the specific capacity-voltage curves were obtained for each. For example... Figure 9 , 10 As shown in Figures 11 and 12, with 0.2V as the voltage cutoff plateau, the actual discharge specific capacities of LMBO-9:1-2h, LMBO-8:2-2h, LMBO-9:1-6h, and LNBO-9:1-2h are 2286mAh / g, 2216mAh / g, 2396mAh / g, and 2390mAh / g, respectively. All composite anodes contain more than 50% reversible active lithium capacity. The microstructure after delithiation was observed using scanning electron microscopy, as shown in Figures 11 and 12. Figure 8 , Figure 13 As shown; where Figure 8In the figure, (a) is a microscopic morphology diagram of the three-dimensional framework of the composite lithium anode material. After the composite anode is completely delithiated, the exposed frame structure is formed by interwoven fibers, with a few particles attached inside the framework. Combined with the distribution diagram, it is clearly shown that metallic lithium is uniformly filled in the three-dimensional network framework structure, and the three-dimensional framework is composed of interwoven Li-B fibers and coexisting nested with multi-element alloy phases and Li2O particles. Figure 13 In the diagram, (a) is a sheet of three-dimensional network skeleton structure, (b) is an enlarged view of a single three-dimensional skeleton structure, (c) is a partial enlarged view of the three-dimensional frame with a few particles attached inside the frame, and (d) is a further enlarged view based on (c), showing that its frame is composed of fibers.

[0094] Nyquist spectra of Sym-1, Sym-2, Sym-3, and Sym-4 were measured using an electrochemical workstation at frequencies ranging from 100,000 to 0.1 Hz. For example... Figure 14 As shown, the diameter of the semicircle in the high-frequency region (the second semicircle) represents the charge transfer impedance (R0). ct The charge transfer impedances of LMBO-9:1-2h, LMBO-8:2-2h, LMBO-9:1-6h and LNBO-9:1-2h are 305.7, 253.5, 140.8 and 255.5 Ω, respectively.

[0095] Sym-1, Sym-2, Sym-3, and Sym-4 were subjected to an A / cm range of 1 mA. 2 1mAh / cm 2 Constant current charge-discharge cycle tests were conducted under these conditions. The fluctuation range of the obtained voltage-time curve reflects the polarization characteristics of the internal electrochemical reaction of the battery. The smaller the fluctuation range, the smaller the polarization, which means that the SEI film interface is stable and lithium ions can be reversibly deposited and dissolved. The length of the interval in which the curve remains stable reflects the battery's cycle reversibility and lifespan. Figure 15 As shown, all four battery groups operated stably for at least 1200 hours at a low polarization voltage. Among them, LMBO-9:1-6h, as a symmetrical battery with positive and negative electrodes, was able to cycle stably for more than 1600 hours at a polarization voltage of less than 45mV.

[0096] 2. Celgard 2400 was used as the diaphragm, and the electrolyte was 1 mol lithium hexafluorophosphate (LiPF6) / ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + fluoroethylene carbonate (FEC) (volume ratio 3:7:1), with a loading of 12.3 mg / cm³. 2 Commercially available LiFePO4 (LFP) was used as the cathode.

[0097] Using the LMBO-9:1-2h material from Example 1 as the negative electrode to assemble a CR2016 coin cell, the Sym-5 cell was obtained.

[0098] Using the LMBO-9:1-2h material from Example 2 as the negative electrode to assemble a CR2016 coin cell, the Sym-6 cell was obtained.

[0099] Using the LMBO-9:1-2h material from Example 3 as the negative electrode to assemble a CR2016 coin cell, the Sym-7 cell was obtained.

[0100] Using the LMBO-9:1-2h material from Example 4 as the negative electrode to assemble a CR2016 coin cell, the Sym-8 cell was obtained.

[0101] Nyquist spectra of Sym-5, Sym-6, Sym-7, and Sym-8 were measured using an electrochemical workstation at frequencies ranging from 100,000 to 0.1 Hz. Figure 16 The charge transfer impedances of the various materials are 132.6, 113.5, 75.1, and 91.6 Ω, respectively. Sym-5 was cycled at 1C, as follows... Figure 17 As shown, the battery still retains 89.65% of its capacity after 375 cycles.

[0102] In summary, this application constructs a boron-containing composite lithium anode material using borate derived from boron ore. Through vacuum melting, the borate reacts with lithium in situ to construct a three-dimensional network skeleton with fibrous interweaving characteristics, forming a symbiotic nested composite structure with multi-element alloy phases. Through a multi-scale synergistic strengthening mechanism, the overall performance of the anode material is improved, significantly enhancing the cycle life of lithium batteries.

[0103] Comparative Example 1

[0104] 1. In an argon glove box where the water and oxygen levels are both below 0.1 ppm, lithium metal ingots are rolled into thin strips with a thickness of 150 μm using a roller press, and then pressed into Li foils using a tablet press to obtain pure Li anode material.

[0105] 2. Using Celgard 2400 as the separator, 1 mol of lithium di(trifluoromethanesulfonyl)imine (LiTFI) / 1,2-dimethoxyethane (DME) + 1,3-dioxocyclopentane (DOL) (volume ratio 1:1), an electrolyte containing 2% Li2NO3 additive, and pure Li as the positive and negative electrodes, CR2016 coin cells were assembled.

[0106] Nyquist spectra were measured using an electrochemical workstation at frequencies ranging from 100,000 to 0.1 Hz. Figure 18Li exhibits a charge transfer impedance of 391.7 Ω, which is significantly greater than that of the previously described composite lithium. At 1 mA / cm² 2 1mAh / cm 2 Under constant current charge-discharge cycle testing conditions, it can only stably cycle for 350 hours. Figure 19 ).

[0107] 3. Celgard 2400 was used as the diaphragm, and the electrolyte was 1 mol lithium hexafluorophosphate (LiPF6) / ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + fluoroethylene carbonate (FEC) (volume ratio 3:7:1), with a loading of 12.3 mg / cm³. 2 Commercially available LiFePO4 (LFP) was used as the positive electrode and pure Li as the negative electrode to assemble CR2016 coin cells. These cells were cycled at 1C, and their specific capacity and coulombic efficiency were as follows: Figure 20 As shown, the battery retains only 38.11% of its capacity after 250 cycles.

[0108] Comparative Example 2

[0109] 1. In an argon glove box with both water and oxygen levels below 0.1 ppm, the mixture was placed in an iron crucible according to a mass ratio of Li:Mg2B2O5 = 9:1. The Mg2B2O5 powder was stirred and dispersed into the molten lithium at 280℃. After dispersion, the temperature was gradually increased to 330℃ at 5℃ / min and held for 2 hours. The crucible was removed from the melting furnace and rapidly cooled to room temperature to obtain an LMBO composite lithium metal ingot. The ingot was rolled into a thin strip (500-1500 μm) in a glove box (with both water and oxygen levels below 0.1 ppm), and then further rolled into a 100 μm strip using a roller press.

[0110] 2. The internal microstructure of the composite material was characterized by scanning electron microscopy (SEM), which can be seen from... Figure 21 The composite material surface was observed to contain numerous unreacted Mg₂B₂O₅ whiskers and already formed Li₂O particles. After assembly into a CR₂O₁₆ coin cell, it achieved a performance of 0.1 mA / cm². 2 When constant current charging is performed at a current density to 1.0V for electrochemical delithiation, no large-scale three-dimensional network skeleton structure can be seen on the surface.

[0111] Comparative Example 3

[0112] 1. In an argon-filled glove box with oxygen levels below 0.1 ppm, a mixture of Li and Mg₂B₂O₅ at a mass ratio of 1:9 was placed in an iron crucible. The Mg₂B₂O₅ powder was dispersed into the molten lithium at 280°C. After dispersion, the temperature was raised to 330°C and maintained for 2 hours with continuous stirring. The temperature was then gradually increased to 480°C, with a holding time of 10 minutes at 50°C intervals. Finally, the temperature was raised to 550°C, stirred, and held for 2 hours. The crucible was then removed from the furnace and cooled to room temperature. Due to the excessive Mg₂B₂O₅ powder content, it could not be completely diffused into the molten lithium, resulting in an unsuccessful alloy ingot.

Claims

1. A method for preparing a boron ore-derived composite lithium anode material, characterized in that: Boron-containing minerals are added to molten lithium for smelting, and after cooling, ingots are obtained. The ingots are then rolled and pressed into sheets to obtain composite lithium anode materials. The boron-containing mineral is selected from at least one of magnesium borate, borax, boronite, and calcite. The mass ratio of molten lithium to boron-containing minerals is 50–90:10–50; The melting is carried out under a protective atmosphere; The smelting process is as follows: first, the temperature is raised to 300-350℃ and held for 0.5-3 hours; then, the temperature is gradually raised to 450-480℃; and finally, the temperature is raised to 500-600℃ and held for 2-6 hours. During the gradient heating process, the temperature is maintained at 45-55℃ for 10-15 minutes at intervals. During the melting process, stirring is carried out. During the heat preservation process at 300-350℃, the stirring speed is controlled at 500-600 rpm. During the gradient heating to 450-480℃, the stirring speed is controlled at 700-800 rpm. During the heat preservation process at 500-600℃, the stirring speed is controlled at 1000-1100 rpm.

2. The method for preparing a boron ore-derived composite lithium anode material according to claim 1, characterized in that: Boron-containing minerals are first vacuum dried at 100–200℃ for 1–10 hours.

3. The method for preparing a boron ore-derived composite lithium anode material according to claim 1, characterized in that: The method for obtaining molten lithium is as follows: the crucible is heated to a temperature range of 200-300°C at a rate of 5-10°C / min, lithium metal is added, the rotation speed is set to 100-400 rpm, and the mixture is stirred and kept at the temperature for 20-30 minutes to obtain the molten lithium.

4. The method for preparing a boron ore-derived composite lithium anode material according to claim 1, characterized in that: The protective atmosphere is argon.

5. The method for preparing a boron ore-derived composite lithium anode material according to claim 1, characterized in that: The ingot is rolled to obtain a thin strip, which is then pressed into a sheet to obtain a composite lithium anode material. The thickness of the thin strip is 100-2000 μm.

6. A boron ore-derived composite lithium anode material prepared by the preparation method according to any one of claims 1-5, characterized in that, The microstructure of the composite lithium anode material is as follows: Li-B fibers are interwoven and coexist with multi-element alloy phases and Li2O particles to form a three-dimensional network skeleton structure, and metallic lithium is uniformly filled in the three-dimensional network skeleton structure, wherein the metal in the multi-element alloy phase is selected from at least one of Mg, Na, Ca and Fe.

7. The application of a boron ore-derived composite lithium anode material prepared by the preparation method according to any one of claims 1-5, characterized in that: The composite lithium anode material is used as an anode material in lithium-ion batteries.

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