A boron-containing composite lithium metal negative electrode material, a preparation method therefor, and an application thereof

Abstract

The application belongs to the field of energy storage materials, and particularly relates to a boron-containing composite lithium metal negative electrode material, a preparation method and application thereof. The boron-containing composite lithium metal negative electrode material is composed of metal lithium, boron and other elements T, and the mass percentage of the metal lithium is 50-85%, the mass percentage of the boron is 10-30%, and the mass percentage of the other alloy elements T is 5-20% based on the total mass of the boron-containing composite lithium negative electrode material, and the total mass percentage of the boron and the other alloy elements T in the composite material is 15-50%. The boron element is provided by a boron-containing compound or jointly provided by a boron-containing compound and elemental boron. The preparation method is designed as follows: the metal lithium, elemental boron and boride are high-temperature smelted under a protective atmosphere. The boride is used as a boron source to generate a lithium boron fiber phase and a second lithium alloy phase in situ with lithium, and the content of the lithium boron fiber can be further regulated by adding elemental boron, so that the structural stability and electrochemical performance of the composite electrode are comprehensively improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of energy storage materials, and particularly relates to a boron-containing composite lithium metal negative electrode material, a preparation method and application thereof. BACKGROUND

[0002] Since the commercialization of rechargeable lithium-ion batteries, after decades of development, extraordinary progress has been made in cycle life, self-discharge rate and safety risk, and has been widely used in various intelligent mobile electronic devices and automotive power batteries. However, the energy density of the existing lithium-ion battery is close to the bottleneck due to the limitation of the theoretical capacity of 372 mAh / g of the graphite negative electrode, and it is difficult to meet the increasing demand for battery energy density in the energy storage market. Metal lithium is considered to be one of the most potential negative electrode materials for the next generation of high specific energy battery systems due to its lowest electrode potential (-3.04 V, compared with the standard hydrogen electrode) and high theoretical specific capacity of 3860 mAh / g. However, in practical application, on the one hand, uncontrollable lithium dendrite growth will cause huge volume fluctuation, leading to interface contact problems, and even cause short circuit, fire and explosion when it pierces the separator; on the other hand, the continuous accumulation of dead lithium and the repeated damage / reconstruction of the solid electrolyte interface (SEI) film will cause continuous consumption of electrolyte and active lithium and continuous increase of interface impedance, resulting in low coulombic efficiency and short service life of the battery, which seriously hinders the practical application of lithium metal negative electrode.

[0003] In view of the above problems of lithium metal negative electrode, a large number of surface engineering and electrolyte engineering strategies have been explored, and good results have been achieved. However, these strategies cannot completely solve the problem of inherent structural volume fluctuation of lithium metal. In addition, due to the poor mechanical strength of lithium metal, it often needs to be attached to a copper foil in practical application, and the huge difference in thermodynamic and electrode potential between lithium and copper leads to poor interface contact problems of lithium-copper composite foil. Therefore, it is necessary to introduce a three-dimensional skeleton to lithium metal based on the requirements of structure and function; the porous skeleton can not only inhibit volume fluctuation and dendrite growth as a lithium deposition host, but also improve the mechanical strength of the substrate to realize self-supporting of the electrode and expand the application space of lithium metal negative electrode.

[0004] The construction of three-dimensional structure composite lithium metal negative electrode can generally be divided into two ways, one is to synthesize a three-dimensional skeleton first, and then composite with lithium through electrodeposition, high-temperature melting or mechanical rolling. This kind of skeleton generally has good continuity and structural stability, but the preparation process is complex, the self-weight is high and usually needs additional surface lithiumophilic modification. The other is to construct a three-dimensional structure directly in the lithium substrate through in-situ reaction, taking various lithium alloys as a typical representative. This kind of method has simple preparation process, high synthesis efficiency and large space for adjusting the specific capacity of the electrode, and is very suitable for industrial planning production. However, this kind of composite negative electrode also usually faces the problems of poor continuity and stability of the skeleton structure.

[0005] Chinese patent CN202211561222.1 discloses a lithium-boron-zinc alloy negative electrode for inhibiting dendrite growth and a preparation method thereof. The scheme introduces a uniform lithium-zinc alloy layer on the surface of the lithium-boron alloy, fully utilizes the advantages of the lithium-boron alloy, makes the alloy negative electrode surface better lithiumophilic, the lithium ion rectification ability stronger, and the local current density smaller.

[0006] Chinese patent CN202111257500.X discloses a porous carbon composite lithium negative electrode with in-situ doping of heteroatoms, a preparation method and application thereof. The scheme constructs a porous carbon skeleton with heteroatom doping, and then mixes and grinds the carbon skeleton with a conductive agent and a binder, and then composites with molten lithium to obtain a porous carbon composite lithium negative electrode, which directionally controls the deposition / dissolution behavior of lithium, and slows down the uneven deposition and dendrite growth of lithium ions.

[0007] Chinese patent CN 116936790 A discloses a lithium alloy negative electrode material, a preparation method thereof, and a lithium ion battery. The scheme introduces non-lithium alloy elements into lithium by melting, so that the non-lithium alloy elements are enriched at the grain boundaries of the metal lithium, thereby relieving the side reaction between the lithium alloy and the electrolyte, maintaining good wettability and stability of the lithium alloy negative electrode, and improving the cycle life thereof.

[0008] Chinese patent CN 110998920 B discloses an electrode material in the form of a lithium-based alloy with magnesium or aluminum as the main alloying element and a manufacturing method thereof. The scheme introduces magnesium or aluminum as the alloying element to improve the rheological properties, adhesion, and melting point of lithium, and further introduces a second alloying element to control the interface properties and electrochemical behavior of the electrode, thereby improving the overall mechanical processing and electrochemical performance of the electrode.

[0009] Lithium-based alloy negative electrodes have attracted widespread attention due to their unique physicochemical properties. However, there is no consensus on how to balance the type and content of alloying elements to ensure that the lithium alloy framework provides better conductive support and the alloy negative electrode maintains a relatively high specific capacity. SUMMARY

[0010] In view of the deficiencies of the prior art, the first object of the present application is to provide a boron-containing composite lithium metal negative electrode material, which aims to construct a long-acting stable three-dimensional skeleton structure and efficient ion / electron channel through in-situ reaction of borides or at least two different valence states of boron sources, to alleviate the problems of severe dendrite growth, large volume fluctuation, short cycle life, and poor mechanical processing performance of lithium metal negative electrodes;

[0011] The second object of the present application is to provide a preparation method of the boron-containing composite lithium metal negative electrode material.

[0012] The present application provides a boron-containing composite lithium metal negative electrode material, which is composed of metal lithium, boron and other elements T, wherein the other elements T are one or more selected from rare earth metals, calcium, magnesium, silicon, aluminum, titanium, iron, chromium, nickel, manganese, molybdenum, niobium, zirconium, antimony, carbon, nitrogen, oxygen, phosphorus, sulfur, selenium, arsenic, bromine and iodine.

[0013] Based on the total mass of the boron-containing composite lithium negative electrode material, the mass percentage of metal lithium is 50-85%, the mass percentage of boron is 10-30%, and the mass percentage of other alloying elements T is 5-20%, and the total mass percentage of boron and other alloying elements T in the composite material is 15-50%; the boron element is provided by a boron-containing compound, or the boron element is provided by a boron-containing compound and elemental boron.

[0014] According to an embodiment of the present application, the other elements T in the boron-containing composite lithium metal negative electrode material are derived from the corresponding boron-containing compounds BxTy added during smelting.

[0015] On the other hand, the present application also provides a preparation method of the boron-containing composite lithium metal negative electrode material, which comprises the following steps:

[0016] Step 1: Under vacuum or argon (water oxygen value less than 100 ppm) atmosphere, the mass ratio of elemental lithium: elemental boron: M is 50-85: 0.01-49.99: 0.01-50; as a preferred, the mass ratio of elemental lithium: elemental boron: M is 70-80: 3-18: 10-30; as a further preferred, the mass ratio of elemental lithium: elemental boron: M is 70-80: 5-15: 15-30; elemental lithium, elemental boron and M are weighed; the M is selected from at least one of borides, boron-containing carbides, boron-containing oxides, boron-containing nitrides, boron-containing phosphides, boron-containing sulfides, boron-containing selenides, boron-containing arsenides, boron-containing bromides, boron-containing iodides; or

[0017] Under vacuum or protective atmosphere, the mass ratio of elemental lithium: M is 50-85: 0.01-50; as a preferred, the mass ratio of elemental lithium: M is 50-85: 3-40; as a further preferred, the mass ratio of elemental lithium: M is 50-85: 5-40, elemental lithium and M are weighed; the M is selected from at least one of borides, boron-containing carbides, boron-containing oxides, boron-containing nitrides, boron-containing phosphides, boron-containing sulfides, boron-containing selenides, boron-containing arsenides, boron-containing bromides, boron-containing iodides;

[0018] Step 2, put the prepared materials into a vacuum / argon smelting furnace, after the lithium is melted, heat and continuously stir for a certain time, fully mix and react; the reaction temperature range is 200℃-700℃, and the reaction time is 5min-100h;

[0019] Step 3, cool and solidify the composite material obtained in step 2 in a special mold to obtain an ingot.

[0020] As preferred, the chemical formula of the boron-containing compound is BxTy; the element T is selected from one or more of rare earth metals, calcium, magnesium, silicon, aluminum, titanium, iron, chromium, nickel, manganese, molybdenum, niobium, zirconium, antimony, carbon, nitrogen, oxygen, phosphorus, sulfur, selenium, arsenic, bromine, and iodine.

[0021] As further preferred, the element T is selected from at least one of carbon, nitrogen, oxygen, phosphorus, and sulfur.

[0022] As preferred, in the preparation method of the boron-containing composite lithium metal negative electrode material, the mass ratio of elemental boron to M is 0.5-1.5:1.5.

[0023] As preferred, the boron powder is crystalline or amorphous boron, and the particle size of the boron powder and boride is 0.01μm-150μm, preferably 0.05μm-30μm, and further preferably 0.1μm-10μm.

[0024] In the protective atmosphere, the water and oxygen value is less than 100ppm. Of course, argon atmosphere can be used in the present application.

[0025] As preferred, in the preparation method of the boron-containing composite lithium metal negative electrode material, after heating to the highest set temperature in step 2, the temperature is kept for 8-25min.

[0026] In the preparation method of the boron-containing composite lithium metal negative electrode material, the obtained ingot is rolled to obtain a thin strip; the thickness of the thin strip is 100-2000μm. Of course, this thickness range also includes 100-1500μm.

[0027] In the preparation method of the boron-containing composite lithium metal negative electrode material, the obtained thin strip is rolled again to obtain an ultrathin strip; the thickness of the ultrathin strip is less than or equal to 100μm. Preferably, it is 5-100μm. If the rolling process can stably produce a thinner product with excellent surface quality, the product can also be used in the present application. The boron-containing composite lithium metal negative electrode material involved and prepared in the present application is used in energy storage devices.

[0028] As further preferred, the energy storage device includes a lithium battery. Of course, it can also include a thermal battery.

[0029] The lithium battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode includes the boron-containing composite lithium metal negative electrode material.

[0030] The Li-B-Si designed and prepared in the application can exhibit more excellent performance when used as a thermal battery. The molar ratio of Li:B:Si is 1:0.05-1:0.01-0.4.

[0031] Compared with the prior art, the application has at least the following beneficial effects:

[0032] The application uses a boron-containing compound M (including at least one of borides, boron-containing carbides, boron-containing oxides, boron-containing nitrides, boron-containing phosphides, boron-containing sulfides, boron-containing selenides, boron-containing arsenides, boron-containing bromides, and boron-containing iodides) as a main boron source to form a LiB fiber phase and other alloy phases nested with the LiB fiber phase through in-situ reaction with lithium. The other alloy phases each have a unique morphological structure, electronic / ion conductivity, and lithium affinity, and can cooperate with the lithium boron fiber to endow the matrix with better mechanical strength, thermodynamic stability, structural stability, oxidation / corrosion resistance, electrode reaction kinetics, and electrochemical performance, thereby improving the machinability of the electrode material, realizing self-supporting of the ultra-thin foil, and inhibiting volume fluctuation and dendrite formation during the electrochemical process, and improving the cycle life of the electrode. On the other hand, by adding elemental boron to regulate the content of the lithium boron fiber to make it the main skeleton supporting phase, and the other alloy phases as auxiliary phases, the composite material can have a stable multi-level skeleton while maintaining a high specific capacity of the electrode.

[0033] The preparation method of the boron-containing composite negative electrode material provided by the application is economical and efficient, has good stability, high repeatability, and can be produced on a large scale.

[0034] The boron-containing composite negative electrode material provided by the application has obviously better electrochemical performance in symmetric batteries with different current densities and capacities, and full batteries with different systems, compared with pure lithium and lithium boron alloy phases.

[0035] The boron-containing composite lithium metal negative electrode material designed and prepared in the application has a stable multi-level skeleton, and the lithium boron alloy phase and the second alloy phase have better interface adhesion, structural stability, and thermal stability

[0036] Therefore, when used as a thermal battery electrode material, it also exhibits excellent performance. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 XRD diffraction pattern of the Li-B-N composite lithium metal negative electrode material;

[0038] Figure 2 Surface and bulk microstructure of the Li-B-N composite lithium metal negative electrode material (a) and (b);

[0039] Figure 3The microstructure of the Li-BN composite lithium metal anode material is shown in (a) and the corresponding (b) N and (c) B element distribution diagrams.

[0040] Figure 4 XRD diffraction pattern of Li-BC composite lithium metal anode material;

[0041] Figure 5 The microstructure of the Li-BC composite lithium metal anode material is shown in (a) and the corresponding (b) B and (c) C element distribution diagrams.

[0042] Figure 6 XRD diffraction pattern of Li-BO composite lithium metal anode material;

[0043] Figure 7 The microstructure of the Li-BO composite lithium metal anode material is shown in (a) and the corresponding (b) and (c) element distribution diagrams of O and B elements.

[0044] Figure 8 XRD diffraction pattern of Li-BP composite lithium metal anode material;

[0045] Figure 9 The microstructure of the Li-BP composite lithium metal anode material is shown in (a) and the corresponding P and B element distribution diagrams in (b) and (c) respectively.

[0046] Figure 10 XRD diffraction pattern of Li-B-Si composite lithium metal anode material;

[0047] Figure 11 The microstructure of the Li-B-Si composite lithium metal anode material is shown in (a) and the corresponding elemental distribution of B and Si (b) in (c).

[0048] Figure 12 XRD diffraction pattern of Li-BN* composite lithium metal anode material;

[0049] Figure 13 for Figure 9 The microstructure of the Li-BN* composite lithium metal anode material is shown in (a) and the corresponding N and B element distribution diagrams in (b) and (c) respectively.

[0050] Figure 14 Discharge voltage-capacity curves of Li-BN composite lithium metal anode material;

[0051] Figure 15 The electrode discharge voltage-capacity curve of Li-BC composite lithium metal anode material;

[0052] Figure 16Discharge voltage-capacity curves of Li-BO composite lithium metal anode material;

[0053] Figure 17 The electrode discharge voltage-capacity curve of Li-BP composite lithium metal anode material;

[0054] Figure 18 Discharge voltage-capacity curves of Li-B-Si composite lithium metal anode material;

[0055] Figure 19 Nyquist plots of symmetrical cells with different boron-containing composite lithium metal anode materials;

[0056] Figure 20 Symmetric cells with different boron-containing composite lithium metal anode materials at 1 mA / cm 2 1mAh / cm 2 Cyclic time-voltage plot under the given conditions;

[0057] Figure 21 The cycle performance of Li-BN|NCM811 full cells;

[0058] Figure 22 For Li-BP|LFP full cell cycle performance;

[0059] Figure 23 For the cycle performance of Li-BO|LCO full cells;

[0060] Figure 24 XRD diffraction pattern of Li-B composite lithium metal anode material;

[0061] Figure 25 Nyquist plot of a symmetrical cell for Li and Li-B composite lithium metal anode materials;

[0062] Figure 26 Symmetric cells using Li and Li-B composite lithium metal anode materials at 1 mA / cm 2 1mAh / cm 2 Cyclic time-voltage plot under the given conditions;

[0063] Figure 27 For Li-B|NCM811 full cell cycle performance;

[0064] Figure 28 For the full cell cycle performance of Li|LFP and Li-B|LFP;

[0065] Figure 29 Cycle performance of Li-B|LCO pouch cells. Detailed Implementation

[0066] The specific embodiments of the present application will be further described with the following detailed description, which is to be taken in an illustrative and explanatory sense and not in a restrictive sense. Various modifications and changes can be made with respect to the present application within the scope of the present disclosure, which will be apparent to those skilled in the art, and any improvement or substitution in the spirit of the present embodiments still falls within the scope of the claims of the present application. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used as received without further purification, and the instruments used in the examples are commercially available.

[0067] The foregoing summary of the present application is not intended to describe each disclosed embodiment or implementation of the present application. Exemplary embodiments are described in greater detail below. Throughout this application, guidance is provided by a series of examples, which can be used in various combinations. In each instance, the list is presented as a representative group, and should not be interpreted as exhaustive.

[0068] In an aspect, the present application provides a boron-containing composite lithium metal anode material, comprising lithium metal, boron and other alloying elements T, wherein the other alloying elements T include one or more of rare earth metals, silicon, calcium, magnesium, aluminum, titanium, iron, chromium, nickel, manganese, molybdenum, niobium, zirconium, antimony, carbon, nitrogen, oxygen, phosphorus, sulfur, selenium, arsenic, bromine, iodine.

[0069] According to embodiments of the present application, the other alloying elements T are introduced in the form of corresponding borides (BxTy), and through in-situ reaction of the borides with lithium, a synergetic lithium-boron fiber phase and a second alloy phase or metal phase nested therein are formed. Compared with the LiB fiber phase and the second alloy phase / metal phase formed by directly adding boron and the corresponding alloying elements in elemental form, the present application has better phase interface combination, smaller phase particle, and more uniform bulk phase distribution.

[0070] According to some embodiments of the present application, based on the total mass of the boron-containing composite lithium anode material, the mass percentage of lithium metal is 50-85%, the mass percentage of boron is 10-30%, and the mass percentage of the other alloying elements T is 5-20%, and the total mass percentage of boron and the other alloying elements in the composite material is 15-50%.

[0071] In some embodiments, to ensure that the boron-containing lithium metal anode material has sufficient specific capacity and sufficient skeleton as a stable three-dimensional support conductive structure, elemental boron is introduced to further regulate the content of the lithium-boron fiber conductive skeleton, so as to coordinate the content of the main skeleton and the overall cost performance of the composite material.

[0072] According to some embodiments of the present application, by introducing borides to react with lithium to form second alloy phases, the unique morphology structure and physical and chemical properties of these second-phase lithium alloys can be coupled with lithium boron fibers to form a more robust skeleton structure, endowing the matrix with efficient charge transfer and ion migration properties, thereby improving the cycle life of the electrode.

[0073] The present application also proposes a preparation method of a boron-containing composite lithium metal negative electrode material, comprising the following steps:

[0074] a. Under vacuum or argon (water oxygen value less than 100 ppm) atmosphere, lithium, boron and boride (BxTy) powders are weighed according to a certain mass ratio;

[0075] b. The weighed lithium, boron and boride powders are put into a vacuum / argon smelting furnace, after the lithium is melted, the temperature is raised and continuously stirred for a certain time, so that the boron and boride powders are fully mixed and reacted with the lithium;

[0076] c. The composite material obtained in step b is naturally (rapidly) cooled and solidified in a special mold, natural cooling refers to furnace cooling, and rapid cooling refers to a cooling speed > 50℃ / min.

[0077] d. The ingot is converted into a thin strip suitable for rolling, and the thickness of the thin strip can be 100-2000 μm;

[0078] e. The thin strip is further converted into an ultrathin strip by rolling, and the thickness of the ultrathin strip is less than or equal to 100 μm.

[0079] In some embodiments, under vacuum or protective atmosphere, the mass ratio of elemental lithium: elemental boron: M is 50-85: 0.01-49.99: 0.01-50; as a preferred, the mass ratio of elemental lithium: elemental boron: M is 70-80: 3-18: 10-30; as a further preferred, the mass ratio of elemental lithium: elemental boron: M is 70-80: 5-15: 15-30; elemental lithium, elemental boron and M are weighed.

[0080] In other embodiments, under vacuum or protective atmosphere, the mass ratio of elemental lithium: M is 50-85: 0.01-50; as a preferred, the mass ratio of elemental lithium: M is 50-85: 3-40; as a further preferred, the mass ratio of elemental lithium: M is 50-85: 5-40, elemental lithium and M are weighed.

[0081] The boron powder used is crystalline or amorphous boron, and the particle size of the boron powder and M is 0.01 μm-150 μm, preferably 0.05 μm-30 μm, and further preferably 0.1 μm-10 μm;

[0082] According to the embodiment of the present application, in order to ensure the full reaction of the metal lithium and M and the uniform distribution of the reactants, the reaction temperature is 200-650℃, or 300-650℃, or 500-650℃, and the reaction time includes the whole process time from the start of heating to the heat preservation and then to the stop of heat preservation, which is 5 min-100 h; in the specific operation, after heating to the highest set temperature, the heat preservation is 8-25 min.

[0083] According to the embodiment of the present application, the boron powder and M can be added into the lithium one after another or simultaneously after the lithium is melted, or can be added into the crucible together with the lithium for heating together.

[0084] According to some other embodiments of the present application, the reactants can only be the metal lithium and the boride.

[0085] The present application further provides a lithium battery in another aspect, which comprises a positive electrode, a separator, an electrolyte and a negative electrode, and can not have the separator when the electrolyte is in a solid state / semi-solid state / half solid state, wherein the negative electrode comprises the boron-containing composite lithium metal negative electrode material according to the first aspect.

[0086] Embodiment 1: Preparation of Li-B-N composite lithium metal negative electrode material

[0087] In an argon glove box with the water oxygen value lower than 0.1 ppm, the mixture is placed in an iron crucible according to the mass ratio of Li:B:BN=7.5:1:1.5, the B and BN powder are stirred and dispersed into the molten lithium at 300-400℃, after the dispersion is completed, the temperature is gradually increased to 650℃ at 5℃ / min, and then heat preserved for 20 min, the crucible is taken out from the smelting furnace and quickly cooled to room temperature, to obtain a Li-B-N composite lithium metal ingot, which is forged into a thin strip (500-1500 μm) in a drying room (dew point <-40℃), and further rolled into a 50 μm thin strip by a rolling machine.

[0088] The sample phase is detected by an X-ray diffraction (XRD) instrument, and the sample is vacuum packaged in a test tank to prevent the influence of water and oxygen in the air on the sample. According to the XRD spectrum Figure 1 , the Li-B-N composite material is composed of Li, LiB and Li3BN2 three phases. The internal microstructure of the composite material is characterized by a field emission scanning electron microscope. The microstructure of the sample after the Li-B-N material is soaked in a 1M naphthalene tetrahydrofuran solution for 1 h is shown in Figure 2 , the LiB phase and Li3BN2 are uniformly wrapped in the metal lithium (a), and the Li3BN2 and LiB are nested with each other (b). As shown in Figure 3 , through further energy spectrum characterization, it can be seen that the Li3BN2 is in a granular shape, and the LiB is in a fibrous shape.

[0089] Example 2: Preparation of Li-B-C composite lithium metal anode material

[0090] In an argon glove box with water and oxygen values below 0.1 ppm, the mixture was placed in an iron crucible according to the mass ratio of Li:B:B4C=8.0:0.5:1.5, and the B and B4C powders were stirred and dispersed into molten lithium at 300-400°C. After dispersion, the temperature was gradually increased to 650°C at a rate of 5°C / min, and the sample was kept at this temperature for 10 min. The crucible was then removed from the smelting furnace and quickly cooled to room temperature. A Li-B-C composite lithium metal ingot was obtained. The ingot was forged into a thin strip (500-1500 μm) in a dry room (dew point <-40°C), and further rolled into a 100 μm thin strip using a rolling machine.

[0091] The sample phase was detected using an X-ray diffraction (XRD) instrument. The sample was vacuum-sealed in a test tank to prevent the influence of water and oxygen in the air on the sample. According to the XRD spectrum Figure 4 ), the Li-B-C composite material was composed of Li, LiB and LiC 12 phases. The internal microstructure of the composite material was characterized by field emission scanning electron microscopy and energy spectrum. The microstructure of the Li-B-C material after immersion in a 1M naphthalene tetrahydrofuran solution for 1 h is shown in Figure 5 . The fibrous LiB phase and the sheet-like LiC 12 phase (a) were observed, and they were nested with each other and uniformly distributed (b, c).

[0092] Example 3: Preparation of Li-B-O composite lithium metal anode material

[0093] In an argon glove box with water and oxygen values below 0.1 ppm, the mixture was placed in an iron crucible according to the mass ratio of Li:B:B2O3=7.0:1.5:1.5, and the B and B2O3 powders were stirred and dispersed into molten lithium at 300-400°C. After dispersion, the temperature was gradually increased to 650°C at a rate of 5°C / min, and the sample was kept at this temperature for 10 min. The crucible was then removed from the smelting furnace and quickly cooled to room temperature. A Li-B-C composite lithium metal ingot was obtained. The ingot was forged into a thin strip (500-1500 μm) in a dry room (dew point <-40°C), and further rolled into a 100 μm thin strip using a rolling machine.

[0094] The sample phase was detected using an X-ray diffraction (XRD) instrument. The sample was vacuum-sealed in a test tank to prevent the influence of water and oxygen in the air on the sample. According to the XRD spectrum Figure 6) shows that the Li-B-O composite material is composed of Li, LiB and Li2O three phases. The internal microstructure of the composite material was characterized by field emission scanning electron microscope and energy spectrum. The microstructure of the sample after the Li-B-N material was immersed in 1M naphthalene tetrahydrofuran solution for 1h is shown in Figure 7 As shown in FIG. 5, the fibrous LiB phase and the granular Li2O phase (a) can be clearly observed, and the Li2O particles are nested and wrapped by the LiB fibers (b, c).

[0095] Example 4: Preparation of Li-B-P composite lithium metal negative electrode material

[0096] In an argon glove box with water and oxygen values less than 0.1 ppm, the mixture was placed in an iron crucible according to the mass ratio of Li:B:BP=7.5:1.0:1.5, and the B and BP powders were stirred and dispersed into molten lithium at 300-400°C. After dispersion, the temperature was gradually increased to 650°C at a rate of 5°C / min, and the temperature was maintained for 10 min. The crucible was taken out of the smelting furnace and quickly cooled to room temperature. A Li-B-C composite lithium metal ingot was obtained. The ingot was forged into a thin strip (500-1500 μm) in a drying room (dew point <-40°C), and further rolled into a 100 μm thin strip using a rolling machine.

[0097] The sample phase was detected by X-ray diffraction (XRD) instrument. The sample was vacuum packaged in the test tank to prevent the influence of water and oxygen in the air on the sample. According to the XRD spectrum Figure 8 ) shows that the Li-B-P composite material is composed of Li, LiB and Li3P three phases. The internal microstructure of the composite material was characterized by field emission scanning electron microscope and energy spectrum. The microstructure of the sample after the Li-B-P material was immersed in 1M naphthalene tetrahydrofuran solution for 1h is shown in Figure 9 As shown in FIG. 6, the fibrous LiB phase and the granular Li3P (a) can be clearly observed, and the Li3P particles are nested and wrapped by the LiB fibers (b, c).

[0098] Example 5: Preparation of Li-B-Si composite lithium metal negative electrode material

[0099] In an argon glove box with water and oxygen values less than 0.1 ppm, the mixture was placed in an iron crucible according to the mass ratio of Li:B:B6Si=7.5:0.5:2.0, and the B and B6Si powders were stirred and dispersed into molten lithium at 300-400°C. After dispersion, the temperature was gradually increased to 650°C at a rate of 5°C / min, and the temperature was maintained for 20 min. The crucible was taken out of the smelting furnace and quickly cooled to room temperature. A Li-B-Si composite lithium metal ingot was obtained. The ingot was forged into a thin strip (500-1500 μm) in a drying room (dew point <-40°C), and further rolled into a 50 μm thin strip using a rolling machine.

[0100] The phase composition of the sample was analyzed using X-ray diffraction (XRD). The sample was vacuum-sealed in a test chamber to prevent the influence of water and oxygen in the air on the sample. Based on the XRD pattern... Figure 10 The data shows that the Li-B-Si composite material consists of Li, LiB, and Li 21 The composite material consists of three phases, Si5. The internal microstructure was characterized by field emission scanning electron microscopy and energy dispersive spectroscopy. The microstructure of the Li-B-Si material after immersion in a 1M naphthalene tetrahydrofuran solution for 1 h is shown below. Figure 11 As shown, fibrous LiB phase and granular Li phase can be clearly observed. 21 Si5(a), and Li 21 Si5 particles are dispersed between LiB fibers (b, c).

[0101] Example 6: Preparation of Li-BN* composite lithium metal anode material

[0102] 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:BN = 7.0:3.0. The BN powder was stirred and dispersed into the molten lithium at 300℃-400℃. After dispersion, the temperature was gradually increased to 650℃ at a rate of 5℃ / min and held for 20 min. The crucible was removed from the melting furnace and rapidly cooled to room temperature to obtain a Li-BN* composite lithium metal ingot. The ingot was forged into a thin strip (500-1500 μm) in a drying room (dew point < -40℃), and then further rolled into a 100 μm thin strip using a roller press.

[0103] The phase composition of the sample was analyzed using X-ray diffraction (XRD). The sample was vacuum-sealed in a test chamber to prevent the influence of water and oxygen in the air on the sample. Based on the XRD pattern... Figure 12 The results showed that the Li-BN* composite material consisted of three phases: Li, LiB, and Li3BN2. Its phase composition was identical to that of the Li-BN material obtained in Example 1, indicating that using boron nitride alone as the boron source could also produce a similar phase structure. The internal microstructure of the composite material was characterized by field emission scanning electron microscopy and energy dispersive spectroscopy. The microstructure of the Li-BN* material after immersion in a 1M naphthalene tetrahydrofuran solution for 1 h is shown below. Figure 13 As shown, fibrous LiB phase and granular Li3BN2 can be clearly observed (a), and Li3BN2 particles are diffusely distributed between LiB fibers (b, c).

[0104] Example 7: Battery fabrication

[0105] (1) Celgard 2400 was used as the diaphragm, and the electrolyte consisted of 1 mol of lithium di(trifluoromethanesulfonyl)imide (LiTFI) / 1,2-dimethoxyethane (DME) + 1,3-dioxocyclopentane (DOL) (volume ratio 1:1) and 2% Li2NO3 additive.

[0106] Using Li-BN as the positive and negative electrodes in Example 1, a CR2016 coin cell symmetrical battery was assembled to obtain battery Sym-1.

[0107] Using Li-BC as the positive and negative electrodes in Example 2, a CR2016 coin cell symmetrical battery was assembled to obtain battery Sym-2;

[0108] Using Li-BO as the positive and negative electrodes in Example 3, a CR2016 coin cell symmetrical battery was assembled to obtain battery Sym-3;

[0109] Using Li-BP as the positive and negative electrodes in Example 4, a CR2016 coin cell symmetrical battery was assembled to obtain battery Sym-4;

[0110] Using Li-B-Si as the positive and negative electrodes in Example 5, a CR2016 coin cell symmetrical battery was assembled to obtain battery Sym-5.

[0111] ① The four types of batteries were tested at 0.5 mA / cm 2 Constant current charging was performed at a current density to 1V, and the specific capacity-voltage curves were obtained for each. For example... Figure 14 , 15 As shown in Figures 16, 17, and 18, with 0.1V as the voltage cutoff plateau, Li-

[0112] The actual discharge specific capacities of BN, Li-BC, Li-BO, Li-BP, and Li-B-Si are 2393 mAh / g, respectively.

[0113] The composite anodes contain more than 50% reversible active lithium capacity, with capacities of 2579 mAh / g, 2045 mAh / g, 2286 mAh / g, and 2239 mAh / g.

[0114] ② Four symmetrical Nyquist cells were obtained using an electrochemical workstation at frequencies ranging from 100,000 to 0.1 Hz.

[0115] Atlas. For example Figure 19 As shown, the diameter of the semicircular arc in the high-frequency region reflects the resistance of the electrode interface film, Li-BN,

[0116] The membrane impedances of Li-BP, Li-BO, and Li-BC are 35, 42, 47.5, and 51 Ω, respectively.

[0117] ③The four batteries were subjected to constant current charge-discharge cycle test under the condition of 1 mA / cm 2 , 1 mAh / cm 2 , and the voltage-time curve of each battery was obtained. The length of the upper and lower interval of the curve reflects the polarization of the electrochemical reaction in the battery, and the length of the stable interval of the curve reflects the cycle reversibility and the life of the battery. As shown in Figure 20 , the four groups of batteries all stably operated for at least 1500 h with a lower polarization voltage (<35 mV).

[0118] (2) Celgard 2400 was used as the separator, 1 mol lithium hexafluorophosphate (LiPF6) / ethylene carbonate (EC) + methyl ethyl carbonate (EMC) + fluoroethylene carbonate (FEC) (volume ratio 3:7:1) was used as the electrolyte, and commercial LiNi 2 Co 0.8 Mn0.1O2 (NCM811) with a loading of 15 mg / cm 0.1 was used as the positive electrode, and the Li-B-N material in Example 1 was used as the negative electrode to assemble a button full battery, and the battery was cycled at 0.5C; as shown in Figure 21 , the battery still had a capacity retention rate of 80% after 250 cycles.

[0119] (3) Celgard 2400 was used as the separator, 1 mol lithium hexafluorophosphate (LiPF6) / ethylene carbonate (EC) + methyl ethyl carbonate (EMC) + fluoroethylene carbonate (FEC) (volume ratio 3:7:1) was used as the electrolyte, and commercial LiFePO4 (LFP) with a loading of 14 mg / cm 2 was used as the positive electrode, and the Li-B-P material in Example 4 was used as the negative electrode to assemble a button full battery, and the battery was cycled at 2C; as shown in Figure 22 , the battery still had a capacity retention rate of 86.4% after 400 cycles.

[0120] (3) Celgard 2400 was used as the separator, 1 mol lithium hexafluorophosphate (LiPF6) / ethylene carbonate (EC) + methyl ethyl carbonate (EMC) + fluoroethylene carbonate (FEC) (volume ratio 3:7:1) was used as the electrolyte, and commercial LiCoO2 (LCO) with a loading of 20 mg / cm 2 was used as the positive electrode, and the Li-B-O material in Example 3 was used as the negative electrode to assemble a soft package full battery, and the battery was cycled at 0.2 / 0.5; as shown in Figure 23 , the battery still had a capacity retention rate of 90.1% after 450 cycles.

[0121] Comparative Example 1

[0122] In an argon glove box with water and oxygen content less than 0.1 ppm, the mixture was placed in an iron crucible according to the mass ratio of Li:B = 8:2, the B powder was stirred and dispersed into molten lithium at 300-400°C, after dispersion, the temperature was gradually increased to 650°C at 5°C / min and kept for 10 min, the crucible was taken out of the smelting furnace and quickly cooled to room temperature, and a Li-B composite lithium metal ingot was obtained. The ingot was forged into a thin strip (500-1500 μm) in a dry room (dew point <-40°C), and further rolled into a 100 μm thin strip using a rolling machine. As shown in Figure 24 The XRD pattern of the sample shows that the sample is composed of pure lithium and LiB two phases.

[0123] Preparation of the battery

[0124] (1) Celgard 2400 was used as the separator, 1 mol lithium bis(trifluoromethylsulfonyl) imide (LiTFI) / 1,2-dimethoxyethane (DME) + 1,3-dioxolane (DOL) (volume ratio 1:1) containing 2% Li2NO3 additive electrolyte.

[0125] Li-B was used as the positive and negative electrode to assemble CR2016 button cells, and battery Sym-6 was obtained;

[0126] Li foil was used as the positive and negative electrode to assemble CR2016 button cells, and battery Sym-7 was obtained;

[0127] The Nyquist plot of the symmetrical battery before cycling was measured by an electrochemical workstation at a frequency of 100000-0.1 Hz. As shown in Figure 25 Li and Li-B show interface impedance of 77Ω and 123Ω, respectively, which is much larger than the aforementioned boron-containing composite lithium metal negative electrode.

[0128] Sym6 and Sym7 were repeatedly charged and discharged at 1 mAh / cm 2 , 1 mA / cm 2 , and the cycle stability was tested. As shown in Figure 26 Li and LiB started to show voltage curve fluctuations at a relatively high polarization voltage (>40 mV) after only about 200 h and 800 h of cycling, and the polarization voltage increased rapidly, indicating that the internal state of the battery began to deteriorate, which is in sharp contrast to the aforementioned boron-containing composite lithium metal negative electrode.

[0129] (2) Celgard 2400 was used as the separator, 1 mol lithium hexafluorophosphate (LiPF6) / ethylene carbonate (EC) + methyl ethyl carbonate (EMC) + fluoroethylene carbonate (FEC) (volume ratio 3:7:1) as the electrolyte, and the load was 15 mg / cm 2 of commercial LiNi0.8 Co 0.1 Mn0.1O2 as the positive electrode, the Li-B material in Comparative Example 1 as the negative electrode, and assembled into a button-type full cell, and cycled at 0.5C; as shown in FIG. 2B, the capacity of the battery rapidly decayed to 61.3% of the initial capacity after 100 cycles. Figure 27

[0130] (3) Celgard 2400 was used as the separator, 1 mol lithium hexafluorophosphate (LiPF6) / ethylene carbonate (EC) + methyl ethyl carbonate (EMC) + fluoroethylene carbonate (FEC) (volume ratio 3:7:1) was used as the electrolyte, and the loading was 15 mg / cm2. Commercial LiFePO4 with a loading of 15 mg / cm2was used as the positive electrode, and the Li-B material in Comparative Example 1 and lithium foil were used as the negative electrode, respectively, to assemble button-type full cells, and the cells were cycled at 2C; as shown in FIG. 3B, the capacity of the cells with Li and Li-B as the negative electrode rapidly decayed after about 60 and 220 cycles, respectively. 2 Figure 28

[0131] (4) Celgard 2400 was used as the separator, 1 mol lithium hexafluorophosphate (LiPF6) / ethylene carbonate (EC) + methyl ethyl carbonate (EMC) + fluoroethylene carbonate (FEC) (volume ratio 3:7:1) was used as the electrolyte, and the loading was 15 mg / cm2. Commercial LiCoO2 with a loading of 15 mg / cm2was used as the positive electrode, and the Li-B material in Comparative Example 1 was used as the negative electrode to assemble soft-pack full cells, and the cells were cycled at 0.2 / 0.5C; as shown in FIG. 4B, the capacity retention rate of the cells was only 63% after 450 cycles. 2 Figure 29

[0132] In summary, the present application uses borides and elemental boron together as the boron source to construct a boron-containing composite lithium metal negative electrode material. The in-situ reaction of the borides with lithium enables the symbiosis and nesting of LiB fiber phases and other alloy phases, and the comprehensive improvement of the mechanical, thermodynamic and electrochemical properties of the matrix, thereby improving the cycle life of lithium batteries.

[0133] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of various equivalent modifications or replacements within the technical range disclosed in the present application, and these modifications or replacements shall be encompassed in the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.​​​​​

Claims

1. A method for preparing a boron-containing composite lithium metal anode material, characterized in that: The boron-containing composite lithium metal negative electrode material is composed of lithium, boron and other elements T, wherein the other elements T are one or more selected from rare earth metals, calcium, magnesium, silicon, aluminum, titanium, iron, chromium, nickel, manganese, molybdenum, niobium, zirconium, antimony, carbon, nitrogen, oxygen, phosphorus, sulfur, selenium, arsenic, bromine and iodine; Based on the total mass of the boron-containing composite lithium negative electrode material, the mass percentage of lithium is 50-85%, the mass percentage of boron is 10-30%, the mass percentage of other alloying elements T is 5-20%, and the total mass percentage of boron and other alloying elements T in the composite material is 15-50%; the boron element is provided by boron-containing compounds and elemental boron; The other elements T in the boron-containing composite lithium metal negative electrode material are derived from the corresponding boron-containing compounds added during smelting; The preparation method comprises the following steps: Step 1: Under vacuum or protective atmosphere, the mass ratio of elemental lithium, elemental boron and boron-containing compounds is 50-85: 0.01-49.99: 0.01-50; elemental lithium, elemental boron and boron-containing compounds are weighed; the boron-containing compounds are selected from at least one of borides, boron-containing carbides, boron-containing oxides, boron-containing nitrides, boron-containing phosphides, boron-containing sulfides, boron-containing selenides, boron-containing arsenides, boron-containing bromides and boron-containing iodides; the chemical formula of the boron-containing compound is BxTy; element T is selected from one or more of rare earth metals, calcium, magnesium, silicon, aluminum, titanium, iron, chromium, nickel, manganese, molybdenum, niobium, zirconium, antimony, carbon, nitrogen, oxygen, phosphorus, sulfur, selenium, arsenic, bromine and iodine; Step 2: Put the weighed materials into a vacuum / argon smelting furnace, heat and continuously stir after the lithium is melted, fully mix and react; the reaction temperature is 200-700℃, and the reaction time is 5min-100h; Step 3: The composite material obtained in step 2 is cooled and solidified in a special mold to obtain an ingot.

2. The method for preparing a boron-containing composite lithium metal anode material according to claim 1, characterized in that: The elemental boron is crystalline or amorphous boron powder, and the particle size of the boron powder and the boron-containing compound is 0.01-150μm.

3. The preparation method of the boron-containing composite lithium metal negative electrode material according to claim 1, characterized in that: In step 1, when elemental boron is used, the mass ratio of elemental lithium, elemental boron and boron-containing compounds is 70-80: 3-18: 10-30.

4. The method of claim 1, wherein the method further comprises: The obtained ingot is rolled to obtain a thin strip; the thickness of the thin strip is 100-2000μm, and the obtained thin strip is further rolled to obtain an ultra-thin strip; the thickness of the ultra-thin strip is less than or equal to 100μm.

5. The preparation method of the boron-containing composite lithium metal anode material according to any one of claims 1-2, characterized in that: The obtained boron-containing composite lithium metal negative electrode material is used in energy storage equipment.

6. The method of claim 5, wherein the method further comprises: The energy storage equipment includes a lithium battery; the lithium battery includes a positive electrode, a negative electrode, a separator and an electrolyte, wherein the negative electrode comprises the boron-containing composite lithium metal negative electrode material.

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