Lithium metal negative electrode material with ion / electron mixed conductor network as well as preparation method and application of lithium metal negative electrode material

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a preparation method of a lithium negative electrode with an ion / electron mixed conductor framework and application of the lithium negative electrode in the lithium ion battery. In order to solve the problems of lithium dendrite growth, volume expansion, corrosion and the like of the existing lithium negative electrode material in the battery cycle process, the invention provides an innovative solution that a double-fiber network skeleton consisting of a LiB compound and VGCF is constructed through a mechanical rolling method and a processing regulation and control process so as to enhance the electrode structure stability and inhibit the generation of lithium dendrites. The rate efficiency, the cycle life and the mechanical property of the prepared lithium negative electrode material are evaluated through a symmetric battery test, microstructure and electrochemical property analysis is carried out through TEM, SEM, XRD and other means, and the lithium negative electrode material has excellent comprehensive mechanical property, can inhibit volume expansion, simplifies the processing flow, and is suitable for large-scale production. And the method is suitable for commercial production of new energy batteries. By implementing the invention, the development of a lithium ion battery technology is expected to be promoted, and the requirements of modern society on an efficient and safe energy storage system are met.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of energy storage materials, and particularly relates to a lithium metal anode material with an ion / electron mixed conductor network and a preparation method and application thereof. BACKGROUND

[0002] With the increasing demand for portable electronic devices and electric vehicles worldwide, the market is increasingly demanding lithium-ion batteries with high energy density, long cycle life, and high safety. The driving range has become a key bottleneck for the development of the electric vehicle industry. Lithium metal has a very high theoretical specific capacity (3860 mAh / g) and the lowest electrochemical potential (-3.040 V vs. standard hydrogen electrode), making it an ideal anode material for improving battery performance. However, the preparation method of traditional lithium anodes has problems such as complex process, high cost, uneven ion and electron transport, etc., which limits the further improvement of battery performance. The dendrite growth, volume expansion and corrosion problems of lithium anode during battery cycling not only shorten the battery life, but also may cause serious safety accidents.

[0003] Chinese patent CN202211561222.1 discloses a lithium-boron-zinc alloy anode for inhibiting dendrite growth and a preparation method thereof. The scheme introduces a uniform lithium-zinc alloy layer on the surface of lithium-boron alloy, which not only makes full use of the advantages of lithium-boron alloy, but also makes the lithium affinity of the alloy anode surface better, the lithium ion rectification ability stronger, and the local current density smaller.

[0004] Chinese patent CN202111257500.X discloses a porous carbon composite lithium anode with in-situ doping of heteroatoms, a preparation method and application thereof. The scheme constructs a porous carbon framework with heteroatom doping, and then mixes and grinds the carbon framework with a conductive agent and a binder to obtain a porous carbon composite lithium anode by compounding with molten lithium, which directionally controls the deposition / dissolution behavior of lithium and slows down the uneven deposition and dendrite growth of lithium ions.

[0005] Chinese patent CN 116936790 A discloses a lithium alloy anode material, a preparation method thereof and a lithium-ion battery. The scheme introduces non-lithium alloy elements into lithium by melting, which enriches at the grain boundaries of lithium metal, thereby alleviating the side reaction of lithium alloy with electrolyte, maintaining good wettability and stability of lithium alloy anode, and improving the cycle life thereof.

[0006] 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.

[0007] Lithium boron compounds have been widely concerned as high specific energy negative electrode. But in the current research, the problem of solving the structure strength of lithium electrode and reducing the total weight has not been effectively solved, not to mention how to design and obtain low density, high strength, high electrical performance and high stability of lithium boron negative electrode.

[0008] The present application proposes a lithium negative electrode preparation method with an ion / electron mixed conductor framework. Through innovative material design and process optimization, the uniform distribution and rapid transmission of ions and electrons in the negative electrode material are realized, solving the problems of lithium dendrite growth, volume change and anode corrosion. The core of the present application is to construct a new type of ion / electron mixed conductor framework, which is formed by a porous framework structure of carbon phase and lithium boron compound fibers. The porous framework can not only act as a lithium deposition host to inhibit volume fluctuation and dendrite growth, but also can improve the mechanical strength of the substrate to realize self-supporting of the electrode, expanding the application space of lithium metal negative electrode. The carbon phase fiber and LiB compound fiber used have high tensile strength, high toughness, large elastic modulus, excellent thermal conductivity and good adsorption performance, which can realize the stability of the framework structure. At the same time, the lithium boron-carbon double fiber composite material is tested for rate efficiency, cycle life, metal tensile and puncture experiments, etc. to evaluate its comprehensive mechanical properties and the influence on the electrochemical performance of lithium battery. At the same time, TEM, SEM, XRD and in-situ electron microscope are used to determine the changes of lithium boron-carbon double fiber in the battery cycle process and its influence on lithium metal deposition. This method has simple preparation process, high synthesis efficiency and large electrode specific capacity regulation space, which is very suitable for industrial standardized production. SUMMARY

[0009] In view of the shortcomings of the prior art, the first object of the present application is to provide a lithium metal negative electrode material with an ion / electron mixed conductor network, which is designed to construct a high-efficiency ion / electron conductor network and double-fiber framework structure by in-situ preparation of LIB compound and conductive fiber laminating dispersion, to provide mutual support for the electrode, improve the deposition electric field uniformity and ion transmission speed, and solve the problems of serious lithium metal negative electrode dendrite growth, negative electrode volume expansion and short cycle life, i.e. excellent electrical performance. At the same time, the lithium metal negative electrode material with ion / electron mixed conductor network designed and prepared by the present application also has the characteristics of low density, high strength, high stability, etc.

[0010] The second object of the present application is to provide a preparation method of the lithium metal negative electrode material with the ion / electron mixed conductor network. A structure configuration of ion / electron double-fiber network conductor framework is provided by composite laminating and in-situ reaction method, and a high-efficiency, low-cost lithium metal negative electrode material preparation method with ion / electron mixed conductor network is provided.

[0011] The present application provides a lithium metal negative electrode material with an ion / electron mixed conductor network, which is composed of metallic lithium, boron and conductive carbon fibers, wherein the conductive carbon fibers are one or more of VGCF and CNT.

[0012] Based on the total mass of the lithium metal negative electrode material with the ion / electron mixed conductor network, the mass percentage of metallic lithium is 50% to 85%, the mass percentage of boron is 10% to 30%, and the mass percentage of carbon fibers is 1% to 50%.

[0013] In another aspect, the present application also provides a preparation method of the lithium metal negative electrode material with the ion / electron mixed conductor network, which comprises the following steps:

[0014] Step 1: Under vacuum or argon (water oxygen value less than 100 ppm) atmosphere, according to the mass ratio of elemental lithium: elemental boron: M = 50 to 85: 0.01 to 49.99: 0.01 to 50, elemental lithium, elemental boron and M are weighed; 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

[0015] When elemental boron is not used, elemental boron is weighed according to the mass ratio of elemental lithium to M of 50 to 85: 3 to 40; M; 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;

[0016] Step 2: Put the weighed materials into a vacuum / argon smelting furnace, heat and continuously stir for a certain time after the lithium is melted, fully mix and react; the reaction temperature is 200℃ to 700℃, and the reaction time is 5min to 100h;

[0017] Step 3: Cool and solidify the composite material obtained in step 2 in a special mold to obtain an ingot.

[0018] Step 4: Roll the ingot obtained in step 3 to obtain a thin strip, and mix and roll the thin strip and the carbon-containing conductive fiber according to the mass ratio of LiB: N = 50 to 85: 0.01 to 50, preferably 60 to 75: 25 to 40, further preferably 68 to 72: 28 to 32, and more preferably 70: 30, to form a double-fiber composite network skeleton; N is selected from at least one of VGCF and CNT.

[0019] For the scheme using elemental boron, the mass ratio of elemental lithium to elemental boron is 60 to 80: 20 to 40; as a further preferred, the mass ratio of elemental lithium to elemental boron is 70 to 80: 20 to 30.

[0020] As preferred, the N is selected from at least one of VGCF, CNT;

[0021] As preferred, the N fiber aspect ratio is 10-200;

[0022] As preferred, the mass ratio of elemental boron to M in the preparation method of the lithium metal negative electrode material with ion / electron mixed conductor network 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 0.01-150 μm, preferably 0.05-30 μm, and further preferably 0.1-10 μm.

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

[0025] As preferred, in the preparation method of the lithium metal negative electrode material with ion / electron mixed conductor network, after heating to the highest set temperature in step 2, the temperature is kept for 8-25 min.

[0026] When the obtained ingot is rolled to obtain a thin strip, the total deformation amount is controlled to be 20%-50%.

[0027] In the preparation method of the lithium metal negative electrode material with ion / electron mixed conductor network, the obtained ingot is rolled to obtain a thin strip; the thickness of the thin strip is 100-2000 μm. Of course, this thickness range also includes 100-1500 μm.

[0028] In the preparation method of the lithium metal negative electrode material with ion / electron mixed conductor network, the obtained thin strip and the carbon-containing conductive fiber are mechanically stacked and rolled to obtain a thin strip; the thickness of the thin strip is less than or equal to 100 μm. Preferably, it is 5-100 μm. If the rolling process can stably prepare a thinner product with excellent surface quality, the product can also be used in the present application. The lithium metal negative electrode material with ion / electron mixed conductor network involved and prepared in the present application is used in energy storage devices.

[0029] As further preferred, the energy storage device includes a lithium battery. Of course, it also includes a thermal battery.

[0030] The lithium battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode includes the lithium metal negative electrode material with ion / electron mixed conductor network.

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

[0032] The application adopts boron-containing compound M (including at least one of boride, boron-containing carbide, boron-containing oxide, boron-containing nitride, boron-containing phosphide, boron-containing sulfide, boron-containing selenide, boron-containing arsenide, boron-containing bromide, boron-containing iodide) as a main boron source to form a LiB fiber phase and other alloy phases coexisting with the LiB fiber phase through in-situ reaction with lithium, and then to form a LiB@VGCF double-fiber ion / electron mixed conductor network skeleton negative electrode with the conductive fiber VGCF through in-situ reaction. The negative electrode has a unique morphology structure, electron / ion conductivity and lithium affinity, and can make the negative electrode have better mechanical properties, thermodynamic stability, structural stability, electrode reaction kinetics and electrochemical performance, so as to improve the machinability of the electrode material, realize mutual support of the electrode structure, inhibit the volume expansion and dendrite formation in the electrochemical process, and improve the cycle life of the electrode. On the other hand, by adding elemental boron to regulate the content of lithium boron fiber to make it become the main skeleton supporting phase, and 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 lithium metal negative electrode material with the ion / electron mixed conductor network provided by the application is economical and efficient, has good stability, high repeatability, and can be produced on a large scale.

[0034] The lithium metal negative electrode material with the ion / electron mixed conductor network provided by the application has obviously better electrochemical performance in symmetrical batteries with different current densities and capacities, and full batteries with different systems, compared with pure lithium and lithium boron alloy phases.

[0035] The lithium metal negative electrode material with the ion / electron mixed conductor network designed and prepared by the application has a stable double-fiber network skeleton, and the lithium boron alloy phase and the second alloy phase have better interface adhesion, structural stability and thermal stability, so that when the lithium metal negative electrode material is used as a thermal battery electrode material, it also exhibits excellent performance. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 XRD diffraction pattern of LiB compound;

[0037] Figure 2 Surface micro-morphology of LiB compound;

[0038] Figure 3 Transmission morphology of LiB compound

[0039] Figure 4 Physical picture of LiB@VGCF (mass ratio of LiB to VGCF fiber is 7:3) double-fiber network skeleton lithium metal negative electrode material;

[0040] Figure 5Microscopic surface morphology profile for LiB@VGCF (LiB ribbon to VGCF fiber mass ratio 7:3) dual fiber network scaffold lithium metal anode material;

[0041] Figure 6 Nyquist plot for Li and LiB@VGCF (LiB ribbon to VGCF fiber mass ratio 7:3) dual fiber network scaffold lithium metal anode material symmetric cell;

[0042] Figure 7 Cycle time-voltage plot for Li and LiB@VGCF (LiB ribbon to VGCF fiber mass ratio 7:3) dual fiber network scaffold lithium metal anode material symmetric cell at 1 mA / cm 2 , 5 mAh / cm 2

[0043] Figure 8 Cycle time-voltage plot for Li and LiB@VGCF (LiB ribbon to VGCF fiber mass ratio 7:3) dual fiber network scaffold lithium metal anode material symmetric cell at 5 mA / cm 2 , 1 mAh / cm 2

[0044] Figure 9 Li|LFP and LiB@VGCF|LFP (LiB ribbon to VGCF fiber mass ratio 7:3) full cell cycle performance;

[0045] Figure 10 Cycle time-voltage plot for LiB anode material symmetric cell at 1 mA / cm 2 , 3 mAh / cm 2

[0046] Figure 11 LiB|LFP full cell cycle performance;

[0047] Figure 12 Cycle time-voltage plot for LiB@VGCF anode material (LiB ribbon to VGCF fiber mass ratio 6:4) symmetric cell at 1 mA / cm 2 , 3 mAh / cm 2

[0048] Figure 13 LiB@VGCF|LFP full cell cycle performance for LiB@VGCF anode material (LiB ribbon to VGCF fiber mass ratio 6:4);

[0049] Figure 14 Cycle time-voltage plot for LiB@VGCF anode material (LiB ribbon to VGCF fiber mass ratio 3:1) symmetric cell at 1 mA / cm​​​​2 , 3 mAh / cm 2 cycle time-voltage plots under the conditions of 1 mA / cm

[0050] Figure 15 cycle performance of LiB@VGCF|LFP full cell assembled with LiB@VGCF negative material (LiB ribbon and VGCF fiber mass ratio 2:1);

[0051] Figure 16 cycle time-voltage plots under the conditions of 1 mA / cm 2 , 3 mAh / cm 2 cycle time-voltage plots under the conditions of 1 mA / cm

[0052] Figure 17 cycle performance of LiB@VGCF|LFP full cell assembled with LiB@VGCF negative material (LiB ribbon and VGCF fiber mass ratio 2:1);

[0053] Figure 18 cycle time-voltage plots under the conditions of 1 mA / cm 2 , 3 mAh / cm 2 cycle time-voltage plots under the conditions of 1 mA / cm

[0054] Figure 19 cycle performance of LiB@VGCF|LFP full cell assembled with LiB@VGCF negative material (LiB ribbon and VGCF fiber mass ratio 7:3, prepared by multi-layer stacking); DETAILED DESCRIPTION

[0055] The specific implementation methods of the present application will be explained in more detail below. These examples are intended to provide illustration and are not intended to limit the present application to only these embodiments. It will be apparent to those skilled in the art within the framework of the present application that appropriate adjustments and changes to the present application are obvious. Any improvement or alternative under the guidance of the present embodiment should be considered as the protection scope covered by the claims of the present application. Unless specifically indicated, all components, percentages and ratios mentioned in the following examples are based on weight calculation. In addition, the reagents used in the examples can be purchased on the market or synthesized by standard methods, and can be used directly without additional treatment. Similarly, the instruments used in the examples can also be purchased on the market.

[0056] The foregoing summary of the application is not intended to describe every implementation or implementation method disclosed in the present application. The following description will provide some specific exemplary embodiments. Throughout the text, guidance is provided through a series of examples, which can be applied in different combinations. In various examples, only representative cases are listed and should not be understood as complete enumeration.

[0057] The present application provides a lithium boron-carbon double fiber lattice skeleton negative electrode. The carbon phase is mainly selected from VGCF (vapor grown carbon fiber) and CNT, and the lithium boron phase adopts an interpenetrating structure, and supports each other to improve the performance of the negative electrode.

[0058] The present application also provides a preparation method of the negative electrode material, comprising the following steps:

[0059] a. Under vacuum or argon (water oxygen value less than 100 ppm) atmosphere, metal lithium and boron are weighed according to a certain mass ratio;

[0060] b. The weighed lithium and boron 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 lithium are fully mixed and reacted;

[0061] 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;

[0062] d. The ingot is converted into an alloy thin strip suitable for rolling, and the thickness of the alloy thin strip is preferably about 50μm;

[0063] e. Selecting carbon phase material; the carbon phase material is VGCF or CNT, and the specification is a diameter of 8-15μm and a length of 100-300μm;

[0064] f. One layer of alloy thin strip, one layer of carbon phase material are stacked (the total thickness of one layer of alloy thin strip / one layer of carbon phase material after stacking is 100 pm), and then gradient rolling method (temperature 200-300°C, pressure 10-50 MPa, speed 0.1-1 m / min, and rolling number 10-30 times) is used to continuously adjust the stacking number and roller spacing to make the bulk phase uniformly distributed and complete the lapping of the double fibers, so as to obtain a 50 pm thick composite material, thereby constructing an ion / electron hybrid conductor network skeleton; or one layer of carbon phase material, one layer of alloy thin strip, and one layer of carbon phase material are stacked (the total thickness of one layer of carbon phase material / one layer of alloy thin strip / one layer of carbon phase material after stacking is 100 pm), and then gradient rolling method (temperature 200-300°C, pressure 10-50 MPa, speed 0.1-1 m / min, and rolling number 10-30 times) is used to continuously adjust the stacking number and roller spacing to make the bulk phase uniformly distributed and complete the lapping of the double fibers, so as to obtain a 50 pm thick composite material, thereby constructing an ion / electron hybrid conductor network skeleton;

[0065] The boron powder can be optional crystalline or amorphous boron, and the particle size range of the boron powder should be 0.01 pm to 150 pm, preferably 0.05 pm to 30 pm, and further preferably 0.1 pm to 10 pm;

[0066] The VGCF fiber aspect ratio range is 10 to 200;

[0067] According to the embodiments of the present application, in order to ensure the sufficient reaction of metal lithium and boron and the uniform distribution of the reactants, the reaction temperature is 200-650°C, or 300-650°C, or 500-650°C, and the reaction time includes the whole process time from the start of heating to the holding and then to the stop of holding, which is 5 min to 100 h; in the specific operation, after heating to the highest set temperature, the holding is 8-25 min.

[0068] And the addition order of lithium and boron is not limited. The boron can be added into the lithium after the lithium is melted, added one after another or simultaneously, or added into the crucible together with the lithium for heating.

[0069] Example 1: Preparation of LiB@VGCF double fiber network skeleton lithium negative electrode

[0070] In an argon glove box with water oxygen value lower than 0.1 ppm, the mixture is placed in an iron crucible according to the mass ratio of Li:B:78:22, the B powder is stirred and dispersed into the molten lithium at 300-400°C, after the dispersion is completed, the temperature is gradually increased to 650°C at a rate of 5°C / min, and then held for 20 min, the crucible is taken out from the smelting furnace and quickly cooled to room temperature, a Li-B metal ingot is obtained, the ingot is forged into a thin strip (500-1500 pm) in a dry room (dew point <-40°C), and a roller press is used to further roll it into a 50 pm LiB fiber thin strip.

[0071] The sample phase was detected by X-ray diffraction (XRD) instrument, and the sample was vacuum packaged in the test groove to prevent the influence of water and oxygen in the air on the sample. According to the XRD spectrum, Figure 1 ), it is shown that the Li-B composite material is composed of Li, LiB and two phases. The internal microstructure of the composite material was characterized by field emission scanning electron microscope. The microstructure of the sample after the Li-B material was immersed in 1 M naphthalene tetrahydrofuran solution for 1 h is shown in Figure 2 , the LiB compound has a compact fiber structure, and the average spacing between the fibers is about 3.1 μm, and the crude fiber diameter can be 5-10 μm, which has the potential of double fiber combination. As Figure 3 , by further transmission electron microscopy, it can be seen that LiB has regularly arranged fibers, and the fiber spacing is 0.334 nm.

[0072] The LiB fiber tape obtained by further rolling with a rolling machine was stacked with VGCF fibers in a coating rolling manner, and then calendering was carried out (the total thickness of the stacked alloy tape / carbon phase material was 100 μm, and the thickness of the alloy tape was 50 μm) (according to the mass ratio, alloy tape:VGCF fiber=7:3), and a 50 μm thick tape was obtained. LiB@VGCF double fiber network skeleton lithium negative electrode Figure 4 ). The density of the LiB@VGCF double fiber network skeleton lithium negative electrode is 2.2 g / cm³. The tensile strength of the LiB@VGCF double fiber network skeleton lithium negative electrode is greater than 10 MPa, specifically 12 MPa, the compressive strength is greater than 20 MPa, specifically 22 MPa, and the stability is more than 80%, specifically 85.2%, after 1000 cycles at a current density of 1 mA / cm².

[0073] The surface morphology of the LiB@VGCF double fiber network skeleton lithium negative electrode was observed by scanning electron microscope Figure 5 , it is observed that the LiB fibers and the VGCF fibers are alternately inserted and staggered, providing mutual support for the electrode structure.

[0074] Preparation of battery

[0075] (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), and the electrolyte containing 2% Li2NO3 additive.

[0076] The LiB@VGCF double fiber network skeleton in Example 1 was used as the positive and negative electrodes to assemble a CR2016 button-shaped symmetrical battery, and a battery Sym-1 was obtained;

[0077] ①The symmetric cell Nyquist plot was obtained by electrochemical workstation at 100000-0.1 Hz frequency. As shown in the figure, the diameter of the high-frequency semicircle arc reflects the size of the electrode interface film resistance, and the film impedance of LiB@VGCF is 110 Ω. Figure 6

[0078] ②The battery was tested by constant current charge-discharge cycle under the condition of 1 mA / cm 2 , 5mAh / cm 2 , and the voltage-time curve of each was obtained. The length of the upper and lower intervals of the curve reflects the polarization of 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 the figure, the battery stably runs at a lower polarization voltage (<35 mV) for at least 1400 h. Figure 7

[0079] ③The battery was tested by constant current charge-discharge cycle under the condition of 5 mA / cm 2 , 1mAh / cm 2 , and the voltage-time curve of each was obtained. As shown in the figure, the battery stably runs at a lower polarization voltage (<35 mV) for at least 495 h. Figure 8

[0080] (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 the commercial lithium iron phosphate with a loading of 1 mol was used as the positive electrode. The LiB@VGCF material in Example 1 was used as the negative electrode to assemble a button full cell, and the cycle was carried out at 1C. As shown in the figure, the battery still has a capacity retention rate of 90% after 150 cycles. Figure 9

[0081] Example 2

[0082] Other conditions are the same as those in Example 1, except that during the rolling compounding, the mass ratio of the alloy thin strip: VGCF fiber is 6:4.

[0083] The tensile strength of the obtained LiB@VGCF fiber network skeleton lithium negative electrode is 12 MPa, the compressive strength is 22 MPa, and the capacity retention rate is still 85.2% after 1000 cycles at a current density of 1 mA / cm².

[0084] The obtained LiB@VGCF double-fiber network skeleton was used as the positive and negative electrodes to assemble a CR2016 button symmetric cell, and the cycle was carried out at 1 mA / cm 2 , 3mAh / cm 2 ​​​​Constant current charge-discharge cycle test was performed under the conditions, and the results are as follows: Figure 12 As shown, the battery operated stably for at least 400 hours at a low polarization voltage (<35mV).

[0085] Celgard 2400 was used as the separator, and 1 mol lithium hexafluorophosphate (LiPF6) / ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + fluoroethylene carbonate (FEC) (volume ratio 3:7:1) was used as the electrolyte. Commercially available lithium iron phosphate was used as the positive electrode, and the LiB@VGCF material from Example 2 was used as the negative electrode to assemble a coin cell. Cyclic testing was conducted at 1C, and the results are as follows: Figure 13 As shown, the battery still retains 95.97% of its capacity after 250 cycles.

[0086] Example 3

[0087] Other conditions are the same as in Example 1, except that during rolling composite, the alloy strip:VGCF fiber ratio is 3:1 by mass.

[0088] The obtained LiB@VGCF dual-fiber network framework was used as the positive and negative electrodes to assemble CR2016 coin cells.

[0089] At 1 mA / cm 2 3mAh / cm 2 Constant current charge-discharge cycle test was performed under the conditions, and the results are as follows: Figure 14 As shown, the battery operated stably for at least 550 hours at a low polarization voltage (<35mV).

[0090] Celgard 2400 was used as the separator, and 1 mol lithium hexafluorophosphate (LiPF6) / ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + fluoroethylene carbonate (FEC) (volume ratio 3:7:1) was used as the electrolyte. Commercially available lithium iron phosphate was used as the positive electrode, and the LiB@VGCF material from Example 3 was used as the negative electrode to assemble a coin cell. Cycling tests were conducted at 1C, and the results are as follows: Figure 15 The battery still retains up to 90.1% of its capacity after 350 cycles.

[0091] Example 4

[0092] The other conditions are the same as in Example 1, except that during the rolling composite process, the alloy strip to CNT fiber ratio is 2:1 by mass.

[0093] The obtained LiB@CNT dual-fiber network framework was used as the positive and negative electrodes to assemble CR2016 coin cells with symmetric polarity. (The last part, "1 mA / cm," appears to be an unrelated fragment and is omitted from the translation.) 2 3mAh / cm2 Galvanostatic charge-discharge cycling tests were performed under the conditions of 0.1 mA / cm Figure 16 , 3mAh / cm , 3mAh / cm

[0094] The results are shown in FIG. 6. The battery stably operated with a low polarization voltage (<35 mV) for at least 550 h. Figure 17

[0095] Example 5

[0096] The other conditions were consistent with Example 1, except that: during the rolling compounding, a roll press was used to further stack the LiB fiber tape and VGCF fibers in a coating rolling manner and then perform calendering (the total thickness of the stacked carbon phase material / alloy tape / carbon phase material was 100 pm, the thickness of the carbon phase material was 25 pm, and the thickness of the alloy tape was 50 pm) (the mass ratio of the alloy tape:VGCF fiber was 7:3), and a 50 pm thick tape was obtained by rolling. The LiB@VGCF double-fiber network skeleton lithium negative electrode was obtained.

[0097] The obtained LiB@VGCF double-fiber network skeleton was used as the positive and negative electrodes to assemble a CR2016 button-shaped symmetrical battery, and galvanostatic charge-discharge cycling tests were performed under the conditions of 0.1 mA / cm 2 , 3mAh / cm 2 The battery stably operated with a low polarization voltage (<35 mV) for at least 600 h.

[0098] 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, commercially available lithium iron phosphate with a loading of 1 mg / cm Figure 19 The results are shown in FIG. 8. The battery still had a capacity retention rate of up to 89.3% after 400 cycles.

[0099] Comparative Example 1

[0100] 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 = 78:22, 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 a rate of 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 Figure Two The scanning electron microscope image of the sample is shown in Figure Five The specific capacity can be observed. After introducing the VGCF fibers, the electrode structure complexity increased, and each fiber provided support to each other.

[0101] The obtained LiB was used as a positive and negative electrode to assemble a CR2016 button-type symmetrical battery, which was subjected to constant current charge and discharge cycle test under the conditions of 1 mA / cm 2 , 3mAh / cm 2 , and the results are shown in Figure 10 The battery stably operated for about 230 h at a lower polarization voltage (<35 mV).

[0102] Celgard 2400 was used as a separator, 1 mol lithium hexafluorophosphate (LiPF6) / ethylene carbonate (EC) + methyl ethyl carbonate (EMC) + fluoroethylene carbonate (FEC) (volume ratio 3:7:1) was used as an electrolyte, and a commercial lithium iron phosphate with a loading of 1.2 mg / cm Figure 11 was used as a positive electrode, and LiB material was used as a negative electrode to assemble a button-type full battery, which was subjected to cycle test at 1C, and the results are shown in

[0103] Comparative Example 2: Preparation of a battery

[0104] (1) Celgard 2400 was used as a separator, 1 mol lithium bis(trifluoromethylsulfonyl) imide (LiTFI) / 1,2-dimethoxyethane (DME) + 1,3-dioxolane (DOL) (volume ratio 1:1) was used as an electrolyte, and 2% Li2NO3 additive was used.

[0105] Li foil was used as a positive and negative electrode to assemble a CR2016 button-type battery, and a battery Sym-2 was obtained;

[0106] The nyquist spectrum of the symmetrical battery was obtained by an electrochemical workstation at a frequency of 100000-0.1 Hz. The nyquist spectrum of the symmetrical battery before cycle was measured by an electrochemical workstation at a frequency of 100000-0.1 Hz. As Figure 6As shown, Li shows an interface impedance of 190Ω, much greater than the aforementioned boron-containing composite lithium metal negative electrode.

[0107] ④The battery was subjected to constant current charge-discharge cycle test under the condition of 1 mA / cm 2 , 5mAh / cm 2 , and the voltage-time curve of each 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 7 , the Li electrode battery stably operated for 500h at a lower polarization voltage (<35mV), and the life was much less than that of the LiBVGCF electrode.

[0108] ⑤The battery was subjected to constant current charge-discharge cycle test under the condition of 5 mA / cm 2 , 1mAh / cm 2 , and the voltage-time curve of each was obtained. As shown in Figure 8 , the battery stably operated for 110h at a lower polarization voltage (<35mV), and the life was much less than that of the LiBVGCF electrode.

[0109] (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 a commercial lithium iron phosphate with a loading of 1 mg / cm was used as the positive electrode. A pure Li was used as the negative electrode to assemble a coin full battery, and the battery was cycled at 1C. As shown in Figure 9 , the battery had a capacity retention rate of only 60% after 90 cycles, and the performance was much lower than that of the LiB@VGCF electrode in Example 1.

[0110] In summary, the LiB fiber is prepared by in-situ reaction of elemental boron and lithium, and is double-coupled with the VGCF fiber by composite calendering, so as to comprehensively improve the mechanical, thermal and electrochemical properties of the electrode structure, and further improve the cycle life of the lithium battery.

[0111] The above is only a specific embodiment 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 scope disclosed in the present application, and these modifications or replacements shall be covered within 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 lithium metal anode material having an ion / electron mixed conductor network, characterized in that: The negative electrode material is a boron-containing composite lithium metal negative electrode material, which is composed of metal lithium, boron and carbon-containing conductive fibers; Based on the total mass of the boron-containing composite lithium negative electrode material, the mass percentage of metal lithium is 20% to 65%, the mass percentage of boron is 10% to 30%, and the mass percentage of carbon-containing conductive fibers is 10% to 30%, the boron element is provided by a boron-containing compound, or the boron element is provided by a boron-containing compound and elemental boron, and the carbon element is provided by VGCF fibers or CNT fibers.

2. The lithium metal anode material with ion / electron mixed conductor network of claim 1, wherein: The ion / electron mixed conductor network is uniformly constructed by LiB@VGCF double fibers.

3. A method of producing a lithium metal anode material having an ion / electron mixed conductor network according to any one of claims 1-2, characterized by: The method comprises the following steps: Step 1: Under vacuum or argon atmosphere, the mass ratio of elemental lithium, elemental boron and M is 50-85:0.01-49.99:0.01-50; 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 When elemental boron is not used, the mass ratio of elemental lithium to M is 50-85:3-40, and elemental lithium and M are weighed; 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; Step 2: Put the weighed materials into a vacuum / argon smelting furnace, heat and continuously stir for a certain time after the lithium is melted, fully mix and react; the reaction temperature is 200-700°C, and the reaction time is 5 minutes to 100 hours; Step 3: The composite material obtained in step 2 is cooled and solidified in a special mold to obtain an ingot; Step 4: The ingot obtained in step 3 is rolled to obtain a thin strip, and the thin strip and carbon-containing conductive fibers are mixed and rolled according to the mass ratio LiB:N=50-85:0.01-50, preferably LiB:N=70:30, to form a double-fiber composite network skeleton; N is selected from at least one of VGCF and CNT.

4. The LiB fiber of claim 3, wherein: The elemental boron is crystalline or amorphous boron, boron powder and boride particle size is 0.01-150μm.

5. The VGCF fiber according to claim 3, characterized by: The VGCF fiber aspect ratio is 10-2000.

6. The method of claim 3, wherein the lithium metal anode material having an ion / electron mixed conductor network is prepared by: The ingot is rolled to obtain a thin strip; the thickness of the thin strip is 100-2000μm, and the obtained thin strip and carbon-containing conductive fibers are mixed and stacked to obtain a composite thin strip; the thickness of the composite thin strip is less than or equal to 100μm.

7. Use of a lithium metal anode material having an ion / electron mixed conductor network according to any one of claims 1-2, characterized in that: The lithium metal negative electrode material with an ion / electron mixed conductor network is used in an energy storage device.

8. Use of a lithium metal anode material having an ion / electron mixed conductor network according to claim 7, characterized in that: The energy storage device includes a lithium battery; the lithium battery includes a positive electrode, a negative electrode, a separator and an electrolyte, wherein the negative electrode includes the lithium metal negative electrode material with an ion / electron mixed conductor network.

9. Use of a lithium metal anode material having an ion / electron mixed conductor network according to claim 8, characterized in that: The energy storage device includes a thermal battery.

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