Negative electrode sheet, method for manufacturing the same, battery cell, battery device, and power using device

Abstract

The application discloses a negative electrode sheet, a preparation method of the negative electrode sheet, a battery monomer, a battery device and a power utilization device. The negative electrode sheet comprises Li7B6 fibers and lithium elements in gaps formed by stacking the Li7B6 fibers, the average gap diameter of the gaps is 1-2 microns, and the mass percentage of B elements is 5-30% based on the total mass of the negative electrode sheet. According to the embodiment of the application, the lithium metal can be uniformly deposited on the negative electrode, the possibility of dendrite and volume expansion is reduced, and the stability of the battery monomer is improved.

Description

Technical Field

[0001] This application relates to secondary batteries, and more particularly to a negative electrode sheet and its preparation method, a battery cell, a battery device, and an electrical device. Background Technology

[0002] Because battery cells can convert chemical energy into electrical energy, they have become one of the important energy sources for human production and life, and are therefore widely used in many fields such as power tools, electric vehicles, and electronic devices to provide them with power.

[0003] With the widespread application of battery cells in various fields, the requirements for their performance are becoming increasingly stringent, among which the stability of battery cells has become a key focus. Therefore, how to improve the stability of battery cells is one of the urgent technical problems to be solved. Summary of the Invention

[0004] This application provides a negative electrode sheet and its preparation method, a battery cell, a battery device, and an electrical device, which enables lithium metal to be uniformly deposited on the negative electrode, reducing the possibility of dendrites and volume expansion, and improving the stability of the battery cell.

[0005] In the first aspect, embodiments of this application provide a negative electrode sheet, which includes Li7B6 fibers and elemental lithium located in the voids formed by the stacking of multiple Li7B6 fibers, wherein the average void diameter is 1 to 2 μm; and the mass percentage of element B is 5% to 30% based on the total mass of the negative electrode sheet.

[0006] The negative electrode in this embodiment utilizes a framework support structure constructed from multiple stacked Li7B6 fibers. Elemental lithium is located within the voids formed by the Li7B6 fiber stacking. Li7B6 possesses excellent lithium affinity, thus guiding the uniform deposition of lithium metal within this void structure, thereby reducing the likelihood of dendrite formation and electrode volume expansion. Furthermore, Li7B6 and elemental lithium do not have an intermediate phase during conversion, which improves the stability of the framework support structure. Simultaneously, the specific content of boron (B) and the specific average void diameter of the multiple voids enhance the strength of the Li7B6 framework support structure while mitigating the problem of uneven lithium metal deposition caused by excessively small average voids due to B. This improves both the stability of the Li7B6 framework structure and the uniform deposition of lithium metal within the framework structure, increases the confinement effect on lithium metal, reduces the scattering of pulverized lithium, thereby reducing the likelihood of dendrite formation and electrode volume expansion, and improving the stability of the individual battery cell.

[0007] In any embodiment of this application, the mass percentage of element B is 5% to 10% based on the total mass of the negative electrode sheet. The specific content setting of element B and the specific setting of the average void diameter of multiple voids in the embodiments of this application can improve the stability of the Li7B6 framework structure while simultaneously improving the uniform deposition of lithium metal in the framework structure, increasing the confinement effect on lithium metal, and reducing the scattering of pulverized lithium. This reduces the possibility of dendrite and electrode volume expansion, thereby improving the stability of the battery cell.

[0008] In any embodiment of this application, the diameter of the Li7B6 fiber is 200–800 nm, and the length of the Li7B6 fiber is 5–10 μm. The diameter and length of the Li7B6 fiber in the embodiments of this application can improve the uniform deposition of lithium metal and obtain a fiber skeleton structure with excellent mechanical properties.

[0009] In any embodiment of this application, the diameter-to-length ratio of the Li7B6 fibers is 0.02:1 to 0.1:1. This diameter-to-length ratio of the Li7B6 fibers in the embodiments of this application can reduce the possibility of loose lithium metal deposition and obtain a fiber skeleton structure with excellent mechanical properties.

[0010] In any embodiment of this application, the thickness of the negative electrode sheet is 15–25 μm.

[0011] This application embodiment also provides a negative electrode sheet, which includes a three-dimensional porous current collector and a composite material located in the pore structure of the three-dimensional porous current collector; the composite material includes Li7B6 fibers and elemental lithium located in the voids formed by the stacking of a plurality of Li7B6 fibers.

[0012] In this embodiment, the negative electrode sheet combines a Li7B6 fiber skeleton structure with a three-dimensional porous current collector to further utilize the supporting effect of the three-dimensional porous current collector, thereby reducing the degree of electrode expansion. At the same time, the physical confinement effect of the three-dimensional porous current collector can also isolate by-products, thereby further improving the stability of the battery cell.

[0013] In any embodiment of this application, the pore size of the three-dimensional porous current collector is 1 to 5 μm.

[0014] The negative electrode sheet with a three-dimensional porous current collector of suitable pore size in the embodiments of this application can further reduce the degree of electrode sheet expansion, and at the same time can also isolate by-products through physical confinement, thereby further improving the stability of the battery cell.

[0015] In any embodiment of this application, the three-dimensional porous current collector includes one or more of three-dimensional carbon fiber and mesh metal current collector.

[0016] In any embodiment of this application, three-dimensional carbon fiber includes one or more of carbon cloth, carbon paper, and carbon felt.

[0017] In any embodiment of this application, the mesh metal current collector includes one or more of stainless steel mesh current collectors, nickel mesh current collectors, copper mesh current collectors, and aluminum mesh current collectors.

[0018] In any embodiment of this application, the thickness of the negative electrode sheet is 15–25 μm.

[0019] Secondly, embodiments of this application provide a method for preparing a negative electrode sheet, comprising: mixing materials containing lithium source and boron source according to a preset ratio; subjecting the mixed materials to gradient heat treatment under an inactive atmosphere, and then performing rolling treatment to obtain a negative electrode sheet.

[0020] This application embodiment achieves the alloying of lithium and boron elements through two exothermic reactions between lithium and boron sources; then, by controlling the amount of lithium and boron sources added, the proportion of boron in the lithium-boron alloy can be adjusted, thereby controlling the proportion and morphology of Li7B6 in the alloy phase; furthermore, by adjusting the temperature and time of heat treatment, the average void diameter of multiple voids can be controlled, thereby obtaining a lithium-boron alloy negative electrode sheet that can uniformly deposit lithium metal and reduce dendrites and volume expansion.

[0021] In any embodiment of this application, the mass ratio of lithium source to boron source is 7:3 to 9:1.

[0022] In any embodiment of this application, the gradient heat treatment includes a first heat treatment and a second heat treatment; the temperature of the first heat treatment is 280-380°C and the time is 50-70 min; the temperature of the second heat treatment is 380-580°C and the time is 100-140 min.

[0023] This application also provides a method for preparing a negative electrode sheet, comprising: mixing materials containing lithium source and boron source according to a preset ratio; subjecting the mixed materials to gradient heat treatment under an inactive atmosphere; and subjecting the gradient heat-treated materials to hot-melt impregnation treatment with a three-dimensional porous current collector to obtain a negative electrode sheet.

[0024] In this embodiment, a three-dimensional porous current collector and a lithium boron alloy with a Li7B6 fiber skeleton structure are composited by hot-melt impregnation to introduce a new support structure—the three-dimensional porous current collector—thereby further reducing the degree of electrode expansion. At the same time, the physical confinement effect of the three-dimensional porous current collector can also isolate by-products, thereby further improving the stability of the battery cell.

[0025] In any embodiment of this application, the mass ratio of lithium source to boron source is 7:3 to 9:1.

[0026] In any embodiment of this application, the gradient heat treatment includes a first heat treatment and a second heat treatment; the temperature of the first heat treatment is 280-380°C and the time is 50-70 min; the temperature of the second heat treatment is 380-580°C and the time is 100-140 min.

[0027] Thirdly, embodiments of this application provide a battery cell including the alloy negative electrode sheet described in the first aspect.

[0028] Fourthly, embodiments of this application provide a battery device including the battery cell described in the third aspect.

[0029] Fifthly, embodiments of this application provide an electrical device including the battery device described in the fourth aspect. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 The diagram shows a schematic of a battery cell provided in some embodiments of this application.

[0032] Figure 2 A schematic diagram of an electrical device provided in some embodiments of this application is shown.

[0033] Figure 3 The diagram shows a cross-sectional view of conventional pure copper as the negative electrode sheet provided in Comparative Example 3 of this application after cycling.

[0034] Figure 4 The diagram shows a cross-sectional view of the lithium-boron alloy provided in Embodiment 1 of this application after cycling.

[0035] The accompanying drawings are not necessarily drawn to scale. Detailed Implementation

[0036] To better understand the above-mentioned objectives, features, and advantages of this application, the solution of this application will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0037] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this application may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of this application, and not all embodiments.

[0038] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode sheet and its preparation method, battery cell, battery device, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0039] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0040] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0041] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0042] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0043] Lithium has a theoretical specific capacity as high as 3860 mAh / g, and batteries that use lithium sheets as the negative electrode are generally called lithium metal batteries. Lithium metal batteries have a high energy density, far exceeding that of lithium-ion batteries that use materials such as graphite as the negative electrode. Therefore, batteries represented by lithium metal batteries are considered the most promising battery system to replace traditional ion batteries.

[0044] However, during the charging and discharging process of the aforementioned batteries, the metal deposited on the negative electrode exhibits uneven deposition and is easily dissolved, which increases the likelihood of dendrite formation and can lead to a short circuit between the positive and negative electrodes. This reduces the stability and reliability of the battery.

[0045] In view of this, embodiments of this application provide a negative electrode sheet and its preparation method, a battery cell, a battery device, and an electrical device, which enable lithium metal to be uniformly deposited on the negative electrode, reducing the possibility of dendrites and volume expansion, and improving the stability of the battery cell.

[0046] Negative electrode sheet

[0047] In the first aspect, embodiments of this application provide a negative electrode sheet, which includes Li7B6 fibers and elemental lithium located in the voids formed by the stacking of multiple Li7B6 fibers, wherein the average void diameter is 1 to 2 μm; and the mass percentage of element B is 5% to 30% based on the total mass of the negative electrode sheet.

[0048] Li7B6 is a phase structure found in lithium-boron alloys. In lithium-boron alloys, lithium and boron form stable compounds, and Li7B6 is one such phase structure.

[0049] The negative electrode sheet of this application embodiment constructs a framework support structure using multiple stacked Li7B6 fibers, with elemental lithium located within the voids formed by the Li7B6 fiber stacking. Since there is no intermediate phase during the conversion of Li7B6 and elemental lithium, the stability of the framework support structure can be improved. Furthermore, currently, negative electrode sheets using metal / alloy sheets or foils are commonly used. The deposited metal in these sheets is uneven and easily dissolved, causing the solid electrolyte interphase (SEI) film on the surface of the negative electrode sheet to continuously break and repair itself. This not only consumes a large amount of electrolyte and reduces the coulombic efficiency of the battery cell, but also corrodes the negative electrode; it can also lead to dendrite breakage and loss of electrical contact with the negative electrode, resulting in capacity loss of the battery cell. The negative electrode sheet of this application embodiment, by constructing a void-like framework support structure and using Li7B6 with good lithium affinity, can guide the uniform deposition of lithium metal within this void structure, thereby reducing the possibility of dendrite formation and electrode volume expansion. Meanwhile, the specific content setting of element B and the specific setting of the average void diameter of multiple voids can improve the strength of the Li7B6 framework support structure while reducing the problem of uneven lithium metal deposition caused by the small average void size due to element B. This can improve the stability of the Li7B6 framework structure, improve the uniform deposition of lithium metal in the framework structure, increase the confinement effect of lithium metal, reduce the scattering of pulverized lithium, thereby reducing the possibility of dendrite and electrode volume expansion and improving the stability of the battery cell.

[0050] In related technologies, uneven metal deposition on the negative electrode sheet can lead to excessive metal concentration in some areas and relative scarcity in others, resulting in loose deposition. Furthermore, metal can encounter blockages during deposition, preventing lithium metal from depositing smoothly onto the electrode surface. This causes more metal to deposit in certain areas, increasing the risk of dendrite growth. During charging and discharging, the continuous deposition and dissolution of metal generates stress on the electrode surface, leading to electrode structure deformation or damage, further exacerbating the uneven deposition. In this application, the average void diameter of multiple voids determines the spatial distribution and transport channels during metal deposition. This improves the effective transport of metal between fibers and ensures deposition at appropriate locations, reducing metal loss during transport due to excessively large voids and improving deposition efficiency. It also reduces the limiting effect of excessively small voids on metal transport and uniform deposition. The appropriate range of boron (B) mass percentage in this application improves framework stability while creating suitable voids for uniform lithium metal deposition. This reduces the limitation on metal deposition caused by excessively high B content and excessively low B content on framework stability.

[0051] In this embodiment, the phase and structure of the lithium-boron alloy negative electrode sheet can be verified by X-ray diffraction.

[0052] In this embodiment, the average gap diameter of multiple gaps can be obtained by SEM testing. Specifically, the electrode is cut along a direction perpendicular to the large surface of the electrode to obtain a cross-sectional sample. The obtained sample is observed using SEM, and a 3*3cm square is randomly selected in the SEM image. The maximum radial dimension of multiple gaps in the square is measured using a scale as the gap diameter, and then the average gap diameter is obtained.

[0053] Optionally, the average pore diameter of the plurality of pores is independently selected from any value or a range between 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, and 2.0 μm.

[0054] In this embodiment, the content of boron (B) has a meaning known in the art and can be detected using ion-selective electrode methods, for example...

[0055] Sample preparation: Take an appropriate amount of lithium-boron alloy sample and digest it to obtain a liquid sample containing boron ions. During digestion, ensure that the analyte is not lost, no interfering substances are introduced, and that the process is safe and rapid.

[0056] Electrode preparation: Select an ion analyzer and perform necessary pretreatment and calibration.

[0057] Measurement procedure: Mix the digested liquid sample with an appropriate electrolyte solution, insert the ion-selective electrode and the reference electrode, connect the potentiometer or electrochemical workstation, and measure the electrode potential.

[0058] Data processing: Based on the relationship between electrode potential and boron ion concentration, the boron content in the sample is determined using a standard curve or calculation formula.

[0059] Optionally, based on the total mass of the negative electrode, the mass percentage of element B is independently selected from any value or a range between any two of 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, and 30%.

[0060] In some embodiments, the mass percentage of element B is 5% to 10% based on the total mass of the negative electrode sheet.

[0061] In the embodiments of this application, a specific content of B can indirectly yield a specific content of Li7B6. Li7B6 can effectively reduce local current density. This reduction in local current density means a more uniform current distribution during charging and discharging, which can reduce excessive metal concentration in specific areas and decrease volume changes during charging and discharging, thereby reducing the possibility of dendrite growth and metal anode structure pulverization. Furthermore, during the first charge and discharge of a battery cell, the adsorption energy of the Li7B6 sites for metal is low, allowing for lateral metal diffusion and planar metal deposition. Simultaneously, Li7B6 itself possesses excellent chemical stability and high mechanical strength, enabling it to withstand various forces during the charging and discharging process of the battery cell, thus improving the strength and stability of the Li7B6 framework support structure.

[0062] However, a certain amount of Li7B6 reduces the average pore diameter of multiple voids, meaning that the metal may encounter blockages during deposition, preventing it from depositing smoothly into the voids. Consequently, more metal is deposited on the surface of the Li7B6 framework, increasing the risk of dendrite growth. During charge and discharge, the continuous deposition and dissolution of metal generates stress on the Li7B6 framework structure, leading to structural deformation or damage, further exacerbating the uneven deposition.

[0063] Therefore, in this embodiment, by adjusting the pore diameter, the ratio of the mass percentage of element B to the average pore diameter of multiple pores is kept within a suitable range. This reduces the possibility of uneven metal deposition caused by a specific content of Li7B6 and enhances the confinement effect of the Li7B6 framework structure on the metal. As a result, the stability of the Li7B6 framework structure can be improved while ensuring uniform metal deposition in the framework structure. This also increases the confinement effect on the deposited metal, reduces the scattering of pulverized lithium, reduces the possibility of dendrites and volume expansion, and improves the stability of the battery cell.

[0064] Optionally, based on the total mass of the negative electrode, the mass percentage of element B is independently selected from any value of 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range between any two.

[0065] In some embodiments, the Li7B6 fiber has a diameter of 200–800 nm and a length of 5–10 μm.

[0066] The diameter and length of Li7B6 fibers refer to the average diameter and length of different Li7B6 fibers at the microscopic level.

[0067] In this embodiment, the diameter and length of the Li7B6 fibers can reduce the local current density by increasing the cross-sectional area through which the metal passes and increasing the path for metal passage. This reduction in local current density means a more uniform current distribution during charging and discharging, which can reduce excessive concentration of deposited metal in specific areas and decrease the degree of electrode volume change during charging and discharging. Simultaneously, the diameter of the Li7B6 fibers in this embodiment can increase the specific surface area, thereby reducing the density of deposited metal and thus reducing the risk of dendrite growth. Furthermore, the diameter of the Li7B6 fibers in this embodiment provides higher mechanical strength, enabling better resistance to volume changes and stress during charging and discharging, thereby enhancing the stability of the Li7B6 framework.

[0068] In this embodiment, the diameter and length of the Li7B6 fibers can be obtained by SEM testing. Specifically, the electrode is cut along a direction perpendicular to the large surface of the electrode to obtain a cross-sectional sample. The obtained sample is observed using SEM, and a 3*3cm square is randomly selected in the SEM image. The diameter and length of multiple Li7B6 fibers in the square are measured using a scale, and then the average value of the diameter and length is obtained.

[0069] Optionally, the diameter of the Li7B6 fiber is independently selected from any value or a range between 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, and 800nm.

[0070] Optionally, the length of the Li7B6 fiber is independently selected from any value of 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or any range between two.

[0071] In some embodiments, the diameter to length ratio of the Li7B6 fiber is 0.02:1 to 0.1:1.

[0072] The diameter-to-length ratio of Li7B6 fibers in this embodiment improves the mechanical strength of the lithium-boron alloy. Compared to lithium metal anode sheets, which require pressure during cycling to achieve dense deposition, the flexibility of pure lithium can lead to lateral stretching and longitudinal deformation. In this embodiment, the mechanical strength of the lithium-boron alloy anode sheet is 10 times that of pure lithium, reducing problems such as wire pulling and adhesion during subsequent cutting. It also reduces stress release during battery cycling, lowering the likelihood of deformation and breakage, and consequently reducing the contact area between the anode sheet and the electrolyte, thereby reducing side reactions.

[0073] Optionally, the ratio of the diameter to the length of the Li7B6 fiber is independently selected from any value among 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.10:1 or any range between both.

[0074] In some embodiments, in order to better reduce the possibility of dendrite formation and volume expansion and improve the stability of the battery cell, the thickness of the negative electrode sheet is 15–25 μm.

[0075] The thickness of the negative electrode sheet in this application embodiment has a meaning known in the art and can be tested using methods known in the art, such as a micrometer (e.g., Mitutoyo 293-100 model, with an accuracy of 0.1 μm).

[0076] Optionally, the thickness of the negative electrode is independently selected from any value or a range between 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, and 25μm.

[0077] This application embodiment also provides a negative electrode sheet, which includes a three-dimensional porous current collector and a composite material located in the pore structure of the three-dimensional porous current collector; the composite material includes Li7B6 fibers and elemental lithium located in the voids formed by the stacking of a plurality of Li7B6 fibers.

[0078] In this embodiment, the negative electrode sheet combines a Li7B6 fiber skeleton structure with a three-dimensional porous current collector to further utilize the supporting effect of the three-dimensional porous current collector, thereby reducing the degree of electrode expansion. At the same time, the physical confinement effect of the three-dimensional porous current collector can also isolate by-products, thereby further improving the stability of the battery cell.

[0079] In some embodiments, the pore size of the three-dimensional porous current collector is 1–5 μm.

[0080] The negative electrode sheet with a three-dimensional porous current collector of suitable pore size in the embodiments of this application can further reduce the degree of electrode sheet expansion, and at the same time can also isolate by-products through physical confinement, thereby further improving the stability of the battery cell.

[0081] In this application, pore size has a meaning known in the art and can be measured using instruments and methods known in the art. For example, it can be calculated using the BET (Brunauer Emmett Teller) method according to GB / T21650.2-2008, and can be tested using a Tri-Star 3020 surface area pore size analyzer from Micromeritics, USA.

[0082] Optionally, the pore size of the three-dimensional porous current collector is independently selected from any value or a range between 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, and 5.0 μm.

[0083] In some embodiments, the three-dimensional porous current collector includes one or more of three-dimensional carbon fiber and mesh metal current collector.

[0084] In some embodiments, three-dimensional carbon fibers include one or more of carbon cloth, carbon paper, and carbon felt.

[0085] In some embodiments, the mesh metal current collector includes one or more of stainless steel mesh current collectors, nickel mesh current collectors, copper mesh current collectors, and aluminum mesh current collectors.

[0086] Those skilled in the art can select specific mesh metal current collectors according to different application scenarios. For example, nickel mesh current collectors may include foamed nickel, and copper mesh current collectors may include foamed copper.

[0087] In some embodiments, in order to better reduce the possibility of dendrite formation and volume expansion and improve the stability of the battery cell, the thickness of the negative electrode sheet is 15–25 μm.

[0088] The thickness of the negative electrode sheet in this application embodiment has a meaning known in the art and can be tested using methods known in the art, such as a micrometer (e.g., Mitutoyo 293-100 model, with an accuracy of 0.1 μm).

[0089] Optionally, the thickness of the negative electrode is independently selected from any value or a range between 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, and 25μm.

[0090] Electrode preparation method

[0091] This application provides a method for preparing a negative electrode sheet, comprising: mixing materials containing lithium source and boron source according to a preset ratio; subjecting the mixed materials to gradient heat treatment under an inactive atmosphere, and then performing rolling treatment to obtain a negative electrode sheet.

[0092] This application embodiment achieves the alloying of lithium and boron elements through two exothermic reactions between lithium and boron sources; then, by controlling the amount of lithium and boron sources added, the proportion of boron element in the lithium-boron alloy can be adjusted, thereby controlling the proportion and morphology of Li7B6 in the alloy phase; furthermore, by adjusting the temperature and time of heat treatment, the average void diameter of multiple voids can be controlled, thereby obtaining a negative electrode sheet that can uniformly deposit metal and reduce dendrites and volume expansion.

[0093] In some embodiments, the lithium source comprises metallic lithium. The purity of the lithium source is 99.0% to 99.9%.

[0094] In some embodiments, the boron source comprises amorphous boron powder. The purity of the boron powder can be 85% to 95%, and the particle size of the boron powder can be 2 to 10 μm.

[0095] In the embodiments of this application, the boron powder has a suitable particle size, which can further control the average void diameter between lithium boron alloy fibers.

[0096] In some embodiments, the boron source can be boron powder prepared from amorphous materials. For example, purified BCl3 can be reduced with pure H2 at high temperatures, such as 1000–1400°C, to obtain boron powder. The chemical equation for the reaction is: 2BCl3 + 3H2 = 2B + 6HCl.

[0097] In some embodiments, the mass ratio of lithium source to boron source is 7:3 to 9:1.

[0098] Optionally, the mass ratio of the lithium source to the boron source is independently selected from any value or a range between 7.0:3.0, 7.1:2.9, 7.2:2.8, 7.3:2.7, 7.4:2.6, 7.5:2.5, 7.6:2.4, 7.7:2.3, 7.8:2.2, 7.9:2.1, 8.0:2.0, 8.1:1.9, 8.2:1.8, 8.3:1.7, 8.4:1.6, 8.5:1.5, 8.6:1.4, 8.7:1.3, 8.8:1.2, 8.9:1.1, and 9.0:1.0.

[0099] In some embodiments, the gradient heat treatment includes a first heat treatment and a second heat treatment; the temperature of the first heat treatment is 280–380°C and the time is 50–70 min; the temperature of the second heat treatment is 380–580°C and the time is 100–140 min.

[0100] In some embodiments, in order to improve the stability of the first exothermic reaction, mechanical pressure can be used at 200–330°C to make the boron source uniform.

[0101] Optionally, the temperature of the first heat treatment is independently selected from any value or a range between 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, and 380℃. The time of the first heat treatment is independently selected from any value or a range between 50 min, 55 min, 60 min, 65 min, and 70 min.

[0102] Optionally, the temperature of the second heat treatment is independently selected from any value or a range between any two of 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, and 580℃. The time of the second heat treatment is independently selected from any value or a range between any two of 100min, 110min, 120min, 130min, and 140min.

[0103] In some embodiments, the diameter and length of Li7B6 fibers can also be adjusted by regulating the B content, heat treatment temperature and time, raw material purity, and raw material particle size.

[0104] In some embodiments, an inactive atmosphere refers to a gas that does not or is difficult to react chemically, which can isolate the reaction system from reactive gases (such as air) in the outside. The specific type of inactive atmosphere is not specifically limited and can be adjusted as needed by those skilled in the art. As an example, the inactive atmosphere can be at least one of nitrogen, neon, and argon.

[0105] This application also provides a method for preparing a negative electrode sheet, comprising: mixing materials containing lithium source and boron source according to a preset ratio; subjecting the mixed materials to gradient heat treatment under an inactive atmosphere; and subjecting the gradient heat-treated materials to hot-melt impregnation treatment with a three-dimensional porous current collector to obtain a negative electrode sheet.

[0106] In this embodiment, a three-dimensional porous current collector and a lithium boron alloy with a Li7B6 fiber skeleton structure are composited by hot-melt impregnation to introduce a new support structure—the three-dimensional porous current collector—thereby further reducing the degree of electrode expansion. At the same time, the physical confinement effect of the three-dimensional porous current collector can also isolate by-products, thereby further improving the stability of the battery cell.

[0107] In some embodiments, in order to improve the bonding force at the interface between the three-dimensional porous current collector and the lithium-boron alloy, a rolling process is further included after the hot melt impregnation process to obtain a negative electrode sheet.

[0108] battery cell

[0109] This application provides a battery cell including the negative electrode sheet described in the first aspect.

[0110] like Figure 4As shown, in the battery including the negative electrode sheet described in the first aspect, after cycling, a dense lithium metal is uniformly deposited in the interstitial space structure of the negative electrode sheet, while the skeleton support structure of the negative electrode sheet remains intact and has good contact with the separator interface. Figure 3 As shown, after cycling, a large number of voids and lithium powder form on the surface of the conventional pure copper battery cell with the negative electrode, creating a large number of gaps with the separator, which leads to increased interfacial resistance and difficulty in electrolyte wetting.

[0111] A battery cell includes an electrode assembly and an electrolyte. The electrode assembly consists of a positive electrode, a negative electrode, and a separator. The battery cell primarily functions by the movement of metal ions between the positive and negative electrodes. The positive electrode includes a positive current collector and a positive active material layer. The positive active material layer is coated on the surface of the positive current collector, and the uncoated positive current collector protrudes beyond the coated positive current collector, serving as the positive electrode tab.

[0112] [Positive electrode plate]

[0113] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0114] In some embodiments, the positive electrode active material includes a material capable of extracting and inserting lithium.

[0115] As examples, positive electrode active materials may include, but are not limited to, one or more of lithium transition metal oxides, metal chalcogenides, lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, lithium titanium oxides, and their respective modified compounds. Lithium transition metal oxides may include, but are not limited to, layered structures and spinel structures. Examples of lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, lithium iron manganese phosphate and carbon composites, and their respective modified compounds.

[0116] In some embodiments, to further improve the energy density of a single battery cell, the positive electrode active material may include materials of the general formula Li. a Ni b Co c M d O e Df One or more of lithium transition metal oxides and their modified compounds. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M may include, but is not limited to, one or more of Ge, Mo, Sn, Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and D may include, but is not limited to, one or more of N, F, S and Cl.

[0117] In some embodiments, the positive electrode active material may simultaneously comprise lithium transition metal oxide and lithium phosphate. This is advantageous for obtaining a battery that balances high capacity and high reliability.

[0118] As an example, the positive electrode active material may include, but is not limited to, LiCoO2, LiNiO2, LiMnO2, and LiNi 1 / 2 Mn 1 / 2O2, LiMn2O4, Li 4 / 3 Ti 5 / 3 O4, LiNi 1 / 2 Mn 1 / 2 O2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.80 Co 0.15 Al 0.05 O2, LiFePO4, LiMnPO4, Li 1.13 Ti 0.57 Fe 0.3 One or more of S2.

[0119] The modified compounds for the above-mentioned positive electrode active materials can be obtained by doping and / or surface coating of the positive electrode active materials.

[0120] In some embodiments, the positive electrode film may optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0121] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene oxide, fluorinated acrylate resins, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0122] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. As an example, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may include, but is not limited to, one or more of polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0123] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing positive electrode active materials, positive electrode conductive agents, positive electrode binders, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to this.

[0124] [Negative electrode plate]

[0125] In some embodiments, the negative electrode sheet includes the lithium-boron alloy negative electrode sheet described in the first aspect. The lithium-boron alloy negative electrode sheet can be obtained by rolling a lithium-boron alloy into foil or sheet.

[0126] In some embodiments, the negative electrode sheet may further include a negative electrode active material and a metal layer disposed on at least one surface of the negative electrode active material, wherein the metal material in the metal layer may include, but is not limited to, one or more of elemental lithium, sodium, and sodium alloys.

[0127] The negative electrode active material may be any material known in the art that can be used in battery cells. As an example, the negative electrode active material may include, but is not limited to, one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include, but are not limited to, one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include, but are not limited to, one or more of elemental tin, tin oxide, and tin alloys.

[0128] Sodium alloys can be alloys formed from metallic sodium with other metallic or non-metallic elements. For example, other metallic elements in a sodium alloy may include one or more of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, and platinum, while non-metallic elements may include one or more of boron, carbon, and silicon.

[0129] [Electrolytes]

[0130] The electrolyte plays a role in conducting ions between the positive and negative electrode plates.

[0131] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and an organic solvent.

[0132] The electrolyte salt may include, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0133] In some embodiments, the organic solvent may include, but is not limited to, one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ester carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE), ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ether.

[0134] In some embodiments, the electrolyte may also include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the battery cell, such as additives that improve overcharge performance, additives that improve high-temperature performance, additives that improve low-temperature performance, etc.

[0135] Optionally, the additive may include one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propanesulfonate lactone (PS), and ethylene sulfate (DTD).

[0136] [Isolation membrane]

[0137] Battery cells using electrolytes, as well as some battery cells using solid electrolytes, also include a separator. The separator is disposed between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes, while allowing metal ions to pass through. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0138] In some embodiments, the material of the separator may include at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0139] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process or a stacking process.

[0140] In some embodiments, the battery cell may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0141] In some embodiments, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0142] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. Figure 1 This is a square-structured battery cell used as an example.

[0143] The method for preparing the battery cell of this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode, the separator, and the negative electrode can be formed into an electrode assembly through a winding process or a stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a battery cell is obtained.

[0144] Battery device

[0145] The battery apparatus mentioned in this application embodiment may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells, which are connected in series, parallel, or mixed connections via a busbar.

[0146] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0147] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0148] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0149] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0150] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0151] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0152] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0153] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0154] The technical solutions described in this disclosure are applicable to various electrical devices that use battery cells or battery devices, such as, but not limited to, mobile devices (e.g., mobile phones, tablets, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc. Battery cells and battery devices are used to store or provide electrical energy.

[0155] Figure 2 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.

[0156] Example

[0157] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0158] Example 1

[0159] 1. Preparation of negative electrode sheet

[0160] (1) Mix lithium metal and boron powder at a mass ratio of 70:30 to obtain a precursor;

[0161] (2) The above precursor is placed in an argon-protected melter for heat treatment. First, the temperature is raised to 330°C at a heating rate of 5°C / min and held for 60 min. Then, the temperature is raised to 200-330°C. Pressure is applied during the heating process to make the boron powder uniform. Then, the temperature is raised to 530°C at a heating rate of 5°C / min and held for 120 min. After cooling to room temperature (25°C), a lithium-boron alloy is obtained.

[0162] (3) The obtained lithium-boron alloy is rolled into a foil with a thickness of 20 μm.

[0163] 2. Assembly of lithium metal battery cells

[0164] (1) Preparation of the positive electrode sheet: The positive electrode active material NCM811, conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were mixed evenly in an appropriate amount of solvent N-methylpyrrolidone (NMP) at a mass ratio of 96:2:2 to obtain a positive electrode slurry; the positive electrode slurry was coated onto the positive electrode current collector aluminum foil, and the positive electrode sheet was obtained through drying, cold pressing, slitting, and cutting. The areal density of the positive electrode sheet was 4 mAh / cm³. 2 .

[0165] (2) Preparation of the isolation membrane: PE porous membrane with a thickness of 5.2 μm was used.

[0166] (3) Preparation of electrolyte: Dimethyl ethylene glycol (DME) was used as solvent, and LiFSI was added to the solvent in batches. The LiFSI was heated and stirred to dissolve, and an electrolyte with a concentration of 1 mol / L was prepared.

[0167] (4) Stack and wind the positive electrode sheet, the separator and the negative electrode sheet prepared above in sequence to obtain the electrode assembly; place the electrode assembly in the outer packaging, dry it and inject the electrolyte, and obtain the lithium metal battery cell through vacuum sealing, standing, formation and shaping processes.

[0168] Example 2

[0169] The experimental steps are basically the same as in Example 1, except that the mass ratio of lithium metal and boron powder in step (1) of step 1 is changed to 75:25.

[0170] Example 3

[0171] The experimental steps are basically the same as in Example 1, except that the mass ratio of lithium metal and boron powder in step (1) of step 1 is changed to 80:20.

[0172] Example 4

[0173] The experimental steps are basically the same as in Example 1, except that the mass ratio of lithium metal and boron powder in step (1) of step 1 is changed to 85:15.

[0174] Examples 5-9

[0175] The experimental steps are basically the same as in Example 3, except that the preparation of the negative electrode sheet is different.

[0176] Preparation of negative electrode sheet:

[0177] (1) Mix lithium metal and boron powder at a mass ratio of 70:30 to obtain a precursor;

[0178] (2) The above precursor is placed in an argon-protected melter for heat treatment. First, the temperature is raised to 330°C at a heating rate of 5°C / min and held for 60 min. Then, the temperature is raised to 200-330°C. Pressure is applied during the heating process to make the boron powder uniform. Then, the temperature is raised to 530°C at a heating rate of 5°C / min and held for 120 min. After cooling to room temperature (25°C), the alloy melt is obtained.

[0179] (3) The three-dimensional porous current collector is completely immersed in the alloy melt in step (2), and after mixing, a negative electrode sheet with a thickness of 20 μm is obtained.

[0180] Comparative Example 1

[0181] The experimental steps are basically the same as in Example 1, except that the mass ratio of lithium metal and boron powder in step (1) of step 1 is changed. The specific values ​​are shown in Table 1.

[0182] Comparative Example 2

[0183] The experimental steps are basically the same as in Example 1, except that the heat treatment temperature in step (2) of step 1 is changed. The specific values ​​are shown in Table 1.

[0184] Comparative Example 3

[0185] The experimental steps are basically the same as in Example 1, except that the negative electrode is changed to pure copper.

[0186] Data Analysis:

[0187] Cyclic performance testing method: At 25℃, the prepared battery cells are charged at a constant current of 0.2C to 4.2V, and then charged at a constant voltage until the current reaches 0.01C. At this point, the battery cell is fully charged, and the charging capacity is recorded, which is the first charge capacity. After the battery cell is left to stand for 5 minutes, it is discharged at a constant current of 0.5C to 2.5V. This completes one charge-discharge cycle, and the discharge capacity is recorded, which is the first discharge capacity. The battery cells are subjected to cyclic charge-discharge tests according to the above method, and the discharge capacity after each cycle is recorded until the discharge capacity of the battery cell decreases to 60% of the first discharge capacity. The number of cycles at this point characterizes the cycle performance of the battery cell. The higher the number of cycles, the better the cycle performance.

[0188] Table 1

[0189]

[0190] As shown in the table above, compared to Comparative Examples 1-3, by controlling the heat treatment conditions and the mass ratio of B element in Examples 1-9, lithium-boron alloys with suitable porosity range and morphology (including the diameter and length of Li7B6 fibers) can be obtained. This lithium-boron alloy, when used as a negative electrode in a battery cell, exhibits good cycle performance.

[0191] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode sheet includes Li7B6 fibers and elemental lithium located in the voids formed by the stacking of multiple Li7B6 fibers, wherein the average void diameter is 1 to 2 μm. Based on the total mass of the negative electrode sheet, the mass percentage of element B is 5% to 30%.

2. The negative electrode sheet according to claim 1, characterized in that, Based on the total mass of the negative electrode sheet, the mass percentage of element B is 5% to 10%.

3. The negative electrode sheet according to claim 1 or 2, characterized in that, The Li7B6 fiber has a diameter of 200–800 nm; and / or, The length of the Li7B6 fiber is 5–10 μm.

4. The negative electrode sheet according to any one of claims 1-3, characterized in that, The diameter to length ratio of the Li7B6 fiber is 0.02:1 to 0.1:

1.

5. The negative electrode sheet according to any one of claims 1-4, characterized in that, The thickness of the negative electrode sheet is 15–25 μm.

6. A negative electrode sheet, characterized in that, The negative electrode sheet includes a three-dimensional porous current collector and a composite material located in the pore structure of the three-dimensional porous current collector; The composite material comprises Li7B6 fibers and elemental lithium located in the voids formed by the stacking of multiple Li7B6 fibers.

7. The negative electrode sheet according to claim 6, characterized in that, The pore size of the three-dimensional porous current collector is 1–5 μm.

8. The negative electrode sheet according to claim 6 or 7, characterized in that, The Li7B6 fiber has a diameter of 500–800 nm and a length of 5–8 μm.

9. The negative electrode sheet according to any one of claims 6-8, characterized in that, The three-dimensional porous current collector includes one or more of three-dimensional carbon fiber and mesh metal current collectors.

10. The negative electrode sheet according to claim 9, characterized in that, The three-dimensional carbon fiber includes one or more of carbon cloth, carbon paper, and carbon felt; and / or, The mesh metal current collector includes one or more of stainless steel mesh current collectors, nickel mesh current collectors, copper mesh current collectors, and aluminum mesh current collectors.

11. The negative electrode sheet according to any one of claims 6-10, characterized in that, The thickness of the negative electrode sheet is 15–25 μm.

12. A method for preparing a negative electrode sheet, characterized in that, include: Materials containing lithium and boron sources are mixed according to a preset ratio; The mixed materials are subjected to gradient heat treatment in an inactive atmosphere, followed by rolling to obtain the negative electrode sheet.

13. The preparation method according to claim 12, characterized in that, The mass ratio of the lithium source to the boron source is 7:3 to 9:

1.

14. The preparation method according to any one of claims 12-13, characterized in that, The gradient heat treatment includes a first heat treatment and a second heat treatment; The temperature of the first heat treatment is 280–380°C, and the time is 50–70 min; The second heat treatment is performed at a temperature of 380–580°C for a time of 100–140 min.

15. A method for preparing a negative electrode sheet, characterized in that, include: Materials containing lithium and boron sources are mixed according to a preset ratio; The mixed materials were subjected to gradient heat treatment under an inactive atmosphere. The negative electrode sheet is obtained by hot-melt impregnation of the material that has undergone gradient heat treatment with a three-dimensional porous current collector.

16. The preparation method according to claim 15, characterized in that, The mass ratio of the lithium source to the boron source is 7:3 to 9:

1.

17. The preparation method according to any one of claims 15-16, characterized in that, The gradient heat treatment includes a first heat treatment and a second heat treatment; The temperature of the first heat treatment is 280–380°C, and the time is 50–70 min; The second heat treatment is performed at a temperature of 380–580°C for a time of 100–140 min.

18. A single battery cell, characterized in that, Includes the negative electrode sheet according to any one of claims 1-11.

19. A battery device, characterized in that, It includes multiple battery cells as described in claim 18.

20. An electrical device, characterized in that, Includes the battery cell of claim 18 or the battery device of claim 19.

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