A method for suppressing the growth of lithium dendrites on the negative electrode of a novel lithium metal battery

Abstract

The present invention discloses a method for suppressing the growth of lithium dendrites on the negative electrode of a novel lithium metal battery, including the preparation of the positive electrode, the surface nanocrystallization of the lithium negative electrode, and the fabrication of a button battery. The surface of metallic lithium is repeatedly ground, generating twin faults and stacking faults on its surface, which serve as lithiophilic active sites on the lithium negative electrode, capable of suppressing the growth of lithium dendrites and enabling the uniform deposition of lithium ions. The operation process of grinding the lithium sheet to make its surface nanocrystallized is simple and one-step forming, without the need for complex treatments such as high-temperature ball milling and mechanical rolling. Moreover, the formed grain boundary density increases sharply, and the grain boundary density of Li after treatment is about 4 times that of untreated Li. During the grinding process, the grains are significantly refined and have reached the nanoscale. There are many uniform active centers at the grain boundaries on the nanocrystallized lithium surface, endowing it with catalytic activity similar to that of quantum dots or single-atom catalysts. After assembling into a battery, the nanocrystallized metallic lithium not only reduces the adsorption energy of adsorbed lithium ions but also enables the uniform deposition of lithium ions, thereby achieving the purpose of suppressing the growth of lithium dendrites.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium metal batteries, and particularly relates to a method for inhibiting the growth of lithium dendrites on the negative electrode of a novel lithium metal battery. Background Art

[0002] Rechargeable lithium (Li) batteries have an extremely high theoretical specific capacity (3860 mAh g -1 ) and the lowest redox potential (-3.04 V vs. standard hydrogen electrode), and are thus considered to be the most promising next-generation high-capacity battery system. However, a major challenge faced by lithium batteries is the nucleation and growth of protrusions during the battery charging process, which limits the battery life and reduces safety. During the charge-discharge cycle, lithium charge deposition is concentrated at the tip of protrusions on the rough lithium negative electrode surface, known as the "tip effect", resulting in uneven lithium ion deposition and preferential growth of lithium dendrites. Extreme growth of lithium dendrites can cause internal short circuits by penetrating the solid electrolyte interface (SEI) and the separator. The SEI is mechanically unstable, cannot adapt to volume changes during cycling, is prone to cracking, and further forms lithium dendrites by consuming fresh lithium metal and electrolyte, resulting in poor lifespan and low Coulomb efficiency.

[0003] To effectively solve the problem of lithium dendrite growth, methods such as modification of liquid electrolytes and controllable synthesis of artificial SEI have been widely studied. Existing research has shown that (4-5 M) lithium bis(fluorosulfonyl)imide (LiFSI) in high-concentration 1,2-dimethoxyethane (DME) can increase the Li metal cycling efficiency to about 99%, and no obvious dendrite formation occurs. Compared with common methods such as modification of liquid electrolytes and controllable synthesis of artificial SEI, regulating the surface micro-morphology of metallic lithium, controllably synthesizing nano-metallic lithium, and inducing uniform deposition of lithium ions will be a direct way to solve the growth of lithium dendrites. However, metallic lithium has high physical and chemical activities, and there are still great challenges in controllably synthesizing nano-structured metallic lithium by chemical methods such as chemical vapor deposition (CVD) and hydrothermal method.

[0004] Metallic lithium is relatively soft and has good plastic deformation ability. Physical methods such as plastic deformation will be a simple and effective method for regulating the surface micro-morphology of metallic lithium and controllably synthesizing nano-metallic lithium. The patent "A Pneumatic Rolling Tool for Nanostructuring Metal Surfaces" (publication number CN114752740A) provides a pneumatic rolling tool for nanostructuring metal surfaces. However, rolling lithium sheets in air will cause oxidation of the lithium sheets; moreover, the device has a complex structure and cannot be transported into a glove box filled with argon to roll lithium sheets. Therefore, it is necessary to find a simple and effective method for inhibiting lithium dendrites. Summary of the Invention

[0005] To overcome the defects of the above-mentioned existing technologies, the present invention directly converts metallic lithium into high-density grain boundaries through a simple grinding process, solving the problem of lithium dendrite growth in lithium batteries. The repeated grinding of lithium metal generates abundant lithium grain boundaries. The lithium metal grain boundaries, as lithiumophilic active sites, induce the uniform nucleation and deposition of lithium ions, ultimately overcoming the lithium dendrite problem. Completely different from the complex chemical approaches for solving the dendrite growth problem in new energy batteries in the past, its simple and effective grinding method will provide new research ideas for the design of high-capacity metal batteries such as lithium, sodium, and zinc.

[0006] To achieve the above-mentioned invention objectives, the present invention provides a method for suppressing lithium dendrite growth at the negative electrode of a new type of lithium metal battery, including the following steps:

[0007] ① Nanostructuring treatment of the lithium negative electrode surface: In a closed space filled with a protective gas, first place sulfuric acid paper on both the upper and lower surfaces of the lithium sheet, place the lithium sheet in a mortar, and repeatedly grind it with a pestle, and then cut it into a negative electrode disc with a cutter.

[0008] ② Preparation of the positive electrode: Mix the active material, conductive agent, and binder in a certain proportion and uniformly prepare a slurry, and apply the slurry on the surface of the current collector; after drying the current collector coated with the slurry in an oven, cut it into a positive electrode disc with a cutter; finally, place it in a hot press for hot pressing.

[0009] ③ Fabrication of a button battery: Use the lithium sheet treated in step ① as the negative electrode, use the disc fabricated in step ② as the positive electrode, add an electrolyte, and assemble it into a battery with a battery case.

[0010] The protective gas in step ① is an inert gas, including argon, nitrogen, etc.; the closed space circulates the protective gas through an air pump to make the water and oxygen concentrations therein below 0.1 ppm; the mortar materials include agate mortar, ceramic mortar, glass mortar, etc.; the grinding time is 5 - 10 min until its area becomes about 1.5 times the original; the diameter of the cut disc is 1.5 cm.

[0011] The active materials in step ② include graphite, Si, LiFePO 4 etc.; the conductive agents include acetylene black, SuperP, Vlucan XC-72, etc.; the binder is prepared from PVDF and N-methylpyrrolidone; the mass ratio of the active material, conductive agent, and binder is 8:1:1; the current collectors include copper foil, aluminum foil, etc.; the drying process is drying at 120 °C for 12 h; the diameter of the cut positive electrode disc is 1.5 cm; the hot pressing process is hot pressing at 0.2 MPa and 65 °C.

[0012] In step ③, the electrolyte includes LBE01, LBE02, etc., and the battery case models include CR2032, CR2025, etc.

[0013] The surface of metallic lithium is repeatedly ground, generating twin faults and stacking faults on its surface. These serve as lithiophilic active sites on the lithium anode, which can inhibit the growth of lithium dendrites and enable uniform deposition of lithium ions.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] Through a simple physical method of grinding, a nanostructure is formed on the surface of lithium metal. The preparation method is simple and feasible, greatly reducing the difficulty of lithium metal nanonization and being applicable to inhibiting the formation of lithium dendrites in lithium metal. The operation process of grinding the lithium sheet surface into nanoscale is simple and can be formed in one step, without going through complex processes such as high-temperature ball milling and mechanical rolling. Moreover, the grain boundary density increases sharply, and the grain boundary density of Li after treatment is about 4 times that of untreated Li. During the grinding process, the grains are significantly refined and have reached the nanoscale.

[0016] The grain boundaries on the surface of surface-nanostructured metallic lithium have many uniform active centers, endowing it with catalytic activity similar to that of quantum dots or single-atom catalysts. After assembling into a battery, the surface-nanostructured metallic lithium not only reduces the adsorption energy of lithium ions but also enables uniform deposition of lithium ions due to its uniform distribution, thus achieving the purpose of inhibiting the growth of lithium dendrites. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 FIG. is the SEM images of untreated lithium and surface-nanostructured lithium. Among them, FIGS. a, b, and e are untreated lithium sheets; FIGS. c, d, and f are surface-nanostructured lithium sheets; FIGS. b and d are the corresponding color SEM images of FIGS. a and c, respectively.

[0018] Figure 2 FIG. is a schematic diagram of the surface nanonization process of the lithium sheet. Among them, FIGS. a - b are schematic diagrams of the grinding process, FIG. c is the force analysis during the grinding process, and FIG. d is a schematic diagram of the process of grain refinement due to the force on the surface of the lithium anode.

[0019] Figure 3 FIG. is the cyclic performance graph of the symmetric battery Li||Li, that is, the charge-discharge curve of the symmetric Li||Li battery. The red corresponds to the Li (untreated)||Li (untreated) battery; the black corresponds to the Li (treated)||Li (treated) battery.

[0020] Figure 4 FIG. is the SEM images of the untreated lithium sheet and the surface-nanostructured lithium sheet after cycling. FIGS. a and b are the SEM images of the untreated lithium sheet after cycling, and FIGS. c and d are the SEM images of the treated lithium sheet after cycling. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited in any way. To avoid repetition, the raw materials in the following embodiments are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0022] Embodiment

[0023] A method for suppressing the growth of lithium dendrites on the negative electrode of a novel lithium metal battery includes the following steps:

[0024] ① Nanostructuring treatment of the lithium negative electrode surface: Inside a glove box filled with argon, first place sulfuric acid paper on the upper and lower surfaces of metallic lithium, place it in a mortar, and repeatedly grind it with an agate pestle for 8 minutes until its area becomes 1.5 times the original. Then cut it into small round pieces with a diameter of 1.5 cm using a cutter.

[0025] ② Preparation (pretreatment) of the positive electrode: Coat the slurry prepared according to the mass ratio of Si: acetylene black: PVDF = 80%: 10%: 10% on the surface of a copper foil; place it in an oven at 120 °C and dry it for 12 hours; then cut it into a positive electrode round piece with a diameter of 1.5 cm using a cutter; finally, place it in a hot press and set the parameters to 0.2 MPa and 65 °C for hot pressing.

[0026] ③ Fabrication of button batteries: Use the lithium sheet treated in step ① as the negative electrode and the round piece fabricated in step ② as the positive electrode, add an electrolyte, and assemble it into a battery using a battery case. That is, use the ground metallic lithium as the negative electrode, the copper foil round piece coated with the active material as the positive electrode, LiFL6 as the electrolyte, and assemble a battery using a CR2032 battery case; and assemble two ground lithium sheets into a Li||Li symmetric battery. There are 4 types of button batteries, namely Li(treated)||Si, Li(treated)||Li(treated); and reference batteries Li(untreated)||Si, Li(untreated)||Li(untreated).

[0027] By Figure 3It can be seen that during the cycle, the voltage of the Li(untreated)||Li(untreated) battery was unstable in the first 40 hours, with a small fluctuation. After 60 hours of cycling, the voltage began to increase rapidly and the battery polarized. The Li(treated)||Li(treated) battery was very stable in the first 300 hours of cycling. After 300 hours, a slow polarization phenomenon began to occur, and the battery was basically ineffective by 330 hours. By comparison, it can be seen that the metal lithium negative electrode treated with surface nano-treatment can effectively inhibit the growth of dendrites and greatly extend the service life of the battery. The lithium grain boundary is a highly active site for the adsorption of lithium ions. The lithium ions are uniformly adsorbed and deposited on the surface of the ground lithium negative electrode, which ultimately inhibits the growth of lithium dendrites. In addition, the uniform charge distribution on the lithium grain boundary helps to grind the uniform lithium ion deposition on the lithium anode. This simple and facile grinding will provide new research ideas for the design of high-capacity and long-cycle-life lithium, sodium, zinc and other metal batteries.

[0028] For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for inhibiting the growth of lithium dendrites on the negative electrode of a novel lithium metal battery, characterized in that, the method comprises the following steps: ① Nanostructuring treatment of the lithium negative electrode surface: In a closed space filled with a protective gas, first place sulfuric acid paper on both the upper and lower surfaces of the lithium sheet, place the lithium sheet in a mortar, and repeatedly grind it with a pestle for 5 - 10 minutes until the area of the lithium sheet becomes 1.5 times the original; then cut it into a negative electrode disc, and the diameter of the cut negative electrode disc is 1.5 cm; ② Preparation of the positive electrode: Mix the active material, conductive agent, and binder in a certain proportion and uniformly prepare a slurry, and coat the slurry on the surface of the current collector; after drying the current collector coated with the slurry in an oven, cut it into a positive electrode disc; finally, place it in a hot press for hot pressing; The active materials described in step ② include graphite, Si, and LiFePO 4 ; the conductive agents include acetylene black, SuperP, and Vlucan XC-72; the binder is prepared from PVDF and N-methylpyrrolidone; the mass ratio of the active materials, conductive agents, and binder is 8:1:1; the current collectors include copper foil and aluminum foil; the drying process is drying at 120 °C for 12 h, and the diameter of the cut positive electrode wafer is 1.5 cm; the hot pressing process is hot pressing at 0.2 MPa and 65 °C; ③ Fabrication of a button battery: Use the lithium sheet treated in step ① as the negative electrode, use the disc fabricated in step ② as the positive electrode, add an electrolyte, and assemble it into a battery with a battery case; the electrolyte includes LBE01 and LBE02, and the battery case models include CR2032 and CR2025.

2. The method according to claim 1, characterized in that, the protective gas in step ① is an inert gas, including argon and nitrogen.

3. The method according to claim 1, characterized in that, in step ①, the closed space enables the protective gas to circulate therein through an air pump to achieve a water and oxygen concentration below 0.1 ppm inside; the mortar materials include agate mortar, ceramic mortar, and glass mortar.

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