阅读说明：本技术 一种用于碱金属基电池的高强度功能隔膜及制备方法和碱金属基电池 (High-strength functional diaphragm for alkali metal-based battery, preparation method of high-strength functional diaphragm and alkali metal-based battery ) 是由 陆盈盈 沈泽宇 于 2020-12-29 设计创作，主要内容包括：本发明涉及碱金属基电池技术领域,针对碱金属电池目前引入无机涂层的人工固态电解质界面膜等对碱金属阳极的效用有限的问题,公开一种用于碱金属基电池的高强度功能隔膜及制备方法和碱金属基电池,隔膜包括聚合物底膜和设置在聚合物底膜上的绝缘涂层；绝缘涂层由为纳米金刚石、纳米蒙脱石、纳米云母中的至少一种和有机粘结剂在聚合物底膜上涂覆制成。本发明采用不导电、高强度且本征化学惰性的无机颗粒,利用碱金属沉积/剥离过程中的应力变化实现纳米颗粒从隔膜到碱金属阳极界面的自转移,作为人工电子隧穿势垒维持SEI膜的低电子电导,组装的碱金属电池库伦效率、循环寿命及安全性均得到了显著提升。(The invention relates to the technical field of alkali metal-based batteries, and discloses a high-strength functional diaphragm for an alkali metal-based battery, a preparation method thereof and the alkali metal-based battery, aiming at the problem that the effect of an artificial solid electrolyte interface film and the like which introduce an inorganic coating to an alkali metal anode of the alkali metal battery is limited, wherein the diaphragm comprises a polymer bottom film and an insulating coating arranged on the polymer bottom film; the insulating coating is prepared by coating at least one of nano diamond, nano montmorillonite and nano mica and an organic binder on the polymer basement membrane. According to the invention, non-conductive, high-strength and intrinsic chemical inert inorganic particles are adopted, self-transfer of nano particles from a diaphragm to an alkali metal anode interface is realized by utilizing stress change in an alkali metal deposition/stripping process, the nano particles are used as an artificial electron tunneling barrier to maintain low electron conductance of an SEI (solid electrolyte interphase) film, and the coulombic efficiency, cycle life and safety of the assembled alkali metal battery are all remarkably improved.)

1. A high-strength functional separator for an alkali metal-based battery, comprising a polymer base film and an insulating coating layer disposed on the polymer base film;

the insulating coating is made by coating a slurry comprising inorganic particles and an organic binder on a polymeric base film.

2. The high-strength functional separator for an alkali metal-based battery according to claim 1, wherein the inorganic particles are at least one of nanodiamond, nanomontmorillonite, and nanomontainite; the particle size of the inorganic particles is 50-500 nm.

3. The high-strength functional separator for alkali metal-based batteries according to claim 1, wherein said organic binder is at least one of polyethylene oxide, polyvinylidene fluoride, Nafion.

4. The high-strength functional separator for an alkali metal-based battery according to claim 1, 2 or 3, wherein the thickness of the insulating coating is 1 to 20 μm.

5. The high-strength functional separator for alkali metal-based battery as claimed in claim 1, wherein the polymer base film is made of at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyimide, and polyacrylonitrile.

6. The high-strength functional separator for alkali metal-based batteries according to claim 1 or 5, wherein the polymer base membrane has a pore size of 0.01 to 1 μm, a porosity of 10 to 60%, and a thickness of 5 to 100 μm.

7. A method for preparing a high-strength functional separator for an alkali metal-based battery according to any one of claims 1 to 6, wherein the inorganic particles are uniformly mixed with the organic binder and the organic solvent to obtain a slurry, and then the slurry is coated on the polymer base film by a coating technique and dried to obtain the high-strength functional separator for the alkali metal-based battery.

8. The method for preparing a high-strength functional separator for an alkali metal-based battery according to claim 7, wherein the slurry contains 20 to 40 mass% of inorganic particles, 2 to 5 mass% of organic binder, and 50 to 70 mass% of organic solvent.

9. The method for preparing a high-strength functional separator for an alkali metal-based battery according to claim 7, wherein the organic solvent is acetonitrile, N-additivated pyrrolidone, or ethanol.

10. An alkali metal-based battery using the high-strength functional separator as claimed in any one of claims 1 to 6.

Technical Field

The invention relates to the technical field of alkali metal-based batteries, in particular to a high-strength functional diaphragm for an alkali metal-based battery, a preparation method of the diaphragm and the alkali metal-based battery.

Background

Alkali metal anodes, such as lithium, sodium, have higher theoretical specific capacities and lower electrode potentials than graphite anodes are a promising approach for pursuing high energy density batteries. However, the alkali metal anodic deposition process has dendrite problems, and faces many serious challenges such as poor cycle stability, high safety hazards, etc., which limits the commercial application of alkali metal batteries.

In an alkali metal battery, the reduction of the electron conductance of the solid electrolyte interface film can effectively inhibit electron tunneling, thereby passivating the alkali metal anode and preventing the continuous side reaction with the electrolyte. Artificial solid electrolyte interfacial films such as LiF, Li₃PO₄、Li₃N and an electrolyte modifying solution such as a perfluoro electrolyte, a high concentration electrolyte, a double salt electrolyte are used to form a solid electrolyte interface film rich in inorganic components to enhance its protective function.

However, artificial inorganic coatings may compromise The ionic conductance and mechanical strength of The solid electrolyte interfacial film, causing its rupture leading to local electronic leakage (He et al, The interfacial glass of lithium fluoride in solid electrolyte membranes on lithium, proc. natl. acad. sci. u.s.a. 2020, 117, 73); the electrolyte spontaneously forms a solid electrolyte interfacial film with random distribution of inorganic crystals and no ability to directionally regulate the electric field around dendrites (Zheng et al, Regulating electrochemical displacement mobility of Lithium: directions commercial regenerative Li Metal Batteries, chem. Soc. Rev. 2020, 49, 2701). The above strategies have therefore limited utility for stabilizing alkali metal anodes. In addition, the preparation process of the method is complicated, the cost is high, the method is not suitable for the existing technical process, and the method is not beneficial to commercial production.

Disclosure of Invention

Aiming at the problems that the artificial solid electrolyte interface film and the like which introduce an inorganic coating into the alkali metal battery at present have limited effect on an alkali metal anode and cause poor cycle stability and high potential safety hazard of the alkali metal battery, the invention aims to provide a high-strength functional diaphragm for the alkali metal-based battery, which can more effectively stabilize the alkali metal anode and ensure that the alkali metal battery obtains better cycle stability.

The invention also aims to provide a preparation method of the high-strength functional diaphragm for the alkali metal-based battery, which has the advantages of simple preparation process and low cost and is beneficial to commercial production.

It is still another object of the present invention to provide an alkali metal-based battery using the high-strength functional separator of the above alkali metal-based battery.

The invention provides the following technical scheme:

a high-strength functional separator for an alkali metal-based battery, the separator comprising a polymer base film and an insulating coating layer disposed on the polymer base film;

the insulating coating is made by coating a slurry comprising inorganic particles and an organic binder on a polymeric base film.

Preferably, the inorganic particles are at least one of nano-diamond, nano-montmorillonite and nano-mica; the particle size of the inorganic particles is 50-500 nm.

The invention breakthroughs the use of non-conductive, high strength, intrinsically chemically inert inorganic particles, such as nanodiamond, nanomontmorillonite and nanomontite, as coating particles, and nanodiamond is preferred. The inorganic particles have high strength and are electrically nonconductive. Because lithium metal has certain viscosity and the mechanical strength of the lithium metal and particles is greatly different, partial particles can fall off from a diaphragm due to external mechanical pressure or stress during internal deposition and are pressed on the surface of the lithium metal, the self-transfer of nano inorganic particles from the diaphragm to an alkali metal anode interface is realized, meanwhile, after electrolyte is injected, a solid electrolyte interface film is formed on the surface of the lithium metal, into which the particles are not pressed, and the inorganic particle embedded solid electrolyte interface film is formed together with the pressed particles, and the inorganic particles form an artificial electron tunneling barrier, so that the electron conductivity of the solid electrolyte interface film is reduced, and the electron leakage is inhibited. Meanwhile, the particles have chemical stability, do not react with alkali metal, have extremely small change of physical and chemical properties along with environmental factors (such as temperature and pressure), have high strength, and can slow down the rupture of a solid electrolyte interface film and inhibit the growth of dendritic crystals.

In the present invention, the organic binder is preferably at least one of polyethylene oxide, polyvinylidene fluoride, and Nafion.

Preferably, the thickness of the insulating coating is 1 to 20 μm.

In the present invention, the polymer base film is preferably made of at least one material selected from the group consisting of polyethylene, polypropylene, polyvinylidene fluoride, polyimide, and polyacrylonitrile.

Preferably, the polymer base membrane has a pore diameter of 0.01 to 1 μm, a porosity of 10 to 60% and a thickness of 5 to 100 μm.

According to the preparation method of the high-strength functional diaphragm for the alkali metal-based battery, the inorganic particles, the organic binder and the organic solvent are uniformly mixed to obtain slurry, and then the slurry is coated on the polymer base membrane by a coating technology and dried to obtain the high-strength functional diaphragm material for the alkali metal-based battery.

Preferably, the mass fraction of the inorganic particles in the slurry is 20-40%, the mass fraction of the organic binder is 2-5%, and the mass fraction of the organic solvent is 50-70%.

Preferably, the organic solvent is acetonitrile, N-pyrrolidone or ethanol.

An alkali metal-based battery using the above high-strength functional separator.

The invention has the following beneficial effects:

compared with the prior art, the invention adopts non-conductive, high-strength and intrinsically chemically inert inorganic particles as the diaphragm functional coating:

firstly, self-transfer of nano particles from a diaphragm to an alkali metal anode interface is realized by utilizing stress change in an alkali metal deposition/stripping process, the nano particles are used as an artificial electron tunneling barrier to participate in the formation of a solid electrolyte interface film, the extremely low electron conductance of the nano particles is always maintained, the continuous side reaction and electron leakage of an alkali metal anode and an electrolyte are inhibited, and the stability and the reversibility of the alkali metal anode are improved;

secondly, realizing the directional distribution of inorganic particles at the interface of the alkali metal anode in a self-transfer mode taking stress response as a mechanism, and pertinently adjusting the electric field distribution around the dendritic crystal, thereby having the capability of adjusting the ion deposition behavior and achieving the purpose of inhibiting the growth of the dendritic crystal;

thirdly, the diaphragm is prepared by a conventional coating technology, self-regulation of the alkali metal anode solid electrolyte interface film is realized in the circulation process after the battery is assembled, the preparation process does not need the support of inert gas atmosphere, and the production amplification is easy to realize;

in addition, the coulomb efficiency, the cycle life and the safety of the alkali metal battery assembled by the high-strength functional diaphragm material prepared by the invention are obviously improved.

Drawings

Fig. 1 is a scanning electron micrograph of the high-strength functional separator of example 1.

Fig. 2 is a graph of leakage current density of a lithium/steel sheet battery assembled from the high strength functional separator of example 1.

In the figure: 1. example 1 assembled lithium/steel cell, 2, lithium/steel cell assembled with Celgard 2400 polypropylene separator.

Figure 3 is a cycle number-coulombic efficiency curve for an assembled lithium copper half cell of example 4,

in the figure: 1. example 4 assembled lithium copper half cell, 2, lithium copper half cell with Celgard 2400 polypropylene separator as separator.

FIG. 4 is a scanning electron micrograph of the first lithium deposition morphology of an assembled lithium copper half cell of example 4.

Figure 5 is a discharge specific capacity curve of an assembled lithium/lithium iron phosphate full cell of example 5,

in the figure: 1. example 5 assembled lithium/lithium iron phosphate full cell, 2, lithium/lithium iron phosphate full cell with Celgard 2400 polypropylene separator as separator.

Figure 6 is a specific discharge capacity curve for an assembled lithium/NCM 811 full cell of example 6,

in the figure: 1. example 6 assembled lithium/NCM 811 full cell, 2, lithium/NCM 811 full cell with Celgard 2400 polypropylene separator as separator.

Detailed Description

The following further describes the embodiments of the present invention.

The starting materials used in the present invention are commercially available or commonly used in the art, unless otherwise specified, and the methods in the following examples are conventional in the art, unless otherwise specified.

In the following examples, Celgard 2400 polypropylene separator is used as an example of a polymer base film.

Example 1

A high-strength functional diaphragm for an alkali metal-based battery comprises a polymer base film and an insulating coating arranged on the polymer base film, wherein the polymer base film is a Celgard 2400 polypropylene diaphragm, the insulating coating is a nano diamond coating with the thickness of 3 mu m, and the average grain diameter of the nano diamond is 100 nm.

The preparation process comprises the following steps:

dissolving 100mg of polyvinylidene fluoride in 2.7mL of N-additive pyrrolidone by taking polyvinylidene fluoride as an organic binder and N-additive pyrrolidone as an organic solvent, adding 1g of nano diamond, and uniformly stirring. Placing the mixed slurry on a Celgard 2400 polypropylene diaphragm, preparing a high-strength functional diaphragm by coating with a scraper, drying in a vacuum oven at 60 ℃ overnight to obtain the high-strength functional diaphragm material for the alkali metal-based battery, wherein the loading capacity of the coating of the obtained functional diaphragm is 0.5 mg.cm^-2。

Example 2

A high-strength functional separator for an alkali metal-based battery, which is different from example 1 in that nano-montmorillonite of the same amount is used instead of nano-diamond.

Example 3

A high-strength functional separator for an alkali metal-based battery, which is different from example 1 in that the same amount of nano mica is substituted for nano diamond.

Example 4

A lithium copper half cell using the high-strength functional separator of example 1 was fabricated by using a nanodiamond-coated counter copper sheet electrode of the high-strength functional separator prepared in example 1, a lithium sheet was a counter electrode, an electrolyte was 1, 3-Dioxolane (DOL)/ethylene glycol dimethyl ether (DME) (1: 1, volume ratio) of 1M lithium bistrifluoromethanesulfonylimide (LiTFSI), and LiNO with a mass fraction of 2%₃And (3) an additive. Assembling the battery in a glove box protected by argon by using a 2032 type button battery to obtain a lithium copper halfA battery.

Example 5

In a lithium/lithium iron phosphate all-cell using the high-strength functional separator of example 1, the nano-diamond coating of the high-strength functional separator prepared in example 1 was faced to an ultra-thin lithium negative electrode and a lithium iron phosphate (LFP) positive electrode (10.5 mg cm)^-2) Assembling a full cell, wherein the electrolyte is 1M lithium bistrifluoromethanesulfonylimide (LiTFSI) 1, 3-Dioxolane (DOL)/ethylene glycol dimethyl ether (DME) (1: 1, volume ratio) and LiNO with the mass fraction of 2%₃And (3) an additive. And (3) assembling the battery in a glove box protected by argon by using a 2032 type button battery to obtain the lithium/lithium iron phosphate full battery.

Example 6

A lithium/NCM 811 full cell using the high strength functional separator of example 1 was prepared by facing the nanodiamond coating of the high strength functional separator prepared in example 1 to an ultra-thin lithium negative electrode and an NCM811 positive electrode (21.5 mg cm)^-2) The whole cell was assembled with an electrolyte of 0.6M lithium difluoroborate (LiDFOB) and 0.6M LiBF₄Fluoroethylene carbonate (FEC)/diethyl carbonate (DEC) (1: 2, volume ratio). The cell assembly was performed using a 2032 type coin cell in an argon-protected glove box to obtain a lithium/NCM 811 full cell.

Performance testing

1. Structural features of nanodiamond diaphragms

Scanning electron microscope test characterization is carried out on the nano-diamond high-strength functional diaphragm prepared in example 1, and an obtained SEM spectrum is shown in figure 1.

As can be seen from fig. 1, the particles in the nanodiamond coating are uniformly distributed and have a thickness of 3 μm.

2. Assembled battery performance of nano-diamond diaphragm

2.1. The leakage current density capacities of the lithium/steel sheet battery assembled from the nanodiamond functional separator of example 1, the lithium/steel sheet battery assembled from the Celgard 2400 polypropylene separator, and pure lithium metal were characterized by using a direct current polarization method, and a direct current voltage of 10mV was used, and the resulting leakage current density curves are shown in fig. 2.

As can be seen from fig. 2, the nano-diamond functional separator can significantly reduce the leakage current density of the battery, which indicates that the high-strength functional separator effectively reduces the electronic conductance of the SEI, thereby inhibiting the electrolyte side reaction and the formation of the interface electric field concentration distribution points.

2.2. The lithium copper half-cells prepared in example 4 were tested for circulating coulombic efficiency (current density 1mA cm)^-2) And the first lithium deposition morphology is tested and characterized by a scanning electron microscope, and the surface capacity of the electro-deposition/stripping lithium metal active substances of the two batteries is 1mAh cm^-2The results are shown in FIGS. 3 and 4.

As can be seen from FIG. 3, the cycle life of the lithium-copper half-cell assembled by adopting the nano-diamond functional diaphragm is prolonged by more than 4 times, and the extremely high coulombic efficiency can be still maintained after 300 cycles.

As can be seen from fig. 4, the nanodiamond particles are attached to the surface of the lithium deposition protrusion, and the lithium deposition particles are in a large-size columnar shape and are arranged closely without moss-like lithium dendrites, which shows that the nanodiamond particles can disperse the electric field intensity at the lithium deposition protrusion, alleviate the tip effect, induce radial deposition of lithium ions, and achieve dense lithium deposition.

2.3. The lithium/lithium iron phosphate full cell prepared in example 5 was tested for specific cycling discharge capacity under 0.5C for charging and discharging, and the results are shown in fig. 5.

It can be seen from fig. 5 that the discharge capacity of the lithium/lithium iron phosphate full cell assembled by the nano-diamond functional diaphragm can be kept stable after 600 cycles, and the voltage hysteresis phenomenon is greatly inhibited.

2.4. The lithium/NCM 811 full cell prepared in example 6 was tested for specific cycling discharge capacity under 0.3C charge and 0.5C discharge conditions, and the results are shown in fig. 6.

As can be seen from fig. 6, the capacity of the lithium/NCM 811 full cell assembled by using the nano-diamond functional separator is maintained at 80% after 112 cycles, which shows that the high-strength functional separator can still significantly improve the cycle performance of the cell even under severe industrial test conditions, and has practical value.