CN112786956B

CN112786956B - All-solid-state electrolyte layer for inhibiting growth of lithium dendrites, preparation method thereof and all-solid-state battery

Info

Publication number: CN112786956B
Application number: CN202110130079.XA
Authority: CN
Inventors: 李瑞杰; 王磊; 黄海强; 陈少杰; 周龙捷
Original assignee: Svolt Energy Technology Wuxi Co Ltd
Current assignee: Svolt Energy Technology Wuxi Co Ltd
Priority date: 2021-01-29
Filing date: 2021-01-29
Publication date: 2022-11-15
Anticipated expiration: 2041-01-29
Also published as: CN112786956A

Abstract

The invention discloses an all-solid-state electrolyte layer for inhibiting growth of lithium dendrites, a preparation method thereof and an all-solid-state battery. The all-solid-state electrolyte layer comprises a polymer film with a through hole and a solid-state electrolyte filled in the through hole; the polymer film is an insulator for lithium ions and electrons. The invention is different from the common lithium protection method for inhibiting the growth of lithium dendrite, the purpose of inhibiting the growth of the lithium dendrite is achieved by designing the structure and the composition of a solid electrolyte layer, no binder or solvent is introduced into the lithium cathode side in the process of preparing the all-solid electrolyte layer, the purpose of preparing the electrolyte layer can be achieved by adopting the traditional equipment, and the method is convenient to operate and low in cost. Can well solve the defects of long time consumption, impurity introduction, easy shedding of the protective layer and high cost of directly forming the protective layer on the lithium metal.

Description

All-solid-state electrolyte layer for inhibiting growth of lithium dendrites, preparation method thereof and all-solid-state battery

Technical Field

The invention belongs to the technical field of solid-state batteries, and relates to an all-solid-state electrolyte layer for inhibiting growth of lithium dendrites, a preparation method thereof and an all-solid-state battery.

Background

With the rapid development of consumer electronics and electric vehicles, the demands for energy density, safety, reliability and service life of batteries are increasing dramatically. Lithium metal has extremely high theoretical specific capacity (3860 mAh/Kg) and lowest potential (-3.04V), so that the lithium metal secondary battery is the preferred system of the next generation of high energy density energy storage devices. The solid-state battery has no electrolyte in the solid-state battery, so that potential safety hazards caused by the leakage of the electrolyte and other problems are well avoided, and meanwhile, the solid-state battery has the advantages of high energy density, no memory effect and the like and is widely concerned by researchers.

However, the growth of lithium dendrites may be caused due to the non-uniform deposition of lithium ions on the lithium metal negative electrode; in addition, the solid electrolyte layer is not completely compact, and pores exist in the solid electrolyte layer, so that the solid electrolyte layer is easily pierced by lithium dendrites in the circulation process, and the anode and the cathode of the battery are short-circuited due to the existence of the lithium dendrites, so that the battery is failed and potential safety hazards are caused.

Most of the existing methods for inhibiting the growth of lithium dendrites are directly used for protection on lithium metal, and the methods for directly protecting the lithium metal have obvious defects: 1. because lithium metal has extremely strong reaction activity, other impurities except the protective layer are inevitably introduced into the lithium metal when the lithium metal is directly protected, so that the purity of the protective layer is not high, and the protective effect is not obvious; 2. the lithium metal will react with N in the air ₂ 、O ₂ 、CO ₂ 、H ₂ O and the like react to cause the self destruction and pollution of lithium metal, so most of the existing lithium protection methods need to be carried out in inert gas atmosphere such as vacuum atmosphere, argon atmosphere and the like, which causes that the method for directly protecting the lithium metal is difficult to carry out large-scale production; and maintaining an inert production atmosphere requires a significant amount of energy, resulting in increased manufacturing costs. The disadvantages of each particular protection method are: 1. a wet coating method is generally used for preparing a protective layer on the surface of lithium, but a solvent and a binder are needed in the coating process, and the protective layer needs to be dried for a long time due to the existence of the solvent, so that the preparation efficiency of the protective layer is reduced, the ionic conductivity of the protective layer is reduced due to the addition of the binder, the mechanical strength and toughness are limited, and the protective layer fails due to fracture and falling of the protective layer caused by violent change of the volume of a lithium metal cathode in the charge-discharge cycle process of a battery; 2. the liquid phase method for preparing the alloy protective layer is a commonly used method for inhibiting lithium dendrite (such as CN111490252A and CN 108565398A), but the method generally has more impurities, so that the impedance of the whole battery is increased, the uniform deposition of lithium ions in the charging and discharging process is influenced, the generation of the lithium dendrite cannot be well inhibited, and the reaction degree of different batches is different, so that the consistency of the alloy protective layer is poor; 3. the polymer film is used as a lithium metal negative electrode protective layer and is generally made of PEO, PVDF, PAN and other polymers added with lithium salt, although the method can be usedThe interface impedance between the solid electrolyte layer and the lithium metal negative electrode can be effectively reduced, but the polymer film generally has insufficient mechanical strength, is difficult to resist the piercing of lithium dendrites, and has little effect on prolonging the cycle life of the battery; 4. the thickness of a protective layer formed by a physical deposition means is difficult to be thickened, generally can only be in a nanometer level, generally does not exceed 200nm, and the regulation space is small; the operability is poor, the time consumption is long, and the formation of a protective layer with dozens of nanometers generally takes hours, so that the large-scale application of a physical deposition means is limited; 5. and (3) coating a graphite or other carbon layer on the surface of the lithium metal by a dry blade coating method to protect the lithium metal. The method has difficulty in controlling the thickness of the protective layer and in preparing the protective layer uniformly.

Therefore, there is a need to find a simpler and more effective lithium metal protection strategy to ensure effective protection of the lithium metal negative electrode during long cycling of the battery.

Disclosure of Invention

In view of the above problems in the prior art, an object of the present invention is to provide an all-solid electrolyte layer that suppresses growth of lithium dendrites, a method of preparing the same, and an all-solid battery.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides an all-solid-state electrolyte layer for suppressing lithium dendrite growth, wherein the all-solid-state electrolyte layer includes a polymer film having a through hole, and a solid-state electrolyte filled in the through hole; the polymer film is an insulator for lithium ions and electrons.

In the prior art, the electrolyte layer of the solid-state battery is generally formed by stacking solid-state electrolyte particles, but because the solid-state electrolyte layer cannot be perfectly uniform in the actual manufacturing process, the problems of uneven thickness, internal defects and the like are inevitable, and the lithium ion conduction capability in the solid-state electrolyte is not completely the same. The growth of lithium dendrites in the solid-state battery is mainly caused by uneven deposition of lithium ions transmitted from the positive electrode side to the negative electrode side, and protruding lithium is formed at positions where the lithium ions are deposited more; further, since these protruding portions are located closer to the positive electrode side, the protruding portions are more likely to attract lithium ions transmitted from the positive electrode side to the negative electrode, and thus have a higher current density at the protruding lithium metal portions, which causes the protruding portions to preferentially grow to form lithium dendrites penetrating the electrolyte layer, and finally short-circuiting the positive and negative electrodes. The schematic diagram is shown in fig. 1, wherein 1 is a solid electrolyte layer, 2 is a positive electrode layer, and 3 is a negative electrode layer.

In order to solve the problems, the invention achieves the purpose of inhibiting the growth of lithium dendrite by improving the structure of an all-solid-state electrolyte layer, and particularly, the all-solid-state electrolyte layer takes a polymer film as a matrix, has no lithium ion and electron conductivity, and can be regarded as an insulating porous film, through holes are distributed on the insulating porous film, and the solid-state electrolyte is filled in the holes.

The technical principle that the all-solid-state electrolyte layer can inhibit the growth of lithium dendrites is as follows: since the pore walls of the insulating porous film are insulators of ions and electrons, lithium ions transported in each pore are strictly constrained to be transported vertically in the pore and cannot pass through the pore walls to adjacent pores, and lithium ions in the electrolyte layer are forcedly transported in the vertical direction without being randomly transported under the restriction of the insulating pore walls; therefore, the lithium ions can be uniformly transmitted to the negative electrode in the electrolyte layer, lithium dendrites formed by overlarge local current density caused by transverse transmission of the lithium ions are avoided, and the purpose of inhibiting the growth of the lithium dendrites is achieved.

The all-solid-state electrolyte layer of the invention has the following advantages because the polymer film is adopted as the matrix: 1. the polymer film is easy to process and can be produced in a large-scale and industrialized manner, so that the process has the potential of large-scale application and the low cost can be ensured; 2. the polymer film has a lower density (can be made of) than other types of substrates<1g/cm ³ ) And can be processed to a thinner thickness (can be processed to<10 μm) so that the use of a thinner, less dense polymer film as the matrix for the solid electrolyte in the battery can increase the mass energy density of the battery; 3. the all-solid-state electrolyte layer has better bonding property when being bonded with the anode and the cathodeThe contact resistance of each component in the battery can be reduced, and the high-performance all-solid-state battery is further favorably obtained.

The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.

Preferably, the thickness of the polymer film is 5 to 50 micrometers, such as 5 micrometers, 8 micrometers, 10 micrometers, 12.5 micrometers, 15 micrometers, 18 micrometers, 20 micrometers, 25 micrometers, 30 micrometers, 35 micrometers, 40 micrometers or 50 micrometers, etc., if the thickness of the polymer film is too small, the processing process is difficult to implement, and the risk of lithium dendrite penetration is increased; if the thickness of the polymer film is too large, the lithium ion transmission path is prolonged, the impedance is increased, the capacity exertion is influenced, the internal resistance is increased, and the self-heating is large. More preferably 5 to 30 microns.

Preferably, the polymer film includes any one of polypropylene (PP), polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyacrylamide (PAM), polyacrylonitrile (PAN), polyethylene oxide (PEO), polyethylene terephthalate (PET), polyimide (PI), or a copolymer formed by monomers of the above polymers, but is not limited to the above-listed substances, and other polymers commonly used in the art to insulate lithium ions and electrons may be used in the present invention, preferably PI.

The shape of the through-hole is not particularly limited in the present invention, and may include any one of a circular hole, a square hole, or a rectangular hole, or a combination of at least two of them, for example.

Preferably, the through-going holes are distributed throughout the polymer film.

Preferably, the through-going holes are evenly distributed throughout the polymer film.

Preferably, the through-going holes are arranged perpendicular to the polymer film. The structure with the vertical channels is beneficial to promoting the transmission of lithium ions in the preset channels and inhibiting the uneven lithium ion deposition on the negative electrode side caused by random transmission and cross transmission of the lithium ions in the electrolyte layer.

Preferably, the through hole is a circular hole.

Preferably, the pore size of the circular pores is 1 to 1000 microns, such as 3 microns, 6 microns, 10 microns, 13 microns, 15 microns, 20 microns, 25 microns, 30 microns, 40 microns, 50 microns, 65 microns, 80 microns, 100 microns, 125 microns, 150 microns, 200 microns, 300 microns, 350 microns, 400 microns, 500 microns, 600 microns, 700 microns, 800 microns, 900 microns, 1000 microns, etc., preferably 20 to 100 microns.

Preferably, the distance between two adjacent circular holes is 1 to 1000 micrometers, such as 3 micrometers, 5 micrometers, 10 micrometers, 13 micrometers, 15 micrometers, 20 micrometers, 30 micrometers, 40 micrometers, 50 micrometers, 70 micrometers, 80 micrometers, 100 micrometers, 125 micrometers, 150 micrometers, 200 micrometers, 300 micrometers, 350 micrometers, 400 micrometers, 500 micrometers, 600 micrometers, 700 micrometers, 800 micrometers, 900 micrometers, 1000 micrometers, etc., preferably 20 to 100 micrometers. The distance between two adjacent round holes refers to the distance between two circle centers.

According to the invention, the pores can be compact by adjusting the aperture of the through hole and the distance between the holes, and the compact, vertical and longitudinal heights of the pores are consistent, so that the performance of the all-solid-state electrolyte layer disclosed by the invention is favorably improved.

Preferably, the solid electrolyte includes any one of a sulfide electrolyte, a halogen electrolyte, an oxide electrolyte or a polymer electrolyte, but is not limited to the above-listed solid electrolyte types, and other solid electrolytes commonly used in the art to achieve the same effect may be used in the present invention, preferably a sulfide electrolyte.

Preferably, the particle size of the solid electrolyte is smaller than the pore size of the through-going pores.

In a second aspect, the present invention provides a method for producing an all-solid electrolyte layer as defined in the first aspect, the method comprising the steps of:

(1) Cutting the through hole in the polymer film by using a die cutting tool;

(2) Dissolving or dispersing a solid electrolyte in a solvent to obtain a solution or dispersion of the solid electrolyte;

(3) And injecting the solution or dispersion liquid of the solid electrolyte into the through holes of the polymer film, and drying to obtain the all-solid electrolyte layer.

In the method, the adopted solvent is stable to the solid electrolyte, so that the structure of the solid electrolyte is prevented from being damaged due to dissolution or dispersion.

According to the method, a through hole is formed in a polymer film in a die cutting mode, liquid containing solid electrolyte is injected into the through hole, the solid electrolyte is filled in the pores of the polymer film after drying, and the structural schematic diagram of the obtained all-solid-state electrolyte layer is shown in figure 2, wherein 4 is the solid electrolyte, and 5 is the polymer film.

The method is simple, the polymer membrane is easy to prepare, the cost is low, the pore size is adjustable, and the method can be suitable for different types of solid electrolytes, for example, the sulfide solid electrolyte with high ionic conductivity has good applicability, and a full solid electrolyte layer with high ionic conductivity can be obtained.

Preferably, the solvent comprises an alcohol.

Preferably, the drying temperature is 45 to 75 ℃, such as 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃ or 75 ℃.

In a third aspect, the present invention provides an all-solid-state battery including the all-solid-state electrolyte layer according to the first aspect, and a positive electrode and a negative electrode respectively located on both sides of the all-solid-state electrolyte layer.

Compared with the prior art, the invention has the following beneficial effects:

the method is different from the common lithium protection method for inhibiting the growth of lithium dendrite, the lithium negative electrode protective layer is not directly prepared on the lithium metal negative electrode, but the aim of inhibiting the growth of the lithium dendrite is achieved by designing the structure and the composition of a solid electrolyte layer. Can well solve the defects of long time consumption, impurity introduction, easy shedding of the protective layer and high cost of directly forming the protective layer on the lithium metal.

Drawings

FIG. 1 is a schematic diagram of lithium dendrite growth caused by non-uniform deposition of lithium ions in a prior art solid-state battery, 1-a solid-state electrolyte layer, 2-a positive electrode layer, and 3-a negative electrode layer.

FIG. 2 is a schematic view of the solid electrolyte layer of the present invention, 4-solid electrolyte, 5-polymer film.

Fig. 3 is a cycle diagram of a symmetrical battery fabricated using the solid electrolyte layer prepared in example 1.

Fig. 4 is a time-voltage cycle chart of a full cell fabricated using the solid electrolyte layer prepared in example 1.

Fig. 5 is a cycle diagram for preparing a symmetrical battery using the electrolyte layer of comparative example 1.

Fig. 6 is a time-voltage cycle chart for preparing a full cell using the electrolyte layer of comparative example 1.

Detailed Description

The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.

Example 1

This example provides a solid electrolyte layer prepared by the following method:

1. a PI film with the thickness of 30 microns is used as a substrate, through circular holes with the diameter of 30 microns are die-cut on the PI film, and the distance between every two holes is 30 microns.

2. Mixing Li ₆ PS ₅ The Cl sulfide solid electrolyte is dissolved in ultra-dry ethanol to prepare a solution, and the solution is injected into the insulating porous film prepared in step 1. And then dried at 70 ℃ for 1.5h to prepare the solid electrolyte layer.

Assembling and testing:

the solid electrolyte layer prepared in the embodiment is used as an intermediate layer, and lithium metal is used as a working electrode and a counter electrode to assemble a symmetrical battery; the battery is placed at 0.6mAh/cm ² The cycling test was performed at current density as shown in fig. 3. As can be seen from FIG. 3, the electrolyte prepared in the present invention was usedThe short circuit phenomenon of the layer-assembled symmetrical battery does not occur after the cycle exceeds 150h, which shows that the electrolyte layer can well inhibit the growth of lithium dendrites.

Lithium metal is used as a negative electrode, the electrolyte layer prepared in the embodiment is used as a diaphragm, and a soft package full battery is assembled by a positive pole piece with nickel cobalt lithium manganate as an active material. The cycling test was performed at 0.1C-rate, the time-voltage diagram of which is shown in fig. 4. As can be seen from fig. 4, with the electrolyte layer fabricated in the present invention, no sign of short circuit occurred for 10 full cell cycles, and the first cycle efficiency was 89%.

Comparative example 1

The comparative example is conventional Li ₆ PS ₅ A Cl sulfide electrolyte layer.

A symmetrical cell of the same construction as in example 1 was made and tested under the same conditions, cycling as shown in fig. 5, with short circuiting due to lithium dendrite puncture occurring when cycling did not exceed 6 hours.

The same pouch full cell as in example 1 was prepared and tested under the same conditions, and the cycle thereof is as shown in fig. 6, which was a micro short circuit due to lithium dendrite penetration occurring at the first cycle.

Example 2

1. a PE film with the thickness of 20 micrometers is used as a base body, through circular holes with the diameter of 25 micrometers are die-cut on the base body, and the distance between every two holes is 30 micrometers.

2. Mixing Li ₆ PS ₅ The Cl sulfide solid electrolyte is dissolved in ultra-dry ethanol to prepare a solution, and the solution is injected into the insulating porous film prepared in step 1. And then drying the electrolyte at 60 ℃ for 2h to prepare a solid electrolyte layer.

A symmetrical battery was prepared in the same manner as in example 1 and tested under the same conditions, and no short circuit occurred after more than 120 hours of cycling.

A pouch full cell was prepared in the same manner as in example 1 and tested under the same conditions, and the first cycle efficiency of the full cell was 90%.

Example 3

1. a PI film with the thickness of 40 micrometers is used as a substrate, through square holes with the side length of 15 micrometers are die-cut on the PI film, and the distance between every two holes is 20 micrometers.

2. The LLZTO oxide solid electrolyte was dispersed in ultra-dry ethanol to prepare a suspension, and the suspension was injected into the insulating porous film prepared in step 1. And then dried at 70 ℃ for 1h to prepare a solid electrolyte layer.

A symmetrical battery was prepared in the same manner as in example 1 and tested under the same conditions, and no short circuit occurred after cycling for more than 170 hours.

A pouch full cell was prepared in the same manner as in example 1 and tested under the same conditions, and the first cycle efficiency of the full cell was 85%.

Example 4

The difference from example 1 is that the thickness of the PI film is 5 μm.

A symmetrical battery was prepared in the same manner as in example 1 and tested under the same conditions, and short-circuiting occurred after cycling for over 53 hours.

Example 5

The difference from example 1 is that the thickness of the PI film is 50 μm.

A pouch full cell was prepared in the same manner as in example 1 and tested under the same conditions, and the first cycle efficiency of the cell was 83%.

As can be seen by comparing example 1 with example 4, a reduction in the thickness of the electrolyte layer increases the risk of lithium dendrite penetration, shortening the cycle life. As can be seen from comparison of example 1 with example 5, an increase in the thickness of the electrolyte layer increases the internal resistance of the battery, which in turn leads to a decrease in the first cycle efficiency of the battery.

Example 6

The difference from example 1 is that Li is added ₆ PS ₅ Solid state electrolysis of Cl sulfidesMass replacement with Polymer solid electrolyte, the specific composition of the polymer solid electrolyte is 75wt% PEO +25wt% LiTFSI.

A pouch full cell was manufactured in the same manner as in example 1 and tested under the same conditions, and the first cycle efficiency of the cell was 79%.

As is clear from a comparison between example 1 and example 6, the polymer electrolyte is unstable at high voltage and is further easily decomposed on the positive electrode high voltage side, which results in a decrease in the first cycle efficiency of the battery.

The applicant states that the present invention is illustrated by the above examples to show the detailed method of the present invention, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be carried out. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of the raw materials of the product of the present invention, and the addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims

1. An all-solid-state electrolyte layer that suppresses growth of lithium dendrites, the all-solid-state electrolyte layer comprising a polymer film having a through-hole, and a solid-state electrolyte filled in the through-hole;

the polymer film is an insulator for lithium ions and electrons;

the through holes are arranged perpendicular to the polymer film;

the lithium ions transmitted in each through hole are constrained in the through hole to be transmitted vertically and cannot pass through the hole wall of the through hole to reach the adjacent through hole;

the thickness of the polymer film is 5-30 microns;

the solid electrolyte is a sulfide electrolyte;

the through holes are uniformly distributed on the whole polymer film, the through holes are round holes, the aperture of each round hole is 20-100 micrometers, and the distance between every two adjacent round holes is 20-100 micrometers;

the all-solid-state electrolyte layer is prepared by the following method, and the method comprises the following steps:

(1) Cutting the through hole in the polymer film by using a die cutting tool;

(3) Injecting the solution or dispersion of the solid electrolyte into the through hole of the polymer film, and drying to obtain an all-solid-state electrolyte layer;

the solvent includes an alcohol.

2. The all-solid electrolyte layer according to claim 1, wherein the polymer film comprises any one of polypropylene PP, polyethylene PE, polystyrene PS, polyvinyl chloride PVC, polyvinylidene chloride PVDC, polytetrafluoroethylene PTFE, polyacrylic acid PAA, polyacrylamide PAM, polyacrylonitrile PAN, polyethylene oxide PEO, polyethylene terephthalate PET, polyimide PI, or a copolymer formed by monomers of the above polymers.

3. The all-solid electrolyte layer according to claim 2 wherein the polymer film is PI.

4. The all-solid electrolyte layer according to claim 1, wherein the through-hole comprises any one of a circular hole, a square hole, or a rectangular hole, or a combination of at least two thereof.

5. The all-solid electrolyte layer according to claim 1, wherein the through-holes are distributed throughout the polymer film.

6. The all-solid electrolyte layer according to claim 1, wherein a particle size of the solid electrolyte is smaller than a pore size of the through-hole.

7. A method of preparing an all-solid electrolyte layer according to claim 1, comprising the steps of:

(1) Cutting the through hole in the polymer film by using a die cutting tool;

(3) Injecting the solution or dispersion of the solid electrolyte into the through holes of the polymer film, and drying to obtain an all-solid electrolyte layer;

the solvent includes an alcohol.

8. The method according to claim 7, wherein the temperature of the drying is 45 to 75 ℃.

9. An all-solid battery comprising an all-solid electrolyte layer according to any one of claims 1 to 6, and a positive electrode and a negative electrode respectively located on both sides of the all-solid electrolyte layer.