CN112786956A

CN112786956A - All-solid-state electrolyte layer for inhibiting growth of lithium dendrites, preparation method thereof and all-solid-state battery

Info

Publication number: CN112786956A
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: 2021-05-11
Anticipated expiration: 2041-01-29
Also published as: CN112786956B

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 method is different from the common lithium protection method for inhibiting the growth of lithium dendrites, the aim of inhibiting the growth of the lithium dendrites is fulfilled 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 aim of preparing the electrolyte layer can be fulfilled 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 (3860mAh/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 air₂、O₂、CO₂、H₂O 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 the maintenance of an inert atmosphere requires a large amount of energy, resulting in an increase in manufacturing costs. Each kind of toolThe disadvantages of the body 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 CN108565398A), 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 method can effectively reduce the interface impedance between the solid electrolyte layer and the lithium metal negative electrode, but the polymer film is generally insufficient in mechanical strength, difficult to resist the penetration of lithium dendrites and not great in the aspect of 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 generally, the formation of a protective layer of dozens of nanometers needs 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 since 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, so that the lithium ion conduction capacities in the solid-state electrolyte are 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: firstly, 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; secondly, polymer films have a lower density (ability to be used) compared to other types of substrates<1g/cm³) 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 cell can increase the mass energy density of the cell; and thirdly, the full-solid electrolyte layer has better laminating property when being laminated with the anode and the cathode, so that the contact impedance of each component in the battery can be reduced, and the full-solid battery with high performance can be 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 5-50 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, and if the thickness of the polymer film is too small, the processing technology 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 μm.

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 aperture of the circular hole is 1 to 1000 micrometers, such as 3 micrometers, 6 micrometers, 10 micrometers, 13 micrometers, 15 micrometers, 20 micrometers, 25 micrometers, 30 micrometers, 40 micrometers, 50 micrometers, 65 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 or 1000 micrometers, and the like, and preferably 20 to 100 micrometers.

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 or 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 pore diameter of the through hole and the distance between the holes can be adjusted to enable the pore space to be compact, and the compact, vertical and longitudinal heights of the pore space 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, through holes are formed in the polymer film in a die cutting mode, liquid containing solid electrolyte is injected into the through holes, the solid electrolyte is filled in the pores of the polymer film after drying, and the structural schematic diagram of the obtained all-solid electrolyte layer is shown in fig. 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 aperture is adjustable, and the method can be suitable for different types of solid electrolytes, for example, sulfide solid electrolytes with high ionic conductivity have good applicability, and all solid electrolyte layers with high ionic conductivity can be obtained.

Preferably, the solvent comprises an alcohol.

Preferably, the drying temperature is 45-75 ℃, 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 Li₆PS₅The 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 example was used as an intermediate layer, and lithium metal was used as a working electrode and a counter electrode, and a symmetrical cell was assembled; the battery is placed at 0.6mAh/cm²The cycling test was performed at current density as shown in fig. 3. As can be seen from fig. 3, the symmetric battery assembled using the electrolyte layer prepared in the present invention did not suffer from the short circuit phenomenon after cycling for more than 150 hours, indicating that the electrolyte layer is excellent in inhibiting 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 electrode plate taking nickel cobalt lithium manganate as an active material. The cycling test was performed at 0.1C-rate, and the time-voltage diagram 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 weeks of full cell cycle, and the first cycle efficiency was 89%.

Comparative example 1

This comparative example is conventional Li₆PS₅A Cl sulfide electrolyte layer.

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

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 occurs a micro short circuit due to penetration of lithium dendrites upon 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 Li₆PS₅The 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 for 2h at 60 ℃ to prepare the 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 cell was prepared in the same manner as in example 1 and tested under the same conditions, and no short circuit occurred after more than 170h 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 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 added₆PS₅The Cl sulfide solid electrolyte was replaced with a polymer solid electrolyte having a specific composition of 75 wt% PEO +25 wt% LiTFSI.

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 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 in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, 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.

2. The all-solid-state electrolyte layer according to claim 1, wherein the polymer film has a thickness of 5 to 50 micrometers, preferably 5 to 30 micrometers.

3. The all-solid-state electrolyte layer according to claim 1 or 2, 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 from monomers of the above polymers, preferably PI.

4. The all-solid electrolyte layer according to any one of claims 1 to 3, wherein the through-hole comprises any one of a round hole, a square hole or a rectangular hole or a combination of at least two thereof;

preferably, the through-going holes are distributed throughout the polymer film;

preferably, the through-going pores are uniformly distributed throughout the polymer film;

preferably, the through-going holes are arranged perpendicular to the polymer film.

5. The all-solid electrolyte layer according to any one of claims 1 to 4, wherein the through-hole is a circular hole;

preferably, the aperture of the round hole is 1-1000 microns, preferably 20-100 microns;

preferably, the distance between two adjacent round holes is 1-1000 microns, and preferably 20-100 microns.

6. All-solid-state electrolyte layer according to any one of claims 1 to 5, wherein the solid-state electrolyte comprises any one of a sulfide electrolyte, a halogen electrolyte, an oxide electrolyte or a polymer electrolyte, preferably a sulfide electrolyte;

7. A method of preparing an all-solid-state electrolyte layer according to any of claims 1 to 6, comprising the steps of:

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

8. The method of claim 7, wherein the solvent comprises an alcohol.

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

10. An all-solid battery comprising the 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.