WO2021098685A1

WO2021098685A1 - Solid-state polymer electrolyte, preparation method therefor, and lithium battery

Info

Publication number: WO2021098685A1
Application number: PCT/CN2020/129495
Authority: WO
Inventors: 刘国华; 陆子恒; 陈佳华; 羿井司; 杨铮; 李�诚; 杨春雷; 钟国华
Original assignee: 深圳先进技术研究院
Priority date: 2019-11-20
Filing date: 2020-11-17
Publication date: 2021-05-27
Also published as: CN110911739A

Abstract

The present invention discloses a solid-state polymer electrolyte, a preparation method therefor, and a lithium battery. The solid-state polymer electrolyte is formed by means of in-situ polymerization of a lithium salt, a polymerization monomer, an additive, an inorganic powder, and an initiator. The disclosed preparation method for the solid-state polymer electrolyte comprises: adding the lithium salt into the polymerization monomer and the additive, mixing same to form a basic electrolyte; adding the inorganic powder into the basic electrolyte, and mixing same to form a first solution; and adding the initiator into the first solution, such that each component undergoes in-situ polymerization, and the solid-state polymer electrolyte is obtained. The solid-state polymer electrolyte according to the present invention has excellent electrochemical stability with an electrochemical window up to 5.5 V, and at the same time, also effectively solves the problem of overly high interface resistance between an electrode and a solid-state electrolyte. The preparation method for the solid-state polymer electrolyte according to the present invention is simple and highly efficient, and can be applied very well in industrial production.

Description

Solid polymer electrolyte, preparation method thereof and lithium battery

Technical field

The invention relates to the technical field of lithium battery electrolyte preparation, in particular to a solid polymer electrolyte, a preparation method thereof and a lithium battery.

Background technique

The development of society and the advancement of science and technology have made lithium-ion batteries have a wide range of application markets. High-energy-density lithium-ion batteries are the main direction pursued by researchers, which require lithium-ion batteries with high-capacity electrodes and stable electrolytes. However, during the application of lithium-ion batteries, there are great safety hazards due to the growth of lithium dendrites, the leakage of liquid electrolyte, and combustion.

At present, gel polymer electrolytes and solid electrolytes have become a hot research field for more and more scholars. Among them, solid electrolytes have received more extensive research due to their higher mechanical strength and ionic conductivity. Higher mechanical strength can inhibit the growth of lithium dendrites, and good ion conductivity is conducive to ion transmission. However, there are serious interface problems between the solid electrolyte and the electrode. Therefore, the strategy of in-situ polymerization has been proposed. The in-situ polymerization method is: use an initiator on the electrode to directly polymerize the nanoparticles and organic molecules, reducing the electrode and the solid electrolyte. The interface resistance between them improves the performance of the battery. However, the solid electrolyte obtained by the current in-situ polymerization method still has the problem of low electrochemical window.

technical problem

In order to solve the problem that the electrochemical window of the solid electrolyte obtained by the in-situ polymerization method in the prior art is not high, the present invention provides a solid polymer electrolyte with an electrochemical window greater than 5 V and a preparation method thereof, and further provides A lithium battery including the solid polymer electrolyte.

Technical solutions

In order to achieve the above-mentioned object of the invention, the present invention provides a solid polymer electrolyte, including in-situ polymerized basic electrolyte, inorganic powder and initiator, wherein the basic electrolyte is a mixture of lithium salt, polymerized monomer and additives.

Further, the inorganic powder is selected from at least one of _{conductive ceramic powder, Al 2} O ₃ , SiO ₂ and TiO _2.

Furthermore, the conductive ceramic powder is at least one of Li _6.4 La ₃ Zr _1.4 Ta _0.6 O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₁₀ GeP ₂ S ₁₂ and Li _1.5 Al _0.5 Ge _1.5 P ₃ O ₁₂ One kind.

Further, the lithium salt is selected from at least one of lithium bis(fluorosulfonyl)imide, lithium bistrifluoromethanesulfonimide, and lithium bisoxalate; the polymerized monomer is selected from ether groups Polymeric monomers; the additives are selected from carbonates.

Further, the polymerized monomer is selected from 1,3-dioxolane or ethylene glycol dimethyl ether; the additive is selected from at least one of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate .

Further, the initiator is selected from at least one of Al(OTF) ₃ , Al(CF ₃ SO ₃ ) ₃ , LiPF ₆ , diethyl aluminum chloride and ethyl aluminum dichloride.

Further, the mass fraction of the base electrolyte is 15% to 95%, the mass fraction of the inorganic powder is 5% to 57%, and the mass fraction of the initiator is 0.2% to 44%.

Furthermore, in the basic electrolyte, the amount concentration of the lithium salt is 1-7 mol/L.

Based on the above solid polyelectrolyte, the present invention also provides a method for preparing the above solid polyelectrolyte, which includes the steps:

S1. Add lithium salt to the polymerized monomer and additives, and mix to form a basic electrolyte;

S2. Add inorganic powder to the basic electrolyte and mix to form a first solution;

S3. Add an initiator to the first solution to polymerize each component in situ to obtain the solid polymer electrolyte.

Further, in step S3, it specifically includes: first adding an initiator to the first solution, stirring and mixing to obtain a second solution, and allowing the second solution to perform in-situ polymerization reaction at 25°C to 70°C.

The present invention further provides a lithium battery including a positive electrode, a negative electrode, and an electrolyte arranged between the positive electrode and the negative electrode, and the electrolyte adopts the above-mentioned solid polymer electrolyte.

Beneficial effect

The preparation method of the solid polymer electrolyte provided by the present invention takes inorganic powder, initiator, lithium salt, polymer monomer and additives as raw materials for polymerization reaction. The preparation method is simple and can be prepared to obtain a stable electrochemical window higher than 5 V. Solid polymer electrolyte with excellent performance.

Description of the drawings

Figure 1 is a physical diagram of a solid polymer electrolyte in an embodiment of the present invention;

2 is an SEM image of the solid polymer electrolyte in Example 1;

3 is a graph of electrochemical impedance of the solid polymer electrolyte in Example 2;

4 is a graph of cyclic voltammetry of the solid polymer electrolyte in Example 2;

Fig. 5 is a graph of the charge-discharge cycle test curve of the lithium battery sample in Example 2 at a rate of 1 C.

The best mode of the present invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention can be implemented in many different forms, and the present invention should not be construed as being limited to the specific embodiments set forth herein. On the contrary, these embodiments are provided to explain the principle of the present invention and its practical application, so that other skilled in the art can understand various embodiments of the present invention and various modifications suitable for specific anticipated applications.

Based on the problem that the electrochemical window of the solid electrolyte obtained by the in-situ polymerization method in the prior art is not high, the inventor of the present invention provides a solid polymer electrolyte with an electrochemical window greater than 5V and a preparation method thereof, and further provides Lithium battery with material electrolyte.

The preparation method of the solid polymer electrolyte provided by the embodiment of the present invention includes the steps:

S1. The lithium salt is added to the polymerized monomer and additives, and mixed to form a basic electrolyte.

The lithium salt may be the lithium salt used in the preparation of lithium batteries in the prior art, for example, it may be selected from (LiFSI), lithium bistrifluoromethanesulfonimide (LiTFSI), lithium bisoxalate borate (LiBOB), and the like.

Furthermore, in the basic electrolyte, the concentration of the lithium salt is 1-7 mol/L.

The polymerization monomer is an ether-based polymerization monomer, which can be selected from 1,3-dioxolane (DOL) or ethylene glycol dimethyl ether (DME).

Additives can help effectively increase the electrochemical window of the electrolyte, and can be selected from carbonates. It is further selected from at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC).

In order to promote the mixing of the above substances, stirring can be carried out at a temperature of 15°C~25°C, and the stirring time can be 0.5~3h.

S2. The inorganic powder is added to the basic electrolyte and mixed to form a first solution.

Further, the inorganic powder is selected from at least one of _{conductive ceramic powder, Al 2} O ₃ , SiO ₂ and TiO _2. Among them, the conductive ceramic powder is Li _6.4 La ₃ Zr _1.4 Ta _0.6 O ₁₂ (LLZTO), Li ₇ La ₃ Zr ₂ O ₁₂ (LLZO), Li ₁₀ GeP ₂ S ₁₂ (LGPS) and Li _1.5 Al _0.5 Ge _1.5 P ₃ At least one of O _{12 (LAGP).} The addition of inorganic powder helps maintain the solid state of the electrolyte.

In order to promote the mixing of inorganic powder and basic electrolyte, stirring can be carried out at a temperature of 15℃~25℃, and the stirring time can be 0.5~3h.

S3. Add an initiator to the first solution to polymerize each component in situ to obtain a solid polymer electrolyte.

The initiator is selected from at least one of Al(OTF) ₃ , Al(CF ₃ SO ₃ ) ₃ , LiPF ₆ , diethyl aluminum chloride and ethyl aluminum dichloride, and the purpose of the initiator is to initiate polymerization of the monomer Carry out in-situ ring-opening polymerization. The initiator usually needs to be heated to polymerize with the polymerized monomer, but for different initiators, the required heating temperature is different, so it is inconvenient to uniformly limit the heating temperature. In order to avoid the self-polymerization reaction of the initiator when it is added to the first solution, the preferred way is to keep the temperature of the first solution lower than the initiation temperature required by the initiator. At this time, stirring can be carried out, and the stirring time can be 0.5~3h ; A further preferred way is: first add the initiator to the first solution, obtain a second solution after mixing, and make the second solution perform in-situ polymerization at a temperature of 25°C to 70°C.

Further, the mass fraction of the base electrolyte is 15%-95%, the mass fraction of the inorganic powder is 5%-57%, and the mass fraction of the initiator is 0.2%-44%.

Based on the above preparation method of solid polyelectrolyte, embodiments of the present invention also provide the above solid polyelectrolyte, which includes in-situ polymerized inorganic powder, initiator, lithium salt, polymerized monomer and additives.

The lithium salt can be selected from (LiFSI), lithium bistrifluoromethanesulfonimide (LiTFSI), lithium bisoxalate borate (LiBOB), and the like.

In the basic electrolyte, the concentration of the lithium salt is 1-7 mol/L.

The additives may be selected from carbonates. It is further selected from at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC).

The inorganic powder is selected from at least one of _{conductive ceramic powder, Al 2} O ₃ , SiO ₂ and TiO _2. Wherein, the conductive ceramic powder is at least one of LLZTO, LLZO, LGPS and LAGP.

The in-situ polymerization reaction realizes the soft contact between the solid electrolyte and the electrode material, the obtained battery structure is uniform, and the interface impedance between the electrode and the solid electrolyte is reduced. The solid polymer electrolyte prepared by the present invention has high ionic conductivity. At the same time, it also has high mechanical strength, and its electrochemical window can reach 5.5V.

The present invention further provides a lithium battery, including a positive electrode, a negative electrode, and an electrolyte arranged between the positive electrode and the negative electrode, and the electrolyte adopts the above-mentioned solid polymer electrolyte.

In order to facilitate subsequent battery assembly, the second solution is first coated on the positive electrode, and then the components are polymerized in situ by heat treatment. So far, the solid polymer electrolyte is directly prepared and formed on the positive electrode. Specifically, the heating temperature is 25-60°C, and the heating time is 0.5-6h.

The lithium battery further assembled with solid polymer electrolyte effectively improves the cycle stability of the lithium battery: when the charge-discharge cycle reaches 400 cycles at a rate of 1C, the coulombic efficiency of the battery is still maintained at about 100%.

The following examples will be combined with specific examples to illustrate the above-mentioned solid polymer electrolyte of the present invention, its preparation method and lithium battery, those skilled in the art understand that the following examples are only the above-mentioned solid polymer electrolyte of the present invention, its preparation The method and the specific example of the lithium battery are not used to limit all of them.

Example 1

Take 0.574g of lithium bis(fluorosulfonyl)imide (LiTFSI) and dissolve it in 2mL of DOL solution. Stir at room temperature for 0.5h until LiTFSI is completely dissolved, forming a high-concentration lithium salt basic electrolyte. In the basic electrolyte, LiTFSI The molar concentration of is 1mol/L.

Weigh 1g of LLZTO powder and add it to the above-mentioned basic electrolyte, and stir for 0.5h at room temperature until the LLZTO powder is uniformly mixed into the basic electrolyte to form a first solution.

1.24 g of lithium hexafluorophosphate (LiPF ₆ ) was added to the first solution, and stirred at a temperature of 60° C. for 30 minutes, until LiPF _{6 was} uniformly dispersed in the first solution to form a second solution.

The second solution is heated to polymerize the components in the second solution in situ to obtain an in-situ polymerized solid polymer electrolyte.

It is worth noting that in this embodiment, in order to facilitate subsequent battery assembly, the second solution is first coated on the LFP positive electrode, and then the components are polymerized in situ by heat treatment, so that the solid polymer electrolyte is directly prepared. It is formed on the positive electrode, the heating temperature is 60°C, and the heating time is 1.5h.

The raw materials for preparing the solid polymer electrolyte in this embodiment include the following components in terms of weight ratio: 53.47% of the base electrolyte, 20.77% of LLZTO powder, and 25.76% of LiPF ₆ .

Example 2

Dissolve 0.574 g of LiTFSI in 2 mL of DOL solution, and stir at room temperature for 0.5 h until the LiTFSI is completely dissolved to form a high-concentration lithium salt basic electrolyte. In the basic electrolyte, the molar concentration of LiTFSI is 1 mol/L .

Weigh 0.5 g of LLZTO powder and add it to the above-mentioned basic electrolyte, and stir for 0.5 h at room temperature until the LLZTO powder is uniformly mixed into the basic electrolyte to form a first solution.

0.93 g of LiPF _{6 was} added to the first solution, and stirred at a temperature of 60° C. for 30 min, until LiPF _{6 was} uniformly dispersed in the first solution to form a second solution.

The second solution is coated on the LFP positive electrode, and then the components are polymerized in situ by heat treatment, so that the solid polymer electrolyte is directly prepared and formed on the LFP positive electrode. The heating temperature of the heat treatment is 60°C, and the heating time It is 1.5h.

The raw materials for preparing the solid polymer electrolyte in this embodiment include the following components in terms of weight ratio: 64.28% of the base electrolyte, 12.49% of LLZTO powder, and 23.23% of LiPF ₆ .

Example 3

Weigh 0.1 g of LLZTO powder and add it to the above-mentioned basic electrolyte, and stir for 0.5 h at room temperature until the LLZTO powder is uniformly mixed into the basic electrolyte to form a first solution.

0.62 g of LiPF _{6 was} added to the first solution, and stirred at a temperature of 60° C. for 30 min, until LiPF _{6 was} uniformly dispersed in the first solution to form a second solution.

The raw materials for preparing the solid polymer electrolyte in this embodiment include the following components in terms of weight ratio: 78.14% of the base electrolyte, 3.04% of LLZTO powder, and 18.82% of LiPF ₆ .

Example 4

Dissolve 2.296 g of LiTFSI in 2 mL of DOL solution, and stir at room temperature for 0.5 h until the LiTFSI is completely dissolved to form a high-concentration lithium salt basic electrolyte. In the basic electrolyte, the molar concentration of LiTFSI is 4 mol/L .

Weigh 1 g of LLZTO powder and add it to the above-mentioned basic electrolyte, and stir at room temperature for 0.5 h until the LLZTO powder is uniformly mixed into the basic electrolyte to form a first solution.

1.24 g of LiPF _{6 was} added to the first solution, and stirred at a temperature of 40° C. for 30 min, until LiPF _{6 was} uniformly dispersed in the first solution to form a second solution.

The second solution is coated on the LFP positive electrode, and then the components are polymerized in situ by heat treatment, so that the solid polymer electrolyte is directly prepared and formed on the LFP positive electrode. The heating temperature of the heat treatment is 60°C, and the heating time For 1h.

The raw materials for preparing the solid polymer electrolyte in this embodiment include the following components in terms of weight ratio: 65.73% of the base electrolyte, 15.30 of LLZTO powder, and 18.97% of LiPF ₆ .

Example 5

Dissolve 4.018 g of LiTFSI in 2 mL of DOL solution, and stir at room temperature for 0.5 h until the LiTFSI is completely dissolved to form a high-concentration lithium salt basic electrolyte. In the basic electrolyte, the molar concentration of LiTFSI is 7 mol/L .

1.24 g of LiPF _{6 was} added to the first solution, and stirred at room temperature for 30 min, until LiPF _{6 was} uniformly dispersed in the first solution to form a second solution.

The raw materials for preparing the solid polymer electrolyte in this embodiment include the following components in terms of weight ratio: 72.87% of the base electrolyte, 12.11% of LLZTO powder, and 15.02% of LiPF ₆ .

Test characterization

Refer to FIG. 1 for the physical diagram of the solid polymer electrolyte prepared in the embodiment of the present invention.

A scanning electron microscope (SEM) was used to scan the solid polymer electrolytes of Example 1 and the obtained scanning results are shown in FIG. 2. It can be seen from the figure that the inorganic powder and the organic polymer are combined with each other.

The electrochemical impedance spectrum of the solid polymer electrolyte in Example 2 obtained by the test is shown in FIG. 3. As can be seen from the figure, the resistance of the prepared electrolyte is 110Ω, and the conductivity is about 10 ^-3 S cm ^-1 .

The cyclic voltammetry curve of the solid polymer electrolyte in Example 2 obtained by the test is shown in Figure 4, and it can be seen from the figure that the electrochemical window of the solid polymer electrolyte reaches 5.5V.

The lithium battery assembled using the solid polyelectrolyte in Example 2 was subjected to a charge-discharge cycle test at a rate of 1C, and the result obtained is shown in FIG. 5. When the cycle reaches 400 cycles, the coulombic efficiency of the battery still remains at about 100%.

Although the present invention has been illustrated and described with reference to specific embodiments, those skilled in the art will understand that forms and forms can be made here without departing from the spirit and scope of the present invention defined by the claims and their equivalents. Various changes in details.

Claims

A solid polymer electrolyte is characterized in that it comprises in-situ polymerized basic electrolyte, inorganic powder and initiator, wherein the basic electrolyte is a mixture of lithium salt, polymerized monomer and additives.
The solid polymer electrolyte according to claim 1, wherein the inorganic powder is selected from at least one of conductive ceramic powder, Al 2 O 3 , SiO 2 and TiO 2.
The solid polymer electrolyte according to claim 2, wherein the conductive ceramic powder is Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 , Li 7 La 3 Zr 2 O 12 , Li 10 GeP 2 S 12 and Li At least one of 1.5 Al 0.5 Ge 1.5 P 3 O 12.
The solid polymer electrolyte according to claim 1, wherein the lithium salt is selected from the group consisting of lithium bis(fluorosulfonyl)imide, lithium bistrifluoromethanesulfonimide, and lithium bisoxalate borate. At least one; the polymerized monomer is selected from ether-based polymerized monomers; the additive is selected from carbonates.
The solid polymer electrolyte according to claim 4, wherein the polymerized monomer is selected from 1,3-dioxolane or ethylene glycol dimethyl ether; and the additive is selected from dimethyl carbonate, carbonic acid At least one of ethyl methyl and diethyl carbonate.
The solid polymer electrolyte according to claim 1, wherein the initiator is selected from Al(OTF) 3 , Al(CF 3 SO 3 ) 3 , LiPF 6 , diethyl aluminum chloride and ethyl two At least one of aluminum chloride.
The solid polymer electrolyte according to any one of claims 1 to 6, wherein the mass fraction of the base electrolyte is 15% to 95%, the mass fraction of the inorganic powder is 5% to 57%, and the The mass fraction of initiator is 0.2%~44%.
8. The solid polyelectrolyte according to claim 7, wherein in the base electrolyte, the concentration of the lithium salt is 1-7 mol/L.
A method for preparing a solid polyelectrolyte according to any one of claims 1 to 8, characterized in that it comprises the steps of:

S1. Add lithium salt to the polymerized monomer and additives, and mix to form a basic electrolyte;

S2. Add inorganic powder to the basic electrolyte and mix to form a first solution;

S3. Add an initiator to the first solution to polymerize each component in situ to obtain the solid polymer electrolyte.
The preparation method according to claim 9, characterized in that, in step S3, it specifically includes, first adding an initiator to the first solution, stirring and mixing to obtain a second solution, and keeping the second solution at 25°C. In-situ polymerization at ~70℃.
A lithium battery comprising a positive electrode, a negative electrode, and an electrolyte arranged between the positive electrode and the negative electrode, wherein the electrolyte adopts the solid polymer electrolyte according to any one of claims 1 to 8.