CN112117488B

CN112117488B - Solid electrolyte, lithium metal negative electrode and preparation method thereof

Info

Publication number: CN112117488B
Application number: CN202010760017.2A
Authority: CN
Inventors: 曹元成; 涂吉; 楼平; 李程; 张炜鑫
Original assignee: Huazhong University of Science and Technology
Current assignee: Huazhong University of Science and Technology
Priority date: 2020-07-31
Filing date: 2020-07-31
Publication date: 2021-11-02
Anticipated expiration: 2040-07-31
Also published as: CN112117488A

Abstract

The invention provides a solid electrolyte, a lithium metal negative electrode and a preparation method thereof. What is needed isThe solid electrolyte is a composite polymer electrolyte compounded by lithium lanthanum titanium oxide and linear polyurethane. The preparation method comprises the following steps: firstly, preparing lithium lanthanum titanium oxide particles with complete crystal phase by a process combining hydrothermal synthesis and high-temperature calcination; and then, blending and stirring the lithium lanthanum titanium oxide particles and the linear polyurethane, and performing solvent evaporation treatment to prepare the solid electrolyte. The lithium ion conductivity of the solid electrolyte prepared by the invention reaches 3.8 multiplied by 10 at room temperature^‑4S cm^‑1. Meanwhile, a battery assembled with the solid electrolyte exhibits excellent cycle performance and excellent specific capacity at room temperature. The lithium metal negative electrode can be obtained by compounding the solid electrolyte and the lithium metal sheet.

Description

Solid electrolyte, lithium metal negative electrode and preparation method thereof

Technical Field

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

Background

In recent years, lithium ion batteries play an important role in production and life of people, have high energy density, are convenient to carry, have long service life, and have wide application. With the rapid development of electronic products towards the trend of portability and miniaturization, all-solid-state thin-film lithium ion batteries are produced, have the advantages of small volume, high energy density, long cycle life, good safety and the like, and the performance of the all-solid-state thin-film lithium ion batteries is determined by a solid electrolyte thin film to a great extent. The solid electrolyte film is equivalent to the electrolyte and the diaphragm in the traditional battery, and not only plays the role of Li⁺Conduction also has a direct effect on the capacity and cyclability of the battery. Lithium lanthanum titanium oxide (Li) with perovskite structure_0.35La_0.55TiO₃) The solid electrolyte material has high ionic conductivity at room temperature, is comparable to liquid electrolyte, has lower activation energy (0.3eV to 0.4eV), is a popular material for the research of the solid electrolyte of the lithium ion battery, and is also an ideal material for the solid film electrolyte.

Invention with publication number CN105206821AThe patent application discloses a synthesis method of a lithium ion battery anode material. Dissolving lithium nitrate, lanthanum nitrate and isopropyl titanate into isopropanol to prepare isopropanol solution; adding spinel type lithium manganate into isopropanol solution, stirring, and carrying out heat treatment for 1-3 h at 300-400 ℃ to obtain Li_0.35La_0.55TiO₃Coated spinel type lithium manganate. However, this synthesis method has a disadvantage of a long reaction time.

Applied materials at ACS published by Li Boyu et al&in the interfaces journal, the title is "Li_0.35La_0.55TiO₃An article of Nanofibres Enhanced Poly (vinylidine fluoride) -Based Composite polymers for All-Solid-State Batteries discloses a lithium lanthanum titanium oxide (Li La Ti-O) (Li La Ti-O) (Li La Ti-O) and Li La Ti-O (Li La Ti-O, Li, La Ti-O, La Ti, Li, La, Ti, Li, La, Ti, Li, La, Ti, La, Ti, Li, Ti, La, Ti, La, Ti, La, Ti, La, Ti, La, Ti, La, Ti, Li, La, Ti, La, Ti, La, Ti_0.35La_0.55TiO₃) A Composite Polymer Electrolyte (CPE) material compounded with a high molecular polymer, polyvinylidene fluoride (PVDF), but the electrolyte has a weak coordination effect on lithium ions.

The invention patent with the publication number of CN110600740A discloses lithium battery slurry, a lithium metal negative electrode composite layer, a lithium metal negative electrode, and a preparation method and application thereof. The lithium battery slurry is a mixed solution of linear thermoplastic polyurethane, lithium salt and a lithium salt dissociation promoter; the mass ratio of the linear thermoplastic polyurethane to the lithium salt dissociation promoter in the mixed solution is 15:0.12: 0.1-15: 12: 10. The lithium battery slurry obtained by taking the linear thermoplastic polyurethane as a base material and the lithium salt dissociation promoter as functional additives can be formed into a film to obtain a composite layer and used for preparing the lithium metal sheet cathode. However, the preparation method of the lithium metal negative electrode has the defects of complicated operation and introduction of some lithium ion non-conductive materials.

Disclosure of Invention

In view of the above-mentioned deficiencies of the prior art, it is an object of the present invention to provide a solid electrolyte, a lithium metal negative electrode and a method for preparing the same.

In order to achieve the above object, the present invention provides a solid electrolyte. The solid electrolyte is a composite polymer compounded by lithium lanthanum titanium oxide and linear polyurethaneA physical electrolyte; in the solid electrolyte, the mass ratio of the lithium lanthanum titanium oxide to the linear polyurethane is 1: (9-11); the thickness of the solid electrolyte is 300-500 mu m; the lithium ion conductivity of the solid electrolyte is 3.8 x 10^-4S cm^-1～5.0×10^-4S cm^-1。

In order to achieve the above object, the present invention also provides a method for preparing the above solid electrolyte, comprising the steps of:

s1, preparation of lithium lanthanum titanium oxide: preparing a first reaction system of lithium nitrate, lanthanum nitrate, tetrabutyl titanate and citric acid according to a predetermined proportion, and carrying out hydrothermal reaction on the first reaction system for 8-16 h at 160-200 ℃; after the hydrothermal reaction is finished, drying and pyrolyzing a first reaction product generated by the reaction, and then calcining the reaction product at 800-1000 ℃ for 1-4 h to prepare lithium lanthanum titanium oxide particles;

s2, preparation of solid electrolyte: preparing a second reaction system of 2, 4-toluene diisocyanate and polypropylene oxide according to a predetermined proportion, placing the lithium lanthanum titanium oxide particles prepared in the step S1 in the second reaction system, and stirring for 3-8 h at the temperature of 50-80 ℃ for reaction; and then pouring a second reaction product generated by the reaction into a mold, and carrying out solvent evaporation treatment to prepare the composite polymer electrolyte, namely the solid electrolyte.

Preferably, in the first reaction system in step S1, the molar mass ratio of the lithium nitrate, the lanthanum nitrate, the tetrabutyl titanate and the citric acid is 0.33: 0.557: 1.00: 0.887.

preferably, in step S1, the pyrolysis process includes: and carrying out pyrolysis treatment on the dried first reaction product at the temperature of 300-400 ℃ at the heating rate of 3-8 ℃/min for 2-6 h.

Preferably, in step S1, the process for preparing the first reaction system includes the following steps:

a1, respectively dissolving the lithium nitrate, the lanthanum nitrate, the tetrabutyl titanate and the citric acid in a solvent according to a preset proportion to obtain a lithium nitrate solution, a lanthanum nitrate solution, a tetrabutyl titanate solution and a citric acid solution;

a2, uniformly mixing the lithium nitrate solution, the tetrabutyl titanate solution and the citric acid solution prepared in the step A1 to obtain a first mixed solution; then dropwise adding the lanthanum nitrate solution with a preset volume under stirring treatment at the temperature of 60-100 ℃;

and A3, stirring for 20-40 min after the lanthanum nitrate solution is dropwise added in the step A2, and preparing to obtain the first reaction system.

Preferably, in step S2, the molar fraction ratio of the 2, 4-toluene diisocyanate to the polypropylene oxide is 1: (1.1-1.3).

Preferably, the ratio of the mass sum of the 2, 4-toluene diisocyanate and the polypropylene oxide to the mass of the lithium lanthanum titanium oxide particles is (8-10): 1.

preferably, in step S2, the process for preparing the second reaction system includes the following steps:

p1, dissolving the 2, 4-toluene diisocyanate in an organic solvent according to a predetermined proportion, and then adding a catalyst in an argon or nitrogen atmosphere to obtain a second mixed solution;

p2, dissolving the polypropylene oxide in the organic solvent to obtain a polypropylene oxide solution; then injecting the polypropylene oxide solution into the second mixed solution prepared in step P1; and preparing the second reaction system.

Preferably, the solvent evaporation treatment in step S2 is performed at ambient temperature in an argon or nitrogen atmosphere; the mould is made of polytetrafluoroethylene.

In order to achieve the above object, the present invention also provides a lithium metal negative electrode. The lithium metal negative electrode is formed by compounding the solid electrolyte and a lithium metal sheet.

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

1. the LLTO/LPU composite polymer electrolyte (CPPE) provided by the invention has a linear structure of polyurethane and an ion-conductive ceramic Lithium Lanthanum Titanium Oxide (LLTO), and the CPPE has excellent electrochemical performance due to the structure, and the mechanism is as follows:

1) the invention synthesizes Linear Polyurethane (LPU) by 2, 4-Toluene Diisocyanate (TDI) and polypropylene oxide (PPO). The coordination of the ether oxygen functional group on the linear polyurethane and the lithium ions is beneficial to the migration of the lithium ions on different linear polymer chain segments, and the diffusion speed of the lithium ions is improved; lithium Lanthanum Titanium Oxide (LLTO) can promote the conduction of lithium ions in the polymer segment, and the Lithium Lanthanum Titanium Oxide (LLTO) and the polymer segment cooperate with each other to improve the electrochemical performance of the solid electrolyte CPPE.

2) The solid electrolyte membrane CPPE prepared by the invention can effectively inhibit lithium dendrites and prevent isolated lithium accumulation, so that the loss of lithium capacity is obviously reduced, and the stable cyclability and high multiplicity of the lithium metal battery are realized; the technical prejudice that the electrolyte can generate lithium crystal branches in the prior art so that the lithium ion diffusion is hindered is effectively overcome.

2. The lithium ion conductivity of the LLTO/LPU composite polymer electrolyte (CPPE) provided by the invention at room temperature reaches 3.8 multiplied by 10^-4S cm^-1. Simultaneously, the assembled LiFePO₄The | CPPE | Li cell exhibited excellent cycling performance at room temperature, and the discharge capacity after 200 cycles was still 149.8mAh · g^-1The capacity retention at 0.5C was as high as 97.8%. Assembled LiNi_0.8Co_0.1Mn_0.1O₂The | CPPE | Li cell exhibited significant rate capacity with an initial capacity of 216.4mAh · g at 0.1C^-1And maintained 138mAh g at 1C^-1Excellent specific capacity of (2). The electrochemical performance of the solid electrolyte CPEE prepared by the method is far higher than that of a lithium battery which is assembled by conventional PPO or liquid electrolyte, and the method has a huge application prospect in the field of lithium metal battery preparation.

3. The preparation method of the solid electrolyte (CPPE) provided by the invention firstly adopts a combined process of hydrothermal synthesis-pyrolysis-high temperature calcination to prepare the Lithium Lanthanum Titanium Oxide (LLTO) conductive ceramic nano-particles with complete crystalline phase, uniform particle size distribution and good electrochemical performance and dispersion performance. Then, the LLTO nano particles are added into a second reaction system of 2, 4-toluene diisocyanate and polypropylene oxide, the synthesis process of linear polyurethane and the dispersion and mixing process of the LLTO nano particles are synchronized, so that the LLTO nano particles can be uniformly dispersed in linear polyurethane polymer molecules and can be diffused into the interior of the polymer composite membrane, a uniform three-dimensional conductive LLTO network structure is formed, and the electrochemical performance of the solid electrolyte CPPE is remarkably improved through the mutual synergistic effect of the linear polyurethane polymer and the LLTO nano particles.

Drawings

Fig. 1 is an XRD spectrum of Lithium Lanthanum Titanyl (LLTO) particles provided in example 1 of the present invention.

Fig. 2 is a diagram of a solid electrolyte (CPPE) and PP separator provided in example 1 of the present invention.

Fig. 3 is an electron microscope image of Lithium Lanthanum Titanium Oxide (LLTO) particles and a solid electrolyte (CPPE) provided in example 1 of the present invention (a in fig. 3 is an electron microscope image of LLTO particles; b in fig. 3 is an electron microscope image of a solid electrolyte (CPPE), and c and d in fig. 3 are cross-sectional electron microscope images of a solid electrolyte (CPPE)), with a scale of 1 μm.

FIG. 4 is a graph showing the performance of examples 1 and comparative examples 1 to 2 of the present invention (in FIG. 4, a is a NCM of a liquid electrolyte using CPPE-LLTO prepared in example 1, PPO-LLTO prepared in comparative example 1 and NCM of a liquid electrolyte provided in comparative example 2₈₁₁Rate capability of Li half cell. In FIG. 4, b, c and d are the NCM of the CPPE-LLTO prepared in example 1, the NCM of the PPO-LLTO prepared in comparative example 1 and the NCM of the liquid electrolyte provided in comparative example 2, respectively₈₁₁Initial charge and discharge curve of Li battery).

FIG. 5 is a graph of cycle performance provided by example 1 of the present invention and comparative examples 1-2.

Detailed Description

The technical solutions of the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings, and it is to be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without any inventive step, are within the scope of the present invention.

The invention provides a preparation method of a solid electrolyte, which comprises the following steps:

Further, in the first reaction system in step S1, the molar mass ratio of the lithium nitrate, the lanthanum nitrate, the tetrabutyl titanate and the citric acid is 0.33: 0.557: 1.00: 0.887.

further, in step S1, the pyrolysis process is as follows: and carrying out pyrolysis treatment on the dried first reaction product at the temperature of 300-400 ℃ at the heating rate of 3-8 ℃/min for 2-6 h.

Further, in step S1, the process of preparing the first reaction system includes the following steps:

Further, in step S2, the molar fraction ratio of the 2, 4-toluene diisocyanate to the polypropylene oxide is 1: (1.1-1.3).

Further, the ratio of the mass sum of the 2, 4-toluene diisocyanate and the polypropylene oxide to the mass of the lithium lanthanum titanium oxide particles is (8-10): 1.

further, in step S2, the process of preparing the second reaction system includes the following steps:

Further, the solvent evaporation treatment described in step S2 is performed at ambient temperature in an argon or nitrogen atmosphere; the mould is made of polytetrafluoroethylene.

The present invention is described in further detail below with reference to specific examples.

Example 1

The preparation of solid LLTO/LPU composite polymer electrolyte (CPPE) comprises the following steps:

s1, synthesis of Lithium Lanthanum Titanium Oxide (LLTO) particles:

1) mixing lithium nitrate, lanthanum nitrate, tetrabutyl titanate and citric acid in a ratio of 0.33: 0.557: 1.00: respectively dissolving the components in absolute ethyl alcohol according to a molar ratio of 0.887 to obtain a lithium nitrate solution, a lanthanum nitrate solution, a tetrabutyl titanate solution and a citric acid solution; wherein, citric acid is taken as a complexing agent;

2) uniformly mixing the lithium nitrate solution, the tetrabutyl titanate solution and the citric acid solution to obtain a first mixed solution; then dropwise adding the lanthanum nitrate solution under mechanical stirring treatment at 80 ℃;

3) after the lanthanum nitrate solution is dropwise added, stirring for 30min to obtain a white suspension, and preparing to obtain the first reaction system;

4) pouring the first reaction system into a reaction kettle with the temperature of 180 ℃ and the volume of 200mL for carrying out hydrothermal reaction for 10 h;

5) after the hydrothermal reaction is finished, cooling a first reaction product generated by the reaction to room temperature, taking out and drying at 80 ℃; then putting the first reaction product into a tubular furnace, and pyrolyzing the first reaction product at 350 ℃ for 4 hours at the heating rate of 5 ℃/min;

6) and calcining the pyrolysis product at 900 ℃ for 2h to prepare Lithium Lanthanum Titanium Oxide (LLTO) particles.

S2, preparation of solid LLTO/LPU composite polymer electrolyte:

1) dissolving 2, 4-Toluene Diisocyanate (TDI) (1.74g, 10mmol) in 20mL of organic solvent chloroform, and adding a catalyst dibutyltin dilaurate (DBTDL) by 5 mol% under an argon atmosphere to obtain a second mixed solution;

2) polypropylene oxide PPO2000(HO-PPO-OH Mw 2000 g/mol)^-110.0g, 5mmol) is dissolved in 30mL of chloroform to obtain a polypropylene oxide solution, and the polypropylene oxide solution is pumped into a second mixed solution by a micro syringe at room temperature to prepare and obtain a second reaction system;

3) placing the lithium lanthanum titanium oxide particles (LLTO) prepared in the step S1 in the second reaction system, and magnetically stirring for 5 hours at the temperature of 60 ℃ to perform reaction; then pouring a second reaction product generated by the reaction into a polytetrafluoroethylene mold, and carrying out solvent evaporation treatment in a nitrogen atmosphere at ambient temperature to prepare the solid LLTO/LPU composite polymer electrolyte, namely the solid electrolyte (CPPE); wherein the addition amount of the lithium lanthanum titanium oxide particles is 10 wt% of the mass of the linear polyurethane.

In the invention, the reaction formula for synthesizing the Linear Polyurethane (LPU) by using 2, 4-Toluene Diisocyanate (TDI) and polypropylene oxide PPO2000 is as follows:

referring to fig. 1, the XRD pattern of Lithium Lanthanum Titanium Oxide (LLTO) particles showed no miscellaneous peaks, indicating that no other impurity phases appeared in the synthesized LLTO particle powder of the present invention. Therefore, the Lithium Lanthanum Titanium Oxide (LLTO) ceramic particles with complete crystal phase can be synthesized by adopting the combined process of hydrothermal reaction and calcination method.

Referring to fig. 2, the LLTO/LPU composite polymer electrolyte membrane prepared according to the present invention showed a gray color with a uniform color compared to the PP separator.

Referring to FIG. 3, a in FIG. 3 is an electron micrograph of LLTO particles, which is seen to be uniform in particle size, light gray in color, and distributed in the range of 0.8-2 μm.

It can be seen in fig. 3 b that the LLTO particles can be uniformly distributed in the LPU matrix and remain dispersed.

Meanwhile, in order to further observe the distribution of the LLTO filler particles in the LPU matrix, cross-sectional SEM characterization was performed on the prepared LLTO/LPU composite polymer electrolyte at different magnifications, and the results are shown as c and d in FIG. 3.

The thickness of the composite electrolyte membrane is shown as about 10 μm in c of fig. 3.

As can be seen in d of FIG. 3, the LLTO particles are uniformly dispersed in the LPU matrix.

Comparative example 1

The difference from example 1 is that: 10.0g of polypropylene oxide (PPO) was dissolved in a commercially available electrolyte (1M lithium hexafluorophosphate EC: DEC ═ 1: 1 Vol%), mixed uniformly to obtain a mixture, and then 10 wt% of lithium lanthanum titanium oxide particles (LLTO) were added to obtain an electrolyte PPO-LLTO.

Comparative example 2

The difference from example 1 is that: commercially available liquid electrolyte 1M lithium hexafluorophosphate EC was used: DEC ═ 1: 1 Vol%.

Performance test of electrolyte: (physicochemical and electrochemical measurements)

1) X-ray diffraction (XRD) measurements were performed on an X' Pert Power diffractometer with Cu ka radiation (λ 1.5418) from 5 ° to 80 ° 2 θ, step size 5 ° min^-1To characterize the crystal structure LLTO nanoparticles.

2) The ionic conductivity of the solid electrolyte (CPPE) was calculated from the following equation

L, S and Rb represent the thickness, area and bulk resistance of CPPE, respectively.

AutoLab (PGDTAT302N) was used at 10^-1To 10⁵Electrochemical Impedance Spectroscopy (EIS) measurements were made at 10mV amplitude over the frequency range in Hz.

3)LiFePO₄The anode is made of active material LiFePO₄Polyvinylidene fluoride (PVDF) and acetylene in N-methyl-2-pyrrolidone (NMP) at a molar ratio of 8: 1: 1, coating the slurry on a carbonized aluminum foil and drying the coated slurry and standing the coated slurry at 80 ℃ for 24 hours under vacuum. LiFePO as active material₄Has a mass loading of about 2mg cm^-2. By sandwiching the solid electrolyte (CPPE) prepared in example 1 or the electrolyte (PPO-LLTO) prepared in comparative example 1 between LiFePO₄Assembling LiFePO between a cathode and a lithium anode₄A half cell of CPPE Li.

By LiFePO₄The CPPE Li was charged and discharged in the cut-off voltage range, and the voltage range from 2.7V to 4.0V was tested using LAND Electronics.

LiNi_0.8Co_0.1Mn_0.1O₂Preparation of | CPPE | Li cells is similar to LiFePO described above₄Batteries, LiNi_0.8Co_0.1Mn_0.1O₂Has a mass loading of about 1.5mg cm^-2。

The present invention also assembled the electrolyte PPO-LLTO provided in comparative example 1 and the liquid electrolyte of comparative example 2 into the LiNi described above_0.8Co_0.1Mn_0.1O₂Li cell as a control.

Li was tested at a voltage range of 3.0 to 4.35V. All the different assembled batteries are assembled in a glove box (H)₂O and O₂The content is less than 0.01 ppm).

It is to be noted that, in the following description, LiNi_0.8Co_0.1Mn_0.1O₂lLi battery abbreviated NCM₈₁₁A | Li battery; LiFePO₄The Li battery is referred to as LFP Li battery for short.

And (3) testing results:

through testing, the lithium ion conductivity of the solid electrolyte (CPPE) prepared in example 1 at room temperature reaches 3.8 x 10^-4S cm^-1. Simultaneously, the assembled LiFePO₄The | CPPE | Li cell exhibited excellent cycling performance at room temperature, and the discharge capacity after 200 cycles was still 149.8mAh · g^-1The capacity retention at 0.5C was as high as 97.9%.

Meanwhile, LiNi_0.8Co_0.1Mn_0.1O₂The | CPPE | Li exhibits a significant rate capacity with an initial capacity of 216.4mAh · g at 0.1C^-1And maintained 138mAh g at 1C^-1Excellent specific capacity of (2).

The above test data indicate that the solid electrolyte (CPPE) prepared by the present invention can be used to develop high performance lithium batteries.

Referring to FIG. 4, a in FIG. 4 is a NCM of a liquid electrolyte using CPPE-LLTO prepared in example 1, PPO-LLTO prepared in comparative example 1 and NCM provided in comparative example 2₈₁₁Rate capability of Li half cell. In FIG. 4, b, c and d are the NCM of the CPPE-LLTO prepared in example 1, the NCM of the PPO-LLTO prepared in comparative example 1 and the NCM of the liquid electrolyte provided in comparative example 2, respectively₈₁₁Initial charge and discharge curves for Li batteries.

Wherein b in FIG. 4 shows the NCM provided in example 1₈₁₁The initial value of CPPE | Li is at low current density of 0.1C, and the discharge capacity is 216.4 mAh.g^-1. As the current density increases, the capacity of the battery also decreases. However, NCM₈₁₁The battery of the | CPPE still maintains 138mAh g at 1C^-1The capacity of (c).

In contrast, the NCM provided in comparative example 1₈₁₁| PPO-LLTO and NCM provided in comparative example 2₈₁₁The discharge capacity of the | LE is only 113.5 mAh.g^-1(c in FIG. 4) and 94.7 mAh.g^-1(d in FIG. 4).

The reason why the difference in discharge capacity between example 1 and comparative examples 1-2 is so large is mainly that: the solid electrolyte (CPPE) prepared in example 1 of the present invention has a linear structure of polyurethane and ion conductive ceramic LLTO. Coordination of the ether oxygen functional group on the linear polyurethane and lithium ions is beneficial to migration of the lithium ions on different linear polymer chain segments, and the diffusion speed of the lithium ions is improved, LLTO can promote the conduction self-characteristics of the lithium ions in the polymer segments, and the ether oxygen functional group and the lithium ions are mutually cooperated, so that the performance of the solid electrolyte CPPE is improved.

However, in comparative example 1, PPO2000 forms a crystalline region for trapping lithium ions, resulting in formation of lithium ion traps in the electrolyte of PPO-LLTO system, such that diffusion of lithium ions is hindered, and thus comparative example 1 is inferior in discharge capacity performance.

In comparative example 2, the liquid electrolyte had a defect of poor compatibility with the lithium anode, resulting in poor discharge capacity performance of comparative example 2.

Referring to FIG. 5, the LFP | CPPE | Li initial discharge capacity of example 1 is 154.6mAh g^-1149.8mAh g after 200 cycles^-1The discharge capacity of (2). The LFP | CPPE | Li battery provided in example 1 has a capacity retention rate as high as 97.9%, indicating that the capacity does not significantly decrease after 200 cycles.

In contrast, the LFP | Li battery using PPO-LLTO provided in comparative example 1 had an initial capacity of 148.7mAh g^-1The capacity retention rate was 94.6%. Whereas the cycle performance curve of LFP LE Li provided in comparative example 2 is irregular.

The reason why the above phenomenon occurs is that: the CPPE electrolyte membrane prepared by the present invention can effectively suppress lithium dendrites and prevent isolated lithium accumulation, so that the loss of lithium capacity is significantly reduced, and at the same time, it is also shown that the CPPE electrolyte membrane prepared by the present invention can realize stable cyclability and high multiplicity of a lithium metal battery.

Examples 2 to 3

The difference from example 1 is that: the mass ratio of lithium lanthanum titanium oxide particles (LLTO) to Linear Polyurethane (LPU) is different, and the rest is the same as that of embodiment 1, and the description is omitted.

Table 1 shows the process parameter settings and their performance parameters in examples 1-3

Examples	Mass ratio of LLTO to LPU	Ionic conductivity of
			Example 1	1:10	5.0×10^-4S cm^-1
Example 2	1：9	4.1×10^-4S cm^-1
			Example 3	1：11	3.8×10^-4S cm^-1

The analysis was performed in conjunction with table 1: the influence of the mass ratio of lithium lanthanum titanium oxide particles (LLTO) to Linear Polyurethane (LPU) on the electrochemical performance of the solid electrolyte CPPE is as follows: setting the mass ratio of LLTO to LPU as 1: when the ionic conductivity is 10, the prepared solid electrolyte has the highest ionic conductivity and excellent electrochemical performance.

Comparative example 3

The difference from example 1 is that: the hydrothermal reaction treatment is not performed in step S1, and the rest is the same as in example 1, and will not be described again.

Comparative example 4

The difference from example 1 is that: the high-temperature calcination process is not performed in step S1, and the rest is the same as in example 1, and will not be described again.

Table 2 shows the process parameter settings and performance parameters of examples 1 and comparative examples 3 to 4

Examples	LLTO synthesis process	Ionic conductivity of
			Example 1	Hydrothermal reaction-pyrolysis-high temperature calcination	5.0×10^-4S cm^-1
Comparative example 3	Pyrolysis-high temperature calcination	3.1×10^-4S cm^-1
			Comparative example 4	Hydrothermal reaction-pyrolysis	2.3×10^-4S cm^-1

Analysis was performed in conjunction with table 2: as can be seen from table 2, the LLTO nanoparticles prepared by the present invention using the LLTO synthesis process combining hydrothermal reaction-pyrolysis-high temperature calcination have better crystalline phase without impurity doping, while in comparative examples 3 and 4, there is a deficiency of different content of impurity phase, and thus, the solid electrolyte provided in example 1 has much higher ionic conductivity than the solid electrolytes prepared in comparative examples 1 and 2.

In summary, the present invention provides a solid state deviceAn electrolyte, a lithium metal negative electrode and a method for preparing the same. The solid electrolyte is a composite polymer electrolyte compounded by lithium lanthanum titanium oxide and linear polyurethane. The preparation method comprises the following steps: firstly, preparing lithium lanthanum titanium oxide particles with complete crystal phase by a process combining hydrothermal synthesis and high-temperature calcination; and then, blending and stirring the lithium lanthanum titanium oxide particles and the linear polyurethane, and performing solvent evaporation treatment to prepare the solid electrolyte. The lithium ion conductivity of the solid electrolyte prepared by the invention reaches 3.8 multiplied by 10 at room temperature^-4S cm^-1. Meanwhile, a battery assembled with the solid electrolyte exhibits excellent cycle performance and excellent specific capacity at room temperature. The lithium metal negative electrode can be obtained by compounding the solid electrolyte and the lithium metal sheet.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A solid state electrolyte characterized by: the solid electrolyte is a composite polymer electrolyte compounded by lithium lanthanum titanium oxide and linear polyurethane; in the solid electrolyte, the mass ratio of the lithium lanthanum titanium oxide to the linear polyurethane is 1: (9-11); the thickness of the solid electrolyte is 300-500 mu m; the lithium ion conductivity of the solid electrolyte is 3.8 x 10^-4 S cm^-1 ～5.0×10^-4 S cm^-1；

The solid electrolyte has a linear structure formed by compounding polyurethane and ion conductive ceramic lithium lanthanum titanium oxide, and the preparation process comprises the following steps:

firstly, preparing lithium lanthanum titanium oxygen conductive ceramic nano particles with complete crystal phase by adopting a combined process of hydrothermal synthesis, pyrolysis and high-temperature calcination; then, adding the lithium lanthanum titanium oxygen conductive ceramic nanoparticles into a second reaction system of 2, 4-toluene diisocyanate and polypropylene oxide, synchronizing the synthesis process of linear polyurethane and the dispersion and mixing process of the lithium lanthanum titanium oxygen conductive ceramic nanoparticles, so that the lithium lanthanum titanium oxygen conductive ceramic nanoparticles can be uniformly dispersed in linear polyurethane polymer molecules and diffused into the interior of the polymer composite membrane, thereby forming a uniform three-dimensional conductive LLTO network structure.

2. A method for producing a solid electrolyte according to claim 1, characterized in that: the method comprises the following steps:

s1, preparation of lithium lanthanum titanium oxide: preparing a first reaction system of lithium nitrate, lanthanum nitrate, tetrabutyl titanate and citric acid according to a predetermined proportion, and carrying out hydrothermal reaction on the first reaction system for 8-16 h at 160-200 ℃; after the hydrothermal reaction is finished, drying and pyrolyzing a first reaction product generated by the reaction, and then calcining the reaction product at 800-1000 ℃ for 1-4 h to prepare lithium lanthanum titanium oxide particles; in step S1, the pyrolysis process is as follows: carrying out pyrolysis treatment on the dried first reaction product at the temperature of 300-400 ℃ at the heating rate of 3-8 ℃/min for 2-6 h;

3. The method for producing a solid electrolyte according to claim 2, characterized in that: in the first reaction system in step S1, the molar mass ratio of the lithium nitrate, the lanthanum nitrate, the tetrabutyl titanate and the citric acid is 0.33: 0.557: 1.00: 0.887.

4. the method for producing a solid electrolyte according to claim 2, characterized in that: in step S1, the process for preparing the first reaction system includes the following steps:

5. The method for producing a solid electrolyte according to claim 2, characterized in that: in step S2, the molar fraction ratio of the 2, 4-toluene diisocyanate to the polypropylene oxide is 1: (1.1-1.3).

6. The method for producing a solid electrolyte according to claim 2, characterized in that: the ratio of the mass sum of the 2, 4-toluene diisocyanate and the polypropylene oxide to the mass of the lithium lanthanum titanium oxide particles is (8-10): 1.

7. the method for producing a solid electrolyte according to claim 2, characterized in that: in step S2, the preparation process of the second reaction system includes the following steps:

p2, dissolving the polypropylene oxide in the organic solvent to obtain a polypropylene oxide solution; then placing the polypropylene oxide solution in the second mixed solution prepared in step P1; and preparing the second reaction system.

8. The method for producing a solid electrolyte according to claim 2, characterized in that: the solvent evaporation treatment described in step S2 is performed at ambient temperature in an argon or nitrogen atmosphere; the mould is made of polytetrafluoroethylene.

9. A lithium metal anode characterized by: the lithium metal negative electrode is formed by compounding the solid electrolyte of claim 1 or the solid electrolyte prepared by the method for preparing the solid electrolyte of any one of claims 2 to 8 with a lithium metal sheet.