CN112117488A - Solid electrolyte, lithium metal negative electrode and preparation method thereof - Google Patents

Abstract

The invention provides a solid electrolyte, a lithium metal negative electrode and a preparation method thereof. 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.

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 negative electrode and a preparation method thereof.

Background technique

In recent years, lithium-ion batteries have played an important role in people's production and life. They have a wide range of applications due to their high energy density, easy portability, and long service life. With the rapid development of electronic products towards portability and miniaturization, all-solid-state thin-film lithium-ion batteries have emerged. All-solid-state thin-film lithium-ion batteries have the advantages of small size, high energy density, long cycle life and good safety. The performance is largely determined by the solid electrolyte membrane. The solid electrolyte film is equivalent to the electrolyte and separator in traditional batteries, which not only plays the role of Li ⁺ conduction, but also directly affects the capacity and cyclability of the battery. The perovskite-structured lithium lanthanum titanium oxide (Li _0.35 La _0.55 TiO ₃ ) solid electrolyte material has high ionic conductivity at room temperature, comparable to liquid electrolytes, and has a low activation energy (0.3eV to 0.4eV), which is It is a popular material for solid-state electrolyte research for lithium-ion batteries, and it is also an ideal material for solid-state thin-film electrolytes.

The invention patent application with publication number CN105206821A discloses a method for synthesizing a positive electrode material for a lithium ion battery. The method includes dissolving lithium nitrate, lanthanum nitrate and isopropyl titanate into isopropyl alcohol to prepare an isopropyl alcohol solution; adding spinel lithium manganate into the isopropyl alcohol solution, stirring, and heating at 300 ℃ The spinel-type lithium manganate coated with Li _0.35 La _0.55 TiO ₃ is prepared by heat treatment at ~400° C. for 1 to 3 hours. However, this synthesis method has the disadvantage of long reaction time.

In an article titled "Li _0.35 La _0.55 TiO ₃ Nanofibers Enhanced Poly(vinylidene fluoride)-Based CompositePolymer Electrolytes for All-Solid-State Batteries" published by Li Boyu et al. in the journal ACS applied materials & interfaces, a lithium lanthanum A composite polymer electrolyte (CPE) material composed of titanium oxide (Li _0.35 La _0.55 TiO ₃ ) and a polymer polyvinylidene fluoride (PVDF), but the electrolyte has the deficiency of weak coordination of lithium ions.

The invention patent with publication number CN110600740A discloses a 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 lithium salt dissociation accelerator; the mass ratio of linear thermoplastic polyurethane, lithium salt and lithium salt dissociation accelerator in the mixed solution is 15:0.12 :0.1～15:12:10. In the invention, the linear thermoplastic polyurethane is used as the base material, and the lithium battery slurry obtained by using the lithium salt and the lithium salt dissociation accelerator as the functional additive can be formed into a film to obtain a composite layer and used for preparing the negative electrode of the lithium metal sheet. However, the preparation method of the lithium metal negative electrode has the disadvantages of complicated operation and the introduction of some materials that do not conduct lithium ions.

SUMMARY OF THE INVENTION

In view of the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a solid electrolyte, a lithium metal negative electrode and a preparation method thereof.

In order to achieve the above purpose of the invention, the present invention provides a solid electrolyte. The solid electrolyte is a composite polymer electrolyte composed of 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 μm; the lithium ion conductivity of the solid electrolyte is 3.8×10 ⁻⁴ S cm ⁻¹ to 5.0×10 ⁻⁴ S cm ⁻¹ .

In order to achieve the above purpose of the invention, the present invention also provides a preparation method of the above solid electrolyte, comprising the following steps:

S1, preparation of lithium lanthanum titanium oxide: prepare a first reaction system of lithium nitrate, lanthanum nitrate, tetrabutyl titanate and citric acid according to a predetermined ratio, and at 160-200 ° C, the first reaction system is hydrothermally The reaction is carried out for 8 to 16 hours; after the hydrothermal reaction is completed, the first reaction product produced by the reaction is dried and pyrolyzed, and then calcined at 800 to 1000 ° C for 1 to 4 hours to prepare lithium lanthanum titanium oxide particles;

S2, preparation of solid electrolyte: prepare a second reaction system of 2,4-toluene diisocyanate and polypropylene oxide according to a predetermined ratio, and place the lithium lanthanum titanium oxide particles prepared in step S1 in the second reaction system In the process, the reaction is carried out under stirring for 3-8 hours at a temperature of 50-80 °C; then the second reaction product produced by the reaction is poured into the mold, and the solvent is evaporated to prepare the composite polymer electrolyte, which is the solid-state electrolyte. .

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

Preferably, in step S1, the process of the pyrolysis treatment is as follows: the first reaction product after drying treatment is subjected to pyrolysis treatment at a heating rate of 3 to 8°C/min at a temperature of 300 to 400°C for 2 to 6 hours .

Preferably, in step S1, the preparation process of the first reaction system includes the following steps:

A1, according to a predetermined ratio, the lithium nitrate, lanthanum nitrate, tetrabutyl titanate and citric acid are respectively dissolved in a solvent to obtain a lithium nitrate solution, a lanthanum nitrate solution, a tetrabutyl titanate solution and a citric acid solution;

A2, the lithium nitrate solution, the tetrabutyl titanate solution and the citric acid solution prepared in step A1 are mixed uniformly to obtain a first mixed solution; then under stirring at 60-100 °C, a predetermined volume is added dropwise The described lanthanum nitrate solution;

A3, after the dropwise addition of the lanthanum nitrate solution described in step A2 is completed, the first reaction system is prepared by stirring for 20-40 min.

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

Preferably, the ratio of the total mass 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 preparation process of the second reaction system includes the following steps:

P1, according to a predetermined ratio, dissolve the 2,4-toluene diisocyanate in an organic solvent, and then add a catalyst under 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; The second reaction system is described.

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

In order to achieve the above purpose of the invention, the present invention also provides a lithium metal negative electrode. The lithium metal negative electrode is composed of the above-mentioned solid electrolyte and lithium metal sheet.

Compared with the prior art, the beneficial effects of the present invention are:

1. The LLTO/LPU composite polymer electrolyte (CPPE) provided by the present invention has a linear structure of polyurethane and ion-conducting ceramic lithium lanthanum titanium oxide (LLTO), which enables CPPE to have excellent electrochemical performance. The mechanism is:

1) In the present invention, linear polyurethane (LPU) is synthesized by 2,4-toluene diisocyanate (TDI) and polypropylene oxide (PPO). The coordination of ether oxygen functional groups on linear polyurethane with lithium ions facilitates the migration of lithium ions on different linear polymer segments and improves the diffusion rate of lithium ions; while lithium lanthanum titanium oxide (LLTO) can be used in polymer segments. Promote the conduction of lithium ions, and the two synergistically improve the electrochemical performance of solid-state electrolyte CPPE.

2) The solid electrolyte membrane CPPE prepared by the present invention can effectively suppress lithium dendrites and prevent isolated lithium accumulation, so that the lithium capacity loss can be significantly reduced, and the stable cyclability and high multiplicity of lithium metal batteries can be achieved; In the prior art, the electrolyte will generate lithium dendrites, which hinders the diffusion of lithium ions.

2. The LLTO/LPU composite polymer electrolyte (CPPE) provided by the present invention has a lithium ion conductivity of 3.8×10 ^-4 S cm ^-1 at room temperature. Meanwhile, the assembled LiFePO ₄ |CPPE|Li battery exhibits excellent cycling performance at room temperature, with a discharge capacity of 149.8 mAh g ^-1 after 200 cycles and a high capacity retention rate of 97.8% at 0.5 C . The assembled LiNi _0.8 Co _0.1 Mn _0.1 O ₂ |CPPE|Li cell exhibits remarkable rate capacity, its initial capacity reaches 216.4 mAh·g ^-1 at 0.1C and maintains an excellent 138 mAh·g ^-1 at 1C Specific capacity. The electrochemical performance of the solid electrolyte CPEE prepared by the invention is much higher than that of the conventional lithium battery assembled with PPO or liquid electrolyte, and 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 present invention firstly adopts a combined process of hydrothermal synthesis-pyrolysis-high temperature calcination to prepare lithium lanthanum titanium oxide (LLTO) conductive ceramic nanoparticles with complete crystalline phase, with a particle size. Evenly distributed, with good electrochemical properties and dispersion properties. Then, LLTO nanoparticles were added to the second reaction system of 2,4-toluene diisocyanate and polypropylene oxide, and the synthesis process of linear polyurethane and the dispersion and mixing process of LLTO nanoparticles were synchronized, so that LLTO nanoparticles could be uniformly dispersed In the linear polyurethane polymer molecules and diffused into the interior of the polymer composite film, a uniform three-dimensional conductive LLTO network structure is formed, and the synergistic effect of the linear polyurethane polymer and LLTO nanoparticles significantly improves the solid electrolyte CPPE electrochemical performance.

Description of drawings

FIG. 1 is an XRD pattern of lithium lanthanum titanium oxide (LLTO) particles provided in Example 1 of the present invention.

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

3 is an electron microscope image of lithium lanthanum titanium oxide (LLTO) particles and 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 solid electrolyte (CPPE) Electron microscope images; c and d in Figure 3 are cross-sectional electron microscope images of solid electrolyte (CPPE), and the scale bar is 1 μm.

Figure 4 is a performance diagram provided by Example 1 and Comparative Examples 1-2 of the present invention (a in Figure 4 is the CPPE-LLTO prepared by using Example 1, the PPO-LLTO prepared by Comparative Example 1 and the liquid electrolyte provided by Comparative Example 2 The rate capability of the NCM ₈₁₁ |Li half-cell. In Fig. 4, b, c, and d are the NCM ₈₁₁ | Initial charge-discharge curves of Li batteries).

FIG. 5 is a cycle performance diagram provided by Example 1 and Comparative Examples 1-2 of the present invention.

Detailed ways

The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

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

S1, preparation of lithium lanthanum titanium oxide: prepare a first reaction system of lithium nitrate, lanthanum nitrate, tetrabutyl titanate and citric acid according to a predetermined ratio, and at 160-200 ° C, the first reaction system is hydrothermally The reaction is carried out for 8 to 16 hours; after the hydrothermal reaction is completed, the first reaction product produced by the reaction is dried and pyrolyzed, and then calcined at 800 to 1000 ° C for 1 to 4 hours to prepare lithium lanthanum titanium oxide particles;

S2, preparation of solid electrolyte: prepare a second reaction system of 2,4-toluene diisocyanate and polypropylene oxide according to a predetermined ratio, and place the lithium lanthanum titanium oxide particles prepared in step S1 in the second reaction system In the process, the reaction is carried out under stirring for 3-8 hours at a temperature of 50-80 °C; then the second reaction product produced by the reaction is poured into the mold, and the solvent is evaporated to prepare the composite polymer electrolyte, which is the solid-state electrolyte. .

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

Further, in step S1, the process of the pyrolysis treatment is as follows: the first reaction product after drying treatment is subjected to a pyrolysis treatment at a heating rate of 3 to 8°C/min at a temperature of 300 to 400°C for 2 to 6 hours .

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

A1, according to a predetermined ratio, the lithium nitrate, lanthanum nitrate, tetrabutyl titanate and citric acid are respectively dissolved in a solvent to obtain a lithium nitrate solution, a lanthanum nitrate solution, a tetrabutyl titanate solution and a citric acid solution;

A2, the lithium nitrate solution, the tetrabutyl titanate solution and the citric acid solution prepared in step A1 are mixed uniformly to obtain a first mixed solution; then under stirring at 60-100 °C, a predetermined volume is added dropwise The described lanthanum nitrate solution;

A3, after the dropwise addition of the lanthanum nitrate solution described in step A2 is completed, the first reaction system is prepared by stirring for 20-40 min.

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

Further, the ratio of the total mass 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 preparation process of the second reaction system includes the following steps:

P1, according to a predetermined ratio, dissolve the 2,4-toluene diisocyanate in an organic solvent, and then add a catalyst under 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; The second reaction system is described.

Further, the solvent evaporation treatment in step S2 is carried out at ambient temperature in an argon or nitrogen atmosphere; the mold is polytetrafluoroethylene.

The present invention will be further described in detail below through specific embodiments.

Example 1

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

S1, Synthesis of Lithium Lanthanum Titanium Oxide (LLTO) Particles:

1) Dissolve lithium nitrate, lanthanum nitrate, tetrabutyl titanate and citric acid in absolute ethanol at a molar ratio of 0.33:0.557:1.00:0.887 to obtain lithium nitrate solution, lanthanum nitrate solution, tetrabutyl titanate solution and citric acid solution; wherein, citric acid is used as complexing agent;

2) Mixing the lithium nitrate solution, the tetrabutyl titanate solution and the citric acid solution uniformly to obtain a first mixed solution; then under mechanical stirring at 80 °C, drop the lanthanum nitrate solution;

3) After the dropwise addition of the lanthanum nitrate solution is completed, stirring for 30min to obtain a white suspension, the first reaction system is prepared;

4) Pour the first reaction system into a 180°C, 200mL reaction kettle, and perform a hydrothermal reaction for 10h;

5) After the hydrothermal reaction is completed, the first reaction product produced by the reaction is cooled to room temperature, then taken out and dried at 80 ° C; then the first reaction product is placed in a tube furnace, and the temperature is 5 ° C/min. The heating rate was pyrolyzed at 350°C for 4h;

6) The pyrolysis product was calcined at 900° C. for 2 h to prepare lithium lanthanum titanium oxide (LLTO) particles.

S2, Preparation of Solid LLTO/LPU Composite Polymer Electrolyte:

1) Dissolve 2,4-toluene diisocyanate (TDI) (1.74 g, 10 mmol) in 20 mL of organic solvent chloroform, then add catalyst dibutyltin dilaurate (DBTDL) 5 mol% under argon atmosphere to obtain a second mixture solution;

2) Dissolve polypropylene oxide PPO2000 (HO-PPO-OH Mw=2000 g·mol ^-1 , 10.0 g, 5 mmol) in 30 mL of chloroform to obtain a polypropylene oxide solution, and pump it into the first In the two mixed solutions, the second reaction system is prepared;

3) The lithium lanthanum titanium oxide particles (LLTO) prepared in step S1 are placed in the second reaction system, and the reaction is carried out under magnetic stirring at a temperature of 60° C. for 5 hours; then the second reaction product produced by the reaction is poured into the polymer. In the tetrafluoroethylene mold, solvent evaporation is performed in a nitrogen atmosphere at ambient temperature to prepare the solid LLTO/LPU composite polymer electrolyte, which is the solid electrolyte (CPPE); wherein, lithium lanthanum titanium oxide particles are added The amount is 10 wt% of the mass of the linear polyurethane.

In the present invention, the reaction formula of 2,4-toluene diisocyanate (TDI) and polypropylene oxide PPO2000 to synthesize linear polyurethane (LPU) is as follows:

Please refer to FIG. 1 , the XRD spectrum of lithium lanthanum titanium oxide (LLTO) particles does not show impurity peaks, indicating that the LLTO particles synthesized by the present invention do not have other impurity phases. This shows that the present invention can synthesize lithium lanthanum titanium oxide (LLTO) ceramic particles with a complete crystalline phase by using a combined process of hydrothermal reaction and calcination.

Please refer to FIG. 2 , compared with the PP separator, the LLTO/LPU composite polymer electrolyte membrane prepared by the present invention is gray and white with uniform color.

Please refer to Fig. 3. In Fig. 3, a is the electron microscope image of the LLTO particle. It can be seen that the particle size is uniform, light gray, and the particle size distribution is in the range of 0.8-2 μm.

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

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

c in Figure 3 indicates that the thickness of the composite electrolyte membrane is about 10 μm.

It can be seen from d in Fig. 3 that the LLTO particles are uniformly dispersed in the LPU matrix.

Comparative Example 1

The difference from Example 1 is that 10.0 g 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% lithium lanthanum was added Titanium oxide particles (LLTO), resulting in electrolyte PPO-LLTO.

Comparative Example 2

The difference from Example 1 is that a commercially available liquid electrolyte 1M lithium hexafluorophosphate EC:DEC=1:1Vol% is used.

Performance Testing of Electrolytes: (Physicochemical and Electrochemical Measurements)

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

2) The ionic conductivity of the solid electrolyte (CPPE) is calculated by the following formula

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

Electrochemical Impedance Spectroscopy (EIS) measurements were performed using AutoLab (PGDTAT302N) in the frequency range of 10 ⁻¹ to 10 ⁵ Hz with an amplitude of 10 mV.

3) The positive electrode of LiFePO ₄ is prepared by stirring the active material LiFePO ₄ , polyvinylidene fluoride (PVDF) and acetylene in N-methyl-2-pyrrolidone (NMP) in a weight ratio of 8:1:1 , the slurry was coated on aluminum carbide foil and dried under vacuum at 80°C for 24h. The mass loading of the active material LiFePO ₄ is about 2 mg cm ⁻² . Half-cells of LiFePO ₄ |CPPE|Li were assembled by sandwiching the solid electrolyte (CPPE) prepared in Example 1 or the electrolyte (PPO-LLTO) prepared in Comparative Example 1 between LiFePO ₄ cathode and lithium anode.

Charge and discharge were performed through LiFePO ₄ |CPPE|Li within the cut-off voltage range, and the voltage range from 2.7V to 4.0V was tested using LANDEtronics.

The preparation of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ |CPPE|Li cells is similar to the above-mentioned LiFePO ₄ cells, and the mass loading of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ is about 1.5 mg cm ⁻² .

The present invention also assembles the electrolyte PPO-LLTO provided in Comparative Example 1 and the liquid electrolyte of Comparative Example 2 into the above-mentioned LiNi _0.8 Co _0.1 Mn _0.1 O ₂ |Li battery as a control sample.

Li was tested over a voltage range of 3.0 to 4.35V. All the different assembled cells were assembled in a glove box ( _H2O and _O2 content less than 0.01 ppm).

It should be noted that, in the following description, the LiNi _0.8 Co _0.1 Mn _0.1 O ₂ |Li battery is abbreviated as NCM ₈₁₁ |Li battery; the LiFePO ₄ |Li battery is abbreviated as LFP|Li battery.

Test Results:

After testing, the lithium ion conductivity of the solid electrolyte (CPPE) prepared in Example 1 at room temperature reached 3.8×10 ^-4 S cm ^-1 . Meanwhile, the assembled LiFePO ₄ |CPPE|Li battery exhibits excellent cycling performance at room temperature, with a discharge capacity of 149.8 mAh g ^-1 after 200 cycles and a high capacity retention rate of 97.9% at 0.5 C .

Meanwhile, LiNi _0.8 Co _0.1 Mn _0.1 O ₂ |CPPE|Li exhibits remarkable rate capacity, its initial capacity reaches 216.4 mAh·g ^-1 at 0.1C, and maintains an excellent specific capacity of 138 mAh·g ^-1 at 1C .

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

Please refer to Figure 4, where a is the rate capability of NCM ₈₁₁ |Li half-cells using the CPPE-LLTO prepared in Example 1, the PPO-LLTO prepared in Comparative Example 1 and the liquid electrolyte provided in Comparative Example 2. In Figure 4, b, c and d are the initial charge-discharge curves of the NCM ₈₁₁ |Li battery with the CPPE-LLTO prepared in Example 1, the PPO-LLTO prepared in Comparative Example 1 and the liquid electrolyte provided in Comparative Example 2, respectively.

Among them, b in Figure 4 shows that the NCM ₈₁₁ |CPPE|Li provided in Example 1 has an initial value of 216.4 mAh·g ^-1 at a low current density of 0.1C. As the current density increases, the capacity of the battery also decreases. However, the battery of NCM ₈₁₁ |CPPE still maintains a capacity of 138mAh·g ^-1 at 1C.

In contrast, the discharge capacities of NCM ₈₁₁ |PPO-LLTO provided by Comparative Example 1 and NCM ₈₁₁ |LE provided by Comparative Example 2 are only 113.5 mAh·g ⁻¹ (c in Fig. 4) and 94.7 mAh·g ⁻¹ (Fig. 4 in d).

The reason for such a large difference in discharge capacity between Example 1 and Comparative Examples 1-2 is that the solid electrolyte (CPPE) prepared in Example 1 of the present invention has a linear structure of polyurethane and ion conductive ceramic LLTO. The coordination of ether oxygen functional groups on linear polyurethane with lithium ions facilitates the migration of lithium ions on different linear polymer segments and improves the diffusion rate of lithium ions, while LLTO in the polymer segments can facilitate the conduction of lithium ions. The two features synergize with each other to jointly improve the performance of solid electrolyte CPPE.

However, in Comparative Example 1, PPO2000 will form a crystalline region that traps lithium ions, resulting in the formation of lithium ion traps in the electrolyte of the PPO-LLTO system, which hinders the diffusion of lithium ions, so the discharge capacity performance of Comparative Example 1 is poor. .

In Comparative Example 2, the liquid electrolyte has the defect of poor compatibility with the lithium anode, resulting in poor discharge capacity performance of Comparative Example 2.

Referring to Figure 5, the initial discharge capacity of the LFP|CPPE|Li provided in Example 1 is 154.6 mAh g ^-1 , and the discharge capacity of 149.8 mAh g ^-1 is still maintained after 200 cycles. The capacity retention rate of the LFP|CPPE|Li battery provided in Example 1 was as high as 97.9%, indicating that after 200 cycles, the capacity did not decrease significantly.

In contrast, the initial capacity of the LFP|Li battery using the PPO-LLTO provided in Comparative Example 1 was 148.7 mAh g ⁻¹ , and the capacity retention rate was 94.6%. However, the cycle performance curve of LFP|LE|Li provided by Comparative Example 2 is irregular.

The reason for the above phenomenon is: the CPPE electrolyte membrane prepared by the present invention can effectively suppress lithium dendrites and prevent the accumulation of isolated lithium, so as to significantly reduce the loss of lithium capacity, and it also shows that the CPPE electrolyte membrane prepared by the present invention can realize lithium metal Stable cyclability and high multiplicity of batteries.

Example 2-3

The difference from Example 1 is that the mass ratios of lithium lanthanum titanium oxide particles (LLTO) and linear polyurethane (LPU) are set differently, and others are the same as those in Example 1, which will not be repeated here.

Table 1 is the process parameter setting and its performance parameters in the embodiment 1-3

Example LLTO to LPU mass ratio Ionic conductivity 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

Combined with Table 1 for analysis: the influence of the mass ratio of lithium lanthanum titanium oxide particles (LLTO) to linear polyurethane (LPU) on the electrochemical performance of solid electrolyte CPPE is: when the mass ratio of LLTO to LPU is set to 1:10, the prepared The solid electrolyte has the highest ionic conductivity and excellent electrochemical performance.

Comparative Example 3

The difference from Embodiment 1 is that the hydrothermal reaction treatment is not carried out in step S1, and the others are the same as those of Embodiment 1, and are not repeated here.

Comparative Example 4

The difference from Example 1 is that high-temperature calcination treatment is not performed in step S1, and other aspects are the same as those in Example 1, which will not be repeated here.

Table 2 is the process parameter setting and its performance parameters in Example 1 and Comparative Examples 3-4

Example LLTO synthesis process Ionic conductivity 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 in conjunction with Table 2: As can be seen from Table 2, the present invention adopts the combined LLTO synthesis process of hydrothermal reaction-pyrolysis-high temperature calcination, and the prepared LLTO nanoparticles have better crystalline phase, no impurity doping, and In Comparative Example 3 and Comparative Example 4, there are deficiencies of different contents of impurity phases. Therefore, the ionic conductivity of the solid electrolyte provided by Example 1 is much higher than that of the solid electrolyte prepared by Comparative Example 1 and Comparative Example 2.

In conclusion, the present invention provides a solid electrolyte, a lithium metal negative electrode and a preparation method thereof. The solid electrolyte is a composite polymer electrolyte composed of lithium lanthanum titanium oxide and linear polyurethane. The preparation method is as follows: firstly, the lithium lanthanum titanium oxide particles with complete crystalline phase are prepared by a combined process of hydrothermal synthesis and high-temperature calcination; then, the lithium lanthanum titanium oxide particles are blended and stirred with linear polyurethane, and solvent evaporation treatment is performed. , a solid electrolyte was prepared. The lithium ion conductivity of the solid electrolyte prepared by the invention at room temperature reaches 3.8×10 ^-4 S cm ^-1 . Meanwhile, the battery assembled with this solid electrolyte exhibits excellent cycle performance and excellent specific capacity at room temperature. In the present invention, 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 embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that it can still be Modifications are made to the technical solutions described in the foregoing embodiments, or some or all of the technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention.

Claims (10)

1. A solid-state electrolyte, characterized in that: the solid-state electrolyte is a composite polymer electrolyte composed of lithium lanthanum titanium oxide and linear polyurethane; in the solid-state electrolyte, the lithium lanthanum titanium oxide and the linear polyurethane The mass ratio of the solid electrolyte is 1:(9～11); the thickness of the solid electrolyte is 300～500μm; the lithium ion conductivity of the solid electrolyte is 3.8×10 ^-4 S cm ^-1 ～5.0×10 ^-4 S cm ^-1 . 2. the preparation method of a solid electrolyte according to claim 1, is characterized in that: comprise the steps: S1, preparation of lithium lanthanum titanium oxide: prepare a first reaction system of lithium nitrate, lanthanum nitrate, tetrabutyl titanate and citric acid according to a predetermined ratio, and at 160-200 ° C, the first reaction system is hydrothermally The reaction is carried out for 8 to 16 hours; after the hydrothermal reaction is completed, the first reaction product produced by the reaction is dried and pyrolyzed, and then calcined at 800 to 1000 ° C for 1 to 4 hours to prepare lithium lanthanum titanium oxide particles; S2, preparation of solid electrolyte: prepare a second reaction system of 2,4-toluene diisocyanate and polypropylene oxide according to a predetermined ratio, and place the lithium lanthanum titanium oxide particles prepared in step S1 in the second reaction system In the process, the reaction is carried out under stirring for 3-8 hours at a temperature of 50-80 °C; then the second reaction product produced by the reaction is poured into the mold, and the solvent is evaporated to prepare the composite polymer electrolyte, which is the solid-state electrolyte. . 3. The preparation method of solid electrolyte according to claim 2, characterized in that: in the first reaction system of step S1, the molar mass ratio of lithium nitrate, lanthanum nitrate, tetrabutyl titanate and citric acid is is 0.33:0.557:1.00:0.887. 4 . The method for preparing a solid electrolyte according to claim 2 , wherein in step S1 , the process of the pyrolysis treatment is: drying the first reaction product after drying at a temperature of 3 to 8° C./min. 5 . The heating rate is at a temperature of 300 to 400 ° C, and the pyrolysis treatment is carried out for 2 to 6 hours. 5. The preparation method of solid electrolyte according to claim 2, characterized in that: in step S1, the preparation process of the first reaction system comprises the following steps: A1, according to a predetermined ratio, the lithium nitrate, lanthanum nitrate, tetrabutyl titanate and citric acid are respectively dissolved in a solvent to obtain a lithium nitrate solution, a lanthanum nitrate solution, a tetrabutyl titanate solution and a citric acid solution; A2, the lithium nitrate solution, the tetrabutyl titanate solution and the citric acid solution prepared in step A1 are mixed uniformly to obtain a first mixed solution; then under stirring at 60-100 °C, a predetermined volume is added dropwise The described lanthanum nitrate solution; A3, after the dropwise addition of the lanthanum nitrate solution described in step A2 is completed, the first reaction system is prepared by stirring for 20-40 min. 6 . The method for preparing a solid electrolyte according to claim 2 , wherein in step S2 , the mole fraction ratio of the 2,4-toluene diisocyanate and the polypropylene oxide is 1: (1.1～ 1.3). 7 . The method for preparing a solid electrolyte according to claim 2 , wherein: 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. 8 . It is (8～10):1. 8. The preparation method of solid electrolyte according to claim 2, characterized in that: in step S2, the preparation process of the second reaction system comprises the following steps: P1, according to a predetermined ratio, dissolve the 2,4-toluene diisocyanate in an organic solvent, and then add a catalyst under 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 placing the polypropylene oxide solution in the second mixed solution prepared in step P1; The second reaction system is described. 9 . The method for preparing a solid electrolyte according to claim 2 , wherein the solvent evaporation treatment in step S2 is carried out at ambient temperature in an argon or nitrogen atmosphere; the mold is polytetrafluoroethylene. 10 . 10. A lithium metal negative electrode, characterized in that: the lithium metal negative electrode is prepared by the solid electrolyte according to claim 1 or by the preparation method of the solid electrolyte according to any one of claims 2-9. A solid electrolyte and a lithium metal sheet are composited.

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