CN108832173B - Garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum and preparation method thereof - Google Patents

Abstract

The invention relates to a garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum and a preparation method thereof, wherein the general composition of the garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum is: Li _6.55-2x Ga _0.15 La ₃ Zr _2-x Mo _x O ₁₂ , and 0.05≤x≤0.25. The garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum in the present invention has higher lithium ion conductivity and greatly reduces the cost. The preparation method of the gallium and molybdenum co-doped garnet type lithium ion solid electrolyte in the present invention is simple in process and low in cost, and the obtained gallium and molybdenum co-doped garnet type lithium ion solid electrolyte has high compactness. improvement.

Description

Garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum and preparation method thereof

technical field

The invention belongs to the technical field of solid electrolyte materials, in particular to a garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum and a preparation method thereof.

Background technique

With the intensification of environmental pollution, people's demand for building an environment-friendly and energy-saving society is becoming more and more intense. Compared with traditional secondary batteries such as nickel-chromium batteries, lead-acid batteries and nickel-hydrogen batteries, lithium-ion batteries have the advantages of higher operating voltage, greater energy density, longer cycle life, and smaller self-discharge rate. , and no pollution, no memory effect, has great potential for development. At present, traditional lithium-ion batteries use organic electrolytes as electrolytes. However, organic liquid electrolytes may volatilize, dry up, and leak during use, affecting battery life. Organic liquids are generally flammable and explosive, and have safety problems. The solid-state battery assembled with solid electrolyte can effectively solve the safety hazards brought by liquid electrolyte, making it possible to use lithium metal as the negative electrode of the battery. In addition, the solid electrolyte can work in a wide temperature range, and its electrochemical window is wider, which expands the application range of electrode materials.

At present, garnet-type lithium-ion solid electrolytes (LLZOs) have received extensive attention due to their high ionic conductivity and good chemical stability. Among them, the garnet-type lithium ion solid electrolyte has two phases: tetragonal and cubic. The ionic conductivity of cubic LLZO is two orders of magnitude higher than that of tetragonal LLZO, ranging from 10 ^-4 to 10 ^{-3 S} / cm. The ionic conductivity of cubic phase LLZO is also slightly higher than that of other oxide solid electrolytes such as NASICON, perovskite, and LISICON. However, the cubic phase is easily transformed into a tetragonal phase at high temperature, therefore, element doping is generally used to effectively increase the concentration of lithium vacancies and stabilize the cubic phase. The most existing one is to obtain higher lithium ion conductivity by doping Ga ³⁺ , but the high price of gallium causes the production cost to be too high.

SUMMARY OF THE INVENTION

(1) Technical problems to be solved

In order to solve the above problems of the prior art, the present invention provides a gallium and molybdenum co-doped garnet-type lithium ion solid electrolyte with high lithium ion conductivity and high lithium ion conductivity, and a preparation method thereof.

(2) Technical solutions

In order to achieve the above-mentioned purpose, the main technical scheme adopted in the present invention includes:

One aspect _of the present invention provides a _{garnet -} type lithium ion solid electrolyte co _- doped with _gallium and _molybdenum . 0.25.

Another aspect of the present invention provides a method for preparing the above-mentioned garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum, comprising the following steps: S1, according to the general formula: Li _6.55-2x Ga _0.15 La ₃ Zr _2-x Mo _x O ₁₂ , weigh Li ₂ CO ₃ powder, ZrO ₂ powder, Ga ₂ O ₃ powder, La ₂ O ₃ powder and MoO ₃ powder in stoichiometric proportions; S2, mix all the powders obtained in step S1 in Grinding together to form the first material to be molded; S3, compressing the first material to be molded, and then calcining to obtain a precursor compound; S4, grinding the precursor compound again to form a second material to be molded; S5, compressing the second material to be molded, and then sintering to obtain a garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum.

According to the present invention, in step S1, the Li ₂ CO ₃ powder weighed according to the stoichiometric ratio includes a 10% capacity balance.

According to the present invention, in step S2, the grinding time is 6-18 hours, and the particle size of the first material to be molded is less than or equal to 10 μm.

According to the present invention, in step S2, ball milling is used for grinding, wherein the rotational speed during ball milling is 350-800 r/min, the ball milling solvent is absolute ethanol or isopropanol, and the ball milling medium is zirconia balls.

According to the present invention, in step S3, the pressing pressure during pressing is 100-300 MPa, the pressure holding time is 3-8 min, the calcination temperature is 800-900°C, and the calcining time is 6-12 h.

According to the present invention, in step S4, the grinding time is 6-18 hours, and the particle size of the second material to be molded is less than or equal to 10 μm.

According to the present invention, in step S5, after compression molding to form compressed tablets, the second material to be molded is used as the master powder, and the compressed tablets after compression molding are buried in the master powder and then sintered.

According to the present invention, in step S5, the pressing pressure during pressing is 100-300 MPa, the pressure holding time is 3-8 min, the sintering temperature is 1100-1200°C, and the sintering time is 6-12 h.

(3) Beneficial effects

The beneficial effects of the present invention are:

In the present invention, Ga ³⁺ and Mo ⁶⁺ are simultaneously doped into the garnet-type lithium ion solid electrolyte for the first time to obtain a garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum (Li _6.55-2x Ga _0.15 La ₃ Zr _{2 -x} Mo _x O ₁₂ ), in which Ga ³⁺ substituted Li sites exhibit extremely high electrical conductivity, which can stabilize the cubic phase without significantly changing lattice parameters, Mo ⁶⁺ substituted Zr sites, which can generate lithium ion vacancies At the same time, due to the presence of molybdenum ions, it can also promote sintering and accelerate the densification process. The atomic radius of Mo is slightly smaller than that of Zr, and it is easy to enter the lattice. After replacing the Zr site, the lattice parameter can be reduced, thereby stabilizing the cubic phase. Mo ⁶⁺ -doped LLZO is very stable for electrode materials and has a wider electrochemical window.

Therefore, the use of Mo ⁶⁺ and Ga ³⁺ co-doping can greatly reduce the amount of gallium, thereby greatly reducing the cost, and at the same time, it can greatly improve the lithium ion conductivity, which is more conducive to the further development of garnet-type lithium ion solid electrolytes . At the same time, the solid-phase reaction method is adopted to synthesize the solid electrolyte in the present invention, the preparation process is simple and the cost is low, and the finally obtained garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum also has the above-mentioned properties, and the compactness is very high. big improvement.

Description of drawings

Fig. 1 is the X-ray diffraction spectrum of the garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum obtained in Example 1 below;

Fig. 2 is the SEM image of the cross-section of the garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum obtained in Example 1 below;

3 is an EIS spectrum of the garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum obtained in Example 1 below.

Detailed ways

In order to better explain the present invention and facilitate understanding, the present invention will be described in detail below with reference to the accompanying drawings and through specific embodiments.

Example 1

This embodiment provides a preparation method of a garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum, which specifically includes the following steps:

S1. Weigh 10.322 g of Li ₂ CO ₃ powder, 9.36 g of ZrO ₂ powder, 0.562 g of Ga ₂ O ₃ powder, 19.548 g of La ₂ O ₃ powder and 0.576 g of MoO ₃ powder, respectively. Among them, 10.322g of Li ₂ CO ₃ powder already contains 10% of the capacity, that is, after the mass of each powder is determined according to the ratio in the general chemical formula Li _6.35 Ga _0.15 La ₃ Zr _1.9 Mo _0.1 O ₁₂ Weigh out more Li ₂ CO ₃ powder with a mass fraction of 10%.

Specifically, since Li ₂ O generated by the decomposition of Li ₂ CO ₃ powder will sublime at a temperature higher than 1000 ° C, the sublimation phenomenon of Li ₂ O will occur during subsequent sintering, which will affect the synthesis of materials. The main purpose of weighing more Li ₂ CO ₃ powder with a mass fraction of 10% is to make up for the Li ₂ O sublimated at high temperature during subsequent sintering, so that the final product just meets the requirements in the general formula. After a large number of experimental studies, it has been shown that when the mass fraction of Li ₂ CO ₃ powder taken in excess is less than 10%, it is not enough to make up for the amount of Li ₂ O sublimated during sintering, and the mass fraction of Li ₂ CO ₃ powder taken in excess is not enough. When it is greater than 10%, a lot of Li ₂ O will react with other substances to generate other impurities, which greatly affects the performance of the final material. Therefore, the mass fraction of Li ₂ CO ₃ powder should be controlled at 10%, which can just make up for the Li ₂ O sublimated at high temperature during sintering and can just form a cubic phase without entering other impurities, ensuring that The final material is a single phase substance.

S2. All powders obtained in step S1 are mixed together and ground to form a first material to be molded, and the particle size of the first material to be molded is less than or equal to 10 μm.

Specifically, the ball milling method was used for grinding, and all the powders were put into an agate ball mill jar, and anhydrous ethanol was used as the ball milling solvent, and zirconia balls were used as the ball milling medium, and the rotational speed was 500 r/min, and the ball was milled in a planetary ball mill for 10 hours. After the ball milling, drying is carried out at 100° C. to obtain a uniformly mixed first material to be molded (in a powder state). Among them, the selection of zirconia balls for the ball milling medium can prevent the introduction of new impurities into the obtained first material to be molded, and all powders are mixed together for grinding, which can make these powders mix more uniformly, and at the same time, the grinding is carried out in step S3. During calcination, the contact area between the powders can be increased to make the reaction more sufficient.

S3, hold the first material to be molded under a pressing pressure of 200 MPa for 5 minutes, and press it into a round tablet, then put it into an alumina crucible, calcined at 850 ° C in air for 6 hours, and naturally cooled to room temperature to obtain precursor complex.

Specifically, the solid-phase reaction method is used in this calcination process. Under heating, the Li ₂ CO ₃ powder in the tablet is first decomposed to form Li ₂ O and CO ₂ , and then Li ₂ O, ZrO ₂ powder, Ga ₂ The O ₃ powder, La ₂ O ₃ powder and MoO ₃ powder react again to obtain a precursor composite, and the precursor composite at this time contains part of Li _6.35 Ga _0.15 La ₃ Zr _1.9 Mo _0.1 O ₁₂ phase and other phases The heterophase is synthesized by the solid-phase reaction method, and the preparation is good in filling, low in cost, large in output and simple in preparation process.

S4, grinding the precursor compound again to form a second material to be molded, and the particle size of the second material to be molded is less than or equal to 10 μm.

Specifically, the ball milling method is used for grinding, and the precursor compound is put into an agate ball mill jar, and anhydrous ethanol is used as the ball milling solvent, and zirconia balls are used as the ball milling medium, and the rotation speed is 500 r/min. . After the ball milling, drying is carried out at 100° C. to obtain a second material to be molded (in powder state) that is evenly mixed. The precursor composite is first ground to make the powder mixed more uniformly, and then sintered, so that the crystal grains of the precursor composite can be sintered together, the reaction is more sufficient, and a sample with excellent compactness can be obtained.

S5, hold the second material to be molded for 5 minutes under the pressing pressure of 200 MPa, and press it into a round tablet, and then use the second material to be molded as the master powder, bury the tablet in the master powder and then compress it in the air for 1200 ℃ After sintering at ℃ for 6 h, and cooling to room temperature naturally, a garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum was obtained.

Specifically, burying the prepared tablet in the mother powder and then sintering can reduce the sublimation of lithium oxide. Here, on the one hand, unreacted substances in the precursor composite can be further reacted by sintering, and on the other hand, the crystal grains in the material are sintered together by high-temperature sintering, thereby improving the density of the material.

Further, after grinding the surface of the obtained gallium and molybdenum co-doped garnet-type lithium ion solid electrolyte (the grinding here is mainly to remove the mother powder attached to the surface), use an agate mortar to grind it into a The powder is then subjected to phase structure analysis by X-ray diffraction (XRD).

It can be seen from Figure 1 that the material is Li _6.35 Ga _0.15 La ₃ Zr _1.9 Mo _0.1 O ₁₂ with diffraction peaks (which are basically consistent with the peaks of cubic phase LLZO (JCPDS 45-109), and the XRD peaks are somewhat different from the standard peaks. The shift is mainly due to the entry of gallium and molybdenum into the unit cell to change the unit cell parameters), and no impurity peaks appear, indicating that the obtained garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum is a pure cubic phase. LLZO has a composition of simple Li _6.35 Ga _0.15 La ₃ Zr _1.9 Mo _0.1 O ₁₂ . And the diffraction peaks are sharp peaks with high intensity, indicating that the obtained garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum has good crystallinity, only a single phase, and the lattice is relatively stable. Therefore, the composition of the obtained garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum is Li _6.35 Ga _0.15 La ₃ Zr _1.9 Mo _0.1 O ₁₂ .

Further, referring to FIG. 2, the microscopic morphology of the section of the prepared gallium and molybdenum co-doped garnet-type lithium ion solid electrolyte was observed by scanning electron microscope (SEM). The obtained gallium and molybdenum co-doped garnet-type lithium ion solid electrolyte has a dense and uniform structure, and the compactness is greatly improved. Among them, the air holes on the fracture surface are mainly caused by the sublimation of lithium oxide, and the blurring of grain boundaries is mainly caused by the melting of excess lithium oxide.

Further, the ionic conductivity of the prepared gallium and molybdenum co-doped garnet-type lithium ion solid electrolyte was measured by alternating current impedance spectroscopy (EIS). During the measurement, silver paste was screen-printed on the top and bottom of the solid electrolyte, and then calcined at 850 °C for 10 min. After cooling to room temperature naturally, a silver film was formed on the surface of the solid electrolyte and used as a blocking electrode. Then, the ionic conductivity was measured at room temperature (25°C). The obtained EIS spectrum of the garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum was shown in Figure 3. Using this spectrum, the gallium was obtained by calculation. The ionic conductivity of the garnet-type lithium ion solid electrolyte co-doped with molybdenum is 6.3×10 ^-4 S/cm. Among them, the abscissa Z' in Fig. 3 represents the real axis, and the ordinate Z" represents the imaginary axis.

Compared with the existing ones, the existing Ga ³⁺ doped LLZOs are generally sintered in oxygen by the liquid phase method to exhibit extremely high electrical conductivity, but the synthesis method is complicated and the cost is high. However, conventional solid-phase sintering in air is currently used. Although the synthesis method is simple, it requires a large amount of gallium doping to obtain high electrical conductivity. The price of gallium is very expensive, causing the cost to be too high. For example, the gallium-doped LLZO sintered in air by the solid-phase method reported by Guo Xin, when the amount of gallium doping is small, is a mixed phase of tetragonal phase and cubic phase, and the conductivity is very low. For example, the conductivity of 0.15Ga-LLZO is 8.5×10 ^-5 S/cm, and it is a mixed phase of cubic phase and tetragonal phase.

In this example, after doping Ga and Mo at the same time, the tetragonal phase disappears and becomes a pure cubic phase, which greatly improves the electrical conductivity. The obtained garnet-type lithium ion solid co-doped with gallium and molybdenum The ionic conductivity of the electrolyte (Li _6.35 Ga _0.15 La ₃ Zr _1.9 Mo _0.1 O ₁₂ ) was 6.3×10 ^-4 S/cm, which achieved a higher lithium ion conductivity while greatly reducing the amount of gallium oxide used. The production cost is reduced, and the preparation method is simple in operation and low in cost. Therefore, the gallium and molybdenum co-doped garnet-type lithium ion solid electrolyte prepared in this embodiment greatly improves the lithium ion conductivity while greatly reducing the cost, which is more conducive to the further development of the garnet-type lithium ion solid electrolyte. develop.

Example 2

This embodiment provides a preparation method of a garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum, which specifically includes the following steps:

S1. Weigh 10.485 g of Li ₂ CO ₃ powder, 9.611 g of ZrO ₂ powder, 0.562 g of Ga ₂ O ₃ powder, 19.548 g of La ₂ O ₃ powder and 0.228 g of MoO ₃ powder, respectively. Among them, 10.458g of Li ₂ CO ₃ powder already contains 10% capacity.

S2. All powders obtained in step S1 are mixed together and ground to form a first material to be molded, and the particle size of the first material to be molded is less than or equal to 10 μm.

Specifically, ball milling was used for grinding, and all the powders were put into an agate ball milling tank, and anhydrous ethanol was used as the ball milling solvent, and zirconia balls were used as the ball milling medium, and the rotational speed was 650 r/min, and the ball was milled in a planetary ball mill for 12 hours. After the ball milling, drying is carried out at 110° C. to obtain a uniformly mixed first material to be molded (in a powder state).

S3, hold the first material to be molded under a pressing pressure of 240 MPa for 6 minutes, and press it into a round tablet, then put it into an alumina crucible, calcined at 900 ° C in air for 10 hours, and naturally cooled to room temperature to obtain precursor complex.

S4, grinding the precursor compound again to form a second material to be molded, and the particle size of the second material to be molded is less than or equal to 10 μm.

Specifically, the ball milling method is used for grinding, and the precursor compound is put into an agate ball mill jar, and anhydrous ethanol is used as the ball milling solvent, and zirconia balls are used as the ball milling medium. . After the ball milling, drying was carried out at 110° C. to obtain a uniformly mixed second material to be molded (in a powder state).

S5, hold the second material to be molded for 6 min under the pressing pressure of 250 MPa, and press it into a round tablet, and then use the second material to be molded as the master powder, bury the tablet in the master powder and then compress it in the air for 1200 ℃ After sintering at ℃ for 10 h, and cooling to room temperature naturally, a garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum was obtained. Its composition is Li _6.45 Ga _0.15 La ₃ Zr _1.95 Mo _0.05 O ₁₂ , and the structure is dense and uniform, and the density is greatly improved. The ionic conductivity of the prepared garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum is 4.1×10 ^-4 S/cm, which is relatively high.

Example 3

This embodiment provides a preparation method of a garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum, which specifically includes the following steps:

S1. Weigh out 10.16 g of Li ₂ CO ₃ powder, 9.118 g of ZrO ₂ powder, 0.562 g of Ga ₂ O ₃ powder, 19.548 g of La ₂ O ₃ powder and 0.864 g of MoO ₃ powder, respectively. Among them, 10.16g of Li ₂ CO ₃ powder already contains 10% of the capacity surplus.

S2. All powders obtained in step S1 are mixed together and ground to form a first material to be molded, and the particle size of the first material to be molded is less than or equal to 10 μm.

Specifically, ball milling was used for grinding, and all the powders were put into an agate ball mill tank, and anhydrous ethanol was used as the ball milling solvent, and zirconia balls were used as the ball milling medium, and the rotational speed was 400 r/min, and the ball was milled in a planetary ball mill for 8 hours. After the ball milling is completed, drying is carried out at 90° C. to obtain a uniformly mixed first material to be molded (in a powder state).

S3, hold the first material to be molded under a pressing pressure of 150 MPa for 4 minutes, and press it into a round tablet, then put it into an alumina crucible, calcined at 800 ° C in air for 8 hours, and naturally cooled to room temperature to obtain precursor complex.

S4, grinding the precursor compound again to form a second material to be molded, and the particle size of the second material to be molded is less than or equal to 10 μm.

Specifically, the ball milling method was used for grinding, and the precursor composite was put into an agate ball mill jar, and anhydrous ethanol was used as the ball milling solvent, and zirconia balls were used as the ball milling medium, and the rotational speed was 400 r/min. . After the ball milling, drying is carried out at 90° C. to obtain a second material to be molded (in powder state) that is evenly mixed.

S5. Hold the second material to be molded for 4 minutes under the pressing pressure of 150 MPa, and press it into a round tablet, and then use the second material to be molded as the master powder, bury the tablet in the master powder and then press it in the air for 1150 ℃ After sintering at ℃ for 8 h, and naturally cooling to room temperature, a garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum was obtained. Its composition is Li _6.25 Ga _0.15 La ₃ Zr _1.85 Mo _0.15 O ₁₂ , and the structure is dense and uniform, and the density is greatly improved. The ionic conductivity of the prepared garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum is 4.8×10 ^-4 S/cm, which is relatively high.

Of course, the present invention is not limited to the above-mentioned embodiments. In step S1, according to the general formula Li _6.55-2x Ga _0.15 La ₃ Zr _{2 -x} Mo _x O ₁₂ , the stoichiometric Li ₂ CO ₃ powder is weighed, ZrO ₂ powder, Ga ₂ O ₃ powder, La ₂ O ₃ powder and MoO ₃ powder, and x is preferably 0.05≦x≦0.25. After a large number of experimental studies, it has been shown that when x is less than 0.05, too little molybdenum is doped, resulting in too few lithium ion vacancies, which is not conducive to the conduction of lithium ions, resulting in a decrease in lithium ion conductivity. When x is greater than 0.25, Mo cannot completely enter the lattice to form impurities in the subsequent preparation process. At the same time, this part of Mo will react with other substances to generate other impurities, so that the garnet co-doped with gallium and molybdenum is finally obtained. Lithium-ion solid electrolytes contain many impurity phases, and the obtained material is not a single-phase substance, which will greatly affect the performance of the material. At the same time, when x is greater than 0.25, the concentration of lithium ions will also be too low, which is not conducive to the conduction of lithium ions. Because lithium ions can quickly migrate through these lithium ion vacancies to form lithium ion conduction, if the concentration of lithium ions is too low, If the amount of lithium ions is too small, the conductivity of lithium ions is likely to decrease.

Therefore, the range of x in the general formula should be strictly controlled within 0.05≤x≤0.25. Within this range, it can be ensured that the obtained garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum only contains a single phase. Enhanced material properties. At the same time, in this range, the lithium ion vacancy and the lithium ion concentration can be optimally matched, and the conduction with the lithium ion can be more powerful, thereby obtaining the best lithium ion conductivity.

In step S2, the grinding time is preferably 6-18 hours, and the particle size of the first material to be molded is preferably ≤10 μm. After a large number of experimental studies, it has been shown that when the particle size of the first material to be molded is too large, it is difficult to react during calcination in step S3, so the particle size of all powders is strictly controlled. The study found that when the particle size of the first molding material formed is ≤10 μm, the reaction between the powders in step S3 can proceed smoothly, and the smaller the particle size, the more sufficient the reaction is. The method of grinding is not limited to ball milling, and other methods can also be used for grinding. When ball milling is selected for grinding, the rotation speed is preferably 350-800 r/min, the ball milling solvent is preferably anhydrous ethanol or isopropanol, and the ball milling medium is preferably zirconia balls. Of course, the ball milling solvent and ball milling medium can also be selected from other substances. It depends on the actual situation. The temperature for drying after ball milling is preferably 80 to 120°C.

In step S3, the compression pressure during compression molding is preferably 100-300 MPa, and the pressure holding time is preferably 3-8 min, and cold pressing or other methods can be selected for compression. The thickness depends on the actual situation and needs. The calcination temperature is preferably 800 to 900° C., and the calcination time is preferably 6 to 12 hours. If the calcination temperature is too low, the solid-phase reaction between the powders cannot proceed normally. If the calcination temperature is too high, the grains that make up the powder will grow at high temperature, thereby affecting the properties of the final material. Therefore, the calcination temperature and calcination time should be strictly controlled. After a large number of experimental studies, it has been shown that when the calcination temperature is controlled at 800-900 °C and the calcination time is controlled between 6-12 h, the precursor composite obtained by calcination has Best activity, best performance.

In step S4, the grinding time is preferably 6-18h, and the particle size of the second material to be molded is preferably ≤10 μm. A large number of experimental studies have shown that when the particle size of the second material to be molded obtained after grinding is controlled to be less than or equal to 10 μm, the density of the material obtained during subsequent sintering is the best.

In step S5, the pressing pressure during pressing is preferably 100-300 MPa, the pressure holding time is preferably 3-8 min, the sintering temperature is preferably 1100-1200°C, and the sintering time is preferably 6-12 h. If the sintering temperature is too low, the resulting garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum will have many pores and poor compactness. If the sintering temperature is too high, Li _6.55-2x Ga _0.15 La ₃ Zr _2-x Mo _x O ₁₂ may react with other substances to generate impurities and affect the performance of the final material. Therefore, the sintering temperature and sintering time should be strictly controlled. After a large number of experimental studies, it was found that when the sintering temperature was controlled at 1100 to 1200 °C and the sintering time was controlled between 6 and 12 hours, the obtained material had the least porosity and was denser. Optimum, and within this range, the greater the sintering temperature and sintering time, the better the compactness.

To sum up, in this example, the garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum was prepared by simultaneously doping gallium and molybdenum elements into the garnet-type lithium-ion solid electrolyte (Li _6.55-2x Ga _0.15 La _{3 )} . Zr _2-x Mo _x O ₁₂ ), in which Ga ³⁺ replaces Li sites and exhibits extremely high electrical conductivity, which can stabilize the cubic phase without significantly changing the lattice parameters, and will generate lithium vacancies, which is beneficial to the ionization of lithium ions. Migration, the migration path of lithium ions is 96h-96h, 24d-96h-24d. Among them, 96h-96h determines its conductivity. When the concentration of lithium ions at 96h increases, the conductivity increases. Mo ⁶⁺ replaces the Zr site, which can generate lithium ion vacancies and increase the concentration of lithium ions at the 96h site. Moreover, the presence of molybdenum ions can also promote sintering and accelerate the densification process. The atomic radius of Mo is slightly smaller than that of Zr, and it is easy to enter the lattice. After replacing the Zr site, the lattice parameter can be reduced, thereby stabilizing the cubic phase. Mo ⁶⁺ -doped LLZO is very stable for electrode materials and has a wider electrochemical window.

Therefore, the use of Mo ⁶⁺ and Ga ³⁺ co-doping can greatly reduce the amount of gallium, thereby greatly reducing the cost, and at the same time, it can greatly improve the lithium ion conductivity, which is more conducive to the further development of garnet-type lithium ion solid electrolytes . At the same time, the solid-phase reaction method is used to synthesize the above-mentioned solid electrolyte in this embodiment, the preparation process is simple and the cost is low, and the finally obtained garnet-type lithium ion solid electrolyte co-doped with gallium and molybdenum also has the above-mentioned properties, and the compactness is improved. Great improvement.

The above are only preferred embodiments of the present invention, and are not intended to limit the invention in other forms. Any person skilled in the art may use the technical content disclosed above to change or remodel to equivalent embodiments of equivalent changes. . However, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solutions of the present invention still belong to the protection scope of the technical solutions of the present invention.

Claims (3)

1. A preparation method of a gallium and molybdenum co-doped garnet type lithium ion solid electrolyte is characterized by comprising the following steps:

s1, according to formula: li_6.55-2xGa_0.15La₃Zr_2-xMo_xO₁₂Weighing stoichiometric ratio of Li₂CO₃Powder of ZrO₂Powder of Ga₂O₃Powder, La₂O₃Powder and MoO₃Powder, wherein x is more than or equal to 0.05 and less than or equal to 0.25;

s2, mixing all the powder obtained in the step S1 together and grinding to form a first material to be molded;

s3, pressing and forming the first material to be molded, and then calcining to obtain a precursor compound;

s4, grinding the precursor compound to form a second material to be molded;

s5, pressing and forming the second material to be molded, and then sintering to obtain the gallium and molybdenum co-doped garnet type lithium ion solid electrolyte;

in step S5, after the second material to be molded is used as a mother powder after being pressed and formed into a tablet, the pressed tablet is embedded in the mother powder and then sintered; the pressing pressure during the pressing forming is 100-300 MPa, the pressure maintaining time is 3-8 min, the sintering temperature is 1100-1200 ℃, and the sintering time is 6-12 h;

in step S2, grinding for 6-18 h, wherein the particle size of the first material to be molded is less than or equal to 10 μm;

in step S2, grinding by adopting a ball milling mode, wherein the rotating speed during ball milling is 350-800 r/min, the ball milling solvent is absolute ethyl alcohol or isopropanol, and the ball milling medium is zirconia balls;

in step S3, the pressing pressure during the press forming is 100 to 300MPa, the pressure maintaining time is 3 to 8min, the calcining temperature is 800 to 900 ℃, and the calcining time is 6 to 12 hours.

2. The method of claim 1, wherein in step S1, the stoichiometrically scaled Li is prepared₂CO₃The powder included a 10% capacity balance.

3. The method for preparing the gallium and molybdenum co-doped garnet-type lithium ion solid electrolyte as claimed in claim 1 or 2, wherein in step S4, the grinding time is 6-18 h, and the particle size of the second material to be molded is less than or equal to 10 μm.

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