Solid electrolyte material, preparation method thereof and solid-state battery

Abstract

The invention discloses a solid-state electrolyte material, a preparation method thereof and a solid-state battery, and relates to the technical field of solid-state batteries, the chemical general formula of the solid-state electrolyte material is Li < 0.33-A < x > La < 0.557 > TiO < 3 + y > B + zC, an auxiliary agent A is Na2CO3 or K2CO3, an auxiliary agent B is a transition metal oxide, an auxiliary agent C is a low-temperature auxiliary agent, x is more than 0 and less than or equal to 0.01, y is more than 0 and less than or equal to 0.08, and z is more than 0 and less than or equal to 0.05. According to the material, on the basis of LLTO, by adding the transition metal oxide with good conductivity, the conductivity of the material can be improved on the premise that the quantity of Li is not increased; by adding the low-temperature additive C, the sintering temperature of the material can be reduced, Li is prevented from volatilizing and overflowing, the material forms a perovskite type crystal with a compact structure at a relatively low temperature, the compactness of the crystal is improved, and the conductivity of the material is further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of micro solid-state batteries, and in particular to a micro solid-state electrolyte material and a preparation method thereof. Background Art

[0002] Compared with traditional liquid electrolytes, solid-state electrolytes have the following advantages: 1) Higher safety performance. Because solid-state electrolytes have a higher melting point and stability, they can avoid safety hazards such as leakage and combustion of liquid electrolytes; 2) Longer service life. Compared with liquid electrolytes, solid-state electrolytes have a longer service life, which greatly reduces the cost and frequency of electrolyte replacement; 3) Better temperature resistance. Solid-state electrolytes have high melting point and higher thermal stability, enabling them to operate at higher temperatures for use in more application scenarios; 4) Higher energy density. Solid-state electrolytes have higher ion conductivity, which can support higher charge density and energy density, thereby improving battery performance.

[0003] Li 0.33 La 0.557 TiO3 (LLTO) is a highly researched oxide solid electrolyte. Its advantages include: 1) good chemical stability: oxide solid electrolytes are highly stable against redox reactions and other electrochemical reactions, which can extend battery life; 2) high ionic conductivity: the high ionic conductivity of oxide solid electrolytes facilitates ion transport within the battery, resulting in faster charge and discharge efficiency and higher energy density; 3) inhibition of lithium dendrite growth: oxide solid electrolytes can effectively inhibit the growth of lithium dendrites, reducing the risk of lithium dendrites penetrating the electrolyte layer and causing short circuits, thereby improving battery safety; 4) high temperature resistance: oxide solid electrolytes typically have high melting points and good thermal stability, maintaining good performance in high-temperature environments, making them suitable for battery applications under high-temperature conditions; 5) no need for solvent addition: compared to some liquid electrolytes, oxide solid electrolytes do not require the addition of solvents during the preparation process, reducing environmental pollution and fire risks, and promoting the sustainable development of batteries. Therefore, as a typical oxide solid electrolyte, LLTO has potential application prospects in solid-state battery technology, which can be used to improve battery performance and safety.

[0004] However, due to the relative density and crystal structure of LLTO, which affect the material's conductivity, a higher sintering temperature (greater than 1100 degrees Celsius) is usually adopted during the preparation process to improve the material's conductivity. This is to obtain LLTO crystals with a high relative density and a perovskite structure. However, when the sintering temperature is increased, Li volatilization and overflow are easily caused, which in turn leads to a decrease in the material's conductivity. To compensate for the Li loss caused by high sintering temperature, the ratio of Li source in the raw material needs to be increased, which in turn leads to increased costs and even makes it difficult to obtain the corresponding LLTO crystal structure.

[0005] It can be seen that the existing technology still needs to be improved and enhanced. Summary of the Invention

[0006] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a solid electrolyte material and a preparation method thereof, aiming to solve the defects of the existing LLTO obtained by high-temperature sintering, such as low density and insufficient conductivity.

[0007] A solid electrolyte material, wherein the chemical formula of the material is: Li 0.33-Ax La 0.557 TiO3+yB+zC, wherein the auxiliary agent A is Na2CO3 or K2CO3, the auxiliary agent B is a transition metal oxide, the auxiliary agent C is a low-temperature auxiliary agent, the x is: 0<x≤0.01, the y is: 0<y≤0.08, and the z is: 0<x≤0.05.

[0008] In the solid electrolyte material, the auxiliary agent A is Na2CO3 or K2CO3.

[0009] In the solid electrolyte material, the additive B includes one or more of CoO, CuO, FeO, NiO, ZnO, and NbO.

[0010] In the solid electrolyte material, the additive C is one of Li2O-B2O3-SiO2 (5:3:1) or La2O3-B2O3-ZnO (2:6:1).

[0011] In the solid electrolyte material, the purity of the Li2O-B2O3-SiO2 (5:3:1) or La2O3-B2O3-ZnO (2:6:1) is ≥99.5%.

[0012] A method for preparing a solid electrolyte material, wherein the method is used to prepare the solid electrolyte material as described above, wherein the solid electrolyte material is a circular sheet, and the method comprises the steps of: Adding additive A to the ceramic component, the ceramic component is mixed, ball-milled, dried, and sieved to obtain a first powder; the ceramic component is composed of lithium hydroxide, lanthanum oxide and titanium oxide; Take additives B and C, grind and sieve them, add them to the first powder, and mix them to obtain a second powder; calcining the second powder at 600-700 degrees to obtain a frit; Grinding, ball milling, and sieving the frit to obtain a third powder; Filling the third powder into a mold and statically pressing it into a round tablet; The disc is placed in a muffle furnace and fired at 900-1000° C. for 4-6 hours. After sintering, it is polished to obtain a disc-shaped solid electrolyte material.

[0013] In the preparation method of the solid electrolyte, in the first powder, the mass of the auxiliary agent A is 0.15% to 1.01% of the first powder, in the second powder, the mass of the auxiliary agent B is 0.21% to 1.05% of the first powder, and the mass of the auxiliary agent C is 0.91% to 1.18% of the first powder.

[0014] In the method for preparing the solid electrolyte material, the static pressure of the third powder in the mold and static pressing into a disc is 100 to 300 MPa.

[0015] In the method for preparing the solid electrolyte material, when firing the solid electrolyte disc, the heating rate of the muffle furnace is 10° C. / min.

[0016] The method for preparing the solid electrolyte material further includes a step of dehumidifying the ceramic components before mixing the ceramic components to remove moisture from the lithium hydroxide, lanthanum oxide and titanium oxide.

[0017] A solid-state battery, wherein the solid-state battery uses the solid electrolyte material as the electrolyte.

[0018] The present invention provides a solid electrolyte material. Based on LLTO, the material is added with additives A, B, and C. The additive A is Na2CO3 or K2CO3, which helps to broaden the ion transmission channel and improve the ion conductivity. The additive B is a transition metal oxide with good conductivity, which can improve the conductivity of the material without increasing the amount of Li. The additive C is a low-temperature additive, which can reduce the sintering temperature of the material, prevent Li volatilization and overflow, and enable the material to form a dense and stable perovskite crystal at a lower temperature, thereby increasing the relative density of the crystal and thus improving the conductivity of the material.

[0019] The second aspect of the present invention provides a method for preparing a solid electrolyte material. By adjusting the raw material composition, adding an additive A that widens the ion channel, adding an additive B with conductive properties, and an additive C that reduces the sintering temperature, the ceramic material can form LLTO crystals with a perovskite structure at a lower sintering temperature. This not only prevents Li overflow, but also the prepared crystals have high density, high relative density, and good conductivity, and can be widely used in solid-state batteries.

[0020] The solid-state battery prepared using this material has good conductivity, high charge density and energy density, as well as higher temperature resistance, and therefore has greater application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The XRD patterns of Example 1, Example 2 and Example 3 are shown.

[0022] Figure 2 These are the impedance spectra of Example 1, Example 2, Example 3, and Example 4.

[0023] Figure 3 This is a scanning electron microscope image of Example 1. DETAILED DESCRIPTION

[0024] The present invention provides a solid electrolyte material, a preparation method thereof, and a solid-state battery. To make the objectives, technical solutions, and effects of the present invention more clear and explicit, the present invention is further described in detail with reference to the following examples. It should be understood that the specific examples described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0025] The present invention provides a solid electrolyte material, which is used for solid-state batteries and has a general chemical formula of Li 0.33- Ax La 0.557 TiO3+yB+zC, wherein the auxiliary agent A is NaOH or KOH, which helps to broaden the ion transmission channel and improve the ion conductivity. The auxiliary agent B is a transition metal oxide with good conductivity, which can improve the conductivity of the material without increasing the amount of Li. The auxiliary agent C is a low-temperature auxiliary agent, which can reduce the sintering temperature of the material, avoid the volatilization and overflow of Li, and enable the material to form a dense and stable perovskite crystal at a lower temperature, thereby increasing the relative density of the crystal and thus improving the conductivity of the material. The x is: 0<x≤0.01, the y is: 0<y≤0.08, and the z is: 0<x≤0.05. By controlling x, y and z, a material with high ionic conductivity, high density, high relative density, and a perovskite-type solid electrolyte is obtained. In a preferred embodiment, the auxiliary agent A is NaOH or KOH, which can broaden the ion transmission path and greatly improve the ion conductivity.

[0026] In a preferred embodiment, the additive B includes one or more of CoO, CuO, FeO, NiO, ZnO, and NbO. Although the amount of these metal oxides added is very small, they can accelerate the migration of lithium ions and improve the conductivity of the material.

[0027] In a preferred embodiment, the additive C is one of Li2O-B2O3-SiO2 (5:3:1) or La2O3-B2O3-ZnO (2:6:1). Among them, the Li2O-B2O3-SiO2 (5:3:1) or La2O3-B2O3-ZnO (2:6:1) has a fluxing effect, which can be transformed into a liquid phase at a relatively low temperature, and then infiltrate the ceramic particles, so that the ceramic particles complete the "dissolution-precipitation" mass transfer process under liquid phase conditions, thereby realizing the formation of perovskite-type crystals at a relatively low sintering temperature, avoiding Li volatilization and overflow, and at the same time densifying the material and having better conductivity. At the same time, lowering the sintering temperature can also save energy, reduce emissions, and reduce costs; the SiO2 in the Li2O-B2O3-SiO2 (5:3:1) or the ZnO2 in the La2O3-B2O3-ZnO (2:6:1) can replace part of the Li position during sintering and crystallization, thereby making the formed lattice structure more stable and having better conductivity.

[0028] However, when the purity of the added Li2O-B2O3-SiO2 (5:3:1) or La2O3-B2O3-ZnO (2:6:1) is insufficient, impurities may be introduced. These impurities may affect crystal formation, forming impurities, resulting in a decrease in the relative density of the material and ultimately a decrease in the conductivity of the material. In a preferred embodiment, the purity of the Li2O-B2O3-SiO2 (5:3:1) or La2O3-B2O3-ZnO (2:6:1) is ≥99.5%, which contains fewer impurities and has a minimal impact on the relative density of the material.

[0029] The second aspect of the present invention further provides a method for preparing a solid electrolyte material, which is used to prepare the solid electrolyte material described above. The solid electrolyte material prepared by the method is a circular sheet material, which is convenient for battery assembly. The method comprises the steps of: Step S10, according to the ratio of the ceramic component, the additive A is added to the ceramic component, the ceramic component is mixed, ball-milled, dried, and sieved to obtain a first powder; the ceramic component is composed of lithium hydroxide, lanthanum oxide and titanium oxide; Step S20: grind and sieve the additives B and C, add them to the first powder, and mix them to obtain a second powder; Step S30, calcining the second powder at 600-700 degrees to obtain a frit; Step S40: Grinding, ball-milling, and sieving the frit to obtain a third powder; Step S50: Filling the third powder into a mold and statically pressing it into a round tablet; Step S60: placing the disc in a muffle furnace and firing at 900-1000° C. for 4-6 hours. After sintering, polishing is performed to obtain a disc-shaped solid electrolyte material.

[0030] In this preparation method, by adjusting the raw material composition and sintering temperature, a perovskite-type crystal is prepared under the condition of a relatively low sintering temperature through two firing processes. The crystal has a high relative density and good conductivity. In step S30, the gas and volatile impurities in the material are discharged through low-temperature calcination at 800 to 900°C, thereby avoiding the appearance of pores in the subsequent sintered product, which affects the relative density and conductivity of the material. At the same time, low-temperature sintering allows the various components to be mixed more evenly, which is more conducive to C exerting its fluxing effect. In step S60, under the action of the auxiliary agent C, a liquid phase can be formed at only a sintering temperature of 900 to 1000°C. The liquid phase is used to infiltrate the ceramic particles, facilitating the "dissolution-precipitation" mass transfer process of the ceramic particles, thereby achieving sintering at a relatively low temperature, forming perovskite-type crystals with a relatively high relative density, and thus having a relatively high conductivity.

[0031] In the first powder, the amount of additive A added will affect the conductive properties of the material. In the second powder, the amount of additives B and C added will affect the conductive properties and sintering temperature of the material. If too much or too little is added, it will be difficult to obtain the corresponding crystalline material. In this regard, in a preferred embodiment, in the first powder, the mass of A is 0.01% to 0.03% of the first powder. In the second powder, the mass of B is 0.19% to 1.02% of the first powder, and the mass of C is 0.89% to 1.12%. The addition amount within this range can reduce the sintering temperature, and the prepared solid electrolyte material has a higher density and relative density, and has better conductivity.

[0032] In a preferred embodiment, the calcination temperature in step S30 is 660° C., and the firing temperature in step S60 is 940° C., which has a better sintering effect. The obtained solid electrolyte material has a higher density and relative density and good conductivity.

[0033] In step S60, since the heating rate affects the molding effect of the material, if the heating rate is too fast, the additive C melts too quickly, resulting in insufficient wetting of the ceramic material, prone to collapse, and poor molding effect, or even unevenness. In this regard, in a preferred embodiment, in step S60, when firing the solid electrolyte disc, the heating rate of the muffle furnace is 8-12°C / min, preferably 10°C / min. Heating at this rate allows the molten additive C to effectively wetting the various components of the ceramic material, preventing collapse. The resulting solid electrolyte disc has a smooth surface, good molding effect, and good conductivity.

[0034] To achieve a better molding result after firing, in step S50, the third powder is placed in a mold and statically pressed to form a rounded block of material. This, in turn, creates a specific corresponding shape after firing. To prevent the third powder from loosening after forming, the static pressure must be controlled. In a preferred embodiment, the static pressure in step S50 is between 100 and 300 MPa. Within this pressure range, the third powder is dense, uniform, and difficult to loosen, resulting in a high relative density of the sintered material.

[0035] It should be noted that the diameter of the disc is 13 mm and the thickness is 1.7 mm. Because the moisture content in the raw materials can affect crystal formation and result in a decrease in relative density, a preferred embodiment includes a dehumidification step for the lithium hydroxide, lanthanum oxide, and titanium dioxide before step S10. Specifically, the ceramic components are dried in an oven or muffle furnace at 80°C to a constant weight to remove moisture from the lithium hydroxide, lanthanum oxide, and titanium dioxide.

[0036] Since the fired disc is not smooth enough, which will affect its conductivity, in step S60, different types of gauze are used to polish the disc surface to make it smoother and flatter, so as to improve its conductivity.

[0037] The third aspect of the present invention also provides a solid-state battery, which uses lithium iron phosphate as the positive electrode, a lithium sheet as the negative electrode, and uses the disc-shaped solid electrolyte material as described above as the electrolyte. Therefore, it has good conductivity, high charge density and energy density, and also has higher temperature resistance, so it has a wider range of applications.

[0038] To further illustrate the solid electrolyte material and its preparation method, and the solid-state battery provided by the present invention, the following examples are provided. Example

[0039] A solid electrolyte material is prepared by the following steps: Step S10, taking 3.435 parts of LiOH, 34.302 parts of La2O3, 30.189 parts of TiO2, 0.6 parts of Na2CO3, 0.376 parts of CoO, and 0.163 parts of Li2O-B2O3-SiO2 (5:3:1), first drying NaOH, Li2OH, La2O3, and TiO2 in an oven at 80°C to a water-free state, then mixing, ball-milling, drying, and passing through an 80-mesh sieve to obtain a first powder; Step S20, CoO and Li2O-B2O3-SiO2 (5:3:1) are stirred and mixed, and ground and passed through an 80-mesh sieve, and then added to the first powder and mixed to obtain a second powder; Step S30, calcining the second powder at 660° C. for 5 h to obtain a frit; Step S40, grinding, ball milling, and passing the frit through a 200-mesh sieve to obtain a third powder; Step S50: Fill the mold with the third powder and statically press at a pressure of 100 MPa for 10 minutes to obtain a round tablet; Step S60: Place the circular pressed piece in a muffle furnace, heat it to 940° C. at a rate of 10° C. / min, and keep it at 940° C. for 5 hours. After sintering, polish it to obtain a solid electrolyte disc.

[0040] The preparation methods of Examples 2-6 are the same as that of Example 1, except that the addition amounts of additives A and B, calcination temperatures, static pressures, and sintering temperatures are different, as shown in Table 1.

[0041] Table 1 Composition and process parameters of the embodiment

[0042] The solid electrolyte materials prepared in Examples 1-3 were subjected to X-ray diffraction analysis. The analysis results are as follows: Figure 1 As shown by Figure 1 It can be seen that Examples 1-3 can all obtain LLTO crystals with a perovskite-type crystal form, and no impurity phase is generated due to the presence of additives.

[0043] The solid electrolytes prepared in Examples 1-4 were subjected to impedance spectrum analysis, as shown in the figure. Figure 2 It can be seen that the impedance of the LLTO solid electrolytes of Examples 1-4 is relatively small, below 900Ω, which indicates that the LLTO solid electrolyte prepared by low-temperature sintering has very high ionic conductivity.

[0044] The solid electrolyte material disc prepared in Example 1 was analyzed by scanning electron microscopy before polishing. The results are as follows: Figure 3 As shown by Figure 3It can be seen that the ceramic sheet of Example 1 has no pores at the microscopic level, unclear grain boundaries, and a dense surface, indicating that the material has a very high relative density.

[0045] In addition, the following comparative examples are given.

[0046] Comparative Example 1 It is basically the same as Example 3, except that Li2O-B2O3-SiO2 (5:3:1) is not added.

[0047] Comparative Example 2 It is basically the same as Example 3, except that FeO is not added.

[0048] Comparative Example 3 It is basically the same as Example 3, except that Na2CO3 is not added to S10. Comparative Example 4 It is basically the same as Example 3, except that there are no steps S30 and S40 during the preparation, and the second powder is directly processed into steps S50 and S60.

[0049] Comparative Example 5 It is basically the same as Example 3, except that the sintering temperature in step S60 is 1100°C.

[0050] The solid electrolyte materials prepared in Examples 1-6 and Comparative Examples 1-5 were tested for density, relative density, and separation conductivity. The specific test results are shown in Table 2.

[0051] Table 2. Performance test results Outer diameter (mm) Thickness (mm) Density (g / side) Relative density (%) Ionic conductivity (ms / cm) Example 1 10.32 1.67 4.78 95.4 0.71 Example 2 10.31 1.72 4.87 97.2 0.78 Example 3 10.28 1.71 4.81 96 0.91 Example 4 10.29 1.69 4.85 96.8 0.51 Example 5 10.35 1.73 4.79 95.6 0.77 Example 6 10.25 1.71 4.81 96 0.77 Comparative Example 1 11.51 1.81 4.58 91.4 0.14 Comparative Example 2 11.43 1.83 4.64 92.6 0.16 Comparative Example 3 10.32 1.69 4.81 96.1 0.41 Comparative Example 4 11.21 1.82 4.59 91.6 0.09 Comparative Example 5 11.32 1.84 4.58 91.5 0.12 As can be seen from Table 2, the solid electrolyte materials described in Examples 1-6 all have high density, relative density and ionic conductivity, indicating that the preparation method of the solid electrolyte described in the present invention can achieve the improvement of the density, relative density and conductivity of LLTO while reducing the sintering temperature.

[0052] However, since Comparative Example 1 did not add Li2O-B2O3-SiO2 (5:3:1), it was unable to form perovskite-type LLTO crystals. As a result, its conductivity was poor, only 0.14ms / cm. Since Comparative Example 2 did not add SiO2, it was difficult to form stable crystals, resulting in insufficient conductivity. Since Comparative Example 3 did not add additive A, the material density and relative density were high, and its conductivity was lower than that of Example 1. Since Comparative Example 4 did not perform the calcination step and the second powder was directly sintered, it was difficult to form crystals at a lower temperature, and ultimately the conductivity was very poor. Since the sintering temperature of Comparative Example 5 was too high, although crystals could be formed with very high density and relative density, the high temperature caused Li to volatilize and overflow, resulting in poor conductivity compared to Example 1.

[0053] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention, and all these changes or substitutions should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A solid electrolyte material, characterized in that The general chemical formula of the material is: Li 0.33-Ax La 0.557 TiO3+yB+zC, wherein the auxiliary agent A is Na2CO3 or K2CO3, the auxiliary agent B is a transition metal oxide, the auxiliary agent C is a low-temperature auxiliary agent, the x is: 0<x≤0.01, the y is: 0<y≤0.08, and the z is: 0<x≤0.

05.

2. The solid electrolyte material according to claim 1, characterized in that The auxiliary agent A is Na2CO3 or K2CO 3， The auxiliary agent B includes one or more of CoO, CuO, FeO, NiO, ZnO, and NbO.

3. The solid electrolyte material according to claim 1, characterized in that The auxiliary agent C is one of Li2O-B2O3-SiO2 (5:3:1) or La2O3-B2O3-ZnO (2:6:1).

4. The solid electrolyte material according to claim 4, characterized in that The purity of the Li2O-B2O3-SiO2 (5:3:1) or La2O3-B2O3-ZnO (2:6:1) is ≥99.5%.

5. A method for preparing a solid electrolyte material, characterized in that: For preparing the solid electrolyte material according to any one of claims 1 to 5, wherein the solid electrolyte material is a circular sheet, the method comprises the steps of: Adding additive A to the ceramic component, the ceramic component is mixed, ball-milled, dried, and sieved to obtain a first powder; the ceramic component is composed of lithium hydroxide, lanthanum oxide and titanium oxide; Take additives B and C, grind and sieve them, add them to the first powder, and mix them to obtain a second powder; calcining the second powder at 600-700 degrees to obtain a frit; Grinding, ball milling, and sieving the frit to obtain a third powder; Filling the third powder into a mold and statically pressing it into a round tablet; The disc is placed in a muffle furnace and fired at 900-1000° C. for 4-6 hours. After sintering, it is polished to obtain a disc-shaped solid electrolyte material.

6. The method for preparing a solid electrolyte according to claim 6, wherein: In the first powder, the mass of the auxiliary agent A is 0.15% to 1.01% of the first powder; in the second powder, the mass of the auxiliary agent B is 0.21% to 1.05% of the first powder; and the mass of the auxiliary agent C is 0.91% to 1.18% of the first powder.

7. The method for preparing a solid electrolyte according to claim 6, wherein: The static pressure of the third powder in the mold and statically pressed into a disc is 100-300 MPa.

8. The method for preparing a solid electrolyte according to claim 6, wherein: When firing the solid electrolyte disc, the heating rate of the muffle furnace is 10°C / min.

9. The method for preparing a solid electrolyte according to claim 6, wherein: Before mixing the ceramic components, there is a step of dehumidifying the ceramic components to remove moisture from lithium hydroxide, titanium oxide and lanthanum oxide.

10. A solid-state battery, characterized in that: The solid-state battery uses the solid electrolyte material according to any one of claims 1 to 4 as an electrolyte.

Images