Modified Li3MX6 Solid Electrolyte Material, Preparation Method, Application Thereof and Lithium Metal Solid-State Battery

Abstract

The present invention belongs to the field of lithium metal solid-state batteries, and particularly relates to a modified Li3MX6 solid electrolyte material, a preparation method, an application thereof, and a lithium metal solid-state battery. The preparation method is as follows: a mixed solution containing LiX, MX3, a regulator of formula 1 (#imgabs0#), and a solvent is frozen under negative pressure and at a temperature of -100 °C to -10 °C, and then the frozen product is annealed to obtain the product. The present invention innovatively uses the structure of formula 1 to participate in the nucleation reaction of LiX and MX3 under negative pressure freezing, and then performs annealing treatment. In this way, based on the electron cloud of the conjugated state N in the structure of formula 1, the nucleation of Li3MX6 can be optimized, and it is helpful to optimize its surface electronic structure and energy band structure, thereby facilitating the optimization of the M 3+ redox in the lithium metal solid-state battery, significantly improving its stability, especially facilitating the improvement of the low-temperature stability of the assembled lithium metal solid-state battery.

Description

Technical Field

[0001] The present invention belongs to the field of solid-state batteries, and particularly relates to the field of solid electrolytes for solid-state batteries. Background Art

[0002] With the rapid development of new energy technologies, lithium-ion batteries have been widely used in electric vehicles, energy storage systems, and portable electronic devices. However, traditional organic liquid electrolyte batteries face problems such as flammability, easy leakage, and low cycle stability, which seriously restrict the safety and long-life development of batteries. Therefore, all-solid-state lithium batteries (ASSLBs, All-Solid-State Lithium Batteries) based on solid electrolytes have become a key development direction for the next-generation energy storage technologies due to their high safety, high energy density, and excellent cycle life. Among them, the ionic conductivity, interfacial stability, and chemical stability of solid electrolytes directly determine the comprehensive performance of the batteries. Therefore, the research on high-performance solid electrolyte materials is crucial.

[0003] In recent years, Li3MX6 has received extensive attention due to its high lithium-ion conductivity, good interfacial wettability, and relatively low interfacial impedance. Compared with sulfide and oxide electrolytes, the structure of Li3MX6 usually exhibits a lower degree of polarization, with lower interfacial stress and more excellent chemical stability. The aforementioned Li3MX6, such as the widely used Li3InCl6, is considered to be one of the most promising electrolytes due to its room-temperature lithium-ion conductivity as high as ~10 -3 S / cm, wide electrochemical window, and good processability, which can effectively promote the development of high-performance solid-state lithium batteries.

[0004] Although Li3MX6 electrolytes exhibit excellent ion transport performance and interfacial adaptability, their chemical stability with lithium metal anodes is still an urgent problem to be solved. The M 3+ ions are easily reduced to metal M by lithium metal in a strong reducing environment, resulting in the destruction of the electrolyte lattice structure and the formation of an electron-conducting phase at the interface, which further accelerates the interfacial side reactions and affects the long-term stability of the batteries. This problem not only reduces the Coulombic efficiency of the batteries but also may accelerate the growth of lithium dendrites, ultimately leading to short circuits and failures. Therefore, how to improve the stability of Li3MX6 electrolytes towards lithium metal and inhibit the irreversible reduction of M 3+ is one of the key scientific issues for improving the performance of lithium metal solid-state batteries.

[0005] To address this problem, the existing improvement methods mainly focus on ion doping, structure regulation, and interfacial modification, etc.

[0006] For example, the Chinese patent document with the publication number CN112216863A discloses a halogenated solid electrolyte material with the chemical formula Liα M β M' γ A δ A' ε ; wherein, M is selected from Group IIIB elements and / or Group IIIA elements, M' is selected from at least one of Group IIA elements, Group IB elements, Group IIB elements, Group IVB elements, Group VIII elements, and Group VIII elements; A is selected from at least one of F-, Cl-, Br-, and I-; A' is selected from SO4 2- and / or SiO3 2- ; 1≤α≤3, 0≤β≤1, 0≤γ≤2, 0<δ≤6, 0≤ε≤1. Again, the Chinese patent document with the publication number CN113845140A discloses a fluorine-doped halide solid electrolyte.

[0007] In summary, there are some reports in the prior art on improving the performance of Li3MX6 by doping, but the modification methods still need to be further expanded, and the performance of the materials, especially the low-temperature performance, needs to be further improved. Summary of the Invention

[0008] Aiming at the problems faced by Li3MX6, the present invention provides a preparation method of a modified Li3MX6 solid electrolyte material, aiming to prepare a Li3MX6 solid electrolyte material with excellent performance.

[0009] The second object of the present invention is to provide the modified Li3MX6 solid electrolyte material prepared by the preparation method and its application in a lithium metal solid battery.

[0010] The third object of the present invention is to provide a lithium metal solid battery comprising the modified Li3MX6 solid electrolyte material.

[0011] When Li3MX6 is applied to a lithium metal solid battery, the M in Li3MX6 3+ ions are easily reduced by lithium metal to metal M, which easily causes the destruction of the electrolyte lattice structure, easily accelerates the interfacial side reaction, and further affects the long-term stability and low-temperature performance of the battery. Aiming at this problem, through in-depth research, the present invention provides the following solutions:

[0012] A preparation method of a modified Li3MX6 solid electrolyte material, which is obtained by freezing a mixed solution containing LiX, MX3, a regulator of formula 1, and a solvent under negative pressure and at a temperature of -100°C to -10°C, and then annealing the frozen product;

[0013] In Li3MX6, LiX, and MX3, the X is F, Cl, Br, or I; the M includes at least one of In, Al, Ga, Sc, La, Sm, and Y;

[0014] Formula 1

[0015] R1 is H or an alkyl group with 1 to 6 carbon atoms;

[0016] R2 is H, an alkyl group with 1 to 6 carbon atoms, an alkoxy group with 1 to 6 carbon atoms, a halogen, trifluoromethyl or nitro;

[0017] Y is CH or N.

[0018] In the present invention, a compound with the structure of Formula 1 is innovatively used to participate in the negative-pressure freezing nucleation reaction of LiX and MX3, and then annealing treatment is carried out. For example, based on the electron cloud of the conjugated state N in the structure of Formula 1, the nucleation of Li3MX6 can be optimized, and it helps to optimize the electronic structure and energy band structure on its surface, thereby facilitating the effective inhibition of M 3+ in the metal lithium solid-state battery from undergoing redox reactions, reducing interfacial side reactions, and thus effectively improving the stability and low-temperature stability of the assembled metal lithium solid-state battery.

[0019] In the present invention, X is Cl and M is In.

[0020] In the present invention, the molar ratio of LiX to MX3 is 3 to 3.2:1.

[0021] The Formula 1 regulator includes a Formula 1A regulator and a Formula 1B regulator. Among them, the weight ratio of the Formula 1A regulator to the Formula 1B regulator is 1:0.2 to 10 (further can be 1:0.5 to 2);

[0022] Formula 1A

[0023] Formula 1B.

[0024] The research of the present invention also shows that the combination of compounds with the structures of Formula 1A and Formula 1B can unexpectedly achieve synergy, which helps to further improve the interfacial stability of Li3MX6 in the metal lithium solid-state battery, and thus improve its stability and low-temperature performance.

[0025] In the Formula 1A and Formula 1B, R1 and R2 can be H or an alkyl group with 1 to 3 carbon atoms.

[0026] The Formula 1 regulator is 1 to 5 wt.% of the total weight of LiX and MX3, and further can be 1 to 3 wt.%.

[0027] In the present invention, the solvent includes at least one of tetrahydrofuran, toluene, and cyclohexanone. For example, it can be a mixed solvent of tetrahydrofuran, toluene, and cyclohexanone with a volume ratio of 60 to 70:15 to 30:15 to 30.

[0028] In the present invention, the negative pressure is a pressure lower than the atmospheric pressure, for example, a pressure below 100 Pa.

[0029] In the present invention, the temperature of the freezing treatment can be from -80°C to -10°C.

[0030] In the present invention, the freezing process includes a gradient freezing treatment process, and its steps sequentially include: the first-stage freezing process at temperature T1, the second-stage freezing process at temperature T2, and the third-stage freezing process at temperature T3;

[0031] Among them, temperature T1 is from -20°C to -10°C; temperature T2 is from -40°C to -30°C; temperature T3 is from -60°C to -50°C.

[0032] Research in the present invention shows that with the assistance of the regulator of formula 1 and further combined with the gradient freezing treatment process, it helps to further optimize the electronic and energy band structures of the material, and helps to further improve the stability and low-temperature performance of the prepared material.

[0033] In the present invention, the time of the freezing treatment is 1 - 10 h, and further can be 2 - 4 h.

[0034] In the present invention, when the gradient freezing treatment process is selected, the time of the first-stage freezing treatment can be 20 - 30 min, the time of the second-stage freezing treatment can be 30 - 40 min, and the time of the third-stage freezing treatment can be 60 - 90 min.

[0035] In the present invention, the atmosphere for annealing is a protective atmosphere.

[0036] In the present invention, the annealing temperature is 200 - 300°C; further can be 210 - 240°C.

[0037] In the present invention, the annealing time is 2 - 10 h, and further can be 4 - 8 h.

[0038] The present invention also provides a modified Li3MX6 solid electrolyte material prepared by the described preparation method.

[0039] The preparation method described in the present invention can endow the material with special physical and chemical characteristics, and the material prepared by the preparation method has excellent adaptability to lithium metal solid-state batteries, and can effectively inhibit the precipitation of M in Li3MX6 3+ and can effectively improve its electrochemical stability, for example, improve its stability at low temperatures.

[0040] The present invention also provides the application of the modified Li3MX6 solid electrolyte material, using it as a solid electrolyte for lithium metal solid-state batteries.

[0041] In the present invention, based on the conventional principles and ideas of solid-state batteries, the modified Li3MX6 solid electrolyte material can be used to prepare the required solid electrolyte sheet and the lithium metal solid-state battery.

[0042] For example, by a pressing method, the modified Li3MX6 solid electrolyte material of the present invention can be pressed into a solid electrolyte sheet. The pressing pressure can be adjusted as needed. For example, it can be 50 - 500 MPa.

[0043] In the present invention, the negative electrode of the lithium metal solid-state battery is a lithium metal negative electrode. The positive electrode can be a positive electrode well-known in the industry. For example, the positive electrode material of the positive electrode includes a positive electrode active material, an electrolyte, and a conductive agent. The positive electrode active material can be components such as NCM ternary materials, lithium cobaltate, lithium nickelate, lithium iron phosphate, etc. The electrolyte is the modified Li3MX6 solid electrolyte material of the present invention. The conductive agent can be conventional conductive agent components such as conductive carbon black and acetylene black. The weights of the positive electrode active material, electrolyte, and conductive agent can be adjusted as needed. For example, they can be 50 - 80:10 - 50:1 - 10; further, they can be 60 - 70:25 - 35:5. In the present invention, the positive electrode can be obtained by pressing the positive electrode material. The pressing pressure can be, for example, 50 - 500 MPa.

[0044] The present invention also provides a lithium metal solid-state battery, including an electrode assembly in which a positive electrode, an electrolyte, and a negative electrode are combined. The electrolyte is the modified Li3MX6 solid electrolyte material of the present invention; the negative electrode is lithium metal.

[0045] Beneficial effects

[0046] The present invention innovatively uses the structure of formula 1 to participate in the negative-pressure freezing nucleation reaction of LiX and MX3, and then annealing treatment is carried out. This helps to optimize the electronic structure and energy band structure on its surface, and further helps to optimize the redox of M in the lithium metal solid-state battery. 3+ This significantly improves its stability, especially helps to inhibit the low-temperature stability of the assembled lithium metal solid-state battery and suppresses interfacial side reactions.

[0047] The research of the present invention also shows that by using the combination of formula 1A and formula 1B, and using the gradient freezing treatment process, the synergy of the process can be further optimized, which helps to further optimize the electronic structure and energy band structure of the Li3MX6 material. This helps to further strengthen the adaptation synergy of the material to lithium metal, and helps to further enhance the stability and low-temperature performance of the assembled lithium metal solid-state battery. Description of the drawings

[0048] Figure 1 It is the Nyquist diagram of the electrochemical impedance of Example 1;

[0049] Figure 2 It is the graph of the cycle test results of the lithium symmetric battery in Example 1;

[0050] Figure 3 It is the charge-discharge cycle diagram of the all-solid-state battery in Example 1. Specific implementation mode

[0051] Example 1

[0052] Step 1:

[0053] Select high-purity LiCl (99.9%) and InCl3 (99.99%), mix and disperse them in a solvent according to the chemical molar ratio of 3:1 to form a mixed solution. The solvent includes tetrahydrofuran, toluene and cyclohexanone with a volume ratio of 70:15:15.

[0054] Step 2:

[0055] Then add a regulator accounting for 2% of the total mass of LiCl and InCl3 to the above mixed solution. The regulator includes Formula 1A1 ( ) and Formula 1B1 ( ) with a weight ratio of 1:1, and stir evenly.

[0056] Step 3:

[0057] Freeze the mixed solution in Step 2 under vacuum. The freezing process includes a process of freezing at -15°C for 25 min, a process of freezing at -35°C for 35 min, and a process of freezing at -60°C for 70 min.

[0058] Step 4:

[0059] Place the frozen product in Step 3 in an inert atmosphere (such as Ar) tube furnace, heat it to 220°C at a rate of 6°C / min, and anneal it at this temperature for 8 hours to obtain the Li3InCl6 solid electrolyte material (also simply referred to as electrolyte).

[0060] Example 2

[0061] Compared with Example 1, the difference is only that the regulator in Step 2 is changed. The experimental groups are as follows:

[0062] Group A: The regulator is a single Formula 1A1, and the dosage of the regulator and other operations and parameters are the same as those in Example 1;

[0063] Group B: The regulator is a single Formula 1B1, and the dosage of the regulator and other operations and parameters are the same as those in Example 1;

[0064] Group C: The regulator is 1 wt.% of the total mass of LiCl and InCl3, and other operations and parameters are the same as those in Example 1;

[0065] Group D: The regulator is 3 wt.% of the total mass of LiCl and InCl3, and other operations and parameters are the same as those in Example 1.

[0066] Other operations and parameters are the same as those in Example 1.

[0067] Example 3

[0068] Compared with Example 1, the difference is only that in Step 3, the freezing process only includes the freezing process at -60 °C, where the total freezing time is 130 min; other operations and parameters are the same as those in Example 1.

[0069] Example 4

[0070] Compared with Example 1, the difference is only that in Step 1, the solvent is toluene, and the solvent dosage and other operating conditions are the same as those in Example 1.

[0071] Example 5

[0072] Compared with Example 1, the difference is only that in Step 4, the annealing temperature is 280 °C and the annealing time is 6 h, and other operating conditions are the same as those in Example 1.

[0073] Comparative Example 1

[0074] Compared with Example 1, the difference is only that in Step 3, no regulator is added, and other operations and parameters are the same as those in Example 1.

[0075] Comparative Example 2

[0076] Compared with Example 1, the difference is only that in Step 3, Comparative Formula A ( ) is used as the regulator, where the regulator dosage and other operating conditions are the same as those in Example 1.

[0077] Comparative Example 3

[0078] Compared with Example 1, the difference is only that in Step 3, Comparative Formula B ( ) is used as the regulator, where the regulator dosage and other operating conditions are the same as those in Example 1.

[0079] Comparative Example 4

[0080] Compared with Example 1, the difference is only that in Step 3, no freezing treatment is carried out, but instead it is kept at 120 °C for 130 min, and other operating conditions are the same as those in Example 1.

[0081] Test:

[0082] Steel Symmetric Battery

[0083] Put the prepared solid electrolyte powder into a mold, apply a pressure of 300 MPa, hold the pressure for 2 min to form an electrolyte sheet, and assemble an ion-blocking symmetric battery with a steel||electrolyte||steel structure (steel symmetric battery). Then, test the electrochemical impedance under a pressure condition of 75 Mpa and a temperature of 25 °C, and calculate the ionic conductivity through the impedance value. The ionic conductivity σ of the solid electrolyte is calculated according to the following formula, where D is the thickness of the electrolyte, R is the impedance value, and S is the effective area for measuring the electrolyte. This process uses a frequency range of 0.01 Hz - 1 MHz. The thickness D = 0.8 mm and the area S = 78.5 mm prepared in this experiment 2 。

[0084]

[0085] Lithium Symmetric Battery

[0086] Assemble the electrolyte sheet into a lithium symmetric battery, and then perform a cycling test at 25 °C using a current of 0.2 mA / cm 2 . The cycling time for each cycle is 1 h. Record the curve of the voltage changing with time, and a drastic change in the voltage is considered to reach the cycle life.

[0087] Lithium-LiCoO2 All-Solid-State Battery:

[0088] Press the electrolyte of each case into a sheet under a pressure of 300 MPa and place it in a polyether ether ketone sleeve as a separator. Then, mix lithium cobaltate, the electrolyte of each case, and carbon black in a mass ratio of 65:30:5 as the positive electrode composite material. Take 10 mg of the positive electrode composite material and spread it on one side of the electrolyte sheet, and press it under a pressure of 300 MPa. Then place a lithium sheet on the other side of the electrolyte sheet as the negative electrode, and use a stainless steel punch as the current collector. Perform a cycling test on the all-solid-state battery, maintain a test pressure of 80 Mpa, with a voltage range of 2.8 to 4.35 V, and test its retention rate under charge and discharge conditions of 0.2C and -5 °C for 500 times.

[0089] All of the above battery assemblies are completed in a glove box filled with an argon atmosphere. The electrochemical impedance spectrum is analyzed on a PARSTAT MC (Princeton, USA) electrochemical workstation, and the battery cycling is carried out on a BlueTec battery tester.

[0090] The results are shown in Table 1:

[0091]

[0092] From Example 1 and Comparative Examples 1 to 4 in Table 1, it can be seen that the structure of Formula 1 is used to participate in the negative-pressure freezing nucleation reaction of LiX and MX3, and then annealing treatment is carried out. This helps to optimize the electronic structure and energy band structure on its surface, and further helps to inhibit the 3+ redox of M in the solid-state lithium metal battery, significantly improving its stability, especially beneficial to improving the low-temperature stability of the assembled solid-state lithium metal battery.

[0093] In addition, from Group A and Group B of Example 1 and Example 2, it can be seen that the combination of Formula 1A and Formula 1B can further optimize the process synergy, and help to further strengthen the stability and low-temperature performance of the assembled solid-state lithium metal battery. From Group C and Group D of Example 1 and Example 2, it can be seen that when the addition amount of the Formula 1 regulator is controlled at 1-3 wt.%, materials with good stability and low-temperature performance can be obtained.

[0094] From Example 1 and Example 3, it can be seen that using the gradient freezing treatment process helps to further strengthen the stability and low-temperature performance of the assembled solid-state lithium metal battery.

[0095] From Example 1 and Example 4, it can be seen that using a hydrophobic solvent for the reaction can prepare materials with excellent performance. Especially when using a composite solvent of tetrahydrofuran, toluene and cyclohexanone, it helps to further strengthen the stability and low-temperature performance of the assembled solid-state lithium metal battery.

[0096] From Example 1 and Example 5, it can be seen that annealing at 200-300 °C can obtain materials with good performance. Especially annealing at a temperature of 210-240 °C helps to further strengthen the stability and low-temperature performance of the assembled solid-state lithium metal battery.

Claims

1. A preparation method of a modified Li3MX6 solid electrolyte material, characterized in that, A mixed solution containing LiX, MX3, a regulator of formula 1 and a solvent is frozen under negative pressure and at a temperature of -100 °C to -10 °C, and then the frozen product is annealed to obtain the product; In Li3MX6, LiX, MX3, X is F, Cl, Br or I; M includes at least one of In, Al, Ga, Sc, La, Sm, Y; Formula 1 R1 is H or an alkyl group with 1 to 6 carbon atoms; R2 is H, an alkyl group with 1 to 6 carbon atoms, an alkoxy group with 1 to 6 carbon atoms, a halogen, trifluoromethyl or nitro; Y is CH or N.

2. The preparation method of the modified Li3MX6 solid electrolyte material according to claim 1, characterized in that, X is Cl and M is In; The molar ratio of LiX to MX3 is 3 to 3.2:

1.

3. The preparation method of the modified Li3MX6 solid electrolyte material according to claim 1, characterized in that, The regulator of formula 1 includes a regulator of formula 1A and a regulator of formula 1B, and the weight ratio of the regulator of formula 1A to the regulator of formula 1B is 1:0.2 to 10; Formula 1A Formula 1B; The regulator of formula 1 is 1 to 5 wt.% of the total weight of LiX and MX3.

4. The preparation method of the modified Li3MX6 solid electrolyte material according to claim 1, wherein, The solvent includes at least one of tetrahydrofuran, toluene, and cyclohexanone.

5. The preparation method of the modified Li3MX6 solid electrolyte material according to claim 1, characterized in that, The freezing process includes a gradient freezing treatment process, and its steps sequentially include: a first freezing process at temperature T1, a second freezing process at temperature T2, and a third freezing process at temperature T3; Among them, temperature T1 is -20 °C to -10 °C; temperature T2 is -40 °C to -30 °C; temperature T3 is -60 °C to -50 °C.

6. The preparation method of the modified Li3MX6 solid electrolyte material according to claim 1 or 5, characterized in that, The freezing treatment time is 1 to 10 h.

7. The preparation method of the modified Li3MX6 solid electrolyte material according to claim 1, characterized in that, The atmosphere for annealing is a protective atmosphere; The annealing temperature is 200 °C to 300 °C; The annealing time is 2 to 10 h.

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