Modified Li3MX6 solid electrolyte material, preparation method, application and lithium metal solid-state battery thereof

Abstract

The invention belongs to the field of metal lithium solid-state batteries, and particularly relates to a modified Li3MX6 solid-state electrolyte material, a preparation method, application and a lithium metal solid-state battery thereof, and the preparation method comprises the following steps: freezing a mixed solution containing LiX, MX3, a regulator in a formula 1 (# imgabs0 #) and a solvent under negative pressure at the temperature of-100 DEG C to-10 DEG C, and then annealing a frozen product to obtain the modified Li3MX6 solid-state electrolyte material. According to the invention, the structure shown in the formula 1 is creatively adopted to participate in the negative pressure freezing nucleation reaction of LiX and MX3, and then annealing treatment is carried out, so that nucleation of Li3MX6 can be optimized based on electron cloud of conjugated state N in the structure shown in the formula 1, an electron structure and an energy band structure on the surface of Li3MX6 can be optimized, redox of M < 3 + > in the metal lithium solid-state battery can be optimized, and the performance of the lithium ion battery can be improved. And especially, the low-temperature stability of the assembled metal lithium solid-state battery is improved.

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 severely restrict the safety and long-life development of batteries. Therefore, all-solid-state lithium batteries (ASSLBs) based on solid electrolytes have become a key development direction for the next-generation energy storage technology 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 battery, so the research on high-performance solid electrolyte materials is crucial.

[0003] In recent years, Li 3 MX 6 has received wide 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 Li 3 MX 6 usually exhibits a lower degree of polarization, with lower interfacial stress and better chemical stability. The so-called Li 3 MX 6 such as the widely used Li 3 InCl 6 , due to its room-temperature lithium-ion conductivity as high as ~10 -3 S / cm, wide electrochemical window, and good processability, is considered to be one of the most promising electrolytes and can effectively promote the development of high-performance solid-state lithium batteries.

[0004] Although Li 3 MX 6 electrolytes exhibit excellent ion transport performance and interfacial adaptability, their chemical stability with lithium metal anodes is still an urgent problem to be solved. Among them, 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 battery. This problem not only reduces the Coulombic efficiency of the battery but also may accelerate the growth of lithium dendrites, ultimately leading to short circuits and failures. Therefore, how to improve the stability of Li 3 MX 6 electrolytes against lithium metal and inhibit M 3+The irreversible reduction is one of the key scientific issues for improving the performance of lithium metal solid-state batteries.

[0005] Regarding this problem, the existing improvement methods mainly lie in ion doping, structure regulation, interface modification, etc.

[0006] For example, the Chinese patent document with the publication number CN112216863A discloses a halogenated solid electrolyte material with the chemical formula Li α M β M’ γ A δ A’ ε ; where 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 SO 4 2- and / or SiO 3 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 Li 3 MX 6 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] Regarding the problems faced by Li 3 MX 6 , the present invention provides a preparation method of a modified Li 3 MX 6 solid electrolyte material, aiming to prepare a Li 3 MX 6 solid electrolyte material with excellent performance.

[0009] The second object of the present invention is to provide the modified Li 3 MX 6 solid electrolyte material prepared by the above preparation method and its application in lithium metal solid-state batteries.

[0010] The third object of the present invention is to provide a lithium metal solid-state battery containing the modified Li 3 MX 6 solid electrolyte material.

[0011] When Li 3MX 6 When applied to a lithium metal solid-state battery, Li 3 MX 6 in which M 3+ ions are easily reduced by lithium metal to metal M, which easily causes damage to the electrolyte lattice structure, accelerates interfacial side reactions, and thus affects the long-term stability and low-temperature performance of the battery. To solve this problem, through in-depth research, the present invention provides the following solutions:

[0012] A preparation method of a modified Li 3 MX 6 solid electrolyte material, which is obtained by freezing a mixed solution containing LiX, MX 3 , 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] Li 3 MX 6 , LiX, MX 3 in which X is F, Cl, Br or I; M includes at least one of In, Al, Ga, Sc, La, Sm, Y;

[0014] Formula 1

[0015] R 1 is H or an alkyl group of C 1 ~C 6 ;

[0016] R 2 is H, an alkyl group of C 1 ~C 6 , an alkoxy group of C 1 ~C 6 , a halogen, a trifluoromethyl group or a nitro group;

[0017] Y is CH or N.

[0018] The present invention innovatively uses a compound with the structure of formula 1 to participate in the negative-pressure freezing nucleation reaction of LiX and MX 3 , and then performs annealing treatment. For example, based on the electron cloud of the conjugated state N in the structure of formula 1, the nucleation of Li 3 MX 6 can be optimized, and it helps to optimize the electronic structure and energy band structure on its surface, and thus is conducive to effectively inhibiting the redox of M 3+ in the lithium metal solid-state battery, reducing interfacial side reactions, and thus effectively improving the stability and low-temperature stability of the assembled lithium metal 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 MX 3 is 3 to 3.2:1.

[0021] The regulator of Formula 1 includes regulator of Formula 1A and regulator of Formula 1B, wherein the weight ratio of the regulator of Formula 1A to the regulator of Formula 1B 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 Li 3 MX 6 in the solid-state lithium metal battery, and further improve its stability and low-temperature performance.

[0025] In the said Formula 1A and Formula 1B, the said R 1 and R 2 can be H or an alkyl group of C 1 to C 3 .

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

[0027] In the present invention, the said 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 atmospheric pressure. For example, it can be a pressure below 100 Pa.

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

[0030] In the present invention, the freezing process includes a gradient freezing treatment process, and its steps successively 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] wherein, temperature T1 is -20 °C to -10 °C; temperature T2 is -40 °C to -30 °C; temperature T3 is -60 °C to -50 °C.

[0032] Research in the present invention shows that with the assistance of the regulator of Formula 1 and in further combination with the gradient freezing treatment process, it helps to further optimize the electronic and energy band structures of the material and 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 to 10 h, and further can be 2 to 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 to 30 min, the time of the second-stage freezing treatment can be 30 to 40 min, and the time of the third-stage freezing treatment can be 60 to 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 to 300 °C; further can be 210 to 240 °C.

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

[0038] The present invention also provides a modified Li 3 MX 6 solid electrolyte material prepared by the preparation method described above.

[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 a lithium metal solid-state battery, and can effectively inhibit the precipitation of M in Li 3 MX 6 and can effectively improve its electrochemical stability, for example, improve its stability at low temperature. 3+

[0040] The present invention also provides the application of the modified Li 3 MX 6 solid electrolyte material, using it as a solid electrolyte for a lithium metal solid-state battery.

[0041] In the present invention, based on the conventional principles and ideas of a solid-state battery, the modified Li 3 MX 6 solid electrolyte material can be used to prepare the required solid electrolyte sheet and lithium metal solid-state battery.

[0042] For example, by a pressing method, the modified Li 3 MX 6 solid electrolyte material described in 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 to 500 MPa.

[0043] In the present invention, the negative electrode of the lithium metal solid-state battery is a metallic lithium 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 material, lithium cobaltate, lithium nickelate, lithium iron phosphate, etc. The electrolyte is the modified Li 3 MX 6 solid electrolyte material. 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, the electrolyte, and the 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 electric core in which a positive electrode, an electrolyte, and a negative electrode are combined. The electrolyte is the modified Li 3 MX 6 solid electrolyte material; the negative electrode is metallic lithium.

[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 MX 3 , and then annealing treatment is carried out. This helps to optimize the electronic structure and energy band structure on its surface, and then is conducive to optimizing the M 3+ redox in the metallic lithium solid-state battery, significantly improving its stability, especially being conducive to suppressing the low-temperature stability of the assembled metallic lithium solid-state battery and suppressing 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 synergistic effect of the process can be further optimized, which helps to further optimize the Li 3 MX 6 electronic structure and energy band structure of the material, so as to help further strengthen the adaptation synergy of the material to metallic lithium, and help further strengthen the stability and low-temperature performance of the assembled metallic lithium 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 of Example 1;

[0050] Figure 3 This is the charge and discharge cycle diagram of the all-solid-state battery of Example 1. DETAILED DESCRIPTION

[0051] Example 1

[0052] Step 1:

[0053] Use high purity LiCl (99.9%) and InCl 3 (99.99%), mixed and dispersed in a solvent in a chemical molar ratio of 3:1 to form a mixed solution, wherein the solvent includes tetrahydrofuran, toluene and cyclohexanone in a volume ratio of 70:15:15.

[0054] Step 2:

[0055] Add LiCl and InCl to the above mixed solution. 3 2% of the total weight of the regulator, the regulator includes the formula 1A1 ( ) and formula 1B1 ( ), stir well.

[0056] Step 3:

[0057] The mixed solution of step 2 is frozen under vacuum, wherein the freezing process includes freezing at -15°C for 25 minutes, freezing at -35°C for 35 minutes, and freezing at -60°C for 70 minutes.

[0058] Step 4:

[0059] The frozen product of step 3 is placed in an inert atmosphere (such as Ar) tube furnace, heated to 220°C at a rate of 6°C / min, and annealed at this temperature for 8 hours to obtain the Li 3 InCl 6 Solid electrolyte materials (also referred to as electrolytes).

[0060] Example 2

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

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

[0064] Group C: LiCl and InCl as regulators 3 1wt.% of the total mass, other operations and parameters are the same as in Example 1;

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

[0066] Other operations and parameters are the same as 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 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 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 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 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 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 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 it is kept at 120°C for 130 min, and other operating conditions are the same as 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 it into an ion-blocking symmetric cell (steel symmetric cell) with a steel||electrolyte||steel structure. 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 change over time, and a significant change in voltage is considered to reach the cycle life.

[0087] Lithium-LiCoO 2 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 a stainless steel punch is used as the current collector. A cycling test was performed on the all-solid-state battery, maintaining a test pressure of 80 Mpa, a voltage range of 2.8 to 4.35 V, and testing its retention rate under 0.2C charge-discharge conditions at -5 °C for 500 times.

[0089] All of the above battery assemblies were completed in a glove box filled with an argon atmosphere. The electrochemical impedance spectroscopy was analyzed on a PARSTAT MC (Princeton, USA) electrochemical workstation, and the battery cycling was performed on a BlueTEC battery tester.

[0090] The results are shown in Table 1:

[0091]

[0092] It can be seen from Example 1 and Comparative Examples 1 - 4 in Table 1 that the structure of Formula 1 is used to participate in LiX, MX 3Negative pressure freezing nucleation reaction, followed by annealing treatment, which helps to optimize the electronic structure and energy band structure of its surface, and then is conducive to inhibiting its M 3+ redox reaction, significantly improving its stability, especially conducive to improving the low-temperature stability of the assembled lithium metal solid-state battery.

[0093] In addition, it can be seen from Group A and Group B of Example 1 and Example 2 that the combination of Formula 1A and Formula 1B can further optimize the process synergy, which helps to further enhance the stability and low-temperature performance of the assembled lithium metal solid-state battery. It can be seen from Group C and Group D of Example 1 and Example 2 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] It can be seen from Example 1 and Example 3 that adopting the gradient freezing treatment process helps to further enhance the stability and low-temperature performance of the assembled lithium metal solid-state battery.

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

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

Claims

1. A method for preparing a modified Li3MX6 solid electrolyte material, characterized in that: Freeze a mixed solution containing LiX, MX3, a regulator of formula 1 and a solvent under negative pressure and a temperature of -100°C to -10°C, and then anneal the frozen product to obtain; In Li3MX6, LiX, and MX3, X is F, Cl, Br, or I; and M includes at least one of In, Al, Ga, Sc, La, Sm, and Y; Formula 1; R1 is H or a C1~C6 alkyl group; R2 is H, C1~C6 alkyl, C1~C6 alkoxy, halogen, trifluoromethyl or nitro; Y is CH or N.

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

1.

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

4. The method for preparing the modified Li3MX6 solid electrolyte material according to claim 1, characterized in that: The solvent includes at least one of tetrahydrofuran, toluene and cyclohexanone.

5. The method for preparing the modified Li3MX6 solid electrolyte material according to claim 1, characterized in that: The freezing process includes a gradient freezing process, the steps of which include: a first freezing process at a temperature T1, a second freezing process at a temperature T2, and a third freezing process at a temperature T3; Among them, temperature T1 is minus 20 to minus 10 degrees Celsius; temperature T2 is minus 40 to minus 30 degrees Celsius; temperature T3 is minus 60 to minus 50 degrees Celsius.

6. The method for preparing the modified Li3MX6 solid electrolyte material according to claim 1 or 5, characterized in that: The freezing treatment time is 1 to 10 hours.

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

8. A modified Li3MX6 solid electrolyte material obtained by the preparation method according to any one of claims 1 to 7.

9. An application of a modified Li3MX6 solid electrolyte material obtained by the preparation method according to any one of claims 1 to 7, characterized in that: Use it as a solid electrolyte for lithium metal solid-state batteries.

10. A lithium metal solid-state battery, comprising a battery cell having a positive electrode, an electrolyte and a negative electrode, characterized in that: The electrolyte is a modified Li3MX6 solid electrolyte material obtained by the preparation method described in any one of claims 1 to 7; and the negative electrode is metallic lithium.

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