Cold sintering preparation method of solid electrolyte and lithium ion battery

Abstract

The invention discloses a cold sintering preparation method of a solid electrolyte and a lithium ion battery, and the cold sintering preparation method of the solid electrolyte comprises the following steps: a primary mixing step: adding a transient liquid phase solvent into a ground NASICON type electrolyte and a lithium salt, and grinding again to obtain an initial mixture; a cold sintering step: carrying out cold sintering on the initial mixture under the conditions that the pressure is 5-500MPa and the temperature is 100-300 DEG C, and then carrying out heat treatment for 0.2-3 hours under the condition that the temperature is 200-800 DEG C to obtain a solid electrolyte; according to the preparation method, on the basis of using the NAS ICON type electrolyte, the preparation method is improved, and the density and the ionic conductivity of the solid electrolyte are greatly improved through combination of cold sintering and heat treatment.

Description

Technical Field

[0001] The invention relates to a cold sintering preparation method of a solid electrolyte and a lithium ion battery, belonging to the technical field of electrolyte preparation and application. Background Art

[0002] With the growing growth of the electric industry, people have higher and higher requirements for battery energy density, stability, safety and other performance. Compared with traditional lithium-ion batteries, solid-state batteries are not easy to leak or burn and have higher safety performance. As an important component, solid electrolytes should have excellent mechanical strength, safety and electrochemical properties. Oxide solid electrolytes have attracted widespread attention due to their good thermal stability, mechanical strength and electrochemical stability. However, due to the existence of interfaces between oxide solid electrolyte particles, their density is quite different from the theory, resulting in low lithium ion transmission efficiency. High-temperature sintering is generally used to reduce the impact of the interface. However, traditional high-temperature sintering to prepare oxide solid electrolytes will lead to the volatilization of lithium and the formation of secondary phases. Although sintering aids can be used to reduce the sintering temperature during the sintering process, the sintering temperature still has to exceed 800°C, and this method of reducing the sintering temperature is difficult to maintain a high ionic conductivity. Summary of the invention

[0003] In order to overcome the shortcomings of the prior art, the first object of the present invention is to provide a cold sintering preparation method for a solid electrolyte. On the basis of using a NASICON type electrolyte, the preparation method is improved, and the density and ionic conductivity of the solid electrolyte are greatly improved by combining cold sintering and heat treatment.

[0004] The second object of the present invention is to provide a lithium ion battery assembled with a solid electrolyte, the battery having good battery cycle performance.

[0005] The first object of the present invention can be achieved by adopting the following technical scheme: A cold sintering preparation method of a solid electrolyte, comprising:

[0006] Initial mixing step: adding a transient liquid phase solvent to the ground NASICON-type electrolyte and lithium salt, and grinding again to obtain an initial mixture;

[0007] Cold sintering step: After the initial mixture is cold sintered at a pressure of 5-500 MPa and a temperature of 100-300° C., heat treatment is performed at a temperature of 200-800° C. for 0.2-3 h to obtain a solid electrolyte.

[0008] Furthermore, the NASICON electrolyte is LATP (Li 1+x Al x Ti 2-x (PO4)3), with a particle size of ≤5μm.

[0009] Further, the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium nitrate (LiNO 3 ) and lithium tetrafluoroborate (LiBF 4 ).

[0010] Further, the transient liquid phase solvent includes at least one of N-methylpyrrolidone (NMP) and water.

[0011] Furthermore, the mass fraction of the transient liquid phase solvent in the initial mixture is 1-99wt%.

[0012] Furthermore, in the cold sintering step, the cold sintering time is 0.2-2h.

[0013] Furthermore, in the cold sintering step, the heat treatment temperature is 300-750°C.

[0014] Furthermore, in the cold sintering step, the heat treatment time is 0.5-2h.

[0015] The second object of the present invention can be achieved by adopting the following technical solution: a lithium ion battery, the lithium ion battery includes an electrolyte; the electrolyte is prepared by the cold sintering preparation method of the solid electrolyte as described above.

[0016] Furthermore, the lithium-ion battery is a lithium iron phosphate battery.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The cold sintering preparation method of the solid electrolyte of the present invention adds lithium salt and liquid transient solvent to the NASICON type electrolyte. After cold sintering, the density can reach more than 80%. Its principle is completely different from the traditional sintering theory. After completion, the electrolyte density exceeds 90% and the ionic conductivity is close to 10 -3 S / cm;

[0019] 2. The lithium ion battery of the present invention is assembled with a solid electrolyte, and the battery has good battery cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a cross-sectional SEM image of Example 1;

[0021] Figure 2 This is the phase analysis diagram of Example 1;

[0022] Figure 3 This is a diagram of the electrochemical impedance test of Example 1;

[0023] Figure 4 This is a battery cycle curve diagram of Example 1;

[0024] Figure 5-15 The cross-sectional SEM images of the solid electrolytes prepared under different parameters based on Example 1;

[0025] Fig.16 Cross-sectional SEM image of Example 2;

[0026] Fig.17 Optical diagram of Example 2;

[0027] Fig.18 Battery cycle curve diagram of Example 2;

[0028] Figure 19-20 Example 2: First cycle charge and discharge curve and first 100 cycle graph of the battery;

[0029] Fig.21 Example 3 cross-sectional SEM image;

[0030] Fig. 22 Battery cycle curve of Example 3. DETAILED DESCRIPTION

[0031] Below, the present invention is further described in conjunction with the accompanying drawings and specific embodiments:

[0032] A cold sintering preparation method for a solid electrolyte, comprising:

[0033] Initial mixing step: adding a transient liquid phase solvent to the ground NASICON type electrolyte and lithium salt, grinding again to obtain an initial mixture; the NASICON type electrolyte is LATP, and its particle size is ≤5μm; the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium nitrate and lithium tetrafluoroborate; the transient liquid phase solvent includes at least one of N-methylpyrrolidone and water, and the mass fraction of the transient liquid phase solvent in the initial mixture is 1-99wt%.

[0034] Cold sintering steps: place the initial mixture in a powder tablet press mold, place the mold in a special cold sintering device, cold sinter for 0.2-2h at a pressure of 5-500MPa and a temperature of 100-300°C, demold after cooling to obtain a green body, place the green body in a muffle furnace, heat treat at a temperature of 300-750°C for 0.5-2h, grind its surface after cooling to obtain a solid electrolyte.

[0035] The electrolyte obtained by the above preparation method is used to prepare a lithium iron phosphate battery.

[0036] The improved cold sintering temperature of 100-400℃ can significantly reduce the heat treatment temperature of NASICON ceramic electrolyte, and the heat treatment temperature does not exceed 750℃. Under the combined effect, the lithium volatilization problem can be effectively avoided.

[0037] Embodiment 1:

[0038] A cold sintering preparation method for a solid electrolyte, comprising:

[0039] Initial mixing step: 45 μL of deionized water was added to the ground 0.3 g of LATP and 0.03 g of LiTFSI, and the mixture was ground again for 10 min to obtain an initial mixture; the particle size of LATP was about 300 nm.

[0040] Cold sintering steps: Place the initial mixture in a mold with a diameter of 15 mm of a powder tablet press, place the mold in a special cold sintering device, and cold sinter for 1 hour at a pressure of 340 MPa and a temperature of 200°C. After cooling, demold the mold to obtain a green body, place the green body in a muffle furnace, heat it to 650°C in air at a rate of 10°C / min for heat treatment for 2 hours, and grind its surface after cooling to obtain a solid electrolyte.

[0041] The cross-sectional SEM image of the solid electrolyte of Example 1 is as follows: Figure 1 The phase analysis diagram is Figure 2 shown.

[0042] Electrochemical impedance spectroscopy was performed using gold as the blocking electrode to obtain the electrochemical impedance spectrum at room temperature. Figure 3 shown.

[0043] The solid electrolyte was used to prepare a lithium-lithium symmetric battery at 60 °C with a charge flow rate of 0.1 mA / cm 2 After 200 hours of circulation, the circulation curve is obtained, as shown in Figure 4 shown.

[0044] The LATP solid electrolyte prepared in Example 1 has a density of more than 90%, and its ionic conductivity is 7.42×10 -4 S / cm. In comparison, the room temperature ionic conductivity of the green body was 7.06×10 -4 S / cm.

[0045] The solid electrolyte prepared by this method can be used to assemble a lithium-lithium symmetric battery at 0.1 mA / cm 2 The stable cycle lasted for more than 200 h at a current density of , and the polarization voltage was less than 50 mV. The test results show that the solid electrolyte provided in Example 1 can achieve a high ionic conductivity at room temperature and can be used in batteries.

[0046] The activation energy E was calculated by comparing the ionic conductivity of LATP solid electrolyte prepared with and without LiTFSI as a function of temperature. a ,like Figure 5As shown in the figure, the results show that the ionic conductivity of the solid electrolyte prepared by adding LiTFSI is higher than that of the LATP solid electrolyte prepared without adding LiTFSI at the same temperature, and the activation energy E a Lower, ion transport efficiency is higher in the LATP solid electrolyte prepared by adding LiTFSI.

[0047] On the basis of Example 1, the preparation parameters were changed to obtain cross-sectional SEM images of the solid electrolyte for comparison. The parameters are shown in Table 1, and the cross-sectional SEM images obtained are shown in Table 1. Figure 5-Figure 15 shown.

[0048] Table 1 Parameters for preparing solid electrolytes

[0049] serial number LATP(g) LiTFSI(g) Cold sintering(℃) Heat treatment(℃) a 0.3 0 / / b 0.3 0 200 / c 0.3 0 200 650 d 0.3 0.03 200 / e 0.3 0 850 / f 0.3 0.03 220 550 g 0.3 0.03 200 650 h 0.3 0.03 200 750 i 0.3 0.03 200 850 j 0.3 0.03 200 900

[0050] Embodiment 2:

[0051] A cold sintering preparation method for a solid electrolyte, comprising:

[0052] Initial mixing step: 130 μL of deionized water was added to the ground 0.5 g of LATP powder and 0.04 g of LiBF4, and the mixture was ground again for 10 min to obtain an initial mixture; the particle size of LATP was about 300 nm.

[0053] Cold sintering steps: Place the initial mixture in a mold with a diameter of 15 mm of a powder tablet press, place the mold in a special cold sintering device, and cold sinter for 1 hour at a pressure of 400 MPa and a temperature of 150°C. After cooling, demold the mold to obtain a green body, place the green body in a muffle furnace, heat it to 740°C at a rate of 10°C / min in air, and heat treat it for 1 hour. After cooling, polish its surface to obtain a solid electrolyte.

[0054] The results of Archimedes drainage method showed that the solid electrolyte has a density of more than 99%.

[0055] The cross-sectional SEM image of the solid electrolyte of Example 2 is as follows: Fig.16 As shown in the optical diagram Fig.17 As shown, it shows a dense structure without abnormal particle growth and internal cracks.

[0056] By conducting electrochemical impedance spectroscopy on the solid electrolyte and using gold as the blocking electrode, the impedance spectrum at room temperature was obtained. The room temperature ionic conductivity was calculated to be 1.02×10 -3 S / cm. The solid electrolyte was used to assemble a lithium-lithium symmetric battery, and its cycle curve was obtained, as shown in Fig.18 As shown. Li-Li symmetric battery at 0.1 mA / cm 2The stable cycle lasted for more than 700 hours at a current density of 1.5 ℃, and the polarization voltage was less than 100 mV. The test results show that the solid electrolyte of Example 2 can achieve high ionic conductivity at room temperature and has good cycle stability. The solid electrolyte was further used to assemble a lithium iron phosphate half-cell. The first cycle charge and discharge curve and the first 100 cycle curves are shown in Figure 2. Fig.19 , Fig. 20 It is shown that the provided solid electrolyte can be used as a high-performance electrolyte for all-solid-state batteries.

[0057] Embodiment 3:

[0058] A cold sintering preparation method for a solid electrolyte, comprising:

[0059] Initial mixing step: add 80 μL of deionized water to the ground 0.5 g of LATP powder and 0.04 g of LiNO3, and grind again for 2-5 min to obtain an initial mixture; the LATP particle size is about 300 nm.

[0060] Cold sintering steps: Place the initial mixture in a mold with a diameter of 15 mm of a powder tablet press, place the mold in a special cold sintering device, and cold sinter for 1 hour at a pressure of 400 MPa and a temperature of 210°C. After cooling, demold the mold to obtain a green body, place the green body in a muffle furnace, heat it to 700°C at a rate of 15°C / min in air, and heat treat it for 1 hour. After cooling, polish its surface to obtain a solid electrolyte.

[0061] The results of Archimedes drainage method showed that the solid electrolyte has a density of more than 95%.

[0062] The cross-sectional SEM images are shown in Fig.21 As shown, it shows a dense structure without abnormal particle growth and internal cracks.

[0063] The electrochemical impedance spectroscopy of the solid electrolyte was carried out by using Au as the blocking electrode to obtain its impedance spectrum at room temperature. The room temperature ionic conductivity was calculated to be 9.04×10 -4 S / cm.

[0064] The solid electrolyte prepared in this embodiment is used to assemble a lithium iron phosphate half-cell, and its cycle curve is obtained, as shown in FIG. Fig. 22 As shown. The assembled lithium iron phosphate half-cell has a gram capacity of more than 160 mAh / g at a rate of 0.1C. After 100 cycles of stable cycling at a subsequent rate of 0.5C, the gram capacity is 143 mAh / g, the capacity retention rate is 97.1%, and the average coulombic efficiency exceeds 99.9%. Test results The solid electrolyte provided in Example 3 can achieve high ionic conductivity at room temperature and has good cycle stability.

[0065] The detection and result calculation methods used in Examples 1-3 are as follows:

[0066] Calculation method of density (relative density):

[0067] First, measure the dry weight of the dried electrolyte sheet sample, recorded as m1, and then put it into ethanol to ensure that the sample is completely immersed in ethanol. After the reading is stable, measure the floating weight of the sample, recorded as m2. Finally, take the sample out of ethanol, wipe the surface with non-woven cloth, and measure its wet weight, recorded as m3. Finally, according to the density of ethanol at the corresponding temperature during the test, ρ 乙醇 To calculate the actual density of the electrolyte sheet sample:

[0068] Density (relative density): ρ r =ρ / ρ 理论 , ρ of LATP 理论 Take 2.947g / cm 3 .

[0069] Conventional high-temperature sintering method: Take a certain amount of solid electrolyte LATP powder and place it in a powder tablet press, set the parameters: pressure: 340MPa, pressure holding time: 5-10min, and make a disc with a diameter of 8mm. Place the disc in a muffle furnace at 850℃ and bake for 2h.

[0070] Ionic conductivity test method: Use an ion sputtering instrument to gold-plate both sides of the solid electrolyte LATP. The sputtering current is 50mA, the single-sided sputtering time is 200s, and the sputtering area is a circle with a diameter of 8mm. The two sides of the solid electrolyte are clamped by a clamp. The contacts of the clamp are in close contact with the gold-plated area, and the test is performed using an electrochemical workstation.

[0071] Calculation formula of ionic conductivity σ:

[0072] Where l is the thickness of the ceramic sheet, R is the measured electrochemical impedance, and A is the area of ​​ion sputtering.

[0073] For those skilled in the art, various other corresponding changes and modifications can be made according to the technical solutions and concepts described above, and all of these changes and modifications should fall within the protection scope of the claims of the present invention.

Claims

1. A cold sintering preparation method for a solid electrolyte, characterized in that: include: Initial mixing step: adding a transient liquid phase solvent to the ground NASICON-type electrolyte and lithium salt, and grinding again to obtain an initial mixture; Cold sintering step: After the initial mixture is cold sintered at a pressure of 5-500 MPa and a temperature of 100-300° C., heat treatment is performed at a temperature of 200-800° C. for 0.2-3 h to obtain a solid electrolyte.

2. The cold sintering preparation method of the solid electrolyte according to claim 1, characterized in that: The NASICON type electrolyte is LATP, and its particle size is ≤5 μm.

3. The cold sintering preparation method of the solid electrolyte according to claim 1, characterized in that: The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium nitrate and lithium tetrafluoroborate.

4. The cold sintering preparation method of the solid electrolyte according to claim 1, characterized in that: The transient liquid phase solvent includes at least one of N-methylpyrrolidone and water.

5. The cold sintering preparation method of the solid electrolyte according to claim 1, characterized in that: The mass fraction of the transient liquid phase solvent in the initial mixture is 1-99wt%.

6. The cold sintering preparation method of the solid electrolyte according to claim 1, characterized in that: In the cold sintering step, the cold sintering time is 0.2-2h.

7. The cold sintering preparation method of the solid electrolyte according to claim 1, characterized in that: In the cold sintering step, the heat treatment temperature is 300-750°C.

8. The cold sintering preparation method of the solid electrolyte according to claim 1, characterized in that: In the cold sintering step, the heat treatment time is 0.5-2h.

9. A lithium ion battery, characterized in that: The lithium-ion battery comprises an electrolyte; the electrolyte is prepared by the cold sintering preparation method of the solid electrolyte as claimed in claim 1.

10. The lithium ion battery according to claim 9, characterized in that The lithium ion battery is a lithium iron phosphate battery.

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