Modified NASICON type solid electrolyte and preparation method thereof

Abstract

The invention discloses a modified NASICON type solid electrolyte and a preparation method, and belongs to the technical field of lithium ion batteries, the preparation raw materials of the solid electrolyte comprise LiAlO2 and a lithium source, an aluminum source, a titanium source and a phosphorus source which form Li < 1 + x > Al < x > Ti < 2-x > (PO4) 3, and x = 0.3-0.5; the preparation method comprises the following steps: uniformly mixing a lithium source, an aluminum source, a titanium source and a phosphorus source, adding LiAlO2 and a dispersing agent, and carrying out ball milling to obtain mixed slurry; drying to obtain mixed powder; sintering to obtain LATP solid electrolyte precursor powder; pressing into sheets, and sintering for the second time to obtain the product. According to the invention, by introducing the sintering aid LiAlO2, an intergranular phase is formed among crystal grains, so that the content of an amorphous phase is reduced, and the conductivity of lithium ions is improved; the LiAlO2 is coated on the surface of the LATP, so that the reaction of lithium metal and the LATP is hindered, and the lithium stability is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a modified NASICON-type solid electrolyte and a preparation method thereof. Background Art

[0002] The NASION-type oxide solid electrolyte Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) has been widely concerned because it has the advantages of high thermal stability, wide potential window and can be prepared in air. It can replace the organic electrolyte in lithium-ion batteries and improve the safety performance of the battery. However, due to its poor grain boundary conductivity, its total conductivity is low, and the serious side reaction between LATP and lithium metal limits the practical application of LATP.

[0003] At present, the main method to improve the conductivity of LATP solid electrolyte is to add low melting point sintering aids such as Li 2 O, Li 3 PO 4 , Li 3 BO 3 etc., to reduce the sintering temperature and promote grain growth, and improve the lithium ion conductivity of LATP. However, it cannot improve the interfacial stability of LATP to lithium metal.

[0004] Therefore, it is of great significance to develop a solid electrolyte with high lithium ion conductivity and relatively stable to lithium metal. Summary of the Invention

[0005] Technical problems to be solved:

[0006] The purpose of the present invention is to overcome the technical problems such as the inability to improve the interfacial stability of LATP to lithium metal in the prior art. The present application provides a modified NASICON-type solid electrolyte and a preparation method thereof, and this material has low cost and simple process, and is suitable for large-scale industrial production.

[0007] Technical solutions:

[0008] To achieve the above purpose, the present application is realized through the following technical solutions:

[0009] A preparation method of a modified NASICON-type solid electrolyte, comprising the following steps:

[0010] Step 1: According to Li 1+x Al x Ti 2-x (PO 4 )3 Among them, for the chemical dosimeter formulation with x = 0.3 - 0.5, lithium source, aluminum source, titanium source, and phosphorus source powders are taken.

[0011] Step 2: Take lithium aluminate LiAlO according to 1 - 15% of the total mass of the lithium source, aluminum source, titanium source, and phosphorus source powders. 2 ;

[0012] Step 3: Add a dispersant and milling beads to the lithium source, aluminum source, titanium source, phosphorus source, and LiAlO 2 and carry out ball milling and stirring to obtain a uniformly mixed slurry.

[0013] Step 4: Dry the uniformly mixed slurry to obtain a mixed powder.

[0014] Step 5: Place the mixed powder in a muffle furnace and calcine it at 700 - 900 °C for 5 - 10 h under air conditions to obtain LATP solid electrolyte precursor powder.

[0015] Step 6: Press the LATP solid electrolyte precursor powder into a tablet and sinter it for the second time at 700 - 900 °C for 4 - 8 h to obtain the modified NASICON-type solid electrolyte.

[0016] Preferably, in Step 1, the lithium source is one or more of lithium carbonate, lithium hydroxide, and lithium oxide; the aluminum source is one or more of aluminum oxide, aluminum hydroxide, and aluminum chloride; the titanium source is titanium dioxide and / or titanium chloride; the phosphorus source is one or more of ammonium dihydrogen phosphate, phosphoric acid, and lithium phosphate.

[0017] Preferably, in Step 1, lithium hydroxide is in an excess of 1 - 10%.

[0018] Preferably, in Step 3, the dispersant is one or more of absolute ethanol, propanol, isopropanol, and ethylene glycol, and the dosage of the dispersant is 3 times the mass of the lithium source, aluminum source, titanium source, phosphorus source, and LiAlO 2 .

[0019] Preferably, in Step 3, the speed of ball milling and stirring is 200 - 400 revolutions per minute, and the stirring time is 10 - 24 h.

[0020] Preferably, in Step 4, the drying temperature is 50 °C - 80 °C, and the drying time is 10 - 24 h.

[0021] Preferably, in Step 5, the heating rate in the muffle furnace is 2 - 10 °C / min.

[0022] Preferably, in Step 6, the pressure for pressing into a tablet is 180 - 200 MPa, and the heating rate for the second sintering is 5 - 10 °C / min.

[0023] The present application also discloses a modified NASICON-type solid electrolyte prepared by any of the above preparation methods.

[0024] Preferably, the modified NASICON-type solid electrolyte further comprises a doping element that replaces Ti 4+ or replaces Al 3+ The doping element that replaces Ti 4+ is Zr 4+ , Hf 4+ , Ge 4+ , Sn 4+ , Te 3+ or Ta 5+ , and the doping element that replaces Al 3+ is Mg 2+ or In 3+ .

[0025] The technical principle of the present invention is that by introducing doping elements, the crystal structure and ion transport characteristics of the NASICON-type solid electrolyte can be changed, thereby improving its ionic conductivity and electrochemical performance. Doping transition metal elements such as Zr, Hf, and Ta can form lattice defects and ion-conducting phases, optimize the crystal structure, and enable the sodium ion conductivity to reach 10 -3 S / cm; in addition, the alkaline earth metal element Mg can also significantly improve the performance of the material; to solve the problems of improving ionic conductivity and lithium stability, fix the modified doping elements. Doping tetravalent cations can significantly improve ionic conductivity, while doping Ta 5+ , Te 3+ is to improve lithium stability.

[0026] Beneficial effects:

[0027] The present application provides a modified NASICON-type solid electrolyte and a preparation method, having the following beneficial effects:

[0028] 1. By adding LiAlO 2 that conducts lithium ions, which is coated on the grain surface during the LATP sintering process, reducing the formation of intergranular amorphous phases and enhancing the conduction ability of lithium ions between grains;

[0029] 2. The added LiAlO 2 is coated on the surface of LATP, hindering the reaction between lithium metal and LATP and improving the interface stability;

[0030] 3. Tetravalent cations such as Zr 4+ and Hf 4+ in the present application can replace Ti 4+ , thereby increasing the ionic conductivity of LATP and reducing Ti 4+reduction; these dopants can stabilize the structure of LATP and prevent Ti 4+ from being reduced to Ti 3+ , thereby improving the stability and performance of the electrolyte;

[0031] 4. Ge in this application 4+ can replace Ti 4+ . When the doping amount of Ge is 0.2, the obtained Li 1.4 Al 0.4 Ti 1.6-x Ge x (PO 4 ) 3 has the highest ionic conductivity of 1.29×10 -3 S / cm; Ge 4+ has a relatively small ionic radius. After doping, it can optimize the ion transport channels and promote lithium ion transport;

[0032] 5. Sn 4+ can replace Ti 4+ . Uniform replacement is beneficial to stabilizing the ceramic crystal structure, reducing the grain size, and increasing the relative density;

[0033] 6. Zr 4+ can replace Ti 4+ . The obtained Li 1.4 Al 0.4 Zr 0.1 Ti 1.5 (PO 4 ) 3 has an ionic conductivity of up to 1.4×10 -3 S / cm at room temperature;

[0034] 7. Mg 2+ can partially replace Al 3+ . This not only increases the Li + concentration, but also expands the material size and lithium ion transport channels, thereby improving the ionic conductivity and density of LATP;

[0035] 8. In 3+ can replace Al 3+ . Introducing In 3+ expands the lithium ion transport path, and at the same time the lattice volume becomes larger, which is beneficial to increasing its density;

[0036] 9. Te 3+ can replace Ti 4+ . When the doping concentration is 0.03, the obtained Li 1.3 Al 0.3 Te 0.03 Ti 1.67 (PO 4 )3 has the highest ionic conductivity of 7.03×10 -4 S / cm; the high electronegativity of Te mainly exists in the +3 valence state, and the interface side reaction between the lithium metal and the ceramic can be effectively inhibited in the doped sample;

[0037] 10. Ta 5+ can replace Ti 4+ to effectively improve the interface problem of the contact between LATP and the lithium metal. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is the SEM image of the modified NASICON-type solid electrolyte material obtained in Example 3 of this application;

[0039] Figure 2 is the XRD pattern of the modified NASICON-type solid electrolyte material obtained in Example 3 of this application;

[0040] Figure 3 is the lithium symmetric battery cycling performance test chart of the modified NASICON-type solid electrolyte material obtained in Example 3 of this application assembled into a lithium symmetric battery at a current density of 0.05 mA / cm -2 ;

[0041] Figure 4 is the lithium symmetric battery cycling performance test chart of the unmodified LATP obtained in Comparative Example 1 assembled into a lithium symmetric battery at a current density of 0.05 mA / cm -2 . DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] To make the objectives, technical solutions and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0043] The chemical reagents used in the embodiments of the present invention are obtained through conventional commercial channels unless otherwise specified.

[0044] In any embodiment of this application, the ball-to-material ratio of ball milling and stirring is 30 to 10:1, and the diameter of the balls is 2 to 20 mm. Most preferably, the ball-to-material ratio of the ball milling and stirring is 25 to 15:1, and the diameter of the balls is 5 to 15 mm.

[0045] The following further illustrates the present invention with examples. The following examples are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention fall within the protection scope of the present invention.

[0046] Example 1

[0047] A preparation method of a modified NASICON-type solid electrolyte, comprising the following steps:

[0048] Step 1: Weigh 19.0918 g of lithium hydroxide, 47.5226 g of titanium dioxide, 5.3529 g of aluminum oxide, and 120.7816 g of ammonium dihydrogen phosphate;

[0049] Step 2: Take lithium aluminate LiAlO according to 1% of the total mass of the lithium hydroxide, aluminum oxide, titanium dioxide and ammonium dihydrogen phosphate powders 2 ;

[0050] Step 3: Add 600 g of isopropanol and milling beads to the lithium hydroxide, aluminum oxide, titanium dioxide, ammonium dihydrogen phosphate and LiAlO 2 and carry out ball milling and stirring at 200 - 400 revolutions per minute for 10 - 24 h to obtain a uniformly mixed slurry;

[0051] Step 4: Dry the uniformly mixed slurry at 50 °C - 80 °C for 10 - 24 h to obtain a mixed powder;

[0052] Step 5: Place the mixed powder in a muffle furnace, under air conditions, heat it at a heating rate of 2 - 10 °C / min to 700 - 900 °C and calcine for 5 - 10 h to obtain LATP solid electrolyte precursor powder;

[0053] Step 6: Press the LATP solid electrolyte precursor powder into tablets at 180 - 200 MPa, and heat it to 700 - 900 °C at a heating rate of 5 - 10 °C / min for secondary sintering for 4 - 8 h to obtain the modified NASICON-type solid electrolyte.

[0054] Example 2

[0055] A preparation method of a modified NASICON-type solid electrolyte, comprising the following steps:

[0056] Step 1: Weigh 19.0918 g of lithium hydroxide, 47.5226 g of titanium dioxide, 5.3529 g of aluminum oxide, and 120.7816 g of ammonium dihydrogen phosphate;

[0057] Step 2: Take lithium aluminate LiAlO according to 5% of the total mass of the lithium hydroxide, aluminum oxide, titanium dioxide and ammonium dihydrogen phosphate powders 2 ;

[0058] Step 3: Add 600 g of isopropanol and milling beads to the lithium hydroxide, aluminum oxide, titanium dioxide, ammonium dihydrogen phosphate and LiAlO 2 and carry out ball milling and stirring at 200 - 400 revolutions per minute for 10 - 24 h to obtain a uniformly mixed slurry;

[0059] Step 4: Dry the uniformly mixed slurry at 50°C to 80°C for 10 to 24 hours to obtain a mixed powder;

[0060] Step 5: Place the mixed powder in a muffle furnace, under air conditions, heat it at a heating rate of 2 - 10°C / min to 700 - 900°C and calcine for 5 - 10 hours to obtain a precursor powder of LATP solid electrolyte;

[0061] Step 6: Press the precursor powder of LATP solid electrolyte into tablets at 180 - 200 MPa, and then heat it at a heating rate of 5 - 10°C / min to 700 - 900°C for secondary sintering for 4 - 8 hours to obtain the modified NASICON-type solid electrolyte.

[0062] Example 3

[0063] A preparation method of a modified NASICON-type solid electrolyte, comprising the following steps:

[0064] Step 1: Weigh 19.0918 g of lithium hydroxide, 47.5226 g of titanium dioxide, 5.3529 g of aluminum oxide, and 120.7816 g of ammonium dihydrogen phosphate;

[0065] Step 2: Take lithium metaaluminate LiAlO according to 10% of the total mass of the lithium hydroxide, aluminum oxide, titanium dioxide, and ammonium dihydrogen phosphate powders 2 ;

[0066] Step 3: Add 600 g of isopropanol and milling beads to the lithium hydroxide, aluminum oxide, titanium dioxide, ammonium dihydrogen phosphate, and LiAlO 2 and carry out ball milling and stirring at 200 - 400 revolutions per minute for 10 - 24 hours to obtain a uniformly mixed slurry;

[0067] Step 4: Dry the uniformly mixed slurry at 50°C to 80°C for 10 to 24 hours to obtain a mixed powder;

[0068] Step 5: Place the mixed powder in a muffle furnace, under air conditions, heat it at a heating rate of 2 - 10°C / min to 700 - 900°C and calcine for 5 - 10 hours to obtain a precursor powder of LATP solid electrolyte;

[0069] Step 6: Press the precursor powder of LATP solid electrolyte into tablets at 180 - 200 MPa, and then heat it at a heating rate of 5 - 10°C / min to 700 - 900°C for secondary sintering for 4 - 8 hours to obtain the modified NASICON-type solid electrolyte.

[0070] The modified NASICON-type solid electrolyte also includes replacing Ti 4+Or replace Al 3+ with a doping element, and the doping element that replaces Ti 4+ is Zr 4+ , Hf 4+ , Ge 4+ , Sn 4+ , Te 3+ or Ta 5+ , and the doping element that replaces Al 3+ is Mg 2+ or In 3+ .

[0071] Replace Ti 4+

[0072] Tetravalent cation doping: Tetravalent cations such as Zr 4+ and Hf 4+ can replace Ti 4+ , thereby increasing the ionic conductivity of LATP and reducing the reduction of Ti 4+ . These dopants can stabilize the structure of LATP and prevent Ti 4+ from being reduced to Ti 3+ , thereby improving the stability and performance of the electrolyte.

[0073] Ge 4+ doping: Ge 4+ can replace Ti 4+ , and when the Ge doping amount is 0.2, the obtained Li 1.4 Al 0.4 Ti 1.6-x Ge x (PO 4 ) 3 has the highest ionic conductivity of 1.29×10 -3 S / cm. The ionic radius of Ge 4+ is relatively small, and after doping, it can optimize the ion transport channels and promote lithium ion transport.

[0074] Sn 4+ doping: Sn 4+ can replace Ti 4+ , and uniform replacement is beneficial to stabilizing the ceramic crystal structure, reducing the grain size, and increasing the relative density.

[0075] Zr 4+ doping: Zr 4+ can replace Ti 4+ , and the obtained Li 1.4 Al 0.4 Zr 0.1 Ti 1.5 (PO 4 ) 3The ionic conductivity at room temperature can reach 1.4×10 -3 S / cm.

[0076] Replace Al 3+

[0077] with Mg 2+ Doping: Mg 2+ can partially replace Al 3+ , not only increasing the Li + concentration, but also expanding the material size and lithium-ion transport channels, thus improving the ionic conductivity and density of LATP.

[0078] In 3+ Doping: In 3+ can replace Al 3+ , introducing In 3+ which expands the lithium-ion transport path and at the same time increases the lattice volume, being beneficial to increasing its density.

[0079] Other doping

[0080] Te 3+ Doping: Te 3+ can replace Ti 4+ , and when the doping concentration is 0.03, the obtained Li 1.3 Al 0.3 Te 0.03 Ti 1.67 (PO 4 ) 3 has the highest ionic conductivity of 7.03×10 -4 S / cm. The high electronegativity of Te mainly exists in the +3 valence state, and the doped sample can effectively inhibit the interfacial side reaction between lithium metal and the ceramic.

[0081] Ta 5+ Doping: Ta 5+ can replace Ti 4+ , effectively improving the interfacial problem of the contact between LATP and lithium metal.

[0082] Comparative Example 1

[0083] The difference between Comparative Example 1 and Example 1 is only that: it is an untreated pure LATP solid electrolyte, that is, the LATP solid electrolyte without adding LiAlO 2 in Step 2.

[0084] The morphology of the LATP powder material prepared in Example 3 of the present invention was observed by scanning electron microscopy, as Figure 1 shown.

[0085] The LATP material prepared in Example 3 of the present invention was subjected to structural characterization by X-ray diffraction, as Figure 2 shown.

[0086] The LATP solid electrolyte powders prepared in Examples 1, 2, and 3 of the present invention and Comparative Example 1 were pressed into tablets for conductivity testing. The results are shown in Table 1 below. It can be seen from Table 1 that the addition of LiAlO 2 can effectively improve the lithium ion conductivity of LATP, and within a certain range, its conductivity increases with the increase of the content of LiAlO 2 .

[0087] Table 1

[0088] Sample <![CDATA[Ionic conductivity (S·cm -1 )]]> Example 1 <![CDATA[1.56×10 -4 > Example 2 <![CDATA[3.34×10 -4 > Example 3 <![CDATA[5.78×10 -4 > Comparative Example 1 <![CDATA[1.04×10 -4 >

[0089] Application Example

[0090] The LATP solid electrolyte tablets obtained in Example 3 and Comparative Example 1 were assembled into lithium symmetric batteries for charge and discharge experiments to test their lithium symmetric battery cycling performance at a current density of 0.05 mA / cm -2 . The results are as Figure 3 and Figure 4 shown.

[0091] It can be Figure 3 seen that the lithium symmetric battery with the LATP solid electrolyte added with 15% LiAlO 2 can stably cycle for 350 h at a current density of 0.05 mA / cm -2 , showing very good lithium stability.

[0092] For the unmodified LATP in Comparative Example 1, its lithium stability is as Figure 4 shown, and it shows a short circuit phenomenon after cycling for 25 h, which is caused by poor interface stability.

[0093] It can be seen from the above that by introducing the sintering aid LiAlO 2 into the LATP solid electrolyte, the present invention not only improves the conductivity of the LATP solid electrolyte, but also greatly improves the interfacial compatibility between the lithium metal and the LATP solid electrolyte.

[0094] The above embodiments are only the preferred embodiments of the present invention, and the scope of protection of the present invention cannot be limited thereby. Any non-substantial changes and substitutions made by those skilled in the art on the basis of the present invention belong to the scope of protection required by the present invention.

Claims

1. A method for preparing a modified NASICON solid electrolyte, characterized in that: The following steps are involved: Step 1: Press Li 1+x Al x Ti 2-x (PO4)3, wherein x = 0.3 to 0.5, lithium source, aluminum source, titanium source and phosphorus source powders are taken in a chemical dosimeter ratio; Step 2: Take lithium aluminate LiAlO2 according to 1-15% of the total mass of lithium source, aluminum source, titanium source and phosphorus source powder; Step 3: Add a dispersant and ball milling beads to the lithium source, aluminum source, titanium source, phosphorus source and LiAlO2, and perform ball milling and stirring to obtain a uniformly mixed slurry; Step 4: drying the uniformly mixed slurry to obtain a mixed powder; Step 5: placing the mixed powder in a muffle furnace and calcining at 700-900° C. for 5-10 hours under air conditions to obtain LATP solid electrolyte precursor powder; Step 6: Press the LATP solid electrolyte precursor powder into tablets, and perform secondary sintering at 700-900°C for 4-8h to obtain a modified NASICON solid electrolyte.

2. The method for preparing the modified NASICON solid electrolyte according to claim 1, characterized in that: In the step 1, the lithium source is one or more of lithium carbonate, lithium hydroxide, and lithium oxide, and the aluminum source is aluminum oxide, aluminum hydroxide, The titanium source is titanium dioxide and / or titanium chloride, and the phosphorus source is one or more of diammonium phosphate, phosphoric acid, and lithium phosphate.

3. The method for preparing the modified NASICON solid electrolyte according to claim 2, characterized in that: In the step 1, the lithium hydroxide is in excess of 1-10%.

4. The method for preparing the modified NASICON solid electrolyte according to claim 1, characterized in that: In the step 3, the dispersant is one or more of anhydrous ethanol, propanol, isopropanol, and ethylene glycol, and the amount of the dispersant is 3 times the mass of the lithium source, aluminum source, titanium source, phosphorus source, and LiAlO2.

5. The method for preparing the modified NASICON solid electrolyte according to claim 1, characterized in that: In the step 3, the ball mill stirring speed is 200 to 400 rpm, and the stirring time is 10 to 24 hours.

6. The method for preparing the modified NASICON solid electrolyte according to claim 1, characterized in that: In step 4, the drying temperature is 50° C. to 80° C., and the drying time is 10 to 24 hours.

7. The method for preparing the modified NASICON solid electrolyte according to claim 1, characterized in that: In the step 5, the heating rate in the muffle furnace is 2-10° C. / min.

8. The method for preparing the modified NASICON solid electrolyte according to claim 1, characterized in that: The pressure of tableting in step six is ​​180-200 MPa, and the sintering heating rate of the secondary sintering is 5-10° C. / min.

9. A modified NASICON solid electrolyte prepared by the preparation method according to any one of claims 1 to 8.

10. The modified NASICON solid electrolyte according to claim 9, characterized in that: The modified NASICON solid electrolyte further comprises replacing Ti 4+ Or replace Al 3+ The doping element replaces Ti 4+ The doping element is Zr 4+ , Hf 4+ ,Ge 4+ Sn 4+ 、Te 3+ or 5+ , the replacement of Al 3+ The doping element is Mg 2+ or In 3+ .

Images