Lithium ion battery for regulating and controlling LAGP interface by using KH2PO4-SN composite interface layer and preparation of lithium ion battery

Abstract

The invention discloses a composite interface layer for a solid electrolyte anode and a preparation method of the composite interface layer, and particularly relates to a lithium ion battery for regulating and controlling an LAGP interface by utilizing a KH2PO4-SN composite interface layer and preparation of the lithium ion battery. A ferroelectric material KH2PO4 is introduced into a lithium metal anode, and the ferroelectric material KH2PO4 and an SN plastic crystal electrolyte form an artificial composite SEI buffer layer between an LAGP solid electrolyte and a lithium metal cathode. By means of spontaneous polarization of KH2PO4, under the action of an external electric field, uniform deposition of lithium ions is guided, meanwhile, Li3PO4 with high ionic conductivity is generated on the lithium surface, and a cured SN buffer layer can provide good contact for LAGP and a lithium metal interface. In addition, the LITFSI in the SN can continue to react with Li < + > in the circulation process to generate LiF. The ferroelectric KH2PO4 capable of generating spontaneous polarization can promote uniform deposition of lithium ions, increase the contact area and limit lithium deposition points, and can also generate a uniform SEI film.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion batteries, and in particular relates to a lithium-ion battery utilizing a KH2PO4-SN composite interface layer to regulate an LAGP interface and a preparation thereof. Background Art

[0002] Li 1.5 A1 0.5 Ge 1.5 (PO4)3 (LAGP) is a kind of oxide solid electrolyte that is currently being studied very hotly. Due to the serious side reaction between LAGP and lithium metal anode, as well as the solid-solid contact between LAGP and lithium metal anode, on the one hand, the interface contact performance is usually poor due to the solid-solid contact between solid LAGP and lithium metal, resulting in increased interface resistance; on the other hand, Ge on the surface of LAGP 4+ Reduction to Ge 2+ This results in the formation of a GeO mixed conductive interface and a significant volume expansion of the LAGP electrolyte, leading to its fragmentation. Existing technologies can incorporate an interfacial buffer layer between the LAGP and the lithium metal anode. For example, by magnetron sputtering an inorganic layer (such as ZnO or Al) onto the LAGP surface, this layer can accommodate the volume changes during lithium stripping and plating. However, this sputtered layer is easily damaged during cycling, and lithium dendrites can continue to grow after a period of cycling. Alternatively, an organic SEI (such as polyethylene oxide (PEO)) can be introduced at the interface. A high content of LiF in the SEI plays a key role in suppressing lithium dendrite growth. LiF effectively mitigates side reactions at the interface between the LAGP and lithium metal anode, regulating the uniform deposition of lithium ions and preventing lithium dendrites from penetrating the SEI layer. Although inorganic layers containing LiF can stabilize the interface between the lithium metal anode and the electrolyte, their inherent brittleness and complex preparation process still hinder the application of solid-state lithium metal batteries. Summary of the Invention

[0003] In view of the deficiencies of the above materials, the purpose of the present invention is to provide a method for regulating the side reactions at the interface between LAGP and lithium metal anode by using KH2PO4-SN composite interface layer, as well as lithium ion battery and its preparation. The present invention introduces KH2PO4 into the lithium negative electrode, and forms an artificial gradient composite SEI buffer layer between the LAGP solid electrolyte and the lithium metal negative electrode with succinonitrile (SN) electrolyte. The spontaneous polarization of KH2PO4 and is used to guide the uniform deposition of lithium ions, while the SN electrolyte buffer layer provides good contact for the interface. In addition, the LITFSI of SN will continue to react with Li during the cycle. + The reaction generates LiF. This structure can improve the uniformity of lithium deposition morphology and avoid the problem of small solid-solid contact surface and limited lithium deposition points.

[0004] In order to achieve the above object, the present invention is implemented through the following technical solutions: In a first aspect, the present invention provides a method for preparing a lithium-ion battery using a KH2PO4-SN composite interface layer to regulate the LAGP interface, comprising the following steps: S1. Add LiTFSI and KH2PO4 to SN, and heat and stir on a heating stirring table to obtain uniformly mixed KH2PO4-SN, which is then solidified at room temperature.

[0005] S2. Heat and stir the prepared KH2PO4-SN on a heating stirring table in a glove box. After KH2PO4-SN becomes liquid, add it dropwise to the surface of LAGP to obtain KH2PO4-SN@LAGP.

[0006] S3. Li metal is used as the negative electrode, KH2PO4-SN@LAGP is used as the electrolyte, and assembled with the positive electrode to obtain a lithium-ion battery that uses the KH2PO4-SN composite interface layer to regulate the LAGP interface.

[0007] In step S1, the mass ratio of SN to LITFSI is 2:3, and the mass of KH2PO4 is 2% of the total mass of SN and LITFSI.

[0008] In step S1, the heating and stirring time is 12 hours, and the heating temperature is 70 degrees Celsius.

[0009] In step S2, Li 1.5 A1 0.5 Ge 1.5 The preparation method of (PO4)3 powder comprises the following steps: Lithium hydroxide, aluminum oxide, germanium dioxide and ammonium dihydrogen phosphate were mixed by Li 1.5 A1 0.5 Ge 1.5 After mixing the stoichiometric ratio of (PO4)3, wet ball milling was carried out in a planetary ball mill to obtain Li 1.5 A1 0.5 Ge 1.5 The precursor of (PO4)3 is sintered, and then ball milled twice, and Li is obtained after drying. 1.5 A1 0.5 Ge 1.5 (PO4)3 powder.

[0010] Furthermore, the ball milling medium is ethanol, the ball milling speed is 400-500 r / min, and the ball milling time is 8-10 hours; the first sintering temperature is 400-500°C for 3-5 hours; the second ball milling time is 8-10 hours; and the drying is vacuum drying at a temperature of 80-100°C for 10-12 hours.

[0011] The LAGP solid electrolyte is prepared by combining Li 1.5 A1 0.5 Ge 1.5 (PO₄)₃ powder is pressed into flakes in a custom mold. The flakes are then cold isostatically pressed, sintered, and polished. The mold pressing pressure is 9.1 to 10 MPa, the cold isostatic pressing pressure is 100 to 150 MPa, and the sintering temperature is 800 to 900°C for 7 to 9 hours. The flakes are then polished using sandpaper of 240, 400, 800, 1200, and 2000 mesh, respectively.

[0012] The amount of KH2PO4-SN@LAGP used in step S2 is 5 μl.

[0013] The battery in step S3 includes a lithium sheet, KH2PO4-SN@LAGP, and a lithium iron phosphate positive electrode.

[0014] In a second aspect, the present invention provides a lithium-ion battery in which a KH2PO4-SN composite interface layer regulates the LAGP negative electrode interface, which is obtained by the preparation method described in the first aspect.

[0015] The beneficial effects achieved by one or more technical solutions of the present invention are as follows: The present invention introduces a composite interface layer between the LAGP electrolyte and the negative electrode lithium metal to further solve the serious side reactions between the LAGP electrolyte and the lithium metal, promote the uniform distribution of lithium ions, and suppress lithium dendrites, thereby improving the lithium battery and full-electric performance of the LAGP lithium-ion battery.

[0016] The present invention forms an artificial composite interface layer (Li@KH2PO4-SN@LAGP) in situ between the LAGP solid electrolyte and the lithium metal negative electrode. The layer consists of two parts: one is the LiF, LiN, and Li3PO4 inorganic interface layer formed in situ by the reaction of the KH2PO4-SN solution with the lithium sheet, and the other is the KH2PO4 on the LAGP electrolyte. Among them, KH2PO4, as a ferroelectric material, generates spontaneous polarization under the action of an external electric field, thereby inducing the uniform deposition of lithium ions and avoiding the growth of lithium dendrites. At the same time, KH2PO4 can also rivet free SN, reducing the side reaction of SN with lithium metal, thereby extending the life of the battery. At the same time, LITFSI will continue to react with Li+ to form LiF during the cycle, maintaining the structural integrity of the composite interface layer.

[0017] The invention forms a composite interface layer between LAGP and lithium metal anode, which reduces the interface side reaction and interface impedance between LAGP solid electrolyte and lithium metal anode. After assembling Li / KH2PO4-SN@LAGP / Li symmetric battery, the critical current density (CCD) of the battery can be increased from 0.7mA / ma / cm2 to 0.7mA / ma / cm3 compared with the Li / SN@LAGP / Li symmetric battery without KH2PO4. 2 Increased to 1.7ma / cm 2 At the same time, at a current density of 0.1 mA / cm2 and 25°C, the cycle life reaches more than 700 hours, while the cycle life of the Li / SN@LAGP / Li symmetric battery without adding KH2PO4 is only 380 hours.

[0018] The Li / KH2PO4-SN@LAGP / LFP full cell achieved a first-cycle discharge capacity of 145.8 mAh / g at a 0.5C rate, with an initial coulombic efficiency of 95.02%. Furthermore, after 100 cycles, the discharge capacity remained at 144.21 mAh / g, achieving a capacity retention rate of 99%. After cycling at a high rate of 0.1C-1C, the discharge capacity of the Li / KH2PO4-SN@LAGP / LFP full cell recovered to 162.74 mAh / g at 0.1C, demonstrating high reversible capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the long cycle diagram of the LFP full battery 0.5c of Example 1 and Comparative Example 1.

[0020] Figure 2 This is the cycle diagram of the LFP full battery of Example 1 and Comparative Example 1 at a rate of 0.1c-1c-0.1c.

[0021] Figure 3 The long-term lithium cycle diagram of Example 1 and Comparative Example 1 at 25 degrees and 0.1 mA cm-1.

[0022] Figure 4a This is the SEM image of the LAGP electrolyte surface of comparative example 1 after cycling for 100 hours at 25 degrees and a current density of 0.1 mA cm-1.

[0023] Figure 4b This is the SEM image of the LAGP electrolyte surface after cycling for 100 h at 25 degrees and a current density of 0.1 mA cm-1 in Example 1.

[0024] Figure 5a This is the SEM image of the lithium sheet surface after cycling for 100 hours at 25 degrees and a current density of 0.1 mA cm-1 in Example 1.

[0025] Figure 5b This is the SEM image of the lithium sheet surface of Comparative Example 1 after cycling for 100 hours at 25 degrees and a current density of 0.1 mA cm-1. DETAILED DESCRIPTION

[0026] The present invention provides a solid electrolyte material, a preparation method thereof, and a solid-state battery. To make the objectives, technical solutions, and effects of the present invention more clear and explicit, the present invention is further described in detail with reference to the following examples. It should be understood that the specific examples described herein are merely illustrative of the present invention and are not intended to limit the present invention. Example

[0027] LiTFSI and KH2PO4 were added to SN at a mass ratio of 2:3, with the mass of KH2PO4 representing 2% of the total mass of SN and LITFSI. The mixture was heated and stirred on a heated stirring plate for 12 hours at 70°C to obtain a uniformly mixed KH2PO4-SN, which was then solidified at room temperature. The prepared KH2PO4-SN was heated and stirred on a heated stirring plate in a glove box. Once the KH2PO4-SN became liquid, it was added dropwise to the surface of LAGP, yielding KH2PO4-SN@LAGP.

[0028] Lithium hydroxide, aluminum oxide, germanium dioxide and ammonium dihydrogen phosphate were mixed by Li 1.5 A1 0.5 Ge 1.5 After mixing the stoichiometric ratio of (PO4)3, wet ball milling was carried out in a planetary ball mill. The ball milling medium was ethanol, the ball milling speed was 400-500 r / min, and the ball milling time was 8-10 h. Li 1.5 A1 0.5 Ge 1.5 (PO4)3 precursor, the obtained precursor is subjected to the first sintering, the first sintering temperature is 400-500℃ for 3-5h, and after sintering, it is subjected to secondary ball milling, the ball milling speed is 400-500r / min, and the ball milling time is 8-10h. After drying in an oven at 80 degrees, Li1.5A10.5Ge1.5(PO4)3 powder is obtained. The LAGP solid electrolyte is prepared by pressing Li 1.5A1 0.5Ge 1.5(PO4 ) 3 powder into a sheet in a special mold at a pressure of 9.1 to 10 MPa. The sheet is then cold isostatically pressed at a pressure of 100 to 150 MPa. The sheet is then sintered in a muffle furnace at a temperature of 800 to 900°C for 7 to 9 hours, and then polished with 240-mesh, 400-mesh, 800-mesh, 1200-mesh, and 2000-mesh sandpaper, respectively.

[0029] Symmetrical cells were assembled in the order of Li / KH2PO4-SN@LAGP / Li, where the amount of KH2PO4-SN was 5ul, and full cells were assembled in the order of Li / KH2PO4-SN@LAGP / LFP, where 5ul of electrolyte was added between the positive electrode and LAGP. Example

[0030] Different from Example 1, the KH2PO4 content in the KH2PO4-SN solution was 4%, and the symmetrical battery was assembled in the order of Li / KH2PO4-SN@LAGP / Li, wherein the amount of KH2PO4-SN was 5ul, and the full battery was assembled in the order of Li / KH2PO4-SN@LAGP / LFP, wherein 5ul of electrolyte was added between the positive electrode and LAGP. Example

[0031] Different from Example 1, the content of KH2PO4 in the KH2PO4-SN solution was 6%, and the symmetrical battery was assembled in the order of Li / KH2PO4-SN@LAGP / Li, wherein the amount of KH2PO4-SN was 5ul, and the full battery was assembled in the order of Li / KH2PO4-SN@LAGP / LFP, wherein 5ul of electrolyte was added between the positive electrode and LAGP. Comparative Example 1 Different from Example 1, KH2PO4 was not added to SN, and symmetrical cells were assembled in the order of Li / SN@LAGP / Li, where the amount of SN was 5 μl, and full cells were assembled in the order of Li / SN@LAGP / LFP, where 5 μl of electrolyte was added between the positive electrode and LAGP.

[0032] Comparative Example 2 Different from Example 1, the lithium sheet and LAGP were not treated in any way. The symmetrical battery Li / LAGP / Li was assembled in the order of lithium sheet, LAGP, and lithium sheet, and the full battery was assembled in the order of Li / LAGP / LFP, with 5 μl of electrolyte added between the positive electrode and LAGP.

[0033] Figure 1The comparison of the full battery of Example 1 and Comparative Example 1 in terms of 0.5C long cycle stability is shown. The capacity of Li / SN@LAGP / LFP decays from 124.6mAh / g to 121.2mAh / g after 100 cycles, and the capacity retention rate is about 97%. The initial capacity of the Li / KH2PO4-SN@LAGP / LFP battery is as high as 145mAh / g at 0.5C, and the capacity retention rate is still around 99.1% after 100 cycles. Compared with the Li / SN@LAGP / LFP full battery without the addition of KH2PO4, the coulombic efficiency stability of the full battery after composite interface modification is also improved, basically maintained at about 100%. At the same time, the discharge specific capacity of the first cycle of 0.5C is also increased from 124.6mAh / g to 145mAh / g.

[0034] Figure 2 The rate performance and charge-discharge curves of Li / KH2PO4-SN@LAGP / LFP and Li / SN@LAGP / LFP full batteries at different rates. 4- When the SN@LAGP / LFP rate was increased from 0.1C to 1C and then back to 0.1C, the discharge capacity recovered to 162.79 mAh / g. This result demonstrates that the composite interface layer enhances the ability of lithium ions to intercalate and deintercalate between the electrolyte and the electrode. However, as the current density gradually increased, the rate performance of the Li / SN@LAGP / LFP full cell rapidly deteriorated, with a discharge capacity of only 16.95 mAh / g at 1C, indicating significant interfacial contact issues between the LAGP without KH2PO4 and the lithium metal anode.

[0035] like Figure 3 As shown, the symmetric Li / KH2PO4-SN@LAGP / Li and Li / SN@LAGP / Li cells were tested at 25℃ and 0.1ma / cm 2 Constant current charge-discharge experiments were conducted under 400 nm CMOS conditions. Li / SN@LAGP / Li cycled for only 380 h, and the polarization voltage continued to increase with cycling time, indicating that interfacial side reactions hindered lithium ion migration. Under the same conditions, Li / KH2PO4SN@LAGP / Li cycled stably for over 700 h, demonstrating that the addition of KH2PO4 accelerates lithium ion migration at the interface.

[0036] As shown in Figure 4, Figure 4a For Li / SN@LAGP / Li symmetric battery at 25℃, 0.1ma / cm 2 The SEM image of the LAGP electrolyte surface after 100 hours of cycling shows that a large amount of dead lithium is attached to the LAGP. Figure 4b For Li / KH2PO4-SN@LAGP / Li symmetric battery at 25℃, 0.1ma / cm2 From the SEM image of the LAGP electrolyte surface after 100 hours of cycling, it can be found that its surface is very smooth and there is no dead lithium attached, indicating that the added KH2PO4 can reduce the side reaction between lithium metal and LAGP and promote the transmission of lithium ions.

[0037] As shown in Figure 5, Figure 5a For Li / KH2PO4-SN@LAGP / Li symmetric battery at 25℃, 0.1ma / cm 2 The SEM image of the lithium sheet surface after 100 hours of cycling shows that the surface of the lithium sheet is very smooth and has no cracks. Figure 5b For Li / SN@LAGP / Li symmetric battery at 25℃, 0.1ma / cm 2 The SEM image of the lithium sheet surface after 100 hours of cycling shows a large number of cracks and uneven areas. The results also show that adding KH2PO4 to the surface can effectively inhibit the side reaction between lithium metal and LAGP electrolyte, reduce the deposition of dead lithium, and inhibit the generation of space charge layer.

[0038] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention, and all these changes or substitutions should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for preparing a lithium-ion battery using a KH2PO4-SN composite interface layer to regulate the LAGP interface, characterized in that: The following steps are involved: S1, potassium dihydrogen phosphate is uniformly stirred in succinonitrile to obtain a mixed solution of succinonitrile and potassium dihydrogen phosphate, and the mixed solution of succinonitrile and potassium dihydrogen phosphate is added dropwise to Li 1.5 A1 0.5 Ge 1.5 Interface of (PO4)3 solid electrolyte. 2.S2. Lithium metal is used as the negative electrode and KH2PO4-SN@LAGP as the electrolyte, and assembled with the positive electrode to obtain a lithium-ion battery in which the LAGP interface is regulated by the KH2PO4-SN composite interface layer.

3. The preparation method according to claim 1, wherein In step S1, the mass of KH2PO4 is 6% of the mass of SN, and then the mixture is stirred by magnetic stirring for 12 hours.

4. The preparation method according to claim 1, wherein In step S1, the stirring temperature of SN and KH2PO4 is 60°C, and the stirring time is 12 hours.

5. The preparation method according to claim 1, wherein In step S1, Li 1.5 A1 0.5 Ge 1.5 The preparation method of (PO4)3 powder comprises the following steps: lithium hydroxide, aluminum oxide, germanium dioxide and ammonium dihydrogen phosphate are mixed in a mixture of Li 1.5 A1 0.5 Ge 1.5 After mixing the stoichiometric ratio of (PO4)3, wet ball milling was carried out in a planetary ball mill to obtain Li 1.5 A1 0.5 Ge 1.5 The precursor of (PO4)3 is sintered, and then ball milled twice, and then dried to obtain Li 1.5 A1 0.5 Ge 1.5 (PO4)3 powder.

6. The preparation method according to claim 4, wherein The ball milling medium is ethanol, the ball milling speed is 400-500 r / min, and the ball milling time is 8-10 hours; the first sintering temperature is 400-500° C. for 3-5 hours; the second ball milling time is 8-10 hours; the drying is vacuum drying at a temperature of 80-100° C. for 10-12 hours.

7. The preparation method according to claim 1, wherein The LAGP solid electrolyte is prepared by combining Li 1.5 A1 0.5 Ge 1.5 (PO4)3 powder is pressed into sheets in a special mold, and then the pressed sheets are pressed under cold isostatic pressing, sintered and polished.

8. The preparation method according to claim 6, wherein The pressing pressure in the mold is 9.1-10 MPa, the cold isostatic pressing pressure is 100-150 MPa, the sintering temperature is 800-900°C, the time is 7-9 hours, and the polishing is carried out in sequence with 240 mesh, 400 mesh, 800 mesh, 1200 mesh, and 2000 mesh sandpaper.

9. The preparation method according to claim 1, wherein The battery includes a lithium sheet, KH2PO4-SN@LAGP and a lithium iron phosphate positive electrode.

10. A lithium-ion battery utilizing a KH2PO4-SN composite interface layer to regulate the LAGP interface, characterized in that: The method is obtained by the preparation method according to any one of claims 1 to 8.

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