Intermediate interface layer for solid-state lithium metal battery and solid-state lithium metal battery

Abstract

The invention discloses a preparation method and application of an interface layer in a solid-state lithium metal battery. The preparation method comprises the following steps: preparing a modified solution, and dissolving anhydrous gallium nitrate Ga (NO3) 3 in absolute ethyl alcohol; dispensing the modified solution on the surface of the LATP solid electrolyte; and drying to obtain Ga (NO3) 3-coated LATP. Through in-situ electrochemical reaction of Ga (NO3) 3 and lithium metal, a multifunctional interface layer composed of LiGa alloy and a LiNxOy compound is constructed. The electronic conductive LiGa alloy can eliminate local electric field concentration at the interface and guide uniform dendrite-free lithium deposition. In LiNxOy, LiNO3 with low interface energy and high affinity can improve interface contact, and Li3N with a low Li < + > migration energy barrier can provide a rapid path for transmission of Li < + > at an interface. In addition, the strong electronic insulativity of LiNxOy can prevent side reactions. Therefore, the LiGa + LiNxOy multifunctional layer prepared by the invention can maintain stable and tight contact of a Li / LATP interface in the whole cycle process, and the electrochemical performance of a lithium / lithium symmetrical battery and a total battery using different positive electrodes is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the field of solid-state batteries, and particularly relates to a method for preparing an interface layer between a solid electrolyte and a lithium metal anode, and a solid-state lithium metal battery. Background Art

[0002] High-energy density and high-safety energy storage devices are requirements for the rapid development of current portable devices and electric vehicles. However, traditional lithium-ion batteries using liquid electrolytes have reached the limit of energy density due to the inherent limitations of their structures. More fatally, liquid electrolytes have serious safety hazards such as flammability and easy leakage. Solid-state batteries (SSBs) consist of non-flammable solid electrolytes (SSEs), lithium metal anodes, and high-voltage cathodes, and have advantages such as high safety, high energy density, and excellent cycle life. They are considered one of the key means to solve the above problems. Developing SSEs with high ionic conductivity and excellent stable SSE / Li interfaces is the key to achieving high-performance SSBs. Among various SSEs, NASICON-type Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (LATP) electrolytes stand out due to their high room-temperature ionic conductivity, wide electrochemical window, good thermal / structural stability, excellent air stability and moisture resistance, low raw material cost, and easy preparation.

[0003] The wide application of LATP in lithium metal batteries is still hindered by many interface problems, including severe side reactions between LATP and metal Li, poor solid-solid interface contact, poor interface ion transport, and rapid growth of lithium dendrites. The compatibility between LATP and metal Li is poor, and spontaneous side reactions will occur after they come into contact. The high-valent Ti 4+ in LATP reduces the formation of an interfacial phase with low ionic conductivity and high electronic conductivity. The formation of the interfacial phase is accompanied by a violent volume expansion, and the stress at the interface continuously accumulates until LATP breaks. This leads to continuous deterioration of the interface resistance, severe polarization, and rapid growth of lithium dendrites.

[0004] In this case, people improve the chemical / electrochemical stability of the Li / LATP interface and improve their physical contact through grain boundary and interface engineering. Specifically, higher ionic conductivity and fewer bulk defects are achieved by exploring new sintering processes (spray drying, direct pulsed laser deposition), introducing sintering aids (Li2CO3, B2O3), element doping (Zn doping, Bi doping), etc. However, due to poor contact between the Li / LATP interfaces, serious side reactions, and low ion transport efficiency, an interlayer is still needed. Each interlayer is inferred and established, and at the same time, according to different requirements, the excellent components required for the interlayer are gradually understood. To solve the problem of poor physical contact at the Li / LATP interface, lithiophilic metals such as Al, Ge, Bi, etc. are introduced by methods such as magnetron sputtering, atomic deposition, and vapor deposition. The presence of the lithiophilic alloy can greatly improve the lithium affinity of the LATP electrolyte and achieve a smaller interfacial resistance. However, the lithiophilic metal layer strategy also faces other problems. Even though the alloy layer can eliminate the stress concentration at the interface through a uniform electric field distribution, due to the problem of side reactions not being solved, the interfacial impedance and polarization voltage still increase during battery cycling. Introducing PVDF, PEO-based polymers or customizing other electronic shielding organic layers (PSiO, KANF, UVEA, F-HNBR, sericin film) by simple drop coating and spin coating methods can effectively block the electron tunneling effect at the interface, physically isolate Li and LATP to avoid side reactions, and provide flexible interfacial contact. Problems such as the temperature dependence, insufficient ionic conductivity, and low mechanical strength of the polymer coating should also be considered, which are usually solved by adding fillers to the polymer coating. The addition of BN, CuF2, BaTiO3, and MoS2 can improve the ionic transport and dendrite inhibition ability of the polymer coating. In-situ transformation / alloying reactions to form a mixed ion-electron hybrid layer composed of a lithium alloy and an ion-conducting phase, such as Li-Zn / LiF, Li-Mg / LiF, Li-Sn / LiCl, and Li-Sn / LiI, etc. are also a method. As a compromise strategy, the construction of the hybrid conductive layer can not only bring about close contact but also has a good effect on suppressing side reactions and fast ion transfer at the interface. To realize the application of LATP-based solid-state lithium batteries, it is necessary to continue to explore and design more ideal interlayers. Summary of the Invention

[0005] The present invention provides a preparation and application of an interface layer for a solid-state lithium metal battery, aiming at serious problems such as poor contact at the LATP / Li interface, uncontrollable side reactions, dendrite growth, and poor interfacial ion transport ability.

[0006] A preparation and application of an interface layer for a solid-state lithium metal battery, the solid electrolyte includes an interface layer, and the interface layer is a LiGa alloy and LiN x Oy Compound, wherein LiN x O y The compound mainly contains LiNO3 and Li3N, that is, LiGa + LiN x O y Interface, the LiGa + LiN x O y Interface is in-situ constructed on the surface of the solid electrolyte.

[0007] The solid electrolyte described includes Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (LATP), Li 1.5 Al 0.5 Ge 1.5 (PO4)3 (LAGP), Li 10 GeP2S 12 (LGPS) and other solid electrolytes that are unstable to lithium metal.

[0008] After impregnating or drop-coating an anhydrous ethanol solution containing gallium nitrate on the surface of the solid electrolyte and then vacuum drying at 30 - 40 °C, a solid electrolyte containing Ga(NO3)3 is obtained. After that, an in-situ reaction occurs upon contact with lithium metal to generate LiGa + LiN x O y .

[0009] The present invention proposes a lithiophilic nitriding interface strategy with fast ion transport ability. Through the in-situ conversion reaction of lithium metal and Ga(NO3)3, a multifunctional nitriding layer composed of LiGa alloy and LiN x O y Compound is designed at the Li / LATP interface. LiN x O y mainly contains Li3N and LiNO3. Li3N has a low migration energy barrier and can provide a fast channel for the transport of lithium ions at the interface. LiNO3 has a high affinity for metallic lithium and LATP, and can achieve close interface contact. LiN x O y has great benefits in terms of uniform lithium flux and contact loss control during cycling. In addition, LiN x O y component can also act as an electron barrier to prevent electrons from tunneling at the interface and protect the LATP pellets from being reduced by metallic lithium. The LiGa alloy with electron-conducting ability can eliminate the local electric field concentration at the interface and guide uniform dendrite-free lithium deposition. Therefore, LiGa+LiN x O yThe multifunctional layer can maintain a stable and intimate contact at the Li / LATP interface throughout the cycling process, and the electrochemical performance of both lithium-lithium symmetric batteries and all-solid-state batteries with different cathodes has been significantly improved.

[0010] A method for preparing an interface layer in a solid-state lithium metal battery, comprising the following steps: Step 1: Prepare a modified solution by dissolving gallium nitrate anhydrous (Ga(NO3)3) in absolute ethanol; Step 2: Drop-coat the modified solution on the surface of the solid electrolyte; Step 3: Dry the solid electrolyte in Step 2 to obtain a solid electrolyte with a Ga(NO3)3 layer; Step 4: React the solid electrolyte with molten lithium in situ to obtain a solid electrolyte with a LiGa + LiN x O y interface.

[0011] The content of Ga(NO3)3 is 10 - 30 mg / mL.

[0012] The amount of the solution drop-coated on the surface of the solid electrolyte is 5 - 20 μL cm -2 .

[0013] The solid electrolyte is selected from solid electrolytes that are unstable to lithium metal, such as Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (LATP), Li 1.5 Al 0.5 Ge 1.5 (PO4)3 (LAGP), Li 10 GeP2S 12 (LGPS), etc.

[0014] Taking Li 1.3 Al 0.3 Ti 1.7 (PO4)3 as an example, Li2CO3, Al2O3, TiO2 and NH4H2PO2 are weighed according to the stoichiometric ratio, and Li 1.3 Al 0.3 Ti 1.7 (PO4) (LATP) solid electrolyte is prepared by the solid-phase sintering method.

[0015] Another technical solution of the present invention is to provide a solid-state lithium metal battery, comprising the solid-state battery electrolyte described above or the solid-state battery electrolyte prepared by the method described above.

[0016] A symmetric battery includes the interface layer for a solid-state lithium metal battery or the interface layer for a solid-state lithium metal battery prepared by the described method.

[0017] The preparation method of the nitrided interface provided by the present invention has the following beneficial effects: (1) The LiGa alloy with electronic conductivity can eliminate the local electric field concentration at the interface and guide uniform dendrite-free lithium deposition; (2) LiNO3 has a high affinity for metallic lithium and LATP, enabling tight interfacial contact and reducing the interfacial resistance.

[0018] (3) Li3N has a low migration energy barrier, providing a fast channel for lithium ion transport at the interface, and enabling low concentration polarization and the balance of interfacial ion diffusion.

[0019] (4) LiN x O y not only has great benefits in terms of uniform lithium flux and controlling contact loss during cycling, but also can act as an electron barrier to prevent electrons from tunneling at the interface, protect the LATP pellets from being reduced by metallic lithium, and inhibit the nucleation and growth of lithium dendrites. Description of the Drawings

[0020] Figure 1 SEM images of the surface (a), cross-section (b) of Ga(NO3)3@LATP prepared in Example 1 of the present invention, and the corresponding elemental energy spectra (c, d).

[0021] Figure 2 High-resolution XPS spectra of Ga 3d (a) and N 1s (b) after the reaction of Ga(NO3)3@LATP prepared in Example 1 of the present invention with metallic lithium.

[0022] Figure 3 EIS impedance spectra (a) before cycling and critical current density (b) of the Li / Ga(NO3)3@LATP / Li symmetric battery prepared in Example 1 of the present invention.

[0023] Figure 4 Voltage-time curves of the Li / Ga(NO3)3@LATP / Li symmetric battery prepared in Example 1 of the present invention at 0.1 mA cm -2 / 0.1mAh cm −2 .

[0024] Figure 5 Rate performance (a) and long-term cycling performance (b) of the Li / Ga(NO3)3@LATP / LFP full battery prepared in Example 1 of the present invention.

[0025] Figure 6Long cycle performance of the Li / Ga(NO3)3@LATP / LMNO full cell prepared in Example 1 of the present invention.

[0026] Figure 7 EIS impedance spectrum before cycling and (b) critical current density of the Li / 10-Ga(NO3)3@LATP / Li symmetric cell prepared in Example 2 of the present invention.

[0027] Figure 8 EIS impedance spectrum before cycling and (b) critical current density of the Li / 30-Ga(NO3)3@LATP / Li symmetric cell prepared in Example 3 of the present invention.

[0028] Figure 9 XRD pattern and (b) surface SEM image of LATP prepared in Comparative Example 1 of the present invention.

[0029] Figure 10 EIS impedance spectrum before cycling and (b) critical current density of the Li / LATP / Li symmetric cell prepared in Comparative Example 1 of the present invention.

[0030] Figure 11 Voltage-time curve of the Li / LATP / Li symmetric cell prepared in Comparative Example 1 of the present invention at 0.1 mA cm -2 / 0.1 mAh cm -2 of.

[0031] Figure 12 Rate performance and (b) long cycle performance of the Li / LATP / LFP full cell prepared in Comparative Example 1 of the present invention.

[0032] Figure 13 Long cycle performance of the Li / LATP / LMNO full cell prepared in Comparative Example 1 of the present invention.

[0033] Figure 14 Voltage-time curve of the Li / Ga@LATP / Li symmetric cell prepared in Comparative Example 2 of the present invention at 0.1 mA cm -2 / 0.1 mAhcm -2 of.

[0034] Figure 15 Voltage-time curve of the Li / LiNO3@LATP / Li symmetric cell prepared in Comparative Example 3 of the present invention at 0.1 mA cm -2 / 0.1 mAhcm -2 of.

[0035] Figure 16The Li / Li3N@LATP / Li symmetric battery prepared in Comparative Example 4 of the present invention has a -2 / 0.1 mAhcm -2 The voltage-time curve of the lower part. DETAILED DESCRIPTION

[0036] The present invention is described in detail below in conjunction with specific embodiments. The present invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solution of this application fall within the protection scope of the present invention. The experimental methods in the following embodiments are conventional methods unless otherwise specified. The test materials used in the following embodiments are all commercially available products. Unless otherwise specified, the reagents are assumed to be directly purchased.

[0037] Example 1 The conventional solid phase sintering method was used to prepare Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (LATP) solid electrolyte. The various raw materials Li2CO3 (99%, Aladdin), Al2O3 (99.99%, Aladdin), TiO2 (99.9%, Aladdin) and NH4H2PO4 (99%, Aladdin) were weighed in a stoichiometric ratio of 1.3:0.3:1.7:3, and an excess of 10 wt% Li2CO3 was added to compensate for the lithium loss during high-temperature sintering. The raw materials and zirconium oxide beads were placed in a ball milling jar with a ball-to-material mass ratio of 10:1, and anhydrous ethanol was used as a dispersion liquid. A planetary ball mill was used for ball milling at 400 rpm for 9 h. After taking out the slurry, it was placed in an oven and dried at 80 °C for 8 h. The dried raw materials were poured into a crucible and placed in a muffle furnace for calcination at 900 °C for 2 h. The heating rate was 2 °C / min, and the temperature was lowered with the furnace. The calcined powder was subjected to secondary ball milling at 400 rpm for 9 h. The dried powder was sieved through a 500-mesh sieve, and 0.16 g of the powder was weighed and poured into a 10 mm steel mold, and pressed at a pressure of 8 MPa for 10 min to obtain the LATP embryo. The LATP embryo was covered with the mother powder and sintered in a muffle furnace at 850 °C for 4 h, with a heating rate of 2 °C / min, to finally obtain the LATP solid electrolyte.

[0038] Place Ga(NO3)3 in a vacuum oven at 40 °C and dry for 48 h. Weigh a certain amount of Ga(NO3)3 powder and dissolve it in anhydrous ethanol to obtain a modified solution with a concentration of 20 mg / mL. Evenly drop 15 μL cm -2The modified solution. After air-drying at 40 °C, the other side was coated, and after air-drying again, the Ga(NO3)3@LATP solid electrolyte was obtained. Using the Ga(NO3)3@LATP solid electrolyte to assemble a battery, during the cycling process, Ga(NO3)3 reacted in situ with lithium metal to obtain LiGa + LiN x O y solid electrolyte with an interface.

[0039] Figure 1 SEM images of (a) the surface, (b) the cross-section of Ga(NO3)3@LATP, and (c, d) the corresponding energy-dispersive X-ray spectroscopy (EDS) maps. It can be seen that the surface of the Ga(NO3)3@LATP solid electrolyte is covered with a flat and dense coating, and the grain boundaries are effectively filled. In addition, the SEM cross-section clearly shows the close contact between the Ga(NO3)3 layer and LATP, and the Ti, Ga, and N elements are clearly stratified in the EDS map.

[0040] Figure 2 High-resolution XPS spectra of (a) Ga 3d and (b) N 1s after the reaction of the Ga(NO3)3@LATP with metallic lithium. In the Ga 3d spectrum after the reaction, two new characteristic peaks were detected at 19.6 eV and 18.5 eV, indicating the presence of LiGa alloy and metallic Ga. In the N 1s spectrum, the three peaks at 407.5, 403.7, and 397.8 eV match LiNO3, LiNO2, and Li3N, respectively, which are LiN 3- compounds generated after the reaction with NO x O y By XPS analysis, it was confirmed that the conversion reaction and alloying reaction between Ga(NO3)3 and lithium metal successfully formed LiGa + LiN x O y multifunctional nitride layer.

[0041] Electrochemical performance test: To assemble a symmetric battery, lithium foil was used as the electrode and Ga(NO3)3@LATP as the electrolyte. The cathode material LiFePO4 (LFP), conductive additive (Super P), and binder (PVDF) were dispersed in N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1. The resulting slurry was coated on aluminum foil with an active material loading of 1.2 - 1.5 mg cm -2 . It was placed in a vacuum oven at 110 °C for 8 h to obtain the LFP cathode sheet. The cathode material Li 1.2 Mn 0.6 Ni 0.2O2 (LMNO), Super P, and PVDF were dispersed in NMP at a mass ratio of 8:1:1. The resulting slurry was coated on an aluminum foil with an active material loading of 1.5 - 2 mg cm -2 . It was placed in a vacuum oven at 110 °C for 8 h to obtain the LMNO positive electrode sheet. Using LFP and Li foil as the positive and negative electrodes respectively, and Ga(NO3)3@LATP as the electrolyte, a Li / Ga(NO3)3@LATP / LFP full cell was assembled. Using LMNO and Li foil as the positive and negative electrodes respectively, and Ga(NO3)3@LATP as the electrolyte, a Li / Ga(NO3)3@LATP / LMNO full cell was assembled. To ensure good transport of Li + at the LFP / LATP and LMNO / LATP interfaces, 2 μL of electrolyte (1 M LiPF6 in EC:DMC = 1:1) was added to the cathode side. Finally, the cells were assembled in an Ar-filled glove box (MIKROUNA, Super 1220 / 750, H2O ≤ 1 ppm, O2 ≤ 1 ppm) using a CR2025 configuration.

[0042] Using the alternating current impedance technique (CHI614C electrochemical workstation), in the range of 1 MHz - 1 Hz with an amplitude of 0.01 V, the ionic conductivity and interfacial impedance of the symmetric cells and full cells were measured. A constant current charge-discharge test was performed on the symmetric cells, with each cycle lasting 2 h. The critical current density (CCD) of the symmetric cells was measured. At a fixed cycle period, the areal capacity of lithium plating / stripping gradually increased (2 h per cycle). In the potential range of 2.4 - 4.2 V (LFP, 1 C = 170 mAh g -1 ) and 2.4 - 4.8 V (LMNO, 1 C = 200 mAh g -1 ), the cells were charged and discharged at different current rates (0.1, 0.2, 0.5, 1.0, and 2.0 C). All electrochemical measurements were carried out at 25 °C.

[0043] Figure 3 For the Li / Ga(NO3)3@LATP / Li symmetric cell, (a) the EIS impedance spectrum before cycling and (b) the critical current density, its initial interfacial resistance was 152.2 Ω cm -2 , and the CCD could reach 1.6 mA cm -2 . As Figure 4 shown, at 0.1 mA cm -2 / 0.1 mAh cm -2The constant current charge-discharge test was carried out on the following symmetric battery. The Li / Ga(NO3)3@LATP / Li symmetric battery showed stable lithium plating / stripping behavior within 3000 h, and the polarization voltage was maintained at about 26 mV, with only a slight increase after long-term cycling. Thanks to LiGa+LiN x O y The intermediate layer improved the interfacial environment of Li / LATP, making the voltage platform very stable and the interfacial ion transport good.

[0044] The Li / LFP and Li / LMNO full batteries assembled using the Ga(NO3)3@LATP solid electrolyte were tested for rate performance and cycle stability. As Figure 5 shown, the Li / Ga(NO3)3@LATP / LFP full battery has excellent rate performance and stable long-cycle performance. The discharge specific capacity can reach 163.8 mAh g at 0.1 C -1 . When the current density increases to 0.2, 0.5, 1, and 2 C, the specific discharge capacities are 154.9, 141.1, 124.7, and 101.5 mAh g -1 respectively. The rapid ion migration at the Li / Ga(NO3)3@LATP interface enables the full battery to have excellent rate performance. When the current density is restored to 0.1 C, the capacity can be restored to 159.6 mAh g -1 (a). After cycling 300 times at 0.5 C, the Li / Ga(NO3)3@LATP / LFP full battery also shows excellent cycle stability, with its capacity stabilized at 118.8 mAh g -1 , the capacity retention rate is 89.3%, and the Coulomb efficiency is greater than 99% (b). Figure 6 Among them, the electrochemical performance of the Li / Ga(NO3)3@LATP / LMNO full battery is also excellent. After cycling 200 times at 0.2 C, the capacity retention rate is still 80.2%.

[0045] Example 2 The process of preparing the LATP solid electrolyte by the solid-phase sintering method is the same as that in Example 1.

[0046] Put Ga(NO3)3 into a 40 °C vacuum oven and dry it for 48 h. Weigh a certain amount of Ga(NO3)3 powder and dissolve it in absolute ethanol to obtain a modified solution with a concentration of 10 mg / mL. Uniformly drop 15 μL cm on the surface of LATP -2The modified solution. After air-drying at 40 °C, the other side was coated, and after air-drying again, 10-Ga(NO3)3@LATP solid electrolyte was obtained. Using 10-Ga(NO3)3@LATP solid electrolyte to assemble a battery, during the cycling process, Ga(NO3)3 reacts in-situ with lithium metal to obtain a solid electrolyte containing LiGa + LiN x O y interface.

[0047] Electrochemical performance test: To assemble a symmetric battery, lithium foil was used as the electrode and 10-Ga(NO3)3@LATP as the electrolyte. Using the AC impedance technique (CHI614C electrochemical workstation), in the range of 1 MHz to 1 Hz with an amplitude of 0.01 V, the ionic conductivity and interfacial impedance of the symmetric battery and the full battery were measured. A constant current charge-discharge test was carried out on the symmetric battery, with each cycle lasting 2 h. The critical current density (CCD) of the symmetric battery was measured. At a fixed cycle period, the areal capacity of lithium plating / stripping gradually increased (2 h per cycle). As Figure 7 shown, the initial interfacial impedance of the Li / 10-Ga(NO3)3@LATP / Li symmetric battery was 265.4 Ω cm -2 (a), and the CCD was 1.1 mA cm -2 (b).

[0048] Example 3 The process of preparing LATP solid electrolyte by solid-phase sintering method was the same as that in Example 1.

[0049] Ga(NO3)3 was placed in a vacuum oven at 40 °C and dried for 48 h. A certain amount of Ga(NO3)3 powder was weighed and dissolved in absolute ethanol to obtain a modified solution with a concentration of 30 mg / mL. 15 μL cm -2 of the modified solution was evenly drop-coated on the surface of LATP. After air-drying at 40 °C, the other side was coated, and after air-drying again, 30-Ga(NO3)3@LATP solid electrolyte was obtained. Using 30-Ga(NO3)3@LATP solid electrolyte to assemble a battery, during the cycling process, Ga(NO3)3 reacts in-situ with lithium metal to obtain a solid electrolyte containing LiGa + LiN x O y interface.

[0050] Electrochemical performance test: To assemble a symmetric cell, lithium foil was used as the electrode and 30-Ga(NO3)3@LATP was used as the electrolyte. The ionic conductivity and interfacial impedance of the symmetric cell and full cell were measured using an alternating current impedance technique (CHI614C electrochemical workstation) in the range of 1 MHz to 1 Hz with an amplitude of 0.01 V. A constant current charge-discharge test was performed on the symmetric cell, with each cycle lasting 2 h. The critical current density (CCD) of the symmetric cell was measured. At a fixed cycle period, the areal capacity of lithium plating / stripping gradually increased (2 h per cycle). As Figure 8 , the initial interfacial impedance of the Li / 30-Ga(NO3)3@LATP / Li symmetric cell was 302.4 Ω cm -2 (a), and the CCD was 0.9 mA cm -2 (b).

[0051] It was demonstrated by Example 2 and Example 3 that the LiGa+LiN x O y layer indeed played a role in stabilizing the Li / LATP interface and improving the electrochemical performance of the symmetric cell. Drop-coating a modified solution with an appropriate concentration also affected the performance of the LATP solid electrolyte. The performance of the Li / Ga(NO3)3@LATP / Li symmetric cell assembled after drop-coating with a 20 mg / mL modified solution in Example 1 of the present invention was the most excellent, and introducing an interface layer with an appropriate thickness could achieve the best effect.

[0052] Comparative Example 1 The process of preparing the LATP solid electrolyte by the solid-phase sintering method was the same as that in Example 1.

[0053] Figure 9 are the (a) XRD pattern and (b) surface SEM image of LATP. The diffraction peaks of the LATP solid electrolyte matched well with the PDF# 35-0754 standard card. The cubic grains on the surface of LATP were closely arranged, showing a dense characteristic, which is the basis for achieving high-performance solid-state batteries.

[0054] Electrochemical performance test: To assemble a symmetric cell, lithium foil was used as the electrode and LATP was used as the electrolyte. The positive electrode material LiFePO4 (LFP), conductive additive (Super P), and binder (PVDF) were dispersed in N-methylpyrrolidone (NMP) with a mass ratio of 8:1:1. The resulting slurry was coated on an aluminum foil with an active material loading of 1.2 - 1.5 mg cm -2 . It was placed in a vacuum oven at 110 °C for 8 h to obtain the LFP positive electrode sheet. The positive electrode material Li 1.2 Mn 0.6 Ni 0.2O2 (LMNO), Super P, and PVDF were dispersed in NMP at a mass ratio of 8:1:1. The resulting slurry was coated on aluminum foil with an active material loading of 1.5 - 2 mg cm -2 . It was placed in a vacuum oven at 110 °C for 8 h to obtain the LMNO positive electrode sheet. Using LFP and Li foil as the positive and negative electrodes respectively, and Ga(NO3)3@LATP as the electrolyte, a Li / Ga(NO3)3@LATP / LFP full cell was assembled. Using LMNO and Li foil as the positive and negative electrodes respectively, and Ga(NO3)3@LATP as the electrolyte, a Li / Ga(NO3)3@LATP / LMNO full cell was assembled. To ensure good transport of Li + at the LFP / LATP and LMNO / LATP interfaces, 2 μL of electrolyte (1 M LiPF6 in EC: DMC = 1:1) was added to the cathode side. Finally, the cells were assembled in an Ar-filled glove box (MIKROUNA, Super 1220 / 750, H2O ≤ 1 ppm, O2 ≤ 1 ppm) using a CR2025 configuration.

[0055] The ionic conductivity and interfacial impedance of the symmetric cells and full cells were measured using an AC impedance technique (CHI614C electrochemical workstation) in the range of 1 MHz - 1 Hz with an amplitude of 0.01 V. A constant current charge-discharge test was performed on the symmetric cells, with each cycle lasting 2 h. The critical current density (CCD) of the symmetric cells was measured. At a fixed cycle period, the areal capacity of lithium plating / stripping gradually increased (2 h per cycle). In the potential range of 2.4 - 4.2 V (LFP, 1 C = 170 mAh g -1 ) and 2.4 - 4.8 V (LMNO, 1 C = 200 mAh g -1 ), the cells were charged and discharged at different current rates (0.1, 0.2, 0.5, 1.0, and 2.0 C). All electrochemical measurements were carried out at 25 °C.

[0056] Figure 3 For the EIS impedance spectrum of the Li / Ga(NO3)3@LATP / Li symmetric cell (a) before cycling and (b) the critical current density, its initial interfacial resistance was 152.2 Ω cm -2 , and the CCD could reach 1.6 mA cm -2 . As Figure 4 shown, at 0.1 mA cm -2 / 0.1 mAh cm -2The Li / Ga(NO3)3@LATP / Li symmetric cell was tested by galvanostatic charge-discharge. The Li / Ga(NO3)3@LATP / Li symmetric cell exhibited stable lithium plating / stripping behavior within 3000 h, with the polarization voltage maintained at about 26 mV and only slightly increasing after long-term cycling. Thanks to the LiGa+LiN x O y interlayer improved the interfacial environment between Li / LATP, making the voltage plateau very stable and the interfacial ion transport good.

[0057] The Li / LFP and Li / LMNO full cells assembled with the Ga(NO3)3@LATP solid electrolyte were tested for rate performance and cycling stability. As Figure 5 shown, the Li / Ga(NO3)3@LATP / LFP full cell had excellent rate performance and stable long-term cycling performance. The discharge specific capacity could reach 163.8 mAh g -1 at 0.1 C. When the current density increased to 0.2, 0.5, 1, and 2 C, the specific discharge capacities were 154.9, 141.1, 124.7, and 101.5 mAh g -1 respectively. The fast ion migration at the Li / Ga(NO3)3@LATP interface enabled the full cell to have excellent rate performance. When the current density was restored to 0.1 C, the capacity could be restored to 159.6 mAh g -1 (a). After cycling 300 times at 0.5 C, the Li / Ga(NO3)3@LATP / LFP full cell also showed excellent cycling stability, with its capacity stabilized at 118.8 mAh g -1 and the capacity retention rate being 89.3%, and the Coulomb efficiency being greater than 99% (b). Figure 6 Among them, the electrochemical performance of the Li / Ga(NO3)3@LATP / LMNO full cell was also excellent. After cycling 200 times at 0.2 C, the capacity retention rate was still 80.2%.

[0058] Example 4 The process of preparing the LATP solid electrolyte by the solid-phase sintering method was the same as that in Example 1.

[0059] Ga(NO3)3 was placed in a vacuum oven at 40 °C and dried for 48 h. A certain amount of Ga(NO3)3 powder was weighed and dissolved in absolute ethanol to obtain a modified solution with a concentration of 10 mg / mL. 15 μL cm was uniformly drop-coated on the surface of LATP -2The modified solution. After drying at 40 °C, the other side was coated and then dried again to obtain the 10-Ga(NO3)3@LATP solid electrolyte. A battery was assembled using the 10-Ga(NO3)3@LATP solid electrolyte. During cycling, Ga(NO3)3 reacted in situ with lithium metal to obtain a solid electrolyte containing LiGa + LiN x O y interface. To ensure good transport of Li + at the LFP / LATP and LMNO / LATP interfaces, 2 μL of electrolyte (1 M LiPF6 in EC: DMC = 1:1) was added to the cathode side. Finally, the battery was assembled in an Ar-filled glove box (MIKROUNA, Super 1220 / 750, H2O ≤ 1 ppm, O2 ≤ 1 ppm) using a CR2025 configuration.

[0060] Using AC impedance technology (CHI614C electrochemical workstation), the ionic conductivity and interfacial impedance of the symmetric cell and full cell were measured in the range of 1 MHz to 1 Hz with an amplitude of 0.01 V. A constant current charge-discharge test was performed on the symmetric cell, with each cycle lasting 2 h. The critical current density (CCD) of the symmetric cell was measured. At a fixed cycle period, the areal capacity of lithium plating / stripping gradually increased (2 h per cycle). In the potential ranges of 2.4 - 4.2 V (LFP, 1 C = 170 mAh g -1 ) and 2.4 - 4.8 V (LMNO, 1 C = 200 mAh g -1 ), the battery was charged and discharged at different current rates (0.1, 0.2, 0.5, 1.0, and 2.0 C). All electrochemical measurements were carried out at 25 °C.

[0061] As Figure 10 shown, for the Li / LATP / Li symmetric cell, (a) the EIS impedance spectrum before cycling and (b) the critical current density. The initial interfacial resistance was relatively large at 1677.2 Ω cm -2 , and the CCD was also relatively low at 0.2 mA cm -2 . Figure 11 Among them, under the conditions of 0.1 mA cm -2 / 0.1 mAh cm -2 , the initial polarization voltage of the Li / LATP / Li symmetric cell was approximately 110 mV, which gradually increased during cycling and short-circuited and failed after 120 h. The main reason for the gradual increase in the polarization voltage is that an uncontrollable side reaction occurs after LATP contacts Li, forming an interfacial phase with low ionic conductivity and high electronic conductivity, resulting in hindered interfacial ion transport and increased interfacial contact loss.

[0062] The rate cycling performance and cycling stability of the Li / LFP and Li / LMNO all-solid-state batteries assembled with the LATP solid electrolyte were further tested. As Figure 12 shown, at the same rate, the discharge specific capacity of the Li / LATP / LFP all-solid-state battery decreased significantly. As the power increased, the capacity decreased rapidly and the polarization voltage increased sharply. At 0.1, 0.2, 0.5, 1, and 2 C, the specific discharge capacities were 143.4, 130.3, 107.5, 78.5, and 26.6 mAh g -1 . After 100 cycles at 0.5 C, the capacity retention rate of the Li / LATP / LFP all-solid-state battery was only 35.9%, and the attenuation rate was very fast. As Figure 13 shown, the long cycling performance of the Li / LATP / LMNO all-solid-state battery was also poor, with a 49.7% attenuation after 160 cycles at 0.2 C.

[0063] Proved by Comparative Example 1, when the LATP solid electrolyte was unmodified, the poor physical contact with lithium metal, serious side reactions, and poor interfacial ion transport efficiency led to poor performance of the symmetric battery and all-solid-state battery. In the present invention, a solid and stable LiGa + LiN x O y multifunctional nitride layer was in-situ generated between Ga(NO3)3 and lithium metal. The LiGa alloy and LiN x O y in LiNO3 have a high affinity for both Li and LATP, and can act as a hinge connecting the two to achieve close physical contact. The high ionic conductivity of Li3N in LiN x O y reduces the energy barrier of Li + , providing a path for the high-speed transfer of Li + . In addition, LiN x O y also has excellent electronic insulation properties, which can block electron injection at the interface, effectively avoid serious side reactions between LATP and Li, and inhibit the nucleation and growth of lithium dendrites.

[0064] Comparative Example 2 The process of preparing the LATP solid electrolyte by the solid-phase sintering method was the same as that in Example 1.

[0065] Liquid metal Ga was coated on both sides of the LATP solid electrolyte by the rubbing method to obtain the Ga@LATP solid electrolyte.

[0066] Electrochemical performance test: A symmetric battery was assembled using a lithium foil as the electrode and Ga@LATP as the electrolyte. As Figure 14 shown, the Li / Ga@LATP / Li symmetric battery at 0.1 mA cm-2 / 0.1 mAh cm -2 Under the condition of, it was cycled for more than 350 h, and the polarization was continuously increasing during the process. Although the single metal Ga conductive layer could uniformly eliminate the stress concentration phenomenon of the electric field at the Li / LATP interface, it did not curb the occurrence of side reactions and did not solve the interface problem well.

[0067] Comparative Example 3 The process of preparing the LATP solid electrolyte by the solid-phase sintering method was the same as that in Example 1.

[0068] Weighed a certain amount of LiNO3 powder and dissolved it in absolute ethanol to obtain a modified solution with a concentration of 20 mg / mL. 15 μL cm of the modified solution was uniformly drop-coated on the surface of LATP. -2 After air drying, the other side was coated to obtain the LiNO3@LATP solid electrolyte.

[0069] Electrochemical performance test: Using lithium foil as the electrode and LiNO3@LATP as the electrolyte, a symmetric cell was assembled. As Figure 15 shown, the Li / LiNO3@LATP / Li symmetric cell short-circuited after 480 h of cycling under the condition of 0.1 mA cm -2 / 0.1 mAh cm -2 and the polarization was 67.2 mV.

[0070] Comparative Example 4 The process of preparing the LATP solid electrolyte by the solid-phase sintering method was the same as that in Example 1.

[0071] Weighed a certain amount of Li3N powder and dissolved it in absolute ethanol to obtain a modified solution with a concentration of 20 mg / mL. 15 μL cm of the modified solution was uniformly drop-coated on the surface of LATP. -2 After air drying, the other side was coated to obtain the Li3N@LATP solid electrolyte.

[0072] Electrochemical performance test: Using lithium foil as the electrode and Li3N@LATP as the electrolyte, a symmetric cell was assembled. As Figure 14 shown, the Li / Li3N@LATP / Li symmetric cell short-circuited after 500 h of cycling under the condition of 0.1 mA cm -2 / 0.1 mAh cm -2 and the polarization was 54.5 mV.

[0073] From the above comparative examples, the conclusion that can be drawn is as follows: The method for preparing the interface layer in the solid-state lithium metal battery provided by the present invention can significantly improve the harsh environment at the Li / LATP interface and achieve a solid-state lithium metal battery with excellent rate performance and long-life stable cycling. Compared with the single-electron conductive layer of gallium metal and the single-ion conductive layers of LiNO3 and Li3N, it shows that in order to more perfectly solve the problems at the Li / LATP interface, the LiGa+LiN that can achieve multiple benefits can be realized. x O y The interface layer is very necessary. The LiGa+LiN prepared by the present invention x O y The multifunctional nitride layer interface modification strategy is expected to be applied in the fields of energy storage power sources and power batteries, etc.

[0074] The applicant declares that the above description is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. An interfacial layer for a solid-state lithium metal battery, characterized in that, The interface layer is LiGa alloy and LiN x O y compound, where LiN x O y compound contains LiNO3, LiNO2 and Li3N, and the LiGa and LiN x O y interface is in-situ constructed on the surface of the solid electrolyte.

2. The interfacial layer for a solid-state lithium metal battery according to claim 1, wherein The solid electrolyte described includes Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3 or Li 10 GeP2S 12 a solid electrolyte that is unstable to lithium metal.

3. The interfacial layer for a solid-state lithium metal battery according to claim 2, wherein After impregnating or drop-coating an absolute ethanol solution containing anhydrous gallium nitrate on the surface of a solid electrolyte and then vacuum-drying at 30 to 40 °C, a solid electrolyte containing Ga(NO3)3 is obtained. In the solid electrolyte containing Ga(NO3)3, Ga(NO3)3 reacts in situ with lithium metal to form an interfacial layer containing LiGa alloy and LiN x O y .

4. A method for preparing an interfacial layer in a solid-state lithium metal battery, characterized in that, It includes the following steps: Step 1: Prepare a modified solution by dissolving gallium nitrate anhydrous Ga(NO3)3 in absolute ethanol; Step 2: Drop the modified solution onto the surface of the solid electrolyte; Step 3: Dry the solid electrolyte in Step 2 to obtain a solid electrolyte with a Ga(NO3)3 layer; Step 4: Assemble a battery using the solid electrolyte containing the Ga(NO3)3 layer in Step 3. During cycling, Ga(NO3)3 reacts in situ with lithium metal to obtain a solid electrolyte containing LiGa + LiN x O y interface layer.

5. The preparation method of the interfacial layer for a solid-state lithium metal battery according to claim 4, characterized in that: The content of Ga(NO3)3 is 10 - 30 mg / mL.

6. The preparation method of the interfacial layer for a solid-state lithium metal battery according to claim 4, wherein: The amount of the solution drop-coated on the surface of the solid electrolyte is 5-20 μL cm -2 .

7. The preparation method of the interfacial layer for a solid-state lithium metal battery according to claim 4, characterized in that: The solid electrolyte described is selected from Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3 or Li 10 GeP2S 12 a solid electrolyte that is unstable to lithium metal.

8. A solid electrolyte, characterized in that, The solid electrolyte is the interface layer for a solid-state lithium metal battery described in any one of Claims 1 - 3 or the interface layer for a solid-state lithium metal battery prepared by the method described in any one of Claims 4 - 8.

9. A solid-state lithium metal battery, characterized in that, It includes the interface layer for a solid-state lithium metal battery described in any one of Claims 1 - 3 or the interface layer for a solid-state lithium metal battery prepared by the method described in any one of Claims 4 - 7 or the solid electrolyte in Claim 8.

10. A symmetric battery, characterized in that, It includes the interface layer for a solid-state lithium metal battery described in any one of Claims 1 - 3 or the interface layer for a solid-state lithium metal battery prepared by the method described in any one of Claims 4 - 7 or the solid electrolyte in Claim 8.

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