Solid electrolyte having lithium salt modification layer

Abstract

The present application relates to a solid electrolyte with a lithium salt modification layer. A lithium metal battery, comprising: a positive electrode; a garnet solid electrolyte disposed on the positive electrode; and a lithium negative electrode disposed on the garnet solid electrolyte, wherein a modification layer is disposed at the interface of the lithium negative electrode and the garnet solid electrolyte, the modification layer comprising an inorganic lithium salt. A method of forming a lithium metal battery, comprising: treating a garnet solid electrolyte with an acid solution; and exposing the acid-treated garnet solid electrolyte to hydrogen fluoride to form a modification layer at the surface layer of the garnet solid electrolyte.

Description

TECHNICAL FIELD

[0001] The present invention relates to a solid electrolyte with a lithium salt modification layer and a method of making the same. BACKGROUND

[0002] Conventional lithium-ion batteries have reached the limit in energy density and safety, which poses a challenge for large-scale applications of electric power devices. For example, garnet-based solid-state lithium metal batteries have a large interfacial resistance between the lithium anode and the garnet electrolyte. Due to the rigid ceramic nature of the garnet electrolyte and poor wettability of lithium, the contact between the lithium metal and the garnet electrolyte is often insufficient, resulting in large polarization and high interfacial resistance.

[0003] The present application discloses an improved lithium anode / garnet electrolyte interface for solid-state lithium metal battery applications and a method of forming the same. SUMMARY

[0004] In some embodiments, a lithium metal battery comprises a cathode; a garnet solid electrolyte disposed on the cathode; a metal lithium anode disposed on the garnet solid electrolyte, wherein there is a modification layer at the interface between the lithium anode and the garnet solid electrolyte, the modification layer comprising an inorganic lithium salt.

[0005] In aspects combinable with any other aspect or embodiment, the modification layer comprises at least one of LiBF4, LiPF6, LiPF2O2, Li2SiF6, LiAlF4, Li3AlF6, LiAsF6, LiSbF6, and their corresponding hydrous compounds.

[0006] In aspects combinable with any other aspect or embodiment, the interfacial area specific resistance (ASR) at the interface between the lithium anode and the garnet solid electrolyte is less than 50 Ω·cm 2 In aspects combinable with any other aspect or embodiment, the ASR is less than 15 Ω·cm 2 .

[0007] In aspects combinable with any other aspect or embodiment, the thickness of the modification layer is in the range of 20 nm to 1000 nm. In aspects combinable with any other aspect or embodiment, the modification layer comprises nanopores with diameters in the range of 1 nm to 100 nm.

[0008] In aspects combinable with any other aspect or embodiment, the lithium anode is in intimate contact with the garnet solid electrolyte through the effect of the modification layer, and there is no void at the interface. In aspects combinable with any other aspect or embodiment, the modification layer is part of the garnet solid electrolyte.

[0009] In aspects combinable with any other aspect or embodiment, the lithium metal battery has a critical current density (CCD) of ~2 mA cm -2 at room temperature (RT).

[0010] In aspects combinable with any other aspect or embodiment, the positive electrode comprises at least one of LiNi d Co e Mn 1-d-e O2(NCM) (0 < d < 1, 0 < e < 1), LiTMO2(TM = Sc, Ti, V, Mn, Fe, Co, Ni, or Cu), Li2TiO3, Li4Ti5O 12 , Li3VO4, LiMn2O4, gLi2MnO3 · (1-g)LiXO2(X = Ni, Co, or Mn, 0 < g < 1), LiNi 0.8 Co 0.15 Al 0.05 O2(NCA), LiNi 0.5 Mn 1.5 O4, LiFePO4. In aspects combinable with any other aspect or embodiment, the garnet solid state electrolyte comprises at least one of: (i) Li 7-3a La3Zr2L a O 12 , L = Al, Ga, or Fe, 0 < a < 0.33; (ii) Li7La 3-b Zr2M b O 12 , M = Bi or Y, 0 < b < 1; (iii) Li 7-c La3(Zr 2-c ,N c )O 12 , N = In, Si, Ge, Sn, V, W, Te, Nb, or Ta, 0 < c < 1. In aspects combinable with any other aspect or embodiment, the lithium negative electrode comprises pure lithium metal or a lithium alloy.

[0011] In some embodiments, a method of forming a lithium metal battery includes treating a garnet solid electrolyte with an acid solution; exposing the acid-treated garnet solid electrolyte to hydrogen fluoride to form a modification layer on the garnet solid electrolyte.

[0012] In aspects combinable with any other aspect or embodiment, the acid solution comprises at least one of H3BO3, H3PO4, H3PO3, H3PO2, H4SiO4, H2SiO3, H2SiO5, H3AIO3, H3ASO4, H3ASO3, and H3SbO3. In aspects combinable with any other aspect or embodiment, prior to the treating step, the acid solution is dissolved by (1) deionized water or (2) an aqueous solution comprising deionized water and at least one organic solvent. In aspects combinable with any other aspect or embodiment, the at least one organic solvent comprises at least one of methanol, ethanol, isopropanol, ethyl acetate, acetone, acetonitrile, N,N-dimethylformamide, N-methylpyrrolidone, N-methylacetamide.

[0013] In aspects combinable with any other aspect or embodiment, the hydrogen fluoride is hydrogen fluoride vapor. In aspects combinable with any other aspect or embodiment, the hydrogen fluoride is a hydrogen fluoride solution.

[0014] In aspects combinable with any other aspect or embodiment, the modification layer comprises an inorganic lithium salt. In aspects combinable with any other aspect or embodiment, the modification layer comprises at least one of LiBF4, LiPF6, LiPF2O2, Li2SiF6, LiAlF4, Li3AlF6, LiAsF6, LiSbF6, and their corresponding aqueous compounds.

[0015] In aspects combinable with any other aspect or embodiment, the modification layer has a thickness in a range from 20 nm to 1000 nm. In aspects combinable with any other aspect or embodiment, the modification layer comprises nanopores having diameters in a range from 1 nm to 100 nm. In aspects combinable with any other aspect or embodiment, the modification layer is part of a garnet solid electrolyte.

[0016] In aspects combinable with any other aspect or embodiment, the method further comprises: adding a positive electrode; placing the garnet solid electrolyte on the positive electrode; and placing a lithium negative electrode on the garnet solid electrolyte; wherein the modification layer is at an interface between the lithium negative electrode and the garnet solid electrolyte.

[0017] In aspects combinable with any other aspect or embodiment, the positive electrode comprises LiNi d Co e Mn 1-d-e O2(NCM) (0 < d < 1, 0 < e < 1), LiTMO2 (TM = Sc, Ti, V, Mn, Fe, Co, Ni, or Cu), Li2TiO3, Li4Ti5O 12 , Li3VO4, LiMn2O4, gLi2MnO 3·(1-g)LiX02(X = Ni, Co or Mn, 0 < g < 1), LiNi 0.8 Co 0.15 Al 0.05 O2(NCA), LiNi 0.5 Mn 1.5 O4, LiFeP04.

[0018] In aspects, combinable with any other aspect or embodiment, the interfacial area specific resistance (ASR) at the interface is less than 15 Ω·cm 2 In aspects, combinable with any other aspect or embodiment, the lithium metal battery has a critical current density (CCD) of ~2 mA cm -2 at room temperature (RT). In aspects, combinable with any other aspect or embodiment, the lithium negative electrode is in continuous contact with the garnet solid electrolyte by the action of the modification layer, no gap is observed at the interface. BRIEF DESCRIPTION OF DRAWINGS

[0019] The present disclosure will become more readily appreciated when considered in conjunction with the following detailed description, and by reference to the accompanying drawings, in which:

[0020] Figure 1 is a schematic diagram of the overall structure of a solid-state battery in some embodiments.

[0021] Figures 2A-2C are scanning electron microscope (SEM) surface layer images ( Figure 2A , 2B ) and cross-sectional images ( Figure 2C ) of the LLZTO with the modification layer in Sample 1 in some embodiments at different magnifications. Figure 2D are element distribution maps of fluorine (F), boron (B), oxygen (O), and lanthanum (La) corresponding to Figure 2B in Sample 1 in some embodiments.

[0022] Figure 3 is an X-ray diffraction (XRD) image of the reaction product of the LLZTO powder with an aqueous solution of H3BO3 and HF in some embodiments.

[0023] Figure 4A and 4B are X-ray photoelectron spectroscopy (XPS) spectral diagrams of the modified LLZTO surface in some embodiments, including the F1s spectrum ( Figure 4A ) and the B1s spectrum ( Figure 4B ) in Sample 1.

[0024] Figure 5A and 5BThe images show cross-sectional SEM images of LLZTO-BF / Li in Sample 1 at different magnifications in some embodiments.

[0025] Figures 6A-6F SEM images of the surface layer of the interfacial phase formed by the reaction between LLZTO-BF and molten lithium in Sample 1 of some embodiments (in some embodiments). Figure 6A (The illustration is a corresponding photograph); corresponding to Figure 6A Elemental distribution diagram of fluorine (F), boron (B), oxygen (O) and lanthanum (La) Figure 6B ); Cross-sectional SEM images of LLZTO with interface phase at different magnifications ( Figure 6C ,6D)( Figure 6D The inset shows the results of energy-dispersive X-ray spectroscopy (EDS) analysis in online scanning mode; and the XPS spectra of the formed interface phase, including the F1s spectrum. Figure 6E ) and B1s spectrum ( Figure 6F ).

[0026] Figure 7 Electrochemical impedance spectroscopy (EIS) curves of a symmetrical lithium battery based on LLZTO-BF in Sample 1 of some embodiments.

[0027] Figure 8A and 8B The voltage-time curves of the Li / LLZTO-BF / Li battery in Sample 1 of some embodiments at 25°C under stepped current density, constant capacity, and constant current cycling conditions are shown below. Figure 8A ), and the long-term galvanostatic cycling curves of symmetric Li cells based on the original LLZTO and LLZTO-BF at 25°C ( Figure 8B ).

[0028] Figures 9A-9F The cycle performance of the NCM523 quasi-solid-state battery in sample 5 at 25°C in some embodiments ( Figure 9A , 9C ) and voltage-capacity curves ( Figure 9B ); and the cycle performance of the quasi-solid-state battery with LFP at 60℃ in sample 6 ( Figure 9D ,9F) and voltage-capacity curves ( Figure 9E ).

[0029] Figure 10 EIS plot of a symmetric lithium battery based on LLZTO-BF in sample 2 of some embodiments.

[0030] Figure 11 EIS plot of a symmetrical lithium battery based on LLZTO-BF in sample 3 of some embodiments.

[0031] Figure 12 EIS plot for a symmetric lithium battery based on LLZTO-BF in Sample 4 in some embodiments.

[0032] Figure 13 Cross-sectional SEM image of raw LLZTO / Li in Comparative Sample in some embodiments, inset is the corresponding photo.

[0033] Figure 14 EIS plot for a symmetric lithium battery based on raw LLZTO in Comparative Sample in some embodiments. DETAILED DESCRIPTION

[0034] Some example embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like elements. Components in the drawings are not necessarily drawn to scale, emphasis instead being placed on illustrating the principles of the example embodiments given. It is to be understood that the application is not limited to the details or methods set forth in the description below or illustrated in the drawings. It is to be further understood that the terminology used herein is for the purpose of description only and should not be considered as limiting.

[0035] In addition, any examples set forth in this application are meant to be illustrative only and are not meant to be limiting in any way, with the intent that the application be given the broadest possible interpretation. Some other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in the field of the application, and which can be apparent to those skilled in the art, are intended to be within the scope of the present disclosure.

[0036] Solid-state batteries (SSB) are of interest due to their high safety and improved energy density. As disclosed herein, based on inorganic solid-state electrolytes (SSE), such as garnet-type SSEs with high ionic conductivity and stability to lithium metal, a solid-state lithium metal battery is disclosed. However, due to its own rigidity and surface impurities, the wettability of SSE with molten lithium is poor. The rigid ceramic does not contact well with the metal lithium, resulting in a large interfacial specific resistance and uneven lithium ion flux during cycling. The concentrated lithium ion flux further causes dendrites to rapidly penetrate along the grain boundaries. Ultimately, the lifetime of the garnet-based solid-state battery is short.

[0037] To solve the above problems, heating, pressurization or the introduction of an organic buffer layer, such as polyethylene oxide (PEO), can be used to reduce the interface ASR. A lithiumophilic thin film (e.g., Al, Si, Ge, Mg, Au, ZnO, AI2O3, etc.) can also be deposited at the lithium anode / garnet electrolyte interface by plasma-enhanced chemical vapor deposition (PECVD), electron beam evaporation (EBE), or atomic layer deposition (ALD). However, this method is complex to operate and expensive, especially for large-scale applications. Other studies attempt to remove Li from the surface of the solid electrolyte. However, the removal of Li from the surface of the solid electrolyte is difficult and the process is complex.+ A passivation layer, including either reaction of carbon introduced at 700 °C with Li2CO3 or direct polishing. Another alternative involves applying very high external mechanical pressure to the lithium anode / garnet electrolyte interface to achieve sufficient contact. This method usually damages the battery, is difficult to implement, and cannot guarantee a sufficiently low interface resistance.

[0038] Each strategy has its own drawbacks, including insufficient interface contact; cost limitations, deposition techniques are costly and complex, and cannot be used for large-scale integration. Therefore, the present invention seeks a simple, effective and scalable method to modify the SSE surface to improve the wettability and electrochemical performance of lithium for future applications of solid-state lithium batteries.

[0039] The present invention relates to a solid electrolyte with a lithium salt modification layer for solid-state lithium batteries. The modification layer is mainly composed of inorganic lithium salts, including at least one of LiBF4, LiPF6, LiPF2O2, Li2SiF6, LiAlF4, Li3AlF6, LiAsF6, LiSbF6, and their corresponding aqueous compounds or combinations thereof.

[0040] The modification layer is introduced in situ to the SSE surface by the following process. The SSE surface is first treated by at least one of H3BO3, H3PO4, H3PO3, H3PO2, H4SiO4, H2SiO3, H2SiO5, H3AlO3, H3AsO4, H3AsO3 and H3SbO3 aqueous solution or combinations thereof. The solvent used to dissolve the above acids can be deionized water or an aqueous solution mixed with deionized water and other organic solvents, including at least one of methanol, ethanol, isopropanol, ethyl acetate, acetone, acetonitrile, N, N-dimethylformamide, N-methyl pyrrolidone, N-methyl acetamide and combinations thereof. Thereafter, HF vapor or solution can be used to modify the SSE surface to form the final modification layer. The modification layer exhibits superior lithiumophilicity. The modification layer can react with the metal anode to form a functional interface phase, thereby greatly improving the affinity between the SSE and the anode and reducing the interface resistance.

[0041] The functional interface phase formed with high surface energy guides the horizontal deposition of lithium, thereby suppressing the formation and growth of dendrites. Based on SSE with a modification layer, the ASR of symmetrical batteries at room temperature (RT) is greatly reduced by about 9 Ωcm 2 , and the critical current density (CCD) is increased by about 2 mA cm -2 . Solid-state batteries with LiFePO4 (LFP) or LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523) as the positive electrode have good long cycle performance and can work normally at high current density.

[0042] Figure 1 A general structure for a solid-state battery in some embodiments. Those skilled in the art will appreciate that the processes described herein can be applied to other configurations of solid-state structures.

[0043] In some embodiments, the lithium-ion battery 100 can include a substrate 102 (e.g., a current collector), a positive electrode 104 disposed on the substrate, a solid-state electrolyte 106 disposed on the positive electrode, a lithium electrode (e.g., a negative electrode) 108 disposed on the solid-state electrolyte, a transition layer 107 disposed between the solid-state electrolyte and the negative electrode, and a second current collector 110 disposed on the negative electrode. They can be placed relatively horizontally or vertically.

[0044] In some embodiments, the battery can include an optional coating disposed on the positive electrode; an optional first interlayer disposed between the coating or the substrate and the solid-state electrolyte; an optional second interlayer disposed between the solid-state electrolyte and the lithium electrode; an optional third interlayer disposed between the solid-state electrolyte and the positive electrode, or a combination thereof.

[0045] In some embodiments, the substrate 102 can be a current collector including at least one of a three-dimensional nickel (Ni) foam, carbon fiber, a foil (e.g., aluminum, stainless steel, copper, platinum, nickel, etc.), or a combination thereof.

[0046] In some embodiments, the optional first, second, and / or third interlayer can be selected from a carbon-based interlayer (e.g., interconnected individual, micro / mesoporous, functionalized, biomass-derived), a polymer-based interlayer (e.g., PEO, polypyrrole (PPY), polyvinylidene fluoride, etc.), a metal-based interlayer (e.g., nickel foam, etc.), an electrolyte (e.g., LiPF6in ethylene carbonate (EC) / dimethyl carbonate (DMC)), an ionic liquid-based (e.g., LiCF3SO3 / CH3CONH2or PEO 18 LiTFSI-10% SiO2-10% IL, the latter in combination with at least one of polyethylene oxide (PEO), lithium bis(trifluoromethane)sulfonimide salt (LiN(CF3SO2)2or LiTFSI), SiO2nanoparticles, and ionic liquids.

[0047] In some embodiments, the solid-state electrolyte 106 can be used to address common safety issues such as leakage, poor chemical stability, and flammability often seen in batteries using liquid electrolytes. In addition, the solid-state electrolyte can also suppress polysulfide shuttling from the positive electrode to the negative electrode, resulting in improved positive electrode utilization and high discharge capacity and energy density. In some embodiments, the solid-state electrolyte can include garnets (e.g., Li7La3Zr2O 12(LLZO), doped LLZO (e.g., with at least one of Al, Mo, W, Nb, Sb, Ca, Ba, Sr, Ce, Hf, Rb, Ta doping), Li 6.4 La3Zr 1.4 Ta 0.6 O 12 or Li 6.5 La3Zr 1.4 Ta 0.5 O 12 (both LLZTO) or combinations thereof, Li 10 GeP2S 12 , Li 1.5 Al 0.5 Ge 1.5 (PO4)3, Li 1.4 Al 0.4 Ti 1.6 (PO4)3, Li 0.55 La 0.35 TiO3, poly(ethyl acrylate) (ipn-PEA) electrolyte interpenetrating polymer network, three-dimensional ceramic / polymer network, in-situ plasticized polymer, composite polymer with well-aligned ceramic nanowires, PEO-based solid-state polymer, flexible polymer, polymer ionic liquid, in-situ formed Li3PS4, Li6PS5Cl.

[0048] In some embodiments, the negative electrode 108 can include lithium metal (Li). In some examples, the battery can include at least one negative electrode protection measure, such as electrolyte additives (e.g., LiNO3, lanthanum nitrate, copper acetate, P2S5, etc.), artificial interfacial layers (e.g., Li3N, (CH3)3SiCl, Al2O3, LiAl, etc.), composite metals (e.g., Li7B6, Li-rGO (reduced graphene oxide), layered Li-rGO, etc., or combinations thereof. In some examples, a thin layer of metal (e.g., Au) can be ion sputter coated to form a contact interface between the negative electrode 108 and the first interlayer or between the negative electrode and the solid-state electrolyte. In some examples, a thin layer of silver (Ag) paste can be brushed onto the surface of the electrolyte 106 to form a tight contact between the negative electrode 108 and the solid-state electrolyte 106.

[0049] In some embodiments, the preferred coating can include at least one of carbon polysulfide (CS), polyethylene oxide (PEO), polyaniline (PANI), polypyrrole (PPY), poly(3,4- ethylenedioxythiophene) (PEDOT), polystyrene sulfonic acid (PSS), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyaniline hydrochloride (PAH), polyvinylidene- hexafluoropropylene (P(VdF-co-HFP)), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), poly(di allyldimethylammonium) bis(trifluoromethylsulfonyl)imide (TFSI) (PDDA TFSI), lithium salts such as lithium bis(trifluoromethyl)sulfonylimide (LiN(CF3SO2)2) (LiTFSI), lithium perchlorate, lithium bis(oxalato)borate (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate (LiCF3SO3) (LiTf), lithium bis(trifluoromethanesulfonyl)amide (Li(C2F5SO2)2N) (LiBETI), and the like, or a combination thereof. In some examples, the coating can additionally include at least one of nitrogen, carbon, cobalt, titanium, tantalum, and tungsten, or at least two or at least three.

[0050] In some embodiments, the cathode 104 can include at least one of LiCoO2, LiNiO2, Li2MnO3, LiNi 0.5 Mn 1.5 O4, LiFePO4, LiNi d Co e Mn 1-d-e O2, or a combination thereof. In some examples, the cathode 104 can include LiNi d Co e Mn 1-d-e O2 (NCM) (0 < d < 1, 0 < e < 1), LiT M O2 (T M = Sc, Ti, V, Mn, Fe, Co, Ni, or Cu), Li2TiO3, Li4Ti5O 12 , Li3VO4, LiMn2O4, gLi2MnO3 · (1-g)LiXO2 (X = Ni, Co, or Mn and 0 < g < 1), LiNi 0.8 Co 0.15 Al 0.05 O2 (NCA), LiNi 0.5 Mn 1.5 O4, LiFePO4, or a combination thereof. In some examples, the cathode 104 can include a composite sulfur cathode including a conductive carbon component (e.g., carbonized dispersed cotton fiber (CDFC)), an electrolyte component (e.g., Li 10 GeP2S 12, β-Li3PS4, Li 9.6 P3S 12 , Li3PS4, Li7P3S 11 , m(Li2S) - n(P2S5) (where m and n are greater than 1) electrolyte materials, etc.) and / or elemental sulfur. In some examples, the composite sulfur cathode can also include an ionic liquid 104d (e.g., PY14FSI, PY14TFSI, P13TFSI, P14TFSI, PYR13TFSI, PP14TFSI, or combinations thereof). Embodiments

[0051] Example 1 - Preparation of Garnet Solid Electrolyte

[0052] LLZTO was synthesized and sintered into ceramic pellets by a conventional solid state method, such as high temperature solid state reaction method. Stoichiometric LiOH H2O (AR), La2O3 (99.99%), ZrO2 (AR) and Ta2O5 (99.99%) were mixed with an excess of 10 wt% LiOH H2O by ball milling. Dry La2O3 powder was obtained by heating at 900 °C for 12 hours. The powder mixture was calcined in an alumina crucible at 950 °C for 6 hours to obtain cubic phase LLZTO powder, which was then ball milled at 250 rpm for 24 hours to obtain a refined powder. The prepared LLZTO fine powder was then pressed and calcined in a platinum crucible at 1250 °C for 30 minutes in air. The pellets were polished and stored in an Ar-filled glovebox. The final ceramic pellets were about 1.0 mm thick and about 13.5 mm in diameter.

[0053] Example 2 - Preparation of LLZTO with a modification layer

[0054] An aqueous solution of H3BO3 was dropped onto the polished LLZTO surface, which was then dried after rinsing the LLZTO surface with HF vapor or HF solution to treat the electrolyte. The H3BO3 reacted with the LiOH instantaneously formed Li-B-O, which was then fluorinated by HF to form a Li-B-F layer on the SSE surface. A SSE with a lithium salt modification layer (LLZTO-BF) was obtained thereafter. + / Li + exchange instantaneously formed LiOH reacted to form Li-B-O, which was then fluorinated by HF to form a Li-B-F layer on the SSE surface. A SSE with a lithium salt modification layer (LLZTO-BF) was obtained thereafter.

[0055] Example 3 - Preparation of LFP / NCM cathodes

[0056] LiFePO4 (LFP) and LiNi 0.5 Co 0.2 Mn 0.3O2 (NCM523) cathode. LFP / NCM523 powder, super P carbon powder (carbon source), vapor grown carbon fiber (VGCF) electronically conductive carbon, and binder PVDF were mixed in a mass ratio of 8:0.5:0.5:1 in N-methyl pyrrolidone (NMP) solvent and ball-milled for 6 hours. The slurry was then coated on an aluminum foil, dried for 4 hours, and then dried under vacuum. The resulting cathode was cut into a 12 mm diameter disc. The loading of LFP was about 5.8 mg cm -2 , and the loading of NCM523 was about 3 mg cm -2 .

[0057] Example 4 - Assembly of symmetric lithium batteries

[0058] The assembly process of the symmetric lithium batteries was as follows: Fresh Li foil was attached to both sides of polished pristine / modified LLZTO, which was then placed at 250 °C for about 3 minutes. In some embodiments, the garnet electrolyte sandwiched between two pieces of lithium foil was placed in a stainless steel plate, heated at a temperature ranging from 250 °C to 400 °C for a time ranging from 1 second to 20 minutes, and then naturally cooled to room temperature.

[0059] In some embodiments, the heating is at a temperature ranging from 250 °C to 400 °C, or 275 °C to 375 °C, or 300 °C to 350 °C (e.g., 340 °C), or 250 °C to 300 °C, or 350 °C to 400 °C, or any value or range disclosed therein. In some embodiments, the time ranges from 1 second to 20 minutes, or 30 seconds to 15 minutes, or 1 minute to 10 minutes, or 3 minutes to 10 minutes, or 5 minutes to 10 minutes, or any value or range disclosed therein.

[0060] All batteries were assembled in CR2025 coin cells, and the entire process was carried out in an argon-filled glovebox. The sealing pressure of the coin cell was in the range of 1 MPa to 10 MPa (e.g., about 5 MPa). Foam nickel was used as a cushion to avoid the breakage of the garnet electrolyte during sealing, lithium pieces as electrodes, and the garnet electrolyte as a separator for charge (e.g., electron, Li + ion) conduction. These types of lithium symmetric batteries can be used to measure the interfacial resistance between lithium and the garnet electrolyte, and also to evaluate the cycling stability of the lithium / garnet electrolyte interface— i.e., charging and discharging (e.g., stripping / deposition of lithium from the lithium piece attached to one side of the garnet electrolyte to the lithium piece attached to the other side of the garnet electrolyte) under applied voltage.

[0061] Example 5 - Assembly of solid-state batteries

[0062] The assembly process of the solid-state battery based on LFP / NCM523 cathode is as follows: first, attach fresh molten lithium on the side of the modified LLZTO, drop 10 pL of electrolyte (1 M LiPF6dissolved in EC / DMC / DEC) onto the cathode sheet, and then place the LLZTO with metal lithium attached on the wet cathode sheet. All batteries are assembled in CR2025 button cells, and the whole process is carried out in an argon-filled glove box.

[0063] Example 6 - Characterization studies

[0064] Material Characterization

[0065] The LLZTO powder and the product of H3BO3 / HF (i.e. phase structure) were characterized by X-ray diffractometry (XRD Rigaku) equipped with Cu Ka radiation (40 kV, 30 mA, 5° / min, 10°-80°). Field emission scanning electron microscopy (FESEM, microstructure images; Magellan-400), energy dispersive X-ray analysis system (EDS Horiba 250) and X-ray photoelectron spectroscopy (XPS, surface chemistry; Thermo Scientific ESCA lab 250) techniques were selected to characterize the material properties.

[0066] Electrochemical Impedance Spectroscopy

[0067] Electrochemical impedance spectroscopy (EIS) was performed on an electrochemical workstation (Autolab PGSTAT302N Netherland) in the frequency range of 10 5 to 0.1 Hz with an alternating current (AC) amplitude of 10 mV.

[0068] Electrochemical Performance

[0069] All assembled batteries were tested on a battery test system (NEWARE BTS-4000). Constant current charge-discharge tests and critical current density (CCD) tests were performed to measure the performance of symmetric lithium batteries. Full cells were tested for charge-discharge at different rates (1C corresponds to 170 mAh g -1 of LFP cathode; 1C corresponds to 200 mAh g -1 of NCM523 cathode) at room temperature or 60 °C.

[0070] Example 7 - Sample preparation

[0071] Sample 1

[0072] 60 μΐ of 1 M aqueous H3B03 solution was dropped onto the polished LLZTO surface. After about 1 minute of reaction, the LLZTO surface was rinsed with anhydrous alcohol. Then the LLZTO surface was treated with 1 M HF vapor for 30 seconds and dried. The modified LLZTO with molten lithium on both sides was assembled into a symmetric lithium battery in a 2025 type coin cell.

[0073] Sample 2

[0074] The preparation of sample 2 was the same as sample 1 except that 100 μΐ of 0.6 M aqueous H3B03 / ethanol mixed solution was used instead of 60 μΐ of 1 M aqueous H3B03 solution.

[0075] Sample 3

[0076] The preparation of sample 3 was the same as sample 1 except that 0.5 M aqueous HF solution was used instead of 1 M HF vapor.

[0077] Sample 4

[0078] The preparation of sample 4 was the same as sample 3 except that the LLZTO was treated with HF solution for 10 seconds.

[0079] Sample 5

[0080] 60 μΐ of 1 M aqueous H3B03 solution was dropped onto the polished LLZTO surface. After about 1 minute of reaction, the LLZTO surface was rinsed with anhydrous alcohol. Then the LLZTO surface was treated with 1 M HF vapor for 30 seconds and dried. The modified LLZTO with molten lithium on one side was pressed against a wet NCM523 cathode sheet, and the solid-state battery was assembled in a 2025 type coin cell, which was operated at 25 °C.

[0081] Sample 6

[0082] The preparation of sample 6 was the same as sample 5 except that the cathode was LFP and the battery was operated at 60 °C.

[0083] Comparative Sample

[0084] The prepared LLZTO was only polished. Then the unmodified LLZTO with molten lithium on both sides was assembled into a symmetric lithium battery in a 2025 type coin cell.

[0085] Example 8 - Sample Characterization

[0086] Figures 2A-2C The scanning electron microscope (SEM) surface images of the LLZTO with a modification layer in sample 1 at different magnifications Figure 2A ,2B ) and cross-sectional images ( Figure 2C ). Figure 2D Elemental maps of fluorine (F), boron (B), oxygen (O), and lanthanum (La) corresponding to Figure 2B in Sample 1.

[0087] The results show that a modification layer with porous structure is covered on the surface of LLZTO. The nanopores of the modification layer have a diameter of about 20 nm. In some aspects, the nanopores of the modification layer can have a diameter in the range of 1 nm to 100 nm, or 1 nm to 50 nm, or 50 nm to 100 nm, or 1 nm to 25 nm, or 75 nm to 100 nm, or any value or sub-range disclosed therein. The corresponding elemental maps show that both boron and fluorine elements are uniformly and densely distributed on the SSE surface, indicating that the boron and fluorine containing compounds are successfully introduced to the SSE surface. Figure 2C The results show that a modification layer with porous structure is covered on the surface of LLZTO. The nanopores of the modification layer have a diameter of about 20 nm. In some aspects, the nanopores of the modification layer can have a diameter in the range of 1 nm to 100 nm, or 1 nm to 50 nm, or 50 nm to 100 nm, or 1 nm to 25 nm, or 75 nm to 100 nm, or any value or sub-range disclosed therein. The corresponding elemental maps show that both boron and fluorine elements are uniformly and densely distributed on the SSE surface, indicating that the boron and fluorine containing compounds are successfully introduced to the SSE surface.

[0088] Figure 3 X-ray diffraction (XRD) pattern of the reaction product of LLZTO powder with aqueous H3BO3 and HF solution. The XRD results show that the main reaction products are LiBF4·H2O and H3BO3, meaning that the mixing of LLZTO with aqueous H3BO3 and HF solution leads to the reaction between the acid and the H + / Li + exchange generated LiOH, forming a Li-B-F layer on the SSE surface, in this case, mainly producing the inorganic lithium salt LiBF4. H3BO3 reacts with the LiOH from the H + / Li + exchange to form Li-B-O, which is then fluorinated by HF to form a Li-B-F layer on the SSE surface.

[0089] Figure 4A and 4B X-ray photoelectron spectroscopy (XPS) spectra of the modified LLZTO surface, including F 1s spectra ( Figure 4A ) and B 1s spectra ( Figure 4B ) in Sample 1. The F 1s spectra ( Figure 4A ) show two peaks at 687.3 eV and 685.3 eV, indicating the presence of BF4 - and LiF. The B 1s spectra ( Figure 4BThe two peaks shown at 195.6 eV and 193.8 eV correspond to BF4, respectively. - The presence of BO groups. Therefore, binding from Figure 1 The data. (Refer to...) Figure 4A and 4B The modified layer was determined to mainly consist of LiBF4·H2O (BF4 - ), H3BO3(BO) and LiF.

[0090] Figure 5A and 5B The images show cross-sectional SEM images of LLZTO-BF / Li in Sample 1 at different magnifications. The modified LLZTO electrolyte exhibits excellent lithiophilicity (i.e., the affinity of the material for lithium), with molten lithium in close contact with the LLZTO. No gaps or defects were observed at the LLZTO-BF (electrolyte) / Li (electrode) interface.

[0091] Figures 6A-6F SEM image of the surface layer of the interfacial phase formed by the reaction between LLZTO-BF and molten lithium in sample 1 ( Figure 6A (The illustration is a corresponding photograph); corresponding to Figure 6A Elemental distribution diagram of fluorine (F), boron (B), oxygen (O) and lanthanum (La) Figure 6B ); Cross-sectional SEM images of LLZTO with interface phase at different magnifications ( Figure 6C ,6D)( Figure 6D The inset shows the results of energy-dispersive X-ray spectroscopy (EDS) analysis in online scanning mode; and the XPS spectra of the formed interface phase, including the F1s spectrum. Figure 6E ) and B1s spectrum ( Figure 6F ).

[0092] Figure 6A The edges of the molten lithium turned black within a short time, and the black area continued to spread along the surface of the electrolyte with the modified layer, indicating a rapid chemical reaction between the modified layer and the molten lithium. The black area is mainly composed of Li and Li₂. x BO y The composition (y = (x + 3) / 2, 0 < x ≤ 5) can serve as a functional SEI to effectively suppress lithium dendrites. Figure 6B In this process, boron and fluorine elements are retained on the surface of the electrolyte with the modified layer. Figure 6C and 6D This indicates that the formed interface is in close contact with LLZTO. Signals for elements B and F were detected at the interface, but signals for La, Zr, and Ta were not detected, suggesting that the thickness of the interface phase is approximately 300 nm. Figure 6E In the spectrum, the F1s spectrum only shows the peak corresponding to LiF at 685.3 eV.Figure 6F In particular, the B 1s spectrum shows a peak at 58.6 eV corresponding to Li x BO y at 191.7 eV. LiF and Li x BO y are both lithium ion conductive and electronically insulating, allowing lithium ion transport and blocking electrons through the interface. In addition, LiF has a high surface energy that can direct the horizontal deposition of lithium. This functional SEI ensures effective suppression of dendrites.

[0093] Figure 7 is the electrochemical impedance spectroscopy (EIS) curve for the symmetric Li cell based on LLZTO-BF in Sample 1, showing a significant reduction to an ASR of ~9 Ω cm 2 at room temperature (e.g., ~25 °C), corresponding to an improved Li / LLZTO interface (e.g., the comparative sample has a much larger ASR of ~450 Ω cm 2 at ~25 °C).

[0094] Figure 8A and 8B is the voltage-time curve of the Li / LLZTO-BF / Li cell under step current density, constant capacity, constant current cycling conditions at 25 °C in Sample 1 ( Figure 8A ), and the long-time constant current cycling curve of the symmetric Li cell based on the original LLZTO (comparative sample) and LLZTO-BF (Sample 1) at 25 °C ( Figure 8B ). Figure 8A indicates that the symmetric lithium battery based on the modified LLZTO exhibits improved CCD, reaching 2 mA cm -2 (0.25 mAh cm -2 ), and no short circuit. As Figure 8B shown, the Li / LLZTO / Li cell (comparative sample) shows large voltage polarization and short circuit within a limited time (below 300 hours), indicating a poor interface, slow and uneven lithium ion transport. The Li / LLZTO-BF / Li cell (Sample 1) exhibits excellent cycle stability under 0.5 mA cm -2 (0.25 mAh cm -2 ) at room temperature for 1200 cycles, indicating that the functional SEI of the Li / SSE interface can suppress lithium dendrites and prolong battery life.

[0095] Figures 9A-9F is the cycle performance ( Figure 9A , 9C ) and voltage capacity curve ( Figure 9B ) of the NCM523 quasi-solid-state battery at 25 °C in Sample 5; and the cycle performance of the quasi-solid-state battery with LFP at 60 °C in Sample 6 ( Figure 9D,9F) and voltage-capacity curves ( Figure 9E ).from Figures 9A-9C It can be seen that the NCM523 / LLZTO-BF / Li battery at 0.1 mA cm -2 Discharge exceeds 160mAh g -1 Capacity, and 1.2 mA cm at 25°C. -2 It operates normally at high current densities without short-circuiting. The battery can operate at 0.2 mA cm⁻¹ -2 The cycle stabilized after more than 200 iterations. Figures 9D-9F It can be seen that the LFP / LLZTO-BF / Li battery exhibits good rate performance, even at 2mA cm⁻¹. -2 It also exhibits low overpotential at 1 mA cm⁻¹ -2 It exhibits good cycling stability at 60℃.

[0096] Figures 10-12 The EIS curves for symmetrical Li batteries based on LLZTO-BF in samples 2-4 are shown below. In each case, samples 2-4 exhibit an improved Li / LLZTO interface, with an ASR (such as improved lithium-ion transport) of approximately 10⁻¹¹ Ωcm at 25 °C. 2 Between (for example, the battery in the control sample has approximately 450 Ωcm at ~25°C) 2 (The larger ASR).

[0097] In comparison, Figure 13 The images show cross-sectional SEM images of the raw LLZTO / Li (i.e., unmodified layer), with insets corresponding to the control sample. The lithium sheet exhibits wrinkling and shrinkage on the raw LLZTO surface, and the porosity observed at the interface indicates poor interfacial contact. This is due to… Figure 14 Confirmed, Figure 14 The EIS curves of symmetric Li cells based on the original LLZTO were compared in the samples. Although samples 1-4 (respectively) Figure 7 and 10 The ASR of -12) at 25℃ is 9-11 Ωcm. 2 The ASR was between [values], but in the control sample at 25°C it was approximately 450 Ωcm. 2 This corresponds to a poor Li / LLZTO interface. In some embodiments, the ASR of the embodiments disclosed herein can be less than 50 Ωcm. 2 or less than 25Ωcm 2 or less than 15Ωcm 2 or less than 10Ωcm 2 .

[0098] Accordingly, as presented herein, the present disclosure relates to solid-state electrolytes with lithium salt-modified layers for solid-state lithium batteries. The modified layer comprises inorganic lithium salts, such as at least one of LiBF4, LiPF6, LiPF2O2, Li2SiF6, LiAlF4, Li3AlF6, LiAsF6, LiSbF6, and their corresponding aqueous compounds.

[0099] The modified layer is introduced in-situ to the SSE surface by the following process. The SSE surface is first treated by at least one of H3BO3, H3PO4, H3PO3, H3PO2, H4SiO4, H2SiO3, H2SiO5, H3AlO3, H3AsO4, H3AsO3, and H3SbO3 aqueous solutions or combinations thereof. The solvent used to dissolve the above acids can be deionized water or aqueous solutions mixed with deionized water and other organic solvents, including at least one of methanol, ethanol, isopropanol, ethyl acetate, acetone, acetonitrile, N,N-dimethylformamide, N-methylpyrrolidone, N-methylacetamide, and combinations thereof. Thereafter, HF vapor or solution can be used to modify the SSE surface to form the final modified layer. The modified layer exhibits superior lithiophilicity. The modified layer can react with the metal anode to form a functional interfacial phase, greatly enhancing the affinity between the SSE and the anode, and reducing the interfacial resistance.

[0100] The functional interfacial phase formed with high surface energy guides the horizontal deposition of lithium, thereby suppressing the formation and growth of dendrites. Based on the SSE with the modified layer, the ASR of the symmetric battery at room temperature (RT) is greatly reduced by about 9 Ωcm 2 , and the critical current density (CCD) is increased by about 2 mA cm -2 . Solid-state batteries with LiFePO4 (LFP) or LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523) as the positive electrode have good long cycle performance and can work normally at high current density.

[0101] The advantages include: (1) in-situ modified layer introduced by aqueous acid strategy; (2) the modification method is simple, efficient, easy to control, and self-terminating; (3) the modified layer with excellent lithiophilicity greatly enhances the affinity of SSE and Li; (4) the functional interface formed by the reaction of the modified layer with lithium effectively suppresses dendrites; (5) greatly reduced Li / SSE interfacial resistance (~9 Ωcm 2 ) and improved CCD (~2 mA cm -2 ) at room temperature; (6) improved cycle performance of solid-state batteries.

[0102] As used herein, “about,” “approximately,” “substantially” and similar terms are intended to have a broad meaning in harmony with the common and accepted usage of the trained person in the field of the subject matter of the present disclosure. It is to be understood by the person skilled in the art that such terms are intended to describe certain aspects believed to be novel to the extent that there is a reasonable expectation that such terms convey the connotation that close-to-the-numerical values so provided would be the most preferred implementation. However, variations from the exact numerical values so provided and still believed to be within the concept are to be permitted. These variations are to be considered to have been prescribed by the terms “about,” “approximately,” “substantially” and like terms or words insofar as implicit to their connotation to the person skilled in the art reading the specification. As such, it is the applicant’s intention that these terms in material statements or claims be given their broadest interpretation using their plain ordinary and accepted meaning consistent with the doctrine of equivalents.

[0103] As used herein, “optional,” “optionally” or similar terms are intended to mean that the subsequently described event or circumstance can or can not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not. The use of the terms “a” or “an” and “the” and similar referents in the context of describing the elements of the application are to be construed to be referring to at least one or one or more of the elements of the preceding description, unless otherwise indicated.

[0104] References to the position of elements (e.g., “top,” “bottom,” “above,” “below,” “intermediate,” etc.) are made merely for the purpose of describing the orientation of various elements in the figures. It should be noted that the orientation of the various elements can differ according to other example embodiments, and such variations are intended to be encompassed by the present disclosure.

[0105] It will be apparent to those skilled in the art that various modifications and variations can be made in view of the above teachings. Thus, it is intended that the claimed subject matter not be limited, except by the appended claims and their equivalents.

Claims

1. A method of forming a lithium metal battery, the method comprising: the lithium metal battery comprising: a positive electrode; a garnet solid electrolyte disposed on the positive electrode; and a lithium negative electrode disposed on the garnet solid electrolyte; wherein the lithium negative electrode is disposed with a modification layer at an interface with the garnet solid electrolyte, the modification layer comprising at least one of LiBF4, LiPF6, LiPF2O2, Li2SiF6, LiAlF4, Li3AlF6, LiAsF6, LiSbF6, and corresponding hydrous compounds thereof; the method of forming the lithium metal battery comprising: treating a polished surface of the garnet solid electrolyte with an acid solution, exposing the acid solution treated garnet solid electrolyte to hydrogen fluoride to form the modification layer at a surface layer of the garnet solid electrolyte; the acid solution comprising at least one of H3BO3, H3PO4, H3PO3, H3PO2, H4SiO4, H2SiO3, H2SiO5, H3AlO3, H3AsO4, H3AsO3, and H3SbO3; prior to the acid solution treating step, dissolving the acid in the acid solution with (1) deionized water, or (2) an aqueous mixed solvent comprising deionized water and at least one organic solvent; the hydrogen fluoride is hydrogen fluoride vapor or a hydrogen fluoride solution.

2. The method of claim 1, wherein, The interface area specific resistance ASR at the interface is less than 50 Ω-cm 2 .

3. The method of claim 2, wherein, the ASR is less than 15 ohm-cm 2 .

4. The method of claim 1, wherein, the modification layer has a thickness in a range of 20 nm to 1000 nm.

5. The method of claim 1, wherein, the modification layer comprises nanopores having diameters in a range of 1 nm to 100 nm.

6. The method of claim 1, wherein, the lithium negative electrode is in close contact with the garnet solid electrolyte with no voids at the interface by virtue of the modification layer.

7. The method of claim 1, wherein, the modification layer is part of the garnet solid electrolyte.

8. The method of claim 1, wherein, The lithium metal battery has a critical current density of ~2 mA cm -2 at room temperature.

9. The method of claim 1, wherein, LiNi d Co e Mn 1-d-e O2, 0 < d < 1, 0 < e < 1, LiTMO2, TM = Sc, Ti, V, Mn, Fe, Co, Ni or Cu, Li2TiO3, Li4Ti5O 12 , Li3VO4, LiMn2O4, gLi2MnO3-(1-g)LiXO2, X = Ni, Co or Mn, 0 < g < 1, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.5 Mn 1.5 O4, LiFePO4.

10. The method of claim 1, wherein, the garnet solid electrolyte comprises at least one of: (i) Li 7-3a La3Zr2LaO 12 wherein L = Al, Ga or Fe and 0 < a < 0.33; (ii) Li7La 3-b Zr2MbO 12 where M = Bi or Y and 0 < b < 1; (iii) Li 7-c La3(Zr 2-c N c )O 12 where N = In, Si, Ge, Sn, V, W, Te, Nb or Ta and 0 < c < 1.

11. The method of claim 1, wherein, the lithium negative electrode comprises pure lithium metal or a lithium alloy.

12. The method of claim 1, wherein, the at least one organic solvent comprises at least one of methanol, ethanol, isopropanol, ethyl acetate, acetone, acetonitrile, N,N-dimethylformamide, N-methylpyrrolidone, N-methylacetamide.

13. The method of claim 1, wherein, further comprising: adding a positive electrode, disposing the garnet solid electrolyte on the positive electrode, and disposing the lithium negative electrode on the garnet solid electrolyte; wherein the modification layer is disposed at an interface of the lithium negative electrode and the garnet solid electrolyte.

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