Sulfur-bromine-hydride-based solid electrolyte compound for all-solid-state battery and method for preparing same

Abstract

The purpose of the present invention is to provide a novel argyrodite-type solid electrolyte for an all-solid-state battery and a method for preparing same, the novel argyrodite-type solid electrolyte simultaneously comprising S2-, BH4-, and Br-, and the present invention provides: a solid electrolyte compound for an all-solid-state battery, represented by chemical formula 1 (Li7-xPS6-x(BH4)x-yBry, (0.5≤χ≤2.5 and 0≤y≤χ)); and a method for preparing same. When the Li7-xPS6-x(BH4)x-yBry solid electrolyte according to the present invention is used, lithium ion conductivity can be improved and the inherent electrochemical stability limitations of argyrodite-type materials can be solved.

Description

Sulfur-bromine-hydride solid electrolyte compound for all-solid-state batteries and method for producing the same

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0080469, filed June 20, 2024, and Korean Patent Application No. 10-2025-0080855, filed June 19, 2025, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a sulfur-bromine-hydride solid electrolyte compound for an all-solid-state battery and a method for producing the same.

[0003] Recent intensive research has led to remarkable progress in all-solid-state batteries, where both the electrolyte and electrodes are solid. Achieving high lithium ion conductivity in solid electrolytes is a critical requirement for their use in all-solid-state batteries. Efforts have been made to develop solid electrolyte materials that exhibit superionic conductivity at room temperature, including sulfides, oxides, halides, and complex hydrides.

[0004] Among the various solid electrolytes reported to date, argyrodite-type sulfide materials have attracted particular attention due to their high ionic conductivity and simple synthetic route. Li7PS6, one of the representative argyrodite-type lithium ion conductors, is a sulfur anion (S 2- , 4a site) has a face-centered cubic lattice (space group F43m, Z = 4), and PS4 3- Polyhedral (S at the P 4b site and S at the 16e site) and additional S2- (4d site) are located at the octahedral and tetrahedral sites, respectively. Lithium ions (24g and 48h sites) form a disordered cage-like arrangement around the S2- (4d site), enabling high lithium ion transport. In addition, S 2- to the halogen anion (Cl - , Br - and I -) and / or oxide anions (O 2- ) is known to further improve ionic conductivity and chemical stability.

[0005] Despite their impressive conducting properties, argyrodite-type solid electrolytes with multiple anions still have inherent limitations related to their limited electrochemical stability. Indeed, most existing argyrodite-type solid electrolytes exhibit a narrow electrochemical window, making them challenging to simultaneously combine with high-voltage cathodes and low-voltage anodes. In particular, due to their very poor stability at low potentials, high-energy-density cathode materials, such as lithium metal (theoretical capacity = 3,860 mAh g-1, potential = -3.04 V vs. standard hydrogen electrode (SHE),) have not been applied to all-solid-state batteries using argyrodite-type solid electrolytes.

[0006] Accordingly, as part of efforts to expand the material diversity of argyrodite-type solid electrolytes with multiple anions and to solve problems related to low potential stability, Li 7-x PS 6-x (BH4) x-y Br y (1.0 ≤ x ≤ 2.0 and 0 ≤ y ≤ x) three different anions, namely S 2- , borohydride anion (BH4 - ) and bromine anion (Br - ) solid electrolyte. Structure S 2- and / or Br - (positions 4a and 4d) BH4 - To replace the Li(BH4) complex hydride, known as a highly reducing solid electrolyte, was used. Experimental results show that x(BH4 - As the amount of ) increases, y(Br -It was found that the argyrodite-type solid electrolyte with a small amount of nickel was stabilized, which improved not only lithium ion conductivity but also stability toward lithium metal. In addition, the manufactured solid electrolyte enabled excellent performance of an all-solid-state battery using a high-nickel-content oxide positive electrode and a lithium metal negative electrode.

[0007] BH4 - Argyrodite-type ion conductors, including , have been studied for lithium solid electrolytes and all-solid-state batteries. However, the continuous compositional changes of sulfide anions, halide anions, and hydride anions within the argyrodite structure explored in this study (Table S1) and the material system including the developed battery are different from those previously reported.

[0008] (Non-patent literature 1) Journal of Power Sources 244 (2013) 707-710

[0009] Argyrodite-type ionic conductors have recently attracted considerable attention as solid electrolyte systems for all-solid-state batteries due to their high ionic conductivity, excellent mechanical deformability, and simple material processability. However, they typically exhibit poor chemical and electrochemical stability at low potentials when operated in batteries with high-energy-density metal electrodes, resulting in poor rate and cycle life characteristics.

[0010] The present invention has been proposed to solve the above-mentioned problems, and the purpose of the present invention is to provide S 2- , BH4 - and Br - The purpose is to provide a new solid electrolyte for an all-solid-state battery including argyrodite at the same time.

[0011] To achieve the above purpose, according to one embodiment of the present invention,

[0012] The present invention provides a hydrogen sulfide-based solid electrolyte compound for an all-solid-state battery represented by the following chemical formula 1.

[0013] [Chemical Formula 1]

[0014] Li 7-x PS 6-x (BH4) x-y Br y , (1.0 ≤x≤ 2.0 and 0 ≤y≤x)

[0015] Additionally, the above x may be 0.0≤x≤2.0, and y may be 0≤y≤2.0.

[0016] Additionally, the above x may be 0.7≤x≤1.2, and y may be 0.75≤y≤1.0.

[0017] Additionally, the above x may be 1.2≤x≤1.7, and y may be 0≤y≤0.5.

[0018] Additionally, the above x may be 1.7≤x≤2.2, and y may be 0≤y≤0.5.

[0019] Additionally, the above x and y may be xy>0.5.

[0020]

[0021] According to one embodiment of the present invention,

[0022] The present invention provides a method for producing a sulfur-bromine-hydride solid electrolyte compound for an all-solid-state battery, comprising the steps of: a) mixing a lithium sulfide compound, a phosphorus sulfide compound, and a lithium bromide compound; b) milling the mixture mixed in step a); c) compressing the mixture milled in step b) into pellets and then heat-treating them; and d) pulverizing the pellets heat-treated in step c) and then ball-milling them with LiBH4.

[0023] Additionally, each of the above steps can be performed in an Ar atmosphere.

[0024] Li according to the present invention 7-x PS 6-x (BH4) x-y Br yWhen using a solid electrolyte, lithium ion conductivity can be improved and the inherent electrochemical stability limitations of argyrodite-type materials can be overcome. Furthermore, compositions with high -x and low -x can promote the formation of the argyrodite phase while simultaneously improving lithium ion conductivity and stability for lithium metal anodes.

[0025] Figure 1 is a Li-based hydrogen sulfide solid electrolyte for an all-solid-state battery according to one embodiment of the present invention. 7-x PS 6-x (BH4) x-y Br y This is a diagram schematically illustrating the synthesis process of (1.0 ≤ x ≤ 2.0 and 0 ≤ y ≤ x).

[0026] In Figure 2, (a) is Li synthesized within the quasi-quaternary phase diagram of Li2SP2S5LiBH4LiBr. 7x PS 6x (BH4) xy Br y The composition of (x = 1.0, 1.5 and 2.0, 0≤y≤x) is shown. (b) is Li 7x PS 6x (BH4) xy Br y XRD pattern for (x = 1.0, 0 ≤ y ≤ x). (c) is Li 7x PS 6x (BH4) xy Br y XRD pattern for (x = 1.5, 0 ≤ y ≤ x). (d) is Li 7x PS 6x (BH4) xy Br y XRD pattern for (x = 2.0, 0 ≤ y ≤ x).

[0027] Figure 3 (a) is Li 7x PS 6x (BH4) xy Br yIn the composition of , (a) is an XRD pattern for a compound with y = 1.125 and x = 1.5, and (b) is an XRD pattern for a compound with y = 0.375 at x = 1.5.

[0028] Figure 4 is Li 7x PS 6x (BH4) xy Br y In the composition, experimental and simulated XRD patterns for x = 1.5 (y = 0.0, 0.375 and 0.75).

[0029] Figure 5 is Li 7x PS 6x (BH4) xy Br y In the composition of , Raman spectra of compounds with x = 2.0 and y = 0.0, x = 1.0 and y = 0.0.

[0030] Figure 6 shows the Nyquist plots of compounds with x = 1.0 and different y values ​​at 25°C (left). The enlarged Nyquist plot in the high-frequency region (right) is shown.

[0031] Figure 7 shows the Nyquist plots of compounds with x = 1.5 and different y values ​​at 25°C (left). The enlarged Nyquist plot in the high-frequency region (right) is shown.

[0032] Figure 8 shows the Nyquist plots of compounds with x = 2.0 and different y values ​​at 25°C (left). The enlarged Nyquist plot in the high-frequency region (right) is shown.

[0033] Figure 9 is an equivalent circuit used to fit the Nyquist plots of Figures 6 to 8.

[0034] Figure 10 is Li 7x PS 6x (BH4) xy Br yArrhenius plots of lithium ion conductivity for Li7PS6Li are shown. Figures (a), (c), and (e) are Arrhenius plots of lithium ion conductivity. Figures (b), (d), and (f) show lithium ion conductivity and activation energy. Figure (g) shows Li7PS6Li 3.5 PS 2.5 Br 3.5 Li 3.5 PS 2.5 (BH4) 3.5 This is the lithium ion conductivity of the quasi-ternary system.

[0035] In Fig. 11, (a) is a schematic diagram of the NCM / Li all-solid-state battery, (b) is the first charge-discharge profile at 0.1C, (c) is the dQ / dV curve, (d) is the charge-discharge profile at 0.05, 0.1, 0.2, 0.5, and 1C (the charge rate is fixed at 0.1C at 0.1, 0.2, 0.5, and 1C), and (e) is the cycling performance of discharge capacity and Coulombic efficiency at 0.5C.

[0036] Figure 12 is a graph showing the cycling performance of discharge capacity and coulombic efficiency at 0.1C.

[0037] Figure 13 is a graph showing the first charge-discharge profile at 0.5C.

[0038] Figure 14 shows the Nyquist plot and fitted curve of a Li / Li symmetric cell using the compound x = 2.0 and y = 0.0 as the solid electrolyte. The inset is the equivalent circuit used for fitting.

[0039] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0040] The terms and words used in this specification and claims should not be construed as limited to their usual or dictionary meanings, but should be construed as meanings and concepts that conform to the technical spirit of the present disclosure, based on the principle that the inventor can appropriately define the concept of the term to best explain his or her own invention.

[0041]

[0042] The present invention provides a hydrogen sulfide-based solid electrolyte compound for an all-solid-state battery represented by the following chemical formula 1.

[0043] [Chemical Formula 1]

[0044] Li 7-x PS 6-x (BH4) x-y Br y , (1.0 ≤ x ≤ 2.0 and 0 ≤ y ≤ x)

[0045] Specifically, in the hydrogen sulfide-based solid electrolyte compound for an all-solid-state battery according to the present invention, in the chemical formula 1, x may be 0.0≤x≤2.0, and y may be 0≤y≤2.0.

[0046]

[0047] Specifically, the hydrogen sulfide-based solid electrolyte compound for an all-solid-state battery according to the present invention can improve lithium ion conductivity by promoting the formation of an argyrodite structure in a low x region (0.7≤x≤1.2, for example, x = 1.0), while in a high x region (1.2≤x≤2.2, for example, x = 1.5 and 2.0), the same change in y hinders the formation of y, because as the x value increases, Li vacancy increases, increasing the ion transfer path and improving ion conductivity.

[0048]

[0049] Specifically, considering the structural analysis and EIS measurement results for the hydrogen sulfide-based solid electrolyte compound for an all-solid-state battery according to the present invention, the lithium ion conductivity of the hydrogen sulfide-based solid electrolyte compound for an all-solid-state battery according to the present invention can be increased at a composition in which x is low (0.7≤x≤1.2) and y is high (0.75≤y≤1.0).

[0050] Accordingly, in the hydrogen sulfide-based solid electrolyte compound for an all-solid-state battery according to the present invention, x in the chemical formula 1 may be 0.7≤x≤1.2, and y may be 0.75≤y≤1.0.

[0051] Considering the structural analysis and EIS measurement results for the hydrogen sulfide-based solid electrolyte compound for an all-solid-state battery according to the present invention, the lithium ion conductivity of the hydrogen sulfide-based solid electrolyte compound for an all-solid-state battery according to the present invention can be increased at a composition in which x is high (1.2≤x≤2.2) and y is low (0≤y≤0.5).

[0052] Accordingly, in the hydrogen sulfide-based solid electrolyte compound for an all-solid-state battery according to the present invention, x in the chemical formula 1 may be 1.2≤x≤1.7, and y may be 0≤y≤0.5.

[0053] In addition, in the hydrogen sulfide-based solid electrolyte compound for an all-solid-state battery according to the present invention, x in the chemical formula 1 may be 1.7≤x≤2.2, and y may be 0≤y≤0.5.

[0054] In addition, in the hydrogen sulfide-based solid electrolyte compound for an all-solid-state battery according to the present invention, in the chemical formula 1, x and y may be 0.5<xy<2.

[0055]

[0056] Furthermore, the electrochemical analysis of the sulfide-based solid electrolyte compound for an all-solid-state battery according to the present invention revealed that a high x composition enhanced the stability toward a lithium metal anode. Based on these results, we developed a high-voltage all-solid-state battery that reversibly cycles between a nickel-rich oxide anode and a lithium metal anode using two different argyrodite-type solid electrolytes for the anode and cathode, respectively.

[0057] The results presented here provide insights into the design strategy of heteroanion ion conductors and the development strategy of high-voltage all-solid-state batteries using these solid electrolytes.

[0058]

[0059] According to one embodiment of the present invention,

[0060] The present invention provides a method for producing a sulfur-bromine-hydride solid electrolyte compound for an all-solid-state battery, comprising the steps of: a) mixing and milling a lithium sulfide compound, a phosphorus sulfide compound, and a lithium bromide compound; b) compressing the mixture milled in step a) into pellets and then heat-treating them; and c) pulverizing the pellets heat-treated in step b) and then ball-milling them with LiBH4.

[0061] The method for producing a sulfur-bromine-hydride solid electrolyte compound for an all-solid-state battery of the present invention can be synthesized through a three-step route including two ball milling steps and one heat treatment step.

[0062] For example, as depicted in Figure 1 (S1), in step a), lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), and lithium bromide (LiBr) were weighed in stoichiometric molar ratios to match the final composition. These materials were then placed in a zirconia ball mill jar containing zirconia balls and ball milled using a planetary mill. In this case, for the composition without LiBr (y=0), only Li2S and P2S5 were used.

[0063] After this, in step b), the mixture obtained through ball milling can be compressed into pellets and transferred to a quartz tube furnace connected to a glove box. The sample is then heat-treated under an Ar atmosphere.

[0064] In step c), the heat-treated pellets were ground into powder and ball-milled using stoichiometrically weighed LiBH4 under the same conditions as in the first step. For compositions without LiBH4 (x=y), the synthesis can be completed after the second step.

[0065] Additionally, each of the above steps can be performed in an Ar atmosphere.

[0066] The following examples are provided only to aid understanding of the present invention, and the present invention is not limited to the following examples.

[0067]

[0068] 1. Experiment

[0069] 1.1 Material Synthesis

[0070] Li 7-x PS 6-x (BH4) x-y Br y(x = 1.0, 1.5, 2.0, 0 ≤ y ≤ x) The solid electrolyte was synthesized through a three-step route including two ball-milling steps and one heat treatment step, which is shown in S1 of Figure 1. In the first step of the synthesis, lithium sulfide (Li₂S, Sigma Aldrich, 99.98%), phosphorus pentasulfide (P₂S5, Sigma Aldrich, 99%), and lithium bromide (LiBr, Sigma Aldrich, 99.995%) were stoichiometrically weighed to match the final composition. These materials were placed in a 45 mL zirconia ball mill jar together with 20 zirconia balls with a diameter of 10 mm, and then milled using a planetary ball mill (PULVERISETTE 7, Fritch) at 400 rpm for 20 h (15 min milling, 5 min pause repeated). For y = 0 (composition without LiBr), only Li₂S and P₂S5 were used.

[0071] In the second step, the ball-milled mixture was compression molded into pellets with a diameter of 10 mm, and then transferred to a quartz tube electric furnace (FDS 001, LIV energy) connected to a glove box and heat-treated at 550°C for 10 hours under an Ar atmosphere.

[0072] In the third step, the heat-treated pellets were pulverized using a pestle and mortar, and then ball-milled again under the same conditions as in the first step with stoichiometrically weighed LiBH₄ (Acros Organics, 95%). Compositions where x = y (without LiBH₄) were synthesized after the second step. All synthetic processes were performed in an Ar atmosphere (O₂ ≤ 0.01 ppm, H₂O ≤ 0.01 ppm).

[0073]

[0074] 1.2 Property Analysis

[0075] For phase analysis, X-ray diffraction (XRD; SmartLab, Rigaku) ​​measurements were performed using CuKα radiation (wavelength λ = 1.5406 Å for Kα1, 1.5444 Å for Kα2) in the range of 2θ = 10°–70° at an interval of 0.01°. The powder for XRD measurements was injected into a thin glass capillary with a diameter of 0.5 mm in an Ar atmosphere and then sealed with liquid paraffin.

[0076] Raman spectroscopy (LabRAM HR Evolution, Horiba) was used for molecular bond analysis.

[0077]

[0078] 1.3 Ionic conductivity measurement

[0079] 100-120 mg of solid electrolyte powder was placed in a PET mold with a diameter of 10 mm and uniaxially compressed at 277.4 MPa. Gold powder (Mitsuwa Chemicals, 99.9%) was then applied to both sides of the solid electrolyte, which was then compressed again at 184.9 MPa. The assembled cell was placed in a stainless steel electrochemical cell and sealed with a torque of 5.0 Nm.

[0080] Ionic conductivity was measured using the alternating current impedance spectroscopy (EIS; MTZ-35, BioLogic) over a temperature range of 25–80°C and a frequency range of 0.01 Hz–1 MHz.

[0081]

[0082] 1.4 Battery assembly and electrochemical testing

[0083] The anode composite is LiNi 0.9 Co 0.05 Mn 0.05O₂(NCM), Li6PS5Cl, and Super C were weighed in a weight ratio of 80:19:1 and mixed for 15 minutes using a mixer (AVM-10, AllforLAB). For cell assembly, 100 mg of solid electrolyte powder was placed in a PET mold with a diameter of 10 mm and uniaxially compressed at 295.8 MPa. 10 mg of the cathode composite was evenly applied thereon and compressed again at 425.3 MPa. A 10 mm diameter pure lithium foil (Honjo Metal Co.) was placed on the opposite side of the solid electrolyte as the anode. The assembled pellet-type cell was sealed in a stainless steel electrochemical cell with a torque of 5.0 Nm.

[0084] The prepared NCM / Li cell was cycled in the CCCV mode (terminal current: 210 × 0.1 × X C-rate (X = 0.1, 0.5) mA g¹, terminal voltage: 4.3 V) in the range of 2.5–4.3 V (voltage reference: Li / Li). The battery cycler used was WBCS3000 (WonATech. Co.), and 1 C = 210 mA g¹ was defined.

[0085] The stability of the lithium metal anode was evaluated using a Li / Li symmetric cell. 100-120 mg of solid electrolyte was placed in a 10 mm diameter PET mold and compressed at 277.4 MPa. A pure lithium flake was then placed on top and further compressed at 18.5 MPa. The cell was then sealed in a stainless steel electrochemical cell with a torque of 5.0 Nm, and all cell assembly processes were performed in an Ar atmosphere.

[0086]

[0087] 2. Results and Discussion

[0088] 2.1 Material Synthesis and Analysis

[0089] Figure 2a is a quasi-ternary diagram showing the compositions in the Li2S-P2S5-LiBH4-LiBr quasi-quaternary system investigated in this study. The polyanion compounds synthesized in this diagram are Li 7-x PS 6-x (BH4) x-y Br y , where the increase of x and y represents the substitution of BH₄ for S² and the substitution of Br for BH₄, respectively. In the present invention, experiments were conducted focusing on the compositions of x = 1.0, 1.5, 2.0 (red, blue, and green dots in Figure 1a) and 0 ≤ y ≤ x.

[0090] First, Li 7-x PS 6-x (BH4) x-y Br y The synthesis route of solid electrolyte was examined. For this purpose, experiments were conducted with two compositions (compositions containing all three anions) of y = 0.375 and y = 1.125 under the fixed condition of x = 1.5. According to previous reports, when LiBH₄ and P2S5 are ball milled, P2S7 4- Byproducts containing polyatomic anions are easily generated, and the intermediate phase β-Li3PS4 is known to be formed through the reaction of Li2S and P2S5 and promote the formation of the final argyrodite structure7].

[0091] Based on these prior studies, two synthetic methods were compared. Both methods involve three steps: ball milling, heat treatment, and re-ball milling, as follows:

[0092]

[0093] 1) The first method is to ball mill Li2S, P2S5, and LiBr together, then perform heat treatment and finally re-ball mill with LiBH4.

[0094] 2) The second method is to perform the first ball milling with only Li2S and P2S5, then add LiBr and LiBH4 in the second ball milling stage, and perform the heat treatment in the same manner.

[0095] This comparative experiment confirmed that Method 1 produced a higher purity azirodite-type compound, as shown in Figure 3. All subsequent syntheses were carried out using Method 1.

[0096] All compositions shown in a of Fig. 2 were synthesized by the above method (see Fig. 1). In the composition of x = 1.0, y = 0.0, both the XRD peaks of the aryrodite phase and the starting material Li2S were observed (b of Fig. 2). As y increased (the amount of Br increased), the peak intensity of the aryrodite phase increased, and the unreacted Li2S peak decreased. In particular, in the composition of x = 1.0, y = 1.0, no peaks corresponding to the starting material or impurity phase were observed, which means that the increase in y promotes the formation of the aryrodite phase.

[0097] On the other hand, at high concentrations of x = 1.5 and 2.0, the phase formation showed an opposite trend. As shown in Fig. 2 c and d, as y increases, the formation of the argyrodite phase is hindered, and the argyrodite peak was not observed for x = 2.0 and y = 2.0. In addition, the intensity of the (111) peak decreases with increasing y, suggesting the continuity of polyanion substitution. No additional diffraction peaks due to superlattice or anion ordering were observed in all compositions, indicating that all anions coexist in a disordered manner at the same crystal sites (4a and 4d). However, the low crystallinity makes it difficult to compare the lattice constants.

[0098] The tendency of aryrodite phase formation was particularly evident in compositions containing two anions. Compositions of y = 0 or x = y are located at the ends of each line in Figure 1a and contain only two anions. For example, x = 1.0, y = 0 corresponds to Li6PS5BH4, and x = 1.0, y = 1.0 corresponds to Li6PS5Br. In the composition of x = y, as x increases, the formation of the aryrodite phase is inhibited, whereas, conversely, in the composition of y = 0, an increase in x promotes the formation of the aryrodite phase. Even in the compositions with high concentrations of x and low concentrations of y, traces of residual starting materials such as Li2S and LiBr were confirmed.

[0099] Figure 5 shows the Raman spectra of x = 1.0, y = 1.0 (Li6PS5Br) and x = 2.0, y = 0.0 (Li5PS4(BH4)2), and these two compositions showed lithium ion conductivities of more than 10³ S / cm at room temperature in EIS analysis. Both compounds were PS4 3- It exhibited symmetric stretching (417 cm¹), symmetric bending (200-210 cm¹), asymmetric stretching (573-575 cm¹), and asymmetric bending (270-280 cm¹) vibration modes of the polyhedron. In addition, at the composition of x = 2.0, y = 0.0, additional peaks corresponding to the bending (1380 cm¹) and stretching (2300 cm¹) vibrations of BH₄ were observed at 1350 cm¹ and 2280 cm¹.

[0100] These results suggest that various anions such as S², Br, and BH₄ can coexist within the same crystal structure, which is consistent with previous reports that these anions can exist in a disordered manner at the 4a and 4d crystal positions.

[0101] In particular, at high concentration compositions such as x = 2.0, it was confirmed that the decrease in y promotes the formation of the aryrodite phase. That is, BH₄ can substitute at a higher rate than Br in the aryrodite structure, and as a result, a stable phase can be maintained even in a structure with little S². This suggests that the low formation / ionization energy of LiBH₄, an ionic crystal (Li and BH₄), and the disordered nature in the polyanion system, together with the low synthesis energy of the disordered structure containing BH₄, contribute to the stabilization of this structure.

[0102]

[0103] 2.2 Lithium ion conductivity

[0104] Li 7-x PS 6-x (BH4) x-y Br y The lithium ion conductivity of the solid electrolytes was evaluated by electrochemical impedance spectroscopy (EIS) measurements using a gold (Au) blocking electrode. For the measurements, pellet samples with a diameter of 10 mm were prepared by cold-pressing. All Nyquist plots exhibited a semicircle shape (see Figures 6 to 8), which could be quantitatively analyzed using the equivalent circuit presented in Figure 9. In addition, all compounds showed a linear increase with increasing temperature in the Arrhenius plot of the logarithmic ion conductivity. The lithium ion conductivities and activation energies at 25°C are summarized in Table 1 below.

[0105]

[0106] Looking at the EIS results of the compositions with x = 1.0, 0 ≤ y ≤ 1.0, it can be confirmed that the y = 1.0 composition exhibits higher lithium ion conductivity and lower activation energy (E) (a and b in Figure 10). The ionic conductivity of the x = 1.0, y = 1.0 composition at 25℃ was measured to be 1.9 × 10³ S cm¹, and the activation energy was 32.5 kJ mol¹, which are well consistent with previous reports. The structural analysis results in this region confirmed that as y increases, the amount of Br introduced increases, resulting in the formation of a single-phase argyrodite structure. Therefore, it is believed that the high ionic conductivity and low activation energy of this composition are due to the formation of a high-purity material.

[0107] Meanwhile, in high-concentration compositions such as x = 1.5 and 2.0, the change in conductivity characteristics according to y showed an opposite trend. As shown in Fig. 10c to f, as y decreased, the ionic conductivity increased. This change in conductivity is because the decrease in y induces the stabilization of the argyrodite phase, as confirmed in the structural analysis above. Meanwhile, the activation energy increased until y increased to half of x, and then tended to decrease again as y increased further. In other words, it is interpreted that the ionic conduction barrier is higher in compositions containing all three anions of S², BH₄, and Br.

[0108] For this reason, in this region, a better argyrodite-type ionic conductor phase was formed at the compositions with low y. For example, for the compositions x = 1.5, y = 0 and x = 2.0, y = 0, the lithium ion conductivities at 25°C were 1.9 × 10³ S cm¹ and 2.8 × 10³ S cm¹, respectively, and the activation energies were 30.2 kJ mol¹ and 31.2 kJ mol¹, respectively.

[0109] The combined results of structural analysis and EIS measurements indicate that the lithium superionic conducting argyrodite phase is formed at compositions with low x and high y (x = 1.0, y = 1.0) or at compositions with high x and low y (x = 2.0, y = 0). These conductivity distributions can also be directly observed in the heat map in Figure 10 g. This result once again demonstrates that compositions containing only two anions have better conductivity properties than compositions containing a mixture of three anions.

[0110] Furthermore, the effect of polyanions on ionic conductivity was particularly pronounced in the region of high x and low y. It is noteworthy that these results contradict the recent report that “the introduction of polyatomic anions removes ion transport barriers.” This difference suggests that the polyatomic effect can vary significantly depending on the structural differences of the anions used, and thus demonstrates the need for further in-depth follow-up studies on this topic. In particular, precise atomic-level analysis is needed to determine how the structural interactions between polyatomic anions, such as BH₄ used in this study, and monoatomic anions affect crystal structure and ion transport.

[0111]

[0112] 2.3 NCM / Li solid-state battery

[0113] Among the compositions synthesized in this study, the compound x = 2.0, y = 0.0 (Li5PS4(BH4)2) showed the highest ionic conductivity among all compositions, and its performance was evaluated by applying it as a solid electrolyte for an NCM / Li all-solid-state battery. Since this solid electrolyte contains highly reducible BH₄ hydride anion, instead of using it directly between the positive and negative electrodes, a design was introduced in which two different types of argyrodite-type solid electrolytes were used as the cathode (positive electrode) electrolyte layer and the anode (negative electrode) electrolyte layer, respectively (see Figure 11).

[0114] Specifically, the solid electrolyte with the composition x = 2.0, y = 0.0 was directly used on the anode side (interface with lithium metal) without any separate surface treatment or interface modification. The cathode composite was composed of a mixture of an NCM cathode with a high nickel content (90%), a Li6PS5Cl solid electrolyte, and a Super C conductive material. Li6PS5Cl is the most widely studied material among argyrodite-type solid electrolytes and is well known to exhibit excellent performance in NCM-based batteries.

[0115] However, in most previous studies, the Li6PS5Cl solid electrolyte is chemically and electrochemically unstable with lithium metal, requiring the use of a lithium metal alloy as the anode. In contrast, in this study, pure lithium metal was directly used as the anode. Detailed procedures for cell fabrication are described in the Experimental section.

[0116] Figure 11b shows the initial cycle voltage curve measured in the range of 2.5–4.3 V (vs. Li / Li) under 0.1C current conditions (1C = 210 mA g¹). At this time, the charge capacity was 235.5 mAh g¹, and the discharge capacity was 194.6 mAh g¹. In addition, the derivative voltage (dQ / dV) curve (Figure 11c) clearly shows peaks corresponding to the oxidation and reduction reactions of each transition metal, indicating that stable electrochemical reactions occurred within the battery.

[0117] This all-solid-state battery also exhibited excellent rate characteristics and cycling stability. After the initial cycle, the capacity was maintained at 94.2%, 88.6%, 81.2%, and 75.7% of the reference capacity of 204.9 mAh g¹ as the discharge rate increased from 0.05 C to 2, 4, 10, and 20 times, respectively (Figure 11d). Furthermore, at 0.1 C, 81.0% of the 189.5 mAh g¹ capacity in the second cycle was maintained after 20 cycles (Figure 12). Even when measured at a higher rate of 0.5 C, the discharge capacity was 115.7 mAh g¹ after 100 cycles (Figures 11e and 13), and the Coulombic efficiency saturated at approximately 100% during cycling, indicating very stable cycling characteristics.

[0118] The interfacial stability between the lithium metal anode and the x = 2.0, y = 0.0 solid electrolyte was further examined through EIS analysis using a lithium symmetric cell (Li / Li) (Fig. 14 and Table 2).

[0119]

[0120] Table 2 above shows the quantitative values ​​of circuit components in the EIS analysis shown in Fig. 14, and the interface resistance (Ω·cm²) is R SEI It was calculated by dividing by 2 and normalizing by surface area.

[0121]

[0122] As a result, the interfacial resistance and charge transfer resistance were measured as 0.18 Ω·cm² and 3.45 Ω·cm², respectively, indicating that the solid electrolyte forms a very stable interface with lithium metal. This stability is interpreted to be due to the highly reducible BH₄ hydride anion.

[0123] These results suggest that various hydride-based anions can serve as very promising candidates for the design of argyrodite-type solid electrolytes that require stability with lithium metal anodes, and show that the range of applications of all-solid-state batteries can be greatly expanded.

[0124]

[0125] 3. Conclusion

[0126] In conclusion, we have integrated multi-anion Li 7-x PS 6-x (BH4) x-y Br y We developed a solid electrolyte to improve lithium ion conductivity and address the inherent electrochemical stability limitations of argyrodite-type materials. Specifically, compositions with high -x and low -x can promote the formation of the argyrodite phase while simultaneously improving lithium ion conductivity and stability toward lithium metal anodes. In addition, BH4 in the structure - Solid electrolytes rich in hydride anions enable superior cycling performance in NCM / Li all-solid-state batteries. Broadly speaking, the insights provided in this study can be applied to various solid electrolytes with atomic anion-based frameworks (e.g., sulfides, oxides, halides, etc.) for broader battery applications.

Claims

1. A sulfur-bromine-hydride solid electrolyte compound for an all-solid-state battery represented by the following chemical formula 1. [Chemical Formula 1] Li 7-x PS 6-x (BH4) x-y Br y , (0.5 ≤x≤ 2.5 and 0 ≤y≤x) 2. In paragraph 1, A sulfur-bromine-hydride solid electrolyte compound for an all-solid-state battery, characterized in that x is 0.0≤x≤2.0 and y is 0≤y≤2.

0.

3. In paragraph 1, A sulfur-bromine-hydride solid electrolyte compound for an all-solid-state battery, characterized in that the above x is 0.7≤x≤1.2 and y is 0.75≤y≤1.

0.

4. In paragraph 1, A sulfur-bromine-hydride solid electrolyte compound for an all-solid-state battery, characterized in that x satisfies 1.2≤x≤1.7 and y satisfies 0≤y≤0.

5.

5. In paragraph 1, A sulfur-bromine-hydride solid electrolyte compound for an all-solid-state battery, characterized in that x is 1.7≤x≤2.2 and y is 0≤y≤0.

5.

6. In paragraph 1, A sulfur-bromine-hydride solid electrolyte compound for an all-solid-state battery, characterized in that the above x and y are xy>0.

5. 7.a) A step of mixing and milling a lithium sulfide compound, a phosphorus sulfide compound, and a lithium bromide compound; b) a step of compressing the mixture milled in step a) into pellets and then heat-treating them; and c) a step of crushing the pellets heat-treated in step b) and then ball-milling them with LiBH4; A method for producing a sulfur-bromine-hydride solid electrolyte compound for an all-solid-state battery of the first paragraph.

8. In paragraph 7, A method for producing a sulfur-bromine-hydride solid electrolyte compound for an all-solid-state battery, characterized in that each of the above steps is performed in an Ar atmosphere.

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