Oxygen-doped Li-Y-Zr-Cl-Br-S sulfide solid electrolyte material and preparation method thereof

Abstract

The invention provides an oxygen-doped Li-Y-Zr-Cl-Br-S sulfide solid electrolyte material and a preparation method thereof, and relates to the technical field of all-solid-state lithium batteries. According to the material, O < 2-> is introduced into a Li-Y-Zr-Cl-Br-S system to form a strong covalent S-O bond, and an S-O mixed anion skeleton is constructed, so that relatively high ionic conductivity can be maintained while the interface stability and the air humidity resistance are improved, the lattice rigidity and the anion stability are enhanced, the interface side reaction rate of a positive electrode under high voltage is reduced, and the service life of the positive electrode is prolonged. Electrolyte decomposition is inhibited, interface impedance increase is slowed down, the cycle life of the battery is prolonged, and the high-performance operation requirement of the all-solid-state battery can be better met.

Description

Technical Field

[0001] This application relates to the field of all-solid-state lithium battery technology, and more specifically, to an oxygen-doped Li-Y-Zr-Cl-Br-S sulfide solid electrolyte material and its preparation method. Background Technology

[0002] All-solid-state lithium batteries, due to their use of non-flammable solid electrolytes, are considered an important development direction for next-generation high-safety energy storage devices. Among them, sulfide-based solid electrolytes such as Li9.6P3S... 12 Li 10 GeP2S 12 Sulfide electrolytes, due to their near-liquid superionic conductivity (up to 10⁻² S / cm) and good mechanical flexibility, have become a class of materials of great interest. However, sulfide electrolytes face serious stability problems: on the one hand, they have poor interfacial chemical stability when in contact with electrode materials, especially when in direct contact with high-voltage cathodes (such as nickel-rich NMC811), where they are easily oxidized and decomposed at high potentials, generating byproducts such as sulfates and sulfur, leading to increased interfacial resistance and rapid capacity decay; on the other hand, sulfide electrolytes are extremely sensitive to environmental humidity, undergoing violent hydrolysis reactions with moisture in the air to generate toxic hydrogen sulfide (H₂S) gas, and the ionic conductivity of the material decreases catastrophically.

[0003] To address the aforementioned shortcomings of sulfide electrolytes, researchers have proposed various improvement schemes, such as partially replacing chlorine (Cl) with bromine (Br) in the sulfide crystals or adding hydrophilic oxide additives to the electrolyte. However, these methods have not fundamentally solved the problems of insufficient interfacial stability and moisture resistance. In contrast, strategies to improve stability by addressing the intrinsic composition of the material have received more attention, such as anionic or cationic substitution of sulfide electrolytes to improve their resistance to oxidative hydrolysis. Among these, partially replacing sulfur ions (S²⁻) with oxygen ions (O²⁻) to form an oxygen-sulfur mixed anionic structure has been shown to significantly improve the material's resistance to air oxidation while largely maintaining its high ionic conductivity and broadening its electrochemical stability window.

[0004] Therefore, this application aims to provide an oxygen-doped Li-Y-Zr-Cl-Br-S sulfide solid electrolyte material and its preparation method, so as to better solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this application is to provide an oxygen-doped Li-Y-Zr-Cl-Br-S sulfide solid electrolyte material and its preparation method, which can solve the technical problems of poor interfacial stability and easy reaction with humid air to generate H2S in existing sulfide electrolytes.

[0006] This application provides an oxygen-doped Li-Y-Zr-Cl-Br-S sulfide solid electrolyte material, whose general chemical formula can be represented as Lia(YxZr(1-x))bCl(cy)BryS(dz)Oz, wherein:

[0007] α is the sizing coefficient of Li, ranging from 5.0 to 7.5, preferably about 6.0 to 6.5, to ensure charge balance and high Li content. + concentration;

[0008] x represents the atomic fraction of Y relative to the total amount of Y+Zr, ranging from 0 to 1, preferably from 0.1 to 0.5. When x=0, it indicates a pure Zr system without Y doping; as x increases, it indicates more Y. 3+ Replace Zr 4+ ;

[0009] b is the total count of (Y, Zr) mixed cations, preferably about 1, which means that each chemical formula unit contains a cation with one (Y, Zr) site and a total valence of about +4;

[0010] c is the sizing coefficient of the total number of halogens Cl+Br, ranging from 1.0 to 2.0, preferably about 1.5, representing the total amount of halide anions, which can be slightly richer than the traditional argyrodite structure to compensate for the change in cation valence state;

[0011] y is the proportioning coefficient of Br, 0≤y≤c, preferably 0.1~1.0, y=0 indicates that it contains only Cl, and increasing y indicates that Br gradually replaces Cl;

[0012] d is the ratio coefficient of total sulfur and oxygen anions, the total number of S+O, ranging from 4.0 to 6.0, preferably about 4.5 to 5.0 (similar to the total number of anions in a typical sulfide structure).

[0013] z represents the oxygen doping amount, where 0 < z ≤ 1.0, preferably 0.05 to 0.2 (i.e., oxygen accounts for 0.5 to 20% of the mixed anions, used to form a crystal structure in which SO coexists).

[0014] In the above general formula, Y 3+ With Zr 4+ It occupies high-valence cation sites in the original sulfide lattice (replacing P in the traditional Li2S–P2S5 system). 5+ By adjusting the ratio x of Y to Zr and the Li content a, the overall charge balance and stable framework of the crystal can be maintained. Introducing an appropriate amount of oxygen doping (O...) 2- Substitute S 2- The formation of higher-energy SO covalent bonds within the crystal significantly enhances the material's chemical stability against oxygen and water in the air. Simultaneously, this mixed anionic structure retains the Li-rich composition of the original sulfide.+ Sites and diffusion channels are identified to ensure that the material retains excellent Li-related properties. + Ion conductivity and a wide electrochemical stability potential window.

[0015] Based on the same inventive concept, this application also provides a method for preparing the above-mentioned oxygen-doped Li-Y-Zr-Cl-Br-S sulfide solid electrolyte material, comprising the following steps:

[0016] The raw materials, including lithium sulfide (Li₂S), lithium chloride (LiCl), lithium bromide (LiBr), and lithium oxide (Li₂O, used to provide O₂), are weighed according to the target stoichiometric ratio. 2- The raw materials include yttrium chloride (YCl3) and zirconium tetrachloride (ZrCl4). Li2S provides the sulfur source, LiCl and LiBr provide the halogen source, Li2O provides the oxygen source, and YCl3 and ZrCl4 provide the corresponding Y and Zr doping element sources. All raw materials should be stored and weighed under anhydrous and oxygen-free conditions.

[0017] The prepared raw materials are placed in a high-energy ball mill jar under an inert atmosphere (such as Ar) and sealed for grinding. A planetary ball mill is used to ball mill the materials at a speed of 200-500 rpm for several hours (for example, premixing at low speed for 1 hour, followed by high-speed ball milling for 20 hours) to ensure that the components are fully mixed and undergo a preliminary solid-phase reaction to form a uniform precursor powder.

[0018] The ball-milled precursor powder was subjected to medium-temperature sintering under an inert atmosphere. Preferably, the powder was sealed in a quartz ampoule or crucible and heated at 300–500°C for several hours (e.g., held at 400°C for 4 hours) to further crystallize the material and complete the formation of the oxygen-doped sulfide phase. The sample was then removed after natural cooling to room temperature.

[0019] The sintered product is ground and sieved in a glove box to obtain a uniform and fine solid electrolyte powder. The obtained powder should be stored under anhydrous conditions for later use and can be used to prepare solid-state battery electrode-electrolyte composite membranes or directly press-form electrolyte separators.

[0020] The material obtained by the above method is the oxygen-doped Li-Y-Zr-Cl-Br-S sulfide solid electrolyte of the present invention, whose crystal structure contains SO mixed anionic bonds and (Y,Zr) co-doped framework cations. This material can be further used to construct various all-solid-state electrochemical devices.

[0021] The beneficial effects of this invention are:

[0022] The solid electrolyte material provided by this invention introduces O into the Li-Y-Zr-Cl-Br-S system. 2-By forming strong covalent SO bonds and constructing a mixed SO anionic framework, the interface stability and resistance to air humidity are improved while maintaining high ionic conductivity. This enhances lattice rigidity and anionic stability, reduces the rate of interfacial side reactions under high voltage at the cathode, inhibits electrolyte decomposition, slows down the growth of interfacial impedance, and extends battery cycle life, thus better meeting the high-performance operation requirements of all-solid-state batteries. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flowchart illustrating the preparation process in an embodiment of the present invention. Detailed Implementation

[0025] To facilitate understanding of the present invention, it will be described more fully below through embodiments, and preferred embodiments are given below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Any other implementation schemes obtained by modifying or equivalently substituting the technical solutions of the present invention without inventive step are all within the protection scope of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0027] The numerical values ​​disclosed in the embodiments of this invention are approximate values, not definitive values. Where error or experimental conditions permit, all values ​​within the error range may be included, and the specific numerical values ​​disclosed in the embodiments of this invention are not limited to those specified.

[0028] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0029] Example

[0030] This embodiment provides a method for preparing an oxygen-doped Li-Y-Zr-Cl-Br-S sulfide solid electrolyte material, with the following chemical formula / ratio: Li6.3(Y0.4Zr0.6)1.0Cl1.0Br0.5S4.5O0.1; preparation steps:

[0031] Li₂S, LiCl, LiBr, Li₂O, YCl₃, and ZrCl₄ were weighed according to stoichiometry. The prepared raw materials were premixed in an Ar atmosphere glove box and then placed in a planetary ball mill for sealed grinding (400 rpm, 16-20 h) to form a uniform precursor powder. The ball-milled precursor powder was then subjected to a closed-loop medium-temperature heat treatment (N₂, 550 °C × 5 h) under an inert atmosphere to further crystallize the material and complete the formation of the oxygen-doped sulfide phase. The sintered product was cooled, ground, and sieved to obtain a uniform and fine solid electrolyte powder.

[0032] Comparative Example 1

[0033] This comparative example provides a method for preparing a solid electrolyte material, with the chemical formula / ratio: Li6.3(Y0.4Zr0.6)1.0Cl1.0Br0.5S4.6, and the preparation steps are the same as in the example.

[0034] Comparative Example 2

[0035] This comparative example provides a method for preparing a solid electrolyte material, with the chemical formula / ratio: Li6.3(Y0.4Zr0.6)1.0Cl1.5S4.6, and the preparation steps are the same as in the example.

[0036] The solid electrolyte materials prepared in the above embodiments and comparative examples were subjected to the following tests:

[0037] XRD: Cu Kα (λ=1.5406 Å), 2θ=10–60°, step 0.02°, compare the shifts of the main diffraction peaks (without Rietveld fitting).

[0038] EIS: φ10 mm disc, thickness ≈1.0 mm, stainless steel blocking electrode, bulk conductivity (σRT) measured at room temperature; activation energy Ea extracted at varying temperatures.

[0039] Battery assembly: NMC811 positive electrode, anode-free (Cu current collector) negative electrode; solid electrolyte is cold-pressed sheet; room temperature 0.1C charge-discharge, 400 cycles; specific capacity is based on the mass of positive electrode active material.

[0040] Air stability: 72 h of continuous exposure in dry air environment with a dew point of -40 °C; record sample mass change (Δm) and H2S sensor readings.

[0041] The test results are shown in the table below:

[0042] index Example (O doping) Comparative Example 1 (No O / Contains Br) Comparative Example 2 (No O / No Br) Main peak location (2θ,°) 29.35 29.10 29.22 Cell variation trend Shrinkage (~0.6%) — Slight shrinkage (compared to control example 1) σRT (S / cm) <![CDATA[2.0×10 -3 ]]> <![CDATA[2.3×10 -3 ]]> <![CDATA[2.5×10 -3 ]]> Ea (eV) 0.36 0.31 0.29 Initial capacity (mAh / g) 160 160 158 400-week retention rate 88% 72% 61% <![CDATA[H2S and Δm (72 h)]]> <1 ppm;Δm<0.8% ~5 ppm@12 h; Δm≈2.3% ≥10 ppm@6 h; Δm≈3.1%

[0043] As can be seen from the test results, in the XRD test of the solid electrolyte material prepared in this application embodiment, the main peak shifted to the right from 29.10° → 29.35° (2θ); the inferred cell a: 10.29 Å → 10.23 Å, with a volume shrinkage of about 0.6%, reflecting the lattice densification and higher lattice energy induced by O²⁻ incorporation. EIS (room temperature): σRT = 2.0×10⁻³ S / cm; Ea = 0.36 eV. Charge-discharge (0.1C, 400 cycles): initial discharge 160 mAh / g; capacity retention 88%; coulombic efficiency ≥99%. Air stability (–40 °C dew point): 72 h exposure Δm < 0.8%, H2S < 1 ppm, not exceeding limits throughout the entire period. As can be seen, the solid electrolyte material prepared in the embodiments of this application, through O doping, results in a rightward shift of the main XRD peak / lattice shrinkage, significant suppression of interfacial side reactions, and significantly better cycle life and air tolerance than the control, while maintaining a conductivity of 10⁻³ S / cm.

[0044] In the XRD analysis of the solid electrolyte material prepared in Comparative Example 1, the main peak is approximately 29.10° (2θ), and no further rightward shift due to O doping was observed; compared to sample A, the cell parameters are larger and the structure is less compact. EIS (room temperature): σRT = 2.3 × 10⁻⁶ -3 S / cm; Ea = 0.31 eV. Charge-discharge (0.1C, 400 cycles): initial discharge 160 mAh / g; capacity retention 72%. Air stability: H2S ≈ 5 ppm within 12 h, Δm ≈ 2.3% after 72 h. The above test results show that although the solid electrolyte material in this comparative example has a slightly higher σRT, its interfacial impedance increases faster with each cycle, and it exhibits significant gas generation under air exposure; its overall durability is inferior to the material prepared in the embodiments of this application.

[0045] In the XRD test of the solid electrolyte material prepared in Comparative Example 2, the main peak is approximately 29.22° (2θ), higher than that of sample B but lower than that of sample A; after removing Br, the lattice shrinks relatively, but still lacks the densification degree induced by O. EIS (room temperature): σRT = 2.5 × 10⁻³ S / cm; Ea = 0.29 eV. Charge-discharge (0.1C, 400 cycles): initial discharge 158 mAh / g; capacity retention 61%. Air stability: H₂S ≥ 10 ppm within 6 h, Δm ≈ 3.1% after 72 h. The above test results show that although the conductivity of the solid electrolyte material in this comparative example is not low, its interface / air stability is the worst, and its cycle decay is the most obvious; verifying that halogen regulation alone is insufficient to solve the interface and moisture resistance problems.

[0046] Furthermore, the different electrolytes prepared in the above examples and comparative examples were used to assemble all-solid-state coin cells with NMC811 cathode and lithium-free anode (using the electrolyte of this invention as the separator, with an initial compaction density of approximately ≥95%, and cycling at room temperature at 0.1C rate). The long-term cycling results showed significant differences. The battery assembled with the oxygen-doped electrolyte of this invention had an initial discharge specific capacity of approximately 160 mAh / g, and after 400 charge-discharge cycles, the capacity retention rate was as high as approximately 88%, demonstrating excellent lifetime stability. In contrast, the control battery using the undoped electrolyte (Comparative Example 1) had a capacity retention rate of approximately 72% under the same conditions, while the battery using the traditional electrolyte (Comparative Example 2), which contains neither oxygen nor bromine, had a capacity retention rate of only approximately 61%. This series of comparative results clearly demonstrates that, through the synergistic effect of oxygen doping and halogen regulation, the electrolyte material of this invention significantly improves the cathode interface stability and cycle durability, effectively suppresses battery capacity decay, and achieves longer cycle life and higher safety and reliability in all-solid-state batteries.

[0047] In summary, the solid electrolyte material provided by this invention, through the introduction of O 2- The formation of strong covalent SO bonds improves the lattice rigidity and anionic stability of the material, resulting in a lower interfacial side reaction rate under high cathode voltage. In other words, oxygen doping effectively suppresses electrolyte decomposition at the cathode interface, slowing down the increase in interfacial impedance during battery cycling and thus extending battery life. After 72 hours of air exposure testing, the H2S gas concentration released by the oxygen-doped electrolyte sample of this invention was less than 1 ppm, far lower than the >5 ppm of the undoped control sample and the >10 ppm of the control sample without oxygen or Br. This demonstrates that oxygen doping significantly reduces the tendency of sulfide electrolytes to react with moisture in the air to produce H2S, greatly improving the material's tolerance to moisture and environmental stability. X-ray diffraction (XRD) analysis shows that, compared to the undoped sample, the main diffraction peak of the material of this invention shifted from approximately 29.1° (2θ) to 29.35°, with a slight decrease in the corresponding cell parameter and a volume shrinkage of approximately 0.6%. This positive shift in the diffraction peak position and the micro-shrinkage of the lattice indicate that O… 2- Successfully incorporated into the lattice and with S 2- The formation of mixed anions enhances the stability of the crystal structure. This structural optimization helps suppress the material's tendency for phase transition or decomposition upon contact with the electrode / air. Although the introduction of a small amount of O may slightly affect the flexibility of the anionic framework, the material of this invention still maintains superionic conductivity close to that of the original sulfide, with a room-temperature ionic conductivity still reaching 10. -3 The S / cm scale can better meet the requirements of high-performance operation of all-solid-state batteries.

[0048] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An oxygen-doped Li-Y-Zr-Cl-Br-S sulfide solid electrolyte material, characterized in that, Its general chemical formula can be represented as Lia (Yx Zr(1-x) )bCl(cy) BryS(dz)Oz, where: a is the sizing coefficient of Li, ranging from 5.0 to 7.5; x is the atomic fraction of Y relative to the total amount of Y+Zr, and its value ranges from 0 to 1; b is the total count of (Y, Zr) mixed cations, preferably about 1; c is the sizing coefficient of the total number of halogens Cl+Br, ranging from 1.0 to 2.0; y is the proportioning coefficient of Br, 0≤y≤c; d is the ratio coefficient of total sulfur and oxygen anions, and the total number of S+O is 4.0 to 6.

0. z represents the oxygen doping level, where 0 < z ≤ 1.

0.

2. A method for preparing the oxygen-doped Li-Y-Zr-Cl-Br-S sulfide solid electrolyte material as described in claim 1, characterized in that, Includes the following steps: The raw materials are weighed according to the target stoichiometric ratio, and the raw materials include lithium sulfide, lithium chloride, lithium bromide, lithium oxide, yttrium chloride and zirconium tetrachloride; The prepared raw materials are placed in a high-energy ball mill jar under an inert atmosphere and sealed and ground to form a uniform precursor powder. The ball-milled precursor powder was subjected to medium-temperature sintering under an inert atmosphere to further crystallize the material and complete the formation of oxygen-doped sulfide phases. The sintered product was ground and sieved to obtain a uniform and fine solid electrolyte powder.

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