A nitrogen-doped Li-Y-Cl-S solid-state electrolyte material, a preparation method and application thereof

Abstract

This application relates to the field of all-solid-state lithium battery materials technology, and discloses a nitrogen-doped Li-Y-Cl-S solid electrolyte material, its preparation method, and its applications. This solid electrolyte material is made of lithium sulfide, yttrium chloride, lithium chloride, and lithium nitride, and has an Fm-3m space group structure. The preparation method includes ball milling and mixing the raw materials under an inert atmosphere to obtain a precursor, followed by heat treatment, sintering, and grinding. This invention utilizes nitrogen ions to replace sulfur ions, causing lattice contraction and enhancing the stability of the bulk structure. Simultaneously, this material can react in situ with a lithium metal anode to generate a lithium nitride-rich interfacial passivation layer. This interfacial layer possesses excellent ionic conductivity and electronic blocking ability, effectively suppressing continuous side reactions between the electrolyte and lithium metal and the nucleation and growth of lithium dendrites, solving the problem of interfacial instability in existing systems, and significantly improving the cycle life and safety performance of all-solid-state batteries.

Description

Technical Field

[0001] This invention relates to the field of all-solid-state lithium battery materials technology, specifically to a nitrogen-doped Li-Y-Cl-S solid electrolyte material, its preparation method, and its application. Background Technology

[0002] All-solid-state lithium metal batteries have become an important development direction for next-generation energy storage technology due to their high safety and high energy density potential. Among various solid electrolyte materials, Li-Y-Cl-S-based sulfur halide solid electrolytes combine the high ionic conductivity of sulfide solid electrolytes with the wide electrochemical oxidation window of halide solid electrolytes, exhibiting good cathode compatibility and conductivity.

[0003] However, Li-Y-Cl-S solid electrolytes face severe interfacial stability challenges when in contact with lithium metal anodes. Due to the low thermodynamic stability of sulfur with lithium metal, continuous redox side reactions occur during battery charge-discharge cycles when the electrolyte is in direct contact with the highly reducing lithium metal anode. These interfacial side reactions generate a decomposition product layer on the anode surface with low ionic conductivity and potentially electronic conductivity, leading to continuous consumption of active material and a sharp increase in interfacial impedance. Furthermore, this interfacial layer generated by the side reactions is usually loosely structured and non-uniform, making it difficult to effectively control lithium-ion deposition behavior. This results in lithium dendrites easily nucleating at the interface and growing along grain boundaries, eventually piercing the electrolyte layer and causing a short circuit. Although existing technologies attempt to isolate the electrolyte from lithium metal by coating with artificial protective layers or introducing inert interlayers, these methods often increase the complexity and cost of the fabrication process, and the added coatings are prone to detachment or cracking during electrode volume changes, making it difficult to achieve long-term stable interfacial protection. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a nitrogen-doped Li-Y-Cl-S solid electrolyte material, its preparation method, and its application, solving the problem of poor interfacial chemical stability of existing Li-Y-Cl-S solid electrolyte materials with lithium metal anodes.

[0005] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of the present invention provides a nitrogen-doped Li-Y-Cl-S solid electrolyte material, which is made from raw materials comprising the following molar proportions:

[0006] (Lithium sulfide): 1.70 parts - 1.99 parts;

[0007] (Yttrium chloride): 1 part;

[0008] LiCl (lithium chloride): 2 parts;

[0009] (Lithium nitride): 0.01 parts - 0.30 parts.

[0010] The solid electrolyte material has a crystal space group of Fm-3m, and its room temperature ionic conductivity is 1.43 mS / cm-2.05 mS / cm, while its electronic conductivity is within a certain range. Magnitude.

[0011] A second aspect of the present invention provides a method for preparing the above-mentioned nitrogen-doped Li-Y-Cl-S solid electrolyte material, comprising the following steps:

[0012] Under an inert atmosphere with a water and oxygen content below 0.1 ppm, Li₂S, ... , LiCl and raw material;

[0013] The weighed raw materials are mixed and subjected to high-energy ball milling to obtain precursor powder; the high-energy ball milling speed is 300rpm-700rpm, the ball milling time is 20 hours-40 hours, and the ball-to-material mass ratio is 8:1-15:1.

[0014] The precursor powder is placed in a sealed environment or inert atmosphere and heated to 200℃-600℃ at a heating rate of 2℃ / min-5℃ / min, and held at that temperature for 3-10 hours for heat treatment sintering.

[0015] The sintered product was cooled to room temperature and then ground and sieved to obtain the nitrogen-doped Li-Y-Cl-S solid electrolyte material.

[0016] A third aspect of the present invention provides an all-solid-state lithium metal battery, comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer, wherein the solid electrolyte layer comprises the aforementioned nitrogen-doped Li-Y-Cl-S-based solid electrolyte material. The negative electrode layer is metallic lithium or a lithium alloy, and the solid electrolyte material forms an interface passivation layer on the surface of the negative electrode layer where the Li3N content decreases with increasing depth.

[0017] This invention provides a nitrogen-doped Li-Y-Cl-S solid electrolyte material, its preparation method, and its applications. It possesses the following beneficial effects:

[0018] 1. This invention introduces nitrogen doping into the Li-Y-Cl-S system, utilizing the characteristic that the radius of nitrogen ions is smaller than that of sulfur ions to induce lattice contraction, thereby enhancing the stability of the crystal structure. While maintaining the high ionic conductivity of the material, the lithium ion transport channel is optimized through the lattice distortion effect, enabling the material to maintain a stable crystal framework during electrochemical cycling and making it less prone to structural collapse.

[0019] 2. When the solid electrolyte material of the present invention comes into contact with the lithium metal anode, it can induce the formation of an interface passivation layer rich in lithium nitride in situ. The interface layer has both high ionic conductivity and low electronic conductivity, which acts as a physical and electronic barrier to block the transfer of electrons into the electrolyte and inhibit the continuous reduction and decomposition of the electrolyte. In addition, the interface layer has high mechanical strength, which can effectively inhibit the nucleation and longitudinal growth of lithium dendrites and prevent the battery from having an internal short circuit.

[0020] 3. The all-solid-state lithium metal battery assembled based on the solid electrolyte of this invention exhibits excellent cycle life and capacity retention. Thanks to the stable bulk structure and the self-limiting growth interface protection layer, the interface impedance of the battery increases slowly during long cycles, the polarization overpotential is low, and the chemical compatibility between the sulfur halide electrolyte and the lithium metal anode is improved, which can meet the requirements of high energy density batteries for long-term stability. Detailed Implementation

[0021] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Preparation Examples 1-5:

[0023] Preparation Example 1:

[0024] This preparation example provides the chemical formula as follows: The preparation method of nitrogen-doped solid electrolyte material includes the following steps:

[0025] In an argon-protected glove box with a water and oxygen content below 0.1 ppm, according to The raw materials were accurately weighed according to the molar ratio. The weighed raw materials were premixed in an agate mortar for 15 minutes, then transferred to a 45 mL stainless steel ball mill jar with 5 mm diameter stainless steel grinding balls at a ball-to-material mass ratio of 10:1. The jar was sealed and removed, and the mixture was ball-milled at 500 rpm for 20 hours in a planetary ball mill to obtain precursor powder. The precursor powder was transferred to a quartz tube in a glove box and vacuum-sealed. It was then placed in a tube furnace and heated to 300 °C at a rate of 5 °C / min, and held for 4 hours (this is the high-temperature solid-state sintering step). The furnace was then allowed to cool naturally to room temperature. The sintered product was ground in a glove box and passed through a 200-mesh sieve to obtain a light yellow solid electrolyte powder. X-ray diffraction (XRD) analysis showed that the crystal structure space group of the obtained powder was Fm-3m. AC impedance spectroscopy and DC polarization analysis showed that the room temperature ionic conductivity of the solid electrolyte powder was 2.05 mS / cm, and the electronic conductivity was [missing value]. .

[0026] Preparation Example 2:

[0027] This preparation example provides the chemical formula as follows: The preparation method of nitrogen-doped solid electrolyte material includes the following steps:

[0028] In an argon-protected glove box with a water and oxygen content below 0.1 ppm, according to The raw materials were accurately weighed according to the molar ratio; after the raw materials were mixed evenly, they were placed into a zirconia ball mill jar, and zirconia grinding balls were added, with a ball-to-material mass ratio of 15:1; high-energy ball milling was carried out at a speed of 400 rpm for 30 hours to obtain precursor powder; the precursor powder was placed into a quartz crucible and heat-treated in a tube furnace filled with high-purity argon gas, with a heating rate of 5℃ / min, a sintering temperature of 550℃, and a holding time of 5 hours; after natural cooling, the product was ground through a 300-mesh sieve to obtain a deep yellow solid electrolyte powder.

[0029] Preparation Example 3:

[0030] This preparation example provides the chemical formula as follows: The preparation method of nitrogen-doped solid electrolyte material includes the following steps:

[0031] In an argon-protected glove box with a water and oxygen content below 0.1 ppm, according to The raw materials were accurately weighed according to the molar ratio; the raw materials were loaded into a stainless steel ball mill jar with a ball-to-material mass ratio of 8:1; the material was pre-milled at 300 rpm for 10 hours, and then the speed was increased to 700 rpm for 15 hours to obtain a fine precursor powder; the precursor was sintered at 600℃ for 3 hours in an argon atmosphere with a heating rate of 3℃ / min; after cooling, it was ground and sieved to obtain a solid electrolyte material.

[0032] Preparation Example 4:

[0033] This preparation example provides the chemical formula as follows: A method for preparing low-concentration nitrogen-doped solid electrolyte materials includes the following steps:

[0034] In an argon-protected glove box with a water and oxygen content below 0.1 ppm, according to The raw materials were accurately weighed according to the molar ratio; a stainless steel ball mill jar and grinding balls were used, with a ball-to-material mass ratio of 12:1, and the mixture was ball-milled at 450 rpm for 25 hours; the resulting precursor powder was encapsulated in a vacuum quartz tube, heated to 500°C at 5°C / min and held at that temperature for 5 hours (sintering); after naturally cooling to room temperature, the powder was removed, ground, and passed through a 200-mesh sieve to obtain solid electrolyte powder.

[0035] Preparation Example 5:

[0036] This preparation example provides the chemical formula as follows: The preparation method of high-concentration nitrogen-doped solid electrolyte materials includes the following steps:

[0037] In an argon-protected glove box with a water oxygen content of less than 0.1 ppm,

[0038] according to The raw materials were accurately weighed according to the molar ratio; the raw materials were thoroughly ground and mixed in an agate mortar for 30 minutes, then placed in a stainless steel ball mill jar with a ball-to-material mass ratio of 10:1, and ball-milled at 500 rpm for 40 hours to ensure reactivity; the precursor was placed in an argon-protected tube furnace and sintered at 400℃ for 8 hours; after cooling, it was ground and sieved to obtain the solid electrolyte material. The room temperature ionic conductivity of the obtained solid electrolyte material was tested to be 1.43 mS / cm, and the electronic conductivity was [missing value]. .

[0039] Preparation Example 6:

[0040] This preparation example provides the chemical formula as follows: The preparation method of nitrogen-doped solid electrolyte materials (low-temperature sintering process) includes the following steps:

[0041] The raw material ratio and ball milling process were exactly the same as in Preparation Example 1. The precursor powder obtained by ball milling was encapsulated in a vacuum quartz tube, placed in a tube furnace and heated to 200°C at a slow heating rate of 2°C / min, and held for 10 hours to promote low-temperature solid-phase reaction (low-temperature sintering). After cooling to room temperature in the furnace, it was ground through a 400-mesh sieve in a glove box to obtain solid electrolyte micro powder.

[0042] Examples 1-3:

[0043] Example 1:

[0044] This embodiment provides a lithium-lithium symmetric battery assembled based on the solid electrolyte material obtained in Preparation Example 1, including the following steps:

[0045] In an argon atmosphere glove box, 120 mg of the nitrogen-doped solid electrolyte powder prepared in Preparation Example 1 was weighed out. The solid electrolyte sheet was placed in a polyether ether ketone (PEEK) mold with an inner diameter of 10 mm and cold-pressed under a pressure of 300 MPa to obtain a dense solid electrolyte sheet with a thickness of about 0.8 mm. Two metal lithium foils with a diameter of 10 mm and a thickness of 50 μm were taken and attached to the upper and lower surfaces of the solid electrolyte sheet, respectively. The above sandwich structure stacked assembly was placed in a stainless steel button battery case (CR2032 type), and gaskets and spring sheets were added to maintain contact pressure. The battery was then packaged using a tablet press to obtain a Li|SE|Li symmetric battery.

[0046] The battery was disassembled after cycle testing, and the lithium anode / electrolyte interface was deeply analyzed using X-ray photoelectron spectroscopy (XPS) combined with argon-ion etching technology. The results showed that the solid electrolyte material formed a rich layer of lithium on the surface of the anode layer. The interface passivation layer, and in the passivation layer The content of [agent] decreases with increasing etching depth.

[0047] Example 2:

[0048] This embodiment provides an all-solid-state lithium metal battery assembled based on the solid electrolyte material obtained in Preparation Example 2, including the following steps:

[0049] Preparation of composite cathode materials: This involves combining cathode active materials... Preparation Example 2: Solid electrolyte powder obtained ( The conductive agent vapor-grown carbon fiber (VGCF) and the conductive agent were placed in an agate mortar at a mass ratio of 70:25:5 and manually ground and mixed for 30 minutes to obtain a uniform composite cathode powder.

[0050] Battery assembly: In an argon glove box, 100 mg of the solid electrolyte powder prepared in Preparation Example 2 was weighed and placed in a 10 mm mold, and pre-pressed flat with a pressure of 100 MPa; then 10 mg of the above composite positive electrode powder was weighed and evenly spread on the surface of the electrolyte layer, and co-pressed under a pressure of 360 MPa to form a positive electrode / electrolyte bilayer sheet; finally, a 10 mm diameter lithium metal sheet was attached to the electrolyte side surface as a negative electrode, placed in the mold battery device, and encapsulated under a constant stacking pressure of 50 MPa to obtain an NCM811 / SE / Li all-solid-state battery.

[0051] Example 3:

[0052] This embodiment provides an all-solid-state lithium metal battery assembled based on the solid electrolyte material obtained in Preparation Example 3, including the following steps:

[0053] Preparation of composite cathode materials: selection As the positive electrode active material, it was combined with the solid electrolyte powder prepared in Preparation Example 3 ( Mix the conductive carbon black (SuperP) and conductive carbon black (SuperP) at a mass ratio of 65:30:5 until homogeneous.

[0054] Battery assembly: 80 mg of solid electrolyte powder from Preparation Example 3 was weighed and placed in a 10 mm mold for pre-pressing; 12 mg of composite positive electrode powder was weighed and laid on it, and pressed into shape under a pressure of 350 MPa; a lithium indium alloy (Li-In) sheet was attached to the other side of the electrolyte layer as a negative electrode (to provide a more stable test benchmark and verify the stability of the material under high voltage), assembled into a test mold and fixed with bolt pressure to obtain an NCA / SE / Li-In all-solid-state battery.

[0055] Comparative Examples 1-4:

[0056] Comparative Example 1:

[0057] The difference compared to Example 1 is that no additives were added during the preparation of the electrolyte. Nitrogen source, adjusted accordingly. The ratio of LiCl to the undoped chemical formula is such that... The stoichiometric ratio is the same, and the remaining preparation steps and battery assembly processes are identical.

[0058] Comparative Example 2:

[0059] The difference compared to Example 1 is that lithium oxide (…) was used. ) to replace lithium nitride ( As a dopant, the oxygen-to-sulfur doping molar ratio remains at x=0.05 (i.e., according to...). (Ingredients), to obtain the chemical formula is The oxygen-doped solid electrolyte is used, and the rest of the preparation process and battery assembly are the same.

[0060] Comparative Example 3:

[0061] The difference from Example 1 is that lithium fluoride (LiF) is used instead of lithium nitride (Li3N) for doping (i.e., to prepare a fluorine-doped electrolyte), otherwise the same.

[0062] Comparative Example 4:

[0063] Compared with Example 1, the difference is that the solid-state sintering step at 300°C in the preparation process was omitted, and only the precursor powder after ball milling was subjected to simple thermal annealing (drying at 100°C to remove stress), while the rest were the same.

[0064] Test Example 1-3:

[0065] Test Example 1: Crystal Structure and Lattice Parameter Analysis

[0066] This test case aims to analyze the crystal structure characteristics of the materials prepared in each embodiment and comparative example using X-ray powder diffraction (XRD) technology, and to calculate the unit cell parameters based on the Bragg equation and the Rietveld refinement method to verify whether nitrogen has been successfully doped into the lattice sites.

[0067] Experimental steps:

[0068] In an argon-protected glove box, a small amount of the solid electrolyte powder used in Examples 1-3 and Comparative Example 1 (as well as the powder used in Preparation Examples 4-6 for reference) was taken and lightly ground with an agate mortar to eliminate preferred orientation.

[0069] The powder sample is laid flat in the groove of a special test sample holder, covered with a polyimide (Kapton) film with a thickness of 8μm, and fixed with a sealing ring to prevent the sample from coming into contact with moisture and oxygen in the air during the test.

[0070] The sealed sample holder was transferred to an X-ray diffractometer (Bruker D8 Advance) using a Cu-Kα radiation source. The tube voltage is set to 40kV and the tube current is 40mA.

[0071] Set the scanning range 2θ to 10° to 80°, the step size to 0.02°, and the scanning speed to 5° / min, and acquire diffraction data.

[0072] The collected diffraction patterns were fitted with the full spectrum and refined with Rietveld using Topas software. The unit cell parameters a and unit cell volume V of each sample were calculated using space group Fm-3m as the reference model.

[0073] The test results are shown in Table 1 below:

[0074] Table 1. Calculation results of lattice parameters for each embodiment and comparative example material.

[0075]

[0076] Conclusion Analysis:

[0077] According to the data in Table 1, the unit cell parameters of Comparative Example 1 to Preparation Example 5 exhibit a clear evolution pattern. The undoped Comparative Example 1 sample has the largest unit cell parameter ( As the nitrogen doping concentration x gradually increases from 0.01 to 0.30, the cell parameter a of the sample changes from... Monotonically decreasing to The unit cell volume V also shrinks accordingly.

[0078] This experimental result directly confirms the lattice substitution mechanism of this invention. In crystal chemistry, Effective ionic radius (approximately) Significantly smaller than Effective ionic radius (approximately) ).when Successfully replaced in the crystal lattice When a solid solution forms at the site, it inevitably leads to lattice contraction, which macroscopically manifests as a shift of diffraction peaks to higher angles in the XRD pattern and a decrease in the calculated unit cell parameters. The data from preparation examples 1-5 strictly follow Vegard's law, indicating that nitrogen atoms do not exist as interstitial atoms or are free at grain boundaries, but are actually incorporated into the main lattice framework of Li-Y-Cl-S.

[0079] Meanwhile, the fitting residuals Rwp of all samples were within a reasonable range, and no raw material residues were observed in the XRD patterns. The characteristic diffraction peaks ruled out the possibility of physical mixing residues, confirming the formation of a single-phase solid solution. It is noteworthy that the cell parameters of Preparation Example 6 (low-temperature process) (…) Slightly larger than the preparation example 1 with the same components ( This indicates that a lower sintering temperature may lead to incomplete elimination of lattice defects or slightly lower solid solubility, but the overall lattice contraction trend after doping is still maintained. This lattice contraction effect caused by the difference in anion radii enhances the binding energy of the crystal framework, providing a thermodynamic basis for the subsequent structural stability exhibited by the material.

[0080] Test Example 2: In-depth analysis of interfacial chemical composition (XPS)

[0081] This test case utilizes X-ray photoelectron spectroscopy (XPS) combined with argon ion etching depth profiling to analyze the chemical composition of the lithium metal anode interface after long-term cycling, aiming to verify the mechanism by which nitrogen-doped solid electrolytes induce the in-situ formation of a nitrogen-containing passivation layer (SEI) on the surface of lithium metal.

[0082] Experimental steps:

[0083] Li|SE|Li symmetric cells assembled in Example 1 (N-doped), Comparative Example 1 (undoped), and Comparative Example 3 (F-doped) were selected. A constant current charge-discharge cycle was performed for 50 hours at the current density to ensure that the interface reaction was fully carried out.

[0084] After the cycle was completed, the battery was carefully disassembled in an argon glove box, and the lithium metal sheet on the side in contact with the solid electrolyte was separated as the sample to be tested.

[0085] The lithium sheet surface was lightly rinsed with DMC (dimethyl carbonate) to remove residual physically adsorbed particles. After drying, it was placed in a vacuum transfer box and quickly transferred to the ultra-high vacuum sample chamber of the XPS instrument (Thermo Fisher ESCALAB 250Xi) to avoid atmospheric contamination.

[0086] A monochromatic Al-Kα ray source was used to perform full-spectrum scanning of the surface and fine spectral scanning of elements such as N1s, S2p, F1s, and Li1s.

[0087] The sample surface was etched using an argon ion beam at a calibrated etching rate of 2 nm / min (relative to...). Data were collected at 0 minutes (surface), 5 minutes (approximately 10 nm deep), and 15 minutes (approximately 30 nm deep) of etching to analyze the longitudinal distribution characteristics of the interface film.

[0088] All binding energy data were charged and corrected based on the C1s peak (284.8 eV).

[0089] The test results are shown in Table 2 below:

[0090] Table 2. Analysis of the binding energy and atomic percentage of characteristic peaks of each element in the lithium anode interface layer after cycling.

[0091]

[0092] Note: “—” in the table indicates that the characteristic signal of the element was not detected or the signal is below the detection limit.

[0093] Conclusion Analysis:

[0094] Based on the data in Table 2, in-depth analysis can clearly reveal the differences in the chemical composition of the interface film (SEI) formed on the surface of lithium metal by different electrolyte systems.

[0095] The sample in Example 1 showed an N1s signal at the interface, with a binding energy around 398.5 eV, corresponding to the characteristic peak of the Li-N bond, confirming that... The presence of different phases was observed. With increasing etching depth (from the surface to a depth of 30 nm), the atomic percentage of nitrogen (N) increased from 4.82% to 11.27%, while the percentage of sulfur (S), representing electrolyte decomposition products, rapidly decreased from 2.15% to 0.45%. This inverse distribution trend indicates that nitrogen was enriched at the interface and preferentially formed phases rich in nitrogen. The inner passivation film. This dense... The layer acts as a physical barrier, effectively blocking direct contact between metallic lithium and sulfur in the electrolyte matrix, thereby inhibiting the continuous reduction and decomposition of sulfur (manifested as extremely low sulfur content in the deep layer).

[0096] In contrast, no N signal was detected in the interface layer of Comparative Example 1 (undoped), and the S content increased sharply with increasing depth (up to 24.18%). This indicates that a violent and uncontrolled side reaction occurred between the electrolyte and metallic lithium, generating a large amount of S. The main decomposition products lead to a continuous thickening of the interface layer.

[0097] Although Comparative Example 3 (F-doped) formed a protective layer mainly composed of LiF at the interface (F content increases with depth), suppressing the decomposition of S (S content is low), subsequent electrochemical performance shows that due to the low ionic conductivity of LiF (approximately...), the decomposition of S was still limited. ) far below (about Its interface impedance is necessarily higher than that of Example 1.

[0098] In summary, XPS data directly confirm the design mechanism of this invention: through in-situ reduction of N atoms in the lattice, a layer rich in N atoms was successfully constructed at the lithium metal interface. The high ionic conductivity and electronic insulation of the self-confined passivation layer is the fundamental reason why the material of this invention achieves high interface stability.

[0099] Test Example 3: Ionic Conductivity and Electronic Conductivity Test

[0100] In this test example, AC impedance spectroscopy (EIS) and DC polarization method were used to measure the room temperature ionic conductivity and electronic conductivity of the solid electrolyte materials obtained in each example and comparative example, so as to evaluate the effect of nitrogen doping on the conductivity of the materials.

[0101] Experimental steps:

[0102] Ionic conductivity testing: In an argon-filled glove box, 150 mg of the electrolyte powder to be tested was weighed and placed in a mold, then cold-pressed at 350 MPa to form a dense disc with a diameter of 10 mm and a thickness of approximately 0.8 mm. A 100 nm thick gold (Au) film was sputtered onto both sides of the disc as ion-blocking electrodes. The sample was loaded into a Swagelok-type test cell mold and connected to an electrochemical workstation. AC impedance spectroscopy was performed at a constant temperature of 25 °C, with a frequency range of 7 MHz to 100 mHz and an amplitude of 10 mV. The total resistance was determined based on the AC impedance spectroscopy data. Combined with sample thickness and area Using the formula Calculate the ionic conductivity.

[0103] Electronic conductivity test: Using the same pressed sample as described above, replace the electrodes on both sides with stainless steel sheets (SS). Apply a constant DC voltage of 0.5V and continuously record the change in current over time until the current reaches a steady state (polarization time set to 1 hour). Analyze the steady-state current value... and applied voltage Using the formula Calculate the electronic conductivity.

[0104] The test results are shown in Table 3 below:

[0105] Table 3. Conductivity test results for each sample (25℃)

[0106]

[0107] Conclusion Analysis:

[0108] According to the data in Table 3, different doping strategies and processes have significantly different effects on conductivity.

[0109] First, appropriate nitrogen doping (Examples 1 and 2) did not reduce the ion transport capacity of the materials; instead, it achieved a slight increase in ionic conductivity. Example 1 (x=0.05) achieved an ionic conductivity of 2.05 mS / cm, which is superior to the undoped Comparative Example 1 (1.82 mS / cm). This is attributed to... The lattice distortion effect induced by the introduction of lithium ions, along with appropriate changes in lattice parameters, broadens the bottleneck size for lithium-ion transport; simultaneously, according to the charge compensation mechanism, replace The introduction of additional interstitial lithium ions into the crystal lattice increases the carrier concentration, and the two work synergistically to reduce the transport activation energy.

[0110] However, when the doping concentration is too high (e.g., in Example 5, x = 0.30), the ionic conductivity decreases to 1.43 mS / cm. This indicates that excessive lattice distortion may disrupt long-range ordered transport channels.

[0111] Compared with different anion doping methods, the ionic conductivity of Comparative Example 3 (F-doped) is only 1.12 mS / cm, significantly lower than that of the N-doped system of this invention. This indicates that... Although it has high stability, it has a strong binding force on lithium ions.

[0112] In terms of process, the electrical conductivity of low-temperature sintering (Reference Example / Preparation Example 6) and no sintering (Comparative Example 4) was significantly reduced, which confirms the necessity of high-temperature heat treatment for eliminating grain boundary defects, improving crystallinity and constructing continuous ion channels.

[0113] Test Example 4: Interfacial Impedance Evolution over Time (Static Stability)

[0114] This test example uses electrochemical impedance spectroscopy (EIS) to monitor the evolution of the interfacial impedance of the assembled lithium-lithium symmetric battery in the open-circuit state with resting time, in order to evaluate the chemical stability of the electrolyte material to the lithium metal anode and the effect of the interfacial passivation layer formation.

[0115] Experimental steps:

[0116] Solid electrolyte powders prepared in Example 1 (N-doped), Comparative Example 1 (undoped), Comparative Example 2 (O-doped), and Comparative Example 3 (F-doped) were selected and assembled into Li|SE|Li symmetric cells according to the method in Example 1. Three cells were assembled in parallel for each sample group to eliminate random errors.

[0117] The assembled battery was placed in a constant temperature and humidity chamber set at 25°C and connected to a multi-channel electrochemical workstation to maintain the open circuit voltage (OCV) state for static aging.

[0118] The impedance test frequency range was set to 1MHz to 100mHz, and the AC disturbance amplitude was 10mV. EIS data was collected at 0 hours (initial state), 24 hours, 120 hours, 300 hours and 500 hours after the battery assembly was completed.

[0119] The arc diameter representing the interfacial charge transfer resistance is extracted from AC impedance spectroscopy data, and the interfacial surface resistance is calculated by normalizing the electrode area. ).

[0120] The test results are shown in Table 4 below:

[0121] Table 4. Lithium / electrolyte interface resistance at different resting times ( Evolutionary data

[0122]

[0123] Conclusion Analysis:

[0124] According to the data in Table 4, the interfacial impedance evolution behavior of each sample shows a completely different trend, which directly reflects the decisive influence of the properties of interfacial products on stability.

[0125] Example 1 exhibits the lowest interface impedance at the initial moment ( Furthermore, the values ​​remained highly stable during the 500-hour settling period, with only a slight increase (ultimately reaching...). This proves that the system was generated in situ. The interface layer possesses both high ionic conductivity and excellent chemical stability. The extremely low grain boundary impedance ensures rapid transport of lithium ions at the interface, while its electronic insulation effectively blocks the tunneling of electrons into the electrolyte, achieving self-limitation of the reaction and thus suppressing the continuous growth of impedance.

[0126] In contrast, the undoped Comparative Example 1 had a lower initial impedance ( However, the impedance increases exponentially over time, surging to [a certain value] after 500 hours. This indicates that the Li-Y-Cl-S system, in the absence of nitrogen protection, underwent a continuous and uncontrollable reductive decomposition reaction with metallic lithium, generating a thick layer of decomposition products (such as polysulfides) with poor ionic conductivity, leading to interface deterioration and failure.

[0127] For other doped systems, Comparative Example 3 (F-doped) exhibited similar stability to Example 1 (with a growth rate of only 17.2%), indicating that the LiF layer does indeed act as a passivation layer, but its absolute impedance value (initially as high as...) was significantly lower. The rate performance of the battery is an order of magnitude higher than that of Example 1. This is because the ionic conductivity of LiF itself is extremely low, forming a huge interfacial transport barrier that severely limits the rate performance of the battery. Comparative Example 2 (O doping) is in an intermediate state, and its generated... The conductivity of the interface layer is weaker than However, while it is stronger than LiF, its stability is not as good. And LiF.

[0128] In summary, the data from Example 1 strongly supports the technical mechanism of this invention: nitrogen doping-induced generation The dominant interface phase is currently the only interface solution in this system that can simultaneously achieve "low interface impedance" and "high long-term stability".

[0129] Test Example 5: Lithium Metal Deposition / Stripping Cycle Stability Test (Dynamic Stability)

[0130] This test case evaluates the tolerance of each group of solid electrolyte materials under dynamic electrochemical conditions through critical current density (CCD) testing and constant current long-cycle testing, specifically examining their performance in inhibiting lithium dendrite growth and maintaining interface stability under high current density.

[0131] Experimental steps:

[0132] The Li|SE|Li symmetric cells (corresponding to Example 1 and each comparative example) were assembled using the same preparation process as in Test Example 4 and placed in a constant temperature environment of 25°C for testing.

[0133] Critical current density (CCD) determination: Set the initial current density to... The single deposition / stripping time is fixed at 1 hour (i.e., half a cycle of 0.5 hours), and after 3 cycles, the time is... The current density is gradually increased step by step until a failure signal is detected.

[0134] Constant current long-cycle test: Select fresh batteries from each group that have not undergone CCD testing, and set a fixed current density. Surface capacity is It undergoes continuous charge and discharge cycles.

[0135] The test results are shown in Table 5 below:

[0136] Table 5 Summary of dynamic cycle performance test data for lithium-symmetric batteries

[0137]

[0138] Conclusion Analysis:

[0139] Based on the data in Table 5, Example 1 demonstrates a comprehensive advantage in terms of dynamic stability, with its critical current density (CCD) reaching [value missing]. It is much higher than that of Comparative Example 1. The CCD value reflects the limiting ability of a solid electrolyte to withstand non-uniformity in lithium-ion flux.

[0140] The high CCD value and long cycle life of over 1200 hours in Example 1 are attributed to in-situ formation. Interface layer. It has high surface energy and mechanical modulus, which can effectively suppress the tip growth effect of lithium dendrites; at the same time, its high ionic conductivity ensures the uniformity of lithium ion flux at the interface.

[0141] Compared to other modified samples, Comparative Example 3 (F-doped) also exhibited a high CCD, but its overpotential was as high as 185.6 mV, implying significant energy loss. These results demonstrate that this invention, by controlling the amount of N doping, constructs a composite material at the interface that combines ionic conductivity with high mechanical strength. The functional layer effectively solves the problem of dendrite short circuits.

[0142] Test Example 6: All-Solid-State Battery Charge and Discharge Performance Test

[0143] This test case involves constant current charge-discharge testing of an assembled NCM811 / SE / Li all-solid-state battery to examine the ability of the solid electrolyte to support the positive electrode capacity in a real full-cell system and its protective effect on the lithium metal anode interface during long-term cycling.

[0144] Experimental steps:

[0145] Five all-solid-state batteries were assembled using materials from Example 2 (NCM811 cathode / N-doped electrolyte), Example 3 (NCA cathode / N-doped electrolyte), and Comparative Example 1 (undoped) and Comparative Example 3 (F-doped).

[0146] Connect the battery to the battery testing system and place it in a 25°C constant temperature chamber for 6 hours to allow the interface to wet and the temperature to equalize.

[0147] Set the test voltage window: 2.8V to 4.3V for NCM811 system, and 2.8V to 4.25V for NCA system.

[0148] Start the formation process: Increase the rate to 0.5C and perform constant current charge-discharge cycles, set a 5-minute rest period between charge and discharge cycles, and run continuously for 200 cycles.

[0149] The test results are shown in Table 6 below:

[0150] Table 6 Performance data of all-solid-state batteries at 0.5C rate for 200 cycles

[0151]

[0152] Conclusion Analysis:

[0153] According to the data in Table 6, the battery of Example 2 exhibited the best overall electrochemical performance. Its first-cycle discharge specific capacity reached 198.4 mAh / g, and after 200 cycles at 0.5C, the capacity retention was as high as 91.5%. This result verifies the effectiveness of the material of this invention at the full-cell level.

[0154] In contrast, Comparative Example 1 (undoped) showed extremely severe degradation, with a capacity retention of less than 40% after 200 cycles. This is attributed to the fact that, in the absence of nitrogen protection, the electrolyte is continuously reduced by metallic lithium during cycling, consuming the active lithium source and increasing internal resistance.

[0155] The comparison with Comparative Example 3 (F-doped) further highlights the The kinetic advantages of the interface. Although the capacity retention of Comparative Example 3 was acceptable, its first-cycle capacity and cycle capacity were significantly lower than those of Example 2. This is consistent with the results of Test Examples 3 and 4: the high interfacial impedance of LiF limits the kinetic performance of the battery.

[0156] In summary, this invention achieves a synergistic improvement in high capacity and long cycle life of sulfur halide electrolytes in full-cell applications by constructing a nitrogen-containing interface with high lithium conductivity and high stability.

Claims

1. A nitrogen-doped Li-Y-Cl-S solid electrolyte material, characterized in that, Made from raw materials comprising the following molar proportions: 1.70-1.99 portions; 1 copy; LiCl: 2 parts; : 0.01-0.30 copies.

2. The nitrogen-doped Li-Y-Cl-S solid electrolyte material according to claim 1, characterized in that, The solid electrolyte material has a crystal space group of Fm-3m, and its room temperature ionic conductivity is 1.43 mS / cm-2.05 mS / cm, and its electronic conductivity is... Magnitude.

3. The method for preparing nitrogen-doped Li-Y-Cl-S solid electrolyte material according to claims 1-2, characterized in that, Includes the following steps: Weigh according to the molar ratio under an inert atmosphere. , , LiCl and raw material; The weighed raw materials are mixed and subjected to high-energy ball milling to obtain precursor powder; The precursor powder is placed in a sealed environment or an inert atmosphere for heat treatment and sintering to obtain the sintered product; The sintered product was cooled to room temperature and then ground and sieved to obtain the nitrogen-doped Li-Y-Cl-S solid electrolyte material.

4. The method for preparing a nitrogen-doped Li-Y-Cl-S solid electrolyte material according to claim 3, characterized in that, The process parameters for the high-energy ball milling treatment are controlled as follows: ball milling speed is 300rpm-700rpm, ball milling time is 20 hours-40 hours, and ball-to-material mass ratio is 8:1-15:

1.

5. The method for preparing a nitrogen-doped Li-Y-Cl-S solid electrolyte material according to claim 3, characterized in that, The heat treatment sintering temperature is 200℃-600℃, and the holding time is 3 hours-10 hours.

6. The method for preparing a nitrogen-doped Li-Y-Cl-S solid electrolyte material according to claim 3, characterized in that, The heating rate during the heat treatment sintering process is controlled at 2℃ / min-5℃ / min.

7. The method for preparing a nitrogen-doped Li-Y-Cl-S solid electrolyte material according to claim 3, characterized in that, The weighing, mixing, and high-energy ball milling of the raw materials were all carried out in an argon atmosphere with a water and oxygen content of less than 0.1 ppm.

8. The method for preparing a nitrogen-doped Li-Y-Cl-S solid electrolyte material according to claim 3, characterized in that, The container for heat treatment and sintering of the precursor powder is a vacuum quartz tube or a tube furnace filled with argon gas.

9. An all-solid-state lithium metal battery, characterized in that, The all-solid-state lithium metal battery includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer. The solid electrolyte layer contains a nitrogen-doped Li-Y-Cl-S solid electrolyte material.

10. The all-solid-state lithium metal battery according to claim 9, characterized in that, The negative electrode layer is metallic lithium or a lithium alloy, and the positive electrode layer comprises a ternary layered oxide positive electrode material or a lithium nickel cobalt aluminum oxide positive electrode material; the solid electrolyte material is contained in an interface passivation layer formed on the surface of the negative electrode layer. The content of [something] decreases with increasing depth.

Images