A sulfide solid electrolyte and its preparation method

Abstract

This invention discloses a sulfide solid electrolyte, its preparation method, and its application, belonging to the field of all-solid-state lithium battery technology. The electrolyte has the general formula Li. 7+x P3S 11‑x M x The precursor, denoted as tantalum (Ta) and / or niobium (Nb), has a molecular weight (x) of 0.01–0.3. Its preparation method includes: high-energy ball milling of raw materials Li₂S, P₂S₅, and M₂S₅ to obtain an amorphous precursor under an inert atmosphere, followed by crystallization through a two-step stepped heat treatment. This invention, through Ta / Nb high-valence cation doping, maintains the high ionic conductivity of the sulfide electrolyte while significantly improving the material's air stability by utilizing its stronger M-S bonds. The electrolyte preparation process is simple and cost-controllable, making it suitable for constructing high-performance, high-safety all-solid-state lithium batteries.

Description

Technical Field

[0001] This invention belongs to the field of electrochemistry and new energy materials technology, specifically relating to a sulfide solid electrolyte material for all-solid-state lithium batteries, its preparation method and its application. Background Technology

[0002] All-solid-state lithium batteries are considered an ideal choice for next-generation energy storage technology due to their high safety and high energy density. Among them, sulfide solid electrolytes are particularly advantageous due to their extremely high ionic conductivity (up to 10). -2 S cm -1 It has attracted much attention due to its scale.

[0003] However, sulfide solid electrolytes, especially those based on the Li2S-P2S5 system, face two major challenges: 1. Extremely sensitive to moisture: It reacts with water vapor in the air to produce highly toxic hydrogen sulfide (H2S) gas, which not only poses a safety hazard but also causes material failure, greatly increasing the cost and difficulty of its production, storage and battery manufacturing (which must be carried out in a harsh drying room or glove box).

[0004] 2. Instability at the high-voltage positive electrode interface: at higher voltages (>4V vs. Li / Li) + Under these conditions, sulfide electrolytes are easily oxidized, leading to increased interfacial impedance and capacity decay.

[0005] Currently, common methods for improving air stability include elemental doping (such as O, Sn, I, etc.) and surface coating. However, these methods often sacrifice the bulk ionic conductivity of the material to varying degrees while improving stability. For example, oxygen doping reduces conductivity; while surface coatings may hinder ion transport.

[0006] Therefore, developing a sulfide solid electrolyte that can maintain high ionic conductivity and excellent air stability is crucial for technological advancement in this field. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a sulfide solid electrolyte and its preparation method. This material maintains high lithium-ion conductivity while significantly improving its stability in atmospheric environment and broadening its electrochemical window.

[0008] To achieve the above objectives, the present invention provides a sulfide solid electrolyte with the general formula: Li 7+ x P3S 11-x M x , where M is Ta and / or Nb, and x ranges from 0.01 to 0.3.

[0009] Furthermore, M is Ta. The ionic radius of Ta is close to that of P, which is advantageous in Li... 7+x P3S 11-x M x Solid solution substitution in the crystal lattice avoids excessive lattice distortion caused by size mismatch, maintaining structural integrity. Simultaneously, the Ta-S bond energy is significantly higher than the PS bond energy, enhancing the overall bonding strength of the crystal structure after doping, thereby improving the material's resistance to water molecule erosion—a key structural factor in improving air stability. After Ta replaces P, additional lithium vacancies are introduced into the lattice to maintain charge balance, providing more channels for Li⁺ migration and partially compensating for potential conductivity losses due to structural densification. Ta exhibits strong electrochemical inertness, and its oxide itself possesses a high dielectric constant and excellent chemical stability; the introduction of Ta can suppress the oxidative decomposition reaction of the electrolyte under high voltage.

[0010] Furthermore, the value of x ranges from 0.05 to 0.15. The key objective of this invention is to suppress the reaction between sulfide electrolytes and water. The principle is to replace some PS bonds with Ta-S / Nb-S bonds to form a hydrolysis-resistant lattice structure. If x < 0.05, the proportion of Ta / Nb in the lattice is less than 5%, the number of replaced PS bonds is limited, and the overall hydrolysis resistance of the lattice is only slightly improved. Another effect of Ta / Nb doping is to introduce lithium vacancies through moderate lattice distortion, providing additional channels for lithium ion migration. If x < 0.05, the amount of lithium vacancies generated is insufficient, and it cannot effectively compensate for the conductivity loss that may result from doping. Furthermore, when x < 0.05, the effect of Ta / Nb on broadening the electrochemical window of the electrolyte is limited, and it cannot effectively suppress high voltage (≥4.3 V vs. Li / Li). + Oxidative decomposition reaction under ( ).

[0011] However, when x is higher than 0.15, excessive Ta can cause problems such as lattice distortion and impurity phase precipitation. Although the ionic radius of Ta / Nb is similar to that of P, excessive substitution will exceed that of Li. 7+x P3S 11-x M x The solid solution limit of the crystal lattice leads to the appearance of impurity peaks, disrupting the original pure phase structure. The presence of impurities blocks lithium-ion transport channels and reduces overall lattice stability, thus exacerbating hydrolysis. Excessive doping causes lattice distortion, shifting from promoting ion transport to hindering it. Excess Ta / Nb compresses lithium-ion transport channels, increasing migration resistance, while impurity formation further reduces ion transport efficiency. Excess Ta / Nb forms a thick impedance layer at the electrolyte-cathode interface. Although Ta / Nb oxides are inherently stable, excessive formation leads to a surge in interfacial charge transfer resistance.

[0012] Furthermore, its room temperature ionic conductivity is not less than 3.0 × 10⁻⁶.-3 S cm -1 .

[0013] On the other hand, the present invention also provides a method for preparing the above-described sulfide solid electrolyte, comprising the following steps: a) Under an inert atmosphere, weigh and mix Li2S, P2S5 and M2S5 raw materials according to stoichiometric ratio; b) The mixture is subjected to high-energy ball milling to obtain an amorphous precursor; c) The precursor is subjected to a step-by-step heat treatment under an inert atmosphere to induce crystallization.

[0014] Furthermore, the stepped heat treatment described in step c) includes: first holding at 200-250℃ for 2-5 hours, and then holding at 400-500℃ for 4-10 hours.

[0015] Furthermore, the high-energy ball milling in step b) has a rotation speed of 400-600 rpm and a milling time of 10-20 h.

[0016] The present invention also provides an all-solid-state lithium battery, comprising a positive electrode layer, a solid electrolyte layer and a negative electrode layer, wherein the solid electrolyte layer comprises a sulfide electrolyte as described above.

[0017] Furthermore, the positive electrode layer comprises a high-voltage positive electrode active material with a charging cut-off voltage of not less than 4.3 V (vs. Li / Li). + ).

[0018] The present invention also provides an application of the sulfide solid electrolyte as described above in an all-solid-state lithium battery.

[0019] The beneficial effects of this invention are: This invention achieves precise Ta / Nb doping without damaging Li 7+x P3S 11-x M xUnder the premise of the original crystal structure, two major gains are achieved: the Ta / Nb ion radius is close to that of P, allowing it to stably dissolve into the crystal lattice and avoid ion transport obstruction caused by lattice distortion; doping maintains charge balance and introduces additional lithium vacancies, providing more channels for Li migration and compensating for the conductivity loss that may result from structural densification. Addressing the industry pain points of sulfide electrolytes being sensitive to moisture and generating highly toxic H2S, this invention achieves a fundamental improvement by replacing some PS bonds with Ta-S / Nb-S bonds; the Ta-S / Nb-S bond energy is significantly higher than that of PS bonds, enhancing the overall lattice bonding strength and greatly improving resistance to water molecule erosion; Ta / Nb possesses excellent electrochemical inertness, and its oxides have high dielectric constants and strong chemical stability, which can suppress the oxidative decomposition reaction of the electrolyte under high voltage; the stable crystal structure formed after doping reduces the interfacial reaction between the electrolyte and the high-voltage cathode. Attached Figure Description

[0020] Figure 1 The electrochemical impedance spectroscopy spectra of the electrolytes in Example 1 and Comparative Example 1 of this invention are shown.

[0021] Figure 2 The X-ray diffraction patterns are those of the electrolytes prepared in Example 1 and Comparative Example 1 of this invention.

[0022] Figure 3 This is a comparison chart showing the retention rate of ionic conductivity of the electrolytes in Example 1 and Comparative Example 1 after exposure to humid air.

[0023] Figure 4 The graph shows the cycle performance of the NCM811|Li all-solid-state battery assembled using the electrolyte from Example 1. Detailed Implementation

[0024] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0025] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0026] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available products or products that can be prepared by known methods.

[0027] The present invention also provides a method for preparing the above-mentioned sulfide solid electrolyte, comprising the following steps: Raw material metering and mixing: Under an inert atmosphere, accurately weigh Li2S, P2S5 and M2S5 powders according to the general formula stoichiometric ratio, and perform preliminary mixing.

[0028] Mechanical alloying: The mixed powder and grinding balls are placed in a high-energy ball mill jar, sealed, and ball milled at 400-600 rpm for 10-20 hours to obtain a uniform amorphous precursor.

[0029] Stepped heat treatment: The amorphous precursor is subjected to programmed temperature-controlled crystallization under an inert atmosphere. a. Low-temperature annealing stage: Increase the temperature to 200-250℃ at a rate of 2-5℃ / min, and hold for 2-5 hours to eliminate internal stress and induce crystal nucleation.

[0030] b. High-temperature crystallization stage: Increase the temperature to 400-500℃ at a rate of 1-3℃ / min, and hold for 4-10 hours to allow the material to fully crystallize and obtain the target product.

[0031] The present invention will be described in detail below through specific embodiments, but the scope of protection of the present invention is not limited thereto. Unless otherwise specified, the equipment and raw materials used in the present invention are conventionally available in the art. All operations are carried out in a glove box filled with high-purity argon gas (H2O < 0.1 ppm, O2 < 0.1 ppm).

[0032] Example 1 Preparation of Li 7.1 P3S 10.9 Ta 0.1 】 Raw material preparation: Weigh precisely according to stoichiometric ratios: Li₂S, P₂S₅, Ta₂S₅.

[0033] Precursor synthesis: Manually premix the above raw materials in an agate mortar for 15 minutes to ensure initial homogeneity.

[0034] High-energy ball milling: The premixed powder was transferred to a 250 mL zirconia ball mill jar, and zirconia grinding balls with diameters of 5 mm and 10 mm (total ball-to-powder mass ratio of 30:1) were added. The ball mill jar was sealed in an argon atmosphere and placed on a planetary ball mill. Milling was performed at 500 rpm for 15 hours, with a 15-minute pause every hour to avoid overheating. After milling, a grayish-black amorphous precursor powder was obtained.

[0035] Stepped heat treatment: a. Take about 1.0 g of ball-milled powder and spread it evenly in an alumina boat.

[0036] b. Place the ark in the middle of the quartz tube of the tube furnace (Hefei Kejing).

[0037] c. First, introduce high-purity argon gas (99.999%) at a flow rate of 200 sccm for 30 minutes to fully remove air.

[0038] d. Under an argon atmosphere, perform the following heat treatment procedure: heat from room temperature to 230°C at a rate of 3°C / min and hold at 230°C for 3 hours; then continue heating to 450°C at a rate of 2°C / min and hold at 450°C for 6 hours.

[0039] e. After heat treatment, cool the furnace to room temperature (<60 °C) and remove it to obtain crystalline Li. 7.1 P3S 10.9 Ta 0.1 Solid electrolyte powder, dark gray in color.

[0040] Example 2 Preparation of Li 7.05 P3S 10.95 Nb 0.05 】 The preparation method is exactly the same as in Example 1, except that the raw material ratio is changed: Li2S: 1.022 g, P2S5: 1.515 g, Nb2S5 (purity 99.9%, Aladdin reagent): 0.113 g.

[0041] Example 3: Preparation of Li 7.2 P3S 10.8 Ta 0.2 】 The preparation method is exactly the same as in Example 1, except that the raw material ratio is changed: Li2S: 1.066 g, P2S5: 1.470 g, Ta2S5: 0.464 g are weighed.

[0042] Comparative Example 1 [Preparation of undoped Li7P3S] 11 】 The preparation method is exactly the same as in Example 1, but without the addition of any dopant source.

[0043] Comparative Example 2 Preparation of Li 7.01 P3S 10.99 Ta 0.01 】 The preparation method is exactly the same as in Example 1, except that the quality of the dopant source is adjusted.

[0044] Comparative Example 3 Preparation of Li 7.3 P3S 10.7Ta 0.3 】 The preparation method is exactly the same as in Example 1, except that the quality of the dopant source is adjusted.

[0045] Test methods and performance characterization The samples obtained from the above embodiments and comparative examples were tested as follows: 1. Structural Characterization X-ray diffraction: The powder samples were analyzed using a Bruker D8 Advance X-ray diffractometer (Cu Kα radiation, λ = 1.5406 Å). The scanning range was 5°–45°, and the scanning speed was 5° / min. The results are as follows: Figure 1 As shown, the main diffraction peaks of the sample in Example 1 are consistent with those of the sample in Comparative Example 1, and there are no obvious impurity phase peaks, proving that Ta / Nb has successfully dissolved into the crystal lattice and formed a pure phase structure.

[0046] 2. Ionic conductivity test Sample preparation: Take about 150 mg of electrolyte powder and put it into a polytetrafluoroethylene mold with a diameter of Φ = 10 mm.

[0047] Tableting: In a glove box, a powder tablet press is used to maintain pressure at 300 MPa uniaxial pressure for 5 minutes to prepare dense electrolyte discs. The thickness of the discs (L, typically 0.8-1.2 mm) is measured using a digital micrometer.

[0048] Battery assembly: Transfer the electrolyte discs into the mold.

[0049] Test method: The assembled SS|Electrolyte|SS symmetric cell was connected to an electrochemical workstation. Its electrochemical impedance spectroscopy was measured at room temperature (25°C) with a frequency range of 1 MHz to 0.1 Hz and an AC amplitude of 10 mV.

[0050] Data processing: The obtained impedance spectrum was fitted using ZView software. Bulk resistance (R0) b The ionic conductivity (σ) is determined by the intersection of the high-frequency region and the real axis in the impedance spectrum. The ionic conductivity (σ) is calculated using the formula σ = L / (R). b Calculate using (π × A), where A is the area of ​​the electrolyte sheet (π × (5 mm)). 2 = 0.785 cm 2 ).

[0051] 3. Air stability test Exposure experiment: The electrolyte powders prepared in the examples and comparative examples were evenly spread in petri dishes in a glove box. The petri dishes were then transferred to a constant temperature and humidity chamber, with the environmental conditions set at 25°C and 50% relative humidity. After 30 minutes of exposure, the samples were quickly returned to the glove box.

[0052] Performance retention rate test: The exposed powder was repressed and assembled into a symmetric cell according to the above-described ionic conductivity test method, and its ionic conductivity (σ_exposed) after exposure was tested. Air stability is characterized by conductivity retention rate, calculated as follows: Retention rate (%) = (σ_exposed / σ_initial) ×100%.

[0053] 4. Electrochemical performance testing of all-solid-state batteries Composite cathode preparation: The electrolyte powder prepared in Example 1 of this invention, NCM811 cathode material, and acetylene black (conductive agent) were thoroughly mixed in an agate mortar at a mass ratio of 70:25:5. 20 mg of this mixture was then added sequentially to a mold along with 80 mg of the electrolyte powder from Example 1 (as a separator layer), and pressed together under a pressure of 360 MPa to form a three-layer structure (cathode|electrolyte|negative electrode) battery cell with a diameter of 10 mm.

[0054] Battery assembly: A lithium metal sheet (200μm thick) is placed on the other side of the electrolyte layer as the negative electrode to form an all-solid-state battery.

[0055] Charge-discharge test: Using the Blue Battery testing system, cycle tests were conducted at 0.5C in a 25°C constant temperature chamber. The initial discharge specific capacity, coulombic efficiency, and cycle capacity retention were recorded. Results are as follows: Figure 4 As shown.

[0056] Conductivity testing: EIS was measured using a blocked electrode after the powder was compressed into tablets. Example 1: Room temperature ionic conductivity reached 7.5 × 10⁻⁶. -3 S cm -1 ( Figure 1 ), which is better than 2.1 × 10 of Comparative Example 1. -3 S cm -1 And in Comparative Example 2, 2.8 × 10 -3 S cm -1 And 2.3 × 10 in Comparative Example 3 -3 S cm -1。

[0057] Phase analysis: XRD ( Figure 2 The results show that the products of each embodiment are all pure phases with no impurity peaks, indicating that Ta / Nb was successfully dissolved.

[0058] Stability test: The sample was exposed to air at a dew point of -10°C for 30 minutes. Example 1 maintained 88% conductivity, while Comparative Example 1 plummeted to 35%. Figure 3 Comparative Example 2 decreased to 56%, and Comparative Example 3 decreased to 63%.

[0059] Full cell performance: A battery was assembled using NCM811 as the positive electrode, the electrolyte from Example 1 as the separator, and lithium foil as the negative electrode. At 500 mA g... -1 At this point, the initial discharge specific capacity is 165 mAh g. -1 After 50 cycles, the capacity retention rate was as high as 98%. In contrast, Comparative Example 1 only achieved a capacity retention rate of 73% after 50 cycles. Figure 4 Comparative Example 2: Initial discharge specific capacity 148 mAh / g; 50-cycle retention 52%; coulombic efficiency 91.3%. Comparative Example 3: Initial discharge specific capacity 155 mAh / g; 50-cycle retention 58%; coulombic efficiency 92%.

[0060] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A sulfide solid electrolyte, characterized in that, Its general formula is: Li 7+x P3S 11-x M x , where M is Ta and / or Nb, and x ranges from 0.01 to 0.

3.

2. The sulfide solid electrolyte according to claim 1, characterized in that, M is Ta.

3. The sulfide solid electrolyte according to claim 2, characterized in that, The value of x ranges from 0.05 to 0.

15.

4. The sulfide solid electrolyte according to claim 1, characterized in that, Its room temperature ionic conductivity is not less than 3.0 × 10⁻⁶. -3 S cm -1 .

5. A method for preparing a sulfide solid electrolyte as described in any one of claims 1-4, characterized in that, Includes the following steps: a) Under an inert atmosphere, weigh and mix Li2S, P2S5 and M2S5 raw materials according to stoichiometric ratio; b) The mixture is subjected to high-energy ball milling to obtain an amorphous precursor; c) The precursor is subjected to a step-by-step heat treatment under an inert atmosphere to induce crystallization.

6. The method according to claim 5, characterized in that, The stepped heat treatment described in step c) includes: first holding at 200-250℃ for 2-5 hours, and then holding at 400-500℃ for 4-10 hours.

7. The preparation method according to claim 5, characterized in that, The high-energy ball milling speed described in step b) is 400-600 rpm, and the ball milling time is 10-20h.

8. An all-solid-state lithium battery, comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, characterized in that, The solid electrolyte layer comprises a sulfide electrolyte as described in any one of claims 1-4.

9. The all-solid-state lithium battery according to claim 8, characterized in that, The positive electrode layer contains a high-voltage positive electrode active material, and its charging cut-off voltage is not less than 4.3 V (vs. Li / Li). + ).

10. The application of the sulfide solid electrolyte as described in any one of claims 1-4 in all-solid-state lithium batteries.

Images