A solid electrolyte with high ionic conductivity, its preparation method and application

Abstract

This invention discloses a modified solid electrolyte with high stability and high ionic conductivity, its preparation method, and its applications. The general chemical formula of this electrolyte is Li. x M a PX b S y Cl z O δ Z c This invention employs a multi-element synergistic gradient doping method by introducing Mg / Zn / Ca, Se / Te, Br / I, and O. Its preparation utilizes a liquid-phase precursor-controlled oxygen atmosphere sintering method. A key step involves gradient heat treatment in an atmosphere containing trace amounts of oxygen, allowing oxygen to selectively accumulate on the particle surface to form a passivation layer. This modified electrolyte maintains high ionic conductivity while exhibiting excellent air stability and a broadened electrochemical window. This invention solves the challenge of simultaneously achieving stability and conductivity in sulfide electrolytes, making it suitable for constructing high-energy-density, long-life all-solid-state lithium batteries.

Description

Technical Field

[0001] This invention belongs to the field of solid-state battery materials technology, specifically relating to a Li6PS5Cl (LPSCL) sulfide-silver-germanium mineral-type solid electrolyte modified by multi-element synergistic gradient doping, its preparation method, and its application in high-performance all-solid-state lithium batteries. Background Technology

[0002] The sulfide solid electrolyte Li6PS5Cl has a high room temperature ionic conductivity (approximately 10). -3 S cm -1 With its relatively good ductility and excellent interfacial contact potential with electrode materials, it is considered one of the core electrolyte materials for all-solid-state batteries. However, its practical application is still limited by the following key bottlenecks: Poor chemical stability: It is extremely sensitive to water and oxygen. When exposed to humid air, it will react rapidly to generate highly toxic H2S, leading to structural damage and permanent performance failure, which greatly increases the environmental and cost requirements for production, storage and battery assembly.

[0003] The electrochemical window is relatively narrow: compared to high-voltage cathode materials (>4.2 V vs. Li / Li). + When materials such as high-nickel NCM and lithium-rich manganese-based materials come into direct contact, oxidation and decomposition easily occur at the interface, forming a high-resistivity interface layer.

[0004] Insufficient (electro)chemical compatibility with lithium metal anode: During long-term cycling, lithium metal undergoes a slow reduction reaction with LPSCL, leading to continuous interface deterioration and uneven growth of lithium dendrites.

[0005] Currently, research on the modification of LPSCL mainly focuses on single-element substitution, such as partially substituting S with O to improve air stability, or partially substituting Cl with Br or I to improve ionic conductivity. However, these single-element modification strategies often cause problems such as decreased conductivity, narrowed synthesis window, or introduction of new phase transitions while solving a specific problem, exhibiting a seesaw effect. Therefore, developing a multifunctional modification strategy that can synergistically improve air stability, electrochemical stability window, and interfacial compatibility without sacrificing (or even improving) ionic conductivity has significant scientific and engineering value. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a modified solid electrolyte through multi-element synergistic gradient doping. This material maintains high ionic conductivity while also possessing excellent air stability, a broadened electrochemical window, and improved anode interface compatibility.

[0007] To achieve the above objectives, the present invention provides a high ionic conductivity solid electrolyte with the general chemical formula: Lix M a PX b S y Cl z O δ Z c ; Oxygen exhibits a concentration gradient distribution from the surface to the interior in electrolyte particles. The surface of the particles is rich in oxygen, forming a passivation layer, while the interior of the particles maintains a high sulfur content. Where M is Mg 2+ Ca 2+ Zn 2+ At least one of the following; used to introduce additional lithium vacancies in the crystal lattice, increase the lithium-ion transference number, and partially replace Li. + To regulate the chemical properties of grain boundaries; X is Se 2- Te 2- At least one of them; used to partially replace S 2- By forming stronger MX bonds (such as P-Se bonds), the lattice energy and overall chemical stability are improved; Z is Br - I - At least one of them; used for partially substituting Cl - By increasing the radius of halide ions, the bottleneck size of lithium-ion transport is expanded, thereby improving ionic conductivity; O is an oxygen dopant (using O) 2- (Form), used to partially replace S 2- It selectively accumulates on the surface and near-surface region of particles, forming a gradient distribution, effectively passivating the surface and improving air stability; Each doping coefficient satisfies: 0≤a≤0.3, 0≤y≤5, 0≤b≤0.2, 0≤z≤1, 0≤δ≤0.5, 0≤c≤0.5 and 0≤x≤6.

[0008] Furthermore, the room temperature ionic conductivity is not less than 3.5 × 10⁻⁶. -3 S cm -1 After being exposed to air at 30% relative humidity for 30 minutes, the ionic conductivity retention rate is not less than 90%, and the H2S release is reduced by more than 90% compared to the unmodified electrolyte.

[0009] On the other hand, the present invention also provides a method for preparing a high ionic conductivity solid electrolyte as described above, employing a liquid-phase precursor-controlled oxygen atmosphere sintering method, comprising the following steps: (1) According to the target stoichiometric ratio, the lithium source, phosphorus source, sulfur source, chlorine source and dopant precursor containing M, X and Z elements are dissolved or dispersed in an anhydrous organic solvent and stirred under an inert atmosphere to form a liquid phase precursor with uniform molecular / ionic level. (2) Remove the solvent from the liquid precursor to obtain an amorphous intermediate powder; (3) The intermediate powder is pressed into tablets and subjected to multi-stage gradient heat treatment under a controllable oxygen partial pressure atmosphere to achieve crystallization and gradient doping; (4) After heat treatment, the product is cooled in the furnace and then post-treated to obtain the solid electrolyte.

[0010] Furthermore, in step (3), the multi-stage gradient heat treatment specifically includes: a) First stage: Under an inert atmosphere, the temperature is increased to 250-350℃ at a heating rate of 2-5℃ / min, and held for 2-5 hours to complete the initial crystallization of the sulfide-silver-germanium mineral phase; b) Second stage: Introduce trace amounts of oxygen into the atmosphere to form an inert mixed atmosphere containing 10~1000 ppm O2. Heat the atmosphere to 400~550℃ at a heating rate of 1~2℃ / min and hold for 4~12 hours to achieve gradient doping of oxygen. The atomic coordination of the electrolyte particles is unsaturated, and the activity is much higher than that of the internal bulk phase. Under a low oxygen partial pressure of 10~1000 ppm, O2 will preferentially react with S on the surface / near the surface, achieving a gradient distribution of oxygen concentration from the surface to the interior. This forms a passivation layer on the surface to improve stability and ensures that the high sulfur content in the bulk phase maintains high ionic conductivity. Slow heating at 1~2℃ / min allows the oxidation reaction on the surface of electrolyte particles to proceed gradually. O can gradually replace the surface at an atomic rate and slowly diffuse along the particle surface to near the surface, forming a continuous, non-porous oxygen-rich passivation layer. If the heating rate is too fast (>2℃ / min), the surface oxidation reaction is completed instantly, easily forming a loose oxide layer. This not only results in poor passivation but also generates grain boundary defects, increasing the resistance to lithium-ion transport.

[0011] c) Third stage: Switch back to a pure inert atmosphere and anneal at 400~550℃ for 1~3 hours to eliminate structural defects introduced by oxidation.

[0012] Furthermore, in step (1), the lithium source is Li2S or metallic Li, the phosphorus source is P2S5, the sulfur source is elemental S, and the chlorine source is LiCl; the dopant precursor containing M, X, and Z elements is at least one of MgS, ZnS, Li2Se, LiBr, and LiI; the anhydrous organic solvent is at least one of acetonitrile and 1,2-dimethoxyethane; and the stirring time is 40-50 h.

[0013] Furthermore, in step (2), the solvent is removed by rotary evaporation or spray drying.

[0014] Furthermore, in step (3), the tableting pressure is 350~400MPa; in step (4), the post-processing is grinding or direct retention.

[0015] Furthermore, the inert atmosphere is high-purity argon, and oxygen is introduced by passing in an argon gas mixture containing O2 or by using a solid oxygen source to decompose and generate oxygen.

[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 high ionic conductivity solid electrolyte as described above.

[0017] Furthermore, the negative electrode layer is a lithium metal, a lithium alloy, or a composite negative electrode containing lithium metal.

[0018] The beneficial effects of this invention are: Multi-element synergistic doping achieves comprehensive performance improvement: Through synergistic doping of Mg / Ca / Zn, Se / Te, Br / I, and O, each dopant element plays a complementary role: Br / I broadens the lithium-ion transport channel, Mg / Zn introduces lithium vacancies to increase the mobility number, resulting in a room-temperature ionic conductivity of up to 8.2 × 10⁻⁶. -3 S cm -1 Se / Te doping enhances the lattice energy, while oxygen gradient doping forms a surface passivation layer. This allows the electrolyte to maintain a conductivity of >90% and reduce H2S release by >90% after 30 minutes of exposure to 30% RH air. Simultaneously, the electrochemical stability window is broadened to 4.8 V vs. Li / Li. + It can be matched with high-voltage cathode materials; Mg / Ca doping can also improve compatibility with lithium metal anodes, form a stable SEI layer at the interface, and suppress lithium dendrite growth.

[0019] Gradient oxygen doping design resolves the contradiction between stability and conductivity: controllable oxygen atmosphere sintering achieves a gradient distribution of oxygen concentration from the surface to the interior of the particles. The oxygen-rich surface forms a passivation layer, effectively improving air stability and oxidation resistance, while maintaining a high sulfur content inside ensures rapid lithium-ion transport. This core-shell structure solves the technical challenge of simultaneously achieving intrinsic conductivity and environmental stability in sulfide electrolytes from both physical and chemical perspectives.

[0020] Innovative manufacturing process enables precise control: The liquid-phase precursor method ensures uniform mixing of raw materials at the molecular / ionic level, avoiding performance fluctuations caused by uneven mixing in traditional solid-phase methods; The controllable oxygen atmosphere gradient sintering process enables precise control of oxygen doping concentration and distribution, avoiding severe degradation of bulk properties caused by traditional oxidation methods, and the process is controllable and reproducible, making it suitable for large-scale industrial production.

[0021] Excellent performance of all-solid-state lithium batteries: When the modified solid electrolyte of this invention is applied to an all-solid-state lithium battery, the battery assembled with NCM811 as the positive electrode and metallic lithium as the negative electrode achieves an initial discharge capacity of 198 mAh g at a 0.5C rate. -1After 200 cycles, the capacity retention rate reaches 95%, which is significantly better than that of batteries using unmodified or single oxygen doping, achieving a combination of high energy density and long cycle life. Attached Figure Description

[0022] Figure 1 : A scanning schematic diagram of the modified electrolyte particles of the present invention. Detailed Implementation

[0023] The present invention will be described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to these embodiments. All simple modifications or equivalent substitutions based on the concept of the present invention are within the scope of protection of the present invention. All experimental operations were carried out in an argon glove box (water oxygen content < 0.1 ppm) or under an inert atmosphere. All reagents used were analytical grade and were treated to be anhydrous and oxygen-free.

[0024] Example 1: Preparation of Li 5.9 Mg 0.1 PSe 0.02 S 4.9 Cl 0.9 Br 0.1 O 0.05 Weigh: Li2S: 0.822g, P2S5: 1.045g, S: 0.032g, LiCl: 0.190g, MgS: ​​0.056g, Li2Se: 0.016g, LiBr: 0.052g.

[0025] The above raw materials were added to a Schlenk flask containing 30 mL of anhydrous acetonitrile and magnetically stirred at room temperature for 48 hours to form a clear yellow solution.

[0026] Acetonitrile was removed by rotary evaporation to obtain a yellow, glassy precursor, which was then ground into a fine powder.

[0027] Take 200mg of powder and press it into a Φ10mm green sheet under 380MPa.

[0028] The green blanks were placed in quartz ampoules, evacuated, and then filled with high-purity Ar (99.999%). Sintering was then carried out in a tube furnace. a) Increase the temperature to 300°C at a rate of 3°C / min and hold for 3 hours.

[0029] b) Introduce 500ppm O2 into the Ar gas stream using a precision flow meter, and continue to heat to 480°C at a rate of 1°C / min, and hold for 8 hours.

[0030] c) Turn off the oxygen and anneal for another 2 hours at 480°C in a pure Ar atmosphere.

[0031] After cooling in the furnace, a dense, grayish-black modified electrolyte sheet E1 is obtained.

[0032] Example 2: Preparation of Li 5.95 Zn 0.05 PS 4.95 Cl 0.7 I 0.3 O 0.1 Weigh out: Li₂S: 0.836g, P₂S₅: 1.114g, LiCl: 0.148g, ZnS: 0.024g, LiI: 0.201g.

[0033] The subsequent steps are the same as in Example 1, except that the second sintering step is carried out at 500°C for 10 hours in an Ar atmosphere containing 200ppm O2.

[0034] The modified electrolyte sheet E2 was obtained.

[0035] Comparative Example 1: Preparation of Unmodified Li6PS5Cl Weigh out: Li₂S: 0.739g, P₂S₅: 1.110g, LiCl: 0.222g.

[0036] The traditional high-temperature solid-state method is adopted: the raw materials are manually ground and mixed, then pressed into tablets and sintered at 550°C for 10 hours in a pure Ar atmosphere.

[0037] Electrolyte tablet C1 was obtained.

[0038] Comparative Example 2: Single oxygen-doped Li6PS5ClO 0.1 Weigh out the same raw materials as in Comparative Example 1, and add 0.015g of Li2O.

[0039] The same solid-phase mixing and sintering process as Comparative Example 1 was used.

[0040] Electrolyte tablet C2 was obtained.

[0041] Comparative Example 3: Weigh the same raw materials as in Example 1, and follow the same steps as in Example 1, except that oxygen is not introduced in step b), otherwise it is the same as in Example 1.

[0042] Comparative Example 4: Weigh the same raw materials as in Example 1, and follow the same steps as in Example 1, except that step c) is not performed. Otherwise, it is the same as in Example 1.

[0043] Table 1. Test data of core performance of materials in each system

[0044] The experimental data from Example 1 and Comparative Examples 1 and 2 show that the conductivity of Example 1 is 7.5 times that of Comparative Example 1 and 10.2 times that of Comparative Example 2. This demonstrates that multi-element synergistic doping, which introduces lithium vacancies with Mg, broadens transport channels with Br, and stabilizes the lattice with Se, can significantly improve ionic conductivity. In contrast, single oxygen doping leads to lattice shrinkage due to O replacing S, reducing lithium-ion transport efficiency and exhibiting the seesaw effect of traditional modification. The conductivity retention rate of Example 1 is 56 percentage points higher than that of Comparative Example 1 and 50 percentage points higher than that of Comparative Example 2, while H2S release is reduced by more than 90%. This indicates that the dual stabilizing effect of gradient oxygen doping and multi-element synergy is far superior to that of the unmodified system and the single oxygen doping system. Single oxygen doping can only slightly improve stability and sacrifices conductivity. Example 1 exhibits a higher initial capacity, with a capacity retention rate improved by approximately 15 percentage points after 200 cycles compared to Comparative Examples 1 and 2. This is attributed to the fact that multi-element synergistic doping broadens the electrochemical window, matching the high-voltage NCM811 cathode and preventing interfacial oxidation and decomposition. Simultaneously, it improves compatibility with the lithium metal anode and suppresses lithium dendrite growth. Therefore, the multi-element synergistic doping strategy of this invention overcomes the seesaw effect of traditional single-modification, achieving simultaneous improvement in conductivity and stability, and is key to solving the core bottleneck of sulfide electrolytes.

[0045] The experimental data from Example 1 and Comparative Example 3 show that Comparative Example 3, which is multi-element doped but without gradient oxygen doping, has an ionic conductivity only slightly lower than that of Example 1, indicating that multi-element doping itself can achieve high conductivity, and oxygen doping is not a factor in improving conductivity. Its air stability is extremely poor, with a conductivity retention rate of only 20%, and the H2S release is close to that of the unmodified Comparative Example 1, indicating that gradient oxygen doping is the core of constructing the surface passivation layer. Without gradient oxygen doping, the multi-element doped electrolyte still retains the intrinsic water and oxygen sensitivity of sulfides. The electrochemical window is only 4.3V, and the full-cell cycle performance is comparable to the unmodified system, indicating that the gradient oxygen passivation layer can significantly improve the electrolyte's oxidation resistance, broaden the electrochemical window, and improve electrode interface compatibility. It is evident that gradient oxygen doping is the core design for achieving high stability in this invention, complementing multi-element synergistic doping. The former is responsible for surface passivation to improve stability, while the latter is responsible for bulk modification to improve conductivity. Together, they construct a high-conductivity core-stable shell structure.

[0046] The experimental data from Example 1 and Comparative Example 4 show that a trace amount of Li2S impurity phase appeared in the phase of Comparative Example 4, indicating that the oxidation reaction in the gradient oxygen doping stage introduces a small amount of lattice defects. These defects cannot be eliminated without annealing, leading to the formation of the impurity phase; the ionic conductivity decreased to 6.5 × 10⁻⁶. -3 S cm -1The reasons for the slight decrease in lithium-ion transport resistance are: lattice defects and trace impurities increase the resistance to lithium-ion transport; air stability and electrochemical window decrease slightly, with conductivity retention at 80% and electrochemical window at 4.6V, indicating that defects reduce the density of the surface passivation layer and weaken its oxidation resistance; full-cell cycle performance decreases, with a retention rate of 88.6% after 200 cycles, lower than the 95% in Example 1, because lattice defects cause the interfacial impedance between the electrolyte and the electrode to rise rapidly with increasing cycles. Therefore, the third-stage pure inert atmosphere annealing is a necessary component of the controlled oxygen atmosphere sintering process of this invention. Its function is to eliminate lattice defects introduced during the oxidation stage, stabilize the crystal structure, ensure the overall performance of the electrolyte, and avoid performance degradation caused by defects.

[0047] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A solid electrolyte with high ionic conductivity, characterized in that, The general chemical formula is: Li x M a PX b S y Cl z O δ Z c Oxygen exhibits a concentration gradient distribution from the surface to the interior in electrolyte particles. The surface of the particles is rich in oxygen, forming a passivation layer, while the interior of the particles maintains a high sulfur content. wherein M is at least one of Mg 2+ , Ca 2+ , Zn 2+ ; X is at least one of Se 2- , Te 2- ; Z is at least one of Br - , I - . Each doping coefficient satisfies: 0≤a≤0.3, 0≤y≤5, 0≤b≤0.2, 0≤z≤1, 0≤δ≤0.5, 0≤c≤0.5 and 0≤x≤6.

2. The high ionic conductivity solid electrolyte according to claim 1, characterized in that, The room temperature ionic conductivity is not less than 3.5*10 -3 S cm -1 After being exposed to 30% relative humidity air for 30 minutes, the ionic conductivity retention rate is not less than 90%, and the H2S release amount is reduced by more than 90% compared with the unmodified electrolyte.

3. A method for preparing a high ionic conductivity solid electrolyte as described in any one of claims 1-2, characterized in that, The liquid-phase precursor-controlled oxygen atmosphere sintering method includes the following steps: (1) According to the target stoichiometric ratio, the lithium source, phosphorus source, sulfur source, chlorine source and dopant precursor containing M, X and Z elements are dissolved or dispersed in an anhydrous organic solvent and stirred under an inert atmosphere to form a liquid phase precursor with uniform molecular / ionic level. (2) Remove the solvent from the liquid precursor to obtain an amorphous intermediate powder; (3) The intermediate powder is pressed into tablets and subjected to multi-stage gradient heat treatment under a controllable oxygen partial pressure atmosphere to achieve crystallization and gradient doping; (4) After heat treatment, the product is cooled in the furnace and then post-treated to obtain the solid electrolyte.

4. The preparation method according to claim 3, characterized in that, In step (3), the multi-stage gradient heat treatment specifically includes: a) First stage: Under an inert atmosphere, the temperature is increased to 250-350℃ at a heating rate of 2-5℃ / min, and held for 2-5 hours to complete the initial crystallization of the sulfide-silver-germanium mineral phase; b) Second stage: Introduce trace amounts of oxygen into the atmosphere to form an inert mixed atmosphere containing 10~1000 ppm O2, heat to 400~550°C at a heating rate of 1~2°C / min, and hold for 4~12 hours to achieve gradient doping of oxygen elements. c) Third stage: Switch back to a pure inert atmosphere and anneal at 400~550℃ for 1~3 hours to eliminate structural defects introduced by oxidation.

5. The preparation method according to claim 3, characterized in that, In step (1), the lithium source is Li2S or metallic Li, the phosphorus source is P2S5, the sulfur source is elemental S, and the chlorine source is LiCl; the dopant precursor containing M, X, and Z elements is at least one of MgS, ZnS, Li2Se, LiBr, and LiI; the anhydrous organic solvent is at least one of acetonitrile and 1,2-dimethoxyethane; and the stirring time is 40-50 h.

6. The preparation method according to claim 3, characterized in that, In step (2), the solvent is removed by rotary evaporation or spray drying.

7. The preparation method according to claim 3, characterized in that, In step (3), the pressure of tableting is 350~400MPa; in step (4), the post-processing is grinding or direct retention.

8. The preparation method according to claim 4, characterized in that, The inert atmosphere is high-purity argon, and oxygen is introduced by passing in an argon gas mixture containing O2 or by decomposing a solid oxygen source.

9. A 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 high ionic conductivity solid electrolyte as described in any one of claims 1-2.

10. The all-solid-state lithium battery according to claim 9, characterized in that, The negative electrode layer is a lithium metal, a lithium alloy, or a composite negative electrode containing lithium metal.

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