A halide solid electrolyte, its preparation method, and a solid-state battery

Abstract

This invention discloses a halide solid electrolyte, its preparation method, and a solid-state battery. The preparation method includes the following steps: 1) mixing the raw materials of the initial halide solid electrolyte with the raw materials of the substituted cations, activating with plasma, and ball milling to obtain a precursor; 2) using lithium halide, employing a vapor-phase permeation crystallization method to perform lithium-ion charge compensation or lithium-ion vacancy compensation on the precursor to obtain the halide solid electrolyte. The method of this invention, by synergistically combining plasma activation, ball milling, and lithium-ion charge or vacancy compensation mechanisms, can both utilize the advantages of high-valence substituted cations and compensate for the negative impacts of substitution. The prepared halide solid electrolyte exhibits excellent antioxidant capacity while ensuring good structural stability and a good lithium-ion transport pathway.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a halide solid electrolyte, its preparation method, and a solid battery. Background Technology

[0002] In recent years, all-solid-state batteries (ASSBs) have become a hot topic in the global scientific research and industry communities and are regarded as the core direction of next-generation battery technology. The reason for their popularity is that organic electrolytes (such as carbonates) are flammable and explosive, with a high risk of thermal runaway (such as electric vehicle battery fire accidents), while solid electrolytes (such as inorganic / organic solid materials) are non-flammable, leak-proof, and have significantly improved thermal stability.

[0003] As people's living standards improve, their requirements for battery energy density are also increasing. Therefore, current battery cathode materials pursue high voltage and high theoretical specific capacity, which increases the requirements for the anti-oxidation ability of the electrolyte on the cathode side. Halogen electrolytes have a high degree of lattice matching with cathode materials, which can reduce interfacial ion transport resistance. Furthermore, due to their wide electrochemical window (>4.1V), low interfacial side reactions, high ionic conductivity, and tunable chemical composition, halide solid electrolytes have become an ideal partner for high-voltage cathode materials.

[0004] However, the current high-voltage positive electrode charging cutoff voltage is as high as 4.4V, 4.5V, or even higher, therefore, it is necessary to further improve the oxidation resistance of the positive electrode side halide solid electrolyte. Common strategies in the literature include: 1. Doping the halide solid electrolyte with high-valence cations to improve conductivity and voltage window; 2. Replacing halide electrolytes with ions of the same valence to optimize structural stability. However, the issue of ionic radius is ignored during element substitution. High-valence cations (e.g., valence > 3) have relatively low ionic radii. Replacing larger-radius elements with smaller-radius elements has the following disadvantages: 1. It causes lattice distortion and structural stability problems, local stress concentration, and lattice contraction due to small-radius substitution. Smaller ions (such as Al)... 3 + (Its ionic radius is 0.535 Å) replaces larger ions (such as Zr) 4+When the ionic radius is 0.72 Å, it introduces local lattice distortion, which may lead to abrupt changes in bond length / bond angle, disrupting the continuity of the original lithium-ion migration channels and forming microcracks. Especially during sintering, stress accumulation will reduce mechanical strength; 2. It generates the risk of phase separation. The solubility of the substituent element is limited, and small-radius ions may not be completely dissolved due to size mismatch, leading to the precipitation of secondary phases and blocking the ion transport path; 3. It narrows the channels. Lattice contraction may squeeze the lithium-ion migration channels, which will increase the transition energy barrier; 4. It increases the grain boundary resistance and increases the difficulty of sintering. Small-radius ion doping may reduce the grain growth rate, resulting in a decrease in density (e.g., relative density <90%) and an increase in the proportion of grain boundary resistance; 5. It increases the complexity of the synthesis process. The diffusion rate of small-radius ions is slow (e.g., Al). 3+ It requires long-term annealing or high-energy ball milling, which can easily introduce impurities.

[0005] Therefore, providing a simple preparation method for halide solid electrolytes that enables them to have excellent antioxidant capacity while ensuring good structural stability and a good lithium-ion transport pathway is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] In view of the above-mentioned technical problems existing in the prior art, the purpose of this invention is to provide a halide solid electrolyte, its preparation method and solid battery.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a halide solid electrolyte, the method comprising the following steps:

[0009] (1) The raw materials of the initial halide solid electrolyte and the raw materials of the substituted cation are mixed, activated by plasma, and ball-milled to obtain the precursor; wherein the valence state a of the substituted cation is greater than the valence state b of the substituted cation in the initial halide solid electrolyte, and the ionic radius of the substituted cation is smaller than the ionic radius of the substituted cation in the initial halide solid electrolyte.

[0010] (2) Using lithium halide, the precursor is subjected to lithium ion charge compensation or lithium ion vacancy compensation by gas phase permeation crystallization method to obtain the halide solid electrolyte.

[0011] The molar amount of charge compensation or vacancy compensation of lithium ions = (ab) × c, where c is the molar percentage of the substitution of cations in the halide solid electrolyte by the substituted cations.

[0012] The method of this invention modifies the material surface by generating highly active particles (e.g., electrons, ions, free radicals) through plasma activation, introducing lithium or oxygen vacancies, accelerating ion diffusion, improving ionic conductivity, and forming an amorphous surface layer to inhibit dendrite penetration. Ball milling can break the chemical bonds of the raw materials and improve the uniformity of the mixture, thus reducing the particle size of the halide solid electrolyte. Furthermore, the present invention performs vapor-phase permeation crystallization on the precursor, which can achieve charge compensation or vacancy compensation, increase carrier concentration, expand the size of ion channels, and reduce the negative impact caused by the small radius when high-valence substituted cations replace the initial halide solid electrolyte.

[0013] In this invention, the advantages of charge compensation or vacancy compensation include: 1. When defects (such as cation vacancies or doped heterovalent ions) are introduced into the material, charge compensation maintains electrical neutrality by adjusting the electron or ion distribution, preventing structural collapse and stabilizing the crystal structure; 2. Charge compensation improves lithium-ion conductivity and optimizes ion transport by introducing vacancies or interstitial ions; 3. Charge compensation provides electron jumping paths, enhancing electronic conductivity; 4. Charge compensation can alleviate interfacial charge accumulation and reduce side reactions; 5. Increased carrier concentration: the additional charge introduced by charge compensation can directly participate in conduction, increasing the number of mobile ions (nn) and thus increasing carrier concentration; 6. Compensated Li⁺ may occupy vacancies or interstitial sites, forming low-barrier continuous migration paths and stabilizing the defect structure.

[0014] This invention utilizes ionic substitution of halide solid electrolytes with substituted cations, combined with vapor-phase permeation crystallization using lithium halides as raw materials, to effectively improve the conductivity and oxidation resistance of halide solid electrolytes, thereby effectively enhancing the initial efficiency, first-cycle discharge capacity, and cycle performance of lithium-ion batteries.

[0015] It should be noted that in this invention, the cation in the initial halide solid electrolyte can be one or more, and the substituted cation can also be one or more.

[0016] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0017] Preferably, the initial halide solid electrolyte in step (1) includes at least one of cubic phase solid electrolyte, layered solid electrolyte, amorphous solid electrolyte, bimetallic doped halide solid electrolyte or halogen-oxygen mixed solid electrolyte.

[0018] This invention does not specifically limit the type of cubic phase solid electrolyte, including but not limited to perovskite-type halide solid electrolytes (general formula: A2BX6 or ABX3) and fluorite-type halide solid electrolytes (general formula: A...). x B y X x+3y In the above general formula, A is a monovalent or divalent cation, such as at least one of Li, Na, K and Ru; B is at least one of a metal cation; and X is at least one of a halide anion.

[0019] This invention does not specifically limit the types of layered solid electrolytes, including but not limited to layered perovskite-type halide solid electrolytes (general formula: A). n+1 B n X 3n+1 Among them, 0.05≤n≤6), CdI2 type layered halide solid electrolyte (general formula: AX2), BiI3 type layered halide (general formula: A2X3), layered bimetallic halide (general formula: A m B n X 3m+n (where 0.75≤m≤5, 0.05≤n≤3.5) or intercalated layered halides (general formula: G x A y B z X n Wherein, 0.25≤x≤4, 0.05≤y≤3, 0.05≤z≤2.5, 0.05≤n≤12). In the above general formula, A is a monovalent or divalent cation, such as at least one of Li, Na, K and Ru; B is at least one of metal cations; X is at least one of halide anions; and G is an intercalated ion such as Li, Na and Mg.

[0020] This invention does not specifically limit the type of amorphous solid electrolyte, including but not limited to amorphous metal halides (general formula: A). x X y Or A x B y X z Where 1≤x≤6, 0.25≤y≤8, 0.05≤z≤12), amorphous-crystalline complex halides (where the general formula of the crystalline component is A). X B y X z Amorphous materials are glass-ceramic phases, where 1≤x≤6, 0.25≤y≤8, 0.05≤z≤12, and the molar ratio of amorphous to crystalline materials is n, where n≥1) and polymer-halide hybrid amorphous systems (where the general formula of the halides is A). x X yWherein, 1≤x≤6, 0.25≤y≤8) is at least one of the following: A is a monovalent or divalent cation, such as at least one of Li, Na, K and Ru; B is at least one of the following metal cations; and X is at least one of the following halide anions.

[0021] In this invention, the general formula of the bimetallic doped halide solid electrolyte is A. x B y X z Wherein, 1≤x≤10, 0.05≤y≤7.5, 0.05≤z≤14, A is a monovalent or divalent cation, such as at least one of Li, Na, K, Ru and Mg; B is at least two metal cations; and X is at least two halide anions.

[0022] In this invention, the general formula of the halogen-oxygen mixed system solid electrolyte is A. x B y X z O c Wherein, 1≤x≤10, 0.05≤y≤7.5, 0.05≤z≤14, 0.05≤c≤8, A is a monovalent or divalent cation, such as at least one of Li, Na, K, Ru and Mg; B is at least one metal cation; and X is at least one halide anion.

[0023] Preferably, the plasma activation method in step (1) includes pulsed discharge plasma activation or continuous discharge plasma activation.

[0024] Preferably, the parameters for plasma solid-phase activation include: power of 5W to 50W, for example, 5W, 7W, 10W, 12W, 15W, 17W, 20W, 22W, 25W, 28W, 30W, 33W, 36W, 40W, 45W, or 50W; and inert gas flow rate of 10sccm to 100sccm, for example, 10sccm, 15sccm, 20sccm, 25sccm, 30sccm, 35sccm, 40sccm, 45sccm, 50sccm, 55sccm, 60sccm, 65sccm, 70sccm, 75sccm, 80sccm, 85sccm, 90sccm, 95sccm, or 100sccm. Duration: 30s~7.5min, for example, 30s, 60s, 1min, 1.5min, 2min, 2.5min, 3min, 3.5min, 4min, 4.5min, 5min, 5.5min, 6min, 6.5min, 7min, or 7.5min, etc. Pressure: 0.1Pa~8Pa, for example, 0.1Pa, 0.5Pa, 1Pa, 1.5Pa, 2Pa, 2.5Pa, 3Pa, 3.5Pa, 4Pa, 4.5Pa, 5Pa, 5.5Pa, 6Pa, 6.5Pa, 7Pa, 7.5Pa, or 8Pa, etc. Temperature: 10℃~85℃, for example, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, or 80℃, etc.

[0025] During plasma solid-state activation, the power should not be too high to avoid phase transitions in the material and the volatilization of lithium in lithium-containing raw materials. At the same time, the power should not be too low, otherwise the activation effect will be insufficient.

[0026] During plasma solid-state activation, the temperature should not be too high to avoid material volatilization. At the same time, the temperature should not be too low either, otherwise it will lead to: 1. Insufficient optimization of lithium-ion migration channels, limited improvement in ionic conductivity, increased electronic conductivity, and increased leakage current; 2. At low temperatures, plasma may not be able to completely decompose raw materials (such as Li2S, P2S5, etc.) or remove surface contaminants (such as LiOH, Li2CO3), and residual Li2S will reduce ionic conductivity; plasma bombardment at low temperatures may introduce local lattice strain (such as amorphous regions), but stress cannot be eliminated through thermal diffusion. When halide solid electrolytes are applied to the cathode and assembled into batteries, the material becomes more brittle and prone to cracking during cycling.

[0027] During plasma solid-phase activation, controlling the pressure within a suitable range is beneficial for regulating the plasma's energy, uniformity, and chemical reaction pathways, which directly affects the defect repair, interface engineering, and densification of halide solid electrolytes, thereby influencing the performance of halide solid electrolytes.

[0028] The duration of plasma solid-state activation should not be too long to avoid phase transitions in the material and the volatilization of lithium in lithium-containing raw materials. At the same time, the duration of plasma solid-state activation should not be too short, otherwise the activation effect will be insufficient.

[0029] As a preferred technical solution for the preparation method of the halide solid electrolyte of the present invention, the activation in step (1) is followed by ultrasonic-assisted ball milling. By employing ultrasonic-assisted ball milling technology, the particle crushing and dispersion effects can be enhanced under the synergistic effect of cavitation and mechanical vibration.

[0030] Preferably, the ultrasonic-assisted ball milling equipment is an ultrasonic planetary ball mill;

[0031] Preferably, during the ultrasonic-assisted ball milling process, the frequency of the ultrasound is 5kHz to 40kHz, for example, it can be 5kHz, 8kHz, 10kHz, 12kHz, 15kHz, 18kHz, 20kHz, 23kHz, 26kHz, 28kHz, 30kHz, 33kHz, 35kHz, 37kHz or 40kHz, etc.

[0032] Preferably, during the ultrasonic-assisted ball milling process, the ball-to-material ratio is (5~30):1, for example, it can be 5:1, 7:1, 10:1, 12:1, 15:1, 18:1, 20:1, 22:1, 25:1, 28:1, or 30:1, etc. The rotational speed is 150rpm~700rpm, for example, it can be 150rpm, 160rpm, 180rpm, 200rpm, 250rpm, 300rpm, 350rpm, 400rpm, 450rpm, 500rpm, 550rpm, 600rpm, 650rpm, or 700rpm, etc. The total ball milling time is 1h~35h, for example, it can be 1h, 3h, 5h, 7h, 9h, 11h, 13h, 14h, 16h, 18h, 20h, 23h, 26h, 28h, 30h, 33h, or 35h, etc. The diameter of the grinding ball is 3mm to 15mm, for example, it can be 3mm, 5mm, 7mm, 9mm, 11mm, 12mm, 13mm or 15mm, etc.

[0033] Preferably, step (2) includes: using a protective gas to carry lithium halide to form a gas flow, and using the gas flow to heat treat the activated material.

[0034] The present invention does not specifically limit the type of protective gas; for example, it can be nitrogen.

[0035] Preferably, the airflow velocity is 10 sccm to 300 sccm, for example, it can be 10 sccm, 20 sccm, 30 sccm, 50 sccm, 60 sccm, 80 sccm, 100 sccm, 120 sccm, 140 sccm, 160 sccm, 180 sccm, 200 sccm, 220 sccm, 240 sccm, 260 sccm, 280 sccm or 300 sccm, etc.

[0036] Preferably, the lithium halide content in the gas flow is 10 mg / L to 25 mg / L, for example, it can be 10 mg / L, 12 mg / L, 15 mg / L, 16 mg / L, 18 mg / L, 20 mg / L, 22 mg / L, 23 mg / L or 25 mg / L, etc.

[0037] Preferably, the heat treatment temperature is 150℃~400℃, for example, it can be 150℃, 160℃, 170℃, 180℃, 200℃, 220℃, 230℃, 240℃, 260℃, 280℃, 300℃, 325℃, 350℃, 370℃, 380℃ or 400℃, etc.

[0038] Preferably, the heat treatment time is 1h to 18h, for example, it can be 1h, 2h, 3h, 5h, 6h, 8h, 10h, 12h, 14h, 16h or 18h.

[0039] In this invention, by controlling the airflow rate, heat treatment temperature, and time, the molar amount of lithium ion charge compensation or lithium ion vacancy compensation can be achieved. For example, if the compensation molar amount is small, the flow rate and time can be set lower; if the compensation molar amount is large, the flow rate and time can be set higher.

[0040] In actual preparation, the molar amount of charge compensation or vacancy compensation of lithium ions can be tested using the following methods:

[0041] X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS), electron energy loss spectroscopy (EELS), resonant inelastic X-ray scattering (RIXS), hard X-ray photoelectron spectroscopy (HAXPES), neutron diffraction (ND) combined with XRD refinement, Mössbauer spectroscopy, electrochemical quartz crystal microbalance (EQCM), in-situ differential electrochemical mass spectrometry (DEMS), atom probe tomography (APT), scanning tunneling microscopy / spectroscopy (STM / STS), and surface localized electronic density of states (DOS) measurement.

[0042] Preferably, the molar percentage of the substituted cation replacing the cation in the halide solid electrolyte is greater than or equal to 0.5, for example, it can be 0.5, 0.52, 0.54, 0.56, 0.58, 0.6, 0.63, 0.65, 0.68, 0.7, 0.72, or 0.75. The advantages of this setting are: 1. Optimized transport channels: Different cations have different ionic radii and polarizabilities. When the molar percentage of the substituted cation replacing the cation in the halide solid electrolyte is greater than or equal to 0.5, more diverse migration channels in terms of size and chemical environment can be created in the crystal lattice. This provides more possible migration paths for lithium ions, avoiding migration bottlenecks that may be caused by a single ion. 2. Reduced migration activation energy. 3. Suppression of phase transition: Using substituted cations to replace the cations in the halide solid electrolyte, and limiting the molar percentage of the substituted cation to the cation in the halide solid electrolyte to greater than or equal to 0.5, can stabilize the crystal lattice, locking the material in a high-conductivity phase and avoiding performance degradation caused by temperature fluctuations.

[0043] In a second aspect, the present invention provides a halide solid electrolyte, which is prepared by the preparation method described in the first aspect.

[0044] Thirdly, the present invention provides a positive electrode, wherein the positive electrode comprises a positive electrode active material and the halide solid electrolyte described in the second aspect.

[0045] Fourthly, the present invention provides a solid-state battery, wherein the solid-state battery includes the halide solid electrolyte described in the second aspect or the positive electrode described in the third aspect.

[0046] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0047] Compared with existing technologies, the present invention has the following beneficial effects:

[0048] The method of this invention combines plasma activation, ball milling, and lithium-ion charge or vacancy compensation mechanisms to leverage the advantages of high-valence cation substitution while mitigating the negative effects of substitution. The resulting halide solid electrolyte exhibits excellent antioxidant capacity while maintaining good structural stability and a favorable lithium-ion transport pathway.

[0049] Using the halide solid electrolyte prepared by this invention to prepare a positive electrode and apply it to a battery can improve the oxidation resistance of the positive electrode and improve the initial discharge capacity and cycle performance of the battery. Detailed Implementation

[0050] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0051] Example 1

[0052] This embodiment provides a method for preparing a halide solid electrolyte, including the following steps:

[0053] (1) Preparation of precursors:

[0054] Weigh 0.5 mol ZrCl4, 0.5 mol ErCl3 and 3.5 mol LiCl, mix the weighed raw materials using plasma activation, and ball mill to obtain the precursor;

[0055] The plasma activation method is a pulsed discharge plasma activation method, and the parameters of the plasma activation method are: power 20W, Ar flow rate 50sccm, duration 2min, pressure 5Pa, and temperature 60℃. The ball milling parameters are: ball-to-material ratio 20:1, rotation speed 500rpm, ball milling time 20h, and grinding ball diameter 8mm.

[0056] (2) Using vapor phase infiltration crystallization to perform lithium ion charge compensation on the precursor:

[0057] A gas stream of LiCl is formed by carrying high-purity nitrogen gas. The content of LiCl in the gas stream is 20 mg / L. The precursor obtained in step (1) is heat-treated using the gas stream. The flow rate of the gas stream is 100 sccm, the temperature of the heat treatment is 300℃, and the heat treatment time is 12 h, to obtain the halide solid electrolyte.

[0058] In this embodiment, the chemical formula of the initial halide solid electrolyte, the chemical formula of the prepared halide solid electrolyte, the molar percentage of substituted cations in the halide solid electrolyte, and the molar amount of lithium ion vacancy compensation are shown in Table 1.

[0059] In this embodiment of the invention, the molar amount of lithium ion vacancy compensation is obtained by X-ray photoelectron spectroscopy (XPS) combined with XRD refinement, specifically by using atomic shift parameters to infer element concentration.

[0060]

[0061] Example 2

[0062] This embodiment provides a method for preparing a halide solid electrolyte, including the following steps:

[0063] (1) Preparation of precursors:

[0064] Weigh 0.5 mol ZrCl4, 0.5 mol ErCl3 and 2.5 mol LiCl, mix the weighed raw materials using plasma activation, and ball mill to obtain the precursor;

[0065] The plasma activation method is a pulsed discharge plasma activation method, and the parameters of the plasma activation method are: power 45W, He flow rate 15sccm, duration 1min, pressure 1Pa, and temperature 85℃. The ball milling parameters are: ball-to-material ratio 5:1, rotation speed 700rpm, ball milling time 4h, and grinding ball diameter 15mm.

[0066] (2) Using vapor phase infiltration crystallization to compensate for lithium ion vacancies in the precursor:

[0067] A gas stream of LiCl is formed by carrying high-purity nitrogen gas. The content of LiCl in the gas stream is 10 mg / L. The precursor obtained in step (1) is heat-treated using the gas stream. The flow rate of the gas stream is 300 sccm, the temperature of the heat treatment is 400℃, and the heat treatment time is 3h, to obtain the halide solid electrolyte.

[0068] In this embodiment, the chemical formula of the initial halide solid electrolyte, the chemical formula of the prepared halide solid electrolyte, the molar percentage of substituted cations in the halide solid electrolyte, and the molar amount of charge compensation of lithium ions are shown in Table 2.

[0069]

[0070] Example 3

[0071] This embodiment provides a method for preparing a halide solid electrolyte, including the following steps:

[0072] (1) Preparation of precursors:

[0073] Weigh out 0.25 mol ZrCl4, 0.25 mol TbCl4, 0.5 mol TmCl2 and 2.5 mol LiCl, mix the weighed raw materials using plasma activation, and ball mill to obtain the precursor;

[0074] The plasma activation method is a pulsed discharge plasma activation method, and the parameters of the plasma activation method are: power 10W, Ar flow rate 90sccm, duration 5min, pressure 7Pa, and temperature 35℃. The ball milling parameters are: ball-to-material ratio 30:1, rotation speed 200rpm, ball milling time 32h, and grinding ball diameter 5mm.

[0075] (2) Using vapor phase infiltration crystallization to perform lithium ion charge compensation on the precursor:

[0076] A gas stream of LiCl is formed by carrying high-purity nitrogen gas. The content of LiCl in the gas stream is 25 mg / L. The precursor obtained in step (1) is heat-treated using the gas stream. The flow rate of the gas stream is 30 sccm, the temperature of the heat treatment is 200℃, and the heat treatment time is 15 h, to obtain the halide solid electrolyte.

[0077] In this embodiment, the chemical formula of the initial halide solid electrolyte, the chemical formula of the prepared halide solid electrolyte, the molar percentage of substituted cations in the halide solid electrolyte, and the molar amount of lithium ion vacancy compensation are shown in Table 3.

[0078]

[0079] Example 4

[0080] The difference from Example 1 is that the power is 4W during the plasma activation process.

[0081] Example 5

[0082] The difference from Example 1 is that the power during plasma activation is 52W.

[0083] Example 6

[0084] The difference from Example 1 is that the temperature during the plasma activation process is 88°C.

[0085] Example 7

[0086] The difference from Example 1 is that in step (2), the content of LiCl in the gas flow is 7 mg / L.

[0087] Example 8

[0088] The difference from Example 1 is that in step (2), the content of LiCl in the gas stream is 28 mg / L.

[0089] Example 9

[0090] The difference from Example 1 is that in step (2), the airflow velocity is 5 sccm.

[0091] Example 10

[0092] The difference from Example 1 is that in step (2), the airflow velocity is 305 sccm.

[0093] Comparative Example 1

[0094] The difference between this comparative example and Example 1 is that the gas flow is replaced with high-purity nitrogen.

[0095] Comparative Example 2

[0096] The difference between this comparative example and Example 1 is that the plasma activation method was not performed.

[0097] Comparative Example 3

[0098] The difference between this comparative example and Example 1 is that ball milling was not performed.

[0099] test:

[0100] (I) Testing the antioxidant capacity of halide solid electrolytes, including specific methods:

[0101] (1) Weigh 20 mg of carbon nanotubes (CNTs) and 80 mg of halide solid electrolyte, place them in a mortar and grind them by hand for 10 min to mix them evenly and obtain a mixture.

[0102] (2) Weigh 100mg of halide solid electrolyte powder and put it into the inner liner of a mold with a diameter of 10mm. Press it into electrolyte sheet using a press (parameter: 400 MPa).

[0103] (3) Spread 25 mg of the mixture from step (1) onto one end of the electrolyte tablet, press it flat with a mold, and then...

[0104] The battery is compacted using a press (parameter: 400 MPa); a Li sheet is introduced at the other end to obtain the battery to be tested.

[0105] (4) Use an electrochemical workstation to perform LSV testing on the above-mentioned battery to be tested. Set the open circuit voltage to 6V and the scan rate to 0.1mV / S to obtain the oxidation window (unit: V). The larger the value, the stronger the antioxidant capacity of the halide solid electrolyte.

[0106] (II) Testing the conductivity of halide solid electrolytes, the test method is as follows:

[0107] (1) Weigh 100mg of halide solid electrolyte powder and put it into the inner liner of the mold (10 mm in diameter). Press it into an electrolyte sheet using a press (parameter: 400 MPa). Then, match stainless steel blocking electrodes at both ends of the electrolyte sheet to assemble a blocking symmetric cell.

[0108] (2) The impedance value of the sample was measured by electrochemical AC impedance spectroscopy using an electrochemical workstation to obtain the solid-state impedance.

[0109] The resistance value R (in Ω) of the solution is specified. The test frequency is from 0.01 Hz to 1 MHz, the test disturbance voltage is 5 mV, and the test temperature is the temperature inside the glove box.

[0110] (3) Take out the electrolyte sheet and use a micrometer to measure the thickness L (in cm) of the solid electrolyte sheet.

[0111] (4) Then, the ionic conductivity of the solid electrolyte at the temperature inside the glove box is calculated using the formula: σLi + =L / (R×S;

[0112] In the formula σLi + —Ionic conductivity of solid electrolytes (S cm) -1 );

[0113] L—Thickness of the solid electrolyte (cm);

[0114] R—Intrinsic resistance (Ω) of solid electrolyte;

[0115] S—Cross-sectional area of ​​solid electrolyte (cm²) 2 )

[0116] (III) Assembling solid-state batteries, specifically including the following steps:

[0117] LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (abbreviated as NCM333) and the halide solid electrolytes prepared in the various examples and comparative examples were mixed at a mass ratio of 85:15 and ground in a mortar for 15 minutes to disperse them evenly, resulting in a mixture of 100 mg.

[0118] Weigh 25 mg of the above mixture and spread it evenly on the electrolyte sheet. Rotate the stainless steel electrode pressure head to the bottom of the mold and rotate the pressure head to spread the powder evenly. Remove the pressure head and place a piece of carbon-coated aluminum foil (10 mm thick) on top of the powder. Press the powder at 400 MPa for 2 minutes using a press and remove excess positive electrode powder with a rubber bulb. Then weigh it a second time to obtain the actual positive electrode material loading. On the other side of the electrolyte sheet, first place a piece of indium foil with a thickness of 100 μm, and then place a piece of lithium copper composite strip with a thickness of 50 μm. The diameter of each of the above layers is 10 mm. Fasten the mold and pressure head, and tighten the nut to obtain the solid-state battery.

[0119] (iv) Testing the electrochemical performance of solid-state batteries using a blue electric shock tester

[0120] (1) First-cycle discharge capacity test: At 35±3℃, charge at a constant current of 0.2C to 3.7V, and charge at a constant voltage of 3.7V to the cutoff current of 0.05C; then discharge at a constant current of 0.1C to discharge the battery to 2.0V to obtain the first-cycle discharge capacity.

[0121] (2) Capacity retention test: At 35±3℃, the battery was charged at a constant current of 0.5C to 3.7V, charged at a constant voltage of 3.7V to the cutoff current of 0.05C, and discharged at a constant current of 0.5C to 2.0V. The discharge capacity of the first cycle at 0.5C was recorded as D1. The charging and discharging process was repeated N times to obtain the discharge capacity of the Nth cycle, which was recorded as D. N The capacity retention rate for the Nth cycle is calculated based on the discharge capacity of the first cycle and the discharge capacity of the Nth cycle. The capacity retention rate for the Nth cycle = (D... N / D1)×100%.

[0122] The test results are shown in Table 4.

[0123]

[0124] In summary, this invention effectively improves the conductivity and oxidation resistance of the halide solid electrolyte by using substituted cations for ion substitution and combining this with vapor-phase permeation crystallization using lithium halides as raw materials. This, in turn, significantly enhances the initial efficiency, first-cycle discharge capacity, and cycle performance of lithium-ion batteries. Comparative Example 2, which did not undergo plasma activation, and Comparative Example 3, which did not undergo ball milling, both resulted in a substantial decrease in the conductivity and oxidation resistance of the halide solid electrolyte, leading to a deterioration in the electrochemical performance of the battery.

[0125] Meanwhile, comparing Example 1 with Examples 4-5, it can be seen that plasma activation power in the range of 5W to 50W is beneficial for halide solid electrolytes to obtain higher conductivity and stronger oxidation resistance, which is beneficial for improving the electrochemical performance of lithium-ion batteries.

[0126] Comparing Example 1 and Example 6, it can be seen that the plasma activation temperature should not be too high, otherwise it will lead to a decrease in the performance of the halide solid electrolyte, and thus reduce the electrochemical performance of the lithium-ion battery.

[0127] Comparing Example 1 with Examples 7-8 and Comparative Example 1, it can be seen that the use of lithium halide in the gas flow is essential in the gas phase permeation crystallization method, and its content is preferably within the range of 10 mg / L to 25 mg / L. Within this preferred range, it is more beneficial to improve the conductivity and oxidation resistance of the halide solid electrolyte, thereby improving the electrochemical performance of the battery.

[0128] Comparing Example 1 with Examples 9-10, it can be seen that in the gas phase permeation crystallization method, the flow rate of the gas flow is preferably in the range of 10 sccm to 300 sccm. Within this preferred range, it is more conducive to improving the conductivity and antioxidant capacity of the halide solid electrolyte, thereby improving the electrochemical performance of the battery.

[0129] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a halide solid electrolyte, characterized in that, The preparation method includes the following steps: (1) The raw materials of the initial halide solid electrolyte and the raw materials of the substituted cation are mixed, activated by plasma, and ball-milled to obtain the precursor; wherein, the valence state a of the substituted cation is greater than the valence state b of the substituted cation in the initial halide solid electrolyte, the ionic radius of the substituted cation is smaller than the ionic radius of the substituted cation in the initial halide solid electrolyte, and the molar ratio of the substituted cation to the cation in the halide solid electrolyte is greater than or equal to 0.5; (2) A protective gas is used to carry lithium halide to form a gas flow, and the precursor is heat-treated at 150°C to 400°C to perform lithium ion charge compensation or lithium ion vacancy compensation on the precursor, so as to obtain the halide solid electrolyte. The molar amount of charge compensation or vacancy compensation of lithium ions = (ab) × c, where c is the molar percentage of the substitution of cations in the halide solid electrolyte by the substituted cations; the initial halide solid electrolyte in step (1) includes at least one of cubic phase solid electrolyte, layered structure solid electrolyte, amorphous system solid electrolyte, bimetallic doped halide solid electrolyte or halogen-oxygen mixed system solid electrolyte.

2. The method for preparing halide solid electrolyte according to claim 1, characterized in that, The plasma activation method in step (1) includes pulsed discharge plasma activation or continuous discharge plasma activation; And / or, The parameters for plasma activation include: power 5W~50W, inert gas flow rate 10sccm~100sccm, duration 30s~7.5min, pressure 0.1Pa~8Pa, and temperature 10℃~85℃.

3. The method for preparing a halide solid electrolyte according to claim 1, characterized in that, After activation in step (1), ultrasonic-assisted ball milling is performed. During the ultrasonic-assisted ball milling process, the frequency of the ultrasound is 5kHz~40kHz. During the ultrasonic-assisted ball milling process, the ball-to-material ratio is (5~30):1, the rotation speed is 150rpm~700rpm, the ball milling time is 1h~35h, and the diameter of the grinding ball is 3mm~15mm.

4. The method for preparing a halide solid electrolyte according to claim 1, characterized in that, The airflow velocity is 10 sccm to 300 sccm; and / or, The lithium halide content in the gas stream is 10 mg / L to 25 mg / L; and / or, The heat treatment time is 1 hour to 18 hours.

5. A halide solid electrolyte, characterized in that, The halide solid electrolyte is prepared by the preparation method according to any one of claims 1-4.

6. A positive electrode, characterized in that, The positive electrode includes a positive electrode active material and the halide solid electrolyte as described in claim 5.

7. A solid-state battery, characterized in that, The solid-state battery includes the halide solid electrolyte of claim 5 or the positive electrode of claim 6.

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