Solid electrolyte with carbon coated surface, preparation method therefor, and use thereof

Abstract

Provided in the present disclosure are a solid electrolyte with a carbon coated surface, a preparation method therefor, and the use thereof. The preparation method comprises the following steps: A) subjecting a solid-state electrolyte to alkaline washing in an alkaline solution, and then aging the alkaline-washed solid-state electrolyte in an air atmosphere to generate Li2CO3 on the surface, so as to obtain an aged solid-state electrolyte, the alkaline solution being an aqueous solution of lithium hydroxide and the concentration of the alkaline solution being less than 0.05 mol / L; B) subjecting the aged solid electrolyte to acid washing in a dilute acid solution, and drying same after the acid washing to obtain a dried powder; C) mixing the dried powder with a solution of an organic carbon source, and enables the carbon source to undergo surface adsorption or in-situ polymerization, so as to obtain an intermediate partially coated with the organic carbon source; and D) calcining the intermediate partially coated with the organic carbon source in an inert atmosphere, so as to obtain the solid electrolyte with a carbon coated surface. By means of the modes of alkaline washing and aging, the present disclosure achieves higher controllability over the carbon-coated surface area and is applicable to more types of electrolytes.

Description

A solid electrolyte with carbon coating, its preparation method and application

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411220756.7, filed on August 30, 2024, entitled "A solid electrolyte with carbon coating on its surface, its preparation method and application", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure belongs to the field of lithium-ion battery technology, and particularly relates to a solid electrolyte with carbon coating on its surface, its preparation method and application. Background Technology

[0004] Since the beginning of the 21st century, developing clean and green renewable energy has become a common goal and a major objective for global energy utilization. Especially in recent years, the rapid development of new energy vehicles, power tools, consumer electronics, and large-scale energy storage has led to the rapid expansion of the global lithium battery market. Currently, the energy structures of various countries are at a critical juncture of transformation, aiming to transition from a traditional energy structure dominated by non-renewable energy sources such as coal and oil to one dominated by renewable and clean energy. Since its initial commercial application in the early 1990s, lithium-ion batteries have experienced extensive development. Due to their advantages over traditional fossil fuels, they significantly avoid consuming non-renewable energy sources such as fossil fuels and offer environmental benefits such as recyclability, leading to their widespread application. Over the past four decades, the performance of lithium batteries has improved dramatically, with advantages such as high energy density, high safety, and zero pollution making them an ideal candidate to replace petroleum energy.

[0005] For power batteries, besides the paramount safety performance, energy density, rate capability, and high / low temperature cycle performance have become crucial performance indicators. To further improve cell performance, modifications are typically made to the internal positive and negative electrodes, electrolyte, and separator. Even though current lithium-ion power batteries have undergone significant development and improvement, some problems still urgently need to be addressed, such as voltage polarization caused by internal resistance and poor rate capability. The root cause is the low lithium-ion conductivity and high internal resistance within the cell system. This problem can be effectively mitigated through a simple positive electrode / electrolyte blending and carbon coating strategy. Inorganic solid electrolytes such as LISICON, NASICON, Garnet, Pyrochlore, and Perovskite are widely used in positive electrode blending processes due to their wide electrochemical window, high ionic conductivity, and high chemical thermodynamic stability. By carbon-coating the electrolyte material surface before blending with the positive electrode, the problem of low ionic and electronic conductivity can be effectively improved.

[0006] Conventional dry and wet carbon coating processes for powders typically result in a core-shell-like fully enclosed structure. While this significantly improves electronic conductivity, it inevitably hinders lithium-ion transport on the grain surface. An ideal carbon-coated electrolyte material should possess high electronic conductivity while maintaining its original ionic conductivity, achieving a balance between high ionic and high electronic conductivity. Summary of the Invention

[0007] This disclosure provides a method for preparing a solid electrolyte with a carbon-coated surface, comprising the following steps:

[0008] A) The solid electrolyte is washed with alkaline solution, and then the alkaline-washed solid electrolyte is aged in air atmosphere to generate Li2CO3 on the surface, thus obtaining the aged solid electrolyte.

[0009] The alkaline solution is an aqueous solution of lithium hydroxide; the concentration of the alkaline solution is less than 0.05 mol / L.

[0010] B) The aged solid electrolyte is acid-washed in a dilute acid solution, and then dried to obtain a dry powder.

[0011] C) The dried powder is mixed with an organic carbon source solution and coated to obtain an intermediate partially coated with an organic carbon source.

[0012] D) The intermediate partially coated with the organic carbon source is calcined under an inert atmosphere to obtain a solid electrolyte with a carbon-coated surface.

[0013] Furthermore, the solid electrolyte includes Garnet-type electrolyte, LISICON-type electrolyte, NASICON-type electrolyte, Pyrochlore-type electrolyte, or Perovskite-type electrolyte.

[0014] Furthermore, the alkaline washing time is 0.5 to 5 minutes.

[0015] Furthermore, the air atmosphere in step A) is a constant humidity air atmosphere with a humidity > 50%;

[0016] The aging temperature is 0–60°C; the aging time is 24–48 hours.

[0017] Further, the dilute acid solution is an aqueous hydrochloric acid solution with a molar concentration of 0.05–0.2 mol / L;

[0018] The pickling time is 10-120 seconds.

[0019] Furthermore, the organic carbon source includes small organic molecules and / or polymers, wherein the small organic molecules include citric acid, glucose, sucrose, malic acid, malonic acid, succinic acid, succinic acid, and lactic acid; the polymers include one or more of polydopamine, polytannic acid, polyvinyl chloride, polyaniline, phenolic resin, furfural resin, epoxy resin, and urea-formaldehyde resin; and the molecular weight of the polymer is 100,000 to 900,000.

[0020] Furthermore, the holding temperature for calcination in step D) is 700–900°C; the calcination time in step D) is 3–6 hours.

[0021] This disclosure provides a solid electrolyte with a carbon-coated surface, prepared according to the preparation method described above, comprising a solid electrolyte substrate and a carbon coating layer on the surface of the solid electrolyte substrate, wherein the carbon coating layer exhibits localized dot-like coating.

[0022] Furthermore, in the solid electrolyte with carbon coating on the surface, the mass fraction of the carbon coating layer is 1-20%, and the area of ​​the carbon coating layer accounts for 10-100% of the total surface area of ​​the solid electrolyte.

[0023] This disclosure provides a lithium-ion battery, including the solid electrolyte with surface carbon coating as described above. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0025] Figure 1 is the XRD phase diagram of carbon-coated LATP nanopowder in Example 5 of this disclosure;

[0026] Figure 2 is the Raman spectrum of carbon-coated LATP nanopowder in Example 5 of this disclosure;

[0027] Figure 3 is a TEM image of the carbon-free LATP nanopowder material in step one of embodiment 5 of this disclosure.

[0028] Figure 4 is a TEM image of 10% local area carbon-coated LATP nanopowder in Example 5 of this disclosure. Detailed Implementation

[0029] This disclosure provides a method for preparing a solid electrolyte with a carbon-coated surface, comprising the following steps:

[0030] A) The solid electrolyte is washed with alkaline solution, and then the alkaline-washed solid electrolyte is aged in air atmosphere to generate Li2CO3 on the surface, thus obtaining the aged solid electrolyte.

[0031] The alkaline solution is an aqueous solution of lithium hydroxide; the concentration of the alkaline solution is less than 0.05 mol / L.

[0032] B) The aged solid electrolyte is acid-washed in a dilute acid solution, and then dried to obtain a dry powder.

[0033] C) The dried powder is mixed with an organic carbon source solution and subjected to a polymerization reaction to obtain an intermediate partially coated with an organic carbon source;

[0034] D) The intermediate partially coated with the organic carbon source is calcined under an inert atmosphere to obtain a solid electrolyte with a carbon-coated surface.

[0035] In this disclosure, the solid electrolyte is an uncoated solid electrolyte, which may be a Garnet-type electrolyte, a Lisicon-type electrolyte, a NASICON-type electrolyte, a Perovskite-type electrolyte, a Pyrochlore-type electrolyte, or other solid electrolyte materials whose structure is insensitive to air and moisture; the Garnet-type electrolyte is Li7La3Zr2O. 12Li5La3Zr2O 12 Li7La3Ta2O 12 or Li7La3Nb2O 12 Electrolyte, in one embodiment, is an element-doped Li 7-3x M x La3Zr2O 12 (M=Al, Ca, Fe, Ga, etc.), Li 7-x La3Zr 2-x M x O 12 (M = Ta, Nb, Sn, Y, Gr, W, etc.), in one embodiment, Li 6.25 Al 0.25 La3Zr2O 12 Li 6.1 Ga 0.3 La3Zr2O 12 Li 6.5 La3Zr 1.5 Nb 0.5 O 12 Or Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The LISICON electrolyte, in one embodiment, is Li... 3+x P 1-x Si x O4 or Li 2+2x Zn 1-x GeO4, in one embodiment, is Li 3.5 P 0.5 Si 0.5 O4 or Li 3.3 Zn 0.45 GeO4; the NASICON-type electrolyte is Li3Zr2Si2PO4. 12 LiZr2(PO4)3, LiTi2(PO4)3, or LiGe2(PO4)3, in one embodiment being its element-doped Li 1+x M x Zr 2-x (PO4)3, Li 1+x M x Ti 2-x (PO4)3 or Li 1+x M x Ge 2-x (PO4)3 (M = Al, Cr, Ga, Fe, Sc, Sn, In, Lu, Y, La, etc.), in one embodiment being LiSn 0.4 Zr 1.6 (PO4)3, Li1.3 Al 0.3 Ti 1.7 (PO4)3 or Li 1.5 Al 0.5 Ge 1.5 (PO4)3; the Perovskite-type electrolyte in one embodiment is LiSr2Ti2NbO9, Li 3x Nd 0.66-x M 0.33-2x TiO3 or Li 3x La 0.66-x M 0.33-2x TiO3 (M is a vacancy), in one embodiment is Li 0.34 La 0.51 TiO 2.94 Li 0.34 La 0.56 TiO3 or Li 0.34 Nd 0.55 TiO3; the Pyrochlore-type electrolyte is, in one embodiment, LiSrM2O6F or Li 2-x La (1+x) / 3 M₂O₆F (M = Nb, Ta), in one embodiment, is Li. 1.25 La 0.58 Nb₂O₆F or LiLa 0.66 Ta2O6F.

[0036] In this disclosure, the solid electrolyte can be prepared by methods commonly used in the art, such as by preparing precursor powder materials through solid-phase reaction or sol-gel methods, and then calcining the precursor powder materials. Alternatively, commercially available products can be purchased, and this disclosure does not make any special requirements in this regard.

[0037] In this disclosure, the solid electrolyte is, in one embodiment, a solid electrolyte powder. The solid electrolyte is soaked and cleaned in a LiOH aqueous solution and then dried so that LiOH is fully wetted and attached to the surface of the powder.

[0038] In this disclosure, the concentration of the LiOH aqueous solution is ≤0.05 mol / L in one embodiment, 0.01–0.05 mol / L in another embodiment, such as 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, or any of the above values ​​as the upper or lower limit in another embodiment; the alkaline washing temperature is 0–50°C in one embodiment, 15–30°C in another embodiment, such as 5°C, 10°C, 20°C, 25°C, 30°C, 40°C, 45°C, or any of the above values ​​as the upper or lower limit in another embodiment; the alkaline washing time is 0.5–5 min in one embodiment, 1–4 min in another embodiment, such as 0.5 min, 1 min, 2 min, 3 min, 4 min, 5 min, or any of the above values ​​as the upper or lower limit in another embodiment.

[0039] In this disclosure, the drying method described in one embodiment is blower drying, which is a commonly used drying method in the art and will not be described in detail here.

[0040] After completing the above alkaline washing, the solid electrolyte powder that has been alkaline washed and dried is placed in a constant temperature and humidity air atmosphere for full exposure and aging, so that the LiOH on the surface of the solid electrolyte reacts with CO2 in the air to generate Li2CO3. The presence of uneven Li on the surface and the non-uniformity of the reaction cause the formation of a Li2CO3 coating layer with uneven thickness and density on the surface of the grains.

[0041] In this disclosure, the humidity of the air atmosphere is >50% in one embodiment, 55% to 90% in another embodiment, such as 51%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, and in another embodiment, a range of values ​​with any of the above values ​​as the upper or lower limit.

[0042] In this disclosure, the aging temperature is 0–60°C in one embodiment, 10–50°C in another embodiment, such as 0°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, or any of the above values ​​as the upper or lower limit in one embodiment; the aging time is 24–48 hours in one embodiment, 30–40 hours in another embodiment, such as 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, 36 hours, 38 hours, 40 hours, 42 hours, 44 hours, 46 hours, 48 ​​hours, or any of the above values ​​as the upper or lower limit in one embodiment.

[0043] After the aging process described above, the aged solid electrolyte is acid-washed in a dilute acid solution and then dried to obtain a dry powder. The Li₂CO₃ coating layer on the surface is removed by acid washing. Under a constant concentration of dilute acid solution, the removal area of ​​the Li₂CO₃ coating layer can be controlled by adjusting the acid washing time. By adjusting the acid washing time, a stepped effect of different coating areas can be achieved within the 0–100% range (10%, 20%, 30%, ... 100%).

[0044] In this disclosure, the acid in the dilute acid solution is hydrochloric acid in one embodiment, and the concentration of the dilute acid solution is 0.05-0.2 mol / L in one embodiment and 0.1-0.15 mol / L in another embodiment. The acid washing time is 10-120 s in one embodiment and 20-100 s in another embodiment, such as 10 s, 15 s, 20 s, 25 s, 30 s, 35 s, 40 s, 45 s, 50 s, 55 s, 60 s, 65 s, 70 s, 75 s, 80 s, 85 s, 90 s, 95 s, 100 s, 105 s, 110 s, 115 s, 120 s in one embodiment, or a range of values ​​with any of the above values ​​as the upper or lower limit.

[0045] After pickling, the pickled slurry is filtered and quickly dried to obtain a dry powder. In this disclosure, the pickled and dried powder material is mixed with an organic carbon source solution, and the mixture is fully reacted and coated under stirring conditions. After complete coating, it is dried to obtain an intermediate partially coated with organic carbon source.

[0046] In this disclosure, the organic carbon source solution, in one embodiment, includes an organic carbon source and a solvent. The organic carbon source, in one embodiment, includes one or more low-molecular-weight and high-molecular-weight polymer materials capable of bonding under Lewis alkaline conditions. The low-molecular-weight materials that bond, in one embodiment, include one or more of citric acid, glucose, sucrose, malic acid, malonic acid, succinic acid, and lactic acid. The high-molecular-weight polymer materials, in one embodiment, include one or more of polydopamine, polytannic acid, polyvinyl chloride, polyaniline, succinic acid conjugated polymers, phenolic resins, furfural resins, epoxy resins, and urea-formaldehyde resins. The molecular weight of the polymer, in one embodiment, is 100,000 to 900,000.

[0047] In this disclosure, the organic small molecules can be directly adsorbed onto the surface of the electrolyte through coordination bonds between functional groups such as carboxyl and hydroxyl groups and metal cations. The polymer coating can be achieved by directly adding polymeric materials that coordinate with metal cations through complexation of their hydroxyl and carboxyl groups, or by adding corresponding small monomers that undergo in-situ polymerization near the metal cations on the electrolyte surface under Lewis alkaline conditions provided by the "π-electron feedback effect," followed by adsorption and coating through strong coordination. Finally, carbonization via high-temperature sintering achieves carbon coating.

[0048] In this disclosure, the solvent in the organic carbon source is, in one embodiment, an alcohol solvent, such as methanol, ethanol, isopropanol, etc.; the mass fraction of the organic carbon source solution is, in one embodiment, 10-50%, in another embodiment, 20-40%, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, and in another embodiment, a range of values ​​with any of the above values ​​as the upper or lower limit.

[0049] In this disclosure, the coating temperature is 10-50°C in one embodiment and 20-40°C in another embodiment, and the coating time is 2-8 hours in one embodiment and 3-6 hours in another embodiment.

[0050] In this disclosure, the drying temperature is 80-120°C in one embodiment, 90-110°C in another embodiment, and 100-105°C in yet another embodiment. The drying time is 4-8 hours in one embodiment and 5-6 hours in yet another embodiment.

[0051] After coating is completed, the coated intermediate is calcined in an inert atmosphere, and then ground to obtain a solid electrolyte powder material with carbon coating on the surface.

[0052] In this disclosure, the inert atmosphere is nitrogen and / or argon in one embodiment; the calcination temperature is 700–900°C in one embodiment, which ensures complete reaction and decomposition of the remaining Li2CO3 on the surface, while the carbon source is completely carbonized; the temperature is 750–850°C in one embodiment, such as 700°C, 720°C, 750°C, 780°C, 800°C, 820°C, 850°C, 880°C, or 900°C; and the temperature is within a range where any of the above values ​​are the upper or lower limits. The calcination time is 3–6 hours in one embodiment and 4–5 hours in another embodiment.

[0053] This disclosure also provides a carbon-coated solid electrolyte, prepared according to the method described above, comprising a solid electrolyte substrate and a carbon coating layer on the surface of the solid electrolyte substrate, wherein the carbon coating layer exhibits localized dot-like coating. In the carbon-coated solid electrolyte, the mass fraction of the carbon coating layer is 1-20%, and in one embodiment, it is 5-15%. The area of ​​the carbon coating layer accounts for 10-100% of the total surface area of ​​the solid electrolyte in one embodiment, and 20-80% in another embodiment.

[0054] This disclosure also provides a lithium-ion battery, including the solid electrolyte with a surface carbon coating as described above.

[0055] This disclosure provides a method for preparing a solid electrolyte with carbon coating, comprising the following steps: A) washing the solid electrolyte in an alkaline solution, and then aging the alkaline-washed solid electrolyte in an air atmosphere to generate Li2CO3 on the surface, thereby obtaining an aged solid electrolyte; the alkaline solution is an aqueous solution of lithium hydroxide; the concentration of the alkaline solution is less than 0.05 mol / L; B) washing the aged solid electrolyte in a dilute acid solution, and drying it to obtain a dry powder; C) mixing the dry powder with an organic carbon source solution and carrying out a polymerization reaction to obtain an intermediate partially coated with an organic carbon source; D) calcining the intermediate partially coated with an organic carbon source in an inert atmosphere to obtain a solid electrolyte with carbon coating. This disclosure first involves alkali washing to fully wet and attach LiOH to the surface of a solid electrolyte, followed by aging in air to generate a Li2CO3 coating layer with uneven surface thickness and density. By utilizing the difference in alkalinity between the Li2CO3 on the surface of the solid electrolyte grains and the electrolyte itself, as well as the difference in adsorption capacity for specific organic molecules, the organic carbon source molecules are controlled to achieve different degrees of polymerization and uneven adhesion polymerization on the surface of the grains without Li2CO3 coverage. After calcination, the final effect of local coating is achieved.

[0056] This disclosure improves the controllability of the carbon coating area on the surface by using alkaline washing and aging, and also makes it applicable to a wider range of electrolytes.

[0057] To further illustrate this disclosure, the following detailed description, in conjunction with embodiments, describes a carbon-coated solid electrolyte, its preparation method, and its applications, but this should not be construed as limiting the scope of protection of this disclosure.

[0058] Example 1

[0059] 1. Solid-state reaction method: First, lithium carbonate, zinc oxide, and germanium oxide are reacted according to Li... 3.3 Zn 0.45The stoichiometric ratio of GeO4 (LZGO) was determined by weighing, with Li source being a volatile element during calcination, thus a 10% excess was added. The weighed lithium, zinc, and germanium source powders were wet-milled in a planetary ball mill for 12 hours to obtain a precursor slurry, which was then dried in an 80°C forced-air drying oven for 12 hours to obtain LZGO electrolyte precursor powder. The precursor was further calcined in a muffle furnace at 900°C for 12 hours, cooled to room temperature with the furnace, and then mechanically crushed using a sand mill to finally obtain nano-LZGO ceramic powder.

[0060] 2. The prepared LZGO powder material was subjected to a concentration of 0.05 mol·L⁻¹. -1 The powder was soaked in LiOH aqueous solution for 0.5 min, filtered, and dried; then aged for 48 h in a room temperature environment with an air humidity of 75%; finally, the powder was placed in a solution with a concentration of 0.05 mol·L⁻¹. －1 The powder was soaked and washed in an HCl solution for 30 seconds, filtered, and then dried to obtain aged dry powder.

[0061] 3. Place the above-mentioned appropriate amount of dried electrolyte powder in a 30% citric acid ethanol solution, mix and stir thoroughly at 25°C for 6 hours, then filter and remove; then place it in a 100°C forced-air drying oven for 6 hours to dry thoroughly, and remove it after cooling to room temperature to obtain the electrolyte powder coated with organic carbon source.

[0062] 4. The above powder is calcined in an inert atmosphere using an atmosphere furnace or tube furnace at a temperature of 900℃. After holding at that temperature for 3 hours, it is cooled with the furnace to obtain LZGO powder material with a carbon coating area of ​​10%.

[0063] Example 2

[0064] 1. Solid-state reaction method: Lithium carbonate, lanthanum oxide, and zirconium titanium oxide are reacted according to the Li... 0.34 La 0.56 TiO3 (LLTO) was weighed according to its stoichiometric ratio, with Li in excess at 10%. The weighed lithium, lanthanum, and titanium sources were added to a zirconium oxide ball mill jar, along with an appropriate amount of ethanol dispersant, and ball milled. The mixture was ball-milled at 500 rpm for 6 hours using a planetary ball mill. The slurry was then removed and dried in an 80°C forced-air drying oven for 12 hours to obtain LLTO electrolyte precursor powder. The precursor was further calcined in a muffle furnace at 900°C for 12 hours, cooled to room temperature with the furnace, and then mechanically crushed using a sand mill to finally obtain nano-LLTO ceramic powder.

[0065] 2. The prepared LLTO powder material was subjected to a concentration of 0.01 mol·L⁻¹. -1The powder was soaked in LiOH aqueous solution for 1 min, filtered, and dried; then aged for 48 h in a room temperature environment with 50% humidity; finally, the powder was placed in a 0.1 mol·L⁻¹ solution. -1 The powder was soaked and washed in an HCl solution for 20 seconds, filtered, and then dried to obtain aged dry powder.

[0066] 3. Place the above-mentioned appropriate amount of dried electrolyte powder in a 50% citric acid ethanol solution, mix and stir thoroughly at 50°C for 2 hours, then filter and remove; then place it in a 100°C forced-air drying oven for 6 hours to dry thoroughly, and remove it after cooling to room temperature to obtain the electrolyte powder coated with organic carbon source.

[0067] 4. The above powder is calcined in an inert gas atmosphere using an atmosphere furnace or tube furnace at a calcination temperature of 900℃. After holding at that temperature for 3 hours, it is cooled with the furnace to obtain LLZO nanopowder material with a carbon coating area of ​​20%.

[0068] Example 3

[0069] 1. Sol-gel method: Lithium nitrate, lanthanum nitrate, zirconium oxynitrate, and tantalum ethoxide are mixed according to the Li... 6.5 La3Zr 1.5 Ta 0.5 O 12 The stoichiometric ratio of LLZTO was determined by weighing, with Li in 10% excess. The weighed lithium, lanthanum, zirconium, and tantalum sources were added to deionized water and mixed, followed by the addition of a complexing agent. After stirring to dissolve and evaporating at 80°C, a transparent gel was obtained. Finally, the gel was dried at 140°C for 24 hours to obtain a dry precursor powder. The precursor was calcined in a muffle furnace at 500°C for 3 hours to remove impurities such as carbon; subsequently, it was calcined at 800°C for 3 hours to obtain nano-LLZTO ceramic powder.

[0070] 2. The prepared LLZTO powder material was subjected to a concentration of 0.05 mol·L⁻¹. -1 The powder was soaked in LiOH aqueous solution for 4 minutes, filtered, and dried; then aged for 24 hours in a room temperature environment with 90% humidity; finally, the powder was placed in a solution with a concentration of 0.2 mol·L⁻¹. -1 The powder was soaked and washed in an HCl solution for 90 seconds, filtered, and then dried to obtain aged dry powder.

[0071] 3. Place the above-mentioned appropriate amount of dried electrolyte powder in a polydopamine ethanol solution with a mass fraction of 10% and a molecular weight of 500,000. Mix and stir thoroughly at 10°C for 8 hours, then filter and remove. Then place it in a forced-air drying oven at 120°C for 4 hours to dry thoroughly. After cooling to room temperature, remove it to obtain electrolyte powder coated with organic carbon source.

[0072] 4. The above powder is calcined in an inert gas atmosphere using an atmosphere furnace or tube furnace at a calcination temperature of 800℃. After holding at this temperature for 3 hours, it is cooled with the furnace to obtain LLZTO nanopowder material with a carbon coating area of ​​20%.

[0073] Example 4

[0074] 1. Solid-state reaction method: Lithium carbonate, germanium oxide, titanium dioxide, and ammonium dihydrogen phosphate are reacted according to the reaction mixture Li... 1.5 Al 0.5 Ge 1.5 The stoichiometric ratio of (PO4)3(LAGP) was determined by weighing, with Li in 10% excess. The weighed lithium, germanium, aluminum, and phosphorus source powders were wet-milled in a planetary ball mill for 12 hours to obtain a precursor slurry. The slurry was then dried in a forced-air dryer at 80°C for 12 hours and ground to obtain the dried precursor powder. The precursor was calcined in a muffle furnace at 900°C for 12 hours to obtain electrolyte micron-sized powder, which was subsequently mechanically crushed using a sand mill to finally obtain nano-LAGP powder material.

[0075] 2. The prepared LAGP powder material was subjected to a concentration of 0.04 mol·L⁻¹. -1 The powder was soaked in LiOH aqueous solution for 2 minutes, filtered, and dried; then aged for 30 hours in a room temperature environment with 80% humidity; finally, the powder was placed in a solution with a concentration of 0.15 mol·L⁻¹. -1 The powder was soaked and washed in an HCl solution for 20 seconds, filtered, and then dried to obtain aged dry powder.

[0076] 3. Place the above-mentioned appropriate amount of dried electrolyte powder in a polydopamine ethanol solution with a mass fraction of 40% and a molecular weight of 100,000. Mix and stir thoroughly at 40°C for 6 hours, then filter and remove. Then place it in a forced-air drying oven at 120°C for 4 hours to dry thoroughly. After cooling to room temperature, remove it to obtain electrolyte powder coated with organic carbon source.

[0077] 4. The above powder is calcined in an inert gas atmosphere using an atmosphere furnace or tube furnace at a calcination temperature of 900℃. After holding at that temperature for 6 hours, it is cooled with the furnace to obtain LAGP nanopowder material with a carbon coating area of ​​40%.

[0078] Example 5

[0079] 1. Sol-gel method: Lithium nitrate, aluminum nitrate, tetrabutyl titanate, and ammonium dihydrogen phosphate are mixed according to the Li... 1.3 Al 0.3 Ti 1.7The stoichiometric ratio of (PO4)3(LATP) was determined by weighing, with Li in 10% excess. The weighed lithium, aluminum, titanium, and phosphorus sources were added to deionized water and mixed, followed by the addition of a complexing agent. After stirring to dissolve and evaporating at 80°C, a transparent gel was obtained. Finally, the gel was dried at 140°C for 24 hours to obtain a dried precursor powder. The precursor was calcined in a muffle furnace at 500°C for 3 hours to remove impurities such as carbon and nitrogen; subsequently, it was calcined in a muffle furnace at 700°C for 3 hours to obtain nano-LATP ceramic powder.

[0080] 2. The prepared LATP powder material was subjected to a concentration of 0.04 mol·L⁻¹ -1 The powder was soaked in LiOH aqueous solution for 5 minutes, filtered, and dried; then aged for 36 hours in a room temperature environment with 80% humidity; finally, the powder was placed in a solution with a concentration of 0.1 mol·L⁻¹. -1 The powder was soaked and washed in an HCl solution for 120 seconds, filtered, and then dried to obtain aged dry powder.

[0081] 3. Place the above-mentioned appropriate amount of dried electrolyte powder in a polydopamine ethanol solution with a mass fraction of 30% and a molecular weight of 900,000. Mix and stir thoroughly at 30°C for 4 hours, then filter and remove. Then place it in an 80°C forced-air drying oven for 8 hours to dry thoroughly. After cooling to room temperature, remove it to obtain electrolyte powder coated with organic carbon source.

[0082] 4. The above powder is calcined in an inert gas atmosphere using an atmosphere furnace or tube furnace at a calcination temperature of 750℃. After holding at this temperature for 6 hours, it is cooled with the furnace to obtain LATP nanopowder material with a carbon coating area of ​​10%.

[0083] Example 6

[0084] LATP nanopowder material with a carbon coating area of ​​20% was prepared according to the method in Example 5. The difference is that in step 2 of Example 6, the nanopowder was immersed and washed in HCl solution for 100 seconds.

[0085] Example 7

[0086] LATP nanoparticles with a carbon coating area of ​​30% were prepared according to the method in Example 5. The difference was that in step 2 of Example 7, the nanoparticles were immersed and washed in HCl solution for 80 seconds.

[0087] Example 8

[0088] LATP nanoparticles with a carbon coating area of ​​50% were prepared according to the method in Example 5. The difference was that in step 2 of Example 8, the nanoparticles were immersed and washed in HCl solution for 60 seconds.

[0089] Example 9

[0090] LATP nanoparticles with a carbon coating area of ​​80% were prepared according to the method in Example 5. The difference was that in step 2 of Example 9, the nanoparticles were immersed and washed in HCl solution for 30 seconds.

[0091] Example 10

[0092] LATP nanoparticles with a carbon coating area of ​​90% were prepared according to the method in Example 5. The difference is that in step 2 of Example 10, the nanoparticles were immersed and washed in HCl solution for 10 seconds.

[0093] Comparative Example 1

[0094] 1. The nano-LLZTO powder material prepared in step 1 of Example 3.

[0095] 2. Place the above-mentioned appropriate amount of dried electrolyte powder in a 50% glucose aqueous solution, mix and stir thoroughly at 25°C for 6 hours, then filter and remove; then place it in a 120°C forced-air drying oven for 12 hours to dry thoroughly, and remove it after cooling to room temperature to obtain the electrolyte powder coated with organic carbon source.

[0096] 3. The above powder is calcined in an inert gas atmosphere using an atmosphere furnace or tube furnace at a temperature of 900℃. After holding at that temperature for 6 hours, it is cooled with the furnace to obtain conventional carbon-coated (fully coated structure) LLZTO nanopowder material.

[0097] Comparative Example 2

[0098] 1. The nano-LATP powder material prepared in step 1 of Example 5.

[0099] 2. Place the above-mentioned appropriate amount of dried electrolyte powder in a 30% citric acid aqueous solution, mix and stir thoroughly at 40°C for 6 hours, then filter and remove; then place it in a 100°C forced-air drying oven for 12 hours to dry thoroughly, and remove it after cooling to room temperature to obtain the electrolyte powder coated with organic carbon source.

[0100] 3. The above powder is calcined in an inert gas atmosphere using an atmosphere furnace or tube furnace at a temperature of 900℃. After holding at that temperature for 12 hours, it is cooled with the furnace to obtain conventional carbon-coated (fully coated structure) LATP nanopowder material.

[0101] Comparative Example 3

[0102] 1. Solid-state reaction method: Lithium carbonate, alumina, titanium dioxide, and ammonium dihydrogen phosphate are reacted according to the Li... 1.3 Al 0.3 Ti 1.7The stoichiometric ratio of (PO4)3(LATP) was determined by weighing, with Li in 15% excess. The weighed lithium, aluminum, titanium, and phosphorus source powders were then wet-milled in a planetary ball mill for 12 hours to obtain a precursor slurry. The slurry was dried by forced-air drying at 80°C for 12 hours and then ground to obtain dried precursor powder. The precursor was calcined in a muffle furnace at 900°C for 12 hours to obtain micron-sized powder, which was then mechanically crushed using a sand mill to finally obtain nano-LATP powder material.

[0103] 2. Place the above-mentioned appropriate amount of dried electrolyte powder in a 30% glucose aqueous solution, mix and stir thoroughly at 30°C for 6 hours, then filter and remove; then place it in a 100°C forced-air drying oven for 12 hours to dry thoroughly, and remove it after cooling to room temperature to obtain the electrolyte powder coated with organic carbon source.

[0104] 3. The above powder is calcined in an inert gas atmosphere using an atmosphere furnace or tube furnace at a calcination temperature of 800℃. After holding at this temperature for 6 hours, it is cooled with the furnace to obtain conventional carbon-coated (fully coated structure) LATP nanopowder material.

[0105] Materials testing and characterization

[0106] 1. Phase characterization: X-ray diffraction was used to characterize the phase structure of the electrolyte powder before and after carbon coating. The results are shown in Figure 1. Figure 1 is the XRD phase spectrum of carbon-coated LATP nanopowder in Example 6 of this disclosure. As can be seen from Figure 1, the synthesized powder after alkaline washing, acid washing, and high-temperature calcination still shows a pure phase, the phase is stable, and it exhibits broadened characteristic peaks, indicating that its grains are fine nano-sized particles.

[0107] 2. Microstructure: The microstructure of the sample grains, including size, surface condition, and coating, was observed and tested using field emission scanning electron microscopy (SEM) or high-resolution transmission electron microscopy (TEM). The results are shown in Figures 3 and 4. Figure 3 is a TEM image of the nm-LATP powder material before coating in Example 6 of this disclosure. Figure 4 is a TEM image of LATP nanoparticles with 20% local carbon coating in Example 6 of this disclosure. As can be seen from Figures 3 and 4, the grain size before and after coating is 100-200 nm. The surface of the grains before coating is smooth and without adhesion. After local coating, the surface shows uniformly dispersed dark-colored dotted graphitized carbon adhesion. The carbon grain size is distributed in the range of 5-20 nm and has a regular shape.

[0108] 3. Electronic and Ionic Conductivity: The electronic conductivity of the powder was quantitatively tested using a four-probe method and a resistivity meter. The ionic conductivity of the cold-pressed ceramic sheet was tested using an AC impedance analyzer on an electrochemical workstation. The results are shown in Table 1. The electronic conductivity test results indicate that the original untreated electrolyte powder has a considerably low conductivity (10⁻⁶). -7 The electronic conductivity (S / cm) is highest at this stage, but the ionic conductivity is the highest. As the carbon coating amount gradually increases, the electronic conductivity shows a rapid upward trend, reaching its highest level in the fully coated state, typically up to 10. -1 S / cm; Ionic conductivity gradually decreases with increasing coating amount, reaching its lowest level in fully coated state; With a small amount of carbon coating (10-30%), a significant increase in electronic conductivity and a slight decrease in ionic conductivity can be achieved; Since graphite is a non-ionic conductor, coating it on the surface of a fast ionic conductor reduces the ion transport channels on the crystal surface, affecting the three-dimensional transport of lithium ions in the electrolyte as a whole. Therefore, for different application conditions, electrolyte powders with appropriate electronic / ionic conductivity ratios should be selected.

[0109] 4. Degree of carbon graphitization: Raman spectroscopy was used to characterize the phase composition and graphitization degree of the surface-coated carbon. The characteristic peak D (1360 cm⁻¹) of pure carbon materials was analyzed. -1 ), G peak (1580cm) -1 By comparing peak intensities or integrated intensities, the degree of graphitization of the carbon source can be quantitatively analyzed. The D peak is caused by the incomplete crystal structure resulting from crystal defects introduced into the carbon after graphitization, corresponding to the defect peak of amorphous materials (denoted as I). D The G peak corresponds to a regular graphitized crystal structure (intensity denoted as I). G Its degree of graphitization R = I D / I G The lower the R value, the closer it is to the graphite structure; the results are shown in Figure 2. Figure 2 is the Raman spectrum of carbon-coated LATP nanopowder in Example 6 of this disclosure. As can be seen from Figure 2, after high-temperature calcination, its graphitization degree R = 1.01, which is close to the conventional organic carbon source coating process, indicating that the organic carbon source has a high degree of graphitization.

[0110] 5. Carbon content and coating area: Quantitative analysis of carbon is performed using an elemental analyzer. Since the carbon coating area is directly proportional to the carbon content, the quantitative relationship between carbon coating content and carbon coating area can be obtained by testing the carbon content of solid electrolytes with no coating (0%), full coating (100%), and other coating areas.

[0111] Table 1. Electronic and ionic conductivity of carbon-coated powders in the embodiments and comparative examples of this disclosure.

[0112] The above description is only some embodiments of this disclosure. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principles of this disclosure, and these improvements and modifications should also be considered within the scope of protection of this disclosure. Industrial applicability

[0113] The purpose of this disclosure is to provide a solid electrolyte with a carbon-coated surface, its preparation method and application. The method in this disclosure can prepare a partially carbon-coated solid electrolyte with higher controllability, maintain the original conductivity level to the greatest extent, reduce the influence of surface coating on the inherent ionic conductivity, and provide electrolyte materials with different properties for the application scenarios of solid electrolytes in battery cells.

[0114] This disclosure provides a method for preparing a solid electrolyte with carbon coating, comprising the following steps: A) washing the solid electrolyte in an alkaline solution, and then aging the alkaline-washed solid electrolyte in an air atmosphere to generate Li2CO3 on the surface, thereby obtaining an aged solid electrolyte; the alkaline solution is an aqueous solution of lithium hydroxide; the concentration of the alkaline solution is less than 0.05 mol / L; B) washing the aged solid electrolyte in a dilute acid solution, and drying it to obtain a dry powder; C) mixing the dry powder with an organic carbon source solution and carrying out a polymerization reaction to obtain an intermediate partially coated with an organic carbon source; D) calcining the intermediate partially coated with an organic carbon source in an inert atmosphere to obtain a solid electrolyte with carbon coating. This disclosure first involves alkali washing to fully wet and attach LiOH to the surface of a solid electrolyte, followed by aging in air to generate a Li2CO3 coating layer with uneven surface thickness and density. By utilizing the difference in alkalinity between the Li2CO3 on the surface of the solid electrolyte grains and the electrolyte itself, as well as the difference in adsorption capacity for specific organic molecules, the organic carbon source molecules are controlled to achieve different degrees of polymerization and uneven adhesion polymerization on the surface of the grains without Li2CO3 coverage. After calcination, the final effect of local coating is achieved.

[0115] This disclosure improves the controllability of the carbon coating area on the surface by using alkaline washing and aging, and also makes it applicable to a wider range of electrolytes.

Claims

1. A method for preparing a solid electrolyte with a carbon-coated surface, comprising the following steps: A) The solid electrolyte is washed with alkaline solution, and then the alkaline-washed solid electrolyte is aged in air atmosphere to generate Li2CO3 on the surface, thus obtaining the aged solid electrolyte. The alkaline solution is an aqueous solution of lithium hydroxide; the concentration of the alkaline solution is less than 0.05 mol / L. B) The aged solid electrolyte is acid-washed in a dilute acid solution, and then dried to obtain a dry powder. C) The dried powder is mixed with an organic carbon source solution and coated to obtain an intermediate partially coated with an organic carbon source. D) The intermediate partially coated with the organic carbon source is calcined under an inert atmosphere to obtain a solid electrolyte with a carbon-coated surface.

2. The preparation method according to claim 1, characterized in that, The solid electrolyte includes Garnet-type electrolyte, LISICON-type electrolyte, NASICON-type electrolyte, Pyrochlore-type electrolyte, or Perovskite-type electrolyte.

3. The preparation method according to claim 1, characterized in that, The alkaline washing time is 0.5 to 5 minutes.

4. The preparation method according to claim 1, characterized in that, The air atmosphere in step A) is a constant humidity air atmosphere with a humidity > 50%; The aging temperature is 0–60°C; the aging time is 24–48 hours.

5. The preparation method according to claim 1, characterized in that, The dilute acid solution is an aqueous hydrochloric acid solution with a molar concentration of 0.05–0.2 mol / L; The pickling time is 10-120 seconds.

6. The preparation method according to claim 1, characterized in that, The organic carbon source includes small organic molecules and / or polymers, wherein the small organic molecules include citric acid, glucose, sucrose, malic acid, malonic acid, succinic acid, succinic acid, and lactic acid; the polymers include one or more of polydopamine, polytannic acid, polyvinyl chloride, polyaniline, phenolic resin, furfural resin, epoxy resin, and urea-formaldehyde resin; and the molecular weight of the polymers is 100,000 to 900,000.

7. The preparation method according to claim 1, characterized in that, The calcination temperature in step D) is 700–900°C; the calcination time in step D) is 3–6 hours.

8. A solid electrolyte with a carbon coating, prepared according to any one of claims 1 to 7, comprising a solid electrolyte substrate and a carbon coating layer on the surface of the solid electrolyte substrate, wherein the carbon coating layer presents as localized dot-like coatings.

9. The solid electrolyte with surface carbon coating according to claim 8, characterized in that, In the solid electrolyte with carbon coating on the surface, the mass fraction of the carbon coating layer is 1-20%, and the area of ​​the carbon coating layer accounts for 10-100% of the total surface area of ​​the solid electrolyte.

10. A lithium-ion battery, characterized in that, Includes the solid electrolyte with surface carbon coating as described in claim 8 or 9.

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