Solid electrolyte with carbon-coated surface as well as preparation method and application of solid electrolyte

Abstract

The invention provides a surface carbon-coated solid electrolyte and a preparation method and application thereof, and the preparation method comprises the following steps: A) carrying out alkali washing on the solid electrolyte in an alkali liquor, and then aging the solid electrolyte subjected to alkali washing in an air atmosphere, so that Li2CO3 is generated on the surface, and an aged solid electrolyte is obtained; the alkali liquor is a lithium hydroxide aqueous solution; the concentration of the alkali liquor is lower than 0.05 mol / L; b) carrying out acid pickling on the aged solid electrolyte in a dilute acid solution, and drying to obtain dry powder after acid pickling; c) mixing the dry powder with an organic carbon source solution, and carrying out surface adsorption or in-situ polymerization on the carbon source 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 to obtain the surface carbon-coated solid electrolyte. According to the method, the controllability of the surface carbon coating area is higher in an alkali washing and aging mode, and the applicable electrolyte types are wider.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a solid electrolyte with a surface carbon coating, and a preparation method and application thereof. Background Art

[0002] Since the beginning of the 21st century, the development of clean energy and green renewable energy has become the goal of the world's joint efforts and vigorous development in the direction of future energy utilization. Especially in recent years, with the rapid development of new energy vehicles, power tools, consumer electronics and large-scale energy storage, the global lithium battery market has expanded rapidly. At present, the energy structure types of various countries are in a critical period of transformation, aiming to transition and transform from traditional non-renewable energy sources such as coal and oil to renewable, green and clean energy. Since the first commercial application of lithium-ion batteries in the 1990s, they have been widely developed. Compared with traditional fossil energy, it greatly avoids the consumption of non-renewable energy such as fossil energy, and has environmental protection advantages such as scrap recycling, so it has been widely used. In the past four decades, the performance of lithium batteries in all aspects has been greatly improved. The advantages of high specific energy, high safety, green and pollution-free make it an ideal candidate to replace petroleum energy.

[0003] For power batteries, in addition to the most important safety performance, energy density, cycle rate performance and high and low temperature cycle performance have become important performance indicators of the battery. In order to further improve the performance of the battery cell, the internal positive and negative electrodes, electrolytes and diaphragms are usually modified to achieve the desired purpose. Even though the current lithium power batteries have been developed and improved more comprehensively, there are still some problems that need to be solved, such as voltage polarization caused by battery internal resistance and poor rate performance. The root cause is the low lithium ion conductivity in the system and the large internal resistance of the battery cell. For this problem, it can be effectively improved 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, high chemical thermodynamic stability and other advantages. By carbon coating the surface of the electrolyte material and then blending the positive electrode, the problem of low positive electrode ion and electronic conductivity can be effectively improved.

[0004] Conventional dry and wet powder carbon coating processes usually have a fully enclosed structure similar to a core-shell structure. Although the electronic conductivity is greatly improved, the process will inevitably hinder the lithium ion transmission on the surface of the grains. The ideal carbon-coated electrolyte material has high electronic conductivity while maintaining the original ionic conductivity to achieve high ionic conductivity and high electronic conductivity. Summary of the invention

[0005] The purpose of the present invention is to provide a solid electrolyte with a surface carbon coating, a preparation method and application thereof. The method of the present invention can prepare a solid electrolyte with a partial surface carbon coating, and has higher controllability, maintains the original conductivity level to the greatest extent, reduces the influence of the surface coating on the inherent ionic conductivity, and can provide electrolyte materials with different performances according to the application scenarios of the solid electrolyte in the battery cell.

[0006] A method for preparing a solid electrolyte with a surface carbon coating comprises the following steps:

[0007] A) washing the solid electrolyte in an alkaline solution, and then aging the washed solid electrolyte in an air atmosphere to generate Li2CO3 on the surface, thereby obtaining an aged solid electrolyte;

[0008] The alkali solution is a lithium hydroxide aqueous solution; the concentration of the alkali solution is lower than 0.05 mol / L;

[0009] B) pickling the aged solid electrolyte in a dilute acid solution, and drying after pickling to obtain a dry powder;

[0010] C) mixing the dry powder with an organic carbon source solution to coat the powder, thereby obtaining an intermediate partially coated with the organic carbon source;

[0011] D) calcining the intermediate partially coated with the organic carbon source under an inert atmosphere to obtain a solid electrolyte coated with surface carbon.

[0012] Preferably, the solid electrolyte includes a Garnet-type electrolyte, a LISICON-type electrolyte, a NASICON-type electrolyte, a Pyrochlore-type electrolyte or a Perovskite-type electrolyte.

[0013] Preferably, the alkali washing time is 0.5 to 5 minutes.

[0014] Preferably, the air atmosphere in step A) is a constant humidity air atmosphere, with humidity > 50%;

[0015] The aging temperature is 0 to 60° C.; the aging time is 24 to 48 hours.

[0016] Preferably, the dilute acid solution is a hydrochloric acid aqueous solution with a molar concentration of 0.05 to 0.2 mol / L;

[0017] The pickling time is 10 to 120 seconds.

[0018] Preferably, the organic carbon source includes organic small molecules and / or polymers, the organic small molecules include citric acid, glucose, sucrose, malic acid, malonic acid, succinic acid, succinic acid, lactic acid; the polymer includes one or more of polydopamine, polytannic acid, polyvinyl chloride, polyaniline, phenolic resin, furfural resin, epoxy resin and urea-formaldehyde resin; the molecular weight of the polymer is 100,000 to 900,000.

[0019] Preferably, the calcination holding temperature in the step D) is 700-900° C.; the calcination time in the step D) is 3-6 hours.

[0020] The present invention provides a solid electrolyte with a surface carbon coating, which is prepared according to the preparation method described above and comprises a solid electrolyte matrix and a carbon coating layer on the surface of the solid electrolyte matrix, wherein the carbon coating layer presents local point coating.

[0021] Preferably, in the solid electrolyte with surface carbon coating, the mass fraction of the carbon coating layer is 1 to 20%, and the area of ​​the carbon coating layer accounts for 10 to 100% of the total surface area of ​​the solid electrolyte.

[0022] The present invention provides a lithium ion battery, comprising the above-mentioned solid electrolyte with surface carbon coating.

[0023] The invention provides a method for preparing a solid electrolyte with a surface carbon coating, comprising the following steps: A) washing the solid electrolyte in an alkaline solution, and then aging the washed solid electrolyte in an air atmosphere to generate Li2CO3 on the surface to obtain an aged solid electrolyte; the alkaline solution is a lithium hydroxide aqueous solution; the concentration of the alkaline solution is lower than 0.05 mol / L; B) washing the aged solid electrolyte in a dilute acid solution, and drying after washing to obtain a dry powder; C) mixing the dry powder with an organic carbon source solution, performing a polymerization reaction, and obtaining an intermediate partially coated with the organic carbon source; D) calcining the intermediate partially coated with the organic carbon source in an inert atmosphere to obtain a solid electrolyte with a surface carbon coating. The present invention firstly uses alkali washing to make the surface of the solid electrolyte fully infiltrated with LiOH, and then ages it in air to generate a Li2CO3 coating layer with uneven surface thickness and density. By utilizing the difference in alkalinity between Li2CO3 on the surface of the solid electrolyte grains and the electrolyte itself, and the difference in adsorption capacity for specific organic molecules, the organic carbon source molecules are controlled to achieve different degrees of polymerization and uneven attachment polymerization on the surface of the grains without Li2CO3 coverage, and finally achieve the effect of local coating after calcination.

[0024] The present invention makes the surface carbon coating area more controllable through the alkaline washing + aging method, and is applicable to a wider range of electrolyte types. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0026] Figure 1 This is the XRD phase spectrum of the carbon-coated LATP nanopowder in Example 5 of the present invention;

[0027] Figure 2 This is the Raman spectrum of the carbon-coated LATP nanopowder in Example 5 of the present invention;

[0028] Figure 3 This is a TEM image of the nano-LATP powder material without carbon coating in step 1 of Example 5 of the present invention;

[0029] Figure 4 This is a TEM image of 10% local area carbon-coated LATP nanopowder in Example 5 of the present invention. DETAILED DESCRIPTION

[0030] The present invention provides a method for preparing a solid electrolyte with a surface carbon coating, comprising the following steps:

[0031] A) washing the solid electrolyte in an alkaline solution, and then aging the washed solid electrolyte in an air atmosphere to generate Li2CO3 on the surface, thereby obtaining an aged solid electrolyte;

[0032] The alkali solution is a lithium hydroxide aqueous solution; the concentration of the alkali solution is lower than 0.05 mol / L;

[0033] B) pickling the aged solid electrolyte in a dilute acid solution, and drying after pickling to obtain a dry powder;

[0034] C) mixing the dry powder with an organic carbon source solution to perform a polymerization reaction to obtain an intermediate partially coated with the organic carbon source;

[0035] D) calcining the intermediate partially coated with the organic carbon source under an inert atmosphere to obtain a solid electrolyte coated with surface carbon.

[0036] In the present invention, the solid electrolyte is a solid electrolyte that has not been coated. The solid electrolyte can be a Garnet electrolyte (garnet electrolyte), a LISICON electrolyte, a NASICON electrolyte, a Perovskite electrolyte (perovskite electrolyte), a Pyrochlore electrolyte (pyrochlore electrolyte) and other solid electrolyte materials whose structures are insensitive to air and moisture; the Garnet electrolyte is Li7La3Zr2O 12 、Li5La3Zr2O 12 、Li7La3Ta2O 12 or Li7La3Nb2O 12 The electrolyte, preferably element-doped Li 7-3x M x La3Zr2O 12 (M=Al, Ca, Fe, Ga, etc.), Li 7-x LqCy 2-x M x O 12 (M = Ta, Nb, Sn, Y, Gr, W, etc.), more preferably Li 6.25 Al 0.25 La3Zr2O 12 , Li 6.1 Ga 0.3 La3Zr2O 12 , Li 6.5 LqCy 1.5 Nb 0.5 O 12 or Li 6.5 LqCy 1.5 Ta 0.5 O 12 ; The LISICON type electrolyte is preferably Li 3+x P 1-x Si x O4 or Li 2+2x Zn 1-x GeO4, more preferably Li 3.5 P 0.5 Si 0.5 O4 or Li 3.3 Zn 0.45 GeO4; the NASICON type electrolyte is Li3Zr2Si2PO 12 , LiZr2(PO4)3, LiTi2(PO4)3 or LiGe2(PO4)3, preferably element-doped Li 1+x M x Zr 2-x (PO4)3、Li 1+x M x Ti2-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.), more preferably LiSn 0.4 Zr 1.6 (PO4)3、Li 1.3 Al 0.3 Ti 1.7 (PO4)3 or Li 1.5 Al 0.5 Ge 1.5 (PO4)3; the Perovskite-type electrolyte is preferably 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), more preferably 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 electrolyte is preferably LiSrM2O6F or Li 2-x La (1+x) / 3 M2O6F (M = Nb, Ta), more preferably Li 1.25 La 0.58 Nb2O6F or LiLa 0.66 Ta2O6F.

[0037] In the present invention, the solid electrolyte can be prepared by the common method in the art, such as preparing a precursor powder material by a solid phase reaction method or a sol-gel method, and then calcining the precursor powder material. The corresponding commercial products can also be purchased, and the present invention does not make special requirements for this.

[0038] In the present invention, the solid electrolyte is preferably a solid electrolyte powder. In the present invention, the solid electrolyte is immersed and cleaned in a LiOH aqueous solution, and then dried so that LiOH is fully infiltrated and attached to the surface of the powder.

[0039] In the present invention, the concentration of the LiOH aqueous solution is preferably ≤0.05mol / L, more preferably 0.01-0.05mol / L, such as 0.01mol / L, 0.02mol / L, 0.03mol / L, 0.04mol / L, 0.05mol / L, preferably a range value with the above arbitrary numerical value as the upper or lower limit; the temperature of the alkali washing is preferably 0-50°C, more preferably 15-30°C, such as 5°C, 10°C, 20°C, 25°C, 30°C, 40°C, 45°C, preferably a range value with the above arbitrary numerical value as the upper or lower limit; the time of the alkali washing is preferably 0.5-5min, more preferably 1-4min, such as 0.5min, 1min, 2min, 3min, 4min, 5min, preferably a range value with the above arbitrary numerical value as the upper or lower limit.

[0040] In the present invention, the drying is preferably air-blast drying, which is a commonly used drying method in the art and will not be described in detail in the present invention.

[0041] After completing the above-mentioned alkali washing, the present invention places the alkali-washed and dried solid electrolyte powder in an air atmosphere of constant temperature and humidity, fully exposes it, and ages it, so that the LiOH on the surface of the solid electrolyte reacts with the CO2 in the air to generate Li2CO3. The presence of uneven Li on the surface and the unevenness of the reaction cause a Li2CO3 coating layer with uneven thickness and density to be generated on the surface of the grains.

[0042] In the present invention, the humidity of the air atmosphere is preferably greater than 50%, more preferably 55% to 90%, such as 51%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, preferably a range value with any of the above values ​​as the upper or lower limit.

[0043] In the present invention, the aging temperature is preferably 0-60°C, more preferably 10-50°C, 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, preferably a range value with the above any numerical value as the upper or lower limit; the aging time is preferably 24-48 hours, more preferably 30-40 hours, 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, preferably a range value with the above any numerical value as the upper or lower limit.

[0044] After the above aging is completed, the present invention pickles the aged solid electrolyte in a dilute acid solution and then dries it to obtain a dry powder. The Li2CO3 coating layer on the surface is removed by pickling. Under the condition of a certain concentration of the dilute acid solution, the removal area of ​​the Li2CO3 coating layer is controlled by controlling the pickling time. By adjusting the pickling time variable, the effect of different step-by-step coating areas in the range of 0 to 100% (10%, 20%, 30%, ... 100%) can be achieved.

[0045] In the present invention, the acid in the dilute acid solution is preferably hydrochloric acid, the concentration of the dilute acid solution is preferably 0.05-0.2 mol / L, more preferably 0.1-0.15 mol / L, the pickling time is preferably 10-120 s, more preferably 20-100 s, such as 10s, 15s, 20s, 25s, 30s, 35s, 40s, 45s, 50s, 55s, 60s, 65s, 70s, 75s, 80s, 85s, 90s, 95s, 100s, 105s, 110s, 115s, 120s, preferably a range value with any of the above values ​​as the upper or lower limit.

[0046] After the acid washing is completed, the slurry is filtered and quickly dried to obtain a dry powder. The powder material after acid washing and drying is mixed with an organic carbon source solution, and fully reacted, attached and coated under stirring conditions. After the coating is complete, it is dried to obtain an intermediate partially coated with an organic carbon source.

[0047] In the present invention, the organic carbon source solution preferably includes an organic carbon source and a solvent, and the organic carbon source preferably includes one or more low-molecular and high-molecular polymer materials that can be bonded under Lewis alkaline conditions; the low-molecular materials that are bonded preferably include one or more of citric acid, glucose, sucrose, malic acid, malonic acid, succinic acid and lactic acid; the high-molecular polymer material preferably includes one or more of polydopamine, polytannic acid, polyvinyl chloride, polyaniline, succinonitrile conjugated polymer, phenolic resin, furfural resin, epoxy resin and urea-formaldehyde resin, and the molecular weight of the polymer is preferably 100,000 to 900,000.

[0048] In the present invention, the organic small molecules can be directly adsorbed on the surface for coating through the coordination bonds between the functional groups carboxyl, hydroxyl and the metal cations in the electrolyte; the polymer material coating can be directly added to the polymer through the coordination and complexation of the hydroxyl, carboxyl and metal cations contained therein, or can be added to the corresponding small molecule monomers, in situ polymerization is initiated under the Lewis alkaline environment provided by the "π electron feedback effect" near the metal cations on the electrolyte surface, and then adsorbed and coated through strong coordination. Finally, carbonization is achieved through high-temperature sintering and carbonization.

[0049] In the present invention, the solvent in the organic carbon source is preferably an alcohol solvent, such as methanol, ethanol, isopropanol, etc.; the mass fraction of the organic carbon source solution is preferably 10-50%, more preferably 20-40%, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, preferably a range value with any of the above values ​​as the upper or lower limit.

[0050] In the present invention, the coating temperature is preferably 10 to 50° C., more preferably 20 to 40° C., and the coating time is preferably 2 to 8 hours, more preferably 3 to 6 hours.

[0051] In the present invention, the drying temperature is preferably 80 to 120° C., more preferably 90 to 110° C., most preferably 100 to 105° C., and the drying time is preferably 4 to 8 hours, more preferably 5 to 6 hours.

[0052] After the coating is completed, the present invention calcines the coated intermediate under an inert atmosphere, takes it out and grinds it to obtain a solid electrolyte powder material with a surface carbon coating.

[0053] In the present invention, the inert atmosphere is preferably nitrogen and / or argon; the calcination temperature is preferably 700-900°C, which can ensure that the residual Li2CO3 on the surface is completely reacted and decomposed, and the carbon source is completely carbonized, more preferably 750-850°C, such as 700°C, 720°C, 750°C, 780°C, 800°C, 820°C, 850°C, 880°C, 900°C, preferably a range value with any of the above values ​​as the upper or lower limit; the calcination time is preferably 3-6 hours, more preferably 4-5 hours.

[0054] The present invention also provides a solid electrolyte with a surface carbon coating, which is prepared according to the preparation method described above, and includes a solid electrolyte matrix and a carbon coating layer on the surface of the solid electrolyte matrix, wherein the carbon coating layer is partially dotted. In the solid electrolyte with a surface carbon coating, the mass fraction of the carbon coating layer is 1 to 20%, more preferably 5 to 15%, and the area of ​​the carbon coating layer preferably accounts for 10 to 100% of the total surface area of ​​the solid electrolyte, more preferably 20 to 80%.

[0055] The present invention also provides a lithium ion battery, comprising the above-mentioned solid electrolyte coated with surface carbon.

[0056] The invention provides a method for preparing a solid electrolyte with a surface carbon coating, comprising the following steps: A) washing the solid electrolyte in an alkaline solution, and then aging the washed solid electrolyte in an air atmosphere to generate Li2CO3 on the surface to obtain an aged solid electrolyte; the alkaline solution is a lithium hydroxide aqueous solution; the concentration of the alkaline solution is lower than 0.05 mol / L; B) washing the aged solid electrolyte in a dilute acid solution, and drying after washing to obtain a dry powder; C) mixing the dry powder with an organic carbon source solution, performing a polymerization reaction, and obtaining an intermediate partially coated with the organic carbon source; D) calcining the intermediate partially coated with the organic carbon source in an inert atmosphere to obtain a solid electrolyte with a surface carbon coating. The present invention firstly uses alkali washing to make the surface of the solid electrolyte fully infiltrated with LiOH, and then ages it in air to generate a Li2CO3 coating layer with uneven surface thickness and density. By utilizing the difference in alkalinity between Li2CO3 on the surface of the solid electrolyte grains and the electrolyte itself, and the difference in adsorption capacity for specific organic molecules, the organic carbon source molecules are controlled to achieve different degrees of polymerization and uneven attachment polymerization on the surface of the grains without Li2CO3 coverage, and finally achieve the effect of local coating after calcination.

[0057] The present invention makes the surface carbon coating area more controllable through the alkaline washing + aging method, and is applicable to a wider range of electrolyte types.

[0058] In order to further illustrate the present invention, a surface carbon-coated solid electrolyte, a preparation method and application thereof provided by the present invention are described in detail below in combination with embodiments, but it should not be construed as limiting the scope of protection of the present invention.

[0059] Example 1

[0060] 1. Use solid phase reaction method: firstly, lithium carbonate, zinc oxide and germanium oxide are reacted according to Li 3.3 Zn 0.45 The stoichiometric ratio of GeO4 (LZGO) is weighed, wherein the Li source is a volatile element during the calcination process, so it is 10% in excess. The weighed lithium source, zinc source and germanium source powders are wet-mechanically ball-milled for 12 hours using a planetary ball mill to obtain a precursor slurry, and then dried in an 80°C forced air drying oven for 12 hours to obtain the LZGO electrolyte precursor powder. The precursor is 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;

[0061] 2. The prepared LZGO powder material was heated to a concentration of 0.05 mol·L -1The powder was immersed in a LiOH aqueous solution for 0.5 min, filtered and dried; then placed in a room temperature environment with an air humidity of 75% for full aging for 48 h; then placed in a concentration of 0.05 mol·L －1 The HCl solution was immersed and cleaned for 30 seconds, and then filtered and dried to obtain aged dry powder;

[0062] 3. Place the above-mentioned appropriately dried electrolyte powder in a 30% by mass citric acid ethanol solution, fully mix and stir at 25°C for 6 hours, and then filter and take it out; then place it in a blast drying oven at 100°C and fully dry it for 6 hours, and take it out after cooling to room temperature to obtain the electrolyte powder coated with the organic carbon source;

[0063] 4. Use an atmosphere furnace or a tubular furnace to calcine the above powder in an inert atmosphere at a calcination temperature of 900° C. After keeping warm for 3 hours, cool the furnace to obtain LZGO powder material with a carbon coating area of ​​10%.

[0064] Example 2

[0065] 1. Solid phase reaction method: lithium carbonate, lanthanum oxide, titanium zirconium oxide according to Li 0.34 La 0.56 The stoichiometric ratio of TiO3 (LLTO) is weighed, in which Li is in excess of 10%. The weighed lithium, lanthanum and titanium sources are added to the zirconium oxide ball mill, and an appropriate amount of ethanol dispersant is added for ball milling. Use a planetary ball mill to ball mill for 6 hours at a speed of 500 rpm, take out the slurry and dry it in an 80°C forced air drying oven for 12 hours to obtain the LLTO electrolyte precursor powder. The precursor is 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;.

[0066] 2. The prepared LLTO powder material was heated to a concentration of 0.01 mol·L -1 The powder was immersed in a LiOH aqueous solution for 1 min, filtered and dried; then placed in a room temperature environment with an air humidity of 50% for full aging for 48 h; then the powder was placed in a concentration of 0.1 mol·L -1 The HCl solution was soaked and washed for 20 seconds, and then filtered and dried to obtain aged dry powder;

[0067] 3. Place the above-mentioned appropriately dried electrolyte powder in a 50% by mass citric acid ethanol solution, fully mix and stir at 50°C for 2 hours, and then filter and take it out; then place it in a blast drying oven at 100°C and fully dry it for 6 hours, and take it out after cooling to room temperature to obtain the electrolyte powder coated with the organic carbon source;

[0068] 4. Use an atmosphere furnace or a tubular furnace to calcine the above powder in an inert gas atmosphere at a calcination temperature of 900° C. After keeping the temperature for 3 hours, cool the furnace to obtain an LLZO nanopowder material with a carbon coating area of ​​20%.

[0069] Example 3

[0070] 1. Sol-gel method: lithium nitrate, lanthanum nitrate, zirconium oxynitrate and tantalum ethoxide are mixed according to Li 6.5 LqCy 1.5 Ta 0.5 O 12 The stoichiometric ratio of (LLZTO) is weighed, in which Li is in excess of 10%. The weighed lithium source, lanthanum source, zirconium source and tantalum source are added to deionized water and mixed, and then a complexing agent is added. A transparent gel can be obtained after stirring and dissolving, heating and evaporating at 80°C. Finally, a dry precursor powder is obtained after drying at 140°C for 24 hours. The precursor is calcined in a muffle furnace at 500°C for 3 hours to remove impurity elements such as carbon; then calcined at 800°C for 3 hours to obtain nano LLZTO ceramic powder.

[0071] 2. The prepared LLZTO powder material was heated to a concentration of 0.05 mol·L -1 The powder was immersed in a LiOH aqueous solution for 4 min, filtered and dried; then aged for 24 h at room temperature with an air humidity of 90%; then the powder was placed in a concentration of 0.2 mol·L -1 The HCl solution was immersed and cleaned for 90 seconds, and then filtered and dried to obtain aged dry powder;

[0072] 3. Place the above-mentioned appropriately dried electrolyte powder in a polydopamine ethanol solution with a mass fraction of 10% and a molecular weight of 500,000, fully mix and stir at 10°C for 8 hours, and then filter and take out; then place in a blast drying oven at 120°C and fully dry for 4 hours, and take out after cooling to room temperature to obtain the electrolyte powder coated with the organic carbon source;

[0073] 4. Use an atmosphere furnace or a tubular furnace to calcine the above powder in an inert gas atmosphere at a calcination temperature of 800° C. After keeping the temperature for 3 hours, cool the furnace to obtain a LLZTO nanopowder material with a carbon coating area of ​​20%.

[0074] Example 4

[0075] 1. Use solid phase reaction method: lithium carbonate, germanium oxide, titanium dioxide, and ammonium dihydrogen phosphate are reacted according to Li 1.5 Al 0.5 Ge 1.5The stoichiometric ratio of (PO4)3(LAGP) is weighed, wherein Li is in excess of 10%. The weighed lithium source, germanium source, aluminum source and phosphorus source powders are wet-milled in a planetary ball mill for 12 hours to obtain a precursor slurry. The slurry is dried at 80°C for 12 hours and then ground to obtain a dry precursor powder. The precursor is calcined at 900°C in a muffle furnace for 12 hours to obtain an electrolyte micron-sized powder, which is then mechanically crushed using a sand mill to finally obtain a nano-LAGP powder material.

[0076] 2. The prepared LAGP powder material was heated to a concentration of 0.04 mol·L -1 The powder was immersed in a LiOH aqueous solution for 2 min, filtered and dried; then aged for 30 h at room temperature with an air humidity of 80%; then the powder was placed in a concentration of 0.15 mol·L -1 The HCl solution was soaked and washed for 20 seconds, and then filtered and dried to obtain aged dry powder;

[0077] 3. Place the above-mentioned appropriately dried electrolyte powder in a polydopamine ethanol solution with a mass fraction of 40% and a molecular weight of 100,000, fully mix and stir at 40°C for 6 hours, and then filter and take out; then place in a blast drying oven at 120°C and fully dry for 4 hours, and take out after cooling to room temperature to obtain the electrolyte powder coated with the organic carbon source;

[0078] 4. Use an atmosphere furnace or a tubular furnace to calcine the above powder in an inert gas atmosphere at a temperature of 900° C. After keeping the temperature for 6 hours, cool the furnace to obtain a LAGP nanopowder material with a carbon coating area of ​​40%.

[0079] Example 5

[0080] 1. Sol-gel method: lithium nitrate, aluminum nitrate, tetrabutyl titanate and ammonium dihydrogen phosphate are mixed according to Li 1.3 Al 0.3 Ti 1.7 The stoichiometric ratio of (PO4)3(LATP) is weighed, in which Li is in excess of 10%. The weighed lithium source, aluminum source, titanium source and phosphorus source are added to deionized water and mixed, and then a complexing agent is added. A transparent gel can be obtained after stirring and dissolving, heating and evaporating at 80°C. Finally, a dry precursor powder is obtained after drying at 140°C for 24 hours. The precursor is calcined in a muffle furnace at 500°C for 3 hours to remove impurity elements such as carbon and nitrogen; then calcined in a muffle furnace at 700°C for 3 hours to obtain nano-LATP ceramic powder.

[0081] 2. The prepared LATP powder material was heated to a concentration of 0.04 mol·L -1The powder was immersed in a LiOH aqueous solution for 5 min, filtered and dried; then aged for 36 h at room temperature with an air humidity of 80%; then the powder was placed in a concentration of 0.1 mol·L -1 The HCl solution was immersed and cleaned for 120 seconds, and then filtered and dried to obtain aged dry powder;

[0082] 3. Place the above-mentioned appropriately dried electrolyte powder in a polydopamine ethanol solution with a mass fraction of 30% and a molecular weight of 900,000, fully mix and stir at 30°C for 4 hours, and then filter and take out; then place in a blast drying oven at 80°C and fully dry for 8 hours, and take out after cooling to room temperature to obtain the electrolyte powder coated with the organic carbon source;

[0083] 4. Use an atmosphere furnace or a tubular furnace to calcine the above powder in an inert gas atmosphere at a calcination temperature of 750° C. After keeping warm for 6 hours, cool the furnace to obtain a LATP nanopowder material with a carbon coating area of ​​10%.

[0084] Example 6

[0085] A LATP nanopowder material with a carbon coating area of ​​20% was prepared according to the method in Example 5. The difference was that in step 2 of Example 6, the immersion cleaning was carried out in the HCl solution for 100 seconds.

[0086] Example 7

[0087] A LATP nanopowder material with a carbon coating area of ​​30% was prepared according to the method in Example 5. The difference was that in step 2 of Example 7, the material was immersed and cleaned in the HCl solution for 80 seconds.

[0088] Example 8

[0089] A LATP nanopowder material with a carbon coating area of ​​50% was prepared according to the method in Example 5. The difference was that in step 2 of Example 8, the material was immersed and cleaned in the HCl solution for 60 seconds.

[0090] Example 9

[0091] The LATP nanopowder material with a carbon coating area of ​​80% was prepared according to the method in Example 5. The difference was that in step 2 of Example 9, the material was immersed and cleaned in the HCl solution for 30 seconds.

[0092] Example 10

[0093] A LATP nanopowder material with a carbon coating area of ​​90% was prepared according to the method in Example 5. The difference was that in step 2 of Example 10, the material was immersed and cleaned in the HCl solution for 10 seconds.

[0094] Comparative Example 1

[0095] 1. The nano LLZTO powder material prepared in step 1 of Example 3.

[0096] 2. Place the above-mentioned appropriate amount of dried electrolyte powder in a 50% glucose aqueous solution by mass, fully mix and stir at 25°C for 6 hours, and then filter and take it out; then place it in a blast drying oven at 120°C and fully dry it for 12 hours, and take it out after cooling to room temperature to obtain the electrolyte powder coated with the organic carbon source;

[0097] 3. Use an atmosphere furnace or a tubular furnace to calcine the above powder in an inert gas atmosphere at a temperature of 900° C. After keeping the temperature for 6 hours, cool the furnace to obtain a conventional carbon-coated (fully coated structure) LLZTO nanopowder material.

[0098] Comparative Example 2

[0099] 1. The nano LATP powder material prepared in step 1 of Example 5.

[0100] 2. Place the above-mentioned appropriately dried electrolyte powder in a 30% by mass aqueous solution of citric acid, fully mix and stir at 40°C for 6 hours, and then filter and take it out; then place it in a blast drying oven at 100°C and fully dry it for 12 hours, and take it out after cooling to room temperature to obtain the electrolyte powder coated with the organic carbon source;

[0101] 3. Use an atmosphere furnace or a tubular furnace to calcine the above powder in an inert gas atmosphere at a temperature of 900°C. After keeping the temperature for 12 hours, cool the furnace to obtain a conventional carbon-coated (fully coated structure) LATP nanopowder material.

[0102] Comparative Example 3

[0103] 1. Solid phase reaction method: lithium carbonate, aluminum oxide, titanium oxide and ammonium dihydrogen phosphate are reacted according to Li 1.3 Al 0.3 Ti 1.7 The stoichiometric ratio of (PO4)3(LATP) is weighed, in which Li is in excess of 15%. The weighed lithium source, aluminum source, titanium source and phosphorus source powders are wet-milled in a planetary ball mill for 12 hours to obtain a precursor slurry. The slurry is air-dried at 80°C for 12 hours and then ground to obtain a dry precursor powder. The precursor is calcined at 900°C for 12 hours in a muffle furnace to obtain a micron-sized powder, which is then mechanically crushed in a sand mill to finally obtain a nano-LATP powder material;

[0104] 2. Place the above-mentioned appropriate amount of dried electrolyte powder in a 30% glucose aqueous solution by mass, fully mix and stir at 30°C for 6 hours, and then filter and take out; then place in a 100°C blast drying oven and fully dry for 12 hours, and take out after cooling to room temperature to obtain the electrolyte powder coated with the organic carbon source;

[0105] 3. Use an atmosphere furnace or a tubular furnace to calcine the above powder in an inert gas atmosphere at a temperature of 800°C. After keeping the temperature for 6 hours, cool the furnace to obtain a conventional carbon-coated (fully coated structure) LATP nanopowder material.

[0106] Material testing and characterization

[0107] 1. Phase characterization: X-ray diffractometer was used to characterize the phase structure of electrolyte powder before and after carbon coating; the results are as follows Figure 1 As shown, Figure 1 is the XRD phase spectrum of the carbon-coated LATP nanopowder in Example 6 of the present invention, Figure 1 It can be seen that after alkali washing, acid washing, high-temperature calcination and other processes, the synthesized powder still shows a pure phase, the phase is stable, and it presents a broadened characteristic peak, indicating that its grains are fine nano-scale particles.

[0108] 2. Micromorphology: Use field emission scanning electron microscope (SEM) or high-resolution transmission electron microscope (TEM) to observe and test the micromorphology of sample grain size, surface state, coating condition, etc. The results are as follows: Figures 3-4 As shown, Figure 3 This is a TEM image of the nm-LATP powder material before coating in Example 6 of the present invention; Figure 4 TEM image of 20% local area carbon-coated LATP nanopowder in Example 6 of the present invention; Figure 3 and Figure 4 It can be seen that the grain size before and after coating is 100-200nm. The surface of the grain before coating presents a smooth and non-attached morphology. After partial coating, its surface presents evenly dispersed dark point-like graphitized carbon attachment. The carbon grain size is distributed in the range of 5-20nm and has a regular shape.

[0109] 3. Electronic and ionic conductivity: The electronic conductivity of the powder was quantitatively tested by the four-probe test method and resistivity meter, and the ionic conductivity of the ceramic sheet after cold pressing of the powder was tested by the AC impedance analyzer of the electrochemical workstation. The results are shown in Table 1. The electronic conductivity test results show that the original untreated electrolyte powder has a very low order of magnitude (10 -7 S / cm), but the ionic conductivity is the highest level. With the gradual increase of carbon coating, the electronic conductivity shows a rapid upward trend and reaches the highest level of electronic conductivity in the fully coated state, usually up to 10 -1S / cm; the ionic conductivity gradually decreases with the increase of the coating amount, and is reduced to the lowest level in the 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 on the surface of a fast ion conductor reduces the ion transport channels on the crystal surface and affects the three-dimensional transport of lithium ions in the electrolyte as a whole. Therefore, according to different application conditions, electrolyte powders with suitable electronic / ionic conductivity quantitative relationships should be reasonably selected.

[0110] 4. Carbon graphitization degree: Raman spectrometer is used to characterize the phase and graphitization degree of the surface coated carbon. The characteristic peak D peak (1360cm -1 )、G peak (1580cm -1 ) for peak intensity or integrated intensity comparison, the degree of graphitization of the carbon source can be quantitatively analyzed. The D peak is caused by the incomplete crystal structure caused by the introduction of crystal defects into the carbon after graphitization, which corresponds to the defect peak of the amorphous phase (intensity is recorded as I D ), the G peak corresponds to the regular graphitized crystal structure (intensity is recorded as I G ), its graphitization degree R = I D / I G The lower the R value, the closer it is to the graphite structure; the results are as follows Figure 2 As shown, Figure 2 is the Raman spectrum of the carbon-coated LATP nanopowder in Example 6 of the present invention, Figure 2 It can be seen that after high-temperature calcination, the graphitization degree R=1.01, which is close to the conventional organic carbon source coating process, indicating that the graphitization degree of the organic carbon source is relatively high.

[0111] 5. Carbon content and coating area: Use an element analyzer to quantitatively analyze the carbon element. Since the carbon coating area is directly proportional to the carbon content, the quantitative relationship between the carbon coating content and the carbon coating area can be obtained by separately testing the carbon content of the solid electrolyte with no coating (0%), full coating (100%) and other coating areas.

[0112] Table 1 Electronic conductivity and ionic conductivity of carbon-coated powders in the embodiments of the present invention and comparative examples

[0113]

[0114] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a solid electrolyte coated with carbon on the surface, The following steps are involved: A) The solid electrolyte is washed with alkali solution, and then the washed solid electrolyte is aged in air atmosphere to generate Li 2 CO 3 , obtaining an aged solid electrolyte; The alkali solution is a lithium hydroxide aqueous solution; the concentration of the alkali solution is lower than 0.05 mol / L; B) pickling the aged solid electrolyte in a dilute acid solution, and drying after pickling to obtain a dry powder; C) mixing the dry powder with an organic carbon source solution to coat the powder, thereby obtaining an intermediate partially coated with the organic carbon source; D) calcining the intermediate partially coated with the organic carbon source under an inert atmosphere to obtain a solid electrolyte coated with surface carbon.

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

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

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

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

6. The preparation method according to claim 1, It is characterized in that The organic carbon source includes organic small molecules and / or polymers, wherein the organic small molecules include citric acid, glucose, sucrose, malic acid, malonic acid, succinic acid, succinic acid, and lactic acid; the polymer includes 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.

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

8. A solid electrolyte with a surface carbon coating, prepared according to the preparation method according to any one of claims 1 to 7, comprising a solid electrolyte matrix and a carbon coating layer on the surface of the solid electrolyte matrix, wherein the carbon coating layer presents a local point coating.

9. The surface carbon-coated solid electrolyte according to claim 8, It is 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, It is characterized in that The invention comprises the surface carbon-coated solid electrolyte as claimed in claim 8 or 9.

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