阅读说明：本技术 一种溶胶凝胶法制备的高电导固体电解质 (High-conductivity solid electrolyte prepared by sol-gel method ) 是由 杨程响 石斌 王庆杰 陈晓涛 陈铤 王振 吴宁宁 张红梅 张亮 吴启兵 于 2019-11-25 设计创作，主要内容包括：本发明涉及固体电解质技术领域,具体涉及一种溶胶凝胶法制备的高电导固体电解质,以硝酸锂、氧化锗、正硅酸乙酯中任意一种或多种组合物为掺杂剂,以磷酸钛铝锂为主料,采用溶胶-凝胶法将掺杂剂嵌入磷酸钛铝锂骨架中,形成NASICON结构,本发明的固体电解质晶界阻抗小,离子电导率高,对热处理温度敏感度低,且适用于工业化生产,集成了传统溶胶凝胶合成温度低、能耗少、产物纯度高、颗粒粒径小、致密度高的特点,采用柠檬酸以及乙二醇为助剂,又防止了环境污染,并且合理控制温度以及搅拌速率,降低了成本。(The invention relates to the technical field of solid electrolytes, in particular to a high-conductivity solid electrolyte prepared by a sol-gel method, which takes any one or more of lithium nitrate, germanium oxide and ethyl orthosilicate as a dopant, takes lithium aluminum titanium phosphate as a main material, and adopts a sol-gel method to embed the dopant into a lithium aluminum titanium phosphate framework to form an NASICON structure.)

1. A high-conductivity solid electrolyte prepared by sol-gel is characterized in that any one or more of lithium nitrate, germanium oxide and ethyl orthosilicate is used as a dopant, Lithium Aluminum Titanium Phosphate (LATP) is used as a main material, and the dopant is embedded into a Lithium Aluminum Titanium Phosphate (LATP) framework by a sol-gel method to form an NASICON structure.

2. The sol-gel prepared high conductivity solid electrolyte of claim 1, wherein the dopant is germanium oxide: 1:1 in weight percent.

3. The sol-gel produced high conductivity solid electrolyte of claim 1 wherein said LATP is Li_1.3Al_0.3Ti_1.7(PO₄)₃。

4. The sol-gel prepared high conductivity solid electrolyte as claimed in claim 1, wherein said LATP is prepared from tetrabutyl titanate, lithium salt, ammonium dihydrogen phosphate, aluminum nitrate, and Li_1.3Al_0.3Ti_1.7(PO₄)₃Calculating and weighing the stoichiometric ratio; namely, lithium salt: aluminum nitrate: tetrabutyl titanate: the molar ratio of ammonium dihydrogen phosphate was 1.3:0.3:1.7: 3.

5. A sol-gel prepared high conductivity solid electrolyte according to claim 1, wherein the lithium salt is any one of lithium nitrate or lithium acetate.

6. The sol-gel prepared high-conductivity solid electrolyte according to claim 1, wherein the sol-gel process comprises the following steps:

step 1: weighing tetrabutyl titanate, adding ammonia water for dissolving, performing suction filtration and washing, slowly adding the washed tetrabutyl titanate into 0.4mol/L citric acid solution, heating, magnetically stirring for 6 hours, and forming clear liquid to obtain solution A;

step 2: weighing lithium salt and ammonium dihydrogen phosphate, uniformly mixing the lithium salt, the ammonium dihydrogen phosphate and citric acid, wherein the molar ratio of the citric acid to the metal cations is 2:1, and adding deionized water to completely dissolve the mixture to obtain a solution B;

and step 3: weighing aluminum nitrate, uniformly mixing the aluminum nitrate and citric acid, wherein the molar ratio of the citric acid to the metal cations is 2:1, and adding deionized water to completely dissolve the mixture to obtain a solution C;

and 4, step 4: weighing a doping agent and ethylene glycol, sequentially adding the solution B, C, the doping agent and the ethylene glycol into the solution A, and magnetically stirring for 8 hours under a heating condition to form white gel; wherein the molar ratio of the ethylene glycol to the citric acid is 1: 1;

and 5: transferring the white gel into a forced air drying oven to be dried to form a dark block, and obtaining a precursor;

step 6: heating the precursor to a pre-sintering temperature in air at a heating rate of 3-5 ℃/min, preserving heat for 8-12h at the pre-sintering temperature, naturally cooling to obtain a light gray block, and performing mechanical dry ball milling for 8-10h to obtain LATP pre-sintering powder;

and 7: and heating the LATP pre-sintered powder to the calcining temperature at the heating rate of 3-5 ℃/min, and preserving the heat at the calcining temperature to obtain a solid electrolyte sintered body.

7. The sol-gel produced high conductivity solid electrolyte of claim 6, wherein the magnetic stirring is performed at a rate of 50 to 150 rpm.

8. The sol-gel produced high-conductivity solid electrolyte according to claim 6, wherein the heating temperature is 85 to 95 ℃.

9. The sol-gel prepared high-conductivity solid electrolyte as claimed in claim 6, wherein the pre-firing temperature is 650-800 ℃.

10. The sol-gel prepared high conductivity solid electrolyte as claimed in claim 6, wherein the calcination temperature is 900-1000 ℃.

Technical Field

The invention relates to the technical field of solid electrolytes, in particular to a high-conductivity solid electrolyte prepared by a sol-gel method.

Background

With the increase of the use amount of energy and the gradual depletion of non-renewable resources in the development of the industrial society, the demand of people on new energy is more and more urgent, and the requirement on the energy storage technology is more and more strict. The lithium ion battery has a very wide development prospect in the aspect of energy storage due to the high energy density and long service life.

At present, the commercial lithium ion battery adopts organic electrolyte, and the organic electrolyte is easy to burn and leak, so that great potential safety hazard exists when the organic electrolyte is used on a large scale. Solid-state batteries have high thermal stability and good safety performance, have attracted much attention in recent years, and are considered to be the key development direction of next-generation lithium ion batteries. The core of the solid-state battery is a solid electrolyte, which is divided into an oxide solid electrolyte and a sulfide solid electrolyte. The sulfide solid electrolyte has high ionic conductivity, but has high hygroscopicity and poor environmental stability, and is difficult to realize commercial application. Most studied are oxide solid electrolytes in which Li1+ xAlxTi2-x (PO4)3(LATP) having a NASICON structure is receiving much attention due to a wide electrochemical window and high ionic conductivity.

In the prior art, oxide solid electrolytes are mainly prepared by means of a coprecipitation method, a sol-gel method, a solvent method, a microwave synthesis method, an electrostatic spinning method, a high-temperature solid phase method and the like, for example, patent number CN201810697845.9 discloses a novel lithium ion conduction oxide solid electrolyte and a preparation method thereof, and specifically, raw materials are weighed according to a designed stoichiometric ratio and are subjected to wet ball milling and mixing; calcining the mixed raw materials step by step to prepare solid electrolyte powder; maintaining the pressure of the solid electrolyte powder for 30-60 min under a proper pressure condition, then embedding the blank body into the powder with the same components, heating to 1100-1200 ℃ at a speed of 1-2 ℃/min, and preserving the heat for 12-24 h to prepare the required solid electrolyte, wherein the calcination temperature is too high, the energy consumption is high, and impurities are difficult to recycle due to direct calcination; CN201710962086.X discloses an oxide solid electrolyte based on lithium halide doping and a low-temperature sintering method thereof, in particular to a solid electrolyte which takes perovskite type, NASICON type and garnet type electrolytes as matrixes, uses the composition of a lithium halide solution and the oxide solid electrolyte and is sintered at low temperature; the preparation method mainly comprises the steps of carrying out ball milling on LATP, LLTO and LLZO solid electrolytes or ball milling and sintering self-made cubic-phase lithium lanthanum zirconium oxygen solid electrolyte powder to prepare cubic-phase LLZO solid electrolyte powder, adding LiX solution into the solid electrolyte powder, pressing into a sheet or coating the sheet into a film, and sintering the sheet or film in a muffle furnace at the low temperature of 100-250 ℃ for 1-10 hours, wherein the raw materials are strictly screened, have high cost and are difficult to obtain; at present, most of the existing oxide solid electrolytes stay in a laboratory stage, and the preparation method has high energy consumption, long time consumption and high dependence of electrical conductivity on heat treatment temperature. In addition, based on the consideration of industrialization factors, the coprecipitation method, the sol-gel method and the high-temperature solid phase method are more suitable for large-scale synthesis, but the prepared solid electrolyte has large grain boundary resistance, low ionic conductivity and sensitivity to heat treatment temperature.

The sol-gel method generally comprises mixing various salts into a solution, heating to form a sol, then carrying out gelation, and carrying out a series of heat treatments to obtain a target product. In the preparation process, factors such as pH value, reaction temperature, reaction concentration, solvent type and the like have great effects on the appearance and electrochemical performance of the product. The method has the advantages of low synthesis temperature, low energy consumption, high product purity, basically no impurity phase, small particle size, high density, effective reduction or avoidance of grain boundary impedance, and suitability for preparing nano active materials.

Disclosure of Invention

The invention provides a high-conductivity solid electrolyte prepared by a sol-gel method to solve the technical problems.

The method is realized by the following technical scheme:

a high-conductivity solid electrolyte prepared by sol-gel takes one or more of lithium nitrate, germanium oxide and ethyl orthosilicate as a dopant, takes titanium aluminum lithium phosphate (LATP) as a main material, and adopts a sol-gel method to embed the dopant into a titanium aluminum lithium phosphate (LATP) framework to form an NASICON structure.

Further preferably, the dopant is germanium oxide: 1:1 in weight percent.

Said LATP is Li_1.3Al_0.3Ti_1.7(PO₄)₃。

The LATP is prepared from tetrabutyl titanate, lithium salt, ammonium dihydrogen phosphate and aluminum nitrate_1.3Al_0.3Ti_1.7(PO₄)₃Calculating and weighing the stoichiometric ratio; namely, lithium salt: aluminum nitrate: tetrabutyl titanate: the molar ratio of ammonium dihydrogen phosphate was 1.3:0.3:1.7: 3.

The lithium salt is any one of lithium nitrate or lithium acetate.

The sol-gel method comprises the following steps:

step 1: weighing tetrabutyl titanate, adding ammonia water for dissolving, performing suction filtration and washing, slowly adding the washed tetrabutyl titanate into 0.4mol/L citric acid solution, heating, magnetically stirring for 6 hours, and forming clear liquid to obtain solution A;

step 2: weighing lithium salt and ammonium dihydrogen phosphate, uniformly mixing the lithium salt, the ammonium dihydrogen phosphate and citric acid, wherein the molar ratio of the citric acid to the metal cations is 2:1, and adding deionized water to completely dissolve the mixture to obtain a solution B;

and step 3: weighing aluminum nitrate, uniformly mixing the aluminum nitrate and citric acid, wherein the molar ratio of the citric acid to the metal cations is 2:1, and adding deionized water to completely dissolve the mixture to obtain a solution C;

and 4, step 4: weighing a doping agent and ethylene glycol, sequentially adding the solution B, C, the doping agent and the ethylene glycol into the solution A, and magnetically stirring for 8 hours under a heating condition to form white gel; wherein the molar ratio of the ethylene glycol to the citric acid is 1: 1;

and 5: transferring the white gel into a forced air drying oven to be dried to form a dark block, and obtaining a precursor;

step 6: heating the precursor to a pre-sintering temperature in air at a heating rate of 3-5 ℃/min, preserving heat for 8-12h at the pre-sintering temperature, naturally cooling to obtain a light gray block, and performing mechanical dry ball milling for 8-10h to obtain LATP pre-sintering powder;

and 7: and heating the LATP pre-sintered powder to the calcining temperature at the heating rate of 3-5 ℃/min, and preserving the heat at the calcining temperature to obtain a solid electrolyte sintered body.

The magnetic stirring speed is 50-150 r/min.

The heating temperature is 85-95 ℃.

The pre-sintering temperature is 650-800 ℃.

The calcination temperature is 900-1000 ℃.

In the sol-gel preparation method, the adding amount of the dopant is calculated by a molar ratio, and specifically is as follows:

① when the doping agent is lithium nitrate, the lithium salt is lithium acetate, the mol ratio of lithium nitrate and lithium acetate is 1: 10;

② when the doping agent is germanium oxide, the lithium salt is lithium nitrate, the mol ratio of germanium oxide and tetrabutyl titanate is 1: 16;

③ when the dopant is ethyl orthosilicate, the lithium salt is lithium acetate, the mol ratio of ethyl orthosilicate and tetrabutyl titanate is 1: 16;

④ when the dopant is germanium oxide and ethyl orthosilicate composition, the lithium salt is selected from lithium nitrate, and the molar ratio of ethyl orthosilicate, germanium oxide and tetrabutyl titanate is 1:1: 14.

The technical principle is as follows:

to solve the problem of preparing solid electrolyte Li by a sol-gel method_1.3Al_0.3Ti_1.7(PO₄)₃The problem of low ionic conductivity, the invention is based on element dopingHetero-modification mechanism to solid electrolyte Li_1.3Al_0.3Ti_1.7(PO₄)₃Processing by doping lithium nitrate, germanium oxide and ethyl orthosilicate and controlling the heat treatment conditions to the solid electrolyte Li_1.3Al_0.3Ti_1.7(PO₄)₃Crystal structure (lattice size, unit cell volume, theoretical density) and ionic conductivity are improved;

according to the method, the heating condition and the magnetic stirring speed are controlled before the gel is formed, the particles randomly jump at the equilibrium position of the condensed substance under the action of temperature, and the particles deviate from the equilibrium position under the action of the stirring force, so that the concentration of movable ions is adjusted, and the improvement of the ionic conductivity, the mobility, the density of defect sites in crystal lattices and the characteristics of crystal boundaries is facilitated.

The method also regulates and controls the height, hopping frequency and average hopping distance of the ion-separated equilibrium position potential barrier by regulating the preburning temperature, and further regulates the mobility and diffusion coefficient.

According to the method, lithium nitrate is used as a doping agent, and an aliovalent element is used for replacing doping to regulate the concentration of a vacancy, so that the loss of high-temperature volatilization of lithium oxide is made up; germanium oxide is used as a doping agent to regulate the size of an ion diffusion channel, so that the ion migration capacity is improved; tetraethoxysilane is used as a doping agent, and the ion conductivity is regulated and controlled by regulating and controlling the property of a space charge layer at an interface through interface modification and interface element enrichment.

The crystal grains with different structures or different orientations are contacted with each other through doping to form a compound with an NASICON structure again, so that the sintering performance is improved, the crystal grain boundary resistance is reduced, the conductivity of the material is improved, the doping substitution work of a Ti position and a P position can be realized, the sintering degree is improved, the crystal grain boundary resistance is reduced, the dosage ratio is strictly controlled, and the conductivity is obviously reduced due to the excessive dosage of a doping agent; the density of defect sites in the crystal lattice cannot be filled up due to too small dosage of the dopant.

According to the method, the solid phase is formed by pre-sintering and then calcined, so that the low-melting-point substance can be filled in the inter-grain gaps in the sintering process in the high-temperature solid-phase synthesis process, and the interface connection is improvedThe density is improved, and the Li + concentration at the crystal boundary is improved, so that the ionic conductivity is improved; when trivalent ions (e.g. Al) replace Ti⁴⁺The lithium ion conductivity is greatly improved along with the great reduction of the porosity in the material at the octahedral position of (A);

citric acid and glycol are adopted as auxiliary agents, so that the method belongs to an environment-friendly method and is low in cost; and then, the carbon source contained in the carbon source is reduced into a carbon simple substance by high-temperature sintering, so that a carbon modification layer is formed, and the oxidation degree is weakened.

The sol-gel method has the following beneficial effects:

the solid electrolyte has small grain boundary impedance, high ionic conductivity and low sensitivity to heat treatment temperature, and is suitable for industrial production; the method integrates the characteristics of low synthesis temperature, low energy consumption, high product purity, small particle size and high density of the traditional sol-gel, adopts citric acid and glycol as additives, prevents environmental pollution, reasonably controls the temperature and stirring speed and reduces the cost.

Detailed Description

The following is a detailed description of the embodiments of the present invention, but the present invention is not limited to these embodiments, and any modifications or substitutions in the basic spirit of the embodiments are included in the scope of the present invention as claimed in the claims.