CN107611476B

CN107611476B - Inorganic solid electrolyte with amorphous substance on surface and preparation method thereof

Info

Publication number: CN107611476B
Application number: CN201710833796.2A
Authority: CN
Inventors: 许晓雄; 张秩华; 黄祯; 赵嫣然; 杨菁; 陈少杰
Original assignee: Zhejiang Feng Li Amperex Technology Ltd
Current assignee: Zhejiang Feng Li Amperex Technology Limited
Priority date: 2017-09-15
Filing date: 2017-09-15
Publication date: 2020-03-31
Anticipated expiration: 2037-09-15
Also published as: CN107611476A

Abstract

The invention provides a preparation method of an inorganic solid electrolyte with an amorphous substance on the surface, which comprises the following steps: A) preparing an amorphous substance with the same chemical composition as the solid electrolyte matrix material by adopting a melting-quenching method or a high-energy ball milling method; B) mixing the amorphous substance, the binder and the solvent to obtain composite material slurry; C) and coating the composite material slurry on the surface of the solid electrolyte matrix material, removing the solvent and the binder, and softening the amorphous substance to obtain the inorganic solid electrolyte with the amorphous substance on the surface.

Description

Inorganic solid electrolyte with amorphous substance on surface and preparation method thereof

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to an inorganic solid electrolyte with an amorphous substance on the surface and a preparation method thereof.

Background

Lithium secondary batteries are widely used in daily life due to their advantages of high output power, high energy density, excellent cycle performance, no memory effect, no environmental pollution, etc., and are the first choice of rechargeable power sources for portable electronic products, and are also considered to be the most competitive power batteries for vehicles.

At present, commercial lithium ion batteries widely use liquid electrolytes and are characterized by higher conductivity and excellent electrochemical performance. However, the liquid electrolyte has a low flash point, and may cause spontaneous combustion due to heating of the electrolyte and even safety problems such as explosion in abnormal conditions such as heavy current discharge, overcharge, and internal short circuit. Meanwhile, in view of safety, various electronic products often use graphite as a negative electrode. However, the theoretical specific capacity of the graphite is only 372mAh/g, and a large irreversible capacity loss exists in the first charging and discharging process, so that the graphite is difficult to be used as a negative electrode material of a high-specific-energy secondary battery. With the continuous development of science and technology and the urgent need for high specific energy negative electrode materials, the research on the use of metallic lithium as the negative electrode material of secondary batteries is receiving attention again. However, its charge density is so high that it can easily polarize other molecules or ions, causing instability factors and safety hazards in the power supply devices filled with the whole liquid electrolyte. Therefore, the development of new materials which are chemically stable to lithium metal and have good lithium ion conductivity characteristics plays an important role in the development of various secondary battery technologies with high energy density and long cycle based on lithium metal negative electrodes.

The all-solid-state lithium secondary battery using the solid electrolyte has incomparable safety with a liquid-state lithium secondary battery, is expected to thoroughly eliminate potential safety hazards in the use process, and more meets the requirements of future development in the fields of electric automobiles and large-scale energy storage. The solid electrolytes currently under extensive study can be roughly classified into two types: inorganic electrolytes and polymer electrolytes. Inorganic electrolytes can be further classified into crystalline and amorphous states, and the crystalline state can be further classified into sulfide and oxide.

Sulfide has high ionic conductivity, but since oxygen-lithium bonds are much stronger than sulfur-lithium ionic bonds at an electrode/solid electrolyte interface, and a commercial positive electrode material is usually an oxide, a high-resistance schottky type space charge layer will be generated at the electrode/electrolyte interface, resulting in a battery having high direct current internal resistance and poor cycle performance. Meanwhile, part of sulfide electrolyte containing high-valence Ge element is unstable to lithium metal (such as LGPS), and mixed conductor layer and high-resistance substance are generated at the interface after contacting with lithium metal.

The oxide electrolyte such as NASICON structure LAGP, LATP, perovskite structure LLTO, garnet structure LLZO, LISICON structure LGZO and the like has the advantages of low cost, good mechanical property, easy processing, good chemical stability, conductivity close to that of sulfide electrolyte, and large application space and practical value. However, although the lithium dendrite growth phenomenon in the battery due to non-uniform deposition and dissolution of lithium can be suppressed by the high shear modulus solid electrolyte, there are some problems that the application of metallic lithium in the oxide electrolyte-based all-solid lithium battery poses a challenge: firstly, the interface resistance is large and the dynamic performance of the battery is poor due to solid point contact between metal lithium and electrolyte; secondly, in the process of charging and discharging, especially under large multiplying power, the volume expansion and contraction of the metal lithium can generate gradually accumulated stress on the interface, and electricityThe mass of the solution is deformed so as to break, further worsening the contact; III, metallic lithium and metallic element with high valence (such as Ti)⁴⁺、Ge⁴⁺) The solid electrolyte has continuous interface reaction penetrating into the electrolyte body to generate an ion-electron mixed conductive area and a low-conductivity byproduct, and the structural strength of interface contact and the electrolyte body is damaged while the conductivity of lithium ion is reduced. Fourthly, spontaneous chemical reaction is generated between the metal lithium and part of electrolyte (such as LLZO) grain boundary substances with low density, and an electronic conductive phase is generated, so that the battery is short-circuited.

The amorphous electrolyte is mainly a thin film prepared by a phase deposition method from amorphous Li-P-O-N, Li-B-Si-O, Li-B-P-O-N and the like. Their ionic conductivity is generally 10^-6The lithium ion battery can only be arranged in an ultrathin battery in a thin layer mode below S/cm, the positive and negative electrode loading capacity of the battery is extremely low, and the requirement of various fields on high energy of the solid lithium battery is not met.

The polymer solid electrolyte, such as a thin film formed by complexing lithium salt and linear polyether, has a simpler preparation process, good film-forming property, high viscoelasticity and lighter weight. But the room temperature conductivity is lower, the mechanical property is poorer, and the penetration of lithium dendrite is difficult to inhibit.

In order to solve the problems of stability and contact of metallic lithium as a negative electrode in an all-solid battery and to achieve high energy density of the all-solid battery, it is necessary to combine the respective advantages of various electrolytes. How to find the balance point of the components, structures and forms of the structure-activity relationship of each component, inhibit the growth of lithium dendrite while preventing the direct contact of the metal lithium and the electrolyte from generating chemical reaction, improve the solid contact interface of the electrolyte/electrode and achieve the long cycle stability of the negative electrode side of the solid-state battery is a technical problem which needs to be solved urgently.

In the aspect of modifying the solid electrolyte by inorganic substances, Masashikobuki and Xiiaogang Han select alumina with a nano-scale thickness by magnetron sputtering on the surface of LLZO, and the Masashikobuki and Xiiaogang consider that Li-Al-O compounds formed on the surface of the electrolyte due to element diffusion can not only increase the contact degree of metallic lithium on the surface of the lithium, but also do not influence the original electrolyte conductanceAnd (4) rate. Mitsuyasu Ogawa sputters a thin layer of Si, Sn and Al on the surface of the metal lithium, and the thin layer of Si can effectively inhibit the reduction of the electrolyte and enhance the interface stability by respectively taking the negative electrode and the sulfide as the electrolyte and taking lithium cobaltate as the positive electrode to assemble the battery. Patent CN 104183871A mentions that Li: BPO₄As a new layer of electrolyte, thermally sprayed to the original electrolyte Li₇La₃Zr₂O₁₂On the substrate. These methods gain good modification effect to a certain extent, but because the modification layer is still crystalline, lithium dendrite may grow in the electrolyte grain boundary, and at the same time, the Li/electrolyte interface is still in rigid contact, the contact area is limited, and interface compatibility cannot be further improved.

In the aspect of modifying the solid electrolyte by the polymer, the LATP is used as the solid electrolyte by Kaoru Dokko, after the lithium manganate material is prepared by spin coating the positive electrode, a layer of PMMA-LiClO is coated on the surface of the negative electrode₄the-EC-DEC semi-liquid electrolyte is used as a lithium metal interface modification layer, and the battery can obtain 60mAh g at ambient temperature^-1But does not show the help of this interfacial layer in improving the cycling stability of the battery. Y Kobayashi uses ethylene oxide co-2- (2-methoxyethoxy) ethyl ether spray to improve the contact of LLTO with lithium metal negative electrodes, but the cycling performance is not yet effectively improved and the 50 cycle cell capacity decays to nearly half of the initial. More importantly, the shear modulus of polymer electrolytes is often very low, especially at operating temperatures (above 60 ℃) much less than that of inorganic solid-state electrolytes. This makes it impossible to prepare thin layers for lower resistance in applications where lithium dendrites would otherwise rapidly grow, breaking through the polymer modification layer, allowing the lithium to contact the inner electrolyte again, causing possible side reactions and worsening of the interfacial conductance.

Summarizing the above technical features, the following two problems can be found:

firstly, the crystalline substance has no obvious effect of modifying the interface, and the intrinsic properties of multiple grain boundaries and high rigidity determine that the crystalline substance cannot both stabilize lithium and make good contact, namely the compatibility is poor.

Secondly, in the existing polymer modification, although the polymer modification is effective in a short time, the potential danger of lithium dendrite exists frequently, and the good compatibility of the electrolyte to the metallic lithium is not really realized.

Disclosure of Invention

In view of the above, the technical problem to be solved by the present invention is to provide an inorganic solid electrolyte with an amorphous surface and a preparation method thereof, and the inorganic solid electrolyte with an amorphous surface is a pure inorganic solid electrolyte with coexistent amorphous and crystalline states and integrated in multiple layers, so as to solve the problems of unstable solid electrolyte/metal lithium interface and poor contact compatibility in an all-solid battery.

The invention provides a preparation method of an inorganic solid electrolyte with an amorphous substance on the surface, which comprises the following steps:

A) preparing an amorphous substance with the same chemical composition as the solid electrolyte matrix material by adopting a melting-quenching method or a high-energy ball milling method;

B) mixing the amorphous substance, the binder and the solvent to obtain composite material slurry;

C) and coating the composite material slurry on the surface of the solid electrolyte matrix material, removing the solvent and the binder, and softening the amorphous substance to obtain the inorganic solid electrolyte with the amorphous substance on the surface.

Preferably, the melt-quenching method is:

preserving the heat of the mixture of the raw material substances for 1-24 hours at 700-900 ℃;

crushing the product, preserving heat for 1-24 hours at 1200-1500 ℃, and quenching by adopting liquid nitrogen to obtain a solid electrolyte matrix material amorphous block;

and crushing the amorphous block of the solid electrolyte matrix material to obtain an amorphous substance with the same chemical composition as the solid electrolyte matrix material.

Preferably, the high-energy ball milling method comprises the following steps:

and (3) placing the ball grinding balls and the solid electrolyte matrix material in a ball grinding tank according to the mass ratio of (5-30): 1, and carrying out ball grinding for 1-50 h at the rotating speed of 400-600 rpm to obtain the amorphous substance with the same chemical composition as the solid electrolyte matrix material.

Preferably, the mass ratio of the amorphous substance to the binder to the solvent is 1 (2-5) to 8.

Preferably, the binder is selected from one or more of cellulose nitrate, polyvinyl alcohol, polyvinylidene fluoride, polyoxyethylene and hydroxycellulose.

The solvent is one or more selected from water, ethanol, acetonitrile, tetrahydrofuran, acetone, dimethyl sulfoxide and terpineol.

Preferably, the softening temperature is 500-700 ℃, and the softening time is 1-24 h.

Preferably, the solid electrolyte matrix is selected from a NASICON structure or a perovskite structure, and the amorphous substance is selected from amorphous lithium aluminum (germanium) titanium phosphate or amorphous lithium lanthanum titanate.

The invention also provides the inorganic solid electrolyte with the amorphous substance on the surface, which is prepared by the preparation method, and the inorganic solid electrolyte comprises a solid electrolyte matrix and an amorphous substance layer compounded on the surface of the solid electrolyte matrix, wherein the amorphous substance is the same as the chemical component of the solid electrolyte matrix material.

Preferably, the amorphous material layer has a thickness of 0.1 to 50 μm.

Compared with the prior art, the invention provides a preparation method of an inorganic solid electrolyte with an amorphous substance on the surface, which comprises the following steps: A) preparing an amorphous substance with the same chemical composition as the solid electrolyte matrix material by adopting a melting-quenching method or a high-energy ball milling method; B) mixing the amorphous substance, the binder and the solvent to obtain composite material slurry; C) and coating the composite material slurry on the surface of the solid electrolyte matrix material, removing the solvent and the binder, and softening the amorphous substance to obtain the inorganic solid electrolyte with the amorphous substance on the surface. The non-grain boundary characteristic of the amorphous substance compounded on the surface of the solid electrolyte matrix can fundamentally kill the growth of lithium dendrites in the grain boundary, and the softer texture can generate plastic deformation to a certain extent, so that the method has greater advantages in the aspects of contact with lithium and stress release. Meanwhile, although the electrolyte has the same chemical element composition with the inorganic crystalline state electrolyte matrix, the reaction of lithium metal and specific elements in the electrolyte is inhibited by utilizing the disorder, large atom disorder degree and uneven element distribution of an amorphous structure, and the original ordered electronic channel is damaged, so that the interior of the amorphous is separated from the surface layer, the metal lithium is prevented from directly contacting with more specific elements to generate chemical reaction, the solid electrolyte of the matrix part is greatly protected, the high impedance of the solid contact interface of the electrolyte/electrode is reduced, and the composite pure inorganic solid electrolyte which is stable to lithium and has good contact is obtained.

Drawings

FIG. 1 is a scanning electron microscope image of an inorganic solid electrolyte having an amorphous material on the surface prepared in example 1;

fig. 2 is an XRD comparison pattern of the surface layer and the inner layer of the inorganic solid electrolyte of which the surface is an amorphous substance in example 1;

FIG. 3 shows the Li/Li symmetrical cell assembled by the inorganic solid electrolyte with amorphous surface in example 1 at 60 deg.C and 0.1mA cm^-2A lower charge-discharge cycle time-voltage plot;

FIG. 4 is a diagram of AC impedance monitoring at 60 ℃ of a Li/Li symmetrical battery assembled by an inorganic solid electrolyte with an amorphous substance on the surface in example 1;

FIG. 5 is an XRD contrast plot of amorphous and crystalline electrolytes prepared in example 2;

fig. 6 is an SEM image of the surface and cross-section of the inorganic solid electrolyte with an amorphous substance on the surface prepared in example 2;

FIG. 7 is a Li/Li symmetrical battery assembled by the inorganic solid electrolyte with amorphous surface in example 2 at 60 deg.C and 0.3mA cm^-2A lower charge-discharge cycle time-voltage plot;

FIG. 8 is an XRD pattern of amorphous and crystalline electrolytes prepared in example 3;

fig. 9 is a cross-sectional SEM image of the inorganic solid electrolyte with an amorphous substance on the surface prepared in example 3;

FIG. 10 shows a schematic view of a liquid crystal display device in example 3The Li/Li symmetrical battery assembled by the inorganic solid electrolyte with amorphous substance on the surface is at 60 ℃ and 0.3mA cm^-2A lower charge-discharge cycle time-voltage plot;

FIG. 11 is an XRD pattern of amorphous and crystalline electrolytes prepared in example 4;

FIG. 12 is a surface layer microtopography of an inorganic solid electrolyte with an amorphous material on the surface prepared in example 4;

FIG. 13 is an AC impedance monitoring of a Li/Li symmetrical battery assembled by an inorganic solid electrolyte with an amorphous surface prepared in example 4 of the present invention at 60 ℃;

FIG. 14 shows a Li/Li symmetrical battery assembled by the inorganic solid electrolyte with amorphous surface prepared in example 4 of the present invention at 60 deg.C and 0.1mA cm^-2A lower charge-discharge cycle time-voltage plot;

FIG. 15 is an XRD pattern of amorphous and crystalline electrolytes prepared in example 5;

FIG. 16 is a scanning electron micrograph of an inorganic solid electrolyte having an amorphous surface prepared according to example 5;

FIG. 17 shows AC impedance monitoring of a Li/Li symmetrical battery assembled from the inorganic solid electrolyte with amorphous material on the surface prepared in example 5 at 60 ℃;

FIG. 18 shows Li in comparative example 1 of the present invention_1.5Al_0.5Ge_1.5(PO₄)₃A cross-sectional scanning electron micrograph of the electrolyte sheet before (a) and after (b) contacting with metallic lithium at 60 ℃ for 72 hours;

FIG. 19 shows Li in comparative example 1 of the present invention_1.5Al_0.5Ge_1.5(PO₄)₃An electrolyte sheet is assembled with an alternating current impedance monitoring chart of the Li/Li symmetrical battery at 60 ℃;

FIG. 20 Li in comparative example 1 of the present invention_1.5Al_0.5Ge_1.5(PO₄)₃The electrolyte sheet is assembled into a Li/Li symmetrical battery at 60 ℃ and 0.1mA cm^-2A lower charge-discharge cycle time-voltage plot;

FIG. 21 shows Li in comparative example 2 of the present invention_1.5Al_0.5Ti_1.5(PO₄)₃Electrolyte sheet and metallic lithium 60 DEG CScanning electron micrographs of the cross section of (a) and (b) before and after 72 hours of lower contact;

FIG. 22 shows Li in comparative example 2 of the present invention_1.5Al_0.5Ti_1.5(PO₄)₃The electrolyte sheet is assembled into a Li/Li symmetrical battery at the temperature of 60 ℃ and the temperature of 0.1mAcm^-2A lower charge-discharge cycle time-voltage plot;

FIG. 23 shows Li in comparative example 2 of the present invention_1.5Al_0.5Ti_1.5(PO₄)₃An electrolyte sheet is assembled into an alternating current impedance monitoring graph of the Li/Li symmetrical battery at 60 ℃;

FIG. 24 shows Li in comparative example 3 of the present invention_0.35La_0.55TiO₃A surface scanning electron micrograph of the electrolyte sheet before (a) and after (b) contacting with metallic lithium at 60 ℃ for 72 hours;

FIG. 25 shows Li in comparative example 3 of the present invention_0.35La_0.55TiO₃The electrolyte sheet is assembled into a Li/Li symmetrical battery at 60 ℃ and 0.3mA cm^-2Time-voltage diagram of the following charge-discharge cycle.

Detailed Description

The invention adopts a melting-quenching method or a high-energy ball milling method to prepare the amorphous substance with the same chemical composition as the solid electrolyte matrix material.

Wherein the melting-quenching method comprises the following steps:

crushing the solid electrolyte matrix material, preserving heat for 1-24 hours at 1200-1500 ℃, and quenching by adopting liquid nitrogen to obtain an amorphous block of the solid electrolyte matrix material;

The source and preparation method of the solid electrolyte matrix material are not particularly limited, and the preparation method known to those skilled in the art can be used.

In the present invention, the solid electrolyte matrix material is preferably prepared as follows:

and uniformly mixing the raw material substances according to the stoichiometric ratio of the chemical formula of the solid electrolyte matrix material to obtain a mixture of the raw material substances, wherein the mixing container is preferably a ball milling tank.

Then, preserving the heat of the mixture for 1-24 hours at 700-900 ℃; preferably, the temperature is kept for 5 to 20 hours under the condition of 750 to 850 ℃. Through the above operation, volatile gas in the mixture is released, and a crystalline electrolyte matrix is obtained.

And (3) crushing the product, and then preserving heat for 1-24 hours at 1200-1500 ℃, preferably for 2-20 hours at 1300-1400 ℃, preferably in a platinum crucible, and pouring into liquid nitrogen for quenching after heat preservation is finished to obtain the amorphous block of the solid electrolyte matrix material.

The invention can also adopt a high-energy ball milling method to prepare amorphous substances with the same chemical components as the solid electrolyte matrix material.

The high-energy ball milling method comprises the following specific steps:

The rotating speed is preferably 450-550 rpm, and the ball milling time is preferably 10-35 hours.

The texture of the ball milling tank is selected from one or more of agate, zirconia and stainless steel. The texture of the ball grinding ball is selected from one or more of agate, zirconia and stainless steel.

In the ball milling process, water and an organic solvent are not added, and only ball milling balls and a solid electrolyte matrix material are subjected to ball milling.

The device for ball milling is preferably a planetary high-energy ball mill.

After the amorphous substance is obtained, the amorphous substance, the binder and the solvent are mixed to obtain the composite material slurry.

The mass ratio of the amorphous substance to the binder to the solvent is 1 (2-5) to 8, and preferably 1 (3-4) to 8.

The binder is selected from one or more of cellulose nitrate, polyvinyl alcohol, polyvinylidene fluoride, polyoxyethylene and hydroxycellulose.

And after obtaining the composite material slurry, coating the composite material slurry on the surface of the solid electrolyte matrix material, wherein the coating method is selected from spray coating, spin coating, blade coating or screen printing.

Applying the amorphous substance to the surface of the solid electrolyte matrix material, removing the solvent and binder and softening the amorphous substance.

In the invention, the softening step is realized by heat treatment, the softening temperature is 500-700 ℃, preferably 550-650 ℃, and the softening time is 1-24 hours, preferably 2-10 hours.

In the softening process, when the temperature is increased to 100-200 ℃ from room temperature, the solvent is removed, and the solvent can be volatilized and removed at room temperature or can be removed by heating; when the temperature is increased to 300-400 ℃, the binder is removed; when the temperature is raised to 500-700 ℃, the softening step is carried out.

Finally, the inorganic solid electrolyte with the amorphous substance on the surface is obtained.

In the present invention, the solid electrolyte matrix is selected from a NASICON structure or a perovskite structure, and the amorphous substance is selected from amorphous lithium aluminum (germanium) titanium phosphate or amorphous lithium lanthanum titanate.

Wherein the solid electrolyte matrix material of NASICON structure is preferably Li_1+xAl_xM_2-x(PO₄)₃Wherein x is 0-0.50, and M is selected from Ti and Ge; the solid electrolyte matrix material of the perovskite structure is preferably Li_xLa_2/3-x/3TiO₃Wherein x is 0 to 0.50

In the present invention, the thickness of the amorphous material layer is 0.1 μm to 50 μm, preferably 0.5 μm to 40 μm, and more preferably 1 μm to 10 μm.

The invention uses the characteristics of inorganic amorphous substances, such as high-temperature softening deformation, high modulus, no crystal boundary, certain lithium ion conductivity and structural nonuniformity on nanometer and micrometer scales caused by long-range disorder short-range ordered atom accumulation, to compound the inorganic amorphous substances on the surface of an inorganic solid electrolyte to form an inorganic solid fast lithium ion conductor with a high-conductivity matrix, and the surface layer is an integrated multilayer electrolyte of amorphous substances which is stable to lithium and has good contact.

The grain boundary-free nature of the amorphous material may fundamentally kill the growth of lithium dendrites in the grain boundaries, while its softer texture may produce plastic deformation to some extent, which would have greater advantages in terms of contact with lithium and stress relief. Meanwhile, although the electrolyte has the same chemical element composition with the inorganic crystalline state electrolyte matrix, the reaction of lithium metal and specific elements in the electrolyte is inhibited by utilizing the disorder, large atom disorder degree and uneven element distribution of an amorphous structure, and the original ordered electronic channel is damaged, so that the interior of the amorphous is separated from the surface layer, the metal lithium is prevented from directly contacting with more specific elements to generate chemical reaction, the solid electrolyte of the matrix part is greatly protected, the high impedance of the solid contact interface of the electrolyte/electrode is reduced, and the composite pure inorganic solid electrolyte which is stable to lithium and has good contact is obtained.

In order to further understand the present invention, the following examples are provided to illustrate the inorganic solid electrolyte with an amorphous surface and the preparation method thereof, and the scope of the present invention is not limited by the following examples.

Example 1

Weighing Li in stoichiometric ratio_1.5Al_0.5Ge_1.5(PO₄)₃Li as raw material for solid electrolyte₂CO₃、Al₂O₃、P₂O₅、GeO₂And mixing and drying, presintering at 700 ℃ for 2h, and then preparing an amorphous block by adopting a melting-quenching method. The melting temperature is 1400 ℃, and the holding time is 2 h. And ball-milling and crushing the amorphous block by a wet method, tabletting under 300MPa, and sintering at 900 ℃ for 5h to prepare the ceramic solid electrolyte sheet.

Accurately weighing cellulose nitrate 2 times the mass of the amorphous powder and ethanol 8 times the mass of the amorphous powder, and placing the cellulose nitrate and the ethanol together in a beaker to stir for 24 hours in an argon atmosphere to obtain composite slurry; coating the composite slurry on Li in sequence by blade coating_1.5Al_0.5Ti_1.5(PO₄)₃And (3) putting the two surfaces of the solid electrolyte sheet into a muffle furnace after the solvent is volatilized, and carrying out heat treatment at 500 ℃ for 2h to obtain the inorganic solid electrolyte with the amorphous substance on the surface, wherein the thickness of the amorphous substance layer on the surface is about 3 microns.

The inorganic solid electrolyte with an amorphous surface is subjected to electron microscope scanning, and the result is shown in fig. 1, and fig. 1 is a scanning electron microscope image of the inorganic solid electrolyte with an amorphous surface prepared in example 1.

XRD detection is carried out on the surface layer and the inner layer of the inorganic solid electrolyte with the amorphous substance on the surface, and the result is shown in figure 2, and figure 2 shows that the inorganic solid electrolyte with the amorphous substance on the surfaceXRD contrast pattern of surface layer and inner layer of electrolyte. As can be seen from FIG. 2, the material of the surface layer was amorphous, had no significant diffraction peak, and the material of the inner layer was pure-phase Li_1.5Al_0.5Ti_1.5(PO₄)₃This shows that a composite integrated electrolyte with an amorphous surface and a crystalline interior can be obtained by this method.

The symmetric battery is assembled by taking metal lithium as an electrode and is at 60 ℃ and 0.1mA cm^-2The results of the charge and discharge tests performed at current density are shown in FIG. 3, where FIG. 3 shows that the Li/Li symmetrical battery assembled by the inorganic solid electrolyte with amorphous material on the surface in example 1 of the present invention is at 60 ℃ and 0.1mA cm^-2Time-voltage diagram of the following charge-discharge cycle. After the test for 200h, the test curve is still stable, the battery is not short-circuited or broken, and the voltage is not obviously increased, which indicates that the composite electrolyte is stable to the lithium metal.

The results of EIS test at 60 ℃ for the change of interface impedance of lithium with time are shown in FIG. 4. FIG. 4 is an AC impedance monitoring chart at 60 ℃ for a Li/Li symmetric battery assembled by the inorganic solid electrolyte with an amorphous material on the surface in example 1 of the present invention. The interfacial resistance of the composite electrolyte and metallic lithium was stable for 14 days, while the interfacial resistance was lower as compared with fig. 19 in comparative example 1.

Example 2

Mixing Li_0.35La_0.55TiO₃Electrolyte raw material La₂O₃、Li₂CO₃And TiO₂Weighing the mixture and agate balls according to the mass ratio of 1:30, and placing the mixture in an agate tank for dry grinding for 50 h. During the period, the ball milling tank is opened every 2 hours, the powder adhered to the inner wall of the ball milling tank is scraped off and ball milling is continued, and finally amorphous Li is obtained_0.35La_0.55TiO₃An electrolyte powder.

Tabletting the obtained powder, and annealing at 1000 ℃ for 3h to obtain Li_0.35La_0.55TiO₃A ceramic electrolyte sheet. The amorphous Li obtained_0.35La_0.55TiO₃Powder and crystalline Li_0.35La_0.55TiO₃The XRD contrast of the ceramic plate is shown in the figure5. FIG. 5 shows the amorphous and crystalline Li prepared in example 2_0.35La_0.55TiO₃XRD contrast pattern of (a).

Weighing amorphous powder, polyvinyl alcohol and dimethyl sulfoxide according to the mass ratio of 1:3:8, stirring and mixing for 50h, and spin-coating the mixture on Li_0.35La_0.55TiO₃Annealing the two side surfaces of the electrolyte sheet at 600 ℃ for 3h to obtain Li with the surface thickness of 0.5 micron as an amorphous layer_0.35La_0.55TiO₃An electrolyte sheet. Surface and cross-sectional SEM see fig. 6, and fig. 6 is an SEM of the surface and cross-section of the inorganic solid electrolyte having an amorphous material on the surface prepared in example 2.

Assembling a Li/electrolyte/Li symmetrical battery at 60 ℃ and 0.3mA/cm²The charge-discharge test of current density, the cycle time-voltage diagram is shown in fig. 7. FIG. 7 is a Li/Li symmetrical battery assembled by the inorganic solid electrolyte with amorphous surface in example 2 at 60 deg.C and 0.3mA cm^-2Time-voltage diagram of the following charge-discharge cycle. The lithium ion battery has good stability to lithium, and the battery is not polarized under the condition of large-current charging and discharging within 250 h. This is illustrated in comparison with FIG. 23 in comparative example 3, which shows Li having an amorphous surface_0.35La_0.55TiO₃The modified lithium ion battery has stability to lithium, and the prepared modified layer has good protection effect.

Example 3

Accurately weighing and measuring Li according to stoichiometric ratio_0.5La_0.5TiO₃LiNO as the raw material of₃、La(NO₃)₃.6H₂O、C₁₆H₃₆O₄Dissolving Ti in proper amount of glycol, stirring for 24 hr, spin coating on alumina film substrate, high temperature sintering at 1000 deg.c for 3 hr, and sintering the alumina film from Li_0.5La_0.5TiO₃The electrolyte is stripped in a grinding and polishing mode to obtain crystalline solid Li_0.5La_0.5TiO₃An electrolyte membrane.

Mixing the above Li_0.5La_0.5TiO₃Ball-milling the electrolyte into powder, keeping the temperature at 1400 ℃ for 2h, and quenching in liquid nitrogen to obtain Li_0.5La_0.5TiO₃Amorphous blockBall milling to obtain Li_0.5La_0.5TiO₃XRD of amorphous powder, amorphous powder and ceramic wafer is shown in figure 8, and figure 8 shows the amorphous and crystalline Li prepared in example 3_0.5La_0.5TiO₃XRD pattern of (a).

Weighing amorphous powder, hydroxy cellulose and terpineol according to the mass ratio of 1:2:8, uniformly mixing by ball milling, screen-printing the slurry to the two side surfaces of the electrolyte film, and drying. And then, preserving the temperature of the composite electrolyte in a muffle furnace at 700 ℃ for 5h, and taking out the composite electrolyte after the amorphous powder on the surface is melted and firmly bonded with the matrix into a whole, thereby obtaining the inorganic solid electrolyte with the amorphous substance on the surface, wherein the thickness of the amorphous substance layer is about 2 mu m. Cross-sectional SEM of the composite electrolyte sheet is shown in fig. 9, and fig. 9 is a cross-sectional SEM of the inorganic solid electrolyte having an amorphous substance on the surface prepared in example 3.

Assembling a Li/electrolyte/Li symmetrical battery for electrochemical characterization, and charging and discharging at 60 ℃ with current density of 0.3mAcm^-2. The test results are shown in FIG. 10, and FIG. 10 shows the Li/Li symmetrical battery assembled by the inorganic solid electrolyte with amorphous surface in example 3 of the present invention at 60 deg.C and 0.3mA cm^-2Time-voltage diagram of the following charge-discharge cycle. The charge and discharge stability of the symmetrical battery exceeds 360h under the condition of high current density, and the phenomenon of polarization voltage increase is avoided. Indicating that the amorphous surface layer can significantly improve its stability to lithium.

Example 4

According to Li_1.5Al_0.5Ti_1.5(PO₄)₃Stoichiometric weighing of Li₂CO₃,TiO₂,Al₂O₃,(NH₄)₂H₂PO₄And mixed, the mixture was wet milled well and heated in a muffle furnace at 300 ℃ for 30 minutes. After cooling, the mixture was ground to a fine white powder and heated to 800 ℃ for about 30 minutes and slowly cooled again in the oven. The fine powder was ground again for 30 minutes and cold-pressed under a pressure of 70MPa to form flakes having a diameter of 50mm and a thickness of 3 mm. The flakes were then sintered at 1100 ℃ for 5 hours and slowly cooled in a furnace to give Li_1.5Al_0.5Ge_1.5(PO₄)₃A ceramic electrolyte sheet.

Uniformly mixing the other part of the raw material powder, heating to 1500 ℃, keeping the temperature for 2 hours, directly pouring the molten liquid into a liquid nitrogen basin for quenching to obtain the amorphous electrolyte, wherein XRD (XRD) is shown in figure 11, and figure 11 is the amorphous Li prepared in example 4_1.5Al_0.5Ti_1.5(PO₄)₃XRD pattern of electrolyte.

Mixing and stirring the amorphous electrolyte powder, polyoxyethylene and acetonitrile according to the mass ratio of 1:3:8 for 24 hours to obtain uniform glue solution. Spin-coating the glue solution on two sides of a ceramic electrolyte sheet, drying, heating to 300 ℃ at a heating rate of 1 ℃/min, keeping the temperature for 5h to fully decompose organic matters in the glue solution, heating to 600 ℃ and keeping the temperature for 5h to melt amorphous powder, and obtaining the inorganic solid electrolyte with the surface being amorphous substances, wherein the thickness of the amorphous substance layer is about 2 mu m.

The surface layer of the inorganic solid electrolyte having an amorphous substance on the surface was subjected to microscopic morphology analysis, and the results are shown in fig. 12, and fig. 12 is a microscopic morphology diagram of the surface layer of the inorganic solid electrolyte having an amorphous substance on the surface prepared in example 4.

The lithium battery is a symmetric lithium battery with electrolyte and electrode assembled by composite electrolyte and lithium sheets, and EIS monitoring and 0.1mA cm are carried out at 60 DEG C^-2The specific data of the charge and discharge test of the current density are shown in fig. 13 and 14. FIG. 13 is an AC impedance monitoring of a Li/Li symmetrical battery assembled by an inorganic solid electrolyte with an amorphous surface prepared in example 4 of the present invention at 60 ℃; FIG. 14 shows a Li/Li symmetrical battery assembled by the inorganic solid electrolyte with amorphous surface prepared in example 4 of the present invention at 60 deg.C and 0.1mA cm^-2Time-voltage diagram of the following charge-discharge cycle.

As is apparent from fig. 12, the large-grained electrolyte surface has a layer of molten material uniformly covering the surface. Meanwhile, the resistance test of fig. 13 shows that the electrolyte can maintain the interface stability for 60 days for lithium after the amorphous layer is formed, and the electrolyte/lithium contact becomes better without increasing or decreasing the resistance due to the applied pressure. Fig. 14 shows that the lithium-lithium symmetric battery can still maintain a stable polarization voltage after 1000 hours of low current charging and discharging.

Example 5

According to Li_1.3Al_0.3Ti_1.7(PO₄)₃Stoichiometric weighing of TiO₂,Al(OH)₃,(NH₄)₂HPO₄And LiOH. H₂And O. The raw materials are subjected to heat treatment at 750 ℃ for 12h after being ball-milled and uniformly mixed, then the raw materials are pressed into slices, and the slices are subjected to heat treatment at 900 ℃ for 24h to obtain the ceramic electrolyte sheet.

Then, the electrolyte sheet is heated to 1400 ℃ and kept for 1h, and is quenched into liquid nitrogen to obtain the amorphous electrolyte, XRD (X-ray diffraction) is shown in figure 15, and figure 15 is an XRD (X-ray diffraction) pattern of the amorphous electrolyte and the crystalline electrolyte sheet prepared in example 5.

Mixing and stirring amorphous electrolyte powder, polyvinylidene fluoride and acetone according to the mass ratio of 1:3:8 to form gel, and blade-coating the gel on the surface of a ceramic electrolyte sheet by using a scraper. And after drying, putting the sample into a muffle furnace, and annealing at 550 ℃ for 5h in the air to obtain the inorganic solid electrolyte with the amorphous substance on the surface, wherein the thickness of the amorphous substance layer is about 10 mu m. The scanning electron micrograph is shown in FIG. 16, and FIG. 16 is the scanning electron micrograph of the inorganic solid electrolyte with an amorphous substance on the surface prepared in example 5. The impedance change of the lithium/composite electrolyte/lithium symmetrical battery monitored at 60 ℃ is assembled, the data is shown in fig. 17, and fig. 17 shows that the inorganic solid electrolyte with the amorphous substance on the surface prepared in the example 5 is assembled into the Li/Li symmetrical battery to monitor the alternating current impedance at 60 ℃.

As is apparent from FIG. 15, amorphous Li was prepared by melt-quenching_1.3Al_0.3Ti_1.7(PO₄)₃. While FIG. 16 shows crystalline Li_1.3Al_0.3Ti_1.7(PO₄)₃The electrolyte sheet has an amorphous layer. FIG. 17 shows that the interface resistance of the composite electrolyte to lithium can be maintained stable for 20 days, and in contrast to FIG. 23 of comparative example 2, Li having an amorphous surface can be obtained_1.3Al_0.3Ti_1.7(PO₄)₃Has a specific ratio of pure Li_1.3Al_0.3Ti_1.7(PO₄)₃Better stability to lithium.

Comparative example 1

Mixing metallic lithium with Li_1.5Al_0.5Ge_1.5(PO₄)₃The electrolyte sheet was placed in direct contact at 60 ℃ for 3 days with Li before and after contact_1.5Al_0.5Ge_1.5(PO₄)₃An SEM photograph of the electrolyte sheet is shown in FIG. 18, and FIG. 18 is Li in comparative example 1 of the present invention_1.5Al_0.5Ge_1.5(PO₄)₃Scanning electron micrographs of the cross section of the electrolyte sheet before (a) and after (b) contact with metallic lithium at 60 ℃ for 72 hours. As can be seen in FIG. 18, a dark reaction layer appears; Li/Li is assembled by taking metallic lithium as an electrode_1.5Al_0.5Ge_1.5(PO₄)₃A/Li symmetrical cell, the cell was subjected to AC impedance test at 60 ℃ to test the change of interfacial impedance of the electrolyte to lithium metal with time, the test results are shown in FIG. 19, FIG. 19 is Li in comparative example 1 of the present invention_1.5Al_0.5Ge_1.5(PO₄)₃Electrolyte sheet assembly Li/Li symmetric cell ac impedance monitoring plot at 60 ℃. As can be seen from the graph, the interfacial resistance increased to about 100 times the initial after 4 days. The symmetrical cell was run at 60 ℃ at 0.1mA cm^-2Current Density Charge/discharge and polarization Voltage Observation results are shown in FIG. 20, and FIG. 20 is Li in comparative example 1 of the present invention_1.5Al_0.5Ge_1.5(PO₄)₃The electrolyte sheet is assembled into a Li/Li symmetrical battery at the temperature of 60 ℃ and the temperature of 0.1mAcm^-2Time-voltage diagram of the following charge-discharge cycle. As can be seen from fig. 20, the polarization voltage of the cell had reached 5V after about 95h, which is about 50 times the initial value. These characterizations demonstrate that pure Li_1.5Al_0.5Ge_1.5(PO₄)₃The electrolyte sheet is unstable to lithium electrodes.

Comparative example 2

Mixing metallic lithium with Li_1.5Al_0.5Ti_1.5(PO₄)₃The electrolyte sheet was placed in direct contact at 60 ℃ for 3 days with Li before and after contact_1.5Al_0.5Ti_1.5(PO₄)₃SEM photograph of electrolyte sheet such asFIG. 21 shows, in FIG. 21, Li in comparative example 2 of the present invention_1.5Al_0.5Ti_1.5(PO₄)₃A scanning electron micrograph of the cross section of the electrolyte sheet (a) and the cross section of the electrolyte sheet (b) before and after contacting with lithium metal at 60 ℃ for 72 hours shows that a dark reaction interface layer appears in fig. 21; Li/Li is assembled by taking metallic lithium as an electrode_1.5Al_0.5Ti_1.5(PO₄)₃a/Li symmetrical cell, the cell is at 60 ℃ and 0.1mAcm^-2AC impedance test was performed at a current, and the test results are shown in FIG. 22, where FIG. 22 is Li in comparative example 2 of the present invention_1.5Al_0.5Ti_1.5(PO₄)₃The electrolyte sheet is assembled into a Li/Li symmetrical battery at 60 ℃ and 0.1mA cm^-2Time-voltage diagram of the following charge-discharge cycle. As can be seen from fig. 22, when the battery was charged and discharged for about 300 hours, the polarization voltage was already about 500 times the initial polarization voltage, and the polarization voltage reached 5V (about 0.01V initially). While the change in the electrolyte/lithium interfacial resistance with time was monitored, as shown in FIG. 23, FIG. 23 is Li in comparative example 2 of the present invention_1.5Al_0.5Ti_1.5(PO₄)₃The electrolyte sheet is assembled into an alternating current impedance monitoring graph of the Li/Li symmetrical battery at 60 ℃. As can be seen from fig. 23, after 3 days, the interface impedance was about 150 times that of the first day. This indicates Li without a modification layer_1.5Al_0.5Ti_1.5(PO₄)₃It is unstable to lithium.

Comparative example 3

Mixing metallic lithium with Li_0.35La_0.55TiO₃The electrolyte sheet was placed in direct contact at 60 ℃ for 3 days with Li before and after contact_0.35La_0.55TiO₃The SEM photograph of the surface of the electrolyte sheet is shown in FIG. 24, and FIG. 24 is Li in comparative example 3 of the present invention_0.35La_0.55TiO₃Surface scanning electron micrographs of (a) and (b) before and after contacting the electrolyte sheet with metallic lithium at 60 ℃ for 72 hours. The surface was found to be darkened and a heterogeneous layer appeared; Li/Li is assembled by taking metallic lithium as an electrode_0.35La_0.55TiO₃a/Li symmetrical cell, the cell is at 60 ℃ and 0.3mAcm^-2Performing AC impedance test under current to test the change of the interface impedance of electrolyte to lithium metal with timeFIG. 25 shows the results of the test, and FIG. 25 shows Li in comparative example 3 of the present invention_0.35La_0.55TiO₃The electrolyte sheet is assembled into a Li/Li symmetrical battery at 60 ℃ and 0.3mA cm^-2Time-voltage diagram of the following charge-discharge cycle. It was found that the polarization voltage of the cell increased to 0.5V (initially 0.02V) after 80h, indicating bare Li_0.35La_0.55TiO₃Is very unstable to lithium.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing an inorganic solid electrolyte with an amorphous substance on the surface is characterized by comprising the following steps:

C) coating the composite material slurry on the surface of the solid electrolyte matrix material, removing the solvent and the binder, and softening the amorphous substance to obtain the inorganic solid electrolyte with the amorphous substance on the surface;

the melting-quenching method comprises the following steps:

crushing the amorphous block of the solid electrolyte matrix material to obtain an amorphous substance with the same chemical composition as the solid electrolyte matrix material;

the high-energy ball milling method comprises the following steps:

2. The preparation method of the amorphous substance, the binder and the solvent according to claim 1, wherein the mass ratio of the amorphous substance to the binder to the solvent is 1 (2-5) to 8.

3. The method of claim 1, wherein the binder is selected from one or more of cellulose nitrate, polyvinyl alcohol, polyvinylidene fluoride, polyoxyethylene, and hydroxycellulose;

4. The preparation method according to claim 1, wherein the softening temperature is 500-700 ℃, and the softening time is 1-24 h.

5. The method according to claim 1, wherein the solid electrolyte matrix is selected from a NASICON structure or a perovskite structure, and the amorphous substance is selected from amorphous lithium aluminum titanium phosphate, amorphous lithium aluminum germanium phosphate, or amorphous lithium lanthanum titanate.

6. The inorganic solid electrolyte with the amorphous surface prepared by the preparation method of any one of claims 1 to 5, which is characterized by comprising a solid electrolyte matrix and an amorphous substance layer compounded on the surface of the solid electrolyte matrix, wherein the amorphous substance is an amorphous substance with the same chemical composition as that of a solid electrolyte matrix material.

7. The inorganic solid electrolyte according to claim 6, wherein the amorphous material layer has a thickness of 0.1 μm to 50 μm.