CN112777632A - Sulfide lithium ion solid electrolyte and preparation method and application thereof - Google Patents

Abstract

The invention discloses a dry air stable sulfide lithium ion solid electrolyte with a chemical formula of Li_6.6Ge_0.6P_{0.4‑ x} M _x S₅I (M = Sn, Sb), x is more than or equal to 0.05 and less than or equal to 0.075; the preparation method comprises the steps of mixing the raw material Li₂S、P₂S₅、GeS₂、LiI、Sb₂S₃Sn and S are uniformly mixed according to a certain dosage, and the mixture is sintered at high temperature in a vacuum environment after high-energy ball milling; the sulfide lithium ion solid electrolyte is also disclosed to be used for preparing an all-solid-state battery; the solid electrolyte material of the present invention has high ionic conductivity and is stable in dry air, and further, the solid electrolyte material of the present invention has high ionic conductivity and is stable in dry airThe technical problems that in the prior art, the sulfide solid electrolyte is sensitive to air, sulfide hydrogen is easily generated when the sulfide solid electrolyte is exposed in the air, the solid electrolyte is invalid, the application of the sulfide solid electrolyte is limited, and the cost for manufacturing a battery is increased are solved.

Description

Sulfide lithium ion solid electrolyte and preparation method and application thereof

Technical Field

The invention belongs to the field of all-solid-state lithium ion batteries, and particularly relates to a dry air stable sulfide lithium ion solid electrolyte, a preparation method thereof and an all-solid-state battery prepared from the electrolyte.

Background

The lithium ion battery occupies the electric automobile market in China at present, is likely to be applied to the power grid energy storage market in a large scale, and is one of key technologies for solving the current energy problem. In an electric vehicle, energy density is the first indicator of power battery performance, while energy storage batteries pay more attention to cost and safety. Meanwhile, with the increase of the sales volume of the electric vehicle, the frequency of safety accidents such as spontaneous combustion explosion and the like is also obviously increased, and the safety problem becomes a key problem which hinders the further application and development of the lithium ion battery. The main reason for the safety problem is the use of flammable organic electrolytes in lithium ion batteries. The all-solid-state battery conducts ions by means of solid electrolyte, is nonflammable and nonvolatile compared with the traditional liquid-state battery, and greatly improves the safety of the battery. Therefore, the lithium ion battery has gained wide attention in academia and industry and is considered to be one of the most potential next-generation lithium ion battery technologies.

Compared with the traditional lithium ion battery, the all-solid-state battery has the advantages of good safety, capability of breaking through the energy density limitation of the existing battery system, good temperature adaptability and the like. The solid electrolyte is a key material of the all-solid battery, and the performance of the solid electrolyte determines the cycle stability, rate capability, safety, service life and the like of the all-solid battery to a great extent. The core of all-solid-state battery research is to find solid-state electrolytes with high ionic conductivity and electrochemical stability and to explore methods for stabilizing the solid-solid interface between the electrolyte and the electrodes. However, most of the existing solid electrolytes have the problems of insufficient ionic conductivity, unstable electrochemical window and various interfaces, so that the comprehensive performance of the existing all-solid batteries cannot meet the application requirements, and no marketable product exists.

The lithium ion solid electrolyte is a key material of the all-solid-state lithium battery. Among the inorganic solid electrolytes reported so far, sulfide electrolytes are attracting much attention because of their high ionic conductivity and good mechanical properties (easy elimination of grain boundary resistance).

However, the sulfide solid electrolyte is very sensitive to air, and the exposure to air is easy to generate sulfide hydrogen and cause the failure of the solid electrolyte, which limits the application of the sulfide solid electrolyte or increases the cost for manufacturing the battery. In the existing research results, the ion conductivity of the air-stable sulfide lithium ion solid electrolyte is generally low, and an all-solid-state battery with good performance is not easy to assemble.

Disclosure of Invention

In view of the above defects or improvement needs of the prior art, an object of the present invention is to provide a dry air stable sulfide lithium ion solid electrolyte, so as to solve the technical problems in the prior art that the sulfide solid electrolyte is sensitive to air, and sulfide hydrogen is easily generated when the sulfide solid electrolyte is exposed to air, and the solid electrolyte is ineffective, thereby limiting the application of the sulfide solid electrolyte and increasing the cost for manufacturing a battery.

The technical scheme adopted by the invention for solving the technical problems is as follows: a sulfide lithium ion solid electrolyte with chemical formula of Li_6.6Ge_0.6P _x0.4-M _x S₅I, wherein M is at least one of Sn and Sb, and x is more than or equal to 0.05 and less than or equal to 0.075. The sulfide lithium ion solid electrolyte has a Argyrodite (Argyrodite) type cubic phase crystal structure.

The crystal structure of the sulfide lithium ion solid electrolyte has a cubic phase

Space group, I and S occupy the vertex and face center of the cube, tetrahedron (P/Ge/Sn) S₄Or (P/Ge/Sb) S₄Or (P/Ge/Sn/Sb) S₄The middle point of each edge of the cube and the body center of the cube are occupied; the cube also has four independent S atoms in the interior, each of the independent S atoms has 18 vacancies around it, and some of the vacancies are filled with Li⁺Occupied, remaining vacancy is Li⁺A migration site.

The invention also aims to provide a preparation method of the sulfide lithium ion solid electrolyte, which comprises the following steps:

(1) mixing Li₂S、P₂S₅、GeS₂、LiI、Sb₂S₃Sn, S according to Li_6.6Ge_0.6P _x0.4-M _x S₅Uniformly mixing the molar ratio of I to obtain a mixed raw material;

(2) performing solid-phase synthesis on the mixed raw materials at 400-600 ℃ under an anaerobic condition to obtain Li_6.6Ge_0.6P_{0.4- x} M _x S₅I, its crystal structure satisfies

A space group;

in the preparation method of the sulfide lithium ion solid electrolyte, the uniform mixing method in the step (1) is planetary ball milling or vibration ball milling; the ball milling speed is 200-400 r/min, and the ball milling time is 10-20 h.

In the preparation method of the sulfide lithium ion solid electrolyte, the oxygen-free condition in the step (2) is a vacuum condition less than 100 Pa.

According to the preparation method of the sulfide lithium ion solid electrolyte, the solid phase synthesis time in the step (2) is 8-24 hours.

The preparation method of the sulfide lithium ion solid electrolyte further comprises the following steps between the step (1) and the step (2): the mixed raw materials are pressed into sheets, so that the components in the mixed raw materials are contacted more closely and the reaction is more sufficient.

The invention also aims to provide the sulfide lithium ion solid electrolyte for preparing the all-solid-state lithium ion battery.

In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:

the invention partially replaces Li with Sb and Sn elements_6.6Ge_0.6P_0.4S₅P in the I can obtain a novel solid electrolyte material Li with higher ionic conductivity_6.6Ge_0.6P _x0.4-M _x S₅I, and at the same time its ionic conductivity (> 10)^–3S/cm) relative to Li_6.6Ge_0.6P_0.4S₅I（5.6×10^–3S/cm) did not decrease significantly, but in dry air, the electrolyte Li_6.6Ge_0.6P _x0.4-M _x S₅I can remain stable, this is including Li_6.6Ge_0.6P_0.4S₅I and the like, which most high ion conductivity sulfide solid electrolytes do not have. Prior efforts have resulted in air stable sulfide solid state electrolytes having either low ionic conductivity (10)^–4S/cm, which greatly limits the performance of the full cell), or contains expensive or highly toxic raw materials, and the electrolyte of the present invention can solve both of these problems. The solid electrolyte material has high ionic conductivity and stable performance in dry air, and can further solve the technical problems that in the prior art, the sulfide solid electrolyte is sensitive to air, sulfide hydrogen is easily generated when the sulfide solid electrolyte is exposed in the air, the solid electrolyte is invalid, the application of the sulfide solid electrolyte is limited, and the cost for manufacturing a battery is increased.

2, the solid electrolyte material Li provided by the invention_6.6Ge_0.6P _x0.4-M _x S₅M in I is at least one of Sn and Sb, and can ensure that M replaces mother phase Li in a small amount_6.6Ge_0.6P_0.4S₅P in I to produce a stable space group of dry air

Li of (2)_6.6Ge_0.6P _x0.4-M _x S₅And x is more than or equal to 0.05 and less than or equal to 0.075, and can prevent the overproduction of the M element.

3, when M is selected as Sb with a certain content in the preferred embodiment of the invention, the ionic conductivity of the obtained electrolyte in dry air at room temperature reaches 5.5 x 10^–3S/cm, and no release of hydrogen sulfide gas and no change of crystal structure.

Drawings

FIG. 1 is a schematic diagram of the crystal structure of the present invention;

FIG. 2 is an XRD of examples 1, 4, 6, 9, 11 of the present invention and an XRD of comparative example 1;

FIG. 3 is an XRD of example 1 of the invention when exposed to dry air for 24 hours;

fig. 4 is a charge and discharge curve in an all solid-state lithium battery prepared as a solid electrolyte in dry air in example 1 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments.

It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

The cubic phase sulfide of the present invention has a chemical formula of Li_6.6Ge_0.6P _x0.4-M _x S₅I; wherein M is one or more of Sn and Sb; wherein x is more than or equal to 0.05 and less than or equal to 0.075; preferably M is Sb; preferably x is in the range of 0.05. ltoreq. x.ltoreq.0.06.

The Li_6.6Ge_0.6P _x0.4-M _x S₅I is a chalcogenide lithium ion solid electrolyte with a crystal structure having cubic phases

Space group, I and S occupy the vertex and face center of the cube, tetrahedron (P/Ge/M) S₄Occupies the midpoints of the sides of the cube and the body center of the cube. The cube also has four independent S atoms in the interior, and 18 Li atoms around the four S atoms⁺Is partially occupied.

The crystal structure of which satisfies

A space group; CuK_αXRD ray diffraction result, at least 2 theta =15.37^o±0.50^o、17.77^o±0.50^o、20.32^o±0.50^o、25.30^o±0.50^o、29.69^o±0.50^o、31.10^o±0.50^o、32.17^o±0.50^o、36.20^o±0.50^o、40.35^o±0.50^o、44.47^o±0.50^o、47.29^o±0.50^o、51.72^o±0.50^o、55.24^o±0.50^o、58.42^o±0.50^oOf (b), wherein 25.30^o±0.50^o、29.69^o±0.50^o、31.10^o±0.50^oThe peak of (a) is relatively strong.

M element partially replaces Li_6.6Ge_0.6P_0.4S₅P in I can obtain a dry air stable solid electrolyte material with high lithium ion conductivity and ion conductivity (more than 10)^–3S/cm）。

M element improves the air stability of the sulfide solid electrolyte through the soft and hard acid-base theory, but when the M element is used for preparing the electrolyte, the air stability of the sulfide solid electrolyte is improvedxWhen the ionic conductivity of the material is more than or equal to 0.075, solid solution cannot be formed continuously due to the limitation of a crystal structure, impurities are generated, and the ionic conductivity of the material is reduced; due to the fact thatIn this way, the temperature of the molten steel is controlled,xpreferably 0.05 to 0.06.

The preparation method of the cubic phase sulfide comprises the following steps: mixing Li₂S、P₂S₅、GeS₂、LiI、Sb₂S₃Sn, S according to Li_6.6Ge_0.6P _x0.4-M _x S₅And (3) weighing the molar ratio of I in an inert atmosphere, uniformly mixing, and calcining for 8-24 hours at 400-600 ℃ under the vacuum degree of less than 100Pa so as to prevent the reactant from reacting with oxygen or moisture in the air to generate impurities.

In the preparation of the solid electrolyte, uniform mixing is very important, and impurities are easy to generate due to the fact that components are inconsistent because of nonuniform mixing; meanwhile, the refining process of the raw materials is also accompanied in the material mixing process, so that the synthesis of sulfide electrolyte in the later period is facilitated; the method of uniform mixing can be selected from mechanical grinding methods such as vibration grinding, turbine grinding, ball milling and the like; for example, when mixing by ball milling, ball milling is carried out at a rotation speed of 200 to 400r/min for 10 to 20 hours. In order to avoid the ball milling tank and the ball milling beads from polluting raw materials during ball milling, the lining of the ball milling tank is made of zirconium oxide or tungsten carbide.

The high temperature is beneficial to the preparation reaction of the sulfide solid electrolyte, and the crystallinity of the crystalline material is improved, so that the ionic conductivity of the sulfide solid electrolyte is improved; however, excessive temperatures tend to cause the sulfide solid electrolyte to produce sulfur vacancy defects. The temperature of calcination is therefore preferably from 450 ℃ to 550 ℃.

The current partial cell production line conditions can reach the atmosphere of dry air in the whole process, so the method is beneficial to the batch preparation of all-solid-state cells.

Example 1

Li in an argon-protected glove box₂S、P₂S₅、GeS₂、LiI、Sb₂S₃With Li_6.6Ge_0.6P_0.35Sb_0.05S₅I are weighed out in molar ratios and mixed as starting materials.

The raw materials and zirconia balls are put into a ball milling tank with a zirconia substrate, the container is sealed, ball milling and mixing are carried out at the rotating speed of 330r/min, and mixed powder is obtained after 12 hours.

And taking out the mixed powder in a glove box, forming the mixed powder under the pressure of 120MPa by a powder tablet machine, putting the formed mixed powder into a glass/quartz tube, vacuumizing until the vacuum degree is less than 100Pa, sealing, and putting the sealed mixed powder into a muffle furnace. The temperature rise speed of the muffle furnace is 100 ℃/h, then solid phase reaction is carried out for 24h at 500 ℃, natural cooling is carried out, and the product Li is obtained_6.6Ge_0.6P _x0.4-M _x S₅I, in this example, the product is Li_6.6Ge_0.6P_0.35Sb_0.05S₅I。

The resultant was taken out from the sealed glass tube in a glove box and crushed and ground in a mortar to obtain a powdery sample having a particle size of 5 to 15 μm. A predetermined amount of a sample was weighed in a glove box and put in a PET tube having an inner diameter of 10mm, and the sample was sandwiched vertically by stainless steel powder molding tools and pressed by a uniaxial press under a pressure of 100 MPa to form an electrolyte sheet having an arbitrary thickness of 8 mm in diameter.

And respectively placing gold powder on two surfaces of the electrolyte sheet to uniformly disperse the gold powder on the surface of the electrolyte sheet, and forming under the pressure of 300 MPa to form the blocking electrode.

The blocking electrode was placed in an argon-protected closed electrochemical cell at 25 ℃ for ac impedance testing. The amplitude of the applied alternating current is 20 mV, and the frequency range is 10 Hz-1 MHz. The room-temperature ionic conductivity of the conductive paste is 5.5 mS/cm. The powder is dried in dry air (dew point-60)^oC) Standing for 24h, and measuring the ionic conductivity by the same method, wherein the ionic conductivity is 5.4 mS/cm at room temperature.

Comparative example 1

According to Li_6.6Ge_0.6P_0.4S₅I composition formula, respectively weighing Li in an argon-protected glove box₂S，P₂S₅、GeS₂LiI and mixed as raw materials. The raw materials and zirconia balls are put into a ball milling tank with a zirconia substrate, the container is sealed, ball milling and mixing are carried out at the rotating speed of 300r/min, and mixed powder is obtained after 15 hours.

Placing the mixed powder in a glove box, taking out, and placing inForming under a powder tablet machine, putting into a glass/quartz tube, vacuumizing until the vacuum degree is less than 100Pa, sealing, and putting into a muffle furnace. The temperature rise speed of the muffle furnace is 100 ℃/h, then solid phase reaction is carried out for 10 h at 550 ℃, natural cooling is carried out, and the product Li is obtained_6.6Ge_0.6P_0.4S₅I。

The resultant was taken out from the sealed glass tube in a glove box and crushed and ground in a mortar to obtain a powdery sample having a particle size of 10 to 20 μm. A predetermined amount of a sample was weighed in a glove box and put in a PET tube having an inner diameter of 10mm, and the sample was sandwiched vertically by stainless steel powder molding tools and pressed by a uniaxial press under a pressure of 160 MPa to form an electrolyte sheet having an arbitrary thickness of 10mm in diameter.

And respectively placing gold powder on two surfaces of the electrolyte sheet to uniformly disperse the gold powder on the surface of the electrolyte sheet, and forming under the pressure of 360 MPa to form the blocking electrode.

The blocking electrode was placed in an argon-protected closed electrochemical cell at 25 ℃ for ac impedance testing. The amplitude of the applied alternating current is 20 mV, and the frequency range is 10 Hz-1 MHz. The room-temperature ionic conductivity of the conductive paste is 5.6 mS/cm. The powder was left to stand in dry air for 24 hours, and its ionic conductivity was measured by the same method and was 1.3 mS/cm, indicating that its crystal structure was broken.

For the sake of simplicity of description, the preparation parameters and product properties of examples 2 to 11 are shown in the following table (preparation parameters and product properties of examples 2 to 11), and the parameters not shown in the table are the same as those of example 1.

Analysis of Experimental results

(1) Measurement of conductivity: comparing the ionic conductivities of examples 1 to 11 with that of comparative example 1, it can be seen that Li was left standing in dry air for 12 hours_6.6Ge_0.6P _x0.4-M _x S₅I sulfide solid electrolytes exhibit higher ionic conductivityAnd (4) conductivity.

(2) X-ray diffraction measurement: the X-ray diffraction measurement of CuK α rays was performed on examples 1 to 11, and it was found that the compound had a peak value of 2 θ =15.33^o±0.50^o、17.74^o±0.50^o、20.31^o±0.50^o、25.20^o±0.50^o、29.65^o±0.50^o、31.00^o±0.50^o、32.17^o±0.50^o、36.00^o±0.50^o、40.35^o±0.50^o、44.42^o±0.50^o、47.29^o±0.50^o、51.78^o±0.50^o、55.21^o±0.50^o、58.45^o±0.50^oOf (b), wherein 25.20^o±0.50^o、29.65^o±0.50^o、31.00^o±0.50^oThe peak of (a) is relatively strong. The diffraction peak in comparative example 11 contains more impurities, indicating that an excessively high proportion of Sn has no longer entered the crystal lattice to form a solid solution instead of P.

(3) Air exposure stability test: the electrolyte (Li) in example 1 was measured_6.6Ge_0.6P_0.35Sb_0.05S₅I) In dry air (dew point-60)^oC) XRD pattern after 24 hours exposure and comparison with XRD pattern of sample stored in glove box after synthesis, the results are shown in fig. 3. It can be seen that there was no significant change in the XRD pattern after the material was exposed to air for 24 hours, indicating that it remained structurally stable in air.

(4) Charging and discharging of the all-solid-state battery: the sulfide solid electrolyte (Li) obtained in example 3 was used_6.6Ge_0.6P_0.34Sb_0.06S₅I) With TiS of particle size 5 um₂With (TiS)₂ Sulfide solid electrolyte material) was mixed at a weight ratio of 7: 3 to obtain a positive electrode composite material. Then, Li is used as a negative electrode material, and a sulfide solid electrolyte Li_6.6Ge_0.6P_0.34Sb_0.06S₅And I, forming a solid electrolyte layer to manufacture the all-solid-state battery. Constant current charging and discharging for the prepared all-solid-state batteryThe measurement was carried out in the range of 1.6V to 3.1V, the charge-discharge magnification was 0.1C, and the temperature was 25 ℃. As a result, as shown in fig. 4, it was found that the all-solid-state battery produced from the sulfide solid electrolyte of the present invention exhibited good performance.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of this invention and is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Claims (8)

1. A sulfide lithium ion solid state electrolyte characterized by: has a chemical formula of Li_6.6Ge_0.6P _x0.4-M _x S₅I, wherein M is at least one of Sn and Sb, and x is more than or equal to 0.05 and less than or equal to 0.075.

2. The sulfide lithium ion solid state electrolyte of claim 1, wherein the crystal structure of the solid state electrolyte has a cubic phase

Space group, I and S occupy the vertex and face center of the cube, tetrahedron (P/Ge/Sn) S₄Or (P/Ge/Sb) S₄Or (P/Ge/Sn/Sb) S₄The middle point of each edge of the cube and the body center of the cube are occupied; the cube is also internally provided with four independent S atoms, each S atom is surrounded by 18 vacant sites, and part of the vacant sites are filled with Li⁺Occupied, remaining vacancy is Li⁺A migration site.

3. A method of preparing the sulfide lithium ion solid state electrolyte of claim 1, comprising the steps of:

(1) mixing Li₂S、P₂S₅、GeS₂、LiI、Sb₂S₃Sn and S are uniformly mixed according to the ratio;

(2) performing solid-phase synthesis on the mixed raw materials at 400-600 ℃ under an anaerobic condition to obtain Li_6.6Ge_0.6P _x0.4-M _x S₅I。

4. The method for preparing a sulfide lithium ion solid state electrolyte according to claim 3, wherein the uniform mixing in the step (1) is planetary ball milling or vibration ball milling; the ball milling speed is 200-400 r/min, and the ball milling time is 10-20 h.

5. The method of claim 3, wherein the oxygen-free condition in step (2) is a vacuum condition of less than 100 Pa.

6. The method for preparing the sulfide lithium ion solid electrolyte according to claim 3, wherein the solid phase synthesis time in the step (2) is 8-24 h.

7. The method for preparing a sulfide lithium ion solid state electrolyte according to claim 3, further comprising between the step (1) and the step (2): the mixed raw materials are pressed into sheets, so that the components are contacted more closely and the reaction is more sufficient.

8. The sulfide lithium ion solid electrolyte according to claim 1, which is used for preparing an all-solid-state lithium ion battery.

Images