CN112510254B

CN112510254B - Novel sulfide solid electrolyte and preparation method and application thereof

Info

Publication number: CN112510254B
Application number: CN202011379643.3A
Authority: CN
Inventors: 杨文�; 尼亚·艾哈迈德; 陈人杰; 于佩雯
Original assignee: Beijing Institute of Technology BIT
Current assignee: Beijing Institute of Technology BIT
Priority date: 2020-11-30
Filing date: 2020-11-30
Publication date: 2022-07-19
Anticipated expiration: 2040-11-30
Also published as: CN112510254A

Abstract

The invention discloses a novel sulfide solid electrolyte, a preparation method and application thereof, wherein the novel sulfide solid electrolyte comprises a compound with a nominal chemical formula as follows: li_3‑0.02xP_1‑0.01xN_xS_4‑0.04xO_3xWherein x is 2,4,6, 8; the novel sulfide solid electrolyte has PS₄ ^3‑/POS₃ ^3‑And (5) structure. The invention lies in Li₃PS₄The glass electrolyte is doped with a proper amount of LiNO₃Then a novel PS is obtained by a simple ball milling and calcining method₄ ^3‑/POS₃ ^3‑The glass ceramic solid electrolyte with a special structure further improves the stability of the sulfide solid electrolyte. The sulfide solid electrolyte synthesized by the method improves the interface stability of the sulfide solid electrolyte and a lithium metal cathode, simultaneously improves the air stability of the electrolyte, and lays a certain theoretical basis for the practical application of all-solid batteries.

Description

Novel sulfide solid electrolyte and preparation method and application thereof

Technical Field

The invention belongs to the technical field of lithium batteries and all-solid-state batteries, relates to a solid electrolyte of a lithium battery, and particularly relates to a novel sulfide solid electrolyte and a preparation method and application thereof.

Background

Since its first commercialization in 1991, lithium ion batteries have dramatically changed our means of communication and transportation due to their higher energy density and longer cycle life. At present, the traditional lithium ion battery taking graphite as a negative electrode is close to the limit of energy density, and still can not meet the urgent requirement of electric automobiles and advanced electronic equipment on the energy density. Therefore, there is an urgent need to develop a new battery system to surpass the conventional lithium ion battery.

The all-solid-state battery utilizes the solid electrolyte to replace the liquid electrolyte in the traditional lithium ion battery to reduce the flammability and prolong the cycle life of the battery, and the alkali metal cathode is applied, so that the energy density and the safety of the lithium ion battery are further improved, and the all-solid-state battery becomes the most promising next-generation lithium ion battery.

The electrode material is a critical part affecting the energy density of the battery. The specific capacity of the metallic lithium is 3860mAh/g, the electrochemical potential is-3.04V (vs standard hydrogen electrode), and the lithium battery anode material is an ideal lithium battery anode material.

Currently, solid electrolytes can be classified into three main categories: inorganic solid electrolyte, polymer solid electrolyte, composite solid electrolyte. Inorganic solid electrolytes include oxide inorganic solid electrolytes, sulfide inorganic solid electrolytes, and the like. Among them, sulfur has a large atomic radius and a large polarizability, causing lattice distortion to form a large ion channel. In addition, the bonding force between sulfur and lithium ions is weak, and the number of movable carriers in a system is large, so that the sulfide solid electrolyte shows good ionic conductivity, and is a main research object at present.

However, the interface compatibility between the sulfide solid electrolyte and the lithium metal cathode is poor, chemical reaction is easy to occur, and phenomena such as lithium dendrite, even 'dead lithium' and the like occur, so that the capacity of the battery is attenuated, and the lithium cathode is difficult to be directly applied to a sulfide all-solid battery.

In addition, sulfide electrolytes are extremely unstable to air and water and produce toxic gases upon contact. Therefore, the development of a novel sulfide solid electrolyte which is stable to a lithium negative electrode and air at the same time has great significance for the practical application of the all-solid-state lithium ion battery.

The present invention has been made to solve the above problems.

Disclosure of Invention

Aiming at the instability of almost all sulfide solid electrolytes to lithium cathodes and air at present, the invention provides a simple preparation method for improving the stability of the sulfide solid electrolytes, thereby improving the stability of the sulfide solid electrolytes in the air and to the lithium cathodes and laying a foundation for further practical application of all-solid lithium ion batteries.

In a first aspect the present invention provides a novel sulphide solid electrolyte comprising a compound of formula nominally: li_3-0.02xP_1-0.01xN_xS_4-0.04xO_3xWherein x is 2,4,6, 8;

the novel sulfide solid electrolyte has PS₄ ^3-/POS₃ ^3-And (5) structure. Here "/" means "and", that is, the novel sulfide solid electrolyte has PS therein₄ ^3-And POS₃ ^3-Structure, but for PS₄ ^3-And POS₃ ^3-The amount of (A) is not limited.

Nominally expressed theoretically in terms of precursor ratios herein, and does not represent the structure of the final product, a novel sulfide solid state electrolyte.

The second aspect of the present invention provides a method for preparing the novel sulfide solid electrolyte, which comprises the following steps:

(1) mixing the precursor Li₂S、P₂S₅And LiNO₃Grinding and mixing in an argon atmosphere according to a certain molar ratio to obtain a mixed precursor;

(2) placing the mixed precursor obtained in the step (1) in a high-energy ball mill, and performing ball milling treatment to obtain mixed powder;

(3) and (3) calcining the mixed powder obtained in the step (2) at a certain temperature to obtain the novel sulfide solid electrolyte.

Preferably, in step (1), LiNO is present based on the total molar mass of the novel sulfide solid-state electrolyte₃The doping ratio of (B) is 2 mol%, 4 mol%, 6 mol% or 8 mol%. More preferably, LiNO₃The doping proportion of (B) is 2 mol%, 4 mol% or 6 mol%.

Preferably, in step (1), the precursor Li is first prepared by using a manual grinding method₂S、P₂S₅And LiNO₃Mixing; in the step (2), the rotation speed of the ball mill is 370-510 rpm, and the ball milling time is 60-70 h.

Preferably, in the step (2), in order to avoid the influence of heat generated in the ball milling process on the reaction product, the ball milling is stopped for 20-30 min every time the ball milling is carried out for 25-30 min.

Preferably, in the step (3), the calcining temperature is 270-290 ℃, and the calcining time is 2-5 h.

Preferably, in step (3), the environment for calcination is an inert atmosphere.

A third aspect of the invention provides a method of improving the conductivity and stability of a sulfide solid state electrolyte, the stability being lithium negative electrode stability and air stability;

the specific method comprises the following steps: doping LiNO in the sulfide solid electrolyte₃Providing the sulfide solid electrolyte with PS₄ ^3-/POS₃ ^3-And (5) structure.

A fourth aspect of the invention provides a use of the sulfide solid electrolyte in an all-solid battery.

Compared with the prior art, the invention has the following beneficial effects:

1. the invention only dopes LiNO with proper amount₃The sulfide solid electrolyte which can stably exist with lithium metal for a long time and has excellent air stability can be obtained through a simple ball milling and calcining method. The sulfide solid electrolyte synthesized by the methodThe interface stability of the sulfide solid electrolyte and the lithium metal cathode is improved, the air stability of the electrolyte is also improved, and a certain theoretical basis is laid for the practical application of the all-solid-state battery.

2. When LiNO is present₃When the doping ratio is 2 percent, the prepared Li_2.96P_0.98N_0.02S_3.92O_0.06The structure of the sulfide solid electrolyte is mainly PS₄ ^3-/POS₃ ^3-，PS₄ ^3-The structure makes the novel sulfide solid electrolyte have higher conductivity, and the POS₃ ^3-The structure enables the novel sulfide solid electrolyte to have higher lithium cathode stability and air stability, especially air stability. Undoped Li₃PS₄The glass electrolyte produced 1.0368cm in 60min³ g^-1H₂S gas, Li_2.96P_0.98N_0.02S_3.92O_0.06The sulfide solid electrolyte has almost no H under the same time and test conditions₂S gas is generated, and the novel sulfide solid electrolyte prepared by the method has good air stability. Further, from Li_2.96P_0.98N_0.02S_3.92O_0.06The comparative graphs of XRD before and after the sulfide solid electrolyte is exposed in air for 60min show that the peak shapes of the sulfide solid electrolyte and the XRD are almost unchanged, and the novel sulfide solid electrolyte is further proved to have excellent air stability.

3. The preparation method is simple in operation process and more beneficial to industrial application.

Drawings

FIG. 1 shows LiNO differently from examples 1 to 5₃XRD spectrogram of the novel sulfide solid electrolyte with doping proportion; wherein (a) represents LiNO₃The doping is 2%; (b) represents LiNO₃The doping is 4%; (c) represents LiNO₃The doping is 6%; (d) represents LiNO₃The doping is 8%;

FIG. 2 shows LiNO differently from examples 1 to 5₃Of novel sulfide solid electrolytes in a doping ratio⁷A Li NMR spectrum; wherein (a)Represents LiNO₃The doping is 2%; (b) represents LiNO₃The doping is 4%; (c) represents LiNO₃The doping is 6%; (d) represents LiNO₃The doping is 8%;

FIG. 3 is a sequence showing the difference in LiNO in examples 1 to 5₃Of novel sulfide solid electrolytes in a doping ratio³¹A P NMR spectrum; wherein (a) represents LiNO₃The doping is 2%; (b) represents LiNO₃The doping is 4%; (c) represents LiNO₃The doping is 6%; (d) represents LiNO₃The doping is 8%;

FIG. 4 shows LiNO differently from examples 1 to 5₃XPS spectrum of novel sulfide solid electrolyte with doping proportion;

FIG. 5 shows the low current density (0.3 mA/cm) of the novel sulfide solid electrolyte of example 2²) Stability of the lower lithium negative electrode;

FIG. 6 shows the high current density (15 mA/cm) of the novel sulfide solid electrolyte of example 2²) Stability of the lower lithium negative electrode;

FIG. 7 shows the high current density (20 mA/cm) of the novel sulfide solid electrolyte in example 2²) Stability of the lower lithium negative electrode;

FIG. 8 is an air stability plot of the novel sulfide solid electrolyte of example 2;

fig. 9 is a comparative XRD pattern before and after exposure of the novel sulfide solid electrolyte of example 2 to air for 1 h.

Detailed Description

The present invention will be described in further detail with reference to specific embodiments, but it should not be construed that the scope of the present invention is limited to the following examples. Various alterations and modifications made by those skilled in the art and ordinary skill in the art without departing from the spirit of the method described above are intended to be included within the scope of the invention.

Preparation of samples

Example 1

Mixing a certain proportion of Li₂S、P₂S₅The precursors are uniformly mixed in a glove, placed in a 45mL zirconium dioxide ball milling tank, and simultaneously added with 5 zirconium oxidesAnd (5) sealing the balls, and transferring the balls into a ball mill. Ball milling was carried out at 370rpm for 60 h. And calcining the ball-milled mixed powder at 270 ℃ for 4h to obtain the sulfide solid electrolyte material without any doping.

Example 2

Will contain 2% LiNO₃Doping ratio of Li₂S、P₂S₅The precursors are uniformly mixed in a glove, placed in a 45mL zirconium dioxide ball milling tank, simultaneously added with 5 zirconium dioxide balls, sealed and transferred into a ball mill. Ball milling was carried out at 370rpm for 60 h. And calcining the ball-milled mixed powder at 270 ℃ and 290 ℃ for 4h to obtain the final sulfide solid electrolyte material, and screening out the optimal calcining temperature.

Example 3

In example 2, LiNO was added₃A sulfide solid electrolyte of example 3 was obtained at an optimum calcination temperature in the same manner as in example 2 except that the doping ratio was adjusted to 4%.

Example 4

In example 2, LiNO was added₃A sulfide solid electrolyte of example 4 was obtained at an optimum calcination temperature in the same manner as in example 2 except that the doping ratio was adjusted to 6%.

Example 5

In example 2, LiNO was added₃A sulfide solid electrolyte of example 5 was obtained at an optimum calcination temperature in the same manner as in example 2, except that the doping ratio was adjusted to 8%.

(II) conductivity test

The ionic conductivity of the solid electrolyte was obtained by analyzing an Electrochemical Impedance Spectroscopy (EIS). The prepared electrolyte material powder (examples 1-5) was pressed at 320MPa into a sheet having a diameter of 10mm and a thickness of about 1mm, and both sides of the sheet were blocked with stainless steel disks to form a symmetrical cell SS/Li_3-0.02xP_1-0.01xN_xS_4-0.04xO_3xand/SS. EIS was tested at an electrochemical workstation (PARSTAT,2273) at a frequency ranging from 10Hz to 1 MHz. The test procedure was carried out under argon atmosphere. The test results are shown in tables 1 and 2.

TABLE 1 Li_2.96P_0.98N_0.02S_3.92O_0.06Conductivity at different calcination temperatures

As can be seen from Table 1, when LiNO was used₃At a doping ratio of 2%, the conductivity before calcination was 3.21X 10^-4S cm^-1. The conductivity is nearly improved by one order of magnitude through high-temperature calcination at 270 ℃. The calcination temperature continues to rise to 290 ℃ and the conductivity decreases conversely, so the optimum calcination temperature is 270 ℃.

TABLE 2 different LiNO₃Doping proportion of conductivity of sulfide solid electrolyte after calcination at 270 DEG C

As shown in Table 2, 2% LiNO₃The doped sulfide solid electrolyte has the highest ionic conductivity of 1.58 x 10^-3S cm^-1Therefore, the optimum doping ratio is 2%.

(III) characterization analysis

Different LiNO₃The XRD test results of the novel sulfide solid electrolyte at the doping ratio are shown in fig. 1.

As shown in FIG. 1, incorporation of different proportions of LiNO₃XRD spectrogram of prepared sulfide solid electrolyte and undoped Li₃PS₄The spectra are consistent without other impurities, indicating LiNO₃Successfully incorporated into the original structure.

Different LiNO₃Method for preparing novel sulfide solid electrolyte with doping ratio⁷The Li NMR spectrum is shown in FIG. 2.

As shown in fig. 2, only one peak appears for all sulfide solid-state electrolytes. And when the doping ratio is 2%, the intensity of the peak is the largest, and the peak shape is the sharpest, indicating that at this ratio, the conductivity of the sulfide solid electrolyte is the highest, which is consistent with the previous test results of conductivity.

Different LiNO₃Of novel sulfide solid electrolytes in a doping ratio³¹The P NMR spectrum is shown in FIG. 3.

As shown in FIG. 3, the precursor is not LiNO₃Then, the obtained sulfide solid electrolyte mainly comprises a high conductive phase PS₄ ^3-And part P₂S₆ ^4-. When the doping ratio is 2%, P₂S₆ ^4-The corresponding peak disappeared. Further, a highly conductive phase PS₄ ^3-S in (1) may be converted to POS by substitution with an O₃ ^3-The structure and PS₄ ^3-Compared with the prior art, the air conditioner has better stability to air. With increasing doping amount, PS₄ ^3-/POS₃ ^3-The corresponding peak gradually decreases, and when the doping ratio increases to 6%, more S is substituted by O and PO appears₂S₂ ^3-And PO₄ ^3-Corresponding peak, and also a small fraction of P₂S₇ ^4-And occurs.

According to different LiNO₃Method for preparing novel sulfide solid electrolyte with doping ratio⁷Li NMR and³¹the analysis result of the P NMR spectrum shows that. When LiNO is present₃At a doping ratio of 2%, Li_2.96P_0.98N_0.02S_3.92O_0.06The structure of the sulfide solid electrolyte is mainly PS of a high conductive phase₄ ^3-And POS with air stability₃ ^3-Therefore, the novel sulfide solid electrolyte at the doping ratio has the highest ionic conductivity and the most excellent air stability.

Different LiNO₃The XPS spectrum of the novel sulfide solid electrolyte with doping ratio is shown in FIG. 4. For undoped and doped Li₃PS₄131.50eV corresponds to PS₄ ^3-Binding energy of the middle P2P peak. In addition, the doped electrolyte has an additional peak at 132.95eV, representing PO_xThe binding energy of the S group is consistent with the data of the binding energy of oxygen-sulfur bonds in other documents. The peak position of S2 p for the doped electrolyte was 161.00eV, and the binding energy was reduced compared to the position of S2 p for the undoped sulfide electrolyte, indicating the formation of oxygen-sulfur bonds in the doped solid state electrolyte. The disappearance of the peak at 168eV for the doped electrolyte compared to the undoped electrolyte indicates that both S and O atoms are chemically bonded to the cation. At the same time, the O1s peak at 531.73eV remained consistent with the P — O bond, further demonstrating that the novel sulfide solid electrolyte obtained by doping forms a new P — O bond. Thus, it was confirmed from XPS data that the amount of the dye in PS was small₄ ^3-O atoms are successfully introduced into the ion-conducting group, so that the chemical and electrochemical stability of the solid electrolyte is improved.

(IV) stability test

Li_2.96P_0.98N_0.02S_3.92O_0.06Stability test for lithium negative electrode

Test method

Adopts a stainless steel mould to assemble Li/Li in a glove box_2.96P_0.98N_0.02S_3.92O_0.06The Li symmetrical battery carries out constant current circulation at room temperature under different current densities to obtain a polarization curve.

As shown in FIG. 5, the symmetric cell was at 0.3mAcm^-2After cycling for 1000h at a current density of (1), the overpotential is only 11mV, indicating that Li_2.96P_0.98N_0.02S_3.92O_0.06The solid electrolyte and the lithium negative electrode have no side reaction in the circulating process under low current density and small interface impedance, and the solid electrolyte and the lithium negative electrode can stably exist for a long time.

When the circulating current density of the symmetrical cell was increased to 15mAcm, as shown in FIGS. 6-7^-2The battery cycle 260h begins to short circuit; continuously increasing the circulating current density to 20mA cm^-2The battery cycle 170h just begins to short, indicating Li_2.96P_0.98N_0.02S_3.92O_0.06Solid state electricityThe electrolyte also has relatively excellent cycling stability for a lithium negative electrode at high cycling current densities.

Li_2.96P_0.98N_0.02S_3.92O_0.06Air stability test

Test conditions

Exposing the electrolyte material at room temperature in an atmosphere of 45-50% air humidity for 60min, and testing H released from the electrolyte by using a hydrogen sulfide sensor₂The content of S, the test results are shown in FIG. 8.

Undoped Li₃PS₄The glass electrolyte produced 1.0368cm in 60min³ g^-1H₂S gas, Li_2.96P_0.98N_0.02S_3.92O_0.06The electrolyte had almost no H at the same time and under the test conditions₂S gas is generated, and the novel sulfide solid electrolyte prepared by the method has good air stability.

FIG. 9 is Li_2.96P_0.98N_0.02S_3.92O_0.06The comparison graph of XRD before and after the electrolyte is exposed in air for 60min shows that the peak shapes of the electrolyte and the electrolyte are almost unchanged, and further proves that the novel sulfide solid electrolyte has excellent air stability.

Claims

1. A method for improving the stability of a lithium cathode of a sulfide solid electrolyte is characterized in that LiNO is doped in the sulfide solid electrolyte₃Providing the sulfide solid electrolyte with PS₄ ^3-/ POS₃ ^3-Structure;

the sulfide solid state electrolyte includes a compound having a nominal formula of: li_3-0.02xP_1- _0.01xN_0.01xS_4-0.04xO_3xWherein x = 2,4,6, 8.

2. The method of claim 1, wherein the preparation of the sulfide solid state electrolyte comprises the steps of:

(1) mixing the precursor Li₂S、P₂S₅And LiNO₃Grinding and mixing in an argon atmosphere to obtain a mixed precursor;

(2) placing the mixed precursor obtained in the step (1) in a ball mill, and carrying out ball milling treatment to obtain mixed powder;

(3) calcining the mixed powder obtained in the step (2) to obtain a sulfide solid electrolyte;

in the step (1), LiNO is added based on the total molar mass of the sulfide solid electrolyte₃The doping proportion of (A) is 2 mol%, 4 mol%, 6 mol% or 8 mol%;

in the step (3), the calcining temperature is 270-290 ℃, and the calcining time is 2-5 h.

3. The method according to claim 2, wherein in step (1), the precursor Li is first prepared by using a manual milling method₂S、P₂S₅And LiNO₃Mixing; in the step (2), the rotation speed of the ball mill is 370-510 rpm, and the ball milling time is 60-70 h.

4. The method according to claim 2, wherein in the step (2), in order to avoid the influence of heat generated in the ball milling process on the reaction product, the ball milling is stopped for 20-30 min every 25-30 min.

5. The method of claim 2, wherein in step (3), the calcination environment is an inert atmosphere.

6. The method according to claim 1, characterized in that the sulfide solid state electrolyte of claim 1 is used in an all-solid-state battery.