CN118136936A - Lithium-rich sulfide solid electrolyte and application thereof - Google Patents

Abstract

The invention belongs to the technical field of batteries, and relates to a lithium-rich sulfide solid electrolyte and application thereof, wherein the electrolyte has the following chemical composition: li _10+xM_1‑xQ_xP₂S_12‑ySe_y, wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, M is a +4 valence element, and Q is a +3 valence element. The lithium-rich solid electrolyte can realize the effect of supplementing lithium to the anode or cathode material in the charge and discharge process, thereby improving the first-circle coulomb efficiency and the cycle stability of the battery; furthermore, the introduction of Se in the system helps to obtain a larger unit cell volume, thereby accelerating the transport of lithium ions; the lithium-rich sulfide electrolyte prepared by the method has high ion conductivity and low activation energy, and has good electrochemical stability on lithium metal.

Description

A lithium-rich sulfide solid electrolyte and its application

Technical Field

The present invention relates to the technical field of solid-state battery materials, and in particular to a lithium-rich sulfide solid electrolyte and a preparation method and application thereof.

Background technique

As an important energy storage device, lithium-ion batteries have been widely used in electric vehicles and electronic products. However, traditional lithium-ion batteries using flammable organic liquid electrolytes and polymer separators have reached their performance limits and have brought serious safety issues. Therefore, the focus of current battery system research has shifted to the use of solid electrolytes (such as polymers, oxides, sulfides, and halide solid electrolytes) with excellent ionic conductivity, stability, and mechanical properties. Among them, the ionic conductivity of sulfide solid electrolytes can reach the level of commercial liquid electrolytes, so they have been widely studied. However, sulfide electrolytes have problems such as narrow electrochemical stability window, high reaction activity, and chemical/electrochemical incompatibility with high-voltage positive electrodes and lithium metal negative electrodes.

Summary of the invention

Based on the problems existing in the above-mentioned prior art, the first purpose of the present invention is to provide a lithium-rich sulfide solid electrolyte and its preparation method and application, so as to solve the problems of low ionic conductivity of solid electrolyte and poor electrochemical stability to lithium metal, and realize the technology of replenishing lithium to the positive or negative electrode from the electrolyte level.

Another object of the present invention is to provide an all-solid-state battery, comprising the above-mentioned lithium-rich sulfide solid electrolyte. The all-solid-state battery has high initial coulombic efficiency and cycle stability.

To achieve the above object, the present invention adopts the following technical solutions:

In a first aspect, the present invention provides a lithium-rich sulfide solid electrolyte, wherein the composition of the lithium-rich sulfide solid electrolyte is Li _10+x M _1-x Q _x P ₂ S _12-y Se _y , and 0<x≤1, 0≤y≤1, wherein: M is a +4-valent element, which is one or more of Si, Ge, and Sn elements; Q is a +3-valent element, including but not limited to one or more of B, Al, Ga, In, and Bi elements.

Since the valence state of the Q element is +3 and the valence state of the M element is +4, according to the charge conservation principle, the sulfide solid electrolyte in the present invention is in a lithium-rich state, and during the charge and discharge process, the lithium-rich electrolyte can replenish lithium to the positive electrode or the negative electrode. In addition, since the electronegativity of the selenium ions therein is relatively small and the binding force on the cations is relatively low, therefore, the introduction of selenium ions into the system is conducive to the migration of lithium ions, thereby improving the ionic conductivity.

In a second aspect, the present invention provides a method for preparing the lithium-rich sulfide solid electrolyte according to the first aspect, the preparation method comprising the following steps:

(1) According to the stoichiometric ratio _of Li10 _{+xM1 - xQxP2S12 -ySey ,} Li source, M source, Q source, P source, S source and Se source are uniformly mixed, and then ball milled for 0.5 to 24 h at a ball milling speed of 300 to 1200 rpm to obtain a sulfide solid electrolyte precursor powder.

(2) Sintering the precursor powder at high temperature to obtain the lithium-rich sulfide solid electrolyte. The sintering heating rate is 1 to 3°C/min, the sintering temperature is 500 to 650°C, and the calcination time is 2 to 24 hours.

The raw materials for preparing the lithium-rich sulfide solid electrolyte include the following components:

Li source: including but not limited to one or more of Li ₂ S, Li ₂ Se, and LiH;

M source: including but not limited to one or more of silicon powder, germanium powder, tin powder, Si ₂ S, Ge ₂ S, Sn ₂ S;

Q source: including but not limited to one or more of boron powder, aluminum powder, indium powder, B ₂ S ₃ , Al ₂ S ₃ , In ₂ S ₃ , and Bi ₂ S ₃ ;

P source: including but not limited to one or more of phosphorus powder, P ₂ S ₅ , P ₄ S ₆ ;

S source: including but not limited to one or more of sulfur powder, Li ₂ S, P ₂ S ₅ , P ₄ S ₆ , B ₂ S ₃ , Al ₂ S ₃ , In ₂ S ₃ , Bi ₂ S ₃ , Li ₂ S;

Se source: including but not limited to one or more of selenium powder, Li ₂ Se, B ₂ Se ₃ , Al ₂ Se ₃ , In ₂ Se ₃ , Bi ₂ Se ₃ , Si ₂ Se, Ge ₂ Se, and Sn ₂ Se.

In the third aspect, the present invention also provides an all-solid-state battery, which is composed of three core parts: a positive electrode, a negative electrode and an electrolyte. In the all-solid-state battery, in addition to the electrolyte layer located between the positive and negative electrodes of the battery using the lithium-rich sulfide solid electrolyte described in the first aspect, at least one of the positive electrode material and the negative electrode material also contains the lithium-rich sulfide solid electrolyte described in the first aspect.

The composition of the positive electrode material or the negative electrode material may be: a positive electrode active material or a negative electrode active material, a solid electrolyte and a conductive agent. The positive electrode active material includes one or more of lithium cobalt oxide, lithium iron phosphate, ternary materials, and lithium-rich manganese-based materials. The negative electrode active material includes one or more of graphite, silicon-based materials, lithium metal, and lithium-indium alloys. The solid electrolyte is the lithium-rich sulfide solid electrolyte described in the first aspect. The conductive agent is one or more of carbon black, carbon nanotubes, carbon fibers, Ketjen black, and acetylene black materials.

Compared with the prior art, the beneficial effects of the present invention are as follows:

1. The lithium-rich sulfide solid electrolyte of the present invention has high ionic conductivity, low activation energy, and exhibits good electrochemical stability to lithium metal.

2. In the solid electrolyte of the present invention, the lithium-rich state of the sulfide solid electrolyte is achieved by partially replacing the +4 element with the +3 valent element according to the charge conservation principle.

3. From the perspective of electrolyte, by adding the lithium-rich sulfide solid electrolyte of the present invention to the positive electrode or the negative electrode, lithium can be replenished to the positive electrode or the negative electrode material in the form of electrolyte during the battery cycle, thereby improving the first-cycle coulombic efficiency and cycle stability of the battery.

4. The lithium-rich sulfide solid electrolyte of the present invention has a low electronegativity of selenium ions, a low binding force on cations, and a large radius of selenium ions, which is beneficial to the migration of lithium ions, thereby improving the electrolyte ion conductivity.

5. The lithium-rich sulfide electrolyte of the present invention is applied to all-solid-state batteries, which can effectively improve the first-cycle discharge specific capacity and coulombic efficiency of the battery.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. By reading the detailed description of the embodiments with reference to the following drawings, other features, purposes and advantages of the present invention will become more apparent.

FIG1 is an X-ray diffraction (XRD) diagram of the solid electrolytes of Examples 1 to 3 of the present invention and Comparative Examples 1 to 2;

FIG2 is an AC impedance diagram of the solid electrolytes of Examples 1 to 3 of the present invention and Comparative Examples 1 to 2;

FIG3 is a diagram showing the Arrhenius equation fitting of the solid electrolytes of Examples 1 to 3 of the present invention and Comparative Examples 1 to 2 at different temperatures, where the numbers in the diagram represent the activation energy obtained by fitting;

FIG4 is a test result of lithium symmetric batteries assembled with solid electrolytes of Examples 1 to 3 of the present invention and Comparative Examples 1 to 2;

FIG5 is a graph showing the cycle performance of all-solid-state batteries assembled with solid electrolytes of Examples 1 to 3 of the present invention and Comparative Examples 1 to 2.

Detailed ways

The lithium-rich sulfide solid electrolyte of the present invention is further described below through specific examples and drawings. It should be understood that the specific examples described herein are only used to help understand the present invention and are not used to specifically limit the present invention.

Example 1

This embodiment provides a lithium-rich sulfide solid electrolyte with a composition of Li _10.1 Sn _0.9 B _0.1 P ₂ S _11.9 Se _0.1 (M=Sn, Q=B, x=0.1, y=0.1), and the specific steps of the preparation method thereof are as follows:

According to the stoichiometric ratio of Li ₂ S: P ₂ S ₅ : SnS ₂ : B powder: S powder: Se powder = 5.05: 1: 0.9: 0.1: 0.05: 0.1, the molar ratio was weighed, and after manual grinding for 15 minutes, it was placed in a stainless steel ball milling jar, and zirconia balls were added at a ball-to-material mass ratio of 20: 1 for ball milling. The ball mill speed was 1200 rpm, and the ball milling time was 2 hours to obtain a uniformly mixed precursor. Then it was placed in a quartz tube, heated to 600°C at a rate of 2°C/min, kept warm for 2 hours, and cooled to obtain Li _10.1 Sn _0.9 B _0.1 P ₂ S _11.9 Se _0.1 electrolyte powder. The whole process was carried out under an argon protective atmosphere.

Example 2

This embodiment provides a lithium-rich sulfide solid electrolyte with a composition of Li _10.3 Sn _0.7 In _0.3 P ₂ S _11.55 Se _0.45 (M = Sn, Q = In, x = 0.3, y = 0.45), and the specific steps of the preparation method thereof are as follows:

Weigh according to the molar ratio of the stoichiometric ratio of Li ₂ S: P ₂ S ₅ : SnS ₂ : In ₂ Se ₃ = 5.15: 1: 0.7: 0.15, grind manually for 15 minutes, put into a ball mill, add zirconium oxide balls according to the ball-to-material mass ratio of 20: 1, the ball mill speed is 1200rpm, the ball milling time is 2 hours, and a uniformly mixed precursor is obtained. Then put it into a quartz tube, heat it to 600℃ at a rate of 2℃/min, keep it warm for 2 hours, and cool it to obtain Li _10.3 Sn _0.7 In _0.3 P ₂ S _11.55 Se _0.45 solid electrolyte powder. The whole process is carried out under argon protective atmosphere.

Example 3

This embodiment provides a lithium-rich sulfide solid electrolyte with a composition of Li _10.1 Sn _0.9 Bi _0.1 P ₂ S _11.85 Se _0.15 (M = Sn, Q = Bi, x = 0.1, y = 0.15), and the specific steps of the preparation method are as follows:

Weigh according to the molar ratio of the stoichiometric ratio of Li ₂ S: P ₂ S ₅ : SnS ₂ : Bi ₂ Se ₃ = 5.05: 1: 0.9: 0.05, grind manually for 15 minutes, put into a ball mill, add zirconium oxide balls according to the ball-to-material mass ratio of 20: 1, the ball mill speed is 1200rpm, the ball milling time is 2 hours, and a uniformly mixed precursor is obtained. Then put it into a quartz tube, heat it to 600℃ at a rate of 2℃/min, keep it warm for 2 hours, and cool it to obtain Li _10.1 Sn _0.9 Bi _0.1 P ₂ S _11.85 Se _0.15 solid electrolyte powder. The whole process is carried out under argon protective atmosphere.

Comparative Example 1

This comparative example provides a solid electrolyte composed of Li ₁₀ SnP ₂ S ₁₂ (M=Sn, x=0, y=0), and the specific steps of the preparation method thereof are as follows:

Weigh according to the molar ratio of Li ₂ S: P ₂ S ₅ : SnS ₂ = 5: 1: 1, grind manually for 15 minutes, put into a ball mill, add zirconium oxide balls according to the ball-to-material mass ratio of 20: 1, the ball mill speed is 1200rpm, the ball milling time is 2 hours, and a uniformly mixed precursor is obtained. Then put it into a quartz tube, heat it to 600℃ at a rate of 2℃/min, keep it warm for 2 hours, and cool it to obtain Li ₁₀ SnP ₂ S ₁₂ solid electrolyte powder. The whole process is carried out under argon protective atmosphere.

Comparative Example 2

This comparative example provides a solid electrolyte having a composition of Li ₁₀ SnP ₂ S _11.9 Se _0.1 (M=Sn, x=0, y=0.1), and the specific steps of the preparation method thereof are as follows:

Weigh according to the molar ratio of the stoichiometric ratio of Li ₂ S: P ₂ S ₅ : SnS ₂ : Li ₂ Se = 4.9: 1: 1: 0.1, grind manually for 15 minutes, put into a ball mill, add zirconium oxide balls according to the ball-to-material mass ratio of 20: 1, the ball mill speed is 600 rpm, the ball milling time is 8 hours, and a uniformly mixed precursor is obtained. Then put it into a quartz tube, heat it to 550°C at a rate of 2°C/min, keep it warm for 10 hours, and cool it to obtain Li ₁₀ SnP ₂ S _11.9 Se _0.1 solid electrolyte powder. The whole process is carried out under argon protective atmosphere.

The solid electrolytes of the embodiments and comparative examples were subjected to the following performance tests:

(1) Structural characterization: XRD test. The test results are summarized in Figure 1.

(2) Ionic conductivity: AC impedance method, the test frequency is 1 MHz to 0.1 Hz, the test results are summarized in Table 1 and Figure 2.

(3) Lithium symmetrical battery: The solid electrolyte of the embodiment or comparative example was pressed into a sheet, and lithium foil was attached to both ends of the electrolyte sheet to assemble a lithium symmetrical battery. The battery was charged and discharged for half an hour each at a current density of 0.1 mA/ ^cm2 using a Xinwei charge and discharge tester. The test results are summarized in FIG4 .

(4) All-solid-state battery: LiNi _0.9 Co _0.05 Mn _0.05 O ₂ (NCM9055) is used as the positive electrode active material. The composite positive electrode material is prepared by grinding NCM9055 and the solid electrolyte powder obtained in the embodiment or the comparative example in an agate mortar at a mass ratio of 7:3 for 30 minutes. Subsequently, 80 mg of the solid electrolyte powder of the embodiment or the comparative example is pressed into a sheet. 10 mg of the composite positive electrode powder is evenly spread on one side of the electrolyte sheet and pressed for 3 minutes, and lithium indium alloy is spread on the other side of the electrolyte sheet for testing. The test voltage is 2.2 to 3.68 V. The first two cycles are tested at a current density of 0.05 C (1C = 180 mAh / g), and then cycled at a current density of 0.1 C. The test results are summarized in Table 2 and Figure 5.

Through the above tests, it can be seen that the solid electrolyte powders prepared in Examples 1 to 3 and Comparative Examples 1 to 2 have good crystallinity and high purity (Figure 1). And compared with Comparative Examples 1 to 2, Examples 1 to 3 show lower impedance (Figure 2) and higher ionic conductivity at room temperature (Table 1), indicating that the present invention has the effect of improving the ionic conductivity of sulfide electrolytes. The activation energy results obtained by fitting the ionic conductivity at different temperatures by the Arrhenius formula are shown in Figure 3. The activation energies of Examples 1-3 are all lower than those of Comparative Examples 1 to 2.

Table 1 Ionic conductivity of each comparative example and embodiment

From the lithium symmetric battery test (Figure 4), it can be seen that the polarization voltage of Comparative Examples 1 and 2 increases when the cycle reaches 130h and 200h, respectively, while the polarization voltage of Examples 1 to 3 is lower than that of Comparative Examples 1 and 2 at the same cycle time, and Example 2 can be stably cycled for more than 600h, indicating that the lithium-rich sulfide solid electrolyte of the present invention has better stability to lithium metal. It can be seen from the battery cycle test that the sulfide solid electrolytes obtained in Examples 1 to 3 have higher first-cycle coulomb efficiency and discharge specific capacity (Table 2). Figure 5 also shows that Examples 1 to 3 have better battery cycle performance. This is precisely because the lithium-rich sulfide solid electrolyte prepared by the present invention realizes the role of lithium replenishment in the cycle process of the all-solid-state battery.

Table 2 First cycle coulombic efficiency and discharge specific capacity of all-solid-state batteries assembled in various comparative examples and embodiments

As mentioned above, the present invention is not limited in any form. Although the present invention has been disclosed as above with a preferred implementation case, any simple modification, equivalent change and modification made to the above implementation case based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims (10)

1. A lithium-rich sulfide solid electrolyte, characterized in that: the composition of the lithium-rich sulfide solid electrolyte is Li _10+x M _1-x Q _x P ₂ S _12-y Se _y , with 0<x≤1, 0≤y≤1, wherein M is a +4-valent element and Q is a +3-valent element. 2. A lithium-rich sulfide solid electrolyte according to claim 1, characterized in that: M is one or more of Si, Ge, and Sn elements. 3. A lithium-rich sulfide solid electrolyte according to claim 1, characterized in that: Q is one or more of B, Al, Ga, In and Bi elements. 4. A method for preparing the lithium-rich sulfide solid electrolyte according to any one of claims 1 to 3, characterized in that it comprises the following steps: (1) according to the stoichiometric ratio of Li _10+x M _1-x Q _x P ₂ S _12-y Se _y , a Li source, an M source, a Q source, a P source, an S source and a Se source are uniformly mixed, and then ball milled to obtain a sulfide solid electrolyte precursor powder; (2) Sintering the precursor powder at high temperature to obtain the lithium-rich sulfide solid electrolyte. 5. The preparation method according to claim 4, characterized in that: the Li source is selected from one or more of Li ₂ S, Li ₂ Se, and LiH; the M source is a simple powder of M or a sulfide of M; the Q source is a simple powder of Q or a sulfide of Q; the P source is selected from one or more of phosphorus powder, P ₂ S ₅ , and P ₄ S ₆ ; the S source is selected from one or more of sulfur powder, Li ₂ S, P ₂ S ₅ , P ₄ S ₆ , B ₂ S ₃ , Al ₂ S ₃ , In ₂ S ₃ , Bi ₂ S ₃ , and Li ₂ S; the Se source is selected from one or more of selenium powder, Li ₂ Se, B ₂ Se ₃ , Al ₂ Se ₃ , In ₂ Se ₃ , Bi ₂ Se ₃ , Si ₂ Se, Ge ₂ Se, and Sn ₂ Se. 6. The preparation method according to claim 4, characterized in that the ball milling time in step (1) is 0.5 to 24 hours and the ball milling speed is 300 to 1200 rpm. 7. The preparation method according to claim 4 is characterized in that: in step (2), the heating rate of the high-temperature sintering is 1-5°C/min, the sintering temperature is 500-650°C, and the sintering time is 2-24h. 8. Use of the lithium-rich sulfide solid electrolyte according to any one of claims 1 to 3 in an all-solid-state battery. 9. An all-solid-state battery, comprising three core parts: a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is a lithium-rich sulfide solid electrolyte as described in any one of claims 1 to 3. 10 . The all-solid-state battery according to claim 9 , wherein the material of at least one of the positive electrode and the negative electrode contains the lithium-rich sulfide solid electrolyte according to any one of claims 1 to 3 .