A lithium-rich sulfide solid electrolyte and its application

Abstract

The present invention belongs to the field of battery technology and relates to a lithium-rich sulfide solid electrolyte and its application. The electrolyte has the following chemical composition: Li 10+x M 1‑x Q x P2S 12‑y Se y , and 0

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state battery materials, and particularly to a lithium-rich sulfide solid electrolyte, a preparation method thereof, and an application thereof. Background Art

[0002] 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 diaphragms have reached their performance limits and brought serious safety problems. Therefore, the current focus of battery system research has shifted to solid electrolytes (such as polymer, oxide, sulfide, and halide solid electrolytes) with excellent ionic conductivity, stability, and mechanical properties. Among them, sulfide solid electrolytes can achieve the level of commercial liquid electrolytes in terms of ionic conductivity, so they have been widely studied. However, sulfide electrolytes have problems such as a narrow electrochemical stability window, high reactivity, and chemical / electrochemical incompatibility with high-voltage positive electrodes and lithium metal negative electrodes. Summary of the Invention

[0003] Based on the problems existing in the above-mentioned prior art, the first object of the present invention is to provide a lithium-rich sulfide solid electrolyte, a preparation method thereof, and an application thereof, so as to solve problems such as low ionic conductivity of the solid electrolyte and poor electrochemical stability to lithium metal, and realize the technology of lithium supplementation to the positive electrode or negative electrode from the electrolyte level.

[0004] Another object of the present invention is to provide a all-solid-state battery including the above-mentioned lithium-rich sulfide solid electrolyte. This all-solid-state battery has a high initial Coulomb efficiency and cycle stability.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] In the first aspect, the present invention provides a lithium-rich sulfide solid electrolyte, and the composition of the lithium-rich sulfide solid electrolyte is Li

[0007] , y , x , , 12-y , , 10+x ,

[0006] , 1-x ,

[0005] M 1-x Q x P2S 12-y Se y where 0 < x ≤ 1 and 0 ≤ y ≤ 1, and 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. [[ID={34]]

[0007] Since the valence state of element Q is +3 and that of element M is +4, according to the principle of charge conservation, the sulfide solid electrolyte in the present invention is lithium-rich. During the charge and discharge process, the lithium-rich electrolyte can replenish lithium to the positive or negative electrode. In addition, since the selenium ions therein have a low electronegativity and a low binding force on cations, the introduction of selenium ions into the system facilitates the migration of lithium ions, thereby improving ionic conductivity.

[0008] 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:

[0009] (1) Press Li 10+x M 1-x Q x P2S 12-y Se y The Li source, M source, Q source, P source, S source and Se source are mixed uniformly in a stoichiometric ratio, 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.

[0010] (2) Sintering the precursor powder at a high temperature to obtain the lithium-rich sulfide solid electrolyte. The sintering temperature is 500-650° C. at a heating rate of 1-3° C. / min and a sintering time of 2-24 h.

[0011] The raw materials for preparing the lithium-rich sulfide solid electrolyte include the following components:

[0012] Li source: including but not limited to one or more of Li2S, Li2Se, and LiH;

[0013] M source: including but not limited to one or more of silicon powder, germanium powder, tin powder, Si2S, Ge2S, Sn2S;

[0014] Q source: one or more of but not limited to boron powder, aluminum powder, indium powder, B2S3, Al2S3, In2S3, Bi2S3;

[0015] P source: including but not limited to one or more of phosphorus powder, P2S5, P4S6;

[0016] S source: including but not limited to one or more of sulfur powder, Li2S, P2S5, P4S6, B2S3, Al2S3, In2S3, Bi2S3, Li2S;

[0017] Se source: including but not limited to one or more of selenium powder, Li2Se, B2Se3, Al2Se3, In2Se3, Bi2Se3, Si2Se, Ge2Se, and Sn2Se.

[0018] In a 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.

[0019] The positive electrode material or negative electrode material may be composed of 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.

[0020] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0021] 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.

[0022] 2. In the solid electrolyte of the present invention, by partially replacing the +4 element with the +3 element, the lithium-rich state of the sulfide solid electrolyte is achieved according to the principle of charge conservation.

[0023] 3. From the perspective of electrolyte, by adding the lithium-rich sulfide solid electrolyte of the present invention to the positive electrode or negative electrode, lithium can be replenished to the positive electrode or 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.

[0024] 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 conducive to the migration of lithium ions, thereby improving the electrolyte ion conductivity.

[0025] 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 capacity and coulombic efficiency of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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.

[0027] Figure 1are X-ray diffraction (XRD) patterns of the solid electrolytes of Examples 1 to 3 of the present invention and Comparative Examples 1 to 2;

[0028] Figure 2 1 is an AC impedance diagram of the solid electrolytes of Examples 1 to 3 of the present invention and Comparative Examples 1 to 2;

[0029] Figure 3 1 is a fitting diagram of the Arrhenius formula at different temperatures for the solid electrolytes of Examples 1 to 3 of the present invention and Comparative Examples 1 to 2, where the numbers represent the activation energy obtained by fitting;

[0030] Figure 4 These are the test results of lithium symmetric batteries assembled with solid electrolytes of Examples 1 to 3 of the present invention and Comparative Examples 1 to 2;

[0031] Figure 5 It is a cycle performance diagram 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 DESCRIPTION

[0032] 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 intended to limit the present invention.

[0033] Example 1

[0034] This embodiment provides a composition of Li 10.1 Sn 0.9 B 0.1 P2S 11.9 Se 0.1 The specific steps of the preparation method of the lithium-rich sulfide solid electrolyte (M=Sn, Q=B, x=0.1, y=0.1) are as follows:

[0035] According to the stoichiometric ratio of Li2S: P2S5: SnS2: 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 mill, and zirconia balls were added at a ball-to-material mass ratio of 20:1, and the ball mill speed was 1200 rpm. The ball milling time was 2 hours to obtain a uniformly mixed precursor. Then it was placed in a quartz tube, heated to 600℃ at a rate of 2℃ / min, kept at this temperature for 2 hours, and cooled to obtain Li 10.1 Sn 0.9 B 0.1 P2S 11.9 Se 0.1 Electrolyte powder. The whole process was carried out under argon protective atmosphere.

[0036] Example 2

[0037] This embodiment provides a composition of Li 10.3 Sn 0.7 In 0.3 P2S 11.55 Se 0.45 The specific steps of the preparation method of the lithium-rich sulfide solid electrolyte (M=Sn, Q=In, x=0.3, y=0.45) are as follows:

[0038] According to the stoichiometric ratio of Li2S: P2S5: SnS2: In2Se3 = 5.15: 1: 0.7: 0.15, the molar ratio was weighed and manually ground for 15 minutes. Zirconia balls were added according to the ball-to-material mass ratio of 20: 1 and the ball milling speed was 1200 rpm. The ball milling time was 2 hours to obtain a uniformly mixed precursor. Then it was placed in a quartz tube and heated to 600 ° C at a rate of 2 ° C / min. It was kept at this temperature for 2 hours and cooled to obtain Li 10.3 Sn 0.7 In 0.3 P2S 11.55 Se 0.45 Solid electrolyte powder. The entire process is carried out under argon protective atmosphere.

[0039] Example 3

[0040] This embodiment provides a composition of Li 10.1 Sn 0.9 Bi 0.1 P2S 11.85 Se 0.15 (M=Sn,Q=Bi,x=0.1,y=0.15) lithium-rich sulfide solid electrolyte, the preparation method thereof has the following specific steps:

[0041] According to the stoichiometric ratio of Li2S: P2S5: SnS2: Bi2Se3 = 5.05: 1: 0.9: 0.05, the molar ratio was weighed and manually ground for 15 minutes. Then, the mixture was placed in a ball mill. Zirconia balls were added according to the ball-to-material mass ratio of 20: 1 and the ball mill speed was 1200 rpm. The ball milling time was 2 hours to obtain a uniformly mixed precursor. Then, the mixture was placed in a quartz tube and heated to 600 ° C at a rate of 2 ° C / min. The mixture was kept at this temperature for 2 hours and cooled to obtain Li 10.1 Sn 0.9 Bi 0.1 P2S 11.85 Se 0.15 Solid electrolyte powder. The entire process is carried out under argon protective atmosphere.

[0042] Comparative Example 1

[0043] This comparative example provides a composition of Li 10 SnP2S 12The specific steps of the preparation method of the solid electrolyte (M=Sn, x=0, y=0) are as follows:

[0044] According to the stoichiometric ratio of Li2S: P2S5: SnS2 = 5:1:1 molar ratio, weigh it, grind it manually for 15 minutes, put it into a ball mill, add zirconium oxide balls according to the ball-to-material mass ratio of 20:1, and mill it at a ball mill speed of 1200 rpm for 2 hours to obtain a uniformly mixed precursor. 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 SnP2S 12 Solid electrolyte powder. The entire process is carried out under argon protective atmosphere.

[0045] Comparative Example 2

[0046] This comparative example provides a composition of Li 10 SnP2S 11.9 Se 0.1 The specific steps of the preparation method of the solid electrolyte (M=Sn, x=0, y=0.1) are as follows:

[0047] According to the stoichiometric ratio of Li2S: P2S5: SnS2: Li2Se = 4.9: 1: 1: 0.1, the molar ratio was weighed and manually ground for 15 minutes. Zirconia balls were added according to the ball-to-material mass ratio of 20: 1 and the ball milling was carried out at a speed of 600 rpm for 8 hours to obtain a uniformly mixed precursor. Then, the precursor was placed in a quartz tube and heated to 550 ° C at a rate of 2 ° C / min. The temperature was kept at this temperature for 10 hours and the Li2Se was obtained after cooling. 10 SnP2S 11.9 Se 0.1 Solid electrolyte powder. The entire process is carried out under argon protective atmosphere.

[0048] The solid electrolytes of the embodiments and comparative examples were subjected to the following performance tests:

[0049] (1) Structural characterization: XRD test, the test results are summarized in Figure 1 middle.

[0050] (2) Ionic conductivity: AC impedance method, the test frequency is 1MHz~0.1Hz, the test results are summarized in Table 1 and Figure 2 middle.

[0051] (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 charge and discharge tester was used at 0.1 mA / cm 2 The test results are summarized in Figure 4 middle.

[0052] (4) All-solid-state battery: using LiNi 0.9 Co 0.05 Mn 0.05 O2 (NCM9055) is 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 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 comparative example is pressed into a sheet. Take 10 mg of the composite positive electrode powder and spread it evenly on one side of the electrolyte sheet and press it for 3 minutes. Lithium indium alloy is spread on the other side of the electrolyte sheet for testing. The test voltage is 2.2~3.68V. The first two cycles are tested at a current density of 0.05C (1C=180mAh / g), and then cycled at a current density of 0.1C. The test results are summarized in Tables 2 and Figure 5 middle.

[0053] The above tests show 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 1-2, examples 1-3 showed lower impedance ( Figure 2 ), the ionic conductivity at room temperature is higher (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 using the Arrhenius formula are as follows Figure 3 As shown, the activation energies of Examples 1-3 are all lower than those of Comparative Examples 1-2.

[0054] Table 1 Ionic conductivity of each comparative example and embodiment

[0055]

[0056] Lithium symmetric battery test ( Figure 4 ) It can be seen that the polarization voltage of Comparative Examples 1 and 2 increased after cycling for 130 hours and 200 hours, respectively. However, at the same cycle time, the polarization voltage of Examples 1-3 was lower than that of Comparative Examples 1 and 2, and Example 2 could be stably cycled for more than 600 hours, indicating that the lithium-rich sulfide solid electrolyte of the present invention has better stability for lithium metal. Battery cycling tests show that the sulfide solid electrolytes obtained in Examples 1-3 have higher first-cycle coulombic efficiency and discharge specific capacity (Table 2). Figure 5 It 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 achieves the function of replenishing lithium during the cycle process of the all-solid-state battery.

[0057] Table 2 First cycle coulombic efficiency and discharge specific capacity of all-solid-state batteries assembled in various comparative examples and embodiments

[0058]

[0059] As mentioned above, the present invention is not limited in any form. Although the present invention has been disclosed as above with preferred implementation cases, any simple modifications, equivalent changes and modifications made to the above implementation cases 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

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 P2S 12-y Se y , and 0 < x ≤ 1, 0 < y ≤ 1. Among them, M is a +4-valent element, Q is a +3-valent element. By partially replacing the +4-valent element with the +3-valent element, the lithium-rich state of the sulfide solid electrolyte is achieved according to the principle of charge conservation; M is one or more of Si, Ge, and Sn elements, and Q is one or more of B, Al, Ga, In, and Bi elements.

2. A method for preparing the lithium-rich sulfide solid electrolyte according to claim 1, characterized in that: The following steps are involved: (1) Press Li 10+x M 1-x Q x P2S 12-y Se y The Li source, M source, Q source, P source, S source and Se source are mixed uniformly in a stoichiometric ratio, and then ball milled to obtain a sulfide solid electrolyte precursor powder; (2) Sintering the precursor powder at a high temperature to obtain the lithium-rich sulfide solid electrolyte.

3. The preparation method according to claim 2, wherein: The Li source is selected from one or more of Li2S, Li2Se, 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, P2S5, and P4S6; the S source is selected from one or more of sulfur powder, Li2S, P2S5, P4S6, B2S3, Al2S3, In2S3, Bi2S3, and Li2S; the Se source is selected from one or more of selenium powder, Li2Se, B2Se3, Al2Se3, In2Se3, Bi2Se3, Si2Se, Ge2Se, and Sn2Se.

4. The preparation method according to claim 2, wherein: The ball milling time in step (1) is 0.5~24 h, and the ball milling speed is 300~1200 rpm.

5. The preparation method according to claim 2, wherein: 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 2-24 h.

6. Use of the lithium-rich sulfide solid electrolyte according to claim 1 in an all-solid-state battery.

7. An all-solid-state battery comprising three core parts: a positive electrode, a negative electrode, and an electrolyte, characterized in that: The electrolyte is the lithium-rich sulfide solid electrolyte according to claim 1.

8. The all-solid-state battery according to claim 7, characterized in that: The material of at least one of the positive electrode and the negative electrode contains the lithium-rich sulfide solid electrolyte according to claim 1.

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