Mixture suitable for in-situ construction of positive electrode coating layer and application of mixture in sulfide solid-state battery

Abstract

The invention provides a mixture suitable for in-situ construction of a positive electrode coating layer and application of the mixture in a sulfide solid-state battery, and relates to the technical field of solid-state batteries, the mixture suitable for in-situ construction of the positive electrode coating layer comprises a positive electrode active material, an additive A and an additive B; the molar ratio of the additive A to the additive B is 1: (0.5-2), and the ratio of the total mass of the additive A and the additive B to the mass of the mixture suitable for in-situ construction of the positive electrode coating layer is (1-5): 100; as the HOMO energy level of the additive A is obviously higher than that of the additive B, a compact inner layer taking inorganic components as main components and a flexible outer layer taking organic components as main components can be sequentially formed in situ on the surfaces of the positive electrode active material particles in the first charging process, and the interface impedance of the positive electrode and sulfide solid electrolyte can be reduced. Therefore, the sulfide solid-state battery prepared by adopting the mixture suitable for in-situ construction of the positive electrode coating layer is relatively good in cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid-state batteries, in particular to a mixture suitable for constructing an anode coating layer in situ and its application in sulfide solid-state batteries. BACKGROUND

[0002] Sulfide solid-state batteries have become a focus of research for next-generation power batteries due to their high energy density and high safety. However, the interface between commercial high-voltage anode materials and sulfide solid-state electrolytes is unstable, resulting in poor battery performance. Specifically, the electrochemical window of sulfide solid-state electrolytes is relatively narrow (<4.0 V), and contact with high-voltage anode materials can easily oxidize and decompose to generate insulating products such as Li2S, resulting in increased interface impedance. The lattice distortion of anode materials during charging and discharging leads to solid-solid interface failure, further exacerbating the increase in interface impedance. Therefore, the existing sulfide solid-state batteries have poor cycle performance. Constructing a coating layer on the surface of the anode material is a mainstream strategy to improve interface stability, but existing coating processes are usually cumbersome, and the coating layers formed have uniformity / density problems and are functionally single, resulting in limited improvement effect. SUMMARY

[0003] The problem solved by the present application is how to further improve the cycle performance of sulfide solid-state batteries.

[0004] To solve the above problems, the present application provides a mixture suitable for constructing an anode coating layer in situ, comprising an anode active material, an additive A and an additive B; the molar ratio of the additive A to the additive B is 1:(0.5 to 2), and the ratio of the total mass of the additive A and the additive B to the mass of the mixture suitable for constructing an anode coating layer in situ is (1 to 5):100; the additive A includes at least one of lithium bis(trimethylsilyl)oxalate borate, lithium trifluoromethylsulfonyl oxalate borate, lithium tetra(2,2,2-trifluoroethoxy)borate, lithium bis(pentafluorophenyl)borate, lithium tris(trimethylsilyl)borate, lithium tris(pentafluorophenyl)phosphate, lithium bis(trifluoroacetyl)phosphate, lithium tetra(trifluoromethyl)oxalate phosphate, lithium tris(vinyl trifluoromethyl)borate and lithium bis(perfluoroisopropoxy)oxalate borate; the additive B includes at least one of perfluorobutyrolactone, dimethyl perfluoroglutarate, perfluorohexanedinitrile, perfluoro-1,4-dioxane-2,5-dione, trifluoroacetyl perfluoro-tert-butyl ester, perfluoro-3-methoxypropionic acid methyl ester, perfluoro-2-methyl-1,3-dioxolan-4-one, perfluorotriethylamine, perfluoro-1,3-dimethylcyclohexane, perfluoro-4-methylmorpholine and perfluoro polyether monomethyl ether.

[0005] Compared with the related art, the mixture suitable for constructing the positive electrode coating layer in situ provided by the application is mixed by the positive electrode active material, the additive A and the additive B in a specific ratio, the mixture suitable for constructing the positive electrode coating layer in situ is mixed with the sulfide solid electrolyte and the conductive agent to manufacture the sulfide solid battery as the composite positive electrode material, since the HOMO energy level of the additive A is obviously higher than that of the additive B, in the process of the first charging, the additive A in the composite positive electrode material is preferentially oxidized and decomposed in the initial low voltage interval, the dense inner layer mainly composed of inorganic components is formed on the surface of the positive electrode active material particles, with the increase of the voltage, the additive B in the composite positive electrode is oxidized and decomposed, the flexible outer layer mainly composed of organic components is formed on the surface of the dense inner layer; the dense inner layer mainly composed of inorganic components can effectively block the side reaction between the high-activity sulfide solid electrolyte and the positive electrode material, inhibit the generation of the resistive components in the interface layer, and is beneficial to reducing the interface impedance of the positive electrode and the sulfide solid electrolyte; the flexible outer layer mainly composed of organic components can ensure the transmission of lithium ions, adaptively fill the interface gap to buffer the volume change in the cycle process, and provide close interface contact, so as to cooperatively improve the interface chemical stability and physical integrity of the positive electrode side, and is beneficial to further reducing the interface impedance of the positive electrode and the sulfide solid electrolyte. Thus, the cycle performance of the sulfide solid battery manufactured by using the mixture suitable for constructing the positive electrode coating layer in situ is good.

[0006] Optionally, the positive electrode active material is selected from LiCoO2, LiNi x Mn y Co z O2, aLi2MnO3•(1-a)LiMO2; wherein x+y+z=1, 0

[0007] The application further provides a preparation method of the sulfide solid battery, comprising: Step S1, uniformly mixing the mixture suitable for constructing the positive electrode coating layer in situ, the sulfide solid electrolyte and the conductive agent to obtain the composite positive electrode material; Step S2, sequentially stacking the composite positive electrode material, the sulfide solid electrolyte and the battery negative electrode to form a multi-layer cell structure, and then packaging to obtain the sulfide solid battery.

[0008] Compared with the related art, the sulfide solid-state battery prepared by the method provided by the application has a specific proportion of the additive A and the additive B introduced into the positive electrode, and in the process of the first charging, a dense inner layer mainly composed of inorganic components and a flexible outer layer mainly composed of organic components can be sequentially formed in situ on the surface of the positive electrode active material particles, which is beneficial to reducing the interface impedance of the positive electrode and the sulfide solid-state electrolyte. Therefore, the sulfide solid-state battery prepared by the method has good cycle performance.

[0009] Optionally, the method further comprises performing two charging and discharging treatments, and the charging and discharging treatment comprises: first charging the sulfide solid-state battery to 4.5 V at a charging rate of 0.1 C, and then discharging the sulfide solid-state battery to 2.5 V at a discharging rate of 0.1 C.

[0010] Optionally, in the step S1, the mass ratio of the mixture suitable for in-situ construction of the positive electrode coating layer, the sulfide solid-state electrolyte and the conductive agent is (70 to 80) : (18 to 28) : 2.

[0011] Optionally, the sulfide solid-state electrolyte is selected from one of Li3PS4, Li 5.5 PS 4.5 Cl 1.5 , Li6PS5Cl, Li 5.5 PS 4.5 Br 1.5 , Li6PS5Br and Li 10 GeP2S 12 .

[0012] Optionally, in the step S1, the conductive agent is selected from one of conductive carbon black, Ketjen black and VGCF.

[0013] Optionally, in the step S2, the battery negative electrode is selected from one of a lithium negative electrode and a lithium-silicon negative electrode.

[0014] The application further provides a sulfide solid-state battery prepared by the preparation method of the sulfide solid-state battery. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 FIG. 1 is a flowchart of the preparation method of the sulfide solid-state battery in the embodiments of the application. DETAILED DESCRIPTION

[0016] In order to make the above objectives, features and advantages of the present application more comprehensible and easier to understand, specific embodiments of the present application are described in detail below with reference to the accompanying drawings. Although some embodiments of the present application are shown in the drawings, it should be understood that the present application can be implemented in various forms, and should not be interpreted as being limited to the embodiments set forth herein, but rather, these embodiments are provided to make the present application more thorough and complete. It should be understood that the drawings and embodiments of the present application are for exemplary purposes only, and are not intended to limit the scope of protection of the present application.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0018] As used herein, the term "includes" and its variants are open-ended, meaning "includes but is not limited to"; the term "based on" is meant to be "based, at least in part, on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optional" means "optional in at least some embodiments". Related terms have meanings ascribed to them below. In the description of the application, the meaning of "a," "an," and "the" includes plural references unless the context clearly dictates otherwise.

[0019] The mixture suitable for constructing the positive electrode coating layer in situ provided by the embodiment of the present application comprises a positive electrode active material, an additive A and an additive B; the molar ratio of the additive A to the additive B is 1:(0.5 to 2), the ratio of the total mass of the additive A and the additive B to the mass of the mixture suitable for constructing the positive electrode coating layer in situ is (1 to 5):100; the additive A comprises at least one of lithium bis(trimethylsilyl)oxalate borate, lithium trifluoromethylsulfonyl oxalate borate, lithium tetra(2,2,2-trifluoroethoxy)borate, lithium bis(pentafluorophenyl)borate, lithium tris(trimethylsilyl)borate, lithium tris(pentafluorophenyl)phosphate, lithium bis(trifluoroacetyl)phosphate, lithium tetra(trifluoromethyl)oxalate phosphate, lithium tris(vinyltrifluoromethyl)borate and lithium bis(perfluoroisopropoxy)oxalate borate; the additive B comprises at least one of perfluorobutyrolactone, dimethyl perfluoroglutarate, perfluorohexanedinitrile, perfluoro-1,4-dioxane-2,5-dione, trifluoroacetyl perfluoro-t-butyl ester, perfluoro-3-methoxypropionic acid methyl ester, perfluoro-2-methyl-1,3-dioxolan-4-one, perfluorotriethylamine, perfluoro-1,3-dimethylcyclohexane, perfluoro-4-methylmorpholine and perfluoropolyether monomethyl ether.

[0020] The mixture suitable for constructing the positive electrode coating layer in situ provided by the embodiment of the present application is mixed by the positive electrode active material, the additive A and the additive B in a specific ratio. The mixture suitable for constructing the positive electrode coating layer in situ is mixed with the sulfide solid electrolyte and the conductive agent to produce the sulfide solid battery as the composite positive electrode material. Since the HOMO energy level of the additive A is obviously higher than that of the additive B, in the process of the first charging, the additive A in the composite positive electrode material is preferentially oxidized and decomposed in the initial low voltage range, and a dense inner layer mainly composed of inorganic components is formed on the surface of the positive electrode active material particles. With the increase of the voltage, the additive B in the composite positive electrode is oxidized and decomposed, and a flexible outer layer mainly composed of organic components is formed on the surface of the dense inner layer. The dense inner layer mainly composed of inorganic components can effectively block the side reaction between the high-activity sulfide solid electrolyte and the positive electrode material, inhibit the generation of the resistive components in the interface layer, and is beneficial to reducing the interface impedance between the positive electrode and the sulfide solid electrolyte. The flexible outer layer mainly composed of organic components can ensure the transmission of lithium ions, adaptively fill the interface gap to buffer the volume change in the cycle process, and provide close interface contact, so as to cooperatively improve the interface chemical stability and physical integrity of the positive electrode side, and is beneficial to further reducing the interface impedance between the positive electrode and the sulfide solid electrolyte. Therefore, the sulfide solid battery produced by using the mixture suitable for constructing the positive electrode coating layer in situ has good cycle performance.

[0021] In some embodiments of the present application, the positive electrode active material is selected from LiCoO2, LiNi x Mn y Co z O2, aLi2MnO3•(1-a)LiMO2; wherein x+y+z=1, 0 0.8 Co 0.1 Mn 0.1 O2.

[0022] As Figure 1 shown, the embodiment of the present application further provides a preparation method of a sulfide solid battery, comprising: Step S1, uniformly mixing the mixture suitable for constructing the positive electrode coating layer in situ, the sulfide solid electrolyte and the conductive agent to obtain a composite positive electrode material; Step S2, sequentially stacking the composite positive electrode material, the sulfide solid electrolyte and the battery negative electrode to form a multi-layer cell structure, and then packaging to obtain a sulfide solid battery.

[0023] The sulfide solid-state battery prepared by the method provided in the embodiments of the present application has a specific proportion of additive A and additive B introduced into the positive electrode, and in the process of the first charging, a dense inner layer mainly composed of inorganic components and a flexible outer layer mainly composed of organic components can be sequentially formed in situ on the surface of the positive electrode active material particles, which is beneficial to reducing the interface impedance of the positive electrode and the sulfide solid-state electrolyte. Therefore, the sulfide solid-state battery prepared by the method of the embodiments of the present application has good cycle performance.

[0024] In some embodiments of the present application, two charging and discharging processes are further included, and the charging and discharging processes include: first charging the sulfide solid-state battery to 4.5 V at a charging rate of 0.1 C, and then discharging to 2.5 V at a discharging rate of 0.1 C.

[0025] In the step S1, the mass ratio of the mixture suitable for in-situ construction of the positive electrode coating layer, the sulfide solid-state electrolyte and the conductive agent is (70-80):(18-28):2.

[0026] In some embodiments of the present application, the sulfide solid-state electrolyte is selected from one of Li3PS4, Li 5.5 PS 4.5 Cl 1.5 , Li6PS5Cl, Li 5.5 PS 4.5 Br 1.5 , Li6PS5Br and Li 10 GeP2S 12 .

[0027] In the step S1, the conductive agent is selected from one of conductive carbon black (Super P), Ketjen black and VGCF.

[0028] In the step S2, the battery negative electrode is selected from one of a lithium negative electrode and a lithium-silicon negative electrode.

[0029] The embodiments of the present application further provide a sulfide solid-state battery prepared by the preparation method of the sulfide solid-state battery.

[0030] The present application will be further described in conjunction with specific embodiments.

[0031] Embodiment 1 M1, the positive electrode active material, the additive A and the additive B are uniformly mixed to obtain a mixture suitable for in-situ construction of a positive electrode coating layer; the molar ratio of the additive A to the additive B is 1:1, and the mass ratio of the total mass of the additive A and the additive B to the mass of the mixture suitable for in-situ construction of the positive electrode coating layer is 3:100; the positive electrode active material is LiNi0.8 Co 0.1 Mn 0.1 O2, the additive A is lithium bis(trimethylsilyl)oxalate borate, and the additive B is perfluorobutyrolactone.

[0032] M2, mixing the mixture suitable for in-situ constructing positive electrode coating layer, the sulfide solid electrolyte and the conductive agent uniformly to obtain a composite positive electrode material; the mass ratio of the mixture suitable for in-situ constructing positive electrode coating layer, the first sulfide solid electrolyte and the conductive agent is 70:28:2, the sulfide solid electrolyte is Li6PS5Cl, and the conductive agent is Super P.

[0033] M3, stacking the composite positive electrode material, a sulfide solid electrolyte and a battery negative electrode in sequence to form a multi-layered cell structure, and then packaging to obtain a sulfide solid battery; the sulfide solid electrolyte is Li6PS5Cl, and the battery negative electrode is a lithium-silicon negative electrode.

[0034] M4, performing twice charging and discharging treatment on the sulfide solid battery, the charging and discharging treatment comprising: first charging the packaged multi-layered cell structure to 4.5V at a charging rate of 0.1C, and then discharging to 2.5V at a discharging rate of 0.1C.

[0035] Example 2 The difference from Example 1 is that in step M1, the molar ratio of the additive A to the additive B is 1:0.5, and the mass ratio of the total mass of the additive A and the additive B to the mass of the mixture suitable for in-situ constructing positive electrode coating layer is 1:100; the additive A is lithium trifluoromethylsulfonyl oxalate borate, and the additive B is dimethyl perfluoroglutarate.

[0036] Example 3 The difference from Example 1 is that in step M1, the molar ratio of the additive A to the additive B is 1:2, and the mass ratio of the total mass of the additive A and the additive B to the mass of the mixture suitable for in-situ constructing positive electrode coating layer is 5:100; the additive A is lithium tetrakis(2,2,2-trifluoroethoxy)borate, and the additive B is perfluorohexanedinitrile.

[0037] Comparative Example 1 The difference from Example 1 is that in step M1, the mixture suitable for in-situ constructing positive electrode coating layer is obtained by uniformly mixing a positive electrode active material and an additive A; the mass ratio of the additive A to the mixture suitable for in-situ constructing positive electrode coating layer is 3:100; the positive electrode active material is LiNi 0.8 Co 0.1 Mn 0.1O2, the additive A is lithium bis (trimethylsilyl) oxalate borate.

[0038] Comparative Example 2 The difference from Example 1 is that step M1 is: mixing the positive electrode active material and additive B uniformly to obtain a mixture suitable for in-situ construction of a positive electrode coating layer; the mass ratio of the additive B to the mass of the mixture suitable for in-situ construction of a positive electrode coating layer is 3:100; the positive electrode active material is LiNi 0.8 Co 0.1 Mn 0.1 O2, the additive B is perfluorobutyrolactone.

[0039] Comparative Example 3 The additive A and the positive electrode active material are added to anhydrous ethanol, mixed uniformly, vacuum rotary evaporation is performed, high-temperature calcination is performed, and the positive electrode particles with inorganic coating layers are obtained; the positive electrode particles with inorganic coating layers, the additive B and the initiator are added to tetrahydrofuran, and under the conditions of heating and nitrogen reflux, the organic coating layer is formed on the surface of the inorganic coating layer, and after centrifugation, drying treatment is performed to obtain the modified positive electrode active material; the molar ratio of the additive A to the additive B is 1:1, and the total mass of the additive A and the additive B to the mass of the modified positive electrode active material is 3:100; the positive electrode active material is LiNi 0.8 Co 0.1 Mn 0.1 O2, the additive A is lithium bis (trimethylsilyl) oxalate borate, and the additive B is perfluorobutyrolactone.

[0040] The modified positive electrode active material, the sulfide solid electrolyte and the conductive agent are mixed uniformly to obtain a composite positive electrode material; the mass ratio of the modified positive electrode active material, the sulfide solid electrolyte and the conductive agent is 70:28:2, the sulfide solid electrolyte is Li6PS5Cl, and the conductive agent is Super P.

[0041] The composite positive electrode material, the sulfide solid electrolyte and the battery negative electrode are stacked in sequence to form a multilayer cell structure, and then packaged to obtain a sulfide solid-state battery; the sulfide solid electrolyte is Li6PS5Cl, and the battery negative electrode is a lithium-silicon negative electrode.

[0042] Experimental Example The sulfide solid-state batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to 1000 cycles at 25°C, 1C, and the capacity retention rate and impedance of the batteries were detected, and the results are shown in Table 1. As can be seen from Table 1, the capacity retention rate after 1000 cycles of the sulfide solid-state batteries prepared in Examples 1 to 3 was higher and the impedance was lower compared to Comparative Examples 1 to 3, indicating that the cycle performance of the sulfide solid-state batteries prepared in Examples 1 to 3 was better.

[0043] Table 1

[0044] Although the present application has been disclosed with reference to the above embodiments, the scope of the present application is not limited to the above. Various changes and modifications can be made thereto without departing from the spirit and scope of the present application, and such changes and modifications are to be included within the scope of the present application.

Claims

1. A mixture suitable for in-situ construction of a positive electrode coating layer, characterized in that, The mixture includes a positive electrode active material, additive A, and additive B; the molar ratio of additive A to additive B is 1:(0.5 to 2), and the mass ratio of the total mass of additive A and additive B to the mass of the mixture suitable for in-situ construction of the positive electrode coating is (1 to 5):100; additive A includes lithium bis(trimethylsilyl)oxalateborate, lithium trifluoromethanesulfonyl oxalateborate, lithium tetrakis(2,2,2-trifluoroethoxy)borate, lithium bis(pentafluorophenyl)borate, lithium tri(trimethylsilyl)borate, lithium tri(pentafluorophenyl)phosphate, and lithium bis(trifluoroacetyl)oxalateborate. The additive B comprises at least one of lithium (trifluoromethyl) phosphate, lithium tetra(trifluoromethyl) oxalate phosphate, lithium tri(vinyltrifluoromethyl) borate, and lithium bis(perfluoroisopropoxy) oxalate borate; wherein the additive B comprises at least one of perfluorobutyrolactone, dimethyl perfluoroglutarate, perfluoroadiponitrile, perfluoro-1,4-dioxane-2,5-dione, trifluoroacetyl perfluorotert-butyl ester, methyl perfluoro-3-methoxypropionate, perfluoro-2-methyl-1,3-dioxane-4-one, perfluorotriethylamine, perfluoro-1,3-dimethylcyclohexane, perfluoro-4-methylmorpholine, and perfluoropolyether monomethyl ether.

2. The mixture suitable for in-situ construction of a positive electrode coating layer according to claim 1, characterized in that, The positive electrode active material is selected from one of LiCoO2, LiNi x Mn y Co z O2, aLi2MnO3•(1-a)LiMO2; wherein, x + y + z = 1, 0 < x < 1, 0 < y < 1, 0 < z < 1, 0 < a < 1, and M is selected from one of Mn, Ni, and Co.

3. A method for preparing a sulfide solid-state battery, characterized in that, include: Step S1: Mix the mixture as described in claim 1 or 2 suitable for in-situ construction of the positive electrode coating layer, the sulfide solid electrolyte, and the conductive agent evenly to obtain a composite positive electrode material; Step S2: Stack the composite positive electrode material, sulfide solid electrolyte and battery negative electrode in sequence to form a multi-layer cell structure, and then encapsulate it to obtain a sulfide solid battery.

4. The method for preparing a sulfide solid-state battery according to claim 3, characterized in that, It also includes performing two charge-discharge processes, which include: first charging the sulfide solid-state battery to 4.5V at a charging rate of 0.1C, and then discharging it to 2.5V at a discharging rate of 0.1C.

5. The method for preparing a sulfide solid-state battery according to claim 3, characterized in that, In step S1, the mass ratio of the mixture suitable for in-situ construction of the positive electrode coating layer, the sulfide solid electrolyte, and the conductive agent is (70 to 80): (18 to 28):

2.

6. The method for preparing a sulfide solid-state battery according to claim 5, characterized in that, The sulfide solid electrolyte is selected from Li3PS4, Li 5.5 PS 4.5 Cl 1.5 Li6PS5Cl, Li 5.5 PS 4.5 Br 1.5 Li6PS5Br and Li 10 GeP2S 12 One of them.

7. The method for preparing a sulfide solid-state battery according to claim 3, characterized in that, In step S1, the conductive agent is selected from one of conductive carbon black, Ketjen black, and VGCF.

8. The method for preparing a sulfide solid-state battery according to claim 3, characterized in that, In step S2, the battery negative electrode is selected from either a lithium negative electrode or a lithium silicon negative electrode.

9. A sulfide solid-state battery, characterized in that, It is prepared using the method for preparing a sulfide solid-state battery as described in any one of claims 3 to 8.

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