Mixtures suitable for in situ construction of positive electrode cladding layers and their use in sulfide solid-state batteries

Abstract

The application provides a mixture suitable for constructing a positive electrode coating layer in situ and application thereof in a sulfide solid-state battery, relates to the technical field of solid-state batteries, and the mixture suitable for constructing the positive electrode coating layer in situ 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), and 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; since the HOMO energy level of the additive A is obviously higher than that of the additive B, 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 in the process of the first charging, and the interface impedance of the positive electrode and the sulfide solid-state electrolyte is reduced. Thus, the cycle performance of the sulfide solid-state battery prepared by using the mixture suitable for constructing the positive electrode coating layer in situ is better.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, and more specifically, to mixtures suitable for in-situ construction of positive electrode coatings and their application in sulfide solid-state batteries. Background Technology

[0002] Sulfide solid-state batteries have become a key research direction for next-generation power batteries due to their high energy density and high safety. However, the interface between commercially available high-voltage cathode materials and sulfide solid electrolytes is unstable, resulting in poor battery performance. Specifically, sulfide solid electrolytes have a narrow electrochemical window (<4.0V), and are easily oxidized and decomposed upon contact with high-voltage cathode materials, generating insulating products such as Li2S, leading to increased interfacial impedance. Lattice distortion of the cathode material during charge and discharge processes causes solid-solid interface failure, further exacerbating the increase in interfacial impedance. Therefore, existing sulfide solid-state batteries have poor cycle performance. Constructing a coating layer on the surface of the cathode material is the mainstream strategy to improve interfacial stability, but existing coating processes are usually cumbersome, and the resulting coating layers suffer from uniformity / density issues and limited functionality, resulting in limited improvement effects. Summary of the Invention

[0003] The problem addressed by this invention is: how to further improve the cycle performance of sulfide solid-state batteries.

[0004] To address the aforementioned problems, this invention provides a mixture suitable for in-situ construction of a positive electrode coating layer, comprising 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 a positive electrode coating layer is (1 to 5):100; additive A comprises lithium bis(trimethylsilyl)oxalateborate, lithium trifluoromethanesulfonyl oxalateborate, lithium tetrakis(2,2,2-trifluoroethoxy)borate, lithium bis(pentafluorophenyl)borate, lithium tri(trimethylsilyl)borate, and lithium tri(trimethylsilyl)borate. Lithium pentafluorophenyl)phosphate, lithium bis(trifluoroacetyl)phosphate, lithium tetra(trifluoromethyl)oxalate phosphate, lithium tri(vinyltrifluoromethyl)borate, and lithium bis(perfluoroisopropoxy)oxalate borate; said additive B includes 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.

[0005] Compared with the related art, the mixture suitable for in-situ construction of a positive electrode coating provided by the present invention is formed by mixing a positive electrode active material, additive A and additive B in a specific ratio. After mixing the mixture suitable for in-situ construction of a positive electrode coating with a sulfide solid electrolyte and a conductive agent, the mixture is used as a composite positive electrode material to fabricate a sulfide solid-state battery. Since the HOMO energy level of additive A is significantly higher than that of additive B, during the first charging process, in an initial low voltage range, additive A in the composite positive electrode material is preferentially oxidized and decomposed, forming a dense inner layer mainly composed of inorganic components on the surface of positive electrode active material particles. As the voltage increases, additive B in the composite positive electrode is subsequently oxidized and decomposed, forming a flexible outer layer mainly composed of organic components 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 highly active sulfide solid electrolyte and the positive electrode material, inhibit the generation of resistive components in the interface layer, and help reduce the interface impedance between the positive electrode and the sulfide solid electrolyte. The flexible outer layer mainly composed of organic components can ensure lithium ion transmission, adaptively fill interface voids to buffer volume changes during cycling, and provide close interface contact, thereby synergistically improving the interface chemical stability and physical integrity on the positive electrode side, and helping to further reduce the interface impedance between the positive electrode and the sulfide solid electrolyte. Therefore, the sulfide solid-state battery prepared by using the mixture suitable for in-situ construction of a positive electrode coating has good cycling performance.

[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<x<1, 0<y<1, 0<z<1, 0<a<1, and M is selected from one of Mn, Ni and Co.

[0007] The present invention also provides a method for preparing a sulfide solid-state battery, comprising: Step S1, uniformly mixing the mixture suitable for in-situ construction of a positive electrode coating described above, a sulfide solid electrolyte and a conductive agent to obtain a composite positive electrode material; Step S2, sequentially stacking the composite positive electrode material, the sulfide solid electrolyte and a battery negative electrode to form a multilayer cell structure, and then performing packaging to obtain a sulfide solid-state battery.

[0008] Compared with related technologies, the sulfide solid-state battery prepared by the method provided in this invention, due to the introduction of a specific ratio of additives A and B into the positive electrode, allows for the sequential in-situ formation of a dense inner layer dominated by inorganic components and a flexible outer layer dominated by organic components on the surface of the positive electrode active material particles during the first charging process. This is beneficial for reducing the interfacial impedance between the positive electrode and the sulfide solid electrolyte. Therefore, the sulfide solid-state battery prepared by the method of this invention exhibits better cycle performance.

[0009] Optionally, the process also includes performing two charge-discharge cycles, wherein the charge-discharge cycle includes 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.

[0010] Optionally, 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.

[0011] Optionally, 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.

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

[0013] Optionally, in step S2, the battery negative electrode is selected from either a lithium negative electrode or a lithium silicon negative electrode.

[0014] The present invention also provides a sulfide solid-state battery, which is manufactured using the sulfide solid-state battery preparation method described above. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the preparation method of the sulfide solid-state battery in an embodiment of the present invention. Detailed Implementation

[0016] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

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

[0018] As used herein, the term "comprising" and its variations are open-ended, meaning "including but not limited to"; the term "based on" means "at least partially based 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"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the description below. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0019] This invention provides a mixture suitable for in-situ construction of a positive electrode coating layer, comprising 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 layer 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, and lithium tri(pentafluorophenyl)borate. The additive B comprises at least one of lithium (fluorophenyl) phosphate, lithium bis(trifluoroacetyl) phosphate, lithium tetra(trifluoromethyl) oxalate phosphate, lithium tri(vinyltrifluoromethyl) borate, and lithium bis(perfluoroisopropoxy) oxalate borate; 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.

[0020] The mixture suitable for in-situ construction of a positive electrode coating layer provided by the embodiment of the present invention is formed by mixing a positive electrode active material, an additive A and an additive B in a specific ratio. After mixing the mixture suitable for in-situ construction of a positive electrode coating layer with a sulfide solid electrolyte and a conductive agent, the mixture is used as a composite positive electrode material to fabricate a sulfide solid-state battery. Since the HOMO energy level of additive A is significantly higher than that of additive B, during the initial charging process, in the initial low voltage range, additive A in the composite positive electrode material is preferentially oxidized and decomposed, forming a dense inner layer mainly composed of inorganic components on the surface of positive electrode active material particles. As the voltage increases, additive B in the composite positive electrode is then oxidized and decomposed, forming a flexible outer layer mainly composed of organic components 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 highly active sulfide solid electrolyte and the positive electrode material, inhibit the generation of resistive components in the interface layer, and help reduce the interface impedance between the positive electrode and the sulfide solid electrolyte. The flexible outer layer mainly composed of organic components can ensure lithium ion transmission, adaptively fill interface voids to buffer volume changes during cycling, and provide close interface contact, thereby synergistically improving the interface chemical stability and physical integrity on the positive electrode side, and helping to further reduce the interface impedance between the positive electrode and the sulfide solid electrolyte. Therefore, the sulfide solid-state battery prepared by using the mixture suitable for in-situ construction of a positive electrode coating layer has good cycling performance.

[0021] In some embodiments of the present invention, the positive electrode active material is selected from LiCoO2, LiNi x Mn y Co z O2 and 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. Illustratively, the positive electrode active material is LiNi 0.8 Co 0.1 Mn 0.1 O2.

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

[0023] The sulfide solid-state battery prepared by the method provided in this invention, due to the introduction of additives A and B in a specific proportion into the positive electrode, allows for the sequential in-situ formation of a dense inner layer dominated by inorganic components and a flexible outer layer dominated by organic components on the surface of the positive electrode active material particles during the first charging process. This helps to reduce the interfacial impedance between the positive electrode and the sulfide solid electrolyte. Therefore, the sulfide solid-state battery prepared by the method of this invention exhibits better cycle performance.

[0024] In some embodiments of the present invention, the method further includes performing two charge-discharge processes, wherein the charge-discharge processes 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.

[0025] In some embodiments of the present invention, 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.

[0026] In some embodiments of the present invention, 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.

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

[0028] In some embodiments of the present invention, in step S2, the battery negative electrode is selected from either a lithium negative electrode or a lithium silicon negative electrode.

[0029] This invention also provides a sulfide solid-state battery, which is manufactured using the sulfide solid-state battery preparation method described above.

[0030] The present invention will be further described below with reference to specific embodiments.

[0031] Example 1 M1. Mix the positive electrode active material, additive A, and additive B evenly to obtain a mixture suitable for in-situ construction of the positive electrode coating layer; the molar ratio of additive A to additive B is 1:1, and the 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 layer is 3:100; the positive electrode active material is LiNi.0.8 Co 0.1 Mn 0.1 O2, wherein additive A is lithium bis(trimethylsilyl)oxalateborate and additive B is perfluorobutyrolactone.

[0032] M2. The mixture suitable for in-situ construction of the positive electrode coating layer, the sulfide solid electrolyte, and the conductive agent are mixed evenly to obtain a composite positive electrode material; the mass ratio of the mixture suitable for in-situ construction of the 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. The composite positive electrode material, sulfide solid electrolyte and battery negative electrode are stacked in sequence to form a multi-layer cell structure, and then packaged 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. The sulfide solid-state battery is subjected to two charge-discharge processes, the charge-discharge process including: first charging the packaged multilayer cell structure to 4.5V at a charging rate of 0.1C, and then discharging it 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 additive A to additive B is 1:0.5, and the 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 1:100; additive A is lithium trifluoromethanesulfonyl oxalate borate, and additive B is dimethyl perfluoroglutarate.

[0036] Example 3 The difference from Example 1 is that, in step M1, the molar ratio of additive A to additive B is 1:2, and the 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 5:100; additive A is lithium tetrakis(2,2,2-trifluoroethoxy)borate, and additive B is perfluoroadiponitrile.

[0037] Comparative Example 1 The difference from Example 1 is that step M1 is as follows: the positive electrode active material and additive A are mixed evenly to obtain a mixture suitable for in-situ construction of the positive electrode coating layer; the mass ratio of additive A 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 LiNi. 0.8 Co 0.1 Mn 0.1O2, wherein additive A is lithium bis(trimethylsilyl)oxalateborate.

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

[0039] Comparative Example 3 Additive A and the positive electrode active material were added to anhydrous ethanol, mixed thoroughly, and then subjected to vacuum rotary evaporation followed by high-temperature calcination to obtain positive electrode particles with an inorganic coating layer. The positive electrode particles with the inorganic coating layer, additive B, and an initiator were added to tetrahydrofuran and reacted under heating and nitrogen reflux conditions to form an organic coating layer on the surface of the inorganic coating layer. After centrifugation and drying, the modified positive electrode active material was obtained. The molar ratio of additive A to additive B was 1:1, and the ratio of the total mass of additive A and additive B to the mass of the modified positive electrode active material was 3:100. The positive electrode active material was LiNi. 0.8 Co 0.1 Mn 0.1 O2, wherein additive A is lithium bis(trimethylsilyl)oxalateborate and additive B is perfluorobutyrolactone.

[0040] The modified positive electrode active material, the sulfide solid electrolyte, and the conductive agent are mixed evenly 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 cathode material, sulfide solid electrolyte, and battery anode are stacked sequentially to form a multilayer cell structure, which is then packaged to obtain a sulfide solid battery. The sulfide solid electrolyte is Li6PS5Cl, and the battery anode is a lithium silicon anode.

[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 and 1C. The capacity retention and impedance of the batteries were tested, and the results are shown in Table 1. As can be seen from Table 1, compared with Comparative Examples 1 to 3, the sulfide solid-state batteries prepared in Examples 1 to 3 have higher capacity retention and lower impedance after 1000 cycles, indicating that the sulfide solid-state batteries prepared in Examples 1 to 3 have better cycle performance.

[0043] Table 1

[0044] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

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 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 layer is (1 to 5):100; additive A is lithium bis(trimethylsilyl)oxalateborate; additive B is perfluorobutyrolactone; during the first charging process, the mixture sequentially forms a dense inner layer mainly composed of inorganic components and a flexible outer layer mainly composed of organic components on the surface of the positive electrode active material particles.

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 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. 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.

4. 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.

5. The method for preparing a sulfide solid-state battery according to claim 4, 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.

6. 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 conductive carbon black and VGCF.

7. 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.

8. 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 7.

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