Gradient sulfurized phosphate coated nickel-rich layered oxide positive electrode and lithium battery thereof

Abstract

The invention relates to the technical field of lithium batteries, in particular to a positive electrode material of a sulfide-based solid-state lithium battery and the lithium battery comprising the positive electrode. Phosphate-coated nickel-rich layered oxide positive electrode powder is modified by sulfur-rich phosphorus sulfide molecules to prepare a gradient vulcanized phosphate-coated nickel-rich layered oxide positive electrode, the gradient vulcanized phosphate-coated nickel-rich layered oxide positive electrode is compounded with sulfide electrolyte and vapor growth carbon fibers (VGCF) to obtain a composite electrode, and then the composite electrode is compounded with an electrolyte sheet to prepare the lithium battery. The gradient sulfurized phosphate coated nickel-rich layered oxide positive electrode and the sulfide solid electrolyte show interface compatibility, and the all-solid-state battery assembled by the gradient sulfurized phosphate coated nickel-rich layered oxide positive electrode, the sulfide solid electrolyte and the lithium metal negative electrode has good electrochemical performance and cycling stability. The protective layer effectively restrains the space charge layer and stabilizes the nickel-rich layered oxide positive electrode / sulfide electrolyte interface, and the practical process of the sulfide-based all-solid-state lithium battery is better promoted due to the characteristics of simple structure, convenience in preparation and large-scale production.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, in particular to a cathode material for a sulfide-based solid-state lithium battery and a lithium battery thereof. Background Art

[0002] With the continuous expansion of the electric vehicle market and the surging energy storage demand, the requirements for the energy density and safety of lithium batteries are getting higher and higher. Commercial lithium batteries generally use flammable liquid electrolytes, which not only exacerbate the potential danger of thermal runaway, but also the growth of lithium dendrites may pierce the separator, resulting in short circuit and thus triggering major safety hazards. As a promising next-generation battery technology, all-solid-state lithium batteries (ASSLBs) are characterized by using solid electrolytes to replace traditional liquid electrolytes. Solid electrolytes have advantages such as non-flammability, high mechanical strength, and high density. These characteristics not only greatly enhance the safety performance of the battery, but also significantly improve the energy density. Given the broad application prospects of all-solid-state lithium batteries, in order to meet the growing urgent demand for high-energy-density batteries in the market, the academic and industrial communities have actively invested in research. On the one hand, efforts are made to develop solid electrolytes with high ionic conductivity to optimize the ion transport performance of the battery; on the other hand, modification research is carried out on high-energy oxide cathode materials to further improve the overall performance of the battery.

[0003] Among many fast ion conductors, sulfide solid electrolytes (such as Li 5.3 PS 4.3 Cl 1.7 , LPSCl) have become one of the most promising key materials in all-solid-state batteries due to their extremely high ionic conductivity (>10 -2 S cm -1 ) at room temperature, excellent mechanical properties, and easy processing. Nickel-rich layered transition metal oxides (such as NCM) have the advantages of high specific capacity (about 200 mAh / g), high working voltage, and low cost, and are the best choice for the cathode material of high-energy-density ASSLBs. However, there are many problems at the interface between sulfide solid electrolytes and NCM cathodes: (1) The physical contact between the two is not dense. During the battery cycling process, the cathode material will undergo large volume changes due to the insertion / extraction of lithium, which will further deteriorate the physical contact at the interface and lead to a decrease in the cycling stability of the battery; (2) There is a difference in chemical potential between the NCM cathode and the sulfide solid electrolyte, and Li + will migrate from the sulfide solid electrolyte to the NCM cathode. Since NCM is an ion-electron mixed conductor, the electron conduction on the cathode side will balance a part of the Li + concentration gradient, which causes more Li + to escape from the sulfide solid electrolyte and form a thick high-impedance Li +The depletion layer (i.e., the space charge layer); (3) The adverse side reactions occurring between the NCM cathode and the sulfide solid electrolyte result in the oxidative decomposition of the sulfide solid electrolyte and the structural collapse of the NCM cathode. Therefore, in order to construct a highly stable NCM / sulfide electrolyte interface and achieve high energy efficiency and long cycle life for sulfide-based ASSLBs, it is very necessary to develop a cathode protective layer material with high structural and chemical similarity to the sulfide solid electrolyte. Summary of the Invention

[0004] To solve the problems of poor interfacial contact, interfacial space charge layer, and interfacial side reactions between the nickel-rich layered oxide cathode and the sulfide solid electrolyte, the present invention provides a surface-modified nickel-rich layered oxide cathode and a sulfide-based solid-state lithium battery including the cathode. The surface of the cathode has improved Li + conductivity, and it has good compatibility with the sulfide solid electrolyte. The interface between the two is more stable, the space charge layer is suppressed, and there are fewer interfacial side reactions. Therefore, the sulfide-based solid-state lithium battery using this cathode has good electrochemical performance and cycle stability.

[0005] The present invention provides a preparation method for a nickel-rich layered oxide cathode coated with gradient sulfide phosphate, which includes the following steps:

[0006] 1) Dissolve the sulfur-rich phosphorus sulfide molecule P4S 10+6n , where n = 1 - 5 and n is a positive integer, in a diglyme solvent, and stir at 60 - 100 °C for 1 - 5 h;

[0007] 2) Disperse a certain amount of the phosphate-coated nickel-rich layered oxide cathode powder into the solution obtained in step 1), and continuously stir at 60 - 100 °C for 8 - 15 h for in-situ sulfidation; continuously stir the solution at 140 - 160 °C until the diglyme solvent completely evaporates to obtain a precursor powder;

[0008] 3) Use absolute ethanol as the solvent, centrifuge and wash the precursor powder at a speed of 7000 - 9000 rpm, and then dry it at 80 - 120 °C to obtain the nickel-rich layered oxide cathode coated with gradient sulfide phosphate.

[0009] Preferably, the mass ratio of the sulfur-rich phosphorus sulfide molecule P4S 10+6n to the phosphate-coated nickel-rich layered oxide cathode powder in step 1) is 1:200.

[0010] Preferably, in step 1), the preparation method of the sulfur-rich phosphorus sulfide molecule P4S 10+6n is as follows: According to P4S 10+6nWeigh the sulfur powder and the powder of P2S5 respectively according to their chemical formulas, mix them to obtain a precursor mixture; subject the precursor mixture to high-temperature heat treatment, and then grind it evenly in a mortar to obtain the sulfur-rich phosphorus sulfide molecules. The high-temperature heat treatment is carried out under an argon atmosphere at 200 - 400 °C for 20 - 30 hours. Among them, the sulfur-rich phosphorus sulfide molecules P4S 10+6n are preferably P4S 16 , P4S 22 and P4S 28 one of them.

[0011] Preferably, in step 2), the preparation method of the phosphate-coated nickel-rich layered oxide cathode is as follows: dissolve the phosphate in absolute ethanol and disperse it by ultrasonic; disperse the commercial uncoated nickel-rich layered oxide cathode powder into the above solution and continuously stir to obtain a precursor solution; continuously stir the precursor solution at 60 - 100 °C until the absolute ethanol completely evaporates to obtain a precursor powder, and then carry out high-temperature heat treatment to obtain the phosphate-coated nickel-rich layered oxide cathode. Among them, the heat treatment conditions are: sintering at 500 - 700 °C for 10 - 15 hours. The mass ratio of the phosphate to the uncoated nickel-rich layered oxide cathode powder is 1:100. Preferably, the phosphate is one of Ti3(PO4)4, AlPO4 and LiZr2(PO4)3.

[0012] The present invention also provides a preparation method of a solid-state lithium battery, and the method includes the following steps:

[0013] 1) Press the sulfide electrolyte powder into a disc with a diameter of 12 mm;

[0014] 2) Prepare the gradient sulfurized phosphate-coated nickel-rich layered oxide cathode powder according to the above method;

[0015] 3) Mix the gradient sulfurized phosphate-coated nickel-rich layered oxide cathode, the sulfide electrolyte powder and the vapor-grown carbon fiber (VGCF) in a weight ratio of 50:48:2 in an agate mortar to prepare a composite cathode;

[0016] 4) Take 6 mg of the composite cathode in step 3) and evenly spread it on one side of the solid electrolyte sheet, and press them together under a pressure of 400 MPa;

[0017] 5) Attach a 12-mm lithium sheet to the other side of the sulfide electrolyte disc to form a "sandwich" solid-state battery structure.

[0018] The sulfide electrolyte is preferably Li 5.3 PS 4.3 Cl 1.7 .

[0019] Beneficial effects

[0020] The present invention proposes a simple and scalable sulfur-rich phosphorus sulfide molecule (P4S 10+6n )-assisted in-situ sulfidation method, which in-situ sulfides a phosphate coating on the surface of a nickel-rich layered oxide cathode to generate a uniform and continuous gradient sulfurized phosphate protective layer through a favorable O-S exchange between P-O bonds and P-S bonds. Among them, PO4 3- reacts with P4S 10+6n to generate PS4 3- and PO 4-x S x 3- . LPSCl belongs to the Argyrodite-type sulfide solid electrolyte, and its crystal structure contains PS4 3- tetrahedral units as the basic framework. For PO 4-x S x 3- , some O atoms are replaced by S atoms to form a tetrahedral structure with mixed anions, which has a high similarity to the structure of PS4 3- and the local structure of LPSCl. In terms of chemical properties, the PS4 3- tetrahedron can construct a three-dimensional network framework through the vertex-sharing mechanism to provide a continuous migration channel for Li + . LPSCl exhibits good ionic conduction ability due to the characteristics of PS4 3- . PO 4-x S x 3- also has chemical activity similar to that of PS4 3- due to the co-action of O and S atoms. Therefore, the gradient sulfurized phosphate protective layer with structural and chemical similarity to LPSCl can greatly improve the interfacial contact while increasing the Li + chemical potential on the surface of the nickel-rich layered oxide cathode, fundamentally suppressing the space charge layer. And thanks to the gradient sulfurization design, the coating has a Li + chemical potential gradient throughout the depth, further reducing the Li + migration barrier and improving the interfacial Li + transport kinetics. The nickel-rich layered oxide cathode coated with gradient sulfurized phosphate shows interfacial compatibility with the LPSCl sulfide solid electrolyte, and the all-solid-state battery assembled with both of them and a lithium metal anode has good electrochemical performance and cycling stability. This protective layer effectively curbs the space charge layer, stabilizes the nickel-rich layered oxide cathode / LPSCl interface, and its simple structure, ease of preparation and large-scale production characteristics better promote the practical application process of sulfide-based all-solid-state lithium batteries. Detailed implementation mode Brief description of the drawings

[0021] Figure 1: Related Characterization of Gradient Sulfurized Phosphate Coated NCM Cathode Material

[0022] Figure 2 : GITT Discharge Curves of PS-NCM811@TiP, NCM811@TiP and NCM811 Cathodes

[0023] Figure 3 : Li+ Diffusion Coefficients of PS-NCM811@TiP, NCM811@TiP and NCM811 Cathodes at Different Discharge States

[0024] Figure 4 : Long Cycle Performance of PS-NCM811@TiP, NCM811@TiP and NCM811 Cathodes at 0.2C

[0025] Figure 5 : Rate Performance of PS-NCM811@TiP, NCM811@TiP and NCM811 Cathodes

[0026] Example 1:

[0027] S1: LPSCl powder was obtained by high-temperature sintering, the LPSCl powder was sieved through a 400-mesh sieve, and the sieved powder was pressed into a solid electrolyte sheet with a diameter of 12 mm under a pressure of 200 MPa.

[0028] S2: Sulfur-rich phosphorus sulfide molecule P4S was obtained by high-temperature sintering under an argon atmosphere 16 .

[0029] S3: NCM811 cathode coated with Ti3(PO4)4 (NCM811@TiP) was obtained by wet chemical method and subsequent high-temperature sintering

[0030] S4: PS-NCM811@TiP cathode was obtained using the P4S 16 -assisted liquid-phase in-situ sulfidation method.

[0031] S5: PS-NCM811@TiP, LPSCl and VGCF were mixed in a weight ratio of 50:48:2 in an agate mortar for 1 h to prepare a composite cathode.

[0032] S6: 6 mg of the composite cathode of S5 was evenly spread on one side of the solid electrolyte sheet and pressed together under a pressure of 400 MPa.

[0033] S7: A 12-mm lithium sheet was attached to the other side of the solid electrolyte sheet in S6 to form a all-solid-state battery with a metallic lithium anode, LPSCl solid electrolyte, and PS-NCM811@TiP composite cathode in sequence.

[0034] Experimental Example 2:

[0035] S1: Obtain LPSCl powder through high-temperature sintering. Sieve the LPSCl powder through a 400-mesh sieve, and press the powder passing through the sieve into a solid electrolyte sheet with a diameter of 12 mm under a pressure of 200 MPa.

[0036] S2: Obtain sulfur-rich phosphorus sulfide molecule P4S through high-temperature sintering under an argon atmosphere 22 .

[0037] S3: Obtain NCM811 cathode coated with Ti3(PO4)4 (NCM811@TiP) through wet chemical method and subsequent high-temperature sintering

[0038] S4: Obtain PS2-NCM811@TiP cathode using the liquid-phase in-situ sulfidation method assisted by P4S 22 .

[0039] S5: Mix PS2-NCM811@TiP, LPSCl, and VGCF in an agate mortar at a weight ratio of 50:48:2 for 1 h to prepare a composite cathode.

[0040] S6: Take 6 mg of the composite cathode from S5 and evenly spread it on one side of the solid electrolyte sheet, and press them together under a pressure of 400 Mpa.

[0041] S7: Attach a 12-mm lithium sheet to the other side of the solid electrolyte sheet in S6 to form a all-solid-state battery with a metallic lithium anode, LPSCl solid electrolyte, and PS2-NCM811@TiP composite cathode in sequence.

[0042] Experimental Example 3:

[0043] S1: Obtain LPSCl powder through high-temperature sintering. Sieve the LPSCl powder through a 400-mesh sieve, and press the powder passing through the sieve into a solid electrolyte sheet with a diameter of 12 mm under a pressure of 200 MPa.

[0044] S2: Obtain sulfur-rich phosphorus sulfide molecule P4S through high-temperature sintering under an argon atmosphere 28 .

[0045] S3: Obtain NCM811 cathode coated with Ti3(PO4)4 (NCM811@TiP) through wet chemical method and subsequent high-temperature sintering

[0046] S4: Obtain PS3-NCM811@TiP cathode using the liquid-phase in-situ sulfidation method assisted by P4S 28 .

[0047] S5: Mix PS3-NCM811@TiP, LPSCl, and VGCF in an agate mortar at a weight ratio of 50:48:2 for 1 h to prepare a composite cathode.

[0048] S6: Take 6 mg of the composite cathode of S5 and evenly spread it on one side of the solid electrolyte sheet, and press them together under a pressure of 400 MPa.

[0049] S7: Attach a 12-mm lithium sheet to the other side of the solid electrolyte sheet in S6 to successively form a all-solid-state battery with a metallic lithium anode, a LPSCl solid electrolyte, and a PS3-NCM811@TiP composite cathode.

[0050] Example 4:

[0051] S1: Obtain LPSCl powder through high-temperature sintering, sieve the LPSCl powder through a 400-mesh sieve, and press the sieved powder into a 12-mm diameter solid electrolyte sheet under a pressure of 200 MPa.

[0052] S2: Obtain sulfur-rich phosphorus sulfide molecule P4S through high-temperature sintering under an argon atmosphere 16 .

[0053] S3: Obtain an AlPO4-coated NCM811 cathode (NCM811@AlP) through a wet chemical method and subsequent high-temperature sintering

[0054] S4: Use P4S 16 -assisted liquid-phase in-situ sulfidation method to obtain a PS-NCM811@AlP cathode.

[0055] S5: Mix PS-NCM811@AlP, LPSCl, and VGCF in a weight ratio of 50:48:2 in an agate mortar for 1 h to prepare a composite cathode.

[0056] S6: Take 6 mg of the composite cathode of S5 and evenly spread it on one side of the solid electrolyte sheet, and press them together under a pressure of 400 MPa.

[0057] S7: Attach a 12-mm lithium sheet to the other side of the solid electrolyte sheet in S6 to successively form a all-solid-state battery with a metallic lithium anode, a LPSCl solid electrolyte, and a PS-NCM811@AlP composite cathode.

[0058] Example 5

[0059] S1: Obtain LPSCl powder through high-temperature sintering, sieve the LPSCl powder through a 400-mesh sieve, and press the sieved powder into a 12-mm diameter solid electrolyte sheet under a pressure of 200 MPa.

[0060] S2: Obtain sulfur-rich phosphorus sulfide molecule P4S through high-temperature sintering under an argon atmosphere 22 .

[0061] S3: Obtain an AlPO4-coated NCM811 cathode (NCM811@AlP) through a wet chemical method and subsequent high-temperature sintering

[0062] S4: Use P4S 22 An auxiliary liquid-phase in-situ sulfidation method is used to obtain the PS2-NCM811@AlP cathode.

[0063] S5: Mix PS2-NCM811@AlP, LPSCl, and VGCF in a weight ratio of 50:48:2 in an agate mortar for 1 h to prepare a composite cathode.

[0064] S6: Take 6 mg of the composite cathode of S5 and evenly spread it on one side of the solid electrolyte sheet, and press them together under a pressure of 400 MPa.

[0065] S7: Attach a 12-mm lithium sheet to the other side of the solid electrolyte sheet in S6 to sequentially form an all-solid-state battery with a metallic lithium anode, an LPSCl solid electrolyte, and a PS2-NCM811@AlP composite cathode.

[0066] Example 6

[0067] S1: LPSCl powder is obtained by high-temperature sintering. The LPSCl powder is passed through a 400-mesh sieve, and the powder passing through the sieve is pressed into a 12-mm-diameter solid electrolyte sheet under a pressure of 200 MPa.

[0068] S2: Sulfur-rich phosphorus sulfide molecule P4S is obtained by high-temperature sintering under an argon atmosphere 28 .

[0069] S3: An NCM811 cathode coated with AlPO4 (NCM811@AlP) is obtained by a wet chemical method and subsequent high-temperature sintering

[0070] S4: Use P4S 28 An auxiliary liquid-phase in-situ sulfidation method is used to obtain the PS3-NCM811@AlP cathode.

[0071] S5: Mix PS3-NCM811@AlP, LPSCl, and VGCF in a weight ratio of 50:48:2 in an agate mortar for 1 h to prepare a composite cathode.

[0072] S6: Take 6 mg of the composite cathode of S5 and evenly spread it on one side of the solid electrolyte sheet, and press them together under a pressure of 400 MPa.

[0073] S7: Attach a 12-mm lithium sheet to the other side of the solid electrolyte sheet in S6 to sequentially form an all-solid-state battery with a metallic lithium anode, an LPSCl solid electrolyte, and a PS3-NCM811@AlP composite cathode.

[0074] Example 7

[0075] S1: Obtain LPSCl powder by high-temperature sintering, sieve the LPSCl powder through a 400-mesh sieve, and press the sieved powder into a solid electrolyte sheet with a diameter of 12 mm under a pressure of 200 MPa.

[0076] S2: Obtain sulfur-rich phosphorus sulfide molecule P4S by high-temperature sintering under an argon atmosphere 16 .

[0077] S3: Obtain LiZr2(PO4)3-coated NCM712 cathode (NCM712@LZP) by wet chemical method and subsequent high-temperature sintering

[0078] S4: Obtain PS-NCM712@LZP cathode using P4S 16 -assisted liquid-phase in-situ sulfidation method.

[0079] S5: Mix PS-NCM712@LZP, LPSCl, and VGCF in a weight ratio of 50:48:2 in an agate mortar for 1 h to prepare a composite cathode.

[0080] S6: Take 6 mg of the composite cathode of S5 and evenly spread it on one side of the solid electrolyte sheet, and press them together under a pressure of 400 MPa.

[0081] S7: Attach a 12-mm lithium sheet to the other side of the solid electrolyte sheet in S6 to form a all-solid-state battery with a metallic lithium anode, LPSCl solid electrolyte, and PS-NCM712@LZP composite cathode

[0082] Example 8

[0083] S1: Obtain LPSCl powder by high-temperature sintering, sieve the LPSCl powder through a 400-mesh sieve, and press the sieved powder into a solid electrolyte sheet with a diameter of 12 mm under a pressure of 200 MPa.

[0084] S2: Obtain sulfur-rich phosphorus sulfide molecule P4S by high-temperature sintering under an argon atmosphere 22 .

[0085] S3: Obtain LiZr2(PO4)3-coated NCM712 cathode (NCM712@LZP) by wet chemical method and subsequent high-temperature sintering

[0086] S4: Obtain PS2-NCM712@LZP cathode using P4S 22 -assisted liquid-phase in-situ sulfidation method.

[0087] S5: Mix PS2-NCM712@LZP, LPSCl, and VGCF in a weight ratio of 50:48:2 in an agate mortar for 1 h to prepare a composite cathode.

[0088] S6: Take 6 mg of the composite cathode of S5 and evenly spread it on one side of the solid electrolyte sheet, and press them together under a pressure of 400 MPa.

[0089] S7: Attach a 12-mm lithium sheet to the other side of the solid electrolyte sheet in S6 to sequentially form a all-solid-state battery with a metallic lithium anode, an LPSCl solid electrolyte, and a PS2-NCM712@LZP composite cathode.

[0090] Example 9

[0091] S1: Obtain LPSCl powder through high-temperature sintering, sieve the LPSCl powder through a 400-mesh sieve, and press the sieved powder into a 12-mm-diameter solid electrolyte sheet under a pressure of 200 MPa.

[0092] S2: Obtain sulfur-rich phosphorus sulfide molecule P4S through high-temperature sintering under an argon atmosphere 28 。

[0093] S3: Obtain an NCM712 cathode coated with LiZr2(PO4)3 (NCM712@LZP) through a wet chemical method and subsequent high-temperature sintering

[0094] S4: Use P4S 28 to obtain a PS3-NCM712@LZP cathode by an assisted liquid-phase in-situ sulfidation method.

[0095] S5: Mix PS3-NCM712@LZP, LPSCl, and VGCF in a weight ratio of 50:48:2 in an agate mortar for 1 h to prepare a composite cathode.

[0096] S6: Take 6 mg of the composite cathode of S5 and evenly spread it on one side of the solid electrolyte sheet, and press them together under a pressure of 400 MPa.

[0097] S7: Attach a 12-mm lithium sheet to the other side of the solid electrolyte sheet in S6 to sequentially form a all-solid-state battery with a metallic lithium anode, an LPSCl solid electrolyte, and a PS3-NCM712@LZP composite cathode.

[0098] Comparative Example 1

[0099] S1: Obtain LPSCl powder through high-temperature sintering, sieve the LPSCl powder through a 400-mesh sieve, and press the sieved powder into a 12-mm-diameter solid electrolyte sheet under a pressure of 200 MPa.

[0100] S2: Mix commercial uncoated NCM811, LPSCl, and VGCF in a weight ratio of 50:48:2 in an agate mortar for 1 h to prepare a composite cathode.

[0101] S3: Take 6 mg of the composite cathode of S2 and evenly spread it on one side of the solid electrolyte sheet, and press them together under a pressure of 400 MPa.

[0102] S4: Attach a 12-mm lithium sheet to the other side of the solid electrolyte sheet in S3 to successively form a all-solid-state battery with a metallic lithium anode, LPSCl solid electrolyte, and a commercial uncoated NCM811 composite cathode.

[0103] Comparative Example 2

[0104] S1: Obtain LPSCl powder through high-temperature sintering, pass the LPSCl powder through a 400-mesh sieve, and press the sieved powder into a 12-mm diameter solid electrolyte sheet under a pressure of 200 MPa.

[0105] S2: Obtain NCM811 cathode coated with Ti3(PO4)4 (NCM811@TiP) through wet chemical method and subsequent high-temperature sintering. S3: Mix NCM811@TiP, LPSCl, and VGCF in an agate mortar at a weight ratio of 50:48:2 for 1 h to prepare a composite cathode.

[0106] S4: Take 6 mg of the composite cathode of S3 and evenly spread it on one side of the solid electrolyte sheet, and press them together under a pressure of 400 MPa.

[0107] S5: Attach a 12-mm lithium sheet to the other side of the solid electrolyte sheet in S4 to successively form a all-solid-state battery with a metallic lithium anode, LPSCl solid electrolyte, and a NCM811@TiP composite cathode.

[0108] Comparative Example 3

[0109] S1: Obtain LPSCl powder through high-temperature sintering, pass the LPSCl powder through a 400-mesh sieve, and press the sieved powder into a 12-mm diameter solid electrolyte sheet under a pressure of 200 MPa.

[0110] S2: Obtain NCM811 cathode coated with AlPO4 (NCM811@AlP) through wet chemical method and subsequent high-temperature sintering.

[0111] S3: Mix NCM811@AlP, LPSCl, and VGCF in an agate mortar at a weight ratio of 50:48:2 for 1 h to prepare a composite cathode.

[0112] S4: Take 6 mg of the composite cathode of S3 and evenly spread it on one side of the solid electrolyte sheet, and press them together under a pressure of 400 MPa.

[0113] S5: Attach a 12-mm lithium sheet to the other side of the solid electrolyte sheet in S4 to successively form a all-solid-state battery with a metallic lithium anode, LPSCl solid electrolyte, and a NCM811@AlP composite cathode.

[0114] Comparative Example 4

[0115] S1: LPSCl powder was obtained by high-temperature sintering. The LPSCl powder was sieved through a 400-mesh sieve, and the powder passing through the sieve was pressed into a solid electrolyte sheet with a diameter of 12 mm under a pressure of 200 MPa.

[0116] S2: LiZr2(PO4)3-coated NCM712 cathode (NCM712@LZP) was obtained by wet chemical method and subsequent high-temperature sintering.

[0117] S3: NCM712@LZP, LPSCl and VGCF were mixed in a weight ratio of 50:48:2 in an agate mortar for 1 h to prepare a composite cathode.

[0118] S4: 6 mg of the composite cathode of S3 was evenly spread on one side of the solid electrolyte sheet and pressed together under a pressure of 400 MPa.

[0119] S5: A 12-mm lithium sheet was attached to the other side of the solid electrolyte sheet in S4 to form a all-solid-state battery with a metallic lithium anode, LPSCl solid electrolyte, and NCM712@LZP composite cathode in sequence.

[0120] The galvanostatic intermittent titration technique (GITT) discharge curves of commercial uncoated NCM811, NCM811@TiP and PS-NCM811@TiP cathode materials were compared. It is obvious that the PS-NCM811@TiP sample has lower polarization and higher discharge capacity. Li + diffusion coefficient (D Li+ ) extraction results show that PS-NCM811@TiP exhibits the highest D Li+ throughout the discharge process, demonstrating improved Li + migration kinetics. The initial discharge capacities of commercial uncoated NCM811, NCM811@TiP and PS-NCM811@TiP cathodes at 0.2C are 130.7, 160.1 and 167.1 mAh / g respectively, and the capacity retention rates after 100 cycles are 30.5%, 41.2% and 88.5% respectively, among which the PS-NCM811@TiP cathode has the highest capacity retention rate.

[0121] The rate performance results of commercial uncoated NCM811, NCM811@TiP, and PS-NCM811@TiP cathodes show that, compared with commercial uncoated NCM811 (26.4 mAh / g) and NCM811@TiP (77.1 mAh / g), PS-NCM811@TiP provides the highest reversible capacity of 104.8 mAh / g at 1C. In addition, when the current is returned from 1C to 0.1C, PS-NCM811@TiP exhibits a discharge capacity of 170.1 mAh / g, almost recovering to the initial level (179.2 mAh / g), indicating excellent electrochemical reversibility. Notably, the discharge specific capacity of NCM811@TiP drops rapidly after 0.1C, indicating that a single Ti3(PO4)4 coating is insufficient to support the stable operation of NCM811 at high current densities.

Claims

1. A preparation method of a gradient sulfurized phosphate-coated nickel-rich layered oxide cathode, characterized in that: It includes the following steps: 1) Dissolve a sulfur-rich phosphorus sulfide molecule P4S 10+6n , where n = 1 - 5 and n is a positive integer, in a diglyme solvent and stir at 60 - 100 °C for 1 - 5 h; 2) Disperse a certain amount of phosphate-coated nickel-rich layered oxide cathode powder into the solution obtained in step 1), and continuously stir at 60 - 100 °C for 8 - 15 h for in-situ sulfidation; continuously stir the solution at 140 - 160 °C until the diglyme solvent completely evaporates to obtain precursor powder; 3) Use anhydrous ethanol as the solvent, centrifuge and wash the precursor powder at a rotation speed of 7000 - 9000 rpm, and then dry it at 80 - 120 °C to obtain a gradient-sulfided phosphate-coated nickel-rich layered oxide cathode.

2. The preparation method according to claim 1, characterized in that: The mass ratio of the sulfur-rich phosphorus sulfide molecule P4S in step 1) 10+6n to the phosphate-coated nickel-rich layered oxide cathode powder is 1:

200.

3. The preparation method according to claim 1, characterized in that: In step 1), the sulfur-rich phosphorus sulfide molecule P4S 10+6n is prepared by the following method. According to the chemical molecular formula of P4S 10+6n , sulfur powder and P2S5 powder are respectively metered, mixed to obtain a precursor mixture; the precursor mixture is subjected to high-temperature heat treatment and then ground evenly in a mortar to obtain the sulfur-rich phosphorus sulfide molecule.

4. The preparation method according to claim 3, characterized in that: Among them, the high-temperature heat treatment is sintering at 200 - 400 °C for 20 - 30 hours under an argon atmosphere.

5. The preparation method according to claim 1, characterized in that: Among them, rich Phosphorus sulfide molecule P4S 10+6n is P4S 16 、P4S 22 、and P4S 28 one of them.

6. The preparation method according to claim 1, wherein: In step 2), the preparation method of the phosphate-coated nickel-rich layered oxide cathode is as follows: dissolve the phosphate in anhydrous ethanol and disperse it by ultrasonic; disperse the commercial uncoated nickel-rich layered oxide cathode powder into the above solution and continuously stir to obtain a precursor solution; continuously stir the precursor solution at 60 - 100 °C until the anhydrous ethanol completely evaporates to obtain precursor powder, and after high-temperature heat treatment, the phosphate-coated nickel-rich layered oxide cathode is obtained.

7. The preparation method according to claim 6, characterized in that: Among them, The heat treatment conditions are: sintering at 500 - 700 °C for 10 - 15 hours.

8. The preparation method according to claim 7, characterized in that: The mass ratio of the phosphate to the uncoated nickel-rich layered oxide cathode powder is 1:

100.

9. The preparation method according to claim 8, characterized in that: The phosphate is one of Ti3(PO4)4, AlPO4 or LiZr2(PO4)3.

10. A nickel-rich layered oxide cathode coated with gradient sulfurized phosphate, characterized in that, Prepared by the preparation method described in claims 1 - 9.

11. A method for preparing a solid-state lithium battery, characterized in that: The method includes the following steps: 1) Press the LPSCl powder into a disc with a diameter of 12 mm; 2) Prepare the gradient-sulfided phosphate-coated nickel-rich layered oxide cathode powder according to the method described in claims 1 - 9; 3) Mix the gradient-sulfided phosphate-coated nickel-rich layered oxide cathode, LPSCl and vapor-grown carbon fiber (VGCF) in a weight ratio of 50:48:2 in an agate mortar to prepare a composite cathode; 4) Take 6 mg of the composite cathode in step 3) and evenly spread it on one side of the solid electrolyte sheet, and press them together under a pressure of 400 MPa; 5) Attach a 12-mm lithium sheet to the other side of the LPSCl disc to form a "sandwich" solid-state battery structure.

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