A gradient sulfidized phosphate-coated nickel-rich layered oxide cathode and lithium battery thereof

Abstract

The application relates to the technical field of lithium batteries, in particular to a positive electrode material of a sulfide-based solid-state lithium battery and a lithium battery containing the positive electrode. A sulfur-rich phosphorus sulfide molecule is used to modify a phosphate-coated nickel-rich layered oxide positive electrode powder, a gradient sulfur-phosphate-coated nickel-rich layered oxide positive electrode is prepared, a composite electrode is obtained by compounding the positive electrode with a sulfide electrolyte and vapor-grown carbon fiber (VGCF), and a lithium battery is prepared by compounding the composite electrode with an electrolyte sheet. The gradient sulfur-phosphate-coated nickel-rich layered oxide positive electrode and the sulfide solid-state electrolyte exhibit interface compatibility, and the full solid-state battery assembled from the two and a lithium metal negative electrode has good electrochemical performance and cycle stability. The protective layer effectively suppresses the space charge layer, stabilizes the nickel-rich layered oxide positive electrode / sulfide electrolyte interface, and has the characteristics of simple structure, easy preparation and large-scale production, which better promotes the practicalization process of the sulfide-based full solid-state lithium battery.

Description

TECHNICAL FIELD

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

[0002] With the continuous expansion of the electric vehicle market and the surge in energy storage demand, the requirements for the energy density and safety of lithium batteries are becoming 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 can pierce the separator, leading to short circuit and thus causing major safety hazards. As a highly potential next-generation battery technology, all-solid-state lithium batteries (ASSLBs) are characterized by the use of solid-state electrolytes to replace traditional liquid electrolytes. Solid-state electrolytes have the advantages of non-flammability, high mechanical strength, and high density, which not only greatly enhance the safety performance of the battery, but also significantly improve the energy density. In view of the broad application prospect of all-solid-state lithium batteries, in order to meet the growing urgent needs of the market for high-energy-density batteries, the academic and industrial circles are actively engaged in research. On the one hand, efforts are made to develop solid-state 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 positive electrode materials, aiming to further improve the overall performance of the battery.

[0003] Among the many fast ion conductors, sulfide solid-state electrolytes (e.g. 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 operating voltage, and low cost, making them the best choice for high-energy-density ASSLBs positive electrode materials. However, there are many problems at the interface between the sulfide solid-state electrolyte and the NCM positive electrode: (1) the physical contact between the two is not dense, and the positive electrode material will undergo a large volume change during the lithium intercalation / deintercalation process, which will further deteriorate the physical contact at the interface, leading to a decrease in the cycle stability of the battery; (2) there is a difference in chemical potential between the NCM positive electrode and the sulfide solid-state electrolyte, and Li + will migrate from the sulfide solid-state electrolyte to the NCM positive electrode. Since NCM is an ion-electron mixed conductor, the electron conduction on the positive electrode side will balance part of the Li + concentration gradient, which leads to more Li + escaping from the sulfide solid-state electrolyte and forming a thick high-impedance Li +depletion layer (i.e. space charge layer); (3) adverse side reactions occurring between the NCM cathode and the sulfide solid-state electrolyte, leading to oxidative decomposition of the sulfide solid-state electrolyte and collapse of the NCM cathode structure. Therefore, in order to construct a highly stable NCM / sulfide electrolyte interface, realize sulfide-based ASSLBs with high energy efficiency and long cycle life, it is necessary to develop a cathode protective layer material with high structural and chemical similarity to the sulfide solid-state electrolyte. SUMMARY

[0004] In order to solve the problems of poor interface contact between the nickel-rich layered oxide cathode and the sulfide solid-state electrolyte, interface space charge layer and interface side reactions, the present application provides a surface-modified nickel-rich layered oxide cathode and a sulfide-based solid-state lithium battery comprising the cathode. The surface of the cathode has improved Li + conductivity, and it has good compatibility with the sulfide solid-state electrolyte, the interface between the two is more stable, the space charge layer is inhibited, and the interface side reactions are less. Therefore, the sulfide-based solid-state lithium battery using the cathode has good electrochemical performance and cycle stability.

[0005] The present application provides a preparation method of a gradient sulfidized phosphate-coated nickel-rich layered oxide cathode, which comprises the following steps:

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

[0007] 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℃ for 8-15h for in-situ sulfidization; continuously stir the solution at 140-160℃ until the diglycol dimethyl ether solvent is completely evaporated to obtain a precursor powder;

[0008] 3) Centrifugal wash the precursor powder with anhydrous ethanol as the solvent at a speed of 7000-9000rpm, and then dry at 80-120℃ to obtain the gradient sulfidized phosphate-coated nickel-rich layered oxide cathode.

[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+6nThe chemical formula of the sulfur powder and P2S5 powder is measured respectively, mixed to obtain a precursor mixture; the precursor mixture is subjected to high-temperature heat treatment, and then is ground uniformly in a mortar to obtain the sulfur-rich phosphorus sulfide molecule. The high-temperature heat treatment is sintering at 200-400°C for 20-30 hours in an argon atmosphere. The sulfur-rich phosphorus sulfide molecule P4S 10+6n is preferably P4S 16 , P4S 22 , and P4S 28 .

[0011] Preferably, in step 2), the preparation method of the phosphate-coated nickel-rich layered oxide positive electrode is as follows: the phosphate is dissolved in anhydrous ethanol and is ultrasonically dispersed; commercial uncoated nickel-rich layered oxide positive electrode powder is dispersed into the above solution, and stirring is continued until anhydrous ethanol is completely evaporated to obtain a precursor powder, which is subjected to high-temperature heat treatment to obtain the phosphate-coated nickel-rich layered oxide positive electrode. The heat treatment condition is sintering at 500-700°C for 10-15 hours. The mass ratio of the phosphate to the uncoated nickel-rich layered oxide positive electrode powder is 1:100. Preferably, the phosphate is one of Ti3(PO4)4, AlPO4, and LiZr2(PO4)3.

[0012] The present application also provides a preparation method of a solid-state lithium battery, which comprises the following steps:

[0013] 1) The sulfide electrolyte powder is pressed into a 12mm-diameter disc;

[0014] 2) The gradient sulfur-phosphated nickel-rich layered oxide positive electrode powder is prepared according to the above method;

[0015] 3) The gradient sulfur-phosphated nickel-rich layered oxide positive electrode, the sulfide electrolyte powder, and the vapor-grown carbon fiber (VGCF) are mixed in a weight ratio of 50:48:2 in a maroon mortar to prepare a composite positive electrode;

[0016] 4) 6mg of the composite positive electrode of step 3) is evenly laid on one side of the solid-state electrolyte disc, and is pressed together under a pressure of 400MPa;

[0017] 5) A 12mm lithium disc is attached 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] This invention proposes a simple and scalable sulfur-rich phosphorus sulfide molecule (P4S). 10+6n The assisted in-situ sulfidation method utilizes favorable OS exchange between PO and PS bonds to generate a uniform and continuous gradient sulfidated phosphate protective layer on the surface of the nickel-rich layered oxide cathode by in-situ sulfidation of a phosphate coating. PO4 3- With P4S 10+6n The reaction produces PS4 3- and PO 4-x S x 3- LPSCl is an Argyrodite-type sulfide solid electrolyte, and its crystal structure contains PS4. 3- Tetrahedral units serve as the basic framework. For PO 4-x S x 3- Some O atoms are replaced by S atoms, forming a tetrahedral structure of mixed anions, similar to PS4. 3- The structure of PS4 is highly similar to the local structure of LPSCl. In terms of chemical properties, PS4... 3- Tetrahedrons can construct 3D network frameworks using a vertex-sharing mechanism, providing a basis for Li + Provides a continuous migration path. LPSCl is available with PS4. 3- Its properties exhibit excellent ion conductivity. PO 4-x S x 3- Due to the combined effect of O and S atoms, it also possesses the properties of PS4. 3- Similar chemical activity. Therefore, a gradient sulfophosphate protective layer with structural and chemical similarity to LPSCl can greatly improve interfacial contact while enhancing the Li content on the nickel-rich layered oxide cathode surface. + Chemical potential, fundamentally suppressing the space charge layer. Furthermore, thanks to the gradient sulfidation design, the coating exhibits Li-like properties throughout its entire depth. + The chemical potential gradient further reduced the Li + Migration barrier improves interface Li + Transport kinetics. The nickel-rich layered oxide cathode coated with gradient phosphate sulfide exhibits interfacial compatibility with the LPSCl sulfide solid electrolyte, and the all-solid-state battery assembled with the lithium metal anode demonstrates good electrochemical performance and cycle stability. This protective layer effectively suppresses the space charge layer, stabilizes the nickel-rich layered oxide cathode / LPSCl interface, and its simple structure, ease of fabrication, and mass production capabilities further promote the practical application of sulfide-based all-solid-state lithium batteries. Detailed Implementation Attached Figure Description

[0021] Figure 1: Related characterization of gradient sulfidized 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 under 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: Obtain LPSCl powder by high-temperature sintering, pass the LPSCl powder through a 400-mesh sieve, and press the undersize powder into a solid electrolyte sheet with a diameter of 12 mm under a pressure of 200 MPa.

[0028] S2: Obtain sulfur-rich phosphorus sulfide P4S7by high-temperature sintering under an argon atmosphere 16 .

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

[0030] S4: Obtain PS-NCM811@TiP cathode using P4S7 16 assisted liquid phase in-situ sulfidation method.

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

[0032] 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.

[0033] S7: Attach a 12 mm lithium sheet to the other side of the solid electrolyte sheet in S6 to form a full solid-state battery of metal lithium anode, LPSCl solid electrolyte, and PS-NCM811@TiP composite cathode.

[0034] Experimental Example 2:

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

[0036] S2: Obtain sulfur-rich phosphorus sulfide molecules P4S 22 .

[0037] S3: Obtain Ti3(PO4)4-coated NCM811 cathodes (NCM811@TiP) by a wet chemical method followed by high-temperature sintering.

[0038] S4: Obtain PS2-NCM811@TiP cathodes using a P4S 22 assisted liquid-phase in-situ sulfuration method.

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

[0040] 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.

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

[0042] Experimental Example 3:

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

[0044] S2: Obtain sulfur-rich phosphorus sulfide molecules P4S 28 .

[0045] S3: Obtain Ti3(PO4)4-coated NCM811 cathodes (NCM811@TiP) by a wet chemical method followed by high-temperature sintering.

[0046] S4: Obtain PS3-NCM811@TiP cathodes using a P4S 28 assisted liquid-phase in-situ sulfuration method.

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

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

[0049] S7: Attach a 12 mm lithium sheet to the other side of the solid-state electrolyte sheet in S6 to form a full solid-state battery of metal lithium negative electrode, LPSCl solid-state electrolyte, and PS3-NCM811@TiP composite positive electrode in sequence.

[0050] Example 4

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

[0052] S2: Obtain sulfur-rich phosphorus sulfide molecules P4S 16 .

[0053] S3: Obtain AlPO4-coated NCM811 positive electrode (NCM811@AlP) by wet chemical method and subsequent high-temperature sintering.

[0054] S4: Obtain PS-NCM811@AlP positive electrode using P4S 16 assisted liquid-phase in-situ sulfidation method.

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

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

[0057] S7: Attach a 12 mm lithium sheet to the other side of the solid-state electrolyte sheet in S6 to form a full solid-state battery of metal lithium negative electrode, LPSCl solid-state electrolyte, and PS-NCM811@AlP composite positive electrode in sequence.

[0058] Example 5

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

[0060] S2: Obtain sulfur-rich phosphorus sulfide molecules P4S 22 .

[0061] S3: Obtain AlPO4-coated NCM811 positive electrode (NCM811@AlP) by wet chemical method and subsequent high-temperature sintering.

[0062] S4: Use P4S 22 The auxiliary liquid in-situ sulfuration method obtains a PS2-NCM811@AlP positive electrode.

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

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

[0065] S7: Attach a 12mm lithium sheet to the other side of the solid-state electrolyte sheet in S6 to form a full solid-state battery of a metal lithium negative electrode, an LPSCl solid-state electrolyte, and a PS2-NCM811@AlP composite positive electrode.

[0066] Example 6

[0067] S1: Obtain LPSCl powder by high-temperature sintering, pass the LPSCl powder through a 400-mesh sieve, and press the sieved powder into a 12mm-diameter solid-state electrolyte sheet under a pressure of 200MPa.

[0068] S2: Obtain sulfur-rich sulfurized phosphorus molecules P4S by high-temperature sintering under an argon atmosphere 28 .

[0069] S3: Obtain NCM811 positive electrode coated with AlPO4 (NCM811@AlP) by wet chemical method and subsequent high-temperature sintering

[0070] S4: Use P4S 28 The auxiliary liquid in-situ sulfuration method obtains a PS3-NCM811@AlP positive electrode.

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

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

[0073] S7: Attach a 12mm lithium sheet to the other side of the solid-state electrolyte sheet in S6 to form a full solid-state battery of a metal lithium negative electrode, an LPSCl solid-state electrolyte, and a PS3-NCM811@AlP composite positive electrode.

[0074] Example 7

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

[0076] S2: Obtain sulfur-rich phosphorus sulfide molecules P4S 16 .

[0077] S3: Obtain LiZr2(PO4)3-coated NCM712 cathodes (NCM712@LZP) by a wet chemical method followed by high-temperature sintering.

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

[0079] S5: Mix PS-NCM712@LZP, LPSCl, and VGCF in a 50:48:2 weight ratio in a maroon 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 full-solid-state battery of a metal lithium anode, an LPSCl solid electrolyte, and a PS-NCM712@LZP composite cathode in sequence.

[0082] Example 8

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

[0084] S2: Obtain sulfur-rich phosphorus sulfide molecules P4S 22 .

[0085] S3: Obtain LiZr2(PO4)3-coated NCM712 cathodes (NCM712@LZP) by a wet chemical method followed by high-temperature sintering.

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

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

[0088] S6: 6 mg of the composite cathode of S5 was evenly spread on one side of the solid-state electrolyte sheet, and they were pressed together under a pressure of 400 MPa.

[0089] S7: A 12 mm lithium sheet was attached to the other side of the solid-state electrolyte sheet in S6, and a full solid-state battery of a metal lithium anode, an LPSCl solid-state electrolyte, and a PS3-NCM712@LZP composite cathode was formed in sequence.

[0090] Example 9

[0091] S1: LPSCl powder was obtained by high-temperature sintering, the LPSCl powder was passed through a 400-mesh sieve, and the powder under the sieve was pressed into a 12-mm-diameter solid-state electrolyte sheet under a pressure of 200 MPa.

[0092] S2: Sulfur-rich phosphorized molecules P4S7were obtained by high-temperature sintering in an argon atmosphere. 28 .

[0093] S3: NCM712 cathodes coated with LiZr2(PO4)3(NCM712@LZP) were obtained by a wet chemical method followed by high-temperature sintering.

[0094] S4: PS3-NCM712@LZP cathodes were obtained using a P4S7assisted liquid-phase in-situ sulfidation method. 28

[0095] S5: The PS3-NCM712@LZP, LPSCl, and VGCF were mixed in a 50:48:2 weight ratio in a maroon mortar for 1 h to prepare a composite cathode.

[0096] S6: 6 mg of the composite cathode of S5 was evenly spread on one side of the solid-state electrolyte sheet, and they were pressed together under a pressure of 400 MPa.

[0097] S7: A 12 mm lithium sheet was attached to the other side of the solid-state electrolyte sheet in S6, and a full solid-state battery of a metal lithium anode, an LPSCl solid-state electrolyte, and a PS3-NCM712@LZP composite cathode was formed in sequence.

[0098] Comparative Example 1

[0099] S1: LPSCl powder was obtained by high-temperature sintering, the LPSCl powder was passed through a 400-mesh sieve, and the powder under the sieve was pressed into a 12-mm-diameter solid-state electrolyte sheet under a pressure of 200 MPa.

[0100] S2: Commercial uncoated NCM811, LPSCl, and VGCF were mixed in a 50:48:2 weight ratio in a maroon mortar for 1 h to prepare a composite cathode.

[0101] ​S3: 6 mg of the composite cathode of S2 was evenly spread on one side of the solid-state electrolyte sheet, and they were pressed together under a pressure of 400 MPa.

[0102] S4: A 12 mm lithium sheet was attached to the other side of the solid-state electrolyte sheet in S3 to form a full solid-state battery of metal lithium anode, LPSCl solid-state electrolyte, and commercial uncoated NCM811 composite cathode in sequence.

[0103] Comparative Example 2

[0104] S1: LPSCl powder was obtained by high-temperature sintering, and the powder was sieved through a 400-mesh sieve. The undersize powder was pressed into a solid-state electrolyte sheet with a diameter of 12 mm under a pressure of 200 MPa.

[0105] S2: Ti3(PO4)4-coated NCM811 cathode (NCM811@TiP) was obtained by a wet chemical method followed by high-temperature sintering.

[0106] S3: NCM811@TiP, LPSCl, and VGCF were mixed in a marquis mortar at a weight ratio of 50:48:2 for 1 h to prepare a composite cathode.

[0107] S4: 6 mg of the composite cathode of S3 was evenly spread on one side of the solid-state electrolyte sheet, and they were pressed together under a pressure of 400 MPa.

[0108] Comparative Example 3

[0109] S1: LPSCl powder was obtained by high-temperature sintering, and the powder was sieved through a 400-mesh sieve. The undersize powder was pressed into a solid-state electrolyte sheet with a diameter of 12 mm under a pressure of 200 MPa.

[0110] S2: AlPO4-coated NCM811 cathode (NCM811@AlP) was obtained by a wet chemical method followed by high-temperature sintering.

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

[0112] S4: 6 mg of the composite cathode of S3 was evenly spread on one side of the solid-state electrolyte sheet, and they were pressed together under a pressure of 400 MPa.

[0113] S5: A 12 mm lithium sheet was attached to the other side of the solid-state electrolyte sheet in S4 to form a full solid-state battery of metal lithium anode, LPSCl solid-state electrolyte, and NCM811@AlP composite cathode in sequence.

[0114] Comparative Example 4

[0115] S1: Obtain LPSCl powder by high-temperature sintering, sieve the LPSCl powder through a 400-mesh sieve, and press the undersize powder into a 12-mm-diameter solid electrolyte sheet under a pressure of 200 MPa.

[0116] S2: Obtain LiZr2(PO4)3-coated NCM712 cathode (NCM712@LZP) by a wet chemical method followed by high-temperature sintering.

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

[0118] 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.

[0119] S5: Attach a 12-mm lithium sheet to the other side of the solid electrolyte sheet in S4 to form a full-solid-state battery of metal 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, and it is clear that the PS-NCM811@TiP sample has lower polarization and higher discharge capacity. + The diffusion coefficient (D Li+ ) extraction results show that PS-NCM811@TiP has the highest D Li+ throughout the discharge process, demonstrating improved Li + ion migration dynamics. 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 capability results of commercial uncoated NCM811, NCM811@TiP and PS-NCM811@TiP cathodes show that PS-NCM811@TiP provides the highest reversible capacity of 104.8 mAh / g at 1C, compared to commercial uncoated NCM811 (26.4 mAh / g) and NCM811@TiP (77.1 mAh / g). Furthermore, when the current is re-turned from 1C back to 0.1C, PS-NCM811@TiP exhibits a discharge capacity of 170.1 mAh / g, almost back 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)4coating is not sufficient to support the stable operation of NCM811 at high current density.

Claims

1. A method for preparing a gradient-sulfidized phosphate-coated nickel-rich layered oxide cathode, characterized by: comprising the following steps: 1) Sulfur-rich sulfurized phosphorus molecules P4S 10+6n n = 1-5, n is a positive integer, dissolved in diethylene glycol dimethyl ether solvent and stirred at 60-100°C for 1-5h; 2) dispersing a certain amount of phosphate-coated Ni-rich layered oxide cathode powder into the solution obtained in step 1) and continuously stirring at 60-100℃ for 8-15h for in-situ sulfidation; continuously stirring the solution at 140-160℃ until the diethylene glycol dimethyl ether solvent is completely evaporated to obtain a precursor powder; 3) centrifugal washing the precursor powder with anhydrous ethanol as solvent at a speed of 7000-9000rpm, and then drying at 80-120℃ to obtain the gradient-sulfidized phosphate-coated Ni-rich layered oxide cathode; In step 1), the sulfur-rich sulfur phosphorus molecule P4S 10+6n The sulfur-rich sulfur phosphorus molecule is prepared by the following method. According to the chemical formula P4S 10+6n Sulfur powder and P2S5 powder are respectively measured according to the chemical formula P4S, mixed to obtain a precursor mixture; the precursor mixture is sintered at 200-400°C for 20-30 hours under an argon atmosphere, and then uniformly ground in a mortar to obtain the sulfur-rich sulfur phosphorus molecule.

2. The method of claim 1, wherein: The sulfur-rich sulfurized phosphorus molecule P4S in step 1 10+6n The mass ratio of the phosphate-coated nickel-rich layered oxide positive electrode powder to the sulfur-rich sulfurized phosphorus molecule P4S in step 1 was 1:

200.

3. The method of claim 1, wherein: wherein the Ni-rich layered oxide is prepared by the following steps: sulfurized phosphorus molecule P4S 10+6n is P4S 16 , P4S 22 , and P4S 28 one of 4. The method of claim 1, wherein: In step 2), the phosphate-coated Ni-rich layered oxide cathode is prepared by the following steps: dissolving phosphate in anhydrous ethanol and ultrasonic dispersion; dispersing commercial uncoated Ni-rich layered oxide cathode powder into the above solution and continuously stirring to obtain a precursor solution; continuously stirring the precursor solution at 60-100℃ until the anhydrous ethanol is completely evaporated to obtain a precursor powder, which is then heat-treated at high temperature to obtain the phosphate-coated Ni-rich layered oxide cathode.

5. The method of claim 4, wherein: wherein, The heat treatment conditions are: sintering at 500-700℃ for 10-15h.

6. The method of claim 4, wherein: The mass ratio of phosphate to uncoated Ni-rich layered oxide cathode powder is 1:

100.

7. The method of claim 4, wherein: The phosphate is one of Ti3(PO4)4, AlPO4 or LiZr2(PO4)3.

8. A gradient-sulfidized phosphate-coated nickel-rich layered oxide cathode, characterized by, Prepared by the preparation method of any one of claims 1-7.

9. A method of producing a solid-state lithium battery, characterized by: The method comprises the following steps: 1) pressing the LPSCl powder into a 12mm diameter disc; 2) preparing the gradient-sulfidized phosphate-coated Ni-rich layered oxide cathode powder according to the method of any one of claims 1-7; 3) mixing the gradient-sulfidized phosphate-coated Ni-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) taking 6mg of the composite cathode of step 3) and evenly spreading it on one side of a solid-state electrolyte disc, and pressing together under a pressure of 400MPa; 5) attaching a 12mm lithium disc to the other side of the LPSCl disc to form a "sandwich" solid-state battery structure.

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