High-nickel ternary positive electrode material of sulfide solid-state battery and modification method of high-nickel ternary positive electrode material

Abstract

The invention provides a sulfide solid-state battery high-nickel ternary positive electrode material and a modification method thereof, and relates to the technical field of lithium batteries. According to the invention, excessive lithium source is added during primary sintering of the high-nickel ternary material, so that more residual alkali exists on the surface of the product after primary sintering, uniformly coated lithium phosphate is formed on the surface in situ through the reaction of the residual alkali on the surface and phosphoric acid, and then the lithium thiophosphate coated high-nickel ternary positive electrode material is formed through the reaction of the lithium phosphate and a phosphorus-sulfur compound; the lithium thiophosphate material is uniformly coated on the surface of the high-nickel ternary positive electrode material through a simple and low-cost method, so that the stability and the ion transmission capability of the positive electrode material in a sulfide solid-state battery can be improved; the obtained lithium thiophosphate-coated high-nickel ternary positive electrode material can be used for sulfide solid-state batteries, and can be applied to the fields of power batteries and energy storage batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a sulfide solid-state battery high-nickel ternary positive electrode material and a modification method thereof. Background Art

[0002] Traditional liquid lithium-ion batteries present serious safety risks due to the shrinkage of the diaphragm at high temperatures and the flammability of the organic electrolyte. All-solid-state lithium-ion batteries, on the other hand, greatly improve safety performance by replacing the diaphragm and organic electrolyte in conventional liquid batteries with a solid-state electrolyte. However, when high-capacity, high-nickel cathode ternary materials come into contact with the sulfide in solid-state batteries, the interface between the two is prone to problems such as interfacial side reactions, space charge layers, and element diffusion due to the difference in potential between the two and the spontaneous decomposition of the sulfide solid electrolyte at high voltage, resulting in poor battery stability.

[0003] At present, the main method is to introduce chemically stable coating materials (commonly used are Al2O3, ZrO2, TiO2, LiNbO3, etc.) on the surface of high-nickel ternary materials to alleviate the interface problems between them and solid electrolytes.

[0004] Sulfide solid-state batteries have a significantly reduced contact area between the cathode material and the electrolyte due to solid-solid point-to-point contact. Therefore, the coating on the cathode material surface needs to have both high chemical stability and high ion conductivity for the sulfide solid electrolyte. However, the chemically stable coating materials commonly used on the surface of high-nickel ternary materials have a single function and are unable to simultaneously meet the requirements of sulfide solid-state batteries for cathode materials to have both high stability and high ion conductivity.

[0005] For example, commonly used coating materials such as Al2O3, ZrO2, and TiO2 do not contain lithium and therefore cannot provide sufficient capacity, which reduces the specific capacity of the cathode material. Furthermore, the general formula lacks lithium ion channels, which hinders lithium ion transport. LiNbO3 is relatively expensive, making it unsuitable for industrial production. Furthermore, many current coating methods are mostly point-based, resulting in uneven coating. Atomic layer deposition (ALD) coating is also an existing technology, but this method is costly and complex, making it unsuitable for mass production. Summary of the Invention

[0006] The present invention is a method for modifying high-nickel positive electrode materials for sulfide solid electrolytes. By sintering and drying, a low-cost lithium thiophosphate material is in situ coated on the surface of the high-nickel positive electrode material to solve the interface problem between the high-nickel ternary positive electrode material and the sulfide solid electrolyte, while promoting the transmission of lithium ions at the interface.

[0007] In a first aspect, the present application provides a method for modifying a high-nickel ternary cathode material for a sulfide solid-state battery, comprising the following preparation steps:

[0008] (1) The high nickel precursor and the excess lithium source are mixed by ball milling, placed in a tube furnace, and sintered at high temperature in an oxygen atmosphere;

[0009] (2) placing the product in step (1) in a phosphoric acid solution, stirring, and filtering;

[0010] (3) Then, the product of step (2) is placed in a tube furnace and calcined at high temperature in an oxygen atmosphere;

[0011] (4) The product of step (3) is placed in an inorganic phosphorus-sulfur compound solution and stirred, and then vacuum dried to obtain a high-nickel ternary positive electrode material coated with lithium thiophosphate; the inorganic phosphorus-sulfur compound is one or more of tetraphosphorus trisulfide, tetraphosphorus pentasulfide, tetraphosphorus heptasulfide, and tetraphosphorus decasulfide.

[0012] Furthermore, the high nickel precursor in step (1) is generally formulated as Ni x Co y Mn z (OH)2; where 1>x≥0.7, 0.3≥y>0, and 0.3≥z>0; in high-nickel materials, x+y+z=1, set to 1>x≥0.7, 0.3≥y>0, and 0.3≥z>0. If x=1, it is a lithium nickelate precursor. The sintered material is LiNiO2, which has an unstable structure and is generally not used as the main material for lithium battery positive electrodes.

[0013] Furthermore, the lithium source is lithium hydroxide and / or lithium carbonate; preferably lithium hydroxide.

[0014] Furthermore, the molar ratio of the high nickel precursor to the lithium source is 1:1.1-1.2.

[0015] Furthermore, the ball milling speed is 300~500 rpm, the zirconium bead particle size is 0.5~2 mm, the ball-to-material ratio is 10~20:1, and the time is 2~4 hours; the high-temperature sintering is a two-stage calcination, the first stage pre-sintering temperature is 300~500℃, the time is 2~4 hours, and then the temperature is raised to 700~950℃, kept warm for 10~20 hours, and the heating rate is 3~9℃ / min.

[0016] Furthermore, the phosphoric acid solution in step (2) is a phosphoric acid aqueous solution with a concentration of 50% to 80%.

[0017] Furthermore, in step (4), the concentration of the phosphorus-sulfur compound in the inorganic phosphorus-sulfur compound solution is 0.1% to 5%, and the solvent is NMP.

[0018] Furthermore, the stirring time in step (4) is 1 to 3 hours.

[0019] Furthermore, the vacuum drying is carried out at a temperature of 50 to 100 degrees Celsius and for a time of 1 to 6 hours.

[0020] In a second aspect, the present application provides a sulfide solid-state battery high-nickel ternary positive electrode material, which is obtained using the improved method of the present application.

[0021] Beneficial effects: 1. This invention adds an excess lithium source during the primary sintering of the high-nickel ternary material, so that there is a large amount of residual alkali on the surface of the product after the primary sintering. The surface residual alkali reacts with phosphoric acid to form a uniformly coated lithium phosphate on the surface, and then reacts with phosphorus-sulfur compounds to form a high-nickel ternary positive electrode material coated with lithium thiophosphate. The lithium thiophosphate material is uniformly coated on the surface of the high-nickel ternary positive electrode material by a simple and low-cost method, which can improve the stability and ion transport capacity of the positive electrode material in sulfide solid-state batteries. The obtained high-nickel ternary positive electrode material coated with lithium thiophosphate can be used in sulfide solid-state batteries, and its application fields include power batteries and energy storage batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a SEM morphology of the high-nickel ternary cathode material obtained in Example 1;

[0023] Figure 2 This is an EDS scan of the high-nickel ternary cathode material obtained in Example 1;

[0024] Figure 3 These are the EIS test characterization results of the high-nickel ternary positive electrode materials obtained in the examples and comparative examples. DETAILED DESCRIPTION

[0025] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below with reference to the specific embodiments of the drawings.

[0026] Example 1, a method for modifying a high-nickel ternary cathode material, comprising the following preparation process:

[0027] (1) 50g Ni 0.9 Co 0.05 Mn 0.05 The (OH)2 nickel-rich precursor and 14.26g LiOH (molar ratio = 1:1.1) were placed in a 1L ball mill, and 700g of 0.5mm zirconium beads were added. The mixture was ball milled at 350 rpm for 3 hours. The mixture was then placed in a tube furnace and heated to 300°C at a rate of 5°C / min under an oxygen atmosphere for 3 hours, then to 850°C and held for 12 hours.

[0028] (2) The product of step (1) was placed in a 75% phosphoric acid aqueous solution, stirred for 2 hours and then filtered.

[0029] (3) The filtered product was placed in a tube furnace and heated to 500°C at a rate of 0.5°C / min under an oxygen atmosphere and kept at this temperature for 2 hours.

[0030] (4) 0.7 g of P4S5 was ultrasonically dissolved and dispersed in 70 g of NMP. The product of step (3) was then placed in the solution, stirred at room temperature for 2 hours, and placed in a vacuum drying oven at 80°C to obtain a high-nickel ternary positive electrode material coated with lithium thiophosphate.

[0031] The SEM morphology of lithium thiophosphate coated high nickel ternary cathode material is as follows Figure 1 ,From the SEM image, it can be seen that the particle size of the high nickel ternary positive electrode material coated with lithium thiophosphate ranges from 2 to 7 microns.

[0032] EDS scanning of lithium thiophosphate coated high nickel ternary cathode material Figure 2 ,from Figure 2 It can be seen that the S and P elements are evenly distributed, confirming that lithium thiophosphate is successfully coated on the surface of the high-nickel material.

[0033] Comparative Example 1, a method for modifying a high-nickel ternary positive electrode material, comprising the following preparation process:

[0034] (1) 50g Ni 0.9 Co 0.05 Mn 0.05 The (OH)2 nickel-rich precursor and 14.26 g of LiOH (molar ratio = 1:1.1) were placed in a 1 L ball mill, and 700 g of 0.5 mm zirconium beads were added. The mixture was ball milled at 350 rpm for 3 hours. The mixture was then placed in a tube furnace and heated to 300°C at a rate of 5°C / min under an oxygen atmosphere for 3 hours, then to 850°C and held for 12 hours.

[0035] (2) The product of step (1) was placed in deionized water, stirred for 2 hours, and then filtered;

[0036] (3) Then, the filtered product was placed in a tube furnace and heated to 500°C at a rate of 0.5°C / min under an oxygen atmosphere and kept at that temperature for 2 hours;

[0037] (4) The product of step (3) was then placed in 70 g of NMP, stirred at room temperature for 2 hours, and dried in a vacuum drying oven at 80° C. to obtain a lithium thiophosphate-coated high-nickel ternary positive electrode material.

[0038] Comparative Example 2, a method for modifying a high-nickel ternary positive electrode material, comprising the following preparation process:

[0039] (1) 50g Ni 0.9 Co 0.05 Mn 0.05The (OH)2 nickel-rich precursor and 14.26 g of LiOH (molar ratio = 1:1.1) were placed in a 1 L ball mill, and 700 g of 0.5 mm zirconium beads were added. The mixture was ball milled at 350 rpm for 3 hours. The mixture was then placed in a tube furnace and heated to 300°C at a rate of 5°C / min under an oxygen atmosphere for 3 hours, then to 850°C and held for 12 hours.

[0040] (2) The product of step (1) was placed in a 75% phosphoric acid aqueous solution, stirred for 2 hours, and then filtered;

[0041] (3) The filtered product was then placed in a tube furnace and heated to 500°C at a rate of 0.5°C / min under an oxygen atmosphere and kept at that temperature for 2 hours;

[0042] (4) The product of step (3) was then placed in 70 g of NMP, stirred at room temperature for 2 hours, and dried in a vacuum drying oven at 80° C. to obtain a lithium phosphate-coated high-nickel ternary positive electrode material.

[0043] Comparative Example 3, a method for modifying a high-nickel ternary positive electrode material, comprising the following preparation process:

[0044] (1) 50g Ni 0.9 Co 0.05 Mn 0.05 The (OH)2 nickel-rich precursor and 14.26g LiOH (molar ratio = 1:1.1) were placed in a 1L ball mill, and 700g of 0.5mm zirconium beads were added. The mixture was ball milled at 350 rpm for 3 hours. The mixture was then placed in a tube furnace and heated to 300°C at a rate of 5°C / min under an oxygen atmosphere for 3 hours, then to 850°C and held for 12 hours.

[0045] (2) The product of step (1) was placed in a 75% phosphoric acid aqueous solution, stirred for 2 hours and then filtered.

[0046] (3) The filtered product was then placed in a tube furnace and heated to 500°C at a rate of 0.5°C / min under an oxygen atmosphere and kept at that temperature for 2 hours.

[0047] (4) Place the product from step 3, 2 g of Al2O3, and 2 g of inorganic solid electrolyte powder into a ball mill, add 600 g of 0.5 mm zirconium beads, and mill at 300 rpm for 5 h.

[0048] The structural formula of the inorganic solid electrolyte powder is Li0.5Al0.5Ge1.5(PO4)3(LAGP).

[0049] (5) The product of step (4) was then placed in 70 g of NMP, stirred at room temperature for 2 hours, and dried in a vacuum drying oven at 80° C. to obtain a high-nickel ternary positive electrode material with aluminum oxide and lithium phosphate co-coated therein.

[0050] Electrochemical performance tests were performed using mold batteries.

[0051] Half-cell assembly: Li-In composite anode + sulfide solid electrolyte + composite cathode

[0052] Composite positive electrode composition: 75% positive electrode active material + 20% sulfide solid electrolyte + 5% conductive carbon VGCF

[0053] Mold battery assembly process: First, place the sulfide solid electrolyte into the mold battery and manually compact it. Then place the composite positive electrode, apply a pressure of 2.5 tons, and maintain the pressure for 3-5 minutes. Next, disassemble the negative electrode side, add the In sheet and a small Li sheet, in the order of Li sheet + In sheet + sulfide solid electrolyte. After the full battery is assembled, apply another 0.1 ton pressure without maintaining the pressure. Finally, let the full battery stand for 6-8 hours before testing. The test results are shown in Table 1.

[0054] Table 1. Discharge capacity and cycle performance of high nickel ternary cathode materials obtained in examples and comparative examples in sulfide solid mold batteries

[0055] distinguish First discharge capacity (mAh / g) Cycle (0.2C / 0.2C, 50 turns) Example 1 221.5 83.5% Comparative Example 1 195.8 36.9% Comparative Example 2 206.7 63.2% Comparative Example 3 202.5 61.8%

[0056] From the data in Table 1, it can be seen that Example 1 exhibits the highest discharge capacity and the best cycle performance. This is due to the fact that the lithium thiophosphate coating layer reduces the interfacial impedance with the sulfide solid electrolyte and slows down the decomposition rate of the sulfide solid electrolyte.

[0057] The first discharge capacity and cycle performance of Example 1 are better than those of Comparative Example 3, which may be because the lithium thiophosphate coating prepared by the in-situ reaction in Example 1 is an in-situ coating, which is more tightly combined with the material and has better adhesion performance on the high-nickel ternary positive electrode material; and the coating layer does not contain Al2O3, ZrO2, TiO2 and other substances, and the lithium ion channel conduction is smoother.

[0058] Figure 3 Figure 1 shows the EIS test results for the Examples and Comparative Examples. Example 1 is a high-nickel material coated with lithium thiophosphate, Comparative Example 1 is an uncoated high-nickel material, Comparative Example 2 is a high-nickel material coated with lithium phosphate, and Comparative Example 3 is a high-nickel material co-coated with aluminum oxide and lithium phosphate. Example 1 has the smallest semicircle in the high-frequency region and the most vertical curve in the low-frequency region, indicating that the lithium thiophosphate-coated high-nickel material (Example 1) has the smallest DCR and the best ion diffusion capacity in sulfide solid-state batteries.

[0059] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for modifying a high-nickel ternary cathode material for a sulfide solid-state battery, characterized in that: The method comprises the following preparation steps: (1) The high nickel precursor and the excess lithium source are mixed by ball milling, placed in a tube furnace, and sintered at high temperature in an oxygen atmosphere; (2) placing the product in step (1) in a phosphoric acid solution, stirring, and filtering; (3) Then, the product of step (2) is placed in a tube furnace and calcined at high temperature in an oxygen atmosphere; (4) The product of step (3) is placed in an inorganic phosphorus-sulfur compound solution and stirred, and then vacuum dried to obtain a high-nickel ternary positive electrode material coated with lithium thiophosphate; the inorganic phosphorus-sulfur compound is one or more of tetraphosphorus trisulfide, tetraphosphorus pentasulfide, tetraphosphorus heptasulfide, and tetraphosphorus decasulfide.

2. The method for modifying a sulfide solid-state battery high-nickel ternary cathode material according to claim 1, characterized in that: The high nickel precursor in step (1) is generally formulated as Ni x Co y Mn z (OH)2; Among them, 1>x≥0.7, 0.3≥y>0, 0.3≥z>0.

3. The method for modifying a sulfide solid-state battery high-nickel ternary cathode material according to claim 1, characterized in that: The lithium source is lithium hydroxide and / or lithium carbonate.

4. The method for modifying a sulfide solid-state battery high-nickel ternary cathode material according to claim 1, characterized in that: The molar ratio of the high nickel precursor to the lithium source is 1:1.1-1.

2.

5. The method for modifying a sulfide solid-state battery high-nickel ternary cathode material according to claim 1, characterized in that: The ball milling speed is 300-500 rpm, the zirconium bead particle size is 0.5-2 mm, the ball-to-material ratio is 10-20:1, and the time is 2-4 hours. The high-temperature sintering is a two-stage calcination, with a pre-sintering temperature of 300-500°C for 2-4 hours in the first stage, followed by heating to 700-950°C and keeping warm for 10-20 hours at a heating rate of 3-9°C / min.

6. The method for modifying a sulfide solid-state battery high-nickel ternary cathode material according to claim 1, characterized in that: The phosphoric acid solution in step (2) is a phosphoric acid aqueous solution with a concentration of 50% to 80%.

7. The method for modifying a sulfide solid-state battery high-nickel ternary cathode material according to claim 1, characterized in that: The concentration of the phosphorus-sulfur compound in the inorganic phosphorus-sulfur compound solution in step (4) is 0.1% to 5%, and the solvent is NMP.

8. The method for modifying a sulfide solid-state battery high-nickel ternary cathode material according to claim 1, characterized in that: The stirring time in step (4) is 1 to 3 hours.

9. The method for modifying a sulfide solid-state battery high-nickel ternary cathode material according to claim 1, characterized in that: The vacuum drying process is carried out at a temperature of 50 to 100 degrees Celsius and for a time of 1 to 6 hours.

10. A high nickel ternary cathode material, characterized in that: The modified product is prepared by the modification method according to any one of claims 1 to 9.

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