Sulfide all-solid-state battery positive electrode material and preparation method thereof

Abstract

The invention belongs to the technical field of battery positive electrode materials, and discloses a sulfide all-solid-state battery positive electrode material and a preparation method thereof. The positive electrode material comprises a positive electrode active material and sulfide solid electrolyte; the sulfide solid electrolyte comprises a sulfide matrix and a coating layer coating the surface of the sulfide matrix, the positive electrode active material and a part of the coating layer are compounded through a fast ion conductor layer which is generated in situ through sintering after the positive electrode active material and the sulfide solid electrolyte are mixed. The surface air stability of the sulfide solid electrolyte is improved through two times of sintering (pre-sintering and sintering), and the interface contact resistance of a sulfide matrix and a positive electrode active material is reduced through an in-situ generated fast ion conductor layer.

Description

Technical Field

[0001] This invention belongs to the field of battery cathode material technology, and more specifically, relates to a sulfide all-solid-state battery cathode material and its preparation method. Background Technology

[0002] Since their large-scale application, lithium-ion power batteries have received widespread market attention. However, the insurmountable problems in some key technologies of battery materials have been hindering their commercial development. Cathode materials are the core materials of power lithium batteries. The energy density of cathode materials is closely related to the driving range of electric vehicles. In the face of the urgent problem of energy shortage, the rapid development of cathode materials with high energy density, long life, high safety, and low cost is crucial for the future.

[0003] Based on the electrolyte, all-solid-state batteries can be divided into three types: sulfide, polymer, and oxide. Among them, sulfide is considered the ultimate route for all-solid-state batteries. However, the main drawbacks of sulfide solid electrolytes are: poor air stability, easily reacting with water or oxygen to generate harmful gases such as H2S, affecting the ionic conductivity of the material; and easy side reactions with the positive electrode active material. Sulfides have a low oxidation potential, while high-nickel positive electrode active materials are also unstable on the surface due to lithium-nickel mixing, inevitably leading to interfacial side reactions at the interface, hindering their application in all-solid-state lithium batteries.

[0004] Currently, to address the direct contact between sulfides and high-nickel cathode active materials, the common approach is to coat the surface of the cathode active material or sulfide material with an inert substance to reduce side reactions. However, during charge and discharge, this inert coating layer forms an isolation layer, hindering ion transport rates in the cathode active material or sulfide material and reducing the electrochemical reactivity of the cathode active material. This is especially true in the areas where the sulfide and cathode active material are not in contact. Due to the presence of the coating layer, lithium-ion transport in the cathode active material will be significantly reduced, increasing internal resistance, polarization, and ultimately affecting the capacity utilization of the cathode active material.

[0005] Therefore, there is an urgent need to propose a new sulfide-based all-solid-state battery cathode material and its preparation method. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a sulfide-based all-solid-state battery cathode material and its preparation method. This invention improves the air stability of the sulfide solid electrolyte surface through two sintering processes (pre-sintering + sintering), and the in-situ generated fast-ion conductor layer reduces the interfacial contact impedance between the sulfide matrix and the cathode active material.

[0007] To achieve the above objectives, the present invention provides a sulfide-based all-solid-state battery cathode material, the cathode material comprising: Positive electrode active material and sulfide solid electrolyte; The sulfide solid electrolyte includes a sulfide matrix and a coating layer covering the surface of the sulfide matrix; The positive electrode active material and part of the coating layer are composites formed in situ by sintering the positive electrode active material and the sulfide solid electrolyte.

[0008] In this invention, the sulfide matrix and the coating material are first mixed and pre-fired to coat the sulfide matrix with a compound coating layer, stabilizing the sulfide matrix structure and improving its air stability, resulting in a pre-fired sulfide solid electrolyte. Then, the pre-fired sulfide solid electrolyte and a positive electrode active material are mixed and sintered. A fast ion conductor layer is generated in situ at the contact point between the coating layer and the positive electrode active material (the fast ion conductor layer is formed by sintering the positive electrode active material and the coating layer material). The sintering process stabilizes the compound coating layer on the surface of the pre-fired sulfide solid electrolyte, preventing side reactions from contacting other substances.

[0009] According to the present invention, preferably, the positive electrode active material is LiNi. x Co y Mn z M 1-x-y-z O2, where M is at least one of Al, Zr, Ti, Nb, W and Ta, 0.8≤x<1, 0.03≤y<0.2, 0.9≤x+y+z≤1.

[0010] According to the present invention, preferably, the mixing mass ratio of the positive electrode active material and the sulfide solid electrolyte is (60-95):(5-40), and more preferably (80-85):(15-20).

[0011] According to the present invention, preferably, the sulfide matrix is ​​Li7P3S. 11 Li3PS4, Li6PS5Cl, Li6PS5Br and Li 10 GeP2S 11 At least one of them.

[0012] According to the present invention, preferably, the material of the coating layer is at least one selected from Al2O3, CoO, NiO2, TiO2, AlF3, TiF4 and NbF5.

[0013] According to the present invention, preferably, the sintering operating conditions include: an inert gas atmosphere, a heating rate of 1-8℃ / min, a sintering temperature of 300-800℃, a sintering holding time of 4-10h, furnace cooling, and a furnace exit temperature of ≤200℃.

[0014] According to the present invention, preferably, the positive electrode material further includes a binder and a conductive agent.

[0015] According to the present invention, preferably, the all-solid-state battery is an all-solid-state lithium-ion battery or an all-solid-state sodium-ion battery.

[0016] Another aspect of the present invention provides a method for preparing the aforementioned sulfide all-solid-state battery cathode material, the method comprising the following steps: S1: The sulfide matrix and coating material are mixed and then pre-calcined to obtain the sulfide solid electrolyte; S2: The positive electrode active material and the sulfide solid electrolyte are mixed, sintered, and sieved to obtain the sulfide all-solid-state battery positive electrode material.

[0017] According to the present invention, preferably, in step S1: The mass ratio of the sulfide matrix and the coating material is 100:(0.05-0.5), preferably 100:(0.1-0.3). The mixing method is ball milling, with a ball milling speed of 300-2000 r / min, preferably 500-1800 r / min, more preferably 1000-1500 r / min, and a time of 2-6 h; The pre-firing operating conditions include: the equipment is a kiln, the inert gas atmosphere (the inert gas is nitrogen and / or argon), the heating rate is 1-8℃ / min, preferably 3-5℃ / min, the sintering temperature is 50-400℃, preferably 100-300℃, and the sintering holding time is 1-8h, preferably 2-4h.

[0018] According to the present invention, preferably, in step S2: The mixing mass ratio of the positive electrode active material and the sulfide solid electrolyte is (60-95):(5-40), preferably (80-85):(15-20). The mixing method is ball milling, with a milling speed of 800-1000 r / min and a time of 4-8 h; The sintering operating conditions include: the equipment is a kiln, the inert gas atmosphere (the inert gas is nitrogen and / or argon), the heating rate is 1-8℃ / min, preferably 3-5℃ / min, the sintering temperature is 300-800℃, preferably 400-500℃, the sintering holding time is 4-10h, preferably 6-8h, the furnace is cooled, and the furnace exit temperature is ≤200℃, preferably ≤100℃. The sieving process involves passing the material through a 300-400 mesh sieve.

[0019] The beneficial effects of the technical solution of the present invention are as follows: 1. This invention improves the air stability of the sulfide solid electrolyte surface through two sintering processes (pre-sintering + sintering): a stable compound coating layer is coated on the surface of the sulfide matrix. Through pre-sintering and sintering, the compound coating layer on the surface becomes more stable, effectively preventing the sulfide solid electrolyte from reacting with binders, conductive agents, trace water, oxygen, and other substances. This reduces the generation of harmful hydrogen sulfide gases, improves the air stability of the sulfide solid electrolyte, and thus improves battery life.

[0020] 2. The in-situ generated fast ion conductor layer reduces the interfacial contact impedance between the sulfide matrix and the positive electrode active material: During the sintering process, a fast ion conductor layer (also known as an in-situ interfacial coating layer) is generated in situ at the contact area between the coating layer of the pre-sintered sulfide solid electrolyte and the positive electrode active material. This avoids direct contact between the sulfide matrix and the positive electrode active material, while also significantly reducing the interfacial impedance between the two, improving ion transport efficiency, and enhancing the charge and discharge efficiency and cycle performance of the solid-state battery.

[0021] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0022] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0023] Figure 1 A schematic diagram of the structure of a sulfide all-solid-state battery cathode material provided by the present invention is shown.

[0024] The annotations in the attached figures are explained as follows: 1. Positive electrode active material, 2. Sulfide matrix, 3. Coating layer, 4. Fast ion conductor layer. Detailed Implementation

[0025] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0026] Example 1

[0027] This embodiment provides a sulfide-based all-solid-state battery cathode material, the preparation method of which includes the following steps: S1: The sulfide matrix Li7P3S 11 The sulfide solid electrolyte is obtained by mixing the Al2O3 coating material with the electrolyte and then pre-calcining it; wherein: The mass ratio of the materials of the sulfide matrix 2 and the coating layer 3 is 100:0.1; The mixing method was ball milling at a speed of 1000 r / min for 2 hours. The pre-firing operating conditions include: the equipment is a kiln, the atmosphere is nitrogen, the temperature is raised to 150°C at a rate of 3°C / min, and the holding time is 2 hours.

[0028] S2: The positive electrode active material LiNi 0.9 Co 0.06 Mn 0.04 O2 and sulfide solid electrolyte are mixed, sintered, and sieved to obtain the sulfide all-solid-state battery cathode material; wherein: The mass ratio of the positive electrode active material 1 to the sulfide solid electrolyte is 80:20; The mixing method was ball milling at a speed of 800 r / min for 4 hours. The sintering operation conditions include: the equipment is a kiln, the atmosphere is argon, the temperature is raised to 400°C at a rate of 3°C / min, the holding time is 6h, and the furnace is taken out after the kiln cools down naturally to below 100°C. The sieving process involves passing the material through a 300-mesh sieve.

[0029] In step S2: a fast ion conductor layer 4 is generated in situ at the part where the coating layer 3 of the pre-calcined sulfide solid electrolyte contacts the positive electrode active material 1 (the fast ion conductor layer 4 is formed by sintering the positive electrode active material 1 and the coating layer 3). The part where the coating layer 3 of the pre-calcined sulfide solid electrolyte does not contact the positive electrode active material 1 can be stabilized by the sintering process, thereby preventing side reactions that occur when the sulfide solid electrolyte comes into contact with other substances.

[0030]

[0031] Test case

[0032] In this test case, the cathode materials obtained from the above embodiments and comparative examples were used to assemble mold batteries, and the initial discharge capacity and cycle retention rate of the mold batteries were tested.

[0033] I. The preparation process of the mold battery is as follows: 1. According to the mass ratio of cathode material:VGCF (one-dimensional carbon nanomaterial) = 100:3, add cathode material and VGCF into a mortar and grind for 10 minutes to obtain composite cathode material; 2. Weigh 60mg of electrolyte (using the same material as the sulfide matrix of the positive electrode), pour it into the mold, manually rotate it until it is uniform and flat, apply pressure of 108MPa, and hold the pressure for 1min; 3. Weigh 25mg of the stable composite cathode material obtained in step 1, pour it into the mold, manually rotate it until it is uniform and flat, apply pressure of 300MPa, and hold the pressure for 1min; 4. Add a lithium-indium alloy sheet (10mm in diameter) to the negative electrode side, apply a pressure of 30MPa, and hold the pressure for 30s; 5. Place the mold into the metal kit, apply pressure of 108 MPa, tighten the kit, and obtain the mold battery.

[0034] II. Initial Discharge Capacity Test: After making the mold battery, place it in a constant temperature chamber at 60℃ for 2 hours. After the open circuit voltage stabilizes, charge the positive electrode with a current density of 0.05C until the cutoff voltage is 3.7V, then charge it at a constant voltage for 30 minutes, and then discharge it with the same current density until the cutoff voltage is 2.1V. Repeat the same process once more. The mold battery at this time is considered an activated battery.

[0035] III. Cycle Retention Rate Test: Using the activated battery, charge-discharge tests were performed at a current density of 1C (200mA / g) in a voltage range of 2.1-3.7V, and the cycle capacity retention was measured after 100 cycles at 45°C.

[0036] The test results are shown in Table 2.

[0037] Table 2

[0038] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A sulfide-based all-solid-state battery cathode material, characterized in that, The cathode material includes: Positive electrode active material and sulfide solid electrolyte; The sulfide solid electrolyte includes a sulfide matrix and a coating layer covering the surface of the sulfide matrix; The positive electrode active material and part of the coating layer are composites formed in situ by sintering the positive electrode active material and the sulfide solid electrolyte.

2. The sulfide all-solid-state battery cathode material according to claim 1, wherein, The positive electrode active material is LiNi. x Co y Mn z M 1-x-y-z O2, where M is at least one of Al, Zr, Ti, Nb, W and Ta, 0.8≤x<1, 0.03≤y<0.2, 0.9≤x+y+z≤1.

3. The sulfide all-solid-state battery cathode material according to claim 1, wherein, The mass ratio of the positive electrode active material to the sulfide solid electrolyte is (60-95):(5-40).

4. The sulfide all-solid-state battery cathode material according to claim 1, wherein, The sulfide matrix is ​​Li7P3S. 11 Li3PS4, Li6PS5Cl, Li6PS5Br and Li 10 GeP2S 11 At least one of them.

5. The sulfide all-solid-state battery cathode material according to claim 1, wherein, The coating material is at least one of Al2O3, CoO, NiO2, TiO2, AlF3, TiF4 and NbF5.

6. The sulfide all-solid-state battery cathode material according to claim 1, wherein, The sintering operating conditions include: inert gas atmosphere, heating rate of 1-8℃ / min, sintering temperature of 300-800℃, sintering holding time of 4-10h, furnace cooling, and furnace exit temperature of ≤200℃.

7. The sulfide all-solid-state battery cathode material according to claim 1, wherein, The positive electrode material also includes a binder and a conductive agent; The all-solid-state battery is either an all-solid-state lithium-ion battery or an all-solid-state sodium-ion battery.

8. The method for preparing the sulfide all-solid-state battery cathode material according to any one of claims 1-7, characterized in that, The preparation method includes the following steps: S1: The sulfide matrix and coating material are mixed and then pre-calcined to obtain the sulfide solid electrolyte; S2: The positive electrode active material and the sulfide solid electrolyte are mixed, sintered, and sieved to obtain the sulfide all-solid-state battery positive electrode material.

9. The method for preparing the sulfide all-solid-state battery cathode material according to claim 8, wherein, In step S1: The mass ratio of the sulfide matrix and the coating material is 100:(0.05-0.5); The mixing method is ball milling, with a speed of 300-2000 r / min and a time of 2-6 h; The pre-firing operating conditions include: the equipment is a kiln, the atmosphere is an inert gas atmosphere, the heating rate is 1-8℃ / min, the sintering temperature is 50-400℃, and the sintering holding time is 1-8h.

10. The method for preparing the sulfide all-solid-state battery cathode material according to claim 8, wherein, In step S2: The mass ratio of the positive electrode active material to the sulfide solid electrolyte is (60-95):(5-40). The mixing method is ball milling, with a milling speed of 800-1000 r / min and a time of 4-8 h; The sintering operating conditions include: the equipment is a kiln, the atmosphere is an inert gas, the heating rate is 1-8℃ / min, the sintering temperature is 300-800℃, the sintering holding time is 4-10h, the furnace is cooled, and the furnace exit temperature is ≤200℃. The sieving process involves passing the material through a 300-400 mesh sieve.

Images