A double-layer coated positive electrode material and its preparation method and application

Abstract

The present invention relates to the technical field of electrode materials, and in particular, to a double-layer coated positive electrode material and a preparation method and application thereof, wherein a double-layer coating layer is prepared on the surface of a positive electrode material (such as NCM811), and the coating material is two types, a metal oxide and a metal salt. The coating material of the present invention is distributed outside the positive electrode material body, and the coated positive electrode material is modified by the coating material, on the one hand, to obtain higher structural stability, inhibit the chemical reaction between the positive electrode material and the electrolyte material, and on the other hand, the overall electrochemical performance is significantly improved, and it is suitable for the application of positive electrode materials for all-solid-state batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and in particular to a double-layer coated positive electrode material and a preparation method and application thereof, and in particular to a novel double-layer positive electrode coating material and a preparation method thereof and application thereof in an all-solid-state battery. Background Art

[0002] At present, lithium-ion batteries have been widely used in the fields of portable electronic products, electric vehicle power batteries, smart grids and other energy storage fields. However, due to the flammability of liquid electrolyte solvents and the fact that the energy density of lithium-ion batteries is approaching its limit, safety accidents such as spontaneous combustion have occurred one after another, and people's attention has shifted to the safety of lithium-ion batteries. All-solid-state batteries do not contain any flammable liquid components. Solid electrolytes (SSE) replace traditional organic electrolytes, play the role of ion transport and diaphragm, and avoid internal short circuits caused by diaphragm shrinkage or rupture and electrolyte leakage. Therefore, the use of all-solid-state inorganic electrolytes to develop theoretically non-flammable all-solid-state batteries will be the best way to fundamentally solve this problem. Solid-state batteries have been recognized as a key technology for the development of the next generation of high-safety, high-energy lithium (ion) batteries.

[0003] However, the high impedance and stability of the solid / solid interface between the components of the composite cathode (including active materials, solid electrolytes and conductive additives) remain one of the key issues hindering the development of current solid-state batteries. Due to the generally narrow electrochemical stability window of solid electrolytes and their considerable chemical reactivity with the cathode, it is difficult to maintain the thermodynamic stability of the interface, so the problem of interface stability between the two is particularly prominent.

[0004] Therefore, it is necessary to provide an improved method to solve the above problems of all-solid-state batteries. Constructing a buffer layer on the surface of the active material is an effective method to solve the high impedance and stability of the interface. There are many choices for coating materials, including metal oxides, metal salts, and the like. Summary of the invention

[0005] The present invention aims to solve the stability problems inside the composite positive electrode and at the positive electrode / electrolyte interface to a certain extent. To this end, the present invention aims to provide a double-layer coated positive electrode material and a preparation method and application thereof.

[0006] The coating material of the present invention is distributed outside the cathode material body. The coated cathode material obtains higher structural stability through the modification of the coating material, suppresses the chemical reaction between the cathode material and the electrolyte material, and significantly improves the overall electrochemical performance, which is suitable for the application of all-solid-state battery cathode materials. Among them, the contact between the metal salt and the electrolyte can provide higher conductivity, and the metal oxide layer directly coating the cathode material can effectively reduce the erosion of the surrounding electrolyte on the particles of the cathode material. At the same time, the combination of the two can form a stable contact, improve the conductivity of the coating layer and suppress the deformation of the active material.

[0007] To achieve the above object, the present invention adopts the technical solution as follows:

[0008] The present invention provides a double-layer coated positive electrode material, the double-layer coated positive electrode material comprising a positive electrode material body and a coating layer obtained by calcining a double-layer coating material on the positive electrode material body, wherein the inner layer of the double-layer coating material is a metal oxide and the outer layer is a metal salt. The double-layer coating material is distributed on the surface of the positive electrode material body to form a coating layer, i.e., a double-layer coated positive electrode material. After calcination, the inner layer is a metal oxide and the outer layer is a metal salt.

[0009] As an embodiment of the present invention, the cathode material body includes one or more of NCM811, NCM622, and NCM8532. The cathode material is a single crystal with a particle size of 2-4 μm.

[0010] As an embodiment of the present invention, the metal oxide includes one or more of TiO2, ZrO2, SiO2, and Al2O3; the metal oxide is nanometer-level, with a diameter of 400-500nm.

[0011] As one embodiment of the present invention, the metal salt includes Mn3(PO4)2, Li3PO4, Li 1.3 Al 0.3 Ti 1.7 One or more of (PO4)3; the metal salt is salt particles with a purity of 99.9% and a particle diameter of 1-5μm.

[0012] As an embodiment of the present invention, the mass percentage of the double-layer coating material to the positive electrode material body is 0.2wt% to 5wt%; wherein the metal oxide accounts for 0.1wt% to 2wt%, and the metal salt accounts for 0.1wt% to 3wt%.

[0013] The present invention also provides a method for preparing the double-layer coated positive electrode material, the preparation method comprising the following steps:

[0014] S1. Premixing the cathode material and the metal oxide, and then adding the metal salt to mix, or directly mixing the three to react, to obtain a mixed material;

[0015] S2. calcining the obtained mixed material to obtain the double-layer coated positive electrode material.

[0016] As an embodiment of the present invention, in step S1, the premixing and mixing are both ball milling; the premixing speed with the metal oxide is 400-600rpm, the time is 2-5h; the mixing speed with the metal salt is 600-900rpm, the time is 5-10h. The premixing and mixing are carried out in a reaction ball milling tank, the reaction ball milling tank includes one of the volumes of 50ml, 75ml, and 100ml; the ball milling beads are selected to have a diameter of 3mm, and the ball-to-material ratio is 1:20 or 1:30.

[0017] As an embodiment of the present invention, in step S2, the calcination temperature is 100°C to 1000°C, the calcination time is 2h to 8h; and the calcination atmosphere is air or an oxygen-containing atmosphere.

[0018] The present invention also provides an application of the double-layer coated positive electrode material in the preparation of an all-solid-state battery.

[0019] The present invention can increase the stability of the interface, reduce impedance, and improve the overall cycle life of the battery through double-layer physical coating. The metal salt used in the present invention contains a large amount of oxygen atoms, which can be better compatible with the high-nickel oxygen-containing positive electrode.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The coated positive electrode material of the present invention is modified by a double-layer coating material, specifically using a metal oxide or metal salt with an ion mobility ti>99.99% and an electron mobility tg<0.01% to coat the surface of the positive electrode material body, so that the side reaction activity when it contacts the electrolyte is greatly reduced, thereby obtaining a higher interface structure stability and inhibiting the chemical reaction between the positive electrode material and the electrolyte material. Compared with the previous use of only a single-layer coating material, it shows better performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0023] Figure 1 This is the first cycle diagram of charge and discharge of the full battery of the material prepared in Example 1 at 0.1C;

[0024] Figure 2This is a SEM image of the material prepared in Example 1 after 100 cycles;

[0025] Figure 3 This is a SEM image of the material prepared in Example 2 after 100 cycles;

[0026] Figure 4 This is the SEM image of the material prepared in Comparative Example 1 after 100 cycles. DETAILED DESCRIPTION

[0027] The present invention is described in detail below in conjunction with embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, some adjustments and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0028] Example 1

[0029] This embodiment provides a double-layer coated positive electrode material, including a positive electrode material body and a coating layer obtained by calcining a double-layer coating material on the positive electrode material body, where the coating material accounts for 2wt% of the mass of the positive electrode material body, wherein the metal oxide accounts for 0.5wt% and the metal salt accounts for 1.5wt%. The preparation steps are as follows:

[0030] Single crystal NCM811 (particle size 2-4μm) and ZrO2 (diameter 400-500nm) were added to the reaction ball mill and ball milled. The ball mill was selected to be 100ml, the ball milling beads were selected to be 3mm in diameter, the ball-to-material ratio was 1:30, and after ball milling at 400rpm / 2h, Li3PO4 particles (purity 99.9%, particle diameter 1-5μm) were added and ball milled at 700rpm / 5h, and then taken out from the ball mill to obtain the coated positive electrode material precursor.

[0031] The obtained coated positive electrode material precursor was placed in a muffle furnace for high-temperature calcination at a temperature of 500° C. for 4 hours to obtain a double-layer coated positive electrode material.

[0032] Example 2

[0033] This embodiment provides a double-layer coated positive electrode material, including a positive electrode material body and a coating layer obtained by calcining a double-layer coating material on the positive electrode material body, where the coating material accounts for 2wt% of the mass of the positive electrode material body, wherein the metal oxide accounts for 0.5wt% and the metal salt accounts for 1.5wt%. The preparation steps are as follows:

[0034] Add single crystal NCM811 (particle size 2-4 μm) and ZrO2 (diameter 400-500 nm) to the reaction ball mill and perform ball milling. The ball milling jar is 100 ml, the ball milling beads are 3 mm in diameter, and the ball-to-material ratio is 1:30. After ball milling at 400 rpm / 2 h, add Li 1.3 Al 0.3 Ti 1.7 (PO4)3 particles (purity 99.9%, particle diameter 1-5 μm) were ball-milled at 700 rpm / 5 h, and then taken out from the ball mill to obtain a coated positive electrode material precursor.

[0035] The obtained coated positive electrode material precursor was placed in a muffle furnace for high-temperature calcination at a temperature of 500° C. for 4 hours to obtain a double-layer coated positive electrode material.

[0036] Comparative Example 1

[0037] This comparative example provides a double-layer coated positive electrode material, and the preparation steps are basically the same as those of Example 1, except that no metal salt Li3PO4 is added for coating.

[0038] Add NCM811 and ZrO2 to the reaction ball mill and perform ball milling. The ball mill is 100ml, the ball milling beads are 3mm in diameter, the ball-to-material ratio is 1:30, and after ball milling at 400rpm / 2h, take it out from the ball mill to obtain a coated positive electrode material precursor (the coating material accounts for 1% of the mass of the positive electrode material).

[0039] The obtained coated positive electrode material precursor was placed in a muffle furnace for high-temperature calcination at a temperature of 500° C. for 4 hours to obtain a double-layer coated positive electrode material.

[0040] Comparative Example 2

[0041] This comparative example provides a double-layer coated positive electrode material, and the preparation steps are basically the same as those of Example 1, with the only difference being that an equal amount of metal salt is coated, and no metal oxide ZrO2 is added for coating.

[0042] The double-layer coated positive electrode material prepared in this comparative example has low conductivity and poor performance after assembling the battery.

[0043] This comparative example provides a double-layer coated positive electrode material, and the preparation steps are basically the same as those in Example 1, except that the positive electrode material body is first mixed with the metal salt Li3PO4 and then mixed with the metal oxide ZrO2.

[0044] The double-layer coated positive electrode material prepared in this embodiment is coated with metal salt first and then with metal oxide, which will lead to poor performance.

[0045] Comparative Example 4

[0046] This comparative example provides a double-layer coated positive electrode material, and the preparation steps are basically the same as those in Example 1, except that the metal salt Li3PO4 is replaced by H2SiO3.

[0047] The double-layer coated positive electrode material prepared in this comparative example has similar performance, but the battery performance is not as good as Li3PO4

[0048] Performance Test:

[0049] The products obtained in the above-mentioned Examples 1-2 and Comparative Example 1 were assembled: in an inert gas glove box with a water and oxygen content of ≤0.01ppm, the prepared composite positive electrode, electrolyte Li6PS5Cl and lithium metal negative electrode sheet were combined together, charged and discharged at 0.1c, the first effect was tested, and the capacity retention rate was tested after 100 cycles. The results are shown in Table 1 as follows: It can be seen from Table 1 that when a double-layer coated positive electrode is used, a higher first effect and capacity retention can be exerted, thereby improving the power performance of the lithium-ion battery. Figure 1 , it can be seen that the double-layer coating of Example 1 can exert a high specific capacity; Figure 2-4 It can be seen that after 100 cycles, the coated materials undergo changes to varying degrees, among which the material morphology of Example 1 is best maintained without cracks or breakage.

[0050] First effect / % Capacity retention rate / % Example 1 85 91.2 Example 2 75 90.8 Comparative Example 1 67 84.3

[0051] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A double-layer coated positive electrode material, characterized in that: The double-layer coated positive electrode material comprises a positive electrode material body and a double-layer coating layer obtained by calcining a double-layer coating material on the positive electrode material body, wherein the inner layer of the double-layer coating material is a metal oxide and the outer layer is a metal salt; The positive electrode material body includes one or more of NCM811, NCM622, and NCM8532; The metal oxide includes one or more of TiO2, ZrO2, SiO2, and Al2O3; The metal salt is Li3PO4.

2. The double-layer coated positive electrode material according to claim 1, characterized in that: The positive electrode material is a single crystal with a particle size of 2-4 μm; the metal oxide is nanometer-level with a diameter of 400-500 nm; the metal salt is salt particles with a purity of 99.9% and a particle diameter of 1-5 μm.

3. The double-layer coated positive electrode material according to claim 1, characterized in that: The mass percentage of the double-layer coating material to the positive electrode material body is 0.2wt% to 5wt%; the metal oxide accounts for 0.1wt% to 2wt% and the metal salt accounts for 0.1wt% to 3wt%.

4. A method for preparing a double-layer coated positive electrode material as claimed in claim 1, characterized in that: The preparation method comprises the following steps: S1, premixing the cathode material and the metal oxide, and then adding the metal salt to mix to obtain a mixed material; S2. calcining the obtained mixed material to obtain the double-layer coated positive electrode material.

5. The preparation method according to claim 4, characterized in that: In step S1, the premixing and mixing are both ball milling mixing; the premixing speed with the metal oxide is 400-600 rpm, and the time is 2-5 hours; the mixing speed with the metal salt is 600-900 rpm, and the time is 5-10 hours.

6. The preparation method according to claim 4, characterized in that: In step S2, the calcination temperature is 100°C to 1000°C, and the calcination time is 2h to 8h.

7. Use of the double-layer coated positive electrode material as claimed in claim 1 in the preparation of an all-solid-state battery.

Images