A rare earth element modified lithium ion battery composite material and a preparation method thereof

Abstract

The present application relates to a kind of rare earth metal element modified lithium ion battery composite material and its preparation method, by in-situ coating doping process, the full coverage spinel surface rich in oxygen vacancy and island distribution nano heterojunction particles are constructed on the surface of electrode material, the spinel surface of nanometer level thickness can provide fast ion diffusion channel, and will not form large area spinel and cause capacity to drop;Due to the structural stability of spinel under high pressure, harmful rock salt phase change can be inhibited;At the same time, the nano heterojunction particles with coherent lattice will also improve the ion diffusion rate and be beneficial to electron conduction due to many octahedral vacancies, good electron conduction is conducive to the formation of CEI interface rich in LiF, protects transition metal, improves cycle stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a rare earth metal element modified lithium ion battery composite material and a preparation method thereof. BACKGROUND

[0002] Layered cathode materials of lithium ion batteries are highly concerned due to their higher theoretical capacity. Typical layered materials include lithium cobalt oxide (LCO), ternary (NCM), lithium-rich manganese-based oxides (LLO), etc. Due to the interaction between electrolyte and cathode material, surface side reactions are one of the important reasons for limiting the cycle life of the battery. The interface side reaction will cause the increase of residual alkali on the surface, which will cause the gelation of the slurry, which will affect the consistency of the electrode preparation, and also increase the polarization of the battery, thereby reducing the cycle performance and stability. The high capacity provided by the high cut-off voltage is partly from the redox reaction of oxygen, which will cause the overflow of oxygen from the surface, thereby causing the problem of transition metal dissolution on the surface. Therefore, improving the surface stability of the layered material is of great significance for the development of the next generation of lithium ion batteries.

[0003] In order to realize the surface stability of the cathode material, various surface modification strategies are widely studied and applied, such as coating, surface reconstruction, etc. However, the thickness of the coating layer is difficult to effectively control, and the over-thick coating layer will cause the problems of capacity decline and poor rate performance. It is reported that some metal oxides such as ZrO2, Al2O3, MgO, etc. are coated on the surface of the material, but most of them exist in the form of amorphous, although they can stabilize the surface structure, but these metal oxides will bring the problems of impedance increase and poor combination with the bulk material, thereby causing poor cycle stability. Surface reconstruction may cause uncontrollable damage to the surface crystal structure, thereby affecting the stability of the surface structure. Therefore, designing a stable interface is of great significance to realize the excellent cycle stability of the layered cathode material under harsh conditions.

[0004] Combining various modification strategies and developing new modification methods to improve the structural stability of the cathode material and thereby improve the cycle life and other electrochemical properties of the material have become an important direction of current research. SUMMARY

[0005] In view of the above technical problems, the purpose of the present application is to provide an effective surface coating strategy, and to construct a coating layer of surface spinel and surface nano-heterojunction particles, and the surface modified cathode material has excellent cycle stability.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A rare earth element modified lithium ion battery composite material, characterized in that the composite material has a core-shell structure, the inner core is a lithium ion battery positive electrode material, the shell layer is an oxygen vacancy rich spinel material interface coated on the surface of the lithium ion battery positive electrode material, the oxygen vacancy rich spinel material fully covers the surface of the lithium ion battery positive electrode material, and nano heterojunction particles are island-shaped distributed on the surface of the oxygen vacancy rich spinel material, and the oxygen vacancy rich spinel material and the nano particle heterostructure both contain rare earth elements.

[0008] Further, the nano heterojunction particle material contains lithium, rare earth elements and oxygen.

[0009] Further, the nano heterojunction particle material has a structural formula of Li x MO 2-y , M is one or more of lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), and yttrium (Y).

[0010] Further, the thickness of the oxygen vacancy rich spinel material interface is 1-5 nm, the nano heterojunction particles are hemispherical, trapezoidal or triangular pyramidal, and the average particle size of the nano heterojunction particles is 1-10 nm.

[0011] The application also provides a preparation method of a rare earth element modified lithium ion battery composite material, characterized in that the method comprises the following steps:

[0012] 1) Dissolve the positive electrode material, a rare earth element source and a metal ion adsorbent in ethanol according to a certain mass ratio, and stir in a water bath until the ethanol evaporates;

[0013] 2) Centrifuge and wash the obtained product three times and dry it;

[0014] 3) Sinter the dried product at a certain temperature, and naturally cool it to room temperature to obtain the surface modified positive electrode material.

[0015] Further, in the step 1), the rare earth element source used is one or more of a sulfate, a nitrate, an acetate and a chloride of a system metal; and the rare earth element is one or more of lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm) and yttrium (Y).

[0016] Further, in the step 1), the metal ion adsorbent is one or more of urotropine, polyvinylpyrrolidone, sodium alginate and acrylonitrile; and urotropine is preferred.

[0017] Further, the mass ratio of the positive electrode material, the rare earth element source and the metal ion adsorbent is 1: (0.01-0.015): (0.01-0.015).

[0018] Further, in the step 1), the temperature of the water bath stirring is 60-80 ℃; in the step 2), the solvent used for centrifugal washing is ethanol, and the temperature of the drying is 80-120 ℃; in the step 3), the sintering condition is 450-600 ℃, and the holding time is 2-6 h.

[0019] Further, the application also provides a use of the composite material as claimed in claims 1-4 or the composite material prepared by the method as claimed in claims 5-9 in a lithium ion battery.

[0020] The application has the following beneficial effects:

[0021] The rare earth element is introduced on the surface of the lithium ion positive electrode material, the double effects of coating and doping are realized, the full-coverage spinel surface rich in oxygen vacancies and the island-distributed nano-heterojunction particles are constructed on the surface of the positive electrode material. The spinel surface with the nano-level thickness can provide a rapid ion diffusion channel, and will not form a large area of spinel to cause capacity decline. Due to the structural stability of the spinel under high pressure, the harmful rock salt phase change can be inhibited. The nano-heterojunction particles which are coherent with the spinel have many octahedral vacancies, so the ion diffusion rate is also improved and the electronic conduction is beneficial, the good electronic conduction is beneficial to form a CEI interface rich in LiF, protect the transition metal, and improve the cycle stability. The positive electrode material with both nano-particles and spinel surface is obtained by the application, and the occurrence of transition metal dissolution and irreversible phase change in the battery cycle can be effectively alleviated. When the positive electrode material is used as a lithium ion positive electrode material, it has good cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Fig. 1 is the (a) XRD pattern and (c, d) SEM images of the lithium-rich material LLO@Ce after surface modification of Example 1 and the original lithium-rich material LLO.

[0023] Figure 2 Fig. 2 is the (a) HAADF-STEM image, (b) EDS mapping image, and (c) atomic resolution HAADF-STEM image of the lithium-rich material LLO@Ce after surface modification of Example 1.

[0024] Figure 3 Fig. 3 is the (a) electrochemical curve and (c) cycle performance comparison chart of the lithium-rich material LLO@Ce after modification of Example 1 and the original lithium-rich material LLO at 0.2 C.

[0025] Figure 4 Fig. 4 is the cycle performance comparison chart of the lithium-rich material LLO@Ce after modification of Example 1 and the original lithium-rich material LLO at 1 C rate.

[0026] Figure 5 The performance comparison chart of the modified lithium-rich material LLO@Ce prepared in Example 1 and the original lithium-rich material LLO at different rates.

[0027] Figure 6 The atomic resolution HAADF-STEM images of the modified lithium-rich material LLO@Ce (a, b) and the original lithium-rich material LLO (c, d) prepared in Example 1 after 100 cycles.

[0028] Figure 7 The TEM images and XPS spectra (c) of the modified lithium-rich material LLO@Ce (a) and the original lithium-rich material LLO (b) prepared in Example 1 after 100 cycles.

[0029] Figure 8 The TEM images of the modified lithium-rich material LLO@Ce and the original lithium-rich material LLO prepared in Example 1 after 100 cycles. DETAILED DESCRIPTION

[0030] In order to make the technical solutions and advantages of the present application clearer, the present application and its beneficial effects will be further described in detail below with reference to specific embodiments and the accompanying drawings, but the embodiments of the present application are not limited thereto. In order to facilitate the understanding of the present application, the present application will be described more fully and specifically below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present application is not limited to the following specific embodiments.

[0031] Unless otherwise defined, all the professional terms used herein have the same meanings as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing the specific embodiments and are not intended to limit the scope of protection of the present application.

[0032] Unless otherwise specified, the various reagents and raw materials used in the present application are commercially available products or products that can be prepared by known methods.

[0033] In order to better understand the present application, the content of the present application will be further illustrated below with reference to the embodiments, but the content of the present application is not limited to the following embodiments.

[0034] In this invention, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0035] Example 1:

[0036] 1) Dissolve 2 g of lithium-rich manganese-based (LLO) cathode material, 0.03 g of Ce(NO3)3·6H2O, and 0.03 g of metal ion adsorbent HMTA in ethanol, and stir in a water bath at 60 ℃ until the ethanol evaporates;

[0037] 2) The product obtained above is centrifuged, washed three times, and dried;

[0038] 3) The dried product is sintered at 450 °C to obtain the surface-modified cathode material.

[0039] Example 2:

[0040] 1) Dissolve 0.03 g of La(NO3)3·6H2O, 0.03 g of HMTA and 2 g of cobalt-free lithium-rich material powder (LRNM) prepared by coprecipitation-solid phase method in ethanol solution, and stir in a water bath at 60 °C until the ethanol evaporates.

[0041] 2) Centrifuge and wash the above product three times and dry it at 80 ℃.

[0042] 3) Place the product in a muffle furnace and keep it at 500 °C for 3 h. Let it cool naturally to room temperature and then remove it to complete the modification (LRNM@La).

[0043] Taking the cobalt-free lithium-rich material powder (LRNM) of secondary particles in this embodiment as an example, surface modification (LRNM@La) was performed on it to verify the effectiveness of this strategy in modifying secondary particle cathode material samples.

[0044] Example 3:

[0045] 1) Dissolve 0.03 g Ce(NO3)3·6H2O, 0.03 g sodium alginate and 2 g single crystal high nickel NCM811 powder in an ethanol solution, and stir in a water bath at 60 °C until the ethanol evaporates.

[0046] 2) Centrifuge and wash the above product three times and dry it at 80 ℃.

[0047] 3) The product was placed in a muffle furnace at 450 °C for 2 h, naturally cooled to room temperature and removed to complete the modification.

[0048] Example Four:

[0049] 1) 0.03 g YbC6H9O6.xH2O, 0.03 g polyvinylpyrrolidone and 2 g of polycrystalline lithium cobalt oxide powder were dissolved in an ethanol solution and stirred in a water bath at 60 °C until the ethanol evaporated.

[0050] 2) The product was centrifuged and washed 3 times and dried at 80 °C.

[0051] 3) The product was placed in a muffle furnace at 550 °C for 3 h, naturally cooled to room temperature and removed to complete the modification.

[0052] The composite cathode material prepared above was then applied to a cathode sheet. The preparation method of the cathode sheet was as follows: the cathode material, polyvinylidene fluoride and SP-P were mixed and ball milled at a mass ratio of 90:5:5 to obtain a cathode slurry, the cathode slurry was coated on the surface of an aluminum foil, and after rolling, vacuum drying was performed at 160 °C overnight, and then cold pressing, die cutting were performed to obtain the cathode sheet.

[0053] The obtained cathode sheet was applied to a R2032 type button cell for electrochemical performance testing. The cathode sheet was used as the working electrode, lithium foil was used as the counter electrode, the separator was a GB-100R separator, and a non-aqueous electrolyte was used as the electrolyte (the specific preparation method was as follows: ethylene carbonate and methyl ethyl carbonate were mixed at a volume ratio of 3:7, and LiPF6 was added to form an electrolyte, the concentration of LiPF6 was 1 mol / L), and a lithium ion button cell was prepared, see the existing preparation method, which will not be repeated here.

[0054] The obtained lithium ion button cell was subjected to constant temperature current charge and discharge test in a constant temperature oven at about 25 °C.

[0055] Figure 1 are the (a) XRD patterns and (c, d) SEM images of the lithium-rich material LLO@Ce after surface modification and the original lithium-rich material LLO of Example 1. The XRD pattern of LLO@Ce shows almost identical peaks as the unmodified powder, indicating that the surface reconstruction did not cause significant changes in the bulk crystal structure. TEM analysis showed that Li x CeO 2-y are uniformly distributed in the form of islands on the surface of LLO.

[0056] Figure 2is the (a) HAADF-STEM image, (b) EDS mapping image, (c) atomic resolution HAADF-STEM image of the lithium-rich material LLO@Ce after surface modification in Example 1. x CeO 2-y distributed on the surface of LLO, and has a good spinel interface with LLO.

[0057] Figure 3 is the cycle performance comparison chart of the lithium-rich material LLO@Ce after modification in Example 1 and the original lithium-rich material LLO at 0.2 C rate. After 100 cycles, the capacity retention rate of LLO@Ce is 96.76%, and the voltage attenuation is inhibited.

[0058] Figure 4 is the cycle performance comparison chart of the lithium-rich material LLO@Ce after modification in Example 1 and the original lithium-rich material LLO at 1 C rate. After 500 cycles, the capacity retention rate of LLO@Ce is 93.12%, showing excellent capacity retention rate.

[0059] Figure 5 is the full cell cycle performance comparison chart of the lithium-rich material LLO@Ce after modification in Example 1 and the original lithium-rich material LLO at 1 C rate, using commercial graphite as the negative electrode. After 400 cycles, the capacity retention rate of LLO@Ce is 90.52%, showing excellent capacity retention rate.

[0060] Figure 6 is the performance comparison chart of the lithium-rich material LLO@Ce after modification in Example 1 and the original lithium-rich material LLO at different rates. As the rate increases, the gap between the capacity of LLO and LLO@Ce becomes larger and larger. At 5 C rate, LLO@Ce can obtain a capacity of 153.6 mAh g-1, while LLO only has 104.2 mAh g-1, which is only two-thirds of LLO@Ce, indicating that x CeO 2-y Nanoparticles and spinel interface provide good electrical conductivity.

[0061] Figure 7 is the high-magnification HAADF-STEM image of the lithium-rich material LLO@Ce after modification in Example 1 and the original lithium-rich material LLO after 100 cycles. After cycling, Li x CeO 2-y without falling off and tightly combined with the material, the composite material structure is stable, while LLO has a large number of holes and cracks.

[0062] Figure 8TEM images of the modified lithium-rich material LLO@Ce prepared in Example 1 and the original lithium-rich material LLO after 100 cycles. The LLO@Ce has a thin and uniform CEI film, and its composition is mainly inorganic LiF, which effectively alleviates the dissolution of transition metals.

[0063] According to the disclosure and teachings of the above specification, a person of ordinary skill in the art will be able to make alterations and modifications to the above embodiments. Therefore, the present application is not limited to the specific embodiments described above, and any obvious improvements, replacements or modifications made by those skilled in the art on the basis of the present application shall fall within the scope of the present application. In addition, although some specific terms are used in the specification, these terms are only for the convenience of description and do not constitute any limitation on the present application.

Claims

1. A rare earth metal element modified lithium-ion battery composite material, characterized in that, The composite material has a core-shell structure. The core is a lithium-ion battery cathode material, and the shell is an oxygen-vacancy-rich spinel material interface covering the surface of the lithium-ion battery cathode material. The thickness of the oxygen-vacancy-rich spinel material interface is 1-5 nm. The oxygen-vacancy-rich spinel material completely covers the surface of the lithium-ion battery cathode material, and there are island-like nano-heterojunction particles distributed on the surface of the oxygen-vacancy-rich spinel material. The oxygen-vacancy-rich spinel material contains rare earth metal elements, and the nano-heterojunction particles contain lithium, rare earth metal elements, and oxygen. The rare earth metal elements are one or more of lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), and yttrium (Y).

2. The rare earth metal element modified lithium-ion battery composite material according to claim 1, wherein the nano-heterojunction particles are hemispherical, trapezoidal or triangular pyramidal, and the average particle size of the nano-heterojunction particles is 1-10 nm.

3. The preparation method of the rare earth metal element modified lithium-ion battery composite material according to claim 1 or 2, characterized in that, Includes the following steps: 1) The positive electrode material, rare earth element source, and metal ion adsorbent are dissolved in ethanol at a certain mass ratio, and stirred in a water bath until the ethanol evaporates; the metal ion adsorbent is one or more of hexamethylenetetramine, polyvinylpyrrolidone, sodium alginate, and acrylonitrile. 2) The product obtained above is centrifuged, washed three times, and dried; 3) The dried product is sintered at a certain temperature, the sintering conditions are 450~600 ℃, held for 2~6 h, and naturally cooled to room temperature to obtain the surface-modified cathode material.

4. The preparation method according to claim 3, characterized in that, In step 1), the rare earth element source used is one or more of the rare earth metal sulfates, nitrates, acetates, and chlorides.

5. The preparation method according to claim 3, characterized in that, The metal ion adsorbent is hexamethylenetetramine.

6. The preparation method according to claim 3, characterized in that, In step 1), the mass ratio of the positive electrode material, rare earth element source, and metal ion adsorbent is 1:(0.01-0.015):(0.01-0.015).

7. The preparation method according to claim 3, characterized in that, In step 1), the temperature of the water bath stirring is 60~80 ℃; in step 2), the solvent used for centrifugal washing is ethanol, and the drying temperature is 80~120 ℃.

8. The use of the rare earth metal element modified lithium-ion battery composite material according to any one of claims 1-2 or the rare earth metal element modified lithium-ion battery composite material prepared by the method according to any one of claims 3-7 in lithium-ion batteries.

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