Preparation method of multi-element doped carbon-coated ternary positive electrode material

Abstract

The application relates to a preparation method of a multi-element doped carbon-coated ternary positive electrode material, and the preparation method is as follows: ternary precursors are placed into a solution, trimeric phosphonitrilic chloride and 4,4'-sulfonyl diphenol are added and stirred, trithylamine is added after stirring for a certain time, continuous stirring is carried out, and after washing, drying is carried out to obtain a PZS (polytrimeric phosphonitrilic chloride-co-4,4'-sulfonyl diphenol) coated ternary positive electrode material; the ternary positive electrode material after coating is mixed with a lithium source in a high-speed mixer, the mixed sample is placed in a tube furnace for sintering, and the sample after sintering is the multi-element doped carbon-coated ternary positive electrode material NCM@C. The multi-element doped carbon layer coating can improve the better conductivity and the stronger hardness, and therefore, the lithium nickel mixed arrangement, soluble lithium, the first discharge specific capacity, the first coulomb efficiency, the capacity retention rate and other parameters are better.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode materials, specifically relating to a method for preparing a ternary cathode material coated with carbon and doped with multiple elements. Background Technology

[0002] Lithium-ion batteries, due to their high theoretical specific capacity, safety, and lack of memory effect, have gradually replaced lead-acid batteries and are widely used. Lithium-ion batteries mainly consist of four main materials: positive electrode material, negative electrode material, separator, and electrolyte, as well as auxiliary materials. The positive electrode material is primarily ternary cathode material or lithium iron phosphate. Compared to lithium iron phosphate, nickel-cobalt-manganese ternary cathode material has a higher theoretical specific capacity and better low-temperature performance, and is widely used in high-end commercial vehicles. However, ternary materials have poor conductivity and come into direct contact with the electrolyte during cycling, leading to poor cycle performance. Therefore, it is necessary to improve the conductivity of ternary materials and isolate them from the electrolyte.

[0003] In existing technologies, the protection of ternary materials by coating them with metal oxides (such as alumina, yttrium oxide, and zirconium oxide) or inorganic non-metallic oxides (such as silicon dioxide) is mainly achieved by isolating the electrolyte. One existing technology involves mixing the ternary cathode material with metal oxides during secondary sintering, followed by sintering at a suitable temperature to achieve metal oxide coating of the ternary cathode material. During cycling, the ternary cathode material generates harmful gases such as HF, which react with the cathode material, leading to a decrease in cell cycle performance. The coated metal oxide can isolate the cathode material from HF, protecting it and thus improving the cell's cycle performance. However, most metal oxide coatings use solid-state methods, resulting in uneven coating and poor conductivity. If the coating amount is too small, the protective effect is greatly weakened; if the coating amount is too large, it will actually reduce the overall conductivity of the material, requiring more conductive agents and binders, thereby reducing the cell's capacity. Existing technology two involves coating with non-metallic oxides. Compared to metal oxides, coating with non-metallic oxides offers more uniform coating, while still isolating the electrolyte and protecting the cathode material, and the coating thickness is controllable. Although inorganic non-metallic oxides have improved conductivity compared to metal oxides, they are still semiconductors with relatively poor conductivity, thus requiring additional conductive agents. Existing technology three involves coating the surface of the ternary cathode material with a carbon layer. The carbon improves the overall conductivity of the material, while the carbon layer isolates the electrolyte from the cathode material. However, ordinary carbon layers have low hardness; if the carbon layer is too thin, it is prone to breakage during cycling, exposing the cathode material; if the carbon layer is too thick, the material's capacity is significantly reduced.

[0004] The key to this invention is to provide a method for a ternary cathode material coated with carbon and doped with multiple elements such as nitrogen, phosphorus, and sulfur. Compared with existing conventional carbon-coated ternary cathode materials, the nitrogen, phosphorus, and sulfur-doped carbon-coated ternary cathode material has superior performance. Summary of the Invention

[0005] Currently, no carbon-coated material capable of providing nitrogen, phosphorus, sulfur, and other multi-element doping has been discovered. This invention provides a novel carbon-coated ternary cathode material, which aims to coat the cathode material, isolate the electrolyte, and improve the overall conductivity of the material.

[0006] A method for preparing a multi-element doped carbon-coated ternary cathode material involves placing a ternary precursor in a solution, stirring, and adding trichlorophosphazene and 4,4'-sulfonyl diphenol. After stirring for a certain period, triethylamine is added, and stirring continues. After washing, the mixture is dried to obtain a PZS (polycyclic trichlorophosphazene-co-4,4'-sulfonyl diphenol)-coated ternary cathode material. The coated ternary cathode material is then mixed with a lithium source in a high-speed mixer. The mixed sample is then sintered in a tube furnace. The sintered sample is the nitrogen, phosphorus, sulfur, and other element-doped carbon-coated ternary cathode material NCM@C. pzs .

[0007] The ternary precursor is preferably NCM712, NCM811, etc.; the ratio of trichlorophosphazene to 4,4'-sulfonyldiphenol and triethylamine is trichlorophosphazene (100-200g): 4,4'-sulfonyldiphenol (100-200g): triethylamine (1-5L); the lithium source is preferably lithium carbonate or lithium hydroxide; the molar ratio of ternary cathode material to lithium source is preferably 1.0-1.1; the mixing parameters of the high-speed mixer are: low speed of high-speed mixer is 50-400r / min, and the rotation time is 5-15min; high speed is 600-900r / min, and the rotation time is 5-35min; the protective gas in the tube furnace is one of oxygen, air, nitrogen and argon, the sintering temperature is 800-950℃, the heating rate is 2-20℃ / min, and the holding time is 1-15h.

[0008] This invention provides a ternary cathode material coated with carbon and doped with multiple elements, prepared by the above method.

[0009] Preferably, the coating thickness of the carbon-coated cathode material is 5-15 nm.

[0010] This invention provides a ternary cathode material with multi-element doped carbon coating, comprising a nitrogen, phosphorus, and sulfur ternary cathode material and a coating layer, wherein the coating layer is composed of carbon, and the molar ratio of nitrogen, phosphorus, and sulfur elements in the ternary cathode material is 4:4:1.

[0011] This invention also relates to the application of mixing and coating the above-mentioned multi-element doped carbon-coated ternary cathode material with PVDF and SP to finally produce a coin cell.

[0012] The preferred ratio of the ternary cathode material coated with carbon multi-element doped with PVDF and SP is 9-10:0.1-0.5:0.1-0.5; the preferred coin cell is CR2302 coin cell.

[0013] For example, the solution described in this invention can be as follows:

[0014] The ternary precursor (including but not limited to NCM712, NCM811, etc.) is placed in a methanol solution, and 20-200g of polyphosphazene trichlorotrichloroacetonide and 20-200g of 4,4'-sulfonyl diphenol are added under continuous stirring. After stirring for 1-30 min, 1-10L of triethylamine is added, and stirring is continued for 10-30 h. After washing, the mixture is placed in a vacuum drying oven and dried for 1-10 h to complete the PZS (polycyclic triphosphazene-co-4,4'-sulfonyl diphenol) coated ternary cathode material. The coated ternary cathode material is then mixed with a lithium source (lithium carbonate or lithium hydroxide) at a molar ratio of 1.0-1.1 in a high-speed mixer. The mixing parameters of the high-speed mixer are: low speed of 50-400 r / min for 5-15 min; high speed of 600-900 r / min for 5-35 min. The mixed sample is placed in a tube furnace for sintering, with the protective gas being one of oxygen, air, nitrogen, or argon. The sintering temperature is 800-950℃, the heating rate is 2-20℃ / min, and the holding time is 1-15h. The sintered sample is NCM@C.

[0015] The finished product was mixed with binder PVDF and conductive agent SP in a ratio of 9:0.5:0.5, 9.5:0.2:0.3 or 9.8:0.1:0.1 and coated. Finally, CR2302 button cells were made and tested with a test voltage of 3.0-4.35V.

[0016] The reaction principle of this invention is as follows: using methanol solution as a solvent, the ternary precursor and PZS precursor are fully dissolved, and then triethylamine solution is added as an initiator to promote the reaction of trichlorophosphazene and 4,4'-sulfonyl diphenol on the surface of the ternary precursor to generate (polycyclic triphosphazene-co-4,4'-sulfonyl diphenol), which then reacts with the lithium source to complete the carbonization of the carbon source and the preparation of the cathode material; finally, the cyclic triphosphazene-co-4,4'-sulfonyl diphenol is coated with the ternary cathode material.

[0017] The present invention has the following technical effects:

[0018] Compared with metal oxide and inorganic non-metal oxide coatings, carbon coating can isolate the electrolyte while improving the conductivity of the material. Compared with existing carbon layer coatings, the multi-element doped carbon layer coating of the present invention can improve conductivity and hardness, thus performing better in parameters such as lithium-nickel mixing, soluble lithium, first discharge specific capacity, first coulombic efficiency, and capacity retention. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0020] Figure 1 This is a cyclic comparison diagram of the three materials used in the examples and comparative examples. Detailed Implementation

[0021] To facilitate understanding of the present invention, various exemplary embodiments of the present invention are now described in detail. This detailed description should not be regarded as a specific limitation of the present invention, but should be understood as a more detailed description of certain aspects, features and embodiments of the present invention.

[0022] Example 1

[0023] 100g of commercially available NCM712 precursor was dispersed in a methanol solution and stirred. Then, 20L of a methanol solution containing 100g of trichlorophosphazene and 113g of 4,4'-sulfonyldiphenol was added dropwise. After 5 minutes, 1L of triethylamine was added, and stirring continued for 18 hours. After the reaction was complete, the precipitate was filtered and dried in a vacuum oven at 80℃ for 5 hours. The dried sample and 48.36g of lithium hydroxide were placed in a high-speed mixer and mixed at a low speed of 200 rpm for 3 minutes, followed by a high speed of 620 rpm for 13 minutes. The mixed material was placed in a tube furnace, and liquid oxygen was introduced before sintering. The temperature was increased at a rate of 6℃ / min to 900℃ and held for 10 hours. The sintered sample was then removed, yielding the multi-element doped carbon-coated ternary cathode material NCM@C. pzs .

[0024] The coating thickness of the carbon-coated cathode material obtained above is 5-15 nm.

[0025] The multi-element doped carbon-coated ternary cathode material includes a nitrogen, phosphorus, and sulfur ternary cathode material and a coating layer. The coating layer is composed of carbon, and the molar ratio of nitrogen, phosphorus, and sulfur in the ternary cathode material is 4:4:1.

[0026] The finished product prepared above was mixed with PVDF and SP in a ratio of 9:0.5:0.5, 9.5:0.2:0.3 or 9.8:0.1:0.1 and coated. Finally, CR2302 button cells were made and tested with a test voltage of 3.0-4.35V.

[0027] Comparative Example 1

[0028] 100g of commercially available NCM712 precursor and 48.36g of lithium hydroxide were placed in a high-speed mixer and mixed at a low speed of 200 rpm for 3 minutes, followed by a high speed of 620 rpm for 13 minutes. The mixed material was then placed in a tube furnace, and liquid oxygen was introduced before sintering. The temperature was increased at a rate of 6℃ / min to 900℃ and held for 10 hours. Subsequently, it was mixed with PVDF and SP in ratios of 9:0.5:0.5, 9.5:0.2:0.3, or 9.8:0.1:0.1 and coated. Finally, CR2302 button cells were fabricated and tested, with a test voltage of 3.0-4.35V.

[0029] Comparative Example 2

[0030] 100g of commercially available NCM712 precursor and 48.36g of lithium hydroxide were placed in a high-speed mixer and mixed at a low speed of 200 rpm for 3 minutes and a high speed of 620 rpm for 13 minutes. The mixed material was then placed in a tube furnace, and liquid oxygen was introduced before sintering. The temperature was increased at a rate of 6℃ / min to 900℃ and held for 10 hours. The resulting sample was then mixed with 1%-5% (by mass) citric acid and ball-milled for 10 hours. Subsequently, the sample was placed in a tube furnace under a nitrogen atmosphere and sintered at 550℃ for 10 hours to obtain NCM@C.

[0031] Table 1 Comparison of XRD patterns of the three materials

[0032] Material Name <![CDATA[I (003) / I(104) ]]> <![CDATA[I (006)+I(102) / I(101) ]]> <![CDATA[Example 1 (NCM@C pzs) > 1.586258456 0.515462346 Comparative Example 1 (NCM712) 1.452562654 0.521562552 Comparative Example 2 (NCM@C) 1.502613646 0.518516256

[0033] Table 1 shows a comparison of the XRD data of the three materials in Example 1, Comparative Example 1, and Comparative Example 2. (003) / I (104) A value above 1.20 indicates that lithium-nickel mixing did not occur in the cathode material. The ratio of the two cathode materials coated with carbon is higher, indicating that the crystal structure of the cathode material coated with carbon is more complete. Among these two cathode materials coated with carbon, the ratio of the cathode material coated with PZS (polycyclic triphosphazene-co-4,4'-sulfonyl diphenol) is higher than that of the cathode material coated with citric acid, indicating that the coating with PZS (polycyclic triphosphazene-co-4,4'-sulfonyl diphenol) is more effective.

[0034] The ratio of I(006) + I(102) / I(101) indicates whether the sintering conditions of the material are suitable. The smaller the ratio, the more stable the structure of the material. (003) / I (104) The structures are similar. Carbon coating is more effective than uncoated carbon coating, and PZS (polycyclic triphosphazene-co-4,4'-sulfonyl diphenol) coating is more effective than citric acid coating.

[0035] Table 2 Comparison of soluble lithium in the three materials

[0036]

[0037]

[0038] Table 2 shows the physicochemical properties of the three materials. As can be seen from the figure, the carbon-coated cathode material, due to the carbon coating on its surface, showed a slight decrease in soluble lithium and pH. However, the decrease in lithium atom percentage was due to a slight increase in the material's mass caused by the carbon coating, thus reducing the lithium atom percentage. In contrast, the physicochemical properties of both PZS (polycyclic triphosphazene-co-4,4'-sulfonyl diphenol) and citric acid coatings were similar and superior to those of the uncoated material, demonstrating that carbon coating does indeed reduce the soluble lithium and pH of the material. Furthermore, the effect of different carbon coatings on soluble lithium and pH is relatively small.

[0039] Table 3. First Coulomb Efficiency of Three Materials

[0040] Material Name <![CDATA[NCM@C pzs ]]> NCM NCM@C First Coulomb efficiency % 87.58 86.63 84.25

[0041] Figure 1 The table shows a comparison of the cycling performance of the three materials. The cathode material coated with PZS (polycyclic triphosphazene-co-4,4'-sulfonyl diphenol) has an initial discharge specific capacity of up to 201.5 mAh / g, while the cathode material coated with citric acid has an initial discharge specific capacity of 193.6 mAh / g, and the uncoated cathode material has an initial discharge specific capacity of 189 mAh / g. Because the cathode material is coated with carbon, the specific surface area of ​​the material is reduced, requiring fewer lithium ions to form the SEI film. Therefore, the cathode material coated with carbon has a higher discharge specific capacity and a higher initial coulombic efficiency, as shown in Table 3.

[0042] It is evident that, compared with metal oxide and inorganic non-metal oxide coatings, the ternary cathode material with multi-element doped carbon coating described in this invention can isolate the electrolyte while improving the conductivity of the material. Compared with existing carbon layer coatings, the multi-element doped carbon layer coating of this invention can improve conductivity and has stronger hardness. Therefore, it performs better in parameters such as lithium-nickel mixing, soluble lithium, first discharge specific capacity, first coulombic efficiency, and capacity retention.

[0043] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a ternary cathode material doped with nitrogen, phosphorus, and sulfur and coated with carbon, characterized in that, Includes the following steps: The ternary precursor was placed in a solution, stirred, and then trichlorophosphazene and 4,4'-sulfonyl diphenol were added. After stirring, triethylamine was added, and the mixture was stirred continuously. After washing, the mixture was dried to obtain a ternary precursor coated with polycyclic trichlorophosphazene-co-4,4'-sulfonyl diphenol. The coated ternary precursor and lithium source were mixed in a high-speed mixer, and the mixed sample was placed in a tube furnace for sintering. The sintered sample is the ternary cathode material coated with multi-element doped carbon. The ternary precursor is either NCM712 or NCM811.

2. The preparation method of a nitrogen, phosphorus, and sulfur multi-element doped carbon-coated ternary cathode material as described in claim 1, characterized in that, The lithium source is lithium carbonate or lithium hydroxide.

3. The preparation method of a nitrogen, phosphorus, and sulfur multi-element doped carbon-coated ternary cathode material as described in claim 1 or 2, characterized in that, The ratio of trichlorophosphazene to 4,4'-sulfonyl diphenol and triethylamine is trichlorophosphazene (100-200g): 4,4'-sulfonyl diphenol (100-200g): triethylamine (1-5L); the molar ratio of ternary precursor to lithium source is 1.0-1.

1.

4. The preparation method of a nitrogen, phosphorus, and sulfur multi-element doped carbon-coated ternary cathode material as described in claim 1, characterized in that, The mixing parameters for the high-speed mixer are as follows: low speed is 50-400 r / min, and the rotation time is 5-15 min; high speed is 600-900 r / min, and the rotation time is 5-35 min.

5. The preparation method of a nitrogen, phosphorus, and sulfur multi-element doped carbon-coated ternary cathode material as described in claim 1, characterized in that, The protective gas in the tube furnace is either nitrogen or argon. The sintering temperature is 800-950℃, the heating rate is 2-20℃ / min, and the holding time is 1-15h.

6. The ternary cathode material coated with carbon and doped with nitrogen, phosphorus, and sulfur multi-element doped by the preparation method according to any one of claims 1-5.

7. The ternary cathode material with nitrogen, phosphorus, and sulfur multi-element doping and carbon coating as described in claim 6, characterized in that, The coating thickness of the carbon-coated cathode material is 5-15 nm.

8. A ternary cathode material with nitrogen, phosphorus, and sulfur multi-element doped carbon coating as described in claim 6 or 7, characterized in that, It includes a multi-element doped ternary cathode material and a coating layer, wherein the coating layer is composed of carbon.

9. The application of the ternary cathode material coated with carbon and doped with nitrogen, phosphorus, and sulfur by the preparation method according to any one of claims 1-5 or the ternary cathode material coated with carbon and doped with carbon and doped with carbon according to any one of claims 6-8 in a coin cell, wherein the ternary cathode material coated with carbon and doped with carbon and doped with carbon is prepared by mixing and coating the ternary cathode material coated with carbon and PVDF and SP.

10. The application of the nitrogen, phosphorus, and sulfur multi-element doped carbon-coated ternary cathode material as described in claim 9 in a coin cell, wherein, The mass ratio of the ternary cathode material coated with carbon with multi-element doping to PVDF and SP is 9-10:0.1-0.5:0.1-0.5; the coin cell is a CR2302 coin cell.

Images