Positive electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of battery materials, and discloses a positive electrode material and a preparation method and application thereof, the preparation method comprises the following steps: mixing a lithium source, a positive electrode precursor material and a composite nanosheet, and sintering to obtain the positive electrode material, the composite nanosheet comprises a carbon material and bimetallic sulfide loaded on the carbon material, and metal elements in the bimetallic sulfide comprise a nickel element and a cobalt element. According to the preparation method of the positive electrode material provided by the invention, the composite nanosheet is introduced, and the carbon material in the composite nanosheet and the bimetallic sulfide cooperate with each other to jointly improve the conductivity, the charge transfer speed, the structural stability and the integrity of the positive electrode material, so that the capacity performance and the cycle stability of the battery running on a high-voltage platform are improved.

Description

Technical Field

[0001] This invention relates to the field of battery materials, specifically to a cathode material, its preparation method, and its application. Background Technology

[0002] As new energy vehicles evolve towards high-voltage platforms, high-nickel cathode materials have become the mainstream choice due to their energy density advantage (>250mAh / g). However, the development of high-nickel cathode materials currently faces three major technical bottlenecks. First, poor structural stability: lattice distortion leads to a volume expansion rate of over 10% during long-cycle operation. Second, interfacial contact failure: poor electrolyte wettability easily leads to increased ion transport impedance. Third, thermal safety risks: the oxygen evolution reaction initiation temperature exceeds 300℃, increasing the probability of thermal runaway by three times.

[0003] To address the aforementioned problems with high-nickel cathode materials, existing technologies often employ single-element doping (e.g., K or Na doping), composite coating (e.g., Al₂O₃ or TiO₂ coating), and gradient doping. However, while single-element doping improves electrolyte wettability, alkali metals are prone to volatilization at high temperatures, leading to structural pulverization, thus failing to simultaneously optimize material conductivity and structural stability. Composite coating can reduce interfacial impedance by approximately 30%, but increases equipment investment by 40%. Gradient doping, due to insufficient sintering density, cannot meet the high compaction density (>2.8 g / cm³) required for large cylindrical electrodes. 3 (Requirements).

[0004] In addition, traditional doping processes usually involve separate solid-phase mixing to achieve elemental doping of cathode materials. However, this method can easily lead to uneven distribution of active sites in the cathode material, reducing the uniformity of the cathode material and thus affecting the electrochemical performance of the battery. Summary of the Invention

[0005] This invention provides a cathode material, its preparation method, and its application, to solve the problems of the inability to simultaneously optimize the conductivity and structural stability of high-nickel cathode materials in the prior art, as well as the uneven distribution of active sites caused by the doping process in the prior art, thereby improving the capacity performance and cycle stability of cathode materials in battery applications.

[0006] In a first aspect, the present invention provides a method for preparing a cathode material, the method comprising the following steps: The cathode material is obtained by mixing a lithium source, a cathode precursor material, and composite nanosheets and then sintering the mixture. The composite nanosheets include carbon materials and bimetallic sulfides supported on the carbon materials. The metal elements in the bimetallic sulfides include nickel and cobalt.

[0007] According to the present invention, the composite nanosheet has a layered structure.

[0008] Preferably, in the composite nanosheet, the mass ratio of the bimetallic sulfide to the carbon material is 1:(3~10).

[0009] According to the present invention, the preparation process of the composite nanosheets includes the following steps: A carbon material is used as the working electrode, and together with the counter electrode and reference electrode, it is placed in an electrolyte for electrodeposition. Then, the working electrode after the electrodeposition reaction is washed and dried in sequence to obtain the composite nanosheet. The electrolyte includes a nickel source, a cobalt source, a sulfur source, and a solvent.

[0010] According to the present invention, in the electrolyte, the ratio of the total molar amount of nickel in the nickel source and cobalt in the cobalt source to the molar amount of sulfur in the sulfur source is (1.8~2.2):(0.8~1.2).

[0011] And / or, in the electrolyte, the molar ratio of nickel in the nickel source to cobalt in the cobalt source is (0.5~1.5):(0.5~1.5).

[0012] And / or, in the electrolyte, the total molar concentration of nickel in the nickel source and cobalt in the cobalt source is 1 mol / L to 3 mol / L.

[0013] Optionally, the nickel source includes at least one of nickel chloride, nickel chloride hydrate, nickel nitrate, nickel nitrate hydrate, nickel sulfate, nickel sulfate hydrate, nickel acetate, and nickel acetate hydrate.

[0014] Optionally, the cobalt source includes at least one of cobalt chloride, cobalt chloride hydrate, cobalt nitrate, cobalt nitrate hydrate, cobalt sulfate, cobalt sulfate hydrate, cobalt acetate, and cobalt acetate hydrate.

[0015] Optionally, the sulfur source includes thiourea (CH4N2S).

[0016] And / or, the voltage range of the electrodeposition reaction is -2V to 1V.

[0017] It should be noted that, in this invention, the "voltage range of the electrodeposition reaction" refers to the voltage range relative to the reference electrode.

[0018] And / or, the scan rate of the electrodeposition reaction is 2 mV·s -1 ~10mV·s -1 .

[0019] And / or, the electrodeposition reaction is accompanied by stirring of the electrolyte.

[0020] And / or, the counter electrode comprises at least one of platinum sheet, graphite, and stainless steel.

[0021] And / or, the reference electrode includes an Ag / AgCl reference electrode, a Hg / Hg2SO4 reference electrode, or a Li / Li... + At least one of the reference electrodes.

[0022] It is understood that in the method for preparing composite nanosheets provided by the present invention, a bimetallic sulfide load is formed on the carbon material of the working electrode until the mass ratio of the bimetallic sulfide to the carbon material is 1:(3~10), at which point the electrodeposition reaction stops, thereby obtaining composite nanosheets.

[0023] Optionally, in the process of preparing the composite nanosheets, the washing reagent used includes deionized water.

[0024] Optionally, the washing process is performed more than twice during the preparation of the composite nanosheets.

[0025] Optionally, the drying process in preparing the composite nanosheets includes vacuum drying.

[0026] Optionally, during the preparation of the composite nanosheets, the drying temperature is 50~100℃.

[0027] Optionally, the drying time during the preparation of the composite nanosheets is 5-10 hours.

[0028] According to the present invention, in the preparation process of the composite nanosheet, the carbon material is further pretreated before being used as the working electrode.

[0029] Preferably, the pretreatment includes: washing the carbon material sequentially with an acid reagent, an organic solvent, and water, and then drying it to obtain the pretreated carbon material.

[0030] Optionally, during the pretreatment of the carbon material, the concentration of the acid reagent used for washing is 0.5 mol / L to 3 mol / L.

[0031] Optionally, during the pretreatment of the carbon material, the acid reagent used for washing includes at least one of HCl, H2SO4, and HNO3.

[0032] Optionally, during the pretreatment of the carbon material, the organic solvent used for washing includes at least one of anhydrous ethanol, acetone, and isopropanol.

[0033] Optionally, during the pretreatment of the carbon material, the washing method includes ultrasonic cleaning.

[0034] And / or, the mass ratio of the lithium source to the composite nanosheet is 1:(0.001~0.003).

[0035] And / or, the chemical formula of the positive electrode precursor material is Ni x Co y Mn z (OH)2, where, 0.6<x<1, 0<y<0.4, 0<z<0.4, x+y+z=1.

[0036] And / or, the ratio of the molar amount of lithium in the lithium source to the total molar amount of transition metal elements in the cathode precursor material is 1:(0.5~1.5).

[0037] Optionally, the lithium source includes lithium hydroxide.

[0038] And / or, the carbon material includes at least one of carbon paper, carbon felt, and carbon nanofibers, preferably carbon paper.

[0039] According to the present invention, the sintering includes a first sintering stage and a second sintering stage performed sequentially.

[0040] Preferably, the heating rate in the first sintering stage is 1℃ / min to 5℃ / min.

[0041] Preferably, the holding temperature during the first sintering stage is 500℃~600℃.

[0042] Preferably, the holding time for the first sintering stage is 5h to 10h.

[0043] Preferably, the heating rate in the second sintering stage is 1℃ / min to 5℃ / min.

[0044] Preferably, the holding temperature during the second sintering stage is 700℃~900℃.

[0045] Preferably, the holding time for the second sintering stage is 8h to 12h.

[0046] According to the present invention, the sintering is carried out in an oxygen atmosphere, and the oxygen flow rate during the sintering process is 1L / min to 5L / min.

[0047] And / or, after sintering, the resulting product is further subjected to crushing and sieving in sequence.

[0048] Optionally, the sieve used for sieving has a mesh size of 300 to 400 mesh.

[0049] In a second aspect, the present invention also provides a cathode material, which is prepared by the cathode material preparation method described in the first aspect.

[0050] Thirdly, the present invention also provides a lithium-ion battery, the lithium-ion battery comprising the positive electrode material described in the second aspect.

[0051] The technical solution of this invention has the following advantages: 1. This invention provides a method for preparing a cathode material, comprising: mixing a lithium source, a cathode precursor material, and composite nanosheets, followed by sintering to obtain the cathode material; wherein the composite nanosheets comprise a carbon material and a bimetallic sulfide supported on the carbon material, and the metal elements in the bimetallic sulfide include nickel and cobalt. The method for preparing the cathode material provided by this invention introduces composite nanosheets during the mixing process of the lithium source and the cathode precursor material, doping the composite nanosheets into the cathode material. The doping of the composite nanosheets does not destroy the overall structural framework of the cathode material, but rather achieves lattice modification through atomic-level substitution and insertion. Bimetallic sulfides in composite nanosheets possess high electronic conductivity, while carbon itself is an excellent conductive medium. The combination of these two materials forms a three-dimensional conductive network structure. The carbon material provides continuous electron transport channels, and the bimetallic sulfide nanosheets are uniformly dispersed within it, significantly reducing charge transfer resistance. Furthermore, the introduction of carbon and bimetallic sulfides into the cathode material allows for synergistic effects, enhancing electron / ion migration during electrochemical reactions, as well as improving the conductivity and charge transport of the cathode material, thereby improving its electrochemical performance. On the other hand, carbon, as a physical support, effectively suppresses the aggregation, volume expansion, or shedding of bimetallic sulfides doped into the cathode material during battery cycling, improving the uniformity of active site distribution and structural stability after bimetallic sulfide doping. Moreover, during charge and discharge, bimetallic sulfides are prone to crystal transformation or volume changes; the rigid structure of carbon buffers the stress generated by these transformations, maintaining the overall structural integrity of the electrode material and extending the battery's cycle life. Furthermore, the bimetallic elements used in bimetallic sulfides are nickel and cobalt. Their ionic radii, valence states, and bond energies with sulfur are more compatible with the lattice structure and electrochemical requirements of the cathode material. Thus, the interaction between nickel and cobalt can reduce the overpotential during battery operation and further improve the electrochemical performance of the battery.

[0052] 2. The composite nanosheets provided by this invention have a layered structure, which can provide a high specific surface area and abundant active sites. Introducing them into cathode materials is beneficial to improving the structural stability and cycle performance of cathode materials.

[0053] 3. The composite nanosheets introduced into the cathode material provided by this invention use a specific carbon paper as the carbon material. It has a three-dimensional porous structure as a physical support carrier, which can more effectively suppress the aggregation, volume expansion or shedding of bimetallic sulfides during battery cycling. The carbon paper and bimetallic sulfides form a self-supporting structure and construct a continuous electron channel, which can effectively reduce the interface resistance of the cathode material, improve the charge transport efficiency in the cathode material, and stabilize the structure of the cathode material. This provides the high capacity and long cycle life advantages of high-nickel cathode materials operating under high voltage platforms.

[0054] 4. The preparation method provided by the present invention controls the decomposition behavior, ion diffusion path and interaction between the composite nanosheets and the cathode precursor material during the mixed sintering process with the lithium source and the cathode precursor through a specific two-stage sintering process, so that the active components in the metal sulfide enter the lattice of the cathode material, rather than the composite nanosheets are only deposited on the surface of the cathode material. The first sintering stage is a low-temperature pre-sintering stage, which promotes the dehydration and decomposition of the cathode precursor material into amorphous oxides. Simultaneously, elements in the bimetallic sulfide migrate to the surface of the amorphous phase. The subsequent second sintering stage is a high-temperature sintering stage, where the amorphous oxide recrystallizes into a layered ternary structure. At this stage, metal ions in the bimetallic sulfide, due to their size matching the transition metal sites in the precursor material, can replace some of the transition metals and enter the cathode material's lattice. Simultaneously, sulfur and carbon paper from the composite nanosheets are introduced into the cathode material during the high-temperature sintering process, doping into the cathode material as sulfur and conductive carbon, respectively. This improves the conductivity and structural stability of the cathode material, thereby enhancing its capacity and cycle stability. Furthermore, the high-temperature stage of the second sintering stage prevents excessive aggregation of metal ions from the composite nanosheets on the cathode material surface and promotes the diffusion of metal ions from the bimetallic sulfide into the cathode material's lattice, achieving doping of the cathode material. Detailed Implementation

[0055] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0056] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0057] Example 1 This embodiment provides a method for preparing a cathode material, including the following steps: (1) Cut the carbon paper into a shape with a length and width of 10cm. Then, use 1mol / L HCl, anhydrous ethanol and deionized water to ultrasonically clean for 15min each. After drying, the pretreated carbon paper is obtained.

[0058] 237.7 g of NiCl₂·6H₂O, 237.9 g of CoCl₂·6H₂O, and 76.12 g of thiourea (CH₄N₂S) were added to deionized water and stirred magnetically for 30 min until the solution became clear, thus preparing a 2 L electrolyte. In the electrolyte, the molar ratio of nickel to cobalt was 1:1, the ratio of the total molar amount of nickel and cobalt to the molar amount of sulfur was 2:1, and the total molar concentration of nickel and cobalt in the electrolyte was 1 mol / L.

[0059] (2) Using the pretreated carbon paper obtained in step (1) as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode, the two electrodes were placed together in the electrolyte prepared in step (1) for electrodeposition reaction. The voltage range of the electrodeposition reaction was set to -1.2~0.2V (vs. Ag / AgCl electrode), and the scan rate was 5mV·s. -1 The reaction was stopped when the mass ratio of carbon paper to NiCoS formed on the carbon paper in the resulting composite nanosheets reached 5:1. Mechanical stirring of the electrolyte was also performed during the electrodeposition process. The working electrode obtained after the electrodeposition reaction was rinsed three times with deionized water and then vacuum dried at 60°C for 6 hours to obtain the composite nanosheets. The resulting composite nanosheets have a layered structure, consisting of carbon paper and NiCoS loaded on the carbon paper.

[0060] (3) 235g of lithium hydroxide and 500g of positive electrode precursor material (Ni 0.83 Co 0.05 Mn 0.12 (OH)2) and 0.5g of the composite nanosheets obtained in step (2) were mixed. Under an oxygen atmosphere with an oxygen flow rate of 2L / min, the mixed product was first heated to 550℃ at a heating rate of 2℃ / min and sintered at 550℃ for 7h. Then, the temperature was raised to 800℃ at a heating rate of 2℃ / min and sintered at 800℃ for 10h. The sintered product was then crushed and sieved with a sieve mesh of 325 to obtain the positive electrode material.

[0061] Example 2 This embodiment provides a method for preparing a cathode material, including the following steps: (1) Cut the carbon paper into a shape with a length and width of 10cm. Then, use 0.5mol / L H2SO4, acetone and deionized water to ultrasonically clean for 15min respectively. After drying, the pretreated carbon paper is obtained.

[0062] 300g of NiCl₂·6H₂O, 200g of CoCl₂·6H₂O, and 80g of thiourea (CH₄N₂S) were added to deionized water and stirred magnetically for 30 minutes until the solution became clear, thus preparing a 1.5L electrolyte. In the electrolyte, the molar ratio of nickel to cobalt was 1.2:0.8, the ratio of the total molar amount of nickel and cobalt to the molar amount of sulfur was 2:1, and the total molar concentration of nickel and cobalt in the electrolyte was 1.4 mol / L.

[0063] (2) Using the pretreated carbon paper obtained in step (1) as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode, the two electrodes were placed together in the electrolyte prepared in step (1) to carry out the electrodeposition reaction. The voltage range of the electrodeposition reaction was set to -1.2~0.2V (vs. Ag / AgCl electrode), and the scan rate was 10mV·s. -1 The reaction was stopped when the mass ratio of carbon paper to NiCoS formed on the carbon paper in the resulting composite nanosheets reached 3:1. Mechanical stirring of the electrolyte was also performed during the electrodeposition process. The working electrode obtained after the electrodeposition reaction was rinsed three times with deionized water and then vacuum dried at 50°C for 10 hours to obtain the composite nanosheets. The resulting composite nanosheets have a layered structure, consisting of carbon paper and NiCoS loaded on the carbon paper. 1.2 Co 0.8 S is composed of.

[0064] (3) 235g of lithium hydroxide and 800g of cathode precursor material (Ni 0.8 Co 0.15 Mn 0.05 (OH)2) and 0.3g of the composite nanosheets obtained in step (2) were mixed. Under an oxygen atmosphere with an oxygen flow rate of 1L / min, the mixed product was first heated to 500℃ at a heating rate of 1℃ / min and sintered at 500℃ for 10h. Then, the temperature was increased to 900℃ at a heating rate of 5℃ / min and sintered at 900℃ for 8h. The sintered product was then crushed and sieved with a sieve mesh of 300 mesh to obtain the positive electrode material.

[0065] Example 3 This embodiment provides a method for preparing a cathode material, including the following steps: (1) Cut the carbon paper into a shape with a length and width of 10cm. Then, use 3mol / L HCl, acetone and deionized water to ultrasonically clean for 10min each. After drying, the pretreated carbon paper is obtained.

[0066] 188g of NiCl₂·6H₂O, 250g of CoCl₂·6H₂O, and 70g of thiourea (CH₄N₂S) were added to deionized water and stirred magnetically for 30 minutes until the solution became clear, thus preparing a 1L electrolyte. In the electrolyte, the molar ratio of nickel to cobalt was 0.86:1.14, the ratio of the total molar amount of nickel and cobalt to the molar amount of sulfur was 2:1, and the total molar concentration of nickel and cobalt in the electrolyte was 1.84 mol / L.

[0067] (2) Using the pretreated carbon paper obtained in step (1) as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode, the two electrodes were placed together in the electrolyte prepared in step (1) to carry out the electrodeposition reaction. The voltage range of the electrodeposition reaction was set to -1.2~0.2V (vs. Ag / AgCl electrode), and the scan rate was 2mV·s. -1 The reaction was stopped when the mass ratio of carbon paper to NiCoS formed on the carbon paper in the resulting composite nanosheets reached 10:1. Mechanical stirring of the electrolyte was also performed during the electrodeposition process. The working electrode obtained after the electrodeposition reaction was rinsed three times with deionized water and then vacuum dried at 100°C for 5 hours to obtain the composite nanosheets. The resulting composite nanosheets have a layered structure, consisting of carbon paper and NiCoS loaded on the carbon paper. 0.86 Co 1.14 S is composed of.

[0068] (3) 235g of lithium hydroxide and 1000g of positive electrode precursor material (Ni 0.9 Co 0.05 Mn 0.05 (OH)2) and 0.7g of the composite nanosheets obtained in step (2) were mixed. Under an oxygen atmosphere with an oxygen flow rate of 5L / min, the mixed product was first heated to 600℃ at a heating rate of 5℃ / min and sintered at 600℃ for 5h. Then, the temperature was increased to 700℃ at a heating rate of 1℃ / min and sintered at 700℃ for 12h. The sintered product was then crushed and sieved with a sieve mesh of 400 mesh to obtain the positive electrode material.

[0069] Example 4 The only difference between this embodiment and Example 1 is that the amount of composite nanosheets added in step (3) is 0.1g. All other contents are the same as in Example 1.

[0070] Example 5 The only difference between this embodiment and Example 1 is that the amount of composite nanosheets added in step (3) is 1g. All other contents are the same as in Example 1.

[0071] Example 6 The only difference between this embodiment and Embodiment 1 is that in step (1), the volume of the electrolyte is configured to be 4L, that is, the total molar concentration of nickel and cobalt in the electrolyte is 0.5mol / L. All other contents are the same as in Embodiment 1.

[0072] Example 7 The only difference between this embodiment and Embodiment 1 is that in step (1), the volume of the electrolyte is configured to be 0.6 L, that is, the total molar concentration of nickel and cobalt in the electrolyte is 3.3 mol / L. All other contents are the same as in Embodiment 1.

[0073] Example 8 The only difference between this embodiment and Embodiment 1 is that the electrodeposition reaction stops in step (2) when the mass ratio of carbon paper in the obtained composite nanosheet to NiCoS formed on the carbon paper is 2:1. All other contents are the same as in Embodiment 1.

[0074] Example 9 The only difference between this embodiment and Example 1 is that in step (2), the electrodeposition reaction stops when the mass ratio of carbon paper in the obtained composite nanosheet to NiCoS formed on the carbon paper is 12:1. All other contents are the same as in Example 1.

[0075] Example 10 The only difference between this embodiment and Embodiment 1 is that step (3) omits the first sintering stage, that is, the mixed product is directly heated to 800°C at a heating rate of 2°C / min under an oxygen atmosphere with an oxygen flow rate of 2L / min, and sintered at 800°C for 10h. All other contents are the same as in Embodiment 1.

[0076] Example 11 The only difference between this embodiment and Embodiment 1 is that step (3) omits the second sintering stage. That is, the mixed product is heated to 550°C at a heating rate of 2°C / min in an oxygen atmosphere with an oxygen flow rate of 2L / min, and sintered at 550°C for 7 hours. Then, the sintered product is crushed and sieved. All other contents are the same as in Embodiment 1.

[0077] Example 12 The only difference between this embodiment and Example 1 is that the carbon paper used to prepare the composite nanosheets is replaced with carbon felt of the same shape and size. All other aspects are the same as in Example 1.

[0078] Comparative Example 1 The only difference between this comparative example and Example 1 is that the preparation of composite nanosheets in steps (1) and (2) and the addition of composite nanosheets in step (3) are omitted. All other contents are the same as in Example 1.

[0079] Comparative Example 2 The only difference between this comparative example and Example 1 is that the 237.7g of NiCl2·6H2O added in step (1) during electrolyte preparation is replaced with 237.9g ​​of CoCl2·6H2O, that is, 237.7g of NiCl2·6H2O is omitted, and 475.8g of CoCl2·6H2O and 76.12g of thiourea (CH4N2S) are added to deionized water and magnetically stirred for 30min until the solution is clear, thus preparing 2L of electrolyte. The composite nanosheets obtained in step (2) are composed of carbon paper and Co2S loaded on the carbon paper. All other contents are the same as in Example 1.

[0080] Comparative Example 3 The only difference between this comparative example and Example 1 is that the 237.9g ​​of CoCl2·6H2O added in step (1) during electrolyte preparation is replaced with 237.7g of NiCl2·6H2O, that is, the 237.9g ​​of CoCl2·6H2O is omitted. Instead, 475.4g of NiCl2·6H2O and 76.12g of thiourea (CH4N2S) are added to deionized water and magnetically stirred for 30 minutes until the solution is clear, thus preparing 2L of electrolyte. The composite nanosheets obtained in step (2) are composed of carbon paper and Ni2S loaded on the carbon paper. All other contents are the same as in Example 1.

[0081] Comparative Example 4 The only difference between this comparative example and Example 1 is that the preparation of the electrolyte in step (1) and the preparation of the composite nanosheets in step (2) are omitted, and the composite nanosheets in step (3) are replaced with pretreated carbon paper, that is, the NiCoS metal sulfide loaded on the pretreated carbon paper is omitted. All other contents are the same as in Example 1.

[0082] Test case The cathode materials provided in Examples 1-12 and Comparative Examples 1-4 were used as cathode materials for lithium-ion batteries to prepare coin cells. The preparation method is as follows: The cathode materials prepared in Examples 1-12 and Comparative Examples 1-4, polyvinylidene fluoride binder, and conductive carbon black were mixed in a mass ratio of 90:5:5. N-methylpyrrolidone was added for homogenization to obtain a cathode slurry. The cathode slurry was then coated onto aluminum foil (area density of 3.5 mg / cm³). 2Next, the positive electrode sheet was dried at 80°C for 6 hours, pressed, and sliced ​​to obtain the positive electrode sheet. The lithium-ion coin cell was assembled using a polypropylene membrane as the separator, a lithium metal sheet as the negative electrode, and an electrolyte of 1 mol / L LiPF6 (solvent: ethylene carbonate and diethyl carbonate in a volume ratio of 1:1).

[0083] Electrochemical performance tests were conducted on lithium-ion coin cells assembled using the cathode materials provided in Examples 1-12 and Comparative Examples 1-4, respectively, using a Wuhan Landian CT2001A battery tester. The test details are as follows: The test temperature was 25℃, and the charge / discharge voltage range was 2.5~4.25V. The battery's initial discharge specific capacity was tested by first cycling at 0.2C / 0.2C for one cycle, and then the capacity retention rate was tested after 50 cycles at 1C / 1C. The test results are shown in Table 1. Table 1

[0084] As can be seen from Table 1, the method for preparing the cathode material provided by this invention introduces composite nanosheets. By introducing composite nanosheets into the cathode material, the carbon material and bimetallic sulfide in the composite nanosheets work synergistically to improve the conductivity, charge transport speed, structural stability and integrity of the cathode material, thereby enabling the battery to have better capacity performance and cycle stability under high voltage platform operation.

[0085] Compared with Example 1, the method for preparing the cathode material provided in Comparative Example 1 lacks the introduction of composite nanosheets, which leads to a deterioration in the cycle performance of the battery.

[0086] Compared with Example 1, the composite nanosheets introduced by the preparation method of the cathode material provided in Comparative Examples 2-3 use single metal sulfides, which cannot simultaneously possess the advantages of capacity performance and stability, thus leading to a decrease in the overall performance of the battery.

[0087] Compared with Example 1, Comparative Example 4 lacks bimetallic sulfides and only uses carbon paper mixed with lithium source and positive electrode precursor materials. It cannot achieve the effect of finding a balance point in the "capacity-stability-conductivity" triangle performance of the battery, resulting in a decline in the overall performance of the battery.

[0088] 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 positive electrode material, characterized in that, The preparation method includes the following steps: The cathode material is obtained by mixing a lithium source, a cathode precursor material, and composite nanosheets and then sintering the mixture. The composite nanosheets include carbon materials and bimetallic sulfides supported on the carbon materials. The metal elements in the bimetallic sulfides include nickel and cobalt.

2. The method for preparing the cathode material according to claim 1, characterized in that, The composite nanosheets have a layered structure; Preferably, in the composite nanosheet, the mass ratio of the bimetallic sulfide to the carbon material is 1:(3~10).

3. The method for preparing the cathode material according to claim 1 or 2, characterized in that, The preparation process of the composite nanosheets includes the following steps: A carbon material is used as the working electrode, and together with the counter electrode and reference electrode, it is placed in an electrolyte for electrodeposition. Then, the working electrode after the electrodeposition reaction is washed and dried in sequence to obtain the composite nanosheet. The electrolyte includes a nickel source, a cobalt source, a sulfur source, and a solvent.

4. The method for preparing the cathode material according to claim 3, characterized in that, In the electrolyte, the ratio of the total molar amount of nickel in the nickel source and cobalt in the cobalt source to the molar amount of sulfur in the sulfur source is (1.8~2.2):(0.8~1.2); And / or, in the electrolyte, the molar ratio of nickel in the nickel source to cobalt in the cobalt source is (0.5~1.5):(0.5~1.5); And / or, in the electrolyte, the total molar concentration of nickel in the nickel source and cobalt in the cobalt source is 1 mol / L to 3 mol / L; And / or, the voltage range of the electrodeposition reaction is -2V to 1V; And / or, the scan rate of the electrodeposition reaction is 2 mV·s -1 ~10mV·s -1 ; And / or, the electrodeposition reaction is also accompanied by stirring of the electrolyte; And / or, the counter electrode comprises at least one of platinum sheet, graphite, and stainless steel; And / or, the reference electrode includes an Ag / AgCl reference electrode, a Hg / Hg2SO4 reference electrode, or a Li / Li... + At least one of the reference electrodes.

5. The method for preparing the cathode material according to claim 3 or 4, characterized in that, In the preparation process of the composite nanosheets, the carbon material is pretreated before being used as the working electrode; Preferably, the pretreatment includes: washing the carbon material sequentially with an acid reagent, an organic solvent, and water, and then drying it to obtain the pretreated carbon material.

6. The method for preparing the cathode material according to any one of claims 1 to 5, characterized in that, The mass ratio of the lithium source to the composite nanosheets is 1:(0.001~0.003); And / or, the chemical formula of the positive electrode precursor material is Ni x Co y Mn z (OH)2, where, 0.6<x<1, 0<y<0.4, 0<z<0.4, x+y+z=1; And / or, the ratio of the molar amount of lithium in the lithium source to the total molar amount of transition metal elements in the cathode precursor material is 1:(0.5~1.5); And / or, the carbon material includes at least one of carbon paper, carbon felt, and carbon nanofibers, preferably carbon paper.

7. The method for preparing the cathode material according to any one of claims 1 to 6, characterized in that, The sintering includes a first sintering stage and a second sintering stage performed sequentially. Preferably, the heating rate in the first sintering stage is 1℃ / min to 5℃ / min; Preferably, the holding temperature during the first sintering stage is 500℃~600℃; Preferably, the holding time in the first sintering stage is 5h~10h; Preferably, the heating rate in the second sintering stage is 1°C / min to 5°C / min; Preferably, the holding temperature during the second sintering stage is 700℃~900℃; Preferably, the holding time for the second sintering stage is 8h to 12h.

8. The method for preparing the cathode material according to any one of claims 1 to 7, characterized in that, The sintering is carried out in an oxygen atmosphere, and the oxygen flow rate during the sintering process is 1L / min to 5L / min; And / or, after sintering, the resulting product is further subjected to crushing and sieving in sequence.

9. A positive electrode material, characterized in that, The cathode material is prepared by the cathode material preparation method according to any one of claims 1 to 8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode material as described in claim 9.

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