A lithium cobalt oxide composite material, a preparation method and application thereof

Abstract

This invention provides a lithium cobalt oxide composite material, its preparation method, and its application. The preparation method includes the following steps: mixing MXene and graphene oxide in a solvent to obtain a suspension; mixing the suspension with lithium cobalt oxide and performing a hydrothermal reaction; then reducing the graphene oxide to obtain the lithium cobalt oxide composite material. This invention utilizes the synergistic effect of graphene and MXene, which have similar structures and layered nanosheet morphologies, exhibiting good compatibility. Through their synergistic effect, not only is a good and efficient transport network formed between the lithium cobalt oxide material, MXene, and graphene, improving the ion and electron transport rates and enhancing the conductivity and stability of the lithium cobalt oxide material, but it also effectively suppresses volume expansion during battery charging and discharging, improving the cycle stability and safety of lithium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a lithium cobalt oxide composite material, its preparation method, and its application. Background Technology

[0002] Lithium cobalt oxide batteries possess advantages such as ultra-high energy density, rapid charge / discharge capability, and good low-temperature performance, giving them a dominant position in the consumer electronics and high-end portable device markets. However, due to the electrostatic repulsion between transition metals, the stability of the crystal structure is compromised when more than 50% of lithium ions are extracted from lithium cobalt oxide. Furthermore, when the charging voltage is too high, lithium cobalt oxide undergoes irreversible structural changes, leading to a severe performance degradation and thus affecting the actual working performance of the cathode.

[0003] To obtain high-performance cathode materials, lithium cobalt oxide materials can be modified, with doping and coating being the most common and efficient methods. Studies have shown that elemental doping is beneficial for stabilizing the layered structure, suppressing phase transitions and volume expansion during charge and discharge, and improving cycle life and thermal stability. For example, Al doping can reduce Co dissolution and oxygen vacancy formation. Coating the material can form a core-shell structure, reducing direct contact between the electrode and the electrolyte, suppressing side reactions, lowering interfacial impedance, and improving rate performance and cycle stability.

[0004] Another effective approach is to combine lithium cobalt oxide with other materials. This composite technology allows lithium cobalt oxide batteries to significantly improve cycle life and safety while maintaining high energy density. However, modifying lithium cobalt oxide through material composites often results in one composite material for one specific modification effect. While using multiple materials in combination to improve performance from multiple angles is common, the significant differences in physicochemical properties between different materials can easily lead to problems such as insufficient high-voltage compatibility and conflicting thermal stability.

[0005] Therefore, there is an urgent need to provide a suitable method for preparing lithium cobalt oxide composite materials to avoid problems such as insufficient high-voltage compatibility and contradictory thermal stability, while improving the conductivity and stability of the cathode material. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a lithium cobalt oxide composite material, its preparation method, and its applications. This invention utilizes graphene and MXene materials in synergy. Both have similar structures and layered nanosheet morphologies, exhibiting good compatibility. Through their synergistic effect, a robust and efficient transport network is formed between the lithium cobalt oxide material, MXene, and graphene, improving the ion and electron transport rates and enhancing the conductivity and capacity of the lithium cobalt oxide material. Furthermore, it effectively suppresses volume expansion during battery charging and discharging, improving the cycle stability of the lithium-ion battery. Moreover, graphene and MXene themselves provide more active sites, increasing capacity.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a lithium cobalt oxide composite material, the method comprising the following steps:

[0009] MXene and graphene oxide materials are mixed in a solvent to obtain a suspension.

[0010] The suspension and lithium cobalt oxide material are mixed and subjected to a hydrothermal reaction to obtain the lithium cobalt oxide composite material.

[0011] This invention utilizes graphene and MXene materials in synergy. Both have similar structures and layered nanosheet morphologies, exhibiting good compatibility. Through their synergistic effect, a robust and efficient transport network is formed between lithium cobalt oxide, MXene, and graphene, improving the ion and electron transport rates and enhancing the conductivity and capacity of the lithium cobalt oxide material. Furthermore, it effectively suppresses volume expansion during battery charging and discharging, improving the cycle stability of the lithium-ion battery. Moreover, graphene and MXene themselves provide more active sites, further increasing capacity.

[0012] Preferably, the mass ratio of the MXene material to the graphene oxide material is (0.5-2):1, for example, it can be 0.5:1, 1:1, 1.5:1 or 2:1, etc.

[0013] In this invention, an appropriate mass ratio helps the two materials achieve good contact and bonding at the microscale, reduces interface defects, and improves the overall stability of the composite material. Under an appropriate mass ratio, MXene and graphene synergistically form an effective conductive channel, enabling electrons to be transported more quickly, thereby improving the overall conductivity of the composite material.

[0014] Preferably, the mass ratio of the lithium cobalt oxide material to the solute in the suspension is (8-10):1, for example, it can be 8:1, 8.5:1, 9:1, 9.5:1, or 10:1. It should be noted that the solute refers to MXene material and graphene oxide material.

[0015] In this invention, a suitable mass ratio helps to achieve an optimal combination of composite material capacity, cycle stability, and conductivity.

[0016] Preferably, the solvent includes water. For example, it could be deionized water.

[0017] Preferably, the temperature of the hydrothermal reaction is 150-300℃, for example, it can be 150℃, 200℃, 250℃ or 300℃.

[0018] In this invention, a suitable hydrothermal reaction temperature can improve the interfacial bonding force between graphene and MXene materials and lithium cobalt oxide materials, forming a stable composite material structure; it can also improve the electron transport rate, thereby increasing the conductivity of the composite material and improving its charge-discharge performance.

[0019] Preferably, the hydrothermal reaction time is 6-24 hours, for example, 6 hours, 12 hours, 18 hours or 24 hours.

[0020] Preferably, the preparation steps of the MXene material include:

[0021] Using a ternary layered metal-ceramic MAX phase as a precursor, the precursor was etched to obtain MXene material. The precursor has the general chemical formula M0. n+1 AX n M includes any one or at least two of Ti, V, Sr, Cr, Ta, Nb, Zr, Mo or Hf; A includes any one or at least two of Al, Ga, In, Ti, Si, Ge, Sn or Pb; X includes C and / or N; and n is 1-3, for example, it can be 1, 2 or 3, etc.

[0022] It should be noted that in the MAX phase, the M atom and the X atom are tightly bonded together by strong ionic and covalent bonds, forming M n+1 X n Layers, these layers are separated by atomic layers of group A elements. M n+1 X n The A layer and the M layer are connected by relatively weak metallic bonds between A atoms and M atoms. Therefore, the A layer can be easily removed by chemical etching, while the M layer... n+1 X nThe hexagonal structure of the layer and its atomic positions are preserved. For example, when n=1, the precursor is phase 211 with the chemical formula M2AX; when n=2, the precursor is phase 312 with the chemical formula M3AX2; and when n=3, the precursor is phase 413 with the chemical formula M4AX3.

[0023] Preferably, the etching agent used in the etching process is hydrofluoric acid or a combination of fluoride salt and hydrochloric acid.

[0024] Preferably, the concentration of the hydrofluoric acid is 30-50 wt%, for example, it can be 30 wt%, 35 wt%, 40 wt%, 45 wt%, or 50 wt%.

[0025] Preferably, in the combination of fluoride and hydrochloric acid, the molar ratio of fluoride to hydrochloric acid is (3-5):1, for example, it can be 3:1, 4:1 or 5:1, etc.

[0026] In this invention, a suitable molar ratio of fluoride salt and hydrochloric acid is used as the etching agent to achieve the transformation from the MAX phase to MXene. This ensures that the etching reaction is sufficient and efficient, improving etching efficiency and obtaining a high yield of MXene in a shorter time. At the same time, it avoids over-etching, which could lead to the destruction or defects of the MXene structure, and also prevents under-etching, ensuring that an ideal MXene product is obtained, with its interlayer structure and surface functional groups being well preserved and controlled. During the etching process, not only is the atom removed, but some functional groups, such as -F and -OH, may also be introduced into the MXene surface. The presence of these functional groups can improve the surface properties of MXene, giving it better hydrophilicity, chemical activity, and surface charge characteristics, which is beneficial for subsequent applications.

[0027] Preferably, the fluoride salt includes any one or a combination of at least two of sodium fluoride, potassium fluoride, or lithium fluoride.

[0028] Preferably, the etching temperature is 50-80℃, for example, it can be 50℃, 55℃, 60℃, 65℃, 70℃, 75℃ or 80℃, etc.

[0029] Preferably, the preparation steps of the graphene oxide material include:

[0030] The intercalating agent and reaction medium are mixed and then added to the graphite material. An oxidant is then added to carry out the oxidation reaction. After the reaction is completed, an oxidant quencher is added to terminate the reaction. Then, post-processing is performed to obtain graphene oxide material.

[0031] In this invention, the intercalating agent, in conjunction with the reaction medium, contacts the graphite material, which can prolong the oxidation window, slow down the reaction rate, and allow the oxidant to penetrate the graphite interlayer more fully. This protects the carbon skeleton from structural collapse caused by localized severe oxidation and increases the functional group density. During the oxidation process, the introduction of oxygen-containing functional groups increases the spacing between graphite sheets, weakens the van der Waals forces between the sheets, and helps to achieve graphite layer exfoliation, laying the foundation for the subsequent preparation of multilayer graphene oxide. The addition of the oxidant quencher helps to remove residual oxidant, prevents over-oxidation, ensures that the oxidation degree of graphene oxide meets expectations, and preserves its ideal structure and properties.

[0032] Preferably, the intercalating agent comprises phosphoric acid.

[0033] Preferably, the volume ratio of the reaction medium to the intercalating agent is (8-10):1, for example, it can be 8:1, 8.5:1, 9:1, 9.5:1 or 10:1, etc.

[0034] Preferably, the reaction medium comprises concentrated sulfuric acid. This invention does not limit the mass fraction of the concentrated sulfuric acid, as long as it is concentrated sulfuric acid with a mass fraction greater than 70%.

[0035] Preferably, the oxidant includes any one or a combination of at least two of potassium permanganate, potassium persulfate, or sodium persulfate.

[0036] Preferably, the mass ratio of the graphite material to the oxidant is 1:(2-8), for example, it can be 1:2, 1:3, 1:4, 1:5, 1:6, 1:7 or 1:8, etc.

[0037] Preferably, the oxidizing quencher includes H2O2.

[0038] Preferably, the amount of the oxidizing quencher added accounts for 4-6% of the mass of the graphite material, for example, it can be 4%, 5% or 6%, etc.

[0039] Preferably, the temperature of the oxidation reaction is 30-40°C, for example, 30°C, 35°C or 40°C.

[0040] Preferably, the preparation steps of the lithium cobalt oxide material include:

[0041] A cobalt source and a lithium source are mixed and then calcined to obtain lithium cobalt oxide material. For example, the cobalt source may be cobalt tetroxide, etc.

[0042] Preferably, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium nitrate, lithium hydroxide, or lithium acetate.

[0043] Preferably, the molar ratio of cobalt in the cobalt source to lithium in the lithium source is 1:(1.0-1.2), for example, it can be 1:1.0, 1:1.1 or 1:1.2, etc.

[0044] Preferably, the calcination temperature is 800-950℃, for example, it can be 800℃, 820℃, 840℃, 860℃, 880℃, 900℃, 920℃ or 950℃, etc.

[0045] Preferably, the reduction process is carried out in an inert atmosphere. For example, the inert atmosphere may be a nitrogen atmosphere or an argon atmosphere.

[0046] Preferably, the reduction reaction temperature is 600-700℃, for example, it can be 600℃, 650℃ or 700℃.

[0047] Preferably, the heat preservation time for the reduction is 2-4 hours, for example, 2 hours, 3 hours or 4 hours.

[0048] Preferably, the preparation method includes the following steps:

[0049] (1) Mix dilute hydrochloric acid (dilute hydrochloric acid refers to hydrochloric acid with a mass fraction of less than 20% and the chemical formula of the solute is HCl) and fluoride salt in a molar ratio of (3-5):1 to obtain an etching agent.

[0050] Using the ternary layered metal ceramic MAX phase as a precursor, the precursor is etched with the etchant at a temperature of 50-80℃ for a time of 40-80h (e.g., 40h, 50h, 60h, 70h, or 80h). After etching, the precursor is washed and dried to obtain Mxene powder.

[0051] (2) Add phosphoric acid to concentrated sulfuric acid to obtain a mixed solution, then add graphite material and mix. After mixing evenly, add oxidant to carry out oxidation reaction. The oxidation reaction temperature is 30-40℃ and the time is 3-5h (e.g., 3h, 4h or 5h).

[0052] After the reaction is complete, an oxidizing agent or quencher is added to terminate the reaction. Then, the mixture is washed, sonicated, and dried to obtain graphene oxide powder.

[0053] The volume ratio of concentrated sulfuric acid to phosphoric acid is (8-10):1, and the mass ratio of graphite material to oxidant is 1:(2-8).

[0054] (3) The cobalt source and the lithium source are ball-milled and mixed at a molar ratio of cobalt to lithium of 1:(1.0-1.2), and then calcined at 800-950℃ to obtain lithium cobalt oxide powder.

[0055] (4) Mix MXene powder and graphene oxide powder in water at a mass ratio of (0.5-2):1 and sonicate to form a suspension.

[0056] The lithium cobalt oxide powder is added to the suspension and ultrasonically mixed for 40-80 minutes (e.g., 40 minutes, 50 minutes, 60 minutes, 70 minutes, or 80 minutes). Then, a hydrothermal reaction is carried out at a temperature of 150-300°C for 6-24 hours. The graphene oxide in the hydrothermal reaction product is then reduced in an inert atmosphere at a temperature of 600-700°C for 2-4 hours to obtain the lithium cobalt oxide composite material.

[0057] The mass ratio of the solute in the lithium cobalt oxide powder to the suspension is (8-10):1.

[0058] In a second aspect, the present invention provides a lithium cobalt oxide composite material, which is prepared by the preparation method described in the first aspect.

[0059] Thirdly, the present invention provides a positive electrode sheet, wherein the positive electrode sheet comprises the lithium cobalt oxide composite material as described in the second aspect.

[0060] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode as described in the third aspect.

[0061] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] This invention utilizes graphene and MXene materials in synergy. Both have similar structures and layered nanosheet morphologies, exhibiting good compatibility. Through their synergistic effect, not only is a good and efficient transport network formed between lithium cobalt oxide material, MXene, and graphene, improving the transport rate of ions and electrons and enhancing the conductivity and stability of lithium cobalt oxide material, but it also effectively suppresses volume expansion during battery charging and discharging, thereby improving the cycle stability and capacity of lithium-ion batteries. Detailed Implementation

[0064] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0065] Example 1

[0066] This embodiment provides a method for preparing a lithium cobalt oxide composite material, the method comprising the following steps:

[0067] (1) Mix dilute hydrochloric acid with a mass fraction of 18% and lithium fluoride in a molar ratio of 4:1 to obtain an etchant.

[0068] Using the ternary layered metal ceramic Ti3AlC2 as a precursor, the precursor was etched in a polytetrafluoroethylene bottle using the etchant at a temperature of 60°C for 48 hours. After etching, the precursor was washed with deionized water in a centrifuge at 7000 rpm until the pH of the supernatant was 7. Then it was dried to obtain Mxene powder.

[0069] (2) Add phosphoric acid to concentrated sulfuric acid (ice bath) to obtain a mixed solution, then add graphite powder and mix. After mixing evenly, slowly add potassium permanganate and stir. Then carry out the oxidation reaction at 35°C for 4 hours.

[0070] After the reaction was completed, H2O2 was added dropwise until the solution turned bright yellow to terminate the reaction. Then, the solution was centrifuged and washed until neutral, and then sonicated to obtain a graphene oxide suspension. Subsequently, the suspension was freeze-dried to obtain graphene oxide powder.

[0071] The volume ratio of concentrated sulfuric acid to phosphoric acid is 9:1, the amount of phosphoric acid used is 10 mL / g graphite powder, and the mass ratio of graphite powder to potassium permanganate is 1:6.

[0072] (3) Cobalt tetroxide and lithium carbonate were added to a ball mill jar at a molar ratio of cobalt to lithium of 1:1.05 and then calcined at 850°C to obtain lithium cobalt oxide powder.

[0073] (4) The synthesized MXene powder and graphene oxide powder were mixed evenly in deionized water at a mass ratio of 1:1 and ultrasonically treated for 2 hours to form a suspension.

[0074] The lithium cobalt oxide powder was added to the suspension and ultrasonically mixed for 60 min. Then it was placed in a high-pressure reactor (with a polytetrafluoroethylene liner) and subjected to a hydrothermal reaction at 200°C for 20 h. After centrifugation and washing, it was transferred to an oven at 80°C to dry, and the dried material was obtained.

[0075] The mass ratio of the solute in the lithium cobalt oxide powder to the suspension is 9:1.

[0076] (5) The dried material is placed in a tube furnace under an argon atmosphere and kept at 650°C for 3 hours to reduce the graphene oxide in the dried material to obtain a lithium cobalt oxide composite material.

[0077] Example 2

[0078] This embodiment provides a method for preparing a lithium cobalt oxide composite material, the method comprising the following steps:

[0079] (1) Mix dilute hydrochloric acid with a mass fraction of 18% and lithium fluoride in a molar ratio of 3:1 to obtain an etchant.

[0080] Using the ternary layered metal ceramic Ti3AlC2 as a precursor, the precursor was etched in a polytetrafluoroethylene bottle using the etchant at a temperature of 50°C for 50 hours. After etching, the precursor was washed with deionized water in a centrifuge at 7000 rpm until the pH of the supernatant was 7. Then it was dried to obtain Mxene powder.

[0081] (2) Add phosphoric acid to concentrated sulfuric acid (ice bath) to obtain a mixed solution, then add graphite powder and mix. After mixing evenly, slowly add potassium permanganate and stir. Then carry out the oxidation reaction at 30°C for 5 hours.

[0082] After the reaction was completed, H2O2 was added dropwise until the solution turned bright yellow to terminate the reaction. Then, the solution was centrifuged and washed until neutral, and then sonicated to obtain a graphene oxide suspension. Subsequently, the suspension was freeze-dried to obtain graphene oxide powder.

[0083] The volume ratio of concentrated sulfuric acid to phosphoric acid is 8:1, the amount of phosphoric acid used is 8 mL / g graphite powder, and the mass ratio of graphite powder to potassium permanganate is 1:4.

[0084] (3) Cobalt tetroxide and lithium cobalt oxide were added to a ball mill jar at a molar ratio of cobalt to lithium of 1:1.02 and then calcined at 900°C to obtain lithium cobalt oxide powder.

[0085] (4) The synthesized MXene powder and graphene oxide powder were mixed evenly in deionized water at a mass ratio of 0.5:1 and ultrasonically treated for 2 hours to form a suspension.

[0086] The lithium cobalt oxide powder was added to the suspension and ultrasonically mixed for 40 minutes. Then, it was placed in a high-pressure reactor (with a polytetrafluoroethylene liner) and subjected to a hydrothermal reaction at 150°C for 24 hours. After centrifugation and washing, it was transferred to an oven at 80°C to dry, and the dried material was obtained.

[0087] The mass ratio of the solute in the lithium cobalt oxide powder to the suspension is 8:1.

[0088] (5) The dried material is placed in a tube furnace under an argon atmosphere and kept at 600°C for 4 hours to reduce the graphene oxide in the dried material to obtain a lithium cobalt oxide composite material.

[0089] Example 3

[0090] This embodiment provides a method for preparing a lithium cobalt oxide composite material, the method comprising the following steps:

[0091] (1) Mix dilute hydrochloric acid with a mass fraction of 18% and lithium fluoride in a molar ratio of 5:1 to obtain an etchant.

[0092] Using the ternary layered metal ceramic Ti3AlC2 as a precursor, the precursor was etched in a polytetrafluoroethylene bottle using the etchant at a temperature of 70°C for 55 hours. After etching, the precursor was washed with deionized water in a centrifuge at 7000 rpm until the pH of the supernatant was 7. Then it was dried to obtain Mxene powder.

[0093] (2) Add phosphoric acid to concentrated sulfuric acid (ice bath) to obtain a mixed solution, then add graphite powder and mix. After mixing evenly, slowly add potassium permanganate and stir. Then carry out the oxidation reaction at 40°C for 3 hours.

[0094] After the reaction was completed, H2O2 was added dropwise until the solution turned bright yellow to terminate the reaction. Then, the solution was centrifuged and washed until neutral, and then sonicated to obtain a graphene oxide suspension. Subsequently, the suspension was freeze-dried to obtain graphene oxide powder.

[0095] The volume ratio of concentrated sulfuric acid to phosphoric acid is 10:1, the amount of phosphoric acid used is 12 mL / g graphite powder, and the mass ratio of graphite powder to potassium permanganate is 1:8.

[0096] (3) Cobalt tetroxide and lithium cobalt oxide were added to a ball mill jar at a molar ratio of cobalt to lithium of 1:1.08 and then calcined at 950°C to obtain lithium cobalt oxide powder.

[0097] (4) The synthesized MXene powder and graphene oxide powder were mixed evenly in deionized water at a mass ratio of 2:1 and ultrasonically treated for 2 hours to form a suspension.

[0098] The lithium cobalt oxide powder was added to the suspension and ultrasonically mixed for 80 minutes. Then, it was placed in a high-pressure reactor (with a polytetrafluoroethylene liner) and subjected to a hydrothermal reaction at 300°C for 6 hours. After centrifugation and washing, it was transferred to an oven at 80°C to dry, and the dried material was obtained.

[0099] The mass ratio of the solute in the lithium cobalt oxide powder to the suspension is 10:1.

[0100] (5) The dried material is placed in a tube furnace under an argon atmosphere and kept at 700°C for 2 hours to reduce the graphene oxide in the dried material to obtain a lithium cobalt oxide composite material.

[0101] Example 4

[0102] The difference between this embodiment and embodiment 1 is that the molar ratio of dilute hydrochloric acid and lithium fluoride in step (1) is 2:1.

[0103] The remaining preparation methods and parameters are consistent with those in Example 1.

[0104] Example 5

[0105] The difference between this embodiment and embodiment 1 is that the molar ratio of dilute hydrochloric acid and lithium fluoride in step (1) is 8:1.

[0106] The remaining preparation methods and parameters are consistent with those in Example 1.

[0107] Example 6

[0108] The difference between this embodiment and embodiment 1 is that phosphoric acid is not added in step (2).

[0109] The remaining preparation methods and parameters are consistent with those in Example 1.

[0110] Example 7

[0111] The difference between this embodiment and embodiment 1 is that H2O2 is not added in step (2).

[0112] The remaining preparation methods and parameters are consistent with those in Example 1.

[0113] Example 8

[0114] The difference between this embodiment and embodiment 1 is that the mass ratio of MXene powder and graphene oxide powder in step (4) is 0.1:1.

[0115] The remaining preparation methods and parameters are consistent with those in Example 1.

[0116] Example 9

[0117] The difference between this embodiment and embodiment 1 is that the mass ratio of MXene powder and graphene oxide powder in step (4) is 2.5:1.

[0118] The remaining preparation methods and parameters are consistent with those in Example 1.

[0119] Example 10

[0120] The difference between this embodiment and embodiment 1 is that the mass ratio of the solute in the lithium cobalt oxide powder and the suspension in step (4) is 12:1.

[0121] The remaining preparation methods and parameters are consistent with those in Example 1.

[0122] Comparative Example 1

[0123] The difference between this comparative example and Example 1 is that step (1) is omitted, and in step (4), MXene powder is replaced with an equal mass of graphene oxide powder.

[0124] The remaining preparation methods and parameters are consistent with those in Example 1.

[0125] Comparative Example 2

[0126] The difference between this comparative example and Example 1 is that step (2) is omitted, and in step (4), the graphene oxide powder is replaced with an equal mass of MXene powder.

[0127] The remaining preparation methods and parameters are consistent with those in Example 1.

[0128] Performance testing

[0129] The preparation of lithium cobalt oxide batteries based on the lithium cobalt oxide composite materials provided in the above embodiments and comparative examples includes the following specific steps: 1) mixing the lithium cobalt oxide composite material with the conductive agent acetylene black and the binder polyvinylidene fluoride in the organic solvent N-methylpyrrolidone to obtain a positive electrode slurry, which is then coated and dried to obtain a positive electrode sheet; 2) using graphite as the negative electrode sheet, assembling the prepared positive electrode sheet, negative electrode sheet and separator in a certain order, and then injecting electrolyte to obtain the lithium cobalt oxide battery.

[0130] Electrochemical performance tests were conducted on the aforementioned lithium cobalt oxide batteries.

[0131] ① Discharge specific capacity: At room temperature (25℃), the first discharge specific capacity was tested in the voltage range of 3V-4.5V using a current density of 0.2C.

[0132] ② Cyclic performance: At room temperature (25℃), the voltage range of 3V-4.5V was tested using a current density of 1C. After 200 cycles, the test was stopped and the capacity retention rate was calculated.

[0133] The test results are shown in Table 1.

[0134] Table 1

[0135]

[0136]

[0137] analyze:

[0138] As shown in Table 1, the present invention uses graphene and MXene materials in synergy. The two materials have similar structures and are both layered nanosheets with good compatibility. Through their synergistic effect, not only can a good and efficient transport network be formed between lithium cobalt oxide material, MXene and graphene, improving the transport rate of ions and electrons and improving the conductivity and stability of lithium cobalt oxide material, but also the volume expansion caused by the charging and discharging process of the battery is effectively suppressed, thereby improving the cycle stability and capacity of the lithium-ion battery.

[0139] As can be seen from the comparison between Example 1 and Examples 4-5, if the molar ratio of dilute hydrochloric acid to lithium fluoride is too small or too large, it will lead to incomplete or over-etching of MXene, reducing the bulk density of the composite material.

[0140] A comparison of Examples 1 and 6-7 shows that without phosphoric acid, the interlayer spacing may be limited and the oxidation uneven during step (2); without H2O2, the carbon skeleton of GO may be over-oxidized and destroyed. Both of these factors lead to a decrease in GO quality, thereby affecting the capacity and cycle stability of the composite material.

[0141] As can be seen from the comparison between Example 1 and Examples 8-9, if the mass ratio of MXene powder to graphene oxide powder is too small or too large, it will not have a good synergistic effect, and the capacity and cycle stability will decrease.

[0142] A comparison of Example 1 and Example 10 shows that if the mass ratio of lithium cobalt oxide powder to solute in the suspension is too large, the positive effects of MXene powder and graphene oxide powder will be reduced.

[0143] As can be seen from the comparison between Example 1 and Comparative Examples 1-2, if MXene powder or graphene oxide powder is not introduced and only a single material is used for composite, the capacity density and capacity retention rate will decrease.

[0144] It should be noted that the present invention is illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for producing a lithium cobalt oxide composite material, characterized by, The preparation method includes the following steps: MXene material and graphene oxide material are mixed in a solvent to obtain a suspension; the mass ratio of MXene material to graphene oxide material is (0.5-2):1; the solvent includes water; The suspension and lithium cobalt oxide material are mixed and subjected to a hydrothermal reaction. Then, the graphene oxide material is reduced to obtain the lithium cobalt oxide composite material. The mass ratio of the lithium cobalt oxide material to the solute in the suspension is (8-10):

1.

2. The production method according to claim 1, characterized by, The temperature of the hydrothermal reaction is 150-300℃; The hydrothermal reaction takes 6-24 hours.

3. The preparation method according to claim 1, characterized in that, The preparation steps of the MXene material include: Using a ternary layered metal-ceramic MAX phase as a precursor, the precursor is etched to obtain MXene material; wherein the general chemical formula of the precursor is M n+1 AX n M includes any one or at least two of Ti, V, Sr, Cr, Ta, Nb, Zr, Mo or Hf; A includes any one or at least two of Al, Ga, In, Ti, Si, Ge, Sn or Pb; X includes C and / or N; and n is 1-3.

4. The production method according to claim 3, characterized by, During the etching process, the etching agent used is hydrofluoric acid or a combination of fluoride salts and hydrochloric acid; The concentration of the hydrofluoric acid is 30-50 wt%. In the combination of fluoride and hydrochloric acid, the molar ratio of fluoride to hydrochloric acid is (3-5):1; The fluoride salt includes any one or a combination of at least two of sodium fluoride, potassium fluoride, or lithium fluoride.

5. The preparation method according to claim 3, characterized in that, The etching temperature is 50-80℃.

6. The method of claim 1, wherein, The preparation steps of the graphene oxide material include: The intercalating agent and reaction medium are mixed and then added to the graphite material. An oxidant is then added to carry out the oxidation reaction. After the reaction is completed, an oxidant quencher is added to terminate the reaction. Then, post-processing is performed to obtain graphene oxide material.

7. The production method according to claim 6, wherein The intercalating agent includes phosphoric acid.

8. The preparation method according to claim 6, characterized in that, The volume ratio of the reaction medium to the intercalating agent is (8-10):

1.

9. The preparation method according to claim 6, characterized in that, The reaction medium includes concentrated sulfuric acid.

10. The preparation method according to claim 6, characterized in that, The oxidant includes any one or a combination of at least two of potassium permanganate, potassium persulfate, or sodium persulfate.

11. The preparation method according to claim 6, characterized in that, The mass ratio of the graphite material to the oxidant is 1:(2-8).

12. The preparation method according to claim 6, characterized in that, The oxidizing quencher includes H2O2.

13. The preparation method according to claim 6, characterized in that, The oxidation reaction is carried out at a temperature of 30-40℃.

14. The preparation method according to claim 1, characterized in that, The preparation steps of the lithium cobalt oxide material include: The cobalt source and lithium source are mixed and then calcined to obtain lithium cobalt oxide material.

15. The preparation method according to claim 14, characterized in that, The lithium source includes any one or a combination of at least two of lithium carbonate, lithium nitrate, lithium hydroxide, or lithium acetate.

16. The preparation method according to claim 14, characterized in that, The molar ratio of cobalt in the cobalt source to lithium in the lithium source is 1:(1.0-1.2).

17. The preparation method according to claim 14, characterized in that, The calcination temperature is 800-950℃.

18. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Mix dilute hydrochloric acid and fluoride salt in a molar ratio of (3-5):1 to obtain an etching agent; Using the ternary layered metal ceramic MAX phase as a precursor, the precursor was etched with the etchant at a temperature of 50-80℃ for 40-80h. After etching, the precursor was washed and dried to obtain Mxene powder. (2) Add phosphoric acid to concentrated sulfuric acid to obtain a mixed solution, then add graphite material and mix. After mixing evenly, add oxidant to carry out the oxidation reaction. The oxidation reaction temperature is 30-40℃ and the time is 3-5h. After the reaction is complete, an oxidizing agent or quencher is added to terminate the reaction. Then, the mixture is washed, sonicated, and dried to obtain graphene oxide powder. The volume ratio of concentrated sulfuric acid to phosphoric acid is (8-10):1, and the mass ratio of graphite material to oxidant is 1:(2-8). (3) The cobalt source and the lithium source are ball-milled and mixed at a molar ratio of cobalt to lithium of 1:(1.0-1.2), and then calcined at 800-950℃ to obtain lithium cobalt oxide powder; (4) Mix MXene powder and graphene oxide powder in water at a mass ratio of (0.5-2):1 and sonicate to form a suspension; The lithium cobalt oxide powder is added to the suspension and ultrasonically mixed for 40-80 minutes. Then, a hydrothermal reaction is carried out at a temperature of 150-300℃ for 6-24 hours. Then, the graphene oxide in the hydrothermal reaction product is reduced in an inert atmosphere at a temperature of 600-700℃ for 2-4 hours to obtain the lithium cobalt oxide composite material. The mass ratio of the solute in the lithium cobalt oxide powder to the suspension is (8-10):

1.

19. A lithium cobalt oxide composite material, characterized in that, The lithium cobalt oxide composite material is prepared by the preparation method described in any one of claims 1-18.

20. A positive electrode sheet, characterized in that, The positive electrode includes the lithium cobalt oxide composite material as described in claim 19.

21. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode as described in claim 20.

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