Preparation method and application of copper sulfide-reduced graphene oxide composite material

Abstract

The invention aims to provide a preparation method and application of a copper sulfide-reduced graphene oxide composite material. The preparation method comprises the following steps: mixing copper chloride and tris (hydroxymethyl) aminomethane to obtain a first mixture, adding a graphene oxide aqueous solution into the first mixture to obtain a second mixture, adding alkali liquor into the second mixture, and then adding thiourea for reaction to obtain a copper sulfide / graphene oxide composite material; and preparing a hydrazine hydrate aqueous solution, mixing the hydrazine hydrate aqueous solution and the copper sulfide / graphene oxide composite material, and carrying out a reduction reaction at a certain temperature. The copper sulphide-reduced graphene oxide composite material can effectively increase reversibility of a phase inversion reaction, and the cycle performance of the composite material can be remarkably improved while the capacity performance is improved.

Description

Technical Field

[0001] The present invention relates to the field of new energy technologies, more particularly to the preparation of materials for secondary batteries, and especially to a method for preparing a copper sulfide-reduced graphene oxide composite material and its applications. Background Art

[0002] The widespread use of secondary batteries (especially lithium-ion batteries) has greatly changed the way people use energy and even their living habits. The development speed of existing lithium-ion batteries has increased exponentially. As the main component of lithium-ion batteries, the positive electrode active materials are facing problems such as resource shortage and high price. The industry is trying to develop other types of materials to replace traditional positive electrode materials such as lithium cobaltate, lithium iron phosphate, and lithium nickel cobalt manganese oxide.

[0003] As a transition metal sulfide, copper sulfide (CuS) has received extensive attention in the exploration of positive electrode materials for lithium-ion batteries due to its high theoretical specific capacity and low manufacturing cost. Compared with common positive electrode materials such as ternary lithium nickel cobalt manganese oxide and lithium iron phosphate series that mainly store lithium through an intercalation mechanism, the lithium storage mechanism of CuS is a special conversion reaction, that is, during the lithium storage process, the CuS phase obtains electrons and is converted into the Cu2S phase. However, although this type of material has a high specific capacity, it has the problem of low reversibility of phase transformation. For example, during the electrode conversion reaction process, a large volume strain will occur, which will cause the collapse of the electrode structure, the destruction of the electron-ion transport network, an increase in interfacial side reactions, and the dissolution and shuttling of active substances, resulting in a significant reduction in the cycling performance, so its application as a positive electrode material is limited. Summary of the Invention

[0004] Based on the above problems, the purpose of the present invention is to provide a method for preparing a copper sulfide-reduced graphene oxide composite material and its applications. The copper sulfide-reduced graphene oxide composite material can effectively increase the reversibility of the phase transformation reaction, and while improving the capacity performance, can also significantly improve its cycling performance.

[0005] To achieve the above purpose, the first aspect of the present invention provides a method for preparing a copper sulfide-reduced graphene oxide composite material. The method for preparing the copper sulfide-reduced graphene oxide composite material includes the steps of: (1) Preparation of copper sulfide / graphene oxide composite material Mix copper chloride and tris(hydroxymethyl)aminomethane to obtain a first mixture, add an aqueous solution of graphene oxide to the first mixture to obtain a second mixture, add an alkali solution to the second mixture and then add thiourea for reaction to obtain a copper sulfide / graphene oxide composite material; (2) Reduction of copper sulfide / graphene oxide composite material Prepare an aqueous hydrazine solution, mix the aqueous hydrazine solution with the copper sulfide / reduced graphene oxide composite, and carry out a reduction reaction at a certain temperature.

[0006] Through the preparation method of the present invention, a composite material in which copper sulfide (CuS) and reduced graphene oxide are evenly dispersed and have a "C-S" network structure can be prepared. Among them, introducing reduced graphene oxide with high electrical conductivity can improve the electrical conductivity of the cathode material, promote the transfer of electrons, and improve its capacity performance. Forming a uniform "C-S" network structure improves the transformation defect of the "S-S" network structure in traditional copper sulfide. The "C-S" network structure reduces the formation energy of the reverse transformation of the structure, thereby promoting the reverse transformation from the Cu2S phase to the CuS phase. In addition, the uniformly distributed "C-S" network structure alleviates the stress change during the CuS phase transformation, reduces the expansion and collapse of the material, and thus can improve the cycling performance of the material.

[0007] The preparation method of the present invention is divided into Step 1 (composite of copper sulfide and graphene oxide) and Step 2 (reduction of the copper sulfide / graphene oxide composite).

[0008] In the first step, tris(hydroxymethyl)aminomethane plays a role in regulating the uniform nucleation of CuS, which makes Cu in copper chloride 2+ uniformly dispersed on graphene oxide (GO), and CuS grows in-situ on graphene oxide. Specifically, before adding the alkali solution, first mix tris(hydroxymethyl)aminomethane and copper chloride, and Cu 2+ can form a complex ion with tris(hydroxymethyl)aminomethane and then be uniformly dispersed on graphene oxide to prevent Cu 2+ from reacting with the alkali solution first to form a Cu(OH)2 precipitate when it exists independently. After adding the alkali solution, add thiourea. Under the action of a strong alkali solution, thiourea can directly hydrolyze to produce S 2- S 2- reacts with Cu 2+ ionized from the complex ion to form CuS uniformly dispersed on graphene oxide. Based on the precipitation equilibrium, the reaction continues until the complex ion is completely ionized and consumed.

[0009] In the second step, further reducing graphene oxide to reduced graphene oxide (rGO) results in a material with more abundant vacancies / defects, stronger electrical conductivity, higher specific surface area, and is more conducive to the progress of electrochemical reactions in terms of performance.

[0010] As a layered material with a large specific surface area, graphene oxide provides a large number of surface active sites for the fixed growth of CuS. CuS is evenly dispersed in GO and fixed on GO, and then forms CuS / rGO after reduction.

[0011] Based on the characteristics that CuS is a semiconductor (with lower conductivity than rGO) and rGO has strong conductivity, the specific morphological structure and conductive properties of CuS / rGO are formed. During the charge and discharge process, electrons will preferentially flow into the rGO network and then be transferred to CuS through the S bonds of CuS, thus forming a "C-S" network structure. Compared with the electron transfer in the S-S bonds of CuS, the C-S bond transfer reaction in CuS / rGO is more rapid and complete, thereby promoting the electrochemical reaction.

[0012] As a technical solution of the present invention, the molar ratio of copper chloride to tris(hydroxymethyl)aminomethane is 1:2 to 5.

[0013] As a technical solution of the present invention, the copper chloride is anhydrous copper chloride, copper chloride monohydrate, copper chloride dihydrate, copper chloride trihydrate or copper chloride tetrahydrate.

[0014] As a technical solution of the present invention, the concentration of the graphene oxide aqueous solution is 0.8 to 1.2 g / L, and the solid-liquid ratio of the first mixture to the graphene oxide aqueous solution is 30 to 55 g / L.

[0015] As a technical solution of the present invention, the alkali solution includes ammonia water with a concentration of 1.9 to 2.1 mol / L and an aqueous sodium hydroxide solution with a concentration of 0.9 to 1.1 mol / L.

[0016] As a technical solution of the present invention, the ammonia water is added first and then the aqueous sodium hydroxide solution. The solid-liquid ratio of the second mixture to the ammonia water is 4 to 15 g / L, and the solid-liquid ratio of the second mixture to the aqueous sodium hydroxide solution is 4 to 15 g / L.

[0017] As a technical solution of the present invention, the thiourea is a thiourea aqueous solution with a concentration of 0.9 to 1.1 mol / L, and the solid-liquid ratio of the second mixture to the thiourea aqueous solution is 3 to 5 g / L.

[0018] As a technical solution of the present invention, after adding the thiourea and reacting, the obtained product is adjusted to a solid-liquid ratio of 35 to 50 g / L with water and left standing for 2 to 5 h. Then, the precipitate is taken and washed alternately with water and ethanol and dried.

[0019] As a technical solution of the present invention, hydrazine hydrate and water are mixed at a volume ratio of 1:5 to 15 for 10 to 20 min to prepare the hydrazine hydrate aqueous solution.

[0020] As a technical solution of the present invention, the solid-liquid ratio of the copper sulfide / graphene oxide composite material to the hydrazine hydrate aqueous solution is 3.5 to 3.7 g / L, the mixing time is 20 to 30 min, the certain temperature is 60 to 70 °C, and the time for the reduction reaction is 2 to 4 h.

[0021] The second invention of the present invention provides an application of the copper sulfide-reduced graphene oxide composite material prepared by the foregoing preparation method of the copper sulfide-reduced graphene oxide composite material in a cathode material of a lithium-ion battery. Specific Embodiments

[0022] The copper sulfide-reduced graphene oxide composite material prepared by the preparation method of the copper sulfide-reduced graphene oxide composite material of the present invention can be used as a cathode material of a lithium-ion battery or as a capacitor material. The preparation method includes Step 1 (composite of copper sulfide and graphene oxide) and Step 2 (reduction of the copper sulfide / graphene oxide composite material).

[0023] The composite step of copper sulfide and graphene oxide includes: mixing copper chloride and tris(hydroxymethyl)aminomethane to obtain a first mixture, adding an aqueous solution of graphene oxide to the first mixture to obtain a second mixture, adding an alkali solution to the second mixture and then adding thiourea to react to obtain a copper sulfide / graphene oxide composite material.

[0024] In this step, the molar ratio of copper chloride to tris(hydroxymethyl)aminomethane is 1:2 to 5. As an example, the molar ratio can be, but is not limited to, 1:2, 1:3, 1:4, 1:5. The copper chloride is anhydrous copper chloride, copper chloride monohydrate, copper chloride dihydrate, copper chloride trihydrate or copper chloride tetrahydrate. The concentration of the aqueous solution of graphene oxide is 0.8 to 1.2 g / L. As an example, it can be, but is not limited to, 0.8 g / L, 0.9 g / L, 1.0 g / L, 1.1 g / L, 1.2 g / L. The solid-liquid ratio of the first mixture and the aqueous solution of graphene oxide is 30 to 55 g / L. As an example, the solid-liquid ratio can be, but is not limited to, 30 g / L, 35 g / L, 40 g / L, 45 g / L, 50 g / L, 55 g / L.

[0025] The alkali solution is added before adding thiourea. The alkali solution includes ammonia water with a concentration of 1.9 to 2.1 mol / L and an aqueous solution of sodium hydroxide with a concentration of 0.9 to 1.1 mol / L. As an example, the concentration of ammonia water can be, but is not limited to, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L. The concentration of the aqueous solution of sodium hydroxide can be, but is not limited to, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L. Ammonia water is added first and then the aqueous solution of sodium hydroxide is added to slowly adjust the alkalinity of the system to avoid rapid ionization of complex ions to Cu under a strong base suddenly. 2+And a Cu(OH)₂ precipitate is formed. The solid-liquid ratio of the second mixture to ammonia water is 4 - 15 g / L. As an example, the solid-liquid ratio can be, but is not limited to, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L, 11 g / L, 12 g / L, 13 g / L, 14 g / L, 15 g / L. The solid-liquid ratio of the second mixture to the aqueous sodium hydroxide solution is 4 - 15 g / L. As an example, the solid-liquid ratio can be, but is not limited to, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L, 11 g / L, 12 g / L, 13 g / L, 14 g / L, 15 g / L.

[0026] The thiourea is an aqueous thiourea solution with a concentration of 0.9 - 1.1 mol / L. As an example, the concentration can be, but is not limited to, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L. The solid-liquid ratio of the second mixture to the aqueous thiourea solution is 3 - 5 g / L. As an example, the solid-liquid ratio can be, but is not limited to, 3 g / L, 4 g / L, 5 g / L. After adding thiourea and reacting, the solid-liquid ratio of the obtained product is adjusted to 35 - 50 g / L with water and left to stand for 2 - 5 h. Then, the precipitate is taken and washed alternately with water and ethanol and dried. As an example, the solid-liquid ratio can be, but is not limited to, 35 g / L, 37 g / L, 39 g / L, 40 g / L, 42 g / L, 44 g / L, 46 g / L, 48 g / L, 50 g / L. The standing time can be, but is not limited to, 2 h, 3 h, 4 h, 5 h. Adjusting the solid-liquid ratio with water can promote diffusion and full reaction, and avoid uneven growth of CuS caused by excessive concentration of thiourea in a certain area. Standing after the reaction is to break the n 2+ complex structure of [Cu(THAM)] to fully form a CuS precipitate.

[0027] In the composite step of copper sulfide and graphene oxide, three reactions are involved, such as the complexation reaction of tris(hydroxymethyl)aminomethane (THAM) and Cu 2+ in Equation 1, the alkaline hydrolysis reaction of thiourea in Equation 2, and the synthesis reaction of Cu 2+ with S 2- in Equation 3.

[0028] Cu 2+ + nTHAM → [Cu(THAM)n] 2+ Equation 1 CS(NH₂)₂ + 2OH - → 2NH₃ + CO₂ + S 2- Equation 2 [Cu(THAM)n] 2+ + S 2- → nTHAM + CuS Equation 3 ​The reduction step of the copper sulfide / graphene oxide composite material includes: preparing an aqueous hydrazine solution, mixing the aqueous hydrazine solution and the copper sulfide / graphene oxide composite material, and performing a reduction reaction at a certain temperature. Among them, the aqueous hydrazine solution can be prepared by mixing hydrazine hydrate and water at a volume ratio of 1:5 to 15 for 10 to 20 minutes. The volume ratio of hydrazine hydrate to water can be, but is not limited to, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15. The solid-liquid ratio of the copper sulfide / graphene oxide composite material to the aqueous hydrazine solution is 3.5 to 3.7 g / L. As an example, the solid-liquid ratio can be, but is not limited to, 3.5 g / L, 3.6 g / L, 3.7 g / L. The mixing time of the copper sulfide / graphene oxide composite material and the aqueous hydrazine solution is 20 to 30 minutes. As an example, the mixing time can be, but is not limited to, 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes, 30 minutes. The reduction reaction time of the copper sulfide / graphene oxide composite material and the aqueous hydrazine solution is 2 to 4 hours. As an example, the time can be, but is not limited to, 2 hours, 3 hours, 4 hours. The reduction reaction temperature of the copper sulfide / graphene oxide composite material and the aqueous hydrazine solution is 60 to 70 °C. As an example, it can be, but is not limited to, 60 °C, 61 °C, 62 °C, 63 °C, 64 °C, 65 °C, 66 °C, 67 °C, 68 °C, 69 °C, 70 °C.

[0029] To better illustrate the purpose, technical solution and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the methods described in the following embodiments are further explanatory descriptions of the present invention and should not be regarded as limitations of the present invention.

[0030] Example 1 This embodiment is a preparation method of a copper sulfide-reduced graphene oxide composite material. This preparation method includes the following steps.

[0031] (1) Preparation of copper sulfide / graphene oxide composite material Mix cupric chloride dihydrate and tris(hydroxymethyl)aminomethane at a molar ratio of 1:4 to obtain a first mixture. Add an aqueous graphene oxide solution with a concentration of 1.0 g / L to the first mixture at a solid-liquid ratio of 42 g / L to obtain a second mixture. First, add ammonia water with a concentration of 2.1 mol / L to the second mixture at a solid-liquid ratio of 7 g / L and mix evenly. Subsequently, add an aqueous sodium hydroxide solution with a concentration of 1.0 mol / L to the second mixture at a solid-liquid ratio of 7 g / L and mix evenly. Then, add an aqueous thiourea solution with a concentration of 1.0 mol / L to the second mixture at a solid-liquid ratio of 4.2 g / L and mix evenly. Then, adjust the solid-liquid ratio of the system to 42 g / L with water, stir evenly, and stand for 3 h to obtain a copper sulfide / graphene oxide composite material, and wash it alternately with water and ethanol and then dry it.

[0032] (2) Reduction of copper sulfide / graphene oxide composite Hydrazine hydrate and water were mixed at a volume ratio of 1:10 for 15 min to prepare an aqueous hydrazine hydrate solution. The copper sulfide / graphene oxide composite and the aqueous hydrazine hydrate solution were mixed at a solid-liquid ratio of 3.5 g / L for 20 min, and then a reduction reaction was carried out at 70 °C for 4 h.

[0033] Example 2 This example is a preparation method of copper sulfide-reduced graphene oxide composite. This preparation method includes the following steps.

[0034] (1) Preparation of copper sulfide / graphene oxide composite Copper dichloride dihydrate and tris(hydroxymethyl)aminomethane were mixed at a molar ratio of 1:5 to obtain a first mixture. An aqueous graphene oxide solution with a concentration of 0.8 g / L was added to the first mixture at a solid-liquid ratio of 50 g / L to obtain a second mixture. In the second mixture, ammonia water with a concentration of 2.0 mol / L was first added at a solid-liquid ratio of 13 g / L and mixed evenly. Subsequently, an aqueous sodium hydroxide solution with a concentration of 0.9 mol / L was added at a solid-liquid ratio of 15 g / L and mixed evenly. Then, an aqueous thiourea solution with a concentration of 1.1 mol / L was added at a solid-liquid ratio of 3.5 g / L of the second mixture and the aqueous thiourea solution and mixed evenly. Then, the solid-liquid ratio of the system was adjusted to 40 g / L with water and stirred evenly, and then left standing for 2 h to obtain a copper sulfide / graphene oxide composite, which was washed alternately with water and ethanol and then dried.

[0035] (2) Reduction of copper sulfide / graphene oxide composite Hydrazine hydrate and water were mixed at a volume ratio of 1:15 for 10 min to prepare an aqueous hydrazine hydrate solution. The copper sulfide / graphene oxide composite and the aqueous hydrazine hydrate solution were mixed at a solid-liquid ratio of 3.7 g / L for 25 min, and then a reduction reaction was carried out at 60 °C for 3 h.

[0036] Example 3 This example is a preparation method of copper sulfide-reduced graphene oxide composite. This preparation method includes the following steps.

[0037] (1) Preparation of copper sulfide / graphene oxide composite Mix cupric chloride and tris(hydroxymethyl)aminomethane in a molar ratio of 1:2 to obtain a first mixture. Add an aqueous solution of graphene oxide with a concentration of 1.2 g / L to the first mixture at a solid-liquid ratio of 30 g / L to obtain a second mixture. First, add ammonia water with a concentration of 1.9 mol / L to the second mixture at a solid-liquid ratio of 5 g / L and mix evenly. Subsequently, add an aqueous solution of sodium hydroxide with a concentration of 0.9 mol / L to the second mixture at a solid-liquid ratio of 12 g / L and mix evenly. Then, add an aqueous solution of thiourea with a concentration of 0.9 mol / L to the second mixture at a solid-liquid ratio of 5.0 g / L and mix evenly. Then, adjust the solid-liquid ratio of the system to 42 g / L with water, stir evenly, and stand for 2 h to obtain a copper sulfide / graphene oxide composite material, and wash it alternately with water and ethanol and then dry it.

[0038] (2)Reduction of copper sulfide / graphene oxide composite material Mix hydrazine hydrate and water in a volume ratio of 1:8 for 10 min to prepare an aqueous solution of hydrazine hydrate. Mix the copper sulfide / graphene oxide composite material and the aqueous solution of hydrazine hydrate at a solid-liquid ratio of 3.6 g / L for 30 min, and then carry out a reduction reaction at 65 °C for 2 h.

[0039] Example 4 This example is a preparation method of a copper sulfide-reduced graphene oxide composite material. This preparation method includes the following steps.

[0040] (1)Preparation of copper sulfide / graphene oxide composite material Mix cupric chloride dihydrate and tris(hydroxymethyl)aminomethane in a molar ratio of 1:4 to obtain a first mixture. Add an aqueous solution of graphene oxide with a concentration of 1.0 g / L to the first mixture at a solid-liquid ratio of 42 g / L to obtain a second mixture. Add ammonia water with a concentration of 2.1 mol / L to the second mixture at a solid-liquid ratio of 14 g / L and mix evenly. Then, add an aqueous solution of thiourea with a concentration of 1.0 mol / L to the second mixture at a solid-liquid ratio of 4.2 g / L and mix evenly. Then, adjust the solid-liquid ratio of the system to 42 g / L with water, stir evenly, and stand for 3 h to obtain a copper sulfide / graphene oxide composite material, and wash it alternately with water and ethanol and then dry it.

[0041] (2)Reduction of copper sulfide / graphene oxide composite material Mix hydrazine hydrate and water in a volume ratio of 1:10 for 15 min to prepare an aqueous solution of hydrazine hydrate. Mix the copper sulfide / graphene oxide composite material and the aqueous solution of hydrazine hydrate at a solid-liquid ratio of 3.5 g / L for 20 min, and then carry out a reduction reaction at 70 °C for 4 h.

[0042] Example 5 This example is a preparation method of a copper sulfide-reduced graphene oxide composite material. This preparation method includes the following steps.

[0043] (1) Preparation of Copper Sulfide / Graphene Oxide Composite Mix cupric chloride dihydrate and tris(hydroxymethyl)aminomethane at a molar ratio of 1:4 to obtain a first mixture. Add an aqueous solution of graphene oxide with a concentration of 1.0 g / L to the first mixture at a solid-liquid ratio of 42 g / L to obtain a second mixture. Add an aqueous solution of sodium hydroxide with a concentration of 1.0 mol / L to the second mixture at a solid-liquid ratio of 14 g / L and mix evenly. Then add an aqueous solution of thiourea with a concentration of 1.0 mol / L to the second mixture at a solid-liquid ratio of 4.2 g / L and mix evenly. Then adjust the solid-liquid ratio of the system to 42 g / L with water, stir evenly, and let it stand for 3 h to obtain the copper sulfide / graphene oxide composite, and wash it alternately with water and ethanol and then dry it.

[0044] (2) Reduction of Copper Sulfide / Graphene Oxide Composite Mix hydrazine hydrate and water at a volume ratio of 1:10 for 15 min to prepare an aqueous solution of hydrazine hydrate. Mix the copper sulfide / graphene oxide composite and the aqueous solution of hydrazine hydrate at a solid-liquid ratio of 3.5 g / L for 20 min, and then carry out a reduction reaction at 70 °C for 4 h.

[0045] Comparative Example 1 This comparative example is a preparation method of a copper sulfide-reduced graphene oxide composite. This preparation method includes the following steps.

[0046] (1) Preparation of Copper Sulfide / Graphene Oxide Composite Add an aqueous solution of graphene oxide with a concentration of 1.0 g / L to cupric chloride dihydrate at a solid-liquid ratio of 42 g / L to obtain a mixture. First, add an aqueous solution of ammonia with a concentration of 2.1 mol / L to the mixture at a solid-liquid ratio of 7 g / L and mix evenly. Subsequently, add an aqueous solution of sodium hydroxide with a concentration of 1.0 mol / L to the mixture at a solid-liquid ratio of 7 g / L and mix evenly. Then add an aqueous solution of thiourea with a concentration of 1.0 mol / L to the mixture at a solid-liquid ratio of 4.2 g / L and mix evenly. Then adjust the solid-liquid ratio of the system to 42 g / L with water, stir evenly, and let it stand for 3 h to obtain the copper sulfide / graphene oxide composite, and wash it alternately with water and ethanol and then dry it.

[0047] (2) Reduction of Copper Sulfide / Graphene Oxide Composite Mix hydrazine hydrate and water at a volume ratio of 1:10 for 15 min to prepare an aqueous solution of hydrazine hydrate. Mix the copper sulfide / graphene oxide composite and the aqueous solution of hydrazine hydrate at a solid-liquid ratio of 3.5 g / L for 20 min, and then carry out a reduction reaction at 70 °C for 4 h.

[0048] Comparative Example 2 This comparative example is a preparation method of a copper sulfide-reduced graphene oxide composite material. This preparation method includes the following steps.

[0049] (1) Preparation of copper sulfide / graphene oxide composite material Mix cupric chloride dihydrate, tris(hydroxymethyl)aminomethane, an aqueous graphene oxide solution with a concentration of 1.0 g / L, ammonia water with a concentration of 2.1 mol / L, and an aqueous sodium hydroxide solution with a concentration of 1.0 mol / L evenly to obtain a mixture (wherein, the molar ratio of cupric chloride dihydrate to tris(hydroxymethyl)aminomethane is 1:4, the solid-liquid ratio of the mixture of cupric chloride dihydrate and tris(hydroxymethyl)aminomethane to the aqueous graphene oxide solution is 42 g / L, the sum of the masses of the mixture of cupric chloride dihydrate, tris(hydroxymethyl)aminomethane and the aqueous graphene oxide solution is m, the ammonia water is m / 7 L, and the aqueous sodium hydroxide solution is m / 7 L). Then add an aqueous thiourea solution with a concentration of 1.0 mol / L at a solid-liquid ratio of 4.2 g / L of the mixture and the aqueous thiourea solution and mix evenly. Then adjust the solid-liquid ratio of the system to 42 g / L with water, stir evenly, and stand for 3 h to obtain a copper sulfide / graphene oxide composite material, and wash it alternately with water and ethanol and then dry it.

[0050] (2) Reduction of copper sulfide / graphene oxide composite material Mix hydrazine hydrate and water at a volume ratio of 1:10 for 15 min to prepare an aqueous hydrazine hydrate solution. After mixing the copper sulfide / graphene oxide composite material and the aqueous hydrazine hydrate solution at a solid-liquid ratio of 3.5 g / L for 20 min, carry out a reduction reaction at 70 °C for 4 h.

[0051] Comparative Example 3 This comparative example is a preparation method of a copper sulfide-reduced graphene oxide composite material. This preparation method includes the following steps.

[0052] (1) Preparation of copper sulfide / graphene oxide composite material Mix cupric chloride dihydrate and tris(hydroxymethyl)aminomethane at a molar ratio of 1:4 to obtain a first mixture. Add an aqueous graphene oxide solution with a concentration of 1.0 g / L to the first mixture at a solid-liquid ratio of 42 g / L to obtain a second mixture. First, add ammonia water with a concentration of 2.1 mol / L to the second mixture at a solid-liquid ratio of 7 g / L and mix evenly. Subsequently, add an aqueous sodium hydroxide solution with a concentration of 1.0 mol / L to the second mixture at a solid-liquid ratio of 7 g / L and mix evenly. Then add an aqueous thiourea solution with a concentration of 1.0 mol / L at a solid-liquid ratio of 4.2 g / L of the second mixture and the aqueous thiourea solution and mix evenly. Then adjust the solid-liquid ratio of the system to 42 g / L with water, stir evenly, and stand for 3 h to obtain a copper sulfide / graphene oxide composite material, and wash it alternately with water and ethanol and then dry it.

[0053] (2)Reduction of Copper Sulfide / Graphene Oxide Composite Place the copper sulfide / graphene oxide composite in a tube furnace and keep it at 530 °C for 3 h. Wash the obtained product repeatedly and then dry it.

[0054] Comparative Example 4 This comparative example is a preparation method of a copper sulfide-reduced graphene oxide composite. This preparation method includes the following steps.

[0055] Add an aqueous solution of graphene oxide with a concentration of 1.0 g / L to cupric chloride dihydrate at a solid-liquid ratio of 42 g / L to obtain a mixture. Then add an aqueous solution of thiourea with a concentration of 1.0 mol / L to the mixture at a solid-liquid ratio of 4.2 g / L and mix evenly to obtain a mixed solution. Place the mixed solution in a high-temperature reaction kettle and keep it at 400 °C for 3 h. Filter the obtained product by suction, wash it repeatedly, and then dry it.

[0056] Make coin cells with the copper sulfide-reduced graphene oxide composites prepared in Examples 1-5 and Comparative Examples 1-4, and conduct battery performance tests.

[0057] Use the copper sulfide-reduced graphene oxide composites prepared in Examples 1-5 and Comparative Examples 1-4, and anhydrous copper sulfide after drying as active materials respectively. Make a slurry by dissolving them in NMP according to the ratio of 80 wt.% active material, 10 wt.% carbon black, and 10 wt.% polyvinylidene fluoride (PVDF). Coat the slurry on an aluminum foil and dry it, then punch small round pieces as the positive electrode sheets. Use lithium sheets as the negative electrode, and use a lithium bis(trifluoromethanesulfonyl)imide and 1,3-dioxolane / ethylene glycol dimethyl ether system (LiTFSI-DOL / DME, the mass ratio of LiTFSI in the electrolyte is 12%, and the volume ratio of DOL / DME is 1:2) as the electrolyte to make coin cells No. 1#-10#. Then let them stand for 15 h, charge at a constant current of 0.5C to 3.0V, then charge at a constant voltage until the current drops to 0.05C, record the charging capacity C1, then discharge at a constant current of 0.5C to 1.0V, and record the discharge capacity C0. Then place the battery in an environment of 25 °C, charge at a constant current of 1C to 3.0V, then charge at a constant voltage until the current drops to 0.05C, and then discharge at a constant current of 1C to 1.0V. Repeat this cycle, and record the discharge capacity of the first cycle and the last cycle.

[0058] Initial Coulombic efficiency = C1 / C0 Capacity retention rate = discharge capacity of the last cycle / discharge capacity of the first cycle × 10% Table 1 Battery performance results of coin cells No. 1#-10#

[0059] As can be seen from the results in Table 1, the initial Coulombic efficiency, the first charge capacity, and the cycling performance of coin cells 1# to 5# are all good. This is because by adding tris(hydroxymethyl)aminomethane, CuS with a uniform arrangement can be in-situ grown on graphene oxide, and then the graphene oxide composite can be reduced by hydrazine hydrate aqueous solution to generate a copper sulfide-reduced graphene oxide composite. In this copper sulfide-reduced graphene oxide composite, the reduced graphene oxide is evenly dispersed and has a "C-S" network structure, which can improve the capacity performance and relieve the stress change during the phase transformation process of CuS during charge and discharge, reducing the expansion and collapse of the material. Therefore, the cycling performance of the material can be improved.

[0060] Comparing Example 1 with Examples 4 to 5, it can be seen that by first using a weak base and then a strong base to adjust the alkalinity of the system, by avoiding the rapid ionization of complex ions to generate Cu 2+ and forming Cu(OH)2 precipitate under strong alkali, the performance of the material can be improved.

[0061] As can be seen from the results of coin cell 6#, in Comparative Example 1, tris(hydroxymethyl)aminomethane was not added, and the CuS in-situ grown on graphene oxide was uneven, greatly affecting the performance of the material.

[0062] As can be seen from the results of coin cell 7#, in Comparative Example 2, copper dichloride dihydrate, tris(hydroxymethyl)aminomethane, graphene oxide aqueous solution, ammonia water, and sodium hydroxide aqueous solution were mixed together, and a large amount of Cu 2+ had already formed Cu(OH)2 precipitate before reacting with S 2- , so the material performance was poor.

[0063] As can be seen from the results of coin cell 8#, the electrochemical performance of the copper sulfide / reduced graphene oxide composite prepared by reducing the copper sulfide / graphene oxide composite by high-temperature sintering is worse than that of reduction by hydrazine hydrate aqueous solution. This is because the vacancies / defects in the material obtained by the reduction method using hydrazine hydrate aqueous solution are richer, and in terms of performance, it shows stronger conductivity and higher specific surface area, so the electrochemical performance is better.

[0064] In coin cell 9#, neither tris(hydroxymethyl)aminomethane was added to promote the dispersion of graphene oxide nor solid-phase reduction was used, so the performance of the obtained material was the worst.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it is not limited to only the embodiments listed. Those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. Preparation method of copper sulfide-reduced graphene oxide composite material, characterized in that, Including the steps: (1) Preparation of copper sulfide / graphene oxide composite Mix cupric chloride and tris(hydroxymethyl)aminomethane to obtain a first mixture, add an aqueous solution of graphene oxide to the first mixture to obtain a second mixture, add an alkali solution to the second mixture and then add thiourea to react to obtain a copper sulfide / graphene oxide composite; (2) Reduction of copper sulfide / graphene oxide composite Prepare an aqueous solution of hydrazine hydrate, mix the aqueous solution of hydrazine hydrate and the copper sulfide / graphene oxide composite and carry out a reduction reaction at a certain temperature.

2. The preparation method of the copper sulfide-reduced graphene oxide composite material according to claim 1, wherein The molar ratio of the cupric chloride to the tris(hydroxymethyl)aminomethane is 1:2 to 5.

3. The preparation method of the copper sulfide-reduced graphene oxide composite material according to claim 1, characterized in that, The cupric chloride is anhydrous cupric chloride, cupric chloride monohydrate, cupric chloride dihydrate, cupric chloride trihydrate or cupric chloride tetrahydrate.

4. The preparation method of the copper sulfide-reduced graphene oxide composite material according to claim 1, wherein, The concentration of the aqueous solution of graphene oxide is 0.8 to 1.2 g / L, and the solid-liquid ratio of the first mixture to the aqueous solution of graphene oxide is 30 to 55 g / L.

5. The preparation method of the copper sulfide-reduced graphene oxide composite material according to claim 1, wherein The alkali solution includes ammonia water with a concentration of 1.9 to 2.1 mol / L and an aqueous solution of sodium hydroxide with a concentration of 0.9 to 1.1 mol / L.

6. The preparation method of the copper sulfide-reduced graphene oxide composite material according to claim 5, characterized in that, First add the ammonia water and then add the aqueous solution of sodium hydroxide. The solid-liquid ratio of the second mixture to the ammonia water is 4 to 15 g / L, and the solid-liquid ratio of the second mixture to the aqueous solution of sodium hydroxide is 4 to 15 g / L.

7. The preparation method of the copper sulfide-reduced graphene oxide composite material according to claim 1, characterized in that, The thiourea is an aqueous solution of thiourea with a concentration of 0.9 to 1.1 mol / L, and the solid-liquid ratio of the second mixture to the aqueous solution of thiourea is 3 to 5 g / L.

8. The preparation method of the copper sulfide-reduced graphene oxide composite material according to claim 1, wherein Mix hydrazine hydrate and water at a volume ratio of 1:5 to 15 for 10 to 20 min to prepare the aqueous solution of hydrazine hydrate.

9. The preparation method of the copper sulfide-reduced graphene oxide composite material according to claim 1, wherein, The solid-liquid ratio of the copper sulfide / graphene oxide composite to the aqueous solution of hydrazine hydrate is 3.5 to 3.7 g / L, the mixing time is 20 to 30 min, the certain temperature is 60 to 70 °C, and the reaction time of the reduction reaction is 2 to 4 h.

10. Application of the copper sulfide-reduced graphene oxide composite prepared by the preparation method of the copper sulfide-reduced graphene oxide composite according to any one of claims 1 to 9 in a positive electrode material of a lithium ion battery.

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