A multi-shell structure material with a concentration gradient of metal elements and a preparation method and application thereof

Abstract

The application relates to the technical field of functional materials, and relates to a hollow multi-shell structure material with a metal element concentration gradient and a preparation method and application thereof. The method comprises the following steps: 1) performing a heating reaction on a carbon source aqueous solution to obtain a carbon sphere template; 2) dispersing the carbon sphere template obtained in step 1) in a metal salt solution to perform primary adsorption and obtain a suspension; 3) adding metal salt into the suspension obtained in step 2) again to perform secondary or multiple adsorption, and then obtaining a solid precursor; 4) placing the solid precursor obtained in step 3) in an inert atmosphere to perform calcination fixation, and then obtaining a solid powder; and 5) performing calcination on the solid powder obtained in step 4) in an oxygen or air atmosphere, and then obtaining the hollow multi-shell structure material with the metal element concentration gradient. The material can maintain a specific capacity of 190 mAh / g, and the performance is far superior to that of commercial materials with the same components.

Description

Technical Field

[0001] The present invention relates to the technical field of functional materials, in particular to a multi-shell structure material with a metal element concentration gradient, a preparation method and an application thereof. Background Art

[0002] The performance of lithium-ion batteries mainly depends on the electrode materials. Among them, the research on negative electrode materials has made continuous breakthroughs in performance since the initial commercial graphite (374mAh / g) to the discovery of silicon, tin, lithium, etc. At present, the specific capacity of positive electrode materials is much lower than that of negative electrode materials. Therefore, positive electrode materials have become a shortcoming restricting the development of lithium-ion batteries. So far, commercial lithium-ion battery positive electrode materials have mainly gone through three stages: LiCoO2 (LCO), LiMn2O4 (LMO) and LiFePO4 (LFP), and LiNi x Co y Mn 1-x-y O2(NCM). The ternary layered oxide NCM developed by Ohzuku's team in 1994 is considered the most promising candidate material for high-performance lithium-ion batteries. Among NCM positive electrode materials, nickel is the main contributor to capacity. Moreover, due to the cost of cobalt resources, research on "nickel-rich" NCM positive electrode materials is becoming increasingly popular. However, "nickel-rich" NCM positive electrode materials face problems such as cation mixing, transition metal dissolution, active lithium loss, and surface reconstruction. These problems lead to rapid degradation of battery performance and also bring about safety issues, limiting its practical application.

[0003] At present, modification measures for "nickel-rich" NCM positive electrode materials include ion doping, surface coating, special structural design, and construction of element concentration gradients. The design of constructing element concentration gradients is favored by researchers because it does not introduce electrochemically inert elements and is low in cost. However, the current construction of concentration gradients is still technically difficult. The co-precipitation method is currently commonly used to construct nickel-rich positive electrode materials with concentration gradients. Due to the complexity of the process and too many influencing factors, the overall element concentration is uncontrollable, and accurate element concentration gradient distribution control cannot be achieved. In addition, a single modification measure cannot suppress a variety of potential failure factors. Current research mainly focuses on the parallel use of multiple modification measures. In this context, how to combine multiple modification measures has become a hot topic and difficulty in current research. Summary of the Invention

[0004] Based on the above-mentioned deficiencies of the prior art, the present invention provides a hollow multi-shell structured material with a metal element concentration gradient, as well as its preparation method and application. Based on the sequential template method, the present invention adopts a two-step metal ion precursor enrichment strategy combined with a two-step calcination strategy to construct a hollow multi-shell structured material with a metal element concentration gradient. By regulating the synthesis conditions, the composition, structure, and morphology of the material are controlled and synthesized. This overcomes the problem of structural collapse of nickel-rich ternary cathode materials during charge and discharge at different scales, thereby achieving a comprehensive improvement in energy density, cycle stability, and rate performance.

[0005] The present invention provides a type of positive electrode material for lithium-ion batteries, as well as its preparation method and application. The present invention adsorbs a carbon sphere template in a solution containing specific metal ions. After adsorption equilibrium is reached, a metal salt is added to the solution to promote the template to adsorb the metal ions again. The distribution of metal ions in the template is controlled by adjusting factors such as adsorption time and adsorption temperature, so that the concentration of metal ions distributed inside and outside the template has a significant difference. The carbon sphere template enriched with metal ions is then placed in a tubular furnace for calcination. First, the calcination is carried out in an inert atmosphere to fix the distribution position of the metal ions. Then, the calcination is carried out in an air or oxygen atmosphere to remove the template to obtain a hollow multi-shell structure material with a metal element concentration gradient. This material has demonstrated excellent electrochemical properties in lithium battery positive electrode applications due to its unique structural advantages.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for preparing a hollow multi-shell structure material having a metal element concentration gradient, that is, a method for preparing a hollow multi-shell structure material in which the metal element concentrations contained in different shells are gradiently distributed, comprising the following steps:

[0008] 1) heating a carbon source aqueous solution, filtering, washing, and drying to prepare micro-nano sized colloidal carbon spheres, which serve as carbon sphere templates for subsequent hollow multi-shell metal oxide synthesis;

[0009] 2) dispersing the carbon sphere template obtained in step 1) in a metal salt solution to obtain a suspension, and after a certain period of stirring, heat preservation and adsorption, the metal salt adsorption reaches a dynamic equilibrium;

[0010] 3) adding a specific metal salt to the suspension after adsorption equilibrium in step 2), stirring, keeping warm and adsorbing for a certain period of time, filtering and drying to obtain a solid precursor;

[0011] 4) calcining the solid precursor obtained in step 3) under an inert atmosphere to obtain a solid powder with the metal ions initially fixed thereon;

[0012] 5) calcining the solid powder obtained in step 4) in air or oxygen atmosphere to obtain a hollow multi-shell structure material with a metal element concentration gradient.

[0013] In this method, a secondary or multiple adsorption strategy is employed to manipulate the distribution of different metal ion precursors within the template, which is key to synthesizing multi-shell materials with metal element concentration gradients. Furthermore, controlling the concentration, composition, and adsorption time of the metal ion solution is crucial for regulating the composition and structure of hollow multi-shell materials with metal element concentration gradients. Considering the varying adsorption capacities of the carbon sphere template for different metal ions, metal salts at varying concentrations are added to the solvent to ensure a solid precursor with a consistent metal concentration ratio. Controlling the solvent composition maximizes metal ion adsorption within the carbon sphere template, thereby generating more shells; controlling the adsorption time ensures sufficient metal ion adsorption. Notably, controlling the metal ion species, concentration, and adsorption time during the secondary adsorption process is crucial for synthesizing multi-shell materials with metal element concentration gradients. By controlling the type of metal salt and the concentration of the metal ions added during the secondary adsorption process, the solid precursor obtained from the primary adsorption process can further adsorb specific metal ions. Regulating the adsorption time controls the distribution of the secondary adsorbed metal ions within the template, resulting in a solid precursor with a metal ion concentration gradient.

[0014] In addition, the choice of high-temperature calcination under an inert atmosphere first is to fix the distribution position of the metal ions in the template and avoid the migration of metal ions during the oxygen calcination to remove the template and synthesize the metal oxide material. In addition, by regulating the calcination atmosphere, calcination temperature and calcination time, the structural parameters of the hollow multi-shell structure material can be regulated. Since the nickel element in the nickel-rich positive electrode material is +2 or +3 valent, the cobalt element is +3 valent, and the manganese element is +4 valent, it is necessary to synthesize the nickel-rich positive electrode material with a layered structure in an oxidizing atmosphere; in addition, theoretically, the higher the nickel content, the lower the sintering temperature, and too high a calcination temperature can easily destroy the multi-shell structure and only obtain nanoparticles, so it is necessary to regulate the calcination temperature to regulate the crystal structure and geometric structure of the material; in addition, the calcination time also has a great influence on the structure of the material. The longer the calcination time, the better the crystallinity of the material. Considering that the multi-shell structure is difficult to maintain at high temperature, it is designed to be kept warm for a long time at a relatively low temperature to obtain a nickel-rich positive electrode material with an ideal layered structure.

[0015] The hydrothermal reaction of the carbon source aqueous solution in step 1) of the present invention prepares micro-nano-sized colloidal carbon spheres. Compared with the traditional mechanical ball milling method, the prepared carbon spheres have uniform particle size and controllable size. At the same time, they contain a large number of active functional groups on the surface, have excellent hydrophilicity and surface reactivity, are more conducive to the adsorption of metal ions, and are commonly used templates for preparing core-shell structure materials.

[0016] The adsorption described in step 2) of the present invention is enhanced adsorption. Enhanced adsorption refers to placing the carbon sphere template and the metal salt solution in a beaker for adsorption at a certain water bath temperature, and regulating the pH value of the metal salt solution to enhance the adsorption of metal ions by the carbon sphere template under appropriate temperature and pH conditions, and obtaining a solid precursor enriched in metal ions after a certain period of adsorption.

[0017] The adsorption described in step 3) of the present invention is adjusted adsorption. Adjusted adsorption refers to adding the metal salt to the precursor solution again in proportion, adsorbing it at a certain water bath temperature, and regulating the adsorption time to adjust the adsorption of the carbon sphere template to the metal ions at an appropriate temperature and time. After a certain period of adsorption, a solid precursor with a gradient distribution of metal ions from the inside to the outside is obtained.

[0018] The calcination in step 4) of the present invention is to gradually solidify the metal ions enriched in the carbon sphere template by controlling the calcination atmosphere, holding time and calcination temperature, so that the metal ions are stably present in the template and avoid migration due to template removal during the subsequent calcination process.

[0019] The calcination described in step 5) of the present invention is to gradually solidify the metal salt adsorbed on the surface of the carbon ball template by controlling the heating rate, holding time and oxygen concentration in the furnace chamber, and cause the template carbon balls to shrink and oxidize and burn, while slowly removing the carbon ball template to form a multi-shell structure metal oxide.

[0020] Preferably, the heating reaction in step 1) is a hydrothermal reaction, and the temperature of the hydrothermal reaction is 160-220°C, for example, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C or 200°C, more preferably 180-205°C, and even more preferably 180-200°C;

[0021] Preferably, the metal salt in step 2) comprises one or more of lithium chloride, nickel chloride, manganese chloride, cobalt chloride, lithium acetate, lithium acetate dihydrate, nickel acetate, nickel acetate tetrahydrate, manganese acetate tetrahydrate, cobalt acetate, cobalt acetate tetrahydrate, lithium sulfate, lithium sulfate dihydrate, nickel sulfate, nickel sulfate tetrahydrate, manganese sulfate, manganese sulfate tetrahydrate, cobalt sulfate, cobalt sulfate tetrahydrate, lithium nitrate, lithium nitrate dihydrate, nickel nitrate, nickel nitrate tetrahydrate, manganese nitrate, manganese nitrate tetrahydrate and cobalt nitrate, cobalt nitrate tetrahydrate; more preferably, it is one or more of lithium acetate dihydrate, nickel acetate, nickel acetate tetrahydrate, manganese acetate tetrahydrate, cobalt acetate, cobalt acetate tetrahydrate, lithium sulfate, lithium sulfate dihydrate, nickel sulfate, nickel sulfate tetrahydrate, manganese sulfate, manganese sulfate tetrahydrate, cobalt sulfate, and cobalt sulfate tetrahydrate; further preferably, it is one or more of lithium acetate dihydrate, nickel acetate tetrahydrate, manganese acetate tetrahydrate, and cobalt acetate tetrahydrate.

[0022] The concentration of the metal salt solution is 0.01-5M, for example, 0.01M, 0.1M, 0.2M, 0.5M, 1M, 2M, 3M, 4M or 5M, more preferably 0.01-3M, and even more preferably 0.01-0.1M;

[0023] The solvent of the metal salt solution includes one or more of water, acetone and ethanol, and more preferably water and / or ethanol.

[0024] Preferably, the adsorption in step 2) is adsorption with heat preservation and stirring;

[0025] The adsorption temperature is 20-60°C, for example, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C or 60°C, more preferably 30-60°C, and even more preferably 40-50°C;

[0026] One adsorption, the adsorption time is 1-48h, more preferably 1-36h, further preferably 12h;

[0027] Preferably, the adsorption in step 3) is a secondary heat preservation and stirring adsorption;

[0028] The adsorption temperature is 20-60°C, for example, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C or 60°C, more preferably 30-60°C, and even more preferably 40-50°C;

[0029] Secondary adsorption, the adsorption time is 0.1-2h, more preferably 0.1-1h, further preferably 0.1-0.5h;

[0030] Multiple adsorption, the adsorption time is 0.1-2h, more preferably 0.1-1h, further preferably 0.1-0.5h;

[0031] The adsorbed mixed liquid is filtered and washed; washed with one or a combination of any two or more of deionized water, methanol, ethanol and isopropanol; for example, it can be deionized water, methanol, ethanol, isopropanol, a combination of deionized water and methanol, a combination of deionized water and ethanol, a combination of deionized water and isopropanol, or a combination of methanol and ethanol; the washing times are 2-5 times, for example, 2 times, 3 times, 4 times or 5 times, more preferably 3-4 times; the washing time is 0.5-24 hours, for example, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 11 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours, more preferably 5-20 hours, and even more preferably 10-15 hours;

[0032] The drying temperature is 50-100°C, for example, 50°C, 60°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, more preferably 50-90°C, and even more preferably 60-80°C.

[0033] The drying time is 6-24 h, for example, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h or 24 h, more preferably 15-24 h, and even more preferably 18-20 h.

[0034] Preferably, the calcination in step 4) is carried out in a muffle furnace, a tubular furnace or a kiln;

[0035] The calcination temperature is 200-800°C, for example, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C or 800°C, more preferably 300-550°C, and even more preferably 400-500°C;

[0036] The calcination time is 0.5-10 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h or 10 h, more preferably 1-6 h, and even more preferably 4-5 h;

[0037] The heating rate of calcination is 0.5-20°C / min, for example, 0.5°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min, 5.5°C / min, 6°C / min, 6.5°C / min, 7°C / min, 7.5°C / min, 8°C / min, 8.5°C / min, 9°C / min, 9.5°C / min or 10°C / min, more preferably 0.5-10°C / min, and even more preferably 1-5°C / min;

[0038] The calcination atmosphere is argon or nitrogen, more preferably argon, with a purity of 99.999% for high-purity argon.

[0039] Preferably, the calcination in step 5) is carried out in a muffle furnace, a tubular furnace or a kiln;

[0040] The first step calcination temperature is 300-500°C, for example, 300°C, 350°C, 400°C, 450°C and 500°C, more preferably 350-450°C;

[0041] The first step calcination time is 1-10 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours, more preferably 5-10 hours;

[0042] The heating rate of the first calcination step is 0.5-10°C / min, for example, 0.5°C / min, 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min, 5.5°C / min, 6°C / min, 6.5°C / min, 7°C / min, 7.5°C / min, 8°C / min, 8.5°C / min, 9°C / min, 9.5°C / min or 10°C / min, more preferably 5-10°C / min;

[0043] The second step calcination temperature is 500-1000°C, for example, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C and 1000°C, more preferably 500-950°C, and even more preferably 600-800°C.

[0044] The second step calcination time is 15-30h, for example, it can be 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, 24h, 25h, 26h, 27h, 28h, 29h or 30h, more preferably 15-25h, and further preferably 18-22h;

[0045] The heating rate of the second calcination step is 0.5-20°C / min, for example, 0.5°C / min, 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min, 5.5°C / min, 6°C / min, 6.5°C / min, 7°C / min, 7.5°C / min, 8°C / min, 8.5°C / min, 9°C / min, 9.5°C / min or 10°C / min, more preferably 0.5-10°C / min, and even more preferably 1-5°C / min;

[0046] The calcination atmosphere is one of air, oxygen, or a mixture of nitrogen and oxygen, wherein the proportion of oxygen in the mixture of nitrogen and oxygen is 10%-100%; more preferably, high-purity oxygen.

[0047] The present invention provides a multi-shell structured material having a metal element concentration gradient synthesized by the aforementioned preparation method. The prepared material not only has a multi-shell structure, but also has different metal element concentrations in different shells, presenting a gradient distribution, typically characterized by a high nickel concentration in the inner shell and a low nickel concentration in the outer shell. The multi-shell structure has 2 to 4 shells, for example, 2, 3, or 4 layers.

[0048] The present invention adopts a secondary / multiple adsorption strategy to regulate the conditions for the adsorption of metal ion precursors by the carbon ball template, such as the concentration of the metal salt precursor solution, adsorption time, adsorption temperature, number of adsorptions and order, and combines the use of a secondary / multiple calcination strategy, that is, first calcining in an inert atmosphere to fix the distribution position of the metal ions, and then calcining in an oxidizing atmosphere to remove the template, and combining the regulation of the calcination temperature, holding time, heating rate, etc., to prepare a hollow multi-shell structure material with a metal element concentration gradient. Material size nanosizing can alleviate the pulverization phenomenon caused by volume change during the cycle. The multi-shell layer can not only effectively buffer the volume expansion during the charge and discharge process, thereby improving the cycle stability of the material, but also form an effective conductive network inside the material, shortening the transmission path of electrons and lithium ions, thereby improving the rate performance of the material. In addition, the higher concentration of nickel content in the inner shell can provide a high specific capacity for the material, while the lower concentration of nickel content in the outer shell can reduce transition metal dissolution, improve the stability of the solid-liquid interface, reduce surface side reactions, and reduce cation mixing, thereby stabilizing the overall structure of the material.

[0049] The hollow multi-shell structure material with a metal element concentration gradient for the positive electrode of a lithium-ion battery can maintain a specific capacity of 190 mAh / g after more than 100 cycles at a rate of 0.3C in a voltage range of 2.5-4.3 V.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] The hollow multi-shell structure material with a metal element concentration gradient prepared by the present invention exhibits excellent cycle stability during high-rate charge and discharge when applied to the positive electrode of a lithium-ion battery. The nano-sizing of the material can alleviate the pulverization phenomenon caused by volume expansion during the cycle, and the multi-shell structure can not only effectively buffer the volume expansion during the charge and discharge process, ensuring the cycle stability of the material; it can also form an effective conductive network inside the material, which is beneficial to the transmission of internal electrons and lithium ions. Moreover, due to the unique nickel concentration gradient distribution of the multi-shell structure of the metal element concentration gradient multi-shell structure material, the migration of transition metals is greatly reduced compared to the solid structure gradient material, so that the electrode material has better stability. The nickel concentration gradient distribution, that is, the nickel content of the inner shell is higher, makes the material have a higher specific capacity as a whole, and the nickel content of the outer shell is lower, so that the material has an excellent solid-liquid interface and structural stability, thereby making the material have excellent stability as a whole. Therefore, the hollow multi-shell structure material with a metal element concentration gradient can maintain a specific capacity of 190 mAh / g after stable cycling at a rate of 0.3C for more than 100 cycles in the voltage range of 2.5-4.3 V, with a capacity retention rate of up to 98%. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a transmission electron microscope bright field image of the material prepared in Example 1 of the present invention;

[0053] Figure 2 This is a transmission electron microscope bright field image of the material prepared in Example 1 of the present invention after embedding and sectioning;

[0054] Figure 3 Transmission electron microscopy-energy dispersive X-ray spectrum line scan of the material prepared in Example 1 of the present invention, and the relative content of Ni element in different shell layers (embedded inside is a transmission electron microscopy photo of the material);

[0055] Figure 4 This is the X-ray diffraction pattern of the material prepared in Example 1 of the present invention;

[0056] Figure 5 This is the X-ray photoelectron spectroscopy test spectrum of the material prepared in Example 1 of the present invention;

[0057] Figure 6 This is the battery cycle performance curve of the material prepared in Example 1 of the present invention;

[0058] Figure 7 This is the differential scanning calorimetry test result of the material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0059] The present invention will be further described in detail below with reference to specific embodiments.

[0060] The present invention provides a method for preparing a hollow multi-shell structure material having a metal element concentration gradient, the method comprising:

[0061] (a) placing a carbon source aqueous solution into a hydrothermal reactor and performing a hydrothermal reaction at 160-220° C. for 100-180 min, followed by filtration, washing, and drying to obtain a carbon sphere template;

[0062] (b) dispersing the carbon sphere template obtained in step (a) in a metal salt solution with a concentration of 0.01-5M to obtain a suspension. The metal salt solution is one or more of lithium chloride, nickel chloride, manganese chloride, cobalt chloride, lithium acetate, nickel acetate, manganese acetate, cobalt acetate, lithium sulfate, nickel sulfate, manganese sulfate, cobalt sulfate, lithium nitrate, nickel nitrate, manganese nitrate, and cobalt nitrate, and adsorbing at 20-60° C. for 1-48 hours to obtain a suspension;

[0063] (c) adding a metal salt having a concentration of 0.01-5M to the suspension obtained in step (b) to obtain a suspension. The metal salt is one or more of lithium chloride, nickel chloride, manganese chloride, cobalt chloride, lithium acetate, nickel acetate, manganese acetate, cobalt acetate, lithium sulfate, nickel sulfate, manganese sulfate, cobalt sulfate, lithium nitrate, nickel nitrate, manganese nitrate, and cobalt nitrate, adsorbing the suspension at 20-60°C for 0.1-2h, filtering the adsorbed mixed solution, washing it 2-5 times with deionized water, methanol, or ethanol, and drying it at 60-100°C for 6-24h to obtain a solid precursor; or repeating the adsorption, filtration, and drying process to obtain a solid precursor after multiple adsorptions.

[0064] (d) calcining the solid precursor obtained in step (c) in a muffle furnace or kiln in an argon or nitrogen atmosphere for 0.5-10 h at a temperature of 200-800° C. at a heating rate of 0.5-20° C. / min, and cooling to obtain a solid powder;

[0065] (e) placing the solid powder obtained in step (c) in a muffle furnace or a kiln in one of air, oxygen, or a mixture of nitrogen and oxygen, wherein the oxygen ratio in the mixture of nitrogen and oxygen is 10%-100%, and the roasting comprises a two-step roasting process, the first step being a roasting temperature of 300-500°C, a roasting time of 1-10h, and a roasting heating rate of 0.5-10°C / min, and the second step being a roasting temperature of 500-1000°C, a roasting time of 15-30h, and a roasting heating rate of 0.5-20°C / min, and after cooling, obtaining the hollow multi-shell structure material having a metal element concentration gradient.

[0066] Example 1

[0067] A method for preparing a hollow multi-shell structure material having a metal element concentration gradient, the method comprising:

[0068] (1) A 1.5 M sucrose aqueous solution was placed in a reactor at 200°C for hydrothermal reaction for 127 min. After natural cooling, the mixture was filtered and washed with water three times and ethanol three times. The product was dried in an oven at 60°C for 24 h to obtain a carbon sphere template with a diameter of 2.9 μm.

[0069] (2) Grind 1 g of the carbon sphere template obtained in step (1) and add it to a metal salt solution with a molar ratio of 100:10:1:1, i.e., 2 M lithium acetate solution, 0.2 M nickel acetate solution, 0.02 M manganese acetate solution, and 0.02 M cobalt acetate. The solvent is a mixture of 30 ml of deionized water and 20 ml of anhydrous ethanol. Stir for 10 minutes, then ultrasonicate for 10 minutes. After the ultrasonication is completed, stir and adsorb at 40°C for 48 hours.

[0070] (3) 0.04 M cobalt acetate and 0.16 M manganese acetate were added to the solution obtained in (2), respectively, and the mixture was heated in a water bath at 40°C with stirring for 10 min, followed by ultrasonic adsorption for 6 min. After adsorption was complete, the suspension was filtered, washed three times with deionized water, and dried in an oven at 60°C for 24 h to obtain a solid precursor.

[0071] (4) The solid precursor obtained in step (3) was placed in a tube furnace, heated to 500°C at 2°C / min under an argon atmosphere, kept at this temperature for 2 h, and then naturally cooled to obtain a black solid powder.

[0072] (5) The black solid powder obtained in step (4) was placed in a tube furnace, heated to 350°C at 10°C / min under an oxygen atmosphere and kept warm for 5 hours, then heated to 650°C at 10°C / min and kept warm for 15 hours to obtain a nickel-rich positive electrode material with a three-shell structure having a nickel concentration gradient, and the outermost shell diameter was about 800 nm.

[0073] Transmission electron microscope photos of nickel-rich cathode materials with nickel concentration gradient three-shell structure Figure 1 As shown, the transmission electron microscopy photos after embedding the slices are as follows Figure 2 shown. Figure 3 The figure shows the transmission electron microscopy-energy dispersive X-ray spectroscopy elemental analysis of the obtained nickel-rich positive electrode material with a three-shell structure with a nickel concentration gradient after embedding and sectioning. It can be seen from the figure that the Ni element on the inner and outer shells presents a gradient distribution, specifically, the Ni element content in the inner shell is high and the Ni element content in the outer shell is relatively low. Figure 4 This is the X-ray diffraction pattern of a nickel-rich cathode material with a three-shell structure and a nickel concentration gradient. It can be seen that the synthesized material belongs to a cubic phase, R-3m space group, and has a layered structure of α-NaFeO4. The two characteristic peaks with the strongest peak intensity correspond to the (003) and (104) crystal planes, respectively. The characteristic peaks of the sample are very sharp, indicating that the material has good crystallinity. There are no impurity peaks in the X-ray diffraction spectrum, indicating that the sample is a pure phase material, and all meet I(003) / I(102)≥1.2, indicating that the degree of cation mixing of the material is low. Figure 5 As shown, the nickel-rich cathode material with a three-shell structure and nickel concentration gradient has a surface Ni element of +2 and +3 valence, Co of +4 valence, and Mn of +4 valence. Figure 6 As shown in the figure, when the nickel-rich cathode material with a nickel concentration gradient three-shell structure is used as a positive electrode material for lithium-ion batteries, it can be stably cycled for more than 100 cycles at a rate of 0.3C in the voltage range of 2.5-4.3V, and the specific capacity can still be maintained at more than 190mAh / g, which is far superior to the nickel-rich cathode material nanoparticles with the same composition. Figure 7 As shown, the exothermic peak temperature of the nickel-rich cathode material with a three-shell structure having a nickel concentration gradient appears at 272.9°C, which is higher than the exothermic peak temperature of 241.1°C of the nickel-rich cathode material nanoparticles, indicating that the nickel-rich cathode material with a three-shell structure having a nickel concentration gradient has excellent thermal stability.

[0074] Example 2

[0075] A method for preparing a hollow multi-shell structure material having a metal element concentration gradient, the method comprising:

[0076] (1) A 2.5 M sucrose aqueous solution was placed in a reactor at 180°C for hydrothermal reaction for 150 min. After natural cooling, it was filtered and washed with water three times and ethanol three times. The product was placed in a 60°C oven and dried for 24 h to obtain a carbon sphere template with a diameter of 2.7 μm.

[0077] (2) Grind 1 g of the carbon sphere template obtained in step (1) and add it to a metal salt solution with a molar ratio of 100:10:1:1, i.e., 1 M lithium acetate solution, 0.1 M nickel acetate solution, 0.01 M manganese acetate solution, and 0.01 M cobalt acetate. The solvent is a mixture of 30 ml of deionized water and 20 ml of anhydrous ethanol. Stir for 10 minutes, then sonicate for 10 minutes. After sonication, stir and adsorb at 40°C for 12 hours.

[0078] (3) 0.04 M cobalt acetate and 0.16 M manganese acetate were added to the solution obtained in (2), respectively, and the mixture was heated in a water bath at 40°C with stirring for 10 min, followed by ultrasonic adsorption for 6 min. After adsorption was complete, the suspension was filtered, washed three times with deionized water, and dried in an oven at 60°C for 24 h to obtain a solid precursor.

[0079] (4) The solid precursor obtained in step (3) was placed in a tube furnace, heated to 500°C at 2°C / min under an argon atmosphere, kept at this temperature for 2 h, and then naturally cooled to obtain a black solid powder.

[0080] (5) The black solid precursor obtained in step (4) is placed in a tube furnace, heated to 400°C at 5°C / min under an oxygen atmosphere and kept warm for 5 hours, then heated to 650°C at 5°C / min and kept warm for 15 hours to obtain a nickel-rich positive electrode material with a two-shell structure having a nickel concentration gradient, and the outermost shell diameter is about 750 nm.

[0081] like Figure 6 As shown, when the above-mentioned nickel-rich positive electrode material with a two-shell structure having a nickel concentration gradient is used as a positive electrode material for lithium-ion batteries, it can maintain a specific capacity of more than 180 mAh / g after stable cycling at a rate of 0.3C for more than 100 cycles in the voltage range of 2.5-4.3 V, and its performance far exceeds that of nickel-rich positive electrode material nanoparticles with the same composition.

[0082] Example 3

[0083] A method for preparing a hollow multi-shell structure material having a metal element concentration gradient, the method comprising:

[0084] (1) A 3M sucrose aqueous solution was placed in a reactor at 210°C for hydrothermal reaction for 120 min. After natural cooling, it was filtered and washed with water three times and ethanol three times. The product was placed in an oven at 60°C and dried for 24 h to obtain a carbon sphere template with a diameter of 3.0 μm.

[0085] (2) Grind 1 g of the carbon sphere template obtained in step (1) and add it to a metal salt solution containing 5 M lithium nitrate solution, 0.5 M nickel nitrate solution, 0.05 M manganese nitrate solution, and 0.05 M cobalt nitrate in a solvent of 30 ml of deionized water and 20 ml of anhydrous ethanol. Stir for 10 min, then sonicate for 10 min. After sonication, stir and adsorb at 20°C for 12 h.

[0086] (3) Add 5M lithium nitrate solution to the solution obtained in (2), stir at 20°C for 10 minutes, then ultrasonicate for 10 minutes, and then adsorb for 2 hours. After adsorption is completed, the suspension is filtered, washed alternately with deionized water and ethanol three times, and dried in an 80°C oven for 24 hours to obtain a solid precursor;

[0087] (4) The solid precursor obtained in step (3) was placed in a tube furnace, heated to 200°C at 0.5°C / min under a nitrogen atmosphere, kept warm for 10 hours, and then naturally cooled to obtain a black solid powder.

[0088] (5) The black solid precursor obtained in step (4) was placed in a tube furnace, heated to 350°C at 0.5°C / min under air atmosphere and kept warm for 5 hours, then heated to 650°C at 5°C / min and kept warm for 15 hours to obtain a nickel-rich positive electrode material with a three-shell structure having a lithium concentration gradient, and the outermost shell diameter was about 850 nm.

[0089] Example 4

[0090] A method for preparing a multi-shell structure material having a metal element concentration gradient, the method comprising:

[0091] (1) A 2M sucrose aqueous solution was placed in a reactor at 160°C for hydrothermal reaction for 200 min. After natural cooling, the mixture was filtered and washed with water three times and ethanol three times. The product was dried in an oven at 60°C for 24 h to obtain a carbon sphere template with a diameter of 2.6 μm.

[0092] (2) Grind 1 g of the carbon sphere template obtained in step (1) and add it to a metal salt solution containing 1 M lithium sulfate solution, 0.1 M cobalt sulfate solution, and a solvent of 30 ml deionized water and 20 ml anhydrous ethanol. Stir for 10 minutes, then sonicate for 10 minutes. After sonication, stir and adsorb at 40°C for 12 hours.

[0093] (3) Add 0.16M nickel sulfate and 0.16M manganese sulfate to the solution obtained in (2), respectively, heat in a water bath at 40°C with stirring for 10 minutes, and then ultrasonically adsorb for 10 minutes. After adsorption is complete, the suspension is filtered, washed three times with deionized water, and dried in an oven at 100°C for 24 hours to obtain a solid precursor;

[0094] (4) The solid powder obtained in (3) was redispersed in a 0.16M nickel sulfate and 0.16M manganese sulfate solution, heated in a water bath at 40°C with stirring for 10 minutes, and then ultrasonically adsorbed for 10 minutes. After adsorption, the suspension was filtered, washed three times with deionized water, and dried in an oven at 100°C for 24 hours to obtain a solid precursor;

[0095] (5) The solid precursor obtained in step (4) was placed in a tube furnace, heated to 800°C at 20°C / min under an argon atmosphere, kept at this temperature for 2 hours, and then naturally cooled to obtain a black solid powder.

[0096] (6) The black solid precursor obtained in step (4) was placed in a tube furnace, and in a mixed atmosphere of oxygen and nitrogen with an oxygen volume fraction of 80%, the temperature was raised to 300°C at 0.5°C / min and kept warm for 10 hours, and then the temperature was raised to 1000°C at 20°C / min and kept warm for 15 hours to obtain a cobalt-rich positive electrode material with a two-shell structure having a cobalt concentration gradient, and the outermost shell diameter was about 700 nm.

[0097] Example 5

[0098] A method for preparing a multi-shell structure material having a metal element concentration gradient, the method comprising:

[0099] (1) A 1.5 M sucrose aqueous solution was placed in a reactor at 200°C for hydrothermal reaction for 135 min. After natural cooling, the mixture was filtered and washed with water three times and ethanol three times. The product was dried in an oven at 60°C for 24 h to obtain a carbon sphere template with a diameter of 2.9 μm.

[0100] (2) Grind 1 g of the carbon sphere template obtained in step (1) and add it to a metal salt solution containing 1 M lithium chloride solution, 1.0 M manganese chloride solution, 0.1 M nickel chloride solution, and 0.1 M cobalt chloride in a mixture of 30 ml deionized water and 20 ml anhydrous ethanol. Stir for 10 min, then sonicate for 10 min. After sonication, stir and adsorb at 60°C for 1 h.

[0101] (3) Add 0.01M nickel chloride and 0.01M cobalt chloride to the solution obtained in (2), respectively, and heat in a water bath at 60°C with stirring for 6 minutes. After adsorption is complete, the suspension is filtered, washed twice with deionized water and methanol alternately, and dried in an oven at 100°C for 24 hours to obtain a solid precursor;

[0102] (4) The solid powder obtained in (3) was redispersed in a 0.01M nickel chloride and 0.01M cobalt chloride solution, heated in a water bath at 60°C with stirring for 6 minutes. After adsorption, the suspension was filtered, washed twice with deionized water and methanol alternately, and dried in an oven at 100°C for 24 hours to obtain a solid precursor;

[0103] (5) The solid powder obtained in (4) was redispersed in a 0.01M nickel chloride and 0.01M cobalt chloride solution, heated in a water bath at 60°C with stirring for 6 minutes. After adsorption, the suspension was filtered, washed twice with deionized water and methanol alternately, and dried in an oven at 100°C for 24 hours to obtain a solid precursor;

[0104] (6) The solid precursor obtained in step (5) was placed in a tube furnace, heated to 400°C at 2°C / min under an argon atmosphere, kept at this temperature for 5 h, and then naturally cooled to obtain a black solid powder.

[0105] (7) The black solid precursor obtained in step (6) was placed in a tube furnace, heated to 350°C at 5°C / min under an oxygen atmosphere and kept warm for 5 hours, then heated to 500°C at 5°C / min and kept warm for 30 hours to obtain a manganese-rich positive electrode material with a two-shell structure having a manganese concentration gradient, and the outermost shell diameter was about 800 nm.

[0106] Example 6

[0107] A method for preparing a multi-shell structure material having a metal element concentration gradient, the method comprising:

[0108] (1) A 1.5 M sucrose aqueous solution was placed in a reactor at 190°C for hydrothermal reaction for 140 min. After natural cooling, it was filtered and washed with water three times and ethanol three times. The product was placed in a 60°C oven and dried for 24 h to obtain a carbon sphere template with a diameter of 2.8 μm.

[0109] (2) Grind 1 g of the carbon sphere template obtained in step (1) and add it to a metal salt solution containing 4 M lithium nitrate solution, 0.4 M nickel nitrate solution, 0.04 M manganese acetate solution, and 0.04 M cobalt acetate in a mixture of 30 ml deionized water and 20 ml anhydrous ethanol. Stir for 10 minutes, then sonicate for 10 minutes. After sonication, stir and adsorb at 40°C for 48 hours.

[0110] (3) 0.04M cobalt acetate and 0.04M manganese acetate were added to the solution obtained in (2), respectively, and the mixture was heated in a water bath at 40°C with stirring for 10 minutes, followed by ultrasonic adsorption for 10 minutes. After adsorption was complete, the suspension was filtered, washed three times with deionized water, and dried in an oven at 60°C for 24 hours to obtain a solid precursor.

[0111] (4) The solid precursor obtained in step (3) was placed in a tube furnace, heated to 500°C at 2°C / min under an argon atmosphere, kept at this temperature for 2 h, and then naturally cooled to obtain a black solid powder.

[0112] (5) The black solid precursor obtained in step (4) is placed in a tubular furnace, and in a mixed atmosphere of nitrogen and oxygen with an oxygen volume fraction of 10%, the temperature is raised to 500°C at 10°C / min and kept warm for 1 hour, and then the temperature is raised to 1000°C at 10°C / min and kept warm for 15 hours to obtain a nickel-rich positive electrode material with a two-shell structure having a nickel concentration gradient, and the outermost shell diameter is about 850nm.

[0113] Example 7

[0114] A method for preparing a multi-shell structure material having a metal element concentration gradient, the method comprising:

[0115] (1) A 1.5 M sucrose aqueous solution was placed in a reactor at 190°C for hydrothermal reaction for 140 min. After natural cooling, it was filtered and washed with water three times and ethanol three times. The product was placed in a 60°C oven and dried for 24 h to obtain a carbon sphere template with a diameter of 2.8 μm.

[0116] (2) Grind 1 g of the carbon sphere template obtained in step (1) and add it to a nickel acetate solution with a nickel acetate concentration of 0.3 M and a solvent of a mixture of 30 ml of deionized water and 20 ml of anhydrous ethanol. Stir for 10 minutes and then sonicate for 10 minutes. After sonication, stir and adsorb at 40°C for 48 hours.

[0117] (3) Add 0.01 M cobalt acetate to the solution obtained in (2), heat in a water bath at 40°C with stirring for 10 minutes, and then ultrasonically adsorb for 10 minutes. After adsorption is complete, the suspension is filtered, washed three times with deionized water, and dried in an oven at 60°C for 24 hours to obtain a solid precursor;

[0118] (4) The solid precursor obtained in step (3) was placed in a tube furnace, heated to 500°C at 2°C / min under an argon atmosphere, kept at this temperature for 2 h, and then naturally cooled to obtain a black solid powder.

[0119] (5) The black solid precursor obtained in step (4) is placed in a tube furnace, and in a mixed atmosphere of nitrogen and oxygen with an oxygen volume fraction of 25%, the temperature is raised to 350°C at 5°C / min and kept warm for 5 hours, and then the temperature is raised to 600°C at 10°C / min and kept warm for 15 hours to obtain a nickel-cobalt oxide material with a three-shell structure having a nickel concentration gradient, and the outermost shell diameter is about 900 nm.

[0120] Example 8

[0121] A method for preparing a multi-shell structure nickel-rich positive electrode material, the method comprising:

[0122] (1) A 1.5 M sucrose aqueous solution was placed in a reactor at 190°C for hydrothermal reaction for 140 min. After natural cooling, it was filtered and washed with water three times and ethanol three times. The product was placed in a 60°C oven and dried for 24 h to obtain a carbon sphere template with a diameter of 2.8 μm.

[0123] (2) Grind 1 g of the carbon sphere template obtained in step (1) and add it to a metal salt solution with a molar ratio of 100:10:1:1, i.e., 2 M lithium acetate solution, 0.2 M nickel acetate solution, 0.02 M manganese acetate solution, and 0.02 M cobalt acetate. The solvent is a mixture of 30 ml of deionized water and 20 ml of anhydrous ethanol. Stir for 10 minutes, then ultrasonicate for 10 minutes. After the ultrasonication is completed, stir and adsorb at 40°C for 48 hours.

[0124] (3) The solid precursor obtained in step (2) was placed in a tubular furnace, and the temperature was raised to 500°C at 2°C / min under an argon atmosphere, and kept warm for 2 hours. Then, the temperature was raised to 350°C at 10°C / min under an oxygen atmosphere and kept warm for 5 hours. Then, the temperature was raised to 650°C at 10°C / min and kept warm for 15 hours to obtain a three-shell nickel-rich positive electrode material, and the outermost shell diameter was about 800 nm.

[0125] The present invention is based on the sequential template method and adopts a secondary adsorption strategy combined with a secondary calcination treatment. The secondary adsorption can regulate the gradient distribution of the metal ion precursor in the template. The secondary calcination treatment is first calcined in an inert atmosphere to fix the position of the metal ions, and then calcined in an oxidizing atmosphere to remove the template, thereby synthesizing a multi-shell structure material with a metal element concentration gradient, and regulating the concentration of the metal ion precursor in the solution, adsorption order, adsorption time, calcination temperature and calcination time and other conditions, so as to accurately control the number of shells and effectively control the gradient distribution of the metal element concentration in the shells.

[0126] Any content not described in detail in the present invention can be based on conventional technical knowledge in the art.

[0127] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and are intended to be encompassed by the claims of the present invention.

Claims

1. A method for preparing a hollow multi-shell structure material having a metal element concentration gradient, comprising the following steps: 1) The carbon source aqueous solution is subjected to a hydrothermal reaction, and after filtration, washing, and drying, a micro-nano-sized colloidal carbon sphere template is obtained; 2) dispersing the colloidal carbon sphere template obtained in step 1) in a metal salt solution to obtain a suspension, stirring, heat preservation, and adsorption to obtain a suspension; 3) adding the metal salt solution again to the suspension obtained in step 2) for secondary adsorption, filtering, and drying to obtain a secondary adsorbed solid precursor; 4) calcining the solid precursor obtained in step 3) at a high temperature under an inert atmosphere to obtain a solid powder; 5) calcining the solid powder obtained in step 4) at a high temperature under an oxygen or air atmosphere to obtain a hollow multi-shell structure material having a metal element concentration gradient; In step 4), the calcination temperature is 200-800°C, the calcination time is 0.5-10 h, and the calcination heating rate is 0.5-20°C / min; The roasting in step 5) comprises a two-step roasting process; The first step is calcination at a temperature of 300-500 °C, a calcination time of 1-10 h, and a calcination heating rate of 0.5-10 °C / min; The second step is calcination at a temperature of 500-1000 °C, a calcination time of 15-30 h, and a calcination heating rate of 0.5-20 °C / min.

2. The preparation method according to claim 1, characterized in that The solvent of the metal salt solution in step 2) is one or more of water, acetone and ethanol; The metal salt includes one or more of lithium chloride, nickel chloride, manganese chloride, cobalt chloride, lithium acetate, nickel acetate, manganese acetate tetrahydrate, cobalt acetate, lithium sulfate, nickel sulfate, manganese sulfate, cobalt sulfate, lithium nitrate, nickel nitrate, manganese nitrate, and cobalt nitrate; The concentration of the metal salt solution in step 2) is 0.01-5M; In step 2), the adsorption temperature is 20-60°C, and the adsorption time is 1-48 h.

3. The preparation method according to claim 1, characterized in that The solvent of the metal salt solution in step 3) is one or more of water, acetone and ethanol; The metal salt includes one or more of lithium chloride, nickel chloride, manganese chloride, cobalt chloride, lithium acetate, nickel acetate, manganese acetate tetrahydrate, cobalt acetate, lithium sulfate, nickel sulfate, manganese sulfate, cobalt sulfate, lithium nitrate, nickel nitrate, manganese nitrate, and cobalt nitrate; The concentration of the metal salt solution in step 3) is 0.01-5M; In step 3), the adsorption temperature is 20-60°C, the adsorption time is 0.1-2 h, the drying temperature is 60-100°C, and the drying time is 6-24 h; The adsorption, filtration and drying processes in step 3) can be repeated multiple times to obtain a solid precursor after multiple adsorptions.

4. The preparation method according to claim 1, characterized in that The inert atmosphere in step 4) is argon or nitrogen.

5. A hollow multi-shell structure material with a metal element concentration gradient, characterized in that: The hollow multi-shell structure material with a metal element concentration gradient is obtained by the preparation method according to any one of claims 1 to 4.

6. The hollow multi-shell structure material with a metal element concentration gradient according to claim 5, characterized in that: The metal element concentration gradient means that the concentration of one metal element in different shell layers from the inside to the outside is distributed from high to low, and correspondingly, the concentration of other metal elements is distributed from low to high. The metal elements with concentration gradient include one or more of lithium, nickel, cobalt and manganese; The hollow multi-shell structure material includes at least one cavity and at least two layers of shell walls.

7. Application of the multi-shell structure material with metal element concentration gradient according to claim 5 or 6 in energy storage.

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