Chromium site high-entropy chromium lithium titanate material, preparation method and application thereof

Abstract

The application discloses a chromium-site high-entropy lithium chromic titanate material and a preparation method and application thereof, and belongs to the technical field of electrochemical energy storage materials.The crystal structure of the chromium-site high-entropy lithium chromic titanate material is a single spinel solid solution phase, and a chemical general formula thereof is Li(Cr 1‑x‑y‑z‑w V x Fe y Mn z Al w )TiO4.The preparation method is fast synthesis by one-step combustion method with chromium trioxide as an oxidizing agent and a carbohydrate as a reducing agent.The chromium-site high-entropy lithium chromic titanate material prepared by the application has high specific capacity and excellent cycle stability, and can be applied as a lithium ion battery negative electrode material.The application effectively solves the problems of limited theoretical capacity and poor rate performance of existing lithium chromic titanate materials, and provides a new way for developing high-performance lithium ion battery negative electrode materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrochemical energy storage materials, and relates to a high-capacity chromium lithium titanate negative material for a lithium ion battery, in particular to a chromium-site high-entropy chromium lithium titanate material and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of portable electronic devices, electric vehicles and large-scale energy storage power grids, the market demands lithium ion batteries with high energy density, high power density, long cycle life and high safety. The performance of the negative electrode material, as a core component of the lithium ion battery, directly determines the overall performance of the battery. Currently, commercial lithium ion batteries mainly use graphite-based carbon materials as the negative electrode. Although such materials have advantages in cost and process maturity, their working potential is close to the deposition potential of metallic lithium, and there is a risk of short circuit and thermal runaway caused by the formation of lithium dendrites during overcharging. In addition, the low first coulomb efficiency and poor compatibility with some electrolytes also limit their application in high-performance batteries.

[0003] Spinel lithium titanate (Li4Ti5O 12 , LTO) has great development prospects as a negative electrode material due to its nearly "zero strain" structure during lithium ion intercalation / deintercalation, which enables it to have an ultra-long cycle life and excellent safety. However, the intrinsic electronic conductivity of LTO is extremely low (about 10 -13 S / cm), and the lithium ion diffusion coefficient is small, which results in poor rate performance and makes it difficult to meet the demand for high-power charging and discharging. At the same time, the theoretical specific capacity of LTO is relatively limited (about 175 mAh / g), which also restricts the further improvement of the energy density of the battery. Therefore, developing new negative electrode material systems has become an important research direction in the industry.

[0004] In comparison, lithium chromium titanate (LiCrTiO4, LCT) of spinel structure, while maintaining similar "zero strain" characteristics and high safety, shows better intrinsic electronic conductivity than LTO, making it more potential in high-rate applications. Existing modification researches on LCT have borrowed relatively mature experiences from LTO, but the overall research depth and breadth are limited, and the ideas are relatively traditional. Existing researches are mostly focused on traditional element doping or surface complexing / coating. For example, by introducing a single element (such as Cr, Al) for doping to optimize the intrinsic conductivity or voltage platform of the material, or by complexing with carbon materials or other active materials to build a conductive network. However, the optimization effect of single element doping has an upper limit, and it is often only possible to improve a certain performance indicator of the material, making it difficult to achieve simultaneous improvement of comprehensive performance. In addition, the existing synthesis methods of LCT, such as high-temperature solid-phase method, sol-gel method, etc., generally have complex process flow, long reaction time, high energy consumption or high cost, etc., which are not conducive to large-scale industrial application.

[0005] In summary, the current modification researches on LCT negative electrode materials have not yet made breakthrough progress in improving its intrinsic specific capacity, and the existing methods are difficult to achieve improvement of the comprehensive performance (such as capacity, rate, structural stability) of the material.

[0006] Therefore, there is an urgent need for a method that can simultaneously improve the comprehensive performance of LCT material, and has a simple process and is easy to industrialize. SUMMARY

[0007] The technical problem to be solved by the present application is the limited theoretical specific capacity and poor rate performance of existing lithium chromium titanate materials.

[0008] To achieve the above application purposes, the technical solutions adopted by the present application are as follows.

[0009] In a first aspect, the present application provides a chromium-site high-entropy lithium chromium titanate (CrHELCT) material, the crystal structure of the chromium-site high-entropy lithium chromium titanate material is a single spinel solid solution phase, and its chemical general formula is Li(Cr 1-x-y-z-w V x Fe y Mn z Al w )TiO4;

[0010] Wherein, x, y, z, w satisfy 0

[0011] Further, the configuration entropy of the above-mentioned chromium-site high-entropy lithium chromite titanate material is greater than 1.3R;

[0012] Wherein, R is the gas constant, and the value is 8.314 J / (mol.K).

[0013] In a second aspect, the present application provides a preparation method of the above-mentioned chromium-site high-entropy lithium chromite titanate material, comprising the following steps:

[0014] S1. According to the stoichiometric ratio of the above-mentioned chemical formula, the chromium source, the titanium source, the lithium source, the vanadium source, the iron source, the manganese source and the aluminum source are weighed, mixed with the carbohydrate and ground to form a precursor;

[0015] Wherein, the chromium source is chromium trioxide (CrO3), and the atomic molar number of carbon elements in the carbohydrate is 2-6 times that of chromium elements in the chromium source;

[0016] S2. The precursor is transferred to an open high-temperature resistant container, and then placed in a reaction device preheated to a set temperature, and fully combusted in an air atmosphere. After the reaction is completed, it is air-cooled to room temperature to obtain a chromium-site high-entropy lithium chromite titanate material;

[0017] Wherein, the set temperature is 750-950℃.

[0018] In the above step S1, the atomic molar number of carbon elements in the carbohydrate is 2-3 times that of chromium elements in the chromium source.

[0019] In the above step S1, the titanium source is at least one of titanium dioxide, titanyl sulfate, and tetrabutyl titanate.

[0020] In the above step S1, the lithium source is at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, and lithium chloride.

[0021] In the above step S1, the vanadium source is at least one of vanadium pentoxide, ammonium metavanadate, and vanadyl sulfate.

[0022] In the above step S1, the iron source is at least one of ferrous sulfate, ferrous sulfate, and high-iron sulfate.

[0023] In the above step S1, the manganese source is at least one of manganese dioxide, manganese sulfate, and manganese acetate.

[0024] In the above step S1, the aluminum source is at least one of aluminum oxide, aluminum sulfate, and aluminum chloride.

[0025] In the above step S1, the carbohydrate is at least one of glucose, sucrose, and starch.

[0026] In the step S1, the mixture is ground with an appropriate amount of liquid medium until the mixture forms a uniform, non-flowing paste-like precursor;

[0027] The liquid medium is polyethylene glycol 400 (PEG400) or polyethylene glycol 400 and water.

[0028] In the step S2, the loading amount of the precursor is 1 / 4 to 3 / 4 of the volume of the open high-temperature-resistant container.

[0029] In the step S2, the combustion reaction starts after the temperature in the reaction device recovers to the set temperature, and the time is 30 to 360 minutes.

[0030] In the step S2, the set temperature is 800℃.

[0031] In a third aspect, the application provides the application of the above-mentioned chromium-site high-entropy lithium chromite titanate material or the chromium-site high-entropy lithium chromite titanate material prepared by the above-mentioned preparation method in lithium ion batteries.

[0032] The application has the following beneficial effects: The application provides a modification method of a "chromium-site high-entropy" lithium chromite titanate material, which breaks through the limitation of traditional single or double element doping, successfully constructs a single spinel structure high-entropy solid solution with good crystallinity, i.e., a chromium-site high-entropy lithium chromite titanate material, by introducing multiple metal elements such as iron (Fe), aluminum (Al), manganese (Mn), and vanadium (V) into the chromium (Cr) lattice site of LCT in a near-equal molar ratio. The high-entropy modification strategy used in the application optimizes the electronic structure and ion transport dynamics of the material, which significantly improves the lithium storage capacity of the material compared with the unmodified lithium chromite titanate, and exhibits excellent cycle stability and structural reversibility at a low rate. At the same time, the combustion synthesis process used in the application utilizes the high-efficiency self-propagating reaction, which greatly shortens the synthesis time, reduces the energy consumption and process complexity, and shows good industrial application potential, providing an effective technical path for developing new high-performance lithium ion battery anode materials. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The XRD pattern of the chromium-site high-entropy lithium chromite titanate material prepared in Example 1 is shown in the figure;

[0034] Figure 2 The discharge specific capacity graph of the chromium-site high-entropy lithium chromite titanate material prepared in Example 1 at 1C rate is shown in the figure;

[0035] Figure 3 The XRD pattern of the chromium-site high-entropy lithium chromite titanate material prepared in Example 2 is shown in the figure;

[0036] Figure 4 The SEM photo of the chromium-site high-entropy lithium chromite titanate material prepared in Example 2 is shown in the figure;

[0037] Figure 5 XRD pattern of the Cr-site high-entropy lithium titanate-chromium material prepared for Example 3;

[0038] Figure 6 XRD pattern of the Cr-site high-entropy lithium titanate-chromium material prepared for Example 4;

[0039] Figure 7 XRD pattern of the Cr-site high-entropy lithium titanate-chromium material prepared for Example 5;

[0040] Figure 8 Discharge specific capacity graph of the Cr-site high-entropy lithium titanate-chromium material prepared for Example 5 at different rates;

[0041] Figure 9 XRD pattern of the Cr-site high-entropy lithium titanate-chromium material prepared for Example 6;

[0042] Figure 10 Discharge specific capacity graph of the Cr-site high-entropy lithium titanate-chromium material prepared for Example 6 at different rates;

[0043] Figure 11 XRD pattern of the lithium titanate-chromium material prepared for Comparative Example 1;

[0044] Figure 12 Discharge specific capacity graph of the lithium titanate-chromium material prepared for Comparative Example 1 at different rates;

[0045] Figure 13 XRD pattern of the lithium titanate-chromium material prepared for Comparative Example 2. DETAILED DESCRIPTION

[0046] In order to make the technical problems, technical solutions and beneficial effects to be solved in the present application more clearly understood, the present application will be further described in detail below in conjunction with the embodiments. Unless otherwise defined, all technical terms used herein have the same meanings as understood by those skilled in the art.

[0047] The present application provides a CrHELCT material and a high-entropy modification method thereof, wherein the crystal structure of the CrHELCT material is a single spinel solid solution phase, and the chemical general formula thereof is Li(Cr 1-x-y-z-w V x Fe y Mn z Al w )TiO4;wherein the molar fractions x, y, z and w of each element satisfy: 0 < x ≤ 0.2, 0 < y ≤ 0.2, 0 < z ≤ 0.1, 0 < w ≤ 0.1 and 0 < x + y + z + w ≤ 0.5.

[0048] LCT has similar "zero strain" characteristics as LTO, and better electrical conductivity than LTO, but slightly smaller electrochemical specific capacity than LTO. In order to improve the electrochemical capacity and comprehensive electrochemical performance of LCT, the present application proposes a "chromium site high-entropy" modification method to prepare CrHELCT material. The modification method of the present application uses LCT as the matrix, and introduces Fe, V, Mn and Al into the Cr site in a specific ratio to construct a multi-principal-element high-entropy solid solution. Among them, the introduction of Fe and V aims to synergistically improve the reversible capacity and electronic conductivity of the material; the introduction of Mn and Al is mainly used to stabilize the spinel structure. The combination of Fe, V, Mn, Al and Cr in LCT produces a high-entropy effect, and through strong "cocktail" synergistic effect and lattice distortion between elements, the electronic structure and lithium ion transport dynamics of the material are synergistically controlled, thereby significantly improving the electrochemical performance of the LCT material, and the comprehensive electrochemical performance of the obtained CrHELCT material is obviously improved.

[0049] The CrHELCT material described in the present application is prepared by a one-step combustion synthesis method based on the principle of self-propagating combustion, the core of which is to use CrO3 as the chromium source and oxidizing agent, and a carbohydrate as the reducing agent, to form a fast and efficient redox reaction system, and to modify LCT through Cr site high-entropy. The preparation method of the CrHELCT material specifically includes the following steps.

[0050] Step one, precursor preparation: accurately weigh the chromium source, titanium source, lithium source, vanadium source, iron source, manganese source and aluminum source according to the stoichiometric ratio of the chemical formula of the target product. Put the weighed solid metal raw materials and carbohydrate reducing agent together in a mortar, add an appropriate amount of liquid medium containing PEG400, and grind thoroughly until the mixture forms a uniform, non-natural flow paste-like precursor.

[0051] In an embodiment of the present application, the chromium source is CrO3; the titanium source is at least one of titanium dioxide, titanyl sulfate, and tetrabutyl titanate; the lithium source is at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, and lithium chloride; the vanadium source is at least one of divanadium pentoxide, ammonium metavanadate, and vanadyl sulfate; the iron source is at least one of diiron trioxide, ferrous sulfate, and high iron sulfate; the manganese source is at least one of manganese dioxide, manganese sulfate, and manganese acetate; the aluminum source is at least one of aluminum oxide, aluminum sulfate, and aluminum chloride; and the carbohydrate is at least one of glucose, sucrose, and starch. Among them, CrO3 not only provides chromium elements, but more importantly, as a strong oxidizing agent, it decomposes and releases oxygen at high temperatures and provides the heat required for reaction initiation, which is the basis for forming a combustion reaction system. If other valence chromium sources (such as Cr2O3) are used, it will not be able to provide enough oxidation potential and instantaneous heat, resulting in incomplete combustion reaction or no reaction.

[0052] In one embodiment of the present application, the atomic mole number of carbon element in the carbohydrate is 2-6 times of the atomic mole number of chromium element in the chromium source. The addition amount of the reducing agent is the key to control the intensity of the combustion reaction and the purity of the product. The appropriate amount of carbon as the reducing agent has a violent oxidation reaction with the oxygen released by the decomposition of CrO3, provides most of the heat required for the synthesis reaction, and provides a strong reducing atmosphere to promote the reduction of each metal oxide and the mutual reaction to form the spinel phase. If the atomic mole ratio of C:Cr is too low, it may lead to unreacted CrO3 residues or the presence of high-valence impurities in the product; if the ratio is too high, the reaction is too violent and difficult to control, and the free carbon remaining after combustion may be too much, which requires a longer subsequent oxidation time to remove it, and may affect the purity and performance of the product. In order to ensure sufficient and rapid reaction, while achieving the best energy utilization and product quality control, it is preferred that the atomic mole number of carbon element in the carbohydrate is 2-3 times of the atomic mole number of chromium element in the chromium source.

[0053] Those skilled in the art can understand that the core of step one of the present application is to finally generate a material that meets the target chemical formula Li(Cr 1-x-y-z-w V x Fe y Mn z Al w )TiO4. Therefore, the weighing of each raw material should be based on the stoichiometric relationship in the formula. In actual high-temperature combustion synthesis process, a small amount of some raw materials (especially lithium-containing compounds) may be volatilized or burned during the violent combustion reaction and subsequent holding process. In order to ensure that the stoichiometric ratio of the final product is as close to the theoretical design value as possible, those skilled in the art will usually make an appropriate excess of the volatile component when batching according to the properties of the selected specific raw material, the reaction temperature and time, which is a common and necessary process compensation means in the art. For example, in a specific embodiment of the present application, the raw material mole feeding ratio of Li:(Cr 1-x-y-z-w V x Fe y Mn z Al w ):Ti=1.1:1:1 is used. Among them, the feeding amount of lithium element is about 10% more than the theoretical value, which aims to compensate for the possible high-temperature lithium loss, so as to ensure the actual content of lithium in the product. The feeding amount of chromium site total metal (Cr, V, Fe, Mn, Al) and Ti strictly follows the theoretical stoichiometric ratio in the formula. This adjustment of the feeding amount of a specific raw material to achieve the target chemical composition, which conforms to the technical common sense in the art, does not deviate from the core limitation of batching based on the stoichiometric relationship of the formula in the present application, and belongs to the protection scope of the present application.

[0054] The skilled in the art can understand that the core of step one of the present application is to obtain a precursor with a specific physical state by grinding, i.e. to ensure that the final material is in the form of a uniform paste without natural fluidity. The scope of protection of the grinding step is not limited to the specific operation parameters and feeding sequence given in the examples. In actual process implementation, as long as the above core objective can be achieved, the skilled in the art can make routine adjustments and optimizations to the grinding time, the type and amount of liquid medium, and the addition sequence of each raw material, etc. according to the actual material properties. For example, in a specific embodiment of the present application, the metal raw material can be mixed with part of the liquid medium and ground to a paste, and then the reducing agent and the remaining liquid medium are added for further mixing; or step-by-step grinding, batch liquid addition, etc. can be used. Any routine adjustment or equivalent replacement made to the technical solution under the premise of not deviating from the core idea of the present application, i.e. ultimately forming a uniform paste-like precursor without fluidity, should be covered within the protection scope of the present application.

[0055] Step two, combustion synthesis reaction: the paste-like precursor obtained in step one is transferred to an open high-temperature-resistant container (such as a corundum crucible), and the container containing the material is quickly placed into a reaction device (such as a muffle furnace) preheated to a target temperature of 750-950°C. The precursor is quickly ignited in a high-temperature environment (air atmosphere) and undergoes a violent combustion reaction. After the reaction is completed, the product is naturally cooled to room temperature in an air atmosphere to obtain a loose and porous foam-like solid. Grinding the foam-like solid can obtain spinel-type chromium-site high-entropy lithium chromite material powder with uniform particle size.

[0056] In an embodiment of the present application, the filling volume of the precursor is about 1 / 4 to 3 / 4 of the volume of the open high-temperature-resistant container. If the filling amount is too small, the thermal effect is weak and the reaction may not be self-sustaining; if the filling amount is too large, the reaction may be too violent, the material may splash, or the heat accumulation may be too high to affect the product morphology.

[0057] In an embodiment of the present application, the temperature of the combustion reaction is 750-950°C. If the temperature is too low, the precursor may not be ignited, leading to difficult start of the combustion reaction or too slow reaction speed, which cannot utilize the self-propagating characteristics and results in poor crystallinity of the product; if the temperature is too high, the reaction degree is difficult to control, which may lead to volatilization loss of part of the low-boiling-point components, abnormal grain growth, and is not conducive to obtaining a material with excellent performance. Preferably, the temperature of the combustion reaction is 800°C, and the product obtained by performing the combustion reaction at this temperature has good crystallinity and ideal particle morphology.

[0058] In an embodiment of the present application, the combustion reaction is started after the temperature of the muffle furnace recovers to the set temperature, and the holding time is 30-360 minutes. The purpose of holding is to promote atomic diffusion, ensure the formation of a single spinel phase that is thermodynamically stable, and obtain sufficient crystallinity.

[0059] The application also provides the use of the above-mentioned CrHELCT material in lithium ion batteries. The material exhibits high specific capacity and good cycle stability at low rates, and is therefore particularly suitable for applications requiring high energy density and cycle life, such as energy storage.

[0060] To adapt the material to a wider range of application conditions (e.g. high-rate charging and discharging), those skilled in the art can perform secondary processing on the material according to conventional techniques. For example, a conductive carbon layer can be formed on the surface of the material particles by conventional carbon source coating and heat treatment processes, or the particle size and morphology can be regulated by conventional nanocrystallization processes to improve the specific capacity and cycle stability of the material at high rates, thereby further optimizing its electrochemical performance.

[0061] Those skilled in the art will understand that secondary processing such as surface coating of a conductive carbon layer, regulation of particle size, etc. on the CrHELCT material of the application is a conventional optimization method when it is applied to a specific lithium ion battery device. These subsequent processes are based on and premised on the specific chemical composition and crystal structure of the CrHELCT material provided by the application. Therefore, whether or not such conventional optimization is performed, or whether it is applied to what specific type of battery device, as long as the active material component includes the CrHELCT material described in the application, it should be considered to fall within the scope of protection of the application.

[0062] The following specific examples will be used to explain the scheme of the application. Those skilled in the art will understand that the following examples are only used to illustrate the application and should not be considered as limiting the scope of the application. If the specific techniques or conditions are not specified in the examples, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be obtained commercially.

[0063] Example 1: Preparation of a CrHELCT material with the chemical formula Li(Cr 0.84 V 0.03 Fe 0.02 Mn 0.05 Al 0.06 )TiO4, the specific steps are as follows.

[0064] (1) CrO3 is used as the chromium source and oxidant, titanium dioxide is used as the titanium source, lithium carbonate is used as the lithium source, ammonium metavanadate is used as the vanadium source, diiron trioxide is used as the iron source, manganese dioxide is used as the manganese source, aluminum oxide is used as the aluminum source, and glucose is used as the reducing agent. The molar ratio of Li:(Cr 0.84 V 0.03 Fe 0.02 Mn 0.05 Al 0.06):Ti=1.1:1:1 of molar ratio, the atomic molar ratio of carbon element in the reducing agent and chromium element in the chromium source is controlled to be 2:1 (i.e. the atomic molar number of carbon element in the reducing agent is 2 times of the atomic molar number of chromium element in the chromium source).

[0065] (2) Mix the raw materials except the reducing agent, add an appropriate amount of deionized water and grind for 15 minutes, add the reducing agent and grind for 5 minutes, and finally add 3% PEG400 of the total mass of solids to continue grinding for 5 minutes to form a uniform, non-natural flow paste-like precursor.

[0066] (3) Transfer the precursor to an open corundum crucible (loading amount is about 1 / 2), and put it into a muffle furnace preheated to 750°C. The material undergoes self-propagating combustion reaction, and after the furnace temperature recovers to 750°C, it is kept for 360 minutes. After the reaction is completed, it is air-cooled to room temperature, ground, and Li(Cr 0.84 V 0.03 Fe 0.02 Mn 0.05 Al 0.06 )TiO4 powder is obtained.

[0067] The configuration entropy of the obtained Li(Cr 0.84 V 0.03 Fe 0.02 Mn 0.05 Al 0.06 )TiO4 material is about 1.315R (R is the gas constant, and its value is 8.314 J / mol·K), indicating that it has successfully realized high entropy. The XRD pattern (X-ray diffraction pattern) Figure 1 ) shows that all the diffraction peaks are consistent with the standard card of spinel structure, and there is no impurity phase peak, indicating that the product is a pure spinel phase with good crystallinity. Electrochemical test shows that its initial specific discharge capacity at 0.1C rate is 168 mAh / g; its capacity retention rate after 100 cycles at 1C rate is 100% (the capacity retention rate is the ratio of the capacity after 100 cycles to the initial capacity) Figure 2 ), showing excellent cycle stability.

[0068] Example 2: Preparation of chromium site high-entropy chromium titanate lithium material, its chemical formula is Li(Cr 0.5 V 0.2 Fe 0.1 Mn 0.1 Al 0.1 )TiO4, the specific steps are as follows.

[0069] (1) CrO3 is used as chromium source and oxidant, tetrabutyl titanate is used as titanium source, lithium acetate is used as lithium source, ammonium metavanadate is used as vanadium source, ferrous sulfate is used as iron source, manganese acetate is used as manganese source, aluminum sulfate is used as aluminum source, and sucrose is used as reducing agent. According to Li:(Cr 0.5 V 0.2 Fe 0.1 Mn0.1 Al 0.1 ):Ti=1.1:1:1 of each raw material, control the atomic mole ratio of carbon element in reducing agent and chromium element in chromium source is 4:1.

[0070] (2) CrO3, ammonium metavanadate, ferrous sulfate and aluminum sulfate were mixed and ground for 15 minutes, titanium tetrabutoxide, lithium acetate and manganese acetate were added and ground for 15 minutes, reducing agent was added and ground for 5 minutes, finally 1% PEG400 and appropriate amount of deionized water were added to form a uniform, non-natural flow paste precursor.

[0071] (3) The precursor was transferred to an open corundum crucible (loading amount was about 1 / 3), and was put into a muffle furnace preheated to 800℃. The material underwent self-propagating combustion reaction, and after the furnace temperature recovered to 800℃, it was kept for 180 minutes. After the reaction was completed, it was air-cooled to room temperature, ground, and Li(Cr 0.5 V 0.2 Fe 0.1 Mn 0.1 Al 0.1 )TiO4 powder was obtained.

[0072] The configuration entropy of the obtained Li(Cr 0.5 V 0.2 Fe 0.1 Mn 0.1 Al 0.1 )TiO4 material was about 1.552R. The XRD pattern ( Figure 3 ) showed that it was a pure spinel phase with good crystallinity. The SEM photo ( Figure 4 ) showed that the grain growth was sufficient, the arrangement was dense, and the average particle size was about 1 micron. Electrochemical test showed that the initial discharge specific capacity at 0.1C rate was 268mAh / g.

[0073] Example 3: Preparation of chromium site high-entropy chromium titanate lithium material, its chemical formula is Li(Cr 0.7 V 0.15 Fe 0.1 Mn 0.025 Al 0.025 )TiO4, the specific steps are as follows.

[0074] (1) CrO3 was used as chromium source and oxidant, titanium dioxide was used as titanium source, lithium hydroxide was used as lithium source, vanadium pentoxide was used as vanadium source, diiron trioxide was used as iron source, manganese dioxide was used as manganese source, aluminum chloride was used as aluminum source, and starch was used as reducing agent. According to Li:(Cr 0.7 V 0.15 Fe 0.1 Mn 0.025 Al 0.025:Ti = 1.1:1:1, and the atomic mole ratio of carbon in the reducing agent to chromium in the chromium source was controlled to be 6:1.

[0075] (2) The raw materials except the reducing agent were mixed, and an appropriate amount of deionized water was added for grinding for 15 minutes. The reducing agent was added for grinding for 5 minutes. Finally, 5% of PEG400 based on the total mass of solids was added for continuous grinding for 5 minutes, to form a uniform, non-naturally flowing paste-like precursor.

[0076] (3) The precursor was transferred to an open corundum crucible (filling amount about 2 / 3), and placed into a muffle furnace preheated to 950°C. The material underwent a self-propagating combustion reaction. After the furnace temperature recovered to 950°C, it was kept for 30 minutes. After the reaction was completed, it was air-cooled to room temperature, ground, and Li(Cr 0.7 V 0.15 Fe 0.1 Mn 0.025 Al 0.025 )TiO4 powder was obtained.

[0077] The configuration entropy of the obtained Li(Cr 0.7 V 0.15 Fe 0.1 Mn 0.025 Al 0.025 )TiO4 material was about 1.415R. The XRD pattern (Fig. 1) showed that it was a pure spinel phase with good crystallinity. Electrochemical tests showed that its initial specific discharge capacity at 0.1C rate was 225mAh / g. Figure 5

[0078] Example 4: Preparation of a chromium-site high-entropy chromium lithium titanate material with the chemical formula Li(Cr 0.55 V 0.15 Fe 0.1 Mn 0.1 Al 0.1 )TiO4, the specific steps are as follows.

[0079] (1) CrO3 was used as the chromium source and oxidant, titanium dioxide was used as the titanium source, lithium chloride was used as the lithium source, vanadium pentoxide was used as the vanadium source, iron trioxide was used as the iron source, manganese dioxide was used as the manganese source, and aluminum oxide was used as the aluminum source. Glucose and starch (mixed in a mass ratio of 1:1) were used as the reducing agent. The molar ratio of Li:(Cr 0.55 V 0.15 Fe 0.1 Mn 0.1 Al 0.1 ):Ti = 1.1:1:1, and the atomic mole ratio of carbon in the reducing agent to chromium in the chromium source was controlled to be 4:1.

[0080] ​(2) Mix the raw materials except the reducing agent, add appropriate amount of deionized water and grind for 15 minutes, add the reducing agent and grind for 5 minutes, finally add 4% PEG400 of the total mass of solids and continue to grind for 5 minutes to form a uniform, non-natural flow paste-like precursor.

[0081] (3) Transfer the precursor to an open corundum crucible (loading amount is about 1 / 3), and put it into a muffle furnace preheated to 800°C. The material undergoes self-propagating combustion reaction, and after the furnace temperature recovers to 800°C, it is kept for 120 minutes. After the reaction is completed, it is air-cooled to room temperature, ground, and Li(Cr 0.55 V 0.15 Fe 0.1 Mn 0.1 Al 0.1 )TiO4 powder is obtained.

[0082] The configuration entropy of the obtained Li(Cr 0.55 V 0.15 Fe 0.1 Mn 0.1 Al 0.1 )TiO4 material is about 1.533R. The XRD pattern ( Figure 6 ) shows that it is a pure spinel phase with good crystallinity. Electrochemical test shows that its initial discharge specific capacity at 0.1C rate is 252mAh / g.

[0083] Example 5: Preparation of chromium site high-entropy chromium lithium titanate material with the chemical formula Li(Cr 0.6 V 0.1 Fe 0.2 Mn 0.05 Al 0.05 )TiO4, the specific steps are as follows.

[0084] (1) CrO3 is used as chromium source and oxidant, titanium dioxide is used as titanium source, lithium carbonate is used as lithium source, ammonium metavanadate is used as vanadium source, high-iron sulfate is used as iron source, manganese sulfate is used as manganese source, and aluminum sulfate is used as aluminum source. Starch is used as reducing agent. According to the molar ratio of Li:(Cr 0.6 V 0.1 Fe 0.2 Mn 0.05 Al 0.05 ):Ti=1.1:1:1, each raw material is weighed, and the atomic molar ratio of carbon element in the reducing agent to chromium element in the chromium source is controlled to be 4:1.

[0085] (2) Mix CrO3, titanium dioxide, lithium carbonate, ammonium metavanadate, high-iron sulfate and aluminum sulfate, add appropriate amount of deionized water and grind for 15 minutes, add manganese sulfate and grind for 5 minutes, add the reducing agent and grind for 5 minutes, finally add 3% PEG400 of the total mass of solids and continue to grind for 5 minutes to form a uniform, non-natural flow paste-like precursor.

[0086] (3) The precursor is transferred to an open corundum crucible (about 1 / 3 of the filling capacity), and placed in a muffle furnace preheated to 850°C. The material undergoes a self-propagating combustion reaction. After the furnace temperature recovers to 850°C, it is kept for 240 minutes. After the reaction is completed, it is air-cooled to room temperature, ground, and Li(Cr 0.6 V 0.1 Fe 0.2 Mn 0.05 Al 0.05 )TiO4 powder is obtained.

[0087] The configuration entropy of the obtained Li(Cr 0.6 V 0.1 Fe 0.2 Mn 0.05 Al 0.05 )TiO4 material is about 1.485R. The XRD pattern ( Figure 7 ) shows that it is a pure spinel phase with good crystallinity. Electrochemical tests show that its initial discharge specific capacity at 0.1C rate is 393mAh / g; the discharge specific capacity graph ( Figure 8 ) at different rates shows that it can still maintain a discharge capacity of about 100mAh / g at a high rate of 2C, and its capacity is basically unchanged after nearly 50 cycles at a rate of 0.2C, showing excellent cycle stability.

[0088] Example 6: Preparation of a chromium-site high-entropy chromium lithium titanate material with the chemical formula Li(Cr 0.58 V 0.08 Fe 0.2 Mn 0.06 Al 0.08 )TiO4, the specific steps are as follows.

[0089] (1) CrO3 is used as the chromium source and oxidizing agent, titanium dioxide is used as the titanium source, lithium carbonate is used as the lithium source, ammonium metavanadate is used as the vanadium source, diiron trioxide is used as the iron source, manganese dioxide is used as the manganese source, and aluminum oxide is used as the aluminum source. Starch is used as a reducing agent. Each raw material is weighed according to the molar ratio of Li:(Cr 0.58 V 0.08 Fe 0.2 Mn 0.06 Al 0.08 ):Ti=1.1:1:1, and the atomic molar ratio of carbon elements in the reducing agent to chromium elements in the chromium source is controlled to be 5:1.

[0090] (2) The raw materials except the reducing agent are mixed, deionized water is added and ground for 15 minutes, the reducing agent is added and ground for 5 minutes, and finally 5% PEG400 of the total mass of solids is added and ground for 5 minutes to form a uniform, non-naturally flowing paste-like precursor.

[0091] (3) Transfer the precursor to an open corundum crucible (filling approximately 1 / 2 full) and place it in a muffle furnace preheated to 950°C. The material undergoes a self-propagating combustion reaction. After the furnace temperature returns to 950°C, maintain the temperature for 30 minutes. After the reaction is complete, air cool to room temperature, grind, and obtain Li(Cr) 0.58 V 0.08 Fe 0.2 Mn 0.06 Al 0.08 )TiO4 powder.

[0092] The obtained Li(Cr) 0.58 V 0.08 Fe 0.2 Mn 0.06 Al 0.08 The configuration entropy of TiO4 material is approximately 1.502R. (XRD pattern) Figure 9 The results show that it is a well-crystallized pure spinel phase. Electrochemical tests show that its initial discharge specific capacity at 0.1C rate is 314 mAh / g; its discharge specific capacity at different rates is shown in the graph (). Figure 10 The results show that it can still maintain a discharge capacity of about 125mAh / g at a higher 2C rate, and its capacity has basically not decreased after nearly 50 cycles at a 0.2C rate, demonstrating excellent cycle stability.

[0093] Comparative Example 1: Pure lithium chromium titanate material without high-entropy modification was prepared using the combustion method described in this invention. Its chemical formula is LiCrTiO4. The specific steps are as follows.

[0094] (1) Using CrO3 as the chromium source, titanium dioxide as the titanium source, lithium sulfate as the lithium source, and starch as the reducing agent. Weigh each raw material according to the molar ratio of Li:Cr:Ti=1.1:1:1, and control the atomic molar ratio of carbon in the reducing agent to chromium in the chromium source to be 6:1.

[0095] (2) Mix the raw materials except for the reducing agent, add an appropriate amount of deionized water and grind for 15 minutes, add the reducing agent and grind for 5 minutes, and finally add PEG400 accounting for 3% of the total solid mass and continue grinding for 5 minutes to form a uniform, non-flowing paste-like precursor.

[0096] (3) Transfer the precursor to an open corundum crucible (filled to about 1 / 2 capacity) and place it in a muffle furnace preheated to 850°C. The material undergoes a self-propagating combustion reaction. After the furnace temperature returns to 850°C, maintain the temperature for 60 minutes. After the reaction is complete, air cool to room temperature and grind to obtain LiCrTiO4 powder.

[0097] The configurational entropy of the obtained LiCrTiO4 material is approximately 1.099R, significantly lower than that of the high-entropy materials in the embodiments of this invention. (XRD pattern) Figure 11) shows that it is a pure spinel phase. Electrochemical tests show that its initial specific discharge capacity at 0.1C rate is 155 mAh / g; its discharge capacity map at different rates ( Figure 12 ) shows that its discharge capacity at a high rate of 2C is only 60 mAh / g, and after nearly 50 cycles at a rate of 0.2C, the capacity attenuation is obvious, and the rate performance and cycle stability are poor.

[0098] Comparative Example 2: A pure lithium chromic titanate material without high-entropy modification was prepared by a traditional high-temperature solid-phase method, and its chemical formula was LiCrTiO4. The specific steps were as follows.

[0099] (1) CrO3 was used as a chromium source, titanium dioxide was used as a titanium source, and lithium hydroxide monohydrate was used as a lithium source. Each raw material was weighed according to the molar ratio of Li:Cr:Ti=1.1:1:1.

[0100] (2) The raw materials were mixed, and an appropriate amount of deionized water was added and ground for 20 minutes. Finally, 3% of PEG400 based on the total mass of the solid was added and ground for another 10 minutes to form a uniform, non-naturally flowing paste-like precursor.

[0101] (3) The precursor was transferred to an open corundum crucible (the filling amount was about 2 / 3), and was placed in a muffle furnace preheated to 800°C for calcination for 360 minutes. After the reaction was completed, the furnace was cooled to room temperature, and the LiCrTiO4 powder was obtained by grinding.

[0102] The XRD pattern of the obtained LiCrTiO4 material ( Figure 13 ) shows that it is a spinel phase. Electrochemical tests show that its initial specific discharge capacity at 0.1C rate is only 137 mAh / g.

[0103] From the test results of the comparative examples and the comparative examples, it can be seen that the first discharge specific capacity of the pure-phase LCT synthesized by the combustion method of the application (Comparative Example 1) is significantly higher than that of the product of the traditional solid-phase method (Comparative Example 2), which shows that the combustion method process of the application is beneficial to improving the basic performance of the material. Further, under the same combustion process conditions, the electrochemical performance of the material modified by "high-entropy of chromium site" (Examples 1-6) is significantly better than that of the unmodified pure-phase LCT (Comparative Examples 1-2). This shows that the combination of "high-entropy of chromium site" material design and combustion synthesis process of the application can synergistically improve the comprehensive electrochemical performance of the LCT material.

Claims

1. A high-entropy lithium chromium titanate material with chromium sites, characterized in that: The crystal structure of the chromium-site high-entropy lithium chromium titanate material is a single spinel solid solution phase, with the general chemical formula Li(Cr) 1-x-y-z-w V x Fe y Mn z Al w TiO4; Among them, x, y, z, and w satisfy 0 < x ≤ 0.2, 0 < y ≤ 0.2, 0 < z ≤ 0.1, 0 < w ≤ 0.1 and 0 < x + y + z + w ≤ 0.5; The configurational entropy of the chromium-site high-entropy lithium chromium titanate material is greater than 1.3R; where R is the gas constant.

2. A method for preparing chromium-site high-entropy lithium chromium titanate materials, characterized in that, It includes the following steps: S1. According to the stoichiometric ratio of the chemical formula described in Claim 1, weigh chromium source, titanium source, lithium source, vanadium source, iron source, manganese source, and aluminum source, and then mix and grind them with carbohydrates to form a precursor; Among them, the chromium source is chromium trioxide, and the atomic mole number of carbon element in the carbohydrates is 2 - 6 times the atomic mole number of chromium element in the chromium source; S2. Transfer the precursor to an open high-temperature resistant container, then place it in a reaction device preheated to a set temperature, and carry out a full combustion reaction in an air atmosphere. After the reaction ends, air-cool it to room temperature to obtain the chromium-site high-entropy lithium chromium titanate material; Among them, the set temperature is 750 - 950 °C.

3. The method for preparing the chromium-site high-entropy lithium chromium titanate material according to claim 2, characterized in that: In step S1, the atomic mole number of carbon element in the carbohydrates is 2 - 3 times the atomic mole number of chromium element in the chromium source.

4. The method for preparing the chromium-site high-entropy lithium chromium titanate material according to claim 2, characterized in that, In step S1: The titanium source is at least one of titanium dioxide, titanium oxysulfate, and tetrabutyl titanate; The lithium source is at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, and lithium chloride; The vanadium source is at least one of vanadium pentoxide, ammonium metavanadate, and vanadyl sulfate; The iron source is at least one of iron(III) oxide, ferrous sulfate, and ferric sulfate; The manganese source is at least one of manganese dioxide, manganese sulfate, and manganese acetate; The aluminum source is at least one of aluminum oxide, aluminum sulfate, and aluminum chloride; The carbohydrates are at least one of glucose, sucrose, and starch.

5. The method for preparing the chromium-site high-entropy lithium chromium titanate material according to claim 2, characterized in that: In step S1, an appropriate amount of liquid medium is added during grinding until the mixed material forms a uniform and non-flowing paste-like precursor; The liquid medium is polyethylene glycol 400, or polyethylene glycol 400 and water.

6. The method for preparing the chromium-site high-entropy lithium chromium titanate material according to claim 2, characterized in that: In step S2, the loading amount of the precursor is 1 / 4 - 3 / 4 of the volume of the open high-temperature resistant container.

7. The method for preparing the chromium-site high-entropy lithium chromium titanate material according to claim 2, characterized in that: In step S2, the combustion reaction starts timing after the temperature in the reaction device returns to the set temperature, and the time is 30 - 360 minutes.

8. The method for preparing the chromium-site high-entropy lithium chromium titanate material according to claim 2, characterized in that: In step S2, the set temperature is 800 °C.

9. Application of the chromium-site high-entropy lithium chromium titanate material described in Claim 1 or the chromium-site high-entropy lithium chromium titanate material prepared by the preparation method described in any one of Claims 2 - 8 in a lithium-ion battery.

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