Manganese iron lithium phosphate positive electrode material with high-entropy interface constructed in situ and preparation method thereof

Abstract

The application provides a manganese iron lithium phosphate positive electrode material with a high-entropy interface constructed in situ and a preparation method thereof. The method can include the following steps: grinding, drying, and screening a manganese source, an iron source, a metal M source, a lithium source, a phosphorus source, and a carbon source to obtain a multi-element doped manganese iron lithium phosphate precursor; step-by-step calcining the multi-element doped manganese iron lithium phosphate precursor in a protective atmosphere, and cooling to obtain a multi-element doped manganese iron lithium phosphate positive electrode material; grinding and screening the multi-element doped manganese iron lithium phosphate positive electrode material for a second time to obtain an amorphous multi-element doped manganese iron lithium phosphate positive electrode material; and annealing the amorphous multi-element doped manganese iron lithium phosphate positive electrode material in a protective atmosphere to obtain a manganese iron lithium phosphate positive electrode material with a high-entropy interface constructed in situ. The manganese iron lithium phosphate positive electrode material prepared by the method has a micron-sized secondary particle structure formed by agglomeration of nanometer-sized primary particles, has a large specific surface area, and has high electrochemical activity.

Description

Technical Field

[0001] This invention relates to the field of battery materials, and more specifically, to a lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface and its preparation method. Background Technology

[0002] Currently, the technology of lithium iron phosphate cathode materials has matured over the past two decades, and it is difficult to further improve the energy density of the material itself. Meanwhile, lithium manganese iron phosphate, an upgraded version of lithium iron phosphate, has received widespread attention in recent years due to its higher energy density. However, due to the difference in valence electrons between Mn and Fe, Mn... 3+ The severe Jahn-Teller effect results in low electrochemical activity and high electrolyte reactivity, often leading to performance inferior to lithium iron phosphate in practical applications, thus limiting the development of this material. Appropriate elemental doping can modulate the crystal structure and optimize the band structure, thereby improving the electrochemical activity and lattice stability to some extent. However, excessive elemental doping may reduce the theoretical energy density, and too many dopants also increase production and recycling costs. Furthermore, elemental doping of precursors often results in significant macroscopic segregation, leading to uneven element distribution during the initial sintering process and insignificant modification effects. Therefore, a method to address these issues is urgently needed.

[0003] Currently, elemental doping modification of lithium manganese iron phosphate can be mainly divided into single-element doping (CN 118145619A, CN 117658094 A), dual-element co-doping (CN 118712368 A), and multi-element synergistic doping (CN 117682496A). However, in different modification methods, even with processes that can achieve uniform mixing of precursors at the nanoscale, such as liquid-phase co-precipitation, hydrothermal methods, or high-energy ball milling, uneven distribution of matter and energy among the micro-elements of the system is inevitable. Microscopic and macroscopic segregation cannot be avoided during the production process, which will greatly reduce the modification effect. If too much doping is used, it may even lead to the coexistence of two or even multiple phases during sintering, resulting in a decrease in the modification effect or poor repeatability. Summary of the Invention

[0004] In view of the shortcomings of the prior art, one of the objectives of this invention is to solve one or more problems existing in the prior art. For example, one objective of this invention is to provide a low-cost, short-process method for preparing high-performance lithium manganese iron phosphate cathode materials.

[0005] This invention provides a method for preparing lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface, which may include the following steps: firstly grinding, drying, and sieving a manganese source, an iron source, a metal M source, a lithium source, a phosphorus source, and a carbon source to obtain a multi-element doped lithium manganese iron phosphate precursor, wherein the metal M is at least one of V, Nb, Ti, Cr, Mg, Zr, W, and Mo; secondly calcining and cooling the multi-element doped lithium manganese iron phosphate precursor under a protective atmosphere to obtain a multi-element doped lithium manganese iron phosphate cathode material; thirdly grinding and sieving the multi-element doped lithium manganese iron phosphate cathode material to obtain an amorphous multi-element doped lithium manganese iron phosphate cathode material; and finally, annealing the amorphous multi-element doped lithium manganese iron phosphate cathode material under a protective atmosphere to obtain a lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface.

[0006] Furthermore, the first grinding can be mechanical liquid phase ball milling, with a ball milling speed of 200 r / min to 800 r / min and a ball milling time of 2 h to 8 h.

[0007] Furthermore, the second grinding can be ball milling, with a ball milling speed of 400 r / min to 1200 r / min and a ball milling time of 0.5 h to 20 h.

[0008] Furthermore, the second grinding process may also include adding a carbon source during the grinding process to perform secondary carbon coating on the multi-element doped lithium manganese iron phosphate cathode material.

[0009] Furthermore, the stepwise calcination can include a first-step calcination, a second-step calcination, and a third-step calcination. The temperature of the first-step calcination can be 120℃~220℃, and the calcination time can be 1h~5h; the temperature of the second-step calcination can be 350℃~550℃, and the calcination time can be 6h~12h; the temperature of the third-step calcination can be 600℃~800℃, and the calcination time can be 6h~12h.

[0010] Furthermore, the annealing temperature can be 750℃~850℃, and the annealing time can be 2h~15h.

[0011] Furthermore, the heating rate for annealing can be from 1℃ / min to 10℃ / min.

[0012] Furthermore, the general chemical formula of lithium manganese iron phosphate cathode materials with in-situ constructed high-entropy interfaces can be Li (m+un / 2+a+0.05) (Mn x Fe 1-x ) m (M u+ ) n (PO4) (m+un / 2+a)@C, where 0≤x≤1, m≥0, n≥0, m+n=1, 0≤a≤0.1, u is the valence state of element M, and a is (PO4). 3- Excess coefficient; manganese source, iron source, metal M source, lithium source, and phosphorus source can be added according to the stoichiometric ratio of each element in the general chemical formula of lithium manganese iron phosphate cathode material with in-situ high-entropy interface; the amount of carbon source added per mole of lithium manganese iron phosphate cathode material with in-situ high-entropy interface can be 10g to 30g.

[0013] Furthermore, it may also include adding a dispersant before the first grinding.

[0014] Furthermore, the manganese source can be at least one of manganese metal oxides, manganese phosphates, manganese sulfates, manganese carbonates, manganese hydroxides, and manganese metal salts; the iron source can be at least one of iron metal oxides, iron phosphates, iron sulfates, iron carbonates, iron hydroxides, and iron metal salts; the metal M source can be at least one of metal M oxides, metal M phosphates, metal M sulfates, metal M carbonates, metal M hydroxides, and metal M metal salts; the lithium source can be at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; the phosphorus source can be at least one of phosphoric acid, lithium dihydrogen phosphate, and transition metal phosphates; and the carbon source can be at least one of sucrose, PVA, dopamine, sodium carboxymethyl cellulose, and starch.

[0015] Another aspect of this invention provides a lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface, the general chemical formula of which can be Li (m+un / 2+a+0.05) (Mn x Fe 1-x ) m (M u+ ) n (PO4) (m+un / 2+a) @C, where 0≤x≤1, m≥0, n≥0, m+n=1, 0≤a≤0.1, u is the valence state of element M, and a is (PO4). 3- The excess coefficient, M, can be at least one of V, Nb, Ti, Cr, Mg, Zr, W, and Mo.

[0016] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0017] (1) The present invention prepares lithium manganese iron phosphate cathode material through the process of "high entropy doping-step calcination-secondary ball milling-annealing". It can simultaneously improve the intrinsic ionic / electronic conductivity of lithium manganese iron phosphate cathode material, construct high ionic conductivity and high entropy interface and refine grains, suppress the dissolution of Mn, avoid micro and macro segregation, and improve the rate performance and cycle stability of the material in multiple dimensions.

[0018] (2) In this invention, the doping element is uniformly incorporated into the cathode material by calcination, and then the doping element is supersaturated and precipitated in situ on the surface by high-temperature annealing, thereby constructing a high-entropy interface. The constructed high-entropy interface has high ionic conductivity and can suppress the dissolution of Mn.

[0019] (3) The lithium manganese iron phosphate cathode material obtained by the present invention is composed of micron-sized secondary particles formed by the agglomeration of nano-sized primary particles. It has a large specific surface area and high electrochemical activity. At the same time, the construction of high-entropy interface greatly improves the interfacial stability of the material. The physicochemical properties of the material preparation are controllable. The process is safe and environmentally friendly, with low technical difficulty, readily available raw materials, low cost, short process, and easy to realize industrial production. The prepared lithium manganese iron phosphate cathode material has excellent performance. Attached Figure Description

[0020] The above and other objects and features of the present invention will become clearer from the following description taken in conjunction with the accompanying drawings, in which:

[0021] Figure 1 The image shows the SEM image of the lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface prepared in Example 1.

[0022] Figure 2 The image shows the XRD pattern of the lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface obtained in Example 1.

[0023] Figure 3 This is a TEM image of the lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface obtained in Example 1.

[0024] Figure 4 The image shows a SEM image of the lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface, prepared in Example 2.

[0025] Figure 5 The image shows the XRD pattern of the lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface obtained in Example 2.

[0026] Figure 6 The 0.1C charge-discharge curves of the lithium iron phosphate cathode material with an in-situ constructed high-entropy interface obtained in Example 2 are shown.

[0027] Figure 7 The 1C charge-discharge curves of the lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface obtained in Example 3 are shown.

[0028] Figure 8 The rate performance diagram shows the in-situ constructed high-entropy interface lithium manganese iron phosphate cathode material prepared in Example 3.

[0029] Figure 9 The diagram shows the cycle performance of the lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface obtained in Example 3.

[0030] Figure 10 The image shows the SEM image of the lithium iron phosphate cathode material prepared in Comparative Example 1.

[0031] Figure 11 The first charge-discharge curve of the lithium manganese iron phosphate cathode material prepared for Comparative Example 1 is shown.

[0032] Figure 12 The cycling performance diagram of the lithium iron phosphate cathode material prepared for Comparative Example 1 is shown. Detailed Implementation

[0033] The following description, in conjunction with the accompanying drawings and exemplary embodiments, details the in-situ construction of a high-entropy interface lithium manganese iron phosphate cathode material and its preparation method according to the present invention.

[0034] Specifically, to avoid the uneven distribution of matter and energy in lithium manganese iron phosphate cathode materials caused by existing technologies such as liquid-phase co-precipitation and hydrothermal methods, resulting in microscopic and macroscopic segregation, this invention proposes a "high-entropy doping-stepwise calcination-secondary ball milling-annealing" process. Through stepwise calcination, the dopant element M is abundantly distributed on the surface of the lithium manganese iron phosphate particles, forming a rich layer that generates a strong pinning effect, preventing further growth of the primary cathode material particles and thus refining the grain size. Through secondary ball milling, the intense impact of the milling process creates numerous defects on the grain surface and within the bulk phase, increasing the energy of the particle surface and the bulk phase itself while significantly reducing crystal stability, thereby generating a large number of highly active particles. During the subsequent annealing process, the elements rearrange themselves under the influence of the thermodynamic minimum energy effect. In order to reduce the total energy of the system, a small amount of dopant elements are further enriched at the grain boundaries, thereby forming a high-entropy interface structure in situ on the surface in one step. This balances the distribution positions of the elements in the lattice, making the element distribution uniform, improving the electrochemical activity of the lithium manganese iron phosphate cathode material, and greatly enhancing the interface stability of the material.

[0035] Furthermore, based on the characteristics of the metal M in lithium manganese iron phosphate (LMFP) with limited substitution of Fe / Mn by sintering temperature and the unlimited co-solubility between metal M ions, this invention can regulate the bulk doping amount and high-entropy interface structure by adjusting the calcination and annealing temperatures and coordinating the metal M ion ratio. This allows for multi-dimensional control through adjusting ion doping amount, lattice vacancy control due to hypervalent ion doping, and multifunctional interface control. Here, the multifunctional interface refers to a high-entropy interface composed of multiple elements, which can optimize the surface band structure of the material, thereby improving conductivity, mechanical properties, and structural stability, thus optimizing the lithium storage structure of LMFP. Moreover, the high-entropy interface formed by in-situ supersaturation and micro-segregation of small elements achieved through the preparation method of this invention can effectively suppress interparticle mass transfer during high-temperature calcination and annealing, weaken agglomeration kinetics during calcination and annealing, and refine primary particles. Therefore, by using multiple supervalent ion doping and employing a "high-entropy doping-step calcination-secondary ball milling-annealing" process, this invention can simultaneously improve the intrinsic ionic / electronic conductivity of lithium manganese iron phosphate cathode materials, construct high ionic conductivity and high-entropy interfaces, refine grains, suppress Mn dissolution, and avoid micro and macro segregation. This can improve the rate performance and cycle stability of the material in multiple dimensions.

[0036] This invention provides a method for preparing lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface. In some embodiments, the method may include the following steps:

[0037] S01, manganese source, iron source, metal M source, lithium source, phosphorus source and carbon source are ground, dried and sieved to obtain multi-element doped lithium manganese iron phosphate precursor, wherein metal M is at least one of V, Nb, Ti, Cr, Mg, Zr, W and Mo.

[0038] S02, multi-element doped lithium manganese iron phosphate precursor is calcined stepwise under a protective atmosphere and cooled to obtain multi-element doped lithium manganese iron phosphate cathode material.

[0039] S03, the multi-element doped lithium manganese iron phosphate cathode material is ground and sieved a second time to obtain amorphous multi-element doped lithium manganese iron phosphate cathode material.

[0040] S04, the amorphous multi-element doped lithium manganese iron phosphate cathode material is annealed under a protective atmosphere to obtain lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface.

[0041] In some implementations, the amounts of manganese source, iron source, metal M source, lithium source, phosphorus source, and carbon source can be proportioned according to the stoichiometric ratio required for the target product, lithium manganese iron phosphate cathode material. In some implementations, the manganese source, iron source, metal M source, lithium source, phosphorus source, and carbon source can be selected from the following raw materials, specifically including:

[0042] The manganese source can be at least one of manganese metal oxides, manganese phosphates, manganese sulfates, manganese carbonates, manganese hydroxides, and manganese metal salts. For example, the manganese source can be one or a mixture of several of manganese trioxide, manganese sulfate, manganese carbonate, and manganese hydroxide.

[0043] The iron source can be at least one of iron metal oxides, iron phosphates, iron sulfates, iron carbonates, iron hydroxides, and iron metal salts. For example, the iron source can be one or a mixture of several of ferric oxide, iron(II,III) oxide, ferric sulfate, and ferric carbonate.

[0044] The metal source M can be at least one of the following: metal oxide, metal phosphate, metal sulfate, metal carbonate, metal hydroxide, and metal acid salt of metal M. For example, one or a mixture of several of the following substances: vanadium pentoxide, magnesium hydroxide, chromium oxide, molybdenum oxide, tungsten oxide, and magnesium sulfate.

[0045] The lithium source can be at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate.

[0046] The phosphorus source can be at least one of phosphoric acid, lithium dihydrogen phosphate, and transition metal phosphates;

[0047] The carbon source can be at least one of sucrose, PVA, dopamine, sodium carboxymethyl cellulose, and starch.

[0048] In some implementations, the first grinding can be performed using mechanical liquid phase ball milling to activate the mixed raw materials. The grinding speed for the first grinding can be 200 r / min to 800 r / min, and the grinding time can be 2 h to 8 h. If the grinding speed is lower than 200 r / min, the mechanical liquid phase activation effect will be poor, the phase dispersion will be uneven, and the particle size will be large; the grinding speed is limited by the equipment capacity and cannot be too high. Mechanical activation will reach an equilibrium state after a certain grinding time. If the grinding time is less than 2 h, it will lead to uneven phase dispersion; if the grinding time is greater than 8 h, increasing the time has little effect on the mechanical activation effect. For example, the grinding speed for the first grinding can be 220 r / min to 760 r / min, 255 r / min to 700 r / min, 302 r / min to 640 r / min, 380 r / min to 550 r / min, or a combination of the above ranges. The grinding time can be 3 h to 7 h, 3.5 h to 6 h, 4 h to 5 h, or a combination of the above ranges. The grinding jar and grinding balls used in mechanical liquid phase ball milling can be made of stainless steel, zirconium oxide, or tungsten carbide, etc. The grinding balls can be used at a ball-to-material ratio of (5-20):1.

[0049] In some embodiments, a dispersant may be added to the raw material before the first grinding to ensure uniform dispersion and facilitate grinding. The dispersant may be any one or more of ethanol, water, ethylene glycol, and acetone, mixed in any proportion. In some embodiments, the dispersant may be added at a solid-liquid ratio of 1:(1–3). For example, it may be added at a solid-liquid ratio of 1:2.

[0050] In some implementations, the drying in step S01 can be achieved using forced-air drying or vacuum drying. The drying temperature can be set to 60°C–120°C, and the time can be 8 hours–24 hours. For example, the drying temperature can be set to 100°C, and the time can be 12 hours. The sieving in step S01 is primarily for separating the pellets. Similarly, the sieving in step S03 is also for separating the pellets.

[0051] In some implementations, stepwise calcination may include a three-step calcination process. The first step involves calcining at 120°C–220°C for 1–5 hours. At these temperatures and times, residual moisture in the precursor is effectively removed. Too short a time or too low a temperature will prevent complete evaporation of residual moisture, affecting subsequent chemical reactions. Too high a sintering temperature will cause the second reaction to occur prematurely, which is detrimental to cathode material preparation. The second step involves calcining at 350°C–550°C for 6–12 hours. At these temperatures and times, the raw materials partially decompose, the organic carbon source carbonizes, and lithium manganese iron phosphate is initially formed. If this process is too short, the precursor cannot decompose completely, and the organic carbon source cannot be fully carbonized; if the time is too long, no significant phase change occurs. The third step involves calcining at 600°C–800°C for 6–12 hours. Under the calcination temperatures and times set above, lithium manganese iron phosphate is fully formed, with atoms moving towards their equilibrium sites, thus increasing the material's crystallinity. If the process time is too short or the sintering temperature is too low, the material's crystallinity will be poor; if the process time is prolonged or the sintering temperature is too high, the primary particles will become larger, which is detrimental to improving electrochemical performance. The three-step calcination temperature and time settings described above, when coordinated, can yield lithium manganese iron phosphate cathode materials with large specific surface area, high electrochemical activity, and excellent performance. For example, in some embodiments, the first-step calcination temperature can be 150℃~200℃, and the calcination time can be 2h~4h. The second-step calcination temperature can be 380℃~500℃, and the calcination time can be 7h~11h. The third-step calcination temperature can be 640℃~750℃, and the calcination time can be 7h~11h. As another example, the first-step calcination temperature can be 170℃~190℃, and the calcination time can be 2.5h~3.5h. The second calcination step can be performed at a temperature of 420℃ to 480℃ for 8 to 10 hours. The third calcination step can be performed at a temperature of 670℃ to 720℃ for 8 to 9 hours. In some embodiments, the protective atmosphere can be argon, nitrogen, or other similar atmospheres. The protective gas introduction rate can be controlled between 100 mL / min and 2000 mL / min. In some embodiments, the heating rate for each calcination step can be between 1℃ / min and 10℃ / min. For example, the heating rate can be between 2℃ / min and 8℃ / min, 4℃ / min and 7℃ / min, 5℃ / min and 6℃ / min, or a combination of these ranges.

[0052] In some embodiments, the second grinding may be performed with the addition of a dispersant, or it may be performed directly without the addition of a dispersant. The dispersant may be any one or more of ethanol, water, ethylene glycol, and acetone, mixed in any proportion. In some embodiments, the second grinding may be performed using ball milling. The ball milling speed may be 400 r / min to 1200 r / min, and the ball milling time may be 0.5 h to 20 h. During the second ball milling process, if the ball milling speed is too slow or the ball milling time is too short, the mechanical energy provided will be weak, the degree of amorphization of the crystals will be low, and it will not be conducive to the occurrence of subsequent reactions. If the ball milling speed is too fast or the ball milling time is too long, on the one hand, it will not be more conducive to the development of the material towards amorphization, and on the other hand, it may accelerate the wear of the equipment, which is not conducive to sustainable production. For example, the ball milling speed may be 500 r / min to 1100 r / min, and the ball milling time may be 1.5 h to 15 h. As another example, the ball milling speed may be 720 r / min to 980 r / min, and the ball milling time may be 3.5 h to 11 h. The grinding jar and grinding balls used in the ball milling process can be made of stainless steel, zirconium oxide, or tungsten carbide, etc. The grinding balls can be used at a ball-to-material ratio of (5-20):1.

[0053] In some embodiments, a carbon source is added during the second grinding process to perform secondary carbon coating on the multi-element doped lithium manganese iron phosphate cathode material. Since uneven carbon coating may occur during the first carbon coating process after the first grinding, or during the amorphization of the crystals during the second ball milling, a carbon source can be added during the second ball milling process to perform secondary carbon coating, thereby obtaining a more uniform carbon coating layer. In some embodiments, the carbon added during the second grinding process can be at least one of sucrose, PVA, dopamine, sodium carboxymethyl cellulose, and starch. In some embodiments, the second grinding process can be divided into two stages. The first stage of grinding does not involve the addition of a carbon source and can be dry grinding. After the first stage of grinding, a carbon source is added for the second stage of grinding. The second stage of grinding can be mechanically activated by liquid hydration.

[0054] In some implementations, the annealing temperature can be 750℃ to 850℃, and the annealing time can be 2h to 15h. If the annealing temperature is below 750℃, the atomic diffusion kinetics are poor, and atoms cannot effectively move to their equilibrium positions; if the annealing time is less than 2h, the chemical reaction cannot reach the expected equilibrium. If the annealing temperature is above 850℃, it will cause the primary particles of the material to increase in size, and the thermodynamic equilibrium state will change uncontrollably, which is not conducive to the material's development towards the expected goal. If the annealing time is greater than 15h, it will not cause further significant changes in the material; therefore, for energy conservation considerations, the annealing time is set to less than 15h. For example, in some implementations, the annealing temperature can be 760℃ to 830℃, and the annealing time can be 4h to 13h; or the annealing temperature can be 780℃ to 810℃, and the annealing time can be 6h to 10h. In some implementations, the heating rate of the annealing treatment can be 1℃ / min to 10℃ / min. For example, the heating rate of the annealing process can be 2℃ / min~8℃ / min, 4℃ / min~7℃ / min, 5℃ / min~6℃ / min or a combination of the above ranges.

[0055] In some implementations, the protective atmosphere for the annealing treatment can be argon, nitrogen, or other similar atmospheres. The protective gas introduction rate can be controlled between 100 mL / min and 2000 mL / min.

[0056] In some implementation schemes, the general chemical formula of the lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface is Li. (m+un / 2+a+0.05) (Mn x Fe 1-x ) m (M u+ ) n (PO4) (m+un / 2+a) @C, where 0≤x≤1, m≥0, n≥0, m+n=1, 0≤a≤0.1, u is the valence state of element M, and a is (PO4). 3- Excess coefficient. For example, in some implementations, the chemical formula of the lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface can be LiMn. 0.72 Fe 0.181 V 0.023 Ti 0.02 Mg 0.03 PO4@C, LiMn 0.55 Fe 0.36 7V 0.023 Nb 0.02 Mg 0.03 PO4@C, LiMn 0.474 Fe 0.316 Nb 0.03 Cr 0.01 W 0.02 Mo0.03 (PO4) 0.95 @C et al. In lithium manganese iron phosphate cathode materials with in-situ constructed high-entropy interfaces, the amount of carbon source added is 10g to 30g per mole. For example, the amount of carbon source added can be a combination of 12g to 25g, 18g to 22g, 19g to 21g or more.

[0057] In another aspect, this invention provides a lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface. This lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface can be prepared by the method described above. In some embodiments, the general chemical formula of the lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface can be Li… (m+un / 2+a+0.05) (Mn x Fe 1-x ) m (M u+ ) n (PO4) (m+un / 2+a) @C, where 0≤x≤1, m≥0, n≥0, m+n=1, 0≤a≤0.1, u is the valence state of element M, and a is (PO4). 3- The excess coefficient, M, is at least one of V, Nb, Ti, Cr, Mg, Zr, W, and Mo.

[0058] To better understand the present invention, specific examples are provided below to further illustrate the content of the present invention, but the content of the present invention is not limited to the examples below.

[0059] Example 1

[0060] A method for preparing lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface includes the following steps:

[0061] Step 1: According to the stoichiometric ratio set for the in-situ constructed high-entropy interface lithium manganese iron phosphate cathode material, accurately weigh 594.58g Mn3O4, 414.97g Fe2O3, 1561.07g LiH2PO4, 11g Li2CO3, 297.41g PVA, 27.32g V2O5, 35.72g TiO2, 18.35g MgO, and 39.57g Nb2O5. Place the weighed raw materials in a zirconia ball mill jar, add 6L deionized water and 500ml ethylene glycol as a dispersant, add 30kg zirconia balls, and perform mechanical activation in a ball mill. Set the ball milling speed to 200r / min and the ball milling time to 15h. After ball milling, place the ball milled slurry in a 100℃ forced-air drying oven and dry for 48h. After drying, remove it and separate the ball and material to obtain the multi-element doped lithium manganese iron phosphate precursor.

[0062] Step 2: Take 50g of the sieved dry precursor powder and pour it into an alumina crucible. Then place it in a tube furnace and hold it at 180℃ for 3 hours under an argon atmosphere. Then raise the temperature to 550℃ and hold it for 10 hours. Finally, hold it at 750℃ for 8 hours and cool it to room temperature with the furnace to obtain carbon-coated multi-element doped lithium manganese iron phosphate, i.e., multi-element doped lithium manganese iron phosphate cathode material.

[0063] Step 3: The black product powder carbon-coated multi-element doped lithium manganese iron phosphate obtained in Step 2 is poured into a stainless steel ball mill jar, and 200g of stainless steel balls are added for secondary ball milling. The ball milling speed is set to 600r / min, and the ball milling time is set to 12h. The first 6 hours are for dry milling, and the last 6 hours are for secondary mechanical activation and organic carbon coating by adding 6g of sucrose and 55ml of ethanol. After ball milling, the ball milling slurry is placed in an 80℃ forced-air drying oven for 24h for forced-air drying. After drying, the ball and material are separated to obtain black lithium manganese iron phosphate, i.e., amorphous multi-element doped lithium manganese iron phosphate cathode material.

[0064] Step 4: Pour the sieved black lithium manganese iron phosphate into an alumina crucible and place it in a tube furnace. Anneal it at 800°C for 8 hours. After cooling to room temperature in the furnace, the lithium manganese iron phosphate cathode material with an in-situ high-entropy interface is obtained.

[0065] The lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface was tested, among which... Figure 1 The image shows a SEM image of the lithium manganese iron phosphate cathode material prepared in this embodiment. As can be seen from the image, the material is composed of nano-sized primary particles agglomerated to form micron-sized secondary particles. Figure 2 The XRD pattern of the lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface prepared in this embodiment shows that the cathode material has a standard olivine structure and good crystallinity. Figure 3 The image shows a TEM image of the lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface prepared in this embodiment. As can be seen from the image, the atoms inside the material crystal are arranged neatly and there is no impurity phase mixing.

[0066] Example 2

[0067] A method for preparing lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface includes the following steps:

[0068] Step 1: According to the stoichiometric ratio set for the in-situ constructed high-entropy interface lithium manganese iron phosphate cathode material, accurately weigh 620.84g Mn3O4, 433.3g Fe2O3, 1566.62g LiH2PO4, 11.03g Li2CO3, 298.47g sucrose, 13.7g V2O5, 23.89g TiO2, 12.27g MgO, 19.85g Nb2O5, and 22.51g NiO. Place the weighed raw materials in a stainless steel ball mill jar, add 6L of anhydrous ethanol as a dispersant, add 15kg of tungsten carbide balls, and perform mechanical activation in a ball mill. Set the ball milling speed to 200r / min and the ball milling time to 12h. After ball milling, place the ball milled slurry in an 80℃ forced-air drying oven and dry for 24h. After drying, remove it and separate the ball and material to obtain the multi-element doped lithium manganese iron phosphate precursor.

[0069] Step 2: Take 50g of the sieved dry precursor powder and pour it into an alumina crucible. Then place it in a tube furnace and hold it at 180℃ for 3 hours under an argon atmosphere. Then raise the temperature to 450℃ and hold it for 8 hours. Finally, hold it at 650℃ for 10 hours and cool it to room temperature with the furnace to obtain carbon-coated multi-element doped lithium manganese iron phosphate, i.e., multi-element doped lithium manganese iron phosphate cathode material.

[0070] Step 3: The black product powder carbon-coated multi-element doped lithium manganese iron phosphate obtained in Step 2 is poured into a stainless steel ball mill jar, and 200g of tungsten carbide balls are added for secondary ball milling. The ball milling speed is set to 500r / min, and the ball milling time is set to 12h. The first 6 hours are dry milling, and the last 6 hours are spent adding 10g of sucrose and 70ml of ethanol for secondary mechanical activation and organic carbon coating. After ball milling, the milled slurry is placed in an 80℃ forced-air drying oven for 24h for forced-air drying. After drying, the ball and material are separated to obtain black lithium manganese iron phosphate, i.e., amorphous multi-element doped lithium manganese iron phosphate cathode material.

[0071] Step 4: Pour the sieved black lithium manganese iron phosphate into an alumina crucible and place it in a tube furnace. Anneal it at 850°C for 10 hours. After cooling to room temperature in the furnace, the lithium manganese iron phosphate cathode material with an in-situ high-entropy interface is obtained.

[0072] The lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface was tested, among which... Figure 4 The image shows the SEM image of the lithium manganese iron phosphate cathode material prepared in this embodiment. As can be seen from the image, the material is formed by the agglomeration of nano-sized primary particles into micron-sized secondary particles. Figure 5 The XRD pattern of the lithium manganese iron phosphate cathode material prepared in this embodiment shows that the material has a standard olivine structure and good crystallinity. Figure 6The figure shows the 0.1C charge-discharge curve of the lithium manganese iron phosphate cathode material prepared in this embodiment. As can be seen from the figure, the first discharge specific capacity of the material at a 0.1C rate is 148.2 mAh / g, indicating that the material has excellent electrochemical performance.

[0073] Example 3

[0074] A method for preparing lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface includes the following steps:

[0075] Step 1: According to the stoichiometric ratio set for the in-situ constructed high-entropy interface lithium manganese iron phosphate cathode material, accurately weigh 594.72g Mn3O4, 415.07g Fe2O3, 1574.35g LiH2PO4, 40.86g Li2CO3, 315.72g sucrose, 25.28g TiO2, 12.98g MgO, 21g Nb2O5, and 23.82g NiO. Place the weighed raw materials in a stainless steel ball mill jar, add 6L of anhydrous ethanol containing 50% deionized water as a dispersant, add 12kg of stainless steel balls, and perform mechanical activation in a ball mill. The ball milling speed is set to 300r / min, and the ball milling time is set to 13h. After ball milling, place the ball milled slurry in a 100℃ forced-air drying oven and dry for 18h. After drying, remove it and separate the ball and material to obtain the multi-element doped lithium manganese iron phosphate precursor.

[0076] Step 2: Take 50g of the sieved dry precursor powder and pour it into an alumina crucible. Then place it in a tube furnace and hold it at 120℃ for 3h under an argon atmosphere. Then raise the temperature to 480℃ and hold it for 10h. Finally, hold it at 625℃ for 10h and cool it to room temperature with the furnace to obtain carbon-coated multi-element doped lithium manganese iron phosphate, i.e., multi-element doped lithium manganese iron phosphate cathode material.

[0077] Step 3: Pour the obtained black powder into a stainless steel ball mill jar, add 200g of stainless steel balls, and perform a second ball milling. The ball milling speed is set to 400r / min, and the ball milling time is set to 10h. The first 5 hours are for dry milling, and the last 5 hours are for adding 12g of sucrose and 80ml of deionized water for secondary mechanical activation and organic carbon coating. After ball milling, the milled slurry is placed in a 100℃ forced-air drying oven for 24h for forced-air drying. After drying, the ball and material are separated to obtain black lithium manganese iron phosphate, i.e., amorphous multi-element doped lithium manganese iron phosphate cathode material.

[0078] Step 4: Pour the sieved black lithium manganese iron phosphate into an alumina crucible and place it in a tube furnace. Anneal it at 825°C for 8 hours. After cooling to room temperature in the furnace, the lithium manganese iron phosphate cathode material with an in-situ high-entropy interface is obtained.

[0079] The lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface was tested, among which... Figure 7 The figure shows the 1C charge-discharge curve of the lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface prepared in this embodiment. As can be seen from the figure, the material has a discharge specific capacity of 134.9 mAh / g at 1.0C, which shows excellent electrochemical performance. Figure 8 The graph shows the rate performance of the lithium manganese iron phosphate cathode material with an in-situ high-entropy interface prepared in this embodiment. As can be seen from the graph, the material has good rate performance. Figure 9 The figure shows the cycling performance of the lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface prepared in this embodiment. As can be seen from the figure, the material has excellent cycling performance.

[0080] Comparative Example 1

[0081] This comparative example is compared with Example 3. The material preparation process is based on Example 3, except that steps 3 and 4, namely the secondary ball milling and annealing treatment, are omitted. The specific operation is as follows:

[0082] Step 1: According to the stoichiometric ratio set for the high-entropy doped lithium manganese iron phosphate cathode material, accurately weigh 594.72g Mn3O4, 415.07g Fe2O3, 1574.35g LiH2PO4, 40.86g Li2CO3, 315.72g sucrose, 25.28g TiO2, 12.98g MgO, 21g Nb2O5, and 23.82g NiO. Place the weighed raw materials in a stainless steel ball mill jar, add 6L of anhydrous ethanol containing 50% deionized water as a dispersant, add 12kg of stainless steel balls, and perform mechanical activation in a ball mill. Set the ball milling speed to 300r / min and the ball milling time to 13h. After ball milling, place the milled slurry in a 100℃ forced-air drying oven and dry for 18h. After drying, remove it and separate the ball and slurry to obtain the multi-element doped lithium manganese iron phosphate precursor.

[0083] Step 2: Take 50g of the sieved dry precursor powder and pour it into an alumina crucible. Then place it in a tube furnace and hold it at 120℃ for 3h under an argon atmosphere. Then raise the temperature to 480℃ and hold it for 10h. Finally, hold it at 625℃ for 10h and cool it to room temperature with the furnace to obtain carbon-coated multi-element doped lithium manganese iron phosphate, i.e., multi-element doped lithium manganese iron phosphate cathode material.

[0084] The obtained high-entropy doped lithium iron phosphate cathode material was tested. Figure 10 The image shows the SEM image of the lithium manganese iron phosphate cathode material prepared in this comparative example. As can be seen from the image, the particle size distribution of the material is uneven, with large primary particles. Figure 11 The figure shows the first charge-discharge curves of the lithium manganese iron phosphate cathode material prepared in this comparative example. As can be seen from the figure, the capacity of the control sample is lower compared with the modified material. Figure 12 The figure shows the cycle performance of the lithium manganese iron phosphate cathode material prepared in this comparative example. As can be seen from the figure, the cycle stability of the comparative sample is worse than that of the modified material.

[0085] Although the invention has been described above in conjunction with exemplary embodiments, those skilled in the art will understand that various modifications and changes can be made to the exemplary embodiments of the invention without departing from the spirit and scope defined by the claims.

Claims

1. A method for preparing lithium manganese iron phosphate cathode material with in-situ constructed high-entropy interface, characterized in that, Includes the following steps: The manganese source, iron source, metal M source, lithium source, phosphorus source and carbon source are first ground, dried and sieved to obtain a multi-element doped lithium manganese iron phosphate precursor, wherein metal M is at least one of V, Nb, Ti, Cr, Mg, Zr, W and Mo. Multi-element doped lithium manganese iron phosphate precursor was calcined stepwise under a protective atmosphere and then cooled to obtain multi-element doped lithium manganese iron phosphate cathode material. The multi-element doped lithium manganese iron phosphate cathode material was ground and sieved a second time to obtain amorphous multi-element doped lithium manganese iron phosphate cathode material. Amorphous multi-element-doped lithium manganese iron phosphate cathode material was annealed under a protective atmosphere to obtain lithium manganese iron phosphate cathode material with an in-situ constructed high-entropy interface. Stepwise calcination includes a first calcination step, a second calcination step, and a third calcination step, wherein... The temperature of the first calcination step is 120 ℃~220 ℃, and the calcination time is 1 h~5 h; The second calcination step involves a temperature of 350 ℃ to 550 ℃ and a calcination time of 6 h to 12 h. The third step of calcination is carried out at a temperature of 600 ℃ to 800 ℃ for a duration of 6 h to 12 h. The annealing temperature is 750 ℃~850 ℃, and the annealing time is 2 h~15 h.

2. The method for preparing lithium manganese iron phosphate cathode material with in-situ constructed high-entropy interface according to claim 1, characterized in that, The first grinding was mechanical liquid phase ball milling, with a ball milling speed of 200 r / min to 800 r / min and a ball milling time of 2 h to 8 h.

3. The method for preparing lithium manganese iron phosphate cathode material with in-situ constructed high-entropy interface according to claim 1 or 2, characterized in that, The second grinding was ball milling, with a ball milling speed of 400 r / min to 1200 r / min and a ball milling time of 0.5 h to 20 h.

4. The method for preparing lithium manganese iron phosphate cathode material with in-situ high-entropy interface according to claim 3, characterized in that, The second grinding process also includes adding a carbon source during the grinding process to perform secondary carbon coating on the multi-element doped lithium manganese iron phosphate cathode material.

5. The method for preparing lithium manganese iron phosphate cathode material with in-situ constructed high-entropy interface according to claim 1 or 2, characterized in that, The general chemical formula of lithium manganese iron phosphate cathode material with in-situ constructed high-entropy interface is Li. (m+un / 2+a+0.05) (Mn x Fe 1-x ) m (M u+ ) n (PO4) (m+un / 2+a) @C, where 0≤x≤1, m≥0, n≥0, m+n=1, 0≤a≤0.1, u is the valence state of element M, and a is (PO4). 3- Excess coefficient; Manganese source, iron source, metal M source, lithium source, and phosphorus source are added according to the stoichiometric ratio of each element in the general chemical formula of lithium iron phosphate cathode material for in-situ construction of high-entropy interface; In each mole of lithium iron phosphate cathode material with an in-situ high-entropy interface, the amount of carbon source added is 10 g to 30 g.

6. The method for preparing lithium manganese iron phosphate cathode material with in-situ constructed high-entropy interface according to claim 1 or 2, characterized in that, It also includes adding a dispersant before the first grinding.

7. The method for preparing lithium manganese iron phosphate cathode material with in-situ constructed high-entropy interface according to claim 1 or 2, characterized in that, The manganese source is at least one of manganese metal oxides, manganese phosphates, manganese sulfates, manganese carbonates, manganese hydroxides, and manganese metal salts. The iron source is at least one of iron metal oxides, iron phosphates, iron sulfates, iron carbonates, iron hydroxides, and iron metal salts; The metal source M is at least one of the following: an oxide of metal M, a phosphate of metal M, a sulfate of metal M, a carbonate of metal M, a hydroxide of metal M, and a metal acid salt of metal M; The lithium source is at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; The phosphorus source is at least one of phosphoric acid, lithium dihydrogen phosphate, and transition metal phosphates; The carbon source is at least one of sucrose, PVA, dopamine, sodium carboxymethyl cellulose, and starch.

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