Lithium manganese iron phosphate positive electrode material for in-situ construction of high-entropy interface and preparation method of lithium manganese iron phosphate positive electrode material

Abstract

The invention provides a lithium manganese iron phosphate positive electrode material for in-situ construction of a high-entropy interface and a preparation method of the lithium manganese iron phosphate positive electrode material. The method comprises the following steps: performing primary grinding, drying and screening on 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 iron manganese phosphate precursor; and calcining the multi-element doped lithium manganese iron phosphate precursor in a protective atmosphere step by step, and cooling to obtain the multi-element doped lithium manganese iron phosphate positive electrode material. Grinding and screening the multi-element doped lithium manganese iron phosphate positive electrode material for the second time to obtain an amorphous multi-element doped lithium manganese iron phosphate positive electrode material; and carrying out annealing treatment on the amorphous multi-element doped lithium manganese iron phosphate positive electrode material in a protective atmosphere to obtain the lithium manganese iron phosphate positive electrode material for in-situ construction of the high-entropy interface. The lithium manganese iron phosphate positive electrode material prepared by the method disclosed by the invention is composed of micron-sized secondary particles agglomerated by nano-sized primary particles, and is large in specific surface area and high in electrochemical activity.

Description

Technical Field

[0001] The present invention relates to the field of battery materials, and more specifically, to a lithium manganese iron phosphate positive electrode material with an in-situ high entropy interface and a preparation method thereof. Background Art

[0002] At present, the technology of lithium iron phosphate cathode materials has become mature in the past 20 years of development, and the energy density of the material itself is difficult to further improve. As an upgraded version of lithium iron phosphate, lithium manganese iron phosphate has attracted 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 makes it have low electrochemical activity and high electrolyte reactivity. In practical applications, its performance is often inferior to that of lithium iron phosphate, which limits the development of this material. Appropriate element doping can regulate the lattice structure of the material and optimize the band structure, thereby improving the electrochemical activity and lattice stability of the material to a certain extent. However, a large amount of element doping may cause a decrease in the theoretical energy density of the material. At the same time, too many doped elements will also increase the production cost and recycling cost of the material. In addition, there is often a large amount of macro-segregation in the element doping of the precursor, which leads to uneven element distribution during the initial sintering process of the material and the modification effect is not obvious. Therefore, there is an urgent need for a method to solve the above problems.

[0003] At present, the element doping modification of lithium manganese iron phosphate can be mainly divided into single element doping (CN 118145619A, CN 117658094 A), double element co-doping (CN 118712368 A) and multi-element synergistic doping (CN 117682496A). However, in different modification methods, even if the liquid phase co-precipitation technology, hydrothermal method or high-energy ball milling are used to make the precursors uniformly mixed at the nanometer level, there will inevitably be uneven distribution of matter and energy between the micro-elements of the system, and the material will inevitably produce micro- and macro-segregation during the production process, which will greatly reduce the modification effect. If the doping is too much, it may even cause the material to coexist in two phases or even multiple phases during the sintering process, which will reduce the modification effect of the material or make the repeatability poor. Summary of the invention

[0004] In view of the deficiencies in the prior art, one of the purposes of the present invention is to solve one or more problems in the prior art. For example, one of the purposes of the present invention is to provide a method for preparing a high-performance lithium manganese iron phosphate positive electrode material with low cost and short process.

[0005] On the one hand, the present invention provides a preparation method of a lithium iron manganese phosphate positive electrode material for in-situ construction of a high entropy interface, which can include the following steps: grinding a manganese source, an iron source, a metal M source, a lithium source, a phosphorus source and a carbon source for the first time, drying and screening to obtain a multi-element doped lithium iron manganese phosphate precursor, wherein the metal M is at least one of V, Nb, Ti, Cr, Mg, Zr, W and Mo; calcining the multi-element doped lithium iron manganese phosphate precursor in a protective atmosphere in steps, cooling to obtain a multi-element doped lithium iron manganese phosphate positive electrode material; grinding the multi-element doped lithium iron manganese phosphate positive electrode material for a second time, screening to obtain an amorphous multi-element doped lithium iron manganese phosphate positive electrode material; annealing the amorphous multi-element doped lithium iron manganese phosphate positive electrode material in a protective atmosphere to obtain a lithium iron manganese phosphate positive electrode material for in-situ construction of a high entropy interface.

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

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

[0008] Furthermore, the second grinding 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 positive electrode material.

[0009] Furthermore, the step-by-step calcination may include a first step calcination, a second step calcination and a third step calcination, wherein the temperature of the first step calcination may be 120°C to 220°C, and the calcination time may be 1h to 5h; the temperature of the second step calcination may be 350°C to 550°C, and the calcination time may be 6h to 12h; the temperature of the third step calcination may be 600°C to 800°C, and the calcination time may be 6h to 12h.

[0010] Furthermore, the annealing temperature may be 750° C. to 850° C., and the annealing time may be 2 h to 15 h.

[0011] Furthermore, the heating rate of the annealing treatment may be 1° C. / min to 10° C. / min.

[0012] Furthermore, the general chemical formula of the lithium manganese iron phosphate cathode material for in-situ construction of a high entropy interface can be Li (m+un / 2+a+0.05) (Mn x Fe 1-x ) m (M u+ ) n (PO 4 ) (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 (PO 4 ) 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 chemical formula of lithium iron manganese phosphate positive electrode material for in-situ construction of high entropy interface; the amount of carbon source added can be 10g to 30g per mole of lithium iron manganese phosphate positive electrode material for in-situ construction of high entropy interface.

[0013] Furthermore, the method may further 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 salts of metal M; 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; the carbon source can be at least one of sucrose, PVA, dopamine, sodium carboxymethyl cellulose and starch.

[0015] Another aspect of the present invention provides a lithium manganese iron phosphate positive electrode material for in-situ construction of a 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 (PO 4 ) (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 (PO 4 ) 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 iron manganese phosphate positive electrode material through the "high entropy doping-step calcination-secondary ball milling-annealing" process, which can simultaneously achieve the improvement of the intrinsic ion / electronic conductivity of the lithium iron manganese phosphate positive electrode material, the construction of a high ion conductivity high entropy interface and grain refinement, inhibit the dissolution of Mn, avoid micro- and macro-segregation, and improve the material's rate performance and cycle stability in multiple dimensions.

[0018] (2) The present invention firstly uniformly incorporates the doping elements into the positive electrode material by calcination, and then precipitates the doping elements in situ on the surface through high-temperature annealing to supersaturate the material, thereby constructing a high-entropy surface interface. The constructed high-entropy surface interface has high ionic conductivity and can inhibit the dissolution of Mn.

[0019] (3) The lithium manganese iron phosphate positive electrode material obtained by the present invention is composed of micron-sized secondary particles formed by the agglomeration of nano-sized primary particles, has a large specific surface area and high electrochemical activity, and at the same time, the construction of a high entropy interface greatly improves the interface stability of the material. The physical and chemical indicators of the material preparation are controllable. The process is safe and environmentally friendly, has low technical difficulty, and the raw materials are easily available, the cost is low, the process is short, and it is easy to realize industrial production. The prepared lithium manganese iron phosphate positive electrode material has excellent performance. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0021] Figure 1 This is an SEM image of the lithium manganese iron phosphate positive electrode material with in-situ constructed high entropy interface prepared in Example 1.

[0022] Figure 2 This is the XRD pattern of the lithium manganese iron phosphate positive electrode material with in-situ constructed high entropy interface prepared in Example 1.

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

[0024] Figure 4 This is the SEM image of the lithium manganese iron phosphate positive electrode material with in-situ constructed high entropy interface obtained in Example 2.

[0025] Figure 5 This is the XRD pattern of the lithium manganese iron phosphate positive electrode material with in-situ constructed high entropy interface prepared in Example 2.

[0026] Figure 6 0.1C charge-discharge curve of the lithium manganese iron phosphate positive electrode material with in-situ high entropy interface prepared in Example 2.

[0027] Figure 7 1C charge-discharge curve of the lithium manganese iron phosphate positive electrode material with in-situ constructed high entropy interface prepared in Example 3.

[0028] Figure 8 This is a rate performance diagram of the lithium manganese iron phosphate positive electrode material with in-situ constructed high entropy interface obtained in Example 3.

[0029] Fig. 9 This is a cycle performance diagram of the lithium manganese iron phosphate positive electrode material with in-situ constructed high entropy interface obtained in Example 3.

[0030] Fig.10 This is the SEM image of the lithium manganese iron phosphate positive electrode material prepared in Comparative Example 1.

[0031] Fig.11 This is the first charge and discharge curve of the lithium manganese iron phosphate positive electrode material prepared in Comparative Example 1.

[0032] Fig.12 This is a cycle performance diagram of the lithium manganese iron phosphate positive electrode material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0033] Hereinafter, the lithium manganese iron phosphate positive electrode material with in-situ high entropy interface construction and the preparation method thereof according to the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.

[0034] Specifically, in order to avoid the uneven distribution of substances and energy produced by lithium iron manganese phosphate positive electrode materials caused by existing technologies such as liquid phase coprecipitation technology and hydrothermal method, and the existence of problems such as micro- and macro-segregation, the present invention proposes a "high entropy doping-step calcination-secondary ball milling-annealing" process. Through step-by-step calcination, the doping element M is distributed in large quantities on the surface of lithium iron manganese phosphate particles to form an enrichment layer, which can produce a strong pinning effect, preventing the further growth of primary particles of the positive electrode material, thereby playing a role in refining the grains. Through secondary ball milling, the strong impact of ball milling causes a large number of defects on the surface of the grains and inside the bulk phase, which greatly reduces the stability of the crystal while increasing the energy of the particle surface and the bulk phase itself, thereby producing a large number of highly active particles. In the subsequent annealing process, the elements are rearranged due to the thermodynamic energy minimum effect. In order to reduce the total energy of the system, a small amount of doping elements are further enriched at the grain boundaries, thereby forming a high-entropy interface structure in situ on the surface and balancing the distribution positions of the elements in the lattice, making the elements evenly distributed, thereby improving the electrochemical activity of the lithium manganese iron phosphate positive electrode material and greatly enhancing the interface stability of the material.

[0035] Moreover, according to the characteristics of the limited substitution of Fe / Mn by the metal M in lithium manganese iron phosphate (LMFP) under the influence of the sintering temperature, and the infinite eutectic characteristics between the metal M ions, the present invention can adjust the bulk doping amount and the high entropy interface structure by adjusting the calcination and annealing temperature, and coordinate the metal M ion ratio, thereby realizing multiple dimensions such as lattice vacancy regulation brought about by adjusting the ion doping amount, supervalent ion doping, and multifunctional interface regulation. The multifunctional interface here refers to a high entropy interface composed of multiple elements, which can optimize the surface band structure of the material, thereby improving the conductivity, improving the mechanical properties of the material, and enhancing the structural stability, thereby optimizing the lithium manganese iron phosphate lithium storage structure. Moreover, the high entropy interface formed by the in-situ supersaturation and microscopic segregation of a small amount of elements achieved by the preparation method of the present invention can effectively inhibit the mass transfer between particles during high-temperature calcination and annealing, weaken the agglomeration dynamics during calcination and annealing, and can refine the primary particles. Therefore, the present invention, through doping with a variety of hypervalent ions and using the "high entropy doping-step calcination-secondary ball milling-annealing" process, can simultaneously achieve the improvement of the intrinsic ion / electronic conductivity of the lithium manganese iron phosphate positive electrode material, the construction of a high ion conductivity high entropy interface and grain refinement, inhibit the dissolution of Mn, avoid micro- and macro-segregation, and improve the material's rate performance and cycle stability in multiple dimensions.

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

[0037] S01, grinding, drying and sieving a manganese source, an iron source, a metal M source, a lithium source, a phosphorus source and a carbon source for the first time 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;

[0038] S02, calcining the multi-element doped lithium manganese iron phosphate precursor in a protective atmosphere in steps, and cooling it to obtain a multi-element doped lithium manganese iron phosphate positive electrode material;

[0039] S03, grinding and sieving the multi-element doped lithium manganese iron phosphate positive electrode material for a second time to obtain an amorphous multi-element doped lithium manganese iron phosphate positive electrode material;

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

[0041] In some embodiments, the amount of manganese source, iron source, metal M source, lithium source, phosphorus source and carbon source used can be proportioned according to the stoichiometric ratio of the target product lithium manganese iron phosphate positive electrode material. In certain embodiments, 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 may 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 may be one or a mixture of manganese trioxide, manganese sulfate, manganese carbonate, manganese hydroxide and the like.

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

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

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

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

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

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

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

[0050] In some embodiments, the drying in step S01 can be performed by air drying or vacuum drying. The drying temperature can be set to 60°C to 120°C, and the drying time can be 8h to 24h. For example, the drying temperature can be set to 100°C, and the drying time can be 12h. The main purpose of the screening in step S01 is to separate the pellets. Similarly, the purpose of the screening in step S03 is to separate the pellets.

[0051] In some embodiments, the step-by-step calcination may include the use of three-step calcination, wherein the temperature of the first calcination may be 120°C to 220°C, and the calcination time may be 1h to 5h. At the calcination temperature and time set above, the residual moisture of the precursor will be fully removed. If the time is too short or the temperature is too low, the residual moisture will not be completely volatilized, affecting the subsequent chemical reaction. If the sintering temperature is too high, the second step reaction will occur in advance, which is not conducive to the preparation of positive electrode materials. The temperature of the second step calcination may be 350°C to 550°C, and the calcination time may be 6h to 12h. At the calcination temperature and time set above, the raw material will be partially decomposed, the organic carbon source will be carbonized, and lithium manganese iron phosphate will be initially formed. If the process time is too short, the precursor cannot be completely decomposed, and the organic carbon source cannot be completely carbonized; if the time is too long, the phase will not change significantly. The temperature of the third step calcination may be 600°C to 800°C, and the calcination time may be 6h to 12h. At the calcination temperature and time set above, lithium manganese iron phosphate is completely formed, each atom moves to the equilibrium site, and the crystallinity of the material is improved. If the process time is too short or the sintering temperature is low, the material crystallinity is poor; if the process time is extended or the sintering temperature is high, the primary particles of the material will become larger, which is not conducive to the improvement of electrochemical performance. The three-step calcination temperature and time set above cooperate with each other to obtain a lithium manganese iron phosphate positive electrode material with a large specific surface area, high electrochemical activity and excellent performance. For example, in some embodiments, the temperature of the first calcination can be 150℃~200℃, and the calcination time can be 2h~4h. The temperature of the second calcination can be 380℃~500℃, and the calcination time can be 7h~11h. The temperature of the third calcination can be 640℃~750℃, and the calcination time can be 7h~11h. For another example, the temperature of the first calcination can be 170℃~190℃, and the calcination time can be 2.5h~3.5h. The temperature of the second step calcination can be 420°C to 480°C, and the calcination time can be 8h to 10h. The temperature of the third step calcination can be 670°C to 720°C, and the calcination time can be 8h to 9h. In certain embodiments, the protective atmosphere can be an atmosphere such as argon, nitrogen, argon, etc. The protective gas introduction rate can be controlled between 100mL / min and 2000mL / min. In certain embodiments, the heating rate of each step calcination can be 1°C / min to 10°C / min. For example, the heating rate can be 2°C / min to 8°C / min, 4°C / min to 7°C / min, 5°C / min to 6°C / min, or a combination of the above ranges.

[0052] In some embodiments, the second grinding can be ground with the addition of a dispersant, or can be ground directly without the addition of a dispersant. The dispersant can be any one or more of ethanol, water, ethylene glycol and acetone mixed in any proportion. In some embodiments, the second grinding can be performed by ball milling. The ball milling speed can be 400r / min to 1200r / min, and the ball milling time can be 0.5h to 20h. 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 is weak, the amorphization degree of the crystal is low, and it is not 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 material to develop in the direction of 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 can be 500r / min to 1100r / min, and the ball milling time can be 1.5h to 15h. For another example, the ball milling speed can be 720r / min to 980r / min, and the ball milling time can be 3.5h to 11h. The materials of the ball milling jar and ball milling beads used in the ball milling process can be stainless steel, zirconium oxide or tungsten carbide, etc. The ball milling beads can be used according to the ball to material ratio (5-20):1.

[0053] In some embodiments, it also includes adding a carbon source during the second grinding process to perform secondary carbon coating on the multi-element doped lithium manganese iron phosphate positive electrode material. Since the carbon coating layer may be uneven during the first carbon coating process after the first grinding or the carbon coating layer may be uneven during the amorphization of the secondary ball milling crystals, a carbon source can be added during the second ball milling process for secondary carbon coating, so that a more uniform carbon coating layer can be obtained. 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 of grinding. No carbon source is added to the first stage of grinding, and dry grinding can be used. After the first stage of grinding, a carbon source is added for the second stage of grinding. The second stage of grinding can be mechanical liquid activation.

[0054] In some embodiments, the annealing temperature can be 750℃~850℃, and the annealing time can be 2h~15h. If the annealing temperature is lower than 750℃, the atomic diffusion kinetics are poor, and the atoms cannot effectively move to the constant position; if the annealing time is less than 2h, the chemical reaction cannot reach the expected equilibrium. If the annealing temperature is higher than 850℃, the primary particles of the material will increase, and the thermodynamic equilibrium state will change uncontrollably, which is not conducive to the development of the material towards the expected goal. If the annealing time is greater than 15h, the material will not undergo further significant changes. From the perspective of energy conservation, the annealing time is set to be less than 15h. For example, in some embodiments, the annealing temperature can be 760℃~830℃, and the annealing time can be 4h~13h; or the annealing temperature can be 780℃~810℃, and the annealing time can be 6h~10h. In some embodiments, the heating rate of the annealing treatment can be 1℃ / min~10℃ / min. For example, the heating rate of the annealing treatment may be 2° C. / min to 8° C. / min, 4° C. / min to 7° C. / min, 5° C. / min to 6° C. / min, or a combination of the above ranges.

[0055] In some embodiments, the protective atmosphere for the annealing treatment may be argon, nitrogen, argon, etc. The rate of introduction of the protective gas may be controlled between 100 mL / min and 2000 mL / min.

[0056] In some embodiments, the chemical formula of the lithium manganese iron phosphate cathode material for in-situ construction of a high entropy interface is Li (m+un / 2+a+0.05) (Mn x Fe 1-x ) m (M u+ ) n (PO 4 ) (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 (PO 4 ) 3- For example, in some embodiments, the chemical formula of the lithium manganese iron phosphate positive electrode material for in-situ construction of a high entropy interface can be LiMn 0.72 Fe 0.181 V 0.023 Ti 0.02 Mg 0.03 PO 4 @C, LiMn 0.55 Fe 0.36 7 V 0.023 Nb 0.02 Mg 0.03 PO 4 @C、LiMn 0.474 Fe0.316 Nb 0.03 Cr 0.01 W 0.02 Mo 0.03 (PO 4 ) 0.95 @C, etc. The amount of carbon source added to each mole of lithium manganese iron phosphate positive electrode material with in-situ high entropy interface construction is 10g to 30g. For example, the amount of carbon source added can be 12g to 25g, 18g to 22g, 19g to 21g or a combination of the above ranges.

[0057] Another aspect of the present invention provides a lithium iron manganese phosphate cathode material with an in-situ high entropy interface. The lithium iron manganese phosphate cathode material with an in-situ high entropy interface can be prepared by the above-mentioned preparation method of the lithium iron manganese phosphate cathode material with an in-situ high entropy interface. In some embodiments, the general chemical formula of the lithium iron manganese phosphate cathode material with an in-situ high entropy interface can be Li (m+un / 2+a+0.05) (Mn x Fe 1-x ) m (M u+ ) n (PO 4 ) (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 (PO 4 ) 3- The excess coefficient, M, is at least one of V, Nb, Ti, Cr, Mg, Zr, W and Mo.

[0058] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with specific examples, but the content of the present invention is not limited to the following examples.

[0059] Example 1

[0060] A method for preparing a lithium manganese iron phosphate positive electrode material with an in-situ high entropy interface comprises the following steps:

[0061] Step 1: According to the stoichiometric ratio of the lithium manganese iron phosphate cathode material for in-situ construction of a high entropy interface, 594.58 g of Mn 3 O 4 , 414.97 g Fe 2 O 3 , 1561.07g LiH 2 PO 4 , 11g Li 2 CO 3 , 297.41g PVA, 27.32g V 2 O 5 , 35.72 g TiO2 , 18.35g MgO, 39.57g Nb 2 O 5 , put the weighed raw materials into a zirconia ball mill, add 6L of deionized water, 500ml of ethylene glycol as a dispersant, add 30kg of zirconia balls, and perform mechanical activation in the ball mill. The ball milling speed is set to 200r / min, and the ball milling time is set to 15h. After the ball milling is completed, the ball milled slurry is placed in a 100℃ blast drying oven and dried for 48h. After drying, it is taken out for ball material separation to obtain a multi-element doped lithium manganese iron phosphate precursor.

[0062] Step 2, take 50g of the sieved dry precursor powder, pour it into a corundum crucible, and then place it in a tubular furnace. Under an argon atmosphere, first keep it at 180°C for 3h, then heat it to 550°C, keep it for 10h, and finally keep it at 750°C for 8h. Cool it to room temperature with the furnace to obtain carbon-coated multi-element doped lithium manganese iron phosphate, that is, multi-element doped lithium manganese iron phosphate positive electrode material.

[0063] Step 3, pour the black product powder carbon-coated multi-element doped lithium manganese iron phosphate obtained in step 2 into a stainless steel ball mill, add 200g stainless steel balls, and perform secondary ball milling. The ball milling speed is set to 600r / min, the ball milling time is set to 12h, dry milling is performed for the first 6 hours, and 6g sucrose and 55ml ethanol are added for the second mechanical activation and organic carbon coating for the last 6 hours. After the ball milling is completed, the ball milled slurry is placed in an 80°C blast drying oven for 24h blast drying. After drying, the ball material is separated to obtain black lithium manganese iron phosphate, that is, an amorphous multi-element doped lithium manganese iron phosphate positive electrode material.

[0064] Step 4, pour the screened black lithium manganese iron phosphate into a corundum crucible, place it in a tubular furnace, anneal it at 800°C for 8 hours, and after cooling to room temperature with the furnace, obtain the lithium manganese iron phosphate positive electrode material with an in-situ high entropy interface.

[0065] The lithium manganese iron phosphate cathode material with in-situ high entropy interface was tested, among which, Figure 1 This is a SEM image of the lithium manganese iron phosphate positive electrode material prepared in this embodiment. It can be seen from the image that the material is composed of micron-sized secondary particles formed by the agglomeration of nano-sized primary particles. Figure 2 This is the XRD spectrum of the lithium manganese iron phosphate positive electrode material with in-situ constructed high entropy interface prepared in this embodiment. It can be seen from the figure that the positive electrode material has a standard olivine structure and has good crystallinity. Figure 3 This is a TEM image of the lithium manganese iron phosphate positive electrode material with an in-situ constructed high entropy interface prepared in this embodiment. It can be seen from the image that the atoms inside the material crystal are arranged neatly without any impurities mixed.

[0066] Example 2

[0067] A method for preparing a lithium manganese iron phosphate positive electrode material with an in-situ high entropy interface comprises the following steps:

[0068] Step 1: According to the stoichiometric ratio of the lithium manganese iron phosphate cathode material for in-situ construction of a high entropy interface, 620.84 g of Mn 3 O 4 , 433.3 g Fe 2 O 3 , 1566.62g LiH 2 PO 4 , 11.03gLi 2 CO 3 , 298.47g sucrose, 13.7gV 2 O 5 , 23.89 g TiO 2 , 12.27g MgO, 19.85g Nb 2 O 5 , 22.51g NiO, the weighed raw materials were placed in a stainless steel ball mill, and 6L of anhydrous ethanol was added as a dispersant, and 15kg of tungsten carbide balls were added, and mechanical activation was performed in the ball mill, the ball milling speed was set to 200r / min, and the ball milling time was set to 12h. After the ball milling was completed, the ball milled slurry was placed in an 80℃ blast drying oven and dried for 24h. After drying, it was taken out for ball material separation to obtain a multi-element doped lithium manganese iron phosphate precursor.

[0069] Step 2, take 50g of the sieved dry precursor powder, pour it into a corundum crucible, and then place it in a tubular furnace. Under an argon atmosphere, first keep it at 180°C for 3h, then heat it to 450°C, keep it for 8h, and finally keep it at 650°C for 10h. Cool it to room temperature with the furnace to obtain carbon-coated multi-element doped lithium manganese iron phosphate, that is, multi-element doped lithium manganese iron phosphate positive electrode material.

[0070] Step 3, pour the black product powder carbon-coated multi-element doped lithium manganese iron phosphate obtained in step 2 into a stainless steel ball mill, add 200g tungsten carbide balls, and perform secondary ball milling. The ball milling speed is set to 500r / min, the ball milling time is set to 12h, dry milling is performed for the first 6 hours, and 10g sucrose and 70ml ethanol are added for the second mechanical activation and organic carbon coating for the last 6 hours. After the ball milling is completed, the ball milled slurry is placed in an 80°C blast drying oven for 24h blast drying. After drying, the ball material is separated to obtain black lithium manganese iron phosphate, that is, an amorphous multi-element doped lithium manganese iron phosphate positive electrode material.

[0071] Step 4, pour the screened black lithium manganese iron phosphate into a corundum crucible, place it in a tubular furnace, anneal it at 850° C. for 10 hours, and after cooling to room temperature with the furnace, obtain the lithium manganese iron phosphate positive electrode material with an in-situ high entropy interface.

[0072] The lithium manganese iron phosphate cathode material with in-situ high entropy interface was tested, among which, Figure 4 This is a SEM image of the lithium manganese iron phosphate positive electrode material prepared in this embodiment. It can be seen from the image that the material is agglomerated by nano-scale primary particles to form micron-scale secondary particles. Figure 5 This is the XRD spectrum of the lithium manganese iron phosphate positive electrode material prepared in this embodiment. It can be seen from the figure that the material has a standard olivine structure and has good crystallinity. Figure 6 This is a 0.1C charge and discharge curve of the lithium manganese iron phosphate positive electrode material prepared in this embodiment. It can be seen from the figure that the first cycle discharge specific capacity of the material at a 0.1C rate is 148.2 mAh / g, and the material has excellent electrochemical performance.

[0073] Example 3

[0074] A method for preparing a lithium manganese iron phosphate positive electrode material with an in-situ high entropy interface comprises the following steps:

[0075] Step 1: According to the stoichiometric ratio set by the lithium manganese iron phosphate positive electrode material for in-situ construction of high entropy interface, 594.72 g Mn 3 O 4 , 415.07 g Fe 2 O 3 , 1574.35g LiH 2 PO 4 , 40.86gLi 2 CO 3 , 315.72 g sucrose, 25.28 g TiO 2 , 12.98g MgO, 21g Nb 2 O 5 , 23.82g NiO, put the weighed raw materials into a stainless steel ball mill, 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 the ball milling is completed, the ball milled slurry is placed in a 100℃ blast drying oven and dried for 18h. After drying, it is taken out for ball-material separation to obtain a multi-element doped lithium manganese iron phosphate precursor.

[0076] Step 2, take 50g of the sieved dry precursor powder, pour it into a corundum crucible, and then place it in a tubular furnace. Under an argon atmosphere, first keep it at 120°C for 3h, then heat it to 480°C, keep it for 10h, and finally keep it at 625°C for 10h. Cool it to room temperature with the furnace to obtain carbon-coated multi-element doped lithium manganese iron phosphate, that is, multi-element doped lithium manganese iron phosphate positive electrode material.

[0077] Step 3, pour the obtained black powder into a stainless steel ball mill, add 200g stainless steel balls, perform secondary ball milling, set the ball milling speed to 400r / min, set the ball milling time to 10h, dry milling for the first 5 hours, and add 12g sucrose and 80ml deionized water for secondary mechanical activation and organic carbon coating in the last 5 hours. After the ball milling is completed, place the ball milled slurry in a 100°C blast drying oven for 24h blast drying, separate the ball material after drying, and obtain black lithium manganese iron phosphate, that is, amorphous multi-element doped lithium manganese iron phosphate positive electrode material.

[0078] Step 4, pour the screened black lithium manganese iron phosphate into a corundum crucible, place it in a tubular furnace, anneal it at 825°C for 8 hours, and after cooling to room temperature with the furnace, obtain the lithium manganese iron phosphate positive electrode material with an in-situ high entropy interface.

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

[0080] Comparative Example 1

[0081] This comparative example is compared with Example 3. The material preparation process is based on Example 3 except for the secondary ball milling and annealing treatment in Step 3 and Step 4. The specific operation is as follows:

[0082] Step 1: According to the stoichiometric ratio set by the high entropy doped lithium manganese iron phosphate positive electrode material, accurately weigh 594.72gMn 3 O 4 , 415.07 g Fe 2 O 3 , 1574.35g LiH 2 PO 4, 40.86 g Li 2 CO 3 , 315.72 g sucrose, 25.28 g TiO 2 , 12.98g MgO, 21g Nb 2 O 5 , 23.82g NiO, put the weighed raw materials into a stainless steel ball mill, 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 the ball milling is completed, the ball milled slurry is placed in a 100℃ blast drying oven and dried for 18h. After drying, it is taken out for ball-material separation to obtain a multi-element doped lithium manganese iron phosphate precursor.

[0083] Step 2, take 50g of the sieved dry precursor powder, pour it into a corundum crucible, and then place it in a tubular furnace. Under an argon atmosphere, first keep it at 120°C for 3h, then heat it to 480°C, keep it for 10h, and finally keep it at 625°C for 10h. Cool it to room temperature with the furnace to obtain carbon-coated multi-element doped lithium manganese iron phosphate, that is, multi-element doped lithium manganese iron phosphate positive electrode material.

[0084] The obtained high entropy doped lithium manganese iron phosphate positive electrode material was tested. Fig.10 This is the SEM image of the lithium manganese iron phosphate positive electrode material prepared in this comparative example. It can be seen from the figure that the particle size distribution of the material is uneven and there are larger primary particles. Fig.11 This is the first charge and discharge curve of the lithium manganese iron phosphate positive electrode material prepared in this comparative example. It can be seen from the figure that the capacity of the comparative sample is lower than that of the modified material. Fig.12 This is a cycle performance diagram of the lithium manganese iron phosphate positive electrode material prepared in this comparative example. It can be seen from the figure that compared with the modified material, the cycle stability of the comparison sample is poor.

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

Claims

1. A method for preparing a lithium manganese iron phosphate positive electrode material with an in-situ high entropy interface, characterized in that: The following steps are involved: Grinding, drying and sieving the manganese source, iron source, metal M source, lithium source, phosphorus source and carbon source for the first time 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; The multi-element doped lithium manganese iron phosphate precursor is calcined step by step under a protective atmosphere, and cooled to obtain a multi-element doped lithium manganese iron phosphate positive electrode material; Grinding the multi-element doped lithium manganese iron phosphate positive electrode material for a second time and sieving to obtain an amorphous multi-element doped lithium manganese iron phosphate positive electrode material; The amorphous multi-element doped lithium manganese iron phosphate positive electrode material is annealed in a protective atmosphere to obtain a lithium manganese iron phosphate positive electrode material with an in-situ constructed high entropy interface.

2. The method for preparing a lithium iron manganese phosphate positive electrode material with an in-situ high entropy interface according to claim 1, characterized in that: The first grinding is mechanical liquid phase ball milling, the ball milling speed is 200r / min~800r / min, and the ball milling time is 2h~8h.

3. The method for preparing a lithium iron manganese phosphate positive electrode material with an in-situ high entropy interface according to claim 1 or 2, characterized in that: The second grinding is ball milling, the ball milling speed is 400r / min~1200r / min, and the ball milling time is 0.5h~20h.

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

5. The method for preparing a lithium manganese iron phosphate positive electrode material with an in-situ high entropy interface according to claim 1, 2 or 3, characterized in that: The step-by-step calcination includes a first step calcination, a second step calcination and a third step calcination, wherein: The first step of calcination is carried out at a temperature of 120°C to 220°C and a calcination time of 1h to 5h; The second step of calcination is performed at a temperature of 350°C to 550°C and a calcination time of 6h to 12h; The calcination temperature in the third step is 600°C to 800°C, and the calcination time is 6h to 12h.

6. The method for preparing a lithium manganese iron phosphate positive electrode material with an in-situ high entropy interface according to claim 1, 2 or 3, characterized in that: The annealing temperature is 750°C to 850°C, and the annealing time is 2h to 15h.

7. The method for preparing a lithium manganese iron phosphate positive electrode material with an in-situ high entropy interface according to claim 1, 2 or 3, characterized in that: The chemical formula of lithium manganese iron phosphate cathode material with in-situ 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; The manganese source, iron source, metal M source, lithium source and phosphorus source are added according to the stoichiometric ratio of each element in the chemical formula of lithium manganese iron phosphate positive electrode material for in-situ construction of high entropy interface; The amount of carbon source added to each mole of lithium manganese iron phosphate positive electrode material with in-situ high entropy interface is 10g to 30g.

8. The method for preparing a lithium iron manganese phosphate positive electrode material with an in-situ high entropy interface according to claim 1, 2 or 3, characterized in that: It also includes adding a dispersant before the first grinding.

9. The method for preparing a lithium manganese iron phosphate positive electrode material with an in-situ high entropy interface according to claim 1, 2 or 3, characterized in that: The manganese source is at least one of manganese metal oxide, manganese phosphate, manganese sulfate, manganese carbonate, manganese hydroxide and manganese metal acid salt; The iron source is at least one of iron metal oxide, iron phosphate, iron sulfate, iron carbonate, iron hydroxide and iron metal acid salt; The metal M source is at least one of 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 phosphate; The carbon source is at least one of sucrose, PVA, dopamine, sodium carboxymethyl cellulose and starch.

10. A lithium manganese iron phosphate positive electrode material with an in-situ high entropy interface, characterized in that: The chemical formula 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- The excess coefficient, M, is at least one of V, Nb, Ti, Cr, Mg, Zr, W and Mo.

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