Hypervalent ion doped lithium manganese iron phosphate composite positive electrode material and preparation method thereof

Abstract

The invention provides a super-valence ion doped lithium manganese iron phosphate composite positive electrode material and a preparation method thereof. The preparation method comprises the following steps: preparing a ferromanganese mixed salt and a hypervalent ion acid radical salt solution; the method comprises the following steps: preparing a weakly acidic base solution, adding a ferromanganese mixed salt and a hypervalent ion acid radical salt solution into the weakly acidic base solution in a parallel flow manner, adding a complexing agent and an oxidizing agent, and filtering, washing and drying after the reaction is finished to obtain a hypervalent ion doped ferromanganese oxide; and preparing a lithium source, a phosphorus source and a carbon source according to an expression of LiMn1-a-bFeaMbPO4 (at) C, mixing the lithium source, the phosphorus source and the carbon source with the hyper-valent ion doped manganese iron oxide, and calcining in an inert atmosphere to obtain the hyper-valent ion doped lithium manganese iron phosphate composite positive electrode material. The preparation method disclosed by the invention is mild in reaction condition, safe and environment-friendly in production process, low in requirement on corrosion resistance of equipment, low in technical difficulty, easily available in raw materials and easy for large-scale production, and the prepared lithium manganese iron phosphate positive electrode material is excellent in performance.

Description

Technical Field

[0001] The present invention relates to the field of lithium batteries, and more particularly, to a supervalent ion-doped lithium iron manganese phosphate composite cathode material and a preparation method thereof. Background Art

[0002] Lithium iron manganese phosphate has the characteristics of low cost, high energy density and high cycle stability. It is considered as an upgraded version of lithium iron phosphate and is one of the alternative materials for the next-generation high-energy density energy storage field. However, compared with lithium iron phosphate, the severe Jahn-Teller effect of trivalent manganese greatly reduces the ionic and electronic conductivities of manganese-rich lithium iron manganese phosphate, which results in the inability to further improve the actual energy density of lithium iron manganese phosphate materials and limits their wide application in the field of high-performance energy storage. Currently, element doping can change the physical and chemical properties of materials at the unit cell level and is an important means to improve the electrochemical performance of lithium iron manganese phosphate materials.

[0003] At present, the industrialization technologies of lithium iron manganese phosphate mainly adopt the high-temperature solid-state sintering method and the co-precipitation method. The high-temperature solid-state sintering method involves mechanically ball-milling and mixing manganese oxide, iron phosphate, lithium carbonate, lithium dihydrogen phosphate, and an external organic carbon source, and then preparing the LMFP@C cathode material by inert atmosphere carbothermal reduction. Using this method, Mn, Fe, and M (doping elements) are separated independently. To achieve uniform doping and ensure good conductivity, high-energy ball milling must be used to achieve particle nanosizing and mixing. This process has problems such as high energy consumption, the main elements cannot be mixed at the molecular and atomic levels, resulting in uneven material phases, and it is difficult to ensure product consistency. In addition, it is very difficult to achieve controllable preparation of materials during the high-energy ball milling nanosizing process, resulting in irregular particle morphologies. Combined with a relatively high carbon incorporation amount, the product has a high specific surface area and poor processing performance. Preparing a precursor with uniform doping of Mn, Fe, and M by the co-precipitation method can effectively solve the problems of the solid-phase method. The co-precipitation methods reported currently mainly include the basic manganese iron precursor route (CN118619369 A), the oxide precursor preparation route (CN 118458832 A), and the lithium iron manganese phosphate precursor preparation route (CN 118458722A). The basic manganese iron precursor route (CN 118619369 A) can prepare a secondary particle-like spherical basic manganese iron precursor. However, a large amount of carbon dioxide and water molecules will surely be released during the subsequent solid-state sintering process of this precursor, reducing the tap density of the material and seriously affecting the volume energy density of lithium iron manganese phosphate. Using the oxide precursor preparation route (CN 118458832 A) can prepare a multi-element doped manganese iron oxide, which has the characteristic of high tap density. However, its intermittent production process and the precursor calcination treatment process greatly increase the economic cost and time cost, and it is difficult to adapt to industrial continuous production. In the lithium iron manganese phosphate precursor preparation route (CN 118458722 A), the lithium iron manganese phosphate precursor obtained after a series of processes such as sand milling and oil bath temperature rise and crystal conversion of the raw materials has the characteristics of high tap density and easy control of element ratios. However, this process is lengthy and the intermittent production efficiency is low, which is not sufficient to support the large-scale production of lithium iron manganese phosphate.

[0004] The supervalent ion doping of materials can effectively adjust the crystal structure of materials and control the development of materials in the direction conducive to enhancing electrochemical performance. Introducing supervalent ions into the lithium iron manganese phosphate lattice can, on the one hand, effectively regulate the energy band structure of materials and reduce the band gap width, thus facilitating the enhancement of the electronic conductivity of materials. On the other hand, in order to maintain charge conservation after introducing supervalent ions into the lattice, unequal substitution phenomena often occur, that is, a small amount of supervalent ions replace a large amount of Mn and Fe ions, which will generate a part of lattice vacancies, thus broadening the ion transport channels. The current main method for supervalent ion doping of lithium iron manganese phosphate is the solid-phase method (CN 117886289 A), and this method often has problems similar to those in the process of synthesizing lithium iron manganese phosphate by the solid-phase method, namely uneven phase, poor controllability, and difficulty in ensuring consistency. Preparing the transition metal source precursor by the co-precipitation method is a means to solve this problem. However, the hydrolysis equilibrium constants of most supervalent ions in aqueous solutions are very high, which is very different from those of Mn(III) and Fe(III), and almost cannot co-precipitate with Mn and Fe thermodynamically. Under normal circumstances, the multi-element doped manganese iron hydrated oxide precursor prepared by the co-precipitation method (CN 117996019 A) decomposes during the subsequent sintering process, generating a large amount of water molecules. The water molecules will undergo redox reactions with the carbon source at high temperatures, consuming the carbon source, making it difficult to control the carbon coating amount of the material. In addition, the removal of water molecules will also cause a huge change in the volume of some raw materials, reducing the contact area between particles, thus affecting the chemical reaction kinetics. Therefore, an innovative supervalent ion co-precipitation scheme must be sought. Summary of the Invention

[0005] Aiming at the deficiencies existing in the prior art, one of the purposes of the present invention is to solve one or more of the problems existing in the above prior art. For example, one of the purposes of the present invention is to provide a method for simply and efficiently producing supervalent ion uniformly doped manganese iron oxide with high tap density, realizing the short-process and low-power consumption preparation of the manganese iron oxide precursor, and further realizing the supervalent element doping of lithium iron manganese phosphate.

[0006] One aspect of the present invention provides a method for preparing a supervalent ion-doped lithium iron manganese phosphate composite cathode material, which may include the following steps: preparing a manganese iron mixed salt and a supervalent ion acid radical salt solution, wherein the supervalent ion acid radical salt is at least one of vanadate, chromate, niobate, titanate, tungstate, molybdate, and aluminate; preparing a weakly acidic bottom liquid, adding the manganese iron mixed salt and the supervalent ion acid radical salt solution into the weakly acidic bottom liquid in a parallel flow manner, and adding a complexing agent and an oxidizing agent. After the reaction ends, filtering, washing, and drying are carried out to obtain supervalent ion-doped manganese iron oxide; according to the expression LiMn 1-a-b Fe a M bThe PO4@C configured lithium source, phosphorus source and carbon source are mixed with the hypervalent ion doped manganese iron oxide and calcined under an inert atmosphere to obtain a hypervalent ion doped lithium manganese iron phosphate composite cathode material, wherein M is selected from at least one of vanadium, chromium, niobium, titanium, tungsten, molybdenum and aluminum, and a + b < 1.

[0007] Further, the pH of the weakly acidic solution can be 2 - 6.

[0008] Further, the complexing agent can be at least one of ammonia water, ammonia gas and sodium ethylenediaminetetraacetate. The oxidizing agent can be at least one of oxygen and air.

[0009] Further, the manganese salt can be at least one of manganese sulfate, manganese sulfite, manganese chloride, manganese nitrate, manganese nitrite, manganese acetate and manganese oxalate;

[0010] Further, the iron salt can be at least one of ferric sulfate, ferrous sulfite, ferric chloride, ferric nitrate, ferrous nitrite, ferric acetate and ferric oxalate.

[0011] Further, the calcination can include heating to 400°C - 500°C at a rate of 2°C / min - 4°C / min and holding for 4 h - 8 h, and then heating to 600°C - 800°C at a rate of 2°C / min - 4°C / min and holding for 6 h - 12 h.

[0012] Further, the lithium source can be at least one of lithium dihydrogen phosphate, lithium hydroxide and lithium carbonate. The phosphorus source can be at least one of lithium dihydrogen phosphate and phosphoric acid; the carbon source is at least one of sucrose, starch, glucose and graphite.

[0013] Further, it can also include adding a dispersant when the lithium source, phosphorus source, carbon source and hypervalent ion doped manganese iron oxide are mixed. The dispersant can be at least one of ethanol, deionized water and ethylene glycol.

[0014] Further, the feeding rate of the complexing agent can be 0.2 - 5 times the feeding rate of the manganese - iron mixed salt. The feeding rate of the manganese - iron mixed salt and the hypervalent ion acid radical salt solution can be 0.01 L / min - 100 L / min. The feeding rate of the oxidizing agent can be 0.01 L / min - 100 L / min.

[0015] Another aspect of the present invention provides a hypervalent ion doped lithium manganese iron phosphate composite cathode material, which can be prepared by the preparation method of the hypervalent ion doped lithium manganese iron phosphate composite cathode material described above.

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

[0017] (1) The hypervalent ion-doped manganese iron oxide prepared by the present invention is micron-sized, has a high tap density, uniform composition, and controllable physical and chemical indexes.

[0018] (2) The preparation method of the present invention has mild reaction conditions, a safe and environmentally friendly production process, low requirements for equipment corrosion resistance, low technical difficulty, easily available raw materials, is easy to scale up production, and the prepared lithium iron manganese phosphate cathode material has excellent performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Through the following description in conjunction with the drawings, the above and other objects and features of the present invention will become clearer, wherein:

[0020] Figure 1 SEM image of the hypervalent ion-doped manganese iron oxide prepared in Example 1;

[0021] Figure 2 XRD pattern of the hypervalent ion-doped manganese iron oxide prepared in Example 1;

[0022] Figure 3 XRD pattern of the lithium iron manganese phosphate cathode material prepared in Example 1;

[0023] Figure 4 SEM image of the lithium iron manganese phosphate cathode material prepared in Example 1;

[0024] Figure 5 SEM image of the hypervalent ion-doped lithium iron manganese phosphate prepared in Example 2;

[0025] Figure 6 XRD pattern of the hypervalent ion-doped lithium iron manganese phosphate prepared in Example 2;

[0026] Figure 7 0.1C charge-discharge curve of the hypervalent ion-doped lithium iron manganese phosphate prepared in Example 2;

[0027] Figure 8 SEM image of the hypervalent ion-doped lithium iron manganese phosphate prepared in Example 3;

[0028] Figure 9 XRD pattern of the hypervalent ion-doped lithium iron manganese phosphate prepared in Example 3;

[0029] Figure 10 Rate performance curve of the hypervalent ion-doped lithium iron manganese phosphate prepared in Example 3;

[0030] Figure 11 Cycling performance graph of the hypervalent ion-doped lithium iron manganese phosphate prepared in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0031] In the following, a preparation method of a supervalent ion-doped lithium iron manganese phosphate composite cathode material according to the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.

[0032] Specifically, the inventors have found that alkali-soluble supervalent metals such as V, Nb, Ti, Cr, W, Mo, and Al will form MO x n- acid anions (M is any one of V, Nb, Ti, Cr, W, Mo, and Al) under highly alkaline conditions. Under the conditions of co-precipitation of Mn and Fe, due to the consumption of OH - ions in the precipitation microdomain, co-precipitation of supervalent ion elements with Mn and Fe elements can be achieved. Based on this, in the present invention, a supervalent ion acid root salt solution is configured. The supervalent ion acid root salt solution is alkaline and can complex supervalent ions with hydroxide ions. After the complexation is completed, by adding the supervalent ion acid root salt solution and the manganese-iron mixed salt into the bottom liquid in a parallel flow manner, on the premise that the supervalent ions complex with hydroxide ions and crystallize to consume hydroxide ions, co-precipitation of Mn 2+ / 3+ and Fe 2+ / 3+ ions with supervalent ions can be achieved, which can ensure the controllability of the whole process, and then realize that the precursor presents a spherical morphology and the particle size is controllable. If the alkali-soluble supervalent metal does not complex with OH - ions first, the solubility product constants of the supervalent doped ions and Mn and Fe precipitates differ too much, which will lead to rapid separate nucleation, resulting in uneven doping and uncontrollable morphology and particle size. By adding a complexing agent and an oxidizing agent, first, the manganese-iron mixed salt, the supervalent ion acid root salt solution and the complexing agent undergo a complexation reaction, and the oxidizing agent oxidizes the low-valent manganese and iron to high-valent manganese and iron, and then an oxidation reaction occurs. Finally, the oxidized manganese and iron ions undergo co-precipitation with the supervalent ions, realizing a complexation-oxidation-co-precipitation reaction, obtaining spherical micron-sized supervalent ion-doped manganese iron oxides, which have the advantages of high tap density and uniform composition. The prepared lithium iron manganese phosphate composite cathode material has excellent physical and chemical properties.

[0033] On the one hand, the present invention provides a preparation method of a supervalent ion-doped lithium iron manganese phosphate composite cathode material. In some embodiments, the preparation method may include the following steps:

[0034] S100, configure a manganese-iron mixed salt and a supervalent ion acid root salt solution, wherein the supervalent ion acid root salt is at least one of vanadate, chromate, niobate, titanate, tungstate, molybdate, and aluminate.

[0035] S200, configure a weakly acidic bottom liquid, add the manganese-iron mixed salt and the supervalent ion acid root salt solution into the weakly acidic bottom liquid in a parallel flow manner, and add a complexing agent and an oxidizing agent to carry out a complexation-co-precipitation-oxidation reaction. After the reaction is completed, filter, wash, and dry to obtain supervalent ion-doped manganese iron oxides.

[0036] S300, according to the formula LiMn 1-a-b Fe a M b PO4@C, configure the lithium source, phosphorus source and carbon source, mix them with the hypervalent ion-doped manganese iron oxide, and calcine them under an inert atmosphere to obtain the hypervalent ion-doped lithium manganese iron phosphate composite cathode material, where M is selected from at least one of vanadium, chromium, niobium, titanium, tungsten, molybdenum and aluminum, and a + b < 1.

[0037] In some embodiments, the hypervalent metal ion is an alkali-soluble hypervalent ion, and complexation of the hypervalent metal with hydroxide can be achieved in the hypervalent ion acid root salt solution.

[0038] In some embodiments, the manganese salt can be at least one of manganese sulfate, manganese sulfite, manganese chloride, manganese nitrate, manganese nitrite, manganese acetate and manganese oxalate.

[0039] In some embodiments, the iron salt can be at least one of iron sulfate, iron sulfite, iron chloride, iron nitrate, iron nitrite, iron acetate and iron oxalate.

[0040] In some embodiments, the pH of the weakly acidic solution can be 2 - 6. In the weakly acidic solution with the above pH, Mn 2+ / Mn 3+ ,Fe 2+ / Fe 3+ can exist stably in ionic form before the addition of the complexing agent and the oxidizing agent. For example, the pH of the weakly acidic solution can be 3 - 5. For another example, the pH of the weakly acidic solution can be 4.

[0041] In some embodiments, the complexing agent can be at least one of ammonia water, ammonia gas and sodium ethylenediaminetetraacetate.

[0042] In some embodiments, the oxidizing agent can be at least one of oxygen and air.

[0043] In some embodiments, the hypervalent ion-doped manganese iron oxide presents a spherical morphology, and its particle size is between 2 μm and 10 μm. For example, its particle size can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, etc.

[0044] In some embodiments, the calcination may include heating to 400°C to 500°C at a rate of 2°C / min to 4°C / min and then holding for 4 h to 8 h, and then heating to 600°C to 800°C at a rate of 2°C / min to 4°C / min and then holding for 6 h to 12 h. For example, the calcination may include heating to 420°C to 480°C at a rate of 2.5°C / min to 3.5°C / min and then holding for 5 h to 7 h, and then heating to 650°C to 750°C at a rate of 2.8°C / min to 3.6°C / min and then holding for 6.5 h to 11 h. For another example, the calcination may include heating to 450°C at a rate of 3°C / min and then holding for 6 h, and then heating to 700°C at a rate of 3.2°C / min and then holding for 9 h.

[0045] In some embodiments, the lithium source may be at least one of lithium dihydrogen phosphate, lithium hydroxide, and lithium carbonate.

[0046] In some embodiments, the phosphorus source may be at least one of lithium dihydrogen phosphate and phosphoric acid.

[0047] In some embodiments, the carbon source is at least one of sucrose, starch, glucose, and graphite.

[0048] In some embodiments, it may further include adding a dispersant when the lithium source, phosphorus source, carbon source, and hypervalent ion-doped manganese iron oxide are mixed. In certain embodiments, the dispersant may be at least one of ethanol, deionized water, and ethylene glycol.

[0049] In some embodiments, the feeding rate of the complexing agent may be 0.2 to 5 times that of the manganese-iron mixed salt. The feeding rates of the manganese-iron mixed salt and the hypervalent ion acid radical salt solution may be 0.01 L / min to 100 L / min. The feeding rate of the oxidant may be 0.01 L / min to 100 L / min.

[0050] In some embodiments, it further includes a lithium source, a phosphorus source, and a carbon source. After being mixed with the hypervalent ion-doped manganese iron oxide, it is mechanically activated, dried, the balls are separated, placed in a crucible, and then put into a tube furnace for sintering.

[0051] In some embodiments, after the manganese-iron mixed salt and the hypervalent ion acid radical salt solution are added in parallel to the weakly acidic bottom liquid, the pH of the reaction system can be controlled at 4 to 9 by adding substances such as ammonia water.

[0052] In some embodiments, the washing in step S200 can be carried out using one or several of deionized water, tap water, weakly acidic solution, and weakly basic solution in any proportion. Drying can be carried out by vacuum drying or air drying. For example, the vacuum degree of vacuum drying can be 0.1 bar to 1 bar, and the temperatures of vacuum drying and air drying can be 20°C to 200°C.

[0053] In some embodiments, to configure a weakly acidic bottom solution, acetic acid, oxalic acid, sulfuric acid, hydrochloric acid, ammonia water, sodium hydroxide, strong acid and weak base salts, etc. can be used to regulate the pH of the bottom solution. The bottom solution can be a metal salt solution such as manganese sulfate, manganous sulfate, ferric sulfate, ferrous sulfate, manganese acetate, ferric acetate, manganese chloride, ferric chloride, etc.

[0054] Another aspect of the present invention provides a hypervalent ion-doped lithium iron manganese phosphate composite cathode material, which can be prepared by the preparation method of the hypervalent ion-doped lithium iron manganese phosphate composite cathode material described above.

[0055] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with specific examples, but the content of the present invention is not limited to the following examples.

[0056] Example 1

[0057] A preparation method of a hypervalent ion-doped lithium iron manganese phosphate composite cathode material may include the following steps:

[0058] Step 1, according to the ratio of each element of the hypervalent ion-doped manganese iron oxide, 1830.31 g of MnSO4, 1227.53 g of FeSO4, 23.63 g of NH4VO3, 65.62 g of NaNbO3, and 85.28 g of Na2TiO3 are respectively weighed, and the manganese iron salts are respectively dissolved in 20 L of deionized water, and the hypervalent ion acid radical salt solution is dissolved in 20 L of deionized water. 50 L of 10% ammonia water is configured to control the pH value of the system. In addition, 40 L of 0.5 mol L -1 manganese iron sulfate bottom solution with a manganese iron ratio of 6:4 is configured, poured into a reaction kettle, and 2000 g of 5% sodium ethylenediaminetetraacetate is added as a complexing agent.

[0059] Step 2, continuously introduce compressed air into the bottom solution of the reaction kettle, and add the manganese iron mixed salt solution and the hypervalent ion acid radical mixed salt solution into the reaction kettle in a co-current manner at a rate of 200 mL min -1 in a ratio of 1:1, and add ammonia water solution to control the pH value of the reaction system between 6 and 8, and the reaction temperature is 50 °C; after the reaction is completed, filter the precipitate, wash it 5 times with 20 L of deionized water at 50 °C, collect the filter cake, place the filter cake in a blast drying oven and dry it at 90 °C for 20 h, then take out the material, and obtain the hypervalent ion-doped manganese iron oxide powder after crushing and sieving.

[0060] Step 3: Weigh 20 g of the hypervalent ion-doped manganese iron oxide powder. According to the set stoichiometric ratio, high-valent metal element:lithium:phosphorus = 1:1.05:1, add 12.05 g of LiH2PO4 as the phosphorus source and lithium source, add 0.18 g of Li2CO3 to supplement lithium, add 2.70 g of sucrose as the organic carbon source, add 50 mL of deionized water as the dispersant, use zirconia as the ball milling beads, with a ball-to-material ratio of 10:1, and the ball mill rotates at 400 r min -1 , ball mill for 4 h for mechanical activation. After mechanical activation, the slurry is dried in a blast dryer at 60 °C for 12 h, and then sieved to separate the balls and materials.

[0061] Step 4: Pour the mixed powder obtained in Step 3 into an alumina crucible, place it in a tubular furnace, under an argon atmosphere, heat it to 450 °C and hold for 6 h for pre-sintering, then heat it to 650 °C and calcine for 6 h, and cool it to 25 °C with the furnace to obtain the hypervalent ion-doped lithium iron phosphate cathode material.

[0062] Figure 1 This is the SEM image of the hypervalent ion-doped manganese iron oxide prepared in Step 2 of this example. It can be seen that the obtained manganese iron oxide is micron-sized spherical particles. Figure 2 This is the XRD pattern of the hypervalent ion-doped manganese iron oxide prepared in Step 2 of this example. It can be seen from the figure that the manganese iron oxide has good crystallinity. Figure 3 This is the XRD pattern of the hypervalent ion-doped lithium iron phosphate cathode material prepared in this example. It can be seen from the figure that the synthesized material is a standard olivine structure and has good crystallinity. Figure 4 This is the SEM image of the hypervalent ion-doped lithium iron phosphate cathode material prepared in this example. It can be seen from the figure that this material is composed of nanoscale primary particles agglomerated into spherical secondary particles.

[0063] Table 1 shows the ICP test results of the hypervalent ion-doped manganese iron oxide prepared in this example.

[0064] Table 1 Elemental composition of hypervalent ion-doped manganese iron oxide

[0065]

[0066] Example 2

[0067] A preparation method of a hypervalent ion-doped lithium iron phosphate composite cathode material may include the following steps:

[0068] Step 1: Weigh 2440.42 g of MnSO4, 613.77 g of FeSO4, 47.26 g of NH4VO3, 32.81 g of NaNbO3, and 113.71 g of Na2TiO3 according to the ratio of each element in the supervalent ion-doped manganese iron oxide. Dissolve the manganese and iron salts in 20 L of deionized water respectively, and dissolve the supervalent ion acid radical salt solution in 20 L of deionized water. Prepare 50 L of 5% ammonia water to control the pH of the system. Additionally, prepare 30 L of a 0.3 mol / L -1 manganese iron sulfate bottom solution with a manganese to iron ratio of 8:2. Pour it into a reaction kettle, and add 2000 g of 5% sodium ethylenediaminetetraacetate as a complexing agent.

[0069] Step 2: Continuously introduce oxygen into the bottom solution of the reaction kettle at a flow rate of 1 L / min -1 , and add the manganese iron mixed salt solution and the supervalent ion acid radical mixed salt solution into the reaction kettle in a co-current manner at a rate of 200 mL / min -1 in a 1:1 ratio, and add ammonia water solution to control the pH value of the reaction system between 7.0 and 8.0. The reaction temperature is 70 °C. After the reaction is completed, filter the precipitate, wash it 3 times with 50 L of deionized water at 70 °C, collect the filter cake, place the filter cake in a blast drying oven and dry it at 90 °C for 20 h. Then take out the material, and after crushing and sieving, the supervalent ion-doped manganese iron oxide powder is obtained.

[0070] Step 3: Weigh 20 g of the supervalent ion-doped manganese iron oxide powder. According to the set stoichiometric ratio, high-valent metal element:lithium:phosphorus = 1:1.05:1, add 11.97 g of LiH2PO4 as the phosphorus source and lithium source, add 0.21 g of Li2CO3 to supplement lithium, add 2.86 g of sucrose as the organic carbon source, add 45 mL of ethanol as a dispersant, use tungsten carbide as the ball milling beads, with a ball-to-material ratio of 10:1, and the ball mill rotates at 400 r / min -1 , and carry out mechanical activation by ball milling for 5 h. After mechanical activation, the slurry is dried in a blast drying oven at 60 °C for 12 h, and then sieved to separate the balls from the material.

[0071] Step 4: Pour the mixed powder obtained in Step 3 into an alumina crucible, place it in a tube furnace, and under an argon atmosphere, heat it to 450 °C and hold for 8 h for pre-sintering, then heat it to 600 °C and calcine for 8 h. After cooling to 25 °C with the furnace, the supervalent ion-doped lithium manganese iron phosphate cathode material is obtained.

[0072] Figure 5 This is the SEM image of the supervalent ion-doped lithium manganese iron phosphate prepared in this example. It can be seen that the secondary particles of the material are micron-sized spherical particles. Figure 6XRD pattern of the hypervalent ion-doped lithium iron manganese phosphate prepared in this example shows that the material has good crystallinity, is in the standard olivine structure, and there are no other impurity phases. Figure 7 Charge-discharge curve of the hypervalent ion-doped lithium iron manganese phosphate prepared in this example at 0.1C. The specific capacity of the material at 0.1C rate is 150.1 mAh g -1 and it has excellent electrochemical performance.

[0073] Table 2 shows the ICP test results of the hypervalent ion-doped manganese iron oxide prepared in this example.

[0074] Table 2 Elemental composition of the hypervalent ion-doped manganese iron oxide

[0075]

[0076] Example 3

[0077] A preparation method of a hypervalent ion-doped lithium iron manganese phosphate composite cathode material may include the following steps:

[0078] Step 1, according to the proportion of each element of the hypervalent ion-doped manganese iron oxide, weigh 2135.36 g of MnSO4, 920.65 g of FeSO4, 94.53 g of NH4VO3, 82.03 g of NaNbO3, and 90.96 g of Na2TiO3 respectively, and dissolve the manganese and iron salts in 20 L of deionized water, and dissolve the hypervalent ion acid radical salt solution in 20 L of deionized water. Prepare 50 L of 20% ammonia water to control the pH of the system. In addition, prepare 30 L of a 0.5 mol L -1 manganese iron sulfate bottom solution with a manganese to iron ratio of 7:3, pour it into the reaction kettle, and add 2000 g of 5% sodium ethylenediaminetetraacetate as a complexing agent.

[0079] Step 2, continuously introduce compressed air into the bottom solution of the reaction kettle, and add the manganese iron mixed salt solution and the hypervalent ion acid radical mixed salt solution into the reaction kettle in a co-current manner at a rate of 100 mL min -1 in a ratio of 1:1, and add ammonia water solution to control the pH value of the reaction system between 7.0 and 8.0, and the reaction temperature is 25°C; after the reaction is completed, filter the precipitate, wash it repeatedly 5 times with 20 L of deionized water at 25°C, collect the filter cake, place the filter cake in a blast drying oven and dry it at 60°C for 24 h, then take out the material, and obtain the hypervalent ion-doped manganese iron oxide powder after crushing and sieving.

[0080] Step 3: Weigh 20 g of the above materials. According to the set stoichiometric ratio, high-valent metal element: lithium: phosphorus = 1:1.05:1, add 11.89 g of LiH2PO4 as the phosphorus source and lithium source, and add 0.21 g of Li2CO3 to supplement lithium. Add 2.83 g of sucrose as the organic carbon source, add 45 mL of ethanol as the dispersant, use stainless steel as the ball-milling beads, with a ball-to-material ratio of 15:1, and the ball mill rotates at 400 r / min -1 , and perform mechanical activation by ball milling for 5 h. After mechanical activation, the slurry is dried in a blast dryer at 60 °C for 12 h, and then sieved to separate the balls and materials.

[0081] Step 4: Pour the mixed powder obtained in Step 3 into an alumina crucible, place it in a tube furnace, under an argon atmosphere, heat it to 400 °C and hold for 8 h for pre-sintering, then heat it to 700 °C and calcine for 6 h, and cool it to 25 °C with the furnace to obtain the super-valent ion-doped lithium iron phosphate cathode material.

[0082] Figure 8 This is the SEM image of the super-valent ion-doped lithium iron phosphate prepared in this example. It can be seen from the figure that the primary particles of the material are spherical, and the secondary particles are micron-sized particles formed by the aggregation of primary particles.

[0083] Figure 9 This is the XRD pattern of the super-valent ion-doped lithium iron phosphate prepared in this example. It can be seen from the figure that the material is a uniform olivine phase and there are no other impurity peaks. Figure 10 This is the rate performance curve of the super-valent ion-doped lithium iron phosphate prepared in this example. It can be seen from the figure that the material has excellent rate performance. Figure 11 This is the cycle performance graph of the super-valent ion-doped lithium iron phosphate prepared in this example. It can be seen from the figure that the material has good stability at a 1.0C rate.

[0084] Table 3 shows the ICP test results of the super-valent ion-doped manganese iron oxide prepared in this example.

[0085] Table 3 Elemental composition of super-valent ion-doped manganese iron oxide

[0086]

[0087] Although the present invention has been described above by combining exemplary embodiments, those skilled in the art should understand that various modifications and changes can be made to the exemplary embodiments of the present invention without departing from the spirit and scope defined by the claims.

Claims

1. A method for preparing a supervalent ion-doped lithium manganese iron phosphate composite positive electrode material, characterized in that: The following steps are involved: A manganese-iron mixed salt and a supervalent ion acid salt solution are prepared, wherein the supervalent ion acid salt is at least one of vanadate, chromate, niobate, titanate, tungstate, molybdate and aluminate; A weakly acidic base liquid is prepared, a manganese iron mixed salt and a supervalent ion acid salt solution are added to the weakly acidic base liquid in parallel, and a complexing agent and an oxidant are added. After the reaction is completed, the mixture is filtered, washed, and dried to obtain a supervalent ion-doped manganese iron oxide; According to the expression LiMn 1-a-b Fe a M b PO4@C is configured with a lithium source, a phosphorus source and a carbon source, which are mixed with a hypervalent ion-doped manganese iron oxide and then calcined under an inert atmosphere to obtain a hypervalent ion-doped lithium manganese iron phosphate composite positive electrode material, wherein M is selected from at least one of vanadium, chromium, niobium, titanium, tungsten, molybdenum and aluminum, and a+b<1.

2. The method for preparing a supervalent ion-doped lithium manganese iron phosphate composite positive electrode material according to claim 1, characterized in that: The pH of the weakly acidic base solution is 2-6.

3. The method for preparing a supervalent ion-doped lithium manganese iron phosphate composite positive electrode material according to claim 1 or 2, characterized in that: The complexing agent is at least one of ammonia water, ammonia gas and sodium ethylenediaminetetraacetate; and the oxidant is at least one of oxygen and air.

4. The method for preparing a supervalent ion-doped lithium manganese iron phosphate composite positive electrode material according to claim 1 or 2, characterized in that: The manganese salt is at least one of manganese sulfate, manganese sulfite, manganese chloride, manganese nitrate, manganese nitrite, manganese acetate and manganese oxalate; The iron salt is at least one of ferric sulfate, ferric sulfite, ferric chloride, ferric nitrate, ferric nitrite, ferric acetate and ferric oxalate.

5. The method for preparing a supervalent ion-doped lithium manganese iron phosphate composite positive electrode material according to claim 1 or 2, characterized in that: The calcination includes heating to 400°C to 500°C at a rate of 2°C / min to 4°C / min, then keeping the temperature for 4h to 8h, and then heating to 600°C to 800°C at a rate of 2°C / min to 4°C / min, then keeping the temperature for 6h to 12h.

6. The method for preparing a supervalent ion-doped lithium manganese iron phosphate composite positive electrode material according to claim 1 or 2, characterized in that: The lithium source is at least one of lithium dihydrogen phosphate, lithium hydroxide and lithium carbonate; the phosphorus source is at least one of lithium dihydrogen phosphate and phosphoric acid; and the carbon source is at least one of sucrose, starch, glucose and graphite.

7. The method for preparing a supervalent ion-doped lithium manganese iron phosphate composite positive electrode material according to claim 1 or 2, characterized in that: The method also includes adding a dispersant when mixing the lithium source, phosphorus source, carbon source and the hypervalent ion-doped manganese iron oxide, wherein the dispersant is at least one of ethanol, deionized water and ethylene glycol.

8. The method for preparing a supervalent ion-doped lithium manganese iron phosphate composite positive electrode material according to claim 1 or 2, characterized in that: The feeding rate of the complexing agent is 0.2 to 5 times of the feeding rate of the manganese-iron mixed salt; the feeding rate of the manganese-iron mixed salt and the supervalent ion acid salt solution is 0.01L / min to 100L / min, and the feeding rate of the oxidant is 0.01L / min to 100L / min.

9. A supervalent ion doped lithium manganese iron phosphate composite positive electrode material, characterized in that: The material is prepared by the method for preparing a supervalent ion-doped lithium manganese iron phosphate composite positive electrode material as described in any one of claims 1 to 8.

Images