Manganese-doped lithium iron phosphate materials, their preparation methods, cathode sheets, lithium-ion batteries, and electrical devices.

Abstract

This invention relates to the field of lithium battery technology, and discloses a manganese-doped lithium iron phosphate material, its preparation method, a positive electrode, a lithium-ion battery, and electrical devices thereof. The chemical formula of the manganese-doped lithium iron phosphate material is LiMn. x Fe 1‑x PO4, where 0

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a manganese-doped lithium iron phosphate material and its preparation method, a positive electrode, a lithium-ion battery, and electrical equipment. Background Technology

[0002] Peridotite-structured polyanionic phosphates, such as LiMPO4 (M = Fe, Mn, Co, Ni, V), have become the most commercially viable cathode materials due to their advantages including low cost, high safety, good cycle stability, and environmental friendliness. Among them, LiFePO4 has been widely used due to its low cost, non-toxicity, safety, stable discharge platform, high discharge capacity, and good cycle stability; however, its relatively low operating voltage platform results in a lower energy density.

[0003] Currently, improving the energy density of LiFePO4 cathode materials has become one of the directions for LiFePO4 modification. The most direct method is to increase its operating voltage to improve energy density. In addition, LiMnPO4, as another olivine-structured polyanionic cathode material that can match the operating voltage of existing electrolytes, has a similar crystal structure to LiFePO4 and a higher operating voltage. Therefore, combining the structural stability, long cycle life, and good thermal stability of LiFePO4 with the higher voltage platform of LiMnPO4, theoretically, LiMnPO4 with higher specific energy could be further improved. x Fe 1-x PO4 (x≥0.5) has become a research hotspot in the lithium-ion battery industry. However, LiMn... x Fe 1-x The volume change of PO4 (x≥0.5) during the two-phase reaction stage of lithium ion insertion / extraction is greater than that of LiFePO4, resulting in greater stress concentration, causing the cathode material particles to break and leading to battery failure.

[0004] Therefore, there is an urgent need to develop an electrode material that can achieve a high voltage platform, high energy density, and high structural stability. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies, such as the low operating voltage of lithium iron phosphate cathode materials and lithium manganese iron phosphate (LiMn). x Fe 1-x To address the problem of excessive stress leading to particle breakage during the two-phase reaction stage of lithium ion insertion / extraction (PO4, x≥0.5), this invention provides a manganese-doped lithium iron phosphate material, its preparation method, a positive electrode, a lithium-ion battery, and electrical equipment. The manganese-doped lithium iron phosphate material of this invention achieves improved voltage platform and energy density while further enhancing its structural stability.

[0006] To achieve the above objectives, the first aspect of the present invention provides a manganese-doped lithium iron phosphate material, wherein the chemical formula of the manganese-doped lithium iron phosphate material is LiMn. x Fe 1-x PO4, where 0 <x≤0.1。

[0007] Preferably, 0.01 <x≤0.1。

[0008] Preferably, the particle size of the manganese-doped lithium iron phosphate material is 120-300 nm.

[0009] Preferably, the surface of the manganese-doped lithium iron phosphate material is coated with a carbon layer, the mass fraction of which is 1.5-1.8 wt%.

[0010] Preferably, the specific surface area of ​​the manganese-doped lithium iron phosphate material is 10-19 m². 2 / g.

[0011] A second aspect of the present invention provides a method for preparing the above-mentioned manganese-doped lithium iron phosphate material, the method comprising the following steps:

[0012] S1. The carbon source, lithium source, iron source and first phosphorus source are ball-milled and then mixed with manganese source and second phosphorus source to obtain precursor material;

[0013] S2. The precursor material is sintered.

[0014] Preferably, the lithium source is at least one selected from lithium hydroxide, lithium acetate, lithium nitrate, lithium carbonate, and lithium dihydrogen phosphate.

[0015] Preferably, the iron source is at least one selected from ferrous phosphate, ferrous oxalate, ferrous nitrate, ferrous hydroxide, ferric phosphate, ferric oxalate, and ferric carbonate.

[0016] Preferably, the first phosphorus source is at least one selected from ferrous phosphate, ferric phosphate, manganese phosphate, lithium dihydrogen phosphate, and lithium phosphate.

[0017] Preferably, the carbon source is at least one selected from oxalic acid, sucrose, cellulose, fructose, polyethylene glycol, glucose, starch, maltose, lactose, citric acid, carbon black, and polyethylene glycol.

[0018] Preferably, the manganese source is at least one selected from manganese nitrate, manganese carbonate, manganese phosphate, manganese oxalate, and manganese sulfate.

[0019] Preferably, the second phosphorus source is phosphoric acid. Preferably, the calcination includes a first sintering stage and a second sintering stage performed sequentially, and the sintering temperature of the second sintering stage is 100-400°C higher than the sintering temperature of the first sintering stage.

[0020] Preferably, the conditions for the first sintering stage include: a heating rate of 1-10 °C / min. -1 The sintering temperature is 300-500℃ and the sintering time is 0.5-2h.

[0021] Preferably, the conditions for the second sintering stage include: a heating rate of 1-10 °C / min. -1 The sintering temperature is 400-800℃ and the time is 5-10h.

[0022] A third aspect of the present invention provides a positive electrode sheet comprising the aforementioned manganese-doped lithium iron phosphate material.

[0023] A fourth aspect of the present invention provides a lithium-ion battery, the lithium-ion battery comprising the above-described positive electrode sheet.

[0024] The fifth aspect of the present invention provides an electrical device comprising the aforementioned lithium-ion battery.

[0025] Through the above technical solutions, on the one hand, manganese doping can increase the cell volume of lithium iron phosphate, widen the lithium-ion diffusion channels, and improve the voltage plateau; on the other hand, compared with high-manganese-doped lithium iron phosphate, the reduction of manganese doping content significantly shortens its Mn content. 3+ / Mn 2+ The platform allows the two-phase reaction to concentrate on Fe. 3+ / Fe 2+ The voltage plateau results in minimal volume changes in the crystal structure during lithium-ion insertion / extraction, preventing material breakage due to large stress and strain. Therefore, the manganese-doped lithium iron phosphate material described in this invention achieves both improved voltage plateau and energy density while further enhancing its structural stability. Attached Figure Description

[0026] Figure 1 The LiMn described in this invention 0.05 Fe 0.95 Scanning electron microscope image of PO4 material;

[0027] Figure 2 The LiMn described in this invention 0.05 Fe 0.95 X-ray diffraction pattern of PO4 material;

[0028] Figure 3 The discharge specific capacity diagram of the manganese-doped lithium iron phosphate materials prepared according to Examples 1 and 2 and Comparative Examples 1 and 2 is shown at 0.5C.

[0029] Figure 4Discharge energy density diagram at 0.5C of the manganese-doped lithium iron phosphate materials prepared according to Examples 1, 2 and Comparative Examples 1, 2. Detailed Description of the Invention

[0030] The following further elaborates on the specific embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for the purpose of illustration and explanation only, and are not intended to limit the present invention.

[0031] In the ranges and any values disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0032] The chemical formula of the manganese-doped lithium iron phosphate material described in the present invention is LiMn x Fe 1-x PO4, where 0 < x ≤ 0.1. According to the manganese-doped lithium iron phosphate material described in the present invention, manganese is the doping element. According to the subsequent experimental results, in LiMn x Fe 1-x PO4, 0 < x ≤ 0.1. By doping a small amount of manganese element into the lithium iron phosphate material, its Mn 3+ / Mn 2+ platform is shortened, making the two-phase reaction concentrated on the Fe 3+ / Fe 2+ platform. During the process of lithium ion insertion / extraction, the volume change of the crystal structure is small, avoiding the fragmentation of the material caused by large stress and strain. Therefore, compared with the lithium iron phosphate material, the manganese-doped lithium iron phosphate material described in the present invention has improved voltage platform and energy density while further enhancing its structural stability.

[0033] In the manganese-doped lithium iron phosphate material described in the present invention, in order to ensure the high stability of the material structure, the range of x is preferably 0.01 < x ≤ 0.1, and the value of x can specifically be, for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.10. In the manganese-doped lithium iron phosphate material, the molar amount of Li is equal to the total molar amount of Fe and Mn, and the molar amount of PO4 3- is equal to the total molar amount of Fe and Mn. The chemical formula of the manganese-doped lithium iron phosphate material can specifically be, for example, LiFe 0.99 Mn 0.01 PO4, LiFe 0.98 Mn 0.02PO4, LiFe 0.97 Mn 0.03 PO4, LiFe 0.96 Mn 0.04 PO4, LiFe 0.95 Mn 0.05 PO4, LiFe 0.94 Mn 0.06 PO4, LiFe 0.93 Mn 0.07 PO4, LiFe 0.92 Mn 0.08 PO4, LiFe 0.91 Mn 0.09 PO4 or LiFe 0.90 Mn 0.10 PO4. The preferred chemical formula of the manganese-doped lithium iron phosphate material is LiFe. 0.95 Mn 0.05 PO4 or LiFe 0.90 Mn 0.10 PO4.

[0034] In the manganese-doped lithium iron phosphate material of the present invention, in order to ensure the structural stability and excellent cycle performance of the material, the manganese-doped lithium iron phosphate material is preferably olivine structure.

[0035] In the manganese-doped lithium iron phosphate material of the present invention, to ensure the charge-discharge performance, energy density, power density, and cycle life of the battery, the particle size of the manganese-doped lithium iron phosphate material is preferably 120-300 nm, more preferably 200-290 nm. The specific surface area of ​​the manganese-doped lithium iron phosphate material is preferably 10-19 m². 2 / g, more preferably 12.4-17.3m 2 / g. The particle size of the manganese-doped lithium iron phosphate material is within the above-mentioned preferred range, which helps to provide more active sites and avoid agglomeration, thereby improving the charge and discharge efficiency and energy density of the battery.

[0036] In the manganese-doped lithium iron phosphate material of the present invention, the surface of the manganese-doped lithium iron phosphate material is coated with a carbon layer. In order to improve the electrochemical performance of the material, the mass fraction of the carbon layer is preferably 1.5-1.8 wt%, more preferably 1.50-1.67 wt%.

[0037] The present invention also provides a method for preparing the above-mentioned manganese-doped lithium iron phosphate material, the method comprising the following steps:

[0038] S1. The carbon source, lithium source, iron source and first phosphorus source are ball-milled and then mixed with manganese source and second phosphorus source to obtain precursor material;

[0039] S2. The precursor material is sintered.

[0040] The method described in this invention is characterized by simple operation, easy process and low cost. Moreover, the manganese-doped lithium iron phosphate material prepared has improved voltage platform and energy density while its structural stability is further enhanced.

[0041] In the method described in this invention, the precursor material can be a polyanionic phosphate with an olivine structure. The preparation method of the precursor material can be a conventional preparation method in the art, specifically, for example, a solid-state reaction method, a sol-gel method, a co-precipitation method, a solvothermal method, or a spray drying method.

[0042] In the method described in this invention, step (S1) may specifically include: mixing a carbon source and water, then adding a lithium source, an iron source, and a first phosphorus source to obtain a mixture; ball milling and dissolving the mixture to obtain a ball-milled solution; adding a manganese source and a second phosphorus source to the diluted ball-milled solution and drying. The ratio of carbon source to water may be (0.5-2) g: 100 mL. The solid content of the diluted ball-milled solution may be 7-15%, preferably 8-12%. The mixture may also include at least one of ammonium phosphate, a water-soluble polymer, and a precursor. The water-soluble polymer may be a water-soluble vinyl copolymer. The precursor may be a sugar precursor. The precursor material may be in hydrated form or a dry powder mixture. The mass of the carbon source accounts for 1-10% of the total mass of the solid phase in the mixture.

[0043] In some embodiments, the ball milling method can be dry milling, wet milling, or a combination of dry and wet milling. The dry milling is carried out in a dry zirconia ball mill jar. The wet milling can use surfactants and solvents to assist in the milling process. The surfactant can be oleic acid. The solvent can be anhydrous ethanol. The process of the combination of dry and wet milling may include first dry milling the mixture and then wet milling it. The ball milling conditions may include: a rotation speed of 300-700 r / min, preferably 350-650 r / min; and a time of 10-20 h, preferably 15-18 h.

[0044] In some embodiments, the dissolution can be achieved by placing the mixture in an oven. The dissolution conditions include: a temperature of 35-60°C, preferably 40-50°C; and a time of 40-60 hours, preferably 45-55 hours.

[0045] In some embodiments, the process of adding a manganese source to the diluted ball milling solution and then drying may specifically include: mixing the ball milling solution and solvent and adding a manganese source, then stirring at a temperature of 20-30°C for 2-5 hours, followed by spray drying to obtain the precursor material. The solvent may be at least one of water, ethanol, and acetone. The spray drying conditions include: inlet and outlet air temperatures of 110-180°C and 50-90°C, preferably 130-160°C and 60-75°C, respectively; and a feed rate of 300-600 mL / h, preferably 400-500 mL / h.

[0046] In the method described in this invention, the lithium source can be at least one selected from lithium hydroxide, lithium acetate, lithium nitrate, lithium carbonate, and lithium dihydrogen phosphate. To improve the electrochemical performance of the material, the lithium source is preferably lithium hydroxide. The lithium source provides lithium ions, thereby enabling the charging and discharging process of the battery.

[0047] In the method described in this invention, the iron source can be at least one selected from ferrous phosphate, ferrous oxalate, ferrous nitrate, ferrous hydroxide, ferric phosphate, ferric oxalate, and ferric carbonate. To improve the stability of the material, the iron source is preferably ferrous phosphate. The iron source can improve electrochemical performance, battery safety, cycle life, and rate performance.

[0048] In the method described in this invention, the first phosphorus source can be at least one selected from ferrous phosphate, iron phosphate, manganese phosphate, lithium dihydrogen phosphate, and lithium phosphate. To improve the charge / discharge performance and safety of the battery, the phosphorus source is preferably ferrous phosphate.

[0049] In the method described in this invention, the carbon source can be at least one selected from oxalic acid, sucrose, cellulose, fructose, polyethylene glycol, glucose, starch, maltose, lactose, citric acid, carbon black, and polyethylene glycol. To improve battery performance and ensure battery stability, the carbon source is preferably citric acid and oxalic acid. The mass ratio of citric acid to oxalic acid can be (1-3):1, specifically, for example, 1:1, 1.5:1, 2:1, 2.5:1, or 3:1. The carbon source can effectively prevent crystal growth and particle agglomeration, improve the electronic conductivity of the material, and provide an effective lithium-ion diffusion channel.

[0050] In the method described in this invention, the manganese source can be at least one selected from manganese nitrate, manganese carbonate, manganese phosphate, manganese oxalate, and manganese sulfate. To avoid material breakage due to stress and strain and to ensure battery stability, the manganese source is preferably manganese nitrate.

[0051] In the method described in this invention, to improve battery performance and ensure battery stability, the second phosphorus source is preferably phosphoric acid. The mass fraction of the phosphoric acid can be 85%-99.99%, preferably 99%-99.99%.

[0052] In the method described in this invention, the calcination includes a first sintering stage and a second sintering stage performed sequentially, wherein the sintering temperature of the second sintering stage is 100-400°C higher than the sintering temperature of the first sintering stage. The calcination process is carried out under a protective gas. The protective gas is a conventional protective gas in the art. The protective gas used can be at least one of nitrogen, argon, and helium, preferably argon, and more preferably, the purity of the argon is 99.6 wt%-99.99 wt%.

[0053] In the method described in this invention, the conditions of the first sintering stage include: a heating rate of 1-10 °C·min. -1 Preferably, it is 5-10℃·min -1 The sintering temperature can be 300-500℃, preferably 350-450℃; the sintering time can be 0.5-2h, preferably 0.5-1.5h.

[0054] In the method described in this invention, the conditions for the second sintering stage include: a heating rate of 1-10 °C·min. -1 Preferably, it is 5-10℃·min -1 The sintering temperature is 400-800℃, preferably 550-750℃; the sintering time is 5-10h, preferably 6-9h.

[0055] In the method described in this invention, to improve the morphology of the manganese-doped lithium iron phosphate material, the method for preparing the above-mentioned manganese-doped lithium iron phosphate material preferably further includes pulverizing and / or sieving the calcined material. The pulverization can be performed using a pulverizer. The particle size D after pulverization is... 50 It can be 1-3µm.

[0056] In some embodiments, the method for preparing the manganese-doped lithium iron phosphate material described above according to the present invention includes: mixing a carbon source and water, then adding a lithium source, an iron source, and a phosphorus source to obtain a mixture; ball milling the mixture at a rotation speed of 300-700 r / min for 10-20 h and dissolving it at a temperature of 35-60 °C for 40-60 h to obtain a ball-milled solution; mixing the ball-milled solution with a solvent and adding a manganese source and a second phosphorus source; then stirring at a temperature of 20-30 °C for 2-5 h; and finally spray drying to obtain a precursor material. The precursor material is then subjected to a first sintering stage and a second sintering stage under a protective gas atmosphere, wherein the sintering temperature of the second sintering stage is 100-400 °C higher than the sintering temperature of the first sintering stage. The conditions of the first sintering stage include a heating rate of 1-10 °C·min. -1 The sintering temperature is 300-500℃, and the time is 0.5-2h. The conditions for the second sintering stage include a heating rate of 1-10℃·min. -1 The sintering temperature is 400-800℃ and the time is 5-10h.

[0057] In other embodiments, the method for preparing the manganese-doped lithium iron phosphate material described above includes: mixing oxalic acid, citric acid, and water, then adding lithium hydroxide and ferrous phosphate to obtain a mixture; ball milling the mixture at a speed of 350-650 r / min for 15-18 h and dissolving it at a temperature of 40-50 °C for 45-55 h to obtain a ball-milled solution; mixing the ball-milled solution with a solvent and adding manganese nitrate and phosphoric acid; then stirring at a temperature of 20-30 °C for 2-5 h; and finally spray drying to obtain a precursor material. The precursor material is then subjected to a first sintering stage and a second sintering stage under a protective gas atmosphere, wherein the sintering temperature of the second sintering stage is 100-400 °C higher than that of the first sintering stage. The conditions for the first sintering stage include a heating rate of 5-10 °C / min. -1 The sintering temperature is 350-450℃, and the time is 0.5-1.5h. The conditions for the second sintering stage include a heating rate of 5-10℃·min. -1 The sintering temperature is 550-750℃, and the sintering time is 6-9 hours. A third aspect of this invention provides the application of the aforementioned manganese-doped lithium iron phosphate material as a positive electrode active material. According to the application described in this invention, batteries using the aforementioned positive electrode active material exhibit high capacity and energy density, as well as good structural stability.

[0058] The present invention also provides a positive electrode sheet comprising the aforementioned manganese-doped lithium iron phosphate material. The positive electrode sheet according to the present invention exhibits excellent charge-discharge performance, charge-discharge efficiency, and cycle stability.

[0059] The present invention also provides a lithium-ion battery comprising the aforementioned positive electrode. The lithium-ion battery according to the present invention has high discharge specific capacity, discharge energy density, cycle life, and rate performance.

[0060] The present invention also provides an electrical device comprising the aforementioned lithium-ion battery. The electrical device according to the present invention has high energy density and good stability.

[0061] The following examples further illustrate the manganese-doped lithium iron phosphate material, its preparation method, positive electrode sheet, lithium-ion battery, and electrical equipment described in this invention. These examples are implemented based on the technical solution of this invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of this invention is not limited to the following examples.

[0062] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0063] Example 1

[0064] 0.5 g oxalic acid, 1.0 g citric acid, and 100 mL water were mixed, followed by the addition of 1.857 g lithium hydroxide and 27.420 g ferrous phosphate to obtain a mixture. This mixture was ball-milled at 500 r / min for 15 h and then dissolved at 45 °C for 48 h to obtain a ball-milled solution. This solution was mixed with water and diluted to a solid content of 8%. 0.723 g manganese nitrate and 4.12 mL phosphoric acid were added, followed by stirring at 25 °C for 3 h. The solution was then spray-dried at inlet and outlet air temperatures of 150 °C and 80 °C, respectively, with a feed rate of 500 mL / h to obtain the precursor material. Under argon atmosphere, the precursor material was heated at a rate of 5 °C / min. -1 The temperature was raised to 400℃ for the first sintering stage for 1 hour, with a heating rate of 5℃·min. -1 The temperature was raised to 650℃ for a second sintering stage for 8 hours, and then cooled to room temperature to obtain LiMn. 0.05 Fe 0.95 PO4 material.

[0065] Characterization tests: LiMn was determined by infrared carbon-sulfur analysis (referencing national standard GB / T 14265-1993 "General Rules for Analysis Methods of Hydrogen, Oxygen, Nitrogen, Carbon and Sulfur in Metallic Materials"). 0.05 Fe 0.95 The carbon layer of the PO4 material has a mass fraction of 1.52 wt%. LiMn can be obtained by nitrogen (N2) adsorption-desorption test (referencing national standard GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method").0.05 Fe 0.95 The specific surface area of ​​PO4 material is 15.3 m². 2 / g. For example... Figure 1 As shown, LiMn can be obtained by scanning electron microscopy (referencing national standard JY / T 010-1996 "General Rules for Analytical Scanning Electron Microscopy Methods"). 0.05 Fe 0.95 The particle size of PO4 material is 250 nm. For example... Figure 2 As shown, X-ray diffraction (XRD) (referencing national standard JY / T 009-1996 "General Rules for X-ray Diffraction Methods of Rotating Target Polycrystalline Materials") reveals that LiMn 0.05 Fe 0.95 The diffraction peaks of the PO4 material correspond well with the standard card of manganese-doped lithium iron phosphate, and the sharp diffraction peaks indicate that it has high purity and crystallinity.

[0066] Assembly of lithium-ion coin cell half-cells: The LiMn prepared in this embodiment... 0.05 Fe 0.95 PO4 materials, conductive carbon black, and polyvinylidene fluoride (LiMn) 0.05 Fe 0.95 A composition was prepared by uniformly mixing PO4 material, conductive carbon black, and polyvinylidene fluoride (PVDF) in a mass ratio of 90:5:5 in N-methylpyrrolidone solvent. The composition had a solid content of 50%. This mixture was then coated onto aluminum foil, which was subsequently dried in a vacuum drying oven at 120°C for 24 hours. After the solvent had completely evaporated, the aluminum foil was cut into 12mm diameter discs using a die-cutting machine. The discs were then processed in a glove box according to the following steps: negative electrode shell, spring sheet, gasket, lithium sheet, and electrolyte (1 mol·L⁻¹). - 1 LiPF6 EC / EMC / DMC), separator (PP, USA), electrolyte (1 mol·L⁻¹) -1 A lithium-ion coin cell was assembled sequentially using LiPF6 EC / EMC / DMC, positive electrode sheet, and positive electrode shell. The lithium-ion coin cell prepared in this embodiment was subjected to 100 constant current / constant voltage charge-discharge cycles at a voltage range of 2.0-4.3V and a rate of 0.5C. The measured discharge specific capacity was recorded. Figure 3 The measured discharge energy density is recorded in Table 1. Figure 4 See Table 1. In this paper, discharge energy density refers to the electrical energy released per unit volume or mass of a battery, with the basic unit being Wh / Kg. The calculation formula is as follows: Discharge energy density (Wh / Kg) = Average discharge voltage (V) × Discharge specific capacity (mAh / g).

[0067] Example 2

[0068] 0.75 g oxalic acid, 0.75 g citric acid, and 100 mL water were mixed, followed by the addition of 1.903 g lithium hydroxide and 26.617 g ferrous phosphate to obtain a mixture. This mixture was ball-milled at 500 r / min for 15 h and then dissolved at 50 °C for 40 h to obtain a ball-milled solution. This solution was mixed with water and diluted to a solid content of 8%. 1.481 g manganese nitrate and 8.44 mL phosphoric acid were added, followed by stirring at 25 °C for 3 h. The solution was then spray-dried at inlet and outlet air temperatures of 130 °C and 60 °C, respectively, with a feed rate of 500 mL / h to obtain the precursor material. Under argon atmosphere, the precursor material was heated at a rate of 5 °C / min. -1 The temperature was raised to 350℃ for the first sintering stage for 1 hour, with a heating rate of 5℃·min. -1 The temperature was raised to 550℃ for a second sintering stage for 6 hours, and then cooled to room temperature to obtain LiMn. 0.10 Fe 0.90 PO4 material. LiMn was obtained by infrared carbon-sulfur analysis (referencing national standard GB / T14265-1993 "General Rules for Analysis Methods of Hydrogen, Oxygen, Nitrogen, Carbon and Sulfur in Metallic Materials"). 0.10 Fe 0.90 The carbon layer of the PO4 material has a mass fraction of 1.67 wt%. Through nitrogen (N2) adsorption-desorption testing (referencing national standard GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption-BET Method"), LiMn can be obtained. 0.10 Fe 0.90 The specific surface area of ​​PO4 material is 17.3 m². 2 / g, by scanning electron microscopy (referencing national standard JY / T 010-1996 "General Rules for Analytical Scanning Electron Microscopy"), LiMn can be obtained. 0.10 Fe 0.90 The PO4 material has a particle size of 200 nm. The LiMn prepared in this example... 0.10 Fe 0.90 The PO4 material was used to assemble lithium-ion coin cells according to Example 1. The lithium-ion coin cells prepared in this example were subjected to 100 constant-current, constant-voltage charge-discharge cycles at a rate of 0.5C within a voltage range of 2.0-4.3V. The measured discharge specific capacity was recorded. Figure 3 The measured discharge energy density is recorded in Table 1. Figure 4 See Table 1.

[0069] Example 3

[0070] 0.375 g oxalic acid, 1.125 g citric acid, and 100 mL water were mixed, followed by the addition of 1.822 g lithium hydroxide and 28.036 g ferrous phosphate to obtain a mixture. This mixture was ball-milled at 300 r / min for 18 h and then dissolved at 40 °C for 60 h to obtain a ball-milled solution. This solution was mixed with water and diluted to a solid content of 12%. 0.142 g manganese nitrate and 8.09 mL phosphoric acid were added, followed by stirring at 20 °C for 5 h. The solution was then spray-dried at inlet and outlet air temperatures of 160 °C and 80 °C, respectively, with a feed rate of 400 mL / h to obtain the precursor material. Under argon atmosphere, the precursor material was heated at a rate of 10 °C / min. -1 The temperature was raised to 350℃ for the first sintering stage for 1.5 hours, with a heating rate of 10℃·min. -1 The temperature was raised to 750℃ for a second sintering stage for 9 hours, and then cooled to room temperature to obtain LiMn. 0.01 Fe 0.99 PO4 material. LiMn was obtained by infrared carbon-sulfur analysis (referencing national standard GB / T14265-1993 "General Rules for Analysis Methods of Hydrogen, Oxygen, Nitrogen, Carbon and Sulfur in Metallic Materials"). 0.01 Fe 0.99 The carbon layer of the PO4 material has a mass fraction of 1.48 wt%. Through nitrogen (N2) adsorption-desorption testing (referencing national standard GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption-BET Method"), LiMn can be obtained. 0.01 Fe 0.99 The specific surface area of ​​PO4 material is 12.4 m². 2 / g, by scanning electron microscopy (referencing national standard JY / T 010-1996 "General Rules for Analytical Scanning Electron Microscopy"), LiMn can be obtained. 0.01 Fe 0.99 The particle size of the PO4 material is 290 nm. The LiMn prepared in this example... 0.01 Fe 0.99 The PO4 material was used to assemble lithium-ion coin cells according to Example 1. The lithium-ion coin cells prepared in this example were subjected to 100 constant current and constant voltage charge-discharge cycles at a rate of 0.5C within a voltage range of 2.0-4.3V. The measured discharge specific capacity and discharge energy density are recorded in Table 1.

[0071] Example 4

[0072] 0.5 g oxalic acid, 1.0 g citric acid, and 100 mL water were mixed, followed by the addition of 1.839 g lithium hydroxide and 27.73 g ferrous phosphate to obtain a mixture. This mixture was ball-milled at 650 r / min for 15 h and then dissolved at 50 °C for 40 h to obtain a ball-milled solution. This solution was mixed with water and diluted to a solid content of 8%. 0.429 g manganese nitrate and 2.99 mL phosphoric acid were added, followed by stirring at 30 °C for 2 h. The solution was then spray-dried at inlet and outlet air temperatures of 150 °C and 80 °C, respectively, with a feed rate of 500 mL / h to obtain the precursor material. Under argon atmosphere, the precursor material was heated at a rate of 5 °C / min. -1 The temperature was raised to 450℃ for the first sintering stage for 0.5 hours, with a heating rate of 5℃·min. -1 The temperature was raised to 550℃ for a second sintering stage for 6 hours, and then cooled to room temperature to obtain LiMn. 0.03 Fe 0.97 PO4 material. LiMn was obtained by infrared carbon-sulfur analysis (referencing national standard GB / T14265-1993 "General Rules for Analysis Methods of Hydrogen, Oxygen, Nitrogen, Carbon and Sulfur in Metallic Materials"). 0.03 Fe 0.97 The carbon layer of the PO4 material has a mass fraction of 1.54 wt%. Through nitrogen (N2) adsorption-desorption testing (referencing national standard GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption-BET Method"), LiMn can be obtained. 0.03 Fe 0.97 The specific surface area of ​​PO4 material is 14.6 m². 2 / g, by scanning electron microscopy (referencing national standard JY / T 010-1996 "General Rules for Analytical Scanning Electron Microscopy"), LiMn can be obtained. 0.03 Fe 0.97 The PO4 material has a particle size of 270 nm. The LiMn prepared in this example... 0.03 Fe 0.97 The PO4 material was used to assemble lithium-ion coin cells according to Example 1. The lithium-ion coin cells prepared in this example were subjected to 100 constant current and constant voltage charge-discharge cycles at a rate of 0.5C within a voltage range of 2.0-4.3V. The measured discharge specific capacity and discharge energy density are recorded in Table 1.

[0073] Comparative Example 1

[0074] The method described in Example 1 is implemented, except that manganese nitrate is not added. Specifically, the method includes:

[0075] 0.5 g oxalic acid, 1.0 g citric acid, and 100 mL water were mixed, followed by the addition of 1.813 g lithium hydroxide and 28.187 g ferrous phosphate to obtain a mixture. This mixture was ball-milled at 500 r / min for 15 h and then dissolved at 45 °C for 48 h to obtain a ball-milled solution. This solution was mixed with water and diluted to a solid content of 12%. The solution was then stirred at 25 °C for 3 h, followed by spray drying at inlet and outlet air temperatures of 150 °C and 80 °C, respectively, with a feed rate of 500 mL / h, to obtain the precursor material. Under argon atmosphere, the precursor material was heated at a rate of 5 °C / min. -1 The temperature was raised to 400℃ for the first sintering stage for 1 hour, with a heating rate of 5℃·min. -1 The material was sintered at 650℃ for 8 hours, then cooled to room temperature to obtain LiFePO4 material. Infrared carbon-sulfur analysis (referring to national standard GB / T 14265-1993 "General Rules for Analysis of Hydrogen, Oxygen, Nitrogen, Carbon and Sulfur in Metallic Materials") showed that the carbon layer mass fraction of the LiFePO4 material was 1.49 wt%. Nitrogen (N2) adsorption-desorption analysis (referring to national standard GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method") showed that the specific surface area of ​​the LiFePO4 material was 10.3 m². 2 / g, the particle size of LiFePO4 material was found to be 300nm by scanning electron microscopy (referencing national standard JY / T 010-1996 "General Rules for Analytical Scanning Electron Microscopy"). The LiFePO4 material prepared in this comparative example was used to assemble lithium-ion coin cells according to Example 1. The lithium-ion coin cells prepared in this comparative example were subjected to 100 constant current and constant voltage charge-discharge cycles at a voltage range of 2.0-4.3V and a rate of 0.5C. The measured discharge specific capacity was recorded. Figure 3 The measured discharge energy density is recorded in Table 1. Figure 4 See Table 1.

[0076] Comparative Example 2

[0077] 0.5 g oxalic acid, 1.0 g citric acid, and 100 mL water were mixed, followed by the addition of 2.110 g lithium hydroxide and 22.962 g ferrous phosphate to obtain a mixture. This mixture was ball-milled at 500 r / min for 15 h and then dissolved at 45 °C for 48 h to obtain a ball-milled solution. This solution was mixed with water and diluted to a solid content of 10%. 4.927 g manganese nitrate and 28.09 mL phosphoric acid were added, followed by stirring at 25 °C for 3 h. The solution was then spray-dried at inlet and outlet air temperatures of 150 °C and 80 °C, respectively, with a feed rate of 500 mL / h to obtain the precursor material. Under argon atmosphere, the precursor material was heated at a rate of 5 °C / min. -1 The temperature was raised to 400℃ for the first sintering stage for 1 hour, with a heating rate of 5℃·min. -1 The temperature was raised to 650℃ for a second sintering stage for 8 hours, and then cooled to room temperature to obtain LiMn. 0.30 Fe 0.70 PO4 material. LiMn was obtained by infrared carbon-sulfur analysis (referencing national standard GB / T14265-1993 "General Rules for Analysis Methods of Hydrogen, Oxygen, Nitrogen, Carbon and Sulfur in Metallic Materials"). 0.30 Fe 0.70 The carbon layer of the PO4 material has a mass fraction of 1.78 wt%. LiMn can be obtained by nitrogen (N2) adsorption-desorption test (referencing national standard GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method"). 0.30 Fe 0.70 The specific surface area of ​​PO4 material is 18.6 m². 2 / g, by scanning electron microscopy (referencing national standard JY / T 010-1996 "General Rules for Analytical Scanning Electron Microscopy"), LiMn can be obtained. 0.30 Fe 0.70 The PO4 material has a particle size of 120 nm. The LiMn prepared in this comparative example... 0.30 Fe 0.70 The PO4 material was used to assemble lithium-ion coin cells according to Example 1. The lithium-ion coin cells prepared in this comparative example were subjected to 100 constant-current, constant-voltage charge-discharge cycles at a rate of 0.5C within a voltage range of 2.0-4.3V. The measured discharge specific capacity was recorded. Figure 3 The measured discharge energy density is recorded in Table 1. Figure 4 See Table 1.

[0078] Table 1

[0079]

[0080] from Figure 3It can be seen that after 100 charge-discharge cycles, the order of discharge specific capacity (Discharge Capacity) of the manganese-doped lithium iron phosphate materials prepared according to Examples 1, 2 and Comparative Examples 1, 2 is: LiFePO4 material > LiMn 0.05 Fe 0.95 PO4 material > LiMn 0.10 Fe 0.90 PO4 material > LiMn 0.30 Fe 0.70 PO4 material.

[0081] From Figure 4 It can be seen that after 100 charge-discharge cycles, the order of discharge energy density (Discharge Energy Density) of the manganese-doped lithium iron phosphate materials prepared according to Examples 1, 2 and Comparative Examples 1, 2 is: LiMn 0.05 Fe 0.95 PO4 > LiMn 0.10 Fe 0.90 PO4 > LiFePO4 > LiMn 0.30 Fe 0.70 PO4. When the manganese-doped lithium iron phosphate material in the present invention is used as the positive electrode material (LiMn x Fe 1-x PO4, where 0 < x ≤ 0.1), compared with LiMn 0.30 Fe 0.70 PO4 (Comparative Example 2), the long-term cycle stability is further improved, and compared with the lithium iron phosphate positive electrode material (Comparative Example 1), it has a higher discharge energy density.

[0082] From the results of Table 1, Figure 3 and Figure 4 it can be seen that the examples of the manganese-doped lithium iron phosphate according to the present invention have a higher discharge specific capacity and energy density, and also have better structural stability, and the overall electrochemical performance is more excellent.

[0083] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A manganese-doped lithium iron phosphate material, characterized in that, The chemical formula of the manganese-doped lithium iron phosphate material is LiMn. x Fe 1-x PO4, where 0 <x≤0.1; The surface of the manganese-doped lithium iron phosphate material is coated with a carbon layer, the mass fraction of which is 1.5-1.8 wt%. The specific surface area of ​​the manganese-doped lithium iron phosphate material is 10-19 m². 2 / g.

2. The manganese-doped lithium iron phosphate material according to claim 1, characterized in that, 0.01<x≤0.1。 3. The manganese-doped lithium iron phosphate material according to claim 1 or 2, characterized in that, The manganese-doped lithium iron phosphate material has a particle size of 120-300 nm.

4. A method for preparing manganese-doped lithium iron phosphate material according to any one of claims 1-3, characterized in that, The method includes the following steps: S1. The carbon source, lithium source, iron source and first phosphorus source are ball-milled and then mixed with manganese source and second phosphorus source to obtain precursor material; S2. The precursor material is sintered.

5. The method according to claim 4, characterized in that, The lithium source is at least one of lithium hydroxide, lithium acetate, lithium nitrate, lithium carbonate, and lithium dihydrogen phosphate.

6. The method according to claim 4 or 5, characterized in that, The iron source is at least one of ferrous phosphate, ferrous oxalate, ferrous nitrate, ferrous hydroxide, ferric phosphate, ferric oxalate, and ferric carbonate.

7. The method according to claim 4 or 5, characterized in that, The first phosphorus source is at least one of ferrous phosphate, iron phosphate, manganese phosphate, lithium dihydrogen phosphate, and lithium phosphate.

8. The method according to claim 4 or 5, characterized in that, The carbon source is at least one selected from oxalic acid, sucrose, cellulose, fructose, polyethylene glycol, glucose, starch, maltose, lactose, citric acid, carbon black, and polyethylene glycol.

9. The method according to claim 4 or 5, characterized in that, The manganese source is at least one of manganese nitrate, manganese carbonate, manganese phosphate, manganese oxalate, and manganese sulfate.

10. The method according to claim 4 or 5, characterized in that, The second phosphorus source is phosphoric acid.

11. The method according to claim 4 or 5, characterized in that, The sintering includes a first sintering and a second sintering performed sequentially, and the sintering temperature of the second sintering stage is 100-400°C higher than the sintering temperature of the first sintering stage.

12. The method according to claim 11, characterized in that, The conditions for the first sintering stage include: a heating rate of 1-10 °C / min. -1 The sintering temperature is 300-500℃ and the sintering time is 0.5-2h.

13. The method according to claim 11, characterized in that, The conditions for the second sintering stage include: a heating rate of 1-10 °C / min. -1 The sintering temperature is 400-800℃ and the time is 5-10h.

14. A positive electrode plate, characterized in that, The positive electrode comprises the manganese-doped lithium iron phosphate material as described in any one of claims 1-3.

15. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode as described in claim 14.

16. An electrical appliance, characterized in that, The electrical equipment includes the lithium-ion battery as described in claim 15.

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