Preparation method and application of lithium manganese iron phosphate positive electrode material with uniformly mixed iron and manganese

Abstract

The invention belongs to the technical field of lithium ion batteries, and relates to a preparation method and application of a lithium manganese iron phosphate positive electrode material with uniformly mixed iron and manganese, and the preparation method comprises the following steps: S1, synthesizing a spherical (Mn < 1-x > Fe < x >) 3 (PO4) 2 * xH2O precursor through a coprecipitation reaction; s2, removing crystal water from (Mn < 1-x > Fe < x >) 3 (PO4) 2 * xH2O in a protective atmosphere to obtain a (Mn < 1-x > Fe < x >) 3 (PO4) 2 precursor; s3, sanding and mixing the (Mn1-xFex) 3 (PO4) 2 precursor, a lithium source, a phosphorus source and water to obtain first slurry; s4, adding a carbon source into the first slurry, uniformly stirring to obtain second slurry, quickly drying, and granulating to obtain dry powder; and S5, roasting the dried powder in a protective atmosphere to obtain the lithium manganese iron phosphate positive electrode material LiMnxFe (1-x) PO4 / C, the lithium manganese iron phosphate secondary particle prepared by the method has a microsphere structure wrapped by nanosheets, the size of the secondary particle is 1-5 microns, the size is uniform, the dispersity is good, the grain size of the primary particle is 50-80 nm, the size of the material is obviously reduced, the path of lithium ions in the transmission process is shortened, and the rate capability of the lithium manganese iron phosphate positive electrode material is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries and relates to a preparation method and application of a lithium iron manganese phosphate positive electrode material in which iron and manganese are uniformly mixed. Background Art

[0002] In recent years, as the energy crisis intensifies, more and more researchers have begun to focus on the development of efficient energy storage technology for new energy sources. Lithium-ion batteries are one of the most stable energy storage devices and are widely used in the field of energy storage due to their high energy density, excellent safety and long service life. As a key component of lithium-ion batteries, cathode materials are the key factor restricting the development of high-performance batteries.

[0003] Among many cathode materials, LiMn x Fe 1-x PO 4 Positive electrode with LiFePO 4 The high capacity of LiMnPO 4 High energy density, is considered to be a promising next-generation commercial cathode material. x Fe 1-x PO 4 Faced with many challenges, LiMn x Fe 1-x PO 4 The material is prone to crystal structure distortion during long cycles, and manganese is easily dissolved during the battery cycle, reacting with the electrolyte, thereby affecting the cycle life. The traditional high-temperature solid phase method is used, that is, the lithium iron manganese phosphate is finally synthesized by mechanically blending the iron source, manganese source, lithium source, and phosphorus source and then sintering at high temperature. Although this method can be mass-produced, the iron and manganese are not mixed evenly, and the final material prepared has poor cycle performance. For example, in the inventions CN117334874A and CN119008888A, the iron and manganese precursors are all iron and manganese oxalate, so there is a problem of uneven distribution of iron and manganese; for example, in the invention CN118919701A, a lithium iron manganese phosphate precursor is obtained by hydrothermal reaction after mixing lithium source, phosphoric acid, iron source, and manganese source. Not only is the output small, it is difficult to prepare on a large scale commercially, and there is also the problem of uneven distribution of iron and manganese.

[0004] Therefore, a lithium iron manganese phosphate positive electrode material that can be prepared on a large scale and achieve uniform mixing of iron and manganese is needed to solve the above technical problems. Summary of the invention

[0005] The technical solution adopted by the present invention to solve the technical problem is: a method for preparing a lithium manganese iron phosphate positive electrode material in which iron and manganese are uniformly mixed, comprising the following steps:

[0006] Step S1: Synthesis of spherical (Mn 1-x Fex ) 3 (PO 4 ) 2 ·xH 2 O precursor;

[0007] Step S2: The (Mn 1-x Fe x ) 3 (PO 4 ) 2 ·xH 2 O is dehydrated under protective atmosphere to obtain (Mn 1-x Fe x ) 3 (PO 4 ) 2 Precursor;

[0008] Step S3: The (Mn 1-x Fe x ) 3 (PO 4 ) 2 The precursor is mixed with a lithium source, a phosphorus source and water, the solid content is controlled, and the mixture is sand-milled to obtain a first slurry;

[0009] Step S4: adding a carbon source to the first slurry obtained in step S3, stirring evenly to obtain a second slurry, and rapidly drying the obtained second slurry by spray drying, and granulating at the same time to obtain a dry powder having a microscopic morphology showing microspheres with a diameter of 1 to 5 μm;

[0010] Step S5: The dried powder obtained in step S4 is calcined under a protective atmosphere to finally obtain a spherical lithium manganese iron phosphate positive electrode material LiMn with a long life and high rate performance. x Fe 1-x PO 4 / C;

[0011] Among them, the value range of x is: 0.2≤x≤0.8.

[0012] Preferably, the lithium iron manganese phosphate positive electrode material LiMn x Fe 1-x PO 4 / C is wrapped into microspheres by uniform nanosheets, the primary particle size is 50-80nm, and the secondary particle size is 1-5μm.

[0013] More preferably, the value range of x is: 0.4≤x≤0.7.

[0014] Preferably, the step S1 specifically comprises: 4 7H 2O、MnSO 4 ·H 2 O and H 3 PO 4 The solutions were continuously mixed and stirred at a molar ratio of 3x:3-3x:2 to perform a coprecipitation reaction;

[0015] The pH range of the coprecipitation reaction is: 5.5≤pH≤7.5;

[0016] During the coprecipitation reaction, a protective atmosphere is introduced for protection;

[0017] The coprecipitation reaction process adopts low-temperature nucleation and high-temperature growth processes. The reaction temperature of the low-temperature nucleation stage is 20-30°C, the reaction temperature of the high-temperature growth stage is 40-60°C, and the total reaction time is 10-24h.

[0018] After the coprecipitation reaction is completed, the mixture is taken out, filtered, washed and dried to obtain (Mn 1-x Fe x ) 3 (PO 4 ) 2 ·xH 2 O precursor.

[0019] Preferably, in step S1, FeSO 4 7H 2 O、MnSO 4 ·H 2 O are dissolved in deionized water to form a cationic solution with a concentration of 1 to 2 M.

[0020] Preferably, in step S3, the lithium source includes: lithium phosphate, lithium carbonate; the phosphorus source includes: ammonium dihydrogen phosphate, diammonium hydrogen phosphate; the lithium source, phosphorus source, (Mn 1-x Fe x ) 3 (PO 4 ) 2 The amount of precursor substances is Li:M:PO 4 It is added in a ratio of 1:0.9~1.1:0.9~1.1, wherein M=Fe+Mn.

[0021] Preferably, in step S4, the carbon source includes: one or more of sucrose, glucose, starch or xylitol; the mass of the carbon source is 5% to 10% of the total mass of the first slurry solid; the spray drying temperature used is 150 to 200° C., and the spray feed rate is 10 to 30 mL / min.

[0022] Preferably, in step S5, the calcination temperature is 600-800° C., and the calcination time is 10-20 hours.

[0023] The beneficial effects of the present invention are:

[0024] 1. The lithium manganese iron phosphate secondary particles of the present invention have a microsphere structure wrapped by nanosheets, the secondary particle size is 1 to 5 μm, the size is uniform, and the dispersion is good. The primary particle size is 50 to 80 nm, which significantly reduces the size of the material, shortens the path of lithium ions in the transmission process, and improves the rate performance of the material. It has been verified by experiments that when the lithium manganese iron phosphate positive electrode material prepared by the preparation method is used in lithium ion batteries, the capacity of the lithium ion battery under the cycle of 3C remains at 136.3 mAh / g, indicating that it has good rate performance.

[0025] 2. The present invention synthesizes an iron-manganese precursor and then synthesizes lithium iron manganese phosphate, which can achieve uniform mixing of iron and manganese, is beneficial to inhibiting manganese dissolution, and improves the lithium iron manganese phosphate positive electrode material LiMn x Fe 1-x PO 4 / C cycle life. Experimental verification shows that when the lithium manganese iron phosphate positive electrode material prepared by this preparation method is used in lithium-ion batteries, the capacity of the lithium-ion battery remains at 141.5mAh / g after 500 cycles at 0.5C, indicating that it has good cycle performance.

[0026] 3. The present invention first synthesizes (Mn 1-x Fe x ) 3 (PO 4 ) 2 ·xH 2 O precursor, by adjusting the experimental conditions such as the rotation speed, reaction temperature, ion concentration, pH and reaction time of the coprecipitation process, a uniform morphology (Mn 1-x Fe x ) 3 (PO 4 ) 2 ·xH 2 O spherical precursor. The iron manganese phosphate precursor is then mixed with the lithium source and the phosphorus source by high-speed sand milling to obtain a first slurry, which makes the raw materials evenly mixed and reduces the particle size. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The (Mn) obtained in Example 1 of the preparation method and application of the lithium manganese iron phosphate positive electrode material uniformly mixed with iron and manganese of the present invention is finally 0.6 Fe 0.4 ) 3 (PO 4 ) 2 ·xH 2 SEM image of O precursor;

[0028] Figure 2 The (Mn 0.6 Fe 0.4 ) 3 (PO 4 ) 2 ·xH 2 TEM-EDS image of O precursor;

[0029] Figure 3 The calcined lithium iron manganese phosphate positive electrode material LiMn of Example 1 of the present invention 0.6 Fe 0.4 PO 4 / SEM image of C;

[0030] Figure 4 The lithium iron manganese phosphate positive electrode material LiMn after calcination in Comparative Example 1 of the present invention 0.6 Fe 0.4 PO 4 / SEM image of C;

[0031] Figure 5 The calcined lithium iron manganese phosphate positive electrode material LiMn of Example 1 of the present invention 0.6 Fe 0.4 PO 4 TEM-EDS image of / C;

[0032] Figure 6 The lithium iron manganese phosphate positive electrode material LiMn after calcination in Comparative Example 1 of the present invention 0.6 Fe 0.4 PO 4 TEM-EDS image of / C

[0033] Figure 7 This is a cycle performance diagram of the lithium manganese iron phosphate positive electrode material finally prepared in Example 1 of the present invention.

[0034] Figure 8 This is a cycle performance diagram of the lithium manganese iron phosphate positive electrode material finally prepared in Comparative Example 1 of the present invention.

[0035] Fig. 9 The lithium iron manganese phosphate positive electrode material LiMn prepared by the methods of Example 1 and Comparative Example 1 of the present invention 0.6 Fe 0.4 PO 4 / C rate performance diagram when used in lithium-ion batteries. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the relevant technologies in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] refer to Figures 1 to 9 As shown, this embodiment provides a method for preparing a lithium manganese iron phosphate positive electrode material based on achieving iron and manganese atomic-level mixing, long cycle life, and high rate performance, comprising the following steps:

[0038] 1. First, spherical (Mn 1-x Fe x ) 3 (PO 4 ) 2 ·xH 2 O precursor. FeSO 4 7H 2 O,MnSO 4 ·H 2 O, and H 3 PO 4 The solution was pumped into a continuously stirred reactor with a capacity of 5 L and a base liquid of 1.8 L at a molar ratio of 3x:3-3x:2. By adjusting the experimental conditions such as the rotation speed, reaction temperature, ion concentration, pH and reaction time of the coprecipitation process, after the reaction was completed, the mixture in the reactor was taken out, filtered, washed, and then placed in a 60°C forced air oven for drying to obtain a uniform morphology (Mn 1-x Fe x ) 3 (PO 4 ) 2 ·xH 2 OSpherical precursor.

[0039] 2. The (Mn 1-x Fe x ) 3 (PO 4 ) 2 ·xH 2 O is dehydrated under protective atmosphere to obtain (Mn 1-x Fe x ) 3 (PO 4 ) 2 Precursor.

[0040] 3. The (Mn 1-x Fe x ) 3 (PO 4 ) 2The precursor is mixed with a lithium source, a phosphorus source and water, the solid content is controlled, and sand milling is performed to obtain a first slurry.

[0041] 4. Then, a carbon source is added to the first slurry, and the mixture is stirred evenly to obtain a second slurry. The second slurry is rapidly dried by spray drying and granulated at the same time to obtain a dry powder having a microscopic morphology of microspheres with a diameter of 1 to 5 μm.

[0042] 5. The spray-dried powder is calcined under a protective atmosphere to obtain a spherical LiMn with a long life and high rate performance. x Fe 1-x PO 4 / C positive electrode material.

[0043] In the embodiments, unless otherwise specified, the required raw materials for preparation are all commercially available products well known to those skilled in the art.

[0044] In step 1 of this embodiment, 0.2≤x≤0.8, preferably x=0.3~0.6, and more preferably x=0.4~0.5; the pH in the reactor is adjusted by pumping in ammonia water, wherein 5.5≤pH≤7.5, preferably pH=6~7. During the reaction, a protective atmosphere is introduced into the reactor for protection, and the protective atmosphere is one or more of argon, nitrogen and helium. The speed of the reactor is 400~600r / min. The reaction process adopts low-temperature nucleation and high-temperature growth process, the reaction temperature of the low-temperature nucleation stage is 20~30℃, the reaction temperature of the high-temperature growth stage is 40~60℃, and the total reaction time is 10~24h, and more preferably, the low-temperature nucleation reaction time is 0~4h, and the high-temperature growth reaction time is 10~24h.

[0045] In this embodiment, in step 2 (Mn 1-x Fe x ) 3 (PO 4 ) 2 ·xH 2 O is heated under a protective atmosphere to remove crystal water, and the heating rate to the roasting temperature is 4-8°C / min; the protective atmosphere is one or more of argon, nitrogen and helium; the roasting temperature is 500-600°C, and the time is 10-20h.

[0046] In this embodiment, in step 3, the lithium source includes lithium phosphate or lithium carbonate, and the phosphorus source includes ammonium dihydrogen phosphate or diammonium hydrogen phosphate. 1-x Fe x ) 3 (PO 4 ) 2 The amount of precursor material is Li:M (M = Fe + Mn):PO 4The material is mixed with deionized water in a ratio of 1:1:1; the mass fraction of the solid content is preferably 10-25%, the sand milling time is preferably 1-5h, and the sand milling speed is preferably 1500-3000r / min.

[0047] In this embodiment, the carbon source in step 4 includes one or more of sucrose, glucose, starch or xylitol; the mass of the carbon source is 5% to 10% of the total mass of the first slurry solid. The temperature of the spray dryer used is 150 to 200° C., and the spray feed rate is 10 to 30 mL / min.

[0048] In this embodiment, the calcination temperature in step 5 is preferably 600-800°C; the heating rate to the calcination temperature is 4-8°C / min; the protective atmosphere is one or more of argon, nitrogen and helium; and the calcination time is 10-20h.

[0049] This embodiment provides the application of the above technical solution based on the realization of atomic-level mixing of iron and manganese, long cycle life, and high rate performance of lithium manganese iron phosphate positive electrode material in lithium-ion batteries. This embodiment does not specifically limit the method of application, and it can be applied according to methods well known in the art.

[0050] The technical solutions provided by this embodiment are described in detail below in conjunction with the embodiments, but they should not be understood as limiting the protection scope of the present invention.

[0051] Example 1

[0052] Will FeSO 4 7H 2 O,MnSO 4 ·H 2 O, and H 3 PO 4 The solution was prepared with deionized water in a molar ratio of 1.2:1.8:2 and pumped into a continuously stirred reactor with a capacity of 5 L and a base liquid of 1.8 L, wherein FeSO 4 7H 2 O,MnSO 4 ·H 2 O were dissolved in deionized water to prepare a cationic solution with a concentration of 1.2 M; the pH was controlled at 6.5 by ammonia water with a concentration of 4.5 M; the early low-temperature nucleation and high-temperature growth process was adopted, the early reaction temperature was 25 ° C, the reaction time was 1 h, and the late high-temperature growth stage reaction temperature was 50 ° C, the reaction time was 17 h; during the reaction process, the reactor speed was 400 r / min, and finally the mixed liquid in the reactor was taken out, filtered, washed, and then placed in a 60 ° C forced air oven to dry to obtain (Mn 0.6 Fe 0.4 ) 3 (PO 4 )2 ·xH 2 O precursor.

[0053] The obtained (Mn 0.6 Fe 0.4 ) 3 (PO 4 ) 2 ·xH 2 The precursor was placed in an argon protected tube furnace and heated to 500°C at a heating rate of 5°C / min and calcined for 10 h to remove the crystal water to obtain (Mn 0.6 Fe 0.4 ) 3 (PO 4 ) 2 Precursor. 0.6 Fe 0.4 ) 3 (PO 4 ) 2 The precursor and lithium phosphate were mixed with deionized water in a molar ratio of 1:1 and then sand-milled at a speed of 2500 r / min for 2 hours to obtain a first slurry, the mass of the solid component of the first slurry accounting for 15% of the total mass of the entire mixture.

[0054] Glucose accounting for 8% of the solid content was added to the first slurry, and the mixture was evenly mixed to obtain the second slurry, which was quickly dried by spray drying. The working temperature of the spray dryer was 160°C, and the spray drying feed rate was 25 mL / min. A dry powder with a microscopic morphology showing microspheres with a diameter of 1 to 5 μm was obtained. The spray-dried powder was placed in an argon-protected tubular furnace, heated to 750°C at a heating rate of 5°C / min, and calcined for 15 hours to obtain a lithium iron manganese phosphate positive electrode material, denoted as LiMn 0.6 Fe 0.4 PO 4 / C.

[0055] Example 2

[0056] Will FeSO 4 7H 2 O,MnSO 4 ·H 2 O, and H 3 PO 4 The solution was prepared with deionized water in a molar ratio of 1.5:1.5:2 and pumped into a continuously stirred reactor with a capacity of 5 L and a base liquid of 1.8 L, wherein FeSO 4 7H 2 O,MnSO 4 ·H 2O were dissolved in deionized water to prepare a cationic solution with a concentration of 1.5 M; the pH was controlled at 6.7 by ammonia water with a concentration of 4.5 M; the early low-temperature nucleation and high-temperature growth process was adopted, the early reaction temperature was 25 ° C, the reaction time was 1 h, and the late high-temperature growth stage reaction temperature was 50 ° C, the reaction time was 15 h; during the reaction process, the speed of the reactor was 400 r / min, and finally the mixed liquid in the reactor was taken out, filtered, washed, and then placed in a 60 ° C forced air oven to dry to obtain (Mn 0.5 Fe 0.5 ) 3 (PO 4 ) 2 ·xH 2 O precursor.

[0057] The obtained (Mn 0.5 Fe 0.5 ) 3 (PO 4 ) 2 ·xH 2 The precursor was placed in an argon protected tube furnace and heated to 550°C at a heating rate of 5°C / min and calcined for 10 h to remove the crystal water to obtain (Mn 0.5 Fe 0.5 ) 3 (PO 4 ) 2 Precursor. 0.5 Fe 0.5 ) 3 (PO 4 ) 2 The precursor and lithium phosphate were mixed with deionized water in a molar ratio of 1:1 and then sand-milled at a speed of 2000 r / min for 5 hours to obtain a first slurry, the mass of the solid component of the first slurry accounting for 18% of the total mass of the entire mixture.

[0058] Glucose accounting for 9% of the solid content was added to the first slurry, and the mixture was mixed to obtain a second slurry. The second slurry was quickly dried by spray drying. The working temperature of the spray dryer was 180°C, and the spray drying feed rate was 25 mL / min. A dry powder with a microscopic morphology of microspheres with a diameter of 1 to 5 μm was obtained. The spray-dried powder was placed in an argon-protected tubular furnace, heated to 700°C at a heating rate of 5°C / min and calcined for 10 hours to obtain a lithium iron manganese phosphate positive electrode material, denoted as LiMn 0.5 Fe 0.5 PO 4 / C.

[0059] Example 3

[0060] Will FeSO 4 7H 2O,MnSO 4 ·H 2 O, and H 3 PO 4 The solution was prepared with deionized water in a molar ratio of 1.2:1.8:2 and pumped into a continuously stirred reactor with a capacity of 5 L and a base liquid of 1.8 L, wherein FeSO 4 7H 2 O,MnSO 4 ·H 2 O were dissolved in deionized water to prepare a cationic solution, the concentration of the cationic solution was 1.5M; the pH was controlled at 6.3 by ammonia water, the concentration of ammonia water was 4M; the early low-temperature nucleation and high-temperature growth process was adopted, the early reaction temperature was 20℃, the reaction time was 2h, and the later high-temperature growth stage reaction temperature was 55℃, the reaction time was 13h; during the reaction process, the speed of the reactor was 500r / min, and finally the mixed liquid in the reactor was taken out, filtered, washed, and then placed in a 60℃ forced air oven to dry to obtain (Mn 0.6 Fe 0.4 ) 3 (PO 4 ) 2 ·xH 2 O precursor.

[0061] The obtained (Mn 0.6 Fe 0.4 ) 3 (PO 4 ) 2 ·xH 2 The precursor was placed in an argon protected tube furnace and heated to 600 °C at a heating rate of 4 °C / min and calcined for 10 h to remove the crystal water to obtain (Mn 0.6 Fe 0.4 ) 3 (PO 4 ) 2 Precursor. 0.6 Fe 0.4 ) 3 (PO 4 ) 2 Precursor and Li 2 CO 3 ,

[0062] NH 4 H 2 PO 4 The mixture was mixed with deionized water in a molar ratio of 2:3:2 and then sand-milled at a speed of 2500 r / min for 4 hours to obtain a first slurry, wherein the mass of the solid component of the first slurry accounted for 12% of the total mass of the mixture.

[0063] Glucose accounting for 7% of the solid content was added to the first slurry, and the mixture was uniformly mixed to obtain a second slurry, which was quickly dried by spray drying. The working temperature of the spray dryer was 200°C, and the spray drying feed rate was 20 mL / min to obtain a dry powder. The spray-dried powder was placed in an argon-protected tubular furnace, heated to 750°C at a heating rate of 6°C / min, and calcined for 10 hours to obtain a lithium iron manganese phosphate positive electrode material, denoted as LiMn 0.6 Fe 0.4 PO 4 / C.

[0064] Comparative Example 1

[0065] Li 2 CO 3 , FeC 2 O 4 ·2H 2 O,MnCO 3 , NH 4 H 2 PO 4 The mixture was mixed with deionized water in a molar ratio of 1:0.8:1.2:2 and then sand-milled at a speed of 2500 r / min for 2 hours to obtain a first slurry, wherein the mass of the solid component of the first slurry accounted for 15% of the total mass of the mixture.

[0066] Glucose accounting for 8% of the solid content was added to the first slurry, and the mixture was evenly mixed to obtain the second slurry, which was quickly dried by spray drying. The working temperature of the spray dryer was 160°C, and the spray drying feed rate was 25 mL / min. A dry powder with a microscopic morphology showing microspheres with a diameter of 1 to 5 μm was obtained. The spray-dried powder was placed in an argon-protected tubular furnace, heated to 700°C at a heating rate of 5°C / min and calcined for 15 hours to obtain a lithium iron manganese phosphate positive electrode material, denoted as LiMn 0.6 Fe 0.4 PO 4 / C.

[0067] Performance and testing

[0068] 1) Figure 1 The (Mn) obtained in Example 1 0.6 Fe 0.4 ) 3 (PO 4 ) 2 ·xH 2 SEM image of O precursor; Figure 2 The (Mn) obtained in Example 1 0.6 Fe 0.4 ) 3 (PO 4) 2 ·xH 2 TEM-EDS image of O precursor; Figure 1 It can be seen that by adjusting the experimental conditions such as the rotation speed, reaction temperature, ion concentration, pH and reaction time of the coprecipitation process, a microspherical manganese iron phosphate precursor with good sphericity and uniform size was obtained, and the diameter of the microspheres was 10-20μm; Figure 2 It can be seen that the precursor iron and manganese elements are evenly distributed, achieving atomic-level mixing of iron and manganese.

[0069] 2) Figure 3 The lithium iron manganese phosphate positive electrode material LiMn after calcination in Example 1 0.6 Fe 0.4 PO 4 / SEM image of C; Figure 4 The positive electrode material LiMn prepared in Comparative Example 1 0.6 Fe 0.4 PO 4 / SEM image of C; Figure 5 The lithium iron manganese phosphate positive electrode material LiMn after calcination in Example 1 0.6 Fe 0.4 PO 4 TEM-EDS image of / C; Figure 6 The lithium iron manganese phosphate positive electrode material LiMn after calcination in Comparative Example 1 0.6 Fe 0.4 PO 4 TEM-EDS diagram of / C; Figure 3 Figure 4 It can be seen that the lithium manganese iron phosphate positive electrode material LiMn is finally synthesized by sand milling and spray drying process in Example 1 and Comparative Example 1. 0.6 Fe 0.4 PO 4 There is no obvious difference in morphology between / C, both of which present microspheres with a size of 1 to 5 μm. Figure 5 Figure 6 It can be seen that LiMn is obtained by first synthesizing an iron-manganese precursor and then mixing it with a lithium source and phosphoric acid. 0.6 Fe 0.4 PO 4 / C positive electrode material, the iron and manganese elements are distributed more evenly, making LiMn 0.6 Fe 0.4 PO 4 The / C structure is more stable and the manganese dissolution is inhibited, so Example 1 exhibits better long cycle performance.

[0070] 3) 0.24 g of the lithium manganese iron phosphate positive electrode material LiMn prepared in Example 1 and Comparative Example 1 were respectively added 0.6 Fe 0.4 PO 4 / C was added into a mortar with a conductive agent super P and polyvinylidene fluoride powder in a mass ratio of 8:1:1 and fully ground for 20 minutes to obtain a mixture; then 900 μL of N-methylpyrrolidone was added into the mixture and fully stirred to obtain a mixed slurry; the mixed slurry was evenly spread on a carbon-coated aluminum foil, dried in a blast oven at 80°C, and finally cut with a cutter with a diameter of 12 mm to obtain a positive electrode sheet; the positive electrode sheet was assembled into a CR2032 battery in a glove box, the negative electrode material was a lithium sheet with a diameter of 13 mm, the separator was Celgard2400, and the electrolyte was 1 mol LiPF 6 Dissolved in EC:DEC:DMC solution with a volume ratio of 1:1:1.

[0071] The performance of the button cells assembled from Example 1 and Comparative Example 1 was tested, and long cycle performance tests were performed at 25 degrees Celsius and at a rate of 0.5 C. The charge and discharge process was constant current charge-constant voltage charge-constant current discharge, and the charge and discharge voltage range was 2.5-4.5V. Figure 7 and Figure 8 The cycle performance diagrams of the lithium manganese iron phosphate positive electrode materials finally prepared in Example 1 and Comparative Example 1 are shown respectively. Figure 7 It can be seen that the LiMn prepared in Example 1 0.6 Fe 0.4 PO 4 When the / C positive electrode material is used in lithium-ion batteries, its capacity can still reach 141.5Ah / g after 500 cycles at 0.5C, and the capacity retention rate is as high as 92.1%; Figure 8 It can be seen that the LiMn prepared in Comparative Example 1 0.6 Fe 0.4 PO 4 When the / C positive electrode material is used in a lithium-ion battery, after 500 cycles at 0.5C, the capacity decays rapidly, and the capacity is only 96.8Ah / g, and the capacity retention rate is only 71.6%. This shows that Example 1 has better cycle performance and can maintain a more stable structure during a long cycle.

[0072] At 25°C, the LiMn prepared in Example 1 and Comparative Example 1 were heated at a rate of 0.1C-0.5C-1C-2C-3C-2C-1C-0.5C-0.1C. 0.6 Fe 0.4 PO 4 The performance of the positive electrode material of / C was tested for rate performance. The charging and discharging process was constant current charging-constant voltage charging-constant current discharging, and the voltage range of charging and discharging was 2.5-4.5V. The rate performance results of Example 1 and Comparative Example 1 are shown in Fig. 9 shown by Fig. 9 It can be seen that Example 1 has better rate performance. Even at a high rate of 3C, the LiMn prepared in Example 1 0.6 Fe0.4 PO 4 / C positive electrode material, its capacity is as high as 136.3 mAh / g (much higher than 123.9 mAh / g of comparative example 1 at the same rate). In summary, example 1 has better cycle performance and rate performance.

[0073] In summary, the lithium iron manganese phosphate prepared by the present invention realizes uniform mixing of iron and manganese atoms, improves the structural stability of the long cycle process, and improves the cycle life of the lithium iron manganese phosphate positive electrode material; at the same time, the lithium iron manganese phosphate secondary particles prepared by the present invention have a microsphere structure wrapped by nanosheets, the secondary particle size is 1-5μm, the size is uniform, and the dispersion is good, the primary particle grain size is 50-80nm, which significantly reduces the size of the material, shortens the path of lithium ions in the transmission process, and improves the rate performance of the lithium iron manganese phosphate positive electrode material. Therefore, the present invention has broad application prospects in the field of lithium ion battery technology.

[0074] It should be emphasized that the above are only preferred embodiments of the present invention and do not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a lithium iron manganese phosphate positive electrode material with uniform iron and manganese mixing, characterized in that: The following steps are involved: Step S1: Synthesis of spherical (Mn 1-x Fe x )3(PO4)2·xH2O precursor; Step S2: The (Mn 1-x Fe x )3(PO4)2·xH2O is dehydrated under protective atmosphere to obtain (Mn 1-x Fe x )3(PO4)2 precursor; Step S3: The (Mn 1-x Fe x )3(PO4)2 precursor is mixed with a lithium source, a phosphorus source and water, the solid content is controlled, and sand milling is performed to obtain a first slurry; Step S4: adding a carbon source to the first slurry obtained in step S3, stirring evenly to obtain a second slurry, and rapidly drying the obtained second slurry by spray drying, and granulating the obtained second slurry to obtain a dry powder; Step S5: The dried powder obtained in step S4 is calcined under a protective atmosphere to finally obtain lithium manganese iron phosphate positive electrode material LiMn x Fe 1-x PO4 / C; The value range of x is: 0.2≤x≤0.

8.

2. The method for preparing the lithium iron manganese phosphate positive electrode material with uniform iron and manganese mixture according to claim 1, characterized in that: The lithium iron manganese phosphate positive electrode material LiMn x Fe 1-x PO4 / C is wrapped into microspheres by uniform nanosheets, with a primary particle size of 50 to 80 nm and a secondary particle size of 1 to 5 μm.

3. The method for preparing the lithium iron manganese phosphate positive electrode material with uniform iron and manganese mixture according to claim 2, characterized in that: The value range of x is: 0.4≤x≤0.

7.

4. The method for preparing the lithium iron manganese phosphate positive electrode material with uniform iron and manganese mixture according to claim 1, characterized in that: The step S1 specifically comprises: continuously mixing and stirring FeSO4·7H2O, MnSO4·H2O and H3PO4 solution at a molar ratio of 3x:3-3x:2 to perform a coprecipitation reaction; The pH value range of the coprecipitation reaction is: 5.5≤pH≤7.5; During the coprecipitation reaction, a protective atmosphere is introduced for protection; The coprecipitation reaction process adopts low-temperature nucleation and high-temperature growth processes, the reaction temperature of the low-temperature nucleation stage is 20-30°C, the reaction temperature of the high-temperature growth stage is 40-60°C, and the total reaction time is 10-24h; After the coprecipitation reaction is completed, the mixture is taken out, filtered, washed and dried to obtain (Mn 1-x Fe x )3(PO4)2·xH2O precursor.

5. The method for preparing the lithium iron manganese phosphate positive electrode material with uniform iron and manganese mixture according to claim 4, characterized in that: In the step S1, FeSO4·7H2O and MnSO4·H2O are dissolved in deionized water to prepare a cationic solution, and the concentration of the cationic solution is 1-2M.

6. The method for preparing the lithium iron manganese phosphate positive electrode material with uniform iron and manganese mixture according to claim 1, characterized in that: In step S3, the lithium source includes: lithium phosphate, lithium carbonate; the phosphorus source includes: ammonium dihydrogen phosphate, diammonium hydrogen phosphate; the lithium source, phosphorus source, (Mn 1-x Fe x The amount of the )3(PO4)2 precursor material is added in a ratio of Li:M:PO4 of 1:0.9~1.1:0.9~1.1, where M=Fe+Mn.

7. The method for preparing the lithium iron manganese phosphate positive electrode material with uniform iron and manganese mixture according to claim 1, characterized in that: In step S4, the carbon source includes: one or more of sucrose, glucose, starch or xylitol; the mass of the carbon source is 5% to 10% of the total mass of the first slurry solid; the spray drying temperature used is 150 to 200° C., and the spray feeding speed is 10 to 30 mL / min.

8. The method for preparing the lithium iron manganese phosphate positive electrode material with uniform iron and manganese mixture according to claim 1, characterized in that: In the step S5, the calcination temperature is 600-800° C., and the calcination time is 10-20 hours.

9. A lithium manganese iron phosphate positive electrode material, characterized in that: The method is prepared by the preparation method according to any one of claims 1 to 8.

10. A lithium ion battery, characterized in that: Comprising the lithium iron manganese phosphate positive electrode material as described in claim 9.

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