Lithium manganese iron phosphate material as well as preparation method and application thereof

Abstract

The embodiment of the invention provides a lithium manganese iron phosphate material and a preparation method and application thereof, the preparation method of the lithium manganese iron phosphate material comprises the following steps: physically mixing lithium iron phosphate, a manganese source, a phosphorus source and a lithium source to obtain a blend, the molar ratio of Mn, P and Li in the manganese source, the phosphorus source and the lithium source being 1: 1: 1; sintering the blend according to the following procedures: keeping the temperature of 200-250 DEG C in a low-temperature section for 1-3 hours; the medium temperature section is kept at 400-500 DEG C for 2-12 hours; the high-temperature section is kept at 600-750 DEG C for 2-10 hours, and the cooling rate in the whole sintering process is 1-10 DEG C / min, so as to obtain the lithium manganese iron phosphate material. The lithium manganese iron phosphate material with stable crystal form and relatively good electrochemical performance can be obtained only by simply mixing the raw materials and then carrying out segmented sintering, and a chemical reagent synthesis process is avoided, so that the cost is saved, the operation is simple, and the industrial applicability is high; and on the other hand, the method can be used for recycling the LiFePO4 material, and the additional value of the lithium iron phosphate is improved by recycling the lithium iron phosphate.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of battery technology, and in particular to a lithium manganese iron phosphate material and a preparation method and application thereof. Background Art

[0002] With the rapid development of new energy vehicles in my country, a large number of lithium-ion power batteries have been applied to new energy vehicles. The life cycle of lithium-ion power batteries is generally 5-8 years, and some are even shorter. The development of new energy vehicles has a history of nearly 10 years. Therefore, with the passage of time, a large number of waste lithium-ion power batteries are generated, and most of them are lithium iron phosphate power batteries and lithium manganese oxide power batteries. For such a large number of waste power batteries, the current common practice is to re-assemble the waste power batteries and apply them to the energy storage field. This method can dispose of a large number of waste lithium-ion power batteries in a short time. However, people also realize that this is only a temporary treatment method. The performance of lithium-ion batteries will eventually decay to the point where they can no longer be used. Therefore, there are also many battery companies or battery recycling companies that are engaged in the recycling and regeneration technology of waste lithium-ion power batteries.

[0003] The prior art mentions that waste lithium iron phosphate batteries are used to regenerate lithium iron phosphate cathode materials through a series of means, but their electrochemical performance is not as good as that of the first synthesized lithium iron phosphate. There are also reports that lithium iron phosphate is resynthesized by acid hydrolysis, and the performance of the lithium iron phosphate material synthesized by this method is basically the same as that of the first synthesized lithium iron phosphate. However, in the development direction of high energy density of lithium-ion power batteries, lithium iron phosphate batteries are almost approaching a bottleneck. Seeking a high energy density electrochemical system has become a consensus in the industry. Lithium iron manganese phosphate has the same crystal structure as lithium iron phosphate, but the energy density of lithium iron manganese phosphate is much higher than that of lithium iron phosphate, and the content of each element of lithium iron manganese phosphate is rich and environmentally friendly. It is considered to be the next generation material system to replace lithium iron phosphate materials. However, the current preparation methods of lithium iron manganese phosphate all use high-purity chemical reagents for synthesis, which is complex and costly. Summary of the invention

[0004] The technical problem solved by the embodiment of the present invention is to provide a method for preparing a lithium iron manganese phosphate material with a simple process, so as to improve the electrochemical performance of the lithium iron manganese phosphate positive electrode material.

[0005] In order to solve the above problems, an embodiment of the present invention provides a method for preparing a lithium manganese iron phosphate material, comprising:

[0006] Physically mixing lithium iron phosphate, a manganese source, a phosphorus source and a lithium source to obtain a blend, wherein the molar ratio of Mn, P and Li in the manganese source, the phosphorus source and the lithium source is 1:1:1;

[0007] The blend is sintered according to the following procedure: the low temperature section is 200°C-250°C, maintained for 1h-3h; the medium temperature section is 400°C-500°C, maintained for 2h-12h; the high temperature section is 600°C-750°C, maintained for 2h-10h. The cooling rate during the entire sintering process is 1°C / min-10°C / min to obtain the lithium manganese iron phosphate material.

[0008] Optionally, the cooling rate is 1°C / min-2°C / min.

[0009] Optionally, after the step of maintaining the temperature in the high temperature section at 600° C.-750° C. for 2 h-10 h, the step further includes: tempering the lithium iron manganese phosphate material to the temperature in the medium temperature section and maintaining the temperature for 2 h-10 h.

[0010] Optionally, the sintering heating rate ranges from 1°C / min to 20°C / min.

[0011] Optionally, the manganese source includes at least one of lithium manganese phosphate, manganese sulfate, manganese carbonate, manganese oxalate, manganese acetate, manganese oxide, manganese trioxide, and manganese dioxide; the phosphorus source includes a mixture of one or more of lithium manganese phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, iron phosphate, manganese phosphate, and manganous phosphate; the lithium source includes a mixture of one or more of lithium manganese phosphate, lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate.

[0012] Optionally, the manganese source, phosphorus source and lithium source are lithium manganese phosphate.

[0013] Optionally, the ratio of iron element to manganese element in the lithium manganese iron phosphate material is 9:1.

[0014] In order to solve the above problems, an embodiment of the present invention provides a lithium manganese iron phosphate material obtained by the above preparation method.

[0015] In order to solve the above problems, an embodiment of the present invention provides an application of the above lithium iron manganese phosphate material in a positive electrode material of a lithium battery.

[0016] Compared with the prior art, the technical solution of the embodiment of the present invention has the following advantages:

[0017] The embodiment of the present invention provides a method for preparing a lithium iron manganese phosphate material, firstly physically mixing lithium iron phosphate, a manganese source, a phosphorus source and a lithium source to obtain a blend, wherein the molar ratio of the elements Mn, P and Li in the manganese source, the phosphorus source and the lithium source is 1:1:1; then the blend is sintered according to the following procedure: the low temperature section is 200℃-250℃ for 1h-3h; the medium temperature section is 400℃-500℃ for 2h-12h; the high temperature section is 600℃-750℃ for 2h-10h, and the cooling rate during the whole sintering process is 1℃ / min-10℃ / min, to obtain the lithium iron manganese phosphate material. It can be seen that the preparation method of the lithium iron manganese phosphate material provided by the embodiment of the present invention can improve the crystallinity of the lithium iron manganese phosphate material by simply mixing the raw materials and then sintering them in stages, and controlling the annealing procedure of the lithium iron manganese phosphate material, thereby improving the electrochemical properties of the lithium iron manganese phosphate material. On the one hand, lithium manganese iron phosphate materials with stable crystal structure and good electrochemical properties can be obtained by simply mixing the raw materials and then sintering them in stages, thus avoiding the chemical reagent synthesis process, which not only saves costs but also is simple to operate and has strong industrial applicability. On the other hand, it can be used to recycle LiFePO4 materials and increase the added value of lithium iron phosphate by recycling and reusing lithium iron phosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0019] Figure 1 This is a flow chart of a method for preparing a lithium iron manganese phosphate material provided by an embodiment of the present invention;

[0020] Figure 2 These are scanning electron microscope images of the raw material LiMnPO4, the raw material LiFePO4, and the lithium manganese iron phosphate materials of Examples 1 to 3 of the present invention;

[0021] Figure 3 The XRD patterns of the lithium manganese iron phosphate materials of Examples 1 to 3 of the present invention and the standard PDF cards of LiMnPO4 and LiFePO4;

[0022] Figure 4 1 is the charge and discharge curve of the button battery prepared from the lithium manganese iron phosphate material of Examples 1 to 3 of the present invention;

[0023] Figure 5 It is a cycle performance test diagram of button batteries prepared from lithium manganese iron phosphate materials of Examples 1 to 3 of the present invention;

[0024] Figure 6 It is a rate performance test diagram of button batteries prepared from lithium manganese iron phosphate materials of Examples 1 to 3 of the present invention;

[0025] Figure 7 1 is the charge and discharge curve of the button cell made of lithium manganese iron phosphate material at different rates according to Example 1 of the present invention;

[0026] Figure 8 1 is the charge and discharge curve of the button cell made of lithium manganese iron phosphate material at different rates according to Example 2 of the present invention;

[0027] Fig. 9 3 are the charge and discharge curves of the button cell made of lithium manganese iron phosphate material at different rates according to Example 3 of the present invention. DETAILED DESCRIPTION

[0028] As can be seen from the background technology, the current preparation methods of lithium manganese iron phosphate mostly use high-purity chemical reagents for synthesis, which has complex processes and high costs.

[0029] This application can improve the crystallinity of lithium iron manganese phosphate material by simply mixing the raw materials and then sintering them in stages, and controlling the annealing process of lithium iron manganese phosphate material, thereby improving the electrochemical performance of lithium iron manganese phosphate material. Thus, lithium iron manganese phosphate material with stable crystal form and good electrochemical performance is obtained, avoiding the chemical reagent synthesis process, not only saving costs, but also simple operation and strong industrial applicability; on the other hand, it can be used to recycle LiFePO4 materials, and by recycling and reusing lithium iron phosphate, the added value of lithium iron phosphate is increased.

[0030] like Figure 1 As shown, in order to solve the above problems, an embodiment of the present invention provides a method for preparing a lithium manganese iron phosphate material, comprising:

[0031] Step S1, physically mixing lithium iron phosphate, a manganese source, a phosphorus source and a lithium source to obtain a blend, wherein the molar ratio of Mn, P and Li in the manganese source, the phosphorus source and the lithium source is 1:1:1;

[0032] In a specific embodiment, the manganese source includes at least one of lithium manganese phosphate, manganese sulfate, manganese carbonate, manganese oxalate, manganese acetate, manganese oxide, manganese trioxide, and manganese dioxide. The phosphorus source includes a mixture of one or more of lithium manganese phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, iron phosphate, manganese phosphate, and manganous phosphate; the lithium source includes one or more of lithium manganese phosphate, lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate.

[0033] It should be noted that the manganese source is used to provide the Mn element, the phosphorus source is used to provide the P element, and the lithium source is used to provide the Li element. The manganese source, phosphorus source, and lithium source described herein may be a raw material containing the three elements of P, Mn, and Li at the same time, or may contain at least one of the three elements of P, Mn, and Li respectively, that is, the manganese source, phosphorus source, and lithium source may refer to one raw material, or two raw materials, or three raw materials, as long as the molar ratio of the elements of Mn, P, and Li in the manganese source, phosphorus source, and lithium source in the raw material is ensured to be 1:1:1.

[0034] In a specific embodiment, the manganese source, phosphorus source and lithium source are lithium manganese phosphate. Lithium manganese phosphate can provide P, Mn and Li elements at the same time, so there is no need to provide phosphorus source and lithium source. In this way, the raw materials and production process can be further simplified.

[0035] The present application utilizes LiFePO4 as a raw material to prepare a lithium manganese iron phosphate material with good conductivity, thereby improving the poor conductivity of batteries with lithium iron phosphate (LiFePO4) as the active material, realizing the recycling of LiFePO4, improving resource utilization, and increasing the energy density of the battery.

[0036] Step S2, sintering the blend according to the following procedure: maintaining the low temperature section at 200°C-250°C for 1h-3h; maintaining the medium temperature section at 400°C-500°C for 2h-12h; maintaining the high temperature section at 600°C-750°C for 2h-10h, and the cooling rate during the entire sintering process is 1°C / min-10°C / min to obtain the lithium manganese iron phosphate material.

[0037] In the present application, the sintering procedure is gradient segmented sintering. The low temperature section corresponds to the decomposition of the carbon source, and the temperature of the low temperature section is 200°C-250°C; the medium temperature section corresponds to the further decomposition of the carbon source, the raw materials are preliminarily decomposed, and a chemical reaction occurs. To prevent the sintering temperature from being too low and causing incomplete reaction, the temperature is controlled at 400°C-500°C, such as 400°C, 405°C, 410°C, 420°C, and 425°C; to make the crystal growth of the high temperature section product perfect and the crystallinity higher, the temperature is controlled at 600°C-750°C, such as 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, etc.

[0038] The sintering time should not be too short or too long. If the sintering time is too short, the raw materials will not react sufficiently, too many impurities will be produced, affecting the purity of the product and ultimately the electrochemical performance; if the sintering time is too long, it will also cause a waste of resources. Therefore, in a specific embodiment, the medium temperature section is maintained at 400℃-500℃ for 2h-12h, specifically, it can be 2h, 3h, 4h, 5h-9h, 10h, etc.

[0039] Of course, before sintering the blend, the blend may be dried first.

[0040] It should be noted that the ratio of Mn and Fe in the final synthesized lithium manganese iron phosphate can be adjusted by adjusting the molar ratio of lithium iron phosphate and raw material lithium manganese phosphate. The molar percentage range of the lithium iron phosphate and the lithium manganese phosphate is related to the proportion of Mn and Fe in the final desired lithium manganese iron phosphate material.

[0041] By adjusting the molar ratio of the raw materials lithium iron phosphate and lithium manganese phosphate, a lithium manganese iron phosphate material with different proportions of manganese and iron can be prepared. In a specific embodiment, the ratio of iron to manganese in the lithium manganese iron phosphate material is 9:1, and the molecular formula is LiMn 0.1 Fe 0.9 PO4, by increasing the proportion of lithium iron phosphate, lithium iron phosphate can be recycled based on lithium iron phosphate as a template. Of course, in other embodiments, the ratio of manganese to iron in the final prepared lithium manganese iron phosphate material can also be other ratios, such as 2:8, 3:7, 4:6, 5:5, etc.

[0042] It has been found through experiments that the annealing procedure in the preparation process of lithium manganese iron phosphate material can improve the crystallinity, thereby improving the battery cycle performance and rate performance. In a specific embodiment, the cooling rate during the entire sintering process is 1°C / min-10°C / min. In order to improve the fusion effect of lithium iron phosphate and lithium manganese phosphate, in a specific embodiment, the sintered product is slowly annealed, and the cooling rate is 1°C / min-2°C / min.

[0043] In another specific embodiment, in order to optimize the crystallinity and improve the electrochemical performance, after the step of maintaining the high temperature section at 600°C-750°C for 2h-10h, the following step may be further included: tempering the lithium manganese iron phosphate material to the temperature of the medium temperature section and maintaining it for 2h-10h. The temperature range of the medium temperature section is 400°C-500°C. By tempering after high temperature, the crystallinity of the lithium manganese iron phosphate material can be further improved.

[0044] In a specific embodiment, the sintering heating rate ranges from 1° C. / min to 20° C. / min.

[0045] The preparation method of the lithium iron manganese phosphate material provided in the embodiment of the present invention, on the one hand, only requires simple mixing of the raw materials and then staged sintering to obtain the lithium iron manganese phosphate material with stable crystal structure and good electrochemical performance, thereby avoiding the chemical reagent synthesis process, which not only saves costs but also is simple to operate and has strong industrial applicability; on the other hand, it can be used to recycle LiFePO4 materials and increase the added value of lithium iron phosphate by recycling and reusing lithium iron phosphate.

[0046] In order to solve the above problems, an embodiment of the present invention further provides a lithium manganese iron phosphate material obtained by the above-mentioned preparation method.

[0047] By simply mixing the lithium iron phosphate and lithium manganese phosphate raw materials and then sintering them in stages, and controlling the annealing procedure of the lithium iron manganese phosphate material, the crystallinity of the lithium iron manganese phosphate material can be improved, thereby improving the electrochemical properties of the lithium iron manganese phosphate material.

[0048] In order to solve the above problems, an embodiment of the present invention further provides an application of the above-mentioned lithium iron manganese phosphate material in a positive electrode material of a lithium battery.

[0049] Specifically, an embodiment of the present invention provides a positive electrode sheet, using the above-mentioned lithium iron manganese phosphate material as an active material. An embodiment of the present invention also provides a lithium ion battery, and the lithium ion battery includes the above-mentioned positive electrode sheet.

[0050] By simply mixing the lithium iron phosphate and lithium manganese phosphate raw materials and then sintering them in stages, and controlling the annealing process of the lithium iron manganese phosphate material, the crystallinity of the lithium iron manganese phosphate material can be improved, thereby improving the cycle performance and charge and discharge capacity of the lithium battery.

[0051] The lithium manganese iron phosphate material and its preparation method and battery of the present invention are further described in detail below in conjunction with specific embodiments.

[0052] Example 1

[0053] Provided is a method for preparing lithium manganese iron phosphate material:

[0054] Step 1, mix LiMnPO4 (LMP) and LiFePO4 (LFP) in a molar ratio of 0.1:0.9.

[0055] Step 2, drying the mixture to obtain a gray product.

[0056] Step 3, the gray product was sintered in stages: first at 200°C for 2h, then at 500°C for 2h, finally at 700°C for 5h, and then at 500°C for 10h. The cooling rate during the entire sintering process was 1°C / min to obtain lithium manganese iron phosphate material (LMFP). The LMFP was subjected to electron microscopy morphology analysis and XRD analysis. The results are as follows: Figure 2 and Figure 3 shown.

[0057] Figure 2 Figure a is the electron microscopy morphology of lithium manganese phosphate, Figure b is the electron microscopy morphology of lithium iron phosphate, Figure c is the electron microscopy morphology of lithium iron manganese phosphate prepared in Example 1, Figure d is the electron microscopy morphology of lithium iron manganese phosphate prepared in Example 2, and Figure e is the electron microscopy morphology of lithium iron manganese phosphate prepared in Example 3.

[0058] Combination Figure 2 and Figure 3 It can be seen that the needle-shaped LMP disappears after sintering, and LMFP basically retains the morphology of LFP. The disappearance of the spindle-shaped particles of lithium manganese phosphate means that lithium manganese phosphate enters lithium iron phosphate after high-temperature treatment. The double peaks of the raw material that are obviously split have merged or fused into a single peak, which confirms that lithium manganese iron phosphate is formed after sintering. Combined with the subsequent electrochemical performance test ( Figure 4 ), in the first cycle charge and discharge curve, the Fe platform at about 3.5V and the Mn platform at about 4.1V appear, and the ratio of specific capacity is consistent with the designed 0.9:0.1, indicating that the molecular formula of the finally prepared lithium manganese iron phosphate is LiMn 0.1 Fe 0.9 PO4.

[0059] Preparation of pole piece

[0060] The active electrode material LMFP (93 wt%) of Example 1, the conductive additive conductive carbon black Super P (2 wt%) and the conductive graphite KS-6 (2 wt%), and the binder PVDF solution (3 wt%) were mixed evenly, and then the mixed slurry was evenly coated on a clean aluminum foil with a scraper, with a coating thickness of 250 μm, and placed in a vacuum transition chamber at 80 ° C for 8 h to dry, and the LMFP loading was about 8 mg cm -2 , rolled with an electric double-roller press, the rolled bottom thickness is about 1.1 mm, and then pressed with a tablet press to prepare an electrode sheet with a diameter of 12 mm.

[0061] Button battery assembly

[0062] The reaction was carried out in a glove box (MBRAUN LABMASTER 130) under Ar atmosphere protection. The electrolyte was 1M LiPF6 (EC / DMC / EMC=1:1:1), 2% VC was used as an additive, the separator was a Celgard-2500 polypropylene microfilm, the electrode sheet prepared in Example 1 was used as the working electrode, and the counter electrode was a fresh lithium sheet.

[0063] The button cell was tested for related performance. The charging and discharging method was constant current charging and discharging, the voltage range was 3.0~4.4V, and the specific capacity, cycle performance, rate performance, etc. of the battery were tested. The test results are shown in Table 1-3 and Figure 4-Figure 7 shown.

[0064] Example 2

[0065] Provided is a method for preparing lithium manganese iron phosphate material:

[0066] Step 1, mix LiMnPO4 and LiFePO4 in a molar ratio of 0.1:0.9.

[0067] Step 2, drying the mixture to obtain a gray product.

[0068] Step 3, the gray product was sintered in stages: first at 200°C for 2h, then at 500°C for 12h, and finally at 700°C for 5h. The cooling rate during the entire sintering process was 1°C / min to obtain lithium manganese iron phosphate material (LMFP). The LMFP was subjected to electron microscopy morphology analysis and XRD analysis. The results are as follows: Figure 2 and Figure 3 Show.

[0069] The active electrode material LMFP (93 wt%) of Example 2, the conductive additives conductive carbon black Super P (2 wt%) and conductive graphite KS-6 (2 wt%), and the binder PVDF solution (3 wt%) were mixed evenly, and then the mixed slurry was evenly coated on a clean aluminum foil with a scraper, with a coating thickness of 250 μm, and placed in a vacuum transition chamber at 80 ° C for 8 h to dry, and the LMFP loading was about 8 mg cm -2 , rolled with an electric double-roller press, the rolled bottom thickness is about 1.1 mm, and then pressed with a tablet press to prepare an electrode sheet with a diameter of 12 mm.

[0070] Button battery assembly

[0071] The reaction was carried out in a glove box (MBRAUN LABMASTER 130) under Ar atmosphere protection. The electrolyte was 1M LiPF6 (EC / DMC / EMC=1:1:1), 2% VC was used as an additive, the separator was a Celgard-2500 polypropylene microfilm, the electrode sheet prepared in Example 2 was used as the working electrode, and the counter electrode was a fresh lithium sheet.

[0072] The button cell was tested for related performance. The charging and discharging mode was constant current charging and discharging, the voltage range was 3.0~4.4V, and the specific capacity, cycle performance, rate performance, etc. of the battery were tested. The test results are shown in Table 1-3. Figure 4-Figure 6 as well as Figure 8 shown.

[0073] Example 3

[0074] Provided is a method for preparing lithium manganese iron phosphate material:

[0075] Step 1, mix LiMnPO4 and LiFePO4 in a molar ratio of 0.1:0.9.

[0076] Step 2, drying the mixture to obtain a gray product.

[0077] Step 3, the gray product was sintered in stages: first at 200°C for 2h, then at 500°C for 2h, finally at 700°C for 5h, and then at 500°C for 10h. The cooling rate during the entire sintering process was 10°C / min to obtain lithium manganese iron phosphate material (LMFP). The LMFP was subjected to electron microscopy morphology analysis and XRD analysis. The results are as follows: Figure 2 and Figure 3 shown.

[0078] The active electrode material LMFP (93 wt%) of Example 3, the conductive additives conductive carbon black Super P (2 wt%) and conductive graphite KS-6 (2 wt%), and the binder PVDF solution (3 wt%) were mixed evenly, and then the mixed slurry was evenly coated on a clean aluminum foil with a scraper, with a coating thickness of 250 μm, and placed in a vacuum transition chamber at 80 ° C for 8 h to dry. The LMFP loading was about 8 mg cm -2 , rolled with an electric double-roller press, the rolled bottom thickness is about 1.1 mm, and then pressed with a tablet press to prepare an electrode sheet with a diameter of 12 mm.

[0079] Button battery assembly

[0080] The reaction was carried out in a glove box (MBRAUN LABMASTER 130) under Ar atmosphere protection. The electrolyte was 1M LiPF6 (EC / DMC / EMC=1:1:1), 2% VC was used as an additive, the diaphragm was Celgard-2500 polypropylene microfilm, the electrode sheet prepared in Example 3 was used as the working electrode, and the counter electrode was a fresh lithium sheet.

[0081] The button cell was tested for related performance. The charging and discharging mode was constant current charging and discharging, the voltage range was 3.0-4.4V, and the specific capacity, cycle performance, rate performance, etc. of the battery were tested. The test results are shown in Tables 1-3. Figure 4-Figure 6 as well as Fig. 9 shown.

[0082] Table 1 Charge and discharge capacity and first cycle coulombic efficiency of Example 1 to Example 3

[0083]

[0084] Table 2 Cyclic performance parameters of Example 1-Example 3

[0085]

[0086] Table 3 Rate performance parameters of Example 1 to Example 3

[0087] Example 1 Example 2 Example 3 <![CDATA[Discharge specific capacity at 0.1C (mAh·g -1 )]]> 146.3 147.9 142.7 <![CDATA[Discharge specific capacity at 0.2C (mAh·g -1 )]]> 137.7 137.9 134.8 <![CDATA[Discharge specific capacity at 0.5°C (mAh·g -1 )]]> 119.9 121.7 116.8 <![CDATA[Discharge specific capacity at 1°C (mAh·g -1 )]]> 98.6 104.8 92.2 <![CDATA[Discharge specific capacity at 25°C (mAh·g -1 )]]> 71.8 84.0 69.1

[0088] Combined with Table 1-3 and Figure 6-Figure 9It can be seen that the lithium manganese iron phosphate battery prepared in Example 2 of the present application has a first-cycle discharge capacity of up to 160 mAh g -1 After 200 long cycles, the capacity retention rate is as high as 86.36%, and the high rate 2C discharge specific capacity is as high as 84.0mAh·g -1 The lithium manganese iron phosphate material prepared by the preparation method of the present application can improve the cycle performance of lithium batteries.

[0089] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0090] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing lithium manganese iron phosphate material, characterized in that: include: Physically mixing lithium iron phosphate, a manganese source, a phosphorus source and a lithium source to obtain a blend, wherein the molar ratio of Mn, P and Li in the manganese source, the phosphorus source and the lithium source is 1:1:1; The blend is sintered according to the following procedure: the low temperature section is 200°C-250°C, maintained for 1h-3h; the medium temperature section is 400°C-500°C, maintained for 2h-12h; the high temperature section is 600°C-750°C, maintained for 2h-10h. The cooling rate during the entire sintering process is 1°C / min-10°C / min to obtain the lithium manganese iron phosphate material.

2. The method for preparing the lithium iron manganese phosphate material according to claim 1, characterized in that: The cooling rate is 1°C / min-2°C / min.

3. The method for preparing the lithium iron manganese phosphate material according to claim 1, characterized in that: After the step of maintaining the temperature at 600° C.-750° C. in the high temperature section for 2 h-10 h, the method further includes: tempering the lithium iron manganese phosphate material to the temperature in the medium temperature section and maintaining the temperature for 2 h-10 h.

4. The method for preparing the lithium manganese iron phosphate material according to any one of claims 1 to 3, characterized in that: The sintering heating rate range is 1℃ / min-20℃ / min.

5. The method for preparing the lithium manganese iron phosphate material according to any one of claims 1 to 3, characterized in that: The manganese source includes at least one of lithium manganese phosphate, manganese sulfate, manganese carbonate, manganese oxalate, manganese acetate, manganese oxide, manganese trioxide, and manganese dioxide; the phosphorus source includes a mixture of one or more of lithium manganese phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, iron phosphate, manganese phosphate, and manganous phosphate; the lithium source includes one or more of lithium manganese phosphate, lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate.

6. The method for preparing lithium iron manganese phosphate material according to claim 5, characterized in that: The manganese source, phosphorus source and lithium source are lithium manganese phosphate.

7. The method for preparing the lithium manganese iron phosphate material according to any one of claims 1 to 3, characterized in that: The ratio of iron to manganese in the lithium manganese iron phosphate material is 9:

1.

8. A lithium iron manganese phosphate material, characterized in that: The method is obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the lithium iron manganese phosphate material as claimed in claim 8 in a positive electrode material for a lithium battery.

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