Modified lithium iron phosphate material, preparation method thereof and battery

Abstract

The application provides a modified lithium iron phosphate material, a preparation method thereof and a battery, and the preparation method comprises the following steps: mixing, grinding and mixing an iron source, a phosphorus source, a lithium source and an additive containing a doping element to obtain a mixed solid material; performing sintering treatment on the mixed solid material to obtain a mixture of Fe2O3 and Li3Fe2(PO4)3; mixing and grinding the mixture of Fe2O3 and Li3Fe2(PO4)3 with a carbon source, and performing calcination treatment to obtain the modified lithium iron phosphate material. Through dry mixing, two-step sintering and the synergistic effect of the specific additive and the carbon source, the lithium iron phosphate material with high tap density, high specific discharge capacity and excellent rate performance can be prepared.

Description

Technical Field

[0001] This application belongs to the field of battery materials technology, and relates to a modified lithium iron phosphate material, its preparation method, and a battery. Background Technology

[0002] Lithium iron phosphate (LiFePO4) has become one of the mainstream cathode materials for power lithium-ion batteries and energy storage batteries due to its advantages such as structural stability, high safety performance, long cycle life, and environmental friendliness. However, the inherent problems of low electronic conductivity, small lithium-ion diffusion coefficient, and low tap density and compaction density of lithium iron phosphate limit its application in scenarios requiring high energy density and high rate performance.

[0003] Currently, the main methods for improving the electrochemical performance of lithium iron phosphate include carbon coating, ion doping, and nano-sizing. However, conventional methods often suffer from problems such as complex processes, high energy consumption, and limited improvement in compaction density. For example, while direct doping with conductive agents or carbon sources can improve conductivity, it can easily reduce the compaction density of the material; and ordinary solid-state sintering processes cannot simultaneously achieve phase uniformity, particle morphology, and electrochemical activity.

[0004] Therefore, there is an urgent need to develop a method for preparing lithium iron phosphate that can improve both the capacity and rate performance of the material and increase the compaction density. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this application is to provide a modified lithium iron phosphate material, its preparation method and battery. This application can obtain a lithium iron phosphate material with high compaction density, high discharge specific capacity and excellent rate performance by dry mixing, two-step sintering and the synergistic effect of specific additives and carbon sources.

[0006] To achieve this objective, the present application adopts the following technical solution: In a first aspect, this application provides a method for preparing a modified lithium iron phosphate material, the method comprising the following steps: Iron source, phosphorus source, lithium source and additives containing doped elements are mixed and ground to obtain mixed solid material; A mixture of Fe2O3 and Li3Fe2(PO4)3 was obtained by sintering the mixed solid materials. A mixture of Fe2O3 and Li3Fe2(PO4)3 was mixed with a carbon source, ground, and then calcined to obtain modified lithium iron phosphate material.

[0007] In one possible implementation, the dopant additive includes any one or a combination of at least two of titanium dioxide, ammonium metavanadate, and niobium pentoxide.

[0008] In one possible implementation, the molar ratio of lithium, iron, phosphorus and dopant elements in the mixed solid material is (1.0~1.04):1:(1.01~1.06):(0.0001~0.08).

[0009] In one possible implementation, the median particle size D50 of the mixed solid material is 0.4 μm to 0.7 μm.

[0010] In one possible implementation, the atmosphere of the sintering process includes air.

[0011] In one possible implementation, the sintering temperature is 600°C to 950°C, preferably 700°C to 850°C.

[0012] In one possible implementation, the holding time for the sintering process is 1 hour to 6 hours.

[0013] In one possible implementation, the mass percentage of Fe2O3 in the mixture of Fe2O3 and Li3Fe2(PO4)3 is 1% to 25%, preferably 5% to 15%.

[0014] In one possible implementation, the carbon source includes any one or a combination of at least two of glucose, PEG, or sucrose.

[0015] In one possible implementation, the mass ratio of the mixture of Fe2O3 and Li3Fe2(PO4)3 to the carbon source is (85~93):(7~15), preferably (88~92):(8~12).

[0016] In one possible implementation, the median particle size D50 of the material obtained by mixing and grinding the mixture of Fe2O3 and Li3Fe2(PO4)3 with a carbon source is 0.4μm~0.7μm.

[0017] In one possible implementation, the atmosphere of the calcination treatment includes nitrogen and / or argon.

[0018] In one possible implementation, the calcination temperature is 650°C to 850°C, preferably 700°C to 800°C.

[0019] In one possible implementation, the calcination treatment time is 5h to 12h.

[0020] Secondly, this application provides a modified lithium iron phosphate material, which is prepared by the preparation method described in the first aspect.

[0021] In one possible implementation, the compaction density of the modified lithium iron phosphate material is ≥2.5 g / cm³.3 .

[0022] Thirdly, this application provides a battery comprising the modified lithium iron phosphate material as described in the second aspect.

[0023] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0024] Compared with the prior art, this application has the following advantages: (1) This application can produce lithium iron phosphate materials with high compaction density, high discharge specific capacity and excellent rate performance by dry mixing, two-step sintering and the synergistic effect of specific additives and carbon sources.

[0025] (2) This application adopts a dry-mixing grinding combined with two-step atmosphere sintering throughout the entire process, without the need for complex liquid phase processes or special equipment, which is easy to industrialize and reduces processing costs by more than 15%. The compaction density of the modified lithium iron phosphate material can reach 2.65 g / cm³. 3 The battery produced exhibits a discharge specific capacity of over 162 mAh / g at 0.1C and over 135 mAh / g at 1C, demonstrating excellent rate performance. Attached Figure Description

[0026] Figure 1 The image shows the XRD pattern of the mixture of Fe2O3 and Li3Fe2(PO4)3 obtained during the preparation of the modified lithium iron phosphate material described in Example 1. Detailed Implementation

[0027] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0028] The scope of this application can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form a valid range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this application. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this application. In this application, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0029] In this application, "at least two combinations" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or at least two combinations" means any one of the listed items, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this application. In this application, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this application, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0030] In this application, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond those listed unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this application, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this application. The term "embodiment" as used in this application means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art can explicitly and implicitly understand that the embodiments described in this application can be combined with other embodiments that do not conflict with existing technologies. The ordinal numbers "first," "second," "third," and "fourth," etc., used in this application in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect," are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0031] In this application, the order in which the steps are written in the methods described in the various embodiments does not imply a strict order of execution. The actual order of execution of each step should be determined according to its function and possible internal logic. Unless otherwise specified, all steps in this application can be executed in the order in which they are written or in any order without technical conflict.

[0032] In a first aspect, this application provides a method for preparing a modified lithium iron phosphate material in some specific embodiments, the method comprising the following steps: Iron source, phosphorus source, lithium source and additives containing doped elements are mixed and ground to obtain mixed solid material; A mixture of Fe2O3 and Li3Fe2(PO4)3 was obtained by sintering the mixed solid materials. A mixture of Fe2O3 and Li3Fe2(PO4)3 was mixed with a carbon source, ground, and then calcined to obtain modified lithium iron phosphate material.

[0033] This application employs solid-phase mixing, where an iron source, phosphorus source, lithium source, and additives containing dopant elements are solid-phase mixed and ground into a mixed solid material. This mixture is then sintered to obtain a mixture of Fe2O3 and Li3Fe2(PO4)3. Simultaneously, during sintering, the dopant elements are incorporated into the crystal lattice of the mixture. Subsequently, the mixture is mixed and ground with a carbon source and then calcined. Fe2O3 and Li3Fe2(PO4)3 are reduced by carbon, promoting the formation of a well-defined particle size distribution and a dense structure, resulting in a high-density lithium iron phosphate material. The carbon source can form a uniform coating layer, further reducing polarization and allowing the material to maintain a high specific capacity at 1C rate.

[0034] The method described in this application employs a combination of dry mixing and grinding with two-step atmosphere sintering throughout the process, eliminating the need for complex liquid phase processes or special equipment, and is easy to industrialize.

[0035] In some embodiments, the mixing and grinding described in this application is carried out using a high-speed mixer or a ball mill.

[0036] In some embodiments, the iron source includes any one or a combination of at least two of anhydrous ferric phosphate, ferric phosphate dihydrate, ferric sulfate, or ferric nitrate. Typical but non-limiting combinations include combinations of anhydrous ferric phosphate and ferric phosphate dihydrate, combinations of ferric phosphate dihydrate and ferric sulfate, or combinations of ferric sulfate and ferric nitrate.

[0037] In some embodiments, the phosphorus source includes anhydrous ferric phosphate and / or ferric phosphate dihydrate.

[0038] In some embodiments, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, or lithium phosphate. Typical but non-limiting combinations include combinations of lithium carbonate and lithium hydroxide, combinations of lithium dihydrogen phosphate and lithium phosphate, or combinations of lithium hydroxide and lithium dihydrogen phosphate.

[0039] In some embodiments, the additive containing doped elements includes any one or a combination of at least two of titanium dioxide, ammonium metavanadate, and niobium pentoxide. Typical but non-limiting combinations include combinations of titanium dioxide and ammonium metavanadate, combinations of ammonium metavanadate and niobium pentoxide, or combinations of titanium dioxide and niobium pentoxide.

[0040] In some embodiments, the molar ratio of lithium, iron, phosphorus and dopant elements in the mixed solid material is (1.0~1.04):1:(1.01~1.06):(0.0001~0.08), for example: 1.0:1:1.01:0.0001, 1.01:1:1.02:0.005, 1.02:1:1.03:0.001, 1.03:1:1.02:0.005 or 1.04:1:1.06:0.008, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] This application can precisely control the ratio of Fe2O3 and Li3Fe2(PO4)3 by controlling the ratio of iron source, phosphorus source and lithium source, thereby controlling the electrochemical performance and compaction characteristics of the final product and effectively avoiding the generation of harmful substances in iron phosphide.

[0042] In some embodiments, the median particle size D50 of the mixed solid material is 0.4 μm to 0.7 μm, for example: 0.4 μm, 0.45 μm, 0.5 μm, 0.6 μm or 0.7 μm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] In some embodiments, the atmosphere of the sintering process includes air.

[0044] In some embodiments, the sintering temperature is 600℃~950℃, for example: 600℃, 650℃, 700℃, 800℃ or 950℃, etc., not limited to the listed values, other unlisted values ​​within this range are also applicable, preferably 700℃~850℃.

[0045] In some embodiments, the holding time for the sintering treatment is 1h to 6h, for example: 1h, 2h, 3h, 4h or 6h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] In some embodiments, the mass percentage of Fe2O3 in the mixture of Fe2O3 and Li3Fe2(PO4)3 is 1% to 25%, for example: 1%, 5%, 10%, 15% or 25%, etc., not limited to the listed values, other unlisted values ​​within this range are also applicable, preferably 5% to 15%.

[0047] In some embodiments, the carbon source includes any one or a combination of at least two of glucose, PEG, or sucrose. Typical but non-limiting combinations include combinations of glucose and sucrose, combinations of PEG and sucrose, or combinations of glucose and PEG.

[0048] The number-average molecular weight of the PEG used in this application is 200-6000.

[0049] In some embodiments, the mass ratio of the mixture of Fe2O3 and Li3Fe2(PO4)3 to the carbon source is (85~93):(7~15), for example: 85:15, 88:12, 90:10, 92:8 or 93:7, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably (88~92):(8~12).

[0050] In some embodiments, after mixing and grinding the mixture of Fe2O3 and Li3Fe2(PO4)3 with a carbon source, the resulting coarse powder and fine powder are graded to obtain two lithium iron phosphate materials with different particle size distributions, thereby further improving the compaction density of the lithium iron phosphate material.

[0051] In some embodiments, the median particle size D50 of the material obtained by mixing and grinding the mixture of Fe2O3 and Li3Fe2(PO4)3 with a carbon source is 0.4μm to 0.7μm, for example: 0.4μm, 0.45μm, 0.5μm, 0.6μm or 0.7μm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0052] In some embodiments, the atmosphere of the calcination treatment includes nitrogen and / or argon.

[0053] In some embodiments, the calcination temperature is 650℃~850℃, for example: 650℃, 700℃, 750℃, 800℃ or 850℃, etc., not limited to the listed values, other unlisted values ​​within this range are also applicable, preferably 700℃~800℃.

[0054] In some embodiments, the calcination time is 5h to 12h, for example: 5h, 6h, 8h, 9h or 12h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0055] Secondly, this application provides a modified lithium iron phosphate material, which is prepared by the preparation method described in the first aspect.

[0056] In some embodiments, the compaction density of the modified lithium iron phosphate material is ≥2.5 g / cm³. 3 .

[0057] Thirdly, this application provides a battery comprising the modified lithium iron phosphate material as described in the second aspect.

[0058] Example 1 This embodiment provides a modified lithium iron phosphate material, which is prepared by the following method: Anhydrous ferric phosphate was used as the iron and phosphorus source, lithium carbonate as the lithium source, and titanium dioxide as an additive. The raw materials were weighed according to the molar ratio Li:Fe:P:Ti = 1.02:1:1.03:0.01, and then dry-mixed evenly in a high-speed mixer before being ground in a mill to obtain a mixed solid material with a D50 of 0.5 μm. The mixed solid materials were placed in a tube furnace and sintered at 750°C for 3 hours in air atmosphere, followed by natural cooling to obtain a mixture of Fe2O3 and Li3Fe2(PO4)3. The XRD pattern of the Fe2O3 and Li3Fe2(PO4)3 mixture is shown in the figure. Figure 1 As shown, XRD quantitative analysis revealed that in the mixture of Fe2O3 and Li3Fe2(PO4)3, Fe2O3 accounted for 12% by mass and Li3Fe2(PO4)3 accounted for 88% by mass. Fe2O3 and Li3Fe2(PO4)3 mixtures and glucose were mixed at a mass ratio of 90:10, and dry-milled in a ball mill until the median particle size D50 was 0.5 μm. The mixture was then calcined at 750 °C for 8 h under a nitrogen atmosphere to obtain modified lithium iron phosphate material.

[0059] Example 2 This embodiment provides a modified lithium iron phosphate material, which is prepared by the following method: Anhydrous ferric phosphate was used as the iron and phosphorus source, lithium carbonate as the lithium source, and titanium dioxide as an additive. The raw materials were weighed according to the molar ratio Li:Fe:P:Ti = 1.02:1:1.03:0.01, and then dry-mixed evenly in a high-speed mixer before being ground in a mill to obtain a mixed solid material with a D50 of 0.5 μm. The mixed solid materials were placed in a tube furnace and sintered at 750℃ for 3 hours in air atmosphere, followed by natural cooling to obtain a mixture of Fe2O3 and Li3Fe2(PO4)3. XRD quantitative analysis showed that Fe2O3 accounted for 12% of the mass of the mixture and Li3Fe2(PO4)3 accounted for 88% of the mass. A mixture of Fe2O3 and Li3Fe2(PO4)3 and glucose was mixed at a mass ratio of 90:10 and dry-milled in a ball mill to prepare two particle sizes: D50=0.3μm (fine powder) and D50=0.7μm (coarse powder). The fine powder and coarse powder were then mixed evenly at a mass ratio of 40:60 and calcined at 750℃ for 8 hours under a nitrogen atmosphere to obtain modified lithium iron phosphate material.

[0060] Example 3 This embodiment provides a modified lithium iron phosphate material, which is prepared by the following method: A mixture of ferric phosphate dihydrate and ferric nitrate was used as the iron and phosphorus sources, lithium hydroxide as the lithium source, and ammonium metavanadate as an additive. The raw materials were weighed according to the molar ratio Li:Fe:P:V = 1.03:1:1.05:0.005, dry-mixed evenly in a high-speed mixer, and then ground in a mill to obtain a mixed solid material with a D50 of 0.6 μm. The mixed solid materials were placed in a tube furnace and sintered at 800℃ for 2 hours in air atmosphere, followed by natural cooling to obtain a mixture of Fe2O3 and Li3Fe2(PO4)3. XRD quantitative analysis showed that Fe2O3 accounted for 8% of the mass of the mixture, while Li3Fe2(PO4)3 accounted for 92%. Fe₂O₃ and Li₃Fe₂(PO₄)₃ were mixed with sucrose at a mass ratio of 88:12, and then dry-milled in a ball mill to prepare two particle sizes: D50=0.25μm (fine powder) and D50=0.75μm (coarse powder). The fine powder and coarse powder were then mixed evenly at a mass ratio of 50:50 and calcined at 780℃ for 10 hours under a nitrogen atmosphere to obtain modified lithium iron phosphate material.

[0061] Example 4 This embodiment provides a modified lithium iron phosphate material, which is prepared by the following method: Anhydrous ferric phosphate was used as the iron and phosphorus source, lithium carbonate as the lithium source, and titanium dioxide as an additive. The raw materials were weighed according to the molar ratio Li:Fe:P:Ti = 1.0:1:1.01:0.0001, added to a high-speed mixer for dry mixing, and then ground in a mill to obtain a mixed solid material with a D50 of 0.4 μm. The mixed solid materials were placed in a tube furnace and sintered at 700℃ for 5 hours in air atmosphere, followed by natural cooling to obtain a mixture of Fe2O3 and Li3Fe2(PO4)3. XRD quantitative analysis showed that Fe2O3 accounted for 5% of the mass of the mixture, while Li3Fe2(PO4)3 accounted for 95%. Fe2O3 and Li3Fe2(PO4)3 mixtures and glucose were mixed at a mass ratio of 88:12 and dry-milled in a ball mill until the median particle size D50 was 0.4 μm. The mixtures were then calcined at 700 °C for 10 h under a nitrogen atmosphere to obtain modified lithium iron phosphate material.

[0062] Example 5 This embodiment provides a modified lithium iron phosphate material, which is prepared by the following method: Anhydrous ferric phosphate was used as the iron and phosphorus source, lithium carbonate as the lithium source, and niobium pentoxide as an additive. The raw materials were weighed according to the molar ratio Li:Fe:P:Nb = 1.04:1:1.06:0.08, and then dry-mixed evenly in a high-speed mixer before being ground in a mill to obtain a mixed solid material with a D50 of 0.7 μm. The mixed solid materials were placed in a tube furnace and sintered at 850℃ for 2 hours in air atmosphere, followed by natural cooling to obtain a mixture of Fe2O3 and Li3Fe2(PO4)3. XRD quantitative analysis showed that Fe2O3 accounted for 15% of the mass of the mixture and Li3Fe2(PO4)3 accounted for 85%. Fe2O3 and Li3Fe2(PO4)3 mixtures and glucose were mixed at a mass ratio of 92:8, and dry-milled in a ball mill until the median particle size D50 was 0.7 μm. The mixture was then calcined at 800 °C for 6 h under a nitrogen atmosphere to obtain modified lithium iron phosphate material.

[0063] Example 6 The only difference between this embodiment and Example 1 is that the mass percentage of Fe2O3 in the mixture of Fe2O3 and Li3Fe2(PO4)3 is controlled to be 3% (the mass ratio of Fe2O3 to Li3Fe2(PO4)3 is 3:97). All other conditions and parameters are exactly the same as in Example 1.

[0064] Example 7 The only difference between this embodiment and Example 1 is that the mass percentage of Fe2O3 in the mixture of Fe2O3 and Li3Fe2(PO4)3 is controlled to be 20% (the mass ratio of Fe2O3 to Li3Fe2(PO4)3 is 20:80). All other conditions and parameters are exactly the same as in Example 1.

[0065] Example 8 The only difference between this embodiment and Example 1 is that the mass ratio of Fe2O3 and Li3Fe2(PO4)3 mixture to glucose is controlled at 93:7. All other conditions and parameters are exactly the same as in Example 1.

[0066] Example 9 The only difference between this embodiment and Example 1 is that the mass ratio of Fe2O3 and Li3Fe2(PO4)3 mixture to glucose is controlled at 85:15. All other conditions and parameters are exactly the same as in Example 1.

[0067] Comparative Example 1 In this comparative example, iron phosphate, lithium carbonate, glucose (at a final carbon content of 10%) and TiO2 in the same proportion as in Example 1 were directly mixed and sintered at 750°C for 10 hours under a nitrogen atmosphere to obtain lithium iron phosphate.

[0068] Performance testing: The compaction density of lithium iron phosphate materials was obtained from the test examples and comparative examples. These materials were then used to fabricate coin cells. The coin cell testing reference standard was GB / T 42161-2022. The specific testing procedure was as follows: 1. After standing for 5 hours, the cells were charged at 0.1C (CC 3.75V) followed by 0.02C (CV), then left to stand for 10 minutes. The cells were then charged at 0.1C (DC 2.0V), left to stand for 10 minutes, and repeated twice. The cycle times were then 0.5C and 1C sequentially. The rate cycling path was two cycles each for 0.1C-0.1C-0.5C-0.5C-1C-1C. The test results are shown in Table 1. Table 1 As shown in Table 1, based on Examples 1 to 9, the compaction density of the modified lithium iron phosphate material prepared by the method described in this application can reach 2.42 g / cm³. 3 The battery produced exhibits a 0.1C discharge specific capacity exceeding 158 mAh / g and a 1C discharge specific capacity exceeding 130 mAh / g. By adjusting the preparation conditions, the compaction density of the modified lithium iron phosphate material can reach 2.65 g / cm³. 3 The battery produced exhibits a discharge specific capacity of over 162 mAh / g at 0.1C and over 135 mAh / g at 1C, demonstrating excellent rate performance.

[0069] A comparison of Examples 1 and 6-7 shows that during the preparation of the modified lithium iron phosphate material described in this application, the mass percentage of Fe2O3 in the mixture of Fe2O3 and Li3Fe2(PO4)3 affects its performance. Controlling the mass percentage of Fe2O3 in the mixture of Fe2O3 and Li3Fe2(PO4)3 to 5%-15% results in a modified lithium iron phosphate material with better performance. If the mass percentage of Fe2O3 in the mixture of Fe2O3 and Li3Fe2(PO4)3 is too low, the material's compaction performance is low, and its electrical properties deteriorate. If the mass percentage of Fe2O3 in the mixture of Fe2O3 and Li3Fe2(PO4)3 is too high, the material's compaction performance is low.

[0070] A comparison of Examples 1 and 8-9 shows that the amount of carbon source added during the preparation of the modified lithium iron phosphate material described in this application affects its performance. When the mass ratio of the mixture of Fe2O3 and Li3Fe2(PO4)3 to the carbon source is controlled at (88-92):(8-12), the modified lithium iron phosphate material has better performance. If the amount of carbon source added is too low, the internal resistance of the material is high and the carbon coating uniformity is insufficient, resulting in the deterioration of the material's electrical properties. If the amount of carbon source added is too high, the compaction ability decreases and the specific surface area of ​​the material is too high, affecting the material's processing performance.

[0071] As can be seen from the comparison between Example 1 and Comparative Example 1, this application adopts solid-phase mixing. Iron source, phosphorus source, lithium source and additive containing doped elements are mixed and ground into a mixed solid material. After sintering, a mixture of Fe2O3 and Li3Fe2(PO4)3 is obtained. Then, the mixture is mixed and ground with carbon source and calcined. Fe2O3 and Li3Fe2(PO4)3 are reduced by carbon, which promotes the formation of particle size distribution and dense structure, and obtains high-density lithium iron phosphate material. The carbon source can form a uniform coating layer, which can further reduce polarization, so that the material can still maintain a high specific capacity at 1C rate.

[0072] The applicant declares that the above description is only a specific implementation of this application, but the protection scope of this application is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application fall within the protection and disclosure scope of this application.

Claims

1. A method for preparing a modified lithium iron phosphate material, characterized in that, The preparation method includes the following steps: Iron source, phosphorus source, lithium source and additives containing doped elements are mixed and ground to obtain mixed solid material; A mixture of Fe2O3 and Li3Fe2(PO4)3 was obtained by sintering the mixed solid materials. A mixture of Fe2O3 and Li3Fe2(PO4)3 was mixed with a carbon source, ground, and then calcined to obtain modified lithium iron phosphate material.

2. The preparation method according to claim 1, characterized in that, The additive containing doped elements includes any one or a combination of at least two of titanium dioxide, ammonium metavanadate, and niobium pentoxide.

3. The preparation method according to claim 1 or 2, characterized in that, In the mixed solid material, the molar ratio of lithium, iron, phosphorus and doping elements is (1.0~1.04):1:(1.01~1.06):(0.0001~0.08); And / or, the median particle size D50 of the mixed solid material is 0.4 μm to 0.7 μm.

4. The preparation method according to any one of claims 1-3, characterized in that, The atmosphere for the sintering process includes air; And / or, the sintering temperature is 600℃~950℃, preferably 700℃~850℃; And / or, the holding time for the sintering treatment is 1h to 6h.

5. The preparation method according to any one of claims 1-4, characterized in that, The mass percentage of Fe2O3 in the mixture of Fe2O3 and Li3Fe2(PO4)3 is 1% to 25%, preferably 5% to 15%.

6. The preparation method according to any one of claims 1-5, characterized in that, The carbon source includes any one or a combination of at least two of glucose, PEG, or sucrose. And / or, the mass ratio of the mixture of Fe2O3 and Li3Fe2(PO4)3 to the carbon source is (85~93):(7~15), preferably (88~92):(8~12); And / or, the median particle size D50 of the material obtained by mixing and grinding the mixture of Fe2O3 and Li3Fe2(PO4)3 with a carbon source is 0.4μm~0.7μm.

7. The preparation method according to any one of claims 1-6, characterized in that, The atmosphere for the calcination treatment includes nitrogen and / or argon; And / or, the calcination temperature is 650℃~850℃, preferably 700℃~800℃; And / or, the calcination treatment time is 5h~12h.

8. A modified lithium iron phosphate material, characterized in that, The modified lithium iron phosphate material is prepared by the preparation method described in any one of claims 1-7.

9. The modified lithium iron phosphate material as described in claim 8, characterized in that, The compaction density of the modified lithium iron phosphate material is ≥2.5 g / cm³. 3 .

10. A battery, characterized in that, The battery comprises the modified lithium iron phosphate material as described in claim 8 or 9.

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