A lithium iron manganese phosphate positive electrode material and a preparation method and electrode material thereof

Abstract

This invention relates to the field of lithium-ion battery technology, and discloses a lithium manganese iron phosphate cathode material, its preparation method, and the electrode material thereof. The chemical formula of the lithium manganese iron phosphate cathode material is: LiMn 0.6 Fe 0.4‑a‑b Ni a Mg b PO4, wherein 0.005≤a≤0.2, 0.005≤b≤0.2. The lithium manganese iron phosphate material provided by this invention has excellent cycle stability, high voltage plateau, and high energy density.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a lithium manganese iron phosphate cathode material and its preparation method, as well as electrode materials. Background Technology

[0002] As is well known, lithium iron phosphate (LFP) cells are widely used in the power battery field due to their excellent cycle performance and safety. However, with the increasing demands for energy density in power batteries, conventional LFP cell design schemes are struggling to meet the requirements of high energy density.

[0003] In recent years, lithium manganese iron phosphate (LMFP) cells have been regarded as the next-generation upgrade of lithium iron phosphate due to their combination of most of the characteristics of lithium iron phosphate and their higher voltage platform. However, the biggest problem with lithium manganese iron phosphate at present is the "Jan Taylor effect" caused by its crystal structure, which leads to manganese dissolution and poor material cycle stability.

[0004] Currently, carbon coating and metal ion doping are two common technical approaches to address the issue of insufficient stability in lithium manganese iron phosphate (LMFP) materials. Carbon coating primarily suppresses side reactions and improves electronic conductivity through surface modification, but its process is complex, the coating layer is prone to inhomogeneity, and its effectiveness in suppressing manganese ion dissolution is limited. Meanwhile, doping with Mg²⁺... + Co² + Ni² + While single metal ions can improve cycle performance to some extent, they often lead to a decrease in the specific energy of the material and may result in a loss of reversible capacity. Overall, existing methods still have limitations in terms of comprehensive performance optimization, making it difficult to balance high stability, high energy density, and long cycle life, and thus cannot meet the actual needs of high-performance power batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a lithium manganese iron phosphate material that simultaneously possesses high energy density and excellent cycle stability.

[0006] To achieve the above objectives, a first aspect of the present invention provides a lithium manganese iron phosphate cathode material, the chemical formula of which is: LiMn 0.6 Fe 0.4-a-b Ni a Mg b PO4, where 0.005≤a≤0.2 and 0.005≤b≤0.2.

[0007] A second aspect of the present invention provides a method for preparing lithium manganese iron phosphate cathode material, the method comprising: (1) The lithium source, manganese source, iron source, nickel source, magnesium source and phosphorus source are mixed and ground to obtain mixture I; the amount of the lithium source, manganese source, iron source, nickel source, magnesium source and phosphorus source is controlled so that the molar ratio of lithium element, manganese element, iron element, nickel element, magnesium element and phosphorus element in the mixture I is 1:0.6:(0.4-ab):a:b:1; wherein, 0.005≤a≤0.2, 0.005≤b≤0.2; (2) The mixture I is sintered to obtain the lithium manganese iron phosphate cathode material.

[0008] A third aspect of the present invention provides an electrode material comprising an active substance, a conductive agent, and a binder; The active material is either the lithium manganese iron phosphate cathode material described in the first aspect, or the lithium manganese iron phosphate cathode material prepared according to the method described in the second aspect.

[0009] The lithium manganese iron phosphate material provided by this invention has excellent cycle stability, high voltage plateau and high energy density.

[0010] The method for synthesizing lithium manganese iron phosphate material provided by this invention is simple and can successfully synthesize Ni and Mg co-doped LMFP material. The reaction is uniform and the particle size is small, with a D50 value of 0.4~0.7μm. Detailed Implementation

[0011] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0012] As previously stated, a first aspect of the present invention provides a lithium manganese iron phosphate cathode material, the chemical formula of which is: LiMn 0.6 Fe 0.4-a-b Ni a Mg b PO4, where 0.005≤a≤0.2 and 0.005≤b≤0.2.

[0013] Preferably, 0.005≤a≤0.1 and 0.005≤b≤0.1.

[0014] In the preferred case, 0.006≤a≤0.02, 0.006≤b≤0.02.

[0015] More preferably, 0.008≤a≤0.015, 0.006≤b≤0.015. The inventors have found that under these preferred conditions, the obtained lithium manganese iron phosphate cathode material has higher energy density and better cycle stability.

[0016] As previously described, a second aspect of the present invention provides a method for preparing lithium manganese iron phosphate cathode material, the method comprising: (1) The lithium source, manganese source, iron source, nickel source, magnesium source and phosphorus source are mixed and ground to obtain mixture I; the amount of the lithium source, manganese source, iron source, nickel source, magnesium source and phosphorus source is controlled so that the molar ratio of lithium element, manganese element, iron element, nickel element, magnesium element and phosphorus element in the mixture I is 1:0.6:(0.4-ab):a:b:1; wherein, 0.005≤a≤0.2, 0.005≤b≤0.2; (2) The mixture I is sintered to obtain the lithium manganese iron phosphate cathode material.

[0017] Preferably, 0.005≤a≤0.1, 0.005≤b≤0.1. More preferably, 0.006≤a≤0.02, 0.006≤b≤0.02.

[0018] More preferably, 0.008≤a≤0.015, 0.006≤b≤0.015. The inventors have found that under these preferred conditions, the prepared lithium manganese iron phosphate cathode material has higher energy density and better cycle stability.

[0019] Preferably, in step (1), the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate.

[0020] Preferably, the manganese source is selected from at least one of manganese carbonate, manganese phosphate, manganese sulfate, manganese nitrate, and manganese oxalate.

[0021] In a preferred embodiment, the iron source is selected from at least one of ferrous oxalate, ferrous acetate, and ferric phosphate.

[0022] Preferably, the nickel source is selected from at least one of nickel carbonate and nickel acetate.

[0023] Preferably, the magnesium source is selected from at least one of magnesium hydroxide, magnesium carbonate, and magnesium chloride.

[0024] In a preferred embodiment, the phosphorus source is selected from at least one of lithium dihydrogen phosphate, lithium hydrogen phosphate, and lithium phosphate.

[0025] The present invention does not have any particular limitation on the mixing method described in step (1). As long as the lithium source, manganese source, iron source, nickel source, magnesium source and phosphorus source can be mixed evenly, those skilled in the art can do so according to the technical means known in the art.

[0026] In a preferred embodiment, the grinding conditions include: a grinding time of 12-15 hours and a grinding speed of 400-500 rpm.

[0027] Preferably, the sintering conditions include a temperature of 350-550℃ and a time of 10-15h.

[0028] This invention employs a solid-state method to synthesize Ni and Mg co-doped LMFP materials. 2+ The lattice distortion caused by doping inhibits lattice growth, resulting in uniform and moderate LMFP particle size. Furthermore, the altered lattice structure suppresses Mn dissolution, thus exhibiting excellent cycling performance. Meanwhile, Mg... 2+ The doping of Li increased + The transmission channel improves Li + The transmission efficiency allows it to have a higher voltage platform, which in turn results in higher energy density.

[0029] As previously described, a third aspect of the present invention provides an electrode material comprising an active substance, a conductive agent, and a binder; The active material is either the lithium manganese iron phosphate cathode material described in the first aspect, or the lithium manganese iron phosphate cathode material prepared according to the method described in the second aspect.

[0030] Preferably, the adhesive is selected from polyvinylidene fluoride.

[0031] Preferably, the conductive agent is carbon black and / or carbon nanotubes.

[0032] In a preferred embodiment, based on the total weight of the electrode material, the content of the active material is 94-96 wt%, the content of the conductive agent is 2-3 wt%, and the content of the binder is 2-3 wt%.

[0033] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, the raw materials and reagents used are all commercially available products.

[0034] Example 1 (1) The lithium source, manganese source, iron source, nickel source, magnesium source and phosphorus source are mixed and then ground in a ball mill jar to obtain mixture I; The amounts of lithium, manganese, iron, nickel, magnesium, and phosphorus sources are controlled so that the molar ratio of lithium, manganese, iron, nickel, magnesium, and phosphorus in the mixture I is 1:0.6:0.38:0.01:0.01:1; The lithium source is lithium carbonate, the manganese source is manganese carbonate, the iron source is iron phosphate, the nickel source is nickel carbonate, the magnesium source is magnesium carbonate, and the phosphorus source is lithium dihydrogen phosphate. The grinding conditions were: a rotation speed of 450 rpm and a grinding time of 12 hours. (2) The mixture I is sintered to obtain lithium manganese iron phosphate cathode material LiMn. 0.6 Fe 0.38 Ni 0.01 Mg 0.01 PO4; The sintering conditions are: temperature 400℃, time 12h.

[0035] Example 2 The method is similar to that in Example 1, except that in step (1), the amounts of lithium source, manganese source, iron source, nickel source, magnesium source and phosphorus source are controlled so that the molar ratio of lithium, manganese, iron, nickel, magnesium and phosphorus in the mixture I is 1:0.6:0.37:0.015:0.015:1; The remaining steps are the same as in Example 1.

[0036] Example 3 The method is similar to that in Example 1, except that in step (1), the amounts of lithium source, manganese source, iron source, nickel source, magnesium source and phosphorus source are controlled so that the molar ratio of lithium, manganese, iron, nickel, magnesium and phosphorus in the mixture I is 1:0.6:0.36:0.02:0.02:1; The remaining steps are the same as in Example 1.

[0037] Comparative Example 1 The method is similar to that in Example 1, except that in step (1), the nickel source and magnesium source are not added, and the amount of lithium source, manganese source, iron source and phosphorus source is controlled so that the molar ratio of lithium, manganese, iron and phosphorus in the mixture I is 1:0.6:0.4:1; The remaining steps are the same as in Example 1.

[0038] Comparative Example 2 The method is similar to that in Example 1, except that no magnesium source is added in step (1), and the amounts of lithium source, manganese source, iron source, nickel source and phosphorus source are controlled so that the molar ratio of lithium, manganese, iron, nickel and phosphorus in the mixture I is 1:0.6:0.39:0.01:1; The remaining steps are the same as in Example 1.

[0039] Comparative Example 3 The method is similar to that in Example 1, except that no nickel source is added in step (1), and the amounts of lithium source, manganese source, iron source, magnesium source and phosphorus source are controlled so that the molar ratio of lithium, manganese, iron, magnesium and phosphorus in the mixture I is 1:0.6:0.39:0.01:1; The remaining steps are the same as in Example 1.

[0040] Comparative Example 4 The method is similar to that in Example 1, except that in step (1), the amounts of lithium source, manganese source, iron source, nickel source, magnesium source and phosphorus source are controlled so that the molar ratio of lithium, manganese, iron, nickel, magnesium and phosphorus in the mixture I is 1:0.78:0.2:0.01:0.01:1; The remaining steps are the same as in Example 1.

[0041] Comparative Example 5 The method is similar to that in Example 1, except that the nickel source in step (1) is replaced with a titanium source (titanium sulfate), so that the molar ratio of lithium, manganese, iron, titanium, magnesium and phosphorus in the mixture I is 1:0.6:0.38:0.01:0.01:1; The remaining steps are the same as in Example 1.

[0042] Test case The lithium manganese iron phosphate (LMFP) cathode material prepared in the above example was mixed with polyvinylidene fluoride (PVDF), conductive carbon black (SP), and carbon nanotubes (CNT) at a mass ratio of 95:2.5:2:0.5, and stirred evenly in N-methylpyrrolidone (NMP) solvent to prepare a cathode slurry with a double-sided areal density of 451 g / m³. 2 Coating: Artificial graphite, conductive carbon black, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 96.5:1:2:0.5 and stirred evenly in deionized water to prepare the negative electrode slurry. The slurry had a double-sided surface density of 200 g / m³. 2 Coating was applied; the cells were then assembled using a lamination process (10 positive electrode layers and 11 negative electrode layers), and 20 mL of electrolyte (containing 1 wt% polystyrene (PS), 2 wt% vinylene carbonate (VC), 1 wt% fluoroethylene carbonate (FEC), 1.0 mol lithium hexafluorophosphate (LiPF6), and a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a 1:1:1 mass ratio) was injected, and the cells were packaged into a pouch cell. The resulting pouch cells were then subjected to capacity, energy, and cycle performance tests.

[0043] The capacity test, energy test, and cycle performance test were conducted in accordance with the standard methods of GB / T31484-2015.

[0044] The specific test results are shown in Table 1.

[0045] Discharge capacity retention after 500 cycles = (Discharge capacity at 500th cycle / Discharge capacity at 1st cycle) × 100% Table 1

[0046] The results above show that the lithium manganese iron phosphate cathode material provided in this embodiment of the invention has higher capacity, energy, and energy density under the same system, and the retention rate is above 96% after 500 room temperature cycles, exhibiting better electrical performance.

[0047] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A lithium manganese iron phosphate cathode material, characterized in that, The chemical formula of the lithium manganese iron phosphate cathode material is: LiMn 0.6 Fe 0.4-a-b Ni a Mg b PO4, where 0.005≤a≤0.2 and 0.005≤b≤0.

2.

2. The lithium iron phosphate cathode material according to claim 1, characterized in that, 0.005≤a≤0.1, 0.005≤b≤0.

1.

3. The lithium iron phosphate cathode material according to claim 1, characterized in that, 0.006≤a≤0.02, 0.006≤b≤0.

02.

4. The lithium manganese iron phosphate cathode material according to claim 1 or 2, wherein, The chemical formula of the lithium manganese iron phosphate cathode material is: LiMn 0.6 Fe 0.38 Ni 0.01 Mg 0.01 PO4.

5. A method for preparing lithium manganese iron phosphate cathode material, characterized in that, The method includes: (1) The lithium source, manganese source, iron source, nickel source, magnesium source and phosphorus source are mixed and ground to obtain mixture I; the amount of the lithium source, manganese source, iron source, nickel source, magnesium source and phosphorus source is controlled so that the molar ratio of lithium element, manganese element, iron element, nickel element, magnesium element and phosphorus element in the mixture I is 1:0.6:(0.4-ab):a:b:1; wherein, 0.005≤a≤0.2, 0.005≤b≤0.2; (2) The mixture I is sintered to obtain the lithium manganese iron phosphate cathode material.

6. The method according to claim 5, characterized in that, In step (1), the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; The manganese source is selected from at least one of manganese carbonate, manganese phosphate, manganese sulfate, manganese nitrate, and manganese oxalate. The iron source is selected from at least one of ferrous oxalate, ferrous acetate, and ferric phosphate. The nickel source is selected from at least one of nickel carbonate and nickel acetate; The magnesium source is selected from at least one of magnesium hydroxide, magnesium carbonate, and magnesium chloride; The phosphorus source is selected from at least one of lithium dihydrogen phosphate, lithium hydrogen phosphate, and lithium phosphate.

7. The method according to claim 5 or 6, characterized in that, In step (1), the grinding conditions include: a time of 12-15 hours and a rotation speed of 400-500 rpm.

8. The method according to claim 5 or 6, characterized in that, In step (2), the sintering conditions include a temperature of 350-550℃ and a time of 10-15h.

9. An electrode material, characterized in that, The electrode material contains active substances, conductive agents, and binders; The active material is the lithium manganese iron phosphate cathode material according to any one of claims 1-4, or the lithium manganese iron phosphate cathode material prepared according to any one of claims 5-8.

10. The electrode material according to claim 9, characterized in that, The adhesive is selected from polyvinylidene fluoride; The conductive agent is conductive carbon black and / or carbon nanotubes.

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