A modified lithium manganese iron phosphate positive electrode material, a positive electrode sheet, a battery and a preparation method

Abstract

The application discloses a modified manganese iron lithium phosphate positive electrode material, a positive electrode sheet, a battery and a preparation method. The modified manganese iron lithium phosphate positive electrode material comprises a manganese iron lithium phosphate base body, a carbon coating layer coated on the surface of the manganese iron lithium phosphate base body and a selenide coating layer coated on the surface of the carbon coating layer. The selenide is selected from a mixture of one or more of copper selenide, cadmium selenide, indium selenide, lead selenide and antimony selenide. The problems of low conductivity, low discharge capacity, poor rate performance, poor cycle retention rate and high manganese dissolution rate of the existing manganese iron lithium phosphate positive electrode material are solved.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, specifically relating to a modified lithium manganese iron phosphate cathode material, cathode sheet, battery, and preparation method. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Lithium manganese iron phosphate is a cathode material for lithium-ion batteries. It has advantages such as high energy density, good safety performance and low cost, and has broad application prospects in electric vehicles, energy storage and other fields.

[0004] Lithium manganese iron phosphate (LFP) has low electronic conductivity and high electrical conduction resistance between electrode material particles, which inevitably leads to poor rate performance. Coating its surface with a conductive material can effectively improve its conductivity. Commonly used coating conductive materials include carbon, metal particles, and organic conductive materials. However, the conductivity of LFP still needs further improvement.

[0005] Furthermore, lithium manganese iron phosphate (LFP) suffers from rapid capacity decay and short cycle life. This is primarily due to the valence state change of manganese in the positive electrode during charging and discharging, leading to the dissolution of manganese ions. This results in a manganese-deficient phase in the positive electrode, causing structural collapse and hindering lithium-ion insertion / extraction, ultimately increasing battery polarization. Simultaneously, manganese dissolved in the electrolyte deposits on the negative electrode surface, damaging the SEI layer structure. This necessitates continuous membrane regeneration and repair, consuming significant amounts of active lithium, causing capacity loss and deteriorating cycle performance. Additionally, high temperatures promote electrolyte hydrolysis, generating HF, which accelerates the dissolution of Mn ions in the positive electrode material, further damaging its structure and causing a rapid capacity decline. Therefore, LFP exhibits poor high-temperature resistance.

[0006] Furthermore, the crystal ions of lithium manganese iron phosphate tend to agglomerate into large particles, affecting its performance. Dispersants are generally needed to grind and disperse the lithium manganese iron phosphate material to improve its performance stability. Currently, the dispersion effect of dispersants is not ideal, making it difficult to effectively disperse lithium manganese iron phosphate. Moreover, there are many types of dispersants, requiring multiple experiments to find the optimal dosage and ratio, making the screening process complex and the preparation process of lithium manganese iron phosphate quite cumbersome. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a modified lithium manganese iron phosphate cathode material, cathode sheet, battery, and preparation method, in order to solve the problems of low conductivity, low discharge capacity, poor rate performance, poor cycle retention, and high manganese dissolution rate of existing lithium manganese iron phosphate cathode materials.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0009] In a first aspect, the present invention provides a modified lithium manganese iron phosphate cathode material, comprising a lithium manganese iron phosphate matrix, a carbon coating layer coated on the surface of the lithium manganese iron phosphate matrix, and a selenide coating layer coated on the surface of the carbon coating layer.

[0010] The selenide is selected from one or more of copper selenide, cadmium selenide, indium selenide, lead selenide, and antimony selenide, or a mixture thereof.

[0011] In some embodiments, the carbon coating layer in the modified lithium manganese iron phosphate cathode material has a mass percentage of 0.5-1.8%.

[0012] In some embodiments, the mass percentage of the selenide coating layer in the modified lithium manganese iron phosphate cathode material is 0.25-4 wt%.

[0013] Preferably, in the modified lithium manganese iron phosphate cathode material, the selenide coating layer has a mass percentage of 1-2 wt%.

[0014] In some embodiments, the chemical formula of the lithium manganese iron phosphate matrix is ​​LiMn. x Fe 1-x-y M y PO4, wherein 0 < X ​​< 1, 0.001 < y ≤ 0.04; selected from at least one of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Y, Zr, Tc, Ru, Rh, Pd, Ag, and Au.

[0015] Preferably, the metallic element is magnesium or titanium.

[0016] More preferably, the metallic element is magnesium.

[0017] Preferably, the molar ratio of the doped metal element to lithium manganese iron phosphate is 0.001~0.04:1; more preferably, it is 0.01~0.03:1.

[0018] Secondly, the present invention provides a method for preparing the modified lithium manganese iron phosphate cathode material, comprising the following steps:

[0019] Carbon-coated lithium manganese iron phosphate is mixed with selenide and sintered in an inert atmosphere for a set time. The sintered product is then cooled and ball-milled to obtain the final product.

[0020] In some embodiments, the selenide accounts for 0.25-4 wt% of the carbon-coated lithium manganese iron phosphate, preferably 1-3 wt%, more preferably 1-2 wt%, and specifically 1.5 wt%.

[0021] In some embodiments, the sintering temperature is 400-1000℃ and the sintering time is 1-10h.

[0022] Preferably, the sintering temperature is 500-700℃, and more preferably 600℃.

[0023] Further preferred, the sintering time is 3-6 hours, preferably 4 hours.

[0024] In some embodiments, the cooling is furnace-in-furnace cooling.

[0025] Prepared LiMn x Fe 1-x-y M y The primary particle size of the PO4 / C@selenide cathode material is 60nm-350nm, and the average particle size D50 is 0.4μm-2μm; the specific surface area of ​​the composite-coated lithium manganese iron phosphate material is 20.0±5.0m². 2 / g.

[0026] Thirdly, the present invention provides a positive electrode sheet prepared from the modified lithium manganese iron phosphate positive electrode material.

[0027] Fourthly, the present invention provides a battery comprising a positive electrode, a negative electrode, and a separator, wherein the positive electrode is prepared from the modified lithium manganese iron phosphate positive electrode material.

[0028] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0029] 1. The selenide-coated modified lithium manganese iron phosphate composite material of the present invention aims to solve the problems of low electronic conductivity, low discharge capacity, poor cycle retention, and manganese dissolution in lithium manganese iron phosphate. Selenides have high electronic conductivity, which can reduce the resistance of the cathode material powder and effectively improve the electrochemical performance of the lithium manganese iron phosphate cathode material.

[0030] 2. The main innovation of this invention is the coating modification of lithium manganese iron phosphate materials. It proposes using carbon-coated magnesium- or titanium-doped lithium manganese iron phosphate cathode materials as the matrix, wherein Mg... 2+ Isovalent doping does not cause lattice structure defects, leading to structural collapse during cycling. It does not directly participate in electrochemical reactions, but rather improves the structural support of lithium manganese iron phosphate, enhances its conductivity, and increases Li... + The conductivity plays a role, and without causing a decrease in the voltage plateau of lithium manganese iron phosphate, it ensures the stable electrochemical performance of the matrix material of this invention.

[0031] Furthermore, the inventors discovered in their experiments that the agglomeration phenomenon of lithium manganese iron phosphate coated with selenide was significantly improved, which is more conducive to improving the electrochemical performance of the cathode material and ensuring its performance stability. Moreover, the screening and use of dispersants can be omitted, reducing research and development steps and production costs.

[0032] Among them, selenides such as indium selenide not only possess excellent electronic conductivity, high density, and chemical stability such as oxidation resistance, but also exhibit high melting points and high mechanical strength, resulting in more stable structures in the coated and doped composite materials. The acid and alkali corrosion resistance of selenides can inhibit the dissolution of manganese, reduce side reactions with the electrolyte, and improve the cycling stability of the material. Furthermore, because the selenide coating reduces the carbon coating amount, it increases the tap density of the material and facilitates lithium-ion diffusion, thereby improving the conductivity of the material while reducing capacity loss after modification.

[0033] 3. In this invention, indium selenide and carbon are composite-coated to form LMFP composite cathode materials using a dry coating method. This process is simple, the conditions are controllable, the crystallinity is high, there are few impurities in the crystals, and the product particle size is relatively uniform. Furthermore, it is cost-effective and environmentally friendly, making it suitable for commercial expansion. Attached Figure Description

[0034] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0035] Figure 1 Example 1: LiMn 0.6 Fe 0.38 Mg 0.02 SEM image of PO4 / C@In2Se3 sample;

[0036] Figure 2 Example 1: LiMn 0.6 Fe 0.38 Mg 0.02 SEM images of PO4 / C@In2Se3 samples;

[0037] Figure 3 Example 1: LiMn 0.6 Fe 0.38 Mg 0.02 Particle size distribution of PO4 / C@In2Se3 sample;

[0038] Figure 4 The graph shows the initial charge-discharge performance of the button batteries of Example 1 and Comparative Example 1 at 25°C and 0.1C rate. Detailed Implementation

[0039] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0040] Example 1

[0041] The coating agent is indium selenide, and the doping element is magnesium.

[0042] 1. Take 50g of nano-grade lithium manganese iron phosphate (LiMn) 0.6 Fe 0.38 Mg 0.02 The matrix (PO4) is designated as A, and the carbon coating content on the surface of A is 0.9 wt%. It was customized by Hunan Wanrun New Energy Battery Materials Co., Ltd.

[0043] 2. Indium selenide was added to A as a coating agent, and the added indium selenide accounted for 1.5 wt% of the mass of A. The mixture was mixed evenly using a high-speed mixer to obtain mixed precursor material B. The speed of the high-speed mixer was 1000 rpm, the mixing time was 60 min, and the mixing temperature was 30℃.

[0044] 3. Place the mixed material B obtained in step 2 into a tube furnace, heat it to 600℃ at a rate of 10℃ / min under a nitrogen atmosphere, hold it at that temperature for 4 hours, and then cool it with the furnace. After cooling, grind and sieve to obtain the composite coated modified lithium manganese iron phosphate composite cathode material LiMn 0.6 Fe 0.38 Mg 0.02 PO4 / C@In2Se3. ( Figure 1 , Figure 2 (SEM image shows uniform particle distribution with no obvious aggregation) Figure 1 and Figure 2 It can be seen that the lithium manganese iron phosphate particles obtained in the examples have a uniform morphology, a rounded surface without obvious micro powder, no excessive agglomeration between particles, and a certain degree of size distribution.

[0045] Example 2

[0046] The coating agent is antimony selenide, and the doping element is magnesium.

[0047] 1. Step 1 is the same as step 1 in <Example 1>;

[0048] 2. Antimony selenide was added to A as a coating agent, with the added antimony selenide accounting for 1.5 wt% of the mass of A. The mixture was mixed evenly using a high-speed mixer to obtain mixed material B. The speed of the high-speed mixer was 1000 rpm, the mixing time was 60 min, and the mixing temperature was 30℃.

[0049] 3. Step 3 is the same as step 3 in Example 1, resulting in a LiMn composite cathode material with composite coating modification, which is a lithium manganese iron phosphate composite cathode material. 0.6 Fe 0.38 Mg 0.02 PO4 / C@Sb2Se3.

[0050] Example 3

[0051] The coating agent is cadmium selenide, and the doping element is magnesium.

[0052] 1. Step 1 is the same as step 1 in <Example 1>;

[0053] 2. Cadmium selenide was added to A as a coating agent, with the added cadmium selenide accounting for 1.5 wt% of the mass of A. The mixture was mixed evenly using a high-speed mixer to obtain mixed material B. The speed of the high-speed mixer was 1000 rpm, the mixing time was 60 min, and the mixing temperature was 30℃.

[0054] 3. Step 3 is the same as step 3 in Example 1, resulting in a LiMn composite cathode material with composite coating modification, which is a lithium manganese iron phosphate composite cathode material. 0.6 Fe 0.38 Mg 0.02 PO4 / C@CdSe.

[0055] Example 4

[0056] The matrix material is doped with Ti.

[0057] 1. Step 1 is the same as step 1 in <Example 1>, except that the substrate is LiMn. 0.6 Fe 0.38 Ti 0.02 PO4;

[0058] 2. Step 2 is the same as step 2 in <Example 1>;

[0059] 3. Step 3 is the same as step 3 in Example 1, to obtain the LiMn manganese iron phosphate composite cathode material. 0.6 Fe 0.38 Ti 0.02 O4 / C@In2Se3.

[0060] Example 5

[0061] The difference from Example 1 is that the doping element of the matrix material is V, while everything else is the same as in Example 1.

[0062] Example 6

[0063] The difference from Example 1 is that the doping element of the matrix material is Cu, while everything else is the same as in Example 1.

[0064] Example 7

[0065] The difference from Example 1 is that the doping element of the matrix material is Mo, while everything else is the same as in Example 1.

[0066] Example 8

[0067] The difference from Example 1 is that the added indium selenide accounts for 1 wt% of A, while all other aspects are the same as in Example 1.

[0068] Example 9

[0069] The difference from Example 1 is that the added indium selenide accounts for 0.5 wt% of A, while all other aspects are the same as in Example 1.

[0070] Example 10

[0071] The difference from Example 1 is that the added indium selenide accounts for 2 wt% of A, while all other aspects are the same as in Example 1.

[0072] Example 11

[0073] The difference from Example 1 is that the added indium selenide accounts for 4 wt% of A, while all other aspects are the same as in Example 1.

[0074] Example 12

[0075] The difference from Example 1 is that the sintering temperature is 800℃, while all other aspects are the same as in Example 1.

[0076] Example 13

[0077] The difference from Example 1 is that the sintering temperature is 1000℃, while all other aspects are the same as in Example 1.

[0078] Example 14

[0079] The difference from Example 1 is that the sintering temperature is 400℃, while all other aspects are the same as in Example 1.

[0080] Comparative Example 1:

[0081] The difference between Comparative Example 1 and Example 1 is that the matrix material does not contain the doping element magnesium and does not use selenide coating agent.

[0082] 1. Step 1 is the same as step 1 in <Example 1>, except that the substrate is different, which is LiMn. 0.6 Fe 0.4 PO4;

[0083] 2. Step 2 is the same as step 2 in <Example 1>;

[0084] 3. Step 3 is the same as step 3 in Example 1, and LiMn is obtained.0.6 Fe 0.4 PO4 / C.

[0085] Comparative Example 2:

[0086] The difference between Comparative Example 2 and Example 1 is that the matrix material does not contain the dopant element magnesium.

[0087] 1. Step 1 is the same as step 1 in <Example 1>, except that the substrate is different, which is LiMn. 0.6 Fe 0.4 PO4;

[0088] 2. Steps 2 and 3 are consistent with steps 2 and 3 in Example 1, yielding LiMn. 0.6 Fe 0.4 O4 / C@In2Se3.

[0089] Comparative Example 3:

[0090] The difference between Comparative Example 3 and Example 1 is that no selenide coating agent is used.

[0091] 1. Step 1 is the same as step 1 in <Example 1>, and the substrate is LiMn. 0.6 Fe 0.38 Mg 0.02 PO4;

[0092] 2. Following steps 2 and 3 as in <Example 1>, LiMn is obtained. 0.6 Fe 0.38 Mg 0.02 PO4 / C.

[0093] Methods for preparing electrodes and coin cells:

[0094] 1. The positive electrode material is the powder obtained in the examples and comparative examples. Weigh 15g of powder and add it to the degassing tank in the ratio of m (positive electrode material): m (SP): m (5%PVDF) = 90: 5: 5 to homogenize. Coat the slurry onto carbon-coated aluminum foil, roll, punch, weigh, and vacuum dry for later use.

[0095] 2. Using dried and prepared electrodes as the positive electrode, lithium foil as the negative electrode, and a microporous polypropylene film as the battery separator, and with electrolyte [missing information], CR2032 button cells were assembled. Electrochemical performance was then compared using a CT3002A Blue Battery Tester, with a charge / discharge voltage range of 2.5 to 4.5V and charge / discharge rates of 0.1C and 1C. The initial charge specific capacity, initial discharge specific capacity, initial efficiency, and cycle performance were evaluated. Specific test data are shown in Table 1.

[0096] Figure 4The four curves represent the electrochemical performance of different materials. Example 1 shows a composite material doped with Mg and coated with selenide (LiMn). 0.6 Fe 0.38 Mg 0.02 (PO4 / C@In2Se3), it can be seen that the specific capacity is improved and the electrochemical polarization is reduced; Comparative Example 1 is a carbon-coated lithium manganese iron phosphate cathode material (LiMn). 0.6 Fe 0.4 PO4 / C), undoped, selenide-coated, with low specific capacity and high electrochemical polarization; Comparative Example 2 is LiMn 0.6 Fe 0.4 O4 / C@In2Se3, Comparative Example 3 is LiMn 0.6 Fe 0.38 Mg 0.02 PO4 / C: Doping with Mg can increase the specific capacity of the material, and coating with selenide can reduce electrical polarization and improve cycle performance.

[0097] Table 1 Electrochemical performance of different substrate materials at 0.1C / 1C rates

[0098]

[0099] Table 1 shows that although the doping elements in Examples 1 and 4 are different, both improved the battery capacity. Coating with different selenides can reduce electrical polarization and improve the battery capacity retention. Comparing Comparative Examples 1, 2, and 3, it can be seen that doping with Ti and Mg can improve the battery capacity. Comparing Comparative Examples 1 and 2, it can be seen that coating with selenides can improve the battery's initial efficiency and capacity retention, indicating that its rate performance and manganese dissolution phenomenon are improved, and electrical polarization is reduced.

[0100] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A modified lithium iron phosphate cathode material, characterized in that: It includes a lithium manganese iron phosphate matrix, a carbon coating layer on the surface of the lithium manganese iron phosphate matrix, and a selenide coating layer on the surface of the carbon coating layer; The selenide is selected from one of cadmium selenide, indium selenide, and antimony selenide; In the modified lithium manganese iron phosphate cathode material, the carbon coating layer has a mass percentage of 0.5-1.8%; in the modified lithium manganese iron phosphate cathode material, the selenide coating layer has a mass percentage of 1-4 wt%. The chemical formula of the lithium manganese iron phosphate matrix is ​​LiMn. x Fe 1-x-y M y PO4, M is the doped metal element, where 0.6≤x<1, 0.01≤y≤0.03; the doped metal element is magnesium or titanium; the molar ratio of the doped metal element to lithium manganese iron phosphate is 0.01~0.03:1; The modified lithium manganese iron phosphate cathode material has a primary particle size of 60nm-350nm, an average particle size D50 of 0.4μm-2μm, and a specific surface area of ​​20.0±5.0m². 2 / g; The preparation method of the modified lithium manganese iron phosphate cathode material includes the following steps: Carbon-coated magnesium- or titanium-doped lithium manganese iron phosphate is mixed with selenide, sintered in an inert atmosphere for a set time, and then cooled and ball-milled to obtain the final product.

2. The modified lithium manganese iron phosphate cathode material according to claim 1, characterized in that: In the modified lithium manganese iron phosphate cathode material, the selenide coating layer has a mass percentage of 1-2 wt%.

3. The modified lithium manganese iron phosphate cathode material according to claim 1, characterized in that: The doped metal element is magnesium.

4. The method for preparing the modified lithium manganese iron phosphate cathode material according to any one of claims 1-3, characterized in that: Includes the following steps: Carbon-coated magnesium- or titanium-doped lithium manganese iron phosphate is mixed with selenide, sintered in an inert atmosphere for a set time, and then cooled and ball-milled to obtain the final product.

5. The method for preparing the modified lithium manganese iron phosphate cathode material according to claim 4, characterized in that: Selenides account for 1-3 wt% of carbon-coated manganese iron phosphate.

6. The method for preparing the modified lithium manganese iron phosphate cathode material according to claim 5, characterized in that: Selenides account for 1-2 wt% of carbon-coated manganese iron phosphate.

7. The method for preparing the modified lithium manganese iron phosphate cathode material according to claim 6, characterized in that: Selenides account for 1.5 wt% of carbon-coated lithium manganese iron phosphate.

8. The method for preparing the modified lithium manganese iron phosphate cathode material according to claim 4, characterized in that: The sintering temperature is 400-1000℃, and the sintering time is 1-10h.

9. The method for preparing the modified lithium manganese iron phosphate cathode material according to claim 8, characterized in that: The sintering temperature is 500-700℃.

10. The method for preparing the modified lithium manganese iron phosphate cathode material according to claim 9, characterized in that: The sintering temperature is 600℃.

11. The method for preparing the modified lithium manganese iron phosphate cathode material according to claim 8, characterized in that: The sintering time is 3-6 hours.

12. The method for preparing the modified lithium manganese iron phosphate cathode material according to claim 11, characterized in that: The sintering time is 4 hours.

13. The method for preparing the modified lithium manganese iron phosphate cathode material according to claim 4, characterized in that: The cooling is furnace-in-process cooling.

14. A positive electrode plate, characterized in that: It is prepared from the modified lithium manganese iron phosphate cathode material according to any one of claims 1-3.

15. A battery, characterized in that: It includes a positive electrode, a negative electrode, and a separator, wherein the positive electrode is prepared from the modified lithium manganese iron phosphate positive electrode material according to any one of claims 1-3.

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