Lithium manganese iron phosphate positive electrode material, preparation method thereof and lithium ion battery
By adjusting the intensity ratio and morphology of the diffraction peaks of lithium manganese iron phosphate cathode material, and optimizing its short rod-shaped morphology and grain size, the problems of low conductivity and slow lithium-ion transport were solved, thereby improving battery capacity and energy density.
Patent Information
- Application Number
- CN202511330376.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-17
- Publication Date
- 2025-12-23
AI Technical Summary
Lithium manganese iron phosphate cathode materials have low conductivity, manganese dissolution leads to lattice distortion, slow lithium-ion transport, and nano-sizing reduces material compaction density, making them difficult to apply in practice.
By adjusting the intensity ratio of each diffraction peak in the XRD diffraction pattern, the short rod-shaped morphology, grain size, and aspect ratio can be controlled, optimizing the preferred orientation of lithium manganese iron phosphate and shortening the lithium-ion transport distance.
It improves the battery capacity and electrochemical performance of lithium manganese iron phosphate, solves the problem of slow lithium-ion transport, and increases the energy density of the material.
Smart Images
Figure CN121192162A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a lithium manganese iron phosphate cathode material, its preparation method, and a lithium-ion battery. Background Technology
[0002] Currently, lithium iron phosphate (LFP) is the most widely used cathode material in the lithium-ion battery field. Compared to other cathode materials (such as ternary cathodes and lithium manganese oxide cathodes), LFP has advantages in terms of high safety and low cost. These advantages enable LFP to be widely used in power batteries and energy storage. However, with the rapid development of new energy vehicles, higher requirements have been placed on vehicle range, making the low energy density of LFP increasingly prominent. A discharge voltage of 3.4V and a theoretical capacity of 170mAh / g make the energy density of LFP pale in comparison to ternary cathodes.
[0003] With the increasing demand for higher energy density phosphate cathode materials, lithium manganese iron phosphate (LiFePO4) cathode materials have received widespread attention in recent years. The chemical formula of LiFePO4 is LiMn2. x Fe 1-x PO4 (0 < x < 1) is obtained by partially replacing Fe with Mn on the basis of lithium iron phosphate. Like lithium iron phosphate, it is a phosphate cathode material, inheriting the advantages of high safety and low cost, and further improving the energy density. While both lithium manganese iron phosphate and lithium iron phosphate have a theoretical capacity of 170 mAh / g, the discharge platform of Mn is 4.1V, which is 21% higher than the 3.4V discharge platform of Fe, allowing lithium manganese iron phosphate to achieve an energy density up to 21% higher than lithium iron phosphate.
[0004] However, while inheriting the advantages of lithium iron phosphate, lithium manganese iron phosphate has the following disadvantages: low conductivity and lattice distortion caused by manganese dissolution. These disadvantages prevent the full utilization of the capacity of lithium manganese iron phosphate, and the low capacity greatly hinders its industrialization. A common method to improve the capacity of lithium manganese iron phosphate is nano-sizing, but nano-sizing significantly reduces the material's compaction density, making it difficult to apply in practice.
[0005] Based on the above research, there is a need to provide a lithium iron phosphate cathode material whose capacity can be fully utilized. Summary of the Invention
[0006] The purpose of this invention is to provide a lithium manganese iron phosphate cathode material, its preparation method, and a lithium-ion battery. The lithium manganese iron phosphate cathode material obtains short rod-shaped lithium manganese iron phosphate by controlling the intensity ratio of each diffraction peak in the XRD diffraction pattern, so that the lithium manganese iron phosphate has a preferred orientation, shortens the lithium ion transport distance inside the particle, and further controls the grain size and aspect ratio, finally obtaining lithium manganese iron phosphate with excellent electrochemical performance.
[0007] To achieve this objective, the present invention employs the following technical solution:
[0008] In a first aspect, the present invention provides a lithium manganese iron phosphate cathode material, wherein the lithium manganese iron phosphate cathode material satisfies the following conditions:
[0009] A / D > 0.25, B / D > 0.7, and C / D > 0.8;
[0010] Wherein, A is the intensity value of the diffraction peak corresponding to the (020) crystal plane in the XRD diffraction pattern of the lithium manganese iron phosphate cathode material, B is the intensity value of the diffraction peak corresponding to the (110) crystal plane in the XRD diffraction pattern of the lithium manganese iron phosphate cathode material, C is the intensity value of the diffraction peak corresponding to the (002) crystal plane in the XRD diffraction pattern of the lithium manganese iron phosphate cathode material, and D is the intensity value of the diffraction peak corresponding to the (131) crystal plane in the XRD diffraction pattern of the lithium manganese iron phosphate cathode material;
[0011] The lithium iron manganese phosphate cathode material has a short rod-like morphology.
[0012] The ratio of the grain size to the aspect ratio of the lithium manganese iron phosphate cathode material is S / LD, and S / LD satisfies: 12≤S / LD≤60.
[0013] Due to the low conductivity of lithium manganese iron phosphate (LMP) cathode materials, ion transport within the particles is slow during charging and discharging, and this problem becomes more severe as the particle size increases. This invention addresses this issue by adjusting the ratio of the diffraction peak intensities corresponding to the (020), (110), and (002) crystal planes to the diffraction peak intensities corresponding to the (131) crystal plane in the XRD diffraction pattern of the LMP cathode material. This causes the particle morphology to tend towards a short rod shape, giving LMP a preferred orientation. For LMP with a short rod morphology, lithium ions preferentially transport along its radial direction, greatly shortening the lithium ion transport distance and effectively solving the problem of slow lithium ion transport in LMP cathode materials, thereby improving the battery capacity of the material.
[0014] Furthermore, this invention effectively controls the grain size and aspect ratio of the lithium manganese iron phosphate cathode material. For short rod-shaped materials with a high aspect ratio, excessively small grain size can lead to insufficient crystallinity, incomplete crystal structure, and incomplete lithium-ion transport channels, which will reduce battery capacity release. Therefore, this invention avoids the above problems by controlling the ratio of grain size to aspect ratio of the lithium manganese iron phosphate cathode material.
[0015] The A / D ratio is greater than 0.25, for example, it can be 0.26, 0.27, 0.28, 0.29, 0.30 or 0.31; the B / D ratio is greater than 0.7, for example, it can be 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81 or 0.82; and the C / D ratio is greater than 0.8, for example, it can be 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91 or 0.92, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0016] The S / LD ratio satisfies: 12≤S / LD≤60 (where the unit of S is nm, and the value of S / LD satisfies 12≤S / LD≤60), for example, it can be 12, 15, 20, 25, 30, 35, 40, 45, 50, 55 or 60, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0017] If the S / LD is too small, the material will not have enough crystallinity, the crystal structure will be incomplete, and the lithium-ion transport channels will be incomplete, which will reduce the battery capacity release. If the S / LD is too large, the particle size will be too large, the lithium-ion transport distance will be increased, and the inner lithium-ion will be difficult to insert and extract, which will also reduce the battery capacity release.
[0018] Preferably, the grain size of the lithium manganese iron phosphate cathode material is S, wherein S satisfies: 60nm≤S≤90nm, for example, it can be 60nm, 65nm, 70nm, 75nm, 80nm, 85nm or 90nm, but is not limited to the listed values, and other unlisted values within the range are also applicable.
[0019] Preferably, the aspect ratio of the lithium manganese iron phosphate cathode material is LD, wherein LD satisfies: 1.5≤LD≤5, for example, it can be 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0020] Preferably, the radial dimension of the lithium manganese iron phosphate cathode material is in the range of 70nm to 150nm, for example, it can be 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 140nm or 150nm, and the length is in the range of 100nm to 350nm, for example, it can be 100nm, 200nm, 250nm, 300nm or 350nm, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0021] Preferably, the lithium manganese iron phosphate cathode material comprises a substrate and a carbon coating layer on the surface of the substrate, wherein the chemical formula of the substrate is LiMn. x Fe 1-x PO4, where 0.5 ≤ x ≤ 0.9, for example, can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85 or 0.9, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0022] Secondly, the present invention provides a method for preparing the lithium manganese iron phosphate cathode material as described in the first aspect, the method comprising the following steps:
[0023] (1) The lithium source, manganese source, iron source, phosphorus source, dispersant, carbon source and solvent are mixed to obtain a mixed slurry;
[0024] (2) The mixed slurry described in step (1) is subjected to high-pressure hydrothermal reaction, and the reactants obtained from the high-pressure hydrothermal reaction are spray-dried and sintered to obtain the lithium manganese iron phosphate cathode material.
[0025] The present invention prepares a mixed slurry from lithium source, manganese source, iron source, phosphorus source, dispersant, carbon source and solvent, then reacts it under high pressure hydrothermal conditions, and finally spray-drying and sintering to obtain the lithium manganese iron phosphate cathode material of the present invention.
[0026] Preferably, the temperature of the high-pressure hydrothermal reaction in step (2) is 140℃~220℃, for example, it can be 140℃, 160℃, 180℃, 200℃ or 220℃, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0027] Preferably, the pressure of the high-pressure hydrothermal reaction in step (2) is 1 MPa to 6 MPa, preferably 2 MPa to 5 MPa. For example, it can be 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa or 6 MPa, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0028] The present invention preferably carries out hydrothermal reaction under specific temperature and pressure. If the reaction pressure is too low, the driving force of the reaction is small, the reaction rate is slow, and the resulting crystal structure is incomplete. If the reaction pressure is too high, higher requirements are placed on the safety of the reaction vessel, which is not conducive to large-scale application.
[0029] Preferably, the high-pressure hydrothermal reaction time in step (2) is 6h to 48h, for example, it can be 6h, 10h, 15h, 20h, 25h, 30h, 35h, 40h, 45h or 48h, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0030] Preferably, the sintering temperature in step (2) is 640℃~780℃, for example, 640℃, 680℃, 720℃ or 780℃, and the time is 5h~24h, for example, 5h, 10h, 15h, 20h or 24h, but not limited to the listed values. Other unlisted values within the range are also applicable.
[0031] Preferably, the outlet temperature of the spray dryer in step (2) is 90℃~140℃, for example, it can be 90℃, 100℃, 120℃ or 140℃, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0032] Preferably, the dispersant in step (1) includes any one or a combination of at least two of ethylene glycol, ethanol, ethylene glycol methyl ether or hexaalkyltrimethylammonium bromide, preferably ethylene glycol methyl ether.
[0033] The type of dispersant used in this invention also affects the morphology of the material; the preferred dispersant is ethylene glycol methyl ether.
[0034] Preferably, the amount of dispersant added in step (1) is 3wt%-8wt% of the total mass of lithium source, manganese source, iron source and phosphorus source, for example, it can be 3wt%, 4wt%, 5wt%, 6wt%, 7wt% or 8wt%, but is not limited to the listed values, and other unlisted values within the range are also applicable.
[0035] Preferably, the carbon source in step (1) includes any one or a combination of at least two of glucose, sucrose, citric acid, PEG (polyethylene glycol), or starch.
[0036] Preferably, the amount of carbon source added in step (1) is 8wt%-15wt% of the total mass of lithium source, manganese source, iron source and phosphorus source, for example, it can be 8wt%, 10wt%, 12wt% or 15wt%, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0037] Preferably, the mixed slurry in step (1) is further milled before step (2).
[0038] Preferably, the particle size D50 of the sand mill is 0.2μm to 0.45μm, for example, it can be 0.2μm, 0.3μm, 0.4μm or 0.45μm, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0039] Preferably, the lithium source in step (1) includes any one or a combination of at least two of lithium carbonate, lithium dihydrogen phosphate, or lithium hydroxide.
[0040] Preferably, the manganese source in step (1) includes any one or a combination of at least two of manganese tetroxide, manganese carbonate, manganese trioxide, manganese phosphate, or manganese oxalate.
[0041] Preferably, the iron source in step (1) includes any one or a combination of at least two of ferric phosphate, ferrous oxalate, or ferric oxide.
[0042] Preferably, the phosphorus source in step (1) includes any one or a combination of at least two of phosphoric acid, lithium dihydrogen phosphate, or ammonium dihydrogen phosphate.
[0043] Thirdly, the present invention provides a lithium-ion battery comprising the lithium manganese iron phosphate cathode material as described in the first aspect.
[0044] Compared with the prior art, the present invention has the following beneficial effects:
[0045] This invention adjusts the ratio of the diffraction peak intensities corresponding to the (020), (110), and (002) crystal planes to the diffraction peak intensities corresponding to the (131) crystal plane in the XRD diffraction pattern of the lithium manganese iron phosphate cathode material, making the particle morphology tend towards a rod shape and giving the lithium manganese iron phosphate a preferred orientation. For lithium manganese iron phosphate with a short rod-shaped morphology, lithium ions will preferentially transport along its radial direction, greatly shortening the lithium ion transport distance and effectively solving the problem of slow lithium ion transport in lithium manganese iron phosphate cathode materials, thereby improving the battery capacity of the material. Furthermore, this invention effectively controls the grain size and aspect ratio of the lithium manganese iron phosphate cathode material. Since for short rod-shaped materials with a high aspect ratio, if the grain size is too small, the material will not have sufficient crystallinity, the crystal structure will not be complete, and the lithium ion transport channels will not be complete, which will reduce the battery capacity release. Therefore, this invention can avoid the above problems by controlling the ratio of the grain size to the aspect ratio of the lithium manganese iron phosphate cathode material. Attached Figure Description
[0046] Figure 1 The image shows the XRD pattern of the lithium manganese iron phosphate cathode material described in Example 1 of this invention.
[0047] Figure 2 This is a SEM image of the lithium manganese iron phosphate cathode material described in Example 2 of the present invention.
[0048] Figure 3 This is a SEM image of the lithium manganese iron phosphate cathode material described in Comparative Example 2 of the present invention. Detailed Implementation
[0049] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.
[0050] Example 1
[0051] This embodiment provides a lithium manganese iron phosphate cathode material, which includes a matrix and a carbon coating layer on the surface of the matrix. The chemical formula of the matrix is LiMn. 0.6 Fe 0.4 PO4;
[0052] The preparation method of the lithium manganese iron phosphate cathode material includes the following steps:
[0053] (1) Lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate were mixed in a molar ratio of Li:Mn:Fe:P = 1.02:0.6:0.4:1. Then, pure water was used as a solvent to prepare a slurry with a solid content of 40 wt%. Subsequently, 5 wt% of ethylene glycol (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a dispersant, and 10 wt% of glucose (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a carbon source.
[0054] (2) The mixed slurry obtained in step (1) is sand-milled in a sand mill until the particle size D50 is 0.35μm;
[0055] (3) The slurry that has been ground by sand is placed in a high-pressure hydrothermal reactor for reaction. The reaction temperature is 220℃, the reaction pressure is 5MPa, and the reaction time is 24h.
[0056] (4) The hydrothermal slurry is spray-dried. The inlet air temperature of the spray drying process is 200℃ and the outlet air temperature is 100℃ to obtain the spray material.
[0057] (5) The sprayed material was sintered under a nitrogen atmosphere at a temperature of 740℃ for 24 hours to obtain the lithium manganese iron phosphate cathode material. The XRD pattern of the lithium manganese iron phosphate cathode material is shown below. Figure 1 As shown, Figure 1 The positions of the diffraction peaks of the (020), (110), (002), and (131) crystal planes are shown in the diagram. The intensity of the diffraction peaks corresponds to the exposure of each crystal plane, representing the preferred orientation of the cathode material.
[0058] Example 2
[0059] This embodiment provides a lithium manganese iron phosphate cathode material, which includes a matrix and a carbon coating layer on the surface of the matrix. The chemical formula of the matrix is LiMn. 0.6 Fe 0.4 PO4;
[0060] The preparation method of the lithium manganese iron phosphate cathode material includes the following steps:
[0061] (1) Lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate were mixed in a molar ratio of Li:Mn:Fe:P = 1.02:0.6:0.4:1. Then, pure water was used as a solvent to prepare a slurry with a solid content of 40 wt%. Subsequently, 5 wt% of ethylene glycol (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a dispersant, and 10 wt% of glucose (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a carbon source.
[0062] (2) The mixed slurry obtained in step (1) is sand-milled in a sand mill until the particle size D50 is 0.35μm;
[0063] (3) The slurry that has been ground by sand is placed in a high-pressure hydrothermal reactor for reaction. The reaction temperature is 180℃, the reaction pressure is 4MPa, and the reaction time is 24h.
[0064] (4) The hydrothermal slurry is spray-dried. The inlet air temperature of the spray drying process is 200℃ and the outlet air temperature is 100℃ to obtain the spray material.
[0065] (5) The sprayed material was sintered under a nitrogen atmosphere at a temperature of 740℃ for 24 hours to obtain the lithium manganese iron phosphate cathode material. The SEM image of the lithium manganese iron phosphate cathode material is shown below. Figure 2 As shown, from Figure 2 It can be seen that the material has a short rod-like morphology.
[0066] Example 3
[0067] This embodiment provides a lithium manganese iron phosphate cathode material, which includes a matrix and a carbon coating layer on the surface of the matrix. The chemical formula of the matrix is LiMn. 0.6 Fe 0.4 PO4;
[0068] The preparation method of the lithium manganese iron phosphate cathode material includes the following steps:
[0069] (1) Lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate were mixed in a molar ratio of Li:Mn:Fe:P = 1.02:0.6:0.4:1. Then, pure water was used as a solvent to prepare a slurry with a solid content of 40 wt%. Subsequently, 5 wt% of ethylene glycol (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a dispersant, and 10 wt% of glucose (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a carbon source.
[0070] (2) The mixed slurry obtained in step (1) is sand-milled in a sand mill until the particle size D50 is 0.35μm;
[0071] (3) The slurry that has been ground by sand is placed in a high-pressure hydrothermal reactor for reaction. The reaction temperature is 140℃, the reaction pressure is 2MPa, and the reaction time is 24h.
[0072] (4) The hydrothermal slurry is spray-dried. The inlet air temperature of the spray drying process is 200℃ and the outlet air temperature is 100℃ to obtain the spray material.
[0073] (5) The spray material is sintered in a nitrogen atmosphere at a temperature of 740°C and a holding time of 24h to finally obtain the lithium manganese iron phosphate cathode material.
[0074] Example 4
[0075] This embodiment provides a lithium manganese iron phosphate cathode material, which includes a matrix and a carbon coating layer on the surface of the matrix. The chemical formula of the matrix is LiMn. 0.5 Fe 0.5 PO4;
[0076] The preparation method of the lithium manganese iron phosphate cathode material includes the following steps:
[0077] (1) Lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate were mixed in a molar ratio of Li:Mn:Fe:P = 1.02:0.5:0.5:1. Then, pure water was used as a solvent to prepare a slurry with a solid content of 40 wt%. Subsequently, 5 wt% of ethylene glycol (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a dispersant, and 10 wt% of glucose (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a carbon source.
[0078] (2) The mixed slurry obtained in step (1) is sand-milled in a sand mill until the particle size D50 is 0.35μm;
[0079] (3) The slurry that has been ground by sand is placed in a high-pressure hydrothermal reactor for reaction. The reaction temperature is 180℃, the reaction pressure is 4MPa, and the reaction time is 24h.
[0080] (4) The hydrothermal slurry is spray-dried. The inlet air temperature of the spray drying process is 200℃ and the outlet air temperature is 100℃ to obtain the spray material.
[0081] (5) The spray material is sintered in a nitrogen atmosphere at a temperature of 740°C and a holding time of 24h to finally obtain the lithium manganese iron phosphate cathode material.
[0082] Example 5
[0083] This embodiment provides a lithium manganese iron phosphate cathode material, which includes a matrix and a carbon coating layer on the surface of the matrix. The chemical formula of the matrix is LiMn. 0.7 Fe 0.3 PO4;
[0084] The preparation method of the lithium manganese iron phosphate cathode material includes the following steps:
[0085] (1) Lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate were mixed in a molar ratio of Li:Mn:Fe:P = 1.02:0.7:0.3:1. Then, pure water was used as a solvent to prepare a slurry with a solid content of 40 wt%. Subsequently, 5 wt% of ethylene glycol (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a dispersant, and 10 wt% of glucose (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a carbon source.
[0086] (2) The mixed slurry obtained in step (1) is sand-milled in a sand mill until the particle size D50 is 0.35μm;
[0087] (3) The slurry that has been ground by sand is placed in a high-pressure hydrothermal reactor for reaction. The reaction temperature is 180℃, the reaction pressure is 4MPa, and the reaction time is 24h.
[0088] (4) The hydrothermal slurry is spray-dried. The inlet air temperature of the spray drying process is 200℃ and the outlet air temperature is 100℃ to obtain the spray material.
[0089] (5) The spray material is sintered in a nitrogen atmosphere at a temperature of 740°C and a holding time of 24h to finally obtain the lithium manganese iron phosphate cathode material.
[0090] Example 6
[0091] This embodiment provides a lithium manganese iron phosphate cathode material, which includes a matrix and a carbon coating layer on the surface of the matrix. The chemical formula of the matrix is LiMn. 0.8 Fe 0.2 PO4;
[0092] The preparation method of the lithium manganese iron phosphate cathode material includes the following steps:
[0093] (1) Lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate were mixed in a molar ratio of Li:Mn:Fe:P = 1.02:0.8:0.2:1. Then, pure water was used as a solvent to prepare a slurry with a solid content of 40 wt%. Subsequently, 5 wt% of ethylene glycol (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a dispersant, and 10 wt% of glucose (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a carbon source.
[0094] (2) The mixed slurry obtained in step (1) is sand-milled in a sand mill until the particle size D50 is 0.35μm;
[0095] (3) The slurry that has been ground by sand is placed in a high-pressure hydrothermal reactor for reaction. The reaction temperature is 180℃, the reaction pressure is 4MPa, and the reaction time is 24h.
[0096] (4) The hydrothermal slurry is spray-dried. The inlet air temperature of the spray drying process is 200℃ and the outlet air temperature is 100℃ to obtain the spray material.
[0097] (5) The spray material is sintered in a nitrogen atmosphere at a temperature of 740°C and a holding time of 24h to finally obtain the lithium manganese iron phosphate cathode material.
[0098] Example 7
[0099] This embodiment provides a lithium manganese iron phosphate cathode material, which includes a matrix and a carbon coating layer on the surface of the matrix. The chemical formula of the matrix is LiMn. 0.9 Fe 0.1 PO4;
[0100] The preparation method of the lithium manganese iron phosphate cathode material includes the following steps:
[0101] (1) Lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate were mixed in a molar ratio of Li:Mn:Fe:P = 1.02:0.9:0.1:1. Then, pure water was used as a solvent to prepare a slurry with a solid content of 40 wt%. Subsequently, 5 wt% of ethylene glycol (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a dispersant, and 10 wt% of glucose (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a carbon source.
[0102] (2) The mixed slurry obtained in step (1) is sand-milled in a sand mill until the particle size D50 is 0.35μm;
[0103] (3) The slurry that has been ground by sand is placed in a high-pressure hydrothermal reactor for reaction. The reaction temperature is 180℃, the reaction pressure is 4MPa, and the reaction time is 24h.
[0104] (4) The hydrothermal slurry is spray-dried. The inlet air temperature of the spray drying process is 200℃ and the outlet air temperature is 100℃ to obtain the spray material.
[0105] (5) The spray material is sintered in a nitrogen atmosphere at a temperature of 740°C and a holding time of 24h to finally obtain the lithium manganese iron phosphate cathode material.
[0106] Example 8
[0107] This embodiment provides a lithium manganese iron phosphate cathode material, which includes a matrix and a carbon coating layer on the surface of the matrix. The chemical formula of the matrix is LiMn. 0.6 Fe 0.4 PO4;
[0108] The preparation method of the lithium manganese iron phosphate cathode material includes the following steps:
[0109] (1) Lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate were mixed in a molar ratio of Li:Mn:Fe:P = 1.02:0.6:0.4:1. Then, pure water was used as a solvent to prepare a slurry with a solid content of 40 wt%. Subsequently, 5 wt% of ethylene glycol methyl ether of the total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate was added as a dispersant, and 10 wt% of glucose of the total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate was added as a carbon source.
[0110] (2) The mixed slurry obtained in step (1) is sand-milled in a sand mill until the particle size D50 is 0.35μm;
[0111] (3) The slurry that has been ground by sand is placed in a high-pressure hydrothermal reactor for reaction. The reaction temperature is 220℃, the reaction pressure is 5MPa, and the reaction time is 24h.
[0112] (4) The hydrothermal slurry is spray-dried. The inlet air temperature of the spray drying process is 200℃ and the outlet air temperature is 100℃ to obtain the spray material.
[0113] (5) The spray material is sintered in a nitrogen atmosphere at a temperature of 740°C and a holding time of 24h to finally obtain the lithium manganese iron phosphate cathode material.
[0114] Comparative Example 1
[0115] This comparative example provides a lithium manganese iron phosphate cathode material, which includes a substrate and a carbon coating layer on the surface of the substrate. The chemical formula of the substrate is LiMn. 0.6 Fe 0.4 PO4;
[0116] The preparation method of the lithium manganese iron phosphate cathode material includes the following steps:
[0117] (1) Lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate were mixed in a molar ratio of Li:Mn:Fe:P = 1.02:0.6:0.4:1. Then, pure water was used as a solvent to prepare a slurry with a solid content of 40 wt%. Subsequently, 5 wt% of ethylene glycol (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a dispersant, and 10 wt% of glucose (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a carbon source.
[0118] (2) The mixed slurry obtained in step (1) is sand-milled in a sand mill until the particle size D50 is 0.35μm;
[0119] (3) The sand-ground slurry is spray-dried. The inlet air temperature of the spray-drying process is 200℃ and the outlet air temperature is 100℃ to obtain the spray material.
[0120] (4) The spray material is sintered in a nitrogen atmosphere at a temperature of 680°C and a holding time of 24h to finally obtain the lithium manganese iron phosphate cathode material.
[0121] Comparative Example 2
[0122] This comparative example provides a lithium manganese iron phosphate cathode material, which includes a substrate and a carbon coating layer on the surface of the substrate. The chemical formula of the substrate is LiMn. 0.6 Fe 0.4 PO4;
[0123] The preparation method of the lithium manganese iron phosphate cathode material includes the following steps:
[0124] (1) Lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate were mixed in a molar ratio of Li:Mn:Fe:P = 1.02:0.6:0.4:1. Then, pure water was used as a solvent to prepare a slurry with a solid content of 40 wt%. Subsequently, 5 wt% of ethylene glycol (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a dispersant, and 10 wt% of glucose (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a carbon source.
[0125] (2) The mixed slurry obtained in step (1) is sand-milled in a sand mill until the particle size D50 is 0.35μm;
[0126] (3) The sand-ground slurry is spray-dried. The inlet air temperature of the spray-drying process is 200℃ and the outlet air temperature is 100℃ to obtain the spray material.
[0127] (4) The sprayed material was sintered under a nitrogen atmosphere at a temperature of 740℃ for 24 hours to obtain the lithium manganese iron phosphate cathode material. The SEM image of the lithium manganese iron phosphate cathode material is shown below. Figure 3 As shown, from Figure 3 It can be seen that the material has a spherical shape.
[0128] Comparative Example 3
[0129] This comparative example provides a lithium manganese iron phosphate cathode material, which includes a substrate and a carbon coating layer on the surface of the substrate. The chemical formula of the substrate is LiMn. 0.6 Fe 0.4 PO4;
[0130] The preparation method of the lithium manganese iron phosphate cathode material includes the following steps:
[0131] (1) Lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate were mixed in a molar ratio of Li:Mn:Fe:P = 1.02:0.6:0.4:1. Then, pure water was used as a solvent to prepare a slurry with a solid content of 40 wt%. Subsequently, 5 wt% of ethylene glycol (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a dispersant, and 10 wt% of glucose (total mass of lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate) was added as a carbon source.
[0132] (2) The mixed slurry obtained in step (1) is sand-milled in a sand mill until the particle size D50 is 0.35μm;
[0133] (3) The slurry that has been ground by sand is placed in a high-pressure hydrothermal reactor for reaction. The reaction temperature is 240℃, the reaction pressure is 6MPa, and the reaction time is 24h.
[0134] (4) The hydrothermal slurry is spray-dried. The inlet air temperature of the spray drying process is 200℃ and the outlet air temperature is 100℃ to obtain the spray material.
[0135] (5) The spray material is sintered in a nitrogen atmosphere at a temperature of 680°C and a holding time of 24h to finally obtain the lithium manganese iron phosphate cathode material.
[0136] Performance testing:
[0137] (1) XRD test: The lithium manganese iron phosphate cathode materials described in the above examples and comparative examples were tested using an XRD diffractometer. The test conditions were: 2-theta range 10-50°, step width 0.02°, scanning speed 5° / min, the intensity values of the diffraction peaks corresponding to each crystal plane were obtained directly from the original data, and the grain size was obtained directly from the XRD test report.
[0138] (2) Morphology: SEM is used to observe the morphology of the sample, calculate and statistically analyze the radial size and length of the primary particles, and calculate the aspect ratio;
[0139] (3) Battery performance test:
[0140] The lithium manganese iron phosphate cathode material, conductive agent (SP), and binder (PVDF) of the above examples and comparative examples were mixed in a weight ratio of 90:5:5, and then an appropriate amount of NMP was added as a solvent for homogenization. The mixture was uniformly coated on carbon-coated aluminum foil and dried in a conventional oven at 120°C for 12 hours, followed by further drying in a vacuum oven at 120°C for 12 hours. The dried electrode was cut into small round pieces with a diameter of 14 mm as cathode sheets.
[0141] Finally, the coin cell was assembled in the glove box: the positive electrode was a lithium electrode, the negative electrode was a polypropylene membrane, the electrolyte was 1 mol / L LiPF6 (the solvent was EC and DMC in a volume ratio of 1:1), and a 2032 coin cell was assembled. After assembly, the battery was first allowed to stand for 24 hours for activation, and then charge and discharge tests were performed on the Xinwei charge and discharge tester: the voltage range was 2.0-4.35V, the charging mode was CC / CV, and the CV cutoff current was 0.04C.
[0142] The Mn / Fe molar ratio, whether high-pressure hydrothermal heating was used, hydrothermal temperature, hydrothermal pressure, and type of dispersant in the above embodiments and comparative examples are shown in Table 1; the particle morphology, aspect ratio, grain size, S / LD, A / D, B / D, C / D, 0.1C discharge capacity, and 1C discharge capacity of the battery are shown in Table 2.
[0143] Table 1
[0144]
[0145] Table 2
[0146]
[0147] As can be seen from Tables 1 and 2 above:
[0148] The samples in Examples 1-8 all had a short rod-like morphology, with an aspect ratio (LD) ranging from 1.5 to 5, a grain size (S) ranging from 60 to 90 nm, and a grain size to aspect ratio ratio (S / LD) ranging from 12 to 60. All samples also satisfied A / D > 0.25, B / D > 0.7, and C / D > 0.8, indicating excellent battery capacity performance. In contrast, the A / D, B / D, and C / D ratios of Comparative Examples 1 and 2 were lower than those of this invention, and the samples had a conventional spherical morphology with an aspect ratio below 1.5. Among them, the grain size of Comparative Example 2 was too large, resulting in a low capacity. Comparative Example 1 had a grain size of 80 nm, but the S / LD ratio was still too large, and the A / D, B / D, and C / D ratios were too low, resulting in a low final capacity. Although Comparative Example 3 also had a short rod-shaped morphology with an aspect ratio as high as 4.8 and met the requirements of A / D > 0.25, B / D > 0.7, and C / D > 0.8, the grain size was too small and the S / LD ratio was too small, indicating that the material had insufficient crystallinity and an incomplete crystal structure, resulting in a low final capacity. Based on the above results, it can be concluded that when the diffraction peak intensities satisfy A / D > 0.25, B / D > 0.7, and C / D > 0.8, the sample tends to grow into a rod-shaped morphology with a high aspect ratio. Lithium ions will preferentially transport along the radial direction of the rod-shaped structure, shortening the lithium ion transport distance and thus improving the discharge capacity of the sample. However, the grain size of the material cannot be too small, otherwise it will lead to insufficient crystallinity, incomplete lithium ion transport channels, and thus low capacity.
[0149] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention 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 technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.
Claims
1. A lithium manganese iron phosphate cathode material, characterized in that, The lithium iron phosphate cathode material meets the following conditions: A / D > 0.25, B / D > 0.7, and C / D > 0.8; Wherein, A is the intensity value of the diffraction peak corresponding to the (020) crystal plane in the XRD diffraction pattern of the lithium manganese iron phosphate cathode material, B is the intensity value of the diffraction peak corresponding to the (110) crystal plane in the XRD diffraction pattern of the lithium manganese iron phosphate cathode material, C is the intensity value of the diffraction peak corresponding to the (002) crystal plane in the XRD diffraction pattern of the lithium manganese iron phosphate cathode material, and D is the intensity value of the diffraction peak corresponding to the (131) crystal plane in the XRD diffraction pattern of the lithium manganese iron phosphate cathode material; The lithium iron manganese phosphate cathode material has a short rod-like morphology. The ratio of the grain size to the aspect ratio of the lithium manganese iron phosphate cathode material is S / LD, and S / LD satisfies: 12≤S / LD≤60.
2. The lithium iron phosphate cathode material according to claim 1, characterized in that, The grain size of the lithium iron manganese phosphate cathode material is S, and S satisfies: 60nm≤S≤90nm; Preferably, the aspect ratio of the lithium manganese iron phosphate cathode material is LD, and LD satisfies: 1.5≤LD≤5.
3. The lithium iron phosphate cathode material according to claim 1 or 2, characterized in that, The radial dimension of the lithium manganese iron phosphate cathode material is in the range of 70nm to 150nm, and the length is in the range of 100nm to 350nm. Preferably, the lithium manganese iron phosphate cathode material comprises a substrate and a carbon coating layer on the surface of the substrate, wherein the chemical formula of the substrate is LiMn. x Fe 1-x PO4, where 0.5 ≤ x ≤ 0.
9.
4. A method for preparing the lithium manganese iron phosphate cathode material as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: (1) The lithium source, manganese source, iron source, phosphorus source, dispersant, carbon source and solvent are mixed to obtain a mixed slurry; (2) The mixed slurry described in step (1) is subjected to high-pressure hydrothermal reaction, and the reactants obtained from the high-pressure hydrothermal reaction are spray-dried and sintered to obtain the lithium manganese iron phosphate cathode material.
5. The preparation method according to claim 4, characterized in that, The temperature of the high-pressure hydrothermal reaction in step (2) is 140℃~220℃; Preferably, the pressure of the high-pressure hydrothermal reaction in step (2) is 1 MPa to 6 MPa, and more preferably 2 MPa to 5 MPa; Preferably, the high-pressure hydrothermal reaction time in step (2) is 6h to 48h.
6. The preparation method according to claim 4 or 5, characterized in that, The sintering temperature in step (2) is 640℃~780℃, and the time is 5h~24h; Preferably, the outlet temperature of the spray dryer in step (2) is 90℃~140℃.
7. The preparation method according to any one of claims 4-6, characterized in that, The dispersant in step (1) includes any one or a combination of at least two of ethylene glycol, ethanol, ethylene glycol methyl ether or hexaalkyltrimethylammonium bromide, preferably ethylene glycol methyl ether; Preferably, the amount of dispersant added in step (1) is 3wt%-8wt% of the total mass of the lithium source, manganese source, iron source and phosphorus source; Preferably, the carbon source in step (1) includes any one or a combination of at least two of glucose, sucrose, citric acid, PEG or starch; Preferably, the amount of carbon source added in step (1) is 8wt%-15wt% of the total mass of lithium source, manganese source, iron source and phosphorus source.
8. The preparation method according to any one of claims 4-7, characterized in that, The mixed slurry described in step (1) was further milled before step (2); Preferably, the sand is milled to a particle size D50 of 0.2μm to 0.45μm.
9. The preparation method according to any one of claims 4-8, characterized in that, The lithium source in step (1) includes any one or a combination of at least two of lithium carbonate, lithium dihydrogen phosphate, or lithium hydroxide; Preferably, the manganese source in step (1) includes any one or a combination of at least two of manganese tetroxide, manganese carbonate, manganese trioxide, manganese phosphate, or manganese oxalate; Preferably, the iron source in step (1) includes any one or a combination of at least two of ferric phosphate, ferrous oxalate, or ferric oxide; Preferably, the phosphorus source in step (1) includes any one or a combination of at least two of phosphoric acid, lithium dihydrogen phosphate, or ammonium dihydrogen phosphate.
10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the lithium manganese iron phosphate cathode material as described in any one of claims 1-3.