Modified lithium iron phosphate-based positive electrode material, preparation method and application thereof
By preparing an amorphous composite interface on the surface of lithium-ion battery cathode material, the problem of uneven carbon coating caused by uneven particle size was solved, improving the energy storage performance and stability of the battery and realizing efficient commercial modification.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SUN YAT SEN UNIV
- Filing Date
- 2025-01-07
- Publication Date
- 2026-08-04
AI Technical Summary
Existing lithium-ion battery cathode materials, such as LiFePO4, have uneven particle size, resulting in uneven carbon coating and the formation of an unstable cathode electrolyte interface. Crack propagation leads to uncontrolled decomposition of the electrolyte, affecting energy storage capacity and cycle stability.
By preparing a uniform amorphous composite interface on the surface of commercial lithium iron phosphate-based materials and treating it with an alkali metal ion solution, a continuous amorphous coating layer is formed, which inhibits crack propagation and improves the energy storage performance of the materials.
It significantly improves the coulombic efficiency, capacity retention, and cycle stability of lithium-ion batteries, and the method is simple, easy to implement, suitable for large-scale commercial modification, and low in cost.
Smart Images
Figure CN119943899B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of secondary battery energy storage technology, specifically to a modified lithium iron phosphate-based cathode material, its preparation method, and its application. Background Technology
[0002] In secondary battery applications, the energy density of materials, especially the energy density of the cathode material, directly affects the overall energy density of the battery. This requires the cathode material to have the highest possible tap density. However, high tap density means that the cathode material must form unique, well-distributed micron-sized aggregates to reduce unnecessary gaps, which objectively requires a non-uniform particle size distribution. Furthermore, commonly used lithium-ion battery cathode materials, such as LiFePO4 and LiCoO2, generally exhibit poor intrinsic conductivity. To meet the requirements of high-power applications, they need kinetic modification, such as constructing nano-sized micron-sized aggregates to shorten the ion diffusion path, and applying a small amount of carbon coating to accelerate charge conduction between particles. However, the carbon coating process must consider not only the influence of coating layer content and annealing process on the intrinsic properties of the cathode material (e.g., stress, defects, actual capacity), but also the dependence of the coating process on particle size. Therefore, achieving a moderately uniform coating layer for cathode materials with large particle size distribution remains a significant challenge, especially considering the practicality of the coating interface layer.
[0003] When an electrode comes into contact with the electrolyte, a so-called solid electrolyte interface spontaneously forms, exhibiting excellent ion conductivity and electronic insulation. A stable solid electrolyte interface is crucial for both electrode stability and stable battery operation. This is especially true for cathode materials; an unstable interface leads to repeated electrolyte decomposition, forming numerous byproducts. This not only consumes electrolyte but also deteriorates the charge conduction process between the electrode and electrolyte. For cathode materials, this interface is also known as the cathode electrolyte interface. For lithium-ion battery cathode materials, such as commercial lithium iron phosphate-based materials (Li...),... x Fe y M z Due to its non-uniform particle size, PO4 contains a large number of exposed, uncoated areas. Upon contact with the electrolyte, it initially forms a primary cathode-electrolyte interface. Through repeated lithium insertion / extraction processes, numerous crack zones are generated within the grains due to the repeated effects of initial and subsequent stresses. When the cracks extend to the carbon-coated areas, the composite coating layer of carbon and the primary cathode-electrolyte interface exhibits strong stability; however, when the cracks extend to the uncoated areas, it leads to the rupture of the primary cathode interface. The deep propagation of the electrolyte and the continuous formation of subsequent amorphous byproducts result in the uncontrolled decomposition of the electrolyte. This is a common problem in commercial lithium iron phosphate-based materials. x Fe y M zOne of the important reasons why the lithium storage properties of PO4 materials still degrade.
[0004] Therefore, there is an urgent need to provide a practical, easy-to-implement, and easily scalable interface preparation method; at the same time, this method does not depend on the size of the parent particles, the coating thickness is adjustable, it does not affect the energy storage specific capacity of the commercial material itself, and it can effectively suppress the runaway decomposition process of the electrolyte caused by crack propagation, thereby further improving the capacity holding rate, cycle stability, coulombic efficiency, etc. of commercial lithium storage cathode materials. Summary of the Invention
[0005] This invention addresses the aforementioned problems by providing a modified lithium iron phosphate-based cathode material, its preparation method, and its applications, enabling the preparation of a uniformly dispersed cathode material in commercial lithium iron phosphate-based materials at room temperature. x Fe y M z The amorphous composite interface of PO4 powder helps to suppress the runaway electrolyte decomposition caused by repeated lithium insertion and extraction cracks, thereby further improving its energy storage capacity holding rate, cycle stability, coulombic efficiency, etc.
[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0007] A method for preparing a modified lithium iron phosphate-based cathode material, specifically comprising dispersing lithium iron phosphate-based material powder containing a small amount of carbon coating in a solution containing alkali metal ions, dispersing, settling, washing, and drying, thereby preparing the surface-modified lithium iron phosphate-based cathode material;
[0008] The lithium iron phosphate-based material powder containing a small amount of carbon coating is a C / Li mixture with a carbon content of 1-10% wt. x Fe y M z PO4 composite material, wherein C is coated on Li in the form of a coating layer x Fe y M z The surface of PO4.
[0009] Preferably, the solute alkali metal cation in the alkali metal ion solution is one or more of sodium, potassium, calcium, magnesium, or aluminum, and the anion is one or more of chloride, bromide, iodide, acetate, or tetrafluoroborate ions; the solvent in the alkali metal ion solution is one or more of deionized water, ethanol, methanol, or ethylene glycol.
[0010] Preferably, the dispersion and settling process is one or a combination of two of the following: stirring dispersion, ultrasonic dispersion, or long-term settling, with a time of 5 min to 24 h.
[0011] Preferably, the concentration of the alkali metal solution is 0.1-2.5 mL. -1.
[0012] Preferably, the ratio of lithium iron phosphate powder to alkali metal ion solution is 1g:(3-50)mL.
[0013] Preferably, the washing process involves one or a combination of deionized water and ethanol, and the washing is performed 1-2 times; the drying process involves drying in an air-atmosphere forced-air drying oven at 50-100℃ for 30 min-24 h.
[0014] Preferably, the surface modification is achieved by locally converting a lithium iron phosphate-based material into an amorphous composite interface through chemical adsorption with an alkali metal ion solution; the amorphous composite interface is continuous and uniform, with adjustable thickness, and contains one or more of potassium, calcium, magnesium, and aluminum; the average thickness of the amorphous composite interface is 5-15 nm.
[0015] The present invention also provides a modified lithium iron phosphate-based cathode material prepared according to the preparation method described above.
[0016] Preferably, the modified lithium iron phosphate-based cathode material has a particle size of 50-500 nm, a tap density of 2.0-5.0 g / cc, and a specific surface area of 10-40 m². 2 / g.
[0017] The present invention also provides an application of the surface-modified lithium iron phosphate-based material in lithium-ion batteries, lithium metal batteries, and solid-state batteries as a secondary lithium battery.
[0018] Specifically, the above-mentioned lithium iron phosphate-based materials are used in the preparation of lithium secondary battery electrode materials.
[0019] More specifically, the amorphous composite interface obtained by the above surface modification method plays a role in suppressing the degradation of commercial lithium iron phosphate-based materials. x Fe y M z Applications of PO4 in runaway electrolyte decomposition caused by repeated lithium insertion and extraction cracks.
[0020] By adopting the above technical solution, the beneficial effects of the present invention are as follows:
[0021] This invention obtains a uniformly coated amorphous composite interface layer of lithium iron phosphate-based material through room-temperature solution chemical adsorption and in-situ local conversion. The coating layer obtained by this method has a uniform and adjustable thickness, does not significantly affect the actual lithium storage specific capacity of the lithium iron phosphate-based material, and when applied to lithium battery cathode materials, it significantly suppresses the runaway electrolyte decomposition induced by lattice cracks accompanying repeated lithium insertion / extraction during charge and discharge processes, effectively improving electrochemical performance such as coulombic efficiency, capacity hold-up, and cycle stability. Furthermore, this method is independent of the parent particle size, the interface thickness is adjustable, and it is simple, easy to implement, and low-cost, making it suitable for further modification of large-scale commercial materials. It compensates for the uneven coating problem caused by large scale differences in carbon coating methods during large-scale preparation, without significantly affecting the intrinsic energy storage specific capacity of commercial electrode materials. Attached Figure Description
[0022] Figure 1 The polycrystalline powder diffraction patterns are those of the samples corresponding to Comparative Example 1 and Example 1 of this invention.
[0023] Figure 2 This is a high-angle annular dark-field image of the sample corresponding to Example 1 of the present invention obtained by transmission electron microscopy;
[0024] Figure 3 This is a transmission electron microscope elemental imaging distribution map of the sample corresponding to Example 1 of the present invention;
[0025] Figure 4 These are transmission electron microscope images of the samples corresponding to Comparative Example 1 and Example 1 of the present invention;
[0026] Figure 5 For Comparative Example 2, Example 2-1, and Example 2-2 of this invention, the corresponding batteries were tested at 200 mA g. -1 The charge and discharge capacity diagram of constant current charge and discharge at current density;
[0027] Figure 6 For Comparative Example 2, Example 2-1, and Example 2-2, the corresponding batteries were tested at 200 mAg. -1 Coulomb efficiency diagram of constant current charge and discharge at current density;
[0028] Figure 7 The images are transmission electron microscope images of the samples corresponding to Comparative Example 3 and Example 3. Detailed Implementation
[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0030] The raw materials and reagents used in the following examples are all commercially available.
[0031] Example 1
[0032] A method for preparing a modified lithium iron phosphate-based cathode material includes the following steps:
[0033] Prepare 30 mL of 0.5 M calcium acetate aqueous solution in a 50 mL centrifuge tube, uniformly disperse 2 g of commercial lithium iron phosphate-based material powder in it, let stand for 6 h, filter, and recover the filtrate for repeated use. Wash the filter cake twice with deionized water and once with anhydrous ethanol, and then dry it in an air-conditioned oven at 80 °C for 6 h to obtain lithium iron phosphate-based material powder with uniformly coated amorphous composite interface, which is the modified lithium iron phosphate-based cathode material.
[0034] The sample corresponding to Example 1 is the modified lithium iron phosphate-based cathode material coated with the amorphous composite interface.
[0035] Comparative Example 1
[0036] Comparative Example 1 corresponds to a commercial lithium iron phosphate-based material powder with a small amount of carbon coating, which was purchased and no post-processing was performed.
[0037] The samples corresponding to Example 1 and Comparative Example 1 were characterized using a polycrystalline powder diffractometer. Figure 1 The polycrystalline powder diffraction (XRD) patterns of the samples are shown. All diffraction peaks of the samples corresponding to Example 1 and Comparative Example 1 are consistent with the orthorhombic standard lithium iron phosphate (PDF No. 40-1499), with no unidentified diffraction peaks. This indicates that the sample corresponding to Example 1 did not introduce any heterogeneous crystalline impurities compared to the sample corresponding to Comparative Example 1, meaning that the calcium ion solution treatment process did not introduce any heterogeneous crystalline phases into the lithium iron phosphate-based material.
[0038] The samples corresponding to Example 1 were analyzed using energy-dispersive X-ray spectroscopy (EDS) of a transmission electron microscope. Figure 2 This is a high-angle annular dark-field image of the sample (HAADF-STEM). Through comparison... Figure 2 Based on the particle size analysis, the particle size of the interface-modified lithium iron phosphate-based material powder after calcium ion solution treatment is approximately 50-500 nm.
[0039] The samples corresponding to Example 1 were analyzed using energy-dispersive X-ray spectroscopy (EDS) with a transmission electron microscope. Figure 3 The image shows the elemental distribution of the sample in scanning transmission mode. The results indicate that a uniform coating layer containing calcium was formed on the particle surface.
[0040] The samples corresponding to Example 1 and Comparative Example 1 were characterized by high-resolution imaging using transmission electron microscopy. Figure 4This is a high-resolution transmission electron microscope (HRTEM) image of the sample. By comparison... Figure 4 It can be seen that the calcium ion solution treatment process forms a continuous amorphous phase with a thickness of about 5 nm on the surface of commercial LiFePO4 grains, which is consistent with... Figure 1 The XRD results are consistent.
[0041] comprehensive Figure 1-4 It is known that a uniform modified amorphous calcium-based composite interface can be formed on the surface of commercial lithium iron phosphate-based material powder by treating with a room temperature calcium ion aqueous solution.
[0042] Example 2
[0043] The battery manufacturing method of Example 2 is the same as that of Comparative Example 2, except that the commercial cathode material used is different. The cathode material of Example 2-1 is commercial lithium iron phosphate powder treated with 0.5M calcium tetrafluoroborate aqueous solution, while the cathode material of Example 2-2 is commercial lithium iron phosphate powder treated with 0.5M calcium chloride aqueous solution.
[0044] Battery assembly preparation: 80 wt.% modified lithium iron phosphate powder, 10 wt.% acetylene black, and 10 wt.% polyvinylidene fluoride were uniformly dispersed in N-methylpyrrolidone to form a slurry. The mixed slurry was uniformly coated onto aluminum foil, dried at 80℃ for 12 hours, and then cut into lithium iron phosphate positive electrode sheets with a diameter of 10 mm. The active material loading was 1.5-4 mg / cm³. -2 A 2032 coin cell was assembled in a glove box using lithium iron phosphate-based positive electrode and lithium sheet as positive and negative electrodes respectively, polypropylene membrane as separator, and 1M LiPF6 ethylene carbonate / diethyl carbonate (mass ratio 1:1) solution as electrolyte.
[0045] Comparative Example 2
[0046] A method for preparing a battery includes the following steps:
[0047] A slurry was formed by uniformly dispersing 80 wt.% commercial lithium iron phosphate powder, 10 wt.% acetylene black, and 10 wt.% polyvinylidene fluoride in N-methylpyrrolidone. The mixed slurry was then uniformly coated onto aluminum foil, dried at 80°C for 12 hours, and cut into lithium iron phosphate positive electrode sheets with a diameter of 10 mm. The active material loading was 1.5-4 mg / cm³. -2 A 2032 coin cell was assembled in a glove box using lithium iron phosphate-based positive electrode and lithium sheet as positive and negative electrodes respectively, polypropylene membrane as separator, and 1M LiPF6 ethylene carbonate / diethyl carbonate (mass ratio 1:1) solution as electrolyte.
[0048] The applicant tested the product's effectiveness, and the results are as follows:
[0049] The batteries obtained in Example 2 and Comparative Example 2 were tested at 200 mAg. -1 Constant current charge-discharge tests were performed under a current and a voltage window of 2.0-4.2V. Figure 5 The graph shows the charge / discharge capacity of the battery. After 500 cycles, the discharge capacity retention of Comparative Example 2 battery is only 51.2%, which means the discharge specific capacity is 64 mAh g. -1 In stark contrast, under the same testing conditions, the discharge capacity retention rate of the battery in Example 2-1 was 67.2%, meaning its discharge specific capacity was 82 mAh g. -1 Under the same test conditions, the discharge capacity retention rate of the battery in Example 2-2 was 74.8%, which means the discharge specific capacity was 92 mAh g. -1 The results showed that after commercial lithium iron phosphate powder was treated with calcium ion solution, an amorphous calcium-based composite interface was formed on its surface, which significantly improved its capacity retention and cycle stability.
[0050] Figure 6 The diagram shows the charge-discharge coulombic efficiency of the batteries. During 500 cycles, the average coulombic efficiency of the battery in Comparative Example 2 was generally below 99%, while the coulombic efficiency of the batteries in Examples 2-1 and 2-2 was generally above 99%. The results indicate that the coulombic efficiency of commercial lithium iron phosphate powder is significantly improved after treatment with calcium ion solution to form an amorphous calcium-based composite interface on the surface.
[0051] Example 3
[0052] A transmission electron microscopy (TEM) sample preparation of a battery electrode material after cycling was carried out by disassembling the battery of Example 2-2 in a glove box after cycling, immersing the positive electrode in diethyl carbonate, washing away the electrolyte adsorbed on the surface, drying it, and scraping the active material on the electrode directly onto a copper grid for TEM characterization.
[0053] Comparative Example 3
[0054] The sample preparation process for Comparative Example 3 is the same as that for Example 3, except that the battery removed is the battery after cycling in Comparative Example 2.
[0055] The applicant further verified the product's effectiveness, and the results are as follows:
[0056] Example 3 and Comparative Example 3 were characterized by transmission electron microscopy. Figure 7High-resolution transmission electron microscopy (TEM) images of the cycled samples are shown. Comparative Example 3, i.e., the cycled commercial lithium iron phosphate powder, after repeated lithium intercalation / deintercalation, exhibits crack propagation zones that extend to the grain boundaries where carbon coating is lacking. Electrolyte penetration leads to the formation of a secondary electrolyte interface phase, resulting in a large amount of amorphous phase within the diffusion zone, originating from the runaway decomposition of the electrolyte. In contrast, Example 3, i.e., the commercial lithium iron phosphate powder coated with a calcium-based amorphous interface, shows that due to the presence of the amorphous calcium-based composite interface, crack propagation to this interface is inhibited by electrolyte penetration. Fourier transforms show that the same crystal structure is maintained within the crack zone and at the boundary, without the formation of a large amount of amorphous phase. The results indicate that the presence of the calcium-based amorphous composite interface effectively inhibits the runaway electrolyte decomposition caused by cracks formed from repeated lithium intercalation / deintercalation in the commercial lithium iron phosphate powder, thereby improving the electrochemical performance of the material, including capacity retention, cycle stability, and coulombic efficiency.
[0057] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical spirit of the present invention should fall within the patent scope covered by the present invention.
Claims
1. A method for preparing a modified lithium iron phosphate-based cathode material, characterized in that, The specific process involves dispersing lithium iron phosphate-based material powder containing a small amount of carbon coating in a metal ion solution, followed by dispersion, settling, washing, and drying to obtain surface-modified lithium iron phosphate-based cathode material. The lithium iron phosphate-based material powder containing a small amount of carbon coating is a C / Li mixture with a carbon content of 1-10% wt. x Fe y M z PO4 composite material, wherein C is coated on Li in the form of a coating layer x Fe y M z PO4 surface; The surface modification is achieved by locally transforming lithium iron phosphate-based materials into an amorphous composite interface through chemical adsorption with a metal ion solution; the amorphous composite interface is continuous and uniform, with adjustable thickness, and contains one or more of calcium, magnesium, and aluminum; the average thickness of the amorphous composite interface is 5-15 nm. The solute in the metal ion solution contains metal cations and anions, wherein the metal cations are one or more of calcium, magnesium, or aluminum, and the anions are one or more of chloride, bromide, iodide, acetate, or tetrafluoroborate ions; the solvent in the metal ion solution is one or more of deionized water, ethanol, methanol, or ethylene glycol. The settling period is 6-24 hours; the concentration of the metal ion solution is 0.1-2.5 mL. -1 The ratio of the amount of lithium iron phosphate-based material powder containing a small amount of carbon coating to the metal ion solution is 1g:(3-50)mL.
2. The method for preparing the modified lithium iron phosphate-based cathode material according to claim 1, characterized in that, The dispersion is one or a combination of stirring dispersion and ultrasonic dispersion.
3. The method for preparing the modified lithium iron phosphate-based cathode material according to claim 1, characterized in that, The washing process consists of one or a combination of deionized water washing and ethanol washing, and the number of washing cycles is 1-2; the drying process is to dry in an air-atmosphere forced-air drying oven at 50-100℃ for 30 min-24 h.
4. A modified lithium iron phosphate-based cathode material prepared by the preparation method according to any one of claims 1-3.
5. The modified lithium iron phosphate-based cathode material according to claim 4, characterized in that, The modified lithium iron phosphate-based cathode material has a particle size of 50-500 nm, a tap density of 2.0-5.0 g / cc, and a specific surface area of 10-40 m². 2 / g.
6. The application of a modified lithium iron phosphate-based cathode material according to claim 4 or 5 in lithium-ion batteries, lithium metal batteries, solid-state batteries, and lithium secondary batteries.