Lithium iron phosphate cathode materials, their preparation methods and applications

Abstract

This invention relates to the field of lithium-ion battery cathode materials, and discloses a lithium iron phosphate cathode material, its preparation method, and its applications. The lithium iron phosphate cathode material includes a matrix and Li₂O₃ sequentially coated on the surface of the matrix. 0.53 WO3 coating and carbon coating; wherein the matrix has the composition shown in Formula I: LiFe b W c Ti d Formula I for PO4; in Formula I, 0.95≤b≤0.99, 0.005≤c≤0.04, 0.001≤d≤0.02, b+c+d=1; based on the total weight of the lithium iron phosphate cathode material, the content of the matrix is ​​95-98.7wt%, and the Li 0.53 The WO3 content is 0.3-3 wt%, and the carbon coating content is 1-2 wt%. The lithium iron phosphate cathode material provided by this invention has a small grain size, and when applied to lithium-ion batteries, it has the advantages of good electrochemical performance and excellent rate performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode materials, specifically to lithium iron phosphate cathode materials, their preparation methods, and applications. Background Technology

[0002] In recent years, with the advancement of new power system construction, electrochemical energy storage stations have been widely used. Lithium iron phosphate (LiFePO4) batteries have broad application prospects due to their low cost and high safety. The cathode material is one of the key components of a battery, often determining its performance and cost. Lithium iron phosphate (LiFePO4) batteries use lithium iron phosphate as the cathode material, which has advantages such as low cost, long cycle life, and high safety. However, LiFePO4 still suffers from poor rate performance, hindering its application in energy storage.

[0003] Nanoparticle size reduction is one of the effective methods to improve rate performance by shortening the lithium-ion transport path through reducing the primary particle size. However, the preparation of nanoparticles typically requires processes such as hydrothermal, solvothermal, reflux, or sol-gel methods. These processes all require organometallic salts or organic solvents and are usually carried out at high temperatures or high pressures, placing high demands on equipment and resulting in significant investment costs. The production of LiFePO4 from the precursor FePO4 is simple and requires less equipment investment, making it the mainstream method for producing lithium iron phosphate. However, lithium iron phosphate inherits the particle size and morphology of iron phosphate, and the grains tend to grow during sintering and lithiation, making it difficult to suppress grain growth. Consequently, the rate performance of the resulting lithium iron phosphate is inferior to that of nano-sized lithium iron phosphate produced by hydrothermal methods. For example, CN 109650366A discloses a lithium iron phosphate and its preparation method. This method uses a mixture of low iron-to-phosphorus ratio iron phosphate and high iron-to-phosphorus ratio iron phosphate as iron phosphate raw materials. The lithium iron phosphate prepared in this way has a high specific capacity and the battery electrode has a high compaction density. The preparation method is simple, but the lithium iron phosphate cathode material prepared by this method has large grains, which is not conducive to the high-rate discharge of lithium iron phosphate.

[0004] Therefore, exploring a method to suppress grain growth and improve rate performance in the process of producing lithium iron phosphate from iron phosphate is of great significance for promoting the application and popularization of lithium iron phosphate. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem of poor rate performance of lithium iron phosphate cathode materials in the prior art.

[0006] To achieve the above objectives, a first aspect of the present invention provides a lithium iron phosphate cathode material, the lithium iron phosphate cathode material comprising a matrix and Li₂S₃ sequentially coated on the surface of the matrix. 0.53 WO3 coating and carbon coating;

[0007] The matrix has the composition shown in Formula I: LiFe b W c Ti d PO4 Form I;

[0008] In Equation I, 0.95≤b≤0.99, 0.005≤c≤0.04, 0.001≤d≤0.02, b+c+d=1;

[0009] Based on the total weight of the lithium iron phosphate cathode material, the matrix content is 95-98.7 wt%, and the Li... 0.53 The WO3 content is 0.3-3 wt%, and the carbon coating content is 1-2 wt%.

[0010] A second aspect of the present invention provides a method for preparing lithium iron phosphate cathode material, the method comprising the following steps:

[0011] (1) In the presence of a solvent, iron phosphate, lithium source, carbon source, tungsten source and titanium source are contacted and mixed to obtain a mixed solution;

[0012] (2) The mixed solution is spray-dried to obtain the precursor;

[0013] (3) The precursor is calcined in an inert atmosphere;

[0014] In step (1), the amount of iron phosphate (calculated as P) and the amount of lithium source (calculated as Li) are the same; the molar ratio of iron phosphate (calculated as P), iron phosphate (calculated as Fe), carbon source (calculated as C), tungsten source (calculated as W), and titanium source (calculated as Ti) is 1:0.95-0.99:0.3-1:0.005-0.04:0.001-0.02.

[0015] In step (3), the calcination conditions include: a heating rate of 2-10℃ / min, a temperature of 600-800℃, and a time of 4-20h.

[0016] During their research, the inventors of this invention discovered that by specifically selecting iron phosphate, lithium source, carbon source, tungsten source, and titanium source as raw materials, and simultaneously controlling the molar ratio of each raw material and the reaction conditions, combined with other technical features, a lithium iron phosphate cathode material was prepared comprising a matrix and Li₂S₃ ... 0.53 The WO3 coating and carbon coating further refine the grain size of the lithium iron phosphate cathode material, broaden the lithium-ion transport channels, and effectively improve the rate performance of the lithium iron phosphate cathode material.

[0017] A third aspect of the present invention provides a lithium iron phosphate cathode material prepared by the method described in the second aspect.

[0018] A fourth aspect of the present invention provides the application of lithium iron phosphate cathode material as described in the first or third aspect in lithium-ion batteries.

[0019] The present invention has the following advantages through the above technical solution:

[0020] (1) The lithium iron phosphate cathode material provided by the present invention includes a matrix and Li₂S₃S ... 0.53 With WO3 and carbon coating layers, this lithium iron phosphate cathode material not only ensures good electrochemical performance but also has excellent rate performance.

[0021] (2) The method for preparing lithium iron phosphate cathode material provided by the present invention refines the grains of lithium iron phosphate, broadens the lithium ion transport channels, and effectively improves the rate performance of lithium iron phosphate cathode material.

[0022] (3) The method for preparing lithium iron phosphate cathode material provided by the present invention is simple, easy to implement, low in cost and highly reproducible. Attached Figure Description

[0023] Figure 1 This is the XRD pattern of the lithium iron phosphate cathode material prepared in Example 1 of this invention;

[0024] Figure 2 This is the XRD pattern of the lithium iron phosphate cathode material prepared in Comparative Example 1 of this invention;

[0025] Figure 3 These are the normalized XRD patterns of the (311) characteristic peaks of the lithium iron phosphate cathode materials prepared in Example 1 and Comparative Example 1 of this invention;

[0026] Figure 4 These are magnified XRD patterns of the lithium iron phosphate cathode materials prepared in Example 1 of the present invention and Comparative Examples 1, 2 and 3.

[0027] Figure 5 This is a scanning electron microscope image of the lithium iron phosphate cathode material prepared in Example 1 of the present invention;

[0028] Figure 6 This is a scanning electron microscope image of the lithium iron phosphate cathode material prepared in Comparative Example 1 of this invention;

[0029] Figure 7 This is an EDS mapping test image of the lithium iron phosphate cathode material prepared in Example 1 of the present invention;

[0030] Figure 8This is an EDS mapping test image of the lithium iron phosphate cathode material prepared in Comparative Example 3 of this invention.

[0031] Figure 9 These are charge-discharge curves of lithium-ion batteries in Application Example 1 and Comparative Application Example 1 of the present invention at a rate of 0.1C.

[0032] Figure 10 These are discharge specific capacity diagrams of lithium-ion batteries of Application Example 1, Comparative Application Example 1, Comparative Application Example 2 and Comparative Application Example 3 of the present invention at different discharge rates;

[0033] Figure 11 This is a graph showing the discharge specific capacity retention rate of lithium-ion batteries in Application Example 1 and Comparative Application Example 1 at a 1C rate.

[0034] Figure 12 This is a graph showing the energy density retention rate of lithium-ion batteries in Application Example 1 and Comparative Application Example 1 at a 1C rate. Detailed Implementation

[0035] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0036] As previously described, a first aspect of the present invention provides a lithium iron phosphate cathode material, the lithium iron phosphate cathode material comprising a matrix and Li₂S₃ sequentially coated on the surface of the matrix. 0.53 WO3 coating and carbon coating;

[0037] The matrix has the composition shown in Formula I: LiFe b W c Ti d PO4 Form I;

[0038] In Equation I, 0.95≤b≤0.99, 0.005≤c≤0.04, 0.001≤d≤0.02, b+c+d=1;

[0039] Based on the total weight of the lithium iron phosphate cathode material, the matrix content is 95-98.7 wt%, and the Li... 0.53 The WO3 content is 0.3-3 wt%, and the carbon coating content is 1-2 wt%.

[0040] In this invention, the grain size of the cathode material was obtained by measuring parameters using a Smart-lab XRD-X-ray powder diffractometer from Rigaku, Japan, and then refined by XRD using the Scherrer equation. The test conditions were as follows: voltage 40kV, current 40mA, step size 0.01°, height limit slit 10mm, divergence slit 1°, anti-scattering slit 1mm, receiving slit open, test scan 2θ angle set to 5°-80°, continuous scanning in 1D mode, scan speed 5° / min.

[0041] The grain size is calculated using the Scherrer formula, as shown below:

[0042]

[0043] Where D is the grain size, K is the Scherrer constant, λ is the X-ray wavelength, and LX is the grain broadening peak shape function parameter of the refined Lorenntzian equation.

[0044] According to some embodiments of the present invention, preferably, the grain size of the lithium iron phosphate cathode material is 100-600 nm, more preferably 200-400 nm.

[0045] According to some embodiments of the present invention, preferably, based on the total weight of the lithium iron phosphate cathode material, the content of the matrix is ​​96.5-98.2 wt%, and the Li... 0.53 The WO3 content is 0.3-2.4 wt%, and the carbon coating content is 1.2-1.7 wt%. More preferably, based on the total weight of the lithium iron phosphate cathode material, the matrix content is 97-98.7 wt%, and the Li... 0.53 The WO3 content is 0.3-1 wt%, and the carbon coating content is 1-2 wt%.

[0046] As mentioned above, a second aspect of the present invention provides a method for preparing lithium iron phosphate cathode materials, the method comprising the following steps:

[0047] (1) In the presence of a solvent, iron phosphate, lithium source, carbon source, tungsten source and titanium source are contacted and mixed to obtain a mixed solution;

[0048] (2) The mixed solution is spray-dried to obtain the precursor;

[0049] (3) The precursor is calcined in an inert atmosphere;

[0050] In step (1), the amount of iron phosphate (calculated as P) is the same as the amount of lithium source (calculated as Li); the molar ratio of iron phosphate (calculated as P), iron phosphate (calculated as Fe), carbon source (calculated as C), tungsten source (calculated as W), and titanium source (calculated as Ti) is 1:0.95-0.99:0.3-1:0.005-0.04:0.001-0.02.

[0051] In step (3), the calcination conditions include: a heating rate of 2-10℃ / min, a temperature of 600-800℃, and a time of 4-20h.

[0052] The method for preparing the lithium iron phosphate cathode material provided by this invention is simple, easy to implement, low in cost, and highly reproducible.

[0053] The inventors discovered that by designing and using iron phosphate, lithium, carbon, tungsten, and titanium sources as raw materials, while controlling other conditions, a lithium iron phosphate cathode material can be prepared that solves the problem of poor rate performance of lithium iron phosphate cathode materials grown from iron phosphate. Analysis revealed that this is due to the presence of W in the tungsten source. 6+ Ti in titanium source 4+ The doping of high-valence elements introduces cation defects into the crystal lattice, increasing the vacancy concentration and improving rate performance. Additionally, W... 6+ and Ti 4+ The charge is larger and the radius is larger than that of Fe. 2+ The smaller size of the lithium ions creates an electrostatic repulsion force on them, while simultaneously widening the transport channels and accelerating the outward migration of lithium ions.

[0054] The inventors further discovered that, through the preparation method provided by this invention, a small portion of W is reduced by C during the preparation process, resulting in Li. 0.53 The WO3 coating on the particle surface forms a thin film of several nm at the grain boundaries, which inhibits grain growth during sintering; moreover, this film is a fast electron conductor, which enhances electron transport between lithium iron phosphate grains.

[0055] The inventors continued their research and discovered that too little carbon content would not improve electronic conductivity, while too much carbon content would result in a loss of specific capacity and reduced compaction; too many dopants would hinder lithium-ion transport, while too few would not have any effect on improvement.

[0056] According to some embodiments of the present invention, preferably, in step (1), the solvent is deionized water.

[0057] According to some embodiments of the present invention, preferably, in step (1), the amount of solvent added satisfies the following condition: the concentration of Fe element in the mixed solution is 0.01-0.08 mol / L, preferably 0.02-0.06 mol / L. The above preferred embodiments are more conducive to obtaining lithium iron phosphate cathode materials with suitable grain size.

[0058] According to some embodiments of the present invention, preferably, the particle size D of the ferric phosphate is... 50 The grain size is 0.5-2 μm, more preferably 0.8-1.5 μm. Using the above-described preferred embodiments is more advantageous for obtaining lithium iron phosphate cathode materials with suitable grain sizes.

[0059] In this invention, D 50 This refers to the particle size at which the cumulative particle size distribution of lithium iron phosphate cathode material reaches 50%, as measured by the Mastersizer3000 laser particle size analyzer. In other words, particles smaller than (or larger than) this particle size account for 50%.

[0060] According to some embodiments of the present invention, preferably, in step (1), the molar ratio of the iron phosphate (calculated as P), the iron phosphate (calculated as Fe), the carbon source (calculated as C), the tungsten source (calculated as W), and the titanium source (calculated as Ti) is 1:0.97-0.99:0.3-0.6:0.005-0.02:0.001-0.01. Using the above preferred embodiments is more conducive to improving electronic conductivity, avoiding loss of specific capacity, reducing compaction, widening the lithium-ion transport channel, and more effectively improving the rate performance of the lithium iron phosphate cathode material.

[0061] According to some embodiments of the present invention, preferably, the contact mixing conditions include: a temperature of 50-90°C and a time of 15-120 min. More preferably, the contact mixing conditions include: a temperature of 60-80°C and a time of 15-60 min.

[0062] In this invention, there is no particular limitation on the type of lithium source. Conventional lithium sources in the art can be used. For example, in step (1), the lithium source is selected from at least one of lithium hydroxide, lithium carbonate and lithium acetate, more preferably lithium acetate and / or lithium hydroxide.

[0063] In this invention, there is no particular limitation on the type of carbon source. Conventional carbon sources in the art can be used. For example, in step (1), the carbon source is selected from at least one of polyethylene glycol, glucose, sucrose, fructose, citric acid, oxalic acid and ascorbic acid, and more preferably at least one of polyethylene glycol, glucose and sucrose.

[0064] According to some embodiments of the present invention, preferably, in step (1), the tungsten source is selected from ammonium paratungstate and / or ammonium tungstate, more preferably ammonium paratungstate.

[0065] According to some embodiments of the present invention, preferably, in step (1), the titanium source is selected from tetrabutyl titanate and / or titanium dioxide, more preferably titanium dioxide.

[0066] The above-described preferred embodiments are beneficial for forming a more uniform carbon coating layer and lattice doping.

[0067] According to some embodiments of the present invention, preferably, in step (2), the spray drying conditions include: a feed rate of 300-2000 mL / h and an inlet air temperature of 200-300°C. More preferably, the spray drying conditions include: a feed rate of 400-1500 mL / h and an inlet air temperature of 220-300°C. Using the above preferred embodiments is beneficial for forming lithium iron phosphate cathode materials with smaller particles and more uniform composition, and can prevent powder particles from sticking to the wall, thereby further improving the yield of the cathode material.

[0068] In this invention, there are no particular limitations on the inert atmosphere in step (3). For example, the inert atmosphere is selected from nitrogen and / or argon, preferably argon. The above-described preferred embodiment is more conducive to reducing production costs.

[0069] According to some embodiments of the present invention, preferably, in step (3), the calcination conditions include: a heating rate of 3-5℃ / min, a temperature of 680-750℃, and a time of 8-12h. Adopting the above preferred embodiments is beneficial for further reducing energy consumption, shortening production time, and obtaining lithium iron phosphate cathode materials with better rate performance and purer and more uniform phases.

[0070] As previously described, a third aspect of the present invention provides a lithium iron phosphate cathode material prepared by the method described in the second aspect. The lithium iron phosphate cathode material is the same as or similar to the lithium iron phosphate cathode material provided in the first aspect of the present invention, and will not be described again here.

[0071] According to some embodiments of the present invention, the lithium iron phosphate cathode material has the advantages of small grain size and excellent rate performance while ensuring other electrochemical properties.

[0072] As previously described, a fourth aspect of the present invention provides the application of lithium iron phosphate cathode material as described in the first or third aspect in lithium-ion batteries.

[0073] According to some embodiments of the present invention, when the lithium iron phosphate cathode material is applied to a lithium-ion battery, it has the advantage of excellent rate performance while ensuring good electrochemical performance.

[0074] The present invention will be described in detail below through examples.

[0075] Unless otherwise specified, the raw materials and equipment used in the following examples are all commercially available products.

[0076] In the following examples, the relevant characteristic parameters were measured using the following methods:

[0077] (1) The content of each element in the lithium iron phosphate cathode material: The content was obtained by testing with an Agilent Technologies 5800 ICP-OES spectrometer.

[0078] (2) Li in lithium iron phosphate cathode materials 0.53 WO3 content: The spectral density was determined using a Rietveld Smart-lab XRD powder diffractometer (Japan). The WO3 content was then refined using Rietveld (by fitting the original data mathematically and calculating the spectral density). 0.53 WO3 content.

[0079] (3) The content of carbon coating in lithium iron phosphate cathode material: The content was obtained by testing with a Cynes HCS-800 infrared carbon-sulfur analyzer.

[0080] (4) Physicochemical properties such as grain size of lithium iron phosphate cathode material: The test was conducted using a Smart-lab XRD-X-ray powder diffractometer from Rigaku, Japan. The test conditions were as follows: voltage 40kV, current 40mA, step size 0.01°, height limit slit 10mm, divergence slit 1°, anti-scattering slit 1mm, receiving slit open, test scanning 2θ angle set to 5°-80°, continuous scanning in 1D mode, scanning speed 5° / min;

[0081] The grain size is calculated using the Scherrer formula, as shown below:

[0082]

[0083] Where D is the grain size, K is the Scherrer constant, λ is the X-ray wavelength, and LX is the grain broadening peak shape function parameter of the refined Lorenntzian equation.

[0084] (5) Morphology of lithium iron phosphate cathode material: The morphology was obtained by scanning electron microscope (SEM) of JSM-7900F model of Nippon Electronics Co., Ltd.

[0085] (6) Elemental distribution of lithium iron phosphate cathode material: obtained by EDS mapping test using Oxford SDD EDS 65mm2 model from Oxford Instruments, UK.

[0086] (7) Specific capacity of lithium iron phosphate cathode material: The specific capacity of the battery was obtained by charging and discharging test using a 3001A model charge and discharge instrument from Wuhan Landian Electronics Co., Ltd.

[0087] In the following examples, unless otherwise specified, the amount of ferric phosphate used in each example is 3g.

[0088] Example 1

[0089] (1) In the presence of a solvent (deionized water), iron phosphate, lithium source, carbon source, tungsten source and titanium source are contacted and mixed to dissolve completely to obtain a mixed solution;

[0090] (2) The above mixed solution was spray-dried to obtain the precursor;

[0091] (3) The above precursor was placed in an inert atmosphere (argon) in a tube furnace for calcination, and then cooled naturally with the furnace to obtain lithium iron phosphate cathode material S1. The corresponding characteristic parameters are shown in Table 1.

[0092] The raw material ratios and specific process conditions are shown in Table 1.

[0093] Examples 2-6

[0094] Using the same method as in Example 1, with the differences shown in Table 1, the rest were the same, and lithium iron phosphate cathode materials S2-S6 were obtained.

[0095] Comparative Examples 1-3

[0096] Using the same method as in Example 1, with the differences shown in Table 1, the rest were the same, and lithium iron phosphate cathode materials DS1-DS3 were obtained.

[0097] Table 1

[0098]

[0099] Note: Molar ratio 1 The molar ratio of the iron phosphate (calculated as P), the iron phosphate (calculated as Fe), the carbon source (calculated as C), the tungsten source (calculated as W), and the titanium source (calculated as Ti); particle size D 50 The particle size D of ferric phosphate 50 .

[0100] Table 1 (continued)

[0101]

[0102] Note: Molar ratio 1 The molar ratio of the iron phosphate (calculated as P), the iron phosphate (calculated as Fe), the carbon source (calculated as C), the tungsten source (calculated as W), and the titanium source (calculated as Ti); particle size D 50 The particle size D of ferric phosphate 50 .

[0103] Test case

[0104] The performance of the lithium iron phosphate cathode materials prepared in the examples was tested, including: crystallinity, microstructure, elemental distribution, material composition, and grain size. The test results for material composition and grain size are shown in Table 2.

[0105] The present invention provides, by way of example, the XRD pattern of the lithium iron phosphate cathode material prepared in Example 1, as shown below. Figure 1 As shown, the Bragg peak refers to the standard card for lithium iron phosphate; the XRD pattern of the lithium iron phosphate cathode material prepared in Comparative Example 1 is shown below. Figure 2 As shown, the Bragg peak refers to the standard card for lithium iron phosphate; the normalized XRD patterns of the (311) characteristic peak of the lithium iron phosphate cathode materials prepared in Example 1 and Comparative Example 1 are shown below. Figure 3 As shown; magnified XRD patterns of the lithium iron phosphate cathode materials prepared in Example 1 and Comparative Examples 1, 2, and 3, as shown. Figure 4 As shown.

[0106] Depend on Figure 1 It can be seen that the XRD pattern of the lithium iron phosphate cathode material prepared in Example 1 corresponds one-to-one with the standard card of lithium iron phosphate, indicating that the synthesized cathode material is indeed lithium iron phosphate. (Refinement reliability factor R) wp =3.3%, indicating that the fitted result is good and the result is reliable.

[0107] Depend on Figure 2 It can be seen that the XRD pattern of the lithium iron phosphate cathode material prepared in Comparative Example 1 corresponds one-to-one with the standard card of lithium iron phosphate, indicating that the synthesized material is indeed a lithium iron phosphate cathode material. (Refinement confidence factor R) wp =4.0%, indicating that the fitted result is good and the result is reliable.

[0108] Depend on Figure 3 It can be seen that the lithium iron phosphate cathode material prepared in Example 1 has a smaller half-width than that prepared in Comparative Example 1, indicating that the lithium iron phosphate cathode material prepared in Example 1 has a smaller grain size than that prepared in Comparative Example 1.

[0109] Depend on Figure 4 It can be seen that the lithium iron phosphate cathode material prepared in Example 1 has Li 0.53The structure of WO3 is present, while the lithium iron phosphate cathode materials prepared in Comparative Examples 1, 2, and 3 do not possess the Li3 structure. 0.53 The structure of WO3.

[0110] The present invention provides, by way of example, a scanning electron microscope image of the lithium iron phosphate cathode material prepared in Example 1, as shown below. Figure 5 As shown, where Figure 5 (b) is Figure 5 Enlarged view of (a); Scanning electron microscope image of the lithium iron phosphate cathode material prepared in Comparative Example 1, as shown. Figure 6 As shown, where Figure 6 (b) is Figure 6 Enlarged view of (a) in the middle.

[0111] Compare Figure 5 and Figure 6 It can be seen that the lithium iron phosphate cathode material prepared in Example 1 has a similar morphology to the lithium iron phosphate cathode material prepared in Comparative Example 1, but the particles of the lithium iron phosphate cathode material prepared in Example 1 are finer than those of the lithium iron phosphate cathode material prepared in Comparative Example 1.

[0112] The present invention provides, exemplarily, an EDS mapping test image of the lithium iron phosphate cathode material prepared in Example 1, as shown below. Figure 7 As shown; where, Figure 7 Image (a) shows the overall EDS mapping of the lithium iron phosphate cathode material prepared in Example 1. Figure 7 (b), (c), (d), (e) and (f) are EDS mapping test diagrams of each element in the lithium iron phosphate cathode material prepared in Example 1;

[0113] The EDS mapping test image of the lithium iron phosphate cathode material prepared in Comparative Example 3 is shown below. Figure 8 As shown; where, Figure 8 (a) shows the overall EDS mapping test result of the lithium iron phosphate cathode material prepared in Comparative Example 3. Figure 8 Figures (b), (c), and (d) show the EDS mapping results of each element in the lithium iron phosphate cathode material prepared in Comparative Example 3.

[0114] After comparison Figure 7 and Figure 8 It can be seen that W and Ti were successfully doped into the crystal lattice.

[0115] Table 2

[0116]

[0117] Application Example 1

[0118] (1) Preparation of button cell: According to the mass ratio (active material: conductive agent: binder = 8:1:1), 0.08g of lithium iron phosphate positive electrode material prepared in Example 1 above was weighed as active material, 0.01g of acetylene black as conductive agent, and 0.01g of polyvinylidene fluoride as binder. The above three materials were placed in a mortar and mixed. After mixing evenly, 0.5 mL of N-methylpyrrolidone was added as dispersant. After mixing again, it was coated on aluminum foil to form a positive electrode sheet. In a glove box under an inert protective atmosphere (argon), a CR2032 button cell was assembled with sodium metal as negative electrode. After standing for 12 hours, lithium-ion battery Y1 was obtained.

[0119] (2) Electrochemical performance test: The charge and discharge voltage range was set to 2.0-4.6V, and the specific capacity of the assembled lithium-ion battery was tested at rates of 0.1C, 0.2C, 5C and 10C respectively.

[0120] Comparative Application Examples 1-3

[0121] (1) Preparation of button cells: Following the method of the application example, except that the lithium iron phosphate cathode materials prepared by Comparative Example 1, Comparative Example 2 and Comparative Example 3 were used for the assembly of button cells, and lithium-ion batteries DY1, DY2 and DY3 were obtained respectively.

[0122] (2) Electrochemical performance test: Same as in application example 1.

[0123] The present invention provides, exemplarily, charge-discharge curves of lithium-ion batteries in Application Example 1 and Comparative Application Example 1 at a 0.1C rate, as follows: Figure 9 As shown; discharge specific capacity graphs of lithium-ion batteries in Application Example 1, Comparative Application Example 1, Comparative Application Example 2, and Comparative Application Example 3 at different discharge rates, as shown. Figure 10 As shown; the discharge specific capacity retention rate of lithium-ion batteries in Application Example 1 and Comparative Application Example 1 at a 1C rate is illustrated in the graph. Figure 11 As shown; the energy density retention rate of the lithium-ion batteries in Application Example 1 and Comparative Application Example 1 at 1C rate is illustrated in the graph. Figure 12 As shown.

[0124] Depend on Figure 9 It can be seen that the lithium-ion battery in Application Example 1 has a higher discharge specific capacity than that in Comparative Application Example 1, indicating that its ion and electron transport is faster.

[0125] Depend on Figure 10 It can be seen that the lithium-ion battery in Application Example 1 has a discharge specific capacity of 160.7 mAh·g at a 0.2C rate. -1 The discharge specific capacity at a 5C rate is 132.50 mAh·g. -1 The discharge specific capacity at a 10C rate is 117.04 mAh·g.-1 The lithium-ion battery in Comparative Application Example 3 has a discharge specific capacity of 154.9 mAh·g at a 0.2C rate. -1 The discharge specific capacity at a 5C rate is 127.1 mAh·g. -1 The discharge specific capacity at a 10C rate is 106.1 mAh·g. -1 The lithium-ion battery in Comparative Application Example 2 has a discharge specific capacity of 155.3 mAh·g at a 0.2C rate. -1 The discharge specific capacity at a 5C rate is 123.3 mAh·g. -1 The discharge specific capacity at a 10C rate is 100.8 mAh·g. -1 The lithium-ion battery in Comparative Application Example 1 has a discharge specific capacity of 157.8 mAh·g at a 0.2C rate. -1 The discharge specific capacity at a 5C rate is 115.3 mAh·g. -1 The discharge specific capacity at a 10C rate is 95.3 mAh·g. -1 The comparison demonstrates that the lithium iron phosphate cathode material provided by this invention exhibits excellent discharge specific capacity and rate performance when applied to lithium-ion batteries.

[0126] Depend on Figure 11 and Figure 12 It is known that the lithium iron phosphate cathode material provided by the present invention can maintain good energy retention and capacity retention when applied to lithium-ion batteries.

[0127] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A lithium iron phosphate cathode material, characterized in that, The lithium iron phosphate cathode material includes a matrix and Li₂ atoms sequentially coated on the surface of the matrix. 0.53 WO3 coating and carbon coating; The matrix has the composition shown in Formula I: LiFe b W c Ti d PO4 Form I; In Equation I, 0.95≤b≤0.99, 0.005≤c≤0.04, 0.001≤d≤0.02, b+c+d=1; Based on the total weight of the lithium iron phosphate cathode material, the matrix content is 95-98.7 wt%, and the Li... 0.53 The WO3 coating content is 0.3-3 wt%, and the carbon coating content is 1-2 wt%.

2. The lithium iron phosphate cathode material according to claim 1, wherein, The grain size of the lithium iron phosphate cathode material is 100-600 nm; And / or, based on the total weight of the lithium iron phosphate cathode material, the content of the matrix is ​​96.5-98.2 wt%, and the Li... 0.53 The content of WO3 is 0.3-2.4 wt%, and the content of the carbon coating layer is 1.2-1.7 wt%.

3. A method for preparing the lithium iron phosphate cathode material according to claim 1 or 2, characterized in that, The method includes the following steps: (1) In the presence of a solvent, iron phosphate, lithium source, carbon source, tungsten source and titanium source are contacted and mixed to obtain a mixed solution; (2) The mixed solution is spray-dried to obtain the precursor; (3) The precursor is calcined in an inert atmosphere; In step (1), the amount of iron phosphate (calculated as P) and the amount of lithium source (calculated as Li) are the same; the molar ratio of iron phosphate (calculated as P), iron phosphate (calculated as Fe), carbon source (calculated as C), tungsten source (calculated as W), and titanium source (calculated as Ti) is 1:0.95-0.99:0.3-1:0.005-0.04:0.001-0.

02. In step (3), the calcination conditions include: a heating rate of 2-10℃ / min, a temperature of 600-800℃, and a time of 4-20h.

4. The method according to claim 3, wherein, In step (1), the amount of solvent added satisfies the following condition: the concentration of Fe element in the mixed solution is 0.01-0.08 mol / L; And / or, the particle size D of the iron phosphate 50 It ranges from 0.5 to 2 μm.

5. The method according to claim 3, wherein, In step (1), the molar ratio of the iron phosphate (calculated as P), the iron phosphate (calculated as Fe), the carbon source (calculated as C), the tungsten source (calculated as W), and the titanium source (calculated as Ti) is 1:0.97-0.99:0.3-0.6:0.005-0.02:0.001-0.01; And / or, the conditions for contact mixing include: a temperature of 50-90°C and a time of 15-120 min.

6. The method according to any one of claims 3-5, wherein, In step (1), the lithium source is selected from at least one of lithium hydroxide, lithium carbonate, and lithium acetate; And / or, the carbon source is selected from at least one of polyethylene glycol, glucose, sucrose, fructose, citric acid, oxalic acid and ascorbic acid; And / or, the tungsten source is selected from ammonium paratungstate and / or ammonium tungstate; And / or, the titanium source is selected from tetrabutyl titanate and / or titanium dioxide.

7. The method according to any one of claims 3-5, wherein, In step (2), the conditions for spray drying include: a feed rate of 300-2000 mL / h and an air inlet temperature of 200-300°C.

8. The method according to any one of claims 3-5, wherein, In step (3), the calcination conditions include: a heating rate of 3-5℃ / min, a temperature of 680-750℃, and a time of 8-12h.

9. The application of the lithium iron phosphate cathode material as described in claim 1 or 2 in lithium-ion batteries.

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