Lithium iron phosphate material, preparation method thereof and lithium ion battery

Abstract

The application relates to the field of lithium ion batteries, and discloses a lithium iron phosphate material, a preparation method thereof and a lithium ion battery. The lattice distortion of the lithium iron phosphate material is 0.058%-0.08%. The lithium iron phosphate has excellent ion migration rate and diffusion coefficient, so that the lithium iron phosphate material has better electrochemical performance; and the prepared lithium ion battery has excellent discharge flux, and still has better discharge capacity in a low-temperature environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a lithium iron phosphate material, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have attracted much attention due to their high theoretical capacity (170 mAh / g), good stability, high safety, environmental friendliness and other advantages, and have been widely used in energy storage, electric tools, electric vehicles, aerospace and other fields. As a key to further improve the performance of the battery, the quality of the positive electrode material directly affects the various performance indicators of the lithium battery. Lithium iron phosphate positive electrode material has become one of the main positive electrode materials currently applied due to its high safety, long cycle life, low cost, wide raw material sources, environmental friendliness and other advantages. However, poor electronic and ionic conductivity is a bottleneck that limits the further application of lithium iron phosphate positive electrode material.

[0003] As a power battery positive electrode material for practical application, poor electronic and ionic conductivity makes lithium iron phosphate (LFP) have a lot of research space in improving the rate performance and prolonging the low-temperature life.

[0004] The low-temperature performance of lithium iron phosphate can be improved by carbon-coated modification. The thickness and uniformity of the carbon coating are also important factors affecting the performance of the composite material. Therefore, finding high-performance and low-cost carbon materials and studying carbon doping and coating uniformity are still key issues that determine whether the positive electrode material can achieve the expected performance. CN112694078A discloses a graphene-coated lithium iron phosphate composite material and a preparation method thereof. Since the cost of graphene is high and the method requires ultrasonic dispersion, the production cost will increase in industrial application, which is not conducive to mass production. CN107359336A discloses a lithium iron phosphate preparation method. In this method, the iron source, phosphorus source, lithium source and carbon source are mixed, calcined, ground, dried and then calcined again to obtain lithium iron phosphate. However, this method is not easy to control and has high production cost, which is not conducive to industrial production.

[0005] The good conductivity of metal can improve the transport of lithium ions on the surface of the material, effectively improve the cycle efficiency, alleviate the capacity decay at high temperature, reduce the electrochemical impedance and improve the electrochemical performance of LFP material. However, the overall impact of metal element doping on the structural stability of LFP is still uncertain, although it is of great significance to the safety and stability of the electrode material and the overall battery. However, before further large-scale application, the impact of doping on the stability of LFP must be fully studied. CN111498825A uses a hydrothermal method to dope titanium tetrachloride into lithium iron phosphate, obtaining high-density lithium iron phosphate. However, this method increases the production cost and is not conducive to commercial application. Therefore, a technical solution is needed to solve one of the above problems. SUMMARY

[0006] The present application aims to overcome the poor structural stability of lithium iron phosphate, which leads to poor rate capability and poor low-temperature performance of the positive electrode material, and provides a lithium iron phosphate material, a preparation method thereof and a lithium ion battery, wherein the lattice distortion of the lithium iron phosphate material is 0.058%-0.08%, and the lithium iron phosphate positive electrode material with uniform particle distribution, low powder impedance, good rate capability and good low-temperature performance can be prepared.

[0007] To achieve the above-mentioned purpose, the present application provides a lithium iron phosphate material in the first aspect, wherein the lattice distortion of the lithium iron phosphate material measured by XRD is 0.058%-0.08%.

[0008] The present application provides a method for preparing the above-mentioned lithium iron phosphate material in the second aspect, wherein the method comprises:

[0009] (1) mixing iron phosphate, a lithium source, an optional carbon source, an M source and an M' source with water to obtain slurry A;

[0010] (2) grinding the slurry A to obtain slurry B containing process product I;

[0011] (3) drying the slurry B to obtain process product II;

[0012] (4) sintering and crushing the process product II to obtain the lithium iron phosphate material;

[0013] wherein the M source and the M' source are each independently selected from a compound containing at least one element selected from Ti, Na, K, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd, and the M source and the M' source are different;

[0014] The median particle size of the M source and the M' source each independently satisfies 0.5µm≤D 50 ≤5µm.

[0015] The present application provides a lithium ion battery in the third aspect, wherein the lithium ion battery comprises the above-mentioned lithium iron phosphate material.

[0016] The lithium iron phosphate material, the preparation method thereof and the lithium ion battery provided by the above-mentioned technical solution have the following beneficial effects.

[0017] The lattice distortion of the lithium iron phosphate material of the present application is 0.058%-0.08%, and the lithium iron phosphate has excellent ion mobility and diffusion coefficient, so that the lithium iron phosphate material has better electrochemical performance; the lithium ion battery prepared has excellent discharge flux, and still has good discharge capacity in a low-temperature environment.

[0018] The present application controls the grinding particle size of the process product so that the lattice distortion is within a suitable range by simultaneously adding M sources and M' sources with specific median particle sizes to the reaction system. The specific multi-element co-doping can produce a synergistic effect, on the one hand, enhancing the lithium ion and electron transport capacity of the lithium iron phosphate material, and on the other hand, effectively improving the compaction density of the lithium iron phosphate material, having the characteristics of small primary particle size and uniform particles, effectively improving the problems of low electronic conductivity and ion mobility of the material. Thus, the capacity and rate performance of the lithium ion battery are improved. The present method is simple to operate, has low energy consumption, and is easy to industrialize. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is the charge-discharge curve of the lithium ion battery made of the lithium iron phosphate material of Example 1 and Comparative Example 1.

[0020] Figure 2 is the SEM image of the lithium iron phosphate material of Example 3. DETAILED DESCRIPTION

[0021] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges and values should be construed to be approximations that allow for significant error and variations. The endpoints of the ranges and values are not to be understood as being limited to the precise values stated. The ranges and values are understood to be approximate and are inclusive of values near the stated values. The endpoints of the ranges of values are not to be understood as being limited to the precise values stated. The ranges and values are understood to be approximate and are inclusive of values near the stated values.

[0022] The present application provides a lithium iron phosphate material, wherein the lattice distortion of the lithium iron phosphate material is 0.058%-0.08%.

[0023] The lattice distortion of the lithium iron phosphate material of the present application is 0.058%-0.08%, and the lithium iron phosphate has excellent ion mobility and diffusion coefficient, so that the lithium iron phosphate material has better electrochemical performance. The lithium ion battery prepared has excellent discharge flux, and still has good discharge capacity in a low temperature environment.

[0024] In the present application, the lattice distortion reflects the degree of lattice distortion caused by micro-stress in the lithium iron phosphate material crystal, the reverse arrangement of part of the atoms in the adjacent two domains, and the local atomic arrangement position error which destroys the balance state between atoms. The present application uses Smartlab Studio II software to perform crystal structure refinement processing on the XRD diffraction pattern of the lithium iron phosphate material under CuKa radiation, and compares with the pure lithium iron phosphate standard XRD pattern to obtain the lattice distortion parameter.

[0025] Further, the lattice distortion of the lithium iron phosphate material is 0.06%-0.075%.

[0026] According to the application, the lattice volume of the lithium iron phosphate material is 290.795-290.85 ų.

[0027] In the application, the XRD diffraction spectrum of the lithium iron phosphate material under CuKa radiation is subjected to crystal structure refinement processing by using the Smartlab Studio II software, so as to obtain the lattice volume parameter.

[0028] In the application, when the lattice volume meets the above range, it indicates that the lithium ion diffusion resistance of the lithium iron phosphate material is small, which is beneficial to improve the conductivity of the material, so as to improve the electrochemical performance of the lithium iron phosphate material.

[0029] Further, the lattice volume of the lithium iron phosphate material is 290.8-290.84 ų.

[0030] According to the application, the lithium iron phosphate material comprises a matrix and optionally a carbon coating layer coated on the surface of the matrix.

[0031] According to the application, the matrix has a composition shown in formula I;

[0032] Li a M y Fe b M’ x PO4 formula I;

[0033] Wherein, 0.0001≤x≤0.01, 0.0001≤y≤0.001; 1≤a≤1.05, 0.95≤b≤0.985.

[0034] Wherein, M and M' are different, and M and M' are each independently selected from at least one of Ti, Na, K, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd.

[0035] In the application, when the lithium iron phosphate material contains the specific M and M' described above, not only the width of the one-dimensional channel of the crystal can be controlled to reduce the charge transfer resistance, but also the morphology and particle size of the lithium iron phosphate material can be controlled to make the particles grow in a directional manner, which is beneficial to the ion diffusion along the b axis. Under the synergistic action of M and M', the lithium iron phosphate material has better electrochemical performance.

[0036] Further, 0.0001≤x≤0.001, 0.0001≤y≤0.001; 1≤a≤1.05, 0.95≤b≤0.985.

[0037] Further, the M is selected from at least one of Na, K, Mg, Y, Zr, Sm, Co, Ni, B, Cu and Gd.

[0038] Further, the M' is selected from at least one of Ti, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd.

[0039] Further, the M is selected from at least one of Na, K and Mg, and the M' is selected from at least one of Ti, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd.

[0040] According to a preferred embodiment of the present application, the M is selected from at least one of Na, K and Mg, and preferentially doped in the Li site; and the M' is selected from at least one of Ti, V, W, Nb, La, Cr, Mo, Ca and Zn, and preferentially doped in the Fe site.

[0041] In the present application, the lithium iron phosphate material contains the above-mentioned specific metal elements, and metal ions are doped in the Fe site and the Li site, respectively. The doping of the Li site in the lithium iron phosphate can expand the olivine crystal lattice, expand the lithium ion channel, promote the migration of lithium ions along the channel, reduce the lithium ion transfer resistance, and increase the diffusion coefficient of lithium ions. The metal ions doped in the Fe site can cause changes in bond length, bond angle and bond energy in the crystal lattice, weaken the interaction of Li-O bond, especially when the valence state of the doped metal ions is different from that of Fe ions, ion vacancies or ion valence changes can be generated, the diffusion path of lithium ions is increased, and the mobility and diffusion coefficient of lithium ions are improved. In addition, the doping of the Fe site can inhibit the crystal growth trend on the (010) plane, which is beneficial to the diffusion of ions along the b axis. Under the synergistic effect of the above-mentioned elements, the capacity, rate and cycle of the lithium iron phosphate material and other electrochemical properties can be improved.

[0042] According to a preferred embodiment of the present application, the multi-element co-doped lithium iron phosphate material comprises a substrate and optionally a carbon coating layer coated on the surface of the substrate.

[0043] In the present application, when the lithium iron phosphate substrate surface contains a carbon coating layer, not only the conductivity between particles can be enhanced to make up for the missing charge number in the lithium ion extraction / insertion process, but also the reducing property of carbon can inhibit the oxidation of ferrous ions to ferric ions to prevent the occurrence of agglomeration.

[0044] According to the present application, the content of carbon in the lithium iron phosphate material is 0-5wt%.

[0045] Further, the content of carbon in the lithium iron phosphate material is 0.5-2wt%.

[0046] According to the present application, the specific surface area of the lithium iron phosphate material is 7-13 m 2 / g.

[0047] Further, the specific surface area of the lithium iron phosphate material is 8-12 m 2 / g.

[0048] According to the present application, the tap density of the lithium iron phosphate material is 2.3-2.6 g / cm 3 .

[0049] Further, the tap density of the lithium iron phosphate material is 2.38-2.58 g / cm 3 .

[0050] According to the present application, the powder resistivity of the lithium iron phosphate material is ≤30 Ω•cm.

[0051] Further, the powder resistivity of the lithium iron phosphate material is ≤20 Ω•cm.

[0052] According to the present application, the median particle size D 50 of the lithium iron phosphate material is 0.5-2.5 µm.

[0053] Further, the median particle size D 50 of the lithium iron phosphate material is 0.8-1.8 µm.

[0054] According to the present application, the K 90 of the lithium iron phosphate material is 2-5.

[0055] In the present application, K 90 =(D 90 -D 10 ) / D 50 . Without special instructions, the particle size parameters (e.g. D 50 , D 90 , D 10 ) are obtained by Malvern 3000 test.

[0056] Further, the K 90 of the lithium iron phosphate material is 2.5-4.5.

[0057] The second aspect of the present application provides a method for preparing the above lithium iron phosphate material, wherein the method comprises:

[0058] (1) mixing iron phosphate, lithium source, optional carbon source, M source and M' source with water to obtain slurry A;

[0059] (2) grinding the slurry A to obtain slurry B containing process product I;

[0060] (3) drying the slurry B to obtain a process product II;

[0061] (4) sintering and crushing the process product II to obtain a lithium iron phosphate material;

[0062] wherein the M source and the M' source are each independently selected from a compound containing at least one element of Ti, Na, K, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd, and the M source and the M' source are different;

[0063] the median particle size of the M source and the M' source each independently satisfies 0.5 µm ≤ D 50 ≤ 5 µm.

[0064] The present application controls the grinding particle size of the process product by simultaneously adding the M source and the M' source with specific median particle size to the reaction system, so that the lattice distortion is within a suitable range. The specific multi-element co-doping can produce a synergistic effect, on the one hand enhancing the lithium ion and electron transport capacity of the lithium iron phosphate material, and on the other hand effectively improving the compaction density of the lithium iron phosphate material, having the characteristics of small primary particle size and uniform particles, effectively improving the problems of low electronic conductivity and ion mobility of the material. Thus, the capacity and rate performance of the lithium ion battery are improved. The present method is simple in operation, low in energy consumption and easy to industrialize.

[0065] Further, the median particle size of the M source and the M' source each independently satisfies 0.6 µm ≤ D 50 ≤ 4.6 µm.

[0066] In the present application, the specific type of the M source and the M' source is not particularly limited, as long as it can contain the above-mentioned elements. Preferably, the M source can be an oxide containing M element and / or a hydroxide containing M element, more preferably an oxide containing M element. Preferably, the M' source can be an oxide containing M' element and / or a hydroxide containing M' element, more preferably an oxide containing M' element.

[0067] Further, the M source is selected from a compound containing at least one element of Na, K, Mg, Y, Zr, Sm, Co, Ni, B, Cu and Gd.

[0068] Further, the M' source is selected from a compound containing at least one element of Ti, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd.

[0069] Furthermore, the M source is selected from compounds containing at least one element from Na, K, and Mg, and the M' source is selected from compounds containing at least one element from Ti, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu, and Gd.

[0070] According to a preferred embodiment of the present invention, the M source is selected from a compound containing at least one element selected from Na, K and Mg, and the M' source is selected from a compound containing at least one element selected from Ti, V, W, Nb, La, Cr, Mo, Ca and Zn.

[0071] According to the present invention, the median particle size D of the iron phosphate is... 50 The range is 0.5-25μm.

[0072] Furthermore, the median particle size D of the iron phosphate 50 It ranges from 1 to 10 μm.

[0073] According to the present invention, the specific surface area of ​​the iron phosphate is 5-13 m². 2 / g.

[0074] Furthermore, the specific surface area of ​​the iron phosphate is 6-10 m². 2 / g.

[0075] According to the present invention, the carbon source is selected from at least one of sugars, organic carboxylic acids, and polymers.

[0076] In this invention, there are no particular limitations on the selection of the carbon source, and conventional carbon sources in the art can be used. Preferably, the sugar is selected from at least one of glucose, sucrose, starch, and cellulose. Preferably, the organic carboxylic acid is selected from citric acid and / or oxalic acid. Preferably, the polymer is selected from at least one of polyethylene glycol, polyvinyl alcohol, and polyethylene.

[0077] According to a preferred embodiment of the present invention, the sugar is selected from glucose and polyethylene glycol. Preferably, the mass ratio of glucose to polyethylene glycol is 1-3:1.

[0078] In this invention, there are no special limitations on the selection of the lithium source, and conventional lithium sources in the art can be used. Preferably, the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate, lithium acetate, lithium oxalate, and lithium nitrate.

[0079] According to the present application, in step (1), the amounts of the M source, the M' source, the lithium source and the iron phosphate are such that n(M):n(M'):n(Li):n(Fe):n(P) is y:x:a:b:1; wherein 0.0001≤x≤0.01, 0.0001≤y≤0.001; 1≤a≤1.05, 0.95≤b≤0.985.

[0080] Further, in step (1), the amounts of the M source, the M' source, the lithium source and the iron phosphate are such that n(M):n(M'):n(Li):n(Fe):n(P) is y:x:a:b:1; wherein 0.0001≤x≤0.001, 0.0001≤y≤0.001; 1≤a≤1.05, 0.95≤b≤0.985.

[0081] According to the present application, the amount of the carbon source added is 0-20wt% based on the mass of the iron phosphate.

[0082] Further, the amount of the carbon source added is 5-15wt% based on the mass of the iron phosphate.

[0083] According to the present application, the solid content of the slurry A is 20-60wt%.

[0084] Further, the solid content of the slurry A is 30-50wt%.

[0085] According to the present application, in step (2), the median particle size D 50 of the process product I is 0.2-0.6µm.

[0086] Further, in step (2), the median particle size D 50 of the process product I is 0.3-0.5µm.

[0087] According to the present application, the grinding comprises: performing coarse grinding on the slurry A to obtain a coarse grinding product, and then performing fine grinding to obtain a slurry B containing the process product I.

[0088] According to the present application, the median particle size D 50 of the coarse grinding product is 1-4µm.

[0089] Further, the median particle size D 50 of the coarse grinding product is 1.5-3.5µm.

[0090] In the present application, the method for grinding is not particularly limited, as long as the median particle size D 50 of the coarse grinding product and the process product I meets the above range. In order to make the electrochemical performance of the lithium iron phosphate material better, the grinding comprises performing coarse grinding and fine grinding in sequence by using a sand grinding method.

[0091] In the application, the rough grinding conditions include: the size of zirconium ball is 0.7-0.8mm, and the rough grinding time is 0.5-1h.

[0092] In the application, the fine grinding conditions include: the size of zirconium ball is 0.3-0.4mm, and the fine grinding time is 1-5h.

[0093] According to the application, in step (3), the drying method is spray drying.

[0094] According to the application, the spray drying atomization frequency is 20-70Hz, and the spray drying temperature is 50-300℃.

[0095] Further, the spray drying atomization frequency is 20-50Hz, and the spray drying temperature is 80-200℃.

[0096] According to the application, in step (4), the sintering temperature is 300-900℃, and the sintering time is 6-10h.

[0097] According to a preferred embodiment of the application, the sintering includes first sintering and second sintering in sequence. In the sintering process, the temperature is first raised to the first sintering temperature, and then raised to the second sintering temperature after the first sintering time, and then kept for the second sintering time.

[0098] According to the application, the first sintering temperature is 300-500℃, and the first sintering time is 2-5h.

[0099] According to the application, the second sintering temperature is 500-900℃, and the second sintering time is 5-15h.

[0100] The third aspect of the application provides a lithium ion battery, wherein the lithium ion battery contains the above lithium iron phosphate material.

[0101] According to the application, the discharge capacity of the lithium ion battery under 0.1C condition is ≥159 mAh / g.

[0102] According to the application, the discharge capacity of the lithium ion battery under 2C condition is ≥136 mAh / g.

[0103] According to the application, the discharge capacity of the lithium ion battery under 0.33C condition at-10℃ is ≥70 mAh / g.

[0104] The application will be described in detail through examples below.

[0105] The composition of the material, the structure or morphology of atoms or molecules inside the material, and the like are obtained by XRD. The model of the XRD diffractometer used is XRD-6000 X-ray powder diffractometer (Japan Shimadzu), and the test conditions of the XRD are as follows: Cu target, Kα ray (wavelength λ = 0.154 nm), tube voltage 40 kV, tube current 200 mA, scanning speed 10 o (2 θ ) / min.

[0106] The surface morphology of the lithium iron phosphate material is characterized by a scanning electron microscope (SEM). The model of the scanning electron microscope used is S-4800 (the manufacturer is Japan Hitachi), and the test conditions of the scanning electron microscope are as follows: acceleration voltage 1 kV, magnification 10K.

[0107] The average particle size of the iron phosphate, the process product I, the coarse grinding product, and the lithium iron phosphate material particles is obtained by Malvern 3000 test.

[0108] The elements and contents in the lithium iron phosphate material are obtained by inductively coupled plasma spectrometer (ICP) test, and the instrument is purchased from PerkinElmer Instrument Co., Ltd., and the model is PE-7000DV.

[0109] Lattice volume and lattice distortion: the XRD diffraction pattern of the lithium iron phosphate material is subjected to crystal structure refinement treatment by using Smartlab Studio II software.

[0110] Specific surface area of iron phosphate and specific surface area of lithium iron phosphate material: the specific surface area tester of Tristar II3020 model of the United States Micromertics Company is used for test.

[0111] Compacted density: the powder compaction density tester is used for test under the pressure of 3t.

[0112] Powder resistivity: the powder resistivity tester of Suzhou Crystal is used for test.

[0113] Carbon content of lithium iron phosphate material: the carbon-sulfur analyzer is used for test.

[0114] In the following examples and comparative examples, the raw materials used are all commercially available products.

[0115] Example 1

[0116] (1) Anhydrous iron phosphate (D 50 8 μm, specific surface area 7 m 2 / g), lithium carbonate (lithium source), glucose, polyethylene glycol (carbon source), MgO (M source; D 50 1 μm), and TiO2 (M' source; D 50The MgO, TiO2, lithium source and iron phosphate were added into pure water in a certain proportion for premixing to obtain slurry A.

[0117] The amounts of the MgO, TiO2, lithium source and iron phosphate were such that n(Mg):n(Ti):n(Li):n(Fe):n(P) was 0.0005:0.0045:1.02:0.97:1.

[0118] (2) The slurry A was coarsely ground, the average size of the zirconium balls was 0.7 mm, the coarse grinding time was 0.5 h, and the median particle size D50 of the coarsely ground product was 2.48 µm. 50 The slurry B (process product I) had a D50 of 0.4 µm. 50 The slurry B (process product I) had a D50 of 0.4 µm.

[0119] (3) The slurry B was spray dried to obtain a precursor, wherein the atomization frequency was 20 Hz, the temperature of the heating air inlet was 120 ℃, and the temperature of the air outlet was 70 ℃.

[0120] (4) The precursor obtained in step (3) was sintered under a nitrogen atmosphere, and the sintering schedule was as follows: 1.5 ℃ / min to 440 ℃, holding for 2 h, 3 ℃ / min to 795 ℃, holding for 7 h. After sintering, the material was crushed and sieved to obtain a lithium iron phosphate material.

[0121] The lithium iron phosphate material had a matrix composition of Li 1.02 Mg 0.0005 Fe 0.97 Ti 0.0045 PO4, and the parameters of the lithium iron phosphate material were shown in Table 1.

[0122] Example 2

[0123] The lithium iron phosphate material was prepared according to the method of Example 1, except that in step (1), the amounts of the MgO, TiO2, lithium source and iron phosphate were such that n(Mg):n(Ti):n(Li):n(Fe):n(P) was 0.0005:0.003:1.02:0.97:1.

[0124] The lithium iron phosphate material had a matrix composition of Li 1.02 Mg 0.0005 Fe 0.97 Ti 0.003 PO4, and the parameters of the lithium iron phosphate material were shown in Table 1.

[0125] Example 3

[0126] The lithium iron phosphate material was prepared according to the method of Example 1, except that in step (1), the amounts of MgO, TiO2, lithium source and iron phosphate were such that n(Mg):n(Ti):n(Li):n(Fe):n(P) was 0.0005:0.0015:1.02:0.97:1.

[0127] The lithium iron phosphate material prepared had a matrix composition of Li 1.02 Mg 0.0005 Fe 0.97 Ti 0.0015 PO4, and the parameters of the lithium iron phosphate material are shown in Table 1.

[0128] Example 4

[0129] The lithium iron phosphate material was prepared according to the method of Example 1, except that in step (1), TiO2was replaced by V2O5, and the amounts of MgO, V2O5, lithium source and iron phosphate were such that n(Mg):n(V):n(Li):n(Fe):n(P) was 0.0005:0.0045:1.02:0.97:1.

[0130] The lithium iron phosphate material prepared had a matrix composition of Li 1.02 Mg 0.0005 Fe 0.97 V 0.0045 PO4, and the parameters of the lithium iron phosphate material are shown in Table 1.

[0131] Example 5

[0132] The lithium iron phosphate material was prepared according to the method of Example 1, except that in step (1), the D 50 of TiO2was 5 μm. The lithium iron phosphate material prepared had a matrix composition of Li 1.02 Mg 0.0005 Fe 0.97 Ti 0.0045 PO4, and the parameters of the lithium iron phosphate material are shown in Table 1.

[0133] Comparative Example 1

[0134] The lithium iron phosphate material was prepared according to the method of Example 1, except that in step (1), no M source and M' source were added, and the amounts of lithium source and iron phosphate were such that n(Li):n(Fe):n(P) was 1.02:0.97:1.

[0135] The lithium iron phosphate material prepared had a matrix composition of Li 1.02 Fe 0.97 PO4, and the parameters of the lithium iron phosphate material are shown in Table 1.

[0136] Comparative Example 2

[0137] The lithium iron phosphate material was prepared according to the method of Example 1, except that in step (1), the MgO was not contained, and the amounts of TiO2 and lithium iron phosphate were such that n(Ti):n(Li):n(Fe):n(P) was 0.0015:1.02:0.97:1.

[0138] The prepared lithium iron phosphate material had a matrix composition of Li 1.02 Mg 0.0005 Fe 0.97 PO4, and the parameters of the lithium iron phosphate material are shown in Table 1.

[0139] Comparative Example 3

[0140] The lithium iron phosphate material was prepared according to the method of Example 1, except that in step (1), the MgO was not contained, and the amounts of TiO2 and lithium iron phosphate were such that n(Ti):n(Li):n(Fe):n(P) was 0.0015:1.02:0.97:1.

[0141] The prepared lithium iron phosphate material had a matrix composition of Li 1.02 Fe 0.97 Ti 0.0015 PO4, and the parameters of the lithium iron phosphate material are shown in Table 1.

[0142] Table 1

[0143]

[0144] Continued Table 1

[0145]

[0146] Test Example 1

[0147] The lithium iron phosphate material prepared in the examples and comparative examples was used to prepare a lithium ion battery, and the specific steps were as follows:

[0148] (1) The lithium iron phosphate material prepared in the above examples and comparative examples, the conductive agent carbon nanotube, and the binder PVDF NMP solution were mixed in a mass ratio of 90:5:5. The specific method was as follows: the dried positive electrode material and the conductive agent were ground in a mortar for 15 minutes, and after uniform grinding, the PVDF solution (5% by mass) was added in proportion, and stirred on a magnetic stirrer for 6 hours; the obtained paste-like slurry was uniformly coated on a current collector aluminum foil, and then dried in a vacuum drying oven at 60°C for 20 hours, and then punched into a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm under a pressure of 100 MPa, and the positive electrode sheet was placed in a vacuum drying oven at 120°C and dried for 12 h.

[0149] (2) battery assembly: with the diameter of 17 mm, the thickness of 1 mm, the metal lithium sheet as the negative electrode, the polyethylene porous membrane coated with the alumina ceramic layer with the thickness of 25 μm as the separator, the equal mixed solution of 1 mol / L of LiPF6, ethylene carbonate (EC) and diethyl carbonate (DEC) as the electrolyte, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte are assembled into the 2025 type button cell in the Ar gas glove box with the water content and oxygen content less than 5 ppm.

[0150] (3) electrochemical performance test: the charge-discharge tester of blue electricity LAND CT2001A of Lantianbo Electronics Co., Ltd. is used to test the charge-discharge of the battery, the charge-discharge voltage range is 2.0 to 3.75 V, the discharge capacity test of the assembled lithium ion battery is carried out at 0.1C, 2C rate respectively, the discharge capacity test of the assembled lithium ion battery is carried out at 0.33C rate at-10℃. The test results of the lithium ion battery are shown in Table 2.

[0151] Table 2

[0152]

[0153] It can be seen from the results that the lithium ion battery prepared by using the lithium iron phosphate material of the application has better electrochemical performance. Under the conditions of low rate (0.1C), high rate (2C) and low temperature, it has excellent discharge capacity.

[0154] Figure 1 is the charge-discharge curve of the lithium ion battery made of the lithium iron phosphate material of Example 1 and Comparative Example 1. It can be seen that the charge-discharge capacity of the battery of Example 1 is higher.

[0155] Figure 2 is the SEM image of the lithium iron phosphate material of Example 1. It can be seen that the particle size distribution is more uniform.

[0156] The above describes the preferred embodiments of the application in detail, but the application is not limited thereto. Within the technical concept of the application, various simple modifications can be made to the technical solutions of the application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as the disclosed content of the application, and all belong to the protection scope of the application.

Claims

1. A lithium iron phosphate material, characterized in that, The lattice distortion of the lithium iron phosphate material is 0.062%-0.075%; The lithium iron phosphate material has a lattice volume of 290.821-290.84 A 3 ; The lithium iron phosphate material comprises a matrix and optionally a carbon coating layer coated on the surface of the matrix; The matrix has a composition shown in Formula I; Li a M y Fe b M’ x PO4Formula I; 0.003≤x≤0.01, 0.0001≤y≤0.001; 1≤a≤1.05, 0.95≤b≤0.985; M and M' are different, and each of M and M' is independently selected from at least one of Ti, Na, K, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd; The median particle size D of the lithium iron phosphate material is 0.5-2.5 pm. 50 is 0.5-2.5 pm.

2. The lithium iron phosphate material of claim 1, wherein, The carbon content in the lithium iron phosphate material is 0-5wt%.

3. The lithium iron phosphate material of claim 1 or 2, wherein, The carbon content in the lithium iron phosphate material is 0.5-2wt%.

4. The lithium iron phosphate material of claim 1 or 2, wherein, The specific surface area of the lithium iron phosphate material is 7-13 m 2 / g; and / or the lithium iron phosphate material has a tap density of 2.3-2.6 g / cm3 3 ; And / or, the powder resistivity of the lithium iron phosphate material is ≤30Ω·cm; and / or the median particle size D50 of the lithium iron phosphate material is 0.8-1.8 pm; 50 0.8-1.8 pm; and / or the lithium iron phosphate material has a K 90 of 2-5.

5. The lithium iron phosphate material of claim 4, wherein, The specific surface area of the lithium iron phosphate material is 8-12 m 2 / g; And / or, the powder resistivity of the lithium iron phosphate material is ≤20Ω·cm; and / or the lithium iron phosphate material has a K 90 of 2.5-4.

5.

6. A method of producing the lithium iron phosphate material according to any one of claims 1 to 5, characterized in that, The method comprises: (1) mixing iron phosphate, a lithium source, optionally a carbon source, an M source and an M' source with water to obtain slurry A; (2) grinding the slurry A to obtain slurry B containing process product I; (3) drying the slurry B to obtain process product II; (4) sintering and crushing the process product II to obtain a lithium iron phosphate material; The M source and the M' source are each independently selected from a compound containing at least one element of Ti, Na, K, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd, and the M source and the M' source are different; The median particle size of the M source and the M' source each independently satisfies 0.5 µm ≤ D50≤ 5 µm. 50 ≤5µm.

7. The method of claim 6, wherein, In step (1), the M source is selected from a compound containing at least one element of Na, K, Mg, Y, Zr, Sm, Co, Ni, B, Cu and Gd; And / or, the M' source is selected from a compound containing at least one element of Ti, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd; and / or the median particle size of the M source and the M' source each independently satisfies 0.6 pm < D50≤ 4.6 pm 50 ≤4.6 pm; and / or the median particle size D50 of the iron phosphate is 0.5-25 pm; 50 0.5-25 pm; And / or, the carbon source is selected from at least one of a sugar, an organic carboxylic acid and a polymer.

8. The method of claim 6 or 7, wherein, The median particle size D of the iron phosphate is 1-10 μm. 50 is 1-10 μm.

9. The method of claim 6 or 7, wherein, In step (1), the amounts of the M source, the M' source, the lithium source and the iron phosphate are such that n(M):n(M'):n(Li):n(Fe):n(P) is y:x:a:b:1; wherein 0.003≤x≤0.01, 0.0001≤y≤0.001; 1≤a≤1.05, 0.95≤b≤0.985; And / or, the amount of the carbon source added is 0-20wt% based on the mass of the iron phosphate; And / or, the solid content of the slurry A is 20-60wt%.

10. The method of claim 9, wherein, In step (1), the amount of the carbon source added is 5-15wt% based on the mass of the iron phosphate.

11. The method of claim 9, wherein, In step (1), the solid content of the slurry A is 30-50wt%.

12. The method of claim 6, wherein, In step (2), the median particle size Dv50 of the process product I is 0.2 to 0.6 pm. 50 0.2 to 0.6 pm. And / or, the grinding comprises: coarsely grinding the slurry A to obtain a coarsely ground product, and then finely grinding to obtain the slurry B containing the process product I.

13. The method of claim 12, wherein, In step (2), the median particle size Dv50 of the process product I is 0.3 to 0.5 pm. 50 0.3 to 0.5 pm.

14. The method of claim 12, wherein, The median particle size D of the coarse grind is 1-4 µm. 50 1-4 µm.

15. The method of claim 14, wherein, The median particle size D of the coarse grind is 1.5-3.5 pm. 50 is 1.5-3.5 pm.

16. The method of claim 6, wherein, In step (3), the drying is by spray drying.

17. The method of claim 16, wherein, The spray drying atomization frequency is 20-70 Hz, and the spray drying temperature is 50-300 DEG C.

18. The method of claim 6, wherein, In step (4), the sintering temperature is 300-900 DEG C, and the sintering time is 6-10 h.

19. The method of claim 18, wherein, The sintering comprises sequentially performing first sintering and second sintering.

20. The method of claim 19, wherein, The first sintering temperature is 300-500 DEG C, and the first sintering time is 2-5 h; And / or, the second sintering temperature is 500-900 DEG C, and the second sintering time is 5-15 h.

21. A lithium-ion battery, characterized by, The lithium ion battery comprises the lithium iron phosphate material according to any one of claims 1-5.

22. The lithium-ion battery of claim 21, wherein, The lithium ion battery has a discharge capacity of ≥ 159 mAh / g under 0.1C condition. And / or, the lithium ion battery has a discharge capacity of ≥ 136 mAh / g under 2C condition. And / or, the lithium ion battery has a discharge capacity of ≥ 70 mAh / g under 0.33C condition at -10 DEG C.

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