Lithium iron phosphate positive electrode material and preparation method therefor, and lithium-ion battery

Abstract

The present invention relates to the technical field of the preparation of lithium-ion positive electrode materials, and discloses a lithium iron phosphate positive electrode material and a preparation method therefor, and a lithium-ion battery. According to an XRD test, the lithium iron phosphate positive electrode material has characteristic diffraction peaks at 2θA1 of 29.4-29.6°, 2θA2 of 29.8-30° and 2θA3 of 43.8-43.9°. The lithium iron phosphate positive electrode material has specific characteristic diffraction peaks according to an XRD test, and therefore the lithium iron phosphate positive electrode material has a high compaction density, thereby significantly improving the capacity and electrochemical properties such as the cycle performance of a lithium-ion battery assembled from the lithium iron phosphate positive electrode material.

Description

Lithium iron phosphate positive electrode material and preparation method thereof, and lithium ion battery Technical Field

[0001] The present invention relates to the technical field of lithium ion positive electrode material preparation, and in particular to a lithium iron phosphate positive electrode material and a preparation method thereof, and a lithium ion battery. Background Art

[0002] Lithium-ion batteries are green secondary batteries with outstanding advantages, including high voltage, high energy density, excellent cycle performance, low self-discharge, and no memory effect. Since their successful development in the 1990s, they have experienced rapid application and development. In recent years, the application range of lithium-ion batteries has become increasingly broad, including energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. Among them, lithium iron phosphate cathode material has become one of the most promising lithium-ion battery cathode materials due to its stable structure, abundant resources, long cycle life, excellent safety, environmental friendliness, and theoretical capacity of up to 170 mAh / g.

[0003] There are many methods for preparing lithium iron phosphate cathode materials, which can be broadly divided into liquid-phase and solid-phase methods. Liquid-phase methods include low-temperature synthesis methods such as chemical precipitation, hydrothermal methods, and sol-gel methods. Solid-phase methods include high-temperature solid-phase sintering, carbothermal reduction, and microwave sintering. Regardless of the synthesis method, implementation in industrial production requires consideration of various factors, including cost, process control difficulty, and performance. The quality of lithium iron phosphate cathode materials has a direct impact on battery performance, including energy density, cycle life, and safety.

[0004] With the rapid development of the energy storage and power battery industries, new demands and challenges have been put forward for lithium iron phosphate cathode materials. Currently, people are conducting extensive research on high-density lithium iron phosphate materials and their precursor iron phosphate materials. CN116553507A discloses a densification treatment process for high-density lithium iron phosphate materials and their precursors. The lithium iron phosphate precursor material is taken and transported to a plasma flame through an inert gas atmosphere for melting to form a spherical single crystal. The material is placed in a graphite sintering furnace, heated and sintered, and then superheated steam is introduced. Under the heat preservation state, a carbon-containing gas is introduced to form a thin layer of carbon coating on the surface of the spherical single crystal. The material is cooled to obtain a high-density lithium iron phosphate material. This method has a complex preparation process, is difficult to control, consumes a lot of energy, and lacks product uniformity and stability.

[0005] CN112408351A discloses a method for preparing high-density iron phosphate and lithium iron phosphate. The method involves preparing a slurry of trivalent iron source and dividing it into two portions; adding a mixed solution of phosphoric acid and liquid caustic soda to one portion and reacting the two portions; after the mixed slurry turns white, adding the other portion to the mixed slurry and reacting the two portions; and finally, washing, filtering, drying, and calcining the mixture to obtain high-density iron phosphate. This method is difficult to control during the preparation process, and simply controlling the stacking pattern and particle size distribution of the secondary iron phosphate particles cannot fundamentally improve the compaction density of the lithium iron phosphate material.

[0006] Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a lithium iron phosphate cathode material, a preparation method thereof, and a lithium ion battery. The lithium iron phosphate cathode material exhibits specific diffraction characteristic peaks as determined by XRD testing, resulting in a high compaction density of the lithium iron phosphate cathode material, thereby significantly improving the electrochemical properties of the lithium ion battery assembled with the lithium iron phosphate cathode material, such as capacity and cycle performance.

[0008] The first aspect of the present invention provides a lithium iron phosphate positive electrode material, wherein, through XRD testing, the positive electrode material has a 2θ A1 =29.4-29.6°, 2θ A2 =29.8-30° and 2θ A3 There is a characteristic diffraction peak at 43.8-43.9°.

[0009] A second aspect of the present invention provides a method for preparing a lithium iron phosphate positive electrode material, wherein the preparation method comprises the following steps:

[0010] (1) mixing an iron phosphate precursor, a lithium source, a carbon source, optionally a metal source M, optionally a Mn source, and a liquid medium, grinding the mixture into a slurry, and drying the mixture to obtain a dried material;

[0011] (2) calcining the dried material under a protective atmosphere to obtain a sintered material;

[0012] (3) crushing and screening the sintered material to obtain the lithium iron phosphate positive electrode material;

[0013] The iron phosphate precursor is tested by XRD at 2θ a1 =16.2-16.9°, 2θ a2 =27.3-28.1°, 2θ a3 =29.0-29.7° and 2θ a4 =30.2-30.9° has a diffraction characteristic peak; the iron phosphate precursor is tested by XRD at 2θ b1 =20-20.7°, 2θb2 =21.5-22.2°, 2θ b3 =23.4-24°, 2θ b4 = There is a characteristic diffraction peak at 25.5-26.2°;

[0014] The 2θ ai The integral area A(2θ ai ) and 2θ bj The integral area A(2θ bj ) satisfy:

[0015] Here, i is an integer from 1 to 4, and j is an integer from 1 to 4.

[0016] A third aspect of the present invention provides a lithium iron phosphate positive electrode material prepared by the above preparation method.

[0017] A fourth aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the above-mentioned lithium iron phosphate positive electrode material.

[0018] Through the above technical solution, the lithium iron phosphate positive electrode material, preparation method and application thereof, and lithium ion battery provided by the present invention achieve the following beneficial effects:

[0019] The lithium iron phosphate positive electrode material provided by the present invention has specific diffraction characteristic peaks through XRD testing, so that the positive electrode material has a high compaction density. When used in lithium-ion batteries, it can effectively improve the electrochemical performance of lithium-ion batteries, showing higher capacity and energy efficiency, lower internal resistance, and better cycle performance.

[0020] Furthermore, the lithium iron phosphate positive electrode material provided by the present invention has a low Fe2P content, which can further increase the capacity and energy density of the positive electrode material, reduce side reactions with the electrolyte, and improve the service life and safety of the lithium-ion battery containing the positive electrode material.

[0021] Furthermore, the lithium iron phosphate positive electrode material provided by the present invention includes a substrate and a carbon coating layer coated on the surface of the substrate, and the carbon coating layer is uniformly coated on the surface of the substrate, thereby further improving the capacity, energy efficiency and cycle performance of the lithium-ion battery containing the positive electrode material, and further reducing the internal resistance.

[0022] Specifically, the lithium iron phosphate positive electrode material provided by the present invention has a density of 2.63 g / cm 3 Under high compaction density, the 0.1C discharge specific capacity of the lithium-ion battery containing this positive electrode material reaches 160mAh / g, the capacity retention rate after 200 cycles at room temperature is 97%, and the 1C energy efficiency reaches 95%, showing excellent electrochemical performance.

[0023] In addition, the present invention provides a corresponding relationship between the unit cell parameter c / a value of the iron phosphate precursor and the compaction density of the lithium iron phosphate, which provides a basis for the development of raw materials and the design of products.

[0024] In the preparation method of the lithium iron phosphate positive electrode material provided in the present invention, on the one hand, by using a precursor material with a specific XRD structure, the iron phosphate precursor has certain structural defects, which can act as a solvent during the sintering process of the precursor and reduce the sintering temperature. On the other hand, by optimizing the grinding, spraying, and sintering process conditions, a lithium iron phosphate positive electrode material with high compaction density and good electrochemical performance is obtained.

[0025] In addition, the preparation method of the lithium iron phosphate precursor of the present invention only optimizes the process parameters and does not require any adjustment to the existing production line. The entire process is non-toxic and harmless, the process is simple, the raw materials are easily available, the equipment requirements are low, and it is easy to promote and apply. It can be widely used in the industrial production of lithium iron phosphate positive electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG1 is an XRD pattern of the iron phosphate precursor prepared in Preparation Example 1 of the present invention.

[0027] FIG2 is a SEM image of the iron phosphate precursor prepared in Preparation Example 1 of the present invention.

[0028] FIG3 is an XRD diagram of the lithium iron phosphate positive electrode materials prepared in Example 1 and Example 2 of the present invention.

[0029] FIG4 is a SEM image of the lithium iron phosphate positive electrode material prepared in Example 1 of the present invention.

[0030] FIG5 is a graph showing the charge and discharge performance of lithium-ion batteries assembled from the lithium iron phosphate positive electrode materials of Example 1 and Example 2. DETAILED DESCRIPTION

[0031] The endpoints of the ranges and any values ​​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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0032] The first aspect of the present invention provides a lithium iron phosphate positive electrode material, characterized in that the positive electrode material has a 2θ A1 =29.4-29.6°, 2θ A2 =29.8-30° and 2θ A3There is a characteristic diffraction peak at 43.8-43.9°.

[0033] In the present invention, when the lithium iron phosphate positive electrode material is tested by XRD, a specific diffraction characteristic peak is present at a specific 2θ position, so that the positive electrode material has a high compaction density. When used in lithium-ion batteries, it can effectively improve the electrochemical performance of lithium-ion batteries, showing higher capacity and energy efficiency, lower internal resistance, and better cycle performance.

[0034] Furthermore, the XRD test shows that the positive electrode material has a B1 =25.4-25.5°, 2θ B2 =35.9-36° and 2θ B3 There is a characteristic diffraction peak at =60.7-60.8°.

[0035] According to the present invention, the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio 0.25≤I(2θ A2 ) / I(2θ B3 )≤0.27.

[0036] In the present invention, when the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) satisfies the above range, the positive electrode material can exhibit a higher compaction density at a relatively low temperature.

[0037] In the present invention, the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio 0.25≤I(2θ A2 ) / I(2θ B3 )≤0.27, for example, it can be 0.250, 0.251, 0.252, 0.253, 0.254, 0.255, 0.256, 0.257, 0.258, 0.259, 0.260, 0.261, 0.262, 0.263, 0.264, 0.265, 0.266, 0.267, 0.268, 0.269, 0.27, and a range consisting of any two values. Preferably, 0.26≤I(2θ A2 ) / I(2θ B3 )≤0.27.

[0038] According to the present invention, the positive electrode material includes a substrate and a carbon coating layer coated on the surface of the substrate;

[0039] Wherein, the matrix has a composition shown in Formula I: Li 1+a Fe b M c Mn d (PO4) 1-2w (P2O7) w Formula I;

[0040] Among them, -0.1≤a≤0.1, 0≤b≤1, 0≤c≤0.5, 0≤d≤1, 0.03≤w≤0.09;

[0041] M is selected from at least one of La, Ce, Cr, Mo, Ca, Hf, Ti, Fe, Zn, Y, Zr, W, Nb, Sm, Co, Ni, V, Mg, Na, B and Al.

[0042] In the present invention, the lithium iron phosphate positive electrode material provided by the present invention includes a substrate and a carbon coating layer coated on the surface of the substrate, and the carbon coating layer is uniformly coated on the surface of the substrate, thereby further improving the capacity, energy efficiency and cycle performance of the lithium-ion battery containing the positive electrode material, and further reducing the internal resistance.

[0043] Furthermore, M is selected from at least one of Al, Zr, W, Fe, Co, V and Ti.

[0044] In the present invention, -0.1≤a≤0.1, for example, it can be -0.09, -0.08, -0.07, -0.06, -0.05, -0.04, -0.03, -0.02, -0.01, 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, and a range consisting of any two values, preferably, -0.05≤a≤0.05; 0≤b≤1, for example, it can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, and a range consisting of any two values, preferably, 0.5≤b≤1; 0 ≤c≤0.5, for example, it can be 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, and a range consisting of any two values. Preferably, 0.001≤c≤ 0.1; 0≤d≤1, for example, it can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, and a range consisting of any two values, preferably, 0≤d≤0.5; 0.03≤w≤0.09, for example, it can be 0.03, 0.031, 0.032, 0.033, 0.034, 0.035, 0.036, 0.037, 0.038, 0.039, 0.04, 0.041, 0.042, 0.043, 0.044, 0.045, 0.046, 0.047, 0.048, 0.049, 0.05, 0.051, 0.052, 0.053, 0.054, 0.055, 0 w, 0.056, 0.057, 0.058, 0.059, 0.06, 0.061, 0.062, 0.063, 0.064, 0.065, 0.066, 0.067, 0.068, 0.069, 0.07, 0.071, 0.072, 0.073, 0.074, 0.075, 0.076, 0.077, 0.078, 0.079, 0.08, 0.081, 0.082, 0.083, 0.084, 0.085, 0.086, 0.087, 0.088, 0.089, 0.09, and a range consisting of any two values, preferably, 0.04≤w≤0.08.

[0045] According to the present invention, based on the total weight of the positive electrode material, the content of the carbon coating layer is 0.5-2 wt%.

[0046] In the present invention, the content of the carbon coating layer is 0.5-2wt%, for example, it can be 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2wt%, and a range consisting of any two values. Preferably, based on the total weight of the positive electrode material, the content of the carbon coating layer is 1-1.5wt%.

[0047] According to the present invention, the lithium iron phosphate cathode material has a secondary particle structure formed by primary particles, and the median particle size D of the primary particles is 50 0.2-2μm.

[0048] In the present invention, the median particle size D of the primary particles is 50 The median particle size D of the primary particles is preferably 0.2-2 μm, for example, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, and a range consisting of any two values. 50 0.5-1.5μm.

[0049] According to the present invention, the compaction density of the lithium iron phosphate positive electrode material is 2.5-2.7 g / cm 3 .

[0050] In the present invention, when the compaction density of the lithium iron phosphate positive electrode material meets the above range, the compaction density is relatively high, which further reduces the contact internal resistance between material particles and improves the energy density of the material.

[0051] In the present invention, the compaction density of the lithium iron phosphate positive electrode material is 2.5-2.7g / cm 3 , for example, it can be 2.5g / cm 3 , 2.51g / cm 3 , 2.52g / cm 3 , 2.53g / cm 3 , 2.54g / cm 3 , 2.55g / cm 3 , 2.56g / cm 3 , 2.57g / cm 3 , 2.58g / cm 3 , 2.59g / cm 3 , 2.6g / cm3 , 2.61g / cm 3 , 2.62g / cm 3 , 2.63g / cm 3 , 2.64g / cm 3 , 2.65g / cm 3 , 2.66g / cm 3 , 2.67g / cm 3 , 2.68g / cm 3 , 2.69g / cm 3 , 2.7g / cm 3 , and the range consisting of any two values, preferably, the compaction density of the lithium iron phosphate positive electrode material is 2.55-2.65g / cm 3 .

[0052] According to the present invention, the tap density of the lithium iron phosphate positive electrode material is 0.6-1.1 g / cm 3 .

[0053] In the present invention, when the tap density of the lithium iron phosphate positive electrode material meets the above range, there is obvious gradation between the particles, which improves the processing performance of the material.

[0054] In the present invention, the tap density of the lithium iron phosphate positive electrode material is 0.6-1.1 g / cm 3 , for example, it can be 0.6 g / cm 3 , 0.61g / cm 3 , 0.62g / cm 3 , 0.63g / cm 3 , 0.64g / cm 3 , 0.65g / cm 3 , 0.66g / cm 3 , 0.67g / cm 3 , 0.68g / cm 3 , 0.69g / cm 3 , 0.7g / cm 3 , 0.71g / cm 3 , 0.72g / cm 3 , 0.73g / cm 3 , 0.74g / cm 3 , 0.75g / cm 3 , 0.76g / cm 3 , 0.77g / cm 3 , 0.78g / cm 3 , 0.79g / cm 3 , 0.8g / cm 3 , 0.81g / cm 3, 0.82g / cm 3 , 0.83g / cm 3 , 0.84g / cm 3 , 0.85g / cm 3 , 0.86g / cm 3 , 0.87g / cm 3 , 0.88g / cm 3 , 0.89g / cm 3 , 0.9g / cm 3 , 0.91g / cm 3 , 0.92g / cm 3 , 0.93g / cm 3 , 0.94g / cm 3 , 0.95g / cm 3 , 0.96g / cm 3 , 0.97g / cm 3 , 0.98g / cm 3 , 0.99g / cm 3 , 1g / cm 3 , 1.1g / cm 3 , and the range of any two values, preferably, the tap density of the lithium iron phosphate positive electrode material is 0.7-1g / cm 3 .

[0055] According to the present invention, the specific surface area of ​​the lithium iron phosphate positive electrode material is 8-20m 2 / g.

[0056] In the present invention, the specific surface area of ​​the lithium iron phosphate positive electrode material is 8-20m 2 / g, for example, 8m 2 / g,9m 2 / g,10m 2 / g,11m 2 / g,12m 2 / g,13m 2 / g,14m 2 / g,15m 2 / g,16m 2 / g,17m 2 / g,18m 2 / g,19m 2 / g,20m 2 / g, and the range of any two values, preferably, the specific surface area of ​​the lithium iron phosphate positive electrode material is 10-15m 2 / g.

[0057] According to the present invention, the volume resistivity of the lithium iron phosphate positive electrode material is 1-100Ω·cm.

[0058] In the present invention, the volume resistivity of the lithium iron phosphate positive electrode material is 1-100Ω·cm, for example, it can be 1Ω·cm, 2Ω·cm, 3Ω·cm, 4Ω·cm, 5Ω·cm, 6Ω·cm, 7Ω·cm, 8Ω·cm, 9Ω·cm, 10Ω·cm, 12Ω·cm, 14Ω·cm, 16Ω·cm, 18Ω·cm, 20Ω·cm, 22Ω·cm, 24Ω·cm, 26Ω·cm, 2 8Ω·cm, 30Ω·cm, 35Ω·cm, 40Ω·cm, 45Ω·cm, 50Ω·cm, 55Ω·cm, 60Ω·cm, 65Ω·cm, 70Ω·cm, 75Ω·cm, 80Ω·cm, 85Ω·cm, 90Ω·cm, 95Ω·cm, 100Ω·cm, and a range consisting of any two values. Preferably, the volume resistivity of the lithium iron phosphate positive electrode material is 10-60Ω·cm.

[0059] According to the present invention, the Fe2P content of the lithium iron phosphate positive electrode material is ≤100 ppb.

[0060] In the present invention, the lithium iron phosphate positive electrode material has a low content of Fe2P, which can further improve the capacity and energy density of the positive electrode material, reduce side reactions with the electrolyte, and improve the service life and safety of the lithium-ion battery containing the positive electrode material.

[0061] In the present invention, the Fe2P content of the lithium iron phosphate positive electrode material is ≤100ppb, for example, it can be 100ppb, 99ppb, 98ppb, 97ppb, 96ppb, 95ppb, 94ppb, 93ppb, 92ppb, 91ppb, 90ppb, 85ppb, 80ppb, 75ppb, 70ppb, 65ppb, 60ppb, 55ppb, 50ppb, 45ppb, 40ppb, 35ppb, 30ppb, 25ppb, 20ppb, 15ppb, 10ppb, 5ppb, 0ppb, and a range consisting of any two values. Preferably, the Fe2P content of the lithium iron phosphate positive electrode material is ≤90ppb.

[0062] According to the present invention, the Fe2P content, volume resistivity and compaction density of the lithium iron phosphate cathode material satisfy the following relationship: MI = 77.13PD - 0.03R - 107.7

[0063] Wherein, R is the volume resistivity of the lithium iron phosphate cathode material, Ω·cm;

[0064] PD is the compaction density of lithium iron phosphate cathode material, g / cm 3 ;

[0065] MI is the Fe2P content of lithium iron phosphate positive electrode material, ppb.

[0066] In the present invention, when the Fe2P content, volume resistivity and compaction density of the positive electrode material satisfy the above relationship, a positive electrode material with a high compaction density can be prepared at a relatively low temperature, and the positive electrode material has good electrical properties.

[0067] According to the present invention, the compacted density of the lithium iron phosphate positive electrode material is related to the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the following relationship: PD=0.084I(2θ A2 )+0.377;

[0068] Where PD is the compaction density of lithium iron phosphate cathode material, g / cm 3 ;

[0069] I(2θ A2 ) is the 2θ in the XRD diffraction pattern of lithium iron phosphate cathode material A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ).

[0070] In the present invention, the inventors have found that the compaction density of the lithium iron phosphate positive electrode material is related to the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the above relationship, by regulating 2θ A2 The peak intensity of the diffraction characteristic peak at can further identify the compaction density of the positive electrode material.

[0071] A second aspect of the present invention provides a method for preparing a lithium iron phosphate positive electrode material, characterized in that the preparation method comprises the following steps:

[0072] (1) mixing an iron phosphate precursor, a lithium source, a carbon source, optionally a metal source M, optionally a Mn source, and a liquid medium, grinding the mixture into a slurry, and drying the mixture to obtain a dried material;

[0073] (2) calcining the dried material under a protective atmosphere to obtain a sintered material;

[0074] (3) crushing and screening the sintered material to obtain the lithium iron phosphate positive electrode material;

[0075] The iron phosphate precursor is tested by XRD at 2θ a1 =16.2-16.9°, 2θ a2 =27.3-28.1°, 2θ a3=29.0-29.7° and 2θ a4 =30.2-30.9° has a diffraction characteristic peak; the iron phosphate precursor is tested by XRD at 2θ b1 =20-20.7°, 2θ b2 =21.5-22.2°, 2θ b3 =23.4-24°, 2θ b4 = There is a characteristic diffraction peak at 25.5-26.2°;

[0076] The 2θ ai The integral area A(2θ ai ) and 2θ bj The integral area A(2θ bj ) satisfy:

[0077] Here, i is an integer from 1 to 4, and j is an integer from 1 to 4.

[0078] In the present invention, by adopting a precursor material with a specific XRD structure, the iron phosphate precursor has certain structural defects, which can act as a solvent during the sintering process of the precursor, thereby reducing the sintering temperature and improving the compaction density of the obtained lithium iron phosphate positive electrode material.

[0079] Furthermore, in the iron phosphate precursor,

[0080] According to the present invention, the unit cell parameters of the a-axis and c-axis of the iron phosphate precursor measured by XRD satisfy the following conditions: 2.2306≤c / a≤2.2330.

[0081] In the present invention, the selection of an iron phosphate precursor having the above-mentioned specific unit cell parameter c / a value can not only achieve a higher compaction density at a lower temperature but also reduce the content of iron phosphide in the lithium iron phosphate, thereby increasing the capacity and energy density of the positive electrode material prepared from the precursor, reducing side reactions with the electrolyte, and improving the service life and safety of the battery.

[0082] In the present invention, the crystal structure of the iron phosphate precursor is hexagonal system, and the space group is P3121.

[0083] In the present invention, the point group structure of the iron phosphate precursor presents equivalent arrangement on the a-axis and the b-axis, and the c-axis is a vertical crystal axis.

[0084] In the present invention, the unit cell parameters of the a-axis and c-axis of the iron phosphate precursor measured by XRD satisfy: 2.2306≤c / a≤2.2330, for example, it can be 2.2306, 2.2307, 2.2308, 2.2309, 2.231, 2.2311, 2.2312, 2.2313, 2.2314, 2.2315, 2.2316, 2.2317, 2.2318, 2.2319, 2.232, 2.2321, 2.2322, 2.2323, 2.2324, 2.2325, 2.2326, 2.2327, 2.2328, 2.2329, 2.2330, and a range consisting of any two values. Preferably, 2.231≤c / a≤2.2326.

[0085] According to the present invention, the iron phosphate precursor has a composition shown in Formula II: (Fe 1-y M y PO4) 1-6x [Fe4(P2O7)3] x Formula II,

[0086] Among them, 0.01≤x≤0.03, 0≤y≤0.1, and M is selected from at least one of Al, Mg, Ca, Sr, V, Cr, Y, Mo, Nb, W, La, Sm, Co, Ni, Cu, Zn, Zr and Ti.

[0087] Furthermore, 0.01≤x≤0.02, 0<y≤0.05, and M is selected from at least one of Al, Mg, Co, Ni, Cu, Zn, Zr and Ti.

[0088] According to the present invention, in the iron phosphate precursor, the molar ratio of the metal element to the phosphorus element n(Me) / n(P) is 0.96-0.98.

[0089] In the present invention, when the molar ratio of the metal element to the phosphorus element in the iron phosphate precursor satisfies the above range, the precursor has certain structural defects, and the excess phosphorus acts as a flux, thereby reducing the sintering temperature and increasing the compaction density of the obtained lithium iron phosphate positive electrode material.

[0090] Furthermore, in the iron phosphate precursor, the molar ratio of the metal element to the phosphorus element n(Me) / n(P) is 0.96-0.97.

[0091] According to the present invention, the median particle size D of the iron phosphate precursor is 50 1-25μm.

[0092] In the present invention, when the median particle size of the iron phosphate precursor satisfies the above range, it is beneficial to improve the grinding efficiency during the preparation of the positive electrode material and reduce energy consumption.

[0093] In the present invention, the median particle size D of the iron phosphate precursor is 50 The median particle size D of the iron phosphate precursor is 1-25 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 15 μm, and a range consisting of any two values. Preferably, the median particle size D of the iron phosphate precursor is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 15 μm, and a range consisting of any two values. 50 2-20μm.

[0094] According to the present invention, the primary particle size of the iron phosphate precursor is 20-200 nm.

[0095] In the present invention, when the primary particle size of the iron phosphate precursor satisfies the above range, the primary particles are uniform and dense, which is conducive to obtaining a high-density lithium iron phosphate positive electrode material.

[0096] In the present invention, the primary particle size of the iron phosphate precursor is 20-200nm, for example, it can be 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 80nm, 85nm, 90nm, 95nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, and a range consisting of any two values. Preferably, the primary particle size of the iron phosphate precursor is 50-150nm.

[0097] According to the present invention, the tap density of the iron phosphate precursor is 0.8-1.3 g / cm 3 .

[0098] In the present invention, when the tap density of the iron phosphate precursor satisfies the above range, it indicates that the precursor has a relatively high density, which is beneficial to further improve the compaction density of the lithium iron phosphate positive electrode material.

[0099] In the present invention, the tap density of the iron phosphate precursor is 0.8-1.3 g / cm 3 , for example, it can be 0.8 g / cm 3 , 0.81g / cm 3 , 0.82g / cm 3 , 0.83g / cm 3 , 0.84g / cm 3 , 0.85g / cm 3 , 0.86g / cm3 , 0.87g / cm 3 , 0.88g / cm 3 , 0.89g / cm 3 , 0.9g / cm 3 , 0.91g / cm 3 , 0.92g / cm 3 , 0.93g / cm 3 , 0.94g / cm 3 , 0.95g / cm 3 , 0.96g / cm 3 , 0.97g / cm 3 , 0.98g / cm 3 , 0.99g / cm 3 , 1g / cm 3 , 1.11g / cm 3 , 1.12g / cm 3 , 1.13g / cm 3 , 1.14g / cm 3 , 1.15g / cm 3 , 1.16g / cm 3 , 1.17g / cm 3 , 1.18g / cm 3 , 1.19g / cm 3 , 1.2g / cm 3 , 1.21g / cm 3 , 1.22g / cm 3 , 1.23g / cm 3 , 1.24g / cm 3 , 1.25g / cm 3 , 1.26g / cm 3 , 1.27g / cm 3 , 1.28g / cm 3 , 1.29g / cm 3 , 1.3g / cm 3 , and the range consisting of any two values, preferably, the tap density of the iron phosphate precursor is 0.9-1.2 g / cm 3 .

[0100] According to the present invention, the specific surface area of ​​the iron phosphate precursor is 6-10m 2 / g.

[0101] In the present invention, when the specific surface area of ​​the iron phosphate precursor satisfies the above range, the precursor has a high reactivity, and when it is used to prepare a lithium iron phosphate positive electrode material, it is beneficial to the diffusion of lithium ions and improves the charge and discharge capacity.

[0102] In the present invention, the specific surface area of ​​the iron phosphate precursor is 6-10m 2 / g, for example, 6m 2 / g,6.1m 2 / g,6.2m 2 / g,6.3m 2 / g,6.4m 2 / g,6.5m 2 / g,6.6m 2 / g,6.7m 2 / g,6.8m 2 / g,6.9m 2 / g,7m 2 / g,7.1m 2 / g,7.2m 2 / g,7.3m 2 / g,7.4m 2 / g,7.5m 2 / g,7.6m 2 / g,7.7m 2 / g,7.8m 2 / g,7.9m 2 / g,8m 2 / g,8.1m 2 / g,8.2m 2 / g,8.3m 2 / g,8.4m 2 / g,8.5m 2 / g,8.6m 2 / g,8.7m 2 / g,8.8m 2 / g,8.9m 2 / g,9m 2 / g,9.1m 2 / g,9.2m 2 / g,9.3m 2 / g,9.4m 2 / g,9.5m 2 / g,9.6m 2 / g,9.7m 2 / g,9.8m 2 / g,9.9m 2 / g,10m 2 / g, and the range of any two values, preferably, the specific surface area of ​​the iron phosphate precursor is 6.5-9.5m 2 / g.

[0103] According to the present invention, the sulfur content in the iron phosphate precursor is ≤400 ppm.

[0104] In the present invention, when the sulfur content in the iron phosphate precursor meets the above range, the lattice distortion caused by impurity ions can be effectively avoided, and the low-temperature performance and cycle performance of the cathode material prepared thereby can be improved.

[0105] In the present invention, the sulfur content in the iron phosphate precursor is ≤400ppm, for example, it can be 400ppm, 350ppm, 300ppm, 250ppm, 200ppm, 150ppm, 100ppm, 50ppm, 40ppm, 30ppm, 25ppm, 20ppm, 15ppm, 10ppm, 5ppm, 0ppm, and a range consisting of any two values. Preferably, the sulfur content in the iron phosphate precursor is ≤200ppm.

[0106] In the present invention, there is no particular limitation on the source of the iron phosphate precursor, as long as the iron phosphate precursor has the structural characteristics defined in the present invention.

[0107] In order to further ensure and improve the electrochemical performance of the lithium iron phosphate positive electrode material, preferably, the iron phosphate precursor of the present invention is prepared according to the following steps:

[0108] S1, dissolving the iron source and the M source in water to form a mixed salt solution A1;

[0109] S2, dissolving a phosphorus source in water and adding a pH adjuster to form a phosphorus source solution A2;

[0110] S3, mixing the mixed salt solution A1, the phosphorus source solution A2 and the oxidant A3, performing a synthesis reaction, and optionally adding an auxiliary agent;

[0111] S4, filtering and washing the product of step S3 to obtain filter cake B1, beating the filter cake to obtain a slurry, optionally adding an auxiliary agent, adjusting the pH value, performing an aging and crystallization reaction, and then filtering and washing to obtain filter cake B3;

[0112] S5, calcining the filter cake to obtain an iron phosphate precursor;

[0113] Wherein, the pH value of the phosphorus source solution A2 is 0.5-2.5;

[0114] The conditions of the aging crystallization reaction include: reaction temperature of 70-90°C, heating rate of 1-3°C / min, and reaction time of 1-3h;

[0115] The calcination conditions include: calcination temperature of 500-800° C., heating rate of 3-8° C. / min, and calcination time of 2-4 h.

[0116] In the present invention, by controlling the pH value of the phosphorus source solution, the aging crystallization reaction and the calcination conditions, the obtained iron phosphate precursor includes both the iron phosphate phase and the iron pyrophosphate phase, and the characteristic peak diffraction intensity of the iron pyrophosphate phase and the iron phosphate phase and the unit cell parameters of the iron phosphate precursor meet specific ranges. Specifically, the iron phosphate precursor described in the first aspect of the present invention is obtained, and when the obtained iron phosphate precursor is used to prepare a lithium iron phosphate positive electrode material, the compaction density of the lithium iron phosphate positive electrode material can be increased while reducing the sintering temperature.

[0117] Specifically, the pH value of the phosphorus source solution is controlled to regulate the oxidation precipitation reaction and generate amorphous iron phosphate; then, the aging temperature, heating rate and aging time in the aging and crystallization stage are regulated to complete the crystallization reaction from amorphous iron phosphate to dihydrate iron phosphate, thereby realizing the regulation of the crystallinity and unit cell parameters of dihydrate iron phosphate; finally, the calcination temperature, heating rate and calcination time in the calcination stage are regulated to complete the dehydration and crystallization reaction from dihydrate iron phosphate to anhydrous iron phosphate, thereby controlling the doping of iron pyrophosphate in iron phosphate and realizing the regulation of the crystallinity and unit cell parameters of anhydrous iron phosphate.

[0118] In the present invention, there is no particular limitation on the mixing method of the mixed salt solution A1, the phosphorus source solution A2, and the oxidant A3, and the timing of adding the auxiliary agent, as long as the mixed salt solution A1, the phosphorus source solution A2, and the antioxidant A3 can be fully mixed, or the aging and crystallization reaction can be carried out in the presence of an auxiliary agent.

[0119] In a specific embodiment of the present invention, the mixed salt solution A1, the phosphorus source solution A2 and the oxidant A3 are added to the reactor in a parallel flow to carry out the synthesis reaction.

[0120] In a specific embodiment of the present invention, the mixed salt solution A1 and the oxidant A3 are firstly fully reacted, and then added into the reactor in a parallel flow with the phosphorus source solution A2 to carry out a synthesis reaction.

[0121] In a specific embodiment of the present invention, the mixed salt solution A1 is used as the base solution, and the phosphorus source solution A2 and the oxidant A3 are added into the reactor in a parallel flow to carry out the synthesis reaction.

[0122] In the present invention, the pH value of the phosphorus source solution A2 is 0.5-2.5, for example, it can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, and a range consisting of any two values. In a preferred embodiment of the present invention, the pH value of the phosphorus source solution A2 is 1-2.

[0123] In the present invention, the conditions of the aging and crystallization reaction include: a reaction temperature of 70-90°C, for example, it can be 70°C, 75°C, 80°C, 85°C, 90°C, and a range consisting of any two values, a heating rate of 1-3°C / min, for example, it can be 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, and a range consisting of any two values, and a reaction time of 1-3h, for example, it can be 1h, 1.5h, 2h, 2.5h, 3h, and a range consisting of any two values; in a preferred embodiment of the present invention, the conditions of the aging and crystallization reaction include: a reaction temperature of 80-85°C, a heating rate of 2-3°C / min, and a reaction time of 1-2h.

[0124] In the present invention, the calcination conditions include: a calcination temperature of 500-800°C, for example, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, and a range consisting of any two values; a heating rate of 3-8°C / min, for example, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min, 5.5°C / min, 6°C / min, 6.5°C / min, 7°C / min, 7.5°C / min, 8°C / min, and a range consisting of any two values; a calcination time of 2-4h, for example, 2h, 2.5h, 3h, 3.5h, 4h, and a range consisting of any two values. In a preferred embodiment of the present invention, the calcination conditions include: a calcination temperature of 600-750°C, a heating rate of 3-5°C / min, and a calcination time of 2-3h.

[0125] According to the present invention, in step (4), the pH value is adjusted to 1-2.5, for example, it can be 1, 1.5, 2, 2.5, or a range consisting of any two values, preferably 1-2.

[0126] In the present invention, there is no particular limitation on the method for adjusting the pH value in step (4). In order to avoid the introduction of impurities, preferably, phosphoric acid is added to adjust the pH value.

[0127] According to the present invention, in step (1), the concentration of the mixed salt solution A1 is 0.1-4 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, and a range consisting of any two values, preferably 0.2-2 mol / L.

[0128] In the present invention, there is no specific limitation on the type of iron source, and the iron source includes but is not limited to ferrous salts. Preferably, the ferrous salt is selected from at least one of ferrous sulfate, ferrous chloride, ferrous nitrate and ferric acetate.

[0129] In the present invention, there is no specific limitation on the type of M source. The M source is a compound that can provide at least one M element selected from Mn, Al, Mg, Co, Ni, Cu, Zn, Zr and Ti, including but not limited to M-containing oxides, M-containing salts, etc.

[0130] In the present invention, in step S1, the iron source and the M source are such that 0≤n(M) / [n(Fe)+n(M)]≤0.1, preferably, 0<n(M) / [n(Fe)+n(M)]≤0.05.

[0131] In the present invention, the concentration of the phosphorus source solution A2 is 0.2-20 mol / L, for example, it can be 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, 11 mol / L, 12 mol / L, 13 mol / L, 14 mol / L, 15 mol / L, 16 mol / L, 17 mol / L, 18 mol / L, 19 mol / L, 20 mol / L, and a range consisting of any two values, preferably 1-15 mol / L.

[0132] In the present invention, the type of phosphorus source is not specifically limited. The phosphorus source includes but is not limited to at least one of phosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate and ammonium monohydrogen phosphate. Preferably, the phosphorus source is selected from at least one of phosphoric acid, sodium dihydrogen phosphate and ammonium dihydrogen phosphate.

[0133] In the present invention, the type of pH adjuster is not specifically limited. Its function is to adjust the pH of the solution. The pH adjuster is an acid solution or an alkaline solution. Preferably, the pH adjuster is selected from at least one of sodium hydroxide, ammonia water, sulfuric acid, hydrochloric acid and nitric acid.

[0134] In the present invention, in step S3, the amount of the mixed salt solution A1 and the amount of the phosphorus source solution A2 are such that n(P):n(Fe) is 1-3:1, preferably 1-1.5:1.

[0135] In the present invention, in step S3, the amount of the mixed salt solution A1 and the amount of the oxidant A3 are such that n(oxidant):n(Fe) is 1-5:1, preferably 1-3:1.

[0136] In the present invention, there is no specific limitation on the type of oxidant, and the oxidant includes but is not limited to hydrogen peroxide, ozone, sodium persulfate, ammonium persulfate, sodium hypochlorite, and sodium ferrate. Preferably, the oxidant is selected from at least one of hydrogen peroxide, sodium persulfate, and ammonium persulfate.

[0137] In the present invention, the conditions of the synthesis reaction include: a reaction temperature of 25-60°C, for example, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, and a range consisting of any two values; a reaction time of 1-6h, for example, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, and a range consisting of any two values.

[0138] Furthermore, the conditions of the synthesis reaction include: reaction temperature of 40-60° C., and reaction time of 1-3 h.

[0139] In the present invention, during the preparation of the iron phosphate precursor, an auxiliary agent is added during the aging and crystallization stage or the synthesis reaction stage, which can induce the deposition and arrangement of crystal nuclei, making the secondary particles of the precursor denser, and at the same time can help remove sulfur impurities in the crystal lattice, thereby affecting the unit cell parameters.

[0140] In the present invention, the auxiliary agent is selected from at least one of sodium cetylbenzenesulfonate, sodium dodecylbenzenesulfonate, triethanolamine, ethylene glycol, polyvinyl pyrrolidone, polyethylene glycol, lignocellulose, and carboxymethyl cellulose. Preferably, the auxiliary agent is selected from at least one of sodium cetylbenzenesulfonate, polyethylene glycol, lignocellulose, and carboxymethyl cellulose.

[0141] In the present invention, based on the total amount of the iron source and the M source, the amount of the auxiliary agent is 0.1wt%-1wt%, for example, it can be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, and a range consisting of any two values, preferably 0.1wt%-0.5wt%.

[0142] In the present invention, when the amount of the auxiliary agent is controlled to meet the above range, it can induce the deposition and arrangement of crystal nuclei, making the secondary particles denser, and at the same time can help remove sulfur impurities in the lattice, thereby further modulating the unit cell parameters in the precursor.

[0143] In the present invention, there is no special requirement for the washing method in step S4, and it can be carried out according to conventional washing methods in the art. Preferably, a washing liquid is used, preferably pure water at 20-90°C, and more preferably pure water at 30-60°C is used for washing.

[0144] According to the present invention, the amounts of the iron phosphate precursor, the lithium source, the metal source M and the Mn source are such that: n(Li):n(Fe):n(M):n(Mn)=1+a:b:c:d, wherein -0.1≤a≤0.1, 0≤b≤1, 0≤c≤0.5, 0≤d≤1.

[0145] In the present invention, there is no particular limitation on the specific amount of the metal source M, as long as the amount of the metal source M and the iron phosphate precursor is such that the content c of the M element in the positive electrode material satisfies 0≤c≤0.5.

[0146] Furthermore, the amounts of the iron phosphate precursor, the lithium source, the metal source M and the Mn source are such that:

[0147] n(Li): n(Fe): n(M): n(Mn)=1+a:b:c:d, where -0.05≤a≤0.05, 0.5≤b≤1, 0.001≤c≤0.1, 0≤d≤0.5.

[0148] According to the present invention, based on the total mass of the iron phosphate precursor, the amount of the carbon source is 8wt%-18wt%, for example, it can be 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, and a range consisting of any two values, preferably 10wt%-15wt%.

[0149] In the present invention, the type of the liquid medium is not specifically limited, as long as a uniform slurry can be formed. For example, the liquid medium is selected from at least one of water, methanol, ethanol, propanol, ethylene glycol, isopropanol, benzyl alcohol, acetone, benzene, toluene, methyl ether, ethyl ether, acetic acid, xylene, tetrahydrofuran, dimethyl carbonate, N-methylpyrrolidone, propylene carbonate, triethylamine, triethanolamine, N,N-dimethylformamide, N,N-diethylformamide, acetonitrile, and ethylene glycol dimethyl ether. The amount of the liquid medium used is also not specifically limited, as long as a uniform slurry can be formed.

[0150] In the present invention, there is no particular limitation on the type of the lithium source. For example, the lithium source is selected from at least one of lithium oxide, lithium hydroxide, lithium chloride, lithium nitrate, lithium nitrite, lithium formate, lithium acetate, lithium oxalate, lithium carbonate, lithium phosphate, dilithium hydrogen phosphate and lithium dihydrogen phosphate. Preferably, the lithium source is selected from at least one of lithium hydroxide, lithium carbonate and lithium dihydrogen phosphate.

[0151] In the present invention, there is no particular limitation on the type of the carbon source. For example, the carbon source is selected from at least one of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, phenolic resin, polyethylene glycol, dopamine, graphene and carbon nanotubes. Preferably, the carbon source is selected from at least one of glucose, sucrose, starch, graphene and polyethylene glycol.

[0152] In the present invention, there is no particular limitation on the type of the metal source M, as long as it can provide a compound of the element M. For example, the metal source M is selected from at least one of oxalates, nitrates, acetates, oxides, hydroxides, carbonates, phosphates, metal clusters, metal complexes and carboxylates that can provide the element M.

[0153] In the present invention, there is no particular limitation on the type of the Mn source. For example, the Mn source is at least one selected from manganese sulfate, manganese nitrate, manganese acetate, manganese chloride, and manganese oxide.

[0154] In the present invention, there is no particular limitation on the grinding method and conditions, as long as the mixture of the iron phosphate precursor, lithium source, carbon source, Mn source, metal source M and liquid medium can be fully ground so that the median particle size D of the slurry obtained by grinding is 50 It is 50-2000nm, preferably 100-1000nm.

[0155] In one embodiment of the present invention, the grinding conditions include: ball milling at a speed of 100-600 rpm using a planetary ball mill for 1-24 h; and / or ball milling at a speed of 300-3000 rpm using a stirred mill and / or a sand mill for 0.5-10 h.

[0156] According to the present invention, the solid content of the slurry is 10-70 wt%, preferably 20-60 wt%.

[0157] According to the present invention, the drying method is spray drying.

[0158] According to the present invention, the spray drying conditions include: air inlet temperature of 190-280°C and air outlet temperature of 60-120°C.

[0159] Furthermore, the spray drying conditions include: air inlet temperature of 200-270°C and air outlet temperature of 70-110°C.

[0160] In the present invention, in step (1), the median particle size D of the spray-dried material is 50 5-50 μm, preferably 8-40 μm; specific surface area 5-15 m 2 / g, preferably 8-13m 2 / g; bulk density is 0.3-1g / cm 3 , preferably 0.5-0.8g / cm 3 ; Moisture ≤5%, preferably ≤3%.

[0161] According to the present invention, in step (2), the conditions for the calcination treatment include: a calcination temperature of 500-900°C, for example, it can be 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, and a range consisting of any two values; the calcination time is 4-20h, for example, it can be 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, and a range consisting of any two values.

[0162] In the present invention, the calcination treatment is carried out under the above conditions, so that the obtained positive electrode material particles are uniform and round, and the carbon coating layer is of moderate thickness, further improving the electronic conductivity and processing performance of the positive electrode material.

[0163] Furthermore, in step (2), the calcination treatment conditions include: calcination temperature of 600-800° C.; calcination time of 6-15 hours.

[0164] In the present invention, the protective atmosphere is selected from nitrogen and / or argon.

[0165] In the present invention, in step (3), the pulverizing equipment is selected from a jet mill and / or a mechanical pulverizer.

[0166] A third aspect of the present invention provides a lithium iron phosphate positive electrode material prepared by the above preparation method.

[0167] A fourth aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery pack includes the above-mentioned lithium iron phosphate positive electrode material.

[0168] In the present invention, when the lithium iron phosphate positive electrode material is applied to a lithium ion battery, it can effectively improve the electrochemical performance of the lithium ion battery, showing higher capacity and energy efficiency, lower internal resistance, and better cycle performance.

[0169] In the present invention, the 0.1C capacity of the lithium-ion battery prepared from the lithium iron phosphate positive electrode material is ≥158 mAh / g, preferably ≥160 mAh / g.

[0170] In the present invention, the 0.5C capacity of the lithium-ion battery prepared from the lithium iron phosphate positive electrode material is ≥151 mAh / g, preferably ≥152 mAh / g.

[0171] In the present invention, the 1C capacity of the lithium-ion battery prepared from the lithium iron phosphate positive electrode material is ≥143.5 mAh / g, preferably ≥145.5 mAh / g.

[0172] In the present invention, the lithium-ion battery prepared from the lithium iron phosphate positive electrode material has a 1C@200 cycle capacity retention rate of ≥97%.

[0173] In the present invention, the first-cycle energy efficiency of the lithium-ion battery prepared from the lithium iron phosphate positive electrode material is ≥90%, preferably ≥91%.

[0174] The present invention will be described in detail below by way of examples.

[0175] The crystallization properties of the iron phosphate precursor, including the unit cell parameters, were measured using a Shimadzu XRD-6000 X-ray powder diffractometer. The instrument was set to 40 kV, 40 mA, a step size of 0.005°, a 10 mm height limit slit, a 1 / 2° divergence slit, an 8 mm anti-scattering slit, and an open receiving slit. The test scan angle was set between 10° and 80°, with continuous scanning in 1D mode at a scan rate of 1.2° / min.

[0176] The content of each element in the iron phosphate precursor and lithium iron phosphate positive electrode material was measured using an Agilent 5800 ICP-OES spectrometer from the United States. The argon partial pressure gauge was controlled at 80-100 psi, the liquid argon boost valve compression control pressure was above 200 psi, nitrogen was 60-100 psi, and compressed air was 80-100 psi. When making a standard curve, a three-point calibration was required based on the sample concentration, and the coefficient of the standard curve was above 0.9999.

[0177] The median particle size of the iron phosphate precursor and the lithium iron phosphate positive electrode material was tested using a Malvern laser particle size analyzer Mastersizer 3000. A certain amount of sodium pyrophosphate dispersant was added, and the sample was added to a light shielding range of 10%-20%. Ultrasonication was performed for 3 minutes before starting the test, and the average of three tests was taken as the median particle size measurement value.

[0178] The primary particle size of the iron phosphate precursor is tested using a scanning electron microscope S-4800 of Hitachi HITACHI, Japan, with a test voltage of 1 kV-5 kV and a test magnification of 1 k-30 k.

[0179] The tap density of the iron phosphate precursor material was tested using a BT-30 tap density tester from Baxter, with the vibration times set to 3000 times and the vibration frequency to 250 times / min.

[0180] The specific surface areas of the iron phosphate precursor and the lithium iron phosphate cathode material were tested using a Tristar II 3020 specific surface area tester from Micromertics, USA, with a degassing temperature of 300° C. and a degassing time of 120 min.

[0181] The compaction density of the lithium iron phosphate positive electrode material was measured using the MCP-PD51 compaction density meter produced by Mitsubishi Chemical of Japan. 1±0.01g of sample was weighed and a pressure of 3T was selected for testing.

[0182] The volume resistivity of the lithium iron phosphate positive electrode material was tested using a MCP-PD51 powder compaction resistance meter produced by Mitsubishi Chemical of Japan. The volume resistivity was measured using a four-probe method under a pressure of 20 kN.

[0183] The raw materials used in the examples and comparative examples are all commercially available products.

[0184] Preparation Example - Preparation of Iron Phosphate Precursor

[0185] Preparation Example 1

[0186] S1. According to the molar ratio of n(Fe):n(Ti)=0.99:0.01, a certain amount of ferrous sulfate and titanyl sulfate were weighed and dissolved in deionized water to prepare a 2 mol / L mixed salt solution A1.

[0187] S2. Weigh a certain amount of concentrated phosphoric acid, add 30% sodium hydroxide to adjust the pH of the solution to 2, and prepare a 2 mol / L phosphorus source solution A2.

[0188] S3. Add a certain amount of mixed salt solution A1, phosphorus source solution A2 and 30% hydrogen peroxide solution A3 into the reactor in parallel for synthesis reaction at a reaction temperature of 40° C. for 1 h.

[0189] S4. After the reaction is completed, the reaction slurry is filtered and washed to obtain a filter cake. The filter cake is beaten to obtain a slurry, which is added to a reactor, 0.1 wt% of lignocellulose is added based on the total mass of ferrous sulfate and titanyl sulfate, phosphoric acid is added to adjust the pH to 1.5, the heating rate is controlled at 2°C / min, the aging temperature is 82°C, and the aging time is 2 hours. After the reaction is completed, the reaction slurry is filtered and washed to obtain a filter cake.

[0190] S5, calcining the filter cake at high temperature for dehydration, controlling the heating rate to 3°C / min, the calcination temperature to 700°C, and the calcination time to 3h, to obtain anhydrous iron phosphate precursor P1. Its composition is (Fe 0.99 Ti 0.01 PO4) 0.91 [Fe4(P2O7)3] 0.015 , where x=0.015, y=0.01.

[0191] Figure 1 is the XRD spectrum of the iron phosphate precursor P1. It can be seen from Figure 1 that the precursor material has a 2θ a1 =16.2-16.9°, 2θ a2 =27.3-28.1°, 2θ a3 =29.0-29.7° and 2θ a4 =30.2-30.9°, there is a characteristic diffraction peak at 2θ b1 =20-20.7°, 2θ b2 =21.5-22.2°, 2θ b3 =23.4-24°, 2θ b4 = There is a characteristic peak at 25.5-26.2°, which suggests that the iron phosphate precursor contains iron pyrophosphate phase;

[0192] Figure 2 is an SEM image of the iron phosphate precursor P1. It can be seen from Figure 2 that the primary particles are uniform and dense, which reduces the differences between particles during the calcination stage, thereby effectively improving the compaction density of the positive electrode material.

[0193] Preparation Example 2

[0194] S1, same as Preparation Example 1.

[0195] S2, same as Preparation Example 1.

[0196] S3, same as Preparation Example 1.

[0197] S4, same as Preparation Example 1.

[0198] S5, calcining the filter cake at high temperature for dehydration, controlling the heating rate to 5°C / min, the calcination temperature to 650°C, and the calcination time to 2h to obtain anhydrous iron phosphate P2. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.886 [Fe4(P2O7)3] 0.019 , where x=0.019, y=0.01.

[0199] Preparation Example 3

[0200] S1, same as Preparation Example 1.

[0201] S2, same as Preparation Example 1.

[0202] S3, same as Preparation Example 1.

[0203] S4. After the reaction is completed, the reaction slurry is filtered and washed to obtain a filter cake. The filter cake is beaten to obtain a slurry, which is added to a reactor, and 0.1 wt% of lignocellulose is added based on the total mass of ferrous sulfate and titanyl sulfate. Phosphoric acid is added to adjust the pH to 1.5, and the heating rate is controlled to 3°C / min, the aging temperature is 80°C, and the aging time is 1 hour. After the reaction is completed, the reaction slurry is filtered and washed to obtain a filter cake.

[0204] S5. The same as in Example 1, anhydrous iron phosphate precursor P3 is obtained. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.904 [Fe4(P2O7)3] 0.016 , where x=0.016, y=0.01.

[0205] Preparation Example 4

[0206] S1, same as Preparation Example 1.

[0207] S2. Weigh a certain mass of concentrated phosphoric acid, add 30% sodium hydroxide to adjust the pH of the solution to 1.5, and prepare a 2 mol / L phosphorus source solution.

[0208] S3, same as Preparation Example 1.

[0209] S4, same as Preparation Example 1.

[0210] S5, the same as Preparation Example 1. Obtain anhydrous iron phosphate precursor P4. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.898 [Fe4(P2O7)3] 0.017 , where x=0.017, y=0.01.

[0211] Preparation Example 5

[0212] S1, same as Preparation Example 1.

[0213] S2. Weigh a certain amount of ammonium dihydrogen phosphate, dissolve it in deionized water, and add 30% dilute sulfuric acid to adjust the pH of the solution to 2 to prepare a 2 mol / L phosphorus source solution.

[0214] S3, same as Preparation Example 1.

[0215] S4, same as Preparation Example 1.

[0216] S5, the same as in Preparation Example 1, to obtain anhydrous iron phosphate precursor P5. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.91 [Fe4(P2O7)3] 0.015 , where x=0.015, y=0.01.

[0217] Preparation Example 6

[0218] S1, same as Preparation Example 1.

[0219] S2. Weigh a certain amount of ammonium dihydrogen phosphate, dissolve it in deionized water, and add 30% dilute sulfuric acid to adjust the pH of the solution to 2 to prepare a 2 mol / L phosphorus source solution.

[0220] S3, same as Preparation Example 1.

[0221] S4. After the reaction is completed, 0.1wt% of lignocellulose is added based on the total mass of ferrous sulfate and titanyl sulfate, phosphoric acid is added to adjust the pH to 1.5, the heating rate is controlled to 2°C / min, the aging temperature is 82°C, and the aging time is 2h. After the reaction is completed, the reaction slurry is filtered and washed to obtain a filter cake. S5. The same as in Example 1, anhydrous iron phosphate precursor P6 is obtained. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.91 [Fe4(P2O7)3] 0.015 , where x=0.015, y=0.01.

[0222] Preparation Example 7

[0223] S1. Weigh a certain amount of ferrous sulfate and dissolve it in deionized water to prepare a 2 mol / L salt solution.

[0224] S2, same as Preparation Example 1.

[0225] S3, same as Preparation Example 1.

[0226] S4, same as Preparation Example 1.

[0227] S5. The same as in Preparation Example 1, anhydrous iron phosphate precursor P7 is obtained. Its composition is: (FePO4) 0.88 [Fe4(P2O7)3] 0.02 , where x=0.02, y=0.

[0228] Comparative Preparation Example 1

[0229] S1, same as Preparation Example 1.

[0230] S2, same as Preparation Example 1.

[0231] S3, same as Preparation Example 1.

[0232] S4, same as Preparation Example 1.

[0233] S5, calcining the filter cake at high temperature for dehydration, controlling the heating rate at 2°C / min, the calcination temperature at 850°C, and the calcination time at 5h to obtain anhydrous iron phosphate precursor DP1. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.958 [Fe4(P2O7)3] 0.007 , where x=0.007, y=0.01.

[0234] Comparative Preparation Example 2

[0235] S1, same as Preparation Example 1.

[0236] S2, same as Preparation Example 1.

[0237] S3, same as Preparation Example 1.

[0238] S4. After the reaction is complete, the reaction slurry is filtered and washed to obtain a filter cake. The filter cake is beaten to obtain a slurry, which is added to a reactor. Lignocellulose is added, and phosphoric acid is added to adjust the pH to 1.5. The temperature is raised at a rate of 0.5°C / min, the aging temperature is 95°C, and the aging time is 4 hours. After the reaction is complete, the reaction slurry is filtered and washed to obtain a filter cake.

[0239] S5. The same as in Preparation Example 1, anhydrous iron phosphate precursor DP2 is obtained. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.946 [Fe4(P2O7)3] 0.009 , where x=0.009, y=0.01.

[0240] Comparative Preparation Example 3

[0241] S1, same as Preparation Example 1.

[0242] S2. The same as Preparation Example 1, except that a certain mass of concentrated phosphoric acid was weighed, and 30% sodium hydroxide was added to adjust the pH of the solution to 3 to prepare a 2 mol / L phosphorus source solution.

[0243] S3, same as Preparation Example 1.

[0244] S4, same as Preparation Example 1.

[0245] S5, calcining the filter cake at high temperature for dehydration, controlling the heating rate to 3°C / min, the calcination temperature to 700°C, and the calcination time to 3h to obtain anhydrous iron phosphate precursor DP3, which has the following composition: (Fe 0.99 Ti 0.01 PO4) 0.952 [Fe4(P2O7)3] 0.008 , where x=0.008, y=0.01.

[0246] The physicochemical indicators of the lithium iron phosphate precursor prepared in the preparation example are shown in Table 1.

[0247] Table 1

[0248] * refers to

[0249] Example - for preparing lithium iron phosphate positive electrode material

[0250] Example 1

[0251] (1) The iron phosphate precursor P1, lithium carbonate, and titanium oxide were added so that n(Fe):n(Li):n(Ti)=0.961:1.04:0.019, and mixed with pure water. Glucose was added in an amount of 12 wt% of the mass of the carbon source and the mass of the iron phosphate precursor P1, and the solid content was controlled to be 40 wt%. The mixture was uniformly mixed by mechanical stirring to obtain a slurry. The slurry was ground by a sand mill (condition: speed 800 rpm) to control the median particle size D of the slurry. 50 The particle size is 380nm; the ground slurry is spray dried and granulated, and the inlet air temperature is controlled at 235℃ and the outlet air temperature is 85℃ to obtain the spray dried material;

[0252] (2) sintering the spray-dried material under a nitrogen atmosphere at a heating rate of 2°C / min, a calcination temperature of 770°C, and a calcination time of 9 hours to obtain a sintered material;

[0253] (3) The sintered material is crushed and sieved by air flow to obtain lithium iron phosphate positive electrode material A1.

[0254] Lithium iron phosphate positive electrode material A1 includes a matrix and a carbon coating layer coated on the surface of the matrix, wherein the matrix is ​​composed of Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0255] The XRD of lithium iron phosphate cathode material A1 is shown in FIG3 . As can be seen from FIG3 , the cathode material has a A1 =29.4-29.6°, 2θ A2=29.8-30° and 2θ A3 =43.8-43.9°, and there is a characteristic diffraction peak at 2θ B1 =25.4-25.5°, 2θ B2 =35.9-36° and 2θ B3 =60.7-60.8°, there is a characteristic diffraction peak. Through analysis, it is speculated that there is lithium iron pyrophosphate phase in the positive electrode material A1. A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio I(2θ A2 ) / I(2θ B3 ) is 0.255. At the same time, the compaction density of the lithium iron phosphate positive electrode material A1 is consistent with the 2θ measured by XRD of the positive electrode material. A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the following relationship: PD=0.084I(2θ A2 )+0.377.

[0256] Example 2

[0257] (1) The same as Example 1, except that the iron phosphate precursor P2 is used to replace the iron phosphate precursor P1, the iron phosphate precursor P2, lithium carbonate, and titanium oxide are added so that n(Fe):n(Li):n(Ti)=0.953:1.04:0.019, and are mixed with pure water to obtain a spray-dried material;

[0258] (2) Same as Example 1.

[0259] (3) The same as in Example 1, obtain lithium iron phosphate positive electrode material A2. Lithium iron phosphate positive electrode material A2 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.953 Ti 0.019 )(PO4) 0.886 (P2O7) 0.057 .

[0260] XRD analysis shows that the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio I(2θ A2 ) / I(2θ B3 ) is 0.267. At the same time, the compaction density of the lithium iron phosphate positive electrode material A2 is consistent with the 2θ measured by XRD of the positive electrode material.A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the following relationship: PD=0.084I(2θ A2 )+0.377.

[0261] Example 3

[0262] (1) The same as Example 1, except that the iron phosphate precursor P3 is used to replace the iron phosphate precursor P1, the iron phosphate precursor P3, lithium carbonate, and titanium oxide are added so that n(Fe):n(Li):n(Ti)=0.959:1.04:0.019, and are mixed with pure water to obtain a spray-dried material;

[0263] (2) Same as Example 1.

[0264] (3) The same as in Example 1, obtain lithium iron phosphate positive electrode material A3. Lithium iron phosphate positive electrode material A3 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.959 Ti 0.019 )(PO4) 0.904 (P2O7) 0.048 .

[0265] XRD analysis shows that the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio I(2θ A2 ) / I(2θ B3 ) is 0.264. At the same time, the compaction density of the lithium iron phosphate positive electrode material A3 is consistent with the 2θ measured by XRD of the positive electrode material. A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the following relationship: PD=0.084I(2θ A2 )+0.377.

[0266] Example 4

[0267] (1) The same as Example 1, except that the iron phosphate precursor P4 was used to replace the iron phosphate precursor P1, and the iron phosphate precursor P4, lithium carbonate, and titanium oxide were added so that n(Fe):n(Li):n(Ti)=0.957:1.04:0.019, and mixed with pure water to obtain a spray-dried material;

[0268] (2) Same as Example 1.

[0269] (3) The same as in Example 1, obtain lithium iron phosphate positive electrode material A4. Lithium iron phosphate positive electrode material A4 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.957 Ti 0.019 )(PO4) 0.898 (P2O7) 0.051 .

[0270] XRD analysis shows that the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio I(2θ A2 ) / I(2θ B3 ) is 0.266. At the same time, the compaction density of the lithium iron phosphate positive electrode material A4 is consistent with the 2θ measured by XRD of the positive electrode material. A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the following relationship: PD=0.084I(2θ A2 )+0.377.

[0271] Example 5

[0272] (1) The same as Example 1, except that the iron phosphate precursor P5 was used to replace the iron phosphate precursor P1, and the iron phosphate precursor P5, lithium carbonate, and titanium oxide were added so as to follow n(Fe):n(Li):n(Ti)=0.961:1.04:0.019, and were mixed with pure water to obtain a spray-dried material;

[0273] (2) Same as Example 1.

[0274] (3) The same as in Example 1, obtain lithium iron phosphate positive electrode material A5. The lithium iron phosphate positive electrode material A5 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0275] XRD analysis shows that the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio I(2θ A2 ) / I(2θ B3) is 0.254. At the same time, the compaction density of the lithium iron phosphate positive electrode material A5 is consistent with the 2θ measured by XRD of the positive electrode material. A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the following relationship: PD=0.084I(2θ A2 )+0.377.

[0276] Example 6

[0277] (1) The same as Example 1, except that the iron phosphate precursor P6 is used to replace the iron phosphate precursor P1, and the iron phosphate precursor P6, lithium carbonate, and titanium oxide are added so that n(Fe):n(Li):n(Ti)=0.961:1.04:0.019, and are mixed with pure water to obtain a spray-dried material;

[0278] (2) Same as Example 1.

[0279] (3) The same as in Example 1, obtain lithium iron phosphate positive electrode material A6. Lithium iron phosphate positive electrode material A6 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0280] XRD analysis shows that the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio I(2θ A2 ) / I(2θ B3 ) is 0.253. At the same time, the compaction density of the lithium iron phosphate positive electrode material A6 is consistent with the 2θ measured by XRD of the positive electrode material. A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the following relationship: PD=0.084I(2θ A2 )+0.377.

[0281] Example 7

[0282] (1) The same as Example 1; except that the iron phosphate precursor P7 is used to replace the iron phosphate precursor P1, the iron phosphate precursor P7, lithium carbonate, and titanium oxide are added so that n(Fe):n(Li):n(Ti)=0.960:1.04:0.019, and are mixed with pure water to obtain a spray-dried material;

[0283] (2) Same as Example 1.

[0284] (3) The same as in Example 1, obtain lithium iron phosphate positive electrode material A7. The lithium iron phosphate positive electrode material A7 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.960 Ti 0.019 )(PO4) 0.88 (P2O7) 0.06 .

[0285] XRD analysis shows that the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio I(2θ A2 ) / I(2θ B3 ) is 0.254. At the same time, the compaction density of the lithium iron phosphate positive electrode material A7 is consistent with the 2θ measured by XRD of the positive electrode material. A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the following relationship: PD=0.084I(2θ A2 )+0.377.

[0286] Example 8

[0287] (1) Same as Example 1, except that the median particle size D of the slurry is controlled. 50 The diameter of the spray-dried material is 450 nm;

[0288] (2) Same as Example 1;

[0289] (3) The same as in Example 1, obtain lithium iron phosphate positive electrode material A8. The lithium iron phosphate positive electrode material A8 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0290] XRD analysis shows that the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio I(2θ A2 ) / I(2θ B3 ) is 0.25. At the same time, the compaction density of the lithium iron phosphate positive electrode material A8 is consistent with the 2θ measured by XRD of the positive electrode material.A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the following relationship: PD=0.084I(2θ A2 )+0.377.

[0291] Example 9

[0292] (1) Same as Example 1, except that the median particle size D of the slurry is controlled. 50 The particle size is 300 nm; spray-dried material is obtained;

[0293] (2) Same as Example 1;

[0294] (3) The same as in Example 1, obtain lithium iron phosphate positive electrode material A9. The lithium iron phosphate positive electrode material A9 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0295] XRD analysis shows that the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio I(2θ A2 ) / I(2θ B3 ) is 0.251. At the same time, the compaction density of the lithium iron phosphate positive electrode material A9 is consistent with the 2θ measured by XRD of the positive electrode material. A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the following relationship: PD=0.084I(2θ A2 )+0.377.

[0296] Example 10

[0297] (1) Same as Example 1.

[0298] (2) Same as Example 1, except that the sintering temperature is 760°C.

[0299] (3) Same as Example 1. Obtain lithium iron phosphate positive electrode material A10. The lithium iron phosphate positive electrode material A10 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0300] XRD analysis shows that the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio I(2θ A2 ) / I(2θ B3 ) is 0.252. At the same time, the compaction density of the lithium iron phosphate positive electrode material A10 is consistent with the 2θ measured by XRD of the positive electrode material. A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the following relationship: PD=0.084I(2θ A2 )+0.377.

[0301] Example 11

[0302] (1) Same as Example 1.

[0303] (2) Same as Example 1, except that the calcination temperature is 780°C.

[0304] (3) Same as Example 1. Obtain lithium iron phosphate positive electrode material A11. Lithium iron phosphate positive electrode material A11 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0305] XRD analysis shows that the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio I(2θ A2 ) / I(2θ B3 ) is 0.255. At the same time, the compaction density of the lithium iron phosphate positive electrode material A11 is consistent with the 2θ measured by XRD of the positive electrode material. A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the following relationship: PD=0.084I(2θ A2 )+0.377.

[0306] Example 12

[0307] (1) Same as Example 1.

[0308] (2) Same as Example 1, except that the calcination temperature is 900°C.

[0309] (3) Same as Example 1. Obtain lithium iron phosphate positive electrode material A12. Lithium iron phosphate positive electrode material A12 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0310] XRD analysis shows that the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio I(2θ A2 ) / I(2θ B3 ) is 0.266. At the same time, the compaction density of the lithium iron phosphate positive electrode material A12 is consistent with the 2θ measured by XRD of the positive electrode material. A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the following relationship: PD=0.084I(2θ A2 )+0.377.

[0311] Example 13

[0312] (1) As in Example 1, the iron phosphate precursor P1, lithium carbonate, titanium oxide, and manganese oxide were added so that n(Fe):n(Li):n(Ti):n(Mn)=0.961:1.04:0.01:0.01, and mixed with pure water to obtain a spray-dried material;

[0313] (2) Same as Example 1.

[0314] (3) The same as in Example 1, obtain lithium iron phosphate positive electrode material A13. The lithium iron phosphate positive electrode material A13 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.961 Ti 0.01 Mn 0.01 )(PO4) 0.91 (P2O7) 0.045 .

[0315] XRD analysis shows that the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θB3 ) ratio I(2θ A2 ) / I(2θ B3 ) is 0.254. At the same time, the compaction density of the lithium iron phosphate positive electrode material A13 is consistent with the 2θ measured by XRD of the positive electrode material. A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the following relationship: PD=0.084I(2θ A2 )+0.377.

[0316] Comparative Example 1

[0317] (1) The same as Example 1, except that the iron phosphate precursor DP1 was used to replace the iron phosphate precursor P1, and the iron phosphate precursor DP1, lithium carbonate, and titanium oxide were added so that n(Fe):n(Li):n(Ti)=0.976:1.04:0.019, and were mixed with pure water to obtain a spray-dried material;

[0318] (2) Same as Example 1.

[0319] (3) The same as in Example 1, a lithium iron phosphate positive electrode material D1 is obtained. The lithium iron phosphate positive electrode material D1 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.976 Ti 0.019 )(PO4) 0.958 (P2O7) 0.021 .

[0320] XRD analysis shows that the positive electrode material D1 has a A1 =29.4-29.6°, 2θ A2 = = 29.8-30°, 2θ A3 There is no characteristic diffraction peak at =43.8-43.9°.

[0321] Comparative Example 2

[0322] (1) The same as Example 1, except that the iron phosphate precursor DP2 is used to replace the iron phosphate precursor P1, the iron phosphate precursor DP2, lithium carbonate, and titanium oxide are added so that n(Fe):n(Li):n(Ti)=0.999:1.04:0.019, and are mixed with pure water to obtain a spray-dried material;

[0323] (2) Same as Example 1.

[0324] (3) The same as in Example 1, obtain lithium iron phosphate positive electrode material D2. The lithium iron phosphate positive electrode material D2 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe0.999 Ti 0.019 )(PO4) 0.946 (P2O7) 0.027 .

[0325] XRD analysis shows that the positive electrode material D2 has a A1 =29.4-29.6°, 2θ A2 = = 29.8-30°, 2θ A3 There is no characteristic diffraction peak at =43.8-43.9°.

[0326] Comparative Example 3

[0327] (1) The same as Example 1, except that the iron phosphate precursor DP3 is used to replace the iron phosphate precursor P1, the iron phosphate precursor DP3, lithium carbonate, and titanium oxide are added so that n(Fe):n(Li):n(Ti)=0.998:1.04:0.019, and are mixed with pure water to obtain a spray-dried material;

[0328] (2) Same as Example 1.

[0329] (3) The same as in Example 1, a lithium iron phosphate positive electrode material D3 is obtained. The lithium iron phosphate positive electrode material D3 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.998 Ti 0.019 )(PO4) 0.952 (P2O7) 0.024 .

[0330] XRD analysis shows that the positive electrode material D3 has a A1 =29.4-29.6°, 2θ A2 = = 29.8-30°, 2θ A3 There is no characteristic diffraction peak at =43.8-43.9°.

[0331] Comparative Example 4

[0332] (1) The same as Example 1, except that the iron phosphate precursor DP1 was used to replace the iron phosphate precursor P1, and the iron phosphate precursor DP1, lithium carbonate, and titanium oxide were added so that n(Fe):n(Li):n(Ti)=0.976:1.04:0.019, and were mixed with pure water to obtain a spray-dried material;

[0333] (2) Same as Example 1, except that the calcination temperature is 795°C.

[0334] (3) The lithium iron phosphate positive electrode material D4 is obtained in the same manner as in Example 1. The lithium iron phosphate positive electrode material D4 comprises a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li1.04(Fe 0.976 Ti 0.019 )(PO4) 0.958 (P2O7) 0.021 .

[0335] XRD analysis shows that the positive electrode material D4 has a A1 =29.4-29.6°, 2θ A2 = = 29.8-30°, 2θ A3 There is no characteristic diffraction peak at =43.8-43.9°.

[0336] Comparative Example 5

[0337] (1) Same as Example 1.

[0338] (2) Same as Example 1, except that the calcination temperature is 480°C.

[0339] (3) Same as Example 1. Obtain lithium iron phosphate positive electrode material D5. The lithium iron phosphate positive electrode material D5 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0340] XRD analysis shows that the positive electrode material D5 has a A1 =29.4-29.6°, 2θ A2 =29.8-30°, 2θ A3 There is no characteristic diffraction peak at =43.8-43.9°.

[0341] In the Examples and Comparative Examples, the median particle size, specific surface area, bulk density and moisture content of the spray-dried materials are shown in Table 2.

[0342] Table 2

[0343] Example

[0344] The physicochemical indicators of lithium iron phosphate positive electrode materials are shown in Table 2.

[0345] Table 2 continued

[0346] 1 Refers to the average particle size of primary particles.

[0347] The Fe2P content, volume resistivity and compaction density of the lithium iron phosphate positive electrode materials obtained in Examples 1 to 11, 14, Comparative Examples 1 to 3 and 5 satisfy the following relationship: MI = 77.13PD-0.03R-107.7.

[0348] Test Case

[0349] This test example is used to illustrate electrode materials, electrodes, lithium-ion batteries, and their preparation methods.

[0350] (1) Preparation of positive electrode sheets: The lithium iron phosphate positive electrode materials prepared in the above examples and comparative examples, the conductive agent carbon nanotubes, and the NMP solution of the binder PVDF were mixed at a mass ratio of 90:5:5. The specific method is as follows: the dried positive electrode material and the conductive agent were ground in a mortar for 15 minutes. After grinding, PVDF solution (mass fraction 5%) was added according to the proportion and stirred on a magnetic stirrer for 6 hours; the obtained paste slurry was evenly coated on the current collector aluminum foil, and then dried in a vacuum drying oven at 60°C for 20 hours. Then, it was stamped into a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm using a pressure of 100 MPa. The positive electrode sheet was placed in a vacuum drying oven at 120°C and dried for 12 hours.

[0351] (2) Battery assembly: A lithium metal sheet with a diameter of 17 mm and a thickness of 1 mm was used as the negative electrode, a polyethylene porous membrane coated with an alumina ceramic layer and a thickness of 25 μm was used as the separator, and an equal amount of a mixture of 1 mol / L LiPF6, ethylene carbonate (EC) and diethyl carbonate (DEC) was selected as the electrolyte. The positive electrode sheet, separator, negative electrode sheet and electrolyte were assembled into a 2025 button battery in an Ar gas glove box with a water content and an oxygen content of less than 5 ppm.

[0352] (3) Electrochemical performance test: The battery was charged and discharged using a LAND CT2001A charge and discharge instrument from Wuhan Rambo Electronics Co., Ltd. The charge and discharge voltage range was 2.5 to 3.75 V. The specific capacity of the assembled lithium-ion battery was tested at rates of 0.1C and 1C, respectively, and the cycle performance was tested at a rate of 1C. The test results are shown in Table 3.

[0353] Table 3

[0354] From the results in Table 2 and Table 3, we can see that 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio I(2θ A2) / I(2θ B3 )≥0.26, the cathode material exhibits higher compaction density, better electrochemical performance, and generates less Fe2P content.

[0355] FIG1 is an XRD diagram of the iron phosphate precursor prepared in Preparation Example 1 of the present invention. It can be seen from FIG1 that at 2θ a1 =16.2-16.9°, 2θ a2 =27.3-28.1°, 2θ a3 =29-29.7° and 2θ a4 =30.2-30.9°, which proves that the iron phosphate precursor contains iron pyrophosphate phase.

[0356] FIG2 is a SEM image of the iron phosphate precursor prepared in Preparation Example 1 of the present invention. It can be seen from FIG2 that the average primary particle size of the iron phosphate precursor is 150 nm.

[0357] FIG3 is an XRD diagram of the lithium iron phosphate cathode material prepared in Example 1 and Example 2 of the present invention. It can be seen from FIG3 that at 2θ A1 =29.50°, 2θ A2 =29.93°, 2θ A3 There is an obvious diffraction characteristic peak at =43.85°, which proves that the positive electrode material contains lithium iron pyrophosphate phase.

[0358] FIG4 is a SEM image of the lithium iron phosphate positive electrode material prepared in Example 1 of the present invention. The positive electrode material has secondary particle structures formed by primary particles.

[0359] FIG5 is a charge and discharge performance diagram of a lithium-ion battery assembled from the lithium iron phosphate positive electrode materials of Example 1 and Example 2. As can be seen from FIG5 , Example 2 has higher charge capacity and discharge capacity.

[0360] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A lithium iron phosphate cathode material, characterized in that, Through XRD testing, the cathode material has diffraction characteristic peaks at 2θ A1 = 29.4 - 29.6°, 2θ A2 = 29.8 - 30° and 2θ A3 = 43.8 - 43.9°.

2. The lithium iron phosphate cathode material according to claim 1, wherein, Through XRD testing, the cathode material has diffraction characteristic peaks at 2θ B1 = 25.4 - 25.5°, 2θ B2 = 35.9 - 36° and 2θ B3 = 60.7 - 60.8°; Preferably, the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ A2 and the peak intensity I(2θ B3 ) of the diffraction characteristic peak at 2θ B3 satisfy the ratio 0.25 ≤ I(2θ A2 ) / I(2θ B3 ) ≤ 0.27, preferably 0.26 ≤ I(2θ A2 ) / I(2θ B3 ) ≤ 0.

27.

3. The lithium iron phosphate cathode material according to claim 1 or 2, wherein, The positive electrode material includes a matrix and a carbon coating layer coated on the surface of the matrix; Among them, the matrix has the composition shown in Formula I: Li 1+a Fe b M c Mn d (PO4) 1-2w (P2O7) w Formula I; Among them, -0.1 ≤ a ≤ 0.1, 0 ≤ b ≤ 1, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 1, 0.03 ≤ w ≤ 0.09; M is selected from at least one of La, Ce, Cr, Mo, Ca, Hf, Ti, Fe, Zn, Y, Zr, W, Nb, Sm, Co, Ni, V, Mg, Na, B, and Al; preferably, M is selected from at least one of Al, Zr, W, Co, V, and Ti; Preferably, based on the total weight of the positive electrode material, the content of the carbon coating layer is 0.5-2 wt%, preferably 1-1.5 wt%.

4. The positive electrode material according to any one of claims 1-3, wherein, The lithium iron phosphate cathode material has a secondary particle structure formed by primary particles, and the median particle size D 50 of the primary particles is 0.2 - 2 μm; Preferably, the tap density of the lithium iron phosphate cathode material is 2.5-2.7 g / cm 3 ; Preferably, the tap density of the lithium iron phosphate cathode material is 0.6-1.1 g / cm 3 ; Preferably, the specific surface area of the lithium iron phosphate cathode material is 8-20 m 2 / g; Preferably, the volume resistivity of the lithium iron phosphate positive electrode material is 1-100 Ω·cm; Preferably, the Fe2P content of the lithium iron phosphate positive electrode material is ≤100 ppb.

5. The cathode material according to claim 4, wherein, The numerical values of the Fe2P content, volume resistivity, and tap density of the lithium iron phosphate positive electrode material satisfy the following relationship: MI = 77.13PD - 0.03R - 107.7 Among them, R is the volume resistivity of the lithium iron phosphate positive electrode material, Ω·cm; PD is the tap density of the lithium iron phosphate cathode material, g / cm 3 ; MI is the Fe2P content of the lithium iron phosphate positive electrode material, ppb; Preferably, the tap density of the lithium iron phosphate cathode material and the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ A2 measured by XRD of the cathode material satisfy the following relationship: PD = 0.084 I(2θ A2 ) + 0.377; Among them, PD is the tap density of the lithium iron phosphate cathode material, g / cm 3 ; I(2θ A2 ) is the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ A2 ) in the XRD diffraction pattern of the lithium iron phosphate cathode material.

6. A preparation method of a lithium iron phosphate cathode material, characterized in that, The preparation method includes the following steps: (1) Mix the iron phosphate precursor, lithium source, carbon source, optionally metal source M, and optionally Mn source with a liquid medium, grind them into a slurry, and then dry to obtain a dried material; (2) Under a protective atmosphere, calcine the dried material to obtain a sintered material; (3) Crush and screen the sintered material to obtain the lithium iron phosphate positive electrode material; Among them, the iron phosphate precursor has diffraction characteristic peaks at 2θ a1 = 16.2 - 16.9°, 2θ a2 = 27.3 - 28.1°, 2θ a3 = 29 - 29.7° and 2θ a4 = 30.2 - 30.9° as detected by XRD test; the iron phosphate precursor has diffraction characteristic peaks at 2θ b1 = 20 - 20.7°, 2θ b2 = 21.5 - 22.2°, 2θ b3 = 23.4 - 24°, 2θ b4 = 25.5 - 26.2° as detected by XRD test; The integrated area A(2θ ai ) of the diffraction characteristic peak at 2θ ai of the iron phosphate precursor and the integrated area A(2θ bj ) of the diffraction characteristic peak at 2θ bj satisfy the following: Among them, i is an integer from 1 to 4, and j is an integer from 1 to 4; In step (2), the temperature of the calcination treatment is greater than or equal to 500 °C.

7. The preparation method according to claim 6, wherein, The lattice parameters of the a-axis and c-axis of the iron phosphate precursor measured by XRD satisfy: 2.231 ≤ c / a ≤ 2.2326 Formula II; Preferably, the iron phosphate precursor has the composition shown in Formula II: (Fe 1-y M y PO4) 1-6x [Fe4(P2O7)3] x Formula II, Among them, 0.01 ≤ x ≤ 0.02, 0 ≤ y ≤ 0.1, M is selected from at least one of Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti; Preferably, in the iron phosphate precursor, the molar ratio of metal element to phosphorus element n(Me) / n(P) is 0.960-0.980; Preferably, the median particle size D 50 of the iron phosphate precursor is 1-25 μm; Preferably, the primary particle size of the iron phosphate precursor is 20-200 nm; Preferably, the tap density of the iron phosphate precursor is 0.8-1.3 g / cm 3 ; Preferably, the specific surface area of the iron phosphate precursor is 6-10 m 2 / g; Preferably, the sulfur content in the iron phosphate precursor is ≤400 ppm.

8. The preparation method according to claim 6 or 7, wherein In step (2), the temperature of the calcination treatment is 500-900 °C, preferably 600-800 °C; Preferably, the time of the calcination treatment is 4-20 h, preferably 6-15 h.

9. The preparation method according to any one of claims 6-8, wherein The dosages of the iron phosphate precursor, the lithium source, the metal source M, and the Mn source are such that: n(Li):n(Fe):n(M):n(Mn) = 1 + a:b:c:d, where -0.1 ≤ a ≤ 0.1, 0 ≤ b ≤ 1, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 1; Preferably, -0.05 ≤ a ≤ 0.05, 0.5 ≤ b ≤ 1, 0.001 ≤ c ≤ 0.1, 0 ≤ d ≤ 0.5; Preferably, based on the total mass of the iron phosphate precursor, the dosage of the carbon source is 8 wt% - 18 wt%; Preferably, the median particle size D of the slurry 50 is 50 - 2000 nm; Preferably, the solid content of the slurry is 10 - 70 wt%; Preferably, the drying method is spray drying; Preferably, the conditions for the spray drying include: an inlet air temperature of 190 - 280 °C and an outlet air temperature of 60 - 120 °C.

10. The preparation method according to any one of claims 6-9, wherein, The metal source M is selected from at least one of oxalates, nitrates, acetates, oxides, hydroxides, carbonates, phosphates, metal clusters, metal complexes, and carboxylates that can provide the element M; Preferably, the carbon source is selected from at least one of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, phenolic resin, polyethylene glycol, dopamine, graphene, and carbon nanotubes.

11. A lithium iron phosphate cathode material prepared by the preparation method according to any one of claims 6 - 10.

12. A lithium-ion battery, characterized in that, The lithium ion battery includes the lithium iron phosphate cathode material according to any one of claims 1 - 5 and 11.

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