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

Abstract

The present invention relates to the field of lithium ion positive electrode material preparation technology, and discloses a lithium iron phosphate positive electrode material and a preparation method thereof, and a lithium ion battery. XRD measurement shows that the lithium iron phosphate positive electrode material has a 2θ A1 =29.4-29.6°, 2θ A2 =29.8-30° and 2θ A3 = 43.8-43.9°. XRD measurement of the lithium iron phosphate positive electrode material reveals that it has a specific diffraction characteristic peak, which indicates that the lithium iron phosphate positive electrode material has a high compaction density and significantly improves the electrochemical performance, such as the capacity and cycling performance, of a lithium ion battery assembled with the lithium iron phosphate positive electrode material.

Description

[Technical Field]

[0001] The present invention relates to the field of lithium ion positive electrode material preparation technology, and particularly to a lithium iron phosphate positive electrode material and its preparation method, and a lithium ion battery. [Background technology]

[0002] Lithium-ion batteries (Li-ion) are green secondary batteries with advantages such as high voltage, high energy density, excellent cycle performance, low self-discharge, and no memory effect. Since their successful development in the 1990s, Li-ion batteries have been rapidly applied and developed. In recent years, they have been used in a wide range of applications, including energy storage systems for hydroelectric, thermal, wind, and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Among these, lithium iron phosphate cathode materials have become one of the most promising cathode materials for Li-ion batteries due to their 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 synthesis, and sol-gel synthesis. Solid-phase methods include high-temperature solid-state sintering, carbothermal reduction, and microwave sintering. Regardless of the synthesis method, factors such as cost, ease of process control, and performance must be considered before industrial production can be implemented. The quality of lithium iron phosphate cathode materials directly affects battery performance, including energy density, cycle life, and safety.

[0004] The rapid development of the storage and power battery industries has presented new demands and challenges for lithium iron phosphate positive electrode materials, and currently, research on densified lithium iron phosphate materials and their precursor iron phosphate materials has been relatively extensive. CN116553507A discloses a densification process for densified lithium iron phosphate materials and their precursors, which involves taking lithium iron phosphate precursor materials, feeding them into a plasma flame in an inert gas atmosphere, melting them to form spherical single crystals, and then placing them in a graphite sintering furnace for heating and sintering. Then, while maintaining the temperature, a carbon-containing gas is passed through to form a thin layer of carbon embedded on the surface of the spherical single crystals, followed by cooling to obtain densified lithium iron phosphate materials. However, this method has a complicated preparation process, is difficult to control, consumes a lot of energy, and lacks uniformity and stability in the products.

[0005] CN112408351A discloses a method for preparing densified iron phosphate and lithium iron phosphate, which involves preparing a trivalent iron source slurry, dividing it into two, adding one portion to a mixed solution of phosphoric acid and liquid alkali to react, and adding the other portion to the mixed slurry to react until the mixed slurry turns white, and finally washing, filtering, drying and calcining to obtain densified iron phosphate. However, this method is difficult to control the production process, and simply controls the deposition method and particle size distribution of the secondary iron phosphate particles, which does not fundamentally increase the compaction density of the lithium iron phosphate material. Summary of the Invention [Problem to be solved by the invention]

[0006] The technical problem to be solved by the present invention overcomes the shortcomings of the prior art by providing a lithium iron phosphate positive electrode material, a preparation method thereof, and a lithium ion battery, which exhibits specific diffraction characteristic peaks in XRD measurement, has a high compaction density, and exhibits significantly improved electrochemical performance, such as capacity and cycle performance, of lithium ion batteries assembled from the lithium iron phosphate positive electrode material. [Means for solving the problem]

[0007] A first aspect of the present invention provides a lithium iron phosphate cathode material, wherein the cathode 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°.

[0008] A second aspect of the present invention provides a method for preparing a lithium iron phosphate cathode material, said method comprising: (1) mixing an iron phosphate precursor, a lithium source, a carbon source, an optional metal source M, and an optional Mn source with a liquid medium, grinding the mixture into a slurry, and then drying the slurry to obtain a dried material; (2) calcining the dried material under a protective atmosphere to obtain a sintered material; (3) crushing and sieving the sintered material to obtain the lithium iron phosphate positive electrode material; Here, the iron phosphate precursor 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°, and the iron phosphate precursor has a characteristic diffraction peak at 2θ = 30.2-30.9° by XRD measurement. 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°. In the iron phosphate precursor, 2θ ai The integral area A(2θ ai ) and 2θ bj The integral area A(2θ bj ) means

number

[0009] A third aspect of the present invention provides a lithium iron phosphate positive electrode material produced by the above preparation method.

[0010] A fourth aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the lithium iron phosphate positive electrode material described above. [Effects of the Invention]

[0011] According to the above technical means, in the lithium iron phosphate positive electrode material and its preparation method and use according to the present invention, the lithium ion battery will achieve the following beneficial effects:

[0012] The lithium iron phosphate positive electrode material of the present invention exhibits specific diffraction characteristic peaks in XRD measurement, which gives the positive electrode material a high compaction density. When the positive electrode material is used in a lithium ion battery, it can effectively improve the electrochemical performance of the lithium ion battery, exhibiting higher capacity, energy efficiency, lower internal resistance, and better cycle performance.

[0013] Furthermore, the lithium iron phosphate cathode material of the present invention has a low FeP content, which can further improve the capacity and energy density of the cathode material and reduce side reactions with the electrolyte, thereby improving the life and safety of lithium-ion batteries containing the cathode material.

[0014] Furthermore, the lithium iron phosphate positive electrode material according to the present invention includes a base and a carbon coating layer coated on the surface of the base, and the carbon coating layer is uniformly coated on the surface of the base, and further improves the capacity, energy efficiency, and cycle performance of a lithium ion battery including the positive electrode material, and further reduces the internal resistance.

[0015] Specifically, the lithium iron phosphate positive electrode material of the present invention has a capacitance of 2.63 g / cm 3Under high pressure and high density, the 0.1C discharge specific capacity of lithium-ion batteries containing this cathode material reaches 160mAh / g, the capacity retention rate at 200 cycles at room temperature reaches 97%, and the 1C energy efficiency reaches 95%, demonstrating excellent electrochemical performance.

[0016] Furthermore, the present invention provides a correlation between the crystal cell parameter c / a value of the iron phosphate precursor and the compacted density of lithium iron phosphate, which provides a basis for the development of raw materials and product design.

[0017] In the preparation method of the lithium iron phosphate positive electrode material provided by the present invention, a precursor material with a specific XRD structure is used, which allows the iron phosphate precursor to have certain defects in its structure, which can act as a co-solvent during the precursor sintering process, thereby reducing the sintering temperature. Meanwhile, by optimizing the grinding, spraying and sintering process conditions, a lithium iron phosphate positive electrode material with high compaction density and excellent electrochemical performance is obtained.

[0018] Furthermore, the method for producing lithium iron phosphate precursor of the present invention only requires optimizing the process parameters, and does not require adjustment of the existing production line. The entire production 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 popularize and apply, and can be widely used in the industrial production of lithium iron phosphate positive electrode materials. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is an XRD diagram of the iron phosphate precursor prepared in Preparation Example 1 of the present invention. [Figure 2] FIG. 1 is an SEM image of an iron phosphate precursor prepared in Preparation Example 1 of the present invention. [Figure 3] 1 is an XRD diagram of the lithium iron phosphate positive electrode material prepared in Example 1 and Example 2 of the present invention; [Figure 4] FIG. 1 is an SEM image of the lithium iron phosphate positive electrode material prepared in Example 1 of the present invention. [Figure 5]FIG. 2 is a graph showing the charge-discharge performance of lithium ion batteries assembled with the lithium iron phosphate positive electrode materials of Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0020] The endpoints of ranges and any values ​​disclosed herein are not intended to be limiting to that exact range or value, but rather should be understood to include values ​​close to those ranges or values. For numerical ranges, combinations between the endpoints of each range, between the endpoints of each range and the individual point values, and between the individual point values, result in one or more new numerical ranges, and these numerical ranges are specifically disclosed herein.

[0021] A first aspect of the present invention provides a lithium iron phosphate cathode material, the cathode material having a 2θ A1 =29.4-29.6°, 2θ A2 =29.8-30° and 2θ A3 It is characterized by the presence of a characteristic diffraction peak at 43.8-43.9°.

[0022] In the present invention, the lithium iron phosphate positive electrode material has a specific diffraction characteristic peak at a specific 2θ when measured by XRD, which indicates that the positive electrode material has a high packing density. When the positive electrode material has a high packing density and is used in a lithium ion battery, it can effectively improve the electrochemical performance of the lithium ion battery, showing higher capacity, energy efficiency, lower internal resistance, and better cycle performance.

[0023] Furthermore, the positive electrode material was measured by XRD and found to have a 2θ B1 =25.4-25.5°, 2θ B2 =35.9-36° and 2θ B3 There is a characteristic diffraction peak at 60.7-60.8°.

[0024] According to the present invention, in the positive electrode material, 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θA2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) and the ratio is 0.25≦I(2θ A2 ) / I(2θ B3 )≦0.27.

[0025] In the present invention, in the positive electrode material, 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 high compaction density at a relatively low temperature.

[0026] In the present invention, in the positive electrode material, 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 ) and the ratio is 0.25≦I(2θ A2 ) / I(2θ B3 )≦0.27, and may be, for example, 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, or a range consisting of any two values, and preferably 0.26≦I(2θ A2 ) / I(2θ B3 )≦0.27.

[0027] According to the present invention, the positive electrode material includes a base and a carbon coating layer coated on a surface of the base, wherein the base has the composition shown in Formula I: Li 1+a Fe b M c Mn d (PO4) 1-2w (P2O7) w Formula I Here, -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.

[0028] In the present invention, the lithium iron phosphate positive electrode material according to the present invention comprises a base and a carbon coating layer coated on the surface of the base, and the carbon coating layer is uniformly coated on the surface of the base, and further improves the capacity, energy efficiency, and cycle performance of a lithium ion battery including the positive electrode material, and further reduces the internal resistance.

[0029] Furthermore, M is selected from at least one of Al, Zr, W, Fe, Co, V and Ti.

[0030] In the present invention, -0.1≦a≦0.1 is set, and may be, for example, -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, or a range consisting of any two values, and preferably -0.05≦a≦0.05, 0≦b≦1 is set, and may be, for example, 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range consisting of any two values, and preferably Alternatively, 0.5≦b≦1 and 0≦c≦0.5, and may be, for example, 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 ranges consisting of any two values, and preferably , 0.001≦c≦0.1, 0≦d≦1, for example, 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, 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, 0.056, 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.Let's call it 08.

[0031] According to the present invention, the content of the carbon coating layer is 0.5-2 wt % based on the total weight of the positive electrode material.

[0032] In the present invention, the content of the carbon coating layer is 0.5-2 wt%, for example, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2 wt%, and may be a range consisting of any two values, and preferably, the content of the carbon coating layer is 1-1.5 wt%, based on the total weight of the positive electrode material.

[0033] According to the present invention, the lithium iron phosphate positive electrode material has a secondary particle structure formed of primary particles, and the median diameter D of the primary particles is 50 is 0.2-2 μm.

[0034] In the present invention, the median diameter D of the primary particles 50 is 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 may be a range consisting of any two values, and preferably, the median diameter D of the primary particles 50 is 0.5-1.5 μm.

[0035] According to the present invention, the compaction density of the lithium iron phosphate positive electrode material is 2.5-2.7 g / cm 3 is.

[0036] In the present invention, when the compaction density of the lithium iron phosphate positive electrode material satisfies the above range, the compaction density is relatively high, the contact internal resistance between material particles is further reduced, and the material energy density is improved.

[0037] In the present invention, the compaction density of the lithium iron phosphate positive electrode material is 2.5-2.7 g / cm 3 For example, 2.5 g / 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 / cm 3 , 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 may be in a range consisting of any two values, and preferably, the compacted density of the lithium iron phosphate positive electrode material is 2.55-2.65 g / cm 3 is.

[0038] According to the present invention, the tap density of the lithium iron phosphate positive electrode material is 0.6-1.1 g / cm 3 is.

[0039] In the present invention, when the tap density of the lithium iron phosphate positive electrode material satisfies the above range, the gradation between particles is significant, and the workability of the material is improved.

[0040] 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, 0.6 g / cm 3 , 0.61g / cm 3 , 0.62g / cm 3 , 0.63g / cm 3 , 0.64g / cm3 , 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 any two values ​​in the range, and preferably, the tap density of the lithium iron phosphate positive electrode material is 0.7-1 g / cm 3 is.

[0041] According to the present invention, the specific surface area of ​​the lithium iron phosphate positive electrode material is 8-20 m 2 / g.

[0042] In the present invention, the specific surface area of ​​the lithium iron phosphate positive electrode material is 8-20 m 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 a range consisting of any two values, preferably, the specific surface area of ​​the lithium iron phosphate positive electrode material is 10-15 m 2 / g.

[0043] According to the present invention, the volume resistivity of the lithium iron phosphate positive electrode material is 1-100 Ω·cm.

[0044] In the present invention, the volume resistivity of the lithium iron phosphate positive electrode material is 1-100 Ω·cm, for example, 1 Ω·cm, 2 Ω·cm, 3 Ω·cm, 4 Ω·cm, 5 Ω·cm, 6 Ω·cm, 7 Ω·cm, 8 Ω·cm, 9 Ω·cm, 10 Ω·cm, 12 Ω·cm, 14 Ω·cm, 16 Ω·cm, 18 Ω·cm, 20 Ω·cm, 22 Ω·cm, 24 Ω·cm, 26 Ω·cm, 28 Ω·cm , 30 Ω·cm, 35 Ω·cm, 40 Ω·cm, 45 Ω·cm, 50 Ω·cm, 55 Ω·cm, 60 Ω·cm, 65 Ω·cm, 70 Ω·cm, 75 Ω·cm, 80 Ω·cm, 85 Ω·cm, 90 Ω·cm, 95 Ω·cm, 100 Ω·cm, and a range consisting of any two values, and preferably, the volume resistivity of the lithium iron phosphate positive electrode material is 10-60 Ω·cm.

[0045] According to the present invention, the content of Fe2P in the lithium iron phosphate positive electrode material is ≦100 ppb.

[0046] In the present invention, the lithium iron phosphate positive electrode material has a low FeP content, which can further improve the capacity and energy density of the positive electrode material and reduce side reactions with the electrolyte, thereby improving the lifespan and safety of lithium-ion batteries containing the positive electrode material.

[0047] In the present invention, the FeP content of the lithium iron phosphate positive electrode material is set to ≦100 ppb, and may be, for example, 100 ppb, 99 ppb, 98 ppb, 97 ppb, 96 ppb, 95 ppb, 94 ppb, 93 ppb, 92 ppb, 91 ppb, 90 ppb, 85 ppb, 80 ppb, 75 ppb, 70 ppb, 65 ppb, 60 ppb, 55 ppb, 50 ppb, 45 ppb, 40 ppb, 35 ppb, 30 ppb, 25 ppb, 20 ppb, 15 ppb, 10 ppb, 5 ppb, 0 ppb, or a range consisting of any two values, and preferably, the FeP content of the lithium iron phosphate positive electrode material is set to ≦90 ppb.

[0048] According to the present invention, the FeP content, volume resistivity, and compaction density of the lithium iron phosphate positive electrode material are as follows: MI=77.13PD-0.03R-107.7 where R is the volume resistivity (Ω cm) of the lithium iron phosphate cathode material, PD is the compacted density (g / cm 3 ) and MI is the Fe2P content (ppb) of the lithium iron phosphate positive electrode material.

[0049] In the present invention, when the FeP content, volume resistivity, and compaction density of the positive electrode material satisfy the above-mentioned relationships, a positive electrode material with a high compaction density can be produced at a relatively low temperature, and a positive electrode material with excellent electrical properties can be obtained.

[0050] According to the present invention, the packed density of the lithium iron phosphate positive electrode material and the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and the numerical value is, PD=0.084 I(2θ A2 ) + 0.377, where PD is the compacted density of the lithium iron phosphate cathode material (g / cm 3 ) and I(2θ A2 ) is the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 )

[0051] In the present invention, the inventor has conducted research to determine the compaction density of the lithium iron phosphate positive electrode material and the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the above relationship, and 2θ A2 It has been discovered that the compaction density of the positive electrode material can be further distinguished by controlling the peak intensity of the diffraction characteristic peak at

[0052] A second aspect of the present invention provides a method for preparing a lithium iron phosphate cathode material, said method comprising: (1) mixing an iron phosphate precursor, a lithium source, a carbon source, an optional metal source M, and an optional Mn source with a liquid medium, grinding the mixture into a slurry, and then drying the slurry to obtain a dried material; (2) calcining the dried material under a protective atmosphere to obtain a sintered material; (3) crushing and sieving the sintered material to obtain the lithium iron phosphate positive electrode material; Here, the iron phosphate precursor 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°, and the iron phosphate precursor has a characteristic diffraction peak at 2θ = 30.2-30.9° by XRD measurement. b1 =20-20.7°, 2θ b2 =21.5-22.2°, 2θ b3 =23.4-24°, 2θ b4There is a characteristic diffraction peak at 25.5-26.2°. In the iron phosphate precursor, 2θ ai The integral area A(2θ ai ) and 2θ bj The integral area A(2θ bj ) means

number

[0053] In the present invention, by using a precursor material with a specific XRD structure, certain defects exist in the structure of the iron phosphate precursor, which act as a co-solvent during the sintering process of the precursor, thereby lowering the sintering temperature and increasing the compaction density of the resulting lithium iron phosphate positive electrode material.

[0054] Furthermore, in the iron phosphate precursor,

number

[0055] According to the present invention, the crystal cell parameters of the a-axis and c-axis of the iron phosphate precursor measured by XRD satisfy the relationship 2.2306≦c / a≦2.2330.

[0056] In the present invention, by selecting an iron phosphate precursor having the above-mentioned specific crystalline cell parameter c / a value, not only can a higher compaction density be achieved at a relatively low temperature, but also the content of iron phosphide in the lithium iron phosphate can be reduced, thereby improving the capacity and energy density of the cathode material prepared from the precursor, reducing side reactions with the electrolyte, and improving the lifespan and safety of the battery.

[0057] In the present invention, the iron phosphate precursor has a hexagonal crystal structure and a space group of P3121.

[0058] In the present invention, the point group structure of the iron phosphate precursor is equivalently arranged on the a-axis and the b-axis. The c-axis is the upright crystal axis.

[0059] In the present invention, for the iron phosphate precursor, the crystal cell parameters of the a-axis and the c-axis measured by XRD satisfy 2.2306 ≦ c / a ≦ 2.2330. For example, it may 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 the range composed of any two values. Preferably, 2.231 ≦ c / a ≦ 2.2326.

[0060] 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 where 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.

[0061] 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.

[0062] According to the present invention, in the iron phosphate precursor, the molar ratio n of the metal element to the phosphorus element, n(Me) / n(P), is 0.96 - 0.98.

[0063] In the present invention, when the molar ratio of metal element to phosphorus element in the iron phosphate precursor satisfies the above range, the precursor has a certain structural defect, and the excess phosphorus acts as a co-solvent, which can lower the sintering temperature and increase the compaction density of the resulting lithium iron phosphate positive electrode material.

[0064] Furthermore, in the iron phosphate precursor, the molar ratio of metal element to phosphorus element, n(Me) / n(P), is set to 0.96 to 0.97.

[0065] According to the present invention, the median diameter D of the iron phosphate precursor 50 is 1-25 μm.

[0066] In the present invention, when the median diameter of the iron phosphate precursor satisfies the above range, it is advantageous for improving the polishing efficiency in the process of producing a positive electrode material and reducing energy consumption.

[0067] In the present invention, the median diameter D of the iron phosphate precursor 50 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, and preferably, the median diameter D of the iron phosphate precursor 50 is 2-20 μm.

[0068] According to the present invention, the iron phosphate precursor has a primary particle size of 20-200 nm.

[0069] In the present invention, when the size of the primary particles of the iron phosphate precursor satisfies the above range, the primary particles are uniform and dense, which is advantageous for obtaining a high-density lithium iron phosphate positive electrode material.

[0070] In the present invention, the primary particle size of the iron phosphate precursor is 20-200 nm, and may be, for example, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, or a range consisting of any two values, and preferably, the primary particle size of the iron phosphate precursor is 50-150 nm.

[0071] According to the present invention, the tap density of the iron phosphate precursor is 0.8-1.3 g / cm 3 is.

[0072] In the present invention, when the tap density of the iron phosphate precursor satisfies the above range, the precursor has a high density, which is advantageous for further improving the compaction density of the lithium iron phosphate positive electrode material.

[0073] In the present invention, the tap density of the iron phosphate precursor is 0.8-1.3 g / cm 3 For example, 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 / 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, 1.11g / 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 any two values ​​in the range, and preferably the tap density of the iron phosphate precursor is 0.9-1.2 g / cm 3 is.

[0074] According to the present invention, the specific surface area of ​​the iron phosphate precursor is 6-10 m 2 / g.

[0075] In the present invention, when the specific surface area of ​​the iron phosphate precursor satisfies the above range, the precursor has high reactivity, which is favorable for the diffusion of lithium ions when the precursor is used to prepare a lithium iron phosphate positive electrode material, thereby improving the charge / discharge capacity.

[0076] In the present invention, the specific surface area of ​​the iron phosphate precursor is 6-10 m 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 any two values ​​in the range, preferably, the specific surface area of ​​the iron phosphate precursor is 6.5-9.5 m 2 / g.

[0077] According to the present invention, the iron phosphate precursor has a sulfur content of ≦400 ppm.

[0078] In the present invention, when the sulfur content in the iron phosphate precursor satisfies the above range, lattice distortion caused by impurity ions can be effectively avoided, thereby improving the low-temperature performance and cycle performance of the resulting positive electrode material.

[0079] In the present invention, the sulfur content in the iron phosphate precursor is set to ≦400 ppm, and may be, for example, 400 ppm, 350 ppm, 300 ppm, 250 ppm, 200 ppm, 150 ppm, 100 ppm, 50 ppm, 40 ppm, 30 ppm, 25 ppm, 20 ppm, 15 ppm, 10 ppm, 5 ppm, 0 ppm, or a range consisting of any two values, and preferably, the sulfur content in the iron phosphate precursor is set to ≦200 ppm.

[0080] In the present invention, the origin of the iron phosphate precursor is not particularly limited as long as the iron phosphate precursor has the structural characteristics defined in the present invention.

[0081] 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: S1, an iron source, and an M source are dissolved in water to form a mixed salt solution A1. S2, dissolve the phosphorus source in water and add a pH adjuster to form phosphorus source solution A2. S3, mixed salt solution A1, phosphorus source solution A2 and oxidizing agent A3 are mixed to carry out a synthesis reaction, and an auxiliary agent is added as needed. S4: The product of step S3 is filtered and washed to obtain cake B1, and the cake is slurried to obtain a slurry. After that, additives are added as needed, and the pH value is adjusted. After aging and crystallization, the product is filtered and washed to obtain cake B3. S5, calcining the cake to obtain an iron phosphate precursor. wherein the pH value of the phosphorus source solution A2 is 0.5-2.5; The conditions of the aging crystallization reaction include: a reaction temperature of 70-90°C, a temperature rising rate of 1-3°C / min, and a reaction time of 1-3 hours; The firing conditions include a firing temperature of 500-800°C, a temperature rise rate of 3-8°C / min, and a firing time of 2-4h.

[0082] In the present invention, by controlling the pH value of the phosphorus source solution and the conditions for the aging crystallization reaction and calcination, the produced iron phosphate precursor simultaneously contains an iron phosphate phase and a ferric pyrophosphate phase, and the characteristic peak diffraction intensities of the ferric pyrophosphate phase and the iron phosphate phase and the crystalline cell parameters of the iron phosphate precursor satisfy specific ranges. Specifically, when the iron phosphate precursor according to the first aspect of the present invention is produced and used to prepare a lithium iron phosphate positive electrode material, the sintering temperature can be reduced and the compaction density of the lithium iron phosphate positive electrode material can be improved.

[0083] Specifically, the oxidation precipitation reaction is adjusted and controlled by controlling the pH value of the phosphorus source solution to produce amorphous iron phosphate. Then, the aging temperature, heating rate, and aging time in the aging crystallization step are adjusted and controlled to complete the crystallization reaction from amorphous iron phosphate to ferric phosphate dihydrate, thereby achieving adjustment and control of the crystallinity and crystal cell parameters of ferric phosphate dihydrate. Finally, the calcination temperature, heating rate, and calcination time in the calcination step are adjusted and controlled to complete the dehydration and crystallization reaction from ferric phosphate dihydrate to ferric phosphate anhydride, thereby controlling the doping of ferric pyrophosphate in the iron phosphate, thereby achieving adjustment and control of the crystallinity and crystal cell parameters of ferric phosphate anhydride.

[0084] In the present invention, there are no particular limitations on the means for mixing the mixed salt solution A1, the phosphorus source solution A2, and the oxidizing agent A3, or on the timing of adding the auxiliary agent, and it is sufficient that the mixed salt solution A1, the phosphorus source solution A2, and the antioxidant A3 are mixed sufficiently and uniformly, or that the aging crystallization reaction is carried out in the presence of an auxiliary agent, as necessary.

[0085] In one specific embodiment of the present invention, the mixed salt solution A1, the phosphorus source solution A2 and the oxidizing agent A3 are added to the reaction kettle in a co-current manner to carry out the synthesis reaction.

[0086] In one specific embodiment of the present invention, the mixed salt solution A1 and the oxidizing agent A3 are first reacted sufficiently, and then added to the reaction kettle in a cocurrent manner together with the phosphorus source solution A2 to carry out the synthesis reaction.

[0087] In one specific embodiment of the present invention, the mixed salt solution A1 is used as a base liquid, and the phosphorus source solution A2 and the oxidizing agent A3 are added in parallel flow to a reaction kettle to carry out the synthesis reaction.

[0088] In the present invention, the pH value of the phosphorus source solution A2 is 0.5-2.5, such as 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 one preferred embodiment of the present invention, the pH value of the phosphorus source solution A2 is 1-2.

[0089] In the present invention, the conditions for the aging crystallization reaction include a reaction temperature of 70-90°C, for example, 70°C, 75°C, 80°C, 85°C, 90°C, and any two of these values; a heating rate of 1-3°C / min, for example, 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, and any two of these values; and a reaction time of 1-3 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, and any two of these values. In one preferred embodiment of the present invention, the conditions for the aging crystallization reaction include a reaction temperature of 80-85°C, a heating rate of 2-3°C / min, and a reaction time of 1-2 hours.

[0090] In the present invention, the firing conditions include a firing temperature of 500-800°C, which may be, for example, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, or any two of these values; a heating rate of 3-8°C / min, which may be, 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, or any two of these values; and a firing time of 2-4 hours, which may be, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, or any two of these values. In one preferred embodiment of the present invention, the firing conditions include a firing temperature of 600-750° C., a temperature increase rate of 3-5° C. / min, and a firing time of 2-3 h.

[0091] According to the present invention, in step (4), the pH value is adjusted to 1-2.5, for example, 1, 1.5, 2, 2.5, and the range consisting of any two values, preferably 1-2.

[0092] In the present invention, in step (4), the means for adjusting the pH value is not particularly limited, but it is preferable to adjust the pH value by adding phosphoric acid in order to prevent the incorporation of impurities.

[0093] According to the present invention, in step (1), the concentration of the mixed salt solution A1 is 0.1-4 mol / L, for example, 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, and preferably 0.2-2 mol / L.

[0094] In the present invention, the type of iron source is not specifically limited, and the iron source includes, but is not limited to, a divalent iron salt. Preferably, the divalent iron salt is selected from at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, and ferric acetate.

[0095] In the present invention, the type of M source is not specifically limited, and the M source is a compound that can provide an M element selected from at least one of Mn, Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti, and includes, but is not limited to, an M-containing oxide, an M-containing salt, and the like.

[0096] In the present invention, in step S1, the iron source and the M source are used to make 0≦n(M) / [n(Fe)+n(M)]≦0.1, and preferably, 0 <n(M) / [n(Fe)+n(M)]≦0.05とする。

[0097] In the present invention, the concentration of the phosphorus source solution A2 is 0.2-20 mol / L, for example, 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, and preferably 1-15 mol / L.

[0098] In the present invention, the type of phosphorus source is not specifically limited, and the phosphorus source includes at least one of phosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate, and ammonium monohydrogen phosphate, but is not limited thereto. Preferably, the phosphorus source is selected from at least one of phosphoric acid, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate.

[0099] In the present invention, the type of pH adjuster is not specifically limited, and its role is to adjust the pH of the solution. The pH adjuster is an acidic solution or an alkaline solution, and preferably, the pH adjuster is selected from at least one of sodium hydroxide, aqueous ammonia, sulfuric acid, hydrochloric acid, and nitric acid.

[0100] 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 adjusted so that n(P):n(Fe) is 1-3:1, preferably 1-1.5:1.

[0101] In the present invention, in step S3, the dosage of the mixed salt solution A1 and the dosage of the oxidizing agent A3 are adjusted so that n(oxidizing agent):n(Fe) is 1-5:1, preferably 1-3:1.

[0102] In the present invention, the type of oxidizing agent is not specifically limited, and the oxidizing agent includes, but is not limited to, hydrogen peroxide, ozone, sodium persulfate, ammonium persulfate, sodium hypochlorite, and sodium ferrate. Preferably, the oxidizing agent is selected from at least one of hydrogen peroxide, sodium persulfate, and ammonium persulfate.

[0103] In the present invention, the synthesis reaction conditions are as follows: 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, or any two of these values; and a reaction time of 1-6 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, or any two of these values.

[0104] Furthermore, the synthesis reaction conditions are that the reaction temperature is 40-60°C and the reaction time is 1-3 hours.

[0105] In the present invention, in the preparation process of the iron phosphate precursor, an auxiliary agent is added in the aging crystallization step or the synthesis reaction step to induce the deposition and arrangement of crystal nuclei, make the secondary particles of the precursor denser, and at the same time, help remove sulfur impurities in the crystal lattice, which can further affect the crystal cell parameters.

[0106] In the present invention, the auxiliary agent is selected from at least one of sodium cetylbenzenesulfonate, sodium dodecylbenzenesulfonate, triethanolamine, ethylene glycol, polyvinylpyrrolidone, polyethylene, lignocellulose, and carboxymethylcellulose. Preferably, the auxiliary agent is selected from at least one of sodium cetylbenzenesulfonate, polyethylene, lignocellulose, and carboxymethylcellulose.

[0107] In the present invention, based on the total dosage of the iron source and the M source, the dosage of the auxiliary agent is 0.1 wt%-1 wt%, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, and may be a range consisting of any two values, and preferably 0.1 wt%-0.5 wt%.

[0108] In the present invention, when the dosage of the auxiliary agent is controlled to satisfy the above range, it can induce the deposition and arrangement of crystal nuclei, make the secondary particles denser, and at the same time help remove sulfur impurities in the crystal lattice, and further realize the adjustment of the crystal cell parameters in the precursor.

[0109] In the present invention, the cleaning means in step S4 is not particularly limited and can be performed according to common cleaning means in this field, preferably using a cleaning liquid, preferably using pure water at 20-90°C, more preferably using pure water at 30-60°C.

[0110] According to the present invention, the dosages of the iron phosphate precursor, the lithium source, the metal source M and the Mn source are: Let 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, and 0≦d≦1.

[0111] In the present invention, the specific dosage of the metal source M is not particularly limited, and the dosage of the metal source M and the iron phosphate precursor should be such that the content c of the M element in the positive electrode material satisfies 0≦c≦0.5.

[0112] Furthermore, depending on the dosage of the iron phosphate precursor, the lithium source, the metal source M, and the Mn source, Let 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, and 0≦d≦0.5.

[0113] According to the present invention, the dosage of the carbon source is 8 wt%-18 wt% based on the total mass of the iron phosphate precursor, for example, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, and a range consisting of any two values, and is preferably 10 wt%-15 wt%.

[0114] In the present invention, the type of the liquid medium is not particularly limited as long as it can form a uniform slurry, and for example, the liquid medium is selected from at least one of water, methanol, ethanol, propanol, ethylene glycol, isopropyl alcohol, benzyl alcohol, acetone, benzene, toluene, methyl ether, 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 to be used is also not specifically limited as long as it can form a uniform slurry.

[0115] In the present invention, the type of the lithium source is not particularly limited, and 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, lithium dihydrogen phosphate, and lithium dihydrogen phosphate. Preferably, the lithium source is selected from at least one of lithium hydroxide, lithium carbonate, and lithium dihydrogen phosphate.

[0116] In the present invention, the type of the carbon source is not particularly limited, and may be, for example, at least one selected from glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, phenolic resin, polyethylene, dopamine, graphene, and carbon nanotubes. Preferably, the carbon source is at least one selected from glucose, sucrose, starch, graphene, and polyethylene.

[0117] In the present invention, the type of the metal source M is not particularly limited as long as it is a compound that can provide 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.

[0118] In the present invention, the type of the Mn source is not particularly limited, and for example, the Mn source is selected from at least one of manganese sulfate, manganese nitrate, manganese acetate, manganese chloride, and manganese oxide.

[0119] In the present invention, the polishing method and conditions are not particularly limited. As long as the mixture of the iron phosphate precursor, the lithium source, the carbon source, the Mn source, the metal source M, and the liquid medium can be sufficiently polished, the median diameter D of the slurry obtained by polishing can be 50 is 50-2000 nm, preferably 100-1000 nm.

[0120] In one specific embodiment of the present invention, the polishing conditions include ball milling using a planetary ball mill at a rotation speed of 100-600 rpm for 1-24 hours, and / or ball milling using a stirring mill and / or a sand mill at a rotation speed of 300-3000 rpm for 0.5-10 hours.

[0121] According to the present invention, the solid content of the slurry is 10-70 wt%, preferably 20-60 wt%.

[0122] According to the present invention, the drying method is spray drying.

[0123] According to the present invention, the spray drying conditions include an inlet air temperature of 190-280°C and an outlet air temperature of 60-120°C.

[0124] Further, the spray drying conditions include an inlet air temperature of 200-270°C and an outlet air temperature of 70-110°C.

[0125] In the present invention, in step (1), the median diameter D of the spray-dried material 50 is 5-50 μm, preferably 8-40 μm, and the specific surface area is 5-15 m 2 / g, preferably 8-13m 2 / g and bulk density is 0.3-1g / cm 3 and preferably 0.5-0.8 g / cm 3 The moisture content is ≦5%, preferably ≦3%.

[0126] According to the present invention, in step (2), the conditions of the firing treatment include a firing temperature of 500-900°C, which may be, for example, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, and any two of these values ​​in a range; and a firing time of 4-20 hours, which may be, for example, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, and any two of these values ​​in a range.

[0127] In the present invention, by carrying out the firing treatment under the above conditions, the particle size of the produced positive electrode material can be made uniform and round, and the carbon coating layer can be made appropriately thin, thereby further improving the electronic conductivity and processability of the positive electrode material.

[0128] Furthermore, in step (2), the conditions of the calcination treatment include a calcination temperature of 600-800°C and a calcination time of 6-15 hours.

[0129] In the present invention, the protective atmosphere is selected from nitrogen gas and / or argon gas.

[0130] In the present invention, in step (3), the grinding equipment is selected from an airflow grinding machine and / or a mechanical grinding machine.

[0131] A third aspect of the present invention provides a lithium iron phosphate positive electrode material produced by the above preparation method.

[0132] A fourth aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the lithium iron phosphate positive electrode material described above.

[0133] In the present invention, when the lithium iron phosphate positive electrode material is used in a lithium ion battery, it can effectively improve the electrochemical performance of the lithium ion battery, exhibiting higher capacity and energy efficiency, lower internal resistance, and better cycle performance.

[0134] In the present invention, the lithium ion battery prepared with the lithium iron phosphate positive electrode material has a 0.1C capacity of ≧158mAh / g, preferably ≧160mAh / g.

[0135] In the present invention, the lithium ion battery prepared with the lithium iron phosphate positive electrode material has a 0.5C capacity of ≧151mAh / g, preferably ≧152mAh / g.

[0136] In the present invention, the lithium ion battery prepared with the lithium iron phosphate positive electrode material has a 1C capacity of ≧143.5mAh / g, preferably ≧145.5mAh / g.

[0137] In the present invention, the lithium ion battery prepared with the lithium iron phosphate positive electrode material has a capacity retention rate of ≥ 97% at 1C @ 200 cycles.

[0138] In the present invention, the lithium ion battery prepared with the lithium iron phosphate positive electrode material has an initial energy efficiency of ≧90%, preferably ≧91%.

[0139] The present invention will be described in more detail below with reference to the following examples. In the following examples, the crystallographic properties of the iron phosphate precursor, such as the crystal cell parameters, were measured using a Shimadzu XRD-6000 X-ray powder diffractometer. The settings were: voltage 40 kV, current 40 mA, step size 0.005°, height limit slit 10 mm, divergence slit 1 / 2°, anti-scattering slit 8 mm, and receiving slit open. The test scan angle 2θ was set to 10°-80°, and continuous scanning was performed in one-dimensional mode at a scan rate of 1.2° / min.

[0140] The content of each element in the iron phosphate precursor and lithium iron phosphate cathode material was measured using an Agilent 5800 ICP-OES spectrometer from the United States. The argon partial pressure meter was controlled at 80-100 psi, the compression control pressure of the liquid argon booster valve was above 200 psi, the nitrogen gas was 60-100 psi, and the compressed air was 80-100 psi. When creating the standard curve, three points of calibration were required according to the concentration of the sample, and the coefficient of the standard curve was 0.9999.

[0141] The median diameters of the iron phosphate precursor and lithium iron phosphate cathode material were measured using a Malvern Mastersizer 3000 laser particle size analyzer. A certain amount of sodium pyrophosphate dispersant was added, and the sample was added until the light blocking rate reached 10%-20%. The test was started after 3 minutes of ultrasonic irradiation, and the average value of three tests was used as the median diameter measurement value.

[0142] The primary particle size of the iron phosphate precursor is measured by a scanning electron microscope, model S-4800, manufactured by Hitachi, Japan, with a measurement voltage of 1 kV-5 kV and a measurement magnification of 1 kV-30 kV.

[0143] The tap density of the iron phosphate precursor material is measured by a Baxter BT-30 tap density tester, set at 3000 vibrations and 250 vibrations / min.

[0144] The specific surface areas of the iron phosphate precursor and the lithium iron phosphate positive electrode material were measured using a Tristar II3020 model specific surface measuring instrument manufactured by Micromertics, USA, with the degassing temperature set at 300°C and the degassing time set at 120 minutes.

[0145] The compaction density of the lithium iron phosphate positive electrode material is measured by using a compaction density meter of model MCP-PD51 manufactured by Mitsubishi Chemical Corporation of Japan, weighing a sample of 1±0.01g, and selecting a pressure of 3T for measurement.

[0146] The volume resistivity of the lithium iron phosphate positive electrode material was measured using a powder compaction resistivity meter, model MCP-PD51, manufactured by Mitsubishi Chemical Corporation of Japan, and the four-probe method was used to measure the volume resistivity under a pressure of 20 kN.

[0147] All of the raw materials used in the examples and comparative examples are commercially available products.

[0148] Preparation Example - Preparation of Iron Phosphate Precursor

[0149] Preparation Example 1 According to the molar ratio of S1, n(Fe):n(Ti) = 0.99:0.01, a certain mass of ferrous sulfate and titanium oxide sulfate are weighed and dissolved in deionized water to prepare a 2 mol / L mixed salt solution A1. S2: Weigh out a certain mass of concentrated phosphoric acid, add 30% sodium hydroxide to adjust the solution pH to 2, and prepare a 2 mol / L phosphorus source solution A2. S3, a certain amount of mixed salt solution A1, phosphorus source solution A2 and 30% hydrogen peroxide A3 are added into the reaction kettle in parallel to carry out the synthesis reaction, the reaction temperature is 40°C and the reaction time is 1 hour. S4: After the reaction is complete, the reaction slurry is filtered and washed to obtain a cake. The cake is slurried and the resulting slurry is added to the reaction kettle. 0.1 wt% lignocellulose is added based on the total mass of ferrous sulfate and titanium dioxide 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 controlled to 82°C, and the aging time is controlled to 2 hours. After the reaction is complete, the reaction slurry is filtered and washed to obtain a cake. S5: The cake is subjected to high-temperature calcination and dehydration, with the temperature rising rate controlled at 3°C / min, the calcination temperature at 700°C, and the calcination time controlled at 3 hours, to obtain anhydrous ferric phosphate precursor P1. Its composition is (Fe 0.99 Ti 0.01 PO4) 0.91 [Fe4(P2O7)3] 0.015 where x=0.015 and y=0.01.

[0150] Figure 1 shows the XRD spectrum of iron phosphate precursor P1. As can be seen from Figure 1, the precursor material exhibits a 2θ a1 =16.2-16.9°, 2θ a2 =27.3-28.1°, 2θ a3 =29.0-29.7° and 2θ a4 There is a characteristic diffraction peak at 2θ = 30.2-30.9°. b1 =20-20.7°, 2θ b2 =21.5-22.2°, 2θ b3 =23.4-24°, 2θ b4= 25.5-26.2°, and it is estimated that the iron phosphate precursor contains ferric pyrophosphate phase.

number

[0151] Figure 2 shows the SEM image of the iron phosphate precursor P1. As can be seen from Figure 2, the primary particles are uniform and dense, and the differences between the particles are reduced during the sintering process, which can effectively increase the compaction density of the positive electrode material.

[0152] Preparation Example 2 S1, same as Preparation Example 1. S2, same as Preparation Example 1. S3, same as Preparation Example 1. S4, same as Preparation Example 1. S5, the cake is subjected to high-temperature calcination and dehydration, with the temperature rising rate controlled at 5°C / min, the calcination temperature at 650°C, and the calcination time controlled at 2 hours to obtain anhydrous ferric phosphate P2. Its composition is (Fe 0.99 Ti 0.01 PO4) 0.886 [Fe4(P2O7)3] 0.019 where x=0.019 and y=0.01.

[0153] Preparation Example 3 S1, same as Preparation Example 1. S2, same as Preparation Example 1. S3, same as Preparation Example 1. S4: After the reaction is complete, the reaction slurry is filtered and washed to obtain a cake. The cake is slurried and the resulting slurry is added to the reaction kettle, where 0.1 wt% of lignocellulose based on the total mass of ferrous sulfate and titanium dioxide sulfate is added. Phosphoric acid is added to adjust the pH to 1.5, and the heating rate is controlled to 3°C / min, the aging temperature to 80°C, and the aging time to 1 hour. After the reaction is complete, the reaction slurry is filtered and washed to obtain a cake. S5, the same procedure as in Example 1 is used to obtain anhydrous ferric phosphate precursor P3. Its composition is (Fe0.99 Ti 0.01 PO4) 0.904 [Fe4(P2O7)3] 0.016 where x=0.016 and y=0.01.

[0154] Preparation Example 4 S1, same as Preparation Example 1. S2: Weigh a certain mass of concentrated phosphoric acid, add 30% sodium hydroxide to adjust the solution pH to 1.5, and prepare a 2 mol / L phosphorus source solution. S3, same as Preparation Example 1. S4, same as Preparation Example 1. S5, the same as in Preparation Example 1. Anhydrous ferric phosphate precursor P4 is obtained. Its composition is (Fe 0.99 Ti 0.01 PO4) 0.898 [Fe4(P2O7)3] 0.017 where x=0.017 and y=0.01.

[0155] Preparation Example 5 S1, same as Preparation Example 1. S2: Weigh out a certain mass of ammonium dihydrogen phosphate, dissolve it in deionized water, add 30% dilute sulfuric acid to adjust the solution pH to 2, and prepare a 2 mol / L phosphorus source solution. S3, same as Preparation Example 1. S4, same as Preparation Example 1. S5, the same as in Preparation Example 1, to obtain anhydrous ferric phosphate precursor P5. Its composition is (Fe 0.99 Ti 0.01 PO4) 0.91 [Fe4(P2O7)3] 0.015 where x=0.015 and y=0.01.

[0156] Preparation Example 6 S1, same as Preparation Example 1. S2: Weigh out a certain mass of ammonium dihydrogen phosphate, dissolve it in deionized water, add 30% dilute sulfuric acid to adjust the solution pH to 2, and prepare a 2 mol / L phosphorus source solution. S3, same as Preparation Example 1. S4: After the reaction is complete, add 0.1 wt% lignocellulose based on the total mass of ferrous sulfate and titanium dioxide sulfate, add phosphoric acid to adjust the pH to 1.5, and control the heating rate to 2°C / min, the aging temperature to 82°C, and the aging time to 2 hours. After the reaction is complete, filter and wash the reaction slurry to obtain a cake. S5, the same procedure as in Example 1 is carried out to obtain anhydrous ferric phosphate precursor P6. Its composition is (Fe 0.99 Ti 0.01 PO4) 0.91 [Fe4(P2O7)3] 0.015 where x=0.015 and y=0.01.

[0157] Preparation Example 7 S1, Weigh out a certain mass of ferrous sulfate and dissolve it in deionized water to prepare a 2 mol / L salt solution. S2, same as Preparation Example 1. S3, same as Preparation Example 1. S4, same as Preparation Example 1. S5, the same as in Preparation Example 1, to obtain anhydrous ferric phosphate precursor P7, whose composition is (FePO4) 0.88 [Fe4(P2O7)3] 0.02 where x=0.02 and y=0.

[0158] Comparative Preparation Example 1 S1, same as Preparation Example 1. S2, same as Preparation Example 1. S3, same as Preparation Example 1. S4, same as Preparation Example 1. S5, the cake was subjected to high-temperature calcination and dehydration, with the temperature rising rate controlled at 2°C / min, the calcination temperature at 850°C, and the calcination time controlled at 5 hours to obtain anhydrous ferric phosphate precursor DP1. Its composition was (Fe 0.99 Ti 0.01 PO4) 0.958 [Fe4(P2O7)3] 0.007 where x=0.007 and y=0.01.

[0159] Comparative Preparation Example 2 S1, same as Preparation Example 1. S2, same as Preparation Example 1. S3, same as Preparation Example 1. S4: After the reaction is complete, the reaction slurry is filtered and washed to obtain a cake. The cake is slurried and the resulting slurry is added to the reaction kettle, where lignocellulose is added and phosphoric acid is added to adjust the pH to 1.5. The heating rate is controlled to 0.5°C / min, the aging temperature is controlled to 95°C, and the aging time is controlled to 4 hours. After the reaction is complete, the reaction slurry is filtered and washed to obtain a cake. S5, the same as in Preparation Example 1, to obtain the anhydrous ferric phosphate precursor DP2. Its composition is (Fe 0.99 Ti 0.01 PO4) 0.946 [Fe4(P2O7)3] 0.009 where x=0.009 and y=0.01.

[0160] Comparative Preparation Example 3 S1, same as Preparation Example 1. S2: Weigh a certain mass of concentrated phosphoric acid, add 30% sodium hydroxide, adjust the solution pH to 3, and prepare a 2 mol / L phosphorus source solution, which is the same as Preparation Example 1. S3, same as Preparation Example 1. S4, same as Preparation Example 1. S5. The cake was subjected to high-temperature calcination dehydration, with the heating rate controlled at 3°C / min, the calcination temperature at 700°C, and the calcination time controlled at 3 hours, to obtain anhydrous ferric phosphate precursor DP3, whose composition was (Fe 0.99 Ti 0.01 PO4) 0.952 [Fe4(P2O7)3] 0.008 where x=0.008 and y=0.01.

[0161] Table 1 shows the physicochemical indices of the lithium iron phosphate precursor produced in the preparation examples.

[0162] [Table 1]

[0163] Example - Used to prepare lithium iron phosphate cathode material

[0164] Example 1 (1) Iron phosphate precursor P1, lithium carbonate, and titanium oxide were added to adjust the ratio of n(Fe):n(Li):n(Ti) = 0.961:1.04:0.019, and mixed with pure water. Glucose was added in an amount such that the ratio of the carbon source mass and the iron phosphate precursor P1 mass was 12 wt%. The solid content was controlled to be 40 wt%. The mixture was uniformly mixed by mechanical stirring to obtain a slurry. The slurry was then polished in a sand mill (the rotation speed was 800 rpm). The median diameter D 50 The polished slurry is granulated by spray drying, and the inlet air temperature is controlled to 235°C and the outlet air temperature is controlled to 85°C to obtain a spray-dried material. (2) In an N2 atmosphere, the spray-dried material is subjected to a sintering process, with the temperature rising rate controlled to 2°C / min, the firing temperature controlled to 770°C, and the firing time controlled to 9 hours, to obtain a sintered material. (3) The sintered material is pulverized by airflow and sieved to obtain lithium iron phosphate positive electrode material A1. The lithium iron phosphate positive electrode material A1 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 is.

[0165] The XRD of the lithium iron phosphate cathode material A1 is shown in FIG. 3. As can be seen from FIG. 3, the cathode material has a 2θ A1 =29.4-29.6°, 2θ A2 =29.8-30° and 2θ A3 There is a characteristic diffraction peak at 2θ = 43.8-43.9°. B1 =25.4-25.5°, 2θ B2=35.9-36° and 2θ B3 = 60.7-60.8°, and the analysis estimated that a lithium ferric pyrophosphate phase was present 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 ) and the ratio I(2θ A2 ) / I(2θ B3 ) is 0.255. At the same time, the compacted density of the lithium iron phosphate cathode material A1 and the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and the numerical value is, PD=0.084 I(2θ A2 )+0.377.

[0166] Example 2 (1) The procedure was the same as in Example 1, except that iron phosphate precursor P1 was replaced with iron phosphate precursor P2, and iron phosphate precursor P2, lithium carbonate, and titanium oxide were added to obtain a spray-dried material with a ratio of n(Fe):n(Li):n(Ti)=0.953:1.04:0.019, which was then mixed with pure water. (2) Same as Example 1. (3) The lithium iron phosphate positive electrode material A2 is obtained in the same manner as in Example 1. The lithium iron phosphate positive electrode material A2 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is Li 1.04 (Fe 0.953 Ti 0.019 )(PO4) 0.886 (P2O7) 0.057 is.

[0167] As can be seen from the XRD analysis, in the positive electrode material A2, 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 ) and the ratio I(2θ A2 ) / I(2θ B3) is 0.267. At the same time, the compaction density of lithium iron phosphate cathode material A2 and the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and the numerical value is, PD=0.084 I(2θ A2 )+0.377.

[0168] Example 3 (1) The procedure was the same as in Example 1, except that iron phosphate precursor P1 was replaced with iron phosphate precursor P3, and iron phosphate precursor P3, lithium carbonate, and titanium oxide were added to obtain a spray-dried material with a ratio of n(Fe):n(Li):n(Ti)=0.959:1.04:0.019, which was then mixed with pure water. (2) Same as Example 1. (3) A lithium iron phosphate positive electrode material A3 is obtained in the same manner as in Example 1. The lithium iron phosphate positive electrode material A3 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is: Li 1.04 (Fe 0.959 Ti 0.019 )(PO4) 0.904 (P2O7) 0.048 is.

[0169] As can be seen from the XRD analysis, in the positive electrode material A3, 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 ) and the ratio I(2θ A2 ) / I(2θ B3 ) is 0.264. At the same time, the compaction density of lithium iron phosphate cathode material A3 and the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and the numerical value is, PD=0.084 I(2θ A2 )+0.377.

[0170] Example 4 (1) The procedure was the same as in Example 1, except that iron phosphate precursor P4 was used instead of iron phosphate precursor P1, and iron phosphate precursor P4, lithium carbonate, and titanium oxide were added to obtain a spray-dried material with a ratio of n(Fe):n(Li):n(Ti)=0.957:1.04:0.019, which was then mixed with pure water. (2) Same as Example 1. (3) The same procedure as in Example 1 is followed to obtain a lithium iron phosphate positive electrode material A4. The lithium iron phosphate positive electrode material A4 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is: Li 1.04 (Fe 0.957 Ti 0.019 )(PO4) 0.898 (P2O7) 0.051 is.

[0171] As can be seen from the XRD analysis, in the positive electrode material A4, 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 ) and the ratio I(2θ A2 ) / I(2θ B3 ) is 0.266. At the same time, the compaction density of the lithium iron phosphate cathode material A4 and the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and the numerical value is, PD=0.084 I(2θ A2 )+0.377.

[0172] Example 5 (1) The procedure was the same as in Example 1, except that iron phosphate precursor P5 was used instead of iron phosphate precursor P1, and iron phosphate precursor P5, lithium carbonate, and titanium oxide were added to obtain a spray-dried material with a ratio of n(Fe):n(Li):n(Ti)=0.961:1.04:0.019, which was then mixed with pure water. (2) Same as Example 1. (3) The same procedure as in Example 1 is followed to obtain a lithium iron phosphate positive electrode material A5. The lithium iron phosphate positive electrode material A5 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 is.

[0173] As can be seen from the XRD analysis, in the positive electrode material A5, 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 ) and the ratio I(2θ A2 ) / I(2θ B3 ) is 0.254. At the same time, the compaction density of the lithium iron phosphate cathode material A5 and the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and the numerical value is, PD=0.084 I(2θ A2 )+0.377.

[0174] Example 6 (1) The procedure was the same as in Example 1, except that the iron phosphate precursor P1 was replaced with the iron phosphate precursor P6, and the iron phosphate precursor P6, lithium carbonate, and titanium oxide were added to obtain a spray-dried material with a ratio of n(Fe):n(Li):n(Ti)=0.961:1.04:0.019, which was then mixed with pure water. (2) Same as Example 1. (3) A lithium iron phosphate positive electrode material A6 is obtained in the same manner as in Example 1. The lithium iron phosphate positive electrode material A6 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is: Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 is.

[0175] As can be seen from the XRD analysis, in the positive electrode material A6, 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 ) and the ratio I(2θ A2 ) / I(2θ B3 ) is 0.253. At the same time, the compacted density of the lithium iron phosphate cathode material A6 and the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and the numerical value is, PD=0.084 I(2θ A2 )+0.377.

[0176] Example 7 (1) The procedure was the same as in Example 1, except that iron phosphate precursor P7 was used instead of iron phosphate precursor P1, and iron phosphate precursor P7, lithium carbonate, and titanium oxide were added to obtain a spray-dried material with a ratio of n(Fe):n(Li):n(Ti)=0.960:1.04:0.019, which was then mixed with pure water. (2) Same as Example 1. (3) A lithium iron phosphate positive electrode material A7 is obtained in the same manner as in Example 1. The lithium iron phosphate positive electrode material A7 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is: Li 1.04 (Fe 0.960 Ti 0.019 )(PO4) 0.88 (P2O7) 0.06 is.

[0177] As can be seen from the XRD analysis, in the positive electrode material A7, 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 ) and the ratio I(2θ A2 ) / I(2θ B3 ) is 0.254. At the same time, the compaction density of the lithium iron phosphate cathode material A7 and the 2θA2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and the numerical value is, PD=0.084 I(2θ A2 )+0.377.

[0178] Example 8 (1) Median diameter of slurry D 50 The procedure is the same as in Example 1, except that the wavelength is controlled to be 450 nm to obtain a spray-dried material. (2) Same as Example 1. (3) A lithium iron phosphate positive electrode material A8 is obtained in the same manner as in Example 1. The lithium iron phosphate positive electrode material A8 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is: Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 is.

[0179] As can be seen from the XRD analysis, in the positive electrode material A8, 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 ) and the ratio I(2θ A2 ) / I(2θ B3 ) is 0.25. At the same time, the compaction density of the lithium iron phosphate cathode material A8 and the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and the numerical value is, PD=0.084 I(2θ A2 )+0.377.

[0180] Example 9 (1) Median diameter of slurry D 50 The procedure was the same as in Example 1, except that the particle diameter was controlled to be 300 nm to obtain a spray-dried material. (2) Same as Example 1. (3) A lithium iron phosphate positive electrode material A9 is obtained in the same manner as in Example 1. The lithium iron phosphate positive electrode material A9 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is: Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 is.

[0181] As can be seen from the XRD analysis, in the positive electrode material A9, 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 ) and the ratio I(2θ A2 ) / I(2θ B3 ) is 0.251. At the same time, the compacted density of the lithium iron phosphate cathode material A9 and the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and the numerical value is, PD=0.084 I(2θ A2 )+0.377.

[0182] Example 10 (1) Same as Example 1. (2) Same as Example 1 except that the sintering temperature was 760°C. (3) A lithium iron phosphate positive electrode material A10 is obtained in the same manner as in Example 1. The lithium iron phosphate positive electrode material A10 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is: Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 is.

[0183] As can be seen from the XRD analysis, in the positive electrode material A10, 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3The peak intensity of the diffraction characteristic peak at I(2θ B3 ) and the ratio I(2θ A2 ) / I(2θ B3 ) is 0.252. At the same time, the compaction density of the lithium iron phosphate cathode material A10 and the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and the numerical value is, PD=0.084 I(2θ A2 )+0.377.

[0184] Example 11 (1) Same as Example 1. (2) Same as Example 1 except that the firing temperature was 780°C. (3) A lithium iron phosphate positive electrode material A11 is obtained in the same manner as in Example 1. The lithium iron phosphate positive electrode material A11 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is: Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 is.

[0185] As can be seen from the XRD analysis, in the positive electrode material A11, 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 ) and the ratio I(2θ A2 ) / I(2θ B3 ) is 0.255. At the same time, the compaction density of the lithium iron phosphate cathode material A11 and the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and the numerical value is, PD=0.084 I(2θ A2 )+0.377.

[0186] Example 12 (1) Same as Example 1. (2) Same as Example 1 except that the firing temperature was 900°C. (3) A lithium iron phosphate positive electrode material A12 is obtained in the same manner as in Example 1. The lithium iron phosphate positive electrode material A12 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is: Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 is.

[0187] As can be seen from the XRD analysis, in the positive electrode material A12, 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 ) and the ratio I(2θ A2 ) / I(2θ B3 ) is 0.266. At the same time, the compacted density of the lithium iron phosphate cathode material A12 and the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and the numerical value is, PD=0.084 I(2θ A2 )+0.377.

[0188] Example 13 (1) In the same manner as in Example 1, iron phosphate precursor P1, lithium carbonate, titanium oxide, and manganese oxide were added to obtain a ratio of n(Fe):n(Li):n(Ti):n(Mn)=0.961:1.04:0.01:0.01, and then mixed with pure water to obtain a spray-dried material. (2) Same as Example 1. (3) The same procedure as in Example 1 is followed to obtain a lithium iron phosphate positive electrode material A13. The lithium iron phosphate positive electrode material A13 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is Li 1.04 (Fe 0.961 Ti 0.01 Mn 0.01 )(PO4) 0.91 (P2O7) 0.045 is.

[0189] As can be seen from the XRD analysis, in the positive electrode material A13, 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 ) and the ratio I(2θ A2 ) / I(2θ B3 ) is 0.254. At the same time, the compacted density of the lithium iron phosphate cathode material A13 and the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and the numerical value is, PD=0.084 I(2θ A2 )+0.377.

[0190] Comparative Example 1 (1) The procedure was the same as in Example 1, except that the iron phosphate precursor P1 was replaced with the iron phosphate precursor DP1, and the iron phosphate precursor DP1, lithium carbonate, and titanium oxide were added to obtain a ratio of n(Fe):n(Li):n(Ti)=0.976:1.04:0.019, which was then mixed with pure water to obtain a spray-dried material. (2) Same as Example 1. (3) A lithium iron phosphate positive electrode material D1 is obtained in the same manner as in Example 1. The lithium iron phosphate positive electrode material D1 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is Li 1.04 (Fe 0.976 Ti 0.019 )(PO4) 0.958 (P2O7) 0.021 is.

[0191] As can be seen from the XRD analysis, the positive electrode material D1 has a 2θ A1 =29.4-29.6°, 2θ A2 ==29.8-30°, 2θ A3 There is no characteristic diffraction peak at 43.8-43.9°.

[0192] Comparative Example 2 (1) The procedure was the same as in Example 1, except that the iron phosphate precursor P1 was replaced with the iron phosphate precursor DP2, and the iron phosphate precursor DP2, lithium carbonate, and titanium oxide were added to obtain a spray-dried material with a ratio of n(Fe):n(Li):n(Ti)=0.999:1.04:0.019, which was then mixed with pure water. (2) Same as Example 1. (3) A lithium iron phosphate positive electrode material D2 is obtained in the same manner as in Example 1. The lithium iron phosphate positive electrode material D2 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is Li 1.04 (Fe 0.999 Ti 0.019 )(PO4) 0.946 (P2O7) 0.027 is.

[0193] As can be seen from the XRD analysis, the positive electrode material D2 has a 2θ A1 =29.4-29.6°, 2θ A2 ==29.8-30°, 2θ A3 There is no characteristic diffraction peak at 43.8-43.9°.

[0194] Comparative Example 3 (1) The procedure was the same as in Example 1, except that the iron phosphate precursor P1 was replaced with the iron phosphate precursor DP3, and the iron phosphate precursor DP3, lithium carbonate, and titanium oxide were added to obtain a spray-dried material with a ratio of n(Fe):n(Li):n(Ti)=0.998:1.04:0.019, which was then mixed with pure water. (2) Same as Example 1. (3) A lithium iron phosphate positive electrode material D3 is obtained in the same manner as in Example 1. The lithium iron phosphate positive electrode material D3 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is Li 1.04 (Fe 0.998 Ti 0.019 )(PO4) 0.952 (P2O7) 0.024 is.

[0195] As can be seen from the XRD analysis, the positive electrode material D3 has a 2θ A1 =29.4-29.6°, 2θ A2==29.8-30°, 2θ A3 There is no characteristic diffraction peak at 43.8-43.9°.

[0196] Comparative Example 4 (1) The procedure was the same as in Example 1, except that the iron phosphate precursor P1 was replaced with the iron phosphate precursor DP1, and the iron phosphate precursor DP1, lithium carbonate, and titanium oxide were added to obtain a ratio of n(Fe):n(Li):n(Ti)=0.976:1.04:0.019, which was then mixed with pure water to obtain a spray-dried material. (2) Same as Example 1 except that the firing temperature was 795°C. (3) A 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 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is Li1.04(Fe 0.976 Ti 0.019 )(PO4) 0.958 (P2O7) 0.021 is.

[0197] As can be seen from the XRD analysis, the positive electrode material D4 has a 2θ A1 =29.4-29.6°, 2θ A2 ==29.8-30°, 2θ A3 There is no characteristic diffraction peak at 43.8-43.9°.

[0198] Comparative Example 5 (1) Same as Example 1. (2) Same as Example 1 except that the firing temperature was 480°C. (3) A lithium iron phosphate positive electrode material D5 is obtained in the same manner as in Example 1. The lithium iron phosphate positive electrode material D5 includes a base and a carbon coating layer coated on the surface of the base, where the composition of the base is: Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 is.

[0199] As can be seen from the XRD analysis, the positive electrode material D5 has a 2θ A1=29.4-29.6°, 2θ A2 =29.8-30°, 2θ A3 There is no characteristic diffraction peak at 43.8-43.9°.

[0200] Table 2 shows the median diameter, specific surface area, bulk density and moisture content of the spray-dried materials in the examples and comparative examples.

[0201] [Table 2-1]

[0202] Example The physicochemical parameters of the lithium iron phosphate cathode material are shown in Table 2.

[0203] [Table 2-2] 1 is the average particle size of the primary particles.

[0204] The FeP content, volume resistivity, and compaction density of the lithium iron phosphate positive electrode materials prepared in Examples 1 to 11, 14, and Comparative Examples 1 to 3 and 5 satisfied MI=77.13PD-0.03R-107.7.

[0205] Measurement example This measurement example is intended to illustrate the electrode material, the electrode, the lithium ion battery, and the preparation method thereof. (1) Preparation of cathode pieces: The lithium iron phosphate cathode material prepared in the above examples and comparative examples, the conductive agent carbon nanotubes, and the adhesive PVDF in NMP solution were mixed in a mass ratio of 90:5:5. Specifically, the dried cathode material and conductive agent were ground in a mortar for 15 minutes to uniformly grind the material, and then a PVDF solution (5% by mass) was added in proportion. The mixture was stirred with a magnetic stirrer for 6 hours. The resulting paste-like slurry was uniformly applied to an aluminum foil current collector and dried in a vacuum oven at 60°C for 20 hours. It was then pressed under a pressure of 100 MPa into a cathode piece with a diameter of 12 mm and a thickness of 120 μm. The cathode piece was then placed in a vacuum oven at 120°C and dried for 12 hours. (2) Battery assembly: A lithium metal sheet with a diameter of 17 mm and a thickness of 1 mm is used as the negative electrode, a 25 μm thick polyethylene porous film with an alumina ceramic layer coated on its surface is used as the separator, and a mixture of equal amounts of 1 mol / L LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC) is selected as the electrolyte. The positive electrode piece, separator, negative electrode piece, and electrolyte are assembled into a 2025-type button battery in an Ar gas glove box with a water content and oxygen content of less than 5 ppm. (3) Electrochemical performance measurement: The charging and discharging of the battery was measured using a LAND CT2001A charge / discharge meter from Wuhan Lanbo Electronics Co., Ltd. The charging and discharging voltage range was 2.5 to 3.75 V. The specific capacity of the assembled lithium-ion battery was measured at 0.1 C and 1 C, respectively, and the cycling performance was measured at 1 C. The measurement results are shown in Table 3.

[0206] [Table 3]

[0207] As can be seen from the results in Tables 2 and 3, 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 ) as a ratio of I(2θ A2 ) / I(2θ B3)≧0.26, the positive electrode material exhibits higher compaction density, better electrochemical performance, and at the same time produces a lower content of Fe2P.

[0208] Fig. 1 is an XRD diagram of the iron phosphate precursor prepared in Preparation Example 1 of the present invention. As can be seen from Fig. 1, 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 ferric pyrophosphate phase.

[0209] FIG. 2 is an SEM image of the iron phosphate precursor prepared in Preparation Example 1 of the present invention. As can be seen from FIG. 2, the average particle size of the primary particles of the iron phosphate precursor is 150 nm.

[0210] FIG. 3 is the XRD diagram of the lithium iron phosphate positive electrode materials prepared in Example 1 and Example 2 of the present invention. As can be seen from FIG. 3, the 2θ A1 =29.50°, 2θ A2 =29.93°, 2θ A3 = 43.85°, which proves that the positive electrode material contains a lithium ferric pyrophosphate phase.

[0211] FIG. 4 is an SEM image of the lithium iron phosphate positive electrode material prepared in Example 1 of the present invention, in which the positive electrode material has secondary particles formed from primary particles.

[0212] FIG. 5 is a graph showing the charge and discharge performance of the lithium ion batteries obtained by assembling the lithium iron phosphate positive electrode materials of Example 1 and Example 2. As can be seen from FIG. 5, Example 2 has higher charge and discharge capacities.

[0213] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications of the technical means of the present invention can be implemented, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations shall also be regarded as the contents disclosed in the present invention and shall fall within the scope of protection of the present invention.

Claims

1. A lithium iron phosphate positive electrode material, wherein the lithium iron phosphate positive electrode material has a 2θ Ａ１ =29.4-29.6°, 2θ Ａ２ = 29.8-30° and 2θ Ａ３ A lithium iron phosphate positive electrode material characterized by the presence of a characteristic diffraction peak at 43.8-43.9°.

2. According to XRD measurement, the lithium iron phosphate positive electrode material has a 2θ Ｂ１ =25.4-25.5°, 2θ Ｂ２ = 35.9-36° and 2θ Ｂ３ = 60.7-60.8°, there is a characteristic diffraction peak, Preferably, in the positive electrode material, 2θ Ａ２ The peak intensity I(2θ) of the diffraction characteristic peak at Ａ２ ) and 2θ Ｂ３ The peak intensity I(2θ) of the diffraction characteristic peak at Ｂ３ ) and 0.25≦I(2θ Ａ２ ) / I(2θ Ｂ３ )≦0.27, and preferably 0.26≦I(2θ Ａ２ ) / I(2θ Ｂ３ 2. The lithium iron phosphate positive electrode material of claim 1, wherein σ is 0.27 or less.

3. the positive electrode material includes a base and a carbon coating layer coated on a surface of the base; wherein the base has the composition shown in Formula I: Li １＋ａ Fe ｂ M ｃ Mn ｄ (PO ４ ) １－２ｗ (P ２ O ７ ) ｗ Formula I Here, -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; 3. The lithium iron phosphate cathode material according to claim 1 or 2, wherein the content of the carbon coating layer is preferably 0.5-2 wt %, preferably 1-1.5 wt %, based on the total weight of the cathode material.

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

5. Fe of the lithium iron phosphate positive electrode material ２ The values ​​of the P content, volume resistivity and compaction density are: MI = 77.13PD - 0.03R - 107.7 is satisfied. where R is the volume resistivity (Ω cm) of the lithium iron phosphate positive electrode material, PD is the compaction density (g / cm) of the lithium iron phosphate cathode material ３ ) and MI is the Fe of the lithium iron phosphate positive electrode material ２ is the P content (ppb), Preferably, the packed density of the lithium iron phosphate positive electrode material and the 2θ value of the lithium iron phosphate positive electrode material measured by XRD Ａ２ The peak intensity I(2θ) of the diffraction characteristic peak at Ａ２ ) and the numerical value is, PD=0.084 I(2θ Ａ２ ) +0.377, where PD is the compaction density (g / cm) of the lithium iron phosphate positive electrode material. ３ ) and I (2θ Ａ２ ) is determined by the 2θ Ａ２ The peak intensity I(2θ) of the diffraction characteristic peak at Ａ２ 5. The lithium iron phosphate positive electrode material of claim 4, wherein

6. (1) mixing an iron phosphate precursor, a lithium source, a carbon source, an optional metal source M, and an optional Mn source with a liquid medium, grinding the mixture into a slurry, and then drying the slurry to obtain a dried material; (2) calcining the dried material under a protective atmosphere to obtain a sintered material; (3) crushing and sieving the sintered material to obtain the lithium iron phosphate positive electrode material; Here, the iron phosphate precursor has a 2θ ａ１ =16.2-16.9°, 2θ ａ２ =27.3-28.1°, 2θ ａ３ = 29-29.7° and 2θ ａ４ = 30.2-30.9°, and the iron phosphate precursor has a characteristic diffraction peak at 2θ = 30.2-30.9° by XRD measurement. ｂ１ =20-20.7°, 2θ ｂ２ =21.5-22.2°, 2θ ｂ３ =23.4-24°, 2θ ｂ４ = 25.5-26.2°, there is a characteristic diffraction peak, In the iron phosphate precursor, 2θ ａｉ The integral area A (2θ ａｉ ) and 2θ ｂｊ The integral area A (2θ ｂｊ ) means [Equation 1] Fulfilling where i is an integer from 1 to 4, and j is an integer from 1 to 4, The method for preparing a lithium iron phosphate positive electrode material, characterized in that in step (2), the temperature of the calcination treatment is 500°C or higher.

7. The iron phosphate precursor has a-axis and c-axis crystal cell parameters measured by XRD of: 2.231≦c / a≦2.2326 Formula II is satisfied, Preferably, the iron phosphate precursor has the composition shown in Formula II: (Fe １－ｙ M ｙ PO ４ ) １－６ｘ [Fe ４ (P ２ O ７ ) ３ ] ｘ Formula II wherein 0.01≦x≦0.02, 0≦y≦0.1, and 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 diameter D of the iron phosphate precursor ５０ is 1-25 μm, Preferably, the iron phosphate precursor has a primary particle size of 20-200 nm; Preferably, the tap density of the iron phosphate precursor is 0.8-1.3 g / cm ３ and Preferably, the iron phosphate precursor has a specific surface area of ​​6-10 m ２ / g, 7. The method according to claim 6, wherein the iron phosphate precursor preferably has a sulfur content of ≦400 ppm.

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

9. The dosages of the iron phosphate precursor, the lithium source, the metal source M, and the Mn source are: Let 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, the dosage of the carbon source is 8 wt %-18 wt %, based on the total mass of the iron phosphate precursor; Preferably, the median diameter D of the slurry ５０ is 50-2000 nm, Preferably, the solids content of the slurry is 10-70 wt %; Preferably, the drying method is spray drying; The preparation method according to any one of claims 6 to 8, wherein the spray drying conditions preferably include an inlet air temperature of 190-280°C and an outlet air temperature of 60-120°C.

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

11. A lithium iron phosphate positive electrode material produced by the preparation method according to any one of claims 6 to 10.

12. A lithium ion battery, characterized in that the lithium ion battery comprises the lithium iron phosphate positive electrode material according to any one of claims 1 to 5 and 11.

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