Iron phosphate precursor, preparation method and application thereof, lithium iron phosphate cathode material, and lithium ion battery

Abstract

The present invention relates to the technical field of the preparation of lithium ion cathode materials, and discloses an iron phosphate precursor, a preparation method and application thereof, a lithium iron phosphate cathode material, and a lithium ion battery. The iron phosphate precursor has diffraction characteristic peaks at 2θ a1 = 16.2 - 16.9°, 2θ a2 = 27.3 - 28.1°, 2θ a3 = 29 - 29.7° and 2θ a4 = 30.2 - 30.9°; there are diffraction characteristic peaks at 2θ b1 = 20 - 20.7°, 2θ b2 = 21.5 - 22.2°, 2θ b3 = 23.4 - 24°, 2θ b4 = 25.5 - 26.2°; the integral area A(2θ ai ) and the integral area A(2θ bj ) satisfy #imgabs0#. The iron phosphate precursor material has specific diffraction characteristic peaks at specific positions, which can reduce the sintering temperature and improve the tap density of the prepared lithium iron phosphate cathode material.

Description

Technical Field

[0001] The present invention relates to the technical field of preparing lithium ion cathode materials, and particularly relates to an iron phosphate precursor, a preparation method and application thereof, a lithium iron phosphate cathode material, and a lithium ion battery. Background Art

[0002] As an important power system, lithium ion batteries are widely used in 3C products such as computers, communication tools and electronic tools, in the fields of electric vehicles such as EV and PHEV, and in energy storage systems. As a lithium ion battery cathode material, lithium iron phosphate has the characteristics of good safety, good stability, low cost, etc., and its market share is continuously increasing. With the rapid development of industrialization, future energy demands pose higher requirements for the energy density of power and energy storage batteries, and also present new demands and challenges for lithium iron phosphate cathode materials.

[0003] At present, the synthesis methods of lithium iron phosphate mainly include high-temperature solid-phase method, hydrothermal method, sol-gel method, etc. The high-temperature solid-phase method has a simple and controllable process flow and is suitable for industrial production; using iron phosphate and a lithium source as raw materials, after mixing evenly, it is calcined to produce lithium iron phosphate. As a precursor material, iron phosphate has a similar structure to lithium iron phosphate. Therefore, the quality of iron phosphate will directly affect battery performance such as energy density, cycle life, and safety. At present, extensive research has been carried out on high-compaction lithium iron phosphate materials and their precursor iron phosphate materials:

[0004] CN115838161A discloses a preparation method of a lithium iron phosphate cathode material with high tap density and high bulk density. LFP seeds are prepared in advance by a hydrothermal method or a solvothermal method, and then the prepared LFP seeds are used to prepare an LFP precursor with a controllable particle size distribution. Furthermore, a lithium iron phosphate cathode material for a lithium ion battery with a certain particle size distribution is obtained through carbon coating. This method regulates the particle size distribution by pre-adding seeds to achieve the size grading of particles. However, it may cause non-uniformity during the calcination process, thereby affecting the electrochemical performance. At the same time, the preparation processes of LFP seeds and the precursor are not easy to control and are not suitable for industrial production. CN104051713A discloses a preparation method of a micro-nano spherical lithium iron phosphate composite cathode material. A soluble lithium compound, an iron compound, and a phosphate are mixed in a molar ratio of lithium:iron:phosphorus of 1:1:1 and dissolved in deionized water to form a solution. The solution is added to a mixed solution of a binder, and then an appropriate amount of heat-conducting oil is added to an oil bath. The uniformly mixed solution is dropped into a beaker of high-temperature heat-conducting oil with a certain stirring speed at a certain rate. After the reaction is complete and filtered, a lithium iron phosphate precursor is obtained. Finally, the washed precursor is carbonized at a high temperature in an inert atmosphere to synthesize a micro-nano spherical lithium iron phosphate composite cathode material with a high tap density. This method introduces a binder, which only changes the morphology of the secondary particles and does not fundamentally solve the problem of bulk density. At the same time, this method requires a high-temperature reaction, and the reaction process is not easy to control and is not suitable for industrial production. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a ferric phosphate precursor, a preparation method and application thereof, a lithium iron phosphate cathode material, and a lithium ion battery. The XRD pattern of the ferric phosphate precursor material has specific diffraction characteristic peaks at specific positions, so that there are certain defects in the structure of the ferric phosphate precursor, which can play the role of a cosolvent during the sintering process of the precursor, reduce the sintering temperature, and improve the bulk density of the prepared lithium iron phosphate cathode material.

[0006] The first aspect of the present invention provides a ferric phosphate precursor, wherein the ferric phosphate precursor has diffraction characteristic peaks at 2θ a1 = 16.2 - 16.9°, 2θ a2 = 27.3 - 28.1°, 2θ a3 = 29 - 29.7° and 2θ a4 = 30.2 - 30.9° as measured by XRD; the ferric phosphate precursor has diffraction characteristic peaks at 2θ b1 = 20 - 20.7°, 2θ b2 = 21.5 - 22.2°, 2θ b3 = 23.4 - 24°, 2θ b4 = 25.5 - 26.2°;

[0007] The integral area A(2θ ai ) of the diffraction characteristic peak at 2θ ai and the integral area A(2θ bj ) of the diffraction characteristic peak at 2θ bj satisfy the following:

[0008] wherein, i is an integer from 1 to 4, and j is an integer from 1 to 4.

[0009] The second aspect of the present invention provides a method for preparing a ferric phosphate precursor, wherein the preparation method includes the following steps:

[0010] (1) Dissolve an iron source and an M source in water to form a mixed salt solution A1;

[0011] (2) Dissolve a phosphorus source in water, add a pH regulator to form a phosphorus source solution A2;

[0012] (3) Mix the mixed salt solution A1, the phosphorus source solution A2 and an oxidant A3, carry out a synthesis reaction, and optionally add an auxiliary agent;

[0013] (4) Filter and wash the product of step (3) to obtain a filter cake B1, beat the filter cake to obtain a slurry, then optionally add an auxiliary agent, adjust the pH value, carry out an aging and crystal transformation reaction, and then filter and wash to obtain a filter cake B2;

[0014] (5) Calcinate the filter cake to obtain a ferric phosphate precursor;

[0015] wherein, the pH value of the phosphorus source solution A2 is 0.5 - 2.5;

[0016] The conditions of the aging and crystal transformation reaction include: the reaction temperature is 70 - 90 °C, the heating rate is 1 - 3 °C / min, and the reaction time is 1 - 3 h;

[0017] The conditions of the calcination include: the calcination temperature is 500 - 800 °C, the heating rate is 3 - 8 °C / min, and the calcination time is 2 - 4 h.

[0018] The third aspect of the present invention provides a ferric phosphate precursor prepared by the above preparation method.

[0019] The fourth aspect of the present invention provides an application of the above ferric phosphate precursor in the preparation of a lithium iron phosphate cathode material.

[0020] The fifth aspect of the present invention provides a lithium iron phosphate cathode material, wherein the lithium iron phosphate cathode material is prepared from the above ferric phosphate precursor.

[0021] The sixth aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery includes the above-mentioned lithium iron phosphate cathode material.

[0022] Through the above technical solutions, the lithium iron phosphate precursor, its preparation method and application, the lithium iron phosphate cathode material, and the lithium-ion battery provided by the present invention obtain the following beneficial effects:

[0023] In the present invention, the XRD pattern of the lithium iron phosphate precursor material has specific diffraction characteristic peaks at specific positions, so that there are certain defects in the structure of the lithium iron phosphate precursor, which can play the role of a cosolvent during the sintering process of the precursor, while reducing the sintering temperature, improving the tap density of the prepared lithium iron phosphate cathode material.

[0024] Furthermore, the primary particles of the lithium iron phosphate precursor provided by the present invention are uniform and dense, and the molar ratio of metal to phosphorus Me / P is stable and adjustable, which can be used to prepare a lithium iron phosphate cathode material with a high tap density.

[0025] Furthermore, in the present invention, the lithium iron phosphate precursor has a specific c / a value of the unit cell parameter, which can not only achieve a higher tap density at a lower temperature but also reduce the content of iron phosphide in the lithium iron phosphate, thereby improving the capacity and energy density of the cathode material prepared from the precursor, reducing the side reaction with the electrolyte, and improving the service life and safety of the battery.

[0026] In addition, the present invention provides the corresponding relationship between the c / a value of the unit cell parameter of the lithium iron phosphate precursor and the tap density of the lithium iron phosphate cathode material, providing a basis for the development of raw materials and the design of products.

[0027] In the preparation method of the lithium iron phosphate precursor provided by the present invention, by controlling the pH value of the phosphorus source solution, the aging and crystal transformation reaction, and the calcination conditions, the XRD pattern of the prepared lithium iron phosphate precursor shows specific characteristic peak diffraction at specific positions. Further, the unit cell parameter of the lithium iron phosphate precursor satisfies a specific range, so that when the prepared lithium iron phosphate precursor is used to prepare the lithium iron phosphate cathode material, the sintering temperature can be reduced while the tap density of the lithium iron phosphate cathode material is improved.

[0028] Furthermore, in the present invention, during the preparation process of the lithium iron phosphate precursor, adding an auxiliary agent in the aging and crystal transformation stage or the synthesis reaction stage can induce the deposition and arrangement of crystal nuclei, make the secondary particles of the precursor more dense, and at the same time help to remove sulfur impurities in the crystal lattice, thereby affecting the unit cell parameter.

[0029] In addition, the preparation method of the iron phosphate precursor of the present invention only optimizes the process parameters and does not require any adjustment to the existing production line. The entire process is non-toxic and harmless, the process is simple, the raw materials are easily available, the equipment requirements are low, it is easy to promote and apply, and it can be widely used in the industrial production of lithium iron phosphate cathode materials.

[0030] The lithium iron phosphate cathode material prepared from the iron phosphate precursor of the present invention has the characteristics of high powder compaction density, low Fe2P content, and uniform carbon coating. When it is used in a lithium ion battery, the lithium ion battery exhibits higher capacity, energy efficiency, lower internal resistance, and better cycle performance. Specifically, the lithium iron phosphate cathode material has a high compaction density of 2.63 g / cm 3 , the discharge specific capacity at 0.1C reaches 160 mAh / g, the capacity retention rate after 80 cycles at room temperature is 100%, and the 1C energy efficiency reaches 95%, showing excellent electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 XRD pattern of the iron phosphate precursor prepared in Example 1 of the present invention.

[0032] Figure 2 SEM image of the iron phosphate precursor prepared in Example 1 of the present invention.

[0033] Figure 3 XRD pattern of the lithium iron phosphate cathode material prepared from the iron phosphate precursor P1.

[0034] Figure 4 SEM image of the lithium iron phosphate cathode material prepared from the iron phosphate precursor P1. DETAILED DESCRIPTION OF THE INVENTION

[0035] The endpoints and any values disclosed in this article for ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this article.

[0036] The first aspect of the present invention provides an iron phosphate precursor, wherein the iron phosphate precursor has diffraction characteristic peaks at 2θ a1 = 16.2 - 16.9°, 2θ a2 = 27.3 - 28.1°, 2θ a3 = 29 - 29.7° and 2θ a4 = 30.2 - 30.9° through XRD testing; the iron phosphate precursor has diffraction characteristic peaks at 2θ b1= 20 - 20.7°, 2θ b2 = 21.5 - 22.2°, 2θ b3 = 23.4 - 24°, 2θ b4 = 25.5 - 26.2°;

[0037] In the iron phosphate precursor, 2θ ai The integrated area A(2θ ai ) of the diffraction characteristic peak at and 2θ bj The integrated area A(2θ bj ) of the diffraction characteristic peak at satisfy:

[0038] where i is an integer from 1 to 4 and j is an integer from 1 to 4.

[0039] The XRD test of the iron phosphate precursor was measured using an XRD-6000 type X-ray powder diffractometer from Shimadzu, Japan. The test conditions were: set voltage 40 kV, current 40 mA, step size 0.005°, height limit slit 10 mm, divergence slit 1 / 2°, anti-scattering slit 8 mm, receiving slit open, set the test scanning 2θ angle to 10° - 80°, continuously scan in 1D mode, and scanning speed 1.2° / min.

[0040] In the present invention, by analyzing the XRD pattern, it can be found that in the iron phosphate precursor of the present invention, there are diffraction characteristic peaks at specific 2θ, and the integrated areas of the diffraction characteristic peaks at different 2θ satisfy a specific proportional relationship, so that there are certain defects in the structure of the iron phosphate precursor, which can play the role of a flux during the sintering process of the precursor, while reducing the sintering temperature, improving the tap density of the prepared lithium iron phosphate cathode material.

[0041] In the present invention, the integrated area A(2θ ai ) of the diffraction characteristic peak at in the iron phosphate precursor refers to ai the total integrated area of the diffraction characteristic peaks at 2θ a1 , 2θ a2 , 2θ a3 and 2θ a4 .

[0042] In the present invention, the integrated area A(2θ bj ) of the diffraction characteristic peak at in the iron phosphate precursor refers to bj the total integrated area of the diffraction characteristic peaks at 2θ b1 , 2θ b2 , 2θ b3 and 2θ b4 .

[0043] Furthermore,

[0044] According to the present invention, the unit cell parameters of the a-axis and c-axis of the iron phosphate precursor measured by XRD satisfy: 2.2306 ≤ c / a ≤ 2.2330.

[0045] In the present invention, the crystal structure of the iron phosphate precursor is hexagonal system, and the space group is P3121.

[0046] In the present invention, the point group structure of the iron phosphate precursor shows an equivalent arrangement on the a-axis and b-axis. The c-axis is the upright crystal axis.

[0047] In the present invention, the iron phosphate precursor has a specific c / a value of the unit cell parameter, which can not only achieve a higher tap density at a lower temperature, but also reduce the content of iron phosphide in lithium iron phosphate, thereby improving the capacity and energy density of the cathode material prepared from the precursor, reducing the side reaction with the electrolyte, and improving the service life and safety of the battery.

[0048] Further, in Formula 2, 2.231 ≤ c / a ≤ 2.2326.

[0049] According to the present invention, the iron phosphate precursor has the composition shown in Formula I:

[0050] (Fe 1-y M y PO4) 1-6x [Fe4(P2O7)3] x Formula I,

[0051] wherein, 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.

[0052] Further, 0.01 ≤ x ≤ 0.02, 0 < y ≤ 0.05, and M is selected from at least one of Mn, Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti.

[0053] According to the present invention, in the iron phosphate precursor, the molar ratio of the metal element to the phosphorus element n(Me) / n(P) is 0.960 - 0.980.

[0054] In the present invention, when the molar ratio of the metal element to the phosphorus element in the iron phosphate precursor satisfies the above range, the precursor has certain structural defects, and the excessive phosphorus acts as a flux, which can reduce the sintering temperature and improve the tap density of the prepared lithium iron phosphate cathode material.

[0055] Further, in the iron phosphate precursor, the molar ratio of the metal element to the phosphorus element, n(Me) / n(P), is 0.960 - 0.970.

[0056] According to the present invention, the median particle size D of the iron phosphate precursor 50 is 1 - 25 μm.

[0057] In the present invention, when the median particle size of the iron phosphate precursor meets the above range, it is beneficial to improve the grinding efficiency in the preparation process of the cathode material and reduce the energy consumption.

[0058] Further, the median particle size D of the iron phosphate precursor 50 is 2 - 20 μm.

[0059] According to the present invention, the primary particle size of the iron phosphate precursor is 20 - 200 nm.

[0060] In the present invention, when the primary particle size of the iron phosphate precursor meets the above range, the primary particles are uniform and dense, which is beneficial to obtaining a high tap density lithium iron phosphate cathode material.

[0061] Further, the primary particle size of the iron phosphate precursor is 50 - 150 nm.

[0062] According to the present invention, the tap density of the iron phosphate precursor is 0.8 - 1.3 g / cm 3 .

[0063] In the present invention, when the tap density of the iron phosphate precursor meets the above range, it indicates that the precursor has a high density, which is beneficial to further improving the tap density of the lithium iron phosphate cathode material.

[0064] Further, the tap density of the iron phosphate precursor is 0.9 - 1.2 g / cm 3 .

[0065] According to the present invention, the specific surface area of the iron phosphate precursor is 6 - 10 m 2 / g.

[0066] In the present invention, when the specific surface area of the iron phosphate precursor meets the above range, the precursor has a high reaction activity. When preparing the lithium iron phosphate cathode material from it, it is beneficial to the diffusion of lithium ions and improves the charge-discharge capacity.

[0067] Further, the specific surface area of the iron phosphate precursor is 6.5 - 9.5 m 2 / g.

[0068] According to the present invention, the sulfur content in the iron phosphate precursor is ≤ 400 ppm.

[0069] 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, and the low-temperature performance and cycling performance of the positive electrode material prepared therefrom can be improved.

[0070] Furthermore, the sulfur content in the iron phosphate precursor is ≤200 ppm.

[0071] The second aspect of the present invention provides a method for preparing an iron phosphate precursor, characterized in that the preparation method comprises the following steps:

[0072] (1) Dissolve an iron source and an M source in water to form a mixed salt solution A1;

[0073] (2) Dissolve a phosphorus source in water, add a pH regulator to form a phosphorus source solution A2;

[0074] (3) Mix the mixed salt solution A1, the phosphorus source solution A2 and an oxidant A3, carry out a synthesis reaction, and optionally add an auxiliary agent;

[0075] (4) Filter and wash the product of step (3) to obtain a filter cake B1, slurry the filter cake, and after obtaining a slurry, optionally add an auxiliary agent, adjust the pH value, carry out an aging and crystal transformation reaction, and then carry out filtration and washing to obtain a filter cake B2;

[0076] (5) Calcinate the filter cake to obtain an iron phosphate precursor;

[0077] Among them, the pH value of the phosphorus source solution A2 is 0.5 - 2.5;

[0078] The conditions of the aging and crystal transformation reaction include: the reaction temperature is 70 - 90 °C, the heating rate is 1 - 3 °C / min, and the reaction time is 1 - 3 h;

[0079] The conditions of the calcination include: the calcination temperature is 500 - 800 °C, the heating rate is 3 - 8 °C / min, and the calcination time is 2 - 4 h.

[0080] In the present invention, by controlling the pH value of the phosphorus source solution, the aging and crystal transformation reaction and the conditions of the calcination, the XRD pattern of the prepared iron phosphate precursor shows specific characteristic peak diffractions at specific 2θ values, and the integral areas of the diffraction characteristic peaks at different 2θ values satisfy a specific proportional relationship. Specifically, the iron phosphate precursor described in the first aspect of the present invention is prepared, and when the prepared iron phosphate precursor is used to prepare a lithium iron phosphate positive electrode material, the sintering temperature can be reduced while the tap density of the lithium iron phosphate positive electrode material is increased.

[0081] Specifically, the pH value of the phosphorus source solution is controlled to regulate the oxidation precipitation reaction to generate amorphous iron phosphate; then, the aging temperature, heating rate, and aging time in the aging and crystal transformation stage are regulated to complete the crystal transformation reaction from amorphous iron phosphate to iron phosphate dihydrate, realizing the regulation of the crystallinity and unit cell parameters of iron phosphate dihydrate; finally, the calcination temperature, heating rate, and calcination time in the calcination stage are regulated to complete the dehydration and crystal transformation reaction from iron phosphate dihydrate to anhydrous iron phosphate, realizing the regulation of the crystal structure in the iron phosphate precursor.

[0082] In the present invention, there are no specific limitations on the mixing method of the mixed salt solution A1, the phosphorus source solution A2, and the oxidant A3, nor on the addition timing of the auxiliary agent, as long as the mixed salt solution A1, the phosphorus source solution A2, and the antioxidant A3 can be fully mixed evenly, or the aging and crystal transformation reaction can be carried out optionally in the presence of the auxiliary agent.

[0083] In a specific embodiment of the present invention, the mixed salt solution A1, the phosphorus source solution A2, and the oxidant A3 are added to the reaction kettle in a co-current manner for the synthesis reaction.

[0084] In a specific embodiment of the present invention, first, the mixed salt solution A1 and the oxidant A3 are fully reacted, and then they are added to the reaction kettle in a co-current manner with the phosphorus source solution A2 for the synthesis reaction.

[0085] In a specific embodiment of the present invention, the mixed salt solution A1 is used as the bottom liquid, and the phosphorus source solution A2 and the oxidant A3 are added to the reaction kettle in a co-current manner for the synthesis reaction.

[0086] In a preferred embodiment of the present invention, the pH value of the phosphorus source solution A2 is 1 - 2.

[0087] In a preferred embodiment of the present invention, the conditions for the aging and crystal transformation reaction include: the reaction temperature is 80 - 85 °C, the heating rate is 2 - 3 °C / min, and the reaction time is 1 - 2 h.

[0088] In a preferred embodiment of the present invention, the conditions for the calcination include: the calcination temperature is 600 - 750 °C, the heating rate is 3 - 5 °C / min, and the calcination time is 2 - 3 h.

[0089] According to the present invention, in step (4), the pH value is adjusted to 1 - 2.5, preferably to 1 - 2.

[0090] In the present invention, there are no specific limitations on the method of adjusting the pH value in step (4). To avoid introducing impurities, preferably, phosphoric acid is added to adjust the pH value.

[0091] According to the present invention, in step (1), the concentration of the mixed salt solution A1 is 0.1 - 4 mol / L; preferably 0.2 - 2 mol / L.

[0092] In the present invention, the type of the iron source is not specifically limited, and the iron source includes but is not limited to divalent iron salts. Preferably, the divalent iron salt is selected from at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, and iron acetate.

[0093] In the present invention, the type of the M source is not specifically limited, and the M source is a compound capable of providing at least one M element selected from Mn, Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti, including but not limited to oxides containing M, salts containing M, etc.

[0094] According to the present invention, in step (1), the iron source and the M source are such that 0 < n(M) / [n(Fe) + n(M)] ≤ 0.1, preferably 0 < n(M) / [n(Fe) + n(M)] ≤ 0.05.

[0095] According to the present invention, the concentration of the phosphorus source solution A2 is 0.2 - 20 mol / L, preferably 1 - 15 mol / L.

[0096] In the present invention, the type of the phosphorus source is not specifically limited, and the phosphorus source includes but is not limited to at least one of phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. Preferably, the phosphorus source is selected from at least one of phosphoric acid, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate.

[0097] In the present invention, the type of the pH regulator is not specifically limited, and its function is to adjust the pH of the solution. The pH regulator is an acid solution or an alkali solution. Preferably, the pH regulator is selected from at least one of sodium hydroxide, ammonia water, sulfuric acid, hydrochloric acid, and nitric acid.

[0098] According to the present invention, in step (3), the dosages of the mixed salt solution A1 and the phosphorus source solution A2 are such that n(P):n(Fe) is 1 - 3:1, preferably 1 - 1.5:1.

[0099] According to the present invention, in step (3), the dosages of the mixed salt solution A1 and the oxidant A3 are such that n(oxidant):n(Fe) is 1 - 5:1, preferably 1 - 3:1.

[0100] In the present invention, the type of the oxidant is not specifically limited, and the oxidant includes but is not limited to hydrogen peroxide, ozone, sodium persulfate, ammonium persulfate, sodium hypochlorite, sodium ferrate. Preferably, the oxidant is selected from at least one of hydrogen peroxide, sodium persulfate, and ammonium persulfate.

[0101] According to the present invention, the conditions for the synthesis reaction include: the reaction temperature is 25 - 60 °C, and the reaction time is 1 - 6 h.

[0102] Further, the conditions for the synthesis reaction include: the reaction temperature is 40 - 60 °C, and the reaction time is 0.5 - 3 h.

[0103] In the present invention, during the preparation process of the iron phosphate precursor, adding an auxiliary agent in the aging and crystal transformation stage or the synthesis reaction stage can induce the deposition and arrangement of crystal nuclei, make the secondary particles of the precursor denser, and at the same time help to remove sulfur impurities in the crystal lattice, thereby affecting the unit cell parameters.

[0104] According to the present invention, the auxiliary agent is selected from at least one of sodium hexadecyl benzene sulfonate, sodium dodecyl benzene sulfonate, triethanolamine, ethylene glycol, polyvinylpyrrolidone, polyethylene glycol, wood cellulose, and carboxymethyl cellulose. Preferably, the auxiliary agent is selected from at least one of sodium hexadecyl benzene sulfonate, polyethylene glycol, wood cellulose, and carboxymethyl cellulose.

[0105] According to the present invention, based on the total amount of the iron source and the M source, the dosage of the auxiliary agent is 0.1 wt% - 1 wt%, preferably 0.1 wt% - 0.5 wt%.

[0106] In the present invention, when the dosage of the auxiliary agent is controlled to meet the above range, it can induce the deposition and arrangement of crystal nuclei, make the secondary particles denser, and at the same time help to remove sulfur impurities in the crystal lattice, thereby further modulating the unit cell parameters in the precursor.

[0107] In the present invention, there is no special requirement for the washing method in step (4), and it can be carried out according to the conventional washing methods in the art. Preferably, a washing liquid is used, preferably pure water at 20 - 90 °C, and more preferably pure water at 30 - 60 °C for washing.

[0108] The third aspect of the present invention provides an iron phosphate precursor prepared by the above preparation method.

[0109] The fourth aspect of the present invention provides an application of the above iron phosphate precursor in the preparation of a lithium iron phosphate cathode material.

[0110] The fifth aspect of the present invention provides a lithium iron phosphate cathode material, wherein the lithium iron phosphate cathode material is prepared from the above iron phosphate precursor.

[0111] According to the present invention, the lithium iron phosphate cathode material includes a matrix and a carbon coating layer coated on the surface of the matrix; wherein, the matrix has the composition shown in Formula II:

[0112] Li 1+a [(Fe 1-y My ) 1-b M’ b PO4 type II;

[0113] where -0.1 ≤ a ≤ 0.1, 0 ≤ b ≤ 0.1, 0 ≤ y ≤ 0.1;

[0114] where 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, and M’ is selected from at least one of La, Ce, Cr, Mo, Ca, Hf, Ti, Mn, Fe, Zn, Y, Zr, W, Nb, Sm, Co, Ni, V, Mg, Na, B, and Al.

[0115] In the present invention, when the lithium iron phosphate cathode material is applied to a lithium-ion battery, it effectively improves the electrochemical performance of the lithium-ion battery, showing higher capacity and energy efficiency, lower internal resistance, and better cycling performance.

[0116] Further, -0.08 ≤ a ≤ 0.08, 0 ≤ b ≤ 0.05, 0 < y ≤ 0.05.

[0117] Further, M is selected from at least one of Mn, Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti, and M’ is selected from at least one of Al, Zr, W, Fe, Mn, Co, V, and Ti.

[0118] According to the present invention, based on the total weight of the cathode material, the content of the carbon coating layer is 0.5 - 2 wt%, preferably 1 - 1.5 wt%.

[0119] According to the present invention, the lithium iron phosphate cathode material has a secondary particle structure formed by primary particles.

[0120] According to the present invention, the median particle size D of the primary particles of the cathode material 50 is 200 - 2500 nm, preferably 500 - 2000 nm.

[0121] According to the present invention, the tap density of the lithium iron phosphate cathode material is 2.50 - 2.70 g / cm 3 , preferably 2.55 - 2.65 g / cm 3 .

[0122] According to the present invention, the specific surface area of the lithium iron phosphate cathode material is 8 - 18 m 2 / g, preferably 10 - 13 m 2 / g.

[0123] According to the present invention, the carbon content of the lithium iron phosphate cathode material is 0.5-2 wt%, preferably 1.0-1.5 wt%.

[0124] According to the present invention, the volume resistivity of the lithium iron phosphate cathode material is 1-100 Ω·cm, preferably 10-50 Ω·cm.

[0125] In the present invention, there is no particular requirement for the preparation method of the lithium iron phosphate cathode material, as long as the iron phosphate precursor described in the first aspect of the present invention is used in the preparation process.

[0126] In a specific embodiment of the present invention, the lithium iron phosphate cathode material is prepared according to the following steps:

[0127] S1. In the presence of a solvent, the iron phosphate lithium precursor is mixed and homogenized with a lithium source, a carbon source, and optionally an M' source to obtain a slurry;

[0128] S2. The solvent in the slurry is removed to obtain a dry material, and then the dry material is calcined in the presence of a protective atmosphere to obtain the lithium iron phosphate cathode material.

[0129] In the present invention, there is no particular limitation on the type of the lithium source, and a conventional type of lithium source in the art can be used. For example, the lithium source is selected from at least one of lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate, lithium oxalate, lithium nitrate, and lithium acetate. Preferably, the lithium source is selected from at least one of lithium hydroxide, lithium carbonate, and lithium dihydrogen phosphate.

[0130] In the present invention, there is no particular limitation on the type of the carbon source, and a conventional type of carbon source in the art can be used. For example, the carbon source is selected from at least one of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine. Preferably, the carbon source is selected from at least one of glucose, sucrose, starch, and cellulose.

[0131] In the present invention, there is no particular limitation on the type of the M' source, as long as it is a compound capable of providing 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 capable of providing the element M'.

[0132] In the present invention, there is no particular requirement for the amount of the solvent in step S1, as long as it can make the iron phosphate lithium precursor, the lithium source, the carbon source, and optionally the M' source fully mixed and uniformly dispersed. There is also no particular limitation on the type of the solvent, and a conventional type of solvent in the art can be used.

[0133] In the present invention, the amounts of the iron phosphate precursor and the phosphorus source are such that 0.9 ≤ n(Li) / n(precursor) ≤ 1.1, and preferably, 0.92 ≤ n(Li) / n(precursor) ≤ 1.08.

[0134] In the present invention, based on the total mass of the iron phosphate precursor, the amount of the carbon source is 0.5 - 2 wt%, preferably 1 - 1.5 wt%.

[0135] In the present invention, the amounts of the iron phosphate precursor and the M' source are such that 0 ≤ n(M') / n(precursor) ≤ 0.1, and preferably, 0 ≤ n(Li) / n(precursor) ≤ 0.05.

[0136] In the present invention, there is no particular limitation on the method for removing the solvent from the slurry in step S2. For example, the solvent in the slurry can be removed by direct evaporation. The evaporation temperature and time can be adjusted according to actual needs. There is no particular limitation on the evaporation method, such as static drying or spray drying.

[0137] In the present invention, there is no particular limitation on the type of the protective atmosphere, such as a nitrogen atmosphere and / or an argon atmosphere.

[0138] In the present invention, the calcination conditions include: the calcination temperature is 500 - 1000 °C, preferably 600 - 800 °C; the calcination time is 4 - 20 h, preferably 6 - 15 h.

[0139] The sixth aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery includes the above-mentioned lithium iron phosphate cathode material.

[0140] The present invention will be described in detail below through examples. In the following examples,

[0141] The crystallization properties such as the unit cell parameters of the iron phosphate precursor were tested using an XRD-6000 type X-ray powder diffractometer from Shimadzu, Japan; the test conditions were: set the voltage at 40 kV, the current at 40 mA, the step size at 0.005°, the height limit slit at 10 mm, the divergence slit at 1 / 2°, the anti-scattering slit at 8 mm, the receiving slit open, set the test scanning 2θ angle to 10° - 80°, continuously scan in 1D mode, and the scanning speed was 1.2° / min.

[0142] The contents of each element in the iron phosphate precursor and the lithium iron phosphate cathode material were tested using a 5800 ICP-OES spectrometer from Agilent, USA;

[0143] The content of the carbon coating layer in the lithium iron phosphate cathode material was tested using a CS-i carbon-sulfur analyzer from Eltra, Germany.

[0144] The median particle size of the iron phosphate precursor and the lithium iron phosphate cathode material was tested using a Malvern laser particle size analyzer Mastersizer 2000;

[0145] The primary particle size of the iron phosphate precursor was tested using a scanning electron microscope of model S-4800 from HITACHI, Japan;

[0146] The tap density of the iron phosphate precursor material was tested using a tap density tester of model BT-30 from Baxter;

[0147] The specific surface area of the iron phosphate precursor and the lithium iron phosphate cathode material was tested using a specific surface area analyzer of model Tristar II 3020 from Micromertics, USA;

[0148] The compaction density of the lithium iron phosphate cathode material was tested using a compaction density tester of model MCP-PD51 from Mitsubishi Chemical, Japan;

[0149] The volume resistivity of the lithium iron phosphate cathode material was tested using a powder compaction resistance tester of model MCP-PD51 from Mitsubishi Chemical, Japan.

[0150] The raw materials used in the examples and comparative examples were all commercially available products.

[0151] Example 1

[0152] (1) According to the molar ratio of n(Fe):n(Ti) = 99:1, a certain mass of ferrous sulfate and titanyl sulfate were weighed and dissolved in deionized water to prepare a 2 mol / L mixed salt solution A1.

[0153] (2) A certain mass of concentrated phosphoric acid was weighed, and the pH of the solution was adjusted to 2 with 30% sodium hydroxide to prepare a 2 mol / L phosphorus source solution A2.

[0154] (3) A certain amount of the mixed salt solution A1, the phosphorus source solution A2 and 30% hydrogen peroxide A3 were added to the reactor in a co-current manner for a synthesis reaction. The reaction temperature was 40 °C and the reaction time was 1 h. Among them, n(P):n(Fe) was 1.05:1, and n(oxidant):n(Fe) was 1.2:1.

[0155] (4) After the reaction, the reaction slurry was filtered and washed to obtain a filter cake. The filter cake was slurried, and the obtained slurry was added to the reactor. 0.1 wt% of lignocellulose was added based on the total mass of ferrous sulfate and titanyl sulfate. Phosphoric acid was added to adjust the pH to 1.5. The heating rate was controlled at 2 °C / min, the aging temperature was 82 °C, and the aging time was 2 h. After the reaction, the reaction slurry was filtered and washed to obtain a filter cake.

[0156] (5) The filter cake is calcined at high temperature for dehydration, controlling the heating rate at 3 °C / min, the calcination temperature at 700 °C, and the calcination time at 3 h to obtain the anhydrous iron phosphate precursor P1. Its composition is (Fe 0.99 Ti 0.01 PO4) 0.91 [Fe4(P2O7)3] 0.015 , where x = 0.015 and y = 0.01.

[0157] Figure 1 is the XRD pattern of the iron phosphate precursor P1. It can be seen from Figure 1 that the precursor material has diffraction characteristic peaks at 2θ a1 = 16.2 - 16.9°, 2θ a2 = 27.3 - 28.1°, 2θ a3 = 29 - 29.7° and 2θ a4 = 30.2 - 30.9°. There are characteristic peaks at 2θ b1 = 20 - 20.7°, 2θ b2 = 21.5 - 22.2°, 2θ b3 = 23.4 - 24°, 2θ b4 = 25.5 - 26.2°. It is speculated that the iron phosphate precursor contains the iron pyrophosphate phase. Through calculation, it is found that

[0158] Figure 2 is the SEM image of the iron phosphate precursor P1. It can be seen from Figure 2 that the primary particles are uniform and dense, reducing the differences between particles during the calcination stage, and thus effectively improving the tap density of the cathode material.

[0159] Example 2

[0160] (1) The same as in Example 1.

[0161] (2) The same as in Example 1.

[0162] (3) The same as in Example 1.

[0163] (4) The same as in Example 1.

[0164] (5) The filter cake is calcined at high temperature for dehydration, controlling the heating rate at 5 °C / min, the calcination temperature at 650 °C, and the calcination time at 2 h to obtain the anhydrous iron phosphate P2. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.886 [Fe4(P2O7)3] 0.019 , where x = 0.019 and y = 0.01.

[0165] Example 3

[0166] (1) The same as Example 1.

[0167] (2) The same as Example 1.

[0168] (3) The same as Example 1.

[0169] (4) After the reaction is completed, the reaction slurry is filtered and washed to obtain a filter cake. The filter cake is slurried, and the obtained slurry is added to the reaction kettle. Based on the total mass of ferrous sulfate and titanyl sulfate, phosphoric acid is added to adjust the pH to 1.5, the heating rate is controlled at 3 °C / min, the aging temperature is 80 °C, and the aging time is 1 h. After the reaction is completed, the reaction slurry is filtered and washed to obtain a filter cake.

[0170] (5) The same as Example 1 to obtain the anhydrous iron phosphate precursor P3. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.904 [Fe4(P2O7)3] 0.016 , where x = 0.016 and y = 0.01.

[0171] Example 4

[0172] (1) The same as Example 1.

[0173] (2) Weigh a certain mass of concentrated phosphoric acid, add sodium hydroxide with a concentration of 30% to adjust the pH of the solution to 1.5, and prepare a 2 mol / L phosphorus source solution.

[0174] (3) The same as Example 1.

[0175] (4) The same as Example 1.

[0176] (5) The same as Example 1 to obtain the anhydrous iron phosphate precursor P4. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.898 [Fe4(P2O7)3] 0.017 , where x = 0.017 and y = 0.01.

[0177] Example 5

[0178] (1) The same as Example 1.

[0179] (2) Weigh a certain mass of ammonium dihydrogen phosphate, dissolve it in deionized water, add dilute sulfuric acid with a concentration of 30% to adjust the pH of the solution to 2, and prepare a 2 mol / L phosphorus source solution.

[0180] (3) The same as Example 1.

[0181] (4) is the same as in Example 1.

[0182] (5) is the same as in Example 1 to obtain an anhydrous iron phosphate precursor P5. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.91 [Fe4(P2O7)3] 0.015 , where x = 0.015 and y = 0.01.

[0183] Example 6

[0184] (1) is the same as in Example 1.

[0185] (2) Weigh a certain mass of ammonium dihydrogen phosphate, dissolve it in deionized water, and adjust the pH of the solution to 2 by adding 30% dilute sulfuric acid to prepare a 2 mol / L phosphorus source solution.

[0186] (3) is the same as in Example 1.

[0187] (4) After the reaction is completed, add 0.1 wt% lignocellulose based on the total mass of ferrous sulfate and titanium oxysulfate, adjust the pH to 1.5 with phosphoric acid, control the heating rate at 2 °C / min, the aging temperature at 82 °C, and the aging time at 2 h. After the reaction is completed, filter and wash the reaction slurry to obtain a filter cake.

[0188] (5) is the same as in Example 1 to obtain an anhydrous iron 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.

[0189] Example 7

[0190] (1) According to the molar ratio of n(Fe):n(Al) = 98:2, weigh a certain mass of ferrous sulfate and sodium aluminate and dissolve them in deionized water to prepare a 2 mol / L mixed salt solution.

[0191] (2) is the same as in Example 1.

[0192] (3) is the same as in Example 1.

[0193] (4) is the same as in Example 1.

[0194] (5) is the same as in Example 1 to obtain an anhydrous iron phosphate precursor P7. Its composition is: (Fe 0.98 Al 0.02 PO4) 0.91 [Fe4(P2O7)3] 0.015, where x = 0.015 and y = 0.02.

[0195] Example 8

[0196] (1) The same as in Example 1.

[0197] (2) Weigh a certain mass of concentrated phosphoric acid, add sodium hydroxide with a concentration of 30% to adjust the pH of the solution to 1.3, and prepare a 2 mol / L phosphorus source solution A2.

[0198] (3) The same as in Example 1.

[0199] (4) After the reaction, filter and wash the reaction slurry to obtain a filter cake. Pulverize the filter cake, add the obtained slurry to the reaction kettle, add phosphoric acid to adjust the pH to 1.5, control the heating rate at 1.5 °C / min, the aging temperature at 75 °C, and the aging time at 1 h. After the reaction, filter and wash the reaction slurry to obtain a filter cake.

[0200] (5) Calcinate the filter cake at high temperature for dehydration, control the heating rate at 6 °C / min, the calcination temperature at 760 °C, and the calcination time at 2 h to obtain an anhydrous iron phosphate precursor P8. Its composition is (Fe 0.99 Ti 0.01 PO4) 0.922 [Fe4(P2O7)3] 0.013 , where x = 0.013 and y = 0.01.

[0201] Comparative Example 1

[0202] (1) The same as in Example 1.

[0203] (2) The same as in Example 1.

[0204] (3) The same as in Example 1.

[0205] (4) The same as in Example 1.

[0206] (5) Calcinate the filter cake at high temperature for dehydration, control the heating rate at 2 °C / min, the calcination temperature at 850 °C, and the calcination time at 5 h to obtain an anhydrous iron phosphate precursor DP1. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.958 [Fe4(P2O7)3] 0.007 , where x = 0.007 and y = 0.01.

[0207] Comparative Example 2

[0208] (1) The same as in Example 1.

[0209] (2) The same as in Example 1.

[0210] (3) is the same as Example 1.

[0211] (4) After the reaction is completed, the reaction slurry is filtered and washed to obtain a filter cake. The filter cake is slurried, and the resulting slurry is added to a reaction kettle. Lignocellulose is added, and phosphoric acid is added to adjust the pH to 1.5. The heating rate is controlled at 0.5 °C / min, the aging temperature is 95 °C, and the aging time is 4 h. After the reaction is completed, the reaction slurry is filtered and washed to obtain a filter cake.

[0212] (5) is the same as Example 1 to obtain the anhydrous iron 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.

[0213] Comparative Example 3

[0214] (1) is the same as Example 1.

[0215] (2) Weigh a certain mass of concentrated phosphoric acid, add sodium hydroxide with a concentration of 30% to adjust the pH of the solution to 3, and prepare a 2 mol / L phosphorus source solution.

[0216] (3) is the same as Example 1.

[0217] (4) is the same as Example 1.

[0218] (5) The filter cake is calcined at high temperature for dehydration, the heating rate is controlled at 3 °C / min, the calcination temperature is 700 °C, and the calcination time is 3 h to obtain the anhydrous iron phosphate precursor DP3. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.952 [Fe4(P2O7)3] 0.008 , where x = 0.008 and y = 0.01.

[0219] The physical and chemical indexes of the iron phosphate precursors prepared in the above examples and comparative examples are shown in Table 1

[0220] Table 1

[0221]

[0222]

[0223] Preparation Example of Cathode Material

[0224] (1) The iron phosphate precursor, lithium carbonate, glucose, and cobalt oxide prepared in the examples and comparative examples were mixed with pure water at a molar ratio of n(precursor):n(Li):n(carbon source):n(M') = 1:1.04:0.068:0.02, and mechanically stirred to mix evenly to obtain a slurry.

[0225] (2) The slurry was evaporated to dryness in a heating furnace tray, and then dried in a vacuum oven at 85 °C for 4 h to obtain a dry material; the dry material was calcined at 770 °C for 9 h in a nitrogen atmosphere, and after screening, a lithium iron phosphate cathode material was obtained.

[0226] The physical and chemical indexes of the lithium iron phosphate cathode material obtained in the above cathode material preparation examples, the composition of the iron phosphate precursor and the lithium iron phosphate cathode material are shown in Table 2.

[0227] Figure 3 is the XRD pattern of the lithium iron phosphate cathode material prepared from the iron phosphate precursor P1. Figure 3 It can be seen that the XRD spectrum of this lithium iron phosphate cathode material corresponds to the lithium iron phosphate standard card, indicating that this cathode material is lithium iron phosphate.

[0228] Figure 4 is the SEM image of the lithium iron phosphate cathode material prepared from the iron phosphate precursor P1. Figure 4 It can be seen that the particle density of this lithium iron phosphate cathode material is good and the surface carbon coating is uniform.

[0229] Table 2

[0230]

[0231]

[0232] Continued Table 2

[0233] <![CDATA[D 50 1 > PD Carbon content BET Volume resistivity Unit μm <![CDATA[g / cm 3 > ％ <![CDATA[m 2 / g]]> Ω·cm Example 1 1.26 2.60 1.21 12.1 25 Example 2 1.28 2.61 1.23 12 23 Example 3 1.31 2.62 1.19 11.9 24 Example 4 1.30 2.61 1.18 11.8 19 Example 5 1.29 2.61 1.19 12.1 20 Example 6 1.32 2.62 1.18 12.2 21 Example 7 1.27 2.60 1.19 11.7 18 Example 8 1.28 2.58 1.19 11.9 22 Comparative Example 1 1.30 2.42 1.20 11.5 131 Comparative Example 2 1.30 2.43 1.20 11.6 129 Comparative Example 3 1.30 2.40 1.21 11.3 155

[0234] 1 refers to the average particle size of the primary particles.

[0235] Test Example

[0236] This test example is used to illustrate the electrode material, electrode, lithium ion battery and their preparation methods.

[0237] (1) Preparation of the positive electrode sheet: The lithium iron phosphate positive electrode materials, conductive agent carbon nanotubes, and NMP solution of binder PVDF prepared in the above-mentioned examples and comparative examples were mixed at a mass ratio of 90:5:5. The specific method is as follows: The dried positive electrode material and conductive agent were ground in a mortar for 15 minutes. After grinding evenly, the PVDF solution (mass fraction 5%) was added according to the ratio, and stirred on a magnetic stirrer for 6 hours; the obtained paste-like slurry was evenly coated on the current collector aluminum foil, and then dried in a vacuum drying oven at 60°C for 20 hours, and then stamped into a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm under a pressure of 100 MPa. The positive electrode sheet was placed in a vacuum drying oven at 120°C and dried for 12 h.

[0238] (2) Battery assembly: A metal lithium sheet with a diameter of 17 mm and a thickness of 1 mm was used as the negative electrode, a polyethylene porous membrane with an alumina ceramic layer coated on the surface and a thickness of 25 μm was used as the separator, and an equal-volume mixture of 1 mol / L LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC) was selected as the electrolyte. The positive electrode sheet, separator, negative electrode sheet, and electrolyte were assembled into a 2025-type button battery in an Ar gas glove box with a water content and oxygen content both less than 5 ppm.

[0239] (3) Electrochemical performance test: The battery was subjected to charge and discharge tests using a LANDCT2001A charge and discharge tester from Wuhan Lanbo Electronics Co., Ltd. The charge and discharge voltage range was 2.5 to 3.75 V. The specific capacity of the assembled lithium-ion battery was tested at rates of 0.1C, 0.5C, and 1C, and the cycle performance was tested at a rate of 1C. The test results are shown in Table 3.

[0240] Table 3

[0241]

[0242] It can be seen from the results of Table 2 and Table 3 that the lithium iron phosphate positive electrode material prepared using the iron phosphate precursor of the present invention has a high tap density. When it is used in a lithium-ion battery, it can significantly improve the discharge capacity and cycle stability of the lithium-ion battery.

[0243] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A ferric phosphate precursor, characterized in that, The iron phosphate precursor has diffraction characteristic peaks at 2θ a1 = 16.2 - 16.9°, 2θ a2 = 27.3 - 28.1°, 2θ a3 = 29 - 29.7° and 2θ a4 = 30.2 - 30.9° as determined by XRD test; the iron phosphate precursor has diffraction characteristic peaks at 2θ b1 = 20 - 20.7°, 2θ b2 = 21.5 - 22.2°, 2θ b3 = 23.4 - 24°, 2θ b4 = 25.5 - 26.2° as determined by XRD test; The integrated area A(2θ ai ) of the diffraction characteristic peak at 2θ ai and the integrated area A(2θ bj ) of the diffraction characteristic peak at 2θ bj satisfy the following: = 1% - 3%, where i is an integer from 1 to 4 and j is an integer from 1 to 4; The integrated area A(2θ ai ) of the diffraction characteristic peak at 2θ of the iron phosphate precursor refers to the total integrated area of the diffraction characteristic peaks at 2θ ai , 2θ a1 , 2θ a2 , 2θ a3 and 2θ a4 ; the integrated area A(2θ bj ) of the diffraction characteristic peak at 2θ of the iron phosphate precursor refers to the total integrated area of the diffraction characteristic peaks at 2θ bj , 2θ b1 , 2θ b2 , 2θ b3 and 2θ b4 . The iron phosphate precursor has a composition as shown in Formula I: (Fe 1-y M y PO4) 1-6x [Fe4(P2O7)3] x Formula I, wherein, 0.01 ≤ x ≤ 0.03, 0 < y ≤ 0.1, M is selected from at least one of Mn, Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti; The method for preparing the iron phosphate precursor comprises the following steps: (1) Dissolve an iron source and an M source in water to form a mixed salt solution A1; (2) Dissolve a phosphorus source in water, add a pH regulator to form a phosphorus source solution A2; (3) Mix the mixed salt solution A1, the phosphorus source solution A2 and an oxidant A3, carry out a synthesis reaction, and optionally add an auxiliary agent; (4) Filter and wash the product of step (3) to obtain a filter cake B1, pulp the filter cake, and after obtaining a slurry, optionally add an auxiliary agent, adjust the pH value, carry out an aging and crystal transformation reaction, and then carry out filtration and washing to obtain a filter cake B2; (5) Calcinate the filter 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 and crystal transformation reaction include: the reaction temperature is 70 - 90 °C, the heating rate is 1 - 3 °C / min, and the reaction time is 1 - 3 h; The conditions of the calcination include: the calcination temperature is 500 - 800 °C, the heating rate is 3 - 8 °C / min, and the calcination time is 2 - 4 h; The auxiliary agent is selected from at least one of sodium hexadecyl benzene sulfonate, sodium dodecyl benzene sulfonate, triethanolamine, ethylene glycol, polyvinylpyrrolidone, polyethylene glycol, wood cellulose and carboxymethyl cellulose.

2. The ferric phosphate precursor according to claim 1, wherein, =1%-2%。 3. The ferric phosphate precursor according to claim 1 or 2, wherein, The lattice parameters of the a-axis and c-axis of the iron phosphate precursor measured by XRD satisfy: 2.2306≤ c / a ≤2.2330。 4. The ferric phosphate precursor according to claim 3, wherein, The lattice parameters of the a-axis and c-axis of the iron phosphate precursor measured by XRD satisfy: 2.231≤ c / a ≤2.2326。 5. The ferric phosphate precursor according to claim 1 or 2, wherein, In the iron phosphate precursor, the molar ratio n(Me) / n(P) of the metal element to the phosphorus element is 0.960 - 0.

980.

6. The ferric phosphate precursor according to claim 5, wherein, In the iron phosphate precursor, the molar ratio n(Me) / n(P) of the metal element to the phosphorus element is 0.960 - 0.

970.

7. The ferric phosphate precursor according to claim 1 or 2, wherein, The median particle size D of the iron phosphate precursor 50 is 1 - 25 μm; And / or, the primary particle size of the iron phosphate precursor is 20 - 200 nm; And / or, the tap density of the iron phosphate precursor is 0.8 - 1.3 g / cm 3 ; and / or, the specific surface area of the iron phosphate precursor is 6-10 m 2 / g; And / or, the sulfur content in the iron phosphate precursor is ≤ 400 ppm.

8. The ferric phosphate precursor according to claim 7, wherein, The median particle size D of the iron phosphate precursor 50 is 2 - 20 μm; And / or, the primary particle size of the iron phosphate precursor is 50 - 150 nm; And / or, the tap density of the iron phosphate precursor is 0.9-1.2 g / cm 3 ; and / or, the specific surface area of the iron phosphate precursor is 6.5-9.5 m 2 / g; And / or, the sulfur content in the iron phosphate precursor is ≤ 200 ppm.

9. A method for preparing a lithium iron phosphate precursor according to any one of claims 1 - 8, characterized in that, The preparation method comprises the following steps: (1) Dissolve an iron source and an M source in water to form a mixed salt solution A1; (2) Dissolve a phosphorus source in water, add a pH regulator to form a phosphorus source solution A2; (3) Mix the mixed salt solution A1, the phosphorus source solution A2 and an oxidant A3, carry out a synthesis reaction, and optionally add an auxiliary agent; (4) Filter and wash the product of step (3) to obtain a filter cake B1, pulp the filter cake, and after obtaining a slurry, optionally add an auxiliary agent, adjust the pH value, carry out an aging and crystal transformation reaction, and then carry out filtration and washing to obtain a filter cake B2; (5) Calcinate the filter 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 and crystal transformation reaction include: the reaction temperature is 70 - 90 °C, the heating rate is 1 - 3 °C / min, and the reaction time is 1 - 3 h; The calcination conditions include: a calcination temperature of 500 - 800 °C, a heating rate of 3 - 8 °C / min, and a calcination time of 2 - 4 h; The M source is a compound capable of providing M element selected from at least one of Mn, Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti; The auxiliary agent is selected from at least one of sodium hexadecylbenzenesulfonate, sodium dodecylbenzenesulfonate, triethanolamine, ethylene glycol, polyvinylpyrrolidone, polyethylene glycol, wood cellulose, and carboxymethyl cellulose.

10. According to the preparation method described in claim 9, wherein, The pH value of the phosphorus source solution A2 is 1 - 2; And / or, the conditions of the aging and crystal conversion reaction include: a reaction temperature of 80 - 85 °C, a heating rate of 2 - 3 °C / min, and a reaction time of 1 - 2 h; And / or, the calcination conditions include: a calcination temperature of 600 - 750 °C, a heating rate of 3 - 5 °C / min, and a calcination time of 2 - 3 h; And / or, in step (4), the pH value is adjusted to 1 - 2.

5.

11. According to the preparation method described in claim 10, wherein, In step (4), the pH value is adjusted to 1 - 2.

12. According to the preparation method described in claim 9 or 10, wherein, In step (1), the concentration of the mixed salt solution A1 is 0.1 - 4 mol / L; And / or, in step (1), the iron source and the M source satisfy 0 < n(M) / [n(Fe)+n(M)] ≤ 0.1; And / or, in step (2), the concentration of the phosphorus source solution A2 is 0.2 - 20 mol / L; And / or, in step (3), the dosage of the mixed salt solution A1 and the dosage of the phosphorus source solution A2 satisfy n(P):n(Fe) = 1 - 3:1; And / or, in step (3), the dosage of the mixed salt solution A1 and the dosage of the oxidant A3 satisfy n(oxidant):n(Fe) = 1 - 5:1; And / or, the synthesis reaction conditions include: a reaction temperature of 25 - 60 °C and a reaction time of 1 - 6 h.

13. According to the preparation method described in claim 9 or 10, wherein, 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%.

14. According to the preparation method described in claim 13, wherein, Based on the total dosage of the iron source and the M source, the dosage of the auxiliary agent is 0.1 wt% - 0.5 wt%.

15. Application of the lithium iron phosphate precursor according to any one of claims 1 - 8 in the preparation of a lithium iron phosphate cathode material.

16. A lithium iron phosphate cathode material, characterized in that, The lithium iron phosphate cathode is prepared from the iron phosphate precursor as described in any one of claims 1 - 8.

17. According to the lithium iron phosphate cathode material described in claim 16, wherein, The lithium iron phosphate cathode material includes a matrix and a carbon coating layer coated on the surface of the matrix; wherein, the matrix has the composition shown in formula II: Li 1+a [(Fe 1-y M y ) 1-b M’ b PO4 type II; where, -0.1 ≤ a ≤ 0.1, 0 ≤ b < 1, 0 < y ≤ 0.1; Wherein, M is selected from at least one of Mn, Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti, and M' is selected from at least one of La, Ce, Cr, Mo, Ca, Hf, Ti, Mn, Fe, Zn, Y, Zr, W, Nb, Sm, Co, Ni, V, Mg, Na, B, and Al.

18. The lithium iron phosphate cathode material according to claim 16 or 17, wherein, M' is selected from at least one of Al, Zr, W, Fe, Mn, Co, V, and Ti.

19. The lithium iron phosphate cathode material according to claim 17, wherein, Based on the total weight of the cathode material, the content of the carbon coating layer is 0.5 - 2 wt%.

20. The lithium iron phosphate cathode material according to claim 19, wherein, Based on the total weight of the cathode material, the content of the carbon coating layer is 1 - 1.5 wt%.

21. The lithium iron phosphate cathode material according to claim 16 or 17, wherein, The lithium iron phosphate cathode material has a secondary particle structure formed by primary particles; and / or, the median particle size D of the primary particles of the positive electrode material 50 is 200 - 2500 nm; And / or, the tap density of the lithium iron phosphate cathode material is 2.50 - 2.7 g / cm 3 ; and / or, the specific surface area of the lithium iron phosphate cathode material is 8-18m 2 / g; And / or, the volume resistivity of the lithium iron phosphate cathode material is 1-100 Ω·cm.

22. The lithium iron phosphate cathode material according to claim 21, wherein, The lithium iron phosphate cathode material has a secondary particle structure formed by primary particles; and / or, the median particle size D of the primary particles of the positive electrode material 50 is 500 - 2000 nm; And / or, the tap density of the lithium iron phosphate cathode material is 2.55-2.65 g / cm 3 ; and / or, the specific surface area of the lithium iron phosphate cathode material is 10-13m 2 / g; And / or, the volume resistivity of the lithium iron phosphate cathode material is 10-50 Ω·cm.

23. A lithium ion battery, characterized in that, The lithium ion battery includes the lithium iron phosphate cathode material according to any one of claims 16-22.

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