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

Abstract

The present invention relates to the field of preparation technologies of lithium-ion cathode materials, and discloses a lithium manganese iron phosphate cathode material, a preparation method thereof, a manganese iron phosphate precursor and a preparation method thereof, and a lithium-ion battery. The cathode material has a structure represented by Formula I, Li d Mn 1-a-b-c Fe a R b PO4 / C Formula I where 0.1 ≦ a ≦ 0.5, 0 ≦ b ≦ 0.08, 0.9 < d ≦ 1.2, R is selected from at least one of Al, Mg, Ca, Sr, V, Cr, Y, Mo, Nb, B, Al, W, La, Sm, Co, Ni, Cu, Zn, Zr and Ti, and the volume resistivity of the cathode material is 10~10 4 Ω·cm. The cathode material contains specific doping elements and has a low volume resistivity, which can effectively improve the electrochemical performance of the lithium-ion battery when it is used in the preparation of the lithium-ion battery.

Description

[Technical Field]

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

[0002] Lithium-ion batteries are an important power supply system and are widely used in 3C products such as computers, communication tools, and electronic tools, electric vehicles such as EVs and PHEVs, and energy storage systems. As a cathode material for lithium-ion batteries, lithium iron phosphate boasts excellent safety, stability, and low cost, resulting in a growing market share. However, lithium iron phosphate has drawbacks such as poor electronic conductivity, a small lithium ion diffusion coefficient, and low energy density, limiting its further development and use in electric vehicles. Lithium manganese iron phosphate is an upgraded version of lithium iron phosphate, and has the same specific capacity (theoretical capacity 170 mAh / g). However, the addition of manganese results in a higher redox potential, thereby improving the material's energy density.

[0003] Currently, the synthesis methods for lithium manganese iron phosphate mainly include high-temperature solid-state method, hydrothermal method, and co-precipitation method. The high-temperature solid-state method has a simple process flow and is suitable for industrial production, but it is difficult to achieve uniform mixing of the manganese iron atomic levels, resulting in poor conformity and uneven particle morphology, which affects the compaction density and discharge capacity. The main advantages of the co-precipitation method are uniform particle structure, easy to adjust and control the dimensional structure, simple operation, and industrial production. The preparation of manganese iron phosphate precursors is the key to synthesizing high-performance materials.

[0004] Currently, research on manganese iron phosphate precursors has been relatively extensive, and CN114057177A discloses manganese iron phosphate and a preparation method thereof, which includes dissolving a divalent manganese salt and a divalent iron salt in water to obtain a mixed salt solution of manganese salt and iron salt, adding a phosphorus source to the mixed salt solution to obtain a precursor solution, adding an alkali co-precipitation to the precursor solution to obtain an iron (I) manganese phosphate slurry containing an iron (I) phosphate precipitate and an iron (I) manganese phosphate precipitate, and washing the iron (I) manganese phosphate slurry with water, filtering, and drying to obtain iron (I) manganese phosphate. Samples prepared by this method exhibit phase separation between iron (I) phosphate and manganese phosphate, resulting in heterogeneous structures and large variations in the metal-to-phosphorus ratio. Therefore, a phosphorus source must be added during the preparation of the positive electrode material, making it difficult to control the metal-to-phosphorus ratio, and limiting the performance of the positive electrode material.

[0005] CN107697899A discloses a method for preparing manganese iron phosphate, which involves first precipitating manganese iron under basic conditions, adding an oxidizing agent to oxidize the manganese iron to manganese iron(III), and then adding a phosphorus source to convert it to phosphate. The preparation process is complicated, with many phase transitions, prone to defects, and difficulty in controlling the particle size and morphology of the precursor. 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 and provides a lithium manganese iron phosphate cathode material and a preparation method thereof, a manganese iron phosphate precursor and a preparation method thereof, and a lithium ion battery. The lithium manganese iron phosphate cathode material contains specific doping elements, has high purity, and the cathode material has low volume resistivity. When used in the preparation of a lithium ion battery, it effectively improves the electrochemical performance of the lithium ion battery, specifically, the lithium ion battery has high specific capacity, high cycle performance, and high energy density. [Means for solving the problem]

[0007] To achieve the above object, a first aspect of the present invention provides a lithium manganese iron phosphate cathode material, the cathode material having a structure represented by Formula I, L id Mn 1-a-b-c Fe a R b PO4 / C Formula I where 0.1 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.08, 0.9 < d ≤ 1.2, and R is selected from at least one of Al, Mg, Ca, Sr, V, Cr, Y, Mo, Nb, B, Al, W, La, Sm, Co, Ni, Cu, Zn, Zr, and Ti, the volume resistivity of the cathode material is 10 to 10 4 Ω·cm, the relationship between the actual molar content ratio m'' of Mn element and Fe element at any position in the cathode material and the theoretical molar content ratio m of Mn element and Fe element at any position in the cathode material is Δm c = |m'' - m| / m ≤ 5%.

[0008] A second aspect of the present invention provides a method for preparing a lithium manganese iron phosphate cathode material, the preparation method comprising: Step S1 of mixing a manganese source, an iron source, a R1 source, and water to obtain a mixed salt solution; Step S2 of mixing a phosphorus source and water, adding a pH adjuster, and obtaining a phosphorus source solution; Step S3 of adding the mixed salt solution, the phosphorus source solution, and an oxidant to a reaction kettle in parallel flow, performing a coprecipitation reaction, filtering, washing, and drying to obtain the manganese iron phosphate precursor; Step S4 of mixing the manganese iron phosphate precursor, a lithium source, a carbon source, and a R2 source to obtain a mixture; Step S5 of firing the mixture in the presence of a protective atmosphere to obtain the lithium manganese iron phosphate cathode material.

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

[0010] A fourth aspect of the present invention provides a manganese iron phosphate precursor material having the structure shown in Formula II: Mn 1-x-y Fe x R1 y P z O4·nH2O formula II, Here, 0.1≦x≦0.5, 0≦y≦0.04, 0.95≦z≦1.10, 0.95≦n≦1.5, and R1 is selected from at least one of Al, Mg, Ca, Sr, V, Cr, Y, Mo, Nb, B, Al, W, La, Sm, Co, Ni, Cu, Zn, Zr, and Ti.

[0011] A fifth aspect of the present invention provides a method for preparing an iron manganese phosphate precursor, said method comprising: Step (1) of mixing a manganese source, an iron source, an R1 source and water to obtain a mixed salt solution; Step (2) of mixing a phosphorus source with water and adding a pH adjuster to obtain a phosphorus source solution; and (3) adding the mixed salt solution, the phosphorus source solution, and the oxidant into a reaction vessel in parallel flow to carry out a co-precipitation reaction, followed by filtering, washing, and drying to obtain the iron manganese phosphate precursor.

[0012] A sixth aspect of the present invention provides an iron manganese phosphate precursor produced by the above preparation method.

[0013] A seventh aspect of the present invention provides a lithium-ion battery comprising the above lithium iron manganese phosphate positive electrode material or a positive electrode material produced from the above iron manganese phosphate precursor.

[0014] According to the above technical solutions, the lithium manganese iron phosphate positive electrode material and its preparation method, the iron manganese phosphate precursor and its preparation method, and the lithium ion battery according to the present invention achieve the following beneficial effects:

[0015] 1. The lithium manganese iron phosphate cathode material of the present invention contains specific doping elements, and the cathode material has low volume resistivity and high purity, effectively preventing the formation of heterophases. When used in the preparation of lithium ion batteries, it can effectively improve the electrochemical performance of the lithium ion batteries, specifically, the lithium ion batteries have high specific capacity, high cycle performance and high energy density.

[0016] Furthermore, the manganese iron element in the lithium manganese iron phosphate positive electrode material of the present invention is uniformly distributed, and the primary particles are small, the carbon coating is uniform, and the compaction density is high, which further improves the electrochemical performance of lithium ion batteries.

[0017] 2. The method for preparing the lithium manganese iron phosphate positive electrode material according to the present invention is obtained by mixing a precursor with a specific composition, a lithium source, a carbon source, and an R2 source, followed by calcination, wherein the precursor contains a specific doping element R1, which enters the metal site to form nanoparticles with a stable structure, and the obtained lithium manganese iron phosphate positive electrode material has high purity and low volume resistivity.

[0018] Furthermore, in the present invention, a manganese source, an iron source, an R1 source, a phosphorus source, and an oxidizing agent are used as raw materials. Specifically, a mixed salt solution containing a manganese source, an iron source, and an R1 source, a phosphorus source solution, and an oxidizing agent are added to a reactor in parallel flow. After the metal ions react with the oxidizing agent and are oxidized, they rapidly combine with the phosphate groups to form precipitates. This effectively avoids the disproportionation reaction of trivalent manganese ions in the aqueous solution and achieves precipitation while oxidizing. Furthermore, the parallel flow of the liquid prevents the sequential precipitation of manganese iron due to an excessively high ion concentration in the solution, which would cause metal segregation, thereby achieving uniform coprecipitation of manganese iron. The resulting manganese iron phosphate precursor has a stable metal stoichiometry, a controllable molar ratio of phosphorus to metal (P / Me), small primary particles, uniform secondary particles, a controllable morphology, a stable structure, a simple synthesis process, environmental friendliness, and pollution-free properties, making it suitable for industrial production.

[0019] Furthermore, by controlling the molar ratio K1 of the phosphorus source and metal (manganese source, iron source, and R1 source) added, the pH of the phosphorus source solution, and the reaction temperature T to satisfy a specific relationship, the molar ratio K of phosphorus to metal in the manganese iron phosphate precursor can be adjusted and controlled, and the performance of the lithium manganese iron phosphate positive electrode material can be adjusted and controlled. The resulting lithium manganese iron phosphate positive electrode material has excellent electrochemical performance.

[0020] The method for preparing lithium manganese iron phosphate positive electrode material according to the present invention 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 applied in the industrial production of lithium manganese iron phosphate positive electrode material. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is an XRD diagram of the iron manganese phosphate precursor prepared in Example 1 of the present invention. [Figure 2] FIG. 1 is an SEM image of the iron manganese phosphate precursor prepared in Example 1 of the present invention. [Figure 3] FIG. 1 is an EDS distribution map of Mn and Fe elements in the cross section of the iron manganese phosphate precursor prepared in Example 1 of the present invention. [Figure 4] FIG. 1 is an XRD diagram of the lithium iron manganese phosphate positive electrode material prepared in Example 1 of the present invention. [Figure 5] FIG. 1 is an SEM image of the lithium iron manganese phosphate positive electrode material prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The endpoints of ranges and any value disclosed herein should be understood to be not limited to such exact ranges or values, but to include values ​​close to those ranges or values. In the case of ranges of numerical values, values ​​between the endpoints of each range, between the endpoints of each range and any single point value, and between any single point value can be combined with each other to create one or more new numerical ranges, and these numerical ranges are considered to be specifically disclosed in the specification.

[0023] The first aspect of the present invention provides a lithium manganese iron phosphate cathode material, and the cathode material has a structure represented by Formula I, Li d Mn 1-a-b-c Fe a R b PO4 / C Formula I where 0.1 ≦ a ≦ 0.5, 0 ≦ b ≦ 0.08, 0.9 < d ≦ 1.2, and R is selected from at least one of Al, Mg, Ca, Sr, V, Cr, Y, Mo, Nb, B, Al, W, La, Sm, Co, Ni, Cu, Zn, Zr, and Ti, The volume resistivity of the cathode material is 10~10 4 Ω·cm, The relationship between the actual molar content ratio m'' of Mn element and Fe element at any position in the cathode material and the theoretical molar content ratio m of Mn element and Fe element at any position in the cathode material is Δm c =|m'' - m| / m ≦ 5% is satisfied.

[0024] In the present invention, the lithium manganese iron phosphate cathode material contains a specific doping element, and the cathode material has a low volume resistivity and high purity. The distribution of manganese and iron elements in the lithium manganese iron phosphate cathode material is uniform, effectively avoiding the formation of hetero phases. Specifically, the difference between the ratio of the actual content and the theoretical content of metal Mn element and Fe element at any position is small. The manganese and iron elements in the lithium manganese iron phosphate cathode material are uniformly distributed without segregation. When it is used in the preparation of a lithium-ion battery, the electrochemical performance of the lithium-ion battery is effectively improved. Specifically, the lithium-ion battery has a high specific capacity, high cycle performance, and high energy density.

[0025] In the present invention, the actual content of Mn element and Fe element at any position in the cathode material is m'' measured by the EDS method.

[0026] In the present invention, the molar content ratio m of Mn element to Fe element at any position in the positive electrode material is set as m = (1 - a - b - c) / a.

[0027] In the present invention, the actual content of Mn element and Fe element ratio When testing m'', the area of the selected position accounts for 1 - 30% of the area of the selected positive electrode material particles. In the present invention, the actual content of Mn element and Fe element ratio When the area of the position selected when testing m'' satisfies the above range, while ensuring the feasibility of the test, the averaging effect can be effectively avoided, thereby better representing the uniformity of the distribution of Mn element and Fe element.

[0028] Furthermore, in formula I, 0.15 ≤ a ≤ 0.45, 0 < b≦0.06 , 0.95 < d ≤ 1.15.

[0029] Furthermore, in formula I, R is selected from at least one of Al, Co, Ni, Mg, Al, W, Nb, Zr, and Ti.

[0030] In a specific embodiment of the present invention, the lithium manganese iron phosphate positive electrode material contains two or more different types of elements R. Specifically, the lithium manganese iron phosphate positive electrode material has a structure represented by formula II, Li d Mn 1-a-b-c Fe a R’ b R’’ c PO4 / C Formula II Here, 0.1 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.04, 0 ≤ c ≤ 0.04, 0.9 < d ≤ 1.2, R’ is selected from at least one of Al, Cu, Zn, Zr, and Ti, and R’’ is selected from at least one of Mg, Ca, Sr, V, Cr, Co, Ni, Y, Mo, Nb, B, W, La, and Sm.

[0031] In one specific embodiment of the present invention, in Formula II, 0.15≦a≦0.45, 0 <b≦0.03、0<c≦0.03、0.95<d≦1.15とする。

[0032] In one specific embodiment of the present invention, in Formula II, R' is selected from at least one of Al, Zr, and Ti, and R'' is selected from at least one of Co, Ni, Mg, Y, La, W, and Nb.

[0033] Furthermore, the volume resistivity of the positive electrode material is 10 to 10 3 Ω·cm.

[0034] Furthermore, the volume resistivity of the positive electrode material is 10 to 500 Ω·cm.

[0035] According to the present invention, the carbon content is 0.5 to 5 wt % based on the total weight of the lithium iron manganese phosphate positive electrode material.

[0036] In the present invention, when the carbon content in the lithium manganese iron phosphate positive electrode material satisfies the above range, the positive electrode material has good electronic conductivity, and further improves the specific capacity, cycle performance and power supply performance of the lithium ion battery manufactured using the positive electrode material.

[0037] Furthermore, the carbon content is 1 to 3 wt % based on the total weight of the lithium iron manganese phosphate positive electrode material.

[0038] Furthermore, Δm c =|m''-m| / m≦3%.

[0039] According to the present invention, the compaction density of the positive electrode material is 1.5 to 3.5 g / cm 3 , preferably 2 to 3 g / cm 3 is.

[0040] According to the present invention, the specific surface area of ​​the positive electrode material is 10 to 60 m 2 / g, preferably 10 to 25 m 2 / g.

[0041] According to the present invention, the lithium iron manganese phosphate positive electrode material has a secondary particle structure formed by primary particles.

[0042] According to the present invention, the average particle size of the positive electrode material is 1 to 50 μm, preferably 7 to 15 μm.

[0043] According to the present invention, the average particle size of the primary particles is 10 to 500 nm.

[0044] In the present invention, the positive electrode material is small primary particles diameter This shortens the diffusion path of lithium ions and improves the ionic conductivity of the positive electrode material, so that when it is used in a lithium ion battery, it effectively improves the electrochemical performance of the lithium ion battery.

[0045] Furthermore, the average particle size of the primary particles is 10 to 200 nm.

[0046] A second aspect of the present invention provides a method for preparing a lithium iron manganese phosphate cathode material, said method comprising: Step S1 of mixing a manganese source, an iron source, an R1 source and water to obtain a mixed salt solution; Step S2: mixing a phosphorus source with water and adding a pH adjuster to obtain a phosphorus source solution; Step S3: adding the mixed salt solution, the phosphorus source solution, and the oxidant into a reaction vessel in parallel flow to carry out a coprecipitation reaction, and then filtering, washing, and drying to obtain the manganese iron phosphate precursor; Step S4: mixing the iron manganese phosphate precursor, a lithium source, a carbon source, and an R2 source to obtain a mixture; and step S5 of calcining the mixture in the presence of a protective atmosphere to obtain the lithium iron manganese phosphate positive electrode material.

[0047] In the present invention, R1 and R2 are used to distinguish the timing of adding the R source, and do not limit the type of element in the R source. Both the R1 source and the R2 source are used to introduce the R source into the positive electrode material.

[0048] In the present invention, a precursor with a specific composition is mixed with a lithium source, a carbon source, and an R2 source, and then calcined to prepare the material, wherein the precursor contains a specific doping element R1, which enters the metal site to form nanoparticles with a stable structure. The resulting positive electrode material for lithium manganese iron phosphate has high purity and low volume resistivity. When the resulting positive electrode material for lithium manganese iron phosphate is used in a lithium ion battery, it can effectively improve the electrochemical performance of the lithium ion battery, specifically, the lithium ion battery has high specific capacity, high cycle performance, and high energy density.

[0049] In the present invention, a manganese source, an iron source, an R1 source, a phosphorus source, and an oxidizing agent are used as raw materials. Specifically, a mixed salt solution containing a manganese source, an iron source, and an R1 source, a phosphorus source solution, and an oxidizing agent are added to a reactor in parallel flow. After the metal ions react with the oxidizing agent and are oxidized, they rapidly combine with the phosphate groups to form precipitates. This effectively avoids the disproportionation reaction of trivalent manganese ions in the aqueous solution and achieves precipitation while oxidation. Furthermore, the parallel liquid transport avoids the sequential precipitation of manganese iron due to an excessively high ion concentration in the solution, which would cause metal segregation, thereby achieving uniform coprecipitation of manganese iron. The resulting manganese iron phosphate precursor has a stable metal stoichiometry, a controllable molar ratio of phosphorus to metal (P / Me), small primary particles, uniform secondary particles, a controllable morphology, a stable structure, a simple synthesis process, environmental friendliness, and pollution-free properties, making it suitable for industrial production.

[0050] According to the present invention, the iron manganese phosphate precursor has the structure shown in Formula II: Mn 1-x-y Fe x R1 y P z O4·nH2O Formula II Here, 0.1≦x≦0.5, 0≦y≦0.04, 0.95≦z≦1.10, 0.95≦n≦1.5, and R1 is selected from at least one of Al, Mg, Ca, Sr, V, Cr, Y, Mo, Nb, B, Al, W, La, Sm, Co, Ni, Cu, Zn, Zr, and Ti.

[0051] Furthermore, in Formula II, 0.15 ≦ x ≦ 0.45, 0 < y ≦ 0.03, 0.95 ≦ z ≦ 1.05, 0.95 ≦ n ≦ 1.2, and R1 is selected from at least one of Al, Co, Ni, Mg, Al, W, Nb, Zr, and Ti.

[0052] According to the present invention, the lithium manganese iron phosphate cathode material has the configuration described in Formula I, LidMn1-a-b-cFeaRb PO 4 / C Formula I where 0.1 ≦ a ≦ 0.5, 0 ≦ b ≦ 0.08, 0.9 < d ≦ 1.2, and R is selected from at least one of Al, Mg, Ca, Sr, V, Cr, Y, Mo, Nb, B, Al, W, La, Sm, Co, Ni, Cu, Zn, Zr, and Ti.

[0053] Furthermore, in Formula I, 0.15 ≦ a ≦ 0.45, 0 < b ≦ 0.06, 0.95 < d ≦ 1.15.

[0054] Furthermore, in Formula I, R is selected from at least one of Al, Co, Ni, Mg, Al, W, Nb, Zr, and Ti.

[0055] According to the present invention, the relationship between the actual molar content ratio m' of Mn element and Fe element at any position in the manganese iron phosphate precursor and the theoretical molar content ratio m0 of Mn element and Fe element at any position in the lithium manganese iron phosphate precursor is Δm p = |m' - m0| / m0 ≦ 5%.

[0056] In the present invention, the manganese iron element is distributed uniformly in the manganese iron phosphate precursor, and in particular, the difference between the actual content ratio of metallic Mn and Fe at any position and the theoretical content ratio is small, indicating that the manganese iron element is distributed uniformly in the manganese iron phosphate precursor and is free from segregation. When the precursor is used to prepare a positive electrode material, the manganese iron phosphorus element is distributed uniformly in the positive electrode material, and segregation of elements in the positive electrode material is avoided. As a result, the capacity performance and cycle performance of a lithium-ion battery containing the lithium manganese iron phosphate positive electrode material are significantly improved.

[0057] In the present invention, the theoretical molar content ratio of Mn element to Fe element at any position in the lithium manganese iron phosphate precursor is m0=(1-xy) / x.

[0058] In the present invention, the actual content of Mn element and Fe element at any position in the precursor is m' measured by EDS method.

[0059] In the present invention, when testing the actual content m' of Mn and Fe elements, the area of ​​the selected position occupies 1-30% of the area of ​​the selected precursor particle. ratio If the area of ​​the selected position when testing m'' satisfies the above range, the feasibility of the test can be ensured while effectively avoiding the averaging effect, thereby better representing the uniformity of the distribution of Mn and Fe elements.

[0060] Furthermore, Δm p =|m'-m0| / m0≦3%.

[0061] According to the present invention, the median diameter D of the iron manganese phosphate precursor 50 is 0.5 to 10 μm, preferably 0.5 to 5 μm.

[0062] According to the present invention, the primary particle size of the iron manganese phosphate precursor is 20 to 200 nm, preferably 20 to 100 nm.

[0063] According to the present invention, the tap density of the iron manganese phosphate precursor is 0.50 to 1.50 g / cm 3 , preferably 0.80 to 1.50 g / cm 3 is.

[0064] According to the present invention, the specific surface area of ​​the iron manganese phosphate precursor is 10 to 100 m 2 / g, preferably 10 to 40m 2 / g.

[0065] In the present invention, the ratio K of the phosphorus content to the total molar amount of metals in the iron manganese phosphate precursor is set to 0.95 to 1.10, that is, the z value in formula II.

[0066] According to the present invention, the method for preparing the iron manganese phosphate precursor satisfies the following relationship: K = (0.033K1 + 0.5) L -0.3 T 0.2 -0.05 Formula III Here, K is the ratio of n(P) to [n(Mn) + n(Fe) + n(R1)] in the manganese iron phosphate precursor, K1 is the molar ratio of the amount of the phosphorus source added in terms of n1(P) to the total amount of the manganese source, the iron source, and the R1 source added in terms of [n1(Mn) + n1(Fe) + n1(R1)], L is the pH value of the phosphorus source solution, and T is the temperature of the coprecipitation reaction.

[0067] In the present invention, the molar ratio K1 of the phosphorus source to the metals (manganese source, iron source, and R1 source) added, the pH of the phosphorus source solution, and the reaction temperature T are controlled to satisfy a specific relationship, thereby enabling the adjustment and control of the phosphorus to metal molar ratio K in the manganese iron phosphate precursor, and further enabling the adjustment and control of the performance of the lithium manganese iron phosphate positive electrode material, and the resulting lithium manganese iron phosphate positive electrode material has excellent electrochemical performance.

[0068] According to the present invention, in formula III, 0.9≦K1≦2, 0 <L≦3、30℃≦T≦90℃とする。

[0069] Furthermore, in formula III, 1≦K1≦1.5, 1.5≦L≦2.5, and 60°C≦T≦90°C.

[0070] According to the present invention, in step S1, the concentration of the mixed salt is 0.1 to 4 mol / L, preferably 0.2 to 2 mol / L.

[0071] In the present invention, the type of manganese source in step S1 is not specifically limited, and any conventional soluble manganese source in the art can be used, including, but not limited to, divalent manganese salts. Preferably, the divalent manganese salt is at least one selected from the group consisting of manganese sulfate, manganese chloride, manganese nitrate, and manganese acetate.

[0072] In the present invention, the type of iron source in step S1 is not specifically limited, and any conventional soluble iron source in the art can be used, including, but not limited to, divalent iron salts. Preferably, the divalent iron salt is at least one selected from the group consisting of ferrous sulfate, ferrous chloride, and ferrous nitrate.

[0073] In the present invention, the types of the R1 source and the R2 source are not specifically limited, and a soluble R-containing compound that can provide at least one of Al, Mg, Ca, Sr, V, Cr, Y, Mo, Nb, B, Al, W, La, Sm, Co, Ni, Cu, Zn, Zr, and Ti conventionally used in the art can be used, including at least one of R-containing sulfates, nitrates, acetates, and chlorides, but is not limited thereto. Preferably, the R source is selected from at least one of titanyl sulfate, zirconium nitrate, and aluminum sulfate.

[0074] In one specific embodiment of the present invention, the R1 source and the R2 source are different in type, specifically, the R1 source is selected from soluble R-containing compounds capable of providing at least one of Al, Cu, Zn, Zr, and Ti, and the R2 source is selected from compounds capable of providing at least one element of Mg, Ca, Sr, V, Cr, Co, Ni, Y, Mo, Nb, B, W, La, and Sm.

[0075] According to the present invention, in step S2, the concentration of the phosphorus source solution is 0.2 to 20 mol / L, preferably 1 to 15 mol / L.

[0076] In the present invention, the type of phosphorus source in step S2 is not specifically limited, and any conventional soluble phosphorus source in the art can be used, including, but not limited to, one of phosphoric acid, sodium phosphate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate, and ammonium monohydrogen phosphate, and preferably at least one of phosphoric acid, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate.

[0077] In the present invention, in step S2, the pH value of the phosphorus source solution is 0 to 3, and preferably, the pH value of the phosphorus source solution is 1.5 to 2.5.

[0078] In the present invention, the pH adjuster used in step S2 is not particularly limited as long as it can adjust the pH value of the phosphorus source solution. For example, the pH adjuster is an acid solution or an alkaline solution, and preferably, the pH adjuster is at least one selected from the group consisting of sodium hydroxide, aqueous ammonia, sulfuric acid, hydrochloric acid, and nitric acid. In the present invention, the amount of the pH adjuster used is also not particularly limited as long as the pH value of the phosphoric acid solution satisfies the above range.

[0079] According to the present invention, in step S3, the molar ratio of the amount of the phosphorus source added in terms of n1(P) to the total amount of the manganese source, the iron source, and the sources added in terms of [n1(Mn) + n1(Fe) + n1(R1)] is 1 to 5:1.

[0080] In the present invention, by controlling the total amount of the phosphorus source, manganese source, iron source, and R1 source to satisfy the above range, it is possible to realize the adjustment and control of the P / Me molar ratio in the positive electrode material, and further realize the adjustment and control of the performance of the lithium manganese iron phosphate positive electrode material, and the obtained lithium manganese iron phosphate positive electrode material has excellent electrochemical performance.

[0081] Furthermore, in step (3), the molar ratio of the amount of the phosphorus source added in terms of n1(P) to the total amount of the manganese source, the iron source, and the R1 source added in terms of [n1(Mn) + n1(Fe) + n1(R1)] is 1 to 3:1.

[0082] According to the present invention, in step S3, the molar ratio of the amount of the oxidizing agent added to the total amount of the manganese source, the iron source, and the R1 source added in terms of [n1(Mn)+n1(Fe)+n1(R1)] is 1 to 10:1.

[0083] Furthermore, by controlling the total amount of the oxidant, manganese source, iron source, and R1 source to satisfy the above relationship, the oxidation degree of the metal elements in the positive electrode material can be controlled, and the resulting lithium manganese iron phosphate positive electrode material has low volume resistivity and high purity. When used in a lithium ion battery, the lithium ion battery will have high specific capacity, high cycle performance, and high energy density.

[0084] Furthermore, in step S3, the molar ratio of the amount of the oxidizing agent added to the total amount of the manganese source, the iron source, and the R1 source added in terms of [n1(Mn)+n1(Fe)+n1(R1)] is 1 to 5:1.

[0085] In the present invention, the type of oxidant in step S3 is not specifically limited, and conventional oxidants in this field can be used, including, but not limited to, ozone, potassium permanganate, sodium persulfate, ammonium persulfate, sodium hypochlorite, and sodium hyalurate. Preferably, the oxidant is at least one selected from the group consisting of ozone, potassium permanganate, sodium persulfate, and ammonium persulfate.

[0086] In the present invention, the speed at which the mixed salt solution, the phosphorus source solution, and the oxidant are flowed into the reaction vessel in step S3 is not specifically limited, and any speed conventional in the art may be used as long as it can achieve uniform co-precipitation of manganese iron.

[0087] According to the present invention, the coprecipitation reaction is carried out under stirring conditions.

[0088] According to the present invention, the rotation speed of the stirring is 200 to 800 r / min, preferably 400 to 800 r / min.

[0089] According to the present invention, after the coprecipitation reaction, an aging reaction is carried out.

[0090] According to the present invention, the conditions for the aging reaction include an aging temperature of 30 to 90° C. and an aging time of 1 to 10 hours.

[0091] Further, the conditions for the aging reaction include an aging temperature of 60 to 90° C. and an aging time of 3 to 6 hours.

[0092] According to the present invention, the cleaning detergent is water at 20 to 90°C.

[0093] Furthermore, the cleaning detergent is water at 60 to 90°C.

[0094] In the present invention, the cleaning detergent is pure water.

[0095] According to the present invention, the drying conditions include a drying temperature of 50 to 200° C. and a drying time of 2 to 8 hours.

[0096] Furthermore, the drying conditions include a drying temperature of 80 to 150°C and a drying time of 3 to 6 hours.

[0097] According to the present invention, in step S4, the mixing is carried out in the presence of a solvent to obtain a mixed slurry, and the solvent in the mixed slurry is removed to obtain the mixed material.

[0098] In the present invention, the manganese iron phosphate precursor, the lithium source, the carbon source, and the R2 source can be mixed sufficiently and uniformly by mixing them preferably in the presence of a solvent, and the obtained lithium manganese iron phosphate positive electrode material has high purity and low volume resistivity.

[0099] In the present invention, the type of solvent is not particularly limited as long as the materials after mixing form a uniform slurry. For example, the solvent may be water, ethanol, etc., and preferably, the solvent is water. The amount of the solvent used is also not particularly limited, and similarly, the basis is that a uniform slurry is formed.

[0100] According to the present invention, the lithium source is selected from at least one of lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate, lithium oxalate, lithium nitrate, and lithium acetate, and preferably, the lithium source is selected from at least one of lithium hydroxide, lithium carbonate, and lithium dihydrogen phosphate.

[0101] According to the present invention, the carbon source is selected from at least one of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine, and preferably, the carbon source is selected from at least one of glucose, sucrose, starch, and cellulose.

[0102] In the present invention, the method for removing the solvent in the mixed slurry is not particularly limited, and any conventional method in this field can be adopted. For example, the solvent in the mixed slurry can be removed by direct evaporation. The evaporation temperature and process can be any conventional technique known to those skilled in the art. For example, the solvent in the mixed slurry can be removed by static drying or spray drying.

[0103] According to the present invention, in step S5, the firing conditions include a firing temperature of 500 to 1000° C. and a firing time of 4 to 20 hours.

[0104] Furthermore, in step S5, the firing conditions include a firing temperature of 600 to 800° C. and a firing time of 6 to 12 hours.

[0105] In the present invention, the protective atmosphere is selected from a nitrogen gas atmosphere and / or an argon gas atmosphere.

[0106] The third aspect of the present invention provides a lithium manganese iron phosphate cathode material produced by a preparation method.

[0107] The fourth aspect of the present invention provides a manganese iron phosphate precursor, and the precursor material has a structure represented by Formula II. Mn 1-x-y Fe x R1 y P z O4·nH2O Formula II Here, 0.1≦x≦0.5, 0≦y≦0.04, 0.95≦z≦1.10, 0.95≦n≦1.5, and R1 is selected from at least one of Al, Mg, Ca, Sr, V, Cr, Y, Mo, Nb, B, Al, W, La, Sm, Co, Ni, Cu, Zn, Zr, and Ti.

[0108] Furthermore, in Formula II, 0.15≦x≦0.45, 0<y≦0.03, 0.95≦z≦1.05, 0.95≦n≦1.2, and R is selected from at least one of Al, Co, Ni, Mg, Al, W, Nb, Zr, and Ti.

[0109] In the present invention, the relationship between the actual molar content ratio m' of Mn element and Fe element at any position in the manganese iron phosphate precursor and the theoretical molar content ratio m0 of Mn element and Fe element at any position in the lithium manganese iron phosphate precursor is Δm p =|m’ - m0| / m0≦5%.

[0110] Furthermore, Δm p =|m’ - m0| / m0≦3%.

[0111] In the present invention, the median diameter of the manganese iron phosphate precursor is 0.5~10 μm, preferably 0.5~10 μm.

[0112] In the present invention, the primary particle size of the iron manganese phosphate precursor is 20 to 200 nm, preferably 20 to 100 nm.

[0113] In the present invention, the tap density of the iron manganese phosphate precursor is 0.5 to 1.5 g / cm 3 , preferably 0.8 to 1.5 g / cm 3 is.

[0114] In the present invention, the specific surface area of ​​the iron manganese phosphate precursor is 10 to 100 m 2 / g, preferably 10 to 40m 2 / g.

[0115] A fifth aspect of the present invention provides a method for preparing an iron manganese phosphate precursor, said method comprising: Step (1) of mixing a manganese source, an iron source, an R1 source and water to obtain a mixed salt solution; (2) mixing a phosphorus source with water and adding a pH adjuster to obtain a phosphorus source solution; and (3) adding the mixed salt solution, the phosphorus source solution, and the oxidizing agent to a reaction vessel in parallel flow to carry out a coprecipitation reaction, followed by filtering, washing, and drying to obtain the iron manganese phosphate precursor.

[0116] In the present invention, the method for preparing the iron manganese phosphate precursor satisfies the following relationship: K = (0.033K1 + 0.5) L -0.3 T 0.2 -0.05 Formula III Here, K is the ratio of n1(P) to [n1(Mn) + n1(Fe) + n1(R1)] in the manganese iron phosphate precursor, K1 is the molar ratio of the amount of the phosphorus source added in terms of n1(P) to the total amount of the manganese source, the iron source, and the R1 source added in terms of [n1(Mn) + n1(Fe) + n1(R1)], L is the pH value of the phosphorus source solution, and T is the temperature of the co-precipitation reaction.

[0117] In the present invention, in formula III, 0.9≦K1≦2, 0 <L≦3、30℃≦T≦90℃とする。

[0118] Furthermore, in formula III, 1≦K1≦1.5, 1.5≦L≦2.5, and 60°C≦T≦90°C.

[0119] According to the present invention, in step (1), the concentration of the mixed salt is 0.1 to 4 mol / L, preferably 0.2 to 2 mol / L.

[0120] In the present invention, the type of manganese source in step (1) is not specifically limited, and any conventional soluble manganese source in the art can be used, including, but not limited to, divalent manganese salts. Preferably, the divalent manganese salt is at least one selected from the group consisting of manganese sulfate, manganese chloride, manganese nitrate, and manganese acetate.

[0121] In the present invention, the type of iron source in step (1) is not specifically limited, and any conventional soluble iron source in the art can be used, including, but not limited to, divalent iron salts. Preferably, the divalent iron salt is at least one selected from the group consisting of ferrous sulfate, ferrous chloride, and ferrous nitrate.

[0122] In the present invention, the type of R1 source in step (1) is not specifically limited, and any conventional soluble R1 source in the art that can provide the M element can be used, including, but not limited to, at least one of sulfates, nitrates, acetates, and chlorides containing M. Preferably, the R1 source is selected from at least one of titanyl sulfate, zirconium nitrate, and aluminum sulfate.

[0123] In the present invention, in step (2), the concentration of the phosphorus source solution is 0.2 to 20 mol / L, preferably 1 to 15 mol / L.

[0124] In the present invention, the type of phosphorus source in step (2) is not specifically limited, and conventional soluble phosphorus sources in the art can be used, including, but not limited to, one of phosphoric acid, sodium phosphate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate, and ammonium monohydrogen phosphate, and preferably at least one of phosphoric acid, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate.

[0125] In the present invention, in step (2), the pH value of the phosphorus source solution is 0 to 3, and preferably, the pH value of the phosphorus source solution is 1.5 to 2.5.

[0126] In the present invention, the pH adjuster in step (2) is not particularly limited as long as it can adjust the pH value of the phosphorus source solution. For example, the pH adjuster is an acid solution or an alkaline solution, and preferably, the pH adjuster is at least one selected from the group consisting of sodium hydroxide, aqueous ammonia, sulfuric acid, hydrochloric acid, and nitric acid. In the present invention, the amount of the pH adjuster used is also not particularly limited as long as the pH value of the phosphoric acid solution satisfies the above range.

[0127] In the present invention, in step (3), the molar ratio of the amount of the phosphorus source added in terms of n1(P) to the total amount of the manganese source, the iron source, and the R1 source added in terms of [n1(Mn) + n1(Fe) + n1(R1)] is 1 to 5:1, preferably 1 to 3:1.

[0128] In the present invention, in step (3), the molar ratio of the amount of the oxidizing agent added to the total amount of the manganese source, the iron source, and the R1 source added in terms of [n1(Mn)+n1(Fe)+n1(R1)] is 1 to 10:1, preferably 1 to 5:1.

[0129] In the present invention, the type of oxidizing agent in step (3) is not specifically limited, and conventional oxidizing agents in this field can be used, including, but not limited to, ozone, potassium permanganate, sodium persulfate, ammonium persulfate, sodium hypochlorite, and sodium hyalurate. Preferably, the oxidizing agent is at least one selected from the group consisting of ozone, potassium permanganate, sodium persulfate, and ammonium persulfate.

[0130] In the present invention, the speed at which the mixed salt solution, the phosphorus source solution, and the oxidant are flowed into the reaction vessel in step (3) is not specifically limited, and any speed conventional in the art may be used as long as it can achieve uniform coprecipitation of manganese iron.

[0131] In the present invention, the coprecipitation reaction is carried out under stirring conditions.

[0132] In the present invention, the rotation speed of the stirring is 200 to 800 r / min, preferably 400 to 800 r / min.

[0133] In the present invention, after the coprecipitation reaction, an aging reaction is carried out.

[0134] In the present invention, the conditions for the aging reaction include an aging temperature of 30 to 90° C. and an aging time of 1 to 10 hours.

[0135] Further, the conditions of the aging reaction include an aging temperature of 60 to 90°C and an aging time of 3 to 6 hours.

[0136] In the present invention, the cleaning detergent is water at 20 to 90°C.

[0137] Furthermore, the cleaning detergent is water at 60 to 90°C.

[0138] In the present invention, the cleaning detergent is pure water.

[0139] In the present invention, the drying conditions include a drying temperature of 50 to 300° C. and a drying time of 2 to 8 hours.

[0140] Furthermore, the drying conditions include a drying temperature of 80 to 200° C. and a drying time of 3 to 6 hours.

[0141] A sixth aspect of the present invention provides an iron manganese phosphate precursor produced by the above preparation method.

[0142] A seventh aspect of the present invention provides a lithium-ion battery comprising the above lithium manganese iron phosphate positive electrode material or a positive electrode material produced from the above iron manganese phosphate precursor.

[0143] The present invention will now be described in detail with reference to examples. Particle size test: Tested and measured by Marvin laser particle size analyzer Mastersizer 2000. Morphological test: The specimens were tested and measured by a scanning electron microscope, model S-4800, manufactured by Hitachi, Japan.

[0144] Actual contents of Mn and Fe elements at any position in the cathode material precursor ratio m' and the actual contents of Mn and Fe elements at any position in the positive electrode material ratio m'' is the 50mm diameter of the Oxford Power Spectrum 2 Tested and measured with EDS on the model.

[0145] Specific surface area: Measured by the Tristar II3020 specific surface tester test of the US Micromertics company. Tap density: Measured using Hyakutoku Co., Ltd.'s BT-30 model tap density tester. Compacted density: measured by testing with a compacted density meter, model MCP-PD51, manufactured by Mitsubishi Chemical Corporation, Japan. Volume resistivity of the positive electrode material: Measured by testing with a powder compaction resistor model MCP-PD51 from Mitsubishi Chemical, Japan. Carbon content: The carbon content in the cathode material was measured by testing with a CS-i carbon-sulfur analyzer from Erdt, Germany. The content of each element in the cathode material and precursor was tested and measured by Agilent 5800 ICP-OES spectrometer, USA.

[0146] All of the raw materials used in the examples and comparative examples are commercially available products.

[0147] Example 1 (1) A certain mass of manganese sulfate, ferrous sulfate, and titanyl sulfate was weighed and dissolved in deionized water in a molar ratio of n(Mn):n(Fe):n(Ti) = 65:34:1 to prepare a 2 mol / L mixed salt solution. (2) A certain mass of sodium dihydrogen phosphate was weighed and dissolved in deionized water, and the pH of the solution was adjusted to 2 by adding 30 wt% dilute sulfuric acid to prepare a 2.8 mol / L phosphorus source solution. (3) Equal volumes of the mixed salt solution, phosphorus source solution, and sodium persulfate solution (2 mol / L) were added to the reactor in parallel to carry out the coprecipitation reaction. The reaction temperature was 90°C, the stirring speed was 500 r / min, and the liquid transfer was completed in 3 hours. After the liquid transfer was completed, the aging reaction was carried out at 90°C, the stirring speed was 500 r / min, and the aging reaction time was 3 hours. Here, n(oxidant) / [n1(Mn) + n1(Fe) + n1(M)] = 1, and K1 = n1(P) / [n1(Mn) + n1(Fe) + n1(M)] = 1.4. (4) After the reaction was completed, the reaction slurry was filtered and washed with purified water in an amount twice the volume of the slurry to obtain a cake, which was then dried at 105°C for 3 hours to obtain iron manganese phosphate precursor P1. Here, the composition of the manganese iron phosphate precursor P1 is Mn 0.648 Fe 0.342 Ti 0.01 P 1.04 O4·H2O and the median diameter D 50 is 2.36 μm and the tap density is 0.96 g / cm 3 and the specific surface area is 26.6m 2The manganese iron titanium ratio in the manganese iron phosphate precursor is n(Mn):n(Fe):n(Ti) = 64.8:34.2:1, and the molar ratio of phosphorus content to total metal content, K = n(P) / [n(Mn) + n(Fe) + n(M)] = 1.04. (5) The above prepared manganese iron phosphate precursor, lithium carbonate (Li2CO3), magnesium carbonate, and glucose (in terms of carbon) were mixed with pure water in a molar ratio of 1:0.52:0.01:0.7, and the mixture was uniformly mixed by mechanical stirring to obtain a slurry. (6) The slurry was steam-dried in a heating oven tray, and then placed in a vacuum oven at 85°C for 4 hours to obtain a dried material. The dried material was then calcined at 650°C for 10 hours in a nitrogen gas atmosphere and sieved to obtain lithium manganese iron phosphate positive electrode material A1. The composition of the lithium manganese iron phosphate cathode material A1 is Li 1.04 Mn 0.642 Fe 0.339 Ti 0.01 Mg 0.01 PO4 / C, the average particle size of its primary particles is 80 nm, and the compacted density is 2.15 g / cm 3 and the specific surface area is 18.6m 2 / g and the carbon content is 1.84 wt%.

[0148] Example 2 (1) A certain mass of manganese sulfate, ferrous sulfate, and titanyl sulfate was weighed and dissolved in deionized water in a molar ratio of n(Mn):n(Fe):n(Ti) = 65:34:1 to prepare a 1 mol / L mixed salt solution. (2) A certain mass of concentrated phosphoric acid was weighed out, diluted with deionized water, and 40 wt% sodium hydroxide was added to adjust the solution pH to 1.5 to prepare a 1.3 mol / L phosphorus source solution. (3) Equal volumes of the mixed salt solution, phosphorus source solution, and ammonium persulfate solution (1.5 mol / L) were added to the reactor in parallel to carry out the coprecipitation reaction. The reaction temperature was 60°C, the stirring speed was 500 r / min, and the liquid transfer was completed in 3 hours. After the liquid transfer was completed, the aging reaction was carried out. The aging temperature was 90°C, the stirring speed was 500 r / min, and the aging reaction time was 3 hours. n(oxidant) / [n1(Mn) + n1(Fe) + n1(M)] = 1.5, and K1 = n1(P) / [n1(Mn) + n1(Fe) + n1(M)] = 1.3. (4) After the reaction was completed, the reaction slurry was filtered and washed with purified water in an amount twice the volume of the slurry to obtain a cake, which was then dried at 105°C for 3 hours to obtain iron manganese phosphate precursor P2. Here, the composition of the manganese iron phosphate precursor P2 is Mn 0.652 Fe 0.338 Ti 0.01 P 1.09 O4·H2O and the median diameter D 50 is 1.65 μm and the tap density is 1.14 g / cm 3 and the specific surface area is 26.5m 2 The manganese iron titanium ratio in the manganese iron phosphate precursor was n(Mn):n(Fe):n(Ti) = 65.2:33.8:1, and the molar ratio of phosphorus content to total metal content, K = n(P) / [n(Mn) + n(Fe) + n(M)] = 1.04, was measured. (5) The above prepared manganese iron phosphate precursor, lithium hydroxide, magnesium carbonate, and sucrose (in terms of C) were mixed with pure water in a molar ratio of 1:1.03:0.01:0.7, and the mixture was uniformly mixed by mechanical stirring to obtain a slurry. (6) The slurry was steam-dried in a heating oven tray, and then placed in a vacuum oven at 85°C for 4 hours to obtain a dried material. The dried material was then calcined at 650°C for 10 hours in a nitrogen gas atmosphere and sieved to obtain lithium manganese iron phosphate positive electrode material A2. The composition of the lithium manganese iron phosphate cathode material A2 is Li 1.03 Mn 0.645 Fe 0.335 Ti 0.01 Mg 0.01PO4 / C, the average particle size of its primary particles is 60 nm, and the compacted density is 2.20 g / cm 3 and the specific surface area is 21.2m 2 / g and the carbon content is 2.09 wt%.

[0149] Example 3 (1) A certain mass of manganese chloride, ferrous sulfate, and titanyl sulfate was weighed and dissolved in deionized water in a molar ratio of n(Mn):n(Fe):n(Ti) = 65:34:1 to prepare a 2 mol / L mixed salt solution. (2) A certain mass of ammonium dihydrogen phosphate was weighed and dissolved in deionized water, and 30 wt% dilute sulfuric acid was added to adjust the solution pH to 2.2 to prepare a 3 mol / L phosphorus source solution. (3) Equal volumes of the mixed salt solution, phosphorus source solution, and sodium permanganate solution (2 mol / L) were added to the reactor in parallel to carry out the coprecipitation reaction. The reaction temperature was 90°C, the stirring speed was 500 r / min, and the liquid transfer was completed in 3 hours. After the liquid transfer was completed, the aging reaction was carried out. The aging temperature was 90°C, the stirring speed was 500 r / min, and the aging reaction time was 3 hours. Here, n(oxidant) / [n1(Mn) + n1(Fe) + n1(M)] = 1, and K1 = n1(P) / [n1(Mn) + n1(Fe) + n1(M)] = 1.5. (4) After the reaction was completed, the reaction slurry was filtered and washed with purified water in an amount twice the volume of the slurry to obtain a cake, which was then dried at 105°C for 3 hours to obtain iron manganese phosphate precursor P3. Here, the composition of the manganese iron phosphate precursor P3 is Mn 0.647 Fe 0.343 Ti 0.01 P 1.02 O4·H2O and the median diameter D 50 is 3.78 μm and the tap density is 1.02 g / cm 3 and the specific surface area is 22.1m 2The manganese iron titanium ratio in the manganese iron phosphate precursor was n(Mn):n(Fe):n(Ti) = 64.7:34.3:1, and the molar ratio of phosphorus content to total metal content, K = n(P) / [n(Mn) + n(Fe) + n(M)] = 1.02, was measured. (5) The above prepared manganese iron phosphate precursor, lithium hydroxide, magnesium carbonate, and sucrose (in terms of C) were mixed with pure water in a molar ratio of 1:1.03:0.01:0.7, and the mixture was uniformly mixed by mechanical stirring to obtain a slurry. (6) The slurry was steam-dried in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours to obtain a dried material. The dried material was then calcined at 650°C for 10 hours in a nitrogen gas atmosphere and sieved to obtain lithium manganese iron phosphate positive electrode material A3. The composition of the lithium manganese iron phosphate cathode material A3 is Li 1.03 Mn 0.640 Fe 0.340 Ti 0.01 Mg 0.01 PO4 / C, the average particle size of its primary particles is 80 nm, and the compacted density is 2.19 g / cm 3 The specific surface area is 18.3m 2 / g and the carbon content is 2.08 wt%.

[0150] Example 4 (1) A 1.8 mol / L mixed salt solution was prepared by weighing out certain masses of manganese chloride, iron chloride, and titanyl sulfate in a molar ratio of n(Mn):n(Fe):n(Ti) = 75:24:1 and dissolving them in deionized water. (2) A certain mass of sodium dihydrogen phosphate was weighed and dissolved in deionized water, and dilute sulfuric acid with a concentration of 30 wt% was added to prepare a 1.8 mol / L phosphorus source solution with a pH of 1.8. (3) The mixed salt solution, phosphorus source solution, and sodium persulfate solution (2.7 mol / L) were added to the reactor in parallel to carry out the coprecipitation reaction. The reaction temperature was 70°C, the stirring speed was 500 r / min, and the liquid transfer was completed in 3 hours. After the liquid transfer was completed, the aging reaction was carried out. The aging temperature was 90°C, the stirring speed was 500 r / min, and the aging reaction time was 3 hours. n(oxidant) / [n1(Mn)+n1(Fe)+n1(M)]=1.5, and K1=n1(P) / [n1(Mn)+n1(Fe)+n1(M)]=1. (4) After the reaction was completed, the reaction slurry was filtered and washed with purified water in an amount twice the volume of the slurry to obtain a cake, which was then dried at 105°C for 3 hours to obtain iron manganese phosphate precursor P4. Here, the composition of the manganese iron phosphate precursor P4 is Mn 0.748 Fe 0.242 Ti 0.01 P 0.99 O4·H2O and the median diameter D 50 is 2.12 μm and the tap density is 0.98 g / cm 3 and the specific surface area is 23.6m 2 The manganese iron titanium ratio in the manganese iron phosphate precursor was n(Mn):n(Fe):n(Ti) = 74.8:24.2:1, and the molar ratio of phosphorus content to total metal content, K = n(P) / [n(Mn) + n(Fe) + n(M)] = 0.99, was measured. (5) The above prepared manganese iron phosphate precursor, lithium hydroxide, magnesium carbonate, and sucrose (in terms of C) were mixed with pure water in a molar ratio of 1:1.03:0.01:0.6, and the mixture was uniformly mixed by mechanical stirring to obtain a slurry. (6) The slurry was steam-dried in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours to obtain a dried material. The dried material was then calcined at 650°C for 10 hours in a nitrogen gas atmosphere and sieved to obtain lithium manganese iron phosphate positive electrode material A4. The composition of the manganese iron lithium phosphate cathode material A4 is Li 1.03 Mn 0.740 Fe 0.240 Ti 0.01 Mg 0.01PO4 / C, the average particle size of its primary particles is 80 nm, and the compacted density is 2.26 g / cm 3 and the specific surface area is 18.4m 2 / g and the carbon content is 1.94 wt%.

[0151] Example 5 (1) A 2 mol / L mixed salt solution was prepared by weighing out certain masses of manganese chloride, ferrous sulfate, and aluminum sulfate in a molar ratio of n(Mn):n(Fe):n(Al) = 70:29:1 and dissolving them in deionized water. (2) A certain mass of sodium monohydrogen phosphate was weighed and dissolved in deionized water, and diluted nitric acid with a concentration of 50 wt% was added to prepare a 2 mol / L phosphorus source solution with a pH of 2. (3) The mixed salt solution, phosphorus source solution, and sodium persulfate solution (1.5 mol / L) were added to the reactor in parallel to carry out the coprecipitation reaction. The reaction temperature was 80°C, the stirring speed was 500 r / min, and the liquid transfer was completed in 3 hours. After the liquid transfer was completed, the aging reaction was carried out. The aging temperature was 90°C, the stirring speed was 500 r / min, and the aging reaction time was 3 hours. n(oxidant) / [n1(Mn) + n1(Fe) + n1(M)] = 0.75, and K1 = n1(P) / [n1(Mn) + n1(Fe) + n1(M)] = 1. (4) After the reaction was completed, the reaction slurry was filtered and washed with purified water in an amount twice the volume of the slurry to obtain a cake, which was then dried at 105°C for 3 hours to obtain iron manganese phosphate precursor P5. Here, the composition of the manganese iron phosphate precursor P5 is Mn 0.703 Fe 0.287 Al 0.01 P 0.99 O4·H2O and the median diameter D 50 is 2.34 μm and the tap density is 1.26 g / cm 3 and the specific surface area is 18.8m 2 The manganese-iron-aluminum ratio in the manganese-iron phosphate precursor was n(Mn):n(Fe):n(Al) = 70.3:28.7:1, and the molar ratio of phosphorus content to total metal content, K = n(P) / [n(Mn) + n(Fe) + n(M)] = 0.99, was measured. (5) The above prepared manganese iron phosphate precursor, lithium hydroxide, niobium pentoxide, and cellulose were mixed with pure water in a molar ratio of 1:1.03:0.005:0.7, and the mixture was uniformly mixed by mechanical stirring to obtain a slurry. (6) The slurry was steam-dried in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours to obtain a dried material. The dried material was then calcined at 650°C for 10 hours in a nitrogen gas atmosphere and sieved to obtain lithium manganese iron phosphate positive electrode material A5. The composition of the manganese iron lithium phosphate cathode material A5 is Li 1.03 Mn 0.696 Fe 0.284 Al 0.01 Nb 0.01 PO4 / C, the average particle size of its primary particles is 90 nm, and the compacted density is 2.15 g / cm 3 The specific surface area is 18.3m 2 / g and the carbon content is 1.92 wt%.

[0152] Example 6 (1) A 2 mol / L mixed salt solution was prepared by weighing out certain masses of manganese chloride, ferrous sulfate, and zirconium nitrate in a molar ratio of n(Mn):n(Fe):n(Zr) = 70:29:1 and dissolving them in deionized water. (2) A certain mass of sodium monohydrogen phosphate was weighed and dissolved in deionized water, and diluted nitric acid with a concentration of 50 wt% was added to prepare a 2.2 mol / L phosphorus source solution with a pH of 1.8. (3) The mixed salt solution, phosphorus source solution, and ammonium persulfate solution (1.5 mol / L) were added to the reactor in parallel to carry out the coprecipitation reaction. The reaction temperature was 75°C, the stirring speed was 500 r / min, and the liquid transfer was completed in 3 hours. After the liquid transfer was completed, the aging reaction was carried out. The aging temperature was 90°C, the stirring speed was 500 r / min, and the aging reaction time was 3 hours. n(oxidant) / [n1(Mn) + n1(Fe) + n1(M)] = 0.75, and K1 = n1(P) / [n1(Mn) + n1(Fe) + n1(M)] = 1.1. (4) After the reaction was completed, the reaction slurry was filtered and washed with purified water in an amount twice the volume of the slurry to obtain a cake, which was then dried at 105°C for 3 hours to obtain iron manganese phosphate precursor P6. The manganese iron phosphate precursor P6 consists of Mn 0.698 Fe 0.292 Zr 0.01 P 1.02 O4·H2O and the median diameter D 50 is 3.08 μm and the tap density is 1.18 g / cm 3 and the specific surface area is 20.6m 2 The manganese-iron-aluminum ratio in the manganese-iron phosphate precursor was n(Mn):n(Fe):n(Zr) = 69.8:29.2:1, and the molar ratio of phosphorus content to total metal content, K = n(P) / [n(Mn) + n(Fe) + n(M)] = 1.02, was measured. (5) The above prepared manganese iron phosphate precursor, lithium hydroxide, tungsten oxide, and sucrose (in terms of C) were mixed with pure water in a molar ratio of 1:1.03:0.01:0.7, and the mixture was uniformly mixed by mechanical stirring to obtain a slurry. (6) The slurry was steam-dried in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours to obtain a dried material. The dried material was then calcined at 650°C for 10 hours in a nitrogen gas atmosphere and sieved to obtain lithium manganese iron phosphate positive electrode material A7. The chemical formula of the lithium manganese iron phosphate cathode material A7 is Li 1.03 Mn 0.691 Fe 0.289 Zr 0.01 W 0.01 PO4 / C, the average particle size of its primary particles is 120 nm, and the compacted density is 2.23 g / cm 3 and the specific surface area is 15.8m 2 / g and the carbon content is 2.10 wt%.

[0153] Example 7 (1) A certain mass of manganese sulfate, ferrous sulfate, and titanyl sulfate was weighed and dissolved in deionized water in a molar ratio of n(Mn):n(Fe):n(Ti) = 65:34:1 to prepare a 2 mol / L mixed salt solution. (2) A certain mass of sodium dihydrogen phosphate was weighed and dissolved in deionized water, and the pH of the solution was adjusted to 2 by adding 30 wt% dilute sulfuric acid to prepare a 2.5 mol / L phosphorus source solution. (3) Equal volumes of the mixed salt solution, phosphorus source solution, and sodium persulfate solution (2 mol / L) were added to the reactor in parallel to carry out the coprecipitation reaction. The reaction temperature was 90°C, the stirring speed was 500 r / min, and the liquid transfer was completed in 3 hours. After the liquid transfer was completed, the aging reaction was carried out at 90°C, the stirring speed was 500 r / min, and the aging reaction time was 3 hours. Here, n(oxidant) / [n1(Mn) + n1(Fe) + n1(M)] = 1, and K1 = n1(P) / [n1(Mn) + n1(Fe) + n1(M)] = 1.25. (4) After the reaction was completed, the reaction slurry was filtered and washed with purified water in an amount twice the volume of the slurry to obtain a cake, which was then dried at 105°C for 3 hours to obtain iron manganese phosphate precursor P7. Here, the composition of the manganese iron phosphate precursor P7 is Mn 0.649 Fe 0.341 Ti 0.01 P 1.03 O4·H2O and the median diameter D 50 is 2.15 μm and the tap density is 0.93 g / cm 3 The specific surface area is 28.9m 2 The manganese iron titanium ratio in the manganese iron phosphate precursor was n(Mn):n(Fe):n(Ti) = 64.9:34.1:1, and the molar ratio of phosphorus content to total metal content, K = n(P) / [n(Mn) + n(Fe) + n(M)] = 1.03, was measured. (5) The above-prepared manganese iron phosphate precursor, lithium carbonate (Li2CO3), aluminum trioxide, and glucose (in terms of carbon) were mixed with pure water in a molar ratio of 1:0.52:0.005:0.7, and the mixture was uniformly mixed by mechanical stirring to obtain a slurry. (6) The slurry was steam-dried in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours to obtain a dried material. The dried material was then calcined at 650°C for 10 hours in a nitrogen gas atmosphere and sieved to obtain lithium manganese iron phosphate positive electrode material A7. The composition of the manganese iron lithium phosphate cathode material A7 is Li 1.04 Mn 0.642 Fe 0.338 Ti 0.01 Al 0.01 PO4 / C, the average particle size of its primary particles is 85 nm, and the compacted density is 2.10 g / cm 3 and the specific surface area is 19.7m 2 / g and the carbon content is 1.86 wt%.

[0154] Example 8 (1) A certain mass of manganese sulfate, ferrous sulfate, and titanyl sulfate was weighed and dissolved in deionized water in a molar ratio of n(Mn):n(Fe):n(Ti) = 65:34:1 to prepare a 2 mol / L mixed salt solution. (2) A certain mass of sodium dihydrogen phosphate was weighed and dissolved in deionized water, and the pH of the solution was adjusted to 2 by adding 30 wt% dilute sulfuric acid to prepare a 2.8 mol / L phosphorus source solution. (3) Equal volumes of the mixed salt solution, phosphorus source solution, and sodium persulfate solution (2 mol / L) were added to the reactor in parallel to carry out the coprecipitation reaction. The reaction temperature was 80°C, the stirring speed was 500 r / min, and the liquid transfer was completed in 3 hours. After the liquid transfer was completed, the aging reaction was carried out at 90°C, the stirring speed was 500 r / min, and the aging reaction time was 3 hours. Here, n(oxidant) / [n1(Mn) + n1(Fe) + n1(M)] = 1, and K1 = n1(P) / [n1(Mn) + n1(Fe) + n1(M)] = 1.4. (4) After the reaction was completed, the reaction slurry was filtered and washed with purified water in an amount twice the volume of the slurry to obtain a cake, which was then dried at 105°C for 3 hours to obtain iron manganese phosphate precursor P8. Here, the composition of the manganese iron phosphate precursor P8 is Mn 0.651 Fe 0.339 Ti 0.01 P 1.02 O4·H2O and the median diameter D 50 is 2.87 μm and the tap density is 0.99 g / cm 3 and the specific surface area is 22.6m 2The manganese iron titanium ratio in the manganese iron phosphate precursor was n(Mn):n(Fe):n(Ti) = 65.1:33.9:1, and the molar ratio of phosphorus content to total metal content, K = n(P) / [n(Mn) + n(Fe) + n(M)] = 1.02, was measured. (5) The above prepared manganese iron phosphate precursor, lithium carbonate (Li2CO3), zirconia, and glucose (in terms of carbon) were mixed with pure water in a molar ratio of 1:0.52:0.01:0.7, and the mixture was uniformly mixed by mechanical stirring to obtain a slurry. (6) The slurry was steam-dried in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours to obtain a dried material. The dried material was then calcined at 650°C for 10 hours in a nitrogen gas atmosphere and sieved to obtain lithium manganese iron phosphate positive electrode material A8. The composition of the manganese iron lithium phosphate cathode material A8 is Li 1.04 Mn 0.644 Fe 0.336 Ti 0.01 Zr 0.01 PO4 / C, the average particle size of its primary particles is 70 nm, and the compacted density is 2.21 g / cm 3 and the specific surface area is 16.8m 2 / g and the carbon content is 1.80 wt%.

[0155] Example 9 (1) A certain mass of manganese sulfate and ferrous sulfate was weighed and dissolved in deionized water in a molar ratio of n(Mn):n(Fe):n(Ti) = 65:34:1 to prepare a 2 mol / L mixed salt solution. (2) A certain mass of sodium dihydrogen phosphate was weighed and dissolved in deionized water, and the pH of the solution was adjusted to 2 by adding 30 wt% dilute sulfuric acid to prepare a 2.8 mol / L phosphorus source solution. (3) Equal volumes of the mixed salt solution, phosphorus source solution, and sodium persulfate solution (2 mol / L) were added to the reactor in parallel to carry out the coprecipitation reaction. The reaction temperature was 90°C, the stirring speed was 500 r / min, and the reaction time was 1 hour. Then, the aging reaction was carried out at 90°C, the stirring speed was 500 r / min, and the aging reaction time was 3 hours. n(oxidant) / [n1(Mn)+n1(Fe)+n1(M)]=1, and K1=n1(P) / [n1(Mn)+n1(Fe)+n1(M)]=1.4. (4) After the reaction was completed, the reaction slurry was filtered and washed with purified water in an amount twice the volume of the slurry to obtain a cake, which was then dried at 105°C for 3 hours to obtain manganese phosphate iron precursor P9. Here, the composition of the manganese iron phosphate precursor P9 is Mn 0.647 Fe 0.343 Ti 0.01 P 1.04 O4·H2O and the median diameter D 50 is 2.48 μm and the tap density is 0.97 g / cm 3 and the specific surface area is 26.2m 2 The manganese iron ratio in the manganese iron phosphate precursor was n(Mn):n(Fe):n(Ti) = 64.7:34.3:1, and the molar ratio of phosphorus content to total metal content, K = n(P) / [n(Mn) + n(Fe) + n(M)] = 1.04, was measured. (5) The above prepared manganese iron phosphate precursor, lithium carbonate, and glucose (in terms of C) were mixed with pure water in a molar ratio of 1:0.52:0.7, and the mixture was uniformly mixed by mechanical stirring to obtain a slurry. (6) The slurry was steam-dried in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours to obtain a dried material. The dried material was then calcined at 650°C for 10 hours in a nitrogen gas atmosphere and sieved to obtain lithium manganese iron phosphate positive electrode material A9. The composition of the manganese iron lithium phosphate cathode material A9 is Li 1.04 Mn 0.647 Fe 0.343 Ti 0.01 PO4 / C, the average particle size of its primary particles is 90 nm, and the compacted density is 2.08 g / cm 3and the specific surface area is 18.8m 2 / g and the carbon content is 1.78 wt%.

[0156] Example 10 (1) A certain mass of manganese sulfate and ferrous sulfate was weighed and dissolved in deionized water in a molar ratio of n(Mn):n(Fe) = 65:35 to prepare a 2 mol / L mixed salt solution. (2) A certain mass of sodium dihydrogen phosphate was weighed and dissolved in deionized water, and the pH of the solution was adjusted to 2 by adding 30 wt% dilute sulfuric acid to prepare a 2.8 mol / L phosphorus source solution. (3) The mixed salt solution, phosphorus source solution, and sodium persulfate solution (2 mol / L) were added to the reactor in parallel to carry out the coprecipitation reaction. The reaction temperature was 90°C, the stirring speed was 500 r / min, and the liquid transfer was completed in 3 hours. After the liquid transfer was completed, the aging reaction was carried out. The aging temperature was 90°C, the stirring speed was 500 r / min, and the aging reaction time was 3 hours. Here, n(oxidant) / [n1(Mn)+n1(Fe)]=1, and K1=n1(P) / [n1(Mn)+n1(Fe)]=1.4. (4) After the reaction is completed, the reaction slurry is filtered and washed with purified water in an amount twice the volume of the slurry to obtain a cake. The cake is dried at 105°C for 3 hours to obtain the manganese iron phosphate precursor P10. Here, the composition of the manganese iron phosphate precursor P10 is Mn 0.650 Fe 0.348 P 1.04 O4·H2O and the median diameter D 50 is 4.88 μm and the tap density is 0.86 g / cm 3 and the specific surface area is 23.2m 2 The manganese iron ratio in the manganese iron phosphate precursor was n(Mn):n(Fe) = 65.2:34.8, and the molar ratio of phosphorus content to total metal content, K = n(P) / [n(Mn) + n(Fe)] = 1.04, was measured. (5) The above prepared manganese iron phosphate precursor, lithium carbonate, magnesium carbonate, and glucose (in terms of C) were mixed with pure water in a molar ratio of 1:0.52:0.01:0.7, and the mixture was uniformly mixed by mechanical stirring to obtain a slurry. (6) The slurry was steam-dried in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours to obtain a dried material. The dried material was then calcined at 650°C for 10 hours in a nitrogen gas atmosphere and sieved to obtain lithium manganese iron phosphate positive electrode material A10. The composition of the manganese iron lithium phosphate cathode material A10 is Li 1.04 Mn 0.645 Fe 0.345 Mg 0.01 PO4 / C, the average particle size of its primary particles is 250 nm, and the compacted density is 2.05 g / cm 3 and the specific surface area is 24.8m 2 / g and the carbon content is 1.86 wt%.

[0157] Comparative Example 1 (1) A certain mass of manganese sulfate, ferrous sulfate, and titanyl sulfate was weighed and dissolved in deionized water in a molar ratio of n(Mn):n(Fe):n(Ti) = 65:34:1 to prepare a 2 mol / L mixed salt solution. (2) A certain mass of sodium dihydrogen phosphate was weighed and dissolved in deionized water to prepare a 2.8 mol / L phosphorus source solution. (3) Equal volumes of the mixed salt solution, phosphorus source solution, and sodium persulfate solution (2 mol / L) were mixed, and 30 wt% dilute sulfuric acid was added to adjust the solution pH to 2. The mixed solution was then added directly to the reactor to carry out the coprecipitation reaction. The reaction temperature was 90°C, the stirring speed was 500 r / min, and the reaction time was 1 hour. Then, the aging reaction was carried out. The aging temperature was 90°C, the stirring speed was 500 r / min, and the aging reaction time was 3 hours. n(oxidant) / [n1(Mn) + n1(Fe) + n1(M)] = 1, and K1 = n1(P) / [n1(Mn) + n1(Fe) + n1(M)] = 1.4. (4) After the reaction was completed, the reaction slurry was filtered and washed with purified water in an amount twice the volume of the slurry to obtain a cake, which was then dried at 105°C for 3 hours to obtain the manganese iron phosphate precursor DP1. The manganese iron phosphate precursor DP1 consists of Mn 0.602 Fe 0.388 Ti 0.01 P 0.95O4·H2O and the median diameter D 50 is 3.85 μm and the tap density is 0.88 g / cm 3 and the specific surface area is 61.5m 2 The manganese iron titanium ratio in the manganese iron phosphate precursor was n(Mn):n(Fe):n(Ti) = 60.2:38.8:1, and the molar ratio of phosphorus content to total metal content, K = n(P) / [n(Mn) + n(Fe) + n(M)] = 0.95, was measured. (5) The above prepared manganese iron phosphate precursor, lithium carbonate, magnesium carbonate, and glucose (in terms of C) were mixed with pure water in a molar ratio of 1:0.52:0.01:0.7, and the mixture was uniformly mixed by mechanical stirring to obtain a slurry. (6) The slurry was steam-dried in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours to obtain a dried material. The dried material was then calcined at 650°C for 10 hours in a nitrogen gas atmosphere and sieved to obtain lithium manganese iron phosphate positive electrode material D1. The composition of the lithium manganese iron phosphate cathode material D1 is Li 1.04 Mn 0.596 Fe 0.384 Ti 0.01 Mg 0.01 PO4 / C, the average particle size of its primary particles is 1000 nm, and the compacted density is 1.85 g / cm 3 and the specific surface area is 36.5m 2 / g and the carbon content is 1.75 wt%.

[0158] Comparative Example 2 (1) A certain mass of manganese sulfate, ferrous sulfate, and titanyl sulfate was weighed and dissolved in deionized water in a molar ratio of n(Mn):n(Fe):n(Ti) = 65:34:1 to prepare a 2 mol / L mixed salt solution. (2) A certain mass of sodium dihydrogen phosphate was weighed and dissolved in deionized water, and the pH of the solution was adjusted to 2 by adding 30 wt% dilute sulfuric acid to prepare a 2.8 mol / L phosphorus source solution. (3) Equal volumes of the mixed salt solution and the phosphorus source solution were mixed and added directly to the reactor. The mixture was heated and stirred at 90°C and 500 rpm. An equal volume of sodium persulfate solution (2 mol / L) was added to the mixture, and the liquid transfer was completed in 3 hours. After the liquid transfer was completed, the aging reaction was carried out at 90°C, 500 rpm, and 3 hours. Here, n(oxidant) / [n1(Mn) + n1(Fe) + n1(M)] = 1, and K1 = n1(P) / [n1(Mn) + n1(Fe) + n1(M)] = 1.4. (4) After the reaction was completed, the reaction slurry was filtered and washed with purified water in an amount twice the volume of the slurry to obtain a cake, which was then dried at 105°C for 3 hours to obtain the manganese iron phosphate precursor DP2. The manganese iron phosphate precursor DP2 consists of Mn 0.613 Fe 0.377 Ti 0.01 P 0.92 O4·H2O and the median diameter D 50 is 3.65 μm and the tap density is 0.68 g / cm 3 and the specific surface area is 52.5m 2 The manganese iron titanium ratio in the manganese iron phosphate precursor was n(Mn):n(Fe):n(Ti) = 61.3:37.7:1, and the molar ratio of phosphorus content to total metal content, K = n(P) / [n(Mn) + n(Fe) + n(M)] = 0.92, was measured. (5) The above prepared manganese iron phosphate precursor, lithium carbonate, magnesium carbonate, and glucose (in terms of C) were mixed with pure water in a molar ratio of 1:0.52:0.01:0.7, and the mixture was uniformly mixed by mechanical stirring to obtain a slurry. (6) The slurry was steam-dried in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours to obtain a dried material. The dried material was then calcined at 650°C for 10 hours in a nitrogen gas atmosphere and sieved to obtain lithium manganese iron phosphate positive electrode material D2. The chemical formula of the positive electrode material is Li 1.04 Mn 0.607 Fe 0.373 Ti 0.01 Mg0.01 PO4 / C, the average particle size of its primary particles is 600 nm, and the compacted density is 1.77 g / cm 3 and the specific surface area is 32.5m 2 / g and the carbon content is 1.18 wt%.

[0159] Comparative Example 3 (1) A certain mass of manganese sulfate, ferrous sulfate, and titanyl sulfate was weighed and dissolved in deionized water in a molar ratio of n(Mn):n(Fe):n(Ti) = 65:34:1 to prepare a 2 mol / L mixed salt solution. (2) A certain mass of sodium dihydrogen phosphate was weighed and dissolved in deionized water, and 30% dilute sulfuric acid was added to adjust the solution pH to 2, thereby preparing a 2.8 mol / L phosphorus source solution. (3) Equal volumes of the mixed salt solution and the phosphorus source solution were added to the reactor in parallel. The reaction temperature was 90°C, the stirring speed was 500 r / min, and alkali was added to adjust the pH. The liquid transfer was completed in 3 hours. After the liquid transfer was completed, the aging reaction was carried out. The aging temperature was 90°C, the stirring speed was 500 r / min, and the aging reaction time was 3 hours. Here, K1 = n1(P) / [n1(Mn) + n1(Fe) + n1(M)] = 1.4. (4) After the reaction was completed, the reaction slurry was filtered and washed with purified water in an amount twice the volume of the slurry to obtain a cake, which was then dried at 105°C for 3 hours to obtain the manganese ferric phosphate precursor DP3. The manganese ferric phosphate precursor DP3 is composed of (Mn 0.621 Fe 0.369 Ti 0.01 )3(PO4)2·H2O, and the median diameter D 50 is 16.85 μm and the tap density is 0.34 g / cm 3 and the specific surface area is 23.5m 2 The manganese iron titanium ratio in the manganese iron phosphate precursor was n(Mn):n(Fe):n(Ti) = 62.1:36.9:1, and the molar ratio of phosphorus content to total metal content, K = n(P) / [n(Mn) + n(Fe) + n(M)] = 0.67, was measured. (5) The manganous iron phosphate precursor prepared above, lithium carbonate, lithium dihydrogen phosphate, magnesium carbonate, and glucose were mixed with pure water in a molar ratio of 1:0.02:1:0.01:0.7, and the mixture was uniformly mixed by mechanical stirring to obtain a slurry. (6) The slurry was steam-dried in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours to obtain a dried material. The dried material was then calcined at 650°C for 10 hours in a nitrogen gas atmosphere and sieved to obtain lithium manganese iron phosphate positive electrode material D3. The composition of the lithium manganese iron phosphate cathode material D3 is Li 1.04 Mn 0.615 Fe 0.365 Ti 0.01 Mg 0.01 PO4 / C, the average particle size of its primary particles is 1.2 μm, and the compacted density is 1.36 g / cm 3 and the specific surface area is 12.8m 2 / g and the carbon content is 1.32 wt%.

[0160] Comparative Example 4 (1) A certain mass of ferrous sulfate was weighed and dissolved in deionized water to prepare a 2 mol / L mixed salt solution. (2) A certain mass of sodium dihydrogen phosphate was weighed and dissolved in deionized water, and 30% dilute sulfuric acid was added to adjust the solution pH to 2, thereby preparing a 2.8 mol / L phosphorus source solution. (3) 1 L of mixed salt solution, 1 L of phosphorus source solution, and 1 L of sodium persulfate solution (2 mol / L) were added in parallel to a 5 L reactor to carry out a coprecipitation reaction. The reaction temperature was 90°C, the stirring speed was 500 r / min, and the liquid transfer time was 1 hour. After the liquid transfer was completed, an aging reaction was carried out. The aging temperature was 90°C, the stirring speed was 500 r / min, and the aging reaction time was 3 hours. Here, n (oxidant) / n1 (Fe) = 1, and K1 = n1 (P) / n1 (Fe) = 1.4. (4) After the reaction was completed, the reaction slurry was filtered and washed with purified water in an amount twice the volume of the slurry to obtain a cake, which was then dried at 105°C for 3 hours to obtain iron phosphate precursor DP4. Here, the composition of the iron phosphate precursor DP4 is FePO4·2H2O, and the median diameter D 50 is 3.78 μm and the tap density is 0.78 g / cm 3 and the specific surface area is 42.3m 2 The molar ratio of phosphorus content to total metal content, K = n(P) / n(Fe), = 1, was measured. (5) The iron phosphate precursor prepared above, trimanganese tetroxide, lithium carbonate, titanium dioxide, and glucose (in terms of C) were mixed with pure water in a molar ratio of 1:0.62:0.52:0.01:0.7, and the mixture was uniformly mixed by mechanical stirring to obtain a slurry. (6) The slurry was steam-dried in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours to obtain a dried material. The dried material was then calcined at 650°C for 10 hours in a nitrogen gas atmosphere and sieved to obtain lithium manganese iron phosphate positive electrode material D4. The composition of the manganese iron lithium phosphate cathode material D4 is Li 1.04 Mn 0.643 Fe 0.347 Ti 0.01 PO4 / C, the average particle size of its primary particles is 600 nm, and the compacted density is 1.65 g / cm 3 and the specific surface area is 32.8m 2 / g and the carbon content is 2.46 wt%.

[0161] Two positions of the prepared manganese iron phosphate precursor were randomly selected, and the actual molar content ratio m' of metallic Mn and Fe at each position was tested by EDS. The measured values ​​are shown in Table 1. The theoretical molar content ratio of metallic Mn and Fe in the manganese iron phosphate precursor is m.

[0162] [Table 1]

[0163] In Comparative Examples 1 and 2, the molar ratios of Mn and Fe at different positions in the precursors differed greatly from the theoretical values, and the ratios at different positions also differed greatly. This is because, compared to the precursor preparation process in Example 1, the precursor preparation process in Comparative Example 1 involves mixing the mixed salt solution, phosphorus source solution, and oxidant before adjusting the pH. This one-step raw material addition method leads to non-uniform reaction and is prone to the phenomenon of ferromanganese segregation. In Comparative Example 2, the mixed salt solution and phosphorus source solution are mixed and reacted, and then the oxidant is added. Some of the metals and phosphorus have already reacted to form precipitates, which prevents complete oxidation and affects the uniform distribution of ferromanganese. In Comparative Example 3, no oxidant is added, and ferromanganese phosphate is produced, with a large deviation in the metal and phosphorus contents.

[0164] The median diameter D of the iron manganese phosphate precursor prepared in the examples and comparative examples 50 The tap density and specific surface area were tested, and the results are shown in Table 2.

[0165] [Table 2]

[0166] Table 3 shows the compositions of the manganese iron phosphate precursor and the lithium manganese iron phosphate positive electrode material prepared in the examples and comparative examples.

[0167] [Table 3]

[0168] Two positions were randomly selected from the prepared lithium manganese iron phosphate positive electrode material, and the actual molar content ratio m'' of metallic Mn and Fe at each position was tested by EDS. The measured values ​​are shown in Table 4. The theoretical molar content ratio of metallic Mn and Fe in the lithium manganese iron phosphate positive electrode material is m.

[0169] [Table 4]

[0170] The average particle size, compaction density, specific surface area, carbon content and volume resistivity of the primary particles in the lithium iron manganese phosphate positive electrode materials prepared in the examples and comparative examples were tested, and the results are shown in Table 5.

[0171] [Table 5]

[0172] As can be seen from Tables 1 to 5, compared with Comparative Examples 1 to 4, in Examples 1 to 10, the difference between the molar ratio of Mn to Fe at different positions in the positive electrode material and its precursor and the theoretical value is small, the distribution of iron and manganese in the positive electrode material and its precursor is uniform, and there is no segregation phenomenon. The positive electrode materials prepared thereby have low volume resistivity and small primary particles, and when used in lithium ion batteries, they can significantly improve the electrochemical performance of the lithium ion batteries.

[0173] Specifically, the difference between the theoretical and theoretical molar ratios of Mn and Fe at different positions in the cathode material precursors of Comparative Examples 1 and 2 was large, resulting in a large difference between the theoretical and theoretical values ​​of Mn and Fe at different positions in the cathode materials of Comparative Examples 1 and 2. At the same time, the segregation distribution of the manganese iron precursor in Comparative Example 1 was nonuniform, and the oxidation reaction of the precursor in Comparative Example 2 was incomplete, resulting in the presence of heterogeneous phases. As a result, the primary particles in the cathode materials of Comparative Examples 1 and 2 were large and the volume resistivity was high. In Comparative Example 3, a phosphorus source had to be added during the preparation of the cathode material, and the distribution of the metal and phosphorus ratio was nonuniform and difficult to control, resulting in a high volume resistivity. In Comparative Example 4, the mixture of iron phosphate and trimanganese tetroxide failed to achieve atomic-level mixing of the elements, resulting in a large deviation in the Mn and Fe molar ratio.

[0174] Test Example

[0175] This example is used to illustrate the electrode materials, electrodes, lithium ion batteries and their preparation methods. (1) Preparation of Positive Electrode Sheet: The lithium manganese iron phosphate positive electrode material prepared in the above examples and comparative examples, the conductive carbon nanotubes, and the PVDF binder in NMP solution were mixed in a mass ratio of 90:5:5. The specific method is as follows: After drying, the positive electrode material and conductive agent were ground in a mortar for 15 minutes to uniformly grind the material. After that, a PVDF solution (5% by mass) was added and stirred with a magnetic stirrer for 6 hours. The resulting paste-like slurry was uniformly applied to an aluminum foil current collector, dried in a vacuum drying oven at 60°C for 20 hours, and then punched out into a 12 mm diameter, 120 μm thick positive electrode sheet at 100 MPa. The positive electrode sheet was then placed in a vacuum drying oven at 120°C and dried for 12 hours. (2) Battery assembly: A metallic lithium 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 an equal mixture of 1 mol / L LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC) is used as the electrolyte. The positive electrode sheet, separator, negative electrode sheet, and electrolyte are assembled into a 2025-type buckle battery in an Ar gas glove box with a water content and oxygen content both less than 5 ppm. (3) Electrochemical performance test: A charge / discharge test was conducted on the battery using a LAND CT2001A charger / discharger from Wuhan Lanbo Electronics Co., Ltd. The charge / discharge voltage range was 2.5 to 4.4 V. The specific capacity test was conducted on the assembled lithium-ion battery at 0.1 C and 1 C multiplication rates, respectively, and a cycle performance test was conducted at 1 C multiplication rate. The test results are shown in Table 6.

[0176] [Table 6]

[0177] From Table 6, it can be seen that the positive electrode material prepared by the present invention has good capacity performance, scalability, and cycle stability. This is because the precursor manganese iron prepared by the present invention has a uniform distribution, the metal and phosphorus ratios can be adjusted and controlled, and the doping of the precursor improves the uniformity of the doped elements. The positive electrode material prepared using the precursor of the present invention as a raw material has small primary particles, a uniform carbon coating, and low volume resistivity, which are advantageous for lithium ion absorption and desorption, resulting in a 0.1C discharge specific capacity of more than 150mAh / g and a 1C discharge specific capacity of more than 140mAh / g. The double doping of the precursor and positive electrode material ensures that its 80-cycle retention rate is greater than 95%.

[0178] FIG. 1 shows the XRD pattern of the manganese phosphate iron precursor prepared in Example 1. As can be seen from FIG. 1, the XRD pattern of the manganese phosphate iron precursor prepared in the present invention corresponds perfectly to that of the MnPO4·H2O standard card, indicating that no phase separation or other impurities are generated.

[0179] FIG. 2 is an SEM image of the manganese iron phosphate precursor prepared in Example 1. As can be seen from FIG. 2, the primary particles of the manganese iron phosphate precursor prepared in the present invention are small, which is advantageous for uniformly mixing the lithium source and the carbon source when used to prepare a lithium manganese iron phosphate positive electrode material, and the carbon source can be uniformly coated on the surface of the positive electrode material.

[0180] FIG. 3 is an EDS distribution diagram of Mn and Fe in the cross section of the manganese ferrous phosphate precursor prepared in Example 1. As can be seen from FIG. 3, the manganese and iron distribution in the manganese ferrous phosphate precursor prepared in the present invention is uniform.

[0181] FIG. 4 shows the XRD pattern of the lithium manganese iron phosphate positive electrode material prepared in Example 1. As can be seen from FIG. 4, the XRD pattern of the lithium manganese iron phosphate positive electrode material prepared in the present invention is completely consistent with the standard pattern, and no phase separation occurs in the manganese iron, and no other impurities are generated.

[0182] FIG. 5 is an SEM image of the lithium manganese iron phosphate positive electrode material prepared in Example 1. As can be seen from FIG. 5, the primary particles of the lithium manganese iron phosphate positive electrode material are small and uniform, and there is no carbon agglomeration on the surface, indicating that the surface of the positive electrode material is uniformly coated with carbon.

Claims

1. 1. A lithium manganese iron phosphate positive electrode material, the lithium manganese iron phosphate positive electrode material having a structure shown in Formula I: Li ｄ Mn １－ａ－ｂ Fe ａ R ｂ PO ４ / C type I wherein 0.1≦a≦0.5, 0≦b≦0.08, and 0.9<d≦1.2, and R is selected from at least one of Al, Mg, Ca, Sr, V, Cr, Y, Mo, Nb, B, W, La, Sm, Co, Ni, Cu, Zn, Zr, and Ti; The volume resistivity of the positive electrode material is 10 to 10 ４ Ω cm, The relationship between the actual molar content ratio m″ of the Mn element to the Fe element at an arbitrary position in the positive electrode material and the theoretical molar content ratio m of the Mn element to the Fe element at an arbitrary position in the positive electrode material is as follows: Δm ｃ =|m''-m| / m≦3%.

2. 2. The lithium manganese iron phosphate positive electrode material according to claim 1, wherein 0.15≦a≦0.45, 0<b≦0.06, and 0.95<d≦1.

15.

3. The compaction density of the positive electrode material is 1.5 to 3.5 g / cm ３ 2. The lithium manganese iron phosphate positive electrode material of claim 1, wherein

4. 1. A method for preparing a lithium iron manganese phosphate cathode material, the method comprising: mixing S1, a manganese source, an iron source, an R1 source and water to obtain a mixed salt solution; S2: Mixing a phosphorus source with water and adding a pH adjuster to obtain a phosphorus source solution; S3. Adding the mixed salt solution, the phosphorus source solution and the oxidant into a reactor in parallel flow to carry out a co-precipitation reaction, and then filtering, washing and drying to obtain the manganese iron phosphate precursor; S4. Mixing the iron manganese phosphate precursor, a lithium source, a carbon source, and an R2 source to obtain a mixture; S5. calcining the mixture in the presence of a protective atmosphere to obtain the lithium manganese iron phosphate cathode material.

5. The actual molar content ratio m' of Mn element to Fe element at any position in the iron manganese phosphate precursor and the theoretical molar content ratio m of Mn element to Fe element at any position in the lithium iron manganese phosphate precursor ０ The relationship between Δm ｐ = |m'-m ０ | / m ０ Meet ≦5% 5. The preparation method according to claim 4.

6. The method for preparing the iron manganese phosphate precursor satisfies the following relationship: K = (0.033K) １ +0.5)·L －０．３ •T ０．２ -0.05 Formula III where K is the ratio of n(P) to [n(Mn) + n(Fe) + n(M)] in the manganese iron phosphate precursor, and K １ is the molar ratio of the amount of the phosphorus source added in terms of n1(P) to the total amount of the manganese source, the iron source, and the R1 source added in terms of [n1(Mn) + n1(Fe) + n1(M)], L is the pH value of the phosphorus source solution, and T is the temperature of the co-precipitation reaction.

7. 5. The method of claim 4, wherein the R1 source and the R2 source are each independently selected from compounds capable of providing at least one element of Al, Mg, Ca, Sr, V, Cr, Y, Mo, Nb, B, W, La, Sm, Co, Ni, Cu, Zn, Zr, and Ti.

8. The preparation method according to claim 4, wherein in step S1, the concentration of the mixed salt is 0.1 to 4 mol / L.

9. The method according to claim 4, wherein the coprecipitation reaction is carried out under stirring conditions.

10. 1. A manganese iron phosphate precursor, said precursor material having the structure shown in Formula II: Mn １－ｘ－ｙ Fe ｘ R1 ｙ P ｚ O ４ ・nH ２ 1. A manganese iron phosphate precursor characterized by having a structure represented by formula II, wherein 0.1≦x≦0.5, 0<y≦0.04, 0.95≦z≦1.10, and 0.95≦n≦1.5, and R1 is selected from at least one of Al, Mg, Ca, Sr, V, Cr, Y, Mo, Nb, B, W, La, Sm, Co, Ni, Cu, Zn, Zr, and Ti.

11. 1. A method for preparing an iron manganese phosphate precursor, the method comprising: Step (1) of mixing a manganese source, an iron source, an R1 source and water to obtain a mixed salt solution; Step (2) of mixing a phosphorus source with water and adding a pH adjuster to obtain a phosphorus source solution; and (3) adding the mixed salt solution, the phosphorus source solution, and the oxidant into a reaction vessel in parallel flow to carry out a coprecipitation reaction, followed by filtering, washing, and drying to obtain the manganese iron phosphate precursor.

12. The method for preparing the iron manganese phosphate precursor satisfies the following relationship: K = (0.033K) １ +0.5)·L －０．３ •T ０．２ -0.05 Formula III where K is the ratio of n(P) in the iron manganese phosphate precursor to [n(Mn) + n(Fe) + n(R1)], and K １ is the molar ratio of the amount of the phosphorus source added in terms of n1(P) to the total amount of the manganese source, the iron source, and the R1 source added in terms of [n1(Mn) + n1(Fe) + n1(R1)], L is the pH value of the phosphorus source solution, and T is the temperature of the co-precipitation reaction.

13. A lithium ion battery comprising the lithium manganese iron phosphate positive electrode material according to any one of claims 1 to 3.

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