Battery cathode materials, their manufacturing methods and applications

Abstract

The battery cathode material includes a core and a first shell layer formed on the core, the core being LiMn x Fe 1-x PO4, and the first shell layer is LiMn y Fe 1-y PO4, where 0

Description

Technical Field

[0001] This application claims the priority of Chinese Patent Application No. 202111125874.6, titled "Battery Cathode Material, Its Manufacturing Method and Application", filed with the China National Intellectual Property Administration on September 24, 2021, and all of its contents are incorporated herein by reference.

[0002] This application relates to the field of lithium-ion batteries, specifically to battery cathode materials and their manufacturing methods and applications.

Background Art

[0003] Poly-anion type lithium iron phosphate LiFePO4 is well-known as the safest lithium-ion battery cathode material, but due to its low theoretical energy density (586 Wh / kg), its wide range of applications is severely limited. Lithium manganese phosphate LiMnPO4 has a structure similar to that of lithium iron phosphate and has a higher theoretical energy density (701 Wh / kg), so it has high availability. However, lithium manganese phosphate has low electronic conductivity and lithium ion diffusion rate (less than 10 1-x ,

[0004] , , , , S / cm, 10 -15 cm 2 / s respectively), which are lower than those of lithium iron phosphate (10 -9 S / cm and 10 -14 cm 2 / s respectively), and there is a problem of divalent Mn dissolution, so it is very difficult to have excellent electrochemical properties. Currently, a feasible solution is to partially replace Mn with Fe to form LiMn x Fe 1-x PO4 (0 < x < 1), make a compromise according to the energy density and kinetic properties, and based on this, perform necessary modification on the material to obtain a material with excellent properties.

Summary of the Invention

[0004] A battery positive electrode material according to a first aspect of the present application includes a core and a first shell layer formed on the core, the core being composed of LiMn x Fe 1-x PO4, and the first shell layer is LiMn y Fe 1-y PO4, where 0 <x≦0.4であり、0.6≦y≦0.9である。

[0005] In one embodiment of the present application, the mass ratio of the core to the first shell layer is 1:(1.5 to 9).

[0006] In one embodiment of the present application, the diameter of the core is between 0.5 μm and 5 μm.

[0007] In one embodiment of the present application, the thickness of the first shell layer is 0.09 μm to 2.7 μm.

[0008] In one embodiment of the present application, the molar ratio of Fe element to Mn element in the battery positive electrode material is 1:(1 to 9).

[0009] In one embodiment of the present application, a second shell layer is further formed on a surface of the first shell layer, and the second shell layer includes LiFePO4 and carbon.

[0010] In one embodiment of the present application, the second shell layer has a thickness of 20 nm to 600 nm.

[0011] In one embodiment of the present application, in the battery positive electrode material, the mass percentage of the core is 10% to 40%, the mass percentage of the first shell layer is 45% to 80%, and the mass percentage of the second shell layer is 10% to 20%.

[0012] In one embodiment of the present application, the battery positive electrode material further comprises a doping element, the doping element comprising one or more of Ti, V, Co, Ni, Cu, Zn, Mg, Al, Ca, Mo, and W, and the mass percentage of the doping element in the battery positive electrode material is 0.1% to 0.5%.

[0013] In one embodiment of the present application, the first shell layer contains the doping element.

[0014] In one embodiment of the present application, the mass percentage of the carbon in the positive electrode material of the battery is 1% to 3%.

[0015] The method for manufacturing a positive electrode material of a battery according to the second aspect of the present application is a step of putting a lithium source, an iron source, a manganese source, a phosphorus source and a solvent into a reaction kettle to perform a first reaction to obtain a core, where the core contains LiMn x Fe 1-x PO4, where 0 < x ≦ 0.4, and the first reaction is carried out at a temperature of 375°C to 500°C and a pressure of 23 Mpa or more, a step of putting a lithium source, an iron source, a manganese source, a phosphorus source, a solvent and the core into a reaction kettle to perform a second reaction to coat a first shell layer on the surface of the core to obtain a core with the first shell layer formed, where the first shell layer contains LiMn y Fe 1-y PO4, where 0.6 ≦ y ≦ 0.9, and the second reaction is carried out at a temperature of 375°C to 500°C and a pressure of 23 Mpa or more, a step of firing the core with the first shell layer formed at 500°C to 800°C to obtain a positive electrode material of a battery.

[0016] In one embodiment of the present application, before firing the core with the first shell layer formed, the manufacturing method further includes a step of putting a lithium source, an iron source, a phosphorus source, a carbon source, a solvent and the core with the first shell layer formed into a reaction kettle to perform a third reaction to coat a second shell layer on the surface of the first shell layer, where the second shell layer contains LiFePO4 and carbon, and the third reaction is carried out at a temperature of 375°C to 500°C and a pressure of 23 Mpa or more.

[0017] In one embodiment of the present application, the lithium source comprises an inorganic lithium salt and an organic lithium salt, the inorganic lithium salt comprising one or more of lithium carbonate, lithium bicarbonate, lithium dihydrogen phosphate, lithium monohydrogen phosphate, lithium phosphate, lithium nitrate, lithium sulfate, lithium chromate, and lithium hydroxide, and the organic lithium salt comprises one or more of lithium oxalate, lithium acetate, lithium benzoate, and Lithium citrate of Contains one or more of the following:

[0018] In one embodiment of the present application, the iron source comprises one or more of iron oxide, iron carbonate, iron oxalate, iron sulfate, iron chloride, and iron acetate.

[0019] In one embodiment of the present application, the manganese source is manganese monoxide, manganese dioxide, manganese hydroxide, manganese carbonate, manganese oxalate, manganese sulfate, manganese nitrate. 、 manganese chloride and manganese acetate.

[0020] In one embodiment of the present application, the phosphorus source comprises one or more of phosphoric acid, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, and lithium dihydrogen phosphate.

[0021] In one embodiment of the present application, the carbon source comprises one or more of glucose, sucrose, polyvinyl alcohol, starch, and citric acid.

[0022] In one embodiment of the present application, the firing is performed in an inert atmosphere, and the inert atmosphere includes one or more of nitrogen gas, argon gas, helium gas, neon gas, krypton gas, xenon gas, and radon gas.

[0023] A secondary battery according to a third aspect of the present application includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode includes a positive electrode plate, the positive electrode plate includes a current collector and a positive electrode material layer disposed on the current collector, and the positive electrode material layer includes the battery positive electrode material according to the first aspect. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 illustrates a battery cathode material according to an embodiment of the present application. [Figure 2] FIG. 1 is a structural schematic diagram of a battery cathode material having structure A. [Figure 3] FIG. 1 is a structural schematic diagram of a positive electrode material having structure B. [Figure 4] 1A-1D illustrate a method for manufacturing a battery cathode material according to an embodiment of the present application. [Figure 5] FIG. 1 illustrates a method for manufacturing a battery cathode material according to another embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, the technical means in the embodiments of the present application will be clearly and completely described with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, but not all of them, and all other embodiments that can be obtained by those skilled in the art based on the embodiments of the present application without any creative work are all within the scope of protection of the present application.

[0026] Lithium manganese phosphate LiMnPO4 has a higher theoretical energy density than lithium iron phosphate, but its electronic conductivity and lithium ion diffusion rate are lower than those of lithium iron phosphate, which is disadvantageous in terms of capacity utilization. In addition, in battery positive electrode materials, the distance over which ions and electrons inside the material must be transported to the outside is long, making the transport of ions and electrons difficult, further limiting the capacity utilization of lithium manganese phosphate positive electrode materials. In order to improve the electrochemical properties of lithium manganese phosphate positive electrode materials, the present application provides a battery positive electrode material, which is made of LiMnPO4, which has a high manganese content and low electronic and ionic conductivity. x Fe 1-x The PO4 (0.6≦x≦1) portion is arranged in the outer layer, and the manganese content is low, resulting in LiMn with high electronic and ionic conductivity. x Fe 1-xSince the PO4 (0 < x ≤ 0.4) portion is disposed in the inner layer, the distance in the electron and ion transport difficult portion (the transport difficult portion is the portion where transport in the material is difficult) is effectively shortened, improving the electrochemical properties of the positive electrode material.

[0027] As shown in FIG. 1, FIG. 1 shows a positive electrode material for a battery according to an embodiment of the present application. As shown in FIG. 1, the positive electrode material for a battery of the present application includes a core 10 and a first shell layer 20 formed on the surface of the core 10, and the first shell layer 20 completely covers the core 10. The core 10 contains a lithium iron manganese phosphate compound represented by Formula I, and the first shell layer 20 contains a lithium iron manganese phosphate compound represented by Formula II.

[0028] LiMn x Fe 1-x PO4, Formula I, where 0 < x ≤ 0.4.

[0029] LiMn y Fe 1-y PO4, Formula II, where 0.6 ≤ y ≤ 0.9.

[0030] In the positive electrode material for a battery, if the diffusion path of ions and electrons from the material core to the outside is long, it is disadvantageous for the transport of ions and electrons. The present application can improve the conductivity of the positive electrode material by doping the Fe element into LiMnPO4. The high proportion of iron element in the material core can improve the diffusion rate of ions and electrons, further improving the electrochemical properties of the positive electrode material. The first shell layer has a high proportion of manganese element, ensuring that the positive electrode material for a battery has a high energy density. With this structure, the positive electrode material for a battery has both a high energy density and high conductivity, and when applied to a battery, it gives the battery a high charge-discharge capacity.

[0031] In some embodiments of the present application, in LiMn x Fe 1-x PO4, the value of x may specifically be 0.1, 0.2, 0.3 or 0.4, but is not limited thereto. In LiMn y Fe 1-yIn PO4, the value of y may be, but is not limited to, 0.6, 0.7, 0.8, or 0.9. By setting x to 0.4 or less, high conductivity of the inner layer can be ensured, and by setting y to 0.6 or more, high energy density of the entire material can be ensured. In some embodiments of the present application, the value of x is 0.2 to 0.3, and the value of y is 0.8 to 0.9. In the battery positive electrode material of the present application, the mass percentage of iron element in the core is greater than the mass percentage of iron element in the first shell layer. The high proportion of iron in the core provides high electrical conductivity to the core, improving the transport rate of ions and electrons in the core and facilitating the transport of ions and electrons within the battery positive electrode material. The first shell layer has a high manganese content, ensuring high energy density of the entire battery positive electrode material.

[0032] Hereinafter, we will explain how the cathode material having the structure of the present application can improve the electrochemical properties of the material, using the cathode material having structure B as a comparison. Taking the cathode material of the present application having structure A as an example, the battery cathode material having structure A is composed of LiMn 0.2 Fe 0.8 PO4(40%) / LiMn 0.8 Fe 0.2 PO4 (60%) and LiMn 0.2 Fe 0.8 The mass percentage of PO4 in the battery positive electrode material is 40%, and LiMn 0.8 Fe 0.2 The mass percentage of PO4 in the battery cathode material is 60%. The cathode material having structure B is composed of LiMn 0.8 Fe 0.2 PO4(60%) / LiMn 0.2 Fe 0.8 PO4 (40%). As shown in Figures 2 and 3, Figure 2 is a structural schematic diagram of a battery cathode material having Structure A, and Figure 3 is a structural schematic diagram of a cathode material having Structure B. Structures A and B have the reversed arrangement of the two layers of materials, i.e., LiMn as a shell layer in Structure A. 0.8 Fe 0.2 PO4 is the core in the case of structure B and LiMn in structure A.0.8 Fe 0.2 PO4 and LiMn 0.2 F e0.8 Mass ratio of LiMn to PO4 and LiMn in structure B 0.8 Fe 0.2 PO4 and LiMn 0.2 F e0.8 The mass ratio of LiMn to PO4 is 3:2 in both cases. That is, the battery positive electrode material having structure A and the positive electrode material having structure B have the same energy density. 0.8 Fe 0.2 PO4 and LiMn 0.2 Fe 0.8 Since PO4 has almost the same material density, Structure A and Structure B have different structural arrangements, but their overall particle sizes are similar.

[0033] For the cathode material with structure B, the core LiMn 0.8 Fe 0.2 The high manganese content and low iron content in PO4 make it difficult for electrons and ions to transport through the core, i.e., the core is a difficult-to-transport layer. For a cathode material having Structure B, the maximum distance for ion and electron transport through the difficult-to-transport layer is 0.843R. To calculate this transport distance, assume that the radius of the cathode material is R and the radius of the core is R1. The core LiMn 0.8 Fe 0.2 Since the mass percentage of PO4 in the positive electrode material is 60%, R and R1 have the following relationship:

number

[0034] From the above formula, R1=0.843R is obtained, that is, for the positive electrode material having structure B, the maximum transport distance of ions and electrons in its difficult-to-transport layer is 0.843R.

[0035] For a battery cathode material having Structure A, assuming that its shell layer is a difficult-to-transport layer, the radius of the battery cathode material is R, and the radius of the core is R2, the maximum transport distance of ions and electrons in the difficult-to-transport layer of the battery cathode material having Structure A is R-R2, which can be calculated specifically as follows:

number

[0036] From the above formula, R2 = 0.737R is obtained, that is, for the battery cathode material having structure A, the maximum transport distance of ions and electrons in the difficult-to-transport layer is 0.263R. Therefore, LiMn 0.8 Fe 0.2 Compared with the cathode material having Structure B with PO4 as the core, the transport distance of ions and electrons in the difficult-to-transport layer of the battery cathode material having Structure A is shorter, with the distance reduction rate being 69%, which is calculated as (0.843R-0.263R) / 0.843R.

[0037] Similarly, LiMn 0.8 Fe 0.2 When the mass percentage of PO4 in the positive electrode material is 70%, the transport distance in the difficult layer for the battery positive electrode material having structure A is 0.331R, and the transport distance in the difficult layer for the battery positive electrode material having structure B is 0.888R. That is, LiMn 0.8 Fe 0.2 Compared with the distribution structure with PO4 as the core, the transport distance of ions and electrons in the difficult-to-transport layer of the battery positive electrode material having Structure A is shorter, with the reduction in distance being 63%. This application compares the transport distance with that of positive electrode materials having other content configurations, as shown in Table 1, which shows the results for the LiMn 0.8 Fe 0.2 1 is a comparison table of transport distances of cathode materials containing PO4.

[0038] Table 1 LiMn with different content 0.8 Fe 0.2 Comparison table of transport distances for cathode materials containing PO4 [Table 1]

[0039] As can be clearly seen from the above calculations, under the premise of having the same energy density, the structural distribution of the present invention can effectively shorten the transport distance of ions and electrons in the difficult-to-transport layer of the battery positive electrode material, thereby improving the electrochemical properties of the battery positive electrode material, and thus the battery positive electrode material can effectively improve the rate performance of the battery.

[0040] In some embodiments of the present application, the mass percentage of the first shell layer in the battery positive electrode material is greater than the mass percentage of the core in the battery positive electrode material, and the mass ratio of the core to the first shell layer is 1:1 (1.5 to 9). The mass ratio of the core to the first shell layer may be, but is not limited to, 1:1.5, 1:2, 1:4, 1:5, 1:6, 1:7, 1:8, or 1:9. Controlling the mass ratio of the core to the first shell layer within the above range can ensure that the battery positive electrode material has high energy density and high internal conductivity. When the mass percentage of the first shell layer is within the above range, the adjustment effect of the core-shell distribution structure on the positive electrode material is high, and the electrochemical properties of the positive electrode material can be effectively improved.

[0041] In some embodiments of the present application, the core diameter is 0.5 μm to 5 μm, and specifically may be, but is not limited to, 0.5 μm, 0.8 μm, 1 μm, 2 μm, 4 μm, or 5 μm. In some embodiments of the present application, the first shell layer has a thickness of 0.09 μm to 2.7 μm. Specifically, the first shell layer has a thickness of 0.09 μm to 2.7 μm, and specifically may be, but is not limited to, 0.09 μm, 0.1 μm, 0.5 μm, 1 μm, 2 μm, or 2.7 μm.

[0042] In some embodiments of the present application, the molar ratio of Fe element to Mn element in the battery positive electrode material is 1:(1-9). The molar ratio of Fe element to Mn element in the battery positive electrode material may be, but is not limited to, 1:1, 1:3, 1:5, or 1:9. For example, the battery positive electrode material may have a composition from the inside to the outside of LiMn 0.2 Fe 0.8 PO4(20%) / LiMn 0.8 Fe 0.2 In the case of PO4 (80%), the molar ratio of Fe to Mn is 1:2.125. By controlling the molar ratio of Fe to Mn in the battery positive electrode material within the above range, it is possible to ensure that the battery has a high energy density.

[0043] In some embodiments of the present application, the battery positive electrode material further includes a doping element, which may include one or more of Ti, V, Co, Ni, Cu, Zn, Mg, Al, and Ca, and may improve ionic and electronic conductivity of the battery positive electrode material. In some embodiments of the present application, both the core and the first shell layer of the battery positive electrode material may be doped with an element to improve electrical conductivity, and in some embodiments, the doping element is located in the first shell layer of the battery positive electrode material. In some embodiments of the present application, the mass percentage of the doping element in the battery positive electrode material is 0.1% to 0.5%. The mass percentage of the doping element in the battery positive electrode material may be, but is not limited to, 0.1%, 0.3%, 0.4%, or 0.5%.

[0044] In some embodiments of the present application, a second shell layer is further formed on the surface of the first shell layer of the battery positive electrode material, and the second shell layer includes LiFePO4 and carbon. Mn dissolves in the electrolyte and accumulates at the interface between the electrode and the electrolyte to form a high-resistance layer, increasing the internal resistance of the battery and reducing the rate and cycle characteristics of the battery. Therefore, coating the surface of the first shell layer with LiFePO4 isolates the first shell layer from the electrolyte and suppresses Mn dissolution. In some embodiments of the present application, the mass percentage of LiFePO4 in the battery positive electrode material is 10% to 20%. The mass percentage of LiFePO4 in the battery positive electrode material may be, but is not limited to, 10%, 13%, 15%, or 20%. In this application, the carbon in the second shell layer improves the conductivity of the battery positive electrode material, enabling high-rate charging and discharging. In some embodiments of the present application, the mass percentage of carbon in the battery positive electrode material is 1% to 5%. The mass percentage of carbon in the battery positive electrode material may be, but is not limited to, 1%, 3%, 4%, or 5%. In some embodiments of the present application, the thickness of the second shell layer is 20 nm to 600 nm. The thickness of the second shell layer may be, but is not limited to, 20 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, or 600 nm. In some embodiments of the present application, the thickness of the second shell layer is 25 nm to 400 nm.

[0045] The battery positive electrode material according to the present application not only has a high energy density but also has high electrical conductivity, enabling high-rate charging and discharging, and when applied to a battery, can effectively improve the cycle characteristics and rate characteristics of the battery.

[0046] The present application further provides a method for manufacturing a battery positive electrode material. FIG. 4 shows a method for manufacturing a battery positive electrode material according to an embodiment of the present application. As shown in FIG. 4, the method includes: Step 100: A lithium source, an iron source, a manganese source, a phosphorus source, and a solvent are placed in a reaction vessel to carry out a first reaction to obtain a core, the core being LiMn x Fe1-x Containing PO4, where 0 < x ≤ 0.4, the first reaction is step 100 with a temperature of 375°C to 500°C and a pressure of 23 Mpa or more, and Putting a lithium source, an iron source, a manganese source, a phosphorus source, a solvent and a core into a reaction kettle to carry out a second reaction to coat a first shell layer on the surface of the core, obtaining a core with the first shell layer formed, where the first shell layer is LiMn y Fe 1-y Containing PO4, where 0.6 ≤ y ≤ 0.9, the second reaction is step 200 with a temperature of 375°C to 500°C and a pressure of 23 Mpa or more, and Firing the core with the first shell layer formed at 500°C to 800°C to obtain a positive electrode material for a battery, including step 300.

[0047] In some embodiments of the present application, the solvent contains water. In some embodiments of the present application, the lithium source includes an inorganic lithium salt and an organic lithium salt. The inorganic lithium salt includes one or more of lithium carbonate, lithium hydrogen carbonate, lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium phosphate, lithium nitrate, lithium sulfate, lithium chromate and lithium hydroxide. The organic lithium salt includes one or more of lithium oxalate, lithium acetate, lithium benzoate, and Lithium citrate of Including one or more of them. In some embodiments of the present application, the iron source includes one or more of iron oxide, iron carbonate, iron oxalate, iron sulfate, iron chloride and iron acetate. In some embodiments of the present application, the manganese source includes one or more of manganese monoxide, manganese dioxide, manganese hydroxide, manganese carbonate, manganese oxalate, manganese sulfate, manganese nitrate 、 Including one or more of manganese chloride and manganese acetate. In some embodiments of the present application, the phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, ammonium hydrogen phosphate, and lithium dihydrogen phosphate.

[0048] In some embodiments of the present application, the first reaction is carried out at a temperature of 375°C to 500°C, under a pressure of 23 MPa to 60 MPa, for a reaction time of 0.5 hours to 10 hours. In some embodiments of the present application, the reaction time of the first reaction is 0.5 hours to 3 hours, and a reaction time of 0.5 hours to 3 hours can form a core with a stable structure. The reaction time of the first reaction may be, but is not limited to, 0.5 hours, 1 hour, 2 hours, 3 hours, 5 hours, or 10 hours. In some embodiments of the present application, the second reaction is carried out at a temperature of 375°C to 500°C, under a pressure of 23 MPa to 60 MPa, for a reaction time of 0.5 hours to 10 hours. In some embodiments of the present application, the reaction time of the second reaction is 0.5 hours to 3 hours, and a reaction time of 0.5 hours to 3 hours can form a first shell layer with a stable structure. In an embodiment of the present application, the first reaction and the second reaction are carried out in an inert atmosphere, and the inert atmosphere includes one or more of nitrogen gas, argon gas, helium gas, neon gas, krypton gas, xenon gas, and radon gas.

[0049] In some embodiments of the present application, the firing temperature is 500° C. to 800° C., and the firing time is 2 hours to 10 hours. The firing temperature may be, but is not limited to, 500° C., 600° C., 700° C., or 800° C., and the firing time may be, but is not limited to, 2 hours, 4 hours, 6 hours, or 10 hours.

[0050] The present application uses a supercritical fluid method to prepare the core and first shell layer. When the reaction temperature is 375°C or higher and the pressure is 23MPa or higher, the solvent in the reactor is in a supercritical fluid state, which can greatly improve the reaction activity and help form a dense crystalline structure. In addition, this method is easy to operate, and a battery cathode material can be obtained with a single calcination, significantly shortening the reaction time.

[0051] In some embodiments of the present application, the method for manufacturing a battery cathode material further includes a step of manufacturing a second shell layer. FIG. 5 illustrates a method for manufacturing a battery cathode material according to another embodiment of the present application. As shown in FIG. 5, the method includes: Step 100 of putting a lithium source, an iron source, a manganese source, a phosphorus source and a solvent into a reaction kettle to carry out a first reaction to obtain a core, where the core contains LiMn x Fe 1-x PO4, where 0 < x ≦ 0.4, and the first reaction is carried out at a temperature of 375°C to 500°C and a pressure of 23 Mpa or more, step 100, and Step 200 of putting a lithium source, an iron source, a manganese source, a phosphorus source, a solvent and the core into a reaction kettle to carry out a second reaction to coat a first shell layer on the surface of the core to obtain a core with the first shell layer formed, where the first shell layer contains LiMn y Fe 1-y PO4, where 0.6 ≦ y ≦ 0.9, and the second reaction is carried out at a temperature of 375°C to 500°C and a pressure of 23 Mpa or more, step 200, and Step 300 of putting a lithium source, an iron source, a phosphorus source, a carbon source, a solvent and the core with the first shell layer formed into a reaction kettle to carry out a third reaction to coat a second shell layer on the surface of the first shell layer, where the second shell layer contains LiFePO4 and carbon, and the third reaction is carried out at a temperature of 375°C to 500°C and a pressure of 23 Mpa or more, step 300, and Step 400 of firing the core with the first shell layer and the second shell layer formed at 500°C to 800°C to obtain a battery positive electrode material, including.

[0052] In some embodiments of the present application, the carbon source includes one or more of glucose, sucrose, polyvinyl alcohol, starch, and citric acid. The third reaction is carried out at a temperature of 375°C to 500°C, a pressure of 23 MPa to 60 Mpa, and a reaction time of 0.5 h to 10 h. The supercritical fluid method is used to help form a dense second shell layer, thereby more effectively suppressing the elution of Mn. In some embodiments of the present application, the third reaction is carried out in an inert atmosphere.

[0053] The manufacturing method of the battery positive electrode material according to the present application is simple, has high operability, and can manufacture a battery positive electrode material with excellent rate characteristics and cycle characteristics.

[0054] The positive electrode plate according to the present application includes a current collector and a positive electrode material layer disposed on the current collector, the positive electrode material layer including the battery positive electrode material according to the present application. In some embodiments of the present application, the preparation of the positive electrode material layer may include mixing a battery positive electrode material, a conductive agent, a binder, and a solvent to form a positive electrode paste, applying the positive electrode paste, and drying the positive electrode paste to obtain the positive electrode material layer. When preparing the positive electrode paste, the binder and the solvent are mixed and stirred thoroughly, followed by adding the conductive agent, stirring, adding the battery positive electrode material, stirring, and sieving to obtain the positive electrode paste. The conductive agent, binder, and solvent are commonly selected in the battery field. For example, the binder may be one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin, sodium carboxymethyl cellulose (CMC), and sodium alginate. The conductive agent may be one or more selected from carbon nanotubes, carbon black, and graphene.

[0055] The secondary battery according to the present application includes a positive electrode, a negative electrode, an electrolyte, and a separator located between the positive electrode and the negative electrode, and the positive electrode includes the positive electrode plate according to the present application.

[0056] In the present application, the negative electrode of the secondary battery may be any negative electrode known in the art. In some embodiments of the present application, the negative electrode may include one or more of a carbon-based negative electrode, a silicon-based negative electrode, a tin-based negative electrode, and a lithium negative electrode. The carbon-based negative electrode may include graphite, hard carbon, soft carbon, graphene, etc. The silicon-based negative electrode may include silicon, silicon carbide, silicon oxide, a silicon metal compound, etc. The tin-based negative electrode may include tin, tin carbide, tin oxide, or a tin metal compound. The lithium negative electrode may include metallic lithium or a lithium alloy. Specifically, the lithium alloy may be at least one of a lithium-silicon alloy, a lithium-sodium alloy, a lithium-potassium alloy, a lithium-aluminum alloy, a lithium-tin alloy, and a lithium-indium alloy. In some embodiments of the present application, the negative electrode current collector is copper foil, the negative electrode active material includes one or more of natural graphite, artificial graphite, hard carbon, soft carbon, lithium titanate, iron trioxide, lithium titanium phosphate, titanium dioxide, silicon, silicon monoxide, tin, and antimony, the binder includes one or more of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR), and the conductive agent includes one or more of acetylene black, Ketjen black, Super-P, carbon nanotubes, carbon nanofibers, activated carbon, and graphene. In the present application, any method known in the art may be used to manufacture the negative electrode.

[0057] In the present application, the separator of the secondary battery may be any separator known to those skilled in the art, for example, the separator may be one or more of a polyolefin microporous membrane, polyethylene terephthalate, polyethylene felt, glass mat, or ultrafine glass fiber paper.

[0058] In the present application, the electrolyte of the secondary battery includes a solution in which an electrolyte lithium salt is dissolved in a non-aqueous solvent. In some embodiments, the electrolyte lithium salt includes one or more of lithium hexafluorophosphate (LiPF), lithium perchlorate (LiClO), lithium tetrafluoroborate (LiBF), lithium hexafluoroarsenate (LiAsF), lithium silicofluoride (LiSiF), lithium tetraphenylborate (LiB(CH)), lithium chloride (LiCl), lithium bromide (LiBr), lithium tetrachloroaluminate (LiAlCl), lithium fluorohydrocarbonylsulfonate (LiC(SOCF)), LiCHSO, LiN(SOCF), and LiN(SOCF) . In some embodiments, the non-aqueous solvent includes one or more of a chain acid ester and a cyclic acid ester. In some embodiments of the present application, the chain acid ester includes one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and dipropyl carbonate (DPC). In some embodiments of the present application, the chain acid ester includes chain organic esters containing fluorine, sulfur, or an unsaturated bond. In some embodiments of the present application, the cyclic acid ester includes one or more of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), γ-butyrolactone (γ-BL), and sultone. In some embodiments of the present application, the cyclic acid ester includes a cyclic organic ester containing fluorine, sulfur, or an unsaturated bond. In some embodiments of the present application, the non-aqueous solvent includes one or more of a chain ether and a cyclic ether solution. In some embodiments of the present application, the cyclic ether comprises one or more of tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane (DOL), and 4-methyl-1,3-dioxolane (4-MeDOL). In some embodiments of the present application, the cyclic ether comprises a cyclic organic ether containing fluorine, sulfur, or an unsaturated bond.In some embodiments of the present application, the chain ether includes one or more of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), 1,2-dimethoxypropane (DMP), and diglyme (DG). In some embodiments of the present application, the chain ether includes a chain organic ether containing fluorine, sulfur, or an unsaturated bond. In some embodiments of the present application, the concentration of the electrolyte lithium salt in the electrolyte solution is 0.1 mol / L to 15 mol / L. In some embodiments of the present application, the concentration of the electrolyte lithium salt is 1 mol / L to 10 mol / L.

[0059] In some embodiments of the present application, the battery can be manufactured using either a layer-by-layer process or a winding process. In some examples of the present application, the battery is manufactured using a layer-by-layer process.

[0060] The secondary battery according to the present application has high cycle characteristics and safety because it uses the battery positive electrode plate according to the present application.

[0061] The technical solution of the present application will be further explained below with reference to several examples. [Example]

[0062] In the method for producing a battery positive electrode material, the battery positive electrode material has a structure in order from the inside to the outside of LiMn 0.2 Fe 0.8 PO4(30%) / LiMn 0.8 Fe 0.2 PO4(60%) / LiFePO4(10%) / C, and its general composition formula is LiMn 0.54 Fe 0.46 PO4 / C. The battery positive electrode active material in the battery positive electrode material is LiMn 0.2 Fe 0.8 PO4, LiMn 0.8 Fe 0.2 PO4 and LiFePO4. LiMn 0.2 Fe 0.8 PO4 (30%), LiMn 0.2 Fe 0.8LiFePO4 (10%) indicates that the mass percentage of LiFePO4 in the battery positive electrode active material is 10%.

[0063] 1) LiMn 0.2 Fe 0.8 PO4 Core Manufacturing Lithium carbonate, iron (II) acetate, manganese acetate, and phosphoric acid were weighed in a stoichiometric ratio and dissolved in water to obtain a mixed solution. The mixed solution was then placed in a high-pressure reactor, and argon gas was introduced into the reactor to maintain an inert atmosphere. The temperature was raised to 380°C under stirring, and the pressure in the reactor was set to 24 MPa. After reacting for 1 hour, the precipitate was collected, washed with water and ethanol, and dried to obtain LiMn 0.2 Fe 0.8 Obtain a PO4 core.

[0064] 2) LiMn 0.8 Fe 0.2 PO4 first shell layer production Lithium carbonate, iron (II) acetate, manganese acetate and phosphoric acid were weighed and dissolved in water in a stoichiometric ratio to obtain a mixed solution, which was then placed in a high-pressure reactor to form LiMn 0.2 Fe 0.8 PO4 core was added, argon gas was introduced into the high-pressure reactor to maintain an inert atmosphere, the temperature was raised to 380°C under stirring, the pressure in the reactor was set to 24 MPa, and the reaction was carried out for 1 hour. After that, the precipitate was collected, washed with water and ethanol, and dried to obtain the core-shell structured LiMn 0.2 Fe 0.8 PO4 / LiMn 0.8 Fe 0.2 Obtain PO4.

[0065] 3) Manufacturing the second shell layer Lithium carbonate, iron (II) acetate, glucose, and phosphoric acid were weighed and dissolved in water in a stoichiometric ratio to obtain a mixed solution, which was then placed in a high-pressure reactor to form a core-shell structured LiMn 0.2 Fe 0.8 PO4 / LiMn 0.8 Fe 0.2PO4 was added, and argon gas was introduced into the high-pressure reactor to maintain an inert atmosphere. The temperature was raised to 380°C while stirring, and the pressure in the reactor was set to 24 MPa. After reacting for 1 hour, the precipitate was collected, washed with water and ethanol, and dried. The product was then calcined at 700°C for 5 hours to obtain the battery positive electrode material LiMn 0.2 Fe 0.8 PO4(30%) / LiMn 0.8 Fe 0.2 PO4(60%) / LiFePO4(10%) / C is obtained.

[0066] 4) Secondary battery manufacturing The resulting battery positive electrode material, conductive agent, and binder were dispersed in N-methylpyrrolidone in a mass ratio of 90:5:5, with the conductive agent being carbon black and carbon nanotubes, the binder being PVDF5130, and the paste having a solid content of 50%. The paste was applied to the surface of aluminum foil and dried, then cut into 61mm x 72mm positive electrode plates, which were then assembled with a separator and graphite negative electrode to obtain a battery. [Example]

[0067] Example 2 differs from Example 1 in that the mass ratio of the core to the first shell layer is different. The battery positive electrode material of Example 2 has a structure of LiMn 0.2 Fe 0.8 PO4(10%) / LiMn 0.8 Fe 0.2 PO4(80%) / LiFePO4(10%) / C, and its general composition formula is LiMn 0.66 Fe 0.34 PO4 / C. The battery positive electrode active material in the battery positive electrode material is LiMn 0.2 Fe 0.8 PO4, LiMn 0.8 Fe 0.2 PO4 and LiFePO4. LiMn 0.2 Fe 0.8 The mass percentage of PO4 in the battery positive electrode active material is 10%, and LiMn 0.8 Fe 0.2 The mass percentage of PO4 in the battery positive electrode active material is 80%. The battery is manufactured using the same method as in Example 1. [Example]

[0068] Example 3 differs from Example 1 in that the mass ratio of the core to the first shell layer is different. The battery positive electrode material of Example 3 has a structure of LiMn 0.2 Fe 0.8 PO4(40%) / LiMn 0.8 Fe 0.2 PO4(45%) / LiFePO4(15%) / C, and its general composition formula is LiMn 0.44 Fe 0.56 PO4 / C. The battery positive electrode active material in the battery positive electrode material is LiMn 0.2 Fe 0.8 PO4, LiMn 0.8 Fe 0.2 PO4 and LiFePO4. LiMn 0.2 Fe 0.8 The mass percentage of PO4 in the battery positive electrode active material is 40%, and LiMn 0.8 Fe 0.2 The mass percentage of PO4 in the battery positive electrode active material is 45%. The battery is manufactured using the same method as in Example 1. [Example]

[0069] Example 4 differs from Example 1 in that the mass ratio of the core to the first shell layer is different. The battery positive electrode material of Example 4 has a structure of LiMn 0.2 Fe 0.8 PO4(10%) / LiMn 0.8 Fe 0.2 PO4(75%) / LiFePO4(15%) / C, and its general composition formula is LiMn 0.62 Fe 0.38 PO4 / C. The battery positive electrode active material in the battery positive electrode material is LiMn 0.2 Fe 0.8 PO4, LiMn 0.8 Fe 0.2 PO4 and LiFePO4. LiMn 0.2 Fe 0.8 The mass percentage of PO4 in the battery positive electrode active material is 10%, and LiMn 0.8 Fe 0.2The mass percentage of PO4 in the battery positive electrode active material is 75%. The battery is manufactured using the same method as in Example 1. [Example]

[0070] Example 5 differs from Example 1 in that the mass ratio of the core to the first shell layer is different. The battery positive electrode material of Example 5 has a structure of LiMn 0.2 Fe 0.8 PO4(20%) / LiMn 0.8 Fe 0.2 PO4(70%) / LiFePO4(10%) / C, and its general composition formula is LiMn 0.6 Fe 0.4 PO4 / C. The battery positive electrode active material in the battery positive electrode material is LiMn 0.2 Fe 0.8 PO4, LiMn 0.8 Fe 0.2 PO4 and LiFePO4. LiMn 0.2 Fe 0.8 The mass percentage of PO4 in the battery positive electrode active material is 20%, and LiMn 0.8 Fe 0.2 The mass percentage of PO4 in the battery positive electrode active material is 70%. The battery is manufactured using the same method as in Example 1. [Example]

[0071] Example 6 differs from Example 5 in that the core components are different. The battery cathode material of Example 6 has a structure of LiMn 0.4 Fe 0.6 PO4(20%) / LiMn 0.8 Fe 0.2 PO4(70%) / LiFePO4(10%) / C, and its general composition formula is LiMn 0.64 Fe 0.36 PO4 / C. The battery positive electrode active material in the battery positive electrode material is LiMn 0.4 Fe 0.6 PO4, LiMn 0.8 Fe 0.2 PO4 and LiFePO4. LiMn 0.4 Fe 0.6 The mass percentage of PO4 in the battery positive electrode active material is 20%, and LiMn0.8 Fe 0.2 The mass percentage of PO4 in the battery positive electrode active material is 70%. The battery is manufactured using the same method as in Example 1. [Example]

[0072] Example 7 differs from Example 5 in that the components of the first shell layer are different. The battery positive electrode material of Example 7 has a structure of LiMn 0.2 Fe 0.8 PO4(20%) / LiMn 0.9 Fe 0.1 PO4(70%) / LiFePO4(10%) / C, and its general composition formula is LiMn 0.67 Fe 0.33 PO4 / C. The battery positive electrode active material in the battery positive electrode material is LiMn 0.2 Fe 0.8 PO4, LiMn 0.9 Fe 0.1 PO4 and LiFePO4. LiMn 0.2 Fe 0.8 The mass percentage of PO4 in the battery positive electrode active material is 20%, and LiMn 0.9 Fe 0.1 The mass percentage of PO4 in the battery positive electrode active material is 70%. The battery is manufactured using the same method as in Example 1. [Example]

[0073] Example 8 differs from Example 5 in that the components of the first shell layer are different. The battery positive electrode material of Example 8 has a structure of LiMn 0.2 Fe 0.8 PO4(20%) / LiMn 0.6 Fe 0.4 PO4(70%) / LiFePO4(10%) / C, and its general composition formula is LiMn 0.56 Fe 0.44 PO4 / C. The battery positive electrode active material in the battery positive electrode material is LiMn 0.2 Fe 0.8 PO4, LiMn 0.6 Fe 0.4 PO4 and LiFePO4. LiMn 0.2 Fe 0.8The mass percentage of PO4 in the battery positive electrode active material is 20%, and LiMn 0.6 Fe 0.4 The mass percentage of PO4 in the battery positive electrode active material is 70%. The battery is manufactured using the same method as in Example 1. [Example]

[0074] Example 9 differs from Example 5 in that the components of the core and the first shell layer are different. The battery positive electrode material of Example 9 is doped with Co in the core and the first shell layer, and the structure is LiMn 0.19 Fe 0.8 Co 0.01 PO4(20%) / LiMn 0.79 Fe 0.2 Co 0.01 PO4(70%) / LiFePO4(10%) / C, and its general composition formula is LiMn 0.591 Fe 0.40 Co 0.009 PO4 / C. The battery positive electrode active material in the battery positive electrode material is LiMn 0.19 Fe 0.8 Co 0.01 PO4, LiMn 0.79 Fe 0.2 Co 0.01 PO4 and LiFePO4.

[0075] The method for producing the battery positive electrode material in Example 9 includes the following steps 1) and 2).

[0076] 1) LiMn 0.19 Fe 0.8 Co 0.01 PO4 Core Manufacturing Lithium carbonate, iron (II) acetate, manganese acetate, cobalt acetate, and phosphoric acid were weighed in a stoichiometric ratio and dissolved in water to obtain a mixed solution. The mixed solution was then placed in a high-pressure reactor, and argon gas was introduced into the reactor to maintain an inert atmosphere. The temperature was raised to 380°C under stirring, and the pressure in the reactor was set to 24 MPa. After reacting for 1 hour, the precipitate was collected, washed with water and ethanol, and dried to obtain LiMn 0.19 Fe 0.8 Co 0.01Obtain a PO4 core.

[0077] 2) LiMn 0.79 Fe 0.2 Co 0.01 PO4 first shell layer production Lithium carbonate, iron (II) acetate, manganese acetate, cobalt acetate and phosphoric acid were weighed in a stoichiometric ratio and dissolved in water to obtain a mixed solution. The mixed solution was then placed in a high-pressure reactor to prepare LiMn 0.19 Fe 0.8 Co 0.01 PO4 core was added, argon gas was introduced into the high-pressure reactor to maintain an inert atmosphere, the temperature was raised to 380°C under stirring, the pressure in the reactor was set to 24 MPa, and the reaction was carried out for 1 hour. After that, the precipitate was collected, washed with water and ethanol, and dried to obtain the core-shell structured LiMn 0.19 Fe 0.8 Co 0.01 PO4 / LiMn 0.79 Fe 0.2 Co 0.01 Obtain PO4.

[0078] The same method as in Example 5 is used to prepare the second shell layer and the battery. [Example]

[0079] Example 10 differs from Example 5 in that the second shell layer does not contain LiFePO4, and the battery cathode material of Example 10 has a structure of LiMn 0.2 Fe 0.8 PO4(25%) / LiMn 0.8 Fe 0.2 PO4 (75%) / C, and its general composition formula is LiMn 0.65 Fe 0.35 PO4 / C. The battery positive electrode active material in the battery positive electrode material is LiMn 0.2 Fe 0.8 PO4 and LiMn 0.8 Fe 0.2 PO4. The same method as in Example 1 is used to prepare the battery. [Example]

[0080] Example 11 differs from Example 5 in that the mass percentage of each layer is different. The battery cathode material of Example 11 has a structure of LiMn 0.2 Fe 0.8 PO4(20%) / LiMn 0.8 Fe 0.2 PO4(75%) / LiFePO4(5%) / C, and its general composition formula is LiMn 0.64 Fe 0.36 PO4 / C. The battery positive electrode active material in the battery positive electrode material is LiMn 0.2 Fe 0.8 PO4, LiMn 0.8 Fe 0.2 PO4 and LiFePO4. The same method as in Example 1 is used to fabricate the battery. [Example]

[0081] Example 12 differs from Example 1 in that the mass ratio of the core to the first shell layer is different. The positive electrode material of Example 12 has a structure of LiMn 0.2 Fe 0.8 PO4(60%) / LiMn 0.8 Fe 0.2 PO4(30%) / LiFePO4(10%) / C, and its general composition formula is LiMn 0.36 Fe 0.64 PO4 / C. The battery positive electrode active material in the battery positive electrode material is LiMn 0.2 Fe 0.8 PO4, LiMn 0.8 Fe 0.2 PO4 and LiFePO4. LiMn 0.2 Fe 0.8 The mass percentage of PO4 in the battery positive electrode active material is 60%, and LiMn 0.8 Fe 0.2 The mass percentage of PO4 in the battery positive electrode active material is 30%. The battery is manufactured using the same method as in Example 1. (Comparative Example 1)

[0082] Comparative Example 1 and Example 1 differ in that the structure of the positive electrode material is different. The positive electrode material of Comparative Example 1 has a structure of LiMn 0.8 Fe 0.2 PO4(70%) / LiMn 0.2Fe 0.8 PO4(20%) / LiFePO4(10%) / C, and its general composition formula is LiMn 0.6 Fe 0.3 PO4 / C. The same method as in Example 1 is used to prepare the battery. (Comparative Example 2)

[0083] Comparative Example 2 differs from Example 1 in that the cathode material of Comparative Example 2 is produced by a hydrothermal method. The method for producing the cathode material of Comparative Example 2 is as follows: Lithium carbonate, iron (II) acetate, manganese acetate, and phosphoric acid were weighed in a stoichiometric ratio and dissolved in water to obtain a mixed solution. The mixed solution was then placed in a hydrothermal reactor, argon gas was introduced into the reactor to maintain an inert atmosphere, and the temperature was raised to 175°C under stirring. After 8 hours of reaction, the precipitate was collected, washed with water and ethanol, and dried to obtain LiMn 0.2 Fe 0.8 Obtaining the PO4 core, Lithium carbonate, iron (II) acetate, manganese acetate and phosphoric acid were weighed and dissolved in water in a stoichiometric ratio to obtain a mixed solution, which was then placed in a hydrothermal reactor to form LiMn 0.2 Fe 0.8 After adding PO4 cores, argon gas was introduced into the hydrothermal reactor to maintain an inert atmosphere, and the temperature was raised to 175°C with stirring. After reacting for 8 hours, the precipitate was collected, washed with water and ethanol, and dried to obtain the core-shell structured LiMn 0.2 Fe 0.8 PO4 / LiMn 0.8 Fe 0.2 Obtaining PO4, Lithium carbonate, iron (II) acetate, glucose, and phosphoric acid were weighed and dissolved in water in a stoichiometric ratio to obtain a mixed solution, which was then placed in a hydrothermal reactor to form a core-shell structured LiMn 0.2 Fe 0.8 PO4 / LiMn 0.8 Fe 0.2PO4 was added, and argon gas was introduced into the hydrothermal reactor to maintain an inert atmosphere. The temperature was raised to 175°C while stirring, and the reaction was carried out for 6.5 hours. The precipitate was collected, washed with water and ethanol, and dried. The product was then calcined at 720°C for 7 hours to obtain the battery cathode material LiMn 0.2 Fe 0.8 PO4(30%) / LiMn 0.8 Fe 0.2 The aim is to obtain PO4 (60%) / LiFePO4 (10%) / C. Although the elements and total contents of the material prepared in Comparative Example 2 are the same as those in Example 1, the shell layer and core layer intermingle to form a transition structure, which prevents the expected design structure from being realized and results in no significant improvement in the transport of electrons and ions in the material. The same method as in Example 1 is used to prepare the battery. (Comparative Example 3)

[0084] Comparative Example 3 and Example 5 differ in that the components of the first shell layer are different. The positive electrode material of Comparative Example 3 has a structure of LiMn 0.2 Fe 0.8 PO4(20%) / LiMn 0.5 Fe 0.5 PO4(70%) / LiFePO4(10%) / C, and its general composition formula is LiMn 0.39 Fe 0.61 PO4 / C. LiMn 0.2 Fe 0.8 The mass percentage of PO4 in the battery positive electrode active material is 20%, and LiMn 0.5 Fe 0.5 The mass percentage of PO4 in the battery positive electrode active material is 70%. The battery is manufactured using the same method as in Example 5.

[0085] Example of comparative effects In order to verify the properties of the battery positive electrode material prepared according to the present application, the present application further provides an effect comparison example.

[0086] 1) The electrochemical characteristics of the batteries in Examples 1 to 12 and Comparative Examples 1 to 3 were measured. At 25°C, the batteries in Examples 1 to 12 and Comparative Examples 1 to 3 were charged at a constant current and constant voltage of 0.1 C in a voltage measurement range of 2.8 to 4.3 V. The off-current was 0.02 C, and the batteries were discharged at a constant current of 0.1 C. The initial charge capacity and discharge capacity were recorded, and the battery parameters were calculated using the formulas: specific discharge capacity = initial discharge capacity of battery (milliampere-hours) / weight of positive electrode material (grams), and energy density = specific discharge capacity (mAh / g) × average discharge voltage (V). The measurement results are shown in Table 2.

[0087] Table 2: Electrochemical characteristic parameters of the batteries in Examples 1 to 12 and Comparative Examples 1 to 3 [Table 2]

[0088] The first shell layer in Example 1 of the present application is LiMn 0.8 Fe 0.2 PO4 and LiMn 0.8 Fe 0.2 The mass percentage of PO4 in the battery positive electrode material is 60%, and LiMn 0.2 Fe 0.8 The mass percentage of PO4 is 30%, and due to this structural distribution, the battery positive electrode material has high conductivity, and therefore the battery has high rate capability. 0.8 Fe 0.2 The mass percentage of PO4 in the battery cathode material is 80%, so the battery has a high energy density, but the LiMn 0.8 Fe 0.2 The PO4 layer is thicker than in Example 1, so the rate characteristics are poor. 0.8 Fe 0.2 Since the mass percentage of PO4 in the battery positive electrode material is 45%, the battery has a high energy density, and its rate characteristics are higher than those of Example 1. In Example 4, the mass percentage of the second shell layer in the battery positive electrode material is 15%, and LiMn 0.8 Fe 0.2The mass percentage of PO4 is 75%, and the whole material has a higher energy density than Example 1. 0.8 Fe 0.2 The mass percentage of PO4 is 70%, and the rate characteristics are similar to those of Example 1. The core components in Example 6 are LiMn 0.4 Fe 0.6 PO4, and compared to Example 5, Example 6 has a higher energy density and its rate characteristics are also relatively low. The first shell layer in Example 7 is LiMn 0.9 Fe 0.1 PO4, and due to the high manganese content, the battery has a higher energy density but its rate capability is poor. 0.6 Fe 0.4 PO4, and its manganese content is lower than that of Example 5, so its rate characteristics are high and its energy density is low. The battery positive electrode material in Example 9 is doped with Co element, and the battery in Example 9 has higher rate characteristics than that of Example 5. The second shell layer in Example 10 does not contain LiFePO4, and the content of the first shell layer is high, so it has high energy density, but the content of the second shell layer is low, so it is less effective in suppressing the manganese dissolution problem, so the battery has low cycle characteristics. The second shell layer in Example 11 contains a certain amount of LiFePO4, and the battery has better cycle characteristics than that of Example 10. LiMn in Example 12 0.8 Fe 0.2 The mass percentage of PO4 in the battery positive electrode material is 30%, and the energy density of the battery is relatively low.

[0089] LiMn in Comparative Example 1 0.8 Fe 0.2PO4 is the core of the material, and its general composition formula is similar to that of Example 5, but its rate characteristics are much lower than that of Example 5. In Comparative Example 2, the positive electrode material was prepared using a hydrothermal method. The material prepared by the hydrothermal method has low crystallinity, so the shell layer and the core intermingle with each other during the subsequent firing process, forming a transition structure, which results in unclear layer separation in the material, making it impossible to achieve the expected designed structure, and resulting in no significant improvement in the transport of electrons and ions in the material. In Comparative Example 3, the first shell layer is LiMn 0.5 Fe 0.5 PO4, its manganese content is low, and the battery energy density is low.

[0090] The above are embodiments of the present application, but they should not be understood as limiting the scope of the present application. It should be noted that those skilled in the art can make some improvements and modifications without departing from the principles of the present application, and these improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A battery positive electrode material comprising a core (10) and a first shell layer (20) formed on the surface of the core (10), The core (10) is LiMn ｘ Fe １－ｘ P.O. ４ and the first shell layer (20) comprises LiMn ｙ Fe １－ｙ P.O. ４ where 0<x≦0.4 and 0.6≦y≦0.9; A battery positive electrode material characterized in that the mass ratio of the core (10) to the first shell layer (20) is 1:(1.5 to 9).

2. A battery positive electrode material comprising a core (10) and a first shell layer (20) formed on the surface of the core (10), the core (10) comprises LiMn x Fe 1-x PO 4 , the first shell layer (20) comprises LiMn y Fe 1-y PO 4 , where 0<x≦0.4 and 0.6≦y≦0.9; The battery positive electrode material is characterized in that the diameter of the core (10) is 0.5 μm to 5 μm.

3. 2. The battery cathode material according to claim 1, wherein the thickness of the first shell layer (20) is 0.09 μm to 2.7 μm.

4. A battery positive electrode material comprising a core (10) and a first shell layer (20) formed on the surface of the core (10), the core (10) comprises LiMn x Fe 1-x PO 4 , the first shell layer (20) comprises LiMn y Fe 1-y PO 4 , where 0<x≦0.4 and 0.6≦y≦0.9; In the battery positive electrode material, a molar ratio of Fe element to Mn element is 1:(1 to 9).

5. A second shell layer is further formed on the surface of the first shell layer (20), and the second shell layer is LiFePO ４ and carbon.

6. The battery positive electrode material according to claim 5, wherein the thickness of the second shell layer is 20 nm to 600 nm.

7. A battery positive electrode material comprising a core (10) and a first shell layer (20) formed on the surface of the core (10), the core (10) comprises LiMn x Fe 1-x PO 4 , the first shell layer (20) comprises LiMn y Fe 1-y PO 4 , where 0<x≦0.4 and 0.6≦y≦0.9; A second shell layer is further formed on the surface of the first shell layer (20), and the second shell layer includes LiFePO 4 and carbon; In the battery positive electrode material, the mass percentage of the core (10) is 10% to 40%, the mass percentage of the first shell layer (20) is 45% to 80%, and the mass percentage of the second shell layer is 10% to 20%.

8. A battery positive electrode material comprising a core (10) and a first shell layer (20) formed on the surface of the core (10), the core (10) comprises LiMn x Fe 1-x PO 4 , the first shell layer (20) comprises LiMn y Fe 1-y PO 4 , where 0<x≦0.4 and 0.6≦y≦0.9; 1. A battery positive electrode material, further comprising a doping element, the doping element comprising one or more of Ti, V, Co, Ni, Cu, Zn, Mg, Al, Ca, Mo, and W, and a mass percentage of the doping element in the battery positive electrode material is 0.1% to 0.5%.

9. 9. The battery cathode material of claim 8, wherein the first shell layer (20) comprises the doping element.

10. A battery positive electrode material comprising a core (10) and a first shell layer (20) formed on the surface of the core (10), the core (10) comprises LiMn x Fe 1-x PO 4 , the first shell layer (20) comprises LiMn y Fe 1-y PO 4 , where 0<x≦0.4 and 0.6≦y≦0.9; A second shell layer is further formed on the surface of the first shell layer (20), and the second shell layer includes LiFePO 4 and carbon; A battery positive electrode material, characterized in that the mass percentage of the carbon in the battery positive electrode material is 1% to 3%.

11. A method for producing a battery positive electrode material, comprising: A step of carrying out a first reaction by placing a lithium source, an iron source, a manganese source, a phosphorus source and a solvent in a reaction vessel to obtain a core (10), wherein the core (10) is LiMn ｘ Fe １－ｘ P.O. ４ wherein 0<x≦0.4, and the first reaction is carried out at a temperature of 375° C. to 500° C. and a pressure of 23 MPa or more; A step of placing a lithium source, an iron source, a manganese source, a phosphorus source, a solvent, and the core (10) in a reaction vessel to carry out a second reaction, thereby coating a first shell layer (20) on the surface of the core (10) to obtain a core (10) having the first shell layer (20) formed thereon, wherein the first shell layer (20) is LiMn ｙ Fe １－ｙ P.O. ４ wherein 0.6≦y≦0.9, and the second reaction is carried out at a temperature of 375° C. to 500° C. and a pressure of 23 MPa or more; and a step of firing the core (10) on which the first shell layer (20) is formed at 500°C to 800°C to obtain the battery positive electrode material.

12. Before firing the core (10) on which the first shell layer (20) is formed, a third reaction is carried out by placing a lithium source, an iron source, a phosphorus source, a carbon source, a solvent, and the core (10) on which the first shell layer (20) is formed in a reaction vessel, thereby coating a second shell layer on the surface of the first shell layer (20), wherein the second shell layer is LiFePO ４ and carbon, and the third reaction is carried out at a temperature of 375° C. to 500° C. and at a pressure of 23 MPa or more.

13. 13. The method of claim 11 or 12, wherein the lithium source comprises an inorganic lithium salt and / or an organic lithium salt, the inorganic lithium salt comprising one or more of lithium carbonate, lithium bicarbonate, lithium dihydrogen phosphate, lithium monohydrogen phosphate, lithium phosphate, lithium nitrate, lithium sulfate, lithium chromate, and lithium hydroxide, and the organic lithium salt comprising one or more of lithium oxalate, lithium acetate, lithium benzoate, and lithium citrate.

14. The manufacturing method described in claim 11 or 12, characterized in that the iron source includes one or more of iron oxide, iron carbonate, iron oxalate, iron sulfate, iron chloride and iron acetate.

15. 12. The method of claim 11, wherein the manganese source comprises one or more of manganese monoxide, manganese dioxide, manganese hydroxide, manganese carbonate, manganese oxalate, manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate.

16. 13. The method of claim 11 or 12, wherein the phosphorus source comprises one or more of phosphoric acid, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, and lithium dihydrogen phosphate.

17. 13. The method of claim 12, wherein the carbon source comprises one or more of glucose, sucrose, polyvinyl alcohol, starch, and citric acid.

18. 13. The manufacturing method according to claim 11 or 12, wherein the firing is carried out in an inert atmosphere, and the inert atmosphere contains one or more of nitrogen gas, argon gas, helium gas, neon gas, krypton gas, xenon gas, and radon gas.

19. 11. A secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode comprises a positive electrode plate, the positive electrode plate comprises a current collector and a positive electrode material layer disposed on the current collector, and the positive electrode material layer comprises the battery positive electrode material according to any one of claims 1 to 10.

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