Manganese iron lithium phosphate composite cathode material and method for manufacturing the same, cathode sheet, secondary battery

Abstract

The present invention provides a manganese iron lithium phosphate-based composite cathode material, a method for manufacturing the same, a cathode sheet, and a secondary battery. [Solution] The manganese iron lithium phosphate composite cathode material contains component A and component B. Component A is a manganese iron lithium phosphate material co-doped with Ni / Ti, and the chemical formula of the material is LiMn 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti y The compound is PO4, where 0 ≤ x ≤ 0.05 and 0 ≤ y ≤ 0.05. Component B contains amorphous carbon. [Effects] The Ni+Ti co-doping strategy adopted in this invention effectively mitigates problems such as energy density and capacity decay in lithium manganese iron phosphate cathode materials, allowing lithium manganese iron phosphate to better demonstrate its clear advantages of high energy density, good safety, and low cost, which is advantageous for improving the capacity and cycle stability of lithium manganese iron phosphate batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of battery active materials, and particularly relates to a lithium iron manganese phosphate-based composite cathode material, a manufacturing method thereof, a cathode sheet, and a secondary battery.

Background Art

[0002] As people put forward higher requirements for the energy density, safety performance and cost control of lithium-ion batteries, the cathode material, as a main component of lithium-ion batteries, has also attracted much attention for its development status. Lithium iron phosphate has advantages such as good safety, low cost, and environmental friendliness, but its plateau voltage is low (~3.4 V) and its energy density is low (580 Wh / kg). The ternary cathode materials of nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) have high energy density, but their development is also restricted by the disadvantages of high cost and poor safety. In comparison, the 4.1 V voltage plateau of lithium iron manganese phosphate provides a higher energy density than lithium iron phosphate, the stable phosphate group provides better safety performance than NCM or NCA ternary cathode materials, and moreover, the cost is lower than that of ternary cathode materials using nickel-cobalt. Summing up the above, the lithium iron manganese phosphate cathode material is expected to become a competitive lithium-ion battery cathode material due to its high energy density, high safety and low cost.

[0003] However, the stable phosphate group in the lithium iron manganese phosphate cathode material guarantees thermodynamic stability, but also causes inhibition of metal ion transport, resulting in a low intrinsic electrical conductivity of the material. Mn in the lithium iron manganese phosphate cathode material 3+ has the Jahn-Teller effect, and the Mn elution in the cycling process causes capacity decay in the cycling process. Furthermore, the Mn plateau voltage decay of the lithium iron manganese phosphate cathode material causes energy density decay, which is also one of the problems that need to be solved urgently for the lithium iron manganese phosphate cathode material.

Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the object of the present invention is to provide a manganese iron lithium phosphate-based composite cathode material, an electrode sheet, and a method for manufacturing the same, thereby enhancing the structural stability and conductivity of the manganese iron lithium phosphate cathode material and improving the capacity and cycle stability of the manganese iron lithium phosphate battery. [Means for solving the problem]

[0005] To achieve the above-mentioned and other related objectives, the present invention provides a manganese iron lithium phosphate composite cathode material comprising component A and component B. Component A is a Ni / Ti co-doped manganese iron lithium phosphate material, and the chemical formula of the Ni / Ti co-doped manganese iron lithium phosphate material is LiMn 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti y The compound is PO4, where 0 ≤ x ≤ 0.05 and 0 ≤ y ≤ 0.05. Component B contains amorphous carbon.

[0006] Furthermore, in the Ni / Ti co-doped manganese iron lithium phosphate material, the ratio of the sum of the molar contents of Ni and Ti to the sum of the molar contents of Mn and Fe is 0.06-0.08:0.92-0.94.

[0007] Furthermore, in the aforementioned Ni / Ti co-doped manganese iron lithium phosphate material, the molar ratio of Ni to Ti elements is 1:1 to 1.6.

[0008] Furthermore, component B coats component A as a network-like thin film.

[0009] Furthermore, in the manganese iron lithium phosphate composite cathode material, the mass percentage of component B is 1% to 2.5%.

[0010] The present invention also provides a method for producing a manganese iron lithium phosphate-based composite cathode material, and the method for producing a manganese iron lithium phosphate-based composite cathode material is A slurry is prepared by mixing a lithium source, a manganese source, an iron source, a nickel source, a titanium source, a phosphorus source, and a carbon source, wherein the molar ratio of elements Li, Mn, Fe, Ni, Ti, and P in the slurry is Li:Mn:Fe:Ni:Ti:P = 1.05:0.6(1-xy):0.4(1-xy):x:y:1, The steps include drying the slurry and then sintering it to produce the manganese iron lithium phosphate composite cathode material, Includes.

[0011] Furthermore, in the slurry, the mass of the carbon source is 8% to 12% of the total mass of the lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source, and carbon source.

[0012] Furthermore, the lithium source is at least one selected from lithium carbonate, lithium hydroxide, lithium acetate, or lithium dihydrogen phosphate.

[0013] Furthermore, the manganese source is at least one selected from manganese oxalate, manganese carbonate, trimanganese tetroxide, manganese phosphate, manganese(II) oxide, or ammonium manganese phosphate.

[0014] Furthermore, the iron source is at least one selected from iron(II) oxalate, iron(II) pyrophosphate, iron phosphate, diferric oxide, or metallic iron.

[0015] Furthermore, the nickel source is at least one selected from nickel oxide, nickel hydroxide, or trinickel tetroxide.

[0016] Furthermore, the titanium source is at least one selected from titanium dioxide, butyl titanate, or metatitanic acid.

[0017] Furthermore, the phosphorus source is at least one selected from iron phosphate, ammonium dihydrogen phosphate, lithium phosphate or lithium dihydrogen phosphate.

[0018] Furthermore, the carbon source is at least one selected from glucose, polyethylene glycol, sucrose, citric acid or graphite.

[0019] Furthermore, sintering is performed under a protective gas atmosphere, the sintering temperature is 650°C to 850°C, and the sintering time is 6h to 12h.

[0020] The present invention further provides a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer on at least one side of the positive electrode current collector, the positive electrode active material layer contains a positive electrode active material, and the positive electrode active material contains the above-mentioned lithium manganese iron phosphate-based composite positive electrode material and / or the lithium manganese iron phosphate-based composite positive electrode material manufactured by the above-mentioned method.

[0021] The present invention further provides a secondary battery including the above-mentioned positive electrode sheet.

Effects of the Invention

[0022] [[ID=Z3]]As described above, the lithium manganese iron phosphate-based composite positive electrode material, electrode sheet and manufacturing method thereof of the present invention have the following advantageous effects. The lithium manganese iron phosphate-based composite positive electrode material LiMn 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti y PO4 / C of the present invention is doped with metal elements Ni and Ti. Ni+Ti co-doping can improve the ion diffusion rate of the material and suppress the phase separation in the cycle process of lithium manganese iron phosphate, thereby effectively reducing the attenuation rate of the Mn plateau. At the same time, the presence of Ni can further increase the crystal structure stability of lithium manganese iron phosphate, which is due to the existence of super-exchange interaction in Ni 2+ -O-Mn 2+ and there is a super-exchange interaction in Mn 3+This is to suppress the change in valence, mitigate the Jahn-Teller effect, and effectively stabilize the crystal structure. This stable crystal structure reduces capacity decay during the lithium-ion battery cycle process, thereby contributing to the maintenance of a relatively high capacity retention rate. Ti doping can reduce particle size because the atomic radius of Ti is smaller than that of Mn and Fe, which can reduce the crystal lattice volume, control particle size, be advantageous for ion transport between particles, and increase the uniformity of Mn and Fe in the material, thereby beneficial for increasing the conductivity of the material. On the other hand, single Ni doping is not clear for particle size control, and single Ti doping is insufficient to stabilize the crystal structure. Therefore, the Ni+Ti co-doping strategy adopted in this invention can effectively mitigate problems such as energy density and capacity decay of the manganese iron lithium phosphate cathode material, thereby allowing manganese iron lithium phosphate to better demonstrate its clear advantages of high energy density, good safety, and low cost, and further is advantageous for improving the capacity and cycle stability of the manganese iron lithium phosphate battery. LiMn provided by the present invention 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti y In PO4 / C, the carbon coating can create a conductive network between particles, thereby improving electronic conductivity. LiMn provided by the present invention 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti y PO4 / C is manufactured by a one-step synthesis method, has a simple manufacturing process, and is applicable to large-scale industrial production. [Brief explanation of the drawing]

[0023] [Figure 1] This is an SEM image of the manganese iron lithium phosphate composite cathode material LiMn0.6Fe0.4Ni0.03Ti0.05PO4 / C manufactured according to Example 2 of the present invention. [Figure 2]This is a 1C charge-discharge curve diagram of a battery prepared using the manganese iron lithium phosphate-based composite cathode material manufactured according to Example 2 and Comparative Examples 1-3 of the present invention. [Modes for carrying out the invention]

[0024] The following describes how the present invention can be implemented through specific examples, but those skilled in the art will readily understand other advantages and effects of the present invention from the contents disclosed herein. The present invention can also be implemented or applied in yet another different specific manner, and the details of each item herein can be modified or changed in various ways based on different perspectives and applications without departing from the spirit of the invention.

[0025] In this invention, unless otherwise stated, the term "plural" means two or more. The character "+" indicates that the preceding and succeeding elements are in an "and" relationship. For example, A+B represents A and B. The character " / " indicates that the preceding and following elements have a kind of "and" or "or" relationship. For example, A / B represents the relationship between A and B, or A or B. The term "and / or" describes the relationship between objects, indicating that three types of relationships are possible. For example, these three types of relationships can be expressed as A and / or B, A or B, or A and B.

[0026] One embodiment of the present invention provides a manganese iron lithium phosphate composite cathode material comprising component A and component B. Component A is a Ni / Ti co-doped manganese iron lithium phosphate material, and the chemical formula of the Ni / Ti co-doped manganese iron lithium phosphate material is LiMn 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti y The compound is PO4, where 0 ≤ x ≤ 0.05 and 0 ≤ y ≤ 0.05. Component B contains amorphous carbon.

[0027] LiMn, a manganese iron lithium phosphate composite cathode material provided by the present invention. 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti y PO4 / C is doped with the metallic elements Ni and Ti, and the Ni and Ti elements are uniformly distributed within the manganese iron lithium phosphate particles. Ni+Ti co-doping can accelerate the ion diffusion rate of the material and suppress phase separation in the cycling process of manganese iron lithium phosphate, thereby effectively reducing the decay rate of the Mn plateau. Specifically, the presence of Ni can further increase the crystalline structure stability of manganese iron lithium phosphate, which is Ni 2+ -O-Mn 2+ A superexchange interaction exists between Mn 3+ This is to suppress the change in valence, mitigate the Jahn-Teller effect, and effectively stabilize the crystal structure. This stable crystal structure reduces capacity decay during the lithium-ion battery cycle process, thereby contributing to the maintenance of a relatively high capacity retention rate. Ti doping can reduce particle size because the atomic radius of Ti is smaller than that of Mn and Fe, which can reduce the crystal lattice volume and control particle size, which is advantageous for ion transport between particles, and also increases the uniformity of Mn and Fe in the material, thereby beneficial for increasing the conductivity of the material. On the other hand, single Ni doping is not clear for particle size control, and single Ti doping is insufficient to stabilize the crystal structure. Therefore, the Ni+Ti co-doping strategy adopted in this invention can effectively mitigate problems such as energy density and capacity decay of the manganese iron lithium phosphate cathode material, thereby allowing manganese iron lithium phosphate to better demonstrate its clear advantages of high energy density, good safety, and low cost, and furthermore, is advantageous for improving the capacity and cycle stability of the manganese iron lithium phosphate battery.

[0028] Furthermore, LiMn provided by the present invention 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti yIn PO4 / C, the carbon coating can create a conductive network between particles, thereby improving electronic conductivity.

[0029] In several examples, the ratio of the sum of the molar contents of Ni and Ti to the sum of the molar contents of Mn and Fe in the Ni / Ti co-doped manganese iron lithium phosphate material is 0.06-0.08:0.92-0.94. A certain amount of Ni+Ti doping is necessary in the manganese iron lithium phosphate material, which allows for a balanced improvement in terms of discharge capacity, capacity retention rate, and other aspects.

[0030] In several examples, the molar ratio of Ni to Ti in the Ni / Ti co-doped manganese iron lithium phosphate material is 1:1 to 1.6. Under the same Ni+Ti doping conditions, a higher Ti doping amount is more advantageous in terms of capacity expression.

[0031] In some embodiments, component B uniformly coats component A as a network-like thin film, and component B uniformly coats the outer layer of component A, thereby further increasing the conductivity of the material.

[0032] In some examples, the mass percentage of component B in the manganese iron lithium phosphate composite cathode material is 1% to 2.5%. X-ray diffraction (XRD) results show that no graphite characteristic peaks appear in the manganese iron lithium phosphate composite cathode material produced by the method of the present invention, explaining that the coating carbon layer exists in the form of amorphous carbon. Therefore, the mass percentage of amorphous carbon in the manganese iron lithium phosphate composite cathode material of the present invention is 1% to 2.5%.

[0033] Another embodiment of the present invention provides a method for producing the manganese iron lithium phosphate-based composite cathode material described above, and the method for producing the manganese iron lithium phosphate-based composite cathode material is A slurry is prepared by mixing a lithium source, a manganese source, an iron source, a nickel source, a titanium source, a phosphorus source, and a carbon source, wherein the molar ratio of elements Li, Mn, Fe, Ni, Ti, and P in the slurry is Li:Mn:Fe:Ni:Ti:P = 1.05:0.6(1-xy):0.4(1-xy):x:y:1. The process includes the step of drying the slurry and then sintering it to produce the manganese iron lithium phosphate composite cathode material.

[0034] LiMn of the present invention 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti y PO4 / C is produced by a one-step synthesis method, making the manufacturing process simple and suitable for large-scale industrial production. The content of each element in the product material can be adjusted by adjusting the raw material input ratio. The content and ratio of each metal element in the product material can be obtained by detecting the content of each metal element using inductively coupled plasma (ICP) measurement. Among these findings, it was discovered that the content of Li in the product material was slightly lower than the input ratio, which is thought to be due to the light mass of Li and the resulting loss of a certain amount of lithium during the roasting process.

[0035] In some embodiments, the mass of the carbon source in the slurry is 8% to 12% of the total mass of the lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source, and carbon source, in order to make the mass ratio of component B in the manufactured manganese iron lithium phosphate-based composite cathode material 1% to 2.5%.

[0036] In some examples, the lithium source is selected from, but is not limited to, at least one of lithium carbonate, lithium hydroxide, lithium acetate, or lithium dihydrogen phosphate. The manganese source is selected from, but is not limited to, at least one of manganese oxalate, manganese carbonate, trimanganese tetroxide, manganese phosphate, manganese(II) oxide, or ammonium manganese phosphate. The iron source is selected from, but is not limited to, at least one of iron(II) oxalate, iron(II) pyrophosphate, iron phosphate, diiryl oxide, or metallic iron. The nickel source is selected from, but is not limited to, at least one of nickel oxide, nickel hydroxide, or trinickel tetroxide. The titanium source is selected from, but is not limited to, at least one of titanium dioxide, butyl titanate, or metatitanic acid. The phosphorus source is selected from, but is not limited to, at least one of iron phosphate, ammonium dihydrogen phosphate, lithium phosphate, or lithium dihydrogen phosphate. The carbon source is selected from, but is not limited to, at least one of glucose, polyethylene glycol (PEG), sucrose, citric acid, or graphite.

[0037] In some embodiments, the slurry is prepared using water as a dispersion medium, and the water includes, but is not limited to, deionized water, pure water, ultrapure water, purified water, etc.

[0038] In some embodiments, the drying method for the slurry is selected from spray drying, but is not limited thereto.

[0039] In some embodiments, sintering is performed under a protective gas atmosphere, with a sintering temperature of 650°C to 850°C and a sintering time of 6 to 12 hours. Here, the protective gas includes, but is not limited to, nitrogen gas, helium gas, and argon gas.

[0040] Another embodiment of the present invention provides a positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer on at least one side of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, the positive electrode active material comprising the manganese iron lithium phosphate composite positive electrode material described above, and / or a manganese iron lithium phosphate composite positive electrode material obtained by the method described above. Compared with conventional manganese iron lithium phosphate materials, the manganese iron lithium phosphate composite positive electrode material provided by the present invention has better structural stability and conductivity, and by using it as a positive electrode active material, the capacity and cycle stability of secondary batteries such as lithium-ion batteries can be improved. Here, the positive electrode current collector is, for example, a foil material formed after surface treatment of nickel, titanium, aluminum, silver, stainless steel, or carbon, and in addition to the foil material, the positive electrode current collector can be used in any one or more of the various forms such as film, mesh, porous, foam, or nonwoven fabric. Here, the thickness of the positive electrode current collector is, for example, 8 μm to 15 μm, and the coating thickness on one side of the positive electrode active material layer is, for example, 20 μm to 100 μm. Furthermore, in one specific embodiment, the positive electrode current collector is, for example, aluminum foil, the thickness of the aluminum foil is, for example, 13 μm, and the coating thickness on one side of the positive electrode active material layer is 50 μm.

[0041] In some embodiments, the positive electrode active material layer includes a positive electrode active material, a binder, and a conductive agent, and the mass ratio of the positive electrode active material, conductive agent, and binder can be, for example, 90-98:1-5:1-5. Here, only the above-mentioned manganese iron lithium phosphate composite positive electrode material can be used as the positive electrode active material, and other materials commonly used as positive electrode active materials can also be added, for example, a material with the chemical formula Li x [Ni y Co z Mn t M (1-y-z-t) ]O 2-δis a material, where M is selected from at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W, Zn, etc., 0.9 < x < 1.1, 0.65 ≤ y < 1.0, 0 ≤ z < 0.5, 0 ≤ t < 0.5, 0 ≤ δ ≤ 0.1, and includes but is not limited to lithium nickel manganese oxide, lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, etc. The binder is selected from any one or more of, for example, polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), ethylene - propylene - diene terpolymer (EPDM), or polyhexafluoropropylene. The conductive agent is selected from any one or more of, for example, conductive carbon black (Super P), acetylene black, carbon nanotubes, and graphene.

[0042] In one specific example, the positive electrode active material is, for example, the manganese iron lithium phosphate composite material described above, the binder is selected from, for example, polyvinylidene fluoride, and the conductive agent is selected from, for example, conductive carbon black. The positive electrode active material, conductive agent, and binder are mixed in, for example, a mass ratio of 90:5:5, then an organic solvent is added, and the system is stirred under the action of a vacuum stirrer until homogeneous to obtain a positive electrode slurry. Here, the organic solvent is selected from, for example, N-methylpyrrolidone (NMP). The positive electrode slurry is uniformly coated onto aluminum foil, dried in an oven, and then a positive electrode sheet is obtained through processes such as cold pressing and slitting. In other examples, the positive electrode sheet may also be obtained by selecting any other method of forming the positive electrode sheet.

[0043] Another embodiment of the present invention provides a secondary battery including the positive electrode sheet described above.

[0044] In some embodiments, the secondary battery may be, but is not limited to, a lithium-ion battery, a sodium-ion battery, a potassium-ion battery, or the like.

[0045] In some embodiments, the secondary battery is a lithium-ion battery and includes an electrolyte, an outer casing, and bare cells installed within the outer casing, the bare cells including the positive electrode sheet, as well as a negative electrode sheet and a separator.

[0046] In one specific embodiment, the manufacturing method of the lithium-ion battery includes the following steps: sequentially stacking a positive electrode sheet, a separator, and a negative electrode sheet, ensuring that a separator is uniformly provided between any positive and negative electrode sheets; obtaining a multilayer laminate by winding; and loading it into the battery casing as a bare cell. Finally, injecting electrolyte into the casing in one or more steps, completely immersing the bare cell in the electrolyte. In other words, injecting electrolyte fills the entire internal space of the battery, completely immersing the positive electrode sheet, separator, and negative electrode sheet in the electrolyte.

[0047] In some embodiments, the negative electrode sheet in the above-described embodiments and / or examples includes a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. Here, the negative electrode current collector is selected from any one of, for example, a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foamed copper current collector, or a stainless steel current collector, etc. The thickness of the negative electrode current collector is, for example, 8 μm to 15 μm, and the single-sided coating thickness of the negative electrode active material layer is, for example, 10 μm to 80 μm. In one specific example, the negative electrode current collector is, for example, a copper foil selected, and the thickness of the copper foil is, for example, 13 μm, and the single-sided coating thickness of the negative electrode active material layer is 50 μm.

[0048] In some embodiments, the negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, a thickener, etc. The mass ratio of the negative electrode active material, the conductive agent, the binder, and the thickener can be, for example, 90 to 96:1 to 2:1 to 3:2 to 5. Here, the negative electrode active material is a compound capable of inserting and desorbing lithium ions, for example, graphite, soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide (SiO x , 0 < x < 2), a silicon carbon compound, or at least one of lithium titanate. The conductive agent is selected from any one or more of, for example, conductive carbon black, acetylene black, ketjen black, carbon nanotubes, and graphene, etc. The binder is selected from any one or more of, for example, polyvinylidene fluoride, polyethylene oxide, polyamide, polypropylene, polyacrylate, polyvinyl ether, polymethyl methacrylate, polyhexafluoropropylene, or styrene butadiene rubber (Polymerized Styrene Butadiene Rubber, SBR), etc. The thickener is selected, for example, carboxymethyl cellulose sodium (Carboxymethyl Cellulose Sodium, CMC-Na), etc.

[0049] In one specific embodiment, the negative electrode active material is selected from, for example, graphite; the conductive agent is selected from, for example, acetylene black; the binder is selected from, for example, styrene-butadiene rubber; and the thickener is selected from, for example, sodium carboxymethylcellulose. The negative electrode active material, conductive agent, binder, and thickener are mixed according to, for example, a mass ratio of 97:1:1:1, deionized water is added, and the mixture is uniformly mixed under the action of a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry is then applied to copper foil, dried in an oven, and then subjected to processes such as cold pressing and slitting to obtain a negative electrode sheet. In other embodiments, the negative electrode sheet may also be obtained by selecting any other method of forming the negative electrode sheet.

[0050] In some embodiments, the electrolyte contains an electrolyte lithium salt, a solvent, and additives. In secondary batteries, the electrolyte plays a role in ion transport and maintaining chemical stability. The various components in the electrolyte can be divided into electrolyte lithium salt, solvent, and additives according to their function and amount used. Lithium salts are mainly used to provide lithium ions and form ion channels. In the overall electrochemical system of the battery, the orientation transfer of lithium ions and electrons generates power, and lithium salts have a relatively large influence on aspects such as the energy density, power density, wide electrochemical window, cycle life, and safety performance of lithium batteries. The solvent is used to dissolve the lithium salt and additives therein. Additives are substances added in small amounts to the electrolyte, and there are many types, each performing different functions, for example, they can have different improvement effects on the high and low temperature performance, cycle performance, and film formation performance of the battery.

[0051] In some embodiments, the electrolyte lithium salt is selected from at least one of lithium hexafluoride phosphate, bis(fluorosulfonyl)imide lithium, bis(trifluoromethyl)sulfonylimide lithium, lithium acetate, lithium methylsulfonate, or lithium trifluoromethylsulfonate, and the mass percentage of the electrolyte lithium salt is 12% to 16% based on the total mass of the electrolyte. The present invention does not limit the type of lithium salt, and a single lithium salt or a mixed lithium salt can be used.

[0052] In some embodiments, the solvent is selected from at least one of a carbonate-based solvent, a carboxylic acid ester solvent, an ether-based solvent, or a nitrile-based solvent, and the mass percentage of the solvent is 70% to 80% based on the total mass of the electrolyte. Among these, carbonate-based solvents are selected from, for example, ethylene carbonate, vinylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, fluorinated ethylene carbonate, polycarbonate, etc. Carboxylic acid ester solvents are selected from, for example, ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, etc. Ether-based solvents are selected from, for example, ethylene glycol dimethyl ether, diethylene glycol diethyl ether, etc. Nitrile-based solvents are selected from, for example, acetonitrile, propionitrile, butyronitrile, valeronitrile, etc. The present invention does not limit the type of solvent, and a single solvent or a mixture of solvents can be used.

[0053] In some examples, the additive is selected from at least one of vinylene carbonate (VC), methylene methanedisulfonate (MMDS), propylene sulfite (PS), ethylene sulfate (1,3,2-dioxathiolane 2,2-dioxide, DTD), and ethylene sulfite (ES), and the mass percentage of the additive is 0.1% to 5% based on the total mass of the electrolyte. The present invention does not limit the type of additive, and a single additive or a mixture of additives can be used.

[0054] In some examples, the separator is, for example, a polyethylene (PE) membrane, a polypropylene (PP) membrane, a glass fiber membrane, or a composite membrane, and the thickness of the separator is, for example, 9 μm to 15 μm, the air permeability is, for example, 150 s / 100 mL to 350 s / 100 mL, and the porosity is, for example, 30% to 50%.

[0055] The present invention will be described in detail below with specific examples. It should also be understood that the following examples are merely for illustrative purposes and should not be considered as limitations on the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described aspects of the present invention are equally within the scope of protection. The specific process parameters, etc., in the examples below are merely examples within an appropriate range; that is, those skilled in the art can select within an appropriate range through the description below and are not limited to the specific numerical values ​​in the examples below.

[0056] [Examples] Example 1 In this embodiment, a type of manganese iron lithium phosphate composite cathode material LiMn 0.6 Fe 0.4 Ni 0.03 Ti 0.03We will manufacture PO4 / C (abbreviated as Ni3Ti3-LMFP), assigning it the number 1, and the specific manufacturing steps are as follows. S1. Using deionized water as a dispersion medium, a slurry is prepared by uniformly mixing a lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source, and carbon source using a sand mill. In the slurry, the molar ratio of elements Li, Mn, Fe, Ni, Ti, and P is Li:Mn:Fe:Ni:Ti:P = 1.05:0.6:0.4:0.03:0.03:1, and the mass of the carbon source is 10% of the total mass of the lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source, and carbon source. In step S2, the slurry obtained in step S1 is spray-dried, then sintered under a nitrogen atmosphere at 750°C for 9 hours. The target material can then be obtained by grinding and pulverizing the product obtained from sintering.

[0057] Example 2 In this embodiment, a type of manganese iron lithium phosphate composite cathode material LiMn 0.6 Fe 0.4 Ni 0.03 Ti 0.05 We manufactured PO4 / C (abbreviated as Ni3Ti5-LMFP), assigned the number 2, and the specific manufacturing steps are as follows: S1. Using deionized water as a dispersion medium, a slurry is prepared by uniformly mixing a lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source, and carbon source using a sand mill. In the slurry, the molar ratio of elements Li, Mn, Fe, Ni, Ti, and P is Li:Mn:Fe:Ni:Ti:P = 1.05:0.6:0.4:0.03:0.05:1, and the mass of the carbon source is 10% of the total mass of the lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source, and carbon source. In step S2, the slurry obtained in step S1 is spray-dried, then sintered under a nitrogen atmosphere at 750°C for 9 hours. The target material can then be obtained by grinding and pulverizing the product obtained from sintering.

[0058] Example 3 In this embodiment, a type of manganese iron lithium phosphate composite cathode material LiMn 0.6Fe 0.4 Ni 0.04 Ti 0.04 We manufactured PO4 / C (abbreviated as Ni4Ti4-LMFP), assigned the number 3, and the specific manufacturing steps are as follows: S1. Using deionized water as a dispersion medium, a slurry is prepared by uniformly mixing a lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source, and carbon source using a sand mill. In the slurry, the molar ratio of elements Li, Mn, Fe, Ni, Ti, and P is Li:Mn:Fe:Ni:Ti:P = 1.05:0.6:0.4:0.04:0.04:1, and the mass of the carbon source is 10% of the total mass of the lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source, and carbon source. In step S2, the slurry obtained in step S1 is spray-dried, then sintered under a nitrogen atmosphere at 750°C for 9 hours. The target material can then be obtained by grinding and pulverizing the product obtained from sintering.

[0059] Example 4 In this embodiment, a type of manganese iron lithium phosphate composite cathode material LiMn 0.6 Fe 0.4 Ni 0.05 Ti 0.03 We manufactured PO4 / C (abbreviated as Ni5Ti3-LMFP), assigned the number 4, and the specific manufacturing steps are as follows: S1. Using deionized water as a dispersion medium, a slurry is prepared by uniformly mixing a lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source, and carbon source using a sand mill. In the slurry, the molar ratio of elements Li, Mn, Fe, Ni, Ti, and P is Li:Mn:Fe:Ni:Ti:P = 1.05:0.6:0.4:0.05:0.03:1, and the mass of the carbon source is 10% of the total mass of the lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source, and carbon source. In step S2, the slurry obtained in step S1 is spray-dried, then sintered under a nitrogen atmosphere at 750°C for 9 hours. The target material can then be obtained by grinding and pulverizing the product obtained from sintering.

[0060] Comparative Example 1 In this comparative example, a type of manganese iron lithium phosphate composite cathode material LiMn 0.6 Fe 0.4 We will manufacture PO4 / C (abbreviated as LMFP), assigning it the number 5, and the specific manufacturing steps are as follows: S1. Using deionized water as a dispersion medium, a slurry is prepared by uniformly mixing a lithium source, manganese source, iron source, phosphorus source, and carbon source using a sand mill. In the slurry, the ratio of the amounts of Li, Mn, Fe, and P elements is Li:Mn:Fe:P = 1.05:0.6:0.4:1, and the mass of the carbon source is 10% of the total mass of the lithium source, manganese source, iron source, phosphorus source, and carbon source. In step S2, the slurry obtained in step S1 is spray-dried, then sintered under a nitrogen atmosphere at 750°C for 9 hours. The target material can then be obtained by grinding and pulverizing the product obtained from sintering.

[0061] Comparative Example 2 In this comparative example, a type of manganese iron lithium phosphate composite cathode material LiMn 0.6 Fe 0.4 Ni 0.08 We manufactured PO4 / C (abbreviated as Ni-LMFP), assigned the number 6, and the specific manufacturing steps are as follows: S1. Using deionized water as a dispersion medium, a slurry is prepared by uniformly mixing a lithium source, manganese source, iron source, nickel source, phosphorus source and carbon source using a sand mill. In the slurry, the ratio of the amounts of Li, Mn, Fe, Ni and P elements is Li:Mn:Fe:Ni:P = 1.05:0.6:0.4:0.08:1, and the mass of the carbon source is 10% of the total mass of the lithium source, manganese source, iron source, nickel source, phosphorus source and carbon source. In step S2, the slurry obtained in step S1 is spray-dried, then sintered under a nitrogen atmosphere at 750°C for 9 hours. The target material can then be obtained by grinding and pulverizing the product obtained from sintering.

[0062] Comparative Example 3 In this comparative example, a type of manganese iron lithium phosphate composite cathode material LiMn 0.6 Fe 0. 4Ti0.08 We will manufacture PO4 / C (abbreviated as Ti-LMFP), assigning it the number 7, and the specific manufacturing steps are as follows: S1. Using deionized water as a dispersion medium, a slurry is prepared by uniformly mixing a lithium source, manganese source, iron source, titanium source, phosphorus source and carbon source using a sand mill. In the slurry, the ratio of the amounts of Li, Mn, Fe, Ti and P elements is Li:Mn:Fe:Ti:P = 1.05:0.6:0.4:0.08:1, and the mass of the carbon source is 10% of the total mass of the lithium source, manganese source, iron source, titanium source, phosphorus source and carbon source. In step S2, the slurry obtained in step S1 is spray-dried, then sintered under a nitrogen atmosphere at 750°C for 9 hours. The target material can then be obtained by grinding and pulverizing the product obtained from sintering.

[0063] The manganese iron lithium phosphate composite cathode materials numbered 1 to 7, manufactured in Examples 1 to 4 and Comparative Examples 1 to 3, will be evaluated for their physicochemical properties.

[0064] Figure 1 shows the LiMn produced in Example 2. 0.6 Fe 0.4 Ni 0.03 Ti 0.05 The image shows an SEM diagram of PO4 / C. From the electron microscope image, it can be confirmed that the manganese iron lithium phosphate material co-doped with Ni / Ti is particulate, and the outer layer of the particles is coated with a network-like thin film of carbon.

[0065] ICP measurements were used to detect the content of each metal element and obtain the metal element ratios in the product material. It was found that the Li element ratio was slightly lower than the input ratio, suggesting that Li has a lighter mass and that a certain amount of lithium loss may have occurred during the roasting process. XRD characterization showed that when x < 0.05, all manufactured materials were pure manganese iron lithium phase, and no characteristic diffraction peaks of Ni or Ti-containing impurities appeared, indicating that both Ni and Ti successfully doped the material matrix. Simultaneously, the XRD results did not show characteristic graphite peaks, indicating that the coating carbon layer exists in the form of amorphous carbon.

[0066] Lithium iron phosphate-based composite cathode materials numbered 1 to 7, produced in Examples 1 to 4 and Comparative Examples 1 to 3, were used as cathode active materials to manufacture lithium-ion batteries according to the following method, and their performance was measured. The measurement results are shown in Table 1 and Figure 2.

[0067] 1. Manufacturing of positive electrode sheets: A composite cathode material of manganese iron lithium phosphate, polyvinylidene fluoride, and conductive carbon black are mixed in a mass ratio of 90:5:5. Then, N-methylpyrrolidone is added, and the mixture is stirred under the action of a vacuum stirrer until the system becomes homogeneous to obtain a cathode slurry. The cathode slurry is uniformly coated onto a 13 μm thick aluminum foil, dried at room temperature, then transferred to an oven for drying, and finally subjected to processes such as cold pressing and cutting to obtain a cathode sheet.

[0068] 2. Manufacturing of the negative electrode sheet: The negative electrode active material graphite, conductive carbon black, carboxymethylcellulose sodium, and styrene-butadiene rubber are mixed in a mass ratio of 97:1:1:1, deionized water is added, and the mixture is uniformly mixed under the action of a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry is applied to a 13 μm thick copper foil, dried at room temperature, then transferred to an oven for drying, and then subjected to processes such as cold pressing and cutting to obtain a negative electrode sheet.

[0069] 3. Manufacturing of the electrolyte: In an argon gas glove box with a moisture content of less than 0.1 ppm and an oxygen content of less than 0.1 ppm, ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate are uniformly mixed in a mass ratio of 3:5:2 to obtain a mixed solvent. Then, dried lithium hexafluoride phosphate and the additive vinylene carbonate are added to the mixed solvent and uniformly mixed to obtain an electrolyte. In the obtained electrolyte, with the total mass percentage of the electrolyte being 100%, the mass percentage of lithium hexafluoride phosphate is 12.5%, the mass percentage of the mixed solvent is 84.5%, and the mass percentage of the additive is 3%.

[0070] 4. Battery manufacturing: A positive electrode sheet, a separator (8 μm polyethylene film), and a negative electrode sheet are wound in sequence, with the separator positioned between the positive and negative electrode sheets to provide isolation, thereby obtaining a cylindrical bare cell. This is then placed in a circular outer shell, dried in a vacuum oven, and the electrolyte prepared above is injected and the cell is sealed. The electrolyte is then converted to obtain a lithium-ion battery.

[0071] 5, battery performance measurement: Under normal temperature conditions, the battery's cycle performance and rate characteristics are measured according to the following method. Battery rate test: After activating the battery for 3 cycles at 0.1C in a 25°C oven, rate cycles are performed at 1C, 2C, 3C, 5C, 7C, and 10C respectively. Finally, a 0.1C charge / discharge measurement is performed to measure battery stability. Battery cycle performance measurement: 50 charge-discharge cycles are performed in a 25°C oven with a current of 1C within a specified potential range, and the discharge capacity of each cycle is recorded. The results of the material and battery electrochemical performance measurements are shown in Table 1. In Table 1, the 10C capacity retention rate is the discharge ratio capacity retention rate under a 10C rate compared to a 1C rate, and the 1C cycle retention rate is the discharge ratio capacity percentage relative to the first cycle after 100 1C cycles under 25°C conditions.

[0072] [Table 1]

[0073] From Table 1 and Figure 2, the following conclusions can be drawn: Compared to LMFP, Ni-LMFP, and Ti-LMFP, lithium-ion batteries manufactured using materials number 1-4 as the cathode active material exhibit higher 1C discharge capacity, 10C capacity retention rate, and 1C cycle retention rate. Among these, lithium-ion batteries manufactured using material number 2 (Ni3Ti5-LMFP) as the cathode active material exhibit the highest 1C discharge capacity, 10C capacity retention rate, and 1C cycle retention rate, resulting in the best battery capacity and cycle stability. This explains why the Ni+Ti co-doping strategy is more advantageous than single Ni doping and single Ti doping in improving the capacity and cycle stability of lithium manganese iron phosphate batteries. The main reasons for this are as follows: The Ni+Ti co-doping strategy can more effectively mitigate problems such as energy density and capacity decay of lithium manganese iron phosphate cathode materials, thereby allowing lithium manganese iron phosphate to better demonstrate its obvious advantages of high energy density, good safety, and low cost, and further contributing to improved capacity and cycle stability of lithium manganese iron phosphate batteries.

[0074] When comparing the electrochemical performance of lithium-ion batteries manufactured using materials numbered 2 to 4 as cathode active materials, it was found that the 1C discharge capacity, 10C capacity retention rate, and 1C cycle retention rate of the batteries increased with increasing Ti doping levels. This explains that, under the assumption of the same Ni+Ti doping amount, a higher Ti doping amount is more advantageous in terms of capacity performance, and is more beneficial for improving the capacity and cycle stability of lithium manganese iron phosphate batteries. [Industrial applicability]

[0075] LiMn, a manganese iron lithium phosphate composite cathode material provided by the present invention. 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti yPO4 / C is doped with the metallic elements Ni and Ti. Ni+Ti co-doping accelerates the ion diffusion rate of the material and can suppress phase separation in the cycling process of manganese iron lithium phosphate, thereby effectively reducing the decay rate of the Mn plateau. At the same time, the presence of Ni can further increase the crystalline structure stability of manganese iron lithium phosphate, which is Ni 2+ -O-Mn 2+ A superexchange interaction exists between Mn 3+ This is to suppress the change in valence, mitigate the Jahn-Teller effect, and effectively stabilize the crystal structure. This stable crystal structure reduces capacity decay during the lithium-ion battery cycle process, thereby contributing to maintaining a relatively high capacity retention rate. Ti doping can reduce particle size because the atomic radius of Ti is smaller than that of Mn and Fe, which can reduce the crystal lattice volume, control particle size, be advantageous for ion transport between particles, and increase the uniformity of Mn and Fe in the material, thereby beneficial for increasing the conductivity of the material. On the other hand, single Ni doping is not clear for particle size control, and single Ti doping is insufficient to stabilize the crystal structure. Therefore, the Ni+Ti co-doping strategy adopted in this invention can effectively mitigate problems such as energy density and capacity decay of the manganese iron lithium phosphate cathode material, thereby allowing manganese iron lithium phosphate to better demonstrate its clear advantages of high energy density, good safety, and low cost, and further is advantageous for improving the capacity and cycle stability of the manganese iron lithium phosphate battery. LiMn provided by the present invention 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti y In PO4 / C, the carbon coating can create a conductive network between particles, improving electronic conductivity. LiMn provided by the present invention 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti yPO4 / C is produced by a one-step synthesis method, has a simple manufacturing process, and is applicable to large-scale industrial production.

[0076] The above-described embodiments are illustrative in illustrating the principles and effects of the present invention and do not limit the present invention. Those skilled in the art can modify or alter the above-described embodiments without violating the spirit and scope of the present invention. Accordingly, any equivalent modifications or alterations completed by those skilled in the art without departing from the spirit and technical concept disclosed by the present invention are still incorporated into the claims of the present invention.

Claims

1. It contains component A and component B, Component A is a Ni / Ti co-doped manganese iron lithium phosphate material, and the chemical formula of the Ni / Ti co-doped manganese iron lithium phosphate material is LiMn ０．６（１－ｘ－ｙ） Fe ０．４（１－ｘ－ｙ） Ni ｘ Ti ｙ PO ４ Here, 0 ≤ x ≤ 0.05 and 0 ≤ y ≤ 0.05, The aforementioned component B contains amorphous carbon, A manganese iron lithium phosphate-based composite cathode material characterized by the following features.

2. The manganese iron lithium phosphate composite cathode material according to claim 1, characterized in that, in the Ni / Ti co-doped manganese iron lithium phosphate material, the ratio of the sum of the molar contents of Ni and Ti to the sum of the molar contents of Mn and Fe is 0.06 to 0.08:0.92 to 0.

94.

3. The manganese iron lithium phosphate composite cathode material according to claim 1 or 2, characterized in that the molar ratio of Ni to Ti elements is 1:1 to 1.6 in the Ni / Ti co-doped manganese iron lithium phosphate material.

4. The aforementioned component B coats the aforementioned component A as a network-like thin film, and / or, The manganese iron lithium phosphate composite cathode material according to claim 1, characterized in that the mass ratio of component B in the manganese iron lithium phosphate composite cathode material is 1% to 2.5%.

5. A slurry is prepared by mixing a lithium source, a manganese source, an iron source, a nickel source, a titanium source, a phosphorus source and a carbon source, wherein the molar ratio of elements Li, Mn, Fe, Ni, Ti and P in the slurry is Li:Mn:Fe:Ni:Ti:P = 1.05:0.6(1-x-y):0.4(1-x-y):x:y:1, The steps include drying the slurry and then sintering it to produce the manganese iron lithium phosphate composite cathode material, A method for producing a manganese iron lithium phosphate-based composite cathode material, characterized by containing the following:

6. A method for producing a manganese iron lithium phosphate composite cathode material according to claim 5, characterized in that the mass of the carbon source in the slurry is 8% to 12% of the total mass of the lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source and carbon source.

7. The lithium source is at least one selected from lithium carbonate, lithium hydroxide, lithium acetate, or lithium dihydrogen phosphate, and / or The manganese source is at least one selected from manganese oxalate, manganese carbonate, trimanganese tetroxide, manganese phosphate, manganese(II) oxide, or ammonium manganese phosphate, and / or The iron source is at least one selected from iron(II) oxalate, iron(II) pyrophosphate, iron phosphate, diferric oxide, or metallic iron, and / or The nickel source is at least one selected from nickel oxide, nickel hydroxide, or trinickel tetroxide, and / or The titanium source is at least one selected from titanium dioxide, butyl titanate, or metatitanic acid, and / or The phosphorus source is at least one selected from iron phosphate, ammonium dihydrogen phosphate, lithium phosphate, or lithium dihydrogen phosphate, and / or The carbon source is at least one selected from glucose, polyethylene glycol, sucrose, citric acid, or graphite. A method for producing a manganese iron lithium phosphate composite cathode material according to claim 5 or 6, characterized in that

8. A method for producing a manganese iron lithium phosphate composite cathode material according to claim 5, characterized in that sintering is performed under a protective gas atmosphere, the sintering temperature is 650°C to 850°C, and the sintering time is 6h to 12h.

9. The positive electrode current collector and the positive electrode active material layer located on at least one side of the positive electrode current collector are included. The positive electrode active material layer contains a positive electrode active material. A positive electrode sheet characterized in that the positive electrode active material includes a manganese iron lithium phosphate-based composite positive electrode material according to any one of claims 1 to 4, and / or a manganese iron lithium phosphate-based composite positive electrode material manufactured by the method according to any one of claims 5 to 8.

10. A secondary battery characterized by including the positive electrode sheet described in claim 9.

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