CN114068908A

CN114068908A - Preparation method of positive electrode material

Info

Publication number: CN114068908A
Application number: CN202010782598.XA
Authority: CN
Inventors: 蒋欣
Original assignee: Xiamen University; Ningde Amperex Technology Ltd
Current assignee: Xiamen University; Ningde Amperex Technology Ltd
Priority date: 2020-08-06
Filing date: 2020-08-06
Publication date: 2022-02-18

Abstract

The application provides a preparation method of a positive electrode material, which comprises the following steps: respectively grinding the one-dimensional conductive agent and the fast ion conductor, sieving, and dispersing into an organic solvent to obtain a first suspension; grinding the base material, sieving, and dispersing into an organic solvent to obtain a second suspension; uniformly mixing the first suspension and the second suspension to obtain mixed slurry, and performing spray drying to obtain a precursor of the positive electrode material; and roasting the precursor of the anode material to obtain the anode material. The application can improve the electronic conductivity and the ionic conductivity of the anode material, thereby improving the performance of the lithium ion battery.

Description

Preparation method of positive electrode material

Technical Field

The application relates to the technical field of electrochemistry, in particular to a preparation method of a positive electrode material.

Background

The lithium ion battery has the characteristics of large specific energy, high working voltage, low self-discharge rate, small volume, light weight and the like, and is widely applied to various fields of electric energy storage, portable electronic equipment, electric automobile power supply and the like.

With the rapid development of electric vehicles and mobile electronic devices, people have higher and higher requirements on energy density, safety, cycle performance and the like of lithium ion batteries, and there is an urgent need to improve a positive electrode material in the lithium ion batteries so as to improve the cycle performance and electrochemical stability of the existing lithium ion batteries.

Disclosure of Invention

The application aims to provide a preparation method of a positive electrode material, so as to further improve the electronic conductivity and the ionic conductivity of the positive electrode material, and further improve the performance of a lithium ion battery. The specific technical scheme is as follows:

the application provides a preparation method of a positive electrode material, which comprises the following steps:

a first suspension preparation step: respectively grinding the one-dimensional conductive agent and the fast ion conductor, sieving, and dispersing the sieved one-dimensional conductive agent and the sieved fast ion conductor into an organic solvent to obtain a first suspension;

a second suspension preparation step: grinding and sieving the base material, and dispersing the sieved base material into an organic solvent to obtain a second suspension;

and (3) suspension mixing step: mixing the first suspension and the second suspension to obtain mixed slurry, and spray-drying the mixed slurry to obtain a precursor of the positive electrode material; and

and (3) roasting: and roasting the precursor of the anode material to obtain the anode material.

In one embodiment of the present application, the atmosphere of the firing step is selected from at least one of argon, helium, neon, or nitrogen, the firing temperature of the firing step is 300 ℃ to 800 ℃, and the firing time of the firing step is 6h to 24 h.

In one embodiment herein, the organic solvent comprises at least one of methanol or ethanol.

In one embodiment of the present application, the solid content of the first suspension is 35 to 65%, the solid content of the second suspension is 35 to 65%, and the solid content of the mixed slurry is 40% to 60%.

In one embodiment of the present application, the mass percentage of the one-dimensional conductive agent is 0.05% to 5% and the mass percentage of the fast ion conductor is 0.05% to 5% based on the total mass of the base material, the one-dimensional conductive agent and the fast ion conductor.

In one embodiment of the present application, the mass ratio of the one-dimensional conductive agent to the fast ion conductor is 0.1: 1 to 10: 1.

in an embodiment of the present application, the matrix material includes at least one of lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganese oxide, or lithium cobalt oxide, a molar ratio of a manganese element to an iron element in the lithium manganese iron phosphate is 0.01 to 10, and the one-dimensional conductive agent includes at least one of a carbon nanotube or a carbon fiber.

In one embodiment of the present application, the fast ion conductor comprises a compound of formula Li_xLa_yZr_zM_aO_bWherein x is more than or equal to 6 and less than or equal to 8, y is more than or equal to 2 and less than or equal to 4, z is more than or equal to 1 and less than or equal to 3, a is more than or equal to 0 and less than or equal to 0.5, b is more than or equal to 11 and less than or equal to 13, and the M element is selected from at least one of Ta elements or W elements.

In one embodiment of the present application, the fast ion conductor comprises Li₁₀GeP₂S₁₂Or Li₇La₃Zr₂O₁₂At least one of (1).

In one embodiment of the present application, the matrix material comprises ZrO₂、SnO₂、ZnO、MgO、Al₂O₃、TiO₂、CeO₂、AlF₃Or Li₃AlF₆At least one of (1).

According to the preparation method of the anode material, a first suspension containing a one-dimensional conductive agent and a fast ion conductor and a second suspension containing a base material are prepared, then the first suspension and the second suspension are mixed into slurry and then are subjected to spray drying to obtain an anode material precursor, the anode material precursor is roasted to obtain the anode material, and the one-dimensional conductive agent in the anode material can be in point-line contact with the base material, so that a more perfect conductive network is formed, and the electronic conductivity of the anode material is improved; the one-dimensional conductive agent can provide a plurality of attachment sites for the fast ion conductors, so that the surface of the one-dimensional conductive agent has more fast ion conductors, the fast ion conductors have the characteristics of wide electrochemical window, stable property and high ionic conductivity, the ionic conductivity of the anode material is improved, and the cycle performance, the electrochemical stability and other performances of an electrochemical device (such as a lithium ion battery) are improved.

Drawings

In order to more clearly illustrate the present application and the technical solutions of the prior art, the following briefly introduces embodiments and drawings required in the prior art, and obviously, the drawings in the following description are only some embodiments of the present application, and other technical solutions can be obtained by those skilled in the art according to the drawings.

Fig. 1 is an electron microscope (SEM) photograph of a cathode material of example 1 of the present application;

fig. 2 is a schematic diagram of the cycle test results of the lithium ion batteries of example 1 and comparative example 1.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is further described in detail below with reference to the accompanying drawings and examples. It is to be understood that the embodiments described are only a few embodiments of the present application and not all embodiments.

In the embodiments of the present application, the present application is explained by taking a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present application is not limited to a lithium ion battery.

As a novel positive electrode active material, compared with a lithium iron phosphate material, although the theoretical specific capacity is 170mAh/g, the voltage platform is higher, so that the material has higher energy density, and meanwhile, the material has an olivine structure the same as that of the lithium iron phosphate and has good safety performance, but the electronic conductivity and the ionic conductivity of the lithium iron manganese phosphate material are lower, so that the lithium ion migration rate is low, and further the electrochemical activity of the positive electrode material using the lithium iron manganese phosphate material is poor. The existing lithium iron manganese phosphate anode material can improve electronic conductivity, but the improvement of ionic conductivity is limited, the cycle performance of the lithium ion battery prepared by the existing lithium iron manganese phosphate anode material is still low, and particularly after high-rate cycle, the capacity is obviously attenuated. In addition, if the matrix material is coated with only a conductive agent, elution of metal (e.g., Mn) from the positive electrode material is not inhibited, and metal ions are deposited on the negative electrode, resulting in continuous regeneration of a Solid Electrolyte Interface (SEI) film, consumption of active lithium in the lithium ion battery, and rapid capacity fade of the lithium ion battery.

In view of the above, the present application provides a method for preparing a positive electrode material, including the following steps:

a first suspension preparation step:

and respectively grinding the one-dimensional conductive agent and the fast ion conductor, sieving, and dispersing the sieved one-dimensional conductive agent and the sieved fast ion conductor into an organic solvent to obtain a first suspension.

A second suspension preparation step:

and grinding the base material, sieving, and dispersing the sieved base material into an organic solvent to obtain a second suspension.

A spray drying step:

and mixing the first turbid liquid and the second turbid liquid to obtain mixed slurry, and spray-drying the mixed slurry to obtain a precursor of the positive electrode material.

And (3) roasting:

and roasting the precursor of the anode material to obtain the anode material.

The number of the screens for sieving the one-dimensional conductive agent, the fast ion conductor and the matrix material is not particularly limited as long as the purpose of the application can be achieved, for example, no large particles are observed by naked eyes after sieving, and the number of the screens can be 300-600 meshes, for example.

The solid contents of the first suspension and the second suspension are not particularly limited, as long as the purpose of the present application can be achieved, for example, the solid content of the first suspension may be 35% to 65%, and the solid content of the second suspension may be 35% to 65%, but should not be too small, otherwise the subsequent spray drying process is difficult. In addition, the solid content of the mixed slurry is also not particularly limited, and is, for example, 40% to 60%, as long as the one-dimensional conductive agent is contained in the positive electrode material in an amount of 0.05% to 5% by mass and the fast ion conductor is contained in the positive electrode material in an amount of 0.05% to 5% by mass after mixing.

The organic solvent for dispersing the one-dimensional conductive agent, the fast ion conductor and the matrix material is not particularly limited as long as the requirements of the application are met, and for example, at least one of ethanol or absolute methanol may be included, and the ethanol may be absolute ethanol.

The baking atmosphere is not particularly limited, for example, at least one of argon, helium, neon or nitrogen can be selected, because the composition or structure of the cathode material may be changed to different degrees at high temperature during baking in the air, so that the particle structure of the cathode material is damaged, the stability of the material is affected, and the inert gas environment can avoid the above condition, which is beneficial to the structural stability of the cathode material.

The spray drying process is not particularly limited as long as the object of the present invention can be achieved, and for example, centrifugal spray drying at a centrifugal speed of 500rpm to 5000rpm may be employed.

The roasting temperature is not particularly limited, but is not too low or too high, because the roasting temperature is too low, the conductive agent and the fast ion conductor are not uniformly distributed, and the performance of the lithium ion battery is not obviously improved; the roasting temperature is too high, so that the material is easy to over-burn, the stability of the material is reduced, and the performance and the safety performance of the lithium ion battery are influenced. The roasting time is too short, the conductive agent and the fast ion conductor are not uniformly distributed, and the performance of the lithium ion battery is not obviously improved; the long roasting time is easy to reduce the stability of the material, and affects the cycle performance and the capacity of the lithium ion battery. In one embodiment of the present application, the firing temperature of the firing step is 300 ℃ to 800 ℃, and the firing time of the firing step is 6h to 24 h.

In one embodiment of the present application, the one-dimensional conductive agent is contained in an amount of 0.05 to 5% by mass, preferably 0.2 to 3% by mass, based on the total mass of the positive electrode material; the mass percentage of the fast ion conductor is 0.05-5%, preferably 0.2-3%, and the balance is the matrix material, so that the positive electrode material has good structural stability, electron conductivity and ion conductivity.

In one embodiment of the present application, the mass ratio of the one-dimensional conductive agent to the fast ion conductor is 0.1: 1 to 10: 1, preferably 0.2: 1 to 5: 1, and is not limited to any theory, when the mass ratio between the one-dimensional conductive agent and the fast ion conductor is too large, the number of the fast ion conductors is relatively small, and no sufficient number of fast ion conductors are attached to the one-dimensional conductive agent, so that the improvement of the structural stability of the positive electrode material is not facilitated; when the mass ratio between the one-dimensional conductive agent and the fast ion conductor is too small, the quantity of the one-dimensional conductive agent is relatively small, the quantity of the fast ion conductor which is not attached to the surface of the one-dimensional conductive agent is increased, the proportion of the matrix material in the anode material is reduced, and the energy density of the lithium ion battery is influenced. By controlling the mass ratio of the one-dimensional conductive agent to the fast ion conductor within the above proportion, the positive electrode material can have good structural stability, electron conductivity and ion conductivity.

In one embodiment of the present application, an olivine-type structured material, such as lithium iron manganese phosphate (LiMn), may be included in the matrix material_1-xFe_xPO₄Abbreviated as LMFP), lithium iron phosphate (LiFePO)₄Abbreviated LFP) or lithium manganese phosphate (LiMnPO)₄) And the material has good safety and higher energy density. Of course, other materials may be included, such as at least one of the ternary materials of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminate (specifically including NCM811, NCM622, NCM523, or NCM333), and the spinel-type materials of lithium cobalt oxide and lithium manganese oxideAt least one of (1).

The molar ratio of the manganese element to the iron element in the lithium manganese iron phosphate is 0.01 to 10, and the energy density of the lithium manganese iron phosphate battery is lower than that of the lithium manganese phosphate battery, while the lithium manganese iron phosphate battery is between the two, but the conductivity of the lithium manganese phosphate battery is lower than that of the lithium iron phosphate battery, so that the molar ratio of the manganese element to the iron element is controlled to be the ratio from the viewpoint of improving the energy density of the battery and enabling the anode material to have higher conductivity.

The one-dimensional conductive agent is not particularly limited, and may include, for example, at least one of carbon nanotubes or carbon fibers, wherein the carbon nanotubes may include at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes. In an alternative embodiment, the carbon nanotubes have a specific surface area of 25g/m²To 300g/m²The specific surface area range can provide more attachment sites for the fast ion conductor, so that the ionic conductivity of the positive electrode material is improved.

In one embodiment of the present application, the aspect ratio of the one-dimensional conductive agent is 100 to 6250, and by controlling the aspect ratio within the above range, more attachment sites can be provided for the fast ion conductor, so that the surface of the one-dimensional conductive agent has more fast ion conductors, thereby further improving the ion conductivity of the material. In an alternative embodiment, the length of the one-dimensional conductive agent is 300nm to 50000nm, preferably 1000nm to 30000nm, more preferably 1000nm to 10000 nm. In an alternative embodiment, the diameter (outer diameter) of the one-dimensional conductive agent is 8nm to 50 nm. By controlling the length and diameter of the one-dimensional conductive agent within the above ranges, the cathode material of the present application can have better electronic conductivity.

The fast ion conductor is not particularly limited as long as the object of the present invention can be achieved, and for example, the fast ion conductor may be a fast ion conductor doped with an M element selected from at least one of Ta element and W element, and the ion conductivity of the fast ion conductor may be further improved by doping the M element, and on the one hand, the fast ion conductor has high ion conductivity, and is mixed with a one-dimensional conductive agent by being attached to a base materialThe particles are in contact with the base material particles, so that the effect of conducting ions and electrons is achieved, and the electronic conductivity and the ionic conductivity of the positive electrode material can be improved; on the other hand, Mn in lithium manganese iron phosphate (LMFP)³⁺、Mn²⁺The working potential is about 4.0V, when the lithium ion battery works under a higher voltage condition, the thermal stability and the electrochemical stability of the lithium ion manganese iron phosphate battery are poor, and the electrochemical performance and the safety performance of the lithium ion manganese iron phosphate battery are further influenced, for example, due to the John-Teller (John-Teller) effect of manganese, the problems of short circuit of the lithium ion battery caused by manganese dissolution, gas expansion generated by reaction of an anode and an electrolyte and the like are solved.

The doping amount of the M element is not particularly limited in the present application as long as the object of the present application can be achieved, and for example, the M element-doped fast ion conductor may be Li doped with Ta element_xLa_yZr_zM_aO_bWherein x is more than or equal to 6 and less than or equal to 8, y is more than or equal to 2 and less than or equal to 4, z is more than or equal to 1 and less than or equal to 3, and 0<a is less than or equal to 0.5, b is less than or equal to 11 and less than or equal to 13, and the doping amount of Ta element is 0.01 mol to 0.5 mol, which represents each 1 mol of Li_xLa_yZr_zM_aO_bContains 0.01 mol to 0.5 mol of Ta element, specifically, 0.3 mol of Ta element doped with Li₇La₃Zr₂O₁₂。

In one embodiment of the present application, the fast ion conductor may include Li₇La₃Zr₂O₁₂(LLZO) or Li₁₀GeP₂S₁₂(LGPS).

In one embodiment of the present application, the fast ion conductor has an ionic conductivity of 1X 10^-4S/cm to 2.7X 10^-2S/cm, can increase the ion content of the positive electrode materialConductivity, and further improves the performance of the lithium ion battery.

In one embodiment of the present application, the surface layer of the matrix material may include ZrO₂、SnO₂、ZnO、MgO、Al₂O₃、TiO₂、CeO₂、AlF₃Or Li₃AlF₆At least one of (1). Without being bound to any theory, the matrix material may have better structural stability due to the stability of the above oxides or fluorides themselves. Of course, the matrix material may have an oxide or fluoride on at least a part of the surface layer, or may have an oxide or fluoride on the entire surface layer. In the present application, the content of the oxide or fluoride is not particularly limited, and may be, for example, 0.1 to 3% by mass based on the total mass of the base material.

According to the preparation method, in the precursor of the anode material obtained by spray drying, the fast ion conductor can be attached to the surface of the one-dimensional conductive agent, the one-dimensional conductive agent attached with the fast ion conductor is mixed among the particles of the base material, and then the fast ion conductor is subjected to a subsequent high-temperature roasting process, so that the one-dimensional conductive agent attached with the fast ion conductor is formed among the particles of the base material and is contacted with the particles of the base material, the effect of conducting ions and electrons is achieved, and the anode material with excellent ionic conductivity and electronic conductivity is obtained. Compared with other anode materials, the anode material obtained by the preparation method can enrich ion and electron transport channels in the anode material, construct an ion-electron mixed conductive network and effectively reduce interface resistance. In addition, the preparation method can obtain the anode materials with different component contents by adjusting parameters such as reaction temperature, one-dimensional conductive agent, fast ion conductor content and the like, and can be suitable for various working conditions. The preparation method has the advantages that the conditions are easy to control, the process is mature, the synthesized positive electrode material has excellent ionic conductivity and electronic conductivity, the particle structure in the positive electrode material is stable, and the electrochemical performance of the lithium ion battery can be effectively improved.

The negative electrode sheet in the present application is not particularly limited as long as the object of the present application can be achieved. For example, the negative electrode tab generally includes a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector is not particularly limited, and any negative electrode current collector known in the art, such as copper foil, aluminum alloy foil, and composite current collector, may be used. The anode active material layer includes an anode active material, and the anode active material is not particularly limited, and any anode active material known in the art may be used. For example, at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, silicon carbon, lithium titanate, and the like may be included.

The separator of the present application includes, but is not limited to, at least one selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, polyimide, and aramid. For example, the polyethylene includes at least one component selected from the group consisting of high density polyethylene, low density polyethylene, and ultra high molecular weight polyethylene. In particular polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of lithium ion batteries by means of a shutdown effect.

The surface of the separation film may further include a porous layer disposed on at least one surface of the separation film, the porous layer including inorganic particles selected from alumina (Al) and a binder₂O₃) Silicon oxide (SiO)₂) Magnesium oxide (MgO), titanium oxide (TiO)₂) Hafnium oxide (HfO)₂) Tin oxide (SnO)₂) Cerium oxide (CeO)₂) Nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO)₂) Yttrium oxide (Y)₂O₃) Silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from one or more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

The porous layer can improve the heat resistance, the oxidation resistance and the electrolyte infiltration performance of the isolating membrane and enhance the adhesion between the isolating membrane and the anode or the cathode.

The battery of the present application further includes an electrolyte, which may be one or more of a gel electrolyte, a solid electrolyte, and an electrolytic solution including a lithium salt and a non-aqueous solvent.

In some embodiments herein, the lithium salt is selected from LiPF₆、LiBF₄、LiAsF₆、LiClO₄、LiB(C₆H₅)₄、LiCH₃SO₃、LiCF₃SO₃、LiN(SO₂CF₃)₂、LiC(SO₂CF₃)₃、LiSiF₆One or more of LiBOB and lithium difluoroborate. For example, the lithium salt may be LiPF₆Since it can give high ionic conductivity and improve cycle characteristics.

The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvent, or a combination thereof.

The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.

Examples of the above chain carbonate compound are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Methyl Ethyl Carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), Vinyl Ethylene Carbonate (VEC), and combinations thereof. Examples of the fluoro carbonate compound are fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1,2, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.

Examples of the above carboxylic acid ester compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonolactone, caprolactone, and combinations thereof.

Examples of the above ether compounds are dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

Examples of such other organic solvents are dimethylsulfoxide, 1, 2-dioxolane, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters and combinations thereof.

This application still provides a positive pole piece, positive pole piece includes anodal active material layer, anodal active material layer include in above-mentioned arbitrary embodiment anodal material, because this anodal material has good structural stability, electron electric conductive property and ionic conductivity, consequently the positive pole piece of this application also has good structural stability, electron electric conductive property and ionic conductivity. Among them, the sheet resistance of the positive electrode active material layer of the present application is 0.1m Ω to 50m Ω, and the test method of the resistance of the positive electrode active material layer will be shown below.

The application also provides an electrode assembly, which comprises a positive electrode piece, a negative electrode piece and an isolating membrane, wherein the isolating membrane is positioned between the positive electrode piece and the negative electrode piece, and the electrode assembly comprises the positive electrode piece in the above embodiment of the application.

The present application also provides an electrochemical device including an electrolyte and the electrode assembly of the above embodiment, having good cycle performance and capacity retention performance.

The present application also provides an electronic device comprising the electrochemical device described in the embodiments of the present application, having a longer service life and higher safety.

The electronic device of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power source, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.

The process of preparing the electrochemical device is well known to those skilled in the art, and the present application is not particularly limited. For example, a lithium ion battery can be manufactured by the following process: the positive electrode and the negative electrode are overlapped through a separation film, the positive electrode and the negative electrode are placed into the shell after being wound, folded and the like according to needs, electrolyte is injected into the shell and the shell is sealed, wherein the used negative electrode is the negative electrode plate provided by the application. In addition, an overcurrent prevention element, a guide plate, or the like may be placed in the case as necessary to prevent a pressure rise or overcharge/discharge inside the lithium ion battery.

Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples. Various tests and evaluations were carried out according to the following methods. Unless otherwise specified, "part" and "%" are based on mass.

Example 1

< preparation of Positive electrode Material >

< preparation of first suspension >

Respectively grinding the one-dimensional conductive agent CNT and the fast ion conductor LLZO, sieving by a 400-mesh sieve, and dispersing the sieved CNT and the sieved LLZO into absolute ethyl alcohol according to the mass ratio of 1: 1 to obtain a first suspension liquid with the solid content of 50%.

< preparation of second suspension >

Grinding a matrix material lithium manganese iron phosphate (LMFP), sieving with a 400-mesh sieve, and dispersing the sieved LMFP into absolute ethyl alcohol to obtain a second suspension liquid with the solid content of 50%. Wherein the molar ratio of manganese to iron in the LMFP is 6: 4.

< mixing of suspension >

And uniformly mixing the first suspension and the second suspension to obtain mixed slurry with the solid content of 50%, and spray-drying the mixed slurry to obtain a precursor of the positive electrode material, wherein the mass percentage of the CNT is 1.5%, the mass percentage of the LLZO is 1.5% and the balance is the matrix material LMFP on the basis of the total mass of the matrix material, the one-dimensional conductive agent and the fast ion conductor.

< calcination >

And roasting the precursor of the anode material in an argon atmosphere at the roasting temperature of 600 ℃ for 15 h.

Wherein the CNT is single wall, the length-diameter ratio is 1000, the length is 20000nm, the diameter is 20nm, and the specific surface area is 42g/m²The ion conductivity of LLZO was 5X 10^-4S/cm。

< preparation of Positive electrode sheet >

Mixing the prepared positive electrode material, acetylene black as a conductive agent and polyvinylidene fluoride (PVDF) as a binder according to the mass ratio of 95: 3: 2, adding N-methylpyrrolidone (NMP) as a solvent, preparing slurry with the solid content of 75%, and uniformly stirring. And uniformly coating the slurry on one surface of an aluminum foil with the thickness of 12 mu m, drying at 90 ℃, cold-pressing to obtain a positive pole piece with the thickness of a positive active material layer of 100 mu m, and repeating the steps on the other surface of the positive pole piece to obtain the positive pole piece with the positive active material layer coated on the two surfaces. Cutting the positive pole piece into the specification of 74mm multiplied by 867mm, and welding the pole lugs for later use.

< preparation of negative electrode sheet >

Mixing artificial graphite serving as a negative electrode active material, acetylene black serving as a conductive agent, Styrene Butadiene Rubber (SBR) serving as a binder and sodium carboxymethyl cellulose (CMC) serving as a thickening agent according to the weight ratio of 95: 2: 1, adding deionized water serving as a solvent, blending into slurry with the solid content of 70%, uniformly stirring, uniformly coating the slurry on one surface of a copper foil with the thickness of 10 mu m, drying at 110 ℃, cold-pressing to obtain a negative electrode piece with the negative electrode active material layer coated on one surface of the negative electrode piece, wherein the thickness of the negative electrode active material layer is 150 mu m, and repeating the coating steps on the other surface of the negative electrode piece to obtain the negative electrode piece with the negative electrode active material layer coated on the two surfaces. Cutting the negative pole piece into a size of 74mm multiplied by 867mm, and welding a pole lug for later use.

< preparation of electrolyte solution >

In a dry argon atmosphere, organic solvents of Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and diethyl carbonate (DEC) were mixed at a mass ratio of 30: 50: 20, and then lithium hexafluorophosphate (LiPF) was added to the organic solvent₆) Dissolving and mixing uniformly to obtain electrolyte, wherein the LiPF is₆The molar concentration in the electrolyte was 1.15 mol/L.

< preparation of lithium ion Battery >

And (3) taking a Polyethylene (PE) porous film with the thickness of 15 mu m as a separation film, stacking the prepared positive pole piece, the separation film and the negative pole piece in sequence to enable the separation film to be positioned between the positive pole piece and the negative pole piece to play a role in separation, and winding to obtain the electrode assembly. And placing the electrode assembly in a shell, injecting the prepared electrolyte, packaging, and carrying out technological processes such as formation, degassing, edge cutting and the like to obtain the lithium ion battery.

Example 2

The same as example 1 was repeated, except that the mass percentages of the one-dimensional conductive agent and the fast ion conductor were 0.05%.

Example 3

The same as example 1 was repeated, except that the mass percentages of the one-dimensional conductive agent and the fast ion conductor were 0.1%.

Example 4

The same as example 1 was repeated, except that the mass percentages of the one-dimensional conductive agent and the fast ion conductor were 0.2%.

Example 5

The same as example 1 was repeated, except that the mass percentages of the one-dimensional conductive agent and the fast ion conductor were 0.5%.

Example 6

The same as example 1 was repeated, except that the mass percentages of the one-dimensional conductive agent and the fast ion conductor were 3%, respectively.

Example 7

The same as example 1 was repeated, except that the mass percentages of the one-dimensional conductive agent and the fast ion conductor were 5%, respectively.

Example 8

The process was performed in the same manner as in example 1, except that the mass percentage of the one-dimensional conductive agent was 0.15%, and the mass percentage of the fast ion conductor was 1.5%, i.e., the mass ratio of the one-dimensional conductive agent to the fast ion conductor was 0.1: 1.

Example 9

The process was performed in the same manner as in example 1, except that the mass percentage of the one-dimensional conductive agent was 0.3%, and the mass percentage of the fast ion conductor was 1.5%, i.e., the mass ratio of the one-dimensional conductive agent to the fast ion conductor was 0.2: 1.

Example 10

The process was performed in the same manner as in example 1, except that the mass percentage of the one-dimensional conductive agent was 2.25% and the mass percentage of the fast ion conductor was 1.5%, i.e., the mass ratio of the one-dimensional conductive agent to the fast ion conductor was 1.5: 1.

Example 11

The same as example 1 except that the mass percentage of the one-dimensional conductive agent was 3% and the mass percentage of the fast ion conductor was 1.5%, that is, the mass ratio of the one-dimensional conductive agent to the fast ion conductor was 2: 1.

Example 12

The process was performed in the same manner as in example 1, except that the mass percentage of the one-dimensional conductive agent was 1.5% and the mass percentage of the fast ion conductor was 0.3%, i.e., the mass ratio of the one-dimensional conductive agent to the fast ion conductor was 5: 1.

Example 13

The process was performed in the same manner as in example 1, except that the mass percentage of the one-dimensional conductive agent was 1.5% and the mass percentage of the fast ion conductor was 0.75%, i.e., the mass ratio of the one-dimensional conductive agent to the fast ion conductor was 2: 1.

Example 14

The process was performed in the same manner as in example 1, except that the mass percentage of the one-dimensional conductive agent was 1.5% and the mass percentage of the fast ion conductor was 2.25%, i.e., the mass ratio of the one-dimensional conductive agent to the fast ion conductor was 0.67: 1.

Example 15

The process was performed in the same manner as in example 1, except that the mass percentage of the one-dimensional conductive agent was 1.5% and the mass percentage of the fast ion conductor was 4.5%, i.e., the mass ratio of the one-dimensional conductive agent to the fast ion conductor was 0.33: 1.

Example 16

The procedure of example 1 was repeated, except that the matrix material was lithium iron phosphate (LFP).

Example 17

The same procedure as in example 1 was repeated, except that the calcination temperature was 300 ℃.

Example 18

The same procedure as in example 1 was repeated, except that the calcination temperature was 500 ℃.

Example 19

The same procedure as in example 1 was repeated, except that the calcination temperature was 800 ℃.

Example 20

The same procedure as in example 1 was repeated, except that the calcination time was set to 8 hours.

Example 21

The same procedure as in example 1 was repeated, except that the calcination time was 20 hours.

Example 22

The same as example 1 was repeated, except that the one-dimensional conductive agent was carbon fiber.

Example 23

The same as example 1 except that the fast ion conductor was LGPS.

Example 24

Except that the fast ion conductor is Li doped with Ta₇La₃Zr₂O₁₂The procedure of example 1 was repeated, except that (Ta-LLZO), wherein the amount of doped Ta element was 0.3 mol.

Example 25

The same as example 1 was repeated, except that the length of the one-dimensional conductive agent was 800nm, the diameter of the one-dimensional conductive agent was 8nm, and the aspect ratio of the one-dimensional conductive agent was 100.

Example 26

The same as example 1 was repeated, except that the length of the one-dimensional conductive agent was 3500nm, the diameter of the one-dimensional conductive agent was 10nm, and the aspect ratio of the one-dimensional conductive agent was 350.

Example 27

The same as example 1 was repeated, except that the length of the one-dimensional conductive agent was 8000nm, the diameter of the one-dimensional conductive agent was 10nm, and the aspect ratio of the one-dimensional conductive agent was 800.

Example 28

The same as example 1 was repeated, except that the length of the one-dimensional conductive agent was 30000nm, the diameter of the one-dimensional conductive agent was 15nm, and the aspect ratio of the one-dimensional conductive agent was 2000.

Example 29

The procedure of example 1 was repeated, except that the length of the one-dimensional conductive agent was 50000nm, the diameter of the one-dimensional conductive agent was 8nm, and the aspect ratio of the one-dimensional conductive agent was 6250.

Example 30

Except that the specific surface area of the one-dimensional conductive agent is 25g/m²Otherwise, the same procedure as in example 1 was repeated.

Example 31

Except that the specific surface area of the one-dimensional conductive agent is 32g/m²Otherwise, the same procedure as in example 1 was repeated.

Example 32

Except that the specific surface area of the one-dimensional conductive agent is 82g/m²Otherwise, the same procedure as in example 1 was repeated.

Example 33

Except that the specific surface area of the one-dimensional conductive agent is 176g/m²Otherwise, the same procedure as in example 1 was repeated.

Example 34

Except that the specific surface area of the one-dimensional conductive agent is 300g/m²Otherwise, the same procedure as in example 1 was repeated.

Comparative example 1

The same procedure as in example 1 was repeated, except that the preparation process of the positive electrode material was different from that of example 1.

The preparation process of the cathode material comprises the following steps:

and directly roasting the LMFP in an argon atmosphere at the roasting temperature of 600 ℃ for 15 h.

Comparative example 2

The preparation process of the cathode material comprises the following steps:

the LMFP was replaced with LFP on the basis of comparative example 1.

Comparative example 3

The preparation process of the cathode material comprises the following steps:

grinding the CNT, sieving with a 400-mesh sieve, and dispersing the sieved CNT in absolute ethyl alcohol to obtain a first suspension with solid content of 50%.

And grinding the LMFP, sieving the ground LMFP by a 400-mesh sieve, and dispersing the sieved LMFP in absolute ethyl alcohol to obtain a second suspension liquid with the solid content of 50%.

And uniformly mixing the first suspension and the second suspension to obtain mixed slurry with the solid content of 50%, and spray-drying the mixed slurry to obtain the precursor of the positive electrode material, wherein the mass percentage of the CNT is 1.5% and the balance is LMFP on the basis of the total mass of the CNT and the LMFP.

Comparative example 4

The preparation process of the cathode material comprises the following steps:

grinding the LLZO, sieving the ground LLZO by a 400-mesh sieve, and dispersing the sieved LLZO into absolute ethyl alcohol to obtain a first suspension with the solid content of 50%.

And uniformly mixing the first suspension and the second suspension to obtain mixed slurry with the solid content of 50%, and spray-drying the mixed slurry to obtain a precursor of the positive electrode material, wherein the total mass of the LLZO and the LMFP is taken as a reference, the mass percentage content of the LLZO is 1.5%, and the balance is the LMFP.

Wherein the ion conductivity of LLZO is 5 × 10^-4S/cm。

Comparative example 5

The preparation process of the cathode material comprises the following steps:

grinding the fast ion conductor LLZO, sieving the ground fast ion conductor LLZO by a 400-mesh sieve, and dispersing the sieved LLZO into absolute ethyl alcohol to obtain a first suspension liquid with the solid content of 50%.

Grinding the base material LMFP, sieving the ground base material LMFP by a 400-mesh sieve, and dispersing the sieved LMFP in absolute ethyl alcohol to obtain a second suspension liquid with the solid content of 50%.

And uniformly mixing the first suspension and the second suspension to obtain mixed slurry with the solid content of 50%, spray-drying the mixed slurry, and roasting at the roasting temperature of 600 ℃ for 15h in an argon atmosphere to obtain the base material with the fast ion conductor on the surface.

Grinding the one-dimensional conductive agent CNT, sieving with a 400-mesh sieve, and dispersing the sieved CNT into absolute ethyl alcohol to obtain a third suspension liquid with the solid content of 50%.

And dispersing the base material with the fast ion conductor on the surface into absolute ethyl alcohol to obtain a fourth suspension liquid with the solid content of 50%.

Uniformly mixing the third suspension and the fourth suspension to obtain solid contentIs 50% of mixed slurry, the mixed slurry is spray-dried and then calcined under the same calcination conditions. Wherein, based on the total mass of the CNT and the LMFP, the mass percentage of the CNT is 1.5 percent, the mass percentage of the LLZO is 1.5 percent, and the rest is the LMFP. CNT is single wall, length-diameter ratio is 1000, length is 20000nm, diameter is 20nm, specific surface area is 42g/m²The ion conductivity of LLZO was 5X 10^-4S/cm。

< Performance test >

The positive electrode material, the positive electrode plate and the lithium ion battery prepared in each example and each comparative example were tested by the following methods:

cathode material SEM, EDS test:

the positive electrode material is made into a pole piece sample, a Scanning Electron Microscope (SEM) and an energy spectrometer (EDS) are used for testing, a focused electron beam of an instrument is used for exciting the surface of the sample to generate secondary information such as secondary electrons, backscattered electrons and characteristic X rays, and the secondary information is collected and detected to be used for analyzing the micro-morphology and the micro-area components of the surface of the sample, wherein the SEM test result of the positive electrode material in example 1 is shown in figure 1, and the EDS test result is shown in table 2. Test conditions for SEM and EDS: working distance 5mm to 30mm, objective aperture 100 μm to 200 μm, acceleration voltage 2kV to 20kV, EDS test conditions: … …, the test apparatus is an OXFORD EDS (X-max-20mm 2).

Testing the resistance of the positive active material layer of the positive pole piece:

before testing, the end faces of upper and lower terminals of a resistance tester are cleaned by using absolute ethyl alcohol to soak dust-free paper, the resistance tester (model BER1200) is checked by using a standard resistor of 20.27m omega or 0.5m omega, the resistance tester is reset to zero after the check, when testing, the pressure is more than or equal to 0.35T, and a positive pole piece is cut into the size of 60mm multiplied by 80mm to carry out resistance testing, wherein the testing method comprises the following steps: the cut pole pieces (about 60mm multiplied by 80mm) are placed on an instrument base, an upper cover plate is covered, the pole pieces cover test hole positions as much as possible, a sample carrying table provided with the pole pieces is placed in a test cavity, then the sample carrying table is moved, the test hole position at the forefront end is clamped to a lower terminal, a protective door is closed, a pneumatic button at the front part of the instrument is pressed down, the lower terminal is pressed down to test the overall resistance and resistivity of the pole pieces in the thickness direction, the sample carrying table is moved to replace the test hole positions after the test at one point is completed, the test interval is 50s, six points are collected for each sample, and then the average value is calculated. The resistance test of the positive active material layer can effectively evaluate the electronic conductivity of the positive pole piece and analyze the contact resistance of the material interface layer.

And (3) testing the discharge specific capacity of 0.1C:

the lithium ion batteries in the embodiments and the comparative examples were subjected to a charge and discharge test using a blue (LAND) series battery test system, and the charge and discharge performance was tested, and the lithium ion batteries were charged at a constant current of 0.1C magnification at normal temperature until the voltage reached 4.2V, and further charged at a constant voltage of 4.2V until the current was less than 0.05C, so that the lithium ion batteries were in a full charge state of 4.2V. Then, constant current discharge was performed at a rate of 0.1C until the voltage was stopped at 2.5V, and the obtained capacity was the 0.1C specific discharge capacity, and the results are shown in tables 1,2, and 3.

And (3) testing the cycle performance:

the lithium ion batteries of the respective examples and comparative examples were repeatedly charged and discharged through the following steps, and the discharge capacity retention rates of the lithium ion batteries were calculated.

First charging and discharging are carried out in an environment of 25 ℃, constant-current and constant-voltage charging is carried out under a charging current of 0.1 ℃ until the upper limit voltage is 4.2V, then constant-current discharging is carried out under a discharging current of 1 ℃ until the final voltage is 2.5V, the discharging capacity of the first cycle is recorded, and then the steps are repeated for 100 charging and discharging cycles, and the discharging capacity of the 100 th cycle is recorded.

The cycle capacity retention rate (discharge capacity at 100 th cycle/discharge capacity at first cycle) × 100%.

The preparation parameters and test results of the respective examples and comparative examples are shown in the following tables 1,2 and 3:

as can be seen from examples 1-15, 17-34 and comparative example 1, when the matrix material is LMFP, the cycle capacity retention rate of the lithium ion battery with the cathode material of the present application is improved.

From example 16 and comparative example 2, it can be seen that when the matrix material is LFP, the retention rate of the cycle capacity of the lithium ion battery with the cathode material of the present application is improved.

As can be seen from examples 1, 12 to 15, 22 to 34 and comparative example 3, when the content of the one-dimensional conductive agent is the same and the roasting condition is the same, the cycle capacity retention rate of the lithium ion battery with the cathode material of the present application is improved, and the 0.1C discharge specific capacity does not change much.

As can be seen from examples 1, 8-11, 22-34 and comparative example 4, when the content of the fast ion conductor is the same and the baking conditions are the same, the cycle capacity retention rate of the lithium ion battery with the cathode material of the present application is improved, and the 0.1C specific discharge capacity is basically maintained.

As can be seen from examples 2 to 7, the cycle performance of the lithium ion battery is improved as the contents of the one-dimensional conductive agent and the fast ion conductor are increased, but the cycle performance is reduced when the contents of the one-dimensional conductive agent and the fast ion conductor are increased to a certain extent.

From examples 17-19, it can be seen that the firing temperature is in the range of 300 deg.C to 800 deg.C, the cycle performance of the lithium ion battery increases as the firing temperature increases, but the cycle performance of the lithium ion battery decreases as the temperature continues to increase. Without being bound to any theory, the inventors believe that the firing temperature may affect the bonding between particles, thereby affecting the lithium ion battery cycle performance.

As can be seen from examples 20 and 21 and comparative example 1, the firing time also has a certain effect on the performance of the positive electrode material, but the cycle capacity retention rate of the lithium ion battery with the positive electrode material of the present application is still improved as a whole.

It can be seen from examples 22-23 and comparative example 1 that the electrochemical performance of the lithium ion battery can be improved by using other one-dimensional conductive agents such as carbon fiber or other fast ion conductors, because the one-dimensional conductive agent is a long-range conductive agent, and can provide sufficient attachment sites for the fast ion conductors, and the fast ion conductors can effectively improve the ionic conductivity of the material and serve as protective layers to inhibit metal dissolution.

From examples 1 and 25 to 29, it can be seen that the cycle performance of the lithium ion battery is improved as the aspect ratio of the one-dimensional conductive agent is increased, but the cycle performance is reduced when the aspect ratio of the one-dimensional conductive agent is increased to a certain degree.

As can be seen from examples 1, 30 to 34, as the specific surface area of the one-dimensional conductive agent increases, the cycle performance of the lithium ion battery increases, but when the specific surface area of the one-dimensional conductive agent increases to a certain extent, the cycle performance decreases.

It can be seen from example 1 and comparative example 5 that the 0.1C specific discharge capacity and the cycle capacity retention rate of comparative example 5 are both decreased, which is probably due to the fact that LLZO in comparative example 5 directly causes an increase in interfacial resistance at the surface of the matrix material, thereby affecting the capacity and cycle performance of the lithium ion battery.

As can be seen from fig. 1, in the cathode material of the present application, the strip-shaped one-dimensional conductive agent is relatively uniformly distributed in the matrix material, and the small-particle fast ion conductor is attached near the one-dimensional conductive agent, so that the cathode material has excellent electron conductivity and ion conductivity.

As is clear from table 4, the positive electrode material of example 1 of the present application contains elements of C, O, P, Mn, Fe, La, and Zr.

The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A preparation method of a positive electrode material comprises the following steps:

2. The preparation method of claim 1, wherein the atmosphere of the firing step is selected from at least one of argon, helium, neon or nitrogen, the firing temperature of the firing step is 300 ℃ to 800 ℃, and the firing time of the firing step is 6h to 24 h.

3. The production method according to claim 1, wherein the organic solvent includes at least one of methanol or ethanol.

4. The production method according to claim 1, wherein the solid content of the first suspension is 35 to 65%, the solid content of the second suspension is 35 to 65%, and the solid content of the mixed slurry is 40 to 60%.

5. The production method according to claim 1, wherein the mass percentage of the one-dimensional conductive agent is 0.05% to 5% and the mass percentage of the fast ion conductor is 0.05% to 5% based on the total mass of the base material, the one-dimensional conductive agent, and the fast ion conductor.

6. The production method according to claim 1, wherein the mass ratio of the one-dimensional conductive agent to the fast ion conductor is 0.1: 1 to 10: 1.

7. the production method according to claim 1, wherein the base material includes at least one of lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganese oxide, or lithium cobalt oxide, a molar ratio of a manganese element to an iron element in the lithium manganese iron phosphate is 0.01 to 10, and the one-dimensional conductive agent includes at least one of carbon nanotubes or carbon fibers.

8. The method of claim 1, wherein the fast ion conductor comprises compound Li_xLa_yZr_zM_aO_bWherein x is more than or equal to 6 and less than or equal to 8, y is more than or equal to 2 and less than or equal to 4, z is more than or equal to 1 and less than or equal to 3, a is more than or equal to 0 and less than or equal to 0.5, b is more than or equal to 11 and less than or equal to 13, and the M element is selected from at least one of Ta elements or W elements.

9. The method of claim 1, wherein the fast ion conductor comprises Li₁₀GeP₂S₁₂Or Li₇La₃Zr₂O₁₂At least one of (1).

10. The production method according to claim 7, wherein the matrix material includes ZrO₂、SnO₂、ZnO、MgO、Al₂O₃、TiO₂、CeO₂、AlF₃Or Li₃AlF₆At least one of (1).