CN113517423B - Positive electrode material, preparation method thereof, pole piece and preparation method thereof - Google Patents

Positive electrode material, preparation method thereof, pole piece and preparation method thereof Download PDF

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CN113517423B
CN113517423B CN202110437251.6A CN202110437251A CN113517423B CN 113517423 B CN113517423 B CN 113517423B CN 202110437251 A CN202110437251 A CN 202110437251A CN 113517423 B CN113517423 B CN 113517423B
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pole piece
positive electrode
low
mixing
iron phosphate
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CN113517423A (en
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莫方杰
孙化雨
汪文静
请求不公布姓名
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Envision Power Technology Jiangsu Co Ltd
Envision Ruitai Power Technology Shanghai Co Ltd
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Envision Power Technology Jiangsu Co Ltd
Envision Ruitai Power Technology Shanghai Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02E60/10—Energy storage using batteries

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Abstract

The invention provides a positive electrode material, a preparation method thereof, a pole piece and a preparation method thereof. The positive electrode material comprises a low-cobalt active material and lithium iron phosphate, and the mass ratio of the low-cobalt active material to the lithium iron phosphate is (90-99). The pole piece comprises the positive pole material. The preparation method of the pole piece comprises the following steps: and mixing the conductive slurry with the positive electrode material to obtain positive electrode slurry, coating the positive electrode slurry on a current collector, drying and rolling to obtain the pole piece. The cathode material provided by the invention can effectively overcome the problem of rapid voltage drop of the low-cobalt active material at the final stage of discharge, and the reaction potential of the electrode at a low potential is improved by blending lithium iron phosphate with a lower reaction potential and cooperating with lithium ion diffusion of the low-cobalt active material at the low potential, so that the energy density of the battery is improved.

Description

Positive electrode material, preparation method thereof, pole piece and preparation method thereof
Technical Field
The invention belongs to the technical field of batteries, and relates to a positive electrode material, a preparation method thereof, a pole piece and a preparation method thereof.
Background
Ternary layered material LiNi x Co y Mn 1-x-y O 2 Because the catalyst has higher theoretical specific capacity of 274mAh/g and high reaction platform voltage of 3.0-4.3V, excellent reaction kinetics, and is widely applied to high energyA power battery system with mass density. However, the ternary material widely used at present has a high Co content (y is more than 0.1), and Co ore is increasingly in short supply as a rare mineral resource. The prior art solves the problems of material cost and limited cobalt ore resources by reducing the content of ternary Co, and develops a low-cobalt active material LiNi x Co y Mn 1-x-y O 2 (y is less than 0.05).
Low cobalt active material LiNi x Co y Mn 1-x-y O 2 The decrease of the Co content in (y is less than 0.05) can reduce the overall conductivity of the material and improve the diffusion barrier of lithium ions in crystal lattices, thereby bringing about a serious reaction kinetics retardation problem and influencing the capacity exertion of the battery. There is a significant voltage drop especially at the end of discharge, which results in a low cobalt active material, liNi x CoyMn 1-x-y O 2 (y is less than 0.05) energy density is reduced, and development and application of the material are influenced.
CN110931738A discloses a complex phase high voltage anode material which is composed of LiNi with a hexagonal layered structure x-a Co y-a Mn z- a M b O 2 A rock salt phase (Li + N) O and a coating agent A, and the chemical general formula is LiNi x-a Co y-a Mn z-a M b O 2 A (Li + N) O.cA; wherein a is more than 0 and less than 0.01, x is more than or equal to 0.33 and less than 1.0, y is more than or equal to 0 and less than or equal to 0.33, z is more than 0.01 and less than 0.5, b is more than 0 and less than 0.02, c is more than 0.001 and less than 0.01, x + y + z =1; m is one or more of Mg, al, ti, zr, sr, Y, ce, B, W, la, sn, zn and Mo; n is one or more of Ni, co and Mn; the coating agent A is TiO 2 、ZrO 2 、Al 2 O 3 、SnO 2 、Li 3 PO 4 、Li 2 B 4 O 7 、Li 4 TiO 4 And Li 2 SiO 3 One kind of (1). However, the above method exists with LiNi, a low cobalt active material x Co y Mn 1-x-y O 2 The energy density is to be improved in the problem of a rapid voltage drop at the end of discharge.
CN111900380A discloses a method for preparing a nickel cobalt lithium manganate single crystal ternary material. The method comprises the following steps: (1) Lithium carbonate and precursor(Ni 0.55 Co 0.15 Mn 0.3 )(OH) 2 Uniformly mixing with a zirconium compound to obtain a mixture; (2) Placing the mixture in a sagger, scribing, cutting into blocks and calcining to obtain the single crystal Li (Ni) 0.55 Co 0.15 Mn 0.3 )O 2 A material block; (3) The material blocks are subjected to coarse crushing, airflow crushing and sieving in sequence to obtain black powder; (4) And (3) mixing the black powder and the additive by a high-speed dry method, and sintering to obtain the additive-coated black powder material. But the ternary material of the method has higher Co content, thereby improving the production cost.
CN111384392A discloses a high-nickel low-cobalt high-voltage-resistant ternary cathode material and a preparation method thereof. The piezoelectric ternary cathode material comprises a coating layer and LiNi doped with a metal element M 0.65 Co 0.07 Mn 0.28 O 2 A matrix, wherein the metal element M is at least two selected from Nb, mg, Y, ti, W, al and Zr; the coating layer contains metal element M' selected from at least two of Mg, Y, ti, W, al and Zr. But the ternary material of the method has higher Co content, thereby improving the production cost.
Disclosure of Invention
In view of the above-mentioned disadvantages in the prior art, the present invention aims to provide a positive electrode material, a preparation method thereof, a pole piece and a preparation method thereof. The positive electrode material provided by the invention solves the problem of low energy density in the low-cobalt active material.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a cathode material, which includes a low-cobalt active material and lithium iron phosphate, wherein a mass ratio of the low-cobalt active material to the lithium iron phosphate is 90-99.
The low-cobalt active material of the invention means that the percentage content of cobalt in other metal elements except lithium in the low-cobalt active material is below 5%.
In the anode material provided by the invention, lithium iron phosphate is matched with a low-cobalt active material, the electrochemical reaction potential of the lithium iron phosphate is 3.0-3.4V, and the theoretical specific capacity is 170mAh/g. The lithium iron phosphate is mixed with a low-cobalt active material, and lithium ion migration of the lithium iron phosphate at a reaction potential can generate a synergistic effect on lithium ion diffusion of the low-cobalt active material at a low potential (3.0-3.4V), so that the reaction potential of an electrode at the low potential is improved, and the overall energy density of the battery is improved.
In the present invention, the mass ratio of the low-cobalt active material to the lithium iron phosphate is 90. In the invention, too much lithium iron phosphate can cause the overall voltage of the battery to be too low, thereby reducing the energy density; if the amount of lithium iron phosphate is too small, the function of lifting the low-potential voltage platform cannot be fully exerted.
The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.
As a preferable technical scheme of the invention, the chemical formula of the low-cobalt active material is LiNi x Co y M 1-x-y O 2 Wherein 0.5. Ltoreq. X.ltoreq.0.9, e.g. x is 0.5, 0.6, 0.7, 0.8 or 0.9 etc., 0. Ltoreq. Y.ltoreq.0.05, e.g. y is 0, 0.01, 0.02, 0.03, 0.04 or.0.05 etc., M is Mn and/or Al.
Preferably, M is Mn.
Preferably, the low cobalt active material is spherical secondary particles or a single crystal.
Preferably, the spherical secondary particles have a D50 particle size of 8-18 μm, such as 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, or the like. The purpose of using this D50 range is to increase the overall compacted density of the material without reducing the reaction kinetics of the active species.
Preferably, the single crystal has a D50 particle size of 2-7 μm, such as 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, or the like. The D50 range is adopted for the purpose of ensuring the reaction kinetics of the material, reducing the side reaction with the electrolyte and ensuring the long-term performance.
As a preferable technical scheme of the invention, the lithium iron phosphate is spherical micro lithium iron phosphate or nano lithium iron phosphate.
Preferably, the D50 particle size of the spherical micro lithium iron phosphate is 5-15 μm, such as 5 μm, 10 μm, or 15 μm. The D50 range is adopted to improve the integral compaction density of the material and ensure the reaction dynamic performance of the material.
Preferably, the D50 particle size of the nano lithium iron phosphate is 0.5-2 μm, such as 0.5 μm, 1 μm, 1.5 μm or 2 μm. The D50 range is adopted for ensuring the electrochemical reaction kinetics of the material and reducing side reactions with the electrolyte.
In a second aspect, the present invention provides a method for producing the positive electrode material according to the first aspect, the method comprising the steps of:
and mixing the low-cobalt active material and the lithium iron phosphate according to the formula ratio to obtain the cathode material.
As the preferable technical scheme of the invention, the mixing is stirring mixing;
preferably, the stirring and mixing is high-speed stirring and mixing.
In the present invention, the stirring rate of the high-speed stirring and mixing is 30 revolutions per minute by rotation and 2000 revolutions per minute or more, the same applies below.
In a third aspect, the present invention provides a pole piece comprising the positive electrode material according to the first aspect.
The pole piece provided by the invention can improve the energy density of the battery because the positive pole material provided by the first aspect is used.
As a preferred technical solution of the present invention, the pole piece includes a current collector and a coating coated on the current collector, and the coating includes the positive electrode material according to the first aspect.
Preferably, the coating further comprises a conductive agent and a binder.
Preferably, the conductive agent comprises conductive carbon black and/or conductive carbon nanotubes.
Preferably, the binder comprises any one of polyvinylidene fluoride, polytetrafluoroethylene or styrene butadiene rubber or a combination of at least two of them.
Preferably, in the coating, the mass ratio of the positive electrode material, the conductive agent and the binder is 100 (1-2) to (0.5-1.5), such as 100.
Preferably, the current collector is an aluminum foil.
In a fourth aspect, the present invention provides a method for preparing a pole piece according to the third aspect, the method includes the following steps:
mixing the conductive slurry with the positive electrode material to obtain positive electrode slurry, coating the positive electrode slurry on a current collector, drying and rolling to obtain the pole piece.
In a preferred embodiment of the present invention, the mixing is stirring.
Preferably, the stirring and mixing is high-speed stirring and mixing.
Preferably, the coating is coating with a doctor blade.
Preferably, the drying temperature is 100-140 ℃, such as 100 ℃, 110 ℃, 120 ℃, 130 ℃ or 140 ℃ and the like.
Preferably, the drying time is 15-25min, such as 15min, 17min, 20min, 23min or 25min, etc.
Preferably, after said rolling, the rolled product is cut.
Preferably, the conductive paste includes formulated amounts of a conductive agent, a binder, and a solvent.
Preferably, the solvent comprises water or a nitrogen methyl pyrrolidone solution.
Preferably, the mass ratio of the solvent to the binder is (35-45) 1, for example 35.
As a further preferable technical scheme of the preparation method of the pole piece, the method comprises the following steps:
(1) Stirring and mixing the low-cobalt active material and the lithium iron phosphate according to the formula ratio at a high speed to obtain a positive electrode material; dispersing and stirring the conductive agent, the binder and the solvent according to the formula ratio to obtain conductive slurry;
(2) And (2) stirring and mixing the positive electrode material in the step (1) and the conductive slurry at a high speed to obtain positive electrode slurry, coating the positive electrode slurry on an aluminum foil by using a scraper, placing the aluminum foil in a forced air drying oven, drying for 15-25min at 100-140 ℃, and then rolling and cutting to obtain the pole piece.
Compared with the prior art, the invention has the following beneficial effects:
the cathode material provided by the invention can effectively overcome the problem of rapid voltage drop of the low-cobalt active material at the final stage of discharge, and the reaction potential of the electrode at a low potential is improved by blending lithium iron phosphate with a lower reaction potential and cooperating with lithium ion diffusion of the low-cobalt active material at the low potential, so that the energy density of the battery is improved.
Drawings
Fig. 1 is a discharge curve at a 2C discharge rate after batteries are prepared from the electrode sheets provided in example 1 and comparative example 1.
Fig. 2 is a discharge curve at a 3C discharge rate after batteries are prepared from the electrode sheets provided in example 1 and comparative example 1.
Detailed Description
In order to better illustrate the present invention and facilitate the understanding of the technical solutions of the present invention, the present invention is further described in detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims.
The following are typical but non-limiting examples of the invention:
example 1
The cathode material provided by this embodiment is composed of a low-cobalt active material and lithium iron phosphate, and the mass ratio of the low-cobalt active material to the lithium iron phosphate is 97. The low-cobalt active material is a single crystal ternary material LiNi 0.75 Mn 0.25 O 2 (D50 is 5 μm), and the lithium iron phosphate is spherical micron lithium iron phosphate (D50 is 10 μm).
The electrode plate provided by this embodiment is composed of a current collector and a coating layer coated on the current collector, the current collector is an aluminum foil, and the coating layer is composed of a positive electrode material, conductive carbon black, a conductive carbon nanotube and a binder polyvinylidene fluoride provided by this embodiment with a mass ratio of 100. The pole piece is coated on two sides, and the thickness of the coating on each side is 2 micrometers.
In this example, the positive electrode material and the electrode sheet were prepared as follows:
(1) Stirring and mixing the low-cobalt active material and the lithium iron phosphate according to the formula ratio at a high speed to obtain a positive electrode material; dispersing and stirring the conductive agent (conductive carbon black and conductive carbon nano tube), the binder (PVDF) and the solvent (N-methyl pyrrolidone NMP) for 2h at a high speed according to the formula ratio to obtain conductive slurry; the mass ratio of the solvent to the binder is 40.
(2) And (2) stirring and mixing the positive electrode material and the conductive slurry in the formula amount in the step (1) at a high speed to obtain positive electrode slurry, coating the positive electrode slurry on an aluminum foil by using a scraper, placing the aluminum foil in a forced air drying oven, drying for 20min at 120 ℃, and then rolling and cutting to obtain the pole piece.
Example 2
The cathode material provided by this embodiment is composed of a low-cobalt active material and lithium iron phosphate, and the mass ratio of the low-cobalt active material to the lithium iron phosphate is 90. The low-cobalt active material is a single crystal ternary material LiNi 0.75 Mn 0.25 O 2 (D50 is 7 μm), and the lithium iron phosphate is spherical micron lithium iron phosphate (D50 is 5 μm).
The electrode plate provided by this embodiment is composed of a current collector and a coating layer coated on the current collector, the current collector is an aluminum foil, and the coating layer is composed of a positive electrode material, conductive carbon black, a conductive carbon nanotube and a binder polyvinylidene fluoride provided by this embodiment, the mass ratio of which is 100. The pole piece is coated on two sides, and the thickness of the coating on each side is 2 micrometers.
In this example, the positive electrode material and the electrode sheet were prepared as follows:
(1) Stirring and mixing the low-cobalt active material and the lithium iron phosphate according to the formula ratio at a high speed to obtain a positive electrode material; dispersing and stirring the conductive agent (conductive carbon black and conductive carbon nano tube), the binder (PVDF) and the solvent (N-methyl pyrrolidone NMP) for 2h at a high speed according to the formula ratio to obtain conductive slurry; the mass ratio of the solvent to the binder is 35.
(2) And (2) stirring and mixing the positive electrode material and the conductive slurry in the formula amount in the step (1) at a high speed to obtain positive electrode slurry, coating the positive electrode slurry on an aluminum foil by using a scraper, placing the aluminum foil in a forced air drying oven, drying for 25min at 100 ℃, and then rolling and cutting to obtain the pole piece.
Example 3
The cathode material provided by this embodiment is composed of a low-cobalt active material and lithium iron phosphate, and the mass ratio of the low-cobalt active material to the lithium iron phosphate is 99. The low-cobalt active material is spherical secondary particle LiNi 0.5 Co 0.05 Mn 0.45 O 2 (D50 is 10 μm), and the lithium iron phosphate is nano lithium iron phosphate (D50 is 0.5 μm).
The electrode plate provided by this embodiment is composed of a current collector and a coating layer coated on the current collector, the current collector is an aluminum foil, and the coating layer is composed of the positive electrode material, conductive carbon black, conductive carbon nanotube and binder polyvinylidene fluoride provided by this embodiment, the mass ratio of which is 100.5. The pole piece is coated on two sides, and the thickness of the coating on each side is 2 micrometers.
In this example, the positive electrode material and the electrode sheet were prepared as follows:
(1) Stirring and mixing the low-cobalt active material and the lithium iron phosphate according to the formula ratio at a high speed to obtain a positive electrode material; dispersing and stirring the conductive agent (conductive carbon black and conductive carbon nano tube), the binder (PVDF) and the solvent (N-methyl pyrrolidone NMP) for 2h at a high speed according to the formula ratio to obtain conductive slurry; the mass ratio of the solvent to the binder is 45.
(2) And (2) stirring and mixing the positive electrode material and the conductive slurry in the formula amount in the step (1) at a high speed to obtain positive electrode slurry, coating the positive electrode slurry on an aluminum foil by using a scraper, placing the aluminum foil in a forced air drying oven, drying for 15min at 140 ℃, and then rolling and cutting to obtain the pole piece.
Example 4
The cathode material provided by this embodiment is composed of a low-cobalt active material and lithium iron phosphate, and the mass ratio of the low-cobalt active material to the lithium iron phosphate is 95. The low-cobalt active material is spherical secondary particle LiNi 0.5 Co 0.05 Mn 0.45 O 2 (D50 is 18 mu m), and the lithium iron phosphate is nano lithium iron phosphate (D50 is 0.5 mu m)m)。
The pole piece that this embodiment provided comprises the mass flow body and is located the coating of coating on the mass flow body, the mass flow body is the aluminium foil, the coating comprises positive electrode material, conductive carbon black, conductive carbon nanotube, binder polyvinylidene fluoride that this embodiment provided of mass ratio is 100.5. The pole piece is coated on two sides, and the thickness of the coating on each side is 2 micrometers.
Comparative example 1
The present comparative example is different from example 1 in that the positive electrode material is entirely composed of the same low cobalt active material as example 1, and does not contain any lithium iron phosphate. The electrode sheet provided by the present comparative example was the same as example 1 except that the positive electrode material of the present comparative example was used.
Comparative example 2
The comparative example differs from example 1 in that the mass ratio of the low-cobalt active material to the lithium iron phosphate was 85. The electrode sheet provided by the present comparative example was the same as example 1 except that the positive electrode material of the present comparative example was used.
Comparative example 3
The comparative example is different from example 1 in that the mass ratio of the low cobalt active material to the lithium iron phosphate is 99.5. The electrode sheet provided by the present comparative example was the same as example 1 except that the positive electrode material of the present comparative example was used.
Test method
The electrode sheets obtained in each example and comparative example were used as a positive electrode, a lithium sheet was used as a negative electrode, and an electrolyte was 1M LiPF 6 (the solvent is a mixed solution of Ethylene Carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1.
Charging at room temperature at 0.33C rate to 4.35V voltage, and then discharging the battery at 2C rate to 3V voltage to obtain a discharge curve shown in FIG. 1; then, the battery was charged to a voltage of 4.35V at a rate of 0.33C, and then the battery was discharged to a voltage of 3V at a rate of 3C, resulting in a discharge curve as shown in fig. 2.
As can be seen from FIGS. 1 and 2, under the 2C rate discharge condition, the discharge voltage plateau of example 1 between 3.3V and 3.5V is significantly improved compared with that of comparative example 1; under the condition of 3C rate discharge, the discharge voltage plateau of the example 1 between 3.2 and 3.4V is obviously improved compared with that of the comparative example 1.
Under the test conditions of 0.33C rate charging and 0.33C rate discharging, the energy density of the button cell is tested, and the test results are shown in the following table:
TABLE 1
Test sample Energy Density (Wh/kg)
Example 1 223
Example 2 213
Example 3 208
Example 4 205
Comparative example 1 207
Comparative example 2 195
Comparative example 3 210
It can be known from the above embodiments and comparative examples that the positive electrode material provided by the embodiments can effectively overcome the problem of rapid voltage drop of the low-cobalt active material at the end of discharge, and the reaction potential of the electrode at the low potential is improved by blending the lithium iron phosphate with the lower reaction potential and cooperating with lithium ion diffusion of the low-cobalt active material at the low potential, thereby improving the energy density of the battery.
The comparative example 1 does not contain lithium iron phosphate, so that a low potential voltage platform is low and the overall energy density is not high.
And in the comparative example 2, the lithium iron phosphate is too much, so that the voltage platform of the whole electrode is too low, and the energy density is reduced.
Comparative example 3 too little lithium iron phosphate resulted in an insignificant gain in the overall energy density of the cell.
The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims (22)

1. The positive electrode material is characterized by comprising a low-cobalt active material and lithium iron phosphate, wherein the mass ratio of the low-cobalt active material to the lithium iron phosphate is (90-99);
the low-cobalt active material is spherical secondary particles or single crystals, the D50 particle size of the spherical secondary particles is 8-18 mu m, and the D50 particle size of the single crystals is 2-7 mu m;
the lithium iron phosphate is spherical micron lithium iron phosphate, and the D50 particle size of the spherical micron lithium iron phosphate is 5-15 mu m;
the chemical formula of the low-cobalt active material is LiNi x Co y M 1-x-y O 2 Wherein x is more than or equal to 0.5 and less than or equal to 0.75, y is more than or equal to 0 and less than or equal to 0.05, and M is Mn.
2. The method for preparing a positive electrode material according to claim 1, comprising the steps of:
and mixing the low-cobalt active material and the lithium iron phosphate according to the formula ratio to obtain the cathode material.
3. The method for producing a positive electrode material according to claim 2, wherein the mixing is stirring mixing.
4. The production method according to claim 3, wherein the agitation mixing is high-speed agitation mixing.
5. A pole piece comprising the positive electrode material of claim 1.
6. The pole piece of claim 5, wherein the pole piece comprises a current collector and a coating coated on the current collector, wherein the coating comprises the positive electrode material of claim 1.
7. The pole piece of claim 6, wherein the coating further comprises a conductive agent and a binder.
8. The pole piece of claim 7, wherein the conductive agent comprises conductive carbon black and/or conductive carbon nanotubes.
9. The pole piece of claim 7, wherein the binder comprises any one of polyvinylidene fluoride, polytetrafluoroethylene or styrene butadiene rubber or a combination of at least two of them.
10. The pole piece of claim 7, wherein the mass ratio of the positive electrode material, the conductive agent and the binder in the coating is 100 (1-2) to (0.5-1.5).
11. The pole piece of claim 6, wherein the current collector is aluminum foil.
12. A method of making a pole piece as claimed in any one of claims 5 to 11, wherein the method includes the steps of:
mixing the conductive slurry with the positive electrode material according to claim 1 to obtain positive electrode slurry, coating the positive electrode slurry on a current collector, drying and rolling to obtain the pole piece.
13. The method for preparing a pole piece according to claim 12, wherein the mixing is stirring mixing.
14. The method for preparing a pole piece according to claim 13, wherein the stirring and mixing is high-speed stirring and mixing.
15. The method of claim 12, wherein the coating is by doctor blade coating.
16. The method for preparing the pole piece according to claim 12, wherein the drying temperature is 100-140 ℃.
17. The method for preparing a pole piece according to claim 12, wherein the drying time is 15-25min.
18. The method for preparing the pole piece according to claim 12, wherein the rolled product is cut after the rolling.
19. The method of claim 12, wherein the conductive slurry comprises formulated amounts of a conductive agent, a binder, and a solvent.
20. The method of claim 19, wherein the solvent comprises water or a nitrogen methyl pyrrolidone solution.
21. The preparation method of the pole piece according to claim 19, wherein the mass ratio of the solvent to the binder is (35-45): 1.
22. The method for preparing the pole piece according to claim 12, wherein the method comprises the following steps:
(1) Stirring and mixing the low-cobalt active material and the lithium iron phosphate according to the formula ratio at a high speed to obtain a positive electrode material; dispersing and stirring the conductive agent, the binder and the solvent according to the formula ratio to obtain conductive slurry;
(2) And (2) stirring and mixing the positive electrode material obtained in the step (1) and the conductive slurry at a high speed to obtain positive electrode slurry, coating the positive electrode slurry on an aluminum foil by using a scraper, placing the aluminum foil in a forced air drying box, drying for 15-25min at 100-140 ℃, and then rolling and cutting to obtain the pole piece.
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