CN114447321A - Positive electrode material, positive plate comprising same and battery - Google Patents
Positive electrode material, positive plate comprising same and battery Download PDFInfo
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- CN114447321A CN114447321A CN202210082272.5A CN202210082272A CN114447321A CN 114447321 A CN114447321 A CN 114447321A CN 202210082272 A CN202210082272 A CN 202210082272A CN 114447321 A CN114447321 A CN 114447321A
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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
- H01M4/366—Composites as layered products
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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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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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
- H01M4/58—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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- 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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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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
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
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- H—ELECTRICITY
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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
Abstract
The invention provides a positive electrode material, a positive electrode plate comprising the material and a battery. The positive electrode active material in the positive electrode material is a secondary spherical particle, the secondary spherical particle comprises an inner core area and an outer shell area, and the outer shell area is positioned on the outer layer of the inner core area; the shell region has an agglomerated compact structure; the inner core area has an agglomerated loose structure; when the positive plate is made of the positive material and applied to a battery, the first effect, the coulombic efficiency, the low-temperature discharge capacity, the high-rate performance and the safety performance of the battery are remarkably improved, and the problem that the low-temperature discharge performance and the rate discharge performance of a battery core are poor in the prior art is solved.
Description
Technical Field
The invention belongs to the technical field of batteries, and relates to a positive electrode material, a positive plate comprising the material and a battery, in particular to a manganese lithium phosphate composite material, a preparation method of the manganese lithium phosphate composite material, a positive plate comprising the composite material and a battery comprising the positive plate.
Background
The battery is applied and popularized in the aspects of portable electrical appliances, power energy storage systems and the like, realizes the wireless revolution of mobile phones, notebook computers and digital cameras, and is a key component of portable electrical appliances and telecommunication equipment required by the current society.
The olivine-type lithium manganese phosphate has high energy density, low cost and excellent cycle performance, is paid much attention by researchers, and has great significance in developing lithium manganese phosphate cathode materials with excellent electrochemical performance. However, the special olivine-type lithium manganese phosphate unit cell structure causes low electronic conductivity and lithium ion diffusion coefficient, the specific discharge capacity under high current density is low, the cycle performance is poor, and the excellent electrochemical performance is not easy to exert.
Meanwhile, most of high-performance lithium manganese phosphate synthesis involves complex processes, the defects limit the large-scale production of the lithium manganese phosphate, and the simplification of the synthesis is a hot topic of scientific research at present.
The conventional lithium manganese phosphate is a monocrystalline substance with higher density obtained by sintering, and the material has higher compacted density and tap density, but the high density cannot relieve the stress load generated by the expansion and contraction of particles during the charge and discharge of the battery, so that primary particles are crushed, and the performance of the battery is influenced.
Disclosure of Invention
Researches show that the hollow structure can provide various paths for diffusion of lithium ions, and the problems of low lithium diffusion speed, polarization and the like of the anode material in the prior art are solved. Meanwhile, the positive plate comprising the material and the battery comprising the positive plate have good rate performance and dynamic performance, and particularly have good low-temperature discharge performance.
In order to overcome the defects of the prior art, the invention provides a positive electrode material, a positive plate comprising the material and a battery, wherein a positive active substance in the positive electrode material is lithium manganese phosphate, and the median particle size of the positive electrode material is selected within a certain range, so that the battery with better dynamic performance, low-temperature discharge performance and high safety performance can be obtained; furthermore, the positive active substance has a core-shell structure, the agglomeration degree of the core is different from that of the shell, and the positive plate prepared by the positive material and the battery assembled by the positive plate have obviously better dynamic performance, low-temperature discharge performance and high safety performance.
The technical scheme provided by the invention is as follows:
a positive electrode material comprises a positive electrode active material and a coating material compounded on the surface of the positive electrode active material; the median particle diameter D50 of the positive electrode material is 2-5 μm;
the positive active material is lithium manganese phosphate.
According to an embodiment of the present invention, the positive electrode active material is a secondary spherical particle including a core region and a shell region, the shell region being located at an outer layer of the core region; the shell region has an agglomerated compact structure; the inner core region has an agglomerated porous structure.
According to an embodiment of the present invention, the chemical formula of the positive active material is LiMnPO4。
According to an embodiment of the invention, the shell area has pores. Illustratively, the shell region has a porosity of 10% to 35%, e.g., 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, or any point in the range consisting of any two of the foregoing endpoints.
According to an embodiment of the invention, the porosity of the inner core region is greater than the porosity of the outer shell region. Illustratively, the core region has a porosity of 60% to 90%, such as 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, or any point in the range consisting of any two of the foregoing endpoints.
The porosity is not particularly limited in the present invention and can be measured by methods known in the art.
According to an embodiment of the present invention, the central position of the inner core region has an agglomerated loose structure, and further, the central position of the inner core region is hollow. Illustratively, the positive electrode material has a structure shown in fig. 8.
According to an embodiment of the invention, the coating material is selected from carbon materials. Preferably, the carbon material is selected from amorphous carbon.
According to an embodiment of the invention, the thickness of the coating material is between 2nm and 8 nm.
According to the embodiment of the invention, the specific surface area of the cathode material is 15-25 m2/g。
According to an embodiment of the present invention, the electron conductivity of the positive electrode material is 1.0 × 10-5S/cm～9.0×10-5S/cm。
According to an embodiment of the present invention, the positive electrode material has a lithium ion diffusion coefficient of 1.0 × 10-14cm2/s～8.0×10-14cm2/s。
According to an embodiment of the present invention, the mass of the positive electrode active material accounts for 97.5 wt% to 99.0 wt% of the total mass of the positive electrode material, for example, 97.5 wt%, 98 wt%, 98.5 wt%, 99 wt%, or any point in the range of the above-mentioned two endpoints.
According to an embodiment of the present invention, the mass of the coating material accounts for 1 wt% to 2.5 wt% of the total mass of the cathode material, for example, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, or any point in the range of the above two endpoints.
According to an embodiment of the present invention, the median particle diameter D50 of the core region of the positive electrode active material is 1.2 μm to 2.6 μm.
According to an embodiment of the invention, the composition of the core region and the shell region is the same and is lithium manganese phosphate LiMnPO4。
According to an embodiment of the present invention, the secondary spherical particles refer to a spherical secondary particle structure formed by stacking primary particles of lithium manganese phosphate.
According to the embodiment of the invention, the inner core region is an agglomerated loose structure with the porosity of 60-90% formed by agglomeration of small-particle-size lithium manganese phosphate primary particles.
According to the embodiment of the invention, the shell area is an agglomerated compact structure with the porosity of 10-35% and formed by agglomeration of primary lithium manganese phosphate particles with large particle sizes.
The invention also provides a positive plate which comprises the positive electrode material.
According to an embodiment of the present invention, the positive electrode sheet may be prepared according to a method known in the art, and may further include, for example, a conductive agent, a binder, or other materials known in the art, which is not particularly limited in the present invention.
According to the embodiment of the invention, the positive plate comprises a positive current collector and a positive active layer positioned on the surface of the positive current collector; the positive electrode active material layer includes the positive electrode material described above.
According to the embodiment of the invention, the mass percentage of each component in the positive electrode active material layer is as follows: 70-99 wt% of positive electrode active material, 0.5-15 wt% of conductive agent and 0.5-15 wt% of binder.
Preferably, the positive electrode active material layer comprises the following components in percentage by mass:
96-98 wt% of positive electrode active material, 1-2 wt% of conductive agent acetylene black, 1-1.5 wt% of conductive agent carbon nano tube and 0.5-1.0 wt% of binder polyvinylidene fluoride (PVDF).
The invention also provides the application of the positive electrode material or the positive electrode plate in a battery.
The invention also provides a battery, which comprises the positive electrode material or the positive electrode sheet.
According to an embodiment of the present invention, the battery includes a positive electrode tab; the positive plate comprises a positive current collector and a positive active layer positioned on the surface of the positive current collector; the positive electrode active layer comprises a positive electrode material, a conductive agent and a binder, and the positive electrode material comprises the positive electrode material.
According to an embodiment of the invention, the battery is a lithium ion battery.
According to an embodiment of the present invention, the battery may be prepared according to a method known in the art, and may further include, for example, a negative electrode, a separator, an electrolyte, and the like, which may be selected according to a method known in the art, and the present invention is not particularly limited.
According to the embodiment of the invention, the volume energy density of the battery is 225-255 KWh/m3The weight energy density is 175-215 Wh/kg.
The invention has the beneficial effects that:
the lithium manganese phosphate anode active material is a microsphere with a core-shell structure, the particle size of the particles is controllable, and a shell in the lithium manganese phosphate anode active material has an agglomerated compact structure; the inner core in the lithium manganese phosphate anode active material has an agglomerated loose structure (even the central position of the inner core is partially hollow), the structure is favorable for improving the infiltration effect of electrolyte, meanwhile, the diffusion distance of lithium ions is shortened due to the internal loose structure, the diffusion path of the lithium ions is shortened, various paths are provided for the diffusion of the lithium ions, and the low diffusion capacity and the polarization effect of the lithium ions of the anode material are obviously improved.
When the positive electrode material is manufactured into a positive plate and applied to a battery, the first charge-discharge efficiency, the coulombic efficiency, the low-temperature performance, the multiplying power performance and the safety performance of a battery core are remarkably improved, the problems of low lithium ion diffusion speed, polarization phenomenon and the like of lithium manganese phosphate in the prior art are solved, and the safety performance and the multiplying power performance of the material are remarkably improved.
The invention provides a preparation method of a battery, which comprises a positive plate, a negative plate, a commercialized battery diaphragm and electrolyte, wherein the commercialized battery is prepared by adopting a standardized operation mode, can be applied to the layer of a soft package battery cell or a cylindrical battery cell, and has higher commercial value and practical significance.
Drawings
Fig. 1 is an XRD pattern of the cathode material of example 1;
fig. 2 is an SEM cross-sectional view of the cathode material of example 1;
fig. 3 is a charge-discharge curve of the button cell of example 1;
fig. 4 is the cycle capacity retention at 25 ℃ for the soft-packed cells of example 1;
fig. 5 is the cycle capacity retention at 45 ℃ for the soft-packed cells of example 1;
fig. 6 is an SEM cross-sectional view of the positive electrode material of comparative example 1;
fig. 7 is a charge-discharge curve of the button cell of comparative example 1;
fig. 8 is a schematic structural view of the positive electrode material of the present invention.
Detailed Description
The invention also provides a preparation method of the cathode material, which comprises the following steps:
1) respectively preparing a precursor solution of the positive active material, a complexing agent solution, a pH adjusting solution and a reaction solution;
2) injecting the precursor solution of the positive active material, the complexing agent solution and the pH adjusting solution in the step 1) into the reaction solution to carry out a first coprecipitation reaction, so as to obtain a solution containing a positive active material precursor crystal nucleus;
3) injecting the complexing agent solution and the pH adjusting solution obtained in the step 1) into the solution containing the anode active material precursor crystal nucleus obtained in the step 2) again, carrying out a second coprecipitation reaction until a target particle size is obtained, and stopping the reaction to prepare Mn3(PO4)2A positive electrode active material precursor;
4) mn obtained in the step 3)3(PO4)2The precursor of the positive active material is uniformly dispersed to Li3PO4Crystal nucleus growth is carried out in the crystal solution to obtain LiMnPO4A precursor;
5) LiMnPO obtained in the step 4)4And mixing the precursor with a carbon source, and roasting at high temperature in an inert atmosphere to prepare the anode material.
According to an embodiment of the present invention, in step 1), the precursor solution of the positive electrode active material includes manganese ions (Mn)2+) And phosphate ion (PO)4 3-)。
According to an embodiment of the invention, the manganese ions are provided by a manganese salt. Further preferably, the manganese salt is selected from (CH)3COO)2Mn、MnSO4、MnC2O4Or MnCl2At least one of (1).
According to an embodiment of the invention, the phosphate ions are provided by a water soluble compound containing phosphate ions. Further, the phosphate ion-containing water-soluble compound is selected from phosphoric acid or other soluble phosphate salts selected from (NH)4)H2PO4、(NH4)2HPO4Or (NH)4)3PO4At least one of (a).
According to an embodiment of the present invention, the manganese ion (Mn)2+) And phosphate ion (PO)4 3-) The total molar concentration of (a) is 1-3 mol/L.
According to an embodiment of the present invention, in step 1), the complexing agent solution contains a complexing agent.
According to an embodiment of the invention, the complexing agent is selected from at least one of oxalic acid, citric acid or EDTA.
According to the embodiment of the invention, the concentration of the complexing agent solution is 1-3 mol/L.
According to an embodiment of the present invention, in step 1), the pH adjusting solution includes an organic acid and/or an inorganic acid. Illustratively, the organic acid is selected from acetic acid or oxalic acid. Illustratively, the inorganic acid is selected from carbonic acid.
According to an embodiment of the present invention, the concentration of the pH adjusting solution is 0.025 to 0.30 mol/L.
According to an embodiment of the present invention, in step 1), the reaction solution is a mixed solvent composed of an alcohol solvent and water.
According to an embodiment of the present invention, the alcohol solvent is selected from at least one of ethylene glycol, glycerol, polyethylene glycol 400 or polyethylene glycol 200.
According to the embodiment of the invention, the volume ratio of the alcohol solvent to the water is (1-5): 1, preferably (2-3): 1.
According to an embodiment of the present invention, step 2) is a nucleation and kernel growth phase of the precursor of the positive active material.
According to an embodiment of the present invention, in the step 2) and the step 3), the reaction conditions of the step 2) and the step 3) are controlled by controlling the addition amounts of the complexing agent solution and the pH adjusting solution.
According to an embodiment of the present invention, in step 2), the reaction conditions include: the pH value is 1.5-2.4, the concentration of the complexing agent is 0.02-0.05 mol/L, and under the condition, the core area with an agglomerated loose structure can be prepared.
According to the embodiment of the invention, in the step 2), the time of the first coprecipitation reaction is 8-20 hours, the temperature of the first coprecipitation reaction is 50-75 ℃, and an inert gas such as nitrogen is continuously introduced in the first coprecipitation reaction process.
According to an embodiment of the present invention, step 3) is a housing production stage of the positive active material precursor.
According to an embodiment of the present invention, in step 3), the molecular formula of the positive active material in the positive material precursor is Mn3(PO4)2。
According to an embodiment of the present invention, in step 3), the reaction conditions include: the pH value is 2.6-3.5, the concentration of the complexing agent is 0.1-0.3 mol/L, and under the condition, the shell area with an agglomerated compact structure can be prepared.
According to the embodiment of the invention, in the step 3), the time of the second coprecipitation reaction is 48-96 h, the temperature of the second coprecipitation reaction is 50-75 ℃, and an inert gas such as nitrogen is continuously introduced in the process of the second coprecipitation reaction.
According to an embodiment of the present invention, the first coprecipitation reaction and the second coprecipitation reaction are performed under stirring conditions, and preferably, the stirring rate in the first coprecipitation reaction is greater than the stirring rate in the second coprecipitation reaction. Illustratively, the stirring speed of the first coprecipitation reaction is 200-650 rpm, and the stirring speed of the second coprecipitation reaction is 150-500 rpm.
According to an embodiment of the present invention, in step 3), the target particle size means that D50 is controlled to be 2 μm to 5 μm.
According to an embodiment of the invention, the step 3) further comprises the steps of performing solid-liquid separation, aging, drying, grinding, screening and impurity removal on the slurry after the reaction to obtain Mn3(PO4)2A positive electrode active material precursor.
According to an embodiment of the present invention, in step 4), the Li3PO4The crystal solution is prepared by the following methodThe following steps:
adding a phosphoric acid solution into a LiOH solution for reaction to form the Li3PO4And (3) crystal solution.
Wherein the phosphoric acid solution is a phosphoric acid water solution, and the molar concentration of the phosphoric acid water solution is 1.0-2.5 mol/L; the LiOH solution is a LiOH aqueous solution, and the molar concentration of the LiOH aqueous solution is 1.0-2.5 mol/L; in the system Li+And PO4 3-The molar ratio of (0.96-1.10) to (1).
According to an embodiment of the invention, in step 4), Li3PO4With Mn3(PO4)2Added in an amount of Li in the system+With Mn2+The molar ratio of (0.96-1.10) to (1).
According to an embodiment of the invention, in step 5), the carbon source is selected from an organic carbon source and/or an inorganic carbon source. Preferably, the organic carbon source is selected from at least one of glucose, sucrose, polyaniline or PEDOT conductive polymer. Preferably, the inorganic carbon source is selected from at least one of carbon nanotubes, conductive graphene and conductive carbon black.
According to an embodiment of the present invention, in step 5), the mixing is, for example, at least one of stirring, ball milling, grinding, and the like.
According to an embodiment of the present invention, in step 5), the inert atmosphere includes at least one of nitrogen, argon, and the like.
According to an embodiment of the invention, in step 5), the carbon source is mixed with LiMnPO4The mass ratio (g/g) of the precursor is (0.07-0.12): 1.
According to the embodiment of the invention, in the step 5), the roasting comprises multi-stage temperature-controlled sintering, and specifically comprises the following steps: heating the anode material from room temperature to 500-600 ℃ at a heating rate of 3 ℃/min, firstly preserving heat for 4-6 h at 500-600 ℃, then heating to 650-800 ℃ and preserving heat for 8-12 h to obtain the anode material.
According to an embodiment of the present invention, in step 5), the carbon source is cracked into amorphous carbon at a high temperature and uniformly deposited on the surface of the cathode active material.
The present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
Example 1
Firstly, preparing anode material
(1) Respectively preparing a binary solution, an oxalic acid solution and an acetic acid solution for later use, wherein the binary solution comprises MnSO4And H3PO4The molar concentration of the binary solution is 1.5mol/L, wherein PO is in the system4 3-With Mn2+In a molar ratio of 1.02: 1; preparing reaction liquid and stirring, wherein the reaction liquid is a mixed solvent of glycerol and water in a volume ratio of 2: 1; the concentration of oxalic acid is 1.25 mol/L; the concentration of acetic acid is 0.15 mol/L;
(2) injecting the binary solution, the oxalic acid solution and the acetic acid solution into the reaction solution to obtain a mixed solution, and carrying out the stage 1 reaction and the stage 2 reaction. The reaction temperature was controlled to 65 ℃ and nitrogen was continuously introduced during the reaction.
Stage 1: injecting the mixed solution into a reactor, controlling the stirring speed at 400rpm/min, controlling the concentration of oxalic acid at 0.03mol/L, regulating and controlling the pH value of the solution at 2.2, forming an intermediate reaction solution, wherein the coprecipitation reaction time of the stage 1 is 12 hours, and the process is a nucleation and kernel growth stage of a precursor to obtain a precursor crystal nucleus;
and (2) stage: injecting an oxalic acid solution and an acetic acid solution into the precursor crystal nucleus solution obtained in the previous step, adjusting the pH value of the system to 3.0, regulating the concentration of a complexing agent to be 0.2mol/L, carrying out coprecipitation reaction at a stirring speed of 350rpm/min, wherein the coprecipitation reaction is a shell production stage of the precursor, and the reaction is stopped until the target particle size reaches 3.5 mu m to obtain Mn3(PO4)2A precursor; the inner core area of the precursor is composed of agglomerated loose tiny particle groupsThe shell area consists of agglomerated and compact large particles, and the particle composition components of the core area and the shell area are both Mn3(PO4)2；
(3) Subjecting the reacted slurry to solid-liquid separation, aging, drying, grinding, screening and impurity removal to obtain Mn3(PO4)2A precursor;
(4) adding a phosphoric acid solution to the LiOH solution to react and form the Li3PO4And (3) crystal solution. The phosphoric acid solution is a phosphoric acid aqueous solution, and the molar concentration of the phosphoric acid aqueous solution is 1.25 mol/L; the LiOH solution is a LiOH aqueous solution, the molar concentration of the LiOH aqueous solution is 1.5mol/L, and Li in the system+And PO4 3-The molar ratio was 1.02: 1. Adding the Mn3(PO4)2The precursor is uniformly dispersed to Li3PO4Crystal nucleus growth is carried out in the crystal solution, the crystal nucleus reaction time is 8 hours, and LiMnPO is obtained after the reaction is finished4Precursor according to Li+With Mn2 +Weighing Li with a molar ratio of 1.04:13PO4With Mn3(PO4)2。
(5) Mixing glucose with LiMnPO4Preparing a precursor according to the mass ratio of 0.10:1, roasting at high temperature in an inert atmosphere, adopting a multi-stage temperature-control sintering mode in the sintering process, heating from room temperature to 580 ℃ at the heating rate of 3 ℃/min, preserving heat for 4h at 580 ℃, then heating to 700 ℃ and preserving heat for 8h, naturally cooling a sample to room temperature to obtain the lithium manganese phosphate with a carbon-coated structure, which is marked as LiMnPO4In the formula,/C, the carbon content was 2.2% (mass ratio) as measured by a carbon sulfur meter, and the specific surface area (BET value) is shown in Table 1.
The particle size D50 of the positive electrode material was 3.8 μm, and the porosity of the core region and the shell region was 75% and 26%, respectively, as determined by a porosity tester.
Fig. 1 is an XRD chart of the lithium manganese phosphate cathode material of example 1, and it can be seen that the standard lithium manganese phosphate material prepared in example 1 has good PDF card matching result.
Fig. 2 is an SEM sectional view of the cathode material of example 1, and it can be seen that the cathode material of example 1 has a core region composed of agglomerated and loose fine particles, an outer shell region composed of agglomerated and dense large particles, and a core region having a loose structure and a part having a hollow structure.
Assembling the button cell: weighing and uniformly mixing the positive active substance, the conductive agent and PVDF according to the mass ratio of 94:3:3, and dispersing by using an N-methylpyrrolidone (NMP) solvent to form slurry; the slurry is evenly coated on an aluminum foil and dried for 12 hours at the temperature of 80 ℃, and the dried pole piece is cut into a circular piece and put into a glove box for standby. The prepared pole piece is used as a positive pole piece, metal lithium is used as a negative pole, Celgard 2400 (microporous polypropylene film) is used as a diaphragm, and 1mol/L LiPF6The 2032 type button cell was assembled using (EC: DMC 1:1) as an electrolyte, and the lithium ion cell was assembled in a glove box using argon as a protective gas.
Thirdly, manufacturing a soft-package battery cell:
(1) preparation of positive plate
The prepared positive electrode material, polyvinylidene fluoride (PVDF) as a binder, acetylene black as a conductive agent, and carbon nanotubes are mixed according to a weight ratio of 96-98: 1-2: 1-1.5: 0.5-1.0, adding N-methyl pyrrolidone (NMP), and stirring under the action of a vacuum stirrer until the mixed system becomes uniform and flowable anode slurry, wherein the solid content of the anode slurry is 54-58%, and the viscosity value of the slurry is controlled to be 2500-4500 mPa.s; uniformly coating the positive electrode slurry on a carbon-coated aluminum foil with the thickness of (10+2) mu m, and controlling the surface density to be 15-18mg/cm2(ii) a Baking the coated aluminum foil in 5 sections of baking ovens with different temperature gradients, and then rolling and cutting to obtain the required positive plate.
(2) Preparation of negative plate
Mixing a negative electrode active material graphite, a thickening agent sodium carboxymethyl cellulose (CMC-Na), a binder styrene butadiene rubber and a conductive agent acetylene black according to a weight ratio of 97:1.2:1.2:0.6, adding deionized water, and obtaining negative electrode slurry under the action of a vacuum stirrer; uniformly coating the negative electrode slurry on a copper foil with the thickness of 8 mu m; and baking the coated copper foil in 3 sections of baking ovens with different temperature gradients, and then performing secondary rolling and slitting to obtain the negative plate.
(3) Preparation of electrolyte
Uniformly mixing ethylene carbonate, propylene carbonate and diethyl carbonate in a glove box filled with argon and qualified in water oxygen content according to the mass ratio of 1:1:1 (the solvent and the additive need to be normalized together), and then quickly adding 1mol/L of fully dried lithium hexafluorophosphate (LiPF)6) And uniformly stirring, and obtaining the required electrolyte after the water and free acid are detected to be qualified.
(4) Preparation of the separator
A7 +3 μm hybrid coated membrane (base polypropylene membrane + PVDF & ceramic hybrid coating) (available from Asahi chemical Co., Ltd.) was selected.
(5) Preparation of lithium ion battery
Stacking the prepared positive plate, the prepared isolating membrane and the prepared negative plate in sequence, wrapping the negative plate by two layers of diaphragms to ensure that the isolating membrane is positioned between the positive plate and the negative plate to play an isolating role, and then winding to obtain a naked battery cell without liquid injection; placing the naked electric core in an outer packaging foil, injecting the prepared electrolyte into the dried naked electric core, and obtaining the soft packaging electric core through the processes of vacuum packaging, standing, formation, shaping, sorting and the like.
Example 2
Firstly, preparing anode material
(1) Respectively preparing a binary solution, an EDTA solution and an oxalic acid solution for standby, wherein the binary solution comprises MnCl2And H3PO4The molar concentration of the binary solution is 1.25mol/L, wherein PO is in the system4 3-With Mn2+In a molar ratio of 0.98: 1; preparing reaction liquid and stirring, wherein the reaction liquid is a mixed solvent of ethylene glycol and water in a volume ratio of 2: 1; the concentration of EDTA is 1.25 mol/L; the concentration of oxalic acid is 0.15 mol/L;
(2) injecting the binary solution, the EDTA solution and the oxalic acid solution into the reaction solution to obtain a mixed solution, and carrying out the stage 1 and stage 2 reactions. The reaction temperature was controlled at 60 ℃ and nitrogen was continuously introduced during the reaction.
Stage 1: injecting the mixed solution into a reactor, controlling the stirring speed at 420rpm/min, controlling the concentration of EDTA at 0.05mol/L, regulating and controlling the pH value of the solution at 2.0, forming an intermediate reaction solution, controlling the coprecipitation reaction time in stage 1 to be 10h, and obtaining a precursor crystal nucleus in the process of nucleation and kernel growth of a precursor;
and (2) stage: injecting an EDTA solution and an oxalic acid solution into the precursor crystal nucleus solution obtained in the previous step, adjusting the pH value of the system to 3.0, regulating the concentration of a complexing agent to be 0.25mol/L, carrying out coprecipitation reaction at a stirring speed of 360rpm/min, wherein the coprecipitation reaction is a shell production stage of the precursor, and the reaction is stopped until the target particle size reaches 3.0 mu m to obtain Mn3(PO4)2A precursor; the inner core area of the precursor consists of loose agglomerated micro particles, the outer shell area consists of dense agglomerated macro particles, and the particle components of the inner core area and the outer shell area are both Mn3(PO4)2；
(3) Subjecting the reacted slurry to solid-liquid separation, aging, drying, grinding, screening and impurity removal to obtain Mn3(PO4)2A precursor;
(4) adding a phosphoric acid solution to the LiOH solution to react and form the Li3PO4And (3) crystal solution. The phosphoric acid solution is phosphoric acid aqueous solution, and the molar concentration of the phosphoric acid aqueous solution is 1.0 mol/L; the LiOH solution is a LiOH aqueous solution, the molar concentration of the LiOH aqueous solution is 1.25mol/L, and Li in the system+And PO4 3-The molar ratio was 1.05: 1. Adding the Mn3(PO4)2The precursor is uniformly dispersed to Li3PO4Crystal nucleus growth is carried out in the crystal solution, the crystal nucleus reaction time is 9 hours, and LiMnPO is obtained after the reaction is finished4Precursor according to Li+With Mn2 +Weighing Li with a molar ratio of 1.02:13PO4With Mn3(PO4)2。
(5) Mixing conductive polymers PEDOT and LiMnPO4Preparing a precursor according to the mass ratio of 0.09:1, roasting at high temperature in an inert atmosphere, heating from room temperature to 560 ℃ at the heating rate of 3 ℃/min in a multi-stage temperature-control sintering mode in the sintering process, preserving heat for 5 hours at 560 ℃, then heating to 680 ℃ and preserving heat for 1 hour0h, naturally cooling the sample to room temperature to obtain the lithium manganese phosphate with the carbon-coated structure, and marking as LiMnPO4The carbon content measured by a carbon sulfur meter was 1.8% (mass ratio), and the specific surface area (BET value) is shown in Table 1. The particle size D50 of the positive electrode material was 3.2 μm, and the porosity of the core region and the shell region was 80% and 28%, respectively, as determined by a porosity tester.
Assembling the button cell: the procedure is as in example 1.
Thirdly, manufacturing a soft-package battery cell: the procedure is as in example 1.
Example 3
Preparation of positive electrode material
(1) Respectively preparing a binary solution, a citric acid solution and a carbonic acid solution for standby, wherein the binary solution comprises MnC2O4And (NH)4)H2PO4The molar concentration of the binary solution is 1.5mol/L, wherein PO is in the system4 3-With Mn2+In a molar ratio of 1.05: 1; preparing reaction liquid and stirring, wherein the volume ratio of polyethylene glycol 200 to water is 1:1, a mixed solvent; the concentration of the citric acid is 2.0 mol/L; the concentration of oxalic acid is 0.1 mol/L;
(2) injecting the binary solution, the citric acid solution and the carbonic acid solution into the reaction solution to obtain a mixed solution, and carrying out the stage 1 reaction and the stage 2 reaction. The reaction temperature was controlled at 55 ℃ and nitrogen was continuously introduced during the reaction.
Stage 1: injecting the mixed solution into a reactor, controlling the stirring speed at 550rpm/min, controlling the citric acid concentration at 0.04mol/L, regulating and controlling the pH value of the solution at 1.6, forming an intermediate reaction solution, wherein the coprecipitation reaction time of the stage 1 is 15 hours, and the process is a nucleation and kernel growth stage of a precursor to obtain a precursor crystal nucleus;
and (2) stage: injecting a citric acid solution and an oxalic acid solution into the precursor crystal nucleus solution obtained in the previous step, adjusting the pH value of the system to 2.8, regulating the concentration of a complexing agent to be 0.3mol/L, carrying out coprecipitation reaction at a stirring speed of 420rpm/min, wherein the coprecipitation reaction is a shell production stage of the precursor, and the reaction is stopped until the target particle size reaches 3.8 mu m to obtain Mn3(PO4)2Precursor ofA body; the inner core area of the precursor consists of loose agglomerated micro particles, the outer shell area consists of dense agglomerated macro particles, and the particle composition components of the inner core area and the outer shell area are both Mn3(PO4)2；
(3) Subjecting the reacted slurry to solid-liquid separation, aging, drying, grinding, screening and impurity removal to obtain Mn3(PO4)2A precursor;
(4) adding a phosphoric acid solution to the LiOH solution to react and form the Li3PO4And (3) crystal solution. The phosphoric acid solution is phosphoric acid aqueous solution, and the molar concentration of the phosphoric acid aqueous solution is 1.5 mol/L; the LiOH solution is a LiOH aqueous solution, the molar concentration of the LiOH aqueous solution is 1.75mol/L, and Li in the system+And PO4 3-The molar ratio was 0.98: 1. Adding the Mn3(PO4)2The precursor is uniformly dispersed to Li3PO4Crystal nucleus growth is carried out in the crystal solution, the crystal nucleus reaction time is 6 hours, and LiMnPO is obtained after the reaction is finished4Precursor according to Li+With Mn2 +Weighing Li with a molar ratio of 1.04:13PO4With Mn3(PO4)2。
(5) Mixing sucrose with LiMnPO4Preparing a precursor according to the mass ratio of 0.08:1, roasting at high temperature in an inert atmosphere, adopting a multi-stage temperature-control sintering mode in the sintering process, heating from room temperature to 600 ℃ at the heating rate of 3 ℃/min, preserving heat for 5h at the temperature of 600 ℃, then heating to 750 ℃, preserving heat for 10h, naturally cooling a sample to room temperature to obtain the lithium manganese phosphate with a carbon-coated structure, which is marked as LiMnPO4The carbon content measured by a carbon sulfur meter was 1.6% (mass ratio), and the specific surface area (BET value) is shown in Table 1. The particle size D50 of the positive electrode material was 4.0 μm, and the porosity of the core region and the shell region was 82% and 31%, respectively, as determined by a porosity tester.
Assembling the button cell: the procedure is as in example 1.
Thirdly, manufacturing a soft-package battery cell: the procedure is as in example 1.
Example 4
(1) Respectively preparing binary solutionsLiquid, EDTA solution and acetic acid solution for standby use, wherein the binary solution Comprises (CH)3COO)2Mn and (NH)4)2HPO4The molar concentration of the binary solution is 2.5mol/L, wherein PO is in the system4 3-With Mn2+In a molar ratio of 1:1, preparing a reaction solution and stirring, wherein the reaction solution is a mixed solvent of polyethylene glycol 400 and water in a volume ratio of 1: 1; the concentration of the lemon is 1.8 mol/L; the concentration of oxalic acid is 0.2 mol/L;
(2) injecting the binary solution, the EDTA solution and the acetic acid solution into the reaction solution to obtain a mixed solution, and carrying out the stage 1 and stage 2 reactions. The reaction temperature was controlled to 65 ℃ and nitrogen was continuously introduced during the reaction.
Stage 1: injecting the mixed solution into a reactor, controlling the stirring speed at 500rpm/min, controlling the concentration of EDTA at 0.04mol/L, regulating and controlling the pH value of the solution at 2.0, forming an intermediate reaction solution, controlling the coprecipitation reaction time in the stage 1 to be 10h, and obtaining a precursor crystal nucleus in the process of nucleation and kernel growth of a precursor;
and (2) stage: injecting an EDTA solution and an acetic acid solution into the precursor crystal nucleus solution obtained in the previous step, adjusting the pH value of the system to 3.0, regulating the concentration of a complexing agent to be 0.25mol/L, carrying out coprecipitation reaction at a stirring speed of 450rpm/min, wherein the coprecipitation reaction is a shell production stage of the precursor, and the reaction is terminated until the target particle size reaches 3.2 mu m to obtain Mn3(PO4)2A precursor; the inner core area of the precursor consists of loose agglomerated micro particles, the outer shell area consists of dense agglomerated macro particles, and the particle composition components of the inner core area and the outer shell area are both Mn3(PO4)2；
(3) Subjecting the reacted slurry to solid-liquid separation, aging, drying, grinding, screening and impurity removal to obtain Mn3(PO4)2A precursor;
(4) adding a phosphoric acid solution to the LiOH solution to react and form the Li3PO4And (3) crystal solution. The phosphoric acid solution is a phosphoric acid aqueous solution, and the molar concentration of the phosphoric acid aqueous solution is 1.25 mol/L; the LiOH solution is LiOH aqueous solution, and the molar concentration of the LiOH aqueous solution is 2.0mol/LIn the system of Li+And PO4 3-The molar ratio is 1: 1. adding the Mn3(PO4)2The precursor is uniformly dispersed to Li3PO4Crystal nucleus growth is carried out in the crystal solution, the crystal nucleus reaction time is 8 hours, and LiMnPO is obtained after the reaction is finished4Precursor according to Li+With Mn2+Weighing Li with a molar ratio of 1.02:13PO4With Mn3(PO4)2。
(5) Mixing glucose with LiMnPO4Preparing a precursor according to the mass ratio of 0.12:1, roasting at high temperature in an inert atmosphere, adopting a multi-stage temperature-control sintering mode in the sintering process, heating from room temperature to 580 ℃ at the heating rate of 3 ℃/min, preserving heat for 6h at 580 ℃, then heating to 720 ℃ and preserving heat for 10h, naturally cooling a sample to room temperature to obtain the lithium manganese phosphate with a carbon-coated structure, which is marked as LiMnPO4In the formula,/C, the carbon content was 2.0% (mass ratio) as measured by a carbon sulfur meter, and the specific surface area (BET value) is shown in Table 1. The particle size D50 of the positive electrode material is 3.4 μm, and the porosity of the core region and the shell region is 76% and 25% respectively, as can be seen from the porosity tester.
Assembling the button cell: the procedure is as in example 1.
Thirdly, manufacturing a soft-package battery cell: the procedure is as in example 1.
Comparative example 1
Preparation of positive electrode material
(1) Respectively preparing a binary solution, a citric acid solution and an oxalic acid solution for standby, wherein the binary solution comprises MnC2O4And H3PO4The total molar concentration of the ternary solution is 1.2mol/L, wherein PO is contained in the system4 3-With Mn2+In a molar ratio of 1.02: 1; preparing reaction liquid and stirring, wherein the reaction liquid is a mixed solvent of ethylene glycol and water in a volume ratio of 3: 1; wherein the concentration of the citric acid is 2.0mol/L, and the concentration of the oxalic acid is 0.15 mol/L;
(2) and injecting the binary solution, the citric acid solution and the oxalic acid solution into the reaction solution to obtain a mixed solution, and carrying out coprecipitation reaction. The reaction temperature was controlled at 70 ℃ and nitrogen was continuously introduced during the reaction.
Injecting the mixed solution into a reactor, adjusting the pH value of a system to 2.2 by finely adjusting the addition amount of oxalic acid solution, regulating the concentration of a complexing agent to be 0.12mol/L, carrying out coprecipitation reaction at the stirring speed of 450rpm/min, stopping the reaction until the target particle size reaches 4.5 mu m, and obtaining Mn3(PO4)2A precursor;
(3) subjecting the reacted slurry to solid-liquid separation, aging, drying, grinding, screening and impurity removal to obtain Mn3(PO4)2A precursor;
(4) adding a phosphoric acid solution to the LiOH solution to react and form the Li3PO4And (3) crystal solution. The phosphoric acid solution is a phosphoric acid aqueous solution, and the molar concentration of the phosphoric acid aqueous solution is 1.0 mol/L; the LiOH solution is a LiOH aqueous solution, the molar concentration of the LiOH aqueous solution is 1.5mol/L, and Li in the system+And PO4 3-The molar ratio is 1.02: 1. adding the Mn3(PO4)2The precursor is uniformly dispersed to Li3PO4Crystal nucleus growth is carried out in the crystal solution, the crystal nucleus reaction time is 10h, and LiMnPO is obtained after the reaction is finished4Precursor according to Li+With Mn2+Weighing Li with a molar ratio of 1.05:13PO4With Mn3(PO4)2。
(5) Mixing glucose with LiMnPO4Preparing a precursor according to the mass ratio of 0.1:1, roasting at high temperature in an inert atmosphere, adopting a multi-stage temperature-control sintering mode in the sintering process, heating from room temperature to 550 ℃ at the heating rate of 3 ℃/min, preserving heat at 550 ℃ for 4h, heating to 660 ℃ for 10h, naturally cooling a sample to room temperature to obtain the lithium manganese phosphate with a carbon-coated structure, and marking as LiMnPO4The carbon content measured by a carbon sulfur meter was 1.8% (mass ratio), and the specific surface area (BET value) is shown in Table 1. The particle size D50 of the anode material is 4.6 μm, and the anode active material LiMnPO can be obtained by the test of a porosity tester4The porosity of (2) was 28%.
Fig. 6 is a SEM cross-sectional view of the cathode material of comparative example 1, and it can be seen that the cathode material prepared in comparative example 1 has a secondary spherical structure formed by close packing of primary particles, is solid spherical particles, and has no hollow or aggregation-bulk structure, and the cathode material of comparative example 1 has a lower porosity than the aggregation-bulk structure prepared in example. The small particles on the surface in fig. 6 are caused by vacuum pumping during the shooting process of the electron microscope.
Assembling the button cell: the procedure is as in example 1.
Thirdly, manufacturing a soft-package battery cell: the procedure is as in example 1.
Test example 1, Charge/discharge test
The button cells of examples 1-4 and comparative example 1 were tested for charging performance at 25 ± 5 ℃ as follows:
1) activating the button cell for 24 h;
2) charging to 4.5V at 0.1C constant current;
3) resting for 10 minutes;
4) constant current discharge is carried out at 0.1 ℃ until the voltage reaches 2.5V.
Fig. 3 shows the charge and discharge curves of the button cell battery of example 1; fig. 7 is a charge-discharge curve of the button cell of comparative example 1. The gram-discharge capacity of the cathode material can be obtained through calculation, and the result is shown in table 1.
Test example 2 rate test
The pouch cells of examples 1-4 and comparative example 1 were tested for rate capability at a temperature of 25 ± 2 ℃ as follows:
1) carrying out capacity test by cycling at 0.33C/0.33C for three times in an environment with the temperature of 25 +/-2 ℃;
2)1C to a lower limit voltage (2.5V);
3) standing for 30 min;
4) after the 1C constant current charging is carried out to the upper limit voltage (4.5V), the constant voltage charging is carried out, and the cutoff current is 0.05C;
5) standing for 30 min;
6) discharging nC to lower limit voltage, wherein nC is 0.2C/0.33C/0.5C/1C/2C/3C/5C/8C/10C/15C;
7) and repeating the steps 3-6 to finish the discharging steps of all multiplying powers.
The rate performance of each battery was calculated (rate ═ 10C discharge capacity/0.33C capacity), and the results are shown in table 1.
Test example 3 test of circulating Capacity
The pouch cells of examples 1 to 4 and comparative example 1 were subjected to a cyclic capacity test at 25 ± 2 ℃ and 45 ± 2 ℃ respectively, and the test procedure included:
and testing the state voltage, the internal resistance, the thickness and the direct current internal resistance of the soft package battery at 25 +/-2 ℃ (45 +/-2 ℃). Voltage range (2.5-4.5V)
1) Placing the battery cell in an environment with the temperature of 25 +/-2 ℃ (45 +/-2 ℃);
2) discharging to lower limit voltage at 0.5C, and standing for 30 min;
3)1C is charged to the upper limit voltage, and the cut-off is 0.05C;
4) standing for 30 min;
5)1C discharging to a lower limit voltage; standing for 30 min;
6) charging to the upper limit voltage at 1C, stopping at 0.05C, and standing for 30 min;
repeating the steps of 5-6 and circulating to n circles.
After 1C/1C and n cycles (n is less than or equal to 5000), the cycle capacity retention rate of each battery is calculated, wherein the first cycle test capacity is recorded as A1, the test capacity after n cycles is recorded as An, the capacity retention rate is An/A1 × 100%, and the capacity retention rate results when n is 1500 are shown in Table 1.
Test example 4, Low temperature Performance test
And testing the state voltage, the internal resistance and the thickness of the soft package battery at 25 +/-2 ℃. Voltage range (2.5-4.5V)
Standing at 1.25 + -2 deg.C for 30 min;
2.0.5C discharge to lower limit voltage;
3. standing for 4 hours;
4.1C, charging to the upper limit voltage, and cutting off the current to 0.05C;
5. standing for 4 hours;
6. the method comprises the following steps of (1) standing in an incubator environment for 4 hours at different temperatures (the following temperature), and discharging to a lower limit voltage at 1C;
standing for 4 hours at 7.25 +/-2 ℃;
repeating the steps 4-7, and circulating until all temperature discharge tests are finished;
discharge temperature: 25 ℃/45 ℃/0 ℃/-10 ℃/-20 ℃.
Test example 5 electronic conductivity test of cathode Material
Sample powders were mixed with 5% PVDF, pressed into cylindrical sheets (. phi.10.0 mm) with a tablet press, and LiMnPO was tested by the four-probe DC technique4Electron conductivity of the/C sample.
Test example 6 lithium ion diffusion coefficient test of positive electrode Material
Constant current intermittent titration method (GITT method) is adopted to test diffusion coefficient (D) of lithium ionsLi +)。
1. Activating the button cell for 24 h;
after the constant current charging is carried out at 2.0.1C until the upper limit voltage (4.5V), the constant voltage charging is carried out, and the current is cut off at 0.05C;
3. standing for 10 minutes;
4.0.1C constant current discharge for 15 min;
5. standing for 30 min;
6. and repeating the steps 4-5 until the discharging process is finished.
The influence of the metal Li cathode on the voltage change of the battery is small, the voltage change in the test process mainly comes from the cathode material, and the diffusion coefficient obtained by the method mainly reflects the diffusion coefficient of the cathode material.
Calculating the diffusion coefficient of the anode material by using the obtained data, and focusing on 4 voltage data, namely the voltage V0 before pulse discharge; constant current discharge instantaneous voltage V1 (pulse instantaneous discharge), the difference value between V0 and V1 mainly corresponds to the influence of ohmic impedance and charge transfer impedance inside the battery on the voltage change; voltage V2 at the end of constant current discharge, corresponding to Li+Voltage changes caused by diffusion into the positive electrode material; voltage V3 at end of standing period corresponding to Li+The active material is diffused inside, and finally the voltage change of the active material in a steady state is realized. Li was calculated from the above data by combining Fick's second law and using the following formula+The diffusion coefficient Ds in a lithium ion battery.
Ds＝(4/πt)(Rs/3)2(△Vs/△Vt)2
Where Rs is the spherical particle radius, t is the discharge pulse duration, Δ Vs ═ V0-V3; Δ Vt ═ V1-V2.
Test example 7 thermal decomposition temperature
Thermal decomposition temperature test-DSC test
And fully charging the soft-packaged cell to 4.5V at the rate of 0.33C, disassembling the soft-packaged cell in a glove box filled with argon to recover the positive pole piece, and washing the pole piece with dimethyl carbonate (DMC) and drying. Placing the positive pole piece and electrolyte into a high-pressure crucible of a thermal analyzer together, and placing the positive pole piece and the electrolyte into a 1mol/L LiPF6(EC: DMC: DMC ═ 1:1:1) as electrolyte, wherein the ratio of the positive pole piece to the electrolyte is 1 mg: 0.6 mu L is prepared, the thermal analysis testing temperature range is 25-500 ℃, and the heating rate is 5 ℃/min.
Test example 8 EIS resistance value test
EIS impedance value test-AC impedance method test
Electrochemical alternating current impedance (EIS) measurement is carried out on an electrochemical workstation of CHI600E Shanghai Chenghua, a soft package cell is adopted for testing, and the battery state is adjusted to be a 50% SOC state; the voltage window is set to be 2.5-4.5V, the amplitude is 5mV, and the frequency range is 10-2～105Hz。
Table 1 results of performance test of positive electrode materials of examples and comparative examples and batteries assembled therewith
The positive electrode materials of the embodiments 1-4 prepared by the preparation method are of a structure with a loose core and a dense shell. The test results in table 1 show that the particles with smaller particle size and the special core-shell structure enable the material to have better lithium ion diffusion capacity and electronic conductivity, and the material dynamic performance is better; when the positive plate is prepared from the positive material and applied to a lithium battery layer, the positive plate has excellent dynamic performance and rate discharge capacity, and meanwhile, the low-temperature discharge performance and the safety performance are also remarkably improved.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The positive electrode material is characterized by comprising a positive electrode active material and a coating material compounded on the surface of the positive electrode active material;
the median particle diameter D50 of the positive electrode material is 2-5 μm;
the positive active material is lithium manganese phosphate.
2. The positive electrode material according to claim 1, wherein the positive electrode active material is a secondary spherical particle including an inner core region and an outer shell region, the outer shell region being located at an outer layer of the inner core region; the shell region has an agglomerated compact structure; the inner core region has an agglomerated porous structure.
3. The positive electrode material as claimed in claim 2, wherein the shell region has pores;
and/or the porosity of the shell region is 10-35%;
and/or the porosity of the core region is 60% to 90%.
4. The positive electrode material according to claim 1, wherein the coating material is selected from a carbon material;
and/or the thickness of the coating material is 2 nm-8 nm.
5. The positive electrode material according to any one of claims 1 to 4, wherein the mass of the positive electrode active material is 97.5 to 99.0 wt% of the total mass of the positive electrode material, and the mass of the coating material is 1 to 2.5 wt% of the total mass of the positive electrode material.
6. The positive electrode material according to any one of claims 1 to 4, wherein the positive electrode material has an electron conductivity of 2.0 x 10-5S/cm～9.0×10-5S/cm；
And/or the lithium ion diffusion coefficient of the cathode material is 1.0 x 10-14cm2/s～8.0×10-14cm2/s。
7. A positive electrode sheet, characterized in that it comprises the positive electrode material according to any one of claims 1 to 6.
8. The positive electrode sheet according to claim 7, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer on a surface of the positive electrode current collector; the positive electrode active material layer includes the positive electrode material according to any one of claims 1 to 6.
9. A battery comprising the positive electrode material according to any one of claims 1 to 6 or the positive electrode sheet according to claim 7 or 8.
10. The battery according to claim 9, wherein the battery has a volumetric energy density of 225 to 255KWh/m3The weight energy density of the battery is 175-215 Wh/kg.
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