CN116143200B - High-compaction micron monocrystal lithium-rich manganese-based positive electrode material, preparation method and lithium battery - Google Patents
High-compaction micron monocrystal lithium-rich manganese-based positive electrode material, preparation method and lithium battery Download PDFInfo
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Abstract
The invention discloses a high-compaction micron monocrystal lithium-rich manganese-based positive electrode material, a preparation method and a lithium battery, and belongs to the technical field of lithium ion battery materials. According to the method, the morphology of monocrystal particles is optimized by adding lithium step by step and calcining twice, molten salt is additionally added during primary calcining, the proper grain size is ensured by elevating the temperature during secondary calcining, and the high-compaction micron monocrystal lithium-rich manganese-based cathode material is obtained, and has good capacity circulation retention rate and rate capability due to the stability of monocrystal crystal structure, the size of micropores in the material is reduced due to high compaction density, and the electrode energy density is improved.
Description
Technical Field
The invention relates to the technical field of lithium ion battery materials, in particular to a high-compaction micron monocrystal lithium-rich manganese-based positive electrode material, a preparation method and a lithium battery.
Background
With the rapid development of new energy electric vehicles, new lithium ion batteries with high energy density are becoming a focus of attention. As an important component for limiting the energy density of lithium ion batteries, the development of a cathode material having a high capacity has become urgent. Compared with layered high-nickel ternary, spinel type and lithium iron phosphate positive electrode materials, the lithium-rich manganese-based positive electrode layered material has the outstanding advantages of ultrahigh specific capacity (more than 250 mAh/g), lower cost and the like, and becomes one of the most ideal positive electrode materials for constructing a high specific energy power battery.
The high capacity of the lithium-rich manganese-based positive electrode material comes from oxygen-oxidation reduction, but the activation of anions under high voltage also causes the damage of a lattice oxygen framework structure, which is unfavorable for the stability of the surface layer structure of the positive electrode material and the cycle stability of a lithium ion battery. The conventional lithium-rich manganese-based positive electrode material is formed by agglomeration of nanoscale primary particles, and the tap density is low, so that practical application of the lithium-rich manganese-based positive electrode material is limited.
Therefore, developing a lithium-rich manganese-based positive electrode material with a high compacted density micron-sized single crystal is of great significance in improving the cycle capacity retention rate of the positive electrode material.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a high-compaction micron monocrystal lithium-rich manganese-based positive electrode material, a preparation method and a lithium battery.
The invention solves the technical problems by adopting the following technical scheme.
The invention provides a preparation method of a high-compaction micron monocrystal lithium-rich manganese-based positive electrode material, which comprises the following steps:
precursor Mn 0.75 Ni 0.25 (OH) 2 Uniformly mixing 50% of lithium-containing compound and molten salt, and then performing primary calcination, wherein the primary calcination is as follows: performing first-stage calcination at 400-600 ℃, and performing second-stage calcination at 700-900 ℃;
washing and drying the materials obtained by primary calcination, uniformly mixing the materials with the rest 50% of lithium-containing compounds, and performing secondary calcination, wherein the secondary calcination is as follows: after the primary calcination is carried out at 400-600 ℃, the secondary calcination is carried out at 800-1100 ℃, and then the material after the secondary calcination is cooled to obtain Li 1.2 Mn 0.6 Ni 0.2 O 2 Is a high-compaction micron monocrystal lithium-rich manganese-based positive electrode material.
The invention also provides the high-compaction micron monocrystal lithium-rich manganese-based anode material prepared by the preparation method.
The embodiment of the invention also provides a lithium battery, and the positive electrode of the lithium battery comprises the high-compaction micron monocrystal lithium-rich manganese-based positive electrode material.
The invention has the following beneficial effects:
the invention provides a high-compaction micron monocrystal lithium-rich manganese-based positive electrode material, a preparation method and a lithium battery.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a scanning electron microscope image of a high-compaction micron single crystal lithium-rich manganese-based positive electrode material prepared in example 3, wherein (a) and (b) are scanning electron microscope images at different magnifications;
fig. 2 is a first cycle charge-discharge plot at a voltage interval of 2.0V-4.8V and a 0.1C rate for the CR2032 coin cell assembled of example 1, example 2, example 3, and example 4;
fig. 3 is a graph showing specific discharge capacities of the CR2032 coin cells assembled in example 1, example 2, example 3, and example 4 at a voltage interval of 2.0V-4.8V and a 0.1C rate;
FIG. 4 is a graph of volumetric energy density at a voltage interval of 2.0V-4.8V and a magnification of 0.1C for the CR2032 button battery assembled of example 1, example 2, example 3, and example 4;
fig. 5 is a graph showing specific discharge capacities of CR2032 coin cells assembled in example 1, example 2, example 3, and example 4 at voltage intervals of 2.0V-4.8V and at different rates;
FIG. 6 is a scanning electron microscope image of the material prepared in comparative example 1, wherein (a) and (b) are scanning electron microscope images at different magnifications;
FIG. 7 is a scanning electron microscope image of the material prepared in comparative example 2, wherein (a) and (b) are scanning electron microscope images at different magnifications;
FIG. 8 is a scanning electron microscope image of the material prepared in comparative example 3, wherein (a) and (b) are scanning electron microscope images at different magnifications;
FIG. 9 is a scanning electron microscope image of the material prepared in comparative example 4, wherein (a) and (b) are scanning electron microscope images at different magnifications;
FIG. 10 is a scanning electron microscope image of the material prepared in comparative example 5, wherein (a) and (b) are scanning electron microscope images at different magnifications;
FIG. 11 is a scanning electron microscope image of the material prepared in comparative example 6, wherein (a) and (b) are scanning electron microscope images at different magnifications.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
In order to solve the technical problems of small compacted density, poor multiplying power performance, poor cycle stability, low energy density and the like of the conventional lithium-rich manganese-based positive electrode material, the invention provides a lithium-rich manganese-based positive electrode material with micron-sized monocrystal morphology and high compacted density, a preparation method thereof and a lithium battery, and the molecular formula of the lithium-rich manganese-based positive electrode material prepared by the invention is Li 1.2 Mn 0.6 Ni 0.2 O 2 The preparation method is simple and convenient, is easy to apply, and the lithium-rich manganese-based positive electrode material has good capacity cycle retention rate and rate capability. The high compaction density reduces the size of the micropores in the material and improves the energy density of the electrode.
The high-compaction micron monocrystal lithium-rich manganese-based positive electrode material, the preparation method and the lithium battery provided by the embodiment of the invention are specifically described below.
In a first aspect, an embodiment of the present invention provides a method for preparing a high-compaction micron single crystal lithium-rich manganese-based positive electrode material, including the following steps:
precursor Mn 0.75 Ni 0.25 (OH) 2 Uniformly mixing 50% of lithium-containing compound and molten salt, and then performing primary calcination, wherein the primary calcination is as follows: performing first-stage calcination at 400-600 ℃, and performing second-stage calcination at 700-900 ℃;
washing and drying the materials obtained by primary calcination, uniformly mixing the materials with the rest 50% of lithium-containing compounds, and performing secondary calcination, wherein the secondary calcination is as follows: after the primary calcination is carried out at 400-600 ℃, the secondary calcination is carried out at 800-1100 ℃, and then the material after the secondary calcination is cooled to obtain Li 1.2 Mn 0.6 Ni 0.2 O 2 Is a high-compaction micron monocrystal lithium-rich manganese-based positive electrode material.
The embodiment of the invention provides a preparation method of a high-compaction micron monocrystal lithium-rich manganese-based positive electrode material, which is used for obtaining the lithium-rich manganese-based positive electrode material with high compaction density by adjusting the calcination times and the calcination temperature. Specific: the material with good monocrystal morphology condition is obtained through stepwise lithium adding and twice calcination, primary sintering is middle-low temperature molten salt auxiliary sintering, morphology of monocrystal particles is optimized, secondary sintering is high-temperature sintering for further improving temperature, size growth of monocrystal particles is facilitated, monocrystal particles with proper particle size and stable existence can be obtained, and due to stability of monocrystal crystal structure, the prepared high-compaction micron monocrystal lithium-rich manganese-based positive electrode material has good capacity circulation retention rate and rate capability, the size of micropores inside the material is reduced due to high compaction density, and electrode energy density is improved.
In an alternative embodiment, the step of primary calcination is as follows: precursor Mn 0.75 Ni 0.25 (OH) 2 Mixing and grinding 50% lithium-containing compound, uniformly mixing with molten salt, placing in a muffle furnace, heating from room temperature to 400-600 ℃ at a heating rate of 3-8 ℃/min, preserving heat for 4-7 h, and cooling along with the furnace; then the temperature is raised from room temperature to 700 ℃ to 900 ℃ at a heating rate of 3 ℃/min to 8 ℃/min, and the temperature is kept for 4h to 7h and then is reduced with the furnace.
The preparation method of the high-compaction micron monocrystal lithium-rich manganese-based positive electrode material provided by the embodiment of the invention comprises the steps of firstly calcining a precursor Mn in one step 0.75 Ni 0.25 (OH) 2 Mixing and grinding 50% of lithium-containing compound, uniformly mixing with molten salt, and then placing in a muffle furnace for calcination, wherein the inventor obtains by multiple experiments: in the primary calcination process, 50% of lithium-containing compound is used, which is favorable for forming single-crystal materials, the usage amount of the lithium-containing compound is less than 50%, such as 20%, 30% and 40%, etc., after primary calcination, particles with primary single-crystal morphology are difficult to obtain, even materials with spinel structures can be obtained, the usage amount of the lithium-containing compound is further increased, such as 60%, 80% and 100%, etc., after primary calcination, the obtained materials are agglomerated into compact secondary particles.
In an alternative embodiment, the method further comprises: preparing a precursor Mn by adopting a coprecipitation method 0.75 Ni 0.25 (OH) 2 Precursor Mn 0.75 Ni 0.25 (OH) 2 Mixing and grinding the mixture with 50% lithium-containing compound for 0.5-2 h, uniformly mixing the mixed dry material with molten salt, and calcining for the first time.
In an alternative embodiment, the molten salt includes at least one of lithium chloride, potassium chloride. The lithium chloride is used for preparing the lithium-rich manganese-based anode material.
In an alternative embodiment, the step of secondary calcination is as follows: washing and drying the materials obtained by primary calcination, uniformly mixing the materials with the rest 50% of lithium-containing compounds, placing the materials in a muffle furnace, and heating the materials from room temperature to 4 at a heating rate of 3-8 ℃/minHeat preservation is carried out for 4 to 7 hours at the temperature of 00 to 600 ℃ and then the temperature is reduced along with the furnace; then the temperature is increased from room temperature to 800-1100 ℃ at the heating rate of 3-8 ℃/min, the temperature is kept for 11-14 h, and then the temperature is reduced along with the furnace, thus obtaining the Li composition 1.2 Mn 0.6 Ni 0.2 O 2 Is a high-compaction micron monocrystal lithium-rich manganese-based positive electrode material.
According to the preparation method of the high-compaction micron monocrystal lithium-rich manganese-based positive electrode material, in the secondary calcination process, a product obtained by primary calcination is washed and dried, and is uniformly mixed with the rest 50% of lithium-containing compound, and then the mixture is placed in a muffle furnace for secondary calcination, and the inventor obtains by multiple experiments: in the secondary calcination process, the calcination temperature is 600 ℃ and 700 ℃, so that the material crystal grains cannot be regularly formed, and the calcination temperature is 1200 ℃ and 1300 ℃, so that the material presents a lithium-deficient sheet layer.
In an alternative embodiment, the lithium-containing compound includes at least one of anhydrous lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, lithium nitrate, lithium oxide, lithium acetate, and lithium oxalate.
From the above, the embodiment of the invention provides a technology of adding lithium in multiple times and calcining in multiple steps, and adopts molten salt to assist, so as to synthesize the micron-sized monocrystal lithium-rich manganese-based positive electrode material with high compaction density.
In a second aspect, the embodiment of the invention provides a high-compaction micron monocrystal lithium-rich manganese-based positive electrode material prepared by the preparation method.
In an alternative embodiment, the high-compaction micron single crystal lithium-rich manganese-based positive electrode material is single crystal particles having a diameter of 2 μm to 4 μm.
In an alternative embodiment, the high compaction micron single crystal lithium-rich manganese-based positive electrode material has a compacted density of 2.8g/cm 3 -4.0g/cm 3 。
In a third aspect, the embodiment of the invention also provides a lithium battery, and the positive electrode of the lithium battery comprises the high-compaction micron monocrystal lithium-rich manganese-based positive electrode material.
The features and capabilities of the present invention are described in further detail below with reference to examples.
The materials used in the following examples were characterized by the following analytical methods:
cycle performance test of CR2032 battery: lanD CT 2001A tester was purchased from Wuhan City blue electric Co.
Example 1
The embodiment provides a preparation method of a high-compaction micron monocrystal lithium-rich manganese-based positive electrode material, which comprises the following specific steps: preparing hydroxide precursor by coprecipitation method. Mixing and grinding the prepared hydroxide precursor and 50% lithium source compound for 1h, uniformly mixing the mixed dry material and lithium chloride, calcining in a muffle furnace, heating from room temperature to 550 ℃ at a heating rate of 5 ℃/min in the first stage, preserving heat for 5h, cooling with the furnace, grinding the material obtained in the first stage for 10 min, and calcining in the second stage; the second stage is heated from room temperature to 900 ℃ at a heating rate of 5 ℃/min, and the temperature is kept for 5 hours and then is reduced along with the furnace. Placing the calcined mixture into deionized water, carrying out suction filtration and washing on the solid-liquid mixture, drying the mixture after the suction filtration in a drying oven, mixing the dried mixture with the rest 50% of lithium source compound in a muffle furnace, carrying out secondary calcination, heating the mixture from room temperature to 550 ℃ at a heating rate of 5 ℃/min in a first stage, carrying out furnace cooling after heat preservation for 5 hours, grinding the material obtained in the first stage for 10 minutes, and carrying out second stage calcination; and in the second stage, the temperature is raised from room temperature to 950 ℃ at a heating rate of 5 ℃/min, and the temperature is kept for 12 hours and then is reduced along with the furnace to obtain the micron-sized monocrystal lithium-rich manganese-based anode material. Rolling the positive electrode material pole piece, and controlling the pole piece compaction density to be 2.8g/cm 3 . The lithium-rich manganese-based positive electrode obtained in example 1 was used as a positive electrode active material at 0.1C (1c=250ma g -1 ) And (3) performing electrochemical constant-current charge and discharge test in a voltage range of 2.0-4.8V.
Example 2
The embodiment provides a preparation method of a high-compaction micron monocrystal lithium-rich manganese-based positive electrode material, which comprises the following specific steps: preparing hydroxide precursor by coprecipitation method. Mixing and grinding the prepared hydroxide precursor and 50% lithium source compound for 1h, uniformly mixing the mixed dry material and lithium chloride, calcining in a muffle furnace, heating from room temperature to 550 ℃ at a heating rate of 5 ℃/min in the first section, preserving heat for 5h, cooling with the furnace, and obtaining the material in the first sectionGrinding the material for 10 minutes, and then performing second-stage calcination; the second stage is heated from room temperature to 900 ℃ at a heating rate of 5 ℃/min, and the temperature is kept for 5 hours and then is reduced along with the furnace. Placing the calcined mixture into deionized water, carrying out suction filtration and washing on the solid-liquid mixture, drying the mixture after the suction filtration in a drying oven, mixing the dried mixture with the rest 50% of lithium source compound in a muffle furnace, carrying out secondary calcination, heating the mixture from room temperature to 550 ℃ at a heating rate of 5 ℃/min in a first stage, carrying out furnace cooling after heat preservation for 5 hours, grinding the material obtained in the first stage for 10 minutes, and carrying out second stage calcination; and in the second stage, the temperature is raised from room temperature to 950 ℃ at a heating rate of 5 ℃/min, and the temperature is kept for 12 hours and then is reduced along with the furnace to obtain the micron-sized monocrystal lithium-rich manganese-based anode material. Rolling the positive electrode material pole piece, and controlling the pole piece compaction density to be 3.2g/cm 3 . The lithium-rich manganese-based positive electrode obtained in example 2 was used as a positive electrode active material at 0.1C (1c=250ma g -1 ) And (3) performing electrochemical constant-current charge and discharge test in a voltage range of 2.0-4.8V.
Example 3
The embodiment provides a preparation method of a high-compaction micron monocrystal lithium-rich manganese-based positive electrode material, which comprises the following specific steps: preparing hydroxide precursor by coprecipitation method. Mixing and grinding the prepared hydroxide precursor and 50% lithium source compound for 1h, uniformly mixing the mixed dry material and lithium chloride, calcining in a muffle furnace, heating from room temperature to 550 ℃ at a heating rate of 5 ℃/min in the first stage, preserving heat for 5h, cooling with the furnace, grinding the material obtained in the first stage for 10 min, and calcining in the second stage; the second stage is heated from room temperature to 900 ℃ at a heating rate of 5 ℃/min, and the temperature is kept for 5 hours and then is reduced along with the furnace. Placing the calcined mixture into deionized water, carrying out suction filtration and washing on the solid-liquid mixture, drying the mixture after the suction filtration in a drying oven, mixing the dried mixture with the rest 50% of lithium source compound in a muffle furnace, carrying out secondary calcination, heating the mixture from room temperature to 550 ℃ at a heating rate of 5 ℃/min in a first stage, carrying out furnace cooling after heat preservation for 5 hours, grinding the material obtained in the first stage for 10 minutes, and carrying out second stage calcination; and in the second stage, the temperature is raised from room temperature to 950 ℃ at a heating rate of 5 ℃/min, and the temperature is kept for 12 hours and then is reduced along with the furnace to obtain the micron-sized monocrystal lithium-rich manganese-based anode material. Rolling treatment is carried out on the positive electrode material pole pieceControlling the compaction density of the pole piece to be 3.6 g/cm 3 . The lithium-rich manganese-based positive electrode obtained in example 3 was used as a positive electrode active material at 0.1C (1c=250ma g -1 ) And (3) performing electrochemical constant-current charge and discharge test in a voltage range of 2.0-4.8V.
Example 4
The embodiment provides a preparation method of a high-compaction micron monocrystal lithium-rich manganese-based positive electrode material, which comprises the following specific steps: preparing hydroxide precursor by coprecipitation method. Mixing and grinding the prepared hydroxide precursor and 50% lithium source compound for 1h, uniformly mixing the mixed dry material and lithium chloride, calcining in a muffle furnace, heating from room temperature to 550 ℃ at a heating rate of 5 ℃/min in the first stage, preserving heat for 5h, cooling with the furnace, grinding the material obtained in the first stage for 10 min, and calcining in the second stage; the second stage is heated from room temperature to 900 ℃ at a heating rate of 5 ℃/min, and the temperature is kept for 5 hours and then is reduced along with the furnace. Placing the calcined mixture into deionized water, carrying out suction filtration and washing on the solid-liquid mixture, drying the mixture after the suction filtration in a drying oven, mixing the dried mixture with the rest 50% of lithium source compound in a muffle furnace, carrying out secondary calcination, heating the mixture from room temperature to 550 ℃ at a heating rate of 5 ℃/min in a first stage, carrying out furnace cooling after heat preservation for 5 hours, grinding the material obtained in the first stage for 10 minutes, and carrying out second stage calcination; and in the second stage, the temperature is raised from room temperature to 950 ℃ at a heating rate of 5 ℃/min, and the temperature is kept for 12 hours and then is reduced along with the furnace to obtain the micron-sized monocrystal lithium-rich manganese-based anode material. Rolling the positive electrode material pole piece, and controlling the pole piece compaction density to be 4.0 g/cm 3 . The lithium-rich manganese-based positive electrode obtained in example 4 was used as a positive electrode active material at 0.1C (1c=250ma g -1 ) And (3) performing electrochemical constant-current charge and discharge test in a voltage range of 2.0-4.8V.
Comparative example 1
Similar to the procedure of example 3, the difference is that: the amount of the lithium-containing compound used in the primary calcination was 30% of the total amount, and the amount of the lithium-containing compound used in the secondary calcination was 70% of the total amount.
Comparative example 2
Similar to the procedure of example 3, the difference is that: the amount of the lithium-containing compound used in the primary calcination was 70% of the total amount, and the amount of the lithium-containing compound used in the secondary calcination was 30% of the total amount.
Comparative example 3
Similar to the procedure of example 3, the only difference is that: in the primary sintering process, the temperature of the secondary calcination is 650 ℃.
Comparative example 4
Similar to the procedure of example 3, the only difference is that: in the primary sintering process, the temperature of the secondary calcination is 1000 ℃.
Comparative example 5
Similar to the procedure of example 3, the only difference is that: in the secondary sintering process, the time for one-stage calcination is 12 hours.
Comparative example 6
Similar to the procedure of example 3, the only difference is that: in the secondary sintering process, the second-stage calcination time is 10 hours.
Test results
Fig. 1 is a scanning electron microscope image of a single crystal lithium-rich manganese-based positive electrode material prepared in example 3, wherein (a) and (b) are scanning electron microscope images with different magnifications, and as can be seen from fig. 1, the surface of particles is smooth and is 2-4um, and primary particles are uniformly dispersed, so that the morphology mechanical strength is high, the particles are not easy to break in the compaction process, and the inter-crystal breaking of the particles can not occur in the long-cycle process.
Fig. 2 is a graph showing the first-cycle charge and discharge curves of the CR2032 coin cells assembled in examples 1, 2, 3 and 4 at a voltage interval of 2.0V-4.8V and a 0.1C rate, and as can be seen from fig. 2, the first-cycle discharge specific capacities of examples 1, 2, 3 and 4 are 201.8 mAh g, respectively -1 、222.8 mAh g -1 、227.6 mAh g -1 And 261.9 mAh g -1 Examples 1, 2, 3 and 4 all present a more pronounced plateau at 4.5V, which corresponds to the activation process of the lithium-rich manganese-based positive electrode material, indicating successful preparation of the lithium-rich manganese-based positive electrode material. In addition, the first-week discharge specific capacities of examples 1, 2, 3 and 4 were gradually increased, corresponding to the increase in pole piece compaction density.
Fig. 3 is a graph showing specific discharge capacities of the CR2032 coin cells assembled in example 1, example 2, example 3 and example 4 at a voltage interval of 2.0V to 4.8V and a rate of 0.1C, and it can be seen from fig. 3 that example 3 exhibits more excellent cycle stability during a long cycle, and the capacity retention rate of example 3 is up to 98.7% for 100 cycles.
Fig. 4 is a graph showing specific discharge capacities of the CR2032 coin cells assembled in example 1, example 2, example 3 and example 4 at voltage intervals of 2.0V to 4.8V and at different rates, and it can be seen in fig. 4 that the volumetric energy densities of example 1, example 2, example 3 and example 4 are increased as the compacted densities are increased, but the cycle stability of the cells is poor due to excessively high compacted densities.
Fig. 5 is a graph showing specific discharge capacities of examples 1, 2, 3 and 4 at different rates, and it can be found that example 3 shows excellent performance at a test rate of 5C, confirming that high compacted density can improve rate performance of lithium-rich manganese-based cathode materials.
Fig. 6 is a scanning electron microscope image of the material prepared in comparative example 1, in which (a) and (b) are scanning electron microscope images of different magnifications, and it can be seen from fig. 6 that, compared with example 3, primary particles having a particle diameter of about 1um are agglomerated into irregular secondary particles, and the morphology of spinel is exhibited, but the morphology of single crystal particles is not exhibited. Presumably, the phenomenon of lithium deficiency due to insufficient lithium content at the time of primary calcination leads to failure in dispersion at the time of particle formation.
Fig. 7 is a scanning electron microscope image of the material prepared in comparative example 2, in which (a) and (b) are scanning electron microscope images at different magnifications, and it can be seen from fig. 7 that the secondary particles are particles having a particle diameter of about 4um, but the primary particle boundaries of the particles are not obvious, compared with example 3. Presumably, this is because the excessive amount of lithium is burned into agglomerated secondary particles at the time of primary calcination, and a small amount of lithium source is not completely mixed and burned at the time of secondary calcination.
Fig. 8 is a scanning electron microscope image of the material prepared in comparative example 3, in which (a) and (b) are scanning electron microscope images of different magnifications, and it can be seen from fig. 8 that agglomerated secondary particles having a particle size of about 5um have a morphology similar to that of the conventional lithium-rich manganese-based positive electrode material, and that a single crystal morphology cannot be fired at a relatively low temperature upon primary calcination, as compared with example 3.
FIG. 9 is a scanning electron microscope image of the material prepared in comparative example 4, in which (a) and (b) are scanning electron microscope images of different magnifications, and it can be seen from FIG. 9 that the material exhibits a better single crystal morphology than example 3, but has a specific discharge capacity of only 198.2mAh g at the first cycle -1 . Presumably, too high a calcination temperature may cause volatilization of lithium, affecting capacity exertion.
Fig. 10 is a scanning electron microscope image of the material prepared in comparative example 5, in which (a) and (b) are scanning electron microscope images of different magnifications, and it can be seen from fig. 10 that the material exhibits primary particles of about 5um in a uniformly dispersed particle size, compared with example 3, and that the grain size is excessively increased due to excessively long calcination time during primary calcination. The longer lithium ion diffusion channel influences the exertion of electrochemical performance, and the specific capacity of the first-week discharge is only 164.3 mAh g -1 。
FIG. 11 is a scanning electron microscope image of the material prepared in comparative example 6, in which (a) and (b) are scanning electron microscope images of different magnifications, and it can be seen from FIG. 11 that the morphology of the material exhibits a partially monocrystalline and partially polycrystalline state as compared with example 3. Reducing the secondary calcination time results in insufficient grain growth of the material.
From the above, it can be seen that the proper increase of the compaction density has an important influence on the cycle performance and the rate performance of the lithium-rich manganese-based positive electrode material, the smaller the compaction density is, the larger the inter-particle distance is, the contact probability and the contact area between particles are reduced, the electron conduction is not facilitated, the reduction of the conductivity can affect the discharge of a large current, and the discharge polarization is increased. However, too high a compaction density increases the extrusion between the primary particles of material, reduces the porosity of the plate, and impedes lithium ion transport. Therefore, the material is difficult to permeate in the electrolyte, and as a direct result, the specific capacity of the material is difficult to develop, and the liquid retention capacity of the battery is poor. In the cycling process, the battery polarization becomes large, the capacity attenuation is serious, the internal resistance is increased, and the cycling stability is poor. The proper compaction density can increase the discharge specific capacity of the battery, reduce the internal resistance, reduce the polarization loss, prolong the cycle life of the battery and improve the utilization rate of the lithium ion battery. When the compacted density is too high or too low, lithium ion transport is not facilitated. The above description shows that the proper compaction density can simultaneously improve the cycle stability and the multiplying power performance of the lithium-rich manganese-based positive electrode material, the preparation is simple and convenient, the application is easy, and the preparation method provided by the embodiment of the invention provides a solution for large-scale synthesis of the lithium-rich manganese-based positive electrode material with high specific energy.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. The preparation method of the high-compaction micron monocrystal lithium-rich manganese-based positive electrode material is characterized by comprising the following steps of:
precursor Mn 0.75 Ni 0.25 (OH) 2 Uniformly mixing 50% of lithium-containing compound and molten salt, and then performing primary calcination, wherein the molten salt comprises at least one of lithium chloride and potassium chloride, and the primary calcination is as follows: performing first-stage calcination for 4-7 h at 400-600 ℃, and then performing second-stage calcination for 4-7 h at 700-900 ℃;
washing and drying the materials obtained by primary calcination, uniformly mixing the materials with the rest 50% of lithium-containing compounds, and performing secondary calcination, wherein the secondary calcination is as follows: performing primary calcination for 4-7 h at 400-600 ℃, performing secondary calcination for 11-14 h at 800-1100 ℃, and cooling the material after secondary calcination to obtain Li 1.2 Mn 0.6 Ni 0.2 O 2 Is a high-compaction micron monocrystal lithium-rich manganese-based positive electrode material;
the prepared high-voltage solid micron single crystal lithium-rich manganese-based positive electrode material is single crystal particles with the diameter of 2-4 mu m, and the compacted density of the high-voltage solid micron single crystal lithium-rich manganese-based positive electrode material is 2.8g/cm 3 -4.0g/cm 3 。
2. The method of claim 1, wherein the step of primary calcination is as follows: precursor Mn 0.75 Ni 0.25 (OH) 2 Mixing and grinding 50% lithium-containing compound, uniformly mixing with molten salt, placing in a muffle furnace, heating from room temperature to 400-600 ℃ at a heating rate of 3-8 ℃/min, preserving heat for 4-7 h, and cooling along with the furnace; then the temperature is raised from room temperature to 700 ℃ to 900 ℃ at a heating rate of 3 ℃/min to 8 ℃/min, and the temperature is kept for 4h to 7h and then is reduced with the furnace.
3. The method of manufacturing according to claim 2, further comprising: preparing a precursor Mn by adopting a coprecipitation method 0.75 Ni 0.25 (OH) 2 The precursor Mn is firstly added 0.75 Ni 0.25 (OH) 2 Mixing and grinding the mixture with 50% lithium-containing compound for 0.5-2 h, uniformly mixing the mixed dry material with molten salt, and calcining for the first time.
4. The method of claim 1, wherein the step of secondary calcination is as follows: washing and drying the materials obtained by primary calcination, uniformly mixing the materials with the rest 50% of lithium-containing compounds, placing the materials in a muffle furnace, heating the materials from room temperature to 400-600 ℃ at a heating rate of 3-8 ℃/min, preserving heat for 4-7 h, and then cooling along with the furnace; then the temperature is increased from room temperature to 800-1100 ℃ at the heating rate of 3-8 ℃/min, the temperature is kept for 11-14 h, and then the temperature is reduced along with the furnace, thus obtaining the Li composition 1.2 Mn 0.6 Ni 0.2 O 2 Is a high-compaction micron monocrystal lithium-rich manganese-based positive electrode material.
5. The method according to claim 1, wherein the lithium-containing compound comprises at least one of anhydrous lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, lithium nitrate, lithium oxide, lithium acetate, and lithium oxalate.
6. A highly compacted micro-single crystal lithium-rich manganese-based cathode material prepared according to the preparation method of any one of claims 1 to 5.
7. A lithium battery, characterized in that the lithium battery positive electrode comprises the high-compaction micron single crystal lithium-rich manganese-based positive electrode material according to claim 6.
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