CN108767254B - Surface structure and chemical composition synchronous regulation and control method of layered lithium-rich cathode material - Google Patents
Surface structure and chemical composition synchronous regulation and control method of layered lithium-rich cathode material Download PDFInfo
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Abstract
The invention discloses a method for synchronously regulating and controlling the surface structure and chemical composition of a layered lithium-rich anode material, which has the following general formula: xLi2MnO3·(1‑x)LiMO2Or Li1+x[M]1‑xO2M is one or more of Mn, Co and Ni; the method comprises the following steps: 1) placing the carbonate precursor into a treating agent solution for surface treatment; 2) and firing the treated carbonate precursor into an oxide, uniformly mixing the oxide with a lithium source compound, and calcining at high temperature to obtain the surface-modified layered lithium-rich cathode material. The main body of the material is of a layered structure, the surface of the material is of a spinel phase, a transition mixed phase is arranged between the layered structure and the spinel phase, and the chemical composition of the surface is different from that of the main body. The method is simple and easy to control, and can endow the anode material with rapid lithium ion diffusion channels, stable cycle life, weak voltage decay and other excellent electrochemical properties.
Description
Technical Field
The invention relates to a method for synchronously regulating and controlling the surface structure and chemical composition of a layered lithium-rich cathode material, belonging to the field of energy materials and electrochemistry.
Background
The lithium ion battery has the advantages of large specific energy, high working voltage, low self-discharge rate, light weight and the like, so that the lithium ion battery becomes the most widely developed and applied power system at present. However, the energy density, power characteristics, safety performance and cost of the lithium ion battery still limit the further development of the lithium ion battery, and particularly, the lithium ion battery is difficult to meet the application requirements of strategic emerging industries such as electric vehicles and the like on high-energy-density power supplies. The energy density of lithium ion batteries mainly depends on the positive electrode material, and increasing the specific capacity or operating voltage of the positive electrode material is the main way to obtain high energy density. Compared with the specific capacity of a carbon negative electrode (350 mAh/g), the current commercialized positive electrode materials, such as layered lithium cobaltate, ternary materials, spinel type lithium manganate and olivine type lithium iron phosphate, have the problem of low specific discharge capacity (less than 200 mAh/g). Therefore, development of a new generation of cathode material with high capacity to obtain a lithium ion battery with high energy density is an urgent need for market application and industry development.
Among the currently developed cathode materials, the layered lithium-rich cathode material xLi2MnO3·(1-x)LiMO2Or Li1+xM1- xO2(M is a transition metal such as Mn, Ni, Co, etc.; 0<x<1) Due to high specific capacity (>250mAh/g), higher working voltage, low cost, environmental protection and the like, and has wide research enthusiasm at home and abroad and wide application prospect. It is generally believed that the material is a layered Li2MnO3(space group C2/m) and layered LiMO2(space group R3m) or both are combined on a nanometer scale. However, the material has the problems of large irreversible capacity, insufficient rate capability, serious voltage decline and the like for the first time, and the commercialization process of the material is hindered. Surface properties of layered lithium-rich cathode materials, e.g. tablesThe surface structure and surface chemical composition are considered to be key factors affecting electrochemical performance. Common surface modification methods, such as surface coating, surface doping, acid treatment and the like, can effectively improve the performance of the material, but can only change one aspect alone, so that more excellent comprehensive electrochemical performance cannot be obtained. How to simultaneously change the surface structure or chemical composition of a material still has great challenges. Therefore, a simple and controllable method is found, the synchronous regulation and control of the surface structure and the chemical composition of the material are realized, and the anode material with high specific capacity, good rate capability, excellent capacity and voltage stability is obtained, so that the method has important practical significance for the rapid development of lithium ion batteries and related industries.
Disclosure of Invention
In order to solve the technical problems, the invention provides a method for synchronously regulating and controlling the surface structure and the chemical composition of the layered lithium-rich cathode material of the lithium ion battery, which is simple and easy to control in operation and can endow the cathode material with excellent electrochemical properties such as a rapid lithium ion diffusion channel, a stable cycle life, weak voltage decay and the like.
The technical scheme adopted by the invention is as follows: a surface structure and chemical composition synchronous regulation and control method of a layered lithium-rich cathode material is disclosed, wherein the general formula of the layered lithium-rich cathode material is as follows: xLi2MnO3·(1-x)LiMO2Or Li1+x[M]1-xO2Wherein M is one or more of transition metals Mn, Co and Ni, 0<x<1; the main body of the layered lithium-rich cathode material particle is of a layered structure, the surface of the layered lithium-rich cathode material particle is of a spinel phase, a transition mixed phase is arranged between the layered structure and the spinel phase, and the chemical composition of the surface of the layered lithium-rich cathode material particle is different from that of the main body, and the layered lithium-rich cathode material particle comprises the following steps:
(1) placing the carbonate precursor into a treating agent solution, uniformly stirring, washing with distilled water, filtering, and drying to obtain a treated carbonate precursor;
(2) calcining the treated carbonate precursor at 400-600 ℃ for 4-8h to obtain an oxide; uniformly mixing the obtained oxide and a lithium source compound according to the ratio of the mole number of lithium to the total mole number of transition metals of 1.1-1.55; calcining the obtained mixture at the temperature of 700-900 ℃ for 8-24h to obtain the surface modified layered lithium-rich cathode material.
In the method for synchronously regulating and controlling the surface structure and the chemical composition of the layered lithium-rich cathode material, the treating agent in the step 1) comprises one or a mixture of more of ammonia water, ammonium sulfate, ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium nitrate, ammonium acetate or ethylenediamine.
In the method for synchronously regulating and controlling the surface structure and the chemical composition of the layered lithium-rich cathode material, magnetic stirring or mechanical stirring is adopted in the stirring mode in the step 1).
In the method for synchronously regulating and controlling the surface structure and the chemical composition of the layered lithium-rich cathode material, the lithium source compound in the step 2) comprises one or a mixture of lithium carbonate, lithium hydroxide or lithium nitrate.
Compared with the prior art, the invention has the beneficial effects that:
according to the method, a treating agent solution is adopted to carry out surface treatment on a carbonate precursor, the surface chemical composition of the precursor is changed based on the coordination reaction of the treating agent and metal ions, and a surface-modified layered lithium-rich cathode material is obtained through a high-temperature solid-phase lithiation reaction; the main body of the layered lithium-rich cathode material is of a layered structure, the surface of the layered lithium-rich cathode material is a spinel phase, the two phases are in gradient transition, and the chemical composition of the surface of the layered lithium-rich cathode material is different from that of the main body; the invention realizes the synchronous regulation and control of the surface structure and chemical components of the anode material, and the obtained special surface endows the anode material with excellent electrochemical properties such as rapid lithium ion diffusion channel, stable cycle life, weak voltage decay and the like; in addition, the method is simple and easy to control in operation, can be used for large-scale industrialization, and has good application prospect.
Drawings
FIG. 1 is a flow chart of the present invention.
FIG. 2 is SEM images of carbonate precursors and untreated carbonate precursors obtained by ammonia water treatment according to the present invention: (a) SEM images of untreated carbonate precursor, (b) SEM images of ammonia treatment for 5min of carbonate precursor, (c) SEM images of ammonia treatment for 10min of carbonate precursor, (c) SEM images of ammonia treatment for 20min of carbonate precursor, and (e) SEM images of ammonia treatment for 40min of carbonate precursor.
FIG. 3 is an EDX energy spectrum of a carbonate precursor and an untreated carbonate precursor obtained by ammonia water treatment for different time periods according to the present invention: (a) EDX spectrum of untreated carbonate precursor, (b) EDX spectrum of carbonate precursor treated with ammonia for 10 min.
FIG. 4 is SEM images of the layered lithium-rich cathode material obtained by treating a carbonate precursor with ammonia water for different times according to the present invention and the layered lithium-rich cathode material obtained by a comparative example: (a) an SEM image of the layered lithium-rich cathode material obtained in the comparative example, (b) an SEM image of the layered lithium-rich cathode material obtained by ammonia water treatment for 5min, (c) an SEM image of the layered lithium-rich cathode material obtained by ammonia water treatment for 10min, (d) an SEM image of the layered lithium-rich cathode material obtained by ammonia water treatment for 20min, and (e) an SEM image of the layered lithium-rich cathode material obtained by ammonia water treatment for 40 min.
FIG. 5 is a linear scanning EDX (EDX) spectrum diagram of the layered lithium-rich cathode material obtained by treating a carbonate precursor with ammonia water for different times according to the invention and the layered lithium-rich cathode material obtained by a comparative example: (a) an EDX energy spectrum of the layered lithium-rich cathode material obtained after ammonia water treatment for 10min, and (b) an EDX energy spectrum of the layered lithium-rich cathode material obtained in the comparative example.
Fig. 6 is XRD patterns of the layered lithium-rich cathode material obtained by treating the carbonate precursor with ammonia water for different times according to the present invention and the layered lithium-rich cathode material obtained by the comparative example.
FIG. 7 is a TEM image of the layered lithium-rich cathode material obtained by treating a carbonate precursor with ammonia water according to the present invention for different periods of time and the layered lithium-rich cathode material obtained by a comparative example: (a) a TEM image of the layered lithium-rich cathode material obtained in the comparative example, (b) a TEM image of the layered lithium-rich cathode material obtained by ammonia water treatment for 10min, and (c) a TEM image of a box a region in fig. b.
Fig. 8 is a first charge-discharge curve of the layered lithium-rich cathode material obtained by treating the carbonate precursor with ammonia water for different times according to the present invention and the layered lithium-rich cathode material obtained by the comparative example.
Fig. 9 is an electrochemical performance diagram of the layered lithium-rich cathode material obtained by treating the carbonate precursor with ammonia water for different times according to the present invention and the layered lithium-rich cathode material obtained by the comparative example: (a) a cycle life chart, (b) a median voltage cycle chart, (c) different cycle times charge-discharge curve charts of the layered lithium-rich cathode material obtained by the comparative example, and (d) different cycle times charge-discharge curve charts of the layered lithium-rich cathode material obtained by ammonia water treatment for 10 min.
Fig. 10 is a graph showing rate performance of the layered lithium-rich cathode material obtained by treating a carbonate precursor with ammonia water for different times according to the present invention and the layered lithium-rich cathode material obtained by the comparative example.
Detailed Description
Comparative example
(1) Weighing spherical Mn synthesized by a hydrothermal method0.6Ni0.2Co0.2CO32.0g of carbonate precursor is burnt for 6 hours at 500 ℃ to obtain the oxide precursor.
(2) The oxide precursor obtained in the above step was uniformly mixed with lithium carbonate in a ratio of [ Li ]: M ═ 1.42:1 ([ Li ] is the number of moles of lithium and [ M ] is the total number of moles of Mn, Ni, and Co metals), and then calcined in a muffle furnace at 750 ℃ for 12 hours to obtain a layered lithium-rich cathode material in the comparative example, labeled as LMNC.
Example 1
(1) Weighing spherical Mn synthesized by a hydrothermal method0.6Ni0.2Co0.2CO32.0g of carbonate precursor is placed in a 50mL beaker, 30mL of 3.0mol/L ammonia water solution is measured and poured into the beaker filled with the carbonate precursor, the mixture is magnetically stirred for 10min, then distilled water is used for washing and filtering for multiple times, and finally the mixture is placed in a forced air drying oven to be dried for 12h at the temperature of 80 ℃ to obtain the carbonate precursor treated by the ammonia water. For comparison, the same method is adopted, and the ammonia water treatment time is changed to 5min, 20min and 40min, so that the corresponding treated carbonate precursors are obtained respectively.
(2) And (2) treating the ammonia water obtained in the step (1) for 5min, 10min, 20min and 40min to obtain carbonate precursors, and respectively burning the carbonate precursors at 500 ℃ for 6h to obtain oxides.
(3) And (2) uniformly mixing the oxide obtained in the step with lithium carbonate according to the proportion of [ Li ] to [ M ] of 1.42:1 (wherein [ Li ] is the mole number of lithium, and [ M ] is the mole number of total metals of Mn, Ni and Co), and calcining the mixture in a muffle furnace at 750 ℃ for 12 hours to obtain the surface-modified layered lithium-rich cathode material. The corresponding surface modified layered lithium rich cathode materials obtained by treatment with ammonia water for 5min, 10min, 20min and 40min are labeled LMNC5, LMNC10, LMNC20 and LMNC40, respectively.
SEM tests were performed on untreated and ammonia-treated carbonate precursors, and as shown in fig. 2(a), the untreated carbonate precursor was spherical particles with a size of about 2 μm and a smooth surface, and as shown in fig. 2(b) and (c), the particle morphology of the precursors treated with ammonia for 5min and 10min was similar to that of the untreated sample and did not change significantly. However, as shown in fig. 2(d), (e), the precursor particles obtained by ammonia water treatment for 20min and 40min have different degrees of erosion on the surface and floccules, and the spherical particles are damaged, which indicates that the ammonia water treatment time is too long, and the ammonia water and the surface of the carbonate precursor have a large degree of chemical reaction, thus damaging the surface morphology. In addition, through the EDX spectroscopy test, as shown in fig. 3(a), the untreated sample surface chemical composition (molar ratio) is 60.73% Mn, 20.06% Ni and 19.21% Co, and the molar ratio of Mn, Ni and Co matches the theoretical value (3:1:1), while the sample treated with ammonia water for 10min, as shown in fig. 3(b), the Ni element content of the surface is significantly reduced to about 14.62% (molar ratio), and the Mn and Co content is slightly increased, indicating that the coordination reaction ratio of ammonia water and Ni is stronger than Mn and Co, and the chemical composition of the surface can be changed after the ammonia water is properly treated.
The microstructure of the layered lithium-rich cathode material obtained by the high-temperature solid-phase lithiation reaction is shown in fig. 4. As shown in fig. 4(a), (b), and (c), the shapes of the particles of the three positive electrode materials LMNC, LMNC5, and LMNC10 are relatively similar, and the spherical shape of the precursor is maintained, and the primary particles on the surface are significantly increased, indicating that the crystallinity is good. As shown in fig. 4(d), the primary particles on the surface of the LMCN20 particles are blurred, and as shown in fig. 4(e), the LMCN40 particles are completely broken in spherical morphology. An EDX energy spectrum test of surface linear scanning is performed on two materials, namely LMNC and LMNC10, as shown in fig. 5(b), it can be seen that the corresponding LMNC layered lithium-rich cathode material is obtained without ammonia water treatment of the precursor, the contents of Mn, Ni and Co are consistent with theoretical values (Mn: Ni: Co: 3:1:1), while the corresponding LMNC10 layered lithium-rich cathode material is obtained by ammonia water treatment of the precursor for 10min, as shown in fig. 5(a), the Ni content of the particle surface is significantly lower than the Co content, that is, the contents of Mn, Ni and Co elements on the particle surface of the carbonate precursor changed after ammonia water treatment are subjected to a high-temperature lithiation reaction, and the same metal element distribution is maintained in the obtained layered lithium-rich cathode material.
By XRD analysis, as shown in FIG. 6, all samples were typically layered alpha-NaFeO2The structure, space group is R3m, and more obvious Li appears between 20-25 DEG2MnO3And the superlattice diffraction peak is a characteristic peak of the layered lithium-rich cathode material, and the space group is C2/m. However, as seen from the enlarged view, XRD diffraction peaks of spinel phase (space group is Fd-3m) were found in the corresponding layered lithium-rich cathode material obtained by ammonia water treatment of the precursor, and the diffraction peaks of spinel phase were more pronounced as the ammonia water treatment time was longer.
As shown in fig. 7, it is found through TME test that, as shown in fig. 7(a), the crystal structure of the layered lithium-rich cathode material LMNC without ammonia water treatment precursor is a pure layered structure, while the layered lithium-rich cathode material LMNC10 obtained after ammonia water treatment of the precursor for 10min has a distinct spinel phase on the particle surface as shown in fig. 7(b), and a mixed structure is formed between the spinel phase and the bulk layered structure, as shown in fig. 7(c), which illustrates that the ammonia water treatment precursor changes its surface chemical composition, and then the formation of the surface spinel phase is self-induced during lithiation.
Electrochemical testing shows that, as seen from the first charge-discharge curve of fig. 8: an obvious spinel phase discharge platform exists in a discharge curve of the layered lithium-rich cathode material obtained by treating the precursor with ammonia water at-2.6V, and an untreated sample does not have the platform. The first discharge capacity of the LMNC sample obtained without ammonia water treatment is 288.7mAh/g, and the first coulombic efficiency is 79.5%, while the LMNC10 sample obtained by ammonia water treatment for 10min has the highest specific discharge capacity of 300.0mAh/g, and the first coulombic efficiency is up to 89.8%. As seen in fig. 9(a), LMNC10 has an optimum cycle life with a capacity retention of 85% after 100 cycles, whereas the comparative LMNC material has a capacity retention of only 65.3% after 100 cycles. In addition, the median voltage of LMNC10 decays most slowly as the cycling progresses (fig. 9(b)), and fig. 9(c) and (d) also demonstrate that the decay of the discharge plateau voltage is slowed down in LMNC10 relative to the pure layered structure LMNC due to the surface introduction of the spinel phase. As seen in the rate capability plot of fig. 10, LMNC10 has good rate capability, which still has 156.2mAh/g at 10C rate, while LMNC has only 111.3mAh/g at 10C rate. The electrochemical performance tests show that after the carbonate precursor is treated by ammonia water for a proper time, a special surface is formed by self-induction in the high-temperature lithiation process, so that the electrochemical performance of the layered lithium-rich cathode material can be obviously improved.
Example 2
(1) Weighing spherical Mn synthesized by a hydrothermal method0.6Ni0.2Co0.2CO32.0g of carbonate precursor is placed in a 50mL beaker, 30mL of 2.0mol/L ammonium sulfate solution is measured and poured into the beaker filled with the carbonate precursor, the mixture is magnetically stirred for 20min, then is washed and filtered for multiple times by distilled water, and finally is placed in a forced air drying oven to be dried for 12h at the temperature of 80 ℃ to obtain the treated carbonate precursor.
(2) And (2) burning the carbonate precursor which is not treated and is obtained in the step (1) and the ammonium sulfate solution for 20min at 500 ℃ for 6h to obtain the oxide.
(3) And (3) uniformly mixing the oxide obtained in the step with lithium carbonate according to the proportion of [ Li ]: [ M ]: 1.42:1, and calcining the mixture in a muffle furnace at 750 ℃ for 12 hours to obtain the lithium-rich cathode material.
Electrochemical tests show that the lithium-rich cathode material obtained after ammonium sulfate treatment has a first discharge specific capacity of 293.0mAh/g and a first charge-discharge efficiency of 88.2% in the voltage range of 0.1C and 2.0-4.6V; the capacity retention rate is 90.5% after 100 cycles at 0.5 ℃; under the condition of large multiplying power of 10C, the reversible capacity is still 146.3m Ah/g, and the electrochemical performance is more excellent than that of a layered lithium-rich cathode material (a comparative sample) obtained by not treating the precursor with ammonium sulfate.
Example 3
(1) Weighing spherical Mn synthesized by a coprecipitation method0.75Ni0.25CO33.0g of carbonate precursor is placed in a 50mL beaker, 30mL of 2.0mol/L ammonium carbonate solution is measured and poured into the beaker filled with the carbonate precursor, mechanical stirring is carried out for 30min, then distilled water is used for washing and filtering for a plurality of times, and finally the beaker is placed in a forced air drying oven to be dried for 12h at the temperature of 80 ℃ to obtain the carbonate precursor treated by ammonia water.
(2) And (2) treating the carbonate precursor which is not treated and is obtained in the step (1) for 30min at 400 ℃ for 8h to obtain an oxide precursor.
(3) And (3) uniformly mixing the oxide precursor obtained in the step with lithium hydroxide according to the proportion of [ Li ] to [ M ] of 1.55:1, and calcining the mixture in a muffle furnace at 700 ℃ for 24 hours to obtain the lithium-rich cathode material.
Electrochemical tests show that the lithium-rich anode material obtained after ammonium carbonate treatment has a first discharge specific capacity of 298.0mAh/g (an untreated sample is 280.0mAh/g) and a first charge-discharge efficiency of 90.3% (the untreated sample is 78.6%) within a voltage range of 0.1C and 2.0-4.6V; capacity retention 91.4% after 100 cycles at 0.5C (78.5% for untreated samples); under the condition of large multiplying power of 10 ℃, the reversible capacity is still 158.6m Ah/g (an untreated sample is 102.3m Ah/g), and the lithium-rich cathode material has more excellent electrochemical performance than a lithium-rich cathode material obtained by not treating a precursor with ammonium carbonate.
Example 4
(1) Weighing spherical Mn synthesized by a coprecipitation method0.50Ni0.25Co0.25CO32.0g of carbonate precursor is placed in a 100mL beaker, 50mL of 2.0mol/L ammonium bicarbonate solution is measured and poured into the beaker filled with the carbonate precursor, mechanical stirring is carried out for 10min, then distilled water is used for washing and filtering for multiple times, and finally the mixture is placed in a forced air drying oven to be dried for 12h at 100 ℃ to obtain the treated carbonate precursor.
(2) And (2) treating the carbonate precursor which is not treated and is obtained in the step (1) by the ammonium bicarbonate solution for 30min, and burning the carbonate precursor at 600 ℃ for 4h to obtain an oxide precursor.
(3) And (3) uniformly mixing the oxide precursor obtained in the step with lithium nitrate according to the proportion of [ Li ] to [ M ] of 1.1:1, and calcining the mixture in a muffle furnace at 900 ℃ for 8 hours to obtain the lithium-rich cathode material.
Electrochemical tests show that the lithium-rich anode material obtained after ammonium bicarbonate treatment has a first discharge specific capacity of 260.0mAh/g (an untreated sample is 232.0mAh/g) and a first charge-discharge efficiency of 88.0% (the untreated sample is 79.3%) within a voltage range of 0.1C and 2.0-4.6V; capacity retention after 100 cycles at 0.5C was 88.5% (75.2% for untreated samples); under the condition of large multiplying power of 10C, the reversible capacity is still 140.6m Ah/g (the untreated sample is 86.2m Ah/g), and the electrochemical performance is more excellent than that of the lithium-rich cathode material obtained by not treating the precursor with ammonium bicarbonate.
Example 5
(1) Weighing spherical Mn synthesized by a hydrothermal method0.6Ni0.2Co0.2CO32.0g of carbonate precursor is placed in a 50mL beaker, 30mL of 2.0mol/L ammonium chloride solution is measured and poured into the beaker filled with the carbonate precursor, magnetic stirring is carried out for 30min, then distilled water is used for washing and filtering for a plurality of times, and finally the beaker is placed in an air-blast drying oven for drying for 12h at the temperature of 80 ℃ to obtain the treated carbonate precursor.
(2) And (2) burning the carbonate precursor which is not treated and is obtained in the step (1) in the ammonium chloride solution for 20min at 500 ℃ for 6h to obtain the oxide.
(3) And (3) uniformly mixing the oxide obtained in the step with lithium carbonate according to the proportion of [ Li ]: [ M ]: 1.42:1, and calcining the mixture in a muffle furnace at 750 ℃ for 12 hours to obtain the lithium-rich cathode material.
Electrochemical tests show that the lithium-rich cathode material obtained after the ammonium chloride treatment has the first discharge specific capacity of 286.0mAh/g and the first charge-discharge efficiency of 85.0% in the voltage ranges of 0.1C and 2.0-4.6V; the capacity retention rate after 100 cycles at 0.5 ℃ is 89.2%; under the condition of large multiplying power of 10C, the reversible capacity is still 134.5m Ah/g, and the electrochemical performance is more excellent than that of a layered lithium-rich cathode material (a comparative sample) obtained by not treating a precursor with ammonium chloride.
Example 6
(1) Weighing the water passing throughSpherical Mn obtained by synthesis0.6Ni0.2Co0.2CO32.0g of carbonate precursor is placed in a 50mL beaker, 30mL of 2.0mol/L ammonium nitrate solution is measured and poured into the beaker filled with the carbonate precursor, magnetic stirring is carried out for 20min, then distilled water is used for washing and filtering for multiple times, and finally the mixture is placed in a forced air drying oven to be dried for 12h at the temperature of 80 ℃ to obtain the treated carbonate precursor.
(2) And (2) burning the carbonate precursor which is not treated and the ammonium nitrate solution obtained in the step (1) for 20min at 500 ℃ for 6h to obtain the oxide.
(3) And (3) uniformly mixing the oxide obtained in the step with lithium carbonate according to the proportion of [ Li ]: [ M ]: 1.42:1, and calcining the mixture in a muffle furnace at 750 ℃ for 12 hours to obtain the lithium-rich cathode material.
Electrochemical tests show that the lithium-rich cathode material obtained after ammonium nitrate treatment has a first discharge specific capacity of 288.4mAh/g and a first charge-discharge efficiency of 86.0% in the voltage range of 0.1C and 2.0-4.6V; the capacity retention rate is 88.2% after 100 cycles at 0.5 ℃; under the condition of large multiplying power of 10C, the reversible capacity is still 141.3m Ah/g, and the electrochemical performance is more excellent than that of a layered lithium-rich cathode material (a comparative sample) obtained by not treating a precursor with ammonium nitrate.
Example 7
(1) Weighing spherical Mn synthesized by a hydrothermal method0.6Ni0.2Co0.2CO32.0g of carbonate precursor is placed in a 50mL beaker, 30mL of 2.0mol/L ammonium acetate solution is measured and poured into the beaker filled with the carbonate precursor, magnetic stirring is carried out for 30min, then distilled water is used for washing and filtering for a plurality of times, and finally the mixture is placed in an air-blast drying oven to be dried for 12h at the temperature of 80 ℃ to obtain the treated carbonate precursor.
(2) And (2) roasting a carbonate precursor which is not treated and is obtained in the step (1) and the ammonium acetate solution for 30min at 500 ℃ for 6h to obtain an oxide.
(3) And (3) uniformly mixing the oxide obtained in the step with lithium carbonate according to the proportion of [ Li ]: [ M ]: 1.42:1, and calcining the mixture in a muffle furnace at 750 ℃ for 12 hours to obtain the lithium-rich cathode material.
Electrochemical tests show that the lithium-rich anode material obtained after the ammonium acetate treatment has the first discharge specific capacity of 289.4mAh/g and the first charge-discharge efficiency of 85.5% in the voltage ranges of 0.1C and 2.0-4.6V; the capacity retention rate after 100 cycles at 0.5 ℃ is 87.6%; under the condition of large multiplying power of 10 ℃, the reversible capacity is still 143.6m Ah/g, and the electrochemical performance is more excellent than that of a layered lithium-rich cathode material (a comparative sample) obtained by not treating a precursor with ammonium acetate.
Example 8
(1) Weighing spherical Mn synthesized by a hydrothermal method0.6Ni0.2Co0.2CO32.0g of carbonate precursor is placed in a 50mL beaker, 30mL of 2.0mol/L ethylenediamine solution is measured and poured into the beaker filled with the carbonate precursor, magnetic stirring is carried out for 40min, then distilled water is used for washing and filtering for multiple times, and finally the mixture is placed in a forced air drying oven to be dried for 12h at the temperature of 80 ℃ to obtain the treated carbonate precursor.
(2) And (2) roasting the carbonate precursor which is not treated and is obtained in the step (1) and treated by the ethylenediamine solution for 40min at 500 ℃ for 6h to obtain the oxide.
(3) And (3) uniformly mixing the oxide obtained in the step with lithium carbonate according to the proportion of [ Li ]: [ M ]: 1.42:1, and calcining the mixture in a muffle furnace at 750 ℃ for 16h to obtain the lithium-rich cathode material.
Electrochemical tests show that the lithium-rich anode material obtained after ethylenediamine treatment has a first discharge specific capacity of 290.4mAh/g and a first charge-discharge efficiency of 86.7% in the voltage range of 0.1C and 2.0-4.6V; the capacity retention rate is 87.2% after 100 cycles at 0.5 ℃; under the condition of large multiplying power of 10C, the reversible capacity is still 139.0mAh/g, and the electrochemical performance is more excellent than that of a layered lithium-rich cathode material (a comparative sample) obtained by treating a precursor without ethylenediamine.
Claims (3)
1. A surface structure and chemical composition synchronous regulation and control method of a layered lithium-rich cathode material is disclosed, wherein the general formula of the layered lithium-rich cathode material is as follows: xLi2MnO3·(1-x)LiMO2Or Li1+x[M]1-xO2In the formula: m is one or more of Mn, Co and NiSeed, x is more than 0 and less than 1; the main body of the layered lithium-rich cathode material particle is of a layered structure, the surface of the layered lithium-rich cathode material particle is of a spinel phase, a transition mixed phase is arranged between the layered structure and the spinel phase, and the chemical composition of the surface of the layered lithium-rich cathode material particle is different from that of the main body, and the layered lithium-rich cathode material particle comprises the following steps:
(1) placing the carbonate precursor into a treating agent solution, uniformly stirring, washing with distilled water, filtering, and drying to obtain a treated carbonate precursor; the treating agent comprises one or a mixture of more of ammonia water, ammonium sulfate, ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium nitrate, ammonium acetate or ethylenediamine;
(2) calcining the treated carbonate precursor at 400-600 ℃ for 4-8h to obtain an oxide; uniformly mixing the obtained oxide and a lithium source compound according to the ratio of the mole number of lithium to the total mole number of transition metals of 1.1-1.55; calcining the obtained mixture at the temperature of 700-900 ℃ for 8-24h to obtain the surface modified lithium-rich cathode material.
2. The method for synchronously regulating and controlling the surface structure and the chemical composition of the layered lithium-rich cathode material according to claim 1, wherein the stirring manner in the step 1) is magnetic stirring or mechanical stirring.
3. The method for synchronously regulating the surface structure and the chemical composition of the layered lithium-rich cathode material as claimed in claim 1, wherein the lithium source compound in the step 2) comprises one or a mixture of lithium carbonate, lithium hydroxide or lithium nitrate.
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