CN112624207A - Full-concentration gradient-distributed lithium-rich manganese-based lithium cathode material and preparation method and application thereof - Google Patents
Full-concentration gradient-distributed lithium-rich manganese-based lithium cathode material and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to the technical field of lithium ion battery electrode materials, and particularly discloses a lithium-rich manganese-based positive electrode material with full-concentration gradient distribution, and a preparation method and application thereof. The preparation method of the anode material comprises the following steps: (1) preparing a transition metal salt solution A with high manganese content and a transition metal salt solution B with low manganese content; slowly pumping the solution B into the solution A, and simultaneously pumping the solution A into the reaction kettle at a certain flow rate; and (3) under the nitrogen atmosphere, regulating and controlling the pH value by controlling the feeding speed of the alkali solution, and carrying out coprecipitation reaction to prepare a precursor material. (2) And uniformly mixing the filtered, cleaned and dried precursor material with lithium salt, and roasting at high temperature to obtain the lithium-rich manganese-based anode material with full concentration gradient distribution, wherein the content of Mn element is linearly reduced from the inside to the surface, and the content of Ni element is linearly increased. The prepared material has high sphericity, narrow particle size distribution, stable material crystal lamellar structure, higher energy density and excellent cycle stability.
Description
Technical Field
The invention relates to the technical field of lithium ion battery anode materials, and particularly discloses a lithium-rich manganese-based lithium anode material with full-concentration gradient distribution, and a preparation method and application thereof.
Technical Field
In recent years, green, convenient and energy-saving electric automobiles are widely popularized, however, compared with traditional fuel automobiles, the electric automobiles still have many problems, such as: the endurance mileage is short, the charging time is long, and the safety performance needs to be improved. The lithium ion battery is a key part for solving the problems as a core component of the electric automobile. The resistance limiting the increase of the endurance mileage of the electric vehicle is mainly that the energy density of the lithium ion battery cannot be further increased, and the resistance is mainly limited by the anode material. Currently, commercial positive electrode materials such as lithium cobaltate, lithium iron phosphate, lithium manganate, low nickel ternary materials (NCM, NCA) and the like generally have the problems of low specific capacity, low energy density and the like, and cannot meet the requirement of developing a high energy density lithium ion battery. Because of the advantages of high discharge specific capacity (more than or equal to 250mAh/g), low material cost, good thermal stability and the like, the lithium-rich manganese-based anode material, xLi2MnO3-(1-x)LiNixCoyMn1-x-yO2,(x<0<1,y<0<1,0<x+y<1) The lithium ion battery has attracted the attention of people and becomes a competitive person for developing the lithium ion battery with high energy density. However, the materials have the problems at present, such as: initial coulombic efficiency low (85% or less), rapid capacity/voltage decay, and poor rate capability, but limited its commercial application. By carrying out surface coating treatment on the lithium-rich manganese-based positive electrode material, the surface of the material can be effectively protected from corrosion of electrolyte, dissolution of transition metal ions and phase change of a surface structure, and the electron/ion conduction rate of the surface of the material can be improved. In addition, bulk phase/surface doping modification is carried out on the anode material by utilizing the heteroatoms, so that the crystal structure of the material can be stabilized, and the lithium-rich manganese base can be improvedThe initial coulomb efficiency, rate capability and cycle capability of the anode material.
Besides surface coating and heteroatom doping modification of the material, the electrochemical performance and structural stability of the material can be effectively improved by regulating and controlling the content and proportion of each element in the lithium-rich manganese-based positive material. According to the invention, the lithium-rich manganese-based lithium anode material with high internal manganese content and high external nickel content and full concentration gradient distribution is designed and prepared, the advantages of high discharge capacity provided by the internal high manganese component and high working voltage and structural stability provided by the external high nickel component are achieved, and the capacity/voltage decline of the material in the circulation is effectively inhibited while the high working voltage and energy density of the lithium-rich manganese-based anode material are maintained.
Disclosure of Invention
Aiming at the defects of the existing lithium-rich manganese-based anode material, the invention designs a preparation method of the lithium-rich manganese-based lithium anode material with full concentration gradient distribution, so that the problem of voltage/capacity decline of the material in circulation is effectively solved while the high energy density of the lithium-rich manganese-based anode material is maintained. The key steps for preparing the material are that when a precursor of the material is prepared by coprecipitation reaction, under the conditions of specific stirring speed, reaction temperature and pH, the feeding concentration of a transition metal salt solution is continuously regulated and controlled to obtain the precursor with the transition metal ion concentration linearly changing from the inside of particles to the surface layer of the particles, high sphericity and uniform particle size distribution, then the filtered, cleaned and dried precursor and lithium salt are uniformly mixed and then are roasted at high temperature, and finally the lithium-rich manganese-based lithium ion battery anode material with full concentration gradient distribution is obtained. Finally, the prepared lithium-rich manganese-based positive electrode material is subjected to morphology and structure analysis and relevant electrochemical performance test.
The technical scheme adopted by the invention comprises the following steps:
1. a preparation method of a lithium-rich manganese-based lithium cathode material with full concentration gradient distribution comprises the following preparation steps:
(1) and mixing nickel salt, cobalt salt and manganese salt according to the element molar ratio of 5-15: 5-15: preparing a transition metal salt solution A according to a proportion of 30-60, and mixing nickel salt, cobalt salt and manganese salt according to an element molar ratio of 10-32: 0 to 104: preparing a transition metal salt solution B according to the proportion of 10-60, and preparing an alkali solution C and an ammonia water solution D with certain concentrations.
(2) Adding reaction base solution E accounting for 20% of the volume of the reaction kettle into the reaction kettle, and adding transition metal salt solution B at a flow rate u1Pumping the transition metal salt solution A into the transition metal salt solution A, and leading the transition metal salt solution A to flow at a flow rate u under the protection of nitrogen2Pumping into a full-automatic control continuous reaction kettle at a certain flow rate u3、u4Respectively pumping the alkali solution C and the ammonia water solution D into a reaction kettle, and regulating and controlling the flow rate u of the alkali solution3To control the pH value of the reaction and maintain the stirring speed R in the kettle1Reaction temperature T1Reacting for a certain time t under the condition of pH value1And obtaining a precursor of the lithium-rich manganese-based positive electrode material with transition metal ions in full-concentration gradient distribution, and then washing, filtering and drying the precursor.
(3) Uniformly mixing the precursor obtained in the step (2) with lithium salt, and then respectively using T2And T3At a temperature of (d) carrying out a pre-calcination (t)2And high-temperature calcination t3And h, cooling to room temperature, crushing and sieving to obtain the lithium-rich manganese-based positive electrode material with the transition metal ions distributed in a full-concentration gradient manner.
2. In a possible embodiment of the present invention, the nickel salt in step (1) is nickel chloride, nickel nitrate, nickel acetate or nickel sulfate, the cobalt salt is cobalt chloride, cobalt nitrate, cobalt acetate or cobalt sulfate, the manganese salt is manganese chloride, manganese nitrate, manganese acetate or manganese sulfate, and the alkali is sodium bicarbonate, sodium carbonate or sodium hydroxide.
3. In a possible embodiment of the invention, u in step (2)1At 10-60 ml/h, u2At 20-120 ml/h, u3At 20-120 ml/h, u4At 20-300 ml/h and satisfy u2＝2u1Stirring speed R1At 300-1000 rpm, reaction temperature T1The reaction pH is 7.5-12 at 40-65 ℃, and the reaction time t1The time is 10 to 55 hours.
4. In a possible embodiment of the invention, the lithium salt in step (3) is hydrogenLithium oxide, lithium carbonate or lithium acetate, pre-firing temperature T2At 200-750 deg.C, pre-roasting time t2At the roasting temperature T of 2-10 h3Roasting at 800-950 deg.c for t3And (4) screening the crushed materials by using a 300-400-mesh sieve within 20-50 h.
Compared with the prior art, the invention has the following advantages:
according to the lithium-rich manganese-based anode material with full concentration gradient distribution, the concentration of transition metal ions is changed linearly, the content of Mn element is gradually reduced from the inside of the particles to the surface of the particles, and the content of Ni element is gradually increased, so that the full concentration gradient change of the content of the transition metal elements from the inside of the material to the surface of the material is realized. In this material, a high manganese content inside provides the material with a high discharge capacity, and a high nickel content outside provides the material with a high operating voltage and structural stability. Therefore, the positive electrode material can effectively inhibit capacity/voltage decline in circulation while maintaining high working voltage and energy density.
Drawings
FIG. 1 is an SEM image of a full-concentration-gradient-distribution lithium-rich manganese-based positive electrode material precursor prepared in example 1 of the present invention
FIG. 2 is a SEM image of a full-concentration-gradient-distribution lithium-rich manganese-based cathode material prepared in example 1 of the present invention and a linear scanning distribution diagram of transition metal elements
FIG. 3 is an XRD (X-ray diffraction) pattern of the lithium-rich manganese-based cathode material with full concentration gradient distribution prepared in example 1 of the invention
FIG. 4 is an SEM image of a precursor of the lithium-rich manganese-based positive electrode material prepared in comparative example 1
FIG. 5 is an SEM image of the lithium-rich manganese-based cathode material prepared in comparative example 1
FIG. 6 is an XRD pattern of the lithium-rich manganese-based positive electrode material prepared in comparative example 1
FIG. 7 is a CV test curve of the first three circles of the positive electrode material of comparative example 1
FIG. 8 is a CV test curve of the first three cycles of the positive electrode material of example 1
FIG. 9 is a graph comparing rate performance of lithium ion half cells corresponding to the positive electrode materials of example 1 and comparative example 1 of the present invention
FIG. 10 is a graph comparing the discharge median voltages of lithium ion half-cells corresponding to the positive electrode materials of example 1 and comparative example 1 of the present invention
FIG. 11 is a graph showing a comparison of discharge energy densities of lithium ion half cells corresponding to the positive electrode materials of example 1 of the present invention and comparative example 1
FIG. 12 is a graph comparing the first charge and discharge capacity, first-turn coulombic efficiency, long cycle performance and electrochemical impedance of lithium ion half-cells corresponding to the positive electrode materials of example 1, example 2 and comparative example 1 of the present invention
Detailed Description
In order to better explain the technical scheme of the invention, the following examples are used to illustrate the preparation process of the invention in detail, but the invention is not limited to the following examples, and various modifications made according to the idea of the invention are within the protection scope of the invention. In order to illustrate the technical effect of the present invention, the following specific operations are designed: preparing the lithium-rich manganese-based anode material with full concentration gradient distribution, analyzing the microstructure and the structure of the lithium-rich manganese-based anode material with full concentration gradient distribution by using SEM and XRD instruments, and then assembling a lithium ion half cell to test the electrochemical performance of the prepared anode material.
1. Preparation of full-concentration gradient distribution lithium-rich manganese-based positive electrode material precursor
(1) According to the lithium-rich manganese-based positive electrode material precursor TM (OH)2Or TMCO3(TM is Ni, Co and Mn elements) and preparing a transition metal salt solution according to the molar ratio of the Ni, Co and Mn elements. Nickel salt, cobalt salt and manganese salt are mixed according to the element molar ratio of 5-15: 5-15: dissolving 30-60% of the transition metal salt solution in deionized water, preparing a transition metal salt solution A, and mixing nickel salt, cobalt salt and manganese salt according to the element molar ratio of 10-32: 0 to 104: 10-60 of transition metal salt solution B, wherein the concentration of the transition metal salt solution A, B is 0.5-4 mol/L.
(2) Preparing a sodium hydroxide or sodium carbonate aqueous alkali C with a certain concentration and preparing an ammonia water solution D with a certain concentration, wherein the concentration of the aqueous alkali is 0.5-6 mol/L, and the concentration of the ammonia water solution is 0.1-10 mol/L.
(3) Adding reaction base liquid E with the volume of 20 percent of the kettle volume into a full-automatic continuous control reaction kettle, and adding transition metal salt solution B at the flow velocity u1Pumping the transition metal salt solution A into the transition metal salt solution A, and leading the transition metal salt solution A to flow at a flow rate u under the protection of nitrogen atmosphere2Pumping into a full-automatic control continuous reaction kettle at a certain flow rate u3、u4Respectively pumping the alkali solution C and the ammonia water solution D into a reaction kettle, and regulating and controlling the flow rate u of the alkali solution3To control the pH of the reaction. Maintaining the stirring speed R in the kettle1Reaction temperature T1Reacting for a certain time t under the condition of pH value1And obtaining a precursor of the lithium-rich manganese-based positive electrode material with transition metal ions in full-concentration gradient distribution, and then washing, filtering and drying the precursor. Wherein u is1At 10-60 ml/h, u2At 20-120 ml/h, u3At 20-120 ml/h, u4At 20-300 ml/h and satisfy u2＝2u1Stirring speed R1300 rpm-1000 rpm, reaction temperature T1The reaction pH is 7.5-12 at 40-65 ℃, and the reaction time t1The time is 10 to 55 hours.
2. Preparation of full-concentration gradient distributed lithium-rich manganese-based positive electrode material
Uniformly mixing a lithium-rich manganese-based positive electrode material precursor with full concentration gradient distribution prepared by a coprecipitation method with a lithium salt, and then carrying out reaction by using T2And T3At a temperature of (d) carrying out a pre-calcination (t)2And high-temperature calcination t3And h, cooling to room temperature, crushing and sieving to obtain the lithium-rich manganese-based positive electrode material with the transition metal ions distributed in a full-concentration gradient manner. Wherein the pre-baking temperature T2At 200-750 deg.C, pre-roasting time t2At the roasting temperature T of 2-10 h3Roasting at 800-950 deg.c for t3And (4) screening the crushed materials by using a 300-400-mesh sieve within 20-50 h. The specific embodiment is as follows:
example 1
1. According to the molar ratio of Ni, Co and Mn elements of 13: 13: 54 preparing a transition metal salt solution A of nickel sulfate, cobalt sulfate and manganese sulfate, wherein the molar ratio of Ni, Co and Mn elements is 32: 4: 44 preparing a transition metal salt solution B of nickel sulfate, cobalt sulfate and manganese sulfate, wherein the concentration of A, B solution is 2 mol/L.
2. Preparing a sodium carbonate solution C with the concentration of 2mol/L and preparing an ammonia water solution D with the concentration of 1.0 mol/L.
3. Adding deionized water with the volume of 20 percent of the kettle volume into a full-automatic continuous control reaction kettle as reaction base liquid E, and adding u of transition metal salt solution B1Pumping the transition metal salt solution A at a flow rate of 15ml/h under the protection of nitrogen atmosphere and respectively adding the solution2＝30ml/h、u3＝10～40ml/h、u4Respectively pumping the transition metal salt solution A, the sodium carbonate solution and the ammonia water solution into a reaction kettle at the flow rate of 30ml/h, and adjusting the feeding flow rate u of the sodium carbonate solution3To control the pH of the reaction system to 9.2 and to maintain the reaction system temperature T1At 55 deg.C and stirring speed R1Reaction t at 900rpm115 h. Continuing to age the reaction slurry after the feeding is finished t4Filtering, washing and drying the precipitate for 12h to obtain the precursor (Ni) of the lithium-rich manganese-based positive electrode material carbonate with the transition metal ions distributed in a full concentration gradient manner0.2813Co0.1062Mn0.6125)CO3。
4. The above-mentioned 20g of carbonate precursor was uniformly mixed with 9.9954g of lithium carbonate, and the mixture was put into a autoclave2Pre-baking at 500 deg.C2At T of 5h3High-temperature roasting at 900 ℃3And (5) obtaining the lithium-rich manganese-based positive electrode material with full concentration gradient distribution, crushing the lithium-rich manganese-based positive electrode material, and screening the crushed material by using a 300-400-mesh sieve to obtain a final product.
Fig. 1 is a scanning electron microscope image of a carbonate precursor prepared in example 1, fig. 2 is a scanning electron microscope image of a lithium-rich manganese-based cathode material with full concentration gradient distribution prepared in example 1 and a linear scanning distribution image of a transition metal element, and it can be confirmed from fig. 1 and fig. 2 that the material prepared in example 1 has the characteristics of good sphericity and narrow particle size distribution (5um to 15 um). Fig. 3 is an X-ray powder diffraction pattern of the cathode material prepared in example 1, and from fig. 3, it can be confirmed that the prepared cathode material has a typical lithium-rich manganese-based layered crystal structure, consists of a material having a hexagonal phase and a monoclinic phase, and maintains a good layered crystal structure.
Example 2
1. According to the molar ratio of Ni, Co and Mn elements of 15: 10: 55 preparing a transition metal salt solution A of nickel chloride, cobalt chloride and manganese chloride, wherein the molar ratio of Ni, Co and Mn elements is 30: 5: 45 preparing a transition metal salt solution B of nickel chloride, cobalt chloride and manganese chloride, wherein the concentration of the A, B solution is 3 mol/L.
2. Preparing a sodium carbonate solution C with the concentration of 3mol/L and preparing an ammonia water solution D with the concentration of 2 mol/L.
3. Adding deionized water with the volume of 20 percent of the kettle volume into a full-automatic continuous control reaction kettle as reaction base liquid E, and adding u of transition metal salt solution B1Pumped into the transition metal salt solution A at a flow rate of 10ml/h, respectively at u under the protection of nitrogen atmosphere2＝20ml/h、u3＝10～40ml/h、u4Pumping the transition metal salt solution A, the sodium carbonate solution C and the ammonia water solution D into a reaction kettle at a flow rate of 20ml/h, and adjusting the feeding flow rate u of the sodium carbonate solution3To control the pH of the reaction system to 9.5 and to maintain the temperature of the reaction system at T 150 ℃ and stirring speed R1Reaction t at 850rpm115 h. Continuing to age the reaction slurry after the feeding is finished t4Filtering, washing and drying the precipitate for 12h to obtain a lithium-rich manganese-based positive electrode material carbonate precursor (Ni) with transition metal ions distributed in a full concentration gradient manner0.2813Co0.1062Mn0.6125)CO3。
4. The above-mentioned 20g of carbonate precursor was uniformly mixed with 9.9954g of lithium carbonate, and the mixture was put into a autoclave2Pre-baking at 500 deg.C2At T of 5h3High-temperature roasting at 850 deg.C3And (3) obtaining the lithium-rich manganese-based positive electrode material with full concentration gradient distribution, crushing the lithium-rich manganese-based positive electrode material, and screening the crushed material by using a 300-400-mesh sieve to obtain the final product.
Scanning electron microscope analysis shows that the particle size distribution and morphology of the material prepared in example 2 are not much different from those of the material prepared in example 1.
Example 3
1. According to the molar ratio of Ni, Co and Mn elements of 13: 13: 54 preparing a transition metal salt solution A of nickel sulfate, cobalt sulfate and manganese sulfate, wherein the molar ratio of Ni, Co and Mn elements is 32: 4: 44 preparing a transition metal salt solution B of nickel sulfate, cobalt sulfate and manganese sulfate, wherein the concentration of A, B is 2 mol/L.
2. Preparing a sodium hydroxide solution with the concentration of 4mol/L and preparing an ammonia water solution with the concentration of 6 mol/L.
3. And (3) taking an ammonia water solution (with the concentration of 2mol/L) with the volume of 20 percent of the kettle volume in the full-automatic continuous control reaction kettle as a reaction bottom liquid E. The transition metal salt solution B is fed at a flow rate u1Pumping 20ml/h of transition metal salt solution A, and respectively adding transition metal salt solution B at a flow rate u under the protection of nitrogen atmosphere2Pumping 40ml/h into a full-automatic control continuous reaction kettle at the same time of flow rate u3＝20～60ml/h、u4Respectively pumping the alkali solution and the ammonia water solution into a reaction kettle at 40ml/h, and adjusting the feeding flow rate u of the sodium hydroxide solution3To maintain the pH of the reaction at 11.2 and the reaction temperature at T 150 ℃ and stirring speed R1800rpm, reaction time t1Continuing aging t after the feed is finished for 30h4Filtering, washing and drying the precipitate for 12h to obtain the precursor (Ni) of the lithium-rich manganese-based positive electrode material hydroxide with the transition metal ions distributed in a full concentration gradient manner0.2813Co0.1062Mn0.6125)OH2。
4. After the above 20g of hydroxide precursor and 15.45g of lithium hydroxide were mixed uniformly, the mixture was subjected to thermal decomposition at T2Pre-roasting at 400 deg.C2At T of 5h3High-temperature roasting at 820 ℃3And (3) obtaining the lithium-rich manganese-based positive electrode material with full concentration gradient distribution for 20h, crushing the lithium-rich manganese-based positive electrode material, and screening the crushed material by using a 300-400-mesh sieve.
Comparative example 1
The difference between comparative example 1 and example 1 is that the conventional secondary particle aggregate lithium-rich manganese-based positive electrode material prepared in comparative example 1 is specifically operated as follows:
1. according to the molar ratio of Ni, Co and Mn elements of 13: 13: and 54, preparing transition metal salt solutions of nickel sulfate, cobalt sulfate and manganese sulfate, wherein the concentration of the transition metal salt solution is 2 mol/L.
2. Preparing a sodium carbonate solution with the concentration of 2mol/L and preparing an ammonia water solution with the concentration of 1.0 mol/L.
3. Adding deionized water with the volume of 20 percent of the kettle volume into a full-automatic continuous control reaction kettle as reaction base liquid E, and adding u under the protection of nitrogen1＝30ml/h、u3＝10～50ml/h、u4Respectively pumping a transition metal salt solution, a sodium carbonate solution and an ammonia water solution into a reaction kettle at the flow rate of 30ml/h, and adjusting the feeding flow rate u of the sodium carbonate solution3To maintain the pH of the reaction system at 9.0 and to maintain the temperature of the reaction system at T1At 55 deg.C and stirring speed R1Reaction t at 900rpm115 h. Continuing to age the reaction slurry after the feeding is finished t4The precipitate was then filtered, washed and dried for 15h to obtain a carbonate precursor (Ni) of the lithium-rich manganese-based positive electrode material0.1625Co0.1625Mn0.675)CO3。
4. The above carbonate precursor (20 g) was mixed with lithium carbonate (10.14 g) uniformly, and the mixture was heated to temperature T2Pre-baking at 500 deg.C2At T of 5h3High-temperature roasting at 900 ℃3And (5) obtaining the lithium-rich manganese-based positive electrode material with full concentration gradient distribution for 25h, crushing the material, and then screening the crushed material by using a 300-400-mesh sieve to obtain the final product.
Fig. 4 is a scanning electron microscope image of a carbonate precursor prepared in comparative example 1, fig. 5 is a scanning electron microscope image of a lithium-rich manganese-based positive electrode material prepared in comparative example 1, fig. 6 is an X-ray powder diffraction image of the positive electrode material prepared in comparative example 1, it can be confirmed from fig. 5 that the material prepared in the comparative example has good sphericity, the particle size distribution is between 5um and 15um, no obvious fine particles and super large aggregate particles exist, and it can be confirmed from fig. 6 that the lithium-rich manganese-based positive electrode material prepared in comparative example 1 still maintains a good lithium-rich manganese-based material layered crystal structure.
Comparative example 2
1. According to the molar ratio of Ni, Co and Mn elements of 32: 4: 44 preparing transition metal salt solutions of nickel sulfate, cobalt sulfate and manganese sulfate, wherein the concentration of the transition metal salt solutions is 2 mol/L.
2. Preparing a sodium hydroxide solution with the concentration of 4mol/L and preparing an ammonia water solution with the concentration of 4 mol/L.
3. An ammonia solution (concentration: 1mol/L) with a volume of 20% of the kettle volume is added into the full-automatic control continuous reaction kettle to be used as a reaction bottom liquid E. Under the protection of nitrogen, at a flow rate u1＝20ml/h、u3＝10～40ml/h、u4Respectively pumping a transition metal salt solution, an alkali solution and an ammonia water solution into a reaction kettle at the flow rate of 20ml/h, and adjusting the feeding flow rate u of a sodium hydroxide solution3To maintain the reaction pH at 11.0 and the reaction system temperature at T 150 ℃ and stirring speed R1Reaction t at 800rpm130 h. Continuing to age the reaction slurry after the feeding is finished t4The precipitate was then filtered, washed and dried to obtain a hydroxide precursor (Ni) of the lithium-rich manganese-based positive electrode material0.1625Co0.1625Mn0.675)OH2。
4. After the above-mentioned 20g of hydroxide precursor and 15.6g of lithium hydroxide were uniformly mixed, the mixture was subjected to thermal decomposition at T2Pre-roasting at 400 deg.C2At T of 5h3High-temperature roasting at 820 ℃3And (3) obtaining the lithium-rich manganese-based positive electrode material after 20h, crushing the lithium-rich manganese-based positive electrode material, and screening the crushed material by using a 300-400-mesh sieve to obtain a final product.
The following are test examples:
the lithium-rich manganese-based positive electrode materials prepared in example 1 and comparative example 1 were mixed with a conductive agent Super P and a binder PVDF according to a ratio of 8: 1: 1, preparing slurry, preparing electrode plates after operations of coating, drying, rolling, cutting and the like, assembling the electrode plates, a lithium negative electrode, a diaphragm and a lithium ion battery high-voltage electrolyte into a button half-cell, and evaluating the electrochemical performance of the button half-cell. The cycle performance of the lithium ion battery assembled by the lithium-rich manganese-based cathode materials prepared in example 1 and comparative example 1 is shown in fig. 12.
As can be seen from fig. 12, the charge transfer resistances of the lithium-rich manganese-based positive electrode material with full concentration gradient distribution obtained in example 1 after 5 cycles and 100 cycles are 30.71 Ω and 110.23 Ω, respectively, which are significantly smaller than the charge transfer resistance of the conventional lithium-rich manganese-based positive electrode material in comparative example 1. This is because the content of the transition metal element in the lithium-rich manganese-based positive electrode material having the full concentration gradient distribution in example 1 linearly changes. The content of Mn element is gradually reduced from the inside of the particle to the outer layer of the particle, the content of Ni element is gradually increased, the characteristics of low Mn and high Ni content of the outer layer are favorable for increasing the conductivity of the surface of the material, and the Mn is reduced3+The dissolution and the precipitation of ions from the surface of the anode material are beneficial to maintaining the structural stability of the material in the circulating process. In addition, from fig. 12, it can be seen that the capacity retention rate of example 1 still reaches 97.36% after 100 cycles at the 0.5C rate, which is 8.34% higher than that of comparative example 1 (89.02%).
Fig. 7 and 8 are comparative graphs of CV tests of the positive electrode materials of comparative example 1 and example 1 in three previous cycles after assembling into a lithium ion half cell, respectively, and it can be found that the positive electrode material prepared in example 1 has better overlapping of CV curves in example 1 than comparative example 1, the structural stability of the positive electrode material prepared in example 1 is better than that of the positive electrode material in comparative example 1 during cycles, and in addition, in the first cycle CV curve in example 1, the oxidation peak at-4.7V is found to be significantly smaller than that of comparative example 1, which indicates that the degree of structural irreversible structural transformation caused by oxygen precipitation in example 1 during the first cycle charging is smaller than that of comparative example 1, and the strength and voltage of the reduction peak in example 1 are higher than those in comparative example 1, which indicates that by designing a lithium-rich manganese-based positive electrode material with a full concentration gradient, the reduction and dissolution processes of manganese ions during the reaction can be significantly inhibited, and can improve the discharge voltage and the structural stability of the material. Fig. 9 is a graph comparing rate performance during a cycle after assembly of example 1 and comparative example 1 into a lithium ion half cell, fig. 10 is a graph comparing median voltage during a cycle after assembly of example 1 and comparative example 1 into a lithium ion half cell, and fig. 11 is a graph comparing specific discharge energy during a cycle after assembly of example 1 and comparative example 1 into a lithium ion half cell. Charging and discharging conditions at 25 deg.C and 0.5C rateUnder the condition that the voltage window is 2.0-4.7V, the initial discharge specific capacity of the lithium-rich manganese-based cathode material prepared in the embodiment 1 is slightly lower than that of the lithium-rich manganese-based cathode material prepared in the comparative example 1, because the content of Mn element in the lithium-rich manganese-based cathode material prepared in the embodiment 1 in full concentration gradient distribution is lower than that in the comparative example 1, the Li is ensured to be slightly lower than that in the comparative example 12MnO3The component content is reduced, the degree of reversible oxygen participation in redox reaction in the charge-discharge process is reduced, but the content of the Ni element is gradually increased, so that the dissolution and precipitation of the Mn element on the surface of the anode material in circulation can be effectively inhibited, and the structural stability and the capacity retention rate of the material in the circulation process are improved. In addition Li2MnO3The conductivity of the components is poor, the rapid lithium ion deintercalation in the charging and discharging process is limited, the surface manganese content of the full concentration gradient lithium-rich manganese-based cathode material is low, and the structural phase change at the surface can be effectively inhibited, so that the cathode material shows more excellent rate performance compared with the material in comparative example 1, as shown in fig. 9. On the other hand, Ni2+/Ni4+Has a redox potential higher than that of Mn3+/Mn4+Therefore, the increase of the content of Ni element is beneficial to the increase of the discharge voltage of the material, while the comparative example 1 has higher content of manganese element, and more manganese element is reduced in the cycle, which further reduces the discharge voltage of the material, so that the example 1 shows higher working voltage and voltage holding ratio in the charge-discharge cycle process, as shown in fig. 10. Therefore, the lithium manganese-rich cathode material with full concentration gradient distribution in example 1 has slightly lower initial discharge specific capacity than that in comparative example 1, but shows higher energy density and excellent cycling stability during cycling because the structure is more stable and the discharge voltage during cycling is also significantly higher than that in comparative example 1, as shown in fig. 11.
The applicant states that the present invention is illustrated by the above examples to show the detailed process equipment and process flow of the present invention, but the present invention is not limited to the above detailed process equipment and process flow, i.e. it does not mean that the present invention must rely on the above detailed process equipment and process flow to be implemented. It is obvious to those skilled in the art that any modification of the present invention, equivalent substitution of each raw material and addition of auxiliary components, selection of specific modes, etc., of the product of the present invention are within the scope of protection and disclosure of the present invention.
Claims (6)
1. A lithium-rich manganese-based lithium cathode material with full concentration gradient distribution is characterized in that the content of Mn element is linearly reduced from the inside to the surface, and the content of Ni element is linearly increased. The prepared material has high sphericity, narrow particle size distribution, stable material crystal lamellar structure, higher energy density and excellent cycle stability.
2. The method for preparing the lithium-rich manganese-based lithium cathode material with full concentration gradient distribution according to claim 1, comprising the following key steps:
(1) preparing a transition metal salt solution A and a transition metal salt solution B with a certain concentration from nickel salt, cobalt salt and manganese salt, wherein the molar ratio of nickel, cobalt and manganese elements in the solution A is 5-15: 5-15: 30-60, wherein the molar ratio of nickel, cobalt and manganese elements in the solution B is 10-32: 0 to 104: 10-60, and preparing an alkali solution C and an ammonia water solution D with certain concentrations;
(2) adding reaction base solution E with the volume of 20 percent of the reaction kettle into the reaction kettle, and adding solution B at the flow rate u1Pumping the solution A into the solution A, and enabling the solution A to flow at a flow rate u under the protection of nitrogen2Pumping into a full-automatic control continuous reaction kettle at a flow rate u3、u4Respectively pumping the alkali solution C and the ammonia water solution D into a reaction kettle, and regulating and controlling the flow rate u of the alkali solution in real time3To control the pH of the reaction and maintain the stirring speed R in the kettle1Reaction temperature T1Reacting for a certain time t under the condition of pH value1Obtaining a lithium-rich manganese-based positive electrode material precursor with transition metal ions distributed in a full concentration gradient manner, and then washing, filtering and drying the precursor;
(3) uniformly mixing the precursor material obtained in the step (2) with lithium salt, and then respectively using T2And T3Temperature of pre-baking t2Roasting at high temperature and for a period of time t3H, cooling to room temperature, crushing and sieving to obtain the lithium-rich manganese-based positive electrode material with transition metal ions in full concentration gradient distribution。
3. The method for preparing the lithium-rich manganese-based lithium cathode material with full concentration gradient distribution according to claim 2, wherein the nickel salt in the step (1) is one or a mixture of more than two of nickel chloride, nickel nitrate, nickel acetate or nickel sulfate; the cobalt salt is one or a mixture of more than two of cobalt chloride, cobalt nitrate, cobalt acetate or cobalt sulfate; the manganese salt is one or more of manganese chloride, manganese nitrate, manganese acetate or manganese sulfate; the alkali is one or more of sodium bicarbonate, sodium carbonate or sodium hydroxide.
4. The method for preparing the lithium-rich manganese-based lithium cathode material with full concentration gradient distribution according to claim 2, wherein u in the step (2)1U is 10 to 60ml/h2U is 20 to 120ml/h3U is 10 to 120ml/h420 to 300ml/h and satisfies u2＝2u1Stirring speed R1300 rpm-1000 rpm, reaction temperature T1The reaction temperature is 40-65 ℃, the reaction pH is 7.5-12, and the reaction time t1Is 10-55 h.
5. The method for preparing the lithium-rich manganese-based lithium cathode material with full concentration gradient distribution as claimed in claim 2, wherein the lithium salt in the step (3) is lithium hydroxide, lithium carbonate or lithium acetate, and the pre-baking temperature T is2At 200-750 deg.C, pre-roasting time t2Is 2 to 10 hours, and the roasting temperature T3At 800-950 ℃ for a roasting time t3And (3) screening the crushed materials by using a 300-400-mesh sieve for 20-50 h.
6. A lithium ion battery, wherein the positive electrode material is the lithium-rich manganese-based lithium positive electrode material with full concentration gradient distribution according to claim 1.
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| CN113772749A (en) * | 2021-11-15 | 2021-12-10 | 中南大学 | Double-gradient-structure nickel-cobalt-manganese ternary positive electrode material precursor, preparation method thereof and ternary positive electrode material |
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