CN109904424B - Method for one-step surface coating and gradient doping integrated double-modification of LNMO (Low noise Metal oxide) positive electrode material - Google Patents
Method for one-step surface coating and gradient doping integrated double-modification of LNMO (Low noise Metal oxide) positive electrode material Download PDFInfo
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Abstract
The invention provides a method for one-step surface coating and gradient doping integrated double-modification of an LNMO positive electrode material. According to the invention, the surface oxygen defect of the high-voltage anode material LNMO is increased by calcining in an inert atmosphere, so that the metal cations of the cladding layer are promoted to diffuse into the surface defect position of the anode material in the cladding process, and the pinning effect is achieved, thereby realizing the integrated double-modification of the surface cladding and surface doping of the high-voltage anode material of the lithium ion battery.
Description
Technical Field
The invention relates to the field of preparation and modification of new energy lithium ion battery anode materials, in particular to a method for one-step surface coating and gradient doping integrated double-modification of an LNMO anode material.
Background
Lithium ion batteries have been widely used as energy storage devices for portable electronic devices due to their characteristics of high energy density, long cycle life, excellent thermal safety performance, environmental friendliness, and the like, and are rapidly expanding into the fields of electric vehicles, large-scale energy storage, and the like. The anode material of the lithium ion battery at present mainly comprises lithium cobaltate, lithium iron phosphate, layered lithium-rich, layered high nickel, high-voltage spinel material and the like. Wherein LiNi is used0.5Mn1.5O4The spinel-structured positive electrode material represented by (LNMO) has high working voltage (4.7V) and high energy density (690 Wh kg)-1) Is superior in thatThe characteristics of rate capability, low cost and the like are widely concerned. However, high voltage positive electrode materials, while exhibiting the advantages of a high operating voltage plateau, are also associated with more significant surface side reactions. Particularly, as the number of cycles increases, the charge-discharge capacity and the cycle reversibility of the battery are continuously degraded, and finally, the battery is out of service, even a safety accident occurs. The research finds that the main reason is that the surface chemical reaction of the lithium ion battery anode material is intensified under the high-voltage working environment, such as irreversible surface phase transition, transition metal dissolution, ginger-Taylor distortion, electrolyte oxidation decomposition and the like.
In order to solve the above problems of the high voltage positive electrode material, some researchers have introduced TiO2、SiO2、CuO、ZrO2、SnO2,、La2O3、Al2O3、MgO、AlF3、MgF2、Li3PO4、AlPO4、YPO4、Li2TiO3The materials are coated on the surface of the high-voltage anode material, so that the structural stability and the thermal safety of the high-voltage anode material are improved. The surface coating method has the advantages that the surface coating layer can be used as a protective layer to effectively prevent the redox reaction of electrolyte on the surface of the active electrode material, so that the generation of surface side reaction and the growth of a solid-electrolyte interface film are inhibited, and the aims of improving the structural stability and the cycling stability of the electrode and optimizing the thermal safety of the battery to a certain extent are fulfilled. However, the single surface coating method has a problem that the coating layer is difficult to be compatible with the surface of the high-voltage positive electrode material, and the phenomenon that the coating layer is easy to fall off in the high-temperature cycle is likely to occur along with the increase of the cycle number. In parallel, some researchers have used ion doping to modify the surface of high voltage positive electrode materials, such as doping with P5+、V5+、Nb5+、Ti4+、Al3+、Cr3+、Si4+、Zr4+And plasma is used for inhibiting the elution of transition metal and lattice oxygen on the surface of the anchor material, so that the effect of stabilizing the surface structure is achieved. However, the surface doping has a single advantage, and thus the key problems such as surface side reactions and the like cannot be effectively solvedAnd (4) sexual problems.
In order to overcome the defects of modification of a high-voltage anode material of a lithium ion battery by single surface coating or surface doping, some researchers integrate the advantages of two modification means for modification of the high-voltage anode material, and realize double modification effects of surface coating and surface doping on the basis of the surface coating by successively calcining twice. However, the approach of implementing surface doping and surface coating dual modification by using a two-step or multi-step method has a complex flow, poor repeatability and is not favorable for industrial application, and meanwhile, the bulk structure of the high-voltage active material suffers from uncontrollable influence when the high-voltage active material undergoes two high-temperature calcination processes in the two-step method.
Disclosure of Invention
Aiming at the defects that although the traditional two-step or multi-step method can generate the effects of a coating layer and surface doping, the coating layer and the surface doping are not formed at the same time, so that an integral structure is difficult to form, and the conventional coating of the LNMO material is usually carried out in the air or oxygen atmosphere, the lower surface oxygen defect density of the LNMO material is not favorable for the metal cations in the coating layer to diffuse to the surface lattice of the active material, and the modification effect of the surface doping and coating integration is difficult to improve, the invention provides a method for realizing the surface doping and surface coating integration double-modification lithium ion battery high-voltage positive electrode material by a one-step method.
Different from the treatment method of coating before doping and calcining twice adopted in the existing double-modification method, the method adopts a one-step method to realize the surface doping coating integrated modification of the high-voltage anode material of the lithium ion battery, namely calcining under inert atmosphere in the coating process to form more surface oxygen defect sites on the surface of LNMO, thereby realizing the gradient diffusion of metal cations in the coating layer to the surface lattice of the anode active material while forming a surface coating layer playing an isolation protection role on the anode material, further forming a solid solution buffer layer doped with the metal cations in a gradient manner, and achieving the effect of surface coating and surface doping integrated double-modification.
The one-step method effectively inhibits the dissolution of transition metal ions of the positive electrode active material, the phase change of the surface structure and improves the surface compatibility of the surface coating layer and the positive electrode material, and simultaneously avoids the degradation of the bulk structure of the high-voltage positive electrode active material caused by multiple calcination processes, thereby obviously improving the structural stability and the electrochemical performance of the high-voltage positive electrode material. More importantly, the 'one-step method' can promote metal cations in the coating layer to diffuse into oxygen defect sites on the surface of the cathode material in the coating process, the surface coating layer and the surface doping are formed, and meanwhile, the surface gradient doping metal cations are utilized to play a pinning role in surface lattices of the cathode active material, so that the integration of the coating layer and the surface doping is realized, the surface integrity of the coating layer and the high-voltage cathode material is greatly improved, and the phenomenon that the coating layer falls off from the surface of the cathode active material in the electrochemical circulation process can be effectively avoided.
The technical scheme for realizing the invention is as follows:
a method for one-step surface coating and gradient doping integrated double-modification of an LNMO positive electrode material comprises the steps of mixing a coating material metal precursor solution with a lithium ion battery positive electrode material solution, fully drying to form gel, calcining the gel in an inert atmosphere, increasing surface oxygen defect positions of the positive electrode material, promoting metal cations in the coating layer to diffuse into the positive electrode material surface oxygen defect positions, forming a surface coating layer, playing a pinning effect on positive electrode material surface lattices, and further performing surface coating and gradient doping integrated double-modification on a lithium ion battery.
The stoichiometric ratio of a cladding layer in the surface modification modified lithium ion battery high-voltage positive electrode material to the positive electrode material is (0.005-0.05): 1.
The coating layer is Li2SiO3、Li2SnO3、Li2ZrO3、Li2RuO3、LiNiO2、Li3VO4、Li4Ti5O12、Li2MoO3、LiNbO3、LiAlO2、LiAlSiO4、Li2GeO3、Li3V2(PO4)3、LiTi2(PO4)3、Li7La3Zr2O12、Li2.5Na0.5V2(PO4)3、Li1.4Al0.4Ti1.6(PO4)3Or Li1.4Al0.4Ge1.6(PO4)3。
The method for one-step surface coating and gradient doping integrated double modification of the LNMO positive electrode material comprises the following specific steps:
(1) weighing a certain mass of a coating material metal precursor, a positive electrode material and citric acid, respectively dissolving or dispersing in a solvent, and then mixing and fully stirring the solution;
(2) stirring and evaporating the mixed solution obtained in the step (1) to obtain a sol substance, and drying to obtain a xerogel-coated active material;
(3) and (3) calcining the xerogel-coated active material obtained in the step (2) in an inert atmosphere, and cooling, cleaning and filtering a reaction product to obtain the surface-coated and gradient-doped integrated double-modified LNMO positive electrode material.
The metal precursor of the coating material in the step (1) is a mixture of a lithium compound and a metal compound: the lithium compound is one of lithium acetate, lithium hydroxide or lithium nitrate, the metal compound is one or two of compounds of Si, Sn, Zr, Ru, Ni, V, Ti, M, Nb, Al, Ge, La and Na, and the mass ratio of the lithium compound to the metal compound is 1: (0.3-2).
The coating material metal precursor in the step (1) is a mixture of a lithium compound, a metal compound and ammonium dihydrogen phosphate, the lithium compound is one of lithium acetate, lithium hydroxide or lithium nitrate, the metal compound is one or two of compounds of Si, Sn, Zr, Ru, Ni, V, Ti, M, Nb, Al, Ge, La and Na, and the mass ratio of the lithium compound to the metal compound to the ammonium dihydrogen phosphate is 1: (0.3-2): (0.45-3).
The solvent in the step (1) is one or more of deionized water, ultrapure water, absolute ethyl alcohol, methanol, ethylene glycol, acetone, diethyl ether, petroleum ether, n-butanol, dichloromethane, acetaldehyde, glycerol and ethyl acetate.
In the step (2), the drying temperature is 90-150 ℃, and the drying time is 8-24 h.
The inert atmosphere in the step (3) is one or more of argon, helium, neon, krypton and xenon; the calcining temperature is 400-600 ℃, and the calcining time is 4-6 h.
The invention has the beneficial effects that: the invention provides a method for realizing surface coating and surface doping integrated double-modification of a high-voltage positive electrode material of a lithium ion battery by a one-step method, which increases the surface oxygen defect of the high-voltage positive electrode material LNMO by calcining in an inert atmosphere, promotes the diffusion of metal cations of a coating layer into the surface defect position of the positive electrode material in the coating process, and plays a pinning role, thereby realizing the surface coating and surface doping integrated double-modification of the high-voltage positive electrode material of the lithium ion battery. On one hand, the double-modified structure can effectively prevent the redox reaction of electrolyte on the surface of the active electrode material through the coating layer, thereby inhibiting the generation of side reaction and the growth of a solid-electrolyte interface film, and achieving the purposes of improving the structural stability and the cycling stability of the material and optimizing the thermal safety of the battery to a certain extent; on the other hand, the solid solution buffer layer is formed by diffusing metal cations of the coating layer to surface lattices of the anode material, so that structural degradation caused by dissolution of transition metal ions can be relieved, and the interface compatibility between the coating layer and the active material is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 shows XRD test and refinement results of original LNMO and LVPO surface double-modified LNMO material prepared by one-step method.
FIG. 2 is a XPS test and fit of the original LNMO and the LVPO surface double modified LNMO material made in a "one-step" process.
FIG. 3 shows HRTEM test and selected FFT results of LVPO surface double-modified LNMO material prepared by one-step method.
FIG. 4 shows the XPS test results of the LVPO surface double-modified LNMO material prepared by the one-step method at different etching depths.
FIG. 5 shows that the LVPO surface double-modified LNMO material prepared by the one-step method has better capacity retention characteristics than the original LNMO.
FIG. 6 shows that the LVPO surface double-modified LNMO material prepared by the one-step method has better rate characteristics than the original LNMO.
FIG. 7 shows EIS measurements and fitting results of virgin LNMO and LVPO surface double modified LNMO material prepared by the "one-step" method after different cycles.
FIG. 8 shows XRD measurements of virgin LNMO and LVPO surface double modified LNMO material made in a "one-shot" manner after 150 weeks of cycling at high temperature (55 ℃ C.).
FIG. 9 shows DSC measurements and fitting results of virgin LNMO and LVPO surface double modified LNMO material made by the "one-shot" method.
Fig. 10 is a schematic diagram of the LVPO surface double-modified LNMO material prepared by the "one-step method", where 1 is a coating layer, 2 is a positive electrode material, and 3 is a surface doped ion.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.
Example 1
"one-step" process for preparing Li3V2(PO4)3(LVPO) surface modified LNMO material, the steps of which are as follows:
weighing a certain amount according to the proportion of 3:2:3:3Dissolving lithium acetate, vanadium pentoxide, ammonium dihydrogen phosphate and citric acid in deionized water, mixing and stirring for 3h, dropwise adding the fully dissolved and mixed solution into an aqueous solution containing 0.2g of LNMO anode material, and continuously mixing and stirring for 8 h; stirring and evaporating the mixed solution at 80 ℃ for 8h to form sol, and drying at 120 ℃ for 24h to obtain xerogel; fully grinding the xerogel, putting the xerogel into a tube furnace, calcining for 6h at 400 ℃ in argon (Ar) atmosphere, naturally cooling to room temperature, cleaning, filtering and drying to obtain Li3V2(PO4)3(LVPO) surface modified LNMO material.
As shown in attached figure 1, XRD test and fine modification results of original spinel structure LNMO and LVPO surface double-modified spinel structure LNMO material prepared by a one-step method are shown. The fitting result shows that the lattice parameter of the LNMO material with double modified surfaces of LVPO is increased, which indicates that the LNMO material with double modified surfaces of LVPO is Mn compared with the original LNMO material3+With a higher relative proportion. According to the consensus of researchers in the field, the LNMO material after surface double modification has more oxygen defect sites.
As shown in fig. 2, XPS testing and fitting results of the original LNMO and the LVPO surface double modified LNMO material prepared by the "one-step" method. The fitting results show that Mn3+The relative proportion of LNMO material modified by double modification on the LVPO surface is higher. This result is consistent with the analysis of FIG. 1.
As shown in fig. 3, HRTEM test and selected FFT results of the LVPO surface double modified LNMO material prepared by the "one-step method". The results show that the degree of order of the surface lattice is obviously reduced while a thin amorphous LVPO coating layer is formed on the surface of the LNMO particles; as is inferred from the results of FIGS. 1 and 2, this is due to Mn in the vicinity of the surface lattice of the active material3+The proportion is increased and the oxygen defect sites are increased; while the LNMO bulk structure is not significantly affected.
As shown in the attached figure 4, the XPS test results of the LVPO surface double-modified LNMO material prepared by the one-step method at different etching depths are shown. The results show that the signal intensity of the V element is gradually reduced along with the increase of the etching depth, and the fact that V ions are diffused into the surface crystal lattice of the positive electrode material LNMO particles from the coating layer in a gradient mode is confirmed, and surface doping is achieved.
As shown in figure 5, the LVPO surface double-modified LNMO material prepared by the one-step method has better capacity retention characteristics compared with the original LNMO material.
As shown in fig. 6, the LVPO surface double modified LNMO material prepared by the "one-step method" has a superior rate property compared to the original LNMO material.
As shown in fig. 7 and table 1, the EIS test and fitting results of the original LNMO and the LVPO surface double modified LNMO material prepared by the "one-step" method after different cycles. The fitting result shows that after the same cycle number, the LNMO material with the LVPO surface double-modified and modified has the interface film resistance (R)sf) And a charge transfer resistance (R)ct) Are all significantly smaller than the original LNMO, where RsfThe reduction of (a) demonstrates that the surface LVPO coating layer can effectively suppress the occurrence of surface side reactions and the growth of a solid-electrolyte interface film; and R isctThe reduction in surface doping proves to be effective in improving the interfacial compatibility between the cladding layer and the active material.
TABLE 1 EIS test and fitting results of the original LNMO and the "one-step" LNMO material after different cycles
As shown in the attached Table 2, the ICP test results of the original LNMO and the LVPO surface double-modified LNMO material prepared by the one-step method after being soaked in the electrolyte for different weeks are shown. Test results show that the elution amount of Mn and Ni elements in the original LNMO is obviously increased along with the increase of the soaking cycle number, and the elution of Mn and Ni elements in the LVPO surface double-modified LNMO material is obviously inhibited, so that the LVPO surface double-modified LNMO material prepared by the one-step method can effectively inhibit the elution of transition metals and stabilize the material bulk structure.
TABLE 2 ICP test results of virgin LNMO and "one-step" LNMO material soaked in electrolyte for different weeks
As shown in FIG. 8, XRD test results of original LNMO and LVPO surface double modified LNMO material prepared by one-step method after 150 weeks of circulation in high temperature environment (55 deg.C) are shown. The test result shows that after high-temperature long circulation, the main peak signal of the original LNMO is obviously weakened and a new mixed peak is generated compared with the original LNMO and the standard card library, and the LVPO surface double-modified LNMO material is basically consistent with the standard card library, thereby proving that the LVPO surface double-modified LNMO material prepared by the one-step method has a stable bulk structure and the structural degradation is effectively inhibited.
As shown in fig. 9, DSC test and fitting results of the virgin LNMO and the LVPO surface double modified LNMO material prepared by the "one-step" method. The test and fitting results show that the LVPO surface double-modified LNMO material has higher heat release temperature and less heat release, and the LVPO surface double-modified LNMO material prepared by the one-step method is proved to have better heat safety performance.
Fig. 10 is a schematic diagram of the LVPO surface double-modified LNMO material prepared by the "one-step method", where 1 is a coating layer, 2 is a positive electrode material, and 3 is a surface doped ion. The doped ions are gradually reduced along with the increase of the etching depth, and the doped ions are diffused into the surface crystal lattice of the anode material LNMO from the coating layer in a gradient manner to form a nail-like surface doped structure.
Example 2
"one-step" process for preparing Li3VO4The surface coating and V surface gradient doping double-modified LNMO material comprises the following steps:
(1) weighing a certain amount of lithium acetate, vanadium pentoxide and citric acid according to the ratio of 3:1:2, dissolving in deionized water, dropwise adding into an aqueous solution in which 0.2g of LNMO anode material is dispersed after dissolving and stirring, and then mixing and stirring for 8 hours;
(2) heating the mixed solution to 80 ℃, stirring and evaporating, and then drying at 120 ℃ for 24 hours to obtain xerogel;
(3) fully grinding the xerogel, putting the xerogel into a crucible, calcining for 6 hours in a tube furnace at 500 ℃ under the atmosphere of argon, naturally cooling to room temperature, cleaning, filtering and drying to obtain Li3VO4And the surface is coated with the LNMO material subjected to double modification through gradient doping on the V surface.
Example 3
"one-step" process for preparing Li2SiO3The surface coating and Si surface gradient doping double-modified LNMO material comprises the following steps:
(1) weighing a certain amount of lithium hydroxide, tetraethoxysilane and citric acid according to the ratio of 2:1:1.5, dissolving in deionized water, dropwise adding into an aqueous solution in which 0.2g of LNMO anode material is dispersed after dissolving and stirring, adjusting the pH of the solution to 7, and then mixing and stirring for 5 hours;
(2) heating the mixed solution to 80 ℃, stirring and evaporating, and then drying at 120 ℃ for 24 hours to obtain xerogel;
(3) fully grinding the xerogel, putting the xerogel into a crucible, calcining for 5 hours in a tube furnace at 500 ℃ under the argon atmosphere, naturally cooling to room temperature, cleaning, filtering and drying to obtain Li2SiO3The surface coating and the gradient doping of the Si surface are carried out on the double-modified LNMO material.
Example 4
"one-step" process for preparing Li2SnO3The surface coating and Sn surface gradient doping double-modified LNMO material comprises the following steps:
(1) weighing a certain amount of lithium acetate, stannic chloride, citric acid and polyethylene glycol according to the proportion of 2:1:0.15:0.005, dissolving in deionized water, dropwise adding into an aqueous solution in which 0.2g of LNMO cathode material is dispersed after dissolving and stirring, and then mixing and stirring for 5 hours;
(2) evaporating the mixed solution at 90 ℃, and then drying at 120 ℃ to obtain a reaction precursor xerogel;
(3) fully grinding the precursor, putting the ground precursor into a crucible, calcining the ground precursor for 5 hours at 500 ℃ in a tube furnace under the argon atmosphere, naturally cooling the calcined precursor to room temperature, cleaning, filtering and drying the calcined precursor to obtain Li2SnO3Surface coating and SnThe surface is doped with double modified LNMO material in a gradient mode.
Example 5
One-step method for preparing LiNbO3The surface coating and Nb surface gradient doping double-modified LNMO material comprises the following steps:
(1) weighing a certain amount of lithium acetate, niobium pentoxide and citric acid according to the proportion of 1:1:3, dissolving in ethanol solution, stirring, and dropwise adding into a solution dispersed with 0.2g LiMn1.5Ni0.5O4Then mixing and stirring the mixture for 5 hours in the aqueous solution of the anode material;
(2) evaporating the mixed solution at 75 ℃, and then drying at 120 ℃ to obtain a reaction precursor xerogel;
(3) fully grinding the precursor, putting the ground precursor into a crucible, calcining the precursor for 4 hours at 500 ℃ in a tube furnace under the argon atmosphere, naturally cooling the calcined precursor to room temperature, cleaning, filtering and drying the calcined precursor to obtain LiNbO3The surface of the LNMO material is coated and subjected to double modification by Nb surface gradient doping.
Example 6
One-step method for preparing LiAlO2The surface coating and Al surface gradient doping double-modified LNMO material comprises the following steps:
(1) weighing a certain amount of lithium acetate, aluminum nitrate and citric acid according to the proportion of 1:1:1.5, dissolving in an ethanol solution, dropwise adding into an aqueous solution in which 0.2g of LNMO cathode material is dispersed after dissolving and stirring, and then mixing and stirring for 7 hours;
(2) evaporating the mixed solution at 70 ℃, and then drying at 110 ℃ to obtain a reaction precursor xerogel;
(3) fully grinding the precursor, putting the ground precursor into a crucible, calcining the precursor for 4 hours at 400 ℃ in a tubular furnace under the argon atmosphere, naturally cooling the calcined precursor to room temperature, cleaning, filtering and drying the calcined precursor to obtain LiAlO2The surface of the LNMO thin film is coated and the surface of the Al is doped with double-modified LNMO materials in a gradient mode.
Example 7
One-step method for preparing LiTi2(PO4)3The surface coating and Ti surface gradient doping double-modified LNMO material comprises the following steps:
(1) weighing a certain amount of lithium acetate, isopropyl titanate, ammonium dihydrogen phosphate and citric acid according to the proportion of 1:2:1:1.5, dissolving in an ethanol solution, dropwise adding into a solution in which 0.2g of LNMO cathode material is dispersed after dissolving and stirring, and then mixing and stirring for 6 hours;
(2) evaporating the mixed solution at 70 ℃ for 4h, and then drying at 100 ℃ to obtain a reaction precursor xerogel;
(3) fully grinding the precursor, putting the ground precursor into a crucible, calcining the ground precursor for 4 hours at 600 ℃ in a tube furnace under the argon atmosphere, naturally cooling the calcined precursor to room temperature, cleaning, filtering and drying the calcined precursor to obtain LiTi2(PO4)3The surface of the LNMO thin film is coated and the gradient of the Ti surface is doped with double-modified LNMO materials.
Example 8
One-step method for preparing LiAlSiO4The surface coating and Al and Si surface gradient doping double-modified LNMO material comprises the following steps:
(1) weighing a certain amount of lithium nitrate, aluminum nitrate, silicon ethoxide and citric acid according to the proportion of 1:1:1:1.5, dissolving in ethanol, dropwise adding into a solution in which 0.2g of LNMO cathode material is dispersed after dissolving and stirring, and then mixing and stirring for 4 hours;
(2) evaporating the mixed solution at 80 ℃ for 4h, and then drying at 120 ℃ to obtain a reaction precursor xerogel;
(3) fully grinding the precursor, putting the ground precursor into a crucible, calcining the ground precursor for 6 hours at 600 ℃ in a tube furnace under the argon atmosphere, naturally cooling the calcined precursor to room temperature, cleaning, filtering and drying the calcined precursor to obtain LiAlSiO4The surface is coated with the LNMO material which is subjected to double modification by gradient doping on the surface of Al and Si.
Example 9
"one-step" process for preparing Li7La3Zr2O12The surface coating and La and Zr surface gradient doping double-modified LNMO material comprises the following steps:
(1) weighing a certain amount of lithium nitrate, lanthanum nitrate, anhydrous zirconium nitrate and citric acid according to the proportion of 7:3:2:8, dissolving in ethanol, dropwise adding into a solution in which 0.2g of LNMO cathode material is dispersed after dissolving and stirring, and then mixing and stirring for 6 hours;
(2) evaporating the mixed solution at 80 ℃ for 6h, and then drying at 110 ℃ to obtain a reaction precursor xerogel;
(3) fully grinding the precursor, putting the ground precursor into a crucible, calcining the ground precursor for 6 hours at 550 ℃ in a tube furnace under the argon atmosphere, naturally cooling the calcined precursor to room temperature, cleaning, filtering and drying the calcined precursor to obtain Li7La3Zr2O12The surface of the LNMO is coated and the gradient of the La and Zr surface is doped with double-modified LNMO material.
Example 10
"one-step" process for preparing Li1.4Al0.4Ti1.6(PO4)3The surface coating and Al and Ti surface gradient doping double-modified LNMO material comprises the following steps:
(1) weighing a certain amount of lithium acetate, aluminum nitrate, isopropyl titanate, ammonium dihydrogen phosphate and citric acid according to the proportion of 1.4:0.4:1.6:1:4, dissolving in ethanol, stirring, dropwise adding into a solution in which 0.2g of LNMO cathode material is dispersed, and then mixing and stirring for 6 hours;
(2) evaporating the mixed solution at 75 ℃ for 6h, and then drying at 120 ℃ to obtain a reaction precursor xerogel;
(3) fully grinding the precursor, putting the ground precursor into a crucible, calcining the ground precursor for 6 hours at 600 ℃ in a tube furnace under the argon atmosphere, naturally cooling the calcined precursor to room temperature, cleaning, filtering and drying the cooled precursor to obtain Li1.4Al0.4Ti1.6(PO4)3The surface is coated with the LNMO material which is subjected to double modification by gradient doping on the surfaces of Al and Ti.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (9)
1. The method for one-step surface coating and gradient doping integrated double modification of the LNMO positive electrode material is characterized by comprising the following steps of: mixing a coating material metal precursor solution with a lithium ion battery anode material solution, fully drying to form gel, calcining the gel in an inert atmosphere to increase the surface oxygen defect position of the anode material, promoting metal cations in a coating layer to diffuse into the surface oxygen defect position of the anode material in the coating process, further performing gradient diffusion into the surface crystal lattice of the anode material LNMO, gradually reducing along with the increase of depth to form a nail-like surface doping structure, playing a pinning effect on the surface crystal lattice of the anode material while forming a surface coating layer, further performing surface coating and gradient doping integrated double modification on the lithium ion battery to obtain a surface modification modified lithium ion battery high-voltage anode material, wherein the coating layer metal cations diffuse to the surface crystal lattice of the anode material to form a solid solution buffer layer, so that the structure degradation caused by the dissolution of transition metal ions can be relieved, and improves the interfacial compatibility between the cladding layer and the active material.
2. The one-step method for surface coating and gradient doping integrated double-modified LNMO positive electrode material as claimed in claim 1, wherein: the coating layer is Li2SiO3、Li2SnO3、Li2ZrO3、Li2RuO3、LiNiO2、Li3VO4、Li4Ti5O12、Li2MoO3、LiNbO3、LiAlO2、LiAlSiO4、Li2GeO3、Li3V2(PO4)3、LiTi2(PO4)3、Li7La3Zr2O12、Li2.5Na0.5V2(PO4)3、Li1.4Al0.4Ti1.6(PO4)3Or Li1.4Al0.4Ge1.6(PO4)3。
3. The one-step method for surface coating and gradient doping integrated double-modified LNMO positive electrode material as claimed in claim 1, wherein: the stoichiometric ratio of a cladding layer in the surface modification modified lithium ion battery high-voltage positive electrode material to the positive electrode material is (0.005-0.05): 1.
4. The one-step method for surface coating and gradient doping integrated double-modified LNMO positive electrode material according to any one of claims 1-3, characterized by the following specific steps:
(1) weighing a certain mass of a coating material metal precursor, a positive electrode material and citric acid, respectively dissolving or dispersing in a solvent, and then mixing and fully stirring the solution;
(2) stirring and evaporating the mixed solution obtained in the step (1) to obtain a sol substance, and drying to obtain a xerogel-coated active material;
(3) and (3) calcining the xerogel-coated active material obtained in the step (2) in an inert atmosphere, and cooling, cleaning and filtering a reaction product to obtain the surface-coated and gradient-doped integrated double-modified LNMO positive electrode material.
5. The one-step method for surface coating and gradient doping integrated double-modified LNMO positive electrode material as claimed in claim 4, wherein: the metal precursor of the coating material in the step (1) is a mixture of a lithium compound and a metal compound: the lithium compound is one of lithium acetate, lithium hydroxide or lithium nitrate, the metal compound is one or two of compounds of Si, Sn, Zr, Ru, Ni, V, Ti, M, Nb, Al, Ge, La and Na, and the mass ratio of the lithium compound to the metal compound is 1: (0.3-2).
6. The one-step method for surface coating and gradient doping integrated double-modified LNMO positive electrode material as claimed in claim 4, wherein: the coating material metal precursor in the step (1) is a mixture of a lithium compound, a metal compound and ammonium dihydrogen phosphate, the lithium compound is one of lithium acetate, lithium hydroxide or lithium nitrate, the metal compound is one or two of compounds of Si, Sn, Zr, Ru, Ni, V, Ti, Mo, Nb, Al, Ge, La and Na, and the mass ratio of the lithium compound to the metal compound to the ammonium dihydrogen phosphate is 1: (0.3-2): (0.45-3).
7. The one-step method for surface coating and gradient doping integrated double-modified LNMO positive electrode material as claimed in claim 4, wherein: the solvent in the step (1) is one or more of deionized water, ultrapure water, absolute ethyl alcohol, methanol, ethylene glycol, acetone, diethyl ether, petroleum ether, n-butanol, dichloromethane, acetaldehyde, glycerol and ethyl acetate.
8. The one-step method for surface coating and gradient doping integrated double-modified LNMO positive electrode material as claimed in claim 4, wherein: in the step (2), the drying temperature is 90-150 ℃, and the drying time is 8-24 h.
9. The one-step method for surface coating and gradient doping integrated double-modified LNMO positive electrode material as claimed in claim 4, wherein: the inert atmosphere in the step (3) is one or more of argon, helium, neon, krypton and xenon; the calcining temperature is 400-600 ℃, and the calcining time is 4-6 h.
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