Detailed Description
The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.
The first aspect of the invention provides a positive electrode material, which is characterized by comprising a substrate and a coating layer coated on the surface of the substrate;
the matrix has a composition represented by formula I:
Li 1+aNixCoyMnzMkO2 formula I;
Wherein in the formula I, a is more than or equal to-0.5 and less than or equal to 0.3, x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 0.1, x+y+z+k is more than or equal to 0 and less than or equal to 1, and M is at least one element selected from Ga, sc, in, Y, ce, co, la, cr, mo, mn, fe, hf, zr, W, nb, sm and Al;
the coating layer has a composition represented by formula II:
Ti 1-αM′αNbγ-βM″βO2+2.5γ-δGδ formula II;
Wherein in the formula II, alpha is more than or equal to 0 and less than or equal to 0.5, gamma is more than or equal to 2 and less than or equal to 30, beta is more than or equal to 0 and less than or equal to 0.4, M 'is at least one element selected from Ru, zr, si, sn, cu, cr, al, mg, zn, fe, co, mn, ni and Mo, M' is at least one element selected from V, ta, bi, W and Sb, and G is at least one element selected from N, F, br, S and Cl.
In the invention, the positive electrode material comprises a matrix and a coating layer coated on the surface of the matrix, and the matrix and the coating layer have specific compositions, so that the surface of the positive electrode material has high ion and electron conduction capacity, and the rate capability of a lithium ion battery containing the positive electrode material is obviously improved.
Further, the positive electrode material comprises a coating layer with a specific composition, so that the interface impedance of the positive electrode material can be effectively reduced, the interface side reaction between the surface of the positive electrode material particles and the electrolyte is inhibited, and the electrochemical performance of a lithium ion battery containing the positive electrode material is obviously improved.
Further, in the formula I, a is more than or equal to-0.05 and less than or equal to-0.05, x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0.01 and less than or equal to 0.06, k is more than or equal to 0 and less than or equal to 0+y+z+k and M is at least one element selected from Ce, co, la, cr, mo, Y, zr, W, nb and Al.
Further, in the formula II, alpha is more than or equal to 0 and less than or equal to 0.1,2 and less than or equal to 24,0 and less than or equal to beta is more than or equal to 0.1, delta is more than or equal to 0 and less than or equal to 0.2, M 'is at least one element selected from Ru, zr, cu, cr, al, mg, zn, co, mn, ni and Mo, M' is at least one element selected from V, ta, bi and W, and G is at least one element selected from N, br, S and Cl.
Further preferably, in formula II, the α includes, but is not limited to, 0.05, 0.07, 0.09, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, etc.;
the γ includes, but is not limited to, 4, 6, 7, 10, 12, 14, 16, 18, 20, 22, 26, etc.;
the beta includes, but is not limited to, 0.05, 0.07, 0.09, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, etc.;
the delta includes, but is not limited to, 0.02, 0.04, 0.05, 0.07, 0.09, 0.15, etc.
In the invention, the coating layer is compact or non-compact, specifically, as shown in a scanning electron microscope image of the positive electrode material shown in figure 1, fine coating particles are uniformly attached to the surfaces of secondary particles of the positive electrode material to form the non-compact coating layer,
In the invention, the compactness of the coating layer is characterized by adopting a scanning electron microscope method.
According to the invention, the coating layer is present in an amount of 0.05 to 0.5 wt.%, based on the total weight of the substrate.
In the invention, when the content of the coating layer in the positive electrode material meets the above range, the positive electrode material has better electrochemical performance.
Further, the coating layer is contained in an amount of 0.1 to 0.3wt% based on the total weight of the substrate.
According to the invention, the thickness of the coating layer is 2-10nm.
In the present invention, the thickness of the coating layer is measured by transmission electron microscopy.
In the present invention, when the thickness of the coating layer satisfies the above range, the positive electrode material can be made to have excellent ion-conducting ability and electron-conducting ability.
Further, the thickness of the coating layer is 3-9nm.
According to the invention, the average particle diameter D 50 of the positive electrode material is 2-30 μm.
In the present invention, the average particle diameter D 50 of the positive electrode material was measured using a malvern particle sizer.
Further, the average particle diameter D 50 of the positive electrode material is 3-20 mu m
According to the invention, the residual alkali content of the surface of the positive electrode material is less than or equal to 1 weight percent.
In the invention, the residual alkali content on the surface of the positive electrode material is measured by an acid-base titration method.
In the invention, when the residual alkali content of the surface of the positive electrode material meets the range, the positive electrode material has better electrochemical performance.
Further, the surface residual alkali amount of the positive electrode material is 0.2-1wt%.
In one specific embodiment of the invention, in the formula II, when 0< alpha is less than or equal to 0.5,2 is less than or equal to gamma is less than or equal to 30,0< beta is less than or equal to 0.5, and 0 is less than or equal to delta is less than or equal to 0.4, namely when the coating layer contains doping elements M 'and M', the forbidden band width of the coating layer is 1.5-2.9eV.
In the invention, the forbidden bandwidth is obtained by calculating the density of states theory.
In the present invention, when the forbidden bandwidth of the coating layer satisfies the above range, the surface of the positive electrode material has high electron transport ability.
Further, when the cladding layer contains doping elements M' and M ", the forbidden bandwidth of the cladding layer is 1.6-2.7eV.
In a preferred embodiment of the invention, in formula II, the electron conductivity of the coating is 10 -4S/cm-10-9 S/cm when 0< alpha > is less than or equal to 0.5,2 < gamma > is less than or equal to 30,0< beta > is less than or equal to 0.5, and 0< delta > is less than or equal to 0.4, i.e. the coating contains doping elements M 'and M'.
In the invention, the electronic conductivity is measured by a four-probe method.
In the present invention, when the electron conductivity of the coating layer satisfies the above range, the surface of the positive electrode material has a high electron transport ability.
Further, when the coating layer contains doping elements M' and M ", the electron conductivity of the coating layer is 10 -4S/cm-10-7 S/cm.
The second aspect of the present invention provides a method for preparing a positive electrode material, which is characterized by comprising the steps of:
S1, firstly mixing a nickel cobalt manganese hydroxide precursor, a lithium source and an optional doping agent M to obtain a mixture I, and calcining, crushing and screening the mixture I in air or oxygen atmosphere to obtain a positive electrode material matrix;
S2, carrying out second mixing on a titanium source, a niobium source, an optional M 'source and an optional G source according to the molar ratio of n (Ti): n (M'): n (Nb): n (M "): n (G) = (1-alpha): alpha (gamma-beta): beta: delta) to obtain a mixture II, and sintering and crushing the mixture II in an air atmosphere to obtain a coating material;
And S3, carrying out third mixing on the positive electrode material matrix and the coating material to obtain a mixture III, and carrying out heat treatment on the mixture III to obtain the positive electrode material.
According to the invention, the positive electrode material which is prepared by carrying out heat treatment on the coating material containing the titanium source, the niobium source and the like and the positive electrode material matrix and comprises the matrix and the coating layer coated on the surface of the matrix has high ion conduction capacity and high electron conduction capacity, so that the multiplying power performance of the lithium ion battery containing the positive electrode material is remarkably improved, the interface impedance of the positive electrode material can be effectively reduced by the coating layer, the interface side reaction between the surface of the positive electrode material particles and electrolyte is inhibited, and the electrochemical performance of the lithium ion battery containing the positive electrode material is remarkably improved.
Furthermore, the preparation method of the positive electrode material provided by the invention has the advantages of simple process, no pollution doping element, simple introduction mode of the coating layer, small dosage, no special requirement on heat treatment atmosphere, low production cost and suitability for large-scale industrial production.
According to the present invention, in step S1, the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium fluoride, lithium nitrate, and lithium acetate.
According to the invention, the dopant M is selected from compounds containing at least one element of Ga, sc, in, Y, ce, co, la, cr, mo, mn, fe, hf, zr, W, nb, sm and Al.
Further, the dopant M is selected from a compound containing at least one element of Ce, co, la, cr, mo, Y, zr, W, nb and Al.
According to the invention, the nickel cobalt manganese hydroxide precursor, the lithium source and the dopant M are used in amounts such that:
0.95≤[n(Li)]/[n(Ni)+n(Co)+n(Mn)+n(M)]≤1.05;
0≤[n(M)]/[n(Ni)+n(Co)+n(Mn)+n(M)]≤0.06。
Further, the nickel cobalt manganese hydroxide precursor, the lithium source, and the dopant M are used in amounts such that:
0.98≤[n(Li)]/[n(Ni)+n(Co)+n(Mn)+n(M)]≤1.02;
0.01≤[n(M)]/[n(Ni)+n(Co)+n(Mn)+n(M)]≤0.05。
According to the invention, the conditions of the calcination include: the calcination temperature is 600-1000 ℃ and the calcination time is 4-20h.
In the invention, the mixture I is calcined under the above conditions, so that a pure-phase positive electrode material matrix can be obtained, and the prepared positive electrode material has excellent stability and electrochemical activity.
Further, the calcining conditions include: the calcination temperature is 650-950 ℃ and the calcination time is 5-18h.
According to the present invention, in step S2, the titanium source is selected from at least one of titanium dioxide, titanium tetrachloride, titanyl sulfate, tetrabutyl titanate, and titanium isopropoxide.
According to the present invention, the niobium source is at least one selected from the group consisting of niobium pentoxide, niobium dioxide, niobium trioxide, niobium hydroxide, niobium pentachloride, niobium pentaethoxide, ammonium niobium oxalate and niobium oxalate,
According to the invention, the M' source is selected from compounds containing at least one element of Ru, zr, si, sn, cu, mo, cr, al, mg, zn, fe, co, mn and Ni.
Further, the M' source is selected from compounds containing at least one element of Ru, zr, cu, cr, al, mg, zn, co, mn, ni and Mo.
According to the invention, the M' source is selected from compounds containing at least one element of V, ta, bi, W and Sb.
Further, the M' source is selected from compounds containing at least one element of V, ta, bi and W.
According to the invention, the G source is selected from compounds containing at least one element of N, F, br, S and Cl.
Further, the G source is selected from compounds containing at least one element of N, br, S and Cl.
According to the invention, the sintering conditions include: the sintering temperature is 350-900 ℃ and the sintering time is 1-12h.
In the invention, under the above conditions, the mixture II containing the niobium source, the titanium source and the like is sintered to prepare the coating material, so that the pure phase doped surface coating layer can be obtained, and the surface of the prepared positive electrode material has excellent ion conduction capability and electron transfer capability.
Further, the sintering conditions include: the sintering temperature is 400-800 ℃ and the sintering time is 3-8h.
According to the present invention, in step S2, the second mixing is at least one of solid phase mixing, sol gel mixing and hydrothermal mixing.
In one embodiment of the present invention, the second mixing is solid phase mixing, and the specific operation steps of the second mixing are as follows:
The titanium source, niobium source, optionally M' source, optionally M "source and optionally G source are mixed with stirring at a speed of 500-900rpm, preferably 600-800rpm, for 2-6h, preferably 3-4h, to obtain said mixture II.
In the present invention, the solid phase mixing may be performed in a mixing apparatus conventional in the art, such as a high-speed mixer.
In one specific embodiment of the present invention, the second mixing is sol-gel mixing, and the specific operation steps of the sol-gel mixing are as follows:
Mixing a titanium source, a niobium source, an optional M' source and an optional G source with a solvent, adjusting the pH, stirring at 50-90 ℃, preferably 60-80 ℃ for 3-7h, preferably 3-5h to obtain a mixed solution, and drying to obtain the mixture II.
In the present invention, the solvent may be a solvent of a kind conventional in the art, for example, ethanol.
In the present invention, the adjustment of the pH can be accomplished using reagents conventional in the art, for example, citric acid to adjust the pH to 8-10.
In one specific embodiment of the present invention, the second mixing is a hydrothermal mixing, and the specific steps of the hydrothermal mixing are as follows:
Mixing a titanium source, a niobium source, an optional M' source and an optional G source with a solvent to obtain a mixture, transferring the mixture into a reaction kettle, preserving heat for 5-12h at 80-250 ℃, and performing solid-liquid separation to obtain solid-liquid which is the mixture II.
Further, in step S2, the second mixing is solid phase mixing and/or sol gel mixing.
In the present invention, the D 50 of the coating is 30-250nm, preferably 50-200nm.
According to the invention, in step S3, the coating material is used in an amount of 0.05-0.5wt% of the positive electrode material.
In the present invention, when the amount of the coating material satisfies the above range, the positive electrode material thus obtained has excellent electrochemical properties.
Further, the amount of the coating material is 0.1 to 0.3wt% of the amount of the positive electrode material.
According to the invention, the conditions of the third mixing include: the mixture is stirred and mixed for 3 to 6 hours at a rotation speed of 500 to 950 rpm.
In the present invention, the third mixing may be implemented in a mixing apparatus conventional in the art, such as a high-speed mixer.
Further, the conditions of the third mixing include: the mixture is stirred and mixed for 4 to 6 hours at the rotating speed of 600 to 850 rpm.
According to the present invention, the conditions of the heat treatment include: the heat treatment temperature is 350-900 ℃, and the heat treatment time is 1-12h.
According to the invention, under the above conditions, the mixture III containing the coating material and the positive electrode material matrix is subjected to heat treatment, so that the coating material and the positive electrode material matrix are fully and uniformly mixed, the coating material can be uniformly dispersed, and the positive electrode material prepared by the method has good electrochemical performance.
Further, the conditions of the heat treatment include: the heat treatment temperature is 400-800 ℃, and the heat treatment time is 3-8h.
In the present invention, the nickel cobalt manganese hydroxide precursor may be a precursor conventional in the art, preferably the nickel cobalt manganese hydroxide precursor is a hydroxide containing Ni, co, mn and optionally a dopant M.
In one specific embodiment of the invention, the nickel cobalt manganese hydroxide precursor is prepared according to the following steps:
(1) Preparing a mixed salt solution of nickel salt, cobalt salt, manganese salt and optionally dopant M according to a molar ratio of Ni: co: mn: m=x: y: z: k; respectively preparing a precipitator solution and a complexing agent solution;
(2) Adding the mixed salt solution, the precipitator solution and the complexing agent solution into a reaction kettle for reaction to obtain precursor slurry, and carrying out solid-liquid separation, washing, drying and screening on the precursor slurry to obtain the nickel-cobalt-manganese hydroxide precursor.
In the present invention, the nickel salt, the cobalt salt, and the manganese salt may be conventional nickel salts, cobalt salts, and manganese salts in the art. In particular, the nickel salt is selected from nickel sulphate and/or nickel chloride; the cobalt salt is selected from cobalt sulfate and/or cobalt chloride; the manganese salt is selected from manganese sulfate and/or manganese chloride.
In the present invention, the precipitant may be at least one of sodium hydroxide, potassium hydroxide, sodium carbonate and ammonium carbonate, which are conventional in the art. The complexing agent may be a complexing agent conventional in the art, such as ammonia.
In the invention, the concentration of the mixed salt is 2-10mol/L; the concentration of the precipitant solution is 5-9mol/L; the concentration of the complexing agent solution is 4-7mol/L.
In the invention, in the step (2), the flow rate of the mixed salt solution entering the reaction kettle is controlled to be 30-45L/h, the flow rate of the precipitant solution entering the reaction kettle is controlled to be 14-26L/h, and the flow rate of the complexing agent solution entering the reaction kettle is controlled to be 5-10L/h.
According to the invention, the dopant M is selected from compounds containing at least one element of Ga, sc, in, Y, ce, co, la, cr, mo, mn, fe, hf, zr, W, nb, sm and Al.
Further, the dopant M is selected from a compound containing at least one element of Ce, co, la, cr, mo, Y, zr, W, nb and Al.
According to the invention, the doping agent M is added in a stoichiometric ratio of 0.ltoreq.n (M)/[ n (Ni) +n (Co) +n (Mn) +n (M) ].ltoreq.0.06.
Further, the addition amount of M is not more than 0.01 and not more than [ n (M) ]/[ n (Ni) +n (Co) +n (Mn) +n (M) ] and not more than 0.05 according to the stoichiometric ratio.
According to the invention, the reaction conditions include: the pH value is 11.2-11.9, the reaction temperature is 50-80 ℃, and the reaction time is 20-80h.
Further, the reaction conditions include: the pH value is 11.5-11.7, the reaction temperature is 60-70 ℃, and the reaction time is 30-50h.
According to the present invention, the conditions for drying include: the drying temperature is 80-120 ℃ and the drying time is 8-12h.
Further, the drying conditions include: the drying temperature is 100-110 ℃, and the drying time is 10-11h.
The second aspect of the present invention provides a positive electrode material produced by the above-described production method.
In the invention, the positive electrode material comprises a substrate and a coating layer coated on the surface of the substrate;
the matrix has a composition represented by formula I:
Li 1+aNixCoyMnzMkO2 formula I;
Wherein in the formula I, a is more than or equal to-0.5 and less than or equal to 0.3, x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 0.06, x+y+z+k is more than or equal to 0 and less than or equal to 1, and M is at least one element selected from Ga, sc, in, Y, ce, co, la, cr, mo, mn, fe, hf, zr, W, nb, sm and Al;
the coating layer has a composition represented by formula II:
Ti 1-αM′αNbγ-βM″βO2+2.5γ-δGδ formula II;
Wherein in the formula II, alpha is more than or equal to 0 and less than or equal to 0.5, gamma is more than or equal to 2 and less than or equal to 30, beta is more than or equal to 0 and less than or equal to 0.4, M 'is at least one element selected from Ru, zr, si, sn, cu, cr, al, mg, zn, fe, co, mn, ni and Mo, M' is at least one element selected from V, ta, bi, W and Sb, and G is at least one element selected from N, F, br, S and Cl.
Further, in the formula I, a is more than or equal to-0.05 and less than or equal to-0.05, x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0.01 and less than or equal to 0.06, x+y+z is more than or equal to 0 and M is at least one element selected from Ce, co, la, cr, mo, Y, zr, W, nb and Al.
Further, in the formula II, alpha is more than or equal to 0 and less than or equal to 0.1,2 and less than or equal to 24,0 and less than or equal to beta is more than or equal to 0.1, delta is more than or equal to 0 and less than or equal to 0.2, M 'is at least one element selected from Ru, zr, cu, cr, al, mg, zn, co, mn, ni and Mo, M' is at least one element selected from V, ta, bi and W, and G is at least one element selected from N, br, S and Cl.
In the invention, the coating layer is compact or non-compact.
In the present invention, the coating layer is contained in an amount of 0.05 to 0.5wt%, preferably 0.1 to 0.3wt%, based on the total weight of the substrate.
In the present invention, the thickness of the coating layer is 2 to 10nm, preferably 3 to 9nm.
In the present invention, the average particle diameter D 50 of the positive electrode material is 2 to 30. Mu.m, preferably 3 to 20. Mu.m.
In the invention, the residual alkali content of the surface of the positive electrode material is less than or equal to 1 weight percent, preferably 0.2 to 1 weight percent.
In the present invention, when the cladding layer contains doping elements M' and M ", the forbidden bandwidth of the cladding layer is 1.5-2.9eV, preferably 1.6-2.7eV.
In the present invention, when the coating layer contains the doping elements M' and M ", the electron conductivity of the coating layer is 10 -4S/cm-10-9 S/cm, preferably 10 -4S/cm-10-7 S/cm.
The third aspect of the invention provides an application of the positive electrode material in a lithium ion battery.
A fourth aspect of the present invention provides a lithium ion battery, wherein the lithium ion battery includes the above-described positive electrode material.
In the invention, the lithium ion battery is a liquid lithium ion battery and comprises a positive electrode, a negative electrode and electrolyte, wherein the positive electrode is made of the positive electrode material.
In the invention, the electrolyte is common commercial electrolyte and is an equivalent mixed solution of LiPF 6, ethylene Carbonate (EC) and diethyl carbonate (DEC) with the composition of 1 mol/L.
In the invention, the lithium ion battery is a solid lithium ion battery and comprises a positive electrode, a negative electrode and a solid electrolyte, wherein the positive electrode is made of the positive electrode material.
In the present invention, the solid electrolyte is at least one selected from the group consisting of a polymer electrolyte, an inorganic solid electrolyte, and a composite solid electrolyte.
The present invention will be described in detail by examples.
The microscopic morphology of the positive electrode material was measured by scanning electron microscopy.
The electrochemical ac impedance of the positive electrode material is measured by the electrochemical workstation.
The forbidden bandwidth of the coating layer is calculated by a state density theory.
The electron conductivity of the coating was measured using a four-probe method.
The residual alkali on the surface of the positive electrode material is measured by an acid-base titration method.
The positive electrode active materials in the following examples and comparative examples were evaluated for electrical properties according to the following methods.
Assembling the liquid button cell:
Firstly, mixing a surface modified positive electrode material for a nonaqueous electrolyte secondary battery, acetylene black and polyvinylidene fluoride (PVDF) according to a mass ratio of 95:2.5:2.5, coating the mixture on aluminum foil, drying the mixture, punching the mixture to form a positive electrode plate with a diameter of 12mm and a thickness of 120 mu m by using a pressure of 100MPa, and then placing the positive electrode plate into a vacuum drying box for drying at 120 ℃ for 12 hours.
The anode uses a Li metal sheet with a diameter of 17mm and a thickness of 1 mm; the separator uses a polyethylene porous film with a thickness of 25 μm; as the electrolyte, 1mol/L of an equivalent mixture of LiPF 6, ethylene Carbonate (EC) and diethyl carbonate (DEC) was used.
And assembling the positive electrode plate, the diaphragm, the negative electrode plate and the electrolyte into the 2025 type button cell in an Ar gas glove box with water content and oxygen content of less than 5 ppm.
Assembling the solid-state button cell:
the preparation method of the positive plate is identical with that of the liquid button cell.
PEO, liTFSI and Li 1.3Al0.3Ti1.7(PO4)3 nano-particles as solid electrolyte are dissolved in acetonitrile according to the weight ratio of 6:3:1, and the mixture is uniformly mixed to form slurry. The slurry is coated on a polytetrafluoroethylene plate in a scraping way, and is dried for 12 hours at 60 ℃ and then peeled off to obtain the solid electrolyte membrane.
And sequentially loading the positive electrode plate, the solid electrolyte membrane and the metal lithium sheet into a battery shell to obtain the solid lithium battery.
The performance of the button cell was evaluated as follows:
(1) And (3) multiplying power performance test: the temperature is 25 ℃, and the multiplying power performance of the material is inspected by 1 circle of circulation under the multiplying power of 0.1C, 0.2C, 0.33C, 0.5C and 1C respectively in the voltage interval of 3.0-4.3V.
(2) And (3) testing charge and discharge performance: the charge and discharge performance of the material was examined at a rate of 0.1C at a temperature of 25 ℃ in a voltage range of 3.0-4.3V.
(3) Ac impedance performance test: the ac impedance test was performed at an amplitude of 5mV in the test frequency range of 0.1Hz-100 kHz.
Preparation example 1
Nickel cobalt manganese hydroxide precursor P1
(1) Preparing 2mol/L nickel sulfate, cobalt sulfate and manganese sulfate mixed salt solution according to the molar ratio of Ni, co and Mn elements of 90:5:5. Preparing 7mol/L sodium hydroxide alkali solution; preparing 6mol/L ammonia water complexing agent solution.
(2) And continuously adding the mixed salt solution, the alkali solution and the ammonia water complexing agent solution into a stirrer in a parallel flow mode for reaction, wherein the stirring speed is 120rpm. Simultaneously controlling the liquid inlet flow of the mixed salt solution to be 40L/h, the liquid inlet flow of the alkali solution to be 20L/h, the liquid inlet flow of the complexing agent solution to be 6L/h, the pH to be 11.5, the temperature to be 60 ℃ and the reaction time to be 30h. When the reaction is completed, the obtained nickel cobalt manganese hydroxide slurry is subjected to solid-liquid separation and washing, a filter cake is dried at 100 ℃ for 10 hours and then is screened, and the product is subjected to water washing, filtering and drying to obtain a nickel cobalt manganese hydroxide precursor P1.
Preparation example 2
Nickel cobalt manganese hydroxide precursor P2
(1) Preparing 2mol/L nickel sulfate, cobalt sulfate, manganese sulfate and zirconium nitrate mixed salt solution according to the mol ratio of Ni, co, mn, zr elements of 60:20:19:1. Preparing 7mol/L sodium hydroxide alkali solution; preparing 6mol/L ammonia water complexing agent solution.
(2) And continuously adding the mixed salt solution, the alkali solution and the ammonia water complexing agent solution into a stirrer in a parallel flow mode for reaction, wherein the stirring speed is 100rpm. Meanwhile, the flow rate of the mixed salt solution is controlled to be 35L/h, the flow rate of the alkali solution is controlled to be 18L/h, the flow rate of the complexing agent solution is controlled to be 6L/h, the pH is controlled to be 11.6, the temperature is 60 ℃, and the reaction is carried out for 38h. When the reaction is completed, the obtained nickel cobalt manganese hydroxide slurry is subjected to solid-liquid separation and washing, a filter cake is dried at 100 ℃ for 10 hours and then is screened, and the product is subjected to water washing, filtering and drying to obtain a nickel cobalt manganese hydroxide precursor P2.
Example 1
S1, uniformly mixing a nickel cobalt manganese hydroxide precursor P1 and lithium hydroxide in a ratio of Li/(Ni+Co+Mn) =1.02 to obtain a mixture I, calcining the mixture I at 720 ℃ for 10 hours in an oxygen atmosphere, and crushing and sieving a product to obtain a positive electrode material matrix;
s2, carrying out second mixing on a titanium source, a niobium source, an M 'source and an M' source by adopting solid phase mixing, and specifically: according to the molar ratio of n (Ti): n (M '): n (Nb): n (M ") =0.95:0.05:1.98:0.02, titanium dioxide, zirconium oxide (M ' source), dinitrile (niobium source) and vanadium pentoxide (M ' source) are stirred and mixed for 2 hours at a rotation speed of 800rpm to obtain a mixture II, the mixture II is sintered for 8 hours at 800 ℃ in an air atmosphere, and after cooling to room temperature, the mixture is crushed and sieved to obtain a coating material, wherein D 50 of the coating material is 200nm, and the composition is Ti 0.95Zr0.05Nb1.98V0.02O7. The band gap of the coating layer was 1.9eV, and the electron conductivity was 10 -4 S/cm.
S3, stirring the coating material and the positive electrode material matrix for 4 hours at the speed of 800rpm to obtain a mixture III, wherein the dosage of the coating material is 0.1wt% based on the dosage of the positive electrode material matrix. Carrying out heat treatment on the mixture III for 5 hours at 500 ℃, after cooling to room temperature, crushing and sieving to obtain a positive electrode material A1, wherein a coating layer of the positive electrode material A1 comprises Ti 0.95Zr0.05Nb1.98V0.02O7, and the matrix comprises the following components: li 1.02Ni0.9Co0.05Mn0.05O2, the content of the coating layer was 0.1wt% based on the total weight of the matrix. D 50 of the positive electrode material A1 is 12 mu m, and the surface residual alkali amount is 0.28wt%.
Fig. 1 is an SEM image of a positive electrode material A1, and it can be seen from fig. 1 that fine coating particles are uniformly attached to the surface of secondary particles of the positive electrode material A1, thereby forming a non-dense coating layer.
Fig. 3 is a TEM image of the positive electrode material A1, and as can be seen from fig. 3, the thickness of the coating layer of the positive electrode material A1 is 8nm.
Example 2
S1, uniformly mixing a nickel cobalt manganese hydroxide precursor P1 and lithium hydroxide in a ratio of Li/(Ni+Co+Mn) =1.02 to obtain a mixture I, sintering the mixture I at 720 ℃ for 10 hours in an oxygen atmosphere, and crushing and sieving a product to obtain a positive electrode material matrix;
s2, mixing a titanium source, a niobium source, an M ' source and a G source in ethanol according to a mol ratio of n (Ti) n (M ')n (Nb) n (M ') n (G) =0.92:0.08:23.94:0.06:0.03, adding citric acid to adjust pH=9.6, stirring at 60 ℃ for 5h to obtain a mixed solution, drying in an oven at 120 ℃ for 8h to obtain a mixture II, sintering the mixture II at 800 ℃ in an air atmosphere, cooling to room temperature, and crushing and sieving to obtain a coating material, wherein D 50 of the coating material is 180nm, and the composition is Ti 0.92Mo0.08Nb23.94Bi0.06O61.97S0.03. The band gap of the coating layer was 2.2eV, and the electron conductivity was 10 -5 S/cm.
S3, stirring the coating material and the positive electrode material matrix for 6 hours at the speed of 800rpm to obtain a mixture III, wherein the dosage of the coating material is 0.2wt% based on the dosage of the positive electrode material matrix. And (3) carrying out heat treatment on the mixture III for 8 hours at 450 ℃, cooling to room temperature, and then crushing and sieving to obtain the anode material A2. The composition of the matrix of the positive electrode material A2 is as follows: li 1.02Ni0.9Co0.05Mn0.05O2, coating layer composition: ti 0.92Mo0.08Nb23.94Bi0.06O61.97S0.03, the content of the coating layer was 0.2wt% based on the total weight of the substrate. The D 50 of the positive electrode material A2 was 13 μm, and the surface residual alkali amount was 0.25wt%. The thickness of the coating layer was 5nm.
Example 3
S1, uniformly mixing a nickel cobalt manganese hydroxide precursor P2 and lithium hydroxide in a ratio of Li/(Ni+Co+Mn+Zr) =1.03 to obtain a mixture I, calcining the mixture I at 720 ℃ for 10 hours in an air atmosphere, and crushing and sieving the product to obtain a positive electrode material matrix;
S2, carrying out second mixing on a titanium source, a niobium source, an M 'source and an M' source by adopting solid phase mixing, and specifically: according to the molar ratio of n (Ti): n (M '): n (Nb): n (M ") =0.9:0.1:4.94:0.06, titanium dioxide, magnesium oxide (M ' source), niobium hydroxide (niobium source) and tantalum pentoxide (M ' source) were stirred at 850rpm for 3 hours to obtain a mixture II, the mixture II was sintered at 750 ℃ for 8 hours under an air atmosphere, and after cooling to room temperature, the mixture was crushed and sieved to obtain a coating material, wherein D 50 of the coating material was 170nm, and the composition was Ti 0.9Mg0.1Nb4.94Ta0.06O14.5. The band gap of the coating layer was 2.1eV, and the electron conductivity was 10 -5 S/cm.
S3, stirring the coating material and the positive electrode material matrix for 6 hours at the rotating speed of 800rpm to obtain a mixture III, wherein the dosage of the coating material is 0.1wt% based on the dosage of the positive electrode material matrix. And (3) carrying out heat treatment on the mixture III for 8 hours at 450 ℃, cooling to room temperature, and then crushing and sieving to obtain the anode material A3. The coating layer of the positive electrode material A3 comprises: ti 0.9Mg0.1Nb4.94Ta0.06O14.5, the composition of the matrix is: li 1.03Ni0.6Co0.2Mn0.19 Zr0.01 O2, the content of the coating layer was 0.1wt% based on the total weight of the matrix. The particle size of the positive electrode material A3 was 13. Mu.m, the residual alkali content on the surface was 0.26wt%, and the thickness of the coating layer was 6nm.
Example 4
S1, uniformly mixing a nickel cobalt manganese hydroxide precursor P2 and lithium carbonate in a ratio of Li/(Ni+Co+Mn+Zr) =1.03 to obtain a mixture I, calcining the mixture I at 750 ℃ for 10 hours in an air atmosphere, and crushing and sieving the product to obtain a positive electrode material matrix.
S2, adopting solid-phase mixing to carry out second mixing on a titanium source, a niobium source, an M ' source and a G source, specifically, according to the mole ratio of n (Ti) to n (M ')ton (Nb) to n (M ') to n (G) to be 0.94:0.06:23.98:0.02:0.04, stirring and mixing titanium dioxide, aluminum oxide (M ' source), niobium pentachloride (niobium source and G source) and tungsten trioxide (M ' source) for 3 hours at the rotating speed of 750rpm to obtain a mixture II, sintering the mixture II for 8 hours at 700 ℃ under the air atmosphere, after cooling to room temperature, crushing and sieving to obtain a coating, wherein D 50 of the coating is 110nm, and the composition is as follows: ti 0.94Al0.06Nb23.98W0.02O61.96Cl0.04. The band gap of the coating layer was 2.6eV, and the electron conductivity was 10 -6 S/cm.
S3, stirring the coating material and the positive electrode material matrix for 4 hours at the speed of 800rpm to obtain a mixture III, wherein the dosage of the coating material is 0.3wt% based on the dosage of the positive electrode material matrix. Carrying out heat treatment on the mixture III for 8 hours at 500 ℃, after cooling to room temperature, crushing and sieving to obtain a positive electrode material A4, wherein a coating layer of the positive electrode material comprises Ti 0.94Al0.06Nb23.98W0.02O61.96Cl0.04, and the composition of a matrix is as follows: li 1.03Ni0.6Co0.2Mn0.19 Zr0.01 O2, the content of the coating layer was 0.3wt% based on the total weight of the matrix. The particle diameter of the positive electrode material A4 was 15. Mu.m, and the amount of residual alkali on the surface was 0.3wt%. The thickness of the coating layer was 5nm.
Example 5
A positive electrode material was prepared as in example 1, except that:
In step S2, the M 'source and the M' source are not contained. The molar ratio of n (Ti): n (Nb) =1:2, titanium dioxide and niobium pentoxide (niobium source) are stirred and mixed for 2 hours at the rotating speed of 800rpm to obtain a mixture II, the mixture II is sintered for 8 hours at 780 ℃ in air atmosphere, and after cooling to room temperature, the mixture is crushed and sieved to obtain a coating material, wherein the D 50 of the coating material is 180nm, and the composition is TiNb 2O7. The band gap of the coating layer was 2.9eV, and the electron conductivity was 10 -9 S/cm.
The positive electrode material A5 is prepared, the matrix composition is Li 1.02Ni0.90Co0.05Mn0.05O2, the coating layer is TiNb 2O7, the content of the coating layer is 0.1wt% based on the total weight of the matrix, the D 50 of the positive electrode material A7 is 11 mu m, the surface residual alkali amount is 0.25wt%, and the thickness of the coating layer is 7nm.
Example 6
A positive electrode material was prepared as in example 1, except that:
in step S1, the nickel cobalt manganese hydroxide precursor P1, lithium hydroxide, and zirconium oxide are mixed in a ratio of Li/(ni+co+mn+zr) =1.02 and M/(ni+co+mn+zr) =0.03.
The prepared positive electrode material A6 has a matrix composition of Li 1.02Ni0.9Co0.02Mn0.05Zr0.03O2, a coating layer of Ti 0.95Zr0.05Nb1.98V0.02O7, D 50 of the positive electrode material A7 of 11 mu m, residual surface alkali content of 0.20wt%, thickness of 6nm, forbidden band width of 1.9eV, and electronic conductivity of 10 -4 S/cm.
Example 7
A positive electrode material was prepared as in example 1, except that:
in the step S2, the sintering temperature is 820 ℃, the sintering time is 10 hours, and the coating material is obtained, wherein the D 50 of the coating material is 210nm.
In the step S3, the use amount of the coating material is 0.5wt% based on the use amount of the positive electrode material matrix, the heat treatment temperature is 350 ℃, and the time is 11h.
The prepared positive electrode material A7 has a matrix composition of Li 1.02Ni0.90Co0.05Mn0.05O2, a coating layer of Ti 0.95Zr0.05Nb1.98V0.02O7, D 50 of the positive electrode material A7 of 13 mu m, residual surface alkali content of 0.26wt%, coating layer thickness of 9nm, a forbidden band width of 2.8eV and electron conductivity of 10 -8 S/cm.
Example 8
A positive electrode material was prepared as in example 1, except that:
In the step S2, the sintering temperature is 1000 ℃, the sintering time is 14 hours, and the coating material is obtained, wherein the D 50 of the coating material is 300nm.
In the step S3, the use amount of the coating material is 0.8wt% based on the use amount of the positive electrode material matrix, the heat treatment temperature is 300 ℃, and the time is 15 hours.
The prepared positive electrode material A8 has a matrix composition of Li 1.02Ni0.90Co0.05Mn0.05O2, a coating layer of Ti 0.95Zr0.05Nb1.98V0.02O7, D 50 of the positive electrode material A8 of 12 mu m, residual surface alkali content of 0.31wt%, coating layer thickness of 10nm, a forbidden band width of 3eV and electronic conductivity of 10 -10 S/cm.
Comparative example 1
S1, uniformly mixing a nickel cobalt manganese hydroxide precursor P1 and lithium hydroxide in a ratio of Li/(Ni+Co+Mn) =1.02 to obtain a mixture I, calcining the mixture I at 720 ℃ for 10 hours in an oxygen atmosphere, crushing and sieving a product to obtain a positive electrode material D1, wherein the composition is as follows: li 1.02Ni0.9Co0.05Mn0.05O2, average particle diameter D 50 of 12 μm and residual surface alkali content of 0.29wt%.
Fig. 2 is an SEM image of the positive electrode material D1, and as can be seen from fig. 2, the secondary particle surface of the positive electrode material D1 is rough, and the inter-particle gaps are fine.
Comparative example 2
S1, uniformly mixing a nickel cobalt manganese hydroxide precursor P2 and lithium carbonate in a ratio of Li/(Ni+Co+Mn+Zr) =1.03 to obtain a mixture I, calcining the mixture I at 750 ℃ for 10 hours in an air atmosphere, crushing and sieving a product to obtain a positive electrode material D2, wherein the composition is as follows: li 1.03Ni0.6Co0.2Mn0.19 Zr0.01 O2, average particle diameter D 50 of 13 μm and residual surface alkali content of 0.32wt%.
Comparative example 3
A positive electrode material was prepared as in example 1, except that:
In step S2, the titanium source is not contained. Specifically, according to the molar ratio of n (M '): n (Nb): n (M ") =1:1.98:0.02, zirconium oxide (M' source), dinitrile pentoxide (niobium source) and vanadium pentoxide (M″ source) are stirred and mixed for 2 hours at a rotation speed of 800rpm to obtain a mixture II, the mixture II is sintered for 8 hours at 800 ℃ in an air atmosphere, and after cooling to room temperature, the mixture is crushed and sieved to obtain a coating material, wherein D 50 of the coating material is 130nm. The band gap of the coating layer was 3.1eV, and the electron conductivity was 10 - 10 S/cm.
The positive electrode material D3 is prepared, a coating layer of the positive electrode material D3 comprises ZrNb 1.98V0.02O7, and a matrix comprises the following components: li 1.02Ni0.9Co0.05Mn0.05O2, the content of the coating layer was 0.1wt% based on the total weight of the matrix. The D 50 of the positive electrode material A1 was 18 μm, the residual alkali content on the surface was 0.4wt%, and the thickness of the coating layer was 9nm.
Comparative example 4
A positive electrode material was prepared as in example 1, except that:
In step S2, a niobium source is not contained. Specifically, according to the molar ratio of n (Ti): n (M '): n (M') = 0.95:0.05:2, titanium dioxide (titanium source), zirconium oxide (M 'source) and vanadium pentoxide (M' source) are stirred and mixed for 4 hours at the rotating speed of 760rpm to obtain a mixture II, the mixture II is sintered for 8 hours at 790 ℃ in air atmosphere, and after being cooled to room temperature, the mixture is crushed and sieved to obtain a coating material, wherein the D 50 of the coating material is 115nm. The band gap of the coating layer was 3.3eV, and the electron conductivity was 10 - 10 S/cm.
The positive electrode material D4 is prepared, wherein a coating layer of the positive electrode material D4 comprises Ti 0.95Zr0.05V2O7, and a matrix comprises the following components: li 1.02Ni0.9Co0.05Mn0.05O2, the content of the coating layer was 0.2wt% based on the total weight of the matrix. The positive electrode material D4 had a D 50 of 17. Mu.m, a residual alkali content of 0.43wt% and a coating layer thickness of 9nm.
Test example 1
The positive electrode materials prepared in examples 1 to 8 and comparative examples 1 to 4 were used as positive electrodes for assembling liquid lithium ion batteries to obtain liquid lithium ion batteries C1 to C8 and DC1 to DC4, respectively. The discharge capacities of the cells at 0.1C, 0.2C, 0.5C and 1C rates were measured in the voltage range of 3.0-4.3V, respectively, and the results are shown in table 1.
TABLE 1
Fig. 4 is an ac impedance diagram of a liquid battery made of the positive electrode material A1, the positive electrode material A2, and the positive electrode material D1, and as can be seen from fig. 4, the semicircle diameter of the high frequency portion in the positive electrode material A1 is smaller than that of the positive electrode material D1 made in comparative example 1, which indicates that the Ti 0.95Zr0.05Nb1.98V0.02O7 coating significantly reduces the interface impedance of the materials. The semicircle diameter of the high frequency part in the positive electrode material A2 was smaller than that of the positive electrode material D1 prepared in comparative example 1, which suggests that Ti 0.92Mo0.08Nb23.94Bi0.06O61.97S0.03 coating significantly reduced the interface impedance of the material.
Fig. 5 is a graph showing the rate performance of liquid lithium ion batteries C1, C2, and DC1 assembled from the positive electrode material A1 prepared in example 1, the positive electrode material A2 prepared in example 2, and the positive electrode material D1 prepared in comparative example 1. As can be seen from fig. 5, the liquid lithium ion battery DC1 has a 0.1C-rate discharge capacity of 219mAh/g, a 0.2C-rate discharge capacity of 214mAh/g, a 0.5C-rate discharge capacity of 205mAh/g, and a 1C-rate discharge capacity of 198mAh/g in the voltage range of 3.0 to 4.3V. The lithium ion battery C1 has a 0.1C rate discharge capacity of 226mAh/g, a 0.2C rate discharge capacity of 221mAh/g, a 0.5C rate discharge capacity of 211mAh/g and a 1C rate discharge capacity of 203mAh/g in a voltage range of 3.0-4.3V. The lithium ion battery C2 has a 0.1C rate discharge capacity of 225mAh/g, a 0.2C rate discharge capacity of 219mAh/g, a 0.5C rate discharge capacity of 210mAh/g and a 1C rate discharge capacity of 203mAh/g in a voltage range of 3.0-4.3V. Compared with the liquid lithium ion battery DC1, the discharge capacity is increased at each multiplying power, which shows that the multiplying power performance is improved after coating.
Fig. 6 is a graph showing the rate performance of the liquid lithium ion battery C3 and DC2 assembled from the positive electrode material A3 prepared in example 3 and the positive electrode material D2 prepared in comparative example 2, and it can be seen from fig. 6 that the liquid lithium ion battery DC2 has a 0.1C rate discharge capacity of 178mAh/g, a 0.2C rate discharge capacity of 175mAh/g, a 0.5C rate discharge capacity of 169mAh/g, and a 1C rate discharge capacity of 164mAh/g in the voltage range of 3.0 to 4.3V. The liquid lithium ion battery C3 has a 0.1C rate discharge capacity of 183mAh/g, a 0.2C rate discharge capacity of 180mAh/g, a 0.5C rate discharge capacity of 174mAh/g and a 1C rate discharge capacity of 168mAh/g in a voltage range of 3.0-4.3V. Compared with the liquid lithium ion battery DC2, the discharge capacity is increased at each multiplying power, which shows that the multiplying power performance is improved after coating.
As can be seen from table 1, the liquid lithium ion batteries assembled from the cathode materials prepared in examples 1 to 8 have higher rate performance than the liquid lithium ion batteries assembled from the cathode materials prepared in comparative examples 1 to 4.
Test example 2
The positive electrode materials prepared in example 4 and comparative example 2 were used as positive electrodes for assembling solid-state lithium ion batteries, in which PEO-Li 1.3Al0.3Ti1.7(PO4)3 was used as a composite solid-state electrolyte. And obtaining a solid-state lithium ion battery C9 and DC5. The discharge capacity of the battery at 0.1C rate was tested in the voltage range of 3.0-4.3V, and the results are shown in table 3.
TABLE 3 Table 3
Battery cell |
0.1C/mAh/g |
C9 |
182 |
DC5 |
173 |
Fig. 7 is a charge-discharge graph of solid lithium ion batteries C9 and DC5 assembled from positive electrode material A4 and positive electrode material D3 at a 0.1C rate, and as can be seen from fig. 7, the solid lithium ion battery DC5 has a 3.0-4.3V voltage range, and the 0.1C rate discharge capacity is 173mAh/g as shown in fig. 6. The discharge capacity of the solid-state lithium ion battery C9 is 182mAh/g as shown in figure 6 in the voltage range of 3.0-4.3V, and the discharge capacity is obviously higher than that of the solid-state lithium ion battery DC5, which shows that after coating, the interface performance between the solid-state electrolyte electrode and the electrolyte is improved.
The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a number of simple variants of the technical solution of the invention are possible, including combinations of the individual technical features in any other suitable way, which simple variants and combinations should likewise be regarded as being disclosed by the invention, all falling within the scope of protection of the invention.