A nickel-based cobalt-free positive electrode material and a preparation method thereof

Abstract

The application provides a nickel-based cobalt-free positive electrode material and a preparation method thereof. The positive electrode material comprises a core and a surface layer. The core is a layered structure multi-component composite lithium oxide which is doped with multiple cations and anions at transition metal sites, oxygen sites and alkali metal sites. The surface layer comprises a substance with a rock salt phase or a spinel phase having an Fm-3m or Fd-3m space group. The positive electrode material has an expression of Li a M b F c (Ni x Mg y Al z H w ) (3‑V1*c) / 3 N d O (4‑V2*d) / 2 ·E e ; wherein 0.60≤x<1.00, 0 The nickel-based cobalt-free positive electrode material has a uniform distribution of the heterostructure substance of the core cation and anion and the surface layer, and has good electrochemical comprehensive performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion secondary battery materials, in particular to a nickel-based cobalt-free positive electrode material and a preparation method thereof. BACKGROUND

[0002] To alleviate the energy crisis and environmental problems caused by fuel vehicles, nickel-rich ternary material is one of the positive electrode materials that can meet the high energy density of lithium ion batteries at present. The nickel-rich ternary positive electrode material includes nickel-rich lithium nickel cobalt manganese oxide (LiNi x Co y Mn z O2) and lithium nickel cobalt aluminum oxide (LiNi x Co y Al z O2) material, and the nickel content is generally greater than 50%. However, the higher the nickel content, the greater the disordered arrangement tendency, which leads to the occupation of lithium ions by nickel ions, causing irreversible structural changes in the material, ultimately resulting in more difficult synthesis of high-nickel ternary materials and poorer cycle performance. During charging, Ni 2+ is converted to Ni 3+ , which causes the collapse of the layered structure and poor cycle stability. The delithiation of the electrode material starts from the surface layer, and as the charging proceeds, the surface layer structure exhibits excessive delithiation, and the layered structure of the high-nickel ternary material is converted to spinel structure and inert rock salt structure, and a thick inert layer is often formed on the surface of the material after the first few charge and discharge. The severe side reactions between the strongly oxidizing transition metal ions on the surface layer and the electrolyte also cause the polarization of the battery to increase and the capacity to rapidly decay.

[0003] Due to the scarcity and strategic value of cobalt, the price has been high for a long time, and reducing the cobalt content is the primary measure to reduce the cost of NCA or NCM positive electrode materials, and developing high-nickel cobalt-free positive electrode materials has become an inevitable trend. However, cobalt-free material reduces the structural stability and electrical conductivity of the material.

[0004] Therefore, it is necessary to provide a nickel-based cobalt-free positive electrode material and a preparation method to solve the problems in the prior art. SUMMARY

[0005] Therefore, the present application provides a nickel-based cobalt-free positive electrode material and a preparation method to solve the problems of high-nickel ternary structure disordered arrangement, phase transition, and unstable surface layer structure and realize cobalt-free.

[0006] To achieve the above-mentioned purpose, the present application provides a nickel-based cobalt-free positive electrode material and a preparation method, which adopts the following technical scheme:

[0007] A nickel-based cobalt-free positive electrode material, comprising an inner core and a surface layer, the inner core comprising a multi-element composite lithium oxide with a unique R-3m layered structure, and the surface layer comprising a substance with a rock salt phase or a spinel phase with a Fm-3m or Fd-3m space group; the inner core of the positive electrode material is doped with multi-element cations and anions at transition metal sites, oxygen sites and alkali metal sites, respectively; the positive electrode material has a formula of Li a M b F c (Ni x Mg y Al z H w ) (3-V1*c) / 3 N d O (4-V2*d) / 2 ·E e ; wherein 0.60≤x<1.00, 0<y≤0.20, 0<z≤0.20, 0<w≤0.02, 0.001≤b≤0.030, 1.00≤a+b≤1.40, 0.001≤d≤0.050, 0.001≤c+e≤0.050, x+y+z+w=1, V1 and V2 are the valence of F element and N element respectively, e is the amount of substance of F element contained in the surface layer E of 1 mol of positive electrode material

[0008] Further, in the formula of the nickel-based cobalt-free positive electrode material, M is a first main group element, the doping position is 3a site, that is, the doping position is alkali metal site; the apparent charge number of F element atom is greater than 3, the ratio r F / r O of the ionic radius of F element to the ionic radius of oxygen is 0.4-0.6, the doping position is 3b site, that is, the doping position is transition metal site; the ratio r 2+ / r H of the ionic radius of H element to the ionic radius of Ni Ni is 0.7-1.1, the doping position is 3b site, that is, the doping position is transition metal site; N is an oxygen group element, the doping position is 6c site, that is, the doping position is oxygen site; the surface layer E is an F element-containing oxide or a lithium-containing compound.

[0009] A preparation method of the nickel-based cobalt-free positive electrode material, comprising the following steps:

[0010] Step (1), cation and anion doping precursor: configure nickel salt, magnesium salt, aluminum salt, H salt, N-containing substance into a mixed salt solution to carry out precipitation reaction, wash and filter to obtain a precursor slurry doped with H cation and N anion uniformly;

[0011] Step (2), metal salt of element with apparent charge number greater than 3 is premixed with precursor by wet method: nano-sized F-containing metal oxide or hydroxide is added into the precursor slurry of step (1), stirred and mixed, vacuum dried to obtain F-homogeneously-mixed premix;

[0012] Step (3), preparation of positive electrode material: the premix obtained in step (2), lithium source and M-containing compound are mechanically mixed and then high-temperature sintered to obtain the positive electrode material

[0013] Li a M b F c (Ni x Mg y Al z H w ) (3-V1*c) / 3 N d O (4-V2*d) / 2 ·E e ;

[0014] The ratio of particle size (D75-D25) / (D90-D10) of the positive electrode material ranges from 0.1 to 0.9, the ratio of specific surface area measured by laser diffraction method to that measured by nitrogen adsorption method ranges from 0.2 to 5.0, and the micro-strain F s ranges from 0.05 to 0.15%.

[0015] Further, in step (1), the nickel salt is at least one of nickel sulfate, nickel chloride, nickel nitrate, nickel oxalate and nickel acetate; the magnesium salt is at least one of magnesium sulfate, magnesium chloride, magnesium nitrate and magnesium acetate; the aluminum salt is at least one of aluminum sulfate, aluminum nitrate, aluminum chloride and aluminum oxalate; the H salt is at least one of Mn, Cr, Ti, Ga, Zr, Nb, Mo and W compounds; and the N-containing substance is at least one of Se powder, SeO2, Na2S and (NH4)2S.

[0016] Further, in step (2), the F is a metal element Zr, Ti, M O , W, V, Nb with apparent charge number greater than 3; and the addition amount of F element is calculated according to the molar ratio of F element to precursor, and the molar ratio ranges from 0.001 to 0.05.

[0017] Further, in step (3), the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium chloride, lithium acetate and lithium halide, and the M-containing compound is at least one of Na- or K-containing hydroxide, oxide, carbonate compound, acetate compound and halide.

[0018] The above technical solution of the present application at least has the following beneficial effects:

[0019] 1. The cathode material prepared by this invention uses Ni, Mg, and Al as the main elements. Based on NCA, Mg is used to replace Co, which increases the valence state of transition metal ions, generates holes, changes the band structure of the material, and thus improves its intrinsic electronic conductivity. It can also suppress nickel mixing and phase transition during charge and discharge. Furthermore, the co-doping of oxygen sites, alkali metal sites, and transition metal sites by anions and cations reduces structural mixing and improves crystal integrity and structural stability.

[0020] 2. When doping with N anions with a large ionic radius, this invention performs N doping during the precursor preparation process, achieving uniform doping of N anions;

[0021] 3. During the charging process, Ni 2+ Transformation into Ni 3+ This can lead to the collapse of the layered structure and a decrease in cycle stability; in the precursor preparation process, this invention selects Ni... 2+ Ni is doped with H ions whose ionic radii are close to those of Ni. 2+ The position of the prepared cathode material means that it does not participate in the electrochemical reaction during charging and plays a supporting role in stabilizing the crystal lattice structure.

[0022] 4. The higher the apparent charge of an ion, the higher the activation energy required for the reaction, i.e., the higher the reaction barrier, and the more difficult the reaction is to proceed. This invention introduces metal ions with an apparent charge greater than 3, allowing some to enter the crystal lattice for doping during high-temperature solid-state reactions, while others remain on the material surface to form a rock salt or spinel phase with higher thermal stability. This constructs a composite structure with both rock salt or spinel and layered phases, improving the material's structural stability while also stabilizing the surface structure, significantly enhancing the material's thermodynamic stability.

[0023] 5. When mixing additives, a wet premixing method is adopted with the precursor slurry. Compared with dry mixing, this improves the dispersion uniformity of the additives, thereby achieving uniformity of the heterogeneous structure material formed by core doping and surface layer.

[0024] 6. The cathode material prepared by this invention has low cost, simple preparation method, uniform doping of core elements with cations and anions, uniform distribution of heterostructure material on the surface, high particle uniformity, and good comprehensive electrochemical performance. Attached Figure Description

[0025] Figure 1 SEM image of the positive electrode material prepared in Example 1 of this invention;

[0026] Figure 2 SEM image of the positive electrode material prepared in Example 2 of this invention;

[0027] Figure 3 Cycling performance comparison results of the positive electrode materials of the inventive examples 1-2 and the comparative examples 1-2;

[0028] Figure 4 Rate performance comparison results of the positive electrode materials of the inventive examples 1-2 and the comparative examples 1-2. DETAILED DESCRIPTION

[0029] To make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will combine the drawings of the embodiments of the present application to clearly and completely describe the technical solutions of the embodiments of the present application. Figures 1-4 The technical solutions of the embodiments of the present application are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the described embodiments of the present application, all other embodiments obtained by those skilled in the art belong to the scope of protection of the present application.

[0030] Embodiment 1

[0031] The nickel-based cobalt-free positive electrode material of the present embodiment is Li 1.05 Na 0.01 W 0.0005 (Ni 0.904 Mg 0.060 Al 0.040 Zr 0.006 ) 0.999 Se 0.001 O 1.998 ·(Li2WO4) 0.001 , and the specific preparation method is as follows:

[0032] (1) Cation and anion doped precursor: configure nickel nitrate, magnesium sulfate, aluminum sulfate, zirconium oxide, and Se powder into a mixed salt solution according to the molar ratio Ni:Mg:Al:Zr:Se=0.9031:0.05994:0.03996:0.00599:0.001, add an alkali solution and an ammonia complexing agent solution to perform a precipitation reaction, the reaction temperature is 170℃, the pH is 11.5, the stirring speed is 215r / min, and the reaction time is 70 hours, then wash the surface impurities of the precursor with deionized water, and filter to obtain a slurry;

[0033] (2) Metal salt of an element with an apparent charge number greater than 3 and precursor wet premixing: add nano WO3 according to the molar ratio of W to precursor of 0.0015:1 in the above slurry, mix by stirring for 50min, and vacuum dry at 120℃ to obtain a precursor premixed with a metal compound with an apparent charge number greater than 3;

[0034] (3) Positive electrode material preparation: the premixed precursor obtained above, lithium hydroxide and sodium hydroxide are mechanically mixed according to a molar ratio of 1:1.05:0.01. Then sintering at 720℃ for 16h under oxygen atmosphere, crushing to obtain a positive electrode material with a ratio of (D75-D25) / (D90-D10) of 0.48, a specific surface area ratio of 1.1 measured by laser diffraction method and nitrogen adsorption method, and a micro-strain F s of 0.06%. In the present application, D50, D75, D25, D90 and D10 are particle size results measured by Mastersizer 3000 with an optical density of 9-11%, representing the particle size corresponding to the particle size distribution of 50%, 75%, 25%, 90% and 10%, respectively; the micro-strain F s is the slope of FWHMcosθ and sinθ, wherein FWHM is the half-height width of the sample obtained by X-ray diffraction test, and θ is the diffraction peak angle.

[0035] The cobalt-free positive electrode material prepared in Example 1 has a specific capacity of 210.2mAh / g at 0.2C, a rate retention rate of 90.8% at 2C, and a capacity retention rate of 94.8% after 50 cycles.

[0036] Example 2

[0037] The nickel-based cobalt-free positive electrode material of the present embodiment is Li 1.05 K 0.005 Zr 0.001 (Ni 0.955 Mg 0.02 Al 0.02 Nb 0.005 ) 0.999 S 0.003 O 1.997 ·(Li2ZrO3) 0.002 , and the specific preparation method is as follows:

[0038] (1) Cation and anion doped precursor: a mixed salt solution is prepared by mixing nickel sulfate, magnesium sulfate, aluminum sulfate, niobium oxide and Na2S according to a molar ratio of Ni:Mg:Al:Nb:S=0.954:0.01998:0.01998:0.003, adding an alkali solution and an ammonia complexing agent solution to carry out a precipitation reaction, the reaction temperature is 80℃, the pH is 11.0, the stirring speed is 300r / min, and the reaction time is 90 hours, then the surface impurities of the precursor are washed with deionized water, and the slurry is obtained by filtration;

[0039] (2) Metal salt with apparent charge number greater than 3 and precursor wet premixing: In the above slurry, nano-sized ZrO2 was added in a Zr to precursor molar ratio of 0.003:1, mixed by stirring for 60 min, and vacuum dried at 150°C to obtain a precursor premixed with a metal compound having an apparent charge number greater than 3;

[0040] (3) Preparation of positive electrode material: The above obtained premixed precursor, lithium hydroxide and potassium hydroxide were mechanically mixed in a molar ratio of 1:1.05:0.005. Then, sintering was carried out at 700°C for 14 h under an oxygen atmosphere, and the positive electrode material was obtained by crushing, with a ratio of (D75-D25) / (D90-D10) of 0.65, a specific surface area ratio of 1.3 measured by laser diffraction method and nitrogen adsorption method, and a micro-strain F s of 0.11%.

[0041] The cobalt-free positive electrode material prepared in Example 2 had a specific capacity of 215.6 mAh / g at 0.2C, a rate retention rate of 90.2% at 2C, and a capacity retention rate of 92.4% after 50 weeks of cycling.

[0042] Comparative Example 1

[0043] The nickel-based cobalt-free positive electrode material of the present comparative example was

[0044] Li 1.05 Na 0.01 W 0.0005 (Ni 0.90 Mg 0.06 Al 0.04 ) 0.999 O2·(Li2WO4) 0.001 , and the specific preparation method was as follows:

[0045] (1) Preparation of precursor: A mixed salt solution was prepared by mixing nickel nitrate, magnesium sulfate and aluminum sulfate in a molar ratio of Ni:Mg:Al=0.8991:0.05994:0.03996, and then a precipitate was obtained by adding an alkali solution and an ammonia complexing agent solution, with a reaction temperature of 170°C, a pH of 11.5, a stirring speed of 215 r / min, and a reaction time of 70 hours. The precursor was then washed with deionized water to remove surface impurities, filtered, and dried to obtain the precursor.

[0046] (2) Preparation of positive electrode material: The above obtained precursor, nano-sized WO3, lithium hydroxide and sodium hydroxide were mechanically mixed in a molar ratio of 1:0.0015:1.05:0.01. Then, sintering was carried out at 720°C for 16 h under an oxygen atmosphere, and the positive electrode material was obtained by crushing.

[0047] The cobalt-free positive electrode material prepared in Comparative Example 1 has a specific discharge capacity of 208.8 mAh / g at 0.2C, a rate retention of 89.2% at 2C, and a capacity retention of 90.5% after 50 cycles.

[0048] Comparative Example 2

[0049] The nickel-based cobalt-free positive electrode material of the present comparative example is

[0050] Li 1.05 K 0.005 Zr 0.001 (Ni 0.96 Mg 0.02 Al 0.02 ) 0.999 S 0.003 O 1.997 ·(Li2ZrO3) 0.002 , and the specific preparation method is as follows:

[0051] (1) Preparation of precursor: nickel sulfate, magnesium sulfate, and aluminum sulfate are configured into a mixed salt solution according to the molar ratio Ni:Mg:Al = 0.959:0.01998:0.01998, and an alkali solution and an ammonia water complexing agent solution are added for precipitation reaction, with a reaction temperature of 80°C, a pH of 11.0, a stirring speed of 300 r / min, and a reaction time of 90 hours. Then, the surface impurities of the precursor are washed with deionized water, and the slurry is obtained by filtration;

[0052] (2) Wet premixing of metal salt of element with apparent charge number greater than 3 and precursor: nano-sized ZrO2 is added to the above slurry according to a molar ratio of Zr to precursor of 0.003:1, and mixed by stirring for 60 min. Vacuum drying at 150°C obtains the premixed precursor of metal compound with an apparent charge number greater than 3;

[0053] (3) Preparation of positive electrode material: the premixed precursor obtained above, lithium hydroxide, and potassium hydroxide are mechanically mixed according to a molar ratio of 1:1.05:0.005. Then, sintering at 700°C for 14h under an oxygen atmosphere, and crushing to obtain the positive electrode material.

[0054] The cobalt-free positive electrode material prepared in Comparative Example 2 has a specific discharge capacity of 209.5 mAh / g at 0.2C, a rate retention of 89.7% at 2C, and a capacity retention of 89.6% after 50 cycles.

[0055] As shown in Table 1 and Figure 3 、 Figure 4 are the battery performance comparison results of the positive electrode materials of Examples 1-2 and Comparative Examples 1-2.

[0056] The 0.2C capacity, 2C rate retention, i.e. 90 week cycle retention of the positive electrode material of Example 1 are 210.2 mAh / g, 90.8%, 94.8% respectively, which are higher than 208.8 mAh / g, 89.2%, 90.5% of Comparative Example 1; the 0.2C capacity, 2C rate retention, i.e. 90 week cycle retention of the positive electrode material of Example 2 are 215.4 mAh / g, 90.2%, 92.4% respectively, which are higher than 209.5 mAh / g, 88.7%, 89.6% of Comparative Example 2; it is indicated that the positive electrode material prepared by the application has good electrochemical performance.

[0057] From Figure 1 , Figure 2 it can be seen that the positive electrode material prepared by the application has good particle uniformity.

[0058] Table 1. Residual alkali and battery performance comparison results of the positive electrode materials of Example 1-2 and Comparative Example 1-2

[0059]

[0060] The above is the preferred embodiment of the application, it should be pointed out that, for the ordinary skilled in the art, without departing from the principles of the application, can also make a number of improvements and refinements, these improvements and refinements should also be considered as the protection scope of the application.

Claims

1. A nickel-based, cobalt-free, positive electrode material, characterized in that, The positive electrode material comprises a core and a surface layer, the core comprises a multi-element composite lithium oxide with a unique R-3m layered structure, and the surface layer comprises a substance with a rock salt phase or a spinel phase with a space group of Fm-3m or Fd-3m; the core is subjected to multi-element doping of cations and anions at transition metal sites, oxygen sites and alkali metal sites respectively; the positive electrode material has an expression of Li a M b F c (Ni x Mg y Al z H w ) (3-V1*c) / 3 N d O (4-V2*d) / 2 ·E e ; wherein 0.60≤x<1.00, 0<y≤0.20, 0<z≤0.20, 0<w≤0.02, 0.001≤b≤0.030, 1.00≤a+b≤1.40, 0.001≤d≤0.050, 0.001≤c+e≤0.050, x+y+z+w=1, V1 and V2 are the valence of F elements and N elements respectively, and e is the amount of substance of F elements in the surface layer E of 1 mol of the positive electrode material. In the expression of the nickel-based cobalt-free positive electrode material, the M element is a first main group element, the doping position is 3a site; the apparent charge number of the F element atom is greater than 3, the ratio r F / O of the ion radius of the F element to the ion radius of the oxygen ion is 0.4-0.6, the doping position is 3b site; the ratio rH / rNi of the ion radius of the H element to the ion radius of Ni 2+ is 0.7-1.1, the doping position is 3b site; the N element is an oxygen group element, the doping position is 6c site; the surface layer E is an oxide containing the F element or a lithium-containing compound; The preparation method comprises the following steps: Step (1), cation and anion doped precursor: a nickel salt, a magnesium salt, an aluminum salt, an H salt, and a N-containing substance are configured into a mixed salt solution to perform a precipitation reaction, washed, and filtered to obtain a precursor slurry uniformly doped with H cations and N anions; Step (2), metal salt of an element with an apparent charge number greater than 3 and the precursor are pre-mixed in a wet manner: a nano-sized metal oxide or hydroxide containing an F element is added to the precursor slurry of step (1), stirred and mixed, vacuum dried, and F uniformly mixed pre-mixed material is obtained; Step (3), cathode material preparation: the premix obtained in step (2), a lithium source and a compound containing M are mechanically mixed and then subjected to high-temperature sintering to obtain a cathode material Li a M b F c (Ni x Mg y Al z H w ) (3-V1*c) / 3 N d O (4-V2*d) / 2 ·E e ; The particle size (D75-D25) / (D90-D10) of the positive electrode material is in the range of 0.1-0.9, the specific surface area ratio measured by laser diffraction method and nitrogen adsorption method is 0.2-5.0, and the micro-strain Fs is 0.05-0.15%. The H salt is at least one of Cr, Ti, Ga, Zr, Nb, Mo, and W compounds; and the N-containing substance is at least one of Se powder, SeO2, Na2S, and (NH4)2S.

2. The method for preparing the nickel-based cobalt-free cathode material according to claim 1, characterized in that, In step (1), the nickel salt is at least one of nickel sulfate, nickel chloride, nickel nitrate, nickel oxalate, and nickel acetate; the magnesium salt is at least one of magnesium sulfate, magnesium chloride, magnesium nitrate, and magnesium acetate; and the aluminum salt is at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, and aluminum oxalate.

3. The method for preparing the nickel-based cobalt-free cathode material according to claim 1, characterized in that, In step (2), the F element is at least one of metal elements Zr, Ti, MO, W, V, and Nb with an apparent charge number greater than 3; the addition amount of the F element is calculated according to the molar ratio of the F element to the precursor, and the molar ratio is 0.001-0.

05.

4. The method for preparing the nickel-based cobalt-free cathode material according to claim 1, characterized in that, In step (3), the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium chloride, lithium acetate, and halogenated lithium, and the M-containing compound is at least one of Na- or K-containing hydroxide, oxide, carbonate compound, acetate compound, and halide.

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