High-manganese layered oxide positive electrode material and synthesis method thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a high-manganese layered oxide positive electrode material and a synthesis method thereof. Through a two-step synthesis process, solid-phase calcination pre-forming (controlling the crystallinity of a layered precursor and uniform distribution of multi-element elements) and molten salt ion exchange (regulating and controlling the composition and performance of a product) are combined, structural regulation and control of atomic-scale element dispersion-interlayer spacing optimization-controllable doping concentration are realized, the composition, lattice parameters and structure of the product are precisely regulated and controlled, and the preparation method is simple and easy to implement. Different requirements are met, and the conductivity and the structural stability in the Li < + > diffusion kinetics and cyclic process are fundamentally improved. The cost of the lithium ion battery cathode material is reduced; when the prepared positive electrode material is used for a lithium ion battery, the first specific discharge capacity under the current density of 0.1 C is larger than 250 mAh / g, the capacity retention ratio after 100 times of circulation is larger than 90%, the cost performance contradiction of an existing positive electrode material is broken, and the preparation process is free of harmful gas emission, safe and reliable.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a high-manganese layered oxide positive electrode material and a synthesis method thereof. BACKGROUND

[0002] As the core carrier of energy storage, lithium ion batteries (LIBs) realize the efficient conversion of chemical energy and electrical energy through the reversible redox reaction of electrode materials, and become the core energy storage technology in the fields of new energy vehicles, renewable energy storage power grids, etc. due to the advantages of theoretical energy density exceeding 300 Wh / kg, cycle life exceeding 1000 times and no heavy metal pollution. The technical progress of LIBs is crucial to the global green economic transformation. Especially with the explosive growth of new energy vehicle production and sales (more than 180 million vehicles worldwide in 2023), the demand for high energy density, long cycle life and low cost LIBs has surged, promoting the accelerated breakthrough of positive electrode material technology.

[0003] However, the commercial application of existing lithium ion batteries is greatly limited by positive electrode materials, including capacity bottleneck and cost pressure. On the one hand, the actual capacity of current mainstream commercial positive electrode materials such as lithium cobalt oxide (LiCoO2) and nickel-based ternary (NCM / NCA) is significantly restricted by the stability of their own crystal structure, making it difficult to break through the high capacity of 200 mAh / g (theoretical capacity 274 mAh / g) (see Adv. Energy Mater., 2021, 11, 2102028; Nat. Commun., 2020, 11, 1550). In addition, they face serious interface side reactions and irreversible structural phase changes, resulting in rapid cycle capacity decay (the capacity retention rate is often less than 80% after 100 cycles), which cannot meet the demand for long cycle life in high-end applications. At the same time, cobalt and nickel resources are scarce, expensive and easily affected by international situation fluctuations, resulting in high preparation cost, which further limits the large-scale application of these materials. On the other hand, positive electrode materials account for 50% of the total material cost and 33% of the total weight of the battery, becoming the key breakthrough for improving the "performance-price ratio" of the battery (see Nat. Energy, 2020, 5, 26-34). Developing high-performance and low-cost positive electrode materials has become the frontier of lithium ion battery technology development.

[0004] High-manganese layered oxide positive electrode materials (general chemical formula: Li x [Mn a M 1-aO2, where a is greater than or equal to 0.7, M is a metal element other than Mn in the transition metal layer), with the absolute advantage of manganese reserves (global reserves of more than 1.7 billion tons, about 35 times the reserves of cobalt and about 11 times the reserves of nickel, with a total reserve of 280 million tons in China, accounting for about 16% of the total global reserves), significant cost advantage (manganese price is about 1 / 15 of cobalt and about 1 / 5 of nickel), high capacity potential (theoretical capacity of more than 300 mAh / g, actual capacity of more than 250 mAh / g, and initial efficiency of more than 90%), environmental friendliness and weak toxicity (see Adv. Energy Mater., 2021, 11, 2102646), it becomes an ideal choice to replace cobalt and nickel-based lithium battery cathode materials on a large scale in the future, and is regarded as the core technology of the next generation of high-performance and cost-effective cathode materials.

[0005] However, such a cathode material system faces multiple technical challenges. First, the high-manganese layered oxide cathode is caused by a high proportion of high-spin trivalent manganese ions (Mn 3+ ) to cause strong Jahn-Teller distortion, resulting in octahedral coordination distortion and lattice distortion, resulting in lower intrinsic structural stability, which is prone to collapse of the layered structure to spinel or rock salt phase structure during electrochemical cycling, accompanied by dissolution of Mn 2+ and other metal ions, causing irreversible capacity and performance decay. For example, the capacity retention rate of traditional manganese-based layered cathodes is only about 70% after 100 cycles (see Adv. Mater., 2022, 34, 2106171). Second, when the charge and discharge voltage exceeds 4.5V (vs Li / Li + ), the lattice oxygen ions (O 2- ) in the structure of the high-manganese layered oxide cathode will undergo redox reactions, causing oxygen ion migration and weakening of the interlayer bond, further exacerbating structural collapse and electrolyte decomposition, exacerbating structural instability, structural damage and performance decay, forming a vicious cycle. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a high-manganese layered oxide cathode material and a synthesis method thereof. By adjusting the solid-phase calcination temperature and time, a layered precursor with good crystallinity and highly uniform distribution of metal elements is formed; by adjusting the molten salt system, ion exchange temperature and time, a high-performance high-manganese layered oxide product is obtained; by precisely adjusting the type of doped elements and the element ratio of Mn-Ni-D, the structural distortion of Mn 3+ and the redox of anions are fundamentally inhibited, and the material structural stability is improved. The technical scheme adopted is:

[0007] A high-manganese layered oxide cathode material, the chemical general formula of which is Li x [Mn a Nib D (1-a-b) ]O2, wherein: 0.6≤x≤1.0, 0.7≤a≤0.95, 0.05≤b≤0.2, 0.005≤(1-a-b)≤0.05; D is a doping element, including one or more of Mg, Al, Ti, Nb, W, Ta, which can anchor Mn and O elements in the transition metal layer structure, inhibit structural distortion and dissolution of Mn 3+ and improve stability.

[0008] Preferably, the D element is Mg, Al, 0.8≤x≤0.9, 0.8≤a≤0.9, 0.05≤b≤0.1.

[0009] As a further preferred, the chemical formula is Li 0.85 [Mn 0.88 Ni 0.11 Mg 0.005 Al 0.005 ]O2, the molar ratio of elements Li, Mn, Ni, Mg, Al is 0.85:0.88:0.11:0.005:0.005, by controlling the content of Li, Mn, Ni, D in the synthesis process, the lattice parameters, the proportion of constituent elements and their distribution of the layered oxide product are precisely controlled, the crystallinity, conductivity, stability and performance of the material are improved, and the synergistic effect of Mn main active center (88%), Ni conductive bridge (11%), Mg and Al structure anchoring (each 0.5%) is realized.

[0010] A synthesis method of a high-manganese layered oxide positive electrode material, comprising the following steps:

[0011] (1) Dissolve the soluble manganese source, the soluble nickel source, the soluble magnesium source, and the soluble aluminum source into aqueous solutions, respectively, and add them into an aqueous solution of sodium carbonate Na2CO3 or sodium hydroxide NaOH in the order of the required chemical formula content drop by drop, to synthesize carbonate or hydroxide precipitates containing Mn, Ni, and D elements, filter out the precipitates and dry them; after drying, mix them with sodium carbonate in the content corresponding to the required chemical formula and ethanol, and then calcine and keep warm in an air atmosphere to obtain a layered precursor with highly uniform distribution of metal elements;

[0012] Alternatively, mix the carbonate or hydroxide precursor containing only Mn and Ni or the manganese source and the nickel source with the doping source and sodium carbonate in the content required by the chemical formula, and then ball mill them with ethanol; then calcine and keep warm in an air atmosphere to obtain a layered precursor with highly uniform distribution of metal elements;

[0013] (2) Mix the layered precursor prepared in step (1) with a molten salt of lithium uniformly, and calcine in an air atmosphere;

[0014] (3) After calcination and cooling to room temperature, the fused salt and soluble product are removed by washing and vacuum drying to obtain the high-manganese layered oxide positive electrode material.

[0015] Preferably, the soluble manganese source is any one or mixture of manganese sulfate MnSO4, manganese nitrate Mn(NO3)2, manganese acetate Mn(CH3COO)2; the soluble nickel source is any one or mixture of nickel sulfate NiSO4, nickel nitrate Ni(NO3)2, nickel acetate Ni(CH3COO)2; the soluble magnesium source is any one or mixture of magnesium sulfate MgSO4, magnesium nitrate Mg(NO3)2; the soluble aluminum source is any one or mixture of aluminum sulfate Al2(SO4)3, aluminum nitrate Al(NO3)3; the doping source can also be an insoluble oxide, preferably MgO, Al2O3, TiO, Nb2O5, WO3, Ta2O5.

[0016] Preferably, the rotation speed during ball milling is 300-500 rpm, and the ball milling time is at least 2 hours, and the grain size of the obtained precursor is 50-200 nm.

[0017] Preferably, excess ethanol is used for ball milling to ensure complete immersion.

[0018] Preferably, in the step (1), the temperature is raised to 700-950 ℃ at a rate of 5 ℃ / min during calcination, and the temperature is maintained for at least 12 hours.

[0019] Preferably, the molten salt system comprises LiCl-KCl or LiCl-LiNO3, and 0.5-1 wt% of LiF is added; the mass ratio of LiCl to KCl is 1:1, and the mass ratio of LiCl to LiNO3 is 9:1; the mass ratio of the layered precursor to the molten salt of lithium is 1:5-15.

[0020] Preferably, in the step (2), the temperature is raised to 280-500 ℃ at a rate of 5 ℃ / min in an air atmosphere, and the temperature is maintained for 6-24 hours.

[0021] Preferably, in the step (3), the precursor is washed with deionized water for 2-5 times, and then vacuum dried at 60 ℃ for 8-16 hours.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] By optimizing the ratio of Mn (as the capacity active center, a≥0.7), Ni (which can enhance the conductivity of the material, increase the valence state of Mn and stabilize the structure) and D (a structure stabilizing element), a multi-element synergistic system of "Mn main active center-Ni conductive bridge-D structure stabilization" is constructed, which can alleviate the problems of Mn 3+The Jahn-Teller distortion and lattice instability caused by anion redox, while improving electronic conductivity and structural stability.

[0024] The present application realizes the structural regulation of "atomic-level element dispersion - interlayer spacing optimization - controllable doping concentration" by a two-step synthesis process, combined with solid-state calcination preforming (controlling the crystallinity of layered precursors and the uniform distribution of multiple elements) and molten salt ion exchange (controlling the composition and performance of the product), accurately regulating the composition, lattice parameters and structure of the product, and adapting to different needs, fundamentally improving the conductivity, Li+ diffusion kinetics and structural stability during the cycle process.

[0025] The present application uses manganese in an amount of more than 70%, greatly reducing the dependence on expensive metals cobalt and nickel (Ni amount ≤20%), in line with the industry trend of "cobalt-free", and using manganese resource advantage to reduce the cost of lithium ion battery cathode material; the prepared cathode material has a first discharge specific capacity > 250 mAh / g at a current density of 0.1C, and a capacity retention rate > 90% after 100 cycles, solving the performance-price ratio contradiction of existing cathode materials.

[0026] The present application is compatible with existing commercial production processes, stabilizes Mn and O through Ni and D elements, improves the structural stability of the material during the electrochemical cycle process, realizes a long cycle capacity retention rate > 90% for 100 times (traditional manganese-based materials only 70%), and reduces the dissolution amount of metal elements such as Mn (Mn concentration in electrolyte is less than 15 ppm), and the preparation process does not produce harmful gas, which is safe and reliable. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Li 0.85 [Mn 0.88 Ni 0.11 Mg 0.005 Al 0.005 ]O2 prepared by the present application example 1;

[0028] Figure 2 X-ray diffraction pattern of Li 0.85 [Mn 0.88 Ni 0.11 Mg 0.005 Al 0.005 ]O2 prepared by the present application example 1;

[0029] Figure 3 First charge-discharge curve of Li 0.85 [Mn 0.88 Ni 0.11 Mg 0.005 Al 0.005 ]O2 prepared by the present application example 1;

[0030] Figure 4 Li 0.85 [Mn 0.88 Ni 0.11 Mg 0.005 Al 0.005 Charge-discharge cycle diagram of Li DETAILED DESCRIPTION

[0031] The accompanying drawings are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification. It will be appreciated that these drawings are given only for purposes of illustration and are not to be used to limit the scope of the application. The embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements. The details of one or more embodiments of the application are set forth herein or in the accompanying drawings with specific reference being made to the drawings in the

[0032] Example 1

[0033] A method for synthesizing a high-manganese layered oxide cathode material, comprising the following steps:

[0034] Step 1. Solid-phase calcination pre-forming

[0035] Co-precipitation-calcination: Provide manganese sulfate, nickel sulfate, magnesium sulfate, and aluminum sulfate raw materials in the required amount, respectively configure aqueous solutions, and add them drop by drop to the sodium carbonate aqueous solution in stoichiometric ratio to synthesize carbonates containing Mn, Ni, and D elements. After drying, mix with stoichiometric sodium carbonate, MgO, Al2O3, and ethanol in a ball mill, with a rotation speed of 300 rpm, and a ball milling time of 8 hours. The resulting precursor has a grain size of 200 nm;

[0036] In an air atmosphere, increase the temperature to the target temperature of 750℃ at a rate of 5℃ / min, and maintain for 12 hours, to obtain a layered precursor with good crystallinity and highly uniform distribution of metal elements;

[0037] Step 2. Molten salt ion exchange

[0038] (1) Molten salt system: includes LiCl-KCl (mass ratio 1:1, melting point 352℃), while adding 0.5wt% LiF, mix the above layered precursor with the molten salt uniformly in a mass ratio of 1:10;

[0039] (2) Exchange process: In an air atmosphere, increase the temperature to the target temperature of 280℃ at a rate of 5℃ / min, and maintain for 12 hours. After decreasing to room temperature, wash with deionized water for 3 times to remove the molten salt and soluble products, and then vacuum dry at 60℃ for 12 hours to obtain the high-manganese layered oxide product; i.e. Li 0.85 [Mn 0.88 Ni 0.11 Mg 0.005Al 0.005 ]O2.

[0040] As Figure 1 shown is the scanning electron micrograph of Li 0.85 [Mn 0.88 Ni 0.11 Mg 0.005 Al 0.005 ]O2; As Figure 2 shown is the X-ray diffraction pattern of Li 0.85 [Mn 0.88 Ni 0.11 Mg 0.005 Al 0.005 ]O2; As Figure 3 shown is the first charge-discharge curve of Li 0.85 [Mn 0.88 Ni 0.11 Mg 0.005 Al 0.005 ]O2, the first discharge capacity is 250 mAh / g at 0.1C current density; As Figure 4 shown is the charge-discharge cycle curve of Li 0.85 [Mn 0.88 Ni 0.11 Mg 0.005 Al 0.005 ]O2, the capacity retention is 98% after 100 cycles (the undoped control group is Li 0.85 [Mn 0.89 Ni 0.11 ]O2, prepared under the same conditions, the capacity retention is about 68% after 100 cycles). The Mn concentration in the electrolyte after cycling is less than 15 ppm.

[0041] Example 2

[0042] A method for synthesizing a high-manganese layered oxide positive electrode material, comprising the following steps:

[0043] Step 1. Solid-phase calcination pre-forming

[0044] (2) Direct calcination: manganese nitrate, nickel nitrate, nickel acetate, doping source magnesium nitrate, aluminum nitrate or MgO, Al2O3, and sodium carbonate are weighed according to the required chemical formula, mixed uniformly in a ball mill at 300 rpm for 8 hours;

[0045] In an air atmosphere, the temperature is increased to the target temperature of 800℃ at a rate of 5℃ / min, and the temperature is kept for 12 hours, to obtain a layered precursor with good crystallinity and highly uniform distribution of metal elements.

[0046] Step 2. Molten salt ion exchange

[0047] (1) Molten salt system: LiCl-KCl (mass ratio 1:1, melting point 352℃) with 0.5wt% LiF added, the layered precursor above was mixed with the molten salt at a mass ratio of 1:5;

[0048] (2) Exchange process: heating to the target temperature (280-500℃) at 5℃ / min in air atmosphere and holding for 6-24 hours, then washing with deionized water for 3 times to remove the molten salt and soluble products, followed by vacuum drying at 60℃ for 12 hours to obtain the high-manganese layered oxide product; i.e. Li 0.85 [Mn 0.88 Ni 0.11 Mg 0.005 Al 0.005 ]O2.

[0049] Of course, the above description is not a limitation of the present application, and the present application is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present application should also be within the scope of the present application.

Claims

1. A high-manganese layered oxide positive electrode material, characterized by, Chemical general formula is Li x [Mn a Ni b D (1-a-b) ]O2, wherein: 0.6≤x≤1.0, 0.7≤a≤0.95, 0.05≤b≤0.2, 0.005≤(1-a-b)≤0.05; D is a doping element, including one or more of Mg, Al, Ti, Nb, W, Ta.

2. The high-manganese layered oxide cathode material of claim 1, characterized in that, D element is Mg, Al, 0.8≤x≤0.9, 0.8≤a≤0.9, 0.05≤b≤0.

1.

3. The method for synthesizing a high-manganese layered oxide cathode material as described in claim 1 or 2, characterized in that, The method comprises the following steps: (1) preparing water solutions of soluble manganese source, soluble nickel source, soluble magnesium source and soluble aluminum source respectively, and adding them into water solution of sodium carbonate Na2CO3 or sodium hydroxide NaOH in the order of required chemical formula content, to synthesize carbonate or hydroxide precipitate containing Mn, Ni and D element, filter out the precipitate and dry it; after drying, mixing it with sodium carbonate in the content corresponding to the required chemical formula and ethanol by ball milling, and then calcining and keeping warm in air atmosphere to obtain layered precursor with highly uniform distribution of metal elements; or, mixing the carbonate or hydroxide precursor containing only Mn and Ni or the manganese source and nickel source with the doping source and sodium carbonate in the content corresponding to the required chemical formula, and ball milling with ethanol; and then calcining and keeping warm in air atmosphere to obtain layered precursor with highly uniform distribution of metal elements; (2) mixing the layered precursor prepared in step (1) with lithium molten salt uniformly, and calcining in air atmosphere; (3) after calcining and cooling to room temperature, washing to remove the molten salt and soluble products, and then vacuum drying to obtain high-manganese layered oxide positive electrode material.

4. The method for synthesizing a high-manganese layered oxide cathode material according to claim 3, characterized in that, The soluble manganese source is any one or mixture of manganese sulfate, manganese nitrate and manganese acetate; the soluble nickel source is any one or mixture of nickel sulfate, nickel nitrate and nickel acetate; the soluble magnesium source is any one or mixture of magnesium sulfate and magnesium nitrate; the soluble aluminum source is any one or mixture of aluminum sulfate and aluminum nitrate; and the doping source is two or more of magnesium nitrate, aluminum nitrate, MgO, Al2O3, TiO, Nb2O5, WO3 and Ta2O5.

5. The method for synthesizing a high-manganese layered oxide cathode material according to claim 3, characterized in that, During ball milling, the rotation speed is 300-500 rpm, and the ball milling time is at least 2 hours, and the grain size of the obtained precursor is 50-200 nm.

6. The method for synthesizing a high-manganese layered oxide cathode material according to claim 3, characterized in that, In step (1), excess ethanol is used for ball milling.

7. The method for synthesizing a high-manganese layered oxide cathode material according to claim 3, characterized in that, In step (1), the temperature is raised to 700-950℃ at a rate of 5℃ / min during calcining, and the temperature is kept for at least 12 hours.

8. The method for synthesizing a high-manganese layered oxide cathode material according to claim 3, characterized in that, The molten salt system comprises LiCl-KCl or LiCl-LiNO3, and 0.5-1wt% of LiF is added; the mass ratio of LiCl to KCl is 1:1, and the mass ratio of LiCl to LiNO3 is 9:1; the mass ratio of layered precursor to lithium molten salt is 1:5-15.

9. The method for synthesizing a high-manganese layered oxide cathode material according to claim 3, characterized in that, In step (2), the temperature is raised to 280-500℃ at a rate of 5℃ / min in air atmosphere, and the temperature is kept for 6-24 hours.

10. The method for synthesizing a high-manganese layered oxide cathode material according to claim 3, characterized in that, In step (3), the product is washed with deionized water for 2-5 times, and then vacuum dried at 60℃ for 8-16 hours.

Images