A lithium-rich / micro-lithium-rich material, a preparation method and application thereof

Abstract

The application discloses a lithium-rich / micro lithium-rich material and a preparation method and application thereof. The lithium-rich / micro lithium-rich material has a structural formula of Li 1+x Mn y Ni z N w O r ; wherein the N element is one or more of Ni, Al, Mg, Ti, Fe, Cu, Cr, Mo, Zr and Ru; the lithium-rich / micro lithium-rich material is a spherical secondary particle, the inside of which is dispersed with a 2-5 mu m spinel phase large single crystal structure, the periphery of the large single crystal structure is wrapped by a primary particle, the primary particle is in a radiating shape; and the outermost layer is a thin shell layer of the spinel phase. The material is prepared by mixing two or more than two kinds of lithium salts in a proper ratio as a molten salt with a precursor material, then performing heat treatment at the lowest melting temperature of the molten salt, and finally calcining. The material has a core-shell structure containing a spinel phase, the overall structure is stable, and when used in a lithium ion battery positive electrode material, the first coulomb efficiency, rate performance and cycle performance are comprehensively improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a lithium-rich / micro-lithium-rich material and a preparation method and application thereof. BACKGROUND

[0002] The lithium-rich manganese-based oxide positive electrode material has the advantages of high capacity, high energy density and low cost, and is expected to meet the development requirements of a new generation of power batteries. Due to the high price of cobalt, the development of lithium-rich cobalt-free positive electrode materials has become a research hotspot, and is expected to be practically applied to the next generation of high-specific-capacity lithium ion batteries as a positive electrode material.

[0003] However, such materials have a layered structure, and the cycle performance gradually highlights, which becomes a problem restricting its practical application. In addition, the problems such as large first-cycle irreversible capacity, serious oxygen release and poor rate performance of such materials greatly limit the application of the materials in lithium ion batteries. Studies have shown that the delithiation degree of the layered structure is high under high specific capacity, which leads to a dramatic change in lattice volume, resulting in stress concentration in the polycrystalline particles, and the intergranular cracks exacerbate the process of material deactivation and interface aging.

[0004] In order to overcome the above shortcomings of lithium-rich materials in the cycle process, the material usually needs to be modified. Generally, the methods for improving its electrochemical performance mainly include element doping and surface modification. In most cases, element doping and surface modification are both through the introduction of heteroatoms from the outside or the acid-base treatment of the material, which will lead to the complexity of the process for preparing the material, the increase of the cost, the harm of the addition of acid and alkali to the environment, etc. Therefore, it is necessary to develop a simple operation and more applicable modification method, which can in-situ modify the material in the process of synthesizing the material, significantly improve its electrochemical performance, and make it applicable to large-scale industrial production, which has strong practical significance. SUMMARY

[0005] The purpose of the present application is to provide a lithium-rich / micro-lithium-rich material and a preparation method and application thereof. The material has a core-shell structure containing a spinel phase, and the overall structure is stable. When used in a lithium ion battery positive electrode material, the first coulombic efficiency, rate performance and cycle performance are comprehensively improved.

[0006] In order to solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0007] A lithium-rich / micro-lithium-rich material is provided, and the structural formula is Li 1+x Mn y Ni z N w O r; wherein the N element is one or more of Ni, Al, Mg, Ti, Fe, Cu, Cr, Mo, Zr, Ru; the parameters x, y, z, w, r satisfy the following conditions: 0 < x < 0.2, 0 < y < 1, 0 < z < 1, 0 < w < 1, 1.8 < r < 3;

[0008] The lithium-rich / micro-lithium-rich material is a spherical secondary particle, and a large single crystal structure of spinel phase of 2-5 μm is dispersed in the lithium-rich / micro-lithium-rich material; the large single crystal structure is surrounded by primary particles, and the primary particles are in a form of emission; and the outermost layer of the lithium-rich / micro-lithium-rich material is a thin shell layer of spinel phase.

[0009] According to the above scheme, the thickness of the thin shell layer is 450-550 nm.

[0010] A preparation method of the lithium-rich / micro-lithium-rich material is provided, and the method comprises the following steps:

[0011] 1) mixing a molten salt and a precursor material to obtain a mixture; wherein the molten salt is two or more kinds of lithium salts in a proper ratio, and the molten salt is melted to form an ionic melt at a certain temperature;

[0012] 2) performing heat treatment on the mixture obtained in step 1) in air or oxygen at the lowest melting temperature of the molten salt, and finally calcining to obtain the lithium-rich / micro-lithium-rich material.

[0013] According to the above scheme, in step 1), the lithium salt is: a lithium nitrate and lithium hydroxide mixed system, the molar amount of lithium hydroxide accounts for 0.393 of the total molar amount; or a lithium carbonate and lithium sulfate mixed system, the molar amount of lithium carbonate accounts for 0.6 of the total molar amount; or a lithium carbonate and lithium fluoride mixed system, the molar amount of lithium carbonate accounts for 0.48 of the total molar amount; or a lithium carbonate and lithium nitrate mixed system, the molar amount of lithium carbonate accounts for 0.993 of the total molar amount; or a lithium carbonate and lithium hydroxide mixed system, the molar amount of lithium carbonate accounts for 0.843 of the total molar amount; or a lithium nitrate and lithium hydroxide mixed system, the molar amount of lithium nitrate accounts for 0.393 of the total molar amount.

[0014] According to the above scheme, in step 1), the molar ratio of lithium elements in the precursor material and the lithium salt is 1:1.02-1:1.25.

[0015] According to the above scheme: in step 1), the precursor material is a carbonate or hydroxide precursor material containing manganese, nickel, or manganese, nickel and N; wherein the N element is one or more of Ni, Al, Mg, Ti, Fe, Cu, Cr, Mo, Zr, Ru.

[0016] According to the above scheme: in step 1), the lithium salt and the precursor material are uniformly mixed by mechanical stirring or manual grinding.

[0017] According to the above scheme: in step 2), the heat treatment time is 2-5 hours.

[0018] According to the above scheme: In step 2), the calcination process is as follows: the temperature is 800-900℃, and the holding time is 12-24h. Preferably, the heating rate is 2-5℃ / min, and the product is removed after natural cooling to room temperature.

[0019] This invention provides an application of the aforementioned lithium-rich / micro-lithium-rich material as a cathode material in lithium-ion batteries.

[0020] The beneficial effects of this invention are as follows:

[0021] 1. This invention provides a lithium-rich / micro-lithium-rich material with a core-shell structure containing a spinel phase. The interior contains large single-crystal spinel phase particles, and the outermost layer is a thin shell layer of spinel phase. Compared with the traditional layered structure, this material significantly improves structural stability. When used in lithium-ion battery cathode materials, it comprehensively improves the first coulombic efficiency, rate performance, and cycle performance.

[0022] 2. This invention provides a method for preparing lithium-rich / micro-lithium-rich materials. Two or more lithium salts are mixed in a certain ratio to form a molten salt, which is then mixed with a precursor material. Utilizing the unique property that the molten salt melts simultaneously at a certain temperature to form an ionic melt, the reaction is maintained at the lowest temperature at which eutectic formation occurs. Because different ions have different binding energies with the transition metal elements in the precursor, the surface and internal structure of the micro-lithium-rich material are affected. The material is then calcined at high temperature to form a composite micro-lithium-rich material with an outer spinel shell and an inner core of large spinel single crystals. The resulting composite micro-lithium-rich material exhibits good structural stability and, when used as a cathode material in lithium-ion batteries, significantly improves the first-cycle coulombic efficiency, cycle life, and rate performance.

[0023] 3. This invention utilizes the characteristic that two or more lithium salts in a suitable molar ratio have the lowest eutectic temperature after mixing. It directly uses lithium salts as both molten salt and lithium source, avoiding the addition of traditional molten salt methods such as potassium chloride and sodium chloride, thereby avoiding the introduction of other impurity cations.

[0024] 4. The process of this invention is simple, low-cost, and produces controllable and high-purity products, which have the potential for large-scale application. Attached Figure Description

[0025] Figure 1 The images show the X-ray diffraction (XRD) patterns of the original sample obtained in Comparative Example 1 and the molten salt sample obtained in Example 1.

[0026] Figure 2 The original sample obtained from Comparative Example 1 ( Figure 2 a and 2b) and the molten salt sample obtained in Example 1 ( Figure 2Scanning electron micrographs (SEM) of c and 2d.

[0027] Figure 3 The original sample obtained from Comparative Example 1 ( Figure 3 a) and the molten salt sample obtained in Example 1 ( Figure 3 b) Thermogravimetric and differential scanning calorimetry (TG-DSC).

[0028] Figure 4 The original sample obtained from Comparative Example 1 ( Figure 4 a and 4b) and the molten salt sample obtained in Example 1 ( Figure 4 Scanning transmission electron microscopy (STEM) images of c and 4d.

[0029] Figure 5 The figures show the electrochemical performance of the original sample obtained in Comparative Example 1 and the molten salt sample obtained in Example 1; where... Figure 5 a and 5b are the electrochemical curves of the original sample and the molten salt sample, respectively; Figure 5 c shows the rate performance of the two samples; Figure 5 d shows the cycling performance of the two samples at a current density of 50 mA / g. Detailed Implementation

[0030] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0031] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0032] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available products or products that can be prepared by known methods.

[0033] Example 1:

[0034] A method for preparing micro-lithium-rich materials using molten salt is provided, comprising the following steps:

[0035] 1) Add 0.5798g Ni 0.25 Mn 0.75 CO3 precursor powder, 0.0860 g LiOH·H2O, and 0.2120 g LiNO3 (calculated by molar ratio, LiOH / (LiNO3+LiOH)=0.393, at which molar ratio the two substances can form a eutectic with a minimum eutectic temperature of 190℃) are thoroughly mixed in a ball mill. Ni 0.25 Mn0.75 The molar ratio of the CO3 precursor to the molten salt was 1:1.15, the rotation speed was 600 r / min, and the mixture was mixed for 2 h.

[0036] 2) The mixture obtained in step 1) was placed in an air condition, heated to 190°C, and kept for 3 h, and then heated to 900°C at a heating rate of 5°C / min, and kept for 10 h, and then naturally cooled to room temperature to obtain a micro-lithium-rich material, which was recorded as a molten salt sample.

[0037] Comparative Example 1

[0038] A method for preparing a micro-lithium-rich material by using a single lithium salt is provided, which comprises the following steps:

[0039] 1) 0.5798 g of Ni 0.25 Mn 0.75 CO3 precursor powder was mixed with 0.2643 g of LiOH·H2O, and then put into a ball mill for uniform mixing, the molar ratio of the Ni 0.25 Mn 0.75 CO3 precursor to lithium hydroxide was 1:1.15, the rotation speed was 600 r / min, and the mixture was mixed for 2 h.

[0040] 2) The mixture obtained in step 1) was placed in an air condition, heated to 300°C, and kept for 3 h, and then heated to 900°C at a heating rate of 5°C / min, and kept for 10 h, and then naturally cooled to room temperature to obtain a micro-lithium-rich material synthesized by using a single lithium salt, which was recorded as an original sample.

[0041] The structure of the product of the present example, the micro-lithium-rich material synthesized by using a molten salt, was determined by an X-ray diffractometer and a scanning electron microscope. The X-ray diffraction spectrum (XRD) showed that the original sample synthesized by using a single lithium salt had an α-NaFeO2 structure, and was an O3-type layered compound without obvious impurity peaks; the structure of the molten salt sample was basically the same, but the peak near 37° was split, which indicated that there was a spinel phase Figure 1 ) in the material.

[0042] Scanning electron microscopy (SEM) Figure 2 It was shown that the synthesized original sample and the molten salt sample were both spherical secondary particles with an average diameter of about 10 μm, and the surface of the particles might have a little flocculation, which might be unreacted lithium salt, etc. The morphology of the two materials did not change obviously, which indicated that the method of molten salt synthesis had no obvious effect on the morphology of the material.

[0043] Figure 3The TG-DSC of the lithium salt and the precursor mixed in proportion, respectively. It can be seen that the weight of the original sample decreases significantly when the temperature rises to about 320℃, indicating that the material reacts at this temperature; while the weight of the molten salt sample has begun to decrease significantly at about 190℃, indicating that the sample mixed with molten salt has begun to react at a lower temperature, and the combination of internal transition metal ions and lithium salt is more closely.

[0044] Figure 4 The two materials are thermal scanning transmission electron micrographs (STEM). Figure a and figure b are the scanning images of the internal cut of the original sample, which can be seen to be a structure of primary particles extending radially outward from the center. When the primary particles in the internal stack are enlarged, many irregular channels are found in the internal, and a thin layer of about 800 nm in thickness is found on the surface, which is found to be a layered phase by electron diffraction test; Figure c and figure d are the samples synthesized with molten salt, which can be seen to have large single crystal structures of about 2-5 μm in the internal, which are dispersed in the internal of secondary particles, surrounded by primary particles, and a thin layer of about 500 nm in thickness on the surface, which is found to be a spinel phase by electron diffraction test.

[0045] The electrochemical performance test of the original material and the molten salt material prepared in this example is tested by assembling a coin-type half-cell, and the cathode uses a lithium metal sheet. The cyclic voltammetry test Figure 5 a, b) shows that the cyclic voltammetry curves of the two materials are similar, except that the redox peak of the molten salt sample at 3.0V is enhanced. Figure 5 c is the rate performance graph of the two samples, which can be seen that the discharge capacity of the half-cell assembled by the molten salt material is about 270 mA / g, 250 mA / g, 240 mA / g, 200 mA / g, 160 mA / g at 0.1C, 0.2C, 0.5C, 1C, 2C current density, while the capacity of the original sample at the same current density is 270 mA / g, 220 mA / g, 170 mA / g, 150 mA / g, 120 mA / g, which shows that the material prepared by the method of molten salt has better rate performance. Figure 5 d is the cycle performance graph of the two materials at a current density of 50 mA / g, which shows that at a current density of 0.4C (1C = 250 mAh g -1 ), the capacity retention rate of the molten salt sample is 91% after 100 cycles, while the capacity retention rate of the original sample is only 88.7%. Therefore, the cycle performance of the molten salt sample is better than that of the original sample.

[0046] Example 2:

[0047] A method for preparing a lithium-rich material by molten salt is provided, comprising the following steps:

[0048] 1) 2.319 g Ni 0.25 Mn 0.75 CO3 precursor powder was mixed with 1.2588 g LiOH H2O and 0.4130 g Li2CO3 (molar ratio LiOH / (Li2CO3+LiOH) = 0.843, the molar amount of lithium hydroxide accounts for 0.843 of the total molar amount, at which the two substances can form a eutectic with a minimum eutectic temperature of 425°C) in a ball mill at a speed of 600 r / min for 4 h. 0.25 Mn 0.75 The molar ratio of the Ni

[0049] 2) The mixture obtained in step 1) was placed in air or oxygen and heated to 425°C for 3 h at a heating rate of 5°C / min, and then heated to 900°C for 10 h, and then naturally cooled to room temperature to obtain the lithium-rich material.

[0050] Example 3:

[0051] A method for preparing a micro-lithium-rich material by molten salt is provided, comprising the following steps:

[0052] 1) 0.5841 g Ni 0.5 Mn 0.5 CO3 precursor powder was mixed with 0.0881 g LiOH H2O and 0.2172 g LiNO3 (molar ratio LiOH / (LiNO3+LiOH) = 0.393, the molar amount of lithium hydroxide accounts for 0.393 of the total molar amount, at which the two substances can form a eutectic with a minimum eutectic temperature of 190°C) in a ball mill at a speed of 200 r / min for 4 h.

[0053] 2) The mixture was placed in air or oxygen and heated to 190°C for 3 h at a heating rate of 5°C / min, and then heated to 850°C for 10 h, and then naturally cooled to room temperature to obtain the micro-lithium-rich material.

[0054] Example 4:

[0055] A method for preparing a micro-lithium-rich material by molten salt is provided, comprising the following steps:

[0056] 1) 0.5841 g Ni 0.5 Mn 0.5The CO3 precursor powder was mixed with 0.1857 g LiOH·H2O and 0.0552 g Li2CO3 (LiOH / (Li2CO3+LiOH) = 0.843 in terms of molar amount, the molar amount of lithium hydroxide accounts for 0.843 of the total molar amount. At this molar ratio, the two substances can form a eutectic with a minimum eutectic temperature of 425°C) in a ball mill at a rotation speed of 200 r / min for 4 h.

[0057] 2) The mixture was heated to 425°C under air or oxygen for 3 h at a heating rate of 7°C / min, and then heated to 900°C for 12 h, and then naturally cooled to room temperature and taken out, to obtain a micro-lithium-rich material.

[0058] The above is only part of the embodiments of the present application, and does not limit the present application in any form; any equivalent changes, modifications and evolution of the above embodiments according to the essential technology of the present application are within the protection scope of the technical solutions of the present application.

Claims

1. A lithium-rich / micro-lithium-rich material, characterized in that, The structural formula of the lithium-rich / micro-lithium-rich material is Li 1+ x Mn y Ni z N w O r ; where N is one or more of Ni, Al, Mg, Ti, Fe, Cu, Cr, Mo, Zr, Ru; x, y, z, w, r satisfy the following conditions: 0 < x ≤ 0.2, 0 < y ≤ 1, 0 < z < 1, 0 ≤ w ≤ 1, 1.8 ≤ r ≤ 3; where: The lithium-rich / micro-lithium-rich material consists of spherical secondary particles, with large single-crystal structures of spinel phase dispersed inside, each 2-5 µm in size. The large single-crystal structures are surrounded by primary particles, which are arranged in a radial pattern. The outermost layer of the lithium-rich / micro-lithium-rich material is a thin shell layer of spinel phase with a thickness of 450-550 nm.

2. A method for preparing the lithium-rich / micro-lithium-rich material as described in claim 1, characterized in that, Includes the following steps: 1) A mixture is prepared by mixing molten salt with precursor material; wherein the molten salt is two or more lithium salts in appropriate proportions; The appropriate proportions of lithium salts are as follows: a mixture of lithium nitrate and lithium hydroxide, wherein the molar amount of lithium hydroxide accounts for 0.393 of the total molar amount; or a mixture of lithium carbonate and lithium sulfate, wherein the molar amount of lithium carbonate accounts for 0.6 of the total molar amount; or a mixture of lithium carbonate and lithium fluoride, wherein the molar amount of lithium carbonate accounts for 0.48 of the total molar amount; or a mixture of lithium carbonate and lithium nitrate, wherein the molar amount of lithium carbonate accounts for 0.993 of the total molar amount; or a mixture of lithium carbonate and lithium hydroxide, wherein the molar amount of lithium carbonate accounts for 0.843 of the total molar amount; or a mixture of lithium nitrate and lithium hydroxide, wherein the molar amount of lithium nitrate accounts for 0.393 of the total molar amount. 2) The mixture obtained in step 1) is heat-treated in air or oxygen at the lowest temperature at which the molten salt forms a eutectic, and then calcined to obtain lithium-rich / micro-lithium-rich material; wherein: the molten salt will melt simultaneously at the holding temperature to form an ionic melt; the heat treatment time is 2-5h; the calcination process is: temperature 800-900 ℃, holding time 12~24h.

3. The preparation method according to claim 2, characterized in that, In step 1), the molar ratio of lithium in the precursor material and lithium salt is 1:1.02 to 1:1.

25.

4. The preparation method according to claim 2, characterized in that, In step 1), the precursor material is a carbonate or hydroxide precursor material containing two elements, manganese and nickel, or three elements, manganese, nickel and N; wherein N is one or more of Ni, Al, Mg, Ti, Fe, Cu, Cr, Mo, Zr and Ru.

5. The preparation method according to claim 2, characterized in that, In step 1), the lithium salt and the precursor material are mixed evenly by mechanical stirring or manual grinding.

6. The application of the lithium-rich / micro-lithium-rich material of claim 1 as a cathode material in lithium-ion batteries.

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