Strontium lanthanum manganate nanodot surface-modified lithium-manganese-rich positive electrode material, and synthesis method and application thereof

Abstract

The invention provides a strontium lanthanum manganate nanodot surface modified lithium-manganese-rich positive electrode material as well as a synthesis method and application thereof. The method comprises the following steps: dissolving La, Sr and Mn raw materials in water according to a stoichiometric ratio to prepare a strontium lanthanum manganate solution, wherein the molecular formula of the strontium lanthanum manganate solution is La0. 7Sr0. 3MnO3; mixing the lithium-rich manganese positive electrode material powder with the strontium lanthanum manganate solution, and drying to obtain mixture powder; and performing high-temperature heat treatment on the mixture powder to obtain the strontium lanthanum manganate nanodot surface modified lithium-rich manganese positive electrode material. The product disclosed by the invention has relatively high electronic conductance and keeps the stability, and the discharge capacity and the cycling stability of the lithium-rich manganese positive electrode material are improved by improving the redox reversibility of lattice oxygen. The lithium-rich manganese positive electrode material modified by 3wt% of strontium lanthanum manganate nanodots is circulated for 300 times at the charge-discharge rate of 1C, the capacity retention ratio is as high as 97.4%, and the voltage attenuation is reduced from 3.03 mV per circle to 2.66 mV. The preparation method is simple and convenient in process, is suitable for low-cost large-scale industrial production and can be widely applied to the field of lithium ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and particularly relates to a lithium-rich manganese cathode material modified by strontium lanthanum manganite nanodots, a synthesis method and an application thereof. Background Art

[0002] As the core energy storage carrier of new energy technology, the improvement of the energy density of lithium ion batteries is the key to promoting the development of electric vehicles and renewable energy. Lithium-rich manganese-based cathode materials (the chemical formula is usually xLi 2 MnO 3 ·(1 - x)LiMO 2 , where M is a transition metal such as Ni, Co, Mn, etc.) due to its unique layered composite structure, has a dual capacity contribution mechanism of both transition metal redox and lattice oxygen activation. Currently, the discharge specific capacity can reach more than 300 mAh / g, which is significantly higher than that of traditional ternary materials (NCM / NCA) and lithium iron phosphate (LFP). This characteristic makes it an ideal choice to break through the current energy density bottleneck (400 Wh / kg) of lithium ion batteries. However, problems such as capacity and voltage decay, oxygen evolution and structural phase transformation during the cycling process of this material seriously restrict its practical application.

[0003] In view of the above problems, in recent years, research teams at home and abroad have made a series of breakthroughs in aspects such as material surface modification, element doping, and preparation process optimization. Among them, surface modification can avoid the direct contact between grains and the electrolyte, reduce the side reactions between the cathode material and the electrolyte and the dissolution of transition metal elements, thereby improving the electrochemical performance of the cathode material. In addition, element doping is widely used to enhance the transition metal-oxygen bond energy and inhibit the layered-spinel phase transformation during cycling, thereby alleviating voltage decay. In terms of the preparation process, wet chemical synthesis technologies such as sol-solution method and hydrothermal method have become important means to improve lithium ion diffusion kinetics because they can precisely control the material morphology and grain size. Although significant progress has been made in the research of lithium-rich manganese-based cathode materials, their commercialization still faces multiple challenges. For example, oxygen evolution at high voltages, side reactions with the electrolyte resulting in shortened cycle life and voltage decay problems need to be further optimized by developing new material modification strategies. In the patent application No. "201711025471.8", a lithium manganate material coated with strontium lanthanum manganite is disclosed, but it is a conventional surface coating modification method. Summary of the Invention

[0004] The present invention aims to provide a lithium-rich manganese cathode material modified by strontium lanthanum manganite nanodots, a synthesis method and an application thereof, so as to alleviate the problems of capacity and voltage decay existing in the lithium-rich manganese cathode material during cycling.

[0005] To achieve the object of the present invention, the technical solution provided by the present invention is: a synthesis method of a lithium-rich manganese cathode material modified by strontium lanthanum manganate nanodots, comprising the following steps:

[0006] 1) Prepare a lithium-rich manganese cathode material xLi 2 MnO 3 ·(1-x)LiMO 2 , where M is one or more of transition metals Ni, Mn, Co, and 0≤x≤1;

[0007] 2) Dissolve La, Sr, and Mn raw materials in water according to the stoichiometric ratio to prepare a strontium lanthanum manganate solution, with the molecular formula La 0.7 Sr 0.3 MnO 3 ;

[0008] 3) Mix the lithium-rich manganese cathode material powder and the strontium lanthanum manganate solution evenly according to a certain mass ratio, and dry to obtain a mixture powder;

[0009] 4) Heat-treat the mixture powder at a high temperature to obtain a lithium-rich manganese cathode material modified by strontium lanthanum manganate nanodots.

[0010] Preferably, in the above step 2), the raw materials for preparing the strontium lanthanum manganate solution are one or more of acetates, nitrates, and sulfates of La, Sr, and Mn; according to the stoichiometric ratio shown in the molecular formula La 0.7 Sr 0.3 MnO 3 , dissolve La, Sr, and Mn salts in water at room temperature and stir well to prepare a strontium lanthanum manganate solution, where the concentration of La 0.7 Sr 0.3 MnO 3 is 1-3 mol / L.

[0011] Preferably, in the above step 3), the mass ratio of strontium lanthanum manganate to the lithium-rich manganese cathode material powder is controlled to be 1% - 5%; the mixture is dried in an oven at 50 - 100 °C for 24 - 48 hours to obtain a dried mixture powder.

[0012] Preferably, in the above step 4), the high-temperature heat treatment temperature of the mixture powder is 500 - 800 °C, and the time is 2 - 5 hours: first grind the mixture powder obtained in step 3 for 1 - 3 hours, then raise the temperature to the target temperature in a muffle furnace at a heating rate of 3 °C / min for high-temperature heat treatment, and finally cool naturally to room temperature to obtain a lithium-rich manganese cathode material modified by strontium lanthanum manganate nanodots.

[0013] The lithium-rich manganese cathode material modified by strontium lanthanum manganate nanodots prepared by the above synthesis method.

[0014] Application of the lithium-rich manganese cathode material modified by strontium lanthanum manganite nanodots on the surface in the field of lithium-ion batteries.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] 1. The present invention synthesizes a lithium-rich manganese cathode material modified by strontium lanthanum manganite nanodots on the surface by a low-cost process. The strontium lanthanum manganite nanodots can not only make the cathode-electrolyte interface have high electronic conductivity and maintain its stability, but also improve the redox reversibility of lattice oxygen, and finally improve the discharge capacity and cycle stability of the lithium-rich manganese cathode material. Taking the lithium-rich manganese cathode material modified by 3wt% strontium lanthanum manganite as an example, it is cycled 300 times at a charge-discharge rate of 1C, and the capacity retention rate is as high as 97.4%. However, the capacity retention rate of the unmodified material is only 62.3% after 300 cycles.

[0017] 2. The method for preparing the strontium lanthanum manganite solution in the present invention is simple, and the surface modification process is convenient, which is suitable for large-scale industrial production at low cost.

[0018] 3. The cathode material prepared by the present invention can be widely applied in the field of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the XRD pattern of the lithium-rich manganese material without surface modification and the surface-modified lithium-rich manganese material in Example 3;

[0020] Figure 2 is the SEM image of the surface-modified lithium-rich manganese material in Example 3;

[0021] Figure 3 is the TEM image of the surface-modified lithium-rich manganese material in Example 3;

[0022] Figure 4 is the cycle performance of the lithium-rich manganese material without surface modification and the surface-modified lithium-rich manganese materials in Examples 1-3 at a charge-discharge rate of 1C;

[0023] Figure 5 is the charge-discharge curve of the lithium-rich manganese material without surface modification;

[0024] Figure 6 is the charge-discharge curve of the surface-modified lithium-rich manganese material in Example 3;

[0025] Figure 7 is the comparison chart of the discharge voltage stability of the lithium-rich manganese material without surface modification and the surface-modified lithium-rich manganese material in Example 3. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The present invention will be described in detail below with reference to the drawings and embodiments.

[0027] Example 1. A lithium-rich manganese cathode material modified by lanthanum strontium manganite nanodots is prepared by the following synthesis method:

[0028] 1) Prepare the lithium-rich manganese cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 ;

[0029] 2) At room temperature, dissolve La, Sr, and Mn acetates in water according to the stoichiometric ratio shown by the chemical formula La 0.7 Sr 0.3 MnO 3 and stir well to prepare a lanthanum strontium manganite solution. Among them, the concentration of La 0.7 Sr 0.3 MnO 3 is 2 mol / L;

[0030] 3) Add the lithium-rich manganese cathode material powder to the lanthanum strontium manganite solution and stir well. Among them, the mass ratio of lanthanum strontium manganite La 0.7 Sr 0.3 MnO 3 to the lithium-rich manganese cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 powder is 1%. Then dry the mixture in an oven at 80 °C for 24 hours to obtain a dry mixture powder;

[0031] 4) First, grind the mixture powder obtained in step 3 for 2 hours, then heat-treat the mixture powder in a muffle furnace at a heating rate of 3 °C / min to 700 °C and hold for 2 hours, and finally cool naturally to room temperature to obtain the lithium-rich manganese cathode material modified by lanthanum strontium manganite nanodots.

[0032] Example 2. A lithium-rich manganese cathode material modified by lanthanum strontium manganite nanodots is prepared by the following synthesis method:

[0033] 1) Prepare the lithium-rich manganese cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 ;

[0034] 2) At room temperature, according to the chemical formula La 0.7 Sr 0.3 MnO 3The stoichiometric ratio is used to dissolve lanthanum acetate, strontium acetate, and manganese acetate in water at room temperature and stir well to prepare a strontium lanthanum manganate solution. Among them, La 0.7 Sr 0.3 MnO 3 has a concentration of 2 mol / L;

[0035] 3) Add the lithium-rich manganese cathode material powder to the strontium lanthanum manganate solution and stir well. Among them, strontium lanthanum manganate La 0.7 Sr 0.3 MnO 3 relative to the lithium-rich manganese cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 powder has a mass ratio of 2%. Then dry the mixture in an oven at 80 °C for 24 hours to obtain a dry mixture powder;

[0036] 4) First, grind the mixture powder obtained in step 3 for 2 hours, then heat-treat the mixture powder in a muffle furnace at a heating rate of 3 °C / min to 700 °C and hold for 2 hours, and finally cool naturally to room temperature to obtain a lithium-rich manganese cathode material surface-modified with strontium lanthanum manganate nanodots.

[0037] Example 3, a lithium-rich manganese cathode material surface-modified with strontium lanthanum manganate nanodots, is prepared by the following synthesis method:

[0038] 1) Prepare a lithium-rich manganese cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 by spray drying and solid-phase sintering;

[0039] 2) At room temperature, according to the chemical formula La 0.7 Sr 0.3 MnO 3 The stoichiometric ratio is used to dissolve lanthanum acetate, strontium acetate, and manganese acetate in water at room temperature and stir well to prepare a strontium lanthanum manganate solution. Among them, La 0.7 Sr 0.3 MnO 3 has a concentration of 2 mol / L;

[0040] 3) Add the lithium-rich manganese cathode material powder to the strontium lanthanum manganate solution and stir well. Among them, strontium lanthanum manganate La 0.7 Sr 0.3 MnO 3 relative to the lithium-rich manganese cathode material Li 1.2 Ni 0.13 Co 0.13 Mn0.54 O 2 The mass ratio of the powder is 3%. Then the mixture is dried in an oven at 80 °C for 24 hours to obtain a dried mixture powder;

[0041] 4) First, grind the mixture powder obtained in step 3 for 2 hours, then heat-treat the mixture powder in a muffle furnace at a heating rate of 3 °C / min to 700 °C and hold for 2 hours, and finally cool naturally to room temperature to obtain a lithium-rich manganese cathode material with lanthanum strontium manganite nanodots on the surface.

[0042] Example 4, a lithium-rich manganese cathode material with lanthanum strontium manganite nanodots on the surface, is prepared by the following synthesis method:

[0043] 1) Prepare a lithium-rich manganese cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 ;

[0044] 2) At room temperature, dissolve La, Sr, and Mn nitrates in water according to the stoichiometric ratio shown by the chemical formula La 0.7 Sr 0.3 MnO 3 and stir well to prepare a lanthanum strontium manganite solution. Among them, the concentration of La 0.7 Sr 0.3 MnO 3 is 1 mol / L;

[0045] 3) Add the lithium-rich manganese cathode material powder to the lanthanum strontium manganite solution and stir well. Among them, the mass ratio of lanthanum strontium manganite La 0.7 Sr 0.3 MnO 3 relative to the lithium-rich manganese cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 powder is 1%. Then dry the mixture in an oven at 80 °C for 24 hours to obtain a dried mixture powder;

[0046] 4) First, grind the mixture powder obtained in step 3 for 2 hours, then heat-treat the mixture powder in a muffle furnace at a heating rate of 3 °C / min to 700 °C and hold for 2 hours, and finally cool naturally to room temperature to obtain a lithium-rich manganese cathode material with lanthanum strontium manganite nanodots on the surface.

[0047] Example 5, a lithium-rich manganese cathode material with lanthanum strontium manganite nanodots on the surface, is prepared by the following synthesis method:

[0048] 1) Prepare the lithium-rich manganese cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 ;

[0049] 2) At room temperature, dissolve La, Sr, and Mn sulfates in water according to the stoichiometric ratio shown in the chemical formula La 0.7 Sr 0.3 MnO 3 and stir well to prepare the strontium lanthanum manganate solution. Among them, the concentration of La 0.7 Sr 0.3 MnO 3 is 1 mol / L;

[0050] 3) Add the lithium-rich manganese cathode material powder to the strontium lanthanum manganate solution and stir well. Among them, the mass ratio of strontium lanthanum manganate La 0.7 Sr 0.3 MnO 3 to the lithium-rich manganese cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 powder is 1%. Then dry the mixture in an oven at 80 °C for 24 hours to obtain a dry mixture powder;

[0051] 4) First, grind the mixture powder obtained in step 3 for 2 hours, then heat-treat the mixture powder in a muffle furnace at a heating rate of 3 °C / min to 700 °C and hold for 2 hours, and finally cool naturally to room temperature to obtain the lithium-rich manganese cathode material surface-modified with strontium lanthanum manganate nanodots.

[0052] Example 6, a lithium-rich manganese cathode material surface-modified with strontium lanthanum manganate nanodots, is prepared by the following synthesis method:

[0053] 1) Prepare the lithium-rich manganese cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 ;

[0054] 2) At room temperature, dissolve La, Sr, and Mn sulfates in water according to the stoichiometric ratio shown in the chemical formula La 0.7 Sr 0.3 MnO 3 and stir well to prepare the strontium lanthanum manganate solution. Among them, the concentration of La 0.7 Sr 0.3 MnO3 The concentration is 2 mol / L;

[0055] 3) Add the lithium-rich manganese cathode material powder to the strontium lanthanum manganite solution and stir well. Among them, the mass ratio of strontium lanthanum manganite La 0.7 Sr 0.3 MnO 3 relative to the lithium-rich manganese cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 powder is 1%. Then dry the mixture in an oven at 80 °C for 24 hours to obtain a dry mixture powder;

[0056] 4) First, grind the mixture powder obtained in step 3 for 2 hours, then heat-treat the mixture powder in a muffle furnace at a heating rate of 3 °C / min to 700 °C and hold for 2 hours, and finally cool naturally to room temperature to obtain a lithium-rich manganese cathode material surface-modified with strontium lanthanum manganite nanodots.

[0057] In the above examples, the lithium-rich manganese cathode material surface-modified with strontium lanthanum manganite nanodots in Example 3 has the best cycle stability and is the best example.

[0058] The test results are as follows:

[0059] As Figure 1 shown, the XRD pattern of the surface-modified lithium-rich manganese cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 (LRMO) in Example 3 shows that the surface modification does not change the phase of the initial lithium-rich manganese material, and a weak signal of strontium lanthanum manganite is also observed in the XRD pattern of Example 3, indicating the formation of a composite phase.

[0060] As Figure 2 shown, the scanning electron microscope image of Example 3 shows that the crystal grains are relatively uniform and the crystal grain size is between 100 and 300 nm.

[0061] As Figure 3 shown, the transmission electron microscope image of Example 3 shows that the size of the strontium lanthanum manganite nanodots is less than 12 nm in the thickness direction and less than 35 nm on the plane.

[0062] As Figure 4As shown, the cycling stability at room temperature, within a voltage window of 2 - 4.8 V, and at a current of 1C indicates that as the content of lanthanum strontium manganite nanodots increases, the cycling stability of the lithium-rich manganese cathode material gradually improves. Among them, the initial discharge specific capacity of the lithium-rich manganese cathode material modified with 3 wt% lanthanum strontium manganite is 219 mAh / g. It is cycled 300 times at a charge-discharge rate of 1C, and the capacity retention rate is as high as 97.4%. While the capacity retention rate of the material without surface modification is only 62.3% after 300 cycles.

[0063] Figure 5 and Figure 6 are the charge-discharge curves of the lithium-rich manganese materials without surface modification and with surface modification in Example 3, respectively, when cycled 300 times at a rate of 1C. It can be clearly found from the charge-discharge curves near the cut-off voltage that the lithium-rich manganese material with surface modification in Example 3 exhibits significantly improved lattice oxygen redox reversibility.

[0064] Figure 7 show the discharge voltage stability of the lithium-rich manganese materials without surface modification and with surface modification in Example 3. The median voltages after 300 cycles at 1C are 2.77 and 2.89 V, respectively, and the voltage decay per cycle is 3.03 mV and 2.66 mV, respectively. This shows that the surface modification with lanthanum strontium manganite nanodots can not only stabilize the discharge capacity but also effectively inhibit voltage decay.

[0065] It should be understood that the above description is for illustrative purposes and not for limitation. By reading the above description, all embodiments and all applications other than the provided examples will be obvious to those skilled in the art.

Claims

1. A method for synthesizing a lithium-rich manganese cathode material modified with strontium lanthanum manganate nanodots, characterized in that: The following steps are involved: 1) The lithium-rich manganese positive electrode material xLi2MnO3•(1-x)LiMO2 is prepared by spray drying and solid phase sintering, where M is one or more transition metals Ni, Mn, and Co, and 0≤x≤1; 2) Dissolve La, Sr, and Mn raw materials in water according to the stoichiometric ratio to prepare lanthanum strontium manganate solution, the molecular formula of which is La 0.7 Sr 0.3 MnO3; 3) mixing the lithium-rich manganese cathode material powder and the strontium lanthanum manganate solution uniformly in a certain mass ratio, and drying to obtain a mixture powder; 4) The mixed powder is subjected to high temperature heat treatment to obtain a lithium-rich manganese positive electrode material with the surface modified with strontium lanthanum manganate nanodots.

2. The method for synthesizing the lithium-rich manganese positive electrode material modified with strontium lanthanum manganate nanodots according to claim 1, characterized in that: In the step 2), the raw materials for preparing the lanthanum strontium manganate solution are one or more of the acetates, nitrates and sulfates of La, Sr and Mn; according to the molecular formula La 0.7 Sr 0.3 La, Sr, and Mn salts are dissolved in water at room temperature and stirred thoroughly to prepare lanthanum strontium manganate solution, wherein La 0.7 Sr 0.3 The concentration of MnO3 is 1~3mol / L.

3. The method for synthesizing the lithium-rich manganese positive electrode material modified with strontium lanthanum manganate nanodots according to claim 1, characterized in that: In the step 3), the mass ratio of strontium lanthanum manganate to lithium-rich manganese positive electrode material powder is controlled to be 1% to 5%, and the mixture is dried in an oven at 50 to 100° C. for 24 to 48 hours to obtain a mixture powder.

4. The lithium-rich manganese positive electrode material modified with strontium lanthanum manganate nanodots and its synthesis method and application according to claim 1, characterized in that: In the step 4), the high-temperature heat treatment temperature is 500-800°C, and the holding time is 2-5 hours. First, the mixture powder obtained in step 3 is ground for 1-3 hours, and then the temperature is raised to the target temperature in a muffle furnace at a heating rate of 3°C / min for high-temperature heat treatment, and finally the temperature is naturally cooled to room temperature to obtain a lithium-rich manganese positive electrode material modified with strontium lanthanum manganate nanodots.

5. A lithium-rich manganese positive electrode material with surface modified strontium lanthanum manganate nanodots prepared according to the synthesis method of claim 1.

6. Application of a lithium-rich manganese positive electrode material modified with strontium lanthanum manganate nanodots prepared by the synthesis method according to claim 1 in the field of lithium-ion batteries.

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