Preparation method and application of carbon-coated modified spinel type lithium manganate material

Abstract

The invention discloses a preparation method and application of a carbon-coated modified spinel type lithium manganate material, and belongs to the technical field of battery materials. The method comprises the following steps: firstly, dissolving glucose hexahydrate in deionized water, and mounting a round-bottom flask filled with spinel type lithium manganate on a rotary evaporator to start rotary heating; slowly dropwise adding the obtained glucose aqueous solution into the round-bottom flask through a peristaltic pump; after the reaction is finished, opening a vacuum pump until the solvent is completely volatilized; and calcining the obtained sample in an N2 atmosphere to finally obtain the carbon-coated spinel type lithium manganate. The carbon-coated modified lithium manganate positive electrode material obtained by the method has relatively high specific discharge capacity and excellent cycling stability and rate capability, and the coated carbon protective layer not only maintains the structural stability of the material, but also improves the surface electron transmission capability of the material, and can optimize the electrochemical performance of spinel type lithium manganate.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and relates to the preparation and application of carbon-coated spinel lithium manganate. The carbon-coated modified lithium manganate improves the conductivity of the material, inhibits the dissolution of Mn, reduces the side reactions between the electrode and the electrolyte, and significantly improves the electrochemical performance. Background Art

[0002] Energy is an important material basis for social and economic development. Traditional fossil energy (coal, oil, natural gas) has greatly promoted the progress of human civilization in the past two centuries by virtue of its high energy density and rich reserves. However, with the continuous growth of global energy demand, the non-renewability of fossil energy and the environmental pollution problems generated during its development and utilization have become increasingly prominent. According to the statistical data of the International Energy Agency (IEA), the global reserves of fossil energy are expected to only meet the demand for the next 50 - 100 years. At the same time, the greenhouse gas emissions generated by the combustion of fossil fuels have become the main cause of global climate change. In this context, the development and utilization of clean energy (solar energy, geothermal energy, hydropower, wind energy, nuclear energy) have attracted much attention. These energies have significant advantages such as renewability and environmental friendliness, and play an active role in coping with energy crises and environmental protection. However, clean energy still faces many challenges in practical applications, among which the most prominent are relatively low energy density and discontinuous energy supply. To overcome the intermittency problem of clean energy, the development of efficient energy storage technologies is particularly important.

[0003] Among many energy storage technologies, lithium-ion batteries are favored due to their high energy density, long cycle life, and wide application. Among them, lithium manganate ( ) as the cathode material of lithium-ion batteries has unique advantages: its spinel structure is stable, manganese is rich in the earth's crust and has a low price, and the material preparation process is relatively simple. However, lithium manganate will show serious capacity attenuation under high-temperature and high-rate charge-discharge conditions, which greatly limits its commercial application. Research shows that the mechanisms of lithium manganate capacity attenuation mainly include the following aspects: First, side reactions occur between the electrode surface and the electrolyte, resulting in excessive growth of the solid electrolyte interface (SEI) film; second, the disproportionation reaction in the electrolyte ( ) leads to the dissolution of manganese; third, the crystal structure distortion caused by the Jahn-Teller effect leads to the destruction of the material structure; finally, the decomposition of the electrolyte under high pressure exacerbates the performance decline of the electrode material. Using 、 Methods such as coating layers can effectively inhibit manganese dissolution and side reactions. However, in existing coating technologies, methods such as ball milling and mixing still have some problems. For example, it is difficult to ensure uniform coating of all particles, and there may be local uncoated or overcoated areas; high-energy impacts may cause particle breakage or surface damage, etc. Summary of the Invention

[0004] To solve the problems existing in the prior art, the purpose of the present invention is to propose a preparation method of LMO-1C cathode material with inexpensive and easily available raw materials, simple preparation process and excellent performance. This method passes through two-step reactions of rotary evaporation and calcination to uniformly coat a carbon nanolayer on the surface of spinel lithium manganate as the cathode material for lithium-ion batteries. To achieve the above purpose, the present invention adopts the following technical solutions: A preparation method of a carbon-coated modified spinel lithium manganate material, through two-step methods of rotary evaporation and calcination, a carbon coating layer is grown on the surface of spinel lithium manganate; specifically includes the following steps:

[0005] (1) Add spinel lithium manganate to a round-bottom flask, install it on a rotary evaporator, and start rotary heating to 90°C - 100°C;

[0006] (2) Add the glucose coating solution to the flask through a peristaltic pump at a rate of 0.2 - 0.5 mL / min, and keep the reaction for 1 - 3 h;

[0007] The mass ratio of the spinel lithium manganate to glucose is 20:(0.1 - 0.4);

[0008] (3) Open the vacuum pump and keep the temperature until the water is completely evaporated to obtain a dry material;

[0009] (4) Put the above material into a tubular furnace and calcine it in an N 2 atmosphere, rise from room temperature to 450 - 500°C at a rate of 3 - 5°C / min, and heat for 4 - 6 h; wait until it cools to room temperature to obtain carbon-coated spinel lithium manganate.

[0010] Further, the mass ratio of the spinel lithium manganate to glucose is 20:(0.1 - 0.2). The preferred mass ratio is 20:0.2.

[0011] The preparation process of the glucose coating solution is: Dissolve 0.1 - 0.4 parts of C 6 H 12 O 6 ·6H 2 O in 20 parts of deionized water.

[0012] A carbon-coated modified spinel lithium manganate material is prepared by the above preparation method.

[0013] The spinel-type lithium manganate material contains an amorphous carbon layer, and the thickness of the carbon layer is 10 nm ± 3 nm.

[0014] The spinel-type lithium manganate material is applied to a lithium-ion battery.

[0015] The spinel-type lithium manganate material is used as the positive electrode material of a lithium-ion battery.

[0016] Specifically, a preparation method of a carbon-coated modified spinel-type lithium manganate material includes the following steps:

[0017] (1) Install a round-bottom distillation flask containing spinel-type lithium manganate on a rotary evaporator;

[0018] (2) Dissolve glucose hexahydrate in deionized water, and obtain a uniform glucose aqueous solution after ultrasonic treatment;

[0019] (3) Slowly add this solution to the round-bottom flask at a rate of 0.5 mL / min through a peristaltic pump, set the oil bath temperature to 90 °C, and continuously rotate for 2 hours;

[0020] (4) Open the vacuum pump to volatilize all the solvents until the material is completely dry;

[0021] (5) Place the obtained material in a tube furnace and perform heat treatment in an N 2 atmosphere. The heat treatment temperature is 500 °C, and it is maintained for 5 h. After cooling to room temperature, LMO-1C is obtained.

[0022] The LMO-1C material is used as the positive electrode material of a lithium-ion battery and is directly used for normal temperature cycling, high temperature cycling, and rate performance testing.

[0023] Compared with the prior art, the technical advantages of the present invention are as follows:

[0024] 1) Using glucose as a precursor, through a two-step method of rotary evaporation and calcination, a layer of carbon is coated on the surface of the spinel-type lithium manganate as a protective layer. This not only effectively isolates the direct contact between the electrode material and the electrolyte, reduces the reaction between the electrode material and HF in the electrolyte, inhibits the dissolution of Mn, thereby improving the structural stability of the material, but also the carbon coating layer improves the electron transfer efficiency on the surface of the material, avoiding the problem of weak conductivity.

[0025] 2) LMO-1C exhibits excellent cycle stability under both normal temperature and high temperature conditions. After 150 cycles at normal temperature, the capacity retention rate is 81.2%. After 80 cycles at high temperature, the capacity retention rate is still 79.5%, both of which are better than other comparative samples. When cycling at different rates, the voltage and capacity of LMO-1C also decay slowly. And after cycling, LMO-1C has smaller impedance and redox peak potential difference, indicating its good electrochemical activity.

[0026] 3) The XRD and XPS results after high temperature show that the carbon-coated spinel lithium manganate has more lithium intercalation active sites and forms a thinner CEI film, thus having excellent stability.

[0027] In summary, by adding glucose to the surface of spinel lithium manganate and then performing heat treatment on it, the present invention obtains lithium manganate with carbon coating. The preparation method is simple, and the raw materials are cheap and easily available. The prepared cathode material exhibits excellent stability and electrochemical activity during cycling at room temperature, high temperature, and different rates. Brief Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below.

[0029] Figure 1 X-ray diffraction patterns of LMO-1C, LMO-0.5C, LMO-2C, and LMO.

[0030] Figure 2 Scanning electron microscopy image of the carbon-coated spinel lithium manganate cathode material LMO-1C prepared by a two-step method.

[0031] Figure 3 Transmission electron microscopy image of the carbon-coated spinel lithium manganate cathode material LMO-1C prepared by a two-step method.

[0032] Figure 4 X-ray photoelectron spectroscopy of the carbon-coated spinel lithium manganate cathode material LMO-1C prepared by a two-step method and its comparative sample LMO, where (a) is the O 1s spectrum; (b) is the Mn 3s spectrum; (c) is the Mn 2p spectrum.

[0033] Figure 5 Among them, (a) is the cycling performance of LMO-1C, LMO-0.5C, LMO-2C, and LMO at 1 C at room temperature; (b) is the first charge-discharge curves of LMO-1C, LMO-0.5C, LMO-2C, and LMO; (c) is the cycling performance of LMO-1C, LMO-0.5C, LMO-2C, and LMO at 1 C and 45 °C at high temperature; (d) is the rate performance of LMO-1C, LMO-0.5C, LMO-2C, and LMO.

[0034] Figure 6Figure (a) shows the cyclic voltammograms of the carbon-coated spinel lithium manganate cathode material LMO-1C prepared by a two-step method and its comparative sample LMO before cycling; Figure (b) shows the cyclic voltammograms of the carbon-coated spinel lithium manganate cathode material LMO-1C prepared by a two-step method and its comparative sample LMO after 150 cycles at room temperature; Figure (c) shows the impedance diagrams of the carbon-coated spinel lithium manganate cathode material LMO-1C prepared by a two-step method and its comparative sample LMO before cycling; Figure (d) shows the impedance diagrams of the carbon-coated spinel lithium manganate cathode material LMO-1C prepared by a two-step method and its comparative sample LMO after 150 cycles at room temperature.

[0035] Figure 7 Figure (a) shows the X-ray diffraction patterns of LMO-1C, LMO-0.5C, LMO-2C, and LMO after 80 cycles at a high temperature of 45 °C; Figure (b) is a partially enlarged view of the (111) peak.

[0036] Figure 8 Figure shows the X-ray photoelectron spectroscopy of the carbon-coated spinel lithium manganate cathode material LMO-1C prepared by a two-step method and its comparative sample LMO after 80 cycles at a high temperature of 45 °C. Among them, Figure (a) is the F 1s spectrum; Figure (b) is the O 1s spectrum; Figure (c) is the C1s spectrum. Detailed implementation manners

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described below in conjunction with specific embodiments. However, the present invention is not limited to the following embodiments.

[0038] Example 1 Preparation of carbon-coated modification of spinel lithium manganate

[0039] Dissolve 0.2 g of C 6 H 12 O 6 ·6H 2 O in 20 g of deionized water, and perform ultrasonic treatment to obtain a uniform glucose aqueous solution;

[0040] Weigh 20 g of spinel lithium manganate in a flask, install it on a rotary evaporator, and heat it to 90 °C while rotating;

[0041] Use a peristaltic pump to slowly add the glucose aqueous solution to the flask at a rate of 0.5 mL / min. After adding, react for 2 h;

[0042] After the reaction is completed, turn on the vacuum pump until the solvent is completely evaporated to obtain a dry material;

[0043] Place the obtained material in a tubular furnace, and in N 2Calcined in an atmosphere, heated to 500 °C at a rate of 5 °C / min, held for 5 h, and after the reaction ended, it was naturally cooled to room temperature to obtain the carbon-coated lithium manganese oxide cathode material LMO-1C.

[0044] Example 2-3

[0045] To explore the influence of different coating amounts on its performance, the addition amounts of C 6 H 12 O 6 ·6H 2 O were changed to 0.1 g and 0.4 g respectively, and other conditions were the same as those in Example 1, and lithium manganese oxides with different carbon coating amounts were synthesized, and the above materials were abbreviated as LMO-0.5C and LMO-2C. At the same time, the untreated lithium manganese oxide LMO was used as a blank comparison material.

[0046] Example 4 Application of Lithium Ion Battery Cathode Material

[0047] The above-synthesized cathode material was made into a pole piece. After assembling a button battery, all electrochemical tests were carried out. First, 5.3 g of 1-methyl-2-pyrrolidone, 0.2 g of polyvinylidene fluoride, and 0.2 g of acetylene black were mixed evenly by stirring, and then 3.6 g of the prepared cathode material was added and stirred until it became a paste, and the content ratio of the solid was about 43%. After using a coater to evenly coat the slurry on the aluminum foil, the aluminum foil was placed in an oven at 80 °C and dried for 2 h. After taking it out, it was put into an electric cold rolling pair-roller machine for cold pressing. Then, a circular positive electrode piece was prepared by a punching machine, and the diameter was uniformly 14 mm. Its mass was weighed with a balance, and finally it was placed in a vacuum drying oven at 80 °C and dried for 5 h. After drying, the positive electrode piece was quickly taken out and placed in a glove box with an oxygen content and a water content lower than 1 ppm, and the button battery was started to be assembled. The battery model was CR-2016, the negative electrode and the reference electrode were lithium metal sheets with a diameter of 16 mm, and the electrolyte was LiPF 6 -based electrolyte. During assembly, first, a nickel mesh serving as a support was placed in the negative electrode case, and then the lithium metal sheet was placed on it as the negative electrode of the button battery. 35 mL of the electrolyte was dropped using a pipette, and then the separator was placed. Another 35 mL of the electrolyte was dropped to completely wet the separator, and then the side of the pole piece loaded with the positive electrode material was placed face down, and finally the positive electrode case was covered and sealed with a sealer to complete the assembly. After assembly, the battery needs to be left standing for 5 h before all electrochemical performance tests are carried out.

[0048] The testing work was carried out using a Dongguan Neware multi-channel tester. The experiment adopted a constant current and constant voltage charging and constant current discharging mode, and the charging and discharging voltage range was set to 3.0-4.3 V, where the current density corresponding to the 1C rate was 148 mAh·g -1To investigate the effect of temperature on battery performance, the tests were carried out at two temperature conditions: 25 °C (room temperature) and 45 °C. The temperature of 45 °C was precisely controlled by an incubator. The test procedures included key parameters such as charge-discharge voltage range, current density, and number of cycles to ensure comprehensive electrochemical performance data were obtained. Through systematic tests, many key electrochemical performance indicators of the material were obtained, including charge-discharge specific capacity, charge-discharge voltage plateau, cycling characteristics, and rate performance, etc.

[0049] Example 5

[0050] (1)Characterization of LMO-1C, LMO-0.5C, and LMO-2C before reaction

[0051] From Figure 1 the XRD patterns, it can be seen that there are no obvious impurity peaks or shifted peaks in LMO-1C, LMO-0.5C, and LMO-2C, indicating that the structure of the material did not damage during carbon coating and maintained good crystallinity. Figure 2 The scanning electron microscopy results show that the surface of LMO-1C is rough, with flaky and massive coatings appearing. Figure 3 The transmission electron microscopy confirmed that LMO-1C was coated with an amorphous carbon layer with a thickness of about 10 nm. From Figure 4 the O 1s spectrum in (a) thereof, it can be seen that the area ratio of oxygen vacancies in LMO-1C is higher, which helps to improve the electrochemical stability of the material. Figure 4 Both (b) and (c) of 4+ show that during the calcination process of forming the carbon coating layer, part of Mn 3+ was reduced to Mn

[0052] (2)Electrochemical performance test of LMO-1C

[0053] Figure 5The results in (a) show that after 150 cycles at a rate of 1 C at room temperature, the discharge specific capacities of LMO, LMO-0.5C, LMO-1C, and LMO-2C materials are 84.2 mAh / g, 102.9 mAh / g, 106.5 mAh / g, and 32.4 mAh / g, respectively. In contrast, LMO-1C has the highest discharge specific capacity, with a capacity retention rate of 81.2%, which is better than other samples. In (b), the initial discharge specific capacity of LMO-1C is the highest at 131.1 mAh / g, while the highest specific capacity of uncoated LMO is 124.4 mAh / g. However, when the carbon coating mass increases to 2%, the first discharge specific capacity of the LMO-2C sample drops sharply to 60.6 mAh / g, showing obvious performance degradation. In (c), after 80 cycles at a rate of 1 C at a high temperature of 45 °C, LMO-1C still has the highest discharge specific capacity of 104.0 mAh / g and a capacity retention rate of 79.5%, indicating that the crystal structure of carbon-coated spinel lithium manganate can still remain stable at high temperatures, effectively inhibiting the occurrence of interfacial side reactions. (d) shows that the discharge specific capacities of carbon-coated LMO-1C can still reach 111.8 mAh / g and 79.2 mAh / g at high rates of 5 C and 10 C, respectively, which are higher than those of LMO-0.5C, LMO-2C, and LMO, indicating that the carbon coating layer can significantly reduce the capacity decay even under high-rate conditions.

[0054] Appropriate carbon coating (0.5%-1%) can form a uniform conductive network on the surface of LMO, effectively improving the electronic conductivity of the material, enhancing the electron transport ability, and thus increasing the initial discharge specific capacity. However, excessive carbon coating (2%) will cause two adverse effects: First, the unreacted glucose molecules aggregate on the surface of LMO, and their poor conductivity greatly affects electron transport; Second, the too thick carbon layer hinders the insertion and extraction processes of lithium ions. These factors work together, ultimately resulting in a significant reduction in the initial discharge specific capacity of the material.

[0055] Figure 6In (a), the area enclosed by the cyclic voltammetry curve of LMO-1C before cycling is higher than that of LMO, further proving that its discharge specific capacity in the first cycle is higher. In (b), as the charge-discharge cycles proceed, significant differences in the degree of polarization are observed among different samples, specifically manifested as changes in the positions and peak areas of the redox peaks. After 150 cycles, the difference in the redox peak positions of LMO-1C (0.424 V) is significantly smaller than that of the unmodified LMO sample (0.443 V). This data confirms that the carbon coating modification effectively reduces the polarization voltage difference of the material, and its redox reversibility is better. In (c) and (d), LMO-1C has a smaller impedance both before and after cycling. Specifically, the ohmic resistance (Rs) and charge transfer resistance (Rct) of the LMO-1C sample before cycling are 0.95 Ω and 485.68 Ω, respectively, which are reduced by 8.65% and 8.42% compared to the uncoated LMO sample. This difference is more significant after cycling: the Rs, SEI film resistance (Rsf), and Rct of the LMO-1C sample are 2.58 Ω, 28.75 Ω, and 12.84 Ω, respectively, but still have obvious advantages compared to the LMO sample, with Rs, Rsf, and Rct reduced by 30.83%, 46.12%, and 45.85%, respectively. The experimental results show that the LMO-1C material exhibits excellent electrical conductivity characteristics, which are mainly attributed to the promotion of charge transport by the surface coating layer. The coating treatment not only effectively reduces the charge transfer resistance of the LMO material but also significantly reduces the CEI film resistance. This dual effect significantly improves the charge transfer rate of the material, thereby improving the rate performance of the material.

[0056] (3)Characterization of LMO-1C after high-temperature cycling

[0057] From Figure 7 the XRD pattern, it can be seen that the (111) peak of LMO-1C after high-temperature cycling shifts 0.06° to the right, which is significantly lower than 0.26° of LMO. This phenomenon indicates that the loss of lithium insertion active sites in the LMO-1C material is less, and the + lithium Figure 8 back-insertion ability is better maintained. From the XPS spectrum, it shows that the intensities of the LiF, C-O, and C=O peaks of LMO-1C are higher, and they are all components of the CEI film, thus proving that the carbon coating inhibits the decomposition of the electrolyte, forms a thinner CEI film on the positive electrode surface, is beneficial to the diffusion of lithium ions, and improves the cycle stability.

[0058] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a carbon-coated modified spinel lithium manganate material, characterized in that: A carbon coating layer is grown on the surface of spinel lithium manganese oxide by a two-step method of rotary evaporation and calcination. The specific steps include: (1) Add spinel lithium manganate into a round-bottom flask, install it on a rotary evaporator, and start rotating and heating to 90°C-100°C; (2) Add the glucose coating solution into the flask at a rate of 0.2-0.5 mL / min via a peristaltic pump and keep the reaction going for 1-3 hours; The mass ratio of the spinel lithium manganate to glucose is 20:(0.1-0.4); (3) Turn on the vacuum pump and maintain the temperature until the water is completely evaporated to obtain dry material; (4) The above materials are placed in a tubular furnace and calcined in a N2 atmosphere, with the temperature rising from room temperature to 450-500°C at a rate of 3-5°C / min and heating for 4-6 hours; after cooling to room temperature, carbon-coated spinel lithium manganate is obtained.

2. The method for preparing a carbon-coated modified spinel lithium manganate material according to claim 1, characterized in that: The mass ratio of the spinel lithium manganese oxide to glucose is 20:(0.1-0.2).

3. The method for preparing a carbon-coated modified spinel lithium manganate material according to claim 1, characterized in that: The mass ratio of the spinel lithium manganese oxide to glucose is 20:0.

2.

4. The method for preparing a carbon-coated modified spinel lithium manganate material according to claim 1, characterized in that: The preparation process of the glucose coating solution is as follows: 0.1-0.4 parts of C6H 12 O6·6H2O was dissolved in 20 parts of deionized water.

5. A carbon-coated modified spinel lithium manganate material, characterized in that: The method is prepared by any one of claims 1 to 4.

6. The carbon-coated modified spinel lithium manganate material according to claim 5, characterized in that: The spinel lithium manganate material comprises an amorphous carbon layer, and the thickness of the carbon layer is 10nm±3nm.

7. The use of a carbon-coated modified spinel lithium manganate material according to claim 5, characterized in that: The spinel lithium manganate material is used in lithium ion batteries.

8. The use of a carbon-coated modified spinel lithium manganate material according to claim 7, characterized in that: The spinel lithium manganate material is used as a positive electrode material for lithium ion batteries.

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