Application of a molybdenum-doped nanocellulose-based lithium manganese silicate as a positive electrode active material in lithium-ion batteries

Abstract

The present invention relates to the application of a molybdenum-doped nanocellulose-based lithium manganese silicate composite positive electrode material in a lithium ion battery. The present invention introduces transition metal Mo to change the electronic environment around manganese ions in Li2MnSiO4 and adjust its electronic conductivity. At the same time, the present invention introduces nanocellulose as a carbon source to improve the electronic conductivity of Li2MnSiO4. The composite positive electrode material of the present invention is used as a positive electrode material for lithium ion batteries, and has high structural stability, high discharge specific capacity and good cycle stability.

Description

Technical Field

[0001] The invention relates to application of a novel molybdenum-doped nano-cellulose-based lithium manganese silicate composite positive electrode material in a lithium ion battery, and belongs to the field of chemical power source materials and lithium ion batteries. Background Art

[0002] Lithium-ion batteries have the advantages of high voltage platform, high specific energy, small self-discharge coefficient, no memory effect, long cycle life, good safety performance, light weight and environmental friendliness. They have broad application prospects in the fields of electric vehicles and hybrid electric vehicles. Lithium-ion batteries achieve the conversion of chemical energy into electrical energy through the movement of lithium ions between the positive and negative electrodes. The more mature lithium-ion battery positive electrode material systems can be roughly divided into two categories: one is transition metal oxides, including layered structured LiCoO2, ternary materials Li(Ni x Co y Mn 1-x-y )O2 and spinel structure LiMn2O4, LiNi 0.5 Mn 1.5 O4; one is the polyanion positive electrode material, including olivine structure LiMPO4 (M = Fe, Mn, Co, Ni) and orthosilicate system Li2MSiO4 (M = Fe, Mn, Co, Ni). Among them, Li2MnSiO4 can theoretically release two Li + , with a theoretical specific capacity of up to 333mAh / g, and due to its good environmental affinity, low price, and high voltage platform, it has become one of the cathode materials with development prospects. However, since the [MnO4] tetrahedron is surrounded by the [SiO4] tetrahedron, and the conductivity of [SiO4] is poor, this leads to very low electronic conductivity of Li2MnSiO4. Moreover, during the charge and discharge process of Li2MnSiO4, it is affected by the Jan-Taylor effect, accompanied by large volume changes and changes in crystal structure, and has poor cycle stability. Therefore, improving the electronic conductivity and structural stability of Li2MnSiO4 cathode materials has become a research hotspot and difficulty. Summary of the invention

[0003] In order to solve the above technical problems, the present invention synthesized a molybdenum-doped nanocellulose-based lithium manganese silicate composite positive electrode material Mo-LMS / CNF, and applied it to the field of lithium-ion batteries for the first time to explore its application possibility in lithium-ion batteries. The composite positive electrode material in the present invention is used as a positive electrode material for lithium-ion batteries, and has high structural stability, high discharge specific capacity and good cycle stability.

[0004] The technical solution of the present invention is as follows:

[0005] Application of molybdenum-doped nanocellulose-based lithium manganese silicate as positive electrode active material in lithium-ion batteries.

[0006] Based on the above technical solution, the method for preparing the positive electrode active material comprises the following steps:

[0007] (1) dissolving a manganese source, a molybdenum source and a lithium source in a mixed solution of ethanol, acetic acid and deionized water at a molar ratio of Mn:Mo:Li of (0.9-0.99):(0.01-0.1):2 to obtain a uniform solution of the manganese source, the molybdenum source and the lithium source;

[0008] (2) adding glucose, nanocellulose (CNF) and tetraethyl orthosilicate (TEOS) to the mixed solution of manganese source, molybdenum source and lithium source obtained in step (1), stirring continuously in a water bath at 70-100° C. until a gel is formed, and then drying to obtain Li2Mn (x) Mo (1-x) SiO4 (x is 0.9-0.99) and nanocellulose composite dry gel.

[0009] (3) placing the product obtained in step (2) in an inert gas atmosphere and calcining at a temperature of 600° C. to 900° C. for 5 to 10 hours to obtain a positive electrode active material powder (Mo-LMS / CNF).

[0010] Based on the above technical solution, preferably, in step (1), the manganese source is one of Mn(CH3COO)2, MnCO3, and Mn(NO3)2; the molybdenum source is (NH4)2MoO4, MoO 12 The lithium source is one of S3, H3PO4·12MoO3, and H2MoO4; and the lithium source is one of CH3COOLi, Li2CO3, and LiOH.

[0011] Based on the above technical solution, preferably, in step (1), the molar ratio of Mn:Mo:Li is 0.97:0.03:2.

[0012] Based on the above technical solution, preferably, in step (1), the volume ratio of ethanol, acetic acid and deionized water in the mixed solution of ethanol, acetic acid and deionized water is 1:1:(1-5), preferably 1:1:3.

[0013] Based on the above technical solution, preferably, in step (2), the nanocellulose is one or more of cellulose nanocrystals, cellulose nanofibers, microcrystalline cellulose and bacterial nanocellulose.

[0014] Based on the above technical solution, preferably, in step (3), the nanocellulose is nanocellulose fibrils (with a diameter of 10-30 nm).

[0015] Based on the above technical solution, preferably, in step (2), the amount of glucose used is relative to Li2Mn (x) Mo (1-x) The amount of nanocellulose is 5%-20% of the mass of SiO4, and the amount of nanocellulose is (x) Mo (1-x) 5%-20% by mass of SiO4, the TEOS and Li2Mn (x) Mo (1-x) The molar ratio of SiO4 is (1-1.5):1, preferably 1:1.

[0016] Based on the above technical solution, preferably, in step (2), the stirring time is 1-5 hours, until a gel is formed.

[0017] Based on the above technical solution, preferably, in step (3), the inert gas is nitrogen or argon.

[0018] Beneficial Effects

[0019] The present invention introduces the transition metal Mo to change the electronic environment around the manganese ions in Li2MnSiO4 and adjust its electronic conductivity. At the same time, the present invention introduces nanocellulose as a carbon source to improve the electronic conductivity of Li2MnSiO4. The abundant oxygen-containing functional groups on the surface of nanocellulose can coordinate or hydrogen bond with the transition metal, thereby forming a carbon-based composite with a more firmly bonded and more stable structure; nanocellulose is a one-dimensional nanomaterial that can provide a "wire-to-wire" connection between particles, thereby improving the electronic conductivity of the material; in addition, nanofibers have a high porosity, which can effectively alleviate the volume expansion problem of the positive electrode material during the charge and discharge process, and can further provide a fast channel for ion transmission.

[0020] Under the combined effect of Mo element regulation and nanocellulose, the initial specific capacity of the composite cathode material can reach up to 235 mAh / g, and it still maintains 93.3 mAh / g after 100 cycles (see Figure 1 ), which is much higher than that of conventional carbon-coated Li2MnSiO4 (almost 0 after 100 cycles), indicating that the Mo element adjustment and the composite modification of nanocellulose can indeed improve the electrochemical performance of Li2MnSiO4. Figure 2 It can be seen that the rate performance of the composite positive electrode material has also been improved, and the discharge specific capacity at different rates is better than that of ordinary carbon-coated Li2MnSiO4. Figure 3 The impedance test showed that the charge transfer impedance of the composite material was low, indicating that the design of the invention improved the electronic conductivity of Li2MnSiO4. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1The cycle curves of Example 1 and Comparative Example at 0.1C;

[0022] Figure 2 The rate performance of Example 1 and the comparative example;

[0023] Figure 3 The impedance curves of Example 1 and the comparative example. DETAILED DESCRIPTION

[0024] The following non-limiting embodiments may enable a person skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0025] Example 1

[0026] 0.0099 mol of Mn(CH3COO)2, 0.0001 mol of (NH4)2MoO4 and 0.022 mol of CH3COOLi were added to a mixture of 20 mL of acetic acid, 20 mL of ethanol and 30 mL of deionized water and stirred until completely dissolved. Then, 20% glucose and 20% nanocellulose fibrils (relative to Li2Mn (x) Mo (1-x) The mass of SiO4 was 20-30nm in diameter (from Northern Century Cellulose Materials Co., Ltd.), and 0.01mol of TEOS was added, stirred at 80℃ for 2h to form a sol-gel state, and then transferred to a 100℃ oven and dried for 12h to obtain a solid. After finely grinding into powder, it was placed in a tubular furnace (nitrogen) for calcination, and the temperature was raised to 650℃ at 5℃ / min and kept for 10h to obtain a composite positive electrode material powder, named Mo-LMS / CNF.

[0027] Example 2

[0028] 0.0097 mol of Mn(CH3COO)2, 0.0003 mol of (NH4)2MoO4 and 0.022 mol of CH3COOLi were added to a mixture of 20 mL of acetic acid, 20 mL of ethanol and 30 mL of deionized water and stirred until completely dissolved. Then, 20% glucose and 20% CNF (relative to Li2Mn (x) Mo (1-x) The mass of SiO4 is 20-30nm in diameter, obtained from Northern Century Cellulose Materials Co., Ltd.), and 0.01mol of TEOS is added, and the mixture is stirred at 80℃ for 2h to form a sol-gel state. The mixture is then transferred to an oven at 100℃ and dried for 12h to obtain a solid. The solid is finely ground into powder and then calcined in a tubular furnace (nitrogen). The temperature is raised to 650℃ at a rate of 5℃ / min and kept for 10h to obtain a composite positive electrode material powder.

[0029] Comparative Example

[0030] 0.01 mol of Mn(CH3COO)2 and 0.022 mol of CH3COOLi were added to a mixture of 20 mL of acetic acid, 20 mL of ethanol and 30 mL of deionized water and stirred until completely dissolved. Then, 20% glucose (relative to Li2Mn (x) Mo (1-x) The mass of SiO4 was 20-30nm in diameter (from Northern Century Cellulose Materials Co., Ltd.), and 0.01mol of TEOS was added, stirred at 80℃ for 2h to form a sol-gel state, and then transferred to a 100℃ oven and dried for 12h to obtain a solid. After finely grinding into powder, it was placed in a tubular furnace (nitrogen) for calcination, and the temperature was increased to 650℃ at 5℃ / min and kept for 10h to obtain the positive electrode powder of the control group, named LMS / C.

[0031] The above embodiments are preferred implementations of the present invention, but the implementations of the present invention are not limited to the above embodiments. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the present invention with the features of other prior arts shall fall within the protection scope of the present invention.

Claims

1. A molybdenum-doped nanocellulose-based lithium manganese silicate as a positive electrode active material in a lithium ion battery, characterized in that: The method for preparing the positive electrode active material comprises the following steps: (1) dissolving a manganese source, a molybdenum source and a lithium source in a mixed solution of ethanol, acetic acid and deionized water at a molar ratio of Mn:Mo:Li of (0.9-0.99):(0.01-0.1):2 to obtain a solution of the manganese source, the molybdenum source and the lithium source; (2) adding glucose, nanocellulose and tetraethyl orthosilicate to the solution of the manganese source, molybdenum source and lithium source obtained in step (1), stirring continuously in a water bath at 70-100° C. until a gel is formed, and then drying to obtain a composite xerogel; (3) placing the dry gel obtained in step (2) in an inert gas atmosphere and calcining at a temperature of 600° C. to 900° C. for 5 to 10 hours to obtain nanocellulose-based molybdenum-doped lithium manganese silicate powder; In step (2), the amount of glucose used is relative to Li2Mn (x) Mo (1-x) The amount of nanocellulose is 5%-20% of the mass of SiO4, and the amount of nanocellulose is (x) Mo (1-x) 5%-20% of SiO4 mass; the tetraethyl orthosilicate and Li2Mn (x) Mo (1-x) The molar ratio of SiO4 is (1-1.5):

1.

2. The use according to claim 1, characterized in that: In step (1), the manganese source is one of Mn(CH3COO)2, MnCO3, and Mn(NO3)2; the molybdenum source is (NH4)2MoO4, MoO 12 The lithium source is one of S3, H3PO4·12MoO3, and H2MoO4; and the lithium source is one of CH3COOLi, Li2CO3, and LiOH.

3. The use according to claim 1, characterized in that: In step (2), the nanocellulose is one or more of cellulose nanocrystals, cellulose nanofibers, microcrystalline cellulose and bacterial nanocellulose.

4. The use according to claim 1, characterized in that: In step (1), the volume ratio of ethanol, acetic acid and deionized water in the mixed solution of ethanol, acetic acid and deionized water is 1:1:(1-5).

5. The use according to claim 1, characterized in that: In step (3), the inert gas is nitrogen or argon.

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