Application of a halogen-containing nanocellulose-based sulfate composite cathode material in lithium-ion batteries

Abstract

The present invention relates to the application of a halogen-containing nanocellulose-based sulfate composite positive electrode material in a lithium ion battery. The present invention introduces highly electronegative halogens such as F, Cl, etc., to change the electronic environment around the transition metal and adjust its electronic conductivity. At the same time, the highly electronegative halogen ions enhance the inductive effect of the sulfate group so that the cation exhibits stronger particle properties, thereby further improving its operating voltage. The composite positive electrode material of the present invention is used as a positive electrode material for a lithium ion battery, and has low cost, high discharge specific capacity and operating voltage.

Description

Technical Field

[0001] The invention relates to application of a halogen-containing nano-cellulose-based sulfate 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 specific energy, low self-discharge coefficient, no memory effect, good safety performance and environmental friendliness, showing broad application prospects in the fields of electric vehicles and hybrid electric vehicles. Lithium-ion batteries are mainly composed of four parts: positive electrode, negative electrode, separator and electrolyte. Among them, the positive electrode material is the most expensive component, and it is also the key factor limiting the further improvement of lithium-ion battery performance. The current commercial lithium-ion battery positive electrode material system can be roughly divided into two categories: one is transition metal oxides, such as layered LiCoO2 and ternary material Li(Ni x Co y Mn 1-x-y )O2; the other is polyanion positive electrode materials, such as olivine-structured LiMPO4 (M=Fe, Mn, Co, Ni). LiCoO2, a representative of layered oxide positive electrode materials, has a high working voltage and good cycle stability, but the expensive and toxic Co element limits its further development; polyanion positive electrode materials are represented by olivine-type LiFePO4, which has low cost and good cycle stability, but its synthesis conditions are harsh and its poor conductivity leads to poor rate performance. Therefore, it is of great research significance to explore and develop new positive electrode materials.

[0003] Sulfate and its derivatives have attracted the attention of researchers due to their low cost and environmental friendliness. Since the electronegativity of S is stronger than that of P, the inductive effect promotes SO4 2- The radical will produce more than PO4 2- The group has a higher working voltage, so sulfate has a high voltage advantage, which will be beneficial to the improvement of the energy density of the positive electrode material. However, as a polyanion salt, LiMSO4 also has the disadvantage of low conductivity of polyanion salts. Therefore, how to improve its electronic conductivity becomes the key to research. Summary of the invention

[0004] In order to solve the problem of low electronic conductivity of LiMSO4, the present invention synthesizes a halogen-containing nanocellulose sulfate positive electrode material nanocellulose-based LiMSO4X, and applies it to the field of lithium-ion batteries to explore its application performance 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 low cost, high discharge specific capacity and working voltage.

[0005] The technical solution of the present invention is as follows:

[0006] Application of a halogen-containing nanocellulose-based sulfate composite positive electrode material in lithium-ion batteries.

[0007] Based on the above technical solution, the preparation method of the composite positive electrode material comprises the following steps:

[0008] (1) Dehydrating FeSO4·7H2O at a temperature of 150-250°C to obtain FeSO4·H2O;

[0009] (2) placing the halogen-containing lithium compound LiX (X=F or Cl) and the FeSO4·H2O obtained in step (1) into a high-pressure reactor, reacting in an oven at 200-400° C. for 3-5 h, recovering the dark powder after cooling, washing it multiple times to remove impurities, and drying it to obtain LiFeSO4X (X=F or Cl);

[0010] (3) Physically mixing an appropriate amount of nanocellulose with the LiFeSO4X obtained in step (2) by mechanical ball milling or ultrasound, and calcining at 700-900° C. for 4-10 h in a nitrogen or argon atmosphere to finally obtain a halogen-containing nanocellulose-based nanocellulose-based sulfate (LiMSO4X) composite positive electrode material powder.

[0011] Based on the above technical solution, preferably, in step (1), the dehydration time of FeSO4·7H2O is 1-5h.

[0012] Based on the above technical solution, preferably, in step (2), the halogen-containing lithium compound is one or both of LiF and LiCl.

[0013] Based on the above technical solution, preferably, in step (2), the molar ratio of the halogen-containing lithium compound LiX to FeSO4·H2O is (0.1-2):1, preferably (0.1-1):1.

[0014] Based on the above technical solution, preferably, in step (2), the drying temperature is 60° C. and the drying time is 5 h.

[0015] Based on the above technical solution, preferably, in step (3), the nanocellulose is one or more of cellulose nanocrystals, cellulose nanofibers, microcrystalline cellulose and bacterial nanocellulose.

[0016] Based on the above technical solution, preferably, in step (3), the nanocellulose is nanocellulose fibrils (with a diameter of 10-30 nm).

[0017] Based on the above technical solution, preferably, in step (3), the amount of the nanocellulose used is 3%-100% relative to the mass of LiFeSO4X, preferably 20%-100%.

[0018] Beneficial Effects

[0019] The present invention introduces highly electronegative halogens such as F, Cl, etc. to change the electronic environment around the transition metal and adjust its electronic conductivity. At the same time, the highly electronegative halogen ions enhance the inductive effect of the sulfate group so that the cation exhibits stronger particle properties, thereby further increasing its operating voltage.

[0020] Nanocellulose, as the most abundant polymer material in nature, has the advantages of low cost, high carbon content, and rich surface oxygen-containing functional groups. The rich oxygen-containing functional groups on the surface of nanocellulose can coordinate with transition metals or form hydrogen bonds, thereby forming a carbon-based complex with a relatively strong bond; in addition, nanocellulose is a one-dimensional nanomaterial that can provide "wire-to-wire" connections between particles, thereby improving the electronic conductivity of the material; nanofibers have a high specific surface area and porosity, which can provide a fast channel for ion transport.

[0021] Due to the strong inductive effect of halogen ions in nanocellulose-based LiMSO4X and the rich three-dimensional porous carbon network provided by nanocellulose, nanocellulose-based LiMSO4X has high electronic conductivity (the charge transfer impedance is only 80Ω, indicating high electronic conductivity, see Figure 2 ) and ion diffusion coefficient. As a positive electrode material for lithium-ion batteries, its reversible capacity is about 140 mAh g -1 and remain stable in subsequent cycles (see Figure 1 ), its operating voltage platform is as high as 3.9V, showing a high energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The cycle curve of the halogen-containing nanocellulose-based sulfate composite cathode material prepared in Example 1 at 0.2C;

[0023] Figure 2 This is the impedance curve of the halogen-containing nanocellulose-based sulfate composite positive electrode material prepared in Example 1. 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] First, 0.01 mol of FeSO4·7H2O was weighed and placed in a vacuum oven at 200°C for 10 hours to dehydrate and obtain FeSO4·H2O; then, 0.01 mol of LiF and FeSO4·H2O were placed in a high-pressure reactor and reacted in an oven at 200°C for 3 hours; the dark powder was recovered after being cooled to room temperature and washed with deionized water three times; finally, it was placed in a vacuum drying oven at 80°C for 5 hours to obtain LiFeSO4F; then, 50% of nanocellulose fibrils (diameter 20-30nm, Northern Century Cellulose Materials Co., Ltd.) were ultrasonically mixed with the obtained LiFeSO4F and placed in a tubular furnace filled with argon, and calcined at 700°C for 5 hours to finally obtain a halogen-containing nanocellulose-based sulfate composite positive electrode material powder.

[0027] Example 2

[0028] First, 0.01 mol of FeSO4·7H2O was weighed and placed in a vacuum oven at 200°C for 10 hours to dehydrate and obtain FeSO4·H2O; then, 0.03 mol of LiF and FeSO4·H2O were placed in a high-pressure reactor and reacted in an oven at 200°C for 3 hours; the dark powder was recovered after being cooled to room temperature and washed with deionized water three times; finally, it was placed in a vacuum drying oven at 80°C for 5 hours to obtain LiFeSO4F; then, 30% of nanocellulose fibrils (diameter 20-30nm, Northern Century Cellulose Materials Co., Ltd.) were ultrasonically mixed with the obtained LiFeSO4F and placed in a tubular furnace filled with argon, and calcined at 700°C for 5 hours to finally obtain a halogen-containing nanocellulose-based sulfate composite positive electrode material powder.

[0029] Example 3

[0030] First, 0.01 mol of FeSO4·7H2O was weighed and placed in a vacuum oven at 200°C for 10 hours to dehydrate and obtain FeSO4·H2O; then, 0.05 mol of LiF and FeSO4·H2O were placed in a high-pressure reactor and reacted in an oven at 200°C for 3 hours; the dark powder was taken out and cooled to room temperature, and then washed with deionized water three times; finally, it was placed in a vacuum drying oven at 80°C for 5 hours to obtain LiFeSO4F; then, 60% of nanocellulose fibrils (diameter 20-30nm, Northern Century Cellulose Materials Co., Ltd.) were ultrasonically mixed with the obtained LiFeSO4F and placed in a tubular furnace filled with argon, and calcined at 700°C for 5 hours to finally obtain a halogen-containing nanocellulose-based sulfate composite positive electrode material powder.

[0031] Example 4

[0032] First, 0.01 mol of FeSO4·7H2O was weighed and placed in a vacuum oven at 200°C for 10 hours to dehydrate and obtain FeSO4·H2O; then, 0.03 mol of LiCl and FeSO4·H2O were placed in a high-pressure reactor and reacted in an oven at 200°C for 3 hours; the dark powder was taken out and cooled to room temperature, and then washed with deionized water three times; finally, it was placed in a vacuum drying oven at 80°C for 5 hours to obtain LiFeSO4F; then, 50% of nanocellulose fibrils (diameter 20-30nm, Northern Century Cellulose Materials Co., Ltd.) were ultrasonically mixed with the obtained LiFeSO4F and placed in a tubular furnace filled with argon, and calcined at 700°C for 5 hours to finally obtain a halogen-containing nanocellulose-based sulfate composite positive electrode material powder.

[0033] 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. Application of a halogen-containing nanocellulose-based sulfate composite positive electrode material in a lithium-ion battery, characterized in that: The preparation method of the composite positive electrode material comprises the following steps: (1) Dehydrating FeSO4·7H2O at a temperature of 150-250°C to obtain FeSO4·H2O; (2) placing the halogen-containing lithium compound LiX and the FeSO4·H2O obtained in step (1) into a reaction vessel, reacting them in an oven at 200° C. for 5 h, recovering a dark powder after cooling, washing and drying, and obtaining LiFeSO4X; (3) mixing the nanocellulose and the LiFeSO4X obtained in step (2) uniformly, and calcining them at 700-900° C. for 5-10 h in an inert gas atmosphere to finally obtain a composite positive electrode material powder; In step (2), the halogen-containing lithium compound is one or both of LiF and LiCl; In step (3), the nanocellulose is one or more of cellulose nanocrystals, cellulose nanofibers, and microcrystalline cellulose; the nanocellulose is nanocellulose fibrils with a diameter of 10-30 nm; In step (3), the amount of nanocellulose is 20%-100% relative to the mass of LiFeSO4X; In step (2), the molar ratio of the halogen-containing lithium compound LiX to FeSO4·H2O is 0.1-1:1; In step (3), mixing is performed by mechanical ball milling or ultrasonic mixing.

2. The use according to claim 1, characterized in that: In step (1), the dehydration time of FeSO4·7H2O is 1-10h.

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

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