阅读说明：本技术 一种原位形成钼酸锂隔膜涂层的制备方法 (Preparation method for in-situ formation of lithium molybdate diaphragm coating ) 是由 刘瑞平 李腾宇 李亚男 于 2021-08-02 设计创作，主要内容包括：本发明涉及一种通过在隔膜上原位形成钼酸锂涂层的制备方法,通过将MoO-(3)纳米棒材料与Super P,PVDF混合,并刮浆涂覆在普通隔膜上于室温下定型,干燥后备用,在室温条件下,与Li金属负极组装成CR2032扣式电池,安装到LAND CT2001A terser电池测试系统上,充放循环100次后即原位形成的钼酸锂隔膜涂层。该方法制备的钼酸锂隔膜涂层不仅可以从根本上改善Li-S电池在实际使用过程中出现的活性物质利用率低、多硫化物穿梭效应这种现象；而且其简便得合成方式也有利于大规模的生产和商业化的推广。(The invention relates to a method for preparing a lithium molybdate coating on a diaphragm by in-situ forming MoO 3 Mixing the nano-rod material with Super P and PVDF, coating slurry on a common diaphragm, shaping at room temperature, drying for later use, assembling the nano-rod material and a Li metal cathode into a CR2032 button cell at room temperature, installing the CR2032 button cell on a LAND CT2001A terser cell test system, and carrying out charge-discharge cycle for 100 times to obtain the in-situ formed lithium molybdate diaphragm coating. The lithium molybdate diaphragm coating prepared by the methodThe phenomena of low utilization rate of active substances and polysulfide shuttling effect in the actual use process of the Li-S battery can be fundamentally improved; and the simple and convenient synthesis mode is also beneficial to large-scale production and commercial popularization.)

1. A preparation method of an in-situ formed lithium molybdate diaphragm coating comprises the following steps: the method is characterized by comprising the following steps:

(1) firstly (NH)₄)₆Mo₇O₂₄·4H₂Dissolving O in nitric acid solution, and ultrasonically stirring for 30min to fully mix;

(2) transferring the mixture obtained in the step (1) into a polytetrafluoroethylene reaction kettle, heating at the temperature of 150-;

(3) sequentially carrying out vacuum filtration and washing on the product obtained in the reaction kettle by using deionized water and ethanol, and finally drying for 10-14 hours in a vacuum drying oven at the temperature of 50-60 ℃ to obtain white MoO₃A nanorod;

(4) adding MoO₃Mixing the nano rods, Super P and PVDF according to a certain mass ratio, fully grinding, dispersing in an NMP solvent, and magnetically stirring at normal temperature for 10-12 hours to obtain a mixed slurry;

(5) coating the mixed slurry on a diaphragm by using a coating machine, shaping at room temperature, and then transferring to a vacuum drying oven for drying for 5-8 h; the dried diaphragm with the coating is punched into a circle by a punching machine, then the circular diaphragm is directly assembled with a Li metal cathode to form a CR2032 button cell without adding a positive electrode in a glove box, and the dosage of the electrolyte is 9 mu L, wherein the electrolyte is composed of 0.1mol of lithium bistrifluoromethanesulfonamide (LiTFSI) and 1.13g of LiNO₃Dissolving in 100ml of a mixed solution consisting of 1, 2-Dioxolane (DOL) and Dimethoxymethane (DME) in a volume ratio of 1: 1;

(6) the assembled cell was mounted on a LAND CT2001A terser cell test system and discharged from 2.8V to 2.4V at 25 ℃ at a current density of 0.1C to form stable Li in situ_0.042MoO₃Standing for 1h, and continuing to discharge to 1.7V, Li_0.042MoO₃Conversion to stable Li₂MoO₄Standing for 1h, charging to 2.8V to make Li₂MoO₄Conversion to Li_0.042MoO₃And continuing the charge-discharge cycle for 100 times, then disassembling the battery, and taking out the diaphragm of the in-situ formed lithium molybdate coating, namely obtaining the in-situ formed lithium molybdate diaphragm coating.

2. The method for preparing an in-situ formed lithium molybdate separator coating according to claim 1, wherein the nitric acid solution in the step (1) has a volume solubility of 15-30% and the ultrasonic stirring time is 30-50 min.

3. The method of claim 1, wherein the MoO in step (4) is performed in a manner that allows the lithium molybdate separator coating to be formed in situ₃The mass ratio of the nano rod, Super P and PVDF is 40-50: 50-40: 10.

Technical Field

The invention relates to a secondary battery, in particular to a rechargeable lithium battery, which is applied to the technical field of electrochemical energy storage devices.

Background

With the increasing popularity of portable electronic devices, Hybrid Electric Vehicles (HEVs) and electric vehicles, there is an increasing need for efficient and economical energy storage systems to accommodate. Since the 90 s of the 20 th century, lithium ion secondary batteries based on intercalation/deintercalation reaction mechanisms have led to the market for portable electronic device batteries by virtue of their mature technologies and advantages of small self-discharge, stable electrochemical performance, long cycle life, and the like. However, although the maximum energy density of the conventional commercial lithium ion battery is close to the limit, the battery cannot meet the requirements of green industry such as electric energy storage. Therefore, it is of great significance to develop a next-generation battery system having a higher energy density.

The Li-S battery has high energy density (the theoretical specific capacity is up to 1672mAh g)^-1The energy density can reach 2600Wh kg^-1) Much higher than the capacity of commercially widely used lithium cobaltate batteries (<150 mAh/g). In addition, the abundant S in the earth has the advantages of high yield, low price, small environmental pollution and the like, so that the Li-S battery has wider development prospect and is expected to become a next-generation energy storage system. Different from the traditional insertion/extraction reaction mechanism, the reaction mechanism of the Li-S battery is based on reversible redox reaction between elemental S and Li, and mutual conversion between electric energy and chemical energy is realized through breaking/generating of a sulfur-sulfur bond. Since the reaction mechanism of Li-S batteries involves multi-step reactions and complex phase changes, their commercial spread has been limited by low active material utilization, reduced battery capacity and reduced life span due to shuttling of intermediate polysulfides across the separator.

Based on this, if a material with good conductivity, effective prevention of polysulfide shuttling effect and accelerated catalytic conversion can be prepared, and a functional coating on the separator can be obtained, it will be possible to solve the problems of the Li-S battery in practical application.

Disclosure of Invention

The object of the present invention is to provide a method for preparing a lithium molybdate coating layer by in-situ formation on a separator. The invention has simple preparation process, high safety and low requirements on equipment and process conditions, and is beneficial to popularization and application.

A preparation method of an in-situ formed lithium molybdate diaphragm coating comprises the following steps: the method is characterized by comprising the following steps:

(1) firstly (NH)₄)₆Mo₇O₂₄·4H₂Dissolving O in nitric acid solution, and ultrasonically stirring for 30min to fully mix;

(2) transferring the mixture obtained in the step (1) into a polytetrafluoroethylene reaction kettle, heating at the temperature of 150-;

(3) sequentially carrying out vacuum filtration and washing on the product obtained in the reaction kettle by using deionized water and ethanol, and finally drying for 10-14 hours in a vacuum drying oven at the temperature of 50-60 ℃ to obtain white MoO₃A nanorod;

(4) adding MoO₃Mixing the nano rods, Super P and PVDF according to a certain mass ratio, fully grinding, dispersing in an NMP solvent, and magnetically stirring at normal temperature for 10-12 hours to obtain a mixed slurry;

(5) coating the mixed slurry on a diaphragm by using a coating machine, shaping at room temperature, and then transferring to a vacuum drying oven for drying for 5-8 h; the dried diaphragm with the coating is punched into a circle by a punching machine, then the circular diaphragm is directly assembled with a Li metal cathode to form a CR2032 button cell without adding a positive electrode in a glove box, and the dosage of the electrolyte is 9 mu L, wherein the electrolyte is composed of 0.1mol of lithium bistrifluoromethanesulfonamide (LiTFSI) and 1.13g of LiNO₃Dissolving in 100ml of a mixed solution consisting of 1, 2-Dioxolane (DOL) and Dimethoxymethane (DME) in a volume ratio of 1: 1; (the composition of the electrolyte is not clear, the amounts of the individual components should be specified)

(6) The assembled cell was mounted on a LAND CT2001A terser cell test system and discharged from 2.8V to 2.4V at 25 ℃ at a current density of 0.1C to form stable Li in situ_0.042MoO₃Standing for 1h, and continuing to discharge to 1.7V, Li_0.042MoO₃Conversion to stable Li₂MoO₄Standing for 1h, charging to 2.8V to make Li₂MoO₄Conversion to Li_0.042MoO₃And continuing the charge-discharge cycle for 100 times, then disassembling the battery, and taking out the diaphragm of the in-situ formed lithium molybdate coating, namely obtaining the in-situ formed lithium molybdate diaphragm coating.

The volume solubility of the nitric acid solution in the step (1) is 15-30%, and the ultrasonic stirring time is 30-50 min.

MoO in step (4)₃The mass ratio of the nano rod, Super P and PVDF is 40-50: 50-40: 10.

has the advantages that:

firstly, the MoO is synthesized and prepared by a simple hydrothermal method₃Nanorods, thereby enabling mass production. And MoO due to nanostructures₃The material has abundant contact area which is helpful for wetting the electrolyte and promoting the next step of in-situ formation of lithium molybdate. Lithium molybdate formed in situ on the diaphragm can effectively adsorb polysulfide to inhibit shuttle of the polysulfide through polar bonding, good catalytic property accelerates the kinetics of redox reaction, and the synergistic effect with Super P can provide a way for ion/electron transmission, so that the utilization efficiency of active substances is improved, and the cycle life and the battery capacity of the Li-S battery are improved.

Thanks to the advantages, the specific capacity of the Li-S battery with the lithium molybdate coating diaphragm can still reach 906.6mAh/g after the battery is cycled for 300 times under the current density of 1C. Compared with the lithium molybdate coating formed in an ex-situ manner, the capacity fading rate is greatly reduced.

The multifunctional lithium molybdate diaphragm coating can not only fundamentally improve the phenomena of low utilization rate of active substances and polysulfide shuttling effect in the practical use process of the Li-S battery; and the simple and convenient synthesis mode is also beneficial to large-scale production and commercial popularization.

Detailed Description

A preparation method of an in-situ formed lithium molybdate diaphragm coating comprises the following steps: the method is characterized by comprising the following steps:

1. firstly, 1-2g (NH)₄)₆Mo₇O₂₄·4H₂Dissolving O in HNO₃/H₂In a beaker of O (1: 5, v/v), stirring for 30min with ultrasound to mix thoroughly.

2. Transferring the solution into a polytetrafluoroethylene reaction kettle lining (100ml), heating and preserving heat for 2h at 200 ℃, and cooling.

3. Sequentially carrying out vacuum filtration and washing on the product obtained in the reaction kettle by using deionized water and ethanol, and finally drying for 12 hours in a vacuum drying oven at 60 ℃ to obtain white MoO₃A nanorod material.

4. Adding MoO₃，Super P，PVDF was mixed in the following mass ratio, ground thoroughly for 30min, then dispersed in 10ml of NMP solvent, and magnetically stirred at room temperature for 12 hours to obtain a mixed slurry.

MoO₃：Super P：PVDF＝45-50：45-40：10

5. And (3) coating the mixed slurry on a common diaphragm by using a coating machine to scrape slurry, keeping the diaphragm for shaping at room temperature for 1 hour, and then transferring the diaphragm into a vacuum drying oven to dry for 6 hours.

6. The dried separator with the coating is punched into a 19mm round shape by a punching machine, and then the dried separator and the Li metal cathode are directly assembled into a CR2032 button cell without adding the anode in a glove box. The electrolyte dosage of 9 mu L is prepared from 0.1mol of lithium bistrifluoromethanesulfonamide (LiTFSI) and 1.13g of LiNO₃Dissolved in 100ml of a mixed solution of 1, 2-Dioxolane (DOL) and Dimethoxymethane (DME) in a volume ratio of 1: 1.

7. The assembled cell was mounted on a LAND CT2001A terser cell test system and discharged from 2.8V to 2.4V at 0.1C current density at 25 ℃ at room temperature to form stable Li in situ_0.042MoO₃Standing for 1h, and continuing to discharge to 1.7V, Li_0.042MoO₃Conversion to stable Li₂MoO₄Standing for 1h, charging to 2.8V to make Li₂MoO₄Conversion to Li_0.042MoO₃The charge and discharge cycle was continued for 100 times. The cell was then disassembled and the separator with the lithium molybdate coating formed in situ was removed.

Examples

The first embodiment is as follows: under room temperature conditions, 1.6g of (NH)₄)₆Mo₇O₂₄·4H₂O dissolved in 90ml HNO₃/H₂In a beaker of O (1: 5, v/v), stirring for 30min with ultrasound to mix thoroughly. Transferring the solution into a polytetrafluoroethylene reaction kettle lining (100ml), heating and preserving heat for 2h at 200 ℃, and cooling. Sequentially carrying out vacuum filtration and washing on the product obtained in the reaction kettle for 5 times by using deionized water and ethanol, and finally drying for 12 hours in a vacuum drying oven at 60 ℃ to obtain white MoO₃A nanorod material. Under the condition of room temperature, MoO₃: super P: PVDF ═ 0.2 g: 0.25 g: mixing 0.05g, grinding for 30min,then, the mixture was dispersed in 10ml of NMP solvent and magnetically stirred for 12 hours to obtain a mixed slurry. And (3) coating the mixed slurry on a common diaphragm by using a coating machine to scrape slurry, keeping the common diaphragm for shaping at room temperature for 1h, then transferring the common diaphragm into a vacuum drying oven for drying for 6h, and punching the dried diaphragm with the coating into a 19mm round shape by using a punching machine for standby. The coated separator was assembled directly with the Li metal negative electrode into a CR2032 button cell using a glove box at room temperature with a positive active material sulfur content of 1mg and an electrolyte of 9 μ l. The assembled cell was mounted on a LAND CT2001A terser cell test system and discharged from 2.8V to 2.4V at 0.1C current density at 25 ℃ at room temperature to form stable Li in situ_0.042MoO₃(ii) a After standing for 1h, continuously discharging to 1.7V, Li_0.042MoO₃Conversion to stable Li₂MoO₄(ii) a Standing for 1h, charging to 2.8V to make Li₂MoO₄Conversion to Li_0.042MoO₃The charging and discharging cycle is 100 times. And then disassembling the battery, and taking out the diaphragm with the coating, wherein the lithium molybdate diaphragm coating is formed in situ. After the full-cell is assembled, the initial capacity at the current density of 1C is 967.1mAh/g, the specific capacity can still reach 526.6mAh/g after the full-cell is cycled for 300 times, and the capacity fading rate is 0.15%.

Example two: under room temperature conditions, 1.6g of (NH)₄)₆Mo₇O₂₄·4H₂O dissolved in 90ml HNO₃/H₂In a beaker of O (1: 5, v/v), stirring for 30min with ultrasound to mix thoroughly. Transferring the solution into a polytetrafluoroethylene reaction kettle lining (100ml), heating and preserving heat for 2h at 200 ℃, and cooling. Sequentially carrying out vacuum filtration and washing on the product obtained in the reaction kettle for 5 times by using deionized water and ethanol, and finally drying for 12 hours in a vacuum drying oven at 60 ℃ to obtain white MoO₃A nanorod material. Under the condition of room temperature, MoO₃: super P: PVDF ═ 0.25 g: 0.2 g: 0.05g by mass, thoroughly ground for 30min, then dispersed in 10ml of NMP solvent, and magnetically stirred for 12 hours to obtain a mixed slurry. Coating the mixed slurry on a common diaphragm by using a coating machine to scrape slurry, keeping the common diaphragm for shaping at room temperature for 1h, then transferring the common diaphragm to a vacuum drying oven for drying for 6h, and using a punching machine to perform punching on the diaphragm with the coating after dryingAnd (5) beating into a 19mm round shape for later use. The coated separator was assembled directly with the Li metal negative electrode into a CR2032 button cell using a glove box at room temperature with a positive active material sulfur content of 1mg and an electrolyte of 9 μ l. The assembled cell was mounted on a LAND CT2001A terser cell test system and discharged from 2.8V to 2.4V at 0.1C current density at 25 ℃ at room temperature to form stable Li in situ_0.042MoO₃(ii) a After standing for 1h, continuously discharging to 1.7V, Li_0.042MoO₃Conversion to stable Li₂MoO₄(ii) a Standing for 1h, charging to 2.8V to make Li₂MoO₄Conversion to Li_0.042MoO₃The charging and discharging cycle is 100 times. And then disassembling the battery, and taking out the diaphragm with the coating, wherein the lithium molybdate diaphragm coating is formed in situ. After the full-cell is assembled, the initial capacity of 1033.6mAh/g under the current density of 1C, the specific capacity can still reach 523.1mAh/g after the cycle is carried out for 300 times, and the capacity fading rate is 0.16%.

Comparative example: the material was deposited on the inner wall of a quartz glass tube by means of chemical vapor deposition using a concentric Mo wire with a synthesis time of 72 hours. Then the obtained alpha-MoO₃Dispersing in ethanol and adding Si nanoparticles: (<1% by weight) to increase the alpha-MoO₃Is reversible. Taking 5mg of Si modified alpha-MoO₃Mixing with 7mg carbon tetrafluoride binder (mixture of polytetrafluoroethylene and acetylene black), pressing on stainless steel mesh collector, directly using as positive and negative lithium sheets, assembling into CR2032 button cell in dry glove box, and performing constant current lithiation at 0.1C current density to form Li_1.33Mo_0.66O₂And finally, disassembling the battery in a glove box, and taking out the stainless steel mesh current collector, wherein lithium molybdate is formed in situ. After the full-cell is assembled, the initial capacity at the current density of 0.1C is 905mAh/g, the specific capacity after 50 times of circulation is 400mAh/g, and the capacity fading rate is 1.1%.