CN103390746B - A kind of method improving lithium ionic cell cathode material lithium titanate performance - Google Patents

Abstract

The present invention successfully realize a kind of be suitable to produce prepare high rate capability, the preparation method of high cycle life ion cathode material lithium lithium titanate.A certain proportion of lithium source and titanium source are carried out ball mill mixing by the method, obtain precursor powder and are placed in high temperature furnace sintering, i.e. can get the lithium titanate (Li of two-phase coexistent after batch mixing₄Ti₅O₁₂-Li₂TiO₃) composite.It is advantageous that: specific capacity and the charge-discharge magnification performance of lithium titanate system can be customized by the ratio controlling lithium source and titanium source；The lithium titanate system prepared by the method, carries out discharge and recharge with the charge-discharge magnification of 10C, and reversible capacity reaches 106mAh/g, and after discharge and recharge 500 times, capability retention is 98.2%, almost without decay；The method environmental protection, large-scale production controlled, applicable.

Description

A method for improving the performance of lithium titanate, a negative electrode material for lithium-ion batteries

technical field

The invention relates to a solid-phase synthesis technique for preparing lithium titanate composite material for lithium-ion secondary battery negative electrodes and improving its electrochemical performance, which belongs to the field of research and production of lithium-ion secondary batteries.

Background technique

In the 21st century, the increasingly serious energy crisis and the impact of the use of fossil energy on the environment have become the weakness of national development, and even endanger national stability. Researchers all over the world have done a lot of work in finding alternative energy sources, such as solar energy and wind energy. However, the temporal discontinuity and spatial dispersion of electric energy generated by these alternative energy sources make their storage an unavoidable problem. Considering factors such as cost, reliability, durability, and safety, direct energy storage systems (supercapacitors, etc.) and energy conversion systems (flywheels, batteries, etc.) have been widely studied and applied to the storage of electrical energy. Among them, the battery system can effectively convert electrical energy into chemical energy and store it, and release it in the form of electrical energy when needed. It is considered to be one of the most suitable systems for electrical energy storage. As we all know, lithium-ion batteries have been widely used in portable electronic devices. Its high energy density makes it the first choice for electric vehicle or hybrid vehicle batteries, and it is also a potential member of the grid energy storage system. As anode materials for lithium-ion batteries, carbon-based materials have been commercialized and widely used in mobile phones and notebooks. However, carbon-based anode materials are prone to precipitate lithium dendrites during rapid charge and discharge, causing internal short circuits in the battery, making it difficult to apply to large equipment such as electric vehicles and hybrid vehicles. The cycle life of silicon and tin-based anode materials with high specific capacity still needs to be further improved.

The lithium titanate (Li ₄ Ti ₅ O ₁₂ ) with a spinel structure has the following two main advantages: (1) The charge and discharge voltage platform of Li ₄ Ti ₅ O ₁₂ is about 1.55V (Vs.Li/Li ⁺ ), The formation of lithium dendrites can be avoided, so that there is no risk of short circuit, making the battery system safer. (2) Li ₄ Ti ₅ O ₁₂ is a "zero-strain" material with almost no volume change during lithium ion intercalation and extraction. This makes the battery with Li ₄ Ti ₅ O ₁₂ as the negative electrode material have good cycle performance and long service life. However, the pure phase Li ₄ Ti ₅ O ₁₂ material has relatively low electronic conductivity and ionic conductivity, and it is difficult to meet the requirements of fast charging and discharging of electric vehicles and hybrid vehicles, which hinders the commercial use of Li ₄ Ti ₅ O ₁₂ chemical production. The current research is mainly focused on improving the electronic conductivity of Li ₄ Ti ₅ O ₁₂ materials and shortening the distance of lithium ion transmission to improve the rate performance of Li ₄ Ti ₅ O ₁₂ materials. Cation doping (Mg, Al, V, etc.), surface modification (coated carbon, polyacene, copper oxide, etc.) are currently the main methods to improve the electronic conductivity of materials. In terms of shortening the lithium ion transmission distance, it is mainly by reducing the particle size or dimension of the Li ₄ Ti ₅ O ₁₂ material.

Recently, the pseudocapacitive effect has been successfully used to improve the rate performance of lithium-ion battery electrode materials, and it has also been found that there is an additional ability to electrochemically reversibly store lithium ions at the phase interface of composite materials, which is beneficial to increase the energy density of electrode materials. It is reported that Li ₄ Ti ₅ O ₁₂ -TiO ₂ nanocomposite anode materials exhibit high specific capacity under high-rate charge-discharge conditions due to the Faradaic pseudocapacitive effect. However, there are no public reports on the preparation of Li ₄ Ti ₅ O ₁₂ -TiO ₂ nanocomposites and their application in lithium-ion batteries.

Contents of the invention

The invention provides a method for preparing a two-phase coexistence composite material Li ₄ Ti ₅ O ₁₂ -Li ₂ TiO ₃ . The synthesis of the material adopts a solid-phase sintering method which is simple, energy-saving and suitable for industrial production. The two-phase coexistence material prepared by this method can effectively combine the Faradaic pseudocapacitive effect with the intercalation and extraction of lithium ions in the active material, so that the composite material Li ₄ Ti ₅ O ₁₂ -Li ₂ TiO ₃ has a higher specific capacity, Excellent charge and discharge rate performance, when the charge and discharge rate is as high as 10C, there is almost no capacity fading after 500 cycles.

The concrete technical scheme of this invention is as follows:

1. Weigh the lithium source and the titanium source according to the Li:Ti molar ratio (4-4.16):5.

2. Put the weighed lithium source and titanium source mixture in a planetary ball mill according to the ball-to-material ratio of (4-10):1 for ball milling and mixing.

3. Dry the precursor obtained by mixing the mixture, place the dried powder in a high-temperature furnace to raise the temperature to 700-850°C at a heating rate of 2-10°C, keep it warm for 5-15 hours, and then cool it naturally to room temperature The two-phase coexistence composite material can be obtained.

The titanium source involved in the above scheme is TiO ₂ with anatase structure, the lithium source is lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, lithium oxalate or the combination of several lithium sources, and the Li:Ti molar ratio is (4～4.16):5.

The ball-to-material ratio involved in the above scheme is (4-10): 1, the rotating speed is 300-500r/min, the ball milling time is 3-6 hours, and the dispersant can use ethanol, deionized water, acetone or several A mixture of dispersants.

The sintering atmosphere involved in the above scheme can be directly sintered in air, or sintered under the protection of argon, nitrogen, helium or carbon dioxide gas.

The heating system involved in the above scheme is 2-10° C./min, the sintering temperature is 700-850° C., and the holding time is 5-15 hours.

Description of drawings

Figure 1: XRD diffraction pattern of Li ₄ Ti ₅ O ₁₂ -Li ₂ TiO ₃ composite prepared by this method.

Figure 2: SEM images of Li ₄ Ti ₅ O ₁₂ -Li ₂ TiO ₃ composites prepared by this method.

Figure 3: Constant current charge and discharge rate performance curve of Li ₄ Ti ₅ O ₁₂ -Li ₂ TiO ₃ composite prepared by this method.

Figure 4: The constant current charge and discharge efficiency curve of the Li ₄ Ti ₅ O ₁₂ -Li ₂ TiO ₃ composite material prepared by this method when the charge and discharge rate is 10C and the number of cycles is 500 times.

detailed description

Implementation case one:

Weigh lithium carbonate and titanium dioxide according to the Li:Ti molar ratio of 4.08:5, and mill the weighed lithium carbonate and titanium dioxide in deionized water at a ball-to-material ratio of 5:1 in a planetary ball mill at a speed of 400r/min for 4 hours. mix. The slurry obtained by mixing was dried in the air, and the precursor powder obtained after drying was placed in a muffle furnace, and the temperature was raised to 750°C at a rate of 2°C/min in the air, and kept for 12 hours, and then naturally returned to room temperature .

The prepared powder samples were analyzed by an X-ray diffraction analyzer (XRD, x'pertMPD) with a scanning range of 10° to 85° and a step speed of 0.03°/min. The XRD diffraction pattern is shown in Figure 1(a). The diffraction peaks of the sample include Li ₄ Ti ₅ O ₁₂ with a spinel structure and a small amount of Li ₂ TiO ₃ . The particle morphology of the prepared samples was measured by a field emission scanning electron microscope (CFSEM, Hitachi S-4800), and the particle size was uniform, basically distributed in 300-600nm, as shown in Figure 2(a).

Grind Li ₄ Ti ₅ O ₁₂ -Li ₂ TiO ₃ composite material and acetylene black in an agate mortar for about 20 minutes to mix thoroughly, then add n-methylpyrrolidone solution containing polyvinyldiene binder and grind thoroughly , wherein the ratio of Li ₄ Ti ₅ O ₁₂ -Li ₂ TiO ₃ composite material: acetylene black: binder is 80:10:10. The ground slurry is evenly spread on a piece of copper foil, dried at 80°C for 5-6 hours, pressed into a disc with a diameter of 1cm, dried in a vacuum oven at 110°C for 12 hours, and then moved into a vacuum chamber filled with 99.99% argon In a gas glove box, a half-cell was assembled with a lithium sheet as a counter electrode and electrochemically tested. The constant current charge and discharge were carried out on the blue battery test system (CT2001A/CT2001C; WuhanKinguoElectronicsCo., Ltd.). The constant current charge and discharge rate performance curve is shown in Figure 3. When the charge and discharge rate is 0.5C, its reversible specific capacity can reach 155mAh/g; when the charge and discharge rate is 10C, the reversible capacity can still be maintained at 104.5mAh/g .

Implementation case two:

Lithium hydroxide and titanium dioxide were weighed according to the molar ratio of Li:Ti 4.04:5, and the weighed lithium hydroxide and titanium dioxide were ball-milled in ethanol at a ball-to-material ratio of 5:1 in a planetary ball mill at a speed of 400r/min for 4 hours Do the mixing. The slurry obtained by mixing the mixture was dried in the air, and the precursor powder obtained after drying was placed in a tube furnace and heated to 750 °C at a rate of 2 °C/min in argon, and kept for 12 hours, and then cooled naturally to room temperature.

The characterization of Li ₄ Ti ₅ O ₁₂ -Li ₂ TiO ₃ composite material and the test of battery electrochemical performance are as in Example 1. The diffraction peaks of the sample include Li ₄ Ti ₅ O ₁₂ with a spinel structure and a small amount of Li ₂ TiO ₃ . The XRD diffraction pattern is shown in Fig. 1(b). The particle size is uniform, basically distributed in 300-600nm, and the SEM image is shown in Figure 2(b). The constant current charge and discharge rate performance curve is shown in Figure 3. When the charge and discharge rate is 0.5C, its reversible specific capacity can reach 146mAh/g; when the charge and discharge rate is 10C, the reversible capacity can still be maintained at 106mAh/g.

Implementation case three:

Lithium nitrate and titanium dioxide were weighed according to the Li:Ti molar ratio of 4.12:5, and the weighed lithium nitrate and titanium dioxide were mixed in a planetary ball mill at a speed of 400r/min for 4 hours in ethanol at a ball-to-material ratio of 5:1. material. The slurry obtained by mixing the mixture was dried in the air, and the precursor powder obtained after drying was placed in a tube furnace and heated to 750 °C at a heating rate of 2 °C/min in nitrogen, and kept for 12 hours, and then naturally cooled to room temperature.

The characterization of Li ₄ Ti ₅ O ₁₂ -Li ₂ TiO ₃ composite material and the test of battery electrochemical performance are as in Example 1. The diffraction peaks of the sample include Li ₄ Ti ₅ O ₁₂ with a spinel structure and a small amount of Li ₂ TiO ₃ . The XRD diffraction pattern is shown in Fig. 1(c). The particle size is uniform, and the basic distribution is 300-600nm. The SEM image is shown in Figure 2(c). The constant current charge and discharge rate performance curve is shown in Figure 3. When the charge and discharge rate is 0.5C, its reversible specific capacity can reach 122.5mAh/g; when the charge and discharge rate is 10C, the reversible capacity can still be maintained at 85mAh/g .

The results of the implementation case show that: with the increase of the proportion of lithium source, the rate performance of the battery is greatly improved, and the cycle life is significantly increased; at the same time, due to the existence of Li ₂ TiO ₃ , it will be accompanied by a decrease in the specific capacity of the battery. Among them, when the Li:Ti molar ratio is 4.08:5, the comprehensive performance is optimized: when the charge-discharge rate is 0.5C, its specific capacity can reach 155mAh/g; when the charge-discharge rate is 10C, the capacity can still maintain 72.56%. In terms of cycle life, when the charge-discharge rate is 10C, after 500 cycles, the capacity retention rate is 98.2%, with almost no decay, as shown in Figure 4.

Claims (2)

1. the method improving lithium ionic cell cathode material lithium titanate performance, it is characterised in that comprise the following steps:

A. by lithium source and titanium source (4～4.16) in molar ratio: 5 add in dispersant, in planetary ball mill, batch mixing 3～6 hours is carried out with 400r/min rotating speed with ratio of grinding media to material 5: 1, the slurry obtained by batch mixing is dried in atmosphere, dried presoma is transferred to grind into powder in agate mortar stand-by；Described lithium source is one or more in lithium carbonate, Lithium hydrate, lithium nitrate, lithium acetate or lithium oxalate；Described titanium source is anatase phase titanium dioxide；

The most mixed powder is placed in high temperature furnace, in nitrogen or argon gas atmosphere, is warming up to 750 DEG C with the speed of 2～10 DEG C/min and sinters 12 hours, i.e. obtain the Li of two-phase coexistent₄Ti₅O₁₂-Li₂TiO₃Lithium titanate composite material, gained composite uniform particle sizes, particle diameter is between 300-600nm.

The method of raising lithium ionic cell cathode material lithium titanate performance the most according to claim 1, it is characterised in that one or more during dispersant uses ethanol, deionized water or acetone in step A.