Low temperature eutectic molten salt method to help lithium battery efficient recovery

　　Author ：Iflowpower – Portable Power Station Supplier

Lithium batteries are widely used in portable electronic products and electric vehicles due to their high energy density and long cycle life. Lithium battery has probably 5-10 years, and the lithium battery production in the next five years is expected to reach hundreds of GWHs every year. This means that a large number of abandoned lithium batteries in the next few decades will be produced, making the recovery of lithium batteries.

At present, the limitations of lithium battery recovery methods The mainstream method of recycling of lithium batteries is fire-making metallurgy and wet magazine law. However, fire-making metallurgy requires extremely high temperature sintering and complex purification process, wet metallurgy requires corrosive acid solution to gradually precipitate metal elements. These two methods are not only costly, and the steps are complex, and environmental pollution is caused.

More importantly, the fire-making metallurgy and wet metallurgical law completely destroyed the particle structure of the positive material, and completely discarded a large number of value stored in material particles (by controlling and optimizing various parameters with ideal performance. Positive material). More efficient method: Direct regeneration method directly regenerates the method of completely destroying the particles in the fire mitr metallurgy and wet metallurgy, but by physically separating the positive electrode material from the discarded battery, and then performs the attenuation positive electrode material deal with.

The positive material after processing regeneration can have high capacity, high-magnification performance, and stable cycle performance, so that it can be used directly in new batteries. Chen Zheng, Chen Zheng, Chen Zheng, the University of California, San Diego, has successfully developed the method of regenerating the positive material with hydrothermal method. The hydrothermal regeneration method can completely restore the original electrochemical properties of the positive electrode material, but the conditions of high pressure are not easily satisfied in actual production.

Recently, they have achieved breakthroughs in direct regenerative positive electrode materials, successfully achieved low temperature eutectic molten salt method regenerated three yuan positive material materials. The method can not only be carried out at normal pressure, but also regenerate the material after the attenuation regenerates its original electrochemical properties. They also collaborate with the Professor of Meng Ying, the California University San Diego, for the first time, through TEM / EELS, etc.

, the first discovery: the surface of the decayed tri-layered material can be regenerated due to phase change. Transition backlay (Layered) structure. The results Ambient-pressureRelithiationofdegradeDlixni0.

5CO0.2Mn0.3O2 (0<little<1) ViaeutecticsolutionsFordirectReutectOflithium-Ionbatterycathodes published in International Journal AdvancenergyMaterials (Impact Factors 21.

875), the first author is Shiyang Dr. Shi Yang. The method still retains the original particle structure of the material, replenishes lithium by the molten lithium salt to attenuate, and accompanying the components and crystal structures of the material in a short sintering process to the original state, showing good application prospects.

Full-text point to analyze the attenuation mechanism of lithium tri-nickel-cobalt-manganese acid (NCM) positive electrode material: two points. First, the loss of lithium: itself presents lithium in the positive electrode material with the battery's circulation, cannot be completely returned to the positive electrode (can result in thickening or other causes of SEI), resulting in a decrease in battery capacity; Second, surface phase change: The surface of the electrolyte contact is more likely to occur, and the original layered structure is transformed into a spinel phase (spinel) and rock salt phase (Rocksalt), which has a lower lithium ion conductivity, so that Polarization, capacity attenuation. The method takes lini0.

5co0.2mn0.3O2 (NCM523) as an example, starting from these two main reasons, first for the material to lift lithium, and then the ideal phase structure is achieved.

The choice of lithium source: This method employs eutectic molten salt as a source of NCM. The eutectic molten salt refers to a salt mixing system that is melted above the eutectic temperature. Due to the low melting point of the eutectic temperature than the melting point of the respective salt components, it can be melted at a lower temperature.

It can be seen by phase diagram (Fig. 1), when the molar ratio of lithium hydroxide and lithium nitrate is 2: 3, the eutectic point is reached, the minimum melting point (about 176 degrees Celsius). Therefore, the lithium salt having the component is used as a source of lithium.

Fig. 1 (a) LINO3-LiOH phase diagram (B) lithium molten salt is a decay NCM 523 material to supplement the lithium reaction temperature determination: attenuated positive electrode material and the DSC curve of the lithium salt mixture showed a heat transfer in 176 degrees Celsius The peak (Fig. 2), the melting of the lithium salt is shown in 250 degrees Celsius, and the corresponding lithium salt begins to react with the attenuated positive electrode material, which is supplemented, and the gas such as oxygen (in the TGA curve Observe the weight loss).

Therefore, 300 degrees Celsius is determined to be a temperature of the reaction, and the reaction time is set to 2 hours or 4 hours. The material after the complement is sintered in 850 degrees Celsius in oxygen for 4 hours, and the NCM523 positive electrode material after regeneration is obtained. Figure 2NCM 523 and Lithium salt mixture (a) DSC curve, (b) TGA curve chemical composition and physical phase recovery: ICP shows that the measurement of chemical components showed that the attenuated NCM523 has a lithium loss, The content of lithium has only 60% of the original content, in addition, in the X-ray diffraction diagram (Fig.

3), the attenuation material (003) peak is significantly left, corresponding to the increase of the layer spacing, direct relationship with lithium loss. After regenerative materials, the ICP results show that the lithium content is restored to the original value, and the (003) peak is removed back to the original position, which proves that the regeneration process successfully supplement lithium supplement positive material material. Fig.

3 Recovery of X-ray diffraction diagram surface crystal structure of NCM523 positive electrode material after attenuation and regeneration: the salt rock phase structure (Fig. 4) is observed in the high resolution TEM image of the attenuated material surface (Fig. 4), and the surface of the lithium layer is displayed.

The intensity increased significantly, which is caused by transition metal elements to lithium, which demonstrates that the surface of the material has changed. The surface of the salt rock phase and the transition metal element in the lithium layer were observed in the surface of the regenerated material. EELS obtains the surface and internal transition metal oxidation state of the attenuation / regenerated material (Fig.

5), further supports the conclusions obtained from the TEM image: the regeneration process can restore salt rocks to the original layered structure of the material, realized Recovery of surface crystal structure. Figure 4 After attenuating (A, C, D, G, H) and regenerated (B, E, F, I, J) High resolution TEM / FFT image and intensity graph 5 attenuated (a) and Recovery of EELS curve of NCM523 positive material after regeneration (b): Recovery of electrochemical properties in 4 hours of molten salt, the capacity, cycle performance and magnification performance of the regeneration material is completely restored to the original material (Figure 6 ). And 2 hours of lithium reaction time is short, the reaction is not complete, so each indicator is lower than the original material.

Figure 6 Electrochemical performance (A) of the NCM523 positive electrode material after the original and regenerated NCM523, (B) Different circulation circles, (c), (C) multiplier performance, (d) summary of voltage curve at different magnification and prospecting the method for first implementation Directly regenerated lithium battery NCM positive electrode material under normal pressure conditions, and the lithium-eutectic molten salt is supplemented with a positive electrode supplemental lithium source to attenuate, and the lithium content of the attenuation material, the body phase / surface Crystal structure, and electrochemical performance to restore to the original state. The method can also be used to regenerate other lithium battery positive materials, such as lithium manganate, lithium iron phosphate, etc., or the positive material of the sodium battery, and the specific step should determine the performance of different material.

This method not only has good application prospects in the field of lithium battery recovery, but also provides a unique idea for the green synthesis of energy materials. Academic research information.