Study On Modification Of LiFePO₄ And LiCoO₂ Waste As The Cathode Material

The lithium-ion batteries（LIBs） are widely used in mobile electronic devices, electric vehicles, large energy storage devices and other fields, and there is a sharp increase in the consumption amount of Li-ion power batteries, Therefore, in the future, a large number of spent Li-ion batteries will be generated and need to be handled properly. Generally, in order to make full use of these spent Li-ion power batteries, the only choice is recycling the valuable materials. If these spent Li-ion power batteries are not handled or mishandled, they will not only lead to a waste of resources, but also pollute the environment.Up to now, many recycling techniques of spent Li-ion batteries have been developed, but these processes are only applicable to the spent digital Li-ion batteries（LiCoO₂ type,Ni-Co-Mn type, etc.） containing Co and Ni. These techniques can not be applied to recycle the spent Li-ion power batteries without Co, Ni, such as LiFePO₄, LiMn₂O₄. And these methods are complicated, high-cost and easy to cause pollution to the environment, so it is necessary to develop new recycling processes and modified methods, which have the advantages of simplicity, low cost and green. Compared with other cathode materials, LiCoO₂ and LiFePO₄ material are respectively representative of the digital lithium-ion batteries and power lithium-ion batteries. Therefore, the subject main studies on the recycling and modified repair of the LiFePO₄ and LiCoO₂ material.（1） The scraps from the producing process of LiCoO₂ batteries are recycled by solvent method and the recycled materials are heat-treated at diffirent temperature. After heat-treated at 250 °C, the discharge capacity and the capacity retention rate are close to or better than those of the pristine scrap materials. Meanwhile, compared with the unheat-treated scrap materials, the heat treatment can decrease the average particle diameter and increase the tap density. The recovery rate of scrap materials can reach 91.88% after two-step recovery processes.（2） A green recycling process is designed and used to recycle spent LiCoO₂ batteries. After these steps of discharing, dismanting, separating and recycling, the whole process has achieved the zero-polluting for the environment. The recycled LiCoO₂ is regenerated after the solid state synthesis with Li₂CO₃, which has good chemical and physical properties.Especially, after regeneration at 900 °C, the properties of LiCoO₂（XRD, morphology, tap density, average particle size, specific surface areas and p H value） are closed to the commercial LiCoO₂, and the discharge specific capacity can reach about 152.4 m Ahg^-1. The test dates show that the regenerated LiCoO₂ at 900 °C can meet the reused requirements.（3） The scraps from the producing process of LiFePO₄ batteries are recycled by solvent method. There is researched on the effect of physical and chemical properties of the recycled LiFePO₄ heat-treated at diffirent temperature. Through XRD pattern analysis, the structure ofthe electrode materials after heat-treatment has not been changed. After the electrochemical performance testing, the discharge capacity of cathode powders after heat treatment at 250 °C could reach about 155 m Ahg^-1. The performance of the recycled cathode powders are closed to the unused materials.（4） In order to recycle the used LiFePO₄ battery effectively, a new green recycling process is developed. This method does not bring secondary pollution to the environment, and recycling byproducts of aluminum have good economic value. After the electrochemical performance testing, the discharge capacity of the recovered cathode powders after heat-treatment at 200 °C could reach about 140.0 m Ahg^-1, and after 70 cycle number the discharge capacity of the cathode materials has good cycle stability. The recycled LiFePO₄ powders have good performance, and meet the reused requirement.