Cycle Life and Recycling of Positive Electrode Materials in Li-Ion Batteries

Katja Lahtinen

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

Li-ion batteries are a primary power source for portable consumer electronics, such as mobile phones and laptops. In addition, they power electric vehicles (EVs) and can be used as a stationary energy storage for renewable energy sources, such as solar and wind power. Lately, the demand for Li-ion batteries has increased rapidly due to the electrification of transportation, and this has induced challenges related to the sustainability of material production. In this thesis, two major factors in improving the sustainability of Li-ion battery positive electrode materials, cycle life and recycling, are investigated. The thesis focuses on understanding, how dopants or impurities affect the positive electrode materials at the different stages of their life from synthesis to recycling. First, adding Mg doping to LiCoO2 in different synthesis stages was investigated. Adding the doping in lithiation step was observed to enhance even Mg distribution to the particles and to improve the morphology, which reduced the increase in the charge transfer resistance and led to the improved cycle life. Precursor doping, on the other hand, induced Mg distribution on the particle surface and decreased the stacking order in the crystal, which decreased the cycle life. Li excess in the samples was observed to decrease the rate capability of all the materials regardless the doping stage but not affect the cyclability of lithiation-doped LiCoO2. In addition to doping with a single element, dual doping of LiCoO2 with Mg and Ti was investigated and compared to the Li excess. The Mg-Ti doping was observed to improve the electrochemical performance of LiCoO2 by enhancing the electric conductivity and suppressing the increase of the charge transfer resistance. Li excess was observed to decrease the cycle life in the voltage range of 3.0–4.2 V. The demand for Li-ion battery raw materials is rapidly increasing alongside the amount of generated waste batteries. In the state-of-art battery recycling processes, all battery parts are recycled at the same process, which leads to impurity metals mixing with the electrode materials. To understand the effect of the metal impurities on the recycling, Li-ion battery waste was recycled using a hydrometallurgical method, and the regenerated chemicals were used in the synthesis of LiCoO2 whose electrochemical performance was then investigated. Cu was observed to be a main impurity in the process, and it decreased the initial capacity of the synthesized materials. However, the regenerated LiCoO2s decreased the increase in impedance, which led to improvements in the rate capability and cycle life. Alternative methods for the state-of-art recycling methods were discussed as well. In this work, a new method to regenerate spent Li-ion battery positive electrode by electrochemical re-lithiation without removing the active material from the current collector was investigated. The effect of doping on the reusability was investigated as well, and Mg-Ti doping was observed to enhance it. The regenerated materials had a slightly poorer cyclability compared to the fresh materials, which was attributed to the decline in the stacking order and the increase in impedance.
Translated title of the contributionLi-ioniakkujen positiivielektrodimateriaalien elinikä ja kierrätys
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Kallio, Tanja, Supervising Professor
  • Kallio, Tanja, Thesis Advisor
Publisher
Print ISBNs978-952-64-0718-0
Electronic ISBNs978-952-64-0719-7
Publication statusPublished - 2022
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • Li-ion battery
  • positive electrode material
  • cycle life
  • recycling
  • doping

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