Studies and applications of the electrode/electrolyte interface in Lithium-ion secondary batteries

• Main Authors: Lee, Meng-Lun, 李孟倫
• Other Authors: Shih, Han C.
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/97045497370353536332

博士 === 國立清華大學 === 材料科學工程學系 === 101 === Rechargeable lithium-ion batteries (LIBs) have been widely used as a power source for many portable electronic devices due to the high energy density, light and environmental friendly. In recent years, many researches have pointed out that aside from the active materials dominating the electrochemical properties of a battery, the most attractive topic is the electrolyte and the related heterogeneous electrolyte and electrode interface/interphase. The interface of electrolyte and electrode not only affect the long term cycling stability but also refers to the safety quality of a battery. In this study, three ways are used to modify the circumstance of the interface: (1) the fundamental surface coating on single particle of active material, (2) one step ahead of depositing compound directly onto the finished electrode, and (3) in contrast to modify the electrolyte transforming the reaction back to the electrode surface. Li4Ti5O12 (LTO)-coated graphite as an anode material for Li-batteries is synthesized. The surface of graphite powders is uniformly coated by the LTO nanoparticles to form a core-shelled structure via a sol-gel process, followed by calcination. The average size of graphite core is 20 µm while the thickness of LTO shell is 60 to 100 nm. We found that LTO-coated graphite has better rate-capability and cycle life at RT and at 55˚C, compared with the pristine graphite. The electrochemical impedance spectroscopy (EIS) results of the cell with LTO-coated graphite anode showed a significant suppression of the impedance rise after 60 cycles. In addition, the Raman spectrum showed that after 60 charge-discharge cycles at 55˚C, the ID/IG ratio of the LTO-coated graphite electrode increased slightly, while that of the pristine graphite electrode increased significantly. Atomic layer deposition (ALD) acts as a novel process to fabricate TiO2 nano-layer with high uniformity by ALD technique on a completive graphite negative electrode of lithium battery is reported. Under accurate thickness control, a TiO2 plated (~40 nm) graphite electrode shows remarkable performance in cycle life. The surface resistance of the electrode has been suppressed after 100 charge-discharge cycles and the stability of surface graphite layer structure has been maintained after 60 cycles. The deposition strategy directly on the electrode shows a resemble purpose as well as the core-shell particle coating of active materials. Quercetin, an organic antioxidant, has been employed as an additive in lithium-ion cells to enhance the electrochemical performance to enhance the cycle life and the overcharging characteristics of LiPF6/EC+ EMC+DMC (1 M) when used as an electrolyte. A LiCoO2/graphite full cell with 0.05% quercetin showed a significant improvement in safety associated with overcharging tolerance and thermal stability, without causing damage on electrochemical properties including C-rate and cycle life. Under the 3C-6V charging circumstance, the LIB with quercetin contained has postponed the vented time for more than 800 s, comparing to the normal battery. Improvements might result from the formation of a passivation microstructure on the electrode’s surface which could both minimize the reaction between electrode and electrolyte and suppress the surface impedance increase of the interface, especially suppresses the increase in the charge-transfer resistance. The studies focused on electrolyte and electrode interface of Li-ion cells provide a viable way to improve the power source for the applications involving electric devices with high rate, long term cycling, and high safety requirements.