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Analyzing Li-ion Batteries Using Combined Atomic Force Microscopy and Raman Microscopy

Lithium batteries, a power source for many portable devices such as cellular phones, laptops, camcorders, etc. are also used in electrical vehicles and aerospace and military applications. The development of lithium batteries is advancing rapidly.

Due to longer life, lower self-discharge rate, and higher energy density compared to other rechargeable batteries, along with higher cost-effectiveness and smaller toxicity, layered lithium cobalt oxide LiCoO2 (Fig. 1) is used as a cathode for commercial applications.

Figure 1. Layered LiCoO2 structure.

The ordinary reversible lithium intercalation of the non-defective lithium battery is key to rechargeable Li battery. However, effects of protracted cycling or prolonged storing pose a threat to performance in course of time. Hence, to improve the life-time of batteries, the distribution of degraded areas on the surface of positive electrodes must be understood.

Experimental Methods
The most valuable methods for structural characterization of the electrodes in rechargeable lithium batteries are Raman spectroscopy and atomic force microscopy (AFM). Results of an LiCoO2 cathode characterization using AFM and Raman techniques on the NTEGRA Spectra (NT-MDT) instrument integrated with Renishaw inVia Raman spectrometer is presented. Simultaneous recording of AFM and Raman images from the same sample area are allowed by the instrument.

Figure 2. Structure of Lithium-ion battery

Figure 2 shows the typical structure of a lithium-ion rechargeable cylindrical cell. The anode, cathode, and electrolyte are the three primary functional components of a lithium-ion battery. Carbonaceous material (graphite is the most popular) is used for the anode, the cathode is made from LiCoO2, and lithium salt in an organic solvent is used as the electrolyte.

The individual lithium-ion cells from different laptop lithium battery packs were examined. The first battery pack, used for about 3 years (about 1200 charging-recharging cycles), had only about 25% of its nominal capacity, and was ~30% charged. The second battery was new and ~65% charged.
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