Impact of Moisture on the Properties of LiNixCoyMn1-x-yO2 (NMC) Cathodes for Lithium-Ion Batteries
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Date
2018-05
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The Ohio State University
Abstract
Lithium-ion battery (LIB) are in high demand for portable electronic devices and EV today. Much attention has been paid to cathode material since it governs the energy density of LIB. LiNi_x Co_y Mn_(1-x-y) O_2 (NMC) materials with various molar ratios of Ni: Mn: Co is now popular options for cathode materials for its lower cost, less toxicity and higher specific capacity comparing to traditional cathode materials such as LiCoO_2. However, the material suffers from performance degradations in contact with moisture in the air. Although this is a particularly important problem, we still have a lack of fundamental understanding about its failure mechanism. Based on literature review, we hypothesized that a high oxidation-state Ni^(3+) in NMC will readily react with moisture to lower its oxidation state into Ni^(2+) and lower the electrochemical capacity of NMC. To prove the hypothesis, we selected and investigated various NMC with different Ni contents: (1). LiNi_(1/3) Co_(1/3) Mn_(1/3) O_2, (2). LiNi_0.5 Co_0.3 Mn_0.2 O_2, (3). LiNi_0.6 Co_0.2 Mn_0.2 O_2, (4) LiNi_0.8 Co_0.1 Mn_0.1 O_2. We stored each type of NMC powder under three different conditions: (i) dry glovebox, (ii) 2% moisturized chamber, and (iii) water. Then, we characterized the samples by using X-ray Powder Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and electrochemical performance test from coin type battery cells. Testing results from the same type of powder in different conditions will be compared with each other to find how the extent of moisture affects the powders, while testing results from different powders in the same condition will be compared with each other to find how the amount of Ni content affects moisture impact.
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Keywords
Active Material, Lithium-ion Battery, Moisture Impact, Degradation