Journal
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume 23, Issue 3, Pages 2438-2448Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/d0cp04598e
Keywords
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Funding
- JSPS KAKENHI [17K19134, 19H05814]
- MEXT (Ministry of Education, Culture, Sports, Science and Technology), Japan
- JST ALCA-SPRING (Specially Promoted Research for Innovative Next Generation Batteries) Project [JPMJAL1301]
- Grants-in-Aid for Scientific Research [19H05814, 17K19134] Funding Source: KAKEN
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The study focused on the tracer diffusion coefficient of lithium ions in LiCoO2 thin film, where D* values varied depending on compositions, and decreased steeply approaching x = 1.0. Our method showed good agreement with electrochemically determined diffusion coefficients, indicating c-axis diffusion occurs through additional diffusion channels.
Lithium diffusion is a key factor in determining the charge/discharge rate of Li-ion batteries. Herein, we study the tracer diffusion coefficient (D*) of lithium ions in the c-axis oriented LiCoO2 thin film using secondary ion mass spectrometry (SIMS). We applied a step-isotope-exchange method to determine D* in the Li-extracted LixCoO2. The observed values of D* ranged from 2 x 10(-12) to 3 x 10(-17) cm(2) s(-1) depending on the compositions in the range of 0.4 < x < 1.0. Approaching the stoichiometric composition (x = 1.0), D* decreases steeply to the minimum, which can be explained by the vacancy diffusion mechanism. Electrochemically determined diffusion coefficients corrected by thermodynamic factors are found to be in good agreement with D* determined by our method, over a wide range of compositions. The c-axis diffusion was explained by the migration of Li+ ions from one layer to another through additional diffusion channels, such as antiphase boundaries and a pair of Li antisite and oxygen vacancies in cobalt oxide layers.
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