LiFePO 4 /C nanoparticle with fast ion/electron transfer capability obtained by adjusting pH values
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LiFePO4/C nanoparticle with fast ion/electron transfer capability obtained by adjusting pH values Yong Li1, Juan Wang1,*
1
, Cheng Cheng Fu1, Xiang Li1, and Liang Liang Wang1
Shaanxi Key Laboratory of Nanomaterials and Nanotechnology, Xi’an University of Architecture and Technology, Xi’an 710055, People’s Republic of China
Received: 28 May 2020
ABSTRACT
Accepted: 30 August 2020
Olivine-structure LiFePO4 is considered as promising cathode materials for lithium-ion batteries. However, the material always sustains poor electron conductivity and restricted lithium-ion diffusion channel, severely hindering its further commercial application. In this work, adjusting the synthesis condition on pH value is a practical approach to reduce the nanoparticle size, which vastly boosts its performance. The pH = 6 sample exhibits the highest specific capacity (149.7 mAh/g at 0.1 C) and capacity retention (96.3% after 50 cycles at 0.1 C, 89.7% after 200 cycles at 1 C) among the other LiFePO4/C powders. Compared to pH = 8 electrode, cyclic voltammetry and electrochemical impedance analysis disclose the reduced charge transfer resistance from 1492 to 993 X. Lithiumion diffusion coefficient from 1.13 9 10–14 to 4.24 9 10–14 cm2s-1suggests that the optimal pH value can effectively minimize particle size, improve contact area, and buffer the diffusion barrier, including electron and ion, thus including the electrochemical property. Our study provides a simple and efficient strategy to design and optimize promising olivine-structural cathodes for lithium-ion batteries.
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Springer Science+Business
Media, LLC, part of Springer Nature 2020
Handling Editor: Mark Bissett.
Address correspondence to E-mail: [email protected]
https://doi.org/10.1007/s10853-020-05192-3
GRAPHIC ABSTRACT
Introduction Lithium-ion batteries (LIBs) have become an indispensable part of our daily life, for the rechargeable cellphones and laptops, as well as electric cars, and have revolutionized modern society [1, 2]. Motivated by the commercialization of LiCoO2 cathode and graphite anode, the olivine LiFePO4 (LFP) was identified as a new polyanion cathode in 1997 [3]. Olivinetype LFP was endowed with environmental friendliness, low raw materials cost, thermal stability, and high operating voltage (*3.4 V vs. Li/Li?). However, the commercial applications of LFP were vastly hindered due to its intrinsic weakness of poor electronic conductivity (10–8 * 10-10scm-1) as well as the inferior one-dimensional diffusion channel for Li? (10–16 to 10-13cm2s-1) [4, 5]. Many reports have verified that the low transferring charge originated from the large miscibility gap between FePO4 and LiFePO4 phases, and the inferior Li? diffusion coefficients resulted from the particular position of LiO6 in the octahedral crystal units of LFP [6, 7]. Many strategies have been widely implemented, including the coating conductive layer and nanosizing particles [8–10]. For the former approach, coating carbon conductive agents, as one of the conventional methods, are usually util
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