Tuning Li-Ion Diffusion in α-LiMn_1–xFe_xPO₄ Nanocrystals by Antisite Defects and Embedded β-Phase for Advanced Li-Ion Batteries

Journal Article · Thu Jul 13 00:00:00 EDT 2017 · Nano Letters

DOI:https://doi.org/10.1021/acs.nanolett.7b01978· OSTI ID:1412728

Hu, Jiangtao ^[1]; Xiao, Yinguo ^[2]; Tang, Hanting ^[1]; Wang, Hongbin ^[1]; Wang, Ziqi ^[1]; Liu, Chaokun ^[1]; Zeng, Hua ^[1]; Huang, Qingzhen ^[3]; Ren, Yang ^[4]; Wang, Chongmin  ^[5]; Zhang, Wei ^[6]; Pan, Feng  ^[1]

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1. Peking Univ. Shenzhen Graduate School, Shenzhen (China). School of Advanced Materials
2. Forschungszentrum Julich (Germany). Julich Centre for Neutron Science. Peter Grunberg Inst.
3. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States). NIST Center for Neutron Research
4. Argonne National Lab. (ANL), Argonne, IL (United States). Electrochemical Technology Program. Chemical Sciences and Engineering Division
5. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab.
6. Brookhaven National Lab. (BNL), Upton, NY (United States). Sustainable Energy Technologies Dept.

Olivine-structured LiMn_1–xFe_xPO₄ has become a promising candidate for cathode materials owing to its higher working voltage of 4.1 V and thus larger energy density than that of LiFePO₄, which has been used for electric vehicles batteries with the advantage of high safety but disadvantage of low energy density due to its lower working voltage of 3.4 V. One drawback of LiMn_1–xFe_xPO₄ electrode is its relatively low electronic and Li-ionic conductivity with Li-ion one-dimensional diffusion. In this paper, olivine-structured α-LiMn_0.5Fe_0.5PO₄ nanocrystals were synthesized with optimized Li-ion diffusion channels in LiMn_1–xFe_xPO₄ nanocrystals by inducing high concentrations of Fe²⁺–Li⁺ antisite defects, which showed impressive capacity improvements of approaching 162, 127, 73, and 55 mAh g^–1 at 0.1, 10, 50, and 100 C, respectively, and a long-term cycling stability of maintaining about 74% capacity after 1000 cycles at 10 C. By using high-resolution transmission electron microscopy imaging and joint refinement of hard X-ray and neutron powder diffraction patterns, we revealed that the extraordinary high-rate performance could be achieved by suppressing the formation of electrochemically inactive phase (β-LiMn_1–xFe_xPO₄, which is first reported in this work) embedded in α-LiMn_0.5Fe_0.5PO₄. Because of the coherent orientation relationship between β- and α-phases, the β-phase embedded would impede the Li⁺ diffusion along the [100] and/or [001] directions that was activated by the high density of Fe²⁺–Li⁺ antisite (4.24%) in α-phase. Thus, by optimizing concentrations of Fe²⁺–Li⁺ antisite defects and suppressing β-phase-embedded olivine structure, Li-ion diffusion properties in LiMn_1–xFe_xPO₄ nanocrystals can be tuned by generating new Li⁺ tunneling. Finally, these findings may provide insights into the design and generation of other advanced electrode materials with improved rate performance.

• Research Organization: Brookhaven National Lab. (BNL), Upton, NY (United States); Peking Univ. Shenzhen Graduate School, Shenzhen (China)
• Sponsoring Organization: USDOE; National Natural Science Foundation of China (NSFC); Shenzhen Science and Technology (China)
• Grant/Contract Number: SC0012704; 2016YFB0700600; 21603007; 51672012; JCYJ20150729111733470; JCYJ20151015162256516
• OSTI ID: 1412728
• Report Number(s): BNL-114552-2017-JA; TRN: US1800333
• Journal Information: Nano Letters, Vol. 17, Issue 8; ISSN 1530-6984
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

25 ENERGY STORAGE
Fe2+-Li+ antisite
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β-LiMn1-xFexPO4