Preparation and electrochemical performance of high voltage LiNi0.5Mn1.5O4 cathode materials coated with different carbon sources
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摘要: LiNi0.5Mn1.5O4正极材料由于其高电压、无钴和高能量密度优势而受到关注,但高电压下易受电解液腐蚀,循环稳定性差限制了其进一步应用。本文采用低温自蔓延法制备出高电压LiNi0.5Mn1.5O4材料,再使用不同糖类作为碳源进行包覆改性研究。结果表明,在400℃/Air条件下,以壳聚糖为碳源制备的LiNi0.5Mn1.5O4复合材料性能明显改善,在148 mA·h/g下循环400次后放电比容量仍有113.3 mA·h/g,容量保持率为91.07%。这主要归功于材料表面裂解的碳层提高了材料的导电性,缓解了电解液的侵蚀,降低了电极反应极化,提高了锂离子扩散速率。本文利用廉价的糖类作为碳源,合成工艺简单,为镍锰酸锂的应用提供了新的思路。Abstract: LiNi0.5Mn1.5O4 cathode material is considered as a promising cathode material due to its advantages of high voltage, cobalt-free and high energy density. But its further application is limited by its poor cyclic stability as the decomposition of electrolyte under high voltage. In this study, LiNi0.5Mn1.5O4 was prepared by low temperature self-propagating combustion method, and then different sugars were used as carbon sources to study the coating modification. The results show that the properties of LiNi0.5Mn1.5O4 composite prepared with chitosan at 400℃/Air is improved significantly. The specific discharge capacity of LiNi0.5Mn1.5O4 composite is 113.3 mA·h/g after 400 cycles at 148 mA·h/g, and the capacity retention rate is 91.07%. This is mainly attributed to the carbon layer on the surface of the material, which improves the electrical conductivity of the material, alleviates the erosion of electrolyte, reduces the electrode reaction polarization, and improves the transport rate of lithium ions. In this study, cheap sugars are used as carbon source, and the synthesis process is simple, which provides a new idea for the application of LiNi0.5Mn1.5O4.
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Key words:
- LiNi0.5Mn1.5O4 /
- carbon coating /
- chitosan /
- lithium ion battery /
- cathode
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图 1 (a) 不同温度和气氛下碳包覆LiNi0.5Mn1.5O4 (LNMO)的XRD图;((b), (c)) 原始材料LNMO及K400A-LNMO的SEM图像;(d) K400N-LNMO及K800N-LNMO的首圈充放电曲线;(e) LNMO及K400A-LNMO的首圈充放电曲线;(f) 倍率曲线
Figure 1. (a) XRD patterns of carbon coating LiNi0.5Mn1.5O4 (LNMO) by different conditions; ((b), (c)) SEM images of the original material LNMO and K400A-LNMO; (d) First charge-discharge curves of K400N-LNMO and K800N-LNMO; (e) First charge-discharge curves of LNMO and K400A-LNMO; (f) Rate cycling capability of carbon coating LNMO by different conditions
A—Air; N—Nitrogen; K400— 400℃; K800—800℃; 1 C—148 mA·h/g
图 6 (a) 循环前后LNMO和K-LNMO的阻抗图;(b) 阻抗的ω−1/2与Z'关系;((c), (d)) LNMO及K-LNMO未充电电池在0、10、20、30、40℃下的阻抗;(e) 等效电路图;(f) LNMO及K-LNMO的活化能拟合曲线
Figure 6. (a) EIS test of LNMO and K-LNMO before and after cycling; (b) Relationship between ω−1/2 and Z' of impedance; ((c), (d)) EIS test of LNMO and K-LNMO at 0, 10, 20, 30, 40℃ before cycling; (e) Fitting circuit; (f) Activation energy fitting curves of LNMO and K-LNMO
Rct—Charge transfer resistance; Rs—Resistance of solution between working electrode and opposite electrode; Zw—Weber impedance; CPE—Phase angle element; Ea—Activation energy; T—Temperature
表 1 电化学循环前后LNMO及K-LNMO的Rct和DLi+
Table 1. Rct and DLi+ of LNMO and K-LNMO before cycling and after cycling
Samples Rct/Ω DLi+/(cm2·S−1) LNMO-before 133.6 1.32×10−15 LNMO-after 1023.1 7.23×10−16 K-LNMO-before 285.5 1.45×10−15 K-LNMO-after 802.6 3.23×10−15 Notes: Rct—Charge transfer resistance; DLi+—Lithium ion diffusion rate. -
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