S-doped carbon nanotubes used as conductive additives to improve the electrochemical performance of LMFP

doi:10.11949/0438-1157.20210956

Abstract

Abstract:

Lithium manganese iron phosphate (LMFP) has a higher energy density compared with lithium iron phosphate (LFP), but its conductivity is lower, resulting in poor rate performance. In this paper, sulfur-doped carbon nanotubes were used to enhance the conductivity of the LMFP electrode, which effectively improved the energy density and power density of the LMFP electrode. Firstly, sulfur-doped carbon nanotubes (SCNT) were obtained by gaseous S doping treatment on carbon nanotubes (CNT), using SO₂ generated by CaSO₃ pyrolysis as dopant. Compared with the undoped CNTs, SCNTs exhibit better conductivity and hydrophilicity. The LMFP electrodes were prepared by using water as solvent and SCNTs aqueous suspension as conductive additive. The rate performance, cyclic stability and AC impedance were tested at room temperature and low temperature of -10℃, respectively. The results showed that the addition of SCNT as conductive agent effectively improved the conductivity and dynamics of LMFP electrode. The reversible capacities of LMFP electrode with SCNT at 0.2C and 5C were 200 mAh/g and 145 mAh/g, respectively, which were significantly higher than that of LMFP electrode with CNT or CB as conductive agent. Finally, the SCNT-added LMFP electrode was matched with graphite to assemble a full battery, showing ultra-high energy density and power density of 185.0 Wh/kg and 665.5W/kg.

Key words: carbon nanotubes, LMFP, dynamics, lithium ion battery, electrochemical, stability

摘要：

磷酸锰铁锂(LMFP)具有比磷酸铁锂(LFP)更高的能量密度，但因电导率更低，倍率性能较差。本文采用掺硫碳纳米管提升LMFP电极的导电性能，有效提高了LMFP电极的能量密度和功率密度。首先，以亚硫酸钙热解产生的SO₂为掺杂剂，对碳纳米管(CNT)进行气相掺硫处理得到掺硫碳纳米管(SCNT)。与未掺杂CNT相比，SCNT表现出更好的亲水性和导电性。将SCNT水相分散液作为导电添加剂，以水为溶剂制备LMFP电极，分别在室温和-10℃的低温环境下进行倍率性能、循环性能和交流阻抗等测试。结果表明，添加SCNT作导电剂有效提高了LMFP电极的导电性和动力学速率，添加SCNT的LMFP电极在0.2C和5C下可逆容量分别为200 mAh/g和145 mAh/g，显著高于添加了CNT或CB导电剂的LMFP电极。将添加SCNT的LMFP电极与石墨匹配组装全电池，表现出185.0 Wh/kg和665.5 W/kg的超高能量密度和功率密度。

关键词: 碳纳米管, 磷酸锰铁锂, 动力学, 锂离子电池, 电化学, 稳定性

CLC Number:

TQ 150

Lu ZHAO, Guoqing NING, Xingxun LI. S-doped carbon nanotubes used as conductive additives to improve the electrochemical performance of LMFP[J]. CIESC Journal, 2021, 72(12): 6388-6398.

赵露, 宁国庆, 李兴洵. 掺硫碳纳米管作导电添加剂改进磷酸锰铁锂电化学性能[J]. 化工学报, 2021, 72(12): 6388-6398.

Figures/Tables 8

Fig.1 TEM images of the CNT [(a), (b)] and SCNT[(c), (d)]; STEM (e) and corresponding EDS mapping (f) of SCNT

Fig.2 Raman spectra (a),XRD pattern (b), XPS spectra (c) of CNT and SCNT; S 2p spectra of SCNT (d)

Fig.3 Contact angles of CNT (a), SCNT-0.8%(mass) (b) and SCNT (c)

Fig.4 SEM images of the LMFP electrode fabricated with the CNT (a) and SCNT (b) as conductive additives

Fig.5 Rate performance (a), cycling performance at 1C (b)，charge-discharge curves respectively at 5C (c), impedance curves (d) of different LMFP electrodes at room temperature

Fig.6 Rate performance (a), charge-discharge curves respectively at 0.2C (c), cycling performance at 1C (b) at -10℃

Fig.7 Rate performance (a), charge-discharge curves respectively at 5C (b), cycling performance at 1C (c) at 40℃

Fig.8 Rate performance (a), capacity retention at different rate (b), charge-discharge curves at 5C (c), cycling performance (d) of LMFP-SCNT//G LMFP-CNT//G and LMFP-CB//G. Charge-discharge curves at different current density (e) and power and energy densities (f) of LMFP-SCNT//G at room temperature

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