Bonnisa Magdaline T, Vadivel Murugan A
Advanced Functional Nanostructured Materials Laboratory, Centre for Nanoscience and Technology, Madanjeet School of Green Energy Technologies, Pondicherry University (A Central University), Dr R. V. Nagar, Kalapet, Puducherry 605014, India.
Dalton Trans. 2020 May 19;49(19):6227-6241. doi: 10.1039/d0dt00919a.
Microwave-driven hydrometallurgical (MW-HM) method has been adopted to extract spinel-type Li4Ti5O12 (LTO) and orthorhombic-type LiFePO4 (LFP) from naturally occurring Ilmenite (FeTiO3) within 2 h unlike the conventional process that requires >30 h. We have successfully demonstrated aliovalent-Nb5+ doping and carbon coating with N, Br co-doping upon the pyrolysis of a polypyrrole-(PPy)-Br2 charge-transfer-(CT)-complex via MW-hydrothermal and MW-solid state heating within 30 min. Further, we also investigated the effect of carbon coating and co-doping of LTO and LFP electrodes at high C-rate performance of the lithium battery. XRD, XPS, FTIR, and Raman spectroscopy results confirmed the co-existence of dual-phase Li4Ti5O12/rutile-TiO2 (LTO-RTO) with substitution-induced transition of Ti4+ → Ti3+ in spinel-LTO due to Nb5+ and N, Br co-doping, which facilitates fast Li+ ion and electron transfer at the electrode-electrolyte interface. Conversely, in situ Nb5+ doped LiFePO4 combined with ex situ carbon-coating with N, Br co-doping improved the overall electronic conductive behavior. The UV-Visible absorption spectra and Tauc plots further support the decrease in the band gap upon co-doping, thus promoting n-type electronic behavior of the electrodes. A significant enhancement in the discharge-capacities of the carbon-coated N, Br co-doped Li4Ti4.97 Nb0.03O12/rutile-TiO2 (NBC-LTNO-RTO) and pristine anode in the range of 174-148 mA h g-1 and 167-125 mA h g-1 was exhibited at different rates in the range of 0.2 C-20 C with 97% and 94% capacity retention, respectively. Instead, the carbon-coated N, Br co-doped LiFe0.99 Nb0.01PO4 (NBC-LFNP) and pristine cathode exhibited discharge capacities in the range of 169-73 mA h g-1 and 136-65 mA h g-1 at different rates in the range of 0.2 C-20 C with 92% and 40% capacity retention for 500 cycles, respectively. Hence, this innovative, rapid, and sustainable chemical process for the fabrication of the modified cathode and anode from the earth abundant ilmenite ore as the single source with high-rate capability and ultra-stability can be used for high-power and safer lithium-ion energy storage.
与需要超过30小时的传统工艺不同，微波驱动的湿法冶金（MW-HM）方法已被用于在2小时内从天然钛铁矿（FeTiO₃）中提取尖晶石型Li₄Ti₅O₁₂（LTO）和正交晶型LiFePO₄（LFP）。我们已经成功地通过微波水热和微波固态加热在30分钟内，在聚吡咯-（PPy）-Br₂电荷转移-（CT）-配合物热解时实现了异价Nb⁵⁺掺杂以及N、Br共掺杂的碳包覆。此外，我们还研究了碳包覆以及LTO和LFP电极的共掺杂对锂电池高C倍率性能的影响。XRD、XPS、FTIR和拉曼光谱结果证实了由于Nb⁵⁺以及N、Br共掺杂，在尖晶石-LTO中存在双相Li₄Ti₅O₁₂/金红石-TiO₂（LTO-RTO）且Ti⁴⁺→Ti³⁺发生了取代诱导转变，这有利于电极-电解质界面处Li⁺离子和电子的快速转移。相反，原位Nb⁵⁺掺杂的LiFePO₄与N、Br共掺杂的异位碳包覆相结合改善了整体电子导电行为。紫外-可见吸收光谱和陶氏图进一步支持了共掺杂后带隙的减小，从而促进了电极的n型电子行为。在0.2C-20C范围内的不同倍率下，碳包覆的N、Br共掺杂Li₄Ti₄.97Nb₀.03O₁₂/金红石-TiO₂（NBC-LTNO-RTO）和原始阳极的放电容量显著提高，分别在174-148 mA h g⁻¹和167-125 mA h g⁻¹范围内，容量保持率分别为97%和94%。相反，碳包覆的N、Br共掺杂LiFe₀.99Nb₀.01PO₄（NBC-LFNP）和原始阴极在0.2C-20C范围内的不同倍率下，放电容量分别在169-73 mA h g⁻¹和136-65 mA h g⁻¹范围内，500次循环的容量保持率分别为92%和40%。因此，这种创新、快速且可持续的化学工艺，以地球上储量丰富的钛铁矿矿石为单一原料制造改性阴极和阳极，具有高倍率性能和超稳定性，可用于高功率和更安全的锂离子储能。
