|Bambang Priyono||Department of Metallurgy and Materials Engineering, Faculty of Engineering, Universitas Indonesia, Kampus Baru UI Depok, Depok 16424, Indonesia|
|Anne Zulfia Syahrial||Department of Metallurgy and Materials Engineering, Faculty of Engineering, Universitas Indonesia, Kampus Baru UI Depok, Depok 16424, Indonesia|
|Mohammad Ridho Nugraha||Department of Metallurgy and Materials Engineering, Faculty of Engineering, Universitas Indonesia, Kampus Baru UI Depok, Depok 16424, Indonesia|
|Achmad Subhan||Research CaResearch Center of Physics, LIPI, PUSPIPTEK, Serpong, Tangerang Selatan, Banten 15314, Indonesiaenter for Physic, LIPI, Puspiptek, Serpong|
Lithium titanate (Li4Ti5O12 or LTO) is a very promising anode material to replace graphite in li-ion batteries due to its safety and fast-charging ability. However, due to the low theoretical capacity of LTO, a strategy must be developed to overcome this problem. Synthesizing LTO by the combined sol-gel and solid-state method, and the addition of tin powder together with activated carbon, is expected to increase the specific capacity of the anode material. The tin powder compositions in this research were 5wt%, 7.5wt% and 12.5wt%. Further, to investigate the influence of activated carbon, 5wt%, 15wt%, and 25wt% activated carbon were added, while the composition of Sn was kept at 7.5wt%. XRD, SEM and BET surface area measurements was performed to characterize the morphology and structure of the samples. The performance of the battery was analyzed using EIS, CV and CD. The results show that TiO2 rutile was present in the LTO samples, with peak rutile decreasing significantly with the addition of carbon. More disperse particle morphology was obtained by the addition of activated carbon. The LTO/Sn anode material exhibits excellent reversible capacities of 191.1 mAh/g at 12.5wt% tin. Additionally, the LTO/Sn@C has the highest specific-capacity at 270.2 mAh/g, with a composition of 5wt% carbon and 7.5wt% Sn. The results show that LTO/Sn@C is a potential anode material for the future.
Activated carbon; Anode; Li4Ti5O12/Sn; Sol-gel; Tin powder
Lithium-ion batteries (LIBs) have diverse applications, ranging from powering electronic devices such as electric vehicles (EVs), to storing renewable energy (such as solar and wind energy) (Yi et al., 2014). State-of-the-art LIBs have used graphite-based material as part of the anode component due to its desirable charge potential profile, with the discharge capacity reaching 372 mAhg-1, and lithium-insertion potential 0V (Li/Li+) (Bayati et al., 2008). However, one of the limiting factors of graphite is its low lithiation potential, poor rate-capability and solvent co-intercalation, thus limiting its potential for EV development. The process of replacing graphite with Li4Ti5O12 (LTO) has been developed to achieve optimal results. Spinel LTO is a good candidate because of its high lithium insertion voltage (1.5 VS (Li/Li+)V), excellent safety profile, cycling performance due to its zero strain insertion material (Priyono et al., 2015), and its applicability is high power conditions (Li et al., 2013). However, the specific capacity (175 mAh/g), electrical conductivity (10-13 S cm-1) and lithium diffusion coefficient (10-9 to 10-13 cm2 s-1) of LTO is low (Ariyoshi et al., 2005). One of the ways to improve the performance rate is by reducing the particle size (Syahrial et al., 2018b), coating the surface with a more conductive material, such as carbon or silver (Kim et al., 2009) or by doping (Sofyan et al., 2016). In addition, tin oxide (Sn or SnO2) can be used as the anode (Aurbach et al., 2002), whose theoretical capacity can reach up to 1491 mAhg-1. However, the expansion of volume associated with the Sn charge-discharge process reaction of the newly formed metallic Sn with lithium, which leads to the formation of Li–Sn alloys with the composition of Li4.4Sn, can reach 300% (Kim et al., 2009).
This volume expansion can lead to the collapse of the electrodes, ultimately decreasing capacity after several cycles (Crosnier et al., 2001). Several innovations have been studied by combining the nanoparticles of the Sn matrix to obtain the LTO-Sn composite (Egashira et al., 2002). In addition, increasing the surface area of the LTO-Sn composite could also be an alternative approach to improving battery performance. In this case, activated carbon is often used to increase the surface area due to its porous structure and ability to provide better support for the anode, since carbon matrices accommodate the change in volume of Sn during the charge–discharge process (Liang et al., 2011).
This paper focuses on optimizing the performance of anode batteries with LTO/Sn and LTO/Sn@C composites. The addition of Sn to LTO is aimed to increase specific capacity and reduce impedance. The LTO in this study was prepared by the sol-gel process and mixing of the Sn element using a ball-mill. Further, the addition of activated carbon is expected to produce LTO/Sn@C with evenly dispersed particles, in an effort to obtain good electrochemical performance. The effect of the tin powder and activated carbon on the LTO anode will be investigated.
The compounds LTO/Sn and LTO/Sn@C were successfully synthesized using sol-gel, the addition of activated carbon and a solid state process, while also obtaining a reasonably high surface area and minimum aggregation. There is no single phase in any of the samples resulting from more than one peak on the CV curve present. The role of the addition of Sn to LTO to form LTO/Sn succeeded in raising the capacity value of the LTO from its theoretical specific capacity of 175 mAh/g. On the other hand, in the LTO/Sn@C the influence of the addition of carbon increases the specific capacity value compared to LTO/Sn. However, the main obstacle to obtaining consistent results in this research may have been the impurities in the carbon contained in the sample, such as the presence of ash, which inhibits the flow of electrons. The CV curve shows that all the samples have more than one peak. This is consistent with the XRD results, where there are phases of TiO2, Sn and LTO in the sample. The addition of Sn and carbon generally succeeded in raising capacity. At a high C-rate, the addition of carbon raises the specific capacity value. LTO with a composition of 7.5 wt.% Sn and 5 w.t% carbon (LSC-5) creates the optimum conditions to achieve a specific capacity of 270.2 mAh/g, which is much higher than the theoretical capacity of LTO of 175 mAh/g.
The authors would like to thank the Direktorat Riset dan Pengabdian Masyarakat Universitas Indonesia (DRPM-UI) for its financial support under the Hibah PITTA grant contract number PITTA/561/FT/2018.
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