Abstract: Li containing binder for improved the first coulombic efficiency and cycleability of Li-ion Batteries Jun-Hwan Ku, a Seung Sik Hwang, a Min-Sang Song, a Jeong-Kuk Shon, a Sang-Min Ji, a Jae-Man Choi, a a Energy Lab, Samsung Advanced Institute of Technology, Electronic Materials Research Complex 130 Samsung-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do, Republic of Korea Lithium-ion batteries occupy a large and increasing share of the energy storage device market as a result of their excellent performance in terms of long-life, energy density and high safety. Among the various electrode materials for LIBs, graphites which are representative of carbon materials have been the most commonly used negative electrode materials due to their low working potential close to lithium metal anode, and remarkable cycling performance. As lithium-ion cells typically operate beyond the thermodynamic stability of organic electrolytes, the reduction products arising from chemical reactions during the first few cycles form passivating films on the carbon anode surface, as we call it 'solid electrolyte interphase (SEI)'. [1] Such SEI, which is comprised of electrochemically insulating layer, plays important roles of preventing the further electrochemical reactions between electrode surface and electrolyte and enabling only lithium ions tunnel through the layer. It is well known that the formation of SEI layers is a determinant factor on the performance of LIBs, affecting cycle-life, life time, power capability and even safety. [2] While the SEI plays an essential part in delivering the best performance in cells, the development of SEI layers are caused by the irreversible reaction accompanying an electrolyte decomposition, which makes the Coulombic efficiency to decrease during the first few cycles. When the stable SEI is not formed, any accidental misuse such as overcharge, high temperature exposure, and mechanic impact might damage the already formed SEI, resulting in more irreversible reaction during charging. The new anode surface, exposed to the electrolyte, immediately reacts with it to form a fresh thin protective film, which eventually leads to a poor cycleability and other undesirable properties in LIBs. Thus, to improve the performance of the cell, not only minimization of the electrolyte degradation but also thinner SEI film which provides an excellent passivating roll is required because thick and resistive SEI film is not favorable to battery operation. Many research studies are thus focused on the improvement of the chemical nature and morphology of SEI. For the modification to SEI films having superior properties, several previous papers reported the polymer binder including the SEI ingredients and their electrochemical effects of LIBs. [3,4] The effects of the surface modification of the graphite electrode by the functional polymer binder, such as poly(acrylic acid), have been reported in several papers. Concretely, it has been demonstrated that the polyion complex layer, which have oxygen species as functional groups, could play the role like artificial SEI to assist the facile penetration of Li ions. Obviously, the stable and efficient operation of LIBs is closely connected with ingredients of surface films, morphology, and coverage feature. Here we report that artificial pre-SEI, which is driven by Li ions containing polymer binder with functional group (-COOLi), can enhance the Coulombic efficiency and cycleability (Fig. 1). Furthermore, electrochemical performance is compared for SEI films that are produced from some different binders, in which different degree of lithium quantity is included in ISOBAM polymer. Fig. 1. (a) 1H-NMR spectra substituted ISOBAM polymer by 20, 50, 80, 100 amounts of Li ions, respectively. (b) Cycleability of SFG6 graphites with all investigated binders. Reference [1] E. Peled, J. Electrochem. Soc. , 1979, 1 26 , 2047. [2] E. Peled, in: J. P. Gabano (ED.), Lithium Batteries, AP, 1983, 43 [3] K. Xu, Chem. Rev. (Washington, D.C.) , 2004, 104 , 4303. [4] S. Komaba, N. Yabuuchi, T. Ozeki, K. Okushi, H. Yui, K. Konno, Y. Katayama, and T. Miura, J. Power Sources , 2010, 195 , 6069.

Abstract: Li 4 Ti 5 O 12 with a cubic spinel structure (space group, F d 3(_) m ) has a high redox potential at around 1.5 V vs. Li + /Li with a theoretical capacity of 175 mA h g −1 . 2 The negligible structural difference between pristine Li 4 Ti 5 O 12 and lithiated Li 7 Ti 5 O 12 at the two-phase equilibrium junction guarantees an outstanding electrochemical reversibility during the charge/discharge process. 3 Furthermore, the high redox potential would prevent not only the lithium metal deposition on the anode at high current conditions but also the formation of the resistive solid electrolyte interphase (SEI) layer, which may lead to an active Li-ion loss and an increase of the cell impedance. 4 No SEI formation at the surface of Li 4 Ti 5 O 12 is a widely accepted argument from the literature point of view. However, in our previous report regarding the electrochemical study of the carbon-free Li 4 Ti 5 O 12 electrode, 5 we noticed the formation and dissolution of the SEI layer through the change in the intensity of Ti 2p XPS core peaks during the charge and discharge process. This fact led us to suspect the stability of Li 4 Ti 5 O 12 vis-à-vis to the electrolyte in spite of its high redox potential. Despite the interesting properties of Li 4 Ti 5 O 12 , only few literature studies were reported on its reactivity to the electrolyte. Based on a detailed XPS study on the electrolyte/electrode interfaces in LiMn 1.6 Ni 0.4 O 4 / Li 4 Ti 5 O 12 system, Dedryvère et al. have reported the formation of organic and inorganic species on the surface of Li 4 Ti 5 O 12 anode after cycling. 6 However, they concluded that those species were first formed at the cathode and then, adsorbed on the surface of Li 4 Ti 5 O 12 either by diffusion or by migration of organic cationic species. In addition, the lower voltage limit of Li 4 Ti 5 O 12 anode couldn’t be also guaranteed to be over 1 V in their study because measuring the voltage of Li 4 Ti 5 O 12 itself is impossible in two-electrode full cell. He et al. also pointed out the formation of SEI film on the Li 4 Ti 5 O 12 electrode cycled between 2.5 and ~ 0 V vs. Li + /Li., but they mainly focused on the SEI formation occurred below 1 V. 7 Moreover, in the aforementioned studies, the results were obtained only at room temperature cycling, and the effects of carbon conducting agent contained in the conventional Li 4 Ti 5 O 12 electrodes were neither considered nor clarified. In this report, for the first time, the Li 4 Ti 5 O 12 / electrolyte interface is investigated at room and high temperature using the carbon-free Li 4 Ti 5 O 12 electrode. The new electrode concept 5,8 allows us to examine the reactivity of Li 4 Ti 5 O 12 to the electrolyte and avoid any kind of parasite reaction which may be induced by the high-surface-area carbon conducting additive. Chemical changes at the surface of Li 4 Ti 5 O 12 were investigated using a step by step X-ray photoelectron spectroscopy (XPS) analysis during charge/discharge cycling. The time-of-flight secondary ion mass spectroscopy (ToF-SIMS) study and scanning electron microscopy (SEM) observation were carried out to examine a quantitative and qualitative change in the surface chemistry and the electrode morphology after cycling, respectively. The differences between the carbon-free and carbon-containing Li 4 Ti 5 O 12 electrodes in terms of stability and cyclability were also discussed. [1] S.S. Zhang, J. Power Sources , 2006, 161 , 1385. [2] T. Ohzuku, A. Ueda, N. Yamamoto, J. Electrochem. Soc. , 1995, 142 , 1431; L. Kavan, M. Gratzel, Electrochem. Solid State Lett. , 2002, 5 , A39. [3] K. Zaghib, M. Simoneua, A. Armand, M. Gauthier, J. Power Sources , 1999, 81-82 , 300; G. Armstrong, A. R. Armstrong, J. Canales, P. G. Bruce, Electrochem. Solid-State Lett. , 2006, 9 , A139; A. N. Jansen, A. J. Kahaian, K. D. Kepler, P. A. Nelson, K. Amine, D. W. Dees, D.R. Vissers, M. M. Thackeray, J. Power Sources , 1999, 81-82 , 902; T. Brousse, P. Fragnaud, R. Marchand, D. M. Schleich, O. Bohnke, K. West, J. Power Sources , 1997, 68 , 412; T. Ohzuku, A. Ueda, N. Yamamoto, J. Electrochem. Soc. , 1995, 142 , 1431. [4] J. Christensen, V. Srinivasan, J. Newman, J. Electrochem. Soc. , 2006, 153 , A560; M. Winter, W. K. Appel, B. Evers, T. Hodal, K. C. Moller, I. Schneider, M. Wachtler, M. R. Wagner, G. H. Wrodnigg, J. O. Besenhard, Monatsch. Chem. , 2001, 132 , 473. [5] M. S. Song, A. Benayad, Y. M. Choi and K. S. Park, Chem. Commun. , 2012, 48 , 516. [6] R. Dedryvère, D. Foix, S. Franger, S. Patoux, L. Daniel and D. Gonbeau, J. Phys. Chem. C, 2010, 114 , 10999. [7] Y. B. He, F. Ning, B. Li, Q. S. Song, W. Lv, H. Du , D. Zhai, F. Su, Q. H. Yang, F. Kang, J. of Power Sources, 2012, 202 , 253. [8] C. J. Kim, N. S. Norberg, C. T. Alexander, R. Kostecki and J. Cabana, Adv. Funct. Mater., 2013, 23 , 1214.

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