Abstract: Abstract not Available.

Abstract: Current battery technology is limited by the decomposition of electrolytes at high voltages ( 〉 4.3 V vs. Li/Li + ), [1] which prevents the use of high voltage cathodes having higher power than current cathode technology. Among various high voltage cathode materials, LiNi 0.5 Mn 1.5 O 4 (LNMO) is one of the most promising candidates due to its high energy and power densities as well as being inexpensive and environmental benign. [2] The high working potential (about 4.7V vs. Li) of Ni 2+ /Ni 3+ and Ni 3+ /Ni 4+ redox couples delivers an energy density equivalent to ~650 W h kg -1 , which is the highest among commercially available cathode materials. [3] Furthermore, the three-dimensional channels in the spinel lattice enhance lithium diffusion rates during intercalation-deintercalation process. While the high operation voltage of LNMO increases power and energy density, it also causes extensive oxidation of the conventional carbonate electrolytes, resulting in large irreversible capacity loss, low coulombic efficiency, and considerable thickening of the solid-electrolyte interphase (SEI) layer. [4]  So far, different additives such as phosphite derivatives, [5] lithium aryl trimethyl borates, [6] lithium difluoro(oxalate)-borate [7] and lithium bis(oxalate)borate (LiBOB) [8] have been used to improve the capacity retention and cycling stability of the LNMO based batteries. [9] Among those additives, LiBOB has been intensively studied because of its distinct thermal stability and beneficial effect of SEI formation. [8, 10] Considering the benefits of LiBOB, we have synthesized a close analog lithium borate salt, lithium bis(2-fluoromalonato)borate (LiBFMB), with higher oxidation stability than LiBOB and solubility in carbonate mixtures. [11] However, LiBFMB has poor stability against both reduction and oxidation because the C-2 hydrogen adjacent to both fluorine and carbonyl groups is acidic and is believed to deterimentally react. To mitigate this issue, we have synthesized a new lithium salt by replacing the acidic hydrogen with a methyl group, forming lithium bis(2-methyl-2-fluoromalonato) borate (LiBMFMB). [12] LiBMFMB based electrolyte showed good cycling performance in both LNMO and graphite based half cells, although its ionic conductivity was still lower than that of LiPF 6 . [12]  In this talk, we report the use of LiBMFMB as an additive in conventional carbonate electrolyte for LNMO based lithium ion batteries, taking advantage of its good SEI formation ability while mitigating its conductivity issue. The LNMO based half-cells with LiBMFMB as an additive exhibited significantly improved cycling performance under a high current rate of 1C, due to a decrease in the decomposition of the LiPF 6 salt and electrolyte solvents and reduction of the SEI layer thickness. [1] J. B. Goodenough, Y. Kim, Chemistry of Materials 2010 , 22 , 587-603. [2] A. Kraytsberg, Y. Ein-Eli, Advanced Energy Materials 2012 , 2 , 922-939. [3] D. Liu, W. Zhu, J. Trottier, C. Gagnon, F. Barray, A. Guerfi, A. Mauger, H. Groult, C. M. Julien, J. B. Goodenough, K. Zaghib, RSC Adv. 2014 , 4 , 154-167. [4] N. P. W. Pieczonka, Z. Liu, P. Lu, K. L. Olson, J. Moote, B. R. Powell, J.-H. Kim, J. Phys. Chem. C 2013 , 117 , 15947-15957. [5] Y.-M. Song, J.-G. Han, S. Park, K. T. Lee, N.-S. Choi, J. Mater. Chem. A 2014 , 2 , 9506-9513. [6] M. Q. Xu, L. Zhou, Y. N. Dong, Y. J. Chen, J. Demeaux, A. D. MacIntosh, A. Garsuch, B. L. Lucht, Energy & Environmental Science 2016 , 9 , 1308-1319. [7] S. Li, W. Zhao, X. Cui, Y. Zhao, B. Li, H. Zhang, Y. Li, G. Li, X. Ye, Y. Luo, Electrochimica Acta 2013 , 91 , 282-292. [8] a) K. Xu, S. Zhang, T. R. Jow, Electrochemical and Solid-State Letters 2005 , 8 , A365; b) Z. Chen, W. Q. Lu, J. Liu, K. Amine, Electrochimica Acta 2006 , 51 , 3322-3326. [9] a) S. S. Zhang, Journal of Power Sources 2006 , 162 , 1379-1394; b) A. von Cresce, K. Xu, Journal of the Electrochemical Society 2011 , 158 , A337-A342. [10] a) N. P. W. Pieczonka, L. Yang, M. P. Balogh, B. R. Powell, K. Chemelewski, A. Manthiram, S. A. Krachkovskiy, G. R. Goward, M. H. Liu, J. H. Kim, Journal of Physical Chemistry C 2013 , 117 , 22603-22612; b) M. Xu, N. Tsiouvaras, A. Garsuch, H. A. Gasteiger, B. L. Lucht, The Journal of Physical Chemistry C 2014 , 118 , 7363-7368. [11] C. Liao, K. S. Han, L. Baggetto, D. A. Hillesheim, R. Custelcean, E.-S. Lee, B. Guo, Z. Bi, D.-e. Jiang, G. M. Veith, E. W. Hagaman, G. M. Brown, C. Bridges, M. P. Paranthaman, A. Manthiram, S. Dai, X.-G. Sun, Advanced Energy Materials 2014 , 4 , 1301368 (1-12).. [12] S. Wan, X. G. Jiang, B. K. Guo, S. Dai, J. B. Goodenough, X. G. Sun, Chemical Communications 2015 , 51 , 9817-9820. Figure 1

Abstract: Abstract not Available.

Abstract: The developments of advanced Li-ion batteries (LIBs) not only depend on the advances in electrode chemistries but also rely on the improvement of the functional electrolyte system (salt, solvent, and additive) for high ionic conductivity and controlled solid electrolyte interphase (SEI) formation capability 1 To increase the energy density of LIBs, high voltage cathode materials ( 〉 4.5 V vs. Li/Li + ) such as the Li-rich compounds, olivine-type LiNiPO 4 , and LiCoPO 4 , as well as spinel-type LiCoMnO 4 , and LiNi 0.5 Mn 1.5 O 4 (LNMO) 2 have been intensively investigated. Particularly, LNMO has attracted more attention because of its fast lithium conduction through the three-dimensional channels and its low cost and environmentally benign. Unfortunately, it causes extensive oxidation of the electrolyte because of its high operation voltage, resulting in thickening of the passivation layer and large irreversible capacity loss. 3 To mitigate severe electrolyte oxidation and improve long cycling performance of LNMO based batteries, different additives have been evaluated. 4  In addition to organic molecules, lithium salts such as lithium bis(oxalato)borate (LiBOB), 5 and lithium difluoro(oxalato)-borate (LiDFOB) 6 have also been evaluated and showed improved long cycling stability. Even though LiBOB and LiDFOB have been extensively studied as additives, the resulting SEI layer and passivation layer generally suffers from high resistance, possibly due to two carbonyl groups being too close to each other. In an effort to reduce the resistance of the SEI layers by increasing the flexibility and yet at the same time enhance the electron delocalization of the anions, we have synthesized a series of fluorinated lithium bis(malonato) borate (LiBMB) salts (Scheme 1), 7-9 the close analog of LiBOB. 10 Besides structurally more flexible, the two hydrogens on the C-2 position of the BMB anion can be substituted by different functional groups, and the electrochemical properties of the salts and their SEI and passivation characteristics can be tuned and optimized. Indeed, improvement has been observed by replacing the acidic hydrogen in lithium bis(2-fluoromalonatoborate) (LiBFMB) with a methyl group in lithium bis(2-methyl-2-fluoromalonato) borate (LiBMFMB) (Scheme 1). 7, 11 Unfortunately, the ionic conductivities of both LiBFMB and LiBMFMB based electrolytes are lower than that of LiPF 6 . To improve the ionic conductivity of these malonatoborate salts, we have further synthesized lithium difluoro-2-alkyl-2-fluoromalonatoborate salts (LiDFMFMB, LiDFEFMB, and LiDFPFMB where alkyl group is methyl, ethyl and propyl, respectively) whose ionic conductivities are close to that of LiPF 6 in the carbonate mixture of EC-ethylene carbonate (EMC) (1-2, by wt.). 9 Electrochemical floating test showed that these half salts are less stable than LiPF 6 above 4.9 V vs Li/Li + , 9 which inspired us to use them as additives in LNMO based batteries. Indeed, these additives exhibited high coulombic efficiency and improved long cycle stability in LNMO||NG full cells, thus providing a cost-effective way to improve the performance of high voltage LNMO batteries. In addition, the additives also exhibit better passivation of the aluminum current collector. References: 1. M. Armand and J. M. Tarascon, Nature , 2008, 451 , 652-657. 2. Q. M. Zhong, A. Bonakdarpour, M. J. Zhang, Y. Gao and J. R. Dahn, J Electrochem. Soc. , 1997, 144 , 205-213. 3. K. Xu, Chemical reviews , 2014, 114 , 11503-11618. 4. S. S. Zhang, J. Power Sources , 2006, 162 , 1379-1394. 5. K. Xu, S. S. Zhang and T. R. Jow, Electrochem. Solid-State Lett. , 2005, 8 , A365. 6. Y. Zhu, Y. Li, M. Bettge and D. P. Abraham, Electrochimica Acta , 2013, 110 , 191-199. 7. Y. C. Li, S. Wan, G. M. Veith, R. R. Unocic, M. P. Paranthaman, S. Dai and X. G. Sun, Adv. Energy Mater. , 2016, 1601397. 8. C. Liao, K. S. Han, L. Baggetto, D. A. Hillesheim, R. Custelcean, E. S. Lee, B. K. Guo, Z. H. Bi, D. E. Jiang, G. M. Veith, E. W. Hagaman, G. M. Brown, C. A. Bridges, M. P. Paranthaman, A. Manthiram, S. Dai and X. G. Sun, Adv. Energy Mater. , 2014, 4 , 1301368 9. X.-G. Sun, S. Wan, H. Y. Guang, Y. Fang, K. S. Reeves, M. Chi and S. Dai, J. Mater. Chem. A , 2017, 5 , 1233-1241. 10. W. Xu and C. A. Angell, Electrochem. Solid State Letters , 2001, 4 , E1-E4. 11. S. Wan, X. G. Jiang, B. K. Guo, S. Dai, J. B. Goodenough and X. G. Sun, Chem Commun , 2015, 51 , 9817-9820. Figure 1

Abstract: The degradation of lithium ion batteries (LIBs) with cycling results from reactions of electrolyte at both anode and cathode, leading to increased cell impedance from continual formation of solid electrolyte interphases (SEIs). One of the economic ways to improve battery cycling performance is to utilize sacrificial additives that could form thin and stable SEIs to prevent continual electrolyte reactions at both electrodes. In this presentation, three trimethylsilyl based malonate esters have been used as additives in 1.0 M LiPF 6 /ethylene carbonate (EC)-dimethyl carbonate (DMC)-diethyl carbonate (DEC) (1-1-1, by v) baseline electrolyte for LiNi 0.80 Co 0.15 Al 0.05 O 2 (NCA) based high voltage lithium ion batteries. The NCA half-cells with 5 wt.% additive exhibit higher capacity retention than that in the baseline electrolyte at different upper cut off voltages, that is, 4.2, 4.3, 4.4 and 4.5 V vs. Li/Li + . Scanning electron microscope (SEM) show that the additive successfully prevents the formation of thick solid electrolyte interphase (SEI) films on the surface of the NCA electrodes. X-ray diffraction (XRD) further reveals that the crystal structure of NCA is also maintained in the electrolyte with 5 wt.% additive at high cut off voltages. Besides beneficial to NCA cathode, the BTMSMFM additive also ensures better cycling performance of the graphite based half-cells and NCA/graphite full-cells, and thus is a promising additive for application in rechargeable lithium ion batteries.