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Wang Z.,South China Normal University | Wang Z.,Dongguan Kaixin Battery Material Co. | Xing L.,South China Normal University | Li J.,South China Normal University | And 5 more authors.
Electrochimica Acta | Year: 2015

Trimethyl borate (TB) is used as an electrolyte additive to improve cyclic stability and rate capability of a layered cathode, LiNi1/3Co1/3Mn1/3O2 (LNCM), under 4.5 V (vs. Li/Li+). Charge/discharge tests demonstrate that the cyclic stability and rate capability of LNCM can be improved significantly by adding TB into a standard (STD) electrolyte, 1.0 mol L-1 LiPF6 in ethylene carbonate/ethyl methyl carbonate/diethyl carbonate (3/5/2, in weight). After 200 cycles at 0.5C between 3.0 and 4.5 V, LNCM exhibits a capacity retention of 89% in 10% TB-containing electrolyte, but only 48% in STD electrolyte. Unlike other additives, which usually decrease the rate capability when they are used for the cyclic stability improvement of LNCM, the discharge capacity of LNCM at 6C is enhanced from 78 mAh g-1 in STD electrolyte to 102 mAh g-1 in 10% TB-containing electrolyte. Physical and electrochemical characterizations demonstrate that these improvements result from the preferential oxidation of TB compared to the STD electrolyte and the formation of a stable and low impedance film on LNCM cathode surface, which suppresses concurrently the decomposition of electrolyte and the dissolution of transition metal ions from LNCM. © 2015 Elsevier Ltd. Source


Wang Z.,South China Normal University | Wang Z.,Dongguan Kaixin Battery Material Co. | Xing L.,South China Normal University | Li J.,South China Normal University | And 3 more authors.
Journal of Power Sources | Year: 2016

Triethylborate (TEB) is used as an electrolyte additive to improve the electrochemical performances of LiNi1/3Co1/3Mn1/3O2 (LNCM) upon cycling at 4.5 V vs. Li/Li+. Charge/discharge tests demonstrate that the cyclic stability of LNCM at room and elevated temperature can be improved effectively by TEB. With addition of 10 wt. % TEB into STD electrolyte (1.0 M LiPF6/EC:EMC:DEC), LNCM achieves a capacity retention of 99.8% after 150 cycles and 94.7% after 120 cycles at room and elevated temperature, respectively, comparing to that of 68.9% and 68.8% of STD electrolyte. In addition, 10 wt. % TEB also improves the rate capability of LNCM at room temperature. Physical and electrochemical characterizations from XRD, SEM, TEM, XPS, ICP-MS, LSV, CA, and EIS reveal that the preferential oxidative reaction of TEB generates a thin, uniform and low interfacial resistance film on the LNCM surface. This film not only suppresses the subsequent decomposition of STD electrolyte, but also prevents the dissolution of transition metal ions from LNCM, resulting in improved cyclic stability and rate capability of LNCM. © 2015 Elsevier B.V. All rights reserved. Source


Wang X.,South China Normal University | Wang X.,Dongguan Kaixin Battery Material Co. | Xing L.,South China Normal University | Liao X.,South China Normal University | And 7 more authors.
Electrochimica Acta | Year: 2015

Trimethylboroxine (TMB) is used as electrolyte additive to improve the cyclic stability of LiCoO2/graphite full cell under high voltage. It is found that capacity retention of LiCoO2/graphite cell at 0.3C rate after 200 cycles between 3.0 ∼ 4.5 V is improved from 29 % to 66 % by applying 0.5 % (by weight) TMB in EC-based electrolyte. Charge-discharge tests on graphite/Li and LiCoO2/Li half cells demonstrate that the improvement in cyclic stability of the full cell results from the contribution of TMB to the enforced stability of LiCoO2 cathode. Cyclic voltammogram shows that TMB is oxidized preferentially to the EC-based electrolyte, while physical characterizations, from SEM, TEM, FTIR and XPS, indicate that TMB helps build a thin but protective film on LiCoO2, which improves the interfacial stability of high voltage electrode/electrolyte. © 2015 Elsevier Ltd. All rights reserved. Source

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