Improving the Performance at Elevated Temperature of High Voltage Graphite/LiNi_0.5Mn_1.5O₄Cells with Added Lithium Catechol Dimethyl Borate

Abstract

Performance of LiNi 0.5 Mn 1.5 O 4 /graphite cells cycled to 4.8 V at 55 • C with the 1.2 M LiPF 6 in EC/EMC (3/7, STD electrolyte) with and without added lithium catechol dimethyl borate (LiCDMB) has been investigated. The incorporation of 0.5 wt% LiCDMB to the STD electrolyte results in an improved capacity retention and coulombic efficiency upon cycling at 55 • C. Ex-situ analysis of the electrode surfaces via a combination of SEM, TEM, and XPS reveals that oxidation of LiCDMB at high potential results in the deposition of a passivation layer on the electrode surface, preventing transition metal ion dissolution from the cathode and subsequent deposition on the anode. NMR investigations of the bulk electrolyte stored at 85 Lithium-ion batteries are widely used for portable electronics and are currently being incorporated into electric vehicles due to their high energy density.1,2 However, there is significant interest in further increasing the energy density of lithium-ion batteries.3 One method to achieve higher energy density is increasing the operating potential of the cathode material. Most commercial lithium-ion batteries contain a lithiated transition metal oxide cathode that typically operates at ∼4.0 V vs. Li/Li + . 3,4 Several novel cathode materials with operating potentials over 4.0 V are currently under investigation, including LiNiPO 4 , 5 LiCoPO 4 , 5,6 and LiNi 0.5 Mn 1.5 O 4 . While the high operating potential of the LiNi 0.5 Mn 1.5 O 4 spinel cathode (4.8 V vs. Li/Li + ) offers high energy density, commercialization has been hampered by severe capacity fade and poor efficiency. 7 The capacity fade is particularly pronounced at moderately elevated temperatures (>45• C) and in full cells employing a graphite anode. 7 The failure mechanisms of LiNi 0.5 Mn 1.5 O 4 cells at high voltage and elevated temperature have been recently investigated. [8][9][10][11][12][13][14] Electrolyte decomposition, electrode/electrolyte interface degradation, and transition metal dissolution are the leading factors reported for performance fade. One effective method for improving the performance of high voltage cathodes involves the incorporation of SEI (solid electrolyte interface) and CEI (cathode electrolyte interface) forming electrolyte additives that are sacrificially oxidized on the surface of electrodes to generate a passivation film which inhibits transition metal dissolution and further electrolyte oxidation.There have been several reports where electrolyte additives have improved the performance of cathodes cycled to high potential. [15][16][17][18]23 Lithium bis(oxalato borate) (LiBOB) has been reported to be one of the better additives for LiNi 0.5 Mn 1.5 O 4 cathodes. 16,17,[20][21][22][23][24][25] The related additive, lithium difluorooxalato borate (LiDFOB) 27-31 has also been reported to improve the properties of Li 1.2 Ni 0.15 Mn 0.55 Co 0.1 O 2 cathodes cycled to high potential 19 In addition to the lithium oxalato borates, 26,32 we have recently reported on the beneficial effect of the incorpor...

Effect of Lithium Borate Additives on Cathode Film Formation in LiNi0.5Mn1.5O4/Li Cells

“…Anodic linear sweep voltammetry of Super C65/Li cells is presented in Figure . Cells containing added LiCDMB have additional electrolyte oxidation above 3.5 V vs Li/Li + as evidenced by increased current; additional oxidation peaks are observed at 3.7, 4.0, and 4.4 V vs Li/Li + , which is consistent with previously published results . Cells containing added LPTB contain new oxidation peaks at 4.25 and 5.5 V vs Li/Li + with comparable intensity to those observed for LiCDMB.…”

“…All lithium borate additives are oxidized at lower potential than the STD electrolyte, and initiation of additive oxidation occurs in the following order LiCDMB > LPTB > LiBOB. All three borate additives have been previously investigated in graphite/LiNi 0.5 Mn 1.5 O 4 cells, confirming compatibility of the additives with graphite anodes. ,, …”

“…Inert metal oxide surface coatings have been previously reported to significantly improve the performance of LiNi 0.5 Mn 1.5 O 4 cathodes. ,− In an effort to generate similar protective surface coatings via electrolyte additives, the development of additives for designed surface modification (ADSM) has been under investigation . Several lithium borates, including lithium bis­(oxalate borate) (LiBOB), lithium alkyl trimethyl borates, lithium aryl trimethyl borates, and lithium catechol dimethyl borate (LiCDMB) (Figure ), have been investigated as electrolyte additives which generate an effective CEI passivation film. ,− The anionic borate additives are electron-rich, easily oxidized, and polarized toward the cathode surface upon initial cell charging. All of the lithium borate electrolyte additives have been reported to generate a borate-rich stable passivating CEI which improves the performance of LiNi 0.5 Mn 1.5 O 4 cathodes.…”

Face to Face at the Cathode Electrolyte Interphase: From Interface Features to Interphase Formation and Dynamics

“…However, not every formed CEI is an ideal compromise, which fulfills all of the following requirements: i) facilitate (or at least does not impede) lithium ion transfer, ii) reduce the interfacial/interphasial resistance, iii) reduce transition metal dissolution, iv) suppress gas generation, v) prevent structural changes of the electrode active material, and vi) prevent side reactions between the electrolyte formulation and the electrode (Figure 7). [89,93,94,98,99,104,109,119,[122][123][124][125][126][127][128][129]…”

Improving the Performance of Graphite/LiNi0.5Mn1.5O4Cells with Added N,N-dimethylformamide Sulfur Trioxide Complex

“…One of the most promising methods to improve the performance of LiNi 0.5 Mn 1.5 O 4 cathode films is via the incorporation of cathode film forming electrolyte additives that are sacrificially oxidized on the cathode surface to generate a cathode passivation layer. 7,11,12 While many different additives have been investigated, lithium bis(oxalate)borate (LiBOB) [13][14][15][16] and other lithium borates 6,7,17,18 are among the most widely investigated electrolyte additives which have been reported to improve the performance of cathodes operating at high potential. However, the borate additives have limitations and thus it is important to develop novel cathode film forming additives to improve the performance of high voltage LiNi 0.5 Mn 1.5 O 4 cathodes.…”