Effect of SEI on Capacity Losses of Spinel Lithium Manganese Oxide/Graphite Batteries Stored at 60°C

Abstract

The discharge capacities of spinel-type Li 1.1 Mn 1.9 O 4 /graphite cells charged in electrolytes with solid electrolyte interphase ͑SEI͒-forming additives are investigated after being stored at 60°C. The presence of Mn deposits on the anode surface, which is responsible for the capacity fading of cells, is clearly shown by means of open-circuit voltage, ex situ X-ray diffraction, and energy-dispersive spectrometry measurements. Unlike fluoroethylene carbonate, using vinylene carbonate as an SEI former leads to a noticeable improvement in the discharge capacity retention of cells that were stored for 20 days at 60°C.Lithium-ion ͑Li-ion͒ batteries have been used as reliable power sources for portable electronic devices. 1 Furthermore, Li-ion batteries are very attractive for applications in electric vehicles, hybrid electric vehicles, and plug-in hybrid electric vehicles owing to their high energy density and long lifetime. A high energy density in batteries can be achieved by increasing the discharge capacity of the cathode or by augmenting the working potential of the cathode materials. 2 Lithium manganese oxides ͑LiMn 2 O 4 ͒ with a spinel structure have been extensively studied for high energy and high power batteries to replace lithium cobalt oxides ͑LiCoO 2 ͒ as cathode materials. LiMn 2 O 4 has the potential to create batteries that are low cost, eco-friendly, have a prolonged lifecycle, and are safe to operate. 3,4 The capacity fading mechanisms of LiMn 2 O 4 are complex, especially at elevated temperatures, and the capacity fading of batteries with spinel LiMn 2 O 4 cannot be explained solely via the loss of cathode materials. Dissolved Mn ions undergo reduction on the anode and thereby lead to self-discharge of the lithiated graphite anode. Even very small amounts of manganese in an electrolyte can affect the calendar life of Li-ion batteries for large-scale power sources. Therefore, it is necessary to restrain the manganese dissolution to attain highly reliable batteries. Recently, it has been established that the partial substitution of manganese ions with transitionmetal ions, such as Co, Cr, or Ni, enhances the structural stability and electrochemical performance of lithium manganese oxides with a spinel structure. 5 Surface coatings with lithium cobalt oxide and other oxides seem to improve the performance of spinel lithium manganese oxides at elevated temperatures. 6,7 It was reported that a considerable degree of Mn dissolution into the electrolyte occurs in the presence of HF that is formed by the hydrolysis of LiPF 6 salts and deposits on the anode surface. [8][9][10] In the present study, we aim to understand the influence of Mn dissolution from a delithiated lithium manganese oxide cathode on the capacity retention behavior of fully charged cells that have been stored at 60°C. We also report intriguing data on the roles of SEIforming additives that could mitigate severe self-discharge in a lithiated graphite anode caused by Mn deposits. ExperimentalAn electrolyte solution composed of a commerc...

Effect of Lithium Bis(oxalato)borate Additive on Electrochemical Performance of Li1.17Ni0.17Mn0.5Co0.17O2Cathodes for Lithium-Ion Batteries

“…• C. [29][30][31] These metal ions then deposit on the anode surface by taking the electrons from the lithiated graphite anode. This electron consumption via the metal reduction on the lithiated graphite anode results in an increase in the anode potential and thus a decrease in the full cell potential.…”

Effects of Dissolved Transition Metals on the Electrochemical Performance and SEI Growth in Lithium-Ion Batteries

“…4,16 Two main routes by which capacity fading may occur due to dissolution are (i) structural changes to the positive electrode and leading to reduced insertion capacity and (ii) accelerated growth of the SEI layer at the negative electrode and the resulting irreversible Li consumption. 15,[17][18][19][20][21][22] Capacity fade due to the structural changes occurring in the positive electrode during partial dissolution is more likely in spinel electrodes, where the extent of dissolution is high, or at high potentials (overcharge). This large degree of dissolution in spinels may cause shrinkage of the active material, which decreased the effective transport properties and kinetics of the electrode.…”

“…They also reported that structural stability is directly related to the extent of dissolution in electrodes. 18 Dissolution may also cause a decrease in cell capacity by increased growth and breakdown of the SEI layer 21,22 on the negative electrode. Although dissolution has been studied extensively in spinel electrode materials and its negative effects on cell capacity have been wellestablished, how dissolution affects the growth of the solid electrolyte interphase (SEI) layer is not well-understood.…”

“…18,25,26 Transition metal ions resulting from dissolution diffuse across the separator and are reduced on the negative electrode. 4,16,19,21,[27][28][29][30][31][32][33] Since the growth of the SEI layer on negative electrodes is one of the major factors leading to capacity fade in Li-ion batteries, it is important to understand the effect of metal dissolution on the properties of the SEI layer. 21,22,[34][35][36][37][38][39][40][41] Understanding the changes occurring in the electrodes and the associated effect on the electrochemical performance of the cell is important in assessing the long-term behavior of these materials.…”

Ageing Behavior of LiNi<SUB>0.80</SUB> Co<SUB>0.15</SUB>Al<SUB>0.05</SUB>O<SUB>2</SUB> Cathode Based Lithium Ion Cells—Influence of Phase Transition Processes

“…In addition different mechanisms on the cathode side are known for calendric aging. In literature, different materials with different aging behaviors are known, especially deactivation of active material, dissolution of particles and side-reactions of active material [17] [18] [19].…”