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

Abstract

Transition metal dissolution is one of the major causes of capacity and power fade in lithium-ion batteries employing transition metal oxides in the positive electrode. Accelerated testing was accomplished by introducing transition-metal salts in the electrolyte in order to study the effects of dissolution on performance. It is shown that metal dissolution causes a reduction in capacity and cycle stability in full cells. The SEI layer resistance in the negative electrode of full cells increases with increasing concentration of transition metal salts. The growth of the SEI layer is non-uniform and is believed to be caused by the reduction of transition metal species in the negative electrode leading to an increase in inorganic component of the SEI layer. Consumption of fossil fuels in the transportation sector is one of the leading causes of greenhouse gas emissions (GHG).1 Efforts to develop cleaner and more efficient alternatives to the internal combustion engine running on petroleum fuels, such as fuel cells and batteries, are on the rise to mitigate this problem. Rechargeable lithium-ion (Li-ion) batteries offer high energy and power densities, good cyclic stability, and low rates of self-discharge. These characteristics are essential for applications in hybrid electric vehicles (HEV), plug-in hybrid vehicles (PHEV), and electric vehicles (EV). Dissolution of transition metals from the positive electrode is a concern for lithium-ion batteries, and manganese dissolution is a major reason for capacity fade in spinel electrodes, including LiMn 2 O 4 . 15Although less susceptible than spinel, metal dissolution does occur in NCM electrodes and has been implicated in a rise in impedance and capacity fade with cycling. 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.20,23 The extent of dissolution in different positive electrode materials was compared by Choi and Manthiram, 18 and amount of Mn dissolution is 16 times greater in LiMn 2 O 4 compared to NCM electrodes. They also reported that structural stability is directly related to the extent of dissolution in electrodes. 18Dissolution 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 dissoluti...

Temperature Dependence of Electrochemical Degradation in LiNi1/3Mn1/3Co1/3O2/Li4Ti5O12 Cells

“…This is expected, considering that the dissolution of Mn from the NMC cathode is highly temperature dependent. The presence of Mn on the LTO electrodes should originate from manganese, which have been dissolved from the NMC electrode, and is in good agreement with the well‐known aging mechanism in LIB cells …”

Aging Analysis of Graphite/LiNi1/3Mn1/3Co1/3O2Cells Using XRD, PGAA, and AC Impedance

“…[11][12][13]18,51 To examine the extent of transition metal deposition on the anode, PGAA was used to quantify the amount of deposited Ni, Mn, Co on harvested graphite anodes. Due to the large penetration depth of neutrons, PGAA examines the entire volume of the investigated anode samples.…”

Dopant Segregation Boosting High‐Voltage Cyclability of Layered Cathode for Sodium Ion Batteries

“…[12,16,17] One of the primary efforts on layered cathodes is further unlocking its capacity potential by narrowing the gap between the practical capacity and theoretical capacity. [26][27][28] The detrimental effects of cracking include fracture caused disintegration, [28] which leads to poor electronic conduction [29,30] and loss of active materials, and new surfaces exposure to electrolyte which results in cathode surface degradation [31][32][33] and electrolyte consumption. [18][19][20] The surface/interface degradations are attributed to the chemical reactions between cathode and electrolyte, which leads to cathode surface phase transition, [21,22] active material dissolution, [23] passivation layer formation, [24] electrolyte consumption, [25] and so on.…”