Study of Mn Dissolution from LiMn[sub 2]O[sub 4] Spinel Electrodes Using Rotating Ring-Disk Collection Experiments

Abstract

The goal of this research was to measure Mn dissolution from a thin porous spinel LiMn 2 O 4 electrode by rotating ring-disk collection experiments. The amount of Mn dissolution from the spinel LiMn 2 O 4 electrode under various conditions was detected by potential step chronoamperometry. The concentration of dissolved Mn was found to increase with increasing cycle numbers and elevated temperature. The dissolved Mn was not dependent on disk rotation speed, which indicated that the Mn dissolution from the disk was under reaction control. The in situ monitoring of Mn dissolution from the spinel was carried out under various conditions. The ring currents exhibited maxima corresponding to the end-of-charge ͑EOC͒ and end-of-discharge ͑EOD͒, with the largest peak at EOC. The results suggest that the dissolution of Mn from spinel LiMn 2 O 4 occurs during charge/discharge cycling, especially in a charged state ͑at Ͼ4.1 V͒ and in a discharged state ͑at Ͻ3.1 V͒. The largest peak at EOC demonstrated that Mn dissolution took place mainly at the top of charge. At elevated temperatures, the ring cathodic currents were larger due to the increase of Mn dissolution rate. The rapid progress in development and widespread use of portable electronic devices have led to a great demand for portable, lightweight power sources. Lithium-ion technology has met these requirements, and has been used commercially for over ten years because it offers high energy and power density, high voltage, longlife, and reliability. The performance of lithium-ion batteries is to a large degree determined by the cathode material. There have been many studies of the cathode materials during the last decade. Although LiCoO 2 has been widely used as the cathode material in the commercial lithium-ion batteries for many years, the lithium manganese oxide spinel LiMn 2 O 4 is a promising alternative cathode material in the future because of its high voltage, low cost, and environmental friendliness. These attractive characteristics make spinel LiMn 2 O 4 a good candidate for large-scale Li-ion batteries for electric vehicle ͑EV͒ and hybrid electric vehicle ͑HEV͒ applications.1 However, capacity fading during charge/discharge cycling is a problem for the spinel, particularly at elevated temperatures. Several factors have been proposed to contribute to the capacity fading such as ͑i͒ the electrochemical reaction with the electrolyte at high voltage, 2,3 (ii) manganese dissolution into the electrolyte due to acid attack and a disproportion reaction at the particle surfaceinstability of the two-phase structure in the charged state leading to the loss of MnO and dissolution of Mn to a more stable single-phase structure, 4,8,9 (iv) formation of tetragonal Li 2 Mn 2 O 4 on the surface of the spinel and the associated Jahn-Teller distortion at the end of discharge, especially under high current density, nonequilibrium conditions, 5,10,11 (v) formation of oxygen-deficient spinels, 12 (vi) cation mixing between the lithium and manganese sites in the spinel lattice, 13 an...

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

“…15 Although 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.…”

“…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.…”

Urea-assisted hydrothermal synthesis of a hollow hierarchical LiNi0.5Mn1.5O4 cathode material with tunable morphology characteristics

“…6 Mn dissolution and severe strain from Jahn-Teller distortion. 3,56,57 In addition, it has been reported that the Mn dissolution of LiMn 2 O 4 spinel is oen accelerated with larger specic surface area, 58,59 which should be also applicable to LiNi 0.5 -Mn 1.5 O 4 , a derivative of LiMn 2 O 4 . The impurity phase tends to react with the electrolyte and thus causes capacity fading.…”

Comparison of Different Synthesis Methods for LiNi0.5Mn1.5O4—Influence on Battery Cycling Performance, Degradation, and Aging

“…Consideringt he different degradation effects of Mn-based spinel materials,t he capacity fadingo fL MO because of Mn dissolution into the electrolyte during cycling was studied extensively. [10,12,[45][46][47][48][49][50][51] Mn dissolution is driven mainly by the disproportionation reaction, which implies the transformation of Mn 3+ + ions into soluble Mn 2+ + and as table Mn 4+ + compound. [45,51] Thed isproportionation of Mn is hinderedi n LNMO because of the reduced Mn 3+ + content in the presence of Ni 2+ + .F urthermore,t he introduction of Ni leads to the enhanceds tability of the delithiated structure in the charged state [11] compared to that of LMO,w hich suffers from structural changes accompanied with the dissolution of Mn.…”

“…[45,51] Thed isproportionation of Mn is hinderedi n LNMO because of the reduced Mn 3+ + content in the presence of Ni 2+ + .F urthermore,t he introduction of Ni leads to the enhanceds tability of the delithiated structure in the charged state [11] compared to that of LMO,w hich suffers from structural changes accompanied with the dissolution of Mn. [46] Additionally,during discharge at high rates,the fastlithiation of the active material leads to an accumulation of Li ions on the surface of the particles. [52] In LMO,t his can cause the average Mn valence to fall below + +3.5, and the onset of Jahn-Teller distortion leads to as pontaneous increase of the unit cell by 16 %.…”