Cobalt substitution in lithium manganate spinels: examination of local structure and lithium extraction by XAFS

Li ion kinetic studies on spinel cathodes, Li(M1/6Mn11/6)O4 (M = Mn, Co, CoAl) by GITT and EIS

“…5,[10][11][12][13][14] The observed reduction in the initial charge-discharge capacity proportional to the amount of the substituent M leads to the conclusion that the Mn 31 ions in the lattice are replaced and the M ion is electrochemically inactive in the voltage range of operation, 3.5-4.3 V vs. Li. 5,[10][11][12][13][14] The main reasons for the capacity fading in LiMn 2 O 4 -type cathodes were ascribed to structural change and Mn dissolution on cycling the cells especially at high temperatures. [3][4][5][7][8][9][16][17][18][19][20][21] The increased impedance contribution of the LiMn 2 O 4 electrode with cycling was also correlated with the observed capacity fading in spinel compounds.…”

“…[5][6][7][8][9][10][11][12][13][14][15][16][17] The latter is also ascribed to the stronger M-O (M~Co, Cr, Al) bond strength compared to that of the Mn-O bond in the spinel structure. 5,[10][11][12][13][14] The observed reduction in the initial charge-discharge capacity proportional to the amount of the substituent M leads to the conclusion that the Mn 31 ions in the lattice are replaced and the M ion is electrochemically inactive in the voltage range of operation, 3.5-4.3 V vs. Li. 5,[10][11][12][13][14] The main reasons for the capacity fading in LiMn 2 O 4 -type cathodes were ascribed to structural change and Mn dissolution on cycling the cells especially at high temperatures.…”

“…17 The fact that the unsubstituted LiMn 2 O 4 shows structural change on cycling at ambient temperature 1,7,9,18,20 but was not seen in the M-substituted spinels at 50 uC 16 is in accordance with the proposed structural stability of the material with doping. [5][6][7][8][9][10][11][12][13][14][15][16][17] Our recent studies 5 and those of Wakihara and co-workers 11,12 have shown improved cathodic performance of the doped spinels Li(M 1/6 Mn 11/6 )O 4 ; M~Co, (Co,Al), (Co,Cr) and (Cr,Al) at ambient temperature (27 uC) as well as at 50 uC (or 55 uC 11,12 ) and this was ascribed to their structural stability. In the present study, galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) studies on the substituted spinels Li(M 1/6 Mn 11/6 )O 4 ; M~Mn, Co and (Co,Al) were carried out to determine the Li ion kinetics and hence to understand the factors which lead to their improved performance.…”

“…[1][2][3][4][5][6] To improve its cycling performance, especially at elevated temperature (¢50 uC), several approaches such as doping at the Mn site, surface modification, and various preparatory conditions have been shown to be successful. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] The partial substitution of Mn as Li(M,Mn) 2 O 4 , (M~Li, Co, Cr, Al, (Co,Al), (Co,Cr), Ni, Mg) at the 16d site is known to increase the average Mn-oxidation state, enabling the compound to be more tolerant to JahnTeller distortion, and an improved cathodic performance is observed. [5][6][7][8][9][10][11][12][13][14][15][16][17] The latter is also ascribed to the stronger M-O (M~Co, Cr, Al) bond strength compared to that of the Mn-O bond in the spinel structure.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] The partial substitution of Mn as Li(M,Mn) 2 O 4 , (M~Li, Co, Cr, Al, (Co,Al), (Co,Cr), Ni, Mg) at the 16d site is known to increase the average Mn-oxidation state, enabling the compound to be more tolerant to JahnTeller distortion, and an improved cathodic performance is observed. [5][6][7][8][9][10][11][12][13][14][15][16][17] The latter is also ascribed to the stronger M-O (M~Co, Cr, Al) bond strength compared to that of the Mn-O bond in the spinel structure. 5,[10][11][12][13][14] The observed reduction in the initial charge-discharge capacity proportional to the amount of the substituent M leads to the conclusion that the Mn 31 ions in the lattice are replaced and the M ion is electrochemically inactive in the voltage range of operation, 3.5-4.3 V vs. Li.…”