Magnetic and electronic properties ofLixCoO2single crystals

Abstract

Measurements of electrical resistivity ͑͒, dc magnetization ͑M͒, and specific heat ͑C͒ have been performed on layered oxide Li x CoO 2 ͑0.25Յ x Յ 0.99͒ using single-crystal specimens. The versus temperature ͑T͒ curve for x = 0.90 and 0.99 is found to be insulating but a metallic behavior is observed for 0.25Յ x Յ 0.71. At T S ϳ 155 K, a sharp anomaly is observed in the -T, M-T, and C / T-T curves for x = 0.66 with thermal hysteresis, indicating the first-order character of the transition. The transition at T S ϳ 155 K is observed for the wide range of x = 0.46-0.71. It is found that the M-T curve measured after rapid cool becomes different from that after slow cool below T F , which is ϳ130 K for x = 0.46-0.71. T F is found to agree with the temperature at which the motional narrowing in the 7 Li NMR linewidth is observed, indicating that the Li ions stop diffusing and order at the regular site below T F . The ordering of Li ions below T F ϳ 130 K is likely to be triggered and stabilized by the charge ordering in CoO 2 layers below T S .

Charging of lithium cobalt oxide battery cathodes studied by means of magnetometry

“…1) agree well with reported literature data [2][3][4]10,13]. This shows that the present way of adjusting and determination of the lithium concentration by electrochemical extraction can be considered as reliable.…”

“…For Co 4+ , a magnetic moment of 1.73 μ B is associated with the respective low spin state S=1/2 [7,10,13].…”

“…In fact, the magnetic susceptibility changes by several 100% with Li de-/intercalation and, therefore, serves as sensitive fingerprint of the charging state. Over the last few years, various groups were concerned with magnetic measurements on Li x CoO 2 cathodes [4,7,[9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Studies over a certain range of concentrations were performed by extracting Li either chemically or electrochemically: chemical Li extraction by Kellerman et al [7] (0.98 ≥ x ≥ 0.60, 6 samples), Hertz et al [9] (1≥ x ≥ 0.51, 9 samples), or Miyoshi et al [10] (0.99 ≥ x ≥ 0.25, 6 samples), electrochemical Li extraction by Sugiyama et al [11] (1 ≥ x ≥ 0.70, 3 samples), Mukai et al [12] (1 ≥ x ≥ 0.10, 8 samples) or Motohashi et al [13] (1≥ x ≥ 0, 9 samples).…”

Impact of lithium composition on the thermoelectric properties of the layered cobalt oxide system LixCoO2

“…It should be noted that their Li x CoO 2 samples were prepared through a complicated route: the samples were obtained with an ion exchange reaction between Na x CoO 2 and Li 2 CO 3 /LiNO 3 , followed by Li extraction utilizing chemical reagents such as NO 2 BF 4 and K 2 S 2 O 8 . 30,31 We suggest that the difference in the synthesis routes may affect the degree of chemical homogeneity, which would be the main source of the discrepancies in the experimental results.…”

Electronic phase diagram of LixCoO2revisited with potentiostatically deintercalated single crystals

“…In addition, the observed 175K phase anomaly shows a significant thermal hysteresis in both resistivity and magnetic susceptibility measurements. 13,15 The persistent existence of one phase signature in a wide range of lithium content suggests that such phase has not been isolated completely from the co-existing phase mixture. The observation of thermal hysteresis also strongly suggests that such hardto-extract phase could be closely related to a phase existence within extremely narrow phase space, i.e., slight deviation due to inhomogeneity could create phase separation of small miscibility gap.…”