Abstract: Changes of crystal structure of manganese dioxide during chemical and following electrochemical lithiation at high temperatures were determined using X-ray diffractometer, and the cathodical discharge properties of the compounds were analysed by simulating thermal batteries with a lithium-boron alloy anode. After chemically lithiated at 410 ℃, with the increase of Li/M n molar ratio, β-MnO2 turns to spinel-structure compounds through layered lithiated manganese dioxide which can change to spinel compounds and Mn2O3 if long-time exposed at 750℃. Intermediate phase LixMnO2 and final spinel phase LiMn2O4 also occurred if MnO2 or LixMnO2 were electrochemically lithiated at 500℃. The voltage of chemically lithiated compounds was not sensitive to Mn's initial valence when they were cathodically discharged, while over-potential was dependent mainly on the channels in which lithium-ions can diffuse inside the crystals.
Electrochemical intercalation performance of chemically lithiated manganese dioxide at high temperature
Abstract：
Changes of crystal structure of manganese dioxide during chemical and following electrochemical lithiation at high temperatures were determined using X ray diffractometer, and the cathodical discharge properties of the compounds were analysed by simulating thermal batteries with a lithium boron alloy anode. After chemically lithiated at 410 ℃, with the increase of Li/Mn molar ratio, β MnO 2 turns to spinel structure compounds through layered lithiated manganese dioxide which can change to spinel compounds and Mn 2O 3 if long time exposed at 750 ℃. Intermediate phase Li xMnO 2 and final spinel phase LiMn 2O 4 also occurred if MnO 2 or Li xMnO 2 were electrochemically lithiated at 500 ℃. The voltage of chemically lithiated compounds was not sensitive to Mn's initial valence when they were cathodically discharged, while over potential was dependent mainly on the channels in which lithium ions can diffuse inside the crystals.
Fig.3 Discharge curves at 5 A/dm2 for specimens with Li/Mn, initial atomic ratios, of (a) 0; (b) 1/4; (c) 1/3; (d) 1/2, after heat-treated at 410 ℃ and (e) 750 ℃; discharging condition: 500 ℃, Li-B anode and LiCl-KCl electrolyte
表1 5 A/dm2放电性能指标
Table 1 Discharge properties at 5 A/dm2
Initial atomic ratios of Li/Mn
Specific capacity at A / (A·s·g-1)
Specific capacity at B / (A·s·g-1)
Value of x in LixMn2O4 for
A
B
232
300
0.93
1.06
149
210
0.94
1.07
108
150
1.21
1.30
14
54
1.025
1.101
Note: specific capacity is the discharge capacity for per unit of initial LixMn2O4.
图4 曲线外延处理示意图
Fig.4 Schematic drawing of discharge curve's epitaxial treatment
图5 放电后的X射线衍射图
Fig.5 XRD spectra for discharged specimens with Li/Mn (initial atomic ratios) of (a) 0; (b) 1/4; (c) 1/3; (d) 1/2, treated at 410 ℃
Fig.6 Pulse-discharge curve for vacancy-rich spinel specimen with Li/Mn initial value of 1/3, cyclically loaded with 5 A/dm2 for 40 s and out of load for 20 s; discharging condition: 500 ℃, Li-B anode, LiCl-KCl electrolyte
Fig.7 Discharge curves at 20 A/dm2 for specimens with Li/Mn (initial atomic ratios) of (a) 0; (b) 1/4; (c) 1/3; (d) 1/2, after treated at 410 ℃ and (e) 1/2, after 750 ℃; discharging condition: 500 ℃, Li-B anode and LiCl-KCl electrolyte
Fig.8 Discharge curves for specially treated product with Li/Mn of 1/4 at current density of (a) 5; (b) 10 and (c) 20 A/dm2; discharging condition: 500 ℃, Li-B anode and LiCl-KCl electrolyte
图9 特殊处理Li/Mn比为1/4产物的放电后的X射线衍射图
Fig.9 XRD pattern for specially treated specimen with Li/Mn ratio of 1/4 after discharged
