10-Li[Li13–2x3NixMn23–x3]O2-AM(2)

the (001) plane (Figure 3d), which is the plane normal to both the set of (110) planes with a crossing lattice spacing of 0.14 nm (d110) and the set of (100) planes with a lattice spacing of 0.25 nm (d100). The ratio of the number of (001) nanoplates to that of (010) nanoplates is found to be approximately 6:1 by sorting out the nanoplates from the XRD analysis and the statistical results of high-resolution TEM (HRTEM) characterizations (see Supporting Information, Section 2), which signi es that the quantity of (010) nanoplates is increased to 1/7 of the total amount of HTN-L

NMO. If the (010) and (001) nanoplates have the same volume, the proportion of the active surface area, that is, the (100)+(010) planes, on the (001) nanoplates is only 21.7%, while it is increased to 93.7% on the (010) nanoplates (see Supporting Information, Section 3). Such analysis implies that the active surface area for Li+ transportation on the (010) nanoplate can be as high as 4.3 times that of the (001) nanoplates. In the present case, although the proportion of the (010) nanoplates in HTN-LNMO is about 1/7, the active surface area in the HTN-LNMO sample

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a)

b)

d003

d 100

c)

d003 d100 d100[100][100]

d)d110

[110][001]

Figure 3. HRTEM results. a) TEM image of HTN-LNMO; the scale bars in the insets both represent 20 nm. b) HRTEM image of the lateral view of HTN-LNMO. c) HRTEM image of the frontal view of a (010) nanoplate. d) HRTEM image of the frontal view of a (001) nanoplate.

has been increased by about 50% in comparison with that in CN-LNMO (see Supporting Information, Section 3). The charge/discharge cycling performance of the HTN-LNMO is illustrated in Figure 4a. The rst charge and discharge capacities were measured as 260 mA h g 1 and 190 mA h g 1, respectively. After 5 cycles, the charge capacity had decreased slightly to 226 mA h g 1, while the discharge capacity had increased to 221 mA h g 1. The discharge capacity increased further to 242 mA h g 1 after 60 cycles due to the tendency of stabilization of the nanoplates after several cycles. The discharge capacity remained at 238 mA h g 1 after 100 cycles. The high-rate performance of the HTN-LNMO materials is evidenced by Figure 4b. A speci c capacity around 197 mA h g 1 is retained even when the discharge rate approaches 6 C, that is, 80% of the capacity at a rate of 0.1 C is retained at a rate of 6 C. The rate capability of the HTN-LNMO materials is further illuminated in Figure 4c, in which the discharge capacity at a 6 C rate and cycleability of the HTN-LNMO are compared with those of the CN-LNMO and LNMO particles. The discharge capacity after 50 cycles at a 6 C rate is measured as 186 mA h g 1 for HTN-LNMO, but only 106 mA h g 1 for CN-LNMO and 40 mA h g 1 for LNMO particles. The capacity of the HTN-LNMO in the 50th cycle is 1.7 times that of the CN-LNMO, and 4.6 times that of the LNMO particles. That is, the HTN-LNMO exhibits excellent capacity and superior cycleability at high-rate charge/discharge, in comparison withCN-LNMO and LNMO particles. It is obvious that the excellent rate-capability of HTN-LNMO originates from the nanometer-size effect on one hand, but most importantly from the signi cantly increased amount of (010) nanoplates, on the other. In conclusion, we have developed a crystal habit-tuned nanoplate material of Li(Li0.17Ni0.25Mn0.58)O2, in which the (0

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Figure 4. Cycleability and rate capability of HTN-LNMO. a) Plots of speci c capacity vs cycle number for electrodes prepared from HTN-LNMO. Test conditions: current density 60 mA g 1 (about 0.2 C), voltage window 2.0–4.8 V. b) Stabilized discharge voltage pro les of HTN-LNMO cycled at different rates: 6, 3, 1, 0.5, 0.1 C from bottom to top. c) Discharge capacity at a 6 C rate and cycleability of HTN-LNMO compared with CN-LNMO and LNMO particles.

nanoplates have been signi cantly increased, to be used as a cathode for high-rate performance LIBs.This material exhibits not only a high reversible capacity but also anexcellent cycleability. At a 6 C rate, the reversible capacity is measured as around 200 mA h g 1, and 186 mA h g 1 after 50 cycles. The excellent high-rate performance has been attributed to the increased active surface area for Li+ transportation in the HTN-LNMO sample, by about 50% in comparison with

© 2010 WILEY-VCH Verlag GmbH& Co. KGaA, Weinheim

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CN-LNMO. The results demonstratethat the proportion of electrochemically active surface for Li+ transportation is a key criterion for evaluating different nanostructures for high-rate performance of LIB materials. Therefore, further increasing the yield of the (010)-nanoplate materials could enhance greatly the rate-performance. Based on these ndings, HTN-LNMO is a promising candidate as a cathode material in LIBs with high energy and high power for application in EVs.

National Science Foundation of China (grant nos. 20833005, 20773102, and 20931160426). Received: April 29, 2010 Published online: August 30, 2010

Experimental SectionPreparation of Materials: HTN-LNMO was prepared by stirring stoichiometric amounts of Ni(CH3COO)2, Mn(CH3COO)2, and Li(CH3COO), and adding oxalic acid as a precipitating agent and acetic acid as an additive. The precursor was pretreated in a poly(tetra uoroethylene) (Te on) container at 150–200°C for normally 6–12 h. Then the mixture was stirred vigorously until dry. The dried mixture was heated at 450°C for 4–5 h, and then calcined in air using a step procedure: at 500°C for 3–5 h, at 750°C for 3–5 h, at 900°C for 8–16 h. All the raw materials of transition metal salts were of analytic …… 此处隐藏：7340字，全部文档内容请下载后查看。喜欢就下载吧 ……