。

To enhance cycleability of Sn–Cu alloy electrode, a protection layer of copper is coated on its surface and heated at 200 ◦C for 24 h at argon atmosphere. The plating time was optimized to be 1min.

As compared with the uncoated anode, the Cu-coated and annealed anode presents higher discharge and charge volts and lower capacity at first cycle. This is probably caused by the polarization of as-coated copper layer when lithium ions pass through it.The coulomb efficiency of the anode increases from 92 to 95% after copper coating as shown in Fig. 5.

The SEM image and surface EDS analysis of the Cucoated anode are shown in Fig. 8. The Cu/Sn ratio is 1.26/1,which indicates that the surface of Cu-coated electrode contains Cu6Sn5 phase and a small quantity of pure copper. Namely, the content of surface changes from Sn-rich as
shown in Fig. 2(b) to Cu-rich as shown in Fig. 8, after copper coating.


Fig. 9 shows surfaces of the uncoated electrode during cycling, where cracks are clearly observed. The cracks appear when lithium is first intercalated into the electrode, and crystalline grains are still observed, as shown in Fig. 9(a). After 17 cycles, a pulverous surface, which seems to be made up of ultrafine powders, can be observed and cracks still exist after 17 cycles, as shown in Fig. 9(b). The pulverous surface indicates structural collapse after several cycles, and its
cycleability is poor.


Fig. 10 shows the surfaces of the copper coated electrode during cycling, where no cracks are observed at first cycle in Fig. 10(a). Small cracks begin to occur after 39 cycles,but no obvious pulverization can be observed as shown in Fig. 10(b). This indicates the copper coating layer acts as an inactive protection layer on the surface, and improves the electrode performance.

Figs. 11 and 12 show the cycling performance of the test cellwith copper coated and uncoated Sn–Cu alloy electrodes. At the first 10 cycles, there is no improvement for cycleability, but an approximate 100mAh/g loss of capacity, as shown in Fig. 11. The capacity retention of the coated and uncoated anodes are over 98% during the first 10 cycles, and still good for coated anode, but gradually deteriorated for uncoated anode in the following cycles, as shown in Fig. 12.


As the electrode is uncoated, the specific capacity increases at the expense of capacity retention. The uncoated electrode has a peak specific capacity in excess of 428mAh/g at the fifth cycle. The first and 50th cycle capacities of the uncoated electrode are 415 and 170mAh/g, respectively, a 59% loss of capacity. As the electrode is copper coated, the capacity retention increases at the expense of specific capacity, whose peak value is 316mAh/g at the first cycle. By
cycle 50, capacity has been reduced to 220mAh/g, and the capacity retention is in excess of 70%. The capacity of the copper coated electrode decreases as compared with that of the uncoated electrode in the beginning, it is larger after 30 cycles. The copper coating on surface of electrode protects it effectively during cycling, and significantly improves the cycleability of the Sn–Cu alloy electrode.


A Sn–Cu alloy electrode for lithium ion battery can be directly prepared by pulsed electrodeposition. Tin is electrochemically deposited on substrate of copper foil. When heated, copper and tin react to form Cu6Sn5 and Cu3Sn. The pulsed electrodeposition leads to smaller crystal grains and takes electrochemically superior to simple electrodeposition. A copper coating is effectively introduced to the surface of Sn–Cu alloy electrode to act as a protection layer by electrodeposition and heating. Although the copper coating decreases capacity of electrode in the beginning, it acts as a protection layer and improves the cycleability of Sn–Cu alloy electrode