Effects of thermal annealing on performance of silicon nitride anode for lithium-ion battery applications

The effects of thermal annealing on the performance of hydrogenated silicon nitride anode (prepared by plasma enhanced chemical vapor deposition, PECVD) are investigated by varying annealing temperatures. The relationship between the annealing temperatures, microstructures and electrochemical behaviors of the anodes is revealed. The capacity of the anodes with low-temperature annealing (<= 400 degrees C) is quite low firstly but increases abruptly after several charge/discharge activation processes. Due to weak strength of hydrogen-containing bonds in the PECVD silicon nitride, dehydrogenation occurs with cycling, which is effective to activate the anodes and thus result in the abrupt increase in the anode capacity. With increasing the annealing temperature to 450 degrees C, the thermal treatment can break the hydrogen-containing bonds (induce dehydrogenation) and activate the anodes; therefore, the anodes with relatively high-temperature annealing (>= 450 degrees C) exhibit a high capacity even with no electrochemical activation processes needed. The mechanical properties of the anodes also depend on the thermal treatment and the anode elastic modulus and hardness increase with increasing the annealing temperature, which results in a poor mechanical stability and thus poor cycling performance of the anode with high-temperature annealing (similar to 600 degrees C). Compared with the anode with lower- or higher-temperature annealing, the anode with an appropriate annealing (similar to 450 degrees C) shows higher and more stable reversible capacity (similar to 1001 mAh g(-1) at 0.6 C over 200 cycles) and better rate performance (similar to 327 mAh g(-1) at 6.0 A g(-1)).