The delithiation capacity-cycle number curve of each sample is shown in Fig. 4. After adding VC, SO2Cl2 and LiBOB to the conventional electrolyte, the lithium removal capacity retention rate of the silicon thin film battery increased from 37.4% to 83.3%, 51.2% and 44.4% after 100 cycles, but the addition of LiBOB and SO2Cl2 resulted in battery capacity. reduce. The addition of ET did not serve to improve cycle performance. Figure 4 Cyclic performance of silicon thin film batteries with different additives In order to find out the reasons for the influence of different additives on the performance of silicon thin film batteries, we conducted a scanning electron microscope observation on the silicon film after 20 cycles, as shown in Fig. 5. Figure 5 (a) shows the surface of the silicon film after VC addition. The surface is relatively dense but rough. Further enlargement also reveals that the surface is covered with knob-like protrusions. This may be due to the growth of the SEI film formed by the VC-containing electrolyte. The accumulation occurred in the middle. After adding VC, the composition of the SEI film changes, and a polymer of lithium polyalkyl carbonate is formed, which makes the SEI film more flexible and adhesive. [14] The main component of the SEI film formed in the conventional electrolyte is an inorganic lithium salt and a small amount of alkyl lithium, which is inferior in flexibility. In contrast, the SEI film formed by the VC-based electrolyte is more suitable for the charging and discharging process of silicon. The volume changes without cracking, thereby improving the cycle stability of the battery. Figure 5(b) shows the surface of the silicon film after the addition of SO2Cl2. It can be seen that there is a porous hole on the surface of the electrode. This may be due to the SO2Cl2 liberating SO2 gas at a higher potential, see equation (3). The cycle performance of the silicon thin film battery containing SO2Cl2 is still not good. It may be that the SEI film formed by SO2Cl2 is loose and porous, the mechanical strength is not high enough, and it is easy to rupture and fall off. Figure 5 Surface morphology of silicon film after 20 cycles with different additive batteries (illustrated as enlarged image) (a) VC; (b) SO2Cl2; (c) LiBOB; (d) ET The surface morphology of the silicon film after adding LiBOB and ET is shown in Figures 5(c) and (d), respectively. It can be seen from the magnified electron microscope image that the surface of the sample containing LiBOB is relatively flat, and the surface of the sample to which ET is added has signs of damage and erosion. This may be due to the fact that it is difficult to form a complete SEI film on the silicon surface due to the electrolyte containing ET, so that the exposed silicon is corroded by a trace amount of HF in the electrolyte, resulting in rapid capacity decay. LiBOB can form a relatively uniform SEI film on the surface of the electrode during the organic solvent reduction and decomposition process, as shown in Figure 5(c). However, the battery capacity of the electrolyte added with LiBOB is still attenuated. In order to find the reason why the SEI film was formed but failed to improve the cycle performance of the silicon film, we analyzed the charge and discharge efficiency of the battery containing different additives in the first 20 cycles, as shown in Fig. 6. The battery containing the VC electrolyte has the highest charge and discharge efficiency (about 99%), followed by the sample containing no additives and containing LiBOB, ET and SO2Cl2. In the first 10 cycles, the charge and discharge efficiency of the battery containing LiBOB was significantly lower than that of the battery containing VC. It can be seen that the battery containing LiBOB not only consumes a lot of irreversible capacity when forming the SEI film for the first time (see Table 2), but also in each cycle. Loss of capacity in the middle. This may be due to the fact that the mechanical strength of the SEI film formed by LiBOB is not high, and cracking occurs during the volume change of silicon, and it is necessary to continuously form the SEI film for repair. This results in an increase in the thickness of the SEI film on the silicon surface, but the effect of improving the stability of the silicon cycle is limited. The samples with ET and SO2Cl2 added have lower charge and discharge efficiency than the samples without any additives. It may be that they have more side reactions and can not form a dense, stable and reliable SEI film, so it does not work well for silicon films. Protection. in conclusion (1) A silicon-based anode with a sandwich structure was designed. The flexible acetylene black coating was used instead of the copper foil as the current collector. The active material was tightly bonded between the acetylene black coating and the polyethylene film. The volume change of silicon during charge and discharge, thereby improving cycle performance. (2) The addition of VC to the conventional LiPF6 electrolyte can form a stable SEI film on the surface of the silicon, thereby greatly improving the cycle performance of the silicon film. The addition of SO2Cl2 and LiBOB can improve the cycle stability of the silicon film to a certain extent, but the addition of ET has no obvious effect. references [1]GAO, B., SINHA, S, FLEMING, L, et al. Alloy formation in nanostructured silicon[J]. Adv. Mater. 2001, 13(11): 816-819. [2]BEATTIE, SD, LARCHER, D., MORCRETTE, M., et al. Si electrodes for Li-ion batteries-A new way to look at an old problem [J]. J. Electrochem. Soc., 2008, 155(2): A158-A163. [3] KASAVAJJULA, U., WANG, C., APPLEBY, AJ. Nano- and bulk-silicon-based insertion anodes for lithium-ion secondary cells [J]. J. Power Sources, 2007, 163(2): 1003 -1039. [4] RANGANATH TEKI, MONI K. DATTA, RAHUL KRISHNAN, et al. Nanostructured Silicon Anodes for Lithium Ion Rechargeable Batteries [J]. Small, 2009, 5(20): 2236-2242. [5]LIBAO CHEN, XIAOHUA XIE, JINGYING XIE, et al. Binder effect on cycling performance of silicon/carbon composite anodes for lithium ion batteries [J]. J. Appli. Electrochem., 2006, 36: 1099-1104. [6]LI, J., CHRISTENSEN, L., OBROVAC, MN, et al. Effect of heat treatment on Si electrodes using polyvinylidene fluoride binder [J]. J. Electrochem. Soc., 2008, 155(3): A234 -A238. [7] KIM, Y.-L., SUN, Y.-K., LEE, S.-M.. Enhanced electrochemical performance of silicon-based anode material by using current collector with modified surface morphology [J]. Electrochi. Acta, 2008, 53(13): 4500-4504. [8] NAM-SOON CHOI, KYOUNG HAN YEW, HO KIM, et al. Surface layer formed on silicon thin-film electrode in lithium bis (oxalato) borate-based electrolyte [J]. J. Power Sources, 2007, 172: 404-409. [9] L. BAGGETTOA, JFM OUDENHOVENA, T. VAN DONGENB, et al. On the electrochemistry of an anode stack for all-solid-state 3D-integrated batteries [J]. J. Power Sources, 2009, 189: 402– 410. [10]OTA, H., SAKATA, Y., INOUE, A., et al. Analysis of vinylene carbonate derived SEI layers on graphite anode[J]. J. Electrochem. Soc., 2004, 151 (10): A1659 -A1669. [11] Cai Zongping, Xu Mengqing, Li Weishan, et al. Research progress of negative film forming additives for lithium ion battery electrolytes[J]. Battery Industry, 2008, 13(1): 68-71. [12] YONG MIN LEE, JUN YOUNG LEE, HEUNG-TAEK SHIM, et al. SEI Layer Formation on Amorphous Si Thin Electrode during Precycling [J]. J. Electrochem. Soc., 2007, 154 (6): A515-A519 . [13] SEUNG-WAN SONG, SEUNG-WON BAEK. Silane-Derived SEI Stabilization on Thin-Film Electrodes of Nanocrystalline Si for Lithium Batteries [J]. Electrochem. and Solid-State Lett., 2009, 12(2): A23 -A27. [14]AURBACH, D., GAMOLSKY, K., MARKOVSKY, B., et al. On the use of vinylene carbonate (VC) as an additive to electrolyte solutions for Li-ion batteries [J]. Electrochim. Acta, 2002 , 47(9): 1423-1439. Metal Roof Panel Bend Machine,Sheet Metal Bending Machines,Steel Bar Bending Machine Willing Technology Co., Ltd. , http://www.txrollformingmachine.com
Study on improving the cycle performance of silicon-based anodes in lithium ion batteries (2)