锂离子电池的优点1）能量密度高。
能量密度可达460-600Wh/kg，其能量密度是铅酸电池的6-7倍；2）相对较高的平均输出电压值。
常用的锂离子电池单体平均工作电压约为3.7V，约为镍-隔电池或者镍-氢电池的3倍3）可以高功率输出，在电动汽车的磷酸铁锂离子电池可以达到15-30C充放电能量，有利于启动加速；4）相对较小的自放电率，无记忆效应，锂电池的自放电率为镍-隔电池或者镍-氢电池的一半甚至更小。
记忆效应指的是电池在充放电循环过程中容量减小的现象，而锂离子电池在循环过程中不出现明显地容量衰减现象；5）使用寿命长，在正常条件下，锂离子电池使用寿命可达6年，循环次数超过1000次。
（6）可快速充电，使用额定电压为4.2 V的充电器只需1~2小时即可充满（7）使用温度范围宽，通常可在-30～+45℃温度范围内使用，通过调整电解液甚至可以在更宽温度范围内使用；（8）绿色电池，对环境友好，无论生产、使用和报废，都不存在镉、铅、汞等对环境有污染的元素；Figure 4b shows the typical charge−discharge voltage profiles of the S@CNTs/Co3S4−NBs, S@Co3S4−NBs and S@CNTs electrodes at 0.2 C (1.0 C = 1,675 mAh g−1). The S@CNTs/ Co3S4−NBs electrode exhibits two typical discharge plateaus at 2.35 and 2.08 V (vs Li+/Li), originated from the reduction of S8 to soluble long-chain polysulfides (Li2Sx, 4 ≤ x ≤ 8) and the formation of insoluble short-chain polysulfides (Li2S/Li2S2), respectively. The single charge plateau of S@CNTs/Co3S4−NBs between 2.25−2.36 V is ascribed to the oxidation of Li2S/ Li2S2 to Li2Sx and eventually S8. These charge and discharge plateaus are consistent with corresponding CV curves (Figure S5). Notably, the S@CNTs/Co3S4−NBs electrode exhibits lower potential hysteresis and higher sulfur utilization ratio than those of the S@Co3S4−NBs and S@CNTs, mainly attributed to the strong chemical affinity of polar Co3S4−NBs with polysulfides and the interconnected CNT network.图4b 显示了S@CNTs/Co3S4−NBs、S@Co3S4−NBs 和S@CNTs 电极在0.2 c (1.0 c = 1675 麻将g−1)上的典型charge−discharge 电压剖面。
S@CNTs/Co3S4−NBs电极展示两个典型的放电高原在 2.35 和 2.08 V (vs li +/李), 起源于 S8 的减少到可溶性长链多硫化物 (Li2Sx, 4 ≤ x ≤ 8) 和形成不溶性短链多硫化物 (Li2S/Li2S2),分别.2.25−2.36 V 之间S@CNTs/Co3S4−的单电荷高原归因于Li2S/Li2S2 对Li2Sx 和最终S8 的氧化作用。
这些电荷和放电高原与相应的CV 曲线一致(图S5)。
值得注意的是, S@CNTs/Co3S4−NBs电极具有比S@Co3S4−NBs和 S@CNTs 更低的潜在滞后率和较高的硫利用率,主要归因于极Co3S4−NBs与多硫化物的强烈化学亲和性和互联的碳纳米管网络。
The rate capability comparison of S@CNTs/Co3S4−NBs,S@Co3S4−NBs, S@CNTs, and S@mixed-CNTs&Co3S4−NBs(the sulfur composite of simply mixed CNTs and Co3S4−NBs)is shown in Figure 4d and Figure S6. When cycled at 0.2, 0.5,1.0, 2.0, and 5.0 C, the S@CNTs/Co3S4−NBs cathode candeliver impressive discharge capacities of 1330, 1165, 988, 859,and 702 mAh g−1, respectively. As the current density turnsback to 1.0 C, the discharge capacity of S@CNTs/Co3S4−NBsrestores to 958 mAh g−1, indicating good structural stability athigh rate. In contrast, the discharge capacities of S@Co3S4−NBs cathode fades sharply from 1240 to 268 mAh g−1 when therate increases from 0.2 to 2.0 C. What is more, the dischargecapacity of S@CNTs fades dramatically to 37 mAh g−1 whenthe current rate increases to 5.0 C. It is clear that the S@CNTs/Co3S4−NBs cathode exhibits much higher ratecapabilities than those of S@Co3S4−NBs and S@CNTs. Thegalvanostatic charge−discharge voltage profiles ofthe S@CNTs/Co3S4−NBs cathode at various current rates were alsomeasured (Figure 4e). The results confirm that theincorporation of interlaced CNT network is very helpful toimprove the rate capability of S@CNTs/Co3S4−NBs. Moreover,the localized and overall electron transfer of the sulfurspecies trapped in S@CNTs/Co3S4−NBs can be effectivelyfacilitated by the interconnected CNT network inserted in andthreaded between the Co3S4−NBs (Figure S7).Synthesis of Hollow Iron Phosphide Nanoparticles. [Caution: Thisreaction should be considered to be highly corrosive andflammable because the high-temperature decomposition of aphosphine can liberate phosphorus, which is pyrophoric. Therefore,this reaction should only be carried out using rigorouslyair-free conditions by appropriately trained personnel.] Hollowiron phosphide nanoparticles were synthesized from colloidaliron nanoparticles by slightly modifying a previously reportedprocess.24 1-Octadecene (ODE, 10.0 mL, 31.3 mmol) andoleylamine (0.2 mL, 0.61 mmol) were added to a 50 mL, threenecked,round-bottom flask that was equipped with a refluxcondenser, a thermometer adapter, a thermometer, a rubberseptum, and a borosilicate-coated stir bar. The contents of theflask were stirred and heated to 120 Cunder vacuum for 30 minto remove any adventitious water and then placed under anAr atmosphere. This ODE/oleylamine solution was then heatedto 190 C, at which point 0.35 mL of pentacarbonyliron wasinjected. The suspension was then maintained at 190 C for20 min. Five milliliters of the hot ODE/oleylamine mixture, whichat this point now contained colloidal Fe nanoparticles, wasthen rapidly injected (using a glass syringe) into a secondAr-filled 50 mL, three-necked flask containing squalane(7.0 mL, 13 mmol) and tri-n-octylphosphine (3.0 mL, 6.7 mmol)that had been heated to 340 C for 1 h. The temperaturedropped as a result of the injection and was brought back upto 320 C and held at that temperature for 1 h. After the reactionwas completed, the heating mantle was turned off and thesolution was allowed to cool to 200 C. The heating mantle wasthen removed to allow the sample to cool more rapidly to roomtemperature. The reaction solution was divided into two centrifugetubes for collection and cleaning. The nanoparticleswere collected by adding hexanes (5 mL) and ethanol (15 mL)to each tube, followed by centrifugation (12 000 rpm, 3 min).The particles were then resuspended in hexanes (5 mL), and thisprocess was repeated twice more. Nanoparticles were redispersedin hexanes after isolation and placed in a vial (20 mL)for use.。